Method for improving thickness stability of thick paste method tobacco sheet

Abstract

The invention belongs to the technical field of heating cigarette processing, and particularly relates to a method for improving the thickness stability of thick paste method tobacco sheets. By adding part of adhesive in the plant fiber pulping process, adding real-time viscosity detection, feedback and microwave heating fine adjustment mechanisms while heating in a water bath, and combining methods of controlling the liquid level of slurry in a headbox, keeping a metal belt to run at a constant speed, controlling a drying program and the like, the thickness stability of slices among batches and in the batches is improved, and the quality of the slices is improved. The stability of physicochemical indexes such as slice quantification, tensile strength and moisture is improved, fluctuation of the product thickness is reduced, repeated adjustment is avoided, the method is simple and convenient, the slurry ratio cannot be changed, and the production efficiency is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of heated cigarette processing, and particularly relates to a method for improving the thickness stability of tobacco sheet by thick slurry method. Background Art

[0002] The tobacco sheet by thick slurry method is prepared by crushing tobacco raw materials and mixing them evenly with a smoking agent, an adhesive, external fibers, water, etc. to form a slurry, then uniformly casting and forming the slurry onto a metal belt through a scraper at the bottom of a headbox, and then drying. The tobacco sheet by thick slurry method has an aroma and taste similar to natural tobacco leaves, the product density and filling value are close to natural tobacco leaves, and it has good mechanical processing performance. Its tar release is 25% lower than that of natural tobacco leaves.

[0003] The thickness of the tobacco sheet by thick slurry method is affected by various factors. Among them, the gap between the scraper and the metal belt, the liquid level of the headbox, the running speed of the metal belt, and the concentration and temperature of the slurry are the main factors affecting the thickness. In particular, the change in slurry temperature directly causes the change in slurry viscosity, which in turn affects the thickness of the casting and forming layer of the thick slurry method, resulting in fluctuations in the product thickness. During the slurry preparation process, factors such as the gap between the scraper and the metal belt, the liquid level of the headbox, the running speed of the metal belt, and the slurry concentration are relatively easy to control. The control of slurry temperature usually increases the slurry temperature by adding a water bath heating device on the outer wall of the tank, but this method of controlling temperature is not accurate enough. Often, the heating will continue even when the control temperature has been reached, and the slurry is more, the heating time is long and not uniform enough, which increases the slurry preparation time and reduces the production efficiency.

[0004] Currently, patents related to the thickness stability of tobacco sheet by thick slurry method mainly focus on aspects such as the coating layer thickness adjustment device and feedback adjustment. For example, patent CN202022970203.7 discloses a constant-state slurry casting and forming device for reconstituted tobacco by thick slurry method for heated cigarettes, which can improve the "paper formation rate" of the reconstituted tobacco by thick slurry method and meet the stability requirements of the thickness and quantitative of the reconstituted tobacco by thick slurry method for heated cigarette sticks. Another example is patent CN202211534531.X, which discloses a method for feedback adjustment of the thickness of tobacco sheet by thick slurry method. Through a linear servo motor, the high-precision servo adjustment of the height of the tool holder is solved, and the thickness of the slurry film is adjusted in real time to solve the problem of lag in the thickness detection of tobacco sheet.

[0005] Based on this, the present invention improves the stability of the thick slurry method slurry from the slurry preparation link by adding a part of the adhesive during the grinding process of plant fibers, adding real-time viscosity detection, feedback and microwave heating fine-tuning mechanisms while heating in a water bath, and combining methods such as controlling the slurry liquid level in the headbox, keeping the metal belt running at a constant speed, and controlling the drying process, reducing the fluctuation of the product thickness and avoiding repeated adjustments, and is simple and convenient, does not change the slurry ratio, and improves the production efficiency. Summary of the Invention

[0006] The object of the present invention is to provide a method for improving the thickness stability of tobacco sheet by thick pulp method. By adding part of the adhesive during the grinding process of plant fibers, adding real-time viscosity detection, feedback and microwave heating fine-tuning mechanism while heating in water bath, and combining methods such as controlling the slurry level in the headbox, keeping the metal belt running at a constant speed, and controlling the drying process, the thickness stability between batches and within batches of the tobacco sheet is improved. Furthermore, the stability of physical and chemical indexes such as the basis weight, tensile strength, and moisture content of the tobacco sheet is improved, the fluctuation of the product thickness is reduced, repeated adjustment is avoided, and the method is simple and convenient, does not change the slurry ratio, and improves the production efficiency.

[0007] Based on the above object, the present invention adopts the following technical solutions:

[0008] A method for improving the thickness stability of tobacco sheet by thick pulp method is realized by adopting a slurry transportation, viscosity detection and headbox system; the slurry transportation, viscosity detection and headbox system includes a slurry tank, a circulation pipeline, two viscosity detection, feedback and microwave heating fine-tuning mechanisms, a headbox, and a PLC controller;

[0009] The discharge end at the bottom of the slurry tank is connected to the feed end of the headbox through the circulation pipeline; two viscosity detection, feedback and microwave heating fine-tuning mechanisms are respectively arranged at the front end and the rear end of the circulation pipeline;

[0010] Each viscosity detection, feedback and microwave heating fine-tuning mechanism includes a viscosity detection device, a temperature detection device and a microwave heating fine-tuning device;

[0011] Specifically, the method includes the following steps:

[0012] (1) Crush the tobacco raw material into powder with a particle size of 30-50 μm; add water and part of the adhesive to the plant fiber, and grind it into fiber pulp with a beating degree of 30-55°SR by a refiner;

[0013] (2) Transfer the fiber pulp in step (1) to a liquid material tank, stir the fuming agent and the remaining adhesive evenly and pump them into the liquid material tank, then add clear water and mix evenly to obtain a liquid material;

[0014] Transfer the evenly mixed liquid material to the slurry tank, add the crushed tobacco powder in step (1) to the slurry tank, mix evenly, and make a slurry; heat the slurry tank in a water bath;

