Polymerization method of polyvinyl chloride emulsion

Abstract

The invention belongs to the technical field of emulsion preparation, and particularly relates to a polyvinyl chloride emulsion polymerization method which comprises the following steps: step 1, adding water into a polymerization kettle, then starting to stir at a low speed, and adding an emulsifier and auxiliary materials into the polymerization kettle at the same time; stirring at a high speed after adding, so that the emulsifier and the small materials are uniformly mixed with the water; then reducing the stirring speed to a low speed for stirring; the auxiliary materials comprise a chelating agent, a dispersing agent, a stabilizing agent and a cross-linking agent; step 2, adding vinyl chloride into a polymerization kettle, then heating the polymerization kettle, and adding an initiator into the polymerization kettle to accelerate polymerization reaction when the temperature rises to a set temperature; 3, after a certain period of time, the polymerization reaction speed is reduced, and then the step 2 is repeated until vinyl chloride is added completely; according to the method, the highest conversion rate of the vinyl chloride can reach 92%, and the utilization rate of the vinyl chloride is greatly increased.

Description

Technical Field

[0001] The invention relates to the technical field of emulsion preparation, in particular to a polymerization method for polyvinyl chloride emulsion. Background Art

[0002] The methods of vinyl chloride polymerization mainly include suspension polymerization, emulsion polymerization and bulk polymerization. Among them, emulsion polymerization has the advantages of fast polymerization speed, high product molecular weight, easy heat dissipation, continuous operation, and the latex can be directly used as the final product. Therefore, the polymerization of polyvinyl chloride emulsion usually adopts emulsion polymerization.

[0003] The main process of emulsion polymerization is as follows:

[0004] 1. Monomer dispersion: by stirring or shaking, the vinyl chloride monomer and the emulsifier form an emulsion in water;

[0005] 2. Adding initiator: After the emulsion is formed, the polymerization reaction of vinyl chloride monomer is initiated by adding initiator;

[0006] 3. Polymerization reaction: Adjust the appropriate temperature according to the size of latex particles, and the monomers begin to polymerize to form high molecular polymers, namely latex particles.

[0007] In the existing emulsion polymerization method, the temperature is set according to the latex particle size requirements, and the polymerization reaction is carried out at this temperature. In the polymerization reaction, the temperature setting affects the maximum size of the latex particles, and the interference force on the minimum size is small, which leads to a large size distribution range of the latex particles (PVC resin particles) in the polyvinyl chloride emulsion produced by it. For example, in the production emulsion, the maximum latex particle diameter is 0.2mm, then the latex particle size range in the emulsion is usually 0.1-0.2mm. In most industries, this emulsion can be used normally. Since the latex particle size range will affect the performance of the emulsion polymer, some industries will have more refined requirements for the latex particle size, such as biomedicine, environment, functional materials, etc. In these industries, the latex particles need to have a smaller size range distribution. In the prior art, the size distribution range of the latex particles is narrowed by more precise adjustment and control of the emulsion concentration, initiator concentration, vinyl chloride concentration, stirring speed and temperature, which will greatly increase the production cost of the polyvinyl chloride emulsion. In addition, during the polymerization process, the concentration of vinyl chloride will change accordingly, which makes it difficult to accurately control the concentration of vinyl chloride during the polymerization process, which further increases the difficulty of controlling the size distribution range of the latex particles; secondly, during the polymerization reaction, some vinyl chloride monomer needs to be retained in the emulsion to ensure that the concentration of vinyl chloride is not too low, which means that the conversion rate of vinyl chloride in the produced polyvinyl chloride emulsion is low. In the current common emulsion polymerization method, the conversion rate of vinyl chloride is 70% to 80%, which will also lead to an increase in the production cost of polyvinyl chloride emulsion.

[0008] Therefore, we propose a polymerization method for polyvinyl chloride emulsion, which is used to narrow the size distribution range of latex particles in the polyvinyl chloride emulsion and improve the conversion rate of vinyl chloride. Summary of the invention

[0009] The object of the present invention is to provide a method for polymerizing polyvinyl chloride emulsion to solve the problems of large size distribution range of latex particles and low vinyl chloride conversion rate in the existing emulsion polymerization method mentioned in the above background technology.

