Method for producing vinyl chloride polymers and vinyl chloride polymers produced thereby

Abstract

To provide: a method for preparing a vinyl chloride-based polymer that can have excellent balance between the CPA and the bulk density of the vinyl chloride-based polymer while reducing the content of an unreacted monomer remaining in a final product; and a vinyl chloride-based polymer prepared by the preparation method.SOLUTION: The present invention relates to: a method for enabling preparation of a vinyl chloride-based polymer showing improved melting rate and mechanical properties and low harmfulness, by pre-mixing and injecting a mixed dispersant comprising polyvinyl alcohol of high hydration and a carbonate metal salt before polymerization, and then polymerizing a vinyl chloride-based monomer; and a vinyl chloride-based polymer prepared by the method.SELECTED DRAWING: None

Description

Technical Field

[0001] This application claims the benefit of priority based on Korean Patent Application No. 10-2021-0086440 filed on July 1, 2021, and all the contents disclosed in the document of the Korean Patent Application are incorporated herein by reference in their entirety.

[0002] The present invention relates to a method for producing a vinyl chloride-based polymer and a vinyl chloride-based polymer produced by the production method, which can achieve a high melting rate, a low content of residual unreacted monomers, and a high bulk density of the polymer by using a mixed dispersant containing a highly hydrated dispersant and a carbonate metal salt in a certain amount.

Background Art

[0003] PVC is a typical thermoplastic resin, which is inexpensive and easy to adjust hardness, and has excellent physicochemical properties such as mechanical strength, weather resistance, and chemical resistance. It is used in various product fields such as films, sheets, and molded products.

[0004] In order to process PVC resin into a final product, a process of mixing suitable additives with the PVC resin according to the properties required for each product field and then extruding is necessary. At this time, the faster the melting of the PVC resin mixture, the easier the chain structure of the vinyl chloride-based polymer is to be broken, and stronger bonds are formed with each other, thereby increasing the mechanical properties of the final product. On the contrary, if the melting rate is low and the chain structure cannot be sufficiently broken, ungelled particles are formed in this process, and the formed ungelled particles act as defects in the final product and reduce the mechanical properties. Therefore, in product fields where high mechanical strength is required, a PVC resin with a higher melting rate is needed.

[0005] On the other hand, CPA (Cold Plasticizer Absorption) is a major physical property that indicates the characteristics of PVC resin, and the higher the CPA, the faster the melting rate tends to be. However, CPA has a trade-off relationship with the bulk density of the vinyl chloride polymer, and the higher the bulk density of the vinyl chloride polymer, the greater the extrusion volume during extrusion processing, resulting in superior productivity. In other words, increasing the CPA of PVC resin in order to produce a PVC resin with excellent mechanical strength leads to a decrease in bulk density, which reduces productivity during processing. Therefore, research is needed on methods to produce PVC resin that balances CPA and bulk density in order to achieve an appropriate level of productivity and mechanical strength. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] KR10-2021-0034418A [Patent Document 2] KR10-2017-0124959A [Overview of the project] [Problems that the invention aims to solve]

[0007] The present invention provides a method for producing a vinyl chloride polymer that offers an excellent balance between CPA and bulk density, while also reducing the content of unreacted monomers remaining in the final product, and a vinyl chloride polymer produced by the said method. [Means for solving the problem]

[0008] To solve the above problems, the present invention provides a method for producing a vinyl chloride polymer and a vinyl chloride polymer. (1) The present invention provides a method for producing a vinyl chloride polymer, comprising the steps of (S1) introducing a mixed dispersant and a carbonate metal salt into a polymerization reactor, and (S2) polymerizing a vinyl chloride monomer in the presence of the mixed dispersant and the carbonate metal salt, wherein the mixed dispersant contains a high-hydration polyvinyl alcohol with a degree of hydration of 80 mol% or more, and the content of the high-hydration polyvinyl alcohol in the mixed dispersant is 50 to 60% by weight.

[0009] (2) The present invention provides a method for producing a vinyl chloride polymer as described in (1), wherein the mixed dispersant and the carbonate metal salt are pre-mixed and then introduced into the polymerization reactor.

[0010] (3) The present invention provides a method for producing a vinyl chloride polymer as described in (1) or (2), wherein the mixed dispersant further comprises a low-hydration polyvinyl alcohol with a hydration degree of less than 80 mol% and a cellulose-based dispersant.

