U.S. patent application number 10/518052 was filed with the patent office on 2005-10-13 for fluoropolymer dispersion and process for producing fluoropolymer dispersion.
Invention is credited to Arase, Takuya, Ino, Tadashi, Tatemoto, Masayoshi.
Application Number | 20050228127 10/518052 |
Document ID | / |
Family ID | 31949466 |
Filed Date | 2005-10-13 |
United States Patent
Application |
20050228127 |
Kind Code |
A1 |
Tatemoto, Masayoshi ; et
al. |
October 13, 2005 |
Fluoropolymer dispersion and process for producing fluoropolymer
dispersion
Abstract
A fluoropolymer solid composition which contains a fine particle
comprising a fluoropolymer, said fluoropolymer having an acid/acid
salt group, said acid/acid salt group being a sulfonic acid group,
--SO.sub.2NR.sup.17R.sup.18, a carboxyl group,
--SO.sub.3NR.sup.1R.sup.2R- .sup.3R.sup.4,
--SO.sub.3M.sup.1.sub.1/L, --COONR.sup.5R.sup.6R.sup.7R.sup- .8 or
--COOM.sup.2.sub.1/L (in which R.sup.17 and R.sup.18 are the same
or different and each represents a hydrogen atom, an alkali metal,
an alkyl group or a sulfonyl-containing group, R.sup.1, R.sup.2,
R.sup.3 and R.sup.4 are the same or different and each represents a
hydrogen atom or an alkyl group having 1 to 4 carbon atoms,
R.sup.5, R.sup.6, R.sup.7 and R.sup.8 are the same or different and
each represents a hydrogen atom or an alkyl group having 1 to 4
carbon atoms, M.sup.1 and M.sup.2 are the same or different and
each represents a metal whose valence is L, and said metal whose
valence is L is a metal belonging to the group 1, 2, 4, 8, 11, 12
or 13 of the periodic table); said fine particle comprising the
fluoropolymer containing, at the proportion of at least 25% by mass
thereof, a spherical fluoropolymer fine particle, and said
spherical fluoropolymer fine particle being substantially
spherical.
Inventors: |
Tatemoto, Masayoshi;
(Settsu-shi, JP) ; Arase, Takuya; (Settsu-shi,
JP) ; Ino, Tadashi; (Settsu-shi, JP) |
Correspondence
Address: |
SUGHRUE MION, PLLC
2100 PENNSYLVANIA AVENUE, N.W.
SUITE 800
WASHINGTON
DC
20037
US
|
Family ID: |
31949466 |
Appl. No.: |
10/518052 |
Filed: |
December 16, 2004 |
PCT Filed: |
June 16, 2003 |
PCT NO: |
PCT/JP03/07591 |
Current U.S.
Class: |
524/805 ;
525/326.2 |
Current CPC
Class: |
H01M 8/1039 20130101;
B01D 71/82 20130101; C08F 6/003 20130101; B01D 67/0009 20130101;
B01D 2325/10 20130101; B01D 2323/46 20130101; C08F 2800/10
20130101; C08F 8/44 20130101; Y02E 60/50 20130101; B01D 2325/42
20130101; H01M 8/1025 20130101; Y02P 70/50 20151101; B01D 2323/06
20130101; B01D 69/141 20130101; H01M 8/1004 20130101; B01D 69/10
20130101; H01M 8/1072 20130101; B01D 69/12 20130101; H01M 2300/0082
20130101; C08F 2/10 20130101; C08F 6/14 20130101; B01D 71/32
20130101; B01D 2325/14 20130101; B01D 67/0011 20130101; C08F 6/003
20130101; C08L 27/12 20130101; C08F 6/14 20130101; C08L 27/12
20130101; C08F 8/44 20130101; C08F 8/12 20130101; C08F 214/262
20130101 |
Class at
Publication: |
524/805 ;
525/326.2 |
International
Class: |
C08K 003/00; C08L
027/12 |
Foreign Application Data
Date |
Code |
Application Number |
Jun 17, 2002 |
JP |
2002-175445 |
Mar 3, 2003 |
JP |
2003-056185 |
Claims
1. A fluoropolymer solid composition which contains a fine particle
comprising a fluoropolymer, said fluoropolymer having an acid/acid
salt group, said acid/acid salt group being a sulfonic acid group,
--SO.sub.2NR.sup.17R.sup.18, a carboxyl group,
--SO.sub.3NR.sup.1R.sup.2R- .sup.3R.sup.4,
--SO.sub.3M.sup.1.sub.1/L, --COONR.sup.5R.sup.6R.sup.7R.sup- .8 or
--COOM.sup.2.sub.1/L (in which R.sup.17 and R.sup.18 are the same
or different and each represents a hydrogen atom, an alkali metal,
an alkyl group or a sulfonyl-containing group, R.sup.1, R.sup.2,
R.sup.3 and R.sup.4 are the same or different and each represents a
hydrogen atom or an alkyl group having 1 to 4 carbon atoms,
R.sup.5, R.sup.6, R.sup.7 and R.sup.8 are the same or different and
each represents a hydrogen atom or an alkyl group having 1 to 4
carbon atoms, M.sup.1 and M.sup.2 are the same or different and
each represents a metal whose valence is L, and said metal whose
valence is L is a metal belonging to the group 1, 2, 4, 8, 11, 12
or 13 of the periodic table); said fine particle comprising the
fluoropolymer containing, at the proportion of at least 25% by mass
thereof, a spherical fluoropolymer fine particle, and said
spherical fluoropolymer fine particle being substantially
spherical.
2. The fluoropolymer solid composition according to claim 1,
wherein the fine particle comprising the fluoropolymer contains the
spherical fluoropolymer fine particle at the proportion of at least
50% by mass thereof.
3. The fluoropolymer solid composition according to claim 1,
wherein the spherical fluoropolymer fine particle has an average
particle diameter of not smaller than 10 nm.
4. The fluoropolymer solid composition according to claim 1,
wherein the spherical fluoropolymer fine particle has an average
particle diameter of 10 to 300 nm.
5. The fluoropolymer solid composition according to claim 1,
wherein the spherical fluoropolymer fine particle has an average
particle diameter of 30 to 160 nm.
6. The fluoropolymer solid composition according to claim 1,
wherein an existence of the acid/acid salt groups on a particle
surface of the fine particles comprising fluoropolymers is more
than that in the particle inside thereof.
7. The fluoropolymer solid composition according to claim 1,
wherein the acid/acid salt group is bound to a fluoroether side
chain represented by the following general formula (I):
--O--(CF.sub.2CFY.sup.1--O).sub.n--(CF- Y.sup.2).sub.m-- (I) in
which Y.sup.1 represents a fluorine atom, a chlorine atom or a
perfluoroalkyl group; n represents an integer of 0 to 3, and n
atoms/groups of Y.sup.1 may be the same or different; Y.sup.2
represents a fluorine atom or a chlorine atom; m represents an
integer of 1 to 5, and m atoms of Y.sup.2 may be the same or
different, said fluoroether side chain being bound, in the manner
of ether bonding, to a carbon atom constituting a perfluoroethylene
unit in a main chain of the fluoropolymer.
8. A fluoropolymer dispersion which comprises the fluoropolymer
solid composition according to claim 1, as dispersed in a liquid
medium.
9. The fluoropolymer dispersion according to claim 8, wherein the
fluoropolymer solid composition amounts to 2 to 80% by mass based
on the total mass of the fluoropolymer dispersion.
10. The fluoropolymer dispersion according to claim 8, wherein the
liquid medium is an aqueous dispersion medium, said aqueous
dispersion medium having a water content of 10 to 100% by mass.
11. A method for producing a fluoropolymer dispersion to give the
fluoropolymer dispersion where a fine particle comprising a
fluoropolymer is dispersed in an aqueous dispersion medium, said
fluoropolymer having a sulfonic acid group and/or carboxyl group,
and said method comprising a hydrolysis step of hydrolyzing, in an
aqueous medium, --SO.sub.2X.sup.1 (X.sup.1 representing a halogen
atom) and/or --COZ.sup.1 (Z.sup.1 representing an alkoxyl group
having 1 to 4 carbon atoms) which a fluoropolymer precursor has
thereby to give the fluoropolymer.
12. The method for producing a fluoropolymer dispersion according
to claim 11, wherein the sulfonic acid group and/or carboxyl group
each is bound to a fluoroether side chain represented by the
following general formula (I):
--O--(CF.sub.2CFY.sup.1--O).sub.n--(CFY.sup.2).sub.m-- (I) wherein
Y.sup.1 represents a fluorine atom, a chlorine atom or a
perfluoroalkyl group; n represents an integer of 0 to 3, and n
atoms/groups of Y.sup.1 may be the same or different; Y.sup.2
represents a fluorine atom or a chlorine atom; m represents an
integer of 1 to 5, and m atoms of Y.sup.2 may be the same or
different, and wherein said fluoroether side chain is bound, in the
manner of ether bonding, to a carbon atom constituting a
perfluoroethylene unit in a main chain of the fluoropolymer.
13. The method for producing a fluoropolymer dispersion according
to claim 11, wherein the aqueous medium is one originating from an
aqueous reaction medium in a polymerization reaction, said
polymerization reaction giving the fluoropolymer precursor.
14. The method for producing a fluoropolymer dispersion according
to claim 13, wherein the polymerization reaction is carried out by
emulsion polymerization.
15. The method for producing a fluoropolymer dispersion according
to claim 11, wherein the aqueous dispersion medium in the
fluoropolymer dispersion is one originating from the aqueous
medium.
16. The method for producing a fluoropolymer dispersion according
to claim 11, wherein the fluoropolymer precursor is one obtainable
by polymerizing a fluorovinyl ether derivative represented by the
following general formula (II):
CF.sub.2.dbd.CF--O--(CF.sub.2CFY.sup.1--O).sub.n--(CFY.sup.-
2).sub.m-A.sup.1 (II) wherein Y.sup.1 represents a fluorine atom, a
chlorine atom or a perfluoroalkyl group; n represents an integer of
0 to 3, and n atoms/groups of Y.sup.1 may be the same or different;
Y.sup.2 represents a fluorine atom or a chlorine atom; m represents
an integer of 1 to 5, and m atoms of Y.sup.2 may be the same or
different; A.sup.1 represents --SO.sub.2X or --COZ.sup.1; X
represents a halogen atom, --OM.sup.3 or --OM.sup.4.sub.1/2,
M.sup.3 represents an alkali metal or
NR.sup.9R.sup.10R.sup.11R.sup.12, M.sup.4 represents an alkaline
earth metal, R.sup.9, R.sup.10, R.sup.11 and R.sup.12 are the same
or different and each represents a hydrogen atom or an alkyl group
having 1 to 4 carbon atoms; and Z.sup.1 represents an alkoxyl group
having 1 to 4 carbon atoms).
17. The method for producing a fluoropolymer dispersion according
to claim 16, wherein the fluoropolymer precursor is a binary or
multinary copolymer obtainable by polymerizing the fluorovinyl
ether derivative and a fluorine-containing ethylenic monomer.
18. The method for producing a fluoropolymer dispersion according
to claim 12, wherein Y.sup.1 is a trifluoromethyl group, Y.sup.2 is
a fluorine atom, n is 0 or 1 and m is 2.
19. The method for producing a fluoropolymer dispersion according
to claim 11, which further comprises a polymerization reaction step
of carrying out a polymerization reaction, said polymerization
reaction providing the fluoropolymer precursor, said fluoropolymer
dispersion being produced in an aqueous system through the
polymerization reaction step and hydrolysis step, and said
fluoropolymer dispersion being produced without drying said
fluoropolymer precursor and the fluoropolymer.
20. The method for producing a fluoropolymer dispersion according
to claim 19, wherein the polymerization reaction is carried out by
iodine transfer polymerization.
21. The method for producing a fluoropolymer dispersion according
to claim 11, wherein the hydrolysis step comprises hydrolysis and
neutralization respectively using with an alkali and an acid in
that order, wherein said fluoropolymer precursor has
--SO.sub.2X.sup.1 (X.sup.1 representing a halogen atom) and/or
--COZ.sup.1 (Z.sup.1 representing an alkoxyl group having 1 to 4
carbon atoms).
22. The method for producing a fluoropolymer dispersion according
to claim 11, wherein the hydrolysis step comprises an alkali
treatment step of treating a fluoropolymer precursor (P) with an
alkali and wherein said fluoropolymer precursor (P) has
--SO.sub.2X.sup.1 (X.sup.1 representing a halogen atom) and/or
--COZ.sup.1 (Z.sup.1 representing an alkoxyl group having 1 to 4
carbon atoms).
23. The method for producing a fluoropolymer dispersion according
to claim 22, wherein the hydrolysis step comprises an alkali
treatment step and thereafter, a subsequent step of neutralization
treatment with an acid.
24. The method for producing a fluoropolymer dispersion according
to claim 22, wherein the hydrolysis step further comprises a step
of removing a low-molecular-weight substance following the alkali
treatment step, and said low-molecular-weight substance being a
residual monomer remaining in the polymerization reaction step, a
polymerization initiator residue, an unrequired
low-molecular-weight polymer, and/or a substance formed upon
treatment of the fluoropolymer precursor (P) with an alkali.
25. The method for producing a fluoropolymer dispersion according
to claim 24, wherein the step of removing a low-molecular-weight
substance is carried out by ultrafiltration technique.
26. The method for producing a fluoropolymer dispersion according
to claim 22, wherein the fluoropolymer precursor (P) has
--SO.sub.2X.sup.1.
27. The method for producing a fluoropolymer dispersion according
to claim 19, wherein the hydrolysis step comprises the
polymerization reaction step of obtaining the fluoropolymer
precursor by polymerizing in the presence of a fluoromonomer (Pm)
and a fluoromonomer (Qm), an alkali treatment step of treatment
with an alkali and a step of neutralization treatment with an acid,
in that order, said fluoromonomer (Pm) having --SO.sub.2X.sup.1
(X.sup.1 representing a halogen atom) and/or --COZ.sup.1 (Z.sup.1
representing an alkoxyl group having 1 to 4 carbon atoms), and said
fluoromonomer (Qm) having --SO.sub.2X.sup.2 (X.sup.2 representing
--OM.sup.3 or --OM.sup.4.sub.1/2 in which M.sup.3 represents an
alkali metal or NR.sup.9R.sup.10R.sup.11R.sup.12 (in which R.sup.9,
R.sup.10, R.sup.11 and R.sup.12 are the same or different and each
represents a hydrogen atom or an alkyl group having 1 to 4 carbon
atoms); and M.sup.4 represents an alkaline earth metal) and/or
--COOZ.sup.2 (Z.sup.2 representing M.sup.5 or M.sup.6.sub.1/2 in
which M.sup.5 represents an alkali metal or
NR.sup.13R.sup.14R.sup.15R.sup.16 (in which R.sup.13, R.sup.14,
R.sup.15 and R.sup.16 are the same or different and each represents
a hydrogen atom or an alkyl group having 1 to 4 carbon atoms);
M.sup.6 represents an alkaline earth metal).
28. The method for producing a fluoropolymer dispersion according
to claim 19, wherein the hydrolysis step comprises the
polymerization reaction step of obtaining the fluoropolymer
precursor by polymerizing in the presence of a fluoromonomer
(Qm)-based polymer and a fluoromonomer (Pm), an alkali treatment
step of treatment with an alkali and a step of neutralization
treatment with an acid, in that order, said fluoromonomer (Pm)
having --SO.sub.2X.sup.1 (X.sup.1 representing a halogen atom)
and/or --COZ.sup.1 (Z.sup.1 representing an alkoxyl group having 1
to 4 carbon atoms), and said fluoromonomer (Qm) having
--SO.sub.2X.sup.2 (X.sup.2 representing --OM.sup.3 or
--OM.sup.4.sub.1/2 in which M.sup.3 represents an alkali metal or
NR.sup.9R.sup.10R.sup.11R.sup.12 (in which R.sup.9, R.sup.10,
R.sup.11 and R.sup.12 are the same or different and each represents
a hydrogen atom or an alkyl group having 1 to 4 carbon atoms); and
M.sup.4 represents an alkaline earth metal) and/or --COOZ.sup.2
(Z.sup.2 representing M.sup.5 or M.sup.6.sub.1/2 in which M.sup.5
represents an alkali metal or NR.sup.13R.sup.14R.sup.15R.sup.16 (in
which R.sup.13, R.sup.14, R.sup.15 and R.sup.16 are the same or
different and each represents a hydrogen atom or an alkyl group
having 1 to 4 carbon atoms); M.sup.6 represents an alkaline earth
metal).
