Vinyl alcohol polymer and method for producing vinyl alcohol polymer

Abstract

The present invention provides a vinyl alcohol polymer that has an average particle size in an appropriate range and that can give polyvinyl chloride having a high bulk density, and a method for producing the vinyl alcohol polymer. A vinyl alcohol polymer according to one embodiment of the present invention comprises: 1 In the 1 H-NMR spectrum, when the sum of the following integral values ​​(a) to (e) is taken as 100, the vinyl alcohol polymer has an integral value (e) of 0.8 to 20. (a) Integration value of the peaks observed at 5.70 to 5.96 ppm (b) Integration value of the peaks identified at 5.97 to 6.63 ppm (c) Integration value of the peaks identified at 6.64 to 7.55 ppm (d) Integration value of the peaks identified at 7.56 to 7.81 ppm (e) Integration value of the peaks identified at 7.82 to 8.04 ppm

Description

[Technical Field]

[0001] The present invention relates to a vinyl alcohol polymer and a method for producing a vinyl alcohol polymer. [Background technology]

[0002] Polyvinyl chloride is generally produced by suspension polymerization of vinyl chloride monomer. Suspension polymerization is often carried out by dispersing vinyl chloride monomer in water using a dispersant such as polyvinyl alcohol. Various dispersants have been investigated from the viewpoints of suppressing foaming during polymerization and producing polyvinyl chloride having a desired average particle size. For example, Japanese Patent Laid-Open No. 2005-350557 (Patent Document 1) describes that foaming during polymerization can be suppressed by using a dispersant for suspension polymerization containing a polyvinyl alcohol resin and a specific compound. Also, Japanese Patent Laid-Open No. 2001-026604 (Patent Document 2) describes that polyvinyl chloride consisting of uniform porous particles can be obtained by using a dispersant for suspension polymerization of a vinyl compound consisting of modified polyvinyl alcohol containing 1 to 10 mol % of α-olefin units having 4 or less carbon atoms. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-350557 [Patent Document 2] Japanese Patent Application Laid-Open No. 2001-026604 Summary of the Invention [Problem to be solved by the invention]

[0004] As a dispersant for suspension polymerization of vinyl chloride monomer, a dispersant that can increase the bulk density while maintaining the average particle size of the polyvinyl chloride produced within an appropriate range, in addition to the above-mentioned properties such as suppressing foaming during polymerization, is desired. A high bulk density of polyvinyl chloride reduces the volume of the container required for storage and improves processability, such as increasing the molding speed when molding by extrusion molding or the like. However, when a conventional dispersant for suspension polymerization is used, it is difficult to increase the bulk density while keeping the average particle size of the produced polyvinyl chloride within an appropriate range, and there is room for improvement.

[0005] An object of the present invention is to provide a vinyl alcohol polymer from which polyvinyl chloride having an average particle size in an appropriate range and high bulk density can be obtained, and a method for producing the vinyl alcohol polymer. [Means for solving the problem]

[0006] Various aspects of the invention are as follows: [1] 1 A vinyl alcohol polymer having an integral value (e) of 0.8 to 20 in a H-NMR spectrum, where the sum of the following integral values (a) to (e) is taken as 100: (a) Integration value of the peaks observed at 5.70 to 5.96 ppm (b) Integration value of the peaks identified at 5.97 to 6.63 ppm (c) Integration value of the peaks identified at 6.64 to 7.55 ppm (d) Integration value of the peaks identified at 7.56 to 7.81 ppm (e) Integration value of the peaks identified at 7.82 to 8.04 ppm [2] The vinyl alcohol polymer according to [1] above, having a degree of saponification of 65 to 80 mol%, a block character of the residual ester group of 0.45 to 0.62, and a ratio a1 / a2 of the absorbance a1 of a 0.1% by mass aqueous solution at a wavelength of 280 nm to the absorbance a2 of the aqueous solution at a wavelength of 320 nm, that is, 1.6 or less. [3] The vinyl alcohol polymer according to the above [1] or [2], wherein the ratio of the weight average molecular weight Mw to the number average molecular weight Mn (Mw / Mn) is 2.6 to 14. [4] The vinyl alcohol polymer according to any one of the above [1] to [3], wherein the ratio of di-chains / tri-chains of the residual ester groups is 0.7 to 1.3, and the ratio of di-chains / tri-chains of the hydroxyl groups is 2.0 to 3.5. [5] The vinyl alcohol polymer according to any one of the above [1] to [4], wherein the residual ester group is an acetoxy group. [6] The vinyl alcohol polymer according to any one of the above [1] to [5], which has a viscosity of 5 to 9 cP in a 4% by mass aqueous solution. [7] The vinyl alcohol polymer according to any one of the above [1] to [6], which has a yellowness index (YI) of 30 to 80 in a 4% by mass aqueous solution. [8] The vinyl alcohol polymer according to any one of the above [1] to [7], wherein when an aqueous solution prepared by dissolving the vinyl alcohol polymer at a concentration of 7% by mass at 5°C for 12 hours is filtered through a 200-mesh filter, less than 0.1% of the components remain on the filter as undissolved substances. [9] The vinyl alcohol polymer according to any one of the above [1] to [8], which is used as a dispersant for suspension polymerization of polyvinyl chloride.

[10] A method for producing a vinyl alcohol polymer, comprising at least the following steps (1) to (3): Step (1) Polymerizing vinyl ester monomers to produce polyvinyl ester Step (2) saponifying the polyvinyl ester to produce a partially saponified polyvinyl ester. Step (3) A step of melt-kneading the partially saponified polyvinyl ester at a heating temperature of 185 to 250°C for a heating time of 1 to 10 minutes.

[11] The method for producing a vinyl alcohol polymer according to

[10] above, wherein the melt-kneading in the step (3) is carried out in the presence of an oxidizing agent, and the amount of the oxidizing agent is 2 parts by mass or less per 100 parts by mass of the polyvinyl ester.

[12] Resin particles made of the vinyl alcohol polymer according to any one of the above [1] to [9].

[13] Resin particles according to

[12] above, in which 95% or more of the particles have a particle diameter of 1.7 mm or more.

[14] 1 A vinyl alcohol polymer in which, in a H-NMR spectrum, when the sum of the following integrals (a) to (e) is taken as 100, integral (c) is 30 to 50 and integral (d) is 0.8 to 10: (a) Integration value of the peaks observed at 5.70 to 5.96 ppm (b) Integration value of the peaks identified at 5.97 to 6.63 ppm (c) Integration value of the peaks identified at 6.64 to 7.55 ppm (d) Integration value of the peaks identified at 7.56 to 7.81 ppm (e) Integration value of the peaks identified at 7.82 to 8.04 ppm

[15] Resin particles made of the vinyl alcohol polymer described in

[14] above.