[0010] To achieve the above object, the present invention provides the following technical solution: a polymerization method of polyvinyl chloride emulsion, the polymerization method of polyvinyl chloride emulsion is as follows:

[0011] Step 1, adding water to the polymerization kettle, and then starting low-speed stirring, while adding emulsifier and small materials to the polymerization kettle; after the addition is completed, high-speed stirring is performed to uniformly mix the emulsifier and small materials with water; then the stirring speed is reduced to low-speed stirring; the small materials include chelating agents, dispersants, stabilizers and cross-linking agents;

[0012] Step 2, adding vinyl chloride to the polymerization kettle, and then heating the polymerization kettle, when the temperature reaches the set temperature, adding an initiator to the polymerization kettle to accelerate the polymerization reaction;

[0013] Step 3: After a certain period of time, the polymerization reaction rate decreases, and then step 2 is repeated until the addition of vinyl chloride is completed;

[0014] Step 4: adding an excess of oxidant to the polymerization kettle to generate free radicals through oxidation reaction to create conditions for further polymerization reaction. After a certain period of time, the polymerization kettle is heated up, and then an excess of reducing agent is added to the polymerization kettle to increase the sensitivity of the residual vinyl chloride monomer to participate in the reaction, promote the vinyl chloride monomer to participate in the polymerization, and generate a polyvinyl chloride emulsion with a smaller latex particle size range;

[0015] The following were added into the polymerization kettle in parts by mass: 498 parts of water, 50 parts of emulsifier, 204.3 parts of small materials, 390 parts of vinyl chloride, 0.05 parts of initiator, 1.8 parts of reducing agent and 1.5 parts of oxidant.

[0016] Preferably, the small material comprises, by mass, 0.3 parts of a chelating agent, 1.6 parts of a diffusing agent, 2.4 parts of a stabilizer and 200 parts of a cross-linking agent.

[0017] Preferably, the chelating agent is one or two of ethylenediaminetetraacetic acid and N-hydroxyethylenediamine;

[0018] The diffusant is an anionic surfactant;

[0019] The stabilizer is mercaptan;

[0020] The cross-linking agent is hydroxyethyl methacrylate.

[0021] Preferably, the emulsifier is selected from one or more of sodium lauryl sulfate, sodium stearate, fatty alcohol ether sulfate, fatty acid soap and fatty alcohol sulfate.

[0022] Preferably, the initiator is ferrous sulfate.

[0023] Preferably, when vinyl chloride is initially added in step 2, the temperature in the polymerization kettle is raised to 40°C; and when the polymerization kettle is heated in step 4, the temperature is raised to 50°C.

[0024] Preferably, when step three repeats step two, the number of repetitions is not less than two times.

[0025] Preferably, when vinyl chloride is added in step 2, the initial amount of vinyl chloride added is not less than half of its total amount; and each subsequent addition of vinyl chloride is not less than half of its remaining amount.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1) In the polymerization process, the present invention gradually increases the size of the latex particles by gradually increasing the temperature to extend the polymerization length of polyvinyl chloride, thereby gradually increasing the maximum size of the latex particles; at the same time, by gradually adding vinyl chloride, the latex particles can be extended in size by polymerizing vinyl chloride monomer; by gradually adding initiators, the concentration of the initiators is slowly increased, so that the initiators inhibit the transitional increase of the latex particle size while initiating the polymerization reaction, so that the latex particles are more inclined to polymerize with the vinyl chloride monomer, thereby reducing the polymerization between the vinyl chloride monomers, and thus avoiding the generation of latex particles with smaller sizes; finally, by separately increasing the temperature, the latex particles with insufficient sizes in the emulsion are polymerized with each other, so that a small number of latex particles with insufficient sizes can grow again, thereby achieving the purpose of reducing the size distribution of the latex particles;

