Note: Descriptions are shown in the official language in which they were submitted.
WO91/049gOPCT/US90/05261 ~
2066596
STABLE EMULSION POLYMERS
AND METHODS OF PREPARING SAME
Reference to Related A~lication `
5This application is a continuation-in-part of U.S. ~
patent application Ser. No. 07/184,480, now U.S. Pat. No. ~--
4,894,397, filed April 21, 1988, the benefit of which is now~`-
claimed for purposes of priority pursuant to 35 U.S.C. 120.
Technical Field
This invention relates to stable, aqueous latexes and to
methods for their preparation. ~-
Background Art `1`~
Aqueous dispersions of polymers, which are referred to `;~-
as "latexes" in the art, are generaLly known to be useful,
15 both alone and in a variety of formulations, as, for example, `~
coatings and impregnants. A wide variety of latexes of
various homopolymeric and copolymeric compositions (such as
styrene-butadiene copolymers, acrylic homopolymers and ^~
copolymers, vinylidene chloride homopolymers and copolymers,
20 etc.) have been developed having specific chemical and/or ~-~
mechanical properties for particular end-use applications. ;-
In particular, aqueous interpolymer latexes resulting -
from the emulsion-polymerization of: certain monovinyl
aromatic monomers such as styrene; certain diolefins such as
25 butadiene; and certain monoethylenically-unsaturated
carboxylic acids such as acrylic acid, are known to be ;
particularly useful as film-forming binders for pigments in
various paper-coating applications.` See, for example, U.S. ~
Pat. No. 3,399,080 to Vitkuske and U.S. Pat. No. 3,404,116 to `~`
30 Pueschner et al. Such emulsion polymerization reactions may
also optionally employ conventional seeding procedures to
obtain optimum control of polymerization and, therefore,
maximum product uniformity (e.g., narrow particle size
distribution). ~"
U.S. Pat. No. 4,151,143 to Blank et al., moreover, `~
discloses a so-called "surfactant-freen polymer emulsion ;`
coating composition and a method for preparing the same. -`-
Blank et al. point out that one problem associated with
emulsion polymerization-produced polymers that are employed
WO91/~4W0 6 ~ 96 PCT/US00/0~261
- 2 - ;
for coatings is the presence of certain surfactants. That
is, certain surfactants, while employed to stabilize
emulsions, tend to adversely affect the water-resistance
;.
and/or corrosion-resistance of the resulting film as well as
5 the adhesion of the coating especially to metal surfaces.
The Blank et al. emulsion polymers, furthermore, are `-
prepared in a so-called ~two-stage~ process. The process
includes a first stage and a second stage. In the first ~-
stage, a conventional carboxyl group-containing polymer is `,;
lO prepared either by a conventional solution-polymerization
technique or by a bulk-polymerization technique, and
thereafter is water-dispersed or solubilized by partial or
full neutralization with an organic amine or base and ;
application of high shear agitation. In the second stage, a ~ `
15 mixture of polymerizable monomers and polymerization catalyst `~-
is added to the first-stage emulsion at an elevated
temperature to effect polymerization of the second-stage
monomers, resulting in the formation of an emulsion coating `~;
composition. Such a coating composition is thus said to be `~
20 ~surfactant-free~
U.S. Pat. No. 4,179,417 to Sunada et al. discloses a
composition for water-based paints, such composition
containing a water-soluble resin and a water-dispersible ``~
~polymer. The water-soluble resin contains 50-99.5 percent by `~
25 weight of either an alpha, beta monoethylenically-unsaturated ~`-"
acid alkyl ester or an alkenyl benzene; 0.5-20 percent by ~-
weight of an alpha, beta monoethylenically-unsaturated acid; `~
and 0-30 percent by weight of a hydroxyalkyl ester of an
alpha, beta monoethylenically-unsaturated acid. These
30 monomers are polymerized in the presence of at least one ;~
unsaturated compound selected from the group consisting of an ~ `
alkyd resin containing a polymerizable unsaturated group, an
epoxy ester containing a polymerizable unsaturated group, a
d~ying oil, a fatty acid of a drying oil, and a diene `
35 polymer. The resulting polymers are water-solubilized by the
addition of ammonia or an amine. The water-dispersible
polymer contains not only hydroxy and/or carboxyl functional~-"
groups but also an alpha, beta monoethylenically-unsaturated`~ ;
acid monomer and/or a hydroxy alkyl ester of such a monomer
i' '. ,',:
WO91/~990 PCT/US90/0~261 ;~
2Q~396 -
- 3 -
as well as certain other ethylenically-unsaturated monomers. -~
T.-,e compositions disclosed in U.S. Pat. No. 4,179,417 are
employed in waterbased paints and can optionally contain a
cross-linking agent.
~anadian Pat. No. 814,528 to Kaminski discloses low
molecular weight alkali-soluble resin, resin solutions and `~ -
methods for their preparation and purification. The
disclosed resins are said to be especially useful as
emulsifiers, leveling agents, and film-formers. Kaminski
lO discloses that the number-average molecular weight of such a -`-;
resin ranges from 700-5000 and that such a resin can have an `~
acid number which ranges between 140-300. The resins are ~```
further disclosed as being useful as emulsifiers in the -
preparation of emulsion polymers, resulting in emulsion
15 polymers that are said to be stable`and substantially free
from coagulum. In connection with such a use, i.e. use as an
emulsifier in an emulsion-polymerization reaction, the resins
are said to require a number-average molecular weight of
between 1,000 and 2,000 and preferably between 1,000 and
20 1,500. Resins having a number-average molecular weight `
greater than 2,000 are said to lead to unstable and
coagulated emulsion polymers when used as the emulsifier in a
conventional emulsion-polymerization reaction. `
Two-stage latex polymers are known to exist in many
25 morphological forms, which are determined by many factors
including the relative hydrophilicity, miscibility and
molecular weights of the first-stage and second-stage
polymers. ``
So-called "core-shell~latexes are formed when such a .
30 second-stage~polymer forms a nshelln (or coating) around a
discrete ncoren (or domain) of the first-stage polymer.
Examples of such core-shell latexes are disclosed in U.S. `
.~
Pat. No. 4,515,914 to Tsurumi et al., where an exemplary
composition containing a first-stage styrene/butadiene
35 polymeric core is encapsulated by a second-stage monovinyl -~
polymeric shell.
So-called "inverted core-shelln latexes are also known.
Lee and Ishikawa, in an article entitled nThe Formation of
'Inverted' Core-Shell Latexes, n and appearing in J. Poly.
