Preparation method and system of hydroxyl modified vinyl chloride-vinyl acetate copolymer resin

Abstract

The invention provides a preparation method and system of hydroxyl modified vinyl chloride-vinyl acetate copolymer resin, and relates to the field of preparation of hydroxyl modified vinyl chloride-vinyl acetate copolymer resin.The preparation method sequentially comprises the steps that kettle coating operation is conducted, and a layer of oleophobic and hydrophilic film is formed on the wall of a polymerization kettle and the surface of a baffle; premixing the catalyst, the dispersing agent and the neutralizer; adding pure water; vinyl acetate and vinyl chloride monomers are respectively added into the polymerization kettle; heating the kettle temperature of the polymerization kettle to the polymerization reaction temperature of the produced vinyl chloride-vinyl acetate copolymer resin through a heating pump, and carrying out copolymerization reaction on vinyl acetate and vinyl chloride monomers under the action of a catalyst; supplementing the vinyl chloride monomer; after the vinyl chloride monomer is supplemented, the kettle temperature of the polymerization kettle is kept at the reaction temperature, and the polymerization reaction is continuously carried out; and finishing the reaction in the polymerization kettle, and discharging. The kettle coating operation is carried out, the adhesive force of a polymer on the kettle wall is reduced, and the heat transfer effect of the kettle wall is guaranteed; and the auxiliary agent is premixed in the auxiliary agent premixing tank, so that uniform dispersion is realized.

Description

Technical Field

[0001] The present invention relates to the technical field of the preparation of hydroxyl-modified vinyl chloride-vinyl acetate copolymer resin, and specifically relates to a preparation method and system for hydroxyl-modified vinyl chloride-vinyl acetate copolymer resin. Background Art

[0002] Vinyl chloride-vinyl acetate (VC-VAC) copolymer is commonly known as vinyl chloride-vinyl acetate copolymer resin, which is the earliest industrialized vinyl chloride copolymer resin. The mass fraction of VAC (vinyl acetate) in the vinyl chloride-vinyl acetate copolymer resin is generally 5% - 40%. Due to the introduction of the VAC group, it has a lower plasticization temperature and melt viscosity. In order to control the composition of the vinyl chloride-vinyl acetate copolymer resin, generally, methods such as changing the feeding ratio of VC and VAC, changing the polymerization temperature, and appropriately controlling the polymerization conversion rate are adopted, so that the composition and molecular weight distribution of the final copolymer will not be too wide.

[0003] The existing preparation methods of vinyl chloride-vinyl acetate copolymer resin, such as a method for preparing vinyl chloride-vinyl acetate copolymer in CN114057927A, have the following problems: 1. Lack of kettle coating operation, it is easy for materials to adhere to the kettle wall, affecting the heat transfer effect on the surface of the kettle wall, and thus affecting the reaction effect; 2. Lack of auxiliary agent premixing step, the auxiliary agent is directly added to the reaction kettle, and it is difficult to disperse evenly in time, affecting the reaction effect. Summary of the Invention

[0004] The present invention provides a preparation method and system for hydroxyl-modified vinyl chloride-vinyl acetate copolymer resin to solve at least one of the technical problems raised in the above background art.

[0005] To solve the above technical problems, the present invention discloses a preparation method for hydroxyl-modified vinyl chloride-vinyl acetate copolymer resin, including: Step 1: Kettle coating operation: Spray the kettle coating liquid into a mist with steam, and condense it on the surface of the polymerization kettle wall and the baffle to form a layer of oil-repellent and hydrophilic film; Step 2: Auxiliary agent premixing operation: Add the catalyst, dispersant, neutralizer according to the formula amount and pure water in proportion into the auxiliary agent premixing tank for mixing; Step 3: Pure water adding operation: Add pure water into the polymerization kettle according to the polymerization formula amount through the pure water storage tank, pure water pump, and flow meter; Step 4: Monomer adding operation: Add all the vinyl acetate in the formula amount directly into the polymerization kettle; then add vinyl chloride monomer; Step 5: Polymerization kettle reaction heating operation: Raise the kettle temperature of the polymerization kettle to the polymerization reaction temperature of the produced vinyl chloride-vinyl acetate copolymer resin through the heating pump, and the vinyl acetate and vinyl chloride monomer undergo copolymerization reaction under the action of the catalyst; Step 6: Vinyl chloride monomer supplementary addition operation: When the cumulative polymerization reaction time is 40 - 60 minutes or the reaction pressure drops by 0.1 - 0.15 MPa, the vinyl chloride monomer supplementary addition operation starts; Step 7: After the vinyl chloride monomer supplementary addition operation is completed, the kettle temperature of the polymerization kettle maintains the reaction temperature and the polymerization reaction continues to occur; Step 8: Completion of the polymerization kettle reaction and discharging operation: After the polymerization reaction is completed, discharging and recovery operations of unreacted vinyl chloride monomer and vinyl acetate are carried out.

[0006] Preferably, in the step 7, the fluctuation range of maintaining the reaction temperature is ±0.2°C.

[0007] Preferably, the step 1 is performed based on a kettle coating device, and the kettle coating device includes an atomizing nozzle. The atomizing nozzle is used to spray on the surface of the polymerization kettle wall and the baffle. The atomizing nozzle is connected to a steam inlet pipe and a kettle coating liquid inlet pipe. The inlet of the kettle coating liquid inlet pipe is connected to a kettle coating liquid constant temperature storage tank through a delivery pump. A discharge branch pipe is also provided near the outlet of the kettle coating liquid inlet pipe. A control valve I is provided on the discharge branch pipe. A control valve II is provided at a position between the discharge branch pipe and the outlet of the kettle coating liquid inlet pipe on the kettle coating liquid inlet pipe. A flow detection device is provided at the inlet of the kettle coating liquid inlet pipe.

