Apparatus and method for continuous production of regenerated cellulose film by slot extrusion

Abstract

The present application relates to the field of thin film preparation, and provides a device and method for continuously preparing regenerated cellulose film by slit extrusion, the device comprising: a dissolving unit (1), a film forming unit (2), and a thin film post-processing unit (7); the dissolving unit (1) is used for preparing a cellulose solution for preparing a thin film; the film forming unit (2) comprises a slit die (201) and a coagulation bath (202), the cellulose solution is extruded from the slit die (201) and enters the coagulation bath (202), and a regenerated cellulose gel is prepared by coagulation; the thin film post-processing unit (7) is used for cleaning, modifying and drying the regenerated cellulose hydrogel to prepare a regenerated cellulose film; and the slit die (201) can be controlled in temperature. The device of the present application can be used for preparing a regenerated cellulose film, precisely controlling the thickness of the thin film, and preparing a thin film with uniform and smooth thickness. The device of the present application can be used for continuously preparing a cellulose film and improving the preparation efficiency of the cellulose film.

Description

Technical Field

[0001] This invention relates to the field of film preparation, and more specifically to an apparatus and method for continuous preparation of regenerated cellulose films by slot extrusion. Background Technology

[0002] Regenerated cellulose film, also known as cellophane or glassine film, is a type of regenerated cellulose film made from natural cellulose such as cotton pulp and wood pulp through an adhesive process. It differs from ordinary paper in that it is not only flexible but also has a transparency similar to glass, hence the name "cellophane." It is mainly used in food packaging, tobacco packaging, pharmaceutical packaging, cosmetic packaging, fireworks packaging, and express delivery packaging, and is considered a low-carbon, environmentally friendly packaging material [China Paper Industry Research Center, China Paper, 38(11)]. Cellulose molecules have extremely strong hydrogen bonds both between and within molecules, making it insoluble in common solvents and difficult to utilize directly.

[0003] Currently, commonly used solvents for dissolving cellulose include copper ammonia, NaOH / CS2, LiCl / DMAc, ionic liquids, N-methylmorpholine-N-oxide (NMMO), and alkali / urea aqueous solvent systems.

[0004] Because the solvent in cellulose solutions is difficult to evaporate, wet forming methods are commonly used in the preparation of regenerated cellulose membranes, such as unidirectional casting, blade coating, and blown film. However, unidirectional casting and blade coating are time-consuming and inefficient, requiring slow coagulation and forming in a mild coagulation bath, and it is difficult to avoid wasting cellulose solution, making them more suitable for laboratory use.

[0005] Li Ruifeng, Gao Shanshan, and others used an extrusion blown film forming method to prepare regenerated cellulose membranes. The cellulose NMMO solution was filtered, heated to 80–100°C, and then subjected to degassing, pressurization, and air blowing before being conveyed to a blown film machine. The membrane then passed through an air gap into a coagulation bath. In the coagulation bath, different biaxially oriented films with varying properties could be obtained by changing the stretching rate and blow-up ratio. The films were then folded into webs by winding rollers, and finally formed through processes such as washing, post-treatment, and drying. Summary of the Invention

[0006] The purpose of this invention is to overcome the problems of long processing time, low efficiency, limited applicability, and poor film thickness uniformity and flatness in existing technologies. It provides an apparatus for the continuous preparation of regenerated cellulose membranes. Using this apparatus, the thickness of the regenerated cellulose membrane can be precisely controlled, resulting in a uniform and flat membrane. The apparatus enables continuous preparation of cellulose membranes, improving the efficiency of cellulose membrane production.

[0007] To achieve the above objectives, the first aspect of the present invention provides an apparatus for continuous preparation of regenerated cellulose membranes by slot extrusion, the apparatus comprising: a dissolution unit, a film forming unit, and a film post-treatment unit.

[0008] Preferably, the dissolution unit is connected to the film-forming unit via a pipe.

[0009] Preferably, a delivery pump and / or metering pump are also included between the dissolving vessel and the slit mold head.

[0010] Preferably, the dissolving unit includes a dissolving vessel and a stirrer, the stirrer being used to uniformly mix the materials in the dissolving vessel, and the dissolving unit being used to prepare a cellulose solution for preparing a film.

[0011] Preferably, the film-forming unit includes a slit die and a coagulation bath, wherein the cellulose solution is extruded from the slit die and enters the coagulation liquid in the coagulation bath to be transformed into a regenerated cellulose hydrogel.

[0012] Preferably, the coagulation bath is configured to be corrosion-resistant.

[0013] Preferably, the film post-processing unit cleans, modifies, dries, and winds up the cellulose hydrogel to obtain a cellulose film.

[0014] The slit die head includes an upper die body, a lower die body, fluid channel I, fluid channel II, a feed pipe, a die cavity, and a die lip.

[0015] The upper mold body and the lower mold body are connected to form a slit mold head.

[0016] A groove is provided on the connecting surface of the lower membrane body and the upper mold body to serve as the mold cavity for storing cellulose solution.

