JPS627218B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for producing a charged film with low electrical resistance, and more specifically, it involves sulfonating vinylidene fluoride polymer powder in its powder state, then turning the sulfonated product into a solution, and forming a cast film from this solution. This invention relates to a method for producing a charged film with low electrical resistance. Polymer charged membranes can be used as ion exchange membranes for desalination of seawater, electrodialysis such as concentrating common salt, electrolysis of various salts, and industrial applications such as reverse osmosis membranes and ultrafiltration membranes as material separation membranes in solution systems. It has a wide range of uses, and further development is expected. When used as an ion exchange membrane, permselectivity, mechanical strength, chemical resistance, and low electrical resistance are desirable;
High mechanical strength, chemical resistance, heat resistance, and permeation flux are desired. One known method for introducing charged groups into a polymer membrane is to react the polymer membrane in its membrane form with a charged group imparting agent to introduce charged groups into the membrane. A disadvantage of this method is that the reaction tends to proceed from the surface, so the degree of reactivity tends to differ between the surface and the inside of the membrane, and this non-uniformity is particularly noticeable when the membrane is thick. For example, a method of sulfonating polyvinylidene fluoride film with fuming sulfuric acid or chlorosulfonic acid is known, but since the reaction tends to proceed from the surface, the way the sulfonation is done differs between the surface and the inside of the film. The degree of oxidation tends to be uneven. As a result of intensive research, the present inventors have come up with a method for obtaining a uniformly sulfonated vinylidene fluoride polymer charged film. That is, in the present invention, vinylidene fluoride polymer powder is sulfonated in powder form using a sulfonating agent in a dispersion medium, and then the sulfonated polymer powder is dissolved in a solvent that can dissolve the sulfonated polymer powder, and a cast film is formed from the solution. This is a method for producing a vinylidene fluoride polymer charged film having low electrical resistance. A feature of the present invention is that the polymer is sulfonated in the form of a powder, and since the surface area is larger than that of a film, the sulfonation progresses more easily and more uniformly than in the case of a film. In addition, since the sulfonated powder is dissolved in a solvent to form a solution and a cast film is made from this solution, the degree of sulfonation on the surface and inside of the film is more uniform than when sulfonation is performed on a film. It is a characteristic. In particular, when sulfonating vinylidene fluoride copolymer or chlorinated polyvinylidene fluoride in the form of a film, sulfonation does not easily progress to the inside, and the film has low membrane resistance even if the sulfonation reaction is carried out for a long time. However, when a cast film is prepared from the sulfonated powder and then a solution as in the present invention, a charged film with low film resistance can be easily obtained. Further, the charged film obtained by the present invention has low electrical resistance and excellent strength. The present invention will be explained in detail below. The vinylidene fluoride polymer powder used in the present invention includes polyvinylidene fluoride, a copolymer containing vinylidene fluoride as a main component and one or more monomers copolymerizable therewith, and polyvinylidene fluoride. It is a chloride powder. The monomer to be copolymerized with vinylidene fluoride is selected from ethylene tetrafluoride, chlorinated ethylene trifluoride, ethylene trifluoride, propylene hexafluoride, and isobutylene hexafluoride. The vinylidene fluoride polymer as described above is more preferably used in the form of suspension polymerized powder particles or powder particles obtained by emulsion polymerization, but is not particularly limited thereto. For example, it is also useful to use a powder produced by pouring a polymer solution obtained by solution polymerization into a polymer non-solvent. First, the vinylidene fluoride polymer powder as described above is dispersed in a solvent. The dispersing solvent may be any solvent that can finely disperse the vinylidene fluoride polymer powder, but it is preferably a solvent that does not easily react with the sulfonating agent.
Examples of such solvents include chloroform, methylene chloride, 1,2 dichloroethane, 1,1,2,
Solvents such as 2.tetrachloroethane are suitable. The amount of dispersion solvent is not particularly limited, but it must be at least enough to soak the entire polymer powder. As the sulfonating agent, for example, chlorosulfonic acid, fuming sulfuric acid, or sulfur trioxide-triethyl phosphate complex can be used. The reaction temperature is not particularly limited, but is room temperature to 100℃.
This degree is desirable in the sense that the reaction proceeds mildly and smoothly. Incidentally, in order to make the reaction more uniform, it is advantageous to carry out the reaction under stirring. The amount of sulfonating agent is not particularly limited, but for example, 10 g of polymer powder,
10 parts of chlorosulfonic acid for 50-200ml of dispersion solvent
A ratio of ml to 1100 ml is often used to allow the reaction to proceed quickly and mildly. The reaction time varies greatly depending on the reaction temperature, but if the sulfonation progresses too much, only a brittle film will be obtained when a cast film is produced later. For example, 10g of polyvinylidene fluoride powder is mixed with 100ml of chloroform.
After adding 50ml of chlorosulfonic acid and reacting for 5 hours at the reflux temperature of chloroform, the powder was cast into a film (20μ) from an acetone solution, and the film resistance was 1Ω in a 0.5N aqueous sodium chloride solution. -Has a value of about cm ² . After a predetermined reaction time, the reaction mixture is allowed to absorb moisture, then poured into water, washed, and dried. The sulfonated powder thus obtained is dissolved in a solvent. Examples of the solvent include dimethylformamide, dimethylacetamide, acetone, dioxane, and tetrahydrofuran. When producing a flat film from these solutions, the film can be obtained by casting the solution onto a glass plate or metal plate and then evaporating the solvent. In addition, it is possible to produce a membrane in any desired shape, and if necessary, it is also possible to cast the membrane on a support and then remove the solvent to form a composite membrane as it is. The vinylidene fluoride-based polymer charged film thus obtained has low film resistance and high mechanical strength. The present invention also uses a method in which two or more sulfonated powders having different degrees of sulfonation are mixed to form a solution, and a cast film is formed from the solution. Generally, when a cast film is formed using only extremely sulfonated powder as a solution, the film resistance is extremely low and a film with good substance permeability is obtained, but the film strength tends to be very weak. . On the other hand, when a cast film is formed using a solution of powder with a low degree of sulfonation, the strength of the film is very strong;
Disadvantages include high membrane resistance and poor substance permeability. In this case, a solution is made of a mixture of powder with a high degree of sulfonation and powder with a low degree of sulfonation (the present invention also includes untreated powder), and a cast film is formed from this solution, which has a low film resistance and A charged film that also maintains film strength can be formed. The charged membrane obtained by the present invention is useful as a substance separation membrane such as an ion exchange membrane or an ultrafiltration membrane. Examples are shown below. Example 1 Polyvinylidene fluoride obtained by suspension polymerization [ηinh of dimethylformamide solution (0.4 g/dl)
=1.8] Disperse 50 g of powder in 500 ml of chloroform in a separable flask, add 100 ml of chlorosulfonic acid dropwise while stirring with a magnetic stirrer, and then raise the temperature to the reflux temperature of chloroform.
Allowed time to react. Sampling was carried out for 1 hour, 2 hours, 3.5 hours, and after completion. After each reaction mixture was allowed to absorb moisture in the air overnight, it was poured into water, washed, and dried. This sulfonated powder was made into an acetone solution with a concentration of 8 wt%, and cast on a glass plate in a desiccator to obtain a brown transparent film. The membrane resistance and ion exchange capacity of these membranes are shown in Table 1.