[16] Resin particles according to

[15] above, in which 95% or more of the particles have a particle diameter of 1.7 mm or more. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a vinyl alcohol-based polymer that has an average particle size within an appropriate range and that can produce polyvinyl chloride having a high bulk density, and a method for producing the vinyl alcohol-based polymer. [Brief explanation of the drawings]

[0008] [Figure 1] 1H-NMR spectra of S1, S3 and S4 obtained in each example. [Figure 2] 1H-NMR spectra of S5 to S7 obtained in each example. [Figure 3] 1H-NMR spectra of C1 to C3 obtained in each comparative example. [Figure 4] FIG. 2 is an enlarged view of a portion of FIG. [Figure 5] FIG. 3 is an enlarged view of a portion of FIG. 2. [Figure 6] FIG. 4 is an enlarged view of a part of FIG. 3. [Figure 7] FIG. 1 shows integral values (a) to (e) in the 1H-NMR spectrum of S1. DETAILED DESCRIPTION OF THE INVENTION

[0009] [Vinyl alcohol polymer] The vinyl alcohol polymer according to one embodiment of the present invention is 1 In the H-NMR spectrum, when the sum of the following integrals (a) to (e) is taken as 100, the integral (e) has a value within a specific range, or the integrals (c) and (d) have a value within a specific range. Preferably, all of the integrals (a) to (e) have values within the specific range. (a) Integration value of the peaks observed at 5.70 to 5.96 ppm (b) Integration value of the peaks identified at 5.97 to 6.63 ppm (c) Integration value of the peaks identified at 6.64 to 7.55 ppm (d) Integration value of the peaks identified at 7.56 to 7.81 ppm (e) Integration value of the peaks identified at 7.82 to 8.04 ppm

[0010] The vinyl alcohol polymer according to one embodiment of the present invention is produced by partially saponifying a polyvinyl ester, which is a polymer of a vinyl ester monomer such as vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl pivalate, or vinyl versatate. The vinyl alcohol polymer produced through the step of partially saponifying polyvinyl ester is represented by the following formula (1) and has structural units represented by (u1) to (u3). [ka] u1 is a structural unit having a carbonyl group and a double bond, u2 is a structural unit having a residual ester group, and u3 is a structural unit having a hydroxyl group. In the above formula, OCOR represents a residual ester group, x, y, and z represent the molar fraction of each structural unit in the polymer, where x + y + z = 1, and x, y, and z are each 0 to 1, but none of x, y, and z is 0. In the above formula, the molecular chain contains an ester, a hydroxyl group, a carbonyl group, and a double bond adjacent to the carbonyl group. The double bond may be a single double bond or a conjugated double bond having two or more double bonds, and both may be present in the vinyl alcohol polymer. n is preferably 1 to 5, and more preferably 1 to 3. The above-mentioned OCOR is a residual ester group (OC(=O)R), where R is a hydrogen atom or an alkyl group having 1 to 20 carbon atoms. In the present invention, it is preferable to use polyvinyl acetate as the polyvinyl ester, and in this case, the residual ester group represents an acetoxy group.

[0011] 1 The integral values (a) to (e) in the H-NMR spectrum are the protons ( 1 The vinyl alcohol polymer according to one embodiment of the present invention has a specific combination of integrals (a) to (e), or all of the integrals (a) to (e) fall within a specific range. This means that the type, number, and arrangement of the double structure, such as whether it is mono- or conjugated, are specific. When a vinyl alcohol polymer having such a specific structure is used as a dispersant for polyvinyl chloride suspension polymerization, polyvinyl chloride having an average particle size within an appropriate range and a high bulk density can be obtained.

[0012] In a first aspect of the present invention, the vinyl alcohol polymer satisfies the following condition (I): [Condition (I)] When the sum of the integral values (a) to (e) is 100, the integral value (e) is 0.8 to 20. (a) Integration value of the peaks observed at 5.70 to 5.96 ppm (b) Integration value of the peaks identified at 5.97 to 6.63 ppm (c) Integration value of the peaks identified at 6.64 to 7.55 ppm (d) Integration value of the peaks identified at 7.56 to 7.81 ppm (e) Integration value of the peaks identified at 7.82 to 8.04 ppm When a vinyl alcohol polymer satisfying the above condition (I) is used as a dispersant for suspension polymerization of polyvinyl chloride, polyvinyl chloride having an average particle size within an appropriate range and a high bulk density can be obtained. From the viewpoint of further increasing the bulk density and further improving the dispersibility of polyvinyl chloride, the integral value (e) is preferably 0.8 to 15, more preferably 0.8 to 10, even more preferably 0.9 to 9, still more preferably 0.95 to 8, and particularly preferably 1 to 7.

[0013] In a second aspect of the present invention, the vinyl alcohol polymer satisfies the following condition (II): [Condition (II)] When the sum of the integrals (a) to (e) is 100, the integral (c) is 30 to 50, and the integral (d) is 0.8 to 10. (a) Integration value of the peaks observed at 5.70 to 5.96 ppm (b) Integration value of the peaks identified at 5.97 to 6.63 ppm (c) Integration value of the peaks identified at 6.64 to 7.55 ppm (d) Integration value of the peaks identified at 7.56 to 7.81 ppm (e) Integration value of the peaks identified at 7.82 to 8.04 ppm

[0014] When a vinyl alcohol polymer satisfying the above condition (II) is used as a dispersant for suspension polymerization of polyvinyl chloride, polyvinyl chloride having an average particle size within an appropriate range and a high bulk density can be obtained. In the above condition (II), from the viewpoint of further increasing the bulk density and further improving the dispersibility of polyvinyl chloride, the integral value (c) is preferably 30 to 45, more preferably 30 to 40, even more preferably 30 to 38, and still more preferably 30 to 37. In the above condition (II), from the viewpoint of further increasing the bulk density and further improving the dispersibility of polyvinyl chloride, the integral value (d) is preferably 0.8 to 8, more preferably 0.8 to 7, even more preferably 0.8 to 6, still more preferably 0.9 to 5.5, and particularly preferably 0.95 to 5.3.

[0015] If a vinyl alcohol polymer does not satisfy either of the conditions (I) or (II), it is difficult to obtain polyvinyl chloride having a high bulk density even when used as a dispersant for suspension polymerization of polyvinyl chloride.

[0016] It is preferable that the vinyl alcohol polymer further satisfies the condition (III). [Condition (III)] When the sum of the integrals (a) to (e) is 100, the integral (a) is 1 to 10, and the integral (b) is 20 to 70. (a) Integration value of the peaks observed at 5.70 to 5.96 ppm (b) Integration value of the peaks identified at 5.97 to 6.63 ppm (c) Integration value of the peaks identified at 6.64 to 7.55 ppm (d) Integration value of the peaks identified at 7.56 to 7.81 ppm (e) Integration value of the peaks identified at 7.82 to 8.04 ppm In the above condition (III), the integral value (a) is preferably 1 to 8, more preferably 1 to 5, and even more preferably 1 to 4, from the viewpoint of further increasing the bulk density and further improving the dispersibility of polyvinyl chloride. In the above condition (III), from the viewpoint of further increasing the bulk density and further improving the dispersibility of polyvinyl chloride, the integral value (b) is preferably 30 to 65, more preferably 40 to 65, even more preferably 45 to 63, still more preferably 48 to 60, and particularly preferably 48 to 59.

[0017] From the viewpoint of further increasing the bulk density and further improving the dispersibility of polyvinyl chloride, the vinyl alcohol polymer according to one embodiment of the present invention preferably satisfies both conditions (I) and (II), both conditions (I) and (III), or both conditions (II) and (III), and more preferably satisfies all of conditions (I), (II), and (III). The above-mentioned integral values (a) to (e) can be adjusted by the production conditions when producing the vinyl alcohol polymer. Specifically, as will be described later, they can be adjusted by the production conditions such as whether or not a peroxide is used, whether or not a heat treatment is performed, the heating temperature, and the heat treatment time.

[0018] (Saponification degree) The vinyl alcohol polymer according to one embodiment of the present invention preferably has a degree of saponification of 65 to 80 mol%. By setting the degree of saponification within this range, the bulk density of polyvinyl chloride produced by using the vinyl alcohol polymer as a dispersant for suspending polyvinyl chloride tends to be increased. From the viewpoint of achieving a better bulk density, the degree of saponification is more preferably 70 to 80 mol%. The degree of saponification can be measured in accordance with JIS K6726.

