Note: Descriptions are shown in the official language in which they were submitted.
~ 1 3 ~ 4 ~ O
LAT~ N3DI~N FOR A COATING COMæOSITION
The present invention relates to a latex
medium for a coating composition.
Coating compositions based on a latex mediu~
are nowadays of a considerable technical and economic
importance. Among these coating compositions particular
mention may be made of papermaking compositions, that
is to say for surface application for paper, and more
particularly paper-coating co~positions, paint
compositions, in particular varnish and paint
compositions for the inside and for the outside,
textile compositions, wood-coating compo~itions,
adhesive compositions, pres~ure-sensitive adhesive
(PSA) compositions, coating compositions for cement ~ ;
mortar, and the like.
Apart from the medium, these coating
compositions co~prise at least one additional compo~ent
chosen from a filler, a pigment, a surfactant, a
thickening agent, an antioxidant, a natural binder ;`~
20 (starch, casein), a dispersing agent, an antifoam -
agent, a biocide, and the like. ~ ~
One of the chief difficulties to be re~olved ~ -
in developing them lies chiefly in that the
compositions of the above type must have surface
25 properties which differ rrom the bulk properties. ~ -
Thus, in the case where these compositions comprise ~ `
fillers and/or pigmsnts, the latex must adhesively bind
the fillers together and to the ~ubstrate. -;
-' . -- ~'`;'`:`'~'`,
---` 2 1 3 ~ ~ ~ 0 ~ ~;
~ 73863-32
In addltlon, the latex partlcles must migrate to the surface of
the coatlng in order that the coating should have a flne smooth
appearance wlthollt asperitles, especlally wlth the alm of
obtainlng good prlntablllty propertles. -
Practlcal experlence shows that obtalnlng correct surface
propertles runs counter to obtalnlng good bulk propertles.
The present lnventlon has made lt posslble to solve
the above problem by proposlng a partlcular latex medlum maklng
lt posslble to obtaln an entlrely advantageous compromlse
between the bulk propertles and the surface propertles. ~;
In fact, accordlng to the lnventlon a medlum has been found for
a coatlng composltlon based on fllm-formlng latlces prepared
~r from unsaturated ethylenlc monomers, characterized ln that the
sald medlum comprlses, per 100 parts by welght of latex A
(calculated on the basls of the sollds content) whlch has a ~;
partlcle slze of between 100 and 500 mn, from 0.1 to 100 parts ~-
by welght of latex B (calculated on the basls of the sollds
, -..:
content)~ whlch has a partlcle slze of between 5 and 40 nm.
Latex A preferably has a partlcle slze of between 120 and 300
nm.
~,' In addltlon, preferably from 0.5 to 20 parts, or better stlll
from 1 to 10 parts of latex B are employed per lO0 parts of
latex A.
~ .
~` ~`'"'.
~' ~
h;~
`: ~
- 21354~o
3 73863-32 ;
Preparation of latex A~
The preparatlon of latex A ls descrlbed in many patent
documents such as, for example, US 5,194,539 and EP 486,374. In
addltlon, latlces A are avallable commerclally.
The polymerlzable monomers conælæt of at least one
monomer chosen from styrene, butadlene, acryllc esters and vlnyl
nltrlles.
Acryllc esters denote esters of acryllc acld and of methacryllc
acld wlth Cl-C12, preferably Cl-C8 alkanolæ such aæ methyl
acrylate, ethyl acrylate, propyl acrylate, n-butyl acrylate,
-: : . : ...
lsobutyl acrylate, 2-ethylhexyl acrylate, methyl methacrylate, :~ -
ethyl methacrylate, n-butyl methacrylate and lsobutyl
i`; :- .;
methacrylate.
Vlnyl nltrlles lnclude those contalning from 3 to 12
carbon atoms, ln partlcular acrylonltrlle and methacrylonltrlle.
Styrene may be replaced entlrely or partlally wlth
alpha-methylstyrene or vlnyltoluene.
