Aqueous aluminum pigment, and preparation method and application thereof

Abstract

The application discloses a kind of water-based aluminum pigments, comprising: aluminum powder and by inside to outside in turn coated on the surface of aluminum powder alumina layer, silica layer one, silane coupling agent layer, silica layer two, aluminum ion capture layer;Aluminum ion capture layer is the organic resin layer containing phosphoric acid group.This application also discloses the preparation method of the above-mentioned water-based aluminum pigment and its application in coating.The application also discloses a kind of water-based paint, and its raw materials include: water-based film-forming resin and the above-mentioned water-based aluminum pigment.The application improves the binding fastness and compactness of each layer by mutual cooperation of alumina layer, silica layer one, silane coupling agent layer and silica layer two, prevents the contact of aluminum pigment and corrosive medium;Through the effect of layer-by-layer cooperation capture formed by silica layer two and aluminum ion capture layer, the capture effect of aluminum ion is greatly improved, and the content of free aluminum ion in coating is reduced;And have good water dispersibility and good metal appearance.

Description

Technical Field

[0001] This invention relates to the field of aluminum pigment technology, and in particular to a water-based aluminum pigment, its preparation method, and its application. Background Technology

[0002] The children's toy industry widely uses paints containing color in their coatings. The combination of aluminum pigments and different colored pigments gives the toys a metallic sheen while being full of color. Toys with a metallic sheen and a variety of colors are more popular with children.

[0003] In the current market environment, most toy coatings using aluminum pigments are oil-based. However, with the development of the coating industry, toy coatings are gradually shifting towards water-based formulations. Considering that most toy products are targeted at children, who inevitably lick or bite the toy surface during use, leading to coating peeling and accidental ingestion, the aluminum pigments in the coating may be decomposed and absorbed by stomach acid, seriously endangering children's health and growth. Therefore, the European Toy Safety Standard EN 71-3:2019+A1:2021 is usually used as the standard to regulate aluminum pigments used in the surface coatings of children's toys.

[0004] Conventional water-based aluminum pigments, due to their processing characteristics, cannot effectively prevent the formation and precipitation of soluble aluminum salts through their surface coatings. Furthermore, they still react with acids in the coating to produce free aluminum. Under these circumstances, they are unlikely to pass the European Toy Safety Standards and therefore cannot be used in children's toy coatings.

[0005] Conventional aluminum pigments are micron-sized flake-like particles, highly reactive, and readily react with acids, alkalis, and water. They often require coating or passivation treatment before application in water-based coatings. Due to the need for corrosion resistance, the most widely used water-based aluminum pigments on the market are typically silica-coated and phosphate-passivated products. Because the silica coating layer has a porous structure, it cannot completely prevent the aluminum pigment from reacting with strong acids, nor can it capture the free aluminum ions generated in the reaction. Phosphate-coated products cannot form a three-dimensional protective layer structure, and they easily react in strong acid systems, generating a large number of free aluminum ions. Both types of products fail to meet the European Toy Safety Standards. Summary of the Invention

[0006] Based on the technical problems existing in the background technology, this invention proposes a water-based aluminum pigment, its preparation method, and its application. This invention employs a multi-layer sandwich coating process. An aluminum oxide layer is formed on the surface of the aluminum pigment using a passivating agent, providing binding sites for the coated silica layer and improving the bonding strength and density of the first silica layer. A silane coupling agent layer fills the pores of the silica layer, further improving the density of the coating layer and preventing contact between the aluminum pigment and corrosive media. Simultaneously, a second silica layer is formed by a secondary reaction between a silane monomer and phytic acid grafted with amino groups. This further improves the density of the coating, preventing contact between the aluminum pigment and corrosive media. Furthermore, the introduction of phytic acid into the second silica layer allows it to capture free aluminum ions. The phytic acid grafted with active amino groups can tightly bind with organic resins containing phosphate groups, improving the stability of the aluminum ion capturing layer. This layer-by-layer capture effect significantly improves the aluminum ion capture effect, reduces the content of free aluminum ions in the coating, and meets the coating's requirements for soluble aluminum content. It also exhibits good water dispersibility and a good metallic appearance.

[0007] This invention proposes an aqueous aluminum pigment, comprising: aluminum powder and, from the inside out, an alumina layer, a first silica layer, a silane coupling agent layer, a second silica layer, and an aluminum ion trapping layer sequentially coated on the surface of the aluminum powder; the aluminum ion trapping layer is an organic resin layer containing phosphate groups.

[0008] The thickness of the alumina layer is 1-3 nm; the thickness of the first silicon dioxide layer is 5-10 nm; the thickness of the silane coupling agent layer is 2-3 nm; the thickness of the second silicon dioxide layer is 5-8 nm; and the thickness of the aluminum ion trapping layer is 10-20 nm.

[0009] Preferably, the organic resin containing phosphate groups is at least one of epoxy resin containing phosphate groups and polyester resin containing phosphate groups.

[0010] The aforementioned epoxy resins containing phosphate groups and polyester resins containing phosphate groups can be purchased from the market. Their molecular weight is preferably 5,000-10,000 and their degree of polymerization is 50-100. The phosphorus content of the epoxy resins containing phosphate groups is 4-6 wt% and the phosphorus content of the polyester resins containing phosphate groups is 6-8 wt%.

