JPH04367767A - Mat black surface-treated steel plate - Google Patents

Abstract

PURPOSE:To improve glossiness and processability while keeping blackness by applying a black inorg. film layer and a Cr hydrated oxide film layer to a Zn type alloy plated steel plate and further forming a thin water-soluble resin coating layer wherein carbon black, colloidal silica and silica white are respectively dispersed in a resin in specific amounts. CONSTITUTION:After a black inorg. film layer (b) and a Cr hydrated oxide film layer (c) are applied to a Zn type alloy plated steel plate (a), a water-soluble or dispersible resin film layer (d) with thickness of 2-3mum wherein 5-10% of silica white being a matting agent is dispersed in a resin composition (e.g. olefin/acrylic resin emulsion) prepared by dispersing 35-45 pts. of carbon black being fine black particles and 30-40 pts. of colloidal silica being a film reinforcing agent in 100 pts. of a resin is formed to said film (c). As a result, a precoat steel plate having the same blackness and matting effect as a conventional post-coat steel plate wherein black electrodeposition painting and mat painting are applied to a steel plate and excellent in the substrate concealability and weldability of a processing part can be prepared.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention is applicable to home appliances, OA equipment,
The present invention relates to a matte black surface-treated steel sheet used for automotive interior parts, building materials, etc., which are designed to give an image of texture and luxury.

0002

[Prior Art] Low cost, high performance, and excellent appearance and quality are used in home appliances, OA equipment, automobile interior parts, etc.
There has been a consistent demand for steel plates used in furniture, construction, etc. In recent years, there has been a strong demand for low-cost steel sheets with low light reflectance for use in light-shielding frames of optical systems, especially as seen in internal parts of optical equipment such as copying machines. In particular, there is a strong desire for a matte black coated steel sheet that is black in color, has a luxurious feel and texture, and has an anti-glare effect. Up until now, cold-rolled steel sheets have been press-formed, then a black electrodeposition coating of approximately 20 μm is applied, and then a 10-20 μm matte coating is applied on top of this, resulting in a two-coat post coat. Conventional manufacturing methods like this require too many steps, resulting in excessive costs.
There were many problems such as the long processing time required.

[0003] In contrast, pretreatment performed by the consumer,
In recent years, there has been a growing movement towards pre-coated steel sheets, which can omit the painting process and produce products with a quality equal to or better than conventional post-coated products at a lower cost. The specific quality level is glossiness (generally expressed as G value) from 1 to 5, blackness (generally expressed as L value) of 20 or less, good appearance uniformity, pencil hardness of 2H or more, etc. In addition to the quality of conventional post-coating, there is no discoloration of the coating during press processing.
No whitening phenomenon was observed in the processed part during 90° bending.

[0004] Various pre-coated steel plates for omitting painting have been put into practical use, one of which is disclosed in Japanese Patent Application Laid-open No. 2-78.
No. 540 discloses a black surface-treated steel sheet, but the G value is as high as 20 to 28, and even under the lowest gloss treatment conditions, the G value is 7, which does not meet the required level, and A slight whitening phenomenon was also observed in the 90° bent portion, and neither of these cases could reach the level required by customers for use in light-shielding frames for optical systems.

[0005]

[Problems to be Solved by the Invention] As mentioned above, inorganic black surface-treated steel sheets have been put into practical use, and the demand for them is increasing. However, when used as internal parts of optical equipment, the following further improvements are required in terms of performance. In other words, (1) to be used in the light-shielding frame of an optical system and to have an anti-glare effect, the G value must be 1-5;
It is necessary that no discoloration (whitening phenomenon) of the coating film be observed in the bent (R=0) processed part.

[0006] The black surface-treated steel sheet disclosed in JP-A-2-78540 has a stable color tone and a uniform appearance, so it is widely used in home appliances, OA equipment, furniture, etc. ing. However, as described above, this technology has not yet been able to satisfy both the G value and workability when used for internal parts of optical equipment.

Accordingly, the present invention provides a matte black surface-treated steel sheet that has improved G value and workability while maintaining L value and appearance uniformity.

[0008]

[Means for Solving the Problems] The matte black surface-treated steel sheet of the present invention is as follows.

[0009] A black inorganic film layer and a chromium hydrated oxide film layer are formed on a Zn-based alloy plated steel sheet, and 35 to 45 parts of carbon black and 30 to 40 parts of colloidal silica are dispersed in 100 parts of resin. For the resin composition that
A matte black surface-treated steel sheet further comprising a water-soluble or water-dispersible resin coating layer having a thickness of 2 to 3 μm and containing 5 to 10% of silica white dispersed therein.

