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THE USE OF CHLORINATED SOLVENTS AS WASHING AGENTS IN THE METAL
AND STEEL INDUSTRIES, AND PARTICULARLY IN THE PRODUCTION OF BRASS
POINTS FOR WRITING INSTRUMENTS, WITH ASSOCIATED PROBLEMS
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Second Section
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Problems related to the use of chlorinated solvents in the production and utilisation of tips for ball-point pens.
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The first part of this document has provided a broad
illustration of metal degreasing methodologies and of the
problems that might arise in the utilisation of chlorinated
solvents.
This second part will analyse the practical implications of a
number of problems recently emerged in the production of refills.
At the beginning of 1993, talking to a solvent technician
working for a multinational company in the sector of chlorinated
solvent production, we learnt that two years ago approximately
all chlorinated solvent manufacturers had to give up the use of
stabilisers like 1,4-dioxan because of toxicological problems.
Such stabilisers were deemed highly toxic because of their very
dangerous vapours.
Moreover, dioxan is considered noxious to the mucous (eyes and
lungs) and is absorbed by the skin.
All the problems occurred in the production of refills all
over the world which caused a lot of troubles to both users and
manufacturers date back to that period, but only very recently an
explanation could be found.
All industrial sector using chlorinated solvents to degrease
metals ran into the same problems.
The identification of their cause was neither simple nor
immediate; solvent manufacturers did not have sufficient
information at their disposal and the problem was totally
unprecedented. Up to that moment REINOL had never encountered
problems in the use of inks for ball pens.
Several tests were carried out both internally and by external
laboratories to come to a correct data interpretation. They were
made necessary by the far-reaching implications of the issue and
by the difficulty in finding a solution.
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Analysis of the first anomalies occurred and search for the cause of writing blocking.
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The first complaints arrived in July 1991; a Korean customer
complained for the presence of defective refills: they usually
started to write, but after a while, the writing specimen became
irregular until it totally stops.
By insisting on moving them some refills started to write and
became gradually normal again.
The stop of writing into the refills is normally due to the
following reasons:
1) The ink thickens and increases viscosity.
To check this instance, our laboratory measured viscosity with
a computerised viscometer Haake Rotovisco Rv-20 equipped with a
PK5-1.0 probe.
Thanks to this equipment our laboratory is able to carry out
the analysis of ink viscosity even with a limited number of
refills.
The ink of these defective refills revealed value in
compliance with the warranted characteristics.
2) Ink crystallisation.
We analysed at the microscope a counter sample of ink sent
back by the customer, but no crystallisation was observed; the
ink on the slide was limpid and pure with no alteration.
3) Formation of a plug at the bottom of the tube due to a
wrong ink formulation or to an early ageing on ink itself.
All tests carried out excluded the possibility that ink might
have formed a dry plug at the bottom of the tube (in this case
the consistency of ink was always normal) and also excluded the
formation of corrosion in the tip shoulder area.
The latter observed at the microscope always appeared
perfectly clean and free from any oxidation (see picture n. 1).
In this respect it is worth remembering that raw materials
used in the production of inks are made of chemically pure
compounds and their formulas are by their very nature constant
and invariable; in the opposite case, their specific features
would be totally upset.
In the case of dyes, for instance, the substance colour
depends on the specific arrangement of atoms in the molecule.
All coloured organic substances are unsaturated compounds,
that reduced with hydrogen loose their colour.
A few cases will now be illustrated to better explain the
above-mentioned concepts:
In this case it was enough to change the arrangement of the
-NH group and the carbonyl group (>C=O) to completely modify
the characteristics of the product obtained (phtalic imide is
colourless whilst isatin is orange).
| Yellow |
Colourless |
Colourless |
To check the quality of the ink we replaced a number of
tip with new ones and then proceeded to the various ageing tests.
All refills treated this way could write normally.
The only unexplored instance left was ink flowing in the tip
internal duct and more specifically the ink close to the ball.
We carried out a new test in our laboratory, we removed the
ball and collected the ink on a slide for subsequent observation
at the microscope.
The ink turned out to be turbid, with unknown clotted
particles.
