Heat-aging-resistant polyvinyl chloride resin and preparation method thereof

Abstract

The invention discloses heat-aging-resistant polyvinyl chloride resin and a preparation method thereof, and belongs to the technical field of polyvinyl chloride resin synthesis. The method comprises the following steps: S1, adding deionized water, a vinyl chloride monomer, an initiator, a dispersant 1, a stabilizer dispersion liquid and a buffer agent into a reaction container, and uniformly stirring; s2, heating to a reaction temperature, and reacting to a set pressure drop; and S3, adding a terminating agent, uniformly stirring, and carrying out post-treatment. The stabilizer dispersion liquid is obtained by mixing a stabilizer, an aqueous solution of a dispersing agent 2 and a defoaming agent and then homogenizing and / or grinding. The stabilizing agent is dispersed in the aqueous solution of the dispersing agent to obtain the stabilizing agent dispersion liquid, and then the stabilizing agent dispersion liquid is added into a PVC polymerization reaction system, so that the stabilizing efficiency of the stabilizing agent on the polyvinyl chloride resin is remarkably improved, and the thermal aging resistance whiteness of the polyvinyl chloride resin powder and the thermal decomposition resistance in the processing process are improved; meanwhile, the amount of a stabilizer required during processing of the polyvinyl chloride resin can be remarkably reduced.

Description

Technical Field

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

[0002] Homopolymer or copolymer polyvinyl chloride resin is prone to thermal decomposition during processing or when the product is used in a heated environment, and produces toxic hydrogen chloride gas, and the decomposition causes problems such as color change and reduced mechanical properties of the product. In order to improve the problem of thermal decomposition of polyvinyl chloride resin, in the process of polyvinyl chloride resin processing products, stabilizers such as alkali metal salts and organic tin are usually used to mix with polyvinyl chloride resin before processing, which can significantly improve the problem of thermal decomposition of polyvinyl chloride resin in the processing process; but because the resin powder particles are spherical with a film, the stabilizer powder or liquid and the polyvinyl chloride resin can only form a mixture between the resin particles and the stabilizer, and the stabilizer cannot enter the resin powder particles. In the process of resin melting, there is no stabilizer or insufficient stabilizer inside the resin powder particles, which will cause the decomposition of the resin powder, resulting in color deviation or reduced mechanical properties of the product. In addition, in order to ensure the thermal stability of polyvinyl chloride resin, the amount of stabilizer added in the process of polyvinyl chloride resin processing products must be large enough.

[0003] In order to improve the heat resistance and 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, in the polymerization process, expensive comonomers that improve heat resistance are added or inorganic salts with heat stability are surface modified before copolymerization and modification of PVC, but a special feeding process is required, the process is complex, the cost is high, and the effect is poor; for example, in a preparation technology of a vinyl chloride polymer with excellent heat stability disclosed in KR20020045354A, more than 5% to 10% of the comonomer weight is required to significantly improve the heat resistance and stability of polyvinyl chloride resin; in a preparation technology of a vinyl chloride polymer with excellent heat stability disclosed in CN103038262B, more than 5% to 10% of the comonomer weight is required to significantly improve the heat resistance and stability of polyvinyl chloride resin; in a preparation technology of a vinyl chloride polymer with excellent heat resistance ... The method of producing a vinyl chloride resin with excellent particle uniformity and thermal stability is to first modify the surface of the inorganic powder hydrotalcite and then add it to the polymerization system. Since the surface chemical modification of the hydrotalcite increases the process difficulty and the surface modifier has a great influence on the dispersion system, it will affect the morphology of the resin particles and require a major adjustment of the polymerization dispersion system of vinyl chloride, which is difficult to industrialize. In addition, the inorganic compound treated with the surface of the organic modifier in the invention still needs to be added during the polymerization reaction, which requires a special feeding process and the timing of feeding is difficult to control. More importantly, the invention can only improve the product quality index and cannot reduce the amount of stabilizer required in the process of polyvinyl chloride resin processing products. Second, after the polymerization is completed, alkali, such as sodium hydroxide, is added to the polyvinyl chloride resin slurry, but this method can only absorb the hydrogen chloride generated when the polyvinyl chloride resin is decomposed, but cannot eliminate the defective structure generated by the decomposition, and cannot fundamentally solve the problem of thermal decomposition of polyvinyl chloride. The third is to add antioxidants, zinc stearate, organic tin and other stabilizers, but they are lost in large quantities during the slurry dehydration process, and the effect is minimal. For example, a method for improving the aging whiteness of polyvinyl chloride resin disclosed in CN101735357A adopts the method of adding antioxidants to the slurry after the polymerization to improve the aging whiteness of polyvinyl chloride resin powder. Since the antioxidant is oily, a large amount of antioxidant is easily lost during the slurry dehydration and the residual antioxidant can only adhere to the surface of the resin particles. The effect of improving the heat aging resistance of the polyvinyl chloride resin powder is minimal, and even no difference can be seen in the test of resistance to thermal decomposition during the processing of polyvinyl chloride resin. Fourth, by restoring the defective structure in the polyvinyl chloride resin powder that has completed polymerization, such as the high-fluidity heat-resistant PVC resin and its preparation method disclosed in CN105754040B, the finished polyvinyl chloride resin powder is continuously mixed with the initiator and the modified monomer in a mixer at 5-30°C for not less than 20 hours, and then reacted by a microwave reactor at 40-50°C for 10-20 minutes or a high-energy vibration mill at 40-50°C for not less than 20 hours. The process is complicated, time-consuming, low-yield, and energy-intensive, and is not feasible for industrialization.

