Finishing paint with high adhesive force and high heat resistance as well as preparation method and application of finishing paint to pre-coating film

Abstract

The invention discloses finish paint with high adhesive force and high heat resistance as well as a preparation method and application of the finish paint to a pre-coating film. The invention relates to a UV (ultraviolet) photoinitiator, which is prepared from the following raw materials in parts by weight: 10 to 25 parts of urethane acrylate A with functionality of 2, 40 to 70 parts of urethane acrylate B with functionality of 4.5, 5 to 15 parts of acrylate reactive diluent, 0.5 to 5 parts of photoinitiator and 0.5 to 20 parts of pigment filler. According to the invention, the balance of high rigidity (Tg = 80.6 DEG C) and moderate flexibility (elongation at break = 9.4%) of the coating is realized through the cooperation of the formula design of the finish paint and the process. The moderate elongation at break is kept while the higher Tg is maintained, so that the heat resistance and the adhesive force are balanced.

Description

Technical Field

[0001] The present invention relates to the field of coatings, and in particular, to a topcoat with high adhesion and high heat resistance, a preparation method thereof, and an application on a pre-coated film. Background Art

[0002] With the wide application of pre-coated film technology in fields such as furniture, PVC floors, and automotive interiors, the performance requirements for topcoats are becoming increasingly stringent. In the field of photocurable coatings, the adhesion and heat resistance of topcoats are the core indicators determining the coating performance and service life. Traditional ultraviolet-curable topcoats mostly use single-functional acrylate resins as the main materials, and it is difficult to balance the crosslinking density and the flexibility of molecular chains, resulting in problems such as insufficient adhesion and thermal deformation of the coating on high-temperature or complex substrate surfaces. For example, low-functional resins can improve flexibility, but the crosslinked network is loose, and the heat resistance is significantly reduced; while high-functional resins can enhance heat resistance, but excessive crosslinking leads to an increase in internal stress and a decrease in the bonding strength to the substrate. In addition, the compatibility between the active diluent and the resin system in the prior art is insufficient, which easily causes phase separation and further weakens the denseness and thermal stability of the coating.

[0003] To address the above problems, the prior art has tried to modify by compounding different functional resins or adding inorganic fillers, but often the performance improvement is limited due to poor functionality matching or uneven dispersion. For example, when using conventional difunctional polyurethane acrylate and multifunctional monomers in combination, it is difficult to form a gradient crosslinked structure, and the relaxation of molecular chain segments intensifies at high temperatures, resulting in easy softening and deformation of the coating. At the same time, problems such as low catalyst efficiency and residual reaction by-products in traditional synthesis processes further affect the regularity of the resin structure, leading to deterioration of the mechanical properties and heat resistance of the coating.

[0004] Based on this, there is an urgent need to develop a new type of photocurable topcoat system, which constructs a three-dimensional crosslinked network with both high adhesion and excellent heat resistance by precisely controlling the resin functionality, molecular structure, and compounding ratio, and at the same time optimizes the synthesis process to improve the resin purity and reaction efficiency, thereby breaking through the bottleneck of the prior art. Summary of the Invention

[0005] The purpose of the present invention is to provide a topcoat with high adhesion and wide-temperature-range toughness, a preparation method thereof, and an application on a pre-coated film, which solves the problems of poor thermal stability and insufficient adhesion of the existing topcoats at high temperatures.

[0006] The present invention realizes the above purpose through the following technical solutions: A topcoat with high adhesion and high heat resistance, comprising the following components in parts by weight: 10 to 25 parts by weight of difunctional polyurethane acrylate A, 40 to 70 parts by weight of 4.5-functional polyurethane acrylate B, 5 to 15 parts by weight of acrylate active diluent, 0.5 to 5 parts by weight of photoinitiator, and 0.5 to 20 parts by weight of pigment filler.

[0007] The present invention has no particular limitation on the parts by weight of difunctional polyurethane acrylate A. For example, it can be difunctional polyurethane acrylate A with a mass of 10 to 25 parts by weight. Exemplarily, the mass percentage of the difunctional polyurethane acrylate A is 10 parts by weight, 15 parts by weight, 20 parts by weight, 25 parts by weight, and any value within the range formed by any two of these point values.

