Low temperature curing epoxy powder coating and method of preparation

Abstract

The present application relates to the technical fields of low-temperature curing of epoxy coating, and discloses a low-temperature curing type epoxy powder coating and a preparation method, specifically: 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane, epichlorohydrin and 2-methylimidazole are used as raw materials, an amino-epoxy ring-opening reaction occurs first, then a ring-closing reaction occurs, and finally an epoxy-amine ring-opening reaction occurs, to obtain a bis-imidazole-based organic silicon curing agent or a tetra-imidazole-based organic silicon curing agent; a bis-imidazole-based fluorine-containing organic silicon curing agent is prepared by the addition reaction of the bis-imidazole-based organic silicon curing agent and methacrylic acid dodecafluoroheptyl ester; the curing agent is blended with an epoxy resin and other raw materials, and is subjected to melt extrusion, crushing and sieving, to obtain the low-temperature curing type epoxy powder coating; the low-temperature curing type epoxy powder coating prepared by the present application has achieved significant improvement in hardness, adhesion and corrosion resistance.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of low-temperature curing technology of epoxy coating, in particular to a low-temperature curing type epoxy powder coating and a preparation method thereof. BACKGROUND

[0002] Coating anti-corrosion coating is essential for pipelines, and epoxy resin coating is one of the most commonly used materials for pipeline anti-corrosion coating. At present, epoxy resin coating mainly includes solvent-based coating, water-based coating and powder coating, and the components of epoxy powder coating are all solids, and its curing process will not have water and solvent volatilization, with the advantages of no VOCs emission, high utilization rate of spraying, easy to realize automatic production, etc.

[0003] The curing agent, as an important component of the epoxy powder coating, its curing temperature is one of the key factors to determine the bonding force of the epoxy powder coating with the pipeline. However, the curing temperature of the epoxy powder coating is generally above 180℃, which leads to high energy consumption of its coating and is difficult to adapt to complex and harsh construction conditions.

[0004] It is found that imidazole curing agent is a kind of low-temperature curing agent with excellent activity, but the imidazole curing agent is difficult to meet the requirement of "storage for more than three months" in practical application due to its high reactivity, which can be cured at room temperature after mixing with epoxy resin. SUMMARY

[0005] In order to reduce the activity of ordinary imidazole curing agent, the imidazole silicone type curing agent is independently developed, the self-made imidazole silicone type curing agent is used as the curing agent of the low-temperature curing type epoxy powder coating, the storage performance of the mixture of the curing agent and the epoxy resin is improved, and the epoxy resin and other raw materials are further blended, and the low-temperature curing type epoxy powder coating with excellent anti-corrosion performance is prepared through melting extrusion, crushing and sieving.

[0006] In order to achieve the above purpose, the technical scheme is adopted as follows:

[0007] A low-temperature curing type epoxy powder coating, the coating formula is: 80-120 parts by weight of epoxy resin; 5-10 parts by weight of low-temperature curing agent; 1-2 parts by weight of leveling agent; 0.5-0.7 parts by weight of defoaming agent; 30-40 parts by weight of pigment; 2-3 parts by weight of filler; 0.5-1.5 parts by weight of polyethylene wax powder;

[0008] The low-temperature curing agent is a bis-imidazole silicone type curing agent, a tetra-imidazole silicone type curing agent or a bis-imidazole fluorine-containing silicone type curing agent.

[0009] A preparation method of a low-temperature curing type epoxy powder coating includes the following steps:

[0010] Step one, based on the mechanism of epoxy ring opening and amine-ene addition reaction, with 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane, epichlorohydrin, 2-methyl imidazole and methyl methacrylate dodecafluoroheptyl ester as raw materials, a low temperature curing agent was synthesized;

[0011] Step two, according to the formula of low temperature curing type epoxy powder coating, the ingredients were prepared by mixing, melting extrusion, crushing and sieving process, and a low temperature curing type epoxy powder coating was prepared.

[0012] Preferably, the preparation method of the bis-imidazole-based silicone curing agent is:

[0013] Through 1 mole equivalent of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane and 2 mole equivalent of epichlorohydrin, amino-epoxy ring opening reaction was first carried out, and then closed ring reaction was carried out under the catalysis of alkali metal hydroxide, to obtain bis-epoxy tetramethyldisiloxane;

[0014] Through 1 mole equivalent of bis-epoxy tetramethyldisiloxane and 2 mole equivalent of 2-methyl imidazole, epoxy-amine ring opening reaction was carried out, to obtain bis-imidazole-based silicone curing agent.

