Note: Descriptions are shown in the official language in which they were submitted.
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EXPR . MAIL #IB 581778714
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RD93034
PROCESS FOR PRODUCING ULTRAFINE SIZED LATEXES
Backaround of the Invention
1. Field of the Invention
The present invention relates to extremely fine-sized aqueous
polymeric dispersions, and particularly acrylic-based dispersions
II~V1I1CJ d Ille~ll p~l-tlCle 31ze o~ les~ than 60 nanometers. More
specifically, the aqueous polymeric dispersions of the present ~
invention are made by incremental addition of monomer and initiator ~ -
solutions to an aqueous solution containing at least one emulsifier
maintained in a minor amount. ~
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2. Technology Description
Heretofore, numeroùs emulsion latexes have existed. However, the
particle slzes of such latexes have generally been large, for
example 120 nanometers or larger.
U.S. Patent No. 4,177,177 to Vanderhoff et al relates to various
method~ for making polymeric emulsions which can be utilized to
produce latexes. The latexes generally have a particle size
greater than 100 nanometers.
U.S. Patent No. 4,228,047 to Pippin et al relates to an aqueous
coating composition comprising a copolymer of at least 95 percent
by weight of vinyl acetate and at least 0.1 percent by weight of
maleic anhydride which allegedly has been found to have improved
starch binder compatibility.
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EXP~ ,MAIL #IB 581778714
,
Japanese Disclosure No. 52103588 to Asahi Dow relates to a carpet-
backing composition containing loO parts by weight (as solids
content) of a copolymer latex: 200 to 350 parts by weight of
inorganic filler and thickener consisting of 30-60 ~eight percent
of a) butadiene: 20-70 weight percent of b) styrene 5-30 weight
percent of c) methyl methacrylate: and 1 to 5 weight percent of d)
ethylene series of unsaturated carboxylic acid and has an average
particle diameter of 60 to 120 nm. By using the latex of small
particle diameter for the carpet bàcking, blistering is prevented.
Belgian Patent No. 812139 to DeSoto, Inc. relates to opaque
coatings obtained from a latex comprised of an aqueous suspension
of small and large resin particles, the large particles having a Tg
less than the small ones and having an average diameter which is
greater than twice that of the small particles, the latter forming
20 to 65 weight percent of the total particles. The particles are
such that neither the large nor the small ones can, on their own,
coalesce when the latex is dried, to form a non-cellular film. The
small particles actually give a powder under such conditions. The
small particles are preferably polystyrene and the large ones a
copolymer o~ vinyl acetate and an ester of a 4 to 18 carbon atom
alkanol and an unsaturated carboxylic acid. The composition
contains a minimum amount of solvent and rapidly gives an opaque
coating of low porosity upon drying. It may be used for lipstick,
crayons, etc.
British Patent No. 1,100,569 to the Dow Chemical Co. relates to
acrylic polymer latexes containing large and small particles
prepared by 1) heating water containing a soluble catalyst to up to
85C in an inert atmosphere, 2) adding 1/3 of a mixture of
monomers, 3) carrying on the polymerization for at least 15
minutes, 4) adding an aqueous solution of an anionic emulsifier and
an aqueous solution of the polymerization catalyst, and 5) adding
the remaining monomer continuously over a period of at least 45
minutes.
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U.S. Patent No. 3,711,435 to DuPont and Co. relates to a stable,
aqueous colloidal dispersion prepared by mixing 1) a copolymer of
20 to 80 weight percent ethylene and 80 to 2~ weight percent of an
aminoalkylacrylate; 2) an acid having a dissociation constant of
10 to 5; and 3) water in proportion to give a solids containing 5
to 30 weight percent and a degree of neutralization of the amino
groups of the polymer of at least 40 percent. The mixing is
effected at a temperature suitable for dispersing the polymer in
particles of size less than 10 nanometers. The resulting
dispersions have very small particle sizes so that they may be
thinly spread over aluminum substrates to give void free coatings,
and as flocculants for removal of suspended matter from water.
N,N-dimethylaminoethylmethacrylate is a suitable comonomer.
Japanese Disclosure No. 52-123478 to Kurraray relates to
compositions prepared by emulsion polymerization of unsaturated
monomers in the presence of a protective colloid which is prepared
by cleaving water-solubilized copolymers in the presence of free
radicals and by heating. The compound contains units of
maleinimide and/or N-substituted maleinimide and units of alpha-
olefin as essential components of the main chain.
An article by Ugelstad, El-Aasser, and Vanderhoff, Journal of
Polymer Science, Polymer Letters Edition, 11, 503: lg73 relates to
the production of latex particles by mini-emulsion polymerization
of a mixed-emulsifier system including a surfactant and a long-
chain alcohol or alkane cosurfactant utilizing ultrasonification.