[0008] The present invention has no particular limitation on the parts by weight of 4.5-functional polyurethane acrylate B. For example, it can be 4.5-functional polyurethane acrylate B with a mass of 40 to 70 parts by weight. Exemplarily, the mass percentage of the 4.5-functional polyurethane acrylate B is 40 parts by weight, 45 parts by weight, 50 parts by weight, 55 parts by weight, 60 parts by weight, 65 parts by weight, 70 parts by weight, and any value within the range formed by any two of these point values.

[0009] The present invention has no particular limitation on the parts by weight of acrylate active diluent. For example, it can be acrylate active diluent with a mass of 5 to 15 parts by weight. Exemplarily, the mass percentage of the acrylate active diluent is 5 parts by weight, 10 parts by weight, 15 parts by weight, and any value within the range formed by any two of these point values.

[0010] The present invention has no particular limitation on the parts by weight of photoinitiator. For example, it can be photoinitiator with a mass of 0.5 to 5 parts by weight. Exemplarily, the mass percentage of the photoinitiator is 0.5 parts by weight, 1 part by weight, 2 parts by weight, 3 parts by weight, 4 parts by weight, 5 parts by weight, and any value within the range formed by any two of these point values.

[0011] The present invention has no particular limitation on the parts by weight of pigment filler. For example, it can be pigment filler with a mass of 0.5 to 20 parts by weight. Exemplarily, the mass percentage of the pigment filler is 0.5 parts by weight, 5 parts by weight, 10 parts by weight, 15 parts by weight, 18 parts by weight, 20 parts by weight, and any value within the range formed by any two of these point values.

[0012] According to a preferred embodiment of the present invention, the difunctional polyurethane acrylate A is prepared by reacting the following components: IPDI, where IPDI is isophorone diisocyanate; PCL 1000, where PCL 1000 is a polycaprolactone polyol with a molecular weight of 1000; PCL 2000, where PCL 2000 is a polycaprolactone polyol with a molecular weight of 2000; CHDM, where CHDM is 1,4-cyclohexanedimethanol; HEA, where HEA is hydroxyethyl acrylate with a content of 97%; polymerization inhibitors, where the polymerization inhibitors are BHT and MEHQ; BHT is dibutylhydroxytoluene, and MEHQ is p-methoxyphenol; catalyst, where the catalyst is DBTL, and DBTL is dibutyltin dilaurate.

[0013] According to a preferred embodiment of the present invention, the molar ratio of the IPDI, the PCL 1000, the PCL 2000, the CHDM, the HEA, the BHT, the MEHQ, and the DBTL is: 1:1.2:1:1:0.067:0.0136:0.0399:0.00158.

[0014] According to a preferred embodiment of the present invention, the amounts of the IPDI, the PCL 1000, the PCL 2000, the CHDM, the HEA, the BHT, the MEHQ, and the DBTL are as follows: 0.1 mol of IPDI, where IPDI is isophorone diisocyanate; 0.12 mol of PCL 1000, where PCL 1000 is a polycaprolactone polyol with a molecular weight of 1000; 0.1 mol of PCL 2000, where PCL 2000 is a polycaprolactone polyol with a molecular weight of 2000; 0.1 mol of CHDM, where CHDM is 1,4-cyclohexanedimethanol; 0.8 ml of HEA, where HEA is hydroxyethyl acrylate with a content of 97%; polymerization inhibitors, where the polymerization inhibitors are 0.3 g of BHT and 0.6 g of MEHQ; 0.1 g of catalyst.

[0015] According to a preferred embodiment of the present invention, the catalyst is DBTL; BHT is dibutylhydroxytoluene, MEHQ is p-methoxyphenol, and DBTL is dibutyltin dilaurate.

[0016] In the solution of the present invention, the specific content of the PCL 1000 improves the reaction activity of the solution of the present invention, and the specific content of the PCL 2000 enhances the chain segment flexibility, synergistically optimizing the coating elasticity and adhesion. The hydroxyl functional groups contained in the PCL 1000 and / or the PCL 2000 react with the IPDI to form a polyurethane prepolymer, forming the coating skeleton structure.

[0017] In the solution of the present invention, the specific content of the CHDM is used as a chain extender to adjust the regularity of the molecular chain segments during the reaction, enhance the hardness and scratch resistance of the coating; its cyclic structure can reduce the thermal shrinkage stress.

[0018] In the solution of the present invention, the specific content of the HEA introduces acrylic double bonds and hydroxyl groups during the reaction, participates in the synthesis of the polyurethane prepolymer, and provides active sites for UV curing.

