A modified polyurethane photocurable coating and its preparation method

Abstract

The present invention discloses a modified polyurethane photocurable coating and a preparation method thereof. First, modified BNNS is introduced into castor oil to prepare a modified chain extender; a prepolymer is obtained by reacting a diol with an isocyanate; the prepolymer is then reacted with the modified castor oil and the modified chain extender in sequence to prepare a modified polyurethane resin; the modified polyurethane resin, an active diluent, a dispersant and a leveling agent are stirred and mixed; then an antifoaming agent is added, stirred and mixed, ground, filtered and discharged, and a photoinitiator is added and stirred and dispersed during use to prepare the modified polyurethane photocurable coating. The ink has dielectric properties and self-healing properties, and at the same time has strong adhesion, good water resistance and solvent resistance.

Description

Technical Field

[0001] The present invention relates to the field of protective coating materials, and particularly to a modified polyurethane photocurable coating and a preparation method thereof. Background Art

[0002] As a protective coating, the modified polyurethane photocurable coating is widely used for the anti-corrosion protection of circuit boards of electronic and electrical equipment, such as smart home appliances, automotive electronics, power / frequency conversion, intelligent industrial control, military ships, outdoor precision equipment, etc. It can protect the circuit board and its related equipment from environmental erosion, thereby improving and extending the service life of the circuit board and ensuring the safety and reliability of the circuit board during use.

[0003] With the increasing requirements for the reliability of electronic components, not only is it required that the coating material has advantages such as solvent resistance, salt spray corrosion resistance, and good adhesion, but also that the coating material has excellent thermal conductivity and dielectric properties. However, currently commonly used coating materials such as acrylic, epoxy, and polyurethane do not have excellent thermal conductivity and dielectric properties. Moreover, during the use of these material coatings, due to the influence of external environments such as collision, corrosion, and photo-degradation, micro-cracks will occur in the coating, resulting in a decrease in the mechanical properties of the material and affecting the functionalization of the coating. Summary of the Invention

[0004] The purpose of the present invention is to provide a modified polyurethane photocurable coating and a preparation method thereof for the deficiencies in the prior art. First, modified polyurethane is synthesized by a stepwise method, introducing -Si-O-CH3-, -BNNS, and UPy groups into the polyurethane side chain, maintaining a large degree of freedom of the silicone structure, BNNS structure, and UPy groups. Then, through crosslinking modification and photocuring technology, a polyurethane with a network structure is obtained, making it have good adhesion performance, water resistance, and solvent resistance. At the same time, its dielectric properties, thermal conductivity, and self-healing performance are improved.

[0005] The purpose of the present invention is achieved through the following technical solutions:

[0006] A modified polyurethane photocurable coating is prepared through the following process:

[0007] Prepare modified castor oil:

[0008] Under a N2 atmosphere, put 15 - 30 parts by weight of castor oil, 1 - 3 parts by weight of succinic anhydride, and 0.15 - 0.3 parts by weight of SnCl2 into a reaction vessel, slowly raise the temperature to 80 - 120 °C, stir and react for 1 - 5 h; wait for the temperature to drop to 70 - 90 °C, add 10 - 15 parts by weight of modified BNNS and 0.01 - 0.1 parts by weight of triethylamine, continue to stir and react for 2 - 6 h to obtain modified castor oil;

[0009] Prepare chain extender:

[0010] Under a nitrogen atmosphere, 5-15 parts by weight of hexamethylene diisocyanate and 0.5-1 part by weight of 2-amino-6-methyl-4-pyrimidinone are placed in a reaction vessel, heated to 90-100 °C, and stirred and reacted for 15-30 h. After the temperature is lowered to room temperature, filtration, washing, and vacuum drying are carried out to obtain NCO-terminated UPy;

[0011] Under a nitrogen atmosphere, 25-30 parts by weight of UPy, 12-16 parts by weight of 2-amino-2-methyl-1,3-propanediol, and an appropriate amount of dimethyl sulfoxide are placed in a reaction vessel, heated to 40-60 °C, and stirred and reacted for 3-8 h. After the temperature is lowered to room temperature, centrifugation, washing, and drying are carried out to obtain a chain extender;

[0012] Prepare a modified polyurethane resin:

[0013] Under a nitrogen atmosphere, diisocyanate and a part of inhibitor are placed in a reaction vessel, heated to 60-80 °C, a diol and a catalyst are added, and the mixture is stirred and kept warm for 1-4 h. Modified castor oil is added, and the mixture is stirred and kept warm for 3-8 h. The temperature is raised to 70-100 °C, the remaining inhibitor and the chain extender are added, and the mixture is stirred and kept warm for 2-3 h to obtain a modified polyurethane resin;

