U.S. patent application number 10/115018 was filed with the patent office on 2002-08-01 for method for improving heat efficiency using silane coatings and coated articles produced thereby.
Invention is credited to Gedeon, Anthony A., Schutt, John B., Stanich, Jeffrey L..
Application Number | 20020102417 10/115018 |
Document ID | / |
Family ID | 27497434 |
Filed Date | 2002-08-01 |
United States Patent
Application |
20020102417 |
Kind Code |
A1 |
Schutt, John B. ; et
al. |
August 1, 2002 |
Method for improving heat efficiency using silane coatings and
coated articles produced thereby
Abstract
Oligomeric silane coating compositions containing, for example,
methyltrimethoxysilane, are used to coat new or used heat exchange
apparatus, such as HVAC systems, to greatly improve the heat
transfer efficiency and prevent or inhibit corrosion. These
oligomeric coating compositions are able to fill microvoids in the
heat exchange surfaces, and penetrate into the microcavities at the
interface of swaged or force fit surfaces, such as fins and tubes.
The oligomeric silane coating compositions are highly active and
will form bonds not only with the metal and metal oxides of the
heat transfer surfaces, but will also displace gasses or liquids at
the heat transfer contact surfaces and form chemical and/or
hydrogen bonds with the oxides and chemical impurities. By so
doing, a parallel heat transfer pathway is formed. The applied
coatings may be as thin as only a few millionths of an inch and
will fill microcavities to a depth of up to about 2000 nanometers.
The coated heat transfer surfaces are non-adherent to deposition of
soils and microorganisms and, therefore, are easier to maintain and
are environmentally safe for use to heat/cool inhabited
structures.
Inventors: |
Schutt, John B.; (Silver
Spring, MD) ; Gedeon, Anthony A.; (Palm Coast,
FL) ; Stanich, Jeffrey L.; (Kenosha, WI) |
Correspondence
Address: |
Sherman & Shalloway
413 North Washington Street
Alexandria
VA
22314
US
|
Family ID: |
27497434 |
Appl. No.: |
10/115018 |
Filed: |
April 4, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10115018 |
Apr 4, 2002 |
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09778942 |
Feb 8, 2001 |
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60181061 |
Feb 8, 2000 |
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60185354 |
Feb 28, 2000 |
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60185367 |
Feb 28, 2000 |
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60236158 |
Sep 29, 2000 |
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Current U.S.
Class: |
428/447 ;
165/133; 427/385.5 |
Current CPC
Class: |
C09D 4/00 20130101; C09D
183/14 20130101; C09D 183/04 20130101; C09D 4/00 20130101; C08L
2666/54 20130101; C08G 77/04 20130101; C08G 77/00 20130101; C09D
4/00 20130101; Y10T 428/31663 20150401; C23C 2222/20 20130101; C08L
2666/54 20130101; C09D 183/14 20130101; C09D 183/04 20130101 |
Class at
Publication: |
428/447 ;
427/385.5; 165/133 |
International
Class: |
B05D 003/02; B32B
009/04 |
Claims
What is claimed is:
1. A method for improving efficiency of heat transfer from a heat
transfer medium flowing in heat transfer contact with a heat
transfer surface of a thermally conductive component of a heat
transfer system across said heat transfer surface, said method
comprising coating at least a portion of said heat transfer surface
with a low viscosity, penetrating, curable, reactive, film-forming,
coating composition and curing the composition to thereby form an
at least substantially continuous glass-like coating on said heat
transfer surface, said coating extending into voids and defects
which may be present in said heat transfer surface, whereby a
thermally conductive corrosion protective layer is provided on said
heat transfer surface.
2. The method of claim 1, wherein said coating composition
comprises an aqueous or non-aqueous oligomeric silane coating
composition formed by admixing (a) at least one silane of the
formula (1)R.sup.1.sub.nSi(OR.sup- .2).sub.4-n (1)where R.sup.1
represents a lower alkyl group, a C.sub.6-C.sub.8 aryl group or a
functional group including at least one of vinyl, acrylic, amino,
mercapto, or vinyl chloride functional groups; (b) silane
condensation catalyst, and (c) lower alkanol solvent, and
optionally, one or more of (d) colloidal aluminum hydroxide; (e)
metal alcoholate of formula (2):M(OR.sup.3).sub.m (2)where M is a
metal of valence 2, 3 or 4, or mixture of two or more such metals;
R represents a lower alkyl group; and, m represents a number or 2,
3 or 4; (f) a silica component selected from the group consisting
of alkali metal silicate, ethyl orthosilicate, ethyl polysilicate,
and colloidal silica dispersed in lower alkanol; (g) color forming
silanol condensation catalyst; (h) epoxysilane; (i) ultrafine
titanium dioxide ultraviolet light absorber; (j) water; and (k)
co-solvent; and curing the applied coating composition.
