JP2008240094A - Manufacturing method of steel sheet for can - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide tin free steel sheet which does not generate minute rust. <P>SOLUTION: In the manufacturing method of the steel sheet for cans by applying plating to the surface of the steel sheet, then forming the film by executing a chemical conversion treatment, the film surface after the chemical conversion treatment is cleaned by cleaning water not containing non-metallic anion and corrosive dissolved substance to prevent the generation of the minute rust. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing a steel plate for a can having a coating that does not generate microrust.

  Conventionally, steel plates with tin chromate coating (tin-free steel plates) have been widely used as various materials for cans, but with the recent diversification of beverages and foods to be stored, weldability, corrosion resistance, and rust resistance In addition to the above, the steel plate surface that is the surface of the can has the required color tone, brightness, and freshness, and the steel plate surface that forms the back of the can has a tin-free steel plate with resistance to contents according to the contents. Has been proposed (see Patent Documents 1 to 5).

  These steel sheets are manufactured on the production line shown in FIG. 1 and are shipped to the can manufacturer by coils. However, minute rust (micro rust) is found on the surface of the steel sheet immediately before shipment, in the middle or in the can manufacturing process. Sometimes.

  The occurrence of micro rust is low, but if it exists on the steel plate surface that becomes the surface of the can, the color tone, brightness, and freshness of that portion will be inhibited, and if it exists on the steel plate surface that becomes the back surface of the can, that portion Therefore, the commercial value as a material for cans of steel plates is impaired.

  In this way, micro rust is extremely small on the steel sheet surface, but it is extremely large as a presence that impairs the properties and commercial value of the steel sheet. It has been demanded.

Japanese Patent Laid-Open No. 05-230694 JP 05-287449 A Japanese Patent Laid-Open No. 05-287591 JP 2004-43897 A Japanese Patent Laying-Open No. 2005-29809

  It is an object of the present invention to provide a tin-free steel sheet that meets the above requirements and does not generate minute rust.

  The present inventor considered that it is necessary to elucidate the cause of rusting in order to prevent rusting of minute rust, and conducted an intensive analysis of the composition of minute rust and investigated the cause of rusting. As a result, it has been found that the cause of the occurrence of micro rust is a micro defect in plating and a deterioration of the coating surface derived from a trace amount of material adhering to the coating surface.

  This invention was made | formed based on the said knowledge, and the summary is as follows.

  (1) In the manufacturing method of the steel sheet for cans which forms a film by performing a chemical conversion treatment after plating on the surface of the steel sheet, the film surface after the chemical conversion treatment contains a nonmetallic anion and a corrosive dissolved substance. A method for producing a steel plate for cans, characterized by washing with no washing water and preventing the occurrence of fine rust.

  (2) In the method of manufacturing a steel plate for cans, which is plated on the surface of the steel plate and then subjected to chemical conversion treatment to form a coating, the steel plate is wound up in a humidity-controlled atmosphere to prevent the generation of fine rust. The manufacturing method of the steel plate for cans characterized by these.

  (3) In the method for manufacturing a steel plate for cans, after plating is performed on the surface of the steel plate, and then a chemical conversion treatment is performed to form a coating, the coating surface is washed with cleaning water that does not contain nonmetallic anions, A method for producing a steel plate for cans, wherein the steel plate is wound in a humidity-controlled atmosphere to prevent the occurrence of fine rust.

  (4) The method for producing a steel plate for cans according to (2) or (3), wherein the dew point of the humidity-controlled atmosphere is 17 ° C. or less.

  (5) The method for producing a steel plate for cans according to any one of (2) to (4), wherein a humidity-controlled gas is blown onto the surface of the steel plate during the winding.

  (6) The surface of the steel plate before plating is washed with washing water that does not contain a nonmetallic anion and a corrosive dissolved substance, and for cans according to any one of (1) to (5), A method of manufacturing a steel sheet.

(7) The (1), wherein the nonmetallic anion is one or more of chlorine ion (Cl ⁻ ), sulfate ion (SO ₄ ²⁻ ), and hydroxide ion (OH ⁻ ). )-(6) The manufacturing method of the steel plate for cans in any one of.

  (8) Any of the above (1) to (7), wherein the corrosive dissolved substance is one kind or two or more kinds of sludge of pretreatment equipment, sludge of plating equipment, and sludge of posttreatment equipment. The manufacturing method of the steel plate for cans as described in a crab.

  (9) The method for producing a steel plate for cans according to any one of (1) to (8), wherein the cleaning water is pure water.

  (10) The method for producing a steel plate for cans according to any one of (1) to (9), wherein the coating is a chromate coating.

