Solvent-free bio-based photocurable prepolymer, its preparation method and application

Abstract

The present invention discloses a solvent-free bio-based photocurable prepolymer and its preparation method and application. By mass fraction, the raw materials for preparing the solvent-free bio-based photocurable prepolymer include: 40-55 parts of castor oil-based polyurethane, 25-35 parts of itaconic acid acrylic diol, 10-20 parts of short-chain acrylate, and 0-20 parts of silane coupling agent. The present invention uses castor oil-based polyurethane and itaconic acid acrylic diol synthesized from bio-based raw materials such as castor oil and itaconic acid to replace petroleum-based materials to prepare photocurable prepolymers, which are green and environmentally friendly. At the same time, the addition of short-chain acrylate and silane coupling agent can avoid the additional addition of solvents, thus solving environmental protection, health and other problems caused by solvent volatilization, and can also effectively improve the UV curing efficiency and the performance of the cured film obtained after curing. The solvent-free bio-based photocurable prepolymer provided by the present invention can be widely applied to fields such as coatings, inks, adhesives, plastics, fibers or composite materials.

Description

Technical Field

[0001] The invention belongs to the technical field of photocurable materials and relates to a solvent-free bio-based photocurable prepolymer and a preparation method and application thereof. Background Art

[0002] Polyurethane (PU) is mainly composed of polyols and isocyanates. It has the advantages of strong bonding performance and good flexibility, and is widely used in many fields. Polyurethane can be classified into solvent-based polyurethane and solvent-free polyurethane. Among them, solvent-based polyurethane has volatile solvents, and the solvent evaporates in the air, which may have adverse effects on the natural environment and the human body. Solvent-free polyurethane has no added solvents, the solid content is 100%, and no harmful substances evaporate during the production and construction process, so it is safer and more environmentally friendly. With the increase of people's awareness of environmental protection and self-protection, people have begun to pursue more green and environmentally friendly polyurethanes with excellent performance. Due to the requirements of energy saving, environmental protection, sustainability and high performance, it is of great practical significance to develop solvent-free polyurethanes with fast curing speed and excellent performance.

[0003] Traditional solvent-based polyurethane needs to be baked or heated for dozens of hours to fully cure, while light-cured coatings cure very quickly and save energy. UV curing refers to the use of medium and short-wave UV light (300-800 nm) under UV radiation. After the photoinitiator absorbs the radiation energy of ultraviolet light, it splits into free radicals, triggering the polymerization, cross-linking and grafting reactions of the prepolymer, and solidifies into a network polymer in a very short time. This allows UV coatings, inks, adhesives, etc. to be converted from liquid to solid within seconds to form patterns. Summary of the invention

[0004] The purpose of the present invention is to provide a solvent-free bio-based photocurable prepolymer and its preparation method and application. On the one hand, the present invention introduces bio-based raw materials such as vegetable oil and itaconic acid into the solvent-free polyurethane system, replacing the use of petroleum-based materials, which is green and environmentally friendly; on the other hand, short-chain acrylates are used to replace solvents such as ethyl acetate, acetone, and butanone, solving the problem that the solvent volatilization in the air of the current solvent-based polyurethane may harm the natural environment and human health; on the other hand, the solvent-free bio-based photocurable prepolymer provided by the present invention can be cured into a film in a short time under the action of a photoinitiator and ultraviolet light, solving the problem of slow curing speed of traditional solvent-based polyurethane.

[0005] According to one aspect of the present invention, a solvent-free bio-based photocurable prepolymer is provided. The raw materials for its preparation include, by weight: 40 to 55 parts of castor oil-based polyurethane, 25 to 35 parts of itaconic acid acrylate diol, 10 to 20 parts of short-chain acrylate, and 0 to 20 parts of silane coupling agent.

