DISPERSION STABILIZER FOR SUSPENSION POLYMERIZATION AND METHOD FOR PRODUCING VINYL RESIN

Abstract

A dispersion stabilizer for suspension polymerization is provided that includes a vinyl alcohol-based polymer (A), wherein a 0.1 mass % concentration aqueous solution of the polymer (A) has an absorbance (a1) of less than 0.25 at a wavelength of 280 nm, the aqueous solution has an absorbance (a2) of less than 0.030 at a wavelength of 320 nm, the polymer (A) has a degree of saponification of not less than 68 mol % and not more than 98 mol %, the polymer (A) has a viscosity-average degree of polymerization of more than 1500 and less than 4500, and the polymer (A) in powder form has a YI value of not less than 5. The dispersion stabilizer is capable of producing a vinyl-based resin that is excellent in polymerization stability, has a small particle size, and has an improved bulk density.

Claims

1. A dispersion stabilizer, comprising a vinyl alcohol-comprising polymer (A), wherein a 0.1 mass % concentration aqueous solution of the polymer (A) has an absorbance (a1) of less than 0.25 at a wavelength of 280 nm, the aqueous solution has an absorbance (a2) of less than 0.030 at a wavelength of 320 nm, the polymer (A) has a degree of saponification of not less than 68 mol % and not more than 98 mol %, the polymer (A) has a viscosity-average degree of polymerization of more than 1500 and less than 4500, and the polymer (A) in powder form has a YI value of not less than 5.

2. The dispersion stabilizer according to claim 1, further comprising a vinyl alcohol-comprising polymer (B), wherein a 0.1 mass % concentration aqueous solution of the polymer (B) has an absorbance (b1) of not less than 0.25 at a wavelength of 280 nm, the aqueous solution has an absorbance (b2) of not less than 0.030 at a wavelength of 320 nm, the polymer (B) has a degree of saponification of not less than 65 mol % and not more than 82 mol %, and the polymer (B) has a viscosity-average degree of polymerization of not less than 500 and not more than 1500.

3. The dispersion stabilizer according to claim 2, wherein a mass ratio (A/B) of the vinyl alcohol-comprising polymer (A) to the vinyl alcohol-comprising polymer (B) is not less than 6/94 and not more than 60/40.

4. A method of producing a vinyl-based resin, comprising suspension-polymerizing a vinyl-comprising monomer in an aqueous medium with the dispersion stabilizer according to claim 1.

5. The method of producing a vinyl-based resin according to claim 4, wherein a mass ratio (vinyl-comprising monomer/aqueous medium) of the vinyl-comprising monomer to the aqueous medium is not less than 0.75.

6. The method of producing a vinyl-based resin according to claim 4, wherein the vinyl-comprising monomer is vinyl chloride.

7. A method of producing a vinyl-based resin, comprising suspension-polymerizing a vinyl-comprising monomer in an aqueous medium with the dispersion stabilizer according to claim 2.

8. A method of producing a vinyl-based resin, comprising suspension-polymerizing a vinyl-comprising monomer in an aqueous medium with the dispersion stabilizer according to claim 3.

9. The method of producing a vinyl-based resin according to claim 5, wherein the vinyl-comprising monomer is vinyl chloride.

Description

EXAMPLES

[0040] The present invention is described below in further detail with reference to Examples. In Examples and Comparative Examples below, “part(s)” and “%” denote, unless otherwise specified, part(s) by mass and mass %, respectively.

[0041] PVAs obtained by Production Examples below were evaluated in accordance with the following methods.

[Viscosity-Average Degree of Polymerization of PVA]

[0042] A viscosity-average degree of polymerization of each PVA was calculated by substantially completely saponifying the PVA, followed by acetylation to make a vinyl ester-based polymer, thereby measuring limiting viscosity in an acetone solution using Nakajima's equation (Akio Nakajima, “Kobunshi Kagaku” (Polymer Chemistry) 6 (1949)).

[Degree of Saponification of PVA]

[0043] A degree of saponification of each PVA was obtained by the method according to JIS K6726 (1994).

[Absorbance of Aqueous Solution]

[0044] A 0.1 mass % aqueous PVA solution was prepared to measure absorbances (optical path length of 10 mm) at wavelengths of 280 nm and 320 nm using an absorptiometer “UV2100” manufactured by Shimadzu Corporation.

[Yellow Index (YI)]

[0045] Hue of PVA: measured using a powder measurement cell in a color meter “SM-T-H1” manufactured by Suga Test Instruments Co., Ltd.

