Note: Descriptions are shown in the official language in which they were submitted.
CA 02808167 2013-02-12
= PF 70760 1
Aqueous polymer dispersion which can be obtained by a radically initiated
emulsion
polymerization in the presence of a molecular weight regulator composition
The present invention relates to an aqueous polymer dispersion comprising a
chain
growth addition polymer obtainable by free-radically initiated emulsion
polymerization of
ethylenically unsaturated, free-radically polymerizable monomers, wherein the
polymerization of the monomers is effected in the presence of a certain
molecular
weight regulator composition. The invention also relates to a process for
preparing the
aqueous polymer dispersion and the use of the polymer dispersion as a binder,
an
adhesive, a sizing agent for fibers, in the manufacture of coatings or in the
manufacture
of paper coating slips.
Aqueous polymer dispersions obtainable by free-radically initiated emulsion
polymerization of ethylenically unsaturated, free-radically polymerizable
monomers
have a variety of use destinations. Binders for paper coating slips, for
instance, are
known that are based on copolymers of vinylaromatic compounds such as, for
example,
styrene, aliphatic dienes such as, for example, 1,3-butadiene and
ethylenically
unsaturated acid such as, for example, acrylic acid or methacrylic acid, or
based on
styrene-acrylate copolymers. Chain transfer agents are used as molecular
weight
regulators to adjust the molecular weight of the chain growth addition
polymers being
prepared by free-radical polymerization to a molecular weight that is suitable
for the
particular use destination. Among the most effective and frequently used
molecular
weight regulators are alkyl mercaptans, i.e., alkanes substituted with a thiol
group, for
example tert-dodecyl mercaptan (TDMC). These compounds have the advantage of
leading to good performance characteristics for paper coating compositions as
well as
regulating the molecular weight of polymers. There is a particular demand for
polymeric
binders with a high binding force and for paper coating slips comprising
polymeric
binders and having good surface strength, for example good dry pick resistance
and
good wet pick resistance. TDMC does meet these requirements, but has the
disadvantage of an unpleasant odor. This can prove troublesome in manufacture
as
well as in the end product. Moreover, TDMC is unwelcome in some use
destinations for
product safety reasons. Alternative molecular weight regulators based on alkyl
esters of
mercaptoalkyl carboxylic acids are advantageous in odor over alkyl mercaptans,
but are
not entirely satisfactory in the performance characteristics, for example the
dry pick
resistance or the wet pick resistance of paper coated with a coating slip.
US 5,354,800 describes a method of producing copolymer dispersions which are
useful
inter alia as binders in paper coating compositions. The method comprises
subjecting
conjugated diene monomer, a further ethylenically unsaturated monomer and also
an
ethylenically unsaturated carboxylic acid monomer to polymerization in the
presence of
PF 70760 CA 02808167 2013-02-12 2
.
a combination of a hydrophilic chain transfer agent and a hydrophobic chain
transfer
agent. Hydrophobic chain transfer agents mentioned include inter alia alkyl
mercaptans
and mercaptoalkyl esters of alkyl carboxylic acids. International patent
application
PCT/EP2010/051833 describes aqueous polymer dispersions prepared from
vinylaromatic compound, conjugated aliphatic diene and ethylenically
unsaturated acid
in a polymerization in the presence of a mercaptoalkyl carboxylic ester of a
02- to C4-
carboxylic acid, more particularly mercaptoethyl propionate, as molecular
weight
regulator.
Molecular weight regulators are typically used in very high purity in respect
of sulfur-
containing compounds in order that unforeseeable and undesired effects of the
sulfur-
containing compounds on the course of the emulsion polymerization and on the
quality
and product properties of the chain growth addition polymer formed may be
minimized.
Molecular weight regulators based on mercaptoalkyl carboxylic esters such as,
for
example, mercaptoethyl propionate have the disadvantage that purification is
very
costly and inconvenient. The reason is that, owing to the nature of the
synthesis, not
only low-boiling constituents (ethylene sulfide for example), middle boilers
(mercaptoethanol for example) but also high-boiling constituents (for example,
oligomeric and polymeric polyethylene sulfides and esters thereof) are
generated side
by side.
Mercaptoethyl propionate is obtainable for example by acid-catalyzed
transesterification
of propionic esters with mercaptoethanol or by acid-catalyzed azeotropic
esterification
of propionic acid with mercaptoethanol in the presence of organic solvents as
entrainers
to remove the water of reaction. The problem is that not only the
mercaptoethanol used
as alcohol component but also the mercaptoalkyl carboxylic ester product are
not only
thermally but also acid labile. As a result, oligomeric polyethylene sulfides
are typically
formed in the course of the synthesis.
Purifying the as-synthesized crude product, i.e., a mixture of mercaptoalkyl
carboxylic
ester and varying amounts of residues of the starting materials -
mercaptoalkanol,
alkylcarboxylic acid, the alkyl carboxylate used for transesterification ¨ and
also
secondary components and reagents and solvents of the synthesis such as, for
example, toluene, cyclohexane, hexane, heptane, xylene, oligomeric
polyethylene
sulfides and ethylene sulfides is possible in principle by distillation.
However, separation
is fairly costly and inconvenient on an industrial scale, since the thermal
lability
necessitates distillation at a low pressure (ideally < 20 mbar) to gently
remove the
desired mercaptoalkyl ester (e.g., mercaptoethyl propionate bp ca. 180 C at 1
bar).
Furthermore, the distillation requires a large number of separation stages to
ensure
removal of the middle boilers (e.g., mercaptoethanol and alkyl carboxylic
acid). In
CA 02808167 2013-02-12
= PF 70760 3
addition, the energy input into the distillation pot has to be so gentle as
not to bring
about a decomposition of the high-boiling oligomeric polyethylene sulfides
with the
formation of low and middle boilers which recontaminate the desired
mercaptoalkyl
carboxylic ester product. For the reasons mentioned, it is generally necessary
to
perform a multiple distillation at greatly reduced pressure using a
distillation plant having
a large number of separation stages to obtain a pure product of value (purity
> 99.8%).
It is an object of the present invention to provide aqueous polymer
dispersions having a
molecular weight set by using a molecular weight regulator which are very
simple and
inexpensive to obtain, have an ideally neutral odor compared with dispersions
obtained
using alkyl mercaptans and shall have very good performance characteristics
when
used as a binder in paper coating slips, more particularly very good dry pick
resistance
and very good wet pick resistance.
We have found that, surprisingly, there is no need for costly and inconvenient
purification of the mercaptoalkyl carboxylic ester in that the as-synthesized
crude
product ¨ or a crude product concentrated by removal of just a proportion of
the low
boilers (e.g., hydrocarbons, ethylene sulfide) ¨ provides a chain transfer
agent
performance which, based on the mercaptoalkyl carboxylic ester content, is
equivalent
and actually even improved pick resistance properties when the chain growth
addition
polymer is used as a binder in paper coating slips.
