U.S. patent application number 14/387764 was filed with the patent office on 2015-03-05 for aqueous fluoropolymer dispersion.
This patent application is currently assigned to DAIKIN INDUSTRIES, LTD.. The applicant listed for this patent is DAIKIN INDUSTRIES, LTD.. Invention is credited to Toshirou Miura, Hiromichi Momose, Nobuhiko Tsuda.
Application Number | 20150065624 14/387764 |
Document ID | / |
Family ID | 49260196 |
Filed Date | 2015-03-05 |
United States Patent
Application |
20150065624 |
Kind Code |
A1 |
Tsuda; Nobuhiko ; et
al. |
March 5, 2015 |
AQUEOUS FLUOROPOLYMER DISPERSION
Abstract
The present invention aims to provide an aqueous dispersion that
contains particles of a fluoropolymer at high concentrations and
has a less variable pH, and in which aggregates are less likely to
be generated even after the aqueous dispersion has been stored for
a long time. The present invention relates to an aqueous
dispersion, including: particles of a fluoropolymer having an
average primary particle size of 0.1 to 0.5 .mu.m in an amount of
50 to 70% by mass; a nonionic surfactant in an amount of 2 to 10%
by mass based on the amount of the fluoropolymer; and ammonium
lauryl sulfate in an amount of 0.0001 to 1% by mass based on the
amount of the fluoropolymer, wherein an amount of a
fluorine-containing anionic surfactant is less than 10 ppm.
Inventors: |
Tsuda; Nobuhiko;
(Settsu-shi, JP) ; Momose; Hiromichi; (Settsu-shi,
JP) ; Miura; Toshirou; (Settsu-shi, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
DAIKIN INDUSTRIES, LTD. |
Kita-Ku, Osaka-Shi |
|
JP |
|
|
Assignee: |
DAIKIN INDUSTRIES, LTD.
Kita-Ku, Osaka-Shi
JP
|
Family ID: |
49260196 |
Appl. No.: |
14/387764 |
Filed: |
March 27, 2013 |
PCT Filed: |
March 27, 2013 |
PCT NO: |
PCT/JP2013/059137 |
371 Date: |
September 24, 2014 |
Current U.S.
Class: |
524/156 |
Current CPC
Class: |
C08L 27/18 20130101;
C08K 5/41 20130101; C08K 2201/019 20130101; C08J 3/07 20130101;
C08K 5/06 20130101; C08L 71/02 20130101; C08J 2327/18 20130101;
C08L 2201/54 20130101; C08K 5/41 20130101; C08L 27/18 20130101;
C08L 71/02 20130101 |
Class at
Publication: |
524/156 |
International
Class: |
C08K 5/41 20060101
C08K005/41; C08K 5/06 20060101 C08K005/06 |
Foreign Application Data
Date |
Code |
Application Number |
Mar 27, 2012 |
JP |
2012-072241 |
Claims
1. An aqueous dispersion, comprising: particles of a fluoropolymer
having an average primary particle size of 0.1 to 0.5 .mu.m in an
amount of 50 to 70% by mass; a nonionic surfactant in an amount of
2 to 10% by mass based on the amount of the fluoropolymer; and
ammonium lauryl sulfate in an amount of 0.0001 to 1% by mass based
on the amount of the fluoropolymer, wherein an amount of a
fluorine-containing anionic surfactant is less than 10 ppm.
2. The aqueous dispersion according to claim 1, wherein the amount
of the ammonium lauryl sulfate is 0.01 to 0.1% by mass based on the
amount of the fluoropolymer.
3. The aqueous dispersion according to claim 1, wherein the
fluoropolymer is polytetrafluoroethylene.
4. The aqueous dispersion according to claim 1, wherein the
nonionic surfactant is a polyoxyethylene alkyl ether.
Description
TECHNICAL FIELD
[0001] The present invention relates to an aqueous dispersion of a
fluoropolymer.
BACKGROUND ART
[0002] An aqueous dispersion containing fluoropolymer particles can
be formed into a film with excellent characteristics such as
chemical stability, non-adhesion, and weather resistance, by
coating, impregnation, or other methods, and is therefore widely
used, for example, for cooking equipment, lining of pipes, and
glass fiber cloth impregnation film.
[0003] Patent Literature 1 discloses an aqueous fluororesin
dispersion containing fluororesin particles and a nonionic
surfactant, and further discloses that condensation is accelerated
by adding ammonium lactate, triethanolamine laurate, sodium lauryl
sulfate, ammonium lauryl sulfate, triethanolamine lauryl sulfate,
or the like in an amount of not more than 0.2% by mass based on the
amount of the fluororesin.
[0004] Patent Literature 2 discloses a method for reducing a
fluorosurfactant content fluoropolymer dispersion containing a
fluorosurfactant, which is stabilized with a nonionic surfactant,
and further discloses that any of various non-fluorinated anionic
surfactants may be used. Examples of the non-fluorinated anionic
surfactants include, but are not limited to, sodium lauryl sulfate,
sodium dodecylbenzylsulfonate, and secondary sodium alkyl
sulfonate. The non-fluorinated anionic surfactants are particularly
preferably ammonium lauryl sulfate or alkali metals, and most
preferably sodium lauryl sulfate.
[0005] Patent Literature 3 discloses a production method of an
aqueous fluoropolymer dispersion, which involves bringing an
aqueous fluoropolymer dispersion containing a fluoropolymer, a
fluorine-containing emulsifier, and a specific organic carboxylic
acid into contact with a weakly basic anion-exchange resin, thereby
adsorbing and removing the fluorine-containing emulsifier; and
bringing the resulting aqueous fluoropolymer dispersion into
contact with a strongly basic anion-exchange resin, thereby
adsorbing and removing the organic carboxylic acid. Patent
Literature 3 further discloses that an anionic surfactant other
than the fluorine-containing emulsifier may be added before or
after condensation in order to improve the stability and
condensation rate. Examples of the anionic surfactant include
ammonium laurate, ethanolamine laurate, ammonium cinnamate,
ammonium lauryl sulfate, sodium lauryl sulfate, triethanolamine
lauryl sulfate, and p-t-butyl ammonium benzoate.
