JP2001038288A - Coated stainless steel panel excellent in non-self- adhesiveness and coating film adhesion - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance non-self-adhesiveness and coating film adhesion by forming a composite coating film compounded with an alkali silicate glass aq. soln., a filler and a tetrafluoro resin on a stainless steel panel having an electrolytically surface-roughened shape satisfying specific relation. SOLUTION: A composite coating film compounded with an alkali silicate glass aq. soln., a filler and a tetrafluoro resin is formed on a stainless steel panel having an electrolytically surface-roughened shape satisfying the relation of 1<=D<=5 and D/3<=H<=D/2 [wherein D is the mean diameter (μm) of the opening parts of pits and H is the mean depth (μm) of pits]. At this time, a composite paint prepared by compounding 10-60 pts.wt. of a particulate filler with a mean particle size of 0.05-5.0 μm and 10-70 pts.wt. of a tetrafluoro resin with 100 pts.wt. of the solid of an alkali silicate glass aq. soln. is applied to the stainless steel panel in a dry film thickness of 7-20 μm and baked at 350-400 deg.C.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coated stainless steel sheet having excellent non-adhesiveness and coating film adhesion, and a method for producing the same.

[0002]

2. Description of the Related Art Polyethersulfone resin (hereinafter, referred to as PES) and ethylene tetrafluoride resin (hereinafter, referred to as PTFE) are used as organic coating materials having non-adhesiveness and heat resistance.
And color pigments are used. However, PES of the heat-resistant paint resin has a softening point of about 200 ° C., so that when heated at a temperature higher than that, hardness cannot be obtained.
In addition, PTFE added to PES for the purpose of imparting non-adhesiveness has the property that food contaminants and the like hardly adhere and can easily be wiped off even if it adheres. Used for components. When a stainless steel plate is used as a base material, sufficient adhesion cannot be obtained with a fluorine-based organic paint. Therefore, a physical surface-roughening treatment such as sandblasting is performed to improve coating film adhesion.

[0003]

However, because of the organic coating material, the coating layer itself is soft, the hardness of the coating film is about F to H in pencil hardness, and the scratch resistance and the wear resistance cannot be satisfied. Although there is a roughening treatment by sandblasting or shot blasting as a means of improving coating adhesion, the former cannot obtain a fine rough surface that satisfies coating adhesion, and the latter does not provide mechanical impact when a thin gauge is used. Therefore, there is a problem that the steel sheet warps. There is also a method using chemical etching such as hydrofluoric nitric acid.However, it is difficult to form pits uniformly on the stainless steel plate surface, for example, because large pits are locally generated. No An object of the present invention is to solve these problems and to obtain a coated stainless steel sheet having excellent non-adhesiveness and coating film adhesion.

[0004]

SUMMARY OF THE INVENTION The present invention has been devised to solve such a problem, and has an average diameter D (μm) of an opening of a pit and an average depth H (μm) of a pit. Is coated on a stainless steel sheet having an electrolytically roughened surface that satisfies the relationship of the following formulas (1) and (2) with a composite coating film containing an aqueous alkali silicate glass solution, a filler and a fluorotetrafluoride resin. Form. 1 ≦ D ≦ 5 (1) D / 3 ≦ H ≦ D / 2 (2) As a composite paint, based on 100 parts by weight of the solid content of the aqueous alkali silicate glass solution Average particle size 0.05-5.
A mixture of 10 to 60 parts by weight of a 0 μm particulate filler and 10 to 70 parts by weight of a tetrafluorinated fluororesin is added to a stainless steel sheet having an electrolytically roughened shape and a dry film thickness of 7 to 20 parts.
It is applied to a thickness of μm and baked at an ambient temperature of 350 to 400 ° C.

[0005]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have studied a method for imparting non-adhesion without impairing the properties of an alkali silicate-based inorganic coating material such as high hardness, scratch resistance and heat resistance.
As a result, they have found that the above characteristics can be obtained by adding a tetrafluoride-based fluororesin to an aqueous solution of an alkali silicate glass in combination. Furthermore, by subjecting the surface of the base stainless steel plate to electrolytic surface roughening treatment, excellent coating film adhesion was obtained. Hereinafter, the present invention will be described in detail. The surface morphology of the stainless steel sheet subjected to electrolytic surface roughening is such that the average diameter D of the pit opening is 1 to 5 μm and the average depth H
Is in the range of D / 3 to D / 2, it has been found that this stainless steel sheet exhibits excellent coating film adhesion that can withstand processing. When the average diameter of the pit opening is less than 1 μm,
Since the depth of the pit boundary is small, the anchor effect of the coating film is weakened, and the composite coating film cannot be firmly fixed. Conversely, if the average diameter of the pit opening exceeds 5 μm, the adhesion of the processed portion will be reduced. This is considered to be due to the fact that as the diameter of the opening increases, the spread of pits is promoted during processing, and the anchor effect with the coating film is lost.

