U.S. patent application number 11/741289 was filed with the patent office on 2008-10-30 for process for removing fluorinated emulsifier from fluoropolmer dispersions using an anion-exchange resin and a ph-dependent surfactant and fluoropolymer dispersions containing a ph-dependent surfactant.
This patent application is currently assigned to 3M Innovative Properties Company. Invention is credited to Michael C. Dadalas, Klaus Hintzer, Ludwig Mayer, James Arthur McDonell, Tilman C. Zipplies.
Application Number | 20080264864 11/741289 |
Document ID | / |
Family ID | 39885714 |
Filed Date | 2008-10-30 |
United States Patent
Application |
20080264864 |
Kind Code |
A1 |
Dadalas; Michael C. ; et
al. |
October 30, 2008 |
PROCESS FOR REMOVING FLUORINATED EMULSIFIER FROM FLUOROPOLMER
DISPERSIONS USING AN ANION-EXCHANGE RESIN AND A pH-DEPENDENT
SURFACTANT AND FLUOROPOLYMER DISPERSIONS CONTAINING A pH-DEPENDENT
SURFACTANT
Abstract
A process of reducing the amount of fluorinated emulsifiers in
fluoropolymer dispersions by contacting the fluoropolymer
dispersion with an anion exchange resin in the presence of a
pH-dependent surfactant, and fluoropolymer dispersions containing
the pH-dependent surfactant and uses thereof.
Inventors: |
Dadalas; Michael C.;
(Eggenfelden, DE) ; Hintzer; Klaus; (Kastl,
DE) ; Mayer; Ludwig; (Burgkirchen, DE) ;
Zipplies; Tilman C.; (Burghausen, DE) ; McDonell;
James Arthur; (Woodbury, MN) |
Correspondence
Address: |
3M INNOVATIVE PROPERTIES COMPANY
PO BOX 33427
ST. PAUL
MN
55133-3427
US
|
Assignee: |
3M Innovative Properties
Company
|
Family ID: |
39885714 |
Appl. No.: |
11/741289 |
Filed: |
April 27, 2007 |
Current U.S.
Class: |
210/656 ;
524/800 |
Current CPC
Class: |
C08F 14/18 20130101;
C08F 14/18 20130101; C08L 27/12 20130101; C08F 2/24 20130101; C08L
27/12 20130101; C08F 6/22 20130101; F16C 17/12 20130101; C02F
2101/14 20130101; C08F 6/16 20130101; C08F 6/22 20130101; C08F 6/16
20130101; C02F 1/42 20130101; Y10T 428/3154 20150401; C02F 2209/06
20130101 |
Class at
Publication: |
210/656 ;
524/800 |
International
Class: |
C02F 1/28 20060101
C02F001/28; C08F 2/16 20060101 C08F002/16 |
Claims
1. A process of reducing the amount of fluorinated emulsifier in a
fluoropolymer dispersion, the process comprising contacting the
fluoropolymer dispersion with an anion exchange resin in the
presence of a pH-dependent surfactant to remove at least a portion
of the fluorinated emulsifier wherein the dispersion is contacted
with the anion exchange resin at a pH at which the pH-dependent
surfactant is in the non-ionic form.
2. The process according to claim 1 wherein the pH-dependent
surfactant has a reduced surface activity in its cationic form
compared to its non-ionic form.
3. The process according to claim 1 wherein the pH-dependent
surfactant, in its non-ionic form, is an amine.
4. The process according to claim 1 wherein the pH-dependent
surfactant in its non-ionic form is a tertiary amine with at least
one of the three residues linked to the N-atom being a polyoxy
alkyl residue and the remaining residues being a non-polar
carbohydrate.
5. The process according to claim 1 wherein the pH-dependent
surfactant in its non-ionic form is a tertiary amine with one of
the three residues linked to the N-atom being a polyoxy alkyl and
the remaining residue(s) being a linear or branched alkyl.
6. The process according to claim 1 wherein the pH-dependent
surfactant in its non-ionic form corresponds to the general formula
##STR00005## with m and n being independent of each other an
integer from 1 to 15 and R being a branched, saturated or
non-saturated, linear or cyclic alkyl, alkylamine, polyamine alkyl,
alkyloxy or polyoxy alkyl residue.
7. The process according to claim 1 wherein the fluoropolymer
dispersion prior to being contacted with the anion exchange resin
comprises at least about 0.02% by weight based on the solid content
of the dispersion of the fluorinated emulsifier.
8. The process according to claim 1 wherein the fluorinated
emulsifier is a perfluorinated carboxylic acid.
9. The process according to claim 1 wherein the fluorinated
emulsifier corresponds to the general formula:
[R.sub.f-O-L-COO].sub.iX.sup.i+ wherein L represents a linear
partially or fully fluorinated alkylene group or an aliphatic
hydrocarbon group R.sub.f represents a linear partially or fully
fluorinated aliphatic group or a linear partially or fully
fluorinated aliphatic group interrupted with one or more oxygen
atoms, X.sup.i+represents a cation having the valence i and i is 1,
2 or 3.
10. An aqueous fluoropolymer dispersion comprising: i) from about
5% to about 70% by weight based on the weight of the dispersion of
a fluoropolymer, and ii) at least about 0.02% by weight based on
the solid content of the dispersion of a pH-dependent surfactant,
the pH-dependent surfactant having depending on the pH of the
dispersion either a cationic or a non-ionic form and wherein the
pH-depedent surfactant is capable in its non-ionic form of
stabilising the dispersion.
11. The aqueous fluoropolymer dispersion according to claim 10
further comprising less than about 0.02% by weight based on the
weight of the solid content of the dispersion of a fluorinated
emulsifier.
