Preparation process of a super concentrated emulsion of styrene-butadiene latex

Abstract

This invention belongs to the field of new material preparation and provides a process for preparing ultra-concentrated styrene-butadiene latex emulsion. The main feature of this process is that, based on existing styrene-butadiene latex concentration processes, a polysiloxane heat-resistant and hydrophobic coating is applied to the wall of the concentration vessel. This improvement eliminates the phenomenon of latex adhering to the vessel wall during concentration, thus preventing skin formation and improving latex utilization. Specifically, using butadiene and styrene as monomers, under the action of emulsifiers and other additives, and under specific temperature and pressure, emulsion polymerization forms a low-concentration latex. After the later stage of concentration, the latex solid content can reach 80-90%. The overall production cost is low, meeting the requirements of green, environmentally friendly, and sustainable development.

Description

Technical Field

[0001] This invention relates to the field of new material preparation, specifically providing a process for preparing ultra-concentrated styrene-butadiene latex emulsion. Background Technology

[0002] Styrene-butadiene latex is a synthetic latex formed by emulsion polymerization of butadiene and styrene as monomers under specific temperature and pressure conditions, with the aid of emulsifiers and other additives. Changing polymerization conditions such as temperature, emulsifier, and styrene content can synthesize various brands and grades, each with different properties and applications. Styrene-butadiene latex not only possesses the elasticity and softness of rubber but also some of the properties of resins, making it widely applicable. The paper and road transportation industries are its main application areas, and it can also be used in architectural coatings and carpet industries. With its broad performance characteristics ranging from rubber to resin, styrene-butadiene latex has the largest demand and is experiencing rapid growth among all types of synthetic latex.

[0003] Among them, the more mature industrial technology route for modified emulsified asphalt uses styrene-butadiene latex as a modifier to modify asphalt while emulsifying it, which can significantly improve the low-temperature performance of asphalt. High-performance modified emulsifiers use butadiene and styrene as the main raw materials to synthesize core-shell structured styrene-butadiene latex. The process mainly consists of six production units: chemical preparation unit, dispersant synthesis unit, polymerization unit, monomer recovery unit, concentration unit, and refrigeration unit.

[0004] In the existing technology, the concentration unit has two concentration kettles, operating in a one-on-one standby state. Under the traditional concentration process, the solid content of the prepared latex is over 60%, which is mainly used for roads.

[0005] In the existing concentration process, after all the latex is transferred into the latex concentration kettle, the latex in the storage tank is heated and stirred. After the heating process and flash evaporation for a period of time, the solid content rises to 60%. At this point, due to the high temperature of the kettle wall, a skin is easily formed, which reduces the concentration efficiency and affects the product production cycle. The waste latex skin generated is polluting to the environment and does not meet the requirements of energy conservation and environmental protection. At the same time, if the latex skin is not cleaned in time, it will be mixed into the latex during the next concentration reaction, making filtration difficult and further exacerbating the latex buildup until the concentration kettle cannot be used normally.

[0006] Therefore, how to solve the above-mentioned skinning problem and further increase the solid content of styrene-butadiene latex has become one of the problems that urgently need to be solved by those skilled in the art. Summary of the Invention

[0007] This invention addresses the gaps in the aforementioned technologies by providing a process for preparing ultra-concentrated styrene-butadiene latex emulsions. The main feature of this process is the application of a polysiloxane heat-resistant and hydrophobic coating to the walls of the concentration vessel, building upon existing styrene-butadiene latex concentration processes. This improvement eliminates the phenomenon of latex adhering to the vessel walls during concentration, preventing skin formation and thus increasing latex utilization. The solid content of the styrene-butadiene latex can reach 80-90% in the later stages of concentration, with low overall production costs, meeting the requirements of green, environmentally friendly, and sustainable development.

[0008] Compared with the prior art, the main improvements of the present invention are as follows:

[0009] First, the hydrophobicity of the concentration vessel is improved by coating the wall of the concentration vessel with a polysiloxane heat-resistant and hydrophobic coating. At the same time, the concentration process is readjusted in conjunction with this improvement, and finally, styrene-butadiene latex with a solid content of up to 80-90% can be obtained.

[0010] The specific technical solution of the present invention is as follows:

[0011] A process for preparing ultra-concentrated styrene-butadiene latex emulsion includes a polymerization step and a concentration step of styrene-butadiene latex.

