Coating composition for passivating ZAM (zinc-aluminum-magnesium) substrates having low to medium aluminum content

Abstract

The present invention provides a coating composition for passivating low and medium Al ZAM substrates, the coating composition comprising at least one water soluble or water dispersible resin selected from the group consisting of polyurethane resins, epoxy resins and polyacrylate resins; at least one silane; at least one corrosion inhibitor and at least one anti-darkening agent selected from amino acids.

Description

Technical Field

[0001] The present invention relates to a coating composition for passivating ZAM substrates, and more specifically for passivating low-Al and medium-Al ZAM substrates. Background Technology

[0002] In recent years, ZAM (zinc-aluminum-magnesium) substrates have become popular due to their superior corrosion resistance compared to traditional HDG (hot-dip galvanized) and GL (hot-dip aluminized zinc) substrates. Based on the aluminum content, ZAM substrates are typically classified into three types: low-Al ZAM, medium-Al ZAM, and high-Al ZAM. Based on the total weight of the ZAM substrate, the weight percentage of Al in low-Al ZAM does not exceed 5%, while for medium-Al ZAM, this figure is higher than 5% but does not exceed 12%. Low-Al and medium-Al ZAM substrates can be considered as HDG substrates with added Al and Mg elements. Furthermore, based on the total weight of the ZAM substrate, the weight percentage of Mg in ZAM is typically in the range of 1% to 3%.

[0003] However, ZAM substrates are prone to darkening during storage due to the formation of magnesium compounds on their surface. Furthermore, when existing passivation coatings are applied to ZAM substrates, noticeable discoloration is observed in humidity tests. Given the stringent surface appearance requirements in the home appliance and automotive industries, passivation coatings must provide excellent anti-darkening properties based on the ZAM substrate. Simultaneously, they must also meet other key performance requirements, including corrosion resistance, alkali resistance, solvent resistance, perspiration resistance, and heat resistance.

[0004] Therefore, there is still a need for a coating composition for passivating ZAM substrates with low to medium aluminum content, which can prevent the substrate surface from darkening and at the same time enable the ZAM substrate surface to be resistant to corrosion, alkali, solvent, sweat and heat. Summary of the Invention

[0005] In one aspect, the present invention provides a coating composition for passivating low-Al and medium-Al ZAM substrates, the coating composition comprising

[0006] (a) at least one water-soluble or water-dispersible resin selected from polyurethane resins, epoxy resins and polyacrylate resins;

[0007] (b) at least one silane;

[0008] (c) at least one corrosion inhibitor; and

[0009] (d) At least one anti-dark staining agent selected from amino acids.

[0010] In another aspect, the present invention provides low-Al and medium-Al ZAM substrates passivated by the coating composition of the present invention.

[0011] Surprisingly, it has been found that by adding appropriate amounts of amino acids (such as aspartic acid, glutamic acid, serine, threonine, cysteine, tyrosine, asparagine, glutamine, and phenylalanine), the resulting passivation coating compositions can significantly improve the anti-darkening performance of low-Al and medium-Al ZAM substrates in humidity tests at 49°C and 95% relative humidity, while other properties (such as corrosion resistance, alkali resistance, solvent resistance, perspiration resistance, and heat resistance) remain satisfactory. Detailed Implementation

[0012] The invention will now be described more fully below, wherein some, but not all, embodiments of the invention are shown. In fact, the invention may be embodied in many different forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that this disclosure will satisfy applicable legal requirements.

[0013] In this disclosure, the expressions “a / an” and “the” include both the plural and singular forms of the term when used to define it.

[0014] The terms “comprise”, “comprising”, etc., are used interchangeably with “contain / containing” and should be interpreted in a non-restrictive, open-ended manner. That is, for example, additional components or elements may exist. If used, expressions such as “composed of” or “substantially composed of” or cognates may be included in “comprises” or cognates.

[0015] The term "acidic" refers to having acidic properties, and an acidic coating composition refers to a coating system with a pH < 7. In some embodiments of the invention, the pH of the coating composition is in the range of 3 to 5.

[0016] The term "passivation layer" refers to a film obtained by curing or drying a passivation composition.

[0017] The term "silane" refers to silanes and their hydrolysis, condensation, polymerization and reaction products, especially silanols, siloxanes and polysiloxanes.

[0018] The term "polyurethane" refers to a polymer composed of organic unit chains linked by carbamate (urethane) bonds. Polyurethane resins are formed by reacting monomers having two or more isocyanate (-N=C=O) groups with monomers having two or more hydroxyl (-OH) groups.

[0019] The terms “isocyanate,” “diisocyanate,” or “polyisocyanate” refer to compounds having one, two, or at least three isocyanate (-N=C=O) groups, respectively.

[0020] The term "polyacrylate resin" is a common name for acrylic polymers and methacrylate polymers (or (meth)acrylate polymers) and their derivatives.