[0019] (Block Character) The block character of the residual ester group in the vinyl alcohol polymer according to one embodiment of the present invention is preferably 0.45 to 0.62, more preferably 0.45 to 0.6, even more preferably 0.45 to 0.55, and particularly preferably 0.45 to 0.5. When the block character is within this range, the bulk density of polyvinyl chloride produced using the vinyl alcohol polymer as a dispersant for suspending polyvinyl chloride tends to be increased. The block character usually takes a value of 0 to 2, with the closer to 0 the higher the blockiness of the distribution of residual ester groups, the closer to 1 the higher the randomness, and the closer to 2 the higher the alternation. The block character (η) of the residual ester group is an index showing the distribution of the residual ester group in the vinyl alcohol polymer, 1 It is determined by analyzing the peaks appearing in the methine region of the H-NMR spectrum. The peaks are split into three due to the triad structure of adjacent substituents, either hydroxyl groups (O) or residual ester groups (A). Specifically, the peaks at the center of the residual ester group peak are (OAO), (AAO), and (AAA), while the peaks at the center of the hydroxyl group are (OOO), (AOO), and (AOA), and the absorption intensities are proportional to the abundance ratio of the structures. The block character (η) is expressed by the following formula (1). For example, when vinyl acetate is used as the raw material, the residual ester group (A) represents the residual acetoxy group (OAc group).

[0020]

number

[0021] (UV absorbance) In one embodiment of the vinyl alcohol polymer of the present invention, it is preferable that the ratio (a1 / a2) of the absorbance a1 of a 0.1% by mass aqueous solution at a wavelength of 280 nm to the absorbance a2 of a 0.1% by mass aqueous solution of the vinyl alcohol polymer at a wavelength of 320 nm is within a certain range. As described above, the vinyl alcohol polymer according to one embodiment of the present invention has double bonds, some of which form conjugated double bonds along the polymer main chain adjacent to the carbonyl groups, as shown in the following formulas (2) and (3):

[0022] [ka] Formula (2) represents a conjugated double bond having two double bonds adjacent to the carbonyl group in the vinyl alcohol polymer, and formula (3) represents a conjugated double bond having three double bonds adjacent to the carbonyl group in the vinyl alcohol polymer. x1 in formula (2) and x2 in formula (3) are each defined as x in formula (1). The absorbance a1 at a wavelength of 280 nm is based on the conjugated double bond having two double bonds close to the carbonyl group represented by the above formula (2), and the more conjugated double bonds there are, the larger the value of a1 becomes. The absorbance a2 at a wavelength of 320 nm is based on the conjugated double bonds having three double bonds close to the carbonyl group represented by the above formula (3), and the more conjugated double bonds there are, the larger the value of a2 becomes.

[0023] The ratio a1 / a2 of the absorbance a1 at a wavelength of 280 nm of a 0.1 mass % aqueous solution of the vinyl alcohol polymer, which is one embodiment of the present invention, to the absorbance a2 at a wavelength of 320 nm of a 0.1 mass % aqueous solution of the vinyl alcohol polymer is preferably 1.6 or less, more preferably 1.5 or less, and is preferably 1.0 or more, more preferably 1.2 or more, and even more preferably 1.3 or more. By using a vinyl alcohol polymer having a1 / a2 in the above range as a dispersant for suspension polymerization, it becomes easier to obtain bulky polyvinyl chloride. From the viewpoint of improving the dispersibility of polyvinyl chloride, the absorbance a1 is preferably 0.15 to 0.70, more preferably 0.20 to 0.60, and the absorbance a2 is preferably 0.10 to 0.50, more preferably 0.15 to 0.40.

[0024] The vinyl alcohol polymer according to one embodiment of the present invention preferably has the above-described degree of saponification, block character of the residual ester group, and ratio a1 / a2 of absorbance a1 at 280 nm to absorbance a2 at 320 nm, all within the above-described ranges. These can be adjusted by varying production conditions, such as the polymerization conditions for the vinyl ester monomer, the partial saponification conditions, whether or not a peroxide is used, whether or not a heat treatment is performed, the heating temperature, and the heat treatment time, when producing the vinyl alcohol polymer, as described below. The same applies to adjustment of various measured values, such as Mw / Mn, the ratio of two-chains to three-chains, and viscosity, as described below.

[0025] The ratio (Mw / Mn) of the weight average molecular weight Mw to the number average molecular weight Mn of the vinyl alcohol polymer according to one embodiment of the present invention is preferably 2.0-18, more preferably 2.6-14, and even more preferably 2.8-14.

[0026] The ratio of di-chains to tri-chains of residual ester groups in the vinyl alcohol polymer according to one embodiment of the present invention (di-chain / tri-chain ratio) is preferably 0.7 to 1.3. Here, the term "tri-chains of residual ester groups" refers to the proportion of three consecutive structural units having residual ester groups in the vinyl alcohol polymer, and the term "dual-chains of residual ester groups" refers to the proportion of two consecutive structural units having residual ester groups in the vinyl alcohol polymer. The ratio of di-hydroxyl groups to tri-hydroxyl groups in the vinyl alcohol polymer according to one embodiment of the present invention (di-hydroxyl / tri-hydroxyl ratio) is preferably 2.0 to 3.5, more preferably 2.1 to 3.3, and even more preferably 2.2 to 3.0. Here, the term "tri-hydroxyl groups" refers to the ratio of three consecutive hydroxyl group-containing structural units in the vinyl alcohol polymer, and the term "dual-hydroxyl groups" refers to the ratio of two consecutive hydroxyl group-containing structural units in the vinyl alcohol polymer.

[0027] These two and three chains are 1It is determined by H-NMR measurement, specifically, 400 MHz at room temperature of a 1.0 wt% DMSO-d6 solution of the target sample. 1 It can be calculated from the ratio of the integral ratios of each peak in H-NMR measurement. Specifically, when the peak integral value of each chemical shift is defined as follows, it is calculated by the following formula: Here, the case where the remaining ester group is an acetyl group will be described, but hereinafter, O represents a hydroxyl group, A represents an acetyl group, and the underline represents a substituent to be integrated.

[0028] [O A O] (relative amount of acetyl groups sandwiched between hydroxyl groups): 5.04-5.19 ppm [A A O+O A A] (relative amount of acetyl groups sandwiched between hydroxyl and acetyl groups): 4.90-5.05 ppm [A A A] (relative amount of acetyl groups sandwiched between acetyl groups): 4.69-4.91 ppm [O O O] (relative amount of hydroxyl groups sandwiched between hydroxyl groups): 3.75-4.15 ppm [A O O+O O A] (relative amount of hydroxyl groups between hydroxyl groups and acetyl groups): 3.60-3.76 ppm [A O A] (relative amount of hydroxyl groups sandwiched between acetyl groups): 3.34-3.61 ppm

[0029] The ratio of two-chain / three-chain remaining ester groups = ([A A A]+0.5[A A O+O A A]) / ([O A O]+0.5[A A O+O A A]) The ratio of hydroxyl groups from two chains to three chains = ([O O O]+0.5[A O O+O O A]) / ([A O A]+0.5[A O O+O O A])

[0030] In one embodiment of the vinyl alcohol polymer of the present invention, when an aqueous solution prepared by dissolving the vinyl alcohol polymer at a concentration of 7% by mass at 5° C. for 12 hours is filtered through a 200-mesh filter, it is preferable that the amount of components remaining on the filter as undissolved matter is less than 0.1%. Such a vinyl alcohol polymer with a small amount of undissolved matter has excellent solubility and is easy to handle as a dispersant.

[0031] The viscosity of the vinyl alcohol polymer according to one embodiment of the present invention is not particularly limited, but from the viewpoint of the stability of the suspension, the viscosity of a 4% by mass aqueous solution of the vinyl alcohol polymer is preferably 5 to 9 cP, more preferably 6 to 7.5 cP. The viscosity is measured at 20°C, and can be measured using a Brookfield viscometer (model LVDV-II+Pro).

