JPS61266416A - Production of acrylonitrile polymer solution - Google Patents

Abstract

PURPOSE:To obtain a polymer solution of good stability and good spinnability by conducting polymerization and spinning sequentially by eliminating both of a polymer washing process and its drying process by polymerizing a polymerizable unsaturated monomer mixture based on acrylonitrile in a solvent mixture of an organic solvent and water. CONSTITUTION:The polymerization of 10-70pts.wt. polymerizable unsaturated monomer mixture comprising 70wt% or above acrylonitrile and 30wt% or below unsaturated monomer copolymerizable therewith is started by using 15-60pts.wt. organic solvent which acts as a solvent for polyacrylonitrile, 15-60pts.wt. water and a radical polymerization initiator. After a polymer is precipitated in the polymerization system, an organic solvent and/or water are added in an amount of 1-10pts.wt. per pt.wt. polymerizable unsaturated monomer mixture fed, and the polymerization is continued. The high-MW acrylonitrile polymer of a reduced viscosity >=2, obtained by the polymerization, is separated from the polymerization system to obtain a polymer of a solvent content <=150wt%. This polymer is dissolved in a solvent for polyacrylonitrile to obtain an acrylonitrile polymer solution of a water content of 1-10wt%.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to a method for preparing a spinning stock solution of an acrylonitrile (IJy) polymer, and in particular a method for drying an acrylonitrile polymer polymerized by aqueous suspension polymerization. It has particularly excellent characteristics as a spinning stock solution with a moisture content of 1 to 10% by weight, which dissolves in organic solvents without any problem, has good stock solution stability and spinnability, and can easily produce threads without defects such as voids. The present invention relates to a method for producing an acrylonitrile polymer solution.

[Conventional technology]

As a method for producing acrylonitrile polymers for fiber production, an aqueous precipitation polymerization method using a water-soluble catalyst such as a redox initiator made of persulfate/acidic sulfite as a polymerization catalyst in an aqueous medium is generally known. The polymer obtained by this method has a relatively high molecular weight compared to the polymer obtained by so-called solution polymerization using dimethylformamide, dimethylacetamide, ethylene carbonate, or r-butyrolactone as a polymerization solvent. be able to.

[Problem that the invention seeks to solve]

However, in the polymer granules separated from the polymerization system after polymerization in an aqueous medium, the water content is 200 to 33% of the polymer weight.
00% by weight, and even if compression dehydration is performed, the dehydration rate will not be high enough to dissolve in dimethyl sulfoxide, dimethyl acetamide, dimethyl formamide, etc., which are good solvents for acrylonitrile polymers, and even if heated to high temperatures, Even if it is dissolved, if the temperature is lowered to the spinning temperature, the stock solution will gel, resulting in extremely poor spinning stability. Further, especially when an inorganic redox initiator is used, an inorganic salt as a catalyst residue remains, which causes nozzle clogging during spinning and deteriorates stability.

As described above, washing and drying steps are essential steps in normal aqueous suspension polymerization, and it is virtually impossible to immediately turn the polymer obtained by aqueous suspension polymerization into a spinning dope using an organic solvent. It has been. Especially when drying is usually 50 to 1
Since the process is carried out under heating at 00°C, there is a possibility that dust may enter the air or the polymer may deteriorate due to heating. Furthermore, from the viewpoint of energy saving, the development of a new process that eliminates the drying step is eagerly awaited. This is where I am.

[Means for solving problems]

Therefore, the present inventors conducted various studies in order to solve the above-mentioned problems, and found that acrylonitrile was produced by using a mixed solvent of a specific ratio of an organic solvent, which is a solvent for polyacrylonitrile, and water as a polymerization solvent. The water content in the acrylonitrile polymer obtained by polymerizing the polymerizable unsaturated monomer mixture as the main component and subsequently separating it from the polymerization system is lower than that obtained by normal aqueous suspension polymerization. Therefore, the solubility of acrylonitrile-based polymers in solvents is good even without forced heating or drying, and the water content can be reduced to 10% without using special dehydration methods.
It became possible to produce a 7-acrylonitrile polymer stock solution with a concentration of less than 7% by weight, and the inventors discovered the possibility of a process that allows continuous polymerization and spinning without the need for a dryer, leading to the completion of the present invention.