[0014] Prepare a modified polyurethane photocurable coating:

[0015] 80-100 parts by weight of the modified polyurethane resin, 30-40 parts by weight of an active diluent, 0.5-2 parts by weight of a dispersant, and 1-3 parts by weight of a leveling agent are put into a reactor and stirred to mix them evenly; then 0.5-1.5 parts by weight of an antifoaming agent is added and stirred to disperse and mix them evenly, followed by grinding, filtration, and discharging. When in use, 3-10 parts by weight of a photoinitiator is added and stirred and dispersed to obtain a modified polyurethane photocurable coating.

[0016] Furthermore, the modified BNNS is prepared by the following method:

[0017] 1-2 parts by weight of γ-glycidoxypropyltrimethoxysilane and 10-15 parts by weight of BNNS are added to an ethanol / H2O solution, heated to 60-80 °C, and stirred and reacted for 6-10 h. After the temperature is lowered to room temperature, filtration, washing, and drying are carried out to obtain modified BNNS.

[0018] Furthermore, in the preparation of the modified polyurethane resin:

[0019] The molar ratio of the diol, the modified castor oil, the chain extender, and the diisocyanate is 3-5:2-3:0.5-1.5:8-10;

[0020] The dosage of the inhibitor is 0.1 - 0.5% of the weight of the diisocyanate.

[0021] The dosage of the catalyst is 0.01 - 0.1% of the weight of the diisocyanate.

[0022] Furthermore, the diisocyanate compound is selected from at least one of hexamethylene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, tetramethyl-m-xylene diisocyanate, and toluene diisocyanate.

[0023] Furthermore, the diol is selected from at least one of polypropylene glycol (PPG2000), polyethylene glycol (PEG 800), polycaprolactone diol (PCL1000), and polybutadiene diol (HTPB1000), and the average molecular weight of the diol is 500 - 3000;

[0024] Furthermore, the inhibitor is p-methoxyphenol, hydroquinone, or 2,6-di-tert-butyl-p-cresol;

[0025] The catalyst is stannous octoate, dibutyltin dilaurate, or tetrabutyl titanate.

[0026] Furthermore, the photoinitiator is selected from at least one of ethyl 2,4,6-trimethylbenzoyl phenylphosphinate, 2,4-diethylthioxanthone, 1-hydroxycyclohexyl phenyl ketone, 2-hydroxy-1-(4-(4-(2-hydroxy-2-methylpropanoyl)benzyl)phenyl)-2-methyl-1-propanone, 2-isopropylthioxanthone, 2-methyl-1-(4-methylthiophenyl)-2-morpholin-1-propanone, 2,4,6-trimethylbenzoyl diphenylphosphine oxide, methyl o-benzoylbenzoate, 2-benzyl-2-dimethylamino-1-(4-morpholinophenyl)butanone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, benzophenone, benzoin diethyl ether, benzoin dimethyl ether, biphenyl benzophenone, 2-hydroxy-2-methyl-1-phenyl-1-propanone, 2-(4-methylbenzyl)-2-(dimethylamino)-1-(4-morpholinophenyl)-1-butanone.

[0027] Furthermore, the reactive diluent is selected from at least one of lauryl methacrylate, lauryl acrylate, isobornyl acrylate, isobornyl methacrylate, isodecyl acrylate, isooctyl acrylate, 2-phenoxyethyl acrylate, and ethoxylated trimethylolpropane triacrylate.

[0028] In the synthesis of polyurethane, the chain length, content, and end-group type of the chain extender can all affect the crystallinity of PU, and thus affect its thermal stability. If the branched structure in the chain extender cannot participate in hydrogen bond assembly, it will hinder the aggregation of hard segments and thus affect the formation of intermolecular hydrogen bonds in PU, thereby reducing the thermal stability of PU.

