Pressurized solvent polymerization preparation method of high-solid-content polyvinyl chloride resin

Abstract

The invention relates to a pressurized solvent polymerization preparation method of high-solid-content polyvinyl chloride resin, and belongs to the technical field of polymer synthesis. The method comprises the following steps: mixing a vinyl chloride monomer, a mixed solvent, a composite initiator, a stabilizer and a molecular weight regulator to obtain a polymerization reaction solution; putting the reaction liquid into a polymerization kettle, pressurizing to 0.5-1.5 MPa, heating to 45-65 DEG C in stages, carrying out polymerization reaction for 4-6 hours, and then adding a terminating agent to terminate the reaction; and performing pressure relief, centrifugal separation, washing and drying on the reaction product to obtain the high-solid-content polyvinyl chloride resin. Through the synergistic effect of pressurization strengthening, mixed solvent compounding and composite initiator synergy, the monomer solubility and the polymerization efficiency are remarkably improved, and high-solid-content polymerization is achieved. The prepared polyvinyl chloride resin has excellent mechanical properties and thermal stability, the process is simple, the solvent can be recycled, and the method is suitable for industrial production.

Description

Technical Field

[0001] This invention relates to the field of polymer synthesis technology, and in particular to a method for preparing high-solids-content polyvinyl chloride resin by pressure solvent polymerization. Background Technology

[0002] Polyvinyl chloride (PVC) resin is one of the world's largest-produced general-purpose plastics, widely used in building materials, pipes, wires and cables, packaging materials, and other fields. Traditional PVC production processes mainly include suspension polymerization, emulsion polymerization, bulk polymerization, and solvent polymerization. Among these, suspension polymerization accounts for 80-85% of global production capacity due to its simplicity and low cost. However, the PVC resin produced by this method has a low solids content, typically only 40-50%, requiring significant energy for subsequent drying, increasing production costs and energy consumption. Furthermore, the product has uneven particle morphology and a wide molecular weight distribution, affecting subsequent processing performance.

[0003] Solvent polymerization, as an important polymerization method, has the advantages of a uniform polymerization system, good heat transfer, and the ability to effectively control the molecular weight distribution of the product, producing PVC resins with high purity and stable performance. However, conventional solution polymerization is mostly carried out under normal pressure, which has obvious drawbacks: the solubility of vinyl chloride monomer in conventional solvents is limited, making it difficult to increase the solid content of the polymerization system, usually not exceeding 60%; at the same time, the polymerization reaction rate is slow under normal pressure, the polymerization time is long, the production efficiency is low, and the viscosity of the system tends to increase during the polymerization process, further exacerbating the difficulty of heat transfer, leading to problems such as cross-linking and degradation of the product, affecting the mechanical properties and heat resistance stability of the resin.

[0004] Furthermore, existing studies have shown that pressure has a significant impact on vinyl chloride polymerization. Increased pressure can improve the solubility of vinyl chloride monomers and affect the kinetics of the polymerization reaction, thereby increasing the polymerization rate and the molecular weight of the product. However, how to combine pressurization technology with solvent polymerization, optimize process parameters, and achieve stable preparation of high-solids-content, high-performance polyvinyl chloride resins while taking into account process feasibility and industrialization costs is a technical problem that urgently needs to be solved in this field. Summary of the Invention

[0005] The purpose of this invention is to address the shortcomings of existing technologies by proposing a method for preparing high-solids-content polyvinyl chloride resin by pressure solvent polymerization.