[0032] The yellowness index (YI) of a 4% by mass aqueous solution of the vinyl alcohol polymer according to one embodiment of the present invention is preferably 30 to 80, more preferably 35 to 70. The yellowness index (YI) correlates with the conjugated double bond component in which n is 4 or more in the above formula (1). When the yellowness index (YI) is 30 or more, the grafting efficiency of the vinyl chloride monomer during the polyvinyl chloride polymerization reaction increases, making it easier to control the particle size and bulk density as desired. When the yellowness index (YI) is 80 or less, side reactions do not proceed excessively, making the polymer more easily soluble in water and improving production efficiency. The yellowness index (YI) can be determined in accordance with ASTM standard D1925.

[0033] The vinyl alcohol polymer according to one embodiment of the present invention is preferably in the form of resin particles made of the vinyl alcohol polymer. Polyvinyl chloride obtained by using the resin particles as a dispersant for suspension polymerization of polyvinyl chloride has little generation of lumps and is of good quality. The average particle size of the resin particles is preferably 0.8 to 3.0 mm, and preferably particles with a particle size of 1.7 mm or larger account for 95% or more by weight. When the average particle size of the resin particles is 0.8 mm or larger, adhesion of the resin particles to each other during dissolution is suppressed, making it less likely for granules to form. Furthermore, when the average particle size of the resin particles is 3.0 mm or smaller, they dissolve completely in a short time, thereby improving the productivity of polyvinyl chloride polymerization. The weight ratio of particles with a particle size of 1.7 mm or larger can be measured by placing 100 g of resin particles on a sieve with a mesh size of 1.7 mm, covering it with a lid, shaking it for 5 minutes, and evaluating the weight ratio of the resin remaining on the sieve to the resin that passed through the sieve. The method for producing the resin particles is not particularly limited, but preferably, as described below, the vinyl alcohol polymer is extruded in the form of a strand using an extruder, air-cooled, and then cut with a strand cutter to pelletize the extruded strand, thereby producing the resin particles.

[0034] The vinyl alcohol polymer and resin particles comprising the vinyl alcohol polymer according to one embodiment of the present invention can be suitably used as a dispersant for suspension polymerization of polyvinyl chloride.

[0035] The vinyl alcohol polymer according to one embodiment of the present invention is preferably produced by a production method including the following steps (1) to (3), although the production method is not limited thereto. Step (1) polymerizing a vinyl ester monomer to produce a polyvinyl ester; Step (2) partially saponifying the polyvinyl ester to produce a partially saponified polyvinyl ester; Step (3) A step of melt-kneading the partially saponified polyvinyl ester at a heating temperature of 185 to 250°C for a heating time of 1 to 10 minutes.

[0036] Step (1) is a step of polymerizing a vinyl ester monomer to produce a polyvinyl ester. [ka] The above reaction formula (I) is a simplified reaction formula used to explain step (1), and shows the reaction formula when vinyl acetate (VAM) is used as the vinyl ester monomer. Ac represents an acetyl group.

[0037] In step (1), examples of the vinyl ester monomer include vinyl formate, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl pivalate, and vinyl versatate. The vinyl ester monomers may be used alone or in combination. Among these, it is preferable to use at least vinyl acetate, and it is more preferable to use only vinyl acetate. The polymerization can be carried out in the substantial absence of olefin comonomers such as ethylene, propylene, or styrene. The polymerization can also be carried out in the absence or substantial absence of chain transfer agents such as aldehydes, ketones, etc., where substantial absence means not intentionally added. Examples of the polymerization method include known methods such as bulk polymerization, solution polymerization, suspension polymerization, emulsion polymerization, etc. The polymerization can be carried out at about −80 to 300° C., and a polymerization initiator such as peroxide or azoisobutyronitrile can be used.

[0038] Step (2) is a step of partially saponifying the polyvinyl ester obtained in step (1) to produce a partially saponified polyvinyl ester. [ka] The above reaction formula (II) is a simplified reaction formula used to explain step (2), and shows the reaction formula for step (2) when vinyl acetate (VAM) is used as the vinyl ester monomer. In step (2), some of the ester groups are saponified to form hydroxyl groups. The reaction temperature in step (2) is, for example, about 10 to 70°C, and preferably about 20 to 50°C.

[0039] Partial saponification can be carried out by contacting the polyvinyl ester with an alkali compound to cause transesterification or direct hydrolysis. Examples of the alkali compound include alkali metal hydroxides such as potassium hydroxide, sodium hydroxide, and lithium hydroxide, and alkali metal alkoxides such as sodium methoxide, sodium ethoxide, potassium methoxide, potassium ethoxide, and potassium t-butoxide.

[0040] The amount of the alkali compound used is not particularly limited, but is preferably 0.0005 to 0.01 mol, and more preferably 0.001 to 0.003 mol, per 1 mol of polyvinyl ester. Examples of solvents that can be used in partial saponification include alcohols such as methanol, ethanol, isopropanol, n-propyl alcohol, n-butanol, isobutanol, sec-butanol, t-butanol, amyl alcohol, and cyclohexanol; cyclic ethers such as tetrahydrofuran and dioxane; ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and pinacoline; sulfoxides such as dimethyl sulfoxide; and hydrocarbons such as toluene, benzene, n-hexane, and cyclohexane. The partially saponified polyvinyl ester is preferably isolated and dried to obtain a powdered partially saponified polyvinyl ester for further processing.

[0041] (Step 3) Step (3) is a step of melt-kneading the partially saponified polyvinyl ester at a heating temperature of 185 to 250° C. for a heating time of 1 to 10 minutes. [ka] The above reaction formula (III) is a simplified reaction formula used to explain step (3), and shows the reaction formula for step (3) when vinyl acetate (VAM) is used as the vinyl ester monomer. In the above reaction formula, OAc represents an acetoxy group, x, y, and z represent the mole fractions of the respective structural units in the polymer, where x + y + z = 1, x, y, and z are each 0 to 1, and none of x, y, and z is 0. In step (3), a double bond and a carbonyl group are introduced into the polymer main chain. The double bond may be a single double bond or a conjugated double bond having two or more double bonds, and both may be present in the vinyl alcohol polymer. n is preferably 1 to 5, and more preferably 1 to 3. In step (3), the partially saponified polyvinyl ester obtained in step (2) is melt-kneaded at a heating temperature of 185 to 250°C for a heating time of 1 to 10 minutes. By performing the melt-kneading at a heating temperature of 185°C or higher, 1 The integrated values (a) to (e) in the H-NMR spectrum can be easily adjusted to the desired ranges. By setting the heating temperature to 250°C or less, the amount of undissolved matter in the vinyl alcohol polymer can be easily reduced. From this perspective, the heating temperature is preferably 190 to 245°C, and the heating time is preferably 2 to 8 minutes. The means for carrying out the melt-kneading is not particularly limited, but it is preferable to use an extruder. The extruder may be a single-screw extruder or a twin-screw extruder, but it is preferable to use a twin-screw extruder. The use of a twin-screw extruder makes it easier to melt-knead the powdery partially saponified polyvinyl ester obtained in step (2), making it easier to obtain the desired vinyl alcohol polymer.

[0042] Furthermore, the melt-kneading is preferably carried out in the presence of an oxidizing agent. 1This makes it easier to adjust the integrated values (a) to (e) in the H-NMR spectrum to the desired ranges. The oxidizing agent is preferably added before adjusting the heating temperature. That is, after adding the oxidizing agent to the partially saponified polyvinyl ester, heat treatment is preferably carried out under the heating temperature and heating time conditions described above. The amount of oxidizing agent added is preferably 2 parts by mass or less, more preferably 1 part by mass or less, and preferably 0.1 parts by mass or more, per 100 parts by mass of polyvinyl ester. The oxidizing agent can also be diluted in a solvent such as water, methanol, or methyl acetate and added, and in this case, it is preferably added as an aqueous solution. The addition of the oxidizing agent is not particularly limited, but is preferably carried out while kneading at a temperature of 10°C to less than 185°C, taking into account the half-life temperature of the oxidizing agent. When the oxidizing agent is diluted in a solvent, it is preferably added at a temperature below the boiling point of the solvent, particularly 100°C or below in the case of an aqueous solution, taking into account the boiling point of the solvent. When an extruder is used, it is preferable to provide an oxidizing agent inlet in the extruder to add the oxidizing agent. Examples of the oxidizing agent include various acids, peroxides, perchlorates, chlorinated isocyanurates, etc. Among these, peroxide-based oxidizing agents such as hydrogen peroxide and peracetic acid are preferred, and hydrogen peroxide is more preferred.