An article by Atik and Thomas, Journal of American Chemical
Society, 103, 4279: 1981 relates to aqueous styrene polymer
microemulsions made by bulk polymerization having a number average
particle size of from about 20 to about 35 nanometers by utilizing
a mixed emulsifier of cetyl-trimethylammonium bromide and hexanol
followed by polymerization with an oil soluble
35 azobisisobutyronitrile and irradiation. However, the solids
2127~19 ~x~ MAIL III~ 5~177~714
content was very low, less than 2 percent and the amount of
emulsifiers utilized was approximately 1.5 times the amount of
polymer by weight.
An article by Jayakrishnan and Shah, Journal of Polymer Science,
Polymer Letters, 22, 31 984 relates to a bulk polymerization of
polystyrene or methyl methacrylate microemulsion particles having
a number average size of from about 10 to about 60 nanometers
utilizing sodium dihexylsulfosuccinate and ethylene oxide-propylene
oxide block copolymers as mixed-emulsifiers and an oil soluble
initiator such as benzoyl peroxide. However, the weight ratio of
the emulsifier to the monomer was approximately one to one and the
microemulsion could not be diluted with water.
Canadian Patent Application No. 2,013,318, assigned to B.F.
Goodrich is directed to a process for producing very fine-sized
aqueous polymeric microemulsions. The process utilizes incremental
addition of a monomer feed solution into an aqueous solution
including one or more emulsifying agents and one or more water
soluble or redox initiators. While this method may be used to
produce such microemulslons, it is deficient in that the emulsion
tend~ to discolor and th~t it is extremely dif~icult to obtain
emulsions having a narrow ~article size range profile.
An article by Okuba et al, "Preparation of Asymmetric Polymer Film
by Emulsion ~lend Technique", Colloid & Polymer Science, 268:1113-
-1117 (1990), teaches blending two different particle size emulsions
together to determine the tackiness properties of such blends. One
of the starting emulsions disclosed is a poly~ethyl acrylate-methyl
methacrylate) emulsion having a particle size of 0.02 microns.
According to the article, this emulsion is prepared by combining
the monomers in a glass flask with water, sodium sulfite, potassium
persulfate and sodium dodecyl sulfate. The order or method of
addition of the different reactants, initiators and emulsifiers is
not specified.
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European Published Patent Application No. 0 429 207, asslgned to
Rohm & Haas is directed to a method of treating or coating a
substrate with an aqueous composition. The coating composition is
an aqueous dispersion of copolymer particles having mutually
incompatible phases and having an average particle size of about 20
to about 70 nanometers. The dispersion is prepared by emulsion
polymerization techniques. In preferred embodiments, the particles
are of a core/shell morphology where the core has a TB of at least
45~C and the shell has a T6 of lower than 35C.
Despite the above teachings, there still exists a need in the art
for a method to produce ultrafine sized emulsion latexes which do
not discolor, have a narrow particle size distribution, are easily
reproducible, and utilizes a mihimal amount of surfactant.
Summarv of the Invention
.
In accordance with the present invention, a process.for producing
ultrafine sized emulsion latexes which do not discolor, have a
narrow particle size distribution, are easily reproducible, and
utilizes a minimal amount of surfactant is provided. The process
is particularly characterized by incrementally feeding monomers and
initiators into an aqueous reaction medium such that the ionicity
of the reaction medium remains constant.
One embodiment of the invention comprises a process for producing
an aqueous-based dispersion containing between about 15 and about
50 percent by weiqht solids comprising the steps of:
(a) incrementally adding one or more ethylenically unsaturated
monomers capable of polymerizing in an aqueous environment to
a reaction vessel containing water and up to 6.3 parts per lOO
parts of said monomers of one or more surfactants;
2 ~ 2 s ~ ~ ~ EXPRI MAIL #IU 581778714
(b) incrementally adding one or more polymerization initiators
to said reaction vessel; and
(c) allowing said one or more ethylenically unsaturated
monomers to polymerize such that the average particle size of
said polymerized monomers is less than 100 nanometers.
In preferred embodiments, the process utilizes monomers derived
from acrylic based acids and esters and yields ultrafine sized
latexes having a mean particle size of less than 50 nanometers.
Another embodiment of the present invention comprises the
dispersion manufactured by the novel process. The polymeric
ultrafine-sized latex is coagulation stable and thus can be diluted
with water. The polymer particles have several physical attributes
such as good film formation, penetration into porous substrates,
very high surface area to volume ratio, monomodality and the like.
The novel dispersions can be used in the manufacture of wood
preservatives, polymer and metal coatings, adhesives, waterproofing
chemicals, textile sizes, agricultural chemicals, pharmaceuticals,
oil field chemicals, inks, paper manu~acture, rheology modifiers,
cosmetics, ultraviolet light scatterers, biomedical and immunoassay
applications.
An object of the present invention is to produce an ultrafine sized
latex emulsion which does not discolor, has a narrow particle size
distribution, is easily produced, and utilizes a minimal amount of
surfactant.