Among the ethylenlcally unsaturated monomers capable ;-
of be1ng polymerlzed wlth the above monomers, and the quantlty
of whlch can range up to 40% by welght of the total of the
monomers, there may be mentloned~
- carboxyllc acld vlnyl esters such as vlnyl acetate,
vlnyl versatate, vlnyl proplDnate, =~
~c
- ~ 2135~o
4 ~:
- ethylenic unsaturated mono- and dicarboxylic
acids 6uch as acrylic acid, methacrylic acid,
itaconic acid, maleic acid, fumarie acid and
monoalkyl e6ter6 of dicarboxylic acid~ of the type
referred to with alkanols which preferably contai~
1 to 4 carbon atoms and their N-substituted
derivatives,
- amides of unsaturated carboxylic acid~ ~uch
as acrylamide, methacrylamide, N~
methalolacrylamide or -methacryl-~;de,
- ethylenic monomers containing a sulphonic
acid group and its alkali metal or a~monium salts,
for example vinylsulphonic acid, -~
vinylbenzenesulphonic acid, alpha-
acrylamidomethylpropanesulphonic acid and 2-
sulphoethylene methacrylate, -
- ethylenically unsaturated monomer6 containing
a seaondary,.tertiary or quaternary amino group or
a heterocyclic group containing nitrogen, for ;-~
example vinylpyridi3es, vinylimidazole, aminoalkyl
: (meth)acrylates and amir.oalkyl (meth)acryla~ides
uch as dimethylaminoethyl acrylate or
methacrylate, di-tert-butylaminoethyl acrylate or -~ `
- methacrylate, dimethyla~ihomethylacrylamide or -
methacrylamide etc., as well ao zwitterionic
monomers such as sulphopropyl (dimethyl) ::~-:; e.i
, .- . ~,.
aminopropyl acrylate etc.,
- esters of (meth)acrylic acids with
.. , ~.'.'
-~ 21354~o ~ :~
alkanediol~ preferably containing 2-8 carbon
atoms, such as glycol mono(meth)acrylate, ~ .";;
hydroxypropyl mono(meth)acrylate, 1,4-butanediol `.
mono(meth)acrylate, and monomers containing two
polymerizable double bonds, ~uch as ethylene ~-
glycol dimethacrylate.
In addition to the abovementioned monomers it
is also possible to use, in minor quantities which are
also between 0.1 and 5 %, unsaturated ethylenic
monomers of a crosslinkable nature, such as glycidyl
(meth)acrylate or vinyl and acrylic silane~
3y way of example of compositions for the
production of latex media there may be mentioned ~ `~
composition~ containing, on a weight basi~, 25-90 %,
preferably 45-75 % of styrene and/or acrylonitrile,
75-10 %, preferably 55-25 %, of butadiene and/or
acrylates, 0-20 %, preferably 1-10 % of unsaturated
carboxylic acid and 0-40 %, preferably 0-15 %, of other
unsaturated ethylenic monomers.
Polymerizat on is carried out in a manner ;~
known per se, in aqueous emulsion, of polymerizable ~-~
monomers in the pre~ence of at least one radical
initiator and preferably in the presence of a transfer
agent, for example of 'he mercaptan type, with a `'`~ J.
25 concentration of monomers in the reaction mixture which - ~
~ . . . ~.
is generally between 20 and 60 % by weight.
Any kind of free-radical initiator -
con~entional in emulsion polymerization can be
~ ~ .
2135~0
suitable. !,
Examples of initiators include hydroperoxides
such as aqueous hydrogen peroxide, diisopropylbenzene
hydroperoxide, Rodium, potassium or ammonium
persulphates and cationic initiators such as
azobisisobutyronitrile or 4,4'-azobis(4-cyanovaleric
acid). ;~
These initiators may be used in combination -`
with a reducing agent such as, for example, bisulphite.
The quantity generally lies between 0.05 and 2 % by
weight relative to the quantity of the monomer~.
The polymerization temperature, a function of
the initiator used, is generally between 50C and
100C, preferably between 70 and 50C. The
stabilization of the particlea is ensured, if need be,
by any known colloidal sta~ilization system such as
anionic, cationic, amphoteric and nonionic emulsifier~
Anionic emulsifiers are, for example, alkali
metal alkyl sulphates, alkylsulphonates, ;~
alkylarylsulphonates and alkyl phosphates, dialkyl
sulphosuccinates and sodium, potassium or ammonium
salts of fatty acids, ~aturated or otherwise. Examples
of cationic emul6ifiers are alkylpyridinium or
alkylammonium salts such as N-ethyldodecyla~monium
25 chloride or bromide or cetylammonium chloride or `
bromide. Nonionic emulsi~iers which are mentioned in
particular are polyoxyethylenated and/or
polyoxypropylenated derivati~es of fatty alcohol~, of
..
