JP4325997B2 - Resin-coated hot-dip galvanized steel sheet and method for producing the same - Google Patents

Description

  The present invention relates to a hot dip galvanized steel sheet on which a coating exhibiting good corrosion resistance is formed without performing chromate treatment, and exhibits excellent properties in corrosion resistance, conductivity, workability, weldability, etc. The present invention relates to a resin-coated hot-dip galvanized steel sheet that is also excellent in tape peelability. The resin-coated hot-dip galvanized steel sheet that is the subject of the present invention can be used for various purposes such as construction equipment, electrical products, and the automobile field. The explanation will proceed with a focus on the case.

  Currently, steel sheets used for automotive parts are often hot dip galvanized on the steel sheet surface from the viewpoint of ensuring corrosion resistance. In addition, in applications where coating is used, a hot-dip galvanized layer is alloyed to form a Zn-Fe alloy layer between the base steel sheet and the plated layer in order to improve paintability (coating adhesion). Alloyed galvanized steel sheets are also widely used.

  With the diversification of the use environment of hot dip galvanized steel sheets in recent years, especially in harsh environments such as places that are strongly affected by sea salt particles in coastal areas and places that are affected by acid rain in heavy industrial areas. Moreover, in long-time use, it is difficult to exhibit sufficient corrosion resistance only by performing normal hot dip galvanization, and realization of a plated steel sheet having higher corrosion resistance is desired. For these reasons, in order to further improve the corrosion resistance of the hot-dip galvanized steel sheet, a hot-dip Zn-5% Al alloy-plated steel sheet and the like, which are more excellent in corrosion resistance than ordinary hot-dip galvanizing, have been proposed.

  By the way, in these various hot dip galvanized steel sheets, corrosion resistance (white rust resistance) may be insufficient, and when used as a coating base, it is difficult to secure adhesion to the paint. As a countermeasure, chromate treatment is also applied to the surface of a hot dip galvanized steel sheet.

  However, when the chromate treatment is performed, the white rust suppressing effect is excellent, but the adhesion with the coating film is not sufficient, and in addition, there is a problem of containing a large amount of harmful hexavalent chromium. . In particular, in recent years, awareness of environmental issues has increased and there is a tendency to avoid chromate treatment, so various treatments (non-chromate treatment) exhibiting the same level of corrosion resistance as chromate treatment are being studied. .

  The present applicant also prepared a coated hot-dip galvanized steel sheet in which a resin film obtained by adding tannic acid and / or sodium vanadate to a polyolefin copolymer resin emulsion intermolecularly associated with ion clusters is formed on the surface of a metal plate. Developed (Patent Document 1). The plated steel sheet described in Patent Document 1 is excellent in corrosion resistance in spite of non-chromate treatment, and also excellent in properties necessary for a plated steel sheet such as conductivity, workability, and weldability.

However, the demand for improvement in corrosion resistance has only increased, and it has become clear that there is a need for improvement in tape peelability. In other words, surface-treated steel sheets such as plated steel sheets are shipped with rolls of strip-shaped steel sheets, and are used as cutting plates after the coil is rewound by the customer. At that time, the end portions of the remaining coils are adhesive tape. May be stored temporarily. Cut plates are processed into AV product cases and parts through processes such as punching, oiling, pressing, and alkaline degreasing. At that time, the product number, size, grade, etc. are displayed on the surface of the case and parts. The sticky adhesive label may be attached for temporary fixing. In such a case, when the customer peels off the adhesive tape or the adhesive label, a phenomenon occurs in which the resin film on the surface of the zinc-based plating peels off from the plating surface together with the tape, which is called tape peeling. When this tape peeling occurs, it becomes a serious product defect.
JP 2003-342746 A

  Therefore, in the present invention, the resin-coated hot-dip galvanized plating having a resin film that has excellent properties such as weldability and workability, has further superior corrosion resistance than conventional ones, and also has excellent tape peel resistance. Providing steel sheets was raised as an issue.

The present invention relates to a resin-coated hot-dip galvanized steel sheet provided with a resin film obtained from an emulsion composition mainly composed of an ethylene-unsaturated carboxylic acid copolymer,
In addition to the ethylene-unsaturated carboxylic acid copolymer, this emulsion composition is
(A) an amine having a boiling point of 100 ° C. or less corresponding to 0.2 to 0.8 mol with respect to 1 mol of carboxyl group of the ethylene-unsaturated carboxylic acid copolymer;
(B) a monovalent metal compound corresponding to 0.02 to 0.4 mol relative to 1 mol of a carboxyl group of the ethylene-unsaturated carboxylic acid copolymer;
(C) a cross-linking agent having two or more functional groups capable of reacting with a carboxyl group is 2 to 28% by mass with respect to 100% by mass of the solid content of the emulsion composition;
(D) 10 to 55% by mass of silica particles with respect to 100% by mass of the solid content of the emulsion composition;
(E) 1-8 mass% of tannic acid and / or ammonium vanadate is contained with respect to 100 mass% of solid content of the emulsion composition.