0010

[Operation] A schematic diagram of the coating structure of the matte black surface-treated steel sheet of the present invention is shown in FIG. In the figure, a is a Zn-based alloy plated steel sheet, b is a black inorganic film, c is a chromate film, and d is a resin film in which black fine particles, a matting agent, etc. are dispersed.

[0011] Normally, in order to obtain a matte black appearance, it is necessary to apply a two-coat coating in which a black coating is applied and then an additional matte coating, and that the coating film is thick. A thin film of 2 to 3 μm, which is the goal of inorganic black steel sheets, is extremely difficult to achieve in terms of the degree of coloring and uniformity. In thick films, the characteristics of the organic resin itself govern the product performance, so desired characteristics such as weldability, scratch resistance, fingerprint resistance, etc. deteriorate. By setting the thickness of the organic resin to 3 μm or less, excellent properties can be obtained due to the combined effect with the inorganic film including the underlying plating. The present invention solves the conventional problems by forming a black organic resin d containing a matting agent after applying a black inorganic film b on the lower layer and a chromate film c on the upper layer.

The key point of the present invention lies in the resin film d shown in the schematic diagram. In other words, silica white is dispersed in this resin film to lower the G value, colloidal silica is dispersed to improve the film strength, and carbon black is dispersed to improve the ability to hide the base of the processed area. Although it is a thin coating film, it has improved G value and workability while maintaining L value and appearance uniformity.

[0013] In general, it is a known technique for matting paints to use extender pigments such as calcium carbonate, mica, aluminum silicate, talc, white silica, or organic polyethylene powder as matting agents. Additionally, in order to improve the film strength of organic resins, composite polymers made by combining inorganic and organic compounds are generally used, but the compounds to be combined include fine oxide sols such as silica, titania, alumina, and zirconia. , inorganic compounds of phosphates, borates, and chromates, fatty acid soaps, fatty acid esters, organic compounds of plastic particles, silane coupling agents,
There are organometallic compounds such as titanium coupling agents. The black fine particles added to improve the base hiding property include carbon black and Fe, Co, Ni, Cu, Mn.
, Mo, Ag, Sn, etc., oxides, sulfides, carbides, and black metal fine powder. As a result of various studies in the present invention, in order to achieve a balance of performance such as gloss and film strength, and to achieve the purpose of a matte black steel sheet, silica white was used as a matting agent, and colloidal as a composite polymer compound was found. It has been found that silica and carbon black are the most effective as black fine particles. There are appropriate particle diameters and amounts for each additive, which will be discussed later.

[0014] Methods for coating with organic resin include coating with a roll coater, coating with a roll squeezer after spray coating, and baking, but the present invention does not particularly limit the coating method. According to the studies conducted by the present inventors, coating using a roll coater can easily ensure uniformity of the film, and can be proposed as the most preferable method.

[0015] Details of each film will be described below.

The base metal of the present invention is a Zn-based alloy plated steel plate. Zn-based alloy plated steel sheet is made of Fe, Ni, C
This is an alloy plating of Zn and metals such as Z, Al, and Sn. From the viewpoint of corrosion resistance and scratch resistance, a Zn-Ni alloy plated steel sheet with a hard plating layer is desirable.

Next, the black inorganic film must contain a black compound as a main component and have excellent adhesion. These films include Fe, Ni, Co, Mn, Mo, Cr, Cu, B
The main ingredients are hydrated oxides and sulfides such as i and V, and heat treatment,
It can be obtained by chemical solution oxidation, electrical anodic oxidation, cathode electrolytic deposition, etc. Since the film is composed of inorganic compounds, the coating weight is 0.1 to 3 in terms of black color and adhesion.
．． It is desirable to control it to 0 g/m2.

