JP2005139477A - Surface-treated steel plate having excellent workability, coil deformation resistance, and corrosion resistance - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface-treated steel plate having excellent press workability and capable of suppressing coil deformation or load collapse while piling cut plates. <P>SOLUTION: An organic resin-made film in which organic lubricant, silane coupling agent, and valve metal compound are blended in aqueous resin is deposited on a surface of the surface-treated steel plate. In the organic resin-made film, the ratio C/all elements of the number of carbon atoms to other elements than hydrogen in an outermost layer is adjusted to be in the range of 0.75 to 0.9, and the ratio (Si + M)/all elements of the number of atoms of Si of the silane coupling agent and a metal (M) of the valve metal compound to other elements than hydrogen is adjusted to be in the range of 0.01-0.05. One or two or more kinds of oxide, hydroxide and phosphate of the valve metal are used for the valve metal compound. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a Cr-free surface-treated steel sheet that can be pressed into a target shape without the need for lubricating oil, and that is also capable of suppressing deformation of a steel strip wound in a coil shape and load collapse at the time of cutting a plate.

  Zinc-based and aluminum-based plated steel sheets used for exterior materials, interior materials, surface materials, vehicle steel sheets, etc., are subjected to chemical treatments such as chromate treatment and phosphate treatment to improve corrosion resistance and coating film adhesion. In most cases. Recently, a Cr-free chemical conversion treatment that does not contain Cr, which has a large environmental load, has been developed. When a steel sheet provided with a chemical conversion film is pressed into a target shape, since the chemical conversion film is poor in lubricity, lubricity is imparted to the surface-treated steel sheet by applying a high-viscosity lubricant prior to pressing.

  When using a lubricant, it is necessary to apply a lubricant before processing and to remove the lubricant after processing. If the surface treatment steel sheet can be processed without oil without omitting the step of applying and removing the lubricant, the number of press working steps can be reduced and the productivity can be improved. Solvent degreasing and alkaline degreasing to wash away the lubricant are no longer necessary, reducing the burden of waste liquid treatment harmful to the environment. From this point of view, surface-treated steel sheets that can be pressed into a target shape without oil are being researched and developed.

For example, a coated steel sheet (Patent Document 1) in which a coating film is formed from a resin composition based on a polyolefin-based polymer that is intermolecularly associated with ion clusters and containing an aziridinyl group-containing organic compound, silica particles, and polyethylene wax, It exhibits excellent lubricity and can be pressed into the target shape even without oil. However, the steel plate surface is slippery, and coil collapse due to loose winding during manufacture and load collapse during cut plate pile-up are likely to occur.
JP-A-8-207199

When a polyethylene resin having an average molecular weight of 5000 or less and an acid value of 0.1 or more is used as a solid lubricant and an organic resin film containing a solid lubricant and an antirust pigment is formed on the surface of a chromated steel plate, no oil is applied. A surface-treated steel sheet that can be pressed and can be prevented from being crushed and collapsed at the time of piling is obtained (Patent Document 2). Surface-treated steel sheet that can be pressed without oiling and has excellent coil deformation resistance by forming an organic composite film containing fatty acid metal salts, fatty acid bisamides, fatty acid amines, fatty acid amide derivatives, etc. on the chromated steel sheet surface. (Patent Document 3). However, none of them is a material that matches the trend of emphasizing environmental conservation because it undergoes a chromate treatment process.
Japanese Patent Laid-Open No. 10-15483 JP 2001-288583 A

Cr-free with improved resistance to press galling and resistance to coil deformation when a layer containing an aqueous resin, silane coupling agent, and phosphoric acid component is used as a base treatment layer, and an upper layer coating of organic resin, fine silica, and polyethylene wax is laminated. A surface-treated steel sheet is obtained (Patent Document 4). However, the manufacturing process is complicated due to the two-stage treatment for forming the lower layer film and the upper layer film, and the corrosion resistance equivalent to that of the chromate film has not been satisfied.
JP 2002-212749 A

  Unlike conventional surface-treated steel sheets or coated steel sheets, the present invention modifies the outermost layer of the organic resin film provided on the surface of the steel sheet to provide corrosion resistance comparable to chromate treatment, as well as pressing to the target shape even without oil coating. An object of the present invention is to provide a surface-treated steel sheet that can be processed and has no collapse of a coil or collapse of a load during piling.

