JPH04226345A - Surface-treated steel sheet excellent in resistance to low-temperature chipping - Google Patents

Abstract

PURPOSE:To enhance resistance to low-temperature chipping of a surface-treated steel sheet by laminating a resin layer whose glass transition temperature is 60-120 deg.C onto a zinc series-plated layer provided on a steel sheet in the amount of 0.1-2.5g/m<2> by dry weight of resin. CONSTITUTION:Layers 12, 22 plated with a zinc series substance such as Zn-Ni are formed on both faces of a steel sheet 10 by means of electroplating and the like. Chromated films 24, 28 containing an amount of not more than 400mg/m<2> in terms of metallic chromium content are laminated onto the plated layers 12, 22, if necessary. The chromated films improve pain adhesion and resistance to corrosion. Furthermore, an organic coating 30 composed of resin whose glass transition temperature is 60-120 deg.C, or an organic coating 30 composed of a mixture of resin whose glass transition temperature is 60-120 deg.C with silica, as coating, is laminated onto the chromated layer 28 to form a surface-treated steel sheet. The surface-treated steel sheet thus obtained has very excellent resistance to low-temperature chipping and water-resistant secondary adhesive properties.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface-treated steel sheet having excellent low-temperature chipping resistance and suitable for use mainly as a steel sheet for automobile bodies.

0002

BACKGROUND OF THE INVENTION The demand for rust prevention for various steel plates is increasing year by year. In particular, rust prevention requirements for automobile steel sheets, electrical products, etc. are severe, and various surface-treated steel sheets that have been subjected to surface treatments to improve rust prevention properties have been developed and put into practical use.

[0003] One of such surface-treated steel sheets is a zinc-plated steel sheet which is coated with zinc plating, zinc-based alloy plating such as zinc-nickel plating, or the like.

[0004] This galvanized steel sheet is a steel sheet that has excellent rust prevention properties under high humidity conditions, but it is exposed to high humidity conditions such as the bag structure and bent parts (hemming parts) of automobile doors.
When applied to areas that are difficult to coat,
There is a problem that corrosion resistance is insufficient. In contrast, recently, an organic composite coated steel sheet in which a chromate and organic coating is applied to a zinc-based plated steel sheet has been proposed.

As described above, surface-treated steel sheets are often used in areas that are likely to be exposed to high humidity conditions, such as the inner surface of a car body.
Conventionally, emphasis has been placed on appearance, such as sharpness and paintability, for the steel plate surface that makes up the exterior surface, so cold-rolled surfaces have been used, and plated steel plates have not been used. For this reason, external rust occurs from paint defects and scratches, which not only impairs the appearance, but also progresses to the point of forming holes, which causes a reduction in the durability of the automobile. Against this background, in recent years, high rust prevention properties have been required on the outside of the vehicle body.
There are now cases where surface treatment is applied to both sides of a steel plate.

[0006] The outer surface of the car body is painted with a film thickness of about 100 μm and is in a relatively dry state, so corrosion progresses more slowly than the steel plate on the inner side of the car body, but scratches in the paint are If it exists, corrosion will progress from that part. Surface-treated steel sheets for exterior use, especially the steel sheet surfaces that serve as the exterior surfaces of automobiles, are required to have performance that does not need to be considered at all on the inside surface, and one such performance is low-temperature chipping resistance. Chipping is a phenomenon in which a pebble or the like hits the car body while the car is running, and the impact causes the plating layer to peel off, exposing the steel sheet base, and is particularly likely to occur at low temperatures.

[0007] Ordinary zinc-based plated steel sheets, especially zinc-nickel plated steel sheets, have poor plating adhesion. Therefore, after coating is applied on the plating layer, the stress of the coating film (electrodeposition coating, intermediate coating, top coating, etc.) is applied to the plating, which tends to cause peeling between the steel sheet base and the plating layer due to low-temperature chipping. Low-temperature chipping resistance is poor compared to cold-rolled steel sheet, which has good low-temperature chipping resistance. When the plating peels off, the sacrificial rust prevention properties of zinc are no longer effective, and external rust progresses. As described above, the zinc-based plated steel sheet used for the outer surface has a problem of poor low-temperature chipping resistance. As described above, there is a problem that there is no steel plate suitable for the exterior of a car body, that is, a steel plate that has both bare corrosion resistance in a highly humid environment on the inside of the car body and resistance to low-temperature chipping on the outside of the car body.

