Safe plasticization method of nitrocellulose

Abstract

The invention discloses a safe plasticizing method for nitrocellulose, and belongs to the technical field of nitrocellulose production. In order to solve the problems that plasticizers are easy to be delaminated and agglomerated, there are many nitrocellulose residues, the safety risk is large, and the quality of plasticized products is low, the invention provides a safe plasticizing method for nitrocellulose, comprising: pre-mixing the plasticizer and water uniformly, emulsifying them through a homogenizing device to obtain an emulsion, and then plasticizing the emulsion with the nitrocellulose. The invention prepares an emulsion by mixing an oil phase plasticizer and water in a suitable proportion, the plasticizer in the emulsion is evenly distributed, and there is no stratification when standing, thus avoiding the safety and quality problems caused by uneven mixing and plasticizing of a kneader, significantly reducing the material adhering to and agglomerated on the inner wall of the equipment, and reducing the difficulty of cleaning the equipment.

Description

Technical Field

[0001] The invention belongs to the technical field of nitrocellulose production, and in particular relates to a safe plasticizing method for nitrocellulose. Background Art

[0002] At present, the kneading process in the production of nitrocellulose lacquer flakes is to dry-mix nitrocellulose and plasticizer in a kneader. The uniformity of the mixture is poor, and some products with high plasticizer content have obvious adhesion and agglomeration inside the equipment; some products with low plasticizer content are easy to form powder and have poor safety, and adhere to the inside of the equipment, posing a safety hazard. The adhered materials require personnel to enter the kneader regularly for manual cleaning, and this operation also poses a great safety risk.

[0003] The fundamental reason for the above problems is that nitrocellulose is a flocculent solid phase, which has good adsorption of plasticizers. However, the process dosage of oil-phase plasticizers is relatively small (less than 1 / 5 of nitrocellulose), and the relative fluidity of the two is very poor, resulting in uneven mixing. Therefore, the plasticizer needs to be dispersed as much as possible to increase its relative fluidity with nitrocellulose so that the two can be mixed more evenly.

[0004] CN201911147738 discloses a method for plasticizing nitro paint flakes, which is implemented according to the following steps: step 1, mixing a plasticizer and water at a volume ratio of 1:0.35-0.45 to obtain a mixture; step 2, adding the mixture of step 1 to a plasticizer disperser, stirring and dispersing it at a speed of 120r / min for 3 minutes by a stirring motor to obtain a dispersion; step 3, conveying the dispersion to a plasticizing kneading machine, spraying nitrocellulose, kneading and plasticizing at the same time, and completing the plasticization of nitro paint flakes after 40-50 minutes. In this method, water is dispersed in the plasticizer by stirring and dispersing to form oil-in-water, but this method will immediately separate the oil-water phases after stopping stirring, making it difficult to form a uniform mixed solution, and thus it is difficult to ensure uniform mixing of the plasticizer and nitrocellulose.

[0005] CN2019111815891 discloses a nitrocellulose lacquer flake plasticizing process method, comprising the following steps: step one, first add 50 to 70 parts of water and 1 part of plasticizer to a reactor with an agitator in sequence, and then turn on the agitator to stir to make the plasticizer evenly distributed in the water; step two, add 4 to 5 parts of nitrocellulose in dry weight to the reactor, and adjust the speed of the agitator, and the speed is based on the ability to suspend the nitrocellulose in water; step three, adjust the temperature in the reactor to 25 to 70°C, and stir the nitrocellulose at this temperature for 40 to 120 minutes to complete plasticization to obtain water-containing nitrocellulose flakes; step four, take out the nitrocellulose flakes after plasticization and dehydrate them. This method also uses stirring and dispersing to disperse the plasticizer in water to form water-in-oil. However, even if a very large amount of water is used, the oil-water phases will still immediately separate after the stirring is stopped, making it difficult to form a uniform mixed liquid. The problem of relatively more plasticizer being absorbed by the nitrocellulose fed first still occurs. At the same time, since a large amount of water is used, special dehydration treatment is required later.

