A method for improving the whiteness and fisheye of polyvinyl chloride

Abstract

The present invention discloses a method for improving the whiteness and fisheyes of polyvinyl chloride (PVC). The method comprises adding a polymerization monomer and an auxiliary agent to a polymerization kettle and carrying out a polymerization reaction according to polymerization reaction conditions to obtain a PVC product. A gas-liquid interface modifier is added to the polymerization kettle in the early or middle to late stages of the polymerization reaction. A pH regulator and a stabilizer are added to the polymerization kettle in the middle to late stages of the polymerization reaction. The method can reduce the thickness of the interface layer, improve the stability of the PVC, and improve the whiteness and fisheyes of the PVC product.

Description

Technical Field

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

[0002] Polyvinyl chloride (PVC), one of the five major engineering plastics, is widely used in industry, construction, and daily life. However, due to differences in process and formulation, various PVC manufacturers (including those from overseas) often experience issues with their products, including excessive fisheyes and poor PVC chain stability. This poor stability can lead to decreased whiteness (both processed and apparent).

[0003] Traditional methods for improving fisheyes include increasing the product's oil absorption rate and adding anti-fisheye agents. However, increasing the product's oil absorption rate significantly reduces the apparent density of PVC. Adding anti-fisheye agents significantly slows down the initial reaction and consumes excessive initiator.

[0004] Traditional methods for improving the stability of polyvinyl chloride include replacing low-polymerization products with high-polymerization degrees and adding stabilizers initially. While improving stability by increasing the degree of polymerization (i.e., reducing the product size) is not suitable for fixed-size products, it is suitable for reducing the size. However, this type of change introduces a series of processing changes, generally preventing industrial use. Initial addition of stabilizers can improve stability, but these stabilizers are typically inhibitory, antioxidant, or terminating types, significantly slowing down the initial 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, comprising adding polymerization monomers and additives into a polymerization kettle and carrying out polymerization reaction according to polymerization reaction conditions to obtain a polyvinyl chloride product; adding a gas-liquid interface mitigating agent into the polymerization kettle in the early stage of the polymerization reaction or in the middle and late stages of the polymerization reaction to reduce the thickness of the interface layer and ensure that more reactions are carried out in the liquid phase; and adding a pH regulator and a stabilizer into the polymerization kettle in the late stage of the polymerization reaction.

[0008] Furthermore, the early stage of the polymerization reaction is before the start of the polymerization reaction; 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 4-7 hours.

[0010] Furthermore, 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 regulator 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.

[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:

[0016] In the present invention, a 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 in 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, and avoiding the problem of a significant decrease in the apparent density of polyvinyl chloride. Moreover, 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 damage to the polyvinyl chloride structure caused by the acidic environment caused by the cleavage of the polyvinyl chloride side chains 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 chains, improving the stability of polyvinyl chloride, and improving the whiteness of polyvinyl chloride. There is no need to improve the stability by increasing the degree of polymerization, thereby achieving industrial use. Moreover, 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

[0017] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions of the present invention. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of the present invention.

[0018] Example 1: A method for improving the whiteness and fisheye of polyvinyl chloride, comprising the following steps:

[0019] The polyvinyl chloride model produced in this embodiment is SG-3;

[0020] 1. First, coat the reactor, that is, apply the anti-sticking agent to the surface of the polymerization reactor to prevent surface scaling;

[0021] 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.

[0022] 3. The polymerization kettle was heated until the temperature in the polymerization kettle reached the set temperature (52°C for SG-3), and constant temperature control was started. The polymerization reaction was started. The reaction was always accompanied by stirring at a certain intensity. The jacket and condenser removed the polymerization heat to ensure constant temperature. After the reaction was carried out stably for 3.25 hours, ammonium bicarbonate and antioxidant 245 were added. The addition of ammonium bicarbonate and antioxidant 245 was stopped 33 minutes before the termination of the reaction. The terminator was added after the polymerization reaction was carried out for 5.5 hours. The polymerization reaction cycle of this embodiment was 5.5 hours. The added amounts of methanol, ammonium bicarbonate and antioxidant 245 were 0.768 kg, 1.28 kg and 2.56 kg (dry basis) respectively (based on 70 m 3 The polymerization kettle is used as a reference), wherein the antioxidant 245 is triethylene glycol bis(β-(3-tert-butyl-4-hydroxy-5-methylphenyl)acrylate).

