JP2006035842A - Resin-coated metal sheet with excellent processing, welding and corrosion resistance properties, and finished piece and production process using the resin-coated metal sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a high-quality resin-coated metal sheet targeting metal sheets such as galvanized steel sheets, which has an excellent conductivity in regard to weldability, especially in spot welding and the like, good processabilities such as bending to prevent occurrence of exfoliation, cracking or powdering of resin film despite skipped use of a processing grease or the like, and further shows excellent corrosion resistance under corrosive atmosphere as a finished piece of resin-coated metal sheet. <P>SOLUTION: The resin-coated metal sheet with excellent processing properties comprises a resin coating layer containing a conductive filler and a corrosion inhibitor, which is formed on the metal sheet. A matrix resin constituting the resin coating layer comprises mainly of a flexible epoxy resin having a modulus of elasticity of 3 GPa or lower. A secondary cure after processing of the resin-coated metal sheet gives a resin-coated metal sheet excellent in weldability and corrosion resistance. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a resin-coated metal plate, a processed product using the metal plate, and a method for producing the resin-coated metal plate. Specifically, the surface of the metal plate, preferably a metal plate plated with zinc or the like, has a conductive filler or anti-corrosion. Resin-coated metal plate excellent in workability, weldability and corrosion resistance, coated with an epoxy matrix resin containing a rusting agent, or an epoxy-based and polyester-based matrix resin layer, and the processed product, and further It relates to the manufacturing method.

  The resin-coated metal plate according to the present invention enables simplification of the coating process when used as a coated steel plate for automobiles, vehicles, ships, etc., and can eliminate the filling of processing grease or the like into the bent portion. Thus, it is useful as a coated steel sheet that increases the productivity and gives a high-quality product excellent in weldability and corrosion resistance.

  For example, a method disclosed in Patent Document 1 is known as a conventional technique related to a method of manufacturing a coated metal sheet processed product, and the present applicant has already disclosed Patent Document 2 as a resin-coated metal sheet excellent in workability and heat resistance. The technology described in is developed and provided.

  The invention described in Patent Document 1 discloses a coated metal plate using a paint containing a polymer having a polymerizable double bond and a crosslinking reactive hydroxyl group and a blocked polyisocyanate compound. Specifically, First, after forming a primary cured coating film having workability (flexibility) by irradiating active energy rays, molding is performed. And after the molding process, it is further baked and the coated polyisocyanate is reacted to completely cure (secondary curing) to give high hardness and stain resistance. When using ultraviolet rays as active energy rays Recommends the use of photoinitiators.

The invention described in Patent Document 2 uses a coating composition containing two or more kinds of cross-linking reactive resin components as a surface coating agent for a steel sheet, and after coating the steel sheet surface with this, a resin coating layer is formed. First, heat is applied at a low temperature, and the resin component that undergoes a cross-linking reaction at a low temperature is subjected to primary crosslinking while leaving an unreacted reactive functional group. Next, after the molding process, the heat for baking performed during top coating is used. It is characterized in that secondary crosslinking is performed with a high-temperature crosslinking reactive resin component. According to the present invention, the resin layer is hardened to some extent by primary crosslinking to improve the top coatability and silk printability, and the poor heat resistance due to insufficient curing of the primary crosslinked resin layer is compensated by secondary crosslinking. It has characteristics. In this invention, a low-temperature crosslinkable epoxy resin is used as a low-temperature-reactive resin component, a melamine-based resin is used as a high-temperature crosslinkable resin component, and the workability is further improved by adding an organic lubricant. .
Japanese Patent Laid-Open No. 6-23319 JP 2001-277422 A

  However, the technique disclosed in Patent Document 1 uses a two-stage curable paint by a combination of ultraviolet curing and thermal curing, and retains workability in the primary curing state. Is due to UV curing. Moreover, the secondary hardening of the coating film by subsequent baking is for ensuring hardness and stain resistance, and corrosion resistance is not considered.

  On the other hand, in Patent Document 2, two or more types of cross-linking reactive resins having different cross-linking start temperatures are used in combination, but at the time of performing the primary curing reaction, an unreacted reactive functional group is used to improve the paintability. In order to leave the group and to impart workability (lubricity) to the coating film, it is essential to add an organic lubricant. That is, the high-temperature crosslinking reactive resin component is added to impart heat resistance to the coating film in the baking coating process, and the workability essentially depends on the organic lubricant. Therefore, the processability is not improved by suppressing the semi-cured state by the low temperature reactive crosslinking agent. Further, the secondary curing by the high-temperature crosslinking reactive resin component is for improving the heat resistance of the coating film, not necessarily for imparting corrosion resistance to the resin coating film.

  The present invention has been developed as an improvement technique of the prior art as described above, and the object thereof is preferably a metal plate plated with zinc or the like, typically a galvanized steel plate, particularly a spot. It has excellent conductivity in consideration of weldability such as welding, and particularly has good moldability such as bending, and even if the use of processing grease etc. is omitted, the resin coating peels off, cracks, powdering, etc. It is another object of the present invention to provide a high-quality resin-coated metal sheet that exhibits excellent corrosion resistance even in a corrosive environment, as a final processed resin-coated metal sheet product.

  Another object of the present invention is to provide a processed product having high corrosion resistance and excellent weldability using the above resin-coated metal plate, and further to provide a useful production method thereof.

