JP3068999B2 - Pre-coated steel sheet with excellent backside grounding - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a precoated steel sheet having a conductive function imparted to a back coating film of a steel sheet, and more particularly to a precoated steel sheet having a back grounding property required for audio products.

[0002]

2. Description of the Related Art In recent years, there has been a high demand for cost reduction of surface-treated steel sheets in the field of home appliances and automobiles, and as precoating of post-coating has progressed further, there is also a high demand for higher functionality by differentiating the coating film performance on the front and back of steel sheets. Especially in the case of pre-coated steel sheets for household appliances, which are often used for outer panels of audio and video products,
There is an increasing demand for coated steel sheets with a grounding property on the backside service coat surface. As a conventional technique in which a thin film is applied to make a steel sheet conductive, an example is given to a weldable coated steel sheet for an automobile as follows, but there is almost no disclosure in the field of a pre-coated steel sheet for home appliances. For example, JP-A-61-23766 and JP-B-62-20024 disclose conductive metal powders as thin-film coatings, and zinc chloride metal is a typical commercial product. However, these coating film performances are disadvantageous in that, for example, crack-free coating films for processing required in the field of home appliances cannot be basically achieved, and they are not very advantageous in terms of productivity and cost.

[0003] Next, a steel plate coated with a water-dispersible resin mixed with a chromium compound to form a thin film has a high corrosion resistance.
Japanese Patent Application Laid-Open No. 162278 and Japanese Patent Application Laid-Open No. 61-584 have been proposed, but none of them has a conductive function of a coating film and is not practical as a back surface grounding property. Further, there are JP-A-60-50181 and JP-A-60-149786 which are formed by coating a thin film of an organic composite silicate resin film obtained by blending a water-dispersible resin with a silane coupling agent and silica sol. However, these may be practically used as spot weldability of steel sheets where the applied voltage is high and the coating film is destroyed by resistance heating under high pressure, but the applied voltage and pressure are small for home appliances. For the grounding property, a contact resistance by soft touch without destruction of the coating film is required, and in this case, the present disclosure is not practical at all.

As described above, the prior art disclosed as a weldable coated steel sheet in the automobile field includes a pre-coated steel sheet in the field of home appliances, and a steel sheet such as a front non-guard / backside conductive sheet required for audio and video products. At present, there are few disclosed cases of precoated steel sheets having different coating functions on the front and back. In addition, the prior art described above,
The disclosure of the type of the conductive metal powder is limited to a single point, and there is no disclosure about the difference in the properties of each metal powder and the difference in the characteristics of the coating film performance.

[0005] In addition, the handling flaws of pre-coated steel sheets, in which the appearance of the product is most important, greatly reduce the commercial value.
Prevention is a pain in your head. For example, in coil coating in a high-productivity line, the coil is in a coil state until the product is primarily stored or secondary processed in a slitter line or the like. In this state, the top coating with high designability and the back coating inevitably come into contact, but at this time, the appearance of the back coating on the top coating surface coming from the coil's own weight becomes a linear mark in the width direction of the board. This appears as indentation flaws at a constant pitch in the longitudinal direction of the coil, causing a significant decrease in productivity.
It is simply called PM resistance. There is no disclosure case proposed for ()) based on the properties of the coating on the back surface.

[0006]

In contrast to the above prior art, the present invention relates to a high productivity line coil coating.
It is an object to impart grounding properties to the backside coating of a precoated steel sheet having a high Tg type top coating having a glass transition point (Tg) of 50 ° C. or higher, and particularly to a top coating having high designability in coil coating. Without affecting the PM resistance of
It is intended to impart a stable grounding property to the back coating film. For this purpose, various conductive pigments are selected in advance for the conductivity of the coating film, and metal N
Based on the knowledge that the i-filler is optimal, the appropriate range including the film thickness is examined for the shape, particle size, and compounding ratio of this metal Ni filler. By specifying the P resistance of the top coating
It is intended to stably impart the grounding property of the back surface coating while maintaining the M property.

