Note: Descriptions are shown in the official language in which they were submitted.
CA 02048297 1998-02-19
PENETRATING STAINS AND SEALANTS
FROM POLYURETHANE DISPERSIONS
Backqround of the Invention
Finishes which are useful on porous substrates such
as wood, concrete, cement, brick and the like typically fall
into two broad classifications: surface coatings and
penetrating finishes. Surface coatings can be very high
molecular weight, can be highly crosslinked, and
characteristically form a continuous film over the substrate.
Varnishes and polyurethane clearcoats are typically classified
as surface coatings.
Penetrating finishes, on the other hand, are
designed to protect a substrate, and typically change a
substrate's color, yet retain the natural textural appearance
of the substrate. Penetrating pigmented stains, non-pigmented
wood preservatives, and water sealants are typical examples of
penetrating finishes. One key attribute of penetrating
finishes is that they are designed so as not to form an
appreciable surface film or coating on the wood/substrate.
They are typically low in molecular weight and very small
particle size. They are durable, well suited for textured,
exposed surfaces such as siding, decks, steps and the like,
can contain water repellants, and are easily applied. The
ability to penetrate into the surface without leaving a
significant or appreciable film on the surface virtually
eliminates the peeling and cracking that varnishes and surface
coatings experience.
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Penetrating finishes can be further subdivided as
clear systems or colored systems. The clear systems typically
contain a water repellant. When applied to a wood or porous
substrate, these compositions serve to protect the substrate
from moisture. In addition to their protective
characteristics, the colored systems are designed to change
the color of the wood or porous surface without hiding the
grain or texture of the substrate.
This invention is directed to penetrating finishes,
particularly, penetrating stains and water sealants. In the
past, commercial architectural penetrating stains and water
sealants have been formulated from oil-based compositions.
Many commercially available wood stains still utilize pure
linseed oil. Oil-based compositions are relatively
inexpensive and provide good spreading characteristics.
However, such stains typically lack good abrasion resistance
and good drying characteristics. They are, furthermore,
typically very high in volatile organic compounds content
(VOC) .
With the advent of environmental laws and
regulations controlling the maximum amounts of VOC permitted
in paints, coatings, stains, sealants and the like, numerous
attempts have been made in the prior art to formulate
penetrating stains which comply with the VOC requirements.
For example, European Patent Application 0 314 378
A1 to Adkins discloses a waterborne alkyd deck stain
containing a medium-long oil length water-reducible alkyd
resin solubilized in water with the use of propylene glycol
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tertiary butyl ether as a coupling solvent. Adkins claims to
have low VOC, good resistance to water, durability to abrasion
and the like.
Likewise, U.S. Patent 4,276,329 to Vasishth et al.
discloses a composition for treating and protecting wood
surfaces comprising a low molecular weight alkyd resin in a
cosolvent of water and glycol ether.
U.S. Patent 4,432,797 to Vasishth et al. discloses a
water based thickened stain containing a film forming resin,
pigment, thickener and water. The resin is taught to be
either an alkyd, a water based acrylic or a water solution of
a modified poly-saccharide polymer.
UK Patent Application 2 215 732 A to Timperley
discloses a water based wood staining composition comprising a
water soluble acrylic resin and a pigment.
UK Patent 1 589 605 to Gorivaerk disclose a method
of preparing a penetrating wood stain of a suspension of
finely divided solids in an oil-in-water emulsion.
SUMr~ARY OF THE INVENTION
The present invention relates to low VOC,
penetrating compositions for staining and protecting porous
surfaces such as wood, concrete, cement, brick and the like.
In particular, this invention relates to stable dispersions of
polyurethane-ureas in water which are small particle size and
whlcn can penetrate into the surface to be coated. The
dispersions of this invention are particularly useful as
environmentally compliant penetrating stains and water
sealants.
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The present invention relates to low VOC stable,
small particle size dispersions of polyurethane-ureas in an
aqueous solvent which are especially suitable as penetrating
stains and water sealants. The dispersions of this invention
have excellent abrasion resistance, shelf stability,
penetration into porous surfaces and W light stability.
