A devolatilization process for a high-melt-index high-transparency lithium-based polymer dope

Abstract

This invention discloses a devolatilization process for high melt flow index and high transparency lithium-based polymer solutions. The process employs falling film evaporation for initial evaporation, followed by deep devolatilization using a twin-screw extruder, with the volatile solvent being condensed and recovered. The devolatilized polymer melt is then extruded by a screw extruder, pelletized by an underwater pelletizer, and dehydrated by a centrifugal dewatering machine to obtain finished polymer granules. This method can be used for the devolatilization of high melt flow index, high transparency, and low water content lithium-based polymer solutions, and the resulting polymer volatile content is ≤0.5% (mass fraction). The granules or cobblestone-like particles are easy for downstream processing applications. This process is simple, low-cost, can be manufactured using existing mature equipment and processes, and is easy to control and industrialize.

Description

Technical Field

[0001] This invention relates to a post-treatment method for polymer adhesives, and particularly to a dry devolatilization process for high melt index and high transparency lithium-based polymer adhesives, belonging to the field of rubber elastomer material preparation technology. Background Technology

[0002] Synthetic rubber production methods include suspension emulsion polymerization, gas-phase polymerization, and solution polymerization, with solution polymerization currently being the dominant technology in global rubber production. In the traditional lithium-based solution copolymerization of styrene-conjugated diene elastomers (SBCs) such as SBS, SIS, SEBS, SEPS, and ethylene propylene rubber, the solvent is typically removed from the polymer using steam condensation, commonly known as "wet devolatilization." Currently, commercially available styrene-butadiene copolymer transparent resins (KR-01 and KR03) also employ heated screw compressors to remove volatile solvents and then granulate (commonly known as dry devolatilization).

[0003] Existing lithium-based polymers are typically produced via wet devolatilization. The solvent, cyclohexane, and water vapor in the polymer or hydride solution are azeotropically condensed in a 98–100°C coagulation reactor. The recovered solvent must be further refined and dehydrated to a water content <20 mg / kg before recycling. This necessitates the addition of post-processing equipment such as coagulation, solvent recovery and refining, particle extrusion dehydration, and oven drying. For molecular weights <8 × 10⁻⁶... 4 Polymer compounds with a melt flow index higher than 12 g / 10 min tend to stick, clump, and clog equipment in coagulation reactors, conveying machinery, pipelines, drying ovens, and woks. Furthermore, wet devolatilization cannot meet the requirements for transparent polymers because organic polymers have barrier properties, making it difficult to remove trace amounts of water remaining in the polymer through drying, resulting in reduced transparency. In general, wet devolatilization of anionic styrene-diene polymers involves numerous equipment, a long process flow, a large footprint, a poor operating environment, wastewater generation, high energy consumption, and significant investment.

[0004] In existing technology (“Research on Wet Deviation Process of Ethylene-Propylene Rubber”, 2010, Chemical Technology), it is disclosed that ethylene-propylene rubber (J-2070) latex was subjected to hydrocondensation and vapor condensation, followed by extrusion devolatilization. The w (total volatile matter) of the extruded sample was <0.5%. Within the extruder speed range of 50–120 r / min, the extruded sample did not degrade, indicating that the devolatilization process is feasible and meets the requirements for ethylene-propylene rubber devolatilization. Chinese Patent (CN108840979A) discloses a SEPS elastomer and its preparation method. The method uses a pre-hydrogenation reaction base latex of polystyrene-polyisoprene-polyethylene block copolymer, which is concentrated by flash evaporation and then directly devolatilized by dry process to obtain the SEPS elastomer. The SEPS elastomer prepared by this method...