  The resin-coated metal plate excellent in electrical conductivity, workability, and corrosion resistance according to the present invention that has solved the above-mentioned problems is that a resin coating layer containing a conductive filler and a rust inhibitor is formed on the metal plate. The matrix resin constituting the resin coating layer is mainly composed of a flexible epoxy resin, or a flexible epoxy resin and a polyester resin, and has a flexural modulus of 3 GPa or less.

  In the present invention, the flexible epoxy resin, which is the main matrix component of the resin coating layer, has good moldability after primary curing and is strong against metal materials both before and after secondary curing. Urethane-modified epoxy resins and / or dimer acid-modified epoxy resins are optimal as those that adhere to the surface and exhibit excellent corrosion resistance, and polyester resins have good moldability after primary curing and good degreasing properties after molding As such, a high molecular weight polyester is optimal. Moreover, as a preferable crosslinking agent mix | blended with these epoxy resins and polyester-type resins as a hardening | curing agent, at least 1 sort (s) selected from the group which consists of block isocyanate, a melamine-type resin, and an amine-type resin is mentioned.

  The preferable content rate of each said component which comprises matrix resin is flexible epoxy resin: 60 mass% or more and 90 mass% or less, and polyester-type resin: 10 mass% or more and 40 mass% or less.

  The typical metal plate to be coated in the present invention is an iron-based metal plate typified by steel, but in addition to non-ferrous metal plates such as copper, brass, titanium, zinc and alloys containing them. The same applies to the case. The steel sheet can be applied to a bare steel sheet, and is also a plated steel sheet that has been plated for the purpose of anticorrosion, typically a hot dip galvanized steel sheet or an electrogalvanized steel sheet.

  In addition, iron phosphide is most preferable as the conductive filler for imparting weldability to the resin-coated metal plate, and the rust preventive agent is selected from aluminum tripolyphosphate, amorphous magnesium silicate, and calcium ion exchange silica. At least one selected from the group is preferably used.

  These conductive fillers and rust preventives are desirably fine powders having a maximum particle size of 15 μm or less in order to improve the workability when bending the resin-coated metal plate. Here, the particle diameter refers to a sphere equivalent diameter obtained by a laser diffraction / scattering microtrack, and the maximum particle diameter of 15 μm means that particles of 15 μm or less occupy 99% of the whole (that is, 99% diameter). Means.

  Moreover, the preferable content rate of each said component which comprises a resin coating layer is 25 mass% or more of matrix resin: 25 mass% or less, Conductive filler: 40 mass% or more and 55 mass% or less, Rust prevention agent: 5 mass% or more 25 It is below mass%.

  Furthermore, as a more preferable embodiment of the present invention, as the matrix resin, the epoxy resin or the epoxy resin and the polyester resin have different crosslinking reaction initiation temperatures, or the crosslinking initiation temperatures are substantially the same and the crosslinking reaction rates are different. Using two or more types of crosslinking agents, the crosslinking agent having the highest crosslinking reaction start temperature or the slowest crosslinking reaction rate is crosslinking agent A, and the crosslinking reaction initiation temperature is the lowest or the crosslinking reaction rate is the fastest. Is a resin-coated metal plate containing an epoxy resin or a reaction product of an epoxy resin and a polyester resin and a crosslinking agent B and an unreacted crosslinking agent A in the resin coating layer. Can be mentioned.

  Still another embodiment of the present invention is a process for producing a processed product using the resin-coated metal plate and the obtained processed product, the process comprising a conductive filler, a rust inhibitor and a crosslinking agent, and a bending elastic modulus. A resin-coated metal sheet having a resin coating layer of 3 GPa or less formed on the metal sheet, and at the same time as or after the molding process, a crosslinking reaction start temperature of the crosslinking agent A or higher and / or It is characterized in that it is heated for more than the cross-linking reaction start time and is allowed to react with the unreacted cross-linking agent A for secondary curing. If this method is employed, corrosion resistance and weldability are excellent under excellent moldability. A resin-coated metal sheet processed product can be obtained. And the resin metal processed goods obtained by this method are also included in the technical scope of the present invention.

  In the resin-coated metal plate of the present invention, a resin coating layer containing a conductive filler and a rust inhibitor is formed on a metal plate, and a flexible epoxy resin or a flexible resin is used as a matrix resin constituting the resin coating layer. By selecting a functional epoxy resin and a polyester-based resin and suppressing the bending elastic modulus of the resin coating layer to 3 GPa or less, the resin coating layer does not cause cracking or powdering or peeling due to bending or the like Thus, it is possible to provide a resin-coated metal plate that has stable and excellent workability, and has excellent corrosion resistance and weldability in the state of the final processed product after processing. Therefore, the resin-coated metal plate can be effectively used widely as an outer plate material for vehicles such as automobiles and trains, ships, and household appliances.

  As described above, the resin-coated metal plate of the present invention has a resin coating layer containing a conductive filler and a rust inhibitor formed on a metal plate, and the main matrix resin constituting the resin coating layer is a flexible epoxy resin, Or it is characterized in that it is specified as a flexible epoxy resin and a polyester resin, and the bending elastic modulus of the resin coating layer is suppressed to 3 GPa or less.

