JP4954758B2 - Method for producing plated steel sheet with excellent corrosion resistance and paint adhesion - Google Patents

Description

  The present invention relates to a method for producing a plated steel sheet excellent in corrosion resistance and paint adhesion, and in particular, has a feature in a method for drying and baking a post-treated film having a non-chromium-based organic post-treated film that does not contain chromium. The present invention relates to a method for producing a plated steel sheet.

  Conventionally, as a galvanized steel sheet used for home appliances, a hot dip galvanized steel sheet that has been chromated has been used, but recently, in consideration of environmental problems, organic non-chromated steel sheets that are chromate substitute materials are used. Development is thriving. Among them, a plated steel sheet obtained by applying a polyolefin resin excellent in blackening resistance and fingerprint resistance, a polyurethane resin or the like on a hot dip galvanized steel sheet and heating and drying is promising.

However, such a plated steel sheet needs to be dried and baked at a high temperature of 100 ° C. or higher after coating in order to improve stability by using resin curing or crosslinking reaction. Conventionally, such drying / baking treatment has been performed by a hot-air drying method. However, in the hot-air drying method, heating efficiency is poor and only the vicinity of the surface of the coating film is heated, and heat penetrates into the coating film. It was difficult to heat uniformly.
Moreover, when it heats with the same temperature increase rate as the case of the conventional hot air drying method, it takes a long time to reach target temperature. Therefore, rapid heating was necessary for efficient production.

Here, examples of the rapid heating technique include induction heating (IH) and near infrared heating (NIR). The induction heating can be rapidly heated according to various requirements by selecting an appropriate AC power source or coil shape. However, because of the method of heating from the inside of the steel plate, bumping of the applied chemical solution is likely to occur. As a result, there are many film defects, it is difficult to obtain the expected performance, and the cost is higher than other heating methods, which is considered not economical. On the other hand, near-infrared light is a heat source having a wavelength of 0.8 to 1.5 μm, and output control is easy, and heat energy is more transparent than mid-infrared and far-infrared, and an economical heating method. Known as.
Patent document 1 is mentioned as an example which heats the post-processing film of a plated steel plate using near infrared rays. In Patent Document 1, (1) a water-based resin, for example, a plated steel sheet on which an acrylic olefin resin or a polyurethane resin ([0039]) is formed, (2) is heated by a near infrared furnace ([0049] etc.) (3) Heating to reach 50 to 250 ° C., more preferably 70 to 200 ° C., and drying and baking ([0051]).
However, with the technique disclosed in Patent Document 1, it is possible to rapidly heat the coating film by near-infrared heating. However, excessively rapid heating causes a phenomenon that only the coating film surface is dried. In some cases, coating film defects called Therefore, until now, in order to prevent the occurrence of cracks, it has been unavoidable that the heating must be limited to a heating rate of 40 ° C./sec or less. As a result, when performing continuous processing, it was necessary to cope with whether the heating equipment was lengthened or the traveling speed of the steel sheet to be processed was slow, and in any case, the manufacturing cost was disadvantageous. . Further, in Patent Document 2 below, the surface of the metal plate is formed with a film comprising 50 to 90% by mass of the crosslinked resin matrix (A) and 10 to 50% by mass of the inorganic rust inhibitor (B). In the treated metal plate, the crosslinked resin matrix (A) is formed by a reaction between an aqueous resin and a crosslinking agent, and has an acid value of 0 to 30 and a hydroxyl value of 5 of a carboxylic acid not neutralized with an alkali metal. By setting it to -50, an organic coated metal sheet having a coating satisfying all of corrosion resistance, alkali resistance, solvent resistance, scratch resistance and adhesion, which has been difficult with conventional non-chromate coatings, has been proposed. ing.

  Moreover, since the shape of the near-infrared heaters that are usually marketed are mostly rod-shaped and spherical, when the object to be heated heats a large area like a steel plate, it is necessary to properly arrange a plurality of heaters. Uneven heating may occur. In other words, overheated parts cause heat shrinkage of the resin and cause distortion, while conversely underheated parts may cause the resin to not sufficiently fuse to the plated steel sheet and cause poor adhesion. There is.

