JP5195169B2 - Plated steel with excellent handling and formability - Google Patents

Description

  The present invention relates to a film-treated plated steel material that has been provided with excellent handleability and formability in a plated steel material that is used after being subjected to a molding process such as a press or a roll foam. More specifically, it is excellent in handling and molding for building parts such as roofs and walls made of plated steel, molded products such as automobiles, machines, and household appliances, or sheet coils. The present invention relates to a plated steel material capable of imparting properties.

  Plated steel materials are widely used as members of building materials, automobiles, home appliances, etc., due to the high anticorrosive function of the plated layer metal material. When such a member is handled industrially, it is necessary to take a slip prevention measure on the surface of the steel material in order to prevent slippage during stacking and slipping during handling. Specifically, a technique of increasing the surface roughness to give irregularities, or adding hard and non-slip particles such as silica into the chemical film is widely used. However, if the surface resistance of the plated steel material is increased with emphasis on handling, it is called flaking when the plated steel material is mechanically deformed using a mold, such as pressing or roll forming. As a result, a phenomenon occurs that the surface layer of the plating layer is scraped off by the mold and falls off. In order to prevent these problems, a method of applying a press oil imparted with lubricity (for example, Patent Document 1) or a method of applying a chemical conversion film imparting a special lubricity to the plating surface layer (for example, Patent Document 2). Is widely used.

  As a method to achieve both handleability and press formability, the handleability depends on the static friction coefficient, and the press formability depends on the dynamic friction coefficient. Therefore, the static friction coefficient is set high and the dynamic friction coefficient is set low to improve the handleability and press formability. A compatible technique (for example, Patent Document 3) is widely used.

  Furthermore, paying attention to the difference in surface pressure during stacking and press molding, a technology that includes multiple types of particle components with different particle sizes and hardness during chemical conversion treatment, and the friction coefficient changes depending on the surface pressure (for example, patent documents) 4) is also open to the public.

JP 63-149025 A JP-A-4-61966 JP 2001-288582 A JP 2001-79982 A

However, none of the techniques has been able to achieve both sufficient handleability and formability.
An object of the present invention is to provide a plated steel material that is excellent in both handleability and formability.

  As a result of intensive studies on the means for solving the above problems, the temperature sensitive polymer is focused on the difference in temperature between the plated steel materials when handling such as sheet storage is required and when press or roll form molding is performed. By applying the functions of beads that are hard shrinkage above the glass transition temperature (Tg) and soften by moisture absorption swelling below the glass transition temperature, the hardness and volume change greatly before and after the glass transition temperature. And the present invention has been completed.

  That is, the present invention has a coating layer containing a zirconium compound, a phosphoric acid compound, and a cobalt compound on at least one side of a plated steel sheet, the main component is composed of N-isopropylacrylamide, and the average particle size is The present invention relates to a plated steel material excellent in handleability and formability, characterized by comprising thermosensitive polymer beads having a glass transition temperature of 30 to 54 ° C. of 0.2 to 2.0 μm.

  Furthermore, in the present invention, the temperature-sensitive polymer beads are preferably made of a copolymer of N-isopropylacrylamide monomer and N, N-dimethylacrylamide monomer in order to improve both handleability and moldability. In this case, it is preferable to use N, N'-methylenebisacrylamide as a crosslinking agent.

  In the plated steel material of the present invention, at room temperature (below the glass transition temperature) where handling is required, the temperature-sensitive polymer beads swell and unevenness is generated on the surface, making it difficult to slip and handling properties are good. Also, as in the molding process, the mold becomes hot and heat is transferred to the plated steel, and when the temperature exceeds the glass transition temperature, the thermosensitive polymer beads shrink and harden, reducing surface irregularities and lubricating. Can be obtained, and the moldability is increased.