[0007]

Means for Solving the Problems In order to solve the above-mentioned problems, the present invention, based on the technical idea defined below, examines in detail the coating design including the surface roughness of the original plate in providing the grounding property on the back surface of the precoated steel sheet. , And at the same time, the suitability has been improved. As the coating resistance at normal temperature without destruction of the coating,
The contact resistance is 1 Ω or less, and it can be obtained stably without variation (ensure surface grounding). The self-weight of the painted coil is about 5 tons, and there is no transfer of the back coating appearance to the top coating surface with high designability due to the coil's own weight (ensure PM resistance). In the formation of the backside coating film, which is compatible with the above, the formation of the conductive metal Ni filler and the appropriateness of the compounding ratio, and the adjustment of the thickness of the coating film and the consistency of the binder resin with the high-molecular polyester resin are investigated.

[0008] Extraction of a roughness element to be controlled as the surface roughness of the base original plate as the target surface. That is, in imparting the grounding property to the back surface of the pre-coated steel sheet, it is necessary to design the back surface in consideration of PM resistance to the top painted surface. For this purpose, it is necessary to ensure the PM resistance of the top coating as a prerequisite, and the appropriate thickness of the top coating and the shape and particle size of the metal Ni filler that becomes the conductor of the back coating, etc. It is necessary to optimize the form of the filler and its compounding ratio. In addition, a detailed study was conducted on the surface roughness of the base plate, particularly the appropriate control of PPI and Ra, etc. in order to stably secure the grounding property of the back surface.

Hereinafter, the constitution of the backside coating film of the present invention will be described first. Regarding the back surface grounding property of the steel sheet of the present invention, first, the back surface of the steel sheet is controlled to have a roughness of 70 to 150 by PPI and 0.5 to 2.0 μm by Ra, and then subjected to an appropriate chemical conversion treatment. Ni fillers having different diameters of 0.1 to 50 μm and having a total resin weight ratio of 10 to 200
%, And the filler has a shape ratio of flake Ni / chain N
It is characterized in that a high-molecular polyester resin paint having a ratio of i of 1 to 10 in terms of a weight ratio of resin is formed as a solid film of 0.5 to 5 μm. The essence is to stably balance PM resistance to the top painted surface and grounding property of the back coating as a coil product, and adjust the filler form and mixing ratio of metal Ni, which is the conductor of the back coating. The point is that the thickness of the back surface coating film is specified, and further, the surface roughness of the base original plate is specified.

The steel sheet applied to the present invention may be any of a bare steel sheet and a galvanized steel sheet, and the zinc-coated steel sheet may be any one obtained by a known plating method. For example, in an electroplating system, Zn
Plating, a Zn-based alloy-plated steel sheet in which the alloy element is at least one of Ni, Cr and Fe may be used. Further, in the electro-dispersion plating system, Zn-Ni, Zn-
SiO ₂ , TiO ₂ , ZrO ₂ , BaC based on Fe
A Zn-based dispersion alloy-plated steel sheet obtained by uniformly dispersing and depositing a metal oxide such as rO ₄ may be used. Further, a hot-dip galvanized steel sheet, a Zn—Al-based alloy-coated steel sheet, and a galvanized steel sheet obtained by alloying them may be used in a hot-dip coating system.

[0011]

The operation limits of the control factors constituting the back surface of the steel sheet of the present invention will be described below. (1) Surface roughness of original plate In order to stably obtain the grounding property of the back coated surface of the present invention without affecting the PM resistance of the top coating film surface, first, the surface roughness of the target original plate back surface should be as follows: In particular, control of PPI and Ra is required. On the other hand, if the PPI is less than 70, the surface of the original plate becomes too smooth, and the thickness of the coating film on the back surface tends to be excessively smooth, and the conductive Ni in the coating film is originally unevenly distributed, so that a stable grounding property is obtained. It is not a good idea under the productivity line because it becomes difficult. On the other hand, if the PPI is more than 150, it is difficult to stably manage the roughness of the original plate from the viewpoint of the life of the roll roughness and the cost of the original plate. Therefore, the PPI of the original plate roughness is preferably 70 to 150, particularly 90 to 120.
Is preferred.