[0017] The feed pipe is used to supply cellulose solution into the mold cavity.

[0018] The connecting surfaces of the upper mold body and the lower mold body at the outlet area along the length direction are each provided with an upper mold lip and a lower mold lip, and the gap between the upper mold lip and the lower mold lip serves as the discharge port of the slit mold head.

[0019] The gap between the upper and lower die lips can be adjusted by moving the lower die lip vertically.

[0020] Fluid channels I and II are respectively provided along the length of the upper mold body and the lower mold body. The temperature of the slit mold head is controlled by the flow of high and low temperature media in fluid channels I and fluid channels II.

[0021] Preferably, the dissolving vessel, pipes, and coagulation bath are equipped with heat-insulating jackets.

[0022] Preferably, the temperatures of the melting vessel, coagulation bath, and pipelines are controlled by circulating high and low temperature media within the insulation jacket.

[0023] Preferably, the film post-processing unit includes a stretching unit for stretching modification of cellulose hydrogel; the stretching unit includes a stretching groove, stretching rollers I and II disposed within the stretching groove for stretching modification of the regenerated cellulose hydrogel within the stretching groove, and transfer pressure rollers III and IV disposed outside the stretching groove with adjustable vertical distance for the cellulose hydrogel; the stretching groove is configured to be corrosion resistant.

[0024] Preferably, the film post-processing unit includes a cleaning unit for washing away impurities remaining in the cellulose hydrogel; the cleaning unit includes stretching roller III, stretching roller IV and a cleaning tank; the cleaning tank is configured to be corrosion resistant.

[0025] Preferably, the film post-processing unit includes a drying unit for drying the cellulose hydrogel; the drying unit includes a five-section hot air drying chamber and a multi-roller assembly.

[0026] Preferably, the five-section hot air drying oven is configured to have separate temperature and humidity control for each section; more preferably, each section of the five-section hot air drying oven is configured to have a temperature control range of 20–180°C and a humidity control range of 5–100%.

[0027] Preferably, the film post-processing unit includes a winding unit for winding the regenerated cellulose film.

[0028] The winding unit includes pressure rollers V and VI, a transfer roller, and a take-up roller; the transfer roller can move vertically up and down to adjust the take-up angle.

[0029] A second aspect of the present invention provides a method for continuous preparation of regenerated cellulose membranes by slot extrusion, the method being carried out in the aforementioned apparatus, the method comprising:

[0030] S1. Place cellulose in dissolving vessel 101, add solvent, stir to dissolve cellulose, and obtain cellulose solution. Degas under vacuum.

[0031] S2. The cellulose solution enters the slit mold 201 and is injected into the coagulation bath 202, where it coagulates in the coagulant to obtain regenerated cellulose gel.

[0032] S3. Regenerated cellulose gel is prepared by stretching unit 3 and washing unit 4 to obtain regenerated cellulose hydrogel.

[0033] S4. The regenerated cellulose hydrogel is dried in the drying unit 5 to obtain a regenerated cellulose membrane; it is then wound up in the winding unit 6.

[0034] Preferably, the concentration of the cellulose solution is 4–20 wt%.

[0035] Preferably, the degree of polymerization of the cellulose is 200 to 1000.

[0036] Preferably, the temperature difference between the dissolution unit 1 and the film-forming unit 2 is controlled to be less than or equal to 30°C; the stretching ratio during the stretching process of the cellulose hydrogel is controlled to be 1:1 to 1:5.

[0037] Preferably, the solvent is one or more of sodium hydroxide solution, copper ammonia solution, NaOH / CS2 solution, alkali / urea solution, and NaOH / thiourea solution; preferably, it is an alkali / urea solution; more preferably, the alkali / urea solution is an aqueous solution of NaOH and urea.

[0038] Preferably, the NaOH and urea aqueous solution comprises: 4-8 wt% NaOH, 10-14 wt% urea, and 78-85 wt% water;

[0039] Preferably, the coagulant is one or more of pure water, ethanol, ethylene glycol, DMSO, hydrochloric acid, sulfuric acid, acetic acid, phosphoric acid, citric acid, phytic acid, and benzoic acid; preferably, it is an aqueous solution of 10-20% acid; more preferably, it is an aqueous solution of 10-20 wt% citric acid.

[0040] Preferably, the drying temperature of the regenerated cellulose hydrogel is 40–65°C; more preferably, a stepped heating drying method is used.

[0041] Preferably, the thickness of the regenerated cellulose hydrogel is 0.01–3 mm; more preferably, it is 1–2 mm.

[0042] Preferably, the thickness of the regenerated cellulose membrane is 0.01–1 mm; more preferably, it is 0.03–0.1 mm.

[0043] The apparatus for continuous and rapid preparation of regenerated cellulose membranes provided by this invention integrates dissolution, extrusion, coagulation, stretching, washing, drying and winding into a continuous process. It has high production efficiency, short production time, and allows for easy adjustment and optimization of each process stage. It is widely applicable to cellulose solution systems of different viscosities.