An additional object of the present invention is to provide a
ultrafine sized latex emulsion which is coagulation stable, has
good film formation, penetration into porous substrates, very high
surface area to volume ratio and monomodality.
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ExpRr MAIL #IB 581778714
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These, as other objects, will readily be apparent to those skilled
in the art as reference is made to the detailed description of the
preferred embodiment.
Detailed Description of the Preferred Embodiment
In describing the preferred embodiment, certain terminology will be
utilized for the sake of clarity. Such terminology is intended to
encompass the recited embodinlent~ as well as all technical
equivalents which operate in a similar manner for a similar purpose
to achieve a similar result.
Th~ ultrafine sized latexes are produced by incrementally adding
one or more ethylenically unsaturated monomers capable of
polymerizing in an aqueous environment and incrementally adding a
polymerization initiator to a reaction vessel containing water and
one or more surfactants and allowing the one or more ethylenically
unsaturated monomer~ to polymerize such that the average particle
size of said polymerized monomers is less than lO0 nanometers. The
term "incremental addition" defines any form of addition of a
small amount of the total monomer and/or initiator to the aqueous
solution over an extended period of time until all of the monomer
and initiator solutions have been added. This includes cyclic
additions, interrupted additions, combinations of the above and the
like. Preferably, the addition of the monomer and initiator is
continuous and at a constant level over a period of time.
Any ethylenically unsaturated monomer which is capable of
polymerizing in an aqueous environment may be selected as a
starting material. Particularly preferred are any of the following
monomers: (meth)acrylic based acids and esters, acrylonitrile,
styrene, divinylbenzene, vinyl acetate, ethylenically unsaturated
carboxylic acids, acrylamide, methacrylamide, vinylidene chloride,
butadiene and vinyl chloride. The dispersion solids that are
produced may take the form of homopolymers (i.e., only one type of
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monomer selected) or copolymers (i.e., mixtures of two or more
types of monomer are selected; this specifically includes
terpolymers and polymers derived from four or more monomers).
Most preferred are the use of acrylic based acids and esters. The
acrylic polymers of the present invention are derived from one or
more acrylate monomers having the formula
R1 0
l 11
H2C=C - C-OR2 (I)
where R1 is preferably hydrogen or an alkyl group having from l to
4 carbon atoms and R2 is an aliphatic group having from l to 20
carbon atoms. In most preferred embodiments, R1 comprises a methyl
group and R2 is an alkyl group having from l to 20 carbon atoms.
Specifically useful monomers falling within the scope of formula
(I) include methyl methacrylate, ethyl acrylate, butyl acrylate,
methacrylic acid, acrylic acid and mixtures thereof.
Other monomers or starting compounds which may be utilized to
produce ultrafine sized latexes are well known to the art.
Example~ are set forth in The Encyclopedia of Chemical Technology,
Xirk-Othmer, John Wiley & Sons, Vol. 14, pp 82-97, (1981). To the
extent necessary, this passage is hereby incorporated by reference.
When producing copolymers that are in part derived from acrylic
monomers, the amount of acrylic monomer typically ranges from about
30 to about 99 percent of the total amount of monomers, with
amounts ranging from about 50 to about 90 percent being more
preferred, and amounts ranging from about 60 to about 80 percent
being most preferred. In addition, when copolymerizing with an
acid, such as methacrylic acid, the copolymer may include up to 60
weight percent of acid. This is much higher than prior art systems
and enables the latexes to be particularly useful in textile
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EXPR~ MAIL #IB 581778714
applications as the resulting materials are easier to dissolve in
base. Further, when producing copolymer dispersions, the separate
monomers may be fed to the aqueous reaction medium from ~ither the
same or different feed vessels.
For several applications, while not necessary, it may be desirable
that the polymers produced be cro5s-linked. This is accomplished
by adding one or more cross-linking agents to the reaction medium.
Examples of cross linking agent include monofunctional compoundsO such as N-alkylol amides of the formula
R5 1l
H2C = C - C - NH - R3 - OR4
where R3 is an alkyl group having from l to lO carbon atoms,
preferably from l to 4 carbon atoms; R4 is hydrogen or an alkyl
group having from l to lO carbon atoms, preferably from l to 4
carbon atoms; and R5 is hydrogen or an alkyl group having from l to
4 carbon atoms. Specific examples of suitable cross-linking agents
include N-methylol acrylamide, N-ethanol acrylamide, N-propanol
acrylamide, N-methylol maleimide, N-ethylol maleamide, N-methylol
maleamic acid, N-methylol maleamic acid esters, the N-alkylol
amides o~ the vinyl aromatic acids such as N-methylol-p-vinyl
benzamide, and the like. Another useful cross-linking agent is
N-(isobutoxymethyl) acrylamide. ~ -
Yarious difunctional compounds or monomers can also be utilized as
effective cross-linking agents. These include compounds containing
two olefinic groups such as divinylbenzene, divinylnaphthalene,
divinylcyclohexane, and the like; various diacrylate or
dimethacrylate esters of aliphatic diols where the ester portion
has from l to lO carbon atoms, and is preferably alkyl where the
diol portion has from 2 to 8 carbon atoms. Examples of these
materials include ethylene glycol dimethacrylate, diethylene glycol
diacrylate, diethylene glycol dimethacrylate and butylene glycol. -~
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Other cross-linking agents are described in the Journal of Applied
Polymer Science, Vol. 34, pp 2389-2397 (1987) John Wiley ~ Sons,
Inc., in an article entitled "New Cross-Linking Agents for Vinyl
Polymers". To the extent necessary, this article is hereby fully
incorporated by ref erence .