  In the surface-treated steel sheet of the present invention, an organic resin film in which an organic lubricant, a silane coupling agent, and a valve metal compound are blended in an aqueous resin is provided on the surface of the steel sheet. The organic resin film has an atomic ratio of carbon to elements other than hydrogen in the outermost layer: C / total elements of 0.75 to 0.9, Si of silane coupling agent, and number of atoms of metal (M) of valve metal compound Ratio: (Si + M) / all elements are adjusted in the range of 0.01 to 0.05. As the valve metal compound, one or more of valve metal oxides, hydroxides and phosphates are used.

The surface-treated steel sheet is affected by press workability and coil deformation resistance depending on the outermost layer of the organic resin film provided on the steel sheet surface.
Since the press workability improves as the affinity of the extreme surface layer of the surface-treated steel sheet is lower, it contains almost no components that increase the affinity (for example, organic polar groups such as carboxyl groups, hydroxyl groups, amine groups, and inorganic hydroxides). By adding a wax to the resin for forming the surface layer and causing the surface to bleed, a surface with few organic functional groups and inorganic compounds that are undesirable for press workability can be obtained. However, if the affinity of the surface is simply reduced, coil collapse and load collapse at the time of cutting the plate are likely to occur. Lubricity when surface-treated steel sheets are stacked on top of each other is the dominant factor in coil deformation and load collapse, and a surface with high affinity is desired for suppressing coil deformation and load collapse.

  Although press workability, coil deformation resistance, and load collapse resistance tend to contradict each other, the concentration of C, Si, M (valve metal) in the outermost layer of the organic resin film is properly controlled, and polar groups with high affinity When the component having s is oriented in the extreme surface layer of the organic resin film and the hard particles are allowed to face the film surface, both press workability, coil deformation resistance and load collapse resistance can be achieved.

[Influence of polar group orientation]
When a component having a polar group with high affinity (hereinafter referred to as “polar group component”) is finely oriented on the extreme surface layer of the organic resin film provided on the surface of the steel sheet, the polar group component is not formed when the surface-treated steel sheets are superimposed. The frequency of overlapping each other increases. The portion where the polar group component overlaps exhibits strong adhesion because the free energy is equal and the affinity is high, and even if the polar group component is small, a high braking effect is exhibited and the lubricity is lowered. As a result, coil deformation when wound in a coil shape and load collapse at the time of cutting a plate are suppressed. On the other hand, since the polar group components do not overlap at the contact interface of the press die / surface-treated steel sheet, the braking effect is small and good lubricity is maintained.

  Organic compounds having carboxylic acid groups, hydroxyl groups, etc. (polyhydric phenols, oxycarboxylic acids, etc.) and epoxy and acrylic organic resins are easy to orient on the steel sheet side in the organic resin film. In order to align it, it is necessary to increase the amount. However, when these organic compounds and organic resins are added excessively, the film properties are likely to change greatly. For example, the addition of a large amount of an organic compound causes many pores in the film, resulting in a decrease in corrosion resistance. Moreover, the addition of a large amount of organic resin reduces the elongation of the film, which is not preferable for workability and post-processing corrosion resistance. Furthermore, the film containing a large amount of carboxylic acid groups also deteriorates the water resistance and alkali resistance.

  When a silane coupling agent having many different polar groups in the molecule compared to an organic compound or organic resin is included in the organic resin film, the silane coupling agent is concentrated at the steel plate / film interface and the extreme surface layer of the film. . Therefore, polar groups can be oriented in the extreme surface layer of the organic resin film with a small addition amount, and the physical properties of the film are hardly deteriorated. In addition, since the molecular weight is smaller than that of the organic resin, the high affinity sites are finely oriented in an island shape, and a surface state suitable for achieving both coil deformation resistance and press workability can be obtained.

[Effect of hard particle distribution]
When surface-treated steel sheets with hard particles such as metal oxides, hydroxides, and phosphates exposed on the surface of the organic resin film are stacked on top of each other, the hard particles are pushed into the organic resin film on the other side and contact the interface. The mechanical meshing force, and hence the braking action, works. As a result, coil deformation when wound into a coil shape and load collapse at the time of cutting a plate are suppressed. In the state where the surface-treated steel sheet is in contact with the press die, the hard particles are pushed into the steel plate side by the pressing force of the press die, so that the mechanical engagement does not occur at the contact surface of the surface-treated steel plate / press die. The lubricity necessary for oil-free press processing is maintained.

