JPH07265790A - Recoated steel plate of superior rear face grounding properties - Google Patents

Abstract

PURPOSE:To provide stably the grounding properties to a rear face film by forming a specified polyester resin film to the rear face of a steel plate and providing specified temperature to the film on the rear face to a top film of glass transition point over the specified temperature. CONSTITUTION:A high molecular polyester resin film of 0.5-5mum as a solid film, having a profile metallic Ni filler of primary average particle diameter of 0.1-50mum with the resin quantity ratio of flake-shaped Ni/chain-shaped Ni of 1-10 as the shape ratio and the total weight of Ni filler of 10-200% by the resin weight ratio to the rear face of a steel plate, is formed. The film on the rear face is set to be 10-40 deg.C to a top film of glass transition point (Tg) of 50 deg.C or over. On the other hand, the surface roughness of the rear face of a coating original sheet is controlled to be 70-150 as a PPI and 0.5-2.0mum as Ra. The grounding properties of the rear face film is provided stably while the formation of coil pressure scars on the top coated surface of high design properties is prevented.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a zinc-plated steel sheet subjected to chemical conversion treatment as a substrate, and more particularly to a precoated steel sheet having a conductive coating on one side of the steel sheet. Regarding the applied precoated steel sheet.

[0002]

2. Description of the Related Art In recent years, there has been a great need for reducing the cost of surface-treated steel sheets in the fields of home appliances and automobiles, and as the precoating of post-coating has progressed further, there is also a strong demand for higher functionality with different functions on the front and back of the steel sheets. Especially for pre-coated steel sheets for home appliances, which are often used as outer panels for audio and video products, there is an increasing demand for coated steel sheets that require earthing on the back surface of the service coat. As an example of a conventional technique for applying electrical conductivity to a steel sheet by applying a thin film coating, the following is an example of a weldable coated steel sheet for automobiles, but there is almost no disclosure in the field of home appliance precoated steel sheet.

For example, as a thin film coated with a conductive metal powder, JP-A-61-23766 and JP-B-62-
There is a publication No. 20024, and a typical market product of these is zinc metal. However, these coating film performances have a drawback that the crack-free coating film for processing required in the field of home electric appliances, for example, cannot be basically achieved, and it is not a good idea including productivity and cost.

Next, a chromium compound was mixed with a water-dispersible resin to improve corrosion resistance of a steel sheet. JP-A-59-162278
JP-A-61-584 and the like have been proposed, but none of them are practical as a back surface grounding property because the coating film lacks a conductive function. Furthermore, a thin film coating of an organic composite silicate resin film obtained by blending a water-dispersible resin with a silane coupling agent and silica sol is made.
181 and JP-A-60-149786. However, although they may be put to practical use as spot weldability of steel sheets where the applied voltage is high and resistance heating under high pressure causes the coating film to break, they are not suitable for the earthing property of home appliances where the applied voltage and pressure are small. On the other hand, soft-touch contact resistance without film destruction is required, and in this case, the disclosed technique is not practical at all.

As described above, the prior art disclosed as the weldable coated steel sheet in the automobile field is the precoated steel sheet in the field of home electric appliances, the steel sheet having the non-front surface / back surface conductivity required for audio and video products, etc. At present, there are almost no disclosure examples of precoated steel sheets with different coating functions on the front and back. In addition, in the above-mentioned prior art, the disclosure regarding the type of the conductive metal powder is merely listed, and the difference in the properties of each metal powder and the behavior and the performance in the coating film. It does not disclose any difference in characteristics.

Pre-coated steel sheets, in which the product appearance is of the utmost importance, must first be sought to prevent handling flaws in the coating film appearance. For example, in the case of coil coating on a high productivity line, the coil is in a coiled state until the product is first stored and secondary processing is performed on a slitter line or the like. In this state, the top coating film and the back surface coating film, which have high design, inevitably come into contact with each other,
At this time, the appearance of the coating film on the back side is transferred as a linear mark in the plate width direction from the coil's own weight to the top coated surface, which appears as indentation marks at a constant pitch in the coil longitudinal direction, greatly reducing productivity. However, there is no disclosure example of this pressure mark prevention measure (hereinafter, simply referred to as PM resistance) proposed from the coating film properties on the back surface.