The amount of the cross linking agent when utilized is generally
from about 0.05 to about l0 percent by weight, desirably from about
0. l to about 5 percent by weight, and most preferably from about
0. l to about l . 0 percent by weight based upon the total weight of
all monomers added.
~lso incr~3mentally added to the aqueous reaction medium is one or
more polymerization initiators, preferably a free radical thermal
initiator. The polymerization initiator may take the form of many
known initiators such as azo, peroxide, persulfate and perester
initiators and may be either water soluble or monomer soluble. The
amount of initiator added to the solution typically ranges from
between about . 05 to about 2 weight percent of the emulsion with
amounts ranging rom about 0. l to about l. 0 weight percent being
particularly pre~erred and amounts ranging from about 0. l to about
0. 5 welght percent belng most pre~erred. The free radical
initiator added is preferably an azo (azobisnitrile) type initiator
(water or oil soluble) such as 2,2'-azobis-isobutyronitrile, 2,2'-
azobis-(2-methylpropanenitrile), 2,2'-azobis-(2,4
dimethylpentanenitrile), 2, 2 ' -azobis- (2-methylbutanenitrile), l, l ' -
azobis-(cyclohexanecarbonitrile), 2, 2 '-azobis-(2;4-dimethyl-4-
methoxyvaleronitrile), 2,2'-azobis-(2,4-dimethylvaleronitrile) and
2, 2 ' -azobis- (2-amidinopropane) hydrochloride.
3 0
Other free radical initiators which may be selected include
peroxide materials such as benzoyl peroxide, cumene hydroperoxide,
~;- hydrogen peroxide, acetyl peroxide, lauroyl peroxide, persulfate
materials such as ammonium persulfate, and peresters such as t-
butylperoxypivalate, ~-cumylperoxypivalate and t-butylperoctoate.
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Examples of commercially suitable initiators which may be selected
include Wako V-50, vazo 52, Vazo 64, Vazo 67 and Lupersol ll.
These commercial initiators may be included with the monomer feed.
In the case of water soluble initiators, such as the peroxides and
persulfates, it is critical that during polymerization the ionicity
of the reaction medium be maintained at a constant. This is
accomplished by removing a portion of the water from the aqueous
reaction medium and adding this removed water to the initiator feed
stream. l'he need for maintaining a constant ionicity is seen when
attempting a conventional post treatment for residual monomer with
ammonium persulfate and sodium metabisulfite. Large quantities of
coagulum form, reducing the efficacy of the process. Similarly, a
conventional initiator feed consisting of ammonium persulfate and
1-3 weight percent of the total water volume will cause
agglomeration of polymer particles throughout the initiator
addition.
It has been found that by maintaining a constant ionicity in the
reaction mixture, agglomeration can be avoided, yielding a more
uniform particle size emulsion. By diluting the water soluble
initiator with the proper quantity of water, the ionic strength of
the initiator system will be the same as the contents of the
reaction vessel at any time during the reaction/initiator feed.
Presumably, this matched ionicity (as expressed in the number of
charges per volume) allows the diffusion controlled migration of
charged species such as ammonium persulfate and ionic surfactants
from droplet to reaction mixture or vice versa.
Use of highly concentrated initiator solutions presumably allows
large changes in the ionic concentration in the area immediately
surrounding an initiator droplet. It is hypothesized that this
massive change in charge density overwhelms the stabilizing forces
~5 exerted on the particles by surfactant and initiator residues.
~ EXPR~ MAIL #IB 581778714
The same ionic balance can be achieved by careful selection of a
charge neutral monomer soluble initiator such as the azo type
initiator commercially sold as VA20 52 (2,2'-azobis-(2,4-
dimethylvaleronitrile)) or VAZo 64 (2,2'-azobis-isobutyronitrile).
In these cases, the entire quantity of initiator is contained
within the monomer feed.
It is believed that the concept of maintaining a constant ionicity
in the reaction medium has not been utilized to form uniform sized
ultrafine polymer latexes until the present invention. The prior
art in the field of ultrafine sized latexes teaches that the
initiator be either contained within the aqueous reaction vessel or
added as a "single shot".
