U.S. patent application number 10/168604 was filed with the patent office on 2003-03-20 for latex with high non-volatile matter content, low viscosity and having a bimodal distribution.
Invention is credited to Betremieux, Isabelle, Loyen, Karine, Meeschaert, Nathalie, Nogues, Pierre, Schneider, Martine.
Application Number | 20030055150 10/168604 |
Document ID | / |
Family ID | 9553865 |
Filed Date | 2003-03-20 |
United States Patent
Application |
20030055150 |
Kind Code |
A1 |
Betremieux, Isabelle ; et
al. |
March 20, 2003 |
Latex with high non-volatile matter content, low viscosity and
having a bimodal distribution
Abstract
The invention concerns a latex consisting of polymers dispersed
in a bimodal distribution, having a non-volatile matter content at
55 % and low viscosity. Said latex is obtained by emulsion
polymerisation of at least a monomer in the presence of a seed of
polymer-based particles with a diameter ranging between 200 and 450
nm. The invention also concerns the use of said latex in various
applications such as pressure sensitive adhesives, floor bonding
adhesives, tile bonding adhesives, additives for mortar, sealants,
sealing joints.
Inventors: |
Betremieux, Isabelle; (Coye
la Foret, FR) ; Loyen, Karine; (Pont-Audemer, FR)
; Meeschaert, Nathalie; (Serquigny, FR) ; Nogues,
Pierre; (Bernay, FR) ; Schneider, Martine;
(Lyon, FR) |
Correspondence
Address: |
WHYTE HIRSCHBOECK DUDEK S C
111 EAST WISCONSIN AVENUE
SUITE 2100
MILWAUKEE
WI
53202
|
Family ID: |
9553865 |
Appl. No.: |
10/168604 |
Filed: |
October 9, 2002 |
PCT Filed: |
December 19, 2000 |
PCT NO: |
PCT/FR00/03587 |
Current U.S.
Class: |
524/458 ;
524/457 |
Current CPC
Class: |
C08F 2/16 20130101; C08F
2/16 20130101; C08F 2/16 20130101; C09J 151/00 20130101; C08F
265/04 20130101; C08F 265/06 20130101; C08F 265/06 20130101; C08F
291/00 20130101; C08F 291/00 20130101 |
Class at
Publication: |
524/458 ;
524/457 |
International
Class: |
C08K 003/20 |
Foreign Application Data
Date |
Code |
Application Number |
Dec 27, 1999 |
FR |
99/16520 |
Claims
1. A latex composed of an aqueous dispersion comprising at least
55% by weight of polymer particles distributed in the following
way: A--from 5 to 30% by weight have a mean diameter (da) of
between 100 and 250 nm, B--from 70 to 95% by weight have a mean
diameter (db) of greater than 500 nm, C--from 0 to 5% by weight
have a mean diameter of between 250 and 500 nm, D--from 0 to 5% by
weight have a mean diameter of less than 100 nm, db/da being
between 3 and 10 and preferably greater than 4.
2. A latex as claimed in claim 1, characterized in that A
represents from 10 to 25% and that B represents from 75 to 90% by
weight of the particles.
3. A process for the preparation of a latex by the emulsion
polymerization at a temperature of between 30 and 90.degree. C. of
at least one ethylenically unsaturated monomer in the presence of
at least one surfactant and of a seed of polymer particles with a
diameter of between 200 and 450 nm representing from 5 to 25% by
weight of the total weight of monomer and seed, the polymerization
being initiated by a mixed water-soluble/fat-soluble system.
4. The process as claimed in claim 3, characterized in that the
seed is introduced before the beginning of the polymerization.
5. The process as claimed in claim 3, characterized in that the
seed is introduced after the beginning of the polymerization and
before achieving 80% conversion of the monomers to be
polymerized.
6. The process as claimed in one of claims 3 to 5, characterized in
that the seed is introduced in the form of a latex.
7. The process as claimed in one of claims 3 to 5, characterized in
that the seed is introduced in the form of a redispersible
powder.
8. The process as claimed in claim 3, characterized in that the
seed is prepared in situ by emulsion polymerization.