3. The method of claim 2, wherein said oligomeric silane coating
composition comprises (I) an aqueous coating composition comprising
a dispersion of divalent metal cations in lower aliphatic
alcohol-water solution of the partial condensate of at least one
silanol of the formula RSi(OH).sub.3, wherein R is a radical
selected from the group consisting of lower alkyl, vinyl, phenyl,
3,3,3-trifluoropropyl, gamma-glycidyloxypropyl, and
gamma-methacryloxypropyl, at least about 70 percent by weight of
the silanol being CH.sub.3Si(OH).sub.3, acid in amount to provide a
pH in the range of from about 2.5 to about 6.2, said divalent metal
cations being present in an amount of from about 1.2 millimoles to
about 2.4 millimoles, per molar equivalent of the partial
condensate, calculated as methyl silane sesquioxide.
4. The method of claim 2, wherein the oligomeric silane coating
composition comprises (II) (A) at least one silane of the formula
(I)R.sup.1Si(OR.sup.2).sub.3 (1)wherein R.sup.1 is a lower alkyl
group, a phenyl group or an N-(2-aminoethyl)-3-aminopropyl group,
and R.sup.2 is a lower alkyl group; (B) acid component selected
from the group consisting of water-soluble organic acids,
H.sub.3BO.sub.3 and H.sub.3PO.sub.3; and (D) water.
5. The method of claim 2, wherein the oligomeric silane coating
composition comprises, (III) a non-aqueous coating composition
formed by admixing (A) at least one silane of formula
(1)R.sup.1.sub.nSi(OR.sup.2).- sub.4-n (1)wherein R.sup.1
represents lower alkyl, phenyl, 3,3,3-trifluoropropyl,
.gamma.-glycidyloxypropyl, .gamma.-(meth)acryloxyp- ropyl,
N-(2-aminoethyl)-3-aminopropyl, or aminopropyl group; R.sup.3
represents lower alkyl group; and n is a number of 1 to 2; and (E)
(i) vinyltriacetoxysilane, (ii) colloidal aluminum hydroxide;
and/or (iii) at least one metal alcoholate of formula
(2)M(OR.sup.3).sub.m (2)wherein M represents a metal of valence m,
R.sup.3 represents lower alkyl group; and m is a number of 2, 3 or
4.
6. The method of claim 2, wherein the oligomeric silane coating
composition comprises, (IV) a non-aqueous coating composition
formed by admixing (A) at least one silane of formula
(1)R.sup.1.sub.nSi(OR.sup.2).- sub.4-n (1)wherein R.sup.1
represents lower alkyl, phenyl, 3,3,3-trifluoropropyl,
.gamma.-glycidyloxypropyl, .gamma.-(meth)acryloxyp- ropyl,
N-(2-aminoethyl)-3-aminopropyl, or aminopropyl group; R.sup.2
represents lower alkyl or acetyl group; and n is a number of 1 to
2; (B) boric acid, optionally dissolved in lower alkanol; (E) (i)
vinyltriacetoxysilane, (ii) colloidal aluminum hydroxide; and/or
(iii) at least one metal alcoholate of formula (2)M(OR.sup.3).sub.m
(2)wherein M represents a metal of valence m, R.sup.3 represents
lower alkyl group m is an number of 2, 3 or 4; and. (F) silica
component selected from the group consisting of ethyl
ortho-silicate, ethyl polysilicate and colloidal silica, dispersed
in lower alkanol.