Below, it describes about the composition of the film layer which is a chemical conversion treatment layer in the plated steel material of this invention.
It is essential that the temperature-sensitive polymer beads are mainly composed of N-isopropylacrylamide polymer gel, have a glass transition temperature of 30 to 54 ° C. and an average particle size of 0.2 to 2.0 μm. “Temperature sensitivity” refers to the characteristic of hygroscopic swelling at a temperature lower than the glass transition temperature to increase the volume, and hard shrinkage above the glass transition temperature.

  A temperature-sensitive polymer bead mainly composed of a polymer gel of N-isopropylacrylamide has a large volume change before and after the glass transition temperature, and is suitable for the present invention. In the plated steel material of the present invention, at room temperature (below the glass transition temperature) where handling is required, the temperature-sensitive polymer beads swell and unevenness is generated on the surface, making it difficult to slip and handling properties are good. Next, when the mold becomes hot and heat is transferred to the plated steel as in the forming process, when the plate temperature exceeds the glass transition temperature, the thermosensitive polymer beads shrink and harden, and the surface of the plated steel Unevenness can be reduced and lubricity can be obtained, resulting in increased moldability.

  The material of the thermosensitive polymer beads used in the present invention is not particularly limited, but in order to change the glass transition temperature of the polymer, an N-isopropylacrylamide polymer, an N-isopropylacrylamide monomer, and A copolymer obtained by copolymerizing N, N-dimethylacrylamide monomer with N, N′-methylenebisacrylamide as a crosslinking agent can be used. When this copolymer is used, the molar ratio of N-isopropylacrylamide monomer to N, N-dimethylacrylamide monomer is preferably in the range of 9: 1 to 4: 1, and 6: 1 to 4: 1. More preferably. The crosslinking agent can be used at 1 to 5%, for example, about 3% of the total molar amount of monomers. Furthermore, the glass transition temperature can be controlled by the solvent desorption rate and the degree of polymer polymerization during bead production. For example, the degree of polymer polymerization in the temperature-sensitive polymer beads used in the present invention is preferably 20,000 to 2,000,000, more preferably 100,000 to 2,000,000, and most preferably the number average molecular weight. Is 1,000,000 to 2,000,000.

  When the average particle size of the temperature-sensitive polymer beads is less than 0.2 μm, it may not be possible to obtain a sufficient contribution to the friction coefficient. When the average particle size is larger than 2.0 μm, there is a risk of dropping from the film during molding. The more preferable average particle diameter of the thermosensitive polymer beads is 0.5 to 2.0 μm, and most preferably 0.8 to 1.5 μm.

  When the glass transition temperature of the thermosensitive polymer beads is less than 30 ° C., sufficient handleability may not be obtained. If it is higher than 54 ° C., the friction coefficient necessary for formability may not be reached. The more preferable glass transition temperature of the thermosensitive polymer beads is 35 to 54 ° C, and most preferably 35 to 50 ° C. The glass transition temperature of the thermosensitive polymer beads is measured by the TMA needle entry temperature method.

  The amount of the thermosensitive polymer beads to be added is not particularly specified, but if the amount of the non-volatile content of the film is less than 0.1% by mass, the effect on sufficient moldability cannot be exhibited. It may fall off during molding and cause film peeling. The more preferable addition amount of the thermosensitive polymer beads is 0.5 to 20% by mass, most preferably 0.5 to 15.0% by mass in the nonvolatile content of the film.

  The zirconium compound in the film (chemical conversion film) is not particularly limited, but may be, for example, ammonium carbonate, potassium salt or sodium salt of zirconium carbonate or zirconium fluoride.

  The phosphoric acid compound in the film is not particularly limited, but may be phosphoric acid and its ammonium salt. Examples thereof include orthophosphoric acid, pyrophosphoric acid, metaphosphoric acid, polyphosphoric acid, phytic acid, phosphonic acid, ammonium phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, sodium phosphate, and potassium phosphate.

  Although the cobalt compound in a film is not specifically limited, For example, it can be cobalt carbonate, cobalt nitrate, cobalt sulfate, cobalt acetate, etc.

