Note: Descriptions are shown in the official language in which they were submitted.
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WO96/21752 PCT~S96/00517
A PROCESS OF COATING METAL SURFAC~S TO PROVUCE A IIIGIILY
llYl)ROPHI~JIC, EI~GHLY CORROSlON I~ESISTANT SURFAC~ WlT~
~ BIORESISTANCE AND LOW ODOR IMPACT CHARACTERISTICS
FIELD OF THE INVENTION
The present invention relates generally to corrosion
resistant coatings for metal surfaces, and more palticularly
to low-odor, bioresistant, hydrophilic, corrosion resistant
coatings for aluminum.
BACKGROUND OF TE~E INVENTION
The present application is a continuatioll-in-part of
applicant's copending patent application Serial No.
0~/137,583, issued as U.S. Patent No. 5,380,374, which is
incorporated herein by reference.
A variety of coatings for aluminum are known to tIle art.
These coatings typically provide corrosion resistance to the
metal, while often simultaneously providiny improved paint or
other organic coating adhesion.
Although most early coatings for rnetals such as aluIninurn
were chromate-based compositions, chromate-free coatirlgs have
recently been developed. These coatings are particularly
useful for applications such as coating alwI~ m food or
bevera~e cans, where it is particularly desirable to avoid
potentially toxic chromium.
~I1romate-free conversion coatings often employ a Group
IVA metal such as titanium, zirconium or halfnium, a source
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of flouride ion and nitric acid for pH adjustment. These
chromate-free conversion coatings are often clear alld are
used to prevent the blackening that normally occurs when
aluminum is boiled in water during pasteurization.
For example, U.S. Patent No. 3,964,936 to Das discloses
the use of zirconium, flouride, nitric acid and boron to
produce a conversion coating for aluminum. U.S. Patent No.
4,148,670 to Kelly discloses a conversion coating comprising
zirconium, fluoride and phosphate. U.S. Patent No. 4,273,592
to Kelly discloses a coating comprising zirconium, flouride
and a Cl 7 polyhydroxy compound, wherein the composition is
essentially free of phosphate and boron. U.S. Patent No.
4,277,292 to Tupper discloses a coating comprising zirconium,
flouride and a soluble vegetable tannin.
U.S. Patent No. 4,338,140 to Reghi discloses a conversion
coating comprising zirconium, fluoride, vegetable tannin an~
phosphate, and optionally including a sequesterinc3 agent to
complex hard water salts such as calcium, magnesium and
iron. U.S. Patent No. 4,470,853 to Das et al. discloses a
coating comprising zirconium, fluoride, vegetable tannin,
phosphate and zinc. U.S. Patent No. 4,786,336 to Schoener et
al. discloses a coating comprising zirconium, fluoride and a
dissolved silicate, while U.S. Patent No. 4,992,11G to
Hallman discloses a conversion coating comprising a
fluoroacid of zirconium and a polyalkenyl phenol.
It should be noted that the conversion coatings of tlle
prior art have not proven particularly effective for certain
applications. In particular, the prior art has not disclosed
a process for coating automotive heat exchanyers so tllat the
s~ face obtained is not only corrosion resistant, but is also
hydrophilic, bioresistant and odor-free. lhese properties
are particularly desired in applications such as the
production of air conditioning evaporators for automobiles.
For example, U.S. Patent No. 5,234,714 to Rasso is
related to a coating system using a chromate/silicate process
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for "providing an aluminum heat excllanger with a
corrosive-resistant hydrophilic coating." Additionally, it
is stated the chemical concentrations "are precisely
controlled in order to avoid producing a coating which emits
a musty odor." The patent describes a process wherein a
"cleaning stage" [this is actually a deoxidation treatment in
the described process], a "chromating" stage, and a
"silicate" stage are employed.
U.S. Patent Nos. 3,762,178 and 4,672,816 to Yarnamada and
Takallaslli, respectively, deal with systems to reduce or
eliminate "musty" odor from auto air conditioning systems
througll use of antibiological agents.