[0043] In step (3), reaction by-products such as esters such as methyl acetate, carboxylic acids such as acetic acid, water, etc. may be removed as necessary. For example, when melt-kneading is performed using an extruder, it is advisable to use an extruder equipped with a vacuum vent.

[0044] The vinyl alcohol polymer according to one embodiment of the present invention can be obtained through steps (1) to (3). When step (3) is performed using an extruder, it is preferable to extrude the vinyl alcohol polymer into a strand shape using the extruder, cool it in air, and then cut it with a strand cutter to pelletize it, thereby obtaining resin particles. Polyvinyl chloride obtained by using the resin particles as a dispersant for suspension polymerization of polyvinyl chloride has little generation of lumps and is of good quality.

[0045] (Polyvinyl chloride manufacturing method) The vinyl alcohol polymer according to one embodiment of the present invention can be used as a dispersant for polyvinyl chloride suspension polymerization. The method for producing polyvinyl chloride using the vinyl alcohol polymer as a dispersant can be, for example, as follows. The process may be carried out by mixing a vinyl alcohol polymer, a vinyl chloride monomer, and water to form a suspension, which is one embodiment of the present invention, and then polymerizing the vinyl chloride monomer. The order in which the vinyl alcohol polymer, vinyl chloride monomer, and water are added is not particularly limited, but for example, the vinyl alcohol polymer may be added to a solution containing the vinyl chloride monomer and water, and then mixed to form a suspension. Mixing can be performed using a known stirring device. The amount of the vinyl alcohol polymer used is preferably 0.01 to 5% by mass, more preferably 0.02 to 0.2% by mass, based on the vinyl chloride monomer.

[0046] Furthermore, dispersants other than the vinyl alcohol polymer of one embodiment of the present invention may be used in combination with the vinyl alcohol polymer of one embodiment of the present invention. Examples of other dispersants include cellulose and cellulose derivatives. Examples of cellulose derivatives include methyl cellulose, ethyl cellulose, hydroxymethyl cellulose, hydroxypropyl methyl cellulose, hydroxybutyl methyl cellulose, hydroxyethyl cellulose, and carboxymethyl cellulose. Furthermore, as the other dispersant, a vinyl alcohol polymer other than the vinyl alcohol polymer of one embodiment of the present invention may be used. The proportion of the vinyl alcohol polymer of one embodiment of the present invention relative to the total amount of the dispersant is preferably 60% by mass or more, more preferably 80% by mass or more, and preferably 90% by mass or more. The vinyl chloride monomer may be added in the amount used for polymerization all at once, or a portion of it may be added at the beginning and the remainder may be added after the start of polymerization. The suspension may further contain one or more additives such as a polymerization initiator, an antioxidant, a pH adjuster, etc. Examples of the polymerization initiator include di-2-ethylhexyl peroxydicarbonate, diethoxyethyl peroxydicarbonate, α-cumyl peroxyneodecanate, t-butyl peroxyneodecanate, t-butyl peroxypivalate, t-butylperoxy-3,5,5-trimethylhexanoate, acetylcyclohexylsulfonyl peroxide, 2,4,4-trimethylpentyl-2-peroxyphenoxyacetate, and lauroyl peroxide. These may be used alone or in combination of two or more. Examples of the antioxidant include hindered phenol-based antioxidants. Examples of pH adjusters include sodium bicarbonate, sodium carbonate, potassium bicarbonate, potassium carbonate, sodium citrate, potassium citrate, sodium tartrate, potassium tartrate, sodium benzoate, and potassium benzoate, and these may be used alone or in combination of two or more.

[0047] After forming the suspension as described above, the suspension is heated to polymerize the vinyl chloride monomer. The temperature during polymerization is about 20 to 90° C. After the polymerization has started, additional vinyl chloride monomer can be added.

[0048] The average particle size of the resulting polyvinyl chloride is preferably 130 to 180 μm, more preferably 140 to 160 μm. Polyvinyl chloride having such an average particle size has good handleability. When the vinyl alcohol polymer according to one embodiment of the present invention is used as a dispersant, polyvinyl chloride having a high bulk density can be obtained. [Example]

[0049] The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

[0050] Example 1 A reactor equipped with a thermometer, stirrer, and condenser was charged with 100 parts by weight of vinyl acetate monomer and 40 parts by weight of methanol. Nitrogen gas was blown in for 30 minutes to replace the atmosphere, and the reactor was then heated to 60°C for 30 minutes. Next, 0.03 parts by weight of 2-ethylhexyl peroxydicarbonate, a polymerization initiator, was added, and the reaction was allowed to proceed at 60°C for 4 hours. After the reaction time, the reaction solution was cooled. The conversion rate was measured after cooling and found to be 40%. Subsequently, the remaining vinyl acetate monomer was removed together with methanol under reduced pressure while adding additional methanol, yielding a methanol solution containing 50% by weight of polyvinyl acetate. A methanol solution of sodium hydroxide was added to this methanol solution so that the amount of sodium hydroxide was 0.003 mol per 1 mol of polyvinyl acetate, and saponification was carried out at 40°C. The solvent was removed by distillation, and the resulting mixture was dried to obtain a powder of partially saponified polyvinyl acetate. The obtained powdery partially saponified polyvinyl acetate was fed into a twin-screw extruder using a feeder and kneaded at room temperature to less than 185°C. While kneading was carried out under these conditions, an aqueous hydrogen peroxide solution (concentration: 30% by mass) was fed through an inlet provided in the barrel and mixed with the partially saponified polyvinyl acetate. The amount of hydrogen peroxide added was adjusted to 0.3 parts by mass per 100 parts by mass of polyvinyl acetate. After adding the aqueous hydrogen peroxide solution, the mixture was melt-kneaded at a heating temperature of 242°C for 7.5 minutes to obtain a vinyl alcohol polymer according to the present invention. The vinyl alcohol polymer was extruded into strands using an extruder, cooled in air, and then cut with a strand cutter to obtain resin particles S1 made of a vinyl alcohol polymer. The S1 was subjected to various evaluations as described below, and the results are shown in Table 1.

[0051] Example 2 A reactor equipped with a thermometer, stirrer, and condenser was charged with 100 parts by weight of vinyl acetate monomer and 40 parts by weight of methanol. Nitrogen gas was blown in for 30 minutes to replace the atmosphere, and the reactor was then heated to 60°C for 30 minutes. Next, 0.03 parts by weight of 2-ethylhexyl peroxydicarbonate, a polymerization initiator, was added, and the reaction was allowed to proceed at 60°C for 4 hours. After the reaction time, the reaction solution was cooled. The conversion rate was measured after cooling and found to be 40%. Subsequently, the remaining vinyl acetate monomer was removed together with methanol under reduced pressure while adding additional methanol, yielding a methanol solution containing 50% by weight of polyvinyl acetate. A methanol solution of sodium hydroxide was added to this methanol solution so that the amount of sodium hydroxide was 0.003 mol per 1 mol of polyvinyl acetate, and saponification was carried out at 40°C. The solvent was removed by distillation, and the resulting mixture was dried to obtain a powder of partially saponified polyvinyl acetate. The obtained powdery partially saponified polyvinyl acetate was fed into a twin-screw extruder using a feeder and kneaded at room temperature to less than 185°C. While kneading was carried out under these conditions, an aqueous hydrogen peroxide solution (concentration: 30% by mass) was fed through an inlet provided in the barrel and mixed with the partially saponified polyvinyl acetate. The amount of hydrogen peroxide added was adjusted to 0.6 parts by mass per 100 parts by mass of polyvinyl acetate. After supplying the aqueous hydrogen peroxide solution, the mixture was melt-kneaded at a heating temperature of 197°C for 6 minutes to obtain a vinyl alcohol polymer according to the present invention. The vinyl alcohol polymer was extruded into strands using an extruder, cooled in air, and then cut with a strand cutter to obtain resin particles S3 made of the vinyl alcohol polymer. The S3 was subjected to various evaluations as described below, and the results are shown in Table 1.