[0005] In recent years, with economic development, the demand for high melt flow index and high transparency resin materials has increased. Traditional transparent resins, including polystyrene, polymethyl methacrylate, polycarbonate, styrene-acrylonitrile resin, K resin, EPDM rubber, polyolefin elastomers, and high melt flow index and high transparency polystyrene-diolefin elastomers (SBC), all have limitations in removing volatiles using wet processes. In particular, high melt flow index and high transparency anionic polymeric polystyrene-diolefin elastomers such as SBS, SIS, and hydrogenated SEBS, along with their manufacturing processes, are proprietary technologies of major manufacturers. Summary of the Invention

[0006] Existing technologies for removing volatiles from polystyrene-diolefin elastomers (SBCs) using wet volatile removal technology suffer from drawbacks such as numerous post-processing equipment, long process flow, high product haze, opacity, easy equipment clogging, large footprint, poor operating environment, wastewater generation, high energy consumption, and large investment.

[0007] The purpose of this invention is to provide a devolatilization process for lithium-based polymers (SBC) and hydride polymers (HSBC) with high melt index, high transparency, and low water content. This process is also suitable for the devolatilization of polymers with low or no melt index. The prepared polymer has a volatile content of ≤0.5% (mass fraction) and appears as granules or coarse pellets, which is convenient for downstream processing applications. This process is simple, low in cost, can be produced using existing mature equipment and processes, and is easy to control and industrialize.

[0008] To achieve the above-mentioned technical objectives, this invention provides a devolatilization process for high melt flow index and high transparency lithium-based polymer solutions. The process involves feeding a dilute polymer solution into a falling film evaporator for initial evaporation. The resulting gas enters a condenser from the top of the falling film evaporator for condensation, recovering the solvent. The concentrated polymer solution obtained from evaporation enters a twin-screw extruder from the bottom of the falling film evaporator. The concentrated polymer solution is heated and volatilized in the twin-screw extruder. The volatilized gas is sequentially drawn into a pre-condenser and a post-condenser for condensation, recovering the solvent. The polymer melt obtained after solvent volatilization is then extruded by a screw extruder, pelletized by an underwater pelletizer, and dehydrated by a centrifugal dewatering machine to obtain the finished polymer granules.

[0009] The technical solution of this invention involves feeding a dilute adhesive solution into a falling film evaporator. The solution is distributed by a distributor located at the top of the evaporator, forming a thin layer on a semi-circular sieve plate within the evaporator, creating a "sprinkler" effect. The falling film evaporator is jacketed and heated using steam as the heating medium. A large amount of solvent in the dilute adhesive solution is evaporated. Simultaneously, the partially solvent-free solution flows under gravity to the next semi-circular sieve plate for further solvent evaporation. This process is repeated, and the evaporated gases (including solvent gases or...) are... The water vapor formed from the moisture used to terminate the adhesive solution is condensed by a condenser and then flows into a condenser tank. This process continues until the solid content of the adhesive solution reaches the required set amount. The concentrated adhesive solution enters the inlet of a twin-screw devolatilizer from the bottom of the falling film evaporator. In the twin-screw extruder, the concentrated adhesive solution is heated, and the residual solvent in the concentrated solution is forcibly extracted from the gas phase outlet of the twin-screw extruder under certain temperature and vacuum conditions, entering the pre-condenser. The condensed solvent enters the pre-condenser tank, while a small amount of uncondensed solvent or water is sent to the post-condenser by a Roots vacuum pump. The condensed solvent then enters the post-condenser tank. Simultaneously, the solvent-removed polymer melt is extruded by a twin-screw extruder, underwater pelletized, centrifuged for dehydration, and conveyed to the finished product silo via a vibrating screen to obtain the granules.

[0010] The key to achieving high melt index and high transparency lithium-based polymer solution de-drifting in this invention lies in the combined process of falling film evaporation tower pre-concentration and twin-screw extrusion. The falling film evaporation tower pre-concentration process avoids the formation of glue residue and agglomeration in high melt index polymers, and can efficiently and continuously pre-concentrate the dilute solution. The twin-screw extrusion can achieve deep de-drifting, ensuring that the w (total volatile matter) of the extruded sample is <0.5%, avoiding residual solvent from affecting the transparency of the polymer. At the same time, the twin-screw extrusion has the characteristic of high production capacity.