Our customer carried out a well-structured laboratory test
with the following results:
1) The ink analysed at the microscope was limpid.
2) The ink contained in refill tips had white insoluble
spots(see Annex A: Customer's "TEST REPORT").
Moreover, tips showed a corroded area on their outer wall as
it can easily be observed in pictures n. 2 and 3.
At the same time, when the first problems arose, our
laboratory sent some refills to SGS Laboratories Ecology
Department for a more accurate examination.
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SGS Ecology
Technical evaluation of possible metal enrichment of ink in
contact with brass parts.
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Since the defect (writing blocking) was believed to be due to
the presence of brass powder not totally extracted during
washing, zinc, copper and lead samples were taken from three
different areas in the refill.
Three samples were obtained:
- in direct contact with the ball
- in the bottom part of the tip
- in the polypropylene tube at 5-6 cm. from the tip.
The latter was considered the reference sample since it does
not come into contact with the metal parts of the refill itself.
The different samples obtained were mineralised with an acid
mixture (HCl -HNO3) and a hot process so as to destroy the
organic matrix and produce a solution.
To check the presence of metals a plasma spectrophotometer
with sequential reading was used.
Results showed (see Table n. 5 and Annex B) a greater
concentration of the three metals in the bottom part of the tip
which according to the SGS laboratory is due to the presence of
brass powder caused by a "non perfect cleaning of the tip
after the lathe operations". This powder creates a wider
contact surface and increases the likelihood of brass
mineralisation. To confirm or reject the assumption put forward
by the SGS Laboratory we had to experimentally reproduce the
defect in our laboratory.
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Table 5
| Parameters |
C (mg/kg) |
B (mg/kg) |
A (mg/kg) |
| Lead |
< 0,5 |
40,9 |
< 0,5 |
| Copper |
< 0,5 |
46,1 |
< 0,5 |
| Zinc |
6,6 |
67,1 |
< 0,5 |
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To this aim, we formulated a number of different inks mixing
with them some brass powder resulting from the tip lathe
operations.
Refills assembled with these mixtures wrote with no defect at
all, neither immediately nor after the ageing test.
Given the tiny amount of defective product, the analysis of A
samples did not produce reliable results.
At this point, we had to go into greater details using an
electronic microscope to find out the nature and origin of the
clot inside the tip.
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We entrusted the Chemical Laboratory of the Chamber of Commerce in Turin with this task.
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With the aim of identifying the nature of the clots which are
probably the root cause of the hole obstruction in our brass ball
point refills, a scanning electron microscope (JEOL 6400)
equipped with an EDS probe was used (X-ray energy dispersion
spectrometer TRACOR Z-MAX 30). See Annex C.
The EDS analysis, as it can be easily observed (Chart n. 2 and
Picture n. 18), highlighted as basic elements agglomerates of
copper with zinc and chlorine. Their arrangement perfectly
overlaps with that of the clot removed from the tip (see Picture
n. 4).
In some cases the procedure highlighted only the presence of
copper particles and this puzzled operators.
The same instrument was used to measure the various elements
present in a brass tip free from corrosion (see Chart n. 1). In
this case no particle of chlorine was observed.
After a first microscopic observation with a magnification
power of x100, the magnification was increased to 1.500 to assess
the crystalline structure of the elements making up the unknown
agglomerate (see Picture n. 5).
Then we started looking for the element with the same
crystalline structure observed at the microscope. After the
analysis of several pure particles and artificially created
products, the optimal result was obtained using some brass powder
(see Picture n. 6).
The size of particles forming the agglomerates is about three
micrometers and their crystalline structure matches that of pure
electrolytic copper powder.
One of the doubts expressed by our experts referred to a
possible contamination of ink at its finale stage, caused by an
imperfect purification during the final stages of the production
process. This could have led to an accumulation of insoluble
particles inside the ball feeding duct during refill
centrifugation.
To side-step this problem, one of the first checks carried out
at the end of the production process is the centrifugation of
some refills assembled with the ink under study. This operation
which takes a long time (30 minutes approximately) is followed by
a microscope analysis of the ink located behind the ball to
verify the actual absence of insoluble parts.