[0006] From the perspective of environmental protection, the present invention provides a solvent-free bio-based photocurable prepolymer. In the present invention, castor oil-based polyurethane and itaconic acid acrylate diol synthesized from bio-based raw materials such as castor oil and itaconic acid, which are widely sourced, inexpensive, and biodegradable, are used to replace petroleum-based materials as the soft and hard segments of polyurethane. This not only makes it environmentally friendly and reduces production costs, but also, the addition of short-chain acrylate and silane coupling agent can not only effectively improve the UV curing efficiency of the bio-based photocurable prepolymer, thereby improving production efficiency, but also effectively improve the mechanical properties of the cured film obtained after curing. The solvent-free bio-based photocurable prepolymer provided by the present invention can be widely applied to different fields such as coatings, inks, adhesives, plastics, fibers or composite materials, with a wide application range and strong applicability.

[0007] The present invention uses short-chain acrylate to replace traditional solvents such as ethyl acetate, acetone, and methyl ethyl ketone, reducing the volatilization of solvents. This can not only solve the problem that solvent volatilization may harm the natural environment and human health in the air, but also has the following advantages: (1) The short-chain acrylate has a small molecular weight and low viscosity, which plays a diluting role in the synthesis process, promoting the progress of the reaction. Therefore, it can well solve the problems of gelation or explosive polymerization caused by excessive viscosity during the synthesis of polyurethane, and can also save the subsequent treatment steps of removing solvents. The utilization rate of raw materials is complete, effectively saving energy and improving reaction efficiency; (2) The short-chain acrylate contains one or more active carbon-carbon double bonds, which is conducive to free radical polymerization, thus being able to well improve the UV curing efficiency, enabling the prepolymer to cure quickly and energy-efficiently, and also improving the properties of the cured film.

[0008] In some embodiments, the short-chain acrylate can be selected from at least one of methacrylate, methyl methacrylate, 2-hydroxyethyl methacrylate, and 2-hydroxyethyl acrylate.

[0009] Silane coupling agents can react with substances such as hydroxyl groups, double bonds, and isocyanates to form a cross-linked molecular structure with repeating units. Traditional silicone materials mainly use heat curing, which has a long curing time and low efficiency, and is not conducive to large-scale production. In the present invention, silicone elements are combined with castor oil-based polyurethane, and itaconic acid acrylate diol is introduced, which not only increases the bio-based content in the prepolymer, but also effectively improves the UV light curing efficiency by increasing the content of carbon-carbon double bonds, thereby improving the production efficiency. At the same time, when itaconic acid acrylate diol and castor oil-based polyurethane are mixed evenly in a suitable ratio and a silane coupling agent is added, the number of interfacial Si-OH can be increased. When used as an adhesive, a dense layer of Si-OH groups can be formed at the bonding interface of the prepolymer, improving the bonding strength and acid and alkali corrosion resistance. In addition, the solvent-free bio-based photocuring prepolymer of the present invention contains more silicon elements, and can form a dense cross-linking density network after curing, effectively improving the mechanical properties of the cured film, and the obtained cured film has high transparency.

[0010] In some embodiments, the silane coupling agent can be selected from at least one of 3-aminopropyltriethoxysilane, γ-glycidoxypropyltrimethoxysilane, and methacryloxy-functional silane.

[0011] In some embodiments, the preparation method of castor oil polyurethane includes the following steps:

[0012] Mix castor oil, isocyanate, a first catalyst, and an inhibitor, and react at 65-78°C under a nitrogen atmosphere for 2-4 hours to obtain it.

[0013] In the synthesis process of the castor oil-based polyurethane of the present invention, solvents do not need to be used, which is green and environmentally friendly.

[0014] In some embodiments, the isocyanate can be selected from at least one of isophorone diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, and toluene diisocyanate.

[0015] In some embodiments, the molar ratio of castor oil to isocyanate can be 1:(1-3).

[0016] In some embodiments, the first catalyst can be selected from at least one of dibutyltin dilaurate, organobismuth, N,N-dimethylcyclohexylamine, N,N'-dimethylpyridine, and triethanolamine.

[0017] In some embodiments, the dosage of the first catalyst can be 0.01-2% of the total weight of castor oil and isocyanate.

[0018] In some embodiments, the inhibitor can be selected from at least one of hydroquinone, 4-methoxyphenol, 2,5-di-tert-butyl-p-cresol, and tert-butylhydroquinone.

[0019] In some embodiments, the amount of the polymerization inhibitor is 0.001 to 1% of the total weight of the castor oil and the isocyanate.

