A heat-resistant aging polyvinyl chloride resin and its preparation method

Abstract

The present invention discloses a heat-resistant aging polyvinyl chloride resin and a preparation method thereof, belonging to the technical field of polyvinyl chloride resin synthesis. The method comprises the following steps: S1. Adding deionized water, vinyl chloride monomer, initiator, dispersant 1, stabilizer dispersion liquid and buffer agent into a reaction vessel and stirring evenly; S2. Heating to the reaction temperature and reacting until the set pressure drop; S3. Adding a terminator and stirring evenly, and then obtaining the product through post-treatment; the stabilizer dispersion liquid is obtained by mixing a stabilizer, an aqueous solution of dispersant 2 and an antifoaming agent, and then through homogenization and / or grinding. By first dispersing the stabilizer in the aqueous solution of the dispersant to obtain the stabilizer dispersion liquid, and then adding the stabilizer dispersion liquid into the reaction system of PVC polymerization, the present invention significantly improves the stabilization efficiency of the stabilizer for the polyvinyl chloride resin, improves the powder anti-heat aging whiteness of the polyvinyl chloride resin and the anti-thermal decomposition performance during the processing, and at the same time can significantly reduce the amount of the stabilizer required for the polyvinyl chloride resin during processing.

Description

Technical Field

[0001] The present invention belongs to the technical field of polyvinyl chloride resin synthesis, and particularly relates to a heat-resistant aging polyvinyl chloride resin and a preparation method thereof. Background Art

[0002] Homopolymer or copolymer polyvinyl chloride resins are prone to thermal decomposition during processing or when products are used in a heated environment, and toxic hydrogen chloride gas is generated. Moreover, due to the decomposition, problems such as color change and reduction of mechanical properties of the products occur. In order to improve the problem of thermal decomposition of polyvinyl chloride resins, during the process of processing polyvinyl chloride resin products, stabilizers such as alkali metal salts and organotin are usually mixed with polyvinyl chloride resins for processing, which can significantly improve the problem of thermal decomposition of polyvinyl chloride resins during processing. However, since the resin powder particles are spherical with a film, the stabilizer powder or liquid can only form a mixture between the resin particles and the stabilizer with the polyvinyl chloride resin, and the stabilizer cannot enter the interior of the resin powder particles. During the process of resin melting due to heat, there is no stabilizer or insufficient stabilizer inside the resin powder particles, resulting in decomposition of the resin powder and problems such as color deviation or reduction of mechanical properties of the products. Furthermore, in order to ensure the thermal stability of polyvinyl chloride resins, the amount of stabilizer added during the process of processing polyvinyl chloride resin products must be large enough.

