Process for the surface treatment of an article by sulphonation and neutralization

Process for the surface treatment of at least a part of an article comprising at least one surface essentially composed of a plastic, the said process comprising at least one sulphonation stage and at least one neutralization stage and being characterized in that the neutralization is carried out by bringing into contact with at least one polyamine compound.

FIELD OF THE INVENTION 
The present invention relates to a process for the surface treatment of an 
article by sulphonation and neutralization. 
TECHNOLOGY REVIEW 
Metals have been used for a long time for the manufacture of substantially 
impermeable articles such as pipes, films or containers, in particular 
bottles or tanks. Plastics nowadays offer many advantages in such 
applications, especially their ease of use, their lightness and their 
lower sensitivity to corrosion. Nevertheless, the majority of current 
plastics are not entirely impermeable to some organic substances and 
especially to some constituents present in fuels. In particular, the 
relative impermeability of commonly used plastics is very substantially 
affected by the incorporation in the fuels of one or a number of alcohols 
such as, for example, ethanol or methanol. In addition, statutory 
provisions regarding the tolerated emissions into the environment from 
fuel tanks are increasingly strict, due especially to environmental 
constraints. It is consequently advisable to be able to have available 
articles offering substantially increased impermeability, in particular to 
the abovementioned new fuels. 
The document (BE-740,763) mentions the treatment of a container 
superficially in order to improve its impermeability, by sulphonation in 
the presence of sulphur trioxide, followed by neutralization. 
Nevertheless, the impermeability offered by a container thus treated 
remains low with respect to the abovementioned requirements. 
It is also known to obtain improved results, according to the document 
JP-58-134,856, by sulphonation in the presence of sulphur trioxide and 
neutralization with ammonia, followed by treatment with an aqueous 
solution containing an alkaline-earth metal salt, in the case of 
containers made of plastic intended to contain a mixture of petrol and 
alcohol. Nevertheless, such a treatment is more complex and of less 
advantageous industrial use in that it requires an additional stage after 
sulphonation and neutralization. 
SUMMARY OF THE INVENTION 
The object of the present invention is consequently to make possible the 
manufacture, according to a simple process, of articles having a high 
impermeability, in particular to the abovementioned fuels. 
The invention relates, to this end, to a process for the surface treatment 
of at least a part of an article comprising at least one surface 
essentially composed of a plastic, the said process comprising at least 
one sulphonation stage and at least one neutralization stage and being 
characterized in that at least one neutralization stage is carried out by 
bringing into contact with at least one polyamine compound.

DETAILED DESCRIPTION OF THE INVENTION 
The articles concerned can be of any type, for example in the form of a 
film, panel, pipe or hollow body and the like. The invention is 
advantageous in the case of a hollow body. It is very particularly 
advantageous in the case of a fuel tank. It also advantageously applies to 
another hollow body, to a pipe or to another article associated with the 
operation of the fuel feed circuit of an engine intended in particular for 
equipping a motor vehicle. 
The plastic is a polymer plastic which is solid under the normal conditions 
of use of the article and which is sulphonatable, such as known in other 
respects. This plastic material can consist of one or a number of 
polymers. In general, use is made of one or a number of thermoplastic 
hydrocarbon polymers having a linear basic molecular structure in which 
the optional substituents are non-aromatic. These polymers can be 
homopolymers, copolymers or their mixtures. As examples of such polymers, 
it is possible to use, for example, polyolefins or vinyl chloride 
polymers. Good results have been obtained from a polyolefin, in particular 
from a polyethylene. Excellent results have been obtained from a high 
density polyethylene (HDPE). 
One or a number of conventional additives, such as antioxidants, 
stabilizers, pigments or others, can obviously be added to the plastic, 
insofar as they do not affect the ability of the article to be sulphonated 
nor substantially its properties, especially mechanical properties, for 
the purpose of its subsequent use. 
The targeted articles comprise at least one surface essentially composed of 
a plastic. They can be, in their entirety, essentially composed of a 
single plastic or comprise a surface essentially composed of a plastic 
and, moreover, one or a number of other plastics or one or a number of 
other materials. Thus, the article can comprise one or a number of other 
layers or one or a number of other parts made of one or a number of other 
materials. It is thus possible to use in particular according to the 
invention a multi-layer article in which only the surface layer to be 
treated is essentially composed of a plastic. In the case of a hollow 
body, the surface layer to be treated can be the internal or external 
layer. Preferably, the internal layer of the hollow body is treated. 
Excellent results have been obtained on articles in their entirety 
essentially composed of a single plastic. 
The process according to the invention can comprise one or a number of 
sulphonation stages. Preferably, it comprises a single sulphonation stage. 