7. The method of claim 2, wherein the oligomeric silane coating
composition comprises, (V) a non-aqueous coating composition formed
by admixing (A) at least one silane of formula
(1)R.sup.1.sub.nSi(OR.sup.2).- sub.4-n (1)wherein R.sup.1
represents lower alkyl, phenyl, 3,3,3-trifluoropropyl,
.gamma.-(meth)acryloxypropyl, N-(2-aminoethyl)-3-aminopropyl, or
aminopropyl group; R.sup.2 represents lower alkyl or acetyl group;
and n is a number of 1 to 2; (A')
.gamma.-glycidyloxypropyloxytrimethoxysilane; (B) boric acid,
optionally dissolved in lower alkanol; (E) (i)
vinyltriacetoxysilane, (ii) colloidal aluminum hydroxide; and/or
(iii) at least one metal alcoholate of formula (2)M(OR.sup.3).sub.m
(2)wherein M represents a metal of valence m, R.sup.3 represents
lower alkyl group m is an number of 2, 3 or 4.
8. The method of claim 2, wherein the oligomeric silane coating
composition comprises (VI) an oligomeric silane coating composition
formed by admixing (A) at least one silane of formula
(1)R.sup.1.sub.nSi(OR.sup.2).sub.4-n (1)wherein R.sup.1 represents
lower alkyl, phenyl, or a functional group containing at least one
of vinyl, acrylic, amino, mercapto, or vinyl chloride functional
group; and R.sup.2 is a lower alkyl group; (B) acid component
comprising a member selected from the group consisting of
water-soluble organic acids, H.sub.3BO.sub.3 and H.sub.3PO.sub.3;
and (D) water.
9. The method of claim 2, wherein the oligomeric silane coating
composition comprises, (VII) an aqueous oligomeric silane coating
composition formed by admixing (A) at least one silane of formula
(1)R.sup.1.sub.nSi(OR.sup.2).sub.4-n (1)wherein R.sup.1 represents
lower alkyl, phenyl, or a functional group containing at least one
of vinyl, acrylic, amino, mercapto, or vinyl chloride functional
group; and R.sup.2 is a lower alkyl group; (C) alkali component;
and (D) water.
10. The method of claim 2, wherein the oligomeric silane coating
composition comprises (VIII) an aqueous coating composition formed
by admixing (A) at least one silane of the formula
(1)R.sup.1Si(OR.sup.2).su- b.3 (1)wherein R.sup.1 is a lower alkyl
group, a phenyl group or a bifunctional silane containing vinyl,
acrylic, amino, or vinyl chloride functional group; and R.sup.2 is
a lower alkyl group; (E) (ii) colloidal aluminum hydroxide, (iii)
metal alcoholate of the formula (2)M(OR.sup.3).sub.m (2)wherein M
is a metal of valence m, R.sup.3 is a lower alkyl group, m is an
integer of 3 or 4, or mixture of (ii) and (iii); and (D) water.
11. The method of claim 2, wherein the oligomeric silane coating
composition comprises (IX) an aqueous coating composition formed by
admixing (A) at least one silane of the formula
(1)R.sup.1Si(OR.sup.2).su- b.3 (1)wherein R.sup.1 is a lower alkyl
group, a phenyl group or a bifunctional silane containing vinyl,
acrylic, amino, or vinyl chloride functional group; and R.sup.2 is
a lower alkyl group; (D) water; (H) lower alkanol; and (G) chromium
acetate hydroxide.
12. The method of claim 2, wherein the oligomeric silane coating
composition comprises (X) an aqueous coating composition formed by
admixing (A) at least one silane of the formula
(1)R.sup.1Si(OR.sup.2).su- b.3 (1)wherein R.sup.1 is a lower alkyl
group, a phenyl group or a functional group including at least one
of vinyl, acrylic, amino, mercapto, or vinyl chloride functional
group; and R.sup.2 is a lower alkyl group; (D) water; (F) alkali
metal silicate, which may be hydrolyzed; (H) lower alkanol; and (E)
(ii) colloidal aluminum hydroxide, (iii) metal alcoholate of the
formula (2)M(OR.sup.3).sub.m (2)wherein M is a metal of valence m,
R.sup.3 is a lower alkyl group, m is an integer of 3 or 4, or
mixture of (ii) and (iii).
13. The method of claim 2, wherein the oligomeric silane coating
composition comprises, (XI) a non-metallic aqueous coating
composition formed by admixing (A) at least one silane of the
formula (1)R.sup.1Si(OR.sup.2).sub.3 (1)wherein R.sup.1 is a lower
alkyl group, a phenyl group or a functional group including at
least one of vinyl, acrylic, amino, mercapto, or vinyl chloride
functional group; and R.sup.2 is a lower alkyl group; (A")
3-(2-aminoethylamino)propyltrimethoxysilane or
3-aminopropyltrimethoxysilane; (D) water; (I) epoxide silane; and
(H) lower alkanol.