[0006] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a method for preparing high-solids-content polyvinyl chloride resin by pressure solvent polymerization, comprising the following steps: S1. Ingredients: Mix 100 parts vinyl chloride monomer, 70-90 parts mixed solvent, 0.02-0.3 parts composite initiator, 0.2-0.5 parts stabilizer and 0.01-0.05 parts molecular weight regulator and stir for 10-20 minutes at a stirring speed of 200-350 r / min to obtain polymerization reaction solution; S2. Pressure Polymerization: Add the polymerization reaction solution obtained in S1 to the polymerization reactor. After sealing the reactor, purge the air with nitrogen 3-5 times (monitor the oxygen content in real time using an online oxygen content detector, and the oxygen content should be ≤0.5% after each purging). Then pressurize to 0.5-1.5MPa, turn on the stirring device, control the stirring speed at 200-350r / min, and raise the temperature in stages to 45-65℃ at a rate of 3-5℃ / min. Maintain constant temperature and pressure for 4-6 hours for the polymerization reaction. Add 0.01-0.03 parts (based on the mass of vinyl chloride monomer) of terminator to the polymerization reactor, maintain the stirring speed at 200-350r / min, and stir for 5-10 minutes to ensure that the terminator is evenly dispersed and completely terminates the polymerization reaction. S3. Post-processing: After the polymerization reaction is completed, stop stirring and heating, and slowly depressurize to atmospheric pressure (the depressurization rate is controlled at 0.05-0.1 MPa / min to avoid excessive depressurization causing resin particle breakage). Discharge the reaction product to the separation equipment at a speed of 3000-5000 r / min for 15-30 min. Remove unreacted monomers and mixed solvents by centrifugation. The unreacted monomers and mixed solvents are separated using a closed distillation column. The tail gas is treated by activated carbon adsorption and condensation recovery before being discharged, which can reduce raw material costs, reduce environmental pollution, and meet the requirements of green chemical development. Then wash with deionized water 3-5 times, each time for 8-12 min, to remove residual initiators, stabilizers and other impurities. Finally, dry at 80-100℃ for 2-4 h to obtain high solids content polyvinyl chloride resin.

[0007] Preferably, the organic solvent in S1 is a mixture of cyclohexane and methyl isobutyl ketone, and the volume ratio of cyclohexane to methyl isobutyl ketone is 1:0.4-0.7.

[0008] Preferably, the composite initiator in S1 is composed of azobisisobutyronitrile and dicyclohexyl peroxide in a mass ratio of 1.5:1.

[0009] Preferably, the stabilizer in S1 is a mixture of a phosphite stabilizer and calcium stearate in a mass ratio of 1:1-2. The phosphite stabilizer can be triphenyl phosphite or phenyl diisooctyl phosphite.

[0010] Preferably, the molecular weight regulator in S1 is one of dodecyl mercaptan and isooctyl mercaptoacetate, used to precisely control the molecular weight and molecular weight distribution of polyvinyl chloride resin, and further improve the processing performance of the product.

[0011] Preferably, in step S2, the temperature is raised to 45-50℃ for 1-2 hours, and then raised to 55-65℃ for 3-4 hours, with the heating rate controlled at 3-5℃ / min.

[0012] Preferably, the terminating agent in S2 is selected from N,N-diethylhydroxylamine or p-tert-butylcatechol.