[0012] The polymerization steps can be found in Volume 5 of "Emulsion Polymerization of Styrene-Butadiene Rubber". The inventor provides specific examples as follows:

[0013] The inorganic phases are fed into the polymerization feed manifold by their respective delivery pumps for mixing, and the mixture enters the low-temperature reactor. The monomers butadiene, styrene, and molecular weight regulators are cooled to 5-10°C by the feed cooler and then enter the aforementioned low-temperature reactor. The stirrer and the coil cooling and jacket of the low-temperature reactor are turned on to cool the reactants. When the reaction temperature cools to 8°C, the initiator is added. During the reaction in the low-temperature reactor, potassium chloride solution and some monomers are added. After the reaction in the low-temperature reactor is completed, the materials in the low-temperature reactor are transported to the high-temperature reactor through the low-temperature latex discharge pump.

[0014] Furthermore, the inventors provide a feasible method for preparing styrene-butadiene latex, comprising the following steps:

[0015] Step S1: Clean the reactor three times with deionized water, purge with nitrogen more than three times to remove a small amount of water and oxygen, then add deionized water, reducing agent, first emulsifier and styrene monomer to the reactor, purge with nitrogen more than three times again to release pressure to a slightly positive pressure, add butadiene and molecular weight regulator, mix evenly, and turn on the stirrer to emulsify;

[0016] Step S2: Cool the material in the reactor to 8°C, add the first initiator, and start the polymerization reaction;

[0017] Step S3: Add a viscosity reducer and a second initiator to the reactor during the 8th hour of reaction, and add water and a second emulsifier during the 9th hour of reaction;

[0018] Step S4: After 10 hours of reaction, the material in the reactor is heated to above 20°C to obtain the styrene-butadiene latex.

[0019] Step S5: Discharge the material after 12 hours of reaction.

[0020] The ingredients, by weight, are as follows:

[0021] The composition includes 70 parts butadiene, 29 parts styrene, 0.13 parts primary emulsifier, 0.2 parts secondary emulsifier, 0.45 parts reducing agent, 0.02 parts primary initiator, 0.1 parts molecular weight regulator, 0.1 parts viscosity reducer, and 0.02 parts secondary initiator; the alternative raw materials are as follows:

[0022] The first emulsifier is selected from disproportionated rosinate potassium soap, sodium dodecylbenzene sulfonate, or a quaternary ammonium salt;

[0023] The second emulsifier is selected from hydrogen peroxide or oleic acid;

[0024] The reducing agent is selected from ferrous sulfate or sodium formaldehyde sulfoxylate;

[0025] The first initiator was selected from cumene hydrogen peroxide;

[0026] The second initiator is selected from methylcyclohexane hydrogen peroxide;

[0027] The molecular weight regulator is selected from n-dodecyl mercaptan or tert-dodecyl mercaptan;

[0028] The viscosity reducer is selected from potassium chloride.

[0029] The concentration step described herein is as follows:

[0030] The polymerized latex is transferred to a concentration vessel; the vessel is stirred until the solid content reaches 70%; hot water is introduced into the concentration vessel, and a negative pressure is drawn to -0.097 MPa. During the process, the liquid level must be controlled to not exceed the third layer of stirring. If necessary, an antifoaming agent is added to eliminate foam. The latex in the concentration tank is heated to 45-80℃, and the heating process takes 2-3 hours; after heating, it is distilled under reduced pressure for 30 hours, and the solid content of the styrene-butadiene latex is analyzed through the sampling port; when the solid content reaches 80-90%, the ultra-concentrated styrene-butadiene latex emulsion is obtained.

[0031] The defoamer used is a conventional defoamer in this field, and no specific restrictions are made here. If the amount of foam is small, defoamer may not be added.

[0032] The concentration temperature is 45-60℃.

[0033] The wall of the concentration vessel is coated with a polysiloxane heat-resistant and hydrophobic coating, which has the characteristics of low surface energy, low coefficient of friction, easy sliding, and excellent hydrophobic properties. The preparation method can be referred to the method described in "Preparation and Performance Study of Polysiloxane Heat-Resistant and Hydrophobic Coating".

[0034] The aforementioned polysiloxane coating is obtained by hydrolysis, condensation, and curing of siloxane monomers. The coating has a low curing temperature, resulting in Si-O bonds with high bond energy. The sesquimeric Si-O-Si structure formed by curing and cross-linking has a high heat resistance temperature, good chemical corrosion resistance, and good dimensional stability, making the coating less susceptible to damage under prolonged high-temperature conditions on the reactor wall. It also features a micro-nano rough lotus leaf-like structure superhydrophobic coating, which prevents the latex from sticking to the reactor wall after the liquid level rises.