If the average depth H of the pits is less than D / 3, the anchor effect is not exhibited, and the adhesion to the coating film is reduced. Conversely, if the average depth H exceeds D / 2, there is no hindrance in characteristics, but it is theoretically unlikely to occur without cost merit. For this reason, the present invention defines the surface morphology of the stainless steel sheet before coating as in the above-described equations (1) and (2). FIG. 1 shows an appearance of an electro-roughened stainless steel sheet before coating according to the present invention observed by an electron microscope (SEM). (A) shows the surface morphology of the stainless steel plate, and (b) shows the state of the cross section of the stainless steel plate. From FIGS. 1A and 1B, it can be seen that fine pits are continuously formed on the surface of the stainless steel plate, and the boundary between adjacent pits is sharply cut. The average diameter D of the pit opening can be obtained from (a),
The pit depth H can be obtained from (b). Next, the conditions of the alternating electrolytic treatment for forming pits satisfying the expressions (1) and (2) will be described.

(Electrolyte) In the present invention, Fe³⁺Including ions
An aqueous ferric chloride solution is used. Fe in the pit³⁺O
H^-→ Fe (OH)_ThreePit inner wall by the reaction of Fe (O
H) _ThreeProtection and form new pits in flat areas
This is in order to use a mechanism that causes the user to make a call. Ferrite type
For stainless steel plates, Fe contained in the electrolyte³⁺ion
Adjust the ferric chloride concentration so that the concentration is 1 to 50 g / L.
It is preferable to adjust them. Fe³⁺Ion concentration is less than 1g / L
When full, the etching power decreases and the stainless steel
Pits near the shape of a semicircular hemisphere cannot be formed.
The anchor effect cannot be obtained. Conversely, Fe³⁺Ion concentration is 5
If it exceeds 0 g / L, the etching power becomes excessive,
No pits are formed because the entire surface is eroded by the entire melting type.
Not.

In an austenitic stainless steel sheet, the concentration of Fe ³⁺ ions contained in the electrolyte is 30 to 120 g / g.
It is preferable to adjust the ferric chloride concentration so as to be L. If the Fe ³⁺ ion concentration is less than 30 g / L, the etching power is reduced, and a pit having a shape close to an ideal semicircular sphere cannot be formed on the surface of the stainless steel plate, and a sufficient anchor effect cannot be obtained. Conversely, if the Fe ³⁺ ion concentration exceeds 120 g / L, the etching power becomes excessive, and the entire surface of the stainless steel is dissolved and eroded, so that no pits are formed.

(Anode electrolysis) The purpose of anodic electrolysis is as follows.
A pit is formed on the surface of a stainless steel plate.
Current density during anode electrolysis is 1.0 to 10.0 KA / m
It is preferred to be in the range of ² . When the anode current density is less than 1.0 KA / m ² , pits cannot be formed on the surface of the stainless steel sheet only by active dissolution. Conversely, when the anode current density exceeds 10.0 KA / m ² , the decomposition reaction to Cl ⁻ ions becomes remarkable, and the working efficiency and the environment deteriorate. The purpose of the (cathode electrolysis) cathode electrolysis of H ₂ generated in the stainless steel surface, thereby forming a protective film of Fe (OH) ₃ in the pit inner wall is to activate the pit non-occurrence portion. In a ferritic stainless steel sheet, the current density during cathode electrolysis is preferably in the range of 0.1 to 3.0 KA / m ² . 0.1K cathode current density
If it is less than A / m ² , it does not reach the value in the H ₂ generation region because it is lower than the limiting current density of the reduction reaction of Fe ^{3+ in} the electrolyte. Conversely, if the cathode current density exceeds 3.0 KA / m ² , excess H ₂ will be generated, and the protective film of Fe (OH) ₃ formed on the inner wall of the pit may be removed. In the austenitic stainless steel sheet, for the same reason, the current density at the time of cathode electrolysis is preferably in the range of 0.5 to 3.0 KA / m ² .