[0028] 2) The present invention realizes multiple polymerization of vinyl chloride by gradually increasing the temperature, thereby realizing the growth of latex particles; since the gradual growth of the latex particles reduces the size distribution of the latex particles, the present invention does not need to control the final concentration of vinyl chloride, and can achieve the purpose of reducing the size distribution of the latex particles. Therefore, the present invention can further polymerize the residual vinyl chloride monomer in the emulsion by adding a reducing agent, thereby improving the conversion rate of vinyl chloride and reducing the production cost of the emulsion;

[0029] 3) In the present invention, the maximum conversion rate of vinyl chloride can reach 92%, which greatly improves the utilization rate of vinyl chloride. DETAILED DESCRIPTION

[0030] The technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0031] In the description of the present invention, it is necessary to understand that the terms "upper", "lower", "front", "back", "left", "right", "top", "bottom", "inside" and "outside" etc., indicating directions or positional relationships, are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific direction, be constructed and operated in a specific direction, and therefore cannot be understood as a limitation on the present invention.

[0032] Example:

[0033] The present invention provides a technical solution: a polymerization method of a polyvinyl chloride emulsion, and the polymerization method of the polyvinyl chloride emulsion is as follows:

[0034] Step 1, add an appropriate amount of water to the polymerization kettle, and then start stirring at a low speed. The low-speed stirring here is to make the stirring shaft in the polymerization kettle adapt to the rotation, and it only needs to be less than 600 rpm, and no specific restrictions are required. Add emulsifiers and small materials to the polymerization kettle while stirring. When the water used in the polymerization kettle is deionized water, since the deionized water does not contain impurities, the emulsifier and small materials can be added at the same time; when the water used in the polymerization kettle is filtered neutral water (conductivity is less than 100μs / cm), since the neutral water is mainly filtered from tap water or purified circulating water, it may contain metal ion impurities, so it is necessary to add small materials first, and the metal ions therein are chelated by the chelating agent in the small materials to remove the metal ions, and then add the emulsifier; to prevent metal ions from interfering with the normal use of the emulsifier. After the emulsifier and the small material are added, high-speed stirring is turned on, and the speed of the stirring shaft in the polymerization kettle is increased to about 1500 rpm. High-speed stirring is not only conducive to the full emulsification and mixing of the emulsifier, the small material and the water, but also can accelerate the mixing speed, thereby reducing the mixing time. After the emulsifier, the small material and the water are evenly mixed, the stirring speed is reduced to low-speed stirring. At this time, the speed of the stirring shaft is maintained at about 200 rpm (the speed of the stirring shaft is maintained stable in the following content). When there are no bubbles in the water, the surface tension of the water in the polymerization kettle is 40-60 mN / m.

[0035] Step 2: Add vinyl chloride to the polymerization kettle. At this time, vinyl chloride will undergo spontaneous and slow polymerization to form latex particles. Then, the polymerization kettle is heated up, and the latex particles begin to increase and the particle size increases. Heating the temperature first and then adding vinyl chloride. When vinyl chloride is added, the temperature in the polymerization kettle fluctuates. At this time, the available spontaneous polymerization time is short and the temperature is unstable. This will cause a large deviation in the size of the latex particles formed during spontaneous polymerization, which is not conducive to the control of the size of the latex particles. However, if vinyl chloride is added first and then heated up, when vinyl chloride spontaneously polymerizes, the temperature of the latex particles formed changes steadily when the temperature is increased, which is conducive to the precise control of the size of the latex particles in the later stage. When the temperature in the polymerization kettle rises to the set temperature (the set temperature is different when the latex particle size requirements are different), an initiator is added to the polymerization kettle. The initiator is used to promote the formation of the polymer, thereby accelerating the speed at which vinyl chloride is polymerized to form latex particles.