., . . - ' ': ~ :~
213S4SO :
,
fatty acids or of alkylphenols.
The polymerization may be carried out continuously,
noncontinuously or semicontinuously with continuous
introduction of a part of the monomers, and may be of
the "seeded" or "incremental" type according to any
known variant for obtaining particles of homogeneous
and heterogeneous structure.
Preparation of latex B~
For convenience in the following description ;~ ;
it will be ~aid that latex B is made up of
nanoparticles. Any monomer containing ethylenic ;~
unsaturation may be chosen as starting material and, in
particular, the monomers and polymerization i~itiators ',i~'~ ,",~
referred to above in the case of latex A.
Among the polymers which may constitute the `
said latex 3 particles there may be mentioned ;-~
homopolymers or copolymers containing units derived
from vinyl, acrylic and vinylaromatic monomers, from
vinyl esters, from alkyl esters of a and unsaturated
acids, from esters o8 unsaturated carboxylic acid~
from vinyl chloride, -rom vinylidene chloride and/or
. ~ .
from dienes.
By way of illustration, the following
monomers may be mentioned more particularly~
~ styrene and its derivatives (vinyltoluene,
ethylvinylbenzene)
- esters, hydroxyesters and amides of `
(meth)acrylic acid, such a~ methyl methacrylate, ;~
'~
213~4~0 ;~
butyl acrylate or (meth)acrylamide
- vinyl esters ~vinyl acetate, vinyl ;
propionate)
- vinyl and vinylidene chloride~
- vinylpyridines (2-vinylpyridine, 4
vi~ylpyridine, 2-methyl-5-vinylpyridine)
- di(ethyl)aminoalkyl (meth)acrylates
- ~ b ~-
- di(ethyl)aminoalkyl(meth)acrylamides .
- allylamide
- ethyleneimine -:
- ~meth)acrylonitrile
- N-vinylimidazole
- dialkylaminomethylstyrenes
- vinylpyrrolidone
- divinylbenzene and itC derivati~es
- - conjugated dienes (butadiene etc.)
- polyallyl derivatives (tetraallylethylene
etc.) .~: .
- polyol (meth)acrylates (ethylene glycol
dimethacrylate e~c.)
- methylenebis(acryl2mide) :~
- bis(acrylamido)acetic acid.
By way OI vinyl and acryli-c monomers which
are suitable for the invention there may be mentioned
more particularly thoae derived from styrene, from
acrylic acid, from acrylic ester of the type of N~
: hydroxysuccinimide acrylic ester~ such as N~
acryloyloxysuccinimide .~nd N-acryloyloxyphthal~mide~
,',~,."'.',',.
r
~35~o
-~ -` - .
g ~
methacrylic acid, monobenzyl maleate, 2-vinylpyridine,
Fityrene methylsulphonate, chloromethylstyrene,
hydroxypropyl methacrylate, hydroxybutyl acrylate,
hydroxyethyl acrylate, acrylonitrile and/or acrolein. ~-~
According to a variant, the particles have ion-forming
or react ve groups at their surfaces, preferably chosen
from OH, SO3H, SO3R, SO4R, COOH, CHO, PhCH2Cl, NH2, NR2,
NR3 with R being a Cl-C3 alkyl radical, CONH2, NH-NH2, ;;
CN, CO2(CH2)~0H with n denoting an integer from 1 to 8,
and N-hydroxyimide ester~
The functional groups present at the surface
of the nanoparticles may also be derived from the ~ ~ -
subsequent chemical conversion, for exa~ple by
nucleophilic 6ubstitution, of one or a number of
15 reacti~e groups carried by the poly~er chain ~:
constituting the nanoparticles.
The nanoparticles according to the invention
have a narrow particle size di6tribution. This
monodi6persity of particle size makes it po6sible to
have acce6s to the true adsorption surface of the
nanoparticles and consequently to the optimum binding
capacity for the latter, especially on fillers and
pigments and on the substrate6 to be covered.
Any particle size distribution whose 6tandara
25 error is lower than or equal to 30 %, and preferably of ;~
the order of 20 %, is considered to be narrow.
The nanoparticles are capable of being
obtained by polymerization of a direct microe~ulsion or `~ P
,~ ` `
-: , 213~o
,~
of the corresponding monomer~. The term microemulsion ~;
i8 intended to denote a thermodynamically stable
dispersion in contrast to a di~persion which i8 only -;
kinetically stable and which coalesces at the end of a
certain period.