[0029] Vegetable oil is an ideal renewable chemical raw material, with rich reserves, little environmental impact, relatively low cost, and is not easily affected by fluctuations in the global oil market. Several common vegetable oils, such as castor oil (CO), soybean oil, rapeseed oil, palm oil, linseed oil, etc., contain active groups such as double bonds and ester groups. After chemical modification, they can be used as starting materials for bio-based polymers. The structure of castor oil in the present invention contains 3 fatty acid carbon chains, each fatty acid carbon chain is composed of 19 carbon atoms, and there are 3 active reaction sites including ester groups, unsaturated carbon-carbon double bonds, and hydroxyl groups, which provide possibilities for the reaction and modification of castor oil. For example, the ester group can be modified by hydrolysis, alcoholysis, amidation, etc., the double bond can be used for polymerization, hydrogenation, epoxidation, etc. reactions, and the hydroxyl group can be used for esterification, etherification, etc. reactions. This special structure provides a theoretical basis for the synthesis of polyurethane, enabling castor oil to replace polyol or chain extender. The long-chain non-polar fatty acid chains in its components can improve the water resistance and elasticity of polyurethane, making the modified polyurethane have good flexibility and flex resistance.

[0030] The structure of boron nitride nanosheets (BNNS) is similar to the two-dimensional nanostructure of graphene, with excellent mechanical properties and thermal conductivity. However, different from conductive materials such as graphene, as an insulating material, BNNS filled in the resin can prepare composites with good insulating properties while improving the mechanical properties of the substrate material. However, the surface functional groups of single-component BNNS are few, and the interaction with the substrate polymer is weak, making it difficult to form a strong interaction, resulting in poor dispersion uniformity of BNNS in the substrate polymer material and thus poor performance.

[0031] First, the present invention modifies the surface of BNNS with a silane coupling agent by the surface grafting method. The silane coupling agent modified on the surface of BNNS increases a large number of polymer segments on the surface of the nanosheets and also loads epoxy groups on the surface of BNNS. Then, succinic anhydride is reacted with castor oil, a biomass raw material, to obtain carboxyl-containing castor oil. Finally, the epoxy groups and the carboxyl groups on the modified castor oil undergo a ring-opening addition reaction, thereby introducing silane and BNNS into the polyol. On the one hand, it improves the dispersion performance of BNNS in the polymer matrix, and also improves the interaction between BNNS and the matrix polymer through the interaction between surface functional groups and polymer molecular chains, enhancing the mechanical properties, insulation properties, and thermal conductivity of the composite material. On the other hand, introducing modified BNNS into castor oil can participate in hydrogen bond assembly, enhancing the thermal stability and friction resistance of PU.

[0032] Compared with traditional anti-corrosion coatings, self-healing coatings represent a shift in the field of corrosion protection. Compared with traditional coatings, self-healing coatings can autonomously repair damage. By continuously reducing loopholes, self-healing coatings ensure long-lasting durability and higher performance, extending the service life of the protective layer. Generally speaking, self-healing crosslinked networks are mainly formed through dynamic and reversible reactions without introducing external substances, and non-covalent bonds are easier to break and reconstruct than reversible covalent bonds. Hydrogen bonds, as an important type of non-covalent bond, have directionality, high reversibility, and responsiveness to various stimuli. However, the binding energy of hydrogen bonds is usually between 25 and 65 kJ / mol, which is a relatively weak type of interaction compared to covalent bonds. It is difficult to obtain a material with good repair performance by simply forming hydrogen bonds between -C=O in the PU structure and -NH- in the BNNS structure to construct a crosslinked network. Therefore, it is usually necessary to construct multiple hydrogen bond interactions in the PU system to endow polyurethane with excellent properties.

[0033] The chemical structure of ureido-4-pyrimidinone (UPy) containing urea and pyrimidine groups makes it easy to form strong quadruple hydrogen bonds. Due to the large number of hydrogen bonds formed between -NH-, -C=O in the PU structure and -NH-, -C=O in UPy, synergistically acting with the dynamic and reversible BNNS groups in the PU structure, and the thermal conductivity of BNNS improving the internal thermal conductivity of the material and increasing the movement effect of polymer molecular segments, the modified polyurethane resin of the present invention has good self-healing performance.

[0034] The polyurethane of the present invention is synthesized by a three-step method: the first step is the reaction of a macromolecular diol (polyester or polyether diol) with an excessive amount of diisocyanate to generate a prepolymer with an NCO-terminal chain; the second step is to introduce a Si-O-CH3 structure and BNNS into castor oil to obtain a modified castor oil-based diol, and then through copolymerization modification, the silicon- and BNNS-containing diol is used as a soft segment to react with the previous prepolymer and incorporated into the main chain structure to obtain a modified prepolymer containing C═C double bonds; the third step is to introduce a UPy group into a small molecule diol to form a modified chain extender, and then react the modified chain extender with the modified prepolymer to obtain a long TPU chain. The present invention uses a step-by-step synthesis method to design and finely control the final main chain and side chain structures by adjusting the structure and molar mass of the diol and the type of diisocyanate, and finally obtains the required PU structure.

