WO2009147911A1 - Solution for self-depositing coating treatment of metal materials and self-depositing coating treatment method - Google Patents

Abstract

The issue is to provide a solution for a self-depositing coating treatment for which the process length has been shortened compared to prior coating processes, that generates almost no by-products that are harmful to the environment such as sludge, that has excellent throwing power in bag-structured interiors, that does not use components that are harmful to the environment such as chromium compounds, that has anti-corrosion properties, and with which a baked finish can be applied to the obtained coating. The solution for a self-depositing coating treatment of metal materials is an aqueous solution comprising a novolak resin having methylol groups, a cross-linking agent, ferric ions, a fluorine component and an oxidant. The above cross-linking agent is a cross-linking agent that has cross-linking groups that can undergo heat-curing reactions with said methylol groups, phenol nuclei and/or phenolic hydroxyl groups. The solids weight concentration ratio of the above novolak resin to the above cross-linking agent is in the range of 1:1 to 1:10. The molar concentration of the above fluorine component is at least 3 times that of the above ferric ions and the pH is in a range of 2 to 6.

Description

Self-deposited coating treatment liquid for metal material, and self-deposited coating treatment method

The present invention can be used alone on a surface of an iron-based metal material that requires corrosion resistance and may be overcoated depending on the application, such as automobile bodies, automobile parts, steel furniture, and home appliances. TECHNICAL FIELD The present invention relates to a surface treatment solution for autodeposition coating treatment for depositing an organic coating having sufficient corrosion resistance and capable of being repeatedly applied with a chemical reaction, a self-deposition coating treatment method, and a metal material having an autodeposition coating. .

Most industrial products using metal materials are painted except for some special applications and materials. The purpose of painting is to prevent oxidation, that is, corrosion, which is the fate of metal, as well as improving aesthetics. Here, the paint used for the metal material can be classified in various ways according to the coating method and components, and is selected according to the performance required for the material to be coated and the possible coating method. Here, when the material to be coated has a complicated structure and a high degree of corrosion resistance is required, such as an automobile body, it is necessary to secure a coating thickness inside the bag structure part called throwing power. is important.

A general method used to ensure corrosion resistance inside the bag structure is a combination of zinc phosphate treatment, which is a chemical conversion treatment for the coating base, and cationic electrodeposition coating. In any method, since the material to be coated is immersed in the treatment bath for chemical conversion treatment and coating, the inside of the bag structure can be brought into contact with the chemical conversion treatment liquid and the paint. However, the zinc phosphate treatment process is hot water washing → preliminary degreasing → degreasing → multistage water washing (usually 2 to 3 stages) → surface adjustment → film formation → multistage water washing (usually 2 to 3 stages) → ion exchange water washing, The cationic electrodeposition coating process is electrodeposition → multi-stage water washing (usually 3 to 5 stages) → ion-exchange water washing → baking, so the treatment process is very long. For example, in the case of an automobile body, the process length exceeds 200 m. It becomes.

In the zinc phosphate treatment process, as is conventionally known, the generation of iron phosphate sludge, which is a side reaction of the film deposition reaction, is unavoidable, and improvement is desired from the viewpoint of environmental problems. In addition, although the recent cationic electrodeposition coatings have been improved, the coating film is deposited by electrolysis, and the coating film is deposited by the electrical resistance of the deposited coating. Occurrence of a difference in film thickness between the plate portion and the inside of the bag structure portion where the coating film is deposited with a delay is an unavoidable problem.

Therefore, technology has been proposed for a long time to solve the problem of iron phosphate sludge generation and the film thickness inside the bag structure, while shortening the process by depositing an organic film by chemical reaction. Such compositions are referred to as autodeposition compositions, or autodeposition compositions, or autodeposition compositions.

For example, Patent Document 1 relates to an autodeposition composition using a vinylidene chloride copolymer. Since vinylidene chloride resin is very excellent in moisture resistance, moisture resistance, and gas barrier properties, it has a very large inhibitory action against corrosion when formed into a coating film. However, as is well known, vinylidene chloride resin has very low heat resistance. Therefore, Patent Document 1 discloses that heat resistance can be improved by copolymerizing a vinylidene chloride monomer with a comonomer such as an acrylic comonomer and inserting a stable comonomer into the chain by heat. However, even if a stable site is inserted in the chain, the low heat resistance of the vinylidene chloride basic structure cannot be fundamentally improved. Therefore, the autodeposition technology using vinylidene chloride is not only applicable to metal materials used in environments exposed to high temperatures, but also cannot be overcoated by baking coating on the autodeposition coating. Had.

Many autodeposition compositions that do not use vinylidene chloride are also disclosed. Examples of resin components used in the autodeposition composition other than vinylidene chloride include styrene butadiene, acrylic polymers and copolymers thereof, polyvinyl chloride, polyethylene, as cited in Patent Documents 2, 3 and 4. Polytetrafluoroethylene, acrylonitrile butadiene and urethane resins are disclosed.

However, in any of the methods, the corrosion resistance of the autodeposition coating film was significantly lower than that using vinylidene chloride. Therefore, in order to improve the corrosion resistance, as shown in Patent Document 3, it is necessary to perform a post-treatment using a chromium compound whose use is currently restricted from the viewpoint of environmental problems after the autodeposition coating.

Therefore, an autodeposition composition combining an epoxy resin and a crosslinking agent has been recently proposed as shown in Patent Document 5. However, as a result of verifying the effects of the present invention by the present inventors, it is difficult to say that the autodeposition coating film using the epoxy resin has sufficient corrosion resistance and the adhesion to the solvent paint is extremely low. And found that it has a fatal defect that can not be overpainted.

Patent Documents 6 and 7 disclose an aqueous coating composition that can be automatically deposited on a metal support, which is made of a water-dispersible phenol resin and a softener polymer. However, since the autodeposition coating film before baking obtained by this method contains a large amount of moisture, the coating film before baking cannot be washed with water. Therefore, there is no problem if it is a flat material to be coated, but in the case of a material having a bag structure part, the paint remaining inside the bag structure part cannot be washed out. Serious defects that significantly affect the corrosion resistance.

Therefore, in the prior art, the process length is shortened compared with the coating process consisting of a combination of zinc phosphate treatment and electrodeposition coating, and no by-product harmful to the environment such as sludge is generated. Providing an auto-deposition coating that has excellent throwing power, does not use environmentally harmful components such as chromium compounds, has corrosion resistance, and can be further baked on top of the resulting coating It was impossible to do.

JP 60-58474 JP 47-32039 JP 48-13428 JP 61-168673 JP2003-176449 Special table 2002-501100 Special Table 2002-501124

The purpose of the present invention is to solve the problems of the prior art. In other words, the process length is shortened compared to the coating process consisting of a combination of zinc phosphate treatment and electrodeposition coating, and almost no by-products that are harmful to the environment such as sludge are produced. Provided is a surface treatment solution for treating a self-deposited film, which is excellent, does not use environmentally harmful components such as chromium compounds, has corrosion resistance, and can be further baked onto the obtained film. That is.