[0036] Step 3: As the polymerization reaction proceeds, after a certain period of time, as the vinyl chloride monomer is consumed, the vinyl chloride concentration decreases, and the polymerization reaction rate decreases. At this time, repeat step 2, that is, continue to add vinyl chloride to the polymerization kettle to promote a new round of polymerization reaction; at the same time, increase the temperature in the polymerization kettle. When the temperature is raised to a new set temperature, add initiator to the polymerization kettle again, and the temperature is increased, so that the size of the latex particles is further increased, so that the polyethylene monomer is polymerized to the latex particles, reducing the generation of new latex particles, so that the size of the latex particles is more uniform.

[0037] Steps 2 and 3 are cycled to further extend the size of the latex particles, and finally the addition of vinyl chloride is completed; at this time, vinyl chloride monomer, latex particles with a size smaller than the set size, and latex particles with a size that meets the standard exist in the polymerization kettle, and it is necessary to further polymerize the vinyl chloride monomer to improve the vinyl chloride conversion rate; and increase the size of the latex particles with a size smaller than the set size, so that the size of the latex particles is more uniform, thereby narrowing the size range of the latex particles in the polymerization kettle. During the cycle, the size range of the latex particles can be further narrowed by increasing the number of cycles. The more cycles, the smaller the size range of the latex particles, and finally 1 / 4 of the size range of the latex particles in the prior art can be reached. For example, the size range of the latex particles in the prior art is 0.10 to 0.20 mm, then through multiple cycles of steps 2 and 3 of the present invention, the size range of the latex particles can be narrowed to 0.175 to 0.20 mm. During the cycle, vinyl chloride and initiator need to be added each time, and the temperature also needs to be increased. In the number of cycles, the temperature difference of the next heating cannot be greater than the temperature difference of this heating. For example, if the temperature of the first heating is 4°C, then the temperature difference of the next heating must not exceed 4°C.

[0038] Step 4: Add an excess of oxidant to the polymerization kettle. The oxidant can inhibit the polymerization reaction by oxidizing the initiator. In addition, the oxidant can also create favorable conditions for the further polymerization of the latex particles by oxidizing the latex particles to produce free radicals. After a certain period of time, the oxidant completes the oxidation purpose, and then the polymerization kettle is heated up. During this heating, the temperature is increased within 3°C. After the heating is completed, an excess of reducing agent is added to the polymerization kettle, and the initiator is reduced by the reducing agent to promote the polymerization reaction again; at the same time, the reducing agent can also increase the sensitivity of the remaining vinyl chloride monomer to participate in the reaction, thereby promoting the remaining vinyl chloride monomer to participate in the polymerization reaction, and then improve the conversion rate of vinyl chloride; after a certain period of time, the vinyl chloride in the polymerization kettle completes the polymerization, and a polyvinyl chloride emulsion with a smaller latex particle size range is generated.

[0039] The following are added to the polymerization kettle by mass: 450-500 parts of water, 48-52 parts of emulsifier, 200-220 parts of small materials, 360-400 parts of vinyl chloride, 0.048-0.052 parts of initiator, 1.8-2.1 parts of reducing agent, and 1.2-1.7 parts of oxidant. Among them, small materials include chelating agents, diffusing agents, stabilizers and crosslinking agents. Chelating agents, diffusing agents, stabilizers and crosslinking agents commonly used in emulsion polymerization reactions can be used, and the addition amount is selected according to the use requirements. The amount of reducing agent is more than that of oxidant, so that the reducing agent can suppress the oxidant, thereby increasing the sensitivity of the residual vinyl chloride monomer, and the initiator can be reduced, thereby continuing to promote the polymerization reaction.

[0040] Preferably, the following are added to the polymerization kettle by weight: 498 parts of water, 50 parts of emulsifier, 204.3 parts of small materials, 390 parts of vinyl chloride, 0.05 parts of initiator, 1.8 parts of reducing agent, 1.5 parts of oxidant. The small materials include by weight: 0.3 parts of chelating agent, 1.6 parts of diffusing agent, 2.4 parts of stabilizer and 200 parts of cross-linking agent.