[0015] (3) Transfer the slurry from the slurry tank to the headbox through the circulation pipeline. Use two viscosity detection, feedback, and microwave heating fine-tuning mechanisms to detect the time taken for a certain volume of slurry to pass through the front and rear ends of the circulation pipeline at regular intervals. Use the PLC controller to perform PID interlock control on the viscosity detection device, temperature detection device, and microwave heating fine-tuning device, calculate the viscosity of the slurry, and monitor the viscosity change until the viscosity remains stable. If the viscosity is unqualified, use the PLC controller to perform PID interlock control on the microwave heating fine-tuning device to make the microwave heating fine-tuning device perform heating fine-tuning to reach the set temperature, and at the same time monitor the temperature and viscosity. There is an opening at the bottom of the headbox, and a doctor blade is provided at the opening. A metal belt running at a constant speed is provided below the headbox. During operation, the slurry in the headbox is discharged from the bottom of the headbox, and then the doctor blade is used to evenly cast the slurry onto the metal belt;

[0016] (4) Then dry the slurry evenly cast onto the metal belt. The drying process successively enters three drying ovens, adopting a low-temperature - high-temperature - low-temperature program. After drying, use a doctor blade to peel it off from the metal belt to obtain the thick-slurry method tobacco sheet.

[0017] Further, in step (1), the plant fiber is one or more of softwood fiber, hardwood fiber, and flax fiber, and the addition amount of the plant fiber (dry weight) is 3 - 6% of the weight of the tobacco powder.

[0018] Further, in step (1), the adhesive is one or more of sodium carboxymethyl cellulose, methyl cellulose, hydroxypropyl methyl cellulose, guar gum, xanthan gum, and tamarind gum.

[0019] Further, in step (1), the mass ratio of the plant fiber, clear water, and the adhesive is 4:(90 - 120):0.1, preferably 4:100:0.1.

[0020] Further, in step (2), the fuming agent is one or two of propylene glycol and glycerol, and the addition amount of the fuming agent is 15 - 22% of the weight of the tobacco powder.

[0021] Further, in step (2), the remaining adhesive is one or more of sodium carboxymethyl cellulose, methyl cellulose, hydroxypropyl methyl cellulose, guar gum, xanthan gum, and tamarind gum, and the addition amount is 3 - 5% of the weight of the tobacco powder.

[0022] Further, in step (2), the addition amount of clear water is 3 - 4 times the weight of the tobacco powder.

[0023] Further, in step (2), a resistance temperature detector (RTD) water bath heating device is also provided outside the slurry tank. Temperature sensors are equipped both in the interlayer (i.e., the water bath layer) of the slurry tank body and inside the slurry tank (in contact with the slurry). The water bath temperature is measured by the temperature sensor in the interlayer of the slurry tank body;

[0024] The RTD water bath heating device is provided with a temperature signal receiving end, an analog-to-digital signal conversion module, a central processor control module, and a heating control module. The temperature sensor is provided with a temperature signal sending end. The signal sending end of the temperature sensor can send the temperature signal to the temperature signal receiving end of the RTD water bath heating device. The temperature signal receiving end sends the temperature signal to the analog-to-digital signal conversion module, and the analog-to-digital signal conversion module then converts the temperature signal into a digital signal and sends it to the central processor control module;

[0025] During operation, the temperature signal of the inside of the slurry tank or the interlayer of the slurry tank is sent to the temperature signal receiving end through the temperature sensor. At the same time, the set temperature is set through the central processor control module of the RTD water bath heating device, and then the received temperature signal is converted into a digital signal through the analog-to-digital signal conversion module and compared with the set temperature value of the central processor control module;

[0026] If the temperature value received by the central processor control module is lower than the set temperature value of the central processor control module, the central processor control module sends a signal to start heating to the heating control module, and the RTD water bath heating device then starts and begins to heat.

[0027] Further, both the temperature sensor and the RTD water bath heating device adopt conventional models in the prior art, and their structures are not the inventive points of the present invention, so they will not be elaborated herein (for example, the temperature sensor model: PT-100, for example, the RTD water bath heating device model: DY2X01-1);

[0028] In the present invention, the electrical signal connection method between the signal sending end of the temperature sensor and the temperature signal receiving end of the RTD water bath heating device adopts a conventional setting in the prior art and is not the inventive point of the present invention, so it will not be elaborated herein.

[0029] Further, when the temperature sensor in the interlayer of the slurry tank detects that the water bath temperature in the interlayer of the slurry tank reaches the set temperature (specifically, for example, 35°C), the temperature sensor sends a signal indicating that the temperature has reached the set temperature (specifically, for example, 35°C) to the temperature signal receiving end of the thermal resistance water bath heating device, and after conversion by the digital-to-analog signal conversion module, it is sent to the central processor control module. At this time, the central processor control module sends a stop heating signal to the heating control module, that is, stops the water bath heating. At this time, the slurry temperature (measured by the temperature sensor in the slurry tank) < the set temperature (specifically, for example, 35°C), and subsequent processes are required to heat up the slurry.

[0030] Further, in step (3), the detection end of the viscosity detection device is arranged on the bottom side wall of the circulation pipeline, the temperature detection device is arranged at a position close to the top side wall in the circulation pipeline, and the heating end of the microwave heating fine-tuning device is arranged between the upper and lower pipe walls in the circulation pipeline.

[0031] Alternatively, as another technical solution, the heating end of the microwave heating fine-tuning device can also be arranged on the outer side wall of the circulation pipeline.

[0032] Further, the viscosity detection device can select the viscosity detection equipment of German MARIMEX company, and the specific model is, for example VA100, the sensor types are, for example: probe (VA-100C), probe (VA-100B), or viscosity detection devices of models such as VA-300L, VA-300M, VA-300H, VA-300X, etc., or a viscosity detection device of model NDJ-5S / 8S / 9S can also be used;

[0033] The temperature detection device can adopt a temperature sensor of model GWP200, or a thermal resistance thermometer of model TR21-C, or a temperature sensor of model PT-100;

[0034] The microwave heating fine-tuning device can adopt a pipeline type electric heater of model CN61M / DN25, or a pipeline type microwave heating device of model MGG-J of Qingdao Maiwei Microwave Chemical Equipment Co., Ltd.;

[0035] Or it can also adopt the structure of a pipeline type microwave heater of a Chinese patent with the application number CN202321125052.2. In this case, the heating end of the microwave heating fine-tuning device is arranged on the outer side wall of the circulation pipeline.

