Method for improving whiteness and fisheye of polyvinyl chloride

Abstract

The invention discloses a method for improving whiteness and fisheye of polyvinyl chloride, which comprises the following steps: adding a polymeric monomer and an auxiliary agent into a polymerization kettle, and carrying out polymerization reaction according to polymerization reaction conditions to obtain a polyvinyl chloride product, the method comprises the following steps: adding a gas-liquid interface relieving agent into a polymerization kettle at the early stage or the middle and later stages of a polymerization reaction, and adding a pH regulator and a stabilizer into the polymerization kettle at the middle and later stages of the polymerization reaction. According to the method, the thickness of an interface layer can be reduced, the stability of polyvinyl chloride is improved, and the whiteness and fisheye of a polyvinyl chloride product are improved.

Description

Technical Field

[0001] The invention relates to the technical field of polymer polymerization, in particular to a method for improving the whiteness and fisheye of polyvinyl chloride. Background Art

[0002] Polyvinyl chloride resin (PVC) is one of the five major engineering plastics and has been widely used in industry, construction and people's lives. At present, different PVC manufacturers (including foreign ones) have problems such as more fish eyes in their products and poor stability of PVC chains due to differences in process and formula. Poor stability will lead to a decrease in whiteness (including processing whiteness and apparent whiteness).

[0003] Traditional methods to improve fisheyes include increasing the oil absorption rate of the product and adding anti-fisheye agents. Among them, increasing the oil absorption rate of the product will significantly reduce the apparent density of polyvinyl chloride. Adding anti-fisheye agents will significantly hinder the early reaction speed and consume too much initiator.

[0004] Traditional methods to improve the stability of polyvinyl chloride include using high-polymerization degree to replace low-polymerization degree products and initially adding stabilizers. Improving stability by increasing the polymerization degree, that is, reducing the product model, is not suitable for fixed-model products, but is suitable for reducing the model. However, the model change brings a series of processing changes and generally cannot be used in industry. Initial addition of stabilizers can improve stability, but stabilizers are generally inhibitory, antioxidant or terminating types, which will significantly hinder the early reaction rate.

[0005] As downstream processing companies have increasingly higher requirements for PVC quality, it is necessary to improve indicators such as fisheye, whiteness, etc. to adapt to market and demand changes. Summary of the invention

[0006] The object of the present invention is to provide a method for improving the whiteness and fisheye of polyvinyl chloride.

[0007] The present invention is implemented by the following technical scheme: a method for improving the whiteness and fisheye of polyvinyl chloride, wherein polymerization monomers and auxiliary agents are added into a polymerization kettle and polymerization reaction is carried out according to polymerization reaction conditions to obtain a polyvinyl chloride product; in the early stage of the polymerization reaction or in the middle and late stages of the polymerization reaction, a gas-liquid interface mitigating agent is added into the polymerization kettle to reduce the thickness of the interface layer and ensure that more reactions are carried out in the liquid phase; in the late stage of the polymerization reaction, a pH regulator and a stabilizer are added into the polymerization kettle.

[0008] Furthermore, the early stage of the polymerization reaction is before the polymerization reaction starts; the middle and late stage of the polymerization reaction is 50%-80% of the polymerization reaction cycle; and the middle and final stage of the polymerization reaction is 50%-90% of the polymerization reaction cycle.

[0009] Furthermore, the polymerization reaction cycle is 4-7h.

[0010] Furthermore, the mass of the gas-liquid interface mitigating agent added is 0.001%-0.01% of the mass of the polymerized monomer added; the mass of the pH adjusting agent added is 0.002%-0.01% of the mass of the polymerized monomer added; and the mass of the stabilizer added is 0.005%-0.015% of the mass of the polymerized monomer added.

[0011] Furthermore, the gas-liquid interface mitigating agent is an alkane derivative with a molecular weight of less than 50.

[0012] Furthermore, the alkane derivative is one or a combination of more than one of methanol, ethanol or ethylene glycol.

[0013] Furthermore, the pH adjuster is one or a combination of more than one of ammonium bicarbonate, sodium bicarbonate or sodium phosphate.

