Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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AQUEOUS WATER-REPELLENT COATINGS
Technical Field
This invention relates to aqueous, air
drying water-repellent latex coating compositions
which include a large proportion of wax and provide
long-term water repellency and durability on exterior
exposure. These coatings are primarily intended for
application to exterior wood surfaces.
Bac~round of the Invention
The coatings industry has long sought to
develop coating compositions that can be applied to
wood surfaces to provide air drying coatings which
demonstrate long-term water repellency and durability
on exterior exposure~
It is known that the presence of a wax in a
coating provides water repellency. In certain prior
coatings, a paraffin wax was melted, dissolved in an
organic solvent and incorporated into the organic
solvent-based coating composition as a solution.
~0 However, only a small proportion of wax can be
incorporated in this manneru This is unsuitable for
many exterior applications where larger amounts of
wax are needed to extend the duration of water
repellency.
Organic solvent-based coating compositions
have been developed which include a large proportion
of paraf~in wax and which provide coatings with the
foregoing properties of water repellency and
durability ~see U.S. Patent No. 4,450,247 which
issued on May 22, 1984 and which is assigned to
DeSoto, Inc., the assignee of this invention)~ Such
coating compositions include a solution of an alkyd
resin in mineral spirits.
But the use of large amounts o organic
solvents in such coating compositions leads to
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numerous environmental and other known disadvantages because of
the presence o-f a solvent. It is desirable to minimize these
disadvantages through the use of coatings which contain minimal
amounts of ~olatile organic solven-ts. Thus, a need e~ists for
aqueous coatings which substantially duplicate the water repel-
lency and the durability of -the patented solvent-based coatings.
In U.S. Patent No. 4,576,987, issued March 18, 1986
which is also assigned to DeSoto, Inc., we disclose aqueous, air
drying water-repeLlent latex coating composi-tions that include an
aqueous microcrystalline wax dispersion, an aqueous latex of
emulsion copolymerized monoethylenically unsaturated monomers and
an aqueous dispersion of an N-methylol -functional self-cross-
linking polyurethane.
The polyurethane component provides several functions,
one of which is to toughen the coating~ This is helpful when the
copolymerized unsaturated monomers are of the type that do not
readily dry in air to form hard films in the absence of a curing
agent. For example, certain polymers of monoethylenically un-
saturated monomers in aqueous emulsion do not coalesce adequately
at Low temperatures (less than about 20 degrees C) so when these
polymers are softened for adequate coalescence, they require the
presence of a curing agent -to provide the desired film hardness.
The use of such a curing agent, however, adds to the cost o~ the
coating composition, and it impairs the adhesion needed when
largely unpiymented coatings are used on decks.
~ t is desirable, therefore, to provide aqueous latex
coating compositions which dry under
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ambient conditions to form durable water-repellent
films and which include a large proportion of wax,
but which do not include substantial amounts of
organic solvents or curing agentsO These coating
compositions should coalesce below about 25 degrees C
and preferably below about 20 degrees C.
Moreover, and even when the copolymer has
sufficient hardness, it is desired to provide
improved adhesion and wear resistance for deck
application.
Disclosure of the Invention
. _
In accordance with this invention, an
aqueous latex coating composition includes a large
proportion of wax and dries in air under amhient
conditions to provide a continuous and durable
water-repellent film.
As used herein, the term '7ambient
conditionsl" refers to atmospheric pressure and
temperaturles in the range of at least about 0 degrees
C to about 30 degrees C. The wax of the present
coating composition slowly and progressively exudes
to the surace of the film to form a water-repellent
surface that persists for a long period of time;
i.e., at least for several months and, preferably
for several year~.
The term "water--repellent" as used herein,
indicates a hydrophobic film which causes water to
bead on the surface of the film without penetrating
the film. The terms "water-resistant" and l'water
resistance", on the other hand, indicate a film that
does not readily degrade or deteriorate in the
presence of water~ but the film does not necessarily
repel water. Most coatings are water resistant to
some degree, few coatings are water repellent.