[0036] Further, the model of the PLC controller used in the present invention can be FX1N-40MT-0001, S7-300, FX3U, S7-1500, etc.

[0037] Further, the viscosity detection, feedback and microwave heating fine-tuning mechanism further includes a flow meter (model: RHM02L). The flow meter is arranged on the right side of the detection end of the viscosity detection device and can detect the flow rate of the slurry.

[0038] Further, by arranging a flow meter in the circulation pipeline before entering the headbox, the flow rate of the slurry is monitored, so as to control the flow rate of the slurry to make the slurry liquid level in the headbox basically fixed at the same height.

[0039] Specifically, the PLC controller can perform logic control and can perform PID interlock control on the viscosity detection device, temperature detection device and microwave heating fine-tuning device;

[0040] During operation, the viscosity, temperature and microwave heating signals are connected to the PLC controller through the viscosity detection device, temperature detection device and microwave heating fine-tuning device; at the same time, the microwave heating fine-tuning device is used as a fine-tuning device for the slurry temperature. The PLC controller monitors the opening or closing of the microwave heating fine-tuning device, so as to realize real-time adjustment of the slurry temperature. The slurry viscosity is used as a process variable (PID input signal), and the microwave heating is used as a control variable (PID output signal). Set the slurry viscosity value, and control the heating power of the microwave heating to reach the viscosity set value;

[0041] After the viscosity detection device sends the viscosity signal to the PLC controller, if the slurry viscosity is higher than the set value, the PLC controller controls to start the microwave heating fine-tuning device for microwave heating and increases the microwave heating power. When the viscosity detection device detects that the slurry viscosity is lower than the set value, the PLC controller controls to gradually close the microwave heating fine-tuning device; during this period, the temperature detection result of the temperature detection device is synchronously sent to the PLC controller for data reference, so as to grasp the final temperature and viscosity change of the slurry in real time.

[0042] Further, the PID interlock control method of the PLC controller for the viscosity detection device, temperature detection device and microwave heating fine-tuning device in the present invention adopts the conventional setting in the prior art and is not the inventive point of the present invention, so it will not be elaborated here.

[0043] Further, in step (3), the two viscosity detection, feedback and microwave heating fine-tuning mechanisms are respectively used to detect once every 10-15 minutes. Detect the time when a certain volume of slurry passes through the front end and the rear end of the viscosity detection, feedback and microwave heating fine-tuning mechanism of the circulation pipeline. The PLC controller performs PID interlock control on the viscosity detection device, temperature detection device and microwave heating fine-tuning device, calculates the viscosity of the slurry, and monitors the viscosity change until the viscosity remains stable.

[0044] Further, in step (3), if the temperature of the slurry is slightly lower than the set value (for example, 35°C) when the slurry enters the circulation pipeline from the slurry tank, the PLC controller can perform PID interlock control on the microwave heating fine-tuning device to make the microwave heating fine-tuning device perform heating fine-tuning, so as to reach the set temperature (for example, 35°C), while monitoring the temperature and viscosity.

[0045] Further, in step (3), if the viscosity is higher than the design value, the microwave heating fine-tuning device is used to perform microwave heating to heat the slurry to the required temperature, and the viscosity detection device at the rear end of the circulation pipeline is used to detect the viscosity until it meets the standard. At this time, the microwave heating is turned off, and then it enters the headbox.

[0046] Further, in step (3), before the slurry enters the headbox, during the process of passing through the circulation pipeline, the temperature of the slurry is controlled at 35±1°C (when not heated, the slurry temperature is generally between 10-33°C according to different seasons), and the viscosity is controlled at 2000-2200 cP.

[0047] Further, in step (3), the deviation of the slurry liquid level height in the headbox is controlled within ±0.5 cm.

[0048] Further, in step (3), the metal belt runs at a constant speed, and the speed is between 8-12 m / min.

[0049] Further, in step (3), the usage time of the slurry is within 4 hours since it is transferred to the slurry tank.

[0050] Further, in step (4), the first-stage low-temperature drying temperature is between 60-80°C, the second-stage high-temperature drying temperature is between 80-100°C, and the third-stage low-temperature drying temperature is between 50-80°C.

[0051] Further, in step (4), the length of each drying oven is 2-4 m, preferably 3 m.

[0052] Further, based on a general inventive concept, the present invention also provides a thick-slurry method tobacco sheet prepared by the above method.

[0053] Compared with the prior art, the beneficial effects of the present invention are:

[0054] 1. By adding a part of adhesive during the grinding process of plant fibers, the present invention enables the fiber pulp to be evenly dispersed in the mixed system of water and adhesive, preventing the liquid material concentration difference caused by the separation of fibers and water during the transfer process of the fiber pulp, thereby affecting the slurry concentration and product thickness.

[0055] For the temperature control of the slurry tank, the traditional method uses water bath heating. The water bath jacket is heated by a thermal resistor, and the start and stop of heating are controlled in real time by detecting the slurry temperature. Due to the temperature inertia of heat conduction, it is easy to cause the slurry temperature to exceed the set temperature, resulting in changes in the slurry viscosity and unstable control of the thin sheet thickness.

[0056] The present invention provides a thermal resistor type water bath heating device outside the slurry tank, and temperature sensors are equipped in the sandwich layer (i.e., the water bath layer) of the slurry tank body and inside the slurry tank. To prevent the slurry temperature from exceeding the set temperature due to the temperature inertia of heat conduction, the water bath heating is stopped when the water bath temperature reaches the set value.