[0035] Through the improvement of the above concentration process, the present invention can obtain styrene-butadiene latex with a solid content of up to 80-90%. The whole process produces no rubber skin, increases product yield, reduces raw material and operating costs, and is also beneficial to environmental protection. Detailed Implementation

[0036] The following detailed embodiments further illustrate the above-described content of the present invention, but should not be construed as limiting the scope of the subject matter of the present invention to the following examples. All technologies implemented based on the above-described content of the present invention fall within the scope of the present invention. Unless otherwise specified, the following embodiments are all implemented using conventional prior art.

[0037] In the following examples, the wall of the concentration vessel is coated with a polysiloxane heat-resistant and hydrophobic coating. This coating has the characteristics of low surface energy, low coefficient of friction, easy sliding, and excellent hydrophobic properties. The preparation method can be referred to the method described in "Preparation and Performance Study of Polysiloxane Heat-Resistant and Hydrophobic Coating".

[0038] Example 1

[0039] A process for preparing ultra-concentrated styrene-butadiene latex emulsion, the specific steps of which are as follows:

[0040] By controlling the flow rates of butadiene, styrene, and various additives in the reactants, the styrene and butadiene are optimally proportioned. The mixture enters the polymerization reaction system, and parameters such as polymerization temperature and pressure are adjusted. The refrigeration and heating systems are stabilized, and all operational parameters of the flash tank are controlled to ensure normal operation, thus producing qualified latex products. A more specific technical solution is as follows, including the following steps:

[0041] Step S1: Clean the reactor three times with deionized water, purge with nitrogen more than three times to remove a small amount of water and oxygen, then add deionized water, reducing agent, first emulsifier and styrene monomer to the reactor, purge with nitrogen more than three times again to release pressure to a slightly positive pressure, add butadiene and molecular weight regulator, mix evenly, and turn on the stirrer to emulsify;

[0042] Step S2: Cool the material in the reactor to 8°C, add the first initiator, and start the polymerization reaction;

[0043] Step S3: Add a viscosity reducer and a second initiator to the reactor during the 8th hour of reaction, and add water and a second emulsifier during the 9th hour of reaction;

[0044] Step S4: After 10 hours of reaction, the material in the reactor is heated to above 20°C to obtain the styrene-butadiene latex.

[0045] Step S5: Discharge the material after 12 hours of reaction; the obtained styrene-butadiene latex has the following properties: solid content ≥36%; pH: 4-6; viscosity: 3-5cp.

[0046] The ingredients, by weight, are as follows:

[0047] The composition includes 70 parts butadiene, 29 parts styrene, 0.13 parts primary emulsifier, 0.2 parts secondary emulsifier, 0.45 parts reducing agent, 0.02 parts primary initiator, 0.1 parts molecular weight regulator, 0.1 parts viscosity reducer, and 0.02 parts secondary initiator; the alternative raw materials are as follows:

[0048] The first emulsifier is selected from disproportionated rosinate soap;

[0049] The second emulsifier is selected from oleic acid;

[0050] The reducing agent is selected from ferrous sulfate;

[0051] The first initiator was selected from cumene hydrogen peroxide;

[0052] The second initiator is selected from methylcyclohexane hydrogen peroxide;

[0053] The molecular weight regulator is selected from tert-dodecyl mercaptan;

[0054] The viscosity reducer is selected from potassium chloride.

[0055] After the reaction is terminated, the latex is introduced into a concentration tank. The specific concentration operation steps are as follows:

[0056] The polymerized latex is transferred to a concentration vessel; the vessel is stirred until the solid content reaches 70%; hot water is introduced into the concentration vessel, and a negative pressure is drawn to -0.097 MPa. During the process, the liquid level must be controlled to not exceed the third layer of stirring. If necessary, defoamer is added to eliminate foam. The latex in the concentration tank is heated to 45-80℃, which takes about 2-3 hours; after heating, it is distilled under reduced pressure for 30 hours, and the solid content of the styrene-butadiene latex is analyzed through the sampling port; when the solid content reaches 80-90%, the ultra-concentrated styrene-butadiene latex emulsion is obtained.

[0057] Examples 2 and 3

[0058] The processes of Examples 2 and 3 are the same as those of Example 1, except that the concentration temperatures are different. The concentration temperatures of Examples 1, 2, and 3 are 45, 50, and 60°C, respectively.

[0059] Comparative Example 1

[0060] Comparative Example 1 is the concentration reaction without coating, with a different concentration temperature. Since Examples 1, 2, and 3 used heat-resistant hydrophobic coatings, lower concentration temperatures of 45, 50, and 60°C could be used. Other steps and characteristics are the same as in Example 1, and the specific process control conditions are shown in Table 1.