To this purpose our experts prepared an X-ray 120
magnification map of insoluble residues obtained during ink
purification at the centrifugation and filtration stage scattered
in an area of 0,85 square centimetres (it should be pointed out
that REINOL utilises a single process, with two filtrations and
one centrifugation stage).
The map (see Annex C) highlights the presence of particles
containing iron, silicon, calcium, sulphur and aluminium in a
smaller percentage, and just one single copper particle.
If we compare the results of this map with the previous one,
we can notice the actual efficacy of the purification process:
indeed none of the particles present in residues is found in ink
at its final stage.
Based on these results one could think that refills stopped
writing because of an excess of brass powder or chips due to an
insufficient cleaning and washing; however, the fineness of
particles (3 micrometers) and the unusually high quantity could
have been traced back to a bad washing of tips, but also to a
cause which remained unknown for the moment.
The chlorine found during the EDS analysis (see Chart n. 2)
was not taken into account at that stage simply because the
hypothesis of corrosion had not been considered yet.
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Verification of results and conclusions
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Experimental test were needed to reproduce the same
circumstances in the laboratory and to check whether the root
cause of the writing defect was in brass contamination or in
other substances normally used in the ball tip production process
and in the subsequent refill assembly.
Inks were therefore contaminated with different percentages of
the following products:
- very fine powder obtained from the machining of tips. Due to
the greater surface in contact with ink, it is much more reactive
than the tip brass;
- new blending oil used for the machining of tips;
- used blending oil with brass chips.
These mixtures were then used in the assembly of some control
refills that were subsequently subjected to a number of tests,
ageing tests included.
All refills thus obtained and assembled were operating
perfectly. This meant that the writing blocking in defective
refills was not due to the presence of brass (powder or chips)
caused by a bad washing of the tip itself.
Some observations had already led us to think that the final
explanation was to be found in a different direction, namely:
- The defect occurred both in tips supplied by experienced and
excellent manufacturers and in products supplied by minor
manufacturers with little experience in the field.
- The same defects recurred using ink supplied by different
manufacturers.
During our study, we received refills from all over the world.
They were filled with both our products and with inks supplied by
competitors - they all had the same defect.
The time frame could be easily identified and it was the same
for all manufacturers.
The EDS analysis clearly highlighted the presence of chlorine
particles that do not belong to the composition of brass, nor to
the formulation of inks.
The use of unwashed tips, dirty with oil, did not produce any
defect, even after one year and a half of tests. Tips remain
shiny and clean.
At page 49 Picture n. 7 shows a tip as it usually appears.
Our laboratory was developing a project for a very important
customer. For the project it used ink formulated in the
laboratory and tips of a very high quality. But there again,
after about six months, all assembled refills stopped writing.
This was the clue to look for different causes. The defect could
no longer be ascribed to a bad ink formulation, that in this case
had been produced in the laboratory with the help of precision
micro-balances and therefore with an error rate of 0,001 grams
for 100 g. of finished products!
The clue to the solution was provided by the observation of a
number of tips with clear signs of acid corrosion on the inner
duct of new tips coming from different manufacturers as it can be
noticed in the following pictures:
- Pictures n. 8,
n. 9,
n. 10,
n. 11,
n. 12,
n. 13,
n. 14,
n. 15
- Picture n. 24
In this case corrosion is caused by the etching of
hydrochloric acid formed through hydrolysis of the chlorinated
solvent and is due to phenomena explained in the previous
section.
It should be noted that hydrochloric acid is by far the most
aggressive in etching brass followed by nitric acid, whilst
sulphuric acid produces a weaker effect.
The term brass encompasses a wide range of Copper and Zinc
alloys, where the latter is in a percentage not exceeding 50%
(usually this percentage varies from 11% to 50%).
Zinc reacts easily to acid and develops hydrogen:
Zn + 2H+ < = > Zn++ + H2
and
Zn + 2HCl < = > ZnCl2 + H2
The greater the amount of impurities in Zinc, the easier the
above-mentioned reaction.
Zinc chloride is deliquescent substance, that is a highly
hygroscopic salt with the property of turning into a solution by
absorbing water from the surrounding atmosphere. This situation
highly increases the reactivity of chloride itself.
