JPS6031328B2 - Method for producing non-aqueous dispersion of carboxylic acid type fluorinated polymer - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for producing a non-aqueous dispersion of a carboxylic acid type fluorinated polymer. The present invention relates to a new manufacturing method capable of obtaining a highly concentrated non-aqueous dispersion, which consists of substituting an aqueous medium with a hydrophilic organic solvent.

Conventionally, since fluorinated polymers generally have resistance to organic solvents, organic solvent solutions of such fluorinated polymers are hardly known.

In particular, no organic solvent is known that can satisfactorily dissolve a fluorinated polymer in which a large number of fluorine atoms are bonded to the carbon atoms of the main chain skeleton. On the other hand, if a solution of the fluorinated polymer as described above can be obtained, various avenues for commercial use will be expanded.

For example, a copolymer of a fluorinated olefin such as tetrafluoroethylene and a fluorinated monomer having a carboxylic acid type side chain is a cation exchange resin with excellent oxidation resistance, chlorine resistance, alkali resistance, and heat resistance. Recently, it has been attracting attention that it can be used as a septum for electrolysis in the production of alkali hydroxide and chlorine, a diaphragm for fuel cells, a diaphragm for general dialysis, and many other uses. If such an organic solvent solution of a carboxylic acid type fluorinated polymer can be obtained, the means and operation for forming a film will be extremely easy, and it will be possible to manufacture membranes of arbitrary complex shapes and extremely thin membranes. Various advantages are brought about by making the solution into a solution, such as facilitating the production of diaphragms by impregnation, and also making it possible to repair pinholes in the diaphragm and appropriately coat the surface of objects with a fluorinated polymer. In the case of a fluorinated polymer having a highly polar and strongly acidic group such as sulfonic acid, as shown in Japanese Patent Publication No. 13333/1983, the sulfonic acid group is an acid, a sulfonamide, or a sulfonate. Only when in a particular form
It is known to be exceptionally soluble in highly polar organic solvents.

However, in the case of fluorinated polymers with carboxylic acid side chains, the only difference is that the side chains are carboxylic acid groups, and they are soluble in organic solvents that well dissolve fluorinated polymers with sulfonic acid side chains. Does not show gender. The applicant previously filed two patent applications regarding organic solvent solutions of carboxylic acid type fluorinated polymers. That is, JP-A-54-10794
The carboxylic acid side chain described in Dogo Publication -COOQ (
Q is a solution in which a fluorinated polymer (as an alkali metal, etc.) is dissolved in a highly polar organic solvent such as alcohol or glycol, or a carboxylic acid described in Tokuhan No. 54-56912. This is a solution in which a fluorinated polymer having pendant side chains containing ester groups is dissolved in a fluorine-containing organic solvent such as trichlorotrifluoroethane or penzotrifluoride. According to the research conducted by the present inventors, it is difficult to increase the concentration of the fluorinated polymer in the organic solvent solution as described above, and a solution having a concentration of about 5% by weight can usually be obtained. Considering film formation from such a solution, it is natural that it is desirable to increase the concentration of the fluorinated polymer as much as possible. As a result of various studies aimed at creating a highly concentrated solution, the inventors of the present invention have come to the following extremely interesting findings.