[0011] Preferably, the second silica layer contains phytic acid grafted with amino groups.

[0012] Preferably, the content of phytic acid grafted with amino groups in the second silica layer is 0.5-1.5 wt%.

[0013] Preferably, in the preparation of phytic acid grafted with amino groups, phytic acid, polyamine and water are mixed and reacted at 70-80℃ for 1-1.5h to obtain phytic acid grafted with amino groups.

[0014] Preferably, in the preparation of phytic acid grafted with amino groups, the polyamine is at least one of ethylenediamine, diethylenetriamine, and triethylenetetramine.

[0015] Preferably, in the preparation of phytic acid grafted with amino groups, the molar ratio of phytic acid to polyamine is 1:0.9-1.1.

[0016] Preferably, in the preparation of phytic acid grafted with amino groups, after the reaction is completed, the mixture is cooled to room temperature, the solid and liquid are separated, washed, and dried to obtain phytic acid grafted with amino groups.

[0017] Preferably, the silane coupling agent is at least one selected from γ-aminopropyltriethoxysilane, N,N-diethyl-3-aminopropyltriethoxysilane, N-β-(aminoethyl)-γ-aminopropyltriethoxysilane, γ-diethylenetriaminopropyltriethoxysilane, γ-glycidyl etheroxypropyltriethoxysilane, β-(3,4-epoxycyclohexyl)-ethyltriethoxysilane, γ-methacryloyloxypropyltriethoxysilane, 3-methacryloyloxypropyltriethoxysilane, propyltriethoxysilane, octyltriethoxysilane, and n-dodecyltriethoxysilane.

[0018] The aluminum powder mentioned above is in the form of flakes; more preferably, it is in the form of oily flakes.

[0019] The above-mentioned oily flake aluminum powder can be purchased from the market; for example, oily flake ball milled aluminum pigment with a solid content of 60-70 wt%.

[0020] The average particle size of the aluminum powder is 11-18 μm; the particle size range of the aluminum powder is 0.8-1.0.

[0021] The present invention also proposes a method for preparing the above-mentioned water-based aluminum pigment, comprising the following steps:

[0022] Aluminum powder, passivating agent and organic solvent are mixed and then passivated.

[0023] After the passivation treatment is completed, add silane monomer one and catalyst one, mix well, and carry out a reaction;

[0024] After one reaction is completed, a silane coupling agent is added to carry out a filling reaction;

[0025] After the filling reaction is completed, silane monomer II, phytic acid grafted with amino groups and catalyst II are added and mixed well to carry out a second reaction;

[0026] After the secondary reaction is completed, organosilicon resin is added to carry out a coating reaction to obtain water-based aluminum pigment.

[0027] Preferably, the passivating agent is at least one of zinc nitrate, ferric nitrate, ferrous nitrate, tin nitrate, and copper nitrate; more preferably, it is zinc nitrate.

[0028] Preferably, the passivation treatment, primary reaction, filling reaction, secondary reaction, and coating reaction are all carried out at temperatures of 40-60°C; more preferably, at 50°C.

[0029] The passivation treatment time is ≥2h; more preferably 2-5h.

[0030] The weight ratio of the aluminum powder and passivating agent is 50-70:1.5-3.5.

[0031] The aforementioned organic solvent is a polar organic solvent that is miscible with water; the organic solvent may be at least one of anhydrous ethanol, ethylene glycol, n-propanol, n-butanol, propylene glycol methyl ether, and ethylene glycol monobutyl ether, more preferably anhydrous ethanol.

[0032] Preferably, silane monomer one and silane monomer two are at least one of methyl orthosilicate, ethyl orthosilicate, and silane prepolymer; more preferably, they are ethyl orthosilicate.

[0033] The aforementioned silane prepolymers can be Si40, Si50, etc.

[0034] Preferably, catalyst one and catalyst two are at least one of concentrated ammonia, ethylenediamine, dimethylethanolamine, and 2-amino-2-methyl-1-propanol; more preferably, they are dimethylethanolamine.

[0035] After the passivation treatment is completed, silane monomer one and catalyst one are added dropwise simultaneously, mixed thoroughly, and a single reaction is carried out. The preferred dropping rate is 2.5-7.5 kg / h, and preferably the addition is completed within 2-4 hours.

[0036] The weight ratio of the above aluminum powder, silane monomer one, and catalyst one is 50-70:10-15:0.5-1.5.

[0037] The reaction time for the above-mentioned single reaction is ≥2h; more preferably 4h.

[0038] The weight ratio of the aluminum powder to the silane coupling agent is 50-70:0.6-2.8.

[0039] The filling reaction time is 0.5-1 hour.

[0040] After the above filling reaction is completed, silane monomer II, phytic acid grafted with amino group, and catalyst II are simultaneously added dropwise, mixed thoroughly, and a secondary reaction is carried out. The preferred dropping rate is 0.8-5 kg / h, and the addition is preferably completed within 2-4 hours.

[0041] The weight ratio of the above aluminum powder, silane monomer II, phytic acid grafted with amino group, and catalyst II is 50-70:5-10:0.05-0.1:0.25-1.

[0042] The time for the above secondary reaction is ≥2h; more preferably 4h.

[0043] The weight ratio of the aluminum powder to the silicone resin is 50-70:3-5.