[0008] Preferably, in the step 1, a kettle coating adjustment process is carried out periodically, and the kettle coating adjustment process includes: Step 11: Obtain the flow control parameter - output flow change curve of the current type of delivery pump under standard conditions; obtain the corresponding first flow control parameter range of the current target kettle coating liquid flow range in the flow control parameter - output flow change curve of the current type of delivery pump under standard conditions; Step 12: Open the control valve I and close the control valve II, and control the actual flow control parameter of the current delivery pump to be the median of the first flow control parameter range Carry out a kettle coating liquid delivery test for a first set duration, and perform multiple detections through the flow detection device within the first set duration; Step 13: When the average detection value of the flow detection device in step 12 The difference from the lower limit of the current target kettle coating liquid flow range is less than a preset value, give a first warning, the flow control parameter - output flow change curve of the current type of delivery pump under standard conditions, the ideal time interval range for adjusting the delivery pump flow, and the equivalent flow loss coefficient for each integer time interval in the ideal time interval range determined based on step 12; Step 14: Determine the second flow control parameter for each integer time interval based on the equivalent flow loss coefficient of each integer time interval obtained in Step 13. Based on the second flow control parameter of each integer time interval and the current target coating liquid flow range, determine the adjustment reliability and flow reliability of the flow control parameter for each integer time interval. Based on the adjustment reliability and flow reliability of the flow control parameter for each integer time interval, determine the comprehensive reliability of each integer time interval; Step 15: Screen the integer time interval with both the adjustment reliability and flow reliability of the flow control parameter greater than 1 and the maximum comprehensive reliability as the target integer time interval, and determine the second flow control parameter corresponding to the target integer time interval as the target flow control parameter; Step S16: Close the first control valve and open the second control valve, and control the operation of the delivery pump with the target flow control parameter until the coating task is completed or until the next coating adjustment process.

[0009] The present invention also discloses a preparation system for a hydroxyl-modified vinyl chloride copolymer resin, which is applied to the preparation method of the hydroxyl-modified vinyl chloride copolymer resin. The preparation system includes: a coating device, an additive premixing tank, a polymerization kettle, a pure water storage tank, a pure water pump, a flow meter, a heating pump, a timer, a pressure sensor, and a temperature sensor. The timer is used to time the polymerization reaction time, the pressure sensor is used to detect the air pressure in the polymerization kettle, and the temperature sensor is used to detect the kettle temperature of the polymerization kettle.

[0010] Preferably, the additive premixing tank is provided with a stirring device. The stirring device includes a stirring rod and a stirring motor. The stirring motor is used to drive the stirring rod. The additive premixing tank includes a tank body and a tank cover. The stirring motor is arranged on the tank cover, and the stirring rod rotates through the tank cover and extends into the tank body.

[0011] Preferably, the additive premixing tank is further provided with a multi-functional screening device, and the multi-functional screening device includes: A box body, which is fixedly connected to the tank cover. The top end of the box body is provided with a feed inlet. A screening box is arranged inside the box body. The upper end of the screening box is open, and the lower end of the screening box is fixedly connected with a support. The lower end of the support is slidably connected to the lower end of the box body. The discharge port at the lower end of the screening box is communicated with the tank body through a hose. Grooves are respectively arranged on the inner walls of the left and right sides of the screening box; A screening mesh. A column is arranged in the middle of the upper end of the screening mesh. The upper end of the column is a conical surface. The upper side of the column is in sealing sliding fit with the inner wall of the feed inlet along the up and down direction. First springs are respectively arranged on the left and right sides of the lower end of the screening mesh. The first springs are installed in the corresponding grooves, and both ends of the first spring are fixedly connected to the lower end of the screening mesh and the lower end of the corresponding groove.

[0012] Preferably, the multi-functional screening device further includes: An installation groove is provided on the left side of the box body, a gear is rotatably installed in the installation groove, the axial direction of the gear is the front-to-back direction, a motor for driving the gear to rotate is arranged in the installation groove, a gear rod 1 and a gear rod 2 are respectively meshed at the upper and lower ends of the gear, the gear rod 1 and the gear rod 2 both penetrate the left side wall of the box body along the left-right direction, the gear rod 1 is also connected to the left part of the lower end of the screening net through a pull rope, and the pull rope slides through the left side wall of the screening box.

[0013] Compared with the prior art, the present invention has the following beneficial effects: The method for preparing hydroxy-modified vinyl chloride copolymer resin developed by the present invention adopts a continuous feeding process to control the reaction pressure to be stable during the polymerization process, thereby ensuring the balance of vinyl chloride and vinyl acetate in the polymerization system, and can prepare vinyl chloride copolymer resin with a high content of vinyl acetate.

[0014] The oleophobic and hydrophilic film formed by the coating liquid can effectively reduce the adhesion of the polymer to the kettle wall. During the polymerization process, if the polymer directly adheres to the kettle wall, it will affect the heat transfer efficiency of the kettle wall, causing local overheating or overcooling, and further affecting the uniformity of the polymerization reaction and product quality. The film layer makes it difficult for the polymer to adhere, keeps the kettle wall clean, and ensures the stable reaction.

[0015] Preventing a large amount of polymer from adhering to the kettle wall can reduce operations such as mechanical scraping for cleaning the kettle wall, reduce wear on the kettle wall, thereby extending the service life of the polymerization kettle and reducing equipment maintenance and replacement costs.

[0016] The uniform film layer can make the heat transfer on the surface of the reactor wall more uniform. In the polymerization reaction, temperature uniformity is crucial to the reaction process. It can ensure the consistency of reaction rate and product performance, reduce the occurrence of side reactions caused by local temperature differences, and improve product quality and production efficiency.

[0017] Premixing in the additive premixing tank can integrate multiple addition steps in the reaction equipment into one addition step, simplifying the operation process of adding additives to the polymerization system, reducing the possibility of operating errors, and better controlling the additive mixing process.

[0018] The decrease in air pressure in the polymerization reactor usually means that a large amount of vinyl chloride monomer has been consumed. Timely addition of vinyl chloride monomer can make the pressure in the reaction system rise and maintain it in an appropriate range, and ensure that the polymerization reaction continues according to the predetermined process, and finally obtain a product that meets the polymerization degree requirements. By adding vinyl chloride monomer in a timely manner, the polymerization reaction can be carried out under relatively stable conditions, which helps to control the polymerization degree of the polymer. And timely addition of vinyl chloride monomer can avoid adding vinyl chloride too early or too late to affect the reaction effect, and the monomer residue is low.

[0019] In the present invention, the chloro-vinyl acetate copolymer resin has regular particle morphology, concentrated particle size distribution, low monomer residue content, and low volatile content, and the comprehensive quality index meets the usage requirements.