(11) The method for producing a steel plate for cans according to (10), wherein the amount of Ox-Cr attached to the chromate film is 10 mg / m ² or more.

  According to the present invention, a tin-free steel plate having a high commercial value can be produced without generating minute rust on the coating surface.

  In order to elucidate the cause of rusting, the present inventor has conducted intensive analysis and investigation on microrust.

  FIGS. 2A and 2B show the results of observing microrust generated on the chromate film surface of the steel sheet with an optical microscope. The minute rust is needle-shaped rust (long in the L direction) of 1 to several mm, and mainly occurs at the center in the width direction of the steel sheet.

  It is known from experience that micro rust occurs in the hot and humid period, but in elucidating the cause of micro rust generation, the quantification of micro rust generation and the dew point in the building where the production line is located The correlation was investigated. FIG. 3 shows the result. It can be seen that minute rusting is concentrated in July to August when the dew point in the building is high.

  Based on this, the present inventor analyzed micro rust by Auger electron spectroscopy (AES). The result is shown in FIG. In the figure, the detected components are indicated by element symbols.

  In FIG. 4, (a1) shows the spectrum of the microrust 1 and the outermost surface around it, and (b1) and (c1) show the spectrum after 60 seconds and the spectrum after 120 seconds, respectively. Moreover, in FIG. 4, (a2) shows the spectrum of the minute rust 2 and the outermost surface around it, and (b2) and (c2) show the spectrum after 60 seconds and the spectrum after 120 seconds, respectively.

  The following can be understood from these figures.

  (A) Fe and oxygen (O) (both rust components) are detected in the minute rust 1 and minute rust 2. That is, the micro rust is obtained by oxidizing Fe existing on the surface of the coating with oxygen (O) in the air.

  (B) Chlorine (Cl) is detected around the minute rust 1 and minute rust 2. Since chlorine is not present in the steel plate or in the air, it is considered that chlorine was introduced due to external factors.

  (C) Around the minute rust 1, only chlorine is detected on the outermost surface, and S and N are detected 120 seconds after sputtering. However, around the minute rust 2, S other than chlorine is detected on the outermost surface. , N, and C are detected, and are detected even after 120 seconds of sputtering.

  This is because the minute rust 1 is generated on the surface of the coating that is easily rusted due to the deterioration of characteristics due to the presence of chlorine, and the minute rust 2 is due to the presence of S, N, and C in addition to chlorine. It means that it was generated on the surface of the coating, whose characteristics deteriorated and became easy to rust.

  Chlorine is derived from the wash water, and S, N, and C are considered to be derived from the steel sheet. The coating surface and the steel plate surface on which minute rust was present were separated from the rust and analyzed by AES.

  5 and 6 show the analysis results of the clean surface where no micro rust exists, in comparison with the spectrum of micro rust 1 and the spectrum of micro rust 2, respectively. 5 and FIG. 6, (a0) shows the spectrum of the clean surface where microrust does not exist, and (b0) and (c0) show the spectrum after 60 seconds and the spectrum after 120 seconds, respectively.

  5 and 6, P, C, N, etc. are present on the outermost surface of the clean surface, but are not present at all after 120 seconds. On the other hand, the surface near the minute rust 1 is also after 120 seconds of sputtering. , S, N, and Cl are present, and in the microrust 2, it is understood that S, N, C, Cr, and Cl are present even after 120 seconds of sputtering.

  In FIG. 7, the analysis result of the steel plate surface in which micro rust existed is shown. From FIG.7 (c), it turns out that microrust has reached even the steel plate surface. Moreover, it turns out that chlorine exists also in the steel plate surface and is detected even for 120 seconds of sputtering.

  This means that the chlorine in the cleaning water used in the cleaning before plating remains in a small amount, but adheres to the surface of the steel plate before plating, forming minute plating defects. As a result, the coating film is formed, and as a result, chlorine from the cleaning water and S, N, C, etc. from the steel sheet concentrate on the coating surface, resulting in degradation of the coating characteristics and rust generation. ) Is formed, indicating that rust has formed.

  That is, the generation of micro rust is as follows: (i) A small amount of chlorine in the cleaning water used for cleaning after chemical conversion treatment remains on the surface of the coating, and / or (ii) Chlorine in the cleaning water used for cleaning the steel sheet surface before plating remains on the surface of the steel sheet before plating, forming minute plating defects. As a result, the surface of the coating formed thereon is easily rusted. This is because a minute region is formed. This elucidation of the cause is one of the findings forming the basis of the present invention.