[0011] (4) The present invention provides a method for producing a vinyl chloride polymer according to any one of the above (1) to (3), wherein the cellulosic dispersant is one or more selected from the group consisting of methylcellulose, hydroxyethylcellulose, and hydroxypropylmethylcellulose.

[0012] (5) The present invention provides a method for producing a vinyl chloride polymer according to any one of the above (1) to (4), wherein the carbonate metal salt is one or more selected from the group consisting of sodium carbonate (Na2CO3), potassium carbonate (K2CO3), and sodium bicarbonate (NaHCO3).

[0013] (6) The present invention provides a method for producing a vinyl chloride polymer according to any one of the above (1) to (5), wherein the mixed dispersant is used in an amount of 0.05 to 0.15 parts by weight per 100 parts by weight of the vinyl chloride monomer.

[0014] (7) In the present invention, there is provided a method for producing a vinyl chloride-based polymer according to any one of the above (1) to (6), wherein the carbonate metal salt is used in an amount of 0.01 to 0.03 parts by weight based on 100 parts by weight of the vinyl chloride-based monomer.

[0015] (8) In the present invention, there is provided a method for producing a vinyl chloride-based polymer according to any one of the above (1) to (7), wherein the polymerization is carried out at 50 to 65 °C.

[0016] (9) The present invention provides a vinyl chloride-based polymer having a content of the vinyl chloride-based polymer in the surface layer measured by XPS analysis of 50% or more.

[0017] (10) The present invention provides a vinyl chloride-based polymer according to the above (9), characterized in that the CPA (cold plasticizer absorption) is 18% or more.

[0018] (11) The present invention provides a vinyl chloride-based polymer according to the above (9) or (10), characterized in that the bulk density is 0.580 g / cm 3 or more.

[0019] (12) The present invention provides a vinyl chloride-based polymer according to any one of the above (9) to (11), which is spherical in particle shape.

Effects of the Invention

[0020] The vinyl chloride-based polymer produced by using the production method of the present invention exhibits both a high CPA and a high bulk density, is excellent in both the productivity during extrusion processing and the mechanical strength during production of the final product, has a low content of unreacted monomers, and is harmless.

Modes for Carrying Out the Invention

[0021] Hereinafter, the present invention will be described in more detail. The terms and words used in this specification and the claims should not be construed as being limited to their ordinary or dictionary meanings. In accordance with the principle that the inventors can appropriately define the concepts of the terms in order to explain their invention in the best way, they should be construed in meanings and concepts consistent with the technical idea of the present invention.

[0022] On the other hand, the term "vinyl chloride polymer" as used in this specification includes a compound produced by polymerizing a vinyl chloride monomer, that is, a mixture in which a vinyl chloride monomer, namely vinyl chloride monomer alone or a vinyl monomer copolymerizable with vinyl chloride monomer is mixed, and may mean a polymer chain derived from a vinyl chloride monomer.

[0023] Method for producing vinyl chloride polymer The present invention includes a step (S1) of charging a mixed dispersant and a metal carbonate salt into a polymerization reactor, and a step (S2) of polymerizing a vinyl chloride monomer in the presence of the mixed dispersant and the metal carbonate salt. The mixed dispersant contains highly hydrated polyvinyl alcohol having a degree of hydration of 80 mol% or more, and the content of highly hydrated polyvinyl alcohol in the mixed dispersant is 50 to 60% by weight. The present invention provides a method for producing a vinyl chloride polymer.

[0024] As described above, there is a trade-off relationship between the CPA and the bulk density of the vinyl chloride polymer. In order to maintain the mechanical strength and productivity during extrusion at an appropriate level, it is necessary to find a suitable balance between the CPA and the bulk density of the vinyl chloride polymer. As a result of research for this purpose, the inventors of the present invention found that when a vinyl chloride monomer is polymerized in the presence of a mixture obtained by previously mixing a mixed dispersant containing highly hydrated polyvinyl alcohol and a metal carbonate salt, the CPA of the vinyl chloride polymer can be increased without impairing the bulk density, and at the same time, the amount of unreacted monomer remaining in the final polymer can be reduced. Thus, the method for producing a vinyl chloride polymer of the present invention was completed.

[0025] The method for producing the vinyl chloride polymer of the present invention will be described below, step by step. Step (S1) of adding the mixed dispersant and carbonate metal salt. The manufacturing method of the present invention includes the step (S1) of introducing a mixed dispersant and a carbonate metal salt into a polymerization reactor before carrying out the polymerization reaction.

