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Description  |
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FIELD OF THE INVENTION
This invention relates generally to methods and compositions for cleaning
and in particular to the cleaning of deposits from the interior of tubes,
tanks, conduits and the like. Most specifically, the present invention
relates to a process and composition for cleaning encrustations from the
lines of paint systems utilizing a particulate containing composition.
BACKGROUND OF THE INVENTION
Presently, the paint delivery systems which are utilized for the finishing
of a wide variety of manufactured items such as motor vehicles, household
appliances and the like are becoming increasingly more sophisticated. A
typical industrial paint delivery system may comprise a central paint
supply having a number of painting stations communicating therewith. Such
paint delivery systems can selectably deliver a variety of different
paints to a given painting station and include complex fluid pathways
involving various tanks, pumps and conduits. These paint delivery systems
tend to become clogged with encrustations in the course of their use and
such deposits can decrease and even block the flow of paint therethrough.
Such clogging is occasioned by deposits of pigment, resins or other
components of the paint within the tanks and lines of the system. In
addition to causing clogging, such deposits can also contaminate the paint
color, and can cause surface defects in the finished, painted product.
Cleaning the paint delivery system reduces the amount of surface repairs
to paint finishes.
The build-up of residues necessitates periodic cleaning of paint delivery
systems and because of the complexity of the systems and the necessity of
avoiding expensive downtime, it is generally preferable that such systems
be cleaned without disassembly. The prior art approach to cleaning
involves passing a variety of solvents, detergents or other cleaners
through the system, and tends to involve numerous steps and multiple
compositions. It should be noted that these processes often do not provide
full removal of deposits, particularly pigment residues.
A typical prior art process can involve flushing five or more different
cleaning compounds of varying polarity through the paint system and can
include 30 separate operational steps. The numerous cleaning compounds are
needed in order to fully remove the residues in the system and to ensure
compatibility of any cleaner residue remaining in the system with
subsequently introduced paint. As a result, the system must be
sequentially rinsed with various materials in a predetermined order such
that the final rinse is with a paint-compatible thinner. Clearly, it would
be most advantageous to reduce the number of steps by utilizing a cleaning
composition which is, fully paint-compatible and to improve the efficiency
of the process by utilizing a composition capable of removing all
residues.
Many prior art cleaning compositions also present problems of waste
disposal. The cleaning compositions may be broadly categorized as either
organic based or aqueous based. The organic based materials can employ
halogenated and/or aromatic solvents as well as reagents such as acetone,
methyl ethyl ketone, and the like. These solvents are toxic, and in many
instances flammable and present problems cf disposal as well as
compatibility with the components of the pain: delivery system. The
aqueous solvents generally comprise highly caustic materials such as
potassium hydroxide or sodium hydroxide or acidic materials such as acetic
acid, all of which present dangers in both handling and disposal. Many of
the aforementioned solvents, particularly the aqueous based ones, are not
compatible with subsequently utilized paint and hence elaborate rinse
procedures are needed before the cleaned equipment may be put back into
service. In addition to the foregoing shortcomings, prior art paint system
cleaning solvents do not provide sufficient cleaning action, particularly
with regard to encrusted pigment deposits and, as a consequence, long
flush times and/or repeated cleaning cycles have been generally required.
It has been known to utilize abrasive materials to clean closed lines and
one such process is disclosed in U.S. Pat. No. 4,572,744 which describes
the use of sand or similar material entrained in a flow of air to clean
the interior of boiler tubes. Also mentioned in the '744 patent is the
similar use of liquid based abrasive slurries to clean pipes.
Heretofore, various attempts have been made to utilize abrasive based
materials for cleaning paint lines and it is known to employ mica, or sand
particles in conjunction with a flush liquid to scour the interior of
paint lines. Problems have arisen with the use of such inorganic abrasives
insofar as they can be relatively hard and tend to damage or clog pumps
and passageways through which they flow. Additionally, such inorganic
abrasive materials are also relatively dense and tend to settle out of a
cleaning fluid unless vigorous agitation is maintained or thickeners are
added to increase the solution viscosity.
It is known to utilize a specific paint system cleaning composition
comprised of sand or mica suspended in a solution of xylene and methyl
isobutyl ketone thickened with a resinous material. Compositions of this
type present problems insofar as the resin and abrasive are difficult to
rinse from the system thereby presenting problems of contamination,
particularly when the resin is not compatible with subsequently employed
paint compositions; additionally, the viscous composition presents
problems of waste disposal insofar as the resin is difficult to incinerate
and inhibits the ready evaporation and recovery of the xylene and ketone.