[0013] Preferably, the preparation mechanism of the pressure solvent polymerization method for preparing high-solids-content polyvinyl chloride resin of the present invention is explained as follows: The core mechanism of this invention is to overcome the technical bottlenecks of low solid content and low polymerization efficiency in conventional solvent polymerization through the synergistic effect of "pressure strengthening + mixed solvent compounding + composite initiator synergy", while ensuring the excellent performance of polyvinyl chloride resin. Firstly, in the mixed solvent system, cyclohexane and methyl isobutyl ketone are compounded at a specific volume ratio. Cyclohexane has good solubility for vinyl chloride monomer and low solubility for polyvinyl chloride resin, which can avoid abnormally high viscosity caused by excessive resin dissolution. Methyl isobutyl ketone can adjust the polarity and boiling point of the mixed solvent. After compounding with cyclohexane, it can further improve the solubility of vinyl chloride monomer, while improving the heat transfer and mass transfer performance of the polymerization system and avoiding local overheating during polymerization. The volume ratio of the two is controlled at 1:0.4-0.7. If the proportion of methyl isobutyl ketone is too high, it will increase the solvent cost and may cause a small amount of polyvinyl chloride resin to dissolve, affecting the product form; if the proportion is too low, it will not be able to effectively improve the monomer solubility and heat transfer effect, making it difficult to achieve high solids content polymerization. Secondly, the azobisisobutyronitrile in the composite initiator has a moderate decomposition temperature (40-60℃), which matches the polymerization temperature of this invention, and a stable decomposition rate. Dicyclohexyl peroxide has high initiation efficiency. The combination of the two can achieve a synergistic initiation effect, which can uniformly initiate the polymerization of vinyl chloride monomer, avoid the widening of molecular weight distribution caused by excessively rapid initiator decomposition, and improve the polymerization reaction rate and ensure complete polymerization. The amount of composite initiator should be controlled at 0.02-0.3 parts. Too little amount will result in a slow polymerization reaction rate and incomplete polymerization; too much amount will result in too many initiation points, a decrease in resin molecular weight, and residual initiator will affect the heat resistance stability of the product. Furthermore, the role of stabilizers is to prevent the degradation of polyvinyl chloride resin during the polymerization process. Phosphite stabilizers have good antioxidant and weather resistance, while calcium stearate has lubricating and thermal stabilizing effects. When the two are combined, they can synergistically improve the thermal stability and processing performance of the resin, solve the problem of insufficient stabilizing effect of a single stabilizer, avoid degradation and yellowing of polyvinyl chloride resin during polymerization, drying and subsequent processing, and improve the resin processing performance at the same time. Furthermore, pressurization is a core technical means to achieve high-solids polymerization: based on the kinetic characteristics of vinyl chloride polymerization, increased pressure can significantly improve the solubility of vinyl chloride monomer in mixed solvents, thereby allowing more monomer to be added to the polymerization system and achieving high-solids polymerization; at the same time, pressurization can accelerate the polymerization reaction rate, shorten the polymerization time, improve production efficiency, and improve the uniformity of the polymerization reaction, reducing resin crosslinking and degradation. If the pressure is too low (below 0.5 MPa), it cannot effectively improve the monomer solubility; if the pressure is too high (above 1.5 MPa), it will increase the equipment cost and operation difficulty of the reactor, and may also cause the vinyl chloride monomer to decompose, affecting product purity and performance; the staged heating method is adapted to the decomposition characteristics of the initiator and the polymerization law of the monomer. The low temperature in the early stage allows the initiator to decompose slowly and form a uniform resin core, while the high temperature in the later stage accelerates the polymerization process, taking into account both product morphology and polymerization efficiency, and avoiding the rapid increase in system viscosity caused by excessively rapid heating in the early stage; Finally, in the post-processing stage, precise control of centrifugation and drying parameters, combined with the distillation recovery of unreacted monomers and solvents, ensures product purity while reducing energy consumption and raw material costs, thus achieving industrially feasible preparation of high-solids-content polyvinyl chloride resin.

[0014] Compared with the prior art, the beneficial effects of the present invention are: 1. High solids content and low energy consumption: This invention, through pressure enhancement, mixed solvent formulation, and synergistic effect of composite initiator, significantly improves the solids content compared to conventional suspension polymerization and atmospheric pressure solvent polymerization, increases the solubility of vinyl chloride monomer, reduces subsequent drying energy consumption, and greatly reduces production costs.

[0015] 2. Excellent product performance: By optimizing the mixing solvent ratio, pressure parameters and polymerization process, the present invention prepares polyvinyl chloride resin with a tensile strength ≥46.8MPa and a thermal decomposition temperature ≥220℃. Compared with products prepared by conventional methods, the mechanical properties and heat resistance stability are significantly improved, and problems such as yellowing and cracking are less likely to occur during subsequent processing, making it more widely applicable.

[0016] 3. Simple process and easy to industrialize: The polymerization process parameters of this invention are controllable, and the pressure (0.5-1.5MPa) is within the bearing range of conventional industrial polymerization reactors, requiring no special equipment modification; the mixed solvent, initiator, and stabilizer are all commonly used industrial raw materials, which are low in cost and easy to obtain; the post-processing is simple, and unreacted monomers and solvents can be recycled, reducing environmental pressure and raw material costs, making it suitable for large-scale industrial production. Detailed Implementation

[0017] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with existing known technologies. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments.