In accordance with the process of the present invention, the
monomer(s) and initiator(s) are fed into an aqueous reaction medium
which comprises water and at least one or more emulsifiers. The
emulsifiers are generally surfactants and hence can be cationic,
nonionic, anionic, amphoteric, copolymerizable surfactants and the
like with anionic generally being desired. Generally, the type of
emulsifiers ùtilized are those which can be utilized in
conventional latex polymerizations. As is recognized by one
skilled in the art, a key criteria Por selecting a surfactant is
its compatibllity with the initiator.
-
Examples of suitable amphoteric surfactants include the alkali
metal, alkaline earth metal, ammonium or substituted ammonium salts -
of alkyl amphocarboxy glycinates and alkyl amphocarboxypropionates,
alkyl amphodipropionates, alkyl amphodiacetates, alkyl
amphoglycinates and alkyl amphopropionates wherein alkyl represents
an alkyl group having 6 to 20 carbon atoms. Other suitable
amphoteric surfactants include alkyliminopropionates, alkyl
iminodipropionates and alkyl amphopropylsulfonates having between
12 and 18 carbon atoms, alkylbetaines and amidopropylbetaines and
alkylsultaines and alkylamidopropylhydroxy sultaines wherein alkyl
12
21 2 7 ~ 1 ~ EXPRE~ MAIL 1~IB 581778714
represents an alkyl group having 6 to 20 carbon atoms.
Anionic surfactants which may be selected include any of the known
hydrophobes attached to a carboxylate, sulfonate, sulfate or
phosphate solubilizing group including salts. Salts may be the
sodium, potassium, calcium, magnesium, barium, iron, ammonium and
amine salts of such surfactants.
Examples of such anionic surfactant5 include water soluble salts of
alkyl benzene sulfonates having between 8 and 22 carbon atoms in
the alkyl group, alkyl ether sulfates having between 8 and 22
carbon atoms in the alkyl group, alkali metal, ammonium and
alkanolammonium salts or organic sulfuric reaction products having
in their molecular structure an alkyl, or alkaryl group containing
from 8 to 22 carbon atoms and a sulfonic or sulfuric acid ester
group.
Preferred are linear sodium and potassium alkyl sulfates.
Particularly preferred is the use of sodium lauryl sulfate (sodium
dodecyl sulfate). Another preferred type of anionic surfactant are
alkyl benzene sulfonates, in which the alkyl group contains between
about 9 to about 15, and even more preferably, between about 11 to
about 13 carbon atoms ln a straight chain or branched chain
configuration and even most preferred a linear straight chain
having an average alkyl group of about 11 carbon atoms.
In some embodiments, mixtures of anionic surfactants may be
utilized, with mixtures of alkyl or alkylaryl sulfonate and sulfate
surfactants being especially preferred. such embodiments comprise
a mixture of alkali metal salts, preferably sodium salts, of aLkyl
benzene sulfonates having from about 9 to 15, and more preferred
between 11 and 13 carbon atoms with an alkali metal salt,
preferably sodium, of an alkyl sulfate or alkyl ethoxy sulfate
having 10 to 20 and preferably 12 to 18 carbon atoms and an average
ethoxylation of 2 to 4.
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EXPR MAIL #IB 581778714
,
Specific anionic surfactants which may be selected include linear
alkyl benzene sulfonates such as dodecylbenzene sulfonate,
decylbenzene sulfonate, undecylbenzene sulfonate, tridecylbenzene
sulfonate, nonylbenzene sulfonate and the sodium, potassium,
ammonium, triethanolammonium and isopropylammonium salts thereof.
Examples of useful nonionic surfactants include condensates of
ethylene oxide with a hydrophobic moiety which has an average
hydrophilic lipophilic balance (HLB~ between about 8 to about 16,
and more preferably, between about l0 and about 12.5. These
surfactants include the condensation products of primary or
secondary aliphatic alcohols having from about 8 to about 24 carbon
atoms, in either straight or branched chain configuration, with
from about 2 to about 40, and preferably between about 2 and about
9 moles of ethylene oxide per mole of alcohol.
Other suitable nonionic surfactants include the condensation
products of about 6 to about 12 carbon atom alkyl phenols with
about 3 to about 30, and preferably between about 5 and about 14
moles of ethylene oxide. Examples of such surfactants are sold
under the trade names Igepol C0 530, Igepol C0 630, Igepol C0 720
and Igepol C0 730 by Rhone-Poulenc Inc. Still other suitable
nonionic surfactants are described in U.S. Patent No. 3,976,586.
To the extent necessary, this patent is expressly incorporated by
reference.
Examples of cationic surfactants include cetyl trimethyl ammonium
bromide.
. .
Other surfactants which may be used include those described in
McCutcheons, "Detergents and Emulsifiers," 1978, North American
Edition, Published by McCutcheon's Division, MC Publishing Corp.,
Glen Rock, New Jersey, UESTA., as well as the various subsequent
editions. To the extent necessary, this reference is expressly
incorporated by reference.
