Note: Descriptions are shown in the official language in which they were submitted.
22749-307
~RUSH APPLIED ALKALI-BASED PAINT STRIPPING COMPOSITIONS
The present invention relates to brush applied
aLkali-based paint stripping compositions, in particular
caustic soda-basecl paint strippers.
Caustic soda-based paint strippers are extremely
eeEective in removing alkyd-based gloss paints. Such
strippers, however, have the disadvantage that in order to
exhibit their highest efficiency they must be applied thickly
to the painted surface to be treated. For this reason they are
usually formulated as pastes which can cling to the surEace to
be treated where, when thus disposed, they can proceed to
li~uify the paint carried by the surface. Unfortunately~ this
mode of action can give rise to a further disadvantage, namely
that unless the surLace is horizontal, liqui~ied paint,
together with water from the paste, can run from the surface
causing unsightly spillage, and perhaps damage if the liquid
which runs comes in contact with substrates such as carpets or
other furnishings.
In our earlier British Published Application
No. 2,069,522 published August 26, 1981 we have described and
claimed a spreadable aqueous paint stripper composition which
forms o~er the surface to be treated a peelable skin. That
earlier paint stripper composition, like other more conven-
tional caustic soda paint strippers, is most suitably applied
using a
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trowel, spatula or other similar tool, beca~se the
applied layer must be relatively thick. As part of the
skin-forming promoter components used in the earlier
composition there may be employed gelling agents, of
which xanthan gums and synthetic clays are preferred.
Furthermore, in one embodiment the earlier compositions
employ a particular combination of gelling agents
cornprising a xanthan gum, preferablv Kelzan gurn, and a
synthetic clay, preferably Laponite. Such a
1~ composition, however, while it contains a mixture of
xanthan aum and svnthetic clav, also contains a
significant proportion of filler and/or fibrous
material, as can be seen from the sDecific Examples,
which always contain in excess of 30% by weight of
filler or at least 10% by weight of fibre where they
contain both xanthan gum and synthetic clay.
Furthermore, in this earlier composition the ratio of
Kelzan to Laponite is in the range of from :1 to 1:1.
We have now found sur?risingly that bv employinq a
mixture of gum and clav in which the ratio of clay to
gum exceeds 1:1 by weight, a gelled caustic soda- or
like alkali-based cornoosition can be provided which is
suitable for brush application, i.e it can be applied
more quickly, especiallv on large, flat areas, and which
in situ exhibits a su~ficiently high thixotropy to
adhere to vertical sur.aces without significant running.
The composition generally dries to a semi-peelable skin
which assists in the removal o~ liquified Daint and any
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running properties of the liquified paint are
considerably reduced.
Accordingly, the present invention provides an
aqueous paint stripper composition suitable for brush
application, which composi-~ion comprises an al~ali in an
amount such that the composition is capable of stripping
alkyd-based gloss p-aint, together with a mixture of a
clay gelling aaent and a gum aellinq agent in aqueous
dispersion, the ratio of clay to gum being in excess of
ln 1:1 on a weight basis.
In the compositions of the invention, the alkali
is most conveniently an alkali metal hydroxide of which
s~dium and potassium hydroxide are preferred. The
alkali metal hvdroxides give a highly al`~aline
composition, and thev are readily available and are
cheap. Howev~r, it is possible to use other alkalis
having a pH in aaueous solution areate than about ln,
such as alkaline silicates, ~or example, sodium
metasilicate, and phosphates, for example, trisodium
phosphate. Other highly alkaline materials, pre~erably
with a pH greater than about 12 and more preferably with
a pH greater than ahout 13, are well known in the art
and could be used in the compositions of the invention,
but sodium hydroxide is generally most preferred for use
as the alkali, other compounds being more expensive and
milder or slower acting. If desired sodium hydroxide
may be provided bv usina a mixture o~ sodium car~onate
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and calcium hydroxide.