These dispersions are particularly suited for use, either
alone or with additional ingredients such as pigments, waxes
and the like, as penetrating stains and water sealants. The
polyurethane-ureas of this invention are predominantly linear
molecules, having relatively no cross-linking, and are very
low in molecular weight. The compositions of this invention
are different from surface coatings and paints in that they do
not form an appreciable film when applied over a porous
substrate such as wood, concrete, cement, brick and the like.
DETAILED DESCRIPTION OF THE INVENTION
The compositions of this invention are penetrating
stains and water sealants which comprise low VOC, stable
dispersions of small particle size polyurethane-ureas in an
aqueous media. Preferably, the particle size of the
polyurethane-urea molecules is less than about 0.2 micron, and
most preferably in the range of about 0.01 to about 0.1
micron. The polyurethane-ureas are predominantly linear
molecules and are low in molecular weight. Prior to
dispersion in water, the polyurethane-urea intermediates have
a weight average molecular weight generally less than about
10,000. When dispersed in an aqueous media, the polyurethane-
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ureas have a theoretical free isocyanate functionality of zero
and a weight average molecular weight generally less than
about 50,000. Additionally, due to the low molecular weight
and linear character of the molecules, the dispersions have
lower viscosities, and thus, can be formulated to higher
solids levels using less solvents.
The compositions of this invention are produced by
first reacting at least one diol, preferably selected from the
group consisting of diols such as
1) polyester diols formed from the reaction of
saturated and unsaturated polyhydric alcohols such
as ethylene glycol, propylene glycol, neopentyl
glycol, 1,4-butanediol, 1,4-butenediol, 1,6-
hexanediol, furan dimethanol, and cyclohexane
dimethanol, with saturated and unsaturated
polycarboxylic acids and derivatives thereof such as
maleic acid, fumaric acid, itaconic acid, succinic
acid, glutaric acid, adipic acid, isophthalic acid,
terephthalic acid, phthalic anhydride, dimethyl
terephthalate, dimer acids and the like;
2) polyesters formed by the reaction of lactones, such
as caprolactone, with a diol;
3) polyether diols such as the products of
the polymerization of a cyclic oxide such
as ethylene oxide, propylene oxide or
tetrahydrofuran;
4) polyether diols formed by the addition of
one or more cyclic oxides to water,
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ethylene glycol, propylene glycol,
diethylene glycol, cyclohexane dimethanol,
glycerol, or Bisphenol A;
5) polycarbonate diols such as the reaction
product of 1,3-propanediol, 1,4-
butanediol, 1,6-hexanediol, diethylene
glycol or tetraethylene glycol with diaryl
carbonates such as diphenyl carbonate or
phosgene;
6) polyacetal diols such as the reaction
product of a glycol such as diethylene
glycol, triethylene glycol or hexanediol
with formaldehyde;
7) low molecular weight diols such as
dihydroxyalkanoic acids including
dimethylolpropionic acid;
and mixtures thereof, with at least one aromatic,
cycloaliphatic or aliphatic diisocyanate-functional
ingredient, preferably selected from the group consisting of
tetramethylene diisocyanate, hexamethylene diisocyanate, 2,4-
toluene diisocyanate, 2,6-toluene diisocyanate, 4,4-
diphenylmethane diisocyanate, isophorone diisocyanates,
Desmodur WTM (a 4,4'-dicyclohexylmethane diisocyanate
available from Mobay), benzene 1,3-bis (1-iso-cyanato-1-
methylethyl)[m-TMXDI], and mixtures thereof.
Optionally, and preferably present during the
reaction is up to about 0.06%, preferably between about 0.01~
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and about 0.04% (by weight based upon total solids of diol and
diisocyanate) of a catalyst such as di-butyl tin dilaurate,
tin octoate and the like.
The preferred ratio of diol to diisocyanate should
be such that there is an excess of isocyanate functionality
over hydroxy functionality. Preferably, the ratio of
equivalents of NCO to OH should be between about 1.01:1 to
about 1.5:1; preferably between about 1.01:1 to a~out 1.3:1.