The ethylene-unsaturated carboxylic acid copolymer has a structure in which an unsaturated carboxylic acid is copolymerized in an amount of 10 to 40% by mass, a structure in which the amine having a boiling point of 100 ° C. or lower is triethylamine, and a glycidyl group-containing cross-linking as a cross-linking agent. In which the agent and the aziridinyl group-containing crosslinking agent are used in combination, the amount of the resin film attached is in the range of 0.1 to 1.5 g / m ² by dry weight, and the silica particles are in the range of 1 to 30 nm. Any configuration having an average particle size is a preferred embodiment of the present invention.

  Moreover, if the surface of the hot dip galvanized steel sheet is subjected to skin pass rolling with an elongation of 0.01% or more, it is effective for improving the adhesion between the plated steel sheet and the resin film. For the purpose of the present invention, it is preferable that the hot dip galvanized steel sheet is not subjected to chromate treatment.

  The method for producing a resin-coated hot-dip galvanized steel sheet according to the present invention is characterized in that the emulsion composition is applied to the surface of a hot-dip galvanized steel sheet and heated and dried to form a resin film on the steel sheet. To do.

  Since an ethylene-unsaturated carboxylic acid copolymer was neutralized and emulsified by using a specific amount of an amine having a boiling point of 100 ° C. or less and a metal compound, an emulsion composition having a very small particle size could be obtained. . In addition, because the optimum composition and amount of various additives could be grasped, various required characteristics were good, and the resin coating was formed with a film that could improve the corrosion resistance after alkali degreasing and tape stripping resistance. A hot-dip galvanized steel sheet could be provided.

  The resin-coated hot-dip galvanized steel sheet of the present invention comprises a resin film formed from a specific emulsion composition. The emulsion composition used in the present invention for forming a resin film has an ethylene-unsaturated carboxylic acid copolymer (including a neutralized state) as a main component and a carboxyl group possessed by the ethylene-unsaturated carboxylic acid copolymer. The amine having a boiling point of 100 ° C. or less corresponding to 0.2 to 0.8 mol (20 to 80 mol%) per mol and 0 mol per mol of carboxyl group of the ethylene-unsaturated carboxylic acid copolymer. It contains a monovalent metal compound corresponding to 0.02 to 0.4 mol (2 to 40 mol%) as a compound for neutralization, but has an amine having a boiling point exceeding 100 ° C and ammonia (derived from ammonium vanadate) (Excluding ammonia) is substantially free.

  The ethylene-unsaturated carboxylic acid copolymer is a copolymer of ethylene and an ethylenically unsaturated carboxylic acid. Examples of the unsaturated carboxylic acid include (meth) acrylic acid, crotonic acid, isocrotonic acid, maleic acid, fumaric acid, itaconic acid, and the like. A copolymer can be obtained by polymerization using a legal method or the like. The copolymer is most preferably random, but may be a block copolymer or a copolymer grafted with an unsaturated carboxylic acid moiety. In addition, (meth) acrylic acid is suitable as the unsaturated carboxylic acid. Further, an olefin monomer such as propylene or 1-butene may be used instead of a part of ethylene, and other known vinyl monomers are partially copolymerized as long as the object of the present invention is not impaired. (About 10 mass% or less).

  The copolymerization ratio of unsaturated carboxylic acid to ethylene is preferably 10 to 40% by mass of unsaturated carboxylic acid when the total amount of monomers is 100% by mass. When the amount of unsaturated carboxylic acid is less than 10% by mass, there are few carboxyl groups that serve as base points for intermolecular association by ion clusters or cross-linking points with cross-linking agents. The corrosion resistance after the degreasing process may be insufficient, and the emulsion stability of the emulsion composition is inferior. A more preferable lower limit of the unsaturated carboxylic acid is 15% by mass. On the other hand, if the unsaturated carboxylic acid exceeds 40% by mass, the corrosion resistance and water resistance of the resin film are inferior, and the corrosion resistance after the degreasing process is lowered, which is not preferable. A more preferred upper limit is 25% by mass.

  Since the ethylene-unsaturated carboxylic acid copolymer has a carboxyl group, it can be emulsified (aqueous dispersion) by neutralization with an organic base or metal ion. In the present invention, an amine having a boiling point of 100 ° C. or lower (hereinafter sometimes simply referred to as “amine (a)”) is used as the organic base. Amines having a boiling point exceeding 100 ° C. are likely to remain on the steel sheet when the resin coating is dried, and the water absorption of the resin coating increases, resulting in a decrease in corrosion resistance. Therefore, the emulsion composition used for film formation in the present invention does not contain amines having a boiling point of more than 100 ° C. As the boiling point, a boiling point under atmospheric pressure is adopted. Further, since the effect of adding ammonia was not recognized, ammonia water or the like for neutralizing the copolymer was not added to the emulsion composition in the present invention. However, as will be described later, an ammonia component may be contained in the film by adding ammonium vanadate, which is a corrosion resistance improving component, to the emulsion composition. However, ammonia not derived from ammonium vanadate is a plated steel sheet of the present invention. It is not included in the resin film.

  Specific examples of the amine (a) include tertiary amines such as triethylamine, N, N-dimethylbutylamine, N, N-dimethylallylamine, N-methylpyrrolidine, tetramethyldiaminomethane, trimethylamine; N-methylethylamine, diisopropyl Secondary amines such as amine and diethylamine; primary amines such as propylamine, t-butylamine, sec-butylamine, isobutylamine, 1,2-dibutylpropylamine, and 3-pentylamine, and the like. The above can be mixed and used. Of these, tertiary amines are preferred, and triethylamine is the most preferred.