[0035] The present invention introduces a Si-O-CH3 structure, a BNNS structure and a UPy group into the side chain of the polyurethane, maintaining a large degree of freedom of the silicone structure, the BNNS structure and the UPy group. On the one hand, it improves the dispersion of BNNS in the polymer matrix, and also improves the interaction between BNNS and the matrix polymer through the interaction between the surface functional groups and the polymer molecular chains, improving the mechanical properties and thermal conductivity of the composite material and endowing the material with excellent dielectric properties; on the other hand, when the siloxane is located in the side chain, its ability to migrate to the surface is higher than when it is located in the main chain. The silicone chain segments will accumulate on the surface of the coating. After film formation, it can significantly reduce the surface free energy of the polyurethane material and use it as a soft segment to prepare a composite coating, showing better mechanical strength and viscoelastic properties. Because of its good lubricity, it can effectively reduce the coating friction resistance, thus contributing to the improvement of the coating wear resistance; on the other hand, by designing the main chain and side chain structures of the polyurethane and introducing BNNS and UPy groups into the PU side chain to form multiple hydrogen bonds, rich hydrogen bonds are introduced into the polymer to construct a multiple crosslinking network, endowing it with rapid self-healing ability and greatly improving the self-healing performance of the material.

[0036] The modified polyurethane photocurable coating of the present invention also adds an active diluent, an antifoaming agent, a leveling agent and a dispersant. The active diluent adjusts the viscosity and curing speed of the coating and improves the hardness, wear resistance, adhesion performance, etc. of the cured film. The antifoaming agent of the present invention is a silicone-based antifoaming agent, the leveling agent is a solvent-free nonionic leveling agent, and the dispersant is a polyester-based wetting dispersant. The antifoaming agent prevents the coating from forming bubbles and pinholes during stirring and construction. The leveling agent can control and improve the fluidity and leveling property of the surface of the coating during construction, reduce the occurrence of shrinkage holes in the coating film, and does not affect the gloss and transparency of the coating film. The dispersant can stabilize the viscosity of the coating in the coating and improve its storage stability. Description of the Drawings

[0037] Figure 1Schematic diagram of the preparation route of the modified castor oil of the present invention;

[0038] Figure 2 Schematic diagram of the preparation route of the chain extender of the present invention. Detailed implementation manners

[0039] To further understand the present invention, the preferred implementation manners of the present invention will be described below in conjunction with embodiments. However, it should be understood that these descriptions are only for further explaining the features and advantages of the present invention, rather than limiting the claims of the present invention.

[0040] The reagents or instruments used in the present invention that are not indicated by the manufacturer can all be conventional products obtained through commercial purchase.

[0041] The following is the specific embodiment part:

[0042] Example 1

[0043] The preparation process of the modified polyurethane photocurable coating in this example is as follows:

[0044] (1) Preparation of modified castor oil

[0045] Add 3 parts by weight of γ-glycidoxypropyltrimethoxysilane (KH560) and 10 parts by weight of boron nitride with a two-dimensional nanosheet structure (BNNS, 500 nm) into an ethanol / H2O solution (ethanol∶H2O = 1∶1, weight / weight), heat up to 70 °C, and stir and react at a speed of 800 rpm for 8 h. After the temperature drops to room temperature, filter, wash with ethanol, and dry at 60 °C for 24 h to obtain modified BNNS;

[0046] Under a N2 atmosphere, put 25 parts by weight of castor oil, 1.5 parts by weight of succinic anhydride (SA), and 0.1 part by weight of SnCl2 into a reaction vessel, slowly heat up to 100 °C, stir and react at a speed of 400 rpm for 3 h. After the temperature drops to 80 °C, add 12 parts by weight of modified BNNS and 0.03 part by weight of triethylamine, and continue to stir and react for 4 h to obtain modified castor oil.

[0047] (2) Preparation of chain extender

[0048] Under a nitrogen atmosphere, put 13 parts by weight of hexamethylene diisocyanate (HDI) and 1 part by weight of 2-amino-6-methyl-4-pyrimidinone into a reaction vessel, heat up to 90 °C, stir and react at a speed of 300 rpm for 26 h. After the temperature drops to room temperature, filter, wash, and vacuum dry at 60 °C for 24 h to obtain NCO-terminated UPy;

[0049] Under a nitrogen atmosphere, 30 parts by weight of UPy, 12 - 15 parts by weight of 2 - amino - 2 - methyl - 1,3 - propanediol (AMPD), and 300 parts by weight of dimethyl sulfoxide (DMSO) were placed in a reaction vessel. The temperature was raised to 60 °C, and the mixture was stirred and reacted for 6 h. After the temperature dropped to room temperature, DMF was added to the reaction system to wash away the residual solvent DMSO, followed by centrifugation and freeze - drying to obtain the chain extender UPy - OH.