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In practice the amount of surfactant present in the aqueous phase
ranges between about 0.5 to about 6.3 percent by weight of the
monomers added. Amounts between about 0.5 and about 3.0 percent by
weight of the total monomers added are more preferred and amounts
between about 1.0 and about 3.0 percent by weight of the total
monomers added are most preferred. In general, the-particle size
of the latex decreases with increasing amounts of surfactant added
up to about 3.0 weight percent. Beyond 3.0 weight percent
surfactant, the decrease in particle size is ~ar less pronounced.
The reaction medium can include between about 0.5 to about lO.0
percent by weight of the monomers added of other optional additives
to provide specific functional properties to the final latex.
Examples of such additives include plasticizers such as
polyethylene glycol, defoamers, pigments, colorants and dyes,
antibacterials, perfumes, pharmaceuticals, enzymes and other
biologically active agents, agricultural chemicals, ultraviolet
active agents, stabilizers and rheology modifiers. -
To produce the novel latexes of the present invention a semi-
continuous or continuoUs polymerization process is utilized. This
involves addlng the monomer, including cross-linklng agent if
nece9sary and initiator solutions incrementally to the reaction
vessel, which is typically heated to temperatures between about
45C and about 90C and includes water and one or more emulsifiers
over a period of time as opposed to a batchwise addition.
optionally, the reaction vessel can contain a small amount of
monomer before commencement of the incremental polymerization to
act as a "seed". Such a small amount of monomer is generally below
30 percent by weight and desirably no more than about 10 percent by
~ weight of the total monomer utilized. The rate of the monomer
- addition is generally governed by various factors such as reaction
vessel size, exothermic reaction temperature increase, cooling
capacity of the reaction vessel, and the like, such that the
reaction temperature is generally maintained at a specific value or
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EXPRi MAIL 1~IB 581778714
range.
The amount of the one or more emulsifiers generally contained in
the reaction vessel is generally at least 50 or 60 percent by
weight, desirably at least 70 percent by weight, more desirably at
least 80 percent by weight, and preferably at least 90 percent by
weight of the total amount of emulsifiers. The remaining
emulsifier, if any, is fed with either the monomer or initiator
feed streams.
1 0 ~,,
The reaction vessel may be maintained at temperatures as low as ;~
ambient temperatures (10C to 20) up to the boiling point of the
aqueous solution. The reaction pressure is generally atmospheric,
but may be elevated if necessary to assist in polymerization.
As discussed above, the monomer feed and the initiator feed may be
the same feed if the initiator is monomer soluble. Further, if the
initiator is water soluble and charged, such as ammonium
persulfate, it is fed such that the ionicity throughout the
reaction vessel is maintained at a constant. This is typically
accomplished by initially transferring an amount of the water from
the reactlon vesgel to the lnitlator feed to create ionic
concentrations in both the feed vessel and the reaction vessel
which are substantially equal.
Feeding the initiator solution on an incremental basis provides for
a generally steady state free radical concentration throughout the
monomer addition. This steady state free radical concentration
avoids the low radical concentrations seen with single charges of
initiators and prolonged f~ed times. It is this continual and
ready availability of free radicals that allows new chain and
particle formation to compete effectively with addition of monomer
to existing particles. As compared to prior art single shot
initiator feed systems, the inventive process markedly improves the
monodispersity of the resulting latex.
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EXPRE. MAIL #Is 581778714
Polymerization continues until all of the monomer(s) and initiator
has been added into the reaction vessel and until nearly all of the
monomer feed has been converted to a polymerized form.
Polymerization is generally continued until a high conversion is
achieved as in excess of 80 percent, desirably at least 90 or 95
percent, and preferably at least 98 percent or even complete
conversion.
Regardless of the particular type of monomers selected for
polymerization in the process as set forth above, the polymer
average particle size is very small. By the term "particle size"
it is meant the volume average median particle size as measured by
photocorellation spectroscopy. Polymeric latexes produced
according to the present invention have a very small volume average
particle size of lO0 nanometers of less, with aver.age preferred
particle sizes of between about l and about 60 nanometers, more
preferred between about 5 and about 40 nanometers, still more
preferred between about lO and about 30 nanometers, and ideally
between about lO and about 20 nanometers. Generally, any of the
above particle size ranges can be produced depending upon the
5pecific end properties desired.
Further, and particularly because of the incremental initiator feed
system used, the range of the produced particle size range is
limited. In practice the standard deviation for each desired size
latex is no more than 4 nanometers.
The above process yields a polymeric latex which is coagulation
stable inasmuch as it can be diluted with water without coagulation
occurring. The solids content of the latex is relatively high as
from about 5 percent to about 55 percent by weight, desirably from
about 15 percent to about 50 percent by weight, more preferably
from about 20 to about 40 percent by weight, and most preferably
from about 25 to about 35 percent by weight based upon the total
3S weight of the aqueous polymeric latex.
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~ EXPRFrC MAIL #IB 581778714
The properties of the polymeric latex are largely dependent upon
the monomers selected for polymerization. For example the glass
transition temperature of the polymers can range from about -54C
to greater than 130C.