  The amount of the amine (a) is in the range of 0.2 to 0.8 mol (20 to 80 mol%) with respect to 1 mol of the carboxyl group in the ethylene-unsaturated carboxylic acid copolymer. This is because, within this range, the corrosion resistance and tape peel resistance are good. If the amine (a) is less than 0.2 mol, it is considered that the particle size of the resin particles in the emulsion becomes large and the above effect is not exhibited. On the other hand, if the amine (a) is used in excess of 0.8 mol, the emulsion composition may thicken and gel, which is not preferable. The upper limit of the more preferable amount of amine (a) is 0.6 mol, more preferably 0.5 mol, and the lower limit of the more preferable amount of amine (a) is 0.3 mol.

  In the present invention, monovalent metal ions are also used for neutralization. Effective for improving solvent resistance and film hardness. Therefore, a monovalent metal compound (hereinafter sometimes simply referred to as “metal compound (b)”) is added to the emulsion composition. The metal compound (b) preferably contains one or more metals selected from sodium, potassium and lithium, and a hydroxide, carbonate or oxide of these metals is preferred. Among these, NaOH, KOH, LiOH and the like are preferable, and NaOH has the best performance and is preferable. In addition, since the effect of adding a metal compound having a valence of 2 or more is not recognized, the emulsion composition used for film formation in the present invention includes a neutralization partner of an ethylene-unsaturated carboxylic acid copolymer. Bivalent or higher metal compounds for are not included.

  The amount of the metal compound (b) is in the range of 0.02 to 0.4 mol (2 to 40 mol%) with respect to 1 mol of the carboxyl group in the ethylene-unsaturated carboxylic acid copolymer. If the amount of the metal compound (b) is less than 0.02 mol, the emulsion stability becomes insufficient, but if it exceeds 0.4 mol, the hygroscopicity (especially with respect to an alkaline solution) of the resulting resin film is obtained. It is not preferable because it increases and the corrosion resistance after the degreasing process deteriorates. A more preferable lower limit of the amount of the metal compound (b) is 0.03 mol, and a more preferable lower limit is 0.1 mol. A more preferable upper limit of the amount of the metal compound (b) is 0.5 mol, and a more preferable upper limit is 0. .2 moles.

  Although the preferable range of each usage-amount of the said amine (a) and the said metal compound (b) is as above-mentioned, all these neutralize the carboxyl group in an ethylene- unsaturated carboxylic acid copolymer. Used to emulsify. Therefore, if the total amount (neutralization amount) is too large, the viscosity of the emulsion composition may rapidly increase and solidify, and excessive alkali will cause corrosion resistance deterioration, and thus volatilize. For this reason, a large amount of energy is required, which is not preferable. However, if the neutralization amount is too small, the emulsifiability is inferior, which is not preferable. Therefore, the total amount of amine (a) and metal compound (b) used should be in the range of 0.3 to 1.0 mole per mole of carboxyl groups in the ethylene-unsaturated carboxylic acid copolymer. preferable.

  The emulsion composition used in the present invention is emulsified by combining an amine (a) having a boiling point of 100 ° C. or less and a monovalent metal compound (b), so that the resin particles in the composition are extremely small of 5 to 50 nm. It exists stably in an aqueous medium in the form of fine particles (oil droplets). For this reason, it is presumed that the film forming property of the resulting resin film, the adhesion to the metal plate, and the densification of the film were achieved, and the corrosion resistance and tape peel resistance were improved. The aqueous medium may contain a hydrophilic solvent such as alcohol or ether in addition to water. The particle size of the resin particles in the emulsion can be measured, for example, by a laser diffraction method using a light scattering photometer (manufactured by Otsuka Electronics Co., Ltd.).

  In the neutralization step (emulsification step) of the ethylene-unsaturated carboxylic acid copolymer with the amine (a) and the metal compound (b), the amine (a) and the metal compound (b) are almost simultaneously converted into a copolymer. It is desirable to add the amine (a) first. The reason is not clear, but if amine (a) is added afterwards, the effect of improving corrosion resistance and tape peel resistance may be insufficient.

  The ethylene-unsaturated carboxylic acid copolymer having a carboxyl group neutralized by a monovalent metal ion derived from the amine (a) and the metal compound (b) forms an intermolecular association by an ion cluster (ionomer). ), And forms a resin film with excellent corrosion resistance and tape peel resistance. However, in order to form a tougher film, it is desirable to crosslink the polymer chains by chemical bonding utilizing a reaction between functional groups. Therefore, the emulsion composition of the present invention contains a crosslinking agent having two or more functional groups capable of reacting with a carboxyl group (hereinafter sometimes simply referred to as “crosslinking agent (c)”) as an essential component. The amount is 2 to 28% by mass in 100% by mass of the solid content (component remaining as a film; nonvolatile content) in the emulsion composition. When using 2 or more types of crosslinking agents together, the total amount shall be 2-28 mass%. When the amount of the cross-linking agent is less than 2% by mass, the effect of cross-linking by chemical bonding becomes insufficient, and the effect of improving the corrosion resistance and tape peel resistance is hardly exhibited. On the other hand, if it exceeds 28% by mass, the crosslinking density of the resin film becomes excessively high, the hardness increases, and it becomes impossible to follow the deformation at the time of pressing, resulting in cracks, resulting in corrosion resistance and paintability. Is not preferable. A more preferable amount of the crosslinking agent (c) is 3 to 15% by mass in 100% by mass of the solid content in the emulsion composition. In addition, as a ratio of the amount of the crosslinking agent (c) to the ethylene-unsaturated carboxylic acid copolymer, it is desirable to appropriately change the amount of the crosslinking agent (c) according to the amount of carboxyl groups in the copolymer. Usually, it is preferable to make a crosslinking agent (c) into 0.5-50 mass parts (more preferably 3-20 mass parts) with respect to 100 mass parts of copolymers.