[0003] In order to improve the heat resistance stability of polyvinyl chloride resin powder, some researchers have conducted research in the following four directions during the polymerization process of polyvinyl chloride resin: First, adding expensive comonomers that can improve heat resistance or surface-modifying inorganic salts with heat stability effects during the polymerization process and then conducting copolymerization modification of PVC. However, a special feeding process is required, the process is complex, the cost is high, and the effect is poor. For example, in the preparation technology of a vinyl chloride-based polymer with excellent heat stability disclosed in KR20020045354A, more than 5% - 10% of the comonomer by weight of the monomer needs to be used to significantly improve the heat resistance stability of polyvinyl chloride resin. In the method for preparing a vinyl chloride-based resin with excellent particle uniformity and heat stability disclosed in CN103038262B, the inorganic powder hydrotalcite is first surface-modified and then added to the polymerization system. Since surface chemical modification of hydrotalcite increases the process difficulty and the surface modifier has a great influence on the dispersion system, it will affect the resin particle morphology and a major adjustment of the vinyl chloride polymerization dispersion system is required, making the industrialization difficult. In addition, in this invention, the inorganic compound surface-treated with the organic modifier still needs to be added during the polymerization reaction process, a special feeding process is required, and the feeding timing is difficult to control. More importantly, this invention can only improve the product quality index and cannot reduce the amount of stabilizer required during the processing of polyvinyl chloride resin products. Second, adding an alkali, such as sodium hydroxide, etc., to the polyvinyl chloride resin slurry after polymerization. However, this method can only absorb hydrogen chloride generated during the decomposition of polyvinyl chloride resin and cannot eliminate the defective structure caused by decomposition, and cannot fundamentally solve the problem of heat decomposition of polyvinyl chloride. Third, adding stabilizers such as antioxidants, zinc stearate, and organotin, but a large amount is lost during the slurry dehydration process, and the effect is very small. For example, in a method for improving the aging whiteness of polyvinyl chloride resin disclosed in CN101735357A, adding an antioxidant to the slurry after polymerization is used to improve the aging whiteness of polyvinyl chloride resin powder. Since the antioxidant is oily, a large amount of antioxidant is easily lost during slurry dehydration, and the remaining antioxidant can only adhere to the surface of the resin particles, and the improvement of the heat aging effect of polyvinyl chloride resin powder is very small. Even in the test of resistance to thermal decomposition during the processing of polyvinyl chloride resin, there is no difference. Fourth, repairing and modifying the defective structure in the polyvinyl chloride resin powder that has completed polymerization. For example, in a high-flow heat-resistant PVC resin and its preparation method disclosed in CN105754040B, the polyvinyl chloride resin powder product is continuously mixed with an initiator and a modified monomer at 5 - 30°C in a mixer for not less than 20 hours, and then reacted at 40 - 50°C for 10 - 20 min in a microwave reactor or reacted at 40 - 50°C for not less than 20 h in a high-energy vibration mill. The process is complex, the time is long, the output is low, and the energy consumption is high, and it is not feasible for industrialization.

[0004] Based on this, there is an urgent need to provide a preparation method for heat-resistant aging polyvinyl chloride resin. Summary of the Invention

[0005] In view of the above deficiencies of the prior art, the object of the present invention is to provide a preparation method of heat-resistant aging polyvinyl chloride resin. By first dispersing the stabilizer in an aqueous solution of the dispersant to obtain a stabilizer dispersion liquid, and then adding the stabilizer dispersion liquid to the reaction system of PVC polymerization, the stabilization efficiency of the stabilizer for polyvinyl chloride resin is significantly improved, the powder anti-heat aging whiteness of polyvinyl chloride resin and the anti-thermal decomposition performance during the processing are improved, and at the same time, the amount of stabilizer required for polyvinyl chloride resin during processing can be significantly reduced.

[0006] To achieve the above object, the specific technical solution of the present invention is as follows:

[0007] A preparation method of heat-resistant aging polyvinyl chloride resin, comprising the following steps:

[0008] S1. Add deionized water, vinyl chloride monomer, initiator, dispersant 1, stabilizer dispersion liquid and buffer to a reaction vessel and stir evenly;

[0009] S2. Heat up to the reaction temperature and react until the set pressure drop;

[0010] S3. Add a terminator and stir evenly, then obtain the polyvinyl chloride resin through stripping, screening of the slurry, dehydration, drying, and screening.

[0011] The stabilizer dispersion liquid is obtained by mixing a stabilizer, an aqueous solution of dispersant 2 and an antifoaming agent, and then homogenizing and / or grinding.

[0012] In the present invention, by first dispersing the stabilizer in an aqueous solution of the dispersant to obtain a stabilizer dispersion liquid, and then adding the stabilizer dispersion liquid to the reaction system of PVC polymerization, the stabilizer is introduced into the primary droplets of vinyl chloride monomer, so that the stabilizer is introduced into the primary particles formed by polyvinyl chloride resin particles, that is, the stabilizer can be dispersed into the interior of the resin particles, significantly improving the stabilization efficiency of the stabilizer for polyvinyl chloride resin, and improving the powder anti-heat aging whiteness and anti-thermal decomposition performance during the processing of polyvinyl chloride resin. At the same time, compared with adding the stabilizer in the reaction stage in the prior art, in the present invention, the stabilizer can be introduced into the primary droplets of vinyl chloride monomer through the stabilizer dispersion liquid, without a special feeding process and without major adjustment of the polymerization process dispersion system.