The stated object is accordingly achieved according to the present invention
by an
aqueous polymer dispersion comprising a chain growth addition polymer
obtainable by
free-radically initiated emulsion polymerization of one or more ethylenically
unsaturated,
free-radically polymerizable monomers, wherein the polymerization of the
monomers is
effected in the presence of a molecular weight regulator composition, and
wherein the
molecular weight regulator composition comprises
(a) at least one mercaptoalkyl carboxylic ester of a C2- to C4-carboxylic
acid, and
(b) at least one oligomeric compound of the formula
R1-X-(A-S-)n-A-Y-R2
where R1 and R2 are independently the same or different, each being H or CH3-
(CH2)m-
C(=0)-,
X and Y are independently the same or different, each being an oxygen atom or
a sulfur
atom,
A is a divalent Ci- to C18-alkylene group,
n is from 1 to 8 and m is from 0 to 2.
To modify the properties of the polymers, the emulsion polymerization is
carried out in
the presence of at least one polymerization regulator. Here it is preferable
to use
CA 02808167 2013-02-12
PF 70760 4
substantially no alkylmercaptan, i.e., alkylmercaptans are not used at all or
at any rate
not in amounts affecting the odor characteristics of the polymer dispersion.
At least one molecular weight regulator composition is used, this composition
comprising at least one mercaptoalkyl carboxylic ester of a C2- to C4-
carboxylic acid as
main constituent (a). The underlying carboxylic acids are acetic acid,
propanoic acid,
isobutanoic acid or n-butanoic acid, preferably propanoic acid. The
mercaptoalkyl
groups may comprise linear, branched or cyclic hydrocarbyl radicals having at
least one
SH group and, for example, up to 18 carbon atoms. Preference is given to
compounds
of the formula
R1-C(=0)-0-R2-SH
where R1 is an alkyl group of 1 to 3 carbon atoms and R2 is a divalent
alkylene group of
1 to18 carbon atoms. Particular preference is given to using 2-mercaptoethyl
propionate
as main component of the molecular weight regulator composition. The
mercaptoalkyl
carboxylic esters (a) are preferably present in the molecular weight regulator
composition at 60% to 95% by weight or 65% to 90% by weight or 70% to 85% by
weight.
The molecular weight regulator composition comprises, as a further constituent
(b), at
least one oligomeric compound of the formula
R1-X-(A-S-)n-A-Y-R2
where R1 and R2 are independently the same or different, each being H or
CH3-(CH2)m-C(=0)-,
X and Y are independently the same or different, each being an oxygen atom or
a sulfur
atom,
A is a divalent C1- to C18-alkylene group,
n is from 1 to 8 and m is from 0 to 2.
Oligomeric compounds (b) of the formula
R1-X-( CH2-CH2-S-)n-CH2-CH2-Y-R2
where R1 and R2 are independently the same or different, each being H or
CH3-CH2-C(--=0)-,
X and Y are independently the same or different, each being an oxygen atom or
a sulfur
atom, and n is from 1 to 8, are preferred, particularly when 2-mercaptoethyl
propionate
is used as main component of the molecular weight regulator composition.
The oligomeric compounds (b) are preferably present in the molecular weight
regulator
composition at 1% to 20% by weight or at 1.5% to 10% by weight or at 2% to 5%
by
weight.
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PF 70760 5
The molecular weight regulator composition by way of further constituents
preferably
additionally comprises small amounts of mercaptoethanol (particularly 2-
mercaptoethanol) and/or ethylene sulfide. Mercaptoethanol may for example be
present
in the molecular weight regulator composition at 0.1% to 10% by weight or at
0.2% to
5% by weight or at 0.3% to 1% by weight. Ethylene sulfide may for example be
present
in the molecular weight regulator composition at 0.05% to 5% by weight or at
0.1% to
2% by weight or at 0.15% to 1% by weight.
The molecular weight regulator composition may further comprise non-sulfur-
containing
constituents, for example propionic acid in an amount of for example 0.1% to
10% by
weight or 0.2% to 5% by weight or 0.3% to 1% by weight; organic solvents, more
particularly aliphatic or aromatic hydrocarbons having 6 to 8 carbon atoms and
an
atmospheric boiling point of 80 to 140 C, for example in an amount of 1% to
20% by
weight or 1.5% to 10% by weight or 2% to 5% by weight.
One embodiment of the invention is for example an aqueous polymer dispersion
wherein the molecular weight regulator composition comprises
(a) 60% to 95% by weight of the mercaptoalkyl carboxylic ester and
(b) 1% to 20% by weight of the oligomeric compound.
One embodiment of the invention is also for example an aqueous polymer
dispersion
wherein the molecular weight regulator composition comprises
(a) 60% to 95% by weight of the mercaptoalkyl carboxylic ester,
(b) 1% to 20% by weight of the oligomeric compound,
(c) 0.1% to 10% by weight of mercaptoethanol, and
(d) 0.05% to 5% by weight of ethylene sulfide.
Further polymerization regulators can be used in addition, but are not
absolutely
necessary. Examples of further polymerization regulators which can optionally
be used
are organic compounds comprising sulfur in bound form such as thiodiglycol,
ethylthioethanol, di-n-butyl sulfide, di-n-octyl sulfide, diphenyl sulfide,
diisopropyl
disulfide, 1,3-mercaptopropanol, 3-mercaptopropane-1,2-diol, 1,4-
mercaptobutanol,
thioglycolic acid, 3-mercaptopropionic acid, mercaptosuccinic acid, thioacetic
acid and
thiourea. Further polymerization regulators are aldehydes such as
formaldehyde,
acetaldehyde and propionaldehyde, organic acids such as formic acid, sodium
formate
or ammonium formate, alcohols such as, in particular, isopropanol and also
phosphorus
compounds such as sodium hypophosphite.
The amount of all the molecular weight regulators is for example in the range
from
0.01% to 5% and preferably in the range from 0.1% to 1% by weight, based on
the
, PF 70760 CA 02808167 2013-02-12 6
, ,
monomers used in the polymerization. The regulators are preferably added
together
with the monomers. However, they may also be wholly or partly present in the
initial
charge. They can also be added in stages at different times than the monomers.
Ethylenically unsaturated, free-radically polymerizable monomers are
polymerized in the
free-radically initiated emulsion polymerization. Examples of suitable
monomers are
vinylaromatic compounds, conjugated aliphatic dienes, ethylenically
unsaturated acids,
ethylenically unsaturated carboxamides, ethylenically unsaturated
carbonitriles, vinyl
esters of saturated C1- to C20-carboxylic acids, esters of acrylic acid or
methacrylic acid
with monohydric C1- to C20-alcohols, ally' esters of saturated carboxylic
acids, vinyl
ethers, vinyl ketones, dialkyl esters of ethylenically unsaturated
dicarboxylic acids, N-
vinylpyrrolidone, N-vinylpyrrolidine, N-vinylformamide, N,N-
dialkylaminoalkylacrylamides, N,N-dialkylaminoalkylmethacrylamides, N,N-
dialkylaminoalkyl acrylates, N,N-dialkylaminoalkyl methacrylates, vinyl
halides, aliphatic
hydrocarbons having 2 to 8 carbon atoms and one or two double bonds, or
mixtures
thereof.