[0020] The present invention solves the following problems raised in the background art: The existing preparation methods of chloro-vinyl acetate copolymer resin, such as a method for preparing vinyl chloride-vinyl acetate copolymer in CN114057927A, have the following problems: 1. Lack of kettle coating operation, which is likely to affect the heat transfer effect on the kettle wall surface due to material adhesion on the kettle wall, thus affecting the reaction effect; 2. Lack of auxiliary agent premixing step, and the auxiliary agent is directly added to the reaction kettle, making it difficult to disperse evenly in a timely manner, which affects the reaction effect. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The drawings are used to provide further understanding of the present invention, and constitute a part of the specification. They are used together with the embodiments of the present invention to explain the present invention, and do not constitute a limitation to the present invention. In the drawings: Figure 1 is a flow schematic diagram of the method of the present invention; Figure 2 is a structural schematic diagram of the kettle coating device of the present invention; Figure 3 is a structural schematic diagram of the auxiliary agent premixing tank of the present invention; Figure 4 is Figure 3 a structural schematic diagram of the multi-functional screening device in

[0022] In the figure: 1. Auxiliary agent premixing tank; 11. Tank body; 12. Tank cover; 2. Stirring motor; 3. Multi-functional screening device; 31. Box body; 3101. Feed inlet; 3102. Installation groove; 32. Screening box; 321. Groove; 33. Support; 34. Hose; 35. Column; 36. First spring; 37. Vertical telescopic rod; 38. Pressing plate; 39. Gear; 310. Rack one; 311. Rack two; 313. Pulling rope; 314. Second spring; 315. Motor; 316. Screening mesh; 4. Kettle coating device; 41. Steam inlet pipe; 42. Kettle coating liquid inlet pipe; 421. Control valve two; 43. Discharge branch pipe; 431. Control valve one; 44. Delivery pump; 45. Kettle coating liquid constant temperature storage tank; 46. Atomizing nozzle; 5. Stirring rod. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0023] The following describes the preferred embodiments of the present invention with reference to the drawings. It should be understood that the preferred embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0024] In addition, in the present invention, descriptions such as "first", "second", etc. are only for descriptive purposes, and do not particularly refer to the meaning of order or sequence, nor are they used to limit the present invention. They are merely used to distinguish components or operations described with the same technical terms, and should not be construed as indicating or implying their relative importance or implicitly indicating the quantity of the indicated technical features. Thus, features defined with "first", "second" may explicitly or implicitly include at least one such feature. In addition, the technical solutions and technical features between various embodiments can be combined with each other, but it must be based on the ability of those of ordinary skill in the art to implement. When the combination of technical solutions results in contradictions or cannot be implemented, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0025] The present invention provides the following embodiments: Example 1, the embodiment of the present invention provides a preparation method of a hydroxyl-modified vinyl chloride-vinyl acetate copolymer resin, as Figure 1 shown, including: Step 1: Coating kettle operation: Spray the coating solution into a mist with steam, condense it on the surface of the polymerization kettle wall and the baffle to form a layer of oil-repellent and hydrophilic film; the polymerization kettle of the present invention is an existing polymerization kettle, and the setting of baffles in the polymerization kettle and the setting of a jacket for the polymerization kettle are all prior arts; Step 2: Auxiliary agent premixing operation: Add the catalyst, dispersant, neutralizing agent according to the formula amount and pure water in proportion into the auxiliary agent premixing tank for mixing (catalyst 0.1 - 0.2 parts, dispersant 0.15 - 0.24 parts, neutralizing agent 0.05 - 0.2 parts, water 25 - 35 parts); Step 3: Pure water adding operation: Add pure water into the polymerization kettle through the pure water storage tank, pure water pump, and flow meter according to the polymerization formula amount; Step 4: Monomer adding operation: Add all the vinyl acetate in the formula amount directly into the polymerization kettle; then add vinyl chloride monomer; Step 5: Polymerization kettle reaction temperature rising operation: Raise the kettle temperature of the polymerization kettle to the polymerization reaction temperature of the produced vinyl chloride-vinyl acetate copolymer resin through a temperature rising pump, and under the action of the catalyst, vinyl acetate and vinyl chloride monomer undergo a copolymerization reaction; Step 6: Vinyl chloride monomer supplementary adding operation: When the cumulative polymerization reaction time is 40 - 60 minutes or the reaction pressure drops by 0.1 - 0.15 MPa, start the vinyl chloride monomer supplementary adding operation (it can be 60 - 70% of the total amount of vinyl chloride monomer, 30 - 40% of the total amount of vinyl chloride monomer added in step 4); Step 7: After the vinyl chloride monomer supplementary adding operation is completed, maintain the kettle temperature of the polymerization kettle at the reaction temperature and continue the polymerization reaction; Step 8: Polymerization kettle reaction end and discharging operation: After the polymerization reaction is completed, perform discharging and recovery operations of unreacted vinyl chloride monomer and vinyl acetate.

[0026] In step 7, the reaction temperature fluctuation range is maintained at ±0.2 °C; the reaction temperature is 60-70 °C.

[0027] The present invention also discloses a preparation system for hydroxyl-modified vinyl chloride-vinyl acetate copolymer resin, which is applied to the preparation method of the hydroxyl-modified vinyl chloride-vinyl acetate copolymer resin. The preparation system includes: a kettle coating device 4 (for performing step 1), an auxiliary agent premixing tank 1, a polymerization kettle, a pure water storage tank, a pure water pump, a flow meter, a heating pump, a timer, a pressure sensor. The timer is used to time the polymerization reaction time, the pressure sensor is used to detect the air pressure in the polymerization kettle, and a temperature sensor is also included. The temperature sensor is used to detect the temperature of the kettle (which can be the temperature of the inner wall of the polymerization kettle). The above devices of the present invention can all be prior art.

[0028] The heating pump generally works in cooperation with a heating medium (such as heat-conducting oil, hot water, etc.). The heating pump causes the heating medium to form a cycle between the jacket (or coil and other heat exchange structures) of the polymerization kettle and the external heating system. The heating medium is heated and raised in temperature in an external heating device (such as a heater), and the heating pump pumps the high-temperature heating medium to the jacket (or coil) of the polymerization kettle to exchange heat with the materials in the polymerization kettle, thereby increasing the temperature in the kettle; after heat exchange, the temperature of the heating medium decreases and is pumped back to the external heating device by the heating pump to be heated again, and so on in a cycle. The jacket of the polymerization kettle is sleeved on the outer wall of the polymerization kettle; In one embodiment, the above materials for the preparation of the hydroxyl-modified vinyl chloride-vinyl acetate copolymer resin of the present invention are respectively in parts by weight: 0.1-0.2 parts of catalyst, 0.15-0.4 parts of dispersant, 0.05-0.2 parts of neutralizer, 13-35 parts of vinyl acetate, 85-100 parts of vinyl chloride monomer, and 160-180 parts of water; Among them, the formula of the above materials for the preparation of the hydroxyl-modified vinyl chloride-vinyl acetate copolymer resin of the present invention can also adopt prior art.

