A transparent powder coating composition and a preparation method thereof

Abstract

The present invention relates to the technical field of powder coatings, and specifically relates to a transparent powder coating composition and a preparation method thereof, including the following mass components, which include a hydroxy-silane-modified GMA acrylic resin component of 50 wt% - 80 wt%, a curing agent component of 15 wt% - 45 wt%, a polycarbonate diol component of 1% - 3%, a degassing agent component of 0.1 wt% - 1.0 wt%, and a leveling agent component of 0.1 wt% - 2 wt%. The glass transition temperature of the hydroxy-silane-modified GMA acrylic resin is 70 - 90 °C, and the number average molecular weight is between 5000 and 8000. The molecular weight of the polycarbonate diol is between 1000 and 2000, and it is added during the synthesis process of the hydroxy-silane-modified GMA acrylic resin and during the premixing process of the powder coating composition. The powder coating composition of the present invention can obtain a cured coating with excellent transparency and scratch resistance, and can improve the corrosion resistance and boiling water adhesion of the coating.

Description

Technical Field

[0001] The invention relates to the technical field of powder coatings, and in particular to a transparent powder coating composition and a preparation method thereof. Background Art

[0002] Powder coating is a solid coating composition applied to a substrate in the form of a free-flowing powder by an electrostatic process. It provides colorful exterior decoration for building materials, home appliances, furniture and industrial metal products. For transparent powder coating systems, the most commonly used is GMA acrylic resin transparent powder coating. The advantages of this type of powder system are good transparency and weather resistance, but the coating has poor scratch resistance and is easily damaged when in contact with solid objects. The surface coating will be scratched due to impact and friction, affecting the surface appearance. Moreover, as the number of scratches on the coating increases, the protective effect of the coating will be reduced, causing the substrate to be corroded. The current method commonly used to improve the scratch resistance of the coating is to add an improved wax anti-scratch agent to the powder coating system, but the addition of such an anti-scratch agent alone will affect the transparency of the cured coating and cannot meet the use requirements.

[0003] To this end, a transparent powder coating composition and a preparation method are provided. Summary of the invention

[0004] The object of the present invention is to provide a transparent powder coating composition and a preparation method thereof. A hydroxyl silane monomer is introduced into the GMA acrylic resin system of the transparent powder coating for modification. When the coating is cured, the floating of the silane chain segment gives the coating smoothness and scratch resistance, and does not affect the transparency of the coating. The hydroxyl and epoxy functional groups in the acrylic resin are respectively cross-linked with a carboxyl curing agent and an isocyanate curing agent to increase the curing density and improve the hardness of the coating. Finally, polycarbonate diol is added to the modified acrylic resin adhesive or in the mixing process of the powder coating composition to assist in improving the hardness, wear resistance and boiling adhesion of the coating. The scratch resistance, boiling adhesion and corrosion resistance of the powder coating composition obtained in combination are greatly improved to solve the problems raised in the above-mentioned background technology.

[0005] To achieve the above-mentioned purpose, the present invention provides the following technical solution: a transparent powder coating composition, comprising the following mass components, including 50wt%-80wt% of a hydroxysilane-modified GMA acrylic resin component, 15wt%-45wt% of a curing agent component, 1%-3% of a polycarbonate diol component, 0.1wt%-1.0wt% of a deaerator component, and 0.1wt%-2wt% of a leveling agent component.

[0006] Preferably, the molecular weight of the polycarbonate diol is between 1000 and 2000, and it is added during the synthesis of the hydroxy silane modified GMA acrylic resin and during the premixing process of the powder coating composition.

[0007] Preferably, the curing agent component is a compound that undergoes a crosslinking reaction with the hydroxy silane modified GMA acrylic resin component, including acid and anhydride curing agents, amine curing agents, and isocyanate curing agents.

[0008] Preferably, the hydroxy silane modified GMA acrylic resin consists of 25wt%-40wt% epoxy acrylate monomer, 30wt%-60wt% methacrylate monomer, 1wt%-5wt% hydroxy silane monomer, 10wt%-25wt% styrene monomer, and 1wt%-3wt% polycarbonate diol monomer with a molecular weight of 1000-2000.

[0009] Preferably, the epoxy acrylate monomer is specifically glycidyl methacrylate, glycidyl acrylate, and acrylate monomers containing epoxy groups.

[0010] Preferably, the methacrylate monomer is specifically methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, and lauryl methacrylate, and acrylate esters with 2 to 11 carbon atoms.

[0011] Preferably, the hydroxy silane monomer in the hydroxy silane modified GMA acrylic resin is specifically a terminal hydroxy vinyl silane monomer.

[0012] Preferably, the glass transition temperature of the hydroxy silane modified GMA acrylic resin is 70°C - 90°C, the epoxy equivalent is 400 - 500, and the number average molecular weight is 5000 - 8000.