[0021] The term "(meth)acrylate" refers to acrylates and / or methacrylate monomers.

[0022] Unless otherwise stated, all percentages and ratios relating to the composition are mentioned by weight.

[0023] This invention provides a coating composition for passivating low-Al and medium-Al ZAM substrates, the coating composition comprising

[0024] (a) at least one water-soluble or water-dispersible resin selected from polyurethane resins, epoxy resins and polyacrylate resins;

[0025] (b) at least one silane;

[0026] (c) at least one corrosion inhibitor; and

[0027] (d) At least one anti-dark staining agent selected from amino acids.

[0028] The coating composition of the present invention comprises a water-soluble or water-dispersible resin selected from the group consisting of polyurethane resin, epoxy resin and polyacrylate resin as component (a). Furthermore, the amount of component (a) is in the range of 5% to 15% by weight based on the total weight of the coating composition. In some embodiments, the amount of component (a) in the coating composition is in the range of 5% to 10% by weight based on the total weight of the coating composition.

[0029] Preferably, component (a) is a combination of polyurethane resin and polyacrylate resin. Surprisingly, by combining polyurethane resin and polyacrylate resin, the surface energy of the resulting passivation layer can be significantly increased, and simultaneously the storage stability of the coating composition, as well as the corrosion resistance, chemical resistance, boiling water resistance, darkening resistance, and heat resistance of the passivation layer, are significantly improved. In some preferred embodiments, the weight ratio of polyurethane resin to polyacrylate resin is in the range of 0.5 to 1.2, preferably in the range of 0.6 to 1.0, and more preferably in the range of 0.7 to 1.0.

[0030] The polyurethane resin suitable for the coating compositions of the present invention can be prepared by reacting at least one polyol selected from the group consisting of polyester polyols and polyether polyols with a diisocyanate or a polyisocyanate.

[0031] Those skilled in the art can select suitable isocyanates. For example, the isocyanate may be hexamethylene diisocyanate, octamethylene diisocyanate, decamethylene diisocyanate, dodecamethylene diisocyanate, tetradecamethylene diisocyanate, trimethylhexane diisocyanate, tetramethylhexane diisocyanate, isophorone diisocyanate, 2-isocyanopropylcyclohexyl isocyanate, dicyclohexylmethane 2,4′-diisocyanate, dicyclohexylmethane 4,4′-diisocyanate, 1,4- or 1,3-bis(isocyanomethyl)cyclohexane, 1,4- or 1,3- or 1,2-diisocyanocyclohexane, 2,4- or 2,6-diisocyano-1-methylcyclohexane, or diisocyanates derived from dimer fatty acids (such as DDI from Henkel). 1410), 1,8-diisocyano-4-isocyano-methyloctane, 1,7-diisocyano-4-isocyano-methylheptane, 1-isocyano-2-(3-isocyanopropyl)cyclohexane, tetramethylphenyl dimethyl diisocyanate (TMXDI), or mixtures of these polyisocyanates. In some embodiments, the isocyanate may be tetramethylphenyl dimethyl diisocyanate (TMXDI) or isophorone diisocyanate or a combination thereof. In some embodiments, the isocyanate is isophorone diisocyanate.

[0032] Preferably, the polyurethane resin used in the coating composition of the present invention does not contain an aromatic structure. The polyurethane resin can be added to the aqueous non-Cr passivated composition in dispersion form. For example, the dispersion can be selected from the group consisting of: Siwo ® PUD1217 (Shanghai Sisheng PolymerMaterials Co., Ltd.), ALBERDINGK ® CUD4820 VP and ALBERDINGK ®CUD4835 VP (Alberdingk Boley), ESACOTE ® PUC1 (Lamberti Asia Pacific Limited), DIC ® HYDRAN MC1030, DIC ® HYDRAN CP-7520 and DIC ® HYDRAN CP-7050 (DIC Corporation). Furthermore, when polyurethane resin is added to a coating composition in dispersion form, the amount of polyurethane resin is calculated based on the amount of polyurethane resin in the dispersion.

[0033] Polyacrylate resin can be added to the coating composition of the present invention in the form of a dispersion or an emulsion. Furthermore, when polyacrylate resin is added to the coating composition in the form of a dispersion or an emulsion, the amount of polyacrylate resin is calculated based on the amount of polyacrylate resin in the dispersion or emulsion.

[0034] Preferably, the polyacrylate resin used as component (a) is prepared by emulsion polymerization of monomers in the presence of a polymerization initiator. Surprisingly, it has been found that polyacrylate resins prepared by emulsion polymerization with appropriate number-average molecular weight (Mn) and average particle size can help improve the alkali resistance of the formed passivation layer.