[0052] Example 3 A reactor equipped with a thermometer, stirrer, and condenser was charged with 100 parts by weight of vinyl acetate monomer and 40 parts by weight of methanol. Nitrogen gas was blown in for 30 minutes to replace the atmosphere, and the reactor was then heated to 60°C for 30 minutes. Next, 0.03 parts by weight of 2-ethylhexyl peroxydicarbonate, a polymerization initiator, was added, and the reaction was allowed to proceed at 60°C for 4 hours. After the reaction time, the reaction solution was cooled. The conversion rate was measured after cooling and found to be 40%. Subsequently, the remaining vinyl acetate monomer was removed together with methanol under reduced pressure while adding additional methanol, yielding a methanol solution containing 50% by weight of polyvinyl acetate. A methanol solution of sodium hydroxide was added to this methanol solution so that the amount of sodium hydroxide was 0.003 mol per 1 mol of polyvinyl acetate, and saponification was carried out at 40°C. The solvent was removed by distillation, and the resulting mixture was dried to obtain a powder of partially saponified polyvinyl acetate. The obtained powdery partially saponified polyvinyl acetate was fed into a twin-screw extruder using a feeder and kneaded at room temperature to less than 185°C. While kneading was carried out under these conditions, an aqueous hydrogen peroxide solution (concentration: 30% by mass) was fed through an inlet provided in the barrel and mixed with the partially saponified polyvinyl acetate. The amount of hydrogen peroxide added was adjusted to 0.3 parts by mass per 100 parts by mass of polyvinyl acetate. After adding the aqueous hydrogen peroxide solution, the mixture was melt-kneaded at a heating temperature of 199°C for 6 minutes to obtain a vinyl alcohol polymer according to the present invention. The vinyl alcohol polymer was extruded into strands using an extruder, cooled in air, and then cut with a strand cutter to obtain resin particles S4 made of the vinyl alcohol polymer. The S4 was subjected to various evaluations as described below, and the results are shown in Table 1.

[0053] Example 4 A reactor equipped with a thermometer, stirrer, and condenser was charged with 100 parts by weight of vinyl acetate monomer and 40 parts by weight of methanol. Nitrogen gas was blown in for 30 minutes to replace the atmosphere, and the reactor was then heated to 60°C for 30 minutes. Next, 0.03 parts by weight of 2-ethylhexyl peroxydicarbonate, a polymerization initiator, was added, and the reaction was allowed to proceed at 60°C for 4 hours. After the reaction time, the reaction solution was cooled. The conversion rate was measured after cooling and found to be 40%. Subsequently, the remaining vinyl acetate monomer was removed together with methanol under reduced pressure while adding additional methanol, yielding a methanol solution containing 50% by weight of polyvinyl acetate. A methanol solution of sodium hydroxide was added to this methanol solution so that the amount of sodium hydroxide was 0.003 mol per 1 mol of polyvinyl acetate, and saponification was carried out at 40°C. The solvent was removed by distillation, and the resulting mixture was dried to obtain a powder of partially saponified polyvinyl acetate. The obtained powdery partially saponified polyvinyl acetate was fed into a twin-screw extruder using a feeder and kneaded at room temperature to less than 185°C. While kneading was carried out under these conditions, an aqueous hydrogen peroxide solution (concentration: 30% by mass) was fed through an inlet provided in the barrel and mixed with the partially saponified polyvinyl acetate. The amount of hydrogen peroxide added was adjusted to 0.6 parts by mass per 100 parts by mass of polyvinyl acetate. After adding the aqueous hydrogen peroxide solution, the mixture was melt-kneaded at a heating temperature of 193°C for 6 minutes to obtain a vinyl alcohol polymer according to the present invention. The vinyl alcohol polymer was extruded into strands using an extruder, cooled in air, and then cut with a strand cutter to obtain resin particles S5 made of a vinyl alcohol polymer. The S5 was subjected to various evaluations described below, and the results are shown in Table 1.

[0054] Example 5 A reactor equipped with a thermometer, stirrer, and condenser was charged with 100 parts by weight of vinyl acetate monomer and 40 parts by weight of methanol. Nitrogen gas was blown in for 30 minutes to replace the atmosphere, and the reactor was then heated to 60°C for 30 minutes. Next, 0.03 parts by weight of 2-ethylhexyl peroxydicarbonate, a polymerization initiator, was added, and the reaction was allowed to proceed at 60°C for 4 hours. After the reaction time, the reaction solution was cooled. The conversion rate was measured after cooling and found to be 40%. Subsequently, the remaining vinyl acetate monomer was removed together with methanol under reduced pressure while adding additional methanol, yielding a methanol solution containing 50% by weight of polyvinyl acetate. A methanol solution of sodium hydroxide was added to this methanol solution so that the amount of sodium hydroxide was 0.003 mol per 1 mol of polyvinyl acetate, and saponification was carried out at 40°C. The solvent was removed by distillation, and the resulting mixture was dried to obtain a powder of partially saponified polyvinyl acetate. The obtained powdery partially saponified polyvinyl acetate was fed into a twin-screw extruder using a feeder and kneaded at room temperature to less than 185°C. While kneading was carried out under these conditions, an aqueous hydrogen peroxide solution (concentration: 30% by mass) was fed through an inlet provided in the barrel and mixed with the partially saponified polyvinyl acetate. The amount of hydrogen peroxide added was adjusted to 0.44 parts by mass per 100 parts by mass of polyvinyl acetate. After supplying the aqueous hydrogen peroxide solution, the mixture was melt-kneaded at a heating temperature of 210°C for 6 minutes to obtain a vinyl alcohol polymer according to the present invention. The vinyl alcohol polymer was extruded into strands using an extruder, cooled in air, and then cut with a strand cutter to obtain resin particles S6 made of a vinyl alcohol polymer. The S6 was subjected to various evaluations as described below, and the results are shown in Table 1.

[0055] Example 6 A reactor equipped with a thermometer, stirrer, and condenser was charged with 100 parts by weight of vinyl acetate monomer and 40 parts by weight of methanol. Nitrogen gas was blown in for 30 minutes to replace the atmosphere, and the reactor was then heated to 60°C for 30 minutes. Next, 0.03 parts by weight of 2-ethylhexyl peroxydicarbonate, a polymerization initiator, was added, and the reaction was allowed to proceed at 60°C for 4 hours. After the reaction time, the reaction solution was cooled. The conversion rate was measured after cooling and found to be 40%. Subsequently, the remaining vinyl acetate monomer was removed together with methanol under reduced pressure while adding additional methanol, yielding a methanol solution containing 50% by weight of polyvinyl acetate. A methanol solution of sodium hydroxide was added to this methanol solution so that the amount of sodium hydroxide was 0.003 mol per 1 mol of polyvinyl acetate, and saponification was carried out at 40°C. The solvent was removed by distillation, and the resulting mixture was dried to obtain a powder of partially saponified polyvinyl acetate. The obtained powdery partially saponified polyvinyl acetate was fed into a twin-screw extruder using a feeder and kneaded at room temperature to less than 185°C. While kneading was carried out under these conditions, an aqueous hydrogen peroxide solution (concentration: 30% by mass) was fed through an inlet provided in the barrel and mixed with the partially saponified polyvinyl acetate. The amount of hydrogen peroxide added was adjusted to 0.8 parts by mass per 100 parts by mass of polyvinyl acetate. After adding the aqueous hydrogen peroxide solution, the mixture was melt-kneaded at a heating temperature of 209°C for 6 minutes to obtain a vinyl alcohol polymer according to the present invention. The vinyl alcohol polymer was extruded into strands using an extruder, cooled in air, and then cut with a strand cutter to obtain resin particles S7 made of a vinyl alcohol polymer. The S7 was subjected to various evaluations as described below, and the results are shown in Table 1.

