JPS62174146A - Weldable heat-resistant coating 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] The present invention relates to a weldable heat-resistant coated steel plate.

In particular, the present invention is suitable for manufacturing parts that are subject to high-temperature oxidation and wet corrosion, such as parts for internal combustion engines, boilers, and heating appliances. This invention relates to a coated steel plate that has heat resistance, corrosion resistance, paint film adhesion, and workability, and can be welded.

Traditionally, for example, mufflers in automobile exhaust systems have
A molded product made of hot-dip aluminum plated steel plate with excellent heat resistance and corrosion resistance was used. However, when the muffler is still cold when the engine is started, moisture and corrosive substances contained in high-temperature exhaust gas condense and remain inside the muffler, and when the muffler heats up due to engine operation, the corrosive substances It is exposed to a corrosive environment in which the condensed water it contains condenses and evaporates. Therefore, mufflers that are simply formed from hot-dip aluminized steel sheets.

The problem was that it would corrode in a short period of time and lose its function as a muffler.

Therefore, depending on the type of muffler, it is proposed to form an organic polymer coating on one side of a hot-dip aluminum plated steel plate and then mold the coated steel plate into a muffler with the organic polymer coating on the inside of the muffler. It was done. However, the painted hot-dip aluminized steel sheets that have been proposed so far have the disadvantage that the heat resistance of the coating film is poor, so the coating film partially peels off due to exhaust gas and corrodes from the peeled part, and the insulating property Since it has an organic coating film, there is a problem in that direct spot welding cannot be performed and series spot welding must be used.

Furthermore, as a recent trend in mufflers, it is desired that the outside of the muffler be painted black from the standpoint of design. In response to this request, a two-sided coated hot-dip aluminized steel sheet was proposed in which conductive metal powder was arranged on one coating film and one coating film was painted black.

However, the double-sided coated hot-dip aluminized steel sheets proposed so far contain conductive metal powder, so
Although sufficient weldability exists.

Because the heat resistance of the paint film is poor, the paint on the inside of the muffler will partially peel off due to exhaust gas, and corrosion will occur from the peeled areas.The black paint on the outside of the muffler will also peel off partially, causing damage to the muffler. There was a drawback that the design quality was impaired. Another method for making an outer black muffler is to first mold the muffler and then paint the outside black, but such a post-coating method is complicated and expensive. I couldn't.

Therefore, one main object of the present invention is to provide a painted steel sheet that has better heat resistance and corrosion resistance than conventional painted hot-dip aluminized steel sheets, and which can be directly spot welded.

One particular object of the present invention is to provide such a coated steel sheet which is colored black on one side.

Thus, the present invention is as follows.

With hot dip aluminized steel sheet.

With a chromate chemical conversion coating layer formed on both sides.

A cured polyamide-imide resin formed on at least one of those chemical conversion coating layers.

An undercoat film layer consisting of a chromate rust preventive pigment and graphite powder that does not have crystal water, and a cured silicone-modified polyester resin with a degree of modification of 30 to 50% and granular aluminum formed on the undercoat film layer. To provide a weldable heat-resistant coated steel sheet comprising a top coat layer made of powder.

The present invention further provides.

With hot dip aluminized steel sheet.

With a chromate chemical conversion coating layer formed on both sides.

An undercoat film layer formed on these chemical conversion film layers is composed of a cured polyamide-imide resin, a chromate rust-preventing pigment that does not contain water of crystallization, and graphite powder.

A silver topcoat layer consisting of a cured silicone-modified polyester resin with a degree of modification of 30 to 50% and granular aluminum powder formed on one of the undercoat layers, and the other of the undercoat layers. To provide a weldable heat-resistant coated steel sheet comprising a black top coat layer consisting of a cured silicone-modified polyester resin having a degree of modification of 30 to 50% and a black top coat layer consisting of a granular aluminum powder and a heat-resistant black pigment formed thereon.

Referring to the attached drawings, the painted steel sheet of the present invention is as follows.

As shown in FIG. 1, a hot-dip aluminized steel plate 1,
A chromate chemical conversion film layer 2 formed on both surfaces thereof, and an undercoat film layer 3 formed on at least one of these chemical conversion film layers 2.

A top coat layer 4 is formed on the undercoat layer 3.