14. The method of claim 2, wherein the oligomeric silane coating
composition comprises, (XII) an aqueous coating composition formed
by admixing (A) at least one silane of the formula
(1)R.sup.1Si(OR.sup.2).su- b.3 (1)wherein R.sup.1 is a lower alkyl
group, a phenyl group or a functional group including at least one
of vinyl, acrylic, amino, mercapto, or vinyl chloride functional
group; and R.sup.2 is a lower alkyl group; (B) boric acid; (C) at
least one alkali component comprising an hydroxide or carbonate of
divalent metal; (D) water; (J) ethyl polysiloxane; and (H) lower
alkanol.
15. The method according to claim 1, for increasing the contact
area between first and second heat transfer surfaces in thermal
contact with each other, thereby improving the heat transfer
efficiency across the thermally contacting heat transfer surfaces,
said method comprising, applying said low viscosity, penetrating
coating composition to the thermally contacting heat transfer
surface of at least one of said first and second heat transfer
surfaces.
16. The method according to claim 15, wherein the coating
composition comprises an aqueous or non-aqueous oligomeric silane
coating composition formed by admixing (a) at least one silane of
the formula (1)R.sup.1.sub.nSi(OR.sup.2).sub.4-n (1)where R.sup.1
represents a lower alkyl group, a C.sub.6-C.sub.8 aryl group or a
functional group including at least one of vinyl, acrylic, amino,
mercapto, or vinyl chloride functional groups; (b) silane
condensation catalyst, and (c) lower alkanol solvent, and
optionally, one or more of (d) colloidal aluminum hydroxide; (e)
metal alcoholate of formula (2):M(OR.sup.3).sub.m (2)where M is a
metal of valence 2, 3 or 4, or mixture of two or more such metals;
R represents a lower alkyl group; and, m represents a number or 2,
3 or 4; (f) silica component selected from the group consisting of
alkali metal silicate, ethyl orthosilicate, ethyl polysilicate, and
colloidal silica dispersed in lower alkanol; (g) color forming
silanol condensation catalyst; (h) epoxysilane; (i) ultrafine
titanium dioxide ultraviolet light absorber; (j)water; (k)
co-solvent; and wherein the oligomeric coating composition is
allowed to cure to a film thickness of from about 5 to about 150
millions of an inch, thereby filling any microvacancies in said
heat transfer surfaces.
17. The method according to claim 1, for improving the efficiency
of heat exchange apparatus of the type wherein a metal heat
transfer surface is swaged or force fit to a metal heat transfer
fluid conveyance, said method comprising, applying to the interface
between the heat transfer surface and the conveyance said low
viscosity, penetrating coating composition whereby the coating
composition will displace gasses and liquids in said interface; and
allowing the coating composition to cure to a film thickness of
from about 5 to about 150 millions of an inch, and fill any
microvacancies in said metal surfaces at said interface.
18. The method according to claim 17, wherein said coating
composition comprises an aqueous or non-aqueous oligomeric silane
coating composition formed by admixing (a) at least one silane of
the formula (1)R.sup.1.sub.nSi(OR.sup.2).sub.4-n (1)where R.sup.1
represents a lower alkyl group, a phenyl group or a functional
group including at least one of vinyl, acrylic, amino, mercapto, or
vinyl chloride functional groups; (b) silane condensation catalyst,
and (c) lower alkanol solvent, and optionally, one or more of (d)
colloidal aluminum hydroxide; (e) metal alcoholate of formula
(2):M(OR.sup.3).sub.m (2)where M is a metal of valence 2, 3 or 4,
or mixture of two or more such metals; R represents a lower alkyl
group; and, m represents a number or 2, 3 or 4; (f) a silica
component selected from the group consisting of alkali metal
silicate, ethyl orthosilicate, ethyl polysilicate, and colloidal
silica dispersed in lower alkanol; (g) color forming silanol
condensation catalyst; (h) epoxysilane; (i) ultrafine titanium
dioxide ultraviolet light absorber; (j) water; (k) cosolvent.