  As a method of preparing a plurality of rod-like near infrared heaters and heating a large area of the transport material, for example, Patent Document 3 discloses. Patent Document 3 discloses a technique in which when a thermoplastic resin sheet is heated with a near-infrared heater, the heating area is divided into several blocks and the temperature of the heater is controlled by each block. However, when the technique described in Patent Document 3 is used, it is difficult to apply in terms of accuracy to uniformly heat the plated steel sheet coated with the organic resin.

  In addition, as a technique for utilizing near infrared rays, the following Patent Document 4 discloses a method for drying printing ink on paper using near infrared rays having a peak wavelength of 0.8 to 2.0 μm, which is rapidly conveyed in a conveyor device. In a method and apparatus for drying inks, particularly inks on rapidly transported paper, in the drying area, separating wet components, in particular solvents, from the material to be dried by incident electromagnetic radiation; And a method comprising a step of transferring from a drying zone by a transfer gas stream. The present invention enables efficient rapid drying of newsprint or thermal paper printed especially in high speed conveyors.

As described above, various methods for using near-infrared rays have been proposed in the past, but drying of a post-treatment film on a plated steel sheet having a non-chromium-based organic post-treatment film that does not contain chromium in the near-infrared plated steel sheet is possible. The baking method has not been sufficiently studied, and a method for producing a plated steel sheet having excellent corrosion resistance and paint adhesion due to sufficient film performance has not been realized.
JP 2000-248380 A JP 2005-281863 A JP-A-11-268111 Japanese translation of PCT publication No. 2002-504442

  Therefore, the present invention has been made in view of the problems of the prior art as described above, and in a method for producing a plated steel sheet that is rapidly heated using near infrared light after applying a non-chromate antirust treatment liquid on the plated steel sheet. An object of the present invention is to provide a method for producing a plated steel sheet having excellent corrosion resistance and paint adhesion by having sufficient film performance.

In order to solve the above-mentioned problems, the present inventor has found a heating condition suitable for rapid heating using near infrared rays, has sufficient film performance, and is a plated steel sheet having excellent corrosion resistance and paint adhesion. The gist of the present invention is as follows, as described in the claims.
(1) After applying a rust preventive treatment liquid containing a water-soluble resin to the surface of the plated steel sheet, the infrared rays are irradiated with near infrared rays having a peak wavelength of radiant energy of 0.8 to 1.5 μm. A method for producing a plated steel sheet excellent in corrosion resistance and paint adhesion, which satisfies the following formula (A) when a coating film is formed by heating at a temperature rate of 50 to 200 ° C./sec. 5 <(PMT-Tg) ² / α <100 (A)
Here, PMT: Steel sheet temperature (° C)
Tg: Glass transition temperature of water-soluble resin (℃)
α: Temperature increase rate (° C / sec)
(2) The production of a plated steel sheet having excellent corrosion resistance and paint adhesion as described in (1), wherein the water-soluble resin is one or two selected from an aqueous polyolefin resin and an aqueous polyurethane resin. Method.
(3) The method for producing a plated steel sheet having excellent corrosion resistance and paint adhesion according to (1) or (2) 2, wherein the water-soluble resin has a glass transition temperature Tg of 30 ° C. to 280 ° C.
(4) The method for producing a plated steel sheet having excellent paint adhesion according to any one of (1) to (3), wherein the steel sheet temperature PMT is 60 ° C to 280 ° C.
(5) The method for producing a plated steel sheet having excellent corrosion resistance and paint adhesion according to any one of (1) to (4), wherein a water spraying process is performed after the heat treatment of the plated steel sheet.