The sulphonation stage is carried out in a conventional way and under 
conventional conditions for a person skilled in the art. The articles to 
be treated are brought into contact with sulphur trioxide, diluted in an 
inert compound, in the liquid or gaseous phase. A dry inert gas, such as 
for example nitrogen, carbon dioxide, sulphur dioxide or air, is 
preferably used. It is important to avoid the presence of water vapour 
which could lead, by reaction with sulphur trioxide, to the formation of 
droplets of sulphuric acid. In general, from 0.1 to 35% by volume of 
sulphur trioxide, preferably from 15 to 30%, is incorporated. The contact 
time is inversely proportional to the sulphur trioxide concentration. It 
can in general be from 0.1 to 20 minutes. The pressure and the temperature 
can be adapted, especially as a function of the other operating 
parameters. The reaction can, in particular, be carried out at ambient 
temperature and ambient pressure. 
Often, after sulphonation, the article or the container in which it is 
contained is purged from residual sulphur trioxide, for example with an 
inert gas such as nitrogen. It is also possible to neutralize the residual 
sulphur trioxide by a very brief injection of ammonia, of the order of a 
few seconds, in particular lasting less than 10 seconds. In the latter 
case, it is then preferable to rinse, most often with water, the article 
or the part of the article which will then be subjected to the 
neutralization stage. 
The process according to the invention can comprise one or a number of 
neutralization stages of all or part of the article. It preferably 
comprises a single neutralization stage of all or part of the article. 
The neutralization stage is carried out by bringing at least a part of the 
article which has to be superficially treated into contact with at least 
one polyamine compound. Polyamine compound is understood to denote an 
aliphatic compound comprising at least two amine functional groups. A 
polyalkylenepolyamine is advantageously used as polyamine compound. Among 
the polyalkylenepolyamines, good results have been obtained in particular 
with triethylenetetramine (TETA). An alkylenepolyamine can also be 
advantageously used as polyamine compound. Among the alkylenepolyamines, 
good results have been obtained with ethylenediamine (EDA). A 
polyalkyleneimine is also advantageously used as polyamine compound. Among 
the polyalkyleneimines, use may be made of homo- or copolymers which are 
unsubstituted, branched or linear, or substituted on the amine functional 
groups by alkyl or acyl groups. The molecular weight of these 
polyalkyleneimines can vary from 300 to 1 000 000. Excellent results have 
been obtained with a polyethyleneimine. 
It is possible to use one or a number of polyamine compounds. For example, 
it is possible to use a mixture of polyamine compounds, from one or a 
number of polyalkylenepolyamines, alkylenepolyamines and/or 
polyalkyleneimines. Such a mixture can especially make it possible to 
combine the advantages of the use of a number of polyalkyleneimines of 
substantially different molecular weights. Preferably, a polyalkyleneimine 
with a molecular weight greater than 500,000 is not used alone. 
Advantageously, a mixture of a number of polyethyleneimines is used. 
During the neutralization stage, the polyamine compound is generally 
present in a proportion of at least 0.05% by volume. It is preferably 
present in a proportion of at least 0.1% by volume and more preferentially 
still in a proportion of at least 1% by volume. The polyamine compound can 
be used pure or diluted. Advantageously, it is used diluted, in particular 
without exceeding 20% by volume and more particularly still without 
exceeding 10% by volume. 
The polyamine compound can especially be diluted in water. The article can 
be brought into contact with a neutralization solution in the liquid or 
gaseous form. In the case of a hollow body, It is simple to fill it with 
an aqueous neutralization solution in liquid form. This solution can in 
particular be used in the form of an atomized jet. 
The contact time for the neutralization stage can easily be optimized by a 
person skilled in the art from a few development tests, in connection with 
the other operating parameters. In practice, a short duration is 
sufficient. Good results have been obtained without having to exceed 5 
minutes. The said contact time is often at least 10 seconds and preferably 
at least 1 minute. 
The neutralization can be carried out within a wide temperature range, for 
example from 0.degree. to 100.degree. C., in particular when the polyamine 
compound is diluted in water. Good results have been obtained at ambient 
temperature. 
The pressure can also be adapted to the other operating parameters. Good 
results have been obtained at atmospheric pressure. 
After neutralization, the article is, if necessary, rinsed and/or dried, in 
order to remove therefrom the residual reaction products and 
neutralization agents. 
The process according to the invention makes possible the surface treatment 
of an article over a sufficient depth in order substantially to improve 
its impermeability. In practice, the treated depth is often of the order 
of 5 to 30 microns. Preferably, it is at least 10 microns. 