[0015] Preferably, the preparation method of the bis-imidazole-based silicone curing agent is:

[0016] Through 1 mole equivalent of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane and 4 mole equivalent of epichlorohydrin, amino-epoxy ring opening reaction was first carried out, and then closed ring reaction was carried out under the catalysis of alkali metal hydroxide, to obtain tetra-epoxy tetramethyldisiloxane;

[0017] Through 1 mole equivalent of tetra-epoxy tetramethyldisiloxane and 4 mole equivalent of 2-methyl imidazole, epoxy-amine ring opening reaction was carried out, to obtain tetra-imidazole-based silicone curing agent.

[0018] Preferably, the preparation method of the bis-imidazole-based silicone curing agent is:

[0019] Through 1 mole equivalent of bis-imidazole-based silicone curing agent and 2 mole equivalent of methyl methacrylate dodecafluoroheptyl ester, amine-α,β-unsaturated double bond addition reaction was carried out, to obtain bis-imidazole-based fluorine-containing silicone curing agent.

[0020] Preferably, the alkali metal hydroxide is one of sodium hydroxide and potassium hydroxide.

[0021] Preferably, the curing temperature of the epoxy powder coating is 120-140℃.

[0022] Preferably, the temperature of melting extrusion is 80-90℃.

[0023] Preferably, the epoxy resin is one of E-12, E-20.

[0024] Preferably, the low-temperature curing type epoxy powder coating is used for coating pipes, and is cured at 120-140 DEG C for 25-30 min, thereby playing a role of corrosion protection.

[0025] The present application has the following beneficial effects:

[0026] The 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane, epichlorohydrin and 2-methylimidazole are used as raw materials, the amino-epoxy group ring-opening reaction is first carried out, then the ring-closing reaction is carried out, and finally the epoxy-amine group ring-opening reaction mechanism is used to prepare the bis-imidazole-based silicone type curing agent or tetra-imidazole-based silicone type curing agent;

[0027] The bis-imidazole-based silicone type curing agent and dodecafluoroheptyl methacrylate are used as raw materials based on the amine-ene addition reaction mechanism between the amine and the alpha, beta-unsaturated double bond to prepare the bis-imidazole-based fluorine-containing silicone type curing agent;

[0028] The epoxy resin, the bis-imidazole-based silicone type curing agent (or the tetra-imidazole-based silicone type curing agent or the bis-imidazole-based fluorine-containing silicone type curing agent), the pigment and filler and other additives are premixed, and then subjected to the melting extrusion, crushing and sieving processes to prepare the low-temperature curing type epoxy powder coating.

[0029] The experimental results prove that the low-temperature curing type epoxy powder coating prepared by the present application has the beneficial technical effects of remarkable improvement in the hardness, adhesion and corrosion resistance. DETAILED DESCRIPTION

[0030] Example 1: The bis-imidazole-based silicone type curing agent is prepared, and the preparation mechanism is as follows:

[0031] In the first step, the amino group of 1 mole equivalent of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane is first subjected to the ring-opening reaction with 2 mole equivalents of the epoxy group of epichlorohydrin, and then subjected to the ring-closing reaction under the catalysis of sodium hydroxide to prepare the bis-epoxy tetramethyldisiloxane.

[0032] In the second step, the epoxy group of 1 mole equivalent of the bis-epoxy tetramethyldisiloxane is subjected to the ring-opening reaction with 2 mole equivalents of the amine group of 2-methylimidazole to prepare the bis-imidazole-based silicone type curing agent.

[0033] The specific experimental steps of the bis-imidazole-based silicone type curing agent are as follows:

[0034] Step I: 2.24 g of epichlorohydrin and 20 mL of deionized water were added to a 250 mL four-necked round-bottom flask equipped with a magnetic stirrer, a dropping funnel, a condenser, and a thermometer. The temperature of the system was raised to 50°C under stirring, and then a solution containing 3 g of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane in 30 mL of tetrahydrofuran was added dropwise for 1 h. After the addition was completed, the temperature was raised to 55°C, and the reaction was maintained for 2 h;

[0035] After the reaction was completed, the temperature of the system was lowered to 40°C, 3 mL of a 10% sodium hydroxide aqueous solution was added, the pH value of the reaction system was controlled at 8, and the reaction was maintained for 3 h at constant temperature. Then, the pH value of the system was adjusted to neutral using a 20% acetic acid solution, and a bis-epoxy tetramethyldisiloxane was prepared.

[0036] Step II: 2.28 g of 2-methylimidazole was added to 60 mL of xylene, and the temperature was raised to 120°C to dissolve the 2-methylimidazole under stirring. Then, 5 g of the bis-epoxy tetramethyldisiloxane was added, and the reaction was continued at 120°C for 2 h. After the reaction was completed, the solvent was removed by distillation under reduced pressure, and a bis-imidazolyl silicone curing agent was prepared.