[0011] As a preferred embodiment, the falling film evaporator is a vertical structure with a length-to-diameter ratio (L / D) of 10–15. The inner wall of the falling film evaporator is equipped with multiple large semi-circular sieve plates. The distance from the chord center of each semi-circular sieve plate to the inner wall is 1 / 5 to 1 / 4 of the diameter of the falling film evaporator. Any two adjacent large semi-circular sieve plates are arranged in a reverse symmetrical and uniform manner, with a spacing of 300–350 mm between them. It is worth further noting that the falling film evaporator employs a multi-layer sieve plate structure. Under gravity, the adhesive gradually evaporates in a thin layer on the sieve plates from top to bottom without the solvent undergoing explosive boiling. The adhesive gradually concentrates during its downward flow, resulting in a short residence time and preventing overheating, thus avoiding gel formation due to prolonged or overheated conditions. Furthermore, the use of a falling film evaporator for adhesive concentration allows for continuous operation, which is beneficial for large-scale production and operation.

[0012] As a preferred embodiment, the semi-circular sieve plate has sieve holes with a diameter of Φ = 7 to 12 mm evenly distributed, and the center distance between any two adjacent sieve holes is 16 to 24 mm.

[0013] As a preferred embodiment, the dilute adhesive solution is fed into the top of the falling film evaporator. After being evenly distributed by a distributor, it forms a film layer on the first semi-circular sieve plate. Under the action of heating and gravity, the solvent in the film layer evaporates, and the dilute adhesive solution with partially evaporated solvent flows to the next semi-circular sieve plate for further evaporation. This process is repeated to control the solid content of the concentrated adhesive solution entering the twin-screw extruder to be 45-55%. If the solid content of the concentrated adhesive solution is too low, the processing load of the subsequent twin-screw extruder will be too high, and the efficiency of vacuum extraction of solvent and condensation recovery will be low. If the solid content of the concentrated adhesive solution is too high or the melt conveying temperature is too low, the melt flow performance will be poor, making conveying difficult and making it difficult to enter the twin-screw devouring extruder.

[0014] As a preferred embodiment, the solid content of the diluted adhesive solution is 8-14%. Generally, the solvent used in anionic polymeric adhesive solutions is cyclohexane (boiling point 80°C, and azeotropic with water). Traditional intermittent batch evaporation and concentration methods are inefficient; the polymer is first heated on the jacketed heating vessel wall or the surface of the heated coil, and is subjected to prolonged heating, leading to thermal polymerization of double bonds in the polymer molecules, resulting in crosslinking and gelation; it is also unfavorable for continuous dry devolatilization methods.

[0015] As a preferred embodiment, the steam pressure inside the falling film evaporator is 1-2 bar, the temperature is 80-90°C, and the operating pressure inside the falling film evaporator is atmospheric pressure.

[0016] As a preferred embodiment, the twin-screw extruder has a total screw length-to-diameter ratio (L / D) of 42 to 58, and the extrusion chamber is divided into 9 sections from the inlet to the die. Among them, the screw length-to-diameter ratio of the first section is L / D of 10 to 12, the screw length-to-diameter ratio of the second, third, fourth, fifth, sixth, seventh, and eighth sections is L / D of 4 to 5, and the fourth, fifth, sixth, seventh, and eighth sections are all provided with gas phase outlets.

[0017] As a preferred embodiment, the parameters of the twin-screw extruder are controlled as follows: die pressure 3.0–5.0 MPa, die temperature 160–185°C, temperature distribution from low to high in each section, with each section ranging from 80–185°C, extruder speed 90–150 r / min, and melt residence time 3–5 min. This preferred parameter control ensures that the w (total volatile matter) of the extruded sample is <0.5%.

