Halogen-free flame-retardant uv-moisture-cured polyurethane triresin and preparation method thereof

Abstract

This invention provides a halogen-free flame-retardant UV-moisture-curing polyurethane conformal insulating resin and its preparation method, belonging to the field of polymer materials technology. The conformal insulating resin of this invention is prepared from the following raw materials in parts by weight: 100 parts HDI trimer, 50-120 parts organosilicon-modified polyol, 10-40 parts chain extender containing a hindered phenol-phosphate structure with bifunctional groups, 15-45 parts hydroxyl-containing acrylate, 2-10 parts photoinitiator, 0.1-1.5 parts polymerization inhibitor, and 20-80 parts reactive diluent. This invention embeds hindered phenol-phosphate synergistic flame-retardant groups into the polyurethane backbone, achieving a UL94V-0 rating and limiting oxygen index ≥32% under halogen-free conditions; the UV-moisture dual-curing mechanism increases the crosslinking degree in the shaded area from 65% to 95%, significantly improving the integrity of the insulation protection.

Description

Technical Field

[0001] This invention relates to the field of polymer materials technology, and in particular to a halogen-free flame-retardant UV-moisture-curing polyurethane three-proof insulating resin and its preparation method. Background Technology

[0002] As electronic devices rapidly evolve towards miniaturization, high integration, and high power density, the performance requirements for protective coatings on printed circuit boards and their components are becoming increasingly stringent. Conformal coatings (moisture-proof, mildew-proof, and salt spray-proof), as core insulating protective materials, must simultaneously possess excellent insulation, flame retardancy, weather resistance, and ease of application.

[0003] Currently, traditional conformal coatings mainly face the following technical bottlenecks: Flame retardant systems are not environmentally friendly: Most conformal coatings on the market use halogenated (such as bromine-based) flame retardants, which can meet the UL94V-0 flame retardant standard, but release a large amount of toxic fumes and corrosive gases when burning, which contradicts the trend of halogen-free environmental protection. Halogen-free flame retardant systems (such as phosphorus-based, nitrogen-based, and inorganic flame retardants) usually require large doses, which can easily lead to a significant decrease in the mechanical properties, adhesion, or insulation of the resin, making it difficult to achieve a balance between flame retardancy and overall performance.

[0004] The problem of UV curing in shaded areas: UV-cured conformal coatings have significant advantages such as rapid curing, low energy consumption, and no solvents, but their inherent shortcomings are that shaded areas that are difficult for light to reach (such as the bottom of components, narrow gaps, and under pins) cannot be fully cured. The degree of crosslinking is usually only about 65%, resulting in incomplete insulation protection and a significant reduction in long-term reliability.

[0005] Insufficient storage stability of dual-curing resins: To overcome the problem of curing in shaded areas, researchers developed a UV-moisture dual-curing system: isocyanate (NCO) groups are introduced into UV resins, and secondary cross-linking is achieved with the help of moisture. However, when the highly reactive NCO groups coexist with the acrylate double bonds, side reactions (such as the reaction of NCO with moisture and the thermal polymerization of acrylate) are very likely to occur during storage, leading to increased resin viscosity, gelation, or even failure. The storage period is usually less than 3 months, which greatly restricts its industrial application.

[0006] Weak resistance to high temperature and damp heat: Ordinary polyurethane conformal coatings are prone to hydrolysis or thermal oxidative degradation in high temperature (≥120℃) or damp heat (85℃ / 85%RH) environments, resulting in a sharp decrease in insulation resistance; in addition, traditional polyurethane has a high surface energy, which makes it easy to adsorb dust and pollutants, and the insulation performance will be further deteriorated in humid environments.

[0007] Flame retardancy and heat aging resistance are difficult to coordinate: Most existing halogen-free flame retardant polyurethanes use additive phosphate flame retardants, which can provide a certain flame retardant effect, but lack a structure that resists heat and oxygen aging. With long-term use, the flame retardant rating is prone to decline due to flame retardant migration or resin degradation.