To ensure that the polyurethane-urea intermediate is
dispersible in an aqueous media, it is essential that a
percentage of the total polymer weight solids, preferably
between about 1% and about 10%, is contributed by diols,
amines and/or epoxies having the ability to contribute ionic
or hydrophilic groups to the polyurethane-urea. For example,
diols, amines and/or epoxies containing carboxylic acid
groups, sulfonic acid groups, phosphoric acid groups, ammonium
salts, phosphonium salts or sulfonium salts.
The reaction is typically carried out by charging
the diol with the catalyst to a reaction vessel, heating the
contents to a temperature of between about 70~C and about
100~C, and adding, via continuous or stepwise addition over a
period of time, preferably between about 1/2 hour to about 4
hours, the diisocyanate-functional materials. Optionally
present can be a solvent such as n-methyl pyrolidinone,
dimethyl formamide, methyl ethyl ketone, toluene, and mixtures
thereof in an amount ranging up to about 20% by weight based
upon the total weight of the materials present in the reaction
vessel. After complete addition of the diisocyanate
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materials, the reaction vessel temperature is maintained
between about 80~ and 100~C for so long as necessary to bring
the residual isocyanate percentage (based upon the total
solids weight of the polymer) below about 3.0%, preferably
into a range between about 1.6% to about 2.4%. This takes
approximately 2 to 4 hours. Residual isocyanate percentage
can be measured by any means well known in the art. The
contents are then cooled to below about 70~C and the ionic
groups present in the product of the above reaction are then
neutralized by the addition of a weak base, such as
triethylamine, trimethylamine, triisopropyl amine, tributyl
amine, triethylene diamine (e.g. DABCO , commercially
avallable from Air Products Co.), N,N-dimethyl-cyclohexyl
amine, N,N-dimethylstearyl amine, N,N-dimethyl aniline, N-
methylmorpholine, N-ethylmorpholine, N-methylpiperazine, N-
methylpyrolidine, N-methylpiperidine, N,N-dimethyl-ethanol
amine, N,N-diethyl-ethanol amine, triethanol amine, N-
methyldiethanol amine, dimethylaminopropanol, 2-
methoxyethyldimethyl amine, N-hydroxyethylpiperazine, 2-(2-
dimethylaminoethoxy)-ethanol and 5-diethylamino-2-pentanone
and mixtures thereof. Most preferred neutralization agents
are the tertiary amines as they are not reactive with the free
isocyanate groups. The amount of weak base added should be
sufficient to neutralize at least about 80% of the ionic
grGupS present in solution. Preferably, the weak base is
added in an amount sufficient to neutralize 100% of the ionic
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groups. The weak base can be added in excess, that is, an
amount greater than that necessary to neutralize the ionic
groups.
The intermediate at this point has a weight average
molecular weight less than about 10,000 and, due to the di-
functional character of both the diols and the diisocyanates,
has predominantly linear molecules.
The intermediate is then dispersed in water, or an
aqueous based solvent. The percentage of solids in the water
or aqueous solvent can range from between about 20% by weight
to about 60% by weight, preferably between about 30% to 50% by
weight.
A disfunctional amine compound such as ethylene
diamine, propylene diamine, butylene diamine, hexamethylene
diamine, cyclohexylene diamine, piperazine, hydrazine,
mixtures thereof, equivalents thereof and the like in an
amount sufficient to react with up to about 80% of the
theoretical amount of residual NCO functionality can
optionally be included in the dispersing media for chain
extension of the polyurethane. Amounts of chain extender
higher than this tend to create dispersions having molecular
weights which are unacceptably high for use as penetrating
stains and water sealants on porous substrates. Chain
extenders having a functionality greater than two should not
be included in any appreciable amount due to their tendency to
cause unacceptably high levels of branching, whereby the
composition then acts as a film-forming polymer rather than a
penetrating composition when applied to wood or another porous
substrate.