29. The method for producing a fluoropolymer dispersion according
to claim 27, wherein the hydrolysis step further comprises a step
of removing a low-molecular-weight substance following the alkali
treatment step, said low-molecular-weight substance being a
residual monomer remaining in the polymerization reaction step, a
polymerization initiator residue, an unrequired
low-molecular-weight polymer, and/or a substance formed upon
treatment of the fluoropolymer precursor with an alkali.
30. The method for producing a fluoropolymer dispersion according
to claim 27, wherein the step of removing a low-molecular-weight
substance is carried out by ultrafiltration technique.
31. The method for producing a fluoropolymer dispersion according
to claim 27, wherein the fluoromonomer (Pm) has --SO.sub.2X.sup.1
and wherein the fluoromonomer (Qm) has --SO.sub.2X.sup.2.
32. The method for producing a fluoropolymer dispersion according
to claim 27, wherein the aqueous medium does not contain an
emulsifier.
33. The method for producing a fluoropolymer dispersion according
to claim 32, wherein the fluoropolymer precursor is one obtainable
by carrying out the polymerization reaction in an emulsifier-free
aqueous reaction medium.
34. A method for producing a fluoropolymer dispersion to give the
fluoropolymer dispersion where a fine particle comprising a
fluoropolymer is dispersed in a liquid medium, said fluoropolymer
having an acid salt group, said acid salt group being
--SO.sub.3NR.sup.1R.sup.2R.sup.3R.sup.4- ,
--SO.sub.3M.sup.1.sub.1/L, --COONR.sup.5R.sup.6R.sup.7R.sup.8 or
--COOM.sup.2.sub.1/L (in which R.sup.1, R.sup.2, R.sup.3 and
R.sup.4 are the same or different and each represents a hydrogen
atom or an alkyl group having 1 to 4 carbon atoms, R.sup.5,
R.sup.6, R.sup.7 and R.sup.8 are the same or different and each
represents a hydrogen atom or an alkyl group having 1 to 4 carbon
atoms, M.sup.1 and M.sup.2 are the same or different and each
represents a metal whose valence is L, and the metal whose valence
is L is a metal belonging to the group 1, 2, 4, 8, 11, 12 or 13 of
the periodic table), and said method comprising a step of
hydrolyzing, in an aqueous medium, --SO.sub.2X.sup.1 (X.sup.1
representing a halogen atom) and/or --COZ.sup.1 (Z.sup.1
representing an alkoxyl group having 1 to 4 carbon atoms) which the
fluoropolymer precursor has thereby to give the fluoropolymer.
35. The method for producing a fluoropolymer dispersion according
to claim 34, wherein the hydrolysis step comprises a polymerization
reaction step for obtaining a fluoropolymer precursor by carrying
out a polymerization in the presence of a fluoromonomer (Pm) and a
fluoromonomer (Qm) and an alkali treatment step of treating with an
alkali, said fluoromonomer (Pm) having --SO.sub.2X.sup.1 (X.sup.1
representing a halogen atom) and/or --COZ.sup.1 (Z.sup.1
representing an alkoxyl group having 1 to 4 carbon atoms), and said
fluoromonomer (Qm) having --SO.sub.2X.sup.2 (X.sup.2 representing
--ONR.sup.9R.sup.10R.sup.11R.sup.12 or --OM.sup.1.sub.1/L in which
R.sup.9, R.sup.10, R.sup.11 and R.sup.12 are the same or different
and each represents a hydrogen atom or an alkyl group having 1 to 4
carbon atoms, M.sup.1 represents a metal whose valence is L, and
the metal whose valence is L is a metal belonging to the group 1,
2, 4, 8, 11, 12 or 13 of the periodic table) and/or --COOZ.sup.2
(Z.sup.2 representing NR.sup.13R.sup.14R.sup.15R.sup.16 or
M.sup.2.sub.1/L in which R.sup.13, R.sup.14, R.sup.15 and R.sup.16
are the same or different and each represents a hydrogen atom or an
alkyl group having 1 to 4 carbon atoms, M.sup.2 represents a metal
whose valence is L, and the metal whose valence is L is a metal
belonging to the group 1, 2, 4, 8, 11, 12 or 13 of the periodic
table).
36. The method for producing a fluoropolymer dispersion according
to claim 34, wherein the hydrolysis step further comprises a step
of removing a low-molecular-weight substance following the alkali
treatment step, said low-molecular-weight substances being a
residual monomer remaining in the polymerization reaction step, a
polymerization initiator residue, an unrequired
low-molecular-weight polymer, and/or a substance formed upon
treatment of the fluoropolymer precursor with an alkali.
37. A fluoropolymer dispersion obtainable by the method for
producing a fluoropolymer dispersion according to claim 11.
38. A dispersion composition for thin film formation which
comprises the fluoropolymer dispersion according to claim 8, and at
least one alcohol selected from the group consisting of methanol,
ethanol, propanol and tetrafluoropropanol.
39. A film/membrane obtainable by cast film formation using the
fluoropolymer dispersion according to claim 8.
40. A film/membrane obtainable by impregnating a porous support
with the fluoropolymer dispersion according to claim 8.
41. An active substance-immobilized material comprising a
fluoropolymer and an active substance which is obtainable by
applying, to a substrate, a liquid composition comprising the
active substance and the fluoropolymer dispersion according to
claim 8.
42. The active substance-immobilized material according to claim
41, wherein the active substance is a catalyst.
43. The active substance-immobilized material according to claim
42, wherein the catalyst is a metal comprising platinum.
44. An electrolyte membrane comprising the active
substance-immobilized material according to claim 42.
45. A solid polymer electrolyte fuel cell comprising the
electrolyte membrane according to claim 44.
46. A method for producing an acid-derivative-type-group-containing
fluorocopolymer which comprises carrying out a polymerization
reaction of a fluorovinyl ether derivative (Rm) represented by the
follwoing general formula (VI):
CF.sub.2.dbd.CF--O--(CF.sub.2CFY.sup.1--O).sub.n--(CFY.sup.-
2).sub.m-A.sup.5 (VI) (wherein Y.sup.1 represents a fluorine atom,
a chlorine atom or a perfluoroalkyl group; n represents an integer
of 0 to 3, and n atoms/groups of Y.sup.1 are the same or different;
Y.sup.2 represents a fluorine atom or a chlorine atom; m represents
an integer of 1 to 5, and m atoms of Y.sup.2 may be the same or
different; A.sup.5 represents --SO.sub.2X.sup.1, --COZ.sup.1 and/or
--CONR.sup.9R.sup.20; X.sup.1 represents a halogen atom, Z.sup.1
represents an alkoxyl group having 1 to 4 carbon atoms, and
R.sup.19 and R.sup.20 are the same or different and each represents
a hydrogen atom, an alkali metal, an alkyl group or a
sulfonyl-containing group) in an aqueous reaction medium to thereby
give the acid-derivative-type-group-containing fluorocopolymer,
said polymerization reaction being carried out with an acid/acid
salt fluorovinyl ether derivative represented by the following
general formula (VII):
CF.sub.2.dbd.CF--O--(CF.sub.2CFY.sup.1--O).sub.n--(CFY.sup.2).sub.-
m--A.sup.6 (VI) (wherein Y.sup.1 represents a fluorine atom, a
chlorine atom or a perfluoroalkyl group; n represents an integer of
0 to 3, and n atoms/groups of Y.sup.1 may be the same or different;
Y.sup.2 represents a fluorine atom or a chlorine atom; m represents
an integer of 1 to 5, and m atoms of Y.sup.2 may be the same or
different; A.sup.6 represents --SO.sub.2X.sup.3,
--SO.sub.2NR.sup.17R.sup.18 and/or --COOZ.sup.3; X.sup.3 represents
--OM.sup.5 or --OM.sup.6.sub.1/2; M.sup.5 represents an alkali
metal or NR.sup.1R.sup.2R.sup.3R.sup.4 in which R.sup.1, R.sup.2,
R.sup.3 and R.sup.4 are the same or different and each represents a
hydrogen atom or an alkyl group having 1 to 4 carbon atoms; M.sup.6
represents an alkaline earth metal; R.sup.17 and R.sup.18 are the
same or different and each represents a hydrogen atom, an alkali
metal, an alkyl group or a sulfonyl-containing group; Z.sup.3
represents M.sup.7 or M.sup.8.sub.1/2; M.sup.7 represents an alkali
metal or NR.sup.5R.sup.6R.sup.7R.sup.8 in which R.sup.5, R.sup.6,
R.sup.7 and R.sup.8 are the same or different and each represents a
hydrogen atom or an alkyl group having 1 to 4 carbon atoms; and
M.sup.8 represents an alkaline earth metal).
47. The method for producing the
acid-derivative-type-group-containing fluorocopolymer according to
claim 46, wherein the polymerization reaction is carried out
without using an existing emulsifiers.
48. A film/membrane obtainable by cast film formation using the
dispersion composition for thin film formation according to claim
38.
49. A film/membrane obtainable by impregnating a porous support
with the dispersion composition for thin film formation according
to claim 38, followed by removal of the liquid medium.
50. An active substance-immobilized material comprising a
fluoropolymer and an active substance which is obtainable by
applying, to a substrate, a liquid composition comprising the
active substance and the dispersion composition for thin film
formation according to claim 38.
Description
TECHNICAL FIELDS
[0001] The present invention relates to a fluoropolymer solid
composition, a fluoropolymer dispersion and a method for producing
a fluoropolymer dispersion.
BACKGROUND ART
[0002] Sulfonic acid group- and/or carboxyl group-containing
fluoropolymers were initially developed mainly for the purpose of
using them as ion exchange membranes to be utilized in common salt
electrolysis, among others. Conventionally, such membrane-like
molded articles are produced by molding --SO.sub.2F
group-containing fluoropolymers by extrusion molding, for instance,
followed by hydrolysis.
[0003] Sulfonic acid group- or like acid group-containing
fluoropolymers have recently attracted attention as materials of
not only ion exchange membranes for common salt electrolysis but
also electrolyte membranes for fuel cells and chemical sensors, and
so forth.
[0004] A solution of a sulfonic acid group-containing fluoropolymer
in a mixed solvent comprising an alcohol is known as a medium for
immobilizing a catalyst on the electrolyte membrane surface in the
manufacture of electrolyte membranes and the like (cf. e.g.
Japanese Kokai Publication Hei-08-236122). However, this solution
has a problem in that it covers active sites of the catalyst in the
process of drying, for instance, and thus cause deteriorations in
performance characteristics of fuel cells (cf. e.g. Makoto Uchida:
"Element technologies of and design guidelines for gas diffusion
electrodes for PEFC", Denkikagaku oyobi Kogyobutsurikagaku (English
title: Electrochemistry), published by The Electrochemical Society
of Japan, 2002, vol. 70, No. 8, p. 639). This solution has a
further problem from the environmental and/or operational
viewpoint. Therefore, aqueous dispersions of sulfonic acid
group-containing fluoropolymers have been demanded.
[0005] Aqueous dispersions of sulfonic acid group-containing
fluoropolymers as such can also be used like solutions, hence can
adequately be used in film/membrane formation by casting or in
immersion, for instance. Thus, they have a wide range of
application.
[0006] A method currently used in preparing aqueous dispersions of
sulfonic acid group-containing fluoropolymers comprises subjecting
membranous molded articles made from --SO.sub.2F group-containing
fluoropolymer to alkali treatment and then to acid treatment to
convert --SO.sub.2F groups to sulfonic acid groups and, further,
treating the molded articles in a mixed solvent composed of water
and a lower alcohol or in water at high temperature and high
pressure conditions.
[0007] The --SO.sub.2F group-containing fluoropolymer so far used
in the art in preparing membranous molded articles are produced
mostly by solution polymerization to obtain pellets for use in
extrusion molding and like methods of producing membranous molded
articles.
[0008] Conceivable as a method of obtaining aqueous fluoropolymer
dispersions as an alternative to solution polymerization is
emulsion polymerization. Generally, the polymers in polymer latexes
prepared by emulsion polymerization are recovered by adding an
electrolyte to the latexes to cause coagulation of polymer
particles. However, it is a problem that the essential auxiliary
components, such as the emulsifier and electrolyte, remain in the
polymers; it is thus difficult to obtain high-quality aqueous
fluoropolymer dispersions. Emulsifiers, in particular, are
difficult to remove, raising a problem in that the driers are
rusted by gases generated in the step of drying the polymers
obtained and/or the polymers are decomposed in the step of
film/membrane formation to produce bubbles and/or become dark
colored, for instance.
[0009] Known as a method of obtaining aqueous fluoropolymer
dispersions without using any conventional emulsifier is the method
which comprises polymerizing a fluoromonomer(s), such as
tetrafluoroethylene or/and vinylidene fluoride, in the presence of
a perfluorovinyl ether containing a sulfonic acid group or carboxyl
group, which may be in the form of a salt (cf. e.g. Japanese Kokai
Publication Sho-59-196308, Japanese Kokai Publication Sho-55-29519
and Japanese Kokai Publication Hei-08-67795). However, regarding
this method, these publications have no description about the use
of --SO.sub.2F group-containing fluorovinyl ether derivative in the
step of subjecting the monomer(s) to polymerization.
[0010] Also known as a method of obtaining aqueous fluoropolymer
dispersions is the method which comprises using a fluoromonomer
having --SO.sub.3Na or the like in the step of polymerization to
give sulfonic acid salt type fluoropolymers without using any
conventional emulsifier (cf. e.g. Japanese Kokai Publication
2001-226436 and Japanese Kokai Publication 2001-226425). However,
the publications cited have no description about the method of
obtaining aqueous dispersions of sulfonic acid group-containing
fluoropolymers.
[0011] As for the method of obtaining aqueous dispersions of
sulfonic acid group-containing fluoropolymers, a method is known,
among others, which comprises treating membranous molded articles
prepared from --SO.sub.2F group-containing fluoropolymer with an
alkali and then with an acid to convert --SO.sub.2F to the sulfonic
acid group and dissolving the membranous molded articles in a mixed
solvent composed of water and a lower alcohol or in water by
treatment under high temperature and high pressure conditions or
treating the membranous molded articles in a solvent essentially
consisting of water with stirring under high temperature and high
pressure conditions to give an aqueous dispersion of particles of 2
to 30 nm in size (cf. e.g. Japanese Kohyo Publication
2001-504872).
[0012] However, the method disclosed in Japanese Kohyo Publication
2001-504872 is inefficient since the fluoropolymer in liquid form
as obtained by polymerization is once made into membranous molded
articles and these are again made liquid. Further, it is a problem
that a high-temperature and high-pressure treatment is required
and, therefore, the corresponding reaction apparatus and energy are
required.
[0013] Furthermore, the polymer particles obtained by the method
disclosed in Japanese Kohyo Publication 2001-504872 are known to
have a rod-like or thread-like shape such that the aspect ratio is
generally 5 to 6 and the major axis length is about 11 nm. However,
in the case of aqueous dispersions prepared by dispersing such
rod-like or thread-like polymer particles, it is necessary to
remove, by evaporation, a large amount of the dispersion medium in
forming films/membranes by casting or impregnation, for instance.
This is very inefficient, and it is difficult to produce thick
films/membranes. A further problem is that cracks are readily
formed in the step of drying.
SUMMARY OF THE INVENTION
[0014] In view of the above-discussed state of the art, it is an
object of the present invention to provide a composition containing
an acid group- and/or acid salt group-containing fluoropolymer
suited for use as an electrode or membrane material, a dispersion
comprising such composition, and a method for producing such
dispersion. Another object of the present invention is to provide a
method for producing the above dispersion without using any
fluorine-containing emulsifier. A further object of the present
invention is to provide a method for producing acid group- or
acid-derivative-type-group-containing fluoropolymers by
polymerizing in an aqueous reaction medium without using any
conventional emulsifier.
[0015] The present invention thus provides a fluoropolymer solid
composition which contains a fine particle comprising a
fluoropolymer,
[0016] said fluoropolymer having an acid/acid salt group,
[0017] said acid/acid salt group each being a sulfonic acid group,
--SO.sub.2NR.sup.17R.sup.18, a carboxyl group,
--SO.sub.3NR.sup.1R.sup.2R- .sup.3R.sup.4,
--SO.sub.3M.sup.1.sub.1/L, --COONR.sup.5R.sup.6R.sup.7R.sup- .8 or
--COOM.sup.2.sub.1/L (in which R.sup.17 and R.sup.18 are the same
or different and each represents a hydrogen atom, an alkali metal,
an alkyl group or a sulfonyl-containing group, R.sup.1, R.sup.2,
R.sup.3 and R.sup.4 are the same or different and each represents a
hydrogen atom or an alkyl group having 1 to 4 carbon atoms,
R.sup.5, R.sup.6, R.sup.7 and R.sup.8 are the same or different and
each represents a hydrogen atom or an alkyl group having 1 to 4
carbon atoms, M.sup.1 and M.sup.2 are the same or different and
each represents a metal whose valence is L, and said metal whose
valence is L is a metal belonging to the group 1, 2, 4, 8, 11, 12
or 13 of the periodic table)
[0018] said fine particle comprising the fluoropolymer containing,
at the proportion of at least 25% by mass thereof, a spherical
fluoropolymer fine particle, and
[0019] said spherical fluoropolymer fine particle being
substantially spherical.