The polymerization of a direct microemul ion ~-~
and the recovery of the said aqueous dispersion at the
end of the polymerization are used, the said direct
microemulsion being obtained beforehand by titration
with the aid of an effective quantity o anionic
surfactantt either of a direct emulsion stabilized with
at least one ionic surfactant, or of an inverse
. : :
emulsion stabilized with at least one nonionic
surfactant, the two emulsions, called initial
emulsions, consisting of at least one monomer in
aqueous dispersion.
The aqueous dispersion of nanoparticles which
is thus obtained may furthermore be subjected to a
purification operation if appropriate.
In a first -t~ge, `herefore, the process
involve~ the formation of this direct microemulsion.
In the case of an inverse initial emulsion
the corresponding micrcemulsion i~ prepared by the 80- ~ -
called inversion method inspired by the Schulman ~ ~
...... ~.. -.. ...
process (J.Phys.Chem. 1959, 63 p. 1677).
It consists, in a first step, in formulating - -~
an emulsion of the water-in-oil type, the oil --~
consisting of the monomer( 8) in question, with the aid ~ -
- ..
- ~. ,...--:
2~ 35 ~ ~ o
11 ~, .~,
of a lipophilic nonionic emulsifier, that i8 to ~ay one
with a low hydrophile-lipophile balance HLB. The oil
forms approximately 70 % by wPight of the mixture. The
quantity of this nonionic surfaetant i~ added 80 as to
obtain a stabilized emulsion.
In general, a small quantity of an anionic
surfactant is also added. Its ~uantity i6 appro~imately
0.5 % by weight relative to the weight of monomer. This
emulsion i8 then inverted by addition of an aqueous
solution of a hydrophilic nonicnic surfactant, that i8
to 6ay of high HLB until phase inversion is observed.
This phenomenon of inver6ion can be detected
macroscopically, since during the titration a change is
observed successively from a milky emulsion to a gel ~ ~;
and then to a transparent, staole, direct mieroemulsion
of low ~iscosity.
The nonionic emulsifier used may be chosen
from polyethoxylated nonylphenol (NP) derivatives. The
lipophilic or hydrophilic nature of these co~pounds ~-
20 varies as a fu~ction of the number of their ethoxy `;~
units. The pairs NP5/NPl 5, NPl 5/NPI 2, NP7/NPI 2 and
NP7/NPI 5 may thus be mentioned as a pair of an ionie
emulsifier of low HLB/nonionic emulsifier of high HLB.
According to a preferred embodiment the ~-
inverse emulsion additionally and before its titration
contains an anionic surfactant. This may be, for :`
exa~ple, sodium dodecylbenzene6ulphonate (DBS), ~odium
1auryl =u1phate (SDS~ or oodlu= dioetyl ~ulpho~eeirat-
r~ ~ r~
2135~o :
(aerosol OT~
The nanoparticle dispersions obtained by this
inverse emul~ion technique contain a large quantity of
surfactants and cannot therefore be employed directly.
The removal of excess surfactants is obtained
subsequently by using a purification technique. This
removal i8 preferably carried out by dialysis which has -~
the advantage of not altering the particle size. No
flocculation phenomenon is observed.
According to another process for the
preparation of nanoparticles of latex ~, at least one
of the monomers containing ethylenic unsaturation,
referred to abo~e and capable of polymerizing in !~
aqueous emulsion, is added incrementally to the reactor
and a polymerization initiator and at least one
~urfactant are added incrementally so that nanolatex
4~ ~ J
particles of particle size smaller than ~ nm are
:: ..
obtained.
The term "incremental addition" includes all
forms of addition of a small part of the monomer and/or
of the initiator to the aqueous solution during a
period of time necessary for all the monomer and all -
the initiator to be added.
This includes cyclic addition~, noncontinuous
25 additions and their combinations. ~ ~
The addition of monomer and initiator is ` ~!"~'"`~'
preferably continuous and kept constant during a
certain period of time.
, . ' .. .''~
/~;
2135~o
i ~ ,
13
The preferred monomers employed are alkyl
acrylates and methacrylates in which the alkyl portio~
contain~ fro~ 1 to 10 carbon ato~s and carboxylic acids
containing ethylenic un~aturation, such as acrylic,
methacrylic, maleic, fumaric and itaconic acid and the
corresponding amides.