CITATION LIST
Patent Literature
[0006] Patent Literature 1: JP 2008-37914 A
[0007] Patent Literature 2: JP 2009-538964 T
[0008] Patent Literature 3: JP 2011-252054 A
SUMMARY OF INVENTION
Technical Problem
[0009] An aqueous dispersion of a fluoropolymer with insufficient
storage stability has a problem in that sludge is generated in the
dispersion at the bottom of a container with time during storage
and still standing. One of the reasons for generation of sludge is
decrease in pH with time. Further, decrease in pH of the aqueous
dispersion may cause mold growing or corrosion of a substrate to
which the aqueous dispersion has been applied.
[0010] Further, a fluorine-containing anionic surfactant used in
the production of the aqueous dispersion is usually removed and
recovered for reducing environmental impact and recycling the
expensive fluorine-containing anionic surfactant. Polymer
aggregates are likely to be generated in an aqueous dispersion from
which the fluorine-containing anionic surfactant has been
removed.
[0011] The present invention aims to provide an aqueous dispersion
which contains particles of a fluoropolymer at high concentrations
and has a less variable pH, and in which aggregates are less likely
to be generated even after the aqueous dispersion has been stored
for a long time.
Solution to Problem
[0012] The present inventors have made various studies, and have
found a solution to the above problem. They found that addition of
ammonium lauryl sulfate in an aqueous dispersion suppresses
variation of pH of the aqueous dispersion and generation of
aggregates. Thus, the present invention has been completed.
[0013] That is, the present invention relates to an aqueous
dispersion, including:
[0014] particles of a fluoropolymer having an average primary
particle size of 0.1 to 0.5 .mu.m in an amount of 50 to 70% by
mass;
[0015] a nonionic surfactant in an amount of 2 to 10% by mass based
on the amount of the fluoropolymer; and
[0016] ammonium lauryl sulfate in an amount of 0.0001 to 1% by mass
based on the amount of the fluoropolymer,
[0017] wherein an amount of a fluorine-containing anionic
surfactant is less than 10 ppm.
[0018] In the aqueous dispersion of the present invention, the
amount of the ammonium lauryl sulfate is preferably 0.01 to 0.1% by
mass based on the amount of the fluoropolymer.
[0019] The fluoropolymer is preferably polytetrafluoroethylene.
[0020] The nonionic surfactant is preferably a polyoxyethylene
alkyl ether.
Advantageous Effects of Invention
[0021] The aqueous dispersion of the present invention containing
particles of a fluoropolymer at high concentrations has a less
variable pH, and aggregates are less likely to be generated in the
aqueous dispersion, even after the aqueous dispersion has been
stored for a long time.
DESCRIPTION OF EMBODIMENTS
[0022] The present invention will be explained in more detail
below.
[0023] The aqueous dispersion of the present invention contains
particles of a fluoropolymer, a nonionic surfactant, and ammonium
lauryl sulfate.
[0024] The aqueous dispersion of the present invention contains
ammonium lauryl sulfate. Therefore, pH of the dispersion is less
variable and aggregates are less likely to be generated in the
aqueous dispersion even after the aqueous dispersion has been
stored for a long time. These effects are specific to ammonium
lauryl sulfate, and surprisingly, sodium lauryl sulfate or other
lauryl sulfates other than ammonium lauryl sulfate is totally
ineffective in suppressing pH variation. Further, addition of
sodium lauryl sulfate or other lauryl sulfates other than ammonium
lauryl sulfate only slightly improves storage stability as compared
to addition of ammonium lauryl sulfate.
[0025] The aqueous dispersion of the present invention contains
ammonium lauryl sulfate in an amount of 0.0001 to 1% by mass based
on the amount of the fluoropolymer. The amount of the ammonium
lauryl sulfate is preferably 0.01 to 0.1% by mass, more preferably
0.02 to 0.1% by mass, and still more preferably 0.025 to 0.1% by
mass, based on the amount of the fluoropolymer. Too small an amount
of the ammonium lauryl sulfate leads to poor storage stability of
the aqueous dispersion. Further, too large an amount of the
ammonium lauryl sulfate surprisingly leads to poor storage
stability of the aqueous dispersion.
[0026] The particles of the fluoropolymer contain fluorine atoms
bonded to carbon atoms.
[0027] The melting point of the fluoropolymer is preferably
130.degree. C. to 370.degree. C. and more preferably 324.degree. C.
to 347.degree. C. The melting point is determined by differential
scanning calorimetry (DSC) at a temperature rise rate of 10.degree.
C./min.
[0028] Examples of the fluoropolymer include, but are not
particularly limited to, polytetrafluoroethylene [PTFE],
tetrafluoroethylene [TFE]/hexafluoropropylene [HFP] copolymers
[FEP], TFE/perfluoro (alkyl vinyl ether) [PAVE] copolymers [PFA],
ethylene/TFE copolymers [ETFE], polyvinylidene fluoride [PVDF], and
polychlorotrifluoroethylene [PCTFE].
[0029] The PTFE fibrillates, and is not limited as long as it has
non-melt processability, and may be a tetrafluoroethylene [TFE]
homopolymer or modified PTFE.
[0030] The "modified PTFE" means one obtained by copolymerising TFE
with a comonomer in such a small amount as not to provide melt
processability to the resulting copolymer. Examples of the monomer
in a small amount include fluoroolefins such as HFP and
chlorotrifluoroethylene [CTFE], fluoro (alkyl vinyl ether) having a
C1-C5 alkyl group, particularly a C1-C3 alkyl group; fluorodioxole;
perfluoroalkylethylene; and .omega.-hydroperfluoroolefin. The
amount of the monomer is preferably not more than 2 mol %, more
preferably not more than 1 mol %, and still more preferably less
than 1 mol %, based on the amount of all monomer units composing
the fluoropolymer. The lower limit is not particularly restricted,
and may be 0.0001 mol %.
