JP5292927B2 - Metal surface treatment method and surface-treated steel sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a metal surface treatment method and a surface-treated steel plate formed by the method capable of suppressing irregular coating even when executing the chromate-free surface treatment of the steel plate having large surface unevenness, and ensuring sufficient corrosion resistance while preventing any increase in the coating film thickness. <P>SOLUTION: In the metal surface treatment method, water-based metal surface treatment agent containing at least silane coupling agent and surfactant is applied on a surface of a galvanized steel plate having the surface roughness of &ge;1 &mu;m and &le;10 &mu;m in terms of Ra, and the steel plate is dried to form a coating film on the surface of the galvanized steel plate. The water-based metal surface treatment agent is formed of liquid particles having the particle diameter of &ge;10 &mu;m and &le;30 &mu;m, the liquid particles are blown to the galvanized steel plate, and the wetting angle of the liquid particles with respect to the surface of the galvanized steel plate is &le;90&deg;. <P>COPYRIGHT: (C)2010,JPO&amp;INPIT

Description

  The present invention relates to a metal surface treatment method and a surface-treated steel sheet, and in particular, a method of performing a chromium-free surface treatment and a chromate-free surface treatment on a steel sheet having a large surface roughness such as an alloyed hot-dip galvanized steel sheet. It relates to a surface-treated steel sheet.

  Contains chromic acid, dichromic acid or their salts as the main component as a technology that provides excellent adhesion to the metal material surface and imparts characteristics such as corrosion resistance, heat resistance, fingerprint resistance, and paintability to the metal material surface. Background Art Conventionally, chromate treatment in which a surface treatment is performed on a metal material surface using a treatment liquid has been widely performed.

  On the other hand, in recent years, a chromate-free treatment that does not use chromate such as chromic acid has been actively developed because the chromate treatment has a large environmental load. Examples of such chromate-free treatment include a method of performing a phosphate treatment, a method of performing a treatment with a silane coupling agent, and a method of performing an organic resin film treatment (see, for example, Patent Document 1).

  Here, conventionally, when a chromate treatment is performed on the surface of a metal material such as a steel plate, it has been carried out by roll coater coating, dip coating (so-called dobbling) of the metal material in a surface treatment solution, spray coating, or the like.

JP 2007-51365 A

  However, as with the chromate treatment, corrosion resistance decreases when chromate-free treatment is applied to steel plates with large surface irregularities such as galvannealed steel plates by roll coater coating, dip coating, or normal spray coating. Or coating unevenness occurs or the thickness of the coating film increases.

  Specifically, roll coater coating is preferable in terms of reducing the amount of surplus surface treatment liquid as much as possible and suppressing the occurrence of coating unevenness. However, in the case of roll coater coating, for example, in order to provide sufficient corrosion resistance as in the case of an electroplated steel sheet, when trying to secure the coating film thickness at the convex part on the steel sheet surface, the thickness of the coating film at the concave part becomes too large. Problems such as an increase in cost and a decrease in workability occur. On the other hand, if the thickness of the coating film is reduced in order to suppress an increase in cost, a decrease in workability, etc., a problem of a decrease in corrosion resistance occurs.

  Furthermore, when roll coater coating is used to apply to uneven steel sheet surfaces such as alloyed hot-dip galvanized steel sheets, there is a problem in that roll wear occurs due to the large unevenness of the surface, and countermeasures against this are required. is there.

  Also, in the case of dip coating, as in the case of roll coater coating, not only the corrosion resistance and the coating film thickness increase, but also the problem of occurrence of coating unevenness occurs.

  On the other hand, in the case of conventional spray coating, uneven coating tends to occur on the coating film. Further, if an excess of the processing liquid is removed with a ringer roll or the like after spray coating, the problem of increase in corrosion resistance and coating thickness occurs as in the case of roll coater coating.

  Therefore, the present invention has been made in view of such problems, and in the metal surface treatment method and the surface-treated steel sheet formed by this method, a chromate-free surface treatment was performed on a steel sheet having large surface irregularities. Even if it is a case, it aims at ensuring sufficient corrosion resistance, suppressing generation | occurrence | production of a coating nonuniformity and not increasing a coating-film thickness.

  As a result of intensive studies to solve the above problems, the present inventors have made the surface treatment agent adhere to the steel sheet in the form of a liquid particle having a small particle diameter and attached to the steel sheet. It was found that the film uniformly adheres along the unevenness and can suppress the occurrence of uneven coating. As a result of further investigation, the present inventors have found that in order to uniformly attach the surface treatment agent to the steel sheet surface, coating unevenness is less likely to occur when the wetting angle of the liquid particles with respect to the steel sheet is 90 degrees or less. It was. Based on the above findings, the present inventors have completed the present invention.

That is, according to an aspect of the present invention, an aqueous metal surface treatment agent containing at least a silane coupling agent and a surfactant is applied to the surface of a galvanized steel sheet having a surface roughness Ra of 1 μm or more and 10 μm or less. In the metal surface treatment method for forming a film on the surface of the galvanized steel sheet by drying it later, the water-based metal surface treatment agent is changed to liquid particles having a particle size of 10 μm or more and 30 μm or less, and then directed to the galvanized steel sheet. The liquid particles are sprayed, the wetting angle of the liquid particles with respect to the surface of the galvanized steel sheet is 90 degrees or less , the aqueous metal surface treatment agent has a pH of 3 to 6, and the surfactant is nonionic. It is a surfactant or a cationic surfactant, and the content of the surfactant is 0.00 with respect to 100 parts by mass of the aqueous metal surface treatment agent. Not more than 5 parts by mass or more parts by weight, the aqueous metal surface treatment agent is further characterized by containing zinc 100ppm or 500ppm or less, the metal surface treatment method is provided.

