JPS627538A - Colored steel plate having excellent high temperature-resistant corrosiveness - 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 (Industrial Application Field) The present invention relates to a colored steel sheet suitable for use in areas where high-temperature corrosion resistance is required, such as automotive exhaust system parts.

(Prior Art and Problems) Conventional high-temperature corrosion-resistant plated steel sheets have generally been, for example, aluminum-based or zinc-based plated steel sheets subjected to chromate treatment. However, such conventional high-temperature corrosion-resistant plated steel sheets are plated with base metals such as aluminum or zinc.
Moreover, since the chromate film formed as a post-treatment has insufficient corrosion resistance and heat resistance, white rust occurs relatively early in a high-temperature corrosive environment.

In addition, conventional plated steel sheets retain the metallic luster of aluminum or zinc even after chromate treatment, but when used for automobile exhaust system parts, such as the outer plate of a muffler, the reflected light from the muffler, especially when driving at night, There was also the problem that this caused problems for the drivers of the following vehicles.

Furthermore, from the viewpoint of appearance quality, there is a strong demand for exhaust system parts to be blackened, just like other underfloor components.

As a way to simultaneously solve the two problems mentioned above, namely, prevention of early white rust on plated steel sheets and blackening of exhaust system parts, it is possible to apply a black heat-resistant paint on the plated steel sheets as a post-treatment. Although this is possible, it is not realistic as the cost would increase dramatically.

(Means for Solving the Problems) The present invention has been made by focusing on the above-mentioned conventional problems, and by forming a colored film with a skeleton of siloxane bonds on the surface of a plated steel sheet. The aim is to solve problems at the same time.

Here, the present invention applies a coating liquid containing one or more monomers or oligomers of di- or trialkoxysilane having an alkyl group containing an organic functional group and a colored heat-resistant pigment to the surface of a plated steel sheet. , Baking is a highly durable film with a colored film with a skeleton of siloxane bonds, which is formed by hardening the film. JjL is a colored steel sheet with excellent corrosion resistance.

In addition to the above-mentioned film, the present invention also provides a coating solution containing one or more monomers or oligomers of di- or trialkoxysilane having an alkyl group containing an organic functional group and containing no pigment, and then baking. The present invention also relates to a colored steel sheet having excellent high-temperature corrosion resistance and having a colored coating having a two-layer structure with a siloxane bond as a skeleton, further comprising a cured transparent coating as an upper or lower coating of the coating.

(effect) This invention will be described in detail below.

The plated steel sheets used as materials in the present invention include those commonly used for high-temperature corrosion-resistant plated steel sheets, such as galvanized steel sheets, zinc alloy plated steel sheets such as zinc-iron, zinc-nickel, and zinc-aluminum, aluminum-plated steel sheets,
Alternatively, a composite plated steel plate made of multiple layers of these platings may be used, which is appropriately selected depending on the required level of corrosion resistance.

According to the present invention, a colored coating having a one-layer or two-layer structure having siloxane bonds as a skeleton is formed on the plated steel sheet, but before that, the plated surface may be subjected to chromate treatment if desired. The chromate treatment can be carried out by conventional reaction-type or coating-type chromate treatment. Additionally, conventional surface cleaning treatments for the thumb and the like can be employed as appropriate.

The structure of the monomer or oligomer of di- or trialkoxysilane (hereinafter referred to as silane compound) having an alkyl group containing an organic functional group used for forming the above-mentioned colored film is represented by the following formula. Alkyl group such as methyl, ethyl, propyl, butyl; R2: an alkyl group or an alkyl group (in the case of dialkoxysilane), or an alkoxy group, i.e. OR□ (in the case of trialkoxysilane); R3: organic functional group Containing alkyl groups (examples of organic functional groups are
(vinyl, amino, chloro, epoxy, hydroxyl, carboxyl, methacryloxy, etc.); n: 0 (for monomers), or an integer of 1 or more but usually 6 or less (for oligomers).

