JPH09299876A - Manufacture of metal sheet coated with organic coating film with high alkali resistance - Google Patents

Abstract

PROBLEM TO BE SOLVED: To prevent a synthetic resin coating film on a steel sheet coated with an organic coating film from being parted even in the case the alkali degreasing conditions are severe. SOLUTION: An emulsion of an aqueous acrylic resin dispersion having 3-20KOH mg/g acid value, 10000 or higher molecular weight, and 0-30 deg.C glass transition temperature is applied to the surface of a chromated and electrolytic zinc-coated steel sheet having Ra 0.5μm or higher center line average roughness as surface roughness and successively the electrolytic zinc-coated steel sheet is heated and dried while the temperature of the steel sheet 13 being kept within a range from 160 deg.C to 230 deg.C.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing an organic film-treated metal strip in which the surface of a metal strip is covered with a thin synthetic resin film.

[0002]

2. Description of the Related Art Metal strips, such as electrogalvanized steel strips, are widely used in electrical equipment housings as a material having excellent surface appearance, workability, and corrosion resistance. In general, the housing is manufactured by punching a blank plate from an electrogalvanized steel strip, applying a press oil to the forming process, subsequently removing the press oil by alkaline degreasing, and further applying a powder coating. Is done by. However, the electrogalvanized steel strip has a problem that stains such as fingerprints are likely to adhere during handling, which may cause problems such as poor appearance after powder coating and deterioration of coating adhesion. Was often there.

The most widely used countermeasure against the stains is a method of coating a thin synthetic resin coating on the surface of the electrogalvanized steel strip, which is called an organic coating treatment. The production of the organic coating-treated electrogalvanized steel strip (hereinafter, may be abbreviated as organic treated galvanized steel strip) is performed by applying an emulsion solution in which a synthetic resin is dispersed in water to the surface of the electrogalvanized steel strip by a roll. The temperature of the electrogalvanized steel strip coated with the emulsion solution and subsequently coated with the emulsion solution is adjusted to 10
It is carried out by heating to a value in the range of 0 to 130 ° C. and drying the coating.

[0004]

As described above, since a thin synthetic resin film is formed on the surface of the organically treated plated steel strip, it has good fingerprint resistance and effectively adheres stains. Can be prevented. Therefore, by using the organically treated plated steel strip instead of the electrogalvanized steel strip, it is possible to effectively prevent the occurrence of defects due to stains such as fingerprints.

However, the above-mentioned organically treated plated steel strip has a problem that the adhesion strength of the organic coating is lowered when the degreasing conditions during alkaline degreasing are severe, and the coating is easily peeled off. A decrease in the adhesion strength of the organic coating causes a decrease in the adhesion strength of the powder coating film formed on the surface layer of the organic coating, so that the above problem is an issue to be solved immediately. The harsh alkaline degreasing condition means that the concentration (PH) of the degreasing agent is high,
In addition, it is a case where the degreasing time is long, for example, the conditions such as the concentration of the degreasing agent sodium silicate; 30 g / l, PH; 11, and the degreasing time of 12 minutes.

As a result of extensive studies on the above problems, the present inventors have set the acid value, molecular weight and glass transition temperature of the synthetic resin coating within appropriate ranges, and the surface of the electrogalvanized steel strip as a raw material. It was found that the peeling of the coating can be prevented even under severe alkaline degreasing conditions by setting the roughness within the appropriate range and the drying heating temperature of the synthetic resin coating within the appropriate range.

The present invention was made on the basis of the above-mentioned findings, and an object thereof is to prevent the adhesion strength of a synthetic resin film from being deteriorated even when the conditions of alkaline degreasing are severe, and to ensure the peeling of the film. An object of the present invention is to provide a method for producing an organic film-treated metal strip that can be prevented.