[0020] The present invention also provides a fluoropolymer
dispersion
[0021] which comprises the above-defined fluoropolymer solid
composition as dispersed in a liquid medium.
[0022] The present invention further provides a method for
producing a fluoropolymer dispersion to give the fluoropolymer
dispersion where a fine particle comprising a fluoropolymer is
dispersed in an aqueous dispersion medium,
[0023] said fluoropolymer having a sulfonic acid group and/or
carboxyl group, and
[0024] said method comprising a step of hydrolyzing, in an aqueous
medium, --SO.sub.2X.sup.1 (X.sup.1 representing a halogen atom)
and/or --COZ.sup.1 (Z.sup.1 representing an alkoxyl group having 1
to 4 carbon atoms) which a fluoropolymer precursor has thereby to
give the fluoropolymer.
[0025] The present invention further provides a method for
producing a fluoropolymer dispersion to give the fluoropolymer
dispersion where a fine particle comprising a fluoropolymer is
dispersed in an aqueous dispersion medium,
[0026] said fluoropolymer having an acid salt group,
[0027] said acid salt group being
--SO.sub.3NR.sup.1R.sup.2R.sup.3R.sup.4, --SO.sub.3M.sup.1.sub.1/L,
--COONR.sup.5R.sup.6R.sup.7R.sup.8 or --COOM.sup.2.sub.1/L (in
which R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are the same or
different and each represents a hydrogen atom or an alkyl group
having 1 to 4 carbon atoms, R.sup.5, R.sup.6, R.sup.7 and R.sup.8
are the same or different and each represents a hydrogen atom or an
alkyl group having 1 to 4 carbon atoms, M.sup.1 and M.sup.2 are the
same or different and each represents a metal whose valence is L,
and said metal whose valence is L is a metal belonging to the group
1, 2, 4, 8, 11, 12 or 13 of the periodic table), and said method
comprising a step of hydrolyzing, in a liquid medium,
--SO.sub.2X.sup.1 (X.sup.1 representing a halogen atom) and/or
--COZ.sup.1 (Z.sup.1 representing an alkoxyl group having 1 to 4
carbon atoms) which a fluoropolymer precursor has thereby to give
the fluoropolymer.
[0028] The present invention further provides a dispersion
composition for thin film formation
[0029] which comprises the above-defined fluoropolymer dispersion
and at least one alcohol selected from the group consisting of
methanol, ethanol, propanol and tetrafluoropropanol.
[0030] The present invention further provides a film/membrane
obtainable by cast film formation using the above-defined
fluoropolymer dispersion or the above-defined dispersion
composition for thin film formation.
[0031] The present invention further provides a film/membrane
obtainable by impregnating a porous support with the above-defined
fluoropolymer dispersion or the above-defined dispersion
composition for thin film formation, followed by removal the liquid
medium.
[0032] The present invention further provides an active
substance-immobilized material comprising a fluoropolymer and an
active substance
[0033] which is obtainable by applying, to a substrate, a liquid
composition comprising the above-mentioned active substance and the
above-defined fluoropolymer dispersion or the above-defined
dispersion composition for thin film formation.
[0034] The present invention further provides an electrolyte
membrane
[0035] which comprises the above-defined active
substance-immobilized material.
[0036] The present invention further provides a solid polymer
electrolyte fuel cell
[0037] which comprises the above-defined electrolyte membrane.
[0038] The present invention still further provides a method for
producing an acid-derivative-type-group-containing
fluorocopolymer
[0039] which comprises carrying out a polymerization reaction of a
fluorovinyl ether derivative (Rm) represented by the following
general formula (VI):
CF.sub.2.dbd.CF--O--(CF.sub.2CFY.sup.1--O).sub.n--(CFY.sup.2).sub.m-A.sup.-
5 (VI)
[0040] (wherein Y.sup.1 represents a fluorine atom, a chlorine atom
or a perfluoroalkyl group; n represents an integer of 0 to 3, and n
atoms/groups of Y.sup.1 are the same or different; Y.sup.2
represents a fluorine atom or a chlorine atom; m represents an
integer of 1 to 5, and m atoms of Y.sup.2 may the same or
different; A.sup.5 represents --SO.sub.2X.sup.1, --COZ.sup.1 and/or
--CONR.sup.19R.sup.20; X.sup.1 represents a halogen atom, Z.sup.1
represents an alkoxyl group having 1 to 4 carbon atoms, and
R.sup.19 and R.sup.20 are the same or different and each represents
a hydrogen atom, an alkali metal, an alkyl group or a
sulfonyl-containing group) in an aqueous reaction medium to thereby
give the acid-derivative-type-group-containing fluorocopolymer,
[0041] said polymerization reaction being carried out by using an
acid/acid salt fluorovinyl ether derivative represented by the
following general formula (VII):
CF.sub.2.dbd.CF--O--(CF.sub.2CFY.sup.1--O).sub.n--(CFY.sup.2).sub.m-A.sup.-
6 (VII)
[0042] (wherein Y.sup.1 represents a fluorine atom, a chlorine atom
or a perfluoroalkyl group; n represents an integer of 0 to 3, and n
atoms/groups of Y.sup.1 may be the same or different; Y.sup.2
represents a fluorine atom or a chlorine atom; m represents an
integer of 1 to 5, and m atoms of Y.sup.2 may be the same or
different; A.sup.6 represents --SO.sub.2X.sup.3,
--SO.sub.2NR.sup.17R.sup.18 and/or --COOZ.sup.3; X.sup.3 represents
--OM.sup.5 or --OM.sup.6.sub.1/2; M.sup.5 represents an alkali
metal or NR.sup.1R.sup.2R.sup.3R.sup.4 in which R.sup.1, R.sup.2,
R.sup.3 and R.sup.4 are the same or different and each represents a
hydrogen atom or an alkyl group having 1 to 4 carbon atoms;
R.sup.5, R.sup.6, R.sup.7 and R.sup.8 are the same or different and
each represents a hydrogen atom or an alkyl group having 1 to 4
carbon atoms; M.sup.6 represents an alkaline earth metal; R.sup.17
and R.sup.18 are the same or different and each represents a
hydrogen atom, an alkali metal, an alkyl group or a
sulfonyl-containing group; Z.sup.3 represents M.sup.7 or
M.sup.8.sub.1/2; M.sup.7 represents an alkali metal or
NR.sup.5R.sup.6R.sup.7R.sup.8 in which R.sup.5, R.sup.6, R.sup.7
and R.sup.8 are the same or different and each represents a
hydrogen atom or an alkyl group having 1 to 4 carbon atoms; and Me
represents an alkaline earth metal).
DETAILED DISCLOSURE OF THE INVENTION
[0043] In the following, the present invention is described in
detail.
[0044] The fluoropolymer solid composition according to the present
invention contains a fine particle comprising a
fluoropolymer(s).
[0045] The fine particle comprising fluoropolymers contains a
spherical fluoropolymer fine particle in the proportion of at least
25% by mass thereof, said spherical fluoropolymer fine particle
being substantially spherical.
[0046] The phrase "contains a spherical fluoropolymer fine particle
in the proportion of at least 25% by mass thereof" as used herein
means that spherical fluoropolymer fine particles amount to 25% by
mass or more of the fine particle comprising fluoropolymers.
[0047] The particle shape of the fine particle comprising
fluoropolymers can be evaluated in terms of aspect ratio.
[0048] By saying "substantially spherical" herein, it is meant that
the aspect ratio is not higher than 3. Generally, the particle
shape becomes closer to spherical as the aspect ratio approaches 1.
The fine particles comprising fluoropolymers preferably have an
aspect ratio of not higher than 3. A more preferred upper limit is
2, and a more preferred upper limit is 1.5.
[0049] Generally, when the fine polymer particles are anisotropic
in particle shape, the dispersion of the fine polymer particles
tends to show a high viscosity. When a dispersion of the fine
polymer particles shows a high viscosity, it unfavorably becomes
difficult to increase the concentration of the fine polymer
particles in the dispersion.
[0050] When the fine particles comprising fluoropolymers comprise
spherical fluoropolymer fine particles which are substantially
spherical, at the proportion of at least 25% by mass thereof, it is
possible, for example, to lower the viscosity of a fluoropolymer
dispersion prepared by using the above-mentioned fluoropolymer
solid composition as compared with the case where the fine particle
comprising fluoropolymers are not substantially spherical in shape,
hence it becomes possible to increase the solid matter
concentration of the fluoropolymer dispersion and, thus, it is
possible to realize high levels of productivity in the step of
film/membrane formation by casting, for instance.
[0051] The fine particles comprising fluoropolymers preferably
comprise the spherical fluoropolymer fine particles at the
proportion of 50% by mass or more thereof.
[0052] The fluoropolymer solid composition comprising spherical
fluoropolymer fine particles within the above content range can be
prepared from a dispersion obtained by emulsion polymerization.
Such composition having a spherical fluoropolymer fine particle
content of 90% by mass or higher can also be obtained from a
dispersion obtained by emulsion polymerization. It is also
possible, by incorporating the fine particles not substantially
spherical into a composition comprising a relatively high
proportion of spherical fluoropolymer fine particles, to provide a
fluoropolymer solid composition adjusted so as to display those
performance characteristics required for the intended purposes.
[0053] The above fine particles comprising fluoropolymers
preferably have an average particle diameter of not smaller than 10
nm. When this is smaller than 10 nm, the particles, when used as an
electrode material, may cover active sites, so that no good cell
characteristics may be obtained in some instances.
[0054] When the average particle diameter is within the above
range, the upper limit may be set at 300 nm, for instance, in
consideration of the stability of the fluoropolymer dispersion
prepared by dispersing fine particles comprising fluoropolymers in
a liquid medium and/or the ease of preparation of the fluoropolymer
precursor to be mentioned later herein. However, average particle
diameters exceeding 300 nm will not significantly influence the
cell characteristics.
[0055] The above-mentioned fine particles comprising fluoropolymers
more preferably have an average particle diameter of 10 to 300 nm.
A more preferred lower limit to the average particle diameter is 30
nm, and a more preferred upper limit is 160 nm.
[0056] The above-mentioned aspect ratio and average particle
diameter can be determined by observing, under a scanning or
transmission electron microscope, an atomic force microscope or the
like, an aggregate of the fine particles comprising fluoropolymers
as obtained by applying the fluoropolymer dispersion onto a glass
substrate, followed by removal of the aqueous dispersion medium,
measuring the major axes and minor axes of at least 20 fine
particles on the picture obtained and calculating the aspect ratio,
namely the average major axis-to-minor axis ratio (major axis/minor
axis), and the average particle diameter, which is the mean of the
major axes and minor axes and which is to be mentioned later
herein.
[0057] The fluoropolymer solid composition of the present invention
preferably contains, at the proportion of at least 25% by mass
thereof, spherical fluoropolymer fine particles not smaller in
average particle diameter than 10 nm among the fine particles
comprising fluoropolymers.
[0058] The fluoropolymer solid composition of the present invention
more preferably contains, at the proportion of at least 25% by mass
thereof, spherical fluoropolymer fine particles whose average
particle diameter is 10 to 300 nm among the fine fluoropolymer
particles.
[0059] Still more preferably, the fluoropolymer solid composition
of the present invention contains, at the proportion of at least
25% by mass thereof, spherical fluoropolymer fine particles whose
average particle diameter is 30 to 160 nm among the fine
fluoropolymer particles.
[0060] The above-mentioned fluoropolymer has acid/acid salt
groups.
[0061] The acid/acid salt groups each refers to an acid group
and/or an acid salt group.
[0062] The acid group is a sulfonic acid group,
--SO.sub.2NR.sup.17R.sup.1- 8 and/or a carboxyl group. R.sup.17 and
R.sup.18 are the same or different and each represents a hydrogen
atom, an alkali metal, an alkyl group or a sulfonyl-containing
group.
[0063] The above alkali metal is not particularly restricted but
may be, for example, Li, Na, K or Cs. The alkyl group is not
particularly restricted but includes an alkyl group having 1 to 4
carbon atoms, such as methyl or ethyl. The alkyl group may be
substituted by a halogen atom(s). The sulfonyl-containing group is
a sulfonyl group- and fluorine-containing alkyl group, for example
a fluorine-containing alkylsulfonyl group, which may have a
substituent(s) at its terminus. As the fluorine-containing
alkylsulfonyl group, there may be mentioned, among others,
--SO.sub.2R.sub.f.sup.1Z.sup.3(R.sub.f.sup.1 representing a
fluorine-containing alkylene group and Z.sup.3 representing an
organic group). As the organic group, there may be mentioned, for
example, --SO.sub.2F, which may take an infinitely connected form
such as --SO.sub.2
(NR.sup.17SO.sub.2R.sub.f.sup.1SO.sub.2).sub.kNR.sup.17SO.sub.- 2--
(in which k represents an integer not smaller than 1 and
R.sub.f.sup.1 represents a fluorine-containing alkylene group), or
the organic group may be
--SO.sub.2(NR.sup.17SO.sub.2R.sub.f.sup.1SO.sub.2).sub.kNR.sup.17S-
O.sub.2F (in which k represents an integer not smaller than 1 but
not greater than 100 and R.sup.17 and R.sub.f.sup.1 are as defined
above), for instance.
[0064] The acid salt group mentioned above comprises a sulfonic
acid group in salt form and/or a carboxyl group in salt form. The
sulfonic acid in salt form is
--SO.sub.3NR.sup.1R.sup.2R.sup.3R.sup.4 or
--SO.sub.3M.sup.1.sub.1/L, and the carboxyl group in salt form is
--COONR.sup.5R.sup.6R.sup.7R.sup.8 or --COOM.sup.2.sub.1/L, wherein
R.sup.1, R.sup.2, R.sup.3 and R.sup.4 are the same or different and
each represents a hydrogen atom or an alkyl group having 1 to 4
carbon atoms, R.sup.5, R.sup.6, R.sup.7 and R.sup.8 are the same or
different and each represents a hydrogen atom or an alkyl group
having 1 to 4 carbon atoms, M.sup.1 and M.sup.2 are the same or
different and each represents a metal having a valence of L.
[0065] The metal having a valence of L is a metal belonging to the
group 1, 2, 4, 8, 11, 12 or 13 of the periodic table. The metal
having a valence of L is not particularly restricted but includes,
for example, Li, Na, K and Cs as the group 1 metal, Mg and Ca as
the group 2 metal, Al as the group 4 metal, Fe as the group 8
metal, Cu and Ag as the group 11 metal, Zn as the group 12 metal,
and Zr as the group 13 metal. The alkyl group having 1 to 4 carbon
atoms is not particularly restricted but preferably is a straight
alkyl group, more preferably a methyl group.
[0066] Preferably, the existence of the acid/acid salt groups on
the particle surface of the fine particles comprising
fluoropolymers is more than that in the particle inside thereof.
For use as ion exchange resins or the like, in particular, it is
desirable that the existence on the particle surface be greater.
When the existence of acid/acid salt groups are greater on the
particle surface than in the particle inside, the dispersion
stability can be improved.
[0067] The fine fluoropolymer particles in which the existence of
the acid/acid salt group on the particle surface is more than in
the particle inside can be obtained by using the so-called
"core/shell" technology in the method for producing the
fluoropolymer dispersion by emulsion polymerization according to
the present invention. Namely, they can be obtained by increasing
the rate of feed of the acid/acid salt group-containing fluorovinyl
ether derivative, which is to be described later herein, at the
late stage of polymerization as compared with the early stage of
polymerization.
[0068] The term "particle inside" as used herein means the central
portion occupying 50% by mass of the whole particle mass. The term
"particle surface" as used herein means the portion of the particle
other than the particle inside defined above.
[0069] The fluoropolymer solid composition of the present invention
may comprise, in addition to the above-mentioned fine particle
comprising fluoropolymers, one or more additives as necessary. The
additives are not particularly restricted but include, among
others, fluororesins such as polytetrafluoroethylene [PTFE],
tetrafluoroethylene/hexafluoropropylene copolymers [FEPs] and
tetrafluoroethylene/perfluoro(alkylvinylether) copolymers [PFAs];
thermoplastic resins such as polyethylene, polypropylene and
polyethylene terephthalate [PET]; thermosetting resins such as
polyamides and polyimides; fine particles of another ion exchange
resin or the like; and fine powders of inorganic materials such as
alumina, silica, zirconia and carbon.