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

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

[0006] To achieve the above purpose, the specific technical solutions of the present invention are as follows:

[0007] A method for preparing a heat-resistant polyvinyl chloride resin comprises the following steps:

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

[0009] S2. Raise the temperature to the reaction temperature and react until the set pressure drops;

[0010] S3. After adding the terminator and stirring evenly, the slurry was stripped, sieved, dehydrated, dried and sieved to obtain the polychloroacetic acid resin;

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

[0012] The present invention first disperses the stabilizer in an aqueous solution of the dispersant to obtain a stabilizer dispersion, and then adds the stabilizer dispersion to the reaction system of PVC polymerization, bringing the stabilizer into the primary droplets of vinyl chloride monomer, thereby introducing the stabilizer into the primary particles formed by polyvinyl chloride resin particles, that is, the stabilizer can be dispersed inside the resin particles, significantly improving the stabilization efficiency of the stabilizer on the polyvinyl chloride resin, and improving the heat aging resistance and whiteness of the polyvinyl chloride resin powder and the anti-thermal decomposition performance during the processing. At the same time, compared with the prior art that adds the stabilizer in the reaction stage, the present invention can bring the stabilizer into the primary droplets of the vinyl chloride monomer through the stabilizer dispersion, without the need for a special feeding process, and without making major adjustments to the dispersion system during the polymerization process.

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

[0014] The present invention uniformly disperses the stabilizer in the aqueous solution of the dispersant by homogenization and / or grinding, so that the stabilizer can be introduced into the primary droplets of the vinyl chloride monomer through the stabilizer dispersion. According to the difficulty of dispersing the stabilizer component, the stabilizer can be uniformly dispersed in the aqueous solution of the dispersant by homogenization, grinding, or homogenization followed by grinding.

[0015] Preferably, the speed during homogenization is 3000-5000 rpm. The stabilizer is uniformly dispersed in the dispersant aqueous solution 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% to 5% of the mass of the vinyl chloride monomer. More preferably, the mass of the stabilizer is 0.1% to 4% of the mass of the vinyl chloride monomer. That is, the amount of the stabilizer dispersion added is calculated based on the mass of the active ingredient stabilizer being 0.05% to 5% of the mass of the vinyl chloride monomer. Preferably, it is 0.1% to 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 is (5-50):(50-95).

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

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

[0021] Preferably, step S1 further comprises adding a comonomer to the reaction system, wherein the comonomer comprises one or more of acrylates, methacrylates, unsaturated polyacid esters, vinyl esters, olefins, vinyl ethers, aromatic vinyl monomers, and vinyl halides.

[0022] More preferably, the acrylic acid esters include methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, tert-butyl acrylate, pentyl acrylate, isopentyl acrylate, cyclohexyl acrylate, and ethylhexyl acrylate; the methacrylic acid esters include methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, tert-butyl methacrylate, pentyl methacrylate, isopentyl methacrylate, ethylhexyl methacrylate, and cyclohexyl methacrylate; the unsaturated polyacid esters include diethyl fumarate, dimethyl itaconate, diethyl itaconate, diisopropyl itaconate, dioctyl itaconate, dimethyl maleate, and diethyl maleate.

[0023] Preferably, the dispersant 1 includes at least one of polyvinyl alcohol, cellulose ether and its derivatives, nonionic surfactants, ionic surfactants, and gelatin; the initiator is at least one of organic peroxides and azo compounds; and 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-aging-resistant polyvinyl chloride resin prepared by the preparation method.