  Although it does not specifically limit as said crosslinking agent (c), Sorbitol polyglycidyl ether, (poly) glycerol polyglycidyl ether, pentaerythritol polyglycidyl ether, trimethylol propane polyglycidyl ether, neopentyl glycol diglycidyl ether, (poly) ethylene Polyglycidyl ethers such as glycol diglycidyl ether and glycidyl group-containing crosslinking agents (epoxy resins) such as polyglycidyl amines; 4,4′-bis (ethyleneiminocarbonylamino) diphenylmethane, N, N′-hexamethylene Two components such as 1,6-bis (1-aziridinecarboxamide), N, N′-diphenylmethane-4,4′-bis (1-aziridinecarboxyamide), toluenebisaziridinecarboxamide Aziridine compounds; tri-1-aziridinylphosphine oxide, tris [1- (2-methyl) aziridinyl] phosphine oxide, trimethylolpropane tris (β-aziridinylpropionate), tris-2,4,6- (1-aziridinyl) -1,3,5-triazine, trifunctional or higher functional aziridine compounds such as tetramethylpropanetetraaziridinylpropionate or aziridinyl group-containing crosslinking agents such as derivatives thereof, isocyanate crosslinking agents, etc. It is mentioned as a preferred example, and one or more of these can be used. In addition, you may use together polyfunctional aziridine and monofunctional aziridine (ethyleneimine etc.). Among these, a glycidyl group-containing crosslinking agent (particularly polyglycidylamines) and an aziridinyl group-containing crosslinking agent are preferable, and it is most preferable to use these in combination. When the glycidyl group-containing crosslinking agent and the aziridinyl group-containing crosslinking agent are used in combination, it is preferable to use 1 to 8% by mass of the glycidyl group-containing crosslinking agent and 1 to 20% by mass of the aziridinyl group-containing crosslinking agent.

  You may make the emulsion composition used by this invention contain 10-55 mass% silica particle (henceforth a silica particle (d)) in conversion of solid content. It is effective for improving corrosion resistance, paintability, scratch resistance, etc., and also effective for improving corrosion resistance after degreasing and tape peeling resistance. When the amount is less than 10% by mass, these effects are hardly exhibited. However, when the amount exceeds 55% by mass, the ratio of the silica particles (d) becomes excessively high and the film-forming property is lowered, and the resin film is formed during the drying process. Cracks may occur, which leads to a decrease in corrosion resistance. Furthermore, the silica particles (d) can act as a polish, improve the lubricity of the coating, reduce the friction coefficient, cause wear of the mold during processing, and shorten the life of the mold. It becomes. The lower limit of the amount of silica particles (d) is more preferably 20% by mass, and the upper limit is 40% by mass.

  In order to obtain the maximum effect of the silica particles (d) as described above, the average particle size of the silica particles (d) is preferably in the range of 1 to 30 nm. As the particle size of the silica particles (d) decreases, the corrosion resistance of the coating improves. This is considered to further increase the corrosion resistance by densifying the resin film and improving the adhesion. From such a point of view, the smaller the particle diameter of the silica particles (d), the better. However, when the particles are extremely fine, the above effect is saturated, so the lower limit of the particle diameter is preferably 1 nm. On the other hand, if the particle diameter of the silica particles (d) exceeds 30 nm, the surface of the resin film is roughened to form a dense resin film. Further, the silica particles (d) can be used as a polishing agent. Since it acts, it leads to deterioration of workability, which is not preferable. A more preferable range of the average particle diameter of the silica particles (d) is 4 to 6 nm.

  Such silica particles (d) are generally known as colloidal silica. In the present invention, for example, “XS” and “SS” of “Snowtex” series (colloidal silica manufactured by Nissan Chemical Industries, Ltd.) are used. , “S”, “N”, “PS-M”, “C”, “40”, “50” and the like can be suitably used.

  The emulsion composition used in the present invention contains tannic acid and / or ammonium vanadate (hereinafter, both may be referred to as “corrosion resistance improving component (e)”). These corrosion resistance improving components (e) are effective in improving the corrosion resistance of the hot dip galvanized steel sheet by forming a non-conductive film on the surface of the hot dip galvanized steel sheet. High level of corrosion resistance can be ensured. In order to exert such an effect effectively, it is necessary to contain 1% by mass or more of one or two of the corrosion resistance improving components (e) in 100% by mass of the solid content of the emulsion composition. However, when the content is excessive and exceeds 8% by mass, the stability of the emulsion is deteriorated and it becomes difficult to form a uniform film, and the corrosion resistance is deteriorated. Further, if the corrosion resistance improving component (e) is present in a large amount exceeding 8 mass% in the film, these components (e) are oxidized in a high temperature and high humidity environment, and the appearance of the hot dip galvanized steel sheet May be noticeably discolored to yellow.