[0008] Therefore, it is of great significance to provide a three-proof insulating resin that combines halogen-free high-efficiency flame retardancy, complete curing without shadow areas, long storage stability, excellent high temperature and humidity resistance, and anti-fouling properties. Summary of the Invention

[0009] The purpose of this invention is to provide a halogen-free flame-retardant UV-moisture-curing polyurethane three-proof insulating resin and its preparation method, in order to solve the technical problems of existing three-proof insulating resins that cannot simultaneously achieve halogen-free flame retardancy and comprehensive performance, incomplete curing of shaded areas during UV curing, poor storage stability of dual-curing resins, insufficient high temperature and damp heat resistance, and difficulty in synergistically combining flame retardancy and resistance to thermo-oxidative aging.

[0010] To achieve the above-mentioned objectives, the present invention provides the following technical solution: This invention provides a halogen-free flame-retardant UV-curable polyurethane three-proof insulating resin, which is prepared from the following raw materials in parts by weight: 100 parts of HDI trimer 50-120 parts of organosilicon-modified polyols 10-40 parts of a bifunctional chain extender containing a hindered phenol-phosphate ester structure. 15-45 parts of hydroxyl-containing acrylates, 2-10 parts of photoinitiator Polymerization inhibitor 0.1~1.5 parts, 20-80 parts of reactive diluent.

[0011] Furthermore, the organosilicon-modified polyol includes hydroxyl-terminated polydimethylsiloxane and / or polysiloxane-polyether copolymer polyol, and the hydroxyl value of the organosilicon-modified polyol is 30~120 mgKOH / g.

[0012] Furthermore, the preparation method of the bifunctional chain extender containing the hindered phenol-phosphate ester structure is as follows: the carboxylic acid containing the hindered phenol group and the polyol containing the phosphate ester group are reacted by esterification under the action of a catalyst.

[0013] Furthermore, the hydroxyl-containing acrylate includes one or more of hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, and hydroxybutyl acrylate; The photoinitiator includes one or more of the following: polymeric macromolecular photoinitiators, polyether-modified α-hydroxy ketone derivatives, 2-hydroxy-2-methyl-1-phenylpropanone, 1-hydroxycyclohexylphenyl ketone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, and 2,4,6-trimethylbenzoyl-dimethylphosphine oxide.

[0014] Furthermore, the polymerization inhibitor includes one or more of hydroquinone, p-hydroxyanisole, p-tert-butylcatechol, 2,6-di-tert-butyl-p-cresol, 2,5-di-tert-butylhydroquinone, 2-tert-butylhydroquinone, and phenothiazine. The reactive diluent includes one or more of isobornyl acrylate, tetrahydrofuran acrylate, 1,6-hexanediol diacrylate, tripropylene glycol diacrylate, trimethylolpropane triacrylate, and pentaerythritol triacrylate.

[0015] This invention also provides a method for preparing the halogen-free flame-retardant UV-moisture-curing polyurethane three-proof insulating resin, comprising the following steps: 1) Under nitrogen protection, HDI trimer, organosilicon-modified polyol and bifunctional chain extender containing hindered phenol-phosphate structure are subjected to a first reaction, and then a catalyst is added to react until the NCO content is controlled at 8~12% to obtain prepolymer; 2) Add hydroxyl-containing acrylate and part of the polymerization inhibitor to the cooled prepolymer to carry out a second reaction until the remaining NCO content is controlled at 2.0~3.5% to obtain the intermediate product; 3) After mixing the intermediate product with the photoinitiator, the remaining polymerization inhibitor and the reactive diluent, vacuum degassing is performed to obtain a halogen-free flame-retardant UV-moisture-curing polyurethane three-proof insulating resin.

[0016] Furthermore, the temperature of the first reaction is 75~90℃, and the reaction time is 1.5~3h; The catalyst is dibutyltin dilaurate or stannous octoate; The amount of the catalyst used is 0.01 to 0.1% of the total mass of HDI trimer, organosilicon-modified polyol, and bifunctional chain extender containing hindered phenol-phosphate ester structure.

[0017] Furthermore, the temperature of the cooled prepolymer is 55~65℃; The temperature of the second reaction is 55~65℃, and the reaction time is 1~2h; The amount of the polymerization inhibitor added is 30-60% of the total mass of the polymerization inhibitor.