[0056] (Comparative Example 1) The vinyl alcohol polymer "Alcotex B72" (sample name C1) manufactured by Synthomer Co., Ltd. was used to carry out the various evaluations described below. The results are shown in Table 2.

[0057] (Comparative Example 2) Various evaluations described below were carried out using a vinyl alcohol polymer, "Kuraray L8" (sample name C2) manufactured by Kuraray Co., Ltd. The results are shown in Table 2.

[0058] (Comparative Example 3) A reactor equipped with a thermometer, stirrer, and condenser was charged with 100 parts by weight of vinyl acetate monomer and 20 parts by weight of methanol. Nitrogen gas was blown in for 30 minutes to replace the atmosphere, and the reactor was then heated to 60°C for 30 minutes. Next, 0.01 parts by weight of 2-ethylhexyl peroxydicarbonate, a polymerization initiator, was added, and the reaction was allowed to proceed at 64°C for 4.5 hours. After the reaction time, the reaction solution was cooled. The conversion rate was measured after cooling and found to be 52%. Subsequently, the remaining vinyl acetate monomer was removed together with methanol under reduced pressure while adding additional methanol, yielding a methanol solution containing 53% by weight of polyvinyl acetate. A methanol solution of sodium hydroxide was added to this methanol solution so that the amount of sodium hydroxide was 0.015 mol per 1 mol of polyvinyl acetate, and saponification was carried out at 42°C. The solvent was distilled off, and the mixture was dried to obtain a powder of partially saponified polyvinyl acetate. The obtained powdery partially saponified polyvinyl acetate was fed into a twin-screw extruder using a feeder and kneaded at room temperature to 165°C. While kneading was carried out under these conditions, glycerin (concentration: 98% by mass) was fed through an inlet provided in the barrel and mixed with the partially saponified polyvinyl acetate. The amount of glycerin added was adjusted to 9.3 parts by mass per 100 parts by mass of polyvinyl acetate. After adding glycerin, the mixture was melt-kneaded at a heating temperature of 180°C for 4 minutes to obtain a vinyl alcohol polymer. The vinyl alcohol polymer was extruded into strands using an extruder, air-cooled, and then cut with a strand cutter to obtain resin particles C3 made of a vinyl alcohol polymer. C3 was used to perform various evaluations described below. The results are shown in Table 2.

[0059] Comparative Example 4 A reactor equipped with a thermometer, stirrer, and condenser was charged with 100 parts by weight of vinyl acetate monomer and 40 parts by weight of methanol. Nitrogen gas was blown in for 30 minutes to replace the atmosphere, and the reactor was then heated to 60°C for 30 minutes. Next, 0.03 parts by weight of 2-ethylhexyl peroxydicarbonate, a polymerization initiator, was added, and the reaction was allowed to proceed at 60°C for 4 hours. After the reaction time, the reaction solution was cooled. The conversion rate was measured after cooling and found to be 40%. Subsequently, the remaining vinyl acetate monomer was removed together with methanol under reduced pressure while adding additional methanol, yielding a methanol solution containing 50% by weight of polyvinyl acetate. A methanol solution of sodium hydroxide was added to this methanol solution so that the amount of sodium hydroxide was 0.003 mol per 1 mol of polyvinyl acetate, and saponification was carried out at 40°C. The solvent was removed by distillation, and the resulting mixture was dried to obtain a powder of partially saponified polyvinyl acetate. The obtained powdery partially saponified polyvinyl acetate was fed into a twin-screw extruder ("BTN-90" manufactured by Plastics Engineering Research Institute) using a feeder and kneaded at room temperature to less than 220°C. While kneading was carried out under these conditions, an aqueous hydrogen peroxide solution (concentration: 30% by mass) was fed through an inlet provided in the barrel and mixed with the partially saponified polyvinyl acetate. The amount of hydrogen peroxide added was adjusted to 1.2 parts by mass per 100 parts by mass of polyvinyl acetate. After adding an aqueous hydrogen peroxide solution, the mixture was melt-kneaded at a heating temperature of 255°C for 8 minutes to obtain a vinyl alcohol polymer. The vinyl alcohol polymer was extruded into strands using an extruder, cooled in air, and then cut with a strand cutter to obtain resin particles C4 made of a vinyl alcohol polymer. Resin particles C4 contained a large amount of undissolved matter, making various measurements difficult.

[0060] [Evaluation method] (Saponification degree) The test was carried out in accordance with JIS K6726. (Block Character) The measurement was carried out according to the method described in the specification, in accordance with the method described in Macromolecules, 1982, 15, 1071.

[0061] (Ratio of di-chains / tri-chains of remaining ester groups and ratio of di-chains / tri-chains of hydroxyl groups) 400MHz at room temperature for a 1.0wt% DMSO-d6 solution of the target sample 1 The ratio was calculated from the integral ratio of each peak in H-NMR measurement. Specifically, it was calculated using the following formula: The ratio of two-chain / three-chain remaining ester groups = ([A A A]+0.5[A A O+O A A]) / ([O A O]+0.5[A A O+O A A]) The ratio of hydroxyl groups from two chains to three chains = ([O O O]+0.5[A O O+O O A]) / ([A O A]+0.5[A O O+O O A]) Here, each [O A O] (relative amount of acetyl groups sandwiched between hydroxyl groups): 5.04-5.19 ppm [A A O+O A A] (relative amount of acetyl groups sandwiched between hydroxyl and acetyl groups): 4.90-5.05 ppm [A A A] (relative amount of acetyl groups sandwiched between acetyl groups): 4.69-4.91 ppm [O O O] (relative amount of hydroxyl groups sandwiched between hydroxyl groups): 3.75-4.15 ppm [A O O+O O A] (relative amount of hydroxyl groups between hydroxyl groups and acetyl groups): 3.60-3.76 ppm [A O A] (relative amount of hydroxyl groups sandwiched between acetyl groups): 3.34-3.61 ppm means.

[0062] (Molecular weight (Mw, Mn), molecular weight distribution Mw / Mn) The molecular weight and molecular weight distribution were calculated by gel permeation chromatography (GPC). Polyethylene oxide (19K) was used as the standard sample, and a SOLDEX SB804 column (two columns connected together) + SOLDEX 802.5 was used. Water was used as the solvent, with an injection volume of 100 μL and a solvent flow rate of 1.0 mL / min. The molecular weight distribution was analyzed using the analysis software Omni SEC DATA based on the signals from the light scattering detector, RI detector, and viscosity detector.

[0063] ( 1 H-NMR measurement) 1 H-NMR was performed using a Bruker 400 MHz instrument. The sample was a 5% by mass solution of deuterated DMSO. Measurements were performed using an exponential function (0.2 Hz), 1024 (Prodigy probe) or 10,000 (standard probe) integration, a 1-second delay, and a 12-microsecond pulse interval, with the DMSO peak (2.49 ppm) as the reference. The above sample (S1 、S3 ~S7, C1~C3) 1 The H-NMR spectra are shown in Figures 1 to 3. 1 The enlarged H-NMR spectra are shown in Figures 4 to 6. 1 The integral values (a) to (e) in the H-NMR spectrum are shown in the figure.