[0031] The number average molecular weight of the PTFE is
preferably 100,000 to 30,000,000, and more preferably not less than
3,500,000 and not more than 8,000,000. The number average molecular
weight is calculated from a standard specific gravity determined by
a water displacement method in accordance with ASTM D-792 using a
sample formed in accordance with ASTM D-4895 98.
[0032] The fluoropolymer is preferably a perfluoropolymer. In
particular, PTFE is preferred. PTFE fibrillates, and is therefore
more likely to aggregate than other fluoropolymers. Accordingly,
storage stability is largely improved by the presence of ammonium
lauryl sulfate.
[0033] The average primary particle size of the particles of the
fluoropolymer is 0.1 to 0.5 .mu.m. The average primary particle
size is preferably 0.1 to 0.4 .mu.m.
[0034] The average primary particle size is determined as follows.
A standard curve of the transmittance of 550 nm incident light
through a unit length of an aqueous dispersion adjusted to a
fluoropolymer concentration of 0.22% by mass versus an average
primary particle size determined by measuring the particle diameter
in a certain specific direction on a transmission electron
micrograph is constructed, and the average primary particle size is
determined from the transmittance based on the standard curve.
[0035] The aqueous dispersion of the present invention contains 50
to 70% by mass of the particles of the fluoropolymer based on the
amount of the aqueous dispersion. The lower limit of the amount of
the particles of the fluoropolymer is more preferably 55% by mass,
and the upper limit thereof is more preferably 65% by mass. The
aqueous dispersion of the present invention thus containing
particles of the fluoropolymer at high concentrations has a less
variable pH, and aggregates are less likely to be generated in the
aqueous dispersion, even after the aqueous dispersion has been
stored for a long time.
[0036] The amount (P) of the particles of the fluoropolymer herein
is determined from the formula: P=Z/X.times.100 (%), wherein an
ignition residue (Z g) is obtained by drying about 1 g (X g) of a
sample in an aluminum cup (diameter: 5 cm) at 100.degree. C. for 1
hour and further drying at 300.degree. C. for 1 hour.
[0037] The aqueous dispersion of the present invention contains a
nonionic surfactant. The nonionic surfactant may be any publicly
known one as long as it is formed of a fluorine-free non-ionic
compound. Examples of the nonionic surfactant include ether type
nonionic surfactants such as polyoxyethylene alkyl phenyl ethers,
polyoxyethylene alkyl ethers, and polyoxyethylene alkylene alkyl
ethers; polyoxyethylene derivatives such as an ethylene
oxide/propylene oxide block copolymer; ester type nonionic
surfactants such as sorbitan fatty acid esters, polyoxyethylene
sorbitan fatty acid esters, polyoxyethylene sorbitol fatty acid
esters, glycerin fatty acid esters, and polyoxyethylene fatty acid
esters; and amine type nonionic surfactants such as polyoxyethylene
alkylamine and alkyl alkanolamide. These are all non-fluorinated
nonionic surfactants.
[0038] A hydrophobic group in a compound composing the nonionic
surfactant may be any of alkyl phenol groups, linear alkyl groups,
and branched alkyl groups, and is preferably a compound free of a
benzene ring, such as a compound free of an alkyl phenol group.
[0039] In particular, the nonionic surfactant is preferably
polyoxyethylene alkyl ethers. The polyoxyethylenealkyl ethers
preferably include a polyoxyethylene alkyl ether structure having a
C10-C20 alkyl group, and more preferably include a polyoxyethylene
alkyl ether structure having a C10-C15 alkyl group. The alkyl group
in the polyoxyethylene alkyl ether structure preferably has a
branched structure.
[0040] Examples of commercially available polyoxyethylene alkyl
ethers include Genapol X080 (product name, produced by Clariant),
TERGITOL 9-S-15 (product name, produced by Clariant), NOIGEN TDS-80
(product name, produced by DAI-ICHI KOGYO SEIYAKU CO., LTD.), and
LEOCOL TD-90 (product name, produced by Lion Corporation).
[0041] The cloud point of the nonionic surfactant is preferably
40.degree. C. to 85.degree. C. A cloud point is a temperature at
which an aqueous solution containing a nonionic surfactant begins
to become cloudy by increasing the temperature of the aqueous
solution. A cloud point can be determined in the usual way as
follows: a nonionic surfactant is dissolved in water so that the
concentration of the nonionic surfactant is 1%; a nonionic
surfactant is dissolved in a 25% aqueous solution of butyl carbitol
so that the concentration of the nonionic surfactant is 10%; or a
nonionic surfactant is dissolved in a 5% aqueous solution of
potassium sulfate so that the concentration of the nonionic
surfactant is 1%.
[0042] The HLB of the nonionic surfactant is preferably 10 to 15.
If the HLB is smaller than 10, improvement in storage stability
which is an object of the present invention is insufficient. If the
HLB is more than 15, the storage stability tends to be poor. The
HLB is still more preferably in the range of 12 to 14. In this
range, an aqueous dispersion with excellent storage stability can
be obtained.
[0043] The aqueous dispersion of the present invention contains the
nonionic surfactant in an amount of 2 to 10% by mass based on the
amount of the fluoropolymer. The amount of the nonionic surfactant
is preferably 2 to 6% by mass, and more preferably 4 to 6% by mass.
Too much a nonionic surfactant increases the viscosity, resulting
in poor handleability, or deterioration of the storage stability.
Too little a nonionic surfactant deteriorates the storage stability
of the aqueous dispersion.