  The influence on the coil deformation resistance does not depend on the type of hard particles, but when a valve metal compound having high oxide insulation resistance is used for the hard particles, corrosion resistance and water resistance can be improved. The improvement in corrosion resistance and water resistance is presumed to be caused by the densification of the organic resin film due to the uniform dispersion of the valve metal compound. Of these, valve metal oxides, hydroxides, and phosphates are effective. On the other hand, inorganic lubricants such as molybdenum disulfide break down the crystal of the lubricant itself and develop lubricity due to the colloidal action of the collapsed crystal. It is difficult to obtain a braking effect that resists load collapse during piling.

  The steel plate (chemical conversion raw plate) on which the organic resin film is formed does not have any particular restrictions on the material, and a normal steel plate, a plated steel plate, a stainless steel plate or the like is used. Examples of the plated steel sheet include a Zn plated steel sheet, an Al plated steel sheet, a Zn—Al alloy plated steel sheet, a Zn—Al—Mg alloy plated steel sheet, a Cu plated steel sheet, and a Sn plated steel sheet.

  Prior to the formation of the organic resin film, the chemical conversion treatment original plate is appropriately subjected to base treatment such as degreasing and phosphate treatment. A target organic resin film is formed by applying an aqueous resin solution containing an organic lubricant, a silane coupling agent, and a valve metal compound to the surface of the chemical conversion treatment original plate and drying it without going through a water washing step. A roll coating method, a spin coating method, a spray method, or the like is employed for application of the aqueous resin liquid. Although drying can be performed at room temperature, it is preferable to shorten the drying time by maintaining the temperature at 50 ° C. or higher in consideration of continuous operation. However, when heated at a high temperature exceeding 200 ° C., organic components contained in the film are thermally decomposed, and quality characteristics such as lubricity and corrosion resistance may be deteriorated.

  The aqueous resin solution contains an organic resin such as urethane, epoxy, polypropylene, olefin such as ethylene-acrylic copolymer, polystyrene, polyester, or copolymer, modified product, acrylic, etc. as a film forming component. It is out. Of these, water-soluble or water-dispersible urethane resins obtained by reaction of polyisocyanates and polyols, particularly self-emulsifying urethane resins are preferred. Examples of polyisocyanates include aliphatic diisocyanates such as phenylene diisocyanate, tolylene diisocyanate, diphenylmethane diisocyanate, and naphthalene diisocyanate, and alicyclic diisocyanates such as cyclohexane diisocyanate, isophorone diisocyanate, norbornane diisocyanate, xylylene diisocyanate, and tetramethylxylylene diisocyanate. . Polyol polyols such as polyester polyols, polyether polyols, polycarbonate polyols, polyacetal polyols, polyacrylate polyols and polybutadienes are used as the polyol.

  Examples of the organic lubricant added to the aqueous resin liquid include fluorine-based, polyethylene-based, and styrene-based waxes, and any of a low melting point wax and a high melting point wax can be used. The low melting point wax bleeds on the surface of the film when the organic resin film is dried and exhibits lubricity. The high melting point wax exists in a dispersed state in the organic resin film, but the outermost layer of the film is exposed on the surface of the film in an island-like distribution to reduce the affinity and develop lubricity.

  As the silane coupling agent, a silane compound containing one or more functional groups such as an amino group, an epoxy group, a mercapto group, an acryloyloxy group, and an alkoxy group is used. Silane coupling agents have a strong tendency to concentrate on the steel sheet side and film surface layer side, and among them, silane coupling agents having amino groups and epoxy groups that exhibit a good braking effect when concentrated on the film surface layer side are preferred. It is.

  The valve metal compound is added as a metal oxide, hydroxide, phosphate or the like. Examples of oxyacid salts include ammonium salts, alkali metal salts, alkaline earth metal salts, hydrates, and the like. The valve metal compound exhibits an effect in any state dissolved or uniformly dispersed in the treatment liquid, and may be added in a form uniformly dispersed in silica sol, alumina sol, titania sol or the like. In particular, when oxides such as hexavalent Mo, W, pentavalent V, etc. that show oxidizing properties and oxyacid salts are included in the organic resin film, the valve metal is formed in the defective portion where the underlying plating layer is exposed through the film. The compound elutes and oxidizes the plating layer, and the self-healing action of reprecipitating the plating layer component and the valve metal compound repairs the film pinholes, processing defects, etc., and improves the corrosion resistance.