  Although not particularly limited, when the element in the film is less than 1% by mass with respect to 100% by mass of Zr, the film strength and adhesion may be slightly reduced and the film may be detached during molding. is there. Similarly, when P is more than 100% by mass, there is a problem in film adhesion, and peeling occurs during molding. A preferable amount of P is 1 to 50% by mass, and most preferably 5 to 50% by mass with respect to 100% by mass of Zr.

  Similarly, when Co is less than 0.1% by mass or more than 20% by mass with respect to 100% by mass of Zr in the film, the adhesion of the film may be lowered, and film peeling may occur during molding. A preferable amount of Co is 0.1 to 10% by mass, and most preferably 0.1 to 5.0% by mass with respect to 100% by mass of Zr.

  In the plated steel material of the present invention, a bead is dispersed by applying an aqueous solution (treatment solution) containing a thermosensitive polymer bead, zirconium compound, phosphate compound, and cobalt compound to the surface of the plated steel material and heating and drying. In addition, a film having a dense three-dimensional structure and excellent barrier properties is formed.

  The coating method for applying the treatment liquid to the surface of the plated steel material is not particularly limited, and any method such as a spray method, a dipping method, a roll coating method, a shower ringer method, and an air knife method is possible.

  The treatment liquid applied to the plated steel material is preferably heat-dried in the range of 40 ° C. to 200 ° C. at the ultimate plate temperature. The heating method is not particularly limited, and any method such as hot air, direct fire, induction heating, infrared, electric furnace or the like can be used.

  In the present invention, in order to improve the wettability to the surface of the plated steel material, a surfactant, an organic solvent, or the like may be added to the treatment liquid as long as the original performance of the film to be formed is not impaired. An antifoaming agent may be added as necessary.

  For the purpose of preventing scratches and wear during processing, molybdenum disulfide, graphite, tungsten disulfide, boron nitride, graphite fluoride, cerium fluoride, melamine cyanurate, fluororesin wax, polyolefin wax It is possible to add lubricants and fillers such as colloidal silica and vapor phase silica.

Although the range of the total film amount in the plated steel material of the present invention is not particularly limited, it is preferably 100 to 1500 mg / m ² . If it is less than 100 mg / m ² , sufficient moldability may not be obtained. Moreover, when it exceeds 1500 mg / m < ² >, a film | membrane becomes weak and there exists a possibility that a moldability, alkali resistance, and coating adhesiveness may fall. A more preferable range of the total coating amount is 100 to 1000 mg / m ² , and most preferably 200 to 1000 mg / m ² .

  In the present invention, the method for producing a plated steel material as a raw material for forming a film is not particularly limited. For example, any of a hot dipping method, an electroplating method, a vapor deposition plating method, a dispersion plating method, a vacuum plating method, and the like may be used. Absent. As a manufacturing method of the hot-dip plating layer, there are a flux method, a Sendzimir method, a method of pre-plating Ni or the like to ensure wettability, and any of them may be used.

  Further, the composition of the plating layer is not particularly limited, but the composite film treatment of the present invention is particularly effective for a plated steel material containing Zn in the plating layer. In addition, you may contain Al, Mg, Si, Ti, Ni, Fe etc. as an alloy component of the plating layer of zinc-based plated steel materials.

  For the purpose of changing the appearance after plating, spraying with water spray or air-water spray, spraying with sodium phosphate aqueous solution or zinc powder, further zinc phosphate powder, magnesium hydrogen phosphate powder or their aqueous solution good.

  Further, for the purpose of further reinforcing the blackening resistance of the plating, surface adjustment with cobalt sulfate, a nickel sulfate solution, or the like may be performed as a pre-treatment for performing a film forming treatment after plating.

  The steel material for forming the plating layer is not particularly limited, and for example, carbon steel, stainless steel, Si-containing steel, Al-containing steel, Mn-containing steel and the like can be used.

  Next, the present invention will be specifically described with reference to examples, but the present invention is not limited to the following specific examples.

