JPS637878A - Precoated steel plate having conductivity - Google Patents

Abstract

PURPOSE:To prevent blocking and to enhance corrosion resistance and conductivity, by applying paint imparting a specific range of a dry film thickness with respect to center line average roughness (Ra) to a steel plate having a specific range of center line average roughness (Ra). CONSTITUTION:In manufacturing a precoated steel plate having electromagnetic shield effect coming to the outer panel of electronic machinery of OA machinery, desired chemical forming treatment is applied to a steel plate to provide surface soughness wherein center line average roughness (hereinafter referred to as Ra) is 0.01-2.0mum. When painting is applied to said steel plate using solvent type paint so that the dry film thickness of the paint comes to 18-110% of Ra of the steel plate, the protruded parts on the surface of the steel plate are partially exposed because of the thin film formed to improve conductivity and, since the recessed parts of said steel plate are covered with the paint, the surface thereof becomes smooth not only to prevent blocking but also to achieve the enhancement of corrosion resistance.

Description

[Detailed Description of the Invention] [Field of Industrial Application] The present invention is a pre-painted steel sheet mainly used for outer panels of electrical/electronic equipment and OA equipment, and eliminates blocking during piling (cutting) or coiling. It also relates to a pre-coated steel sheet that has corrosion resistance, electrical conductivity, and electromagnetic cross-fertilization and shielding effects. [Prior art and problems to be solved by the invention] In recent years,
The problem is that electromagnetic waves generated from electrical/electronic equipment, OA equipment, etc. cause malfunctions or noise in other electrical/electronic equipment, OA equipment, etc. (This phenomenon is called electromagnetic interference, hereinafter abbreviated as EMI). It becomes. This problem can be prevented by covering the entire device with a conductive material and grounding it, but in recent years, plastics, an insulating material, and pre-painted steel sheets with an insulating coating on the front and back are often used as materials for device casings. As a result, demand for countermeasures against EMI problems is increasing.

Regarding plastics, EMI countermeasures include metal spraying, metal vapor deposition, and coating the plastic surface with conductive substances such as paint mixed with conductive pigments (for example, Japanese Patent Laid-Open No. 59
-107938), or mixing a conductive substance into plastics (for example, JP-A-59-102953)
), but all of them have drawbacks such as insufficient conductivity, technical difficulties, and high cost.

For pre-coated steel sheets, there are no specific methods proposed as EMI countermeasures, and countermeasures include leaving one side of the steel sheet untreated or only chemically treated, or scraping off a portion of the coating. In this method, there is a problem of reduced corrosion resistance of the exposed part of the steel sheet.In particular, in the method in which one side is left untreated or chemically treated only, the surface of the steel sheet or the chemically treated surface is damaged during piling (cutting) or coiling. There is a problem of plotting that damages the decorative (painted) surface. Furthermore, the method of partially scraping off the coating film also has the disadvantage of increasing the number of production steps.

Although the purpose is different, a method of applying a paint mixed with metal powder to the steel plate has been proposed as a method of imparting conductivity to the pre-coated steel plate (for example, Japanese Patent Laid-Open No. 1898-1898)
43) However, like the method in which one side is left untreated or treated only with chemical conversion treatment, this method also has the problem of protrusions of metal powder mixed in during piling or coiling, as well as the problem of protrusions caused by EMI countermeasures. The conductivity is insufficient for use.

[Means for solving problems]

The present invention provides a pre-coated steel sheet that is free from blocking during piling or coiling as described above and has good corrosion resistance and electrical conductivity, and its gist is as follows: 1. Surface roughness is center line average roughness (Ra) of 0.01
~2.0 μm steel plate, apply paint at a ratio of 10 to Ra of the steel plate.
A pre-coated steel sheet having conductivity characterized by being coated with a dry film thickness of ~110%, and 2. having conductivity as described in item 1 above, characterized in that the paint is solvent-based. Pre-painted steel plate, and 3. The pre-coated steel sheet having electrical conductivity as described in item 1 above is characterized in that a chemical conversion treatment is applied between the steel sheet and the coating film. ? Examples of the steel sheet of the invention include cold-rolled steel sheet, hot-dip galvanized steel sheet, electrogalvanized steel sheet, alloy-plated steel sheet, stainless steel, electrolytic chromic acid treated steel sheet (TFS), and the like. If the Ra of the steel plate is outside the range of 0.01 to 2.0 μm, adjust it to within the range by skin pass or the like.