[0041] The chelating agent is selected from one or both of ethylenediaminetetraacetic acid and N-hydroxyethylidene diamine. Metal ions can affect the speed and quality of the polymerization reaction, and in severe cases can even lead to instability of the emulsion system. The use of chelating agents to control metal ions can prevent metal ions from interfering with the polymerization of the emulsion. Ethylenediaminetetraacetic acid and N-hydroxyethylidene diamine can effectively remove metal ions, thereby improving the stability and quality of the emulsion.

[0042] The dispersant is an anionic surfactant, which can promote the dispersion and suspension of the emulsion system, effectively disperse the vinyl chloride monomer evenly in the water, and thus promote the effective progress of the polymerization reaction.

[0043] The stabilizer is mercaptan. As a stabilizer, mercaptan can play a regulating role in the production of emulsion and improve the stability of emulsion, thereby maintaining the uniformity of emulsion and extending the service life of emulsion. In addition, after adding oxidant, the active hydrogen of mercaptan reacts with oxidant to form new free radicals, which participate in addition reaction in subsequent polymerization reaction, that is, mercaptan can also be used as an emulsifier, thereby promoting the residual polymerization reaction of residual vinyl chloride monomer, and further improving the conversion rate of vinyl chloride.

[0044] The cross-linking agent is hydroxyethyl methacrylate. In the production of emulsion, hydroxyethyl methacrylate and other monomers undergo copolymerization reaction to prepare an emulsion with specific properties, thereby improving the heat resistance, chemical corrosion resistance and other properties of the product after the emulsion is used.

[0045] The emulsifier is an anionic emulsifier, for example, one or more of sodium lauryl sulfate, sodium stearate, fatty alcohol ether sulfate, fatty acid soap and fatty alcohol sulfate; the anionic emulsifier can form a negative charge by adsorbing on the surface of micelles, thereby stabilizing the emulsion.

[0046] The initiator is a preparation that can participate in redox reaction, such as ferrous sulfate; after the initiator is oxidized, the action of the initiator is inhibited, thereby reducing the speed of the collective reaction; later, the use of a reducing agent promotes the speed of the polymerization reaction again, thereby increasing the size of the latex particles, allowing the vinyl chloride monomer to participate in the polymerization, and thereby increasing the conversion rate of vinyl chloride.

[0047] The factors that can affect the size of latex particles in the emulsion polymerization method include: monomer concentration, emulsifier concentration, initiator concentration, polymerization temperature and stirring speed; wherein, the present invention avoids excessive monomer concentration by repeatedly adding vinyl chloride, thereby avoiding the problem that the latex particle size is too large during the initial polymerization and the latex particle size is too small during the later polymerization. After the initial addition, the emulsifier is not added, and it can be assumed that its concentration remains unchanged in the present invention. In the present invention, when the initiator concentration is gradually increased and other conditions remain unchanged, the increase in the initiator concentration will cause the maximum size of the latex particles to become smaller; and when other conditions remain unchanged, the increase in temperature will cause the maximum size of the latex particles to become larger. Through the dual influence of the initiator concentration and the increase in temperature, the size of the latex particles is slowly increased, thereby stabilizing the size of the latex particles, and preventing the size of the latex particles from changing too much in the generated emulsion. During the polymerization of the vinyl chloride of the present invention, the stirring speed is constant, and it can be considered that the stirring speed will not affect it.

[0048] Preferably, when step 3 is repeated on step 2, the number of repetitions is not less than two times, and when vinyl chloride is initially added in step 2, the temperature in the polymerization kettle is raised to 40°C; when the polymerization kettle is heated in step 4, the temperature is raised to 50°C, and during the heating process, the single heating temperature does not exceed 4°C. After repeating twice, the cycle ends and all the vinyl chloride is added. When vinyl chloride is added in step 2, the initial addition amount of vinyl chloride is not less than half of its total amount; each subsequent addition of vinyl chloride is not less than half of its remaining amount; for example, when adding 50 parts of vinyl chloride, 30 parts are added when vinyl chloride is added for the first time, 15 parts are added when vinyl chloride is added for the second time, and 5 parts are added when vinyl chloride is added for the last time. Adding according to this amount, latex particles with a size range of 0.15 to 0.20 mm can be obtained.