[Production Examples]

Production of PVA (A1)

[0046] In a polymerization vessel, 1400 parts of vinyl acetate (hereinafter, may be abbreviated as VAc) and 600 parts of methanol were charged and the atmosphere was purged with nitrogen and then heated to the boiling point, followed by adding 0.05% azobisisobutyronitrile and 10 parts of methanol to VAc for polymerization. The polymerization was terminated at a rate of polymerization of 40%, and under a reduced pressure, methanol was added to remove the residual VAc together with the methanol to outside the system to provide a solution of polyvinyl acetate (hereinafter, may be abbreviated as PVAc) in methanol (concentration of 40%). Subsequently, saponification reaction was then initiated using sodium hydroxide as a saponification catalyst at a molar ratio of 0.0047 to PVAc in a 30% solution of PVAc in methanol at a temperature of 40° C. Gelation was found after 23 minutes and the contents were taken out once, followed by pulverization using a mixer. It was returned to 40° C. again and reacted for 1 hour in total of the reaction time at 40° C. After termination of the reaction, it was dried under a reduced pressure to remove methanol, followed by heat treatment at atmospheric pressure in air atmosphere for 1 hour at 80° C., then for 1 hour at 90° C., and further for 4 hours at 120° C. to produce PVA (A1). The PVA (A1) had a viscosity-average degree of polymerization of 1550 and a degree of saponification of 80 mol %, and a 0.1% concentration aqueous solution thereof had the absorbance (a1) of 0.008 at a wavelength at 280 nm and the absorbance (a2) of 0.004 at 320 nm, and the PVA (A1) had a YI value of 41.

Production of PVA (A2-A7, A9, A12-A14)

[0047] PVAs (A2-A7, A9, A12-A14) shown in Table 1 were produced in the same manner as PVA (A1) other than changing the polymerization conditions such as the amounts of vinyl acetate and methanol to be charged, the amount of the initiator used for polymerization, and the target rate of polymerization, the saponification conditions such as the amount of sodium hydroxide, and the heat treatment conditions such as the time and the temperature.

Production of PVA (A8, A10)

[0048] PVAs (A8, A10) shown in Table 1 were produced in the same manner as PVA (A1) other than using acetaldehyde as a chain transfer agent for polymerization in the same manner as the method described in JP 8-283313 A to control the degree of polymerization by the amount to be used and changing the polymerization conditions such as the amounts of vinyl acetate and methanol to be charged, the amount of the initiator used for polymerization, and the target rate of polymerization, the saponification conditions such as the amount of sodium hydroxide, and the heat treatment conditions such as the time and the temperature.

Production of PVA (A11)

[0049] PVA (A11) was obtained without heat treatment in the production procedure of PVA (A1). PVA (A11) was produced in the same manner as PVA (A1) other than not performing heat treatment.

Production of PVA (B1-B3)

[0050] PVAs (B1-B3) shown in Table 1 were produced in the same manner as PVA (A8) other than changing, in the same manner as the method described in JP 8-283313 A, the polymerization conditions such as the amount of acetaldehyde used for polymerization, the amounts of vinyl acetate and methanol to be charged, the amount of the initiator used for polymerization, and the target rate of polymerization, the saponification conditions such as the amount of sodium hydroxide, and the heat treatment conditions such as the time and the temperature.

TABLE-US-00001 TABLE 1 Amount Used Vinyl Alcohol-Based Polymer (A) Vinyl Alcohol-Based Polymer (B) for Suspension Degree Degree Polymerization of Degree of Degree (ppm/ Absorb- Absorb- Saponi- of Absorb- Absorb- Saponi- of Mass Vinyl-Based ance ance fication Polymer- ance ance fication Polymer- Ratio Compound) Type (a1) (a2) YI (mol %) ization Type (b1) (b2) (mol %) ization (A/B) (A) (B) Formulation (A1) 0.008 0.004 41 80 1550 None 100/0  880 0 Example 1 Formulation (A1) 0.008 0.004 41 80 1550 (B1) 0.581 0.444 72 700  27/73 240 640 Example 2 Formulation (A2) 0.008 0.004 39 80 1750 (B1) 0.581 0.444 72 700  27/73 240 640 Example 3 Formulation (A3) 0.008 0.004 41 80 2000 (B1) 0.581 0.444 72 700  27/73 240 640 Example 4 Formulation (A4) 0.009 0.004 38 88 2400 (B1) 0.581 0.444 72 700  27/73 240 640 Example 5 Formulation (A5) 0.008 0.004 39 95 2400 (B1) 0.581 0.444 72 700  27/73 240 640 Example 6 Formulation (A6) 0.005 0.002 9 88 2400 (B1) 0.581 0.444 72 700  27/73 240 640 Example 7 Formulation (A7) 0.013 0.007 60 88 3800 (B1) 0.581 0.444 72 700  27/73 240 640 Example 8 Formulation (A8) 0.202 0.025 14 88 1550 (B1) 0.581 0.444 72 700  27/73 240 640 Example 9 Formulation (A4) 0.009 0.004 38 88 2400 (B2) 0.401 0.196 72 700  27/73 240 640 Example 10 Formulation (A4) 0.009 0.004 38 88 2400 (B3) 0.302 0.079 72 700  27/73 240 640 Example 11 Formulation (A4) 0.009 0.004 38 88 2400 (B1) 0.581 0.444 72 700  9/91 79 801 Example 12 Formulation (A4) 0.009 0.004 38 88 2400 (B1) 0.581 0.444 72 700  55/45 484 396 Example 13 Formulation (A4) 0.009 0.004 38 88 2400 (B1) 0.581 0.444 72 700  5/95 40 840 Example 14 Formulation (A9) 0.008 0.004 40 74 800 (B1) 0.581 0.444 72 700  27/73 240 640 Example 15 Formulation (A10) 0.452 0.201 40 74 800 (B1) 0.581 0.444 72 700  27/73 240 640 Example 16 Formulation (A11) 0.002 0.001 2 80 1550 (B1) 0.581 0.444 72 700  27/73 240 640 Example 17 Formulation (Al2) 0.008 0.004 41 65 2400 (B1) 0.581 0.444 72 700  27/73 240 640 Example 18 Formulation (A13) 0.008 0.004 41 99 2400 (B1) 0.581 0.444 72 700  27/73 240 640 Example 19 Formulation (A14) 0.008 0.004 40 74 5000 (B1) 0.581 0.444 72 700  27/73 240 640 Example 20