  There are no particular restrictions on the metal plate on which the resin coating layer is formed. In addition to iron-based metal plates represented by the most versatile steel plates, non-ferrous metal plates such as copper, aluminum and titanium, and alloy plates containing them Is included. Prior to forming the resin coating layer, these metal plates may be subjected to plating treatment such as hot dip galvanization, electrogalvanization, etc., and by performing phosphate treatment or chromate treatment, Of course, it is also effective to further improve the corrosion resistance and adhesion. Especially when steel plates are applied, zinc-based plating (including hot dip galvanization and electrogalvanization) steel plates that exhibit an excellent rust prevention effect by sacrificial anodic action even when cracks and pinhole defects are formed in the coating. Preferably used. The shape of the metal plate is not limited. In addition to the most common flat plate shape, a deformed plate shape formed into a corrugated plate shape, an L shape, or a U shape by press molding, and a bowl shape or an annular shape. Etc. are also included.

  The resin coating layer formed on these metal plates contains a conductive filler and a rust preventive agent in order to ensure weldability and corrosion resistance, but it is possible to omit the resin coating after molding processing as a part of an automobile or the like. As a so-called post metal plate for the purpose, in order to ensure stable and excellent moldability, the main matrix resin of the coating layer is specified as a flexible epoxy resin, or an epoxy resin and a polyester resin, and the resin coating The bending elastic modulus of the layer is suppressed to 3 GPa or less.

  Various resins such as polyolefin resins, polyester resins, polyamide resins, aminoplast resins, phenolic resins, alkyd resins are known as resins for forming coating layers on metal plates used as automotive outer plate materials. The coating layer's corrosion resistance (salt water resistance), weather resistance, paint film adhesion, etc. are fully considered, but the flexibility of the coating itself is not so much considered, so the matrix resin also In particular, there is little recognition that one having excellent flexibility is selected.

  However, as a so-called post-coated steel sheet as in the present invention, in a resin-coated metal plate in which a resin coating layer is formed before the molding process, the molding process including the bending process is added after the resin coating is formed. Naturally, the bending force accompanying the processing is also applied to the resin coating layer. Therefore, even if it has excellent coating performance in the state before the molding process, the coating layer must not be peeled off due to bending or the like, and cracking or powdering should not occur. It must be able to guarantee moldability.

  Therefore, even when bending is performed after the resin coating is formed, the results of repeated studies on the resin coating that does not cause the coating defects as described above and can stably guarantee excellent moldability. As described above, if a flexible epoxy resin, or a flexible epoxy resin and a polyester resin are selected as the main matrix resin, and the bending elastic modulus of the resin coating layer is suppressed to 3 MPa or less, those requirements are satisfied. I knew that it would be possible to satisfy all the characteristics.

  By the way, when the bending elastic modulus of the resin coating layer exceeds 3 MPa, the resin coating layer peels off or cracks or powdering occurs when various molding processes are performed as automotive outer plate materials, etc. This is because the layer cannot be maintained. In order to ensure the required characteristics, a more preferable flexural modulus is 2.5 MPa or less. In addition, the flexible epoxy resin that satisfies the requirements for the flexural modulus means a characteristic that can withstand repeated bending of 300 times or more in a repeated bending test (MIT bending test) as shown in FIG. .

  The lower limit of the bending elastic modulus is not particularly limited, but if it is too low, obstacles such as the coating film being easily damaged appear, so it is preferably 1.0 MPa or more, more preferably 1.2 MPa or more. .

  Particularly preferred as a flexible epoxy resin that meets these required properties is a urethane-modified epoxy resin that has been improved in flexibility by introducing a urethane bond into the molecular structure of the epoxy resin, or is flexible by modification with dimer acid. Examples thereof include dimer acid-modified epoxy resins having improved properties.

  As the polyester resin, if the molecular weight is too small, the processability is lowered, and conversely, if the molecular weight is too large, it becomes difficult to dissolve in the solvent. Therefore, it is desirable to use a resin having a number average molecular weight of about 50,000 to 200,000. . This number average molecular weight is a value calculated in terms of polystyrene using a gel permeation chromatograph “150-CALC / GPC (GPC)” manufactured by Waters and using hexafluoroisopropanol as a solvent.

  The blending ratio of the flexible epoxy resin and the polyester resin is preferably flexible epoxy resin: 60 to 90% by mass and polyester resin: 10 to 40% by mass. This is because when the blending ratio of the polyester resin is less than 10% by mass, the alkali resistance of the coating film tends to be insufficient, whereas when it exceeds 40% by mass, the workability after the primary curing tends to decrease. The blending ratio of the flexible epoxy resin and the polyester resin is determined by calculating the absorbance of the absorption spectrum derived from the ester bond of the polyester obtained using a Fourier transform infrared spectrometer (FT-IR). This can be confirmed by quantifying the components (measurement of the blending ratio).

  Although there is no special restriction | limiting also in the hardening | curing agent used as a crosslinking agent of the said epoxy resin, The block isocyanate illustrated below, an melamine resin, and an amine type hardening | curing agent are preferable.

  (1) Blocked isocyanate: An isocyanate group blocked with caprolactam or oxime.

  (2) Melamine resin: n-butylated melamine resin, isobutylated melamine resin, methylated melamine resin and the like.