Next, the composition of the composite paint and the production conditions will be described. The aqueous alkali silicate glass solution is SiO ₂ :
23-37 wt%, Na ₂ O: as a main component 6-18% by weight. The particulate filler is added to prevent bubbling and pinhole-like defects after baking. In the baking step, the coating film is dried from the surface side, but in the case of a coating film using water as a solvent, water vapor tends to remain inside the coating film. This residual water vapor becomes bubbles, which causes foaming and pinhole-like defects. When the particulate filler is dispersed and mixed in the coating film, the water vapor remaining inside the coating film is easily radiated to the outside of the coating film along the filler particles, so that foaming and pinhole-like defects can be prevented. . The particulate filler that can be used in the present invention is not particularly limited as long as it is insoluble in an aqueous alkali silicate glass solution at room temperature, does not change its form such as melting or incineration at the baking temperature after coating, and can maintain its particle state.

For example, colloidal alumina, glass powder particles, metal-containing oxides (such as titanium oxide), borides and the like can be used. These particulate fillers can be used alone or as a mixture of two or more, and the average particle size of the particulate filler is preferably in the range of 0.05 to 5.0 μm.
When the average particle size of the particulate filler is less than 0.05 μm, the effect of adding the particles is not recognized. When the average particle size exceeds 5.0 μm, secondary aggregates are easily formed. Transferability to the metal plate during roll coating is poor.
The compounding amount of the particulate filler is in the range of 10 to 60 parts by weight, preferably 20 to 50 parts by weight, based on 100 parts by weight of the solid content of the aqueous alkali silicate glass solution. If the amount is less than 10 parts by weight, the effect of preventing foaming and pinhole-like defects is poor.
If the amount is more than 0 parts by weight, the dispersibility of the paint becomes poor, and the workability of the paint is affected. In addition, the amount of alkali silicate glass forming the composite film is insufficient, and the film strength and durability are reduced.

As the tetrafluorinated fluororesin, PTF
E, ethylene tetrafluoride-propylene hexafluoride copolymer resin (hereinafter, referred to as FEP), ethylene tetrafluoride-perfluoroalkyl vinyl ether copolymer resin (hereinafter, referred to as PFA), ethylene-tetrafluoroethylene copolymer resin ( Hereinafter, referred to as ETFE). The compounding amount of the tetrafluorinated fluororesin is 10% of the solid content of the aqueous alkali silicate glass solution.
10 to 70 parts by weight, preferably 20 to 70 parts by weight per 0 parts by weight
The ratio is 60 parts by weight. When the amount is less than 10 parts by weight, no improvement in non-adhesiveness is not recognized. When the amount is more than 70 parts by weight, the dispersibility of the coating material deteriorates and the coating becomes difficult. In addition, the hardness and heat resistance of the coating film decrease. The composite paint prepared as described above is applied to a metal plate by a known method such as spraying, roll coating, or gravure coating so that the dry film thickness becomes 7 to 20 μm. When the dry film thickness of the composite coating film is less than 7 μm, there is no concealing property, and the non-adhesiveness is inferior because a layer such as PTFE is not sufficiently formed. If the coating thickness exceeds 20 μm, not only is it difficult to apply a single coat, but also the adhesion and processability are reduced.
In the present invention, the production can be performed by one coating, so that the cost can be reduced.

The baking temperature after coating is a temperature higher than the melting point of the tetrafluorinated fluororesin. For example, since the melting point of PTFE is 327 ° C. and the melting points of other tetrafluorinated fluororesins are similar, baking is performed at an ambient temperature of 350 to 400 ° C. Color pigments are also added to the composite paint, but pigments that do not change color even at high temperatures, for example, a Cu—Fe—Mn-based composite oxide pigment can be used.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be described below in detail with reference to embodiments. Example 1 A SUS430 2B finishing material having a thickness of 0.5 mm was subjected to ordinary electrolytic degreasing and pickling, and subjected to electrolytic surface roughening treatment under various conditions, and then to a solid content of 100 parts by weight of an aqueous alkali silicate glass solution. On the other hand, a composite paint containing 40 parts by weight of a particulate filler (colloidal alumina) having an average particle diameter of 3 μm and 50 parts by weight of a PTFE resin was spray-coated so that the dry film thickness became 15 μm, and baked at 400 ° C. . The obtained test pieces were examined for coating film adhesion. The adhesion of the coating film was evaluated by sandwiching a plate of the same thickness as the test piece, bending it 180 degrees so that the painted surface became a convex portion, and observing the peeling state of the coating film on the processed convex portion with a 10 × microscope. Then, those with no peeling of the coating film were evaluated with ○, and those with remarkable peeling of the coating film were evaluated with x. In addition, as a comparative example, the same investigation was performed on a test piece in which the composite paint used in the present invention was applied to the 2B finishing material and the sandblasted material after the usual electrolytic degreasing and pickling treatment, but without performing the roughening treatment by alternating electrolysis. Was done.