[0007]

In contrast to the above-mentioned conventional techniques, the present invention is applied to coil coating in a high productivity line.
An object of the present invention is to impart stable grounding property to a back surface coating film of a precoated steel sheet having a high Tg type top coating film having a glass transition point (Tg) of 50 ° C. or higher. In this case, the point to be noted is that it is necessary to stably impart the grounding property to the back surface coating film in consideration of PM resistance to the surface of the high Tg type top coating film having a high design property in coil coating. is there. In order to do so, first, various conductive pigments are selected in advance in order to specify the Tg range of the high-molecular polyester resin that is the binder resin for the back surface coating, and to make the coating conductive, and to make it metallic Ni
Based on the finding that the filler is optimal, the suitable range including the film thickness for the shape, particle size and mixing ratio of this metallic Ni filler is examined, and further, the surface roughness of the back coated surface of the applied original plate It is intended to stably impart the grounding property of the back surface coating film while maintaining the PM resistance of the top coating film by specifying.

[0008]

In order to solve the above-mentioned problems, the present invention is based on the following technical concept, and for the back surface coating design including the surface roughness of the original plate for imparting the back surface earthing property of the pre-coated steel plate. This is an optimization. Sandwiching the front and back of a coated steel sheet with thin copper plate pieces, the contact resistance with the back surface coating is 1 Ω or less when a slight voltage and load are applied from above, which is stable and does not vary depending on the location. Being able to secure the back side grounding. The weight of the coated coil is approximately 5 tons, and the appearance of the backside coating film is not transferred to the top coating film with high designability due to the weight of the coil itself (securing PM resistance). In forming a back surface coating film for achieving both and, compatibility of the form and compounding ratio of the conductive metal Ni filler and the film thickness thereof with the polyester resin of the binder are obtained, and the back surface coating film formed Tg is specified from the viewpoint of PM resistance of the top coating film.

Extraction of roughness elements to be controlled as the surface roughness of the base original plate which is the target surface. That is, in order to impart the back surface earthing property of the precoated steel sheet, it is necessary to design the back surface with due consideration of PM resistance to the top coated surface. To this end, first, the Tg of the back surface coating film considering the PM resistance of the top coating film and its appropriate film thickness, the shape of the metallic Ni filler that becomes the conductor of the back surface coating film, the filler form such as the particle size, and the mixing ratio thereof. It is necessary to optimize the In addition, in order to stably secure the back surface grounding property, the surface roughness form of the base original plate, in particular, the appropriate control of PPI and Ra is required to be examined in detail, and as a result, the present invention has been proposed. It is a thing.

The back coating composition of the present invention will be described below. In order to stably impart the grounding property to the back surface coating film of the steel sheet of the present invention, first, the back surface of the steel sheet is PPI 70 to 15
0, Ra, the roughness is controlled to 0.5 to 2.0 μm, and appropriate chemical conversion treatment is applied to both sides of the steel sheet.
When a high-molecular polyester resin is used as a binder and Ni fillers having different shapes with a particle size of 0.1 to 50 μm are blended, the shape ratio of the filler is flake Ni / chain Ni ratio in terms of resin component weight ratio. 1-10, the N
The total amount of the i filler is 10 to 200% by weight of the resin content, and the Tg of the coating film is 0 to 40.
It is characterized in that it is formed at a temperature of 0 ° C. and a solid film of 0.5 to 5 μm is formed.

The essence is that a coil product has a stable grounding property of the back coating film in consideration of PM resistance of the top coated surface. In order to make the former back coating film that does not affect PM resistance to the top coating film, it is basically necessary to lower the Tg of the back coating film from that of the top coating film, and Ni which is a conductor of the back coating film. The point is that the form and blending ratio of the filler are specified, the film thickness of the back coating film is specified, and further the surface roughness of the base original plate is specified. It should be additionally noted that if the back coating film of the present invention is required to have colorability, there is no problem if it is made into a coating material with a color pigment within the scope of the prior art.

The steel sheet applied to the present invention may be either a bare steel sheet or a zinc-based plated steel sheet, but the zinc-based plated steel sheet may be any one obtained by a known plating method, For example, in electroplating systems, Zn
A Zn-based alloy-plated steel sheet whose plating and alloying elements are one or more of Ni, Cr, and Fe may be used. In the electrodispersive plating system, Zn-Ni, Zn-
Fe based SiO ₂ , TiO ₂ , ZrO ₂ , BaC
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, hot-dip galvanized steel sheets, Zn-Al alloy plated steel sheets, and galvanized steel sheets obtained by alloying them may be applied in the hot-dip galvanizing system.