As a result of intensive studies on means for solving the above problems, the present inventors have invented a surface treatment solution for autodeposition coating treatment, a method for autodeposition coating treatment, and a metal material having an autodeposition coating that is not found in the prior art. It came.

That is, the surface treatment liquid for autodeposition coating treatment according to the present invention comprises a resole resin obtained by reacting phenols and aldehydes in the presence of an alkali catalyst in the F / P ratio range of 2.5 to 3. , Obtained by mixing and stirring a hydroxyphenol having two or more hydroxyl groups on adjacent aromatic ring carbon and a phenol, further adding a phenol, an aldehyde and an acid catalyst, and polymerizing the F / A novolak resin having a methylol group having a P ratio of 0.7 to 1.0, and a crosslinking agent having a crosslinking group capable of thermosetting reaction with the methylol group, phenol nucleus and / or phenolic hydroxyl group, The solid content mass concentration ratio with the crosslinking agent is in the range of 1: 1 to 1:10, and the ferric ion and at least three times the mole of the ferric ion And every elemental fluorine (preferably dissolved elemental fluorine in), further comprising an oxidizing agent is an aqueous solution in the range pH of 2 to 6.

The novolak resin preferably has at least a methylol group substituted with an aromatic ring and a phenol moiety having two or more hydroxyl groups on adjacent aromatic ring carbons, and has a structural formula shown in Formula 1. More preferred.

Wherein m and n are integers of 1 to 5, p is an integer of 0 to 5, R1 is methylol, R2 is independently hydroxyl or alkylaryl, R3 is independently methylol, hydroxyl or alkylaryl, a is 0 or 1)

It is preferable that the crosslinking group capable of thermosetting reaction of the crosslinking agent is an isocyanate group.

Further, the cross-linking agent is preferably a polyfunctional blocked isocyanate obtained by adding at least 2 mol of polyisocyanate in which one isocyanate group is blocked with a blocking agent to 1 mol of polyol.

Moreover, it is preferable that the polyol in the crosslinking agent has a bisphenol A structure of at least one molecule.

The concentration of the novolak resin is preferably 1 to 5% by mass as the solid content concentration in the aqueous solution.

It is preferable that the oxidizing agent is at least one selected from perchloric acid, hypochlorous acid, dissolved oxygen, ozone, permanganic acid, and hydrogen peroxide.

The oxidation-reduction potential of the surface treatment solution for autodeposition coating treatment measured with a platinum electrode is preferably 300 to 500 mV.

In addition, the present invention is a method in which a metal material is previously degreased and cleaned with a water washing treatment, and then contacted with the aqueous solution described in the surface treatment solution for autodeposition coating treatment. This is a metal material self-deposition coating treatment method, wherein the coating film is thermally cured by removing excess treatment liquid adhering to the substrate and then performing a baking treatment.

Further, the present invention has an autodeposition coating layer deposited on the surface of an iron-based metal material by the above method, and the thickness of the autodeposition coating layer after baking hardening is 10 to 30 μm. It is a metal material.

Here, the meaning of each term used in the claims and the specification will be described. As long as the “ferric ion” is an ion represented by Fe ³⁺ , the existence form in the treatment liquid for surface treatment is not particularly limited, and for example, indicates a state in which Fe ³⁺ or a ligand is coordinated. . Examples of conditions elemental fluorine is coordinated to ferric ^{_ion, FeF 2+,} FeF 2 ^+, can be cited FeF ₃ and the like. The “elemental fluorine” is not particularly limited to its form such as a molecular state or an ionic state, and means the whole elemental fluorine supplied by a fluorine-containing compound such as hydrogen fluoride and / or a salt thereof. Furthermore, the concentration of “elemental fluorine” is the total molar concentration of various elements of fluorine present in the system. For example, elemental fluorine supplied by the fluorine-containing compound depending on the pH of the aqueous _{^{solution, F -, HF, HF 2}} - can take the dissociated form, such as, a concentration of the fluorine element as referred to herein, all in an aqueous solution The total molar concentration of F. Further, when a complex is formed with ferric ions, the complex includes “ferric ions” and also includes “fluorine element”. The “dissolved fluorine element” is not particularly limited to its form such as molecular state or ion state, but is present as solid particles without being dissolved in the surface treatment liquid for autodeposition coating treatment of the present invention. Fluorine elements contained in salts and the like are excluded. Furthermore, the concentration of “dissolved fluorine element” is the total molar concentration of various dissolved fluorine elements present in the system. The “novolak resin” means a resin obtained by polymerizing phenols with aldehydes under an acid catalyst. “Resol” means a resin obtained by polymerizing phenols with aldehydes in the presence of an alkali catalyst. Here, “phenol” means an aromatic compound having a phenolic hydroxyl group. “Aldehydes” are compounds having one or more aldehyde groups in one molecule or compounds that can easily generate aldehyde groups in a reaction system. “Alkyl” means C1-C10 linear or branched, substituted or unsubstituted alkyl. “Aryl” is a substituted or unsubstituted C6-C14 1- to 3-cyclic aryl (wherein one or more C atoms constituting the ring may be substituted with S, N, or O). Means.

By using the surface treatment liquid for autodeposition coating treatment of the present invention, hot water washing → preliminary degreasing → degreasing → multistage water washing (usually 2 to 3 stages) → surface adjustment → film formation → multistage water washing (usually 2 to 3 stages) → Ion exchange water washing → Electrodeposition coating → Multi-stage water washing (usually 3 to 5 stages) → Ion exchange water washing → Baking process compared to the conventional process consisting of a combination of zinc phosphate treatment and electrodeposition coating It can be shortened. Furthermore, according to the method of the present invention, no by-product harmful to the environment such as sludge is produced, and no harmful components such as chromium compounds are used in the autodeposition coating treatment bath, so the influence on the environment is small. Moreover, since the self-deposited film of the present invention has excellent corrosion resistance and excellent throwing power inside the bag structure, it is effective for improving the corrosion resistance of an object having a complicated structure. Furthermore, the autodeposition coated metal material of the present invention can be baked over the autodeposition coating. Therefore, it can be used in combination with various coatings.

By using isocyanate as the cross-linking agent, it is possible to form an autodeposition coating with better corrosion resistance.

By using polyfunctional blocked isocyanate as a cross-linking agent, it is possible to form an autodeposition film with even better corrosion resistance.

By using a cross-linking agent having at least one molecule of bisphenol A structure, an effect of forming a self-deposited film having further excellent corrosion resistance can be obtained.

When the concentration of the novolak resin is 1 to 5% by mass as the solid content concentration in the aqueous solution, the film has a sufficient film thickness to obtain corrosion resistance and the consumption of components can be suppressed.

When the novolak resin and the cross-linking agent have a solid mass concentration ratio of 1: 1 to 1:10, a uniform autodeposition coating appearance can be obtained and corrosion resistance can be improved.

By making the oxidant at least one selected from perchloric acid, hypochlorous acid, dissolved oxygen, ozone, permanganic acid, and hydrogen peroxide, the self-deposition coating treatment liquid is self-impaired without impairing the stability. There is an effect of promoting the precipitation reaction.