Examples of such silane compounds include vinyltriethoxysilane, γ-methacryloxypropyltrimethoxysilane, γ-7 minobrobyltriethoxylane, γ-glycidoxypropyltrimethoxysilane, β-(3,4
Examples include so-called silane coupling agents such as -epoxycyclohexyl)ethyltrimethoxysilane, N-β-(aminoethyl)-T-aminopropyltrimethoxysilane, and T-chloropropyltrimethoxysilane, which are available as commercially available products. There are things you can do. Also included are reactants of these silane compounds and organic resins. The monomers or oligomers of these silane compounds are dissolved in a suitable solvent such as water or isopropyl alcohol,
A coating solution is prepared by dissolving it in an organic solvent such as phthyl alcohol or xylene. The solid content concentration of the coating liquid is adjusted depending on the desired film thickness, solution viscosity, etc.

When forming a colored film on the surface of a plated steel sheet, the coating solution contains a colored heat-resistant pigment in addition to the above silane compound in order to color the film. When used as automobile exhaust system parts, it is preferable that the heat-resistant pigment be black.
Depending on the intended use and the required level of heat resistance, not only black but also other suitable colored heat-resistant pigments can be used. Examples of black heat-resistant pigments include (Cu + Cr, Mn) oxide, (
There are mixed oxide pigments such as Cu + Cr) oxides. In addition, other colored heat-resistant pigments include (Co, A1
．． Cr) oxide pigment (blue pigment).

The amount of colored heat-resistant pigment added is 1% by volume based on the total solid content.
It is preferably within the range of 0 to 50%. If it is less than 10%, it will be difficult to obtain sufficient coloring. On the other hand, the proportion of pigment is 50
%, the deterioration of film performance such as heat resistance, corrosion resistance, and workability becomes noticeable.

It is generally preferred that the particle size of the pigment is less than or equal to about 1 micrometer.

Further, antirust pigments may be added as appropriate to improve corrosion resistance.

On the plated surface of a plated steel sheet, a coating solution containing a silane compound or oligomer containing a colored heat-resistant pigment as described above is applied, and the coating film is baked to obtain a colored cured film. This application can be done by dipping, roll coating, spray painting,
It can be carried out by conventional application means such as barcode coating and brush coating. The coating amount of the pigmented coating solution is 1 to 1 after baking hardening.
It is preferable to set it within a range where a film with a thickness of 10 μm can be obtained. When the thickness of the pigment-containing film is less than 1 μm, coloring is insufficient, and when it exceeds 10 μm, processability may deteriorate.

The curing conditions for the coating film vary depending on the type of silane compound used, but generally the heating temperature is 150 to 35
The temperature is 0° C. and the heating time is about 30 seconds to 60 minutes. By heating and baking, the alkoxy groups of the silane compound are thermally decomposed to form siloxane bonds in which 0 and Si are alternately bonded, and a colored cured film having the siloxane bonds as a skeleton is obtained. If this baking is insufficient, the desired film performance cannot be obtained, so the curing conditions are set so that the alkoxy groups are almost completely thermally decomposed by baking. However, if the heating temperature is too high, there is a risk that the organic functional groups in the silane compound that should remain in the film will decompose.
High temperatures above °C should be avoided. The presence of organic functional groups in this film is important for improving performance such as adhesion, corrosion resistance, and processability of the film.

The colored steel sheet of the present invention, which has a colored cured film of a silane compound added with a colored heat-resistant pigment on the plated surface thus formed, exhibits excellent corrosion resistance and heat resistance. Furthermore, when the amount of the colored heat-resistant pigment added is small, the coating film adhesion is sufficient and the processability is also good. However, if a large amount of pigment is added, processability tends to deteriorate to some extent, so when using it for applications that require advanced processing, a two-layered film as described below should be applied on the plating surface. It is preferable to form. Furthermore, in order to obtain even better corrosion resistance and heat resistance, a two-layer structure coating as described below is preferable.

