WO2010002543A1

WO2010002543A1 - Treatment solution for autodeposition coating of metallic materials and autodeposition coating treatment method

Info

Publication number: WO2010002543A1
Application number: PCT/US2009/046406
Authority: WO
Inventors: Takahiro Fujino; Satoshi Kawabe
Original assignee: Lord Corporation
Priority date: 2008-06-07
Filing date: 2009-06-05
Publication date: 2010-01-07
Also published as: TW201006959A; JP5518307B2; WO2009147911A1; JP2009293101A

Abstract

A surface treatment solution for autodeposition coating treatment of metallic materials, which is an aqueous solution comprising a novolac resin, a crosslinking agent, ferric ions, elemental fluorine and an oxidizing agent, characterized in that: the crosslinking agent is a crosslinking agent which has a crosslinking group capable of causing a thermosetting reaction between the methylol group and a phenol nucleus and/or a phenolic hydroxyl group, the solid component mass concentration ratio of the novolac resin to the crosslinking agent being in the range of 1 :1 to 1 :10, the molar concentration of the elemental fluorine being at least 3 times the ferric ions, and the pH being in the range of 2 to 6. A surface treatment solution for autodeposition coating treatment is provided, with which the process length is shorter than conventional coating processes, wherein almost no environmentally harmful byproducts such as sludge are generated, which has excellent throwing power within recessed structures, which does not use environmentally harmful components such as chromium compounds, which is corrosion resistant, and which allows for further overcoating with baked paints on the coating that is produced.

Description

TREATMENT SOLUTION FOR AUTODEPOSITION COATING OF METALLIC MATERIALS AND AUTODEPOSITION COATING TREATMENT METHOD

FIELD OF THE INVENTION

[0001] The present invention relates to a surface treatment solution for autodeposition coating treatment and to an autodeposition coating treatment method for depositing an organic coating, by way of a chemical reaction, on the surfaces of ferrous metallic materials for which corrosion resistance is required, such as automobile bodies, automobile parts, steel furnishings and home appliances, on which, depending on the usage, overcoats of paint may be applied, the organic coating having sufficient corrosion resistance alone and allowing for overcoating with paint; the present invention also relates to metallic materials having an autodeposition coating.

BACKGROUND OF THE INVENTION

[0002] With the exception of some special applications and materials, almost all industrial parts using metallic materials are coated. The purpose of this coating is not only to improve the appearance, but also to prevent oxidation, which is to say, corrosion, to which metals are subject. Here, the coatings used for metallic materials can be classified in different ways according to the application method and the components, and are selected according to the properties required of the coated material and the application methods that are possible. Here, in cases where the coated material has a complex structure and there is a demand for a high level of corrosion resistance, such as for automobile bodies, it is important to maintain coating thickness at the interior of recessed structures, which is a capacity referred to as throwing power.

[0003] A common method used to maintain corrosion resistance at the interior of recessed structures is to combine a zinc phosphate treatment, which is a chemical conversion treatment for coating substrates, and cationic electrodeposition coating. In any of these methods, the chemical conversion treatment and the coating are performed with the material to be coated immersed in a treatment bath, so that the chemical conversion solution and the coating material can be brought into contact with the interior of the recessed structure. However, the zinc phosphate treatment process comprises: hot water washing -> preliminary degreasing -> degreasing -> multistage water washing (normally 2 to 3 stages) -> surface conditioning -> coating chemical conversion -> multistage water washing (normally 2 to 3 stages) -> ion exchange water washing; and the cationic electrodeposition coating process further comprises: electrodeposition coating -> multistage water washing (normally 3 to 5 stages) -> ion exchange water washing -> baking; thus, the treatment process is a very long with, for example, in the case of automobile bodies, a process length of more than 200 m.

[0004] As is conventionally known, in the zinc phosphate treatment process, it is not possible to avoid production of iron phosphate sludge as a side reaction to the coating deposition reaction, and thus there is a demand for improvement from the point of view of environmental problems. Furthermore, while cationic electrodeposition coating has recently improved, because the mechanism is one in which the coating is precipitated as a result of electrolysis and the coating is thrown as a result of the electrical resistance of the precipitated coating, there is an unavoidable problem in that this produces a difference in the thicknesses of the films on the outer panels where the coating is initially precipitated and the interior of the recessed structures where the coating is subsequently deposited.

[0005] For some time, techniques have been proposed that have been directed at shortening the process and solving the problem of the generation of iron phosphate sludge as well as the problem of the coating thickness at the interior of recessed structures, by depositing an organic coating by way of a chemical reaction; compositions of this sort are called autodeposition compositions, self precipitating compositions or self depositing compositions.

[0006] For example, JP-60-058474-A relates to an autodeposition composition using a vinylidene chloride copolymer. Because vinylidene chloride resin has excellent moisture proof properties, moisture resistance and gas barrier properties, when used as a coating, the effect of limiting corrosion is extremely great. However, as is well known, vinylidene chloride resin has extremely low heat resistance. Here, Patent Document 1 discloses that it is possible to improve the heat resistance by inserting a heat stable comonomer into the chain by way of copolymehzing a vinylidene chloride monomer with a comonomer such as an acrylic comonomer. However, even if a stable unit is inserted into the chain, it is not possible to fundamentally improve the low heat resistance of the basic vinylidene chloride structure. Accordingly, there were problems in that it was not possible to use autodeposition techniques that employed vinylidene chloride for metallic materials that would be used in environments where they would be exposed to high temperatures, in addition to which, it was not possible to overcoat the autodeposition coating with baked paints.

[0007] Many autodeposition compositions have been disclosed that do not use vinylidene chloride. As cited in JP-47-032039-A, JP-48-013428-A, JP-61-168673-A, styrene butadiene, acrylic polymers and copolymers thereof, polyvinyl chloride, polyethylene, polytetrafluoroethylene, acrylonithle butadiene and urethane resins have been disclosed as examples of resin components other than vinylidene chloride that can be used for autodeposition compositions.

[0008] However, with any of these methods, the corrosion resistances of the autodeposition coatings were markedly lower than those using vinylidene chloride. Here, as indicated in Patent Document 3, in order to improve the corrosion resistance, following the autodeposition coating, it was necessary to perform after-processing using chromium compounds, the use of which is currently limited due to concerns about environmental problems.

[0009] Then, as indicated in JP-2003-176449-A, in recent years, autodeposition compositions have been proposed, which combine epoxy resin and a crosslinking agent. However, as a result of investigating the results of the aforementioned invention, the present inventors discovered that the anticorrosion properties of the autodeposition coating using epoxy resin were not sufficient, in addition to which, there was a fatal flaw in that the adhesion with solvent coatings was extremely low, so that overcoats were not possible.

[0010] JP-2002-501100-B and JP-2002-501124-B disclose an aqueous coating composition comprising a water dispersible phenol resin and a polymer softening agent, characterized by being capable of autodeposition on a metal support. However, because the autodeposition coating produced by this method contains a large quantity of water before baking, it is not possible to wash the coating with water before baking. Accordingly, there are no problems if the material to be coated is flat, but in the case of materials having a recessed structure, because it is not possible to wash out the coating that remains at the interior of the recessed structure, serious defects occur, which have a major impact on corrosion prevention, such as swelling and peeling off the coating after baking.

[0011] Accordingly, in the prior art, it was not possible to provide an autodeposition coating with which the process length was shorter than the coating process in which zinc phosphate processing and electrodeposition coating were combined, wherein environmentally harmful byproducts such as sludge were not produced, which had excellent throwing power within recessed structures, which did not use environmentally harmful components such as chromium compounds, which was corrosion resistant, and which allowed for additional overcoating with baked paints on the resulting coating.