[0044] The amount of the nonionic surfactant (N) herein is
calculated from the formula: N=[(Y-Z)/X].times.100 (%), wherein an
ignition residue (Y g) is obtained by heating about 1 g (X g) of a
sample in an aluminum cup (diameter: 5 cm) at 100.degree. C. for 1
hour, and an ignition residue (Z g) is obtained by further heating
the resulting ignition residue (Y g) at 300.degree. C. for 1
hour.
[0045] The aqueous dispersion of the present invention preferably
contains an aqueous medium. The aqueous medium may be water, or may
contain non-fluorine-containing organic solvents and/or
fluorine-containing organic solvents such as alcohols, ethers,
ketones, and paraffin wax, in addition to water.
[0046] The aqueous dispersion of the present invention contains a
fluorine-containing anionic surfactant in an amount of less than 10
ppm. Due to the above reason, the smaller the amount of the
fluorine-containing anionic surfactant is, the better. The
fluorine-containing anionic surfactant is a compound having a
fluorine atom and showing interface activity. The aqueous
dispersion of the present invention thus containing little of or no
fluorine-containing anionic surfactant has a less variable pH, and
aggregates are less likely to be generated in the aqueous
dispersion, even after the aqueous dispersion is stored for a long
time.
[0047] The amount of the fluorine-containing anionic surfactant may
be determined in such a way that methanol in an amount equal to the
amount of a measuring aqueous dispersion is added to the aqueous
dispersion, soxhlet extraction is performed, and high-performance
liquid chromatography [HPLC] is then performed.
[0048] Examples of the fluorine-containing anionic surfactant
include perfluorocarboxylic acids and the salts thereof,
perfluorosulfonic acids and the salts thereof, and fluoroether
compounds. Examples of the fluorocarboxylic acids include
perfluoroalkyl carboxylic acids such as perfluorooctanoic acid.
[0049] The fluorine-containing anionic surfactant is preferably a
fluorine-containing anionic surfactant represented by the formula
(5): Rf.sup.1-Y.sup.1 (5)
(in the formula, Rf.sup.1 represents a linear or branched C2-C12
fluoroalkyl group to which a divalent oxygen atom may be inserted,
Y.sup.1 represents --COOM.sup.1, --SO.sub.3M.sup.2,
--SO.sub.2NM.sup.3M.sup.4, or --PO.sub.3M.sup.5M.sup.6, and the
above M.sup.1, M.sup.2, M.sup.3, M.sup.4, M.sup.5, and M.sup.6 are
the same or different from one another, and each represent H or a
univalent cation). Examples of the univalent cation include --Na,
--K, and --NH.sub.4. The Rf.sup.1 is more preferably a linear or
branched C2-C6 fluoroalkyl group to which a divalent oxygen atom
may be inserted.
[0050] Y.sup.1 is preferably --COOH, --COONa, --COOK, or
--COONH.sub.4, and more preferably --COONH.sub.4.
[0051] The fluorine-containing anionic surfactant is more
preferably a fluorine-containing anionic surfactant represented by
the formula (6):
CF.sub.3--(CF.sub.2).sub.n1--Y.sup.1 (6)
(in the formula, n1 represents an integer of 1 to 5, and Y.sup.1 is
as defined above) or a fluorine-containing anionic surfactant
represented by the formula (7):
Rf.sup.2O--Rf.sup.3O--Rf.sup.4--Y.sup.1 (7)
(in the formula, Rf.sup.2 represents a C1-C3 fluoroalkyl group, and
Rf.sup.3 and Rf.sup.4 are each independently a linear or branched
C1-C3 fluoroalkylene group, the total number of carbons of
Rf.sup.2, Rf.sup.3, and Rf.sup.4 being not more than 6; and Y.sup.1
is as defined above).
[0052] Examples of the fluorine-containing anionic surfactant
represented by the formula (6) include
CF.sub.3(CF.sub.2).sub.4COONH.sub.4,
CF.sub.3(CF.sub.2).sub.3COONH.sub.4,
CF.sub.3(CF.sub.2).sub.2COONH.sub.4,
CF.sub.3(CF.sub.2).sub.3SO.sub.3Na, and
CF.sub.3(CF.sub.2).sub.3SO.sub.2NH.sub.2.
[0053] Examples of the fluorine-containing anionic surfactant
represented by the formula (7) include a fluorine-containing
anionic surfactant represented by the formula:
CF.sub.3O--CF(CF.sub.3)CF.sub.2O--CX.sup.1(CF.sub.3)--Y.sup.1
(in the formula, X.sup.1 represents H or F, and Y.sup.1 is as
defined above), a fluorine-containing anionic surfactant
represented by the formula:
CF.sub.3O--CF.sub.2CF.sub.2CF.sub.2O--CFX.sup.1CF.sub.2--Y.sup.1
(in the formula, X.sup.1 represents H or F, and Y.sup.1 is as
defined above), and a fluorine-containing anionic surfactant
represented by the formula:
CF.sub.3CF.sub.2O--CF.sub.2CF.sub.2O--CFX.sup.1--Y.sup.1
(in the formula, X.sup.1 represents H or F, and Y.sup.1 is as
defined above).
[0054] The number average molecular weight of the
fluorine-containing anionic surfactant is preferably not more than
1000, and more preferably not more than 500 because such a
surfactant is easily removed. In addition, the fluorine-containing
anionic surfactant preferably has 5 to 12 carbons. The number
average molecular weight herein is measured on the polystyrene
equivalent basis by GPC (gel permeation chromatograph)
measurement.
[0055] The aqueous dispersion of the present invention may contain,
if necessary, other resins as long as the features of the present
invention are not impaired.
[0056] Examples of the other resins include, but are not
particularly limited to, polyethylene oxide (dispersion
stabilizer), polyethylene glycol (dispersion stabilizer), phenol
resins, urea resins, epoxy resins, melamine resins, polyester
resins, polyether resins, acrylic silicone resins, silicone resins,
silicone polyester resins, and polyurethane resins.