[0050] (3) Preparation of modified polyurethane photocurable coating

[0051] Under a nitrogen atmosphere, 18 parts by weight of HDI and 0.04 parts by weight of p - methoxyphenol were placed in a reaction vessel, mixed evenly, and the temperature was raised to 85 °C. Then, 50 parts by weight of polybutadiene diol (HTPB - 1000) and 0.01 parts by weight of a catalyst were added. The mixture was stirred and kept at a constant temperature for 3 h. Next, 40 parts by weight of modified castor oil was added, and the mixture was stirred and kept at a constant temperature for 5 h. The temperature was then raised to 75 °C, 4.1 parts by weight of the chain extender UPy - OH and 0.01 parts by weight of p - methoxyphenol were added, and the mixture was stirred and kept at a constant temperature for 3 h to obtain a modified polyurethane resin; the stirring speed during this process was 400 rpm;

[0052] By weight, 80 parts of the modified polyurethane resin, 30 parts of lauryl methacrylate, 5 parts of 1 - hydroxycyclohexyl phenyl ketone, 2 parts of a leveling agent, 1 part of an antifoaming agent, and 1 part of a dispersant were weighed. The modified polyurethane resin, lauryl methacrylate, dispersant, and leveling agent were put into a reactor and dispersed at a speed of 900 rpm for 10 min; then the antifoaming agent was added, and the mixture was dispersed at a speed of 1300 rpm for 15 min, followed by grinding, filtering, and discharging. When in use, 1 - hydroxycyclohexyl phenyl ketone was added and dispersed at a speed of 700 rpm for 10 min to obtain the modified polyurethane photocurable coating.

[0053] The implementation methods of Example 2 and Example 3 were the same as those of Example 1, except that in the process of preparing the modified polyurethane photocurable coating, there were differences in the raw materials and their contents. In each example, the specific raw materials and their contents are shown in Table 1, with the unit being parts by weight.

[0054] Table 1

[0055]

[0056]

[0057] Comparative Example 1

[0058] Under a nitrogen atmosphere, 18 parts by weight of HDI and 0.04 part by weight of p-methoxyphenol were placed in a reaction vessel, mixed evenly and heated to 85 °C. Then, 50 parts by weight of polybutadiene diol (HTPB-1000) and 0.01 part by weight of a catalyst were added, and the mixture was stirred and kept at a constant temperature for 3 h. Next, 40 parts by weight of castor oil was added, and the mixture was stirred and kept at a constant temperature for 5 h. After that, the temperature was raised to 75 °C, 4.1 parts by weight of 2-amino-2-methyl-1,3-propanediol and 0.01 part by weight of p-methoxyphenol were added, and the mixture was stirred and kept at a constant temperature for 3 h to obtain a polyurethane acrylate resin. The stirring speed during this process was 400 rpm;

[0059] By weight, 80 parts of polyurethane acrylate resin, 30 parts of lauryl methacrylate, 5 parts of 1-hydroxycyclohexyl phenyl ketone, 2 parts of a leveling agent, 1 part of an antifoaming agent and 1 part of a dispersant were weighed. The modified polyurethane resin, lauryl methacrylate, dispersant and leveling agent were put into a reactor and dispersed at a speed of 900 rpm for 10 min; then the antifoaming agent was added, and the mixture was dispersed at a speed of 1300 rpm for 15 min, followed by grinding, filtering and discharging. When in use, 1-hydroxycyclohexyl phenyl ketone was added and dispersed at a speed of 700 rpm for 10 min to obtain a modified polyurethane photocurable coating.