[0008]

The present invention has an acid value of 3 to 20 KOHmg / g and a molecular weight of 10,000 after drying.
The above is an emulsion solution of a water-dispersible synthetic resin having a glass transition temperature of 0 to 30 ° C., which is subjected to chromate treatment and has a surface roughness of 0.5 μm or more in terms of center line average roughness Ra. Apply to the surface and continue to increase the temperature of the metal strip to 1
A method for producing an organic film-treated metal strip having excellent alkali resistance, which comprises heating to a value in the range of 60 to 230 ° C. According to the present invention, the acid value, which represents the content of free fatty acids in the synthetic resin film, is set to a value within an appropriate range. Since the upper limit of the acid value is set appropriately, the amount of the neutralization reaction product of the alkali content of the degreasing agent and the free fatty acid is increased when performing the alkaline degreasing after molding and processing the metal band treated with the organic coating. Suppressed. Since the neutralization reaction product is produced in the synthetic resin film and reduces the adhesion strength of the film, the suppression of the amount of the neutralization reaction product produced results in the improvement of the adhesion force of the film. Further, since the lower limit of the acid value is properly set, hydrogen bonding between the synthetic resin coating and the chromate coating is promoted, and the adhesive strength of the synthetic resin coating is improved.
Furthermore, since the lower limit of the molecular weight of the synthetic resin coating is set appropriately, the alkali resistance of the synthetic resin coating is improved. Furthermore, since the lower limit of the glass transition temperature is set appropriately, excessive softening of the hardness of the synthetic resin coating is avoided, and the adhesion of the synthetic resin coatings during coil winding is reliably prevented. Further, since the upper limit value of the glass transition temperature is properly set, the hardness of the synthetic resin film is prevented from being excessively hardened, and the work adhesion of the synthetic resin film is improved. Furthermore, since the lower limit value of the surface roughness of the metal band is set appropriately, the anchor effect improves the adhesiveness of the synthetic resin film. Furthermore, since the lower limit of the heating temperature of the metal band coated with the synthetic resin is set appropriately, hydrogen bonding between the synthetic resin coating and the chromate coating is promoted,
The adhesion of the synthetic resin coating is improved. Further, since the upper limit of the heating temperature of the metal strip is set appropriately, the discoloration of the synthetic resin film, which is likely to occur when the heating temperature of the metal strip is excessively high, is reliably prevented. As described above, in the present invention, since the adhesion of the synthetic resin film can be improved by setting the appropriate conditions, even if the alkaline degreasing condition is severe, it is possible to reliably prevent the peeling of the synthetic resin film. You can Therefore, it is possible to efficiently produce an organic coating-treated metal strip having excellent alkali resistance.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a cross-sectional view showing a simplified structure of an organic coating-treated electrogalvanized steel strip according to the present invention (hereinafter sometimes abbreviated as organic-treated plated steel strip). 2 is a schematic view showing a simplified configuration of an organic film treatment apparatus capable of suitably manufacturing the organically treated plated steel strip shown in FIG. 1, and FIG. 3 is a synthetic resin film (hereinafter abbreviated as organic film). Is a graph showing the relationship between the acid value and the film peeling area ratio, and FIG. 4 is a graph showing the relationship between the plate temperature of the organically treated plated steel strip and the film peeling area ratio,
Figure 5 shows the plate temperature of the organically treated plated steel strip and the yellowness b of the organic coating.
It is a graph which shows the relationship with a value.

Referring to FIG. 1, an organically treated plated steel strip 1
Is composed of an electrogalvanized steel strip 13 as a base material and an organic coating 5 formed on the surface thereof. The electrogalvanized steel strip 13 includes a base material steel strip 3 and a base material steel strip 3 And a chromate film 2 formed on the surface of the zinc plating layer 4.
The base material steel strip 3 constituting the electrogalvanized steel strip 13 is, for example, low carbon aluminum killed steel, and its metal structure is a recrystallized structure annealed after cold rolling. Low carbon aluminum killed steel has excellent workability and can perform complex forming. The dimensions of the base material steel strip 3 are, for example, plate thickness; 0.5 to 1.6 mm, plate width;
It is 00 to 1300 mm. The material of the base material steel strip 3 is not limited to low carbon aluminum killed steel, but may be low carbon steel, stainless steel, or the like, and may be other metal instead of steel.

