A synthesis process of low-refractive-index polysiloxane resin

Abstract

The present application relates to the technical field of optical resins, and specifically discloses a process for synthesizing a low-refractive-index polysiloxane resin. The synthesis process uses amino-di-terminated polydimethylsiloxane and isocyanate as the main raw materials. Amino-di-terminated polydimethylsiloxane and isocyanate are added in a molar ratio of 1:(1-2) and reacted under an inert gas atmosphere to obtain a low-refractive-index polysiloxane resin. The present application can directly react to obtain the target product in a solvent-free state. The refractive index of the target product is controlled at 1.41-1.44, and the elongation at break can reach 200-400%, with excellent elasticity. The target product can be directly melt-extruded, which is greener and more environmentally friendly than the solvent method. The target product is more suitable for the production of elastomeric multilayer optical films.

Description

Technical Field

[0001] The present application relates to the technical field of optical resins, and more specifically, to a synthesis process of low-refractive-index polysiloxane resins. Background Art

[0002] Multilayer polymer optical films offer high reflectivity, high transmittance, and lightweight properties, making them widely applicable in liquid crystal displays, solar cells, lasers, and other fields. These films utilize the principle of optical interference, alternating layers of materials with different refractive indices through a dispenser according to a predetermined design. This method suppresses reflected light and enhances transmitted light, resulting in optical films with enhanced transparency and color reproduction.

[0003] By increasing the refractive index difference between two adjacent layers of the resin material in an optical film, the film's optical power, thickness, and reflection bandwidth can be improved. However, currently, the low-refractive-index materials used in optical films are primarily polymethyl methacrylate (refractive index 1.49) and polyethylene (refractive index 1.50). While the development of low-refractive-index materials is of great value, the refractive index of resin materials still needs to be lowered.

[0004] Due to the physical and chemical properties of the siloxane bond, polysiloxane elastomers have good UV resistance and oxidation stability. At present, the industry's research on improving the refractive index of polysiloxane elastomers is as follows:

[0005] Patent application number CN201780034603.5 modifies a polysiloxane elastomer with a fluorinated monomer, using a silane monomer containing a chlorosilane functional group, a silane monomer containing at least one fluoroalkyl group, a silane monomer containing a (meth)acryloyl functional group, an ether monomer, and a silicone resin as the main reaction raw materials to synthesize a highly fluorinated silicone resin. Although the refractive index of this resin can be reduced to below 1.4, the resin is expensive, and the increased degree of fluorination affects its compatibility with other resins, making it prone to weak interfacial bonding during co-extrusion.

[0006] Patent application number CN202211647789.0 modifies hydroxyalkylsilane monomers and polysiloxane in an organic solvent. This resin can be applied to a substrate surface using various methods, including roller coating, dip coating, and inkjet coating, and then cured by thermal curing. This resin requires an organic solvent for use, and currently no method has been demonstrated to enable lamination and extrusion with other resins. Even if extrusion were possible, the organic solvent would need to be removed before subsequent lamination and distribution steps could be performed.

[0007] Based on the above situation, the current modification and preparation methods for low-refractive-index polysiloxane elastomers all need to be carried out in the presence of organic solvents, and the products produced need to undergo post-processing before melt co-extrusion. Summary of the Invention

[0008] In order to solve the problem that organic solvents are required for the modification of existing polysiloxane resins, the present application provides a low-refractive-index polysiloxane resin synthesis process, which can synthesize low-refractive-index resins in one step without solvent, and the resin particles can be directly used in the production of elastomeric multilayer optical films.

[0009] The present application provides a low refractive index polysiloxane resin synthesis process, which adopts the following technical solution:

[0010] A low-refractive-index polysiloxane resin comprises the following steps:

[0011] Amino di-terminated polydimethylsiloxane and isocyanate are used as main raw materials, the amino di-terminated polydimethylsiloxane and isocyanate are added in a molar ratio of 1:(1-2), and react under an inert gas atmosphere to obtain a low-refractive-index polysiloxane resin.

[0012] Furthermore, the amino double-terminated polydimethylsiloxane is aminopropyl double-terminated polydimethylsiloxane.