[0035] Preferably, the polyacrylate resin has a number average molecular weight (Mn) in the range of 100,000 Daltons to 500,000 Daltons, as determined by gel permeation chromatography (GPC) according to DIN 55672-1. More preferably, the polyacrylate resin has a number average molecular weight in the range of 100,000 Daltons to 300,000 Daltons, and more preferably 100,000 Daltons to 200,000 Daltons.

[0036] Preferably, the polyacrylate resin has a particle size in the range of 50 nm to 400 nm, preferably 100 nm to 300 nm, and more preferably 100 nm to 200 nm as measured by DLS (dynamic light scattering).

[0037] Those skilled in the art can select appropriate conditions and procedures for emulsion polymerization based on the actual application. In some preferred embodiments, the polyacrylate resins used in this invention are prepared by emulsion polymerization without the use of any fluorinated emulsifiers. For example, the polyacrylate resin dispersion or emulsion may be selected from the group consisting of: NeoCrylXK350 (DSM NeoResins), GUANGSHU® GS-406 (Changzhou Guangshu Chemical Technology Co., Ltd.), Capast ® CP 7012 (Caprol Chemical (Shanghai) Co., Ltd.) and Gardobond PC8918 CA (Chemetall).

[0038] Monomers used to prepare polyacrylate resins are known in the art. For example, these monomers may be methyl acrylate, methyl methacrylate, acrylic acid, methacrylic acid, ethyl acrylate, ethyl methacrylate, propyl acrylate, propyl methacrylate, isopropyl acrylate, isopropyl methacrylate, butyl acrylate, butyl methacrylate, isobutyl acrylate, isobutyl methacrylate, tert-butyl acrylate, tert-butyl methacrylate, amyl acrylate, amyl methacrylate, hexyl acrylate, hexyl methacrylate, ethylhexyl acrylate, ethylhexyl methacrylate, 3,3,5-trimethylhexyl acrylate, 3,3,5-trimethylhexyl methacrylate, stearyl acrylate, stearyl methacrylate, lauryl acrylate or lauryl methacrylate, cycloalkyl acrylates and / or cycloalkyl methacrylates, such as (meth)acrylic acid. Cyclohexyl esters, alkyl-substituted cyclohexanol (meth)acrylates, and alkanol-substituted cyclohexane (meth)acrylates, such as 2-tert-butyl and 4-tert-butylcyclohexyl (meth)acrylates, 4-cyclohexyl-1-butyl (meth)acrylates, and 3,3,5,5-tetramethylcyclohexyl (meth)acrylates; isobornyl (meth)acrylate; isomenthyl (meth)acrylate; cyclopentyl (meth)acrylate, alkyl-substituted cyclopentanol (meth)acrylates, and alkanol-substituted cyclopentane (meth)acrylates; adamantyl (meth)acrylate; cyclododecane (meth)acrylate; cycloundecane methyl (meth)acrylate; dicyclohexyl methyl (meth)acrylate; cyclododecane methyl (meth)acrylate; menthyl (meth)acrylate and combinations thereof.

[0039] The epoxy resin suitable for the aqueous non-Cr passivation composition can be any aqueous epoxy resin known in the art capable of forming a film.

[0040] Those skilled in the art can select appropriate epoxy resins for this invention. For example, the epoxy resin can be selected from the group consisting of: bisphenol A type epoxy resin, bisphenol F type epoxy resin, glycidyl ether epoxy resin (such as polyphenol type glycidyl ether epoxy resin), glycidyl ester epoxy resin, silicone modified epoxy resin, and polyurethane modified epoxy resin.

[0041] Component (b) may be selected from the group consisting of various silanes. For example, the silanes used in this invention may be selected from acyloxysilanes, alkylsilanes, alkyltrialkoxysilanes, aminosilanes, aminoalkylsilanes, aminopropyltrialkoxysilanes, bis(meth)acrylate silanes, mono(meth)alkylsilanes, poly(meth)alkylsilanes, bis-(trialkoxysilylpropyl)amines, bis-(trialkoxysilyl)ethane, sulfur-containing silanes, bis-(trialkoxysilyl)propyltetrathiones, ureosilanes (such as (ureopropyltrialkoxy)silanes), vinylsilanes (especially vinyltrialkoxysilanes and / or vinyltriacetoxysilanes), and / or at least one corresponding silanol and / or siloxane.

[0042] Preferably, the silane may be selected from the group consisting of: tetraethoxysilane, 3-glycidoxyalkyltrialkoxysilane, 3-methacryloxyalkyltrialkoxysilane, aminoalkylaminoalkylalkyldialkoxysilane, β-(3,4-epoxycycloalkyl)alkyltrialkoxysilane, (3,4-epoxycycloalkyl)alkyltrialkoxysilane, bis(trialkoxysilylalkyl)amine, bis-(trialkoxysilyl)ethane, (3,4-epoxyalkyl)trialkoxysilane, γ-aminoalkyltrialkoxysilane. Alkane, γ-methacryloxyalkyltrialkoxysilane, γ-ureidoalkyltrialkoxysilane, glycidoxyalkyltrialkoxysilane, N-(3-(trialkoxysilyl)alkyl)alkylene diamine, N-β-(aminoalkyl)-γ-aminoalkyltrialkoxysilane, N-(γ-trialkoxysilyl)dialkylene triamine, polyaminoalkylalkyldialkoxysilane, tris(3-(trialkoxysilyl)alkyl)isocyanurate, (ureidopropyltrialkoxy)silane, and vinyltriacetoxysilane. More preferably, the silane may be selected from the group consisting of 3-aminopropyltriethoxysilane, 3-epoxypropyltrimethoxysilane, tetraethoxysilane, and 3-vinyltrimethoxysilane.

