Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
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CEMENT pAtNT
THIS INnIENTICN relates, broadly, to a cement paint. More partic~llarly,
it relates to a water-bused cement paint; and it relates to a process for
formulating
the water-based cemeint paint.
. Accordinl~ to the .invention there is provided a water-based cement
paint, the paint bein;~ a p2~int which includes, as constituents thereof,
cement
particles and water, tile cement particles being uncured cement particles, the
paint
else including, as a constituent, ca(loidall~r-sized particles pf polymeric
material
capable of farming ~ sfiable colloid in water, the paint being fn the form of
a
1 ~ . homogeneous blend ~~;fi said constituents, the cemjnt particles forming
5 - ~O~o by
mass of the paint and the cotloidally~si~ed particles forming O,~S -
10°!o by mass of
tho paint.
it is a feature of the paint of the present invention that the paint can be
~0 formulated as a stabG;~ blend of its canstituent_S, in that the blend has
an extended
shelf life in the absen~;~e of air. By stable is meant not only that the blend
has seed
extended shelf-life in fibs absence Qf air, but also that It has little or no
tendency,
when sealed in a pair~'t can, to.separate quickly into its constituent parts,
and after
mixing by skirring In a .;saint can prior to case, will not require further
mixing far at least
~5 B4 minutes. By an e~~tended shelf fife is meant that tile palm, in th~
absence of air
(for example when corWined Err a sealed paint eon), will b~ usable for sevsral
months
AMENpED SHEET
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or more, requiring no more than stirring to provide it with acceptable
homogeneity
prior to use.
The uncured cement particles are capable of being cured, i.e. in this
context being capable in bulk of setting and hardening into a mass, by contact
with
water and are conveniently run-of-the-mill portland cement particles, which
may be of
white or grey portland cement, depending on the intended colour of the paint
and on
any pigment used in the paint. The ordinary particle size of uncured portland
cement
is suitable for the present invention; and the cement particles may form 10 -
30% by
mass of the paint, preferably 12 - 18% by mass of the paint.
The colloidally-sized polymeric particles will have a particle size in the
range 1 - 100nm and, as indicated above, will be capable of forming a stable
colloidal suspension in water. Suitable colloidally-sized particles may be
fibrous in
shape, being elongated and typically having a length at least several time
their
maximum transverse dimension. The colloidally-sized particles may be of a
material
selected from the group of polymeric materials consisting of sodium
carboxymethyl-
cellulose, hydroxyethyl-cellulose, carboxymethyl-cellulose, polyvinyl-alcohol
and
mixtures thereof. Preferably the colloidally-sized polymeric particles are of
sodium
carboxymethyl -cellulose. The polymeric particles may form 1 - 6% by mass of
the
paint, preferably 1.5 - 3% by mass of the paint.
In a particular embodiment of the invention, the cement particles may
be run-of-the-mill portland cement particles, the cement particles forming 10 -
30% by
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mass of the paint and the colloidally-sized particles forming 1 - 6% by mass
of the
paint. In a more preferred embodiment they form respectively 12 - 18% and 1.5 -
3% by mass. As indicated above, the cement particles may be grey portland
cement
particles, or, instead, the cement particles may be white portland cement
particles.
Without being bound by theory, the Applicant believes that the
colloidally-sized particles act by adhering in the paint blend to the surfaces
of the
cement particles, to form a sufficiently continuous coating thereon to protect
the
cement particles from water in the blend and to resist or prevent premature or
so-
called in-can curing of the cement in the blend. Too low a proportion of the
polymeric
particles is expected to result in premature or in-can curing of the cement,
while too
high a proportion can adversely affect early water resistance of the paint,
when it has
been applied to provide a painted layer on a substrate, and can also adversely
affect
curing of the cement in the layer on the substrate. Routine experimentation
will thus
be required to determine, as with the cement proportions, acceptable or
optimum
proportions of the polymeric particles in the paint.
As indicated above, the particles may be fibrous in shape, i.e. they may
have a shape which resembles that of fibres, so that they are indeed in the
form of
fibres; and a particularly preferred embodiment the polymeric material is
sodium
carboxymethyl cellulose.
The paint may include a particulate elastomer. In particular, the
elastomer may be capable of curing on exposure to the atmosphere when forming
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part of a paint layer painted on a substrate, to provide the paint layer with
early or
short-term film strength, desirable flexibility and sheen, durability and ease
of
application. The elastomer is desirably also be capable of providing, when
cured,
resistance to water penetration through the layer into the substrate, the
resistance
lasting at least until the curing of the cement in the paint reaches a
sufficient stage to
take over from the elastomer in providing the paint layer with these
properties on a
long-term basis. Suitable elastomers may be selected from the group of
elastomeric
materials consisting of latex, synthetic rubber, styrene, butadiene and
mixtures
thereof, latex being preferred. When the elastomer is a latex, it may form 5 -
60% by
mass of the paint, preferably 20 - 50%. The averaqe particle size of the latex
may
be in the range 0.08 - 1 Nm, preferably 0.1 - 0.7pm, all the particles
conveniently
falling in these size ranges. As with the cement and colloidally-sized
polymeric
particles, routine experimentation can also be used to establish acceptable or
optimum proportions and particle sizes for the elastomer particles in the
paint blend.