[0008]

In order to solve these problems, improvements have been made to improve the low-temperature chipping resistance of the outer surface of the steel plate and the bare corrosion resistance of the inner surface in a highly humid environment.

As a method for improving the low-temperature chipping resistance, the initial plating disclosed in JP-A No. 63-143286 is carried out at a low current density, and the surface of the steel sheet is coated with zinc-
A method of forming an epitaxial layer of nickel plating and then applying zinc-nickel plating by increasing the current density, which is characterized by preferentially and selectively dissolving and removing zinc in the plating layer, which is disclosed in JP-A-1-108400. a method of
0.9<Ni/(Zn+Ni)<1.0 (molar ratio),
Concerning the structure of the plating itself, such as a method of applying 50 to 1000 mg/m2 of zinc-nickel plating under the conditions of pH 2 or less and current density of 5 to 200 A/dm2, followed by zinc-nickel plating with a predetermined nickel content, i.e.,
Various methods for increasing plating adhesion have been disclosed.

[0010] According to each of the above methods, the low-temperature chipping resistance is certainly improved compared to ordinary zinc-plated steel sheets. However, in either method, the low-temperature chipping resistance does not reach the level of cold-rolled steel sheets, which are excellent in this, and further improvement of the low-temperature chipping resistance is desired.

[0011] Furthermore, a chromate or phosphate treated film layer is provided on the plating disclosed in JP-A-64-78832, and furthermore, the Tg point is 55°C or less and the hardness at room temperature after baking is a pencil. A method is disclosed in which an organic resin coating layer having a hardness of H to 2B is provided with a thickness of 0.1 to 2.0 μm.

[0012] The peeling area in a low-temperature chipping property test of a plated steel sheet is usually calculated by converting only the exposed area of the base metal (peeling between the base metal and the plating), and not the remaining plating area. According to the surface-treated steel sheet of JP-A-64-78832 mentioned above,
Peeling between the base metal and plating has decreased. However, at a Tg point of 55°C or lower, which is an essential requirement for this method, considerable peeling is observed in areas that are not converted in the low-temperature chipping resistance test (between the resin and the electrodeposited coating), making it impractical for use as exterior panels for automobiles. It has been found. This is presumed to be because the adhesion between the resin and the electrodeposited coating becomes weak when the Tg point is below 55°C.

[0013] In addition to ensuring such low-temperature chipping resistance and paint adhesion, steel plates for exterior use are also desired to have excellent corrosion resistance and paintability as described above.

An object of the present invention is to solve the above-mentioned problems of the prior art, and to ensure that both the front and back surfaces of the steel plate used for parts such as the bag structure have appropriate functions.
The object of the present invention is to provide a galvanized surface-treated steel sheet that has excellent low-temperature chipping resistance, external rust resistance, and water-resistant secondary adhesion, and has excellent bare corrosion resistance on the other side, and is easy to manufacture. .

[0015]

[Means for Solving the Problems] In order to achieve the above object, the present inventors have made extensive studies and have found that the phosphate treatment that is commonly performed on galvanized surface-treated steel sheets is resistant to low-temperature chipping. It was found that it decreased the sex. In zinc-plated surface-treated steel sheets for automobiles, in order to improve paint adhesion (secondary adhesion), phosphate treatment is performed after the plating layer is formed to form a water-insoluble phosphate film. Research by the present inventors has revealed that by having this phosphate film, the secondary adhesion of the obtained surface-treated steel sheet is improved, but the low-temperature chipping resistance is reduced.

[0016] Further, the present inventors have conducted further studies and found that a predetermined organic coating layer, that is, a resin having a glass transition point of 60 to 120°C, is deposited on the zinc-based plating layer in an amount of 0 in terms of dry weight.
．． It has been found that by setting the amount to 1 to 2.5 g/m2, not only the peeling of the plating but also the peeling between the resin and the electrodeposited coating film is significantly improved in the low-temperature chipping property test. In addition, such an organic coating layer has necessary and sufficient electrodeposition coating properties, but the composition of the organic coating layer is a mixture of resin and silica, and the glass transition point of the coating is 60 to 12.
By controlling the adhesion amount at 0° C. to 0.1 to 2.5 g/m 2 in terms of dry weight, the electrodeposition coating properties near the upper limit of the film thickness can also be significantly improved.