[0013] Preferably, the preparation method of the stabilizer dispersion liquid is as follows: Add an aqueous solution of dispersant 2 and an antifoaming agent to a reactor, stir evenly, then add the stabilizer, and homogenize and / or grind until the particle size of the suspended particles in the dispersion liquid is 1 - 1500 nm. More preferably, homogenize and / or grind until the particle size of the suspended particles in the dispersion liquid is 100 - 1000 nm.

[0014] In the present invention, the stabilizer is uniformly dispersed in the aqueous solution of the dispersant through homogenization and / or grinding, so that the stabilizer can be introduced into the primary droplets of vinyl chloride monomer through the stabilizer dispersion liquid. According to the difficulty of dispersing the stabilizer components, the stabilizer can be uniformly dispersed in the aqueous solution of the dispersant by means of homogenization, grinding, or first homogenization and then grinding.

[0015] Preferably, the rotation speed during homogenization is 3000 - 5000 rpm. The stabilizer is uniformly dispersed in the aqueous solution of the dispersant by high-speed shearing.

[0016] Preferably, the dispersant 2 includes at least one of polyvinyl alcohol, cellulose ether and its derivatives, gelatin, polyoxyethylene ether and its derivatives.

[0017] Preferably, the mass of the stabilizer in the reaction system is 0.05% - 5% of the vinyl chloride monomer. More preferably, the mass of the stabilizer is 0.1% - 4% of the vinyl chloride monomer. That is, the addition amount of the stabilizer dispersion liquid is calculated based on the mass of the effective component stabilizer being 0.05% - 5% of the mass of the vinyl chloride monomer. Preferably 0.1% - 4%.

[0018] Preferably, the mass fraction of the dispersant in the aqueous solution of the dispersant 2 is 0.5% - 8%; the mass ratio of the stabilizer to water in the stabilizer dispersion liquid is (5 - 50):(50 - 95).

[0019] Preferably, the stabilizer includes at least two of calcium stearate, zinc stearate, barium stearate, hydrotalcite, phosphite esters, epoxy compounds, pentaerythritol and its derivatives, zeolite, β-diketone compounds.

[0020] Preferably, the defoamer includes at least one of mineral oil defoamers, polyether defoamers, silicone defoamers; the mass of the defoamer is 0.1% - 0.3% of the total mass of water and the stabilizer.

[0021] Preferably, in step S1, a comonomer is further added to the reaction system, and the comonomer includes one or several of acrylate esters, methacrylate esters, unsaturated polyacid esters, vinyl esters, olefins, vinyl ethers, aromatic vinyl monomers, vinyl halides.

[0022] More preferably, the acrylate esters include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, tert-butyl acrylate, amyl acrylate, isoamyl acrylate, cyclohexyl acrylate, 2-ethylhexyl acrylate; the methacrylate esters include methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, tert-butyl methacrylate, amyl methacrylate, isoamyl methacrylate, 2-ethylhexyl methacrylate, cyclohexyl methacrylate; the unsaturated polyacid esters include diethyl fumarate, dimethyl itaconate, diethyl itaconate, diisopropyl itaconate, dioctyl itaconate, dimethyl maleate, diethyl maleate.

[0023] Preferably, the dispersant 1 includes at least one of polyvinyl alcohol, cellulose ethers and their derivatives, nonionic surfactants, ionic surfactants, and gelatin; the initiator is at least one of organic peroxides and azo compounds; the terminator includes at least one of hindered phenols, phosphites, aromatic amines, thioesters, thiophenols, hydroxylamines, and thiosemicarbazides.

[0024] Preferably, the buffer includes at least one of ammonia water, sodium bicarbonate, sodium carbonate, disodium hydrogen phosphate, sodium dihydrogen phosphate, and sodium citrate.

[0025] Preferably, the reaction temperature in step S2 is 39-70°C, and the pressure drop is 0.1-0.5 MPa.

[0026] The present invention also provides a heat-resistant aging polyvinyl chloride resin prepared by the preparation method.