[0057] The aqueous dispersion of the present invention preferably
has a pH of 7 to 12, and more preferably has a pH of 8 to 11 for
good storage stability. Since the aqueous dispersion of the present
invention contains ammonium lauryl sulfate, the special effect of
maintaining the pH for a long period of time is provided.
[0058] The aqueous dispersion of the present invention may contain
an additive for enhancing the coating property and the property of
a resulting coating film.
[0059] The additive may be selected depending on the intended use
of a resulting coated article, and examples of the additive
include, but are not particularly limited to, leveling agents,
solid lubricants, wood flour, quartz sand, carbon black, diamond,
tourmaline, germanium, alumina, silicone nitride, fluorite, clay,
talc, extender pigments, various bulking agents, conductive
fillers, bright materials, pigments, fillers, pigment dispersants,
anti-settling agents, water absorbers, surface conditioners,
thixotropy imparting agents, viscosity modifiers, anti-gelling
agents, ultraviolet absorbers, light stabilizers, plasticizers,
anti-flooding agents, anti-skinning agents, anti-scratch agents,
mildew proofing agents, anti-microbial agents, antioxidants,
antistatic agents, silane coupling agents, defoaming agents, drying
agents, and cissing inhibitors.
[0060] Examples of the bright materials include mica, metal powder,
glass beads, glass bubbles, glass flakes, and glass fibers. The
aqueous dispersion of the present invention containing such a
bright material may be formed into a coating film with excellent
outward appearance. The amount of the bright material is preferably
0.1 to 10.0% by mass based on the solids content of the aqueous
dispersion.
[0061] Examples of the metal powder include, but are not
particularly limited to, powder of an elemental metal such as
aluminum, iron, tin, zinc, gold, silver, and copper; and powder of
an alloy such as aluminum alloy and stainless. The metal powder may
be in any form, and may be in the form of particles, flakes, or the
like. The aqueous dispersion of the present invention may be a
clear coating material not containing such metal powder as coloring
components.
[0062] Examples of the viscosity modifier include methyl cellulose,
alumina sol, polyvinyl alcohol, and a carboxylated vinyl
polymer.
[0063] Examples of the defoaming agent include non-polar solvents
such as toluene, xylene, C9-C11 hydrocarbons; and silicone oil.
[0064] Examples of the drying agent include cobalt oxide.
[0065] The aqueous dispersion of the present invention can be
preferably produced by a production method including the steps of
polymerizing fluoromonomers in the presence of the
fluorine-containing anionic surfactant to obtain an aqueous
dispersion containing particles of a fluoropolymer; adding the
nonionic surfactant into the aqueous dispersion; removing the
fluorine-containing anionic surfactant from the aqueous dispersion;
and adding ammonium lauryl sulfate into the aqueous dispersion from
which the fluorine-containing anionic surfactant has been
removed.
[0066] The production method preferably includes the step of adding
an alkali into the aqueous dispersion to adjust the pH to 7 to 12,
and preferably to 8 to 11 before or after the step of adding
ammonium lauryl sulfate for improving the storage stability of the
resulting aqueous dispersion. Examples of the alkali include
alkali-metal hydroxides and ammonia. Preferred among these is
ammonia.
[0067] Examples of the fluorine-containing monomer contributing to
the polymerization include, but are not particularly limited to,
TFE, HFP, PAVE, vinylidene fluoride [VDF], and CTFE. These
fluorine-containing monomers used for the polymerization may be
used alone or two or more of these may be used in combination. If
necessary, a non-fluorine-containing monomer such as ethylene may
also be used in the polymerization.
[0068] The polymerization is so-called emulsion polymerization, and
can be performed by a publicly known method. The temperature,
pressure, and other conditions of the polymerization may be
appropriately set depending on the kinds and amounts of the
fluorine-containing monomer and the fluorine-containing anionic
surfactant, and the kind of an intended fluoropolymer. Publicly
known polymerization stabilizers and polymerization initiators may
be used.
[0069] The fluorine-containing anionic surfactant may be removed by
any method, and may be removed by performing, for example,
conventionally known condensation and purification. Any one of the
conventionally known operations may be performed only at once, or
any one or combination of the operations may be performed twice or
more.
[0070] Examples of the method for removing the fluorine-containing
anionic surfactant include a cloud point concentration method
according to WO2004/050719, treatment with an anion exchanger
according to JP 2002-532583 T, and ultrafiltration according to JP
S55-120630 A. For example, the method for removing the
fluorine-containing anionic surfactant may be a method including
contacting an aqueous dispersion containing a nonionic surfactant
with an anion-exchange resin including a strongly basic resin
preliminarily converted into the OH form, under basic environment;
and phase-separating and condensing the resulting aqueous
dispersion.
[0071] The phase-separation condensing can be performed in such a
way that an aqueous dispersion containing a nonionic surfactant is
heated and separated into a fluoropolymer-non-containing phase
(supernatant phase) and a fluoropolymer-containing phase (condensed
phase), and the fluoropolymer non-containing phase is removed and
the fluoropolymer-containing phase is recovered.
[0072] The aqueous dispersion of the present invention may
preferably be used as a coating material, and specifically used as
a top coating material, an intermediate coating material, or a
coating material for lining.
[0073] The coating may be performed by various methods similar to
conventional coating methods, such as a dipping method, a spray
method, a roll coating method, a doctor blade method, a spin flow
coating method, and a curtain flow coating method.
[0074] The aqueous dispersion of the present invention may be
applied directly to a substrate. In order to improve adhesion, it
is desirable that a primer layer be formed and the aqueous
dispersion be applied thereto. Examples of the substrate to be used
include, but are not particularly limited to, substrates made of
various metals, porcelain enamel, glass, or various ceramics.