[0049] The above shows and describes the basic principles and main features of the present invention and the advantages of the present invention. For those skilled in the art, it is obvious that the present invention is not limited to the details of the above exemplary embodiments, and the present invention can be implemented in other specific forms without departing from the spirit or basic features of the present invention; therefore, no matter from which point of view, the embodiments should be regarded as exemplary and non-restrictive. The scope of the present invention is limited by the attached claims rather than the above description, and it is intended to include all changes within the meaning and scope of the equivalent elements of the claims in the present invention, and they should not be regarded as limiting the claims involved.

[0050] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A polymerization method for polyvinyl chloride emulsion, characterized in that: The polymerization method of the polyvinyl chloride emulsion is as follows: Step 1, adding water to the polymerization kettle, and then starting low-speed stirring, while adding emulsifier and small materials to the polymerization kettle; after the addition is completed, high-speed stirring is performed to uniformly mix the emulsifier and small materials with water; then the stirring speed is reduced to low-speed stirring; the small materials include chelating agents, dispersants, stabilizers and cross-linking agents; Step 2, adding vinyl chloride to the polymerization kettle, and then heating the polymerization kettle, when the temperature reaches the set temperature, adding an initiator to the polymerization kettle to accelerate the polymerization reaction; Step 3: After a certain period of time, the polymerization reaction rate decreases, and then step 2 is repeated until the addition of vinyl chloride is completed; Step 4: adding an excess of oxidant to the polymerization kettle to generate free radicals through oxidation reaction to create conditions for further polymerization reaction. After a certain period of time, the polymerization kettle is heated up, and then an excess of reducing agent is added to the polymerization kettle to increase the sensitivity of the residual vinyl chloride monomer to participate in the reaction, promote the vinyl chloride monomer to participate in the polymerization, and generate a polyvinyl chloride emulsion with a smaller latex particle size range; The following were added into the polymerization kettle in parts by mass: 498 parts of water, 50 parts of emulsifier, 204.3 parts of small materials, 390 parts of vinyl chloride, 0.05 parts of initiator, 1.8 parts of reducing agent and 1.5 parts of oxidant.

2. The polymerization method of a polyvinyl chloride emulsion according to claim 1, characterized in that: The small material comprises, by weight, 0.3 parts of a chelating agent, 1.6 parts of a diffusing agent, 2.4 parts of a stabilizer and 200 parts of a cross-linking agent.

3. A method for polymerizing a polyvinyl chloride emulsion according to claim 2, characterized in that: The chelating agent is selected from one or two of ethylenediaminetetraacetic acid and N-hydroxyethylenediamine; The diffusant is an anionic surfactant; The stabilizer is mercaptan; The cross-linking agent is hydroxyethyl methacrylate.

4. The polymerization method of a polyvinyl chloride emulsion according to claim 1, characterized in that: The emulsifier is selected from one or more of sodium lauryl sulfate, sodium stearate, fatty alcohol ether sulfate, fatty acid soap and fatty alcohol sulfate.

5. The polymerization method of a polyvinyl chloride emulsion according to claim 1, characterized in that: The initiator is ferrous sulfate.

6. The polymerization method of a polyvinyl chloride emulsion according to claim 1, characterized in that: When vinyl chloride is initially added in step 2, the temperature in the polymerization kettle is raised to 40°C; when the polymerization kettle is heated in step 4, the temperature is raised to 50°C.

7. The polymerization method of a polyvinyl chloride emulsion according to claim 1, characterized in that: When step three repeats step two, the number of repetitions is not less than two times.

8. The polymerization method of a polyvinyl chloride emulsion according to claim 1, characterized in that: When vinyl chloride is added in the step 2, the initial amount of vinyl chloride added is not less than half of its total amount; and each subsequent addition of vinyl chloride is not less than half of its remaining amount.