U.S. Patent No. 5,203,402 to Nisllishita describes a heat
exchanger design along with an organic-based coating to
produce a llydropllilic layer. The coating is composed of a
colloidal silica suspended in an organic matrix. The
suspension is cured and the "silanol groups of the colloidal
silica are chemically combined with part of hydroxyl groups
of the resin," reportedly resulting in a change of properties
of ~he silica and "making smells less liable to attach to the
colloidal silica."
U.S. Patent No. 5,201,119 to Minzuno descri~es design of
a heat excllanger with use of two separate coating systems.
The first typically incorporating a chromium contaillirlg
conversion coating for corrosion protection and the second
coating incorporating an antimicrobial agent [specifically,
2,2'-ditlliobis(pyridine-1-oxide)] to prevent microbial grow~h.
Canadian Pat. Appl. No. 2083454 AA 9, Intl. Cl.
C23C-022/37 to Melzer describes a method for coating aluminurn
and aluminum containing metals with a "no-rinse coating" for
increased corrosion protection. The process described
details the use of aqueous solutions of "multivalent chrolniuln
compoullds comprising including in said aqueous solution a
fluoride containing compound." The compositions which may be
used are described in U.S. Patent Nos. 4,475,957 and
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4,921,552 to Sander, et al, and others so listed in the
application. The process and compositions described render a
surface protected by a polymer (such as a
"poly(alkyleneo~y)-" type) Witll a multivalent transition
metal incorporated into the matrix.
V.S. Patent No. 4,338,140 to Reyhi is related to coating
metal for improved corrosion resistance with solutions
containing zirconium, fluoride and tannin compounds at pll
values from 2.0 to 3.5. U.S. Patent No. 4,470,~53 to Das is
related to a coating composition comprised of zirconium,
fluoride, tannin, ~llospllate, and zinc in tlle ~H range of 2.3
to 2.95. U.S. ~atent No. 5,380,374 to Tomlinson describes
compositions combilling Group IV-B with Group II-A elements
for producing corrosion resistant coatings on metals.
U.S. Pat. Appl. No. 08/138,136 to Tomlinson describes
compositiorls for combining Group IV-B with Group IA elements
for producing hydrophilic, corrosion resistant coatings on
metals in low p~l and high speed applications.
The above patents do not describe tlle process as
desclibed below for providing a Group IV-B/silicate coatin-3,
nor is it obvious that the invention described below would
produce a coating witll all the desired properties. A need
tllerefore exists for a process of coatiny aluminum so that
the surface obtained is not only corrosion resistant but is
also hydrophilic, bioresistant and odor-free. Tlle present
invention addresses that need.
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' SUMMARY OF THE INVENTION
~ BLiefly describing one aspect of t11e invention, there is
provided a process for improving the corrosion resistance of
metal surfaces by treating the metal with a solution of
flLloride, zirconium and a protic acid, subsequently treating
said metal surface with a solution of water-soluble silicate
at an alkaline p1~, and then drying the metal surface.
One object of Lhe present inventio1l is to provide
coatings for alwnir1l1m that are corrosion resistant,
11ydrophilic, bioresistant and odor-free.
Further objects and advantages of the present inve11tion
will be ayparent from the following description.
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DESCRIPTION OF Tl~E PREFERRED EMBODIMENT
Eor the purposes of promoting an understandir1y of the
principles of the invention, reference will now be made to
preferred embodiments and speciEic language will be used to
describe the same. It will nevertheless be understood that
no limitation of the scope of t11e invention is L1lereby
intended, sucl1 alterations and furtl1er modifications in tlle
disclosed embodiments, and suc~1 furtller app]ications of tlle
prir~ciples of the invention as illustrated therei11, being
co11te1llplated as would nor1nally occur to one skilled in the
art to wl1ich the invention pertains.
As previously indicated, tlle present invenLion relates to
a process for producing a c11romium-free, 11iy11ly corrosion
resistant coating on the surface of a metal substrate. The
cllemical compositions used in the process produce a
l1ydrop11ilic, corrosion resistant coatiny on iron, alurninu
and magnesium alloys.