That is, the carboxylic acid type fluorinated polymer can be produced as a highly concentrated aqueous dispersion by emulsion polymerization in an aqueous medium. It is possible to replace it with a solvent. Although the reason is not necessarily clear, the dispersion state is not destroyed even when replaced with a hydrophilic organic solvent, and a non-aqueous dispersion liquid that maintains a stable dispersion state can be obtained. Furthermore, the non-aqueous dispersion thus obtained can be applied to film formation, etc. in the same way as an organic solvent solution. For example, an aqueous latex of a carboxylic acid type fluorinated polymer can be separated into an aqueous medium layer and a latex layer with increased polymer concentration by an appropriate centrifugation operation, and a hydrophilic organic solvent is added to the concentrated latex layer. , repeating the centrifugation operation reduces the aqueous medium content in the concentrated latex layer and achieves replacement by the hydrophilic organic solvent. The carboxylic acid type fluorinated polymer is dispersed in the hydrophilic organic solvent while maintaining the dispersion state of the aqueous latex. Then, by such substitution treatment, a non-aqueous dispersion liquid having a polymer concentration similar to that in the aqueous latex can be obtained.
Thus, the present invention has been completed based on the above findings, and uses a fluorinated ethylenically unsaturated monomer and a polymerizable functional monomer having a carboxylic acid group or a functional group convertible to a carboxylic acid group. copolymerized in an aqueous medium by the action of a polymerization initiation source, and the functional monomer content is 5 to 5.
An aqueous dispersion containing 40 mol% of a carboxylic acid type fluorinated polymer in a dispersed state is obtained, and the aqueous medium of the aqueous dispersion is replaced with a hydrophilic organic solvent without destroying the dispersion state of the aqueous dispersion. The present invention provides a novel method for producing a non-aqueous dispersion of a carboxylic acid type fluorinated polymer. According to the present invention, a non-aqueous dispersion with a high concentration of about 5% by weight can be easily obtained using a wide variety of hydrophilic organic solvents, and the mechanical or chemical stability of the dispersion can be easily obtained. is extremely good.

The viscosity of the dispersion can be freely adjusted depending on the purpose and use by selecting the type of solvent used. By casting the non-aqueous dispersion, a good copolymer film free from defects such as pinholes can be obtained. In the present invention, it is important to use a polymerizable monomer containing a carboxylic acid group or a functional group convertible to a carboxylic acid group as the functional monomer.

The carboxylic acid type functional monomer (1) is usually desirably a fluorovinyl compound, taking into account the chlorine resistance, oxidation resistance, etc. of the resulting polymer; CF2=CX-(OCF2CFY)so)m
-(CFYI')n-A (where, ku is 0 to 3, m is 0
~1, n is an integer of 0 to 12, X is a fluorine atom or -CF3, Y, Y' is a fluorine atom or a carbon number of 1 to
10 perfluoroalkyl groups. Also, A is 1C
N, one COF, one COO day, one COOR,, -C0OM
or -CONR2R3, where R is carbon number 1 to = 10
an alkyl group, R2 and R3 are hydrogen atoms or R,
An example is a fluorovinyl compound represented by (M is an alkali metal or a quaternary ammonium group). From the viewpoint of performance and availability, X is a fluorine atom, Y is -CF3,
Y' is a fluorine atom of 0 to 1, m is 0 to 1, and n is 0 to 1.
8, and A is -COOR due to copolymerization reactivity etc.
, is preferable. Preferred representative examples of such fluorovinyl compounds include CF2=CF○(CF2), ~8CO
OCH3, CF2=CF○(CF2), ~8COOC2
Horse, CF2 = CF(CF2).

~8COOCH3,CF2:CFOCF2CF(OC
F3) OCF2CF2COOCH3, etc. Next, examples of the fluorinated ethylenically unsaturated monomer m) include ethylene tetrafluoride, ethylene trifluoride chloride, propylene hexafluoride, ethylene trifluoride, vinylidene fluoride, and vinyl fluoride. , preferably a fluorinated olefin compound represented by the general formula CF2=CZZ' (where Z, Z' are a fluorine atom, a chlorine atom, a hydrogen atom or -CF3).

Among these, perfluoroolefin compounds are preferred, and tetrafluoroethylene is particularly preferred. In the present invention, the functional monomer (1) and the ethylenically unsaturated monomer (b)
It is also possible to use two or more of each of the monomer compounds of 8 alkyl group or aromatic nucleus)
An olefin compound represented by m), CF2=CFO
Fluorovinyl ether such as Rf (Rr represents a perfluoroalkyl group having 1 to 10 carbon atoms), CF2=CF
-CF=CF2, CF2=CF○(CF2), ~40C
One or more types of divinyl monomers such as F=CF2 and other functional monomers such as sulfonic acid type functional groups can also be used in combination.

Preferred representative examples of the olefin compound (m) include ethylene, propylene, butene-1, isobutylene, styrene, Q-methylstyrene, bentene-1, and hexene-1.
, heptene-1,3-methyloptene-1,4-methylbentene-1, etc. Among them, ethylene, propylene, propylene,
Particular preference is given to using isoptylene and the like.