[0037] The chemical structural formula of the bis-imidazolyl silicone curing agent is as follows:

[0038] ;

[0039] The hydrogen nuclear magnetic resonance spectrum of the bis-imidazolyl silicone curing agent is as follows:

[0040] 1 H NMR (DMSO-d6, 400 MHz) δ: 0.10 (s, 12H), 0.74-0.77 (t, 4H), 1.44-1.50 (m, 4H), 2.46 (s, 6H), 2.64-2.74 (m, 4H), 2.75-2.81 (m, 4H), 2.96-3.00 (m, 2H), 3.87-3.97 (m, 4H), 4.01-4.06 (m, 2H), 4.21-4.22 (d, 2H), 6.96-6.98 (m, 4H).

[0041] Example Two: A tetra-imidazolyl silicone curing agent was prepared, and the preparation mechanism is as follows:

[0042] First Step: The amino groups of 1 mole equivalent of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane were first subjected to ring-opening reaction with 4 mole equivalents of epoxy groups of epichlorohydrin, and then subjected to ring-closing reaction under the catalysis of sodium hydroxide, to prepare a tetra-epoxy tetramethyldisiloxane.

[0043] Second step: through the ring opening reaction of 1 mole equivalent of epoxy group of tetraepoxy tetramethyl disiloxane and 4 mole equivalent of secondary amine group of 2-methyl imidazole, a tetraimidazolyl silicone type curing agent is prepared;

[0044] The specific experimental steps of the tetraimidazolyl silicone type curing agent are as follows:

[0045] Step I: 4.47 g of epichlorohydrin and 40 mL of deionized water are added to a 250 mL four-necked round-bottom flask equipped with a magnetic stirrer, a dropping funnel, a condenser tube and a thermometer, and the temperature of the system is increased to 50°C under stirring, then a tetrahydrofuran solution (30 mL) containing 3 g of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane is added dropwise, the dropping time is 1 h, after the dropping is completed, the temperature is increased to 55°C, and the reaction is kept for 2 h;

[0046] After the reaction is completed, the temperature of the system is decreased to 40°C, 4.8 mL of 10% sodium hydroxide aqueous solution is added, the pH value of the reaction system is controlled to be 8, the reaction is kept for 3 h at constant temperature, then the pH value of the system is adjusted to neutral by using 20% acetic acid, and tetraepoxy tetramethyl disiloxane is prepared;

[0047] Step II: 4.56 g of 2-methyl imidazole is added to 80 mL of xylene, the temperature is increased to 120°C, and 2-methyl imidazole is dissolved by stirring, then 5 g of tetraepoxy tetramethyl disiloxane is added, the reaction is continued at 120°C for 2 h, after the reaction is completed, the solvent is removed by distillation under reduced pressure, and a tetraimidazolyl silicone type curing agent is prepared;

[0048] The chemical structural formula of the tetraimidazolyl silicone type curing agent is as follows:

[0049] ;

[0050] The hydrogen nuclear magnetic resonance spectrum of the tetraimidazolyl silicone type curing agent is as follows:

[0051] 1 H NMR(DMSO-d6, 400MHz) δ: 0.15(s, 12H), 0.68-0.72(t, 4H), 1.45-1.52(m, 4H), 2.42(s, 12H), 2.45-2.52(m, 8H), 2.53-2.60(m, 4H), 3.82-3.93(m, 8H), 4.00-4.06(m, 4H), 4.12-4.14(d, 4H), 6.96(s, 8H).

[0052] Example Three: A bisimidazolyl fluorine-containing silicone type curing agent is prepared, and the preparation mechanism is as follows:

[0053] The bismidazolyl fluorine-containing silicone type curing agent is prepared by reacting the secondary amine group of 1 mole equivalent of the bismidazolyl silicone type curing agent with the alkenyl group of 2 mole equivalents of dodecafluoroheptyl methacrylate;

[0054] The specific experimental steps of the bismidazolyl fluorine-containing silicone type curing agent are as follows:

[0055] Into a 250 mL three-necked flask equipped with a thermometer, a stirrer and a condenser reflux device, 3 g of the bismidazolyl silicone type curing agent, 4.58 g of dodecafluoroheptyl methacrylate and 60 mL of ethanol are added, and the mixture is uniformly stirred mechanically, and the temperature is raised to 60°C. After 8 h of reaction at this temperature, the product is filtered, washed and vacuum dried at 60°C for 8 h to obtain the bismidazolyl fluorine-containing silicone type curing agent;