12. Process of preparing a composition containing a coagulated
fluoropolymer said process comprising: i) providing an aqueous
fluoropolymer dispersion containing: a) from about 5% to about 70%
by weight based on the weight of the dispersion of a fluoropolymer,
and b) at least about 0.02% by weight based on the solid content of
the dispersion of a pH-dependent surfactant wherein the
pH-dependent surfactant has, depending on the pH of the dispersion,
either a cationic or a non-ionic form and is capable in its
non-ionic form of stabilising the dispersion; ii) reducing the pH
of the dispersion to a level at which the pH-dependent surfactant
is in its cationic form, iii) coagulating the dispersion.
13. The process according to claim 12, wherein the dispersion
further comprises less than about 0.02% by weight based on the
solid content of the dispersion of a fluorinated emulsifier.
14. The process according to claim 12 further comprising adding one
or more coating ingredients to the dispersion before carrying out
iii).
15. A coated substrate comprising a coagulated fluoropolymer
obtainable by the process according to claim 12.
16-17. (canceled)
Description
[0001] The present invention relates to a process of reducing the
amount of fluorinated emulsifier in fluoropolymer dispersions using
anion exchange resins in the presence of one or more pH-dependent
surfactants. The invention also relates to fluoropolymer
dispersions containing the pH-dependent surfactants but containing
no or only low amounts of fluorinated emulsifiers, and to uses of
these dispersions.
BACKGROUND
[0002] Fluoropolymers, i.e. polymers having a fluorinated backbone,
have been long known and used in a various applications because of
their desirable properties such as heat resistance, chemical
resistance, weatherability, UV-stability etc. Various
fluoropolymers are for example described in "Modern
Fluoropolymers", edited by John Scheirs (ed), Wiley Science 1997.
The fluoropolymers may have a partially fluorinated backbone,
generally at least 40% by weight fluorinated, or a fully
fluorinated backbone. Particular examples of fluoropolymers include
polytetrafluoroethylene (PTFE), copolymers of tetrafluoroethylene
(TFE) and hexafluoropropylene (HFP), typically referred to as FEP,
perfluoroalkoxy copolymers (PFA), ethylene-tetrafluoroethylene
(ETFE) copolymers, terpolymers of tetrafluoroethylene,
hexafluoropropylene and vinylidene fluoride (THV) and
polyvinylidene fluoride polymers (PVDF).
[0003] The fluoropolymers may be used to coat or impregnate
substrates to provide desirable properties thereto such as for
instance chemical resistance, weatherability, water- and oil
repellence, lubricity etc. For example, aqueous dispersions of
fluoropolymers may be used to coat or impregnate substrates such as
metals, fabrics, textiles, glass fibers or paper.
[0004] A frequently used method for producing aqueous dispersions
of fluoropolymers involves aqueous emulsion polymerization of one
or more fluorinated monomers. Usually, one or more concentration
steps follow the polymerization reaction to increase the content of
solids in the raw dispersion. The aqueous emulsion polymerization
of fluorinated monomers generally involves the use of an
emulsifier. Typically, the emulsifiers are perfluorinated anionic
surfactants. The fluorinated emulsifier stabilises the
fluoropolymer in the aqueous medium and prevents the fluoropolymer
from coagulating in the dispersion. Typical examples of fluorinated
emulsifiers are perfluorinated carboxylic acids, such as, for
example, perfluorooctanoic acids and salts thereof, in particular
ammonium perfluorooctanoic acid (APFO). Fluorinated emulsifiers are
generally expensive compounds and in several cases fluorinated
emulsifiers have been found to be poorly biodegradable.
Accordingly, measures have been taken to remove fluorinated
emulsifiers from the aqueous fluoropolymer dispersions.
[0005] WO 00/35971 describes a method in which the amount of
fluorinated emulsifier in aqueous dispersions is reduced by
contacting the dispersion with an anion exchange resin to which the
(anionic) fluorinated emulsifier binds. Non-ionic surfactants are
added to the dispersion prior to the ion-exchange to stabilise the
fluoropolymer in the dispersion in the absence of the fluorinated
emulsifier. The resulting emulsifier-free or emulsifier-reduced
fluoropolymer dispersions can be conveniently used in applications
where the fluoropolymers are applied to a substrate directly from
the dispersion.
[0006] However, in certain applications where the fluoropolymer is
not applied to a substrate directly from the dispersion, for
example, where the fluoropolymer is applied as a coagulum, e.g. as
a paste or solid, it may be desirable to avoid or at least to
reduce the presence of non-ionic surfactants. In these applications
the fluoropolymer is separated from the dispersion prior to
application to the substrate which is typically done by
destabilising the dispersion and separating the fluoropolymer from
the aqueous medium (also referred to as phase-separation or
coagulation). Non-ionic surfactants, however, have been observed to
prevent or inhibit the phase separation when using common phase
separation techniques such as, for example, salting out (i.e.
increasing the ionic strength of the dispersion by adding salts or
acids), shear force-induced coagulation, or solvent-induced
coagulation (e.g. adding organic solvents). Instead of the
formation of distinct phases, a fluoropolymer phase and a water
phase, slurries are often contained. If the fluoropolymers can be
collected from those poorly phase-separated mixtures at all, they
typically contain rather large amounts of residual non-ionic
surfactants and water, the presence of which impacts on the
physical properties of coatings prepared from these poorly
phase-separated fluoropolymers. For example, due to the presence of
the surfactants the fluoropolymer coating may adsorb water, for
instance from ambient humidity, leading to poor properties as
regards, for example, surface hardness, water resistance,
self-lubrication or friction-resistance etc.