  The emulsion composition used in the present invention may contain a wax. The wax is effective in improving the lubricity and scratch resistance of the resulting resin film. Furthermore, it is preferable to improve the deep drawability and punchability required during press working and punching, wear resistance of the mold, blackening resistance of the sliding surface during processing, and impart excellent workability. Can be used. Moreover, since solid lubricants, such as carbon disulfide and graphite, have the same effect, they can be used. Furthermore, Co-containing compounds and Ni-containing compounds are effective in improving blackening resistance.

  In order to exert the above effect of the wax, it is preferable that the wax is 0.5 to 20% by mass in 100% by mass of the solid content of the emulsion composition. When the amount of the wax is less than 0.5% by mass in terms of solid content, the resulting resin film has insufficient lubricity, and it is impossible to improve the scratch resistance and to obtain satisfactory processability. On the other hand, if it exceeds 20% by mass, the resulting resin film has sufficient lubricity, but the film adhesion (paintability) when electrodeposition coating, powder coating, or post-coating by silk printing is applied. ). Moreover, the corrosion resistance and detaping resistance after degreasing also deteriorate. This is because the wax softens, liquefies, or blooms due to heating in the post-coating process or changes over time, and concentrates at the interface between the resin film and the post-coating film or between the metal plate and the resin film. This is thought to be because the adhesion to the post-coating coating film and the adhesion to the metal plate deteriorate. A more preferable upper limit value of the wax is 10% by mass, and a further preferable upper limit value is 5.0% by mass.

  The wax is not particularly limited, and natural wax, synthetic wax, and the like can be used. As natural waxes, for example, carnauba wax, rice wax, candelilla wax, montan wax and derivatives thereof, mineral oil wax, microcrystalline wax, paraffin wax and the like, and derivatives having a carboxyl group added thereto may also be used. Can do.

  Synthetic waxes include polyethylene, polyethylene oxide, polypropylene, ethylene and propylene copolymer wax, and oxide wax of copolymer wax of ethylene and other monomers. This system can be used in various ways including terpolymer systems by changing the copolymerization partner. Furthermore, maleic acid addition wax, fatty acid ester, and the like can be mentioned. In addition, a wax of a fluororesin such as polytetrafluoroethylene, polyvinyl fluoride, polyvinylidene fluoride, and tetrafluoroethylene can also be used.

  As the wax, it is preferable to select a wax having a softening point of 80 to 140 ° C. among those exemplified above. When the softening point is lower than 80 ° C., the wax particles soften and liquefy as the mold temperature rises during press working or punching, and liquefaction occurs on the sliding surface between the resin-coated steel sheet and the mold. This is not preferable because a wax breakage phenomenon occurs, processability is reduced, and scuffing or seizure with a mold occurs. In addition, blackened material may adhere to the sliding portion and the product appearance may be significantly deteriorated. Furthermore, also from the viewpoint of the corrosion resistance after the degreasing process and the tape peel resistance, it was found that the softening point is too low. On the other hand, when the softening point exceeds 140 ° C., the lubricity by the wax becomes insufficient, the improvement in punchability, die wear resistance, deep drawability, etc. is not recognized, and the corrosion resistance after degreasing is slightly lowered. There was a trend.

  As the wax, spherical polyethylene wax is most preferable. In this case, in order to obtain the maximum effect of the spherical polyethylene wax, the particle diameter of the wax particles is preferably 0.1 to 3 μm. If the particle size of the wax particles is smaller than 0.1 μm, it is difficult to achieve significant improvements in lubricity, punchability, mold wear resistance and deep drawability. On the other hand, when the particle diameter of the wax particles exceeds 3 μm, it is difficult to uniformly disperse in the finely divided emulsion composition, so that the adhesion of the resin film to the metal plate may be lowered. A more preferable spherical polyethylene wax has a particle size of 0.3 to 1.0 μm.

  Examples of the spherical polyethylene wax as described above include “Daijet E-17” (manufactured by Kyoyo Chemical Co., Ltd.), “KUE-1”, “KUE-5”, “KUE-8” (manufactured by Sanyo Chemical Industries). "W-100", "W-200", "W-300", "W-400", "W-500", "W-640", "W" of "Chemical Pearl" series (Mitsui Chemicals) Commercially available products such as “-700” and “Elepon E-20” (manufactured by Nikka Chemical Co., Ltd.) can be suitably used.

  The emulsion composition used in the present invention comprises an essential component of an ethylene-unsaturated carboxylic acid copolymer, an amine (a) having a boiling point of 100 ° C. or less, a monovalent metal compound (b), a crosslinking agent (c), silica It contains particles (d), a corrosion resistance improving component (e), and further contains a wax or the like as necessary, but the ethylene-unsaturated carboxylic acid copolymer as the main component is 50% by mass of the solid content of the emulsion composition. It is desirable to adjust the amounts of the other components so as to achieve the above.