Further, in order to improve adhesion, a surface of a substrate is
preferably made rough, for example, by sandblasting.
[0075] The aqueous dispersion applied to a substrate is then dried
under usual conditions. Dry to touch is achieved by drying
preferably at room temperature to 150.degree. C., and more
preferably at 80.degree. C. to 150.degree. C. for 5 to 20
minutes.
[0076] A dried coating film is sintered (processed). The sintering
(processing) temperature and time may be changed depending on the
kind or melting temperature of the fluororesin. For example,
sintering is performed at the melting temperature or higher of the
fluororesin, and is performed usually at 360.degree. C. to
415.degree. C. for 5 to 30 minutes.
[0077] A primer layer may be formed in such a way that a primer is
applied, dried, and sintered, and the aqueous dispersion of the
present invention is then applied thereto, and dried and sintered
(2-coat 2-bake process); a primer is applied and dried, and the
aqueous dispersion of the present invention is then applied thereto
and dried, and both the primer and the aqueous fluropolymer
dispersion are simultaneously sintered (2-coat 1-bake process); or
a primer is applied and dried, an intermediate coating material
containing a bright material, which is the aqueous dispersion of
the present invention, is applied thereto and dried, a top coating
material, which is a clear coating material other than the aqueous
dispersion of the present invention, is applied thereto and dried,
and these are simultaneously sintered (3-coat 1-bake process). In
addition, after application of a primer, an intermediate coating
material containing a bright material, and a top coating material
as a clear coating material, which are both the aqueous dispersion
of the present invention, may subsequently be applied.
[0078] Coated articles listed below can be produced by application
of the aqueous dispersion of the present invention. Examples of the
coated articles include cooking equipment such as frying pans,
grill pans, pressure cookers, other various pans, rice cookers,
rice cake machines, ovens, hot plates, bread molds, knives, and gas
cookers; food and beverage containers such as electric pots and ice
cube trays; equipment for food industry such as mixing rolls, mill
rolls, conveyers, and hoppers; industrial products such as rolls
for office automation devices [OA], belts for OA devices,
separation pawls for OA devices, paper making rolls, and calender
rolls for film production; metal molds and molds for molding foamed
polystyrene and the like, release plates for forming dies such as
release plates for producing plyboards and decorative plates;
kitchen equipment such as range hoods; frozen food processing
equipment such as conveyer belts; tools such as saws, files, dies,
and borers; household products such as irons, scissors, and knives;
metal foils and electric wires; sliding bearings of food processing
machines, packaging machines, and spinning machines; slide members
of cameras and watches; auto parts such as pipes, valves, and
bearings; and snow shovels, plows, parachutes, ship bottoms,
boilers, and industrial containers (particularly for semiconductor
industry).
[0079] The aqueous dispersion of the present invention may be used,
for example, in impregnation involving impregnating a porous medium
such as a nonwoven fabric and a resin molded product in the aqueous
dispersion, drying the medium, and preferably sintering the medium;
or in cast film formation involving applying the aqueous dispersion
to a substrate such as glass, drying the applied dispersion,
immersing the resulting product in water as needed, and removing
the substrate to obtain a thin film. For example, the aqueous
dispersion is used as aqueous dispersion coating materials, binders
for electrodes, and water repellents for electrodes.
[0080] The aqueous dispersion of the present invention may
preferably be used as a processing aid. Use of the aqueous
fluoropolymer dispersion of the present invention as a processing
aid in combination with a host polymer or the like improves the
melt strength at melt processing of the host polymer, and the
mechanical strength, electrical characteristics, flame retardancy,
anti-dropping property, and sliding property of the resulting
polymer.
[0081] The aqueous dispersion of the present invention containing
PTFE as the fluoropolymer is preferably used as a processing aid
after combining with a hot melt processable fluororesin. The
aqueous dispersion of the present invention is preferred as a
material of PTFE, which is described, for example, in JP H11-49912
A, JP 2003-24693 A, U.S. Pat. No. 5,804,654, JP H11-29679 A, and JP
2003-2980 A. The aqueous dispersion of the present invention is as
good as the processing aids described in the publications.
[0082] The aqueous fluoropolymer dispersion of the present
invention containing polytetrafluoroethylene as the fluoropolymer
(B) is preferably formed into co-coagulation powder by mixing with
an aqueous dispersion of a hot melt processable fluororesin and
coagulating the mixture. The co-coagulation powder is preferred as
a processing aid. Examples of the hot melt processable fluororesin
include FEP, PFA, ETFE, and EFEP. Preferred among these is FEP.
[0083] The aqueous dispersion of the present invention containing
PTFE as the fluoropolymer is preferably used as a dust-control
treatment agent. The dust-control treatment agent may be used as
follows: it is mixed with a dust-emitting substance, and the
mixture is subjected to compression-shearing action at a
temperature of 20.degree. C. to 200.degree. C. to fibrillate
polytetrafluoroethylene, thereby emission of dust of dust-emitting
substance is suppressed. For example, the dust-control treatment
agent may be used in the methods disclosed, for example, in JP
2827152 B and JP 2538783 B. The dust-control treatment agent is
used in the fields of building-products, soil stabilizers,
solidifying materials, fertilizers, landfill of incineration ash
and harmful substance, and explosion proof equipment, and
cosmetics.
[0084] The aqueous dispersion of the present invention may
preferably be used for the dust-control treatment agent composition
according to WO 2007/004250, and may be used in the dust-control
treatment according to WO 2007/000812.
[0085] The aqueous dispersion of the present invention containing
PTFE as the fluoropolymer is preferably used as a material of PTFE
fibers obtained by a dispersion spinning method. The dispersion
spinning method is a method for providing PTFE fibers by mixing a
PTFE aqueous dispersion with an aqueous dispersion of a matrix
polymer, extruding the mixture to form an intermediate fiber
structure, and sintering the intermediate fiber structure to
decompose the matrix polymer and sinter the PTFE particles.