The zinc plating layer 4 is a plating layer formed by electrogalvanizing, and its material is, for example, pure zinc. The amount of the galvanized layer 4 attached is, for example, 5 to 5.
It is 30 g / m ² (one side). The material of the zinc plating layer 4 is not limited to pure zinc, but may be a zinc nickel alloy or the like. The chromate film 2 is a film that improves the corrosion resistance of the galvanized layer 4, and is formed by a chromate treatment. The chromate treatment is performed by applying or spraying a chromate treatment liquid on the surface of the zinc plating layer 4. The chromate treatment liquid is an aqueous solution containing chromic acid, a chromate salt, and a mineral acid as a main component, and the chromate film 2 is composed of a salt containing chromium as a main component, an oxide, a hydrate, and the like. The amount of the chromate film 2 attached is, for example, 10 to 30 mg / m ² .

The surface roughness of the electrogalvanized steel strip 13 is preferably 0.5 μm or more in terms of center line average roughness Ra. This is because the anchor effect increases as the surface roughness increases, and the mechanical adhesion between the electrogalvanized steel strip 13 and the organic coating 5 formed on the surface thereof improves.

The organic coating 5 is a coating made of acrylic resin, for example. Acrylic resins are colorless and transparent resins, and there are many types. Examples of the acrylic resin used as the organic coating 5 include polymers or copolymers of acrylic acid, methacrylic acid, acrylic acid esters, and methacrylic acid esters. In addition, examples of acrylic acid esters include methyl acrylate, ethyl acrylate, and butyl acrylate. In this embodiment, as the acrylic resin, a polymer or copolymer of acrylic acid, butyl acrylate, or methyl acrylate, which is water dispersible and hard to attach dirt, is used. The organic film 5 is
It is formed by applying the emulsion solution in which the acrylic resin is dispersed in water to the electrogalvanized steel strip 13 and heating and drying.

The organic coating 5 has an acid value of 3 to 20K.
OH mg / g, its molecular weight is 10,000 or more, its glass transition temperature is 0 to 30 ° C., and its film thickness is 0.5 to
The thickness is preferably 5.0 μm. The thickness of the organic coating 5 is limited to the above range because the effect of preventing the adhesion of stains such as fingerprints is not sufficient if the thickness is less than 0.5 μm.
This is because the stain adhesion preventing effect is saturated when the film thickness exceeds 5.0 μm. The reason why the acid value of the organic coating film 5 is limited to the above range will be described below with reference to FIG.

The acid value of the organic coating 5 is shown on the horizontal axis of FIG. 3, and the film peeling area ratio is shown on the vertical axis. The acid value is a value representing the content of the free acid in the resin, and is represented by the number of milligrams of potassium hydroxide (KOH) required to neutralize the free acid contained in 1 g of the resin. The coating peeling area ratio is a value representing the peeling resistance of the organic coating due to alkali degreasing, and the value is the PH of the organically treated plated steel strip.
11, 12 in the alkaline degreasing solution adjusted to a temperature of 40 ℃
After immersing for a minute, taking out and drying, apply cellophane tape, peel it off, and calculate the ratio of the peeled area of the organic film adhered to the cellophane tape to the total area of the cellophane tape applied. .
From FIG. 3, in the case where the acid value of the organic film is in the range of 3 to 20 KOHmg / g, the film peeling area ratio is very small, the film peeling hardly occurs, and the acid value is 20 KOHmg / g.
It can be seen that when it is more than g or less than 3 KOHmg / g, the film peeling area ratio rapidly increases and the adhesiveness and peeling resistance of the film remarkably decrease.