[0018] Furthermore, the mixing temperature is 40~50℃, the mixing time is 0.5~1h, and the mixing speed is 300~600rpm; The vacuum degree of the vacuum degassing is ≤-0.095MPa, the vacuum degassing time is 15~30min, and the vacuum degassing temperature is 40~50℃.

[0019] The beneficial effects of this invention are: 1) This invention embeds hindered phenol-phosphate synergistic flame-retardant groups into the polyurethane main chain, achieving UL94V-0 rating and limiting oxygen index ≥32% under halogen-free conditions; the UV-wet dual-curing mechanism increases the crosslinking degree of the shaded area from 65% to 95%, significantly improving the insulation protection integrity.

[0020] 2) This invention utilizes organosilicon segments to migrate to the material surface at high temperatures to form a dense ceramicized silica protective layer. This layer works synergistically with the polyphosphoric acid / carbon layer formed by the decomposition of phosphate esters. Through the synergistic flame retardancy of silicon and phosphorus, the heat insulation and oxygen barrier effects are significantly enhanced, further suppressing dripping, increasing the oxygen index, and achieving higher flame retardancy efficiency. The high bond energy of the organosilicon Si-O-Si bonds endows the resin with excellent thermal stability and high-temperature resistance. The thermal decomposition initiation temperature is increased by 30~50℃ compared to the unmodified resin, and the long-term service temperature range is widened to -40℃~150℃, meeting the insulation protection requirements under higher temperature conditions.

[0021] 3) The present invention achieves storage stability of more than 6 months through the combination of polymerization inhibitors and inert gas packaging process, and the organosilicon segments do not interfere with the storage stability of the system. Detailed Implementation

[0022] This invention provides a halogen-free flame-retardant UV-curable polyurethane three-proof insulating resin, which is prepared from the following raw materials in parts by weight: 100 parts of HDI trimer 50-120 parts of organosilicon-modified polyols 10-40 parts of a bifunctional chain extender containing a hindered phenol-phosphate ester structure. 15-45 parts of hydroxyl-containing acrylates, 2-10 parts of photoinitiator Polymerization inhibitor 0.1~1.5 parts, 20-80 parts of reactive diluent.

[0023] In this invention, the content of the organosilicon-modified polyol is preferably 60-110 parts by mass, and more preferably 70-100 parts by mass.

[0024] In this invention, the organosilicon-modified polyol includes hydroxyl-terminated polydimethylsiloxane and / or polysiloxane-polyether copolymer polyol, preferably hydroxyl-terminated polydimethylsiloxane; the hydroxyl value of the organosilicon-modified polyol is 30~120mgKOH / g, preferably 40~110mgKOH / g, and more preferably 50~100mgKOH / g.

[0025] In this invention, the content of the bifunctional chain extender containing the hindered phenol-phosphate ester structure is preferably 15 to 35 parts by mass, and more preferably 20 to 30 parts.

[0026] In this invention, the preparation method of the bifunctional chain extender containing the hindered phenol-phosphate ester structure is as follows: the carboxylic acid containing the hindered phenol group and the polyol containing the phosphate ester group are reacted by esterification under the action of a catalyst.

[0027] In this invention, under nitrogen protection, a hindered phenolic carboxylic acid and a polyol containing phosphate ester groups are added in a molar ratio of 1.5:1. The hindered phenolic carboxylic acid is 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid, and the polyol containing phosphate ester groups is bis(2-hydroxyethyl) phosphate. Simultaneously, 0.5-1.5% by weight of p-toluenesulfonic acid as a catalyst and toluene as a dehydrating agent are added. The temperature is raised to 100-110°C for the reaction, and the reaction time is 5-7 hours. During the reaction, the mixture is kept moist by a water separator. The water generated during esterification is separated until the water level in the separator no longer increases. After the reaction is complete, the reaction solution is cooled to room temperature and washed with a 4-6% sodium carbonate aqueous solution until neutral to remove the catalyst and unreacted carboxylic acids containing hindered phenol groups. The solution is then washed twice with water, separated to obtain the organic phase, dried with anhydrous magnesium sulfate overnight, filtered, and then distilled under reduced pressure at 60-80℃ and a vacuum degree ≤-0.095MPa to remove toluene, yielding a light yellow viscous product, which is the bifunctional chain extender containing a hindered phenol-phosphate ester structure.