SUMMARY OF THE INVENTION
[0007] There is a desire to provide a process for removing
fluorinated emulsifiers from fluoropolymer dispersions using
surfactants that stabilise the dispersion but are easily removable
from the dispersion and/or allow for a good or complete separation
of the fluoropolymer from the dispersion by phase separation
(coagulation).
[0008] Additionally, there is a need to provide stable aqueous
fluoropolymer dispersions containing no or only very low amounts of
fluorinated surfactants allowing effective and easy coagulation of
the fluoropolymer.
[0009] Furthermore, there is a need to provide fluoropolymers
coagulated from aqueous dispersions containing low amounts of
fluorinated surfactants and low amounts of non-ionic
surfactants.
[0010] In the following there is provided a process for reducing
the amount of fluorinated emulsifier in a fluoropolymer dispersion.
The process comprising contacting the dispersion with an anion
exchange resin in the presence of a pH-dependent surfactant. The
pH-dependent surfactant attains either a cationic or a non-ionic
form, depending on the pH of the dispersion in which it is present.
The pH-dependent surfactant is capable of stabilising the
dispersion when the surfactant is in its non-ionic form. The
dispersion is contacted with the anion exchange resin at a pH at
which the surfactant is in its non-ionic form.
[0011] In another aspect, there is provided an aqueous
fluoropolymer dispersion comprising: [0012] i) from about 5% to
about 70% by weight based on the weight of the dispersion of a
fluoropolymer, and [0013] ii) at least about 0.02% by weight based
on the solid content of the dispersion of the pH-dependent
surfactant.
[0014] Furthermore, there is provided a process of preparing a
composition containing a coagulated fluoropolymer said process
comprising: [0015] i) providing an aqueous fluoropolymer dispersion
containing: [0016] a) from about 5% to about 70% by weight based on
the weight of the dispersion of a fluoropolymer, and [0017] b) at
least about 0.02% by weight based on the solid content of the
dispersion of the pH-dependent surfactant and wherein the
dispersion has a pH at which the surfactant is in its non-ionic
form; [0018] ii) reducing the pH of the dispersion to a level at
which the surfactant is in its cationic form, [0019] iii)
coagulating the dispersion.
[0020] Additionally, there are also provided electrodes or bearings
comprising the coagulated fluoropolymers obtainable by the process
described above.
DETAILED DESCRIPTION OF THE INVENTION
The Fluoropolymers
[0021] The fluoropolymer dispersions from which the fluorinated
emulsifier is to be removed or in which the amount thereof is to be
reduced can originate from any source but are typically aqueous
fluoropolymer dispersions obtained by the emulsion polymerization
with fluorinated emulsifiers. The preparation of aqueous
fluoropolymer dispersions is known in the art and are described,
for example, in EP 0 030 663 or U.S. Pat. No. 3,142,665,
incorporated herein by reference. Typically, the raw dispersion,
i.e. the dispersion directly obtained after emulsion
polymerization, comprises between about 5% and about 35% by weight
of fluoropolymer. Concentrated dispersions, i.e. dispersions having
a fluoropolymer content of from about 35% and to about 70% by
weight, are usually obtained in a separate concentration step by
concentrating the raw dispersion, e.g. by ultrafiltration,
evaporation, thermal decantation or electrodecantation.
[0022] The fluoropolymers contained in the dispersions described
herein include melt-processable as well as non-melt-processible
fluoropolymers.
[0023] Examples of non-melt processible fluoropolymers include
polytetrafluoroethylene (PTFE) and so-called modified PTFE, which
is a polymer of tetrafluoroethylene modified or copolymerized with
minor amounts, e.g. up to or less than 1% wt based on PTFE of
another fluorinated monomer such as, for example,
hexafluoropropylene or a perfluorinated vinyl ether.
[0024] Melt-processible fluoropolymers include so-called
fluorothermoplasts. Fluorothermoplasts typically have a distinct
melting point.
[0025] Still further, the fluoropolymer may comprise a so-called
micro-powder, typically a low molecular weight
polytetrafluoroethylene. Due to the low molecular weight of the
PTFE, micro-powders are melt processible.
[0026] The fluoropolymers of the dispersion may also be amorphous,
including those that upon curing result fluoroelastomers.
Fluoroelastomers have elastomeric properties. This means the
polymer can be extended and retains its original length when the
force necessary to extend the polymer is no longer applied.
Typically, amorphous fluoropolymers have no melting point or have
no distinct melting point.
[0027] Examples of suitable fluoropolymers include polymers based
on tetrafluorethylene (TFE), such as TFE homopolymers (PTFE) or TFE
copolymers. TFE copolymers may be copolymers with monomers
containing at least one unsaturated carbon-carbon functionality.
These monomers may be not fluorinated such as, e.g., ethylene (E)
or propylene (P), or they may be fluorinated, such as vinylidene
fluoride (VDF), hexafluoropropylene (HFP) or both. Other examples
of suitable fluoropolymers are VDF-based homopolymers or
copolymers, chlorotrifluoroethylene (CTFE)-based homopolymers or
copolymers. Further examples are modified PTFE, micro-powder,
copolymers of VDF and perfluorovinyl ether (PVE), copolymers of
TFE, E and/or P and PVE, copolymers of TFE, HFP and PVE, copolymers
of TFE, VDF and HFP and optionally CTFE, copolymers of VDF, TFE and
PVE, copolymers of TFE, E or P, HFP and PVE or mixtures
thereof.
[0028] The particle size of the fluoropolymer in the aqueous
fluoropolymer dispersion is typically between 50 nm and 400 nm
(number average diameter). Smaller particle sizes are contemplated
as well, for example between 20 nm and 50 nm, which may typically
be obtained by microemulsion polymerization techniques.