According to the present invention, in a method of manufacturing a plated steel sheet that is rapidly heated using near infrared rays after applying a non-chromate antirust treatment liquid containing a water-soluble resin on the plated steel sheet, sufficient film formation of the resin in the treatment liquid is achieved. For this reason, it is possible to provide a method for producing a plated steel sheet with excellent corrosion resistance and paint adhesion by providing an amount of heat input under an appropriate heating condition, and a good film performance can be obtained with a compact drying and baking equipment. Specifically, the following industrially useful remarkable effects and effects are exhibited.
1) In a method for manufacturing a plated steel sheet that is rapidly heated using near infrared rays after applying a non-chromate rust-preventing treatment solution on the plated steel sheet, sufficient film formation (crosslinking) is required as a heating condition that makes the heat input within an appropriate range. By being made, the manufacturing method of the plated steel plate excellent in corrosion resistance and paint adhesion can be provided.
2) When the water-soluble resin is composed of one or two selected from water-based polyolefin resin and water-based polyurethane resin, it is possible to realize high film performance such as blackening resistance and fingerprint resistance with a versatile material. .
According to the invention of 3), since the glass transition temperature Tg of the water-soluble resin is 30 ° C. to 280 ° C., it is possible to prevent sticking in which the films adhere to each other after film formation and the decomposition reaction of the resin itself.
4) Since the steel sheet reached temperature PMT is 60 ° C. to 280 ° C., the evaporation of the solvent is easy, and the decomposition reaction of the resin itself can be prevented. 5) By carrying out water spraying after the heat treatment of the plated steel sheet, soluble unreacted substances remaining on the surface of the resin can be removed, paint adhesion can be further improved, and cooling can be performed. By combining the device, the device can be made more compact.

  Exemplary embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In addition, in this specification and drawing, about the component which has the substantially same function structure, duplication description is abbreviate | omitted by attaching | subjecting the same code | symbol. FIG. 1 is a diagram illustrating a production line for a plated steel sheet to which the present invention is applied.

  The plated steel sheet to which the present invention is applied is a rust preventive treatment containing a water-soluble resin on the surface of a steel sheet plated with hot dip zinc or the like in a plating line not shown in FIG. 1 by an applicator roll shown in FIG. It is a steel plate in which a resin film is formed on the surface by heating with a near-infrared (NIR) heating and drying apparatus after applying the liquid.

  The aqueous resin used for this invention can be apply | coated by the coating method generally used, For example, a roll coater, a spray, a ringer roll, a bar coater, immersion etc. can be used.

  FIG. 2 is a diagram for explaining the definition of near infrared (NIR).

  As shown in FIG. 2, near-infrared rays generally refer to short-wavelength infrared rays having a wavelength band of 0.8 to 1.5 μm.

FIG. 3 is a diagram for explaining the heating principle of near infrared (NIR).

The principle of near infrared (NIR) heating is that energy is resonantly absorbed in the material by near infrared irradiation, and the absorbed energy vibrates molecules (or atoms) and generates frictional heat between the vibrated molecules. And heated. Since the infrared absorption characteristics of water have peaks with high absorption at 3 μm and 6 μm, efficient heating is possible by using infrared light having a wavelength matching this peak. In general, the infrared wavelength suitable for heating is preferably slightly shorter than the absorption peak.
As shown in FIG. 3, conventional IR heating and hot air heating are heated from the surface because the heat energy is absorbed by the coating surface, but near infrared (NIR) is absorbed in the process of transmission. Therefore, the entire coating film can be heated uniformly, and output control is easy and economical. FIG. 4 is a diagram illustrating a resin film forming process in the present invention.

  As shown in FIG. 4, a rust-proofing treatment liquid (chemical) containing a water-soluble resin applied to the surface of a plated steel sheet evaporates a solvent such as water or alcohol when heated, and the resin is fused (crosslinked). By doing so, a film is formed.

  The present invention provides a method for producing a plated steel sheet having sufficient film performance and excellent corrosion resistance and paint adhesion by finding a heating condition suitable for rapid heating using near infrared (NIR). After applying a rust preventive treatment liquid containing a water-soluble resin to the surface of the plated steel sheet, the peak wavelength of the radiant energy is irradiated with near infrared rays of 0.8 to 1.5 μm, When a coating film is formed by heating at a heating rate of 50 to 200 ° C./sec, the following formula (A) is satisfied.