(3) Amine curing agent:
Aliphatic polyamines; diethylenetriamine, dipropylenetriamine, triethylenetetramine, tetraethylenepentamine, dimethylaminopropylamine, diethylaminopropylamine, dibutylaminopropylpyramine, hexamethylenediamine, N-aminoethylpiperazine, bis-aminopropylpiperazine , Trimethylhexamethylenediamine and the like.

  Alicyclic polyamines; 3,3′-dimethyl-4,4′-diaminodicyclohexylmethane, 3-amino-1-cyclohexylaminopropane, 4,4′-diaminodicyclohexylmethane, isophoronediamine, 1,3- Bis (aminomethyl) cyclohexane, N-dimethylcyclohexylamine, heterocyclic diamine and the like.

  -Aromatic polyamines; xylylenediamine, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenyl ether, diaminodiphenylsulfone, m-phenylenediamine, and the like.

  Polyamideamine; also called polyamide resin or polyaminoamide.

  Of the crosslinking agents, blocked isocyanates and melamine resins react with the hydroxyl groups of the epoxy resin, and amine curing agents react with the epoxy groups of the epoxy resin. The blending ratio of the epoxy resin and the crosslinking agent is 0.8 or more and 1.2 or less in a ratio of [equivalent of reactive functional group contained in epoxy resin] / [equivalent of reactive functional group in crosslinking agent]. Preferably they are 0.9 or more and 1.1 or less.

  In the present invention, as described above, it is important to have excellent workability in the state before the molding process and to have excellent corrosion resistance in the state after the molding process. It is desirable that two or more of the above-mentioned curing agents are used in combination with the epoxy resin main component, and the two-stage curing type is used. Specifically, at least two kinds of crosslinking agents having different crosslinking initiation temperatures or substantially the same crosslinking initiation temperature and different crosslinking reaction rates are used in combination, and in the state of the resin coating layer before molding processing, the crosslinking initiation temperature is A cross-linking agent having a relatively high or relatively low cross-linking reaction rate is left in an unreacted state, and only a cross-linking agent having a relatively low cross-linking initiation temperature or a relatively high cross-linking reaction rate is used. A certain degree of flexibility is retained in the resin coating layer by reacting and primary curing. Then, in the heat treatment process for paint baking generally performed after the molding process, the secondary curing is performed by reacting with a crosslinking agent having a high crosslinking initiation temperature or a slow crosslinking reaction rate that has remained in an unreacted state. Thus, excellent corrosion resistance is provided as the final resin coating layer.

  Here, the crosslinking reaction initiation temperature refers to a film obtained by mixing a base epoxy resin (or epoxy resin and polyester resin) and a crosslinking agent and forming a film at room temperature, using a differential thermal analysis (DTA) apparatus. And the temperature when the epoxy resin and the crosslinking agent start to react and start to generate an exothermic reaction.

  The crosslinking reaction rate was determined by using a thermosetting resin curing characteristic measuring device “JSR type curlastometer” manufactured by Ichuchu Machinery Co., Ltd., test temperature: normal temperature to 200 ° C., load resistance: 20 kgf at load cell rated load, Sample size: The outer diameter was 28 mm, the outer height was 8 mm, and the sample thickness was 2 mm. The curing curve of the test resin was measured and determined by the time required to cure 10 to 90% of the maximum load.

  The cross-linking agent A having a high cross-linking reaction start temperature is preferably one having a cross-linking reaction start temperature of 135 ° C. or higher, although it depends on the cross-linking reaction start temperature of the cross-linking agent B and the temperature of the final coating forming step. Blocked isocyanates are effective. In the melamine resin, mainly hydroxyl groups and active hydrogen react with the epoxy resin. Blocked isocyanates block active isocyanates using active hydrogen-containing compounds as blocking agents and volatilize the blocking agents by heating to activate them. By controlling the thermal dissociation temperature of the blocking agents, the crosslinking reaction initiation temperature Can be changed arbitrarily. Therefore, the blocked isocyanate can also be used as the crosslinking agent B having a low crosslinking reaction initiation temperature.

  As the crosslinking agent B having a low crosslinking reaction initiation temperature, a crosslinking agent exhibiting crosslinking reactivity at a temperature of about 130 ° C. or lower is preferable, and the above-mentioned blocked isocyanate or amine-based crosslinking agent is preferably used. In addition to the crosslinking agents A and B, it is of course possible to use another crosslinking agent having a crosslinking reaction initiation temperature therebetween.

  The crosslinking agent A is preferably a crosslinking agent that is slower than the crosslinking reaction rate of the crosslinking agent B and generally causes a crosslinking reaction at about 160 to 180 ° C. × 10 minutes. The crosslinking agent B is 140 to 150 ° C. × 1. A crosslinking agent that causes a crosslinking reaction in about a minute is preferred. That is, the cross-linking agents A and B merely mean a relative slow / fast cross-linking reaction rate, and neither is absolute. Of course, in addition to two kinds of crosslinking agents having different reaction rates, another crosslinking agent having a crosslinking reaction rate between them may be used in combination.