[0029] The dispersion may be monomodal, bimodal or multimodal with
respect to particle sizes, molecular weight distribution and/or
average molecular weight. Such a dispersion may contain
fluoropolymers of the same or different chemical composition, for
example one component may be a non melt-processible polymer and the
other component may be a thermoplast.
[0030] An example of a dispersion that is bimodal with respect to
particle size is a dispersion containing a first fluoropolymer
having an average particle size (number average) of greater than
200 nm and a second fluoropolymer having a particle size (number
average) of less than 100 nm. The fluoropolymer may also be in the
form of core-shell particles. Core-shell particles include
particles of which an inner layer (core) comprises a fluoropolymer
that has a different chemical composition and or molecular weight
compared to the polymer in the outer layer of the particles. To
produce core-shell particles, the corresponding monomer or monomer
mixture that is to form the shell is added at the final stage of
the polymerization. The final polymerization stage is typically
defined as the stage during which the last 25% by weight or less of
polymer solids are produced. In a particular embodiment, the shell
may constitute not more than 20% by weight or not more than 15% by
weight of the particle weight. Examples for the preparation of
core-shell polymers are described, for instance, in EP 1 529 785 or
EP 0 030 663.
The Fluorinated Emulsifier
[0031] Typically, aqueous fluoropolymer dispersions are prepared
using emulsifiers. The fluorinated emulsifier used in aqueous
emulsion polymerization is typically an anionic fluorinated
surfactant. Commonly used fluorinated surfactants are non-telogenic
and include those that correspond to the formula (I):
i) (Y--R.sub.f-Z)n-M, (I)
wherein Y represents hydrogen, Cl or F; R.sub.f represents a linear
or branched perfluorinated alkylene having 4 to 10 carbon atoms; Z
represents COO.sup.- or SO.sub.3.sup.-; M represents a cation
including monovalent and multivalent cations, e.g. an alkali metal
ion, an ammonium ion or a calcium ion and n corresponds to the
valence of M and typically has a value of 1, 2 or 3.
[0032] Representative examples of fluorinated emulsifiers according
to above formula (I) are perfluoroalkanoic acids and salts thereof
such as perfluorooctanoic acid and its salts, in particular
ammonium salts, such as ammonium perfluoro octanoic acid
(APFO).
[0033] Other fluorinated emulsifiers which may be used in aqueous
polymerization of fluoropolymers include fluorinated carboxylic
acids or salts thereof corresponding to the general formula
(II):
i) [R.sub.f--O-L-COO.sup.-].sub.iX.sup.i+ (II)
wherein L represents a linear partially or fully fluorinated
alkylene group or an aliphatic hydrocarbon group, R.sub.f
represents a linear partially or fully fluorinated aliphatic group
or a linear partially or fully fluorinated aliphatic group
interrupted with one or more oxygen atoms, X.sup.i+ represents a
cation having the valence i and i is 1, 2 or 3. Examples of cations
include H.sup.+, ammonium, monovalent metal cations, divalent metal
cations and trivalent cations. Typical cations are H.sup.+ K.sup.+,
Na.sup.+ and NH.sub.4.sup.+.
[0034] For the sake of convenience, the term `fluorinated
carboxylic acid` is hereinafter used to indicate the free acid as
well as salts thereof. Generally, the fluorinated carboxylic acid
are low molecular weight compounds, for example a compound having a
molecular weight for the anion part of the compound of not more
than 1000 g/mol, typically not more than 600 g/mol and in
particular embodiments, the anion of the fluorinated carboxylic
acid may have a molecular weight of not more than 500 g/mol.
[0035] Fluorinated emulsifiers of this type are described in great
detail in US 2007/0015937 by Hintzer et al, which is incorporated
herein by reference. All fluorinated emulsifiers and in particular
the individual compounds described in US 2007/0015937 may be used
in this invention.
The pH-Dependent Surfactant
[0036] The process of removing the fluorinated emulsifier is
carried out in the presence of a pH-dependent surfactant (or a
mixture thereof). A pH-dependent surfactant is understood to mean a
surfactant that attains either a non-ionic or a cationic form
depending on the pH of the environment at which it is present.
Non-ionic form means the surfactant molecule does not contain an
ionic group, i.e. a positively or negatively charged group.
Cationic form means the surfactant molecule has one or more,
preferably one or two cationic groups.
[0037] Preferably, the surfactant is cationic at a pH of or below
about 6.0 or at a pH of or below about 5.0 or of or below about pH
4.0. Preferably, the surfactant is non-ionic at a pH of or above
about 7.0, at a pH of or above about 8.0 or at a pH of or above
about 9.0. For example, the surfactant may be cationic at a pH of
or below about 4 and non-ionic at a pH of or above 11.
[0038] The surfactant is capable of stabilising the fluoropolymer
dispersion when the dispersion is at a pH at which the surfactant
is in its non-ionic form.
[0039] The surfactant is not capable of stabilising the
fluoropolymer dispersion when it is in its cationic form or it is
less capable compared to it being in the non-ionic form. This may
be because the pH-dependent surfactant is less surface active at a
pH at which it is in its cationic form than at a pH at which its is
in its non-ionic form. The surfactant may also have no surface
activity at a pH at which it is in its cationic form. The
surfactant may also be incapable or less capable of stabilisation
when being in the cationic form because it may be susceptible to
de-aggregation by increasing the ionic strength of the dispersion
(i.e. adding soluble salts or acids to the dispersion), which may
result in the precipitation of the surfactant or to its
concentration in the aqueous phase falling below its critical
micelle concentration (cmc), i.e. the concentration at which the
surfactant becomes surface active. Surface activity is the
capability of a surfactant to reduce the surface tension of water.