According to a preferred embodiment of the present invention, on the cured film of the colored heat-resistant pigment-containing silane compound formed as described above, a transparent coating containing a monomer or oligomer of the silane compound and substantially free of pigment is provided. By further applying the solution and baking and hardening the coating film by heating, a colored steel sheet having a two-layered hardened film consisting of a colored lower layer film and a transparent upper layer film on the plated surface is obtained. The coating means and curing conditions for this upper layer film may be the same as those for forming the colored lower layer film described above. The silane compound used for forming the upper layer film is preferably the same as that used for forming the lower layer film from the viewpoint of adhesion, but other silane compounds can also be used.

According to another preferred embodiment of the present invention, a colored steel sheet having a two-layer structure in which a transparent film as described above is formed as a lower layer below a colored heat-resistant pigment film can also be obtained in the same manner as described above.

In this way, by forming the cured film of the silane compound into a two-layer structure, corrosion resistance and heat resistance are further improved, and even more excellent high-temperature corrosion resistance is ensured.

In addition, if the amount of colored heat-resistant pigment added to either the lower layer or the upper layer is large, processability may not be sufficient with just one layer of the colored film, but a transparent film containing substantially no pigment may be used. By forming a two-layer structure in which the layers are stacked as an upper layer or a lower layer, it is possible to improve workability that has deteriorated. However, if the film thickness of the transparent film is too small, it will be difficult to obtain the above improvements, and if the film thickness is too large, the processability will deteriorate, so the amount of coating of the transparent coating liquid without pigments 065 to 3.0 after curing, whether it is applied as an upper or lower layer.
It is preferably within a range that allows a μ-film to be obtained.

For the purposes of the present invention, the term "transparent film that does not substantially contain pigment" includes a film that contains a small amount of pigment, for example, 5% by volume or less. Such coatings are substantially transparent, and the same effect is obtained according to the invention as in the case of cured coatings formed from coating liquid 7 containing no pigment at all.

The colored steel sheet according to the present invention has a dense film of siloxane bonds formed on the plating surface, which prevents oxygen, water, chlorine ions, etc. that promote metal corrosion from coming into contact with the steel sheet surface, and at the same time prevents corrosion current from coming into contact with the steel sheet surface. is extremely small, so almost no corrosion occurs.

In addition, it does not change over time unlike carbon-based organic films such as epoxy resins, hardly changes in quality even at temperatures of several hundred degrees, and does not exhibit phenomena such as cracking even in the face of rapid temperature changes.

Therefore, the colored steel sheet according to the present invention exhibits excellent high-temperature corrosion resistance, has good workability due to the high flexibility of the coating, and can be colored into any desired color with the pigment contained in the coating. This makes it particularly suitable for manufacturing automotive exhaust system parts such as mufflers. However, the use of the colored steel sheet of the present invention is not limited to the production of such parts, but also a wide range of other uses that require high temperature corrosion resistance, such as heating equipment parts such as kerosene stoves, various combustor materials, etc. can also be used. Furthermore, depending on the application, the colored steel sheet of the present invention may be either a single-sided coated type or a double-sided coated type.

When manufacturing an automobile muffler using the colored steel sheet of the present invention, for parts where muffler internal corrosion is a problem (e.g. muffler end plate), the material should be an aluminum-plated steel sheet or an aluminum/galvanized steel sheet <AQ
50% or more). On the other hand, parts of the muffler where internal corrosion is not a problem (muffler outer shell, heat shield plate, etc.) are made of aluminum-plated steel sheets, zinc-coated steel sheets,
It is preferable to use an aluminum-plated steel sheet (A (25% or more), an alloyed galvanized steel sheet, a zinc-nickel-plated steel sheet, etc.).

The present invention will be further explained below with reference to Examples.

On the implementation plate (1 layer film) Various plated steel plates of A to F below, width 70 x length 150 x thickness 1 [Ryu] are coated with milk fat, and then silane compounds (monomers or oligomers) and black heat-resistant pigments listed below are applied. In the coating liquid it contains? i? fl and in an oven at a temperature of 300℃ for 5 minutes.
The film was cured by baking for a minute to obtain a steel plate with a black appearance.