[0044] The coating reaction takes 5-7 hours.

[0045] After the above coating reaction is completed, the solid and liquid are separated, and then kneaded evenly to obtain water-based aluminum pigment.

[0046] The method of solid-liquid separation is not limited to the above-mentioned method; centrifugation, pressure filtration, etc. are also acceptable, with pressure filtration being preferred. A kneader can be used to knead the mixture evenly.

[0047] The above-mentioned water-based aluminum pigments can be dispersed in anhydrous ethanol for use. When dispersed in anhydrous ethanol, the solid content of the water-based aluminum pigments can be 50-60 wt%.

[0048] The present invention also proposes the application of the above-mentioned water-based aluminum pigment in coatings.

[0049] The above-mentioned coating is a coating for children; more preferably, it is a coating for children's toys.

[0050] The present invention also proposes a water-based coating, the raw materials of which include: water-based film-forming resin and the above-mentioned water-based aluminum pigment.

[0051] The aforementioned aqueous film-forming resins can be polyurethane resins, epoxy resins, acrylic resins, etc.

[0052] The aforementioned water-based coatings may also contain fillers, dispersants, antioxidants, leveling agents, flame retardants, etc.

[0053] In the above-mentioned water-based coatings, the content of water-based aluminum pigment can be 8-12 wt%.

[0054] This invention first uses a passivating agent to form an alumina layer on the surface of aluminum powder. Then, a silane monomer is used to form a first silica layer through a primary reaction. The alumina layer provides binding sites for the coating of the first silica layer, improving the bonding strength and density of the first silica layer. Next, it reacts with a silane coupling agent to form a silane coupling agent layer. The silane coupling agent layer can fill the pores of the first silica layer, further improving the density of the coating. Then, a second reaction is carried out with a silane monomer and phytic acid grafted with amino groups to form a second silica layer. On the one hand, this can further improve the density of the coating and prevent the aluminum pigment from contacting the corrosive medium. On the other hand, the introduction of phytic acid into the second silica layer can capture free aluminum ions. Furthermore, the phytic acid grafted with active amino groups can tightly bind with organic resins containing phosphate groups, improving the stability of the aluminum ion capturing layer. This allows the aluminum pigment to maintain good dispersibility in water-based coatings, avoiding the problems of difficulty in dispersion and orientation, difficulty in obtaining excellent metallic luster, and easy discoloration in water-based coatings.

[0055] Finally, an aluminum ion capturing layer is formed by coating with an organic resin containing phosphate groups. The phosphate groups can react and combine with free aluminum ions, thereby capturing free aluminum ions and avoiding problems caused by the release of free aluminum ions. The silica layer and the aluminum ion capturing layer can form a layer-by-layer synergistic capturing effect, which greatly improves the aluminum ion capturing effect, greatly improves the acid resistance of water-based aluminum pigments, and reduces the content of free aluminum ions in the coating, so as to meet the requirements of children's paint for soluble aluminum index.

[0056] Furthermore, the present invention has good water dispersibility, and the water-based aluminum pigment has excellent stability; in addition, the present invention, after undergoing multi-layer sandwich coating treatment, still maintains good whiteness, brightness and metallic feel.

[0057] Testing revealed that this invention meets the European toy safety standards EN 71-3:2019+A1:2021 and can be used in surface coatings for children's toys. A comparative test using a plastic coating system at 50°C for 30 days showed that, compared to commercially available water-based aluminum paste, the water-based aluminum pigment of this invention exhibits better stability in plastic coatings. Furthermore, a comparative test using a strongly acidic aqueous solution at 40°C for 30 days showed that, compared to commercially available water-based aluminum paste, the water-based aluminum pigment of this invention exhibits better corrosion resistance in strongly acidic solutions. Attached Figure Description

[0058] Figure 1 These are comparative photographs of the whiteness of scraper coatings made from water-based aluminum pigments in Example 1 and Comparative Example 2. The left side is Comparative Example 2, and the right side is Example 1.

[0059] Figure 2 These are comparison photographs of the gloss of scraper coatings made from water-based aluminum pigments in Example 1 and Comparative Example 2, with Comparative Example 2 on the left and Example 1 on the right. Detailed Implementation

[0060] The technical solution of the present invention will be described in detail below through specific embodiments. However, it should be clearly stated that these embodiments are for illustrative purposes only and are not intended to limit the scope of the present invention.

[0061] The water used in the following examples and comparative examples is deionized water.

[0062] Example 1

[0063] A water-based aluminum pigment comprises: aluminum powder and, from the inside out, an aluminum oxide layer, a first silica layer, a silane coupling agent layer, a second silica layer, and an aluminum ion trapping layer sequentially coated on the surface of the aluminum powder; the aluminum ion trapping layer is an epoxy resin layer containing phosphate groups, the passivating agent is zinc nitrate, and the silane coupling agent is γ-aminopropyltriethoxysilane; the second silica layer contains phytic acid grafted with amino groups;

[0064] In the preparation of phytic acid grafted with amino groups, 0.1 mol of phytic acid, 0.1 mol of diethylenetriamine and 100 mL of water were mixed, heated to 75 °C and reacted for 1.2 h. After cooling to room temperature, the mixture was filtered, washed and dried to obtain phytic acid grafted with amino groups.