[0013] Furthermore, the weight average molecular weight of the aminopropyl double-terminated polydimethylsiloxane is 2,000 to 10,000.

[0014] Furthermore, the weight average molecular weight of the aminopropyl dicapped polydimethylsiloxane is 5000.

[0015] Furthermore, the isocyanate is one or more of hexamethylene diisocyanate, isophorone diisocyanate, 4,4'-dicyclohexylmethane diisocyanate, 4,4'-diphenylmethane diisocyanate, phenyl isocyanate, and 4,4',4"-triphenylmethane triisocyanate.

[0016] Furthermore, the isocyanate is diisocyanate.

[0017] Furthermore, the diisocyanate is 4,4'-dicyclohexylmethane diisocyanate.

[0018] Furthermore, the amino di-terminated polydimethylsiloxane and isocyanate are reacted in a molar ratio of 1:1.

[0019] Furthermore, the reaction temperature under the inert gas atmosphere is 0-210° C., and the insulation reaction time is 2-4 hours.

[0020] Furthermore, the reaction temperature under the inert gas atmosphere is 170-210° C., and the insulation reaction time is 2-4 hours.

[0021] Furthermore, the inert gas is nitrogen or argon.

[0022] Furthermore, after the reaction is completed, the reaction product is dried at 80-95° C. for 2-6 hours.

[0023] By adopting the above technical solution, this application has at least the following advantages:

[0024] First, in terms of process, the present application uses aminopropyl diblocked polydimethylsiloxane and isocyanate as the main raw materials, directly adds isocyanate dropwise into the aminopropyl diblocked polydimethylsiloxane, and directly reacts under the protection of inert gas. After drying, the reaction product can be directly put into the extruder for melt extrusion, without the need to remove a large amount of organic solvent, saving energy consumption for solvent treatment, and the synthesis process is simple, the reaction temperature range is wide, the operation is controllable, and it is green and environmentally friendly.

[0025] Second, in terms of product performance, the target product obtained in this application has been tested with an Abbe refractometer (25°C) and a prism coupler (636nm). The test results show that the refractive index of the product is 1.41 to 1.44, which is a low refractive index. After mechanical property testing, the elongation at break of the product can reach 200 to 400%, and it has excellent elasticity.

[0026] Third, in-depth research into the process of this application revealed that the weight-average molecular weight of aminopropyl dicapped polydimethylsiloxane significantly influences the refractive index and elongation at break of the resin. Within a specific weight-average molecular weight range, a resin with a refractive index ≤ 1.4250 and an elongation at break ≥ 390% can be obtained. The functionality of the isocyanate also has a certain influence on the refractive index and elongation at break of the resin. The reaction of diisocyanate with aminopropyl polydimethylsiloxane yields a resin that balances a decrease in refractive index with an increase in elongation at break. DETAILED DESCRIPTION

[0027] This application is further described in conjunction with the following examples, comparative examples and test data.

[0028] Aminopropyl double-terminated polydimethylsiloxane: a customized product with a weight-average molecular weight of 2000-10000;

[0029] Hexamethylene diisocyanate, purity ≥98%;

[0030] Isophorone diisocyanate, purity ≥98%;

[0031] 4,4'-Dicyclohexylmethane diisocyanate, purity ≥98%;

[0032] 4,4'-diphenylmethane diisocyanate, purity ≥98%;

[0033] Phenyl isocyanate, purity ≥98%;

[0034] 4,4',4"-Triphenylmethane triisocyanate, purity ≥98%.

[0035] Example 1

[0036] A low-refractive-index polysiloxane resin synthesis process is carried out according to the following steps:

[0037] Weigh 50.06 g of aminopropyl di-terminated polydimethylsiloxane with a weight-average molecular weight of 5000 into a three-necked flask, and slowly add 2.62 g of 4,4'-dicyclohexylmethane diisocyanate dropwise while introducing nitrogen. After the addition is complete, heat to 170°C under a nitrogen atmosphere and continue stirring at 200 rpm for 4 hours. After pouring out, dry at 95°C for 4 hours to obtain the target product.