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Preferably, all hydroxy-functional ingredients are
exclusively di-functional. A minor amount of the total number
of OH equivalents can be contributed by higher-functional
alcohols; however, an appreciable percentage of such alcohols
is not desired as this results in an intermediate, and thus a
final polymer, which exhibits high molecular weight and
extensive branching. The most preferred hydroxy-functional
starting materials are a combination of 1) the polyester diols
formed from the reaction of saturated and unsaturated dihydric
alcohols such as ethylene glycol, propylene glycol, neopentyl
glycol, 1,4-butanediol, 1,4-butenediol, 1,6-hexanediol, furan
dimethanol, and cyclohexane dimethanol with saturated and
unsaturated polycarboxylic acids such as maleic acid, fumaric
acid, itaconic acid, succinic acid, glutaric acid, adipic
acid, isophthalic acid, terephthalic acid, phthalic anhydride,
dimethyl terephthalate, dimer acids and the like; and 2) a
diol containing hydrophilic groups. One such preferred
polyester diol is RucoflexTM 1015-120 (a mixture of polyester
diols based on neopentyl glycol, hexanediol and adipic acid,
commercially available from Ruco Polymer Corporation). A
particularly preferred diol containing hydrophilic groups is
dimethylolpropionic acid. When used, these two diols are
preferably present in percentages such that the Rucoflex
material contributes between about 40% to about 70% of the OH
functionality of the total materials.
The isocyanate-functional materials are most
preferably exclusively diisocyanates selected from the group
consisting of Desmodur WTM (4,4~-dicyclohexylmethane
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diisocyanate), m-TMXDI (benzene 1,3-bis (l-isocyanato-l-
methylethyl)), IPDI (isophorone diisocyanates) and mixtures
thereof. Most preferred is a combination of Desmodur WTM and
m-TMXDI.
As with the alcohols, a minor percentage of the
isocyanate-functional materials can have a functionality
greater than two, however, for the same reasons, an
appreciable percentage of such isocyanate ingredients is not
acceptable due to the effect on molecular weight and chain
branching of both the intermediate and the final product.
When a mixture of two or more diisocyanates is used, the ratio
of NCO equivalents contributed by the individual isocyanates
is not critical.
The dispersing media is preferably water. Preferred
is water with a small percentage of diamine present or added
for chain extension with the residual NCO. The amount of
dispersing media should be between about 40% and about 80% by
weight of total reaction ingredients. More preferably, the
percentage of dispersing media is between about 50% and 80% by
weight. When a chain extension agent is used, it should
preferably be present or added in an amount sufficient to
react with up to about 80% of the residual NCO functionality.
The final, chain-extended dispersion, should have a weight
average molecular weight less than about 50,000.
Once dispersed into the dispersing media, the
composition can be modified with other standard ingredients
commonly used to formulate penetrating stains, wood
preservatives and water sealants. For example, the
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dispersions of this invention can be combined with other
ingredients such as pigments, colorants, paraffins, waxes, W
light stabilizers, rheology modifiers, mildewcides, biocides,
fungicides, and other conventional additives to form excellent
penetrating stains, preservatives and/or sealants for wood,
concrete, cement, brick and other porous architectural
surfaces. Colorants and pigment dispersions, when used, are
typically added in amounts up to about 15~ by volume of the
total composition. Paraffin and ethylene waxes, used to
impart water resistance to penetrating finishes, when used,
are typically added in amounts up to about 2-3% by weight of
the total composition.
It is highly preferred that a surface tension
modifying ingredient be added to the composition to lower the
surface tension of the carrier. It has been found that it is
preferred to add such a surface tension modifying ingredient
as this enables the composition to more easily penetrate into
the porous substrate to which it is applied. Suitable
solvents for use as surface tension modifying ingredients
include the 2,2,4-tri-methyl-alkyl diol monoisobutyrate
solvents available from Eastman Chemical marketed under the
TexanolTM brand name, glycols such as ethylene glycol,
propylene glycol, dipropylene glycol, and the like, glycol
ethers such as 2-butoxy ethanol (Butyl CellosolveTM),
diethylene glycol monobutyl ether (Butyl CarbitolTM), and the
like, and alcohols such as methanol, ethanol, propanol and the
like; and mixtures thereof. Generally, the surface tension
modifying agent should be included in an amount sufficient to
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lower the surface tension of the carrier to a level where the
composition will achieve the desired penetration into the
porous substrate. Typically, the amount of surface tension
modifying agent required is from between about 0.25% to about
5.0~ by volume based upon the total volume of the composition.