The Applicant has successfully used both pure acrylic latexes and styrene-
acrylic
latexes.
Accordingly, the paint may include, as a constituent thereof, an uncured
particulate elastomer capable of curing upon exposure to the atmosphere. The
elastomer may, in particular, be a latex forming 5 - 60% by mass of the paint,
and
having an average particle size in the range 0.08 - 1 pm; and in a preferred
version
of the paint, the latex may form 20 - 50% by mass of the paint, the paint
having a
particle size in the range 0.1 - 0.7 Nm.
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Optionally, the paint includes a thickener. The thickener may be any
suitable commercially available thickener, used in appropriate or
manufacturer's
recommended proportions to obtain a desired degree of thickening of the paint
blend.
5 The Applicant has found that, in general, hydroxyalkyl-celluloses are
suitable for this
purpose, examples being hydroxyethyl-cellulose, methyl hydroxyethyl-
cellulose,
ethyl hydroxyethyl-cellulose, methyl hydroxypropyl-cellulose, or the like. The
thickener can desirably affect the application properties of the paint, can
inhibit
separation of constituents of the blend from one another in the can and
settling
therein of solids, and can generally provide good stability and extended shelf-
life. A
preferred version of the paint includes 0.1 - 0.6% by mass of a hydroxyalkyl-
cellulose
thickener.
Furthermore, the paint optionally includes a suitable pigment, to provide
it with a desired colour and/or opacity. While the proportion of pigment used
can vary
widely, a proportion of 1 - 15% by mass has been found to be suitable.
Inorganic
pigments such as oxides, in particular metal oxides, are preferred, as being
compatible with the cement in the paint, the pigments being typically present
in
proportions forming 2 - 10% by mass of the paint, preferably 3 - 5%, and
having an
average particle size of 0.05 - 100Nm, preferably 1 - 20pm, all the pigment
particles
conveniently falling in these size ranges. It follows that the paint may
include 1 -
15% by mass of a pigment; and in particular the pigment may be a particulate
inorganic pigment forming 2 - 10% by mass of the paint and having an average
particle size in the range 0.05 - 100 pm.
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The paint may include, as optional constituents, one or more suitable
in-can biocides, one or more dry-film fungicides and/or algicides, one or more
defoamers and one or more dispersants. Commercially available products may be
used for these purposes, in the usual proportions prescribed by the
manufacturers.
The Applicant has successfully used, as formaldehyde-releasing biocidal
agents, in-
can biocides selected from methyl-isothiazalone, chloromethyl-isothiazalone,
benzyl-
isothiazalone and suitable mixtures thereof. In paints, according to the
present
invention, the Applicant has used 0.1 - 0.3% by mass of said formaldehyde-
releasing
agents to resist microbiological attack on the colloidally-sized polymeric
particles in
the can, together with 0.05 - 1 %, preferably 0.5 - 1 %, by mass dry-film
fungicide
and/or algicide, and with 0.05 - 0.5%, preferably 0.1 - 0.4%, by mass defoamer
and
0.05 - 0.5% by mass dispersant.
As with the cement, polymeric material and elastomer, routine
experimentation can be employed, both for the selection of the various said
optional
constituents and for selection of their proportions in the paint, bearing in
mind both
technical and economic considerations, for optimum or at least acceptable
results.
Typically, once the proportions of all the constituents have been established,
water
will make up the balance.
To formulate the paint blend the colloidally-sized polymer particles may
be dispersed in water to form a colloidal suspension of the particles therein,
the
cement then being admixed into the colloidal suspension, followed optionally
by the
particulate elastomer. Conveniently, any in-can biocide, fungicide/algicide
and/or
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defiaamer used is adm :peed with the water or colloidal suspension prior to
the r"ement,
and any pigment, thickener andlor dispersant used 16 admixed with the outer
cpnstifuents, after addiihon of the elastomer to the cailvidal suspenslan. In
particular,
tho pigment, thicken~~~r andlor dispersant ' may' 'be dispars~d {dissolved
andlor w
suspended) in water b~"fore addition thereof to the blend of the other
c.~nstituents.
The inver~tian accordingly extends to a process for formulating a water-
based cement paint as defined above, the process including ~e steps of:
suspending the collaidally~si~ed polymer particles in water to form a
colloidal
suspension; arid
admixing the cn:ment particles with the colloidal suspension to form a palm
which is a blend of fhe waxen cement and colloidally-sized polymor particles.
h5 The process m~~y include the step of admixing the elagtom~~ particles with
the
water to form the collcuidal suspension, before the admixing of the cement
particles
with th~ suspension.
The varisous other Bald optional constituents may be admixed with th~
~0 water, polymer partfcl~~~s, cement particles and elastomer particles in any
desired or
convenient sequence.