In the caAe of copolymers derived partly from ;~
acrylic monomer~, a quantity of acrylic mono~er which
is typically between 30 and 99 % of the total weight of
the monomerA, preferably from 50 to 90 %, is employed.
For certain applications it i de irable that
~ ,:
the latex B should be crosslinked. To do this, a
crosslinking agent is added to the reaction mixture for
aqueous emulsion polymerization, which is chosen ~rom
N-alkylol amides such as N-methylolacrylamide, N-
methylolmaleimide, certain difunctional monomers such
as divinylbenzne, divinylnaphthalene and
divinylcyclohexane, as well as various diacrylates Ruch ;~
as ethylene glycol dimethacrylate.
, . ~. ~ .
The quantit e6 of crosslinking agents are
generally between 0.05 and 10 %, from 0.1 to 5 % and `
preferably from 0.1 ~o 1.0 %, based on the total weight -
of all the monomers added. '.. ".'.
As indicated above, any polymerization
25 initiator can be employed. ` -
However, in the case where the initiator is
water-soluble, which is the case with peroxides and
, ~ ., .,,~i
persulphates, it i6 critical to keep the ionicity o
~ . . .;~
'"' "'`"`'
.. ..
.. .
. . .
213~4~0
14
the reaction mixture constant by removing a proportion
of the water from the reaction mixture and by adding
thi6 same water to the initiator feed stream.
It has been found, in fact, that by keeping a
constant ionicity in the reaction mixture the
agglomeration of the particles is avoided and particle~
exhibiting a narrower particle ~ize distribution are
obtained. By diluting the water-soluble initiator with
an appropriate quantity of water the ionic strength of
the reacticn mixture is kept constant.
A semiconti~uous or continuous polymerization ;
proces~ may be employed for preparing latices B. This ~ r';!~
makes use of the addition, in an incremental manner, of
the monomer, of the crosslinking agent if noed be and ~ fi
of the lnitiator solution~ to the reactor, which is
heated to a temperature which is generally between
approximately 45 and 90C, water and at least one
surfacta~t being ircluded during a certain period of ;-;~
time, in contrast to the noncontinuous ~'batch" process. `~
The reactor may optionally contain a small
quantity of monomer before the beginning of the
incremental polymerization, for the purpose of acting -
as a "seed". Such a small quantity of monomer is
generally lower than 30 % and preferably lower than
...-. .,,. - , .. . .
10 % of the total weight of the monomer employed.
The rate of addition of the monomer is
generally governed by various factors such as the -;"
dimension~ of the reactor, the temperature increase due
2 1 3 5 4 ~ o
to the exothermic reaction, the cooling capacity and
the like, 80 that the reaction temperature i8 generally
~aintained in a specific range.
. . .:
The reaction mixture i8 maintained at a
temperature between the ambient temperature (10 to
25C) and the boiling point of the aqueous golution.
~ -Y.'~
The reaction is generally performed at atmospheric
pressure but it can be increased to promote the
polymerization.
The monomer feed and the initiator feed must
be combined as the ~ame single feed in the case where
the initiator is ~oluble.
In addition, if the initiator is water~ -
soluble and is an ionic salt such as ammonium
15 persulphate, this initiator is introduced into the ` ~-
reactor so that the ionicity in the reaction mixture is
maintained at a constant level. This objective is
typically obtained by initially tran~ferring a
proportion of the water .ro~ the reaction mixture to
20 the initiator feed in order to give ri~e to ion
concentrations which are appreciably equal both in the
feed and in the reactor. -
Feeding the reactor using an incremental
method generally makes it pos ible to obtain a a
2S stabilized concen~ration of free radicals, which ~akes
it possible to avoid the low radical concentration~
observed during single initiator charges and prolonged `~
.-, .. . : ~
feed period~. It i~ the continuous availability of fre~
,,,
21354~0 ~ ~
~ .
16 73863-3~ ~
radicals that allows the formation of the new chaln and of the ~--
particle to cornpete effectlvely with the addltion of monomer to
already exlstlng particles, whlch results ln latex B particles ~-
exhiblting an improved monodlspersity (that is to say a narrow
partlcle slze distribution).
The terms "partlcle size dlstrlbutlon" or "partlcle
slze" are lntended according to the invention to mean the ;
: . ~ ".
dlmenslon of the mean dlameter of the volume of the partlcle,
. ~ . , .. ~ ..:
measured by photocorrelatlon spectroscopy. Latex B partlcles
have a partlcle 9 ize which ls generally between 5 and 40 nm and :~
preferably between lO and 30 nm. ~.