Obviously, the inorganic abrasive residue presents significant waste
disposal problems insofar as it cannot be readily incinerated.
The present invention overcomes various shortcomings of prior art cleaning
compositions and methods insofar as it provides a group of simple to use
compositions which are readily compatible with a variety of paint
formulations and which can be readily incinerated or recycled.
The cleaning compositions of the present invention include a particulate
organic abrasive material. Organic, polymeric materials are not generally
thought of as being abrasive; however the present invention relies in part
upon the counter intuitive finding that organic materials can function
very well to facilitate the cleaning of encrustations from paint delivery
systems. The polymeric particles utilized in this invention are of
relatively low density and hence may be maintained in suspension without
resort to thickeners or vigorous agitation. Although these organic
materials perform an excellent job of cleaning residues from paint lines,
they are not sufficiently abrasive to damage pumps, valves and the like.
The compositions of the present invention may be advantageously utilized
in cleaning the lines and tanks of paint delivery systems as well as for
other cleaning purposes where some degree of abrasive action is required.
The relatively low viscosity of the cleaning compositions of the present
invention simplifies their disposal or recycling and the fact that they
contain no inorganic solids allows for their ready incineration. These and
other advantages of the present invention will be readily apparent from
the drawings, discussion, description and claims which follow.
SUMMARY OF THE INVENTION
There is disclosed herein a method for cleaning encrustations from the
interior surface of a vessel. The method includes the steps of providing a
cleaning composition comprising a vehicle having a particulate, organic,
polymeric material dispersed therein and establishing and maintaining a
flow of the cleaning composition through the vessel. The particulate
material may in some instances be selected from the group consisting
essentially of: polypropylene, polyvinylchloride, polyethylene,
polytetrafluoroethylene, copolymers thereof, and mixtures thereof. In
particular instances, the particulate material is of a particle size no
greater than one half inch, although in some instances a particle size of
no more than 200 microns is desired and in yet other instances a particle
size range of approximately 50-150 microns is preferred for the organic
material. In yet other instances, it is preferred that the specific
gravity of the material be less than 1.5.
The vehicle may comprise a liquid including therein an organic solvent and
this solvent may be selected from the group consisting essentially of:
aliphatic hydrocarbons, aromatic hydrocarbons, lactones, lactams,
terpenes, alcohols, organic acids, amines, amides, ketones, aldehydes,
esters, halocarbons, ethers, glycols and combinations thereof. In other
instances the liquid vehicle may include water whereas in yet other
instances the vehicle may be acidic or alkaline. The composition may
further include ancillary ingredients such as detergents, surfactants, or
thickeners.
In general it will be preferred that the particulate matter comprise
between 2 and 20 volume percent of the composition although particular
applications may require greater or lesser amounts. In implementing the
process, a flow of the cleaning composition may be established through the
vessel by pumping the material therethrough. In those instances where the
vessel is a tube it may be advantageous to maintain a linear flow of at
least 50 feet per minute therethrough. Also included within the scope of
the instant invention is the aforementioned composition.
DETAILED DESCRIPTION OF THE INVENTION
The present invention recognizes the fact that inclusion of a particulate,
organic, polymeric material in a cleaning composition improves the ability
of that composition to remove encrusted deposits from the interior
surfaces of vessels such as tanks and tubes. This finding is
counterintuitive in the sense that the polymeric materials tend to be
relatively soft compared to the components of the encrustations which they
remove. As was mentioned previously, heretofore employed compositions
relied upon the use of extremely hard abrasive materials which were
difficult to use and caused damage to equipment.
The composition of the present invention includes in its simplest form a
vehicle, which is preferably a solvent for at least some components of the
encrustations, and the aforementioned polymeric material. The vehicle may
be organic or inorganic depending upon the particular cleaning task. Among
the organic materials which may be used are solvent such as aliphatic
hydrocarbons, aromatic hydrocarbons, lactones such as butyrolactone,
lactams, particularly pyrrolidones, terpenes, alcohols, organic acids,
amines, amides, ketones, aldehydes, esters, halogenated solvents, ethers,
glycols and the like either taken singly or in combination. Some
particular solvents include xylene, propylene carbonate, m-pryol and the
like. Inorganic vehicles will generally be aqueous based and can be acidic
or alkaline. Either the organic or inorganic vehicles can include
detergents, surfactants, and other such ancillary ingredients as is well
known to those of skill in the art. In some instances it may be
advantageous to blend organic and aqueous solvents. The basic requirement
of a vehicle is that it be inert to the organic particulate material.