[0044] The cellulose membrane prepared using the above-mentioned device has the advantages of high efficiency, precise control of membrane thickness and width, and uniform and flat membrane thickness. Attached Figure Description

[0045] Figure 1 A simplified diagram of an apparatus for the continuous preparation of regenerated cellulose membranes provided in an embodiment of the present invention;

[0046] Figure 2 A front view of the slit mold head provided for an embodiment of the present invention;

[0047] Figure 3 This is a cross-sectional view of the slit die head of the present invention.

[0048] Explanation of reference numerals in the attached figures

[0049] 1—Dissolution unit 2—Film forming unit

[0050] 3—Stretching unit 4—Cleaning unit

[0051] 5—Drying unit; 6—Winding unit

[0052] 7—Thin Film Post-Processing Unit 101—Dissolving Vessel

[0053] 102—Agitator; 105—Metering pump

[0054] 106—Pipeline 201—Slit Die

[0055] 202—Coagulation bath 203—Pair of pressure rollers I

[0056] 204—Pressure roller II; 205—Upper film body

[0057] 206—Lower mold body; 207—Fluid channel I

[0058] 208—Fluid Channel II 209—Infeed Pipe

[0059] 210—Mold cavity 211—Lower mold lip

[0060] 212—Drafting roller; 213—Upper die lip

[0061] 301—Drafting groove; 302—Drafting roller I

[0062] 303—Drafting Roller II 401—Washing Tank

[0063] 304—Pair of pressure rollers III; 305—Pair of pressure rollers IV

[0064] 402—Drafting Roller III 403—Drafting Roller IV

[0065] 501—Five-section hot air drying oven; 502—Multi-roller unit

[0066] 601—Pair of pressure rollers V 602—Pair of pressure rollers VI

[0067] 603—Transfer roller; 604—Take-up roller Detailed Implementation

[0068] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0069] The first aspect of this invention provides an apparatus for the continuous preparation of regenerated cellulose membranes by slot extrusion, such as... Figure 1 As shown, the device includes: a dissolution unit 1, a film forming unit 2, and a film post-processing unit 7;

[0070] The dissolution unit 1 is connected to the film extrusion unit via pipe 106.

[0071] The dissolution unit 1 is used to prepare the cellulose solution for the preparation of the film.

[0072] According to one embodiment of the present invention, the cellulose dissolving unit 1 includes a dissolving vessel 101 and a stirrer 102; the dissolving vessel 101 also includes a vacuum port, a quick-opening feed port, and a nitrogen inlet; the vessel body is pressure resistant to 2 MPa. Using this dissolving vessel 101 to prepare the cellulose solution, air bubbles in the cellulose solution can be removed by vacuuming; nitrogen gas is introduced through the nitrogen inlet to transport the cellulose solution into the film-forming unit 2.

[0073] According to one embodiment of the present invention, the film-forming unit 2 includes a slit die 201 and a coagulation bath 202. The cellulose solution is extruded from the slit die 201 and enters the coagulation liquid in the coagulation bath 202 to be transformed into a cellulose hydrogel.

[0074] According to one embodiment of the present invention, the dissolving vessel 101, the coagulation bath 202, and the pipe 106 are provided with heat-insulating jackets; the temperature of the dissolving vessel 101, the coagulation bath 202, and the pipe 106 is controlled to be -35 to 200°C by circulating a high- and low-temperature medium in the heat-insulating jackets. This embodiment ensures consistent temperature control throughout the process from obtaining the cellulose solution to preparing the regenerated cellulose membrane.

[0075] According to one embodiment of the present invention, a delivery pump and / or a metering pump 105 are further provided between the dissolving vessel 101 and the slit die 201; the delivery pump delivers the cellulose solution to the slit die 201, and the metering pump 105 can realize the quantitative and stable delivery of the cellulose solution.

[0076] According to one embodiment of the present invention, such as Figure 2 , Figure 3As shown, the slit die head 201 includes an upper die body 205, a lower die body 206, a fluid channel I 207, a fluid channel II 208, a feed pipe 209, a die cavity 210, a lower die lip 211, and an upper die lip 213.

[0077] The upper mold body 205 and the lower mold body 206 are connected by fastening screws to form a slit mold head.

[0078] The feed pipe 209 is located in the lower mold body 206 and connected to the mold cavity 210, and is used for feeding cellulose solution.

[0079] The mold cavity 210 is an internal groove of the lower membrane body 206, used for storing cellulose solution.

[0080] The upper mold body 205 and the lower mold body 206 are respectively provided with an upper mold lip 213 and a lower mold lip 211 along the length direction at their front ends, and the gap between the mold lips serves as the discharge port of the slit mold head 201.

[0081] The gap between the upper die lip 213 and the lower die lip 211 can be adjusted by moving the lower die lip 211 vertically.