Of course, the propertles of latex B depend to a large
extent on the monomers chosen for their preparation. `
The constltuent monomers of latlces B may have a glass
transltlon temperature Tg of between -54C and +130C. Of
course, these Tg values rnust be chosen as a functlon of the type - i
of chosen coatlng composltlons. A slmple rule, but not unl~ue ~ .:
ln the case of the medlum accordlng to the lnventlon, ls that,
advantageously, the Tg of latex B is slmllar to the Tg of latex
A. Thls rule can be applled ln particular to palnts.
When the medium accordlng to the lnventlon ls employed ;~^
ln papermaking compositlons, the latex A
. ~- ., ~
...... .
., .,~
;
.~
~135~
17 ~ -
employed i8 generally a latex A of aa organic copolymer
chosen from a styrene/butadiene, styrene/acrylate and
styrene/butadiene/acrylate copolymer.
Pigment is added to the medium, such as, for
exam~le, a mineral clay such as kaolin, calcium
carbonate, titanium oxide, satin white, hydrargillite,
talc, barium sulphate, plaster, as well as various
adjuvants such as dispersing age~ts, natural binders
such as starch, biocides, foa~ suppressor~, slip agents ~ ;
and the like.
A coating composition generally comprises: - ;
- 100 parts by weight of pigment, , ;
- 2 to 25 parts by weight o~ medium, `
- 1 to 10 parts by weight of adjuv~nts 8uch as
those referred to above.
The medium content i8 lower (2 to 8 days) in :~
the case of compositions for photogravure
(Rotogravure); it is greater (6 to 15 beams) in the `-
case of offset compositions. ~ c
The coating compositions according to the
invention exhibit a better coating ratio, that is to
say that, compared with Xnown compositions, the "`''.::.' '' ;'`'.'``?~
compositions according to the invention make it
possible to obtain a satisfactory paper coating while
employing less composition.
In addition, the medium according to the
invention enables the fillers to be hidden better and - `
makes it possible to obtain a better ink uptake, which `~
o ,: ,
18 ,:.
makes the papermaking compositions according to the
invention more particularly advantageous for
photogravure ("Rotogravure").
The compositions according to the invention .~
5 are also aimed at pressure-sensitive adhesive (PSA) .:-~ .,,.i.
compositions comprising a medium according to the
invention. The compositions are traditionally based on
an acrylic latex A such as, for example, tho~e
described in patentfi US-A-5,164,441 and GB-A 1,257,940. .
~atex B is preferably hard with a Tg higher ..
than QC and prepared with the same monomers (generally `.-` ,
an alkyl (meth)acr,vlate and a (meth)acrylic acid). -~
In accordance with the inYention it has been
found that the simultaneous addition of 0.01 to 0.3 % ~". ~:
15 by weight of a water-~oluble polymer such as .
carboxymethyl cellulose to latex B makes it possible to .. `~
obtain an asymmetric tack (adhesiveness) due to the
rise of latex B to the surface at the time of drying. ";a~
In addition, the uGe of hard nanolatices B (Tg higher
than or equal ~o 0) reduces "blocking" that i8 to say
"tack", in other words the adhesiveness. ~ `
The present invention i8 also aimed more .
specifically at paint compositions comprising the : ~-., ~,.~
medium according to the invention in which the latices ,,,~., ";,.,
A and B are preferably essentially based on acrylic or
styrene-acrylate copolymer based on at least one `~
alpha/beta un~aturated monoolefinic carboxylic monomer
such as ~meth)acrylic acids and on at least one
~'-~. '..
,~ """,""',''.,, ~
2 ~L 3 ~ 4 5 o ~ :
19'
(meth)acrylic acid e~ter of a pri~ary or secondary
alcohol containing from 1 to 18 carbon atoms and
optionally on styrene. Such latice~ A are, for example,
de~cribed in US-A-3,320,198 and in EP-A 5,010,000 which
are mentioned as reference.
In paints for the exterior it i8 reco~mended
that latex A 6hould ha~e a Tg lower than 0C and that
latex B should ha~e a Tg higher than 0C, preferably
hisher than 10C.
In fact, in this particular case, the paint
employed outside will exhibit a high resistance to
soiling due to the migration of the particles of latex
B to the surface.