  First, an ethylene-unsaturated carboxylic acid copolymer, which is an essential component, is put together with an aqueous medium into, for example, a homogenizer apparatus and the like, and heated under a temperature of 70 to 250 ° C. as necessary. a) and the metal compound (b) are appropriately added in the form of an aqueous solution or the like (the amine (a) is added first or the amine (a) and the metal compound (b) are added almost simultaneously), and high shear Stir with force. The crosslinking agent (c), silica particles (d), corrosion resistance improving component (e), wax and the like may be added at any stage, but after the addition of the crosslinking agent (c), the crosslinking reaction proceeds to gel. It is desirable not to apply heat.

  The emulsion composition includes a diluent solvent, an anti-skinning agent, a leveling agent, an antifoaming agent, an emulsifier, an emulsifying agent, a film-forming aid, a coloring pigment, a thickener, and a silane as long as the object of the present invention is not impaired. A coupling agent, other resin, etc. may be added as appropriate.

  As a hot dip galvanized steel plate (original plate) on which a film obtained from the above emulsion composition is formed in the present invention, a normal hot dip galvanized steel plate (GI) and an alloyed hot dip galvanized steel plate (GA) obtained by alloying the same Furthermore, any of hot dip zinc Zn-5% Al alloy plated steel sheet (GF) can be used.

  It is also useful to perform skin pass rolling on the surface of the hot dip galvanized steel sheet used in the present invention, if necessary. By performing such skin pass rolling, the oxide layer on the surface of the hot-dip galvanized plating is destroyed, and therefore the reactivity between the resin film and the hot-dip galvanized layer is improved, and the corrosion resistance of the resin film is further improved. Become. In order to exert such an effect, the elongation rate of the skin pass rolling is preferably 0.01% or more. However, if the elongation rate is increased, pickup to the work roll is likely to occur. Is good.

  Moreover, when the hot dip galvanized steel sheet surface has a certain degree of roughness, the adhesion between the resin film and the hot dip galvanized layer can be improved. In order to exert such an effect, the center line average roughness Ra on the surface of the hot dip galvanized steel sheet is preferably 0.1 μm or more. However, when Ra is larger than 2.0 μm, it is difficult to form a film uniformly and the corrosion resistance is not improved.

  The surface of the hot dip galvanized steel sheet used as the original plate in the present invention is assumed to be substantially not chromated, but may be subjected to various chromate treatments or non-chromate treatments as necessary. The surface of the hot dip galvanized steel sheet can be subjected to various known pretreatments such as Co treatment, Ni treatment, and inhibitor treatment.

  In order to form a resin film on the original plate, the emulsion composition is applied to one or both surfaces of a metal plate surface using a known coating method, that is, a roll coater method, a spray method, a curtain flow coater method, or the like. And heat drying. The heating and drying temperature is preferably a temperature at which the crosslinking reaction between the crosslinking agent and the carboxyl group proceeds. In addition, when spherical polyethylene wax is used as the lubricant, it is preferable to perform drying in the range of 70 to 130 ° C. because maintaining the spherical shape improves the workability in the subsequent processing step. .

The adhesion amount (thickness) of the resin film is preferably 0.1 to 1.5 g / m ² after drying. If it is too thin, it is difficult to uniformly coat the steel sheet, and it is difficult to obtain the desired balanced film properties such as workability, corrosion resistance, and paintability. However, if the adhesion amount exceeds 1.5 g / m ² , the grounding property (conductivity) and the interlayer resistance when used for a computer housing or the like are deteriorated and the weldability is lowered, which is not preferable. Furthermore, the amount of peeling of the resin film is increased during press working, causing adhesion and accumulation of the peeling film on the mold, resulting in trouble with press molding and wasteful manufacturing cost. The lower limit of the more preferable resin film adhesion amount is 0.3 g / m ² , and the upper limit is 1.2 g / m ² .

  By forming the resin film, the resin-coated hot-dip galvanized steel sheet of the present invention is obtained. This resin-coated hot-dip galvanized steel sheet can be used as it is after undergoing a processing step depending on the application, or electrodeposition coating, powder coating, and silk printing (about 130 to 160 ° C., about 20 to 30 minutes) under conventional conditions. You may use it.

  The present invention will be described in more detail with reference to the following examples. However, the following examples are not intended to limit the present invention, and all modifications are included in the present invention without departing from the spirit of the present invention. The test methods used in the following examples are as follows.

〔Test method〕
(1) Corrosion resistance (normal)
About the flat test piece which sealed the back side and the edge, the salt spray test prescribed | regulated to JISZ2371 was implemented, and the time until white rust generate | occur | produces 1% (area ratio) was measured. The evaluation criteria were as follows: ◎: 120 hours or more, ○: 72 to less than 120 hours, Δ: 48 to less than 72 hours, ×: less than 48 hours.

(2) Corrosion resistance after the degreasing step The resin-coated hot-dip galvanized steel sheet is immersed for 2 minutes in 20 g / liter of an alkaline degreasing agent (“CL-N364S” manufactured by Nihon Parkerizing Co., Ltd.) prepared at 60 ° C. After drying, a salt spray test was performed according to JIS Z2371, and the time until 1% of white rust was generated was measured. The evaluation criteria were: ◎: 72 hours or more, ○: 48 to less than 72 hours, Δ: less than 24 to 48 hours, ×: less than 24 hours.