[0026] The mixed dispersant used in this step is intended to disperse the vinyl chloride monomer, which will be added in a later step, in the solvent. It may be a mixture of two or more different dispersants, and at least one of the two or more dispersants included in the mixed dispersant may be a high-hydration polyvinyl alcohol with a hydration degree of 80 mol% or higher. Particularly preferably, the hydration degree of the high-hydration polyvinyl alcohol may be 85 mol% or higher. When polyvinyl alcohol with such a high hydration degree is used in mixture with other dispersants, there is an advantage in that the stability of the final generated particles can be further enhanced. On the other hand, the polyvinyl alcohol used as a dispersant in this step is in a form in which polyvinyl acetate is hydrated and a portion of the acetate is replaced with alcohol, and the hydration degree is defined as the degree to which the acetate is replaced with alcohol.

[0027] The content of high-hydration polyvinyl alcohol in the mixed dispersant may be 50 to 60% by weight. If the content of high-hydration polyvinyl alcohol in the mixed dispersant is excessively low, the stability of the particles will decrease during the polymerization process, leading to the generation of a large amount of scale, and it will not be possible to obtain vinyl chloride polymer particles in a consistent form. Furthermore, the bulk density of the final vinyl chloride polymer may be excessively low, which may cause a problem of reduced extrusion volume. Conversely, if the content of high-hydration polyvinyl alcohol in the mixed dispersant is excessively high, the voids inside the resulting vinyl chloride polymer particles will decrease, potentially lowering the plasticizer absorption rate. As a result, the discharge of residual monomers into the atmosphere will not be smooth, and the content of unreacted monomers remaining in the final product may increase rapidly.

[0028] The mixed dispersant may further contain, in addition to the high-hydration polyvinyl alcohol described above, a low-hydration polyvinyl alcohol of less than 80 mol% and a cellulose-based dispersant. When both high-hydration and low-hydration polyvinyl alcohol are used, basic physical properties such as polymer particle size and plasticizer absorption rate can be easily controlled, and polymer particles with relatively fast melting properties can be obtained while satisfying the basic physical properties required for the product, as the skin layer is not too thick. The hydration degree of the low-hydration polyvinyl alcohol may be less than 80 mol%, preferably 50 to 75 mol%, and the low-hydration polyvinyl alcohol may contain two or more types of polyvinyl alcohol having hydration degrees within the above range.

[0029] The mixed dispersant may be used in an amount of 0.05 to 0.15 parts by weight, preferably 0.08 to 0.12 parts by weight, per 100 parts by weight of the vinyl chloride monomer. If the amount of the mixed dispersant used is excessively small, the role of the mixed dispersant described above may not be sufficiently performed, and polymerization stability may decrease. If the amount of the mixed dispersant used is excessively large, the dispersant components may remain and act as impurities in the final product, adversely affecting the quality of the product.

[0030] The cellulose-based dispersant can act as a protective colloidal aid to stabilize the reactants during the polymerization process. One or more cellulose-based dispersants selected from the group consisting of methylcellulose, hydroxyethylcellulose, and hydroxypropylmethylcellulose may be used.

[0031] The carbonate-based metal salt used in this step acts as a pH adjuster and can reduce the content of unreacted monomers that may remain in the final product. The carbonate-based metal salt used may be one that can be dissolved in water and ionized, and specifically, one or more selected from the group consisting of sodium carbonate (Na2CO3), potassium carbonate (K2CO3), and sodium bicarbonate (NaHCO3) may be used.

[0032] The carbonate metal salt may be used in an amount of 0.01 to 0.03 parts by weight, preferably 0.015 to 0.025 parts by weight, per 100 parts by weight of the vinyl chloride monomer. If the amount of carbonate metal salt used is excessively small, the role of the carbonate metal salt described above cannot be sufficiently performed, and if the amount of carbonate metal salt used is excessively large, the carbonate metal salt component will affect the dispersant and reduce the dispersion stability, which may cause the size of the polymer particles to become excessively large.

[0033] On the other hand, in this step, the mixed dispersant and the carbonate metal salt may be pre-mixed and then added to the polymerization reactor. By pre-mixing and adding the mixed dispersant and the carbonate metal salt before the start of the polymerization reaction, rather than after the start of the polymerization reaction, the content of the vinyl chloride polymer in the surface layer of the final product can be further increased, thereby increasing the melting rate.