The thermosensitive polymer resin beads were produced by the following method.
N-isopropylacrylamide (NIPA) and N, N-dimethylacrylamide (DMAA) are used as monomers, N, N′-methylenebisacrylamide (MBAA) is used as a crosslinking agent, and water and dimethylformamide (DMF) are used at a temperature of 40 ° C. ) In a mixed solvent. Temperature-sensitive polymer beads were prepared by changing the monomer and cross-linking agent composition ratio and the DMF concentration.

Table 1 shows the average particle diameter and glass transition temperature of the temperature-sensitive polymer beads used.
Table 2 shows the temperature-sensitive polymer bead content in the prepared chemical conversion coating, and the composition ratio of the Zr compound, the P compound, and the Co compound in terms of elements. This composition ratio was determined based on data analyzed by fluorescent X-ray analysis and ICP emission analysis. The compounds used in the treatment liquid are as shown in the following symbols.
Zr: B1: ammonium zirconium carbonate
B2: Sodium zirconium fluoride P: C1: Ammonium phosphate
C2: Sodium phosphate Co: D1: Cobalt carbonate

  The chemical conversion coating is applied to the surface of the plated steel with a roll coater so that a predetermined amount of dry coating can be obtained by diluting with deionized water to a predetermined concentration, and immediately using a hot air dryer. It was produced by heating and drying so that the ultimate plate temperature was 80 ° C.

Table 3 shows the processing conditions and test evaluation results for the prepared test pieces. In addition, the symbol of the used plated steel materials is as follows.
M1: Hot-dip Zn plating (plating adhesion amount 90 mg / m ² )
M2: Molten 11% Al-3% Mg-0.2% Si-Zn plating
(Amount of plating 90 mg / m ² )
M3: Zn electroplating (plating amount 20 mg / m ² )
M4: Electric 11% Ni—Zn plating (plating adhesion amount 20 mg / m ² )
M5: Molten 55% Al-1.6% Si—Zn plating (plating adhesion amount 90 mg / m ² )

The evaluation items and test methods are shown below.
(1) Handling property The static friction coefficient when the plated steel materials were face to face was measured using a tripod gear manufactured by HEIDON. The measurement was performed at room temperature of 20 ° C. The evaluation criteria are as follows, and ◎ and ○ were accepted.
◎: Static friction coefficient 0.3 or more ○: Static friction coefficient 0.2 or more and less than 0.3 △: Static friction coefficient 0.1 or more and less than 0.2 ×: Static friction coefficient less than 0.1

(2) Formability The coefficient of dynamic friction at the mating surface of the plated steel material and the flat plate mold was measured using HEIDON's tripo gear. The surface pressure at the time of measurement was 500 kgf (about 5 kN), and the measurement was performed at 70 ° C. The evaluation criteria are as follows, and ◎ and ○ were accepted.
◎: Dynamic friction coefficient 0.15 or less ○: Dynamic friction coefficient 0.15 to 0.2 or less △: Dynamic friction coefficient 0.2 to 0.25 or less ×: Dynamic friction coefficient 0.25 or more XX: Molding test Sometimes noticeable film peeling

As shown in Table 3, it is clear that the plated steel material of the conditions of the present invention has good performance in both handleability and formability.
On the other hand, none of the plated steel materials under comparative conditions can simultaneously satisfy the handling and formability performances.

Claims (3)

  At least one surface of the plated steel sheet has a coating layer containing a zirconium compound, a phosphoric acid compound, and a cobalt compound, the main component is composed of N-isopropylacrylamide, and the average particle size is 0.2-2. A plated steel material excellent in handleability and formability, comprising temperature-sensitive polymer beads having a glass transition temperature of 30 to 54 ° C. at 0 μm.   The plated steel material according to claim 1, wherein the temperature-sensitive polymer beads comprise a copolymer of N-isopropylacrylamide monomer and N, N-dimethylacrylamide monomer.   The plated steel material according to claim 2, wherein the copolymer uses N, N'-methylenebisacrylamide as a crosslinking agent.