:
Wo~l/04990 PCT/US90/0~261
~,~6s;~j96 '
- 4 -
Sci., 21, 147-154 (1983), shows that such ~inverted~ latexes ~`
are those where the second-stage polymer becomes the ~core~ ;~
domain and is encapsulated by the first-stage polymeric ~-
shell. These inverted latex compositions can be formed when
5 the first-stage polymer is more hydrophilic than the second-
stage polymer. Lee and Ishikawa studied the formation of the
~invertedn core-shell morphology using two polymer pairs: a
soft polymer pair [ethyl acrylate/methacrylic acid (EA/MAA)
(90110)]/tstyrene/butadiene (S/B)(60/40)] and a hard polymer
10 pair [EA/S/MAA (50/40/10)]/[S (100)]. The ratio of monomers
in each polymer is in parts-by-weight. Soft polymers have a ~i
relatively Iow glass-transition temperature (~g), generally
below~about 20 degrees Celsius, while hard polymers have a `~-
relatively high Tg, generally above about 20 C. It was
15 found, in the case of the soft polymer pair systems, that the~ ~
formation of inverted core-shell morphology was equally ~-
complete regardless of the molecular weight of the ~
hydrophilic polymer molecules, whereas in the case of the ~`
hard polymer~pair systems it was found that the efficiency of
;;20~inversion depended upon the molecular weights of the
~ hyd~rophilic and hydrophobic polymers. The Lee and Ishikawa
- ~ ~study further suggests that the formation of inverted core~
shell latexes depends not only on the hydrophilicity, the
interfacial tension, and the molecular weight of the ~`i
25 hydrophilic polymer molecules, but aIso on the extent of ~;
phase seporat;ion between the two polymers. Lee and Ishikawa
also point out a particular ~alkali-swellability~ aspect of ~`~
the first-stage polymer, in connection with those inverted ```-~
~emulsion systems which they investigated. ;~
Muroi et al., in an article titled ~Morphology of Core-
Shell Latex Particles,~ and appearing in J. Poly. Sci., 22, i `
1365-1372 (1984), evaluated certain latex particles which are
formed when either an ethyl acrylate-methacrylic acid (EA-
~ M~A)~containing mixture or a methyl acrylate-methacrylic acid`~
- ~ 3S (MA-MAA) containing mixture was polymerized in the presence ;~i
of either poly methyl acrylate/methacrylic acid seeds or poly
ethyl acrylate/methacrylic acid seeds. These investigators
discovered (1) that the shell was composed of the more
hydrophilic poly (MA/MAA) molecules which were relatively
.; ~
.,~,.
WO91/04990 PCT/US90/05261
_ 5 _ 2066 596
high in MAA content and (2) that the core was composed of `
both poly (MA/MAA) and poly (EA/MAA) molecules, with the -`~
thus-investigated copolymeric particles being relatively
uniform from surface to center with respect to distribution
5 of all other components (i.e., except for MAA). The monomer ~
content of MAA, in particular, was found to increase in the ;
direction of the shell surface. ~ -
More particularly, Muroi et al. studied five -
compositions, including one where the first-stage feed was
10 MA/MAA (90/10) and the second-stage feed was EA/MAA (90/10).
These investigators discovered that as the pH of the
resulting latex was increased, as a result of the addition of
NaOH, the optical density decreased, indicating complete
dissolution of all the latex particles.
In view of the above, it is desirable to provide a
~stable latex emulsion that is capable of employing a
relatively broad spectrum of hard and soft monomers wherein
such monomers possess nacidicn as well as "basic"
functionality.
Summarv Disclosure of Invention
The present invention is directed to a stabilized latex~ -
emulsion and the process for preparing it. The process `
comprises the steps of: ;
a) reacting latex-forming monomers under predete~mined
emulsion-polymerization reaction conditions to form a
hydrophilic first-stage polymer; and
b) contacting the first-stage polymer with an
effective amount of at least one hydrophobic latex-
forming monomer under predetermined emulsion-
polymerization reaction conditions to form a hydrophobic
second-stage polymer, wherein the second-stage
hydrophobic polymer partitions into the first-stage ~;
hydrophobic polymer thereby producing an inverted core-
shell emulsion polymer,
wherein the improvement comprises the additional
step of adjusting the pH of the inverted core-shell ~-
emulsion polymer by an amount effective to dissolve the
first-stage hydrophilic polymer, the first-stage
hydrophilic polymer being dissolvable and the second-
WO91/04990 G~ 9C PCT/US90/05261 `~
- 6 - :
stage hydrophobic polymer being insoluble upon
adjustment of pH, for thereby producing a stabilized
latex emulsion adhesive comprising a continuous aqueous -
phase containing the first-stage hydrophilic polymer and
a discontinuous phase containing discrete, stabilized
particles of the second-stage hydrophobic polymer. -
Industrial Applicability ;-
The latexes of this invention exhibit excellent
mechanical properties as a result of the stabilization of the
lO second-stage polymer. Many latexes of this invention exhibit
superior coating properties for those applications known in
the art. Such applications include uses in floor polish,
varnishes, including water-borne graphic arts varnishes, -
paints, inks, adhesives, and the like.
Best Mode For Carrvinq Out The Invention
The polymer particles of this invention are broadly
characterized as latex particles comprising a hydrophilic ~-
first-stage polymer dissolved in a continuous aqueous phase
- containing discrete domains of a hydrophobic second-stage ~`
20 polymer. As employed herein the term "hydrophilic~ means `~
that the polymer is capable of being dissolved in an aqueous ~`
medium upon adjustment of the pH. First-stage polymers -`-
containing acid-functional groups (i.e., possessing ~'acidic~
functionality) will be solubilized upon addition of alkali;
first-stage polymers containing basic functional groups
(i.e., possessing nbasic" functionality) will be solubilized
upon addition of acid.
The term nhydrophobicn as used herein includes a polymer
which will not be dissolved in any aqueous medium by
30 adjusting the pH. ;
For purposes of this invention, the term N inverse core~
shell latex" means a latex formed in a two-stage
polymerization process wherein the second-stage polymer tends
to form a ncore" domain in the first-stage polymer. The
35 first-stage polymer may either encapsulate the second-stage ~
polymer, or may form a nshellN around the second-stage `- -
polymer ncore", or may incorporate the second-stage polymer `
into its swollen matrix. It is also possible to engraft a
` !
WO9l/04990 PCT/US90/05261
2 Q ~ 9 6 ~ ~
. :`'.
- 7 - -
portion of the second-stage polymer onto the first-stage
polymer to thereby further stabilize the first-stage polymer.
~ Emulsion polymerizationn as the term is employed herein
is a process that requires a polymerizable monomer or several
5 polymerizable co-monomers, an initiator, and water as the
continuous phase. This invention may also optionally utilize
such commonly-employed emulsion-polymerization ingredients as
chain-transfer agents to regulate the molecular weight of the
resulting first-stage polymer and/or second-stage polymer, as
10 well as conventional free-radical polymerization catalysts
and/or conventional cross-linking agents, if desired.
The first step in the emulsion polymerization process of ~-
this invention is selecting the monomers which will produce
the hydrophilic first-stage polymer. The monomers should be
15 selected so that there is at least one monomer from each of
the two monomer groups, namely (i) specified monomers that -
are at least partially water-insoluble and (ii) specified
~acidic~ or ~basic" functional group-containing monomers. -
As employed herein, the term ~water insoluble monomers"
is intended to include those monomers that form polymers
which, upon pH adjustment, do not become appreciably water-
soluble.
As employed herein, the term ~functional group- `~
containing monomers~ includes those monomers that form
25 polymers whose solubility characteristics become appreciably -~`
changed upon pH adjustment.
Typical monomers that are at least partially water-
~insoluble, for purposes of the present invention, are certain
open-chain conjugated dienes as well as certain vinyl
30 monomers such as monovinyl aromatic monomers.