[0057] 2. To further improve production efficiency, the present invention sets up a viscosity detection, feedback, and microwave heating fine-tuning mechanism on the circulation pipeline connecting the slurry tank and the headbox. The PLC controller can perform logical control and can perform PID interlock control on the viscosity detection device, temperature detection device, and microwave heating fine-tuning device;

[0058] During operation, the viscosity, temperature, and microwave heating signals are connected to the PLC controller through the viscosity detection device, temperature detection device, and microwave heating fine-tuning device; at the same time, the microwave heating fine-tuning device is used as a fine-tuning device for the slurry temperature, and the PLC controller monitors the opening or closing of the microwave heating fine-tuning device, so as to realize real-time adjustment of the slurry temperature. The slurry viscosity is used as a process variable (PID input signal), and the microwave heating is used as a control variable (PID output signal). The set slurry viscosity value is set, and the heating power of the microwave heating is controlled to reach the viscosity set value;

[0059] After the viscosity detection device sends the viscosity signal to the PLC controller, if the slurry viscosity is higher than the set value, the PLC controller controls the start of the microwave heating fine-tuning device for microwave heating and increases the microwave heating power. When the viscosity detection device detects that the slurry viscosity is lower than the set value, the PLC controller controls the gradual closing of the microwave heating fine-tuning device; during this period, the temperature detection result of the temperature detection device is synchronously sent to the PLC controller for data reference, so as to grasp the final temperature and viscosity changes of the slurry in real time.

[0060] The present invention starts microwave heating for temperature fine-tuning to play a role in temperature compensation and prevent thickness non-uniformity caused by slurry viscosity differences; then controls the slurry use time to prevent the slurry state from changing due to too long placement time of the slurry, which in turn affects the thickness of the slurry cast on the metal strip; since the slurry casting thickness is closely related to the headbox liquid level and the metal strip running speed, etc., the slurry flow rate is controlled to keep the slurry liquid level in the headbox basically fixed at the same height and keep the metal strip running at a constant speed.

[0061] 3. During the drying process of the slurry, a low-temperature - high-temperature - low-temperature program is adopted. In the first stage, low-temperature drying is used to prevent cracks or bubbles from appearing on the surface due to too fast drying of the slurry. In the second stage, high-temperature drying is used to quickly remove most of the water in the slurry. In the third stage, low-temperature drying is used to prevent the shrinkage of the thin sheet caused by too large a temperature difference when the thin sheet exits the metal belt.

[0062] The present invention improves the surface flatness and uniformity of the thin sheet through a three-stage temperature control program of low-temperature - high-temperature - low-temperature. Through the comprehensive application of the above methods, the thickness stability of the thin sheets between batches and within batches is improved, and further, the stability of physical and chemical indexes such as the basis weight, tensile strength, and moisture content of the thin sheets is improved. Brief Description of the Drawings

[0063] Figure 1 It is a flowchart of the method for improving the thickness stability of tobacco thin sheets by the thick slurry method according to the present invention;

[0064] Figure 2 It is a connection diagram of some components in the slurry transportation, viscosity detection, and flow slurry system according to the present invention; wherein, 1. slurry tank, 11. interlayer, 2. circulation pipeline, 21. detection end of the viscosity detection device, 22. temperature detection device, 23. heating end of the microwave heating fine-tuning device, 3. headbox;

[0065] Figure 3 It is a curve chart of time and slurry viscosity in step (3) of the method for improving the thickness stability of tobacco thin sheets by the thick slurry method according to the present invention;

[0066] Figure 4 It is a curve chart of temperature and slurry viscosity in step (3) of the method for improving the thickness stability of tobacco thin sheets by the thick slurry method according to the present invention. Detailed Embodiments

[0067] To facilitate the understanding of the present invention, the present invention will be described more comprehensively and meticulously below in combination with embodiments, but the protection scope of the present invention is not limited to the following specific embodiments.

[0068] Unless otherwise defined, all professional terms used hereinafter have the same meaning as commonly understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the protection scope of the present invention.

[0069] Unless otherwise specifically stated, all kinds of raw materials, reagents, instruments, and equipment used in the present invention can be obtained through market purchase or can be prepared by existing methods.

[0070] Example 1

[0071] A method for improving the thickness stability of tobacco thin sheets by the thick slurry method, the process is as Figure 1 shown, and the specific steps are as follows:

[0072] (1) Crush the tobacco raw materials into powders of about 50 μm.

[0073] Add clear water and part of the adhesive to the plant fiber, and grind it into a fiber pulp with a beating degree of 35°SR by a refiner (since when ordinary plant fibers are ground in a refiner, if only circulated and ground in clear water, due to the hydrophobic groups of the fiber molecular polymer chains, they cannot be evenly dispersed in water, which will lead to inconsistent concentrations during the transfer of the fiber pulp to the liquid material tank in each batch. There will often be a phenomenon that plant fibers will stay behind, resulting in a higher fiber content in the subsequent batches or accumulation in the fiber tank and unable to be pumped away. If part of the adhesive is added, a uniform dispersion system can be formed for the fiber pulp to ensure the stability of the subsequent slurry viscosity and formula);

[0074] The plant fiber is softwood fiber, and the addition amount is 3% of the weight of the tobacco powder; the adhesive is sodium carboxymethylcellulose; the mass ratio of the plant fiber, clear water and the adhesive is 4:100:0.1.

[0075] (2) Transfer the fiber pulp in step (1) to the liquid material tank, stir the fuming agent and the remaining adhesive evenly and pump them into the liquid material tank, then add clear water and mix evenly to obtain the liquid material;

[0076] The fuming agent is glycerol, and the addition amount of the fuming agent is 16% of the weight of the tobacco powder; the remaining adhesive is sodium carboxymethylcellulose, and the addition amount is 3% of the weight of the tobacco powder; the addition amount of clear water is 3.2 times the weight of the tobacco powder;

[0077] The method of the present invention is realized by adopting a slurry transportation, viscosity detection and flow slurry system; specifically, as Figure 2 shown, the slurry transportation, viscosity detection and flow slurry system includes a slurry tank 1, a circulation pipeline 2, two viscosity detection, feedback and microwave heating fine-tuning mechanisms, a flow box 3, and a PLC controller (not marked in the figure);

[0078] Transfer the evenly mixed liquid material to the slurry tank 1, add the crushed tobacco powder in step (1) to the slurry tank 1, mix evenly, and make a slurry; perform water bath heating on the slurry tank 1;