9. The process as claimed in any one of claims 3 to 8,
characterized in that the seed is composed essentially of
(meth)acrylic polymers.
10. The process as claimed in any one of claims 3 to 9,
characterized in that the surfactant is chosen from anionic
surfactants, such as alkylaryl ether sulfate or alkyl ether
sulfates, nonionic surfactants, such as ethoxylated alkylphenol or
ethoxylated fatty alcohols.
11. The process as claimed in any one of claims 3 to 10,
characterized in that the mixed system is composed of a molar ratio
of the water-soluble initiator to the fat-soluble initiator of
between 0.01/1 and 1/0.01.
12. The process as claimed in any one of claims 3 to 11,
characterized in that the water-soluble initiator is chosen from
sodium, potassium and ammonium persulfates, water-soluble azo
derivatives, such as 4,4'-azobis(4-cyanovaleric acid) or
2,2'-azobis(2-amidinopropane) dihydrochloride, for example. The
systems involving a reducing agent, an oxidizing agent and
sometimes even an activating agent. The oxidizing agents are
generally hydroperoxides, such as aqueous hydrogen peroxide
solution, tert-butyl hydroperoxide, tert-amyl hydroperoxide, cumyl
hydroperoxide or the sodium salt of the mixture of m- and
p-diisopropylbenzene dihydroperoxide. The most commonly employed
reducing agents are sodium formaldehydesulfoxylate, sodium
metabisulfite or ascorbic acid. Activating agents are generally
metal salts, such as iron sulfate, copper sulfate or cobalt
acetate.
13. The process as claimed in any one of claims 3 to 12,
characterized in that the fat-soluble initiator is chosen from
peroxides and hydroperoxides which are insoluble in water,
peroxyesters, peroxydicarbonates or fat-soluble azo derivatives,
such as azobisisobutyronitrile, azobiisobutyrodimethyl ester or
azobiisobutyrodiethyl ester.
14. A use of the latices capable of being obtained according to the
process of claims 3 to 13 in adhesive applications, such as
pressure-sensitive adhesives used to stick on labels or floor
covering adhesives.
Description
[0001] The invention relates to the field of latices with a high
solids content and with a low viscosity and in particular to
latices comprising polymer particles dispersed according to a
bimodal particle size distribution. It also relates to a process
for the synthesis of such latices and to their applications.
[0002] According to the invention, the term "latex with a high
solids content" is understood to mean aqueous dispersions of
polymer particles comprising at least 55% by weight of said
particles.
[0003] The synthesis of a latex with a high solids content very
often presents viscosity problems. This is because, at these solids
contents, the viscosity reaches very high values, which presents
stirring problems during the synthesis process and also
applicational problems.
[0004] In order to obtain both high solids contents and low
viscosities, it is well known that the particle size of the latices
must observe certain rules (see, on that subject, in particular
Woods, M. E., Krieger, I. M., J. Colloid Interface Sci., 34, 91
(1970), Johnson, P. H., Kesley, R. H., Rubber World, 138, 877
(1958), England, D., Kay, M., J. Colloid and Interface Sci., 34,
249, (1970)), such that:
[0005] At identical solids contents, a latex with a large particle
size is more fluid than a latex with a small particle size.
[0006] A latex composed of a mixture of two populations of
particles is more fluid than a latex composed of a single
population of particles, provided that the small particles do not
represent more than 30 to 20% of the fraction by volume of the
particles and that the ratio in size of the large particles to the
small particles is sufficiently high.
[0007] A latex composed of two populations of particles is more
viscous than a latex composed of three population, provided that
the criteria of concentration and of differences in sizes described
above are observed.
[0008] In short, the preparation of a latex having both a high
solids content and a low viscosity remains a difficult problem.
However, numerous documents have attempted to solve it. Thus, EP
568 834 A1, EP 814 103 A2, EP 818 471 A1 and WO 9816560 disclose
the use of seed dispersions with different particle size which are
introduced at the start or during the synthesis, these seeds grow
larger as the monomers and initiators, of water-soluble type, are
run in, which makes it possible to obtain final particle sizes
which result in a good solids content/viscosity compromise.
[0009] In application EP 814 096, products with a high solids
content and a low viscosity are obtained by virtue of a
single-stage process with the use of a water-miscible cosolvent
introduced into the preemulsion of monomers.