Corrosion resistance of steel sheets is improved by chemical conversion treatment such as chromate-based, zinc phosphate-based, iron phosphate-based, etc., so it is more preferable to perform such chemical conversion treatment. In addition, chromate-based chemical conversion treatment provides a smoother surface finish compared to zinc phosphate-based and iron phosphate-based chemical conversion treatments, so the coating film on the decorative surface will be smoother.
If the surface has high gloss and is prone to blocking, chromate-based materials are more useful for improving blocking resistance than zinc phosphate-based or iron phosphate-based materials. In this case as well, the Ra of the steel sheet is reduced to 0.01 to 2.0 by means such as crystal grain refinement.
It is processed so that it becomes 0 μm.

The steel plate used in the present invention has an Ra of 0.01 to 2.0 μm. If the Ra of the steel plate is 2.0 μm or more, the unevenness on the surface of the steel plate is too large, making it difficult to obtain good blocking properties with a thin film of the level of the present invention, and if the Ra of the steel plate is 0.01 μm or less, the thin film of the level of the present invention cannot be achieved. However, sufficient conductivity cannot be obtained. However, if the coating film on the decorative surface has a high surface gloss and is prone to blocking, the Ra of the steel plate should be 0.01 to 0.
．． 5 μm is more preferable.

Ra of the steel plate in the present invention is measured according to JIS B 0601.

The paint used for painting is preferably a solvent-based paint.

If a water-based paint is used, under the drying conditions during the production of pre-coated steel sheets (board temperature reaches 200-230°C in around 60 seconds), the surface finish will become rough due to intense water evaporation during drying, which is a unique phenomenon of water-based paints. This is because it will be in a state of

Pre-coated steel sheets, which are generally used for the outer panels of electrical/electronic equipment and OA equipment, are designed to withstand severe processing, so a soft paint with relatively low hardness is used for the coating on the decorative side. Therefore, if the surface of the paint film on the back side becomes rough and eroded, stacking them by piling or coiling and leaving them for a long time will cause a phenomenon in which the rough surface of the back side is transferred to the front surface, so-called plotting. That's what I do.

The type of resin is not particularly limited, but examples include melamine/alkyd type, polyester type, fluorine type, acrylic type, silicone/polyester type, and epoxy type.

The paint may contain additives such as anti-rust pigments, other pigments, or lubricants, if necessary. The average particle size of pigments and other additives is preferably 1 μm or less. If the average particle size becomes too large, blocking may occur. Examples of antirust pigments include chromium-based and strontium-based pigments, and other pigments include yellow iron oxide, red iron oxide, phthalocyanine blue, carbon black, and titanium oxide. Examples of the lubricant include polyethylene.

In particular, if the paint film on the decorative side has a high surface gloss and is prone to blocking, it is preferable to use a clear paint that does not contain pigments on the back side because the surface will be smooth. You can choose as appropriate.

In the present invention, the dry film thickness of the paint is set to lθ to 110 of the Ra of the steel plate.
%. This is because if it is less than 10%, the problem of blocking cannot be solved and the corrosion resistance will be insufficient, and if it is more than 110%, the conductivity will be insufficient. (Function) In the present invention, blocking is prevented by coating a steel plate with a dry film thickness of 10 to 110% of Ra on a steel plate with an Ra of 1 to 2, θ μm, and further corrosion resistance and conductivity are improved. This also results in better performance.