[0020] In some embodiments, the method for preparing itaconic acid acrylic diol may include the following steps:

[0021] Mix itaconic acid, epoxy acrylate and a second catalyst, and react at 75 to 100 °C under a nitrogen atmosphere for 2 to 6 hours to obtain it.

[0022] In some embodiments, the epoxy acrylate may be selected from at least one of epoxy resin, diglycidyl ether, methyl glycidyl ether, lauric acid glycidyl ether, and tertiary carbonate glycidyl ether.

[0023] In some embodiments, the molar ratio of itaconic acid to epoxy acrylate may be 1:(1 to 2.5).

[0024] In some embodiments, the second catalyst may be selected from at least one of N,N-dimethylethanolamine, N,N-dimethylbenzylamine, triethylamine, tetrabutylammonium bromide, and triphenylphosphine.

[0025] In some embodiments, the amount of the second catalyst may be 0.5 to 2% of the total weight of itaconic acid and epoxy acrylate.

[0026] According to another aspect of the present invention, a method for preparing the above solvent-free bio-based photocurable prepolymer is provided, including the following steps:

[0027] Mix the castor oil-based polyurethane, itaconic acid acrylic diol, short-chain acrylate and silane coupling agent, and react at 65 to 78 °C under a nitrogen atmosphere for 2 to 4 hours to obtain it.

[0028] According to still another aspect of the present invention, a solvent-free bio-based photocurable material is provided. By mass, it includes the following components: 75 to 90 parts of the solvent-free bio-based photocurable prepolymer provided by the present invention, 10 to 25 parts of an active diluent, and 0.001 to 2 parts of a photoinitiator.

[0029] For the solvent-free bio-based photocurable material provided by the present invention, when in use, mix the solvent-free bio-based photocurable prepolymer, the active diluent, and the photoinitiator uniformly in proportion to obtain a mixture, and then coat the mixture and irradiate it under ultraviolet light. Among them, the wavelength of the ultraviolet light is 245 to 430 nm, the irradiation time is 1 to 5 min, and preferably, the wavelength of the ultraviolet light is 365 nm.

[0030] The solvent-free bio-based photocurable material provided by the present invention has the characteristics of high adhesive strength, high refractive index, fast curing speed, and good transparency. The photocurable film formed after photocuring has a high degree of crosslinking and mechanical properties, and can be applied to fields such as UV curable coatings, UV curable inks, and UV curable adhesives.

[0031] In some embodiments, the reactive diluent can be selected from at least one of dipropylene glycol diacrylate, 1,6-hexanediol diacrylate, glycidyl acrylate, and glycidyl methacrylate.

[0032] In some embodiments, the photoinitiator can be selected from at least one of 2-hydroxy-2-methyl-phenylpropanone-1, 1-hydroxy-cyclohexyl phenyl ketone, 2-hydroxy-2-methyl-p-hydroxyethyl ether phenyl propanone-1, 2-methyl-1-(4-methylthiophenyl)-2-morpholin-1-propanone, 2,4,6-trimethylbenzoyl-ethoxy-phenyl phosphine oxide, bis(2,4,6-trimethylbenzoyl)phenyl phosphine oxide, and 4-p-tolylthio benzophenone. Description of the Drawings

[0033] Figure 1 It is a schematic diagram of the synthesis route of castor oil-based polyurethane (CPU) in Example 1 of the present invention; in the figure, CO represents castor oil, and IPDI represents isophorone diisocyanate.

[0034] Figure 2 It is a schematic diagram of the synthesis route of itaconic acid acrylate diol (EIA) in Example 1 of the present invention; in the figure, IA represents itaconic acid, E10p represents glycidyl tert-carbonate, and DMEA represents N,N-dimethylethanolamine.

[0035] Figure 3 It is the infrared spectrogram of glycidyl tert-carbonate (E-10p), itaconic acid acrylate diol (EIA), castor oil (CO), castor oil-based polyurethane (CPU), the solvent-free bio-based photocurable prepolymer (ICPU) prepared in Example 1, and the solvent-free bio-based photocurable prepolymer (ECPU) prepared in Example 2.