  Here, based on FIG.8 and FIG.9, the process in which microrust is produced | generated is demonstrated.

The process of pre-plating applied to the processing Maehara steel A, then washed with washing water, to prepare a pre-plating the steel plate 1 ₁ to be subjected to the plating process 9. After the plating 4 is applied in the plating step 9, a chemical conversion treatment is further performed to form a film 5, which is used as a steel plate for cans ₁₂ and wound up to form a steel plate coil for cans 1 ₂ ′.

Before winding, but to clean the steel sheet for cans 1 _2, when the non-metallic anions 6 present in the wash water, the foreign matter 7, attached to the surface of a steel sheet for cans 1 _second coating 5, and the residual (Fig. 9), a foreign substance residual minute region x ₁ is formed (see FIG. 8). In the foreign substance remaining minute region x ₁ , the coating characteristics deteriorate with time, and changes to the easily rusted minute region x ₂ , and minute rust z ₁ is generated in this region (see FIG. 8).

Of the non-metallic anions present in the wash water, those that are particularly likely to generate microrust are chlorine ions (Cl ⁻ ), sulfate ions (SO ₄ ²⁻ ), and hydroxide ions (OH ⁻ ). Further, among the corrosive dissolved substances, the sludge of the pretreatment equipment, the sludge of the plating equipment, and the sludge of the posttreatment equipment are particularly likely to generate micro rust.

  Sludge is a solid substance present in each facility, which is a chemical impurity, an electrode impurity, and the like, and is a substance that is soluble in water.

During winding of the steel sheet, the humidity near the steel sheet for cans 1 ₂ is high (i.e., the dew point is high) and, juicy air is trapped between the steel plates. Thereafter, when the temperature decreases, condensation occurs, and in cooperation with the nonmetallic anion 6 and the foreign matter 7, the change to the easily rusting microregion x ₂ and the generation of micro rust z ₁ are promoted (see FIG. 8). .

Further, the treatment before plating subjected to the processing Maehara steel A, then washed with washing water, to prepare a pre-plating the steel plate 2 ₁ to be subjected to the plating process 9. At this time, the non-metallic anions 6 or foreign matter 7 of the washing water is, the pre-plating the steel plate 2 ₁ surface, it is a trace amount remains, the foreign matter remaining small area y ₀ is formed (FIG. 9, reference).

After plating 4 subjected in the plating step 9, when forming the film 5 is subjected to chemical conversion treatment, the foreign matter remaining small area y _0, the plating 4 is not done properly, the plating defect minute region y ₁ is formed (See FIG. 8).

The steel plate 2 ₂ for cans formed with a film by chemical conversion treatment is washed and wound to form a steel plate coil 2 ₂ ′ for cans, but the coating 5 formed in the plating defect micro-region y ₁ is easy as time passes. changes to rusting minute region y _2, in this region, small rust z ₂ is generated (FIG. 8, reference).

During winding, the dew point of the surrounding steel sheet for cans 1 ₂ is high (i.e., the dew point is high) and, juicy air is trapped between the steel plates. Thereafter, when the temperature drops, condensation, in cooperation with the non-metallic ions 6 and foreign matter 7, to promote the formation of fine rust z ₁ changes to Ekihatsusabi minute regions y _2.

Therefore, in the present invention, the coating surface of the steel plate for cans is washed with washing water not containing chlorine ions (Cl ⁻ ), sulfate ions (SO ₄ ²⁻ ), and hydroxide ions (OH ⁻ ), and the humidity is adjusted. It is necessary to wind up the steel plate for cans in a humidity-controlled atmosphere. This is the second feature of the present invention.

  The humidity control atmosphere is formed by adjusting the dew point, but in order to confirm the relationship between the adjustment of the dew point and rusting, the present inventor uses a tin-free steel plate cleaned with purified water and a tin-free steel plate cleaned with pure water. The following tests were conducted.

  Six pieces of 250 mm × 250 mm × 0.20 mm tin-free steel plates were stacked in an air with a dew point adjusted and packed to prepare a test specimen. The test body was pressurized with a hydraulic jack and stored in a test chamber, and the presence or absence of rust generation and the number of rusts were periodically observed. FIG. 10 shows microrust generated in the test. FIG. 11 shows the relationship between the dew point and the number of days until rusting in the test results.

  In the case of the test body packed in the air whose dew point was adjusted to 25 ° C., rust as shown in FIG. 10 occurred on the coating surface of the tin-free steel plate washed with purified water after 9 days. On the other hand, no rust was generated on the surface of the tin-free steel sheet washed with pure water after 9 days.