5 <(PMT-Tg) ² / α <100 (A)
Here, PMT: Steel sheet temperature (° C)
Tg: Glass transition temperature of water-soluble resin (℃)
α: Temperature increase rate (° C / sec)
After applying a rust preventive treatment liquid containing a water-soluble resin to the surface of the plated steel sheet, the temperature rise rate of the steel sheet is set to 50 to 200 ° C. using near infrared rays having a peak wavelength of radiant energy of 0.8 to 1.5 μm. The amount of heat input to the film represented by the above formula (A) is shown when the film is formed by heating to a certain reaching plate temperature (PMT: Peak Metal Temperature) while maintaining at / sec (PMT-Tg ) ² / α is in the range of 5-100.

The reason for limiting the above formula (A) is that when (PMT-Tg) ² / α is less than 5, film formation (crosslinking) becomes insufficient and sufficient film performance cannot be obtained, while (PMT-Tg This is because, when ² / α exceeds 100, the secondary adhesion of the paint deteriorates.

  FIG. 5 is a diagram showing the behavior when the amount of heat input to the resin film is large. As the resin serving as the binder, a mixed system is often employed in order to achieve both barrier properties and film flexibility, such as a combination of an olefin resin and a urethane resin. In the case of rapid heating with a heating rate α of 50 ° C / sec or more, if the amount of heat input is too large, the interface between the resins will be distorted, causing minute cracks in the film, and the adhesiveness of the paint due to the inter-resin destruction when the tape is peeled In addition to deterioration, the corrosion resistance also deteriorates.

  The glass transition temperature Tg (° C) of a water-soluble resin refers to the temperature at which the inflection point changes from a hard glass region to a soft rubber region. When the glass transition temperature Tg (° C) is exceeded, the resin softens and melts. It is easy to wear (crosslink).

  The reason for setting the heating rate α of the plated steel sheet to 50 ° C./sec or more is that if it is less than 50 ° C./sec, the effect of the present invention for making the heat drying apparatus compact cannot be obtained, and the heating rate α If it is large, it overshoots and exceeds the PMT set value, so 200 ° C / sec is the upper limit.

  Examples of water-soluble resins applicable to the present invention include water-soluble polymers such as polyacrylic acid, polyacrylamide, polyvinyl alcohol, and polyethylene glycol, acrylic resins dispersed in water, urethane resins, epoxy resins, and polyester resins. , One or more selected from aqueous emulsion resins such as polyamide resins, polyolefin resins, ethylene-acrylic acid copolymer resins, polyacetal resins, and polybutyral resins.

  Among these, among the non-chromate organic resins, a water-soluble resin composed of one or two selected from an aqueous polyolefin resin and an aqueous polyurethane resin is preferable because of excellent blackening resistance and fingerprint resistance.

  In the present invention, the glass transition temperature Tg of the water-soluble resin is not limited, but is preferably 30 ° C. to 280 ° C., more preferably 40 to 130 ° C.

    When the glass transition temperature Tg is 30 ° C. or less, the film is reactive after film formation, so when the samples are laminated, the films adhere to each other (sticking), and the film peels off when the sample is taken out. Moreover, it is because decomposition | disassembly reaction of organic substance itself will occur when it exceeds 280 degreeC.

  In the present invention, the range of the steel sheet reached temperature PMT is not limited, but is preferably 60 ° C. to 280 ° C., more preferably 80 ° C. to 150 ° C.

  Basically, it is necessary to heat more than Tg in order to cause a welding reaction between resins (this is not the case when a reaction accelerator is contained). In order to actually evaporate the solvent (water, alcohol, solvent) in the applied drug, it is necessary to heat the plate at 60 ° C. or higher. In addition, heating at 280 ° C. or higher causes a decomposition reaction of the organic matter itself.