The invention incorporates at least three process
stages. The first stage is a Group IV/mixed oxide treatme1lt
with no or minimal etcl1iny of the surface. The second is a
silicate deposition stage with, for example, sodium and/or
potassium silicate being suitable here. The tl1ird stage i.s a
final "dryir1y" stage, preferably at elevated temperature. It
is during this final dryiny stage that metal-oxide-Group IV
metal-oxide-silicate/siloxyl linkages are fully establis11ed.
The following discussion and examples will address
treatment of aluminum alloys in general an~ alwninu1n alloy
l1eat excha1lge units specifically. The treatme11ts so
describe~ are applicable to ferrous, ZillC, arld ma9Ilesilllll
alloys as well as all1minu1n.
Depending ~1pon the final requirements of the coati1l9, a
multiplicity of stages may be used prior to t11ose indicated
above. For example, when usiny an aluminum substrate wllere
_
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hydropl1ilicity of the surface is hi~JI1ly desirable (such as an
air conditioning evaporator) a first stage prior to tllose
listed above can incorporate components to mildly etch the
oxide and simultaneously deposit mixed metal/non[netal salts
(such as a Zr/K/Al/F matrix). l'l1e sur~aces so ob~ained will
provide the base layer for the three stages described in tl1e
above, rather than the natural metal oxide that exists on the
base alloys. The resultant coating when all stages have been
used will be slightly roughened and have many hydropllilic
components to provide a superior water-break-free surface. A
specific exarnple of this is presented below.
If corrosion resistance is desired above what is provide~
by the three required stages, a pretreatment stage may be
used wherein elements or compounds are deposited to enhar1ce
tl1is inllereIIt characteristic. For example, it has been seer
that nonetching "pretreatments" in mixed Group IV/Group
II/[borate, silicate, and/or phospl1ate] solutiolls may be
beneficial in this regard. Also, creating a thick and
uniform oxi~e layer by standard anodization processes
general]y increases corrosion resistallce as the coatilly coats
this "built" oxide.
It is to be appreciated that the coatings obtained by tlle
disclosed process are "non-nutrient" and have essentially no
odor impact. These are consequences of the inorganic nature
of tl1e coating obtained, and will also be inherent to each
variant described when no organic component is use~ to
supplelnent any characteristics of tl1e coating system. The
coating does not contain components that microorganisllls use
for metabolism and therefore does not promote this type of
yrowtll.
It is also to be noted that borates have been showr1 to
exhibit bioinhibition in certain environments, and in the
coatings herein described where boric acid and/or polyborates
have been used bioinhibitio1l has been demonstrated.
Finally, it is to be appreciated that the absence of any
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significant long-term odor impact is believed to be due to
tlle lack of promotion of biological growth on tllese types of
s~stems. Tlle lack of short-terrn odor impact is likely due to
tlle tightly bound and relatively neutral (witll regard to
oxidation po~ential against carbonaceous components iII the
air stream) ollter siloxyl surface obtained in tl-lis process.
The lack of short-term odor impact is believed to be inllerellt
to tlle process, so that only the "long-term" odor impact is
significant-ly augmented by the use of bioinhibitory
components in or on the final surface.
The aqueous stages are yenerally at elevated ternperature
(>70~F) and exposure times usually rull from 30 seconds to 5
rninutes per stage. A notable exception would include wllerl a
"hydrophilic pretreatment" is used as described al~ove. Illi5
has ~een done down to 50~F [pretreatmerlt - K/Zr/Al/F/I~NO3
system~ with excellent results as etc~ling is moderate and a
heavy deposition of salts is obtained. Superior corrosioll
resistance is obtained quickly a~ter the three prirnary stages
(generally 30 seconds per aqueous stage) and extended
exposures are usually not required.
One or more rinse stages can be used sequentially
following any stage. l'here oEten is a more pronounced nee~t
for rinsing with parts such as lleat exchange units that are
complicated geometrically. Fres~l water is continuolJ.sly
introduced to the rinse baths to maintain cleanlilless.