The gist of the present invention is to provide a polymerizable unsaturated monomer mixture of 10 to 70% by weight consisting of at least 70% by weight of acrylonitrile and 30% by weight or less of other copolymerizable polymerizable unsaturated monomers. 15 to 60 parts, an organic solvent that serves as a solvent for polyacrylonitrile! Polymerization is initiated using a radical polymerization initiator with a charging composition consisting of part f and 15 to 60 parts by weight of water, and if necessary, water and the organic solvent are added alone after the time when polymer precipitation is observed in the polymerization system. Add 1 to 10 parts by weight to 1 part by weight of the charged polymerizable unsaturated monomer mixture, separate the resulting acrylonitrile polymer from the polymerization system, and add an organic solvent as necessary. The content of the polymerization medium used for polymerization washing was reduced to 100% by weight or less by dissolving it in a polyacrylonitrile solvent, and spinning with a polymer concentration of 10 to 25% by weight and a water content of 1 to 10% by weight was performed. There is a method for obtaining an acrylonitrile polymer solution for use.

The acrylonitrile polymer used in the present invention contains 70% by weight or more of acrylonitrile and 30% by weight or less of other copolymerizable unsaturated monomers. Fibers, films, etc. made from polymers containing 70% or more acrylonitrile have better weather resistance than those containing less than 70% by weight.
It has advantages such as excellent whitening and heat resistance.

Examples of polymerizable unsaturated monomers that can be copolymerized with acrylonitrile include unsaturated carboxylic acids such as acrylic acid, methacrylic acid, and itaconic acid, and their salts, methyl acrylate, ethyl acrylate, butyl acrylate, and octyl acrylate. , acrylic esters such as methoxyethyl acrylate, acrylic phenyl, cyclohexyl acrylate, methyl methacrylate, ethyl methacrylate, butyl methacrylate, octyl methacrylate, methoxyethyl methacrylate, phenyl methacrylate, cyclohexyl methacrylate, etc. Vinyl esters such as methacrylic acid esters, alkyl vinyl ketones, vinyl acetate, vinyl propionate, vinyl butyrate, vinyl benzoate, and vinyl sulfonic acids such as nyl sulfonic acid, methallyl sulfonic acid, p-styrene sulfonic acid, and those salts,
Vinyl chloride, vinyl chloride, vinyl bromide and other vinyl halides or vinylidene halides, vinyl pyridine, vinyl imidazole, basic vinyl compounds such as dimethylaminoethyl methacrylate, acrolein, methacrylate tolyl, α-chloro Mention may be made of unsaturated monomers such as acrylonitrile.

As the organic solvent used in carrying out the present invention, any common solvent for polyacrylonitrile can be used, and examples thereof include dimethylformamide, dimethylacetamide, dimethylsulfoxide, r-butyrolactone, and the like. As mentioned above, the amount used is in the range of 15 to 65% by weight in the mixed composition during polymerization. 15
If it is less than 10% by weight, there is no advantage compared to normal aqueous precipitation polymerization, and the water content in the polymer after separation from the polymerization system is particularly high, so it is impossible to obtain a spinning dope containing less than 10% by weight of water. If the amount is more than 65% by weight, the organic solvent used acts as a chain transfer agent, lowering the molecular weight of the polymer and causing a decrease in the performance of the fiber obtained by spinning, especially strength and elastic modulus, which is not preferable.

As the polymerization initiator, common radical initiators such as 2,
azo compounds such as 2'-azobisisobutyronitrile, 2°2'-azobis+2,4-dimethylvaleronitrile), aliphatic diacyl peroxides, or organic acid peroxides such as peroxy esters; Alternatively, persulfates and redox initiators in combination with these and reducing agents can be mentioned, but from the point of view of omitting the washing and drying steps, which is the purpose of the present invention, organic compounds such as azo compounds or organic peroxides can be used. It is preferred to use a system initiator.

The amount used is 0.00 parts by weight of the charged polymerizable unsaturated monomer in terms of polymerization stability and molecular weight of the resulting polymer.
05 to 0.05 parts by weight, preferably 0.001 to 0.0
Use 2 parts by weight.

When polymerization of the above charge composition is started, polymer precipitation occurs as the polymerization progresses, the viscosity of the polymerization system increases, and a state in which stirring of the system is usually impossible occurs, resulting in a high polymerization rate. I won't be able to do that.

In the present invention, at the time when polymer precipitation is observed in the polymerization system, 1 part by weight of the polymerizable unsaturated monomer mixture to 1 part by weight of the polymerization medium selected from water and/or the above-mentioned organic solvent is added. By additionally adding ~10 parts by weight, polymerization can be carried out to a high polymerization rate with sufficient stirring without deteriorating the polymerization behavior of the polymerization system.