(3) Tape peel resistance Adhesive tape (Flamen Tape No. 9510 manufactured by Sliontec Co., Ltd .; rubber adhesive) is applied to a resin-coated hot-dip galvanized steel sheet, and the atmosphere is 40 ° C. and 98% RH with a constant temperature and humidity device. After storing for 24 hours, the tape was peeled off according to JIS K 5400, and the remaining area ratio of the film was measured. The evaluation criteria were as follows: A: film remaining rate 100%, ○: film remaining rate 90-99%, Δ: film remaining rate 89-70%, x: film remaining rate 70% or less.

(4) Weldability Using a 1% Cr-Cu dome-shaped (tip diameter: 6 mm, 40 mmR) electrode, a 5t ^1/2 nugget is formed with a pressure of 2156 N (220 kgf) and 14 cycles (60 Hz). 1000 spot spot welding was carried out at a current 1 kA higher than the welding current, and the ratio of the good welding points in all the welding points was determined to be weldability (%). In addition, the occurrence of scattering (occurrence of surface sparks) at all hit points was visually evaluated. The evaluation criteria were ◎: very good, ○: good, Δ: bad, ×: extremely bad.

(5) Color tone change under high temperature and high humidity environment The color tone change before and after leaving the resin-coated hot-dip galvanized steel sheet in an environment of temperature: 50 ° C. and humidity: 98% RH was visually evaluated. The evaluation criteria were ◎: very good (no change in color tone), ○: good (no change in color tone), Δ: bad (a little change in color tone), x: very bad (a great change in color tone).

(6) Interlayer resistance According to JIS-C2550-9, test voltage: 0.5 V, measurement current range: 0 to 1 A, total area of contacts: 10 cm ² , standard test pressure: 2 N / mm ² ± 5%, interlayer resistance Was measured. The evaluation criteria were as follows: A: less than 0.1 to 1.0Ω, ○: less than 1.0 to 5.0Ω, Δ: 5.0 to less than 10.0Ω, and x: 10.0Ω or more.

(7) Workability In order to evaluate the deep drawing workability of the resin-coated hot-dip galvanized steel sheet, a single press test was carried out using an 80-ton crank press machine, The presence of mold galling and blackening was visually evaluated. The evaluation criteria were ◎: very good, ○: good, Δ: bad, ×: extremely bad.

Experimental Example 1 (Influence of type and amount of organic base and metal salt)
In order to prepare an emulsion composition, an ethylene-acrylic acid copolymer (acrylic acid 20% by mass, melt index (MI) 300) 160 is added to 626 parts by mass of water (hereinafter simply referred to as “parts”) in an autoclave. Further, an organic base and a metal compound in the amounts shown in Table 1 were added, and the mixture was stirred at a high speed in an atmosphere of 150 ° C. and 5 Pa to obtain an ethylene-acrylic acid copolymer emulsion.

  Subsequently, a glycidyl group-containing cross-linking agent (“Epiclon CR5L” (abbreviated as CR5L); “Epiclon” is a registered trademark; manufactured by Dainippon Ink & Chemicals, Inc.) as a cross-linking agent is added to the above emulsion in an amount of 5% by mass ( When the solid content (nonvolatile content) of the emulsion composition is 100% by mass: the same applies hereinafter, and an aziridinyl group-containing crosslinking agent (4,4′-bis (ethyleneiminocarbonylamino) diphenylmethane; “Chemite DZ-22E” "Chemite" is a registered trademark; manufactured by Nippon Shokubai Co., Ltd.) and is a silica particle having a solid content of 5 mass% and a particle size of 4 to 6 nm ("Snowtex XS"; manufactured by Nissan Chemical Industries, Ltd.) Was added in an amount of 35% by mass in solid content and 5% by mass of ammonium vanadate and stirred to prepare an emulsion composition.

This emulsion composition was applied to the surface of a hot-dip galvanized steel sheet (Zn deposition amount 60 g / m ² ; sheet thickness 0.8 mm; skin pass elongation rate: 1.0%; surface roughness Ra: 1.0 μm) Heat-drying was performed at a temperature of 100 ° C. to obtain a resin-coated hot-dip galvanized steel sheet having a resin film with an adhesion amount of 0.5 g / m ² . The obtained resin-coated hot-dip galvanized steel sheet was evaluated for corrosion resistance (normal state), corrosion resistance after degreasing, and tape peel resistance by the above-described evaluation methods, and the results are shown in Table 1.

Experimental Example 2 (Influence of the amount of crosslinking agent)
As shown in Table 2, the amount of triethylamine used was fixed at 40% and the amount of NaOH used was fixed at 15%, and the amounts of the glycidyl group-containing crosslinking agent (CR5L) and the aziridinyl group-containing crosslinking agent (DZ-22E) were as shown in Table 2. Except for the change, a resin-coated hot-dip galvanized steel sheet was obtained in the same manner as in Experimental Example 1, and the characteristics were evaluated. The results are shown in Table 2.

Experimental Example 3 (Influence of the amount of silica particles)
The kind and amount of the cross-linking agent were the same as in Experimental Example 1, and a resin-coated hot-dip galvanized steel sheet was obtained in the same manner as in Experimental Example 2 except that the addition concentration of silica particles was changed as shown in Table 3, and the characteristics were evaluated. did. The results are shown in Table 3.