Even copper melts in any acid if exposed to air.
With hydrogen halide acids, like for instance hydrochloric
acid, copper oxide forms insoluble copper salts which
precipitate:
2Cu + HCl < = > 2CuCl + H2
This acid etching is followed by the formation of zinc, lead
and copper salts.
Brass oxidation and the consequent formation of the so-called
"saline efflorescence" leads to the formation of
insoluble particles mixed with ink in the duct behind the ball.
An example of this acid etching on brass, with the consequent
formation of saline crystals, was already registered in
nickel-plated tips at the end of the machining process in 1984
(see Picture n.17).
To avoid this problem, manufacturers started to machine tips
only after the nickel-plating process.
In other cases acid etching may be caused by factors not
linked to washing products but to the raw materials used during
the forming process (Picture n. 17).
The ensuing copper and zinc oxides are highly reactive to
certain ink ingredients and produce insoluble substances, usually
copper and/or zinc carboxilates. These compounds alter the normal
rheology of the ink, decreasing its ability to flow into the
capillary duct.
The degeneration process occurs in three distinct stages:
Stage 1: At this stage a weakening of the writing specimen
occurs; it is due to a narrowing of the tip inner duct and
therefore to a smaller amount of ink flowing through.
Stage 2: Salts continue to increase with consequent writing
"gaps".
Stage 3: It is the final stage of the degeneration process
when tips just cease to write altogether.
Some refills however, if subjected to centrifugation, start to
write again reasonably well, gradually improving until the ink
flowing out has not brought out with it all saline particles.
The salt content of these refills is smaller and has not
caused a total duct occlusion yet.
In refills which do not start writing again the salt content
has totally blocked the capillary duct.
If we slightly blow the refills, writing starts and gradually
becomes normal again. Even after ageing test, the performance of
refills processed this way remains normal.
This is in line with the results of some tests carried out by
our competitors. They demonstrated that by replacing or washing
the tips of defective refills, but using the same ink, the
problem did not crop up again.
Furthermore, there is the possibility that in some tip lots,
the capillary duct might have already been totally obstructed.
In the light of these data, the results of all the tests
carried out by external laboratories fine an easier explanation:
- The high copper and zinc percentage in the tip ink stressed
by the SGS analysis confirms the high content of the two metals
in ionic form, which therefore passes into ink.
- Copper and zinc particles found in all tests carried out by
the Chemical Laboratory of the Chamber of Commerce are in fact
Zinc and Copper salts, as it can be easily observed from Charts
n. 1 (EDS analysis carried out on a brass tip with no writing
defect: no chlorine, copper or zinc particle is found to be part
of the brass alloy) and n. 2 (EDS analysis of the waxy clot
behind the ball of a tip belonging to a defective refill: the two
above-mentioned salts are not only made of copper and zinc, but
also of a certain amount of chlorine.
- This explains why replacing the tips of defective refills
with new tips all anomalies are avoided.
Corroded tips probably account for a negligible and sporadic
part of production.
To check the accuracy of our conclusions, we experimentally
reproduced the defect in our laboratory. We dipped for few
minutes some etch-free tips in a 0,1 normal solution of
hydrochloric acid (which amounts to 3,5 g. of HCl dissolved in a
litre of water). After a few days the tips had the same problems
of those contained in defective refills; this is clearly shown in
Picture n. 19 and 20.
Over a subsequent set of tests carried out at the Chemical
Laboratory of the Chamber of Commerce, we tried to ascertain the
origin of saline efflorescence using manifestly defective refills
and tips coming from Korea.
Here are the findings of the analysis of saline formations:
1) Brass undergoes a selective oxidation of its components;
2) Displayed saline efflorescence is primarily made of Zinc
and Lead salts.
Picture n. 21 and 22 are very helpful in explaining these
findings.
At the same time a scanning electron microscope was used to
observe a saline formation found in a recently produced tip (see
Picture n. 23).
The EDS analysis clearly shows that this crystal is made of
Zinc salts.
Result of the EDS analysis carried out on a new and
corrosion-free brass tip.
Result of the EDS analysis carried out on the clot behind the
ball of the tip of a defective refill.
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