[0043] Component (b) is added in an amount of 5% to 20% by weight, and preferably 8% to 15% by weight, based on the total weight of the coating composition.

[0044] Component (c) is a corrosion inhibitor used to prevent metal corrosion. Furthermore, it can improve the stability of the coating composition during storage.

[0045] Component (c) may be an organophosphonic acid, an inorganic phosphoric acid, or their salts; or an acid corrosion inhibitor, such as a fluorinated acid corrosion inhibitor, like hexafluorotitanic acid, hexafluorozirconic acid, or a combination thereof.

[0046] Inorganic phosphoric acid or phosphate is preferably added in at least one of the following forms: monophosphate (= based on PO4) 3- orthophosphate, based on HPO4 2- The monohydrogen phosphate, or based on H2PO4 - The phosphates include zinc dihydrogen phosphate, diphosphate, triphosphate, phosphorus pentoxide, and phosphoric acid (= orthophosphoric acid H3PO4). Phosphates can be monometallic phosphates, mixtures of phosphoric acid and metals, mixtures of phosphoric acid and metal salts / oxides, diphosphates, triphosphates, polyphosphates of phosphorus pentoxide, etc. In one embodiment, component (c) is zinc dihydrogen phosphate.

[0047] Organophosphonic acids and salts can be added as component (c) to the coating compositions of the present invention. The organophosphonic acids and salts suitable for use in the present invention may include, but are not limited to, diphosphonic acids and diphosphonic acids having alkyl chains. Examples include 1-hydroxyethane-1,1-diphosphonic acid (HEDP), aminotris(methylenephosphonic acid) (ATMP), ethylenediamine-tetra(methylenephosphonic acid) (EDTMP), diethylenetriamine-penta(methylenephosphonic acid) (DTPMP), diethylenetriamine-penta(methylenephosphonic acid) (DTPMP), hexamethylenediamine-tetra(methylenephosphonic acid) (HDTMP), hydroxyethyl-amino-di(methylenephosphonic acid) (HEMPA), and / or phosphonobutane-1,2,4-tricarboxylic acid (PBTC).

[0048] Based on the total weight of the coating composition, the amount of component (c) in the coating composition is in the range of 1% to 10% by weight, for example, in the range of 1% to 5% by weight.

[0049] Component (d) is an anti-darkening agent selected from the group of amino acids. Compared with hot-dip galvanized (HDG) and hot-dip aluminized zinc (GL) substrates, ZAM substrates exhibit better corrosion resistance, but are prone to darkening during storage due to the formation of magnesium compounds on the substrate surface.

[0050] Surprisingly, by adding appropriate amounts of certain amino acids, the resulting coating compositions enabled low-Al and medium-Al ZAM substrates to resist darkening while maintaining other properties such as corrosion resistance, solvent resistance, heat resistance, and alkali resistance.

[0051] The amino acids used as anti-dark staining agents are hydrophilic amino acids, including amino acids with polar side chains and charged side chains, such as serine, threonine, cysteine, tyrosine, asparagine, glutamine, aspartic acid, glutamic acid, lysine, arginine, and histidine.

[0052] Preferably, component (d) as the anti-dark-growth agent is at least one selected from the group consisting of: aspartic acid, glutamic acid, serine, threonine, cysteine, tyrosine, asparagine, glutamine, and phenylalanine. In some embodiments, at least one amino acid selected from phenylalanine, glutamine, threonine, and tyrosine is used as the anti-dark-growth agent. And in one specific embodiment, threonine is used as the anti-dark-growth agent.

[0053] Based on the total weight of the coating composition, the amount of component (d) as the anti-darkening agent is in the range of 0.05% to 2% by weight, and preferably 0.1% to 1% by weight.

[0054] The coating compositions of the present invention may further comprise at least one additive. Those skilled in the art can select one or more additives for use in the aqueous non-Cr passivation compositions of the present invention, depending on the specific application. For example, these additives may be defoamers such as BYK028 (BYK Chemie); wetting agents such as SF104E (Evonik); and coalescing agents such as dipropylene glycol monobutyl ether.

[0055] In some embodiments, polyester resin and phenolic varnish resin may also be added as additives.