[0029] In the present invention, the catalyst can be a peroxide (such as benzoyl peroxide, methyl ethyl ketone peroxide, diisopropyl peroxydicarbonate, etc.), an azo compound (such as azobisisobutyronitrile), etc.; The dispersant can be polyvinyl alcohol; The neutralizer can be an alkaline substance such as sodium hydroxide or potassium hydroxide; The beneficial effects of the above technical solutions are: The method for the hydroxyl-modified vinyl chloride-vinyl acetate copolymer resin developed by the present invention adopts a continuous feeding process to control the reaction pressure in the polymerization process to be stable, thereby ensuring the balance of vinyl chloride and vinyl acetate in the polymerization system, and a vinyl chloride-vinyl acetate copolymer resin with a high content of vinyl acetate can be prepared.

[0030] The oleophobic and hydrophilic film formed by the coating liquid can effectively reduce the adhesion of the polymer to the kettle wall. During the polymerization process, if the polymer directly adheres to the kettle wall, it will affect the heat transfer efficiency of the kettle wall, causing local overheating or overcooling, and further affecting the uniformity of the polymerization reaction and product quality. The film layer makes it difficult for the polymer to adhere, keeps the kettle wall clean, and ensures the stable reaction.

[0031] Preventing a large amount of polymer from adhering to the kettle wall can reduce operations such as mechanical scraping for cleaning the kettle wall, reduce wear on the kettle wall, thereby extending the service life of the polymerization kettle and reducing equipment maintenance and replacement costs.

[0032] The uniform film layer can make the heat transfer on the surface of the reactor wall more uniform. In the polymerization reaction, temperature uniformity is crucial to the reaction process. It can ensure the consistency of reaction rate and product performance, reduce the occurrence of side reactions caused by local temperature differences, and improve product quality and production efficiency.

[0033] Premixing in the additive premixing tank can integrate multiple addition steps in the reaction equipment into one addition step, simplifying the operation process of adding additives to the polymerization system, reducing the possibility of operating errors, and better controlling the additive mixing process.

[0034] The decrease in air pressure in the polymerization reactor usually means that a large amount of vinyl chloride monomer has been consumed. Timely addition of vinyl chloride monomer can make the pressure in the reaction system rise and maintain it in an appropriate range, and ensure that the polymerization reaction continues according to the predetermined process, and finally obtain a product that meets the polymerization degree requirements. By adding vinyl chloride monomer in a timely manner, the polymerization reaction can be carried out under relatively stable conditions, which helps to control the polymerization degree of the polymer. And timely addition of vinyl chloride monomer can avoid adding vinyl chloride too early or too late to affect the reaction effect, and the monomer residue is low.

[0035] In the present invention, the chlorovinyl copolymer resin particles have regular shape, concentrated particle size distribution, low monomer residue, low volatile content, and the comprehensive quality indicators meet the use requirements.

[0036] The present invention solves the following problems raised by the background technology: The existing preparation methods of chlorovinyl acetate copolymer resins, such as a method for preparing vinyl chloride-vinyl acetate copolymers in CN114057927A, have the following problems: 1. Lack of kettle coating operation, which easily causes the material to adhere to the kettle wall, affecting the heat transfer effect on the kettle wall surface, thereby affecting the reaction effect; 2. There is no premixing step for the additives. The additives are directly added to the reactor, which makes it difficult to disperse them evenly in time, affecting the reaction effect.

[0037] Embodiment 2, on the basis of embodiment 1, as Figure 2 As shown, Step 1 is performed based on the kettle coating device 4, which includes an atomizing nozzle 46 for spraying the polymerization kettle wall and the baffle surface. The atomizing nozzle 46 (the principle of steam atomizing liquid is prior art and an existing atomizing nozzle can be used) is connected to a steam inlet pipe 41 and a kettle coating liquid inlet pipe 42. The inlet of the kettle coating liquid inlet pipe 42 is connected to a kettle coating liquid constant temperature storage tank 45 through a delivery pump 44. A discharge branch pipe 43 is also provided near the outlet of the kettle coating liquid inlet pipe 42, and a control valve 431 is provided on the discharge branch pipe 43. A control valve 421 is provided on the kettle coating liquid inlet pipe 42 at a position between the discharge branch pipe 43 and the outlet of the kettle coating liquid inlet pipe 42. A flow detection device is provided at the inlet of the kettle coating liquid inlet pipe 42.

[0038] In step 1, a kettle coating adjustment process is performed periodically. The kettle coating adjustment process includes: Step 11: Obtain the flow control parameter-output flow change curve of the current type of delivery pump 44 under standard conditions; obtain the first flow control parameter range corresponding to the current target kettle coating liquid flow range (determined according to the current kettle coating demand) in the flow control parameter-output flow change curve of the current type of delivery pump 44 under standard conditions; Step 12: Open the control valve 431 and close the control valve 421, and control the actual flow control parameter of the current delivery pump 44 to be the median of the first flow control parameter range. Perform a kettle coating liquid delivery test for a first set duration (which can be 3 min), and perform multiple detections through the flow detection device within the first set duration. Step 13: When the average detection value of the flow detection device in step 12 has a difference less than a preset value from the lower limit of the current target kettle coating liquid flow range, give a first warning, including the flow control parameter-output flow change curve of the current type of delivery pump 44 under standard conditions, the ideal time interval range for adjusting the delivery pump 44 flow rate, and the equivalent flow loss coefficient for each integer time interval within the ideal time interval range determined based on step 12; Step 14: Determine the second flow control parameter for each integer time interval based on the equivalent flow loss coefficient for each integer time interval obtained in step 13, determine the flow control parameter adjustment reliability and flow reliability for each integer time interval based on the second flow control parameter for each integer time interval and the current target kettle coating liquid flow range, and determine the comprehensive reliability for each integer time interval based on the flow control parameter adjustment reliability and flow reliability for each integer time interval. Step 15: Screen the integer time interval with a flow control parameter adjustment reliability and a flow reliability both greater than 1 and the largest comprehensive reliability as the target integer time interval, and determine the second flow control parameter corresponding to the target integer time interval as the target flow control parameter; Step S16: Close the control valve 1 431, open the control valve 2 421, and control the operation of the delivery pump with the target flow control parameter until the kettle coating task is completed or until the next kettle coating adjustment process.