As described above, when the acid value of the organic coating film 5 is within a proper range, the peeling of the coating film does not occur even if the alkaline degreasing is performed under the severe conditions as described below. You can As described above, the acid value represents the content of free fatty acid in the resin, so that the acid value of the resin is an appropriate value, the content of free fatty acid in the resin is an appropriate value, and excess free fatty acid is It means that it does not exist. Since the free fatty acid exhibits acidity, it undergoes a neutralization reaction with the alkali content of the degreasing agent during alkaline degreasing to form a reaction product in the organic coating. Since the neutralization reaction product reduces the adhesion of the coating as the amount of production increases, when the excess free fatty acid is present, the adhesion of the coating is significantly reduced. On the other hand, when the acid value of the organic coating 5 is a proper value, the neutralization reaction product is prevented from being excessively produced, so that the adhesion of the organic coating 5 is prevented from being lowered and the coating is peeled off. Is prevented. Moreover, since the lower limit of the acid value of the organic coating 5 is set appropriately, hydrogen bonding between the organic coating 5 and the chromate coating 2 is promoted, and the bonding force between both is increased. As a result, the adhesion of the organic coating 5 is improved, and the organic coating 5 is prevented from peeling off.

The coating 5 has a glass transition temperature of 0 to 3
The reason why the temperature is limited to 0 ° C. is as follows. When the glass transition temperature is lower than 0 ° C., the hardness of the organic coating 5 becomes too small, and when the organically treated plated steel strip 1 is wound into a coil, the organic coatings 5 adhere to each other. When the glass transition temperature exceeds 30 ° C., the hardness of the organic coating film 5 becomes excessively large, and the processing adhesion of the coating film deteriorates. On the other hand, when the glass transition temperature is 0 to 30 ° C., the hardness of the organic coating film 5 is appropriate, so that the occurrence of the above-mentioned problems can be avoided. The molecular weight of the organic coating 5 is 10
It is limited to 000 or more because the alkali resistance of the organic coating 5 is significantly improved in that range.

As described above, the organically treated plated steel strip 1 of this embodiment has an acid value of 3 to 20 KOHmg / g, a glass transition temperature of 0 to 30 ° C., a molecular weight of 10,000 or more, and a thickness of 0.5 to 5. Since the organic coating 5 having a thickness of 0.0 μm is formed on the surface, even if alkali degreasing is performed under harsh conditions, a decrease in adhesion of the organic coating 5 is avoided, and peeling of the organic coating is reliably prevented. . Further, since the thickness of the organic coating is formed within the appropriate range, it is possible to reliably prevent the attachment of stains such as fingerprints. Therefore, the organically treated plated steel strip 1 of the present embodiment has excellent alkali resistance and fingerprint resistance.

With reference to FIG. 2, the organic film processing apparatus 7 comprises a first cooling means 8, a coating means 9, a drying furnace 10, a heating means 21, and a second cooling means 12. . The organic film processing apparatus 7 of the present embodiment is arranged downstream of the electrogalvanizing apparatus 6. The first cooling device 8, which is a first cooling means, is a device for adjusting the temperature of the electrogalvanized steel strip 13 (hereinafter sometimes abbreviated as galvanized steel strip), and is supplied from a fan (not shown). The cooling air is sprayed onto the plated steel strip 13 to control its temperature.

The roll coater device 9 as a coating means is a device for coating an emulsion solution in which a water-dispersible acrylic resin is dispersed in water on the surface of the plated steel strip 13.
Coating roll 14, lifting roll 15, intermediate roll 1
6, a tray 17, and a refrigerator 18. The coating roll 14, the lifting roll 15, and the intermediate roll 16 are arranged with a predetermined gap therebetween, and the axes of the rolls are parallel to each other and to the surface of the plated steel strip 13.

The lifting roll 15 is immersed in a tray 17 filled with the emulsion solution, and a part of the emulsion solution is lifted by the rotation of the lifting roll 15, and the intermediate roll 16 is applied to the coating roll 14. It is transferred and applied to the surface of the plated steel strip 13. The coating roll 14, the lifting roll 15 and the intermediate roll 16 are
Driven together, the gap between each of these rolls determines the thickness of the emulsion solution to be applied to the plated steel strip 13. The emulsion solution has a thickness of, for example, 5 to 12 μm, and the emulsion solution has an acrylic resin concentration of, for example, 35%. In addition, in the gap between the coating roll 14 and the plated steel strip 13, the emulsion solution transferred to the coating roll 14 is entirely coated with the plated steel strip 13.
It is set to be applied to. The emulsion solution is stored in the tray 17 while being cooled to a predetermined temperature by the refrigerator 18. In addition, each component which comprises the roll coater apparatus 9 is arrange | positioned on both sides of the plated steel strip 13 by the same structure.