[0023] 4. Discharging: The discharging process is the process of sending 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, sodium bicarbonate or ammonia water is added to adjust the pH to meet the needs of subsequent processes.

[0024] 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.

[0025] 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.

[0026] 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 in Example 1.

[0027] 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 Example 1.

[0028] Example 2: A method for improving the whiteness and fisheye of polyvinyl chloride, comprising the following steps:

[0029] The polyvinyl chloride model produced in this embodiment is SG-5;

[0030] 1. First, coat the reactor, that is, apply the anti-sticking agent to the surface of the polymerization reactor to prevent surface scaling;

[0031] 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.

[0032] 3. The polymerization kettle is heated until the temperature in the polymerization kettle reaches the set temperature (57°C for SG-5), thermostatic control is started, and the polymerization reaction begins. The reaction is always accompanied by stirring of 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 (based on 70m 3 The polymerization kettle is used as the benchmark), wherein the antioxidant 1076 is octadecyl β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate.

[0033] 4. Discharging: The discharging process is the process of sending 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, sodium bicarbonate or ammonia water is added to adjust the pH to meet the needs of subsequent processes.

[0034] 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.

[0035] 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 Example 2.

[0036] 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 in Example 2.

[0037] Comparative Example 2-4: The difference from Example 2 is that antioxidant 1076 is not added, and the other steps and parameters are exactly the same as Example 2.

[0038] Example 3: A method for improving the whiteness and fisheye of polyvinyl chloride, comprising the following steps:

[0039] The polyvinyl chloride model produced in this embodiment is SG-7;

[0040] 1. First, coat the reactor, that is, apply the anti-sticking agent to the surface of the polymerization reactor to prevent surface scaling;

[0041] 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.

[0042] 3. The polymerization kettle was heated until the temperature in the polymerization kettle reached the set temperature (64°C for SG-7), thermostatic control was started, and the polymerization reaction began. The reaction was always accompanied by stirring of a certain intensity. The jacket and condenser removed the polymerization heat to ensure constant temperature. After the reaction was stable for 2 hours, ammonium bicarbonate, sodium phosphate and antioxidant 1141 were added. The addition of ammonium bicarbonate, sodium phosphate and antioxidant 1141 was stopped 24 minutes before the termination of the reaction. The terminator was added after the polymerization reaction was carried out for 4 hours. The polymerization reaction cycle of this embodiment was 4 hours. The added amounts of ethanol and ethylene glycol, ammonium bicarbonate + sodium phosphate (1:1) and antioxidant 1141 were 0.768 kg, 1.28 kg and 2.56 kg (dry basis) respectively (based on 70 m 3 The polymerization kettle is used as the benchmark), wherein the antioxidant 1141 is 2,4-dimethyl-6-(1-methylpentadecyl)-phenol.

[0043] 4. Discharging: The discharging process is the process of sending 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, sodium bicarbonate or ammonia water is added to adjust the pH to meet the needs of subsequent processes.

[0044] 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.

[0045] Comparative Example 3-2: The difference from Example 3 is that no ethanol and ethylene glycol were added, and the other steps and parameters were exactly the same as those in Example 3.

[0046] Comparative Example 3-3: The difference from Example 3 is that ammonium bicarbonate and sodium phosphate are not added, and the other steps and parameters are exactly the same as those of Example 3.

[0047] 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 Example 3.

[0048] The products prepared in Examples 1-3 and all comparative examples were tested for whiteness and fisheyes. The whiteness was tested using a colorimeter; the fisheye was tested using an automatic fisheye analyzer.