[0018] Example 1: A method for preparing high-solids-content polyvinyl chloride resin by pressure solvent polymerization, comprising the following steps: S1. Ingredients: Weigh 100g vinyl chloride monomer, 80ml mixed solvent (51.6ml cyclohexane, 28.4ml methyl isobutyl ketone), 0.16g composite initiator (0.096g azobisisobutyronitrile, 0.064g dicyclohexyl peroxide), 0.35g stabilizer (0.14g triphenyl phosphite, 0.21g calcium stearate), and 0.03g molecular weight regulator (isooctyl mercaptoacetate). Mix and stir for 15min at a stirring speed of 280r / min to obtain the polymerization reaction solution. S2. Pressure polymerization: Add the polymerization reaction solution obtained in S1 to the polymerization reactor, seal it, and purge with nitrogen four times (oxygen content ≤0.5% after each purging). Pressurize to 1.0 MPa, turn on the stirrer at 280 r / min, raise the temperature to 48℃ at a rate of 4℃ / min, and keep the temperature constant for 1.5 h. Then raise the temperature to 60℃ at the same rate and keep the temperature constant for 3.5 h. Add 0.02 g of terminator (N,N-diethylhydroxylamine), and keep stirring for 8 min to terminate the reaction. S3 Post-processing: After the polymerization reaction is completed, stirring and heating are stopped, and the pressure is released to atmospheric pressure at a rate of 0.08 MPa / min. The product is centrifuged at 4000 r / min for 20 min, washed with deionized water 3 times for 10 min each time, and dried at 90℃ for 3 h to obtain high solid content polyvinyl chloride resin, unreacted monomers and mixed solvents. A closed distillation column is used, and the tail gas is treated by activated carbon adsorption and condensation recovery before being discharged.

[0019] Example 2: A method for preparing high-solids-content polyvinyl chloride resin by pressure solvent polymerization, comprising the following steps: S1. Ingredients: Weigh 100g vinyl chloride monomer, 70ml mixed solvent (50ml cyclohexane, 20ml methyl isobutyl ketone), 0.02g composite initiator (0.012g azobisisobutyronitrile, 0.008g dicyclohexyl peroxide), 0.2g stabilizer (0.1g phenyl diisooctyl phosphite, 0.1g calcium stearate), and 0.01g molecular weight regulator (dodecyl mercaptan). Mix and stir for 10min at a stirring speed of 200r / min to obtain the polymerization reaction solution. S2. Pressure polymerization: Add the polymerization reaction solution obtained in S1 to the polymerization reactor, seal it, and purge with nitrogen four times (oxygen content ≤0.5% after each purging). Pressurize to 0.5MPa, turn on the stirrer at 200r / min, raise the temperature to 45℃ at a rate of 3℃ / min, and keep the temperature constant for 1h. Then raise the temperature to 55℃ at the same rate and keep the temperature constant for 3h. Add 0.01g of terminator (N,N-diethylhydroxylamine), and keep stirring for 5min to terminate the reaction. S3 Post-processing: After the polymerization reaction is completed, stirring and heating are stopped, and the pressure is released to atmospheric pressure at a rate of 0.05 MPa / min. The product is centrifuged at 3000 r / min for 15 min, washed with deionized water 4 times for 8 min each time, and dried at 80℃ for 4 h to obtain high solid content polyvinyl chloride resin. Unreacted monomers and mixed solvents are processed in a closed distillation column. The tail gas is treated by activated carbon adsorption and condensation recovery before being discharged.

[0020] Example 3: A method for preparing high-solids-content polyvinyl chloride resin by pressure solvent polymerization, comprising the following steps: S1. Ingredients: Weigh 100g vinyl chloride monomer, 90ml mixed solvent (53ml cyclohexane, 37ml methyl isobutyl ketone), 0.3g composite initiator (0.18g azobisisobutyronitrile, 0.12g dicyclohexyl peroxide), 0.5g stabilizer (0.17g triphenyl phosphite, 0.33g calcium stearate), and 0.05g molecular weight regulator (isooctyl mercaptoacetate). Mix and stir for 20min at a stirring speed of 350r / min to obtain the polymerization reaction solution. S2. Pressure polymerization: Add the polymerization reaction solution obtained in S1 to the polymerization reactor, seal it, and purge with nitrogen 5 times (oxygen content ≤0.5% after each purging). Pressurize to 1.5MPa, turn on the stirrer at 350r / min, raise the temperature to 50℃ at a rate of 5℃ / min, and keep the temperature constant for 2h. Then raise the temperature to 65℃ at the same rate and keep the temperature constant for 4h. Add 0.03g of terminator (p-tert-butylcatechol), and keep stirring for 10min to terminate the reaction. S3 Post-processing: After the polymerization reaction is completed, stirring and heating are stopped, and the pressure is released to atmospheric pressure at a rate of 0.1 MPa / min. The product is centrifuged at 5000 r / min for 30 min, washed with deionized water 5 times for 12 min each time, and dried at 100℃ for 2 h to obtain high solid content polyvinyl chloride resin, unreacted monomers and mixed solvents. A closed distillation column is used, and the tail gas is treated by activated carbon adsorption and condensation recovery before being discharged.