  The crosslinking agent A is preferably contained in the total amount of the resin coating layer in the range of 1 to 20% by mass, and if it is less than 1% by mass, the resin coating layer is insufficient in hardness and the corrosion resistance of the resin coating layer tends to decrease. Therefore, it is not preferable. More preferably, it is 2 mass% or more. However, if the amount exceeds 20% by mass, the amount of unreacted crosslinking agent increases and the strength of the coating film decreases, which is not preferable. More preferably, it is 10 mass% or less. On the other hand, if the cross-linking agent B is less than 1% by mass, it is inferior in scratch resistance, and if it exceeds 20% by mass, the cross-linking reaction of the primary cured product proceeds too hard and the workability is deteriorated. Absent. More preferably, it is 10 mass% or less. Further, if the total content of the crosslinking agents A and B (the total including those when other crosslinking agents are used in combination) exceeds 30% by mass, the secondary hardened layer becomes insufficient in corrosion resistance due to the remaining crosslinking agent. It is not preferable. More preferably, it should be suppressed to 20% by mass or less.

  In the resin-coated metal plate before molding processing according to the present invention, the crosslinking agents A and B are present in a state in which the crosslinking agent A is substantially unreacted with the epoxy resin, and the crosslinking agent B is an epoxy resin. It is ideal that it is contained in the resin coating layer in a reacted state. That is, a preferable resin coating layer includes a flexible epoxy resin that is primarily cured by a reaction between the epoxy resin constituting the matrix resin and the crosslinking agent B having the lowest crosslinking reaction initiation temperature or the fastest crosslinking reaction rate. The cross-linking agent A having the highest cross-linking reaction start temperature or the slowest cross-linking reaction rate remains in an unreacted state as a composite composition resin layer, and has appropriate flexibility. In addition, in the state after the resin-coated metal plate is molded and then subjected to the bake-curing treatment and secondarily cured, the crosslinking agent A also participates in the crosslinking reaction, and has a high crosslinking density and is strong and has excellent corrosion resistance. A coating will be formed.

  In addition, about the kind and compounding ratio of the crosslinking agent for primary curing and the crosslinking agent for secondary curing, the conditions at the time of forming as a post-coated metal plate, the baking curing conditions for the secondary curing, etc. It may be selected appropriately according to the situation. For example, when the present invention is applied to an automobile outer plate, a resin-coated steel material that has undergone primary hardening is molded by an automobile manufacturer, and heating for secondary hardening is performed in a paint baking process of a paint line. However, since the coating baking is usually performed at about 170 ° C. for about 20 to 30 minutes, the secondary curing crosslinking agent (crosslinking agent A) is made to correspond to the coating baking conditions. The cross-linking agent (cross-linking agent B) for the next curing is selected to cause a cross-linking reaction under the temperature and time conditions below that. As described above, the selection of the primary curing agent and the secondary curing crosslinking agent should be appropriately selected and determined each time according to the situation of the site where the resin-coated metal material of the present invention is applied, and is uniformly determined. It shouldn't be.

  In this invention, in addition to the said matrix resin component, the mixing | blending of the antirust agent shown below and an electroconductive filler is made essential. In other words, the rust preventive agent is for enhancing the corrosion resistance of the metal material by providing the resin coating layer itself with a rust preventive property, and the conductive filler is a spot welding widely used when put into practical use as an outer plate material for automobiles or ships. This is to cope with sex.

  Examples of preferred rust preventives are as follows.

1) Silica-based rust inhibitor:
・ Colloidal silica; “Snowtex O”, “Snowtex N”, “Snowtex 20”, “Snowtex 30”, “Snowtex 40”, “Snowtex C”, “Snowtex S” (all Nissan Chemical) (Trade name made by Kogyo)
Fumed silica; “AEROSIL R971”, “AEROSIL R812”, “AEROSIL R811”, “AEROSIL R974”, “AEROSIL R202”, “AEROSIL R805”, “AEROSIL 130”, “AEROSIL 200”, “AEROSIL 300”, “AEROSIL 300CF” and the like (both are trade names manufactured by Nippon Aerosil Co., Ltd.)
-Ion exchange silica; "SHIELDEX C3O3", "SHIELDEX AC-3", "SHIELDEX C-5" etc. (all are trade names manufactured by Fuji Silysia Chemical Co., Ltd.)
-Aluminum-modified silica; "Adelite AT-20A2" (trade name, manufactured by Nippon Aerosil Co., Ltd.)
2) Phosphate rust inhibitor:
・ Aluminum tripolyphosphate; “Taika K-WHITE 80”, “Taika K-WHITE 84”, “Taika K-WHITE 105”, “Taika K-WHIT G105”, “Taika K-WRITE 90”, etc. Product name),
・ Phosphate: Zinc phosphate, iron phosphate, aluminum phosphate, aluminum dihydrogen phosphate, phosphorus / zinc silicate, aluminum zinc phosphate, calcium zinc phosphate, etc.
・ Phosphonic acid, phosphonate; zinc phosphite, calcium phosphite, aluminum phosphite, etc.
3) Molybdate rust preventive: calcium molybdate, aluminum molybdate, barium molybdate, zinc calcium molybdate, zinc molybdate, etc.
4) Phosphorus / molybdate rust preventives; Phosphorus / aluminum molybdate, etc.
5) Phytic acid and phytate rust preventives;
6) Silicate (silicate) rust preventive agent; calcium silicate, amorphous magnesium silicate compound, etc.
7) Vanadium rust preventive agent; vanadium oxide, etc.
8) Vanadium acid / phosphoric acid mixture system rust inhibitor;
9) Polyaniline rust preventive agent; sulfonic acid doped polyaniline, etc.
10) Cyanamide-based rust preventive agent; cyanamide zinc, etc.
Is mentioned.

