Photo-thermal dual-curing coating and preparation method thereof

Abstract

The invention belongs to the technical field of environment-friendly chemical engineering and new materials, and particularly relates to a photo-thermal dual-curing coating and a preparation method thereof. The invention relates to a photo-thermal dual-curing coating which is prepared by subpackaging a component A and a component B, the component A comprises 40-50% of hydroxy acrylic resin; 20-25% of an acrylate monomer; 1-3% of a photoinitiator; 10-15% of titanium dioxide; 1-3% of an auxiliary agent; the balance is barium sulfate; and the component B is an isocyanate curing agent. The acrylate monomer replaces an organic solvent to serve as a diluent and other reactive components, the possibility of generating VOC is reduced, under the action of the photoinitiator, the acrylate monomer and unsaturated double bonds in the resin are subjected to free radical polymerization under ultraviolet irradiation, a primary polymer network is formed, and the curing effect of the resin is improved. In the heat treatment process of the hydroxyl acrylic resin and the isocyanate curing agent, hydroxyl of the resin and an isocyanate group of the curing agent are subjected to an addition reaction to form a urethane bond and construct a compact three-dimensional cross-linked network, so that the coating has good curing performance and physical performance.

Description

Technical Field

[0001] This invention belongs to the field of environmental protection chemical and new materials technology, specifically relating to photo-thermal dual-curing coatings and their preparation methods. Background Technology

[0002] VOCs are important precursors to PM2.5 and ozone, posing a serious threat to the atmospheric environment and human health. Therefore, with the increasing global awareness of environmental protection, countries are imposing increasingly strict restrictions on the emission of volatile organic compounds (VOCs) in coating products. Traditional solvent-based coatings, which contain a large amount of organic solvents, are the main source of VOC emissions and are being replaced by low-VOC water-based coatings.

[0003] Water-based coatings, which are the mainstream low-VOC coatings in related technologies, have a lower VOC content, but the film-forming process relies on the evaporation of water and the coalescence of cosolvents. They have a slow drying speed, high energy consumption, and their water resistance, chemical resistance, and hardness are usually inferior to those of solvent-based coatings.

[0004] Therefore, there have been related technical reports attempting to reduce VOCs through physical adsorption or chemical coating, but these methods often come at the cost of sacrificing the adhesion, mechanical strength, and durability of the coating. Thus, developing a coating product that achieves low VOC emissions while also possessing excellent overall performance has become a pressing technical problem to be solved in this field. Summary of the Invention

[0005] In order to develop a coating product with low VOC emissions and excellent comprehensive performance, including high hardness, strong adhesion and excellent durability, this application provides a photo-thermal dual-curing coating and its preparation method.

[0006] In the first aspect, this application provides a photo-thermal dual-curing coating, which adopts the following technical solution: A photo-thermal dual-curing coating is a two-component system, consisting of component A and component B packaged in a weight ratio of 3-5:1. Component A consists of the following raw materials by mass percentage: Hydroxyacrylate resin 40-50%; 20-25% acrylate monomer; Photoinitiator 1-3%; Titanium dioxide 10-15%; Additives 1-3%; Barium sulfate is the balance; Component B is an isocyanate curing agent.

[0007] By adopting the above technical solution, the entire formulation system relies on acrylate monomers to replace organic solvents as diluents and other reactive components, reducing the possibility of VOC generation. The two-component system is packaged in a specific weight ratio for easy storage and use, giving the coating good curing and physical properties. Under the action of photoinitiator, the acrylate monomers and the unsaturated double bonds in the resin undergo rapid free radical polymerization under ultraviolet light irradiation to form a preliminary polymer network. In the subsequent heat treatment process, the hydroxyl groups of the resin and the isocyanate groups of the curing agent undergo an addition reaction to form urethane bonds, constructing a dense three-dimensional cross-linked network.

[0008] Preferably, the photoinitiator is a compound of any one of 1173 photoinitiator, TPO photoinitiator, and 819 photoinitiator with ZnO NPs.