Next, when Ra is less than 0.5 μm, it is necessary to excessively increase the compounding ratio of the metal Ni filler necessary for imparting the grounding property to the back surface coating, and the uniform dispersion of the Ni filler in the paint pan is required. Or the lowering of the processing adhesion, or the surface roughness of the back coating film due to the Ni filler is easily transferred to the top coating film surface, and it is difficult to impart a back grounding property that is also compatible with the so-called PM resistance of the top coating film, Not very good, including cost. On the other hand, if Ra exceeds 2.0 μm, it is difficult to stably manage the roughness of the original plate from the viewpoint of the life of the roll roughness and the cost of the original plate. Accordingly, Ra as a raw plate roughness is 0.5 to
2.0 μm is preferred, and particularly preferably 0.8 to 1.5 μm.

(2) Form and Mixing Ratio of Ni Filler for Imparting Conductivity of Back Coating First, as a high-molecular polyester resin as a binder resin for forming a back coating according to the present invention, there is a conventional technology. What is necessary is just to be obtained. When coloring the back surface coating film, an appropriate coloring pigment can be blended in the category of the prior art. It is important to control the shape, particle size, and mixing ratio of the metal Ni filler used for imparting conductivity to the back surface coating film within the following specific ranges. Among the forms of the Ni filler, the shape is most preferably flaky in order to transfer the appearance of the back surface coating to the top coating having high designability in the coil coating, that is, to obtain stable PM resistance. It is preferable to use a linear and a chain Ni filler in combination.

First, the total amount of the Ni filler is allowed to be 10 to 200% in terms of resin weight ratio. If the total amount of Ni is less than 10%, lowering of the backside grounding property is caused. In addition,
To secure the grounding property in this state, the coating thickness should be 0.5 μm.
However, it is difficult to achieve the PM resistance of the top coating film as a coil product, including the appearance of the back coating film, with this film thickness. On the other hand, if it exceeds 200%, the uniform dispersibility of the Ni filler in the paint is impaired, and the lowering of the grounding property on the back is unavoidable. Under a high productivity line, it is not very advantageous including workability and cost. . Therefore, the total amount of the Ni filler in the coating film is preferably from 10 to 200% by weight, more preferably from 20 to 100% by weight.

Next, regarding the suitable form of the Ni filler and the compounding ratio thereof, if the shape ratio of flake Ni / chain Ni is less than 1 in terms of the weight ratio of the resin, the ratio of chain Ni becomes excessive and the difference in specific gravity is reduced. Disturbance of uniform dispersibility in the paint occurs, and the lowering of the Ni transfer rate into the paint film lowers the function of forming an electric circuit by Ni on the back surface paint film, leading to an increase in paint film resistance and a decrease in grounding properties. It is not very desirable to present. On the other hand, if the Ni ratio exceeds 10, the flake-like Ni tends to segregate on the surface layer of the coating film, so that the formation of a conductive circuit with the chain-like Ni tends to be short-circuited. Is difficult to obtain, which is not so preferable. Therefore, the shape ratio of flake-like Ni / chain-like Ni is 1 to 1 in terms of resin weight ratio.
0 is preferable, and 3 to 7 is particularly preferable.

In such Ni fillers having different forms, it is necessary to control the particle size within an appropriate range. The Ni
If the particle size is less than 0.1 μm, Ni is too fine and tends to segregate on the surface of the coating film, which hinders the formation of an electric circuit of the coating film by the essential Ni, which in turn makes the grounding property of the back surface unstable. Therefore, it is not very preferable. On the other hand, if the particle size of Ni exceeds 50 μm, the back surface coating film is liable to be roughened, which causes a decrease in PM resistance to the top coated surface as a coil product, which is not preferable in terms of commercial value. Therefore, the particle size of the Ni filler is preferably 0.1 to 50 μm, and more preferably 5 to 20 μm.