[0038] Example 2

[0039] A low-refractive-index polysiloxane resin synthesis process is carried out according to the following steps:

[0040] Weigh 20.02 g of aminopropyl di-terminated polydimethylsiloxane with a weight-average molecular weight of 2000 into a three-necked flask, and slowly add 2.62 g of 4,4'-dicyclohexylmethane diisocyanate dropwise while introducing nitrogen. After the addition is complete, heat to 170°C under a nitrogen atmosphere and continue stirring at 200 rpm for 4 h. After pouring out, dry at 95°C for 4 h to obtain the target product.

[0041] Example 3

[0042] A low-refractive-index polysiloxane resin synthesis process is carried out according to the following steps:

[0043] 100.11 g of aminopropyl di-terminated polydimethylsiloxane with a weight-average molecular weight of 10,000 was weighed into a three-necked flask, and 2.62 g of 4,4'-dicyclohexylmethane diisocyanate was slowly added dropwise while introducing nitrogen. After the addition was complete, the temperature was raised to 170°C under a nitrogen atmosphere and the mixture was stirred at 200 rpm for 4 h. After pouring out, the mixture was dried at 95°C for 4 h to obtain the target product.

[0044] The difference between Examples 1-3 is that the weight average molecular weights of the aminopropyl diblocked polydimethylsiloxanes are different. The three aminopropyl diblocked polydimethylsiloxanes with different weight average molecular weights were reacted with 4,4'-dicyclohexylmethane diisocyanate at a molar ratio of 1:1. The target products were tested using an Abbe refractometer (25°C) and a prism coupler (636nm). The test results are as follows:

[0045]

[0046] The test results show that: first, the test results of the Abbe refractometer and the prism coupler are not much different, indicating that the refractive index measurement value of the target product is accurate; second, the overall refractive index of the resin is low, and as the weight-average molecular weight of aminopropyl dimethylsiloxane increases, the refractive index of the resin tends to decrease; third, as the weight-average molecular weight of aminopropyl dimethylsiloxane increases, the elongation at break of the resin tends to first increase and then decrease. When the weight-average molecular weight of aminopropyl dimethylsiloxane is 5000, the elongation at break reaches more than 390%.

[0047] Example 4

[0048] A low-refractive-index polysiloxane resin synthesis process is carried out according to the following steps:

[0049] 50.04 g of aminopropyl di-terminated polydimethylsiloxane (weight-average molecular weight 5000) was weighed into a three-necked flask. 1.19 g of phenyl isocyanate was slowly added dropwise while purging with nitrogen. After the addition was complete, the mixture was heated to 170°C under a nitrogen atmosphere and stirred at 200 rpm for 4 h. After decanting, the mixture was dried at 95°C for 4 h to obtain the desired product.

[0050] Example 5

[0051] A low-refractive-index polysiloxane resin synthesis process is carried out according to the following steps:

[0052] Weigh 50.31 g of aminopropyl di-terminated polydimethylsiloxane with a weight-average molecular weight of 5000 into a three-necked flask, and slowly add 3.67 g of 4,4',4"-triphenylmethane triisocyanate dropwise while introducing nitrogen. After the addition is complete, heat to 170°C under a nitrogen atmosphere and continue stirring at 200 rpm for 4 hours. After pouring out, dry at 95°C for 4 hours to obtain the target product.

[0053] Examples 1, 4-5 are compared in a single manner. The difference lies in the different functionalities of the isocyanates. The three isocyanates with different functionalities were reacted with aminopropyl di-terminated polydimethylsiloxane at a molar ratio of 1:1. The target products were tested using an Abbe refractometer (25°C) and a prism coupler (636nm). The test results are as follows:

[0054]

[0055] The test results show that: first, as the number of isocyanate groups increases, the functionality increases and the refractive index of the resin increases; second, as the functionality of the isocyanate increases, the elongation at break of the resin shows a trend of first increasing and then decreasing.

[0056] Example 6

[0057] A low-refractive-index polysiloxane resin synthesis process is carried out according to the following steps:

[0058] 50.05 g of aminopropyl di-terminated polydimethylsiloxane (weight-average molecular weight 5000) was weighed into a three-necked flask. 1.68 g of hexamethylene diisocyanate was slowly added dropwise while purging with nitrogen. After the addition, the mixture was heated to 170°C under a nitrogen atmosphere and stirred at 200 rpm for 4 h. After decanting, the mixture was dried at 95°C for 4 h to obtain the desired product.