That is, by forming a thin film in this range, a portion of the convex portion on the surface of the steel sheet is exposed, and this exposed portion conducts electricity, so it is thought that the conductivity is improved. In addition, since the recesses are covered with paint, the surface becomes quite smooth, and even when piled up by piling or coiling, the paint film has a buffering effect, so it is difficult to coat untreated steel sheets or steel sheets that have only been chemically treated. It does not damage the cosmetic surface, and its durability is also improved.

(Example〕 Examples will be described below along with comparative examples.

Example 1 A chromate-based chemical conversion treatment was applied to a hot-dip galvanized steel sheet with a zinc coating amount of 120 g/rr' so that the chromium amount was 30 mg/rrt'. This was coated using a roll coating method using a solvent-based polyester paint whose solid content was arbitrarily adjusted within the range of 1 to 20%.

Ra of hot-dip galvanized steel sheet is 0.2μm, 0.4μm
, 0.7 μm. Five types were used: 1.1 μm Et and 2.3 μm (comparative example).

Figure 1 shows the conductivity measurement results when the paint film thickness was varied under these conditions, Figure 2 shows the blocking test results, and Figure 3 shows the corrosion resistance test results. The method for measuring Ra of the steel plate was in accordance with JIS B 0801.

The coating film thickness was measured by gravimetric method. Conductivity measurement is the fourth
This was done using the method shown in the figure. For the blocking property test, the test piece prepared by the above method and the decorative surface are stacked facing each other.
After applying a load of 100 kg/cm' and leaving it in an atmosphere at 70° C. for 1 hour, the unevenness of gloss that occurred on the decorative surface was evaluated. The decorative surfaces were a solvent-based polyester silver metallic painted surface (60 degrees specular gloss 50%, dry film thickness 20 μm) created using a roll coater, and a solvent-based polyester black painted surface (60 degrees specular gloss 70%). , dry film thickness 18 μm) was used. The blocking property was evaluated as follows.

○ No uneven gloss is observed.

Δ It can be used practically depending on the application, but there may be slight unevenness in gloss.

× Significant uneven gloss is observed.

Corrosion resistance was tested according to JIS Z 2371 by evaluating the incidence of white rust on the surface after a 192-hour salt spray test, and the evaluation was as follows. 0 The incidence of white rust is less than 10% O~△ The incidence of white rust is 10% or more and less than 33%△
Incidence rate of white rust is 33% or more and less than 50% Δ~× Incidence rate of white rust is 50% or more and less than 70%× Incidence rate of white rust is 70% or more Example 2 Melting amount of zinc deposit xa3g/go Galvanized steel sheet (Ra
O. 7 μm) with chromate-based chemical conversion treatment with a chromium content of 40
It was applied at a concentration of mg/m'. This is coated with a solvent-based acrylic clear paint using a roll coating method to achieve a dry film thickness of 0.
．． It was coated to a thickness of 5 μm. Comparative Example 1 10% by weight of nickel-based conductive powder (particle size 15 μm) was added to a steel plate that had undergone the chemical conversion treatment under the same conditions as Example 2.
The mixed solvent-based acrylic paint was applied by roll coating so that the dry film thickness was 3 μm.

Comparative Example 2 10% by weight of carbon-based tetraelectric powder (particle size 0.1 μm) was added to a steel plate that had undergone the chemical conversion treatment process under the same conditions as Example 2.
The mixed solvent-based acrylic paint was applied by roll coating so that the dry film thickness was 3 μm.

Example 3 A water-based acrylic clear paint was applied to a steel plate that had undergone the chemical conversion treatment under the same conditions as in Example 2 using a roll coating method so that the dry film thickness was 0.5 μm.

Table 1 shows the conductivity measurement results, blocking properties, and corrosion resistance test results of Example 2, Comparative Example 1, Comparative Example 2, and Example 3. The test conditions, evaluation method, and measurement method were the same as in Example 1.