[0027] Compared with the prior art, the present invention is beneficial in that:

[0028] (1) The present invention first disperses the stabilizer in an aqueous solution of the dispersant to obtain a stabilizer dispersion, and then adds the stabilizer dispersion to a PVC polymerization reaction system to bring the stabilizer into primary droplets of vinyl chloride monomer, thereby introducing the stabilizer into primary particles formed by polyvinyl chloride resin particles. That is, the stabilizer can be dispersed inside the resin particles, thereby significantly improving the stabilization efficiency of the stabilizer on the polyvinyl chloride resin, and improving the heat aging resistance and whiteness of the polyvinyl chloride resin powder and the anti-thermal decomposition performance during the processing process.

[0029] (2) Unlike the prior art which adds stabilizers during the reaction stage, the present invention can introduce the stabilizer into the primary droplets of vinyl chloride monomer via the stabilizer dispersion, without requiring a special feeding process or major adjustments to the dispersion system during the polymerization process.

[0030] (3) The method of the present invention can significantly reduce the amount of stabilizer used. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 This is a physical picture of the stabilizer dispersion prepared in Comparative Example 3;

[0032] Figure 2 It is a dynamic aging diagram of the polyvinyl chloride resin of Examples 7, 9-11 and Comparative Examples 5, 8-9;

[0033] Figure 3 It is a dynamic aging diagram of the polyvinyl chloride resin of Example 8 and Comparative Example 6;

[0034] Figure 4 It is a dynamic aging diagram of the copolymerized polyvinyl chloride resin of Example 8 and the homopolymerized polyvinyl chloride resin of the commercial product. DETAILED DESCRIPTION

[0035] The technical solution of the present invention will be described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. 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.

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

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

[0038] S2. Raise the temperature to the reaction temperature and react until the set pressure drops;

[0039] S3. After adding the terminator and stirring evenly, the slurry was stripped, sieved, dehydrated, dried and sieved to obtain the polychloroacetic acid resin;

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

[0041] Depending on the difficulty of dispersing the stabilizer component, the stabilizer can be evenly dispersed in the aqueous solution of the dispersant by homogenization, grinding, or homogenization followed by grinding.

[0042] The dispersant 1 and dispersant 2 used in the present invention may 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, nonionic surfactants, ionic surfactants, and gelatin; the dispersant 2 is selected from at least one of polyvinyl alcohol, cellulose ether and its derivatives, gelatin, polyoxyethylene ether and its derivatives.

[0043] In the reaction system, the amount of the stabilizer dispersion added 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% to 5%, preferably 0.1% to 4%, of the vinyl chloride monomer.

[0044] In some embodiments, the mass fraction of the dispersant in the aqueous solution of dispersant 2 is 0.5% to 8%, preferably 2% to 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 to 50): (50 to 95), preferably (10 to 40): (60 to 90).

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

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

[0047] In some embodiments, step S1 further comprises adding a comonomer to the reaction system, wherein the comonomer comprises one or more of acrylates, methacrylates, 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 an organic peroxide and an azo compound. The terminator includes at least one of hindered phenols, phosphites, aromatic amines, thioesters, thiophenols, hydroxylamines, and thiosemicarbazides. 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 in conjunction with specific embodiments, but the present invention is not limited thereto.

[0051] Preparation of stabilizer dispersion:

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

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

[0054] Wherein, no polyether defoamer was added in Comparative Example 3.

[0055] Example 6

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

[0057] To a 5000mL homogenizing tank, add 2700g of an aqueous solution of polyvinyl alcohol TCR-7524 with a degree of alcoholysis of 80mol%, the concentration of the aqueous solution is 4wt%, start stirring at 800rpm, add 337.5g of calcium stearate, 225.0g of zinc stearate, 1012.5g of hydrotalcite, 56.3g of phosphite, 112.5g of epoxy soybean oil, 33.75g of tetrapentanol, 22.5g of β-diketone and 4.5g of polyether defoamer under stirring, control the material temperature to be less than 30°C, the speed of the homogenizing pump is 4000rpm, and homogenization is carried out for 30min.

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

[0059] Table 1 Stabilizer dispersion test results

[0060]

[0061] As can be seen from Table 1, homogenizing for 30 to 60 minutes, grinding for 30 to 60 minutes, or homogenizing for 10 minutes and then grinding for 30 minutes can all obtain a stabilizer dispersion with uniform dispersion and a particle size D50 less than 1000 nm. In Comparative Examples 1 and 2, the homogenization or grinding time is too short, the particle size D50 is as high as 12 μm, and the dispersion is poorly dispersed, and stratification occurs after standing for 20 minutes. In Comparative Example 3, no defoamer is added, and the stabilizer dispersion obtained has a lot of foam and agglomerates visible to the naked eye. Figure 1 .