[0065] The preparation method of the above-mentioned water-based aluminum pigment includes the following steps:

[0066] 60 kg of aluminum powder (oil-based, flake-shaped, ball-milled aluminum powder with an average particle size of 11 μm and a particle size range of 0.8-1.0) was added to a stainless steel stirred reactor, followed by 300 kg of anhydrous ethanol. The reactor temperature was set to 50 °C, and stirring and heating were started. After heating was completed, an ethanol solution of zinc nitrate (containing 2.5 kg of zinc nitrate and 25 kg of ethanol) was added, and the mixture was kept at the same temperature and stirred for 3 hours for passivation treatment.

[0067] After the passivation treatment is completed, 12 kg of 8 wt% dimethylethanolamine aqueous solution and 12 kg of tetraethyl orthosilicate are simultaneously added dropwise to the reaction vessel at a rate of 3 kg / h. After the addition is completed, the mixture is kept warm and stirred for a reaction of 2 hours.

[0068] After one reaction was completed, 3 kg of 50 wt% γ-aminopropyltriethoxysilane ethanol solution was added, and the mixture was kept warm and stirred for 1 hour to carry out the filling reaction.

[0069] After the filling reaction is completed, 4 kg of 16 wt% dimethylethanolamine aqueous solution and 4 kg of 2 wt% phytic acid aqueous solution with grafted amino group are mixed to obtain a mixture. Then, the mixture and 8 kg of tetraethyl orthosilicate are dropped into the reaction vessel at a dropping rate of 2 kg / h. After the dropping is completed, the mixture is kept warm and stirred for a second reaction for 2 h.

[0070] After the secondary reaction is completed, 4 kg of phosphate-containing epoxy resin (DH-7325 from Suzhou Qingtian New Materials Co., Ltd.) is added to the reactor and the mixture is kept warm and stirred for 6 hours for coating reaction. Then it is cooled to 30°C, filtered by a filter press, and then kneaded evenly by a kneader to obtain water-based aluminum pigment.

[0071] Example 2

[0072] A water-based aluminum pigment comprises: aluminum powder and, from the inside out, an aluminum oxide layer, a first silica layer, a silane coupling agent layer, a second silica layer, and an aluminum ion trapping layer sequentially coated on the surface of the aluminum powder; the aluminum ion trapping layer is a polyester resin layer containing phosphate groups, the passivating agent is copper nitrate, and the silane coupling agent is γ-glycidoxypropyltriethoxysilane; the second silica layer contains phytic acid grafted with amino groups;

[0073] In the preparation of phytic acid grafted with amino groups, 0.1 mol of phytic acid, 0.1 mol of ethylenediamine and 100 mL of water were mixed, heated to 70 °C and reacted for 1.5 h. After cooling to room temperature, the mixture was filtered, washed and dried to obtain phytic acid grafted with amino groups.

[0074] The preparation method of the above-mentioned water-based aluminum pigment includes the following steps:

[0075] 50 kg of aluminum powder (oil-based, flake-shaped, ball-milled aluminum powder with an average particle size of 15 μm and a particle size range of 0.8-1.0) was added to a stainless steel stirred reactor. Then, 250 kg of anhydrous ethanol was added. The reactor temperature was set to 50 °C, and stirring and heating were started. After the heating was completed, an ethanol solution of copper nitrate (containing 1.5 kg of copper nitrate and 15 kg of ethanol) was added. The mixture was kept at the temperature and stirred for 2 hours for passivation treatment.

[0076] After the passivation treatment is completed, 10 kg of 5 wt% dimethyl ethanolamine aqueous solution and 10 kg of methyl orthosilicate are simultaneously added dropwise to the reaction vessel at a rate of 2.5 kg / h. After the addition is completed, the mixture is kept warm and stirred for a reaction of 2 hours.

[0077] After one reaction was completed, 2 kg of 30 wt% γ-glycidyl etheroxypropyltriethoxysilane ethanol solution was added, and the mixture was kept warm and stirred for another 0.5 h for the filling reaction.

[0078] After the filling reaction is completed, 2.5 kg of 10 wt% dimethylethanolamine aqueous solution and 2.5 kg of 2 wt% phytic acid aqueous solution with grafted amino groups are mixed to obtain a mixed solution. Then, the mixed solution and 5 kg of methyl orthosilicate are simultaneously added dropwise to the reaction vessel at a dropping rate of 1.25 kg / h. After the dropping is completed, the mixture is kept warm and stirred for a second reaction for 2 hours.

[0079] After the secondary reaction is completed, 3 kg of phosphate-containing polyester resin (AKN-6105 from Foshan Qianyou Chemical Co., Ltd.) is added to the reactor and the mixture is kept warm and stirred for 6 hours for coating reaction. Then it is cooled to 30°C, filtered by a filter press, and then kneaded evenly by a kneader to obtain water-based aluminum pigment.