[0056] When additives are added, the amount can be determined by those skilled in the art. Generally, based on the total weight of the coating composition of the present invention, the amount of additional additives can be in the range of 1% to 10% by weight, or 1% to 5% by weight.

[0057] The coating composition is prepared by mixing components (a), (b), (c), (d) and optional additives in appropriate amounts. Furthermore, those skilled in the art can determine the order of mixing and all conditions.

[0058] Passivation of low-Al and medium-Al ZAM substrates is performed by a method comprising the following steps:

[0059] i) Use a degreasing agent (1 wt% Gardoclean, commercially available from Chemitre) at 50°C. ® Clean low-Al or medium-Al ZAM surfaces with S5185 aqueous solution for 5 to 10 seconds to remove grease;

[0060] ii) Rinse the low-Al or medium-Al ZAM substrate with deionized water until a continuous water film is formed, and then dry these surfaces with hot air;

[0061] iii) Applying the coating composition of the present invention to the degreased surface of a low-Al or medium-Al ZAM substrate using a bar coater; and

[0062] iv) Place the coated substrate in an oven at 280°C for 5 to 10 seconds to form 1.0 g / m 2 A certain amount of passivation layer.

[0063] After passivation, the obtained substrate was subjected to a series of performance tests, including resistance to darkening, corrosion resistance, solvent resistance, heat resistance, and alkali resistance. Furthermore, compared to coating compositions that do not contain amino acids as anti-darkening agents, the coating compositions of the present invention enable low-Al and medium-Al ZAM substrates to resist darkening, while other properties are also satisfactory. Example

[0064] The following examples further illustrate how the invention can be carried out.

[0065] Example 1

[0066] A coating composition for passivating low-Al and medium-Al ZAM substrates, the coating composition comprising

[0067] (a) at least one water-soluble or water-dispersible resin selected from polyurethane resins, epoxy resins and polyacrylate resins;

[0068] (b) at least one silane;

[0069] (c) at least one corrosion inhibitor; and

[0070] (d) At least one anti-dark staining agent selected from amino acids.

[0071] Example 2

[0072] According to the coating composition of Example 1, the anti-darkening agent is selected from hydrophilic amino acids and preferably selected from at least one of the following groups: aspartic acid, glutamic acid, serine, threonine, cysteine, tyrosine, asparagine, glutamine, and phenylalanine.

[0073] Example 3

[0074] According to any one of Examples 1 to 2, the amount of the anti-darkening agent in the coating composition is in the range of 0.05% to 2% by weight based on the total weight of the coating composition, and preferably 0.1% to 1% by weight.

[0075] Example 4

[0076] The coating composition according to any one of Examples 1 to 3, wherein the coating composition further comprises at least one additive selected from defoamers, wetting agents and coalescing agents.

[0077] Example 5

[0078] According to any one of Examples 1 to 4, the coating composition wherein component (a) is a combination of polyurethane resin and polyacrylate resin, and the weight ratio of polyurethane resin to polyacrylate resin is in the range of 0.5 to 1.2, preferably in the range of 0.6 to 1.0, and more preferably in the range of 0.7 to 1.0.

[0079] Example 6

[0080] The coating composition according to any one of Examples 1 to 5, wherein the polyacrylate resin has a number average molecular weight (Mn) in the range of 100,000 Daltons to 500,000 Daltons as determined by gel permeation chromatography (GPC) according to DIN 55672-1. Preferably, the polyacrylate resin has a number average molecular weight in the range of 100,000 Daltons to 300,000 Daltons, and more preferably in the range of 100,000 Daltons to 200,000 Daltons.

[0081] Example 7

[0082] According to any one of Examples 1 to 6, the coating composition wherein the silane is selected from the group consisting of: tetraethoxysilane, 3-glycidoxyalkyltrialkoxysilane, 3-methacryloyloxyalkyltrialkoxysilane, aminoalkylaminoalkylalkyldialkoxysilane, β-(3,4-epoxycycloalkyl)alkyltrialkoxysilane, (3,4-epoxycycloalkyl)alkyltrialkoxysilane, bis(trialkoxysilylalkyl)amine, bis-(trialkoxysilyl)ethane, (3,4-epoxyalkyl)trialkoxysilane, γ- Aminoalkyltrialkoxysilane, γ-methacryloxyalkyltrialkoxysilane, γ-ureidoalkyltrialkoxysilane, glycidoxyalkyltrialkoxysilane, N-(3-(trialkoxysilyl)alkyl)alkylene diamine, N-β-(aminoalkyl)-γ-aminoalkyltrialkoxysilane, N-(γ-trialkoxysilyl)dialkylene triamine, polyaminoalkylalkyldialkoxysilane, tris(3-(trialkoxysilyl)alkyl)isocyanurate, (ureidopropyltrialkoxy)silane, and vinyltriacetoxysilane. More preferably, the silane may be selected from the group consisting of 3-aminopropyltriethoxysilane, 3-epoxypropyltrimethoxysilane, tetraethoxysilane, and 3-vinyltrimethoxysilane.