The surface treatment process according to the invention can advantageously 
be combined with the prior working of the constituent material(s) of the 
article. 
The invention consequently also relates to a process for the manufacture of 
an article comprising at least one surface essentially composed of a 
plastic, the said process comprising at least one working stage and one 
surface treatment as defined above. 
Working stage is understood to denote any known technique which can be used 
for the conversion of one or a number of materials and which makes it 
possible to produce an article. In the case of the working of one or a 
number of plastics, mention may be made, as non-limiting examples of 
working stage, of injection, extrusion, extrusion blow-moulding or 
calendering. In the specific case of a hollow body made of one or a number 
of plastics, it is preferable to carry out an extrusion blow-moulding as 
the working stage. 
It can prove to be advantageous for the working stage to be quickly, in 
particular immediately, followed by the surface treatment. 
Alternatively, the surface treatment can be carried out on the plastic from 
which at least one surface of the article will essentially be composed, 
even before the working stage, in particular on the polymer powder which 
has not yet been treated with additive. 
EXAMPLES 
Examples 1R and 6R which follow are given by way of comparison. 
Examples 2 to 5, 7 and 8 illustrate the invention in a non-limiting way. 
The permeability is expressed therein in g.mm/m.sup.2.d, i.e. in grams of 
fuel times millimeters of thickness of the article per square meter of 
surface area for exchange with the outside and per day. It is in fact 
logical to assess the permeability of an article proportionally to its 
thickness and inversely proportionally to the surface area for exchange 
with the outside which it possesses, rather than to refer to a 
permeability expressed solely in grams of fuel per day. In fact, such a 
measurement would not take into account the effect of scale well known to 
a person skilled in the art, for example in the case of a hollow body, 
between a bottle, with a reduced thickness and surface area, and a fuel 
tank, with a greater thickness and greater exchange surface area. 
Functioning permeability is understood to denote this property when it has 
become stable as a function of time. The time period necessary to arrive 
there is obviously related especially to the characteristics specific to 
the article and cannot be defined absolutely. By way of order of 
magnitude, it can, in particular, be estimated that the permeability of a 
bottle is functioning after approximately 1 month whereas approximately 3 
months are necessary to reach the same state in the case of a tank. 
EXAMPLE 1R 
A bottle made of high density polyethylene (HDPE), with an internal volume 
of 360 cm.sup.3, a thickness of 2 mm and an internal surface area of 280 
cm.sup.2, was produced by extrusion blow moulding. The HDPE used was of 
Phillips type with a mean density of 0.946 g/m.sup.3 and HLMI (High Load 
Melt Index measured according to the ASTM standard 1238-1987) of 5.4 to 
6.8 g/10 min and containing 1 g/kg of IRGANOX.RTM. 1076 stabilizer. 
The internal surface of this bottle was brought into contact by injection 
and maintained for 10 minutes at ambient temperature and at atmospheric 
pressure with a gas flow containing 15% by volume of sulphur trioxide 
diluted in nitrogen. 
The bottle was then purged with nitrogen for 5 minutes at ambient 
temperature and at atmospheric pressure. 
It was then filled at ambient temperature and at atmospheric pressure with 
200 cm.sup.3 of an aqueous solution containing 10% by volume of ammonia 
and then agitated for 5 minutes. 
The bottle was finally emptied, rinsed with water and dried in an oven at 
60.degree. C. overnight. 
Evaluation of the permeability of this bottle was carried out with a 
mixture containing 92.5% by volume of lead-free CEC RF 08-A-85 petrol with 
an octane number of 95, 5% by volume of methanol and 2.5% by volume of 
ethanol (mixture known in the United States under the name TF2=Test Fuel 
2). The bottle was filled with 300 cm.sup.3 of this mixture, stoppered, 
weighed and stored in a room at 40.degree. C. 
After 1 month, under functioning conditions, its permeability, measured by 
loss in weight according to ECE standard 34-1979 (Appendix 5), was 14.3 
g.mm/m.sup.2.d. 
By way of comparison, the same untreated bottle lost, under functioning 
conditions, 71 g.mm/m.sup.2.d. 
EXAMPLE 2 
A bottle identical to that according to Example 1R was treated in the same 
way, apart from the fact that the neutralization was carried out by 
filling the bottle with an aqueous solution containing 10% by volume of 
Lupasol.RTM. WF polyethyleneimine with a molecular weight equal to 20,000. 
After 1 month, under functioning conditions, its permeability, measured by 
loss in weight according to ECE standard 34-1979 (Appendix 5), was 1.43 
g.mm/m.sup.2.d. 