EXAMPLE
[0086] The present invention is described in more detail below with
reference to examples, but is not limited only to these
examples.
[0087] The values of examples were determined by the following
methods.
(1) Average Primary Particle Size
[0088] A standard curve of the transmittance of 550 nm incident
light through a unit length of an aqueous dispersion adjusted to a
resin solids concentration of 0.22% by mass versus an average
primary particle size determined by measuring the particle diameter
in a certain direction on a transmission electron micrograph was
constructed. The average primary particle size was determined from
the transmittance based on the standard curve.
(2) Fluoropolymer Concentration (P)
[0089] The fluoropolymer concentration was determined from the
formula: P=Z/X.times.100 (%), wherein an ignition residue (Z g) was
obtained by drying about 1 g (X g) of a sample in an aluminum cup
(diameter: 5 cm) at 100.degree. C. for 1 hour and further drying at
300.degree. C. for 1 hour.
(3) Fluorine-Containing Anionic Surfactant Concentration
[0090] The fluorine-containing anionic surfactant concentration was
determined in such a way that methanol in an amount equal to the
amount of the resulting aqueous dispersion was added to the aqueous
dispersion, soxhlet extraction was performed, and high-performance
liquid chromatography [HPLC] was performed under the following
conditions. The fluorine-containing anionic surfactant
concentration was calculated using a standard curve of a known
fluorine-containing anionic surfactant concentration obtained from
HPLC measurement using the above eluate and conditions.
(Measurement Condition)
[0091] Column: ODS-120T (4.6.phi..times.250 mm, produced by TOSO
CORPORATION) [0092] Developer solution: Acetonitrile/0.6% by mass
aqueous [0093] perchloric acid solution=1/1 (vol/vol %) [0094]
Amount of sample: 20 .mu.L [0095] Flow rate: 1.0 ml/min [0096]
Detection wavelength: UV 210 nm [0097] Column temperature:
40.degree. C.
(4) Amount (N) of Nonionic Surfactant
[0098] The amount of the nonionic surfactant was determined as
follows: the amount N is calculated from the formula :
N=[(Y-Z)/X]100(%), wherein an ignition residue (Y g) was obtained
by heating about 1 g (X g) of a sample in an aluminum cup
(diameter: 5 cm) at 100.degree. C. for 1 hour, and an ignition
residue (Z g) was obtained by heating the resulting ignition
residue (Y g) at 300.degree. C. for 1 hour, and the amount of a
stabilizer was subtracted from the amount N. The amount of the
stabilizer was calculated based on the amount added at the time of
preparation.
(5) Storage Stability
[0099] An aqueous dispersion (500 ml) contained in a plastic
container was allowed to stand in a room at a constant temperature
of 40.degree. C. for 6 months. The aqueous dispersion after
allowing to stand was gently stirred and allowed to pass through a
400-mesh stainless steel screen, and an aggregated matter left on
the screen was dried at 300.degree. C. for 1 hour. The amount of
the aggregated matter was expressed as percentage of the resin
solids content (based on the fluoropolymer in the original aqueous
dispersion). If the storage stability is poor, a large amount of
aggregated matter generates.
Production Example 1
[0100] A nonionic surfactant (TD-90, produced by Lion Corporation)
was added to a PTFE aqueous dispersion 1-1 obtained in Example 8 of
JP 2005-036002 A (average primary particle size: 274 nm, PTFE
concentration: 22% by mass, fluorine-containing anionic surfactant:
CF.sub.3(CF.sub.2).sub.2O(CF.sub.2).sub.2COONH.sub.4, amount of
fluorine-containing anionic surfactant: 4280 ppm based on PTFE) so
that a dispersion containing 15 parts by mass of the nonionic
surfactant based on 100 parts by mass of the PTFE was prepared.
Subsequently, a 20-mm diameter column was filled with 250 ml of a
OH-form anion-exchange resin (product name: AMBERJETAMJ4002,
produced by Rohm and Haas), and the temperature of the column was
adjusted to 40.degree. C. The PTFE aqueous dispersion 1-1 was
allowed to pass through the column at SV=1. Further, the aqueous
dispersion after passing through the column was maintained at
63.degree. C. for 3 hours, and separated into a supernatant phase
and a condensed phase. The condensed phase was recovered as a PTFE
aqueous dispersion 1-2.
[0101] The PTFE aqueous dispersion 1-2 has a fluoropolymer
concentration (PC) of 67.4% by mass and a nonionic surfactant
concentration (NC) of 3.5 parts by mass based on 100 parts by mass
of PTFE, and contains 1 ppm of a fluorine-containing anionic
surfactant based on the PTFE.
Production Example 2
[0102] A nonionic surfactant (TDS-80, produced by DAI-ICHI KOGYO
SEIYAKU CO., LTD.) was added to the modified PTFE aqueous
dispersion 2-1 obtained in Experimental Example 2 of JP 2006-117912
A (average primary particle size: 283 nm, PTFE concentration: 29%,
fluorine-containing anionic surfactant:
CF.sub.3(CF.sub.2).sub.6COONH.sub.4, amount of fluorine-containing
anionic surfactant: 2400 ppm based on PTFE) so that a dispersion
containing 15 parts by mass of the nonionic surfactant based on 100
parts by mass of the PTFE was prepared. Subsequently, a 20-mm
diameter column was filled with 250 ml of an OH-form anion-exchange
resin (product name: AMBERJET AMJ4002, produced by Rohm and Haas),
and the temperature of the column was adjusted to 40.degree. C. The
PTFE aqueous dispersion 2-1 was allowed to pass through the column
at SV=1. Further, the aqueous dispersion after passing through the
column was maintained at 63.degree. C. for 3 hours, and separated
into a supernatant phase and a condensed phase. The condensed phase
was recovered as a PTFE aqueous dispersion 2-2.
