JP2001018322A - Conductive black surface-treated metallic plate with outstanding resistance to flaw and fingerprint - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide outstanding properties such as resistance to flaw and fingerprint and further, upgrade the blackness and conductivity by applying a conductive black coating film and a clear coating film to a metallic plate. SOLUTION: The conductive black surface-treated metallic plate has a conductive black coating film 4 and a clear coating film 5 applied to a metallic plate 1. The black coating film 4 is applied for imparting conductivity and blackness, and further, the resistance to flaw is also enhanced by controlling the particle diameter and coating film thickness of a conductive filler. For the conductive filler, it is desirable to use a carbon black of a small particle diameter from the viewpoint of imparting the blackness. The clear coating film 5 is effective for imparting the conductivity and at the same time, shows the effect to significantly enhance especially the resistance to flaw and fingerprint and besides, the effect to significantly increase the blackness. Thus it is possible to obtain an appearance showing the high blackness and reduce the total thickness of a coating film applied to the metallic plate 1 and further, cut down on a painting cost from the viewpoint of favorably expanding the field of use applications.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a conductive black surface-treated metal plate excellent in both scratch resistance and fingerprint resistance. The black surface-treated metal plate of the present invention is suitably used for internal parts such as copiers and printers, which are required to have a low gloss and black appearance and are required to have a grounding property and an electromagnetic shielding property.

[0002]

2. Description of the Related Art Internal parts such as copiers and printers
For the purpose of shielding light, a low-gloss black appearance is required, and grounding properties, electromagnetic wave shielding properties, and the like are also required. Conventionally, as a black surface-treated metal plate applied to such an application, a metal plate in which a plating surface itself is blackened by an oxidation treatment or the like on a plating surface on which special plating such as Zn-Ni plating or Zn-Co-Mo plating is applied. Had been used in general.

[0003] However, since the black oxide film is a hard film, if it is subjected to a process such as bending, the black film cannot follow the elongation and cracks, resulting in a problem that the appearance of the product is remarkably deteriorated. there were. Further, in the above-mentioned metal plate, it is necessary to perform special plating such as Zn-Ni plating or Zn-Co-Mo plating on the original plate, and there is a problem that not only the performance is restricted but also the cost is increased.

In order to overcome the above problems, a so-called "conductive pre-coated metal plate" has been developed in which a metal plate is coated with a coating obtained by adding a conductive pigment to a resin having excellent processability. In this precoated metal plate, various conductive pigments (metals or metal compounds such as nickel, zinc oxide, conductive titanium oxide, and iron phosphide) are added to the film for the purpose of imparting conductivity. However, in order to effectively exert the effect of improving the conductivity by the addition of the conductive pigment, the thickness of the coating must be reduced as much as possible. As a result, the conductive pigment protrudes from the surface of the coating, resulting in handling and processing. At times, there has been a problem that flaws are very likely to occur on the protruding portion. In addition, there has been a problem that when a process such as a bending process is performed, cracks in the coating film and peeling of the conductive pigment are observed.

[0005] Among the above problems, in order to prevent the occurrence of flaws,
Add wax to the coating to improve the lubricity of the coating,
As a result, a method for improving the scratch resistance is generally employed. However, even with the addition of wax,
It is extremely difficult to remove the adverse effects due to protrusion due to the addition of the conductive pigment, the effect of improving the lubricity by adding the wax is insufficient, and it is not possible to obtain a precoated metal plate that is sufficiently satisfactory in terms of scratch resistance. is there.

Further, in the precoated metal plate, as described above, the conductivity decreases as the coating thickness increases. For the purpose of preventing a decrease in conductivity, even if a conductive pigment is added to the coating film, the resin covers the conductive pigment according to the film thickness, so the film thickness must be reduced. There was also a problem that a desired degree of blackness could not be obtained, and it could not be applied to applications requiring a high degree of blackness.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and an object of the present invention is to provide both excellent scratch resistance and anti-fingerprint properties, and furthermore, the blackness and An object of the present invention is to provide a conductive black surface-treated metal plate having improved conductivity.