. ~ ;~
The polymeric latexes of the present invention, due to their
extremely fine size, are useful in many applications such as wood
preservatives, polymer and metal coatings, adhesives, waterproofing
chemicals, textile sizes, agricultural chemicals, pharmaceuticals,
oil field chemicals, inks, paper making, rheology modifiers,
cosmetics, personal care products, ultraviolet light scatterers and
sunscreens, biomedical and immunoassay applications. Even though
they are latexes in structure, they often approximate solution type
properties. In addition, they may be used alone or in combination
with other materials, such as higher mean particle size emulsions
to yield products having specifically designed uses.
The invention will be better understood by reference to the
following examples. -
Example 1
An aqueous polymeric latex of methyl methacrylate is prepared as
~ollows: 100 parts per hundred ~PHM) methyl methacrylate are mixed
with 0.5 PHM VAZ0 52, a thermal initiator (2,2'-azobis-(2,4-
2S dimethylvaleronitrile)) soluble in methyl methacrylate. This
monomer/initiator solution is metered evenly over 3 hours into a
l-liter glass reaction vessel which contains 185 PHM water and 3
PHM sodium dodecyl sulfate. The reactor is maintained at 85C and
constantly stirred. At the end of the monomer addition, the
reactor is maintained at 85C for another 1 hour. The reaction
mixture is then brought to almost complete conversion by treatment
with 0.015 PHM t-butyl hydroperoxide and 0.015 PHM sodium
metabisulfite, at a temperature of 6~C. This synthesis results in
an aqueous polymeric latex containing 35 weight percent solids.
The average particle size mea~ured by a Niacomp 370A is 14
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nanometers. This polymeric latex is translucent due to the small
particle size of the latex particles. The latex is blue in color
and has a Tg of about 105C.
Example 2
An aqueous polymeric latex of butyl acrylate, methyl methacrylate
and methacrylic acid is prepared using the same method as in
Example 1. The composition of the monomer/initiator solution is 65
PHM butyl acrylate, 25 PHM methacrylic acid, 10 PHM methyl
methacrylate, and 1 PHM VAZ0-64 (2,2'-azobis-isobutryonitrile).
This process yields a latex of 25 weight percent total solids and
a volume weiyhted mean particle size of 14 nanometers. The latex is
clear, blue in color, and has a T~ of about -5C.
Example 3
An aqueous polymeric latex of styrene, butyl acrylate and
methacrylic acid is prepared as follows: 65 PHM butyl acrylate, 25
PHM methacrylic acid and 10 PHM styrene are thoroughly mixed
together to form one feed solution. In a separate feed vessel,
0.25 PHM ammonium peroxydisulfate is added to 65 PHM water. In a
separate reaction ve9sel 3 PHM sodium dodecyl sulfate is added to
244 PHM water and heated to 85C with continuous stirring. The
reason for preparing the separate aqueous initiator solution is to
enable a constant ionicity in the reaction vessel throughout the
synthesis procedure. Ten percent of the total volume of the
ammonium peroxydisulfate solution is added to the heated mixture
and the initiator and monomer solutions begin feeding at a rate
30 that allows even metering of the feed solutions over a three hour
interval. The reaction mixture is stirred for an additional 30
minutes and subsequently cooled to 62C. 0.10 PHM sodium
metabisulfite is dissolved in 24 PHM water and metered into the
reaction mixture over a 1 hour interval. The reaction temperature
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EXPRI MAIL #IB 581778714
is then increased to 85C for 1 hour. The mixture i5 then cooled
to room temperature and filtered. This charge results in an
aqueous polymeric latex containing 23.3 weight percent solids. The
volume median particle size measured by photocorrelation
spectroscopy is 34 nanometers. The latex is clear, blue in color,
and has a T~ of about -5C.
Example 4
To a solution containing 4.17 PHM of sodium lauryl sulfate and 313
PHM water is added 0.25 PHM ammonium persulfate dissolved in 0.52
PHM water. After an initiation period of five minutes a mixture of
53 PIIM butyl acrylate and 47 PHM methyl methacrylate is metered
into the solution over an interval of 2 hours. The temperature is
then raised to 92C for 1/2 hour then subsequently cooled and
filtered. A blue-gray latex is yielded having a solids level of
24.85%. This latex has an average particle size of less than 30
nanometers and has a T~ of -5C.
ExamPle 5
To a solution containing 2.57 PHM sodium lauryl sulfate and 241 PHM
water is added 0.15 PHM ammonium persulfate dissolved in 0.3 PHM
water. After an initiation period of five minutes a mixture of 43
PHM butyl acrylate and 57 PHM methyl methacrylate is metered into
the solution over an interval of 2 hours. The temperature is then
raised to 92C for 1/2 hour then subsequently cooled and filtered.
A blue-gray latex is yielded at a solids level of 23.10%. This
latex has an average particle size of less than 30 nanometers and
has a T~ of 0C.