[0082] Fluid channels I 207 and II 208 are respectively provided along the length direction inside the upper mold body 205 and the lower mold body 206. The temperature of the slit mold head 201 is controlled by the flow of high and low temperature media in the fluid channels I 207 and II 208.

[0083] According to one embodiment of the present invention, the temperature of the slit die head is controlled by the flow of a high- or low-temperature medium through fluid channel I 207 and fluid channel II 208.

[0084] According to one embodiment of the present invention, the coagulation bath 202 further includes a pair of pressure rollers I 203 and a pair of pressure rollers II 204 for the transfer of regenerated cellulose hydrogel.

[0085] The coagulation bath is designed to be corrosion resistant. Preferably, the inner side of the coagulation bath 202 is coated with an acid- and alkali-resistant coating. The coagulation bath 202 can be used to hold acidic or alkaline coagulation solutions.

[0086] According to one embodiment of the present invention, the film post-processing unit 7 is used for cleaning, modifying, drying and winding the cellulose hydrogel obtained by the film forming unit 2.

[0087] According to one embodiment of the present invention, the film post-processing unit 7 includes a stretching unit 3, which includes stretching roller I 302, stretching roller II 303, and stretching groove 301 with adjustable distance, and counter-pressure roller III 304 and counter-pressure roller IV 305 with adjustable vertical distance; the stretching unit 3 is used for stretching and orientation processing modification of cellulose hydrogel.

[0088] The inner side of the drawing groove 301 is designed to be corrosion resistant. Preferably, the drawing groove 301 contains an acid- and alkali-resistant coating.

[0089] According to one embodiment of the present invention, the film post-processing unit 7 includes a cleaning unit 4, which includes a stretching roller III 402, a stretching roller IV 403, and a cleaning tank 401; the cleaning unit 4 is used to wash away impurities such as alkali, urea, and salt remaining in the cellulose hydrogel.

[0090] The inner side of the cleaning tank 401 is designed to be corrosion resistant. Preferably, the inner side of the cleaning tank 401 includes an acid- and alkali-resistant coating.

[0091] According to one embodiment of the present invention, the film post-processing unit includes a drying unit 5 for drying cellulose hydrogel; the drying unit 5 includes a five-section hot air drying box 501 and a multi-roller assembly 502.

[0092] According to the present invention, preferably, the five-section hot air drying oven 501 can be individually temperature-controlled in different areas, and the temperature control range of each section of the five-section hot air drying oven 501 is 20-180℃. By adopting multi-section drying oven 501 with zoned temperature control, a gradual drying process from low temperature to high temperature is achieved, and the shrinkage and wrinkling of the regenerated cellulose membrane are avoided through the tension and thermal orientation of multiple rollers.

[0093] According to one embodiment of the present invention, the film post-processing unit includes a winding unit 6, which includes a pressure roller V 601, a pressure roller VI 602, a transfer roller 603, and a take-up roller 604. The winding unit 6 is used for winding up the regenerated cellulose film.

[0094] A second aspect of the present invention provides a method for continuous preparation of regenerated cellulose membranes by slot extrusion, the method being carried out in the aforementioned apparatus, the method comprising:

[0095] S1. Place cellulose in dissolving vessel 101, add solvent, stir to dissolve cellulose, and obtain cellulose solution. Degas under vacuum.

[0096] S2. The cellulose solution enters the slit mold 201 and is injected into the coagulation bath 202, where it coagulates in the coagulant to obtain regenerated cellulose gel.

[0097] S3. Regenerated cellulose gel is prepared by stretching unit 3 and washing unit 4 to obtain regenerated cellulose hydrogel.

[0098] S4. The regenerated cellulose hydrogel is dried in the drying unit 5 to obtain a regenerated cellulose membrane; it is then wound up in the winding unit 6.

[0099] According to the present invention, preferably, the concentration of the cellulose solution is 4 to 20 wt%; the regenerated natural polymer membrane prepared from the natural polymer solution of the aforementioned concentration has superior mechanical strength and elongation at break.

[0100] According to the present invention, preferably, the degree of polymerization of the cellulose is 200 to 1000; in the present invention, natural polymer materials with a degree of polymerization higher than 1000 cannot be completely dissolved, which is not conducive to extrusion film formation.

[0101] According to the present invention, preferably, the cellulose solution is extruded from the slit die 201 by increasing the air pressure of the dissolving vessel 101.

[0102] According to the present invention, preferably, the temperature difference between the dissolution unit 1 and the film-forming unit 2 is controlled to be less than or equal to 30°C; the stretching ratio of the cellulose hydrogel stretching process is controlled to be 1:1 to 1:5.

[0103] By controlling the temperature of the natural polymer solution during regeneration and before regeneration, the natural polymer solution can be stably formed, ensuring that the regenerated natural polymer film is uniform and flat.

