Search

JP-7856653-B2 - Polyvinyl alcohol-based resin, dispersant for suspension polymerization, method for producing vinyl polymer particles, and method for producing polyvinyl alcohol-based resin

JP7856653B2JP 7856653 B2JP7856653 B2JP 7856653B2JP-7856653-B2

Inventors

  • 藤田 和真

Assignees

  • 株式会社クラレ

Dates

Publication Date
20260511
Application Date
20220726
Priority Date
20210730

Claims (7)

  1. The polymer component contains virtually only polyvinyl alcohol. When prepared as a 0.1 mass% aqueous solution, the absorbance Abs 320 at a path length of 10 mm and wavelength of 320 nm is 0.09 or higher. When a 0.1 mass% aqueous solution is prepared, the ratio of the absorbance Abs 320 to the absorbance Abs 370 at a path length of 10 mm and a wavelength of 370 nm (Abs 320 / Abs 370 ) is 4.9 or less. A polyvinyl alcohol-based resin having a total content of divalent and trivalent metal elements of less than 30 μmol/g.
  2. The polyvinyl alcohol-based resin according to claim 1, wherein the above ratio (Abs 320 / Abs 370 ) is 2.0 or greater.
  3. The polyvinyl alcohol-based resin according to claim 1 , wherein the absorbance Abs 320 is less than 0.30.
  4. The polyvinyl alcohol-based resin according to claim 1 , wherein the viscosity at 20°C when prepared as a 4% by mass aqueous solution is 4.5 mPa·s or more and 8.0 mPa·s or less.
  5. A dispersant for suspension polymerization containing a polyvinyl alcohol-based resin according to any one of claims 1 to 4.
  6. A method for producing vinyl polymer particles, comprising the step of suspend polymerization of a vinyl compound using the suspension polymerization dispersant described in claim 5.
  7. The process includes a step of stirring and heating the saponified polyvinyl ester in a container. The above stirring and heating is performed at a temperature of 90°C to 180°C for 350 minutes to 1,300 minutes while circulating gas within the container. A method for producing a polyvinyl alcohol-based resin, wherein the flow rate of the above gas is 2 parts by mass or more and 11 parts by mass or less per hour per 100 parts by mass of the above saponified polyvinyl ester.

Description

The present invention relates to a polyvinyl alcohol-based resin, a dispersant for suspension polymerization, a method for producing vinyl polymer particles, and a method for producing a polyvinyl alcohol-based resin. In the industrial production of vinyl polymers such as polyvinyl chloride, suspension polymerization is widely practiced, in which vinyl compounds such as vinyl chloride are dispersed in an aqueous medium in the presence of a dispersant (sometimes called a dispersion stabilizer), and polymerization is carried out using an oil-soluble catalyst. Generally, factors that govern the quality of vinyl polymers obtained by suspension polymerization of vinyl compounds include polymerization rate, water-monomer ratio, polymerization temperature, type and amount of oil-soluble catalyst, type of polymerization tank, stirring speed of the contents in the polymerization tank, and type of dispersant, but the influence of the type of dispersant is particularly significant. The performance requirements for dispersants used in the suspension polymerization of vinyl compounds include the ability to stably produce vinyl polymer particles with a small amount of additive. Conventionally, dispersants used in the suspension polymerization of vinyl compounds have included cellulose derivatives such as methylcellulose and carboxymethylcellulose, as well as partially saponified polyvinyl alcohol, either alone or in appropriate combinations. Regarding polyvinyl alcohol (hereinafter also referred to as "PVA") used as a dispersant for suspension polymerization, Patent Document 1 describes "a polyvinyl alcohol-based resin having an absorbance (X) of 0.3 or more at a wavelength of 320 nm in the ultraviolet absorption spectrum when it is a 0.1% by weight aqueous solution, and a ratio (Y/X) of the absorbance at a wavelength of 380 nm (Y) to the absorbance at a wavelength of 320 nm (X) of 0.09 or more." International Publication No. 2020/184397 <Polyvinyl alcohol-based resin> The polyvinyl alcohol-based resin (PVA-based resin) of the present invention contains substantially only PVA as a polymer component, has an absorbance Abs 320 of 0.09 or more when it is a 0.1% by mass aqueous solution with a path length of 10 mm and a wavelength of 320 nm, has a ratio of Abs 320 to Abs 370 (Abs 320 / Abs 370 ) of 4.9 or less when it is a 0.1% by mass aqueous solution with a path length of 10 mm and a wavelength of 370 nm, and has a total content of divalent and trivalent metal elements of less than 30 μmol/g. The PVA-based resin has a low content of divalent and trivalent metal elements, and when used as a dispersant for suspension polymerization, it is possible to produce vinyl polymer particles with small particle sizes even with a small amount of additive. The reason why this PVA-based resin can produce vinyl polymer particles with small particle sizes even with a small amount of additive is not entirely clear, but the following is speculated. PVA, which is generally used as a dispersant for suspension polymerization, has a terminal structure represented as R-CO-(CH=CH) n- (where R is an alkyl group and n is a natural number). The polyene structure in the above terminal structure is formed by a dehydration reaction that occurs when PVA is heat-treated. On the other hand, regarding the absorption spectrum of PVA, the absorption at a wavelength of 320 nm is thought to belong to the -CO-(CH=CH) 3- structure, and the absorption at a wavelength of 370 nm is thought to belong to the -CO-(CH=CH) 4- structure. In other words, in this PVA-based resin, an absorbance Abs 320 of 0.09 or higher, and an absorbance ratio (Abs 320 / Abs 370 ) of 4.9 or lower, means that it has a sufficient amount of -CO-(CH=CH) 3- structure and also a sufficient amount of -CO-(CH=CH) 4- structure. Thus, this PVA-based resin has a large amount of relatively long polyene structures (n=3,4), and as a result, sufficient surfactant activity is generated. Therefore, when used as a dispersant for suspension polymerization, polymerization stability is increased, and it is thought that vinyl polymer particles with small particle sizes can be produced even with a small amount of additive. Furthermore, vinyl polymer particles obtained by using this PVA-based resin as a dispersant for suspension polymerization also have good plasticizer absorption capacity. Furthermore, the PVA-based resin having the above absorption spectrum can be obtained by stirring and heating under predetermined conditions while circulating a gas, as will be described in detail later. This is presumed to be because stirring and heating while circulating a gas facilitates the dehydration reaction described above, resulting in a longer polyene structure. Therefore, by using this method, a good end structure can be introduced by heat treatment without using divalent or trivalent metal salts and hydroxides. For this reason, even though the total content of divalent and trivalent metal elements in this PVA-based