[0009] By adopting the above technical solution, the photoinitiator and ZnO NPs are combined to produce a synergistic effect, which can effectively initiate the curing reaction under ultraviolet light irradiation, ensuring the good curing effect of the coating. The photoinitiator that does not contain active hydrogen and has good compatibility with isocyanate is selected to ensure the storage stability of the product.

[0010] Preferably, the photoinitiator is a compound of 1173 photoinitiator and ZnO NPs in a ratio of (6-8):1.

[0011] By adopting the above technical solution, the 1173 photoinitiator and ZnO NPs are compounded in a ratio of (6-8):1, which has better photoinitiation activity and can initiate the photocuring reaction in a shorter time, thereby improving the UV curing efficiency of the photo-thermal dual-curing coating. This allows the coating to be initially cured more quickly to form a coating of a certain strength. In addition, it has good solubility in the coating system and can be uniformly dispersed in the coating, ensuring the uniformity of the curing effect.

[0012] Preferably, the acrylate monomer is selected from any one of cyclotrimethylolpropane methyl acetal acrylate, propylene laurate, and isobornyl acrylate.

[0013] By adopting the above technical solution, cyclotrimethylolpropane methyl acetal acrylate, propylene laurate, and isoborneol acrylate as acrylate monomers can adjust the viscosity of the coating, improve the fluidity and workability of the coating, and also participate in the photocuring and thermocuring reactions to increase the crosslinking density and hardness of the coating, thereby enhancing the wear resistance, chemical corrosion resistance and weather resistance of the coating.

[0014] Preferably, the acrylate monomer is cyclotrimethylolpropane methyl acetal acrylate.

[0015] By adopting the above technical solution, using cyclotrimethylolpropane methyl acetal acrylate as the acrylate monomer, compared with other acrylate monomers, it has the advantages of low shrinkage, low irritation, and high dilution. It can reduce shrinkage and deformation during the curing process of the coating, reduce irritation to the human body, and at the same time better dissolve and dilute other components, thereby improving the coating's workability and product quality.

[0016] Secondly, this application provides a method for preparing a photo-thermal dual-curing coating, employing the following technical solution: A method for preparing a photo-thermal dual-curing coating includes the following steps: a) Premixing: Hydroxy acrylic resin, acrylate monomer, titanium dioxide and barium sulfate are mixed and dispersed at high speed to obtain a slurry; b) Grinding: The slurry obtained in step a) is ground to a fineness ≤15μm; c) Post-processing: Under light-protected conditions, add photoinitiator and additives to the material obtained in step b), stir and mix evenly to obtain component A; d) Use isocyanate curing agent as component B and package it with component A to obtain a light-heat dual-curing coating.

[0017] By adopting the above technical solution, the raw materials are prepared into a photo-thermal dual-curing coating according to specific steps. The two-component system is packaged separately for easy storage and use. The high-speed dispersion in the premixing step ensures that the raw materials are fully mixed. The grinding ensures that the fineness of the slurry meets the standard and guarantees the quality of the coating. The addition of a photoinitiator in the dark can prevent it from initiating the reaction prematurely. Finally, a photo-thermal dual-curing coating with good performance is obtained.

[0018] Preferably, the high-speed dispersion in step a) is performed at a rotation speed of 800-1200 rpm for 20-30 minutes.

[0019] By adopting the above technical solution, when preparing photo-thermal dual-curing coatings, the hydroxyl acrylic resin, acrylate monomer, titanium dioxide and barium sulfate are dispersed at a high speed of 800-1200 rpm for 20-30 minutes, which can make the raw materials fully mixed to form a uniform slurry, which helps to prepare high-performance photo-thermal dual-curing coatings in subsequent processes.

[0020] Thirdly, this application provides a coating formation method, which adopts the following technical solution: after mixing component A and component B of the photo-thermal dual-curing coating according to any one of claims 1-7, the mixture is applied to the surface of a substrate, and the following curing steps are performed sequentially: UV curing: Curing by UV light for 10-60 seconds; Heat curing: Curing at 60-80℃ for 4 hours.