[0104] According to the present invention, preferably, the solvent is one or more of sodium hydroxide solution, copper ammonia solution, NaOH / CS2 solution, alkali / urea solution, and NaOH / thiourea solution; preferably, it is an alkali / urea solution; more preferably, the alkali / urea solution is an aqueous solution of NaOH and urea; more preferably, the aqueous solution of NaOH and urea comprises: 4-8 wt% NaOH, 10-14 wt% urea, and 78-85 wt% water. Using the aforementioned solvent, the cost is low, the dissolution speed is fast and the efficiency is high, and the gelation time of the natural polymer solution is extended. The regenerated natural polymer hydrogel and regenerated natural polymer membrane prepared have better mechanical strength and elongation at break, and have excellent optical transmittance.

[0105] According to the present invention, preferably, the coagulant is one or more of pure water, ethanol, ethylene glycol, DMSO, hydrochloric acid, sulfuric acid, acetic acid, phosphoric acid, citric acid, phytic acid and benzoic acid; preferably, it is an aqueous solution of 10-20% acid; more preferably, it is an aqueous solution of 10-20 wt% citric acid; the regenerated natural polymer membrane prepared using the aforementioned coagulant has superior mechanical strength and elongation at break, while ensuring high production efficiency.

[0106] Preferably, the drying temperature of the regenerated cellulose hydrogel is 40-65°C; more preferably, a stepped heating drying method is adopted; the aforementioned drying method is used to achieve a gradual drying process from low temperature to high temperature, and the tension and thermal orientation of the regenerated natural polymer film are adjusted by the multi-roller group 502 to avoid shrinkage and wrinkling of the regenerated natural polymer film.

[0107] According to the present invention, preferably, the thickness of the regenerated cellulose hydrogel is 0.01-3 mm; more preferably, it is 1-2 mm.

[0108] According to the present invention, preferably, the thickness of the regenerated cellulose membrane is 0.01 to 1 mm; more preferably, it is 0.03 to 0.1 mm.

[0109] The present invention will be described in detail below through embodiments.

[0110] Example 1

[0111] a. Add NaOH / thiourea solution (sodium hydroxide:thiourea:water = 8:10:82) to dissolving kettle 101. The temperatures of dissolving kettle 101, coagulation bath 202 and pipe 106 are -12℃, 10℃ and 10℃ respectively. Add refined bamboo dissolving pulp (DP=1500) and stir at high speed to dissolve cellulose. The concentration of cellulose is 4wt%. Vacuum degassing is performed, and then air is introduced into the dissolving kettle to make the pressure inside the kettle 0.8MPa.

[0112] b. Turn on metering pump 105 and control the extrusion speed to 5m / min. The cellulose solution is injected into the coagulant through the slit extrusion die (the gasket thickness is 1.0mm, the width is 5cm, and the slit extrusion die temperature is 10℃) to obtain regenerated cellulose gel, 10wt% citric acid solution, and the temperature is 10℃.

[0113] c. The regenerated cellulose gel is stretched by pressure roller I 203, pressure roller II 204, and stretching roller 212 (each roller speed is 5m / min, and the stretching ratio is 1:3). After being stretched by stretching roller I 302 and stretching roller II 303 (roller speed is 5m / min), the regenerated cellulose gel enters the cleaning tank 401 and is cleaned by stretching roller III 402 and stretching roller IV 403 to obtain regenerated cellulose hydrogel. The solvent in stretching unit 3 is 5wt% sulfuric acid solution, and the solvent in cleaning unit 4 is pure water.

[0114] d. The regenerated cellulose hydrogel enters the drying unit 5 and the winding unit 6 to produce a regenerated cellulose membrane roll; the initial temperature of the five-stage hot air drying oven 501 is 30℃, and then the temperature is gradually increased by 5℃ to a final temperature of 55℃, with a humidity of 10% in each stage; the rotation speed of each roller in the multi-roller group 502 and the winding unit is 5m / min; the angle between the regenerated cellulose membrane and the take-up roller 604 is 120°.

[0115] The resulting regenerated cellulose membrane had low transparency, did not turn white, was 0.12 mm thick, and was 36.0 mm wide. The entire process took 185 minutes.

[0116] Example 2

[0117] a. Add NaOH / urea solvent (NaOH:urea:water = 7:12:81) to dissolving kettle 101. The temperatures of dissolving kettle 101, coagulation bath 202 and pipe 106 are -12℃, 5℃ and 5℃ respectively. Add refined bamboo dissolving pulp (DP=350) and stir at high speed to dissolve cellulose. The concentration of cellulose is 4wt%. Vacuum degassing is performed, and then air is introduced into the dissolving kettle to make the pressure inside the kettle 0.8MPa.

[0118] b. Turn on metering pump 105 and control the extrusion speed to 5m / min. The cellulose solution is injected into the coagulant through the slit extrusion die (the gasket thickness is 1.0mm, the width is 5cm, and the slit extrusion die temperature is 5℃) to obtain regenerated cellulose gel. The coagulant is a 10wt% citric acid solution at a temperature of 5℃.