[0018] As a preferred embodiment, the gases volatilized by heat in the twin-screw extruder are extracted by a Roots vacuum pump and sequentially condensed in the pre-condenser and post-condenser. The vacuum level inside the extrusion chamber of the twin-screw extruder is -0.3 to -0.5 bar. If the vacuum level is too high, the solvent is not easily condensed and recovered from the condenser. Using a Roots vacuum pump to remove the small amount of solvent gas removed from the twin-screw extruder will not damage the Roots vacuum pump. However, using a commonly used vacuum pump to pump out gases and small amounts of moisture can damage the vacuum pump piston.

[0019] As a preferred embodiment, the heat transfer medium used in both the pre-condenser and post-condenser is industrial water at 5–20°C. Both the pre-condenser and post-condenser operate at atmospheric pressure. Each is equipped with a condenser tank. Both the condenser and the condenser tank are equipment well-known to those skilled in the chemical industry.

[0020] The underwater pelletizer of this invention uses cooling water that is reused through a circulation system, and the recovered solvent is sent to the polymerization unit for recycling.

[0021] The falling film evaporator of this invention uses a jacketed steam heating system.

[0022] The twin-screw extruder of this invention is derived from the continuous horizontal devouring extruder of Jiangsu Chengmeng Equipment Company.

[0023] The twin-screw heating method of the present invention is electric heating.

[0024] The underwater pelletizer, granule centrifugal dewatering machine, vibrating screen, finished product silo, and water circulation system of this invention are all equipment well-known to those in the chemical industry.

[0025] Compared with existing wet devolatilization technologies, the technical solution of this invention offers the following advantages:

[0026] Compared to existing wet devolatilization technologies, the dry devolatilization equipment and process of this invention offer several advantages for lithium-based polymers, including fewer post-processing devices, a shorter process flow, smaller footprint, less clogging of equipment and pipelines, a better operating environment, no need for barrier agents (such as calcium stearate and other inorganic powders) for underwater pellets, no wastewater generation, low energy consumption, low investment, transparent products, and pellet moisture content of less than 0.5%. Apart from a falling film evaporator and a twin-screw extruder, it eliminates the need for large-scale equipment such as wet-process extrusion dehydrators (SDUs), drying ovens, and liquid water vapor condensation systems. Furthermore, dry devolatilization pellets are more suitable for blending with polyolefin resins; the recovered solvent moisture content is <20mg / Kg, and the solvent recovery rate is >97%, allowing for direct use as a polymerization solvent, thus saving energy.

[0027] The falling film evaporation-twin-screw extrusion combined devolatilization process of the present invention has advantages such as good operational flexibility, high processing capacity and efficiency, and is easy to control and adjust.

[0028] Except for the falling film evaporator and the twin-screw extruder, which require special design, the other equipment in this invention are all general equipment used in the chemical industry. Overall, the equipment is not complicated and can be designed using existing experience, making it easy to industrialize. Attached Figure Description

[0029] Figure 1 The present invention provides a combined dry devolatilization process using falling film evaporation and twin-screw extrusion.

[0030] Figure 2 This is the existing dual-machine dry devolatilization process. Detailed Implementation

[0031] The present invention will be further described in detail with reference to the following specific embodiments, which do not constitute a limitation on the scope of protection of the claims or the implementation method of the present invention.

[0032] The volatile matter content of rubber was determined according to GB2958-82.

[0033] Mooney viscosity was determined according to GB / T 1232-1992.

[0034] The devolatilization process of the high melt flow index and high transparency lithium-based polymer solution of the present invention is as follows: Figure 1 .

[0035] The devolatilization process of this invention mainly includes a falling film evaporation unit and a granulation unit. The falling film evaporation unit mainly consists of a falling film evaporation tower, a condenser, and a condensation tank. The granulation unit includes a twin-screw extruder, an underwater pelletizer, a pellet centrifugal dewatering machine, a vibrating screen, a finished product silo, and a water circulation system. The twin-screw extruder also has a solvent recovery assembly, including a pre-condenser, a pre-condensation tank, a vacuum pump, a post-condenser, and a post-condensation tank.