[0021] Comparative Example 1: Based on Example 1, the difference is that the mixed solvent of cyclohexane and methyl isobutyl ketone was replaced with an equal volume of single cyclohexane, and the rest was the same as in Example 1.

[0022] Comparative Example 2: Based on Example 1, the difference is that the azobisisobutyronitrile and dicyclohexyl peroxide composite initiator is replaced with an equal mass of single dicyclohexyl peroxide, and the rest is the same as in Example 1.

[0023] Comparative Example 3: Based on Example 1, the difference is that the segmented heating was changed to a direct one-time heating to 60°C, and the reaction was carried out at this temperature for 5 hours. The rest is the same as Example 1.

[0024] Comparative Example 4: Based on Example 1, the difference is that the depressurization rate in post-treatment S3 is increased to 0.5 MPa / min (far higher than the required 0.05-0.1 MPa / min), and the rest is the same as Example 1.

[0025] Comparative Example 5: Based on Example 1, the difference is that polymerization is carried out under normal pressure, and the rest is the same as Example 1.

[0026] Performance testing: 1. Solid content test of polymerization system: After the terminator is added to the polymerization reaction and stirred evenly, immediately take about 5-10 g of a representative original reaction mixture from the sampling port of the polymerization reactor and quickly transfer it to a weighing bottle (m0) that has been weighed to constant weight. Seal the bottle to prevent solvent evaporation and accurately weigh the total mass of the bottle and the original mixture, and record it as m1 (accurate to 0.1 mg). Place the weighing bottle containing the mixture (with the cap off) into a vacuum drying oven and dry it at 60℃ under high vacuum for 2-4 hours until constant weight is reached (the difference between two consecutive weighings is ≤1.0 mg). Cool the solid resin after removing the solvent and monomer, along with the container, to room temperature and weigh it accurately, and record it as m2. Solid content of polymerization system (%) = [(m2-m0) / (m1-m0)]×100%.

[0027] 2. Tensile strength test: Referring to GB / T 1040.2-2006 standard, polyvinyl chloride resin is mixed with necessary additives (such as stabilizers) and plasticized and mixed at 165-175℃ for 5-10 minutes on a two-roll mill. Then, it is pressed into a sheet with a thickness of 1-2 mm and punched into V-shaped dumbbell specimens with a standard cutter. On a universal testing machine, the specimen is clamped and the gauge length is set to 25 mm or 50 mm. The test is carried out at a tensile speed of 50 mm / min until the specimen breaks. The maximum tensile force is recorded and the tensile strength (MPa) is calculated.

[0028] 3. Thermal decomposition temperature test: Referring to ISO 11358 standard, take 5-10 mg of dried polyvinyl chloride resin sample and use a thermogravimetric analyzer (TGA) to heat from 50℃ to 600℃ at a heating rate of 10℃ / min under a dynamic nitrogen atmosphere (flow rate 50 mL / min). Record the sample mass change curve with temperature in real time and take the temperature corresponding to 5% mass loss (T5%), in ℃.

[0029] 4. Molecular weight distribution index test: Referring to ISO 13844 standard, polyvinyl chloride resin was dissolved in tetrahydrofuran to prepare a solution with a concentration of approximately 1-2 mg / mL. The solution was filtered through a 0.45 μm microporous membrane and then subjected to gel permeation chromatography equipped with a differential refractive index detector. Tetrahydrofuran was used as the mobile phase at a flow rate of 1.0 mL / min. Narrow distribution polystyrene standards were used for calibration, and the molecular weight distribution index was calculated.