[0028] In this invention, the content of the hydroxyl-containing acrylate is preferably 18 to 42 parts by weight, and more preferably 20 to 40 parts by weight.

[0029] In this invention, the hydroxyl-containing acrylate includes one or more of hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, and hydroxybutyl acrylate, preferably one or more of hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl methacrylate, and hydroxybutyl acrylate, and more preferably one or more of hydroxyethyl acrylate, hydroxyethyl methacrylate, and hydroxybutyl acrylate.

[0030] In this invention, the content of the photoinitiator is preferably 3 to 9 parts by weight, and more preferably 4 to 8 parts by weight.

[0031] In this invention, the photoinitiator includes one or more of the following: polymerizable macromolecular photoinitiator, polyether-modified α-hydroxy ketone derivative, 2-hydroxy-2-methyl-1-phenylpropanone, 1-hydroxycyclohexylphenyl ketone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, and 2,4,6-trimethylbenzoyl-dimethylphosphine oxide. Preferably, it is one or more of the following: polyether-modified α-hydroxy ketone derivative, 2-hydroxy-2-methyl-1-phenylpropanone, 1-hydroxycyclohexylphenyl ketone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, and 2,4,6-trimethylbenzoyl-dimethylphosphine oxide. More preferably, it is one or more of the following: 2-hydroxy-2-methyl-1-phenylpropanone, 1-hydroxycyclohexylphenyl ketone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, and 2,4,6-trimethylbenzoyl-dimethylphosphine oxide.

[0032] In this invention, the content of the polymerization inhibitor is preferably 0.3 to 1.2 parts by mass, and more preferably 0.5 to 1 part.

[0033] In this invention, the polymerization inhibitor includes one or more of hydroquinone, p-hydroxyanisole, p-tert-butylcatechol, 2,6-di-tert-butyl-p-cresol, 2,5-di-tert-butylhydroquinone, 2-tert-butylhydroquinone, and phenothiazine, preferably one or more of hydroquinone, p-hydroxyanisole, p-tert-butylcatechol, 2,5-di-tert-butylhydroquinone, 2-tert-butylhydroquinone, and phenothiazine, and more preferably one or more of hydroquinone, p-hydroxyanisole, p-tert-butylcatechol, 2-tert-butylhydroquinone, and phenothiazine.

[0034] In this invention, the content of the active diluent is preferably 25 to 75 parts by weight, and more preferably 30 to 70 parts by weight.

[0035] In this invention, the active diluent comprises one or more of isobornyl acrylate, tetrahydrofuran acrylate, 1,6-hexanediol diacrylate, tripropylene glycol diacrylate, trimethylolpropane triacrylate, and pentaerythritol triacrylate, preferably one or more of isobornyl acrylate, tetrahydrofuran acrylate, 1,6-hexanediol diacrylate, trimethylolpropane triacrylate, and pentaerythritol triacrylate, and more preferably one or more of isobornyl acrylate, tetrahydrofuran acrylate, 1,6-hexanediol diacrylate, and pentaerythritol triacrylate.

[0036] This invention also provides a method for preparing the halogen-free flame-retardant UV-moisture-curing polyurethane three-proof insulating resin, comprising the following steps: 1) Under nitrogen protection, HDI trimer, organosilicon-modified polyol and bifunctional chain extender containing hindered phenol-phosphate structure are subjected to a first reaction, and then a catalyst is added to react until the NCO content is controlled at 8~12% to obtain prepolymer; 2) Add hydroxyl-containing acrylate and part of the polymerization inhibitor to the cooled prepolymer to carry out a second reaction until the remaining NCO content is controlled at 2.0~3.5% to obtain the intermediate product; 3) After mixing the intermediate product with the photoinitiator, the remaining polymerization inhibitor and the reactive diluent, vacuum degassing is performed to obtain a halogen-free flame-retardant UV-moisture-curing polyurethane three-proof insulating resin.