Experimental Example 4 (Influence of silica particle size)
The type and amount of the cross-linking agent were the same as in Experimental Example 1, and the resin-coated hot-dip galvanized steel sheet was obtained in the same manner as in Experimental Example 2 except that the average particle diameter of the silica particles was changed as shown in Table 4. Characterized. The results are shown in Table 4.

Experimental Example 5 (Effect of corrosion resistance improving component)
Resin-coated molten zinc was used in the same manner as in Experimental Example 2 except that the type and amount of the cross-linking agent were the same as in Experimental Example 1 and the amounts of tannic acid and ammonium vanadate as the corrosion resistance improving components were changed as shown in Table 5. A plated steel sheet was obtained and characterized. The results are shown in Table 5.

Experimental Example 6 (Influence of adhesion amount)
The type and amount of the cross-linking agent were the same as in Experimental Example 1, and a resin-coated galvanized steel sheet was obtained and evaluated in the same manner as in Experimental Example 2 except that the amount of resin film deposited was changed as shown in Table 6. . The results are shown in Table 6.

Experimental Example 7 (Effect of original plate type and skin pass elongation)
The type and amount of the cross-linking agent were the same as in Experimental Example 1, and the resin-coated hot-dip galvanized steel sheet was obtained and evaluated in the same manner as in Experimental Example 2 except that the skin pass elongation was changed as shown in Table 7. . Experiment No. In No. 87, an electrogalvanized steel sheet (Zn adhesion amount 20 g / m ² ; plate thickness 0.8 mm) was used as the original sheet. The evaluation results are shown in Table 7.

Experimental Example 8 (Influence of original plate type and surface roughness)
The type and amount of the crosslinking agent were the same as in Experimental Example 1, and the resin-coated molten zinc was the same as in Experimental Example 2 except that the surface roughness (centerline average roughness Ra) of the original plate was changed as shown in Table 8. A plated steel sheet was obtained and characterized. Experiment No. 96, no. The same electrogalvanized steel plate as 87 was used as the original plate. The evaluation results are shown in Table 8.

  As is apparent from each table, the inventive examples were excellent in corrosion resistance, corrosion resistance after degreasing, and tape peel resistance. Further, the weldability, conductivity, and workability were sufficiently satisfactory for practical use. Although some reference examples outside the preferred range of the present invention were slightly inferior to the characteristics of the present invention, comparative examples that did not satisfy the requirements of the present invention clearly had inferior characteristics to the present invention.

Claims (9)

A resin-coated hot-dip galvanized steel sheet provided with a resin film obtained from an emulsion composition mainly composed of an ethylene-unsaturated carboxylic acid copolymer,
In addition to the ethylene-unsaturated carboxylic acid copolymer, this emulsion composition is
(A) an amine having a boiling point of 100 ° C. or less corresponding to 0.2 to 0.8 mol with respect to 1 mol of carboxyl group of the ethylene-unsaturated carboxylic acid copolymer;
(B) a monovalent metal compound corresponding to 0.02 to 0.4 mol relative to 1 mol of a carboxyl group of the ethylene-unsaturated carboxylic acid copolymer;
(C) a cross-linking agent having two or more functional groups capable of reacting with a carboxyl group is 2 to 28% by mass with respect to 100% by mass of the solid content of the emulsion composition;
(D) 10 to 50 % by mass of silica particles with respect to 100% by mass of the solid content of the emulsion composition;
(E) 1-8% by mass of tannic acid and / or ammonium vanadate with respect to 100% by mass of the solid content of the emulsion composition
A resin-coated hot-dip galvanized steel sheet containing an amine having a boiling point exceeding 100 ° C., ammonia not derived from ammonium vanadate, and a metal compound having a valence of 2 or more.   The resin-coated hot-dip galvanized steel sheet according to claim 1, wherein the ethylene-unsaturated carboxylic acid copolymer is copolymerized with 10 to 40 mass% of an unsaturated carboxylic acid.   The resin-coated hot-dip galvanized steel sheet according to claim 1 or 2, wherein the amine having a boiling point of 100 ° C or lower is triethylamine.   The resin-coated melt according to any one of claims 1 to 3, wherein a glycidyl group-containing crosslinking agent and an aziridinyl group-containing crosslinking agent are used in combination as a crosslinking agent having two or more functional groups capable of reacting with a carboxyl group. Galvanized steel sheet. The resin-coated hot-dip galvanized steel sheet according to any one of claims 1 to 4, wherein an adhesion amount of the resin film is in a range of 0.1 to 1.5 g / m ² by dry weight.   The resin-coated hot-dip galvanized steel sheet according to any one of claims 1 to 5, wherein the silica particles have an average particle diameter in the range of 1 to 30 nm.   The resin-coated hot-dip galvanized steel sheet according to any one of claims 1 to 6, wherein the surface of the hot-dip galvanized steel sheet is subjected to skin pass rolling with an elongation of 0.01% or more.   The resin-coated hot-dip galvanized steel sheet according to any one of claims 1 to 7, wherein the hot-dip galvanized steel sheet is not subjected to chromate treatment.   The emulsion composition according to claim 1 is applied to the surface of a hot dip galvanized steel sheet and dried by heating to form a resin film on the steel sheet. Method.