[0080] Example 3

[0081] A water-based aluminum pigment comprises: aluminum powder and, from the inside out, an aluminum oxide layer, a first silica layer, a silane coupling agent layer, a second silica layer, and an aluminum ion trapping layer sequentially coated on the surface of the aluminum powder; the aluminum ion trapping layer is an epoxy resin layer containing phosphate groups, the passivating agent is zinc nitrate, and the silane coupling agent is γ-diethylenetriaminopropyltriethoxysilane; the second silica layer contains phytic acid grafted with amino groups;

[0082] In the preparation of phytic acid grafted with amino groups, 0.1 mol of phytic acid, 0.1 mol of triethylenetetramine and 100 mL of water were mixed, heated to 80 °C and reacted for 1 h. After cooling to room temperature, the mixture was filtered, washed and dried to obtain phytic acid grafted with amino groups.

[0083] The preparation method of the above-mentioned water-based aluminum pigment includes the following steps:

[0084] 70 kg of aluminum powder (oil-based, flake-shaped, ball-milled aluminum powder with an average particle size of 18 μm and a particle size range of 0.8-1.0) was added to a stainless steel stirred reactor, followed by 350 kg of anhydrous ethanol. The reactor temperature was set to 50 °C, and stirring and heating were started. After heating was completed, an ethanol solution of zinc nitrate (containing 3.5 kg of zinc nitrate and 35 kg of ethanol) was added, and the mixture was kept at the temperature and stirred for passivation treatment for 5 hours.

[0085] After the passivation treatment is completed, 15 kg of 10 wt% dimethylethanolamine aqueous solution and 15 kg of tetraethyl orthosilicate are simultaneously added dropwise to the reaction vessel at a rate of 3.75 kg / h. After the addition is completed, the mixture is kept warm and stirred for a reaction of 2 hours.

[0086] After the first reaction was completed, 4 kg of 70 wt% γ-diethylenetriaminopropyltriethoxysilane ethanol solution was added, and the mixture was kept warm and stirred for 1 hour for a filling reaction.

[0087] After the filling reaction is completed, 5 kg of 20 wt% dimethylethanolamine aqueous solution and 5 kg of 2 wt% phytic acid aqueous solution with grafted amino group are mixed to obtain a mixed solution. Then, the mixed solution and 10 kg of tetraethyl orthosilicate are simultaneously added dropwise to the reaction vessel at a dropping rate of 2.5 kg / h. After the dropping is completed, the mixture is kept warm and stirred for a second reaction for 2 hours.

[0088] After the secondary reaction is completed, 5 kg of phosphate-containing epoxy resin (DH-7325 from Suzhou Qingtian New Materials Co., Ltd.) is added to the reactor and the mixture is kept warm and stirred for 6 hours for coating reaction. Then it is cooled to 30°C, filtered by a filter press, and then kneaded evenly by a kneader to obtain water-based aluminum pigment.

[0089] In the water-based aluminum pigments prepared in Examples 1-3 above, the thickness of the alumina layer is 1-3 nm; the thickness of the first silicon dioxide layer is 5-10 nm; the thickness of the silane coupling agent layer is 2-3 nm; the thickness of the second silicon dioxide layer is 5-8 nm; and the thickness of the aluminum ion trapping layer is 10-20 nm.

[0090] By selecting a suitable preparation method, this invention can ensure that each layer has an appropriate thickness. The layers with appropriate thicknesses work together to meet the coating's requirements for soluble aluminum content and corrosion resistance while maintaining a good appearance.

[0091] Comparative Example 1

[0092] A method for preparing a water-based aluminum pigment includes the following steps:

[0093] 60 kg of aluminum powder (oil-based, flake-shaped ball-milled aluminum powder with an average particle size of 11 μm and a particle size range of 0.8-1.0) was added into a stainless steel stirred reactor, and then 300 kg of anhydrous ethanol was added. The reactor temperature was set to 50°C, and stirring and heating were started.

[0094] After the heating is completed, 12 kg of 8 wt% dimethylethanolamine aqueous solution and 12 kg of tetraethyl orthosilicate are simultaneously added dropwise into the reactor at a rate of 3 kg / h. After the addition is completed, the reactor is kept warm and stirred for 2 hours.

[0095] After one reaction was completed, 3 kg of 50 wt% γ-aminopropyltriethoxysilane ethanol solution was added, and the mixture was kept warm and stirred for 1 hour to carry out the filling reaction.

[0096] After the filling reaction is completed, 4 kg of 16 wt% dimethylethanolamine aqueous solution and 4 kg of 2 wt% phytic acid aqueous solution with grafted amino group are mixed to obtain a mixture. Then, the mixture and 8 kg of tetraethyl orthosilicate are dropped into the reaction vessel at a dropping rate of 2 kg / h. After the dropping is completed, the mixture is kept warm and stirred for a second reaction for 2 h.

[0097] After the secondary reaction is completed, 4 kg of phosphate-containing epoxy resin (DH-7325 from Suzhou Qingtian New Materials Co., Ltd.) is added to the reactor and the mixture is kept warm and stirred for 6 hours for coating reaction. Then it is cooled to 30°C, filtered by a filter press, and then kneaded evenly by a kneader to obtain water-based aluminum pigment.

[0098] The difference between Comparative Example 1 and Example 1 is that Comparative Example 1 does not undergo passivation treatment, while the water-based aluminum pigment is prepared according to the steps of Example 1.

[0099] Comparative Example 2

[0100] Commercially available oily, flake-shaped ball-milled aluminum powder coated with silica with an average particle size of 11 μm.