Further, for example, by using a divinyl monomer in combination, it is possible to crosslink the resulting copolymer and improve the mechanical strength when it is made into a molded product such as a film or stiffness. In the carboxylic acid type fluorinated polymer of the present invention, the composition ratios of the functional monomer 1), the fluorinated olefin compound (0), and the olefin compound (plate) and other components are determined firstly. It is related to the performance of fluorinated polymers, for example, when used as ion exchange membranes for electrolytic cells, and also to the stability of the dispersion state during substitution treatment with hydrophilic organic solvents from aqueous dispersions to non-aqueous dispersions. It is important because it is related. First, the amount of the functional monomer (1) is directly related to the ion exchange capacity and also to the stability of the dispersion state, but it is 5 to 40 mol% in the copolymer, etc., and 10 to 30 mol%. % is suitable. If the amount of the functional monomer 1) is too large, it will impair the mechanical strength of the ion exchange membrane, etc.
Furthermore, the ion exchange performance decreases due to an increase in the water content, and if the excess amount is too small, the ion exchange function is not exhibited, and the retention stability of the dispersion state during the replacement treatment is impaired, so it is preferable. do not have. In the present invention, the reason why the presence of carboxylic acid type side chains in the fluorinated polymer is related to the stability of the dispersion state is not necessarily clear.

However, in centrifugal separation of aqueous dispersions, etc., carboxylic acid type fluorinated polymers maintain a stable dispersion state in the concentrated latex layer, whereas fluorinated polymers without functional groups such as carboxylic acid groups Since the occurrence of latex destruction is observed at the same level of concentration during coalescence, it is thought that the carboxylic acid type side chains make some contribution to the stability of the dispersed state. It goes without saying that the above explanations are provided to assist in understanding the present invention and do not limit the present invention in any way. Therefore, the remainder of the compound (1) in the copolymer of the present invention is occupied by the compound (0) and the other compound (m), but the amount of the olefin compound (m) is important because it is greatly related to the electrical, mechanical properties, chlorine resistance, etc. when used as an ion exchange membrane.

Therefore, when using the olefin compound (m) in combination,
Olefin compound (m)/Fluorinated olefin compound (
The molar ratio of 0) is preferably 5/95 to 70/30, particularly 10/90 to 60/40. Furthermore, when fluorovinyl ether, divinyl ether, etc. are used in combination, it is suitable to use the proportion in the copolymer of 30 mol% or less, preferably about 2 to 20 mol%. In a preferred embodiment of the invention, the ion exchange capacity is
They are selected from a wide range of 0.5 to 2.2 milliequivalents/gram dry resin, but the unique feature is that even if the ion exchange capacity is increased, the molecular weight of the resulting copolymer can be increased; The mechanical properties and durability of the combination do not deteriorate.

Although the ion exchange capacity varies depending on the type of copolymer within the above range, it is preferably 0.8 meq/g dry resin or more, particularly 1.0 meq/g dry resin or more. It is preferable in terms of mechanical properties and electrochemical performance as an exchange membrane. In addition, the molecular weight of the carboxylic acid type fluorinated polymer in the present invention is important because it is related to the mechanical performance and film formability as an ion exchange membrane, and when expressed in the value of To, it is 150o0 or more, preferably 170~
It is preferably about 34,000, particularly about 180 to 30,000. In this specification, the word "To" is defined as follows.

That is, the volumetric flow rate is related to the molecular weight of the copolymer.
The temperature in seconds is defined as TQ. Here, the volume flow rate is the diameter of the polymer under a pressure of 30 kg/1 at a constant temperature.
The amount of copolymer melted and flowed out from an orifice with a length of 2 willows on the side is expressed in units of /sec. still,
"Ion exchange capacity" was determined as follows. That is,
The H-type cation exchange resin membrane was heated to 600 m
The mixture was left to stand for 0.5 hours, completely converted to H type, and thoroughly washed with water so that no HC residue remained. Thereafter, 0.5 mm of this H-type membrane was left standing at room temperature for 2 days in a solution prepared by adding 25 mm of water to 0.1 N NaoH25. The membrane was then taken out and the amount of NaOH in the solution was reduced to 0.1N H
It is determined by back titration with C sleeve. In the present invention, in the copolymerization reaction between the functional monomer and the fluorinated olefin compound, the amount of aqueous medium used is adjusted to a weight ratio of aqueous medium/functional monomer of 20/1 or less, preferably 10/1.
It is preferable to carry out the control at a value of /1 or less.