It is also possible to add phosphoric acid, phosphate, fluoride, etc. as other optional components to the aqueous resin liquid. Phosphoric acid, phosphate, fluoride, etc. are highly reactive and improve the adhesion of the organic resin film to the substrate. When an Al-containing zinc-based plated steel sheet is used for the chemical conversion treatment original sheet, the blackening of the surface-treated steel sheet is suppressed when a compound such as Fe, Co, or Ni is added to the aqueous resin solution. Moreover, an inorganic pigment, an organic pigment, an organic dye, etc. can be mix | blended and a predetermined color tone can also be provided to an organic resin film.
An organic resin film is formed on the surface of the original plate by applying and drying an aqueous resin solution to the chemical conversion treatment original plate. However, in order to ensure good coil deformation resistance, load collapse resistance when cutting a plate, and press workability. The C concentration of the outermost layer of the film and the total concentration of the silane coupling agent and the valve metal compound are important factors. The C concentration of the outermost layer of the film can be controlled by the aqueous resin type and wax type to be used and their addition amount, and when using a low melting point type wax, the drying temperature. The total concentration of the silane coupling agent and the valve metal compound can be controlled by the type and amount of additive used and, if sol is used, the particle size.

  The low C concentration means that there are many organic polar groups such as carboxyl groups, hydroxyl groups, amino groups, inorganic oxides, hydroxides, phosphates, etc. that increase the affinity on the surface of the film. It is not preferable for press workability. Although press workability is improved with C concentration, when the C concentration is too high, components having a braking effect are reduced, and resistance to coil deformation, load collapse resistance, and the like are lowered. Silane coupling agents and valve metal compounds improve the braking effect as it concentrates on the outermost layer of the coating, but lowers the press workability. Insufficient concentration causes insufficient braking effect and resistance to coil deformation and load collapse. The properties etc. are reduced.

  From the results of investigations and researches by the present inventors, the atomic ratio of C to all elements other than hydrogen in the outermost layer of the film is in the range of 0.75 to 0.9, and the silane coupling agent for all elements other than hydrogen is Atom ratio of Si and valve metal compound (M): (Si + M) / When maintaining all elements in the range of 0.01 to 0.05, press workability, coil deformation resistance, load collapse resistance It was found that a balance could be achieved. The concentration of C, Si, M, etc. in the outermost layer of the film can be measured by ESCA, Auger (AES) or the like.

Two types of galvanized steel sheets A and B were used for the chemical conversion treatment original plate, and the organic resin film was formed on the original plate surface by applying and drying the aqueous resin liquid shown in Table 1. The film thickness of the organic resin film was variously changed depending on the coating amount of the aqueous resin liquid. Table 2 shows the film thickness of the formed organic resin film, the C concentration of the outermost layer of the film, and the total concentration of the silane coupling agent and the valve metal compound.
A: coating weight 20 g / m ^2, electro-galvanized steel sheet having a thickness of 0.8mm B: coating weight 20 g / m ^2, melting Zn-6 mass% Al-3 mass% Mg alloy plated steel sheet having a thickness of 0.8mm

A test piece was cut out from each surface-treated steel sheet on which an organic resin film was formed and subjected to a corrosion test, a friction test, a press work test, and a coil deformation test.
[Corrosion test]
The end face of the test piece was sealed and sprayed with a 5% NaCl aqueous solution at 35 ° C. in accordance with JIS Z2371. After spraying salt water for a predetermined time, the surface of the test piece was observed. The area ratio of white rust generated on the surface of the test piece is measured. The white rust generation area ratio is 5% or less ◎, 5-10% ○, 10-30% △, 30-50% ▲, The corrosion resistance of the flat portion was evaluated with x being 50% or more.