  By having such a configuration, according to the metal surface treatment method of the present invention, even when a chromate-free treatment is performed on the surface of a steel plate having large irregularities such as an alloyed hot-dip galvanized steel plate, While suppressing the occurrence of unevenness, the coating film can have sufficient corrosion resistance.

  Further, in the metal surface treatment method, the particle size of the liquid particles may be adjusted according to the average film thickness after drying of the film. Specifically, for example, when the average film thickness after drying of the film is relatively large, the particle size of the liquid particles is adjusted to be relatively large, and conversely, the average film thickness after drying of the film is compared. If the particle size is small, the effect of suppressing uneven coating can be further improved by adjusting the particle size of the liquid particles to be relatively small.

  Moreover, in the said metal surface treatment method, it is preferable to spray the said liquid particle from the position spaced apart 50 mm or more from the surface of the said galvanized steel plate.

  Moreover, in the said metal surface treatment method, it is preferable that the speed | rate when the said liquid particle contacts the said galvanized steel plate shall be 0.1 m / s or more and 5 m / s or less.

  In the metal surface treatment method, the water-based metal surface treatment agent may be applied using a gas-liquid mixed spray in which a gas and a liquid are mixed and discharged to the outside.

At this time, it is preferable that the cross-sectional area of the discharge port of the aqueous metal surface treatment agent in the gas-liquid mixed spray is 3 mm ² or more.

  Further, the gas-liquid mixed spray may be coated with fluoride in the vicinity of the discharge port including the discharge port of the aqueous metal surface treatment agent.

Further, according to another aspect of the present invention, the surface of a galvanized steel sheet having a surface roughness Ra of 1 μm or more and 10 μm or less has a film formed by the metal surface treatment method described above, A surface-treated steel sheet having an average film thickness T after drying of 0.1 μm to 2 μm and a standard deviation σ of the film thickness satisfying the following formula (I) is provided.
σ ≦ 0.21T + 0.78 (I)

  According to the present invention, in the metal surface treatment method and the surface-treated steel sheet formed by this method, the aqueous metal surface treatment agent is applied as fine liquid particles, and the wetting angle of the liquid particles is adjusted. Even when a chromate-free surface treatment is applied to a steel sheet with large surface irregularities, it is possible to form a film with a uniform thickness along the irregularities on the surface of the steel sheet and to suppress the occurrence of uneven coating. Sufficient corrosion resistance can be ensured while not increasing the coating film thickness.

  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.

<Reason for uneven coating due to chromate-free treatment>
First, before explaining the details of the present invention in detail, as a premise, when performing chromate treatment, even if it is an alloyed hot-dip galvanized steel sheet with large irregularities on the surface, the occurrence of uneven coating, a decrease in corrosion resistance, While problems such as an increase in the thickness of the coating film do not occur, in the case of chromate-free treatment, the results of the study by the present inventors will be described as to why each problem occurs.

  In the case of chromate treatment, since chromate such as chromic acid is a strong acid, zinc on the surface of the galvanized steel sheet is dissolved in chromate. However, the reaction between chromate and zinc (dissolution of zinc by chromate) forms a passive film on the galvanized steel sheet that does not react with chromate (does not dissolve in chromate). As a result, the zinc on the surface of the galvanized steel sheet is protected by a passive film, so chromate can no longer dissolve zinc, and the reaction between chromate and zinc without dissolving more zinc than necessary. Stops. Thus, in the case of a chromate film, the formation of a passive film prevents the chromate and zinc from reacting more than necessary, so an alloyed hot dip galvanized steel sheet using dip coating or conventional spray coating is used. Even if the steel sheet having a large unevenness on the surface is processed, uneven coating is less likely to occur.

  On the other hand, in the case of chromate-free treatment, uneven coating tends to occur in dip coating or conventional spray coating. As a result of studying the reason by the inventors, the following knowledge was obtained. The surface treatment agent used for chromate-free treatment forms a passive film that does not react with the surface treatment agent (does not dissolve in the surface treatment agent) and is slower than chromate. Therefore, if the chromate-free surface treatment agent is kept in contact with the galvanized steel sheet for a long time, the dissolution reaction of zinc proceeds before the passive film is formed, and it is unstable on the formed chromate-free film layer. Layers (layers that are easy to peel) tend to be laminated. It was found that when this unstable layer partially peels, unevenness occurs in the reaction between the surface treatment agent and zinc, and uneven coating tends to occur.

  Furthermore, as described above, when a chromate-free surface treatment agent is used, since the zinc dissolution reaction proceeds before the passive film is formed, excess zinc is eluted and the film swells, It has also been found that a large amount of sludge may be generated in the surface treatment agent.

  That is, the chromate-free surface treatment agent (aqueous solution) can be dissolved in water again even if the water is once evaporated and only the solid content is taken out. On the other hand, when the chromate-free surface treatment agent (aqueous solution) reacts with zinc, it forms a product (passive film) that cannot be dissolved in zinc. However, in the case of chromate-free treatment, the formation of this passive film was slower than in the case of chromate treatment, which was found to be the reason that it was difficult to suppress the dissolution of excess zinc compared to the chromate film. .