[0021] By adopting the above technical solution, the A and B components of the two-component photo-thermal dual-curing coating are mixed and coated on the substrate surface. First, it is cured by ultraviolet light irradiation for 10-60 seconds, and the photoinitiator is used to initiate the photocuring reaction, so that the coating can be quickly and initially cured, improving the construction efficiency. Then, it is heat-cured at 60-80℃ for 4 hours, and the isocyanate curing agent and hydroxy acrylic resin undergo a heat-curing reaction, which further cures the coating completely, ensuring that the coating has good comprehensive properties such as hardness, wear resistance, and chemical resistance, forming a high-performance coating.

[0022] Preferably, the substrate is wood, metal, or plastic.

[0023] By adopting the above technical solutions, photo-thermal dual-curing coatings can be applied to different types of substrates such as wood, metal or plastic, thus expanding the application range of coatings.

[0024] In summary, this application has the following beneficial effects: 1. In this application, the entire formulation system relies on acrylate monomers instead of organic solvents as diluents and other reactive components, reducing the possibility of VOC generation. The photoinitiator is combined with ZnO NPs to enhance the photoinitiation effect. The acrylate monomers and the unsaturated double bonds in the resin undergo rapid free radical polymerization under ultraviolet light irradiation to form a preliminary polymer network. The hydroxyl groups of the resin and the isocyanate groups of the curing agent undergo addition reactions to form urethane bonds, constructing a dense three-dimensional cross-linked network. 2. In this application, the raw materials are prepared into a photo-thermal dual-curing coating according to specific steps. The two-component system is packaged separately for easy storage and use. The high-speed dispersion in the premixing step ensures that the raw materials are fully mixed. Grinding ensures that the slurry fineness meets the standard to guarantee the quality of the coating. The addition of the photoinitiator in the dark can prevent premature initiation of the reaction, ultimately resulting in a high-performance photo-thermal dual-curing coating. 3. This application mixes component A and component B of a two-component photo-thermal dual-curing coating and applies them to the surface of a substrate. A photoinitiator is used to initiate a photocuring reaction under ultraviolet light irradiation, which enables the coating to cure rapidly and improves construction efficiency. The isocyanate curing agent undergoes a thermocuring reaction with the hydroxyl acrylic resin, which further cures the coating completely, ensuring that the coating has good comprehensive properties such as hardness, wear resistance, and chemical resistance, forming a high-performance coating. Detailed Implementation

[0025] The present application will be further described in detail below with reference to the embodiments.

[0026] Performance testing experiment The coatings obtained from each embodiment and comparative example were selected and prepared into corresponding samples. The test methods for their film hardness, VOC content, salt spray resistance, and adhesion were as follows: 1. Pencil hardness test: conducted according to the national standard GB / T 6739-2006 "Determination of paint film hardness by pencil method for paints and varnishes".

[0027] 2. VOC content test: The VOC content mixture before curing was tested according to the method (gas chromatography) specified in Appendix A of the national standard GB 18582-2020 "Limits of Hazardous Substances in Wall Coatings for Buildings".

[0028] 3. Salt spray resistance test: According to the national standard GB / T 1771-2007 "Determination of resistance to neutral salt spray of paints and varnishes", the corrosion width of the scratch spread on one side is measured.

[0029] 4. Adhesion test: conducted according to the national standard GB / T 9286-1998 "Cross-cut test for paint and varnish film" (1mm spacing, 6 cuts).

[0030] The above experiment was conducted in parallel 5 times, and the average value was recorded.

[0031] Examples 1-3 A photo-thermal dual-curing coating is a two-component system, prepared by dispensing component A and component B in a weight ratio of 3:1; the components A and their amounts are shown in the table below (kg); the isocyanate curing agent of component B is HDI trimer, the HDI trimer brand name is MIRANCO H300, purchased from Meiri New Materials Co., Ltd.

[0032] Table 1: Component A and its weight (kg) in Examples 1-3 The acrylate monomer in the table above is cyclotrimethylolpropane methyl acetal acrylate, purchased from Shanghai Hechuang Chemical Co., Ltd.; the titanium dioxide is rutile titanium dioxide with a particle size of 0.2-0.3 μm. The barium sulfate particle size is 0.6-0.8 μm; The additives are a mixture of leveling agent and defoamer in a 1:1 weight ratio; The photoinitiator was 1173 photoinitiator, purchased from Nanjing Milan Chemical Co., Ltd.