[0036] Figure 4 It is the stress-strain diagram of the cured films (ECPU1-5) obtained by curing the solvent-free bio-based photocurable materials prepared in Examples 1-5 of the present invention.

[0037] Figure 5 It is the storage modulus ( E' ) and loss factor (tanδ) of the cured films (ECPU1-5) obtained by curing the solvent-free bio-based photocurable materials prepared in Examples 1-5 of the present invention as a function of temperature. Detailed Embodiments

[0038] The present invention will be further described in detail below in conjunction with the embodiments. The embodiments are only for explanation and do not limit the present invention in any way. Unless otherwise specified, the raw materials and reagents used in the embodiments are conventional products that can be obtained commercially; the experimental methods without specific conditions noted in the embodiments are usually carried out under the conventional conditions in the art or according to the conditions recommended by the manufacturers.

[0039] Example 1 Solvent-free Bio-based Photocurable Material

[0040] (1) Preparation of Castor Oil-based Polyurethane (CPU)

[0041] The schematic diagram of the synthesis route of the castor oil-based polyurethane in this example is as Figure 1 shown; its preparation method specifically includes the following steps:

[0042] Add 25.1 g of castor oil, 16.1 g of isophorone diisocyanate (purity 99%), 0.4 g of dibutyltin dilaurate, and 0.04 g of 4-methoxyphenol into a three-necked flask equipped with a thermometer, and stir at 70 °C under a nitrogen atmosphere for 3 h to obtain castor oil-based polyurethane.

[0043] Among them, the molar ratio of castor oil to isophorone diisocyanate is about 1:2.7, the addition amount of the catalyst dibutyltin dilaurate is 1% of the total mass of castor oil and isophorone diisocyanate, and the addition amount of the inhibitor 4-methoxyphenol is 0.1% of the total mass of castor oil and isophorone diisocyanate.

[0044] (2) Preparation of Itaconic Acid Acrylic Diol (EIA)

[0045] The schematic diagram of the synthesis route of the itaconic acid acrylic diol in this example is as Figure 2 shown; its preparation method specifically includes the following steps:

[0046] Add 13.4 g of itaconic acid, 45.6 (purity 99%) of tert-carbonic acid glycidyl ether, and 0.7 g of N,N-dimethylethanolamine into a three-necked flask equipped with a thermometer, and stir at 95 °C under a nitrogen atmosphere for 6 h to obtain itaconic acid acrylic diol.

[0047] Among them, the molar ratio of itaconic acid to tert-carbonic acid glycidyl ether is 1:2, and the addition amount of the catalyst N,N-dimethylethanolamine is about 1% of the total mass of itaconic acid and tert-carbonic acid glycidyl ether.

[0048] (3) Preparation of Solvent-free Bio-based Photocurable Prepolymer

[0049] Add 41.3 g of castor oil-based polyurethane, 27.0 g of itaconic acid acrylic diol, and 11.5 g of hydroxyethyl acrylate (purity 99%) into a three-necked flask equipped with a thermometer, and stir for 3 h at 70 °C under a nitrogen atmosphere to obtain a solvent-free bio-based photocurable prepolymer.

[0050] (4) Solvent-free bio-based photocurable material

[0051] Mix 16 g of the solvent-free bio-based photocurable prepolymer, 4 g of the reactive diluent dipropylene glycol triacrylate (purity 99%), and 0.2 g of the photoinitiator 2-hydroxy-2-methyl-1-phenylpropanone (purity 99%) evenly to obtain a solvent-free bio-based photocurable material.

[0052] Example 2 Solvent-free bio-based photocurable material

[0053] Different from Example 1, in the step of "(3) Preparation of solvent-free bio-based photocurable prepolymer", add 5.97 g of 3-aminopropyltriethoxysilane and mix and react with 41.3 g of castor oil-based polyurethane, 27.0 g of itaconic acid acrylic diol, and 11.5 g of hydroxyethyl acrylate; the remaining steps are the same as those in Example 1.

[0054] Example 3 Solvent-free bio-based photocurable material

[0055] Different from Example 1, in the step of "(3) Preparation of solvent-free bio-based photocurable prepolymer", add 8.96 g of 3-aminopropyltriethoxysilane and mix and react with 41.3 g of castor oil-based polyurethane, 27.0 g of itaconic acid acrylic diol, and 11.5 g of hydroxyethyl acrylate; the remaining steps are the same as those in Example 1.