[0056] The chemical structural formula of the bismidazolyl fluorine-containing silicone type curing agent is as follows:

[0057] ;

[0058] The hydrogen nuclear magnetic resonance spectrum of the bismidazolyl fluorine-containing silicone type curing agent is as follows:

[0059] 1 H NMR (DMSO-d6, 400 MHz) δ: 0.17 (s, 12H), 0.75-0.79 (t, 4H), 1.11-1.13 (d, 6H), 1.48-1.54 (m, 4H), 2.33-2.41 (m, 4H), 2.44 (s, 6H), 2.46-2.56 (m, 4H), 2.60-2.67 (m, 2H), 2.69-2.75 (m, 4H), 3.82-3.93 (m, 4H), 4.00-4.06 (m, 2H), 4.12-4.14 (d, 2H), 4.55-4.70 (m, 4H), 6.51-6.82 (m, 2H), 6.98 (s, 4H).

[0060] Example Four: (1) A low-temperature curing type epoxy powder coating A, comprising the following raw materials in parts by weight:

[0061] 100 parts of epoxy resin E-12 (epoxy value of 0.110-0.140 / 100 g);

[0062] 3 parts of bismidazolyl silicone type curing agent;

[0063] 1.5 parts of leveling agent (model BYK-360P);

[0064] 0.6 parts of benzoin;

[0065] 34 parts of pigment titanium white powder;

[0066] 2.6 parts of filler barium sulfate;

[0067] 0.9 parts of polyethylene wax powder;

[0068] The preparation method of the low-temperature curing type epoxy powder coating A is as follows: the epoxy resin E-12, the bis-imidazole-based silicone type curing agent, the leveling agent, the benzoin, the pigment titanium dioxide, the filler barium sulfate, and the polyethylene wax powder are added into a mixer, stirred and uniformly mixed, then the mixed material is transferred into a double-screw extruder, the extrusion temperature is set to 85℃, the screw extrusion speed is 55r / min, the extruded material is cooled to room temperature, then is crushed and sieved to 200 meshes to obtain the low-temperature curing type epoxy powder coating A.

[0069] (2) The low-temperature curing type epoxy powder coating B is prepared, which is only different from the low-temperature curing type epoxy powder coating A in that the bis-imidazole-based silicone type curing agent is replaced by a tetra-imidazole-based silicone type curing agent.

[0070] (3) The low-temperature curing type epoxy powder coating C is prepared, which is only different from the low-temperature curing type epoxy powder coating A in that the bis-imidazole-based silicone type curing agent is replaced by a bis-imidazole-based fluorine-containing silicone type curing agent.

[0071] Performance test: the low-temperature curing type epoxy powder coating prepared in the application is sprayed on a tinplate substrate by an electrostatic spraying method (the substrate is selected according to the content of GB / T 9271-2008 “Standard Test Panels for Paint and Varnish”), after the spraying is completed, the substrate with the coating is placed in an oven, first heated at 80℃ for 15min, then the temperature is increased to 140℃ and continues to be heated for 10min to obtain a coating sample with a thickness of 100μm;

[0072] I. Gelation time: the gelation time of the low-temperature curing type epoxy powder coating is tested according to GB / T 16995-1997 “Determination of Gelation Time of Thermosetting Powder Coatings at Given Temperature”, 0.25mL of the powder coating sample is placed on a test plate preheated to 120℃ or 140℃, when the powder on the test plate just melts, the timing starts, at this time, a needle with low heat capacity is used to stir the melted powder by drawing a small circle on it every 2-3 seconds, when the silk formed by drawing the powder up 1cm breaks or cannot be drawn up from the melted powder, the timing stops, at this time, the recorded time is the gelation time of the sample;

[0073] II. Hardness: the surface hardness of the coating sample is tested according to GB / T 6739-2022 “Paint and Varnish - Determination of Film Hardness by Pencil Method”;

[0074] III. Adhesion: the adhesion of the coating sample is tested according to GB / T 9286-2021 “Paint and Varnish - Crosshatch Test”;

[0075] Four, corrosion resistance: according to HG / T 2006-2022 “Thermosetting and thermoplastic powder coatings” to test the corrosion resistance of the coating sample, alkali resistance, acid resistance and salt spray resistance;

[0076] The above test results are shown in Table 1 below;

[0077] Table 1 Performance test results of low-temperature curing epoxy powder coatings

[0078]

[0079] The comparative example: using dicyandiamide curing agent to replace the dually imidazole-based organic silicon curing agent in the low-temperature curing epoxy powder coating A, the powder coating prepared is not gelled at 120℃ and 140℃;

[0080] From the experimental results in Table 1, it can be seen that:

[0081] Compared with the low-temperature curing epoxy powder coating A and the low-temperature curing epoxy powder coating C, the low-temperature curing epoxy powder coating B has the shortest gelling time, the curing activity of the curing agent is significantly improved, and the hardness and adhesion of the epoxy powder coating layer are also significantly improved;

[0082] Compared with the low-temperature curing epoxy powder coating A and the low-temperature curing epoxy powder coating B, the low-temperature curing epoxy powder coating C has achieved a significant technical effect in corrosion resistance.