  In the case of a specimen packed in air with a dew point adjusted to 15 ° C, rust is generated on the surface of the tin-free steel sheet cleaned with purified water and on the surface of the tin-free steel sheet cleaned with pure water after 9 days. Rust did not occur after 9th.

  From FIG. 11, it can be seen that the dew point of air confined in the gap between the steel plates greatly affects the generation of microrust. That is, even when purified water containing chlorine is used as cleaning water, microrust does not occur if the dew point around the steel sheet is lowered.

  In addition, when pure water not containing chlorine is used as cleaning water instead of purified water containing chlorine, the generation of rust can be prevented without lowering the dew point.

  Based on this, in the present invention, the dew point of the atmosphere around the steel sheet when winding the steel sheet is appropriately set according to the type of cleaning water used in the production line. In addition, since the dew point of the air trapped in the gap between the steel plates greatly affects the generation of micro rust, the wind-up is performed while blowing a humidity-control gas such as conditioned air on the surface of the steel plate during winding. May be.

  Since the occurrence of micro rust is also related to the thickness of the coating, the present inventor investigated the minimum film thickness at which micro rust does not occur using a tin-free steel plate.

The Ox-Cr layer that forms the coating of the tin-free steel sheet contains sulfate ions (SO ₄ ^2- ) and F residual substances, and has the property that water adsorbs and penetrates easily. In order to prevent it, the required thickness is required.

  During chemical conversion treatment, a coating is formed by changing the amount of Ox-Cr attached, and the steel plate washed with purified water is left in a humidity bath at a temperature of 30 ° C, a relative humidity of 80%, and a dew point of 26 ° C. The number of rust to be measured was measured. The result is shown in FIG.

From FIG. 12, it can be seen that if Ox-Cr of 10 mg / m ² or more adheres to the plating layer to form a coating, the generation of rust can be greatly suppressed even with a steel plate washed with purified water.

Based on this, in the present invention, the amount of Ox—Cr attached is preferably 10 mg / m ² or more. In addition, the plated steel plate which performs a chemical conversion treatment is not limited to a specific steel plate.

  Next, examples of the present invention will be described. The conditions of the examples are one example of conditions adopted for confirming the feasibility and effects of the present invention, and the present invention is limited to this one example of conditions. Is not to be done. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

(Example)
The present invention was carried out on a production line, and the relationship between the presence or absence of rust and the dew point was investigated to confirm the effect of the present invention.

  The result is shown in FIG. FIG. 13B shows the relationship between the presence of rust and the dew point when pure water is used as the cleaning water and the dew point of the atmosphere around the winder is adjusted. FIG. 13C shows the winder. The relationship between the presence or absence of rust and the dew point when the nearby dew point is adjusted is shown.

  For comparison, FIG. 13A shows the relationship between the presence or absence of rust generation and the outside air dew point in a conventional winding environment. In the conventional winding environment, when the outside air dew point is 20 ° C. or higher, minute rust is generated when 5 days have passed since the film was formed.

  On the other hand, when the dew point of the atmosphere around the winder is adjusted, when the dew point is 25 ° C. or higher, minute rust is generated when 8 days have elapsed since the film was formed. As described above, the critical dew point at which minute rust is generated and the critical days until the rust are moved to the high dew point side and the high day side (see FIG. 13B).

  When the dew point in the vicinity of the winder is adjusted to 17 ° C. or less, microrust does not occur on the coating surface (see FIG. 13C).

  As described above, according to the present invention, it is possible to manufacture a tin-free steel plate in which minute rust is not generated on the coating surface. Therefore, the present invention has great applicability not only in the steel plate manufacturing industry but also in the can manufacturing industry.