[0056] Example 4 Solvent-free bio-based photocurable material

[0057] Different from Example 1, in the step of "(3) Preparation of solvent-free bio-based photocurable prepolymer", add 11.94 g of 3-aminopropyltriethoxysilane and mix and react with 41.3 g of castor oil-based polyurethane, 27.0 g of itaconic acid acrylic diol, and 11.5 g of hydroxyethyl acrylate; the remaining steps are the same as those in Example 1.

[0058] Example 5 Solvent-free bio-based photocurable material

[0059] Different from Example 1, in the step of " (3) Preparation of solvent-free bio-based photocurable prepolymer", 14.93 g of 3-aminopropyltriethoxysilane was further added and mixed with 41.3 g of castor oil-based polyurethane, 27.0 g of itaconic acid acrylate diol, and 11.5 g of hydroxyethyl acrylate for reaction; the remaining steps were the same as those in Example 1.

[0060] Test Example 1 Infrared Spectroscopy Test

[0061] Epoxy novolac glycidyl ether (E-10p), itaconic acid acrylate diol (EIA), castor oil (CO), castor oil-based polyurethane (CPU), solvent-free bio-based photocurable prepolymer without silane coupling agent prepared in Example 1 (ICPU), and solvent-free bio-based photocurable prepolymer prepared in Example 2 (ECPU) were subjected to infrared spectroscopy detection, and the results are as Figure 3 shown.

[0062] From Figure 3 the results, it can be seen that compared with the spectrum of E-10p, in the infrared spectrum of EIA synthesized by ring-opening reaction of E10p with IA, the characteristic absorption peak of the epoxy group belonging to 908 cm -1 disappeared, and at the same time, the characteristic absorption peak belonging to the hydroxyl group at 3494 cm -1 appeared, indicating that the ring-opening esterification of IA to E-10p was completed. Comparing the infrared spectrum of CO, in the spectrum of CPU, the infrared characteristic absorption peak of isocyanate group appeared at 2269 cm -1 , and at the same time, a new infrared characteristic absorption peak appeared at 3347 cm -1 , which belongs to the infrared characteristic peak of -N-H- stretching vibration in urethane, indicating that the reaction of CO with IPDI was completed. At the same time, comparing the infrared spectra of CO and CPU, the hydroxyl absorption peak disappeared at 3467 cm -1 , while the urethane characteristic peak of ICPU increased at 3347 cm -1 , and the stretching vibration absorption peak of C=O appeared at 1741 cm -1 and increased, and the characteristic peak of -NCO shrank, indicating that the isocyanate group of CPU and the hydroxyl group of EIA basically completed the reaction, that is, it can explain the successful synthesis of ICPU. In ECPU, the -NCO characteristic absorption peak of isocyanate completely disappeared, indicating that IPDI reacted completely with CO, EIA, and 3-aminopropyltriethoxysilane. These infrared characteristic peaks can explain the basic chemical structures of EIA, CPU, ICPU, and ECPU, indicating that the synthesis has been successful.

[0063] Test Example 2 Performance Test

[0064] 1. General Performance Test

[0065] The cured films (ECPU1-5) obtained after curing the solvent-free bio-based photocurable materials prepared in Examples 1-5 under 365 nm ultraviolet light irradiation were tested for pencil hardness, curing time, gel fraction, and acid and alkali resistance. The viscosity of the solvent-free bio-based photocurable materials prepared in Examples 1-5 was tested, and the test results are shown in Table 1.

[0066] (1) Pencil hardness test: The hardness of the cured film was tested according to the national standard GB / T6739-1996 method (where pencil hardness 6H is the hardest, 6B is the softest, and the hardness range is 6B-HB-6H). The pencil hardness tester uses the three-point contact method to measure the surface of the cured film (where two points are rollers and one point is the pencil lead). The angle between the pencil and the surface of the cured film is 45°. Use the pencil hardness tester to slide on the surface of the cured film with a force of 1 ± 0.05 kg, and observe the damage of the cured film. When no more than 2 damages occur in 5 tests, replace the hardness pencil with a larger grade for testing. When the damage of the cured film exceeds 2 times, the grade of this pencil can be read and the next grade of this grade can be recorded.