Hot-dip aluminized steel sheet used as a base plate for painting 1
The total amount of plating on both sides is 30-80g/M, the amount of Si in the plating layer is 6-9% by weight, and the thickness is 0.4-80g/M.
Preferably, the diameter is 1.6 mm.

The coated steel sheet of the present invention has chromate chemical conversion treatment film layers 2 formed on both surfaces of such a hot-dip aluminized steel sheet 1. This chemical conversion coating layer 2 is intended to improve the adhesion between the plating layer and the undercoat coating layer, and to enhance the corrosion resistance of the coated steel sheet. Formation of the chemical conversion coating layer 2 was carried out using a hot-dip aluminized steel sheet l whose surface had been cleaned.
This can be done by treatment with a chromate chemical conversion treatment solution. The chromate chemical conversion treatment liquid is preferably one based on chromic acid-phosphoric acid-(acidic) sodium fluoride, but other acidic chromate chemical conversion treatment liquids can be used.

Regardless of the treatment solution used, it is important to control the conditions so that the amount of chromium deposited in the chemical conversion film formed is 10 to 50 mg/nf (one side). If the amount of chromium deposited is substantially lower than 10 mg/rd, it is impossible to expect improvement in paint film adhesion and corrosion resistance. A tendency to swell and peel has been observed. Moreover, an unnecessarily excessive amount of chromium deposit increases the cost of the product. The hot-dip aluminum-plated steel sheet 1 taken out from the chemical conversion treatment solution is washed with hot water.

Squeeze with a roll and dry with hot air.

The coated steel sheet of the present invention is provided with an undercoat film consisting of a hardened polyamide-imide resin, a chromate rust-preventing pigment without crystal water, and graphite powder on at least one of the chromate chemical conversion treatment film layers 2 formed in this manner. It has layer 3. The undercoat film N3 is formed by applying an undercoat consisting of a polyamide-imide resin paint mixed with a chromate rust-preventing pigment and graphite powder that does not contain water of crystallization, and then applying 260
This can be done by baking at a temperature of ~320°C.

Chromate-based anticorrosive pigments that do not have water of crystallization suitable for use include strontium chromate, calcium chromate, barium chromate, barium potassium chromate, basic lead chromate and basic lead silichromate, with strontium chromate being preferred. . The amount of the chromate rust-preventing pigment that does not have crystal water in the undercoat paint is preferably 8 to 52 parts by weight per 100 parts by weight of the solid content of the polyamide-imide resin. Resin solid content 1
Using substantially less than 8 parts by weight of anticorrosion pigment per 100 parts by weight of the resin solids may fail to achieve sufficient corrosion resistance; The use of rust pigments not only makes the undercoat film layer 3 porous and deteriorates its physical properties, but also impairs the adhesion of the paint film, which in turn has the disadvantage of reducing the corrosion resistance of the product.

The graphite powder blended into the undercoat film layer 3 is 99.9%.
Those with the above-mentioned high purity and a very high degree of crystal orientation are preferable. The graphite powder used may be natural, but synthetic graphite is easier to control the particle size and is more cost-effective. The purpose of adding graphite powder is to make the undercoat film layer 3 electrically conductive. For this purpose, it is generally necessary to have at least 5 parts by weight of graphite powder present in the base coat layer 3 per 100 parts by weight of cured polyamideimide resin. That is, the amount of graphite powder blended into the undercoat needs to be 5 parts by weight or more per 100 parts by weight of resin solid content. However, resin solid content 100
The blending of graphite powder in an amount substantially exceeding 50 parts by weight should be avoided, since it makes the coating film porous, impairing its adhesion to the top coating film, and thus impairing its corrosion resistance.

Furthermore, for the purpose of the present invention, it is preferable to use graphite powder having an average particle size of 1/3 to 2/3 of the thickness of the undercoat film layer 3. If the graphite powder is unduly fine, the conductivity of the undercoat film and, by extension, the weldability of the coated steel sheet will be reduced, and if it is unduly coarse, the adhesion of the paint film will be poor. The thickness of the undercoat film layer 3 is determined from the viewpoint of adhesion with the topcoat film and corrosion resistance of the product.

The thickness is usually 3 to 8 μm.

In addition to the graphite powder, suitable amounts of a suitable metal powder, such as granular aluminum, may, if desired, be present in the base coat layer as an additional conductivity-imparting agent.