Example 3 The amount of zinc deposited. Hot-dip galvanized steel sheets with various Ra values of t2og/m" were continuously subjected to chemical conversion treatment and painting using continuous coil coating equipment, and then wound into coils. Chromate-based materials were used for the chemical conversion treatment. use,
The coating was applied so that the amount of chromium was 30 mg/m. One side is coated with solvent-based melamine/alkyd clear paint with varying film thickness, and the other side is a decorative surface with solvent-based polyester silver metallic color paint (60 degree specular gloss 50%, dry film thickness 20 μm). ), brown metallic paint (60 degree specular gloss 50%, dry film thickness 18 μm)
, white paint (60 degree specular gloss 70%, dry film thickness 20μ
m) was arbitrarily selected from the three types and used.

Table 2 shows the measurement results of the Ra of the steel plate, the dry film thickness of the melamine/alkyd clear paint, the conductivity, and the test results of blocking and corrosion resistance.

The Ra of the steel plate, the dry film thickness of the paint, the method for measuring conductivity, and the test method for corrosion resistance were conducted in the same manner as in Example 1. Blocking properties are determined by leaving the wound coil for a week and then unwinding it.
The uneven gloss that occurred on the decorative surface was evaluated. The evaluation method was the same as in Example 1. Example 4 Hot-dip galvanized steel sheet (Ra
0.8 μm), chromate-based (chromium adhesion amount: 30 mg/rr1'') and zinc phosphate-based (adhesion amount: 0.8 μm) were used as chemical conversion treatments.
2g/rn'), iron phosphate type (adhesion amount 0.2g/m')
) and samples without chemical conversion treatment were prepared. Each of these was coated with a solvent-based melamine/alkyd paint to a thickness of 0.4 μffI'EL and 0.8 μm using a roll coater.

Table 3 shows the conductivity measurement results, blocking and corrosion resistance test results.

The measurement method and experimental method were the same as in Example 1.