[0070] Generally, the fluoropolymer solid composition of the
present invention can be obtained by drying the fluoropolymer
dispersion to be described later herein. As for the procedure for
obtaining the fluoropolymer solid composition from the
fluoropolymer dispersion, there may be mentioned, for example, the
method which comprises concentrating the fluoropolymer dispersion
and drying the concentrate at a temperature of 80 to 400.degree.
C.
[0071] When applied to a substrate, the fluoropolymer solid
composition of the present invention may take the form of a coating
film formed on the substrate by heating for drying at the
above-mentioned temperature of 80 to 400.degree. C. and then
further heating to a temperature not less than the melting point of
the fine particle comprising fluoropolymers.
[0072] The particle shape and average particle diameter of the fine
particles comprising fluoropolymers as referred to hereinabove are
those after the above heating for drying, and the requirements
imposed thereon are to be met only in the state not yet subjected
to heating at a temperature not less than the melting point of the
fine particles comprising fluoropolymers.
[0073] The fluoropolymer dispersion of the present invention
comprises the above-mentioned fine particles comprising
fluoropolymers as dispersed in a liquid medium.
[0074] The liquid medium is a liquid capable of wetting the fine
particles comprising fluoropolymers. The liquid medium is not
particularly restricted but preferably occurs as a liquid at room
temperature.
[0075] Where good dispersibility is required of the fine particles
comprising fluoropolymers, not only water but also alcohols such as
methanol; nitrogen-containing solvents such as N-methylpyrrolidone
[NMP]; ketones such as acetone; esters such as ethyl acetate; polar
ethers such as diglyme and tetrahydrofuran [THF] and the like;
carbonate esters such as diethylene carbonate and other polar
organic solvents may be mentioned as the liquid medium, and one of
these or a mixture of two or more of these can be used as such. For
producing films or membranes by casting, impregnation or a like
technique, as mentioned later herein, alcohols may be used as the
liquid medium for leveling properties improvement, and
polyoxyethylenes for film-forming properties improvement.
[0076] The fluoropolymer dispersion of the present invention may be
one comprising the above-mentioned fluoropolymer solid composition
as dispersed in a liquid medium or one prepared from the dispersion
obtained by the polymerization reaction as such without taking the
form of the above-mentioned fluoropolymer solid composition.
[0077] When the fluoropolymer dispersion comprises a fluoropolymer
solid composition as dispersed in a liquid medium, the
fluoropolymer solid composition preferably amounts to 2 to 80% by
mass relative to the whole mass of the fluoropolymer dispersion.
The amount of the fine particles comprising fluoropolymers in the
fluoropolymer dispersion generally corresponds to the mass of the
solid matter in the fluoropolymer dispersion. When the content of
the fluoropolymer solid composition in the fluoropolymer dispersion
is lower than 2% by mass, the amount of the liquid medium becomes
fairly large, and decreases in productivity may result in
film/membrane formation. Conversely, when it exceeds 80% by mass,
the viscosity becomes excessively high and the dispersion tends to
become difficult to handle. A more preferred lower limit is 5% by
mass, and a more preferred upper limit is 60% by mass.
[0078] The fluoropolymer dispersion of the present invention is
preferably one in which the dispersion medium is an aqueous
dispersion medium. In this case, the fluoropolymer dispersion of
the present invention comprises fine particles comprising
fluoropolymers as dispersed in an aqueous dispersion medium, namely
it comprises the fine particles comprising fluoropolymers and the
aqueous dispersion medium. The fluoropolymer dispersion comprises
the fine particles comprising fluoropolymers as the dispersoid and
the aqueous dispersion medium as the dispersion medium.
[0079] The "aqueous dispersion medium" so referred to herein is the
dispersion medium in the fluoropolymer dispersion and comprises
water. So long as it comprises water, the aqueous dispersion medium
may be composed of water and, further, a water-soluble organic
solvent. The aqueous dispersion medium may contain one or more of
those additives which are generally used in aqueous dispersions,
for example surfactants and stabilizers.
[0080] The aqueous dispersion medium preferably has a water content
of 10 to 100% by mass. When the content is below 10% by mass,
deteriorated dispersibility will result and unfavorable effects on
the environment and human body may also be produced. A more
preferred lower limit is 40% by mass.
[0081] The fluoropolymer dispersion of the present invention can be
produced by the method for producing a fluoropolymer dispersion
according to the present invention which essentially comprises
converting a sulfonic acid or carboxylic acid halide of a
fluoropolymer precursor obtained by the polymerization reaction to
the acid salt group by hydrolysis in an aqueous medium, or by
converting this acid salt group to the acid group by treatment with
an acid in an aqueous medium. When the acid/acid salt group is
--SO.sub.2NR.sup.17R.sup.18, the fluoropolymer dispersion of the
present invention can be prepared in the form of a dispersion which
comprises a fluoropolymer solid composition containing fine
particles of the --SO.sub.2NR.sup.17R.sup.18-containing
fluoropolymer as dispersed in a liquid medium.
[0082] In the present specification, among those methods of
producing fluoropolymer dispersions according to the present
invention, the method for obtaining the acid salt group is
sometimes referred to as "method (i) for producing a fluoropolymer
dispersion", and the method for obtaining the sulfonic acid group
and/or carboxylic acid group as the acid group is sometimes
referred to as "method (ii) for producing a fluoropolymer
dispersion".
[0083] The method (i) for producing a fluoropolymer dispersion
according to the present invention is intended to obtain
fluoropolymer dispersions which comprises fine particles comprising
fluoropolymers as dispersed in the liquid medium mentioned
above.
[0084] In the method (i) for producing a fluoropolymer dispersion
according to the present invention, the fluoropolymer has acid salt
groups. The acid salt group is the same as the sulfonic acid group
in salt form or the carboxyl group in salt form as described
hereinabove referring to the fluoropolymer solid composition.
[0085] The method (i) for producing a fluoropolymer dispersion
according to the present invention comprises the same step as the
step of obtaining the acid salt group in the method (ii) for
producing a fluoropolymer dispersion which is to be described later
herein.
[0086] Therefore, like the method (ii) for producing a
fluoropolymer dispersion, which is to be described later herein,
the method (i) for producing a fluoropolymer dispersion according
to the present invention comprises the step of hydrolyzing
--SO.sub.2X.sup.1 (X.sup.1 representing a halogen atom) and/or
--COZ.sup.1 (Z.sup.1 representing an alkoxyl group having 1 to 4
carbon atoms) of a fluoropolymer precursor in a liquid medium to
give the corresponding fluoropolymer.
[0087] The term "fluoropolymer precursor" as used herein means a
polymer to give fluoropolymer through the above-mentioned step of
hydrolysis in a liquid medium.
[0088] The method (i) for producing a fluoropolymer dispersion
according to the present invention has the same characteristic
features as the method (ii) for producing a fluoropolymer
dispersion which is to be described later herein. In one of the
features, the above-mentioned hydrolyzing step may comprise the
polymerization reaction step comprising the polymerization in the
presence of a fluoromonomer (Pm) and a fluoromonomer (Qm) and the
alkali treatment step of treating with an alkali.
[0089] The above-mentioned fluoromonomer (Pm) has --SO.sub.2X.sup.1
(X.sup.1 representing a halogen atom) and/or --COZ.sup.1 (Z.sup.1
representing an alkoxyl group having 1 to 4 carbon atoms), and the
above-mentioned fluoromonomer (Qm) has --SO.sub.2X.sup.2 (X.sup.2
representing --ONR.sup.9R.sup.10R.sup.11R.sup.12 or
--OM.sup.1.sub.1/L in which R.sup.9, R.sup.10, R.sup.11 and
R.sup.12 are the same or different and each represents a hydrogen
atom or an alkyl group having 1 to 4 carbon atoms and M.sup.1
represents a metal whose valence is L) and/or --COOZ.sup.2 (Z.sup.2
representing NR.sup.13R.sup.14R.sup.15R.sup.16 or --M.sup.2.sub.1/L
in which M.sup.2 represents a metal whose valence is L).
[0090] The method (ii) for producing a fluoropolymer dispersion
according to the present invention is intended for producing
fluoropolymer dispersions which comprises fine particles comprising
fluoropolymers as dispersed in an aqueous medium.
[0091] The above "method (ii) for producing a fluoropolymer
dispersion", which is to produce fluoropolymer dispersions in which
the dispersion medium is an aqueous dispersion medium and the
dispersoid fluoropolymer has a sulfonic acid group and/or carboxyl
group, is conceptually different from the above "method (i) for
producing a fluoropolymer dispersion", in which method the
dispersion medium is a liquid medium and the fluoropolymer has an
acid salt group. By merely saying "method for producing a
fluoropolymer dispersion" in the present specification, it is meant
that the above-mentioned method (ii) for producing a fluoropolymer
dispersion and method (i) for producing a fluoropolymer dispersion
are referred to without distinction therebetween.
[0092] In carrying out the method (ii) for producing a
fluoropolymer dispersion according to the present invention, the
fluoropolymer has a sulfonic acid group and/or carboxyl group.
[0093] The sulfonic acid group and/or carboxyl group is preferably
one bound to a fluoroether side chain represented by the following
general formula (I):
--O--(CF.sub.2CFY.sup.1--O).sub.n--(CFY.sup.2 ).sub.m-- (I)
[0094] (wherein Y.sup.1 represents a fluorine atom, a chlorine atom
or a perfluoroalkyl group; n represents an integer of 0 to 3, and n
atoms/groups of Y.sup.1 are the same or different; Y.sup.2
represents a fluorine atom or chlorine atom; m represents an
integer of 1 to 5, and m atoms of Y.sup.2 may be the same or
different). The sulfonic acid group and/or carboxyl group is bound
to the fluoroether side chain so that it may be adjacent to
--(CFY.sup.2).sub.m-- in the above general formula (I).
[0095] The above fluoroether side chain is preferably one forming
an ether bond with a carbon atom constituting the fluoroethylene
unit in the main chain of the fluoropolymer. The term
"fluoroethylene unit" as used herein means the part derivative from
the perfluorovinyl group of a monomer constituting the
fluoropolymer in the molecular structure of the fluoropolymer.
Generally, the perfluorovinyl group is a group derived from the
fluorovinyl ether derivative composed of the above-mentioned
perfluorovinyl group and the above-mentioned fluoroether side chain
bound to each other. The term "forming an ether bond" refers to the
ether bonding of the fluoroether side chain represented by the
above general formula (I) via a divalent oxygen atom in such a form
as
--(CF.sub.2--CF.sub.2)--O--(CF.sub.2CFY.sup.1--O).sub.n--(CFY.sup.2).sub.m-
--
[0096] as a result of substitution of a fluorine atom bound to a
carbon atom constituting the perfluoroethylene unit
[--(CF.sub.2--CF.sub.2)--].
[0097] The method (ii) for producing a fluoropolymer dispersion
according to the present invention is to produce the
above-mentioned fluoropolymer dispersions, and the method (ii) for
producing a fluoropolymer dispersion comprises the hydrolysis step
of hydrolyzing --SO.sub.2X.sup.1 and/or --COZ.sup.1 of the
fluoropolymer precursor in an aqueous medium to give the
fluoropolymer.
[0098] The term "aqueous medium" as used herein means a medium in
which the hydrolysis is carried out in the above-mentioned
hydrolysis step and which comprises water. The hydrolysis is
carried out in an aqueous dispersion comprising an aqueous medium
and a fluoropolymer precursor. The aqueous system in which this
hydrolysis is carried out comprises at least an aqueous medium as
the dispersion medium and fine particles of the above-mentioned
fluoropolymer precursor as the dispersoid before the start of the
hydrolysis and, after completion of the above-mentioned hydrolysis
step, it comprises at least the above-mentioned fine particles
comprising fluoropolymers as the dispersoid. So long as it
comprises water, the above-mentioned aqueous medium may comprise
water and a water-soluble organic solvent.
[0099] When, in carrying out the method for producing a
fluoropolymer dispersion according to the present invention, the
fluoropolymer precursor has --SO.sub.2X.sup.1-- and/or --COZ.sup.1,
the above hydrolysis step preferably comprises the alkali treatment
step in which the fluoropolymer precursor is treated with an alkali
(such step hereinafter sometimes referred to as "alkali treatment
step (A.sub.alk)"). The above hydrolysis step is hereinafter
referred to as "hydrolysis step (A)". The --SO.sub.2X.sup.1--
and/or --COZ.sup.1-containing fluoropolymer precursor mentioned
above is hereinafter referred to as "fluoropolymer precursor (P)".
The fluoropolymer precursor (P) has preferably
--SO.sub.2X.sup.1.
[0100] The above symbol X.sup.1 represents a halogen atom. The
halogen atom X.sup.1 is not particularly restricted but may be any
of fluorine, chlorine, bromine and iodine atoms. Preferably,
however, it is a fluorine atom or a chlorine atom, more preferably
a fluorine atom.
[0101] The above symbol Z.sup.1 represents an alkoxyl group having
1 to 4 carbon atoms. The alkoxyl group having 1 to 4 carbon atoms
as represented by Z.sup.1 is not particularly restricted but
preferably is an n-alkoxyl group, more preferably a methoxy
group.
[0102] The group --SO.sub.2X.sup.1-- is preferably --SO.sub.2F, and
the group --COZ.sup.1 is preferably --COOCH.sub.3.
[0103] When the alkali treatment step (A.sub.alk) is carried out,
the groups --SO.sub.2X.sup.1 and/or --COZ.sup.1 of the
fluoropolymer precursor (P) are converted to acid salt groups. The
term "acid salt group" as used herein means a sulfonic acid and/or
carboxyl group in salt form. The acid salt group preferably forms
an alkali metal salt or an alkaline earth metal salt.
[0104] The hydrolysis step (A) preferably comprises the alkali
treatment step (A.sub.alk) and further the subsequent step of
neutralization treatment with an acid (hereinafter sometimes
referred to as "acid treatment step (A.sub.acd)"). When the acid
treatment step (A.sub.acd) is carried out, the acid salt group
obtained by the alkali treatment step (A.sub.alk) is converted to
the sulfonic acid group and/or carboxyl group.
[0105] The end point of the hydrolysis reaction in the hydrolysis
step (A) can be detected as a point of time at which the alkali and
acid are no more consumed and the pH stabilizes.
[0106] The hydrolysis step (A) preferably comprises the alkali
treatment step (A.sub.alk) and, further, a subsequent step of
removing a low-molecular-weight substance (hereinafter sometimes
referred to as "low-molecular-weight substance elimination step
(A.sub.rmv)"). The low-molecular-weight substances are, for
example, the residual monomers remaining in the polymerization
reaction step, polymerization initiator residues, unrequired
low-molecular-weight polymers and/or substances formed upon
treatment of the fluoropolymer precursor (P) with an alkali. In
cases where there exist the residues of the emulsifier and the like
used in the polymerization reaction, these can also be removed.
[0107] The low-molecular-weight substance elimination step
(A.sub.rmv) can be carried out by centrifugation method,
electrophoresis method or ultrafiltration method, for instance. The
ultrafiltration method is preferably used, however, since it is
superior in productivity. The ultrafiltration method is not
particularly restricted but may be any of the methods by using an
ultrafiltration apparatus comprising an ultrafiltration membrane
for removing a low-molecular-weight substance. Thus, it includes,
among others, the centrifugal ultrafiltration method and the
circulating ultrafiltration method. The ultrafiltration membrane
and the ultrafiltration membrane-containing ultrafiltration
apparatus are adequately selected according to the molecular
weights and types of the low-molecular-weight substances to be
removed, the aqueous medium species, the molecular weight and type
of the fluoropolymers, and other factors. Suited for use as the
ultrafiltration membrane-containing ultrafiltration apparatus are
commercially available ones. For the laboratory use, there may be
mentioned Centriprep (product of Amicon) and Millitan (product of
Millipore), for instance. It is also possible, in the
ultrafiltration step, to concentrate the fluoropolymer obtained.
The fluoropolymer solid composition obtained by concentration or
evaporating to dryness the fluoropolymer dispersion purified by
using the above-mentioned ultrafiltration method is preferred in
view of its low impurity content.
[0108] The low-molecular-weight elimination step (A.sub.rmv) may be
carried out either before or after the acid treatment step
(A.sub.acd).