[0119] c. The regenerated cellulose gel is stretched by pressure roller I 203, pressure roller II 204, and stretching roller 212 (each roller speed is 5m / min, and the stretching ratio is 1:3). After being stretched by stretching roller I 302 and stretching roller II 303 (roller speed is 5m / min), the regenerated cellulose gel enters the cleaning tank 401 and is cleaned by stretching roller III 402 and stretching roller IV 403 to obtain regenerated cellulose hydrogel. The solvent in stretching unit 3 is 5wt% sulfuric acid solution, and the solvent in cleaning unit 4 is pure water.

[0120] d. The regenerated cellulose hydrogel enters the drying unit 5 and the winding unit 6 to produce a regenerated cellulose membrane roll; the initial temperature of the five-stage hot air drying oven 501 is 40℃, and then the temperature is gradually increased by 5℃ to a final temperature of 65℃, with a humidity of 10% in each stage; the rotation speed of each roller in the multi-roller group 502 and the winding unit is 5m / min; the angle between the regenerated cellulose membrane and the take-up roller 604 is 120°.

[0121] The resulting regenerated cellulose membrane had high transparency, a thickness of 0.12 mm, and a width of 46 mm. The entire process took 185 minutes.

[0122] Example 3

[0123] S1. Add NaOH / urea solvent (NaOH:urea:water = 7:12:81) to dissolving kettle 101. The temperatures of dissolving kettle 101, coagulation bath 202 and pipe 106 are -12℃, 5℃ and 5℃ respectively. Add refined bamboo dissolving pulp (DP=350) and stir at high speed to dissolve cellulose. The concentration of cellulose is 8wt%. Vacuum degassing is performed, and then air is introduced into the dissolving kettle to make the pressure inside the kettle 0.8MPa.

[0124] S2. Turn on metering pump 105 and control the extrusion speed to 5m / min. The cellulose solution is injected into the coagulant through the slit extrusion die (the gasket thickness is 1.0mm, the width is 80cm, and the slit extrusion die temperature is 5℃) to obtain cellulose gel. The coagulant is a 15wt% citric acid solution at a temperature of 5℃.

[0125] S3. Cellulose gel is stretched by pressure roller I 203, pressure roller II 204, and stretching roller 212 (each roller speed is 5m / min, and the stretching ratio is 1:3). After stretching by stretching roller I 302 and stretching roller II 303 (roller speed is 5m / min), the cellulose gel enters the cleaning tank 401 and is cleaned by stretching roller III 402 and stretching roller IV 403 to obtain cellulose hydrogel. The solvent in stretching unit 3 is 5wt% sulfuric acid solution, and the solvent in cleaning unit 4 is pure water.

[0126] d. Cellulose hydrogel enters the drying unit 5 and the winding unit 6 to produce cellulose membrane rolls; the initial temperature of the five-stage hot air drying oven 501 is 40℃, and then the temperature is gradually increased by 5℃ to a final temperature of 65℃, with a humidity of 10% in each stage; the rotation speed of each roller in the multi-roller group 502 and the winding unit is 5m / min; the angle between the regenerated cellulose membrane and the winding roller 604 is 120°.

[0127] The final cellulose membrane had high transparency, a thickness of 0.12 mm, and a width of 785 mm. The entire process took 60 minutes.

[0128] Example 4

[0129] The difference from Example 2 is that the temperatures of the dissolving vessel 101, the coagulation bath 202, and the pipe 106 in step a are -12°C, 12°C, and 12°C, respectively, while other conditions are the same as in Example 2.

[0130] The resulting regenerated cellulose membrane had high transparency, a thickness of 0.12 mm, and a width of 42 mm. The entire process took 180 minutes.

[0131] Example 5

[0132] a. Add NaOH / urea solvent (NaOH:urea:water = 11:4:85) to the dissolving vessel, add chitosan (DP = 550), and stir at high speed. Adjust the temperature of the reaction vessel to -30℃ and maintain it for 3 hours. Then, thaw and stir until the temperature reaches 5℃. Repeat this freezing-thawing process twice to dissolve the chitosan. The concentration of chitosan is 2wt%. Degas under vacuum, and then introduce air into the dissolving vessel to make the pressure inside the vessel 0.8MPa. The temperatures of the coagulation bath 202 and the pipe 106 are 0℃ and 0℃, respectively. The remaining conditions are the same as in Example 1.

[0133] The resulting regenerated cellulose membrane had high transparency, a thickness of 0.11 mm, and a width of 40 mm. The entire process took 220 minutes.

[0134] Example 6

[0135] The natural polymer material added in step a is cellulose (DP=1000); the other conditions are the same as in Example 2.

[0136] The final cellulose membrane had high transparency, a thickness of 0.12 mm, and a width of 46.0 mm. The entire process took 185 minutes.

[0137] Example 7

[0138] Unlike Example 2, the rotation speed of the stretching roller II303 was controlled at 25 m / min to achieve different stretching in the longitudinal direction of the hydrogel, and the stretching ratio was controlled at 1:5. The final cellulose membrane had high transparency, a thickness of 0.03 mm, and a width of 40 mm. The whole process took 130 min.