(3) Appropriate Thickness of Backside Coating In order to impart stable grounding properties to the backside coating, it is necessary to appropriately mix the Ni filler having the above-mentioned specific properties. There is naturally a limit.
When the thickness of the coating film is less than 0.5 μm, for example, in roll coating or the like, the coating film lacks uniform paintability due to the breakage of the coating film and the productivity is poor. In addition, PM resistance to the top painted surface as a coil product
It is not a good idea because it makes it difficult to balance gender. Also,
If it exceeds 5 μm, the grounding property and adhesion as the back surface coating film become unstable, and this is not very advantageous including the cost. Therefore, a suitable backside coating thickness for achieving both PM resistance to the top painted surface and backside grounding property is preferably 0.5 to 5.0 μm, and more preferably 1 to 3 μm.

[0018]

The effects of the present invention will be described below in detail with reference to examples. 0.7m thick steel plate with roughness controlled in specific range
m, line speed 70 on both sides of steel plate 914mm wide
50 mg total chromium deposition as a base treatment under m / min
/ M ² after being subjected to a silica sol-containing chromate treatment,
Immediately, a roll coating process of 2C2B (2 coats 2 bake) is started. Top coat (2C2B), which has high design properties, uses a high-molecular-weight polyester resin paint of an organic solvent type for both primer coating and top coating, and a flexible coating of 600 EU primer (manufactured by Nippon Paint) as a primer coating is 5 μm as a solid coating. Painted, and on top of it Flexcoat 500 paint (Nippon Paint) as top coating
Is a solid film whose thickness is controlled to 17 μm, baked under standard conditions, and water-cooled and dried.

On the other hand, the back surface coating on the back surface of the steel sheet controlled to a specific roughness is carried out according to a known roll coating method.
The Ni-filler-containing high-molecular polyester resin paint specified in Examples of the present invention described in Table 7 is applied and baked in a specific film thickness. The back painted surface manufactured by the method of the present invention manufactured in this manner is a revolutionary technology that is not present in the related art and has both stable back grounding properties without sacrificing PM resistance to the top painted surface having high designability. You can see that.

(1) Effect of Back Surface Roughness of Steel Sheet In order to stably obtain grounding properties of the back coating film of the present invention, it is important to specify the surface roughness of the steel sheet. PPI and Ra specified by the present invention as the surface roughness of the back surface of the steel sheet
No. was applied to the examples regarding the appropriate range of No. 1 to No. 24, and the comparative example is No. 24. 25-No. 32. In addition, as an example of application to various types of plated steel sheets manufactured by the prior art as the base original sheet, the examples are described as Nos. 73 and No. 97-N
o. Shown at 105. As is clear from this, when both the PPI and Ra are out of the specific range of the present invention, it is difficult to achieve both PM resistance to the top coated surface in coil coating and essential back grounding. In other words, in order to stably obtain the grounding property of the back coating film in consideration of PM resistance to the top coating surface with high designability according to the present invention, regardless of the plating system, the appropriateness of the back surface roughness of the base steel sheet It is necessary to control the roughness so that the effectiveness of controlling the PPI and Ra in the range specified by the present invention can be clearly understood.

(2) Appropriate Compounding of Conductive Metal Ni Filler for Back Coating Film The present invention is the most important feature of the proper compounding of Ni in imparting the back surface grounding property. This is in that the distribution form of the contained metal Ni filler is appropriately distributed, and in addition, a stable grounding property is obtained in consideration of the PM resistance of the top painted surface. For that purpose, it is necessary to mix the metal Ni filler having a different shape in a specific range including its form. First, an embodiment of the present invention is described as an effect of the combination of particle sizes of flake-like Ni (NoF) and chain-like Ni (NoC) having different shapes.
o. 33-No. No. 65, and the comparative example is No. 66-N
o. 70.