  Among the above rust preventives, aluminum tripolyphosphate, amorphous magnesium silicate, calcium ion exchange silica (“SHIELDEX C3O3”, etc.) is particularly preferably used in the present invention. Among these three types of rust preventives, aluminum tripolyphosphate and amorphous magnesium silicate compound are more preferable because they exhibit an effect of improving corrosion resistance superior to calcium ion-exchanged silica.

  The addition amount (content) of the anticorrosive agent contained in the resin coating layer in the present invention is preferably in the range of 5 to 25% by mass in terms of solid content, and if it is less than 5% by mass, the anticorrosion performance tends to be insufficient. On the other hand, if the amount exceeds 25% by mass, the moldability may be adversely affected. A more preferable blending amount of the rust inhibitor is 10% by mass or more and 20% by mass or less. In addition, content of the said rust preventive agent is the content, when only 1 type of the said 3 types of rust preventive agents extracted as a preferable thing is contained, and when 2 or more types are contained, those total content Amount.

  It is desirable to use the rust preventive agent after pulverizing the particle size to be equal to or less than the thickness of the resin coating layer (generally about 10 μm). This is because if the particle size of the rust inhibitor exceeds the thickness of the coating film, the workability deteriorates. The average particle size is preferably about 15 μm or less.

  Among the rust preventives, aluminum tripolyphosphate exhibits excellent rust preventive ability due to pH buffering action and passive film forming action. Of course, aluminum tripolyphosphate can be used as it is, but an Mg-treated product or Ca-treated product obtained by treating this with Mg or Ca is preferable because it exhibits better rust prevention performance.

  Further, the calcium ion-exchangeable silica also exhibits excellent rust prevention ability due to pH buffering action. A preferable concentration of the calcium component in the calcium ion-exchangeable silica is 1% by mass or more and 10% by mass or less.

  The amorphous magnesium silicate compound also exhibits excellent rust preventive ability due to pH buffering action and passive film formation. The amorphous magnesium silicate compound is produced by reacting an alkali metal silicate and a water-soluble magnesium salt in an aqueous solution using an Mg / Si atomic ratio of 0.025 to 1.0. The precipitate is filtered, then washed, dried and pulverized. Amorphous form can be confirmed by X-ray diffraction.

  Next, as the conductive filler blended for improving weldability, metal powder (Zn, Ni, Cu, Ti, Sn, Ag, Au, etc.), alloy powder (iron phosphide, ferrosilicon, ferroaluminum, Ferromanganese, AlMg, stainless steel, etc.) are exemplified, but iron phosphide is particularly preferred among these. This is because the use of iron phosphide as the conductive filler improves not only the weldability but also the moldability. Zinc rich paint (Zn), which is widely used for the purpose of preventing rust and improving conductivity, promotes powdering during processing, and should be used with care.

  When iron phosphide is used as the conductive filler, if the added amount (content) exceeds 60% by mass in the solid content ratio in the total amount of the resin coating layer, the weldability is improved but the workability is reduced. On the other hand, if it is less than 40% by mass, the workability is good but sufficient weldability is difficult to obtain. Therefore, the content of iron phosphide is preferably 40% by mass or more and 60% by mass or less, more preferably 45% by mass or more and 55% by mass or less.

  The particle size of the iron phosphide used as the conductive filler is preferably 15 μm or less, more preferably 12 μm or less in terms of the maximum particle size, and if it exceeds 15 μm, the workability deteriorates. In addition, although the particle size of iron phosphide is small, there is no problem, but those having a particle size of 6 μm or less are difficult to obtain as a commercial product, so the lower limit of the particle size is 6 μm. The particle diameter means a sphere equivalent diameter as described above.

  In addition to the above components, the resin coating layer may contain fumed silica as an anti-settling agent. Further, the resin coating layer further contains a diluent solvent, anti-skinning agent, leveling agent, antifoaming agent, emulsifier, colorant, thickener, film-forming aid as long as the object of the present invention is not impaired. It is also possible to contain these appropriately.

  The thickness of the resin coating layer is preferably 3 μm or more because if it is too thin, the rust prevention property is inferior and iron phosphide particles may be lost. On the other hand, it is preferable to set it as 15 micrometers or less from the point of weldability.

  There is no particular limitation on the method of forming the resin coating layer on the metal plate, and any composition such as a roll coating method, a spray method, a curtain flow coating method, or the like can be used for the composition constituting the resin coating layer. Then, it may be applied to one or both sides of a metal plate and dried by heating. In this case, the temperature or time of the heat drying is not less than the temperature at which the primary crosslinking reaction proceeds, that is, the temperature higher than the crosslinking reaction start temperature of the crosslinking agent B and less than the temperature at which the secondary crosslinking reaction does not occur, that is, the crosslinking agent A. A temperature lower than the crosslinking reaction initiation temperature, or a time longer than the time at which the primary crosslinking reaction proceeds, that is, a time longer than the time at which the crosslinking reaction of the crosslinking agent B ends, and less than the time at which the secondary crosslinking reaction starts, ie, the crosslinking agent. A time shorter than the crosslinking reaction start time of A is employed. The specific heat drying temperature and time vary depending on the types of the crosslinking agents A and B, but are usually about 80 to 120 ° C. and about 1 to 10 minutes.