[0014] Furthermore, the stabilizer is one or a combination of triethylene glycol bis(β-(3-tert-butyl-4-hydroxy-5-methylphenyl)acrylate) (antioxidant 245), β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate octadecyl ester (antioxidant 1076) or 2,4-dimethyl-6-(1-methylpentadecyl)-phenol (antioxidant 1141).

[0015] Advantages of the present invention: In the present invention, the buffer gas-liquid interface agent is added in the early stage of the polymerization reaction or in the middle and late stages of the polymerization reaction, thereby avoiding the increase of the thickness of the interface layer due to the polymerization reaction of vinyl chloride, reducing the thickness of the interface layer, reducing the number of fish eyes of polyvinyl chloride, improving the oil absorption rate of polyvinyl chloride, avoiding the problem of a significant decrease in the apparent density of polyvinyl chloride, and the buffer gas-liquid interface agent added in the early stage of the polymerization reaction will not react with the initiator, thereby avoiding the influence on the polymerization reaction. The pH regulator is added in the late stage of the polymerization reaction, thereby avoiding the destruction of the polyvinyl chloride structure by the acidic environment caused by the cleavage of the polyvinyl chloride side chain in the late stage of the polymerization reaction to generate hydrogen chloride. The stabilizer is added in the late stage of the polymerization reaction, thereby avoiding the cleavage of the polyvinyl chloride side chain, improving the stability of the polyvinyl chloride, and improving the whiteness of the polyvinyl chloride. There is no need to improve the stability by increasing the degree of polymerization, thereby achieving industrial use. The stabilizer is added in the late stage of the polymerization reaction, thereby avoiding the reaction with the initiator to hinder the reaction speed in the early stage of the polymerization reaction. DETAILED DESCRIPTION

[0016] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solution of the present invention. 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.

[0017] Embodiment 1: A method for improving the whiteness and fisheye of polyvinyl chloride, comprising the following steps: The polyvinyl chloride model produced in this embodiment is SG-3; 1. First, coat the kettle, that is, effectively apply the anti-sticking agent to the surface of the polymerization kettle to prevent surface scaling; 2. The system feeds the polymerization kettle, i.e., the raw materials of vinyl chloride, pure water, dispersant, initiator and methanol are added into the reactor according to the feeding program control; the weight of polyethylene is 25.2 tons, the weight of pure water is 23.94 tons, the weight of initiator is 12.6 kg, and the weight of dispersant is 17.85 kg.

[0018] 3. The polymerization kettle is heated up. When the temperature in the polymerization kettle reaches the set temperature (SG-3 is set at 52°C), constant temperature control is started, and polymerization reaction is started. During the reaction, stirring is always accompanied by a certain intensity. The jacket and condenser remove the polymerization heat to ensure constant temperature. After the reaction is carried out stably for 3.25 hours, ammonium bicarbonate and antioxidant 245 are added. The addition of ammonium bicarbonate and antioxidant 245 is stopped 33 minutes before the termination of the reaction. The terminator is added after the polymerization reaction is carried out for 5.5 hours. The polymerization reaction cycle of this embodiment is 5.5 hours; the addition amounts of methanol, ammonium bicarbonate and antioxidant 245 are 0.768 kg, 1.28 kg and 2.56 kg (dry basis) respectively (based on 70m 3 The polymerization kettle is used as the reference), wherein the antioxidant 245 is triethylene glycol bis(β-(3-tert-butyl-4-hydroxy-5-methylphenyl)acrylate).

[0019] 4. Discharging: The discharging process is to send the slurry after the reaction in the polymerization kettle is completed and the terminator slurry is added to the discharging tank and the unreacted monomers are recovered. In this process, sodium hydroxide or sodium bicarbonate or ammonia water is added to adjust the pH to meet the needs of subsequent processes.

[0020] Comparative Example 1-1: The difference from Example 1 is that methanol, ammonium bicarbonate and antioxidant 245 are not added, and the other steps and parameters are exactly the same as those of Example 1.

[0021] Comparative Example 1-2: The difference from Example 1 is that no methanol is added, and the other steps and parameters are exactly the same as those of Example 1.

[0022] Comparative Example 1-3: The difference from Example 1 is that no ammonium bicarbonate is added, and the other steps and parameters are exactly the same as those of Example 1.