[0008]

Means for Solving the Problems The conductive black surface-treated metal plate having excellent scratch resistance and fingerprint resistance according to the present invention, which has solved the above-mentioned problems, is provided on a metal plate by applying a conductive black coating. The gist is that the film and the clear coating film are coated.

In the above-mentioned black coating film, one containing carbon black in the coating film or the black coating film having a thickness of 0.3
Controlling the thickness of the clear coating film to be 0.05 to 3 μm is a preferred embodiment of the present invention.

Further, those satisfying the following expression (1) are useful because the conductivity is further enhanced. 10B / A + 3C ≦ 10 (1) In the formula, A is the amount (% by weight) of the carbon black contained in the black coating, B is the thickness of the black coating (μm), C is the clear coating It means the thickness (μm) of the film.

Those satisfying the following formulas (2) and (3) are useful because the blackness can be further increased. A × B ≧ 10 (2) A × B + 20C ≧ 15 (3) In the formula, A and B have the same meanings as before.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION The present inventors have enthusiastically focused on the above-mentioned precoated metal plate in order to provide a conductive black surface-treated metal plate excellent in both scratch resistance and fingerprint resistance. Have been considering. As described above, the conventional conductive pre-coated metal plate is prepared by adding a conductive pigment to the coating film from the viewpoint of imparting conductivity, and controlling the coating film thickness such that the conductive pigment projects to the surface layer of the coating film. Thus, although conductivity is imparted, there is a problem that the scratch resistance is poor. A method of increasing the lubricity of the coating film by adding wax to the coating film with the aim of improving the scratch resistance has also been proposed, but the effect is not so large, and the method for sufficiently improving the scratch resistance has been proposed. Did not reach. Furthermore, a precoated metal plate capable of improving fingerprint resistance in addition to scratch resistance has not yet been provided.

Therefore, as a result of intensive studies to provide a pre-coated metal plate having not only excellent conductivity but also excellent scratch resistance and further improved fingerprint resistance, a conductive black coating was formed on the metal plate. Film (undercoat) and clear coating (overcoat)
It has been found that the desired object can be achieved by forming a two-layered film in which the layers are sequentially coated, and the present invention has been completed.

As described above, the conductive black surface-treated metal plate of the present invention has a conductive black coating (conductive black coating; undercoat layer) and a clear coating film (overcoat layer) on the metal plate. These are sequentially applied. Hereinafter, the function of each coating film will be described in detail.

Conductive black coating (undercoat layer) The conductive black coating (hereinafter sometimes abbreviated as a black coating) is coated for the purpose of imparting conductivity and blackness, and is further provided with a conductive filler. Controlling the particle size and coating thickness of (such as carbon black) also has the advantage of improving the scratch resistance.

Specifically, it is recommended to use a conductive filler having a smaller particle size than a metal filler in order to impart conductivity and improve scratch resistance. This is because the use of a material having a small particle size can reduce the unevenness of the black coating film and improve the scratch resistance. Furthermore, since the particle size is small, the filler does not fall off even when bent,
There is an advantage that the bending workability is also improved. In the present invention, it is recommended to use carbon black having a small particle size from the viewpoint of imparting blackness. This carbon black may be used alone, or two or more carbon blacks may be added.

Further, the thickness of the black coating is 0.3 to 10
It is preferable to control to μm. When the film thickness is less than 0.3 μm, a predetermined blackness cannot be provided. It is more preferably at least 0.6 μm, even more preferably at least 0.8 μm. However, if the thickness of the black coating film is too large, the conductivity is reduced. Therefore, it is preferable to control the thickness to 10 μm or less. More preferably 6 μm or less, and still more preferably 4 μm
μm or less.

Clear coating film (overcoat layer) This clear coating film is effective for imparting conductivity,
In particular, it has the effect of significantly improving scratch resistance and fingerprint resistance, and further has the effect of significantly increasing blackness, which is the most important point of the present invention.

