U.S. patent application number 11/151865 was filed with the patent office on 2005-12-08 for method of removing organic materials using aqueous cleaning solutions.
This patent application is currently assigned to Princeton Trade & Technology Inc.. Invention is credited to Labib, Mohamed Emam.
Application Number | 20050272625 11/151865 |
Document ID | / |
Family ID | 28792366 |
Filed Date | 2005-12-08 |
United States Patent
Application |
20050272625 |
Kind Code |
A1 |
Labib, Mohamed Emam |
December 8, 2005 |
Method of removing organic materials using aqueous cleaning
solutions
Abstract
Removal of water-insoluble organic residues from inorganic
surfaces can be accomplished in aqueous cleaning solutions
containing an oxidant at a preselected temperature wherein the pH
is adjusted with respect to the isoelectric point of the surface
material to be removed so that the pH is above the pK.sub.a and the
isoelectric point of the surface for acid materials, and below the
pK.sub.a and the isoelectric point of the surface for basic
materials. Surfactants can also be added to the cleaning
solution.
Inventors: |
Labib, Mohamed Emam;
(Princeton, NJ) |
Correspondence
Address: |
MERCHANT & GOULD PC
P.O. BOX 2903
MINNEAPOLIS
MN
55402-0903
US
|
Assignee: |
Princeton Trade & Technology
Inc.
Princeton
NJ
|
Family ID: |
28792366 |
Appl. No.: |
11/151865 |
Filed: |
June 13, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11151865 |
Jun 13, 2005 |
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08974148 |
Nov 19, 1997 |
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6905550 |
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08974148 |
Nov 19, 1997 |
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08643690 |
May 6, 1996 |
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Current U.S.
Class: |
510/407 |
Current CPC
Class: |
C11D 11/0041 20130101;
C11D 1/83 20130101; C11D 3/3947 20130101; C11D 1/835 20130101; C11D
7/06 20130101; C11D 7/08 20130101; C11D 3/042 20130101; C09D 9/00
20130101; C03C 23/0075 20130101; C11D 1/65 20130101; C11D 3/044
20130101; C11D 11/0023 20130101 |
Class at
Publication: |
510/407 |
International
Class: |
C11D 017/00 |
Claims
I claim:
1. A method of cleaning inorganic surfaces to remove water
insoluble organic materials therefrom comprising a) treating said
surfaces with an aqueous solution including i) an oxidant in an
amount sufficient to convert non-polar residues to polar residues;
ii) a pH adjusting agent in an amount sufficient to provide a pH
greater than the isoelectric point for acid-type materials and less
than the isoelectric point for basic-type materials.
2. A method according to claim 1 wherein the temperature of the
cleaning solution is maintained between about 40-100.degree. C.
3. A method according to claim 1 wherein the oxidant is hydrogen
peroxide.
4. A method according to claim 1 wherein the pH adjustment agent is
ammonium hydroxide.
5. A method according to claim 1 wherein the pH adjustment agent is
hydrogen chloride.
6. A method according to claim 1 wherein the aqueous solution
further includes a surfactant.
7. A method according to claim 6 wherein the surfactant is a
mixture of an anionic and a nonionic surfactant.
8. A method according to claim 6 wherein the surfactant is a
mixture of a cationic and a nonionic surfactant.
9. A method according to claim 6 wherein the surfactant is a
mixture of an anionic and a cationic surfactant.
10. A mixture according to claim 6 wherein the aqueous solution
further includes a defoaming agent.
Description
[0001] This invention relates to a method of cleaning using
water-based cleaning solutions. More particularly, this invention
relates to a method of removing organic residues from inorganic
surfaces using water-based solutions.
BACKGROUND OF THE INVENTION
[0002] The conventional wisdom is that organic solvents are
required to remove most organic residues from the surfaces of
equipment used to make organic chemicals, pharmaceuticals and
foodstuffs. Organic residues are generally non-polar, or only
slightly polar, and thus aqueous solutions do not wet the residues
and do not remove them from equipment surfaces. Organic solvent
cleaning works by solubilizing organic residues; an organic residue
is contacted with a quantity of organic solvent until all of the
residue has dissolved. Depending on the particular organic residue,
one or several organic solvents may be required to thoroughly clean
equipment surfaces made of metal, ceramic, glass or polymers.