[0019] In the solution of the present invention, the specific content of the BHT / MEHQ inhibits the pre-polymerization initiated by free radicals during storage or reaction to ensure the stability of the formulation.

[0020] In the solution of the present invention, the specific content of the DBTL accelerates the polycondensation reaction of isocyanate and hydroxyl groups during the reaction, shortens the reaction time and reduces the risk of side reactions.

[0021] According to a preferred embodiment of the present invention, the reaction comprises the following steps: S1. Mix the PCL 1000, PCL 2000, and CHDM, heat up, dehydrate under vacuum, and cool to obtain mixture 1; S2. Mix the mixture 1 obtained in step S1 with IPDI, stir and heat up, and then add the DBTL to obtain mixture 2; S3. Add HEA, BHT, and MEHQ to the mixture 2 obtained in step S2 to obtain the bifunctional polyurethane acrylate A.

[0022] According to a preferred embodiment of the present invention, in step S1, after mixing, heat up to 110°C, dehydrate under vacuum for 40 minutes, and cool to 25°C.

[0023] According to a preferred embodiment of the present invention, in step S2, the reaction temperature is 55 - 60°C, and the reaction is carried out for 0.5 h.

[0024] According to a preferred embodiment of the present invention, in step S3, the reaction temperature is 65 - 70°C, and the reaction is carried out for 0.5 h.

[0025] In the present invention, in step S2, the reaction temperature is 55 - 60°C, for example, it can be 55°C, 57°C, 60°C, and any value within the range formed by any two of these point values.

[0026] In the present invention, in step S3, the reaction temperature is 65 - 70°C, for example, it can be 65°C, 67°C, 70°C, and any value within the range formed by any two of these point values.

[0027] The present invention also provides a method for preparing the primer, which includes mixing a difunctional polyurethane acrylate A with an acrylate active diluent, a photoinitiator, and a pigment extender.

[0028] In the solution of the present invention, the monofunctional acrylate monomer with a specific content, as an active diluent, reduces the viscosity of the system to improve the workability; through homopolymerization or copolymerization, it participates in the UV curing crosslinking to adjust the balance between the flexibility and hardness of the coating.

[0029] According to a preferred embodiment of the present invention, the acrylate active diluent is selected from at least one of acrylate active diluent TMCHA, acrylate active diluent IBOA, and acrylate active diluent CTFA, and the photoinitiator is selected from at least one of MBP, 184, and TPO-L; the pigment extender is SiO 2 。

[0030] In the solution of the present invention, the photoinitiator with a specific content decomposes under UV light to generate free radicals, triggering the polymerization reaction of the acrylic double bond to achieve rapid curing.

[0031] In the solution of the present invention, the pigment extender with a specific content provides color hiding power; excessive addition may reduce the flexibility and curing efficiency of the coating.

[0032] According to a preferred embodiment of the present invention, the 4.5-functional polyurethane acrylate B is prepared by reacting the following components in parts by weight: 100 parts by weight of HT100, 20-50 parts by weight of HEA, 20-50 parts by weight of PETA, 0.5 part by weight of BHT, 1.0 part by weight of MEHQ, and 0.2 part by weight of DBTL.

[0033] In the present invention, the 4.5-functional polyurethane acrylate B is named as such because the average functionality is calculated to be 4.5 based on the integral areas of the double bond and the main chain characteristic peaks in the nuclear magnetic resonance hydrogen spectrum (1H-NMR) of the polyurethane acrylate prepared by the reaction.

[0034] According to a preferred embodiment of the present invention, the HT100 is an HDI trimer, which is an aliphatic polyisocyanate curing agent with a mass fraction of —NCO ≈ 22.0%; the HEA is hydroxyethyl acrylate with a content of 97%; the PETA is pentaerythritol triacrylate; the BHT is dibutylhydroxytoluene, the MEHQ is p-methoxyphenol; the DBTL is dibutyltin dilaurate.

[0035] In the solution of the present invention, the specific content of the HT100 (HDI trimer) serves as the main source of isocyanate (NCO) groups, reacts with polyols or hydroxyl-containing monomers to form the polyurethane main chain, and at the same time provides crosslinking sites through the trimer structure to enhance the rigidity of the material; its 3 NCO groups can undergo an addition reaction with the hydroxyl groups in HEA and PETA to form urethane bonds, constituting the polymer network skeleton.