The reduced viscosity of the acrylonitrile polymer obtained by the above polymerization (measured at 25°C as a 0.5% solution in dimethylformamide) is over a very wide range of 2.0 or more, especially 2.5 or more, and it has a high molecular weight. A major feature is that it can be combined.

In addition, fibers obtained by spinning acrylonitrile polymers with high molecular weights are 7 JP/d or more, especially 1 JP/d or more.
It can have a strength of 0//d or more and a high modulus of elasticity.

Polymerization methods for obtaining this high molecular weight polymer include a one-tank batch polymerization method in which a mixture of a certain composition is charged into a flask and a solvent is added after polymer precipitation, or a one-tank batch polymerization method in which a mixture of a certain composition is continuously poured into a flask. Any two-stage or more multi-stage continuous polymerization method can be employed, in which the polymer is supplied to the first tank, polymerization is started, and the polymerization medium is added in the second tank or thereafter.

The polymer obtained by the above polymerization method is separated from the polymerization system and dissolved, and the polymer content is 10 to 30% by weight and the water content is 1.
A ~10% by weight acrylonitrile polymer solution is prepared.

In the present invention, since the polymerization medium in the polymerization system is a mixed solvent of organic solvent and water, the solvent content after filtration and compression dehydration is 1.
Even if the proportion is as high as 50% by weight or less, preferably 100% by weight or less, the solubility in organic solvents is good, and a polymer solution with a desired polymer concentration and water content can be easily prepared. can. On the other hand, in ordinary aqueous suspension polymerization, even if the solvent content after compression dehydration is the same as in the present invention, the solubility in organic solvents is poor and the desired polymer solution cannot be obtained. Furthermore, even if solvent replacement is performed, it is necessary to repeat dispersion in a solvent and compression dehydration several times or more, which is very disadvantageous from an economic standpoint or from the perspective of establishing a continuous process.

In this way, in the present invention, 1 to 10% by weight is added to the polymer solution.
Since it contains water in the range of , the solution viscosity is lower than that of a water-free system, and oral changes in viscosity are also reduced, which is very advantageous in terms of industrial production.

If the water content is less than 1% by weight, the effect of reducing and stabilizing the viscosity of the solution will be low;

Exceeding this is undesirable as it may lead to gelation of the solution.

Further, the polymer concentration in the solution is preferably in the range of 10 to 30% by weight; if it is less than 10% by weight, spinning stability will be lacking and productivity will be poor, and if it exceeds 30% by weight, the solution viscosity will be high. I don't like it.

The method for spinning the acrylonitrile polymer solution obtained by the above method includes the usual dry spinning method, dry-wet spinning method,
Any wet spinning method can be employed.

In this way, the present invention enables continuous polymerization and spinning without the two steps of washing and drying, and creates a system with very few impurities that eliminates the contamination of dust and the generation of solvent-insoluble polymers. I can do it.

In addition, when using a high molecular weight polymer with a reduced viscosity of 2.5 or more, the fiber obtained by spinning has high strength with few defects,
It can have a high modulus of elasticity.

〔Example〕

Hereinafter, the present invention will be explained in more detail with reference to Examples.

Example 1 The charge composition shown in Table 1 was charged into a two-hole four-bottle flask equipped with a stirrer, a thermometer, a reflux condenser, and a nitrogen introduction tube, and after purging with nitrogen, the mixture was heated and polymerized. I started it. After the start of polymerization, when the system became cloudy, additional solvents shown in Table 1 were added, and the mixture was heated for about 4 hours to complete the polymerization. The obtained polymer slurry was subjected to centrifugal dehydration and compression dehydration to obtain a polymer wet powder containing 100% by weight of residual solvent. Dimethylformamide (DMF) was added to this wet powder to prepare a polymer solution with a desired polymer concentration.

If you want to further lower the water content, add enough DMF to the wet powder so that the polymer does not dissolve, and then disperse the polymer.
After filtration and compression dehydration, DMF was added again to the solution to a desired polymer concentration and dissolved by heating to obtain a polymer solution.