[0103] The PTFE aqueous dispersion 2-2 has a fluoropolymer
concentration (PC) of 69.3% and a nonionic surfactant concentration
(NC) of 2.8 parts by mass based on 100 parts by mass of the PTFE,
and contains 1 ppm of a fluorine-containing anionic surfactant
based on the PTFE.
Example 1
[0104] To the PTFE aqueous dispersion 1-2 obtained in Production
Example 1 was added TD-90 in an amount of 6.0% by mass based on the
amount of the PTFE and LATEMUL AD25 (25% aqueous solution of
ammonium lauryl sulfate) produced by Kao Corporation in an amount
of 500 ppm (in terms of active ingredients) based on the amount of
the PTFE. Further, the PTFE concentration was adjusted to 60% by
mass and the pH was adjusted to 9.8 using ion exchange water and
ammonia water. The resulting aqueous dispersion contained 6.0% by
mass of the nonionic surfactant based on the amount of the PTFE,
and 0.05% by mass of the ammonium lauryl sulfate based on the
amount of the PTFE.
[0105] The resulting aqueous dispersion was allowed to stand at
25.degree. C. for 6 months, and measured for the pH and the
percentage of an aggregate. The pH was 9.6, and the percentage of
an aggregate was 1%.
Comparative Example 1
[0106] A dispersion having a PTFE concentration of 60% by mass and
a pH of 9.8 was obtained in the same manner as in Example 1 except
that EMAL 2F30 (30% aqueous solution of sodium lauryl sulfate salt)
produced by Kao Corporation was added in an amount of 500 ppm (in
terms of active ingredients) based on the amount of the PTFE
instead of LATEMUL AD25 of Example 1. The resulting aqueous
dispersion contained 6.0% by mass of the nonionic surfactant based
on the amount of the PTFE, and 0.05% by mass of the sodium lauryl
sulfate based on the amount of the PTFE.
[0107] The resulting aqueous dispersion was allowed to stand at
25.degree. C. for 6 months, and the pH and the percentage of an
aggregate were measured to be 4.3 and 3%, respectively.
Comparative Example 2
[0108] A dispersion having a PTFE concentration of 60% by mass and
a pH of 9.8 was obtained in the same manner as in Example 1 except
that a 5% aqueous solution of ammonium laurate obtained by
neutralizing lauric acid produced by Wako Pure Chemical Industries,
Ltd. with ammonia was added in an amount of 500 ppm (in terms of
active ingredients) based on the amount of the PTFE, instead of
LATEMUL AD25 of Example 1. The resulting aqueous dispersion
contained 6.0% by mass of the nonionic surfactant based on the
amount of PTFE, and 0.05% by mass of the ammonium laurate based on
the amount of PTFE.
[0109] The resulting aqueous dispersion was allowed to stand at
25.degree. C. for 6 months, and the pH and the percentage of an
aggregate were measured to be 8.4 and 6%, respectively.
Examples 2 to 5
[0110] Aqueous dispersions were each prepared in such a way that to
the PTFE dispersion 2-2 obtained in Production Example 2 was added
TDS-80 in an amount of 6.0% by mass based on the amount of the PTFE
and LATEMUL AD25 (25% aqueous solution of ammonium lauryl sulfate)
produced by Kao Corporation in an amount of 100 ppm (in terms of
active ingredients), 250 ppm (in terms of active ingredients), 500
ppm (in terms of active ingredients), or 1000 ppm (in terms of
active ingredients) based on the amount of the PTFE; and the PTFE
concentration was adjusted to 62% by mass and the pH was adjusted
to 9.8 using ion exchange water and ammonia water. The resulting
aqueous dispersions each contained 6.0% by mass of the nonionic
surfactant based on the amount of the PTFE, and the ammonium lauryl
sulfate in an amount of 0.01% by mass, 0.025% by mass, 0.05% by
mass, or 0.1% by mass, based on the amount of the PTFE.
[0111] The resulting aqueous dispersions were allowed to stand at
40.degree. C. for 6 months, and the pHs and the amounts of
aggregates of the aqueous dispersions were measured. Table 1 shows
the results.
Comparative Example 3
[0112] A dispersion was prepared in the same manner as in Example 4
except that EMAL 2F30 (30% aqueous solution of sodium lauryl
sulfate salt) produced by Kao Corporation was used instead of
LATEMUL AD25 in Examples 2 to 4. The resulting dispersion contained
6.0% by mass of the nonionic surfactant and 0.05% by mass of the
sodium lauryl sulfate based on the amount of the PTFE.
[0113] The resulting aqueous dispersion was allowed to stand at
40.degree. C. for 6 months, and measured for the pH and the amount
of an aggregate. Table 1 shows the results.
TABLE-US-00001 TABLE 1 Amount of non-fluorinated Aggregate
Non-fluorinated anionic surfactant Initial pH after (%) after
anionic surfactant (% by mass) pH 6 months 6 months Example 1
Ammonium lauryl sulfate 0.05 9.8 9.6 1 Example 2 Ammonium lauryl
sulfate 0.01 9.8 9.6 18 Example 3 Ammonium lauryl sulfate 0.025 9.8
9.6 15 Example 4 Ammonium lauryl sulfate 0.05 9.8 9.7 9 Example 5
Ammonium lauryl sulfate 0.1 9.8 9.7 16 Comparative Sodium lauryl
sulfate 0.05 9.8 4.3 3 Example 1 Comparative Ammonium laurate 0.05
9.8 8.4 6 Example 2 Comparative Sodium lauryl sulfate 0.05 9.8 5.8
23 Example 3
[0114] The aforementioned results show that use of ammonium lauryl
sulfate enhances storage stability remarkably, and further provides
excellent performance of pH stability.
* * * * *