In some applications, such as where there may be a danger of
staining the surface under the pain-t, it may be desirable to select a milder
alkal:i, and in that case trisodium phosphate typically may be used.
The concentration of alkali iTI the composition will be selected
accordirlg to known criteria, and this selection is believed to be within
the competence oE the man skilled in the art. When sodium hydroxide is
employed it is possible to employ concentrations of up to about 25% by
weight or higher, but it is preferred to use no more than about 12% by
weight of sodium hydroxide or such other percentage as may be prescribed
in order to avoid restrictions in use resulting from regulations for
handling poisons. The lower concentration limit is determined by the paint
stripping task for which the composition is intended, and could be as
low as about 1% by weight or even lower. However, the usual concentration
range for sodium hydroxide is from about 3% to about 12% by weight, and
preferably from about 5% to about 12% by weight. Within those particular
ranges any specific concentration may be selected having regard to the
required speed o:E s-tripping, and the thickness of the paint layers to be
removccl .
~() When other alkalis are used the preferred concentration is judged
on a similar basis. Potassium hydroxide may be used at concentrations of
up to about 17% by weight or even at higher concentrations up to about 35%
by weight, with about 10 to about 17% by weight being preferred. On the
other hand, a typical concentration range for the alkaline salts mentioned
above is Erom about 30% to about ~0% by weight.
The compositions of the invention contain a mixture of at leas-t
two specific gelling agents comprising at least one gum and at least one
clay. The gum gelling agent generally will be a carbohydrate high polymer,
ancl pre:Eerably the gum is a xanthan gum, a high molecular weight natural
polysaccharide produced in a pure culture fermentation process by the
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microor~anism X~nthomonas campestris. One example o~ a commercially
available xantham gum is Kelzan ~Trade Mark), wllich is obtainable from
Kelco Inc., a division of ~erck and Co. Inc. Another, and more preferred,
examplo of a commorciall~ available xanthan gum is K9 C57, also available
~rom Kolco Inc.
In the compositions of the invention the clay may be any natural
or synthotic clay which provides a thickening effect, typically ~ clay
wllicll swells in the presence o~ water. Preferred clays are the synthetic
clays comprising one or more montmorillonite type materials such as ben-
tonite or hectorite.
Thus, especially preferred syn~hetic clays are:
1. Those sold as Laponite ~Trade Mark) clays, which are synthe-
tic hectorites and which comprise a magnesium silica-te containing lithium,
and Eluorine or hydroxide groups in a layered structure, and which are
available rom Laporte Industries Limited;
2. Those known as "specially produced" montmorillonito clays,
for example, that sold under the Trade Mark Bentone El~ and availnble from
Steetley Chemicals, and whicll is a magnesium montmorillonite ~hydrous
magnesium silicate); and
3. Combinations thereof.
rhe amount o~ gelling agent used is selected on the ~asis of
the thickness required ~or the composition having regard to the requirement
~or brush application and the properties of tlle particular gelling agent
used. Generally, the gelling agents will not be used in concentrations
in excess of about 10% by weight, wllile a convenient lower limit is about
0.5% by weight, based on the total weigllt of the composition. Preferably,
however, the gelling agents are employed in amowlts o~ ~rom about 2.0%
to about ~.0% by WCig]lt of clay and about 1.0% to about 2.0% by weight o~
gum, the ratio of clay to gum being in the rnnge o~ from about 5:1 to
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just above l:l.
Ihe compositions of the invention may also include other in-
~redients employed in pain-t stripping compositions such as wetting agents,
dycs, pigments and water-miscible organic solv~nts. All such additional
ingrcdicnts must of coursc be compatible with the other essential ingred-
iCI1ts, and in particular must be compati~le with the alkalinity of the
compositions, as well as being water-miscible. The selection of these
convel1tiol1al ingredients and suitable concentrations for them is believed
to bc withil1 tho competence of the man skilled in the ar~.