  In this invention, although the process after heat processing of a plated steel plate is not ask | required, it is preferable to wash with water by implementing a water spraying process after heat processing. In the near-infrared heating method in which the film is rapidly heated from the inside of the film, a soluble unreacted substance tends to remain on the surface of the film that finally becomes the film forming part. If this remains as it is, it may adversely affect the adhesion with the paint, so it is desirable to provide a water spraying (washing) step. Further, since this water spraying also acts as cooling, the apparatus can be made more compact.

FIG. 6 is a diagram illustrating a near infrared (NIR) heating device used in the present invention.

Based on FIG. 6, the structure of the heat drying apparatus 10 used for the manufacturing method of the plated steel plate which concerns on one Embodiment of this invention is demonstrated. 6A is a plan view showing a configuration of the heating and drying apparatus 10 according to an embodiment of the present invention, and FIG. 6B is a cross-sectional view taken along line AA in FIG. 6 (c) is a cross-sectional view taken along the line BB of (a).

  As shown in FIG. 6, the heating and drying apparatus 10 is an apparatus for heating and drying the organic resin coated on the plated steel sheet S, and includes a reflecting plate 12, a near infrared heater 14 including a filament inside, an air The nozzle 16 and the glass 18 are mainly provided.

  The plated steel sheet S has a width of about 1100 to 1500 mm, passes through at 30 to 300 m / min, and is heated while passing under the near infrared heater 14.

  The reflector 12 is provided to efficiently perform heating by the near infrared heater 14 and is disposed so as to cover the upper surface side of the near infrared heater 14. Near infrared rays radiated from the near infrared heater 14 directly hit the plated steel sheet S, and partly hit the plated steel sheet S after being reflected by the reflecting plate 12. Moreover, in this embodiment, although the reflecting plate 12 is formed in the substantially W shape in cross section, the plated steel plate S can be heated more uniformly by forming in this way a substantially W shape. . However, the shape of the reflecting plate 12 is not limited to a substantially W shape, and any structure can be used as long as the near infrared ray emitted from the near infrared heater 14 can be reflected and applied to the plated steel sheet S. There may be.

  The near-infrared heater 14 has a filament (not shown) disposed therein, and a gas such as halogen is present around the near-infrared heater 14. For example, the near-infrared heater 14 may have a length in the direction parallel to the plate passing direction of the plated steel sheet S of about 250 mm and an output of about 3 to 5 kW.

  Further, as described above, the near infrared ray radiated from the filament has a peak wavelength of radiant energy of 0.7 to 1.0 μm from the viewpoint of preventing the occurrence of coating defects such as armpits and the life of the filament. Is preferred.

The filament which concerns on this embodiment radiates | emits near infrared rays, the longitudinal direction is parallel to the plate | board passing direction of the plated steel plate S, and the plurality is arrange | positioned along the width direction of the plated steel plate S at intervals of 15-25 mm. As described above, the interval between the adjacent filaments is set to 15 to 25 mm along the width direction of the plated steel sheet S. If the interval between the filaments is less than 15 mm, the number of filaments to be used increases, which is uneconomical. In addition, it is not preferable because the diameter of the near infrared heater 14 needs to be reduced and technically difficult. On the other hand, if the interval between the filaments exceeds 25 mm, temperature unevenness occurs in the width direction of the plated steel sheet S, and a high-output heater that is difficult to manufacture with current technology is not preferable.

  Moreover, as shown in FIG.6 (c), the distance of the filament which concerns on this embodiment, and the plated steel plate S is comprised so that it may become 50-200 mm. As described above, the distance between the filament and the plated steel sheet S is set to 50 to 200 mm. When the distance between the filament and the plated steel sheet S is less than 50 mm, the plated steel sheet S flutters up and down while moving, This is not preferable because there is a risk of damage to equipment such as the near infrared heater 14. On the other hand, if the distance between the filament and the plated steel sheet S exceeds 200 mm, the heating efficiency is deteriorated, and it is not preferable because a large-power near-infrared heater 14 and a near-infrared heater 14 need to be added.

  In the heating and drying apparatus 10 according to the present embodiment, in order to heat with a filament between the center of the plated steel sheet S in the width direction and starting from the both ends of the plated steel sheet S to a position 40 to 60 mm apart, plating is performed. Whether or not each filament is used for heating is controlled according to the width of the steel sheet S.