[0036] According to a preferred embodiment of the present invention, the PETA is pentaerythritol triacrylate, which is a multifunctional acrylate monomer containing three acrylate groups and has high reactivity, and is used to increase the crosslinking density and hardness of the coating.

[0037] In the solution of the present invention, the specific content of the PETA reacts with HDI trimer (HT100) in the formulation to construct the rigid skeleton of the highly functional polyurethane acrylate B, enhancing the heat resistance (Tg≥70°C) and mechanical strength of the coating. In the solution of the present invention, the specific content of the HEA (hydroxyethyl acrylate) has both hydroxyl reactivity and acrylate double bond functions, participates in the synthesis of the polyurethane main chain, and provides the active sites required for UV curing; the hydroxyl groups react with the NCO groups of HT100, and the acrylate double bonds undergo free radical polymerization in the presence of a photoinitiator, enhancing the crosslinking density of the final product.

[0038] In the solution of the present invention, the specific content of the BHT (dibutylhydroxytoluene) serves as an antioxidant type inhibitor, inhibits the free radical side reactions caused by oxygen or heat during storage or processing, ensures the stability of the system; terminates the chain reaction by capturing free radicals, preventing the premature polymerization of prepolymers or monomers.

[0039] In the solution of the present invention, the specific content of the MEHQ (p-methoxyphenol) preferentially combines with free radicals, inhibits the self-polymerization of acrylate monomers, and extends the pot life of the system; acts synergistically with BHT to form a dual protection mechanism, which is especially suitable for UV curing systems containing acrylate double bonds.

[0040] In the solution of the present invention, the specific content of the DBTL (dibutyltin dilaurate) catalyzes the addition reaction of isocyanate and hydroxyl groups, accelerates the formation of the polyurethane main chain, shortens the reaction time; promotes the efficient bonding of NCO groups and hydroxyl groups by reducing the reaction activation energy, ensuring the uniformity of the reaction system. According to a preferred embodiment of the present invention, the reaction comprises the following steps: S1. Mix the PETA, MEHQ and BHT and stir, then add the material HT100 to obtain mixture 1; S2. Mix the mixture 1 obtained in step S1 with DBTL to obtain mixture 2; S3. Add HEA to the mixture 2 obtained in step S2 to obtain the 4.5-functional polyurethane acrylate B.

[0041] According to a preferred embodiment of the present invention, in step S2, the reaction temperature is 50 - 60 °C, for example, it can be 50 °C, 55 °C, 60 °C, and any value within the range formed by any two of these point values. The reaction time is 1.5 h.

[0042] According to a preferred embodiment of the present invention, in step S3, the reaction temperature is 65 - 70 °C, for example, it can be 65 °C, 68 °C, 70 °C, and any value within the range formed by any two of these point values. The reaction time is 1.5 - 2 h, for example, it can be 1.5 h, 1.8 h, 2 h, and any value within the range formed by any two of these point values. Under this preferred specific embodiment, the solution of the present invention has a higher reaction yield.

[0043] The present invention also provides a method for preparing a topcoat, which includes mixing a 2-functional polyurethane acrylate A, a 4.5-functional polyurethane acrylate B, an acrylate active diluent, a photoinitiator, and a pigment filler.

[0044] According to a preferred embodiment of the present invention, the acrylate active diluent is acrylate active diluent TMCHA and.

[0045] According to a preferred embodiment of the present invention, the photoinitiator is selected from at least one of MBP, 184, and TPO-L.

[0046] According to a preferred embodiment of the present invention, the pigment filler is SiO 2 The present invention also provides the application of the topcoat on a pre-coated film.

[0047] The beneficial effects of the present invention are as follows: The present invention realizes the synergistic improvement of high temperature resistance (Tg≥70°C) and high adhesion of the coating through the compounding of bifunctional resins and the staged gradient cross-linking process: Using 4.5-functional polyurethane acrylate B (containing HDI trimer HT100, PETA, and HEA) as the main component (40-70%), its high NCO content (≈22.0%) and multi-functional monomers form a dense cross-linked network, making Tg≥70°C, much higher than that of conventional photocurable coatings (Tg<50°C). At high temperatures, the molecular chain rigidity is maintained, resisting softening and deformation, and protecting the stability of the substrate. Compounding 2-functional resin A (10-25%) introduces flexible chain segments to reduce the internal stress during curing; adding HEA in the later stage of resin B synthesis, the flexible chains penetrate the pores of the substrate, combining mechanical anchoring and chemical bonding to enhance the interfacial bonding. The gradient cross-linking process constructs a network combining rigidity and flexibility, buffering thermal stress and avoiding interfacial peeling. Detailed implementation methods