The emulsion polymer consists of so-called main monomers, preferably to an
extent of
at least 40% by weight, more preferably to an extent of at least 60% by weight
and even
more preferably to an extent of at least 80% by weight. The main monomers are
selected from C1-C20-alkyl (meth)acrylates, vinyl esters of carboxylic acids
comprising
up to 20 carbon atoms, vinylaromatics having up to 20 carbon atoms,
ethylenically
unsaturated nitriles, vinyl halides, vinyl ethers of alcohols comprising 1 to
10 carbon
atoms, aliphatic hydrocarbons having 2 to 8 carbon atoms and one or two double
bonds, or mixtures thereof. Examples are alkyl (meth)acrylates with a C1-C10-
alkyl
radical, such as methyl methacrylate, methyl acrylate, n-butyl acrylate, ethyl
acrylate
and 2-ethylhexyl acrylate. Mixtures of alkyl (meth)acrylates are also suitable
in
particular. Vinyl esters of carboxylic acids having 1 to 20 carbon atoms are
for example
vinyl laurate, vinyl stearate, vinyl propionate, vinyl versatate and vinyl
acetate. Useful
vinylaromatic compounds include vinyl toluene, alpha-methylstyrene, p-
methylstyrene,
alpha-butylstyrene, 4-n-butylstyrene, 4-n-decylstyrene and preferably styrene.
Examples of nitriles are acrylonitrile and methacrylonitrile. The vinyl
halides are
chlorine-, fluorine- or bromine-substituted ethylenically unsaturated
compounds,
preferably vinyl chloride and vinylidene chloride. Examples of vinyl ethers
are vinyl
methyl ether and vinyl isobutyl ether. Vinyl ethers of alcohols comprising 1
to 4 carbon
atoms are preferred. As hydrocarbons having 2 to 8 carbon atoms and one or two
olefinic double bonds there may be mentioned ethylene, propylene, butadiene,
isoprene
and chloroprene.
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= PF 70760 7
Preferred main monomers are C1-C10-alkyl (meth)acrylates and mixtures of the
alkyl
(meth)acrylates with vinylaromatics, more particularly styrene (also referred
together as
polyacrylate binders) or hydrocarbons having 2 double bonds, more particularly
butadiene, or mixtures of such hydrocarbons with vinylaromatics, more
particularly
styrene (also referred together as polybutadiene binders). In polybutadiene
binders, the
weight ratio of butadiene to vinylaromatics (more particularly styrene) can be
for
example in the range from 10:90 to 90:10 and preferably in the range from
20:80 to
80:20. Polybutadiene binders are particularly preferred.
In addition to the main monomers, the polymer may comprise further monomers,
for
example monomers having carboxylic acid, sulfonic acid or phosphonic acid
groups.
Carboxylic acid groups are preferred. Examples are acrylic acid, methacrylic
acid,
itaconic acid, maleic acid or fumaric acid and aconitic acid. The proportion
of
ethylenically unsaturated acids in the emulsion polymer is generally below 5%
by
weight. Further monomers also include, for example, hydroxyl-containing
monomers,
more particularly C1-C10-hydroxyalkyl (meth)acrylates, or amides such as
(meth)acrylamide.
In one embodiment of the invention, the chain growth addition polymer is
constructed of
butadiene or mixtures of butadiene and styrene to an extent of at least 60% by
weight or
of Cl to C20 alkyl (meth)acrylates or mixtures of Cl to C20 alkyl
(meth)acrylates and
styrene to an extent of at least 60% by weight.
One embodiment of the invention utilizes as monomers
(Al) 19.8 to 80 parts by weight, preferably 25 to 70 parts by weight, of at
least one
vinylaromatic compound,
(B1) 19.8 to 80 parts by weight, preferably 25 to 70 parts by weight, of at
least one
conjugated aliphatic diene,
(Cl) 0.1 to 15 parts by weight of at least one ethylenically unsaturated acid
and
(D1) 0 to 20 parts by weight, preferably 0.1 to 15 parts by weight, of at
least one
further monoethylenically unsaturated monomer other than the monomers (Al) to
(Cl),
wherein the sum total of the parts by weight of the monomers (Al) to (D1) is
100.
One embodiment of the invention utilizes as monomers
(A2) 19.8 to 80 parts by weight, preferably 25 to 70 parts by weight, of at
least one
vinylaromatic compound,
(B2) 19.8 to 80 parts by weight, preferably 25 to 70 parts by weight, of at
least one
monomer selected from Cl to 018 alkyl esters of acrylic acid and Cl to 018
alkyl
esters of methacrylic acid,
CA 02808167 2013-02-12 ,
PF 70760 8 ,
(02) 0.1 to 15 parts by weight of at least one ethylenically unsaturated acid
and
(D2) 0 to 20 parts by weight, preferably 0.1 to 15 parts by weight, of at
least one
further monoethylenically unsaturated monomer other than the monomers (A2) to
(C2),
wherein the sum total of the parts by weight of the monomers (A2) to (D2) is
in each
case 100.
Monomers useful for group (Al) or (A2) include vinylaromatic compounds, for
example
styrene, a-methylstyrene and/or vinyltoluene. Among this group of monomers,
styrene
is preferred. 100 parts by weight of the monomer mixtures used altogether in
the
polymerization comprise for example from 19.8 to 80 parts by weight and
preferably
from 25 to 70 parts by weight of at least one monomer of group (Al) or (A2).
Monomers of group (B1) are for example 1,3-butadiene, isoprene, 1,3-
pentadiene,
dimethy1-1,3-butadiene and cyclopentadiene. Of this group of monomers, 1,3-
butadiene
and/or isoprene is/are preferred. 100 parts by weight of the monomer mixtures
used
altogether in the emulsion polymerization comprise for example from 19.8 to 80
parts by
weight, preferably from 25 to 70 parts by weight and more particularly from 25
to 60
parts by weight of at least one monomer of group (B1).
Monomers of group (Cl) or (02) are for example ethylenically unsaturated
carboxylic
acids, ethylenically unsaturated sulfonic acids and vinylphosphonic acid.
Preferred
ethylenically unsaturated carboxylic acids are a,13-monoethylenically
unsaturated mono-
and dicarboxylic acids having 3 to 6 carbon atoms in the molecule. Examples
thereof
are acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid,
crotonic acid,
vinylacetic acid and vinyllactic acid. Useful ethylenically unsaturated
sulfonic acids
include for example vinylsulfonic acid, styrenesulfonic acid,
acrylamidomethylpropanesulfonic acid, sulfopropyl acrylate and sulfopropyl
methacrylate. Acrylic acid and methacrylic acid are particularly preferred,
acrylic acid in
particular.