[0030] 5. Yellow Index Test: Without adding colorant, the polyvinyl chloride resin sample is hot-pressed into a smooth sheet of uniform thickness (about 1 mm) at 180±2℃ and a certain pressure using a molding method. After rapid cooling, it is punched into round pieces of the specified size. The sample pieces are placed in a forced-air drying oven at a constant temperature of 180±2℃. Timing is started, and a sample piece is taken out at certain time intervals (such as 10 minutes, 20 minutes). After cooling, its yellow index (YI value) is measured using a colorimeter (whiteness meter). The original unaged sample piece must be used as a reference during the measurement.

[0031] Table: Performance tests were conducted on a high solids content polyvinyl chloride resin from Examples 1-3 and Comparative Examples 1-5.

[0032] Table 1. Performance Test Results

[0033] Data Analysis: 1. Solid content analysis of the polymerization system: The solid content of Examples 1-3 was around 70.6-71.1%, significantly higher than that of Comparative Examples 1-5 (55.6%-63.5%). This result directly verifies the core role of pressurization technology. Increased pressure effectively improves the solubility of vinyl chloride monomer in the mixed solvent, thereby achieving high solid content polymerization. In particular, Comparative Example 5 (atmospheric pressure polymerization) had the lowest solid content (55.6%), which is in stark contrast to Example 1 (70.9%). This strongly proves that pressurization is the key to breaking through the solid content bottleneck of conventional solvent polymerization. The solid content of Comparative Example 1 (single cyclohexane solvent) was only 58.1%, indicating that the compounding of mixed solvents is crucial for improving monomer solubility and solid content. The solid content of Comparative Example 2 (single initiator) and Comparative Example 3 (non-segmented heating) also decreased to 61.6% and 62.4%, respectively, further indicating that the synergistic initiation effect of the composite initiator and the segmented heating strategy make a positive contribution to maintaining an efficient and stable polymerization process and ultimately achieving high solid content.

[0034] 2. Tensile strength analysis: The tensile strength of Examples 1-3 of this invention is ≥46.8MPa, which is significantly better than that of Comparative Example 5, which is polymerized under normal pressure. This indicates that while polymerizing with high solid content, the molecular structure of the resin still maintains good regularity and no obvious structural defects appear due to the increase in the concentration of the polymerization system. The tensile strength of Comparative Examples 1-3 all decreased to varying degrees, especially the tensile strength of Comparative Example 4 (rapid pressure relief) which was the lowest (38.5 MPa). This proves that excessively rapid pressure relief will cause the resin particles to break, destroy their microstructure, and thus impair mechanical properties.

[0035] 3. Thermal Decomposition Temperature Analysis: Thermal decomposition temperature (T5%) is a key indicator for measuring the thermal stability of resin. As shown in Table 1, the T5% of Examples 1-3 are all above 220°C (Example 3 reaches 231°C), exhibiting excellent thermal stability. However, the T5% of all comparative examples are below 200°C, indicating significant performance degradation. This is mainly due to the synergistic effect of the stabilizer system. The phosphite and calcium stearate compound stabilizer used in Examples 1-3 can effectively inhibit thermal degradation during polymerization and post-treatment. The pressurization and segmented heating process avoids local overheating, reduces defects in resin molecular chains and the formation of unstable structures, thereby improving intrinsic thermal stability. Comparative Example 5 (atmospheric pressure) and Comparative Example 1 (single solvent, T5% = 191°C) show that an undesirable polymerization environment directly leads to a significant decrease in thermal stability.

[0036] 4. Molecular Weight Distribution Index Analysis: The closer the molecular weight distribution index (Mw / Mn) is to 1, the narrower the molecular weight distribution and the more uniform the processing and physical properties of the resin. The Mw / Mn of Examples 1-3 are concentrated in the narrow range of 1.82-1.91, demonstrating excellent molecular weight controllability. This is mainly due to the synergistic initiation of the composite initiator and the precise control of the molecular weight regulator. For example, in Comparative Example 2 (single initiator, Mw / Mn=2.81), the use of dicyclohexyl peroxide dicarbonate resulted in excessively rapid initiation and a significantly wider molecular weight distribution. In contrast, in Examples 1-3, the combined use of azobisisobutyronitrile and dicyclohexyl peroxide dicarbonate stably provided free radicals at different temperature stages, achieving uniform initiation. The use of thiol ester regulators effectively controlled chain growth, resulting in a narrow molecular weight distribution product. The narrow molecular weight distribution is an important reason why Examples 1-3 have high and stable tensile strength.