More particularly, with respect to the hydrophilic
first-stage polymer of the present invention, a suitable ;
monomer that is at least partially water-insoluble is
selected from the group consisting of styrene, methyl -
styrene, alpha-methyl styrene, ethyl styrene, isopropyl
styrene, tertiary-butyl styrene, ethyl methacrylate, methyl
methacrylate, butyl acrylate, butyl methacrylate, 2-ethyl
hexylacrylate, ethyl acrylate, vinyl acetate, methyl
acrylate, open-chain conjugated dienes, 2-hydroxyethyl
WQ 91tO4990 - PCT/US90/0~261 ~
206~596
- 8 -
methacrylate, 2-hydroxyethyl acrylate, methylol acrylamide,
glycidyl acrylate, glycidyl methacrylate, and combinations
thereof. Preferably, the hydrophilic first stage polymer is
produced from a monoalkenyl aromatic monomer such as methyl
5 styrene, alpha-methyl styrene, tertiary-butyl styrene or,
most preferably, styrene.
With respect to the hydrophobic second-stage polymer of
the present invention, a suitable monomer that is at least --
partially water-insoluble is selected from the group
10 consisting of styrene, methyl styrene, alpha-methyl styrene,
ethyl styrene, isopropyl styrene, tertiary butyl styrene, ~`~
ethyl methacrylate, methyl methacrylate, butyl acrylate, -~-
butyl methacrylate, 2-ethyl hexylacrylate, ethyl acrylate,
vinyl acetate, methyl acrylate, open-chain conjugated dienes, ~-~
15 2-hydroxyethyl methacrylate, 2-hydroxyethyl acrylate,
methylol acrylamide, glycidyl acrylate, glycidyl ~ ~-
methacrylate, an aromatic or an acrylate or a methacrylate
having a functionality of at least 2, and combinations -
thereof.
One suitable aromatic monomer having a functionality of
at least two, for example, is divinyl benzene. Suitable
acrylate monomers having a functionality of at least two or
greater, for example, include: 1,3-butane diol diacrylate;
1,4-butane diol diacrylate; ethylene glycol diacrylate;
25 diethy~ene glycol diacrylate; triethylene glycol diacrylate;
tetraethylene glycol diacrylate; 1,6-hexane diol diacrylate;
pentaerythritol tetraacrylate; and trimethylol propane -
triacrylate. Suitable methacrylate monomers having a
functionality of at least 2, for example, include: 1,3-
30 butane diol dimethacrylate; 1,4-butane diol dimethacrylate;
ethylene-glycol dimethacrylate; diethylene glycol ~;
dimethacrylate; triethylene glycol dimethacrylate;
tetraethylene glycol dimethacrylate; 1,6-hexane diol
~imethacrylate; pentaerythritol tetramethacrylate; and
35 trimethylol propane trimethacrylate. `;
As employed herein, the term ~monovinyl aromatic -
monomer" includes those monomers wherein a radical of the `~
formula
... ~ ., .. .. ... . . . ... . . . . , .... . .... . ., .. ~ ~
WO91/04990 PCT~US90/0~261
R 2 0 6 6 5 9 6
.`
CH2=C~
is attached directly to an aromatic nucleus containing from 6to 10 carbon atoms, wherein R is hydrogen or a lower alkyl
such as an alkyl having from 1 to 4 carbon atoms, including -
those monomers wherein the aromatic nucleus portion is
substituted with alkyl or halogen substituents. Suitable ``
lo monovinyl aromatic monomers, for purposes of the present
invention, are styrene; alpha-methyl styrene; ortho-, meta-
and para-methyl styrene; ortho-, meta- and para-ethyl `
styrene; O-methyl-para-isopropyl styrene; ~E3-chloro -~-
styrene; para-bromo styrene; ortho, ~ara-dichloro styrene;
15 ortho, y~-dibromo styrene; vinyl naphthalene; diverse `
vinyl(alkyl-naphthalenes) and vinyl(halonaphthalenes), and ;~-
co-monomeric mixtures thereof. j -
The term nopen-chain conjugated diene~ is meant to -~
include, for example, 1,3-butadiene, 2-methyl-1,3-butadiene,
20 2,3-dimethyl-1,3-butadiene, pentadiene, 2-neopentyl-1,3- `~
butadiene and other hydrogen analogs of 1,3-butadiene and, in
addition, the substituted 1,3-butadienes, such as 2-chloro- ~
1,3-butadiene, 2-cyano-1,3-butadiene, the substituted - -
straight-chain conjugated pentadienes, the straight-chain and
25 branched-chain conjugated hexadienes, other stràight and
branched-chain conjugated dienes typically having from 4 to -~;
about 9 carbon atoms, and co-monomeric mixtures thereof.
The functional group-containing monomers of the present
invention can have basic or acidic functionalities such as
30 amino or carboxy functionality. Typical functional group-
containing monomers include nacidic" group-containing
monomers such as acrylic acid methacrylic acid, other
unsaturated acid monomers, an; combinations of these, and
nbasicn group-containing monomers such as vinyl pyridines,
35 amino acrylates and methacrylates, and combinations of these.
Typical amines include the vinyl pyridines, dimethvl
aminoethyl methacrylate and tert-butyl amino ethyl ;
methacrylate.
WO91/~990~ 9 6 PCT/US90/05261 -
66~
,
-- 1 0 -- ~ .::
The acrylic monomers employed in the process of the
present invention include acrylic acid or methacrylic acid, -
either alone or admixed wrth at least one other unsaturated
monomer such as an ester of acrylic or methacrylic acid, 2~
5 hydroxyethyl methacrylate, methacrylonitrile, acrylonitrile,
and the like, and combinations of these. ;~
Other unsaturated a¢id monomers can also be substituted
in minor part for the preferred acrylic acids of the present
invention. Such unsaturated acid monomers include maleic
lO acid, crotonic acid, fumaric acid, itaconic acid, vinyl
benzoic acid, isopropenyl benzoic acid, and~combinations ~`
thereof.
The qlass-transition;temperature (Tg) of the first-stage
polymer is an important factor in achieving the desired film
15 forming properties of a~particular stabilized latex product.
Therefore, monomers are selected such that~the first-stage
polymer will exhibit a Tg suitable for a pàrticular end-use
application.
The~first-staqe monomers are, accordingly, selected so
20 ~that~a~hydrophilic first-stage polymer will be producèd.
Additionall~, the~monomers are selected with a view toward
the ultimate use of;the Iatex film that is to be produced as
well~as the chemical~resistance required of the thus-produced
latex~film.~ If~tho resulting emulsion is to be crosslinked,
25~ for;~example,~then~crosslinkable monomers should be used to
form~the~first-stage~polymer.
Preferred~monomer formulations for the first-stage
polymer~i~nclude;ethyl acrylate (EA) and methacrylic acid
;~ (MAA) and, particularly,~ the combination 80 EA/20 MAA.