[0027] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0028] (1) In the present invention, the stabilizer is first dispersed in the aqueous solution of the dispersant to obtain a stabilizer dispersion liquid, and then the stabilizer dispersion liquid is added to the reaction system of PVC polymerization, and the stabilizer is brought into the primary droplets of vinyl chloride monomer, so that the stabilizer is introduced into the primary particles formed by the polyvinyl chloride resin particles, that is, the stabilizer can be dispersed into the interior of the resin particles, significantly improving the stabilization efficiency of the stabilizer for the polyvinyl chloride resin, and improving the powder heat-resistant aging whiteness and heat decomposition resistance during the processing of the polyvinyl chloride resin.

[0029] (2) Compared with adding the stabilizer in the reaction stage of the prior art, in the present invention, the stabilizer can be brought into the primary droplets of vinyl chloride monomer through the stabilizer dispersion liquid, without a special feeding process and without major adjustment of the polymerization process dispersion system.

[0030] (3) The method of the present invention can significantly reduce the dosage of the stabilizer. Description of the Drawings

[0031] Figure 1 The physical diagram of the stabilizer dispersion liquid prepared in Comparative Example 3;

[0032] Figure 2 The dynamic aging diagram of the polyvinyl chloride resins of Examples 7, 9 to 11 and Comparative Examples 5, 8 to 9;

[0033] Figure 3 The dynamic aging diagram of the polyvinyl chloride resins of Example 8 and Comparative Example 6;

[0034] Figure 4 The dynamic aging diagram of the copolymerized polyvinyl chloride resin of Example 8 and the market-average polyvinyl chloride resin. Detailed implementation manners

[0035] The technical solutions of the present invention will be described clearly and completely below. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the protection scope of the present invention.

[0036] The preparation method of the heat-resistant aging polyvinyl chloride resin of the present invention includes the following steps:

[0037] S1. Add deionized water, vinyl chloride monomer, initiator, dispersant 1, stabilizer dispersion liquid and buffer agent to a reaction vessel and stir evenly;

[0038] S2. Heat up to the reaction temperature and react until the set pressure drop;

[0039] S3. Add a terminator and stir evenly, then obtain the polyvinyl chloride resin after stripping, screening the slurry, dehydrating, drying and screening;

[0040] The preparation method of the stabilizer dispersion liquid is as follows: Add an aqueous solution of dispersant 2 and an antifoaming agent to a reactor, stir evenly, then add a stabilizer, and homogenize and / or grind until the particle size of the suspended particles in the dispersion liquid is 1 to 1500 nm. Preferably, it is 100 to 1000 nm.

[0041] According to the difficulty of dispersing the stabilizer components, the stabilizer can be evenly dispersed in the aqueous solution of the dispersant by means of homogenization, grinding, or homogenization first and then grinding.

[0042] The dispersant 1 and dispersant 2 used in the present invention can be the same substance or different substances. In some embodiments, the dispersant 1 is selected from at least one of polyvinyl alcohol, cellulose ether and its derivatives, non-ionic surfactants, ionic surfactants, and gelatin; the dispersant 2 is selected from at least one of polyvinyl alcohol, cellulose ether and its derivatives, gelatin, and polyoxyethylene ether and its derivatives.

[0043] In the reaction system, the addition amount of the stabilizer dispersion is calculated based on the mass of the active ingredient. In some embodiments, the mass of the stabilizer in the reaction system is 0.05% - 5% of the vinyl chloride monomer, preferably 0.1% - 4%.

[0044] In some embodiments, the mass fraction of the dispersant in the aqueous solution of dispersant 2 is 0.5% - 8%, preferably 2% - 4%. For example, the mass fraction of the dispersant in the aqueous solution of dispersant 2 can be 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, etc. The mass ratio of the stabilizer to water in the stabilizer dispersion is (5 - 50):(50 - 95), preferably (10 - 40):(60 - 90).

[0045] In some embodiments, the stabilizer is selected from at least two of calcium stearate, zinc stearate, barium stearate, hydrotalcite, phosphite esters, epoxy compounds, pentaerythritol and its derivatives, zeolite, β-diketone compounds.