The drying oven 10 is an oven for drying the emulsion solution applied to the surface of the plated steel strip 13, and the first drying zone 10a and the second drying zone 1 are arranged from the upstream side.
0b, the third dry zone 10c and the fourth dry zone 10d are arranged in this order. In each dry zone 10a-10d,
Thermocouples 19 for detecting the temperature inside the furnace are provided, and a radiation thermometer 20 for detecting the temperature of the organically treated plated steel strip 1 is provided on the outlet side of the drying furnace 10.

The gas burner 21, which is the heating means, is provided in each of the drying zones 10a to 10d, and mixes and burns natural gas and air to raise the temperature in the furnace.
The installation position of the gas burner 21 is actually the plated steel strip 13
Although it is a side wall facing the plate width end face of FIG. 2, the gas burner 21 is shown in the lower part of the furnace wall in FIG. 2 for convenience of illustration.
Natural gas is supplied to the gas burner 21 from the gas tank 23 via the gas supply pipe line 24. The gas supply line 24 is provided with a pressure reducing valve 25 and a flow rate adjusting valve 26, which adjust the pressure and flow rate of natural gas. The combustion air is supplied from the air compressor 27 to the gas burner 21 via the air supply pipe line 28. The air supply conduit 28 is provided with a pressure reducing valve 29 and a flow rate adjusting valve 30, which adjust the pressure and flow rate of the combustion air.
This configuration is exactly the same for each of the dry zones 10a to 10d. A second cooling device 12 which is the second cooling means.
Is a device for cooling the organically treated plated steel strip 1 and blows cooling air from a fan (not shown) onto the organically treated plated steel strip 1 to cool it.

The electrogalvanized steel strip 13 is adjusted to a predetermined temperature in the first cooling device 8 and then conveyed to the roll coater device 9 via the support roll 34. The plated steel strip 13 conveyed to the roll coater 9 is coated with the emulsion solution adjusted to a predetermined temperature so as to have a predetermined thickness, and is carried into the drying furnace 10. Drying oven 10
The organically treated plated steel strip 1 carried into the first dry zone 10
a, support roll 35, second to fourth drying zones 10b to 10d
The heating temperature is controlled so that the heating temperature reaches a predetermined temperature. The organically treated plated steel strip 1 carried out from the drying furnace 10 is conveyed to the second cooling device 12 via the support roll 36, and is cooled to a predetermined temperature. The organically treated plated steel strip 1 conveyed from the second cooling device 12 is further conveyed to the downstream side via the support roll 37.

The temperature control of the organically treated plated steel strip 1 in the drying furnace 10 is carried out so that the temperature detected by the radiation thermometer 20 becomes a value within a predetermined temperature range.
It is performed by controlling the temperature in the furnace of 10d.
Further, the control of the furnace internal temperature is performed by controlling the combustion calorific value of the gas burner 21 so that the furnace internal temperature matches a preset set temperature, and the combustion calorific value of the gas burner 21 is controlled. It is done by adjusting the flow rates of natural gas and air supplied to.

The set value of the temperature in the furnace is determined in advance for each target heating temperature of the organically treated plated steel strip 1 based on the operation result value. Table 1 shows an example of set values of the furnace temperature when the target heating temperature is 180 ° C. Table 1 shows the set values of the furnace temperature, stratified by the plate thickness of the organically treated plated steel strip 1 and the transport speed. From Table 1,
It can be seen that the set value of the furnace temperature is set to be higher as at least one of the plate thickness and the transfer speed is increased, and that the transfer speed is set to be smaller as the plate thickness is increased. .