[Friction test]
Using a dynamic friction coefficient measuring device (HEIDON-14; manufactured by Shinto Kagaku Co., Ltd.), sliding a stainless steel ball having a diameter of 10 mm on the surface of a test piece under the conditions of a load of 100 gf and a sliding speed of 150 mm / min. Was measured.
[Pressing test]
The test piece was pressed by a single press test using a clamp press apparatus, and the sliding surface of the molded product was visually observed. A specimen with no wrinkles on the sliding surface was marked with ◎, a specimen with wrinkles detected at a rate of less than 10 area% on the sliding surface, and a sliding wrinkle with a ratio of 10-50 area%. The press workability was evaluated with Δ for the test piece and x for the test piece with sliding wrinkles exceeding 50 area%.

[Coil deformation test]
After producing 10 tons of each surface-treated steel sheet and winding it on a coil, the coil was taken out from the payoff reel and placed on a coil car. When the coil loosening width of the inner circumference of the coil generated when the coil car is reciprocated three times to the left and right is measured, the relationship shown in FIG. 1 is established between the measured value of the coil loosening width and the static friction coefficient of the surface-treated steel sheet. It was. Therefore, the resistance to coil deformation was simply evaluated with a surface-treated steel sheet having a static friction coefficient of 0.15 or more as “◯” and a surface-treated steel sheet with less than 0.15 as “x”. The static friction coefficient was measured by the following method.

The surface treated steel plates 1R and 1L having a width of 50 mm and a length of 40 mm are bonded to the molds 2R and 2L, and the surface treated steel plate 3 having a width of 30 mm is sandwiched between the surface treated steel plates 1R and 1L. The contact area between 1 L and the surface-treated steel sheet 3 was set to 12 cm ² (FIG. 2). The surface-treated steel sheet 3 was drawn from between the surface-treated steel sheets 1R, 1L at a drawing speed v: 100 mm / min while applying a pressing force F: 600 kgf. A value F ₁ / F obtained by dividing the pulling force F ₁ when the surface-treated steel sheet 3 starts moving under this condition by the applied pressure F was calculated as a coefficient of static friction.

  As can be seen from the investigation results in Tables 3 and 4, the atomic ratios of C / all elements and (Si + M) / all elements were maintained in the ranges of 0.75 to 0.9 and 0.01 to 0.05, respectively. The surface-treated steel sheet provided with the organic resin film was excellent in flat portion corrosion resistance, and both press workability and coil deformation resistance were good. On the other hand, the surface-treated steel sheet provided with the organic resin film with the treatment liquid No. 9 having a low atomic ratio of C / all elements has a large kinetic friction coefficient and inferior press workability, and there is a shortage of polar groups on the outermost layer of the film. . The surface-treated steel sheet provided with an organic resin coating with a treatment solution No. 10 with a low atomic ratio of (Si + M) / all elements is inferior in coil deformation resistance, and the component having an anchor effect on the outermost layer of the coating is on the coating surface. It is admired that there is a shortage. The surface-treated steel sheet provided with the organic resin film with the treatment liquid No. 11 containing no valve metal compound was inferior in corrosion resistance although it had good coil deformation resistance and press workability.

  As explained above, by properly managing C / all elements, (Si + M) / all elements of the organic resin film formed on the surface of the steel sheet, press workability and coil deformation resistance, load resistance at the time of cutting the plate pile A surface-treated steel sheet that is compatible with collapsibility is obtained. The coil wound with the surface-treated steel sheet is restrained from being deformed, and is easy to handle because there is little loosening, and the manufacturing process can be simplified because it can be press-formed into a target shape without oil. Therefore, it is used as a material suitable for a wide range of applications such as exterior materials, interior materials, and cover materials.

Graph explaining the correlation between the coefficient of static friction and the coil winding looseness width Illustration of static coefficient of friction measurement

Claims (2)

  An organic resin film in which an organic lubricant, a silane coupling agent, and a valve metal compound are mixed in an aqueous resin is provided on the surface of the steel plate, and the atomic ratio of carbon to elements other than hydrogen in the outermost layer of the organic resin film: C / total The atomic ratio of the element is 0.75 to 0.9, Si of the silane coupling agent and the metal (M) of the valve metal compound: (Si + M) / all elements are in the range of 0.01 to 0.05. Surface-treated steel sheet with excellent workability, coil deformation resistance, and corrosion resistance.   The surface-treated steel sheet according to claim 1, wherein a valve metal compound is contained as one or more of oxide, hydroxide, and phosphate.

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