JPH0586963B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to polyvinyl alcohol (hereinafter referred to as
Abbreviated as PVA. ) type polymer, and particularly relates to a method for manufacturing a PVA type polymer with little coloring. (Conventional technology) PVA is known as a typical water-soluble polymer.
Fibers, films, molded products, adhesives, fiber processing agents,
It is used in a wide range of fields such as emulsifiers and suspending agents. Due to the quality of fibers, films, molded products, etc.
It is required that there is no coloration caused by raw materials. Furthermore, when PVA is used as an aqueous solution, such as laundry starch or office starch, the aqueous solution is required to be colorless and transparent. Conventionally, PVA is generally produced by saponifying vinyl ester polymers, and industrially, vinyl acetate is solution polymerized in an alcohol solvent such as methanol, and after removing unreacted vinyl acetate, PVA is produced by saponifying vinyl ester polymers. , an alkali such as caustic soda is added to an alcoholic solution of the polymer, saponified by an alcoholysis reaction, dried and pulverized, and then sold as a powdered product. Vinyl ester polymerization is generally carried out by radical polymerization. As polymerization initiators used in solution polymerization of vinyl esters, azo polymerization initiators and organic peroxide polymerization initiators are generally used. Organic peroxides such as benzoyl peroxide are sensitive to temperature and impact and require extreme care when handling, so azo polymerization initiators are mainly used. Examples of azo polymerization initiators include 2,2'-azohisisobutyronitrile, 2,
Cyano group-containing types such as 2'-azobis-2,4-dimethylvaleronitrile are known. However, as described above, PVA obtained by the known production method has a yellowish coloration, which is particularly noticeable in the case of PVA with a low degree of polymerization. Methods for reducing the coloring of PVA include adding an organic acid such as oxalic acid during the polymerization of vinyl ester (Japanese Patent Publication No. 1644-1973) or adding pyrophosphoric acid (Japanese Patent Publication No. 47-24533). A method for preventing the alcoholysis of vinyl esters, a method for bleaching PVA by adding sodium hypochlorite, etc. during the saponification process (Japanese Patent Publication No. 36-19591),
A method of adding sulfuric acid or the like to improve the thermal stability in the drying process (Japanese Patent Publication No. 52-26589), a method of drying using a moist heat drying method (Japanese Patent Publication No. 17385-1983), etc. have been proposed. However, with these methods, the effects are small, the addition of chemicals causes corrosion of equipment, and when PVA is used in the reaction system, the added chemicals cause side reactions and cannot be used. There was a problem. Furthermore, the coloring of PVA itself and the coloring of its aqueous solution do not necessarily correspond, and the current situation is that even if the coloring of PVA decreases, the coloring of the aqueous solution may not decrease. In addition to the above-mentioned azo polymerization initiators, dimethyl 2,2'-azobisisobutyrate is also known (in "Vinyl Acetate Resins" edited by Ichiro Sakurada).
P71 Kobunshi Kankankai Publishing) has never produced PVA by polymerizing vinyl ester using an azo polymerization initiator that does not contain cyano groups and saponifying the polymer. (Problems to be Solved by the Invention) The present invention does not cause corrosion of equipment due to the addition of chemicals, does not limit the field of use, does not require significant improvement of existing equipment, and, of course, does not require PVA itself. The purpose of this invention is to provide a method for producing PVA that can significantly reduce the coloring of its aqueous solution. (Means for Solving the Problems) As a result of intensive research to achieve the above object, the present inventors surprisingly found that when vinyl ester is polymerized, an azo-based and cyano-based By using a polymerization initiator that does not contain cyano groups, the coloring of PVA and its aqueous solution obtained by saponifying, drying and pulverizing vinyl ester polymers is different from that of using an azo polymerization initiator that contains cyano groups. It was discovered that the coloring of PVA and its aqueous solution was significantly reduced compared to similarly obtained PVA and its aqueous solution, and the present invention was achieved. That is, the present invention involves polymerizing a vinyl ester using an azo polymerization initiator and saponifying the resulting polymer to produce a PVA polymer. PVA characterized by using a polymerization initiator that does not contain
The gist of this paper is the method for producing the polymer. Examples of the azo-based polymerization initiator that does not contain a cyano group used in the present invention include dimethyl 2,2'-azobisisobutyrate, (1-phenylethyl)azodiphenylmethane, 2,2 ′−
Examples include azobis(2,4,4-trimethylpentane), but from the viewpoint of degradability of the polymerization initiator, dimethyl 2,2'-azobisisobutyrate, (1
-phenylethyl)azodiphenylmethane is preferred. Vinyl esters used in the present invention include:
Examples include vinyl formate, vinyl acetate, vinyl propionate, and vinyl acetate is industrially advantageous. For the vinyl ester polymerization in the present invention, for example, known bulk, solution, suspension or emulsion polymerization may be employed, but solution polymerization is industrially advantageous. Solvents for solution polymerization include alcohols such as methanol and ethanol, methyl acetate,
Esters such as ethyl acetate, benzene, etc. can be used, but methanol or ethanol is industrially advantageous. The degree of polymerization of the polymer can be arbitrarily adjusted by adjusting the ratio of vinyl ester and solvent in polymerization. The amount of the azo polymerization initiator that does not contain a nitrile group to be added during polymerization in the present invention is not particularly limited, but is preferably
It is 0.0005 to 0.5 mol%. Known methods are appropriately employed for the temperature and stirring conditions during polymerization and for removing unreacted vinyl ester after polymerization. During polymerization, monomers other than vinyl esters, such as maleic acid, itaconic acid, acrylic acid, acrylic esters, acrylamide, vinyl sulfonate, allyl acetate, alkyl vinyl ether, hydroxyalkyl vinyl ether, α-olefin, etc., may be used as necessary. like, generally
It is possible to copolymerize materials used for modifying PVA. The method of saponifying the polymer to obtain PVA may be any known method and is not particularly limited, but industrially, caustic soda, caustic potash, ammonia, etc. are added to a solution of the polymer in alcohol such as methanol or ethanol. Advantageous is a method of alcoholysis by adding an alkali or an acid such as hydrochloric acid or sulfuric acid. Known methods can be used for drying and pulverizing the saponified product. (Example) Next, the present invention will be specifically explained using Examples and Comparative Examples. Note that "parts" in the examples indicate "parts by weight" unless otherwise specified. Example 1 In a reaction vessel equipped with a stirrer, a thermometer and a reflux condenser, 600 parts of vinyl acetate and 300 parts of methanol are added.
After purging the system with nitrogen while stirring, the internal temperature was raised to 60°C. In this system, dimethyl 2,2'-azobisisobutyrate (manufactured by Wako Pure Chemical Industries, Ltd.)
100 parts of a methanol solution containing 0.8 parts was added to initiate polymerization. Polymerization was stopped after 6 hours. The solid content concentration in the system at the time of termination of polymerization was 48%, and the polymerization yield was 80%. By introducing methanol vapor,
After expelling unreacted vinyl acetate monomer, a 45% methanol solution of the polymer was obtained. While stirring 100 parts of this methanol solution at 40°C, 16 parts of a methanol solution containing 2.0 parts of caustic soda was added thereto, and after saponification reaction for 2 hours, excess caustic soda was neutralized with acetic acid. . The resulting white gel was crushed and dried at 90°C for 2 hours under a nitrogen stream to reduce the volatile content to 2.5%.
Got PVA. The degree of saponification of PVA was 98.5 mol%, and the degree of polymerization was 870. The whiteness (W value) and degree of coloration (ΔN value) (measured using a color difference meter manufactured by JEOL Ltd., Model Z-1001DP) were measured for the obtained 60-mesh pass product of PVA. The W value was 96.3 and the ΔN value was 1.2. In addition, the chromaticity (JIS K
- Conforms to 0101. ) was 4. in this way,
PVA and its aqueous solution showed little coloring. The results are shown in Table 1. Comparative Example 1 PVA was obtained in the same manner as in Example 1 except that 2,2'-azobisisobutyronitrile was used instead of dimethyl 2,2'-azobisisobutyrate. The polymerization yield was 82%. Also, obtained
The volatile content of PVA is 2.8%, the degree of saponification is 98.6 mol%,
The degree of polymerization was 850. As a result of measuring the whiteness and degree of coloration of the obtained PVA in the same manner as in Example 1, the W value was
89.9, and the ΔN value was 8.3. Further, the chromaticity of the 20% aqueous solution was 15. Thus, both PVA and the aqueous solution had a high degree of coloring. The results are shown in Table 1. Example 2 In the same reactor as used in Example 1,
600 parts of vinyl propionate, 300 parts of methanol, and 6 parts of lauryl vinyl ether were charged, and further, 100 parts of a methanol solution containing 0.5 part of (1-phenylethyl)azodiphenylmethane was added to initiate polymerization. Polymerization was stopped after 6 hours,
Next, the same procedure as in Example 1 was carried out to obtain modified PVA. The polymerization yield was 75%. In addition, the volatile content of the obtained modified PVA was 2.9%, the degree of saponification was 98.1 mol%,
The degree of polymerization was 790. The whiteness and degree of coloration of the obtained modified PVA were measured in the same manner as in Example 1, and the W value was
95.8, and the ΔN value was 2.1. The chromaticity of the 20% aqueous solution was 6. In this way, there was little coloration in either case. The results are shown in Table 1. Comparative Example 2 Instead of using 0.5 part of (1-phenylethyl)azodiphenylmethane, 2,2'-azobis2,
A modified PVA was obtained in the same manner as in Example 2 except that 0.3 part of 2,4-dimethylvaleronitrile was used.