Industrial and Yuka ■ Plate A: AQ plated steel plate (area weight 30 g/r
d>B: AQ plated steel sheet (area weight 60g/a)
C: Zn-5% 8-plated steel plate (fabric weight ff1) 00 g
/rd) D: Zn-Ni plated steel plate (area weight 2
0g/+d)E: Alloyed Zn-plated steel plate (date amount 40g
/rr F: Electrolytic Zn-plated steel sheet (Weight 40g/m
) 2 Radigo L (at: r-glycidoxypropyltrimethoxysilane (monomer) (b): γ-aminopropyltriethoxysilane (oligomer) (C): β-(3,4-epoxycyclohexyl) Ethyltrimethoxysilane (monomer) The coating solution is a 20% isopropyl alcohol solution of each of the above silane compounds, and a Cu-Cr-Mn oxide black heat-resistant pigment (Nippon Ferro Co., Ltd.) in an amount of 30% by volume based on the total solid content. 9＠, trade name: NF-1335-P). Each coating solution was applied to the plated steel plate using a bar coater so that the coating thickness after curing was approximately 4 μm. did.

The plated steel sheet having a single-layer hardened film made of the pigment-containing silane compound on the surface is subjected to the following (1) to (4).
It was evaluated by various corrosion resistance tests.

+1) Salt spray test 35 according to the method specified in JIS Z 2371
A salt spray test is conducted for 480 hours in which the test piece is sprayed with a 5% NaCl aqueous solution at .degree.

(2) Combined corrosion test 4 hours of salt water spray above - dry (60'C) 2 hours - wet (
50° C., relative humidity 95%) A dry and wet repeated salt water spray test is conducted for 100 cycles, with one cycle being 4 hours.

(3) Heat Corrosion Test After heating at 300° C. for 100 hours, the sample is cooled in air and subjected to the above salt spray test for 144 hours.

(4) Thermal Shock Corrosion Test After heating at 300° C. for 100 hours, the sample was cooled with water and subjected to the above salt spray test for 144 hours.

Each of the above tests was conducted on three test pieces, and the average value of the white rust or red rust occurrence area ratio (%) is summarized as the test results in Table 1 below. For comparison, Table 1 also shows similar test results when each plated steel sheet was subjected to chromate treatment.

As can be seen from the results in Table 1, in the case of a chromate film, either red rust occurred or significant white rust was observed even in the absence of red rust, and the corrosion resistance was poor in all tests. On the contrary,
When a single-layer colored cured film of a silane compound is formed on a plating surface, regardless of the type of silane compound, the occurrence of red rust is almost completely prevented, and a suppressive effect on the occurrence of white rust is also observed.

, 1fJLl (two-layer film)
[A coating solution containing γ-aminopropyl 1° triethoxysilane (oligomer) as a silane compound was applied to the various plated steel sheets A to D used in Example 1 in the same manner as in Example 1. Pigment-containing black underlayer cured
A 5° film was formed, and a transparent upper cured film was formed thereon using a coating solution having the same composition except that no pigment was added. That is, the coating liquid used was a 20% isopropyl alcohol solution of the above silane compound T, tp'')1
"1"°1°"hlcL"6"+Jfje&:Nt
The same Cu-Cr-Mn oxide black heat-resistant pigment used in Example 1 was added and mixed in an amount of 30% by volume.

Coating is done using a bar coater for both the lower and upper layers.
The amount of each coating solution deposited was such that the thickness of the coating after curing was approximately 4 μm for the lower layer pigment-containing layer and approximately 1 μm for the upper layer transparent layer (2 layers A). In addition, there is a transparent film on the lower layer (approx. 1μ→,
A pigment-containing film (approximately 4 μm) was also formed on the upper layer in a two-layer structure (layer B) in the same manner. Both the pigment-containing layer and the transparent layer were baked under the same conditions (300°C x 5 minutes). I went there.

Each of the obtained steel plates having a two-layer structure had a black appearance. The obtained steel plate was evaluated by various corrosion resistance tests similar to those in Example 1. The results are the results of Example 1 (
The chromate layer alone is shown in Table 2 below, together with the chromate layer (forming a colored single-layer film). Table 2 also shows the test results when a single-layer film and a two-layer film of T-aminopropyltriethoxysilane oligomer were formed on a bare steel plate in the same manner as in Examples 1 and 2.