The coated steel sheet of the present invention has a top coat layer 4 made of a cured silicone-modified polyester resin having a degree of modification of 30 to 50% and granular aluminum powder on the undercoat layer 3 as described above. The top coat layer 4 can be formed by applying a top coat made of a silicone-modified polyester resin paint mixed with granular aluminum powder on the undercoat layer 3, and baking at a temperature of 220 to 260°C. .

The purpose of adding granular aluminum powder to the top coating layer 4 is to make the coating electrically conductive and to make the painted screen plate weldable. For this purpose, the aluminum powder used is preferably granular with an aspect ratio close to 1,
The blending amount needs to be 60 parts by weight or more per 100 parts by weight of the cured silicone-modified polyester resin. In other words, the blending of granular aluminum powder into the top coat paint is as follows.

The amount should be 60 parts by weight or more per 100 parts by weight of resin solid content.

However, blending of granular aluminum powder in an amount exceeding 150 parts by weight per 100 parts by weight of resin solid content should be avoided since it will make the coating film bolus and deteriorate corrosion resistance.

Further, for the purpose of the present invention, it is preferable to use granular aluminum powder having an average particle size of 1/3 to 2/3 of the thickness of the top coat layer 4. If the granular aluminum powder is unduly fine, the conductivity of the topcoat film and, by extension, the weldability of the coated steel sheet will be reduced, and if the granular aluminum powder is unduly coarse, the adhesion of the paint film will be poor. Note that the thickness of the top coat layer 4 is preferably 8 to 25 μm from the viewpoint of product design, corrosion resistance, and durability.
The thickness is usually 12 to 20 μm.

The unillustrated surface of the coated steel sheet according to the present invention shown in FIG. 1 is the surface that will be the outside of a member such as a muffler, and has only the chromate chemical conversion coating layer 2 formed on the surface of the hot-dip aluminum plated steel sheet.

Alternatively, one or two heat-resistant resin coatings may be formed on the chemical conversion coating layer 2. On both sides of the hot-dip aluminized steel plate 1.

Chemical conversion coating layer 2. FIG. 2 shows an example in which an undercoat film layer 3 and a topcoat film layer 4 are respectively formed. In the painted steel sheet of FIG. 2, the two base coat layers 3 and the two top coat layers 4 can each be identical to each other and can be formed at the same time. If you want to make the outer surface of a member such as a muffler black, form the undercoat film layer 3 as described above on both sides of a hot-dip aluminum plated steel sheet that has been subjected to chromate chemical conversion treatment, and then On one side of the undercoat film layer 3, a topcoat paint for forming a silver-colored topcoat film, which is a mixture of silicone-modified polyester resin paint and granular aluminum powder, is applied, and on the other basecoat film N3. A top coat of silicone-modified polyester resin paint mixed with granular aluminum powder and a heat-resistant black pigment is applied to form a blank-colored top coat, and these are simultaneously baked at a temperature of 220°C to 260°C. Thus, a painted steel plate according to the present invention having one side in silver color and the other side in black color can be obtained, and this can be formed into a member such as a muffler with the blank side facing outward.

The composition of a top coat suitable for forming a black top coat is a silicone-modified polyester resin paint with a degree of modification of 30 to 50%, and a resin solid content of 100 parts by weight and 20 to 100 parts by weight of granules. Aluminum powder and 5~
It may contain 20 parts by weight of a heat-resistant black pigment. Examples of heat-resistant black pigments include calcined black pigments, graphite, and the like. If desired, graphite powder may be added in addition to the heat-resistant black pigment. Graphite powder also contributes to the electrical conductivity of the top coat. If desired, a small amount (up to 5 parts by weight per 100 parts by weight of cured resin) of silica powder can be incorporated into the black topcoat layer as a quenching agent. Further, if desired, a piece of aluminum powder may be added to the silver topcoat layer as a reinforcing heat-resistant pigment in an amount of 20 parts by weight or less per 100 parts by weight of the cured resin.

Hereinafter, the present invention will be further explained with reference to specific examples.

Example Hot-dip aluminum plated steel plate (thickness 0.6 mm, width 250 mm, length 600 mm, coating weight 40 g/%
Both sides) were adjusted to a component concentration of 4% by weight [Ridorine 35N
- I J (alkaline degreasing liquid manufactured by Nippon Paint Co., Ltd.) after being immersed at 60°C for about 10 seconds, and then taken out from the liquid.