〔Effect of the invention〕

As described above, according to the present invention, it is possible to provide a pre-coated steel sheet that eliminates blocking during piling or coiling, has corrosion resistance, conductivity, and has electromagnetic bonding and shielding effects, and its effects are significant. It is what it is.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between the ratio of film thickness to Ra and conductivity of the steel plate in Example 1. FIG. 2 is a graph showing the relationship between the ratio of film thickness to Ra and blocking property of the steel plate in Example 1. FIG. 3 is a graph showing the relationship between the ratio of film thickness to Ra and corrosion resistance of the steel plate in Example 1. FIG. 4 is an explanatory diagram showing a method for measuring conductivity. 1...4-terminal microresistance meter (measuring range 1 mΩ to 100
Ω full scale) 2, 3...Contact piece with integrated current terminal and voltage terminal 4...
Load (IQOg) 5... Paint film (However, if chemical conversion treatment has been applied, there may be a multilayer film of two or more layers including chemical conversion treatment under the coating film) 6... Steel plate 'fflo sagi... )''C>Mother; Curvature Figure 4 M Ding-lu Procedural Amendment Document 1988-B Month-No-Otsu Date of 1986 Patent Case No. 7ζOξFuri No. 3. Person making the amendment Relationship with the case Applicant 4. Agent address: 3308 Marunouchi Yaesu Building, 2-6-2 Marunouchi, Chiyoda-ku, Tokyo. Details of the amendment: As shown in the attached document, we amend the following paragraph in the specification of the application. 2. Correct "Figure 1" to "Figure 3" in the drawings as shown in the attached sheet. 1. Name of the invention Pre-coated steel plate with electrical conductivity 2. Claim 1 Surface roughness is 0.01 to 2 in center line average roughness (Ra)
．． On a 0 μm steel plate, apply paint at a ratio of 18 to 1 relative to the Ra of the steel plate.
A conductive pre-coated steel sheet characterized by being coated with a dry film thickness of 10%. 2. The precoated steel sheet having electrical conductivity as set forth in claim 1, wherein the paint is solvent-based. The precoated steel sheet having electrical conductivity according to claim 1, characterized in that a chemical conversion treatment is applied between the 3TL4 sheet and the coating film. 3. Detailed Description of the Invention [Field of Industrial Application] The present invention is a pre-coated steel sheet mainly used for outer panels of electric/electronic equipment and OA equipment, which eliminates blocking during piling (cutting) or coiling, and has corrosion resistance. -Relates to pre-coated steel sheets that are conductive and have electromagnetic cross-over and shielding effects. [Prior art and problems to be solved by the invention] In recent years,
The problem is that electromagnetic waves generated from electrical/electronic equipment, OA equipment, etc. cause malfunctions or noise in other electrical/electronic equipment, OA equipment, etc. (this phenomenon is called electromagnetic interference, hereinafter abbreviated as EMI). It becomes. This problem can be prevented by covering the entire device with conductive material and grounding it, but in recent years, the material for the housing of devices is often plastic, which is an insulating substance, or pre-coated steel sheets with an insulating coating on the front and back. As EMI is being used more and more, there is an increasing demand for countermeasures against EMI problems. Regarding plastics, EMI countermeasures include metal spraying, metal vapor deposition, coating the plastic surface with conductive materials such as paint mixed with conductive pigments (for example, Japanese Patent Laid-Open No. 59
-207938), or mixing conductive substances into plastics (for example, Japanese Patent Application Laid-Open No. 59-102953)
), but all of them have drawbacks such as insufficient conductivity, technical difficulties, and high cost. For pre-coated steel sheets, there are no specific methods proposed as EMI countermeasures, and countermeasures include leaving one side of the steel sheet untreated or only chemically treated, or scraping off a portion of the coating. In this method, there is a problem of reduced corrosion resistance of the exposed part of the steel sheet.In particular, in the method in which one side is left untreated or chemically treated only, the surface of the steel sheet or the chemically treated surface is damaged during piling (cutting) or coiling. There is a problem of plotting that damages the decorative (painted) surface. Furthermore, the method of partially scraping off the coating film also has the disadvantage of increasing the number of production steps. Although the purpose is different, a method of applying a paint mixed with metal powder to the steel plate has been proposed as a method of imparting conductivity to the pre-coated steel plate (for example, Japanese Patent Application Laid-Open No. 1898-1891).