Organic solvents in general use for removing organic residues
include petroleum fractions, chlorinated hydrocarbons, toluene,
acetone, alcohols, esters and the like.
[0003] However, environmental laws and regulations that regulate
the use and emissions of organic solvents into the atmosphere are
becoming more stringent, and more expensive disposal is required,
thus making the use of organic solvents for cleaning more
expensive. On the other hand, regulations from the Federal Drug
Administration (FDA) and other agencies that monitor the
pharmaceutical industry are also requiring a higher level of
cleanliness for the manufacture of pharmaceutical products. A very
high level of cleanliness for equipment must be ensured for each
batch of material produced. Depending on the organic residue
present, one or several organic solvents may be required to
thoroughly clean the equipment. Organic residues that include
ionizable functional groups, such as carboxylic acid groups,
hydroxy groups or amine groups, adhere strongly to metal and glass
surfaces.
[0004] Certain organic materials are water soluble, and thus
water-based solutions can be used to remove water soluble organic
materials from various surfaces. However, most organic materials
are insoluble in water and thus washing in water does not remove
these insoluble organics from surfaces.
[0005] Thus water-based cleaning solutions that can effectively
remove organic residues from the equipment used to make organic
chemical products and pharmaceuticals would be highly
desirable.
SUMMARY OF THE INVENTION
[0006] In accordance with the present invention, organic materials
which are non-polar and insoluble in water are reacted to form
polar materials that can be removed from metal, ceramic, glass or
polymeric surfaces using water-based cleaning solutions.
[0007] The water-based cleaning solutions of the invention contain
an oxidant that adjusts the oxidation potential of aqueous cleaning
solutions and a pH adjusting agent, and optionally a surfactant.
Contact between the present cleaning solutions and insoluble
organic residues are continued at a preselected temperature until
the non-polar residues are converted to polar residues which can be
solubilized or loosened from various inorganic surfaces and rinsed
away with water.
[0008] Water-insoluble organic residues to be removed from
inorganic surfaces to which they adhere are taken into the aqueous
cleaning solution of the invention as particulates, rather than
solubilized as is done using organic solvents.
BRIEF DESCRIPTION OF THE DRAWING
[0009] FIG. 1 is a graph of cleaning performance versus pH for
diphenyl amine on stainless steel.
[0010] FIG. 2 is a schematic view of a system used to measure
cleaning of glass substrates.
[0011] FIG. 3 is a graph of cleaning performance versus pH for
stearic acid on stainless steel.
[0012] FIG. 4 is a graph of cleaning performance versus pH for
diphenyl amine on glass.
[0013] FIG. 5 is a graph of cleaning performance versus time for
different temperatures for stearic acid on glass.
DETAILED DESCRIPTION OF THE INVENTION
[0014] The surface chemistry of substrates such as stainless steel
and other metals, ceramics such as alumina and zirconia,
dielectrics such as quartz and glass and the like, depends on the
chemistry of their surface oxides and hydroxides. Adhesion of
various insoluble organic materials follows acid-base reactions.
The mechanism of adhesion between an organic material and a surface
in aqueous solution will be explained using stainless steel as an
example. Solid surfaces such as stainless steel have surface oxide
and hydroxide groups present. In an aqueous environment, several
layers of water become hydrogen-bonded to the hydroxylated surface.
The hydroxyl groups can be ionized at the solid-water interface,
as
-MOH+H.sup.+.about.-MOH.sub.2.sup.+ and
-MO--+H.sup.+.about.-MOH
[0015] Thus the ionization depends on the pH of the aqueous
solution. For oxide, there is a pH at which the number of positive
charges equals the number of negative charges at the surface, which
is defined as the isoelectric point of the surface (IEP) If the pH
is lower than the IEP, the solid surface is positively charged. If
the pH is higher than the IEP, the solid surface is negatively
charged.
[0016] The isoelectric points of several solids useful herein are
given below in Table I.
1 TABLE I Surface IEP stainless steel 8.5 quartz 2.5 molybdenum 3.7
aluminum 9.0 titanium 6.0 tantalum 5.2
[0017] Thus in order to repel a material (organic residue) from a
particular surface, both should have the same charge sign. If they
do not, the organic residue will be attracted to, and adhere to,
the metal or glass surface, and cleaning will not take place.