Example 1

[0051] In a 5 liter autoclave, 100 parts of a deionized aqueous solution in which PVA (A1) was dissolved in an amount of 880 ppm relative to vinyl chloride were charged, and deionized water was additionally charged to have 1200 parts of deionized water in total. Then, 0.65 parts of a 70% solution of cumyl peroxyneodecanoate in toluene and 1.05 parts of a 70% solution of t-butyl peroxyneododecanoate in toluene were charged in the autoclave. An operation in which nitrogen was introduced into the autoclave to produce a pressure of 0.2 MPa and then the nitrogen was purged was repeated 5 times in total. Inside the autoclave was thus sufficiently purged with nitrogen to remove oxygen, followed by charging of 940 parts of vinyl chloride. The contents in the autoclave were raised in temperature to 57° C. to initiate polymerization of the vinyl chloride monomer with stirring. The pressure in the autoclave was 0.80 MPa at the beginning of the polymerization. Approximately 3.5 hours after the initiation of polymerization, the polymerization was terminated at a pressure in the autoclave of 0.70 MPa and unreacted vinyl chloride monomers were removed. The polymerization reaction product was then taken out and dried at 65° C. for 16 hours to obtain vinyl chloride resin particles. The particles thus obtained were evaluated in the methods below.

(Evaluation of Vinyl Chloride Resin Particles)

[0052] The vinyl chloride resin particles thus obtained were evaluated for (1) an average particle size, (2) a particle size distribution, and (3) a bulk density in accordance with the following methods. Evaluation results are shown in Table 2.

(1) Average Particle Size

[0053] Using Tyler-mesh screens, a particle size distribution was measured by dry screen analysis in accordance with JIS Z8815. From the results, an average particle size was calculated using a Rosin-Rammler plot. Evaluation results are shown in Table 2.

(2) Particle Size Distribution

[0054] In the vinyl chloride polymer particles thus obtained, a content of JIS standard screen 42 mesh-on resin particles was indicated by mass %. Evaluation results are shown in Table 2.

[0055] A: less than 0.5%

[0056] B: not less than 0.5% and less than 1%

[0057] C: not less than 1%

[0058] In the vinyl chloride polymer particles thus obtained, a content of JIS standard screen 60 mesh-on resin particles was indicated by mass %.

[0059] A: less than 5%

[0060] B: not less than 5% and less than 10%

[0061] C: not less than 10%

[0062] Smaller values of the contents of both 42 mesh-on resin particles and 60 mesh-on resin particles indicate to contain fewer coarse particles, to have a sharper particle size distribution, and to have more excellent polymerization stability.

(3) Bulk Density

[0063] A bulk density of the vinyl chloride resin was measured in accordance with JIS K6721. Evaluation results are shown in Table 2.

Example 2

[0064] Suspension polymerization of vinyl chloride was carried out in the same manner as that in Example 1 other than using a deionized aqueous solution in which PVA (A1) (240 ppm based on vinyl chloride) and PVA (B1) (640 ppm based on vinyl chloride) were dissolved, instead of the deionized aqueous solution of PVA (A1), to produce vinyl chloride resin particles. Evaluation results of the vinyl chloride resin particles are shown in Table 2.