[0083] Example 8

[0084] According to any one of Examples 1 to 7, the coating composition wherein the corrosion inhibitor is at least one selected from the group consisting of phosphorus-containing compounds and acid corrosion inhibitors, preferably at least one selected from the group consisting of 1-hydroxyethane-1,1-diphosphonic acid, zinc dihydrogen phosphate, hexafluorotitanic acid and hexafluorozirconic acid.

[0085] Example 9

[0086] The coating composition according to any one of Examples 1 to 8, wherein the coating composition further comprises at least one additive selected from defoamers, wetting agents and coalescing agents.

[0087] Example 10

[0088] A low-Al ZAM substrate, which is passivated by a coating composition according to any one of Examples 1 to 9.

[0089] Example 11

[0090] According to the low-Al ZAM substrate of Example 10, the weight percentage of Al is in the range of 0.5% to 5% by weight, and preferably 1% to 3% based on the total weight of the low-Al ZAM substrate.

[0091] Example 12

[0092] According to any one of Examples 10 to 11, the low Al ZAM substrate contains Mg by weight percentage in the range of 1% to 3% by weight, and preferably 1% to 2% by weight, based on the total weight of the low Al ZAM substrate.

[0093] Example 13

[0094] A medium Al ZAM substrate, which is passivated by a coating composition according to any one of Examples 1 to 9.

[0095] Example 14

[0096] According to the medium Al ZAM substrate of Example 13, the weight percentage of Al is in the range of 0.5% to 5% and preferably 1% to 3% by weight, based on the total weight of the medium Al ZAM substrate.

[0097] Example 15

[0098] According to any one of Examples 13 to 14, the medium Al ZAM substrate, wherein the weight percentage of Mg is in the range of 1% to 3% by weight, and preferably 2% to 3% by weight, based on the total weight of the medium Al ZAM substrate. Example

[0099] The invention will be better understood from the following non-limiting examples. These examples do not limit the scope of the invention as described and claimed.

[0100] <Raw materials>

[0101]

[0102] Other raw materials are standard raw materials, and there are no special restrictions on their specific types.

[0103] Examples 1 to 4 and Comparative Example C1: Preparation of coating compositions for passivating low-Al ZAM substrates

[0104] A series of coating compositions for passivating low-Al ZAM substrates were prepared by mixing certain amounts of the components according to the formulations in Table 1.

[0105] Table 1:

[0106]

[0107] Examples 5 to 8 and Comparative Example C2: Preparation of coating compositions for passivating intermediate Al ZAM substrates

[0108] A series of coating compositions for passivating medium Al ZAM substrates were prepared by mixing certain amounts of the components according to the formulations in Table 2.

[0109] Table 2:

[0110]

[0111] Passivation of low Al ZAM substrates

[0112] To obtain samples for performance testing, low-Al ZAM substrates were treated with coating compositions obtained from Examples 1 to 4 and Comparative Example C1 to passivate them by a method comprising the following steps:

[0113] i) Use a degreasing agent (1 wt% Gardoclean, commercially available from Chemitre) at 50°C. ® Clean low-Al ZAM surfaces with S5185 aqueous solution for 5 to 10 seconds to remove grease;

[0114] ii) Rinse the low-Al ZAM substrate with deionized water until a continuous water film is formed, and then dry the surfaces with hot air;

[0115] iii) Applying one of the coating compositions obtained in Examples 1 to 4 and Comparative Example 5 to a degreased surface of a low-Al ZAM substrate using a bar coater; and

[0116] iv) Place the coated substrate in an oven at 280°C for 5 to 10 seconds to form 1.0 g / m 2 A certain amount of passivation layer.

[0117] Passivation of medium Al ZAM substrate

[0118] To obtain samples for performance testing, a medium Al ZAM substrate was treated with coating compositions obtained from Examples 5 to 8 and Comparative Example C2 to passivate it by a method comprising the following steps:

[0119] i) Use a degreasing agent (1 wt% Gardoclean, commercially available from Chemitre) at 50°C. ® S5185 aqueous solution) cleans medium Al ZAM surfaces for 5 to 10 seconds to remove grease;

[0120] ii) Rinse the medium Al ZAM substrate with deionized water until a continuous water film is formed, and then dry the surfaces with hot air;

[0121] iii) Applying one of the coating compositions obtained in Examples 5 to 8 and Comparative Example C2 to a degreased surface of a medium Al ZAM substrate using a bar coater; and

[0122] iv) Place the coated substrate in an oven at 280°C for 5 to 10 seconds to form 1.0 g / m 2 A certain amount of passivation layer.

