Composition for stripping paints, varnishes or lacquers

This composition for stripping paints, varnishes or lacquers coating a substrate is characterized in that it consists of or comprises: PA1 (A) 1 to 100 parts by weight of a mixture (A1) of at least one aromatic solvent chosen from benzaldehyde, toluene, xylene and anisole and (A2) of benzoic acid; PA1 (B) 99 to 0 parts by weight of water; PA1 (A)+(B) representing in total 100 parts by weight. In particular, (A) consists of a commercial benzaldehyde which contains benzoic acid.

FIELD OF THE INVENTION 
The present invention relates to a composition for stripping paints, 
varnishes or lacquers coating a substrate. 
BACKGROUND OF THE INVENTION 
In the field of stripping paints, varnishes or lacquers, the current 
tendency is to develop efficient aqueous formulations using the least 
possible amount of solvent, in order to limit the effects on the 
environment. However, the aqueous formulations which are currently 
developed are relatively inefficient and, for this reason, none of them 
are mentioned in the Kirk-Othmer Encyclopaedia of Chemical Technology (4th 
edition, 1996, vol. 17). 
International patent application WO/07227 discloses the addition of water 
to solvent or to mixtures of solvents which are considered to be efficient 
paint strippers. That document describes compositions containing: 
(1) at least one organic solvent chosen from ethyl acetate, methyl ethyl 
ketone and toluene; 
(2) water; 
(3) at least one thickener, and 
(4) at least one surfactant. 
The efficacy of these composition is simply proportional to the amount of 
organic solvent used and, in any case, is lower than the efficacy of the 
pure solvent. This is true in particular for toluene, which is the solvent 
most capable of stripping paints out of the three mentioned. 
Moreover, in the case of fully solvent-laden formulations, it is common to 
use acidic or basic activators, (generally, less than 20% by weight of the 
total formulation). Among the acidic activators usually found are citric 
acid, formic acid and acetic acid. Formic acid is the most effective and 
the one most commonly used (Kirk-Othmer Encyclopaedia of Chemical 
Technology, 4th edition, 1996, vol. 17). However, this acid can cause 
serious burns and it is thus of prime importance to develop formulations 
activated with less corrosive acids. 
The aim of the present invention is to propose a composition for stripping 
paints, varnishes and lacquers which does not have the drawbacks of the 
prior art. 
SUMMARY OF THE INVENTION 
To this end, it has not been discovered, surprisingly, that benzoic acid, 
which has not been mentioned in the literature as an acidic activator, is 
highly efficient for this acid-activated function, provided that it is 
combined with an aromatic solvent, which can advantageously be commercial 
benzaldehyde, which already contains the abovementioned benzoic acid. 
Moreover, it has been discovered that the resulting stripping compositions 
can contain a large amount of water while at the same time, however, 
conserving high stripping efficiency. The reason for this is that 
advantageous synergism has been obtained between the water and commercial 
benzaldehyde, it being possible for the latter to be replaced by another 
aromatic solvent supplemented with benzoic acid. 
The subject of the present invention is thus, firstly, a composition for 
stripping paints, varnishes or lacquers coating a substrate, characterized 
in that it consists of or comprises: 
(A) 1 to 100 parts by weight of a mixture (A1) of at least one aromatic 
solvent chosen from benzaldehyde, toluene, xylene and anisole and (A2) of 
benzoic acid; 
(B) 99 to 0 parts by weight of water; 
(A)+(B) representing in total 100 parts by weight. 
In accordance with a first particularly advantageous embodiment of the 
composition according to the invention, (A) consists of commercial 
benzaldehyde which, in this case, already contains benzoic acid. (A) can 
then advantageously represent 5 to 10 parts by weight of (A)+(B). 
According to another embodiment, for all of the systems, the various 
components can, for example, be present in the following proportions: 
(A1) aromatic solvent(s): 30-70 parts by weight 
(A2) benzoic acid: 0.05-10 parts by weight 
(B) water: 30-70 parts by weight. 