SUMMARY OF THE INVENTION

[0012] An object of the present invention is to solve the problems of the prior art. In other words, a surface treatment solution for autodeposition coating treatment is provided with which the process length is shorter than the coating process in which zinc phosphate processing and electrodeposition coating were combined, wherein almost no environmentally harmful byproducts such as sludge are produced, which has excellent throwing power within recessed structures, which does not use environmentally harmful components such as chromium compounds, which is corrosion resistant, and which allows for additional overcoating with baked paints on the resulting coating.

[0013] As a result of the earnest study into means for solving the problems described above, the present inventors succeeded in inventing a surface treatment solution for autodeposition coating treatment, an autodeposition coating treatment method and a metallic material having an autodeposition coating, which are not found in the prior art.

[0014] In other words, the surface treatment solution for autodeposition coating treatment according to the present invention is an aqueous solution comprising: a novolac resin having a methylol group and having an F/P ratio of 0.7 to 1.0, produced by mixing and stirring a resole resin, which is producible by reacting a phenol and an aldehyde in the presence of an alkaline catalyst at an F/P ratio in the range of 2.5 to 3, a hydroxyphenol having two or more hydroxyl groups on adjacent aromatic ring carbons, and a phenol, and further adding a phenol, an aldehyde and an acidic catalyst and polymerizing; and a crosslinking agent, which has a crosslinking group capable of causing a thermosetting reaction between the methylol group and a phenol nucleus and/or a phenolic hydroxyl group, at a solid component mass concentration ratio of the novolac resin to the crosslinking agent in the range of 1 :1 to 1 :10; further comprising ferric ions, elemental fluorine (preferably dissolved elemental fluorine) at a molar concentration that is at least 3 times the ferric ions, and an oxidizing agent, the pH being in the range of 2 to 6.

[0015] The novolac resin preferably has at least a methylol group substituted on an aromatic ring and, on two or more mutually adjacent aromatic ring carbons, phenolic sites having hydroxyl groups, and more preferably has the structural formula shown in Formula 1. [Chem. 2]

[Formula 1]

(In the formula, m and n are integers from 1 to 5, p is an integer from O to 5, R1 is methylol, R2 is independently hydroxyl or alkylaryl, R3 is independently methylol, hydroxyl or alkylaryl, and a is 0 or 1.)

[0016] The crosslinking group of the crosslinking agent that is capable of causing a thermosetting reaction is preferably an isocyanate group.

[0017] Furthermore, it is preferable that the cross-linking agent be a polyfunctional blocked isocyanate, wherein at least 2 mol of polyisocyanate, wherein one of the isocyanate groups has been blocked in advance with a blocking agent, are added to 1 mol of polyol.

[0018] Furthermore, the polyol in the crosslinking agent preferably has at least one molecule of bisphenol A structure.

[0019] The concentration of the novolac resin is preferably 1 to 5 mass% as a solid component concentration in the aqueous solution.

[0020] The oxidizing agent is preferably at least one oxidizing agent selected from perchloric acid, hypochlorous acid, dissolved oxygen, ozone, permanganic acid, and hydrogen peroxide.

[0021] The redox potential of the surface treatment solution for autodeposition coating treatment, measured with a platinum electrode, is preferably 300 to 500 mV. [0022] Furthermore, the present invention is a metallic material autodeposition coating treatment method characterized by contacting a metallic material, the surface of which has been cleaned by degreasing and water washing in advance, with the aqueous solution described as the surface treatment solution for autodeposition coating treatment, then furthermore removing the excess of the treating solution that has adhered to the surface of the metallic material in a washing process, and next thermosetting the coating by performing a baking treatment.

[0023] In addition, the present invention is an autodeposition coated metallic material characterized by comprising an autodeposition coating layer, deposited on the surface of a ferrous metallic material by the method described above, and in that the film thickness of the autodeposition coating layer after being hardened by baking is 10 to 30 μm.

[0024] Here, the meanings of the terms used in the claims and the specification of the present invention are explained. With regard to the term "ferric ion", so long as this is an ion represented by Fe³⁺, there are no particular restrictions on the state in which it is present in the surface treatment solution, and this indicates, for example, Fe³⁺ and states in which a ligand is coordinated thereto. Examples of elemental fluorine coordinated to a ferric ion include FeF²⁺, FeF₂ ⁺, FeF₃. The term "elemental fluorine" refers to elemental fluorine in general, which is supplied by fluorine containing compounds such as hydrogen fluoride and/or salts thereof, with no particular restrictions on the state thereof, which may be a molecular state, an ionic state or the like. Furthermore, the concentration of the "elemental fluorine" is the total molar concentration of the various forms of elemental fluorine present in the system. For example, the elemental fluorine supplied by the fluorine containing compounds mentioned above can be disassociated as F^", HF, HF₂ ^" or the like, depending on the pH of the aqueous solution, and the elemental fluorine concentration as referred to herein is the total molar concentration of the fluorine in the aqueous solution. Furthermore, if this forms a complex with a ferric ion, that complex includes a "ferric ion" and also includes "elemental fluorine". Furthermore, there are no particular restrictions on the state of the "dissolved elemental fluorine", which may be the molecular state, the ionic state or the like; but this excludes elemental fluorine that is contained in salts or the like that are present as undissolved solid particles in the surface treatment solution for autodeposition coating treatment of the present invention. Furthermore, the concentration of "dissolved elemental fluorine" is the total molar concentration of the various forms of dissolved elemental fluorine present in the system. Furthermore, "novolac resin" refers to a resin wherein a phenol is polymerized with an aldehyde in the presence of an acid catalyst. Furthermore, "resole" refers to a resin wherein a phenol is polymerized with an aldehyde in the presence of an alkaline catalyst. Here, the expression "a phenol" refers to an aromatic compound bearing a phenolic hydroxyl group. "An aldehyde" is a compound having one or more aldehyde groups in one molecule, or a compound that readily produces an aldehyde group in the reaction system. The term "alkyl" refers to a straight chain or branched chain, substituted or non-substituted Ci to C10 alkyl. The term "aryl" refers to a substituted or unsubstituted Cβ to Ci₄ mono- to tricyclic aryl (here, one or more of the carbon atoms constituting the rings may be substituted by sulfur, nitrogen or oxygen).

[0025] By using the surface treatment solution for autodeposition coating treatment of the present invention, it is possible to shorten the process length as compared to the conventional technique, comprising hot water washing -> preliminary degreasing -> degreasing -> multistage water washing (normally 2 to 3 stages) -> surface conditioning -> coating chemical conversion -> multistage water washing (normally 2 to 3 stages) -> ion exchange water washing -> electrodeposition coating -> multistage water washing (normally 3 to 5 stages) -> ion exchange water washing -> baking, which is to say, the coating process that combines zinc phosphate treatment and electrodeposition coating. Furthermore, because the method of the present invention does not produce environmentally harmful byproducts such as sludge and the autodeposition coating treatment bath does not use harmful components such as chromium compounds, there is little impact on the environment. Furthermore, the autodeposition coating of the present invention has excellent corrosion resistance and excellent throwing power within recessed structures, and therefore is effective in improving the corrosion resistance of coated objects having complex structures. In addition, the autodeposition coated metallic materials of the present invention allow for overcoating with baked paints on the autodeposition coating. Accordingly, this can be used in combination with various types of paints.

[0026] By using an isocyanate as the crosslinking agent, an effect is achieved that allows for the formation of an autodeposition coating having better corrosion resistance. [0027] By using a polyfunctional blocked isocyanate for the crosslinking agent, an effect is achieved that allows for the formation of an autodeposition coating having still better corrosion resistance.