[0034] Polymerization step (S2) As mentioned above, the polymerization reaction can be carried out by adding a vinyl chloride monomer to a polymerization reactor after the mixed dispersant and carbonate metal salt have been added. In particular, the polymerization reaction in this step may be carried out by suspension polymerization.

[0035] The vinyl chloride monomer may be one type of vinyl chloride monomer, or a mixed monomer containing a vinyl chloride monomer and a vinyl monomer capable of copolymerization with the vinyl chloride monomer. The mixed monomer may contain 1 to 50 parts by weight of a copolymerizable vinyl monomer based on 100 parts by weight of the vinyl chloride monomer. Including the copolymerizable vinyl monomer within the above range has the advantage of stable suspension polymerization while providing excellent processability for the final product, the vinyl chloride polymer. The vinyl monomer may be one or more selected from the group consisting of olefin compounds such as ethylene and propylene; vinyl esters such as vinyl acetate and vinyl propionate; unsaturated nitriles such as acrylonitrile; vinyl alkyl ethers such as vinyl methyl ether and vinyl ethyl ether; unsaturated fatty acids such as acrylic acid, methacrylic acid, itaconic acid, and maleic acid; and anhydrides of these fatty acids.

[0036] In this step, a solvent for suspension polymerization may be used, and the solvent may be deionized water. The amount of solvent used may be appropriately adjusted according to the size of the polymerization reactor and the amount of monomer used, for example, 70 parts by weight or more per 100 parts by weight of vinyl chloride monomer. The solvent may be added in the preceding S1 step, mixed together with the mixed dispersant and the carbonate metal salt.

[0037] In this step, a polymerization initiator may be used to start the polymerization reaction. The polymerization initiator may be used in an amount of 0.02 to 0.2 parts by weight per 100 parts by weight of the vinyl chloride monomer to be polymerized. If less than 0.02 parts by weight of the polymerization initiator is used, the polymerization reaction time will be prolonged, the conversion rate to vinyl chloride polymer will be low, and productivity may decrease. If more than 0.2 parts by weight is used, the polymerization initiator may not be completely consumed during the polymerization process and may remain in the final vinyl chloride polymer slurry, potentially reducing thermal stability. More specifically, the polymerization initiator may be used in an amount of 0.04 to 0.12 parts by weight per 100 parts by weight of vinyl chloride monomer.

[0038] Examples of polymerization initiators include, specifically, peroxide compounds such as dicumyl peroxide, dipentyl peroxide, di-3,5,5-trimethylhexanoyl peroxide, or dilauryl peroxide; peroxydicarbonate compounds such as diisopropyl peroxydicarbonate, di-sec-butyl peroxydicarbonate, or di-2-ethylhexyl peroxydicarbonate; peroxyester compounds such as t-butyl peroxypivalate, 1,1,3,3-tetramethylbutyl peroxyneodecanoate, or t-butyl peroxyneodecanoate; azo compounds such as azobis-2,4-dimethylvaleronitrile; hydroperoxide compounds such as t-butyl hydroperoxide; or sulfate compounds such as potassium persulfate or ammonium persulfate. However, one or more of these may be used in combination.

[0039] In this step, the polymerization may be carried out at a temperature range of 50 to 65°C, more specifically, 50 to 60°C. Furthermore, since the polymerization reaction of vinyl chloride polymers is exothermic, a heat removal step via a reactor jacket and reflux condenser (R / CN) may be performed to minimize temperature changes during the polymerization process. When the polymerization reaction is carried out at the aforementioned temperature range, foam formation can be prevented while repolymerization and scale formation can be suppressed. Additionally, the decomposition of the polymerization initiator remaining at the end of the reaction is induced at this temperature range, allowing for the production of a vinyl chloride polymer with even better physical properties after the reaction.

[0040] In this step, additives such as antioxidants, bases, crosslinking agents, polymerization regulators, chain transfer agents, antistatic agents, scale inhibitors, and surfactants may be added. The type and content of these additives are not particularly limited and may be of the types and in amounts commonly known in the industry. These additives may be added at any point during the polymerization process, either all at once or continuously.

[0041] Vinyl chloride polymer The present invention provides a vinyl chloride polymer that can be produced using the vinyl chloride polymer production method described above. Specifically, the present invention provides a vinyl chloride polymer having a vinyl chloride polymer content of 50% or more in the surface layer as measured by XPS analysis.