[0039] Steps 13 and 14 are calculated respectively based on the following formulas: ; is the median of the range of the first flow control parameter in the flow control parameter-output flow change curve of the delivery pump 44 of the current type under standard condition 1 corresponding value; are the jth and (j - 1)th detection values of the flow detection device obtained in Step 12 respectively; t is the time interval between two consecutive detections of the flow detection device in Step 12; is the ith integer time interval in the ideal time range for the delivery pump flow adjustment; is the equivalent flow loss coefficient of the ith integer time interval in the ideal time range for the delivery pump 44 flow adjustment; ; is the second flow control parameter corresponding to the ith integer time interval in the ideal time range for the delivery pump 44 flow adjustment, is the flow control parameter in the flow control parameter-output flow change curve of the delivery pump of the current type under standard condition; ; ; ; is the allowable difference between the subsequent flow adjustment control parameter and the previous flow adjustment control parameter of the delivery pump 44; is the comprehensive reliability of the second flow control parameter of the ith integer time interval in the ideal time range for the delivery pump 44 flow adjustment; are the maximum value and the median of the current target kettle coating liquid flow range respectively; are the flow control parameter adjustment reliability and the flow reliability of the ith integer time interval in the ideal time range for the delivery pump 44 flow adjustment respectively.

[0040] As described above, standard condition 1 means that the parameters of the coating solution in the coating solution constant temperature storage tank 45 are standard parameters (such as key parameters such as the composition and temperature of the coating solution are all corresponding theoretical required values / standard values); The flow control parameter - output flow change curve of the current type of transfer pump 44 under standard condition 1 is obtained by transporting the coating solution in the coating solution constant temperature storage tank 45 under standard condition 1 with a qualified transfer pump 44 at the beginning of use. By continuously adjusting the flow control parameter of the transfer pump 44, the corresponding output flow detection value (the detection value of the flow detection device set at the outlet of the transfer pump 44) is obtained. Based on the output flow detection value, the flow control parameter - output flow change curve of the current type of transfer pump 44 under standard condition 1 is obtained (the abscissa is the flow control parameter, and the ordinate is the average detection value of the flow detection device when the actual flow control parameter of the corresponding transfer pump 44 is the flow control parameter corresponding to the abscissa); Steps 12 and 16 of the present invention are both executed based on standard condition 1; The current type of transfer pump 44 is the same type of transfer pump 44 as the current transfer pump (the same type of transfer pump 44 has the same size, structure, parameters, etc.); Among them, the present invention can also set a second flow detection device on the coating solution inlet pipe 42 on the inlet side of the discharge branch pipe 43. When the ratio of the second flow detection device to the flow detection device is less than a preset ratio, an alarm is given to remind to clean the coating solution inlet pipe; In the present invention, the flow control parameter can be the rotation speed of the pump; The beneficial effects of the above technical solutions are as follows: When the transfer pump 44 is used for a long time, due to factors such as its own performance attenuation, the actual flow at the outlet of the transfer pump 44 under the same flow control parameter will be different from the output flow (as the standard flow) corresponding to the flow control parameter - output flow change curve of the current type of transfer pump 44 under standard condition 1. Perform a coating adjustment process periodically to ensure that the appropriate delivery flow of the coating solution is determined; Obtain the flow control parameter - output flow change curve of the current type of transfer pump 44 under standard condition 1, and based on this, determine the target flow control parameter determined in the current coating adjustment process to control the transfer pump 44 to work and transport the coating solution to the atomizing nozzle, avoiding the unreliability of selecting the parameters of the transfer pump 44's last work as the basis for adjustment (such as the inapplicability of the last work parameters due to the cleaning of the transfer pump 44 or the inapplicability of the abnormal work parameters last time); The early warning mechanism in step 13 is triggered in time when the flow is close to the lower limit of the current target coating solution flow range, avoiding the coating effect not meeting the requirements due to too low flow.

[0041] By calculating the comprehensive reliability at different time intervals (Step 14, Step 15), the system automatically selects the optimal adjustment period (target integer time interval). This can not only avoid the waste of energy consumption caused by overly frequent adjustment, but also prevent the risk of flow out of control caused by too long adjustment period, achieving the best balance between efficiency and stability. Automatically screening the target integer time interval and target flow control parameters reduces the error of manual experience judgment and makes the pot coating process more standardized and automated. Precise adjustment based on reliability analysis (Step 14) avoids over-adjustment of the pump.

[0042] Through the equivalent flow loss coefficient calculation in Step 13 and the reliability model in Step 14, the system establishes a mathematical model for flow adjustment, providing a more accurate parameter prediction and optimization basis for the subsequent pot coating process. Through the above flow control, it is convenient to be at an appropriate flow rate, so as to obtain an appropriate atomization particle size (the atomization particle size corresponding to each pot coating liquid for meeting the requirements of the pot coating effect can be determined based on tests, and then the appropriate atomization liquid flow range can be determined based on steam parameters and atomization liquid parameters to ensure an appropriate atomization particle size).

[0043] Example 3, on the basis of Example 1 or 2, as Figure 3 、 Figure 4 shown, the auxiliary premixing tank 1 is provided with a stirring device, the stirring device includes a stirring rod and a stirring motor 2, the stirring motor 2 is used to drive the stirring rod 5, the auxiliary premixing tank 1 includes a tank body 11 and a tank cover 12, the stirring motor 2 is arranged on the tank cover 12, and the stirring rod 5 rotates through the tank cover 12 and then extends into the tank body 11. The stirring rod 5 of the present invention is an existing stirring rod / stirring shaft; The auxiliary premixing tank 1 is also provided with a multi-functional screening device 3, and the multi-functional screening device 3 includes: A box body 31, the box body 31 is fixedly connected to the tank cover 12, a feed inlet 3101 is arranged at the top end of the box body 31, a screening box 32 is arranged in the box body 31, the screening box 32 is open at the upper end, the lower end of the screening box 32 is fixedly connected with a bracket 33, the lower end of the bracket 33 is slidably connected to the lower end of the box body 31, and the discharge port at the lower end of the screening box 32 is communicated with the tank body 11 through a hose 34; grooves 321 are respectively arranged on the inner walls of the left and right sides of the screening box 32; A screening mesh 316, a column 35 is arranged in the middle of the upper end of the screening mesh 316, the upper end of the column 35 is a conical surface, the upper side of the upper part of the column 35 is in sealing sliding fit with the inner wall of the feed inlet 3101 along the up and down direction, first springs 36 are respectively arranged on the left and right sides of the lower end of the screening mesh 316, the first springs 36 are installed in the corresponding grooves 321, and both ends of the first springs 36 are fixedly connected with the lower end of the screening mesh 316 and the lower end of the corresponding side groove 321 respectively.