[0010] In application WO 9807767, products with a high solids
content and a low viscosity are obtained by virtue of a
single-stage process with a very low amount of inhibitor with
respect to the monomers (<50 ppm) and flow rates for
introduction of the preemulsion of monomers which gradually
increase over time.
[0011] DE 19727060 discloses a process for the production of
aqueous polymer dispersions having an essentially monomodal
particle size distribution and a diameter of greater than 400 nm by
emulsion polymerization using two initiating systems, the first of
which is a redox system, in the presence of 0.01. to 2% by weight
of the total weight of seed and monomers of a seed with a diameter
of between 10 and 100 nm.
[0012] The main problem which the invention attempts to solve is
that of obtaining a latex with a suitable bimodal distribution by a
simple and easily controllable polymerization process.
[0013] This is because the Applicant Company has found that a latex
with two populations can exhibit a good solids content/viscosity
compromise if it is composed of a population of large particles,
the size of which is greater than 500 nm, and of a population of
small particles, the size of which is less than 250 nm. The solids
content/viscosity compromise is even better if the large particles
mean diameter/small particles mean diameter ratio is greater than
3, preferably greater than 4.
[0014] In point of fact, it is well known to a person skilled in
the art that it is difficult, in emulsion polymerization, to obtain
large particle sizes (>450 nm) with short manufacturing times
and in particular in the presence of particles with a smaller size.
The present invention provides a solution to this problem based on
the use of specific initiating systems combining water-soluble
initiators and fat-soluble initiators.
[0015] The Applicant Company has found that the abovementioned
problems can be solved by emulsion polymerization in the presence
of a seed having a well defined mean diameter. The polymerization
being initiated by a mixture of two initiating systems, one
water-soluble and the other fat-soluble.
[0016] The advantage of this invention with respect to the prior
art using seeds is that, by virtue of the use of mixed
water-soluble/fat-soluble initiating systems, the enlarging of
populations with different size originating from seeds becomes
easier to control. For this, it is sufficient to dissolve the
fat-soluble initiator in one of the populations to promote its
growth at the expense of that of the others. This is particularly
advantageous since, in the case of a mixture of small and large
particles, it is difficult, with water-soluble initiating
conventional in emulsion polymerization, to bring about the growth
of large particles. This is because, in this case, most of the
monomers are consumed by the small particles because they have a
greater capture surface area. This phenomenon is all the more of a
nuisance since, in order to obtain a very low viscosity with a high
solids content, it is necessary (see above) to obtain a
concentration by volume of large particles of greater than 75% and
better still greater than 80%.
[0017] Furthermore, the solution provided by the Applicant Company
does not require the use of a cosolvent which generates volatile
products during the use of a latex and that neither does it require
the presence of an inhibitor in the monomers, which renders it much
more advantageous from a safety viewpoint on an industrial
plant.
[0018] One of the subject matters of the invention is a latex
composed of an aqueous dispersion comprising at least 55% by weight
of polymer particles distributed in the following way:
[0019] A--from 5 to 30% by weight have a mean diameter of between
100 and 250 nm,
[0020] B--from 75 to 95% by weight have a mean diameter of greater
than 500 nm,
[0021] C--from 0 to 5% by weight have a mean diameter of between
250 and 500 nm,
[0022] D--from 0 to 5% by weight have a mean diameter of less than
100 nm.
[0023] The mean diameter of the B particles (dB)/mean diameter of
the A particles (dA) ratio is between 3 and 10 and preferably
greater than 4.
[0024] According to a preferred form, the latex of the invention
includes from 10 to 15% by weight of particles (A) and from 75 to
90% of particles (B).
[0025] By reducing the amount of A, C and D particles to a minimum,
the latex of the invention becomes an essentially monomodal latex
having a mean diameter of greater than 500 nm.
[0026] Another of the subject matters of the invention is a process
for obtaining a latex such as that described above based on the
controlled growth of a or of a mixture of populations of particles
which are obtained either by the introduction of seeds or by
successive renucleations during the same manufacturing sequence.
Renucleation makes it possible, at various stages in the
polymerization, to manufacture small polymer particles.
