JPH0588253B2 - - Google Patents

Description

[Detailed description of the invention]

[Industrial Field of Application] The main proportion of the present invention is an acrylonitrile structural unit, which is shaped into a fiber by conventional wet, wet-dry, and dry spinning methods, and is suitable for manufacturing not only clothing fibers but also carbon fibers. Fibers useful as precursors, cloth-like industrial furnace materials, fibers for tents and canvas, or sewing threads, or as an asbestos substitute reinforcing agent for reinforcing cement, membrane-like and hollow-fiber filters used in the medical industry, and gas barriers. The present invention relates to a method for producing a highly polymerized acrylonitrile-based polymer that can be used to make a transparent film and the like. [Prior Art] Conventionally, as a method for industrially producing acrylonitrile polymers, persulfate/
An aqueous precipitation polymerization method using a redox polymerization catalyst consisting of acidic sulfite, etc., and a polyacrylonitrile solvent such as dimethyl sulfoxide (DMSO), dimethylformamide (DMF), dimethylacetamide (DMAc), ethylene carbonate, or γ-butyrolactone. Examples include homogeneous solution polymerization and emulsion polymerization. However, the reduced viscosity of the acrylonitrile polymer obtained by these polymerizations is usually 2.0 or less, and the strength of the fiber obtained by spinning this polymer is usually 5.0 g/d or less, but it cannot be used as a clothing fiber. has sufficient characteristics. Although acrylonitrile fibers have superior hydrolysis resistance, solvent resistance, and weather resistance compared to condensed fibers such as polyester and polyamide, they are only rarely used in industrial applications as precursors for carbon fibers. The reason it is only used is largely due to its low strength. However, the requirements for the properties of precursors for carbon fibers have also become higher, and
Considering its use as an industrial material, the emergence of acrylonitrile polymers with improved properties is awaited. One method for this is to use an acrylonitrile polymer with a high degree of polymerization. However, in the solution polymerization method, the solvent acts as a chain transfer agent, and the degree of polymerization cannot be achieved.In the suspension polymerization method or the emulsion polymerization method, although the degree of polymerization can be increased to a certain extent, it tends to result in branched polymers such as branching. Solubility becomes significantly worse. Various studies have been carried out to solve these problems. For example, a method of polymerizing a polymerizable monomer mixture containing 80% by weight or more of acrylonitrile in a mixed medium of dimethyl sulfoxide and water (Japanese Patent Publication No. 36-10996), the dimethyl sulfoxide/water ratio is 65% by weight. /35～85/
Acrylonitrile in a mixed solvent equivalent to 15 80
~20% by weight of at least one polymerizable monomer more hydrophobic than acrylonitrile, and 10% by weight or more of at least one acrylic acid or sulfoalkyl ester of methacrylic acid, Or a method of polymerizing a monomer mixture containing those salts at a monomer concentration of 60% by weight or less (Japanese Patent Publication No. 48-36430), or a dimethylacetamide/water ratio of 95/5 to 75/25. Method using a mixture as a polymerization medium (Japanese Patent Application Laid-Open No. 52-47088
No.) etc. are mentioned as manufacturing methods for improving the degree of acrylonitrile polymer. However, in all of these methods, the reduced viscosity of the polymer is 2.0 or less, and the viscosity of the polymerization system increases abnormally at a relatively low polymerization rate, making stirring impossible and causing problems in terms of polymerization control and productivity. Become. Another method is to polymerize a reaction product of an alkali metal salt of a carboxylic acid and a trialkylaluminum (Tokuko Sho
47-26978), an acrylonitrile polymer with a high degree of polymerization was obtained. However, this system results in anionic polymerization, and water cannot be used as a polymerization medium.
Polymerization operations, polymerization equipment, and industrial production also pose problems. [Problems to be Solved by the Invention] In order to solve the above problems, the present invention starts the polymerization of a mixture containing a polymerizable monomer using a water-organic solvent as a polymerization medium, and the polymer precipitates out. The purpose of the present invention is to provide a method for continuously producing an acrylonitrile polymer with a high degree of polymerization stably and at a high polymerization rate by further supplying water to the polymerization system after the system becomes non-uniform. shall be. [Means for Solving the Problems] The gist of the present invention is that 10 to 70% by weight of a polymerizable unsaturated monomer containing at least 70 mol% of acrylonitrile, 15 to 60% by weight of an organic solvent, and water.
Polymerization of a mixed composition consisting of 15 to 60% by weight is started using a radical initiator, and after the polymer precipitates and the system becomes non-uniform, water is added to add 1 part by weight of polymerizable monomer. The objective is to continuously produce an acrylonitrile-based polymer having a stable and high degree of polymerization by supplying 1 to 10 parts by weight of the acrylonitrile-based polymer to a high degree of polymerization. The conventional method for improving the degree of polymerization of acrylonitrile-based polymers is to add water, alcohol, etc., which are poor solvents for polyacrylonitrile, to the solution polymerization mixture to suppress chain transfer to the solvent and improve the degree of polymerization. However, it has not gone beyond solution polymerization.