30 Styrene (S) and~acrylic acid (AA) form another preferred
composition, particularly, the combination 60 S/40 AA. A '!`.'`'.~.-.','~
~ third~preferred monomer composition, for purposes of `~
- ~ ~preparing the hydrophilic first-stage polymer, is methyl
ethacrylate (MMA), butyl acrylate ~BA) and methacrylic acid`
35~(MAA), especiàlly 58~MMA/30 BA/12 MAA. `~
Sufficient functional group-containing monomer is
present to ensure that the first-stage polymer will dissolve ~`
upon adjustment of the pH. For this and other purposes, the `;
` ratio of water-insoluble monomer to functional-group monomer -~
; : ' ' ~` `
WO91/04990 PCT/US90/0~261
- 11 - 20~6596
is from 20:1 to 1:3. A more preferred ratio is from 10:1 to `-
l:1~ The most preferred embodiment is where the water-
~ .
insoluble monomer to functional-group monomer ratio varies ~`
from 7:1 to 3:2. ~;
A chain-transfer agent is preferably added to the first
stage monomers during emulsion polymerization to regulate the
molecular weight of the first-stage polymer. (As those
skilled in the art well know,- the addition of a chain-
transfer agent will enable one to regulate not only the -;
10 number-average molecular weight but also the weight-average -
molecular weight of the first-stage polymer.) The number- ~
average molecular weight should generally not exceed about ~ -
20,000, otherwise the first-stage polymer will usually cause
the system to become exceedingly viscous upon pH adjustment. ~-~
15 However, employing higher molecular weight might be useful -~
for some compositions, especially those where high viscosity ``
is desirable.
As employed herein the phrase nmolecular weightN refers
to the number-average (Mn) molecular weight, unleæs indicated ;~
20 otherwise.
The first-stage polymer must be capable of dissolving -~
upon proper adjustment of the pH. For this and other
purposes, such as viscosity considerations, the preferred
molecular weight for the first-stage polymer is from about
3,000 to 15,000. The most preferred molecular weight is from
about 5,000 to lO,000.
Selection of appropriate chain-transfer agents for ;
molecular weight control is important for obtaining
homogeneous, low molecular weight polymers. Chain-transfer
30 agents must be efficient, must exhibit high transfer
activity, must produce controllable molecular weight
distribution, and must not adversely affect the
polymerization rates. Conventional chain-transfer aqents
which meet these standards, such as mercapto carboxylic acids
35 having 2 to 8 carbon atoms, and their esters, may be
employed. Examples of suitable chain-transfer agents, still
more particularly, are mercaptoacetic acid, 2-
mercaptopropionic acid, 3-mercaptopropionic acid, 2-
mercaptobenzoic acid, mercaptosuccinic acid,
WO91/04990 PCT/US90/05261
~96 - 12 -
mercaptoisophthalic acid, and alkyl esters thereof, and
combinations thereof. It may also be desirable to employ a
mercapto monocarboxylic acid and/or a mercapto dicarboxylic
acid containing 2 to 6 carbon atoms such as mercaptopropionic
5 acid and the alkyl ester thereof, or the butyl or isooctyl ~
ester of mercaptopropionic acid. ~` `
Other organic-type chain-transfer agents, including
halogenated hydrocarbons such as bromoform, carbon ; -
tetrachloride and bromotrichloromethane, may also be
l0 desirable.
- For example, when producing stabilized latex emulsion ~`~
adhesives, the chain-transfer agent is preferably selected
from the group consisting of bromotrichloromethane, butyl
mercaptopropionate, dodecyl mercaptan, mercaptoethanol, octyl `
15 mercaptan, and combinations of these.
In general, there is a reduction in polymerization rate -
and an increase in steady-state monomer concentration with `~
increasing addition levels of chain-transfer agent. '`'''!'':~`'',
GeneraIly, no greater than about 6 mole percent (mol %) of ~^-
20 chain-transfer agent is employed, based on total molar weight` `~
of the monomer charged. On the other hand, as the addition -``
level of chain-transfer agent is reduced, both the
polydispersity index or ratio as well as the molecular weight -
of the polymer tend to increase, because a lesser amount of
25 chain-transfer agent res~lts in a reduced level of chain-
transfer activity. (For the meaning of ~polydispersity ~
ratio" , please refer to U.S. Pat. No. 4,529,787 to Schmidt et ~--
al.) Accordingly, no less than about 0.5 mol % chain- ~-`
transfer agent is normally employed. If it is desirable to ~
30 make polymers of greater molecular w;eight and/or ~";
polydispersity values, then the amount of chain-transfer
- agent employed can be reduced to below 0.5 mol %, say, to atm~
least about 0.3 mol %. Depending upon the end-use, however, ~`
it~may be desirable to use from about 1-3 mol % of a chain-
35 transfer agent.
, . . ~ .
The chain-transfer agent is normally added to the ;`~
reaction mix incrementally, along with the monomers of the
first stage. A portion of the chain-transfer agent may be
added to a functional group-containing monomer precharge, ;
WO91/~990 PCT/US90/05261 ~-~
~ .
- 13 ~ 206~396
usually in the same relative proportion as the functional
group monomer. For most purposes, the precharge preferably
contains about-10 weight percent (wt.-%) of the entire charge ~
of chain-transfer agent. The choice of type and amount of ;
S chain-transfer agents, and their effects, are well known to ~-
those skilled in the art. ;`
Initiation is a factor to consider in connection with
the emulsion polymerization process; and choice of suitable
initiator is important for the preparation of homogeneous
10 products. For example, to enhance initiator efficiency, to
provide desired polymerization rates, and to provide product
of a particular fine-particle size, it may be preferable to
gradually add initiator to a particular reaction mixture.
Precharging initiator prior to the onset of polymerization,
15 or rapidly adding initiator along with the monomers, may
yield premature destruction of initiator from the high ~-~
concentrations of radical thereby produced. Employing high --`
polymerization temperatures may also induce early consumption
of initiator. For the above and other purposes, low~
20 temperature initiators are preferred. Best results are
attained with persulfate initiators æuch as sodium persulfate
or potassium persulfate or barium persulfate and, especially, ;~
with ammonium persulfate (APS). Mixtures of such initiators ;
may also be employed.
In general, from about 0.25 to 2 wt.-% of initiator,
based on the total weight of all initiator and monomer
charged, is employed. The particular identity and quantity ;-
of initiator selected will of course depend, in part, upon
the desired polymerization rate, the co-monomer mixture
30 addition rate, the polymerization reaction temperature, and
the like.
If desired, a post-addition of initiator may be employed
to drive the reaction to completion. The choice of type of
initiator, and amount of initiator, as well as the effect
35 will be apparent to those skilled in the art.
An emulsifier, typically an anionic emulsion-
polymerization surfactant such as sodium lauryl sulfate, can
be utilized to promote desired emulsion polymerization and to
stabilize a particular polymerization reactian. Other
.` '` :
WO91/04990 ~ 9~ PCT/US90/05261 ;~
- 14 - `~;
emulsifiers, such as alkali metal sulfates, sulfonates and/or ~
sulfosuccinic esters and so-called nnon-ionics~, as well as `;
combinations of these, can aIso be utilized.