[0013] A preparation method of a transparent powder coating composition, wherein the synthesis method of the hydroxy silane modified GMA acrylic resin is prepared by the following steps of free radical polymerization reaction:

[0014] S1. Add a solvent to the reaction vessel, stir and heat to the reflux state, mix the terminal hydroxy vinyl silane monomer, glycidyl methacrylate monomer, alkyl methacrylate monomer, styrene monomer, and initiator evenly, and drop them into the refluxing solvent within 3h - 3.5h. After the dropping is completed, react for 2h under the reflux state;

[0015] S2. Continue to slowly dropwise add the mixed solution of the remaining initiator and solvent under the condition of solvent reflux, and finish the dropping within 10 min, then carry out reflux reaction for 2 h;

[0016] S3. After the reflux reaction ends, add polycarbonate diol, and start to distill off the solvent. When the temperature of the reaction system reaches 180 °C, apply a vacuum of -0.09 MPa for 0.5 h, then release the vacuum, discharge the material and cool it to obtain the hydroxyl silane-modified GMA acrylic resin.

[0017] Preferably, by physically premixing the hydroxyl silane-modified GMA acrylic resin, curing agent, leveling agent, degassing agent and polycarbonate diol, then using a twin-screw extruder for melt extrusion, tablet pressing, cooling and crushing into fine powder, and finally passing through a 200-mesh sieve, a transparent powder coating composition is obtained.

[0018] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0019] In the present invention, the hydroxyl silane monomer is introduced into the GMA acrylic resin system of the transparent powder coating for modification. When the coating is cured, the floating of the silane chain segments endows the coating with smoothness and provides scratch resistance, and does not affect the transparency of the coating. The combination crosslinking of the hydroxyl and epoxy functional groups in the acrylic resin with the carboxyl curing agent and isocyanate curing agent increases the curing density and improves the hardness of the coating. Finally, adding polycarbonate diol in the modified acrylic resin binder or during the mixing process of the powder coating composition helps to improve the hardness, wear resistance and boiling water resistance adhesion of the coating. The scratch resistance, boiling water resistance adhesion and corrosion resistance of the obtained powder coating composition are greatly improved. Description of the Drawings

[0020] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following will briefly introduce the drawings required for the description of the specific embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0021] Figure 1 It is the composition table of the transparent powder coating composition of the present invention;

[0022] Figure 2 It is the flow chart of the preparation method of the transparent powder coating composition of the present invention. Detailed Embodiments

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0024] Please refer to Figures 1 to 2 , the present invention provides a technical solution:

[0025] A transparent powder coating composition, comprising the following mass components: 50wt%-80wt% of a hydroxyl silane-modified GMA acrylic resin component, 15wt%-45wt% of a curing agent component, 1%-3% of polycarbonate diol, 0.1wt%-1.0wt% of a degassing agent, and 0.1wt%-2wt% of a leveling agent.

[0026] The polycarbonate diol is premixed during the mixing process with the hydroxyl silane-modified GMA acrylic resin or in the powder coating composition. It can be mixed with other coating components after being completely mixed in the acrylic resin, or can be melt-mixed as a separate component with the powder coating composition during the extrusion process. The polycarbonate diol used in the present invention has a molecular weight of 1000-2000 and can be purchased from Asahi Kasei of Japan under the DURANOL brand, such as DURANOL T5652. Adding polycarbonate diol to the powder coating system helps to improve the hardness, abrasion resistance, and boiling water adhesion of the coating.

[0027] The curing agent that can crosslink with the hydroxyl silane-modified GMA acrylic resin of the present invention can be a compound or a composition containing carboxyl groups, amino groups, and isocyanate groups. Among them, the curing agent component containing carboxyl groups is preferably a polycarboxylic acid, such as dodecanedioic acid, and the isocyanate curing agent is preferably a caprolactam-blocked isocyanate, such as K7150 of Lu'an Jiantongda New Materials Co., Ltd.

[0028] The hydroxyl silane-modified GMA acrylic resin comprises: 25wt%-40wt% of an epoxy acrylate monomer, 30wt%-60wt% of a methacrylate monomer, 1wt%-5wt% of a hydroxyl silane monomer, 10wt%-25wt% of a styrene monomer, and 1wt%-3wt% of a polycarbonate diol monomer with a molecular weight of 1000-2000.

[0029] The epoxy acrylate monomer is an epoxy acrylate monomer containing glycidyl methacrylate, glycidyl acrylate, etc. The present invention preferably uses glycidyl methacrylate.

[0030] The methacrylate monomer may be an acrylate having 2 to 11 carbon atoms such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, cyclohexyl methacrylate, 2-ethylhexyl methacrylate, and lauryl methacrylate, for example, methyl methacrylate and ethyl methacrylate.