[0139] Comparative Example 1

[0140] Casting Method 1:

[0141] A NaOH / urea solvent (NaOH:urea:water = 7:12:81) was prepared, and refined bamboo dissolving slurry (DP = 350) was added. The mixture was pre-cooled to -12℃ and stirred at high speed to dissolve the cellulose, achieving a cellulose concentration of 6 wt%. The solution was then centrifuged to remove bubbles, and the supernatant was poured into a clean 1 mm thick mold. The mold was then smoothly placed in a 5 wt% citric acid aqueous solution coagulation bath. After standing for 12 hours, the solution was washed with deionized water until its conductivity approached that of pure water. After air drying at room temperature for 24 hours, the cellulose film was obtained. The final film was whitish in color, had low transparency, and poor mechanical properties.

[0142] Comparative Example 2

[0143] Casting Method 2:

[0144] A NaOH / urea solvent (NaOH:urea:water = 7:12:81) was prepared, and refined bamboo dissolving slurry (DP = 350) was added. The mixture was pre-cooled to -12°C and stirred at high speed to dissolve the cellulose, achieving a cellulose concentration of 6 wt%. The solution was then centrifuged to remove bubbles, and the supernatant was poured into a clean 1 mm thick mold. The mold was then smoothly placed in a 15 wt% citric acid aqueous solution as a coagulation bath. After standing for 5 minutes, the solution was washed with deionized water until its conductivity approached that of pure water. After air-drying at room temperature for 24 hours, a cellulose film was obtained. The final regenerated cellulose film exhibited severe shrinkage and wrinkles, resulting in poor mechanical properties. The entire process took approximately 28 hours.

[0145] Comparative Example 3

[0146] a. Add NaOH / urea solvent (NaOH:urea:water = 7:12:81) to the dissolving kettle. The temperatures of the dissolving kettle 101, coagulation bath 202 and pipe 106 are -12℃, 30℃ and 30℃ respectively. Add refined bamboo dissolving pulp (DP=350) and stir at high speed to dissolve the cellulose. The concentration of cellulose is 4wt%. Vacuum degassing is performed, and then air is introduced into the dissolving kettle to make the pressure inside the kettle 0.8MPa.

[0147] b. Turn on metering pump 105 and control the extrusion speed to 5 m / min, so that the cellulose solution is injected into the coagulant through a slit extrusion die (gap thickness is 1.0 mm, width is 5 cm, slit extrusion die temperature is 25℃) to obtain regenerated cellulose gel. The coagulant is a 15 wt% citric acid solution at 25℃; the remaining steps are the same as in Example 1.

[0148] The final regenerated cellulose hydrogel was 0.1 mm thick and 50 mm wide. The whole process took 125 minutes. The resulting membrane had low transparency, severe whitening, and poor mechanical properties.

[0149] Comparative Example 4

[0150] Unlike Example 2, the coagulant was a 5 wt% citric acid solution, and the cellulose solution could not gel, making continuous preparation impossible.

[0151] Comparative Example 5

[0152] Unlike Example 2, in step c, the speed of the drafting roller is adjusted to control the drafting ratio to 1:5.5, and the other operating conditions are the same as in Example 2.

[0153] The hydrogel breaks down in the coagulation bath, making continuous preparation impossible.

[0154] Compared with Comparative Examples 1 and 2, the preparation method of the present invention can achieve rapid and continuous preparation of regenerated natural polymer membranes; compared with Comparative Example 3, the regenerated natural polymer membrane prepared by adopting the aforementioned technical solution of the present invention is smooth, uniform in thickness, highly transparent, and has good mechanical properties.

[0155] Compared with Comparative Examples 4 and 5, the polymer film prepared by the method of the present invention is continuous and does not break during processing.

[0156] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various specific technical features in any suitable manner. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately. However, these simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A method for continuous preparation of regenerated cellulose membranes via slot extrusion, characterized in that, The method is carried out in a slit extrusion continuous preparation of regenerated cellulose membrane, the apparatus comprising: a dissolution unit (1), a film forming unit (2), and a film post-treatment unit (7). The dissolving unit (1) is used to prepare a cellulose solution for film preparation; the dissolving unit includes a dissolving vessel (101), which is connected to a slit mold (201) via a pipe (106); the dissolving vessel (101), the coagulation bath (202) and the pipe (106) are each provided with a heat-insulating jacket; The film-forming unit (2) includes a slit die (201) and a coagulation bath (202). The cellulose solution is extruded from the slit die (201) and enters the coagulation bath (202) to coagulate and obtain a regenerated cellulose hydrogel. The film post-processing unit (7) modifies, cleans, and dries the regenerated cellulose hydrogel to prepare a regenerated cellulose membrane; the slit die (201) can regulate the temperature; the method includes: S1. Place cellulose in a dissolving vessel (101), add solvent, stir to dissolve cellulose, and obtain cellulose solution. Degas under vacuum. S2. The cellulose solution enters the slit mold (201) and is injected into the coagulation bath (202), where it coagulates in the coagulant to obtain regenerated cellulose gel. S3. Regenerated cellulose gel is prepared by stretching unit (3) and washing unit (4) to obtain regenerated cellulose hydrogel; S4. The regenerated cellulose hydrogel is dried by the drying unit (5) to obtain a regenerated cellulose membrane; optionally, it is wound by the winding unit (6); wherein, the temperature difference between the dissolution unit (1) and the film forming unit (2) is controlled to be less than or equal to 30°C; the stretching ratio of the cellulose hydrogel is controlled to be 1:1 to 1:5; the concentration of the cellulose solution is 4 to 20 wt%, the solvent is an aqueous solution of NaOH and urea, and the solvent components are 4 to 8 wt% NaOH, 10 to 14 wt% urea and 78 to 85 wt% water; the coagulant is an aqueous solution of 10 to 20% acid; the thickness of the regenerated cellulose hydrogel is 0.01 to 3 mm.