<Examination of surface treatment method for suppressing occurrence of uneven coating>
Based on the above knowledge, the present inventors examined a surface treatment method for suppressing the occurrence of uneven coating by suppressing the dissolution of excessive zinc. Specifically, in the case of conventional spray application, the present inventors first attached the surface treatment agent more than the necessary amount for forming a film by the reaction between zinc and the surface treatment agent, It was considered that the reaction between zinc and the surface treatment agent would proceed excessively in order to remove the excess treatment agent (in this case, occurrence of spotted or linear coating unevenness was observed on the steel sheet surface). Therefore, the present inventors thought that a method in which a necessary minimum amount of a surface treatment agent was previously attached to the surface of a galvanized steel sheet was effective. As a method for attaching the minimum necessary amount of the surface treatment agent in advance, for example, application using a roll coater is conceivable. However, in the case of roll coater coating, a film having a uniform thickness (chromate-free film) is formed on a smooth roll surface, and this film is transferred to the steel sheet surface. Therefore, when a chromate-free film is formed on a steel sheet having a large surface unevenness such as an alloyed hot-dip galvanized steel sheet, the film thickness varies depending on the surface unevenness of the steel sheet (thickness of the recess). Becomes thicker and the film thickness of the convex portion becomes thinner). That is, in the case of roll coater application, the surface of the roll and the convex portion of the surface of the steel sheet come into contact with each other, so the surface of this convex portion becomes the reference and becomes the surface of the chromate-free film. In this case, since the surface treatment agent is press-fitted and filled in the recesses on the steel plate surface, a film having a non-uniform thickness is formed. In the case of conventional spray coating, the particle size of the liquid particles is as large as several hundred μm to several mm, for example, to form a film having a thickness of 0.1 μm to 2 μm on the steel sheet after drying. Since the amount of solid content in the surface treatment agent needs to be considerably reduced, the reaction between the surface treatment agent and zinc on the steel sheet surface is significantly delayed, and the surface treatment agent flows out, so that uneven coating tends to occur. . Although there is a technique called electrostatic coating, it is difficult to use this technique for water-based paints.

  Therefore, the present inventors have made a chromate-free surface treatment agent on a steel plate with a large surface irregularity such as an alloyed hot-dip galvanized steel plate by attaching a chromate-free surface treatment agent in the form of fine liquid particles to the steel plate surface. It has been found that even when a treatment agent is applied, the surface treatment agent can be uniformly adhered along the unevenness of the steel sheet surface, thereby suppressing the occurrence of coating unevenness. When spraying such fine liquid particles, the surface of the concave portion on the surface of the steel sheet is used as a reference, and the surface treatment agent is in contact, and the surface treatment agent is not pressed into the concave portion as in the case of roll coater application. It becomes easy to form a uniform film along the unevenness of the steel sheet surface. Such a film cannot be formed by conventional roll coater coating, dip coating, spray coating, or the like.

  Further, as a result of further investigation, the present inventors have set the wetting angle of the liquid particles to the steel sheet to 90 ° or less in order to uniformly attach the chromate-free surface treatment agent on the steel sheet having a large uneven surface. Thus, the distance between the steel plate and the surface of the liquid particles adhering to the steel plate can be made almost constant, and it has been found that uneven coating is less likely to occur.

<About the metal surface treatment method according to the present invention>
That is, in the metal surface treatment method according to the present invention, a chromate-free aqueous metal surface treatment agent is applied to the surface of a galvanized steel sheet with large irregularities on the surface, and then dried, so that the chromate-free surface is applied to the surface of the galvanized steel sheet. This is a method of forming a film. In the metal surface treatment method of the present invention, when the water-based metal surface treatment agent is applied, the water-based metal surface treatment agent is made into fine liquid particles (particle size of 10 μm or more and 30 μm or less) and then directed toward the surface of the galvanized steel sheet. Liquid particles are sprayed to adhere the liquid particles onto the galvanized steel sheet. At this time, by adjusting the wetting angle of the liquid particles with respect to the surface of the galvanized steel sheet to a predetermined range (90 degrees or less), the surface treatment agent is formed into a film having a uniform thickness along the unevenness of the surface of the galvanized steel sheet. be able to.

(About galvanized steel sheet)
As the galvanized steel sheet used in the present invention, one having a surface roughness of Ra of 1 μm or more and 10 μm or less is used, and examples thereof include galvannealed steel sheets. Here, Ra can be measured using a surface roughness measuring instrument (for example, manufactured by Kosaka Laboratory Ltd.).

  Moreover, it is preferable that the temperature at the time of passing of a galvanized steel plate shall be 60 to 90 degreeC from a viewpoint of accelerating | stimulating reaction with a surface treating agent and zinc, when apply | coating. Below 60 ° C., when the film thickness is about 2 μm, a non-reactive portion may remain in the liquid particles. On the other hand, if it exceeds 90 ° C., the film may be dried before reacting in the region where the film thickness is about 0.1 μm. The temperature of the galvanized steel sheet can be adjusted, for example, by installing a hot air blower or the like on the front surface of the spray for applying the surface treatment agent.

(About water-based metal surface treatment agent)
The aqueous metal surface treatment agent of the present invention is an aqueous solution in which at least a silane coupling agent and a surfactant are contained in water as a solvent. Further, phosphoric acid, a vanadium compound, a fluoro compound, and the like are used as necessary. May be included.

The general formula of the silane coupling agent is represented by R—Si (OR ′) ₃ (where R is a functional group, aminopropyl group, glycidoxy group, methacryloxy group, N-phenylaminopropyl group, mercato group) R ′ is a methyl group or an ethyl group, and this silane coupling agent is hydrolyzed to form a silanol group upon contact with water, as shown in the following formula.
R—Si (OR ′) ₃ + 3H ₂ O → R—Si (OH) ₃ + 3R′OH
Silanol groups are polymerized by self-condensation and at the same time chemically bonded to hydroxyl groups on the metal surface by acid-base reaction. On the other hand, the functional group R is firmly bonded to the coating component by chemical bonding or crosslinking. As such a silane coupling agent, for example, 3-aminopropyltriethoxysilane, 3-aminopropyltrimethoxysilane, 3-glycidoxypropyltrimethoxysilane and the like can be used.