[0033] It was prepared using the following steps: 1. Premixing: Hydroxy acrylic resin, acrylate monomer, titanium dioxide and barium sulfate are mixed and dispersed at high speed to obtain a slurry; the dispersion speed is 1000 rpm and the time is 25 minutes. b) Grinding: Grind the slurry obtained in step a) to a fineness ≤15μm; c) Post-processing: Under light-protected conditions, add photoinitiator and additives to the material obtained in step b), stir and mix evenly to obtain component A; d) Use isocyanate curing agent as component B and package it with component A to obtain a light-heat dual-curing coating.

[0034] Comparative Example 1 A coating that differs from Example 1 in that component A does not contain a photoinitiator.

[0035] Comparative Example 2 A coating that differs from Example 1 in that component A does not contain acrylate monomers.

[0036] Comparative Example 3 A coating that differs from Example 1 in that it does not contain component B isocyanate curing agent and is UV-cured only.

[0037] Comparative Example 4 A coating, which differs from Example 1 in that the acrylate monomer is replaced by an equal amount of the organic solvent ethyl acetate.

[0038] After mixing components A and B in Examples 1-3 and Comparative Examples 1-4, the mixture was applied to the surface of a wood substrate, and the following curing steps were performed sequentially: UV curing: Curing by UV light exposure for 40 seconds; Thermosetting: Curing at 65°C for 4 hours; The cured coating was used as the test specimen.

[0039] Test samples corresponding to the above embodiments and comparative examples were extracted and tested according to the aforementioned performance testing methods. The film hardness, salt spray resistance, and adhesion were tested respectively. The VOC content of the coatings before curing was tested, and the average test results were recorded in the table below.

[0040] Table 2: Performance test results of Examples 1-3 and Comparative Examples 1-4 As can be seen from Table 2, the photo-thermal dual-curing coatings in Examples 1-3, thanks to their component ratios and photo-thermal dual curing, have excellent performance in all aspects. Their film hardness is 2H, VOC content is 0.5g / L, corrosion width is 1.6-1.8mm, adhesion is grade 0, and they have excellent durability, corrosion resistance and low VOC emissions.

[0041] The coatings in Comparative Examples 1-4 have a film hardness of BH, a VOC content of 0.5-450 g / L, a corrosion width of 1.6-5.6 mm, and an adhesion grade of 1-5. Compared with Example 1, the film hardness is significantly reduced and the corrosion width is significantly increased. In Comparative Example 1, the hardness was HB, the adhesion was level 2, the corrosion width was 3.5mm, the UV curing step completely failed, the coating relied solely on thermal curing for cross-linking, and the cross-linking density was seriously insufficient, resulting in a significant decrease in its mechanical properties and protective performance. The adhesion in Comparative Example 2 was grade 1, and the corrosion width was 4.2 mm. The lack of UV curing involving acrylate monomers affected the initial structure and crosslinking density of the entire coating film, resulting in a decrease in performance. In Comparative Example 3, the adhesion was grade 5, the film hardness was B, and the thermosetting reaction was completely absent. The reasons are analyzed as follows: Under ultraviolet irradiation, only the initiator generates free radicals to photocur with the acrylate monomers and unsaturated double bonds in the resin, which will result in the incomplete curing of the shaded areas. In addition, without the isocyanate curing agent, the overall polyurethane cross-linking network cannot be formed, resulting in low cross-linking degree and poor cohesion of the paint film, which manifests as a significant overall decrease in hardness, adhesion and corrosion resistance.

[0042] The VOC content in Comparative Example 4 was 450 g / L, indicating that using organic solvents as diluents would generate a large amount of VOCs, which would seriously pollute the environment.

[0043] Examples 4-5 A photo-thermal dual-curing coating differs from Example 1 in that the amount of component B is different. The weights of components A and B are shown in the table below.