The acid-functional monomers of group (Cl) or (C2) can be used in the
polymerization
in the form of the free acids and also partially or completely neutralized
with suitable
bases. Preference is given to using aqueous sodium hydroxide solution, aqueous
potassium hydroxide solution or ammonia as neutralizing agent. 100 parts by
weight of
the monomer mixtures used in the emulsion polymerization comprise for example
from
0.1 to 15 parts by weight, preferably from 0.1 to 10 parts by weight or from 1
to 8 parts
by weight of at least one monomer of group (Cl) or (02).
CA 02808167 2013-02-12
PF 70760 9
,
As monomers of group (62) there may be used esters of acrylic acid and of
methacrylic
acid with monohydric Ci- to 018-alcohols such as methyl acrylate, methyl
methacrylate,
ethyl acrylate, ethyl methacrylate, n-propyl acrylate, n-propyl methacrylate,
isopropyl
acrylate, isopropyl methacrylate, n-butyl acrylate, n-butyl methacrylate,
isobutyl acrylate,
isobutyl methacrylate, sec-butyl acrylate, sec-butyl methacrylate, tert-butyl
acrylate, tert-
butyl methacrylate, pentyl acrylates, pentyl methacrylates, 2-ethylhexyl
acrylate, 2-
ethylhexyl methacrylate. 100 parts by weight of the monomer mixtures used
altogether
in the polymerization comprise for example from 19.8 to 80 parts by weight and
preferably from 25 to 70 parts by weight of at least one monomer of group
(62).
Other monoethylenically unsaturated compounds are contemplated for use as
monomers of group (02). Examples thereof are ethylenically unsaturated
carboxamides
such as in particular acrylamide and methacrylamide, ethylenically unsaturated
carbonitriles such as in particular acrylonitrile and methacrylonitrile, vinyl
esters of
saturated Ci- to Gm-carboxylic acids, preferably vinyl acetate, allyl esters
of saturated
carboxylic acids, vinyl ethers, vinyl ketones, dialkyl esters of ethylenically
unsaturated
dicarboxylic acids, N-vinylpyrrolidone, N-vinylpyrrolidine, N-vinylformamide,
N,N-
dialkylaminoalkylacrylamides, N,N-dialkylaminoalkylmethacrylamides, N,N-
dialkylaminoalkyl acrylates, N,N-dialkylaminoalkyl methacrylates, vinyl
chloride and
vinylidene chloride. Monomers useful for group (D1) include the monomers of
group
(D2) and also esters of acrylic acid and of methacrylic acid with monohydric
Ci- to C18-
alcohols such as methyl acrylate, methyl methacrylate, ethyl acrylate, ethyl
methacrylate, n-propyl acrylate, n-propyl methacrylate, isopropyl acrylate,
isopropyl
methacrylate, n-butyl acrylate, n-butyl methacrylate, isobutyl acrylate,
isobutyl
methacrylate, sec-butyl acrylate, sec-butyl methacrylate, tert-butyl acrylate,
tert-butyl
methacrylate, pentyl acrylates, pentyl methacrylates, 2-ethylhexyl acrylate, 2-
ethylhexyl
methacrylate. This group of monomers is optionally used to modify the
polymers. 100
parts by weight of the monomer mixtures used in the emulsion polymerization
comprise
for example from 0 to 20 parts by weight or from 0.1 to 15 parts by weight and
more
particularly from 0.5 to 10 parts by weight of at least one monomer of group
(D1) or
(D2).
In one embodiment of the invention, the further monomers (D1) and (02) are
each used
in amounts of 0.1-15 parts by weight; the vinylaromatic compound is selected
from
styrene, methylstyrene and their mixture; the conjugated aliphatic diene is
selected from
1,3-butadiene, isoprene and their mixture; and the ethylenically unsaturated
acid is
selected from one or more compounds of the group consisting of acrylic acid,
methacrylic acid, itaconic acid, maleic acid, fumaric acid, crotonic acid,
vinylacetic acid,
vinyllactic acid, vinylsulfonic acid, styrenesulfonic acid,
acrylamidomethylpropane-
CA 02808167 2013-02-12
PF 70760 10
sulfonic acid, sulfopropyl acrylate, sulfopropyl methacrylate, vinylphosphonic
acid and
salts thereof.
The emulsion polymerization typically utilizes initiators that form free
radicals under the
reaction conditions. The initiators are used for example in amounts up to 2%
by weight
and preferably at least 0.9% by weight, for example in the range from 1.0% to
1.5% by
weight, based on the monomers to be polymerized. Suitable polymerization
initiators
include, for example, peroxides, hydroperoxides, hydrogen peroxide, sodium
persulfate,
potassium persulfate, redox catalysts and azo compounds such as 2,2-azobis(4-
methoxy-2,4-dimethylvaleronitrile), 2,2-azobis(2,4-dimethylvaleronitrile) and
2,2-
azobis(2-amidinopropane) dihydrochloride. Examples of further suitable
initiators are
dibenzoyl peroxide, tert.-butyl perpivalate, tert.-butyl per-2-ethylhexanoate,
di-tert-butyl
peroxide, diamyl peroxide, dioctanoyl peroxide, didecanoyl peroxide, dilauroyl
peroxide,
bis(o-toly1) peroxide, succinyl peroxide, tert-butyl peracetate, tert-butyl
permaleate, tert-
butyl perisobutyrate, tert-butyl perpivalate, tert-butyl peroctoate, tert-
butyl perbenzoate,
tert-butyl hydroperoxide, azobisisobutyronitrile, 2,2"-azobis(2-
methylbutyronitrile), 2,2"-
azobis(2,4-dimethylvaleronitrile) and 2,2"-azobis(N,W-
dimethyleneisobutyroamidine)
dihydrochloride. Initiators are preferably selected from the group consisting
of
peroxodisulfates, peroxosulfates, azo initiators, organic peroxides, organic
hydroperoxides and hydrogen peroxide. Particular preference is given to using
water-
soluble initiators, for example sodium persulfate, potassium persulfate,
ammonium
persulfate, sodium peroxodisulfate, potassium peroxodisulfate and/or ammonium
peroxodisulfate. The polymerization can also be initiated by means of high-
energy rays
such as electron beams or irradiation with UV light.
To avoid high levels of undesirable arylcyclohexenes, it will prove
particularly
advantageous to perform the emulsion polymerization in at least two stages,
wherein
the beginning of the addition of the monomeric vinylaromatic compound (A)
takes place
at a different time than the beginning of the addition of the monomeric
conjugated
aliphatic diene. Preferably, at least a portion of the monomeric vinylaromatic
compounds, for example at least 3.5% by weight of the total amount of all
monomeric
vinylaromatic compounds, is initially charged in the aqueous medium under
polymerization conditions, or added to the polymerization mixture before the
addition of
monomeric conjugated aliphatic dienes is commenced.
The present invention also provides a process for preparing an aqueous polymer
dispersion comprising one or more of the abovementioned ethylenically
unsaturated,
free-radically polymerizable monomers being polymerized by free-radically
initiated
emulsion polymerization in the presence of the above-described molecular
weight
regulator composition.