Furthermore, a chromium hydrated oxide film can be obtained by chromate treatment. The chromate treatment is not particularly limited, but a coating-drying type coating chromate, a reaction chromate that involves dipping or spraying and then washing with water, and an electrolytic chromate can be applied. The coated chromate is a water-soluble Cr3+ and Cr6+ compound, preferably chromic anhydride (CrO3
) or using a reducing agent to reduce Cr3+/Cr6+ = 0.1 to 0.
Immediately after applying a water-soluble chromate treatment solution containing chromic acid partially reduced to 60% or a complex component containing silica sol, phosphoric acid, organic polymer compound, etc. on the black film,
Obtained by forced drying at ~120°C. The reactive chromate can be obtained by using a commercially available treatment solution consisting of a chromic acid compound and an anionic compound. Further, electrolytic chromate can be obtained by performing cathodic electrolysis in a chromic acid aqueous solution containing chromic acid, an anion, and a metal ion as main components at pH 0.5 to 5, and then washing with water. The amount of adhesion is preferably 10 to 200 mg/m2 in terms of Cr. 200
If it exceeds mg/m2, problems such as deterioration of adhesion due to cohesive failure of the chromate film itself and contamination of the welding electrode will occur. 10
If it is less than mg/m2, the effect of chromate on corrosion resistance and adhesion is not sufficient.

It is necessary to take care that the resin coating layer does not harm the appearance, weldability, etc. (FIG. 8), and the upper limit of the coating amount is 3μ. In addition, it is necessary to provide uniform appearance, especially texture, to ensure the ability to hide the base of the processed part during press working, and to provide corrosion resistance and scratch resistance, so the lower limit for the amount of film is It is 2μ. Furthermore, a resin film in which carbon black is dispersed is effective as a remedy for uneven appearance in a black inorganic film.

[0020] The resin (composite polymer) is a film obtained by coating a composite polymer in which a water-soluble or water-dispersible organic polymer compound is combined with an inorganic compound and, if necessary, a curing agent, and hardening the coating by baking or the like. There are other organic polymer compounds that are solvent-soluble or UV-curable, but because of the environmental issues with solvents and workability issues during handling, water-soluble or water-dispersible organic polymer compounds are more economical and productive. , is the most versatile.

The matting agent to be dispersed in the resin is silica white (
SiO2.nH2O) is most preferred. The particle size is selected depending on the desired appearance color tone and gloss, and commercially available silica white with a particle size of 20 to 100 nm can be used (FIG. 2). The scattering reflectance of light varies depending on the particle size of silica white, which affects the matting effect. That is, particles with an extremely small particle size increase gloss, which has the opposite effect on the matting effect (reducing gloss), which is the objective of the present invention. Moreover, if the particle size is too large, the silica white will break through the resin film, making the surface rough and making it difficult to obtain a uniform appearance, and in particular, the scratch resistance will deteriorate. Therefore, the appropriate particle size of silica white is 20 to 100 nm. The amount added is such that the weight ratio (silica white/(resin + carbon black + colloidal silica)) to the mixed resin is 5 to 10% in terms of uniform appearance, gloss, etc. (Figure 3
). If it is less than 5%, a decrease in glossiness, that is, no matting effect is observed. On the other hand, if it exceeds 10%, the appearance becomes non-uniform and unevenness tends to occur, and the surface becomes rough and the scratch resistance deteriorates. For this reason, the weight ratio to the mixed resin is 5 to 10%, preferably 6 to 8%.

Furthermore, the black fine particles to be dispersed in the resin are most preferably carbon black. The particle size is selected depending on the desired appearance color tone and gloss, and commercially available particle size 50
~170nm carbon black can be used (Figure 4)
. Although fine carbon black with a particle size of less than 50 nm has excellent blackening ability, it has no effect on gloss, and rather increases gloss, which has the opposite effect on reducing gloss, which is the objective of the present invention. Moreover, if it exceeds 170 nm, it will tend to settle in the water-soluble organic resin and will be unevenly distributed in the resin, making it difficult to obtain a uniform appearance and deteriorating the scratch resistance. Therefore, the appropriate particle size of carbon black is preferably around 100 nm. Practically speaking, a commercially available product in which carbon black is dispersed can be used as a dispersion. The amount added should be 15/100 or more by weight (carbon black/resin) to the resin from the viewpoint of color tone and uniformity of appearance and electrical conductivity, but it should be 35/100 or more from the viewpoint of hiding the base of the processed area. It is necessary that there be. If it is less than 35/100, a whitening phenomenon occurs at the 90° bent portion (R=0) after press working. In addition, if the weight ratio of carbon black exceeds 45/100, secondary agglomeration of carbon black causes the carbon black to break through the resin film and protrude, causing the surface to become rough, causing scratches and powdering, and resulting in poor adhesion and corrosion resistance. deteriorates. For this reason, the weight ratio to the resin is set to (35-45)/100 (FIG. 5). In addition to carbon black, black fine particles include Fe, Co, Ni, and C.
u, Mn. Oxides such as Mo, Ag, and Sn, sulfides, carbides, and black metal fine powders can also be used, but they are inferior to carbon black in terms of base-hiding properties.