EXAMPLE 3 
A bottle identical to that according to Example 1R was treated in the same 
way as according to this example, apart from the fact that the 
neutralization was carried out by filling the bottle with pure 
ethylenediamine (Merck Index, 10th edition, 3741). 
After 1 month, under functioning conditions, its permeability, measured by 
loss in weight according to ECE standard 34-1979 (Appendix 5), was 2.85 
g.mm/m.sup.2.d. 
EXAMPLE 4 
A bottle identical to that according to Example 1R was treated in the same 
way as according to this example, apart from the fact that, for the 
neutralisation, the bottle was filled with an aqueous solution comprising 
10% by volume of triethylenetetramine (Merck Index, 10th edition, 9483). 
After 1 month, under functioning conditions, its permeability, measured by 
loss in weight according to ECE standard 34-1979 (Appendix 5), was 2.14 
g.mm/m.sup.2.d. 
EXAMPLE 5 
A bottle identical to that according to Example 1R was treated in the same 
way as according to this example, apart from the fact that, for the 
neutralization, the bottle was filled with an aqueous solution comprising 
10% by volume of a mixture of equal parts by volume of LUPASOL.RTM. WF 
polyethyleneimine (PEI) and ethylenediamine (EDA). 
After 1 month, under functioning conditions, its permeability, measured by 
loss in weight according to ECE standard 34-1979 (Appendix 5), was 1.43 
g.mm/m.sup.2.d. 
EXAMPLE 6R 
A fuel tank made of high density polyethylene (HDPE), with an internal 
volume of 60 liters, a mean thickness of 5 mm and an internal surface area 
of 15 m.sup.2, was produced by extrusion blow moulding. The HDPE used had 
a mean density of 0.948 g/cm.sup.3, an HLMI of 3.4 g/10 min and contained 
0.2 g/kg of carbon black and 2 g/kg of IRGANOX.RTM. B 225 stabilizer. 
The internal surface of this tank was brought into contact by injection and 
maintained for 2 minutes at 49.degree. C. and at atmospheric pressure with 
a gas flow containing 15% by volume of sulphur trioxide diluted in 
nitrogen. 
The tank was then purged with nitrogen for 2 minutes at ambient temperature 
and at atmospheric pressure. 
It was then filled at ambient temperature and at atmospheric pressure with 
a mixture comprising 70% by volume of ammonia and 15% by volume of air 
dampened with 15% by volume of water in the form of fine atomized droplets 
for 100 seconds. 
The tank was finally emptied, rinsed with water and dried in an oven at 
60.degree. C. overnight. 
Evaluation of the permeability of the tank was carried out with a mixture 
containing 90% by volume of lead-free CEC RF 08-A-85 petrol, with an 
octane number of 95, and 10% by volume of ethanol (mixture known in the 
United States under TF1=Test Fuel 1). The tank was filled with 30 liters 
of this mixture, stoppered, weighed and stored in a room at 40.degree. C. 
After 3 months, under functioning conditions, its permeability, measured by 
loss in weight according to ECE standard 34-1979 (Appendix 5), was 10 
g.mm/m.sup.2.d. 
The permeability of this tank was also evaluated according to the SHED 
measurement as described in "Measurement of fuel evaporative emission from 
gasoline powered passenger cars and light trucks, technical enclosure SAE 
J171, June 82". After 3 months, under functioning conditions, the 
permeability of the tank, measured according to this method, was 8.3 
g.mm/m.sup.2.d. 
EXAMPLE 7 
A fuel tank identical to that according to Example 6R was treated in the 
same way, apart from the fact that, for the neutralization, the tank was 
filled with 3 liters of an aqueous solution containing 5% by volume of 
LUPASOL.RTM. polyethyleneimine with a molecular weight of between 600,000 
and 1,000,000 and then agitated for 3 minutes. 
After 3 months, under functioning conditions, its permeability, measured by 
loss in weight according to ECE standard 34-1979 (Appendix 5), was 1 
g.mm/m.sup.2.d. 
At the same time, the permeability of the tank, measured according to the 
abovementioned SHED method, was 0.83 g.m./m.sup.2.d. 
EXAMPLE 8 
A fuel tank identical to that according to Example 6R was treated in the 
same way, apart from the fact that, for the neutralization, the tank was 
filled with 3 liters of an aqueous solution containing 5% by volume of a 
mixture containing equal parts of Lupasol.RTM. P polyethyleneimine with a 
molecular weight of between 600,000 and 1,000,000 and LUPASOL.RTM. G 
polyethyleneimine with a molecular weight of approximately 2,000 and then 
agitated for 3 minutes. 
After 3 months, under functioning conditions, the permeability of the tank, 
measured according to the abovementioned SHED method, was 0.67 
g.mm/m.sup.2.d.