Moreover, although the organic coating layer described above has sufficient paint adhesion, it is possible to improve the adhesion by applying a chromate film of 400 mg/m2 or less before forming this organic coating layer. It is possible to obtain excellent paint adhesion and also exhibit excellent corrosion resistance.

Furthermore, by having such a chromate film and an organic coating layer, even if phosphate treatment is performed, substantial formation of a phosphate film that reduces low-temperature chipping resistance can be prevented. can.

Further, chromate treatment was applied to the zinc-based plating layer on the other side of the surface-treated steel sheet produced in this way, with a coating amount of 5 to 400 mg/m2 in terms of metallic chromium, and further, a chromate treatment with a number average molecular weight of 2000 mg/m2 was applied. By applying a mixture of a resin composition based on the above epichlorohydrin-bisphenol A type epoxy resin and silica at a dry weight of 0.2 to 3.0 g/m2, excellent bare corrosion resistance is also imparted. be able to.

That is, the present invention has a zinc-based plating layer on at least one side, with or without chromate treatment with a coating amount of 400 mg/m2 or less in terms of metallic chromium, and with a glass transition temperature is 60-12
The adhesion amount of the resin layer at 0℃ is 0.1 to 2.5 g/dry weight.
The present invention provides a surface-treated steel sheet having excellent low-temperature chipping resistance, characterized by having m2.

[0021] The present invention also has a zinc-based plating layer on at least one side, and the coating amount on the upper layer is 4 in terms of metallic chromium.
With or without chromate treatment of 00 mg/m2 or less, the upper layer is a mixture layer containing resin and silica and having a glass transition temperature of 60 to 120°C, with a dry weight of 0.1 to 2.5 g/m2. The present invention provides a surface-treated steel sheet having excellent low-temperature chipping resistance, characterized by having m2. Here, the content of silica in the mixture layer is preferably 50% by weight or less. In addition, the zinc-based plating layer on the side where the resin layer or mixture layer is provided has a zinc-nickel plating layer with a nickel content of 16 wt% or more as the first layer with a coating amount of 0.05 g/m2 to 1.0 g/m2 Yes. However, it is preferable to have a zinc-nickel plating layer with a nickel content of 9 to 15 wt% as the second layer.

Furthermore, the present invention has a zinc-based plating layer on both sides, and one side (I) has the upper layer subjected to chromate treatment with a coating amount of 400 mg/m 2 or less in terms of metallic chromium, or not. The upper layer has a glass transition temperature of 60~
The amount of adhesion of the resin layer at 120℃ is 0.1 to 2.5 by dry weight.
g/m2, and the upper layer of the other side (II) is treated with chromate with a coating amount of 5 to 400 mg/m2 in terms of metallic chromium, and is further coated with epichlorohydrin-bisphenol having a number average molecular weight of 2000 or more. Characterized by a layer of a mixture of a resin composition based on type A epoxy resin and silica having a dry weight of 0.2 to 3.0 g/m2.One side has excellent low temperature chipping resistance and other aspects have excellent corrosion resistance. The purpose of this invention is to provide a steel sheet with an excellent surface treatment.

Furthermore, the present invention has a zinc-based plating layer on both sides, and one side (I) is coated with or without chromate treatment with a coating amount of 400 mg/m2 or less in terms of metal chromium on the upper layer. The upper layer has a mixture layer (A) containing resin and silica and having a glass transition temperature of 60 to 120°C with a dry weight of 0.1 to 2.5 g/m2, and the other side (II) is 5 to 4 in terms of metallic chromium in the upper layer.
A mixture layer (B) of silica and a resin composition based on an epichlorohydrin-bisphenol A type epoxy resin having a number average molecular weight of 2000 or more was subjected to chromate treatment with a coating weight of 00 mg/m2, and the dry weight The object of the present invention is to provide a surface-treated steel sheet, characterized in that one side has excellent low-temperature chipping resistance and the other side has excellent corrosion resistance. Here, it is preferable that the content of silica in the mixture layer (A) is 50% by weight or less. In addition, the zinc-based plating layer on one side (I) is a first layer of a zinc-nickel plating layer with a nickel content of 16 wt% or more at a coating amount of 0.05 g/m2.
~1.0 g/m2, and preferably has a zinc-nickel plating layer with a nickel content of 9 to 15 wt% as the second layer.