[0048] Main raw materials: HT100 (HDI trimer): Purchased from Wanhua Chemical Group Co., Ltd. PETA (pentaerythritol triacrylate): Purchased from Sartomer (Guangzhou) Chemical Co., Ltd. IPDI (isophorone diisocyanate): Molecular weight 222.29, purchased from Wanhua Chemical Group Co., Ltd. PCL 1000 (polycaprolactone polyol): Molecular weight 1000, purchased from Guangzhou Haoyi Chemical Technology Co., Ltd. PCL 2000 (polycaprolactone polyol): Molecular weight 2000, purchased from Hunan Juren Chemical New Materials Technology Co., Ltd. CHDM (1,4-cyclohexanedimethanol): Molecular weight 144.21, purchased from Green Link (Jining) Chemical Technology Co., Ltd. HEA (hydroxyethyl acrylate, 97%): Molecular weight 116.11, purchased from Jinan Aochen Chemical Co., Ltd. BHT (dibutylhydroxytoluene): Molecular weight 220.35, purchased from Hunan Jushuo Biotechnology Co., Ltd. MEHQ (p-methoxyphenol), molecular weight 138.16, purchased from Hubei Dechao Chemical Co., Ltd. DBTL (dibutyltin dilaurate): Molecular weight 631.56, purchased from Shandong Jinyuanyuan New Materials Co., Ltd. Acrylate active diluent TMCHA: Purchased from Changxing Chemical Industry (Guangdong) Co., Ltd. Acrylate active diluent IBOA: Purchased from Changxing Chemical Industry (Guangdong) Co., Ltd. Acrylate reactive diluent CTFA: Purchased from Changxing Chemical Industry (Guangdong) Co., Ltd.; Photoinitiator TPO-L: Purchased from Wuhan Xinyang Ruihe Chemical Technology Co., Ltd.; Photoinitiator 184: Purchased from Hubei Hongxin Ruiyu Fine Chemical Co., Ltd.; Photoinitiator MBP: Purchased from Hunan Juren Chemical New Materials Technology Co., Ltd.; SiO 2 : Molecular weight 60.08, purchased from Wuhan Jinqu New Materials Co., Ltd.; 2-functional polyether polyurethane acrylate (Huihe HU9807): Purchased from Dongguan Huihe New Materials Co., Ltd.; 2-functional polyether polyurethane acrylate (Zicai ZC6487): Purchased from Shenzhen Zicai Technology Co., Ltd.; 6-functional polyester acrylate (Dymax BDT-1006): Purchased from Dymax Corporation; 6-functional polyurethane acrylate (Huihe 8200): Purchased from Dongguan Huihe New Materials Co., Ltd.; 2-functional polyether polyurethane acrylate (Kunlong HM320): Purchased from Jiangxi Kunlong New Materials Co., Ltd.

[0049] II. Examples Example 1:

[0050] A method for preparing a high-adhesion and high-heat-resistant topcoat, which includes first preparing a 2-functional polyurethane acrylate A and a 4.5-functional polyurethane acrylate B, and then mixing the 2-functional polyurethane acrylate A, the 4.5-functional polyurethane acrylate B, an acrylate reactive diluent, a photoinitiator, and a pigment filler to prepare the topcoat.

[0051] 1. The preparation steps of the 2-functional polyurethane acrylate A include: S1. Mix 0.12 mol of PCL 1000, 0.1 mol of PCL 2000, and 0.1 mol of CHDM, heat up to 110°C, dehydrate under vacuum for 40 minutes, cool to 25°C, and obtain mixture 1; S2. Mix the mixture 1 obtained in step S1 with 0.1 mol of IPDI, stir and heat up to a temperature of 55 - 60°C, react for 0.5 h, and then add 0.1 g of DBTL to obtain mixture 2; S3. Add 0.8 ml of hydroxyethyl acrylate with 97% HEA content, 0.3 g of BHT, and 0.6 g of MEHQ to the mixture 2 obtained in step S2, and react at a reaction temperature of 65°C for 0.5 h to obtain the 2-functional polyurethane acrylate A; 2. The preparation steps of 4.5-functional polyurethane acrylate B are as follows: S1. Mix 30 g of PETA, 1.0 g of MEHQ, and 0.5 g of BHT, stir, add 100 g of HT100 to the materials, and let it warm up naturally to obtain Mixture 1. S2. Mix Mixture 1 obtained in Step S1 with 0.2 g of DBTL, and control the reaction temperature at 55 °C to obtain Mixture 2. S3. Add 30 g of HEA to Mixture 2 obtained in Step S2, slightly warm up to 65 °C, and continue the reaction for 2 h to obtain the 4.5-functional polyurethane acrylate B.