Preferably, where a pigment is employed, it is used in an amount
such tha-t the stripper, when applied at the thickness necessary ~o achieve
a desired stripping ef~ect, iust obscures the underlying paint layer.
In use the compositions of the invention are applied to a
painted surface usin~ a brush having alkali resistantsynthetic bristles,
e.g. of nylon or polypropylene - not animal bristle - typically as a plural-
ity of separately applied layers. The composition is then left until the
paint has been softened; typically this will be a period of from about l
to about 6 hours, although longer periods of contact may be desirable when
many coats of paint are to be removed.
2~ The layer of composition is then removed as a semi-peelable skin
using a scrapor, pallet knife or similar tool, although actual scraping
oE thc undorlying surfacc should no-t be necessary. The skin is liEted away
frolll tllo surfacc together with the softened paint, and complex shapes can
bc rca~ily stripped without having to scrape paint from every crevice.
1'hc compositions of the invention have been described above in
thoir ready-to-use Eorm. It is to be understood, however, that the com-
positions of the invention may be produced for distribution and sale in
dry powder form. Accordingly, the present invention in anotl1er aspect
providos a composition in dry powder form which when mixed with water can
form a spreadable aqueous paint stripper composition as describe~ herein.
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The dry powder composition may be the same as the spreadable
aqueous composition, except for the inclusion of water. However, since at
least some of the alkali materials described above may not be conveniently
harldled in dry form, it may be preferred to formulate the dry composition
wi~h a Illixture of calcium hydroxide (lime) and an alkali metal salt, the
an:ion ot which forms an insoluble salt with calcium. The ingredients of
such a mixture when mixed with water provide an alkali metal hydroxide e.g.
sodium hydroxide, but when in dry -Eorm are more easily handled than the
corresponding alkali metal hydroxide.
Preferably, the alkali metal salt and the calcium hydroxide are
employed in substantially stoichiometric amounts, the percentage of each in
the dry composition being such as to provide a corresponding percentage of
alkali metal hydroxide in accordance with the above description, preferably
about 5 to about 12% by weight of hydroxide.
Preferably the dry powder composition includes a mixture of
lime and sodium carbonate to provide sodium hydroxide when mixed with water.
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The following Examples illustrate compositions in
accordance with the invention and their use.
Example 1
A composition was prepared from the following
ingredients:
%w/w
Water 70.10
Caustic Soda 48~ w/w solution. 25.00
Laponite*S (Synthetic thickening clay) 3.25
K 9 C 57 (Development xanthan gum from
Relco Inc., U.S.A. supplied by
Alginate Industries Limited) 1.~5
100.00
A panel was prepared with ten cozts of commercial alkyd
gloss paint and aged for several months to allow the
paint to become mature. The above composi~ion was
applied using a polypropvlene brush to obtain a thick
layer. After ten minutes, a further layer was applied
above the flrst layér using a "cross hatch" technicue.
The panel was dis?osed with the coated surface
vertical and after two hours it was found that a
flexible dry coherent skin had formed which could easily
be removed intact with a pallet knife. During the two
hour period little or no "running" was observed from the
vertical panel, and when the ?anel was washed down with
a wet cloth it was found that all ten coats of paint had
been removed.
In addition it was Eound that the formulation was
*Trade Mark
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stable for prolonged periods and afforded an acceptable
shelf-life. Also, it not only possessed film-forming
properties but had sufficient thixotropy to remain in
place when coated on an inverted surface.
Example 2
A composition was prepared from the following
ingredients:
% w/w
Water 70.10
Caustic Soaa 48%
w~w solution 25.00
Bentsne* EW (Svnt~e~ic
thickeninq clay) 3.25
20 K 9 C 57 (xanthan gum~ 1.65
10 0 . o o
In use, results were obtained similar to those
described above Eor the composition of Example 1.
*'I'ra~l~ M~rk