  As the surfactant, a nonionic surfactant or a cationic surfactant can be used, and specific examples include polyethylene oxide, polypropylene oxide adducts, and acetylene glycol compounds. Moreover, it is preferable that content of surfactant is 0.001 mass part or more and 5 mass parts or less with respect to 100 mass parts of aqueous metal surface treatment agents. By defining the type of surfactant and the content of the surfactant as described above, the wetting angle of the liquid particles can be 90 degrees or less.

  In the present invention, the pH of the aqueous metal surface treatment agent is preferably about 3 to 6 (weakly acidic). By setting the pH of the treatment agent in the above range, the aqueous metal surface treatment agent of the present invention has reactivity with the galvanized layer on the steel sheet surface, the weakly acidic aqueous metal surface treatment agent dissolves the galvanized layer, A chromate-free film is formed by concentrating zinc in the treatment agent. However, since zinc is an amphoteric metal, the pH of the surface treatment agent can be acid or alkali (since zinc is an amphoteric metal, it becomes water-soluble by changing the pH to the acidic side or alkaline side), or excessive ammonia is used in combination ( An ammine complex may be formed to make zinc water-soluble). As the pH adjuster, for example, acetic acid, lactic acid, hydrofluoric acid, ammonium salt, amines and the like can be used.

  Moreover, it is preferable to further contain 100 ppm or more and 500 ppm or less of zinc in the aqueous metal surface treatment agent. Thus, it becomes easy to adjust the wetting angle of the liquid particles by containing a small amount of zinc in the aqueous metal surface treatment agent. In this case, if the zinc content is less than 100 ppm, the effect of easily adjusting the wetting angle cannot be obtained, and if it exceeds 500 ppm, the silane coupling agent in the aqueous metal surface treatment agent reacts with zinc. , Because the treatment agent is altered.

  In the present invention, the particle size of the liquid particles sprayed on the surface of the galvanized steel sheet is 10 μm or more and 30 μm or less. The size (particle size) of this liquid particle is the target value of the average film thickness of the chromate-free film after drying, the proportion of non-volatile components in the metal surface treatment agent, and the unit of liquid particles of the metal surface treatment agent that collides with the steel sheet. It is determined according to time and the number per unit area. Specifically, for example, when forming a chromate-free film having an average film thickness after drying of 0.1 μm to 2 μm, the case where the nonvolatile component in the metal surface treatment agent is about 10% is taken as an example. When the average film thickness after drying is about 0.1 μm to 0.5 μm, the particle size of the liquid particles is about 10 μm ± 5 μm, and when the average film thickness after drying is about 0.5 μm to about 1.5 μm If the particle size of the liquid particles is about 20 μm ± 10 μm and the average film thickness after drying is more than 1.5 μm to about 2 μm, the particle size of the liquid particles may be adjusted to about 30 μm ± 10 μm. Note that the size (average particle size) of the liquid particles can be experimentally determined from the relationship between the nozzle type, pressure, and flow rate.

  Thus, when forming a chromate-free film on the surface of a steel sheet with large irregularities such as an alloyed hot-dip galvanized steel sheet, the metal surface treatment agent is adjusted by adjusting the diameter of the liquid particles according to the average film thickness after drying. After drying, a film having a uniform thickness can be formed along the irregularities on the surface of the steel sheet. That is, in the metal surface treatment method of the present invention, the particle size of the liquid particles may be adjusted according to the average film thickness after drying the chromate-free coating. Specifically, for example, when the average film thickness after drying of the film is relatively large, the particle size of the liquid particles is adjusted to be relatively large, and conversely, the average film thickness after drying of the film is compared. If the particle size is small, the effect of suppressing uneven coating can be further improved by adjusting the particle size of the liquid particles to be relatively small.

  This is because, as described above, when the film thickness after drying of the film is thin, by reducing the particle size of the liquid particles, an area that does not react with the steel sheet surface cannot be formed in the liquid particles, and thus uneven coating occurs. It is thought that it becomes difficult. On the contrary, when the film thickness after drying of the film is thin, if the particle size of the liquid particles is increased, an area that does not react with the surface of the steel sheet is formed in the liquid particles, which is considered to cause uneven coating. .

  On the other hand, if the particle size of the liquid particles is reduced when the film thickness after drying is small, the coating efficiency of the metal surface treatment agent may be deteriorated. In such a case, if the operation is performed so as to increase the density of the liquid particles (so that the distance between the liquid particles is close), the liquid particles tend to aggregate, and as a result, the particle diameter of the liquid particles is reduced. Since it becomes large, the painting efficiency can be improved.

  When the water-based metal surface treatment agent is applied onto the galvanized steel sheet with large unevenness on the surface as described above, a uniform film is formed along the unevenness on the surface of the steel sheet, and the film thickness after drying is minimized. Can be suppressed.

  However, the method for adjusting the particle size of the liquid particles is not limited to the method for adjusting the particle size of the liquid particles according to the film thickness after drying of the film as described above, but the target of the average film thickness of the chromate-free film after drying. It can be appropriately determined according to the value, the ratio of the non-volatile component in the metal surface treatment agent, the unit time of the liquid particles of the metal surface treatment agent that collides with the steel plate, the number per unit area, and the like.