CA 02808167 2013-02-12
PF 70760 11
To augment the dispersal of the monomers in the aqueous medium, the protective
colloids and/or emulsifiers customarily used as dispersants can be used. A
detailed
description of suitable protective colloids is given in Houben-Weyl, Methoden
der
organischen Chemie, volume XIV/1, Makromolekulare Stoffe, Georg-Thieme-Verlag,
Stuttgart, 1961, pages 411 to 420. Suitable emulsifiers include surface-active
substances whose number average molecular weight is typically below 2000 g/mol
or
preferably below 1500 g/mol, while the number average molecular weight of the
protective colloids is above 2000 g/mol, for example in the range from 2000 to
100 000 g/mol and more particularly in the range from 5000 to 50 000 g/mol.
Suitable
emulsifiers include, for example, ethoxylated C8-C36 fatty alcohols having a
degree of
ethoxylation in the range from 3 to 50, ethoxylated mono-, di- and tri-C4-C12-
alkylphenols having a degree of ethoxylation in the range from 3 to 50, alkali
metal salts
of dialkyl esters of sulfosuccinic acid, alkali metal and ammonium salts of 08-
012 alkyl
sulfates, alkali metal and ammonium salts of 012-018 alkylsulfonic acids and
alkali
metal and ammonium salts of 09-018 alkylarylsulfonic acids. Cation-active
emulsifiers
are, for example, compounds having at least one amino or ammonium group and at
least one C8-C22 alkyl group. When emulsifiers and/or protective colloids are
used as
auxiliaries to disperse the monomers, the amounts used thereof are for example
in the
range from 0.1% to 5% by weight, based on the monomers.
Useful protective colloids include for example degraded starch, more
particularly
maltodextrin. Useful starting starches for preparing degraded starches include
all native
starches such as starches from maize (corn), wheat, oats, barley, rice,
millet, potato,
peas, tapioca, sorghum or sago. Also of interest are those natural starches
which have
a high amylopectin content such as wax maize starch and wax potato starch. The
amylopectin content of these starches is above 90%, usually in the range from
95 to
100%. Starches modified chemically by etherification or esterification can
also be used
for preparing the polymer dispersions of the present invention. Such products
are
known and commercially available. They are prepared for example by
esterification of
native starch or degraded native starch with inorganic or organic acids, their
anhydrides
or chlorides. Of particular interest are phosphated and acetylated degraded
starches.
The most common method to etherify starches consists in treating starch with
organic
halogen compounds, epoxides or sulfates in aqueous alkaline solution. Known
starch
ethers are alkyl ethers, hydroxyalkyl ethers, carboxyalkyl ethers and allyl
ethers. The
reaction products of starches with 2,3-epoxypropyltrimethylammonium chloride
are also
useful. Particular preference is given to degraded native starches, more
particularly
native starches degraded to maltodextrin. Further suitable starches include
cationically
modified starches, i.e., starch compounds having amino groups or ammonium
groups.
The degraded starches have for example an intrinsic viscosity qi of less than
0.07 dl/g
CA 02808167 2013-02-12
PF 70760 12
or less than 0.05 dl/g. The intrinsic viscosity ni of the degraded starches is
preferably in
the range from 0.02 to 0.06 dl/g. The intrinsic viscosity ni is determined in
accordance
with DIN EN1628 at a temperature of 23 C.
In one embodiment of the invention, the emulsion polymerization is effected in
the
presence of seed particles. The initial charge then comprises polymer seed,
more
particularly a polystyrene seed, i.e., an aqueous dispersion of finely divided
polymer,
preferably polystyrene, having a particle diameter of 20 to 40 nm.
The emulsion polymerization takes place in an aqueous medium. The aqueous
medium
may comprise for example completely ion-free water or else mixtures of water
and a
miscible solvent such as methanol, ethanol or tetrahydrofuran. As soon as the
particular
polymerization temperature desired is reached or within the time span of 1 to
15
minutes, preferably 5 to 15 minutes after reaching the polymerization
temperature, the
metered addition of the monomers is commenced. They can be for example pumped
into the reactor continuously within for example 60 minutes to 10 hours,
usually within 2
to 4 hours. The reaction mixture is preferably heated in the initial charge to
the
temperature required for the polymerization to proceed. These temperatures are
for
example in the range from 80 to 130 C, preferably 85 to 120 C. The
polymerization can
also be performed under pressure, e.g., at pressures up to 15 bar, e.g., at 2
to 10 bar.
Adding the monomer can take place as a batch process, continuously or in
stages.
After the polymerization has ended, further initiator may optionally be added
to the
reaction mixture and a postpolymerization performed at the same temperature as
the
main polymerization or else at a lower or higher temperature. To complete the
polymerization reaction, it will in most cases suffice to stir the reaction
mixture at the
polymerization temperature for for example 1 to 3 hours after addition of all
the
monomers. The pH in the polymerization can be for example in the range from 1
to 5.
After polymerization, the pH is adjusted to a value of between 6 and 7 for
example. In
the aqueous polymer dispersion obtained, the dispersed particles have an
average
particle diameter of preferably 80 to 200 nm. The average particle diameter of
the
polymer particles can be determined by dynamic light scattering on a 0.005% to
0.01%
by weight aqueous polymer dispersion at 23 C by means of an Autosizer IIC from
Malvern Instruments, England. The reported data are all based on the cumulant
z-
average diameter of the measured autocorrelation function as per ISO standard
13321.
In one embodiment, the solids content of the aqueous polymer dispersion of the
present
invention is in the range from 40% to 60% by weight. The solids content can be
effected
for example through appropriate adjustment of the water quantity and/or of the
monomer quantities used in the emulsion polymerization.
. * PF 70760 CA 02808167 2013-02-1213
, ,
The aqueous polymer dispersions of the present invention can be used as a
binder, an
adhesive, a sizing agent for fibers, in the manufacture of coatings or in the
manufacture
of paper coating slips. The aqueous polymer dispersions of the present
invention are
5 useful both for sizing textile fibers and for sizing mineral fibers, more
particularly glass
fibers. Owing to their high adhesiveness, particularly when comonomers are
used that
lead to a low glass transition temperature for the copolymer (below 20 C for
example),
they can also be used as an adhesive and in the manufacture of coatings. The
aqueous
polymer dispersions of the present invention are preferably used as binders in
paper
10 coating slips and as binders for fibers, more particularly textile
fibers.
The present invention accordingly also provides a paper coating slip
comprising
(i) inorganic pigments and
(ii) an above-described aqueous polymer dispersion obtainable according to the
15 present invention
and optionally further added substances.
Paper coating slips, in addition to water, generally comprise pigments,
binders and
auxiliaries for setting the requisite rheological properties, for example
thickeners. The
20 pigments are typically dispersed in water. The paper coating slip
comprises pigments in
an amount of preferably at least 80% by weight, for example 80% to 95% by
weight or
80% to 90% by weight, based on the total solids content. White pigments are
contemplated in particular. Suitable pigments include, for example, metal salt
pigments
such as, for example, calcium sulfate, calcium aluminate sulfate, barium
sulfate,
25 magnesium carbonate and calcium carbonate, of which carbonate pigments,
more
particularly calcium carbonate are preferred. The calcium carbonate may be
natural
ground calcium carbonate (GCC), precipitated calcium carbonate (PCC), lime or
chalk.