The present invention will be explained in detail below.

The present invention was made based on the above-mentioned knowledge, and this point will be explained in more detail with reference to the drawings.

As shown in FIG. 2, in the conventional double-sided surface-treated steel sheet for automobile bodies, a plating layer 12 such as zinc-nickel plating is formed on a cold rolled steel sheet 10, and the upper layer of the plating layer 12 is painted. , that is, cationic electrodeposition coating 16,
Phosphate film 14 formed by phosphate treatment to improve the adhesion of intermediate coat 18 and top coat 20
has. Furthermore, in order to provide even higher corrosion resistance, some steel sheets have a chromate layer 24 and an organic coating layer 26 on the side that corresponds to the inner surface of the vehicle body.

Conventional surface-treated steel sheets having such a structure have low low-temperature chipping resistance, and various improvement methods as described above have been proposed, but none of these methods can provide the desired low-temperature chipping resistance. As mentioned above, even if only the bare corrosion resistance of the inner surface of the vehicle body is improved, corrosion progresses from the scratches on the outer surface of the vehicle body, making it impossible to obtain a good surface-treated steel sheet for automobiles.

As a result of extensive studies, the inventors of the present invention found that by forming a phosphate film 14 through phosphate treatment, which is well-known as a base treatment for painting, conventional surface-treated steel sheets can be made more resistant to low temperatures. It was found that the chipping property was reduced.

The reason for this is not clear, but it is thought to be as follows.

[0030] The commonly used phosphate treatment allows the paint to firmly adhere to the upper layer. This is thought to be because the phosphate film 14 has large phosphate crystals and a high surface roughness, which allows the paint to obtain a physical anchoring effect. Therefore, it is thought that the phosphate crystals increase the contact area between the electrodeposition coating and the plating, thereby promoting transmission of residual stress in the paint, causing distortion in the plating, and reducing plating adhesion.

However, if this phosphate film is not formed, but instead an electrodeposition coating 16, an intermediate coating 18, a top coating 20, etc. are formed, sufficient adhesion, especially water-resistant secondary adhesion, cannot be obtained. First, it is well known that it is impossible to put it to practical use as a steel plate for automobiles, especially as a steel plate for exterior use.

[0032] Furthermore, a chromate or phosphate treatment film layer is provided on the plating, and the Tg point is 55°C or less, and the hardness at room temperature after baking hardening is a pencil hardness of H to 2B.
Although there was no peeling of the plating on steel sheets provided with an organic resin film layer of 0.1 to 2.0 μm, peeling of the coating occurred during low-temperature chipping, which is thought to be due to a decrease in the adhesion between the resin and the electrodeposited coating. It's still not practical.

On the other hand, the surface-treated steel sheet of the present invention has
A predetermined organic coating layer 30 substantially free of this phosphate film 14 and having a glass transition temperature of 60% is formed on at least one surface to improve low temperature chipping resistance and water resistant secondary adhesion. It has a layer of resin having a temperature of ~120°C or a mixture layer having a glass transition temperature of 60°C to 120°C, with a dry weight of 0.1 to 2.5 g/m 2 .

In other words, as a result of further intensive studies, the present inventors have found that by forming the organic coating layer 30 on the plating layer 12, the transmission of residual stress of each paint layer to the plating layer is alleviated, and the plating is removed. It has also been found that it is possible to suppress not only the peeling of the paint film but also the peeling of the paint film.

Moreover, it has also been found that by having such an organic coating layer 30 and a predetermined chromate film, even if phosphate treatment is performed, a phosphate film is not substantially formed. Note that "substantially no phosphate film is formed" means that the amount is 0.2 g/m2 or less.