[0031] In the present invention, no special requirements are imposed on the hydroxy silane monomer, as long as it is a terminal hydroxy vinyl silane monomer and does not crosslink with the acrylate monomer, for example, SO001OH (terminal hydroxy vinyl silane) selected from Shenzhen Tianqi New Materials. The silane structure is introduced into the acrylic resin by free radical polymerization to improve the smoothness and scratch resistance of the coating. And the hydroxyl group and epoxy group act together with the carboxyl group and isocyanate during the curing crosslinking process to increase the denseness of the coating and further improve the scratch resistance of the coating.

[0032] The glass transition temperature of the hydroxy silane-modified GMA acrylic resin is 70°C - 90°C, the number average molecular weight is 5000 - 8000, and the epoxy equivalent is 400 - 500. The acrylic resin with a high glass transition temperature helps to improve the hardness of the coating, reduce scratches, and improve the corrosion resistance.

[0033] The synthesis method of the hydroxy silane-modified GMA acrylic resin is prepared by the following steps of free radical polymerization reaction:

[0034] S1. Add a solvent to the reaction vessel, stir and heat to the reflux state, mix the terminal hydroxy vinyl silane monomer, glycidyl methacrylate monomer, alkyl methacrylate monomer, styrene monomer, and initiator evenly, and drop them into the refluxing solvent within 3h - 3.5h. After the dropping is completed, react for 2h under the reflux state;

[0035] S2. Continue to slowly drop the mixed solution of the remaining initiator and solvent under the condition of solvent reflux, complete the dropping within 10min, and then reflux and react for 2h;

[0036] S3. After the reflux reaction is completed, add polycarbonate diol, start to distill off the solvent. When the temperature of the reaction system reaches 180°C, apply a vacuum of -0.09MPa for 0.5h, then release the vacuum, discharge and cool to obtain the hydroxy silane-modified GMA acrylic resin of the present invention.

[0037] By physically premixing the hydroxy silane-modified GMA acrylic resin, curing agent, leveling agent, degassing agent, and polycarbonate diol, then using a twin-screw extruder for melt extrusion, tablet pressing, cooling, and crushing into fine powder, and finally passing through a 200-mesh sieve, the transparent powder coating composition of the present invention is obtained.

[0038] Synthesis Example 1

[0039] 100 parts by weight of xylene was added to a three-necked flask equipped with an N2 inlet, stirring equipment, and condensation equipment, and it was continuously heated and stirred until reflux. A mixed solution of 30 parts by weight of glycidyl methacrylate, 35 parts by weight of methyl methacrylate, 20 parts by weight of styrene, 10 parts by weight of ethyl methacrylate, 3 parts by weight of hydroxyvinylsilane, 2 parts by weight of butyl acrylate, and 5 parts by weight of benzoyl peroxide was added dropwise within 3 h. The reflux reaction was maintained for 2 h, and a mixed solution of 0.5 part by weight of benzoyl peroxide and 10 parts by weight of xylene was added, and the reaction was carried out again for 2 h. After the reaction was completed, the temperature was lowered to 100 °C, 1 g of polycarbonate diol was added, and then distillation was carried out under heating and reduced pressure to remove the solvent in the polymer resin to obtain the hydroxy-silane-modified acrylic resin 1 of the present invention. The epoxy equivalent of the hydroxy-silane-modified acrylic resin 1 was 470, the number-average molecular weight was measured to be 5500, and the glass transition temperature was 65 °C.

[0040] Synthesis Example 2-3 and Comparative Synthesis Example 1

[0041] According to the components shown in Table 1 below, the hydroxy-silane-modified GMA acrylic resins 2-3 and Comparative Synthesis Example 1 were synthesized by the process method of Synthesis Example 1.

[0042] Table 1

[0043]

[0044] SO001OH of the present application was from Shenzhen Tianqi New Materials Technology Co., Ltd., hydroxyvinylsilane.

[0045] DURANOL T5652 of the present application was from Asahi Kasei of Japan, polycarbonate diol with a molecular weight of 2000.

[0046] Examples 1-5 and Comparative Example 1

[0047] In Application Examples 1-5 and Comparative Example 1, the physical dry mixing of the powder coating components given in Table 2 was carried out, and then the powder coating components were melt-mixed, pressed into sheets, cooled, and crushed into fine powders using a twin-screw extruder. Finally, it was sieved through a 200-mesh sieve to obtain the transparent powder coating composition of the present invention.

[0048] Table 2

[0049]

[0050] K7150 of the present application was from Liuan Jietongda New Materials Co., Ltd., isocyanate curing agent.

[0051] DURANOLT5652 of the present application was from Asahi Kasei of Japan, polycarbonate diol with a molecular weight of 2000.

[0052] The leveling agent used in K7572 of this application is from Lu'an Jietongda New Materials Co., Ltd.