[0064] (UV absorbance) A 0.1% by mass aqueous solution of a vinyl alcohol polymer was prepared, and the absorbance at 280 nm and 320 nm was measured using an Evolution 600 UV-Vis Spectrophotometer (Thermo Fisher, Pittsburgh, PA, USA).

[0065] (viscosity) A 4% by mass aqueous solution of the vinyl alcohol polymer was prepared, and the viscosity was measured at 20°C using a Brookfield viscometer (model LVDV-II+Pro) with a #18 spindle at 100 rpm.

[0066] (Percentage of particles with a particle diameter of 1.7 mm or more) Each sample was sieved to assess the proportion of particles with a particle size of 1.7 mm or more.

[0067] (yellowness) The yellowness index (YI) was determined in accordance with ASTM standard D1925 by preparing a 4% by mass aqueous solution of the vinyl alcohol polymer.

[0068] [Production and evaluation of polyvinyl chloride] Vinyl alcohol polymer S1 、S3 Polyvinyl chloride was produced as follows using each of S1 to S7 and C1 to C4 as a dispersant, and various evaluations were carried out. (Production of polyvinyl chloride) Polymerization was carried out in a 200 L reactor equipped with a dual Pfaudler impeller. 100 kg of water and a vinyl alcohol polymer (PVA) from each Example or Comparative Example as a dispersant were added so that the concentration was 400 ppm relative to the vinyl chloride monomer, and the polymerization vessel was then depressurized to remove air. Next, 70 kg of vinyl chloride monomer, 150 ppm of t-butyl peroxyneodecanate relative to the vinyl chloride monomer, and 385 ppm of cumyl peroxyneodecanate relative to the vinyl chloride monomer were added. Polymerization was carried out at 57°C with stirring at 450 rpm, and the pressure in the polymerization vessel was 7.0 kg / cm. 2 When the temperature dropped to 0°C, the unreacted vinyl chloride monomer was recovered, the contents were taken out, and dehydrated and dried to obtain polyvinyl chloride. Furthermore, separately from the above, polyvinyl chloride was obtained in the same manner as above, except that the amount of vinyl alcohol polymer added was adjusted to 500 ppm relative to the vinyl chloride monomer. The polyvinyl chloride obtained was evaluated as follows.

[0069] (bulk density) The bulk density (g / cm) of the polyvinyl chloride produced in each example and comparative example 3) was measured in accordance with JIS K 6721. The bulk density was measured for both polyvinyl chloride produced using 400 ppm of vinyl alcohol polymer and polyvinyl chloride produced using 500 ppm of vinyl alcohol polymer, and the data for the higher bulk density was used and shown in the table.

[0070] (Average particle size) The average particle size (μm) of polyvinyl chloride (PVC) produced in each example and comparative example was measured using a particle size distribution analyzer. The average particle size was measured for both polyvinyl chloride produced using 400 ppm of vinyl alcohol polymer and polyvinyl chloride produced using 500 ppm of vinyl alcohol polymer.

[0071] (The occurrence of mamako) The polyvinyl chloride produced in each of the Examples and Comparative Examples was visually inspected for the occurrence of this defect.

[0072] [Table 1]

[0073] [Table 2]

[0074] It was found that polyvinyl chloride produced using the vinyl alcohol polymers of each Example satisfying the requirements of the present invention as dispersants for polyvinyl chloride suspension polymerization had an average particle size of 130 to 180 μm, which was within the appropriate range, and had a high bulk density. On the other hand, polyvinyl chloride produced using the vinyl alcohol polymers of Comparative Examples which do not satisfy the requirements of the present invention as dispersants for polyvinyl chloride suspension polymerization either had low bulk densities or could not be evaluated.

Claims

1. １ In a H-NMR spectrum, when the sum of the following integrals (a) to (e) is taken as 100, the integral (a) is 1 to 8, the integral (b) is 30 to 65, the integral (c) is 30 to 45, the integral (d) is 0.8 to 8, and the integral (e) is 0.8 to 10, and the vinyl alcohol polymer is represented by the following formula (1), which has a structural unit having a carbonyl group and a double bond, a structural unit having a residual ester group, and a structural unit having a hydroxyl group. (a) Integrated value of the peak observed at 5.70 to 5.96 ppm (b) Integrated value of the peak observed at 5.97 to 6.63 ppm (c) Integrated value of the peak observed at 6.64 to 7.55 ppm (d) Integrated value of the peak observed at 7.56 to 7.81 ppm (e) Integrated value of the peak observed at 7.82 to 8.04 ppm 【Chemical 1】 u1 is a structural unit having a carbonyl group and a double bond, u2 is a structural unit having a residual ester group, and u3 is a structural unit having a hydroxyl group. In the above formula, OCOR is a residual ester group (O—C(═O)R), and R is a hydrogen atom or an alkyl group having 1 to 20 carbon atoms. x, y, and z represent the mole fraction of each structural unit in the polymer, where x + y + z = 1, x, y, and z are each 0 to 1, none of x, y, and z is 0, and n is 1 to 5.

2. 2. The vinyl alcohol polymer according to claim 1, wherein the degree of saponification is 65 to 80 mol%, the block character of the residual ester group is 0.45 to 0.62, and the ratio a1 / a2 of the absorbance a1 of a 0.1 mass% aqueous solution at a wavelength of 280 nm to the absorbance a2 of the aqueous solution at a wavelength of 320 nm is 1.6 or less.

3. 3. The vinyl alcohol polymer according to claim 1, wherein the ratio of the weight average molecular weight Mw to the number average molecular weight Mn (Mw / Mn) is 2.6 to 14.

4. 4. The vinyl alcohol polymer according to claim 1, wherein the di-chain / tri-chain ratio of the residual ester groups is 0.7 to 1.3, and the di-chain / tri-chain ratio of the hydroxyl groups is 2.0 to 3.

5.

5. The vinyl alcohol polymer according to any one of claims 1 to 4, wherein the residual ester group is an acetoxy group.

6. The vinyl alcohol polymer according to any one of claims 1 to 5, wherein a 4% by mass aqueous solution has a viscosity of 5 to 9 cP.

7. The vinyl alcohol polymer according to any one of claims 1 to 6, wherein the yellowness index (YI) of a 4% by mass aqueous solution is 30 to 80.

8. The vinyl alcohol polymer according to any one of claims 1 to 7, wherein when an aqueous solution prepared by dissolving the vinyl alcohol polymer at a concentration of 7% by mass at 5°C for 12 hours is filtered through a 200-mesh filter, less than 0.1% by weight of components remain on the filter as undissolved substances.

9. The vinyl alcohol polymer according to any one of claims 1 to 8, which is used as a dispersant for suspension polymerization of polyvinyl chloride.

10. The method for producing a vinyl alcohol polymer according to any one of claims 1 to 9, comprising at least the following steps (1) to (3): Step (1) Polymerizing vinyl ester monomers to produce polyvinyl ester Step (2) saponifying the polyvinyl ester to produce a partially saponified polyvinyl ester. Step (3) A step of melt-kneading the partially saponified polyvinyl ester at a heating temperature of 185 to 250°C for a heating time of 1 to 10 minutes.

11. 11. The method for producing a vinyl alcohol polymer according to claim 10, wherein the melt-kneading in the step (3) is carried out in the presence of an oxidizing agent, and the amount of the oxidizing agent is 2 parts by mass or less per 100 parts by mass of the polyvinyl ester.

12. Resin particles comprising the vinyl alcohol polymer according to any one of claims 1 to 9.

13. The resin particles according to claim 12, wherein 95% by weight or more of the particles have a particle diameter of 1.7 mm or more.

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