[0042] When vinyl chloride polymers are produced using suspension polymerization, the final product is obtained in a form in which the vinyl chloride polymer is present internally and its surface is surrounded by a dispersant. In this case, the band that forms the surface is called the skin layer, and generally, the thicker the skin layer, the slower the melting rate, and therefore the longer the melting time tends to be. The thickness of such a skin layer can be estimated from the content of vinyl chloride polymer in the surface obtained by XPS analysis of the surface of the obtained polymer particles, and specifically, the lower the content of vinyl chloride polymer in the surface, the thinner the skin layer is considered to be.

[0043] In connection with this, when using the method for producing vinyl chloride polymers of the present invention described above, the content of dispersant on the surface of the polymer particles decreases, the content of vinyl chloride polymer increases, and a vinyl chloride polymer with a thin skin layer can be obtained. Specifically, when using the method for producing vinyl chloride polymers of the present invention, a vinyl chloride polymer having a vinyl chloride polymer content of 50% or more in the surface layer can be obtained. The vinyl chloride polymer of the present invention can have a faster melting rate because it has a thin skin layer.

[0044] The content of the vinyl chloride polymer in the surface layer can be measured using XPS analysis by the following method. 1) Assume that the only materials forming the surface of vinyl chloride polymers are PVC, PVA, and PVAc.

[0045] 2) Using PVC produced by bulk polymerization without the use of a dispersant, calculate the relative ratio of C to Cl in the PVC particles (C:Cl = 2.17:1). Since PVC produced by bulk polymerization consists only of PVC, the relative ratio calculated above is the relative ratio of C to Cl in pure PVC. Next, using the calculated relative ratio, calculate the PVC content from the Cl content measured in the surface layer of the target vinyl chloride polymer.

[0046] 3) The PVAc content is calculated using a specific BE value that appears at the carbonyl peak present in the PVAc within the C peak. 4) The remaining C peak after subtracting the PVC and PVAc content from the total content is determined to represent the PVA content.

[0047] 5) The content of PVC is defined as (PVC / (PVC+PVA+PVAc))*100%, based on the total amount of PVC, PVA, and PVAc calculated by the above process.

[0048] For the XPS equipment used in the aforementioned measurements, standard equipment may be used, for example, K-ALPHA+ (manufacturer: Thermofisher).

[0049] Furthermore, the vinyl chloride polymer of the present invention may have a CPA (cold plasticizer absorption) of 18% or more. Specifically, the vinyl chloride polymer of the present invention has a thin skin layer thickness, a fast melting rate, and accordingly, a high CPA of 18% or more is possible. In addition, the vinyl chloride polymer of the present invention has a bulk density of 0.580 g / cm³ 3 The above is also acceptable. While bulk density has a trade-off relationship with CPA, the vinyl chloride polymer particles of the present invention have a shape that is relatively closer to spherical compared to vinyl chloride polymers produced by existing methods, and therefore can exhibit high bulk density along with high CPA. The vinyl chloride polymer of the present invention may be in the form of spherical parts, and more specifically, it may be in the form of spherical parts with an aspect ratio of 1 to 1.2.

[0050] The following are preferred embodiments to aid in understanding the present invention. However, the following embodiments are merely illustrative and not intended to limit the scope of the present invention.

[0051] Example 1 Internal volume 1 m³ with reflux condenser and agitator 3 In a stainless steel polymerization reactor, 130 parts by weight of polymerization water, 0.02 parts by weight of sodium carbonate, 0.055 parts by weight of polyvinyl alcohol with a degree of hydration of 88 mol%, 0.025 parts by weight of polyvinyl alcohol with a degree of hydration of 72 mol%, 0.009 parts by weight of polyvinyl alcohol with a degree of hydration of 55 mol%, 0.011 parts by weight of hydroxypropyl methylcellulose, and 0.088 parts by weight of t-butyl peroxyneodecanoate (BND) were added, and the reactor was degassed using a vacuum pump while stirring. Subsequently, 100 parts by weight of vinyl chloride monomer was added, and the reaction proceeded while maintaining the temperature inside the polymerization reactor at 57.2°C. During the polymerization reaction, the pressure inside the reactor was 1.0 kg / cm². 2 Polymerization was stopped when the reaction rate decreased, and 0.05 parts by weight of triethylene glycol-bis-[3-(3-t-butyl-5-methyl-4-hydroxyphenyl)propionate] was added as an antioxidant. After that, the unreacted monomers were recovered, and the resin slurry was recovered in a polymerization reactor.