[0013]

The operation limits for the respective 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, there is no problem in PM resistance of the top coating surface, and the surface roughness of the back surface of the original substrate is first Especially, it is necessary to control PPI and Ra. On the other hand, when the PPI is less than 70, the surface of the original plate is excessively smoothed and the back surface coating film thickness tends to be excessively smooth, and conductive Ni in the coating film is originally non-uniformly distributed, so that stable grounding properties can be obtained. It's hard to do, so it's not a good idea under the productivity line. On the other hand, if the PPI is more than 150, it is difficult to stably control the roughness of the original plate from the viewpoint of roll roughness life and original plate cost, and the PM resistance of the top coating film surface is deteriorated, which is not a cost effective measure. Therefore, the PPI of the original plate roughness is preferably 70 to 150, especially 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 metallic Ni filler necessary for imparting the earth property of the back surface coating film, and the uniform dispersion of the Ni filler in the paint pan. Or a decrease in processing adhesion, or the surface roughness of the back coating film due to the Ni filler is easily transferred to the top coating surface, and it is difficult to impart the back surface grounding property that is compatible with the so-called PM resistance of the top coating, Not a good idea, including cost. On the other hand, if Ra exceeds 2.0 μm, it becomes difficult to stably control the roughness of the original plate from the viewpoint of roll roughness life and original plate cost, and PM resistance of the top coating film surface is deteriorated, which is not a good idea. Therefore, Ra of the original plate roughness is 0.5 to
2.0 μm is preferable, and 0.8 to 1.5 μm is particularly preferable.

(2) Form and Mixing Ratio of Ni Filler that Gives Conductivity to Backside Coating First, as the high molecular polyester resin of the binder resin forming the backside coating of the present invention, it is within the scope of the prior art. Anything can be obtained. Further, for the coloring of the coating film as needed, it is possible to easily color the back surface coating film by using a commercially available coloring pigment as a conventional coating material. It is important to control the shape, particle size and mixing ratio of the metallic Ni filler used for imparting conductivity to the back surface coating within the following specific ranges. Of the forms of Ni filler, the shape is most preferably flake-like for transferring the appearance of the back surface coating film to the top coating film having high designability in coil coating, that is, stably obtaining PM resistance, and flakes. It is preferable to use a combination of linear and chain Ni fillers.

First, regarding the total amount ratio of the Ni filler,
A resin weight ratio of 10 to 200% is allowed. This Ni
If the compounding ratio is less than 10%, the back side grounding property is deteriorated. In this state, the coating thickness should be 0.5μ
It is necessary to make the thickness less than m, but with this film thickness, coating film breakage easily occurs and it is difficult to achieve both PM resistance of the top coating film as a coil product including the appearance of the back surface coating film. Further, if it exceeds 200%, the uniform dispersibility of the Ni filler in the paint is impaired, and the essential backside grounding property is deteriorated. Therefore, it is a good idea including workability and cost under a high productivity line. Not. Therefore, the total amount of Ni filler is preferably 10 to 200%, and more preferably 20 to 100% in terms of the resin content weight ratio.

Next, regarding the suitable form of Ni filler and its compounding ratio, when the flake Ni / chain Ni shape ratio is less than 1.0 in terms of resin content weight ratio, the ratio of chain Ni becomes excessive and the specific gravity Due to the difference, the uniform dispersibility in the paint is hindered, the transfer rate of Ni into the coating film decreases, the function of forming an electric circuit by Ni in the back surface coating film decreases, and the resistance of the coating film increases, resulting in an increase in grounding property. It is less preferable because it exhibits a decrease.
Further, when the ratio of Ni exceeds 10, flaky Ni is likely to segregate on the surface layer of the coating film, and a conductive circuit formation with chain Ni is likely to be short-circuited, resulting in stable groundability of the back coating film. Is difficult to obtain, which is not preferable. Flaky N
The shape ratio of i / chain Ni is 1 to 10 in terms of resin weight ratio.
Therefore, 3 to 7 is preferable.

In such Ni fillers having different morphologies, it is necessary to control the particle size of the Ni filler within an appropriate range. The Ni
If the particle size is less than 0.1 μm, Ni is too fine and segregates easily on the surface of the coating film, which interferes with the formation of the electric circuit of the coating film due to the essential Ni, which in turn makes the grounding property of the back surface unstable. Therefore, it is not so preferable. The particle size is 50μ
If it exceeds m, the back surface coating film is liable to be rough, which leads to a decrease in PM resistance on the top coated surface of the coil product, which is not so preferable from the standpoint of commercial value. Therefore, the N
The particle size of the i filler is preferably 0.1 to 50 μm, and more preferably 5 to 20 μm.