The method of the present invention brings the polymerization system to a non-uniform state in which the polymer is precipitated at the initial stage of polymerization, significantly increases the polymerization rate, produces a high degree of polymerization, and prevents the phenomenon of agglomeration that is likely to occur at this time into the polymerization system. Furthermore, this is suppressed by supplying additional water. In addition, since the polymerization medium is an organic solvent-water system, the degree of polymerization can be easily changed by changing this ratio, and organic radical polymerization initiators that cannot be used in normal aqueous suspension polymerization can be used. This can also be said to be an advantage. In other words, the continuous method for producing an acrylonitrile polymer of the present invention can be said to be a completely new method for continuously producing an acrylonitrile polymer that takes advantage of the characteristics of both the current aqueous precipitation polymerization and solution polymerization. The high degree of polymerization of the acrylonitrile-based polymer of the present invention requires that the amount of acrylonitrile be 70 mol% or more to meet the chemical or physical properties required for fibers or film materials obtained by shaping this polymer. This is more preferable from the point of view.
Other polymerizable unsaturated monomers copolymerized with the acrylonitrile of the present invention include methyl acrylate or methacrylate, ethyl acrylate or methacrylate, n- or iso- or t-butyl acrylate or methacrylate, 2-ethylhexyl acrylate or methacrylate, Monomers such as acrylic acid, methacrylic acid, itaconic acid, α-chloroacrylonitrile, 2-hydroxyethyl acrylonitrile, hydroxyalkyl acrylate or methacrylate, acrylamide, methacrylamide, vinyl chloride, vinylidene chloride, vinyl bromide, vinyl acetate, vinyl propionate, etc. I can list several types. These polymerizable unsaturated monomers can be copolymerized with acrylonitrile alone or in combination, but the copolymerization ratio is preferably 30 mol % or less, as described above. As the polymerization medium of the present invention, an organic solvent and water are continuously supplied to proceed with polymerization.
% by weight, water in the range of 15-60% by weight. As the organic solvent used here, any ordinary acrylonitrile solvent can be used, such as dimethylformamide (DMF), dimethylacetamide (DMAc), dimethylsulfoxide (DMSO), ethylene carbonate (EC), etc. can be mentioned. Since the polymerization medium is a mixed solvent of organic solvent and water, the selection range of polymerization initiators is wide in terms of solubility, and any conventional radical initiator can be used. For example, azo compounds such as azobisisobutyronitrile and 2,2'-azobis(2,4-dimethylvaleronitrile), organic peroxides such as fatty acid diacyl peroxides or peroxy esters, or persulfuric acid. Examples include salts and redox initiators in combination with these salts and reducing agents. In particular, when the absence of impurities is required, for example, when producing a polymer for a precursor for carbon fibers, when an organic radical initiator is used, the polymerization system of the present invention has no polymerizable impurities. A system containing only saturated monomers, water-organic solvent, and initiator is created with few impurities. This means that
The system using a redox initiator is advantageous in terms of economy and the ability to obtain a polymer free of impurities because the absolutely necessary washing step for the polymer can be omitted. It can be said that it is a more preferable embodiment to use an initiator of When polymerization of a polymerizable mixture with the above composition is started and the polymerization continues as it is, the polymer precipitates and the entire polymerization system usually becomes lumpy, and in severe cases, stirring becomes impossible and continuation of the polymerization becomes impossible. Become. A major feature of the present invention is that in order to prevent this clumping during polymerization, water is additionally supplied to the second and subsequent polymerization vessels, and the polymerization is carried out stably and continuously to a high polymerization rate. . Further, the amount of additional water to be supplied is desirably 1 to 10 parts by weight, preferably 2 to 8 parts by weight, per 1 part by weight of the charged polymerizable unsaturated monomer. If the additional supply amount of the polymerization medium is less than 1 part by weight based on the charged polymerizable monomer, agglomeration of the polymerization system cannot be prevented, and if it exceeds 10 parts by weight, the polymer concentration in the resulting polymerization slurry will be low. , unfavorable in terms of productivity and economy. The method for polymerizing the acrylonitrile polymer of the present invention described above uses two or more polymerization tanks, and in the first tank, a mixture containing a polymerizable monomer is continuously supplied to start polymerization. A multi-stage continuous polymerization method can be adopted in which polymerization is continued by additionally supplying a polymerization medium from the second tank onwards. In this case, the supply of the polymerizable unsaturated monomer is not limited to the first tank, but from the second tank onwards.
Alternatively, it is always possible to divide the supply into the first tank and the second tank or thereafter. Among these polymerization methods, polymerization is started by continuously supplying a polymerizable unsaturated monomer, a polymerization medium, and an initiator with a fixed composition in the first tank, and water is additionally supplied in the second tank. The two-vessel continuous polymerization method, which continuously advances polymerization to a stable and high polymerization rate, improves productivity and
From the point of view of economy, this embodiment can be said to be a more preferable embodiment of the present invention. In addition, in the text or in the examples shown below, the amount supplied is based on the weight based on 1 part by weight of the polymerizable unsaturated monomer, and the reduced viscosity ηred is 0.5% by weight.
This is a value measured at 25°C in a dimethylformamide solution. Further, as a representative example of a polymerization apparatus, a two-tank continuous polymerization apparatus is schematically shown in FIG. [Example] Hereinafter, the present invention will be explained in more detail using Examples. Example 1 Polymerization was carried out as shown in Table 1 using a two-tank continuous polymerization apparatus shown in FIG.