[0067] (2) Viscosity test: The shear rate-viscosity test was carried out on the solvent-free bio-based photocurable materials (uncured) prepared in Examples 1-5. The Anton Paar MCR502 modular intelligent advanced rheometer was used to test the uncured photocurable materials. The test standard was in accordance with GB / T2794-2013 "Determination of Viscosity of Adhesives", and the viscosity of the measured photocurable materials was recorded.

[0068] (3) Curing time: The curing time was timed from when the ultraviolet lamp was turned on and stopped when the surface of the photocurable material was dry, and the curing time was recorded.

[0069] (4) Acid and alkali resistance test: A certain mass of the cured film was immersed in 10% hydrochloric acid and 10% sodium hydroxide for 48 hours, dried and weighed, and the change in mass before and after immersion was observed, and the performance results of the cured film were recorded.

[0070] (5) Gel fraction test: The gel content in the cured film was determined by the acetone extraction method. At room temperature, accurately weigh a cured film with a mass of w0 and immerse it in a sealed glass bottle containing 20 mL of acetone for 48 h, then take out the cured film and place it in a vacuum oven at 60 °C to dry to a constant weight. The mass of the cured film after drying was denoted as w1, and the gel fraction of the cured film could be calculated according to the formula.

[0071] Gel fraction = (w1 / w0) × 100%

[0072] Among them, w1 represents the mass (mg) of the photocured film after drying, and w0 represents the mass (mg) of the photocured film before immersion in acetone.

[0073] Table 1 General performance test results

[0074]

[0075] As can be seen from the results in Table 1, the surfaces of all samples were completely cured after 5 minutes of curing, indicating a very fast curing speed. At the same time, all the cured films showed no changes after being immersed in acid and alkali solutions for 48 hours, indicating that the cured films had good acid and alkali resistance. This was attributed to the silane coupling agent and the multiple branched chains and abundant methoxy groups contained in EIA, which could form a dense cross-linked network on the surface of the cured film to prevent the penetration of polar substances into the photocured film, thus endowing the photocured film with good chemical erosion resistance. With the increase in the proportion of silane coupling agent KH-550, the pencil hardness of the cured material decreased. The reason was that the flexible long chains contained in the added KH-550 and the flexible long chains inherent in EIA helped to increase the flexibility of the cured film. The gel fraction reflected the solvent resistance of the UV cured film. The gradual decrease in the gel fraction might be because too much silane coupling agent was added, resulting in too many cross-linking points and too high a cross-linking degree, leading to a decrease in the double bond activity on the surface.

[0076] 2. Mechanical property testing

[0077] The cured films (ECPU1 - 5) obtained by curing the solvent-free bio-based photocurable materials prepared in Examples 1 - 5 under 365 nm ultraviolet light irradiation for 5 minutes were subjected to mechanical property testing. The tensile property testing of the photocured films was carried out using a UTM5000 electronic universal testing machine. The crosshead speed was 10 mm / min, and the sample size was 20mm×10mm×0.5mm. The results are as Figure 4 shown.

[0078] From Figure 4 it can be seen that ECPU1 had the highest tensile strength, which was 30.31 MPa. With the increase in the addition amount of the silane coupling agent, the tensile strength decreased while the elongation at break increased. This was because the -Si-O-C2H5 groups of KH-550 formed a large number of Si-O-Si flexible structures after hydrolysis and condensation, enhancing the flexibility of the cured film. However, at the same time, due to the formation of a large number of cross-linking sites on the surface by the silane coupling agent, the film-forming property of the prepolymer decreased, resulting in a decrease in mechanical properties and a reduction in tensile strength.