By setting the redox potential measured at the platinum electrode to 300 to 500 mV, there is a sufficient amount of oxidant to oxidize all the iron ions present in the bath to ferric ions and maintain their oxidation state. Thus, the precipitation reaction of the autodeposition film can be promoted and the destabilization of the autodeposition film treatment liquid due to ferrous ions can be suppressed.

According to the autodeposition coating treatment method according to the present invention, by using the treatment liquid according to the present invention, there is an effect that an autodeposition coating having more excellent corrosion resistance can be formed.

Since the metal material is an iron-based metal material, it is easier to form a self-oxidation film, and the film having excellent corrosion resistance can be formed.

The inventors of the present invention have disclosed a metal material, a resole resin obtained by reacting a phenol and an aldehyde with an F / P ratio in the range of 2.5 to 3 in the presence of an alkali catalyst, and an adjacent aromatic ring carbon. The F / P ratio obtained by mixing and stirring a hydroxyphenol having two or more hydroxyl groups and a phenol, and adding and polymerizing a phenol, an aldehyde and an acid catalyst is 0.7. A solid content of the novolak resin and the crosslinking agent comprising a novolak resin having a methylol group of ˜1.0 and a crosslinking agent having a crosslinking group capable of thermosetting reaction with the methylol group, phenol nucleus and / or phenolic hydroxyl group. A mass concentration ratio in the range of 1: 1 to 1:10, ferric ions, at least a three-fold molar concentration of fluorine elements of ferric ions, and an oxidizing agent; Further comprising, by contact with the surface treatment solution pH ranges from 2 to 6, it was made possible to be deposited the autodeposition coating having excellent corrosion resistance on a metal material surface.

Furthermore, the novolac resin preferably has the structural formula shown in Formula 1.

Wherein m and n are integers of 1 to 5, p is an integer of 0 to 5, R1 is methylol, R2 is independently hydroxyl or alkylaryl, R3 is independently methylol, hydroxyl or alkylaryl, a is 0 or 1)

The surface treatment liquid for autodeposition coating treatment of the present invention can be applied to ferrous metal materials and galvanized steel sheets. However, the most suitable metal material is an iron-based metal material. The iron-based metal material here refers to steel-based metals such as cold-rolled steel plates and hot-rolled steel plates, and iron-based metals such as cast iron and sintered materials.

Applications of the metal material of the present invention are automobile bodies, automobile parts, steel furniture, home appliances, etc., and depending on each application, only the self-deposited film of the present invention or other top coating such as solvent coating Can be used in combination.

The novolak resin containing at least one methylol group in the basic molecular structure is one of the essential components in the present invention. The present invention is a surface treatment solution for treating an autodeposition coating of a metal material, wherein the iron-based metal material is brought into contact with a specific aqueous solution. Therefore, the components used in the treatment method of the present invention must first be water-soluble or water-dispersible. Furthermore, the resin component that is the main component of the self-deposited film must have self-deposition property to the ferrous metal material under the treatment conditions presented in the present invention, and the thermosetting property in the baking treatment after self-deposition. It is necessary to have both.

The present inventors have found that by using a novolak resin having a special structure shown in Formula 1, the conditions necessary for the present invention can be satisfied and excellent performance can be obtained. In Formula 1, m and n are integers of 1 to 5, p is an integer of 0 to 5, R1 is methylol, R2 is independently hydroxyl or alkylaryl, R3 is independently methylol, hydroxyl or alkylaryl, a is 0 or 1. Further, preferred alkylaryl of R2 and R3 is a benzyl group or a tolyl group.

Resins generally called novolak resins and resol resins are polymerized using phenols and aldehydes. Here, the reaction molar ratio at the time of reacting phenols (P) and aldehydes (F) is called F / P ratio. A resin generally referred to as a novolak is obtained by polymerizing phenols with aldehydes using an acid catalyst. Novolac is polymerized with a small F / P ratio in order to prevent the molecular structure from becoming three-dimensional, and aldehydes added to phenols are used in the polymerization reaction of phenols. Therefore, even when formaldehyde is used as an aldehyde, in the novolak resin generally referred to, formaldehyde is used for polymerization of phenols, and there is no methylol group due to addition of formaldehyde. The novolak resin according to the best mode is not particularly limited, but the F / P ratio is preferably 0.7 to 1.0, more preferably 0.75 to 0.95, and 0.75 to 0. .9 is more preferred.

A novolak resin having no methylol group is not suitable for the use of the present invention because it has a remarkably low affinity with water and does not disperse in water and does not have a functional group that is crosslinked by heat. A resol resin that polymerizes formaldehyde and phenols at a high F / P ratio under an alkali catalyst is a thermosetting resin having a methylol group, but the stability of the aqueous dispersion in an acidic aqueous solution is remarkable. Since it is low, it cannot be used in the present invention.

The novolak resin represented by Formula 1 used in the present invention has at least one methylol group. By having a methylol group, thermosetting is imparted to the novolac resin. Furthermore, by having a methylol group, the hydrophilicity of the novolak resin can be improved. However, sufficient water solubility and water dispersibility cannot be provided only by methylol groups. In addition, novolak resin only provided with a methylol group cannot obtain autoprecipitation. Therefore, by introducing dihydroxyphenol having an ionic group into a novolak resin having a methylol group, its water solubility and water dispersibility were improved, and autoprecipitation was further imparted.

As shown in Formula 1, 2,3-dihydroxynaphthalene-6-sulfonic acid is most preferable as the dihydroxyphenol having an ionic group used in the novolak resin of the present invention. Sulfonic acid groups can impart sufficient water solubility and water dispersibility to the novolak resin, and self-precipitating properties can be imparted by two ortho-hydroxy groups. In the synthesis of the novolak resin, 2,3-dihydroxynaphthalene-6-sulfonic acid alkali metal salt can be used.

The novolak resin having a methylol group in the structural formula shown in Formula 1 used in the present invention reacts phenols with aldehydes in advance under an alkaline catalyst, preferably at an F / P ratio in the range of 2.5 to 3. After synthesizing the resole resin, 2,3-dihydroxynaphthalene-6-sulfonic acid sodium salt and phenols were mixed and stirred in the resole resin, and further polymerized by adding phenols, aldehydes and an acid catalyst. Can be synthesized. The final novolak F / P ratio is the molar ratio of all phenols (including hydroxyphenols) and aldehydes. Therefore, the phenols and aldehydes used in the resol resin synthesis are also included in the final F / P ratio. Further, whether or not a methylol group is present in the synthesized novolak resin can be determined by measuring the absorption of the methylol group appearing in the vicinity of 1000 cm ⁻¹ by infrared spectroscopy.

Here, phenol, catechol, resorcinol, pyrogallol, cresol and the like can be used as phenols, and formaldehyde, acetaldehyde, acetone, benzaldehyde and the like can be used as aldehydes. Among these, the most preferred aldehyde is formaldehyde marketed as formalin.