[0046] In some embodiments, the defoamer is selected from at least one of mineral oil defoamers, polyether defoamers, and silicone defoamers; the mass of the defoamer is 0.1% - 0.3% of the total mass of water and the stabilizer.

[0047] In some embodiments, step S1 further includes adding a comonomer to the reaction system, and the comonomer includes one or more of acrylate esters, methacrylate esters, vinyl esters, unsaturated polyacid esters, olefins, vinyl ethers, aromatic vinyl monomers, and vinyl halides.

[0048] In some embodiments, the reaction temperature in step S2 is 39 - 70 °C, and the pressure drop is 0.1 - 0.5 MPa.

[0049] In some embodiments, the initiator is at least one of organic peroxides and azo compounds. The terminator includes at least one of hindered phenols, phosphite esters, aromatic amines, thioesters, thiophenols, hydroxylamines, and semicarbazides. The buffer includes at least one of ammonia water, sodium bicarbonate, sodium carbonate, disodium hydrogen phosphate, sodium dihydrogen phosphate, and sodium citrate.

[0050] The present invention will be further described below with reference to specific embodiments, but it is not limited to the present invention.

[0051] Preparation of the stabilizer dispersion:

[0052] The preparation methods of the stabilizer dispersions of Examples 1 - 5 and Comparative Examples 1 - 3 are as follows:

[0053] Add an aqueous solution of 2700 g of polyvinyl alcohol TCR-7507P with a degree of alcoholysis of 72 mol% to a 5000 mL homogenization tank. The concentration of the aqueous solution is 4 wt%. Start stirring at 800 rpm. While stirring, add 211.8 g of calcium stearate, 317.6 g of zinc stearate, 1279.6 g of hydrotalcite, and 4.5 g of polyether defoamer. Control the material temperature to be less than 30 °C. The rotational speed of the homogenization pump is 4000 rpm. Homogenize for a certain period of time first, and then transfer it to a grinder for grinding for a certain period of time to obtain the product.

[0054] Among them, polyether defoamer was not added in Comparative Example 3.

[0055] Example 6

[0056] The preparation method of the stabilizer dispersion in this example is as follows:

[0057] Add an aqueous solution of 2700 g of polyvinyl alcohol TCR-7524 with a degree of alcoholysis of 80 mol% to a 5000 mL homogenization tank. The concentration of the aqueous solution is 4 wt%. Start stirring at 800 rpm. While stirring, add 337.5 g of calcium stearate, 225.0 g of zinc stearate, 1012.5 g of hydrotalcite, 56.3 g of phosphite, 112.5 g of epoxidized soybean oil, 33.75 g of pentaerythritol, 22.5 g of β-diketone, and 4.5 g of polyether defoamer. Control the material temperature to be less than 30 °C. The rotational speed of the homogenization pump is 4000 rpm. Homogenize for 30 min to obtain the product.

[0058] The homogenization, grinding time, and laser particle size test results of each example and comparative example are shown in Table 1.

[0059] Table 1 Test results of stabilizer dispersion

[0060]

[0061] As can be seen from Table 1, a stabilizer dispersion with uniform dispersion and a particle size D50 less than 1000 nm can be obtained by homogenizing for 30 - 60 min, grinding for 30 - 60 min, or homogenizing for 10 min first and then grinding for 30 min. In Comparative Examples 1 and 2, the homogenization or grinding time was too short, the particle size D50 was as high as 12 μm, and the dispersion of the dispersion was poor. Stratification occurred after standing for 20 min. In Comparative Example 3, no defoamer was added, and the obtained stabilizer dispersion had a lot of foam and visible aggregates, see Figure 1 .

[0062] Comparative Example 4

[0063] The preparation method of the modified stabilizer in this comparative example is as follows: Add 4000 g of hydrotalcite to a 10 L high-speed mixer with an oil bath jacket, start the stirring speed at 1000 rpm, add glycerol-stearate and stir for 5 min, start heating to 180 °C, continue stirring for 30 min, and discharge and cool to room temperature to obtain modified hydrotalcite.