[0109] When, in carrying out the method for producing a
fluoropolymer dispersion according to the present invention, the
fluoropolymer precursor is the product of polymerization in the
presence of a fluoromonomer (Pm) containing --SO.sub.2X.sup.1
and/or --COZ.sup.1 and a fluoromonomer (Qm) containing
--SO.sub.2X.sup.2 (X.sup.2 representing --OM.sup.3 or
--OM.sup.4.sub.1/2 in which M.sup.3 represents an alkali metal or
NR.sup.1R.sup.2R.sup.3R.sup.4, R.sup.1, R.sup.2, R.sup.3 and
R.sup.4 are the same or different and each represents a hydrogen
atom or an alkyl group having 1 to 4 carbon atoms and M.sup.4
represents an alkaline earth metal) and/or --COOZ.sup.2 (Z.sup.2
representing M.sup.5 or M.sup.6.sub.1/2 in which M.sup.5 represents
an alkali metal or NR.sup.5R.sup.6R.sup.7R.sup.8, R.sup.5, R.sup.6,
R.sup.7 and R.sup.8 are the same or different and each represents a
hydrogen atom or an alkyl group having 1 to 4 carbon atoms and
M.sup.6 represents an alkaline earth metal), the hydrolysis step
preferably comprises the polymerization reaction step for obtaining
the fluoropolymer precursor, the alkali treatment step comprising
treatment with an alkali (hereinafter sometimes referred to as
"alkali treatment step (B.sub.alk)") and the step of neutralization
with an acid (hereinafter sometimes referred to as "acid treatment
step (B.sub.acd)"), in that order. The above hydrolysis step is
hereinafter referred to as "hydrolysis step (B)". The fluoromonomer
(Pm) is preferably one having --SO.sub.2X.sup.1, and the
fluoromonomer (Qm) is preferably one having --SO.sub.2X.sup.2.
[0110] The symbol X.sup.2 represents --OM.sup.3 or
--OM.sup.4.sub.1/2; M.sup.3 represents an alkali metal or
NR.sup.1R.sup.2R.sup.3R.sup.4, R.sup.1, R.sup.2, R.sup.3 and
R.sup.4 are the same or different and each represents a hydrogen
atom or an alkyl group having 1 to 4 carbon atoms and M.sup.4
represents an alkaline earth metal. The alkyl group having 1 to 4
carbon atoms is not particularly restricted but may be any of
methyl, ethyl, propyl and butyl groups. The alkali metal is not
particularly restricted but may be Li, Na, K, Cs, for instance, and
the alkaline earth metal is not particularly restricted but may be
Mg or Ca, for instance.
[0111] The symbol Z.sup.2 represents M.sup.5 or M.sup.6.sub.1/2,
and M.sup.5 represents an alkali metal or
NR.sup.5R.sup.6R.sup.7R.sup.8, R.sup.5, R.sup.6, R.sup.7 and
R.sup.8 are the same or different and each represents a hydrogen
atom or an alkyl group having 1 to 4 carbon atoms and M.sup.6
represents an alkaline earth metal. The alkali metal, alkaline
earth metal and alkyl group having 1 to 4 carbon atoms each is not
particularly restricted but includes the same ones as mentioned
above referring to X.sup.2.
[0112] In the above polymerization reaction step, the fluoropolymer
precursor can be obtained, for example, by carrying out the
polymerization in the presence of a fluoromonomer (Pm1) represented
by the following general formula (III):
CF.sub.2.dbd.CF--O--(CF.sub.2CFY.sup.1--O).sub.n--(CFY.sup.2).sub.m-A.sup.-
2 (III)
[0113] (wherein Y.sup.1 represents a fluorine atom, a chlorine atom
or a perfluoroalkyl group; n represents an integer of 0 to 3 and
the n atoms/groups of Y.sup.1 may be the same or different; Y.sup.2
represents a fluorine atom or a chlorine atom; m represents an
integer of 1 to 5 and m atoms of Y.sup.2 may be the same or
different; A.sup.2 represents --SO.sub.2X.sup.1 and/or --COZ.sup.1,
X.sup.1 represents a halogen atom and Z.sup.1 represents an alkoxyl
group having 1 to 4 carbon atoms) and a fluoromonomer (Qm1)
represented by the general formula (IV):
CF.sub.2.dbd.CF--O--(CF.sub.2CFY.sup.1--O).sub.n--(CFY.sup.2).sub.m-A.sup.-
3 (IV)
[0114] (wherein Y.sup.1, n, Y.sup.2 and m are defined above;
A.sup.3 represents --SO.sub.2X.sup.2 and/or --COOZ.sup.2, X.sup.2
represents --OM.sup.3 or --OM.sup.4.sub.1/2, M.sup.3 represents an
alkali metal or NR.sup.1R.sup.2R.sup.3R.sup.4, R.sup.1, R.sup.2,
R.sup.3 and R.sup.4 are the same or different and each represents a
hydrogen atom or an alkyl group having 1 to 4 carbon atoms, M.sup.4
represents an alkaline earth metal, Z.sup.2 represents M.sup.5 or
M.sup.6.sub.1/2, M.sup.5 represents an alkali metal or
NR.sup.5R.sup.6R.sup.7R.sup.8, R.sup.5, R.sup.6, R.sup.7 and
R.sup.8 are the same or different and each represents a hydrogen
atom or an alkyl group having 1 to 4 carbon atoms, and M.sup.6
represents an alkaline earth metal). The fluoropolymer precursor
obtained in the above polymerization step can take, in the aqueous
medium, the core/shell structure in which the core is a polymer
chain comprising the monomer (Pm) and the shell is a polymer chain
comprising the monomer (Qm), since the above-mentioned
--SO.sub.2X.sup.2 and/or --COOZ.sup.2 is hydrophilic and the
above-mentioned --SO.sub.2X.sup.1 and/or --COZ.sup.1 is
hydrophobic. In the above polymerization reaction step, the
fluoromonomer (Qm) and polymer chains comprising the fluoromonomer
(Qm) have emulsifying activity and, therefore, it is no more
necessary to add such an emulsifier as is generally used in the
conventional cases of emulsion polymerization, hence emulsifier
removal in a subsequent step is not necessary.
[0115] When the above alkali treatment step (B.sub.alk) is carried
out, --SO.sub.2X.sup.1 and/or --COZ.sup.1 which the polymer chain
comprising the fluoromonomer (Pm) has are converted to acid salt
groups and, when the above acid treatment step (B.sub.acd) is then
carried out, the acid salt groups are converted to sulfonic acid
and/or carboxyl groups and --SO.sub.2X.sup.2and/or --COOZ.sup.2
which the polymer chains comprising the fluoromonomer (Qm) has are
converted to sulfonic acid groups and/or carboxyl groups.
[0116] The end point of the hydrolysis reaction in the hydrolysis
reaction (B) can be detected as a point of time at which the alkali
and acid are no more consumed and the pH stabilizes.
[0117] In the hydrolysis step (B), the fluoropolymer precursor may
be, for example, a seed polymerization product obtained by carrying
out the polymerization in the presence of the above-mentioned
fluoromonomer (Pm) and a fluoromonomer (Qm)-based polymer obtained
by polymerizing the above-mentioned fluoromonomer (Qm). Like
polymer chains comprising the fluoromonomer (Qm) and fluoromonomer
(Pm), the above seed polymerization product has emulsifying
activity and, therefore, it is no more necessary to add such an
emulsifier as is generally used in the conventional cases of
emulsion polymerization, hence emulsifier removal in a subsequent
step is not necessary. The method for producing a fluoropolymer
dispersion according to the present invention requires no such
subsequent step and, in this respect, can be said to be a method
capable of efficiently producing sulfonic acid group- and/or
carboxyl group-containing fluoropolymer dispersions and
fluoropolymer solid compositions.
[0118] The above hydrolysis step (B) preferably comprises the
alkali treatment step (B.sub.alk) and further a subsequent step of
removing a low-molecular-weight substance (hereinafter sometimes
referred to as "low-molecular-weight substance elimination step
(B.sub.rmv)"). The low-molecular-weight substances are, for
example, residual monomers remaining in the polymerization reaction
step, polymerization initiator residues, unrequired
low-molecular-weight polymers, and/or substances obtained by
treatment of the fluoropolymer precursor with alkali, such as those
mentioned hereinabove referring to the low-molecular-weight
substance elimination step (A.sub.rmv). Like the
low-molecular-weight substance elimination step (A.sub.rmv), other
low-molecular-weight substances can also be removed.
[0119] The low-molecular-weight substance elimination step
(B.sub.rmv) can be carried out in the same manner as the
low-molecular-weight substance elimination step (A.sub.rmv), and
use is preferably made of the same ultrafiltration method as the
ultrafiltration method in the low-molecular-weight substance
elimination step (A.sub.rmv).
[0120] The above low-molecular-weight substance elimination step
(B.sub.rmv) may be carried out either before or after the acid
treatment step (B.sub.acd).
[0121] When the fluoropolymer precursor is
--SO.sub.2X.sup.1-containing one (X.sup.1 representing a halogen
atom), it generally tends to coagulate and be unstable upon
addition of an acid. In accordance with the method for producing a
fluoropolymer dispersion according to the present invention,
however, an alkali is added and therefore, unless the alkali is
added hastily, the fluoropolymer precursor can avoid coagulating
and can be maintained in a state stably dispersed in an aqueous
medium and --SO.sub.2X.sup.1 can be quantitatively converted to a
sulfonic acid salt group.
[0122] The method for producing a fluoropolymer dispersion
according to the present invention is intended to obtain
fluoropolymer dispersions and comprises the hydrolysis step for
hydrolyzing --SO.sub.2X and/or --COZ.sup.1 which the fluoropolymer
precursor has in an aqueous medium to give the corresponding
fluoropolymer. The term "fluoropolymer precursor" as used herein
means a polymer which gives the fluoropolymer through the
above-mentioned hydrolysis step.
[0123] The above symbol X represents a halogen atom, --OM.sup.3 or
--OM.sup.4.sub.1/2, M.sup.3 represents an alkaline metal or
NR.sup.9R.sup.10R.sup.11R.sup.12, and M.sup.4 represents an
alkaline earth metal. The halogen atom represented by X includes
those enumerated hereinabove referring to X.sup.1.
[0124] The above-mentioned --SO.sub.2X is preferably --SO.sub.2F,
and the above-mentioned --COZ.sup.1 is preferably
--COOCH.sub.3.
[0125] When subjected to the above hydrolysis step, --SO.sub.2X
and/or --COZ.sup.1 which the fluoropolymer precursor has is
converted to --SO.sub.3-- and/or --COO-- either via an acid salt
group or without taking the form of an acid salt group depending on
the kind of X and or Z.sup.1. The above hydrolysis step may be
carried out using an alkali, and an acid for neutralization.
[0126] When the fluoropolymer precursor has --SO.sub.2X.sup.1
(X.sup.1 representing a halogen atom) and/or --COZ.sup.1 (Z.sup.1
representing an alkoxyl group having 1 to 4 carbon atoms), the
hydrolysis can be carried out using an alkali, and an acid for
neutralization in that order. Upon treatment with an alkali,
--SO.sub.2X.sup.1 and/or --COZ.sup.1 which the fluoropolymer
precursor has is converted to an acid salt group and, then, upon
treatment with an acid, the above acid salt group can be converted
to the sulfonic acid group and/or carboxyl group.
[0127] The alkali to be used in the above hydrolysis step is not
particularly restricted but may be any of those alkalis which are
generally used in hydrolysis, including alkali metal or alkaline
earth metal hydroxides, among others. As such hydroxides, there may
be mentioned sodium hydroxide, potassium hydroxide and lithium
hydroxide, for instance.
[0128] The acid to be used in the above hydrolysis step is not
particularly restricted but may be any of those acids which are
generally used in hydrolysis, including mineral acids, among
others. As such mineral acids, there may be mentioned hydrochloric
acid and sulfuric acid, for instance.
[0129] The alkali and acid to be used in the above hydrolysis step
can be used also in the hydrolysis step (A) and hydrolysis step
(B).
[0130] The above hydrolysis step can be carried out in the aqueous
medium mentioned above.
[0131] The aqueous medium may be one originating in the aqueous
polymerization reaction medium to be mentioned later herein. The
polymerization reaction is intended to obtain the above-mentioned
fluoropolymer precursor. The polymerization reaction for obtaining
such fluoropolymer precursor in accordance with the present
invention is herein sometimes referred to as "polymerization
reaction step". The polymerization reaction for obtaining the
fluoropolymer precursor is preferably carried out by emulsion
polymerization, as mentioned later herein. In the case of emulsion
polymerization, the above polymerization reaction is carried out in
an aqueous reaction medium. The term "aqueous reaction medium" as
used herein means a medium in which the polymerization reaction is
allowed to proceed and which comprises water. When it is carried
out in such aqueous reaction medium, the above polymerization
reaction is carried out in an aqueous dispersion composed of the
aqueous reaction medium and fine particles comprising
fluoropolymers precursor formed as the polymerization reaction
proceeds. The aqueous dispersion in which the polymerization
reaction is carried out comprises the aqueous reaction medium as
the dispersion medium and the fine particles comprising
fluoropolymers precursor as the dispersoid. So long as it comprises
water, the aqueous reaction medium may be composed of water and a
water-soluble organic solvent. Preferably, however, it is free of
any water-soluble organic solvent. The aqueous reaction medium may
contain one or more of those additives which are generally used in
aqueous dispersions, for example surfactants, stabilizers, and
those existing emulsifiers and emulsifying agents which are to be
described later herein. In cases where the aqueous medium is one
derived from the aqueous reaction medium, the aqueous reaction
medium as such can be used, after the polymerization reaction step,
as the aqueous medium in the above-mentioned hydrolysis step of
carrying out the hydrolysis reaction therein.
[0132] The aqueous medium in the hydrolysis step as such can be
used, after the hydrolysis step, as the aqueous dispersion medium
for the fluoropolymer dispersion. In this case, the aqueous
dispersion medium is one derived from the aqueous medium mentioned
above.
[0133] The above-mentioned aqueous medium is the dispersion medium
in the aqueous dispersion in which the above-mentioned hydrolysis
is carried out, the aqueous dispersion medium is the dispersion
medium in the fluoropolymer dispersion obtained through the
hydrolysis step in which the above-mentioned hydrolysis is carried
out, and the aqueous reaction medium is the dispersion medium in
the aqueous dispersion in which the polymerization reaction is
carried out. In this respect, the aqueous medium, aqueous
dispersion medium and aqueous reaction medium are conceptually
different from one another.
[0134] When the method for producing a fluoropolymer dispersion
according to the present invention comprises the above-mentioned
hydrolysis step and, further, the polymerization reaction step, as
described later herein, the fluoropolymer dispersion can be
produced in an aqueous system through the polymerization reaction
step and hydrolysis step. The phrase "in an aqueous system" means
"in a medium comprising water". The method for producing a
fluoropolymer dispersion according to the present invention can be
carried out in a medium comprising water from the above-mentioned
polymerization reaction step to the fluoropolymer dispersion
production through the above-mentioned hydrolysis step. In cases
where, in carrying out the method for producing a fluoropolymer
dispersion according to the present invention, the polymerization
reaction in the polymerization reaction step is carried out by
emulsion polymerization, as mentioned above, the aqueous reaction
medium can be used as such medium comprising water; this aqueous
reaction medium can be used, after completion of the polymerization
reaction step, as the aqueous medium in the following hydrolysis
step, and this aqueous medium can be used, after completion of the
hydrolysis step, as the aqueous dispersion medium in the
fluoropolymer dispersion.
[0135] When the fluoropolymer dispersion production through the
above polymerization reaction step and hydrolysis step is carried
out in an aqueous system, as mentioned above, the method for
producing a fluoropolymer dispersion according to the present
invention can produce the fluoropolymer dispersion without drying
the fluoropolymer precursor and fluoropolymer. The phrase "without
drying the fluoropolymer precursor and fluoropolymer" means that
the fluoropolymer precursor and fluoropolymer each occurs in the
aqueous medium. In cases where the fluoropolymer precursor and
fluoropolymer each occurs in the aqueous medium, the
above-mentioned acid salt group-containing intermediate possibly
formed, according to the species of X in --SO.sub.2X and/or the
species of Z.sup.1 in --COZ.sup.1, in the course of the formation
of the fluoropolymer from the fluoropolymer precursor through the
hydrolysis step is formed in the aqueous medium and remains in the
aqueous medium until it is converted to the sulfonic acid group-
and/or carboxyl group-containing fluoropolymer.
[0136] The reaction temperature in the hydrolysis step is not
particularly restricted. Thus, the reaction maybe carried out at
room temperature but, from the reaction rate viewpoint, the
reaction is preferably carried out at 30 to 100.degree. C. The
concentration of the fluoropolymer precursor in carrying out the
hydrolysis is not particularly restricted but, when it is 5-15% by
mass relative to the aqueous medium, the dispersion comprising the
aqueous medium and fluoropolymer precursor has a viscosity within a
preferred range and the particles of the fluoropolymer precursor
are distributed uniformly, hence the hydrolysis proceeds smoothly.
The reaction temperature may be selected in the same manner in the
hydrolysis step (A) as well as in the hydrolysis step (B).