Suitable calcium carbonate pigments are available for example as Covercarb
60,
Hydrocarb8 60 or Hydrocarb 90 ME. Further suitable pigments include, for
example,
30 silicas, aluminas, aluminum hydrate, silicates, titanium dioxide, zinc
oxide, kaolin,
argillaceous earths, talc or silicon dioxide. Suitable further pigments are
available for
example as Capim MP 50 (Clay), Hydragloss 90 (Clay) or Talcum 010.
The paper coating slip comprises at least one binder. The polymer dispersion
prepared
35 according to the present invention can be used in the paper coating slip
as sole binder
or in combination with further binders. The most important functions of
binders in paper
coating slips are to bind the pigments to the paper and the pigments to each
other and
to some extent fill voids between pigment particles. For every 100 parts by
weight of
pigments, the amount of organic binder used in terms of binder solids, i.e.
without
40 water or other solvent liquid at 21 C, 1 bar) is for example in the
range from 1 to 50
CA 02808167 2013-02-12 ,
, PF 70760 14 ,
parts by weight, preferably in the range from 1 to 25 parts by weight or in
the range from
to 20 parts by weight.
Useful further binders include natural-based binders, more particularly
binders based on
5 starch, and also synthetic binders other than the polymers prepared
according to the
present invention, more particularly emulsion polymers obtainable by emulsion
polymerization. Chain growth addition polymers prepared according to the
present
invention are preferably present as the sole synthetic binder. A binder based
on starch
is in this context to be understood as referring to any native, modified or
degraded
starch. Native starches can consist of amylose, amylopectin or mixtures
thereof.
Modified starches may comprise oxidized starch, starch esters or starch
ethers.
Hydrolysis can be used to reduce the molecular weight of the starch (degraded
starch).
Possible degradation products include oligosaccharides or dextrins. Preferred
starches
are cereal starch, maize starch and potato starch. Particular preference is
given to
cereal starch and maize starch and very particular preference is given to
cereal starch.
Paper coating slips of the present invention may additionally comprise further
additives
and auxiliary materials, for example fillers, co-binders and thickeners to
further optimize
viscosity and water retention, optical brighteners, dispersants, surfactants,
lubricants
(e.g., calcium stearate and waxes), neutralizing agents (e.g., NaOH or
ammonium
hydroxide) for pH adjustment, defoamers, deaerators, preservatives (biocides
for
example), flow control agents, dyes (soluble dyes in particular), etc. Useful
thickeners in
addition to synthetic polymers (crosslinked polyacrylate for example) include
particularly
celluloses, preferably carboxymethylcellulose. Optical brighteners are, for
example,
fluorescent or phosphorescent dyes, particularly stilbenes.
The paper coating slip of the present invention preferably comprises an
aqueous paper
coating slip; water is present therein particularly due to the make-up form of
the
constituents (aqueous polymer dispersions, aqueous pigment slurries); the
desired
viscosity can be set by adding further water. Customary solids contents of
paper coating
slips range from 30% to 70% by weight. The pH of the paper coating slip is
preferably
adjusted to values in the range from 6 to 10, more particularly in the range
from 7 to 9.5.
One embodiment of the invention relates to a paper coating slip wherein the
polymers of
the aqueous polymer dispersion prepared according to the invention are used in
an
'amount of 1 to 50 parts by weight, based on the total amount of pigments, and
wherein
the pigments are present in an amount of 80 to 95 parts by weight, based on
the total
solids content and are selected from the group consisting of calcium sulfate,
calcium
aluminate sulfate, barium sulfate, magnesium carbonate, calcium carbonate,
silicas,
aluminas, aluminum hydrate, silicates, titanium dioxide, zinc oxide, kaolin,
argillaceous
CA 02808167 2013-02-12
PF 70760 15
earth, talc and silicon dioxide, and wherein the paper coating slip further
comprises at
least one auxiliary selected from the group consisting of thickeners, further
polymeric
binders, co-binders, optical brighteners, fillers, flow control agents,
dispersants,
surfactants, lubricants, neutralizing agents, defoamers, deaerators,
preservatives and
dyes.
The invention also provides paper or card coated with a paper coating slip of
the
present invention and also a process for coating paper or card, which
comprises
preparing or providing an aqueous polymer dispersion according to the
invention;
and
using this polymer dispersion, at least one pigment and optional further
auxiliaries
to prepare a paper coating slip; and applying the paper coating slip to at
least one
surface of paper or card.
The paper coating slip is preferably applied to uncoated base papers or
uncoated card.
The amount is generally in the range from 1 to 50 g, and preferably in the
range from 5
to 30 g (in terms of solids, i.e., without water or other solvent liquid at 21
C, 1 bar) per
square meter. Coating can be effected by means of customary methods of
application,
for example via size press, film press, blade coater, air brush, doctor blade,
curtain
coating or spray coater. Depending on the pigment system, the aqueous
dispersions of
the water-soluble copolymers can be used in paper coating slips for the
basecoat and/or
for the topcoat.
Polymer dispersions according to the present invention are inexpensive to
produce,
since there is no need for costly and inconvenient purification of the
mercaptoalkyl
carboxylic ester. Compared with dispersions produced in accordance with the
prior art
using tert-dodecyl mercaptan as chain transfer agent, the odor and level of
volatiles in
the gas phase above the final dispersion is distinctly lower (not more than 5
ppm of
mercaptoethyl propionate for example). Paper coating slips according to the
present
invention also have good performance characteristics. They have good run
ability in
paper coating processes and a high binding force. The coated papers and cards
have
good surface strength, more particularly very high wet and dry pick
resistance. They are
readily printable in the customary printing processes, such as relief
printing, gravure,
offset, digital, inkjet, flexographic, newsprint, letterpress, sublimation
printing, laser
printing, electrophotographic printing or a combination thereof.
Examples
Unless the context suggests otherwise, percentages are always by weight. A
reported
content is based on the content in aqueous solution or dispersion.
CA 02808167 2013-02-12
PF 70760 16
Solids contents are determined by drying a defined amount of the particular
aqueous
polymer dispersion (about 5 g) at 140 C in a drying cabinet to constant
weight. Two
separate measurements are carried out in each case and averaged.
Glass transition temperature is determined in accordance with DIN 53765 using
a
TA8000 series DSC820 instrument from Mettler-Toledo Int. Inc.
The average particle diameters of the polymer particles are determined by
dynamic light
scattering on a 0.005% to 0.01% by weight aqueous polymer dispersion at 23 C
by
means of an Autosizer IIC from Malvern Instruments, England. The cumulant z-
average
diameter of the measured autocorrelation function (ISO standard 13321) is
reported.