[0018] To accomplish cleaning of an insoluble organic acid, the pH
of the solution should be higher than the pK.sub.a of the acid and
the IEP of the surface to be cleaned. To accomplish cleaning of an
organic base, the pH of the surface should be lower than the
pK.sub.a of the organic base and the IEP of the solid surface.
Weakly ionized materials such as diphenyl amine, can be cleaned
using the present invention. Further, ionizable materials having a
high molecular weight hydrophobic moiety, not cleanable in water,
can also be cleaned in accordance with the present invention. In
order for cleaning to occur, the interface between the organic
residue and the solid surface must be in a state of net
electrostatic repulsion for cleaning to be possible. Using these
criteria, a determination of whether effective cleaning can be
accomplished, and the pH needed, can be made.
[0019] The most important ingredient of the present cleaning
solution is the oxidizing agent that produces an oxidation
potential for a particular organic residue and will generate polar
functional groups in the residue. The oxidation potential can be
varied in accordance with the type of oxidant and its concentration
in the aqueous cleaning solution, and it must be higher than the
minimum oxidation potential required to oxidize the particular
organic residue sought to be removed.
[0020] The pH is another important criterion for the present
aqueous cleaning solutions. The pH level of the cleaning solution
must be such that the electrostatic charge sign of the surface to
be cleaned remains the same during cleaning. The dissociation of
surface hydroxides on the substrate in an aqueous solution takes
place at the isoelectric point, when the surface has zero charge.
In order for cleaning to occur, the pH of the cleaning solution
must be greater than the isoelectric point for the cleaning of
acid-type materials, and lower than the isoelectric point for the
cleaning of basic-type materials. The pH level should also be
adjusted so as to avoid corrosion of the metal surfaces to be
cleaned at too high a pH, and to avoid etching of glass surfaces to
be cleaned, i.e., at too high or too low a pH.
[0021] The oxidation potential and pH can be selected so they
operate in the passivation region of metal surfaces, such as
stainless steel. The formulations can be tailored to the
corrosivity of other metals as well, such as copper or aluminum.
The oxidation potential can be adjusted by adding peroxides,
permanganates, periodates and bromates, and by the addition of an
oxidizing ion such as ceric ions in small amounts. If the solution
oxidation potential does not provide an immediate response to the
oxidation potential at the interface between the residue and the
solid surface to be cleaned, the level of the oxidant must be
adjusted and checked periodically during the cleaning process.
[0022] A conventional surfactant or detergent can also be added to
the present cleaning solutions. The amount and type of surfactant
can also be varied so as to increase the surface charge of the
residue with respect to the surface charge of the surface to be
cleaned. When the particles of residue are taken into the cleaning
solution, the surfactant type and amount are adjusted so the
particles do not readily re-deposit on the surfaces being cleaned.
The surfactant also must be non-reactive with the quantity of
oxidant used in the cleaning solution.
[0023] When cleaning is done below the IEP, i.e., the residue
behaves as an organic base (positively charged), a mixture of
cationic and nonionic surfactants are effective for non-soluble
residues that generate a positive charge during cleaning, including
amines or materials that generate amines. For example, for cleaning
amine residues, cationic surfactants of the type
R--N--CH.sub.3Cl
[0024] wherein R is an alkyl group suitably of 8-16 carbon atoms
can be employed. One example is hexadecyltrimethylammonium chloride
at a level of about 0.1-10%. The cationic surface can be mixed with
a nonionic surfactant, such as a monolaurylether of polyethylene
glycol, used as a wetting agent. These surfactants also stabilize
organic residues dislodged during the cleaning. The nonionic
surfactant can be present in amounts of 0.1-5%.
[0025] When cleaning is done above the IEP, when the residue
behaves as an organic acid, a mixture of anionic and nonionic
surfactants can be used. Suitable anionic surfactants include long
chain alkyl-substituted sulfonic acids, such as
dodecylbenzosulfonic acid, in an amount of about 0.1-10%.