Claims

1. A low-temperature curing epoxy powder coating, characterized in that, The coating formulation is as follows: 80-120 parts by weight of epoxy resin; 5-10 parts by weight of low-temperature curing agent; 1-2 parts by weight of leveling agent; 0.5-0.7 parts by weight of defoamer; 30-40 parts by weight of pigment; 2-3 parts by weight of filler; 0.5-1.5 parts by weight of polyethylene wax powder; The low-temperature curing agent is a bisimidazole-based silicone curing agent, a tetraimidazole-based silicone curing agent, or a bisimidazole-based fluorinated silicone curing agent. The chemical structural formula of the bisimidazole-based silicone curing agent is: ； The chemical structural formula of the tetraimidazolium-based silicone curing agent is: ； The chemical structural formula of the bisimidazole-based fluorinated organosilicon curing agent is: 。 2. The method for preparing a low-temperature curing epoxy powder coating according to claim 1, characterized in that, Includes the following steps: Step 1: Based on the mechanism of epoxy ring-opening and amine addition reaction, a low-temperature curing agent is synthesized using 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane, epichlorohydrin, 2-methylimidazolium and dodecafluoroheptyl methacrylate as raw materials. Step 2: Prepare the ingredients according to the formula of the low-temperature curing epoxy powder coating, and obtain the low-temperature curing epoxy powder coating through mixing, melt extrusion, crushing and sieving processes.

3. The method for preparing a low-temperature curing epoxy powder coating according to claim 2, characterized in that, The preparation method of the bisimidazole-based organosilicon curing agent is as follows: Diepoxytetramethyldisiloxane was prepared by reacting 1 molar equivalent of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane with 2 molar equivalents of epichlorohydrin first with an amino-epoxy ring-opening reaction, and then with a ring-closing reaction under the catalysis of an alkali metal hydroxide. A diimidazole-based organosilicon curing agent was prepared by reacting 1 molar equivalent of diepoxytetramethyldisiloxane with 2 molar equivalents of 2-methylimidazole in an epoxy-secondary amine ring-opening reaction.

4. The method for preparing a low-temperature curing epoxy powder coating according to claim 2, characterized in that, The preparation method of the tetraimidazolyl organosilicon curing agent is as follows: Tetraepoxytetramethyldisiloxane was prepared by first reacting 1 molar equivalent of 1,3-bis(3-aminopropyl)-1,1,3,3-tetramethyldisiloxane with 4 molar equivalents of epichlorohydrin in an amino-epoxy ring-opening reaction, followed by a ring-closing reaction catalyzed by an alkali metal hydroxide. Tetraimidazole-based organosilicon curing agent was prepared by reacting 1 molar equivalent of tetraepoxytetramethyldisiloxane with 4 molar equivalents of 2-methylimidazole in an epoxy-secondary amine ring-opening reaction.

5. The method for preparing a low-temperature curing epoxy powder coating according to claim 2, characterized in that, The preparation method of the bisimidazole-based fluorinated organosilicon curing agent is as follows: A fluorinated organosilicon curing agent based on imidazolium was prepared by reacting 1 molar equivalent of a bisimidazole-based organosilicon curing agent with 2 molar equivalents of dodecafluoroheptyl methacrylate via a secondary amine-α,β-unsaturated double bond addition reaction.

6. A method for preparing a low-temperature curing epoxy powder coating according to any one of claims 3-4, characterized in that, The alkali metal hydroxide is one of sodium hydroxide and potassium hydroxide.

7. The method for preparing a low-temperature curing epoxy powder coating according to claim 2, characterized in that, The curing temperature of the epoxy powder coating is 120-140℃.

8. The method for preparing a low-temperature curing epoxy powder coating according to claim 2, characterized in that, The temperature of the melt extrusion is 80-90℃.

9. The low-temperature curing epoxy powder coating according to claim 1, characterized in that, The epoxy resin is of type E-12 or E-20.

10. A low-temperature curing epoxy powder coating according to claim 1, characterized in that, The low-temperature curing epoxy powder coating is used to coat pipes and cures at 120-140℃ for 25-30 minutes to provide corrosion protection.

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