  The heating temperature and heating time for the secondary curing performed after the molding process may be determined in consideration of the crosslinking reaction start temperature and the crosslinking reaction speed of the crosslinking agent A. Usually, heating for paint baking is used. More generally, it is performed at about 150 to 250 ° C. for about 20 to 40 minutes. By performing this secondary curing reaction, the resin coating layer having insufficient hardness in the state after the molding process, the unreacted crosslinking agent A left in the three-dimensional crosslinking is hardened and is excellent. Thus, a hard resin coating layer having excellent corrosion resistance and scratch resistance is formed.

  EXAMPLES Hereinafter, the present invention will be described in more detail with reference to examples. However, the present invention is not limited by the following examples as a matter of course, and appropriate modifications are made within a range that can meet the purpose described above and below. Of course, it is possible to implement them, and they are all included in the technical scope of the present invention. The test methods employed in the following examples are as follows.

[Crosslinking reaction start temperature]
A matrix resin (epoxy resin or epoxy resin and polyester resin) and a cross-linking agent are mixed and applied on a tetrafluoroethylene plate to a dry thickness of about 1 mm, and then dried at room temperature to form a film. Get a membrane. Using this dried coating film as a sample, the temperature was raised by heating using a differential thermal analysis (DTA) apparatus, and the crosslinking reaction initiation temperature was determined from the obtained chart as shown in FIG.

[Bend elastic modulus after primary curing]
1) Perform a three-point bending test using only an aluminum substrate, and determine the slope of the load-deflection diagram.
2) A three-point bending test is performed after forming a resin coating layer on the substrate, and the gradient of the load-deflection diagram is obtained in the same manner.
3) From the ratio of the gradients obtained in 1) and 2) above, obtain the flexural modulus of the resin film.
<Measurement conditions>
Measuring device: Intron's ultra-precision material testing machine "Mode 15848"
Load cell used: 10N capacity,
Measurement method: Crosshead displacement method,
Measurement temperature: 23 ° C (room temperature),
Distance between fulcrums: 40mm,
Test speed: 0.5 mm / min,
Data processing: Intron data processing system “Merlin”,
Test piece shape: See FIG.

[Processability after primary curing]
1) Perform deep drawing under the following conditions.
Unloading: Diameter 90 mm, Punch: 50 mm, Die: 52 mm, BHF (wrinkle pressing pressure): 980 N, Molding speed: 160 mm / min),
2) Forced tape peeling on the surface after processing,
3) Measurement of weight loss,
<Criteria>
-○: Less than 3 g / m ² (excellent),
Δ: 3 g / m ² or more and less than 5 g / m ² (good),
*: 5 g / m ² or more (defect).

[Corrosion resistance after secondary curing]
1) Preparation of the alignment sample: After the alignment sample is prepared as shown in FIGS. 3 and 4, the following processing (according to a general automobile coating method) is performed.
1-1) Alkaline degreasing (treated with 3% aqueous sodium orthosilicate solution at 40 ° C for 2 minutes),
1-2) Washing with water (30 seconds),
1-3) Phosphate treatment (60 ° C x 2 minutes using the following phosphoric acid aqueous solution),
Phosphoric acid aqueous solution (Nippon Parkerizing Co., Ltd., trade name “Palbond L3080”), acid concentration in the solution is TA: 23Po, FA: 0.9Po, where Po is 10N phosphoric acid aqueous solution with 0.1N NaOH Represents the amount required to titrate, TA as an indicator; phenolphthalein or FA; value using bromophenol,
1-4) Cationic electrodeposition coating (target film thickness: 20 μm),
2) The corrosion resistance cycle test shown in FIG.
3) Judgment criteria;
Open the sample after 20 cycles and check the red rust occurrence rate of the mating part and evaluate it according to the following criteria.
○: Less than 0.5%, Δ: 0.5% or more and less than 5%, ×: more than 5%.

[Weldability after secondary curing]
Perform continuous spot welding under the following test conditions, and evaluate the number of times that continuous spotting is possible
<Test conditions>
-Tip diameter: 6 mm
・ Pressure force: 200 kgf,
・ Energization cycle: 12 cycles
-Welding current: 8.0 kA,
<Criteria>
*: Less than 400 dots (poor weldability),
Δ: 400 or more and less than 600 (permissible range)
・ ○: 600 points or more, less than 800 points (good),
・ ◎: More than 800 dots (excellent weldability).

[Alkali resistance test after primary curing]
After performing spray degreasing under the following conditions, the surface gloss of the portion where the spray is applied is visually observed and evaluated according to the following criteria.
<Spray degreasing conditions>
-Spray solution composition: sodium orthosilicate aqueous solution (2%) manufactured by Nihon Parkerizing Co., Ltd.
・ Spray pressure: 0.7kg,
-Distance from spray to sample plate; 145mm,
・ Spray pattern: cone,
・ Washing after degreasing; 30 seconds,
<Evaluation criteria>
・ ○: No shine
・ △: There is shine.