[0006] It can be seen that the existing technologies all use stirring to disperse plasticizers and water, which is essentially still two phases of oil and water, and no uniform emulsion is formed. In the subsequent mixing process with nitrocellulose, the uniformity of plasticization cannot be ensured. Summary of the invention

[0007] In order to solve the problems that the plasticizer will immediately stratify and agglomerate after the stirring is stopped in the traditional stirring and dispersing emulsification of plasticizers, there will be a lot of nitrocellulose residues sticking and agglomerated during the kneading production process of nitrocellulose lacquer flakes, there are great safety risks in production and cleaning, and the quality of mixed plasticization is poor, the adhesion and agglomeration phenomenon on the inner wall of the kneading machine is improved, and the quality of the mixed plasticization products of the equipment is improved.

[0008] The present invention adopts a method of pre-homogenizing and emulsifying the plasticizer, and then wet-mixing the emulsified plasticizer solution with the nitrocellulose material in a kneader, so as to achieve the purpose of reducing the safety production risk and improving the phenomenon of adhesion and agglomeration on the inner wall of the kneader. Compared with the traditional stirring and dispersing emulsification method, the stability of the plasticizer emulsification is improved, and the emulsion will not be stratified when it is left to stand for a long time, and the uniformity of the plasticizer dispersion is maintained, thereby improving the mixed plasticization quality of the plasticizer and the nitrocellulose; compared with the existing dry mixing of the kneader, firstly, the material adhering to the inner wall of the equipment is greatly reduced, making the equipment easier to clean and improving the safety of the production process; secondly, the plasticizer in the emulsion improves its own "fluidity" by using water as a medium, so that the nitrocellulose and the plasticizer are mixed more evenly, thereby improving the product quality.

[0009] In order to solve the above technical problems, the present invention provides a safe plasticizing method of nitrocellulose, comprising the following steps:

[0010] A. Emulsification: premix the plasticizer and water in a premixing tank, stir the premixed system evenly and then emulsify it through a homogenizing device to obtain an emulsion; wherein the bottom of the premixing tank is conical or elliptical, and the discharge port is located at the center of the tank bottom; the inlet of the homogenizing device is DN50-DN55, the outlet is DN35-DN40, and the cavity has three layers of tightly matched rotors and stators, with gaps of 1.0-1.5mm, 0.5-1.0mm and 0.3-0.5mm respectively;

[0011] B. Plasticization: Heat the kneader jacket to 50-65°C in advance, then add the nitrocellulose into the kneader, start the kneader for stirring, then add the emulsion containing the plasticizer into the kneader, stir for 40-65 minutes to complete safe mixing and plasticization, and obtain the nitrocellulose material with uniform distribution of plasticizer; wherein, the mass ratio of nitrocellulose, plasticizer and water is 81:18-20:160-370 based on dry weight.

[0012] Wherein, in the above-mentioned safe plasticizing method of nitrocellulose, during premixing, the rotation speed of the premixing tank is controlled to be 200-500r / min.

[0013] Among them, in the above-mentioned nitrocellulose safe plasticization method, during emulsification, the rotation speed of the homogenizing equipment is controlled to be 2500-5000r / min.

[0014] Wherein, in the above-mentioned safe plasticization method of nitrocellulose, the water content of the nitrocellulose is 28-32wt%.

[0015] Among them, in the above-mentioned nitrocellulose safe plasticization method, the plasticizer is dibutyl phthalate, tri-n-butyl acetyl citrate, epoxy soybean oil, dioctyl phthalate, diisodecyl phthalate, dioctyl adipate, dioctyl azelaic acid, dioctyl sebacate, epoxy stearate or tricresyl phosphate.