That is, by forming the above-mentioned black coating film, the flaw resistance is improved to some extent.
It is not enough to improve scratch resistance under severe processing conditions. Furthermore, since the above-mentioned black coating film is painted with a dark black, there is a demerit that a fingerprint is conspicuous when handled by hand, and the appearance quality is deteriorated. In view of such circumstances, the black coating film was coated with a clear coating film in order to provide a surface-treated metal plate having excellent scratch resistance even under severe processing conditions and further excellent fingerprint resistance. .

First, the effect of improving the scratch resistance by forming a clear coating film will be described.

The reason why the scratch resistance is improved by applying the clear coating film to the black coating film is that the unevenness of the black coating film can be further reduced. In order to improve the scratch resistance, it is important to control the thickness of the clear coating film. Furthermore, if additives such as a wax and a crosslinking agent are added to the clear coating film, it becomes possible to easily adjust the lubricity and strength of the coating film, and as a result, it is possible to further enhance the scratch resistance. it can. Additives used in the present invention are not particularly limited as long as they are normally used in a coating film and can effectively exert the above-mentioned effects, and include, for example, a melamine-based crosslinking agent and a crosslinking agent such as a blocked isocyanate-based crosslinking agent. Is mentioned.

Next, the effect of improving the fingerprint resistance by forming a clear coating film will be described.

Here, the "fingerprint" which is a problem to be solved by the present invention is described.
Will be described briefly. As is well known, a fingerprint is a trace of secretion from a finger and is a kind of transparent oil. Therefore, the surface layer portion of the black coating film to which the fingerprint is not attached and the surface layer portion of the black coating film to which the fingerprint is attached have different light reflectance and absorptance, and the fingerprint becomes very noticeable, resulting in poor appearance. I will invite you. As a solution, it is conceivable not to attach the fingerprint itself, but it is extremely difficult. Therefore, the viewpoint was changed, and the fingerprint resistance was improved by applying a clear coating film whose light reflectance and absorptance were similar to those of the fingerprint so that the fingerprint became inconspicuous even when attached. In order to improve the fingerprint resistance, it is important to control the thickness of the clear coating film as in the case of the above-described effect of improving the scratch resistance.

As described above, the thickness of the clear coating film is controlled from the viewpoints of improving scratch resistance and fingerprint resistance and further increasing the blackness (described later), and effectively exerts these functions. In order to achieve this, it is preferable that the film thickness be 0.05 μm or more. It is more preferably at least 0.1 μm, further preferably at least 0.2 μm. If the film thickness is too large, the conductivity is adversely affected.
It is preferable to set it to μm. It is more preferably 2 μm or less, and still more preferably 1.5 μm.

As described above, the two-layer coating structure in which the clear coating is coated on the black coating significantly improves the scratch resistance as compared with the single-layer coating consisting of the black coating alone. In addition, the formation of a clear coating film is extremely effective in that the improvement in fingerprint resistance, which cannot be achieved with the single-layer coating film structure, can be obtained, but the blackness of the black coating film is greatly improved. There is also an advantage that it becomes possible. as a result,
Besides being applicable to applications requiring a higher appearance of blackness; compared to a single-layer coated metal plate, the metal plate of the present invention can reduce the total coating thickness coated on the metal plate,
This is extremely useful in that the application field can be expanded and the cost can be reduced, for example, the coating cost can be reduced.

In order to further clarify the effect of the two-layer coated metal plate of the present invention on the increase in blackness and the like from a single-layer coated metal plate not coated with a clear coating, FIGS.
This will be described in detail with reference to FIG. In addition, these figures are examples in which a surface-treated steel sheet using a chromate-treated steel sheet in which a chromate film is coated on a plated steel sheet as a metal plate is a typical example, but it is needless to say that the present invention is not limited to this. No.