[0028] By using a substance having at least one molecule of bisphenol A structure for the crosslinking agent, an effect is achieved that allows for the formation of an autodeposition coating having yet better corrosion resistance.

[0029] By causing the concentration of the novolac resin to be 1 to 5 mass% as a solid component concentration in the aqueous solution, the coating is thick enough to prevent corrosion, and it is also possible to limit the consumption of components.

[0030] By causing the solid mass concentration ratio of the novolac resin to the crosslinking agent to be from 1 :1 to 1 :10, an effect is achieved whereby the autodeposition coating has a uniform appearance and the corrosion resistance is improved.

[0031] By using at least one oxidizing agent selected from perchloric acid, hypochlorous acid, dissolved oxygen, ozone, permanganic acid and hydrogen peroxide for the oxidizing agent, an effect is achieved whereby the autodeposition reaction is promoted without degrading the stability of the treatment solution for autodeposition coating treatment.

[0032] By causing the redox potential measured with a platinum electrode to be 300 to 500 mV, all of the iron ions present in the bath are oxidized to ferric ions and a sufficient quantity of oxidizing agent is present to maintain that oxidation state, so that the deposition reaction for the autodeposition coating is promoted and it is possible to limit destabilization of the autodeposition coating treatment solution by ferrous ions.

[0033] According to the autodeposition coating treatment method of the present invention, by using the treatment solution of the present invention, an effect is achieved whereby an autodeposition coating having excellent corrosion resistance can be formed.

[0034] As a result of the metallic materials being ferrous metallic materials, an effect is achieved whereby an autodepositable film is more easily formed, and this film can be formed so as to have excellent corrosion resistance.

DETAILED DESCRIPTION OF THE INVENTION

[0035] The present inventors made it possible to deposit an autodeposition coating having excellent corrosion resistance on the surface of a metallic material by contacting the metallic material with a surface treatment solution comprising a novolac resin having a methylol group and having an F/P ratio of 0.7 to 1.0, produced by mixing and stirring a resole resin, which is producible by reacting a phenol and an aldehyde in the presence of an alkaline catalyst at an F/P ratio in the range of 2.5 to 3, a hydroxyphenol having two or more hydroxyl groups on adjacent aromatic ring carbons, and a phenol, and further adding a phenol, an aldehyde and an acidic catalyst and polymerizing; and a crosslinking agent, which has a crosslinking group capable of causing a thermosetting reaction between the methylol group and a phenol nucleus and/or a phenolic hydroxyl group, at a solid component mass concentration ratio of the novolac resin to the crosslinking agent in the range of 1 :1 to 1 :10; further comprising ferric ions, elemental fluorine at a concentration that is at least 3 times the ferric ions, and an oxidizing agent, the pH being in the range of 2 to 6.

[0036] Furthermore, the novolac resin preferably has the structural formula shown in Formula 1. [Chem. 3]

[Formula 1]

(In the formula, m and n are integers from 1 to 5, p is an integer from 0 to 5, R1 is methylol, R2 is independently hydroxyl or alkylaryl, R3 is independently methylol, hydroxyl or alkylaryl, and a is 0 or 1.)

[0037] The surface treatment solution for autodeposition coating treatment of the present invention can suitably be used for ferrous metallic materials and galvanized steel sheets. However, the most suitable metallic materials are ferrous metallic materials. The term ferrous metallic materials, as used here, indicates steel sheets such as cold rolled steel and hot rolled steel, as well as ferrous metals such as cast iron and sintered materials. [0038] The metallic materials of the present invention are used for automobile bodies, automobile parts, steel furnishings, household appliances and the like, and depending on the various applications, these can be used with the autodeposition coating of the present invention alone, or in combination with other top coatings such as solvent coatings.

[0039] The novolac resin containing at least one methylol group in the basic molecular structure is an essential component of the present invention. The present invention is a surface treatment solution for autodeposition coating treatment of metallic materials, which is characterized by contacting a ferrous metallic material with a certain specific aqueous solution. Accordingly, it is a primary necessity that the components used in the treatment method of the present invention be water-soluble or water dispersible. Furthermore, the resin component, which is a primary component of the autodeposition coating must be capable of autodeposition onto a ferrous metallic material under the processing conditions set forth in the present invention, and it must also be capable of thermosetting in a baking process following autodeposition.

[0040] The present inventors discovered that, by using the novolac resin having the special structure indicated by Formula 1 , the conditions necessary for the present invention as described above are satisfied and excellent properties can be produced. In Formula 1 , m and n are integers from 1 to 5; p is an integer from 0 to 5; R1 is methylol; R2 is independently hydroxyl or alkylaryl; R3 is independently methylol, hydroxyl or alkylaryl; and a is 0 or 1. Furthermore, benzyl groups and tolyl groups are preferred alkylaryls for R2 and R3.

[0041] The resins generally referred to as novolac resins and resole resins are polymerized using a phenol and an aldehyde. Here, when the phenol (P) and the aldehyde (F) are reacted, the molar reaction ratio is referred to as the F/P ratio. In general, resins referred to as novolacs are produced by polymerizing a phenol with an aldehyde, using an acidic catalyst. Novolac is polymerized at a low F/P ratio in order to prevent the molecular structure from becoming three-dimensional, and the aldehyde that is added to the phenol is used in the polymerization reaction of the phenol. Accordingly, even if formaldehyde is used as the aldehyde, in what is generally referred to as novolac resin, the formaldehyde is used in the phenol polymerization, so that a methylol group is not present as a result of adding the formaldehyde. There are no particular restrictions on the novolac resin in this best mode, but an F/P ratio of 0.7 to 1.0 is preferred, 0.75 to 0.95 is more preferred and 0.75 to 0.9 is still more preferred.

[0042] Because novolac resins in which methylol groups are not present have extremely low affinity with water and do not, therefore, disperse in water, and because they do not have functional groups that are cross-linked by heat, they are not suitable for use in the present invention. Meanwhile, resole resins, wherein formaldehyde and a phenol are polymerized at a high F/P ratio in the presence of an alkaline catalyst, are thermosetting resins having a methylol group but, because a dispersion of resole resin in an acidic aqueous solution has extremely low stability, it cannot be used in the present invention.

[0043] The novolac resin shown in Formula 1 , which can be used in the present invention has at least one methylol group. The presence of the methylol group gives the novolac resin thermosetting properties. Furthermore, the presence of the methylol group can improve the hydrophilic properties of the novolac resin. However, it is not possible to give this sufficient water solubility and water dispersiblility by way of the methylol group alone. Furthermore, it is not possible to achieve autodeposition, simply by providing a novolac resin with a methylol group. Here, by introducing a dihydroxyphenol group having an ionizable group into a novolac resin having a methylol group, the water solubility and water dispersibility thereof are improved and this is made capable of autodeposition.

[0044] The dihydroxyphenol having an ionizable group, which is used in the novolac resin of the present invention, is most preferably 2,3-dihydroxynaphthalene-6-sulfonic acid, as shown in Formula 1. The novolac resin is given sufficient water solubility and water dispersibility by the sulfonic acid group, and is made capable of autodeposition by the two hydroxyl groups in the ortho positions. Note that when the novolac resin is synthesized, an alkali metal salt of 2,3-dihydroxynaphthalene-6-sulfonic acid may be used.