  In the present embodiment, the reason why the filament used for heating is between the both ends of the plated steel sheet S and the position separated by 40 to 60 mm outward is to prevent a temperature drop at the end of the plated steel sheet S. This is because the outside of the plated steel sheet S is heated outside. Further, the thickness of 40 to 60 mm is less than 40 mm, which is not preferable because the end portion of the plated steel sheet S is not sufficiently heated and the temperature difference between the central portion and the end portion of the plated steel sheet S becomes too large. On the other hand, if it exceeds 60 mm, the end portion of the plated steel sheet S is excessively heated, and the temperature difference between the central portion and the end portion of the plated steel sheet S becomes too large.

  Moreover, it is preferable that the filament which concerns on this embodiment is multiply arranged along the advancing direction of the plated steel plate S. FIG. By comprising in this way, even if it speeds up a plate-feeding speed, it can heat to target target temperature.

  The air nozzle 16 is provided to ventilate the inside of the heating and drying apparatus 10. That is, the air nozzle 16 is used to prevent the moisture in the heating and drying apparatus 10 from rising due to the water evaporated from the organic resin coating film, and the air evaporation rate from the organic resin coating film from slowing down. It plays the role of sending air from the nozzle 16 and removing moisture to the outside.

  The glass 18 is disposed between the filament and the plated steel sheet S in order to protect the near-infrared heater 14 described above and allow the air fed from the air nozzle 16 to flow smoothly.

  As mentioned above, although preferred embodiment of this invention was described referring an accompanying drawing, it cannot be overemphasized that this invention is not limited to this example. It will be apparent to those skilled in the art that various changes and modifications can be made within the scope of the claims, and these are naturally within the technical scope of the present invention. Understood.

First, implementation conditions of the present invention will be described. A hot-dip galvanized steel sheet is coated with an aqueous resin composed of polyolefin and polyurethane, with Nb compound, P compound, and Ti compound added as rust preventive agents so that the film thickness after drying with a roll coater is 1.0 μm. And heated with a near-infrared heater.
Here, in this example, the corrosion resistance after strong alkaline degreasing and the evaluation of the secondary adhesion of the paint were performed as follows.
It is necessary to ensure corrosion resistance after strong alkaline degreasing. Users who have obtained plated steel sheets manufactured by the method according to the present embodiment usually perform degreasing treatment before painting, but this degreasing treatment The degreasing solution to be used ranges from a weak alkali of about pH 9 to a strong alkali of about pH 13, and the higher the pH, the more easily the plating layer (for example, Zn) dissolves and the corrosion resistance deteriorates. It is necessary to ensure corrosion resistance.
For corrosion resistance after strong alkaline degreasing, wash the sample with 2min sample in 60 ° C strong alkaline degreasing liquid (Fine Cleaner L4460, A agent 1.2%, B agent 0.8%, manufactured by Nihon Parkerizing Co., Ltd.) After coating with tape on the end face and the back face, a salt spray test (SST: JIS-Z2371) was conducted. The white rust occurrence state after 120 hours was observed, and the ratio (%) of the white rust occurrence area was determined. Evaluation was made and those having a white rust generation area ratio (white rust area ratio) of 5% or less were considered to have good corrosion resistance after strong alkaline degreasing. .