[0137] When, after completion of the alkali hydrolysis reaction,
the reaction mixture is subjected to ultrafiltration, as described
later herein, the residual monomers remaining in the polymerization
reaction step, polymerization initiator residues, unrequired
low-molecular-weight polymers and/or substances formed upon alkali
treatment of the fluoropolymer precursor can be removed and, if
there are an emulsifier and like additive(s) remaining after the
polymerization reaction, these can also be removed.
[0138] The above-mentioned fluoropolymer precursor is one obtained
by subjecting to polymerization a fluorovinyl ether derivative
represented by the following general formula (II):
CF.sub.2.dbd.CF--O--(CF.sub.2CFY.sup.1--O).sub.n--(CFY.sup.2).sub.m-A.sup.-
1 (II)
[0139] (wherein Y.sup.1 represents a fluorine atom, a chlorine atom
or a perfluoroalkyl group; n represents an integer of 0 to 3, and n
atoms/groups of Y.sup.1 may be the same or different; Y.sup.2
represents a fluorine atom or a chlorine atom; m represents an
integer of 1 to 5, and m atoms of Y.sup.2 may be the same or
different; A.sup.1 represents --SO.sub.2X or --COZ.sup.1; X.sup.1
represents a halogen atom, --OM.sup.3 or --OM.sup.4.sub.1/2,
M.sup.3 represents an alkali metal or
NR.sup.9R.sup.10R.sup.11R.sup.12, M.sup.4 represents an alkaline
earth metal, R.sup.9, R.sup.10, R.sup.11 and R.sup.12 may be the
same or different and each represents a hydrogen atom or an alkyl
group having 1 to 4 carbon atoms, and Z.sup.1 represents an alkoxyl
group having 1 to 4 carbon atoms).
[0140] When the fluoropolymer precursor is one obtained by
subjecting the above fluorovinyl ether derivative to
polymerization, the --SO.sub.2X or --COZ.sup.1 group to be
hydrolyzed in the above-mentioned hydrolysis step is one derived
from the fluorovinyl ether derivative represented by the above
general formula (II).
[0141] In the fluorovinyl ether derivative, n in the above general
formula (II) represents an integer of 0 to 3. Preferably, n is 0 or
1. In the above general formula (II), m represents an integer of 1
to 5. Preferably, m is 2.
[0142] In the above general formula (II), Y.sup.1 represents a
fluorine atom, a chlorine atom or a perfluoroalkyl group, and n
atoms/groups of Y.sup.1 may be the same or different. In the
general formula (II), Y.sup.2 represents a fluorine atom or a
chlorine atom, and m atoms of Y.sup.2 may be the same or different.
The above perfluoroalkyl group is not particularly restricted but
may be, for example, trifluoromethyl or pentafluoroethyl. In the
above general formula (II), Y.sup.1 is preferably a trifluoromethyl
group, and Y.sup.2 is preferably a fluorine atom.
[0143] As X in the above general formula (II), there may be
mentioned the same ones as mentioned above. Among the halogen
atoms, X representing a fluorine atom or chlorine atom, Y.sup.1
representing a fluorine atom or chlorine atom, and Y.sup.2
representing a fluorine atom or chlorine atom may be the same or
different.
[0144] As for Z.sup.1 in the above general formula (II), there may
be mentioned the same species as mentioned hereinabove.
[0145] Preferred as the fluorovinyl ether derivative are those in
which, in general formula (II), Y.sup.1 is a trifluoromethyl group,
Y.sup.2 is a fluorine atom, n is 0 or 1, and m is 2.
[0146] The above fluoropolymer precursor is generally a copolymer
of the above fluorovinyl ether derivatIve and a monomer(s)
copolymerizable with the fluorovinyl ether derivative, and
preferably is a binary or multinary copolymer obtained by
polymerizing the above fluorovinyl ether derivative with a
fluorine-containing ethylenic monomer. The fluorine-containing
ethylenic monomer is not particularly restricted but may be any
vinyl group-containing one. This is different from the
above-mentioned fluorovinyl ether derivative.
[0147] As the fluorine-containing ethylenic monomer, there may be
mentioned, for example, haloethylenic monomers represented by the
following general formula:
CF.sub.2.dbd.CF--R.sub.f.sup.1
[0148] (wherein R.sub.f.sup.1 represents a fluorine atom, a
chlorine atom, --R.sub.f.sup.2 or --OR.sub.f.sup.2, and
R.sub.f.sup.3 represents a straight or branched fluoroalkyl group
having 1 to 9 carbon atoms, which may contain an ether oxygen atom
or atoms), and hydrogen-containing fluoroethylenic monomers
represented by the general formula:
CHY.sup.3.dbd.CFY.sup.4
[0149] (wherein Y.sup.3 represents a hydrogen atom or a fluorine
atom, Y.sup.4 represents a hydrogen atom, a fluorine atom, a
chlorine atom, R.sub.f.sup.3 or --OR.sub.f.sup.3; R.sub.f.sup.4
represents a straight or branched fluoroalkyl group having 1 to 9
carbon atoms, which may contain an ether oxygen atom or atoms).
[0150] Preferably, the fluorine-containing ethylenic monomer
comprises at least one monomer selected from the group consisting
of CF.sub.2.dbd.CF.sub.2, CH.sub.2.dbd.CF.sub.2, CF.sub.2.dbd.CFCl,
CF.sub.2.dbd.CFH, CH.sub.2.dbd.CFH, CF.sub.2.dbd.CFCF.sub.3, and
fluorovinyl ethers represented by CF.sub.2.dbd.CF--O--R.sub.f.sup.4
(R.sub.f.sup.4 representing a fluoroalkyl group having 1 to 9
carbon atoms or a fluoropolyether group having 1 to 9 carbon
atoms). Preferably, R.sub.f.sup.4 in the fluorovinyl ethers is a
perfluoroalkyl group having 1 to 3 carbon atoms.
[0151] The fluorine-containing ethylenic monomer is preferably a
perhaloethylenic monomer, in particular a perfluoroethylenic
monomer, more preferably CF.sub.2.dbd.CF.sub.2. The
fluorine-containing ethylenic monomer may comprise one single
species or two or more species.
[0152] In addition to the fluorine-containing ethylenic monomer,
another copolymerizable monomer may further be added for providing
the fluorocopolymer with various functional properties so long as
the fundamental performance characteristics of the fluoropolymer
are not deteriorated. The other copolymerizable monomer is not
particularly restricted but may be adequately selected from among
copolymerizable monomers to achieve the purpose of controlling the
rate of polymerization, controlling the polymer composition,
controlling the mechanical properties such as elasticity modulus,
or introducing crosslinking sites, for instance. As examples, there
may be mentioned, among others, monomers having two or more
unsaturated bonds, for example perfluorodivinyl ether, and cyano
group-containing monomers.
[0153] The above fluoropolymer precursor preferably has a
fluorovinyl ether derivative unit content of 5 to 40 mole percent.
If such content is lower than 5 mole percent, the fluoropolymer
obtained therefrom, when used as an electrolyte, may show
deteriorated performance characteristics. At content levels
exceeding 40 mole percent, the mechanical strength of the
films/membranes obtained using the fluoropolymer obtained may be
insufficient in certain cases. In cases where, in the fluoropolymer
solid composition of the present invention, the sulfonic acid group
and/or carboxyl group concentration on the fluoropolymer particle
surface is more than that in the fluoropolymer particle inside, the
fluorovinyl ether derivative unit content on the fluoropolymer
particle surface is required to be within the above range. A more
preferred lower limit is 8 mole percent, and a more preferred upper
limit is 35 mole percent.
[0154] The term "fluorovinyl ether derivative unit" as used herein
means the part derived from the fluorovinyl ether derivative in the
molecular structure of the fluoropolymer precursor. The
"fluorovinyl ether derivative unit content" so referred to herein
is the proportion of the number of moles of the fluorovinyl ether
derivative from which the fluorovinyl ether derivative-unit is
derived to the number of moles of the monomers from which all the
monomer units in the fluoropolymer precursor are derived. "All the
monomer units" refers to the sum of the parts derived from all the
monomer in the molecular structure of the fluoropolymer precursor.
Therefore, meant by saying "the monomers from which all the monomer
units are derived" is the total amount of the monomers which have
become constituents of the fluoropolymer precursor. The fluorovinyl
ether derivative unit content is the value obtained by infrared
absorption spectrometry [IR] or fused-state NMR at 300.degree.
C.
[0155] The method for producing a fluoropolymer dispersion
according to the present invention comprises the above-mentioned
hydrolysis step and further the polymerization reaction step in
which the polymerization reaction is carried out. The
polymerization reaction is intended to obtain the fluoropolymer
precursor. The polymerization reaction is preferably carried out in
an aqueous reaction medium.
[0156] The above polymerization reaction is preferably carried out
by emulsion polymerization. As for the method of emulsification, it
maybe the method using, for emulsification, one of those
emulsifiers which are in general use in the conventional emulsion
polymerization processes (hereinafter referred to as "existing
emulsifiers"), the method using, for emulsification, an agent other
than the existing emulsifiers but having emulsifying activity
(hereinafter referred to as "emulsifying agent"), or the method
using, for emulsification, both of an existing emulsifier and an
emulsifying agent. The term "emulsion polymerization" as used
herein means the polymerization which is carried out in the
above-mentioned aqueous reaction medium using an existing
emulsifier and/or an emulsifying agent.
[0157] The existing emulsifier is not particularly restricted but
may be any of those generally used as emulsifiers in the
conventional emulsion polymerization processes but, herein, it
means an organic compound having surfactant activity and having no
unsaturated bond. The term "surfactant activity" as used herein
means that the compound is capable of forming micelles. The
unsaturated bond in question is generally a carbon-carbon double
bond. The organic compound having surfactant activity and having no
unsaturated bond may be an anionic surfactant, cationic surfactant,
nonionic surfactant or betaine type surfactant. From the
emulsifying power viewpoint, however, it is preferably an anionic
surfactant. The anionic surfactant is not particularly restricted
but includes, among others, fluorine-containing emulsifiers such as
fluorine-containing carboxylic acids represented by
X.sup.4(CF.sub.2).sub.sCOOH (X.sup.4 representing a fluorine atom
or a hydrogen atom and s representing an integer of 6 to 20) or
C.sub.tF.sub.2t+1O[CF(CF.sub.3)CF.sub.2O].sub.uCF(- CF.sub.3)COOH
(t representing an integer of 1 to 5 and u representing an integer
of 1 to 5) or salts of such fluorine-containing carboxylic acids;
and fluorine-containing sulfonic acids represented by
C.sub.vF.sub.2v+1(CH.sub.2).sub.wSO.sub.3H (v representing an
integer of 6 to 20 and w representing-an integer of 0 to 4) or salt
of such fluorine-containing sulfonic acids. As the salts, there may
be mentioned, for example, alkali metal salts, ammonium salts,
amine salts, quaternary ammonium salts, etc. As the anionic
surfactant, there may specifically be mentioned ammonium
perfluorooctanoate [C.sub.7H.sub.15COONH.sub.4] and ammonium
perfluorononanoate [C.sub.8H.sub.17COONH.sub.4], among others, in
view of their weathering resistance and water resistance.
[0158] As the emulsifying agent, there maybe mentionedsulfonic acid
salts, among others.
[0159] The emulsifying agent includes, among others, acid/acid salt
fluorovinyl ether derivatives represented by the following general
formula (VII):
CF.sub.2.dbd.CF--O--(CF.sub.2CFY.sup.1--O).sub.n--(CFY.sup.2).sub.m-A.sup.-
6 (VII)
[0160] (wherein Y.sup.1 represents a fluorine atom, a chlorine atom
or a perfluoroalkyl group; n represents an integer of 0 to 3, and n
atoms/groups of Y.sup.1 may be the same or different; Y.sup.2
represents a fluorine atom or a chlorine atom; m represents an
integer of 1 to 5, and m atoms of Y.sup.2 may be the same or
different; A.sup.6 represents --SO.sub.2X.sup.3,
--SO.sub.2NR.sup.17R.sup.18 and/or --COOZ.sup.3; X.sup.3 represents
--OM.sup.5 or --OM.sup.6.sub.1/2, M.sup.5 represents an alkali
metal or NR.sup.1R.sup.2R.sup.3R.sup.4, R.sup.1, R.sup.2, R.sup.3
and R.sup.4are the same or different and each represents a hydrogen
atom or an alkyl group having 1 to 4 carbon atoms, M.sup.6
represents an alkaline earth metal; R.sup.17 and R.sup.18 are the
same or different and each represents a hydrogen atom, an alkali
metal, an alkyl group or a sulfonyl-containing group; Z.sup.3
represents M.sup.7 or --M.sup.8.sub.1/2, M.sup.7 represents an
alkali metal or NR.sup.5R.sup.6R.sup.7R.sup.8, R.sup.5, R.sup.6,
R.sup.7 and R.sup.8 are the same or different and each represents a
hydrogen atom or an alkyl group having 1 to 4 carbon atoms, and
M.sup.8 represents an alkaline earth metal). Preferred are acid
salt fluorovinyl ether derivatives represented by the general
formula (V):
CF.sub.2.dbd.CF--O--(CF.sub.2CFY.sup.1--O).sub.n--(CFY.sup.2).sub.m-A.sup.-
1 (V)
[0161] (wherein Y.sup.1, Y.sup.2, n and m are as defined above, the
n Y.sup.1 atoms/groups may be the same or different and the m
Y.sup.2 atoms may be the same or different; A.sup.4 represents
--SO.sub.2X.sup.3 or --COOZ.sup.3, and X.sup.3 and Z.sup.3 are as
defined above). When such an acid/acid salt fluorovinyl ether
derivative or such an acid salt fluorovinyl ether derivative as
mentioned above is used, emulsification can be attained even if the
aqueous reaction medium contains no existing emulsifier. Therefore,
there is no need for removal of the existing emulsifier after
emulsion polymerization, unlike in the conventional art. The
above-mentioned acid/acid salt fluorovinyl ether derivative or acid
salt fluorovinyl ether derivative shows emulsifying activity on the
occasion of emulsion polymerization and, in addition, it is
ethylenic and therefore can be added as a monomer in the
polymerization reaction for polymerization thereof to constitute at
least part of the molecular structure of the fluoropolymer
precursor. The fluoropolymer precursor obtained by polymerizing the
above acid/acid salt fluorovinyl ether derivative or acid salt
fluorovinyl ether derivative can also have emulsifying
activity.
[0162] In the above-mentioned hydrolysis step (B), the
fluoromonomer (Qm) may have --SO.sub.2X.sup.3 as A.sup.6 in the
general formula (VII) among the above acid/acid salt fluorovinyl
ether derivatives, namely as A.sup.4 in the general formula (V)
among the above acid salt fluorovinyl ether derivatives. The
fluoromonomer (Qm) and the polymer chain comprising the
fluoromonomer (Qm) have emulsifier activity and, therefore, the
aqueous medium need not contain an existing emulsifier. In this
case, the fluoropolymer precursor (Q) is generally one obtained by
carrying out the polymerization reaction in an aqueous reaction
medium containing no existing emulsifier, as mentioned above.
[0163] The above emulsion polymerization may be carried out by
using an existing emulsifier or by using an emulsifying agent
without any existing emulsifier. The use of an emulsifying agent
without any existing emulsifier is preferred since no emulsifier
removal is required after the polymerization reaction and since,
when the above-mentioned acid/acid salt fluorovinyl ether
derivative or acid salt type fluorovinyl ether derivative is used,
no emulsifier removal is required and, further, such derivative
having emulsifying activity can efficiently be used as a monomer.
Depending on the polymerization conditions in carrying out the
above emulsion polymerization, the number of particles of the
fluoropolymer precursor obtained may decrease, namely the particle
size may increase, hence the load on the ultrafiltration membrane
may increase in the low-molecular-weight substance elimination step
mentioned above in some cases and, further, the films/membranes
produced in the step of film/membrane formation may become
heterogeneous in certain cases. In such cases, an existing
emulsifier is preferably used.
[0164] For increasing the number of particles of the fluoropolymer
precursor, it is possible to carry out the so-called "seed
polymerization" which comprises carrying out the polymerization by
using a large amount of an existing emulsifier or an emulsifying
agent, diluting the dispersion obtained, and further continuing the
polymerization.
[0165] The existing emulsifier and/or emulsifying agent to be used
in the above emulsion polymerization is generally used in an amount
of 0.01 to 10% by mass based on the aqueous reaction medium.
[0166] The polymerization reaction can be carried out in the
conventional manner except that the above-mentioned emulsifying
agent can be used as well.