[0016] Beneficial effects of the present invention:

[0017] The method of the present invention prepares an emulsion with an oil-phase plasticizer and water in an appropriate ratio, wherein the plasticizer is evenly distributed in the emulsion and will not be stratified when left standing, thereby ensuring that the ratio of the plasticizer to water is always constant, thereby improving the quality of the mixed plasticization of the plasticizer and the nitrocellulose, and at the same time ensuring that the kneading machine contains enough water in the mixed plasticization process, thereby improving the safety of the production process and avoiding the related safety and quality problems caused by the uneven mixed plasticization of the kneading machine. The method of the present invention significantly reduces the materials adhered to and agglomerated on the inner wall of the equipment, making the equipment easier to clean and greatly reducing the difficulty of cleaning the equipment; after plasticization, only water needs to be filtered (without dehydration), and the emulsification water can be recycled, thereby avoiding the generation of wastewater and having the benefits of energy saving and environmental protection. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 It is a process flow chart of the present invention. DETAILED DESCRIPTION

[0019] Specifically, the safe plasticization method of nitrocellulose comprises the following steps:

[0020] A. Emulsification: premix the plasticizer and water in a premixing tank, stir the premixed system evenly and then emulsify it through a homogenizing device to obtain an emulsion; wherein the bottom of the premixing tank is conical or elliptical, and the discharge port is located at the center of the tank bottom; the inlet of the homogenizing device is DN50-DN55, the outlet is DN35-DN40, and the cavity has three layers of tightly matched rotors and stators, with gaps of 1.0-1.5mm, 0.5-1.0mm and 0.3-0.5mm respectively;

[0021] B. Plasticization: Heat the kneader jacket to 50-65°C in advance, then add the nitrocellulose into the kneader, start the kneader for stirring, then add the emulsion containing the plasticizer into the kneader, stir for 40-65 minutes to complete safe mixing and plasticization, and obtain the nitrocellulose material with uniform distribution of plasticizer; wherein, the mass ratio of nitrocellulose, plasticizer and water is 81:18-20:160-370 based on dry weight.

[0022] Since the plasticizer is an "oily" substance with a higher density than water, it will immediately settle at the bottom of the container without stirring. However, there is a certain distance between the stirring and the bottom of the tank. When the liquid level is lower than the stirring, the material cannot be dispersed, and the plasticizer is deposited at the bottom of the tank. If the premixing tank is a flat-bottomed tank, the plasticizer cannot be completely discharged, resulting in a reduction in the plasticizer content in the emulsion. For the subsequent process, the amount of plasticizer fed is low, that is, the plasticizer content obtained in the nitrocellulose is low, which affects the product quality. At the same time, if the premixing tank is a flat-bottomed tank, the outlet position is generally on the side of the tank body and higher than the bottom of the tank. For heterogeneous materials, the plasticizer discharged from the discharge port is sometimes present and sometimes absent, and the uniformity is worse. Therefore, the present invention adopts a conical or elliptical bottom of the premixing tank, and the discharge port is located at the center of the bottom of the tank. First, the plasticizer fed into it is discharged as much as possible to maintain the plasticizer content of the prepared emulsion; second, it is to maintain the uniformity of the plasticizer discharged from the premixing tank.

[0023] When the oil-water two-phase medium (plasticizer and water) is mixed to form oil-in-water or water-in-oil, it cannot exist stably. It is necessary to use strong cutting dispersion to break up the medium into fine particles, improve the surface tension of the system, and finally form a stable and uniform dispersion system. The present invention uses a homogenizing device to efficiently and evenly dissolve the oil phase plasticizer into another immiscible water phase. The working chamber of the homogenizing device is composed of a total of 6 layers of three-stage dual interlocking rotors and stators. Under the driving action, axial suction occurs to suck the material into the cavity, and the high shear and high-frequency mechanical effects generated by the high-speed rotation of the rotor make the material in the narrow gap between the stator and the rotor. The material is subjected to intense mechanical and hydraulic shear, centrifugal kneading, liquid layer conflict, impact tearing and other cyclic high-pressure forces, and the material is instantly uniform and fine, and a long-term stable suspension and emulsion are obtained.

[0024] In the present invention, the inlet DN50-DN55 of the homogenizing equipment is controlled to be larger than the outlet DN35-DN40, firstly to facilitate the inhalation of materials; secondly to form a pressure difference, forming high pressure in the working chamber of the equipment, and facilitating the homogenization of oil and water. At the same time, the gaps of the three-stage coupled rotor and stator in the cavity of the homogenizing equipment are respectively 1.0-1.5mm, 0.5-1.0mm, and 0.3-0.5mm, thereby forming a variety of cyclic high-pressure forces such as mechanical and hydraulic shearing, centrifugal kneading, liquid layer collision, impact tearing, etc. that are gradually enhanced in the cavity, so that the materials are gradually dispersed, finely and evenly dispersed, and finally a stable and uniform dispersion system is formed.