Furthermore, in the surface-treated steel sheet of the present invention, excellent corrosion resistance, particularly water-resistant secondary adhesion, can be obtained by applying chromate treatment as the lower layer of the organic coating layer 30.

Furthermore, zinc plating is applied to the other side, and chromate treatment is applied with a coating amount of 5 to 400 mg/m2 in terms of metallic chromium, and the number average molecular weight is 2.
000+ epichlorohydrin-bisphenol A
By applying a mixture of a resin composition based on molded epoxy resin and silica at a dry weight of 0.2 to 3.0 g/m2, corrosion resistance is ensured in areas where it is difficult to coat the interior surface of the vehicle body. It can also improve resistance to pitting and corrosion from the side, and in combination with the aforementioned excellent low-temperature chipping resistance on the outside of the car body, it can exhibit extremely excellent performance as a steel plate for the outside of an automobile body.

The present invention will be explained in detail below.

The surface-treated steel sheet of the present invention has plating layers 12 and 22 made of zinc-based plating on both sides of the steel sheet 10. The zinc-based plating in the present invention is not particularly limited, but includes pure zinc plating, binary alloy plating such as Zn-Ni and Zn-Fe, and ternary alloy plating such as Zn-Ni-Cr and Zn-Co-Cr. based alloy plating, Zn-Co-Cr-Al2
There are various types of plating such as composite dispersion plating such as O3, and there are no particular limitations on the method of forming the plating, such as electroplating,
Various methods such as hot-dip plating are applicable.

Further, when the applied plating is zinc-nickel plating, in order to improve the adhesion between the steel sheet 10 and the plating layer 12, the lower part of the plating layer is made of Ni.
It is preferable to form the Zn-Ni plating with a coating content of 16 wt% or more in an amount of 0.05 to 1.0 g/m2. The upper layer has a nickel content of 9 to 1
It is preferable to have a zinc-nickel plating layer of 5 wt%.

[0041] Moreover, on such a zinc-based plating layer,
By applying the chromate films 24 and 28 in the following amount in terms of metal chromium, good paint adhesion and corrosion resistance can be obtained by having such chromate films 24 and 28.

In the surface-treated steel sheet of the present invention, the amount of chromate film 28 deposited is 400 mg/m in terms of metallic chromium.
2 or less. If it exceeds 400 mg/m2, chromium elution occurs, which is unfavorable from an environmental standpoint. In addition, the amount of chromate film 24 deposited is 5 to 400 m in terms of metallic chromium.
g/m2. If it is less than 5 mg/m2, it will be difficult to form a uniform chromate film 24 and bare corrosion resistance will be insufficient. Moreover, if it exceeds 400 mg/m2, chromium elution will occur, which is unfavorable from an environmental standpoint.

The method for forming the chromate films 24 and 28 is not particularly limited, and any known chromate treatment method such as coating type, electrolytic type, or reaction type can be applied. Moreover, various additives such as silica may be added to the chromate treatment liquid as necessary.

In the surface-treated steel sheet of the present invention, the chromate layer 28 is provided with an organic coating 30 made of a resin having a glass transition point of 60 to 120°C, or a resin having a glass transition point of 60 to 120°C as a coating. It has an organic coating layer 30 made of a mixture of silica. With such a configuration, very good low temperature chipping resistance and water resistant secondary adhesion can be obtained. Additives may be added to this organic coating layer 30 if necessary.

The range of the glass transition point of the organic coating layer 30 applied to the present invention is 60 to 120° C. for both the resin alone and the resin and silica mixture layer. 6
At temperatures below 0°C, the residual stress of each paint layer is not applied to the plating layer 12, and the transmission of impact is stopped at the organic coating layer 30, so peeling from the steel sheet base does not occur.
As described above, the adhesion between the organic coating layer 30 and the coating layer formed thereon is low, and peeling occurs between the two, making it impossible to obtain a good surface-treated steel sheet. On the other hand, if the glass transition point of the organic coating layer 30 exceeds 120°C, the viscosity of the paint will be high and the solubility in various solvents will be low, making it difficult to apply uniformly and still maintain a good surface. Unable to obtain treated steel plate.