[0059] Example 7

[0060] A low-refractive-index polysiloxane resin synthesis process is carried out according to the following steps:

[0061] 50.12 g of aminopropyl di-terminated polydimethylsiloxane (weight-average molecular weight 5000) was weighed into a three-necked flask. 2.23 g of isophorone diisocyanate was slowly added dropwise while purging with nitrogen. After the addition was complete, the mixture was heated to 170°C under a nitrogen atmosphere and stirred at 200 rpm for 4 h. After decanting, the mixture was dried at 95°C for 4 h to obtain the desired product.

[0062] Example 8

[0063] A low-refractive-index polysiloxane resin synthesis process is carried out according to the following steps:

[0064] Weigh 50.08 g of aminopropyl di-terminated polydimethylsiloxane with a weight-average molecular weight of 5000 into a three-necked flask, slowly add 2.50 g of 4,4'-diphenylmethane diisocyanate dropwise while introducing nitrogen. After the addition is complete, heat to 170°C under a nitrogen atmosphere and continue stirring at 200 rpm for 4 h. After pouring out, dry at 95°C for 4 h to obtain the target product.

[0065] Examples 1 and 6-8 are compared in a single manner. The difference lies in the different types of diisocyanates, their structures and molecular weights. The four different types of diisocyanates were reacted with aminopropyl di-terminated polydimethylsiloxane at a molar ratio of 1:1. The target products were tested using an Abbe refractometer (25°C) and a prism coupler (636nm). The test results are as follows:

[0066]

[0067] The test results show that: First, the structure of the isocyanate group affects the refractive index of the resin. The introduction of groups such as methylene and methyl groups helps to reduce the refractive index of the resin. At the same time, the molecular weight and segment structure also have different effects on the refractive index of the resin. Second, as the molecular weight of the diisocyanate gradually increases, the elongation at break of the resin also gradually increases. Taking all factors into consideration, the reaction of 4,4'-dicyclohexylmethane diisocyanate with aminopropyl diblocked polydimethylsiloxane can not only reduce the refractive index of the resin, but also significantly improve the elongation at break of the resin.

[0068] Example 9

[0069] A low-refractive-index polysiloxane resin synthesis process is carried out according to the following steps:

[0070] 50.08 g of aminopropyl di-terminated polydimethylsiloxane (weight-average molecular weight 5000) was weighed into a three-necked flask. 3.36 g of hexamethylene diisocyanate was slowly added dropwise while purging with nitrogen. After the addition was complete, the mixture was heated to 170°C under a nitrogen atmosphere and stirred at 200 rpm for 4 h. After decanting, the mixture was dried at 80°C for 6 h to obtain the desired product.

[0071] Example 6 and Example 9 form a single comparison, and the difference is only the molar ratio. The molar ratio in Example 6 is 1:1, and the molar ratio in Example 9 is 1:2. The target product was tested by Abbe refractometer (25°C) and prism coupling instrument (636nm), and the test results are as follows:

[0072]

[0073] The test results show that an increase in the molar ratio will simultaneously increase the resin's refractive index and elongation at break.

[0074] Examples 10-12

[0075] A low-refractive-index polysiloxane resin synthesis process differs from Example 1 in that the reaction temperature and other related parameters are different, as follows:

[0076]

[0077] The target product was tested by Abbe refractometer (25℃) and prism coupler (636nm), and the test results are as follows:

[0078]

[0079] The test results show that the change of reaction temperature has little effect on the refractive index of the resin. The higher the reaction temperature, the more complete the reaction between the raw materials, which has a positive effect on improving the elongation at break of the resin.

[0080] Comparative Example 1

[0081] A low-refractive-index polysiloxane resin synthesis process is carried out according to the following steps:

[0082] Weigh 50.03 g of aminopropyl di-terminated polydimethylsiloxane with a weight-average molecular weight of 5000 into a three-necked flask, add 50.13 g of tetrahydrofuran, and stir. Separately, weigh 2.62 g of 4,4'-dicyclohexylmethane diisocyanate, dissolve it in 2.62 g of tetrahydrofuran, and slowly add dropwise to the three-necked flask. React at 25°C for 6 h, pour out, and dry at 95°C for 48 h to obtain the target product.