Manual or automatic rnonitoring o~ pl~ or conductivity can be
used to determine and maintain cleanliness of the rinse
stages.
A deionized water rinse stage is preferred prior to tlle
silicate treatment in order to keep it free of contaminant-:s
from tlle first stage(s). Aqueous silicate sols are generally
stable at very lliyl~ concentrations provided tlle p~ is
maintained, genera]ly, above 10.0 and the solution is kept
free of ionic contaminaTIts. The components of tlle first
treatmellt stage will and do (at the surface - silicate
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solutiol1 interface) induce polymerization leading to an
[SiO2~x matrix. It is by this mechanism, along with the
"substrate-O-[Group IV Metal]-O-Si-[SiO2]x" production, tl1at
the final coating is obtained and, therefore, it is desirable
to keep the silicate solutions free oE any contamination.
More particularly describirly stage l, the acidic, aqueous
coating solution composition can be prepared from a variety
of acids and salts which contain group IV-B metals,
specifically Zr, l~f, or Ti. Fluoride may be added by tl1e
complex metal fluoride of the Group IVB metal, as an acid or
salt of such a complex fluoride, by the many simple fluoride
salts. Examples include KF, NaF, etc., acid fluorides such
as ~F, and preferably as H2ZrF6 and KF. The essential
acid component may be added from the acid metal (Group IV- B)
5 r luoride or otl1er mineral acids such as HNO3, II2SO4,
~lF, etc., and preferably as ~IN~3.
In one embodiment the invention incorporates Group lV-B
metals (zirconium in the examples ~elow) in solution with
Group II-A metals (calcium in the examples below) at pl~
levels of 1.5 to 4.5 for the first treatment stage.
~ ependent on concentration of the Group II-A and IV-B
metals (generally, the higher level of metal concentratio11
necessitates lower pH levels and, with increasing levels of
metal and acid, a heavier coating is obtained) and fluoride
in a mole ratio to Group IV-B and dissolved metal (e.g.,
aluminum) of at least 4 moles fluoride to each mole of
metal. Fluoride must be balanced to maintain the working
solution such that the metals remain soluble while little or
no e~chi11g of the substrate occurs. This is dependent on
acid and metal concentrations as the fluoride will move Erom
the hiyl1er order metal fluorides to t11e lower order and
preferentially to the metallic (oxide) surface. A small
alnount of etching oE an oxide surface is acceptable, but mucl
oE t11e metal oxide resident on tl1e surEace prior to coating
is maintained and gives additional protection iIl a corrosive
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--10--
environment. Temperatllre of the workinc3 solution can range r
from 70~F to 180~F witll 120 to 140~F bein~ preferred. Tlle
surface so obtained is ready for the next stage of the
process.
By example, acceptable coatin~s can be formed from
solutions contailling from 0.00015 M to 0.055 M, Group IV-B
metal, with 0.00025 M to 0.03 Group II-A metal in Stage 1.
Tlle best ratio of Group IV-B to Group II-A metal will be
dependeIlt on the method of coatincJ solution contact (spray,
dip, etc.), the working bath temperature, pll, and fluoride
concentration.
In one aspect of the invention, Stage 1 comprises a 5
minute immersion at a temperature of 140~F, with
concentrations of 150 to 600 ppm Zr, 80 ppm Ca, and 200 to
740 p~m F at a pH from 2.4 to 2.8. This embodiment of tlle
invention gives sllperior corrosion protection when used in
conjllnctioll wilh Stage 2.
Workiny solutiolls can be made up to tlle solubility limits
of the components in Stage 1 in combination to provide
accepLable coatin~s, but lower levels as described above are
preferred, as dissolved substrate metal ions enterillg tlle
coating solution during processing may cause precipitation of
bath components in saturated and near saturated solutiolls.