It can be measured according to standard procedures, for example
using the ring method (cf DIN 53914:1980-03).
[0040] Examples of suitable pH-dependent surfactants include
primary, secondary or tertiary amines or polyamines of appropriate
structure to have surface activity when being in the non-ionic form
and having reduced surface activity when being in the cationic
form. The amines are capable of abstracting a proton from an acid
to form a salt by which the amines are converted in the cationic
form. Preferably, the amines are tertiary amines or polyamines
containing at least one tertiary amine moiety with at least one of
the three residues of the tertiary amine being a polyoxy alkyl
residue and the remaining residue(s) being a non-polar residue.
[0041] The non-polar residues may be, for example, saturated or
non-saturated, linear, branched or cyclic alkyls, alkylaryls, alkyl
ethers, aryl ethers, alkylaryl ethers, alkyl esters, aryl esters,
alkylaryl esters or silicones. Preferred non-polar residues are
branched, linear or cyclic alkyl residues, preferably comprising
more than 8 and less than 30, more preferably more than 10 and less
than 20, and most preferably between 12 and 18 C atoms.
[0042] The polyoxy alkyl residues may be linear or branched,
substituted or non-substituted, wherein substituted means the
residue bears further moieties, such as alkyl residues, alkoxy
residues, alkyl amines, amino groups, halogen groups, hydroxyl
groups, ester groups, thiol group, aromatic groups etc. Preferred
polyoxy alkyl residues include ethoxylates or propoxylates or
combinations thereof.
[0043] Suitable amine ethoxylates include those corresponding to
the general formulae (III) or (IV):
i) R.sub.1R.sub.2--N--(CH.sub.2CH.sub.2O).sub.nH (III)
or
##STR00001##
with R.sub.1, R.sub.2 and R being a non-polar residue, such as
being independent from each other a branched, linear or cyclic
alkyl, alkyloxy or polyoxy alkyl residue. Each non polar residue
may comprise, independent from each other, 4 or more, 6 or more, 8
or more and less than 30, more preferably more than 10 and less
than 20, most preferably between 6 and 18 C atoms. In some
embodiments one or more of the residues R.sub.1, R.sub.2 or R may
be alkyl-substituted (preferably with a methyl or ethyl group) in
the 1-position (i.e. the position adjacent to the N-atom) or
di-alkyl-substituted in the 1-position.
[0044] In formulae (III) and (IV) n and m represent an integer and
being independently from each other 1, 2, 3, 4, 5, 6, 7, 8, 9, 10,
11, 12, 13 or 14 or 1 to 10, 1 to 6 or 1 to 4. Preferably, the sum
of n and m may be less than 30, more preferably less than 25, most
preferably less than 20. The sum of n and m may also be 2, 3, 4, 5,
8, 10, 12, 20 or 25.
[0045] The total number of C-atoms in the molecule may be less than
50 or less than 40.
[0046] In one embodiment one or more residues of the tertiary amine
linked to the N-atom may correspond to the formula (V):
i) R'--(OCH.sub.2--CR''H).sub.x-- (V)
with R' being hydrogen, a branched, linear or cyclic alkyl or aryl
residue and R'' being hydrogen or an alkyl group including, for
example, a methyl, ethyl, propyl, isopropyl, or butyl group.
Preferably, R' is a methyl, ethyl, propyl or isopropyl group; x
represents an integer of from 1, 2, 3, or 1 to 10, 1 to 6 or 1 to
4.
[0047] In another embodiment, x is an integer from 1 to 10, R'' is
H or CH.sub.3 and R' is selected from the group consisting of H or
straight or branched alkyls, such as methyl, ethyl, propyl,
isopropyl etc.
[0048] Examples of readily available pH-dependent surfactants
include but are not limited to those marketed under the tradename
TRITON RW-Series by Dow Chemical Company, Midland, Mich., USA, such
as for example TRITON RW-20, RW-50, RW-70, RW-100, RW-150.
[0049] Other examples of commercially available pH-dependent
surfactants include but are not limited to those shown in table 1.
Further examples of pH-dependent surfactants are described, for
example in U.S. Pat. No. 4,605,773, which is incorporated herein by
reference.
[0050] Table 1: pH-dependent surfactants available under the
tradename GENAMIN from Clariant, Basel, CH
TABLE-US-00001 GENAMIN Chemical Class Structure Amine ethoxylates
##STR00002## T 200 Tallow amine R = tallow; x + y = 20 ethoxylates
T 150 R = tallow; x + y = 15 T 120 R = tallow; x + y = 12 T 020 R =
tallow; x + y = 2 S 250 Stearyl amine R = stearyl; x + y = 25
ethoxylates S 200 R = stearyl; x + y = 20 S 150 R = stearyl; x + y
= 15 S 120 R = stearyl; x + y = 12 S 080 R = stearyl; x + y = 8 S
020 R = stearyl; x + y = 2 O 200 Oleyl amine R = oleyl; x + y = 20
ethoxylates O 080 R = oleyl; x + y = 8 O 050 R = oleyl; x + y = 5 O
020 R = oleyl; x + y = 2 Alkylproyplenediamine ethoxylates
##STR00003## LCL 030 R = lauryl, x + y + z = appr. 3.5 OCL 030 R =
oleyl, x + y + z = appr. 3.5 TCL 030 R = tallow, x + y + z = appr.
3.5 N,N-bisaminopropyltallow fatty amine ##STR00004## 3119 R =
tallow Tallow fatty propylene
R--(NH--CH.sub.2CH.sub.2CH.sub.2).sub.x--NH.sub.2 poly amine TP3A R
= tallow; x = 2 TP4A R = tallow; x = 3 Fatty propylene
R--NH--CH.sub.2CH.sub.2CH.sub.2--NH.sub.2 diamine LAP 100; R =
lauryl; R = oleyl;, R = tallow OAP 100, TAP100
[0051] The pH-dependent surfactant may be aromatic or non-aromatic.