[0027] The populations of particles are thus obtained either by
addition of seed of different sizes at the beginning and/or during
the polymerization process in an aqueous dispersion or by micellar
or coagulative nucleation, brought about at various moments in the
synthesis process, according to the amounts and the nature of the
surfactants introduced but also according to the nature of the
monomers, as is known by a person skilled in the art.
[0028] The polymerization being provided by a mixed system of
water-soluble/fat-soluble initiators.
[0029] According to one form, the process of the invention is
carried out by the polymerization of at least one ethylenically
unsaturated monomer in the presence of 5 to 25% by weight with
respect to the total weight of the polymers of a seed composed of
polymer particles with a mean diameter of between 200 and 450
nm.
[0030] It being possible for the seed to be introduced at the
beginning of the polymerization or during the polymerization but
before achieving the polymerization of 80% of the monomers to be
polymerized.
[0031] It being possible for the seed to be introduced either in
the form of a latex or in the form of a redispersible powder or
else prepared in situ by emulsion polymerization.
[0032] The mixed initiating systems chosen subsequently make it
possible to bring about the growth of the particles in order to
obtain the final particle size of the latex which will result in
the desired Theological and applicative properties.
[0033] The mixed initiating systems are composed of one or more
water-soluble initiator systems and of one or more fat-soluble
initiators which can be introduced simultaneously during the
synthesis process or according to well defined sequences.
[0034] The mixed system can be composed of a molar ratio of the
water-soluble initiator to the fat-soluble initiator of between
0.01/1 and 1/0.01.
[0035] The water-soluble initiators are the initiators commonly
used in emulsion polymerization, among which may be mentioned,
nonexhaustively:
[0036] sodium, potassium and ammonium persulfates,
[0037] water-soluble azo derivatives, such as
4,4'-azobis(4-cyanovaleric acid) or 2,2'-azobis(2-amidinopropane)
dihydrochloride, for example.
[0038] The systems involving a reducing agent, an oxidizing agent
and sometimes even an activating agent. The oxidizing agents are
generally hydroperoxides, such as aqueous hydrogen peroxide
solution, tert-butyl hydroperoxide, tert-amyl hydroperoxide, cumyl
hydroperoxide or the sodium salt of the mixture of m- and
p-diisopropylbenzene dihydroperoxid. The most commonly employed
reducing agents are sodium formaldehydesulfoxylate- , sodium
metabisulfite or ascorbic acid. Activating agents are generally
metal salts, such as iron sulfate, copper sulfate or cobalt
acetate.
[0039] The fat-soluble initiators are chosen according to their
solubility in the mixture of monomers to be polymerized and of the
corresponding polymer. They are peroxides or hydroperoxides which
are insoluble in water, peroxyesters, peroxydicarbonates or
fat-soluble azo derivatives, such as azobisisobutyronitrile,
azobiisobutyrodimethyl ester or azobiisobutyrodiethyl ester.
Moreover, the latter will preferably be used when a mixture of
monomers is to be polymerized which comprises a high proportion of
acrylic or methacrylic derivatives because of their high solubility
in these mixtures of monomers and of their polymer. Among azo
initiators, azobisisobutyrodiethyl ester is often chosen because of
its liquid state at ambient temperature, which makes it easier to
handle.
[0040] In the case of fat-soluble initiators exhibiting high
decomposition temperatures, it may also be necessary to use
reducing agents, such as described in the context of the
water-soluble initiators, in order to activate the polymerization
reaction. A metal compound can advantageously increase the
initiating rates.
[0041] The other important components of the formulation are, as
for any polymerization in aqueous dispersion, the surfactants and
the monomers.
[0042] As regards the surfactants, their nature and their level are
to be optimized according to the desired particle size and also
according to the nature of the monomers to be polymerized.
Generally, it is preferable to use a mixture of anionic and
nonionic surfactants. The anionic surfactants are chosen, for
example, from alkylaryl ether sulfate or alkyl ether sulfates. The
nonionic surfactants are chosen from ethoxylated alkylphenol or
ethyoxylated fatty alcohols.
