JPH0556267B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a weldable heat-resistant coated steel plate. In particular, the present invention has heat resistance, corrosion resistance, coating adhesion, and processability suitable for manufacturing parts that are subject to high-temperature oxidation and wet corrosion, such as parts for internal combustion engines, boilers, and heating equipment. , and additionally relates to weldable painted steel sheets. BACKGROUND ART Conventionally, for example, mufflers in exhaust systems of automobiles have been made of molded molten aluminum-plated steel sheets with excellent heat resistance and corrosion resistance. 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. exposed to a corrosive environment in which condensed water containing harmful substances condenses and evaporates. Therefore, a muffler simply formed from a molten aluminum-plated steel plate has the disadvantage that it corrodes in a short period of time and loses its function as a muffler. Therefore, depending on the type of muffler, an organic polymer coating film is formed on one side of a molten aluminum plated steel plate, and the coated steel plate is formed into a muffler so that the organic polymer coating film is on the inside of the muffler. was proposed. However, the painted hot-dip aluminum plated steel sheets that have been proposed so far have the disadvantage that the paint film has poor heat resistance, and the paint film partially peels off due to exhaust gas, causing corrosion from the peeled part. Since it has an insulating organic coating film, there was a problem in that direct spot welding could not be performed and series spot welding had to 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 demand, a double-sided coated hot-dip aluminum plated steel sheet was proposed in which conductive metal powder was placed on both coatings and one coating was black.
However, the double-sided coated hot-dip aluminum coated steel sheets that have been proposed so far contain conductive metal powder, so although they have sufficient weldability,
Because the heat resistance of the paint film is poor, the paint surface on the inside of the muffler will partially peel off due to exhaust gas, and corrosion will occur from the peeled part, and the black paint surface on the outside of the muffler will also partially peel off, causing problems with the design of the muffler. The disadvantage was that the sex was impaired. Another method for producing a 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 help it. Therefore, one of the main objects of the present invention is to provide a painted steel sheet that has superior heat resistance and corrosion resistance than conventional painted hot-dip aluminum coated steel sheets, and is also capable of direct spot welding. One particular object of the invention is to provide such a coated steel plate which is colored black on one side. Thus, the present invention provides a molten aluminum plated steel sheet, a chromate chemical conversion coating layer formed on both surfaces thereof, a hardened polyamide-imide resin formed on at least one of these chemical conversion coating layers, and crystal water. an undercoat layer consisting of a chromate-based rust-preventing pigment and graphite powder, and an overcoat layer formed on the undercoat layer consisting of a cured polyamide-imide resin and granular aluminum powder. The present invention provides a heat-resistant coated steel plate that can be welded. Furthermore, the present invention provides a molten aluminum plated steel sheet, a chromate chemical conversion coating layer formed on both surfaces of the steel sheet, a hardened polyamide-imide resin formed on the chemical conversion coating layer, and a chromate coating layer that does not have crystallization water. an undercoat film layer consisting of a rust-preventive pigment and graphite powder; a silver topcoat layer formed on one of the undercoat layers and consisting of a cured polyamide-imide resin and granular aluminum powder; To provide a weldable heat-resistant coated steel sheet comprising: a black top coat layer consisting of a hardened polyamide-imide resin, granular aluminum powder and a heat-resistant black pigment, formed on the other base coat layer. Referring to the attached drawings, the painted steel sheet of the present invention is
As shown in FIG. 1, a molten aluminum plated steel sheet 1, a chromate chemical conversion coating layer 2 formed on both surfaces thereof, and an undercoat coating layer formed on at least one of these chemical conversion coating layers 2. 3 and
A top coat layer 4 is formed on the undercoat layer 3. The molten aluminum plated steel plate 1 used as the original plate for painting has a total plating amount of 30 to 80 on both sides.