  In the present invention, the wetting angle of the liquid particles with respect to the steel sheet when the liquid particles collide with the steel sheet is 90 degrees or less. As a result of the inventor's investigation, in order to uniformly deposit the chromate-free surface treatment agent on the steel sheet having a large uneven surface, the wetting angle of the liquid particles with respect to the steel sheet is set to 90 degrees or less. This is because the distance between the steel plate and the surface of the liquid particles adhering to the steel plate can be made almost constant, so that the knowledge that coating unevenness hardly occurs is obtained.

  The wetting angle of the liquid particles with respect to the steel plate is preferably 60 degrees or less. In this case, when the treated surface (painted surface) of the steel sheet is substantially perpendicular to the ground, the present inventors have confirmed that it has an effect of reducing coating unevenness on the coated surfaces on both surfaces of the steel sheet. . Furthermore, when the wetting angle of the liquid particles with respect to the steel sheet is 30 degrees or less, when the painted surface is horizontal to the ground, the effect of reducing spot-like or linear coating unevenness is also achieved on the painted surface on the lower surface side. It has been confirmed by the present inventors.

  On the other hand, when the wetting angle of the liquid particles with respect to the steel plate exceeds 90 degrees, some of the liquid particles are in contact with the steel plate (for example, the surface on the center side of the liquid particles is in contact with the steel plate surface, and the end of the liquid particles The surface on the part side is separated from the steel plate surface). Therefore, since the formation of the film by the reaction between the surface treatment agent and zinc on the surface of the galvanized steel sheet is limited only to the portion where the liquid particles and the steel sheet are in contact with each other, the film is formed unevenly on the surface of the steel sheet. Unevenness will occur. In addition, when the surface treatment agent is applied in a region where the steel plate is passed through in a direction perpendicular to the ground, the surface treatment agent may hang downward, and the wetting angle of the liquid particles with respect to the steel plate exceeds 90 degrees. In the state, the linear coating unevenness may become remarkable.

  Moreover, in order to adjust the wetting angle of the liquid particles with respect to the steel plate, for example, a surfactant having a small wetting angle may be selected and added to the surface treatment agent in a predetermined amount. Specifically, as described above. Furthermore, as described above, it is easy to adjust the wetting angle if a small amount of zinc is previously contained in the surface treatment agent.

  Here, the wetting angle of the liquid particles with respect to the steel sheet is, for example, that a droplet of a surface treatment agent is dropped on a galvanized steel sheet placed horizontally with respect to the ground, and the state of the liquid droplet is observed from the side. Can be measured.

  When the surface tension of the surface treatment agent is set to 40 mN / m or less (preferably less than 20 mN / m), when the distance between the galvanized steel sheet and the nozzle of the present invention is 50 mm or more, the surface is made fine particles. The treatment agent is preferable because it is difficult to reaggregate.

(About application method of water-based metal surface treatment agent)
The water-based metal surface treatment agent used in the metal surface treatment method of the present invention has been described in detail above. Subsequently, a specific method for applying such a water-based metal surface treatment agent will be described.

  In the present invention, it is preferable to spray the liquid particles obtained by atomizing the water-based metal surface treatment agent by spraying from a position separated from the surface of the galvanized steel sheet by 50 mm or more, preferably 200 mm or more. This is because the steel plate vibrates easily in the thickness direction (spray nozzle direction) when there is a fluctuation in tension, so the nozzle cannot be installed close to the steel plate so as not to damage the spray nozzle. is there.

  However, if the interval between the nozzle and the steel plate is too wide, uneven coating tends to occur. This is because when the gap between the nozzle and the steel plate is widened, the liquid particles impinging on the steel plate include low-velocity liquid particles. This is because the ratio of bad contact with liquid particles increases. Therefore, when the distance between the steel plate and the nozzle is 50 mm or more, it is particularly desirable that the wetting angle be 90 degrees or less.

  Moreover, in this invention, it is preferable that the speed | velocity when the liquid particle which atomized the water-system metal surface treating agent contacts a galvanized steel plate shall be 0.1 m / s or more and 5 m / s or less. If the speed of the liquid particles exceeds 5 m / s, when the aqueous metal surface treatment agent collides with the steel plate surface and the liquid particles spread, the probability that air remains between the steel plate and the liquid particles increases, so that the drying is performed. There is a risk that foaming may occur during the process. From such a point of view, it is more preferable that the speed of the liquid particles is 1 m / s or less, since air is hardly involved between the steel plate and the liquid particles. On the other hand, if the speed of the liquid particles is less than 0.1 m / s, the liquid particles may not adhere to the steel sheet when the speed of the liquid particles fluctuates. The flow rate of the liquid particles can be controlled by adjusting the pressure of the gas (air or the like) when discharging the liquid particles from a spray or the like.

In addition, in the application experiment of the liquid particles of the water-based metal surface treatment agent using water as a preliminary experiment conducted by the present inventors, the liquid particles (that is, water droplets in this experiment) are alloyed in the above speed range. It was found that it adhered to the surface of the hot-dip galvanized steel sheet sparsely and not uniformly. At this time, the surface tension of water was about 50 to 70 mN / m. The reason for this is that when the surface of the galvannealed steel sheet is uneven, the effective speed at which the water particles collide with the steel sheet surface is, for example, 10 It is considered that 10 to 30 μm of water particles were repelled from the surface of the steel sheet because it was as small as about 50% to 50%. In general, the change in the internal pressure (PP ′) is proportional to the surface tension σ and inversely proportional to the particle radius r (PP ′ = 2σ / r). It is considered easy to play. Further, since the change in internal pressure is only proportional to the surface tension, it is considered that the influence of adhesion to the steel sheet is small even if the surface tension is changed. On the other hand, when the wetting angle of the liquid particles with respect to the steel sheet surface is as small as 90 degrees or less, once the liquid particles come into contact with the steel sheet, energy is minimized by reducing the wetting angle. The liquid particles are considered to be applied to the steel sheet.