The polymerization yield was 76%. Also, the resulting denaturation
The volatile content of PVA is 2.4%, the degree of saponification is 98.3 mol%,
The degree of polymerization was 800. The whiteness and degree of coloration of the obtained modified PVA were measured in the same manner as in Example 1, and the W value was
88.1, and the ΔN value was 10.3. Further, the chromaticity of the 20% aqueous solution was 20. In this way, the degree of coloration was high in all cases. The results are shown in Table 1. Example 3 In the same reactor as used in Example 1,
650 parts of vinyl acetate and 250 parts of ethanol were charged, and after purging the system with nitrogen, the internal temperature was raised to 67°C. To this system, 100 parts of an ethanol solution containing 0.4 parts of dimethyl 2,2'-azobisisobutyrate was added to initiate polymerization. After 5 hours, polymerization was stopped. The solid content in the system at the time of polymerization termination was 59%, and the polymerization yield was
It was 90%. This solution was dried under reduced pressure to remove unreacted vinyl acetate monomer with ethanol, and the obtained polymer was redissolved in methanol to obtain a 40% methanol solution. This methanol solution 100
While stirring the mixture at 40°C, add caustic soda to it.
15 parts of a methanol solution containing 0.14 parts of water and 0.8 parts of water were added, and after reaction for 30 minutes, excess caustic soda was neutralized with acetic acid. The obtained white gel was crushed and dried in the same manner as in Example 1. The volatile content of the obtained PVA was 3.1
%, saponification degree was 80.5 mol%, and polymerization degree was 410. The whiteness and degree of coloration of the obtained PVA were measured in the same manner as in Example 1, and the results are shown in Table 1. The chromaticity of the 20% aqueous solution was also measured in the same manner, and the results are shown in Table 1. In both cases, there was little coloring. Comparative Example 3 PVA was obtained in the same manner as in Example 3, except that 2,2'-azobisisobutyronitrile was used instead of dimethyl 2,2'-azobisisobutyrate. The polymerization yield was 89%. Also, obtained
The volatile content of PVA is 2.9%, the degree of saponification is 80.3 mol%,
The degree of polymerization was 400. The whiteness and degree of coloration of the obtained PVA were measured in the same manner as in Example 1, and the results are shown in Table 1. The chromaticity of the 20% aqueous solution was also measured in the same manner, and the results are shown in Table 1. In all cases, the degree of coloration was high.

【table】

[Table] Here, the smaller the value of whiteness (W value), the more
Alternatively, the greater the degree of coloration (ΔN value), the greater the degree of coloration. Furthermore, the greater the chromaticity value of the 20% aqueous solution, the greater the degree of coloring. (Effects of the Invention) According to the present invention, a PVA-based polymer with less coloring can be obtained without impairing the yield or the physical properties of the obtained polymer compared to conventional methods. Also,
An aqueous solution with little coloring can be prepared from the obtained PVA-based polymer. Therefore, the PVA polymer obtained by the method of the present invention can be used in applications that require no coloring, such as fibers, films, and molded products, and in applications such as laundry starch and office starch. It is especially suitable for applications where the aqueous solution is required to be nearly colorless and transparent.
It goes without saying that it can also be used in applications where other polymers are used.

Claims (1)

[Claims] 1. When a vinyl ester is polymerized using an azo polymerization initiator and the obtained polymer is saponified to produce a polyvinyl alcohol polymer, as a polymerization initiator, an azo polymer and A method for producing a polyvinyl alcohol polymer, characterized by using a polymerization initiator that does not contain a cyano group. 2. The manufacturing method according to claim 1, wherein the vinyl ester is vinyl acetate. 3. The production method according to claim 1, wherein the azo-based polymerization initiator that does not contain a cyano group is dimethyl 2,2'-azobisisobutyrate.