[0026] When cleaning is required at a neutral pH or at about the
IEP, nonionic surfactants alone can be used. These surfactants
promote the wetting of the inorganic surfaces, and can be used at a
level of about 0.1-5% added to the standard cleaning solution at a
hydrogen peroxide concentration of about 5%.
[0027] When cleaning is required under acidic pH conditions, the pH
can be adjusted between 3 to 5 with citric acid for example at a
temperature of about 75.degree. C. The concentration of hydrogen
peroxide in that case is preferably increased to between 5-15%.
Difficult to clean materials such as non-wettable oils on glass,
stainless steel or ceramic surfaces, can be removed with such a
solution, particularly if ultrasonic agitation is also used.
[0028] A combination of an anionic surfactant and a cationic
surfactant can also be used at a high (10.5) pH. The pH can be
maintained at a high level with the addition of ammonium hydroxide
or sodium hydroxide. If required, a silicone defoaming agent can
also be employed.
[0029] Regardless of the choice of surfactant, non-foaming
surfactants should be chosen, or a defoaming agent should be added,
such as cetyl alcohol.
[0030] The temperature of the cleaning solution during cleaning
operations should be generally between about 40.degree. C. to
100.degree. C. Within this temperature range, generally an increase
in temperature increases the rate of removal of the organic
residues from substrate surfaces. If the temperature is high enough
to melt the organic residue, cleaning is easier since fluids are
removed faster than solid organic materials using the present
cleaning solutions.
[0031] Mechanical force can also be applied to aid in the removal
of organic residues from substrate surfaces. In general, removal of
organic residues from a surface is aided by the use of mechanical
agitation, such as the use of jets, or stirring, or ultrasound
agitation, all of which improve the rate of residue removal,
particularly for stubborn residues such as charred sugars, polymers
and silicone grease.
[0032] In order to ensure an optimum level of cleaning activity,
the pH, oxidation potential, temperature and agitation parameters
must be maintained and monitored. Timely addition of reagents and
the maintenance of temperature and agitation will maintain the
effectiveness of the present cleaning solutions so that the maximum
amount of residue may be removed from surfaces in a minimum amount
of time, while avoiding the use of excess environmentally unsafe
oxidant materials.
[0033] One of the major benefits of the present cleaning technology
is that the rate of cleaning is remarkably increased, often by a
factor of ten. This can be seen in FIG. 1, which compares the
cleaning performance for removing diphenyl amine from a stainless
steel surface using a 4.5% aqueous solution of hydrogen peroxide at
a temperature of 45.degree. C. Curve A shows cleaning performance
of this solution after ten minutes at various pH, versus water
alone (curve B). It is apparent that above a pH of 8, the removal
of the diphenyl amine is very rapid in the solution of the
invention. Partially ionizable residues can also be cleaned more
rapidly when peroxide solutions of the invention are employed.
[0034] Suitable oxidants useful in the present water-based cleaning
solutions include peroxides, perborates, percarbonates and the
like, as well as other materials that can change the oxidation
potential of aqueous solutions. A widely available, non-toxic,
inexpensive and easy to use oxidant is hydrogen peroxide. Hydrogen
peroxide dissociates upon reaction to produce water and oxygen,
both innocuous, and no solids are formed that could interfere with
the cleaning of substrates. Organic peroxides such as peracetic
acids, or peroxybenzoic acid, and tetrabutyl peroxy compounds are
also useful and the latter can diffuse into polymeric matrices and
interstices. The selection of the peroxide to be used is chosen
based on the nature of the residue. Other widely available and
inexpensive materials, such as hypochlorite solutions (bleach) are
corrosive and generate particulates. Thus hypochlorites are not
preferred. Perborates and percarbonates must be used above the
temperatures at which they spontaneously dissociate.
[0035] In addition to cleaning water insoluble organic materials,
organic materials that are soluble in water can form insoluble
materials when they are exposed to elevated temperatures. For
example, cooking foods at too high a temperature will form
insoluble residues that can no longer be removed with aqueous
solutions, even those including surfactants. The present cleaning
solutions will remove these charred or chemically altered
materials.
[0036] The invention will be further described by the following
examples. However, the invention is not meant to be limited to the
details described therein.
[0037] In the examples, small glass and metal substrates were used.