[0101] Comparative Example 3

[0102] Commercially available acrylic resin-coated aluminum silver paste with an average particle size of 11μm does not contain an alumina layer, a silica layer one, a silane coupling agent layer, or a silica layer two.

[0103] Comparative Example 4

[0104] A method for preparing a water-based aluminum pigment includes the following steps:

[0105] 60 kg of aluminum powder (oil-based, flake-shaped, ball-milled aluminum powder with an average particle size of 11 μm and a particle size range of 0.8-1.0) was added to a stainless steel stirred reactor, followed by 300 kg of anhydrous ethanol. The reactor temperature was set to 50 °C, and stirring and heating were started. After heating was completed, an ethanol solution of zinc nitrate (containing 2.5 kg of zinc nitrate and 25 kg of ethanol) was added, and the mixture was kept at the same temperature and stirred for 3 hours for passivation treatment.

[0106] After the passivation treatment is completed, 12 kg of 8 wt% dimethylethanolamine aqueous solution and 12 kg of tetraethyl orthosilicate are simultaneously added dropwise to the reaction vessel at a rate of 3 kg / h. After the addition is completed, the mixture is kept warm and stirred for a reaction of 2 hours.

[0107] After one reaction was completed, 3 kg of 50 wt% γ-aminopropyltriethoxysilane ethanol solution was added, and the mixture was kept warm and stirred for 1 hour to carry out the filling reaction.

[0108] After the filling reaction is completed, 4 kg of 16 wt% dimethylethanolamine aqueous solution and 4 kg of 2 wt% phytic acid aqueous solution with grafted amino group are mixed to obtain a mixture. Then, the mixture and 8 kg of tetraethyl orthosilicate are dropped into the reaction vessel at a dropping rate of 2 kg / h. After the dropping is completed, the mixture is kept warm and stirred for a second reaction for 2 h.

[0109] After the secondary reaction is completed, 4 kg of acrylic resin is added to the reactor and the mixture is kept warm and stirred for 6 hours for coating reaction. Then it is cooled to 30°C, filtered by a filter press, and then kneaded evenly by a kneader to obtain water-based aluminum pigment.

[0110] The difference between Comparative Example 4 and Example 1 is that the epoxy resin containing phosphate groups was replaced with acrylic resin, while the water-based aluminum pigment was prepared according to the steps of Example 1.

[0111] Comparative Example 5

[0112] A method for preparing a water-based aluminum pigment includes the following steps:

[0113] 60 kg of aluminum powder (oil-based, flake-shaped, ball-milled aluminum powder with an average particle size of 11 μm and a particle size range of 0.8-1.0) was added to a stainless steel stirred reactor, followed by 300 kg of anhydrous ethanol. The reactor temperature was set to 50 °C, and stirring and heating were started. After heating was completed, an ethanol solution of zinc nitrate (containing 2.5 kg of zinc nitrate and 25 kg of ethanol) was added, and the mixture was kept at the same temperature and stirred for 3 hours for passivation treatment.

[0114] After the passivation treatment is completed, 12 kg of 8 wt% dimethylethanolamine aqueous solution and 12 kg of tetraethyl orthosilicate are simultaneously added dropwise to the reaction vessel at a rate of 3 kg / h. After the addition is completed, the mixture is kept warm and stirred for a reaction of 2 hours.

[0115] After one reaction was completed, 3 kg of 50 wt% γ-aminopropyltriethoxysilane ethanol solution was added, and the mixture was kept warm and stirred for 1 hour to carry out the filling reaction.

[0116] After the filling reaction is completed, 4 kg of 16 wt% dimethylethanolamine aqueous solution and 4 kg of 2 wt% phytic acid aqueous solution with grafted amino groups are mixed to obtain a mixed solution. Then, 8 kg of tetraethyl orthosilicate is added dropwise to the reaction vessel at a rate of 2 kg / h. After the addition is completed, the mixture is kept warm and stirred for a second reaction for 2 h. Then, it is cooled to 30°C, filtered by a filter press, and kneaded evenly by a kneader to obtain water-based aluminum pigment.

[0117] The difference between Comparative Example 5 and Example 1 is that Comparative Example 5 does not undergo the epoxy resin coating reaction treatment containing phosphate groups, while the water-based aluminum pigment is prepared according to the steps of Example 1.

[0118] Comparative Example 6

[0119] A method for preparing a water-based aluminum pigment includes the following steps:

[0120] 60 kg of aluminum powder (oil-based, flake-shaped, ball-milled aluminum powder with an average particle size of 11 μm and a particle size range of 0.8-1.0) was added to a stainless steel stirred reactor, followed by 300 kg of anhydrous ethanol. The reactor temperature was set to 50 °C, and stirring and heating were started. After heating was completed, an ethanol solution of zinc nitrate (containing 2.5 kg of zinc nitrate and 25 kg of ethanol) was added, and the mixture was kept at the same temperature and stirred for 3 hours for passivation treatment.

[0121] After the passivation treatment is completed, 12 kg of 8 wt% dimethylethanolamine aqueous solution and 12 kg of tetraethyl orthosilicate are simultaneously added dropwise to the reaction vessel at a rate of 3 kg / h. After the addition is completed, the mixture is kept warm and stirred for a reaction of 2 hours.