To make an acrylic paint containing
styrene/acrylate, the latex mediu~, preferably
neutralized with a base (for example agueous a~monia or
amine) i8 mixed in a known manner with a pigment
dispersion containing usual adjuva~ts as well as
pigments and pulverulent filler materials.
It has been found surprisingly and
unexpectedly that the medium according to the invention
permits wet abrasion resistance without affecting `~
stability.
In addition, as latex B tends to migrate to
the external surface of the paint, the "hardness" of
this surface can be modified by a suitable choice of
the Tg of the constituent (co)polymer of latex B. ~ -
In this paint application latex B prefarably -~
. '
213~0
exhibits a Tg of between -50 and +50C, preferably
between -30 and +30C.
The following exa~ples are given by way of ^ -
illustration, no limitation whatever being implied.
In all that follows all that precedes, unleo~
the contrary is expressly mentioned, the parts and
percentages are by weight. -
EXAMP~E 1
Pre~aration of a latex A
The following monomers are introduced into a
25-litre reactor made of stainless steel, fitted with a
stirrer and a jacket for circulating water enabling the
temperature inside the reactor to be regulated at 80C
during the polymerization:
15 - 83 parts by weight of water,
- 9 parts by weight of styrene,
- 75.5 parts by weight of butyl acrylate,
- 10 parts by weight of 2-ethylhexyl acrylate, ;
- 0.5 parts by weight of ethylene glycol
dimethacrylate,
- 2.7 parts by weight of acrylic acid,
- 0.5 parts by weight of acrylamide,
- 0.5 parts by weight of sodium sulphoethyl -~
methacrylate
- 0.1 parts by weight of sodium
alkylsulphonate,
- 1.6 parts by weight of ammonium persulphate.
The polymerization is performed at 80C for ;~
~`','-'.''~
2~3~4~0
21
10 h.
The neutralized latex Lo has a mea~ particle
size of 0.15 ~m, a Tg of -40C, a solids content of --~
53.3 %, a pH of 6 and a Brookfield viscosity, measured ~ `~
at 50 rev/min, of 280 mPa 8.
EXAMPLE 2
2-1 Preparation of a latex B~
In a 1-litre reactor made of stainlesE steel
fitted with a stirrer and a jacket for circulating ; --- ~q;
10 water enabling the tempe`rature inside the reactor to be -
regulated, a reaction stream consisting of the
following is introduced into the reactor:
65 parts of butyl ac~ylate, ~ ~
25 parts of methacrylic acid, ~ æ"~".
10 parts of methyl methacrylate.
1 part of Vazo-64(3) (2,2'-azobisisobutyronitrile in
solution in methyl methacrylate). :~
This feed solution is introduced in a ~-
controlled manner into the reactor which contains 185
parts of water and 3 parts of sodium dodecyl sulphate.
The reactor is kept at 85C with constant
stirring.
At the end of the addition of monomer the
reactor is still kept at 85C for another hour. The
reaction mixture is then taken to an almost complete
conversion by treatment with 0.015 parts of t-butyl
hydroperoxide and 0.015 parts of sodium metabisulphite
at a temperature of 62C.
" """";''~
~' 21354~0
22
A latex with a solid~ co~tent of 25 % is ~ --
obtained, with a particle size of 14 nm.
The latex is light in colour and has a Tg of
approximately -5C.
2-2 Pre~aration of latex B (2)
0.15 parts of am~onium per~ulphate ~,'',. '~:,:!~"'
predissolved ia 0.3 parts of water are added to a
solution containing 2.57 parts of sodium lauryl
sulphate a d 241 parts of water. After an initiation -~
period of 5 minutes a mixture of 43 partQ of butyl
acrylate and 57 parts of butyl methacrylate i8 W`7-'~
introduced into the solution over 2 hours. The
temperature i8 raised to 92C over 30 minutes and then
the mixture is cooled and filtered.
A blue-grey latex is obtained which has a
solid content of 23.10 %.
This latex has a particle ~ize smaller than
30 nm and a Tg of 0C.
2-3 Preparation of latex B (3)
The operating method of example 2-2 is ;~
reproduced exactly except that 47 ~0 of methyl
methacrylate, 43 % of butyl acrylate and 10 % of -
methacrylic acid are employed.
This latex thus obtained has a particle size ~-
smaller than 40 nm and a Tg of ~20C.
2-4 Preparation o$ latex B (4)
-,-~: . :: .