g/m ² , the amount of Si in the plating layer is 6 to 9% by weight, and the plate thickness is preferably 0.4 to 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 molten aluminum plated 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. The chemical conversion coating layer 2 can be formed by treating the surface-cleaned molten aluminum plated steel sheet 1 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 may be used. No matter what treatment solution is used, the amount of chromium deposited in the chemical conversion film formed will be
It is important to control various conditions so that the amount is 10 to 50 mg/m ² (one side). Chromium adhesion amount is 10mg/m ²
If it is substantially lower than 50 mg/m 2 , it is impossible to improve the adhesion and corrosion resistance of the paint film, and as the amount of chromium deposit exceeds 50 mg/m ² , the paint film may swell or peel due to the presence of moisture. A tendency towards Moreover, an unnecessarily excessive amount of chromium deposit increases the cost of the product. After washing the molten aluminum plated steel sheet 1 taken out from the chemical conversion treatment solution 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-preventive pigment without crystal water, and graphite powder on at least one of the chromate chemical conversion coating layers 2 formed in this manner. It has layer 3. Undercoat film layer 3
The formation of 260~
This can be done by baking at a temperature of 320℃. Chromate-based antirust 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 thread 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
Using substantially less than 8 parts by weight of anticorrosion pigment per 100 parts by weight may not result in sufficient corrosion resistance;
Use of an excessive amount of anti-corrosion pigment that substantially exceeds 52 parts by weight not only makes the undercoat film layer 3 porous and deteriorates its physical properties, but also deteriorates the adhesion of the paint film, which may actually reduce the corrosion resistance of the product. There is an inconvenience that lowers sex. 99.9% graphite powder is blended into the undercoat layer 3.
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 artificial graphite is easier to control 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, blending of graphite powder in an amount that substantially exceeds 50 parts by weight per 100 parts by weight of resin solids makes the coating film porous, impairing its adhesion with the topcoat film, and ultimately impairing its corrosion resistance, so it must be avoided. It won't happen. Further, 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, in turn, the weldability of the coated steel sheet will be reduced, and if it is unduly rough, the adhesion of the paint film will be poor. In addition, the thickness of the undercoat film layer 3 is 3 to 3 from the viewpoint of adhesion with the top coat film and corrosion resistance of the product.
The thickness is usually 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 hardened polyamide-imide resin and granular aluminum powder on the undercoat layer 3 as described above.
has. The top coat layer 4 can be formed by applying a top coat made of a polyamide-imide resin paint mixed with granular aluminum powder onto the undercoat layer 3, and baking at a temperature of 260 to 320°C. The purpose of adding granular aluminum powder to the top coating layer 4 is to make the coating conductive and to make the coated steel sheet weldable. For this purpose, the aluminum powder used is preferably granular with an aspect ratio close to 1, and the amount thereof needs to be 60 parts by weight or more per 100 parts by weight of the cured polyamide-imide resin. That is, the amount of granular aluminum powder added to the top coat is 60 parts by weight or more per 100 parts by weight of resin solid content. However,
Addition of more than 150 parts by weight of granular aluminum powder per 100 parts by weight of resin solids makes the coating film porous and deteriorates corrosion resistance, and must be avoided. 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 top coat
As a result, the weldability of the painted steel sheet deteriorates, and if it is unduly rough, the adhesion of the paint film will deteriorate. Note that the thickness of the top coat layer 4 is 8 to 25 μm, preferably 12 to 20 μm, from the viewpoint of product design, corrosion resistance, and durability.
It is normal to set it to m. 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 is a state in which only the chromate chemical conversion treatment film layer 2 is 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 molten aluminum plated steel plate 1,
FIG. 2 shows an example in which a chemical conversion coating layer 2, an undercoat coating layer 3, and a top coating coating layer 4 are 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. When it is desired to make the outer surface of a member such as a muffler black, the undercoat film layer 3 as described above is formed on both sides of the molten aluminum plated steel plate which has been subjected to chromate chemical conversion treatment, and On one of these undercoat film layers 3, a topcoat paint for forming a silver color topcoat film, which is made by blending granular aluminum powder with the polyamide-imide paint as described above, is applied. A top coat of polyamide-imide paint mixed with granular aluminum powder and a heat-resistant black pigment is applied to form a black top coat, and both are simultaneously heated at 260°C to 260°C.
