Note: Descriptions are shown in the official language in which they were submitted.
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~M 35692
SOLVENT CLEANING OF' ARTICLES
This invention relates to solvent cleaning
applications in which contaminated articles such as, for
example, metals, textiles, glass, plastics, electronic
components and printed circuit boards are cleaned using
a solvent or solvent vapour and more particularly to
the use of low molecular weight ethers as solvents in
solvent cleaning applications.
Solvent cleaning applications wherein contaminated
articles are immersed in or washed with halogenated
hydrocarbon solvents and/or the vapours thereof are well
known and are in common use. Applications involving
several stages of immersion, rinsing and drying are
common and it is well known to use the solvent at
ambient temperature (often accompanied by ultrasonic
agitation) or at an elevated temperature up to the
boiling point of the solvent. Examples of solvents used
in these cleaning processes are 1,1,2-trichloro-
1,2,2-trifluoroethane, 1,1,1-trichloroethane,
trichloroethylene, perchloroethylene and methylene
chloride. These solvents are used alone or in mixtures
with cosolvents such as aliphatic alcohols or other low
molecular weight, polar additives and depending to some
extent upon the articles to be cleaned are often
stabilised against degradation induced by light, heat
and the presence of metals.
In the known common solvent cleaning applications
and especially in those applications where the solvent
is used at an elevated temperature, there is a tendency
for solvent vapour to be lost from the cleaning system
into the atmosphere. Further losses may occur in
loading and unloading the solvents into cleaning plant
and in recovering used solvent by distillation. Whilst
care is usually exercised to minimize losses of solvent
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into the atmosphere, for instance by improved plant
design and vapour recovery systems, the expense of
totally preventing lasses is exhorbitant and most
practical cleaning applications result in some loss of
solvent vapour into the atmosphere.
Until recently, the use of the common cleaning
solvents has been regarded as safe practice in that the
solvents are stable, of low toxicity, non-flammable
materials believed to be environmentally benign.
However recent evidence suggests that some at least of
the common solvents may have a long-term deleterious
effect on the stratosphere, the so-called ozone layer,
so that a replacement solvent is seen to be desirable.
According to the invention there is provided the
use in solvent cleaning applications of solvents
comprising low molecular weight fluorine-containing
ethers of boiling point in the range of about 20°C to
about 12. 0 ° C .
The ether has a boiling point in the range 20°C to
120°C, preferably from 25°C to 85°C, such that it may
be used in conventional and existing cleaning equipment.
For any particular cleaning application, an ether may be
selected having a boiling point close to that of the
solvent the ether is replacing.
The ethers can be obtained by reaction of a
halogenated aliphatic olefin with an optionally
halogenated aliphatic alcohol in known manner and thus
contain at least three carbon atoms in the molecule.
Usually the ether will contain not more than five carbon
atoms although it may contain six or more carbon atoms
providing its boiling point is below about 120°C.
The ether contains at least one and will usually
contain two or more fluorine atoms but will not
generally be perfluorinated. In addition to fluorine
atoms, the ether may contain chlorine atoms, bromine
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atoms and hydrogen atoms. Ethers containing chlorine
and/or hydrogen may contain one or two chlorine atoms
and/or one or two hydrogen atoms.
Examples of alcohols which may be used to produce
the ethers are methanol, ethanol, propanol and butanol
and halogenated derivatives thereof. Alkenes which may
be used include tetrafluoroethylene, hexafluoropropene,
chlorotrifluoroethylene and the chlorofluoropropenes
and hydrogen-containing analogues of these compounds for
example trifluoroethylene and chlorodifluoroethylene.