[0060] Comparative Example 2

[0061] Under a nitrogen atmosphere, 18 parts by weight of HDI and 0.04 part by weight of p-methoxyphenol were placed in a reaction vessel, mixed evenly and heated to 85 °C. Then, 50 parts by weight of polybutadiene diol (HTPB-1000) and 0.01 part by weight of a catalyst were added, and the mixture was stirred and kept at a constant temperature for 3 h. Next, 40 parts by weight of castor oil was added, and the mixture was stirred and kept at a constant temperature for 5 h. After that, the temperature was raised to 75 °C, 4.1 parts by weight of 2-amino-2-methyl-1,3-propanediol and 0.01 part by weight of p-methoxyphenol were added, and the mixture was stirred and kept at a constant temperature for 3 h to obtain a polyurethane acrylate resin. The stirring speed during this process was 400 rpm;

[0062] 3 parts by weight of γ-glycidoxypropyltrimethoxysilane (KH560) and 10 parts by weight of two-dimensional nanosheet-structured boron nitride (BNNS, 500 nm) were added to an ethanol / H2O solution (ethanol∶H2O = 1∶1, weight / weight), and the temperature was raised to 70 °C. The mixture was stirred and reacted at a speed of 800 rpm for 8 h. After the temperature dropped to room temperature, it was filtered, washed with ethanol and dried at 60 °C for 24 h to obtain modified BNNS;

[0063] By weight, weigh 80 parts of polyurethane acrylate resin, 30 parts of lauryl methacrylate, 15 parts of epoxy acrylate, 12 parts of modified BNNS, 5 parts of 1-hydroxycyclohexyl phenyl ketone, 2 parts of leveling agent, 1 part of defoaming agent and 1 part of dispersant. Put the modified polyurethane resin, lauryl methacrylate, modified BNNS, dispersant and leveling agent into a reactor and disperse them at a speed of 900 rpm for 10 min; then add the defoaming agent and disperse it at a speed of 1300 rpm for 15 min, grind, filter and discharge. When in use, add 1-hydroxycyclohexyl phenyl ketone and disperse it at a speed of 700 rpm for 10 min to obtain the modified polyurethane UV-curable coating.

[0064] Comparative Example 3

[0065] The difference between Comparative Example 3 and Example 1 is that:

[0066] (3) Preparation of modified polyurethane UV-curable coating

[0067] Under a nitrogen atmosphere, put 18 parts by weight of HDI and 0.04 parts by weight of p-hydroxyanisole into a reaction vessel, mix them evenly and heat up to 85 °C, add 50 parts by weight of polybutadiene diol (HTPB-1000) and 0.01 parts by weight of catalyst, stir and keep the temperature for reaction for 3 h, add 40 parts by weight of modified castor oil, stir and keep the temperature for reaction for 5 h, heat up to 75 °C, add 4.1 parts by weight of 2-amino-2-methyl-1,3-propanediol and 0.01 parts by weight of p-hydroxyanisole, stir and keep the temperature for reaction for 3 h to obtain the modified polyurethane resin; the stirring speed in this process is 400 rpm;

[0068] By weight, weigh 80 parts of modified polyurethane resin, 30 parts of lauryl methacrylate, 5 parts of 1-hydroxycyclohexyl phenyl ketone, 2 parts of leveling agent, 1 part of defoaming agent and 1 part of dispersant. Put the modified polyurethane resin, lauryl methacrylate, dispersant and leveling agent into a reactor and disperse them at a speed of 900 rpm for 10 min; then add the defoaming agent and disperse it at a speed of 1300 rpm for 15 min, grind, filter and discharge. When in use, add 1-hydroxycyclohexyl phenyl ketone and disperse it at a speed of 700 rpm for 10 min to obtain the modified polyurethane UV-curable coating.

[0069] Comparative Example 4

[0070] The difference between Comparative Example 4 and Example 1 is that:

[0071] (1) The castor oil is not modified;

[0072] (3) Preparation of modified polyurethane UV-curable coating

[0073] Under a nitrogen atmosphere, 18 parts by weight of HDI and 0.04 parts by weight of a polymerization inhibitor were placed in a reaction vessel, mixed evenly and heated to 85 °C. Then, 50 parts by weight of polybutadiene diol (HTPB-1000) and 0.01 parts by weight of a catalyst were added, and the mixture was stirred and kept at a constant temperature for 3 h. Next, 40 parts by weight of castor oil were added, and the mixture was stirred and kept at a constant temperature for 5 h. Then, the temperature was raised to 75 °C, 4.1 parts by weight of a chain extender UPy-OH and 0.01 parts by weight of a polymerization inhibitor were added, and the mixture was stirred and kept at a constant temperature for 3 h to obtain a modified polyurethane resin. The stirring speed during this process was 400 rpm;

[0074] By weight, 80 parts of the modified polyurethane resin, 30 parts of lauryl methacrylate, 12 parts of modified BNNS, 5 parts of 1-hydroxycyclohexyl phenyl ketone, 2 parts of a leveling agent, 1 part of an antifoaming agent and 1 part of a dispersant were weighed. The modified polyurethane resin, lauryl methacrylate, modified BNNS, dispersant and leveling agent were put into a reactor and dispersed at a speed of 900 rpm for 10 min; then the antifoaming agent was added, and the mixture was dispersed at a speed of 1300 rpm for 15 min, followed by grinding, filtering and discharging. When in use, 1-hydroxycyclohexyl phenyl ketone was added and dispersed at a speed of 700 rpm for 10 min to obtain a modified polyurethane UV-curable coating.