[0052] 3. The preparation steps of the topcoat are as follows: S4. Use 15 g of 2-functional polyurethane acrylate A and 76.5 g of 4.5-functional polyurethane acrylate B prepared in the previous steps, mix them with 29 g of acrylate active diluent TMCHA, 0.5 g of MBP, 0.5 g of 184, 0.5 g of TPO-L, and 2 g of silica, and stir evenly in a dispersion kettle to obtain the finished topcoat.

[0053] Example 2:

[0054] 1. The preparation steps of 2-functional polyurethane acrylate A are as follows: S1. Mix 0.12 mol of PCL 1000, 0.1 mol of PCL 2000, and 0.1 mol of CHDM, heat up to 110 °C, dehydrate under vacuum for 40 minutes, and cool to 25 °C to obtain Mixture 1. S2. Mix Mixture 1 obtained in Step S1 with 0.1 mol of IPDI, stir and heat up to a temperature of 55 - 60 °C, react for 0.5 h, and then add 0.1 g of DBTL to obtain Mixture 2. S3. Add 0.8 ml of hydroxyethyl acrylate with a HEA content of 97%, 0.3 g of BHT, and 0.6 g of MEHQ to Mixture 2 obtained in Step S2, and react at a reaction temperature of 65 °C for 0.5 h to obtain 2-functional polyurethane acrylate A. 2. The preparation steps of 4.5-functional polyurethane acrylate B are as follows: S1. Mix 30 g of PETA, 1.0 g of MEHQ, and 0.5 g of BHT, stir, add 100 g of HT100 to the materials, and let it warm up naturally to obtain Mixture 1. S2. Mix Mixture 1 obtained in Step S1 with 0.2 g of DBTL, and control the reaction temperature at 55 °C to obtain Mixture 2. S3. Add 30 g of HEA to the mixture 2 obtained in step S2, slightly raise the temperature to 65 °C, and continue the reaction for 2 h to obtain the 4.5-functional polyurethane acrylate B.

[0055] 3. The steps for preparing the topcoat include: S4. Use 20 g of 2-functional polyurethane acrylate A and 70 g of 4.5-functional polyurethane acrylate B prepared in the previous steps, mix them with 6.5 g of acrylate active diluent TMCHA, 0.5 g of MBP, 0.5 g of 184, 0.5 g of TPO-L, and 2 g of silica, and stir evenly in a dispersion kettle to obtain the finished topcoat.

[0056] Example 3:

[0057] 1. The steps for preparing 2-functional polyurethane acrylate A include: S1. Mix 0.12 mol of PCL 1000, 0.1 mol of PCL 2000, and 0.1 mol of CHDM, then raise the temperature to 110 °C, dehydrate under vacuum for 40 minutes, and cool to 25 °C to obtain mixture 1; S2. Mix the mixture 1 obtained in step S1 with 0.1 mol of IPDI, stir and raise the temperature to 55 - 60 °C, react for 0.5 h, and then add 0.1 g of DBTL to obtain mixture 2; S3. Add 0.8 ml of hydroxyethyl acrylate with 97% HEA content, 0.3 g of BHT, and 0.6 g of MEHQ to the mixture 2 obtained in step S2, and react at 65 °C for 0.5 h to obtain 2-functional polyurethane acrylate A; 2. The steps for preparing 4.5-functional polyurethane acrylate B include: S1. Mix 30 g of PETA, 1.0 g of MEHQ, and 0.5 g of BHT, then stir, add 100 g of HT100, and let the temperature rise naturally to obtain mixture 1; S2. Mix the mixture 1 obtained in step S1 with 0.2 g of DBTL, and control the reaction temperature at 55 °C to obtain mixture 2; S3. Add 30 g of HEA to the mixture 2 obtained in step S2, slightly raise the temperature to 65 °C, and continue the reaction for 2 h to obtain the 4.5-functional polyurethane acrylate B.