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The coating composition consists essentially of (1) from
about S percent to about 50 percent, preferably from 15 percent to
40 percent, by weight of an aqueous wax dispersion lncluding a
petroleum wax, a polyethylene was and a surfactant; and (2~ from
bout 50 percent to about 95 percent, preferably from 60 percen~ to
85 percent, by weight of an aqueous latex of emulsion
copolymeri~ed monoethylenically unsaturated monomers.
Thus, according to one aspect, the present invention
provides an aqueous coating composition which dries to provide a
continuous film from which a wax will slowly and progressively
exude to provide a water-repellent surface that confers long-term
water resi.stance consisting essentially of from about 5 percent to
about 50 percent of an aqueous wax dispersion including a
petroleum wax, a polyethylene wax and a surfactant; and from about
50 percent to about 95 percen~ of an aqueous latex of emulsion
copolymerized acrylic copolymer comprising monoethylenically
unsaturated monomers having a sufficiently low glass transition
temperature to coalesce on air drying, said proportions being by
weight of solids based on the total solids not including any
pigment which may be present.
As a feature of this invention, improved adhesion and
wear resistance are provlded by the inclu~ion o~ an aqueous
emulslon of an unsaturated oil or fatty acid thereof together with
a catalyst for the drying reaction, typlcally a cobalt
naphthenate. The proportion o~ this optional component may range
from 5 percent to 50 percent, preferably from 10 percent to 40
percent.
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The proportions disclosecl herein are by weight of sollds
based on the total weight of solids :Ln the composition not
including any pigment which may be present.
The aqueous latex of emulsion copolymerized
monoethylenically unsaturated monomers preferably have a
sufficiently low glass ~ransition temperature (Tg) to coalesce on
air drying and provide a durable film. In general, aqueous
emulsion copolymers having a (Tg) of from about 5 degrees C to
about 2~ degrees C are useful herein since these provide coatings
which are soft enough to air dry in A~he presence of little or no
organic solvent, and which are hard enough to be u~eful without
added curing agent.
Film formation from emulsions involves loss of water by
evaporation, followed by coalescence of the emulsifled polymer
particles to provide a continuous adherent film. There i5 a
minimum
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temperature for each polymer system below which
coalescence of the particles (or film formation) will
not take place. This temperature is related to the
"glass transition teMperature" (designated Tg) of the
S polymer. This is the point of transition between a
hard solid and a plastic or semi-fluid condition.
The Tg of a monomer is the glass transition
temperature of a homopolymer of the monomerO Such
values are commonly determined by differential
thermal analysis or by calculation from the monomers
and their preparation in a known manner.
Emulsion-containing coating compositions can
be applied at temperatures below the Tg of the
polymer, and it is usual, therefore, to include a
small proportion of a coalescing solvent in the
formulation. These solvents can be stirred into the
emulsion and dissolve in the polymer particles,
resulting in a softening of the polymer and a
momentary lowering of the Tg as the deposited coating
dries. This helps the polymer particles to coalesce
and produce a continuous film, whereupon the
coalescing solvent evaporates. Solvents used for
-this purpose include certain glycol esters and
ether-esters as will be described herein.
As indicated, the aqueous wax dispersion
comprises a blend of at least about 30 percent of a
petroleum wax ~preferably, a paraffin wax), at least
about 10 percent of a polyethylene wax and a
surfactant. Preferably, the aqueous wax dispersion
includes from about 40 percent to about 70 percent of
a paraffin wax, from about 15 percent to about 25
percent of a polyethylene wax and enough surfactant
to stabili~e the dispersion, usually at least about 5
percent. More preferably, the aqueous wax dispersion
inc~udes from about 50 percent to about 60 percent
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paraffin wax, about ~0 percent polyethylene wax and
a~ least about ~0 percent of a fatty acid salt
surfactant (wit~. ammonia or an alkali metal).
As indicated above, the foregoing
proportions are by weight of solids based on the
total ~eight of solids in the composition not
including any pigment which may be present.
Wax selection is more critical in the
present coating compositions than in the
solven~-based or the aqueous coatiny compositions
discussed above. Higher melting point waxes and
carnauba wax may be used as the petroleum wax; but,
as described herein, paraffin waxes are preferred.