[0075] Above, the antifoaming agent used in Examples 1-3 and Comparative Examples 1-4 was a silicone-based antifoaming agent, the leveling agent was a solvent-free nonionic leveling agent, and the dispersant was a polyester-based wetting dispersant, which were conventional reagents for coatings and could all be obtained by purchase.

[0076] The finished coatings prepared in Examples 1-3 and Comparative Examples 1-4 were applied to ITO glass of 50 mm × 50 mm, and then placed under an ultraviolet curing machine and irradiated with ultraviolet light of 365 nm wavelength for 3 min to obtain a cured film with a controlled thickness of 20 μm. Then, it was dried at room temperature for 24 h and the following tests were carried out:

[0077] (1) Water absorption rate: The ITO glass coated with the cured film was immersed in distilled water at room temperature for 24 h, and the mass of the sample before and after immersion was weighed.

[0078] (2) Alkali resistance and alcohol resistance tests: At room temperature, the samples were immersed in 10% NaOH aqueous solution and ethanol for 24 h respectively, and rubbed by hand to observe the degree of color fading. The degree of color fading was indicated by "+", with +: slight color fading; ++: medium color fading; +++: severe color fading.

[0079] (3) Measuring the water contact angle at the top of the cured coating by the sessile drop method. The liquid drop was set to 3 μL / drop, and the measurement temperature was about 20 °C.

[0080] (4) Adhesion test: Adopted "GB / T9286-1998 Cross-Cut Test for Paints and Varnishes Films".

[0081] (5) Dielectric constant test: "GB / T 1409-2006 Dielectric Permittivity and Dissipation Factor".

[0082] (6) Thermal conductivity: "ASTM D 5470-01 Standard Test Method for Thermal Conductivity of Thinned Thermal Insulating Solid Electrical Insulation Materials".

[0083] (7) Storage stability: Weigh 50 g of the samples of Examples 1-3 and Comparative Examples 1-4 into cans and seal them. After placing them at 60 °C for 30 d, observe whether gel, precipitation or other phenomena occur in the system. If not, record it as stable; otherwise, record it as unstable.

[0084] (8) Self-healing performance: Use a utility knife to scratch the ITO glass coated with the cured film, then keep the sample at 40 °C for different times, and observe the healing situation through an optical microscope.

[0085] The test results are shown in Table 1.

[0086] Table 1

[0087]

[0088] According to the disclosure of the above specification, those skilled in the art to which the present invention pertains can also make appropriate changes and modifications to the above embodiments. Therefore, the present invention is not limited to the specific embodiments disclosed and described above, and some modifications and changes to the present invention should also fall within the protection scope of the claims of the present invention. In addition, although some specific terms are used in this specification, these terms are only for convenience of description and do not constitute any limitation to the present invention.