It was washed with hot water at about 70°C for about 10 seconds. Next, a mixture of "Allodin #407 J" adjusted to a component concentration of 4% by weight and "Allodin #47" adjusted to a component concentration of 0.6% by weight ([Allodin #407 J and "Allodin #47")
was immersed in Nippon Paint Co., Ltd.'s chromic acid-phosphoric acid-based acidic chromate chemical conversion treatment solution at 60°C for about 10 seconds, removed from the solution, washed with hot water at about 70°C for about 10 seconds, and rolled. It was squeezed and dried with hot air at about 100°C. In this way, chemical conversion coatings with a chromium adhesion amount of 25 mg/rIr (one side) were formed on both surfaces of the hot-dip aluminized steel sheet.

1 per 100 parts by weight of resin solids to a polyamide-imide resin paint (polyamide-imide resin varnish with an average molecular weight of about 4500, solid content 22% by weight in N-methylpyrrolidone).
0 parts by weight of strontium chromate and an average particle size of 2 μm
Alternatively, 6 μm highly oriented graphite powder (Graphite POG 2 or POG 10 manufactured by Kyowa Carbon Co., Ltd.) in the amount shown in Table 1 was added with stirring to prepare an undercoat paint. Each undercoat paint is applied to both sides of the chemical conversion treated hot-dip aluminum plated steel plate using a roll coating method,
Approximately 40 ℃ when the conveyor is open with a furnace atmosphere temperature of 280℃
It was baked for seconds to form an undercoat film layer with a dry film thickness of about 6 μm.

A silicone-modified polyester resin paint with a degree of modification of 40% (solid content: 50%) was added with granular aluminum powder (manufactured by thermal spraying, average particle size of approx. 20 μm) was added with stirring to create a silver top coat. Furthermore, 20% of a fired black pigment as a heat-resistant pigment is added to the silicone-modified polyester resin paint as a heat-resistant pigment per 100 parts by weight of resin solid content.
Parts by weight and amounts of highly oriented graphite powder (Graphai manufactured by Kyowa Carbon Co., Ltd.) shown in Table 1: POG 40.
(average particle size of approximately 20 μm) and granular aluminum powder in the amount shown in Table 1 (manufactured by thermal spraying method, average particle size of approximately 20 μm)
) was added with stirring to create a blank color topcoat paint.

A silver topcoat was applied on one side of the previously formed undercoat layer, and a black topcoat was applied on the other using a roll coating method, and the furnace atmosphere temperature was set at 230°C.
Baking for about 60 seconds in a conveyor oven at .degree. C. produced silver and black topcoat layers each having a dry coating thickness of about 20 .mu.m.

Regarding each side of the obtained double-sided coated steel plate.

Paint film adhesion, heat resistance, and corrosion resistance were tested in the following manner. Further, for each coated steel plate, weldability between silver surfaces and between a silver surface and a black surface was tested in the following manner.

(1), Paint film adhesion DuPont impact deformation (punch radius = 1/2 inch.

Dropping Ikg from a height of 50cm) test and 180 degree 2t or 4t (dropping 2 or 4 plates of the same thickness as the test piece)
After undergoing a bending test, the peeling state of the coating film was evaluated according to the following criteria.

A: No peeling of the paint film B: Slight peeling of the paint film C: Severe peeling of the paint film D = Significant peeling of the paint film (2), Weldability Model: NDN 25 Direct, manufactured by Dengensha Manufacturing Co., Ltd.
Using a spot welder, electrode: 4Iφ, pressure crab 200
The test was conducted under the following conditions: kg, current 77 kA, current application time: 10 cycles, and evaluation was made based on the primary criteria.

A: Sufficient nuggets were formed. B: Nuggets were formed. C: Current was applied, but nuggets were insufficiently formed. D = No current was applied at all. heated at a temperature of After being left in a constant temperature and humidity chamber at 20° C. and 60% RH for 24 hours, the adhesion of the coating film was examined by a cross-cut test in accordance with JIS-G 3312, and the heat resistance of the test piece was evaluated according to the following criteria.

A: No peeling of the paint film at all. B: Slight peeling of the paint film. C: Slight peeling of the paint film. D: Significant peeling of the paint film. (4). Corrosion resistance JIS-Z. 500 salt spray tests in accordance with 2371
Evaluation was performed based on the following 9 criteria.