(3) Tg of Back Coating Film In forming the back coating film of the present invention as described above, in order to basically guarantee the PM resistance of the top coating film, the Ni filler is contained. It is necessary to control the Tg of the back coating film within a suitable range. When the Tg of the back surface coating film is less than 0 ° C., the coating film is basically soft and handling flaws easily occur in a secondary processing step such as pressing. On the contrary, the PM resistance of the back surface coating film decreases, or the unevenness of the back surface coating film due to the Ni filler of the bone agent, which is difficult to remedy only by adjusting the gloss of the coating film, is promoted, which is the resistance of the top coating film surface. In any case, the softness of the back surface coating film often causes a decrease in commercial value, such as a decrease in PM property, which is not preferable. Further, when the Tg of the back coating film exceeds 40 ° C., the Tg difference from the top coating film decreases, so that PM resistance to the top coating film and adhesion as the back coating film decrease, which is not preferable. . Therefore, the Tg of the back coating film of the present invention using a high molecular polyester resin as a binder is 0 to 40 ° C.
Is preferable, and 15 to 25 ° C. is preferable.

(4) Appropriate coating film thickness on the back surface In order to impart a stable grounding property to the back surface coating, it is necessary to mix the Ni filler having the above-mentioned specific characteristics, but the film thickness is naturally limited. There is. When the coating film thickness is less than 0.5 μm, for example, in roll coating, uniform coating property is lacked due to film breakage and the productivity is poor.
In addition, it is difficult to achieve both PM resistance on the top coated surface as a coil product, which is not a good idea. On the other hand, if it exceeds 5 μm, the grounding property and the adhesiveness of the back surface coating film become unstable, which is not a good idea including the cost. Therefore, a suitable back surface coating film thickness for achieving both PM resistance to the top coated surface and back surface grounding property is 0.5 to 5.0 μm, preferably 1 to 3 μm.

[0021]

EXAMPLES The effects of the present invention will be described in detail below with reference to examples. The thickness of the back side of the steel plate is 0.7m with the roughness controlled to a specific range.
Line speed 70 for both sides of a steel plate with a width of m and a width of 914 mm
After a silica sol-containing chromate treatment with a total chromium deposition amount of 50 mg / m ² was applied as a pretreatment for coating by the conventional technique at m / min, the roll coating process of 2C2B (2-coat-2bake) is immediately started. Highly designed top coating (2C2
In B), both of the primer coating and the top coating, organic solvent-based polymer polyester resin coatings are used, and Flexcoat 600EU primer (manufactured by Nippon Paint) is coated as a solid coating with a thickness of 5 μm, and the top coating is applied on top of it. Flexcoat 500 paint (manufactured by Nippon Paint Co., Ltd.) having a Tg of 60 ° C. as a film is controlled to have a solid film thickness of 17 μm, and then baked under standard conditions.
It is water-cooled and dried. On the other hand, for the back surface coating on the back surface of the steel sheet controlled to have a specific roughness, a Ni roll-containing high-molecular polyester resin coating material specified by the examples of the present invention described in Tables 1 to 8 is prepared by a known roll coating method. Painted and baked with a specific film thickness. The back coated surface produced by the method of the present invention thus manufactured is PM resistant to the top coated surface having a high design.
It can be seen that this is an epoch-making technology that does not exist in the prior art and that also has stable back surface grounding properties without sacrificing the property.

(1) Effect of Back Surface Roughness of Steel Sheet In order to stably obtain the groundability of the back surface coating film of the present invention, it is essential 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. 1-No. 24, a comparative example No. 25-No. 32. In addition, as an example applied to various plated steel sheets manufactured by the conventional technique as the base original plate, No. 73 and No. 73. 97-N
o. Shown at 105. As is clear from this, if both the PPI and Ra of the surface roughness of the back surface of the steel plate deviate from the specific ranges of the present invention, it becomes difficult to achieve both PM resistance to the top coating surface and essential back surface grounding property in coil coating. I understand. That is, in order to stably obtain the grounding property of the back coating film in consideration of PM resistance to the top coating surface having a high design according to the present invention, the back surface roughness of the base steel sheet is suitable regardless of the plating system. It is necessary to manage the roughness, especially P
The effectiveness of controlling PI and Ra within the range specified by the present invention can be clearly understood.