[0037] 5. Yellow Index Analysis: The YI values ​​of Examples 1-3 are all below 2.5, indicating excellent color, while the YI values ​​of Comparative Examples 1-5 are all above 4.0, indicating obvious yellowing. This comprehensively reflects the high purity and excellent thermal history of the resin in Examples 1-3 (such as the YI increase in Comparative Example 3 due to a one-time heating). A low YI value means that the resin is less likely to change color in subsequent processing, resulting in a higher product grade.

[0038] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing high-solids-content polyvinyl chloride resin by pressure solvent polymerization, characterized in that, Includes the following steps: S1. Ingredients: Mix 100 parts vinyl chloride monomer, 70-90 parts mixed solvent, 0.02-0.3 parts composite initiator, 0.2-0.5 parts stabilizer and 0.01-0.05 parts molecular weight regulator and stir for 10-20 minutes at a stirring speed of 200-350 r / min to obtain polymerization reaction solution; S2. Pressure polymerization: Add the polymerization reaction solution obtained in S1 to the polymerization reactor, seal it and purge the air with nitrogen 3-5 times, pressurize to 0.5-1.5MPa, and heat to 45-65℃ in stages at a stirring speed of 200-350r / min for 4-6h. Then add 0.01-0.03 parts of terminator and stir to terminate the reaction. S3. Post-processing: After the reaction is complete, control the depressurization rate and depressurize to atmospheric pressure. The product is then centrifuged, washed, and dried to obtain high solids content polyvinyl chloride resin.

2. The method for preparing high-solids-content polyvinyl chloride resin by pressure solvent polymerization according to claim 1, characterized in that, The mixed solvent in S1 is a mixture of cyclohexane and methyl isobutyl ketone, with a volume ratio of cyclohexane to methyl isobutyl ketone of 1:0.4-0.

7.

3. The method for preparing high-solids-content polyvinyl chloride resin by pressure solvent polymerization according to claim 1, characterized in that, The composite initiator in S1 is composed of azobisisobutyronitrile and dicyclohexyl peroxide in a mass ratio of 1.5:

1.

4. The method for preparing high-solids-content polyvinyl chloride resin by pressure solvent polymerization according to claim 1, characterized in that, The stabilizer in S1 is a mixture of phosphite stabilizer and calcium stearate in a mass ratio of 1:1-2. The phosphite stabilizer can be triphenyl phosphite or diisooctyl phosphite.

5. The method for preparing high-solids-content polyvinyl chloride resin by pressure solvent polymerization according to claim 1, characterized in that, The molecular weight regulator in S1 is dodecyl mercaptan or isooctyl mercaptoacetate.

6. The method for preparing high-solids-content polyvinyl chloride resin by pressure solvent polymerization according to claim 1, characterized in that, After nitrogen is introduced into S2 to replace the air, the oxygen content is monitored in real time by an online oxygen content detector, and the oxygen content is ≤0.5% after each replacement.

7. The method for preparing high-solids-content polyvinyl chloride resin by pressure solvent polymerization according to claim 1, characterized in that, The segmented heating in S2 is as follows: first, the temperature is raised to 45-50℃ and reacted for 1-2 hours, then the temperature is raised to 55-65℃ and reacted for 3-4 hours, with the heating rate controlled at 3-5℃ / min.

8. The method for preparing high-solids-content polyvinyl chloride resin by pressure solvent polymerization according to claim 1, characterized in that, The terminator in S2 is N,N-diethylhydroxylamine or p-tert-butylcatechol.

9. The method for preparing high-solids-content polyvinyl chloride resin by pressure solvent polymerization according to claim 1, characterized in that, The pressure relief rate in S3 is controlled at 0.05-0.1 MPa / min.

10. The method for preparing high-solids-content polyvinyl chloride resin by pressure solvent polymerization according to claim 1, characterized in that, The centrifugation conditions in S3 are: centrifugation at 3000-5000 r / min for 15-30 min; washing conditions are: washing with deionized water 3-5 times, each time for 8-12 min; and drying conditions are: drying at 80-100℃ for 2-4 h.

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