From the foregoing it should be apparent that there are a wide variety of
solvents which may be employed in the present invention. The principal
requirements for solvent selection are that the solvent not dissolve the
organic, polymeric particulate material and that it not damage the system
being cleaned. Within these bounds one can readily select a variety of
solvent materials.
The organic particulate material may comprise any one of a number of
polymeric materials provided that such materials do not dissolve in the
vehicle and do not melt, decompose or otherwise react at the cleaning
temperature. Among some polymeric materials which were found to have
significant utility are polypropylene, polyethylene, polyvinylchloride,
and halogenated polymers such as polytetrafluoroethylene. The size of
polymer particles utilized will depend upon the particular application
however it has generally been found that larger particles provide for a
more rapid cleaning action as compared to smaller particles. However it
should be kept in mind that as the particles get larger it becomes more
difficult to maintain them in a dispersed form in the vehicle and very
large particles tend to clog pumps, lines and the like. Although the
present invention is not limited to any particular size of particles, as a
general rule it has been found that for systems using reciprocating or
impeller type pumps particle sizes of 200 microns or less generally
function the best and that particles within a size range of 50-150 microns
are usually the most preferred. It should be noted however, that many new
paint delivery systems employ diaphragm type pumps, and that pumps of this
type are less prone to clogging of the particles than are heretofore
employed pumps. Consequently, in a diaphragm pumped system, relatively
large particles of polymeric material (i.e., as large as 1/2 inch
diameter) may be employed. The fact that polymeric materials of the type
employed herein are of relatively low density (typically no greater than
1.5) helps to prevent them from settling out even if they are large.
There are a number of suppliers of particulate polymeric material which may
be used herein. Hercules, Inc. of Bloomington, Del. supplies particulate
polypropylene under the trade name of "Hercoflat".RTM.. This material is
very stable over a wide temperature range and in a variety of solvents. It
has a specific gravity of approximately 0.9, which facilitates its
suspension in a variety of solvents. Hercoflat .RTM. grade 1200 has a mean
average particle size, of 200 microns, whereas grade 1150 has a particle
size of approximately 150 microns. In some instances it has been found
advantageous to utilize Hercoflat .RTM. grade 135 which has a mean
particle size of approximately 35 microns.
A similar polypropylene material is sold by Micro Powders, Inc. of
Scarsdale, N.Y. under the trade name Propyl-Tex 140 and comprises
polypropylene having a particle size of approximately 50-55 microns.
Shamrock Technologies of Newark, N.J. sells polypropylene powders having
particle sizes ranging from 18 to 90 microns under the trade name "Texture
Series," and these materials are suitable for the present invention. The
Allied Corporation of Norristown, N.J. sells a polyethylene particulate
material under the trade name of "A-C".RTM. 316A polyethylene. This
material comprises 40 mesh polyethylene having a density of approximately
0.98 G/CC. The B.F. Goodrich Chemical Group of Cleveland, Ohio provides a
variety of polyvinylchloride materials under the trade name "Geon".RTM..
These materials are quite inert and have a specific gravity of
approximately 1.4 and are available in a variety of particle sizes. Of
particular advantage is Grade 141 which comprises approximately 100 micron
size particles and Grade 142 which comprises particles of approximately
75-80 microns in size. In addition to the foregoing, there are a wide
variety of other polymers and other suppliers which are known to one of
skill in the art who could readily locate such sources of supply, and in
light of the teaching herein, obtain material useful in the practice of
the present invention.
Use of a polymeric "abrasive" material confers particular advantage in a
cleaning process. The polymeric materials generally have a low adhesion to
metallic parts such as components of a paint delivery system thereby
minimizing rinse steps in the cleaning process and reducing contamination
of subsequently painted articles. Such contamination is a particular
problem in the use of inorganic abrasive materials, many of which, such as
mica or silica sand, have a high affinity for metallic surfaces. The
relatively low density of the polymeric material prevents it from settling
out thereby allowing the composition to be shipped, stored and utilized
without numerous mixing steps. Most organic polymers useful in the present
invention have a specific gravity of 1.5 or less and many have a specific
gravity below one whereas most of the commonly employed inorganic abrasive
materials have specific gravities greater than 2.5. Because of the fact
that the particulate material of the present invention remains in
suspension readily, the need for resins or other thickening materials is
eliminated thereby resulting in a savings of cost and facilitating waste
disposal and solvent recovery in addition to preventing contamination of
subsequently applied paint by the resin. Elimination of resins and/or
thickeners results in a cleaner of low viscosity. Such low viscosity
material is easy to pump through the system and is capable of reaching and
cleaning narrow passages in the system. It has been found that typical
compositions of the present invention have a viscosity comparable to
water. Times for discharge of a standard #4 Ford viscosity measuring cup
are approximately 10 seconds. As mentioned previously, the organic
polymeric materials of the present invention are completely incineratable
whereas the inorganic materials are not. A final point to be noted is that
the organic polymeric materials are relatively soft and therefore do not
abrade or damage pumps or other equipment through which they pass.