[0043] The level of surfactant used depends on the process. This is
because, generally, if it is a matter of bringing about the growth
of particles already present, it is more advantageous to use mainly
a nonionic surfactant. On the other hand, if it is a matter of
nucleating a population of particles, it is advantageous to use
anionic surfactant.
[0044] The principle of this invention is general; however, the
seed of large particles or the large particles generated in situ
are predominantly composed of acrylic or methacrylic monomers
because of the good solubility of the majority of fat-soluble
initiators in these monomers and their polymers. For the subsequent
stage of growth of the particles and of renucleation of one or more
populations of smaller particles, the monomers used are not
necessarily the same as those which are used during the preparation
of the seed and can just as easily be the family of acrylic and
methacrylics as of vinyl monomers, such as, for example, vinyl
chloride, vinylidene fluoride or vinyl acetate, or of styrene
monomers.
[0045] As regards the polymerization process, whether or not this
is in the presence of seed, the monomers are introduced
continuously into the reactor with a rate of addition similar to
their rate of consumption.
[0046] The preferred process consists in preparing a seed of large,
predominantly acrylic, particles in situ or ex situ, in causing it
to expand with a mixture of monomers and fat-soluble initiator, in
continuing the growth of these large particles by continuously
adding a preemulsion of monomers and one or more water- and
fat-soluble initiators, and in creating one or more populations of
small particles by renucleation in the presence of surfactant or by
injection of a second seed which is small in size.
[0047] It has been seen above that the choice of the initiators is
a key element of the invention, and the time and the way in which
they are introduced constitute parameters which are just as
important.
[0048] This is because the choice will be made to introduce the
fat-soluble initiator as one lot or by running in at the moments in
the process where it is desired to bring about the growth of the
large particles without renucleating small particles. On the other
hand, the water-soluble initiator may be preferably introduced when
it is desired to renucleate small particles where to bring about
the growth of the latter at the expense of the larger particles.
The water-soluble initiator and the fat-soluble initiator will be
introduced in parallel when it is a matter of bringing about the
growth of a mixture of large and of small particles at equivalent
rates.
[0049] The fat-soluble initiator can be introduced in several ways;
the preferred way consists in dissolving it in the seed of large
particles; however, it is also possible to introduce it
continuously into the process by dissolving it in the preemulsion
of monomers or in the form of an emulsion or dispersion stabilized
by a mixture of surfactants and/or of protective colloids, as
disclosed in patents FR 74-12907, EP 010 986 or FR 76 07124.
[0050] The water-soluble initiator is introduced in the form of an
aqueous solution, as one lot or by running in, as is known by a
person skilled in the art.
[0051] The polymerization temperatures are between 30 and
90.degree. C., according to the initiating system chosen.
[0052] A stage of removal of the residual monomers can be carried
out at the end of running in the monomers either by a stationary
temperature phase or by the introduction of polymerization
initiators.
[0053] The present invention also relates to the use of the latices
capable of being obtained according to the process defined above in
adhesive applications, such as pressure-sensitive adhesives used to
stick on labels or floor covering adhesives.
[0054] The following examples illustrate the invention without
limiting the scope thereof.
EXAMPLES
[0055] The particle sizes are measured by separative capillary
liquid chromatography using the CHDF 2000 apparatus supplied by
Matec Applied Science.
[0056] The viscosity is measured with a Brookfield according to the
ISO 2555 standard.
Example 1
Synthesis of the Seed Dispersion
[0057] 1358.4 g of water, 10.0 g of a 30% aqueous solution of
ethoxylated nonylphenol sulfate comprising 32 EO, 10.0 g of a 65%
aqueous solution of ethoxylated nonylphenol comprising 30 EO and
41.5 g of sodium acetate trihydrate are introduced into a jacketed
glass reactor equipped with a mechanical stirrer of anchor type.
The contents are brought to 80.degree. C. with stirring. 327.3 g of
the preemulsion of monomers and 7.6 g of the sodium persulfate
solution are added as one lot at this temperature. 10 minutes
later, the remainder of the preemulsion is introduced continuously
over a time of 5 h at 80.degree. C., while the remainder of the
sodium persulfate solution is introduced separately over 5 h
30.