[0037] In this invention, the temperature of the first reaction is 75~90℃, preferably 77~88℃, and more preferably 80~85℃; the time of the first reaction is 1.5~3h, preferably 1.7~2.8h, and more preferably 2~2.5h. The catalyst is dibutyltin dilaurate or stannous octoate, preferably dibutyltin dilaurate; The amount of the catalyst is 0.01 to 0.1% of the total mass of the HDI trimer, the organosilicon-modified polyol, and the bifunctional chain extender containing the hindered phenol-phosphate ester structure, preferably 0.02 to 0.09%, and more preferably 0.03 to 0.08%.

[0038] In this invention, the temperature of the cooled prepolymer is 55~65℃, preferably 58~62℃, and more preferably 60℃; The temperature of the second reaction is 55~65℃, preferably 58~62℃, and more preferably 60℃; the time of the second reaction is 1~2h, preferably 1.2~1.8h, and more preferably 1.4~1.6h.

[0039] In this invention, the amount of the polymerization inhibitor added is 30-60% of the total mass of the polymerization inhibitor, preferably 35-55%, and more preferably 40-50%.

[0040] In this invention, the mixing temperature is 40~50℃, preferably 42~48℃, and more preferably 44~46℃; the mixing time is 0.5~1h, preferably 0.6~0.9h, and more preferably 0.7~0.8h; the mixing speed is 300~600rpm, preferably 350~550rpm, and more preferably 400~500rpm. The vacuum degree of the vacuum degassing is ≤-0.095MPa, preferably ≤-0.098MPa, and more preferably ≤-0.1MPa; the vacuum degassing time is 15~30min, preferably 18~27min, and more preferably 20~25min; the vacuum degassing temperature is 40~50℃, preferably 42~48℃, and more preferably 44~46℃.

[0041] The technical solutions provided by the present invention will be described in detail below with reference to the embodiments, but they should not be construed as limiting the scope of protection of the present invention.

[0042] Example 1

[0043] Under nitrogen protection, 3,5-di-tert-butyl-4-hydroxyphenylpropionic acid and bis(2-hydroxyethyl) phosphate were added to a reactor equipped with a stirrer, thermometer, and water separator at a molar ratio of 1.5:1. Simultaneously, 1% p-toluenesulfonic acid (by mass of the total reactants) was added as a catalyst, and an appropriate amount of toluene was added as a dehydrating agent. The mixture was heated to 105°C and refluxed under atmospheric pressure and nitrogen protection for 6 hours. During this period, water generated during esterification was continuously separated using the water separator. When the water level in the separator stopped increasing, the reaction was stopped. The reaction solution was cooled to room temperature, washed with a 5% sodium carbonate aqueous solution until neutral, and then washed twice with water. The organic phase was obtained by separation and dried overnight with anhydrous magnesium sulfate. After filtration, the toluene was removed by vacuum distillation at 70°C and a vacuum degree of -0.095 MPa, yielding a light yellow viscous product, which is a bifunctional chain extender containing a hindered phenol-phosphate structure. The hydroxyl value was determined to be 112 mg KOH / g by titration. Under nitrogen protection, 100 parts of HDI trimer, 85 parts of organosilicon-modified polyol (hydroxyl-terminated polydimethylsiloxane PDMS, hydroxyl value 80 mgKOH / g) and 25 parts of the above-prepared bifunctional chain extender containing hindered phenol-phosphate ester structure were added to the reactor, heated to 80℃, and stirred for 2 hours. Then, 0.05% of dibutyltin dilaurate as a catalyst was added, and the reaction continued. The NCO content was monitored by di-n-butylamine titration until the NCO content reached 10.2%, and NCO-terminated polyurethane prepolymer was obtained. The prepolymer was cooled to 60°C, and 30 parts of hydroxyethyl acrylate (HEA) and 0.3 parts of polymerization inhibitor (the polymerization inhibitor is a combination of p-hydroxyanisole and phenothiazine, with a mass ratio of p-hydroxyanisole to phenothiazine of 2:1) were added. The reaction was continued at 60°C for 1.5 h until the remaining NCO content dropped to 2.8%, and the intermediate product was obtained. The above intermediate product was cooled to 45°C, and 6 parts of photoinitiator (2-hydroxy-2-methyl-1-phenylpropanone and 1-hydroxycyclohexylphenyl ketone in a mass ratio of 1:1), 0.5 parts of polymerization inhibitor (a combination of p-hydroxyanisole and phenothiazine in a mass ratio of 2:1), and 50 parts of reactive diluent (isoborneol acrylate and 1,6-hexanediol diacrylate in a mass ratio of 3:1) were added. The mixture was dispersed and mixed at high speed at 45°C and 400 rpm for 0.8 h. Then, it was transferred to a vacuum degassing kettle and degassed under vacuum at -0.098 MPa and 45°C for 20 min. Finally, it was filtered (using a 400-mesh filter) in a nitrogen-filled glove box (with residual oxygen ≤0.5%) and sealed in packaging to obtain halogen-free flame-retardant UV-moisture-curing polyurethane three-proof insulating resin.