【table】

[Table] Table 2 shows the results of polymerization carried out as shown in Table 1.

[Table] A polymer with a slightly high degree of polymerization was obtained at the initial stage of polymerization, but a high degree of polymerization with an average reduced viscosity of about 2.3 was obtained at a high polymerization rate. Example 2 Polymerization was carried out under exactly the same conditions as in Table 1, except that the ratio of organic solvent to distilled water was changed, and the results shown in Table 3 were obtained. In this way, the degree of polymerization can be easily changed by simply changing the organic solvent/water ratio. The reduced viscosity indicates the average value after the system stabilizes, excluding the initial stage of polymerization.

[Table] The supply amount and other conditions were all the same as in Example 1. Comparative Example 1 Aqueous suspension polymerization using a redox polymerization initiator was carried out by a continuous polymerization method using one polymerization tank.

〔Effect of the invention〕

By using the production method of the present invention, an acrylonitrile polymer having a high degree of polymerization with a reduced viscosity of 2 or more, particularly 2.5 or more can be easily obtained, and an organic initiator such as azobisisobutyronitrile can be used. When used, the polymerization system is a simple system of water-organic solvent-monomer-initiator, and the washing step can be omitted, which is advantageous in terms of economy. In addition, despite having a fairly high degree of polymerization, it has better solubility in solvents compared to polymers obtained by conventional manufacturing methods, and fibers with high Young's modulus can be produced without special spinning methods. It can be shaped into Fibers with such a high Young's modulus have higher strength than conventional fibers with a low Young's modulus. The carbon fiber can be elongated at a certain magnification, has high strength, and has an elongation of 1.7% or more. It is also extremely useful when used as a canvas material, and when used as a cement reinforcing material, it can be made into a hardened product with high bending strength due to its excellent alkali resistance.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the composition of the polymerizable mixture used in the method of the present invention at the time of preparation. FIG. 2 schematically shows a two-tank continuous polymerization apparatus, which is the most preferred embodiment for carrying out the present invention.

Claims (1)

[Claims] 1 Using a two-stage or more multi-stage continuous polymerization apparatus, 10 to 70% by weight of a polymerizable unsaturated monomer containing at least 70 mol% of acrylonitrile, 15 to 60% by weight of an organic solvent, and 15% of water Polymerization of a mixed composition consisting of ~60% by weight is started using a radical initiator, and after the polymer precipitates and the system becomes non-uniform, water is added to the polymerizable unsaturated monomer 1. 1. A method for continuously producing an acrylonitrile polymer, which comprises supplying 1 to 10 parts by weight of an acrylonitrile polymer and carrying out continuous polymerization.