[0027]

[Table 1]

The production of the organically treated plated steel strip 1 includes a coating step of coating the emulsion solution on the surface of the plated steel strip 13 and a drying step of heating and drying the plated steel strip 13 coated with the emulsion solution. The cooling step of cooling the organically treated plated steel strip 1 that has been heated and dried is sequentially performed in this order.

In the coating step, the emulsion solution is coated with the gap between the coating roll 14 of the roll coater 9 and the plated steel strip 13 adjusted to a predetermined value as described above.

In the drying step, the plated steel strip 13 coated with the emulsion solution as described above is heated to a predetermined temperature and dried. In the present embodiment, it is preferable to heat the plate temperature of the plated steel strip 13 coated with the emulsion solution (hereinafter, also referred to as plate temperature) to a value in the range of 160 to 230 ° C. The reason why the plate temperature is limited to the temperature range will be described below with reference to FIGS. 4 and 5.

The horizontal axis of FIG. 4 represents the plate temperature, and FIG.
The vertical axis represents the film peeling area ratio. The method for measuring the film peeling area ratio shown in FIG. 4 is exactly the same as that shown in FIG. It can be seen from FIG. 4 that the film peeling area ratio decreases as the plate temperature increases, and that the film peeling area ratio is very small and the film peeling hardly occurs when the plate temperature is 160 ° C. or higher. It is understood that this is because the hydrogen bonding reaction between the organic film 5 and the underlying chromate film 2 is promoted as the plate temperature rises, and the bonding force between the two increases.

The horizontal axis of FIG. 5 represents the plate temperature,
The vertical axis of FIG. 5 represents the yellowness b value of the organic coating 5. b
The value is an index showing the degree of yellowness of the organic coating 5, and means that the higher the b value, the stronger the yellowness. From FIG. 5, it can be seen that when the plate temperature exceeds 230 ° C., the b value sharply increases and discoloration occurs.

In the present embodiment, the plate temperature is 160-
This is the reason why the temperature is limited to 230 ° C.
In addition, it is particularly preferable to set the plate temperature to a value in the range of 160 to 200 ° C. from the viewpoint of energy saving. in this way,
In the present embodiment, it is possible to efficiently manufacture an organically treated plated steel strip that is excellent in film peeling resistance and film discoloration resistance.

In the cooling step, the organically treated plated steel strip 1
Is cooled to a temperature of 50 ° C. or lower. As a result, even if the organic coating 5 of the organically treated plated steel strip 1 is wound around and carried on a bridle roll (not shown) that is arranged subsequently, there is no possibility that it will adhere to the roll surface.

The material of the metal strip coated with the organic treatment film is not limited to the electrogalvanized steel strip, and other plated steel strips, stainless steel strips and other metal strips may be used.

[0036]

EXAMPLE An acrylic resin emulsion was applied to a chromate-treated electrogalvanized steel sheet 13 and heated and dried to produce an organically treated plated steel strip 1. The electrogalvanized steel sheet 13 as a raw material has a plate thickness of 0.8 mm, a galvanized amount (one side) of 20 g / m ² , and a surface roughness of 2.0 μm in terms of center line average roughness Ra. In addition, the chromium adhesion amount of the electrogalvanized steel sheet 13 after chromate treatment is 1
It is 5 mg / m ² , and the film thickness of the organic coating 5 of the organically treated plated steel strip 1 after drying is 2.0 μm. Table 2 shows Examples in which the acid value, molecular weight, glass transition temperature and drying temperature of the organic coating 5 all satisfy the conditions of the present invention and Comparative Examples which deviate from the conditions of the present invention.