As the crosslinking group of the crosslinking agent having a methylol group, a phenol nucleus, and a crosslinking group capable of thermosetting reaction with a phenolic hydroxyl group used in the present invention, a methylol group, a carboxyl group, a glycidyl group, and a secondary class in which a glycidyl group is opened An alcohol group, an isocyanate group, and the like can be used, and among them, an isocyanate group is preferable.

Further, the cross-linking agent is preferably a polyfunctional blocked isocyanate obtained by adding at least 2 mol of polyisocyanate in which one isocyanate group is blocked with a blocking agent to 1 mol of polyol. Isocyanate groups are optimal as the crosslinking agent of the present invention, because the blocking with a blocking agent can suppress the reaction with water, and the application of heat causes the blocking agent to dissociate and cause a crosslinking reaction. .

As the polyisocyanate that can be used in the present invention, known ones can be used. For example, 1,4-tetramethylene diisocyanate, ethyl (2,6-diisocyanato) hexanoate, 1,6-hexamethylene diisocyanate, 1,12-dodecamethylene diisocyanate, 2,2,4- or 2,4,4 -Aliphatic diisocyanates such as trimethylhexamethylene diisocyanate, 1,3,6-hexamethylene triisocyanate, 1,8-diisocyanate-4-isocyanatomethyloctane, 2-isocyanatoethyl (2,6-diisocyanate) Nato) diisocyanate having a cyclic structure such as aliphatic triisocyanate such as hexanoate and isophorone diisocyanate, m- or p-phenylene diisocyanate, toluene-2,4- or 2,6-diisocyanate, diphenylmethane 4,4'-diisocyanate, naphthalene-1,5-diisocyanate, diphenyl-4,4'-diisocyanate, 4,4'-diisocyanate-3,3'-dimethyldiphenyl, 3-methyl-diphenylmethane-4,4 Aromatic diisocyanates such as' -diisocyanate and diphenyl ether-4,4'-diisocyanate can be used.

The polyisocyanate suitable for the present invention is 1,6-hexamethylene diisocyanate from the viewpoint of the flexibility of the resulting film, and toluene-2,4- or 2,6-diisocyanate from the viewpoint of the reactivity of the isocyanate group. .

As the isocyanate group blocking agent used in the present invention, known ones can be used. For example, alcohol such as methanol, ethanol, n-propyl alcohol, iso-propyl alcohol, n-butyl alcohol, iso-butyl alcohol, tert-butyl alcohol, phenol, methylphenol, chlorophenol, p-iso-butylphenol, p Phenols such as tert-butylphenol, p-iso-amylphenol, p-octylphenol, p-nonylphenol, active methylene compounds such as malonic acid dimethyl ester, malonic acid diethyl ester, acetylacetone, methyl acetoacetate, ethyl acetoacetate, Such as formaldoxime, acetoaldoxime, acetone oxime, cyclohexanone oxime, acetophenone oxime, benzophenone oxime, 2-butanone oxime, etc. Shim acids, .epsilon.-caprolactam, .delta.-valerolactam, lactams such as γ- butyrolactam, and thiosulfate salts.

By selecting a blocking agent having a low dissociation temperature from the isocyanate group, the baking temperature of the coating in the autodeposition coating treatment of the present invention can be lowered. However, when the dissociation temperature is too low, the stability of the surface treatment solution for autodeposition coating treatment may be impaired. Therefore, it is preferable to use oximes such as formaldoxime, acetoaldoxime, acetone oxime, cyclohexanone oxime, acetophenone oxime, benzophenone oxime, 2-butanone oxime, and thiosulfate. The blocking agent used here is preferably ½ times the molar amount when the polyisocyanate to be used is a diisocyanate and 2/3 times the molar amount when it is a triisocyanate. When the blocking agent is used, the reaction with the water of the crosslinking agent after reacting with the polyol is suppressed, and heat is applied to the autodeposition coating before baking while maintaining the stability of the autodeposition surface treatment solution. This has the effect of curing the coating film.

Examples of polyols that can be used in the present invention include polyether polyols such as polypropylene glycol, polyethylene glycol, and polytetramethylene glycol, polyethylene abates, polydiethylene abates, polypropylene abates, polytetramethylene abates, and poly-ε. -Polyester polyols such as caprolactone, polycarbonate polyols, acrylic polyols, epoxy polyols, trimethylolpropane, bisphenol A, bisphenol F, bisphenol AD and the like.

Among them, epoxy polyol and bisphenol A having at least one molecule of bisphenol A structure in the molecular structure are preferable. Here, “having at least one molecule of bisphenol A structure” means that the polymer is incorporated in a linear chain of a polymer such as the epoxy polyol or has a bisphenol A repeating unit in part. Or a homopolymer of bisphenol A or bisphenol A itself. Bisphenol A has a benzene ring in the basic skeleton, and since the two benzene rings are connected by a methylene chain with two methyl groups, the resin itself has robustness (rigidity) and high chemical resistance. is a structure that has both _{(HO-C 6 H 4 -C} (CH 3) 2 -C 6 H 4 -OH). Therefore, the use of a polyol having a bisphenol A structure in the polyfunctional blocked isocyanate of the present invention dramatically improves the corrosion resistance obtained by the present invention.

The concentration of the novolak resin is preferably 1 to 5% by mass, more preferably 1 to 3% by mass as the solid content concentration in the aqueous solution. As described above, the novolak resin having a methylol group has autoprecipitation properties and thermosetting properties. Therefore, when the concentration is less than 1% by mass, sufficient self-deposition property cannot be obtained, and a self-deposition coating thickness sufficient to obtain the corrosion resistance which is one of the effects of the present invention cannot be obtained. On the other hand, if it is larger than 5% by mass, not only the consumption of the autodeposition bath component due to the removal of the treatment liquid by the object to be coated will increase, but also the removed treatment liquid will be removed in the water washing process and go to the wastewater treatment process. Since it is sent, unnecessary waste increases. Therefore, the more preferable upper limit concentration of the novolak resin is 3% by mass.

The solid mass concentration ratio of the novolak resin and the crosslinking agent in the aqueous solution is preferably 1: 1 to 1:10, more preferably 1: 1 to 1: 5, and even more preferably 1: 1. To 1: 3. Since the novolak resin used in the present invention has at least one molecule of methylol group in its molecular structure, heat is applied without adding a crosslinking agent by a crosslinking reaction between methylol groups, that is, an ether bond or methylene crosslinking. Can be cured. However, the present inventors have found that it is important to further increase the crosslinking density by adding a crosslinking agent in order to obtain practically sufficient corrosion resistance as the object of the present invention.

Further, by combining a novolak resin having a methylol group and a block polyisocyanate having a bisphenol A structure, unprecedented corrosion resistance is exhibited. However, as a result of intensive studies by the present inventors, it has been found that the corrosion resistance of the autodeposition coating is not improved if the amount of the crosslinking agent added is increased unnecessarily.

The coating film formed of novolac resin has inherently hard properties. In addition, the hardness of the coating film increases as a result of complicated crosslinking with a cross-linking agent, and eventually the coating film becomes very brittle. As a result of investigations by the present inventors, it has been found that a hard and brittle coating film using a novolak resin is inferior in adhesion. Furthermore, a hard and brittle coating film is not suitable for practical use because it is easily damaged by impact applied to the coating film and deformation of the coated metal material.