[0045] The novolac resin having the methylol group in the structural formula shown in Formula 1 , which is used in the present invention, can be synthesized by way of first synthesizing a resole resin by reacting a phenol with an aldehyde in the presence of an alkaline catalyst, preferably at an F/P ratio in the range of 2 .5 to 3, and then mixing and stirring sodium 2,3-dihydroxynaphthalene-6-sulfonate and a phenol with the resole resin, and then adding a phenol, an aldehyde and an acidic catalyst and polymerizing. Note that the final novolac F/P ratio is the molar ratio of the phenols (including hydroxy phenols) to the aldehydes. Accordingly, the phenols and aldehydes used in the synthesis of the resole resin are also included in the final F/P ratio. Furthermore, whether or not a methylol group is present in the synthesized novolac resin can be determined by measuring methylol group absorption, which appears in the vicinity of 1000 cm^"1, with infrared spectroscopy.

[0046] Here, phenol, catechol, resorcinol, pyrogallol, cresol and the like can be used as the phenol; and formaldehyde, acetaldehyde, acetone, benzaldehyde and the like can be used as the aldehyde. Among these, the most preferred aldehyde is formaldehyde, which is sold as formalin.

[0047] In terms of the crosslinking group in the crosslinking agent having a crosslinking group that is capable of a thermosetting reaction with the methylol group, the phenol nucleus and the phenolic hydroxyl group used in the present invention, methylol groups, carboxyl groups, glycidyl groups, secondary alcohol groups wherein a glycidyl group has been ring opened, isocyanate groups and the like can be used, and from among these, isocyanate groups are preferred.

[0048] Furthermore, it is preferable that the aforementioned crosslinking agent be a polyfunctional blocked isocyanate, in which at least 2 mol of poly-isocyanate, wherein one of the isocyanate groups has been blocked in advance with a blocking agent, are added to 1 mol of polyol. This is most suitable as a crosslinking agent for the present invention because, by blocking the isocyanate group with the blocking agent, reactions with water can be suppressed, but the blocking agent disassociates on application of heat, so that the crosslinking reaction occurs.

[0049] Well-known polyisocyanates can be used as the polyisocyanate that can be used in the present invention. For example, aliphatic diiosocyanates such as 1 ,4-tetramethylene diisocyanate, ethyl(2,6-diisocyanate)hexanoate,

1 ,6-hexamethylene diisocyanate, 1 ,12-dodecamethylene diisocyanate, and 2,2,4- or 2,4,4-trimethyl hexamethylene diisocyanate; aliphatic thisocyanates such as 1 ,3,6-hexamethylene tri isocyanate,

1.δ-diisocyanate^-isocyanatomethyloctane and

2-isocyanatoethyl(2,6-diisocyanate)hexanoate; diosocyanates having cyclic structures, such as isophorone diisocyanate; and aromatic diisocyantes such as 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'-dinnethyldiphenyl,

3-methyl-diphenylnnethane-4,4'-diisocyanate, and diphenylether-4,4'-diisocyanate can be used.

[0050] From the point of view of the flexibility of the resulting coating, 1 ,6-hexamethylene diisocyanate, and from the point of view of the reactivity of the isocyanate group, toluene-2,4- or 2,6-diisocyanate, are suitable polyisocyanates for the present invention.

[0051] Well-known blocking agents can be used for the isocyanate blocking agent used in the present invention. Examples include, alcohols such as methanol, ethanol, n-propyl alcohol, iso-propyl alcohol, n-butyl alcohol, iso-butyl alcohol and tert-butyl alcohol; phenols such as phenol, methylphenol, chlorphenol, p-iso-butylphenol, p-tert-butylphenol, p-iso-amylphenol, p-octyl phenol and p-nonylphenol; active methylene compounds such as malonic acid dimethylester, malonic acid diethyl ester, acetylacetone, methyl acetoacetate and acetoacetic acid ethyl; oximes such as formaldoxime, acetoaldoxime, acetone oxime, cyclohexanone oxime, acetophenone oxime, benzophenone oxime and 2-butanone oxime; lactams such as ε-caprolactam, δ-valerolactam and γ-butyrolactam; and thiosulfuric acid salts.

[0052] By selecting a blocking agent that disassociates from the isocyanate group at low temperatures, it is possible to lower the baking temperature for the coating in the autodeposition coating treatment of the present invention. However, if the disassociation temperature is too low, there is a risk of negatively impacting the stability of the surface treatment solution for autodeposition coating treatment. Thus, the use of oximes such as formaldoxime, acetoaldoxime, acetone oxime, cyclohexanone oxime, acetophenone oxime, benzophenone oxime and 2-butanone oxime and thiosulfuric acid salts is preferred. Note that, when the polyisocyanate used is a diisocyanate, it is preferable that one half that mole amount of blocking agent be used, and when the polyisocyanate used is a tri isocyanate, it is preferable that two thirds that mole amount of blocking agent be used, with respect to the isocyanate group. If such a blocking agent is used, an effect is produced whereby the reaction of the crosslinking agent with water subsequent to the polyol reaction is suppressed, the stability of the treatment solution for autodeposition surface treatment is maintained, and the coating hardens as a result of applying heat to the unbaked autodeposition coating. [0053] Polyols that can be used in the present invention include: polyether polyols such as polypropylene glycol, polyethylene glycol and polytetramethylene glycol, polyester polyols such as polyethylene adipate, polydiethylene adipate, polypropylene adipate, polytetramethylene adipate and poly-ε-caprolactone; polycarbonate polyol, acryl polyol, epoxy polyol, trimethylol propane, bisphenol A, bisphenol F and bisphenol AD.

[0054] Among these, epoxy polyol and bisphenol A, which have at least one molecule of bisphenol A structure in the molecular structure are preferred. Here, "have at least one molecule of bisphenol A structure" means that this is incorporated into the straight chain of a polymer, as with the aforementioned epoxy polyol, or a polymer having a bisphenol A repeating unit as a portion thereof, or a bisphenol A homopolymer, or bisphenol A itself. Bisphenol A has benzene rings in its basic skeleton, with two benzene rings being connected by a methylene chain having two methyl groups, so that the resin itself has a structure which is both robust (rigid) and has high chemical resistance (HO-C₆H₄-C(CH₃^-C₆H₄-OH). Accordingly, by using a polyol having a bisphenol A structure as the polyfunctional blocked isocyanate of the present invention, the corrosion resistance achieved by the present invention is dramatically improved.

[0055] The concentration of the novolac resin is preferably 1 to 5 mass% as a solid component concentration in the aqueous solution, more preferably 1 to 3 mass%. As described above, novolac resin having a methylol group is capable of autodeposition and thermosetting. Accordingly, when the concentration is less than 1 mass%, sufficient autodeposition capacity cannot be achieved, so that it is not possible to produce an autodeposition coating thickness sufficient to achieve the corrosion resistance that is one of the effects of the present invention. Furthermore, if 5 mass% is exceeded, the consumption of the autodeposition bath components increases, because of the treatment solution that is taken away by the object being coated, and this may also lead to increases in unnecessary waste products, as a result of the treatment solution that has been taken away being delivered to the wastewater treatment process after being removed in the water washing process. Accordingly, it is more preferable that the upper concentration limit for the novolac resin be 3 mass%.

[0056] The solid component concentration ratio of the novolac resin to the crosslinking agent in the aqueous solution is preferably from 1 :1 to 1 :10, more preferably from 1 :1 to 1 :5, and still more preferably from 1 :1 to 1 :3. The novolac resin used in the present invention has at least one molecule of methylol in the molecular structure and therefore can be hardened upon application of heat, even if a crosslinking agent is not added, due to the crosslinking reactions between the methylol groups, which is to say, ether bonds or methylene bridges. However, the present inventors discovered that, in order to achieve the corrosion resistance that is an object of the present invention, it was important to increase the crosslinking density by further adding a crosslinking agent.