[0044] The multi-functional screening device 3 further includes: two crushing components, which are respectively arranged on the left and right sides of the column 35. The crushing component includes: A vertical telescopic rod 37. The fixed end of the vertical telescopic rod 37 is installed at the upper end of the box body 31. The telescopic end at the lower end of the vertical telescopic rod 37 slides through the upper end of the box body 31. The lower end of the vertical telescopic rod 37 is fixedly connected with a pressing plate 38, and the pressing plate 38 is located directly above the screening mesh 316. The vertical telescopic rod 37 can be an existing electric telescopic rod, hydraulic rod or pneumatic rod; The multi-functional screening device 3 further includes: An installation groove 3102 is opened on the left side of the box body 31. A gear 39 is rotatably installed in the installation groove 3102. The axial direction of the gear 39 is the front-rear direction. A motor 315 for driving the gear 39 to rotate is arranged in the installation groove 3102. The upper and lower ends of the gear 39 are respectively meshed with a first rack 310 and a second rack 311. The first rack 310 and the second rack 311 both penetrate through the left side wall of the box body 31 along the left-right direction. The first rack 310 is also connected to the left part of the lower end of the screening mesh 316 through a pulling rope 313, and the pulling rope 313 slides through the left side wall of the screening box 32.

[0045] The working principle and beneficial effects of the above technical solution are as follows: When any one of the catalyst and the dispersant is a granular material and it is necessary to screen a suitable particle size, the multi-functional screening device 3 of the present invention is connected to the tank cover 12. If screening is not required for both, the multi-functional screening device 3 of the present invention is not connected; Such as Figure 4 , when there is no material falling in the feed inlet 3101, the upper side of the column 35 is sealed with the inner side wall of the feed inlet 3101, so as to prevent dust and impurities from entering the screening box 32 through the column 35. When the sealing cover on the feed inlet 3101 is damaged or forgotten to be covered, the above dust-proof function can still be realized. When feeding in the feed inlet 3101, the column 35 descends under the action of the weight of the material until the feed inlet 3101 is opened, and the material enters the screening box 32 and then falls onto the screening mesh 316; The vertical telescopic rod 37 extends downward, driving the pressing plate 38 to press and crush the particles that cannot pass through the screening mesh 316, and cooperating with the first spring 36 to realize the vibrating screening of the screening mesh 316. The dual mechanism ensures that the particle size of the material is uniform, and avoids slow dissolution speed due to too large particles.

[0046] When the screening is completed (restored to as Figure 4When in the (**status**) or when the screening box 32 discharges materials slowly through the hose 34 after screening is completed, the motor 315 can be controlled to drive the gear 39 to rotate counterclockwise. The counterclockwise rotation of the gear 39 drives the first rack 310 to move leftward and the second rack 311 to move rightward. First, the first rack 310 drives the screening mesh 316 to move downward through the pulling rope 313 until the upper end of the column 35 is located at the lower end of the pressing plate 38 (the upper end of the column 35 is located inside the screening box 32). Then, the first rack 310 continues to move leftward and the second rack 311 continues to move rightward. The second rack 311 pushes the screening box 32 to move rightward, compressing the second spring 314. Then, the motor 315 is controlled to return to its original position, thereby realizing the vibration of the screening mesh 316 and the screening box 32, avoiding the slow discharge of granular materials on the screening mesh 316 and avoiding the slow discharge of materials on the screening mesh 316 through the hose 34.

[0047] And the above functions are realized by one motor 315, which is convenient to control.

[0048] Example 4, based on any one of Examples 1-3, in step 2, during several times of auxiliary agent premixing operations (all under the corresponding standard condition two) for the current batch, the following process is carried out when the first auxiliary agent premixing operation is executed: Step 21: Obtain the stirring time-concentration change curve and the stirring time-concentration non-uniformity change curve of the catalyst, dispersant, and neutralizing agent under standard condition two and the standard stirring speed; and obtain the stirring speed-mixing time change curve that meets the requirements for mixing of the catalyst, dispersant, and neutralizing agent under standard condition two; Step 22: Control the speed of the stirring motor of the stirring device to be the standard stirring speed, and add the catalyst, dispersant, neutralizing agent, and water to the auxiliary agent premixing tank according to the formula amount (the formula amount for a single auxiliary agent premixing operation), and stir for a second time. The concentrations of the catalyst, dispersant, and neutralizing agent are detected N times from the first time to the second time (the second time is after the first time and can be the first time + 1 min); the first time is the stirring time when the non-uniformity in the stirring time-concentration non-uniformity change curve of each of the catalyst, dispersant, and neutralizing agent in step 21 is less than the corresponding preset non-uniformity (which can be set to 0.2) and the ratio of the concentration to the corresponding final concentration is greater than the corresponding preset value (which can be 0.95); Step 23: Construct a mixture concentration matrix based on the concentrations detected in step 22. The first row, second row, and third row in the mixture concentration matrix are the concentration ratios of the catalyst, dispersant, and neutralizing agent respectively; The i-th column in the first row is: the concentration of the catalyst detected in the i-th detection in step 22 ÷ the concentration of the catalyst corresponding to the sampling time (the abscissa of the stirring time-concentration change curve of the catalyst) of the catalyst detected in the i-th detection in step 22 in the stirring time-concentration change curve of the catalyst obtained in step 21; that is ;

[0049] Step 24: Determine that the average value of each row in Step 23 is the first concentration ratio of the corresponding material for each row, and determine the rate of change of the concentration ratio of the corresponding material based on each row in Step 23; Step 25: Give an alarm when the first concentration ratio of the material corresponding to any row is less than the corresponding first concentration preset ratio (such as 0.6); When the first concentration ratio of the material corresponding to any row is greater than the corresponding first concentration preset ratio and less than the corresponding second preset concentration ratio (such as 0.8), determine the target stirring speed based on the first concentration ratio and the rate of change of the concentration ratio of the material corresponding to each row and the stirring speed - mixing time change curve that meets the requirements under standard condition two for the catalyst, dispersant, and neutralizer; Step 26: During the remaining times of performing the auxiliary agent premixing operation for several times in the current batch, work at the target stirring speed. The stirring time is the mixing time that meets the requirements corresponding to the target stirring speed in the stirring speed - mixing time change curve that meets the requirements for the corresponding material (any one of the catalyst, dispersant, and neutralizer).

[0050] The target stirring speed is calculated based on the following formula: ; are respectively the initial times when the stirring time - concentration change curves of the catalyst, dispersant, and neutralizer obtained in Step 21 maintain at the final concentration); are respectively the first concentration ratios in the catalyst, dispersant, and neutralizer; are respectively the rates of change of the concentration ratios of the catalyst, dispersant, and neutralizer; are respectively the absolute values of the differences between the second time and the time when the concentration stabilizes at the final concentration in the corresponding stirring time - concentration change curves of the catalyst, dispersant, and neutralizer obtained in Step 21; is the stirring speed corresponding to the time in the stirring speed - mixing time change curve of the catalyst obtained in Step 21 corresponding to the corresponding time.