In addition, paint secondary adhesion is distinguished from paint primary adhesion, and paint primary adhesion is paint adhesion without applying a load after coating, whereas paint secondary adhesion is It means the paint adhesion after applying a load corresponding to the user environment after painting. As an evaluation method, for example, for paint primary adhesion, there is a method of performing tape peeling evaluation after coating, and for paint secondary adhesion, a method of performing tape peeling evaluation after being immersed in boiling water for a predetermined time after coating. There is.
In this example, for coating secondary adhesion, melamine alkyd paint (Amirac # 1000, manufactured by Kansai Paint Co., Ltd.) was applied to the surface of the plated steel sheet used as a sample using a bar coater so as to have a dry film thickness of 20 μm. After that, it was baked at 120 ° C. for 25 minutes to prepare a coated test plate. After being left overnight, the coated test plate was immersed in boiling water for 30 minutes, taken out and left for 1 day. Next, a grid cut crease with a 1 mm interval is placed in a painted test plate, and Erichsen 7 mm extrusion is performed. Cellophane tape (registered trademark of Nichiban Co., Ltd.) is applied to the extrusion, and the state of the coating film after forced peeling Observed. A rating of 10 (no peeling) to 1 (complete peeling) was given stepwise depending on the remaining rate of the coating film. Of these, those with a rating of 9 and 10 were considered to have good paint secondary adhesion. Moreover, it is preferable that the film thickness after drying of the organic resin film coat | covered with a plated steel plate is 0.7-2.0 micrometers. When dried by the method according to the present embodiment, if the film thickness after drying exceeds 2.0 μm, the electrical resistance increases and the weldability deteriorates, which is not preferable. On the other hand, when the film thickness after drying is less than 0.7 μm, it is not preferable because sufficient corrosion resistance cannot be secured.

FIG. 7 is a diagram showing the temperature-time relationship in the resin film drying step.
(PMT−Tg) ² / α in the formula (A) of the present invention indicates the area of the upper portion from the glass transition temperature Tg of the triangle showing the temperature profile shown in FIG. 7, and represents the amount of heat contributing to the crosslinking reaction of the resin. Equivalent to.

FIG. 8 is a diagram showing the influence of heat input on the resin film formation.
In the range where (PMT-Tg) ² / α in the formula (A) of the present invention shown on the horizontal axis in FIG. 8 exceeds 5, the white rust ratio (%) after SST120Hr becomes 5% or less, and (PMT-Tg ) The coating adhesion score was 9 or more when ² / α was less than 100, and the effect of the present invention was confirmed.

It is a figure which illustrates the production line of the plated steel plate to which this invention is applied. It is a figure explaining the definition of near infrared rays (NIR). It is a figure explaining the heating principle of infrared rays (NIR). It is a figure explaining the resin film formation process. It is a figure which shows the behavior in case there are many heat inputs to a resin film. It is a figure which illustrates the near-infrared (NIR) heating apparatus used for this invention. It is a figure which shows the temperature-time relationship in the drying process of a resin film. It is a figure which shows the influence of the heat input which has on resin film formation.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Heating and drying apparatus 12 Reflecting plate 14 Near-infrared heater 16 Air nozzle 18 Glass 20 Detection part (sensor)
S plated steel sheet

Claims (5)

After applying a rust preventive treatment liquid containing a water-soluble resin to the surface of the plated steel plate, the infrared rays are irradiated with near infrared rays having a peak wavelength of 0.8 to 1.5 μm, and the temperature rise rate of the plated steel plate is A method for producing a plated steel sheet having excellent corrosion resistance and paint adhesion, characterized by satisfying the following formula (A) when a coating film is formed by heating at 50 to 200 ° C / sec.
5 <(PMT-Tg) ² / α <100 (A)
Here, PMT: Steel sheet temperature (° C)
Tg: Glass transition temperature of water-soluble resin (℃)
α: Temperature increase rate (° C / sec)   The method for producing a plated steel sheet excellent in corrosion resistance and paint adhesion according to claim 1, wherein the water-soluble resin is one or two selected from an aqueous polyolefin resin and an aqueous polyurethane resin.   The method for producing a plated steel sheet having excellent corrosion resistance and paint adhesion according to claim 1 or 2, wherein the water-soluble resin has a glass transition temperature Tg of 30C to 280C.   The method for producing a plated steel sheet having excellent paint adhesion according to any one of claims 1 to 3, wherein the steel sheet temperature PMT is 60 ° C to 280 ° C.   The method for producing a plated steel sheet excellent in corrosion resistance and paint adhesion according to any one of claims 1 to 4, wherein a water spraying process is performed after the heat treatment of the plated steel sheet.

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