Examples 1-3: styrene-butadiene copolymer dispersions
Example 1 (comparative example)
tert-dodecyl mercaptan as molecular weight regulator
A 200 liter pressure reactor equipped with an MIG stirrer and 3 metering
devices is
initially charged, at room temperature and under nitrogen, with 29 kg of
deionized water,
2.2 kg of polystyrene latex (30 nm) and 5% by weight each of feeds 1A and 1B.
Next
the reactor contents are heated to 90 C with stirring (180 rpm) and, when 85 C
is
reached, 1 kg of a 7% by weight aqueous sodium persulfate solution is added.
After 10
minutes, the metered addition is commenced, at the same time, of the
remainders (95%
in each case) of feed 1A and feed 1B, and of feed 2, and continued at uniform
flow rates
for 360 minutes in the case of the remainders of feeds 1A and 1B and for 390
minutes
in the case of feed 2. Throughout the entire metering time, the streams of
feed 1A and
feed 1B are homogenized shortly before entry into the reactor. Thereafter, the
reactor
contents are left to postreact at 90 C for a further 2 hours. Thereafter, the
reactor
contents are cooled down to room temperature and adjusted to pH 6.5 with 15%
by
weight aqueous NaOH solution, and the pressurized container is let down to
atmospheric pressure.
Feed 1A, homogeneous mixture of
22.9 kg of deionized water
5.4 kg of 15% by weight aqueous sodium dodecylsulfate solution
3 kg of acrylic acid
0.52 kg of 15% by weight aqueous sodium hydroxide solution
Feed 1B, homogeneous mixture of
56.07 kg of styrene
. . PF 70760 CA 02808167 2013-02-1217
0.8 kg of tertiary-dodecyl mercaptan
26.65 kg of butadiene
Feed 2
27.34 kg of 3.5% by weight aqueous sodium persulfate solution
The resulting aqueous dispersion (D1) had a solids content of 49% by weight,
based on
the total weight of the aqueous dispersion. Glass transition temperature was
determined
as 17 C and particle size as 160 nm. Gel content 75%
Example 2 (comparative example)
High purity mercaptoethyl propionate as molecular weight regulator
Example 1 is repeated except that feed 1B has the following composition:
Feed 1B, homogeneous mixture of
56.07 kg of styrene
0.31 kg of mercaptoethyl propionate (99.5% pure)
26.65 kg of butadiene
The resulting aqueous dispersion (D2) had a solids content of 49.5% by weight,
based
on the total weight of the aqueous dispersion. Glass transition temperature
was
determined as 16 C and particle size as 158 nm. Gel content 75%
Example 3
Example 1 is repeated except that feed 1B has the following composition:
Feed 1B, homogeneous mixture of
56.07 kg of styrene
0.41 kg of molecular weight regulator composition comprising
mercaptoethyl propionate (74 parts by weight)
oligomeric polyethylene sulfides (10 parts by weight)
mercaptoethanol (1 part by weight)
ethylene sulfide (0.5 part by weight)
toluene (13.5 parts by weight)
26.65 kg of butadiene
The resulting aqueous dispersion (D3) had a solids content of 49.4% by weight,
based
on the total weight of the aqueous dispersion. Glass transition temperature
was
determined as 18 C and particle size as 157 nm. Gel content 74%
CA 02808167 2013-02-12 .
PF 70760 18
Aqueous polymer dispersions D1 to D7, prepared according to the examples, are
used
as binders for paper coating slips.
Paper coating slip preparation:
The coating slip is prepared in a stirred assembly into which the individual
components
are fed in succession. The pigments are added in pre-dispersed form (as a
slurry). The
other components are added after the pigments, the order corresponding to the
order in
the reported coating slip formulation. Final solids content is set by adding
water.
Coating slip formulation:
70 parts of finely divided carbonate (Hydrocarb 90, Omya)
30 parts of finely divided clay (Hydragloss 90, Omya)
10 parts of coating slip binder (emulsion polymers of Examples 1-7)
0.5 part of rheology modifier (carboxymethylcellulose)
The coating slip is applied to one side of uncoated base paper using a semi-
commercial
coating machine, and dried via IR radiator. The weight of the coat applied is
about
10 g/m2.
The coated paper was tested for surface strength using test methods known to a
person
skilled in the art. The following test methods were used:
IGT dry pick resistance
IGT wet pick resistance
The results are summarized in Table 1.
Measurement of dry pick resistance with IGT test printer (IGT dry)
Strips were cut out of the in-test papers and printed with the IGT test
printer. The
printing inks used are specific test inks from Lorillieux, which transmit
different tensile
forces. The test strips are fed through the press at continuously increasing
speed
(maximum speed 200 cm/s). To evaluate the result, the point at which 10 picks
have
occurred on the paper surface after the start of printing is determined on the
sample
printing strip. The measure reported for dry pick resistance is the speed in
cm/sec
present at this point during printing and also the test ink used. The higher
this printing
speed at the tenth pick point, the better the quality rating of the paper
surface.
Measurement of wet pick resistance with IGT test printer (IGT wet)
Strips were cut out of the in-test papers and printed with the IGT test
printer. The printer
was set up such that the test strips are moistened with water prior to the
printing
CA 02808167 2013-02-12
* . PF 70760 19
operation. The printing inks used are specific test inks from Lorilleux (No.
3807), which
transmit different tensile forces. Printing is done at a constant speed of 0.6
cm/s. Picks
out of the paper surface are visible as unprinted spots. To determine wet pick
resistance, a color densitometer is used to determine color density in %
compared with
the full hue. The higher the reported color density, the better the wet pick
resistance.
Table 1: results measured for dry and wet pick resistance
D1 D2 D3
(comparator) (comparator)
Top side dry pick resistance [cm/s] 43 46 45
Bottom side dry pick resistance [cm/s] 46 48 53
Top side wet pick resistance [%] 72 72 77
Bottom side wet pick resistance [%1 76 79 86
Odor test
The coated papers were odor rated by a trained group of people. The procedure
involved in odor tests of this kind is known to a person skilled in the art.
The odor level
of the samples was assessed on a scale from 1 to 6, where 1 denotes very good
and 6
denotes very bad. The results are summarized in Table 2.
Table 2: results of odor test
Odor rating
Example 1 (tert-dodecyl mercaptan) 4
Example 2 (high purity mercaptoethyl propionate) 3
Example 3 (74% purity mercaptoethyl propionate) 3
Example 3 exhibits significantly better wet pick resistance both on the top
side and the
bottom side of the coated paper and also significantly better dry pick
resistance on the
bottom side of the coated paper. The coated paper has an acceptable odor, this
odor
being better than that of a paper coated with Example 1.
Examples 4-5: styrene-butadiene-acrylonitirile copolymer dispersions
Example 4 (comparative example, comprising acrylonitrile)
tert-dodecyl mercaptan as molecular weight regulator
A 200 liter pressure reactor equipped with an MIG stirrer and 3 metering
devices is
initially charged, at room temperature and under nitrogen, with 29 kg of
deionized water,
2.1 kg of polystyrene latex (30 nm) and 5% by weight each of feeds 1A and 1B.