[0079] A resistance thermal water bath heating device (not marked in the figure) is also provided outside the slurry tank 1. Temperature sensors (not marked in the figure) are equipped in the sandwich layer 11 (i.e., the water bath layer) of the slurry tank 1 body and inside the slurry tank 1 (in contact with the slurry). The water bath temperature is measured by the temperature sensor in the sandwich layer 11 of the slurry tank 1 body;

[0080] The thermoresistive water bath heating device is provided with a temperature signal receiving end, an analog-to-digital signal conversion module, a central processor control module, and a heating control module. The temperature sensor is provided with a temperature signal sending end. The signal sending end of the temperature sensor can send the temperature signal to the temperature signal receiving end of the thermoresistive water bath heating device. The temperature signal receiving end sends the temperature signal to the analog-to-digital signal conversion module, and the analog-to-digital signal conversion module then converts the temperature signal into a digital signal and sends it to the central processor control module;

[0081] During operation, the temperature signal of the slurry tank 1 or the interlayer 11 of the slurry tank 1 is sent to the temperature signal receiving end through the temperature sensor. At the same time, the set temperature is set through the central processor control module of the thermoresistive water bath heating device, and then the received temperature signal is converted into a digital signal through the analog-to-digital signal conversion module and compared with the set temperature value of the central processor control module;

[0082] If the temperature value received by the central processor control module is lower than the set temperature value of the central processor control module (specifically set to 35 °C in this embodiment), the central processor control module sends a signal to start heating to the heating control module, and the thermoresistive water bath heating device immediately starts and begins to heat (to save time, improve efficiency, and at the same time prevent the drawback that when the traditional method monitors the start and stop of heating by detecting the slurry temperature, the slurry temperature often exceeds the set temperature due to the temperature inertia of heat conduction. In this application, temperature sensors are equipped both in the interlayer 11 of the slurry tank 1 body and inside the slurry tank 1, and the signal control between the temperature sensor and the thermoresistive water bath heating device is used to regulate the water bath temperature of the slurry tank 1 body and the temperature inside the tank);

[0083] Specifically, both the temperature sensor and the thermoresistive water bath heating device adopt conventional models in the prior art, and their structures are not the invention points of the present invention, so they will not be elaborated further (for example, the temperature sensor model: PT-100, for example, the thermoresistive water bath heating device model: DY2X01-1). In the present invention, the electrical signal connection method between the signal sending end of the temperature sensor and the temperature signal receiving end of the thermoresistive water bath heating device adopts a conventional setting in the prior art and is not the invention point of the present invention, so it will not be elaborated further;

[0084] When the temperature sensor in the jacket 11 of the slurry tank 1 detects that the water bath temperature in the jacket 11 of the slurry tank 1 reaches 35°C, the temperature sensor sends a signal indicating that the temperature has reached 35°C to the temperature signal receiving end of the thermal resistance type water bath heating device, and after conversion by the digital-to-analog signal conversion module, it is sent to the central processor control module. At this time, the central processor control module sends a stop heating signal to the heating control module, that is, stops the water bath heating. At this time, the slurry temperature < 35°C (specifically 30°C (measured by the temperature sensor in the slurry tank 1)), which is lower than the set value (35°C), and subsequent processes are required to heat up the slurry.

[0085] (3) As Figure 2 shown, the discharge end at the bottom of the slurry tank 1 is connected to the feed end of the headbox 3 through the circulation pipeline 2; two viscosity detection, feedback, and microwave heating fine-tuning mechanisms are respectively arranged at the front end and the rear end of the circulation pipeline 2;

[0086] Each viscosity detection, feedback, and microwave heating fine-tuning mechanism includes a viscosity detection device (not marked in the figure), a temperature detection device 22, and a microwave heating fine-tuning device (not marked in the figure);

[0087] The detection end 21 of the viscosity detection device is arranged on the bottom side wall of the circulation pipeline 2, the temperature detection device 22 is arranged at a position close to the top side wall inside the circulation pipeline 2, and the heating end 23 of the microwave heating fine-tuning device is arranged between the upper and lower pipe walls inside the circulation pipeline 2 (the heating end 23 can be a pipe-shaped structure, or can also be arranged on the front pipe wall or the rear pipe wall inside the circulation pipeline 2), or the heating end of the microwave heating fine-tuning device can also be arranged on the outer side wall of the circulation pipeline 2 (this situation is not marked in the figure);

[0088] The viscosity detection device can select the viscosity detection equipment of German MARIMEX company, and the specific model is, for example VA100, the sensor types are, for example: probe (VA-100C), probe (VA-100B), or viscosity detection devices of models such as VA-300L, VA-300M, VA-300H, VA-300X, or a viscosity detection device of model NDJ-5S / 8S / 9S can also be used;

[0089] The temperature detection device 22 can adopt a temperature sensor of model GWP200, or a thermal resistance thermometer of model TR21-C, or a temperature sensor of model PT-100;

[0090] The microwave heating fine-tuning device can adopt a pipeline-type electric heater of the CN61M / DN25 type, or a pipeline-type microwave heating device of the MGG-J model produced by Qingdao Maiwei Microwave Chemical Equipment Co., Ltd.; or it can also adopt the structure of a pipeline-type microwave heater in a Chinese patent with the application number CN202321125052.2. In this case, the heating end of the microwave heating fine-tuning device is arranged on the outer side wall of the circulation pipeline 2;

[0091] The model of the PLC controller used in the present invention can be FX1N-40MT-0001, S7-300, FX3U, S7-1500, etc.;

[0092] The viscosity detection, feedback and microwave heating fine-tuning mechanism further includes a flowmeter (model: RHM02L). The flowmeter is arranged on the right side (not marked in the figure) of the detection end 21 of the viscosity detection device and can detect the flow rate of the slurry;

[0093] The PLC controller can perform logic control and can perform PID interlock control on the viscosity detection device, the temperature detection device 22 and the microwave heating fine-tuning device;