  Here, for example, Japanese Patent Application Laid-Open Nos. 2006-341144, 2004-906, and 2004-122705 disclose techniques for applying ink on paper as fine particles. However, since these techniques are application on paper, they cannot be applied to application on a steel sheet as they are. This is because in the case of inkjet, since the discharge speed of the particles is high, if the surface treatment agent is applied onto the steel plate at the same speed, air entrainment occurs and coating unevenness occurs.

  In the metal surface treatment method of the present invention, an aqueous base liquid containing a silane coupling agent, a surfactant, silica, a water-soluble organic resin, and water as a solvent is used as an aqueous metal surface treatment agent. Therefore, it is preferable to use a gas-liquid mixed spray for applying the water-based metal surface treatment agent by mixing gas and liquid and discharging them to the outside.

At this time, since the surface treatment agent has reactivity with the metal, the cross-sectional area of the discharge port of the aqueous metal surface treatment agent in the gas-liquid mixed spray is preferably 3 mm ² or more.

  Furthermore, depending on the nozzle material of the gas-liquid mixed spray, when it becomes difficult to generate fine liquid particles when the wetting angle becomes small, a material that can ensure a wetting angle of 90 degrees or more for the material of the tip including the nozzle discharge port, for example, It is preferable to apply a fluoride coating.

<About the surface-treated steel sheet according to the present invention>
Although the metal surface treatment method according to the present invention has been described in detail above, the surface-treated steel sheet after the treatment by the metal surface treatment method as described above will be described below.

The surface-treated steel sheet according to the present invention has a chromate-free film formed by the above-described metal surface treatment method on the surface of a galvanized steel sheet having a surface roughness Ra of 1 μm to 10 μm. In the surface-treated steel sheet of the present invention, the formed chromate-free film has an average film thickness T after drying of 0.1 μm to 2 μm, and the standard deviation σ of the film thickness satisfies the following formula (I).
σ ≦ 0.21T + 0.78 (μm) (I)

(About film thickness measurement method)
Here, the average film thickness T after drying of the film is obtained as an average value of, for example, a result of measuring a thickness of about 10 points using a high-resolution scanning electron microscope (SEM) by preparing a cross-sectional sample of a steel plate. be able to. Further, the standard deviation σ of the film thickness can be obtained by calculating the standard deviation using the result of measuring about 10 points in the same manner as the average film thickness T.

  In addition, as another method for measuring the film thickness, for example, when the components in the film are known, measurement using fluorescent X-rays is performed, for example, the amount of a specific component such as Si or P and after drying The relationship with the weight of the surface treatment agent is obtained in advance. Then, after creating a calibration curve based on this relationship, the amount of specific components such as Si and P existing on the steel sheet surface is measured by measurement using fluorescent X-rays to determine the adhesion weight. By dividing this weight by the area of the fluorescent X-ray measurement region (in this case, 35 mm diameter), the adhesion weight per unit area is obtained. Furthermore, by obtaining the specific gravity in advance from the relationship between the volume and weight of the surface treatment agent after drying, the adhesion weight per unit area can be converted into a film thickness.

(Relationship between standard deviation of film thickness and average film thickness)
Next, the relationship between the standard deviation σ of the film thickness and the average film thickness T (formula (I)) will be described in detail with reference to FIGS. In addition, FIG. 1 is explanatory drawing which shows an example of the state of the film | membrane formed by performing chromate free surface treatment on the steel plate with the large unevenness | corrugation of the surface. FIG. 2 is a graph showing an example of the relationship between the standard deviation σ and the average film thickness T in the surface-treated steel sheet thickness according to the present invention.

  As shown in FIG. 1, in the surface-treated steel sheet on which the coating 2 is formed by performing chromate-free surface treatment on the galvanized steel sheet 1, generally, when the film thickness of the convex portion 11 on the surface becomes a limit value or less. Corrosion occurs from that portion (see the circled portion S in FIG. 1). Moreover, when the film thickness of the film 2 varies, there may be a portion where the corrosion is below the limit value.

On the other hand, the thickness T _thin corresponding to the _thin film thickness is expressed by the following formula (II) in consideration of variations in the film thickness.
T−α × σ = T _thin (II)

Accordingly, when the thickness T _thin becomes equal to or less than the limit value T _{limit for} occurrence of corrosion, corrosion occurs. That is, the following formula (III) is established.
T−α × σ <T _limit (III)

Conversely, if the following formula (III) ′ holds, corrosion does not occur.
T−α × σ ≧ T _limit (III) ′

As a result of carrying out the salt spray test (SST) for 72 hours in accordance with JIS Z2371, the present inventors have found that α = 0.21 in the above formulas (III) and (III) ′, the thickness T that is the limit value for occurrence of corrosion. _{It was found that when limit} = 0.078 μm, the average film thickness T and the standard deviation σ of the film thickness are related as shown in FIG. In addition, “◯” in FIG. 2 indicates an example when rust generation is 10% or more of the entire area, and “X” indicates an example when rust generation is less than 10% of the total area. ing. As a result, it was found that the relationship between the standard deviation σ of the film thickness and the average film thickness T for ensuring sufficient corrosion resistance is the above formula (I).

  Furthermore, the present inventors realize the relationship of the above formula (I) in the conventional coating method in the range where the film thickness is small (2 μm or less) particularly in the alloyed hot-dip galvanized steel sheet having a large surface irregularity. It was found that the relationship of the formula (I) can be satisfied by the coating method using fine liquid particles according to the present invention.