[0023] Comparative Example 1-4: The difference from Example 1 is that no antioxidant 245 is added, and the other steps and parameters are exactly the same as those of Example 1.

[0024] Embodiment 2: A method for improving the whiteness and fisheye of polyvinyl chloride, comprising the following steps: The polyvinyl chloride model provided in this embodiment is SG-5; 1. First, coat the kettle, that is, effectively apply the anti-sticking agent to the surface of the polymerization kettle to prevent surface scaling; 2. The system feeds the polymerization kettle, i.e., the raw materials of vinyl chloride, pure water, dispersant, initiator and ethanol are added into the reactor according to the feeding program control; the weight of polyethylene is 26 tons, the weight of pure water is 24.7 tons, the weight of initiator is 13 kg, and the weight of dispersant is 18.2 kg.

[0025] 3. The polymerization kettle is heated up. When the temperature in the polymerization kettle reaches the set temperature (SG-5 is set at 57°C), constant temperature control is started, and polymerization reaction is started. During the reaction, stirring is always accompanied by a certain intensity. The jacket and condenser remove the polymerization heat to ensure constant temperature. After the reaction is carried out stably for 2.25 hours, sodium bicarbonate and antioxidant 1076 are added. The addition of sodium bicarbonate and antioxidant 1076 is stopped 27 minutes before the termination of the reaction. The terminator is added after the polymerization reaction is carried out for 4.5 hours. The polymerization reaction cycle of this embodiment is 4.5 hours; the addition amounts of ethanol, sodium bicarbonate and antioxidant 1076 are 0.768 kg, 1.28 kg and 2.56 kg (dry basis) respectively (at 70 m 3 The polymerization kettle is used as the reference), wherein the antioxidant 1076 is β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate.

[0026] 4. Discharging: The discharging process is to send the slurry after the reaction in the polymerization kettle is completed and the terminator slurry is added to the discharging tank and the unreacted monomers are recovered. In this process, sodium hydroxide or sodium bicarbonate or ammonia water is added to adjust the pH to meet the needs of subsequent processes.

[0027] Comparative Example 2-1: The difference from Example 2 is that ethanol, sodium bicarbonate and antioxidant 1076 are not added, and the other steps and parameters are exactly the same as those of Example 2.

[0028] Comparative Example 2-2: The difference from Example 2 is that no ethanol is added, and the other steps and parameters are exactly the same as those of Example 2.

[0029] Comparative Example 2-3: The difference from Example 2 is that no sodium bicarbonate is added, and the other steps and parameters are exactly the same as those of Example 2.

[0030] Comparative Example 2-4: The difference from Example 2 is that the antioxidant 1076 is not added, and the other steps and parameters are exactly the same as those of Example 2.

[0031] Embodiment 3: A method for improving the whiteness and fisheye of polyvinyl chloride, comprising the following steps: The polyvinyl chloride model provided in this embodiment is SG-7; 1. First, coat the kettle, that is, effectively apply the anti-sticking agent to the surface of the polymerization kettle to prevent surface scaling; 2. The system feeds the polymerization kettle, i.e., the raw materials of vinyl chloride, pure water, dispersant, initiator, ethanol and ethylene glycol are added into the reactor according to the feeding program control; the weight of polyethylene is 26.5 tons, the weight of pure water is 25.175 tons, the weight of initiator is 13.2 kg, and the weight of dispersant is 18.5 kg.

[0032] 3. The polymerization kettle is heated up. When the temperature in the polymerization kettle reaches the set temperature (SG-7 is set at 64°C), constant temperature control is started, and polymerization reaction is started. During the reaction, stirring is always accompanied by a certain intensity. The jacket and condenser remove the polymerization heat to ensure constant temperature. After the reaction is stable for 2 hours, ammonium bicarbonate, sodium phosphate and antioxidant 1141 are added. The addition of ammonium bicarbonate, sodium phosphate and antioxidant 1141 is stopped 24 minutes before the termination of the reaction. The terminator is added after the polymerization reaction is carried out for 4 hours. The polymerization reaction cycle of this embodiment is 4 hours; the addition amounts of ethanol and ethylene glycol, ammonium bicarbonate + sodium phosphate (1:1) and antioxidant 1141 are 0.768 kg, 1.28 kg and 2.56 kg (dry basis) respectively (at 70 m 3 The polymerization kettle is used as the reference), wherein the antioxidant 1141 is 2,4-dimethyl-6-(1-methylpentadecyl)-phenol.