Next
PF 70760 CA 02808167 2013-02-12 20
.
the reactor contents are heated to 90 C with stirring (180 rpm) and, when 85 C
is
reached, 1 kg of a 7% by weight aqueous sodium persulfate solution is added.
After 10
minutes, the metered addition is commenced, at the same time, of the
remainders (95%
in each case) of feed 1A and feed 1B, and of feed 2, and continued at uniform
flow rates
for 360 minutes in the case of the remainders of feeds 1A and 1B and for 390
minutes
in the case of feed 2. Throughout the entire metering time, the streams of
feed 1A and
feed 1B are homogenized shortly before entry into the reactor. Thereafter, the
reactor
contents are left to postreact at 90 C for a further 2 hours. Thereafter, the
reactor
contents are cooled down to room temperature and adjusted to pH 6.5 with 15%
by
weight aqueous NaOH solution, and the pressurized container is let down to
atmospheric pressure.
Feed 1A, homogeneous mixture of
8.5 kg of deionized water
1.7 kg of 15% by weight aqueous sodium dodecylsulfate solution
2 kg of acrylic acid
0.48 kg of 15% by weight aqueous sodium hydroxide solution
Feed 1B, homogeneous mixture of
19.1 kg of styrene
0.72 kg of tertiary-dodecyl mercaptan
20.1 kg of butadiene
7.2 kg of acrylonitrile
Feed 2
10.7 kg of 3.5% by weight aqueous sodium persulfate solution
The resulting aqueous dispersion (D4) had a solids content of 48% by weight,
based on
the total weight of the aqueous dispersion. Glass transition temperature was
determined
as 8 C and particle size as 160 nm. Gel content 77%
Example 5
Example 4 is repeated except that feed 1B has the following composition:
Feed 1B, homogeneous mixture of
19.1 kg of styrene
0.32 kg of molecular weight regulator composition comprising
mercaptoethyl propionate (74 parts by weight)
oligomeric polyethylene sulfides (10 parts by weight)
mercaptoethanol (1 part by weight)
CA 02808167 2013-02-12
= PF 70760 21
ethylene sulfide (0.5 part by weight)
toluene (13.5 parts by weight)
20 kg of butadiene
7.2 kg of acrylonitrile
The resulting aqueous dispersion (D5) had a solids content of 49.4% by weight,
based
on the total weight of the aqueous dispersion. Glass transition temperature
was
determined as 9 C and particle size as 157 nm. Gel content 75%
The dry and wet pick resistance measurements and the results of the odor test
are
collated in Tables 3 and 4.
Table 3: results measured for dry and wet pick resistance
D4 (comparator) D5
Top side dry pick resistance [cm/s] 49 51
Bottom side dry pick resistance [cm/s] 50 52
Top side wet pick resistance [%] 75 78
Bottom side wet pick resistance [%] 80 83
Table 4: results of odor test
Odor rating
Example 4 (tert-dodecyl mercaptan) 5
Example 5 (74% purity mercaptoethyl propionate) 4
Examples 6-7: styrene-butadiene copolymer dispersions prepared in the presence
of
degraded starch
Example 6 (comparative example)
tert-dodecyl mercaptan as molecular weight regulator
A 200 liter pressure reactor equipped with an MIG stirrer and 3 metering
devices is
initially charged, at room temperature and under nitrogen, with 9.46 kg of
deionized
water, 2 kg of polystyrene latex (30 nm), 24 kg of degraded starch (50%) and
5% by
weight each of feeds 1A and 1B. Next the reactor contents are heated to 90 C
with
stirring (180 rpm) and, when 85 C is reached, 0.9 kg of a 7% by weight aqueous
sodium persulfate solution is added. After 10 minutes, the metered addition is
commenced, at the same time, of the remainders (95% in each case) of feed 1A
and
feed 1B, and of feed 2, and continued at uniform flow rates for 360 minutes in
the case
of the remainders of feeds 1A and 1B and for 390 minutes in the case of feed
2.
CA 02808167 2013-02-12 .
PF 70760 22
Throughout the entire metering time, the streams of feed 1A and feed 1B are
homogenized shortly before entry into the reactor. Thereafter, the reactor
contents are
left to postreact at 90 C for a further 2 hours. Thereafter, the reactor
contents are
cooled down to room temperature and adjusted to pH 6.5 with 15% by weight
aqueous
NaOH solution, and the pressurized container is let down to atmospheric
pressure.
Feed 1A, homogeneous mixture of
15.5 kg of deionized water
1.4 kg of 15% by weight aqueous sodium dodecylsulfate solution
1.58 kg of acrylic acid
0.27 kg of 15% by weight aqueous sodium hydroxide solution
Feed 1B, homogeneous mixture of
22.5 kg of styrene
0.36 kg of tertiary-dodecyl mercaptan
15.4 kg of butadiene
Feed 2
6.3 kg of 3.5% by weight aqueous sodium persulfate solution
The resulting aqueous dispersion (D6) had a solids content of 50% by weight,
based on
the total weight of the aqueous dispersion. Glass transition temperature was
determined
as 18 C and particle size as 165 nm. Gel content 79%
Example 7
Example 6 is repeated except that feed 1B has the following composition:
Feed 1B, homogeneous mixture of
22.7 kg of styrene
0.18 kg of molecular weight regulator composition comprising
mercaptoethyl propionate (74 parts by weight)
oligomeric polyethylene sulfides (10 parts by weight)
mercaptoethanol (1 part by weight)
ethylene sulfide (0.5 part by weight)
toluene (13.5 parts by weight)
15.4 kg of butadiene
The resulting aqueous dispersion (D7) had a solids content of 50.4% by weight,
based
on the total weight of the aqueous dispersion. Glass transition temperature
was
determined as 19 C and particle size as 168 nm. Gel content 77%
CA 02808167 2013-02-12
= PF 70760 23
The dry and wet pick resistance measurements and the results of the odor test
are
collated in Tables 5 and 6.
Table 5: results measured for dry and wet pick resistance
D6 (comparator) D7
Top side dry pick resistance [cm/s] 45 45
Bottom side dry pick resistance [cm/s] 42 46
Top side wet pick resistance [%] 35 38
Bottom side wet pick resistance [%] 32 40
Table 6: results of odor test
Odor rating
Example 6 (tert-dodecyl mercaptan) 3
Example 7 (74% purity mercaptoethyl propionate) 2
The examples with impure (74% purity) mercaptoethyl propionate generally have
better
wet pick resistance not only on the top side but also on the bottom side of
the coated
paper and also better dry pick resistance.
The papers coated with dispersions comprising impure (74% purity)
mercaptoethyl
propionate generally have better odor than papers coated with dispersions
comprising
tert-dodecyl mercaptan. Unexpectedly, there is no odor difference between
papers
based on pure or impure mercaptoethyl propionate despite the increased level
of
normally odor-intensive sulfides in the impure mercaptoethyl propionate.