The selection of the monomers that make up the
5 hydrophobic second-stage polymer is important. These -~^
monomers can be selected from the group of monomers set forth ~'
hereinabove (described in connection with the first-stage ~`~
polymer); however, such monomers as well as their relative `-~
ratios are selected so that the resulting polymer will not be ;~
10 water soluble upon pH adjustment. Further, the resulting -`
second-stage polymer must be capable of partitioning into the -~
first-stage polymer, so as to form ~domains" on or within the ~`
first-stage polymer. Accordingly, the second-stage polymer
must be relatively incompatible with the first-stage polymer.
The molecular weight of the second-stage polymers may ~-
also be modified or regulated by use of the chain-transfer
agents discussed hereinabove. One function of the second- -'
stage polymer may be to enhance film strength. For that ;
purpose the molecular weight should be significantly higher -
20 than that employed for the first-stage polymer. Generally, `-`.
molecular weights of 15,000 to 200,000 are acceptable for the
second-stage polymers of this invention. Higher molecular `
weights, if desired, can be obtained by methods known in the ~-
art, such as cross-linking. Preferred molecular weights are
from 20,000 to 150,000. The most preferred molecular weight
range for the second-stage polymer is 25,000 to 100,000.
In general, the weight ratio of first-stage polymer to
second-stage monomer can range from about 1:20 to 1:1. ~
Preferably, the ratio is from about 1:15 to 1:2. In the most ~`
30 preferred embodiments, the ratio of first-stage polymer to
second-stage monomer is from about 1:10 to 1:3.
In general, the process of the present invention is
conducted at the temperature range for conventional emulsion ;
polymerization, known to those skilled in the art. For most ~-
35 purposes, the reaction temperatures are maintained at about
70 C. to about 90 C. and preferably at about 80 C. Lower `
temperatures, if desired, may be utilized using re-dox
polymerization techniques, as is well known to those skilled`~
in the art. It is generally preferred that the second-stage ~--
WO91/049~0 PCT/US90/05261 ~ ~
2066~96 ~: ~
- 15 -
monomers be polymerized at a temperature above the glass-
transition temperature ~Tg) for the first-stage polymer.
This will soften the first-stage polymer, will permit the
second-stage polymer to form domains therein, and will permit
5 the first-stage polymer to flow more readily, the result
being that the first-stage polymer will better encapsulate
the second-stage polymer product.
- To assist in stabilizing the polymer product, and to
ensure completion of the reaction, it may be desirable to ~
10 maintain the reaction mixture at the desired reaction ` ;
temperature for a period of about 1 hour, or more, after the -~
final additions of co-monomers, initiator, and chain-transfer
agent. ~-
.
The second-stage emulsion polymer is formed from ~-~
15 monomers which polymerize so as to form a "hydrophobicn
polymer, as defined hereinabove. Monomers similar to those
employed for the first stage can be used in the second stage, -~
except that lesser amounts of functional group-containing
polymers are employed to prevent solubilization upon
20 dissolution of the first-stage polymers. In this instance,
it is preferred that the second-stage polymer contain no more
than about 10 mol % of functional monomer.
Copolymers of monomers such as monovinyl aromatic
monomers, monoethylenically-unsaturated carboxylic acids and
25 esters thereof, conjugated dienes, acrylonitrile, vinyl
acetate, vinyl dichloride, and the like, and combinations of
these, can thus be employed as second-stage monomers.
Because of considerations such as desired polymer properties,
availability and compatability with the polymer formed (by ~-~
30 polymerizing the aforementioned monomer charge), it has been
found that copolymers of styrene and acrylate esters and/or
methacrylate esters -- such as methyl methacrylate, butyl
methacrylate, 2-ethylhexyl acrylate, and the like, and
combinations of these -- are preferred.
3S In order to promote desired core-shell inversion, it may ;
be desirable to adjust the pH of the first-stage polymer ~;
reaction mixture to swell and plasticize the first-stage
polymer, thereby to promote second-stage polymer domain
, ''.~:
W091/04990 6~6 PCT/US90/0~26
- 16 -
formation in the first-stage polymer. A plasticizer or a
coalescing agent may similarly promote domain formation. .
- The reaction conditions for second-stage emulsion
polymerization reaction are similar to those of the first- ~ -
5 stage reaction1 ~t~ least with regard to initiator, chain- ~
transfer agent, emulsifier, and reaction parameters. After ~`
desired polymerization has occurred, the solids content of
the resulting aqueous polymer latex can be adjusted to the
level desired by adding water thereto or by distilling water -
l0 therefrom. Generally, a desired level of polymeric solids
content is from about 20 to about 65 wt.-%, and preferably `~`~
rrom about 30 to about 55 wt.-%, on a total weight basis.
In selecting reaction conditions for the second-stage ~`
polymerization reaction, it should be understood that `~
15 sufficient initiator may still be present from the first-
stage reaction to conduct the second-stage reaction. ~ -`
Addition of more chain-transfer agent may, however, be ; `
necessary to bring about the desired second-stage
polymerization reaction, depending upon the desired molecular ~
20 weight of the second-stage polymer. On the other hand, use !,, ,;,
of additional emulsifier is often unnecessary in the second- `
stage polymarization reaction. ~
Those skilled in the art will therefore appreciate that ~;
reaction parameters and adjuvants can be modified, as needed, ~`""`
25 to provide optimum second-stage reaction conditions.
The emulsion-polymerization process can, moreover, be `;~
conducted as a batch process, or as a semi-continuous ` -
process, as desired. ;~
Further, the addition rate of first-stage monomer may be -~`
30 important, particularly if there is difficulty in obtaining "`
uniformity of composition, for example, due to the tendency
of certain monomers to partition to different phases. A ;~
particular example is a first stage of styrene and acrylic ~ ~
a~cid wherein monomer-starved conditions are necessary. In ~`
35 such a case, a one-hour addition may be unsatisfactory, `-
whereas a three-hour addition might be preferable. Usually, `--
an addition rate of about 0.5 to about 4 hours is sufficient -~`
for most semi-continuous polymerization reactions, dependent,
of course, on the type and amount of initiator, the monomers
`''~'':;``'
WO91/04990 PCT/US90tO5261
2066S96
- 17 -
employed, and the polymerization rate, as is well known to
those skilled in the art.
The rate of addition of the second-stage monomer may
also be important. Providing a high rate of second-stage
5 monomer addition may make the first-stage polymer more- ~-
soluble. This can affect morphology and grafting. Similar ;
rates of addition, as compared to first-stage addition, are ~
normally employed but this also depends on polymerization ~`
rates.
Once the inverted core-shell latex has been formed, the
pH of the emulsion is adjusted to dissolve the first-stage ~;
polymer. If acidic functional group monomers are selected -
for the first-stage polymer, addition of a suitable base is
appropriate. If basic functional group monomers are selected
15 for the first-stage polymer, addition of an acid is
appropriate.
Suitable bases which can be used to adjust the pH
include organic and inorganic bases. Examples of suitable
organic bases include amines, morpholine, and alkanol amines.
20 Examples of suitable inorganic bases include ammonia, NaOH,
KOH, and LiOH. ~;
Suitable acids for adjusting pH include various known ~-~
organic and inorganic acids such as acetic acid, hydrochloric
acid, and phosphoric acid.