When the ratio of the crosslinking agent to the novolak resin having a methylol group is less than 1 time, the crosslinking density is low and sufficient corrosion resistance cannot be obtained. On the other hand, if it is larger than 10 times, the crosslinking density is too high and the coating film becomes brittle, which is not suitable for practical use.

Furthermore, a solvent component for improving the water solubility of the components in the surface treatment liquid, particularly the crosslinking agent, and improving the appearance of the film after baking and curing can be added to the present invention. Suitable solvents for the present invention include ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethylene glycol monohexyl ether, diethylene glycol monohexyl ether, and 2,2,4-trimethylpentanediol-1,3-monoisobutyrate Etc.

The present invention relates to a surface treatment solution for autodeposition coating treatment. Here, the self-precipitation reaction is carried out by dissolving ferrous metal material having a pH of 2 to 6, and ferrous ions dissolved in the bath by oxidation reaction of metallic iron with ferric ions, and methylol. In the novolak resin having a group, the two hydroxy groups in the ortho position of the 2,3-dihydroxynaphthalene-6-sulfonic acid molecule chelate with ferrous ions, so that the novolak resin is insolubilized and deposited as an autodeposition coating film. is there.

Furthermore, surplus ferrous ions that have not been used in the autodeposition reaction are rapidly oxidized to ferric ions by the oxidizing agent in the autodeposition treatment bath of the present invention. Oxidized ferric ions can cause the stability of the autodeposition treatment bath as it is, but by coordination of the fluorine element contained in the treatment bath of the present invention, the novolac resin in the treatment bath This suppresses the chelating reaction and maintains the stability of the treatment bath.

Here, as a source of iron ions, soluble iron salts such as iron nitrate, iron sulfate, iron chloride, etc. can be used, and any of the ferrous salts and ferric salts can be used for autoprecipitation. By oxidizing with an oxidizing agent in the surface treatment liquid for coating treatment, ferric ions can be formed in the treatment liquid. Further, iron powder, iron oxide, iron hydroxide, or the like may be dissolved in hydrofluoric acid.

The concentration of ferric ions for causing the autodeposition reaction is 0.1 to 3 g / L, preferably 0.5 to 2.5 g / L, more preferably 1 to 2 g / L. . The concentration of ferric ion can be measured by a general method in the art. For example, using a surface treatment solution for autodeposition coating treatment obtained by previously decomposing and separating a resin component by acid and heating, an atomic absorption method, It can be measured by ICP emission analysis or chelate analysis by EDTA. Moreover, the preferable density | concentration of a fluorine element is a 3 times molar concentration of a ferric ion. Although an upper limit is not specifically limited, For example, it is 10 times or less molar concentration of a ferric ion. The concentration of elemental fluorine can be measured by a common method in the industry. For example, the surface treatment solution for autodeposition coating treatment of the present invention is subjected to distillation operation, and the concentration of elemental fluorine in the distilled solution is determined by ion chromatography or capillary. It can be measured by an electrophoresis apparatus. When the ferric ion concentration is less than 0.1 g / L, it becomes difficult to cause an oxidation dissolution reaction of iron in an amount suitable for autodeposition. Also, if it is greater than 3 g / L, the concentration of iron contained in the deposited self-deposited coating increases, and the amount of moisture taken into the coating together with iron ions increases. It becomes easy to peel off in the water washing process.

As a supply source of elemental fluorine, hydrofluoric acid, ammonium fluoride, acidic ammonium fluoride, sodium fluoride, sodium hydrogen difluoride, potassium fluoride, potassium hydrogen difluoride and the like can be used. Here, when using a fluoride other than hydrofluoric acid, the pH of the surface treatment solution for autodeposition coating treatment may be adjusted using an acid such as nitric acid or sulfuric acid.

The preferred pH of the surface treatment solution for autodeposition coating treatment of the present invention is 2 to 6, more preferably 2.5 to 5, more preferably 2.5 to 4. In addition, the measuring method of pH shall be based on the method of JISZ8802. As described above, the autodeposition coating treatment method of the present invention starts from the dissolution reaction of the iron-based metal material by hydrofluoric acid in the surface treatment solution for autodeposition coating treatment and the oxidation reaction of metallic iron by ferric ions. It is what. Accordingly, when the pH is higher than 6, the dissolution reaction of the metal material hardly occurs and the reduction reaction of ferric ion does not easily occur. On the other hand, if the pH is less than 2, the dissolution reaction of the metal material with respect to the precipitation reaction of the autodeposition coating becomes too large, and the stability of the surface treatment solution for autodeposition coating treatment may be impaired.

The oxidizing agent is preferably at least one selected from perchloric acid, hypochlorous acid, dissolved oxygen, ozone, permanganic acid, and hydrogen peroxide. Hydrogen peroxide is an oxidant suitable for the present invention because it is easily available and it is not necessary to consider the influence on the autodeposition treatment bath because the by-product of its own reduction reaction is water.

The concentration of the oxidizing agent in the autodeposition treatment bath of the present invention can be controlled by the oxidation-reduction potential measured with a commercially available ORP electrode using a platinum electrode as a working station. Here, from the self-deposition reaction mechanism of the present invention, it is preferable that an excess oxidizing agent exists in the treatment bath in a state where all ferrous ions are oxidized to ferric ions. That is, the amount of oxidizing agent is preferably an amount sufficient to oxidize all iron ions present in the bath to ferric ions and maintain their oxidized state. By maintaining the oxidation-reduction potential at or above the minimum value given by the selected oxidant, it becomes possible to maintain this state, where the preferred oxidation-reduction potential when taking hydrogen peroxide as an example. Is at least 300 mV or more, more preferably 350 mV or more, and even more preferably 400 mV or more. Although an upper limit is not specifically limited, It is 500 mV or less.

Furthermore, in the method for treating a self-deposited film of a metal material according to the present invention, the surface of the iron-based metal material is previously degreased and washed with water, and then brought into contact with the aqueous solution described in the surface treatment solution for self-deposited film treatment. Then, the excess aqueous solution adhering to the surface of the metal material is further removed by a water washing step, and then the coating is thermally cured by performing a baking treatment.

Here, as the degreasing treatment, solvent degreasing, alkali degreasing and the like that have been generally used can be used, and the method of the degreasing is not limited and spraying, dipping, electrolysis and the like are not limited. Moreover, there is no restriction | limiting also about the water washing process performed after a degreasing process and an autodeposition coating process, It can select from pouring, spraying, immersion, etc. The quality of water used for washing is not particularly limited, but ion-exchanged water is a preferable choice in consideration of bringing in small components into the autodeposition coating treatment bath and remaining in the coating.

The autodeposition coating treatment according to the present invention is performed by an immersion method in which an object to be coated is immersed in a treatment bath. With respect to the treatment bath in which the dipping method is performed, it is only necessary to provide stirring to such an extent that the component concentration in the treatment bath is kept uniform. Further, the preferable immersion time is 1 to 10 minutes, and the more preferable immersion time is 2 to 5 minutes.