Table 1 shows the conditions of the electrolytic surface roughening treatment and the evaluation results. The anode current density and the cathode current density described in the table indicate the maximum current density when a trapezoidal wave or a sine wave (AC wave) is used as an alternating power supply. The electrolyte is
A ferric chloride aqueous solution containing a liquid temperature of 30 ° C. and an Fe ³⁺ ion concentration of 30 g / L was used. As can be seen from the D value and the H value of the pit forms of the present invention examples (Nos. 1 to 10), there is a relationship of D / 3 ≦ H ≦ D / 2 between the average diameter D and the average depth H of the opening. It showed a semicircular sphere that was established, and it was confirmed that good adhesion was exhibited. On the other hand, Comparative Examples (Nos. 11 to 16) in which the surface roughening treatment was performed under non-specified electrolytic conditions and Comparative Examples (Nos. 17 to 18) in which the electrolytic surface roughening treatment was not performed had poor coating film adhesion. Was enough.

[0016]

[Table 1]

Example 2: SUS304 having a thickness of 0.6 mm
The 2B finishing material was subjected to ordinary electrolytic degreasing and pickling, and subjected to electrolytic surface roughening treatment under various conditions. Then, the same paint as in Example 1 was applied and the same property evaluation was performed. Note that the electrolytic solution has a liquid temperature of 5
An aqueous ferric chloride solution containing 0 g and an Fe ³⁺ ion concentration of 75 g / L was used. Table 2 shows the electrolytic surface roughening conditions and the evaluation results. The pit form of the present invention example (No. 19 to 28) is D
The average diameter D and the average depth H of the opening as can be seen from the values and H values.
And a semi-spherical shape satisfying the relationship of D / 3 ≦ H ≦ D / 2 was established, and it was confirmed that good adhesion was exhibited. On the other hand, a comparative example (N
o. Nos. 29 to 34), the coating film adhesion was insufficient.

[0018]

[Table 2]

Example 3 Electrolytic surface roughening conditions were changed for each type of stainless steel, and electrolytic surface roughening treatment was performed under constant conditions between the same steel types. SUS430 (plate thickness 0.5 mm, 2B finishing material) was subjected to ordinary electrolytic degreasing and pickling, and the invention sample No. The treatment was carried out under the electrolytic surface roughening conditions of No. 2. That is, when the liquid temperature is 30 ° C. and the Fe ³⁺
Using an aqueous ferric chloride solution containing an ion concentration of 30 g / L, the anode current density was 3.0 KA / m ² , the cathode current density was 1.5 KA / m ² , the alternating electrolysis cycle was 2.5 Hz, and the treatment time was 30 seconds. SUS304 (plate thickness: 0.6 mm, 2B finished material) was subjected to ordinary electrolytic degreasing / pickling, and the present invention sample No. The treatment was performed under the conditions of electrolytic surface roughening of 20. That is, the liquid temperature is 50 ° C.
Using an aqueous solution of ferric chloride containing a ³⁺ ion concentration of 75 g / L,
The anode current density was 3.0 KA / m ² , the cathode current density was 1.5 KA / m ² , the alternating electrolysis cycle was 2.5 Hz, and the processing time was 30 seconds.

SUS430 and SU subjected to electrolytic surface roughening
In S304, the composite paint shown in Table 3 is spray-coated,
Bake at 00 ° C. The properties of the obtained coated stainless steel sheet were evaluated by the following methods. (1) Contact Angle (Wettability) Using a FACE automatic contact angle meter CA-Z (manufactured by Kyowa Interface Science Co., Ltd.) in a constant temperature room at 20 ° C., the contact angle θ of the dropped pure water was measured. The measurement was performed seven times with one test piece, and the average value of five values excluding the maximum value and the minimum value was displayed. (2) Non-sticky contaminated liquid (sugar: egg: soy sauce = 1: 1: 1 by weight ratio)
5 ml of the dropped test piece was placed in an oven at 260 ° C.
After heating for 5 minutes, the test piece was taken out, and the ease of wiping off the contaminated liquid was observed and evaluated according to the following criteria. 5: No sticking 4: Can be removed by rubbing lightly 3: Can be removed by strongly rubbing 2: Can hardly be removed 1: Can not be removed at all

(3) Pencil hardness (coating film hardness) "JIS K5400 8.4.2 Pencil scratch value
In accordance with the "hand-drawing method", the coating film surface was scratched with a pencil of various hardness, and the limit pencil hardness at which the coating film was not scratched was determined. (4) Heat resistance With respect to the test pieces heated at 400 ° C. for 3 hours, changes in the surface state were visually observed, and those with no change were marked with “○”, those with slight discoloration were marked with “△”, and those with marked discoloration were marked. The evaluation was made with an X mark. Table 3 summarizes the results of the respective characteristic evaluations.