[0033] 4. Discharging: The discharging process is to send the slurry after the reaction in the polymerization kettle is completed and the terminator slurry is added to the discharging tank and the unreacted monomers are recovered. In this process, sodium hydroxide or sodium bicarbonate or ammonia water is added to adjust the pH to meet the needs of subsequent processes.

[0034] Comparative Example 3-1: The difference from Example 3 is that ethanol, ethylene glycol, ammonium bicarbonate, sodium phosphate and antioxidant 1141 are not added, and the other steps and parameters are exactly the same as those of Example 3.

[0035] Comparative Example 3-2: The difference from Example 3 is that no ethanol and ethylene glycol are added, and the other steps and parameters are exactly the same as those of Example 3.

[0036] Comparative Example 3-3: The difference from Example 3 is that no ammonium bicarbonate and sodium phosphate are added, and the other steps and parameters are exactly the same as those of Example 3.

[0037] Comparative Example 3-4: The difference from Example 3 is that antioxidant 1141 is not added, and the other steps and parameters are exactly the same as those of Example 3.

[0038] The products prepared in Examples 1-3 and all comparative examples were tested for whiteness and fisheyes. The whiteness was tested by a colorimeter; the fisheye was tested by an automatic fisheye meter.

[0039] The test results are shown in Table 1: Table 1: Test results of products prepared in Examples 1-3 and all comparative examples

[0040] Apparent whiteness: directly use a whiteness meter to test the whiteness value of PVC products (powder); Processing whiteness: Use the produced PVC product (powder) to perform white sheet calendering to obtain white sheets. Use a whiteness meter to test the whiteness of the sheet surface to obtain the whiteness value.

[0041] Fisheye: Add carbon black to the PVC product (powder) to generate black flakes, and use an automatic fisheye meter to test the number of fisheyes in the PVC product (powder).

[0042] Processing whiteness and apparent whiteness are two indicators used to characterize the stability of polyvinyl chloride. The greater the processing whiteness and apparent whiteness, the greater the stability of the polyvinyl chloride.

[0043] It can be seen from the data in Table 1 that the apparent whiteness and processing whiteness of the prepared polyvinyl chloride in Comparative Examples 1-1, 2-1 and 3-1 are significantly lower than those in Examples 1-3, respectively, by not adding a gas-liquid interface mitigating agent, a pH adjusting agent and a stabilizer. This indicates that the addition of a gas-liquid interface mitigating agent in the early stage of the polymerization reaction or in the middle and late stages of the polymerization reaction reduces the fisheye data and improves the fisheye of the polyvinyl chloride. Furthermore, the addition of a pH adjusting agent and a stabilizer in the late stage of the polymerization reaction enhances the apparent whiteness and processing whiteness, improves the whiteness of the polyvinyl chloride, and improves the stability of the polyvinyl chloride.

[0044] It can be seen from the data in Table 1 that in Comparative Examples 1-2, Comparative Example 2-2, and Comparative Example 3-2, no gas-liquid interface mitigating agent is added in the early stage of the polymerization reaction or in the middle and late stages of the polymerization reaction, and a pH regulator and a stabilizer are added at the end of the polymerization reaction. It can be seen that the processing whiteness and the apparent whiteness have no obvious changes compared with Examples 1-3, respectively; while the number of fisheyes increases significantly. Therefore, it is further proved that adding a gas-liquid interface mitigating agent in the early stage of the polymerization reaction or in the middle and late stages of the polymerization reaction can significantly reduce the number of fisheyes in polyvinyl chloride.