[0023] In a composite polymer containing an inorganic compound, colloidal silica is most preferably used as the inorganic compound. In order to ensure the strength of the organic resin film, the particle size of colloidal silica is preferably 1 to 20 nm and needs to be uniformly dispersed in the resin (FIG. 6). If the particle size exceeds 20 nm, it is difficult to obtain the strength of the organic film, and the ability to hide the base during processing deteriorates. The amount added is determined by the weight ratio (colloidal silica/resin) to the resin from the viewpoint of film strength, color tone and uniformity of appearance.
0 to 40)/100 (Figure 7). If it is less than 30/100, it will not be effective in securing the film strength during processing, and if it is less than 40/100, it will not be effective in securing the film strength during processing.
If it exceeds 100, colloidal silica will break through the resin film and protrude due to secondary aggregation of colloidal silica.
The surface becomes rough, causing scratches and powdering, and adhesion and corrosion resistance deteriorate.

[0024] The particle diameters of these fine particles dispersed in the resin can be measured and controlled using a spectroscopic analyzer that utilizes laser scattered light.

[0025] Furthermore, when uniformity of the painted appearance is particularly strictly required, it is also effective to add a surfactant having a leveling effect to the resin to the present matte black resin. It is effective if the amount added is 50 ppm or more based on the matte black resin, and 50 to 100 ppm may be practical.

[0026]

[Examples] The present invention will now be described with reference to Examples. The terms and evaluation methods in Examples are as follows.

(1) Matte black appearance L value: represents lightness (JIS Z 8370), and L≦20 is required for a black steel plate. G value: Glossiness measured by 60° specular reflection using a black glass plate as a standard value of 90.1. G≦5 is required for a matte steel plate. Appearance uniformity: The appearance after coating with matte resin was visually evaluated. 5...No unevenness at all. 4... Slight unevenness that does not pose a problem in practical use. 3... Some streak-like unevenness is observed. 2...Striped unevenness is clearly observed. 1...Conspicuous unevenness.

(2) Workability R=0, 90° bending was performed, and the outer R-processed portion was visually evaluated to evaluate the degree of whitening phenomenon. 5...No abnormality at all. 4...Whitening phenomenon is observed up to 1/4 of the total length. 3...Whitening phenomenon is observed up to 1/2 of the total length. 2...Whitening phenomenon is observed up to 3/4 of the total length. 1...Whitening phenomenon is observed over the entire length.

(3) Scratch resistance Scratches caused by pencil hardness were visually evaluated based on the degree of damage to the surface film, and expressed as the hardness of the pencil before the scratches appeared (JIS
K5400).

(4) Spot weldability Painted plates were combined and weldability was determined by applying a pressure of 200 kg and varying the welding current at a constant current cycle of 10 Hz (electrode diameter 4.5 mmφ, Cu-Zn electrode). ○…There is no occurrence of splintering, etc., and welding can be easily performed. △...Welding can be performed by changing the welding current, but splintering occurs and the appearance is poor. ×...Welding cannot be performed even if the welding current is changed.

Example 1 Zinc-nickel alloy plated steel sheet (Ni content 11.5%,
A black inorganic film was formed by spraying a plating amount of 20g/m2 and an average roughness of 1.2μ with a mixed solution of sodium nitrate and phosphoric acid. After electrolytic chromate treatment, carbon was added to 100 parts of resin. An olefin/acrylic resin emulsion in which 40 parts of black (particle size 99 nm and 164 nm) and 35 parts of colloidal silica (particle size 7 nm) are dispersed, and aluminum silicate (particle size 50 nm) is added as a matting agent therein. , talc (particle size 3μ
m), 5 to 15% of silica white (particle size 60 nm), respectively.
Disperse and dry with a roll coater to a film thickness of 2.5±0.1
It was coated with μ coating and baked at a board temperature of 120°C. Table 1 shows the evaluation results.