According to the metal surface treatment method and the surface-treated steel sheet according to the present invention as described above, coating unevenness may be slightly observed, but compared with conventional roll coater coating, dip coating, conventional spray coating, etc. Thus, uneven coating can be remarkably improved. Specifically, as shown in the examples described later, it was confirmed that equivalent corrosion resistance was obtained even when the adhesion amount per unit area (g / m ² ) on the steel sheet surface was reduced by about 75%.

Moreover, the point which is excellent in the method of making a chromate free surface treating agent the shape of a fine liquid particle and making it adhere to a steel plate like this invention is mainly the following three points.
(1) In the case of alloyed hot-dip galvanized steel sheets, etc., the unevenness of the surface is as large as 1 μm to 10 μm in Ra, but even in this case, the film is formed with the same thickness on both the concave and convex portions. A surface treatment agent can be applied. That is, according to the present invention, it is possible to form a chromate-free film having a uniform film thickness on both the concave and convex portions of the steel sheet surface, which could not be realized by the conventional coating method.
(2) Since the fine liquid particle surface treatment agent that does not adhere to the steel plate is recovered without reacting with zinc, the concentration of zinc in the recovered liquid as seen in dip coating or conventional spray coating is reduced. There is no increase.
(3) After attaching the surface treatment agent in the form of fine liquid particles, the chromate-free film can be formed by leaving it to dry. Moreover, since it is not necessary to make the film thickness uniform with a ringer roll or the like after application of the surface treatment agent, coating unevenness does not occur.

  Next, the present invention will be described more specifically with reference to examples.

  In this example, first, as the galvanized steel sheet, an galvannealed steel sheet having irregularities and Ra on the steel sheet surface as shown in Table 1 below and containing about 8% by mass to 12% by mass of Fe was used. .

  Further, as the water-based metal surface treatment agent, 3-glycidoxypropyltrimethoxysilane, an organosilicon compound in which 3-glycidoxypropyltriethoxysilane is mixed 2: 1, several percent of a Zr fluoro compound, phosphorus A drug A containing a chemical solution containing acid, vanadium oxysulfate, and polyethylene oxide as a surfactant as a non-volatile component ratio shown in Table 1 was used.

  The aqueous metal surface treatment agent was adjusted with acetic acid so that the pH was 3 to 6 in order to promote the reaction with zinc (accelerate the film formation rate).

  In addition, the wetting angle was adjusted to the wetting angle shown in Table 1 below by adjusting the acetic acid concentration and the addition amount of polyethylene oxide and ethanol. Further, as a comparative example, a surface treatment agent having a wetting angle of about 100 was prepared by adjusting the addition amounts of polyethylene oxide and ethanol (Comparative Examples 2 and 4).

  The surface treatment agent prepared as described above was applied to the surface of a galvanized steel sheet using a coating apparatus as shown in FIG. As shown in FIG. 3, the plate-passing direction when applying the surface treatment agent was perpendicular to the ground, and a plurality of two-fluid nozzles were used for applying the surface treatment agent. Specifically, in the present example, two two-fluid nozzles were installed in the vertical direction (through plate direction) and in the horizontal direction (steel plate width direction). An air nozzle for preventing scattering of the processing agent is installed below the two-fluid nozzle, and a hood for preventing scattering of the processing agent is installed above the two-fluid nozzle to suck the scattered processing agent. . In this embodiment, the surface treatment agent is applied to one side of the steel plate, but it can also be applied to both sides of the steel plate. Further, the temperature of the steel sheet on the entry side was controlled to be 60 ° C. to 90 ° C. from the viewpoint of promoting the reaction of the surface treatment agent. This temperature was adjusted by installing a hot air blower in front of the nozzle.

The particle size of the liquid particles is controlled to be 10 μm to 30 μm by adjusting the air pressure (1 to 3 kg / cm ² ) and the amount of liquid (5 to 10 L / hr) using a two-fluid nozzle. did. The distance between the steel plate and the nozzle port was set to 200 mm so as not to damage the nozzle, considering that the steel plate vibrates in the thickness direction due to tension fluctuation. The cross-sectional area of the nozzle port was also 5 mm ² (1 mm × 5 mm) in consideration of the distance (200 mm) between the steel plate and the nozzle port and the reaction between the surface treatment agent and the nozzle. Furthermore, in order to suppress the reaction between the nozzle opening and the surface treatment agent, Teflon (registered trademark) processing was applied to the nozzle tip. In addition, the coating amount of the surface treatment agent from the nozzle was adjusted so that a predetermined coating film was formed on the assumption that the amount of nonvolatile components was about 10%.

After the surface treatment agent is applied to the steel sheet surface as described above, it is naturally dried to form a chromate-free film on the steel sheet, and the impact speed (m / s) of the liquid particles on the steel sheet surface with respect to the steel sheet after the film formation. ), Average film thickness before drying (μm), average film thickness after drying (μm), variation in film thickness (μm), and calculated values of formula (I) were measured or calculated by the methods described above. Furthermore, in order to evaluate corrosion resistance about this steel plate, the salt spray test (SST) was implemented for 72 hours and 120 hours based on JISZ2371, and the case where the rust generation | occurrence | production area was less than 10% of the whole was set as the pass. In addition, regarding the appearance of the surface of the steel sheet, the presence or absence of uneven coating was observed, and × when the uneven coating occurred, Δ when the slight coating unevenness occurred, and ○ when almost no uneven coating occurred It was evaluated. The results are shown in Table 1 below.