[0025] Since the kneading machine contains enough water in the mixing and plasticizing process, the safety of the production process is improved. At the same time, according to the test, if the water is too little, the purpose of dispersing the plasticizer in water cannot be achieved, which is not conducive to emulsification. Secondly, the amount of emulsion feed will be reduced accordingly (because the plasticizer index content of nitro paint flakes is 18-20%), and the relative fluidity of nitrocellulose and plasticizer during mixing and plasticizing is poor, which makes the uniformity of mixing nitrocellulose and plasticizer worse, and the residual materials on the inner wall of the kneading and plasticizing equipment are easy to adhere and agglomerate; if the water is too much, the mixing and plasticizing time of nitrocellulose will be prolonged, the production efficiency will be reduced, and a large amount of water will be not conducive to the subsequent plasticizing process. Therefore, the mass ratio of plasticizer to water in step A of the present invention is controlled to be 18-20:160-370.

[0026] After the emulsion is obtained in step A of the method of the present invention, it is transported to an emulsion tank for standby use. The plasticizer is evenly distributed in the emulsified system and will not stratify when left standing, ensuring that the ratio of the plasticizer to water is always maintained constant. The emulsion can be subsequently transported by a centrifugal pump.

[0027] Since the kneading machine contains enough water in the mixing and plasticizing process, the safety of the production process is improved. And because the plasticizer is evenly distributed in the water and mixed more evenly with the nitrocellulose, the material adhering to the inner wall of the equipment is greatly reduced, making the equipment easier to clean.

[0028] During premixing, the rotation speed of the premixing tank needs to be controlled at 200-500 r / min to ensure the uniformity of the emulsified feed. If the rotation speed of the premixing tank is too low, the plasticizer is easy to agglomerate and sink to the bottom, the emulsified feed contains more plasticizer in the early stage and almost all water in the later stage, the emulsion is relatively uneven and the stability is relatively poor. If the rotation speed of the premixing tank is too high, it is difficult to achieve in production and wastes energy.

[0029] When the present invention is emulsifying, the speed of the homogenizing device needs to be controlled at 2500-5000r / min to ensure multiple high-pressure shearing forces during emulsification to obtain a long-term stable emulsion. If the speed of the homogenizing device is too low, the effect of multiple shearing forces during emulsification is reduced, the homogenization and dispersion effect cannot be achieved, and a homogenous emulsion cannot be formed; if the speed of the homogenizing device is too high, the slight vibration and energy consumption of the device are increased, and the reliable stability of continuous operation in production is reduced.

[0030] In step A of the present invention, a common plasticizer in the art can be used, such as dibutyl phthalate, tri-n-butyl acetyl citrate, epoxy soybean oil, dioctyl phthalate, diisodecyl phthalate, dioctyl adipate, dioctyl azelate, dioctyl sebacate, epoxy stearate octyl or tricresyl phosphate. In step B, a common nitrocellulose in the art can be used, and its water content is generally 28-32wt%.

[0031] The present invention is further described in detail below by way of examples, but the protection scope of the present invention is not limited to the scope of the examples.

[0032] Example 1

[0033] 77 kg of DBP plasticizer and 690 kg of water were added to a mixing tank and stirred for pre-mixing. Then, the pre-mixed solution was stirred evenly and then emulsified by a homogenizer to obtain an emulsion containing plasticizer, which was transported to an emulsion tank. The inlet (DN50) of the homogenizer was larger than the outlet (DN40), and the cavity had three layers of tightly fitted rotors and stators with gaps of 1.5 mm, 1.0 mm, and 0.5 mm, respectively.