Examples 3-14

[0065] Suspension polymerization of vinyl chloride was carried out in the same manner as that in Example 2 other than changing the type and amount of the PVA (A) and the PVA (B) to be used as shown in Table 1 to produce vinyl chloride resin particles. Evaluation results of the vinyl chloride resin particles are shown in Table 2.

Comparative Examples 1-6

[0066] Suspension polymerization of vinyl chloride was carried out in the same manner as that in Example 2 other than changing the type and amount of the PVA (A) and the PVA (B) to be used as shown in Table 1 to produce the PVA (A) and the PVA (B) vinyl chloride resin particles. Evaluation results of the vinyl chloride resin particles are shown in Table 2.

TABLE-US-00002 TABLE 2 Evaluation Result of Vinyl Chloride Resin Particles Vinyl Average Particle Size Chloride Particle Distribution Bulk Monomer/ Size 42 60 Density Formulation Water (μm) mesh on mesh on (g/cc) Example 1 Formulation 940/1200 135.2 B A 0.489 Example 1 Example 2 Formulation 940/1200 124.3 A A 0.491 Example 2 Example 3 Formulation 940/1200 126.7 A A 0.502 Example 3 Example 4 Formulation 940/1200 130.5 A A 0.513 Example 4 Example 5 Formulation 940/1200 131.5 A A 0.546 Example 5 Example 6 Formulation 940/1200 138.4 B A 0.552 Example 6 Example 7 Formulation 940/1200 137.9 A A 0.523 Example 7 Example 8 Formulation 940/1200 127.1 B A 0.565 Example 8 Example 9 Formulation 940/1200 152.9 B A 0.475 Example 9 Example 10 Formulation 940/1200 135.1 A A 0.530 Example 10 Example 11 Formulation 940/1200 139.8 A A 0.520 Example 11 Example 12 Formulation 940/1200 140.9 A A 0.501 Example 12 Example 13 Formulation 940/1200 146.9 A A 0.565 Example 13 Example 14 Formulation 940/1200 152.3 B A 0.471 Example 14 Comparative Formulation 940/1200 182.5 C B 0.432 Example 1 Example 15 Comparative Formulation 940/1200 170.2 C B 0.443 Example 2 Example 16 Comparative Formulation 940/1200 199.2 C B 0.435 Example 3 Example 17 Comparative Formulation 940/1200 Not Capable of Suspension Polymerization due to Example 4 Example 18 Insolubility in Water Comparative Formulation 940/1200 210.2 C C 0.441 Example 5 Example 19 Comparative Formulation 940/1200 Not Capable of Suspension Polymerization due to Example 6 Example 20 Insolubility in Water

[0067] As shown in Table 2, in the cases of using the dispersion stabilizers of PVA (A) that had an absorbance of a 0.1 mass % concentration aqueous solution, a degree of saponification, a viscosity-average degree of polymerization, and a YI value in powder form within predetermined ranges, vinyl chloride resin particles were produced that exhibited very stable polymerization, even in the conditions of a high ratio of vinyl-based monomers liable to cause instability, contained fewer coarse particles, and had a high bulk density (Examples 1-14). In particular, the dispersion stabilizers of the PVA (A) and the PVA (B) had the above properties even more excellent (Examples 2-14). Accordingly, the production method of the present invention has extremely high industrial utility.

[0068] In all the cases of using PVA (A9) with a degree of polymerization of 800 (Comparative Example 1), using PVA (A10) producing a 0.1 mass % concentration aqueous solution with an absorbance (a1) of 0.452 at a wavelength of 280 nm and an absorbance (a2) of 0.201 at a wavelength of 320 nm (Comparative Example 2), and using PVA (A11) having a YI value of 2 (Comparative Example 3), the vinyl chloride resin particles thus obtained had a large particle size and were coarse, had greater 42 mesh-on and 60 mesh-on ratios indicating unstable polymerization, and had a low bulk density.

[0069] Although suspension polymerization of vinyl chloride were attempted using PVA (A12) with a degree of saponification of 65 mol %, PVA (A12) was not dissolved in water possibly because of the low degree of saponification and it was not possible to carry out polymerization (Comparative Example 4). In the case of using PVA (A13) with a degree of saponification of 99 mol %, the vinyl chloride resin particles thus obtained had a large particle size and were coarse, had greater 42 mesh-on and 60 mesh-on ratios indicating unstable polymerization, and had a low bulk density (Comparative Example 5). Although suspension polymerization of vinyl chloride was attempted using PVA (A14) with a viscosity-average degree of polymerization of 5000, PVA (A14) was not dissolved in water possibly because of the low viscosity-average degree of polymerization and it was not possible to carry out polymerization (Comparative Example 6).