[0044] Table 3: Weight ratio of component A to component B in Examples 4-5 Group weight ratio Example 4 4：1 Example 5 5：1 Comparative Examples 5-6 A photo-thermal dual-curing coating differs from Example 1 in that the amount of component B is different. The weights of components A and B are shown in the table below.

[0045] Table 4: Weight ratio of component A to component B in Comparative Examples 5-6 Group weight ratio Comparative Example 5 1：1 Comparative Example 6 10：1 Test samples corresponding to Examples 4-5 and Comparative Examples 5-6 were extracted and tested according to the aforementioned performance testing methods. The hardness, salt spray resistance, and adhesion of the paint film were tested respectively. The VOC content of the coating before curing was tested, and the average test results were recorded in the table below.

[0046] Table 5: Performance test results of Examples 4-5 and Comparative Examples 5-6 As can be seen from Table 5, compared with Example 1, the corrosion width of Examples 4-5 is significantly increased by 2.2-2.8 mm, and the adhesion changes from level 0 to level 1. It can be concluded that the optimal weight ratio of component A to component B is 3:1. Compared with Example 1, Comparative Examples 5-6 showed a decrease in hardness from 2H to B, an increase in corrosion width to 3.5-5.2, and an increase in adhesion from grade 0 to grade 2-3.

[0047] The possible reasons are as follows: In Comparative Example 5, the excessive amount of component B led to an excessive amount of isocyanate, which in turn caused a side reaction with moisture in the air, resulting in embrittlement and porosity of the paint film, ultimately leading to a significant decrease in corrosion resistance and adhesion; In Comparative Example 6, the severe deficiency of component B meant an extreme lack of -NCO groups. Most of the -OH groups on the hydroxyl acrylic resin molecular chains could not find a reaction target and could not form effective chemical crosslinking points, resulting in extremely low crosslinking density and poor cohesive strength, which manifested as a very soft paint film.

[0048] Examples 6-10 A photo-thermal dual-curing coating, which differs from Example 1 in that the photoinitiator is a compound of 1173 photoinitiator and ZnO NPs.

[0049] Table 6: Combination ratio of 1173 photoinitiator to ZnO NPs in Examples 6-10 Group Compound ratio Example 6 6:1 Example 7 7:1 Example 8 8:1 Example 9 5:1 Example 10 10:1 Test samples corresponding to Examples 6-10 above were extracted and tested according to the aforementioned performance testing methods. The hardness of the paint film, salt spray resistance, and adhesion were tested respectively. The VOC content of the coating before curing was tested, and the average value of the test results was recorded in the table below.

[0050] Table 7: Performance Test Results of Examples 6-10 As shown in Table 7, Examples 6-8 all exhibited excellent durability and corrosion resistance. Compared with Example 1, the film hardness of Example 6 reached 3H, and the corrosion width decreased to 1.5mm, significantly improving the corrosion resistance and durability of the coating. This demonstrates the synergistic effect of the photoinitiator and ZnO NPs compound, and the optimal ratio of photoinitiator to ZnO NPs is 6:1. Compared with Example 6, Examples 9-10 showed a decrease in film hardness to HB, an increase in corrosion width to 3.5-4.2mm, and a decrease in adhesion from grade 0 to grade 1, demonstrating that the optimal ratio of 1173 photoinitiator to ZnO NPs is (6-8):1.

[0051] Examples 11-12 A photo-thermal dual-curing coating, differing from Example 6 in the choice of photoinitiator in combination with ZnO NPs.

[0052] Table 8: Types of photoinitiators combined with ZnO NPs in Examples 11-12 Group Types of photoinitiators Example 11 TPO photoinitiator Example 12 819 photoinitiator In the table above, TPO photoinitiator and 819 photoinitiator were purchased from Nanjing Milan Chemical Co., Ltd.

[0053] Test samples corresponding to Examples 11-12 above were extracted and tested according to the aforementioned performance testing methods. The hardness of the paint film, salt spray resistance, and adhesion were tested respectively. The VOC content of the coating before curing was tested, and the average value of the test results was recorded in the table below.