From this, when the particle size falls below the lower limit of the range specified by the present invention, the Ni filler is too fine and tends to segregate on the surface of the coating film cross section, so that stable electric circuit formation by the Ni filler is expected. When the applied voltage and the load are small, the contact resistance of the coating film increases, and it becomes difficult to provide the expected grounding on the back surface. On the other hand, if the particle size is out of the upper limit of the present invention, the pick-up property of the Ni filler to the coating roll will vary, and the distribution of the Ni filler in the coating film will be destabilized, and satisfactory back grounding properties will be obtained. In some cases, this causes projections of the Ni filler on the surface of the back coating film, which leads to a decrease in the PM resistance of the top painted surface.

In any case, the particle size of the Ni filler for imparting a stable grounding property to the back surface coating while maintaining the PM resistance of the top coating surface can be controlled within a specific range of the present invention. It is important. Next, in the present invention, the shape ratio of the Ni filler is flaky (F) / chain (C).
It is important to control the ratio within a proper range by the weight ratio of the resin component. With respect to the shape ratio of the invention of the present application, the example is No. 7
1 to No. No. 75, and the comparative example was No. 75. 76-No. 7
FIG.

As is apparent from the above, when the shape ratio of Ni is out of the specific range of the present invention, the back coating appearance, the PM resistance of the top coating surface, the adhesion of the back coating film, and the back grounding property. It can be seen that it is difficult to achieve compatibility between the properties of the coating film and the productivity and the commercial value of the coated product are reduced. Further, with respect to the total amount of the Ni filler, which is a weight ratio of the binder resin to the high-molecular polyester resin, the examples of the present invention are referred to as Nos. 78-No. 88
And the comparative example is shown in FIG. 89-No. Shown at 90.

In order to impart a stable grounding property to the back coating film of the present invention, it is necessary to raise the distribution density of the Ni filler in the cross section and the surface of the coating film appropriately. In this sense, the specific control of the total amount of Ni is required. Required. However, also in this case, the effect on the PM resistance of the top coating film surface needs to be sufficiently considered. As can be seen from the examples and comparative examples,
If the total amount of Ni is out of the specific range of the present invention, the properties of the backside coating film do not satisfy the gist of the present invention, and the commercial value of the precoated steel sheet is greatly impaired. As described above, in order to properly form an electric circuit on the back surface coating and secure stable grounding while considering PM resistance to the top coating, Ni fillers having different particle sizes and shapes are used in the present application. It can be seen that it is essential to control to the appropriate range of the invention.

(3) Appropriate coating thickness on the back side It is necessary to control the thickness of the back coating of the present invention within an appropriate range. Regarding this point, the embodiment of the present invention is referred to as “ 91
-No. No. 94, and the comparative example is No. 95-No. 96
Shown in As is clear from this, when the specific thickness of the present invention is deviated, the PM resistance to the top coating film having high commercial value is reduced.
It is also difficult to secure the grounding property of the originally intended back coating, as well as the property, and it is not very advantageous including the cost. It should be noted that, with respect to the coloring requirement of the backside coating film of the present invention, it is sufficiently possible to form a colored coating film by using a commercially available coloring pigment as needed and appropriately blending it into the coating material.

[0027]

[Table 1]

[0028]

[Table 2]

[0029]

[Table 3]

[0030]

[Table 4]

[0031]

[Table 5]

[0032]

[Table 6]

[0033]

[Table 7]