Examples of ethers which may be used, and their
boiling points, inc7.ude the following:-
Boiling
Point (°C)
1,1-difluoroethyl methyl ether 47
1,1,2,2-tetrafluoroethyl methyl ether 36.5
1-chloro-1,2,2-trifluoroethyl methyl ether 70.6
1-1-dichloro-2,2-difluoroethyl methyl ether 104.8
1-chloro-2,2-difluoroethyl methyl ether 27.5 1
1,1.1,2,3,3-hexafluoropropyl methyl ether 54.5
1,1-difluoroethyl ethyl.ether 65
1,1,2,2-tetrafluoroethyl ethyl ether 56
1-chloro-1,2,2-trifluoroethyl ethyl ether 82
1,1,1,2,3,3-hexafluoropropyl ethyl ether 64.5
1,1,2,2-tetrafluoroethyl n-propyl ether 71.7 3
1-chloro-1,2,2-trifluoroethyl n-propyl ether 109
1,1,1,2,3,3-hexafluoropropyl n-propyl ether 92
1-chloro-1,2,2-trifluoroethyl isopropyl ether 100
1-chloro-2,2-difluoroethyl isopropyl ether 53
1,1,1,2,3,3-hexafluoropropyl isopropyl ether 76
1,1,2,2-tetrafluoroethyl n-butyl ether 49
1,1,1,2,3,3-hexafluoropropyl n-butyl ether 108
1,2,2-trifluoroethyl 1,1,1-trifluoroethyl ether 75
1,1,2,2-tetrafluoroethyl 1,1-difluoroethyl ether 77
di(1,1-difluoroethyl) ether 103
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1-chloro-1,2,2-trifluoroethyl 1,1-difluoroethyl
ether 102
1,1,2,2-tetrafluoroethyl 1,1-
di(trifluoromethyl)methyl ethex 85
At 130 mm Hg
At 630 mm Hg
At 62'7 mm Hg
At 121 mm Hg
IO 5 At 113 mm Hg
Mixtures of ethers, including azeotropic
mixtures, may be used if desired as may mixtures of an
ether with one or more cosolvents. The same cosolvents
may be used as are used with the principal solvents in
known cleaning applications and in particular polar
compounds such as alcohols are preferred cosolvents.
Cleaning compositions comprising the ether and a
cosolvent, notably a lower alkanol cosolvent, are
, provided according to another feature of the invention.
Azeotropic mixtures of ethers and alcohols represent
preferred embodiments of the invention. Lower aliphatic
alcohols containing 1 to ~ carbon atoms are useful in
such mixtures.
The ethers used according to the invention tend
to be more stable than 'the commonly-used solvents and
generally will not require stabilisation against
degradation. However, stabilisers may be added if
desired or if required for particularly onerous cleaning
applications and the stabilisers used in the common
solvents may be employed, notably nitroalkanes and
epoxides.
The ethers may be used as replacements for the
solvents) used in any of the known cleaning
applications and have the advantage of being generally
CA 02039828 2000-04-12
60557-5662
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more stable towards aluminium than the solvents they
replace. The ethers may be used to replace part of the
solvents) used in known cleaning applications.
The invention is illustrated by the following
examples.
L~YAMt~T D 1
This Example illustrates the use of
2-chloro-1,1,2-trifluoroethyl methyl ether
in cleaning flux residues from copper-coated boards.
A known weight of solder cream was applied to
i~test boards (5 cm x 7 cm) cut from copper-coated FR4
(epoxy/glass fibre laminate) board and the cream was
reflowed in a MICRO VPS~'soldering unit. The solder
cream used was a 62% tin/38~ lead solder available as
Multicore'~PRAB 3.
2-chloro-1,1,2-trifluoroethyl methyl ether
(boiling point 65°C at 630mm Hg) was boiled in a beaker
fitted with an upper cooling coil through which cold
water was circulated to create a boiling liquid phase
and a vapour phase and the contaminated board was dipped
into the boiling liquid for 60 seconds and then held in
the vapour for 30 seconds.
Residual ionic contamination of the test board,
expressed as mg sodium chloride per square centimetre
was determined using a Protonique'~Contaminometer. The
ionic contamination of an unwashed test~board was
determined and the ~ removal of ionic contamination was
calculated. 61~ of the ionic flux residues were removed
fr«rn the test boards.