By baking at a temperature of 320°C, a painted steel plate according to the present invention having one side silver colored and the other side black colored is obtained, and this is applied to a member such as a muffler with the black side facing outward. Just mold it. The composition of a top coat suitable for forming a black top coat is a polyamide-imide resin paint, 3 to 100 parts by weight of granular aluminum powder, and 5 to 20 parts by weight of heat-resistant aluminum powder per 100 parts by weight of resin solids. It may contain a black pigment.
Examples of heat-resistant black pigments include fired 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 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 matting agent. Further, if desired, scaly aluminum powder may be added to the silver top coat layer as a reinforcing heat-resistant pigment in an amount of, for example, 20 parts by weight or less per 100 parts by weight of the cured resin. Hereinafter, the present invention will be further explained by giving specific examples. Example Molten aluminum plated steel plate (thickness 0.6mm, width
250mm, length 600mm, plating amount 40g/m ² sides)
``Ridrin 35N-'', which has an ingredient concentration of 4% by weight.
1" (an alkaline degreasing liquid manufactured by Nippon Paint Co., Ltd.) at 60°C for about 10 seconds, it was taken out from the liquid and washed with hot water at about 70°C for about 10 seconds. Next, a mixture of "Alodine #407" adjusted to a component concentration of 4% by weight and "Alodine #47" adjusted to a component concentration of 0.6% by weight ("Alodine #407" and "Alodine #47" are manufactured by Nippon Paint Co., Ltd. 60% in chromate-phosphoric acid-based acid chromate chemical conversion treatment solution)
After soaking for about 10 seconds at
It was washed with hot water at about 100°C for about 10 seconds, squeezed with a roll, and dried with hot air at about 100°C. In this way,
A chemical conversion coating with a chromium adhesion amount of 25 mg/m ² (one side) was formed on both surfaces of a molten aluminum plated steel sheet. Polyamide-imide resin paint (average molecular weight approximately 4500
Polyamideimide resin varnish (solid content in N-methylpyrrolidone: 22% by weight), 10 parts by weight of strontium chromate per 100 parts by weight of resin solids, and highly oriented graphite powder with an average particle size of 2 μm or 6 μm (Kyowa Carbon Co., Ltd.) Graphite POG
2 or the amounts shown in Table 1 of POG 10) were added with stirring to prepare an undercoat paint. Each undercoat paint is applied to both sides of the above-mentioned chemical conversion-treated molten aluminum plated steel plate using the roll coating method, and baked in a conveyor oven with an internal furnace atmosphere temperature of 280°C for about 40 seconds to form a dry coating film with a thickness of about 6 μm. A membrane layer was formed. The resin solid content is added to the polyamide-imide paint mentioned above.
The amount of granular aluminum powder shown in Table 1 per 100 parts by weight (manufactured by thermal spraying, average particle size of approx.
20 μm) was added with stirring to create a silver-colored top coat. Furthermore, per 100 parts by weight of resin solid content, 20 parts by weight of fired black pigment as a heat-resistant pigment and highly oriented graphite powder (Graphite manufactured by Kyowa Carbon Co., Ltd.: POG 40) in the amount shown in Table 1 were added to the above polyamide-imide paint. , average particle size about 20μ
m) and the amount of granular aluminum powder (manufactured by thermal spraying, average particle size: about 20 μm) shown in Table 1 were added with stirring to prepare a black top coat. A silver top coat is applied on one side of the previously formed undercoat layer, and a black top coat is applied on the other using a roll coating method. 60
Baked for seconds, the dry coating thickness is approximately
A 20 μm silver and black top coat layer was formed. Each side of the obtained double-sided coated steel plate was tested for coating film adhesion, heat resistance, and corrosion resistance in the following manner. In addition, each coated steel plate was tested for weldability between silver surfaces and between a silver surface and a black surface in the manner described below. (1) Paint film adhesion Dupont impact deformation (punch radius = 1/2 inch,
1Kg dropped from a height of 50cm) test and 180 degrees
After being subjected to a 2t or 4t (two or four plates of the same thickness as the test piece) bending test, the peeling state of the coating film was evaluated using 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 Direct spot of model: NDN 25 manufactured by Dengensha Manufacturing Co., Ltd. Using a welding machine, electrode: 4mmφ,
Tests were conducted under the conditions of pressurizing force: 200 kg, current: 7 kA, and energization time: 10 cycles, and evaluations were made based on the following criteria. A: Sufficient nuggets are formed B: Nuggets are formed C: Current is applied, but nuggets are insufficiently formed D: No current is applied at all (3) Heat resistance Temperature indicated for the time indicated in a hot air circulation dryer heated to. 24 in a constant temperature and humidity room at 20℃ and 6%RH
After standing for a period of time, 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 A': Very slight 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 (4) Corrosion resistance JIS-Z 500 salt spray tests according to 2371
The tests were carried out for several hours and evaluated using the following 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 blistering of the paint film and occurrence of rust 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. Also,
Table 1 shows the weldability test results between the silver surfaces and between the silver surface and the black surface of each test piece.

【table】

【table】 [Brief explanation of the drawing]

The accompanying drawings are enlarged cross-sectional views of painted steel plates according to the present invention, with FIG. 1 showing one coated on one side and FIG. 2 showing one coated on both sides. 1: Molten aluminum plated steel sheet, 2: Chromate chemical conversion coating layer, 3: Undercoat coating layer, 4: Top coating coating layer.

Claims (1)

[Scope of Claims] 1. A molten aluminum plated steel sheet, chromate chemical conversion coating layers formed on both surfaces thereof, and a hardened polyamide-imide resin and crystals formed on at least one of these chemical conversion coating layers. Consisting of an undercoat layer consisting of a water-free chromate rust preventive pigment and graphite powder, and an overcoat layer formed on the undercoat layer consisting of a hardened polyamide-imide resin and granular aluminum powder. Weldable heat-resistant painted steel plate. 2. The undercoat film layer has a thickness of 3 to 8 μm, and contains a cured polyamide-imide resin, 8 to 52 parts by weight of a chromate-based rust preventive pigment per 100 parts by weight of the resin, and 5 to 50 parts by weight per 100 parts by weight of the resin. 2. The coated steel sheet according to claim 1, wherein the coated steel sheet is made of graphite powder of 30% or less, and the particle size of the graphite powder is 1/3 to 3/2 of the thickness of the undercoat layer. 3 The top coat layer has a thickness of 8 to 25 μm, and a cured polyamide-imide resin and the resin 100
60 to 150 parts by weight of granular aluminum powder, and the particle size of the granular aluminum powder is 1/3 to 3/2 of the thickness of the top coat layer. Painted steel plate as described in section. 4. A molten aluminum plated steel sheet, a chromate chemical conversion coating layer formed on both sides thereof, a hardened polyamide-imide resin formed on the chemical conversion coating layer, and a chromate-based rust-preventing pigment that does not have crystal water. and a silver topcoat layer consisting of a cured polyamide-imide resin and granular aluminum powder formed on one of the undercoat layers; A weldable heat-resistant coated steel sheet comprising: a black topcoat film layer formed on the other film layer of a hardened polyamide-imide resin, granular aluminum powder, and a heat-resistant black pigment; 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-based rust preventive pigment per 100 parts by weight of the resin, and 5 to 50 parts by weight per 100 parts by weight of the resin. 5. The coated steel sheet according to claim 4, wherein the coated steel sheet is made of graphite powder of 50% or less, and the particle size of the graphite powder is 1/3 to 3/2 of the thickness of the undercoat layer. 6. The silver color topcoat layer has a thickness of 8 to 25 μm and is composed of a cured polyamide-imide resin and 60 to 150 parts by weight of granular aluminum powder per 100 parts by weight of the resin, and the particle size of the granular aluminum powder is The coated steel sheet according to claim 4 or 5, which has a thickness of 1/3 to 3/2 of the thickness of the top coat layer. 7. The black topcoat layer has a thickness of 8 to 25 μm, and contains a cured polyamideimide resin, 3 to 100 parts by weight of granular aluminum powder per 100 parts by weight of the resin, and 5 to 20 parts by weight per 100 parts by weight of the resin.
Part by weight of heat-resistant black pigment, and the particle size of the granular aluminum powder is 1/1 of the thickness of the top coat layer.
The coated steel plate according to any one of claims 4 to 6, which has a thickness of 3 to 3/2.