The operating method of example 2-2 is
reproduced exactly except that 20 % of methyl ;-
.. ""' ~'.
, ~
23
methacrylate, 70 % of butyl acrylate and 10 % of -~ "
methacrylic acid are e~ployed. This latex thus obtainod .;
ha6 a particle size smaller tha~ 40 nm and a Tg of
-20C.
EXAMPLE 3:
Pre~aration of the media
The media Ll, L2, L3 and L~ are prepared Qimply
by mixing, at slightly acidic pH, 100 parts of latex A
and 10 parts of lati~es B~l), B(2), B(3) and B(4) `~
10 respecti~ely. The media Ll, L2, L3 and L~ thu~ obtained .`~
ha~e solid~ contents of approximately 50 %.
Preparation of the ~aint:
The pigment pa6te which ha~ the following
composition (in parts by weight) is prepared simply by .
15 mixing in a paint disperser:
Water 3000 - ~.
Tylose MH 6000 XP ~ (thickener)40
Coatex P 50 ~g (acrylic dispersant) 37 ;;
Clérol TPE 714 ~ (antifoam) 20 :~
Proxel BD ~ (biocide) 9 ..
TiO2 RL68 530
Omyalite 90 (calcium carbonate of
particle size ~ l~m) 2130
D~rcol 50 (calcium carbonate of
particle size smaller than 5 ~m)3200
to 89.66 parts of this pigment paste are added 15 part~
of a modium chosen from ~2~ L3 and L~ and 0.9 parts of
water, to obtain a paint P2, P3 and P~, re~pecti~ely,
: .- , ~-~ .
- . ~: :;
: ~` :`:
~ 1 3 5 4 5 0 ~ ~
i ., , ~ ~
which has a Pigment Volume Concentration (PVC) of
approximately 75 %. - ~`
Characteristics of the media L" L3, L, and of the
~aint8 P2~ P3~ P~
The following are determined on the media L
L3 and L, and the paints P2, P, and P,: ;
- Brookfield viscosity at 50 rev/min (v)
- storage stability 28 days at 55C.
To do thi~, a sample of medium or o~ paint i8 `,`:. ,~ ; `
10 heated at 55C for 28 days in a receptacle protected `-
from air. The stability (S) of the medium or of the -
paint is given by the ratio of the Brookfield
viscositieE of the paints, measured at 50 rev/min at
20~ after 30 day~, to the initial visco~ity.
Also measured on the media L2, L3 a d L~ are~
the pH, the solid~ content (%) and the minimum fil~
forming temperature (MFFT in C), that is to say the
lowest temperature at which a film is obtained. A wet
abrasion resistance (WAR) test is performed on the `~
20 paints P2, P3 and P~, which i~ performed with the aid o~ ;
a C-- abrasiometer according to DIN Standard 53778. ~he
WAR is evaluated as the number of cycles at the end of
which the paint i8 eroded.
The results obtained are collated in Table 1
below insofar as the media are concerned and in Table 2
below in~ofar a~ the paints are concerned.
'' ', :' ' ''`""
`' ,`'`'',''`.",`'~``'`
`;~
, ' ' '~
` 2 1 3 5 ~ ~ o
TABLE 1 .
- ., .;,..........
~-di~= ~ pH SC ~ (=P- ~) 5 Z8 d/ MFFT
._ ,',, ` ',- ~.'`~
L? 7.7 47.9 2080 0.75 0 ; ` ~
.~ ,, _ _ - ___ -', ,. . ' ` ,' -.-.'-.
L3 8 47.8 1200 0.65 0
, . .__
Ls 7.8 48.0 600 1.05 0
, ....... . ,__ ' `,~
TABLE 2
,__ "'~
Paint Medi~ V S 28 d/ WAR (~o.
.___. employed (mPa 8)55C of cyrle~)
Pl L2 4080 1 3910
._
p3 L3 4440 1.15 1370 .
_ .~
P~ L~ 4120 1.1 3400
, __ _ ,,_, ,~,__ ~ .. ,.. ,,.,,,,",
Po LA 3560 1.05 2550
Paint Po i8 a control paint prepared only
with the medium LA.
From Tables 1 and 2 above it appears that
paints which have satis$actory viscosities and which
remain perfectly stable at the end of the 28 days at
55C are obtained. ~:
It is noted, furthermore, that the addition
of binder B with Tg = 0C greatly improves the WAR.
~ ' : ~! . , . ~ .!