In addition, coatings with one-layer structure and two-layer structure (two-layer A
) having a steel plate B (i.e., area weight 160 g/n (A of
The workability of the Q-plated steel sheet was evaluated by a 180° bending test. In this bending test, the specimen was
After bending, a tape peeling test was conducted at the bent portion and the peeled area (%) was measured. The test results are shown graphically in the accompanying drawings as peeling area versus bending radius expressed in 1t (t: steel plate thickness = 1ms).

As is clear from Table 2, by forming a two-layer film of a silane compound on a plated steel sheet, not only red rust but also white rust, which was observed in the case of the single-layer film in Example 1, was generated. It can be seen that the corrosion resistance was suppressed to a very low level, and the corrosion resistance was improved compared to a single layer coating. There is no big difference in the results between the two layers A and B, but there is a tendency for 2NB, whose lower layer is a transparent film, to have slightly better corrosion resistance. However, if the material is a bare steel sheet rather than a plated steel sheet, the silane compound
Even if a layer film is formed on the surface, red rust is observed, and the corrosion resistance is insufficient.

Also, from the graph in the attached drawing, the workability of the steel plate is also good for the two-layer structure! It can be seen that (2-layer A) is superior. For example, the peeling area in a bending test is the bending radius 1t (=l
sl), the single-layer coating is 100%, while the two-layer coating is approximately 40%, and the bending half iV 2 L (=
2 +w) Teha I N skin FfjaM approx. 50%, 2rF
i film is about 13%.

(Effects of the Invention) According to the present invention, a colored hardened film with a skeleton of siloxane bonds is formed by coating and baking a coating liquid containing a specific silane compound and a heat-resistant colored pigment on the surface of a plated steel sheet. It has significantly improved corrosion resistance and heat resistance compared to chromate-treated plated steel sheets, and corrosion is effectively suppressed even in high-temperature corrosive environments. Furthermore, by forming a colored film with a two-layer structure in which a transparent cured film of a silane compound is stacked as an upper or lower layer, it is possible to improve not only corrosion resistance and heat resistance but also processability. Furthermore, since it can be colored in any desired color by incorporating heat-resistant pigments, the appearance quality of exhaust system parts that are required to be blackened, for example, can be significantly improved compared to conventional chromate-treated plated steel sheets.

[Brief explanation of the drawing]

The attached drawing is a graph showing the relationship between the peeling area (%) of the bent part and the bending radius (T-thickness of the steel plate) in a 180° bending test, where the dotted line is for a single colored coating, and the solid line is for an additional transparent layer. The case of a two-layer film layered on top is shown.

Claims (4)

[Claims] (1) A coating liquid containing one or more di- or trialkoxysilane monomers or oligomers having an alkyl group containing an organic functional group and a colored heat-resistant pigment is applied onto the plated surface of a plated steel sheet, and baked. A colored steel sheet with excellent high-temperature corrosion resistance and having a colored film with a skeleton of siloxane bonds, which is obtained by hardening. (2) A colored steel sheet with excellent high-temperature corrosion resistance according to claim 1, wherein the plated steel sheet is a steel sheet for automobile exhaust system parts. (3) A coating liquid containing one or more di- or trialkoxysilane monomers or oligomers having an alkyl group containing an organic functional group and a colored heat-resistant pigment is applied onto the plated surface of the plated steel sheet, and baked. Applying a coating solution containing the colored film obtained by curing and one or more monomers or oligomers of di- or trialkoxysilane having an alkyl group containing an organic functional group and substantially free of pigment, A colored steel sheet having excellent high-temperature corrosion resistance and having a colored film having a skeleton of siloxane bonds and a film obtained by baking and hardening. (4) A colored steel sheet with excellent high-temperature corrosion resistance according to claim 3, wherein the plated steel sheet is a steel sheet for automobile exhaust system parts.