The metal substrates were 316 (SS316) grade stainless steel, a high
carbon, high chromium, high nickel corrosion resistant steel. The
test plates used were 2 inches square and {fraction (1/16)} inch
thick. These stainless steel substrates were cleaned in preparation
for the testing as follows: the test substrates were rinsed with
acetone, dipped in trichloroethylene for 30 seconds, rinsed with
methanol and then with acetone, dipped in HCl for 30 seconds,
dipped in nitric acid for 30 seconds, rinsed with hot deionized
water, then with acetone and dried.
[0038] The glass substrates were pyrex glass 3 inch squares 1/8
inch thick. These substrates were cleaned by first washing with
detergent, dipping in chromic acid for 30 seconds, then in HCl for
30 seconds, rinsing with deionized water and drying.
[0039] Other test substrates were made from aluminum, molybdenum,
tantalum, titanium, and zirconia cut into 2 inch squares.
[0040] Various organic materials were deposited on the test
substrates as will be detailed in the examples below. Various
cleaning solutions and deposition methods were used for the removal
of the organic materials.
[0041] The degree of cleaning was determined for the metal
substrates by visual inspection. The degree of cleaning was
determined by dividing the amount of cleaned area by the total area
of the sample. The visual inspection can be augmented using a
microscope.
[0042] Cleaning of glass substrates was measured by optical
spectroscopy. The system used is shown in FIG. 2. Referring to FIG.
2, a source of monochromatic light 12 is mounted so that the light
passes to a photospectrometer 14. The incoming light beam (400
nanometers) was passed through a quartz cuvette 16 (a quartz
container for the solutions to be measured) and the absorbance
measured to calibrate the clean cuvette. After depositing the
organic residue and cleaning the glass substrate, absorbance of the
resultant cuvette was measured again. The difference in the mass of
deposited material before and after cleaning is calculated as a
measure of cleaning performance in accordance with the following
equation:
C.sub.p(%)=(A.sub.o-A.sub.t)/(A.sub.o-A.sub.c).times.100
[0043] wherein A.sub.o is absorbance before cleaning, A.sub.t is
absorbance at time "t" (after cleaning) and A.sub.c is absorbance
of the clean quartz cuvette.
EXAMPLE 1
Cleaning of Dehydrated Carbohydrate
[0044] A 1 Molar solution in water of glycerol was made by heating
in water at 80.degree. C. for one hour. The glycerol deposited onto
a stainless steel substrate, was heated at 200.degree. C. for one
hour. A sticky residue formed which was not removable in cold
water, but was removable in warm (60.degree. C.) water after 10
minutes.
[0045] The sticky residue was removed immediately in a solution
containing 4.5% of hydrogen peroxide and 4.5% of ammonium hydroxide
in water (standard cleaning solution, hereinafter SCS) at
60.degree. C.
EXAMPLE 2
Cleaning of Insoluble Esters
[0046] A 0.5 Molar solution of isoamyl acetate in acetone was made
at 80.degree. C. and evaporated to leave a residue on a test
substrate. This residue was heated at 180.degree. C. for one hour
to form a brownish sticky residue that could not be removed in
either cold or warm water.
[0047] The residue was removed in SCS at 60.degree. C. within one
minute.
EXAMPLE 3
Cleaning of Cycloketones
[0048] Cyclohexanone was deposited on warmed (70.degree. C.)
substrates. This material was not removable with cold or warm
water, but was removed in less than one minute in SCS at 60.degree.
C.
EXAMPLE 4
Cleaning of Epoxy Resin
[0049] Bisphenol A and epichlorohydrin were mixed together on a
substrate and dried to form an adherent clear epoxy resin layer.
This residue could only be removed by treatment with SCS at
70.degree. C. with scrubbing.
EXAMPLE 5
Cleaning of Silicone Grease
[0050] A commercial silicone grease was deposited on a substrate,
which was not removable with cold or warm water. However, it was
removed in SCS at 70.degree. C. after about 10 minutes.
EXAMPLE 6
Cleaning of Insoluble Organic Acid on Stainless Steel
[0051] A 1 Molar solution of stearic acid in boiling isopropanol
was used to deposit stearic acid on glass. Removal of stearic acid
from the substrate was strongly pH dependent, as shown in FIG. 3, a
graph of cleaning performance versus pH at 55.degree. C. measured
after 10 minutes.