[0062] Comparative Example 4

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

[0064] Preparation of heat-resistant polyvinyl chloride: The following examples and comparative examples all use an aqueous solution of PVA

[0065] Example 7

[0066] This embodiment provides a method for preparing a heat-resistant polyvinyl chloride resin, comprising the following steps:

[0067] Into a 27000mL autoclave, 1090.40g of 1wt% PVA TCR-7524 with an alcoholysis degree of 80mol%, 742.40g of 1wt% PVA BR-60 with an alcoholysis degree of 72mol%, 2.64g of 40wt% PVA TCR-4040 with an alcoholysis degree of 55mol%, 12528.00g of deionized water, 105.85g of the stabilizer dispersion prepared in Example 5, 5.18g of peroxy neodecanoate TRIGONOX 99-W50, 8.36g of tert-butyl peroxy neodecanoate TRIGONOX 23-W50, after closing the reactor and replacing with nitrogen three times, add 8468.00g of vinyl chloride monomer, raise the temperature to 56℃ to start the reaction, and the pressure reaches 0.4MPa. Add 10.59g of hindered phenol antioxidant, stir for 10min, then put the material through a 40-mesh sieve, dehydrate by centrifugation, dry at 60℃, and then sieve with a 60-mesh sieve to obtain heat-resistant polyvinyl chloride resin powder.

[0068] Example 8

[0069] The preparation method of the heat-resistant polyvinyl chloride resin of this embodiment is basically the same as that of Example 7, except that 8468.00 g of vinyl chloride monomer is replaced by 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-aging-resistant polyvinyl chloride resin in this embodiment is basically the same as that in Embodiment 7, except that the mass of the stabilizer dispersion prepared in Embodiment 5 added is 21.17 g.

[0072] Example 10

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

[0074] Embodiment 11

[0075] The preparation method of the heat-resistant aging polyvinyl chloride resin of this embodiment is basically the same as that of Embodiment 7, and the only difference is that the stabilizer dispersion prepared in Embodiment 5 is replaced by the stabilizer dispersion prepared in Embodiment 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, the only difference being that the stabilizer dispersion prepared in Example 5 is replaced by 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, the only difference being that the stabilizer dispersion prepared in Example 5 is replaced by 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, the only difference is that the stabilizer dispersion prepared in Example 5 is replaced by the modified stabilizer prepared in Comparative Example 4, and the mass of the modified stabilizer is 42.34 g.

[0086] The polyvinyl chloride resin prepared in the embodiment and the comparative example was 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 thermal aging are shown in Tables 3 and Figure 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 are tested according to GB / T 5761-2018 "Suspension method general purpose polyvinyl chloride resin".

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

[0090] Table 2 Performance results of polyvinyl chloride resin

[0091]

[0092] From the data in Table 2, it can be seen that compared with Comparative Example 5 in which no stabilizer dispersion is added, Example 7 adds a well-dispersed stabilizer dispersion in the polymerization system of the homopolymer resin, which has no effect on the particle size of the polyvinyl chloride resin and can significantly improve the powder whiteness of the resin powder (the powder whiteness is increased from 82.98% to 88.49%). In particular, by comparing Example 8 with Comparative Example 6, it can be found that adding a stabilizer dispersion in the polymerization system of the copolymer resin can significantly improve the aging whiteness index of the copolymer resin powder (the powder whiteness is increased from 76.63% to 84.31%). By comparing Example 7 with Comparative Example 7, it can be found that the use of a poorly dispersed and agglomerated stabilizer dispersion in Comparative Example 7 will lead to abnormal polymerization and obtain coarse material. By comparing Examples 7, 9, and 10, it can be found that as the amount of stabilizer dispersion increases, the powder whiteness is higher. By comparing Example 7 with Example 11, it can be found that compared with the use of an inorganic stabilizer alone, the use of an inorganic and organic composite stabilizer can significantly improve the powder whiteness of the polyvinyl chloride resin. In addition, the whiteness of the powder aged at 160°C for 10 min of the resin in Comparative Example 9 is improved compared with that in Comparative Example 5, indicating that the method of Comparative Example 9 can improve the quality index of PVC resin, but compared with Examples 7 and 11, its quality improvement is limited.