(2) Appropriate Blending of Conductive Metal Ni Filler for Back Side Coating The invention of the present application is the main purpose for imparting back side grounding property to the blending of this Ni filler. This is because the distribution form of the metallic Ni filler contained in is properly distributed, and in addition, the stable grounding property is obtained while considering the PM resistance of the top coated surface.
For that purpose, it is necessary to mix a metallic Ni filler having an irregular shape in a specific range including its form. First, flaky Ni (NoF) and chain Ni (No) having different shapes
As a particle size combination effect of C), the embodiment of the present invention is No.
33-No. 65, a comparative example No. 66-No.
70.

From this, when the particle size falls below the lower limit of the range specified by the present invention, the Ni filler becomes too fine and segregates easily in the surface layer of the cross section of the coating film, so that a stable electric circuit can be formed by the Ni filler. It is difficult to expect, and when the applied voltage and the load are small, the contact resistance of the coating film increases, and it becomes difficult to impart the expected grounding property to the back surface. On the other hand, when the particle size exceeds the upper limit of the present invention, the Ni filler pickup property on the coating roll varies, and the Ni filler distribution in the coating film becomes unstable. It becomes difficult to obtain the Ni filler, and in some cases, this causes the Ni filler to project to the surface of the back coating film, which leads to a reduction in PM resistance of the top coated surface. In any case, it is important to control the suitable particle size of the Ni filler for imparting a stable grounding property to the back coating film while maintaining the PM resistance of the top coating surface within the specific range of the present invention. I know there is.

Next, in the present invention, it is necessary to appropriately control the shape ratio of the Ni filler. When Ni flakes different in shape from flakes (F) and chains (C) are used in combination, the shape ratio (F / C) is specified as the resin weight ratio. Regarding the shape ratio of the present invention, No. 71-No. No. 75 shown in FIG. 76-
No. 77. If the F / C Ni shape ratio of the present invention deviates from a specific range, the back surface coating appearance and the P resistance of the top coating surface
It can be seen that it is not a good idea because it is difficult to achieve both physical properties of the coating film such as M property, adhesiveness of the coating film on the back surface and earthing property on the back surface, and productivity is lowered.

Further, as the total amount of the Ni filler with respect to the high-molecular polyester resin, the No. 7
8 to No. 88, and a comparative example No. 89-No. 9
It shows in 0. In order to impart stable grounding properties to the back surface coating film of the present invention, it is necessary to raise the distribution density of the Ni filler in the coating film cross section and surface, and in this sense, specific control of the total Ni content is essential. Is. However, in this case as well, it goes without saying that PM resistance to the top coating film surface is taken into consideration. As can be seen from the examples and comparative examples, when the total amount of Ni deviates from the specific range of the present invention, the back coating film properties do not satisfy the above-mentioned gist, and it is understood that the commercial value of the precoated steel sheet, which is the gist of the present invention, is impaired. . As mentioned above,
In order to ensure stable grounding by appropriately forming the electric circuit of the back coating film while considering PM resistance to the top coating film, the present invention in which the shape and particle size of the metallic Ni filler are blended in an appropriate ratio It turns out that control within the scope of the invention is essential.

(3) Appropriate thickness of back surface coating film In the present invention, the back surface coating film thickness also needs to be controlled within an appropriate range. In this regard, the embodiment of the present invention No. 91-No. 94 and N for the comparative example
o. 95-No. 96. As is clear from this, if the specific film thickness of the invention of the present application is deviated, it becomes difficult to maintain the PM property on the top coating film surface having high commercial value, and also to secure the grounding property of the originally desired back coating film, It is not a good idea, including costs. In addition, it goes without saying that the coloring of the back surface coating film of the present invention can be dealt with in the category of the conventional coating material using a commercially available pigment.

(4) Appropriate Tg of back side coating film Regarding the Tg of the back side coating film satisfying the groundability of the present invention, the PM resistance to the front and back side coating film surface as a precoated steel sheet is
It is to maintain sex basically. Regarding the Tg range of the back surface coating film specified by the present invention, Examples No. 106 ~
No. 111, and a comparative example No. 112-No. 1
13 shows. As is clear from this, when the Tg of the back coating film specified by the present invention is deviated, scratches due to insufficient hardness of the coating film on the low Tg side and frequent occurrence of handling flaws on the back coating film in the product processing process occur. Invite.