[0057] Furthermore, by combining the novolac resin having a methylol group and the blocked poly-isocyanate having the bisphenol A structure, unprecedented corrosion resistance is achieved. However, as a result of the earnest study on the part of the inventors, it was determined that unduly increasing the amount of crosslinking agent added does not increase the corrosion resistance of the autodeposition coating.

[0058] Coatings formed from novolac resin are inherently hard. As the hardness of the coating film is further increased by way of complex crosslinking with a crosslinking agent, this ultimately becomes an extremely brittle resin. As a result of the study on the part of the inventors, it was determined that hard brittle coating films using novolac resin have inferior adhesion. Furthermore, hard brittle coating films are not suitable for practical use, as they are easily damaged by impact to the coating film or deformation of the metallic material on which they are applied.

[0059] If the ratio of the crosslinking agent to the novolac resin having the methylol group is less than one times the amount, the crosslinking density is low and sufficient corrosion resistance cannot be achieved. Furthermore, if this is greater than ten times the amount, the crosslinking density is excessive, so that the coating film becomes brittle and is not suitable for practical application.

[0060] Furthermore, in order to increase the water solubility of the components in the surface treatment solution, and particularly the crosslinking agent, and in order to improve the appearance of the coating after this is hardened by baking, a solvent component can be added. Solvents that are suitable for the present invention include ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, ethyleneglycol monohexyl ether, diethylene glycol monohexyl ether and 2,2,4-thmethylpentanediol-1 ,3-monoisobutyrate. [0061] The present invention relates to a surface treatment solution for autodeposition coating treatment. Here, the autodeposition reaction is one wherein, because of ferrous ions that are solved into the bath by a dissolution reaction of the ferrous metallic material due to the pH being 2 to 6 and an oxidization reaction of the metallic iron by the ferric ions, the two hydroxyl groups in the ortho positions on the 2,3-dihydroxynaphthalene-6-sulfonic acid molecule in the novolac resin that has the methylol group chelate the ferrous ion, whereby the novolac resin is rendered insoluble and precipitates as an autodeposition coating.

[0062] Furthermore, the excess ferrous ions, which were not used in the autodeposition reaction, are rapidly oxidized to ferric ions by the oxidizing agent in the autodeposition treatment bath of the present invention. The oxidized ferric ions, by themselves, can cause degradation of the stability of the autodeposition treatment bath, but as a result of coordination with the elemental fluorine contained in the treatment bath of the present invention, the chelation reaction with the novolac resin in the treatment bath is suppressed, so that the stability of the treatment bath is maintained.

[0063] Here, soluble iron salts such as iron nitrate, iron sulfate and iron chloride can be used as the iron ion source, and whether ferrous salts or ferric salts are used, these will become ferric ions in the treatment solution as a result of oxidization by the oxidizing agent in the surface treatment solution for autodeposition coating treatment. Furthermore, iron powder, iron oxide, iron hydroxide and the like may be used dissolved in hydrofluoric acid.

[0064] In order to bring about the autodeposition reaction, the concentration of ferric ions is 0.1 to 3 g/l, preferably 0.5 to 2.5 g/l, and more preferably 1 to 2 g/l. Note that the ferric ion concentration can be measured by methods common in this field of industry and, for example, using the surface treatment solution for autodeposition coating treatment in which the resin component has been broken down and separated in advance by way of acid and heating, this can be measured by way of the atomic absorption method, ICP emission analysis, or chelation analysis using EDTA. Note that a preferred concentration for the elemental fluorine is at least three times the molar concentration of the ferric ions. There is no particular restriction on the upper limit, but an example is no greater than 10 times the molar concentration of ferric ions. Note that the elemental fluorine concentration can be measured by methods common in this field of industry and, for example, the surface treatment solution for autodeposition coating treatment of the present invention can be subjected to a distillation process and the elemental fluorine concentration in the distillate can be measured by ion chromatography or with a capillary electrophoresis device. If the ferric ion concentration is less than the 0.1 g/l, it is difficult to cause an oxidation/dissolution reaction of a quantity of iron suitable for autodeposition. Furthermore, if this is greater than 3 g/l, the concentration of iron incorporated in the autodeposition coating increases, and thus the amount of water incorporated in the coating that accompanies the iron ions, increases, as a result of which, the autodeposition coating tends to peel off in subsequent water washing processes.

[0065] Hydrofluoric acid, ammonium fluoride, ammonium acid fluoride, sodium fluoride, sodium hydrogen difluoride, potassium fluoride, potassium hydrogen difluoride and the like can be used as the elemental fluorine source. Here, if fluorides other than hydrofluoric acid are used, the pH of the surface treatment solution for autodeposition coating treatment may be adjusted using acids such as nitric acid or sulfuric acid.

[0066] A preferred pH for the surface treatment solution for autodeposition coating treatment of the present invention is from 2 to 6, from 2.5 to 5 is more preferred, and from 2.5 to 4 is more preferred. Note that the pH measurement method is in accordance with the method of JIS Z8802. As described above, the surface deposition coating treatment method of the present invention begins with the dissolution reaction of the ferrous metallic material in the surface treatment solution for autodeposition coating treatment as a result of the hydrofluoric acid, and the oxidation reaction of the metallic iron as a result of the ferric ions. Accordingly, if the pH is greater than 6, the dissolution reaction of the metallic material will not readily occur, and the reduction reaction of the ferric ions will not readily occur. Furthermore, if the pH is less than 2, the dissolution reaction of the metallic material will be excessive in terms of the deposition reaction of the autodeposition coating, and there is a risk of degrading the stability of the surface treatment solution for autodeposition coating treatment.

[0067] The oxidizing agent is preferably at least one oxidizing agent selected from perchloric acid, hypochlorous acid, dissolved oxygen, ozone, permanganic acid, and hydrogen peroxide. Hydrogen peroxide is readily available and is a suitable oxidizing agent for the present invention because, since the byproduct of its own reduction reaction is water, there is no need for concern in terms of the influence on the autodeposition treatment bath.

[0068] The concentration of the oxidizing agent in the autodeposition treatment bath of the present invention can be managed by way of the redox potential, which is measured by market available ORP electrodes using a platinum electrode as the working electrode. Here, from the point of view of the autodeposition reaction of the present invention, it is preferable that there be excess oxidizing agent in the treatment bath when all of the ferrous ions have been oxidized to ferric ions. In other words, it is preferable that the amount of oxidizing agent be an amount that is sufficient to oxidize all of the iron ions present in the bath to ferric ions and maintain them in that oxidization state. It is possible to maintain the state described above by maintaining the redox potential at or above the minimum value given by the selected oxidizing agent; here, the preferred redox potential in the case of the example of hydrogen peroxide is at least 300 mV or more, more preferably 350 mV or more and still more preferably 400 mV or more. There are no particular restrictions on the upper limit, but this is no greater than 500 mV.

[0069] Furthermore, the method of autodeposition coating treatment of metallic materials of the present invention is one wherein the surface of a ferrous metallic material is first cleaned by degreasing and water washing, whereafter this is brought into contact with the aqueous solution described above as the surface treatment solution for autodeposition coating treatment, whereafter excess aqueous solution that has adhered to the surface of the metallic material is removed in a water washing process, and then the coating is thermoset by way of a baking process.