FIG. 1 is a schematic view showing the structure of the steel sheet of the present invention, in which 1 is a steel sheet, 2 is a plating layer, 3 is a chromate film, 4 is a conductive black coating, and 5 is a clear coating. Meaning respectively. FIG. 2 is a schematic diagram showing the configuration of a conductive precoated steel sheet that does not cover a clear coating film, and the other configuration is the same as that of the steel sheet of the present invention shown in FIG. Note that carbon black is added as a conductive filler to the conductive black coating film.

The blackness is determined according to JIS Z 8722-198.
Measure according to the color tone measurement method specified in 1. Specifically, the color tone of the sample is calculated by measuring the diffuse reflection light excluding the specular reflection light from the light incident on the sample, and simulates the color tone actually felt visually. As described above, since the color tone is determined by the wavelength of the diffusely reflected light with respect to the incident light and the intensity thereof, when the amount of the diffusely reflected light is extremely small, a "black color" is felt.

As shown in FIG. 2, a single-layer coated steel sheet in which a metal plate is coated only with a conductive black coating film, from the viewpoint of imparting conductivity, a conductive filler is added to the coating film and the film thickness is increased. Therefore, it is inevitable that the unevenness of the coating film becomes large. Even if carbon black having a small particle size is used as the conductive filler and the unevenness of the coating film can be smoothed to some extent, it is difficult to exhibit the effect of improving the scratch resistance under severe processing conditions.

Further, in the single-layer coated steel sheet, most of the incident light is absorbed because a black coating film is formed on the surface layer.
Since the surface layer has unevenness of the coating film, the reflected light is diffused and reflected more, and as a result, only an appearance having a slightly whitish blackness can be obtained.

On the other hand, the reason why the blackness of the double-layer coated steel sheet of the present invention (FIG. 1) in which the clear coating is further coated on the black coating is considered as follows.

When light is applied to the steel sheet of the present invention in which a black coating film is coated with a clear coating film, the reflected light and the like include specular reflection and diffuse reflection in the clear coating film, transmission through the clear coating film, and black color. A total of four modes of specular reflection and diffuse reflection in the coating film, multiple reflection when reflected light is reflected by the clear coating film, and light absorption in the clear coating film and the black coating film are considered. Among them, the influence of the formation of the clear coating film on the degree of blackness is diffused reflected light and the like.

That is, due to the effect of multiple reflection and light absorption, the amount of diffuse reflected light coming out of the coating film is surely reduced as compared with the case where no clear coating film is formed. Furthermore,
As shown in FIG. 1, the irregularity of the conductive black coating film is smoothed by forming the clear coating film, so that the regular reflection light increases, and as a result, the diffuse reflection light decreases. It is considered that the combination of these effects results in extremely low diffuse reflection, resulting in an increase in blackness.

The operation of the double-coated steel sheet of the present invention is as described above, but it is recommended to satisfy the above-mentioned expression (1) for the purpose of further improving the conductivity. In the present invention, as a factor for controlling the conductivity, attention is paid to a factor [carbon black addition amount (A) and film thickness (B)] on the black coating film side and a factor [film thickness (C)] on the clear coating film side. After examining the effect of the black coating thickness (B / A) and the clear coating thickness (C) per 1% by weight of the carbon black on the improvement in conductivity, the above relational expression (1) was specified. It is up to you. When the above formula (1) exceeds 10, the conductivity becomes insufficient. More preferably, it is 4.5 or less, and still more preferably, it is 4.0 or less.

Further, aiming at a further action of increasing blackness,
It is recommended that the above relational expressions (2) and (3) be satisfied. In the present invention, as a factor for controlling the degree of blackness, as in the case of the above-mentioned conductivity, the above-mentioned A, B and C were examined and the results were examined. The product (A × B), that is, equation (2) is important,
On the other hand, it is found that the film thickness (C) is important as a factor on the clear coating side, and that the blackness increasing effect is not observed unless the relationship between the black coating side and the clear coating side is both within the predetermined range. , Equation (3). Equation (2) above
And (3) are more preferably 20 or more.