[0064] Preparation of heat-resistant polyvinyl chloride: An aqueous solution of PVA is used in the following examples and comparative examples.

[0065] Example 7

[0066] This example provides a preparation method of a heat-resistant aging polyvinyl chloride resin, including the following steps:

[0067] Add 1090.40 g of PVA TCR-7524 with a concentration of 1 wt% and a degree of alcoholysis of 80 mol%, 742.40 g of PVA BR-60 with a concentration of 1 wt% and a degree of alcoholysis of 72 mol%, 2.64 g of PVA TCR-4040 with a concentration of 40 wt% and a degree of alcoholysis of 55 mol%, 12528.00 g of deionized water, 105.85 g of the stabilizer dispersion prepared in Example 5, 5.18 g of cumyl peroxyneodecanoate TRIGONOX 99-W50, and 8.36 g of tert-butyl peroxyneodecanoate TRIGONOX 23-W50 into a 27000 mL high-pressure reactor. After closing the reactor and replacing the nitrogen 3 times, add 8468.00 g of vinyl chloride monomer, heat to 56 °C to start the reaction. When the pressure reaches 0.4 MPa, add 10.59 g of hindered phenol antioxidant, stir for 10 min, then discharge and screen through a 40-mesh sieve, dehydrate by centrifugation, dry at 60 °C, and then screen through a 60-mesh sieve to obtain heat-resistant polyvinyl chloride resin powder.

[0068] Example 8

[0069] The preparation method of the heat-resistant aging polyvinyl chloride resin in this example is basically the same as that in Example 7, except that 8468.00 g of vinyl chloride monomer is replaced with 8044.60 g of vinyl chloride monomer and 423.40 g of vinyl acetate monomer.

[0070] Example 9

[0071] The preparation method of the heat-resistant aging polyvinyl chloride resin in this example is basically the same as that in Example 7, except that the mass of the stabilizer dispersion prepared in Example 5 added is 21.17 g.

[0072] Example 10

[0073] The preparation method of the heat-resistant aging polyvinyl chloride resin in this example is basically the same as that in Example 7, except that the mass of the stabilizer dispersion prepared in Example 5 added is 63.51 g.

[0074] Example 11

[0075] The preparation method of the heat-resistant aging polyvinyl chloride resin in this example is basically the same as that in Example 7, except that the stabilizer dispersion prepared in Example 5 is replaced with the stabilizer dispersion prepared in Example 6.

[0076] Comparative Example 5

[0077] The preparation method of the polyvinyl chloride resin in this comparative example is basically the same as that in Example 7, except that no stabilizer dispersion is added.

[0078] Comparative Example 6

[0079] The preparation method of the polyvinyl chloride resin in this comparative example is basically the same as that in Example 8, except that no stabilizer dispersion is added.

[0080] Comparative Example 7

[0081] The preparation method of the polyvinyl chloride resin in this comparative example is basically the same as that in Example 7, except that the stabilizer dispersion prepared in Example 5 is replaced with the stabilizer dispersion prepared in Comparative Example 1.

[0082] Comparative Example 8

[0083] The preparation method of the polyvinyl chloride resin in this comparative example is basically the same as that in Example 7, except that the stabilizer dispersion prepared in Example 5 is replaced with the stabilizer dispersion prepared in Comparative Example 3.

[0084] Comparative Example 9

[0085] The preparation method of the polyvinyl chloride resin in this comparative example is basically the same as that in Example 7, except that the stabilizer dispersion prepared in Example 5 is replaced with the modified stabilizer prepared in Comparative Example 4, and the mass of the modified stabilizer is 42.34 g.

[0086] The polyvinyl chloride resins prepared in the examples and comparative examples were subjected to relevant tests. The test results of laser particle size, apparent density, oil absorption value, and powder whiteness are shown in Table 2, and the test results of torque rheology dynamic heat aging are shown in Table 3 and Figures 2 - 3 .

[0087] The laser particle size was measured using a Malvern 2000 laser particle size analyzer.

[0088] The apparent density, oil absorption value, and powder whiteness were tested according to GB / T 5761-2018 "Suspension Polymerization General Purpose Polyvinyl Chloride Resins".