The pH-dependent surfactant may be fluorinated or non-fluorinated
but is preferably non-fluorinated.
[0052] Although not necessary, further anionic surfactants other
than the fluorinated emulsifiers, and preferably non-fluorinated
ones may be present in the dispersion or may be added to it.
[0053] The pH-dependent surfactant may have a critical micelle
concentration (cmc) at room temperature of from about 10-3 to about
10-6 mol/l. The cmc and surface tension can be determined by
standard methods, for example by the ring method using a
tensiometer (Kriiss tensiometer K100, Kruss GmbH, Hamburg
Germany).
Process of Removing the Fluorinated Emulsifier from Fluoropolymer
Dispersions
[0054] The fluorinated emulsifier is removed from the fluoropolymer
dispersion containing it by contacting the dispersion with an anion
exchange resin in the presence of the pH-dependent surfactant.
[0055] The pH-dependent surfactant is present during the anion
exchange in an amount sufficient to stabilise the fluoropolymer
dispersion. Typical amounts are at least about 0.02%, or at least
about 0.5%, preferably at least about 1.0% by weight based on the
solid content of the dispersion. The upper limit may be chosen such
that the viscosity of the dispersion still allows covenient
handling and processing and/or that the pH-dependent surfactant can
be easily removed from the coagulated polymer or the dipersion.
This amount may be up to about 100%, up to about 25% or up to about
10% by weight based on the solid content of the dispersion.
Typically, the pH-dependent surfactant may be present in amounts
from 0.5 to about 15 or from about 1 to about 7% by weight based on
the solid content. The optimum effective amount can be easily
determined b one skilled in the art through routine
experimentation. For example, the destabilisation of the dispersion
can be determined visibly by the occurrence of coagulation, or can
be measured by pressure build-up at constant flow rate (or
reduction of the flow rate at constant pressure) in the anion
exchange resin.
[0056] When subjecting the dispersion to the anion exchange, the pH
of the dispersion has a pH at which the pH-dependent surfactant is
capable to stabilise the fluoropolymer dispersion. Typically, this
is when the surfactant is in its non-ionic form.
[0057] Preferably, the anion exchange resin used in the process
according to the invention is basic. The anion exchange resin may
be a weak, medium strong or a strong basic. The terms strong,
medium strong and weak basic anion exchange resin are defined in
"Encyclopedia of Polymer Science and Engineering", John Wiley &
Sons, 1985, Volume 8, page 347 and "Kirk-Othmer", John Wiley &
Sons, 3rd edition, volume 13, page 687. Strong basic anion exchange
resin typically contain quaternary ammonium groups, medium strong
resins usually have tertiary amine groups and weak basic resins
usually have secondary amines as the anion exchange functions.
Examples of anion exchange resins that are commercially available
for use in this invention include but are not limited to
AMBERLITE.RTM. IRA-402, AMBERJET.RTM. 4200, AMBERLITE.RTM. IRA-67
and AMBERLITE.RTM. IRA-92 all available from Rohm &Haas,
PUROLITE.RTM. A845 (Purolite GmbH) and LEWATIT.RTM. MP-500 (Bayer
AG), LEWATIT.RTM. MP-62 (Bayer AG), or DOWEX 550A (Dow Chemical
Company) or DOWEX MARATHON A2 (Dow Chemical Company).
[0058] The resin employed in the present invention may have a
Gaussian distribution of bead sizes about the average bead
diameter, the beads may be polydisperse or the beads may be
monodisperse. The resin may be in a "non-fixed resin bed" or in a
"fixed resin bed". In a fixed resin bed the ion-exchange resin is
not agitated. Fixed resin bed typically covers column technology,
in which the resin rests and removal of the substance occurs
through a chromatographic process. The term non-fixed resin bed is
used to indicate that the resin is agitated, for example, being
fluidized, stirred or shaken.
[0059] The dimension of the ion exchange resin (volume of resin
containing column) are adapted to the concentration of fluorinated
emulsifier and volume of the fluoropolymer dispersion to be
treated. In case of resins loaded with the pH-dependent
surfactants, the volume of the resin and/or its loading degree is
such that the amount of the pH-dependent surfactant that could be
released from the resin is equal or preferably exceeds the amount
of fluorinated emulsifier to be removed from the dispersion.
[0060] In accordance with the process of removing the fluorinated
emulsifier, the fluoropolymer dispersion is contacted with an
effective amount of anion exchange resin and for a time sufficient
to reduce the level of fluorinated emulsifier to the desired level.
It is also possible to contact the dispersion with more than one
resin, for example a series of anion exchange resins according to
the invention. As an alternative or in addition to adding the
pH-dependent surfactant to the dispersion prior to the ion-exchange
step, resins may be used that have been loaded with the
pH-dependent surfactant and which release the pH-dependent
surfactant during the ion-exchange. In this embodiment, the resins
may be loaded with the same or a different pH-dependent surfactant
that has been added to the dispersion prior to the
ion-exchange.
[0061] The fluoropolymer dispersions may be contacted with the
anion exchange resin by mildly agitating or not agitating the
mixture of fluoropolymer dispersion and anion exchange resin. Ways
to agitate include shaking a vessel containing the mixture,
stirring the mixture in a vessel with a stirrer or rotating the
vessel around its axel. The rotation around the axel may be
complete or partial and may include alternating the direction of
rotation. Rotation of the vessel is generally a convenient way to
cause the agitation. When rotation is used, baffles may be included
in the vessel. A further attractive alternative to cause agitation
of the mixture of exchange resin and fluoropolymer dispersion is
fluidizing the exchange resin. Fluidization may be caused by
flowing the dispersion through the exchange resin in a vessel
whereby the flow of the dispersion causes the exchange resin to
swirl. Strong shear forces, however, may support coagulation of the
dispersion and are preferably avoided.