A: No blistering of the paint film or occurrence of rust A゛: Very little blistering of the paint film or occurrence of rust B: Slight occurrence of blistering of the paint film or occurrence of rust C: Swelling of the paint film or occurrence of rust D= Significant paint film blistering and rust occurrence The results of the paint film adhesion, heat resistance, and corrosion resistance tests for the silver and black surfaces of each test piece are shown in Tables 1 and 2, respectively. show.

Further, Table 1 shows the weldability test results between the silver surface and the dirt floor and between the silver surface and the black surface of each test piece.

[Brief explanation of drawings]

The attached drawings are enlarged sectional views of a coated steel plate according to the present invention, with FIG. 1 showing a coated steel plate on one side, and FIG. 2 showing a coated steel plate on both sides. 1: Melt-dip aluminum plated steel sheet 2: Chromate chemical conversion treatment film layer 3: Undercoat film layer 4: Topcoat film layer

Claims (7)

[Claims] (1) A hot-dip aluminized steel sheet, a chromate chemical conversion coating layer formed on both surfaces thereof, and a hardened polyamide-imide resin formed on at least one of these chemical conversion coating layers, free of crystallization water. An undercoat film layer consisting of a chromate rust preventive pigment and graphite powder, and a hardened modification degree formed on the undercoat film layer of 3.
A weldable heat-resistant coated steel sheet comprising: a top coat layer comprising 0 to 50% silicone-modified polyester resin and granular aluminum powder; (2) The undercoat film layer has a thickness of 3 to 8 μm, a cured polyamide-imide resin, 8 to 52 parts by weight of a chromate rust-preventive pigment per 100 parts by weight of the resin, and 5 parts by weight per 100 parts by weight of the resin. ~50 parts by weight of graphite powder, and the particle size of the graphite powder is 1/1 of the thickness of the base coat layer.
The coated steel sheet according to claim 1, which has a hardness of 3 to 3/2. (3) A silicone-modified polyester resin with a top coat layer having a thickness of 8 to 25 μm and a cured degree of modification of 30 to 50%, and 60 to 15% per 100 parts by weight of the resin.
0 parts by weight of granular aluminum powder, and the particle size of the granular aluminum powder is 1/3 of the thickness of the top coat layer.
The coated steel plate according to claim 1 or 2, which has a coating ratio of 3/2 to 3/2. (4) A hot-dip aluminized steel sheet, a chromate chemical conversion coating layer formed on both sides of the steel sheet, a hardened polyamide-imide resin formed on the chemical conversion coating layer, and a chromate-based barrier that does not contain crystal water. An undercoat layer consisting of rust pigment and graphite powder, and a silver topcoat consisting of a cured silicone-modified polyester resin with a degree of modification of 30 to 50% and granular aluminum powder formed on one of the undercoat layers. a black topcoat layer formed on the coating layer and on the other of the undercoat coating layers, consisting of a cured silicone-modified polyester resin with a degree of modification of 30 to 50%, granular aluminum powder, and a heat-resistant black pigment; A weldable heat-resistant painted steel plate consisting of. (5) The undercoat film layer has a thickness of 3 to 8 μm, a cured polyamide-imide resin, 8 to 52 parts by weight of a chromate rust-preventing pigment per 100 parts by weight of the resin, and 5 parts by weight per 100 parts by weight of the resin. ~50 parts by weight of graphite powder, and the particle size of the graphite powder is 1/1 of the thickness of the base coat layer.
The coated steel plate according to claim 4, which has a coating ratio of 3 to 3/2. (6) A silicone-modified polyester resin with a silver color top coat layer having a thickness of 8 to 25 μm and a cured degree of modification of 30 to 50%, and 60 to 150 parts by weight of granular aluminum per 100 parts by weight of the resin. Consisting of powder,
The coated steel sheet according to claim 4 or 5, wherein the particle size of the granular aluminum powder is 1/3 to 3/2 of the thickness of the top coat layer. (7) A silicone-modified polyester resin with a black top coat layer having a thickness of 8 to 25 μm and a cured degree of modification of 30 to 50%, 20% per 100 parts by weight of the resin.
~100 parts by weight of granular aluminum powder and 5 to 20 parts by weight of a heat-resistant black pigment per 100 parts by weight of the resin, and the particle size of the granular aluminum powder is 1/3 to 3/2 of the thickness of the top coat layer. A painted steel board according to any one of claims 4 to 6.