The composition of the coating film in the present invention is as described above, and the metal plate under the coating film is not particularly limited, and may be a cold-rolled steel sheet, a hot-dip galvanized steel sheet, an electro-galvanized steel sheet, a galvannealed steel sheet. , An aluminum plate, a stainless steel plate, a copper plate, a copper-plated steel plate, a tin-plated steel plate, and the like. Such a steel sheet or the like may be directly coated with the black coating film and the clear coating film directly in sequence, but if the surface of the steel sheet or the like is contaminated with a contaminant such as oil, the coating film and It is recommended that the steel sheet be subjected to a known metal surface treatment for the purpose of improving the adhesion of the steel sheet. Known surface treatment methods include, for example, phosphoric acid-based surface treatment, chromic acid-based surface treatment, and the like.

The paint used for the black coating film and the clear coating film is not particularly limited, and includes various resins such as polyester, acrylic, urethane, silicone, and fluorine resins. In consideration of workability, use of a polyester resin is recommended.

In order to further impart various properties, a crosslinking agent, a rust preventive pigment, a matting agent, an aggregate, a wax,
Additives such as extenders, coloring pigments, leveling agents, and defoamers may be added as appropriate.

Next, a method for manufacturing a surface-treated metal sheet according to the present invention will be described. The surface-treated metal plate can be manufactured by applying a coating solution containing a coating film component to the surface of the metal plate by an arbitrary coating method and drying. The method of applying the coating liquid is not limited at all. For example, a roll coater may be applied to the surface of a long strip of a metal plate that has been subjected to a pre-coating treatment (for example, a phosphate treatment or a chromate treatment) or the like. A known coating means such as a spraying method, a spraying method and a curtain flow coater method may be employed.

In consideration of the uniformity of the coating thickness, the processing cost, the coating efficiency, etc., the most preferable in practical use is:
This is a method of applying with a roll coater. Incidentally, the zinc-coated steel sheet, for the purpose of improving the adhesion to the coating film and the corrosion resistance of the surface-treated steel sheet, those subjected to a pre-coating treatment such as a phosphate treatment or a chromate treatment, of course, of the present invention, It can be used as a “metal plate”.

Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the following examples, and the present invention is not limited thereto. Of course, the present invention can be modified and implemented, and all of them are included in the technical scope of the present invention.

[0042]

EXAMPLES Using the chromated metal plate (chromium coating weight 50 mg / m ²⁾ was electro-galvanized steel sheet (zinc deposition amount 20g / m ^2), the carbon black basecoat (a polyester resin to the metal plate After coating with the added paint) to coat the black coating film, the clear coating film was coated by applying a clear polyester resin. At that time, the amount of carbon black added in the undercoat paint,
In addition, the thicknesses of the black coating film and the clear coating film were variously changed as shown in Table 1, and each test material was obtained. The following properties were evaluated for each test material obtained in this manner.

[Conductivity] The coating resistance (kΩ) of the test material was measured with a tester and evaluated according to the following criteria. ◎: excellent resistance less than 1.0 kΩ ○: good resistance 1.0 kΩ or more and less than 10 kΩ ×: inferior resistance 10 kΩ or more

[Scratch Resistance] The surface of the coating film of the test material was rubbed with a nail, and the appearance change of the rubbed portion was observed according to the following criteria. ◎: Excellent No change in appearance ：: Good Slight trace ×: Poor

[Fingerprint Resistance] Acetone solution saturated with white petrolatum at 50 ° C. was used as an artificial fingerprint solution, and the test material was immersed in the solution for 1 minute. It measured with the color difference meter (SZ-S # 90). The change in color tone is represented by ΔE. A larger ΔE indicates a larger change in color tone. The fingerprint resistance was evaluated based on the obtained ΔE value according to the following criteria. ：: Excellent ΔE = 1 or less Adhesion of fingerprints is not conspicuous at all ○: Good ΔE = 1 or more and less than 3 Adhesion of fingerprints is hardly conspicuous ×: Poor ΔE = 3 or more Adhesion of fingerprints is conspicuous

[Blackness] Color difference meter (S
The blackness was evaluated according to the following criteria based on the L value measured using (ZS−90). The lower the value of the L value, the darker the color. ：: excellent L value = less than 31 ：: good L value = 31 or more and less than 33 ×: inferior L value = 33 or more The obtained results are also shown in Table 1.