843) However, like the method in which one side is left untreated or chemically treated, this method also has the problem of blocking caused by the protrusions of the metal powder mixed in during piling or coiling, as well as EMI countermeasures. The conductivity is insufficient for use. (Means for Solving the Problems) The present invention provides a pre-coated steel sheet that is free from blocking during piling or coiling as described above and has good corrosion resistance and conductivity, and its gist is as follows: ．． Surface roughness is center line average roughness (Ra) of 0.01
A conductive material characterized by coating a paint on a steel plate of ~2.0 μm, preferably 0.2 to 1.5 μm, to a dry film thickness of 18 to 110% of the Ra of the steel plate, preferably 30 to 90*. 2. 3. The conductive pre-coated steel sheet according to item 1 above, wherein the paint is solvent-based; The first method is characterized in that a chemical conversion treatment is applied between the steel plate and the coating film.
The pre-painted steel sheet has electrical conductivity as described in 2. Examples of the steel sheet of the present invention include cold-rolled steel sheet, hot-dip galvanized steel sheet, electrogalvanized steel sheet, alloy-plated steel sheet, stainless steel, electrolytic chromic acid treated steel sheet (TFS), and the like. If the Ra of the steel plate is outside the range of 0.01 to 2.0 μm, adjust it to within the range by skin pass etc. Corrosion resistance of steel sheets is improved by chemical conversion treatment such as chromate-based, zinc phosphate-based, iron phosphate-based, etc., so it is more preferable to perform such chemical conversion treatment. In addition, chromate-based chemical conversion treatment provides a smoother surface finish compared to zinc phosphate-based and iron phosphate-based chemical conversion treatments, so the coating film on the decorative surface will be smoother.
If the surface has high gloss and is prone to blocking, chromate-based materials are more useful for improving blocking resistance than zinc phosphate-based or iron phosphate-based materials. In this case as well, the Ra of the steel sheet is reduced to 0.01 to 2.0 by means such as crystal grain refinement.
It is processed so that it becomes 0μ1. The steel plate used in the present invention has an Ra of 0.01 to 2.0 μm. If the Ra of the steel plate is 2.0 μm or more, the unevenness on the surface of the steel plate is too large, making it difficult to improve blocking properties with a thin film of the level of the present invention, and if the Ra of the steel plate is 0.01 μm or less, the thin film of the level of the present invention cannot be achieved. However, sufficient conductivity cannot be obtained. Generally R
More preferably, a is 0.2 to 1.5 μm. However, if the decorative coating film has a high surface gloss and is prone to blocking, the Ra of the steel plate should be 0. Ol～0
．． 5 μm is more preferable. Ra of the steel plate in the present invention is measured according to JIS B 0801. The paint used for painting is preferably solvent-based. If a water-based paint is used, under the drying conditions during the production of pre-coated steel sheets (the board temperature reaches 200-230°C in around 60 seconds), the surface finish will deteriorate due to the intense evaporation of water during drying, which is a unique phenomenon of water-based paints. This is because it will be in a rough state. Pre-coated steel sheets, which are generally used for the outer panels of electrical/electronic equipment and OA equipment, are designed to withstand severe processing, so a soft paint with relatively low hardness is used for the coating on the decorative side. Therefore, if the coating surface on the back side is rough, stacking them by piling or coiling and leaving them for a long time will cause the rough skin on the back side to be transferred to the front surface, which is called plotting. . The type of resin is not particularly limited, but examples include melamine/alkyd type, polyester type, fluorine type, acrylic type, silicone/polyester type, and epoxy type. The paint may contain additives such as anti-corrosion pigments, other pigments, and lubricants as necessary. The average particle size of pigments and other additives is II. tm or less is preferable. If the average particle size becomes too large, blocking may occur. Examples of antirust pigments include chromium-based pigments, and other pigments include yellow iron oxide, red iron oxide, phthalocyanine blue, carbon black, and titanium oxide. Examples of the lubricant include polyethylene. In particular, if the paint film on the decorative side has a high surface gloss and is prone to blocking, it is preferable to use a clear paint that does not contain pigments on the back side because the surface will be smooth. Just choose as appropriate. In the present invention, the dry film thickness of the paint is 18 to 110 of the Ra of the steel plate.