Exam~le 6
To a solution containing 3.1 PHM sodium lauryl sulfate and 245 PHM
water heated to 85C are added continuously and simultaneously two
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- EXPRE~ MAIL #IB 581778714
separate feeds. One feed is comprised of 0.32 PHM ammonium
persulfate dissolved in 85 PHM of water and the other feed is
comprised of l0 PHM of styrene, 25 PHM methacrylic acid, and 65PHM
butyl acrylate. Feeding of each separate feed occurs for
approximately 2.5 hours and each feed stream is metered into the
reaction vessel in such a way that both feed streams are completed
depleted after approximately 2-5 hours. A solution containing 0.l
PHM sodium metabisulfite dissolved in 24 PHM water is then metered
into the reaction mixture over an interval of l/2 hour. The
temperature is maintained for l hour and the reaction mixture is
subsequently cooled to room temperature and is filtered. A blue-
clear latex is yielded having a solids level of 23.3% and an
average particle size of about 14 nanometers.
. . .
QUANTITATIVE AND QUALITATIVE TESTING
Wood Penetration Properties
A test is performed to determine the wood penetration ability of
the inventive latexes versus commercially available products. The
following test procedure is used:
l. 10% solids solutions of each latex are prepared by
diluting each latex with an appropriate amount of distilled
water.
-:
2. A pine dowel is cut into 3 inch sections and each dowel is
immersed in each latex solution for 3 hours.
3. Each dowel is dried at ambient conditions overnight.
4. A 2% Nigrosine stain solution is prepared and each dried ~-
dowel is immersed in the solution for 24 hours.
~ '
5. Each dowel is removed and dried at ambient conditions
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overnight.
6. Cross-sectional pieces of each dowel are cut and evaluated
for stain penetration.
.
The sample latexes tested are:
Sample A: Example 4 Latex :.
Sample B: Example 5 Latex
Sample C: Joncryl 537, 46% solids neat (S. C. Johnson)
3ample D: Reichhold 40-423, 46% solids neat (Reichhold
Chemical)
Sample E: UCAR 429, 47% solids neat (Union Carbide)
The particle size and relative penetration of the stain for each
sample is shown in Table 1:
.
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. ~ :
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EXPRE MAIL #IB 581778714
~able l
SampleParticle Size Penetration
A <30 nm minimal
B <30 nm minimal
C 90 nm slight
D lO0 nm appreciable
E 150 nm extensive
'
The minimal penetration seen when utilizing the inventive materials
demonstrates that the smaller particle sized latexes penetrate wood
better than conventional latexes. Accordingly, the inventive
materials form significantly better wood protective coatings than
commercial materials.
Surface Tenslon Pro~erties
The surface tensions of lO percent solids solutions of Samples A,
C, D and E are analyzed using a SensaDyne bubble surface
tensiometer. The results are shown in Table 2. The measure for
surface tension is in dynes/cm.
Table 2
SampleParticle SizeSurface Tension ~-~
A <30 nm 57.3 ;~ ~;
C 90 nm 40.8
D lO0 nm 57.2
E 150 nm 47.9
~ Penetrating ability is highly dependent upon wetting ability. If
~ a product does not wet a surface well, it will have little chance
~ of penetrating the surface. The higher surface tension of Sample
-~ 35 A, the inventive sample, places this product at a distinct
,: -:
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EXPRF~C MAIL #IB 581778714
disadvantage in penetration studies. However, the previous Example
demonstrates that Sample A has much better wood penetration than
the commercial samples (C, D and E). Thus, it is hypothesized that
the particle size of the samples is much more important than
surface tension in determining the penetrating ability of a latex.
In addition, the above tests are performed using 10~ solids
solutions. It is theorized that when using the Samples in a "neat"
form that Samples A and B~would demonstrate even more enhanced
positive results.
Textile Sizinq Properties
The latex of Example 6 is compared with the commercial products
Permaloid 150 and Permaloid 172, both manufactured by Rhône-Poulenc
Inc. for use as textile sizes. All samples are evaluated at
concentrations of 7% and applied to polyester filament yarn via a
lab scale slasher. The abrasion resistance of the latex of Example
6 is approximately equal to that of Permaloid 150 .and Permaloid
172. The advantage rendered by use of the inventive latex is the
absence of neutralization prior to application. Conventional
sizes, such as Permaloid 150 and Permaloid 172, are applied as
solution polymers prepared by the alkali induced solubilization of
a conventional latex polymer. The inventive ultrafine latex based
textile sizes are applied directly to the yarn without
neutralization. This eliminates the need for alkali or the
monitoring of ammonia release normally associated with the sizing '
-of filament yarns and hence provides significant advantages as -
compared to commercially available materials. -~
: .
Having described the invention in detail and by reference to the
preferred embodiments thereof, it will be apparent that
modifications and variations are possible without departing from
the scope of the appended claims.
24
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