2. The method according to claim 1, wherein, The degree of polymerization of the cellulose is 200 to 1000.

3. The method according to claim 1, wherein, The coagulant is a 10-20 wt% citric acid aqueous solution.

4. The method according to claim 1, wherein, The drying temperature of the regenerated cellulose hydrogel is 40~65℃; and / or The regenerated cellulose hydrogel has a thickness of 0.01~3mm; and / or The thickness of the regenerated cellulose membrane is 0.01~1mm.

5. The method according to claim 1, wherein, The regenerated cellulose hydrogel is dried using a stepped temperature increase method; and / or The regenerated cellulose hydrogel has a thickness of 1-2 mm; and / or The thickness of the regenerated cellulose membrane is 0.03~0.1mm.

6. The method according to claim 1, wherein, The slit die head (201) includes an upper die body (205), a lower die body (206), fluid channel I (207), fluid channel II (208), a feed pipe (209), a die cavity (210), a lower die lip (211), and an upper die lip (213); The upper mold body (205) and the lower mold body (206) are connected to form a slit mold head (201). The lower membrane body (206) and the upper mold body (205) are connected by a groove on the lower membrane body (206) as the mold cavity (210) for storing cellulose solution; The feed pipe (209) is used to feed the cellulose solution into the mold cavity; The connecting surfaces of the upper mold body (205) and the lower mold body (206) at the outlet area along the length direction are respectively provided with an upper mold lip (213) and a lower mold lip (211), and the gap between the upper mold lip (213) and the lower mold lip (211) serves as the discharge port of the slit mold head (201); Fluid channels I (207) and II (208) are respectively provided in the mold body along the length direction of the upper mold body (205) and the lower mold body (206). The temperature of the cellulose solution flowing in the slit mold head (201) is controlled by the flow of high and low temperature media in fluid channels I (207) and fluid channels II (208).

7. The method according to claim 1, wherein, The dissolving unit also includes a stirrer (102) for uniformly mixing the materials in the dissolving vessel (101).

8. The method according to claim 6, wherein, The size of the gap between the upper die lip (213) and the lower die lip (211) can be adjusted by moving the lower die lip (211) in the vertical direction.

9. The method according to claim 1, wherein, The coagulation bath (202) also includes rotating pressure rollers I (203) and II (204) for the transfer of cellulose hydrogel; the coagulation bath (202) is configured to be corrosion resistant.

10. The method according to claim 1, wherein, The film post-processing unit (7) includes a stretching unit (3) for stretching modification of cellulose hydrogel; the stretching unit (3) includes a stretching groove (301), stretching roller I (302) and stretching roller II (303) disposed in the stretching groove (301), the stretching roller I (302) and stretching roller II (303) being used to stretch and modify the regenerated cellulose hydrogel in the stretching groove (301), and a transfer pressure roller III (304) and a pressure roller IV (305) disposed outside the stretching groove (301) and with an adjustable vertical distance for the cellulose hydrogel; the stretching groove (301) is configured to be corrosion resistant; The film post-processing unit (7) includes a cleaning unit (4) for washing away impurities remaining in the cellulose hydrogel; the cleaning unit (4) includes stretching roller III (402), stretching roller IV (403) and cleaning tank (401); the cleaning tank (401) is configured to be corrosion resistant. The film post-processing unit (7) includes a drying unit (5) for drying the cellulose hydrogel after cleaning to prepare a cellulose membrane; the drying unit (5) includes a five-section hot air drying box (501) and a multi-roller assembly (502). The film post-processing unit (7) includes a winding unit (6) for winding the regenerated cellulose film; the winding unit (6) includes a pressure roller V (601) and a pressure roller VI (602), a transfer roller (603) and a take-up roller (604); the transfer roller (603) can move vertically up and down to adjust the winding angle.

11. The method according to claim 10, wherein, The five-section hot air drying oven (501) is designed to have separate temperature and humidity control for each section. The temperature control range of each section of the five-section hot air drying oven (501) is 20~180℃, and the humidity control range is 5~100%.

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