[0037]

[Table 2]

Further, Table 3 shows the results of performance evaluation of the above-mentioned Examples and Comparative Examples with respect to alkali resistance, blocking resistance, processing adhesion and discoloration resistance. Each of the above performance evaluations was performed by the following method using a sample collected from the organically treated plated steel strip 1. (1) Alkali resistance The sample is immersed in a sodium silicate-based alkaline degreasing agent adjusted to a liquid temperature of 50 ° C. and a pH of 12.8 for 3 minutes, taken out and dried, and then a cellophane tape is attached, and an organic film after the cellophane tape is removed. The residual rate was obtained and evaluated based on the following criteria. ◯: Coating residual rate 100%, Δ: Coating residual rate 70% or more and less than 100%, ×: Coating residual rate less than 70% (2) Blocking resistance Temperature is 40 ° C., pressure is 150 kgf /
It was pressed for 24 hours at cm ² , and it was evaluated whether or not the organic coatings were adhered to each other and blocked (lumped) after pressing. ◯: No organic film adhered, ×: Organic film adhered (3) Processing adhesion 5 weights of 500 gf were used using a DuPont impact tester.
The sample was processed by dropping it from a height of 0 cm onto the sample, a cellophane tape was attached to the processed part, and the presence or absence of peeling of the organic coating after the removal of the cellophane tape was evaluated. ◯: No peeling, ×: Peeling (4) Discoloration resistance The yellowness b value of the organic coating surface was measured and evaluated. ◯: b value of 2 or less, no discoloration, ×: b value of 2 or more, discoloration (yellowing)

[0039]

[Table 3]

From Table 3, it can be seen that the evaluation results of all the performances of the examples are good, and the performances of the comparative examples have bad evaluation results. Thus, in the organically treated plated steel strip 1 according to the present invention, the adhesion of the organic coating 5 is good, and the peeling of the organic coating can be reliably prevented even if the alkaline degreasing conditions are severe. Further, it also has excellent performances with respect to blocking resistance, processing adhesion and discoloration resistance.

[0041]

As described above, according to the present invention, since the acid value, the molecular weight, the glass transition temperature, the surface roughness of the metal strip, and the heating temperature of the synthetic resin film are properly set, the alkali resistance, It is possible to efficiently produce a metal band treated with an organic film, which is excellent in blocking property, process adhesion and discoloration resistance. For this reason, even if the alkaline degreasing conditions at the shipping destination of the organic coating film-treated metal strip are severe, the peeling of the organic coating film can be reliably prevented.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing a simplified configuration of an organic coating-treated electrogalvanized steel strip according to the present invention.

FIG. 2 is a schematic view showing a simplified configuration of an organic film treatment apparatus capable of suitably manufacturing the organically treated plated steel strip shown in FIG.

FIG. 3 is a graph showing the relationship between the acid value of an organic film and the film peeling area ratio.

FIG. 4 is a graph showing the relationship between the plate temperature of an organically treated plated steel strip and the film peeling area ratio.

FIG. 5 is a graph showing the relationship between the plate temperature of the organically treated plated steel strip and the yellowness b value of the organic coating.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Organic coating treatment electrogalvanized steel strip 2 Chromate coating 3 Base material steel strip 4 Zinc coating layer 5 Organic coating 7 Organic coating treatment device 8 1st cooling means 9 Coating means 10 Drying furnace 12 2nd cooling means 13 Electrogalvanized steel Obi 21 heating means

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasutaka Kawaguchi 5 Ishizu Nishimachi, Sakai City, Osaka Prefecture Sakai Works, Nisshin Steel Co., Ltd. Sakai Works (72) Inventor Hirofumi Takezu 5 Ishizu Nishimachi, Sakai City, Osaka Prefecture Nisshin Steel Co., Ltd. Technical Research Institute

Claims (1)

[Claims] 1. The acid value after drying is 3 to 20 KOHmg / g.
And a water-dispersible synthetic resin emulsion solution having a molecular weight of 10,000 or more and a glass transition temperature of 0 to 30 ° C. is subjected to chromate treatment and has a surface roughness of 0.5 μm in terms of center line average roughness Ra. A method for producing an organic film-treated metal strip having excellent alkali resistance, which comprises coating the surface of a metal strip as described above and subsequently heating the temperature of the metal strip to a value in the range of 160 to 230 ° C.