[0122] After the first reaction was completed, 4 kg of 16 wt% dimethylethanolamine aqueous solution and 4 kg of 2 wt% phytic acid aqueous solution with grafted amino were mixed to obtain a mixture. Then, the mixture and 8 kg of tetraethyl orthosilicate were added dropwise into the reaction vessel at a rate of 2 kg / h. After the addition was completed, the mixture was kept warm and stirred for a second reaction for 2 h.

[0123] After the secondary reaction is completed, 4 kg of phosphate-containing epoxy resin (DH-7325 from Suzhou Qingtian New Materials Co., Ltd.) is added to the reactor and the mixture is kept warm and stirred for 6 hours for coating reaction. Then it is cooled to 30°C, filtered by a filter press, and then kneaded evenly by a kneader to obtain water-based aluminum pigment.

[0124] The difference between Comparative Example 6 and Example 1 is that Comparative Example 6 does not undergo the filling reaction treatment with γ-aminopropyltriethoxysilane, while the water-based aluminum pigment is prepared according to the steps of Example 1.

[0125] Comparative Example 7

[0126] A method for preparing a water-based aluminum pigment includes the following steps:

[0127] 60 kg of aluminum powder (oil-based, flake-shaped ball-milled aluminum powder with an average particle size of 11 μm and a particle size range of 0.8-1.0) was added into a stainless steel stirred reactor, and then 300 kg of anhydrous ethanol was added. The reactor temperature was set to 50°C, and stirring and heating were started.

[0128] After heating, 4 kg of phosphate-containing epoxy resin (DH-7325 from Suzhou Qingtian New Materials Co., Ltd.) was added to the reactor, and the mixture was kept warm and stirred for 6 hours for coating reaction. Then it was cooled to 30°C, filtered by a filter press, and then kneaded evenly by a kneader to obtain water-based aluminum pigment.

[0129] Comparative Example 8

[0130] A method for preparing a water-based aluminum pigment includes the following steps:

[0131] 60 kg of aluminum powder (oil-based, flake-shaped, ball-milled aluminum powder with an average particle size of 11 μm and a particle size range of 0.8-1.0) was added to a stainless steel stirred reactor, followed by 300 kg of anhydrous ethanol. The reactor temperature was set to 50 °C, and stirring and heating were started. After heating was completed, an ethanol solution of zinc nitrate (containing 2.5 kg of zinc nitrate and 25 kg of ethanol) was added, and the mixture was kept at the same temperature and stirred for 3 hours for passivation treatment.

[0132] After the passivation treatment is completed, 12 kg of 8 wt% dimethylethanolamine aqueous solution and 12 kg of tetraethyl orthosilicate are simultaneously added dropwise to the reaction vessel at a rate of 3 kg / h. After the addition is completed, the mixture is kept warm and stirred for a reaction of 2 hours.

[0133] After one reaction was completed, 3 kg of 50 wt% γ-aminopropyltriethoxysilane ethanol solution was added, and the mixture was kept warm and stirred for 1 hour to carry out the filling reaction.

[0134] After the filling reaction is completed, 8 kg of 8 wt% dimethylethanolamine aqueous solution and 8 kg of tetraethyl orthosilicate are simultaneously added dropwise into the reaction vessel at a rate of 2 kg / h. After the addition is completed, the vessel is kept warm and stirred for a second reaction for 2 hours.

[0135] After the secondary reaction is completed, 4 kg of phosphate-containing epoxy resin (DH-7325 from Suzhou Qingtian New Materials Co., Ltd.) is added to the reactor and the mixture is kept warm and stirred for 6 hours for coating reaction. Then it is cooled to 30°C, filtered by a filter press, and then kneaded evenly by a kneader to obtain water-based aluminum pigment.

[0136] The difference between Comparative Example 8 and Example 1 is that the phytic acid aqueous solution without grafted amino groups was not added, while the aqueous aluminum pigment was prepared according to the steps of Example 1.

[0137] The aluminum pigments from Examples 1-3 and Comparative Examples 1-8 were uniformly dispersed in anhydrous ethanol to obtain aluminum silver pastes with a solid content of 55 wt%.

[0138] Experiment 1

[0139] Each group of aluminum silver paste was used to prepare water-based plastic coatings according to the same formula (where the content of aluminum silver paste was 8wt%), and the coatings were formed on plastic boards. The soluble aluminum index in each group of coatings was tested according to the method specified in EN 71-3:2019+Al:2021. The test results are shown in Table 1.

[0140] Table 1 Test Results

[0141]

[0142] As shown in Table 1, the coating prepared by the water-based aluminum pigment of the present invention can effectively reduce the generation of soluble aluminum, meeting the requirements of the European toy safety standard EN 71-3:2019+Al:2021. However, the soluble aluminum content of Comparative Examples 1-5 and 7-8 does not meet the requirements of the European toy safety standard. The result of Comparative Example 6 is close to the limit. The soluble aluminum content is high when there is no passivation treatment, only silica coating, only other resin coating, other resin coating, no phosphate group resin coating, no silane coupling agent coating, only phosphate group resin coating, and no phytic acid grafted with amino groups in the second silica layer. It is necessary to use the alumina layer, silica layer one, silane coupling agent layer, silica layer two, and aluminum ion capturing layer of the present invention in combination to meet the requirements.