[0051] The second of the above standard conditions is as follows: the composition and ratio of the catalyst, dispersant, and neutralizer, as well as the water temperature during stirring, are all corresponding theoretical values / standard values; the standard stirring speed corresponds to the second standard condition. Stirring tests can be carried out using a qualified stirring device that can be initially used (at this time, the efficiency of the stirring device is relatively high). It can be determined that under the second standard condition, all aspects such as the stirring efficiency and stirring effect when the stirring motor operates at the standard stirring speed meet the requirements. The standard stirring speed is selected by optimizing various aspects such as stirring efficiency and stirring effect; in the stirring time-concentration change curve of the catalyst under the second standard condition and the standard stirring speed, the abscissa is the stirring time, and the ordinate is the concentration of the catalyst; in the stirring time-concentration non-uniformity change curve, the abscissa is the stirring time, and the ordinate is the concentration non-uniformity; For example, the mixed solution can be sampled simultaneously at different positions in the auxiliary agent premixing tank to detect the concentration of the catalyst. Based on the ratio of the standard deviation of the detected catalyst concentration in all simultaneously sampled mixed solutions to the average value of the detected catalyst concentration in all simultaneously sampled mixed solutions, it is the concentration non-uniformity. The stirring time-concentration change curve of the catalyst is constructed based on the average value of the detected catalyst concentration in all simultaneously sampled mixed solutions, and the stirring time-concentration non-uniformity change curve of the catalyst is constructed based on this concentration non-uniformity; during the above tests, the catalyst, dispersant, neutralizer, and water can be added to the auxiliary agent premixing tank simultaneously for testing; the dispersant and neutralizer also use this method to obtain the corresponding curves; In the stirring speed - mixing time change curve that meets the requirements of the catalyst, dispersant, and neutralizer under the second standard condition, the abscissa is the stirring speed of the corresponding material, and the ordinate is the mixing time that meets the requirements of the material under the second standard condition and the stirring speed corresponding to the abscissa; it can be obtained based on the test; For an auxiliary agent premixing tank of the same type as the auxiliary agent premixing tank during the test of the present invention (with the same structural composition, etc.), when the conditions are the same, the curve of step 21 is also applicable; The beneficial effects of the above technical solution are as follows: By obtaining the "stirring time - concentration change curve", "stirring time - concentration non-uniformity change curve", and "stirring speed - mixing time change curve that meets the requirements", the mixing kinetic characteristics of the catalyst, dispersant, and neutralizer are comprehensively quantified. For example: the concentration change curve can clarify the time threshold for each material to reach the target concentration (such as the catalyst needs to be stirred for 15 minutes to reach 95% of the final concentration); The concentration non-uniformity curve can locate the critical point of uniform mixing (such as the non-uniformity of the dispersant drops below 0.2 after stirring for 10 minutes), avoiding abnormal polymerization reactions caused by local concentration deviations.

[0052] Taking "theoretical composition ratio + high - efficiency stirring speed" as the standard conditions to ensure the reproducibility and comparability of curve data. For subsequent batches, if they deviate from the standard curve, it is possible to directly locate the decline in equipment efficiency or material abnormalities (such as the slowdown of the concentration increase rate caused by the attenuation of catalyst activity).

[0053] Select the first time to the second time when the concentration is relatively uniform for concentration detection, and construct a concentration ratio matrix (the ratio of the real - time concentration to the theoretical concentration of the catalyst, dispersant, and neutralizer) to achieve synchronous monitoring of the multi - material mixing state and reduce the amount of the matrix, making the calculation more accurate: When the first concentration ratio of a certain material < 0.6, give an alarm to promptly detect feeding errors or stirring device failures; the analysis of the rate of change of the concentration ratio can predict the mixing trend.

[0054] Based on the concentration ratio and rate of change measured in the first batch, combined with the "stirring speed - mixing time curve", calculate the target stirring speed through a formula to achieve the following optimizations: When the material mixing efficiency decreases (such as when the catalyst concentration ratio is only 0.7), automatically increase the stirring speed (such as from 200 r / min to 250 r / min) to shorten the mixing time; Avoid the lag of traditional fixed - speed adjustment (such as adjusting the speed manually when it is found that the mixing is insufficient, which may have led to unqualified products in multiple batches, and it is very difficult to adjust the speed accurately at one time).

[0055] From "experience control" to "data - driven": Through multi - dimensional curve modeling and real - time data feedback, achieve precise control of the mixing process; Process standardization and replicability: For pre - mixing tanks of the same type of additives, the standard curve can be directly reused to accelerate the implementation of new processes.

[0056] Obviously, those skilled in the art can make various changes and modifications to the present invention without departing from the spirit and scope of the present invention. Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and its equivalent technologies, the present invention also intends to include these changes and modifications.

Claims

1. A preparation method of a hydroxyl-modified vinyl chloride-vinyl acetate copolymer resin, characterized in that: Including: Step 1: Kettle coating operation: Spray the kettle coating liquid into a mist with steam, and condense it on the surface of the polymerization kettle wall and baffle to form a layer of oil-repellent and hydrophilic film; Step 2: Auxiliary agent premixing operation: Add the catalyst, dispersant, and neutralizing agent according to the formula amount and pure water in proportion into the auxiliary agent premixing tank for mixing; Step 3: Pure water adding operation: Add pure water into the polymerization kettle according to the polymerization formula amount through the pure water storage tank, pure water pump, and flowmeter; Step 4: Monomer adding operation: Add all the vinyl acetate of the formula amount directly into the polymerization kettle; then add vinyl chloride monomer; Step 5: Polymerization kettle reaction heating operation: Raise the kettle temperature of the polymerization kettle to the polymerization reaction temperature of the produced vinyl chloride-vinyl acetate copolymer resin through the heating pump, and the vinyl acetate and vinyl chloride monomer undergo a copolymerization reaction under the action of the catalyst; Step 6: Vinyl chloride monomer supplementary adding operation: When the cumulative polymerization reaction time is 40 - 60 minutes or the reaction pressure drops by 0.1 - 0.15 MPa, start the vinyl chloride monomer supplementary adding operation; Step 7: After the vinyl chloride monomer supplementary adding operation is completed, the kettle temperature of the polymerization kettle maintains the reaction temperature and the polymerization reaction continues to occur; Step 8: Polymerization kettle reaction end and discharging operation: After the polymerization reaction is completed, perform discharging and recovery operations of unreacted vinyl chloride monomer and vinyl acetate; 2. The preparation method of a hydroxyl-modified vinyl chloride-vinyl acetate copolymer resin according to claim 1, characterized in that: In the step 7, the fluctuation range of maintaining the reaction temperature is ±0.2°C.