[0061] Table 1. Relevant parameter data for the preparation process of ultra-concentrated latex in Examples 1-3 and Comparative Example 1

[0062] Concentration temperature (°C) Example 1 45 Example 2 50 Example 3 60 Comparative Example 1 80 (Uncoated)

[0063] Experimental Example

[0064] The inventors also applied the obtained styrene-butadiene latex super-concentrated emulsion to base asphalt for performance testing and verification. The asphalt used in the test was 90# base asphalt with a softening point of 46℃.

[0065] Emulsified asphalt is made from asphalt and soap solution.

[0066] 1. Prepare soap solution: (50g MPT-ml, 480g water), heat to 60°C to dissolve, then add hydrochloric acid to adjust pH to 1.9-2.7.

[0067] 2. Pour the soap solution (60°C) into the colloid mill.

[0068] 3. Heat the asphalt, then slowly pour it into the colloid mill while stirring. After it is completely poured in, emulsify for 1 minute.

[0069] 4. Clean the colloid mill, add 4g of each of the latex from Examples 1-3 and Comparative Example 1 to 1000g of emulsified asphalt, stir evenly, and then steam the sample.

[0070] While ensuring the solid content of the products, the latex solid content, softening point and ductility of the modified emulsified asphalt in Examples 1-3 were tested respectively. The results are shown in Table 2.

[0071] Table 2. Data on the verification of latex properties and modified asphalt properties in Examples 1-3 and Comparative Example 1.

[0072] Solid content / % Modified asphalt softening point / ℃ Modified asphalt ductility / cm Anti-fouling effect Example 1 83 57 ＞100 good Example 2 81 56 ＞100 good Example 3 80 55 ＞100 good Comparative Example 1 70 54 32 Difference

[0073] The above calculations and test results show that the ultra-concentrated emulsion preparation process provided by this invention can reduce the concentration temperature by using a hydrophobic coating. By controlling different concentration temperature conditions, and through latex solid content and modified emulsified asphalt performance tests, the ultra-concentrated emulsion preparation process has no impact on the polymerization reaction and product quality. This verifies that the ultra-concentrated latex preparation process has been successfully developed, ultimately achieving zero rubber skin production, increased product yield, reduced raw material and operating costs, and is also beneficial to environmental protection.

[0074] The technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. The description of the above embodiments can help understand the principles and methods of the present invention. However, the above embodiments are not unique and should not be construed as limiting the present invention. At the same time, those skilled in the art can make flexible changes to the specific implementation methods and application scope based on the principles and methods of the present invention.

Claims

1. A process for preparing ultra-concentrated styrene-butadiene latex emulsion, comprising a polymerization step and a concentration step of styrene-butadiene latex, characterized in that: In the concentration step, the hydrophobicity of the concentration vessel is improved by coating the wall of the concentration vessel with a polysiloxane heat-resistant and hydrophobic coating, and finally a styrene-butadiene latex with a solid content of up to 80-90% is obtained. The concentration steps for styrene-butadiene latex are as follows: The polymerized latex is transferred to a concentration vessel; the vessel is stirred until the solid content reaches 70%; hot water is introduced into the concentration vessel and negative pressure is applied. Throughout the process, the liquid level must be controlled to not exceed the third layer of stirring. The latex in the concentration tank is heated to 45-60℃, which takes 2-3 hours; after heating, it undergoes vacuum distillation for 30 hours, and the solid content of the styrene-butadiene latex is analyzed through a sampling port; when the solid content reaches 80-90%, the ultra-concentrated styrene-butadiene latex emulsion is obtained.

2. The process for preparing ultra-concentrated styrene-butadiene latex emulsion according to claim 1, characterized in that, The polymerization steps of styrene-butadiene latex are as follows: Step S1: Clean the reactor three times with deionized water, purge with nitrogen more than three times, remove a small amount of water and oxygen, then add deionized water, reducing agent, first emulsifier and styrene monomer to the reactor, purge with nitrogen more than three times again, depressurize to a slightly positive pressure, add butadiene and molecular weight regulator, mix evenly, turn on the stirrer to emulsify; Step S2: Cool the material in the reactor to 8°C, add the first initiator, and start the polymerization reaction; Step S3: Add a viscosity reducer and a second initiator to the reactor during the 8th hour of reaction, and add water and a second emulsifier during the 9th hour of reaction; Step S4: After 10 hours of reaction, the material in the reactor is heated to above 20°C to obtain the styrene-butadiene latex; Step S5: Discharge the material after 12 hours of reaction; the obtained styrene-butadiene latex has the following properties: solid content ≥36%; pH: 4-6; viscosity: 3-5cp; The viscosity reducer is selected from potassium chloride.

3. The process for preparing ultra-concentrated styrene-butadiene latex emulsion according to claim 1, characterized in that, Add defoamer during concentration to eliminate foam.