Claims

1. A method for preparing a modified polyurethane light-curing coating, characterized in that: Preparation of modified castor oil: 1-2 parts by weight of γ-glycidyloxypropyltrimethoxysilane and 10-15 parts by weight of BNNS are added to a mixed solution of ethanol / H2O, the temperature is raised to 60-80°C, the mixture is stirred for reaction for 6-10 hours, and after the temperature is lowered to room temperature, the mixture is filtered, washed and dried to obtain modified BNNS; Under N2 atmosphere, 15-30 parts by weight of castor oil, 1-3 parts by weight of succinic anhydride and 0.15-0.3 parts by weight of SnCl2 are placed in a reaction container, the temperature is slowly raised to 80-120°C, and the reaction is stirred for 1-5 hours; when the temperature drops to 70-90°C, 10-15 parts by weight of modified BNNS and 0.01-0.1 parts by weight of triethylamine are added, and the reaction is continued with stirring for 2-6 hours to obtain modified castor oil; Preparation of chain extender: Under a nitrogen atmosphere, 5 to 15 parts by weight of hexamethylene diisocyanate and 0.5 to 1 part by weight of 2-amino-6-methyl-4-pyrimidone are placed in a reaction container, the temperature is raised to 90 to 100° C., and the reaction is stirred for 15 to 30 hours. After the temperature drops to room temperature, the mixture is filtered, washed, and vacuum dried to obtain NCO-terminated UPy; Under a nitrogen atmosphere, 25 to 30 parts by weight of UPy, 12 to 16 parts by weight of 2-amino-2-methyl-1,3-propanediol and an appropriate amount of dimethyl sulfoxide are placed in a reaction container, the temperature is raised to 40 to 60° C., and the mixture is stirred for reaction for 3 to 8 hours. After the temperature drops to room temperature, the mixture is centrifuged, washed and dried to obtain a chain extender; Preparation of modified polyurethane resin: In a nitrogen atmosphere, placing a diisocyanate and a part of the polymerization inhibitor in a reaction container, heating to 60-80° C., adding a diol and a catalyst, stirring and keeping the reaction for 1-4 hours, adding the modified castor oil, stirring and keeping the reaction for 3-8 hours, heating to 70-100° C., adding the remaining polymerization inhibitor and the chain extender, stirring and keeping the reaction for 2-3 hours, and obtaining a modified polyurethane resin; Preparation of modified polyurethane light-curing coating: 80-100 parts by weight of modified polyurethane resin, 30-40 parts by weight of active diluent, 0.5-2 parts by weight of dispersant and 1-3 parts by weight of leveling agent are put into a reactor and stirred to make them evenly mixed; then 0.5-1.5 parts by weight of defoamer are added and stirred to make them evenly dispersed and mixed, the material is ground and filtered, and when used, 3-10 parts by weight of photoinitiator is added and stirred to disperse, so as to prepare the modified polyurethane light-curing coating.

2. The method for preparing the modified polyurethane light-curing coating according to claim 1, characterized in that: In the preparation of modified polyurethane resin: The molar ratio of the diol, modified castor oil, chain extender and diisocyanate is 3-5:2-3:0.5-1.5:8-10; The amount of the polymerization inhibitor is 0.1 to 0.5% by weight of the diisocyanate; The amount of the catalyst used is 0.01-0.1% by weight of the diisocyanate.

3. The method for preparing the modified polyurethane light-curing coating according to claim 2, characterized in that: The diisocyanate compound is at least one selected from the group consisting of hexamethylene diisocyanate, isophorone diisocyanate, diphenylmethane diisocyanate, tetramethyl-m-xylylene diisocyanate and toluene diisocyanate.

4. The method for preparing the modified polyurethane light-curing coating according to claim 2, characterized in that: The diol is selected from at least one of polypropylene glycol, polyethylene glycol, polycaprolactone glycol and polybutadiene glycol, and the average molecular weight of the diol is 500-3000.

5. The method for preparing the modified polyurethane light-curing coating according to claim 2, characterized in that: The polymerization inhibitor is p-hydroxyanisole, hydroquinone or 2,6-di-tert-butyl-p-cresol.

6. The method for preparing the modified polyurethane light-curing coating according to claim 2, characterized in that: The catalyst is stannous octoate, dibutyltin dilaurate or tetrabutyl titanate.

7. The method for preparing the modified polyurethane light-curing coating according to claim 1, characterized in that: The photoinitiator is selected from at least one of 2,4,6-trimethylbenzoylphenylphosphonic acid ethyl ester, 2,4-diethylthioxanthone, 1-hydroxycyclohexylphenyl ketone, 2-hydroxy-1-(4-(4-(2-hydroxy-2-methylpropionyl)benzyl)phenyl)-2-methyl-1-propanone, 2-isopropylthioxanthone, 2-methyl-1-(4-methylthiophenyl)-2-morpholine-1-propanone, 2,4,6-trimethylbenzoyldiphenylphosphine oxide, methyl o-benzoylbenzoate, 2-benzyl-2-dimethylamino-1-(4-morpholinephenyl)butanone, benzophenone, benzoin diethyl ether, benzoin dimethyl ether, biphenyl benzophenone, 2-hydroxy-2-methyl-1-phenyl-1-propanone, and 2-(4-methylbenzyl)-2-(dimethylamino)-1-(4-morpholinephenyl)-1-butanone.

8. The method for preparing the modified polyurethane light-curing coating according to claim 1, characterized in that: The active diluent is at least one of lauryl methacrylate, lauryl acrylate, isobornyl acrylate, isobornyl methacrylate, isodecyl acrylate, isooctyl acrylate, 2-phenoxyethyl acrylate, and ethoxylated trimethylolpropane triacrylate.

9. A modified polyurethane photocurable coating prepared by the method for preparing the modified polyurethane photocurable coating according to any one of claims 1 to 8.

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