  As shown in Table 1, it was found that when the variation in film thickness increases, the area of rust generation in SST increases. This is thought to be due to the occurrence of a thin film thickness and a deterioration in the corrosion resistance of this film. In particular, when the film thickness was 0.5 μm or more, it was found that the area of rust generation increased with SST for 120 hours. In addition, it was found that uneven coating occurs (or slightly occurs) for those having a large wetting angle between the surface treatment agent and the steel sheet (Comparative Examples 2, 4, and 8).

  FIG. 4 shows a surface-treated steel plate ((a)) on which a chromate-free coating is formed by roll coater coating, and a surface-treated steel plate ((b) on which a chromate-free coating is formed by spray coating using fine liquid particles of the present invention. ) And (c)) are examples of scanning electron microscope (SEM) photographs. In FIG. 4, the lowermost layer is a steel plate, the layer immediately above it is a galvanized layer, and the black portion above it is a chromate-free coating layer. As shown in FIG. 4, in the case of conventional roller coater coating, a film is formed on the basis of the convex part on the surface of the galvanized layer, and the surface treatment agent is press-fitted into the concave part, resulting in a large variation in the film thickness. It can be seen that the thickness of the concave portion is large and the thickness of the convex portion is small. On the other hand, according to the spray coating using the fine liquid particles of the present invention, it can be seen that a film having a uniform thickness can be formed along the unevenness of the surface of the galvanized layer.

FIG. 5 shows the relationship between the coating amount (QM adhesion amount) and the rust generation area ratio (SST72h-WR) after SST was performed for 72 hours. In FIG. 5, ◇ indicates the case of roll coater application, and □ indicates the case of spray application using the fine liquid particles of the present invention. As shown in FIG. 5, when the surface treatment agent was applied with a variation in film thickness of the formula (I) or less, the corrosion resistance for SST 72 hours could be secured with an average adhesion amount of 0.3 g / m ² . However, in the roll coating method not satisfying the formula (I), the corrosion resistance for SST 72 hours was secured at an average adhesion amount of 0.45 g / m ² . Therefore, the amount of the surface treatment agent used can be reduced by 25% or more . In addition, when coating a steel sheet with large irregularities on the surface, spray coating using fine liquid particles is simple and easy without any roll replacement, as compared with roll coater coating, which has a measure for preventing roll abrasion.

  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.

It is explanatory drawing which shows an example of the state of the film | membrane formed by performing chromate free surface treatment on the steel plate with the large unevenness | corrugation of the surface. It is a graph which shows an example of the relationship between the standard deviation (sigma) and the average film thickness T in the surface-treated steel sheet thickness which concerns on this invention. It is a schematic diagram which shows the structure of the coating device of the surface treating agent used in the Example of this invention. Surface-treated steel sheet ((a)) on which a chromate-free film is formed by roll coater coating, and surface-treated steel sheets ((b) and (c) on which a chromate-free film is formed by spray coating using fine liquid particles of the present invention. )) Is a scanning electron microscope (SEM) photograph showing an example. It is a graph which shows the relationship between the adhesion amount (QM adhesion amount) of a membrane | film | coat, and the rust generation | occurence | production area ratio (SST72h-WR) after implementing SST for 72 hours.

Explanation of symbols

1 Galvanized steel sheet 2 Chromate-free coating 11 Convex part 13 Concave part

Claims (8)

By applying an aqueous metal surface treatment agent containing at least a silane coupling agent and a surfactant to the surface of a galvanized steel sheet having a surface roughness of 1 μm or more and 10 μm or less at Ra, the surface of the galvanized steel sheet is dried. In the metal surface treatment method for forming a film on the surface,
After making the water-based metal surface treatment agent liquid particles having a particle size of 10 μm or more and 30 μm or less, the liquid particles are sprayed toward the galvanized steel sheet,
The wetting angle of the liquid particles with respect to the surface of the galvanized steel sheet is 90 degrees or less ,
The aqueous metal surface treatment agent has a pH of 3 to 6,
The surfactant is a nonionic surfactant or a cationic surfactant,
The content of the surfactant is 0.001 part by mass or more and 5 parts by mass or less with respect to 100 parts by mass of the aqueous metal surface treatment agent.
The water-based metal surface treatment agent further contains 100 ppm or more and 500 ppm or less of zinc . Wherein the particle diameter of liquid particles, and adjusting in response to the average film thickness after drying of the coating, according to claim 1 a metal surface treatment method according. From a position spaced surface 50mm or more of the galvanized steel sheet, characterized in that spraying the liquid particles, metal surface treatment method according to claim 1 or 2. The liquid particles are characterized by less speed 0.1 m / s or more 5 m / s when in contact with the galvanized steel sheet, the metal surface treatment method according to any one of claims 1-3. The metal surface treatment according to any one of claims 1 to 4 , wherein the water-based metal surface treatment agent is applied using a gas-liquid mixed spray in which a gas and a liquid are mixed and discharged to the outside. Method. The metal surface treatment method according to claim 5 , wherein a cross-sectional area of a discharge port of the aqueous metal surface treatment agent in the gas-liquid mixed spray is 3 mm ² or more. 7. The metal surface treatment method according to claim 5 , wherein the gas-liquid mixed spray is coated with fluoride in the vicinity of the discharge port including the discharge port of the water-based metal surface treatment agent. . On the surface of the galvanized steel sheet having 10μm or less surface roughness than 1μm in Ra, has a film formed by the metal surface treatment method according to any one of claims 1 to 7
The film has an average film thickness T after drying of 0.1 μm or more and 2 μm or less,
The surface-treated steel sheet characterized in that the standard deviation σ of the thickness of the film satisfies the following formula (I).
σ ≦ 0.21T + 0.78 (I)

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