[0089] The dynamic thermal aging of torque rheology was tested using a Brabender torque rheometer. The test conditions were: 175 °C and 35 rpm. The formulation was 100 phr of PVC resin powder and 3 phr of stabilizer. The heat stabilizer added during the polymerization process in each example or comparative example was deducted from the 3 phr in the torque rheology test for comparison. That is, the total amount of heat stabilizer added during the polymerization process and the torque rheology test in each example and comparative example was 3% of the PVC resin powder.

[0090] Table 2 Performance Results of Polyvinyl Chloride Resin

[0091]

[0092] It can be seen from the data in Table 2 that compared with Comparative Example 5 without the addition of a stabilizer dispersion liquid, in Example 7, a well-dispersed stabilizer dispersion liquid was added to the polymerization system of the homopolymer resin, which had no effect on the particle size of the polyvinyl chloride resin and could significantly improve the powder whiteness of the resin powder (the powder whiteness increased from 82.98% to 88.49%). In particular, by comparing Example 8 and Comparative Example 6, it was found that adding a stabilizer dispersion liquid to the polymerization system of the copolymer resin could significantly improve the aging whiteness index of the copolymer resin powder (the powder whiteness increased from 76.63% to 84.31%). By comparing Example 7 and Comparative Example 7, it was found that in Comparative Example 7, a stabilizer dispersion liquid with poor dispersion and agglomeration was used, which would lead to abnormal polymerization and obtain coarse materials. By comparing Examples 7, 9, and 10, it was found that as the amount of the stabilizer dispersion liquid increased, the powder whiteness was higher. By comparing Example 7 and Example 11, it was found that compared with using only an inorganic stabilizer, using a compound stabilizer of inorganic and organic could significantly improve the powder whiteness of the polyvinyl chloride resin. In addition, the 160 °C 10 min aging powder whiteness of the resin in Comparative Example 9 had a certain improvement compared with that in Comparative Example 5, indicating that the method in Comparative Example 9 could improve the quality index of the PVC resin, but compared with Example 7 and Example 11, the quality improvement was limited.

[0093] Table 3 Torque Rheology Dynamic Thermal Aging Test Results of Polyvinyl Chloride Resin

[0094]

[0095] Figure 2 is the dynamic aging diagram of the polyvinyl chloride resins of Examples 7, 9 to 11 and Comparative Examples 5, 8 to 9. Figure 3 is the dynamic aging diagram of the polyvinyl chloride resins of Example 8 and Comparative Example 6.

[0096] From Table 3 and Figures 2 - 3It can be seen that, compared with Comparative Example 5 without the addition of the stabilizer dispersion liquid, in Example 7, a well-dispersed stabilizer dispersion liquid was added to the polymerization system of the homopolymer resin, and the thermal decomposition time was increased from 820 s to 1942 s, and the processing heat resistance aging performance of the polyvinyl chloride resin powder was greatly improved. Similarly, compared with Comparative Example 6 without the addition of the stabilizer dispersion liquid, in Example 8, adding the stabilizer dispersion liquid to the polymerization system of the copolymer resin can also significantly improve the processing heat resistance aging performance of the polyvinyl chloride resin powder and solve the problem of poor processing stability of the copolymer resin. By comparing Examples 7, 9, and 10, it can be found that as the dosage of the stabilizer dispersion liquid increases, the heat resistance aging performance of the polyvinyl chloride resin powder is better. By comparing Example 7 and Example 11, it can be found that compared with using only inorganic stabilizers, using a compound stabilizer of inorganic and organic can significantly improve the heat resistance aging performance of the polyvinyl chloride resin powder. In addition, during the dynamic thermal aging evaluation of the resin in Comparative Example 9 during the processing process, the thermal decomposition time was comparable to that of Comparative Example 5, indicating that the method of Comparative Example 9 cannot improve the thermal stability of the resin powder during processing.