[0022]

[Table 3]

As is apparent from Table 3, Example No. 1 of the present invention in which a particulate filler and a PTFE resin were added in combination to an aqueous alkali silicate glass solution. All of Nos. 35 to 44 had a high contact angle of water of 115 to 128 degrees, had water repellency, and exhibited good non-adhesiveness. The hardness of the paint film is 7H in pencil hardness.
It was found that the heat resistance was good and the coating film properties were excellent. In contrast, Comparative Example No. containing no PTFE. Comparative Example N containing a small amount of PTFE 45 and PTFE
o. In the case of No. 46, the pencil hardness and the heat resistance were good, but the non-adhesiveness was poor. Conversely, Comparative Example No. In the case of No. 48, although good non-adhesiveness was shown, pencil hardness and heat resistance were slightly inferior. Further, even when the amount of PTFE was within the range of the present invention, the dry coating film thickness of Comparative Example No. 5 was as thin as 5 μm. In the case of No. 47, the non-adhesiveness was inferior. The commercially available organic non-adhesive coated steel sheet (Comparative Example No. 51)
In particular, the pencil hardness was inferior from F to H, and the discoloration of the surface was conspicuous in heat resistance. Comparative Example No. containing no particulate filler. In Comparative Example No. 49, appearance defects due to foaming and pinhole-like defects occurred after baking, and the average particle diameter was as large as 8 μm even when the amount of the particulate filler was within the range of the present invention. In No. 50, coating was impossible due to aggregation of the composite paint.

[0024]

As described above, the coated stainless steel sheet of the present invention has higher hardness, scratch resistance and anti-scratch property of the alkali silicate-based inorganic coating material than the conventional organic resin-based non-adhesive coating material. It has excellent non-adhesiveness while maintaining properties such as abrasion resistance and heat resistance, and can be suitably used for products used in a high-temperature environment such as a range top plate.

[Brief description of the drawings]

FIG. 1 is an appearance of an electro-roughened stainless steel sheet before painting according to the present invention [electron microscope (SEM) photograph]. (A) Surface morphology of electrolytically grained stainless steel sheet (b) Cross section of electrolytically grained stainless steel sheet

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI theme coat ゛ (Reference) B05D 7/24 302 B05D 7/24 302L B32B 15/08 102 B32B 15/08 102B 17/06 17/06 27 / 20 27/20 Z C09D 7/12 C09D 7/12 Z 127/12 127/12 C25F 3/06 C25F 3/06 // C09D 1/04 C09D 1/04 (72) Inventor Yasuji Maeda Ichikawa, Chiba 7th Takatani Shinmachi 1st day New Steel Works Co., Ltd. Painting & Composite Materials Research Dept. F-term (reference) 4D075 BB26Z BB63X BB93Z CA02 CA06 CA13 DA04 DB04 DC10 EB02 EB05 EB16 EC13 EC54 4F100 AA40B AB04A AK17B BA02 BA07 CA23B EH48 GB GB90 JJ03 JK12 JL11 YY00B 4J038 CD121 HA456 KA08 KA20 NA10 PC02

Claims (2)

[Claims] 1. A stainless steel having an electrolytically roughened shape in which the average diameter D (μm) of the pit opening and the average depth H (μm) of the pit satisfy the following formulas (1) and (2). A coated stainless steel sheet with excellent non-adhesion and coating adhesion, formed by forming a composite coating film containing an aqueous alkali silicate glass solution, a filler and a fluorotetrafluororesin on a steel plate. 1 ≦ D ≦ 5 (1) D / 3 ≦ H ≦ D / 2 (2) 2. A solid content of an aqueous alkali silicate glass solution of 10.
A composite paint comprising 10 to 60 parts by weight of a particulate filler having an average particle diameter of 0.05 to 5.0 μm and 10 to 70 parts by weight of a tetrafluorinated fluororesin, based on 0 parts by weight. Non-adhesiveness and coating adhesion, characterized in that it is applied to a stainless steel sheet having the above described electrolytically roughened shape so that the dry film thickness is 7 to 20 μm and baked at an ambient temperature of 350 to 400 ° C. Method for producing coated stainless steel sheet with excellent quality.