Comparative Example 1 A polymerization slurry obtained by an aqueous precipitation polymerization method using a redox initiator using potassium persulfate as an oxidizing agent and sodium sulfite as a reducing agent and sulfuric acid as a pH adjuster was subjected to compression dehydration in the same manner as in Example 1. I tried to make a polymer solution, but it did not dissolve because it was difficult to keep the moisture content below 10%. Therefore, I replaced the solvent with dimethylformamide, and then added dimethylformamide to make the spinning stock solution. And so. Table 1 shows the results of Example 1 and Comparative Example.

Polymerization scale is 50! The stability of the obtained polymer solution when it was left at a constant temperature was determined according to Table 1 except for the polymer solution for Experimental Electron 2, Glecursor ■, ■, and the water content of 0% as a control. It is also shown in FIG.

Example 2 The polymer solutions obtained in Example 1 and Comparative Example 1 were wet-spun according to a conventional method to obtain a precursor (with a fineness of 1.3 d).
Numbers ■～■) were obtained. 230% of this precursor in the air
After flameproofing treatment in an oxidizing atmosphere at ~270°C, N,
Carbonization treatment was performed by applying a temperature increasing gradient of 600 to 1250° C. under air flow. The resulting carbon fiber performance is shown in Table 2.

Table 2 Metal content measurement: Tables 1 and 2 by ordinary atomic absorption method
As shown in the table, in the present invention, a spinning dope with good stability can be obtained without washing or drying, and the carbon fibers spun and fired from this solution have high performance. In comparison, Comparative Example 1 has a high moisture content and poor solubility in dimethylformamide (even if it has a composition that can be dissolved, a large amount of impurities remains in the resulting fiber, causing a decrease in the performance of the precursor and carbon fiber). It can be seen that it is impossible to omit the washing and drying steps.

Example 3 Using a two-tank continuous polymerization apparatus, polymerization was carried out by continuously supplying the polymer according to the conditions shown in Table 3.

Table 3 - Internal temperature; 1st tank 55℃, 2nd tank 60℃ ・1st tank 101, 2nd tank 501 Both are glass lined tanks 1・Total stay time 7 hours 50
A! Transfer to glass lined tank and add 25011HJl
The remaining monomer was removed by heating to 60° C. under reduced pressure, and a portion of the monomer was removed, washed, and dried. The polymer had a polymerization rate of 63% and a reduced viscosity of 4.3.

The composition of the wet powder after demonomerization is polymer/DMF/
Water = 100784/16, and 300 parts of dimethylformamide was added thereto and dissolved by heating, resulting in a polymer concentration of 2.
A polymer solution with a water content of 0% and a moisture content of 3.2% was obtained.

Example 4 Carbon fiber obtained by spinning and firing the polymer solution obtained in Example 3 according to a conventional method has a strength of 498 kg/lx
", and the elastic modulus was 25.9 ton/mm."

The amount of metal remaining in the precursor is below the limit of quantification, indicating that polymerization and spinning can be carried out continuously without washing or drying.

[Brief explanation of drawings]

FIG. 1 shows the stability of the stock solution of the polymer obtained according to the present invention in terms of retention time and the corresponding change in viscosity.

Claims (1)

[Scope of Claims] 1. At least 70% by weight or more of acrylonitrile;
Polymerizable unsaturated monomer mixture 1 consisting of 30% by weight or less of a polymerizable unsaturated monomer copolymerizable with other acrylonitrile
0 to 70 parts by weight, 15 to 60 parts by weight of an organic solvent serving as a solvent for polyacrylonitrile, and 15 to 60 parts by weight of water. Polymerization is initiated using a radical polymerization initiator, and the polymer is added to the polymerization system. After the point of precipitation, a polymerization medium selected from organic solvents, water or mixtures thereof,
1 to 1 part by weight of the charged polymerizable unsaturated monomer mixture
Add 10 parts by weight, separate the high molecular weight acrylonitrile polymer with a reduced viscosity of 2 or more obtained by polymerization from the polymerization system, and dissolve the acrylonitrile polymer with a solvent content of 150% by weight or less in a solvent to determine the water content. A method for producing an acrylonitrile polymer solution, characterized in that the acrylonitrile polymer solution is 1 to 10% by weight. 2. The manufacturing method according to claim 1, wherein the radical polymerization initiator is an azo compound or a peroxide. 3. After separating the high molecular weight acrylonitrile polymer with a reduced viscosity of 2 or more from the polymerization system, perform solvent replacement to reduce the solvent content to 1.
2. The manufacturing method according to claim 1, wherein the acrylonitrile polymer is dissolved in a solvent in an amount of 50% by weight or less.