[0079] 3. Dynamic thermomechanical analysis

[0080] The cured films (ECPU1 - 5) obtained by curing the solvent-free bio-based photocurable materials prepared in Examples 1 - 5 under 365 nm ultraviolet light irradiation for 5 minutes were subjected to storage modulus measurement ( E') and the test of loss factor (tanδ), the dynamic thermomechanical analysis (DMA) test instrument uses the DMA242C dynamic mechanical analyzer of Netzsch Company in Germany. The sample holder uses a tensile holder, the oscillation frequency is 1 Hz, the sample size is 20 mm×6 mm×0.5 mm, the heating rate is 3℃ / min, and the temperature range is -50~150℃. The crosslinking density is calculated according to the rubber elasticity dynamics theory v e , as shown in the following formula, where E’ is the storage modulus at T g + 30℃, R is the gas constant, T is the absolute temperature of the photocurable material at T g + 30℃:

[0081]

[0082] The results are as Figure 5 shown in Table 2, where the loss factor (tanδ) is the same as the glass transition temperature value T g . With the increase of the silane coupling agent, the flexible chain Si-O-Si in it increases, resulting in a decrease in the glass transition temperature. At the same time, the chain-chain interaction of the long-chain fatty acid leads to the relative migration of the network. The combination of these properties leads to a looser network, thus showing additional fluidity and finally reducing T g .

[0083] Table 2 Test results of storage modulus and glass transition temperature

[0084]

[0085] 4. Adhesion performance test

[0086] The cured films obtained by curing the solvent-free bio-based photocurable materials prepared in Examples 1 to 5 under 365 nm ultraviolet light irradiation for 5 min were subjected to shear strength tests on different substrates according to the national standard GB / T 7124-2008 "Determination of Tensile Shear Strength of Adhesives (Rigid Material to Rigid Material)". The results are shown in Table 3.

[0087] Table 3 Shear strength of photocured films on different substrates

[0088]

[0089] As can be seen from the results in Table 3, the photocured film of the solvent-free bio-based photocuring material provided by the present invention has a strong shear strength on the PVC-aluminum plate. With the increase in the addition amount of the silane coupling agent, the shear strength on the PVC-aluminum plate and the glass-glass increases significantly. On the PVC-aluminum plate, the shear strength of Example 3 is the strongest. This is mainly because the silane coupling agent contains methoxy groups that can react with the hydroxyl groups on the substrate surface, and the other end of the isocyanate also contains various organic functional groups, including epoxy groups, amino groups, and hydroxyl groups, etc., which can enhance the adhesion and adhesion to different substrates. The increase in the addition amount of the silane coupling agent makes the -Si-O-C2H5 groups form a Si-O-Si structure after hydrolysis and condensation, and at the same time, the hydrogen bond force in the system is enhanced, thereby improving the shear strength. However, at the same time, the excessive Si-O-Si flexible long-chain structure on the surface leads to too many connection sites on the surface of the photocured film, resulting in a subsequent decrease in the shear strength.

[0090] 5. Optical property testing

[0091] The haze of the photocured films obtained by curing the solvent-free bio-based photocuring materials prepared in Examples 1 to 5 under 365 nm ultraviolet light irradiation for 5 minutes was tested according to the standard GB / T 2410-2008 "Determination of Transmittance and Haze of Transparent Plastics". The haze test was carried out using the TH-100 instrument of Hangzhou Caipu Technology Co., Ltd. The film was closely attached to the test area for testing. Each sample was tested three times repeatedly, and the average value was taken as the haze value result. According to the standard GB / T 7962.1-1987 "Test Methods for Colorless Optical Glass, Test Methods for Refractive Index and Dispersion Coefficient", an Abbe refractometer was used to measure the refractive index of the photocured film. The samples were tested 3 times on average, and the average value was taken as the final result. The test results are shown in Table 4.

[0092] Table 4 Haze and refractive index testing of photocured films

[0093]

[0094] As can be seen from the results in Table 4, with the addition of the silane coupling agent, the haze of the photocured film can be well reduced, from 48.17% to 5.40%. Example 3 has the lowest haze of 5.40%. The refractive index decreases from 1.4786 to 1.4776, indicating that the addition of KH-550 has little effect on the refractive index of the photocured film. The good optical properties enable the ECPU photocured film to have a relatively wide application scenario in the fields of optical devices, coatings, etc.