This can also be dealt with in the solutions disclosed so ~ar
by other metllods. For example, addition of a chelarlt such as
Versenex 80 to a bath for treatment of ferrous substrate will
yield a solu~le ion complex with dissolved FeX~, extendillc~
the life and efficiency of the workillg solution. It should
be rloted that the presence of iron in woLI~ing solutions for
alumillulll and oTher metals may decrease tlle corrosion
protectioll obtained. A chelarlt 511Ch as EDTA,
trielllaIIolamine, or Versenex ~0 will preferentially coln~lex
~he iron in solution and inll;bit its incorporatioll into the
conversion coatillys for a]uminuTTI or mac~nesiuln.
Additionally, insoluble calcium salts which may form in
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W096/21752 PCT~S96/00517
- tlle higher temperature range mentioned may be rnore soluble at
the lower temperatures and, ~herefore, the woLking solution
sllould be used at the lower end of tlle temperature range wller
tlle calcium content of the working solutioll is at tlle lligl
end of the levels stated. Also, addition of a
tr;~olypllosphate (as Na5P3010 or other polypllosphate salt)
will assist in maintaining lligll levels of calcium in the
treatlllerlt bath.
Addition of boron in the form of boric acid, borate
salts, or fluoroborates to tlle workiny solution has beell
sllown to improve certain properties of the coatinys obtained
as described. l'he preferred range for boron is 50 to 100
ppm, typically present at 10 to 200 ppm.
Addition of p~losphate to tlle workillcJ bal~l can add to
corrosion protection and paint adhesion to tlle coating
o~tained. It is commonly believed tllat the incorporation of
pllospllate into certain conversion coatings enllances
protection from "pittiny" corrosion; as wllen a pit is
illitiated in a corrosive environment, the phosphate present
will ~irst dissolve into tlle pit area and, there, form
insoluble salts witll base (substrate) metal ions or other
coating components, effectively sealinc3 the pit.
Additioll of ZillC to the working solution llas been ShOWII
to produce coatings with improved corrosion resistance on
ferrous substrates. It is believed tlle zinc accelerates
coating deposition and, wllen incorporated into tl~e coatillg
(if reduced) may provide galvanic protection to tlle metal
substrate. The typical range for zinc is 5 to 100 ppm,
preferably lU to 30 ppm.
Aluminum added to the working solution increases tlle rate
of deposition of insoluble salts in the coating. Aluminulll
may be added in any form of soluble alumillum salt, preferably
as a hydrated alulllillulllrlitrate. Typically, alwllinunl may be
presellt at 50 to 1,000 ppm, pre~erably at 100 to 200 ppm.
Working solutions composed of Inixture(s) of the above
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components may be applied by spray or dip coat applications.
After the coating in the first stage has formed tl1e surface
should be ril1sed with clean water. The rinse(s) may be
deionized or tap water and should remove any soluble salts
whicl1 might be present on tlle surface.
Tlle first stage is generally monitored by a simple
acid-base titration and pH. A l0 or l00 mL bath sample is
taken (whichever is desired for accuracy and convenience - a
l~0 mL sample gives the more accurate result) and titrated to
me~hyl orange (/pH = 4.5) witl1 0.l0 N NaOH. This measure
tells tlle available "free acid" in the bath and is used in
conjunction with tl1e pl~ mea.surement. T1le same or otller
(equivalent size) batl1 sample is titrated to pllenol~LIIaleill
(/pll = 8.5). This measure gives the Group lV-B available to
enter into the surface coating. When aluminum or other
"metal hydroxide" forming element is present in solution
(such as whe1l alurninuln evaporators are being ~rocessed? it
must be considered that this will add to this titratiorl
value. This can be dealt witl1 (if deemed necessary) by use
of complexa11ts, excess fluoride addition duriny titration, or
multiple indicator systems if deemed necessary. We 1lave
found tl1at for coating alwninum evaporators, tlle titratiorl oE
l00 mL of tllis bath against 17.0 +/- 5.0 mL 0.l0 N NaOl1
provides excellent results, as when tlle "free acid" is
maintained by concentrate addition aluminum reaclles a
steady-state concentration and an equilibriunl between
dissolution/deposition develops.