Various resins can be used as the resin for the organic coating layer 30 of the present invention as long as they have the above-mentioned glass transition point, such as epoxy resins, urethane resins, acrylic resins, phenolic resins, polyolefin resins, etc. is exemplified.

Note that two or more of the above resins may be used in combination.

[0048] Even if the resin has a glass transition point below the range of the present invention, it is possible to add additives such as various curing agents and modifiers to raise the glass transition point to 60°C or higher. be. In the present invention, the amount of the organic coating layer 30 deposited is 0.1 to 2.5 g/m2 in terms of dry weight. If the amount of the organic coating layer 30 is less than 0.1 g/m2, it is difficult to uniformly form the organic coating layer 30 on the chromate film 28, and chromium is eluted. Furthermore, if the amount of the organic coating layer 30 deposited exceeds 2.5 g/m2, the electrodeposition coating 16, which is normally performed after the formation of the organic coating layer 30, may not be possible. Moreover, even if it can be done, there is a risk that the film will be non-uniform. In addition, when using a mixture of multiple resins as mentioned above, the total amount should be 0.1 to 2.5 g/m2.
That is.

There are no particular limitations on the method of forming the organic coating layer 30, and various solvents are used depending on the resin to be applied, the resin is dissolved therein, and the method is coated by spray coating, dip coating, roll coating, etc. After coating, a conventional drying method such as heating or ultraviolet irradiation may be used.

Further, the organic coating layer 26 of the present invention includes a mixture of silica and a resin composition based on an epichlorohydrin-bisphenol A type epoxy resin having a number average molecular weight of 2000 or more as an upper layer of the chromate layer 24. Apply at a dry weight of 0.2 to 3.0 g/m2. With such a configuration, bare corrosion resistance can be significantly improved. Epoxy resins include glycidyl epoxy, glycidyl amine, aliphatic epoxides, alicyclic epoxides, etc., but epichlorohydrin-bisphenol A type epoxy resin is used in the steel sheet of the present invention from the viewpoint of toughness and corrosion resistance. A specific example is Epicote 1
Commercially available products such as 010, 1009, 1007, and 1004 (all manufactured by Shell Chemical) can be mentioned.

The average molecular weight Mn of such a resin composition is preferably 2,000 or more. Silica contributes to the stabilization of corrosion products, and the resin functions as a binder for this silica. The number average molecular weight of the resin is 200
If it is less than 0, the resin length will be short and the resin will not have a mesh structure, so it will not function as a binder for silica, significantly impairing corrosion resistance and paint adhesion, and also inhibiting interaction with silica in paint. Compatibility also deteriorates. There is no particular upper limit to the number average molecular weight, but if it exceeds 100,000, the resistance of the film increases and may impede electrodeposition coating properties and spot weldability, so it is preferably 100,000.
The following shall apply.

Further, dialkanolamine is preferably added to the oxirane ring at the end of the epoxy resin. this is,
The aim is to increase the number of highly reactive primary hydroxyl groups to facilitate bonding with silica. Examples of the dialkanolamine used here include diethanolamine, dipropanolamine, and dibutanolamine.

Furthermore, if necessary, it is possible to modify a part of the resin composition with urethane, or it is also possible to incorporate an amine resin such as melamine or benzoguanamine into the paint as a crosslinking agent. good.

In the surface-treated steel sheet of the present invention having the above-described structure, an electrodeposition coating 16, an intermediate coating 18, a top coating 20, etc. are applied on the organic coating layer 30, and an electrocoating coating 16, an intermediate coating 18, a top coating 20, etc. The electrodeposition coating 16 is applied to various uses such as steel plates for automobiles. As described above, the surface-treated steel sheet of the present invention has excellent coating film adhesion even without a phosphate film.

[0055]

[Examples] Hereinafter, the present invention will be explained in more detail by giving specific examples of the present invention.

(Example 1) A cold-rolled steel sheet was pickled, degreased, and then plated to produce a plated steel sheet. For some zinc-nickel plating, the initial plating is performed at a low current density so that the Ni content is 16% or more in the area where the coating weight is 0.3 g/m2 at the initial plating, and then the current density is increased. In addition, measures for plating adhesion were taken by performing Zn-Ni plating with an average Ni content of 12%. Table 3 shows the plating type, area weight, and presence or absence of measures for plating adhesion of the produced plated steel sheets.