Paraffin waxes generally contain about 14 different
stralght chain and branched hydrocarbons ranging from
~l~H38 to C32~66 and solidify between about
27 degrees C and about 70 degrees C (between about
80.5 degrees F and about 158 degrees F).
According to this invention, the preferred
2CI paraffin waxes have melting points in the range of
about 50 degrees C to about 70 degrees C, more
preferably from 55 degrees C to 65 degrees C, for
long-term durability of water-repellent properties,
however the melting point range is not critical~
The aqueous wax dispersion also includes a
polyethylene wax, which preferably has a number
average molecular weight greater than about 10,000.
In the aforementioned '247 patent, it was
necessary to stably incorporate the wax in an organic
solvent-based solutionJ But since little solvent is
used herein and since the waxes used are not
themselves water dispersible, the wax dispersion is
maintained with the aid of a surfactant.
The sur~actant, which is preferably anionic
or nonionic, provides a dispersion of fine particle
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size. If the surfactant i5 anionicl a defoaming
agent may be employed to reduce bubble formation. If
the surfactant is nonionic, a defoaming agent is
usually not required. The selection of a particular
surfactant, however, i5 not critical to the present
invention.
The most common types of anionic surfactants
are alkali metal salts of straight chain carboxylic
sulfonic acids of about 11 to about 17 carbon atoms.
Other types of compounds frequently used as anionic
surfactants are water-soluble salts of amines and
fatty acids (triethanolamine oleate); sulfated higher
alcohols (sodium lauryl sulfate); sulfonated
compounds (sulfonated castor oil) and aromatic
petroleum sulfonates.
Anionic surfactants that are useful herein
include sodium lauryl sulfate; sodium lauryl
sulfonate; sodium dodecyl benzene sulfonate; sodium
diisopropyl naphthalene sulfonate ~an aerosol
acrylaryl sulfonate surfactant that is commercially
available from American Cyanamid Co., Wayne, NJ under
the product name Aerosol OS may be used); and
disodium isodecyl sulfosuccinate, disodium alkyl
amidoethanol sulfosuccinate, and disodium alkyl àmido
polyethoxy sul~osuccina~e (aerosol disodium monoester
sulfosuccinate surfactants available from Ameri~an~
Cyanamid Co. under the product names Aerosol A-~68,
Aerosol 413 and Aerosol 200, respectively, may be
used). Other suitable anionic surfactants include
Lutensit A-ES surfactant, which is commercially
available from BASF Corp., Holland, MI.
Particularly suitable surfactants include at
least one ammonium or alkali metal salt of a C10 to
C22 saturated or unsaturated carboxylic acid; for
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example, the sodium and potassium salts of myristic,
palmitoleic anA oleic acids.
Suitable nonionic surfactants include
ethoxylated nonyl lor dodecyl) phenols which, for
example, are commercially available from DeSoto,
Inc.~ Des Plaines, IL under the trade name Flo Mo 6N
~or Flo Mo 6D); polyethylene glycol ethers of
straight chain fatty alcohols including Arnox 1007
~~ which is available from the Arjay Chemical Division
of Magna Corp., Houston, TX~ and ethoxylated castor
oils including Chemax C0-30 which is available from
Chemax, Inc., Greenville, SC.
The aqueous emulsion of copolymerized
monoethylenically unsaturated monomers having a
sufficiently low glass transition temperature to
coalesce on air drying is subject to wide variation
because so many copolymers are known which are
broadly applicable. Acrylic copolymers which
comprise monoethylenically unsaturated monomers, at
21) least 50 percent of which are esters of acrylic acid
or methacrylic acid with a Cl to C8 alcohol, are
particularly contemplated, however, since these
copolymers are durable on exterior exposure.
Suitable monoethylenicaLly unsaturated
~5 monomers also include butyl acrylate, vinyl acetate,
methyl acrylate, ethyl acrylate, methyl methacrylate,
styrene, ~-ethyl hexylacrylate, vinyl toluene,
acrylonitrile, vinylidene chloride and the like.
Minor amounts, generally, less than about 5 percent
by weight (based on the weight of the emulsion) of
monomers having a functional group other than an
ethylenic group, for example, acrylic acid,
acrylamide, methylol acrylamlde, aminoacrylates, or
hydroxyethyl acrylates, and the like may also be
present.