3. The preparation method of a hydroxyl-modified vinyl chloride-vinyl acetate copolymer resin according to claim 1, characterized in that: The step 1 is executed based on the kettle coating device (4), and the kettle coating device (4) includes an atomizing nozzle (46), and the atomizing nozzle (46) is used for spraying on the surface of the polymerization kettle wall and baffle. The atomizing nozzle (46) is connected to a steam inlet pipe (41) and a kettle coating liquid inlet pipe (42). The inlet of the kettle coating liquid inlet pipe (42) is connected to a kettle coating liquid constant temperature storage tank (45) through a delivery pump (44). A discharge branch pipe (43) is also provided near the outlet of the kettle coating liquid inlet pipe (42). A control valve I (431) is provided on the discharge branch pipe (43). A control valve II (421) is provided at a position between the discharge branch pipe (43) and the outlet of the kettle coating liquid inlet pipe (42) on the kettle coating liquid inlet pipe (42). A flow detection device is provided at the inlet of the kettle coating liquid inlet pipe (42).

4. The preparation method of a hydroxyl-modified vinyl chloride-vinyl acetate copolymer resin according to claim 3, characterized in that: In the step 1, a kettle coating adjustment process is performed periodically, and the kettle coating adjustment process includes: Step 11: Obtain the flow control parameter - output flow change curve of the current type of delivery pump (44) under standard conditions; obtain the corresponding first flow control parameter range of the current target kettle coating liquid flow range in the flow control parameter - output flow change curve of the current type of delivery pump (44) under standard conditions; Step 12: Open control valve 1 (431), close control valve 2 (421), and control the actual flow control parameter of the current delivery pump (44) to be the median value within the range of the first flow control parameter. Conduct a coating kettle liquid delivery test for a first set duration, and perform multiple detections through a flow detection device within the first set duration. Step 13: When the difference between the average detection value of the flow detection device in Step 12 and the lower limit of the current target kettle coating liquid flow range is less than a preset value, a first warning is given, and based on the flow control parameter-output flow change curve of the current type of delivery pump (44) under standard condition 1, the ideal time interval range for flow regulation of the delivery pump (44), and the equivalent flow loss coefficient for each integer time interval in the ideal time interval range determined based on Step 12; Step 14: Determine the second flow control parameter of the corresponding integer time interval based on the equivalent flow loss coefficient of each integer time interval obtained in step 13. Based on the second flow control parameter of each integer time interval, the current target kettle coating liquid flow range, determine the flow control parameter adjustment reliability and flow reliability of each integer time interval. Based on the flow control parameter adjustment reliability and flow reliability of each integer time interval, determine the comprehensive reliability of each integer time interval; Step 15: Screen the integer time interval with a flow control parameter adjustment reliability and a flow reliability both greater than 1 and the largest comprehensive reliability as the target integer time interval, and determine the second flow control parameter corresponding to the target integer time interval as the target flow control parameter; Step S16: Close the first control valve (431), open the second control valve (421), and control the operation of the delivery pump (44) with the target flow control parameter until the kettle coating task is completed or until the next kettle coating adjustment process.

5. A preparation system for a hydroxyl-modified vinyl chloride-vinyl acetate copolymer resin, which is applied to the preparation method of a hydroxyl-modified vinyl chloride-vinyl acetate copolymer resin according to any one of claims 1-4, and is characterized in that: The preparation system includes: a kettle coating device, an auxiliary agent premixing tank (1), a polymerization kettle, a pure water storage tank, a pure water pump, a flowmeter, a heating pump, a timer, a pressure sensor, and a temperature sensor. The timer is used to time the polymerization reaction time, the pressure sensor is used to detect the air pressure in the polymerization kettle, and the temperature sensor is used to detect the temperature of the kettle body of the polymerization kettle.

6. The preparation system of a hydroxyl-modified vinyl chloride-vinyl acetate copolymer resin according to claim 5, characterized in that: The auxiliary agent premixing tank (1) is provided with a stirring device. The stirring device includes a stirring rod and a stirring motor (2). The stirring motor (2) is used to drive the stirring rod (5). The auxiliary agent premixing tank (1) includes a tank body (11) and a tank cover (12). The stirring motor (2) is arranged on the tank cover (12), and the stirring rod (5) rotates through the tank cover (12) and then extends into the tank body (11).

7. The preparation system of a hydroxyl-modified vinyl chloride-vinyl acetate copolymer resin according to claim 6, characterized in that: The auxiliary agent premixing tank (1) is further provided with a multi-functional screening device (3). The multi-functional screening device (3) includes: A box body (31). The box body (31) is fixedly connected to the tank cover (12). The top end of the box body (31) is provided with a feed inlet (3101). A screening box (32) is arranged inside the box body (31). The upper end of the screening box (32) is open. The lower end of the screening box (32) is fixedly connected with a support (33). The lower end of the support (33) is slidably connected to the lower end of the box body (31). The discharge port at the lower end of the screening box (32) is communicated with the tank body (11) through a hose (34). Grooves (321) are respectively arranged on the inner walls of the left and right sides of the screening box (32); A screening mesh (316). A column (35) is arranged in the middle of the upper end of the screening mesh (316). The upper end of the column (35) is a conical surface. The upper side of the column (35) is in sealing sliding fit with the inner wall of the feed inlet (3101) along the up and down direction. First springs (36) are respectively arranged on the left and right sides of the lower end of the screening mesh (316). The first springs (36) are installed in the corresponding grooves (321). The two ends of the first spring (36) are respectively fixedly connected to the lower end of the screening mesh (316) and the lower end of the corresponding side groove (321).

8. The preparation system of a hydroxyl-modified vinyl chloride-vinyl acetate copolymer resin according to claim 7, characterized in that: The multi-functional screening device (3) further includes: Installation groove (3102), the installation groove (3102) is opened on the left side of the box body (31), a gear (39) is rotatably installed in the installation groove (3102), the axial direction of the gear (39) is the front-back direction, a motor (315) for driving the gear (39) to rotate is arranged in the installation groove (3102), a first rack (310) and a second rack (311) are respectively meshed with the upper and lower ends of the gear (39), the first rack (310) and the second rack (311) both penetrate through the left side wall of the box body (31) along the left-right direction, the first rack (310) is also connected to the left part of the lower end of the screening mesh (316) through a pulling rope (313), and the pulling rope (313) slidably penetrates through the left side wall of the screening box (32).

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