[0052] Example 2 The procedure was carried out in the same manner as in Example 1, except that 0.050 parts by weight of polyvinyl alcohol with a degree of hydration of 88 mol%, 0.028 parts by weight of polyvinyl alcohol with a degree of hydration of 72 mol%, 0.010 parts by weight of polyvinyl alcohol with a degree of hydration of 55 mol%, and 0.012 parts by weight of hydroxypropyl methylcellulose were used as the polyvinyl alcohol, and a resin slurry was obtained.

[0053] Example 3 The procedure was carried out in the same manner as in Example 1, except that 0.06 parts by weight of polyvinyl alcohol with a degree of hydration of 88 mol%, 0.022 parts by weight of polyvinyl alcohol with a degree of hydration of 72 mol%, 0.008 parts by weight of polyvinyl alcohol with a degree of hydration of 55 mol%, and 0.010 parts by weight of hydroxypropyl methylcellulose were used as the polyvinyl alcohol, and a resin slurry was obtained.

[0054] Comparative Example 1 The procedure was carried out in the same manner as in Example 1, except that sodium carbonate was not added, to obtain a resin slurry.

[0055] Comparative Example 2 The procedure was carried out in the same manner as in Example 1, except that sodium carbonate was not added, and 0.045 parts by weight of polyvinyl alcohol with a degree of hydration of 88 mol%, 0.037 parts by weight of polyvinyl alcohol with a degree of hydration of 72 mol%, 0.008 parts by weight of polyvinyl alcohol with a degree of hydration of 55 mol%, and 0.010 parts by weight of hydroxypropyl methylcellulose were added to obtain a resin slurry.

[0056] Comparative Example 3 In Example 1 described above, sodium carbonate was added, but the procedure was carried out similarly except that the addition of sodium carbonate was done after the addition of the monomer, and a resin slurry was obtained.

[0057] Comparative Example 4 In Example 2 described above, sodium carbonate was added, but the procedure was the same except that the addition was made after the addition of the monomer, and a resin slurry was obtained.

[0058] Comparative Example 5 In Example 3 described above, sodium carbonate was added, but the procedure was the same except that the addition was made after the addition of the monomer, and a resin slurry was obtained.

[0059] Comparative Example 6 The procedure was carried out in the same manner as in Example 1, except that 0.045 parts by weight of polyvinyl alcohol with a degree of hydration of 88 mol%, 0.037 parts by weight of polyvinyl alcohol with a degree of hydration of 72 mol%, 0.008 parts by weight of polyvinyl alcohol with a degree of hydration of 55 mol%, and 0.010 parts by weight of hydroxypropyl methylcellulose were added to obtain a resin slurry.

[0060] Comparative Example 7 The procedure was carried out in the same manner as in Example 1, except that 0.065 parts by weight of polyvinyl alcohol with a degree of hydration of 88 mol%, 0.020 parts by weight of polyvinyl alcohol with a degree of hydration of 72 mol%, 0.008 parts by weight of polyvinyl alcohol with a degree of hydration of 55 mol%, and 0.007 parts by weight of hydroxypropyl methylcellulose were added to obtain a resin slurry. The content of highly hydrated polyvinyl alcohol in the mixed dispersant used in the above examples and comparative examples, and the timing of sodium carbonate addition are summarized in Table 1 below.

[0061] [Table 1]

[0062] Experimental Example 1. Measurement of CPA and bulk density of vinyl chloride polymers The resin slurries produced in the above examples and comparative examples were dehydrated and dried to obtain particulate vinyl chloride polymers. The CPA and bulk density of the obtained vinyl chloride polymers were measured. CPA was measured according to ASTM D 3367-95, and bulk density was measured according to ASTM D 1895 Method A. The results are shown in Table 2 below.

[0063] [Table 2]

[0064] As shown in the results above, the vinyl chloride polymer of the present invention maintained excellent bulk density while having the highest CPA among the examples and comparative examples. This means that the vinyl chloride polymer of the present invention exhibits both excellent mechanical properties and a high melting rate. In particular, the results above confirm that a vinyl chloride polymer with such high CPA and excellent bulk density can be produced by having a high-hydration polyvinyl alcohol content of 50-60% by weight in the mixed dispersant and by pre-adding the carbonate metal salt before adding the monomer.