If the amount of the aqueous medium used is too large, the copolymerization reaction rate will drop significantly and it will take a long time to obtain a high copolymer yield. Also, too much aqueous medium makes it difficult to achieve high molecular weights when high ion exchange capacities are used. Furthermore, the following difficulties are recognized when using a large amount of an aqueous medium. For example, there are disadvantages in operational aspects such as an increase in the size of the reactor and separation and recovery of the copolymer. Next, in the present invention, it is preferable to employ a copolymerization reaction pressure of 7 kg/〆 or more.

If the copolymerization reaction pressure is too low, the copolymerization reaction rate cannot be maintained at a level that is practically satisfactory, and there are also difficulties in forming a high molecular weight copolymer. Furthermore, if the copolymerization reaction pressure is too low, the ion exchange capacity of the resulting copolymer will become extremely high, and the mechanical strength and ion exchange performance will tend to decrease due to increased water content.
In addition, the copolymerization reaction pressure is desirably selected from 50k9/c cedar or less, taking into consideration the reaction apparatus or work operation in industrial implementation. Although it is possible to employ a copolymerization reaction pressure higher than this range, it is not possible to proportionately improve the objects of the present invention. Therefore, in the present invention, it is optimal to select the polymerization reaction pressure from the range of 7 to 50 k9/c, preferably 9 to 30 k9/c. In the copolymerization reaction of the present invention, conditions and operations other than the above-mentioned reaction conditions are not particularly limited and may be adopted over a wide range.

For example, the optimum copolymerization reaction temperature can be selected depending on the type of polymerization initiation source, reaction molar ratio, etc., but normally, too high or low temperature is disadvantageous for industrial implementation.
It is selected from about 20 to 9000, preferably about 30 to 8000. Therefore, in the present invention, it is desirable to select a polymerization initiation source that exhibits high activity at the above-mentioned suitable reaction temperature.

for example,. Although it is possible to employ highly active ionizing radiation even at room temperature or lower, it is usually more advantageous to employ an azo compound or a peroxy compound for industrial implementation. Polymerization initiation sources suitably employed in the present invention include disuccinic acid peroxide, benzoyl peroxide, lauroyl/
diacyl peroxide such as dibentafluoropropionyl peroxide, 2,2'-azobis(2-ami[dinopropane) hydrochloride, 4,4'-azopis(4-cyanowallerianic acid), azobis Azo compounds such as isobutyronitrile, peroxyesters such as t-butylperoxyisobutyrate and t-butylperoxypivalate, diisopropyl peroxydicarbonate, di-2-ethylhexyl peroxydicarbonate, etc. These include hydroperoxides such as peroxydicarbonate and diisopropylbenzene hydroperoxide, inorganic peroxides such as potassium persulfate and ammonium persulfate, and their redox systems. In the present invention, the concentration of the polymerization initiator is 0.0% relative to all monomers.
0001-3% by weight, preferably 0.001-2% by weight
That's about it.

By lowering the initiator concentration, it is possible to increase the molecular weight of the resulting copolymer and maintain a high ion exchange capacity. If the initiator concentration is too high, the tendency to decrease the molecular weight increases, which is disadvantageous to the production of high ion exchange capacity, high molecular weight copolymers. Other surfactants and dispersants used in ordinary aqueous medium polymerization,
Buffers, pH adjusters, etc. can also be added. In addition, as long as it does not inhibit the copolymerization reaction between the fluorinated olefin compound and the specific functional monomer and has low chain transfer, for example, fluorinated or fluorinated chlorinated solvents known as fluorocarbon solvents may be used. Inert organic solvents such as saturated hydrocarbons can also be added. Therefore, in the copolymerization in an aqueous medium in the present invention, it is preferable to control the concentration of the produced copolymer to 4% by weight or less, preferably 3% by weight or less.

If the concentration is too high, problems such as an increase in the load, difficulty in heat removal, and insufficient diffusion of the fluorinated olefin monomer will occur. In the present invention, the aqueous dispersion obtained as described above is subjected to a substitution treatment with a hydrophilic organic solvent.