On the contrary, since the coating film is soft, the PM resistance of the top coating film on the back surface coating film is deteriorated, and at the same time, the PM resistance of the top coating film surface is deteriorated by the conductive Ni filler of the back surface film. Also, even if the grounding property of the back surface is satisfied, the scratches on the appearance of the coating film and the decrease in adhesion are large, and the commercial value is lost. On the other hand, when the Tg exceeds the upper limit of the present invention, the coating film becomes harder, so that the adhesiveness as the back surface coating film and the PM resistance to the top coating film also decrease, so that the commercial value is obtained. Overall decline. In any case, it is understood that the Tg of the back surface coating film must be controlled within the range of the present invention in terms of commercial value.

[0030]

[Table 1]

[0031]

[Table 2]

[0032]

[Table 3]

[0033]

[Table 4]

[0034]

[Table 5]

[0035]

[Table 6]

[0036]

[Table 7]

[0037]

[Table 8]

(Note) * 1. Plating system EZ: Electric 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: Electrical _{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 the steel sheet in the width direction. PPI (number of irregularities per inch of length), Ra (average surface roughness) * 3. Metal Ni Filler Properties in Backside Coating F: Flake Ni, C: Chain Ni The blending ratio of Ni fillers having different F / C shapes is shown by resin weight ratio. The primary average particle size of the filler is expressed as [(major axis + minor axis) / 2]. Coating film Tg is TMA (probe method)
According to measurement.

* 4. Uniformity of coating film appearance (visual appearance) ◎: Uniform, ◯: Slightly roping, Δ: Partial roping, ×: Full surface roping or stripe unevenness * 5. Grounding property of backside coating Sandwich the front and back of a steel plate with copper pieces, and measure the contact resistance between the upper and lower copper pieces 5 times at different locations and take the average value (applied voltage 1 V, load 50 g / cm ² ). ◎: 0.5Ω or less, ◯: 1Ω or less, △: 2Ω or less, ×:
Over 5Ω

* 6. Adhesion to back side coating Primary adhesion; OT adhesion Repeatedly bending the same processed part 3
Peel off the cellophane tape. Secondary adhesiveness: Immersed in pure water, boiled and left for 2 hours and then for 24 hours, and then evaluated in the same manner as the primary adhesiveness. ⊚: No peeling of coating film, ◯: 5% or less of peeling, Δ: 10% or less of peeling, ×: More than 10% of peeling * 7. Resistance to pressure marks against top coatings The top and back surfaces of steel sheets are brought into contact with each other, and the load 6
The degree of indentation on the top coated surface after 0 kg / cm ² and 40 ° C. × 48 hrs elapsed was visually judged. ◎: No change, ◯: Very slight indentation through watermark, △: Thin indentation, ×: Clear indentation

[0042]

As described above, according to the present invention, in order to meet the needs for imparting the backside grounding property of the coated steel sheet, various studies including securing the stability thereof have been performed. As a result, the following surface roughness characteristics of the steel sheet original plate are included. We have come up with a proposal for a coating film for the back surface. That is, an appropriate range of PPI and Ra was specified as the back surface roughness of the original plate. The metallic Ni filler was adopted as the conductive circuit forming ability of the back surface coating film, but its shape and particle size were specified, and their appropriate compounding ratio was specified. The back coating has a proper range of Tg and it is specified. The film thickness range is specified as the back coating thickness. Due to these synergistic effects, the invention of the present application stably imparts the grounding property of the back surface coating film without impairing the pressure mark resistance of the top coating surface with high designability in coil coating under a high productivity line. As a revolutionary pre-coated steel sheet that was unprecedented in the past, we have succeeded in providing it to the market. In addition, it should be added that the coloring request to the back coating film of the present invention thus formed can be dealt with by appropriately blending a coloring pigment within the scope of the conventional art.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Office reference number FI technical display location B32B 15/08 104 Z 7148-4F

Claims (2)

[Claims] 1. The back surface of a steel sheet has a primary average grain size of 0.
The ratio of flake Ni / chain Ni in the resin component weight ratio is 1 to 1 with the shape ratio of the irregularly shaped metallic Ni filler of 1 to 50 μm.
0, the total amount of Ni filler is 10 to 200 in terms of resin weight ratio.
% Of the high molecular polyester resin coating film as a solid coating film having a glass transition point (Tg) of 50 ° C. or higher and a coating film Tg of 10 to 40% on the back surface thereof. Pre-coated steel sheet with excellent backside grounding characteristics, characterized in that the temperature is in ° C. 2. The surface roughness of the back surface of the original plate for coating is 7 in PPI.
The precoated steel sheet having excellent grounding property on the back surface according to claim 1, which is controlled to 0 to 150 and Ra to 0.5 to 2.0 μm.