[0045] It can be seen from the data in Table 1 that in Comparative Examples 1-3, Comparative Examples 2-3, and Comparative Examples 3-3, no pH regulator is added at the end of the polymerization reaction, a stabilizer is added, and a gas-liquid interface mitigation agent is added in the early stage of the polymerization reaction or in the middle and late stages of the polymerization reaction. It can be observed that the fisheye data are not significantly changed compared with Examples 1-3, and the apparent whiteness and processing whiteness data are significantly reduced compared with Examples 1-3, further proving that no pH regulator is added at the end of the polymerization reaction, a stabilizer is added, and a gas-liquid interface mitigation agent is added in the early stage of the polymerization reaction or in the middle and late stages of the polymerization reaction, although the whiteness of polyvinyl chloride can be improved and the fisheye of polyvinyl chloride can be reduced, the whiteness effect of polyvinyl chloride is slightly worse than that of Examples 1-3, respectively. Therefore, it is explained that only the stabilizer is added at the end of the polymerization reaction, so that the stability of polyvinyl chloride is not as obvious as that of adding the pH regulator and the stabilizer at the end of the polymerization reaction.

[0046] It can be seen from the data in Table 1 that in Comparative Examples 1-4, Comparative Examples 2-4, Comparative Examples 3-4, or in which no stabilizer is added at the end of the polymerization reaction, a pH regulator is added, and a gas-liquid interface mitigation agent is added in the early stage of the polymerization reaction or in the middle and late stages of the polymerization reaction, it can be observed that the fisheye data are not significantly changed compared with Examples 1-3, and the apparent whiteness and processing whiteness data are significantly reduced compared with Examples 1-3, further proving that no stabilizer is added at the end of the polymerization reaction, a pH regulator is added, and a gas-liquid interface mitigation agent is added in the early stage of the polymerization reaction or in the middle and late stages of the polymerization reaction, although the whiteness of polyvinyl chloride can be improved and the fisheye of polyvinyl chloride can be reduced, the whiteness effect of polyvinyl chloride is slightly worse than that of Examples 1-3, respectively. Therefore, it is explained that only the pH regulator is added at the end of the polymerization reaction, so that the stability of polyvinyl chloride is not as obvious as that of adding the pH regulator and the stabilizer at the end of the polymerization reaction.

[0047] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for improving the whiteness and fisheye of polyvinyl chloride, wherein a polymerization monomer and an auxiliary agent are added to a polymerization kettle and subjected to polymerization reaction under polymerization reaction conditions to obtain a polyvinyl chloride product, characterized in that: In the early stage of the polymerization reaction or in the middle and late stages of the polymerization reaction, a gas-liquid interface mitigating agent is added to the polymerization kettle. In the late stage of the polymerization reaction, a pH regulator and a stabilizer are added to the polymerization kettle.

2. A method for improving the whiteness and fisheye of polyvinyl chloride according to claim 1, characterized in that: The early stage of the polymerization reaction is before the polymerization reaction starts; the middle and late stage of the polymerization reaction is 50%-80% of the polymerization reaction cycle; and the middle and final stage of the polymerization reaction is 50%-90% of the polymerization reaction cycle.

3. A method for improving the whiteness and fisheye of polyvinyl chloride according to claim 2, characterized in that: The polymerization reaction cycle is 4-7h.

4. A method for improving the whiteness and fisheye of polyvinyl chloride according to claim 1, characterized in that: The added mass of the gas-liquid interface mitigating agent is 0.001%-0.01% of the added mass of the polymerized monomer; the added mass of the pH adjusting agent is 0.002%-0.01% of the added mass of the polymerized monomer; and the added mass of the stabilizer is 0.005%-0.015% of the added mass of the polymerized monomer.

5. The method for improving the whiteness and fisheye of polyvinyl chloride according to claim 1, characterized in that: The gas-liquid interface mitigating agent is an alkane derivative with a molecular weight of less than 50.

6. A method for improving the whiteness and fisheye of polyvinyl chloride according to claim 5, characterized in that: The alkane derivative is one or a combination of more than one of methanol, ethanol or ethylene glycol.

7. A method for improving the whiteness and fisheye of polyvinyl chloride according to claim 1, characterized in that: The pH adjuster is one or a combination of ammonium bicarbonate, sodium bicarbonate or sodium phosphate.

8. The method for improving the whiteness and fisheye of polyvinyl chloride according to claim 1, characterized in that: The stabilizer is one or a combination of triethylene glycol bis(β-(3-tert-butyl-4-hydroxy-5-methylphenyl)acrylate), β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate octadecyl alcohol or 2,4-dimethyl-6-(1-methylpentadecyl)-phenol.

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