Depending on the surface condition of the material to be coated, a pickling process may be employed. The treatment process in this case is degreasing → multi-stage washing (usually 2 to 3 stages) → acid washing → multi-stage water washing (usually 1 to 2 stages) → self-deposition coating formation → multi-stage water washing (usually 2 to 3 stages) → baking .

Further, the present invention has an autodeposition coating layer deposited on the surface of an iron-based metal material by the above method, and the thickness of the autodeposition coating layer after baking hardening is 10 to 30 μm. It is a metal material. Within this range, it has sufficient corrosion resistance, and appearance defects such as cracks and shrinkage are less likely to occur.

〔Example〕

Examples will be given below together with comparative examples to specifically explain the effects of the surface treatment liquid for autodeposition coating treatment of the present invention and the metal material subjected to autodeposition coating treatment. In addition, the to-be-treated metal material, degreasing agent, and paint used in the examples are arbitrarily selected from commercially available materials, and the surface treatment liquid for autodeposition coating treatment of the present invention, and the autodeposition coating There is no limitation on the combination of materials in the actual application of the treated metal material.

(Test plate)
The abbreviations and breakdown of the test plates used in the examples and comparative examples are shown below.
・ CRS (Cold rolled steel sheet: JIS-G-3141)

(Self-deposition coating solution composition and treatment process)

Production Example 1: Synthesis of a novolak resin containing a methylol group Using dimethylaminobenzene as an alkali catalyst, 60 g of phenol (reagent) and 135 g of 37% by mass formaldehyde (reagent) are mixed and stirred at 70 ° C., and F / P ratio Of 2.6, and a water-soluble resol resin having a solid content of 55% by mass was obtained. A solution obtained by adding 40 g of 2,3-dihydroxynaphthalene-6-sulfonic acid sodium salt (reagent), 35 g of catechol (reagent), and 50 g of water to 200 g of the water-soluble resol resin is heated to 90 ° C. Stir for 3 hours. After stirring, 210 g of resorcinol (reagent) and 200 g of water to which 5 g of 85% by mass phosphoric acid (reagent) was added were added and stirred for 1 hour while maintaining the temperature at 90 ° C. After stirring, 70 g of 37% by mass formaldehyde (reagent) is added little by little, and it is visually confirmed that the viscosity of the composite increases, and a novolak resin having an F / P ratio of 0.84 and a solid content concentration of 53% is obtained. It was. As a result of analyzing the synthesized product by infrared spectroscopy, absorption indicating the presence of a methylol group was confirmed.

Production Example 2: Synthesis of novolak resin Using 85% by mass phosphoric acid (reagent) as an acid catalyst, 61 g of phenol (reagent) and 42 g of 37% by mass formaldehyde (reagent) were mixed and stirred at 70 ° C., and F / P ratio Was novolak resin having a solid content of 55% by mass. To 140 g of the novolak resin, 40 g of 2,3-dihydroxynaphthalene-6-sulfonic acid sodium salt (reagent), 35 g of catechol (reagent), 30 g of 37% by mass formaldehyde (reagent) and 30 g of water were added. The product was heated to 90 ° C. and stirred for 3 hours. After stirring, 210 g of resorcinol (reagent) and 200 g of water to which 5 g of 85% by mass phosphoric acid (reagent) was added were added and stirred for 1 hour while maintaining the temperature at 90 ° C. After stirring, 70 g of 37% by mass formaldehyde (reagent) is added little by little, and it is visually confirmed that the viscosity of the synthesized product increases, and a novolak resin having an F / P ratio of 0.3 and a solid content concentration of 53% is obtained. It was. As a result of analyzing the synthesized product by infrared spectroscopy, absorption indicating the presence of a methylol group could not be confirmed.

Production Example 3: Synthesis of cross-linking agent In a dry nitrogen atmosphere, 174 g of toluene diisocyanate (Coronate T80: manufactured by Nippon Polyurethane Industry Co., Ltd.) was added with 87 g of 2-butanone oxime so that the reaction temperature did not exceed 40 ° C. Added while cooling from outside. After holding at 40 ° C. for 1 hour, the reaction vessel was warmed to 70 ° C. Thereto, 113 g of bisphenol A (reagent) and 0.02 g of dibutyltin laurate (STANN BL: manufactured by Sansha Co., Ltd.) were added and held at 120 ° C. for 2 hours, and then solidified with ethylene glycol monobutyl ether (reagent). It diluted so that a partial concentration might be 30 mass%.

Production Example 4: Synthesis of cross-linking agent In a dry nitrogen atmosphere, 174 g of toluene diisocyanate (Coronate T80: manufactured by Nippon Polyurethane Industry Co., Ltd.) was added with 87 g of 2-butanone oxime so that the reaction temperature did not exceed 40 ° C. Added while cooling from outside. After holding at 40 ° C. for 1 hour, the reaction vessel was warmed to 70 ° C. Thereto, 45 g of 1,1,1-tris (hydroxymethyl) propane (reagent) and 0.02 g of dibutyltin laurate (STANN BL: manufactured by Sansha Co., Ltd.) were added and held at 120 ° C. for 2 hours. The solution was diluted with ethylene glycol monobutyl ether (reagent) so that the solid content was 30% by mass.

Examples 1 to 5 and Comparative Example 1
A commercially available fine cleaner L4460 (manufactured by Nihon Parkerizing Co., Ltd.), which is a commercially available alkaline degreasing agent, was diluted to 2% by mass with water and heated to 40 ° C., and sprayed on a test plate with a spray device to perform degreasing treatment. The surface of the test plate after the degreasing treatment was washed with ion-exchanged water using a spray device. The test plate whose surface was degreased and cleaned was prepared by using a novolak resin containing a methylol group in Production Example 1, a crosslinking agent in Production Example 3, iron powder (reagent), hydrofluoric acid (reagent), and hydrogen peroxide ( After immersing in the autodeposition coating treatment bath shown in Table 1 prepared using a reagent), it was washed with ion-exchanged water using a spray device, and then baked at 160 ° C. for 20 minutes. The immersion time in the autodeposition bath was set so that the film thickness was 15 μm. The autodeposition coated metal materials obtained in each of the examples and comparative examples were evaluated according to the methods described later.

Examples 6 to 9 and Comparative Examples 2 and 3
A commercially available fine cleaner L4460 (manufactured by Nihon Parkerizing Co., Ltd.), which is a commercially available alkaline degreasing agent, was diluted to 2% by mass with water and heated to 40 ° C., and sprayed on a test plate with a spray device to perform a degreasing treatment. The surface of the test plate after the degreasing treatment was washed with ion-exchanged water using a spray device. The test plate whose surface was degreased and cleaned was prepared by using a novolak resin containing a methylol group in Production Example 1, a crosslinking agent in Production Example 4, iron powder (reagent), hydrofluoric acid (reagent), and hydrogen peroxide ( After being immersed in the autodeposition coating treatment bath shown in Table 2 prepared using a reagent), it was washed with ion-exchanged water using a spray device, and then baked at 160 ° C. for 20 minutes. In addition, a commercially available amino alkyd intermediate coating (trade name Amirac TP-37 Gray: manufactured by Kansai Paint Co., Ltd., film thickness 35 μm, spray coating, baked at 140 ° C. for 20 minutes), and commercially available amino alkyd top coating (product) Name Amirac TM-13 White: manufactured by Kansai Paint Co., Ltd., film thickness 35 μm, spray coating, baking at 140 ° C. for 20 minutes). The autodeposition coated metal materials obtained in each of the examples and comparative examples were evaluated according to the methods described later.