[0143] Experiment 2

[0144] Each group of aluminum silver paste was used to prepare water-based plastic coatings according to the same formula (where the content of aluminum silver paste was 8wt%). Then, the coatings were placed in a constant temperature environment of 50℃ for 30 days to conduct an accelerated hydrogen evolution test on the plastic coatings. The cumulative gas release results after 30 days are shown in Table 2.

[0145] Table 2. Test results (unit: ml)

[0146]

[0147] As can be seen from Table 2, the waterborne aluminum pigment of the present invention has a hydrogen evolution and gas release of 0 in 30 days when used in plastic coating systems, which meets the limit and also meets the requirement that the hydrogen evolution and gas release limit of conventional plastic coating systems is less than 20 ml in 7 days. The storage stability of the waterborne aluminum pigment of the present invention is significantly better than that of comparative examples 1-8.

[0148] Experiment 3

[0149] Take 5g of each group of aluminum silver paste and disperse it evenly in 250g of pH=1 HCl aqueous solution. Place it in a constant temperature environment of 40℃ for 30 days to carry out hydrogen evolution acceleration test by immersion in strong acid solution. The cumulative gas release results after 30 days are shown in Table 3.

[0150] Table 3. Detection Results (Unit: ml)

[0151]

[0152] As can be seen from Table 3, in Examples 1-3, after being placed in a strong acid system at 40°C with pH=1 for 30 days, the amount of gas released was only 0-18.9 mL, and the main gas release phase was in the first two days of the test. The amount of gas released did not continue to increase afterward, indicating that the water-based aluminum pigment of the present invention can remain stable in a strong acid solution and has good acid resistance. In contrast, Comparative Examples 1-8 reacted very rapidly in a strong acid system with pH=1.

[0153] Experiment 4

[0154] The aluminum silver pastes from Example 1 and Comparative Example 2 were used to prepare water-based plastic coatings (the film-forming resin was a water-based polyurethane emulsion resin, and the amount of aluminum silver paste added was 10 wt%). A 50 μm thick wet film was then formed on a scraper, and the results were compared using the scraper. Figure 1-2 As shown.

[0155] Figure 1 These are comparative photographs of the whiteness of scraper coatings made from water-based aluminum pigments in Example 1 and Comparative Example 2. The left side is Comparative Example 2, and the right side is Example 1.

[0156] Figure 2 These are comparison photographs of the gloss of scraper coatings made from water-based aluminum pigments in Example 1 and Comparative Example 2, with Comparative Example 2 on the left and Example 1 on the right.

[0157] Depend on Figure 1-2 It can be seen that the whiteness, brightness and metallic feel of the water-based plastic coating made of the water-based aluminum pigment of the present invention are not significantly different from those of Comparative Example 2.

[0158] In summary, the water-based aluminum pigment of this invention, while ensuring the same hue as commercially available aluminum pigments, has excellent stability and corrosion resistance. Furthermore, the water-based aluminum pigment of this invention meets the requirements of the EN 71-3:2019+A1:2021 European toy safety standard and can be used in children's coatings.

[0159] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A water-based aluminum pigment, characterized in that, include: Aluminum powder and, from the inside out, an aluminum oxide layer, a first silica layer, a silane coupling agent layer, a second silica layer, and an aluminum ion trapping layer are sequentially coated on the surface of the aluminum powder; the aluminum ion trapping layer is an organic resin layer containing phosphate groups. The second layer of silica contains phytic acid grafted with amino groups.

2. The water-based aluminum pigment according to claim 1, characterized in that, The organic resin containing phosphate groups is at least one of epoxy resin containing phosphate groups and polyester resin containing phosphate groups.

3. A method for preparing a water-based aluminum pigment as described in claim 1 or 2, characterized in that, Includes the following steps: Aluminum powder, passivating agent and organic solvent are mixed and then passivated. After the passivation treatment is completed, add silane monomer one and catalyst one, mix well, and carry out a reaction; After one reaction is completed, a silane coupling agent is added to carry out a filling reaction; After the filling reaction is completed, silane monomer II, phytic acid grafted with amino groups and catalyst II are added and mixed well to carry out a second reaction; After the secondary reaction is completed, an organic resin containing phosphate groups is added to carry out a coating reaction, thereby obtaining a water-based aluminum pigment.

4. The method for preparing water-based aluminum pigment according to claim 3, characterized in that, The passivating agent is at least one of zinc nitrate, ferric nitrate, ferrous nitrate, tin nitrate, and copper nitrate.

5. The method for preparing water-based aluminum pigment according to claim 3, characterized in that, The passivation treatment, primary reaction, filling reaction, secondary reaction, and coating reaction are all carried out at temperatures of 40-60℃.

6. The method for preparing water-based aluminum pigment according to claim 3, characterized in that, Both silane monomer one and silane monomer two are at least one of methyl orthosilicate, ethyl orthosilicate, and silane prepolymer.

7. The method for preparing water-based aluminum pigment according to claim 3, characterized in that, Catalyst 1 and Catalyst 2 are both at least one of concentrated ammonia, ethylenediamine, dimethylethanolamine, and 2-amino-2-methyl-1-propanol.

8. The application of a water-based aluminum pigment as described in claim 1 or 2 in a coating.

9. A water-based coating, characterized in that, Its raw materials include: water-based film-forming resin and water-based aluminum pigment as described in claim 1 or 2.

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