[0036] The specific devolatilization process of the high melt flow index and high transparency lithium-based polymer adhesive of this invention is as follows: The dilute adhesive is fed into the falling film evaporator from the top. Under pressure, it is distributed by a distributor, forming a thin layer evenly on the first semi-circular sieve plate within the evaporator. The falling film evaporator is heated by jacketed steam, causing a large amount of solvent in the adhesive to evaporate. Simultaneously, the adhesive flows to the next semi-circular sieve plate under gravity to continue solvent evaporation. This process is repeated. The evaporated solvent gas or adhesive is then removed by water vaporization. Water vapor is output from the top of the falling film evaporator. After condensation in the condenser, the liquid is recovered and sent to the condenser tank until the solid content of the adhesive reaches the required set amount. The concentrated adhesive enters the inlet of the twin-screw extruder from the bottom of the falling film evaporator. The concentrated adhesive evaporates under heat in the extrusion chamber of the twin-screw extruder. The evaporated solvent is forcibly extracted from the gas phase outlet of the twin-screw extruder by a vacuum pump and first enters the pre-condenser. The condensed solvent is recovered and sent to the pre-condenser tank. The small amount of uncondensed solvent or water is sent to the post-condenser by a Roots vacuum pump. The condensed solvent is recovered and sent to the post-condenser tank. The devolatilized polymer melt is then extruded by a twin-screw extruder, underwater pelletized, centrifuged for dehydration, and conveyed to the finished product silo by a vibrating screen to obtain polymer granules.

[0037] Example 1

[0038] Select Figure 1 The dry devolatilization process for lithium-based polymers was used to devolatilize 14.6% polystyrene-isoprene block copolymer SIS-1106. The SIS-1106 solution containing cyclohexane solvent came from the SIS workshop of the synthetic rubber plant of Sinopec Baling Petrochemical Company.

[0039] The selected falling film evaporator has an inner diameter of 0.4m and a height of 4.0m. It is equipped with an external jacket for steam heating. The chord center point of the sieve plate is 80mm away from the wall of the falling film evaporator. The diameter of the sieve holes on the sieve plate is Φ7mm, the spacing between the holes is 16mm, and the distance between the upper and lower sieve plates is 300mm.

[0040] The twin-screw devourer was selected as the TSD-65 devourer manufactured by Jiangsu Chengmeng Equipment Co., Ltd. The main motor is 55kw with a maximum output speed of 300rpm. The screw outer diameter is Φ61.5mm, the barrel inner diameter is φ=62mm, the screw length-to-diameter ratio is L / D=42, and the barrel is composed of 8 sections connected in series, including 5 sections of vacuum exhaust cylinder.

[0041] The heat transfer area of ​​the condensers used for solvent recovery is 4m². 2 All other equipment is standardized and manufactured according to specifications.

[0042] First, the falling film evaporator is preheated with steam at 1.4 bar for 20 minutes. Then, a screw pump is used to send the glue solution with a volumetric flow rate of 950 L / h to the distributor at the top of the falling film evaporator. The pressure inside the tower is maintained at atmospheric pressure and the temperature at 85°C. The residence time of the glue solution is 22 minutes. The evaporated cyclohexane gas enters the condenser from the top of the tower for recovery. The concentration of the pre-concentrated glue melt entering the twin-screw inlet from the bottom of the tower is 51.8% (mass fraction).

[0043] The TSD-65 devourer uses an electric heating and temperature control system to control the temperature of each zone. The temperatures at the feed inlet, zones 1-8, 1-8, 1-2, 1-3, 1-4, 1-5, 6-7, 1-8, and the die head are set to 80℃, 90℃, 100℃, 115℃, 130℃, 145℃, 160℃, 165℃, 170℃, and 180℃, respectively. Zones 4-8 each have five gas phase outlets. The screw speed is 180 rpm, the melt residence time is 180 seconds, and the die head pressure is 4.0 MPa. The Roots suction vacuum is -0.38 bar. The heat transfer area of ​​each condenser is 4 m². 2 The molten pellets are cooled by circulating water at 20°C; the underwater pelletizer uses circulating water at 20°C to cool the pellets.