1 Preemulsion of monomers: Water 2567.6 g 30% Ethoxylated
nonylphenol sulfate in water 376.7 g 65% Ethoxylated nonylphenol in
water 145.7 g Methyl methacrylate 800.0 g 2-Ethylhexyl acrylate
8100.0 g Vinyl acetate 800.0 g Acrylic acid 300.0 g Sodium
persulfate solution: Water 272.0 g Sodium persulfate 35.0 g
[0058] The seed resulting from this example has a solids content of
65.6% and a particle size of 410 nm.
Example 2
Synthesis of Latex with Two Populations in the Presence of a Mixed
Initiating: Persulfate/DEAB
[0059] DEAB is Azobisisobutyrodiethyl Ester
[0060] 207.4 g of water, 376.0 g of the seed synthesized in Example
I-1 and 30.0 g of a solution of monomers and of fat-soluble
initiator are introduced into a jacketed glass reactor equipped
with a mechanical stirrer of anchor type. The contents are brought
to 80.degree. C. with stirring. All of the preemulsion of monomers
is introduced continuously over a time of 4 h at 80.degree. C.,
while the remainder of the sodium persulfate solution is introduced
over 4 h 30.
[0061] 2 h 30 after having begun to run in the preemulsion of
monomers, 51.9 g of a surfactant solution are added as one lot to
the reactor.
2 Solution of monomers and of fat-soluble initiator: Methyl
methacrylate 2.2 g Vinyl acetate 2.2 g 2-Ethylhexyl acrylate 22.4 g
Acrylic acid 0.8 g DEAB 2.4 g Preemulsion of monomers: Water 168.3
g 30% Ethoxylated nonylphenol sulfate in water 23.4 g 65%
Ethoxylated nonylphenol in water 14.0 g Methyl methacrylate 74.6 g
Vinyl acetate 74.6 g 2-Ethylhexyl acrylate 755.2 g Acrylic acid
28.0 g DEAB 2.4 g Sodium persulfate solution: Water 36.0 g Sodium
persulfate 4.0 g Surfactant solution: Water 23.5 g 30% Ethoxylated
nonylphenol sulfate in water 25.0 g 65% Ethoxylated nonylphenol in
water 3.4 g
[0062] The latex resulting from this example has a solids content
of 67.0% and a Brookfield viscosity of 250 mPa.s.
Example 3
Synthesis of Comparative Latex with Two Populations in the Presence
of a Simple Initiating: Sodium Persulfate
[0063] 207.4 g of water, 376.0 g of the seed synthesized in Example
1, 1.20 g of sodium persulfate and 27.6 g of a solution of monomers
are introduced into a jacketed glass reactor equipped with a
mechanical stirrer of anchor type. The contents are brought to
80.degree. C. with stirring. All of the preemulsion of monomers is
introduced continuously over a time of 4 h at 80.degree. C., while
the remainder of the sodium persulfate solution is introduced over
4 h 30.
[0064] 2 h 30 after having begun to run in the preemulsion of
monomers, 51.9 g of a surfactant solution are added as one lot to
the reactor.
3 Solution of monomers and of fat-soluble initiator: Methyl
methacrylate 2.2 g Vinyl acetate 2.2 g 2-Ethylhexyl acrylate 22.4 g
Acrylic acid 0.8 g Preemulsion of monomers: Water 168.3 g 30%
Ethoxylated nonylphenol sulfate in water 23.4 g 65% Ethoxylated
nonylphenol in water 14.0 g Methyl methacrylate 74.6 g Vinyl
acetate 74.6 g 2-Ethylhexyl acrylate 28.0 g DEAB 2.4 g Sodium
persulfate solution: Water 40.5 g Sodium persulfate 4.4 g
Surfactant solution: Water 23.5 g 30% Ethoxylated nonylphenol
sulfate in water 25.0 g 65% Ethoxylated nonylphenol in water 3.4
g
[0065] The latex resulting from this example at a solids content of
66.3% and a Brookfield viscosity of 2 200 mPa.s.
[0066] Particle Size Analysis
4 Size (nm) Distribution by weight (%) Small particles/ Small
particles/ Reference Large particles Large particles Example 2
124/596 22/78 Example 3 154/632 40/60
* * * * *