[0034] The kneader jacket is heated to 50°C in advance, and then 486 kg of nitrocellulose (containing 28% water) is added to the kneader, and the kneader is turned on for stirring. Then, the emulsion containing the plasticizer is added to the kneader, and after stirring for 40 minutes, safe mixing and plasticization are completed to obtain a nitrocellulose material with a plasticizer content of 18% and uniform distribution. The material mixed and plasticized by the kneader is filtered, and the liquid phase water is recovered and temporarily stored, and the solid phase enters the next process.

[0035] Example 2

[0036] 82kg of DBP plasticizer and 1145kg of water were added to a mixing tank and stirred for premixing. Then, the premixed solution was stirred evenly and then emulsified by a homogenizer to obtain an emulsion containing plasticizer, which was transported to an emulsion tank. The inlet (DN50) of the homogenizer was larger than the outlet (DN40), and the cavity had three layers of tightly fitted rotors and stators with gaps of 1.25mm, 0.75mm, and 0.4mm, respectively.

[0037] The kneader jacket is heated to 57°C in advance, and then 500 kg of nitrocellulose (containing 30% water) is added to the kneader, the kneader is turned on for stirring, and then the emulsion containing the plasticizer is added to the kneader, and after stirring for 52 minutes, safe mixing and plasticization are completed to obtain a nitrocellulose material with a plasticizer content of 19% and uniform distribution. The material mixed and plasticized by the kneader is filtered, and the liquid phase water is recovered and temporarily stored, and the solid phase enters the next process.

[0038] Example 3

[0039] 87kg of DBP plasticizer and 1600kg of water were added to a mixing tank and stirred for pre-mixing. Then, the pre-mixed solution was stirred evenly and then emulsified by a homogenizing device to obtain an emulsion containing plasticizer, which was transported to an emulsion tank. The inlet (DN50) of the homogenizing device was larger than the outlet (DN40), and the cavity had three layers of tightly fitted rotors and stators with gaps of 1.0mm, 0.5mm, and 0.3mm, respectively.

[0040] The kneading machine jacket is heated to 65°C in advance, and then 514 kg of nitrocellulose (containing 32% water) is added to the kneading machine, and the kneading machine is turned on for stirring. Then, the emulsion containing the plasticizer is added to the kneading machine, and after stirring for 65 minutes, safe mixing and plasticization are completed to obtain a nitrocellulose material with a plasticizer content of 20% and evenly distributed. The material mixed and plasticized by the kneading machine is filtered, and the liquid phase water is recovered and temporarily stored, and the solid phase enters the next process.

Claims

1. A safe plasticizing method for nitrocellulose, characterized in that: The following steps are involved: A. Emulsification: premix the plasticizer and water in a premixing tank, stir the premixed system evenly and then emulsify it through a homogenizing device to obtain an emulsion; wherein the bottom of the premixing tank is conical or elliptical, and the discharge port is located at the center of the tank bottom; the inlet of the homogenizing device is DN50~DN55, the outlet is DN35~DN40, and the cavity has three layers of tightly matched rotors and stators, with gaps of 1.0~1.5mm, 0.5~1.0mm and 0.3~0.5mm respectively; during premixing, the speed of the premixing tank is controlled to be 200~500r / min; during emulsification, the speed of the homogenizing device is controlled to be 2500~5000r / min; B. Plasticization: Heat the kneader jacket to 50-65°C in advance, then add the nitrocellulose into the kneader, start the kneader for stirring, then add the emulsion containing the plasticizer into the kneader, stir for 40-65 minutes to complete safe mixing and plasticization, and obtain the nitrocellulose material with uniformly distributed plasticizer; wherein, the mass ratio of nitrocellulose, plasticizer and water is 81:18-20:160-370 based on dry weight.

2. The safe plasticizing method of nitrocellulose according to claim 1, characterized in that: The water content of the nitrocellulose is 28-32wt%.

3. The safe plasticizing method of nitrocellulose according to claim 1 or 2, characterized in that: The plasticizer is dibutyl phthalate, tri-n-butyl acetyl citrate, epoxy soybean oil, dioctyl phthalate, diisodecyl phthalate, dioctyl adipate, dioctyl azelate, dioctyl sebacate, epoxy stearate octyl or tricresyl phosphate.

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