[0053] The test method is as follows: Spray each of the coating compositions prepared in Table 2 onto the surface of a glass substrate by high-voltage electrostatic spraying, and bake the substrate at 200 °C for 10 minutes to fully cure it.

[0054] Transparency: Spray a transparent powder coating on a standard transparent thin glass plate and bake it for curing. Visually compare the transparency of the standard transparent thin glass plate and the transparent powder coating-coated layer under transmitted light and rate it. 1 is poor, 10 is excellent, and the standard transparent thin glass plate is rated 10.

[0055] Film thickness: Measure it with a film thickness gauge A-3430 from BYK, Germany.

[0056] Leveling performance: Conduct leveling rating according to the leveling effect rating standard plate of PCI, USA. 1 is poor, 10 is excellent.

[0057] Corrosion resistance: Conduct copper-accelerated acetate spray (CASS) test according to the test standard ASTM B368-21. This test method is used to determine the corrosion resistance of the coating in the corrosive environment generated by CASS. After the test lasts for 168 hours, wash the test plate and dry it, and check for blisters and corrosion at the edges along the scribed lines. Evaluate the corrosion resistance of the coating according to the degree of rust on the plate surface. The maximum rust range of the scribed lines is 3.0 mm.

[0058] Scratch resistance: Judge the scratch resistance of the coating according to the pencil hardness test standard GBT6739. 6H is the hardest and 6B is the softest.

[0059] Adhesion after boiling water: Place the coating sample plate prepared in this invention in boiling water under normal pressure for 2 hours, and then conduct rating according to GB / T 9286-2021 Paints and varnishes - Cross-cut test, which is divided into grades 0 - 5.

[0060] Table 3

[0061]

[0062] Finally, it should be noted that: The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; Although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: They can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; And these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A transparent powder coating composition, characterized in that: Includes the following quality components: Hydroxysilane-modified GMA acrylic resin component 50wt%-80wt%, curing agent component 15wt%-45wt%, polycarbonate diol component 1%-3%, degassing agent component 0.1wt%-1.0wt%, leveling agent component 0.1wt%-2wt%; The hydroxysilane-modified GMA acrylic resin is composed of 25wt%-40wt% of epoxy acrylate monomer, 30wt%-60wt% of methacrylate monomer, 1wt%-5wt% of terminal hydroxyl vinyl silane monomer, 10wt%-25wt% of styrene-based monomer and 1wt%-3wt% of polycarbonate diol monomer with a molecular weight of 1000-2000; The epoxy acrylate monomer is specifically glycidyl methacrylate or glycidyl acrylate.

2. A transparent powder coating composition according to claim 1, characterized in that: The molecular weight of the polycarbonate diol is between 1000-2000.

3. A transparent powder coating composition according to claim 1, characterized in that: The curing agent component is a compound that undergoes a cross-linking reaction with the hydroxysilane-modified GMA acrylic resin component, and the curing agent component is any one of an acid and anhydride curing agent, an amine curing agent, and an isocyanate curing agent.

4. A transparent powder coating composition according to claim 1, characterized in that: The methacrylate monomer is selected from at least one of the following: methyl methacrylate, ethyl methacrylate, propyl methacrylate, n-butyl methacrylate, isobutyl methacrylate, 2-ethylhexyl methacrylate and lauryl methacrylate.

5. A transparent powder coating composition according to claim 1, characterized in that: The glass transition temperature of the hydroxysilane-modified GMA acrylic resin is 70° C.-90° C., the epoxy equivalent is 400-500, and the number average molecular weight is 5000-8000.

6. A method for preparing the transparent powder coating composition according to any one of claims 1 to 5, characterized in that: The steps include: S1. Add a solvent to a reaction vessel, stir and heat to reflux, mix the terminal hydroxy vinyl silane monomer, glycidyl methacrylate monomer, methacrylate monomer, styrene monomer and initiator evenly, and add dropwise to the refluxing solvent within 3h-3.5h. After the addition is complete, react under reflux for 2h; S2, continue to slowly drop the remaining mixed solution of initiator and solvent under the condition of solvent reflux, complete the dropwise addition within 10 minutes, and then reflux for 2 hours; S3, after the reflux reaction is completed, polycarbonate diol is added, and the solvent is removed by distillation. When the temperature of the reaction system reaches 180° C., a vacuum of -0.09 MPa is applied for 0.5 h, and then the vacuum is released, the material is discharged and cooled, and a hydroxysilane-modified GMA acrylic resin is obtained; S4, physically premixing the hydroxysilane-modified GMA acrylic resin, curing agent, leveling agent, degassing agent and polycarbonate diol, and then using a twin-screw extruder to melt-extrude, tablet, cool and crush into fine powder, and finally pass through a 200-mesh sieve to obtain a transparent powder coating composition.

Images