* ~,~le n~a~k
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Preferably the monoethylenically unsaturated
monomers are selected so as to produce a copoly~er
having a glass ~ransition temperature (Tg) below
about room temperature so that the individual
copolymer particles, when applied on a selected
surface as a coating, will coalesce by ~hemselves to
provide a substantially continuous polymeric film
without the need to apply external heat.
The aqueous emulsion of copolymerized
monoethylenically unsaturated monomers may further
include an amount of a water immiscible organic
solvent sufficient to lower the Tg, and thus the
coalescing temperature~ of the copolymeri~ed monomers
to the desired value.
15When using higher glass transition
temperature emulsion polymers, especially those
having a Tg above 20 degrees C, water immiscible
organic soLvents a~e helpful as coalescing agents in
amounts of from lrrl5 percent based on the weight of
the emulsion. These water-immiscible solvents are
illustrated by ester alcohols like 2,2,4
trimethyltentanediol-1,3 monoisobutyrate, mineral
spirits, 2-phenoxy ethanol, methyl octyl ketone,
2-ethyl hexanol and aromatic hydrocarbon mixtures
such as Solvesso 150.
Any ethylenically unsaturated oil, or fatty
acid derived therefrom, may be used herein, including
drying oils, semi-drying oils, and the fatty acids
therein. These are illustrated by dehydrated castor
oil, linseed oil, linseed fatty acid and the like.
These oils are used as emulsions in water using
surfactants well known for the purpose, as
illustrated previously. The preferred surfactants
include polysorbitan esters, as is also well known.
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The drying catalysts may be any of those
customarily used to speed the oxidative drying of
unsaturated oilsO These are usually octoates or
naphthenates of metals, especially cobalt. The
catalyst is normally used in an amount of 0.01
percent to 2 percent of the weight of the oil.
While several aqueous components are
combined ~o form the present coating composition, all
proportions expressed herein are by weight based on
the solids content of the particular components,
except in the examples.
The composition may also include pigments,
preferably comprising finely divided silica in
admixture with a platy clay. The pigment masks any
observable blushing of the coating. Blushing is the
tendency of a coating to whiten or become opaque upon
exposure to moisture. Thickeners, such as
hydroxyethyl cellulose, may be employed to provide
the desired coating rheology. Preservatives may also
be present as well as defoamers to minimize foaming
as the various components are blended together. The
~se of such materials will be apparent to those
skilled in the art, but those materials are not
essential aspects of this invention. The foregoing
proportions do not include the weight of any pigment
(or thickener, preservative or defoamer~ that may be
present .
The specified combination o~ components
enables a large propor~ion o~ wax solids to be s~ably
incorporated into an aqueous medium which solidi~ies
on air drying to provide a continuous and durable
water-repellent film. The wax slowly and
progressively exudes to the surface of the coating
over a long period of time to provide the desired
long-term water resistance. Moreover, the mixture of
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paraffin wax and polyethylene wax with the aqueous
emulsion of copoly~erized monoethylenically
unsaturated monomers provides a durable film having
immediate water-repellent properties.
Preferred embodiments of the invention are
illustrated in the following Examples.
Examele 1
Component Pounds Gallons
water 120 12
hydroxyethyl cellulose 1.5 0.11
propyl mercuric
acetate preservative 2 0.15
tetrapotassium
pyrophosphate 1 0.04
defoaming agentl 3 0.33
platy clay2 10 0.42
finely divided silica 70 2.64
"
The above components are dispersed in a
Hockmeyer blender and then the following components
are added, one at a time:
Component Pounds Gallons
acrylic copolymer emulsion
at about 46 percent
solids4- 320 29.91
water 50 5.00
defoaming agent 2 0.22
aqueous wax dispersion
at about 39 percent
solids5- 80 8.00
water 220 22
premix the following and add
water 20 2.00
35 hydroxyethyl cellulose 1 0.07
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2,2,4 trimethyltentane-
diol-1,3 monoisobutyrate 10 1.00
1. Any water-dispersible defoaming agent suitable for
;~ 5 use in water-based coating compositions may be
used including Foamaster DF-122NS (Diamond
Shamrock Corp., Morristown, NJ)~ SAG Silicone
Antifoam 4220 (Union Carbide Corp., Danbury, CT)
and Albon 781 (Finetex, Inc., Elmwood Park, NJ).