[0044] Example 2

[0045] Compared with Example 1, the difference is that in Example 2, the amount of organosilicon-modified polyol is adjusted to 50 parts, and the amount of bifunctional chain extender containing hindered phenol-phosphate ester structure is 40 parts, while the rest is the same as in Example 1.

[0046] Example 3

[0047] Compared with Example 1, the difference is that in Example 3, the amount of organosilicon-modified polyol is 120 parts, and the amount of bifunctional chain extender containing hindered phenol-phosphate ester structure is 10 parts. In the second reaction, the remaining NCO content was controlled to be reduced to 3.5%, and the rest was the same as in Example 1.

[0048] Example 4

[0049] Compared with Example 1, the difference is that in Example 4, the organosilicon-modified polyol is a polysiloxane-polyether copolymer polyol (hydroxyl value of 95 mgKOH / g), and the photoinitiator is 2,4,6-trimethylbenzoyl-diphenylphosphine oxide (TPO) and 1-hydroxycyclohexylphenyl ketone in a mass ratio of 1:1. The rest is the same as in Example 1.

[0050] Comparative Example 1

[0051] Compared with Example 1, the difference is that in Comparative Example 1, the organosilicon-modified polyol was replaced with an unmodified polyether polyol (polyoxypropylene glycol), and the rest is the same as in Example 1.

[0052] Comparative Example 2

[0053] Compared with Example 1, the difference is that in Comparative Example 2, the bifunctional chain extender containing the hindered phenol-phosphate ester structure was replaced with 1,4-butanediol, and the rest is the same as in Example 1.

[0054] Comparative Example 3

[0055] Compared with Example 1, the difference is that in Comparative Example 3, after adding hydroxyl-containing acrylate in the second reaction, the reaction continued until the remaining NCO content dropped to 0.3%, and the rest was the same as in Example 1.

[0056] Comparative Example 4

[0057] The difference between Comparative Example 4 and Example 1 is that no polymerization inhibitor was added.

[0058] The performance of the three-proof insulating resins prepared in Examples 1-4 and Comparative Examples 1-4 was tested. The test method was as follows: Limiting Oxygen Index (LOI): GB / T 2406.2-2009 "Determination of Combustion Behavior by Oxygen Index Method for Plastics - Part 2: Room Temperature Test"; UL 94 Vertical Flammability Rating: UL 94, "Tests on the Flammability of Plastic Materials Used in Equipment and Appliance Components"; Crosslinking degree (gel rate) in the shaded area: Simulated curing in the shaded area (aluminum foil was used to cover 50% of the area, and only the unshaded part was irradiated, and then the whole area was placed in 25℃ / 60%RH humidity for 7 days for curing), the cured film at the center of the shaded area was taken and weighed W0 (0.5g), extracted with acetone by Soxhlet extraction for 24 hours, and then dried to constant weight W1. The calculation formula is: Crosslinking degree (%) = (W1 / W0) × 100%; Storage stability (40℃ accelerated test): The resin was sealed in an aluminum foil bag (nitrogen-filled) and placed in a 40℃ constant temperature oven. Samples were taken every 7 days, and viscosity changes were tested using a rotational viscometer (Brookfield DV2T, 25℃, rotor S63, speed 20 rpm). The viscosity change rate after 30 days was calculated. A change rate ≤25% was considered acceptable (corresponding to 6 months of storage at room temperature). The failure time was recorded when gelation (non-flowing) occurred. Thermal decomposition initiation temperature (Td,5%): Thermogravimetric analysis (TGA) is performed under a nitrogen atmosphere, with the temperature increased to 600℃ at a heating rate of 10℃ / min. The temperature (Td,5%) corresponding to a 5% mass loss of the test sample is then determined.