[0070] Here, for the degreasing treatment, conventionally commonly used solvent degreasers, alkaline degreasers and the like can be used, and there is no restriction whatsoever on the procedure, which can be flushing, spraying, immersion, electrolysis or the like. Furthermore, there are no restrictions whatsoever on the water washing after the degreasing treatment and after the autodeposition coating treatment, which can be selected from flushing, spraying, immersion and the like. There are no particular restrictions on the quality of the water used for water washing, but with consideration for micro components getting into the autodeposition coating treatment bath and remaining in the coating, ion exchange water is a preferred choice. [0071] The autodeposition coating treatment of the present invention is performed by the immersion method, wherein the object to be coated is immersed in a treatment bath. It suffices that the treatment bath in which the immersion method is performed be provided with stirring sufficient to maintain a uniform concentration of components in the treatment bath. Furthermore, a preferred immersion time is 1 to 10 minutes, and a more preferred immersion time is 2 to 5 minutes.

[0072] An acid washing process may also be employed, depending on the condition of the surface of the material to be coated. In this case, the treatment process comprises degreasing -> multistage water washing (normally 2 to 3 stages) -> acid washing -> multistage water washing (normally 1 to 2 stages) -> autodeposition coating formation -> multistage water washing (normally 2 to 3 stages) -> baking.

[0073] Furthermore, the present invention includes an autodeposition coated metallic material characterized by having an autodeposition coating layer that was deposited on the surface of a ferrous metallic material by the method described above, and in that the film thickness of the autodeposition coating layer after hardening by way of baking is 10 to 30 μm. Within this range, the corrosion resistance is sufficient and defects in the appearance such as cracks and shrinkage do not readily occur.

EXAMPLES

[0074] Hereafter, working examples and comparative examples are given so as to describe the effects of the surface treatment solution for autodeposition coating treatment and the autodeposition coating treated metallic material in concrete terms. Note that any market available materials may be selected as the metallic material to be treated, the degreasing agent and the paint used in the working examples, and there are no restrictions on the combinations of materials for the various actual applications of the surface treatment solution for autodeposition coating treatment and autodeposition coating treated metallic material of the present invention.

[0075] Test Pieces

The code and the specifics for the test pieces used in the working examples and comparative examples are as indicated below. ^• CRS (Cold Rolled Steel Plate: JIS-G-3141 )

[0076] Autodeposition Coating Treatment Solution Composition and Treatment Process

[0077] Manufacturing Example 1 : Synthesis of Novolac Resin Having a Methylol Group

Using dimethylamino benzene as an alkaline catalyst, 60 g of phenol (reagent) and 135 g of 37 mass% formaldehyde (reagent) were mixed by stirring at 70⁰C, to produce an aqueous resole resin having an F/P ratio of 2.6 and a solid content of 55 mass%. To 200 g of the aqueous resole resin, were added 40 g of sodium 2,3-dihydroxynaphthalene-6-sulfonate (reagent), 35 g catechol (reagent) and 50 g of water, and this was heated to 90⁰C and stirred for 3 hours. After stirring, 210 g of resorcinol (reagent) and 200 g of water with an added 5 g of 85 mass% phosphoric acid (reagent) were added, and this was stirred for 1 hour with the temperature maintained at 90°C. After stirring, 70 g of 37 mass% formaldehyde (reagent) were gradually added, an increase in the viscosity of the synthesized product was visually observed, and novolac resin having an F/P ratio of 0.84 and a solid component concentration of 53% was produced. The results of infrared spectrographic analysis of the synthesis product confirmed absorption indicating the presence of methylol groups.

[0078] Manufacturing Example 2: Synthesis of Novolac Resin Using 85 mass% phosphoric acid (reagent) as the acid catalyst, 61 g of phenol (reagent) and 42 g of 37 mass% formaldehyde (reagent) were mixed by stirring at 70⁰C to produce a novolac resin having an F/P ratio of 0.8 and a solid content of 55 mass%. To 140 g of the novolac resin were added 40 g of sodium 2,3-dihydroxynaphthalene-6-sulfonate (reagent), 35 g of catechol (reagent), 30 g of 37 mass% formaldehyde (reagent) and 30 g of water, which was heated to 90°C and stirred for 3 hours. After stirring, 210 g of resorcinol (reagent) and 200 g of water with an added 5 g of 85 mass% phosphoric acid (reagent) were added and this was stirred for 1 hour with the temperature maintained at 90°C. After stirring, 70 g of 37 mass% formaldehyde (reagent) were gradually added, an increase in the viscosity of the synthesized product was visually observed, and novolac resin having an F/P ratio of 0.3 and a solid component concentration of 53% was produced. The results of infrared spectrographic analysis of the synthesis product were not able confirm absorption indicating the presence of methylol groups.

[0079] Manufacturing Example 3: Synthesis of Crosslinking Agent In a dry nitrogen atmosphere, 87 g of 2-butanone oxime were added to 174 g of toluene diisocyanate (Koronate T80, made by Nippon Polyurethane Industry Co., Ltd.) under cooling from the exterior so that the reaction temperature did not exceed 40⁰C. After maintaining this at 40⁰C for 1 hour, the reaction vessel was heated to 70°C. Thereupon, 113 g of bisphenol A (reagent) and 0.02 g of dibutyl tin laurate (STANN BL: made by Sankyo Organic Synthesis Co., Ltd.) were added, and after maintaining this at 120⁰C for 2 hours, this was diluted with ethylene glycol monobutyl ether (reagent), so as to produce a solid component concentration of 30 mass%.

[0080] Manufacturing Example 4: Synthesis of Crosslinking Agent In a dry nitrogen atmosphere, 87 g of 2-butanone oxime were added to 174 g of toluene diisocyanate (Koronate T80: made by Nippon Polyurethane Industry Co., Ltd.) under cooling from the exterior so that the reaction temperature did not exceed 40°C. After maintaining this at 40°C for 1 hour, the reaction vessel was heated to 70⁰C. Thereupon, 45 g of 1 ,1 ,1-ths(hydroxymethyl)propane (reagent) and 0.02 g of dibutyl tin laurate (STANN BL: made by Sankyo Organic Synthesis Co., Ltd.) were added, and after maintaining this at 120°C for 2 hours, this was diluted with ethylene glycol monobutyl ether (reagent), so as to produce a solid component concentration of 30 mass%.

[0081] Working Examples 1 to 5 and Comparative Example 1 Degreasing treatment was performed by spraying the test sheets with the market available alkaline degreaser, Fine Cleaner L4460 (Nihon Parkerizing Co., Ltd.) which had been diluted to 2 mass% in water and heated to 40°C, using a sprayer. After the degreasing treatment, the surface of the test sheets were washed with ion exchange water, using a sprayer. The test sheets, the surfaces of which had been degreased and washed, were immersed in the autodeposition coating treatment baths shown in Table 1 , which were prepared using the novolac resin containing methylol groups from Manufacturing Example 1 , the crosslinking agent from Manufacturing Example 3, iron powder (reagent), hydrofluoric acid (reagent) and hydrogen peroxide (reagent), whereafter these were washed with ion exchange water using a sprayer, and subsequently baked for 20 minutes at 160⁰C. The immersion time in the autodeposition bath was established so as to produce a film thickness of 15 μm. The autodeposition coated metallic materials produced in the working examples and comparative examples were evaluated according to the methods described below.