[0065] Experimental Example 2. Measurement of Melting Rate To 300 g of the resin produced in the above examples and comparative examples, 15 g of Ca-Zn-based stabilizer, 21 g of polyethylene chloride (CPE7000, manufacturer: Weipren), 29 g of TiO, and 36 g of CaCO3 were added, and the mixture was mixed for 6 minutes using a mixer (manufacturer: HANIL ELECTRIC, product name: HMF-3100S). After that, 56 g of the mixture was placed in a Brabender plastograph mixer and the melting time was measured for 6 minutes under conditions of 165°C and 45 rpm. The results are shown in Table 3 below.

[0066] [Table 3]

[0067] As predicted from the previous experimental example 1, the embodiment of the present invention measured the fastest melting time. This means that the vinyl chloride polymer of the present invention exhibits superior mechanical properties compared to the comparative examples. In particular, when comparing Examples 1-3 and Comparative Examples 3-5, which differ only in the timing of sodium carbonate addition, it can be confirmed that the melting time of Comparative Examples 3-5, in which sodium carbonate is added after the monomer, is about 7 seconds longer. From this, it can be confirmed that the mechanical properties of the polymer finally produced can change depending on the timing of the addition of sodium carbonate, i.e., the carbonate metal salt.

[0068] Experimental Example 3. Measurement of the content of vinyl chloride-based polymer in the surface layer. The resin slurries obtained in the examples and comparative examples were dehydrated and dried to obtain particulate vinyl chloride polymers, and the content of the vinyl chloride polymer in the surface layer of the particles was measured. The content was calculated under the following conditions.

[0069] The content of vinyl chloride polymer in the aforementioned surface layer was calculated using XPS analysis by the following method. A K-ALPHA+ (manufacturer: Thermofisher) was used as the XPS analysis equipment.

[0070] 1) Assume that the only materials forming the surface of vinyl chloride polymers are PVC, PVA, and PVAc. 2) Using PVC produced by bulk polymerization without the use of a dispersant, calculate the relative ratio of C to Cl in the PVC particles (C:Cl = 2.17:1). Since PVC produced by bulk polymerization consists only of PVC, the relative ratio calculated above is the relative ratio of C to Cl in pure PVC. Next, using the calculated relative ratio, calculate the PVC content from the Cl content measured in the surface layer of the target vinyl chloride polymer.

[0071] 3) The PVAc content is calculated using a specific BE value that appears at the carbonyl peak present in the PVAc within the C peak. 4) The remaining C peak after subtracting the PVC and PVAc content from the total content is determined to represent the PVA content.

[0072] 5) The content of PVC is defined as (PVC / (PVC+PVA+PVAc))*100%, based on the total amount of PVC, PVA, and PVAc calculated by the above process. The results are shown in Table 4 below.

[0073] [Table 4]

[0074] Examples 1-3 show a higher content of vinyl chloride polymer in the surface layer compared to the comparative example, which means that the vinyl chloride polymer according to the examples of the present invention has the thinnest skin layer thickness and is easily melted.

[0075] Experimental Example 4. Measurement of the content of residual vinyl chloride monomers. The resin slurries obtained in the above examples and comparative examples were dehydrated to a moisture content of approximately 15%, then divided into 20g portions and placed into paper cups (9cm in diameter, 12cm in height). These portions were then dried in an 80°C oven for 8 hours. After that, the slurries were placed in vials, and the content of residual vinyl chloride monomers was measured by HS-GS (Headspace-Gas chromatography) (measurement conditions: 1g of resin was sealed in a 20ml vial, and the components of the vinyl chloride monomers released at 90°C for 20 minutes were analyzed). The measurement results are shown in Table 5 below.

[0076] [Table 5]

[0077] As can be seen from the table above, the vinyl chloride polymer produced in the examples of the present invention showed remarkably low levels of residual vinyl chloride monomer components. This means that the vinyl chloride polymer of the present invention is not only superior in terms of melting rate and mechanical properties, but also has advantages over vinyl chloride polymers produced by existing methods in terms of toxicity.

Claims

1. The content of vinyl chloride polymers in the surface layer, as measured by XPS analysis, is 50% or more. The CPA (cold plasticizer absorption) is 18% or higher. A vinyl chloride polymer characterized by having a bulk density of 0.580 g / cm³ or more.

2. The vinyl chloride polymer according to claim 1, which is in the form of spherical parts.

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