[0059] Water contact angle (hydrophobicity): GB / T 30693-2014 "Measurement of water contact angle between plastic film"; Insulation resistance retention rate (damp heat aging): GB / T 1410-2006 "Test methods for volume resistivity and surface resistivity of solid insulating materials".

[0060] The test results are shown in Table 1.

[0061] Table 1. Performance test results of the three-proof insulating resins prepared in Examples 1-4 and Comparative Examples 1-4

[0062] As shown in Table 1, Examples 1, 2, and 4 all achieved UL94 V-0 rating with a limiting oxygen index (LOI) ≥ 32.8%; while the LOI of Comparative Example 1 (without silicone) was only 24.5%, and the LOI of Comparative Example 2 (without phosphate chain extender) was only 22.0%, fully demonstrating the necessity of silicon-phosphorus synergistic flame retardancy. The degree of crosslinking in Examples 1-4 was ≥ 93.2%, but the degree of crosslinking in Comparative Example 3 (with only 0.3% residual NCO) was only 68.5%, indicating that the UV-wet dual-curing mechanism plays a crucial role in the complete curing of the shaded area. After accelerated aging at 40℃ for 30 days, the viscosity increase in Examples 1-4 was ≤ 14%, suggesting a storage period of over 6 months at room temperature; while Comparative Example 4 (without polymerization inhibitor) gelled within 7 days, demonstrating the indispensable necessity of the polymerization inhibitor combination. Example 3, with the highest silicone content, exhibited the highest 5% thermogravimetric temperature (Td, 5%, 320°C) and water contact angle (110°). In contrast, Comparative Example 1, with no silicone, showed a Td, 5% decrease to 275°C and a water contact angle of only 85°, demonstrating that silicone modification significantly improves the material's thermal stability and anti-fouling properties. After damp heat aging, Examples 1-4 all maintained over 90% electrical resistance; however, Comparative Example 3, with incomplete curing in the shaded area, only maintained 78.5% of its resistance, further demonstrating the importance of complete curing for the material's long-term insulation performance.

[0063] As can be seen from the above embodiments, the present invention provides a halogen-free flame-retardant UV-moisture-curing polyurethane conformal insulating resin and its preparation method. The conformal insulating resin is prepared from the following raw materials in parts by weight: 100 parts of HDI trimer, 50-120 parts of organosilicon-modified polyol, 10-40 parts of a bifunctional chain extender containing a hindered phenol-phosphate ester structure, 15-45 parts of a hydroxyl-containing acrylate, 2-10 parts of a photoinitiator, 0.1-1.5 parts of a polymerization inhibitor, and 20-80 parts of an reactive diluent. The present invention embeds hindered phenol-phosphate ester synergistic flame-retardant groups into the polyurethane main chain, achieving a UL94V-0 rating and a limiting oxygen index ≥32% under halogen-free conditions. The UV-moisture dual-curing mechanism increases the crosslinking degree in the shaded area from 65% to 95%, significantly improving the integrity of the insulation protection.

[0064] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A halogen-free flame-retardant UV-curable polyurethane three-proof insulating resin, characterized in that, It is prepared from the following raw materials in parts by weight: 100 parts of HDI trimer 50-120 parts of organosilicon-modified polyols 10-40 parts of a bifunctional chain extender containing a hindered phenol-phosphate ester structure. 15-45 parts of hydroxyl-containing acrylates, 2-10 parts of photoinitiator Polymerization inhibitor 0.1~1.5 parts, 20-80 parts of reactive diluent.