To the Applicant Company's knowledge, benzaldehyde is not mentioned in the 
literature with regard to paint stripping. However, this solvent proved to 
be of high performance in paint stripping if it is not distilled and used 
under inert atmosphere. In this case, it always contains a variable 
proportion of benzoic acid. In commercial bottles, the level of benzoic 
acid remains equal to or less than 10% by weight, but, during the (air) 
stripping operation, this level, can rise considerably (it being possible 
for the air-oxidation to be catalysed by the film of paint). The inventors 
have frequently observed a benzoic acid salt during stripping with a 
formulation containing commercial benzaldehyde, and have thus discovered 
that the water/pure benzaldehyde/benzoic acid combination was particularly 
effective. One astute way of preparing the pure benzaldehyde/benzoic acid 
mixture is to use commercial benzaldehyde. This combination is of even 
higher performance than the water/toluene/benzoic acid combination and can 
comprise a majority of water. Commercial benzaldehyde is thus able to 
function both as a solvent and as an activator. 
The composition according to the invention can also contain at least one 
additive chosen from: 
activators, such as sodium benzoate and, when the aromatic solvent is 
benzaldehyde, toluene, in a proportion in particular of from 0.1 to 10 
parts by weight relative to (A)+(B) (as indicated below, the sodium 
benzoate also acts as a corrosion inhibitor); 
thickeners, such as cellulosic and acrylic thickeners, in a proportion in 
particular of from 0.1 to 10 parts by weight relative to (A)+(B); as an 
example of a cellulosic thickener, mention may be made of Methocell 311 
sold by the company Dow Chemical Co., whose production process is featured 
in American patent U.S. Pat. No. 3,388,082 entitled "hydroxypropyl methyl 
cellulose ethers"; 
corrosion inhibitors, such as monoethanolamine, sodium benzoate or citric 
acid, in a proportion in particular of from 0.1 to 10 parts by weight 
relative to (A)+(B); 
evaporation retardants, such as paraffin, in a proportion in particular of 
from 0.1 to 10 parts by weight relative to (A)+(B); and 
surfactants, such as nonionic surfactants, in a proportion in particular of 
from 0.1 to 10 parts by weight relative to (A)+(B); as examples of 
nonionic surfactants, mention may be made of the ethoxylated surfactants 
of the "Metox" series sold by the company "SEPPIC". 
The water and the aromatic solvent (preferably commercial benzaldehyde or 
toluene, for example) are immiscible. The result of this is to give a 
water/aromatic solvent emulsion. This emulsion is very unstable and 
separation of the two phases is rapidly observed. In order to use this 
emulsion as it is, the mixture needs to be stirred vigorously. The 
emulsion can also be stabilized by adding a surfactant or a surfactant 
system. The stabilization can also be achieved by adding a thickener. 
The aqueous formulations described can be used for stripping by the general 
public (thickened formulations), professional building stripping 
(thickened formulations), industrial stripping (non-thickened 
formulations), and, lastly, aeronautical stripping (thickened 
formulations). These thickened or unthickened formulations can, as already 
indicated, contain an activator, an evaporation retardant or a corrosion 
inhibitor. 
The examples which follow will make it possible to obtain a clearer idea of 
the invention. All the proportions mentioned in the examples are parts by 
weight.

EXAMPLE 1 
Commercial benzaldehyde "B", containing 1% by weight of benzoic acid, or a 
70/30 water/commercial benzaldehyde mixture referred to hereinbelow as 
"70/30 W/B", was used as stripping composition. 
The stripping tests were carried out on a glycerophthalic paint applied on 
wood. When an old paint is involved, a high degree of crosslinking is 
present. Two disks of cotton impregnated with solvent are placed on the 
samples and covered with the lid of a Petri dish in order to limit 
evaporation. The stripping was continued for 24 hours and quantified by a 
grading system between 0 (no action) and 5 (stripping of all the layers of 
paint to leave the support naked). The conventions adopted for attributing 
the intermediate grades are given below: 
Grade 0=no action 
Grade 1=appearance of a few blisters 
Grade 2=formation of a few flakes 
Grade 3=removal of the first layers with formation of flakes 
Grade 4=removal of all the layers except the last 
Grade 5=support stripped naked by removal of all of the layers. 