The rate of addition of the base or acid to the latex
emulsion is usually not important. Sufficient base or acid
should be added to achieve dissolution of the f irst-stage
polymer. The degree of dissolution of the first-stage
polymer can be estimated by measuring the change in optical -:;
30 density (O.D.) of the emulsion before and after addition of `;``-
the pH-adjusting agent.
For various applications, it is sometimes desirable to
employ small amounts of various known additives in the latex. -
Typical examples of such additives are bacteriocides, ``
35 antifoamers, etc. Such additives can be added in a `
conventional manner to such latexes. -~
The resulting stabilized emulsion can be used to produce -`
a variety of coatings known in the art, including films, `
polishes, varnishes, paints, inks, and adhesives. ~ `
' ''`'
'.,, ~;:
WO91l04~0 PCT/US90/0~261 ~
6~96 ~ 18 - ;
The process of this invention can typically be conducted -
as semi-continuous polymerization as follows. Unless
otherwise specified, percentages shall refer to weight
percent.
General Pre~aration Example - `
Internally subjected to a nitrogen (N2) atmosphere, a
suitable reactor is filled with water and emulsifier and ~-~
stirred until a homogeneous solution is formed. The solution
is heated, utilizing conventional heating equipment, to the `~
lO desired reaction temperature. `
The first-stage monomers and chain-transfer agent are ~ `~
combined to produce a first-stage mixture. A pre-charge of
about 15% of the first-stage mixture is introduced into the
reactor. An initiator, dissolved in water, is thereafter
15 added into`the reactor to induce the pre-charge to
polymerize.
The balance of the first-stage monomers and chain- ;~
transfer agent are thereafter slowly added to the reaction -`~
mixture, over a time period of about 20 minutes to 2 hours.
Assuming that an acidic monomer is included in the
first-stage mixture, the pH of the first-stage emulsion-
polymerization reaction mixture is optionally raised to about
4.5 to 7 to cause the first-stage polymer to "swell". (If a ~ -
desired second-stage polymerization mixture has not been
25 prepared beforehand, such can now be prepared.) -
Thereafter, and over a time period of about 60 minutes, ~
the second-stage polymerization mixture (of second-stage ;`
monomers) is added at the desired reaction temperature. ~
After a short holding period of about 5 to about 30 minutes, ~`-
30 the pH of the reaction mix is slowly raised (over ca. 50
minutes) to about 8 to lO to release the first-stage polymer `~`
into solution. ~`~
Alternatively, it might be desirable to prepare a so- ``
called ~mastern batch of first-stage polymer and subsequently
35 utilize such in conjunction with certain desired second-stage
polymerization reactions.
The following examples are intended to better illustrate
the invention but are not intended to limit the scope ~ `
thereof. ~
WO91/04990 PCT/US90/0~261
- 19- 2066~96
EXAMPLE 1
To a 1-liter round-bottom flask fitted with a paddle
stirrer and containing S00 g of H20 at 80 C. under a N2
atmosphere was added 0.5 g of the emulsifier sodium lauryl
5 sulfate. Next, 1.0 g of the free-radical initiator
(NH4)2S2O8 was added to the flask. First-stage monomer, -
namely 80 g of ethyl acrylate (EA) and 20 g of methacrylic
acid (MAA), was added over a time period of 30 minutes, along
with the addition of 2.0 g of the chain-transfer agent butyl
lo mercaptopropionate. The monomer-containing mixture was then
held at 80 C. for approximately 15 minutes. The second-stage
monomer, namely 100 g of methyl methacrylate (MMA), was added
into the thus-heated monomer-containing mixture over a time
period of 30 minutes. The resultant mixture was thereafter
15 held at 80 C. for 1 hour with stirring. The pH of the
stirred mixture was approximately 2.5, and the optical ~
density (O.D.), measured on a Bausch and Lomb Spec 70 unit~ `
(at 500 nm in a lO mm cell at 0.2% N.V.) was found to be 1.4. -~
Next, the pH was adjusted to 9.5 using a 28 weight- ~ ~
20 percent aqueous ammonium hydroxide solution (28 wt.-% aq. ~-
NH40H soln.). The second-stage MMA polymer was stabilized by
dissolution of the first-stage EA/MAA polymer. The o.D. -~
after pH adjustment was found to be 0.37. `~-
The relative O.D. values of the thus-produced emulsions ~
25 as well as the actual size of the relative emulsion polymeri`
particles were reduced, which provided evidence of
dissolution of the inverted first-stage shell. ;
EXANPLE 2 `-`
The procedure of Example 1 was followed, except that lO0 -
30 g of styrene (S) was used as the second-stage monomer in -
place of tHe 100 g of MMA. Similar results were obtained;
and an emulsion l?tex was formed. When the O.D. was measured- `
at a pH of appro: lately 2.5, the O.D. was found to be `--
grèater than 2. After adjustment to approximately pH 9, the ~`
35 O.D. was found to be reduced to 0.82. `~
EXAMPLE 3 `~
The procedure of Example l was again followed, except ~-
that no emulsifier was added to the first-stage "
polymerization step. Similar results were obtained. When
WO91/04990 ~ ~6 PCI'/IS90/05261 ~;
. - 2 0 -
measured at a pH of approximately 2.5, the O.D. was found to
be 0.4. After adjustment to approximately pH 9, the O.D. was -~
found to be 0.18. ;;`
EXAMPLE 4 -
To provide a clear model to show inverse core/shell ~
emulsion polymerization and also to obtain additional ~--
confirmation of release and stabilization of the domains by
base solubilization of the first stage, a monomodal first-
stage alkali-soluble emulsion polymer was formulated as
10 follows. Such an emulsion was made via a so-called "seeded~
approach, wherein a fine particle size 80/20 EA/MAA polymer,
made by emulsion-polymerization techniques, was used as the -~
"seedn for the second-stage manufacturing step of the same
composition. ~
The resulting alkali-soluble, relatively low molecular `-
weight thus-produced nseedn was then characterized, at low
and high pH, utilizing known transmission electron microscopy
(T.E.M.) techniques and was shown to be both monodisperse, 94 i``
nm (nanometers), and alkali-soluble. Such a seed was then
20 utilized in connection with second-stage monomers of both
styrene (S) and methyl methacrylate (MMA) at 5:1 and 1:1
S/MMA weight ratios, and resultant mixtures were subjected to
emulsion polymerization. `
When measured at a pH of approximately 2.5, the O.D. of
25 each such mixture was found to be 1.1. After adjustment to
approximately pH 9, the O.D. of each such mixture was found
to be 0.66. -``
The resulting emulsions were then characterized by known
T.E.M techniques. In all cases, phase inversion was noted.
30 At high pH, the EA/MAA first-stage polymer was shown to be in
a dissolved state and the discrete second-stage domains "~`,``!`'`,`
remained. These results correlated well with the particle
size distributions at low and high pH. The distributions '`!`,~`
te~nded to show lower, monomodal particle sizes at high pH,
indicating the presence of the second-stage domains after the
EA/MAA phase was solubilized. The T.E.M. analytical results
also correlated well with the observatian of the lower O.D.
value of the emulsions after the pH was raised from 2.5 to 9.