(Note) * 1. Plating EZ: Electro zinc plating ZN: Electric Zn-Ni alloy plating (Ni; 11.5%) EC: Electric Zn-Cr-Ni alloy plating (Cr; 10)
%, Ni; 2%) EF : Electrical Zn-Fe alloy plating (Fe; 15%) ZS: Electrical _{Zn-Ni-SiO 2 (Ni} ; 12%, Si
O ₂ ; 3%) ZT: Electric Zn—Ni—TiO ₂ (Ni; 12%, Ti
O _2; 3%) ZB: Electrical _{Zn-Ni-BaSO 4 (Ni} ; 12%, B
aSO _4; 3%) ZS: Electrical _{Zn-Fe-SiO 2 (Fe} ; 10%, Si
O _2; 3%) GZ: molten Zn plating GA: molten Zn-Al plating (Al; 5%) GF: alloyed hot-dip Zn plating (Fe; 8~11%)

* 2. Surface roughness The roughness of a steel sheet in the width direction. PPI (number of irregularities per 1 inch length) Ra (average surface roughness) * 3. Metal Ni Filler Properties in Back Coating Film F: Flake Ni, C: Chain Ni The compounding ratio of Ni fillers having different shapes of F / C is represented by resin weight ratio. The primary average particle size of the filler is expressed as [(major axis + minor axis) / 2].

* 4. Uniformity of coating film appearance (visual appearance) ：: uniform, 〇: slightly roping, △: partial roping, ×: entire roping or stripe unevenness * 5. Grounding property of the back coating film A copper piece is sandwiched between the front and back of the steel sheet, and the contact resistance between the upper and lower copper pieces is measured five times at different locations, and the average value is set (applied voltage 1 V, load 50 g / cm ² ). ◎: 0.5Ω or less, Δ: 1Ω or less, Δ: 2Ω or less, ×:
Over 5Ω

* 6. Backside coating adhesion Primary adhesion; Repeated processing of the same processed part with OT contact bending 3
Time cellophane tape peeling. Secondary adhesion: After being immersed in pure water and boiled for 2 hours and then left for 24 hours, the same evaluation as the primary was performed. ：: No peeling of coating film, Δ: 5% or less of peeling, Δ: 10% or less of peeling, ×: Over 10% of peeling * 7. Pressure mark resistance to top coatings The top painted surface / back painted surface of the steel sheet is faced and the load is 6
0kg / cm ² , 40 ° C. × 48 hrs. ◎: No change, Δ: Very slight indentation through the mark, Δ: Thin indentation, ×: Clear indentation

[0038]

As described above, according to the present invention, as a result of various studies including the need for imparting the grounding property to the back side of the coated steel sheet, including securing the stability thereof, the present invention includes the following surface roughness characteristics of the original steel sheet. We came up with a design for the backside coating. That is, there is a specific range in particular for the PPI and Ra as the back surface roughness of the original plate. A metal Ni filler is used as the conductive circuit forming ability of the back coating film, and there is a specific range of the filler form and the compounding ratio. The film thickness is specified as a thin film. In addition, due to the synergistic effect of these, there is no indentation transfer (pressure resistance resistance) of the back coating appearance to the top painted surface with high designability in coil coating under high productivity line, The present invention has provided the market with an unprecedented groundbreaking technology that can stably impart grounding properties.

────────────────────────────────────────────────── ⁷ Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI B32B 15/08 104 B32B 15/08 104Z (56) References JP-A-63-778 (JP, A) JP-A-5-185030 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B05D 1/00-7/26 B32B 15/08 B32B 15/08 104

Claims (2)

(57) [Claims] 1. A steel sheet having a primary average particle size of 0.1 to one side of a steel sheet.
The ratio of flake-like Ni / chain-like Ni is 1 to 1 in terms of resin weight ratio by using a 1 to 50 μm irregular-shaped metal Ni filler as a shape ratio.
0, the total amount of Ni filler is 10 to 2
A precoated steel sheet having an excellent backside grounding property, characterized in that a solid coating of a high-molecular-weight polyester resin coating of 100% is formed in a thickness of 0.5 to 5 μm. 2. The back surface roughness of a coating original plate is 7 in PPI.
2. The precoated steel sheet according to claim 1, wherein the precoated steel sheet is controlled to have a Ra of 0 to 150 and a Ra of 0.5 to 2.0 [mu] m.