However, it should be appreciated that many standard stain and
sealant additives are commercially available in a media which
imparts some surface tension modifying activity. In
particular, it should be appreciated that many commercially
available rheology modifiers are sold in glycol and glycol
ether media. The media may contribute some surface tension
modifying properties. For example, the RheolateTM materials
are commercially available in a butyl carbitol media.
Additionally, some mildewcides and fungicides are commercially
available in petroleum distillate media. These media
additionally may impart some surface tension modifying
characteristics. In general, media which would be expected
to impart surface tension modifying activity and which are
present in an appreciable amount should be included when
calculating the total percentage of surface tension modifying
agents.
The following examples demonstrate the methods of
preparation of the penetrating finishes of this invention.
The examples are intended to be representative of the
formulations which can be made and are not intended to limit
the scope of the invention.
EXAMPLE I--PREPARATION OF THE DISPERSION
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2048~9~
Charge 112.2g of n-methyl pyrolldlnone, 591.96g of
Rucoflex 1015-120 (1.3 eq of OH), 69.74g of
dlmethylolproplonlc acld (1.04 eq of OH) and 1.6g of dlbutyl
tln dllaurate (10% solutlon ln n-methyl pyrolidinone) to a
reactlon vessel equlpped with a nltrogen blanket. Begin
stirrlng and lncrease temperature to about 80O~. Begln a two
hour addition of 161;6g of Desmodur W (1.23 eq of NCO) and
188.03g of m-TMXDI (1.54 eq of NCO). After addition of all
lsocyanate-functlonal materlals, hold the reactlon at 80~C
for approxlmately 3 hours. Add 63.02g of triethylamine to
neutralize the ionlc groups and hold the reaction for another
1/2 hour. Disperse the resultant materlal lnto 1,500g of
water and add 10.4g of ethylene dlamlne.
Disperslons prepared accordlng to the above
generally have the followlng characteristlcs:
Molecular welght <50,000 (wt. ave)
Partlcle Slze: <0.1 mlcron
EXAMPLE II--WOOD STAIN
The followlng represents a typlcal penetratlng
staln compositlon using the polyurethane-urea dlsperslon of
Example I to whlch standard commercially avallable tintlng
colorants and plgment dlsperslons may be added.
Water 610.20 g
Dispersion of Example I 170.80
Texanol* 15.84
Troysan Mlldew-/Funglclde 10.50
Magneslum Slllcate (Flaky) 10.00
Rheolate* 255 Thlckener 9.00
Mlchemlube* 511 Wax 7.00
Rheolate* 278 Thlckener 3.00
Tlnuvln* UV Absorber 3.00
*Trade-mark
14
A 62795-1g0
~o~ 8~ q ~
Mln-u-gel* 440 Attapulglte Clay2.00
Anlonlc Surfactant 1.00
pH buffer 1.00
Proxcel* Bioclde 0.40
Defoamer 0.40
844.14 g
EXAMPLE III--WATER SEALANT
The followlng represents a typlcal, non-plgmented,
water sealant composltlon uslng the polyurethane-urea
dlsperslon of Example I.
Water 614.11 g
Dlsperslon of Example I 205.87
2-butoxy ethanol 16.68
Mlchemlube* 511 Wax 4.00
2-amlno-2-methyl-1-
propanol (pH buffer) 2.00
Dow Versene* 100 1.00
843.66 g
In preparlng the above water sealant, lt ls hlghly preferred
to render lnactlve metalllc lons whlch might be present in
the water and would tend to precipltate out of solution upon
addltlon of the surface tenslon modlfying agent.
*Trade-mark
62795-190