[0167] The above polymerization reaction may be carried out using a
polymerization initiator. The polymerization initiator is not
particularly restricted but may be any of those generally used in
the polymerization of fluoropolymers, for example organic
peroxides, inorganic peroxides, and azo compounds. The use of
ammonium persulfate [APS] is particularly preferred. The level of
addition of the polymerization initiator is preferably 0.01 to 1%
by mass relative to the total amount of all the monomers to be
subjected to the polymerization reaction.
[0168] The aqueous reaction medium in the above polymerization
reaction preferably has a pH of 4 to 7. At pH levels within the
above range, the polymerization reaction can progress smoothly and
the hydrolysis of --SO.sub.2X and/or --COZ.sup.1, which the
fluorovinyl ether derivative during polymerization reaction and/or
the fluoropolymer precursor has, can be minimized.
[0169] When the acid salt fluorovinyl ether derivative of general
formula (V) is used as an emulsifying agent, the fluoropolymer
precursor obtained by the above polymerization reaction has the
above-mentioned --SO.sub.2X.sup.3 and/or --COOZ.sup.4. The
--SO.sub.2X.sup.3 can be converted to the sulfonic acid group by
acid treatment with an acid and, as for the method of such acid
treatment, the same method as in the above-mentioned acid treatment
step (A.sub.acd) and acid treatment step (B.sub.acd) can be used.
It is thought that the above-mentioned --COOZ.sup.4 can be
converted to the carboxyl group by the same acid treatment as in
the above acid treatment step (A.sub.acd) and acid treatment step
(B.sub.acd).
[0170] In carrying out the method for producing a fluoropolymer
dispersion according to the present invention, the above-mentioned
polymerization reaction may be carried out in the manner of the
so-called iodine transfer polymerization technique according to
which the copolymerization is carried out in the presence of an
iodine compound to give a block copolymer. When such iodine
transfer polymerization is carried out, the films/membranes to be
described later herein, which are obtained from the polymer, can
show good mechanical strength characteristics even when the
above-mentioned fluorovinyl ether derivative unit content is
relatively low.
[0171] The iodine compound to be used in the above iodine transfer
polymerization includes, among others, perfluoroalkylene diiodides
such as 1,3-diidoperfluoropropane, 1,4-diiodoperfluorobutane,
1,3-diiodo-2-chloroperfluoropropane,
1,5-diiodo-2,4-dichloroperfluoropent- ane,
1,6-diiodoperfluorohexane, 1,8-diiodoperfluorooctane,
1,12-diiodoperfluorododecane and 1,16-diiodoperfluorohexadecane,
unsaturated bond-containing perfluoroalkenyl iodides such as
CF.sub.2.dbd.CFI and CF.sub.2.dbd.CFOCF.sub.2CF.sub.2I,
diiodomethane, and 1,2-diiodoethane. One of these species or a
combination of two or more of them may be used.
1,4-Diiodoperfluorobutane is preferred, among others. The iodine
compound may be used in an amount of 0.01 to 1% by mass relative to
the total amount of all the monomers subjected to the
polymerization reaction.
[0172] The method for producing an
acid-derivative-type-group-containing fluorocopolymer according to
the present invention comprises polymerizing a fluorovinyl ether
derivative (Rm) represented by the following general formula
(VI):
CF.sub.2.dbd.CF--O--(CF.sub.2CFY.sup.1--O).sub.n--(CFY.sup.2).sub.m-A.sup.-
5 (VI)
[0173] (wherein Y.sup.1 represents a fluorine atom, a chlorine atom
or a perfluoroalkyl group; n represents an integer of 0 to 3, and n
atoms/groups of Y.sup.1 may be the same or different; Y.sup.2
represents a fluorine atom or a chlorine atom; m represents an
integer of 1 to 5, and m atoms of Y.sup.2 may be the same or
different; A.sup.5 represents --SO.sub.2X.sup.1, --COZ.sup.1 and/or
--CONR.sup.19R.sup.20; X.sup.1 represents a halogen atom, Z.sup.1
represents an alkoxyl group having 1 to 4 carbon atoms, and
R.sup.19 and R.sup.20 are the same or different and each represents
a hydrogen atom, an alkali metal, an alkyl group or a
sulfonyl-containing group) in an aqueous reaction system, said
polymerization reaction being carried out using an acid/acid salt
fluorovinyl ether derivative represented by the general formula
(VII) given hereinabove. As the aqueous reaction medium, there may
be mentioned those spices mentioned hereinabove.
[0174] The above polymerization reaction is preferably carried out
by emulsion polymerization.
[0175] The method for producing an
acid-derivative-type-group-containing fluorocopolymer according to
the present invention may comprise the polymerization reaction
using an existing emulsifier in combination. Since, however, the
above-mentioned acid/acid salt fluorovinyl ether derivative
functions as the above-mentioned emulsifying agent, emulsification
is possible without using any existing emulsifier, as described
hereinabove referring to the polymerization reaction using an
emulsifying agent; further, the
acid-derivative-type-group-containing fluorocopolymer obtained can
have emulsifying activity. When no existing emulsifier is used,
there is no need for existing emulsifier removal after
polymerization and, therefore, the process can become economical
and simplified, high-purity products can be obtained with ease, and
there are not such inconveniences that will be caused when the
existing emulsifier used remains at the case of forming the
acid-derivative-type-group-containing fluorocopolymer into
films/membranes. Such inconveniences include foaming or
discoloration of films/membranes as caused by decomposition of the
existing emulsifier, and corrosion of the drier inside wall.
[0176] In producing an acid-derivative-type-group-containing
fluorocopolymer according to the present invention, the
polymerization reaction is preferably carried out without using any
existing emulsifier.
[0177] The method for producing an
acid-derivative-type-group-containing fluorocopolymer according to
the present invention produces an
acid-derivative-type-group-containing fluorocopolymer according to
the present invention, and the
acid-derivative-type-group-containing fluorocopolymer may be in the
form of a dispersion (first dispersion) obtained by the
above-mentioned polymerization reaction and comprising an
acid-derivative-type-group-containing fluorocopolymer particles as
dispersed in an aqueous medium, or in the form of a second
dispersion obtained by subjecting the first dispersion obtained by
the polymerization reaction to such after-treatment as aggregation,
flocculation and/or stabilizing treatment, or in the form of the
acid-derivative-type-group-containing fluorocopolymer particles
obtained by taking out from the above-mentioned first or second
dispersion, followed by drying, or in the form of a powder which is
an aggregate of such particles.
[0178] The acid-derivative-type-group-containing fluorocopolymer
has A.sup.5 in the above general formula (VI) as originating from
the fluorovinyl ether derivative (Rm) and is common to the
above-mentioned fluoropolymer precursor in that it can have
--SO.sub.2X.sup.1 or --COZ.sup.1 (X.sup.1 and Z.sup.1 being as
defined above) as A.sup.5. As for the chemical structure of the
above-mentioned acid-derivative-type-gr- oup-containing
fluorocopolymer, the fluoropolymer precursor is preferably obtained
by subjecting a fluorovinyl ether derivative represented by the
above general formula (II) to polymerization and the above general
formula (II) is common in chemical structure to the above general
formula (VI). Therefore, when the
acid-derivative-type-group-containing fluorocopolymer is subjected
to the same treatment as in the above-mentioned hydrolysis of the
fluoropolymer precursor, the above-mentioned --SO.sub.2X.sup.1
and/or --COZ.sup.1 can be hydrolyzed in an aqueous medium. In cases
where A.sup.5 which the above acid-derivative-type-group-containing
fluorocopolymer has is --CONR.sup.19R.sup.20 (R.sup.19 and R.sup.20
being as defined above), --CONR.sup.19 is generally hydrolyzed in
an aqueous medium by the same treatment as in the above-mentioned
hydrolysis step.
[0179] When the above-mentioned
acid-derivative-type-group-containing fluorocopolymer, which can
have a proton-conductive functional group obtained upon hydrolysis
of A.sup.5 in the above general formula (VI), said A.sup.5
originating from the fluorovinyl ether derivative (Rm), is used in
producing membranes having ion exchanging ability or proton
transferring activity, for example electrolyte membranes, the
copolymer can provide the membranes with improved performance
characteristics.
[0180] The fluoropolymer dispersion of the present invention can
also be obtained with ease by dispersing the fluoropolymer solid
composition in a liquid medium, as described above. The method for
dispersing the fluoropolymer solid composition of the present
invention in a liquid medium is not particularly restricted but
mention may be made of the method comprising using a stirrer such
as a dissolver, the method using a medium mill such as a sand
grinder, and the method based on ultrasonication, among others.
From the simplicity viewpoint, in particular, the ultrasonication
method is preferred.
[0181] The fluoropolymer dispersion of the present invention may be
one resulting from substituting a certain liquid medium falling
within the above-mentioned range of liquid media with another
certain liquid medium in the conventional manner. For example, a
fluoropolymer dispersion in a high-boiling liquid medium can be
obtained by adding the relatively high-boiling liquid, such as
N-methylpyrrolidone, to a fluoropolymer dispersion in a relatively
low-boiling liquid medium, such as water, and removing the
low-boiling liquid medium by heating for evaporation.
[0182] Such fluoropolymer dispersion obtainable by the
above-mentioned method for producing a fluoropolymer dispersion
also constitutes an aspect of the present invention.
[0183] The fluoropolymer dispersion of the present invention, if
necessary after incorporation of an alcohol therein, can be
suitably used in forming thin films/membranes by impregnating
porous supports for film/membrane formation or by casting for
film/membrane formation, as described later herein. The
fluoropolymer dispersion of the present invention can also be used
in thick film/membrane formation, if necessary after incorporation
of polyethylene glycol or the like therein.
[0184] The alcohol to be incorporated according to need is not
particularly restricted but may be any of those generally
incorporated in polymer dispersions for thin film formation. Thus,
there may be mentioned, for example, straight or branched alkanols
having 1 to 5 carbon atoms, which may be substituted by a fluorine
atom or atoms. Those alkanols having 1 to 3 carbon atoms are
preferred. Such alkanols are not particularly restricted but
include methanol, ethanol, propanol, isopropanol,
tetrafluoropropanol, etc. As the tetrafluoropropanol, there may be
mentioned 2,2,3,3-tetrafluoropropanol.
[0185] The dispersion composition for thin film formation of the
present invention comprises the above-mentioned fluoropolymer
dispersion and at least one alcohol selected from the group
consisting of methanol, ethanol, propanol and tetrafluoropropanol.
Preferred as the tetrafluoropropanol is
2,2,3,3-tetrafluoropropanol. The above-mentioned alcohol may be
used singly or two or more of them may be used.
[0186] The level of addition of the above alcohol(s) is preferably
10 to 80% by volume relative to the fluoropolymer dispersion. By
adding the alcohol(s) at the above addition level, it is possible
to adjust the surface tension of the dispersion composition for
thin film formation, so that when films/membranes are formed using
the dispersion composition for thin film formation, as described
later herein, uniform films/membranes can be obtained.
[0187] The dispersion composition for thin film formation may
further contain one or more other components or ingredients other
than the fluoropolymer dispersion and alcohol, unless the
film-forming properties of the dispersion composition for thin film
formation are impaired. As the other components/ingredients, there
may be mentioned, among others, alcohols other than the
above-defined alcohols, film-forming auxiliaries, and active
substances to be mentioned later herein.
[0188] The above-mentioned fluoropolymer dispersion or dispersion
composition for thin film formation can be judiciously used in
forming films/membranes. The "films/membranes" include, within the
meaning thereof, films/membranes including the so-called thin
films/membranes and, further, films, sheets, and the like. The
films/membranes may be those obtained by film/membrane formation by
casting, impregnation, or coating, for instance. They do not
include the substrates, porous supports or the like used in the
step of film/membrane formation.
[0189] The film/membrane of the present invention is one obtained
by film/membrane formation by casting using the above-mentioned
fluoropolymer dispersion or dispersion composition for thin film
formation. The phrase "film/membrane formation by casting"
generally refers to the manufacture of thin films/membranes by
applying the fluoropolymer dispersion or dispersion composition for
thin film formation to the surface of a substrate such as a glass
late, drying the dispersion/composition at ordinary temperature
and/or with heating, and peeling off the thus-formed film/membrane
from the substrate surface, if necessary after immersing in water.
When the above drying is carried out at ordinary temperature alone,
the film/membrane obtained after application of the fluoropolymer
dispersion or dispersion composition for thin film formation may
readily soluble in water or the like in certain instances and,
therefore, drying is preferably carried out at least with heating.
The term "ordinary temperature" as used herein means a temperature
of or in the vicinity of 300.degree. C., and the "heating"
generally refers to a temperature of 80 to 400.degree. C.
Preferably, the drying temperature is not lower than 200.degree.
C.
[0190] The film/membrane of the present invention is also one
obtained by impregnating a porous support with the above-mentioned
fluoropolymer dispersion or dispersion composition for thin film
formation and then removing the liquid medium. Generally, the
liquid medium can be removed by drying at ordinary temperature
and/or with heating. The film/membrane obtained by impregnation
with the fluoropolymer dispersion or dispersion composition for
thin film formation, when dried only at ordinary temperature, may
readily soluble in water or the like in certain instances and,
therefore, the drying is preferably carried out at least with
heating. The "drying with heating" following the impregnation can
be carried out at a temperature not lower than the melting point of
the fluoropolymer, for example at 200 to 350.degree. C.
[0191] The above-mentioned porous support is not particularly
restricted but may be an organic or inorganic material having a
porous structure. Thus, there may be mentioned, among others,
porous materials made of glass wool, a ceramic material, alumina, a
porous polytetrafluoroethylene [PTFE] film, carbon, a nonwoven
fabric or any of various polymers.
[0192] The films/membranes obtained by casting for film/membrane
formation and the films/membranes formed on porous supports
preferably have a film/membrane thickness of 5 to 50 .mu.m. When
the thickness is less than 5 .mu.m, the films/membranes will be
poor in mechanical strength characteristics and, when the thickness
exceeds 50 .mu.m, the films/membranes, when used in solid polymer
electrolyte type fuels cells, for instance, will unfavorably cause
deteriorations in performance characteristics of the fuel
cells.
[0193] For obtaining thick films/membranes, it is preferable for
the concentration of particles comprising the fluoropolymer in the
fluoropolymer dispersion to be high, since, then, the number of
repetitions of casting can be reduced and the volume shrinkage in
the step of drying can be suppressed. Low concentrations are
undesirable since, in particular when films/membranes with a
thickness of scores of millimeters are to be obtained, it is
necessary to repeat several times the step of casting of the
fluoropolymer dispersion and the step of drying.
[0194] The active substance-immobilized material of the present
invention comprises the fluoropolymer and an active substance and
is one obtained by applying, to a substrate, a liquid composition
comprising the active substance and the above-mentioned
fluoropolymer dispersion or dispersion composition for thin film
formation. Upon application of the liquid composition to a
substrate, the fluoropolymer and active substance are immobilized
on the substrate.
[0195] The above-mentioned active substance is not particularly
restricted but may be judiciously selected, according to the
intended use of the active substance-immobilized material, from
among those substances capable of having activity in the active
substance-immobilized material. For example, a catalyst can
judiciously be used in certain instances.
[0196] The above-mentioned catalyst is not particularly restricted
but may be any of those generally used as electrode catalysts.
Thus, for example, mention may be made of metals comprising
platinum, ruthenium, etc.; and organic metal complexes generally
comprising one or more metals as central metals and comprising
platinum or ruthenium as at least one of the central atoms. The
metal comprising platinum or ruthenium or the like is preferably a
platinum-containing metal, although it may be a
ruthenium-containing metal such as simple substance ruthenium. The
platinum-containing metal is not particularly restricted but
includes, among others, simple substance platinum (platinum black);
platinum-ruthenium alloys. Generally, the catalyst is used in the
form supported on a carrier such as silica, alumina or carbon.
[0197] The above-mentioned liquid composition comprises at least
the above-mentioned fluoropolymer dispersion or dispersion
composition for thin film formation and the above-mentioned active
substance, if necessary together with another component(s). As the
other component, there may be mentioned, for example, film-forming
auxiliaries.
[0198] The above-mentioned substrate is not particularly restricted
but includes, among others, the above-mentioned porous supports,
resin molded articles, and metal sheets/plates. Preferred are, for
example, electrolyte membranes and porous carbon electrodes for
fuel cells. The electrolyte membranes comprise preferably
fluoropolymer, and it may comprise the above-mentioned
fluoropolymer.
[0199] The "application of the liquid composition to a substrate"
comprises applying the liquid composition to the substrate and, if
necessary after drying, further heating the whole generally at a
temperature not lower than the melting point of the fluoropolymer.
So long as the fluoropolymer and active substance can be
immobilized on the substrate, the heating conditions are not
particularly restricted but, for example, several minutes, for
example 2 to 30 minutes, of heating at 200 to 350.degree. C. is
preferred.