[0052] It is apparent that no cleaning took place up to a pH of 8
for SCS and above 8 for water.
EXAMPLE 7
Cleaning of Aromatic Amine on Stainless Steel
[0053] Diphenyl amine was deposited from 2-propanol solution onto a
stainless steel substrate. The deposit was not wetted nor cleanable
in cold water. At a temperature above about 52.degree. C., the
material melted and could be removed.
EXAMPLE 8
Cleaning of Aromatic Amine on Glass
[0054] Diphenyl amine was deposited as in Example 7 onto glass
substrates.
[0055] As can be seen in FIG. 4, a graph of cleaning performance
versus pH, the substrates were not cleanable except at a pH below
2. At high pH, the substrate was etched.
EXAMPLE 9
Cleaning of Stearic Acid from Various Substrates
[0056] Stearic acid was deposited as in Example 6 onto different
metal substrates. Removal from aluminum in hot water only occurred
at a pH over 11, which caused corrosion of the substrate.
[0057] Stearic acid was deposited onto molybdenum and was removable
from aqueous solution at 55.degree. C. at a pH over 6.
[0058] On tantalum, stearic acid was only removable from aqueous
solution at 55.degree. C. at a pH over 5.
[0059] On titanium, stearic acid was only removable from aqueous
solution at 55.degree. C. at a pH over 6.
EXAMPLE 10
Cleaning of Stearic Acid Versus Temperature
[0060] Stearic acid was deposited onto glass substrates and removed
with hydrogen peroxide solution (4.5%) at various temperatures. The
results are shown in FIG. 5 wherein the pH was maintained at 7. It
can be seen that temperature has a marked influence on removal of
the organic residue.
EXAMPLE 11
Cleaning of Burned Oil on a Zirconia Surface
[0061] Oil was deposited on zirconia and burned. The residue was
removed by a cleaning solution of 10% hydrogen peroxide, 2%
hexadecyl trimethyl ammonium chloride, 2% cationic surfactant and
0.5% of cetyl alcohol as a defoaming agent. The pH of the solution
was 3.5. Maintaining the solution at 75.degree. C., the organic
residue was removed from the zirconia surface.
EXAMPLE 12
Cleaning of Hydrophobic Resinous Oils on a Zirconia Surface
[0062] A cleaning solution containing 7% hydrogen peroxide, 5%
anionic surfactant and 2% cationic surfactant in water was adjusted
to a pH of 10.5, which is above the IEP of zirconia. Silicon
defoaming agents can be added as required. This solution removed
the resinous residue from a zirconia surface.
EXAMPLE 13
Cleaning of Glucose and Charred Sugars on a Zirconia Surface
[0063] A glucose solution was heated to 180.degree. C. and
deposited on a zirconia substrate. Cleaning was accomplished using
potassium periodate at a basic pH of 10.5 and a temperature of
75.degree. C.
EXAMPLE 14
Cleaning of Charred Starch on Metal and Glass Surfaces
[0064] A starch was heated to a brown color in an oven and
deposited on 316 stainless steel and glass. This material was very
difficult to remove with SCS but the addition of a small amount of
alcohol aided the cleaning process.
EXAMPLE 15
Cleaning of Ethyl Cellulose on a Stainless Steel Surface
[0065] An ethyl cellulose latex containing plasticizers such as
dibutyl sebacate or trimethyl citrate was deposited on 316
stainless steel and made to adhere to the substrate by heating in
an oven at 80.degree. C. for 18 hours. This residue is not
cleanable in either hot or cold water, or in conventional alkaline
surfactants. This very inert material was cleaned with SCS alone at
75.degree. C. This material was also cleaned with SCS to which
phosphate and anionic surfactants were added at a pH of 10.5, in 10
minutes.
[0066] Although the invention has been illustrated in terms of
specific embodiments, it will be apparent to those skilled in the
art that various insoluble organic materials can be removed from
glass and metal surfaces in like manner. The pH and temperature can
be readily optimized in accordance with the above examples. Thus
the invention is to be limited only by the scope of the appended
claims.
* * * * *