%. If it is less than 18%, the blocking problem cannot be solved and the corrosion resistance will be insufficient, and if it is more than 110%, the conductivity will be insufficient. The dry film thickness of the paint is more preferably in the range of 30 to 90% of the steel plate Ra. [Function] In the present invention, RaO. By coating a steel plate with a dry film thickness of 18 to 110% of Ra on a steel plate having a thickness of 1 to 2.0 μm, blocking can be prevented and corrosion resistance and conductivity can also be improved. In other words, by forming a thin film in this range, some of the convex parts on the surface of the steel sheet are exposed, and this exposed part conducts electricity, so it is thought that the conductivity is good. In addition, since the recesses are covered with paint, the surface becomes quite smooth, and even when piled up by piling or coiling, the paint film has a buffering effect, so it is difficult to coat untreated steel sheets or steel sheets that have only been chemically treated. It does not damage the decorative surface and also improves corrosion resistance. [Example] Examples will be described below along with comparative examples. Example 1 A chromate-based chemical conversion treatment was applied to a hot-dip galvanized steel sheet with a zinc coating amount of 120 g/rn' so that the chromium amount was 30 mg/rn'. This was coated using a roll coating method using a solvent-based polyester paint whose solid content was arbitrarily adjusted within the range of 1 to 20%. Ra of hot-dip galvanized steel sheet is 0.2μm, 0.4μm
, 0.7 μm, 1.1 μm . 1.5 μrn, 2.
Seven types were used: 0 μm and 2.3 μm (comparative example). Figure 1 shows the conductivity measurement results when the paint film thickness was varied under these conditions, Figure 2 shows the blowing test results, and Figure 3 shows the corrosion resistance test results. The method for measuring Ra of the steel plate was in accordance with JIS B 0601. The coating thickness was measured using the gravimetric method. The conductivity was measured using the method shown in Figure 4. In the blocking property test, the test pieces prepared by the above method and the decorative surface were stacked facing each other, a load of 100 kg/crn' was applied, and the unevenness of gloss that occurred on the decorative surface was checked after leaving them in an atmosphere at 70°C for 1 hour. evaluated. The decorative surface is a solvent-based polyester silver metallic painted surface (80
degree specular gloss 50%, dry film thickness 20μll), and solvent-based polyester black painted surface (60 degree specular gloss 70%).
%, dry film thickness 18 μm). The blocking property was evaluated as follows. O: No uneven gloss is observed. Δ It can be used for practical purposes depending on the application, but slight unevenness in gloss is observed. × Significant uneven gloss is observed. The corrosion resistance test was conducted according to JIS Z 2371, and was evaluated based on the incidence of white rust generated on the surface after a 192-hour salt spray test, and the evaluation was as follows. ○ Occurrence rate of white rust is less than 10% O ~ Δ Occurrence rate of white rust is 10% or more and less than 33% Δ
The incidence of white rust is 33% or more and less than 50% Δ~× The incidence of white rust is 50% or more and less than 70%× The incidence of white rust is 70% or more Hot dip galvanized steel sheet (R
a O. 7 μm) was coated with a chromate-based chemical conversion treatment so that the amount of chromium was 40 mg/rri”.A solvent-based acrylic clear paint was applied to this using a roll coat method so that the dry film thickness was 0.5 μm. Comparative Example 1 10% by weight of nickel-based conductive powder (particle size 15 μm) was applied to a steel plate that had undergone the chemical conversion treatment under the same conditions as Example 2.
The mixed solvent-based acrylic paint was applied by roll coating to a dry film thickness of 3 μm. Comparative Example 2 10% by weight of carbon-based conductive powder (particle size 0.1 μm) was added to a steel plate that had undergone the chemical conversion treatment under the same conditions as Example 2.
The mixed solvent-based acrylic paint was applied by roll coating so that the dry film thickness was 3 μm. Example 3 A water-based acrylic clear paint was applied to a steel plate that had undergone the chemical conversion treatment under the same conditions as in Example 2 using a roll coating method so that the dry film thickness was 0.5 μm. Table 1 shows the conductivity measurement results, blocking properties, and corrosion resistance test results of Example 2, Comparative Example 1, Comparative Example 2, and Example 3. The test conditions, evaluation method, and measurement method were the same as in Example 1. Example 4 Hot-dip galvanized steel sheets with a uniform zinc coating amount of 120 g/m' and various Ra values were continuously subjected to chemical conversion treatment and painting in a continuous coil coating facility, and then wound into a coil shape. Chromate-based products are used for chemical conversion treatment,
The coating was done so that the amount of chromium was 3 (IB/m').On one side, a solvent-based melamine/alkyd clear paint was applied with varying film thickness, and on the other side, a solvent-based polyester silver/silver paint was applied as a decorative surface. Metallic color paint (6 (1 degree specular gloss 50%, dry film thickness 20 μm), brown metallic color paint (60 degree specular gloss 50%, dry film thickness 18 μm)