[0123] Performance testing

[0124] The low-Al and medium-Al ZAM substrates after passivation of the coating composition of the present invention were tested as follows:

[0125] < Anti-dark phase change >

[0126] The following are evaluations of anti-dark mutation properties:

[0127] The fabrication size is 50 mm. Sample specimen of a 100 mm passivated metal substrate;

[0128] The parameters L, a, and b at the center of the specimen were measured using a HunterLab UltraScan spectrophotometer. The specimen was then placed vertically in a chamber with constant temperature and humidity (50°C and 98% relative humidity) for 120 hours by securing the back of the specimen to the chamber with tape. The parameters L, a, and b at the center of the specimen were then measured using a HunterLab UltraScan spectrophotometer to determine the ΔE value.

[0129] ΔE refers to the color difference of the passivation layer before and after surface treatment, calculated according to the following formula:

[0130]

[0131] The results are rated as follows:

[0132] (Meaning it meets the requirements): ΔE ≤ 3 and white rust area ≤ 5%;

[0133] Δ (meaning meeting the requirements): ΔE ≤ 6 and white rust area ≤ 5%;

[0134] (Indicating non-compliance): Other situations

[0135] < Corrosion resistance >

[0136] Corrosion resistance is evaluated according to GB / T 10125-2012 by a neutral salt spray test (NSST) lasting 120 hours.

[0137] The results are rated as follows:

[0138] (Meaning it meets the requirements): White rust area < 5%;

[0139] (Indicating non-compliance): Other situations

[0140] Solvent resistance

[0141] Solvent resistance is evaluated as follows:

[0142] The fabrication size is 50 mm. Sample specimen of a 100 mm passivated metal substrate;

[0143] The parameters L, a, and b at the center of the specimen were measured using a HunterLab UltraScan spectrophotometer. The specimen was then wiped 30 times at a 45° angle and a pressure of 500 g using a Φ10 mm cotton swab soaked in 80% ethanol. The parameters L, a, and b at the center of the specimen were then measured again using a HunterLab UltraScan spectrophotometer to determine the ΔE value.

[0144] The results are rated as follows:

[0145] (Indicating that the requirement is met): ΔE ≤ 3

[0146] (Indicating non-compliance): Other situations

[0147] < Heat resistance >

[0148] The following are evaluations of heat resistance:

[0149] The fabrication size is 50 mm. Sample specimen of a 100 mm passivated metal substrate;

[0150] The parameters L, a, and b at the center of the specimen were measured using a HunterLab UltraScan spectrophotometer.

[0151] The specimens were placed in an oven at 240°C for 20 minutes; and then...

[0152] Remove the specimen and cool it to room temperature (5°C-40°C). Then, measure the parameters L, a, and b at the center of the specimen using a HunterLab UltraScan spectrophotometer to determine the ΔE value.

[0153] The results are rated as follows:

[0154] (Indicating that the requirement is met): ΔE ≤ 3

[0155] (Indicating non-compliance): Other situations

[0156] < Alkali resistance >

[0157] The following are evaluations of alkali resistance:

[0158] The fabrication size is 75 mm. Sample specimen of a 150 mm passivated metal substrate;

[0159] The thickness of the passivation layer was measured using an infrared film thickness meter; and

[0160] The degreasing agent (commercially available from Chemidel (China, Shanghai) containing 2 wt% Gardoclean) was used. ® The aqueous solution of S5185 was heated to 50°C and sprayed for 2 min. The specimen was then removed, washed and dried, and then subjected to a neutral salt spray test (NSST) for 72 hours according to GB / T10125-2012.

[0161] The results are rated as follows:

[0162] (Meaning it meets the requirements): White rust area < 5%

[0163] (Indicating non-compliance): Other situations

[0164] The test results based on low-Al and medium-Al ZAM substrates are summarized in Tables 3 and 4, respectively:

[0165] Table 3:

[0166]

[0167] Table 4:

[0168]

[0169] As shown in Tables 3 and 4, by adding amino acids (such as phenylalanine, glutamine, threonine, and tyrosine) in appropriate amounts, the resulting coating compositions enable low-Al and medium-Al ZAM substrates to better resist darkening while maintaining other properties such as corrosion resistance, solvent resistance, heat resistance, and alkali resistance.

Claims

1. A coating composition for passivating low-Al and medium-Al ZAM substrates, the coating composition comprising (a) at least one water-soluble or water-dispersible resin selected from polyurethane resins, epoxy resins and polyacrylate resins; (b) at least one silane; (c) at least one corrosion inhibitor; and (d) At least one anti-dark staining agent selected from amino acids.

2. The coating composition according to claim 1, wherein, The anti-darkening agent is selected from hydrophilic amino acids and preferably from at least one of the following groups: aspartic acid, glutamic acid, serine, threonine, cysteine, tyrosine, asparagine, glutamine, and phenylalanine.

3. The coating composition according to any one of claims 1 to 2, wherein, Based on the total weight of the coating composition, the amount of the anti-darkening agent is in the range of 0.05% to 2% by weight, and preferably 0.1% to 1% by weight.