As for the substitution treatment means, various means can be employed as long as they do not destroy the dispersion state of the aqueous dispersion. For example, a combination of separation of the aqueous medium layer by centrifugation and addition of a hydrophilic organic solvent, a combination of separation of the aqueous medium layer and addition of a hydrophilic organic solvent by the electric shock method or freezing method, or a combination of separation of the aqueous medium layer by centrifugal separation and addition of a hydrophilic organic solvent, or Examples include a method of removing water by evaporation after adding a hydrophilic organic solvent. Usually far 0
A method of gradually separating the aqueous medium layer through repeated operations of separating the aqueous medium layer by a separation method, adding a hydrophilic organic solvent to the concentrated layer, and subjecting it to centrifugation can be effectively employed. . Various hydrophilic organic solvents may be used for the substitution treatment in the present invention.

Usually, it is desirable to employ a water-soluble organic solvent for the purpose of smoothly and advantageously displacing and separating the aqueous medium, and preferably one that dissolves 0.5% by weight or more of water in 20 oo. Specific examples include alcohols, ketones, organic acids, aldehydes, and amines. In addition, hydrophilic organic solvents that are easily compatible with water, such as pyrrolidones, esters, and ethers, may also be used even if their solubility in water is not necessarily high, and a mixed solvent system may also be used. In the operation of adding a hydrophilic organic solvent to the concentrated layer to replace the aqueous medium layer, the operation can be repeated depending on the tolerance of water remaining in the non-aqueous dispersion, and usually several times is sufficient. It is.

The amount of the organic solvent to be added is not particularly limited, but it is usually 0.5 to 20 parts by weight based on the weight of the polymer. According to the present invention, the concentration of the non-aqueous dispersion can be as high as 6% by weight, but usually from 5% by weight to 5% by weight.
, preferably in a concentration of 1% to 4% by weight.

The viscosity of the non-aqueous dispersion can vary from 10 centipoise to 1,000,000 centipoise depending on the concentration of the dispersion and the type of hydrophilic organic solvent used, but for purposes such as obtaining a good copolymer film by casting etc. Usually 100
It is used in the range of centipoise to 10,000 poise. The non-aqueous dispersion obtained in the present invention can be used in the same manner as an organic solvent solution, and can be used for various purposes and uses.

And since it is possible to achieve a concentration as high as 6% by weight,
The range of applications has been expanded, and the effects of use are excellent. For example, by casting the non-aqueous dispersion or impregnating it into a porous material such as asbestos or polytetrafluoroethylene, and drying and removing the hydrophilic organic solvent, it can be used for electrolysis, dialysis, fuel, etc. It is suitable for making films of arbitrary shapes, sheet-like products, etc. for use in batteries, etc., and is also suitable for repairing damaged parts such as pisoholes and tears in films made in this way or other films for corneal membranes. It is extremely effective. Furthermore, by using the non-aqueous dispersion of the present invention, it becomes extremely convenient to coat the surfaces of objects such as substrates and electrodes. next,
Examples of the present invention will be explained in more detail.
It goes without saying that the present invention is not limited in any way by this explanation.

Incidentally, parts in the examples are parts by weight unless otherwise specified. Example 10.2 Into the stainless steel pressure-resistant reaction vessel, add ion-exchanged water for 100 minutes, C8F, 7COON for 0.2 hours, Na2HP04/12 days 20 for 0.5 hours, NaH2P
04/2nd 20 0.3 evening, (NH4) 2S208 0
．． 026 evening preparation, then 20 evening CF2=CF○(C
F2) 3COOCH3 was charged.

After sufficiently degassing with liquid nitrogen, the temperature was raised to 57o0, and tetrafluoroethylene was introduced to 11.0k9/c to carry out a reaction. During the reaction, tetrafluoroethylene was continuously introduced into the system and the pressure was maintained at 11.0 k9/s. After 4.5 hours, unreacted tetrafluoroethylene was purged to terminate the reaction.