[0058] 3. The steps for preparing the topcoat include: S4. Use the 25 g of difunctional polyurethane acrylate A and 63.5 g of 4.5-functional polyurethane acrylate B prepared in the aforementioned steps, mix them with 8 g of acrylate active diluent TMCHA, 0.5 g of MBP, 0.5 g of 184, 0.5 g of TPO-L, and 15 g of silica, and stir evenly in a dispersion kettle to obtain the finished topcoat product.

[0059] Comparative Example 1 Take 15 g of difunctional polyether polyurethane acrylate (Zicai ZC6487) and 75.5 g of 4.5-functional polyurethane acrylate B, mix them with 5 g of acrylate active diluent TMCHA, 0.5 g of MBP, 0.5 g of 184, 0.5 g of TPO-L, and 2 g of silica, and stir evenly in a dispersion kettle to obtain the finished topcoat product.

[0060] Comparative Example 2 Take 15 g of difunctional polyether polyurethane acrylate (Huihe HU9807) and 76.5 g of 6-functional polyester acrylate (Dymax BDT-1006), mix them with 5 g of acrylate active diluent TMCHA, 0.5 g of MBP, 0.5 g of 184, 0.5 g of TPO-L, and 2 g of silica, and stir evenly in a dispersion kettle to obtain the finished topcoat product.

[0061] Comparative Example 3 Take 15 g of difunctional polyether polyurethane acrylate (Kunlong HM320) and 72.5 g of 6-functional polyurethane acrylate (Huihe 8200), mix them with 9 g of acrylate active diluent TMCHA, 0.5 g of MBP, 0.5 g of 184, 0.5 g of TPO-L, and 15 g of silica, and stir evenly in a dispersion kettle to obtain the finished topcoat product.

[0062] III. Performance Testing Methods for Testing Tg and Elongation at Break Due to interference from external curing factors, the Tg and elongation at break data of the cured topcoat coating fluctuate slightly. The coatings for testing Tg and elongation at break are obtained in the following manner: Coat the paint on a high-gloss PET film, cover it with a high-gloss OPP release film, and cure the coating with a high-pressure mercury lamp in an oxygen-free environment.

[0063] Specific Steps: 1. Coating Preparation: Evenly apply the topcoat paint on the surface of the high-gloss PET film, controlling the wet film thickness (it is recommended to use a wire bar or a doctor blade, with a thickness tolerance of ±5 μm); cover with a high-gloss OPP release film to avoid oxygen penetration interference during curing and ensure an oxygen-free environment; use a high-pressure mercury lamp for photocuring, controlling the light intensity (such as 80 - 120 mW / cm²) and the exposure time (adjusted according to the resin photoinitiator system). Curing Environment Control: Keep the temperature at 25 ± 2 °C and the humidity at 50 ± 5% throughout the curing process to reduce the influence of temperature and humidity on the curing rate and the internal stress of the coating; after curing, peel off the release film and let it stand for 24 hours to eliminate the residual stress.

[0064] 2. Glass Transition Temperature (Tg) Test According to the ISO6721 - 11 standard, cut 5 - 10 mg of samples from the coating, avoiding contamination or mechanical damage; encapsulate them in an aluminum crucible to ensure good contact with the DSC instrument, heat from 15 °C to 250 °C at a rate of 10 °C / min; cool to 15 °C at the same rate; then heat to 250 °C again at a rate of 10 °C / min and record the heat flow curve. Take the inflection point or the midpoint of the second heating curve as the Tg value and compare with the baseline calibration data.

[0065] 3. Elongation at Break Test (Tensile Test)

[0066] According to the ISO 527 standard, cut the coating into dumbbell-shaped specimens (the width of the gauge section is 10 mm and the length is 50 mm), use laser scribing or non-contact optical marking for the gauge (the line width ≤ 0.1 mm) to avoid stress concentration caused by mechanical scribing. Use a universal material testing machine, set the tensile rate to 5 mm / min (for flexible coatings) or 50 mm / min (for rigid coatings), ensure that the coaxiality deviation is ≤ 0.2 mm / m when clamping the specimen to avoid early yielding, record the stress-strain curve, read the gauge length at break, and calculate the elongation at break according to the formula: 100% (L 断 -L 0 ) / L 0 , where L 0 is the initial gauge length and L 断 is the gauge length after break. Results of Tg and Elongation at Break: Table 1: Results of Tg and Elongation at Break for Each Example and Comparative Example