STAGE 2
Stage 2 is comprised of a stable aqueous solutioll of,
preferably, at least 5 percent by weigllt sodiunl silicate
(eg., ~rade 42 sodium silicate) in water. Tl1e silicate may
be any stable silicate sol but sodiwn silicate will be used
for tllis discussion. It has been seen tllat tlle odor impact
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WO96121752 PCT~S96/00517
of the surface is reduced as the concentration of the
silicate is increased, reaching a rninimum above 5 percent w/w
~ as sodium silicate.
'lhe temperature of this stage can range from arnbient
(a~out 70~F) up to about 1~0~F. Tlle preferred range is 90~F
to 120~F, 110~F being most preferred at a 10% sodium silicate
concentratiorl .
Superior corrosion protection is obtained when the
silicate concen~ratioIl is at least 2% w/w. This parameter
can depend on the exact nature of tlle prior stage(s) and, due
to all considerations, a 10% w/w solution maintairled at a pll
of 11.1 +/- 0.5 is recommended for optimal performarlce in
heat exchanger applications.
As stated above, gelation of this stage can occur if tlle
p~I becomes too low and/or a hiyll level of corltaminatioIl is
experienced. It must be cautioned here as well that tl]e
al]~alinity must not be excessive so as not to attack the
layer provi~ed in Stage 1 above (or otller plior supplernental
stages) and then the substra~e itself. This, of course,
becomes more pronounced in the higher end of the recomInellded
temperature range.
The control for staye 2 is done by morli~oring of pII (kept
in the range stated above) and a simple acid-base Litration.
For titration, five milliliters of batll solution are taken,
diluted to approxiIllately S0 nlL witIl deionized or distilled
water, and titrated with 0.10 N HCl to phenolpthalein (/pH =
8.5). When Grade #42 sodium silicate is used, the equatioll:
[0.5 x mL 0.10 N ~Cl = % silicate]
can be used. A graph of mL acid versus % #42 silicate can
also be used, witIl 0.5 being the approximate slope of the
line. More specific measures of the Na2O/SiO2 ratio can
also be used, but have not been necessary in ~referred
embodiments to date.
Additionally, tIle second stage as described here may be
augInented for reduction in solids formatiorl by maintaining a
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-14-
proper concentration of chelant in the solution. A wide
variety of cllelarlts will complex hard water minerals and
metals from prior stage(s) wllich will reduce the formatiorl of
insoluble Group IIA [or other] silicate salts. Several
classes of cllelants have been found to be effective to a
su~stantial extent: tripolyphosphates (such as
Na2P2O5, trisodium phosphate, KTPP potassium
pyrophospllate), phosphonates (such as De~uest 20U0, 2010,
2060), EDTA and Versene 120, sodium gluconates, and ~orax.
lO Th;s augmentatioll may allow the manufacturincJ process to
achieve greater production qualltities througll tllis stage
before dumping and recharging becomes necessary. lndications
are that silicate scale build llp on racks and equipment
surfaces that come into internlitterlt contact with the
solution may be reduced, as well.
It must ~e cautioned Ihat hiyll concerltrations of
chelallt(s) may affect with tlle oxide matrix that forms in
Stage 2 and change characteristics of the coating. The
beneEits to the manufacturillg process must ~e balance(l willl
the desired characteristics of the coatiny in each particular
case.
STAGE 3
Stage 3 is the "drying" stage and is the point in the
process where the coating composition becomes "fixed." There
is IlO augmentation of the coating after this point otller tha
to paint over it, which may require a "pre-paint treatmerlt"
to enhance adhesion. l'his stage is generally at an elevated
temperature for a duration long enough to complete the
formation of covalent nlixed metal oxide linkages. A gra~ual
increase in surface and part tenlperature, as moisture wi]l be
leaving the coating as linkages form and as the a~ueous
portion of tlle residual coating solutions eva~orates, is
preEerred. The peak surface temperature should be from 200
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WO96/21752 PCT~S96/00517
to 450~F, 250 to 275~F being preferred in tlle described
embodiment. The ternperature of the coated surface should
remain at the drying temperature for at least 5 millutes to
ensure completion of tlle "drying" reacLions alld eventllal
evaporation of all water associated with the surface.