2. The halogen-free flame-retardant UV-moisture-curing polyurethane three-proof insulating resin according to claim 1, characterized in that, The organosilicon-modified polyols include hydroxyl-terminated polydimethylsiloxane and / or polysiloxane-polyether copolymer polyols, with hydroxyl values ​​of 30~120 mgKOH / g.

3. The halogen-free flame-retardant UV-moisture-curing polyurethane three-proof insulating resin according to claim 1 or 2, characterized in that, The preparation method of the bifunctional chain extender containing the hindered phenol-phosphate ester structure is as follows: the carboxylic acid containing the hindered phenol group and the polyol containing the phosphate ester group are reacted by esterification under the action of a catalyst.

4. The halogen-free flame-retardant UV-moisture-curing polyurethane three-proof insulating resin according to claim 3, characterized in that, The hydroxyl-containing acrylates include one or more of hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, hydroxypropyl methacrylate, and hydroxybutyl acrylate. The photoinitiator includes one or more of the following: polymeric macromolecular photoinitiators, polyether-modified α-hydroxy ketone derivatives, 2-hydroxy-2-methyl-1-phenylpropanone, 1-hydroxycyclohexylphenyl ketone, 2,4,6-trimethylbenzoyl-diphenylphosphine oxide, and 2,4,6-trimethylbenzoyl-dimethylphosphine oxide.

5. The halogen-free flame-retardant UV-moisture-curing polyurethane three-proof insulating resin according to claim 4, characterized in that, The polymerization inhibitor includes one or more of hydroquinone, p-hydroxyanisole, p-tert-butylcatechol, 2,6-di-tert-butyl-p-cresol, 2,5-di-tert-butylhydroquinone, 2-tert-butylhydroquinone, and phenothiazines. The reactive diluent includes one or more of isobornyl acrylate, tetrahydrofuran acrylate, 1,6-hexanediol diacrylate, tripropylene glycol diacrylate, trimethylolpropane triacrylate, and pentaerythritol triacrylate.

6. A method for preparing the halogen-free flame-retardant UV-moisture-curing polyurethane three-proof insulating resin according to any one of claims 1 to 5, characterized in that, Includes the following steps: 1) Under nitrogen protection, HDI trimer, organosilicon-modified polyol and bifunctional chain extender containing hindered phenol-phosphate structure are subjected to a first reaction, and then a catalyst is added to react until the NCO content is controlled at 8~12% to obtain prepolymer; 2) Add hydroxyl-containing acrylate and part of the polymerization inhibitor to the cooled prepolymer to carry out a second reaction until the remaining NCO content is controlled at 2.0~3.5% to obtain the intermediate product; 3) After mixing the intermediate product with the photoinitiator, the remaining polymerization inhibitor and the reactive diluent, vacuum degassing is performed to obtain a halogen-free flame-retardant UV-moisture-curing polyurethane three-proof insulating resin.

7. The preparation method of the halogen-free flame-retardant UV-moisture-curing polyurethane three-proof insulating resin according to claim 6, characterized in that, The temperature of the first reaction is 75~90℃, and the reaction time is 1.5~3h; The catalyst is dibutyltin dilaurate or stannous octoate; The amount of the catalyst used is 0.01 to 0.1% of the total mass of HDI trimer, organosilicon-modified polyol, and bifunctional chain extender containing hindered phenol-phosphate ester structure.

8. The preparation method of the halogen-free flame-retardant UV-moisture-curing polyurethane three-proof insulating resin according to claim 7, characterized in that, The temperature of the prepolymer after cooling is 55~65℃; The temperature of the second reaction is 55~65℃, and the reaction time is 1~2h; The amount of the polymerization inhibitor added is 30-60% of the total mass of the polymerization inhibitor.

9. The method for preparing the halogen-free flame-retardant UV-moisture-curing polyurethane three-proof insulating resin according to claim 7 or 8, characterized in that, The mixing temperature is 40~50℃, the mixing time is 0.5~1h, and the mixing speed is 300~600rpm; The vacuum degree of the vacuum degassing is ≤-0.095MPa, the vacuum degassing time is 15~30min, and the vacuum degassing temperature is 40~50℃.

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