2. Attapulgus clay ~Attagel 50, which is commercially
available from Engelhard Minerals ~ Chemical
Corp., Menlo Park, NJ) may be used.
3. Imsil A-15 ~commercially available from Illinois
Minerals Co., Cairo, IL) may be used.
4. An aqueous emulsion copolymer of methyl
methacrylate and ethyl acrylate in a weight ratio
of 2:1 cor.taining 1 percent by wei~ht of acrylic
acid. Rohm and Haas product AC-61 (Rohm and Haas
,! CO., Philadelphia, PA) may be used.
5. Miche~.ube 270 (Michelman Chemicals, ~nc.,
Cinncinati, OH) may be used.
The aqueous wax dispersion that was used
~ncluded about 38-39 percent non-volatile materials
based on the weight of the composition. The
dispersion had a nitrogen content of about 0.01
percent, an acid value of about 0.4 milligrams (mg)
potassium hydroxide per gram of sample, and an amine
value of about 0.2 milli-equivalents per gram of
sample.
The non-volatile materials of the wax
dispersion include about 56 percent paraf~in wax,
about 17 percent high molecular weight polyethylene
wax and, as surfactants, about 27 percent carboxylic
acid salts o~ myristic, palmitoleic and oleiç acids
by weight. The ~erm "hlgh molecular weight" is used
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in the accepted manner with reference to polyethylene
wax to indicate such waxes having number average
molecular weights greater than about 10,000.
A composition of the type described in the
S foregoing example may be appliecl to a wood surface/
such as an unsealed cedar board, to provide a clear
coa~ing which dries in air without heating and
provides a continuous film to protect the wood. Some
exudation o wax occurs shortly after drying as
indicated by the beading of water placed on the film;
and the exudation of wax continues with t imè to
provide long-term exterior durability as indicated by
wea~herometer testing and by exterior exposure. The
coating may be further pigmented, if desired, to
incorporate desired coloration.
From the standpoint of commercial practice,
the concentration of non-volatile solid materials in
the final composition is preferably from about 5
,! percent to about 40 percent. Also, the pigment can
be omitted or it can be used in a larger amount than
in the foregoing Example. Thus, this invention can
he practiced using a pigment to binder weight ratio
of from about 0 to about 1Ø
Example 2
25 Component Pounds
wate~ 120
hydroxyethyl cellulose 2
propyl mercuric
acetate preservative
30 tetrapotassium
pyrophosphate
defoaming agentl
platy clay2- 35
finely divided silica3- 100
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The above components are dispersed in a
Hockmeyer blender and then the following components
are added, one at a time:
Com~onent Pounds
,
premix the following and add
water 100
acrylic copolymer emulsion
at about 46 percent
solids4- . 256.8
10 premix the following and add
water 80
hydroxyethyl cellulose 4
2,2,4 trimethyltentane-
diol~l,3 m~noisobutyrate 7
15 continue to add one at a time
ethylene glycol 17 -
dioctyl sodium
sulfosuccinate 0.75
defoaming agent
20 linseed oil emulsion 90
cobalt naphthenate
(6 percent in mineral
spirits) 2
water lB0
25 aqueous wax di~persion
at about 39 percent
solids5- 100
The linseed oil emulsion used in the above
30 Example is as follows:
Component Pounds
linseed oil 744
sorbitan trioleate 6
sorbitan monolaurate 14
admix the above at high speed for 5 minutes and add
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water . 200
sorbitan trioleate
polysorbate 7
nonylphenoxy polyethanol
(HLB = 13~ 39
admix the above at high speed for lO minutes
cobalt naphthenate (6
percent in mineral spirits) lO
defoaming agent lO
wa~er lO0
This composition is similar to that provided
in Example 1, but the dried coatings possess greater
flexibility adhesion on horizontal surfaces. Better
freeze-thaw and wear resistance are also provided.
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