[0083] The target product was tested by Abbe refractometer (25℃) and prism coupler (636nm), and the test results are as follows:

[0084]

[0085] The test results show that: First, the solvent method used in Comparative Example 1, where the weight ratio of the reactants to the tetrahydrofuran solvent exceeds 1:1, results in a longer reaction time for the resin synthesized by this method, and the subsequent solvent treatment time is multiplied. The dried target product also requires further heating or vacuum treatment to prevent residual solvent from volatilizing after melt extrusion, which could lead to unstable performance of the extruded optical film. Second, the solvent-free reaction significantly improves the elongation at break of the resin.

[0086] Practical Application:

[0087] The resin particles obtained in Example 1 and the extruded polyester TPU (model Covestro 88375A) were melted, passed through a melt metering pump and a filter screen, and then transferred to a designed multi-layer feed block. The resin particles obtained in Example 1 formed film layer I, and the extruded polyester TPU formed film layer II. Film layer I and film layer II were alternately laminated according to the designed optical thickness. The laminated film was biaxially stretched to obtain an optical film 1.

[0088] The resin particles obtained in Comparative Example 1 and the extruded polyester TPU (model Covestro 88375A) were melted, passed through a melt metering pump and a filter screen, and then transferred to a designed multi-layer feed block. The resin particles obtained in Comparative Example 1 formed film layer I, and the extruded polyester TPU formed film layer II. Film layer I and film layer II were alternately laminated according to the designed optical thickness. The laminated film was biaxially stretched to obtain optical film 2.

[0089] Optical Film 1 and Optical Film 2 have the same number of laminated layers, the same single-layer optical thickness, the same stacking order, and the same process parameters such as biaxial stretching. The visible light transmittance and near-infrared reflectivity of the optical films were measured using a solar film tester LS162; the haze of the optical films was measured using a haze meter; and the tensile strength and elongation at break of the optical films were measured using a universal testing machine. The test results are as follows:

[0090]

[0091] According to the above test results, it can be seen that the optical film 1 has low haze and high visible light transmittance, and the optical properties of the optical film 1 are excellent; at the same time, the optical film 1 has high tensile strength and high elongation at break, and the mechanical properties of the optical film 1 are also more excellent.

[0092] The technical features of the above-mentioned embodiments can be combined arbitrarily. In order to make the description concise, not all possible combinations of the technical features in the above-mentioned embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0093] Furthermore, the above-described embodiments merely represent several implementation methods of the present invention, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the patent. It should be noted that a person of ordinary skill in the art can make a number of variations and improvements without departing from the concept of the present invention, and these variations and improvements fall within the scope of protection of the present invention. Therefore, the scope of protection of the patent for this invention shall be based on the appended claims.

Claims

1. A process for synthesizing a low-refractive-index polysiloxane resin, characterized in that: The method comprises the following steps: under solvent-free conditions, using amino diblocked polydimethylsiloxane and 4,4'-dicyclohexylmethane diisocyanate as main raw materials, adding the amino diblocked polydimethylsiloxane and 4,4'-dicyclohexylmethane diisocyanate in a molar ratio of 1:(1-2), reacting in an inert gas atmosphere to obtain a low-refractive index polysiloxane resin; wherein the amino diblocked polydimethylsiloxane is aminopropyl diblocked polydimethylsiloxane, and the weight-average molecular weight of the aminopropyl diblocked polydimethylsiloxane is 5000-10000; the reaction temperature in the inert gas atmosphere is 170-210° C., and the heat preservation reaction time is 2-4 hours; after the reaction is completed, drying the reaction product at 80-95° C. for 2-6 hours.

2. A process for synthesizing a low-refractive-index polysiloxane resin according to claim 1, characterized in that: The weight average molecular weight of the aminopropyl double-terminated polydimethylsiloxane is 5000.

3. A process for synthesizing a low-refractive-index polysiloxane resin according to claim 1, characterized in that: The amino diblocked polydimethylsiloxane and isocyanate react in a molar ratio of 1:1.

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