Examples 11 to 13
A commercially available fine cleaner L4460 (manufactured by Nihon Parkerizing Co., Ltd.), which is a commercially available alkaline degreasing agent, was diluted to 2% by mass with water and heated to 40 ° C., and sprayed on a test plate with a spray device to perform degreasing treatment. The surface of the test plate after the degreasing treatment was washed with ion-exchanged water using a spray device. The test plate whose surface was degreased and washed was a novolak resin containing a methylol group in Production Example 1, Elastron H38 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), a commercial block isocyanate crosslinking agent, iron powder (reagent), After immersing in an autodeposition coating treatment bath shown in Table 3 prepared using hydrofluoric acid (reagent) and hydrogen peroxide solution (reagent) for 5 minutes, it was washed with ion-exchanged water using a spray device, Baking was performed at 160 ° C. for 20 minutes. In addition, a commercially available amino alkyd intermediate coating (trade name Amirac TP-37 Gray: manufactured by Kansai Paint Co., Ltd., film thickness 35 μm, spray coating, baked at 140 ° C. for 20 minutes), and commercially available amino alkyd top coating (product) Name Amirac TM-13 White: manufactured by Kansai Paint Co., Ltd., film thickness 35 μm, spray coating, baking at 140 ° C. for 20 minutes). The autodeposition coated metal material obtained in each example was evaluated according to the method described later.

Comparative example 4
A commercially available fine cleaner L4460 (manufactured by Nihon Parkerizing Co., Ltd.), which is a commercially available alkaline degreasing agent, was diluted to 2% by mass with water and heated to 40 ° C., and sprayed on a test plate with a spray device to perform a degreasing treatment. The surface of the test plate after the degreasing treatment was washed with ion-exchanged water using a spray device. The test plate whose surface was degreased and washed was a novolak resin containing a methylol group in Production Example 1, Elastron H38 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.), a commercial block isocyanate crosslinking agent, iron powder (reagent), After immersing in an autodeposition coating treatment bath shown in Table 3 prepared using hydrofluoric acid (reagent) and hydrogen peroxide solution (reagent) for 5 minutes, it was washed with ion-exchanged water using a spray device, Baking was performed at 160 ° C. for 20 minutes. The mixing ratio of ferric chloride and iron powder was 1 g / L with ferric chloride as iron and the remaining iron as iron powder. In addition, a commercially available amino alkyd intermediate coating (trade name Amirac TP-37 Gray: manufactured by Kansai Paint Co., Ltd., film thickness 35 μm, spray coating, baked at 140 ° C. for 20 minutes), and commercially available amino alkyd top coating (product) Name Amirac TM-13 White: manufactured by Kansai Paint Co., Ltd., film thickness 35 μm, spray coating, baking at 140 ° C. for 20 minutes). The autodeposition coated metal material obtained in each example was evaluated according to the method described later.

Comparative example 5
A commercially available fine cleaner L4460 (manufactured by Nihon Parkerizing Co., Ltd.), which is a commercially available alkaline degreasing agent, was diluted to 2% by mass with water and heated to 40 ° C., and sprayed on a test plate with a spray device to perform degreasing treatment. The surface of the test plate after the degreasing treatment was washed with ion-exchanged water using a spray device. The test plate whose surface was degreased and washed was obtained by adding 3% by mass of the novolak resin containing the methylol group of Production Example 1 as a solid content, 1.5 g / L of iron powder (reagent), and hydrofluoric acid (reagent). After dipping for 5 minutes in an autodeposition coating treatment bath in which ORP was adjusted to 400 mV using 1.6 g / L of fluorine and hydrogen peroxide solution (reagent) as a fluorine, it was washed with ion-exchanged water using a spray device, and then Baking was performed at 160 ° C. for 20 minutes. The obtained autodeposition coated metal material was evaluated according to the method described later.

Comparative examples 6-8
A fine alkaline L4460 (manufactured by Nihon Parkerizing Co., Ltd.) was diluted with water to 2% by mass with a commercially available alkaline degreasing agent and heated to 40 ° C. and sprayed on a test plate with a spray device to perform degreasing treatment. The surface of the test plate after the degreasing treatment was washed with ion-exchanged water using a spray device. Using the novolak resin of Production Example 2, the cross-linking agent of Production Example 3, iron powder (reagent), hydrofluoric acid (reagent), and hydrogen peroxide (reagent), the test plate whose surface was degreased and washed was used. After being immersed in the adjusted autodeposition coating treatment bath shown in Table 4, it was washed with ion-exchanged water using a spray device, and then baked at 160 ° C. for 20 minutes. The immersion time in the autodeposition bath was set so that the film thickness was 15 μm. The self-deposited coated metal material obtained in each comparative example was evaluated according to the method described later.

Comparative Example 9
A fine alkaline L4460 (manufactured by Nihon Parkerizing Co., Ltd.) was diluted with water to 2% by mass with a commercially available alkaline degreasing agent and heated to 40 ° C. and sprayed on a test plate with a spray device to perform degreasing treatment. The surface of the test plate after the degreasing treatment was washed with ion-exchanged water using a spray device. The test plate whose surface was degreased and washed was immersed in a treatment bath in which NSD-1000 (vinylidene chloride type: Nippon Parkerizing Co., Ltd.), a commercially available autodeposition coating treatment agent, was adjusted to the center of the catalog value for 2 minutes. Then, it wash | cleaned with ion-exchange water using the spray apparatus, and then baked at 100 degreeC for 20 minutes. In addition, a commercially available amino alkyd intermediate coating (trade name Amirac TP-37 Gray: manufactured by Kansai Paint Co., Ltd., film thickness 35 μm, spray coating, baked at 140 ° C. for 20 minutes), and commercially available amino alkyd top coating (product) Name Amirac TM-13 White: manufactured by Kansai Paint Co., Ltd., film thickness 35 μm, spray coating, baking at 140 ° C. for 20 minutes). The adhesion of the test plate coating film that was applied to the top coat was evaluated according to the method described below.

(Appearance and film thickness evaluation of self-deposited coated metal materials)
The appearance of the test plates treated with the autodeposition coating treatment methods of the examples and comparative examples was visually determined. The film thickness was measured using an electromagnetic film thickness meter (Fischerscope MMS: manufactured by FISCHER).