WO91/04990 PCT/US90/0~261 ~
- 21 - 20~6596 :~:
EXAMPLE 5
- To a l-liter round-bottom flask equipped wit:~ a
conventional paddle stirrer, and internally subjected to a N2
atmosphere, was added 48 g of water and 0.8 g of sodium
lauryl sulfate emulsifier (28%). These ingredients were then
mixed until homogeneous, while heating to a temperature of 80
C.
The following first-stage monomers were next Gombined
along with 2.6 g of the chain-transfer agent
10 bromotrichloromethane, to produce a first-stage monomer
mixture: ~
Methyl methacrylate 76.7 g '! "
Butyl acrylate 19.8 g
2-Ethylhexyl acrylate 19.8 g .
Methacrylic acid ~ 15.9 g
Fifteen percent, namely 20.2 g, of the thus-produced
first-stage monomer mixture was then added to the reaction
flask, as a pre-charge. With the temperature of the flask
contents at 80 C., 2 g of the initiator ammonium persulfate
(APS), pre-disæolved in 5 g of water, was added to the
reaction flask. ~ ~
After reacting the pre-charge ingredients at 80 C. for `; `
10 minutes, the balance of the chain-transfer agent~
containing first-stage monomer mixture was added to the -
25 flask, over a time period of 30 minutes, while maintaining ~
the desired 80 C. reaction temperature. -`
After the addition of the remainder of the first-stage ``
monomer mixture to the flask was completed, the resultant ``
reaction mixture was held at 80 C. for one additional hour. ``
30 Then, a premix of 10.1 g of an 80~ aqueous solution of 2-
dimethylamino-2-methyl-1-propanol, 1.4 g of 28 wt.-~ aq. ~j `
N~40H solr., and 20 g of water was added to the re~ction
mixture, using the same feed rate as for the first- tage
m~homer mixture. After such addition was completed, the `~
35 resultant reaction mixture wàs then held at 80 C. for 5
minutes. The pH was thereafter found to be 7.0-7.5. `
While the first-stage polymer mixture was reacting, the -
following second-stage monomer mixture was prepared~
,
,~
W091/~4990 9~ PCT/US90/05261
- 22 -
Methyl methacrylate 9l.4 g
Butyl methacrylate 157.5 g
2-Ethylhexyl acrylate 66.5 g
The second-stage monomer mixture was then added to the
5 thus-neutralized first-stage poIymer mixture, over a time
period of 60 minu~es, at a temperature of 80 C. After such `
addition of the second-stage monomer mixture was completed,
the resultant batch was held at a temperature of 80 C. for 5
minutes.
Next, a pre-mix of 5.6 g of 28 wt.-% aq. NH40H soln. and
20 g of water was added at the same feed rate as for the `-
second monomer feed. The resultant reaction mixture was then
maintained at 80 C. for 50 minutes. ~
The resulting latex emulsion wàs thereafter cooled and ~`-
filtered. The emulsion was observed to exhibit the
characteristics of an ~invertedn core-shell emulsion, within ~
which the first-stage polymer had become solubilized. 1i`
EXAMPLE 6 -
The procedures of Example 5 were again followed, except
20 that the following second-stage monomers were employed:
Methyl methacrylate 28.4 g
Styrene 63.0 g
Butyl methacrylate 157.5 g
2-Ethylhexyl acrylate 66.l g ~
25 Results similar to Example 5 were obtained. ;j`~i;
EXAMPLE 7
A latex for use in a floor polish, which can providei`;~
both the low molecular weight leveling resins and the high ~i
molecular weight colloidal components, can be made from the ~
30 latexes produced according to the present invention, using `-'
known procedures and formulations.
As an example, an emulsion polymer was prepared
according to the above general preparation example (2-hour
flrst-stage monomer addition) utilizing the following raw ~ ;~
35 materials:
: .:
. . `
WO91/04990 PCT/US90/05261
2066596
- 23 -
Step 1: Preparation of Em~uLsion Polymer ~;-
~ i~r
Staae 1 monomers:
Styrene 72.0 g
Acrylic Acid 48.0 g ~
Iso-octyl Mercapto propionate4.8 g `-
Staae 2 monomers:
Styrene 210.0 g -~
-Butyl Acrylate 56.0 g ~-
Methacrylic Acid 14.0 g
10 Aqueous phase:
- Sodium Lauryl Sulfate 12.0 g
Ammonium Persulfate 4.0 g
De-ionized Water 575.0 g `-
Step 2: Floor Finish Prepared Employinq Step 1 Polymer -~
An 18.7% non-volatile, high-gloss floor polish was
formulated, in a conventional manner, from the above `~
emulsion. The ingredients are listed below: ~`
In~redients
Water 121.4 g
Non-ionic emulsifier* 2.5 g `
- (Triton X 4Q5) ` `
~; ~ 1% Fluorocarbon Leveling 1.3 g -~
~, .-
Surfactant (Zonyl FSJ) ~`;
28% NH40H (aq. soln.) 5.8 g '.,!~1',',',
Olei¢ Acid 1.3 g
26~ Non-volatile Wax 39.8 g
- Emulsion (a 1:1 blend of
AC-392 and Eplene E-43 `
polyethylene waxes) ;~
20~ Zinc Ammonium~Carbonate3.0 g
Solution ~"~
Emulsion polymer 72.6 g ~`
Footnote
*T~e identified emulsifier, Triton X 405, is ~ commercially~
35 available 70 wt.-~ soln. of a 40-EO octylphenol surfactant. -~
EXANPLE 8
An architectural coating was prepared using the polymer
prepared according to Example 5. The coating had the
following formulation:
,~:
WO91/04990 PCT/US90/05261 ;
~66~9 - 24 - ` ~
Paint Base~
Propylene Glycol 176.3 g. ---
Disperse Ayd W22l 29~39 g.
Drew Plus T45002 5.88 g. ~
Water 53.78 g. ;`
Titanium Dioxide tKronos 2190)734.65 g.
Paint: ~
Paint Base lO0.0 g. ` -
Polymer From Example 5 216.0 g. I ~
Anti-foam (BYK 073) -0.6 g. ~ `
Dibutyl phthalate 3.8 g. `~
, "
l- nDisperse Ayd W22n is a blend of anionic and non-ionic
surfactants, sold by Daniel Products, Jersey City, NJ.
15 2- nDrew Plus T4500~ is an anti-foam agent; for water-based
paints, based on mineral oil and a silica derivative,
sold by Drew Ameroid.
The above paint possessed good gloss as well as good
coating and adhesion properties. ~`~
~ The next three examples are directed to the production
of adhesives.
EXAMPLE 9
A first-stage hydrophilic polymer emulsion was produced ;
as follows. To a 2-liter round-bottom flask fitted with a
25 conventional paddle stirrer and containing 580.7 g of water
at 80 C. under a N2 atmosphere was added 8.0 g of a first
emulsifier, sodium lauryl sulfate, together with 8.5 g of a ~```
second emulsifier, sodium dodecyl diphenyl oxide disulfonate.