[0067] As can be seen from Table 1, for the topcoat prepared in Example 1 of the present invention, the Tg (°C) of its coating can reach 80.6 °C and the elongation at break is 9.4%. Both its Tg and elongation at break are very excellent and reach a balance. In Comparative Example 1, a commercially available difunctional polyether polyurethane acrylate (Zicai ZC6487) was used to replace the difunctional polyurethane acrylate A to prepare the topcoat, and the Tg (°C) of its coating dropped to 60.8 °C, and the elongation at break was 8.7%, indicating that the difunctional polyurethane acrylate A is very important for the Tg of the material. In Comparative Example 2, a difunctional polyether polyurethane acrylate (Huihe HU9807) and a hexafunctional polyester acrylate (Dymax BDT-1006) were used to prepare the topcoat, and its elongation at break dropped to 4.1%. In summary, using the difunctional polyurethane acrylate A and 4.5-functional polyurethane acrylate B modified by the present invention to prepare the topcoat, the high elongation at break indicates that the coating has good flexibility and deformation ability, can adapt to the stress generated by the thermal expansion or mechanical deformation of the substrate, and retains an appropriate elongation at break while maintaining a relatively high Tg, thereby balancing heat resistance and adhesion. The above-described embodiments merely represent several implementation manners of the present invention. The description thereof is relatively specific and detailed, but it should not be construed as a limitation to the scope of the present invention. It should be noted that for those of ordinary skill in the art, without departing from the concept of the present invention, several deformations and improvements can still be made, and these all belong to the protection scope of the present invention.

Claims

1. A topcoat with high adhesion and high heat resistance, characterized in that: The invention comprises the following components in parts by weight: 10 to 25 parts by weight of 2-functionality polyurethane acrylate A, 40 to 70 parts by weight of 4.5-functionality polyurethane acrylate B, 5 to 15 parts by weight of acrylate reactive diluent, 0.5 to 5 parts by weight of photoinitiator, and 0.5 to 20 parts by weight of pigment and filler; The bifunctional polyurethane acrylate A is prepared by reacting the following components: IPDI, PCL 1000, PCL 2000, CHDM, HEA, BHT, MEHQ, DBTL; the molar ratio of the IPDI, the PCL 1000, the PCL 2000, the CHDM, the HEA, the BHT, the MEHQ, and the DBTL is 1:1.2:1:1:0.067:0.0136:0.0399:0.00158; The 4.5-functionality polyurethane acrylate B is prepared by reacting the following components in parts by weight: 100 parts by weight of HT100, 20-50 parts by weight of HEA, 20-50 parts by weight of PETA, 0.5 parts by weight of BHT, 1.0 parts by weight of MEHQ, and 0.2 parts by weight of DBTL.

2. The topcoat according to claim 1, characterized in that The 4.5-functionality polyurethane acrylate B is prepared by a reaction comprising the following steps: S1, mixing the PETA, MEHQ and BHT, and adding material HT100 to obtain mixture 1; S2, mixing the mixture 1 obtained in step S1 with DBTL to obtain a mixture 2; S3, adding HEA to the mixture 2 obtained in the step S2 to obtain the polyurethane acrylate B with a functionality of 4.

5.

3. The topcoat according to claim 2, characterized in that In step S2, the reaction temperature is 50-60° C. and the reaction is carried out for 1.5 hours.

4. The topcoat according to claim 2, characterized in that In step S3, the reaction temperature is 65-70° C. and the reaction time is 1.5-2 hours.

5. A method for preparing a topcoat as claimed in any one of claims 1 to 4, characterized in that: The method comprises mixing 2-functionality polyurethane acrylate A, 4.5-functionality polyurethane acrylate B, acrylate reactive diluent, photoinitiator and pigment filler.

6. The method according to claim 5, characterized in that The acrylate reactive diluent is acrylate reactive diluent TMCHA.

7. The method according to claim 5, characterized in that The photoinitiator is selected from at least one of MBP, 184 and TPO-L.

8. The method according to claim 5, characterized in that The pigment and filler are SiO 2。 9. The use of the topcoat according to any one of claims 1 to 4, characterized in that: Application of the topcoat on a pre-coated film.

Images