[0062] Contacting of the dispersion with the resin can be practiced
in a so-called batch-wise manner or in a continuous manner. In a
batch-wise process, a vessel is charged with the anion exchange
resin and fluoropolymer dispersion. The mixture in the vessel is
then agitated for a time sufficient to reduce the residual
fluorinated emulsifier to the desired level after which the
dispersion and exchange resin are separated, e.g. through
filtration. The vessel may then be charged anew with fluoropolymer
dispersion and exchange resin and the process is then repeated.
[0063] In a continuous process, fluoropolymer dispersions from
which fluorinated emulsifier is to be removed may be continuously
added at one end to a (preferably mildly agitating) vessel that
contains an anion exchange resin, and fluoropolymer dispersion
having a reduced amount of fluorinated emulsifier may be withdrawn
at another end of the vessel in a continuous fashion. In a
continuous process, the equipment will be designed such that the
residence time of the dispersion in the vessel is sufficient to
reduce the amount of fluorinated emulsifier to the desired level.
In a particular embodiment of a continuous process, a plurality,
e.g. 2 or more, (preferably mildly agitating) vessels each charged
with anion exchange resin may be used. Accordingly, the
fluoropolymer dispersion may be continuously added and withdrawn
from the first vessel. The fluoropolymer dispersion from the first
vessel may be fed continuously in the next vessel from which it is
continuously withdrawn and this process can be repeated if more
than 2 vessels are used. If a plurality of vessels is used, they
are typically arranged in a cascading arrangement.
[0064] Anion exchange resins charged with fluorinated emulsifier
can be regenerated by eluting the anion exchange resin according to
the processes disclosed in for example U.S. Pat. No. 4,282,162, WO
01/32563 and EP 1 069 078 and the fluorinated emulsifer may then be
recovered from the eluate. The recovered fluorinated emulsifer may
thereafter be re-used for example in an aqueous emulsion
polymerization of one or more fluorinated monomers to produce a
fluoropolymer.
The Fluoropolymer Dispersions
[0065] Accordingly, there is also provided a fluoropolymer raw
dispersion and a concentrated dispersion comprising
[0066] from about 5% to about 35% (raw dispersion) or from about
35% to about 70% by weight of fluoropolymer (concentrated
dispersion),
[0067] at least about 0.02%, preferably at least about 0.5%, more
preferably at least about 1.0% or from about 0.02% to about 20%, or
from about 0.5% to about 12% or from about 1 to about 8% by weight
based on the solid content of the dispersion of the pH-dependent
surfactant.
[0068] The dispersion may further comprise no or less than about
0.02%, preferably less than about 0.01%, more preferably less than
about 0.005% by weight based on the solid content of the dispersion
of a fluorinated emulsifier.
[0069] The dispersions are suitable for the preparation of
fluoropolymer coatings and fluoropolymer coating compositions.
Therefore, further coating ingredients may be added to the
dispersion. Consequently, the dispersions may also comprise further
coating ingredients. Typical coating ingredients may be for
example:
[0070] further polymers, such as further fluorinated polymers,
non-fluorinated polymers, including but not limited to
polysulfones, polyethersulfones, polyetherketones, polyamides,
polyimides, polyether imides, polyamide-imides, polybismaleimides,
polyacetals, silicones, silicates or mixture thereof which may
improve the rheology of the dispersion or the resulting coating or
may improve the adhesion of the fluoropolymer coating to the
substrate; or
[0071] fillers, such as, for example, carbon fibers, glass fibers,
glass spheres, ceramic fibers, borosilicates, silicates and
mixtures thereof, or
[0072] metal particles or agglomerates, such as for example silver
particles, gold particles, iron particles etc, or carbon particles
or graphite and mixtures thereof, for example for the preparation
of catalytic surfaces, electroconducting or heat conducting
surfaces or electrode surfaces (as for example disclosed in U.S.
Pat. No. 4,603,118); or
[0073] friction reducing agents such as sulphate salts or sulfide
salts such as for example metal salts such as molybdenium sulfide,
zinc sulfide, barium sulphate or mixtures thereof, for example for
the preparation of bearings (as disclosed in U.S. Pat. No.
4,847,135); or
[0074] pigments, such as for example soot, carbon black or titanium
dioxide.
[0075] The substrate to be coated may have a smooth or porous
surface. The substrate may be an inorganic composite such as
enamel, ceramics or, preferably, metals. Suitable metals include,
but are not limited to, for example, steel, stainless steel,
bronze, aluminium, iron or copper. Also suitable substrates are
fibres, such as textiles, paper, glass fabrics or fabrics
containing organic polymers, such as for example polyester,
polypropylene, polyethylene, or poylacetates. Prior to application
of the composition to these substrates, the substrate may be
roughened to further enhance adhesion of the coating to the
substrate. Typically, sand blasting or etching is used to roughen a
metal substrate.
[0076] A particular suitable application of the fluoropolymer
dispersion is the preparation of bearings such as, for example,
sliding-contact bearings, bush bearings, friction-type contact
bearings etc. Another particular suitable application of the
fluoropolymer dispersion is the preparation of electrodes.
[0077] Therefore, there is also provided the use of the composition
obtainable by the process described above for coating a substrate.
Typically, the substrate comprises a metal and more typically, the
substrate is a bearing of an electrode.