[0094] During operation, viscosity, temperature and microwave heating signals are connected to the PLC controller through the viscosity detection device, the temperature detection device 22 and the microwave heating fine-tuning device; at the same time, the microwave heating fine-tuning device is used as a fine-tuning device for the slurry temperature. The PLC controller monitors the opening or closing of the microwave heating fine-tuning device, so as to realize real-time adjustment of the slurry temperature. The slurry viscosity is used as a process variable (PID input signal), and the microwave heating is used as a control variable (PID output signal). The set slurry viscosity value is set, and the heating power of the microwave heating is controlled to reach the viscosity set value;

[0095] After the viscosity detection device sends the viscosity signal to the PLC controller, if the slurry viscosity is higher than the set value, the PLC controller controls the start of the microwave heating fine-tuning device for microwave heating and increases the microwave heating power. When the viscosity detection device detects that the slurry viscosity is lower than the set value, the PLC controller controls the gradual closing of the microwave heating fine-tuning device; during this period, the temperature detection result of the temperature detection device 22 is synchronously sent to the PLC controller for data reference, and the final temperature and viscosity change of the slurry can be grasped in real time;

[0096] Specifically, the PID interlock control method of the PLC controller for the viscosity detection device, the temperature detection device 22 and the microwave heating fine-tuning device in the present invention adopts the conventional settings in the prior art and is not the inventive point of the present invention, so it will not be elaborated here.

[0097] Transfer the slurry from the slurry tank 1 to the headbox 3 slowly through the circulation pipeline 2. By detecting the time taken for a certain volume (200 mL) of the slurry to pass through the front end and the back end of the circulation pipeline 2 by the viscosity detection, feedback and microwave heating fine-tuning mechanism, the viscosity of the slurry is calculated (through multiple experiments and detections by the inventor in the early stage, a curve graph of the passing time of the slurry through the circulation pipeline 2 and the slurry viscosity, as shown in Figure 3 is obtained; and a curve graph of the temperature and the slurry viscosity, as shown in Figure 4 is obtained);

[0098] Use the viscosity detection, feedback and microwave heating fine-tuning mechanism to detect once every 15 minutes. Use the PLC controller for PID interlocking control of the viscosity detection device, the temperature detection device 22 and the microwave heating fine-tuning device to calculate the viscosity of the slurry and monitor the viscosity change until the viscosity remains stable. At this time, the performance of the adhesive reaches the optimum (by adjusting the slurry temperature to control the viscosity, this will not change the slurry formula and is conducive to production);

[0099] Since the temperature of the slurry (specifically 30 °C) is slightly lower than the set value (35 °C) when the slurry enters the circulation pipeline 2 from the slurry tank 1, it is necessary to perform PID interlocking control on the microwave heating fine-tuning device through the PLC controller to make the microwave heating fine-tuning device perform heating fine-tuning to reach the set temperature (35 °C), and at the same time monitor the temperature and viscosity;

[0100] If the viscosity is higher than the design value, use the microwave heating fine-tuning device to perform microwave heating to heat the slurry to the required temperature, and use the viscosity detection device 21 at the back end of the circulation pipeline 2 to detect the viscosity until it meets the standard. At this time, turn off the microwave heating and then enter the headbox 3.

[0101] Specifically, in step (3), before the slurry enters the headbox 3, during the process of passing through the circulation pipeline 2, the slurry temperature is controlled at 35 ± 1 °C (when not heated, the slurry temperature is generally between 10 - 33 °C according to different seasons), and the viscosity is controlled at 2000 - 2200 cP.

[0102] Monitor the slurry flow rate through the flow meter set on the circulation pipeline 2 before entering the headbox 3, so as to control the slurry flow rate to make the slurry liquid level in the headbox 3 basically fixed at the same height, and the height deviation is controlled within ±0.5 cm;

[0103] The bottom of the headbox 3 is provided with an opening (not marked in the figure), and a scraper is provided at the opening (not marked in the figure). A uniformly running metal belt is provided below the headbox 3. The running speed of the metal belt is 8 m / min. During the running process, the slurry in the headbox 3 is discharged from the bottom of the headbox 3, and then the scraper is used to uniformly cast the slurry onto the metal belt;

[0104] The slurry shall be used within 4 hours after being transferred to the slurry tank 1.

[0105] (4) Then, the slurry uniformly cast on the metal belt is dried. The drying process sequentially enters three drying chambers, adopting a low temperature - high temperature - low temperature procedure. Specifically, the first - stage low - temperature drying temperature is between 60 - 80 °C, the second - stage high - temperature drying temperature is between 80 - 100 °C, and the third - stage low - temperature drying temperature is between 50 - 80 °C (the length of each drying chamber is 3 m); after drying, it is peeled off from the metal belt with a scraper to obtain the thick - pulp - method tobacco sheet.

[0106] Meanwhile, a control sample 1 is made. The difference between control sample 1 and Example 1 is that: in step (1), no partial adhesive is added during the grinding of plant fibers, and all adhesives are added during the liquid - material preparation in step (2), and the others refer to Example 1.

[0107] For each batch of slurry, samples are taken at the same longitudinal position of the sheet every few minutes. 5 groups of samples are taken for each batch, with a total of 10 groups, and then the slurry concentration, viscosity, and finished - product thickness are detected. The thickness is detected in accordance with GB / T451.3 - 2002. The specific results are shown in Tables 1, 2, and 3 as follows:

[0108] Table 1 Comparison of the concentration and viscosity of the first and second batches of slurry in control sample 1

[0109] Measurement Name Concentration (%) Viscosity (cP) Temperature (°C) First Batch of Slurry 21.05 1342 38 Second Batch of Slurry 24.34 1950 37

[0110] Table 2 Comparison of the concentration and viscosity of the first and second batches of slurry in Example 1

[0111] Measurement Name Concentration (%) Viscosity (cP) Temperature (°C) First Batch of Slurry 24.41 1853 38 Second Batch of Slurry 24.55 1907 39

[0112] Table 3 Comparison of the thickness of 10 groups of sheet samples in two batches of control sample 1 and Example 1

[0113] Measurement Name Average Thickness (mm) Coefficient of Variation (%) Control Sample 1 0.140 6.81 Example 1 0.144 1.72

[0114] It can be seen from Tables 1, 2, and 3 that: in the control sample, no partial adhesive is added during the grinding of plant fibers, and all adhesives are added during the liquid - material preparation in step (2), resulting in uneven dispersion of plant fibers in water, different concentrations of the aqueous solutions of plant fibers in the two batches entering the liquid - material tank, and thus affecting the slurry concentration, viscosity, and the uniformity of sample thickness. In Example 1, partial adhesive is added during the grinding of plant fibers, and through the dispersion effect of the adhesive, the plant fibers are evenly dispersed in water, the concentrations of the aqueous solutions of plant fibers in the two batches entering the liquid - material tank are the same, the concentrations and viscosities of the two batches of slurry are close, and the uniformity of sample thickness is better.