a+), 3f of white paint (60 degree specular gloss 70%, dry film thickness 20 μm)! were arbitrarily selected and used. Table 2 shows the measurement results of the Ra of the steel plate, the dry film thickness of the melamine/alkyd clear paint, the conductivity, and the test results of blocking and corrosion resistance. The Ra of the steel plate, the dry film thickness of the paint, the method of measuring conductivity, and the method of testing corrosion resistance were the same as in Example 1. Blocking properties are determined by leaving the wound coil for a week and then unwinding it.
The uneven gloss that occurred on the decorative surface was evaluated. The evaluation method was the same as in Example 1. Example 5 Zinc adhesion amount 120g/rr? hot-dip galvanized steel sheet (R
a O. 8μm) as a chemical conversion treatment: chromate-based (chromium adhesion amount: 30mg/m'), zinc phosphate-based (adhesion amount: 0)
．． 2g/rn'') and samples without chemical conversion treatment were prepared.These were coated with solvent-based melamine/alkyd paints of 0.4μm and 0.8μm, respectively.
It was coated with a roll coater in an amount of μl. Table 3 shows the conductivity measurement results, blocking and corrosion resistance test results. The measurement method and experimental method were the same as in Example 1. Example 6 Cold-rolled steel sheets (Ra 0.4 μm) were treated with chromate-based (chromium deposition amount: 30 mg/m'), iron phosphate-based (chromium deposition amount: 0.2 g/d) as chemical conversion treatments, and .
A sample was prepared without chemical conversion treatment. These were coated with solvent-based melamine/alkyd paint to a thickness of 0.2 μm and 0.4 μm using a roll coater, respectively. Table 4 shows the conductivity measurement results, blocking and corrosion resistance test results. The method for measuring conductivity and the experimental method for blocking are shown in Example 1.
I did the same thing. Corrosion resistance was evaluated by the incidence of rust on the surface after being left for 100 hours in an atmosphere with a temperature of 49±1° C. and a humidity of 95 or higher. O Rust occurrence rate is less than 10%O~△ Rust occurrence rate is 10% or more and less than 33%△ Rust occurrence rate is 33% or more and less than 50%Δ~× Rust occurrence rate is 50% or more~70 Less than %x Rust occurrence rate is 70% or more Example 7 As a steel plate. 55! kA1-Zn plating (plating amount: 244 g/m2), Fe-Zn plating (plating amount: 90 g/m2), electrolytic galvanizing (zinc coating amount: 40 g/m2)
g/m2), stainless steel (StlS 304)
, and electrolytic chromic acid treated steel sheets (TFS), and one coated with chromate-based chemical conversion treatment so that the amount of chromium was 30 B/m2 and one without coated steel were prepared. For those that have undergone chemical conversion treatment,
Furthermore, a solvent-based polyester paint was applied using a roll coating method. Table 5 shows the conductivity measurement results, blocking, and corrosion resistance test results. The method for measuring conductivity and the experimental method for blocking are shown in Example 1.
I did the same thing. The corrosion resistance test was conducted in the same manner as in Example 1 (
(according to JIS Z 2371), and was evaluated based on the incidence of rust on the surface. The judgment was as follows. ○ Rust occurrence rate is less than 10% Q~Δ Rust occurrence rate is 10% or more and less than 33% △ Rust occurrence rate is 33% or more and less than 50% Δ~× Rust occurrence rate is 50% or more ~ 70 Less than % It is possible to provide a pre-coated steel sheet with a cross-shielding effect, and the effect is excellent. 4. BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a graph showing the relationship between the ratio of film thickness to Ra and conductivity of a steel plate in Example 1. FIG. 2 is a graph showing the relationship between the ratio of film thickness to Ra and blocking property of the steel plate in Example 1. FIG. 3 is a graph showing the relationship between the ratio of film thickness to Ra and corrosion resistance of the steel plate in Example 1. FIG. 4 is an explanatory diagram showing a method for measuring conductivity. 1...4-terminal microresistance meter (measuring range 1 mΩ to 100
Ω full scale) 2, 3...Contact piece with integrated current terminal and voltage terminal 4...
Load (100g) 5... Paint film (However, if chemical conversion treatment has been applied, there may be a multilayer film of two or more layers including chemical conversion treatment under the coating film) 6... Steel plate

Claims (1)

[Scope of Claims] 1. A paint is applied to a steel plate having a surface roughness of 0.01 to 2.0 μm in center line average roughness (Ra) to a dry film thickness of 18 to 110% of the Ra of the steel plate. A pre-coated steel sheet having electrical conductivity. 2. The precoated steel sheet having electrical conductivity as set forth in claim 1, wherein the paint is solvent-based. 3. The precoated steel sheet having electrical conductivity according to claim 1, wherein a chemical conversion treatment is applied between the steel sheet and the coating film.