[0082] Working Examples 6 to 9 and Comparative Examples 2, 3 Degreasing treatment was performed by spraying the test sheets with the market available alkaline degreaser, Fine Cleaner L4460 (Nihon Parkerizing Co., Ltd.) which had been diluted to 2 mass% in water and heated to 40⁰C, using a sprayer. After the degreasing treatment, the surface of the test sheets were washed with ion exchange water, using a sprayer. The test sheets, the surfaces of which had been degreased and washed, were immersed in the autodeposition coating treatment baths shown in Table 2, which were prepared using the novolac resin containing methylol groups from Manufacturing Example 1 , the crosslinking agent from Manufacturing Example 4, iron powder (reagent), hydrofluoric acid (reagent) and hydrogen peroxide (reagent), whereafter these were washed with ion exchange water using a sprayer, and subsequently baked for 20 minutes at 160⁰C. In addition, a market available amino alkyd intermediate coat paint (product name: Amilac TP-37 Gray: made by Kansai Paint Co., Ltd., film thickness 35 μm, sprayer application, baking for 20 minutes at 140°C) and a market available amino alkyd topcoat paint (product name: Amilac TM-13 White: made by Kansai Paint Co., Ltd., film thickness 35 μm, sprayer application, baking for 20 minutes at 140⁰C) were applied. The autodeposition coated metallic materials produced in the working examples and comparative examples were evaluated according to the methods described below.

[0083] Working Examples 11 to 13

Degreasing treatment was performed by spraying the test sheets with the market available alkaline degreaser, Fine Cleaner L4460 (Nihon Parkerizing Co., Ltd.) which had been diluted to 2 mass% in water and heated to 40°C, using a sprayer. After the degreasing treatment, the surface of the test sheets were washed with ion exchange water, using a sprayer. The test sheets, the surfaces of which had been degreased and washed, were immersed for 5 minutes in the autodeposition coating treatment baths shown in Table 3, which were prepared using the novolac resin containing methylol groups from Manufacturing Example 1 , the market available blocked isocyanate crosslinking agent, Elastron H38 (made by Dai-ichi Kogyo Seiyaku Co., Ltd.), iron powder (reagent), hydrofluoric acid (reagent) and hydrogen peroxide (reagent), whereafter these were washed with ion exchange water using a sprayer, and subsequently baked for 20 minutes at 160°C. In addition, a market available amino alkyd intermediate coat paint (product name: Amilac TP-37 Gray: made by Kansai Paint Co., Ltd., film thickness 35 μm, sprayer application, baking for 20 minutes at 140⁰C) and a market available amino alkyd topcoat paint (product name: Amilac TM-13 White: made by Kansai Paint Co., Ltd., film thickness 35 μm, sprayer application, baking for 20 minutes at 140⁰C) were applied. The autodeposition coated metallic materials produced in the working examples were evaluated according to the methods described below.

[0084] Comparative Example 4

Degreasing treatment was performed by spraying the test sheet with the market available alkaline degreaser, Fine Cleaner L4460 (Nihon Parkerizing Co., Ltd.) which had been diluted to 2 mass% in water and heated to 40°C, using a sprayer. After the degreasing treatment, the surface of the test sheet was washed with ion exchange water, using a sprayer. The test sheet, the surface of which had been degreased and washed, was immersed for 5 minutes in the autodeposition coating treatment bath shown in Table 3, which was prepared using the novolac resin containing methylol groups from Manufacturing Example 1 , a market available blocked isocyanate crosslinking agent, Elastron H38 (made by Dai-ichi Kogyo Seiyaku Co., Ltd.), iron powder (reagent), hydrofluoric acid (reagent) and hydrogen peroxide (reagent), whereafter this was washed with ion exchange water using a sprayer, and subsequently baked for 20 minutes at 160⁰C. Note that the blending ratio for the ferric chloride and the iron powder was such that the iron content from the ferric chloride was 1 g/l, and the remaining iron content was from the iron powder. In addition, a market available amino alkyd intermediate coat paint (product name: Amilac TP-37 Gray: made by Kansai Paint Co., Ltd., film thickness 35 μm, sprayer application, baking for 20 minutes at 140°C) and a market available amino alkyd topcoat paint (product name: Amilac TM-13 White: made by Kansai Paint Co., Ltd., film thickness 35 μm, sprayer application, baking for 20 minutes at 140°C) were applied. The autodeposition coated metallic materials produced in the comparative examples were evaluated according to the methods described below.

[0085] Comparative Example 5

Degreasing treatment was performed by spraying the test sheet with the market available alkaline degreaser, Fine Cleaner L4460 (Nihon Parkerizing Co., Ltd.) which had been diluted to 2 mass% in water and heated to 40⁰C, using a sprayer. After the degreasing treatment, the surface of the test sheet was washed with ion exchange water, using a sprayer. The test sheet, the surface of which had been degreased and washed, was immersed for 5 minutes in an autodeposition coating treatment bath, which was prepared with an ORP of 400 mV, using the novolac resin containing methylol groups from Manufacturing Example 1 at a solid content of 3 mass%, 1.5 g/l of iron powder (reagent), 1.6 g/l of hydrofluoric acid (reagent) for the fluorine and hydrogen peroxide (reagent), whereafter this was washed with ion exchange water using a sprayer, and subsequently baked for 20 minutes at 160⁰C. The autodeposition coated metallic material produced was evaluated according to the methods described below.

[0086] Comparative Examples 6 to 8

Degreasing treatment was performed by spraying the test sheets with the market available alkaline degreaser, Fine Cleaner L4460 (Nihon Parkerizing Co., Ltd.) which had been diluted to 2 mass% in water and heated to 40⁰C, using a sprayer. After the degreasing treatment, the surface of the test sheets were washed with ion exchange water, using a sprayer. The test sheets, the surfaces of which had been degreased and washed, were immersed in the autodeposition coating treatment baths shown in Table 4, which were prepared using the novolac resin from Manufacturing Example 2, the crosslinking agent from Manufacturing Example 3, iron powder (reagent), hydrofluoric acid (reagent) and hydrogen peroxide (reagent), whereafter these were washed with ion exchange water using a sprayer, and subsequently baked for 20 minutes at 160°C. The immersion time in the autodeposition bath was established so as to produce a film thickness of 15 μm. The autodeposition coated metallic materials produced in the comparative examples were evaluated according to the methods described below.

[0087] Comparative Example 9

Degreasing treatment was performed by spraying the test sheet with the market available alkaline degreaser, Fine Cleaner L4460 (Nihon Parkerizing Co., Ltd.) which had been diluted to 2 mass% in water and heated to 40⁰C, using a sprayer. After the degreasing treatment, the surface of the test sheet was washed with ion exchange water, using a sprayer. The test sheet, the surface of which had been degreased and washed, was immersed for 2 minutes in a treatment bath prepared with NSD-1000 (vinylidene chloride type, made by Nihon Parkerizing Co., Ltd.) adjusted based on the catalog value, whereafter this was washed with ion exchange water using a sprayer, and subsequently baked for 20 minutes at 100°C. In addition, a market available amino alkyd intermediate coat paint (product name: Amilac TP-37 Gray: made by Kansai Paint Co., Ltd., film thickness 35 μm, sprayer application, baking for 20 minutes at 140°C) and a market available amino alkyd topcoat paint (product name: Amilac TM-13 White: made by Kansai Paint Co., Ltd., film thickness 35 μm, sprayer application, baking for 20 minutes at 140⁰C) were applied. The adhesion of the test sheet coating after completing topcoat application was evaluated according to the methods described below.

[0088] Evaluation of the Appearance and Film Thickness of Autodeposition Coating Treated Metallic Materials

The appearance of the test sheets that had been subjected to the autodeposition coating treatment method in the working examples and comparative examples were judged visually. Furthermore, the coating thicknesses were measured using an electromagnetic coating thickness measurement instrument (Fisherscope MMS, made by Fischer)

[0089] Evaluation of the Performance of the Autodeposition Coated Metallic Material

The performances of the working examples and comparative examples were evaluated. The evaluation items and codes are as shown below. Note that the coating at the point in time when the autodeposition coating treatment is complete is referred to as an autodeposition coating and the coating at the point in time when the topcoat application is complete is referred to as a 3-coat coating.