[0093] Table 3 Torque rheological dynamic thermal aging test results of polyvinyl chloride resin

[0094]

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

[0096] From Table 3 and Figure 2~3It can be seen that compared with comparative example 5 without adding stabilizer dispersion, in embodiment 7, a well-dispersed stabilizer dispersion is added to the polymerization system of the homopolymer resin, and the thermal decomposition time is increased from 820s to 1942s, and the processing heat aging resistance of the polyvinyl chloride resin powder is greatly improved. Similarly, compared with comparative example 6 without adding stabilizer dispersion, in embodiment 8, a stabilizer dispersion is added to the polymerization system of the copolymer resin, which can also significantly improve the processing heat aging resistance of the polyvinyl chloride resin powder and improve the problem of poor processing stability of the copolymer resin. By comparing embodiments 7, 9, and 10, it can be found that as the amount of stabilizer dispersion increases, the heat aging resistance of the polyvinyl chloride resin powder is better. By comparing embodiments 7 and 11, it can be found that compared with the use of inorganic stabilizers alone, the use of inorganic and organic composite stabilizers can significantly improve the heat aging resistance of the polyvinyl chloride resin powder. In addition, the thermal decomposition time of the resin in comparative example 9 is equivalent to that of comparative example 5 during the dynamic heat aging evaluation of the processing process, indicating that the method of comparative example 9 cannot improve the thermal stability of the resin powder during processing.

[0097] It is well known that under the same polymerization degree, 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 and the homopolymer polyvinyl chloride resin (Yunnan Energy Investment SG8) of the market were subjected to torque dynamic thermal aging test. The test conditions were 175°C and 35rpm. Figure 4 The dynamic aging diagram of the copolymerized polyvinyl chloride resin of Example 8 and the homopolymerized polyvinyl chloride resin of the commercial product is shown in the figure. It can be seen from the figure that although the mass of the stabilizer added when preparing the polyvinyl chloride resin in Example 8 is only 0.5% of the vinyl chloride monomer, compared with the homopolymerized polyvinyl chloride resin of the commercial product, even if the amount of the heat stabilizer is reduced by 67% during processing, the same thermal stability as the homopolymerized polyvinyl chloride resin of the commercial product can still be maintained, indicating that the method of the present invention can reduce the amount of stabilizer required in the process of processing polyvinyl chloride resin products.

[0098] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. A method for preparing a heat-resistant polyvinyl chloride resin, characterized in that: The following steps are involved: S1. Add deionized water, vinyl chloride monomer, initiator, dispersant 1, stabilizer dispersion and buffer to the reaction vessel and stir evenly; S2. Raise the temperature to the reaction temperature and react until the set pressure drops; S3. After adding the terminator and stirring evenly, the slurry was stripped, sieved, dehydrated, dried and sieved to obtain the polychloroacetic acid resin; The stabilizer dispersion is obtained by mixing a stabilizer, an aqueous solution of a dispersant 2 and a defoamer, and then homogenizing and / or grinding.

2. The method for preparing a heat-aging-resistant polyvinyl chloride resin according to claim 1, characterized in that: The preparation method of the stabilizer dispersion is as follows: add an aqueous solution of dispersant 2 and a defoamer into a reactor, stir evenly, add a stabilizer, and homogenize and / or grind until the particle size of suspended particles in the dispersion is 1-1500 nm.

3. The method for preparing a heat-aging-resistant 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.

4. The method for preparing a heat-aging-resistant polyvinyl chloride resin according to claim 1, characterized in that: The mass of the stabilizer in the reaction system is 0.05% to 5% of the vinyl chloride monomer.

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

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

7. The method for preparing a heat-aging-resistant polyvinyl chloride resin according to claim 1, characterized in that: The defoamer comprises at least one of a mineral oil defoamer, a polyether defoamer and a silicone defoamer; the mass of the defoamer is 0.1% to 0.3% of the total mass of water and the stabilizer.

8. The method for preparing a heat-aging-resistant polyvinyl chloride resin according to claim 1, characterized in that: Step S1 also includes adding a comonomer to the reaction system, wherein the comonomer includes one or more of acrylates, methacrylates, vinyl esters, unsaturated polyacid esters, olefins, vinyl ethers, aromatic vinyl monomers, and vinyl halides.

9. The method for preparing a heat-aging-resistant 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, nonionic surfactants, ionic surfactants, and gelatin; And / or, the initiator is at least one of an organic peroxide and an azo compound; And / or, the terminator includes at least one of hindered phenols, phosphites, aromatic amines, thioesters, thiophenols, hydroxylamines, and thiosemicarbazides.

10. The heat-aging resistant polyvinyl chloride resin prepared by the preparation method according to any one of claims 1 to 9.

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