Since water and benzaldehyde are immiscible, the water/benzaldehyde mixture 
is in the form of an emulsion. This very unstable emulsion is homogenized 
by drawing the mixture up from and squirting it back into the bottle 
several times before impregnating the cotton. 
TABLE 1 
______________________________________ 
Stripping power at 20.degree. C. of "B" and "W/B 
(70/30)" on a glycerophthalic paint applied 
on wood. 
Grade 
Time B W/B (70/30) 
______________________________________ 
5 min. 0 1 
10 min. 0 3 
15 min. 1 4 
20 min. 3 4 
25 min. 4 4 
30 min. 4 4 
1 h 5 5 
2 h 5 5 
24 h 5 5 
______________________________________ 
After one hour, "B" and "W/B (70/30)" have completely stripped the support 
naked. However, it is observed that formulation "W/B (70/30)" is faster 
than B. There is thus synergism between the water and the benzaldehyde, 
which is reflected on this glycerophthalic paint by an effect of 
acceleration to short times (less than 30 min.). 
EXAMPLE 2 
The stripping tests in this example were carried out on an epoxy paint 
applied by cataphoretic electroplating onto a phosphate-treated steel. Two 
disks of cotton impregnated with solvent were placed on the samples and 
covered with the lid of a Petri dish in order to limit evaporation. The 
stripping was carried out for 24 hours and quantified by a grading system 
between 0 (no action) and 5 (support stripped naked). The conventions 
adopted for assigning the intermediate grades are given below: 
Grade 0=no action 
Grade 1=20% of the surface is blistered 
Grade 2=40% of the surface is blistered 
Grade 3=60% of the surface is blistered 
Grade 4=80% of the surface is blistered 
Grade 5=total removal of the film of paint. 
The results obtained are given in Table 2 below: 
TABLE 2 
______________________________________ 
Stripping power at 20.degree. C. of "B" and "W/B 
(70/30)" on an epoxy paint applied to steel. 
(B = commercial benzaldehyde). 
Grade 
Time B W/B (70/30) 
______________________________________ 
10 min. 0 0 
20 min. 0 0 
30 min. 0 0 
1 h 0 0 
2 h 0 5 
4 h 0 5 
24 h 5 5 
______________________________________ 
The epoxy paint detaches from its support after 2 hours with the 
composition "W/B (70/30)". On the other hand, it takes 24 hours for the 
same effect to be achieved with "B". These results clearly show the 
superiority of the composition of "W/B" type and thus the synergism effect 
compared with "B". 
EXAMPLE 3 
In this example, the paint to be stripped and the stripping conditions are 
rigorously identical to those of Example 2. 
This example shows the effect of sodium benzoate as an activator on the 
composition of "W/B" type. The sodium benzoate was used in a proportion of 
1% by weight relative to the benzaldehyde. The results obtained are given 
in Table 3. 
TABLE 3 
______________________________________ 
Effect of sodium benzoate on the "W/B 
(70/30)" mixture for stripping an epoxy paint 
at T = 20.degree. C. B = commercial benzaldehyde. 
Grade 
W/B (70/30) + 
Time W/B (70/30) 
sodium benzoate 
______________________________________ 
1 h 0 2 
1 h 10 1 5 
1 h 20 2 5 
1 h 30 3 5 
1 h 40 5 5 
______________________________________ 
It is observed that the effect of the sodium benzoate is to accelerate the 
stripping using the "W/B (70/30)" composition. 
EXAMPLE 4 
In this example, paints from the motor vehicle industry were used: 
glacier-white 389 polyester lacquers from Herberts, supplied by the 
company Etalon (France). The thickness of the coating is 35 to 45 .mu.m. 
The metal plates used are made of phosphate-treated steel and have a 
rectangular coated area of 90.times.190 mm. The performance levels on 
these plates are generally similar to other paints that are easier to 
strip than polyester paints, which is generally the case for 
glycerophthalic, alkyd and acrylic paints. The results are featured in 
Table 4. 