(Performance evaluation of self-deposited coated metal materials)
The performance evaluation of Examples and Comparative Examples was performed. Evaluation items and abbreviations are shown below. The coating film at the time of completion of the autodeposition coating treatment is referred to as a self-deposition coating film, and the coating film at the time of completion of the top coating is referred to as a 3coats coating film.
(1) SST: Salt spray test (self-deposited coating)
(2) SDT: salt warm water test (self-deposited coating)
(3) 1 ^st ADH: Primary adhesion (3coats coating film)
(4) 2 ^nd ADH: water resistant secondary adhesion (3-coat coating film)

・ SST
5 mass% salt water was sprayed for 600 hours (according to JIS-Z-2371) onto a self-deposited coated film plate that had been cross-cut with a sharp cutter. After spraying, the maximum swelling width on both sides from the cross cut part was measured.

・ SDT
The self-deposited coated plate with a cross cut cut with a sharp cutter was immersed in a 5 mass% NaCl aqueous solution heated to 50 ° C for 240 hours. After dipping, the cross-cut portion that was washed with tap water and dried at room temperature was peeled off with an adhesive tape, and the maximum peel width on both sides of the coating film was measured.

・ 1 ^st ADH
Cut 100 grids at 2mm intervals with a sharp cutter on the 3coats coating. Cellotape (registered trademark) was peeled off from the grid area, and the remaining number of grids was counted.

· 2 ^nd ADH
The 3coats coated plate was immersed in deionized water at 40 ° C. for 240 hours. After immersion, 100 grids with 2 mm intervals were cut with a sharp cutter. The tape was peeled off from the grid area, and the remaining number of grids was counted.

Table 5 shows the evaluation results of the autodeposition coatings obtained in Examples 1 to 5 and Comparative Example 1. In Examples 1 to 5, a uniform appearance was obtained at all levels, and corrosion resistance was excellent. On the other hand, Comparative Example 1 was not evaluated for corrosion resistance because cracks occurred on the entire surface of the autodeposition coating after baking.

Table 6 shows the evaluation results of the self-deposited films obtained in Examples 6 to 9 and Comparative Examples 2 and 3. Since Examples 6 to 9 did not introduce a bisphenol A structure into the cross-linking agent, they exhibited practically sufficient corrosion resistance although slightly inferior to Examples 1 to 5. Also, the adhesion after the intermediate top coating was good. On the other hand, the self-deposited coated metal material of Comparative Example 2 was inferior in corrosion resistance because the film thickness was low, although adhesion was obtained. In Comparative Example 3, the corrosion resistance evaluation was not performed because cracks occurred in the autodeposition coating after baking.

Table 7 shows the evaluation results of the autodeposition coatings obtained in Examples 11 to 13 and Comparative Example 4. In Examples 11 to 13, a uniform appearance was obtained at all levels, and the corrosion resistance was excellent. Also, the adhesion after the intermediate top coating was good. On the other hand, in the comparative example 4, the coating film before baking peeled in the washing process which is the next process of an autodeposition coating process.

Table 8 shows the evaluation results of the self-deposited film obtained in Comparative Example 5. In Comparative Example 5, an autodeposited film was obtained, but the result was markedly inferior in corrosion resistance because no crosslinking agent was used.

Table 9 shows the evaluation results of the autodeposition coating obtained in Comparative Examples 6 to 8. The novolak resin used in Comparative Examples 6 to 8 was inferior in corrosion resistance because it did not have a methylol group. In addition, the stability of the treatment bath was extremely low, and precipitates were generated 1 hour after the autodeposition coating treatment. On the other hand, in all Examples, no precipitate was generated even when the treatment liquid after the autodeposition coating treatment was stored for one month, and sludge was hardly generated by the autodeposition coating treatment.

Table 10 shows the evaluation results of the self-deposited film obtained in Comparative Example 9. Since Comparative Example 9 was a commercially available autodeposition coating agent, it exhibited relatively good corrosion resistance. However, in the adhesion evaluation after the intermediate top coating, all the coatings on the grid area were peeled off.

From the above, the effects of the present invention are clear.

Claims (11)

1. An aqueous solution containing a novolak resin, a crosslinking agent, ferric ions, elemental fluorine, and an oxidizing agent,
   The novolak resin comprises two or more resole resins obtained by reacting phenols and aldehydes in the presence of an alkali catalyst in an F / P ratio of 2.5 to 3, and two or more adjacent aromatic ring carbons. A hydroxyphenol having a hydroxyl group and a phenol are mixed and stirred, and further polymerized by adding a phenol, an aldehyde and an acid catalyst, and having an F / P ratio of 0.7 to 1.0. A novolac resin having a methylol group,
   The crosslinking agent is a crosslinking agent having a crosslinking group capable of thermosetting reaction with the methylol group, phenol nucleus and / or phenolic hydroxyl group,
   The solid content mass concentration ratio of the novolac resin and the crosslinking agent is in the range of 1: 1 to 1:10,
   A surface treatment solution for autodeposition coating treatment of a metal material, wherein the molar concentration of the fluorine element is at least 3 times that of the ferric ion and the pH is in the range of 2 to 6.
2. The surface treatment solution for autodeposition coating treatment of a metal material according to claim 1, wherein the novolak resin has a structural formula shown in Formula 1.
   

   

   Wherein m and n are integers of 1 to 5, p is an integer of 0 to 5, R1 is methylol, R2 is independently hydroxyl or alkylaryl, R3 is independently methylol, hydroxyl or alkylaryl, a is 0 or 1)
3. The surface treatment liquid for autodeposition coating treatment of a metal material according to claim 1 or 2, wherein the crosslinking group capable of thermosetting reaction of the crosslinking agent is an isocyanate group.
4. The metal material according to claim 3, wherein the cross-linking agent is a polyfunctional blocked isocyanate obtained by adding at least 2 mol of polyisocyanate in which one isocyanate group is blocked with a blocking agent to 1 mol of polyol. Surface treatment solution for autodeposition coating treatment.
5. The surface treatment liquid for autodeposition coating treatment of a metal material according to claim 4, wherein the polyol in the cross-linking agent has at least one molecule of bisphenol A structure.
6. 6. The surface treatment liquid for autodeposition coating treatment of a metal material according to claim 1, wherein the concentration of the novolak resin is 1 to 5% by mass as a solid content concentration in the aqueous solution. .
7. The metal material self-deposition according to any one of claims 1 to 6, wherein the oxidizing agent is at least one selected from perchloric acid, hypochlorous acid, dissolved oxygen, ozone, permanganic acid, and hydrogen peroxide. Surface treatment solution for coating treatment.
8. The surface treatment solution for autodeposition coating treatment according to claim 7, wherein the oxidation-reduction potential measured with a platinum electrode is 300 to 500 mV.
9. The surplus adhered to the surface of the metal material in the water washing step after the metal material whose surface has been cleaned in advance by degreasing and washing treatment is brought into contact with the surface treatment liquid described in any one of claims 1 to 8. An autodeposition coating treatment method for a metal material, wherein the coating solution is thermally cured by removing the treatment liquid and then performing a baking treatment.
10. 10. The metal material autodeposition coating treatment method according to claim 9, wherein the metal material is an iron-based metal material.
11. An autodeposition film layer having an autodeposition coating layer deposited on the surface of a metal material by the method described in claim 9 and having a film thickness of 10 to 30 μm after baking and hardening. Coated metal material.