It is a figure which shows the manufacturing line of a plated steel plate. (A), (b) is a figure which shows the result of having observed the microrust which rusted on the chromate film surface of the steel plate with the optical microscope. It is a figure which shows the relationship between the dew point of the building with a manufacturing line, and the generation | occurrence | production time of microrust. It is a figure which shows the result of having analyzed micro rust by Auger electron spectroscopy (AES). (A1) shows the spectrum of the microrust 1 and the outermost surface around it, and (b1) and (c1) show the spectrum after 60 seconds and the spectrum after 120 seconds, respectively. (A2) shows the spectrum of the minute rust 2 and its outermost surface, and (b2) and (c2) show the spectrum after 60 seconds and the spectrum after 120 seconds, respectively. It is a figure which shows the result of having analyzed the clean surface in which micro rust does not exist with AES in contrast with the spectrum of micro rust 1. FIG. (A0) shows the spectrum of the clean surface where microrust does not exist, and (b0) and (c0) show the spectrum after 60 seconds and the spectrum after 120 seconds, respectively. (A1) shows the spectrum of the outermost surface of the minute rust 1, and (b1) and (c1) show the spectrum after 60 seconds and the spectrum after 120 seconds, respectively. It is a figure which shows the result of having analyzed the clean surface in which micro rust does not exist with AES in contrast with the spectrum of micro rust 2. FIG. (A0) shows the spectrum of the clean surface where microrust does not exist, and (b0) and (c0) show the spectrum after 60 seconds and the spectrum after 120 seconds, respectively. (A2) shows the spectrum of the outermost surface of the microrust 2. (b2) and (c2) show the spectrum after 60 seconds and the spectrum after 120 seconds, respectively. It is a figure which shows the result of having analyzed the steel plate surface in which microrust existed by AES. It is a figure explaining the process in which micro rust produces | generates. It is a figure which shows typically the structure of the film of the steel plate for cans. It is a figure which shows the microrust produced | generated by the test. It is a figure which shows the relationship between a dew point and the days until rusting. It is a figure which shows the relationship between the adhesion amount of Ox-Cr, and rust generation | occurrence | production. It is a figure which shows the relationship between the presence or absence of rust generation | occurrence | production, and a dew point. (A) shows the relationship between the presence or absence of rust generation and the outside air dew point in a conventional winding environment, and (b) shows the case where pure water is used as cleaning water and the dew point of the atmosphere around the winder is adjusted. The relationship between the presence or absence of rust and the dew point is shown. (C) shows the relationship between the presence or absence of rust and the dew point when the dew point near the winder is adjusted.

Explanation of symbols

₁ , 2 Raw steel plate before treatment 1 ₁ , 2 _{1 1} Steel plate before plating 1 ₂ , 2 ₂ Steel plate for cans 1 ₂ ', 2 ₂ ' Steel plate coil for cans 1 ₃ , 2 ₃ Steel plates for rewinding cans 3 Coating 4 Plating 5 Coating 6 Non-metallic anion 7 Foreign matter 8 Residual substance 9 Plating process x ₁ , y ₀ Foreign matter remaining micro area x ₂ , y ₂ Easy rusting micro area y ₁ Plating defect micro area z ₁ , z ₂ Micro rust

Claims (11)

  In the method for producing a steel sheet for cans, which is formed by coating the surface of the steel sheet and then performing a chemical conversion treatment, the coating surface after the chemical conversion treatment is washed with water that does not contain nonmetallic anions and corrosive dissolved substances. A method for producing a steel plate for cans, characterized in that the generation of micro-rust is prevented.   In the method for producing a steel plate for cans, which is formed by coating the surface of the steel plate and then performing a chemical conversion treatment, the steel plate is wound in a humidity-controlled atmosphere to prevent the occurrence of micro-rust. Manufacturing method for steel plate for can.   In the method for producing a steel plate for cans, after the surface of the steel plate is plated and then subjected to chemical conversion treatment to form a coating, the coating surface is washed with washing water that does not contain nonmetallic anions, and then the steel plate is A method for producing a steel plate for cans, characterized in that it is wound up in a humidity-controlled atmosphere to prevent the occurrence of minute rust.   The manufacturing method of the steel plate for cans according to claim 2 or 3, wherein a dew point of said humidity control atmosphere is 17 ° C or less.   The method for producing a steel plate for cans according to any one of claims 2 to 4, wherein a humidity control gas is blown onto the surface of the steel plate during the winding.   The method for producing a steel plate for cans according to any one of claims 1 to 5, wherein the surface of the steel plate before plating is washed with washing water that does not contain nonmetallic anions and corrosive dissolved substances. . The nonmetallic anion is one or more of chlorine ion (Cl ⁻ ), sulfate ion (SO ₄ ²⁻ ), and hydroxide ion (OH ⁻ ). The manufacturing method of the steel plate for cans of any one of Claims 1.   The said corrosive melt | dissolution substance is 1 type, or 2 or more types of the sludge of a pre-processing equipment, the sludge of a plating equipment, and the sludge of a post-processing equipment, The any one of Claims 1-7 characterized by the above-mentioned. Manufacturing method of steel plate for cans.   The method for producing a steel plate for cans according to any one of claims 1 to 8, wherein the washing water is pure water.   The said coating film is a chromate film, The manufacturing method of the steel plate for cans of any one of Claims 1-9 characterized by the above-mentioned. The manufacturing method of the steel plate for cans according to claim 10, wherein the amount of Ox-Cr attached to the chromate film is 10 mg / m ² or more.