[0200] The electrolyte membrane of the present invention comprises
the above-mentioned active substance-immobilized material. The
electrolyte membrane may contain a substance(s) other than the
active substance-immobilized material unless the properties of the
active substance-immobilized material are deteriorated thereby.
[0201] The solid polymer electrolyte fuel cell of the present
invention comprises the above-mentioned electrolyte membrane. The
solid polymer electrolyte fuel cell is not particularly restricted
so long as it comprises the above-mentioned electrolyte membrane.
Generally, it may be one comprising those constituents which
constitute the solid polymer electrolyte fuel cell, such as
electrodes, gas, etc.
[0202] The above-mentioned dispersion composition for thin film
formation, the film/membrane obtained by casting, the membrane
formed on a porous support, the active substance-immobilized
material, the electrolyte membrane and the solid polymer
electrolyte fuel cell each is obtained from an acid/acid salt
group-containing fluoropolymer, preferably a sulfonic acid
group-containing fluoropolymer.
BEST MODES FOR CARRYING OUT THE INVENTION
[0203] The following examples illustrate the present invention in
further detail. These examples are, however, by no means limitative
of the scope of the present invention.
EXAMPLE 1
[0204] (1) A 300-ml stainless steel autoclave of the agitator type
was charged with a solution of 2.4 g of
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2SO.su- b.3Na and 20 mg of ammonium
persulfate [APS] in pure water and, after cooling to 0.degree. C.,
the autoclave inside space was thoroughly deaerated and substituted
with tetrafluoroethylene [TFE] gas and then evacuated. Then, 20 g
of CF.sub.2.dbd.CFOCF.sub.2CF.sub.2SO.sub.2F deaerated with N.sub.2
gas was injected into the autoclave, hexafluoropropylene [HFP] gas
was further injected under pressure until a pressure of 0.08 MPa
and, finally, TFE gas was injected under pressure until 0.9 MPa,
immediately followed by the start of temperature raising. The
temperature was programmed so that it arrived at 60.degree. C. in
about 10 minutes, when the pressure was 1.2 MPa. Immediately
thereafter, the pressure began to fall and dropped to 0.7 MPa after
1.5 hours. Thereafter, the polymerization was continued while
maintaining the pressure at 0.7 to 0.9 MPa. After 4 hours, the
polymerization was finished by temperature raising and pressure
release. A fluoropolymer precursor composed of tetrafluoroethylene
[TFE] and CF.sub.2.dbd.CFOCF.sub.2CF.sub.2SO.sub.2F was obtained in
the state of a colorless, transparent dispersion, and the unreacted
portion of CF.sub.2.dbd.CFOCF.sub.2CF.sub.2SO.sub.2F weighed about
4 g. The solid content of the fluoropolymer precursor in the
dispersion was 16% by mass, and the
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2SO.sub.2F unit content in the
fluoropolymer precursor was 16 mole percent. The
CF.sub.2.dbd.CFOCF.sub.2- CF.sub.2SO.sub.2F unit content values
described herein each is the value obtained by subjecting each
fluoropolymer precursor to coagulation with an acid and washing and
then to infrared absorption spectroscopic measurement [IR] or
fused-state NMR measurement at 300.degree. C.
[0205] (2) The fluoropolymer precursor dispersion (50 ml) obtained
as described above under (1) was two-fold diluted with pure water,
the dilution was stirred in a 200-ml beaker, the temperature was
raised to 55.degree. C., and the --SO.sub.2F groups of the
fluoropolymer precursor were hydrolyzed by adding dropwise a 10%
(by mass) aqueous solution of potassium hydroxide while maintaining
the pH at 10. After about 3 hours, no more decrease in pH was
observed. However, the hydrolysis step was continued for further 2
hours and then finished. During this period, no fluoropolymer
precipitation was perceived by the eye.
[0206] (3) The reaction mixture obtained as described above under
(2) was treated for hydrolysis by adding 1 N hydrochloric acid, and
the fluoropolymer was purified and concentrated by centrifugal
ultrafiltration using Centriprep YM-10 (product of Amicon) with
simultaneous removal of low-molecular-weight substances. The
fluoropolymer dispersion obtained had a fluoropolymer concentration
of 32% by mass and contained a fluoropolymer having stable
--SO.sub.3K groups with a small proportion of --SO.sub.3Na
groups.
[0207] (4) To the fluoropolymer dispersion obtained as described
above under (3) was added a mixture of ethanol and isopropanol (1:1
by volume) in an amount half the volume of the dispersion to give a
dispersion composition for thin film formation. The thus-obtained
dispersion composition for thin film formation had a viscosity of
about 0.08 Pa.s. The dispersion composition for thin film formation
was applied onto a glass sheet and then dried at room temperature
to give a colorless, transparent film. The film formed was
heat-treated at 300.degree. C. for 10 minutes for fixation. The
whole was then immersed in pure water, and the thin film was peeled
off from the glass sheet. The thin film obtained had a thickness of
5-10 .mu.m. The viscosity given above is the value obtained by
carrying out the measurement at 25.degree. C. using a type B
viscometer.
EXAMPLE 2
[0208] A fluoropolymer precursor was obtained in the state of a
dispersion in the same manner as in (1) of Example 1 except that an
amount of 2% by mass, relative water, of ammonium
perfluorooctanoate [C.sub.7F.sub.15COONH.sub.4] was used as the
emulsifier in lieu of CF.sub.2.dbd.CFOCF.sub.2CF.sub.2SO.sub.3Na
and that the charging of hexafluoropropylene [HFP] gas under
pressure was omitted. The dispersion obtained was colorless and
transparent, the solid content of the fluoropolymer precursor in
the dispersion was 18% by mass, and the
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2SO.sub.2F unit content in the
fluoropolymer precursor was 16.5 mole percent.
[0209] The fluoropolymer precursor dispersion obtained was treated
in the same manner as described above under (2), (3) and (4) in
Example 1. The --SO.sub.2F groups in the fluoropolymer precursor
could be converted to --SO.sub.3K groups, and coating films could
be formed as well.
EXAMPLE 3
[0210] A fluoropolymer precursor was obtained in the state of a
dispersion in the same manner as in (1) of Example 1 except that
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2SO.sub.3Na was not used. A certain
extent of fluoropolymer precursor coagulated in the dispersion
obtained, and the fluoropolymer precursor particles were large in
size, hence the dispersion was opaque.
[0211] The dispersion obtained was subjected to alkali hydrolysis
in the same manner as in (2) of Example 1. Although the
fluoropolymer particles coagulated in the early reaction stage, the
hydrolysis reaction could be brought to completion.
[0212] The reaction mixture after the above hydrolysis was
ultrafiltered by the same centrifugal ultrafiltration method as
described above under (3) in Example 1. Although the fluoropolymer
sedimented because of the large sizes of particles thereof, the
fluoropolymer, when stirred in pure water, could be dispersed
again.
[0213] A dispersion composition for thin film formation comprising
the fluoropolymer dispersion after purification was prepared in the
same manner as mentioned above under (4) in Example 1 and applied
to a glass sheet, followed by drying at room temperature. The
resulting film was milk-white because of its being not homogeneous.
When heated at 300.degree. C., however, the film became colorless
and transparent. It was thus possible to obtain thin
films/membranes.
EXAMPLE 4
[0214] A transparent dispersion was obtained in the same manner as
in (1) of Example 1 except that 100 mg of 1,4-diiodoperfluorobutane
[I(CF.sub.2).sub.4I] was added together with
CF.sub.2.dbd.CFOCF.sub.2CF.s- ub.2SO.sub.2F. Then, the residual
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2SO.sub.2- F was removed by 30
minutes of degassing treatment under reduced pressure at 40.degree.
C. with purging with N.sub.2 gas and, then, CF.sub.2.dbd.CFCF.sub.3
gas was charged under pressure until 0.6 MPa and, further,
CF.sub.2.dbd.CF.sub.2gas was charged under pressure until 1 MPa.
Upon raising the temperature to 60.degree. C., pressure drop
immediately began. The polymerization was continued for 1.5 hours
while feeding CF.sub.2.dbd.CF.sub.2 gas to maintain the pressure at
0.9 to 1.0 MPa. Thereafter, the polymerization reaction was
terminated by pressure release, whereby a colorless and transparent
fluoropolymer precursor dispersion was obtained.
[0215] The fluoropolymer precursor dispersion obtained, when
treated in the same manner as described above under (2), (3) and
(4) in Example 1, could give the corresponding fluoropolymer
dispersion and coating films.
[0216] As the above results indicate, the fluoropolymer dispersion
of Example 3 as produced by using the fluoropolymer precursor
obtained by the polymerization reaction in the aqueous reaction
medium containing neither the monomer having emulsifying activity
nor the emulsifier could be obtained in the state of a dispersion
and could be formed into films/membranes. The fluoropolymer
dispersion of Example 1 or 2 as produced by using the fluoropolymer
precursor obtained by the polymerization reaction in the aqueous
reaction medium containing the monomer having emulsifying activity
or the emulsifier showed better dispersibility and film-forming
ability, among others. The fluoropolymer dispersion of Example 4 as
produced by using the fluoropolymer precursor obtained by using the
iodine transfer polymerization technique had no dispersibility,
film-forming ability or like problems.
EXAMPLE 5
[0217] (1) A 3,000-ml stainless steel autoclave of the agitator
type was charged with 300 g of a 10% aqueous solution of
C.sub.7F.sub.15COONH.sub.- 4 and 1,170 g of pure water, followed by
thorough evacuation and nitrogen substitution. After thorough
evacuation of the autoclave, tetrafluoroethylene [TFE] was injected
into the autoclave until a gage pressure of 0.2 MPa and the
temperature was raised to 50.degree. C. Then, 100 g of
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2SO.sub.2F was charged and TFE gas
was introduced to increase the pressure to a gage pressure of 0.7
MPa. A solution of 0.5 g of ammonium persulfate [APS] in 60 g of
pure water was then injected into the autoclave to initiate the
polymerization reaction.
[0218] For filling up that portion of TFE consumed by
polymerization, TFE was continuously fed to maintain the autoclave
inside pressure at 0.7 MPa. Further,
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2SO.sub.2F was continuously fed in
an amount corresponding to 53% by mass of the TFE fed to continue
the polymerization reaction.
[0219] At the time when the TFE fed amounted to 522 g, the pressure
in the autoclave was released to terminate the polymerization
reaction. The reaction mixture was then cooled to room temperature
to give 2,450 g of a slightly turbid aqueous dispersion with a
fluoropolymer precursor content of about 33% by mass.
[0220] A portion of the above aqueous dispersion was taken and
coagulated with nitric acid, and the coagulate was washed with
water and dried and subjected to fused-state NMR measurement. The
fluorovinyl ether derivative unit content in the fluoropolymer
precursor was 19 mole percent.
[0221] (2) A 50-ml portion of the fluoropolymer precursor
dispersion obtained in the above step (1) was 5-fold diluted with
pure water. The dilution was stirred in a 500-ml beaker, the
temperature was raised to 55.degree. C., and the --SO.sub.2F groups
which the fluoropolymer precursor had were hydrolyzed while
maintaining the pH at 10 or above by adding dropwise a 10% (by
mass) aqueous solution of sodium hydroxide. After about 3 hours, no
more decrease in pH was observed. However, the hydrolysis was
further continued for 2 hours and then terminated. Fluoropolymer
precipitation was not noticed by the eye.
[0222] (3) Acid hydrolysis was effected by adding 1 N hydrochloric
acid to the reaction mixture obtained in the above step (2), and
the fluoropolymer was purified and concentrated and
low-molecular-weight substances were removed simultaneously by
centrifugal ultrafiltration using Centriprep YM-10 (product of
Amicon). The fluoropolymer dispersion obtained had a fluoropolymer
concentration of 43% by mass and contained the corresponding
fluoropolymer having stable --SO.sub.3K groups.
[0223] The fluoropolymer dispersion was 100-fold diluted with pure
water, and a sample for particle shape measurement was prepared by
dropping the dilution onto an aluminum sheet, followed by drying at
60.degree. C. The sample was subjected to atomic force microscopy
[AFM], 20 particles in the picture obtained were extracted at
random, and the aspect ratio and average particle diameter thereof
were determined and found to be 1.0 and 100 nm, respectively.
[0224] (4) To the fluoropolymer dispersion obtained as described
above under (3) was added a mixture of ethanol and isopropanol (1:1
by volume) in an amount half the volume of the dispersion to give a
dispersion composition for thin film formation. The thus-obtained
dispersion composition for thin film formation had a viscosity of
about 0.08 Pa.s. The dispersion composition for thin film formation
was applied onto a glass sheet and then dried at room temperature
to give a colorless, transparent film. The film formed was
heat-treated at 300.degree. C. for 10 minutes for fixation. The
whole was then immersed in pure water, and the thin film was peeled
off from the glass sheet. The thin film obtained had a thickness of
12 to 17 .mu.m. The viscosity given above is the value obtained by
carrying out the measurement at 25.degree. C. using a type B
viscometer.
[0225] (5) The fluoropolymer dispersion obtained in the above step
(3) was evaporated to dryness using a rotary evaporator to give a
fluoropolymer solid composition. Observation of the surface of the
fluoropolymer solid composition under a scanning electron
microscope [SEM] gave the same results as described above under
(3).
[0226] (6) A 5-g portion of the fluoropolymer solid composition
obtained in the above step (5) was placed in a 200-ml beaker, 95 g
of NMP was added, and the mixture was sonicated for 15 minutes with
occasional shaking. A slightly turbid fluoropolymer dispersion was
obtained.
EXAMPLE 6
[0227] (1) A 3,000-ml stainless steel autoclave of the agitator
type was charged with 600 g of a 10% aqueous solution of
C.sub.7F.sub.15COONH.sub.- 4 and 870 g of pure water, followed by
thorough nitrogen substitution. The autoclave was evacuated
sufficiently and, then, TFE gas was charged until a gage pressure
of 0.2 MPa, and the temperature was raised to 50.degree. C.
Thereafter, 20 g of CF.sub.2.dbd.CFOCF.sub.2CF.sub.2SO.sub.2F was
injected, and the gage pressure was raised to 0.7 MPa by
introducing TFE gas. The polymerization was then initiated by
injecting an aqueous solution of 0.5 g of ammonium persulfate [APS]
in 60 g of pure water.
[0228] For filling up that portion of TFE consumed by
polymerization, PFE was continuously fed to maintain the autoclave
inside pressure at 0.7 MPa. Further,
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2SO.sub.2F was continuously fed in
an amount corresponding to 30% by mass of the TFE fed to continue
the polymerization reaction.
[0229] At the time when the TFE fed amounted to 400 g, a portion of
the fluoropolymer precursor dispersion was collected as a sample.
Then, 120 g of CF.sub.2.dbd.CFOCF.sub.2CF.sub.2SO.sub.2F was
charged under pressure and the polymerization was further
continued. Since the pressure rapidly decreased at that point of
time and, therefore, TFE was fed in an increased amount but this
was not immediately consumed by polymerization. After pressure
recovery, the polymerization was continued while continuously
feeding CF.sub.2.dbd.CFOCF.sub.2CF.sub.2SO.sub.2F in an amount of
60% by mass of the TFE consumed by polymerization.
[0230] At the time when the TFE fed amounted to 200 g, the pressure
in the autoclave was released to terminate the polymerization
reaction. The reaction mixture was then cooled to room temperature
to give 2,470 g of a slightly turbid aqueous dispersion with a
fluoropolymer precursor content of about 33% by mass.
[0231] A dried fluoropolymer precursor was obtained from the above
aqueous dispersion in the same manner as in Example 5. As a result
of fused-state NMR measurement, the
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2SO.sub.2F unit content in the
fluoropolymer precursor was found to be 10 mole percent and the
CF.sub.2.dbd.CFOCF.sub.2CF.sub.2SO.sub.2F unit content in the above
aqueous dispersion to be 13 mole percent.
[0232] The desired fluoropolymer dispersion was obtained through
the same hydrolysis step and purification/concentration step as in
Example 5.
[0233] The polymer particles in the fluoropolymer dispersion
obtained had an aspect ratio of 1.1 and an average particle
diameter of 60 nm.
INDUSTRIAL APPLICABILITY
[0234] The method for producing a fluoropolymer dispersion
according to the present invention, which has the above-described
constitution, can produce, in an aqueous system, fluoropolymer
dispersions each resulting from dispersion of an acid/acid salt
group-containing fluoropolymer through the polymerization reaction
step and hydrolysis step. The fluoropolymer dispersions obtained
and the fluoropolymer solid compositions derived therefrom can be
adequately used in producing electrolyte membranes in solid polymer
electrolyte fuel cells, in particular.
* * * * *