[0057] A chromate treatment solution was applied to the surface of the plated steel sheet thus produced using a roll coater, and then chromate treatment was performed by drying it in an electric furnace. On one side of several steel plate surfaces prepared in this way,
An organic coating layer was formed using the resin shown in Table 1 and the resin shown in Table 2 on the other side. The formation of the organic coating layer is as follows:
The resin to be applied was dissolved in a corresponding solvent, silica was added as appropriate, and the coating was applied using a bar coater, followed by drying in an electric furnace. Table 3 shows the resin type, silica content, glass transition temperature, and resin coating amount of the formed organic coating layer.

[0058] Some of the samples are
Phosphate treatment was performed. The processing conditions are as shown below.

(Phosphate treatment) Normal alkali degreasing was performed, followed by phosphate treatment (immersion in Palbond 3020 manufactured by Nippon Parkerizing Co., Ltd. for 120 seconds). Table 3 shows the presence or absence of phosphate treatment and the presence or absence of phosphate film. Regarding the phosphate coating, if the coating amount was 0.2 g/m2 or more, the coating was present, and if it was less than 0.2 g/m2, the coating was not coated. The amount of chromium eluted from each sample obtained here was measured before and after the alkaline degreasing step before electrodeposition coating. In the measurement, the amount of chromium deposited on the steel plate before and after degreasing was measured by fluorescent X-ray analysis, and the difference was regarded as the amount of chromium eluted for evaluation. The evaluation criteria are as follows. ◎ Less than 1 mg/m2 ○ Less than 1 to 2 mg/m2 △ Less than 2 to 5 mg/m2 × More than 5 mg/m2 The results are shown in Table 3.

(Corrosion Resistance) The bare corrosion resistance of one side of the surface-treated steel sheet produced as described above was investigated. A combined cycle corrosion test was conducted in which the following conditions were used as one cycle, and the test was evaluated based on the number of cycles at which red rust occurred.

Power Top U-600 (manufactured by Nippon Paint Co., Ltd.) was electrodeposited on one side of the surface-treated steel sheet thus prepared at a voltage of 250 V and a bath temperature of 28° C. for 180 seconds.
Electricity was applied and baking was performed at 170°C for 20 minutes. After electrodeposition coating, the sample was further spray-painted with an automotive intermediate coat and a top coat. Using each sample thus obtained, a diamond shot test and a water resistant secondary adhesion test were conducted.

(Diamond shot test) Diamond: 10 mg (±1 mg) Test temperature: -20°C Shot speed: 210 km/h A diamond shot test was conducted under each of the above conditions. After the test, a peel test was performed using tape. The evaluation method was the total peeled area of 10 shots. Note that the shot speed of 210 km/h is stricter than normal test conditions in Japan (normal shot speed of 170 km/h or less).

(Waterproof secondary adhesion test) Each sample was immersed in 40°C warm water for 240 hours. After taking out each sample, within 10 minutes, divide the sample into 2m squares in a grid pattern.
Make 100 scratches at m intervals using a cutter knife,
A peel test was conducted using cellophane tape. Evaluation was performed by measuring the number of peeled pieces. ◎ No peeling ○ Number of peeled pieces: 1 or less △ Number of peeled pieces: 2 to 10 × Number of peeled pieces: 11 or more The results of each test are shown in Table 3.

[0064] Table 1: Resin type

0065
]Table 2 Resin types

[0066]

[Table 1]

[0067]

[Table 2]

[0068]

[Table 3]

[0069]

[Table 4]

[0070]

[Table 5]

From the results shown in Table 3 above, the surface-treated steel sheet of the present invention has much better low-temperature chipping resistance than the conventional surface-treated steel sheet that does not have an organic coating on the side that is applied to the outer surface. It can be seen that it has a sexual nature.

Furthermore, since the surface-treated steel sheet of the present invention has an organic coating on the other side, it exhibits excellent corrosion resistance.