Furthermore, unreacted CF2=CF○(CF2)3COOCH3
was extracted and separated by adding trichlorotrifluoroethane to obtain a stable aqueous dispersion having a concentration of 1% by weight. The composition of CF2=CF○(CF2)3COOCH3 in the copolymer was 20.3 mol%. The aqueous dispersion was separated into an aqueous medium and a polymer concentrated layer using a centrifuge. The aqueous medium layer was removed, the same amount of water was newly added, and the centrifugation operation was repeated again. The operation was repeated three times to remove the electrolyte used in the polymerization.

Next, a mixed solvent of N-methylpyrrolidone and methanol (N-methylpyrrolidone/methanol = 2.5/
1 weight ratio) was added to prepare a dispersion liquid, and the centrifugation operation was repeated again. Finally, an organic solvent having the above composition was added to the concentrated layer again to produce a non-aqueous dispersion having a copolymer concentration of 2% by weight. The viscosity of the dispersion was 1000 centipoise. The dispersion was cast onto a thoroughly washed glass plate, and 50 qo
A good film of the copolymer having a thickness of 300 m was obtained by leaving it in an electric furnace for 5 hours at 150 oo.

By hydrolyzing the film, the ion exchange capacity is increased to 1
．． An ion exchange membrane of 43 milliequivalents/ta dry resin was obtained. Example 2 A non-aqueous dispersion with a copolymer concentration of 35% by weight was produced in the same manner as in Example 1, except that the organic solvent used in Example 1 was changed from a mixed solvent of N-methylpyrrolidone and methanol to propanol. .

- The viscosity of the dispersion was 250 centipoise, and a good film was obtained by leaving it on a glass plate at 5,000 centipoise for two hours. Example 3 In Example 1, CF2=CF○(CF2)3COOC
Polymerization was carried out in the same manner except that H3 was charged in place of H3 and the reaction was carried out at a polymerization pressure of 13k9/c to obtain a 19% by weight aqueous dispersion of a copolymer having a composition of 16.0 mol%.

Claims (1)

[Scope of Claims] 1. A fluorinated ethylenically unsaturated monomer and a polymerizable functional monomer having a functional group that can be converted into a carboxylic acid group or a carboxylic acid group are combined by the action of a polymerization initiation source. copolymerized in an aqueous medium, and the functional monomer content is 5 to 5.
An aqueous dispersion containing 40 mol% of a carboxylic acid type fluorinated polymer in a dispersed state was obtained, and the aqueous medium of the aqueous dispersion was replaced with a hydrophilic organic solvent without destroying the dispersion state of the aqueous dispersion. A method for producing a non-aqueous dispersion of a carboxylic acid type fluorinated polymer. 2 The functional monomer has the general formula CF_2=CX(OCF_2
CFY) l-(O)_m-(CFY')_n-A (in the formula, l is an integer of 0 to 3, m is 0 to 1, n is an integer of 0 to 12, and X is a fluorine atom or −CF_3, Y, Y
' is a fluorine atom or a perfluoroalkyl group having 1 to 10 carbon atoms, and A is -CN, -COOR_1, -COO
M or -CONR_2R_3, where R_1 is carbon number 1
~10 alkyl groups, R_2, R_3 are hydrogen atoms or R
_1 and M is an alkali metal or a quaternary ammonium group). 3 The fluorinated ethylenically unsaturated monomer has the general formula CF_
2. The manufacturing method according to claim 1, which is a fluorinated olefin compound represented by 2=CZZ' (where Z and Z' are a fluorine atom, a chlorine atom, or -CF_3). 4 The functional monomer has a general formula ▲ Numerical formula, chemical formula, table, etc. 3. The manufacturing method according to claim 2, wherein the fluorovinyl compound is a fluorovinyl compound represented by COOR and R is a lower alkyl group. 5. The manufacturing method according to claim 3, wherein tetrafluoroethylene is used as the fluorinated ethylenically unsaturated monomer. 6. The manufacturing method according to claim 1, which is carried out at a copolymerization reaction temperature of 20 to 90°C. 7. The manufacturing method according to claim 1, which is carried out at a copolymerization reaction pressure of 7 kg/cm^2 or more. 8. The production method according to claim 1, wherein the copolymerization reaction is carried out while controlling the concentration of the carboxylic acid type fluorinated polymer in the produced aqueous dispersion to 40% by weight or less.