4. The coating composition according to any one of claims 1 to 3, wherein, It further comprises at least one additive selected from defoamers, wetting agents and coalescing agents.

5. The coating composition according to any one of claims 1 to 4, wherein, Component (a) is a combination of polyurethane resin and polyacrylate resin, wherein the weight ratio of polyurethane resin to polyacrylate resin is in the range of 0.5 to 1.2, preferably in the range of 0.6 to 1.0, and more preferably in the range of 0.7 to 1.

0.

6. The coating composition according to any one of claims 1 to 5, wherein, The polyacrylate resin has a number average molecular weight (Mn) in the range of 100,000 Daltons to 500,000 Daltons, as determined by gel permeation chromatography (GPC) according to DIN 55672-1; preferably, the polyacrylate resin has a number average molecular weight in the range of 100,000 Daltons to 300,000 Daltons, and more preferably in the range of 100,000 Daltons to 200,000 Daltons.

7. The coating composition according to any one of claims 1 to 6, wherein, The silane is selected from the group consisting of: tetraethoxysilane, 3-glycidoxyalkyltrialkoxysilane, 3-methacryloxyalkyltrialkoxysilane, aminoalkylaminoalkylalkyldialkoxysilane, β-(3,4-epoxycycloalkyl)alkyltrialkoxysilane, (3,4-epoxycycloalkyl)alkyltrialkoxysilane, bis(trialkoxymethylsilylalkyl)amine, bis-(trialkoxymethylsilyl)ethane, (3,4-epoxyalkyl)trialkoxysilane, γ-aminoalkyltrialkoxysilane, γ-methacryloxyalkyltrialkoxysilane, γ-ureidoalkyltrialkoxysilane, glycidoxysilane, β-(3,4-epoxycycloalkyl)alkyltrialkoxysilane, γ-aminoalkyltrialkoxysilane, γ-methacryloxyalkyltrialkoxysilane, γ-ureidoalkyltrialkoxysilane, β-(3,4-epoxycycloalkyl)alkyltrialkoxysilane, γ-aminoalkyltrialkoxysilane, γ-methacryloxyalkyltrialkoxysilane, γ-ureidoalkyltrialkoxysilane, β-glycidoxyalkyltrialkoxysilane, β-(3,4-epoxycycloalkyl) ... The silane may be selected from the group consisting of glyceryloxyalkyltrialkoxysilane, N-(3-(trialkoxysilyl)alkyl)alkylene diamine, N-β-(aminoalkyl)-γ-aminoalkyltrialkoxysilane, N-(γ-trialkoxysilyl)dialkylene triamine, polyaminoalkylalkyldialkoxysilane, tris(3-(trialkoxysilyl)alkyl)isocyanurate, (ureopropyltrialkoxy)silane, and vinyltriacetoxysilane; more preferably, the silane may be selected from the group consisting of 3-aminopropyltriethoxysilane, 3-epoxypropyltrimethoxysilane, tetraethoxysilane, and 3-vinyltrimethoxysilane.

8. The coating composition according to any one of claims 1 to 7, wherein, The corrosion inhibitor is at least one selected from the group consisting of phosphorus-containing compounds and acid corrosion inhibitors. Preferably, the corrosion inhibitor is at least one selected from the group consisting of 1-hydroxyethane-1,1-diphosphonic acid, zinc dihydrogen phosphate, hexafluorotitanic acid, and hexafluorozirconic acid.

9. The coating composition according to any one of claims 1 to 8, wherein, It further comprises at least one additive selected from defoamers, wetting agents and coalescing agents.

10. The coating composition according to any one of claims 1 to 9, wherein, The coating composition is acidic.

11. A low-Al ZAM substrate, which is passivated by a coating composition according to any one of claims 1 to 10.

12. The low-Al ZAM substrate according to claim 11, wherein, Based on the total weight of the low-Al ZAM substrate, the weight percentage of Al is in the range of 0.5% to 5% by weight, and preferably 1% to 3%.

13. The low-Al ZAM substrate according to any one of claims 11 to 12, wherein, Based on the total weight of the low-Al ZAM substrate, the weight percentage of Mg is in the range of 1% to 3% by weight, and preferably 1% to 2% by weight.

14. A medium Al ZAM substrate, which is passivated by a coating composition according to any one of claims 1 to 10.

15. The intermediate Al ZAM substrate according to claim 14, wherein, Based on the total weight of the medium Al ZAM substrate, the weight percentage of Al is in the range of 0.5% to 5% by weight, and preferably 1% to 3%.

16. The intermediate Al ZAM substrate according to any one of claims 14 to 15, wherein, Based on the total weight of the medium Al ZAM substrate, the weight percentage of Mg is in the range of 1% to 3% by weight, and preferably 2% to 3% by weight.

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