The ether was heated to 190°C and the vapour
pressures above the ether were determined over the range
50 - 190°C. A slight increase in vapour pressure was
observed at approximately 120°C but there was no visible
evi_cience of solvent breakdown at this temperature.
* 'Trade-mark
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In a Comparative Test, using
1,1,2-trichloro-1,2,2-trifluoroethane as the solvent,
45% of the ionic flux residues were removed.
EXAMPLE 2-3
These Examples illustrate the use of mixtures of
2-chloro-1,1,2-trifluoroethyl methyl ether and methanol
far cleaning flux residues from copper coated printed
circuit boards.
In Example 2, a mixture of 2-chloro-1,1,2-
trifluoroethyl methyl ether and methanol was boiled
until a constant boiling mixture was obtained. This
azeotrope contained 18.5% by weight of methanol and
boiled at 56.8°C at normal pressure.
The azeotropic mixture was used to remove ionic
residues from the test boards as described in Example 1.
66.9% of the ionic resudes were removed.
In Example 3, the procedure of Example 2 was
repeated except that a mixture of the ether (95% by
weight) and methanol (5% by weight) was used instead of
the azeotropic mixture. 65.1% of the ionic residues were
removed.
EXAMPLE 4
This Example demonstrates the stability of
2-chloro-1,1,2- trifluoroethyl methyl ether in the
presence of aluminium.
The ether was refluxed in contact with aluminium
for 48 hours. The aluminium test piece was partly
immersed in the liquid and partly in the vapour above
the liquid.
In the test, no increase in chloride ion or
fluoride ion was observed in the liquid phase and the GC
trace of the solvent after the test showed no change.
There was no significant weight change in the metal test
piece which emerged from the test clean and bright with
no evidence of corrosion.
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The results demonstrate that the ether has high
stability in the presence of aluminium and is suitable
for use in aluminium cleaning applications. Stabilisers
may be added to inhibit the build up of acidity in the
ether when it is used to clean metals.
EXAMPLE 5
This Example illustrates the use of
tetrafluoroethyl methyl ether in cleaning flux residues
from copper-coated boards.
Tetrafluoroethyl methyl ether, boiling point
33-35°C (630 mm Hg) and density (25°C) 1.28g/ml, was
used to clean flux residues from copper coated boards
as described in Example 1. 62% of the ionic flux
residues were removed.
EXAMPLE 6-8
These Examples illustrate certain azeotropic
mixtures suitable for use in the process according to
the present invention.
Tetrafluoroethyl methyl ether forms an azeotrope
, with methanol containing 4% by weight methanol and
boiling at 34.5°C.
The ether forms an azeotrope with 1,1,2-trichloro-
1,2,2 -trifluoroethane containing 39.5% by weight of the
haloethane and boiling at about 34.9°C.
The ether forms a ternary azeotrope with
1,1,2-trichloro- 1,2,2-trifluoroethane and methanol
containing 41% by weight of the haloethane and 3% by
weight of methanol and boiling at about 34.5°C.
EXAMPLE 9
This Example illustrates the use of a ternary
azeotropic mixture in the process according to the
present invention.
The ternary azeotropic mixture of
tetrafluoroethyl methyl ether,
1,1,2-trichloro-1,2,2-trifluoroethane and methanol
prepared in Example 8 was used to remove solder flux
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residues from circuit boards by the procedure described
in Example 1. 48.2 of the ionic flux residues were
removed.
EXAMPLE 10-11
These Examples illustrate further azeotropic
mixtures for use in the process according to the present
invention.
Tetrafluoroethyl ethyl ether, boiling point 56°C
and density 1.21 g/ml, forms an azeotrope with methanol
containing 10.6 by weight of methanol and boiling at
48.6°C.
The ether forms an azeotrope with ethanol
containing 38.5 by weight of 1,1,2-trichloro-1,2,2-
trifluoroethane and boiling at 46.3°C.