[0095] The above are only some embodiments of the present invention. For those of ordinary skill in the art, without departing from the inventive 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 solvent-free bio-based photocurable prepolymer, characterized in that: The raw materials for its preparation include, by weight: 40-55 parts of castor oil-based polyurethane, 25-35 parts of itaconic acid acrylic acid diol, 10-20 parts of short-chain acrylate, and 0-20 parts of silane coupling agent; The short-chain acrylate is selected from at least one of methyl methacrylate, hydroxyethyl methacrylate, and hydroxyethyl acrylate; The preparation method of the castor oil-based polyurethane comprises the following steps: Mix castor oil, isocyanate, the first catalyst and the polymerization inhibitor, and react at 65-78° C. in a nitrogen atmosphere for 2-4 hours to obtain; The molar ratio of castor oil to isocyanate is 1:(2.7-3); the amount of the first catalyst is 0.01-2% of the total weight of castor oil and isocyanate; the amount of the inhibitor is 0.001-1% of the total weight of castor oil and isocyanate; The preparation method of itaconic acid acrylic acid diol comprises the following steps: Itaconic acid, an epoxy compound and a second catalyst are mixed, and reacted at 75-100° C. in a nitrogen atmosphere for 2-6 hours to obtain; Wherein, the molar ratio of itaconic acid to the epoxy compound is 1:(1-2.5); the amount of the second catalyst is 0.5-2% of the total weight of itaconic acid and the epoxy compound; The epoxy compound is selected from at least one of epoxy resin, diglycidyl ether, methyl glycidyl ether and tert-butyl glycidyl ester.

2. The solvent-free bio-based photocurable prepolymer according to claim 1, characterized in that: The silane coupling agent is selected from at least one of 3-aminopropyltriethoxysilane, γ-glycidyloxypropyltrimethoxysilane and methacryloxy functional silane.

3. The solvent-free bio-based photocurable prepolymer according to claim 2, characterized in that: The isocyanate is selected from at least one of isophorone diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, and toluene diisocyanate; the first catalyst is selected from at least one of dibutyltin dilaurate, organic bismuth, N,N-dimethylcyclohexylamine, N,N'-dimethylpyridine, and triethanolamine; and the inhibitor is selected from at least one of hydroquinone, 4-methoxyphenol, 2,5-di-tert-butyl-p-cresol, and tert-butylhydroquinone.

4. The solvent-free bio-based photocurable prepolymer according to claim 1, characterized in that: The second catalyst is selected from at least one of N,N-dimethylethanolamine, N,N-dimethylbenzylamine, triethylamine, tetrabutylammonium bromide and triphenylphosphine.

5. The method for preparing a solvent-free bio-based photocurable prepolymer according to any one of claims 1 to 4, characterized in that: The steps include: The castor oil-based polyurethane, itaconic acid acrylic acid diol, short-chain acrylate and silane coupling agent are mixed, and reacted at 65-78° C. in a nitrogen atmosphere for 2-4 hours to obtain the product.

6. Use of the solvent-free bio-based photocurable prepolymer according to any one of claims 1 to 4 in the fields of coatings, inks, adhesives, plastics, fibers or composite materials.

7. A solvent-free bio-based photocurable material, characterized in that: The composition comprises the following components by weight: 75-90 parts of the solvent-free bio-based photocurable prepolymer according to any one of claims 1 to 4, 10-25 parts of a reactive diluent and 0.001-2 parts of a photoinitiator.

8. The solvent-free bio-based photocurable material according to claim 7, characterized in that: The active diluent is selected from at least one of tripropylene glycol diacrylate, 1,6-hexanediol diacrylate, glycidyl acrylate and glycidyl methacrylate; the photoinitiator is selected from at least one of 2-hydroxy-2-methyl-1-phenyl-1-propanone, 1-hydroxy-cyclohexyl benzophenone, 2-hydroxy-2-methyl-p-hydroxyethyl ether phenyl acetone, 2-methyl-1-(4-methylthiophenyl)-2-morpholinyl-1-propanone, 2,4,6-trimethylbenzoyl-ethoxy-phenyl phosphine oxide, bis(2,4,6-trimethylbenzoyl)phenyl phosphine oxide and 4-p-toluene mercaptobenzophenone.

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