Experimental Example 1) After blending epoxy resin (or epoxy resin and polyester resin) and a curing agent in the formulation shown in Table 1, conductive filler (iron phosphide or zinc powder) and rust inhibitor in the ratio shown in Table 2 (Aluminum tripolyphosphate or magnesium / silica) and an anti-settling agent (trade name “R972” manufactured by Nippon Aerosil Co., Ltd.) are added. In addition, each compounding raw material is dissolved and dispersed in a mixed solvent of xylene / propylene glycol monomethyl ether acetate / n-butanol = 4/3/1 (mass ratio) so that the solid content concentration is 50% by mass. Prepared.

  2) While cooling the formulation obtained above, it is stirred for 10 minutes at 3000 rpm using a homogenizer.

  3) Using the uniform dispersion obtained above, apply a non-chromate ground treatment on an alloyed hot-dip galvanized steel sheet with a bar coater so that the dry coating thickness is 10 μm.

  4) The coated steel sheet is placed in a continuous heating furnace and heated at PMT (maximum temperature reached) 140 ° C. to remove the solvent and perform primary curing.

  5) A workability evaluation test is performed using the obtained primary cured resin-coated steel sheet.

  6) Further, the 4) obtained primary cured resin-coated steel sheet is secondarily cured by heating at 230 ° C. PMT.

  7) The secondary cured resin-coated metal plate is subjected to corrosion resistance and weldability evaluation tests.

  The results are collectively shown in Table 3.

It is a model figure of a DTA chart for explaining a crosslinking reaction start temperature. It is a schematic diagram which shows the test piece shape for a bending elastic modulus measurement. It is plane explanatory drawing which shows the assembly | attachment of the combined sample for a corrosion resistance test. Similarly, it is side explanatory drawing which shows the assembly | attachment of the matching sample for a corrosion resistance test. It is explanatory drawing which shows the cycle test method for corrosion resistance evaluation. It is explanatory drawing which shows the repeated bending test method used for the characteristic evaluation of a flexible epoxy resin.

Claims (13)

  A resin coating layer containing a conductive filler and a rust preventive agent is formed on a metal plate, and the matrix resin constituting the resin coating layer is mainly composed of a flexible epoxy resin and has a flexural modulus of 3 GPa or less. A resin-coated metal plate excellent in workability, weldability and corrosion resistance.   The resin-coated metal plate according to claim 1, wherein the matrix resin contains a polyester resin.   The resin-coated metal plate according to claim 1 or 2, wherein the flexible epoxy resin is a urethane-modified epoxy resin and / or a dimer acid-modified epoxy resin.   The resin-coated metal plate according to claim 2 or 3, wherein the matrix resin contains flexible epoxy resin: 60 to 90 mass% and polyester resin: 10 to 40 mass%.   The resin-coated metal plate according to any one of claims 1 to 4, wherein the epoxy resin uses at least one selected from the group consisting of a blocked isocyanate, a melamine resin, and an amine resin as a crosslinking agent.   The resin-coated metal plate according to claim 1, wherein the conductive filler is iron phosphide.   The resin-coated metal sheet according to any one of claims 1 to 6, wherein the rust inhibitor is at least one selected from the group consisting of aluminum tripolyphosphate, amorphous magnesium silicate, and calcium ion exchange silica.   The resin-coated metal plate according to any one of claims 1 to 7, wherein each of the conductive filler and the rust inhibitor is a powder having a maximum particle size of 15 µm or less.   The resin-coated metal plate according to claim 1, wherein the metal plate is plated.   The resin coating layer contains a matrix resin: 25% by mass to 55% by mass, a conductive filler: 40% by mass to 55% by mass, and a rust inhibitor: 5% by mass to 25% by mass. Item 11. The resin-coated metal plate according to any one of Items 1 to 9.   As the matrix resin, an epoxy resin or an epoxy resin and a polyester-based resin have different crosslinking reaction initiation temperatures, or two or more kinds of crosslinking agents having the same crosslinking initiation temperature and different crosslinking reaction rates are used. When the crosslinking agent having the highest reaction initiation temperature or the slowest crosslinking reaction rate is the crosslinking agent A, and the crosslinking agent having the lowest crosslinking reaction initiation temperature or the fastest crosslinking reaction rate is the crosslinking agent B, the resin coating layer The resin-coated metal plate according to any one of claims 1 to 10, wherein a primary curing reaction product of an epoxy resin or an epoxy resin and a polyester-based resin and a crosslinking agent B and an unreacted crosslinking agent A are included. .   A resin-coated metal plate on which the resin coating layer according to claim 11 is formed, which includes a conductive filler, a rust preventive agent, and a crosslinking agent on the plated metal plate and has a flexural modulus of 3 GPa or less, A resin-coated metal sheet processed article excellent in weldability and corrosion resistance, characterized by being subjected to secondary curing by reacting with an unreacted crosslinking agent A simultaneously with or after the molding process. A resin-coated metal plate on which a resin coating layer according to claim 11 is formed, which includes a conductive filler, a rust inhibitor, and a crosslinking agent and has a flexural modulus of 3 GPa or less on the metal plate, At the same time as the molding process or after the molding process, the crosslinking agent A is heated at or above the crosslinking reaction start temperature and / or the crosslinking reaction start time, and the unreacted crosslinking agent A is reacted to perform secondary curing. Of resin-coated metal sheet processed products with excellent heat resistance and corrosion resistance.

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