[0073]

[Effects of the Invention] Since the surface-treated steel sheet of the present invention has excellent low-temperature chipping resistance, it can be widely used for automobile bodies, and is especially suitable for use as automobile outer panels.

[Brief explanation of the drawing]

FIG. 1 is a diagram conceptually showing a surface-treated steel sheet having excellent low-temperature chipping resistance according to the present invention.

FIG. 2 is a diagram conceptually showing a conventional surface-treated steel sheet.

[Explanation of symbols]

10 Cold rolled steel plate 12 Zinc-based plating layer 14 Phosphate film 16　Electrodeposition coating 18 Intermediate coating 20 Top coat painting 22 Zinc-based plating layer 24 Chromate film 26 Organic coating layer 28 Chromate film 30 Organic coating layer

Claims (8)

[Claims] Claim 1: Has a zinc-based plating layer on at least one side, and has a coating amount of 400 mg/metal chromium on the upper layer.
m2 or less, with or without chromate treatment, and having a resin layer with a glass transition temperature of 60 to 120°C as an upper layer with a dry weight of 0.1 to 2.5 g/m2. A surface-treated steel sheet with excellent low-temperature chipping resistance. Claim 2: At least one side has a zinc-based plating layer, and the amount of adhesion on the upper layer is 400 mg/metal chromium equivalent.
m2 With or without chromate treatment, the upper layer contains resin and silica and has a glass transition temperature of 60
The adhesion amount of the mixture layer at ~120℃ is 0.1 to 2 by dry weight.
．． 5g/m2 A surface-treated steel sheet having excellent low-temperature chipping resistance. 3. The surface-treated steel sheet with excellent low-temperature chipping resistance according to claim 2, wherein the silica content in the mixture layer is 50% by weight or less. 4. The zinc-based plating layer on the side where the resin layer or mixture layer is provided has a nickel content of 16 as the first layer.
Zinc-nickel plating layer with a coating weight of 0.05 wt% or more
g/m2 to 1.0 g/m2, and further comprising a zinc-nickel plating layer having a nickel content of 9 to 15 wt% as the second layer. steel plate. 5. Both sides have a zinc-based plating layer, and one side (I) has a zinc-based plating layer on the top layer of 400 mg/m in terms of metallic chromium.
2 A resin layer with a glass transition temperature of 60 to 120°C with a dry weight of 0.1 to 2.5 g/m2 on the upper layer, with or without chromate treatment with a coating weight of 0.1 to 2.5 g/m2 on the other side. The upper layer of surface (II) is treated with chromate at a coating weight of 5 to 400 mg/m2 in terms of metallic chromium, and is further made based on epichlorohydrin-bisphenol A type epoxy resin with a number average molecular weight of 2000 or more. A surface-treated steel sheet having excellent low-temperature chipping resistance on one side and excellent corrosion resistance on the other side, characterized by having a layer of a mixture of a resin composition and silica in a dry weight of 0.2 to 3.0 g/m2. [Claim 6] Both sides have a zinc-based plating layer, and one side (I) has a zinc-based plating layer on the upper layer of 400 mg/m in terms of metallic chromium.
2 A mixture layer (A) containing resin and silica and having a glass transition temperature of 60 to 120° C. is applied with or without chromate treatment with a coating amount of 0.1 to 0.1 to 120° C. on a dry weight basis. 2.5g/m2, and the other side (II
) contains 5 to 400 mg/m2 in terms of metallic chromium in the upper layer.
chromate treatment with a coating weight of .2-3.
0g/m2 A surface-treated steel sheet having one side with excellent low-temperature chipping resistance and the other side with excellent corrosion resistance. 7. The surface-treated steel sheet with excellent low-temperature chipping resistance according to claim 6, wherein the silica content in the mixture layer (A) is 50% by weight or less. 8. The zinc-based plating layer on the one surface (I) is a first layer of a zinc-nickel plating layer having a nickel content of 16 wt% or more at a coating amount of 0.05 g/m2.
-1.0 g/m2, and the other surface having excellent low temperature chipping resistance according to claims 5, 6 and 7, further comprising a zinc-nickel plating layer having a nickel content of 9 to 15 wt% as the second layer. A surface-treated steel sheet with excellent corrosion resistance.