TABLE 4 
______________________________________ 
Stripping power at 20.degree. C. of "B", "W/B", and 
"W/B/T" (T = toluene) on a polyester paint. 
B = commercial benzaldehyde 
Formulation Stripping time in min. 
______________________________________ 
B 12 
W/B (50/50) 12 
W/B/T (50/45/5) 
7 
W/B (95/5) 10 
W/B/T (95/5/5) 
7 
______________________________________ 
The stripping power of "B" on this polyester paint is conserved even when 
it is diluted to 50% or 95% in water. Addition of 5% toluene to the dilute 
mixtures leads to a very marked improvement in their stripping power. This 
example shows the possibility of making mixtures which contain a lot of 
water and which are very effective (90% water and 10% solvent). 
Examples 3 and 4 thus show that sodium benzoate and toluene can be very 
good activators of W/B mixtures. 
EXAMPLE 5 
In this example, the paint to be stripped and the stripping conditions are 
rigorously identical to those of Example 4. 
This example shows the specificity of benzaldehyde to give excellent paint 
stripping performance. For this, small molecules (which are thus more 
capable of diffusing in the film of paint) and which contain the aldehyde 
function --CHO were tested. Molecules whose structure is very close to 
that of benzaldehyde were also tested. 
The results are given in Table 5. 
TABLE 5 
______________________________________ 
Stripping power at 20.degree. C. of molecules 
containing the aldehyde function on a 
polyester paint. 
Compound Stripping time 
______________________________________ 
Formaldehyde &gt;1 h 
Formamide &gt;1 h 
Methyl formate &gt;1 h 
4-Methoxybenzaldehyde &gt;1 h 
1,3,5-Trimethyl- &gt;1 h 
benzaldehyde 
Benzyl alcohol &gt;1 h 
Benzaldehyde 12 min. 
______________________________________ 
EXAMPLES 6 to 11 (of the Invention) and 12 Comparative) 
The paint to be stripped and the stripping conditions are rigorously 
identical to those of Example 4. The stripping compositions used are 
featured in Table 6, in which the following abbreviations have been used: 
W=water 
B=commercial benzaldehyde 
T=toluene 
X=xylene 
AN=anisole (methoxybenzene) 
BA=benzyl alcohol 
ba=benzoic acid 
The results obtained are also given in Table 6. 
TABLE 6 
______________________________________ 
Stripping power at 20.degree. C. of mixtures based on 
aromatic compounds supplemented with benzoic 
acid on a polyester paint 
Stripping time 
Example Composition in min. 
______________________________________ 
6 W/B (50/50) 12 
7 W/T/ba (50/45/5) 
13 
8 W/B (95/5) 10 
9 W/T/ba (90/5/5) 
40 
10 W/AN/ba (50/45/5) 
20 
11 W/X/ba (50/45/5) 
32 
12 W/BA/ba (50/45/5) 
700 
______________________________________ 
EXAMPLE 13 
The stripping test is identical to that of Example 4. It was carried out on 
a thickened on of the type: 
______________________________________ 
Water 50 
Anisole 40 
Commercial benzaldehyde 10 
Ethoxylated methyl ester fraction 
1 
comprising 20 ethylene oxide units, 
marketed by the company "SEPPIC" under 
the name "Metox 20 EO" 
Cellulosic thickener marketed by the 
1.3 
company "Dow Chemical Co." under the 
name "Methocell 311" 
______________________________________ 
This thickened, very stable formulation leads to a time of 18 min. on an 
Etalon polyester plate. 
The preceding examples can be repeated with similar success by substituting 
the generically or specifically described reactants and/or operating 
conditions of this invention for those used in the preceding examples. 
The entire disclosure of all applications, patents and publications, cited 
above and below, and of corresponding French application 96/15040, are 
hereby incorporated by reference. 
From the foregoing description, one skilled in the art can easily ascertain 
the essential characteristics of this invention, and without departing 
from the spirit and scope thereof, can make various changes and 
modifications of the invention to adapt it to various usages.