The invention wil( now be described, by way ~of nan~llmiting illustrative
example, with referent~e to the following worked Examples:
i4MENDED ~WEE'C
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EXAMPLE 1
In an initial trial a batch comprising 182 kg (1780 of a colloidal
. suspension was prepared by admixing, into 160 water, 12 kg of colloidally-
sized cellulose fibres, 5 kg of in-can biocide, 5 kg of defoamer, and 10f of
acrylic latex available under the Trade Mark "REV 6115" from Revertex
Chemicals (Proprietary) Limited of 200 Lansdowne Road, Jacobs, Durban,
Republic of South Africa. The cellulose fibres were those available under the
Trade Mark "NORILOSE 6064" from Protea Chemicals Limited of 1 Berrange
Road, Wadeville, Gauteng, Republic of South Africa; the biocide was that
available under the Trade Mark "ROCIMA 623N" from (ACIMA) Servochem
(Proprietary) Limited of 8 Struwig Street, Jet Park, Republic of South Africa;
and the defoamer was that available under the Trade Mark "DEFOAMER-
AF306" from Servochem.
To 178 of the colloidal suspension was added 100 kg of ordinary white
portland cement available from Lafarge South Africa (Proprietary) Limited of
Century Club Estates, 21 Woodlands Drive, Woodmead, Gauteng, Republic of
South Africa to obtain about 270 kg of a blend of the cement and the colloidal
suspension.
To the cement-containing blend were added a further 230 of the "REV
6115" acrylic latex, to form a water-based cement paint according to the
invention.
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Finally, additional optional constituents were added to the paint, namely
100f water into which was admixed 30 kg of titanium dioxide pigment having a
particle size in the range 1 - 20pm to form a pigment suspension, together
with
1.6 kg of hydroxyethyl-cellulose available from Dow/Servochem under the
Trade Mark "CELLOSIZE QP52000" and 0.2 kg of dispersant available from
Rohm and Haas/Servochem under the Trade Mark "OROTAN N4000". This
made up a batch of paint having a mass of 617 - 631 kg and a volume of 570
- 580f.
To form the colloidal suspension the biocide, defoamer and cellulose
fibres were added slowly to the water with medium-speed stirring, the stirring
being continued for 10 minutes after the addition was complete. The
suspension was left' to digest without stirring for an hour, after which the
acrylic latex was added over 5 minutes with medium-speed stirring.
To obtain the cement-containing blend, the cement was added slowly to
the colloidal suspension with mixing by medium-speed stirring, after which the
mixing was continued for a further 10 minutes to obtain a paste, which was
left
to digest overnight.
The remaining acrylic latex was added, after the digestion overnight, to
the paste slowly with mixing by medium-speed stirring, which continued for 15
minutes after the addition was complete, to obtain the paint.
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The pigment suspension was made by adding the thickener slowly to
the water with medium-speed stirring, after which the stirring was continued
for 10 minutes. The pigment was then admixed into the water containing the
5 thickener over a period of 15 - 25 minutes with medium-speed stirring.
Finally, the pigment suspension was added to the paint with mixing
over a period of 5 minutes by means of medium-speed stirring to colour the
paint.
EXAMPLE 2
In a subsequent trial Example 1 was repeated except that the "REV 6115"
latex was replaced by the same mass of the latex available from Servochem
under the Trade Mark "PRIMAL SF-016"; and the white portland cement was
replace by the same mass of ordinary grey portland cement, also obtained
from Lafarge South Africa (Proprietary) Limited. The titanium dioxide pigment
was omitted, the batch sizes and volumes being reduced to 587 - 601 kg and
500 - 510 respectively.
GYennpi ~ ~
In another subsequent trial Example 1 was repeated except that the white
portland cement was replaced by the same mass of ordinary grey portland
cement from the same supplier; and the titanium dioxide pigment was
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replaced by the same mass of red iron (ferrous) oxide pigment of the same
particle size.
EXAMPLE 4
In a further subsequent trial Example 1 was repeated except that the
"NORILOSE 6064" cellulose fibres admixed into the 160 water were
increased from 12 kg to 18 kg; and the "REV 6115" latex was replaced by the
same mass of "PRIMAL SF-016" latex.
The initial trial of the present invention as illustrated by Example 1
showed substantial increases in in-can shelf-life, compared with a control
which had
the same composition except that it omitted the colloidally-sized cellulose
fibres, and
promised to render feasible provision of a water-based cement paint which is
in
single-pack form and can be stored for a substantial shelf-life of several
months or
more in a paint tin or paint can. Such paint would be useful for coating
substrates, in
particular cementitious substrates, for both waterproofing and colouring
purposes.
The subsequent trials detailed in Examples 2 - 4 provided paints which
lived up to the promise of Example 1 in that they embodied the advanges
promised
by Example 1, and exhibited (Examples 2 and 3), or promise to exhibit (Example
4)
said long shelf-lives. The paint can be used without frequent stirring after
the can
has been opened and cures rapidly by virtue of its acrylic latex content,
nevertheless
continuing to cure for long-term utility by virtue of its cement content. The
cement
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content also bonds with cement in cement-containing substrates to which the
paint is
often expected to be applied, the cement curing and bonding after application
thereof
to the substrate.