[0047]

[Table 1]

From Table 1, it can be considered as follows.

First, Nos. 1 to 24 are double-coated steel sheets of the present invention in which a black coating film is coated with a clear coating film and the thickness of each coating film is appropriately controlled. No. 25-28, 32-37 not controlled within the preferred range of the invention
As compared with the above, all of scratch resistance, fingerprint resistance and blackness increasing effect are better.

On the other hand, Nos. 29 to 31 are single-layer coated steel sheets coated only with a black coating film without coating a clear coating film, and are inferior in scratch resistance and fingerprint resistance and have an increased blackness. No effect is obtained.

Nos. 38 to 44 are obtained by examining the effects of the above equations (1) to (3) on the steel sheet of the present invention. The above formula (1) satisfies the preferred upper limit of the present invention.
No. 42 and No. 44 do not satisfy the preferable upper limit.
43, it is more excellent in conductivity. The formulas (2) and (3) of the present invention, in which Nos. 38 to 41 and No. 43 are preferred in the present invention, are more excellent in blackness increasing effect than Nos. 42 and 44 which do not satisfy the preferred upper limit.

[0052]

Since the present invention is constituted as described above, it is excellent in both scratch resistance and fingerprint resistance, and furthermore, a conductive black having improved blackness and conductivity. A surface-treated metal plate could be provided.

[Brief description of the drawings]

FIG. 1 is a schematic diagram for explaining a configuration of the present invention.

FIG. 2 is a schematic diagram for explaining the configuration of a black single-layer coated steel sheet that does not cover a clear coating film.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tadashige Nakamoto 1 Kanazawa-cho, Kakogawa-shi, Hyogo F-term in Kobe Steel Works Kakogawa Works (reference) 4D075 AE03 CA02 CA22 CA34 DA06 DB02 DC16 EA43 EC01 EC11 4F100 AA22 AA37B AA37H AB01A AB03 AK01B AK01C AK17 AK25 AK36H AK41 AK51 AK51H AK52 BA03 BA07 BA10A BA10C CA02 CA13B CA21B CC00B CC00C EJ69 GB48 GB51 HB00C JD08 JG01B JK00 JL00Y

Claims (6)

[Claims] 1. A conductive black surface-treated metal plate having excellent scratch resistance and fingerprint resistance, wherein a metal plate is coated with a conductive black coating film and a clear coating film. . 2. The conductive black surface-treated metal plate according to claim 1, wherein the black coating contains carbon black in the coating. 3. The thickness of the black coating film is 0.3 to 10 μm.
The conductive black surface-treated metal plate according to claim 1, wherein the metal plate is controlled to: 4. The thickness of the clear coating film is 0.05 to 3
The conductive black surface-treated metal plate according to any one of claims 1 to 3, wherein the metal plate is controlled to μm. 5. The conductive black surface-treated metal plate according to claim 1, wherein the conductivity is further enhanced by satisfying the following expression (1). 10B / A + 3C ≦ 10 (1) In the formula, A represents the amount (% by weight) of carbon black contained in the black coating film, and B represents the thickness (μm) of the black coating film.
Means the thickness (μm) of the clear coating film, respectively. 6. The conductive black surface-treated metal plate according to claim 1, wherein the blackness is further enhanced by satisfying the following expressions (2) and (3). A × B ≧ 10 (2) A × B + 20C ≧ 15 (3) In the formula, A is the added amount (% by weight) of carbon black contained in the black coating, and B is the black coating. Film thickness (μm), C
Means the thickness (μm) of the clear coating film, respectively.