Process for Preparing Coating Compositions
[0078] The dispersions described above may be used for coating a
substrate. They can be applied to the substrate as dispersion and
subsequently sintered. Preferably the coating composition is not a
dispersion but is a solid mass or a paste. Preferably the coating
composition is a coagulum (i.e. the fluoropolymer phase obtained by
destabilising the dispersion). The coagualum may be prepared by
[0079] a) destabilizing the dispersion [0080] b) (optionally)
adding one or more further coating ingredients to the dispersion
[0081] c) coagulating the fluoropolymer [0082] d) collecting the
coagulum, wherein a) b) c) and d) can be carried out simultaneously
or subsequently. It is also possible to carry our a) before, after
or simultaneously with b).
[0083] Detabilizing the dispersion is typically carried out by
reducing the pH to a level at which the pH-depedent surfactant has
a reduced surface activity. Typically, this is the case when the
surfactant is in its cationic form.
[0084] Coagulating the fluoropolymer may already be achieved by
reducing the pH as described above. However, the pH-reduction may
not necessarily lead to an immediate coagulation. Coagulation may
be initiated or supported in various ways: for example, shear force
may be applied, the ionic strength of the dispersion may be
increased by adding further cations ("salting out") or by adding
organic solvents or other flocculation agents such as polycations
etc.
[0085] Organic solvents may also be added after or during the
coagulation which may help to increase the particle sizes of
cogulate and/or may lead to a further removal of water from the
coagulum ("agglomeration"). Preferred organic solvents are those
that are not soluble in water or only soluble in water up to an
amount of 15% by weight at room temperature and ambient pressure.
Typical organic solvents include, for example, toluene, xylene,
carbohydrates with boiling points from about 80 to 110.degree. C.,
liquid mineral oils, liquid parrafines etc.
[0086] Salts for "salting out" are preferably water soluble salts,
including for example, magnesium chloride, sodium chloride,
potassioum chloride, ammonium chloride or the corresponding
nitrates, sulfates or mixtures thereof.
[0087] The coagulate can be collected by standard methods such as
filtration, sedimentation, centrifugation, or decantation.
[0088] The coagulum may be applied to the substrate by standard
techniques such as, for example, calendering or rolling etc.
Typically, the coagulum is applied to roughened metal substrates as
described above.
[0089] The invention is further illustrated with reference to the
following examples, without however the intention to limit the
invention thereto.
METHODS AND EXAMPLES
Particle Sizes:
[0090] Particle sizes of fluoropolymer dispersions may be
determined by dynamic light scattering using a Malvern Zetasizer
1000 HSA in according to ISO/DIS 13321. Prior to the measurements
the polymer latexes were diluted with 0.001 mol/L KCl solution. The
measurements are made at 25.degree. C.
Fluorinated Emulsifier Content:
[0091] The content of fluorinated emulsifier can be measured by gas
chromatography (head space), by converting the emulsifier into the
methyl ester (using sulfuric acid and methanol) and using the
methyl ester of perfluorododecanoic acid as internal standard.
Solid Content:
[0092] The solid content was determined according to ISO 12086 (2 h
120.degree. C., 35 min 380.degree. C.).
Surfactant Content:
[0093] Content of surfactant in the dispersion can be determined by
using HPLC. In case of highly concentrated dispersion dilution may
be required.
Comparative Example 1 (C1)
[0094] To 500 g of a 35% solid containing aqueous PTFE dispersion
prepared by emulsion polymerization of tetrafluoroethylene using
ammonium perfluoro octanoic acid (APFO) as emulsifier and
containing 1500 ppm APFO were added 5% wt. (based on the solids) of
the non-ionic surfactant Triton X-100 (Dow Chemical Comp.) under
stirring. The dispersion had a pH of 3. The dispersion was then
submitted to anion exchange to reduce the APFO. Anion exchange was
carried out in a standard ion exchange column (5.times.50 cm) using
400 ml of AMBERLITE.TM. IRA 402 (available from Rohm & Haas) as
anion exchange resin. The resin was brought in its OH.sup.- form by
adjusting it with NaOH solution. The resulting dispersion had an
APFO content of 6 ppm.
[0095] 26 g of zinc sulphide (filler material) were added to the
dispersion under mild stirring. Then 7 ml of an aqueous ammonium
sulphate solution (40% wt of ammonium sulphate) were added upon
which coagulation started. The coagulation was supported by
applying shear force (Turrax mixer, 8,000 rpm, 15 minutes). The
coagulated polymer formed a slurry without any phase separation.
Addition of 90 ml xylene did not lead to a phase separation neither
did it lead to an agglomeration of the coagulum.
Example 1
[0096] To 500 g of the same PTFE dispersion of the comparative
example above were added 5% wt (based on the solid content of the
dispersion) of an aqueous solution containing 25% by wt of TRITON
RW 150 (an ethoxylated amine available from Dow Chemical Company,
Midland, Mich., USA). The pH of the dispersion was adjusted to pH
10 by adding an aqueous ammonia solution (25% wt of ammonia). The
dispersion was then submitted to the same ion-exchange process as
described in C1 above. The resulting dispersion had an APFO content
of 5 ppm. The pH of the dispersion was then reduced to a pH of 3 by
adding a 10% aqueous oxalic acid solution. Then 26 g of zinc
sulphide were added to the dispersion under mild stirring. The salt
concentration was increased by adding 7 ml of an aqueous ammonium
sulphate solution (40% wt of ammonium sulphate) by which
coagulation was initiated. Coagulation was completed by applying
shear force using a Turrax mixer (8,000 rpm, 15 minutes). The
coagulated dispersion showed a distinct phase separation. The
coagulum could be agglomerated by adding 90 ml of xylene.
* * * * *