[0044] As a result, the prepared SIS-1106 elastomer was a transparent, flat granule with a volatile content of 0.42% (by weight), a melt index of 14.63 g / 10 min, a yield of 124.8 kg / h, a cyclohexane recovery rate of 98.4%, and a water content of 18.5 mg / kg.

[0045] Example 2

[0046] The equipment and process conditions in Implementation 1 remain unchanged, except that the SBS-805 adhesive solution with a dry adhesive mass fraction of 12.4% in cyclohexane (of which the dry adhesive mass fraction is 34% cyclohexane oil KN4010) is used. The adhesive solution comes from the SBS workshop of the synthetic rubber plant of Sinopec Baling Petrochemical Company, and the flow rate of the SBS-805 adhesive solution entering the top of the falling film evaporator is 750L / h.

[0047] As a result, the concentration of the pre-concentrated gel melt entering the twin-screw inlet from the bottom of the tower was 53.2% (mass fraction); the die head pressure was 4.0 MPa; the prepared SBS-805 oil-extended gel was a transparent granule; the volatile matter content was measured to be 0.49% (by weight); the melt index was 2.87 g / 10 min; the yield was 123.7 kg / h; the cyclohexane recovery rate was 97.6%; and the water content was 18.5 mg / kg.

[0048] Example 3

[0049] The equipment and process conditions in Implementation 1 remain unchanged, except that the SBS-788 adhesive solution with a dry adhesive mass fraction of 16.7% in cyclohexane is used. The adhesive solution comes from the SBS workshop of the synthetic rubber plant of Sinopec Baling Petrochemical Company. The flow rate of the adhesive solution entering the top of the falling film evaporator is 950 L / h, and the screw speed is 210 rpm.

[0050] As a result, the concentration of the pre-concentrated gel melt entering the twin-screw inlet from the bottom of the tower was 55.8% (mass fraction), the die head pressure was 4.2 MPa, the prepared SBS-788 elastomer was a transparent granule, the volatile matter was measured to be 0.38% (by weight), the melt index was 10.63 g / 10 min, the yield was 139.8 kg / h, the cyclohexane recovery rate was 97.2%, and the water content was 18.4 mg / kg.

[0051] Comparative Example 1

[0052] The SIS-1106 adhesive, TSD-65 devolatilizer, and related process conditions in Example 1 remain unchanged. The only difference is that the pre-concentration unit of the falling film evaporator is replaced with an SCP devolatilizer (concentrator). The barrel has an inner diameter of 320mm, a double-jacketed design, and is internally steam-flushed. The barrel consists of two sections connected in series, with a length-to-diameter ratio (L / D) of 7:1. It features dual rotors rotating at different speeds in the same direction, controlled by a frequency converter, with a maximum speed of 50rpm. The barrel has two vacuum exhaust chambers connected to a vacuum condensation system via vacuum pipes and valves. See the flowchart for details on the dual-machine setup. Figure 2 The entire equipment was manufactured by Jiangsu Chengmeng Equipment Company and assembled at the Sinopec Baling Petrochemical Company's synthetic rubber plant.

[0053] The results showed that the TSD deep devolatilization twin-screw pelletizer had a die pressure of only 1.6 MPa, produced 60.2 kg / h of transparent SIS-1106 pellets, had a maximum feed rate of 468 L / h for the SCP devolatilization reaction concentrater to SIS-1106 solution, a maximum solution concentration of 32.8% (by weight), and a maximum discharge rate or feed rate to the TSD unit of 199.5 L / h; the solvent recovery rate was 91.4%.