As mentioned previously, there are a variety of compositions which may be
formulated in accord with the teaching of the present invention. Presented
herein for purposes of illustration and not limitation are some particular
formulations which have been found to be advantageous in cleaning lines of
paint delivery systems.
EXAMPLE 1
This composition comprises approximately 48.5% xylene, 17.2% dibasic ester,
a paint solvent sold by the DuPont Corporation of Wilmington, Del.;
approximately 24% isobutyl isobutyrate, an ester solvent for paint and
approximately 9.3% Hercoflat .RTM. 1150 polypropylene powder. The
foregoing ingredients were mixed together by simple agitation and were
employed as will be described hereinbelow in a cleaning process.
EXAMPLE 2
This composition was for a line cleaner having a higher flash point than
that of Example 1, consequently the xylene was replaced with a high flash
point aromatic solvent sold under the trade name Cyclosol 53 by Shell
Chemical which is a subsidiary of The Shell Oil Company of Houston, Tex.
EXAMPLE 3
This example relates to a composition having a higher volatility than the
foregoing and is comprised of approximately 30.2% methyl isobutyl ketone;
30.2% xylene; 30.2% of the aforementioned dibasic ester solvent and
approximately 9.4% Hercoflat .RTM. 1150 polypropylene.
EXAMPLE 4
This example relates to a water compatible cleaning composition comprised
of approximately 49% water; 29% 2-Butanol; 9.8% methyl ethyl ketone; 9.8%
Hercoflat 1150 polypropylene powder; 0.2% choline base (45%), an organic,
industrial alkali; approximately 2% of Polytergent B-300; a nonylphenol
detergent sold by the Olin Corporation of Stanford, Conn.
EXAMPLE 5
This example employed a 35 micron particle size polymeric material. The
composition consisted of 30.4% of the aforementioned dibasic ester
solvent; 30.4% of methyl isobutyl ketone; 30.4% of xylene and 8% of
Hercoflat .RTM. 1135 polypropylene powder.
All of the aforementioned compositions were fabricated and tested under
similar conditions by pumping them through glass tubes which had been
coated with paint residue upon the interior surface thereof. The
compositions were pumped at room temperature and a flow rate of 50 ft/min.
Visual inspection of the tubes indicated that all of the aforementioned
compositions. were quite satisfactory in effecting cleaning thereof. The
composition of Example 1 was the very best with the remaining compositions
being of slightly decreasing efficiency.
In the following series of examples, the effect of varying the amount of
organic particulate material was assessed. Various cleaning compositions
were prepared as follows:
EXAMPLE 6
This sample comprised N-methylpyrrolidone 25%; cyclohexanone 7%; Cyclosol
53, as previously described 18%; triethanolamine (85%) 3%; diacetone
alcohol 9%; polytergent B-300, as previously described 1.5%; dibasic
ester, as previously described 16.5% and propylene glycol monomethyl
ether, a solvent provided by the Olin Corporation of Stanford, Conn.,
16.5%. It should be noted that no organic particulate was included.
EXAMPLE 7
This sample comprised n-methylpyrrolidone 22.7%; cyclohexanone 6.3%;
Cyclosol 53 16.3%; triethanolamine (85%) 2.7%; diaceatone alcohol 8.2%;
polytergent B-300 1.3%; dibasic ester 18%; propylene glycol monomethyl
ether, 14.9% and Hercoflat .RTM. 1150 9.3%.
EXAMPLE 8
This sample comprised n-methylpyrrolidone 21;2%; cyclohexanone 5.9%;
Cyclosol 53 15.3%; triethanolamine (85%) 2.5%; diaceatone alcohol 7.6%;
polytergent B-300 1.3%; dibasic ester 17%; propylene glycol monomethyl
ether 14% and Hercoflat.RTM. 1150 15%.