[0049] The test results are shown in Table 1:

[0050] Table 1: Test results of the products prepared in Examples 1-3 and all comparative examples

[0051]

[0052] Apparent whiteness: directly use a whiteness meter to test the whiteness value of PVC products (powder);

[0053] Processing whiteness: Use the production PVC product (powder) to perform white sheet calendering to obtain white sheet. Use a whiteness meter to test the whiteness of the sheet surface to obtain the whiteness value.

[0054] Fisheye: Add carbon black to PVC products (powder) to generate black flakes. Use an automatic fisheye meter to test the number of fisheyes in the PVC products (powder).

[0055] 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 polyvinyl chloride.

[0056] It can be seen from the data in Table 1 that the apparent whiteness and processing whiteness of the polyvinyl chloride prepared in Comparative Example 1-1, Comparative Example 2-1, and Comparative Example 3-1 are significantly lower than those in Example 1-3, respectively, by not adding a gas-liquid interface mitigating agent, a pH regulator, 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, and the addition of a pH regulator 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.

[0057] It can be seen from the data in Table 1 that in Comparative Examples 1-2, 2-2, and 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 are not significantly changed compared with Examples 1-3, respectively; while the number of fisheyes is significantly increased. 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.

[0058] As can be seen from the data in Table 1, in Comparative Examples 1-3, 2-3, and 3-3, no pH regulator was added at the end of the polymerization reaction, a stabilizer was added, and a gas-liquid interface mitigation agent was 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 did not change significantly compared with Examples 1-3, and the apparent whiteness and processing whiteness data decreased significantly compared with Examples 1-3, further proving that no pH regulator was added at the end of the polymerization reaction, a stabilizer was added, and a gas-liquid interface mitigation agent was added in the early stage of the polymerization reaction or in the middle and late stages of the polymerization reaction. Although the whiteness of the polyvinyl chloride can be improved and the fisheye of the polyvinyl chloride can be reduced, the whiteness effect of the polyvinyl chloride is slightly worse than that of Examples 1-3, respectively. Therefore, it is explained that only the addition of a stabilizer at the end of the polymerization reaction makes the stability of the polyvinyl chloride less obvious than that of the addition of a pH regulator and a stabilizer at the end of the polymerization reaction.

[0059] As can be seen from the data in Table 1, in Comparative Examples 1-4, Comparative Examples 2-4, and 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 or middle-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 decreased compared with Examples 1-3, further demonstrating that in which no stabilizer is added at the end of the polymerization reaction, a pH regulator is added, and in which a gas-liquid interface mitigation agent is added in the early or middle-late stages of the polymerization reaction, although the whiteness of the polyvinyl chloride can be improved and the fisheye of the polyvinyl chloride can be reduced, the whiteness effect of the polyvinyl chloride is slightly worse than that of Examples 1-3, respectively. Therefore, it is explained that in which only the pH regulator is added at the end of the polymerization reaction, the stability of the polyvinyl chloride is not as significant as in which the pH regulator and the stabilizer are added at the end of the polymerization reaction.

[0060] 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 principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for improving the whiteness and fisheye of polyvinyl chloride, comprising adding a polymerization monomer and an auxiliary agent into a polymerization kettle and carrying out 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; The gas-liquid interface mitigating agent is an alkane derivative with a molecular weight of less than 50; the alkane derivative is one or a combination of more than one of methanol and ethanol; the added mass of the gas-liquid interface mitigating agent is 0.001%-0.01% of the added mass of the polymerization monomer; the added mass of the pH adjuster is 0.002%-0.01% of the added mass of the polymerization monomer; the added mass of the stabilizer is 0.005%-0.015% of the added mass of the polymerization monomer; the stabilizer is one or a combination of more than one of triethylene glycol bis(β-(3-tert-butyl-4-hydroxy-5-methylphenyl)acrylate), β-(3,5-di-tert-butyl-4-hydroxyphenyl) propionate or 2,4-dimethyl-6-(1-methylpentadecyl)-phenol.

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

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

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