Next, 2.0 g of the free-radical initiator (NH4)2S208 was
30 added to the flask contents. Thereafter, first-stage
monomers, namely, 310.0 g of ethyl acrylate (EA) and 78.0 g
of methacrylic acid (MAA), were added to the agitated flask ~;
contents over a time period of 60 minutes, along with 7.8 g
o~f the chain-transfer agent butyl mercaptopropionate. The ~
35 monomer-containing agitated flask contents were then held at `
80 C. for 30 minutes; and, thereafter, 5.0 g of a 28 wt -%
aq. NH40H soln. was added, to maintain a pH value of from 5
to 6.
~ ' '
WO 91/04990 PCI'/US90/05261 ~
2 0S6596 ~` ~
- 25 -
Next, the second-stage polymer was produced as follows.
To a 2-liter round-bottom flask fitted with a conventional
paddle stirrer and containing 366.7 g of water at 78 C. under
a N2 atmosphere was added 100 g of the first-stage
5 hydrophilic polymer-containing emulsion along with 15 g of a
4-mole E0 nonyl phenol surfactant. Next, 1.3 g of the free-
radical initiator (NH4)2S2O8 was added to the flask.
Thereafter, second-stage ~onomer, namely lO g of MAA, 433 g -~
of butyl acrylate (BA), and 4 g of 1,4-hexanediol diacrylate, ~;
lo were simultaneously added to the agitated flask contents over -`
a time period of 90 minutes. The resultant mixture was then: `
held at 80 C. for one hour, while maintaining agitation. The
pH of the thus-agitated emulsion was approximately 5.5 and ~<
the viscosity was approximately 75 centipoises (cps). Next, ~-
- 15 the pH of the thus-agitated emulsion was adjusted to 7.0-7.5,
utilizing 5.0 g of the above-mentioned 28 wt.-% aq. NH40H ~~
soln. With the addition of the NH40H solution, the first- ~;~
stage EA/MAA polymer particles were observed to dissolve in~:~
their emulsion and the viscosity of such an emulsion was
20 observed to increase to approximately 1000 cps. ;
The thus-produced pH-adjusted second-stage polymeric ~`
emulsion was thereafter applied to commercially-available ~`
polyester film to provide a one-mil thick dry film of ~;
pressure-sensitive adhesive possessing so-called ~removable
25 performancen characteristics (i.e., the adhesive and so-
called nface stockn onto which the adhesive is coated are
together cleanly removable from a surface). The dried film
- was observed to have a glass-transition temperature (Tg) of `;
minus 48 C. When the adhesive side of the adhesive-coated --
30 polyester film was applied to a stainless steel panel, such `
was observed to provide an initial 30-minute 180-degree peel
value of 22 ounces per inch width. (PSTC-l, 180-degree peel, `
modified for residence time of 30-minutes dwell.) 24-hour
aging of the polymeric adhesive on the stainless steel panel ~ ;
35 at 70 C. provided a peel value of 26 ounces or less. (PSTC~
1, 180-degree peel, modified for a residence time of 24 hours `
at 70 C.) The Polyken Tack value of the polymeric adhesive
was observed to be 420 g or less per square centimeter -~
(Polyken Probe Tack Test, A-l-1); and the rolling-ball tack
WO91/04990 PCT/US90/0~261
2066~96 ~- ~
- 2
(Rolling Ball Tack Test, PSTC-6) was observed to be 5 inches -
or less. ;-~
EXAMPLE 10
The procedure for Example 9 was repeated except that 4.3 --
5 g of diethylene glycol dimethacrylate was utilized to produce ;--
~the second-stage polymer, in lieu of the 4.0 g of hexanediol
diacrylate. An emulsion polymer, similar to that of Example ``
9, was formed. The initial 30-minute 180-degree peel value
was determined to be 48 ounces per inch width; the 70-degree ~
10 C, 24-hour aged 180-degree peel value was observed to be 110 - -`
ounces; the Polyken tack was observed to be 600 g per square
centimeter; and the rolling-ball tack was observed to be 4 `
inches. ~`
Thus, while Example 9 produced a "removablen pressure~
15 sensitive adhesive, Example lO produced a somewhat more ` -
"permanent" pressure-sensitive adhesive. ~``
EXAMPLE 11
A heat-sealable (e.g., blister-pack) variety of adhesive `
was prepared as follows.
The above-discussed procedures of Ex~mple 9 were again -~
followed to produce yet another quantity of the first-stage`~
hydrophilic polymer emulsion.
Another second-stage hydrophobic polymer was then
produced as follows.
To the 2-liter round-bottom flask, which was fitted with~`
the conventional paddle stirrer and which contained 270 g of
water at 78 C. under a N2 atmosphere, was added 250 g of the
first-stage hydrophilic polymer-containing emulsion along
with 15 g of a 4-mole E0 nonyl phenol surfactant. Next, 1.3
30 g of the free-radical initiator (NH4)2S208 was added to the
flask. Thereafter, second-stage monomer, namely 10 g of MAA,
225 g of BA, and 150 g of methyl methacrylate (MMA), were
simultaneously added to the agitated fiask contents over a
time period of 90 minutes to produce a second-stage monomer
35 mixture. The thus-produced second-stage monomer mixture was
then held at 80 C. for one hour, while maintaining agitation. ``
The pH of the thus-agitated emulsion was approximately 5.5
and the viscosity was approximately 30 centipoises (cps). -
Next, the pH of the thus-agitated emulsion was adjusted to
WO91/~990 PCT/US90/05261
- 27 _ 20~6~96 ;
7.0-7.5, utilizing 12.5 g of the 28 wt.-% aq. NH40H soln.
With the addition of the NH40H solution, the first-stage
EA/MAA polymer particles were observed to dissolve in their ~
emulsion, and the viscosity of such emulsion was found to --
5 have increased to approximately 1900 cps. This emulsion was` -;
then reduced to 40 wt.-% solids with water, resulting in a :
viscosity of 8S cps. The pH-adjusted second-stage polymeric
emulsion was thereafter applied to commercially`-available so-
called ~SBSn paper stock to provide a dry film of heat- `
10 sealable adhesive. When the adhesive-coated paper stock was `-
heat sealed onto rigid PVC blister stock for 1-1/2 seconds,
at 50 pounds (per square inch gauge) and at a temperature of
at least 121 C., an adhesive bond was formed that required
complete ~fiber tearn (i.e., failurè) of the SBS paper stock
15 to separate the PVC blister material from the SBS paper
stock.
What has bee~ described herein is a novel, stable i"`
emulsion polymer and methods for preparing the same. It will
be apparent that the foregoing examples illustrate certain
20 preferred embodiments and are not limitàtive of scope. Thus, ``~`
while the polymer and the methods of the present invention ;~
have been described with reference to preferred embodiments, ~;
the present invention is not limited thereto. On the
contrary, alternatives, changes and modifications will become
25 appa`rent to those skilled in the art upon reading the --~
- foregoing description. F~ example, as Examples 9 through 11 ``~
illustrate, the present invention can be utilized to prepare "
certain adhesives. Still other variations will be obvious to ` `~
those skilled in this art. Accordingly, such alternatives, -~-
30 changes and modifications are to be considered as forming a -
part of th~ invention insofar as they fall within the spirit
and scope of the appended claims. ~
~.
:; .'~:,
,'.
: ~
`"',;-`~
..:
