JP2001276731A - Heat resistant coated steel plate for high grade processing - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a silicone resin coated heat resistant steel plate excellent in processability for a coating film. SOLUTION: A rough surface side of the steel plate having, on at least one side thereof, a rough surface having a degree of surface roughness Ra of 0.3-2.0 μm and a 60 degree specular gloss of 70 or less is coated with a coating material wherein 50-120 pts.wt. isocyanate and epoxy resin, in total, is added to 100 pts.wt. monomethyl silicone resin and at a ratio of (weight of isocyanate per equivalent weight of isocyanate group)/(weight of epoxy resin per equivalent weight per equivalent weight of epoxy group)=0.5-3.0 in such a manner that the dry coating thickness becomes 2-20 μm, and the rough side surface of the steel plate is heated and dried.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applicable to applications requiring high workability and heat resistance, for example, cooking equipment (oven range, fish roaster, gas table stove, etc.), automobile exhaust system members. The present invention relates to a heat-resistant coated steel sheet for high working suitable for oil-burning heating equipment (combustion cylinder, hot air outlet, etc.).

[0002]

2. Description of the Related Art When a coated steel sheet is used for the above-mentioned applications, if the heat resistance of the coating film is 400 ° C. or higher and the workability is about 2 to 3 tons and it does not peel off by 180 ° bending,
Almost usable. However, even if a heat-resistant paint such as a polyethersulfone or silicone resin is applied to a heat-resistant steel sheet such as a stainless steel sheet or an Al-based plated steel sheet by an ordinary method of producing a precoat, the above-described coating method is applied. No film satisfying both the film heat resistance and the processability was obtained. For example, when a monomethylsilicone resin paint is applied to a 2B-finished stainless steel sheet, the heat resistance of the coating film is 400 ° C. or more, but the coating film is peeled off by a 180 ° bending process of about 10 t. As-plated molten Al-9
When the same coating was performed on a% Si alloy-plated steel sheet, the workability was slightly good but still insufficient. For this reason, when a silicone resin-based heat-resistant paint is used, it is the present situation that an unpainted steel sheet is processed into a product and then painted.

As a method for improving the workability of a heat-resistant steel sheet coated with a silicone resin-based paint, monomethylsilano-
There is a method of using a paint obtained by adding 10 to 50 parts by weight of an isocyanate and an epoxy resin to 100 parts by weight of a sol (Japanese Patent Application Laid-Open No. 8-245922). If this paint is applied to, for example, a 2B-finished stainless steel sheet or as-plated hot-dip Al-9% Si alloy-plated steel sheet, even if the workability of the coated steel sheet is 3 to 9 tons by 180 ° bending, the coating film does not peel off. However, this level of workability has not been able to withstand severe processing yet.

[0004]

SUMMARY OF THE INVENTION The present invention provides a heat-resistant coated steel sheet coated with a silicone resin-based paint that can withstand a 180-degree bending process of about 2 to 3 tons.

[0005]

The heat-resistant coated steel sheet of the present invention has a surface roughness Ra of 0.3 to 2.0 μm and a 60 ° mirror gloss of 70 or less. On the surface side, a total of 50 parts by weight of isocyanate and epoxy resin are added to 100 parts by weight of monomethyl silicone resin.
-120 parts by weight, and a paint added in a ratio of (weight of isocyanate per equivalent of isocyanate group) / (weight of epoxy resin per equivalent of epoxy group) = 0.5-3.0. It is characterized in that it is applied so as to have a thickness of 2 to 20 μm and then dried by heating.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have prepared a coated steel sheet containing 10 to 50 parts by weight of isocyanate and epoxy resin per 100 parts by weight of monomethylsilanol sol while maintaining the heat resistance of the coated steel sheet. Investigations on various methods for improving the workability revealed that the surface of the base steel sheet should be appropriately roughened and the amount of isocyanate and epoxy resin added to the paint should be increased. Here, "appropriately roughening the steel sheet surface" means that the surface roughness Ra (center line average roughness) is 0.3.
And 2.0 μm, and the 60-degree specular gloss in the specular gloss measurement method specified in JIS Z8741 is 7
0 or less.

[0007] The surface of the 2B-finished stainless steel sheet or the as-plated hot-dip Al-9% Si alloy-plated steel sheet has a continuous wave of waves with small steepness, so that the anchoring effect of the coating film is hardly obtained. The 60-degree specular gloss is usually 200 or more. However, the surface roughness Ra is 0.3 μm.
When it is at least m, an anchoring effect can be obtained, and the scratch resistance during processing and use can be improved. If the surface roughness Ra is too large, it becomes difficult to uniformly apply the paint on the surface, so that the surface roughness Ra is set to 2.0 μm or less. Surface roughness Ra
May be measured by a contact-type roughness meter, but when there is pitting of 1 μm or less such as a steel sheet whose surface is roughened by electrolytic etching, it is preferable to use a non-contact roughness meter.

By the way, the surface roughness Ra only indicates the size of the unevenness, but does not indicate the continuous state of the unevenness. For example, even if the surface roughness Ra is the same, the gloss of the flat portion P as shown in FIG. 1 is larger than that of the flat portion P as shown in FIG. It is necessary to manage some of P. That is, since the incident light is specularly reflected in the flat portion P and irregularly reflected in the uneven portion, the gloss increases as the number of the flat portions P increases. Also,
Even if the irregularities show a continuous state, the anchoring effect of the coating film cannot be sufficiently obtained when the period of each irregularity is large as shown in FIG. Even on such a surface, the ratio of regular reflection of incident light increases,
Gloss increases. Melt A temper-rolled by Darroll
In 1-9% Si alloy plated steel sheet, the surface roughness Ra is 1.
Although there are irregularities of about 0 to 1.5 μm, the 60-degree specular gloss is 90 or more. Therefore, if the gloss is controlled to be low, the anchoring effect can be increased. In the present invention, the gloss is set to 70 or less, preferably 50 or less, more preferably 10 or less as a 60-degree specular gloss.

As a method of setting the surface roughness Ra to 0.3 to 2.0 μm and the 60-degree specular gloss to 70 or less, a known method such as shot blasting and electrolytic etching may be used. For example, Transactions of the Insititu
AC etching in nitric acid or hydrochloric acid described in te of Metal Finishing 1979 Vol. 57, p138, and in the case of stainless steel plates, alternating electrolytic etching described in JP-A-8-259499 may be used.

The base steel sheet is desirably a heat-resistant stainless steel sheet, an Al-plated steel sheet, an Al-plated stainless steel sheet, and the like, and an appropriate steel type is selected according to the use and the working degree. When using an Al-based plated steel sheet for a long time with heating at 450 ° C or higher, the A
The alloy layer may grow to the surface by l-Fe interdiffusion, and the coating film may be peeled off. When used at such a high temperature, as described in JP-A-9-228018,
The N in the solid solution state in the steel suppresses the Al-Fe interdiffusion between the Al plating layer and the steel base, and reduces the alloying start temperature to 55.
A hot-dip Al-plated steel sheet raised to 0 ° C. may be used. In applying the silicone resin-based coating material, it is preferable to perform an appropriate pretreatment. For example, a stainless steel plate may be subjected to a pickling treatment after a degreasing treatment, and an aluminum-based plated steel plate may be subjected to a coating or reaction type chromate treatment, a phosphoric acid chromate treatment or the like after degreasing.

[0011] The coating of the silicone resin-based paint on the base steel sheet is based on 100 parts by weight of the monomethyl silicone resin.
Isocyanate and epoxy resin in total of 50 to 120
A paint is used in which parts by weight and (weight of isocyanate per equivalent of isocyanate group) / (weight of epoxy resin per equivalent of epoxy group) = 0.5 to 3.0 are added. Here, as the monomethyl silicone resin,
Monomethylsilanol sol (CH ₃ ) Si (—OH) ₂ —O — [(CH ₃ ) Si having many hydroxyl groups in the molecular chain
_{(-OH) -O-] n - (} OH-) 2 Si (CH 3) are preferred. This monomethylsilanol sol preferably has a molecular weight of about 5,000 to 20,000 in terms of polystyrene.
If the molecular weight is less than 5000, the film-forming property is poor and 1 μm
It is difficult to secure the above film thickness, and if it exceeds 20,000, the stability of the sol is poor, the coating material easily gels, and the formed film is not dense, so that the processing adhesion also decreases. Would.

When the silicone resin is a monomethylsilanol sol, isocyanate and an epoxy resin are added thereto, and the mixture is coated on a base steel plate and dried by heating at 150 to 280 ° C. to obtain a monomethylsilanol sol. The hydroxyl group and the isocyanate group and the epoxy group react with each other, and the hydroxyl group and the isocyanate group in the epoxy resin react to form a composite film having good adhesion to the base steel sheet and ductility. However, the isocyanate and the epoxy resin are added in a total amount of 50 to 120 parts by weight of the isocyanate and the epoxy resin with respect to 100 parts by weight of the monomethyl silicone resin (in the case of monomethylsilanol sol, the non-volatile content). Part. When the addition amount is less than 50 parts by weight, the processing adhesion does not improve, and when it exceeds 120 parts by weight, the amount of the organic component with respect to the inorganic component increases. The scratch resistance decreases. Further, cracks are remarkably generated due to shrinkage of the film accompanying the combustion of the organic resin component, and the film is peeled off.

The isocyanate and epoxy resin to be added are (weight of isocyanate per equivalent of isocyanate group) / (weight of epoxy resin per equivalent of epoxy group) = 0.5 to 3.0. I do. If it is less than 0.5, the proportion of isocyanate is low, so that not only the ductility of the film and the work adhesion are reduced, but also the proportion of the epoxy resin which is hard to be cured by heating increases, so that the coated steel sheet is wound around a coil. Blocking and pressure marks tend to occur when cutting or piling a cut plate, and the film is easily eluted only by rubbing with a cloth impregnated with alcohol or the like. On the other hand, if it is larger than 3.0, the effect of improving the adhesion to the base steel sheet by adding the epoxy resin does not appear.

Examples of isocyanates include hexamethylene diisocyanate (HDI), diphenylmethane diisocyanate (MDI), and tolylene diisocyanate (TDI).
DI), such as diisocyanate or polyisocyanate, or blocked isocyanate obtained by blocking isocyanate. However, in consideration of the stability of the paint at room temperature, isocyanate having high reactivity is used. Preference is given to blocked isocyanates having blocked groups.
Examples of the epoxy resin include a bisphenol type and a novolak phenol type.

The coating of the paint on the steel sheet is performed, for example, by spraying.
A known method such as a method, a roll coating method, or a bar coating method may be used. It is desirable that the coating amount is 2 to 20 μm in dry film thickness. If the thickness is less than 2 μm, the surface of the steel sheet is rough.
Unevenness cannot be covered, and it is difficult to apply uniformly.
On the other hand, if it exceeds 20 μm, a remarkable crack is generated in the processed portion, and the portion is separated. This coating amount is more desirably in the range of 3 to 10 μm in dry film thickness.

After application to the steel sheet, the steel sheet is heated so that the maximum temperature of the steel sheet is about 150 to 280 ° C. so that the resin film does not peel off or is damaged even when the steel sheet is processed. . When the heating is performed at a temperature lower than 150 ° C., a solvent remains in the film, and crosslinking of the resin becomes insufficient. Therefore, the processing adhesion decreases, and the film surface causes blocking during coil winding or piling of a cut plate. . On the other hand, when the temperature exceeds 280 ° C., the film becomes too dense, so that the processing adhesion decreases. In consideration of blocking and processing adhesion, the temperature is preferably set to 170 to 250 ° C. To reach this temperature, the steel sheet may be heated at a furnace temperature of 200 to 300 ° C. for 40 to 180 seconds.

The coating may contain additives such as pigments, catalysts, aggregates, rust-preventive pigments, etc. in order to improve or impart design properties, scratch resistance, coating strength, catalytic function, corrosion resistance, etc. is there. In that case, as the pigment, Mn, F
Examples thereof include oxides or composite oxides of e, Cr, Cu, Ti, and Al, and metal powders such as Al powders. Further, as the aggregate, potassium titanate fiber and the like can be mentioned. Further, examples of the rust preventive pigment include calcium molybdate which is a non-chromium compound (chromium-free) which is environmentally friendly. These additives may be added alone or in combination, but the amount of addition is 10 to 200 parts by weight based on 100 parts by weight of the total weight of the monomethyl silicone resin, isocyanate and epoxy resin. If it is less than 10 parts by weight, the effect of addition is small, and if it exceeds 200 parts by weight, the film becomes brittle and peels off during processing. It is preferable that the size be 0.1 to 20 μm in average particle size. If it is less than 0.1 μm, it is expensive to make fine particles, and if it exceeds 20 μm, it is difficult to disperse it in the film.

[0018]

EXAMPLE 1 A black pigment (MnCuCrO _x ) was added to 100 parts by weight of monomethylsilanol sol (solid content) having a molecular weight of 10,000.
After adding 100 parts by weight of a calcined pigment and 40 parts by weight of a rust preventive pigment (calcium molybdate), a block type isocyanate (hexamethylene diisocyanate,
Isocyanate weight per equivalent of isocyanate group;
650) and an epoxy resin (bisphenol A type, epoxy weight per equivalent of epoxy group; 170) were added at various ratios to prepare a heat-resistant paint. Next, the paint was degreased and pickled to obtain a SUS430 stainless steel plate (sheet thickness 0.4 mm, 2DR finish) having a surface roughness Ra of 0.81 and a 60-degree specular gloss of 52. It was applied by a method so that the thickness of the dried coating film became 6 μm, and was heated for 80 seconds so that the ultimate plate temperature reached 190 ° C. Then, the following test was performed on the obtained coated steel sheet. Table 1 shows the test results.

(1) Work adhesion test A test piece (size: 80 x 40 mm) is bent at 180 degrees (1 to 3 tons), and a cellophane tape is applied to the processed portion and then taped to be peeled off. The symbol ◎ indicates that no film peeling was observed, the symbol を indicates that the film peeled slightly, and the symbol X evaluated that the film peeled from the base steel sheet. (2) Scratch resistance test A test piece (dimension 50 × 50 mm) was heated in an oven at 400 ° C. for 30 minutes, and after cooling, a coating test with a pencil was carried out. Those with a pencil hardness of 2H or more were evaluated with the symbol ◎, those with H to F were evaluated with the symbol 、, and those with HB or less were evaluated with the symbol ×. (3) Blocking resistance test The test pieces (dimensions: 100 x 50 mm)
Apply a surface pressure of 30 kg / cm ² and place in a constant temperature room at 50 ° C.
After standing for 4 hours, the symbol ○ indicates that no blocking was observed, and the symbol X indicates that blocking was considerably observed.
Was evaluated.

[0020]

[Table 1] (Note 1) The organic resin in the added amount of the organic resin means isocyanate and epoxy resin. (Note 2) The mixing ratio of isocyanate / epoxy resin is (weight of isocyanate per equivalent of isocyanate group) /
(Weight of epoxy resin per equivalent of epoxy group). (Note 3) In Comparative Example 2, the addition amount of the organic resin was appropriate, but blocking occurred because the ratio of the epoxy resin to the isocyanate was large. (Note 4) In Comparative Example 3, since the amount of the organic resin added was small,
The remarkable peeling occurred in the film by high processing of 2t or less.

Example 2 In Example 1, the coating and drying conditions and the film thickness of the paint having the composition shown in Table 1 and No. 1 were changed. A blocking test was performed. Table 2 shows the test results.

[0022]

[Table 2] (Note) In Comparative Example 12, the steel sheet could not be uniformly coated.

Example 3 A stainless steel plate (plate thickness: 0.4 mm) or an Al-plated steel plate (plated coating weight: 60 g / m ² ) with different finishes and treatments was applied to paints having the composition No. 1 in Table 1 of Example 1. Barco
The coating was applied to a dry film thickness of 6 μm (constant) by a coating method, and heated at a maximum ultimate plate temperature of 190 ° C. for 80 seconds to cure the film. As a test, a processing adhesion test and a scratch resistance test of Tree Example 1 were performed. Table 3 shows the test results.

[0024]

[Table 3] (Note 1) A is a SUS430 stainless steel sheet, B is a SUS304 stainless steel sheet, and C is ordinary steel Al.
D is a SUS430Al-plated steel sheet. (Note 2) Abbreviations of finishing (processing) are as follows.
M: 2DR finish, N: nitric acid etching, O: alternating electrolytic etching, P: darroll finish, Q: BA finish,
R: 2B finish, S: No. 4 finish, T: 2D finish, U: Bright rolling finish (Note 3) Comparative Examples Nos. 21, 22, 25, 27, and 28 have small surface roughness Ra of the base steel sheet. Also, since the 60 degree gloss is 70 or more, neither the processing adhesion nor the scratch resistance is good. (Note 4) In the case of Comparative Examples Nos. 23, 24 and 29, the surface roughness Ra of the base steel sheet is sufficient and the processing adhesion is good, but the 60 ° gloss is high and the steel sheet surface has many flat portions. For,
The scratch resistance after heating is poor at that part.

[0025]

As described above, the heat-resistant coated steel sheet of the present invention exerts an anchoring effect on the resin film because the surface roughness Ra of the base steel sheet is 0.3 to 2.0 μm. Also, since the surface is a rough surface having a 60-degree specular gloss of 70 or less,
There are few flat parts, and the anchoring effect can be obtained over the entire surface. For this reason, the adhesiveness of the resin film is improved. In addition, the paint for forming the resin film is a total of 50 to 120 parts by weight of an isocyanate and an epoxy resin for enhancing adhesion, which are added to 100 parts by weight of monomethylsilicone resin in total, and
And (isocyanate per equivalent of isocyanate group)
(Weight of epoxy resin) / (weight of epoxy resin per equivalent of epoxy group) = 0.5 to 3.0, so that the coating film has high paint composition and high adhesion. For this reason, the coated steel sheet of the present invention can withstand a 180 ° bending process of about 2 to 3 tons due to the excellent anchoring effect of the base steel sheet and the improved adhesion of the film.

[Brief description of the drawings]

FIG. 1 is a schematic diagram showing high gloss surface roughness.

FIG. 2 is a schematic diagram showing low gloss surface roughness.

FIG. 3 is a schematic diagram showing a high gloss surface roughness.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification FI theme coat ゛ (Reference) C09D 183/04 C09D 183/04 (72) Inventor Masayoshi Tatana 5th Ishizu Nishimachi, Sakai City, Osaka Nisshin Steel Co., Ltd. (72) Keiji Izumi, Inventor Keiji Izumi, 5th Ishizu Nishimachi, Sakai City, Osaka Prefecture Nissin Steel Co., Ltd. Minoru Saito, 72 Inventor Minoru Ishizu Nishimachi, Sakai City, Osaka Prefecture 4D075 BB04X BB24Z BB66X BB91X CA13 DA06 DB02 DC13 DC38 EB33 EB38 EB42 EB56 4J038 DG161 DG162 DL031 DL032 NA11 NA12 NA14 PA19 PB06 PB07 PB09 PC02

Claims (1)

[Claims] 1. The method according to claim 1, wherein the surface roughness Ra is 0.3 to 2.0 μm.
A monomethyl silicone resin 1 is provided on the rough surface side of a steel plate having at least one rough surface having a 60-degree specular gloss of 70 or less.
50 to 120 parts by weight of the isocyanate and the epoxy resin in total with respect to 00 parts by weight, and (weight of isocyanate per equivalent of isocyanate group) / (weight of epoxy resin per equivalent of epoxy group) A heat-resistant coated steel sheet for high working, characterized in that a paint added at a ratio of 0.5) to 3.0 is applied so as to have a dry coating thickness of 2 to 20 μm, and dried by heating.