[0115] Example 2

[0116] A method for improving the thickness stability of tobacco sheet by thick slurry method. The difference between Example 2 and Example 1 is as follows:

[0117] In step (1), the tobacco raw material is crushed into powder of about 40 μm, the beating degree of the fiber pulp is 40°SR, the plant fibers are two kinds of softwood fibers and hardwood fibers, and the addition amounts of softwood fibers and hardwood fibers are 2% and 2% of the weight of the tobacco powder respectively. The adhesive is sodium carboxymethylcellulose; the mass ratio of plant fiber, clear water and adhesive is 4:100:0.1.

[0118] In step (2), the smoking agents are two kinds of propylene glycol and glycerol, and the addition amounts of propylene glycol and glycerol are 5% and 15% of the weight of the tobacco powder respectively; the remaining adhesive is sodium carboxymethylcellulose, and the addition amount is 4% of the weight of the tobacco powder; the addition amount of clear water is 3.5 times the weight of the tobacco powder;

[0119] In step (3), the running speed of the metal belt is 12 m / min.

[0120] Meanwhile, a control sample 2 is made. The difference between control sample 2 and Example 2 is as follows: In step (2), only a temperature sensor is arranged inside the slurry tank 1 in the slurry tank 1, and no viscosity detection device and microwave heating fine-tuning device are arranged. In step (4), the drying process of the slurry on the metal belt is carried out at a constant temperature of about 90°C for drying.

[0121] Samples are taken at the same longitudinal position of the sheet at intervals of several minutes for each batch of slurry. For the first two batches, 5 groups of samples are taken for each batch, a total of 10 groups. Then, the finished product thickness, basis weight, tensile strength and moisture are detected respectively according to GB / T451.3-2002, GBT451.2-2002, GBT12914-2008, YC T 345-2010. The specific results are shown in Tables 4, 5, 6 as follows:

[0122] Table 4 Comparison of slurry concentration and viscosity between control sample 2 and Example 2

[0123] Measurement Name Concentration (%) Viscosity (cP) Temperature (°C) Control Sample 2 24.56 1778 39 Example 2 24.63 2156 35

[0124] Table 5 Comparison of thickness and basis weight of 10 groups of sheet samples between control sample 2 and Example 2

[0125]

[0126] Table 6 Comparison of tensile index and moisture of 10 groups of sheet samples between control sample 2 and Example 2

[0127]

[0128] It can be seen from Tables 4, 5, and 6 that: In the control sample 2, only a temperature sensor is provided inside the slurry tank 1. Due to the lag of water bath heating, the actual slurry temperature exceeds the set temperature, which affects the slurry viscosity. It may also cause changes in the performance of the adhesive in the slurry due to too high temperature, affecting the slurry uniformity, and further affecting the sample thickness and quantitative uniformity.

[0129] As described above, it is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention. Therefore, the protection scope of the present invention should be subject to the protection scope of the claims.

Claims

1. A method for improving the thickness stability of tobacco sheet by thick slurry method, characterized in that, It is achieved by adopting a slurry transportation, viscosity detection and flow slurry system; the slurry transportation, viscosity detection and flow slurry system includes a slurry tank, a circulation pipeline, two viscosity detection, feedback and microwave heating fine-tuning mechanisms, a flow slurry box, and a PLC controller; The discharge end at the bottom of the slurry tank is connected to the feed end of the flow slurry box through the circulation pipeline; two viscosity detection, feedback and microwave heating fine-tuning mechanisms are respectively arranged at the front end and the rear end of the circulation pipeline; Each viscosity detection, feedback and microwave heating fine-tuning mechanism includes a viscosity detection device, a temperature detection device and a microwave heating fine-tuning device; The method includes the following steps: (1) Crush the tobacco raw materials into powders with a size of 30 - 50 μm; add water and part of the adhesive to the plant fibers, and grind them into fiber pulp with a beating degree of 30 - 55°SR using a refiner; (2) Transfer the fiber pulp in step (1) to a liquid material tank, stir the fuming agent and the remaining adhesive evenly and pump them into the liquid material tank, then add clear water and mix evenly to obtain a liquid material; Transfer the evenly mixed liquid material to the slurry tank, add the crushed tobacco powder in step (1) to the slurry tank, mix evenly to make a slurry; perform water bath heating on the slurry tank; (3) Transfer the slurry from the slurry tank to the flow slurry box through the circulation pipeline. Respectively use the two viscosity detection, feedback and microwave heating fine-tuning mechanisms to detect the time for a certain volume of slurry to pass through the front end and the rear end of the circulation pipeline of the viscosity detection, feedback and microwave heating fine-tuning mechanisms at regular intervals. Use the PLC controller to perform PID interlock control on the viscosity detection device, temperature detection device and microwave heating fine-tuning device, convert to obtain the viscosity of the slurry, and monitor the viscosity change until the viscosity remains stable; The bottom of the flow slurry box is provided with an opening, a scraper is provided at the opening, and a uniformly running metal belt is provided below the flow slurry box. During operation, the slurry in the flow slurry box is discharged from the bottom of the flow slurry box, and then the scraper is used to uniformly spread the slurry onto the metal belt; (4) Then dry the slurry uniformly spread on the metal belt. The drying process sequentially enters three drying ovens, adopting a low-temperature - high-temperature - low-temperature program. After drying, use a scraper to peel it off from the metal belt to obtain the thick slurry method tobacco sheet.