[Table] The film resistance of this example and the following examples is as follows:
The values were measured using a Kohllaus bridge at room temperature in a 0.5N aqueous sodium chloride solution. Example 2 Polyvinylidene fluoride obtained by suspension polymerization [ηinh of dimethylformamide solution (0.4 g/dl)
= 1.0] 300 g of powder was dispersed in 3 kg of carbon tetrachloride, and chlorine was blown in at 60 to 70° C. while irradiating with a mercury lamp to carry out a chlorination reaction for about 40 hours. The degree of chlorination (weight percent of chlorine in the polymer) of the resulting polymer was 14%. 20 g of this chlorinated polyvinylidene fluoride [dimethylformamide solution (ηinh = 0.87 of 0.4 g/dl)] powder was placed in a separable flask, dispersed in 200 ml of chloroform, and 100 ml of chlorosulfonic acid was added dropwise to the reflux temperature of chloroform. The temperature was raised and the reaction was carried out for 6 hours. Post-treatment was carried out in the same manner as in Example 1, and then an 8% acetone solution was prepared.
From this, a cast film was created in a desiccator. A pale brown transparent membrane was obtained, with a membrane thickness of 20μ, membrane resistance of 6.8Ω- ^cm2 , and ion exchange capacity of 2.54m.
It was eq/g dry resin. Comparative Example For comparison, the chlorinated polyvinylidene fluoride used in Example 2 was dissolved in acetone, a cast film was created from this, and this film was mixed with 200% of chloroform.
ml, into a mixture of 100 ml of chlorosulfonic acid,
The chloroform was refluxed for 6 hours. This film (film thickness
20μ) membrane resistance was 439Ω-cm ² . Example 3 Copolymer powder obtained by suspension polymerization with a weight ratio of 90% vinylidene fluoride and 10% trifluorochloroethylene
Disperse 20g in 200ml of chloroform and add 100ml to this.
of chlorosulfonic acid was added, and the chloroform was refluxed for 2 hours. The same post-treatment as in the other Examples was carried out, and then a brown cast film was obtained from an 8% acetone solution in exactly the same manner. The thickness of this film is 30μ and the film resistance is 2Ω.
-It was warm at ^cm2 . Example 4 Copolymer powder same as the raw material powder used in Example 3
Disperse 20g in 200ml of chloroform and add 100ml to this.
of chlorosulfonic acid was added and refluxed. After refluxing for 1 hour, the second half of the amount was taken out and refluxing was further continued for 1 hour. These reactants were processed and dried as in other examples. The weight ratio of the powder treated for 1 hour and the powder treated for 2 hours is 1 hour treated powder / 2 hour treated powder = 30 /
Mixed at a mixing ratio of 70(A) and 50/50(B), 8wt each
% acetone solution, and a cast film was prepared in a desiccator. The membrane resistance of each membrane was as follows. (Film thickness: 30μ) Film Film resistance (Ω-cm ² ) A 43 B 67 Both A and B magnetic films had strong film strength, and B was particularly strong.

Claims (1)

[Claims] 1 Polyvinylidene fluoride, vinylidene fluoride as the main component, ethylene tetrafluoride, ethylene trifluorochloride,
A vinylidene fluoride polymer that is either a copolymer with one or more monomers selected from trifluoroethylene, hexafluoropropylene, and hexafluoroisobutylene, and a chlorinated product of these polymers. A method for producing a charged vinylidene fluoride polymer film, which comprises sulfonating a powder in a dispersion medium, dissolving the sulfonated powder in a solvent, and forming a cast film from the solution.