[0032]

[Table 1]

[0033]No. 1 is a comparative example in which carbon black with a particle size of 99 nm is dispersed and no matting agent is added, and the G value is 2.
It had a glossy appearance of 8. No. 2 to 10 have a particle size of 99n
Various matting agents were investigated using carbon black of No. As shown in Nos. 8 to 10, the addition of silica white had a great matting effect, and when it was added in an amount of 5% or more, the G value decreased to 5 or less. The L value increases with the addition of silica white, and No. 15% silica white as shown in Comparative Example 10
The added product had an L value of 20.3, which did not satisfy the blackness.

[0034]No. No. 11 is a comparative example in which carbon black with a particle size of 164 nm is dispersed and no matting agent is added.
It had a glossy appearance with a value of 22. No. Nos. 12 to 20 are carbon black with a particle size of 164 nm, and various matting agents were investigated. Similar to Examples 8 to 10, the addition of silica white had a matting effect. In this case as well, No. As shown in Comparative Example 20, the one with 15% silica white added has an L value of 21.
．． 2 and blackness could no longer be satisfied.

[0035] Also, No. 21 shows the characteristics of a conventional example in which a cold-rolled steel sheet was coated with black electrodeposition and then matte coated. The G value was 4.3 and the L value was 18.7. Note that because the coating film was thick, approximately 41 μm, welding was not possible.

[0036]No. As shown in Examples 8, 9, 18, and 19, by adding 5 to 10% of silica white as a matting agent, both the G value and L value can be obtained as in the conventional example, and welding is easy. I was able to go to

Example 2 A black inorganic film was formed on the surface of a zinc-nickel alloy plated steel sheet by a spray method, and after electrolytic chromate treatment, carbon black (particle size 99%) was added to 100 parts of resin.
Silica white was further dispersed as a matting agent into an olefin/acrylic resin emulsion in which 40 parts (nm) and 35 parts of colloidal silica (particle size 7 nm) were dispersed, and the amount and particle size of silica white added were varied. The material was coated with a dry film thickness of 2.5±0.1μ using a roll coater, and the plate temperature was 120℃.
Burned into. Table 2 shows the evaluation results.

[0038]

[Table 2]

Comparative example in which the particle size of silica white is less than 20 nm (
No. 2 to 4), the matting effect is small and the G value is No.
This is higher than the conventional example of No. 22. Silica white particle size is 10
Comparative examples (Nos. 17 to 21) with a thickness exceeding 0 nm had very low G values, but were inferior in appearance uniformity and scratch resistance. In addition, a comparative example (No.
8), the matting effect is small, and the comparative example (No.
．． 12, 13) are inferior in appearance uniformity and scratch resistance. No
．． As shown in Examples 5 to 7, 9 to 11, and 14 to 16, by adding 5 to 10% of silica white with a particle size of 20 to 100 nm, film performance equivalent to that of the conventional example can be obtained, and welding was easy to do.

Example 3 A black inorganic film was formed on the surface of a zinc-nickel alloy-plated steel sheet by a spray method, and after electrolytic chromate treatment, the particle size and number of carbon black added were varied to form a black inorganic film based on 100 parts of resin. Olefin in which carbon black and 35 parts of colloidal silica (particle size 7 nm) are dispersed
Further, 7.5% of silica white (particle size 60 nm) was dispersed into the acrylic resin emulsion as a matting agent, and a dry film thickness of 2.5 ± 0.1 μ was coated using a roll coater, and the plate temperature was raised to 120°C. Burnt it. Table 3 shows the evaluation results.

[0041]

[Table 3]

[0042] In the comparative example (No. 1) in which the particle size of carbon black was less than 50 nm, the base hiding ability of the processed portion was poor. The comparative example (No. 10) in which the particle size of carbon black was more than 170 nm was inferior in appearance uniformity and scratch resistance. In addition, in the comparative example (No. 3) in which the amount of carbon black added was less than 35 parts, the base hiding property of the processed part was poor, and in the comparative example (No. 7) in which the amount of carbon black added was more than 45 parts, the appearance uniformity and scratch resistance were poor. Inferior. No. As shown in Examples 2, 4, 5, 6, 8, and 9, carbon black with a particle size of 50 to 164 nm was
By adding 5 parts, film performance equivalent to that of the conventional example was obtained, and welding could be easily performed.

Example 4 A black inorganic film was formed on the surface of a zinc-nickel alloy-plated steel sheet by a spray method, and after electrolytic chromate treatment, the particle size and number of colloidal silica added were varied, and the amount of colloidal silica was added to 100 parts of resin. carbon black (particle size 99n)
m) Into an olefin/acrylic resin emulsion in which 40 parts and colloidal silica are dispersed, 7.5% of silica white (particle size 60 nm) is further dispersed as a matting agent, and a dry film thickness of 2.5 is coated with a roll coater. It was coated with a coating of ±0.1μ and baked at a board temperature of 120°C. Table 4 shows the evaluation results.