Extended periods at elevated temperatures should be
avoided, as sllould rapid descents in ternperature (such as
that experieIlced in quenching operations). The coatiny is
considered to be an amorphous mixed metal oxide/siloxyl type
and will normally ~lave a different coefficiellt of thermal
expansion/contraction than the substrate and, therefore,
excessively rapid or extreme ternperature fluctuations are to
be avoided in this stage.
ln the preferred embodirnent for typical air conditiorlillg
evaporators for automobiles, it has been determined that, in
general, 15 minutes at 300~F yields a satisEactory coating
wiLh regard to the described desired characteristics. This
parameter has been tested for many sizes and models (as have
tlle oLher stages) and the stated values work well in ovens
wllere there is some circulation of heated air thloucJIl the
parts.
As with most chemical treatment operations, automatic
controls may be used to add chemicaI concentrates to tlle
treatmerlt stages during processing with the described
process. Conductivity or pll regulation of the feed pumps is
use~ to keep the S~age 1 and Stage 2 concentra~ions in the
desired ranges. Once the first two stages have reached a
sta~le "steady" state with regard to tlle specified pll and
titration values for a yiven operation, the conductivity (or
pl~) control is set to feed concentrate to rnaintain the value
in the treatment stage. The "steady" state is reaclled when
reaction product (SllCh as A13 ) has built up in the stages
to its peal~ level. This state can be reached in a new batl
~y addition of a "charge supplement" of the known reaction
product(s) at t~leir steady-state levels.
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-16-
Reference will llOW be made to specific exarmples using the
processes described above. It is to be understood tllat tlle
exanlples are provided to more completely describe preferred
ernbodiments, and that no limitation to the scope of the
invention is intende~ thereby.
EX~MPLE 1
A first solution containir1y 150 ppm Zr and 200 ppm F at a
pT~ of 2.4 is prepared and the solution is rnaintained at a
temperature of about l40~F. An air conditionir1y heat
exchanger is immersed in the first solution for five minutes.
A second solution of about 2% silicate, at a pl1 of about
lO, is prepared and mair1tai1led at a ternperature of about
90~F. l'he heat excharlger which ~las been immersed in the
first solution above is subsequently immersed in the second
solution-
l'he treated heat exchanger is drie~ in an oven for one
hour to produce a low-odor, bioresistant, hydrophilic,
corrosion resistant coating.
EXAMPLE 2
A first solution containi11g 600 ppm Zr and 750 ppm F at a
pTI of 2.8 is prepared alld the solution is maintained at a
temperature of about 140~F. An air conditionirlg heat
exchanger is immersed in the first solution for five mil1lltes.
A second solution of about 10% silicate, at a p~l of about
12, is prepared and maintained at a ternperature of about
90~F. l'he heat exchanger whic11 has been immersed in the
first solution above is subsequently immersed in the second
solution.
The treated l1eat exchanger is dried in an oven for one
CA 02209924 1997-07-09
WO96/21752 PCT~S96/00517
,
hour to produce a low-odor, bioresistant, hydropllilic,
corrosion resistant coating.
~,
EXAME'L~ 3
A first solution containillg 150 ppm Zr, 80 ppnl Ca and 200
ppln F at a pl~ of l.5 is prepared and the solution is
maimtained at a temperature of aboul 1~0~F. An air
conditioning heat exchanger is immersed in tlle Eirst solution
for five minutes.
A second soluti.on of about 2% silicate, at a pll oE about
lO, is prepared and maintairled at a temperature of about
90~F. The heat exchanger which has been immersed in the
Eirst solution above is subsequent].y immersed in the second
solul.ion.
The treated heat exchallger is dried in a-l oven for one
hour to produce a low-odor, bioresistant, hydrophilic,
corrosion resistant coating.
EXAMPLE 4
A first solution containing 600 ppm Zr, 80 ppln Ca and 7~0
ppm F at a pll of 4.5 is prepared and the solution is
maintained at a tempera~ure oE about 1~0~F. An air
conditioning heat exchanger is immersed in the first solution
for five minutes.