Claims

1. A devolatilization process for a high melt index high transparency lithium polymer dope, characterized by: The diluted adhesive solution is fed into a falling film evaporator for initial evaporation. The resulting gas enters a condenser from the top of the evaporator for condensation and solvent recovery. The concentrated adhesive solution enters a twin-screw extruder from the bottom of the evaporator. The concentrated adhesive solution is heated and evaporated in the twin-screw extruder. The evaporated gas is sequentially drawn into a front condenser and a rear condenser for condensation and solvent recovery. The polymer melt obtained after solvent evaporation is extruded by a screw extruder, pelletized by an underwater pelletizer, and dehydrated by a centrifugal dehydrator to obtain finished adhesive granules. The falling film evaporator has a vertical structure with a length-to-diameter ratio L / D = 10~15. The vertical inner wall of the falling film evaporator is equipped with multiple large semi-circular sieve plates. The distance from the chord center of each large semi-circular sieve plate to the inner wall of the tower is 1 / 5 to 1 / 4 of the diameter of the falling film evaporator. Any two large semi-circular sieve plates are arranged in a reverse symmetrical and uniform manner, and the distance between any two large semi-circular sieve plates is 300~350mm. The dilute adhesive solution is fed into the top of the falling film evaporator. After being evenly distributed by the distributor, it is uniformly distributed on the first semi-circular sieve plate to form a film layer. Under the action of heating and gravity, the solvent in the film layer evaporates. At the same time, the dilute adhesive solution with some solvent evaporated flows to the next semi-circular sieve plate to continue evaporating. This process is repeated to control the solid content of the concentrated adhesive solution entering the twin-screw extruder to be 45-55%.

2. The devolatilization process of a high-melt-index high-transparency lithium polymer glue solution according to claim 1, characterized in that: The semi-circular sieve plate has sieve holes with a diameter of Φ=7~12mm evenly distributed, and the center distance between any two adjacent sieve holes is 16~24mm.

3. The devolatilization process of a high-melt-index high-transparency lithium polymer glue solution according to claim 1, characterized in that: The solid content of the diluted adhesive solution is 8-14%.

4. The devolatilization process of a high-melt-index high-transparency lithium polymer glue solution according to claim 1, characterized in that: The steam pressure inside the falling film evaporator is 1~2 bar, the temperature is 80~90℃, and the operating pressure inside the falling film evaporator is atmospheric pressure.

5. The devolatilization process of a high-melt-index high-transparency lithium polymer glue solution according to claim 1, characterized in that: The twin-screw extruder has a total screw length-to-diameter ratio (L / D) of 42 to 58, and the extrusion chamber is divided into 9 sections from the inlet to the die. The screw length-to-diameter ratio of the first section is 10 to 12, and the screw length-to-diameter ratios of the second, third, fourth, fifth, sixth, seventh, and eighth sections are all 4 to 5. Gas phase outlets are provided in the fourth, fifth, sixth, seventh, and eighth sections.

6. The devolatilization process for a high melt flow index and high transparency lithium-based polymer solution according to claim 1, characterized in that: The parameters of the twin-screw extruder are controlled as follows: die pressure 3.0–5.0 MPa, die temperature 160–185 °C, temperature distribution of each section from low to high, temperature range of each section from 80 to 185 °C, extruder speed 90–150 r / min, and melt residence time 3–5 min.

7. The devolatilization process for a high melt flow index and high transparency lithium-based polymer solution according to claim 1, characterized in that: The gas that evaporates due to heat in the twin-screw extruder is extracted by a Roots vacuum pump and sequentially condensed in the front condenser and the rear condenser. The vacuum degree in the extrusion chamber of the twin-screw extruder is -0.3 to -0.5 bar.

8. The devolatilization process for a high melt flow index and high transparency lithium-based polymer solution according to claim 1, characterized in that: The heat transfer medium used in the pre-condenser and post-condenser is industrial water at 5~20℃.

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