[0097] As is well known, under the condition of the same degree of polymerization, the processing thermal stability of homopolymer polyvinyl chloride resin is better than that of copolymer polyvinyl chloride resin. The copolymer polyvinyl chloride resin obtained in Example 8 of the present invention was subjected to a torque dynamic thermal aging test with a commercial homopolymer polyvinyl chloride resin (Yunnan Energy Investment SG8). The test conditions were 175 °C and 35 rpm. Figure 4 is the dynamic aging diagram of the copolymer polyvinyl chloride resin in Example 8 and the commercial homopolymer polyvinyl chloride resin; it can be seen from the figure that although the mass of the stabilizer added during the preparation of the polyvinyl chloride resin in Example 8 was only 0.5% of the vinyl chloride monomer, compared with the commercial homopolymer polyvinyl chloride resin, even when the dosage of the heat stabilizer during processing was reduced by 67%, the same thermal stability could still be maintained, indicating that the method of the present invention can reduce the dosage of the stabilizer required during the processing of polyvinyl chloride resin products.

[0098] Although the embodiments of the present invention have been shown and described, for those of ordinary skill in the art, it can be understood that various changes, modifications, substitutions, and variations can be made to these embodiments without departing from the principle and spirit of the present invention. The scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a heat-resistant aging polyvinyl chloride resin, characterized in that, It includes the following steps: S1. Add deionized water, vinyl chloride monomer, initiator, dispersant 1, stabilizer dispersion, and buffer into a reaction vessel and stir evenly; S2. Heat up to the reaction temperature and react until the set pressure drop; S3. Add a terminator and stir evenly, then obtain the polyvinyl chloride resin through stripping, screening of the slurry, dehydration, drying, and screening; The preparation method of the stabilizer dispersion is as follows: Add an aqueous solution of dispersant 2 and an antifoaming agent into a reactor, stir evenly, and then add a stabilizer, homogenize and / or grind until the particle size of the suspended particles in the dispersion is 1 - 1500 nm; In the reaction system, the mass of the stabilizer is 0.05% - 0.5% of the vinyl chloride monomer.

2. The preparation method of a heat-resistant aging polyvinyl chloride resin according to claim 1, characterized in that, The dispersant 2 includes at least one of polyvinyl alcohol, cellulose ether and its derivatives, gelatin, polyoxyethylene ether and its derivatives.

3. The preparation method of a heat-resistant aging polyvinyl chloride resin according to claim 1, characterized in that In the aqueous solution of the dispersant 2, the mass fraction of the dispersant is 0.5% - 8%; the mass ratio of the stabilizer to water in the stabilizer dispersion is (5 - 50):(50 - 95).

4. The preparation method of a heat-resistant aging polyvinyl chloride resin according to claim 1, characterized in that, The stabilizer includes at least two of calcium stearate, zinc stearate, barium stearate, hydrotalcite, phosphite esters, epoxy compounds, pentaerythritol and its derivatives, zeolite, β - diketone compounds.

5. The preparation method of a heat-resistant aging polyvinyl chloride resin according to claim 1, characterized in that, The antifoaming agent includes at least one of mineral oil antifoaming agents, polyether antifoaming agents, silicone antifoaming agents; the mass of the antifoaming agent is 0.1% - 0.3% of the total mass of water and the stabilizer.

6. The preparation method of a heat-resistant aging polyvinyl chloride resin according to claim 1, characterized in that, In step S1, a comonomer is further added to the reaction system, and the comonomer includes one or several of acrylate esters, methacrylate esters, vinyl esters, unsaturated polyacid esters, olefins, vinyl ethers, aromatic vinyl monomers, vinyl halides.

7. The preparation method of a heat-resistant aging polyvinyl chloride resin according to claim 1, characterized in that, The dispersant 1 includes at least one of polyvinyl alcohol, cellulose ether and its derivatives, ionic surfactants, gelatin; and / or, the initiator is at least one of organic peroxides, azo compounds; and / or, the terminator includes at least one of hindered phenols, phosphite esters, aromatic amines, thioesters, thiophenols, hydroxylamines, semicarbazides; 8. A heat - aging resistant polyvinyl chloride resin prepared by the preparation method according to any one of claims 1 - 7.

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