A second solution of about 10% silicate, at a pll of about
12, is prepared and [naintained at a temperature of about
goo~. The heat exchanger which llas been immersed in the
first solution above is subsequently immersed in the second
solution.
The treated heat exchanger is dried in an oven for one
llour to produce a low-odor, bioresistant, hydropllilic,
corrosion resistant coating.
CA 02209924 1997-07-09
Wo96/21752 PCT~S96/OOS17
-18-
~XAMPL~S 5-8
Further samples were treated as described in Examples 1-4
ahove, but also including the additional steps of rillsing tlle
metal witll deionized water after each immersion step. After
drying, the treated heat exchangers had a low-odor,
bioresistant, hydrophilic, corrosion resistant coating.
EX~MPLE 9
A first solution contairling 0.00015 M Zr, 0.00025 M Ca
and 200 ppm F at a p~ of 1.5 is prepared and tlle solution is
~ 10 mailltained at a temperature of about 140~F. An air
condi.tioniny heat exchallger is ilmnersed in the first solution
for five Inin~ltes.
A second solution of abollt 2% silicate, at a pl-~ of about
10, is prepared and maintained at a temperature of about
90~F. The lleat exchanger wllich has been immersed in the
first solution above is subsequently immersed in the second
solution.
llle treated heat excllanger is dried in an oven ~or one
hour to produce a low-odor, bioresistant, hydrophilic,
corrosion resistant coating.
EXAMPLE 10
A first solution containing 0.055 M Zr, O.OU025 M Ca alld
7gO ~pm F at a pH of 4.5 is prepared and the solution is
maintained at a temperature of about 1~0~F. An air
conditioning heat exchanger is immersed in tlle first solution
for five minutes.
A second solution of about 10% silicate, at a pll of about
- 12, is prepared and maintai.ned at a temperature o~ abollt
90~F. Tlle lleat exc~langer wllich llas been immersed in tlle
first solution above is subsequently immersed in the second
solution .
CA 02209924 lss7-07-os
WO96/21752 PCT~S96/005I7
--19-- .
The treated heat exchanger is dried in an oven for one
hour ~o produce a low-odor, bioresistarlt, hydropIIilic,
corrosion resistant coating.
EXAMPLE 11
A first solution containiny 0.00015 M Ti, 0.00025 M Ca
and 200 ppm F at a pH of 2.0 is prepared and tlle solutioIl is
maintained at a temperature of about 1~0~F. An air
conditioning heat exchanger is immersed in the first solution
for five miIlutes.
A second solution of about 5% silicate, at a pll of about
~ . 11, is prepared and maintained at a temperature of about
90~F. The heat exchanger which has beerl immersed in tlle
first solution above is subsequently immersed in the second
sol~l~i.o]l.
The treated lleat exchaIlger is dri.ed in an oven for one
hour to produce a low-odor, bioresistant, hydrophilic,
corrosion resistant coating.
EXAMPLE 12
A ~irst solution containirly 0.055 M Ti, 0.00025 M Ca and
740 ppm F at a pII of 2.5 is prepared and tlIe solutioll is
maintained at a temperature of a~out 140~F. An air
conditioning heat exchanger is immersed in the first soluLion
for five miIllltes.
A second solution of about 10% silicate, at a pII of about
12, is prepared and maintained at a telnperature of about 90~F.
The heat exchanger which has been immersed in tlle ~irst
sollltioIl above is subsequently immersed in the second
solution.
The trea~ed heat exchanger is drie~ in an oven for oIle
hour to prodllce a ].ow-odor, bioresistant, hydrophilic,
corrosion resistant coatiny.
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WO96/21752 PCT~S96/00517
-20-
While the inventiorl has been illustrated and described in
de~ail in the foregoing description, the same is to be
considered as illustrative and not restrictive in character,
it being urlderstood that only tlle preferred embodirnent has
been shown and described and that all changes and
modi~ications that come within the spirit of the invention
are desired to be protected.