2. The method according to claim 1, wherein In step (1), the plant fiber is one or more of softwood fiber, hardwood fiber, and flax fiber, and the addition amount of the plant fiber is 3 - 6% of the weight of the tobacco powder; In step (1), the adhesive is one or more of sodium carboxymethylcellulose, methylcellulose, hydroxypropyl methylcellulose, guar gum, xanthan gum, and tamarind gum; In step (1), the mass ratio of the plant fiber, clear water, and adhesive is 4:(90 - 120):0.

1.

3. The method according to claim 1, wherein In step (2), the fuming agent is one or two of propylene glycol and glycerol, and the addition amount of the fuming agent is 15 - 22% of the weight of the tobacco powder; In step (2), the remaining adhesive is one or more of sodium carboxymethylcellulose, methylcellulose, hydroxypropyl methylcellulose, guar gum, xanthan gum, and tamarind gum, and the addition amount is 3 - 5% of the weight of the tobacco powder; In step (2), the addition amount of clear water is 3 - 4 times the weight of the tobacco powder.

4. The method according to claim 1, wherein In step (2), a resistance temperature detector (RTD) water bath heating device is further provided outside the slurry tank. Temperature sensors are equipped in both the interlayer of the slurry tank body and inside the slurry tank. The water bath temperature is measured by the temperature sensor in the interlayer of the slurry tank body. The RTD water bath heating device is provided with a temperature signal receiving end, an analog-to-digital signal conversion module, a central processor control module, and a heating control module. The temperature sensor is provided with a temperature signal sending end. The signal sending end of the temperature sensor can send the temperature signal to the temperature signal receiving end of the RTD water bath heating device. The temperature signal receiving end sends the temperature signal to the analog-to-digital signal conversion module, and the analog-to-digital signal conversion module then converts the temperature signal into a digital signal and sends it to the central processor control module. The temperature signal of the inside of the slurry tank or the interlayer of the slurry tank is sent to the temperature signal receiving end through the temperature sensor. At the same time, the set temperature is set through the central processor control module of the RTD water bath heating device. Then, the received temperature signal is converted into a digital signal through the analog-to-digital signal conversion module and compared with the set temperature value of the central processor control module. If the temperature value received by the central processor control module is lower than the set temperature value of the central processor control module, the central processor control module sends a signal to start heating to the heating control module, and the RTD water bath heating device is immediately started and begins to heat.

5. The method according to claim 4, characterized in that, When the temperature sensor in the interlayer of the slurry tank detects that the water bath temperature in the interlayer of the slurry tank reaches the set temperature, the temperature sensor sends a signal that the temperature has reached the set temperature to the temperature signal receiving end of the RTD water bath heating device, and after conversion through the analog-to-digital signal conversion module, it is sent to the central processor control module. At this time, the central processor control module sends a signal to stop heating to the heating control module, that is, to stop the water bath heating. At this time, the slurry temperature < the set temperature, and subsequent processes are required to heat up the slurry.

6. The method according to claim 1, wherein In step (3), the detection end of the viscosity detection device is arranged on the bottom side wall of the circulation pipeline, the temperature detection device is arranged at a position close to the top side wall inside the circulation pipeline, and the heating end of the microwave heating fine-tuning device is arranged between the upper and lower pipe walls inside the circulation pipeline. Alternatively, the heating end of the microwave heating fine-tuning device can also be arranged on the outer side wall of the circulation pipeline. The PLC controller can perform logic control and can perform PID interlock control on the viscosity detection device, temperature detection device, and microwave heating fine-tuning device. The viscosity, temperature, and microwave heating signals are connected to the PLC controller through the viscosity detection device, temperature detection device, and microwave heating fine-tuning device. At the same time, the microwave heating fine-tuning device is used as a fine-tuning device for the slurry temperature. The PLC controller is used to monitor the opening or closing of the microwave heating fine-tuning device, so as to realize the real-time adjustment of the slurry temperature. The slurry viscosity is used as a process variable, and the microwave heating is used as a control variable. The set slurry viscosity value is set, and the heating power of the microwave heating is controlled to reach the viscosity set value. After the viscosity detection device sends the viscosity signal to the PLC controller, if the viscosity of the slurry is higher than the set value, the PLC controller controls the start of the microwave heating fine-tuning device for microwave heating and increases the microwave heating power. When the viscosity detection device detects that the viscosity of the slurry is lower than the set value, the PLC controller controls the gradual shutdown of the microwave heating fine-tuning device; during this period, the temperature detection results of the temperature detection device are synchronously sent to the PLC controller for data reference, so as to grasp the final temperature and viscosity changes of the slurry in real time.

7. The method according to claim 1, characterized in that, In step (3), the two viscosity detection, feedback and microwave heating fine-tuning mechanisms are used to detect once every 10 - 15 minutes, and the time for a certain volume of slurry to pass through the front end and the back end of the viscosity detection, feedback and microwave heating fine-tuning mechanisms of the circulation pipeline is detected. The PLC controller performs PID interlock control on the viscosity detection device, temperature detection device and microwave heating fine-tuning device, converts to obtain the viscosity of the slurry, and monitors the viscosity change until the viscosity remains stable.

8. The method according to claim 1, wherein In step (3), before the slurry enters the headbox, during the process of passing through the circulation pipeline, the temperature of the slurry is controlled at 35 ± 1 °C, and the viscosity is controlled at 2000 - 2200 cP; In step (3), the usage time of the slurry is within 4 hours since it is transferred to the slurry tank.

9. The method according to claim 1, characterized in that In step (4), the first-stage low-temperature drying temperature is between 60 - 80 °C, the second-stage high-temperature drying temperature is between 80 - 100 °C, and the third-stage low-temperature drying temperature is between 50 - 80 °C; In step (4), the length of each drying oven is 2 - 4 m.

10. A thick-slurry method tobacco sheet prepared by the method according to any one of claims 1 - 9.

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