[0054] Table 9: Performance Test Results of Examples 11-12 As shown in Table 9, the corrosion width of Examples 11-12 increased compared to Example 6, reaching 2.5-2.8 mm. This indicates that among the photoinitiators compounded with ZnO NPs, photoinitiator 1173 had the best effect.

[0055] Examples 13-14 A photo-thermal dual-curing coating, differing from Example 1 in that the acrylate monomers are propylene laurate and isoborneol acrylate, respectively; propylene methacrylate was purchased from Shandong Jinyueyuan New Material Co., Ltd.; and isoborneol acrylate was purchased from Shanghai Hechuang Chemical Co., Ltd.

[0056] Table 10: Types of acrylate monomers in Examples 13-14 Group Photoinitiator Example 13 lauryl methacrylate Example 14 Isoborneol acrylate Test samples corresponding to Examples 13-14 above were extracted and tested according to the aforementioned performance testing methods. The hardness of the paint film, salt spray resistance, and adhesion were tested respectively. The VOC content of the coating before curing was tested, and the average value of the test results was recorded in the table below.

[0057] Table 11: Performance Test Results of Examples 13-14 As can be seen from Table 11, in Examples 13-14, the adhesion was grade 0, the film hardness was 2H, the VOC content was 0.5g / L, and the corrosion width was 1.8-2.0mm. This shows that high-performance coatings can be obtained by using different monomers.

[0058] This specific embodiment is merely an explanation of this application and is not intended to limit it. After reading this specification, those skilled in the art can make modifications to this embodiment without contributing any inventive step, but such modifications are protected by patent law as long as they fall within the scope of the claims of this application.

Claims

1. A photo-thermal dual-curing coating, characterized in that: It is a two-component system, prepared by separating component A and component B in a weight ratio of (3-5):1; Component A consists of the following raw materials by mass percentage: Hydroxyacrylate resin 40-50%; 20-25% acrylate monomers; Photoinitiator 1-3%; Titanium dioxide 10-15%; Additives 1-3%; Barium sulfate is the balance; Component B is an isocyanate curing agent.

2. The photo-thermal dual-curing coating according to claim 1, characterized in that: The photoinitiator is composed of any one of 1173 photoinitiator, TPO photoinitiator, and 819 photoinitiator combined with ZnO NPs.

3. The photo-thermal dual-curing coating according to claim 2, characterized in that: The photoinitiator is composed of 1173 photoinitiator and ZnO NPs in a ratio of (6-8):

1.

4. The photo-thermal dual-curing coating according to claim 1, characterized in that: The acrylate monomer is selected from any one of cyclotrimethylolpropane methyl acetal acrylate, propylene laurate, and isobornyl acrylate.

5. The photo-thermal dual-curing coating according to claim 4, characterized in that: The acrylate monomer is cyclotrimethylolpropane methyl acetal acrylate.

6. A method for preparing a photo-thermal dual-curing coating as described in any one of claims 1-5, characterized in that: Includes the following steps: a) Premixing: Hydroxy acrylic resin, acrylate monomer, titanium dioxide and barium sulfate are mixed and dispersed at high speed to obtain a slurry; b) Grinding: Grind the slurry obtained in step a) to a fineness of ≤15μm; c) Post-processing: Under light-protected conditions, add photoinitiator and additives to the material obtained in step b), stir and mix evenly to obtain component A; d) Use isocyanate curing agent as component B and package it with component A to obtain a light-heat dual-curing coating.

7. The method for preparing the photo-thermal dual-curing coating according to claim 6, characterized in that: The high-speed dispersion described in step a) is performed at a rotation speed of 800-1200 rpm for 20-30 minutes.

8. A method for forming a coating, characterized in that: After mixing component A and component B of any of the photo-thermal dual-curing coatings described in claims 1-7, the mixture is applied to the surface of a substrate with a coating thickness of 20-40 μm, and the following curing steps are performed sequentially: UV curing: Curing by UV light for 10-60 seconds; Heat curing: Curing at 60-80℃ for 4 hours.

9. The coating formation method according to claim 8, characterized in that: The substrate can be wood, metal, or plastic.

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