(1 ) SST: Salt spray test (autodeposition coating)

(2) SDT: Hot salt water test (autodeposition coating)

(3) 1^stADH: Primary adhesion (3-coat coating)

(4) 2^ndADH: Water resistant secondary adhesion (3-coat coating)

[0090] SST

An autodeposition coated plate, into which a crosscut had been made with a sharp cutter, was sprayed for 600 hours with 5 mass% saline (according to JIS-Z-2371 ). After the spraying, the maximum blister width on both sides of the crosscut was measured.

[0091] SDT

An autodeposition coated plate, into which a crosscuts had been made with a sharp cutter was immersed for 240 hours in 5 mass% aqueous sodium chloride solution heated to 50⁰C. After immersion, the crosscut area, which had been washed with water and dried at ambient temperature, was subjected to peel off with adhesive tape, and the maximum coating peel off width on both sides was measured. [0092] 1^st ADH

One hundred grid squares were cut at 2 mm intervals into the 3-coat coating with a sharp cutter. The grid area was subjected to peel off with Cellotape™ and the number of grid squares remaining was counted.

[0093] 2^nd ADH

The 3-coat coating sheet was immersed in deionized water at 40⁰C for 240 hours. After immersion, a 100 square grid was cut at 2 mm intervals with a sharp cutter. The grid area was subjected to peel off with Cellotape and the number of grid squares remaining was counted.

[0094] Table 5 shows the results of evaluating the autodeposition coatings produced in Working Examples 1 to 5 and Comparative Example 1. In Working Examples 1 to 5, a uniform appearance was produced and the corrosion resistance was excellent, for all standards. Conversely, in Comparative Example 1 , cracks were produced over the entire surface of the autodeposition coating after baking, and therefore corrosion resistance was not evaluated.

[0095] Table 6 shows the results of evaluating the autodeposition coatings produced in Working Examples 6 to 9 and Comparative Examples 2 and 3. Working Examples 6 to 9 were slightly inferior to Working Examples 1 to 5 because a bisphenol A structure was not introduced into the cross-linking agent, but they showed sufficient corrosion resistance for practical use. Furthermore, after applying an intermediate coat, the adhesion was also good. Conversely, while the autodeposition coated metallic material of Comparative Example 2 achieved adhesiveness, the film thickness was low, which resulted in inferior corrosion resistance. In Comparative Example 3, cracks were produced over the entire surface of the autodeposition coating after baking, and therefore corrosion resistance was not evaluated.

[0096] Table 7 shows the results of evaluating the autodeposition coatings produced in Working Examples 11 to 13 and Comparative Example 4. In Working Examples 11 to 13, a uniform appearance was produced and the corrosion resistance was excellent, for all standards. Furthermore, after applying an intermediate coat, the adhesion was also good. Conversely, in Comparative Example 4, the unbaked coating peeled in the water washing process, which was the process subsequent to the autodeposition coating treatment process. [0097] Table 8 shows the results of evaluating the autodeposition coating produced in Comparative Example 5. In Comparative Example 5, an autodeposition coating was produced, but the result was a markedly inferior corrosion resistance, because a cross-linking agent was not used.

[0098] Table 9 shows the results of evaluating the autodeposition coatings produced in Comparative Examples 6 to 8. Because the novolac resin used in Comparative Examples 6 to 8 did not have a methylol group, the corrosion resistance was inferior. Furthermore, the stability of the treatment bath was very low, and sedimentation occurred one hour after autodeposition coating treatment. Conversely, in all of the working examples, there was no sedimentation, even after storing the treatment solution for one month after autodeposition coating treatment, and almost no sludge was produced as a result of the autodeposition coating treatment.

[0099] Table 10 shows the results of evaluating the autodeposition coating produced in Comparative Example 9. Because Comparative Example 9 was that of a market available autodeposition coating treatment agent, a relatively good corrosion resistance was exhibited. However, in evaluating the adhesion after applying an intermediate coat, all of the coating in the grid area peeled off.

[0100] From the foregoing, the effects of the present invention are clear.

[Table 1]

[Table 2]

[Table 3]

[Table 4]

[Table 5]

[Table 6]

[Table 8]

[Table 9]

[Table 10]

Claims

1. A surface treatment solution for autodeposition coating treatment of metallic materials, which is an aqueous solution comprising a novolac resin, a crosslinking agent, ferric ions, elemental fluorine and an oxidizing agent, characterized in that: said novolac resin is a novolac resin having a methylol group and having an F/P ratio of 0.7 to 1.0, produced by mixing and stirring a resole resin, which is producible by reacting a phenol and an aldehyde in the presence of an alkaline catalyst at an F/P ratio in the range of 2.5 to 3, a hydroxyphenol having two or more hydroxyl groups on adjacent aromatic ring carbons, and a phenol, and further adding a phenol, an aldehyde and an acidic catalyst and polymerizing; said crosslinking agent is a crosslinking agent having a crosslinking group capable of causing a thermosetting reaction between said methylol group and a phenol nucleus and/or a phenolic hydroxyl group; the solid component mass concentration ratio of said novolac resin to said crosslinking agent is in the range of 1 :1 to 1 :10; the molar concentration of said elemental fluorine is at least 3 times said ferric ions, and the pH is in the range of 2 to 6.

2. The surface treatment solution for autodeposition coating treatment of metallic materials recited in Claim 1 , characterized in that said novolac resin has the structural formula shown in Formula 1.

[Chem. 1]

[Formula 1]

3. The surface treatment solution for autodeposition coating treatment of metallic materials recited in Claim 1 or Claim 2, wherein said crosslinking group of the crosslinking agent that is capable of causing a thermosetting reaction is an isocyanate group.

4. The surface treatment solution for autodeposition coating treatment of metallic materials recited in Claim 3, wherein said crosslinking agent is a polyfunctional blocked isocyanate wherein at least 2 mol of polyisocyanate, wherein one of the isocyanate groups has been blocked in advance with a blocking agent, are added to 1 mol of polyol.

5. The surface treatment solution for autodeposition coating treatment of metallic materials recited in Claim 4, characterized in that the polyol in said crosslinking agent has at least one molecule of bisphenol A structure.

6. The surface treatment solution for autodeposition coating treatment of metallic materials recited in any one of Claim 1 to Claim 5, characterized in that the concentration of said novolac resin is 1 to 5 mass% as a solid component concentration in the aqueous solution.

7. The surface treatment solution for autodeposition coating treatment of metallic materials recited in any one of Claim 1 to Claim 6, wherein the oxidizing agent is at least one oxidizing agent selected from perchloric acid, hypochlorous acid, dissolved oxygen, ozone, permanganic acid and hydrogen peroxide.

8. The surface treatment solution for autodeposition coating treatment recited in Claim 7, characterized in that the redox potential, measured with a platinum electrode, is 300 to 500 mV.

9. A metallic material autodeposition coating treatment method characterized by contacting a metallic material, the surface of which has been cleaned by degreasing and water washing in advance, with the surface treatment solution recited in any one of Claims 1 to 8, then furthermore removing the excess of said treating solution that has adhered to the surface of said metallic material in a washing process, and next thermosetting the coating by performing a baking treatment.

10. The metallic material autodeposition coating treatment method recited in Claim 9, characterized in that said metallic material is a ferrous metallic material.

11. An autodeposition coated metallic material characterized by comprising an autodeposition coating layer, deposited on the surface of the metallic material by the method recited in Claim 9 or Claim 10, and in that the film thickness of the autodeposition coating layer after being hardened by baking is 10 to 30 μm.