[0044]

[Table 4]

[0045] In the comparative example (No. 10) in which the particle size of colloidal silica was over 20 nm, the ability to hide the base of the processed portion was poor. Further, in the comparative example (No. 2) in which the amount of colloidal silica added was less than 25 parts, the base hiding property of the processed part was poor, and in the comparative example (No. 6) in which the amount of added colloidal silica was more than 40 parts, the scratch resistance was poor. No. 1
, 3-5, 7-9, particle size 3-20
By adding 30 to 40 parts of colloidal silica of nm size, a film performance equivalent to that of the conventional example (No. 11) was obtained, and welding could be easily performed.

Example 5 A black inorganic film was formed on the surface of a zinc-nickel alloy plated steel sheet by a spray method, and after electrolytic chromate treatment, carbon black (particle size 99%) was added to 100 parts of resin.
In addition to the olefin/acrylic resin emulsion in which 40 parts of colloidal silica (particle size: 7 nm) and 35 parts of colloidal silica (particle size: 7 nm) are dispersed, silica white (particle size: 60 nm) is added as a matting agent.
Disperse 7.5% and use a roll coater to reduce the dry film thickness to 1.
．． It was coated with different thicknesses of 1 to 3.9μ and baked at a board temperature of 120°C. Table 5 shows the evaluation results.

[0047]

[Table 5]

The L value does not change with film thickness, but the G value tends to decrease with film thickness. No. with film thickness less than 2μ
．． In Comparative Examples 1 and 2, No. Compared to the conventional example No. 8, the G value is higher, the base hiding ability of the processed part is inferior, and the film thickness is 3.
No. beyond μ In Comparative Examples 6 and 7, the scratch resistance of the coating deteriorated and it became difficult to weld. No. 2 with a film thickness of 2 to 3 μm. In Examples 3 and 4, No. The coating performance was equal to or better than that of the conventional example No. 8, and welding could be easily performed.

[0049]

[Effects of the Invention] The matte black surface-treated steel sheet of the present invention has low gloss in terms of quality, excellent workability, corrosion resistance, and scratch resistance.
As a new steel sheet with anti-fingerprint properties, it can be used in the field of conventional matte-coated steel sheets, greatly contributing to higher quality products and lower costs.

[0050] Also, in terms of manufacturing, roll coater applicability etc. can be easily applied within the range of operation using conventional coating techniques.
Because high-speed, short-time processing is possible, processing can be performed within conventional electroplating lines, and manufacturing can be done at low cost.

[Brief explanation of the drawing]

FIG. 1 is a schematic cross-sectional view of a matte black surface-treated steel sheet of the present invention.

FIG. 2 is a diagram showing the relationship between L value (lightness), G value (glossiness), surface appearance, and particle size of white silica in a matte black resin film.

FIG. 3 is a diagram showing the relationship between L value, G value, surface appearance, and the amount of white silica added in the matte black resin film.

FIG. 4 is a diagram showing the relationship between L value, G value, surface appearance, and particle size of carbon black in a matte black resin film.

FIG. 5 is a diagram showing the relationship between processability, scratch resistance, and the amount of carbon black added in a matte black resin film.

FIG. 6 is a diagram showing the relationship between processability and particle size of colloidal silica in a matte black resin film.

FIG. 7 is a diagram showing the relationship between processability, scratch resistance, and the amount of colloidal silica added in a matte black resin film.

FIG. 8 is a diagram showing the relationship between processability, weldability, and film thickness of a matte black resin film.

[Explanation of symbols] a...Zn-based alloy plated steel plate b...Black inorganic coating c...Chromate coating

Claims (1)

[Claims] Claim 1: A Zn-based alloy plated steel sheet having a black inorganic film layer and a chromium hydrated oxide film layer, and further comprising a resin 10
A resin composition in which 35 to 45 parts of carbon black and 30 to 40 parts of colloidal silica are dispersed relative to 0 parts, and a thickness of 2 to 3 in which 5 to 10% of silica white is further dispersed.
A matte black surface-treated steel sheet characterized by having a water-soluble or water-dispersible resin coating layer of μ.