EXAMPLE 9
This composition consisted of n-methylpyrrolidone 19.9%; cyclohexanone
5.6%; Cyclosol 53 14.4%; triethanolamine (85%) 2.4%; diaceatone alcohol
7.1%; polytergent B-300 1.2%; dibasic ester 15.9%; propylene glycol
monomethyl ether 13.2% and Hercoflat.RTM. 11.50 20.1%.
In evaluating the foregoing four samples it was found that the material of
Sample 6, lacking the polymeric material was the poorest cleaning agent
and that the cleaning efficiencies of the compositions increased as the
level of polymeric material increased. It was also noted that the
composition of Example 9 began to show some pumping problems owing to the
heavy polymer loading; although as noted hereinabove, use of other pumps,
such as diaphragm pumps will permit use of particulate material of large
size and heavy loading.
In general it will be appreciated from the foregoing that a wide variety of
solvent materials may be employed in the use of the present invention and
that significant advantage in cleaning ability attends upon the use of the
organic, polymeric material. The upper limit of the percent of polymeric
material in the vehicle is established by flow conditions of the liquid
through a given system and that upper limit will depend inter alia upon
system conditions as well as the particular solvents employed. Generally,
2-20% polymer will provide good cleaning action. It will also be noted
that similar results have been obtained using a variety of other solvents
and polymeric materials other than polypropylene.
The compositions of the present invention may be employed for cleaning a
variety of vessels, and it will be understood that as used herein the term
"vessel" refers to any object or piece of equipment from which encrusted
deposits are to be cleaned. Specifically, the term "vessel" includes
tanks, conduits, tubes, hoses, nozzles and similar parts of paint delivery
systems, chemical processing equipment, food handling equipment and the
like. The particular sequence of cleaning steps will depend upon the
nature of the article being cleaned as well as the characteristics of the
encrustations which are being removed.
In a typical process for the cleaning of a paint delivery system, the
system is first drained of paint and the lines thereof are blown out with
compressed air to remove any residual paint. At this point it is generally
advantageous to remove the filters, debris screens and like items in the
system. The painting system is then filled with one of the cleaning
solvent compositions of the present invention and the delivery pumps
thereof are activated to pass the solvent through the lines of the system.
Circulation of the fluid is maintained for a time sufficient to loosen
residues in the line. Generally it is sufficient to maintain circulation
from 6 to 8 hours and it has been found that adequate cleaning is obtained
if a minimum flow rate of 50 feet per minute is maintained through the
lines. It should be noted that the solutions are generally employed at
room temperature for sake of simplicity although it may be advantageous in
some instances to hasten cleaning action by heating the solution. Such
heating may be readily accomplished by disposing a heating unit in series
with the paint lines.
After the initial circulation of cleaning solvent is completed, it has
generally been found advantageous to rinse the system so as to remove
traces of the cleaning composition. Such rinsing is preferably
accomplished with a solvent compatible with subsequently introduced paint.
In many instances rinsing will be most advantageously accomplished by
utilizing a solvent similar to the vehicle of the cleaning composition,
but lacking the polymeric material therein. In other instances cleaning
will be found to be accomplished most efficiently by utilizing a dual
stage process wherein a first charge of contaminated cleaning composition
is drained from the system and a second charge of fresh composition is
introduced and circulated for another period of time. Obviously, such
process may be followed with a rinse step. In those instances where a dual
stage process is employed the second charge of cleaning composition will
usually be only very lightly contaminated and may be saved and reused as a
first charge of cleaning compositions for subsequent operations. Clearly,
this process may be varied in many ways depending upon the particular
application. As noted previously, cleaning may be carried out at an
elevated temperature; likewise, the cleaning composition may be agitated
or vibrated as for example, by ultrasonic energy, to enhance scrubbing
action.
Obviously, many other variations of the present invention, both in terms of
compositions and methods of application may be had in light of the
foregoing teaching. For example, cleaning of the external surfaces of
articles may be readily accomplished by spraying the organic particulate
containing compositions disclosed herein onto the surfaces of articles.
Such a process is particularly advantageous for degreasing articles or for
stripping paint therefrom. In a similar manner, the compositions disclosed
herein may be employed in combination with scrub pads, brushes or other
mechanical applicators to effect cleaning. These and other such variations
are clearly within the scope of the present invention. It is to be
understood that the foregoing description, discussion and examples are
merely meant to illustrate particular embodiments of the invention and are
not meant to be limitations upon the practice thereof. It is the following
claims, including all equivalents which define the scope of the invention.
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