19. The method according to claim 1, wherein said heat transfer
surface comprises a fin and tube heat transfer device.
20. A heat transfer system comprising a metal heat transfer
surface, wherein said metal heat transfer surface is coated with a
cured low viscosity, penetrating, curable, reactive, film-forming,
coating composition whereby the cured coating composition has a
film thickness of from about 5 to about 150 millions of an inch,
and fills any microvacancies in said metal surfaces.
21. The heat transfer system according to claim 20, wherein the
heat transfer surface of said heat transfer system comprises a fin
and tube heat exchange device.
22. The heat transfer system according to claim 20, wherein the
heat transfer surface comprises an evaporator, said coating being
resistant to adhesion of microorganisms.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority from Provisional
Applications Nos. 60/181,061, 60/185,354, 60/185,367, and
60/236,158, filed Feb. 8, 2000, Feb. 28, 2000, Feb. 28, 2000, and
Sep. 29, 2000, respectively.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] This invention relates to use of silane based coating
compositions for coating heat exchange systems, such as HVAC
systems, whereby heating efficiencies and corrosion protection are
both substantially improved. More particularly, the present
invention is concerned with improving performance and useful
lifetime of heat exchange systems wherein the heat exchange
surfaces are coated with a very thin coating of glass-like silane
based coating composition which penetrate into very small spaces at
the interface between and in the heat exchange surfaces to provide
a parallel path for heat transfer and prevent corrosion, thereby
greatly improving short- and long-term efficiency.
[0004] 2. Discussion of the Prior Art
[0005] Silane, silanol and siloxane compounds have been used for
many years, as both solvent-based and aqueous-based, formulations,
with or without modification with organic substituents, for such
applications as coupling agents for glass or other inorganic
substrates to organic compounds; non-permanent (limited life) water
repellants for concrete and woven fabric materials; synthetic
rubber like compounds for adhesives and sealers; adhesion modifiers
for organic paints and inorganic coatings; and other property
enhancing uses which take advantage of having the ability to form
moderate to strong hydrogen bonds to organic and inorganic
surfaces, more tenaciously than most classes of polymeric
coatings.
[0006] U.S. Pat. Nos. 3,944,702, 3,976,497, 3,986,997 and 4,027,073
describe coating compositions which are acid dispersions of
colloidal silica and hydroxylated silsequioxane in an alcohol-water
medium.
[0007] U.S. Pat. No. 4,113,665 discloses chemically resistant
ambient curable coatings based on a binder of which the major
portion is prepared by reacting, in an acidic solution,
trialkoxysilanes (e.g., methyltriethoxysilane) with aliphatic
polyols, silicones or both. Barium fillers, such as barium
metaborate, may be added to provide resistance to sulfur dioxide.
Zinc oxide or metallic zinc may be included for further corrosion
resistance. The compositions may be applied to, e.g., steel
petroleum tanks, by spraying, concrete, vitreous surfaces.
[0008] U.S. Pat. No. 4,413,086 describes water reducible coating
compositions containing organosilane-polyol which is a reaction
product between certain hydrophilic organic polycarbinols and
organosilicon material, e.g., organosilane, curing agent (e.g.,
aminoplast resin), organic solvent (optional), essentially
unreacted polyol (optional), essentially unreacted hydrolyzed and
condensed organosilane (optional), water (optional) and pigment
(optional).
[0009] U.S. Pat. No. 4,648,904 describes an aqueous emulsion of (a)
hydrolyzable silane, inclusive of methyltrimethoxysilane, (b)
surfactant (e.g., Table I, col. 4) and (c) water. The coatings may
be used for rendering masonry water repellant.
[0010] U.S. Pat. No. 5,275,645 is purported to provide an
improvement to the acid-catalyzed organosilane coating compositions
of the above-mentioned U.S. Pat. No. 4,113,665. According to this
patent a protective coating is obtained at ambient temperature from
a coating composition containing organosilanes having an Si--O
bond, using an amine catalyst and an organometallic catalyst.
[0011] U.S. Pat. No. 5,879,437 describes a coating composition
containing a tetraalkyl silicate or monomeric or oligomeric
hydrolysis product thereof, present in a proportion of 40-90% by
weight based on the non-volatile content of the composition and a
hydrous oxide sol (Type A or Type B), in an amount such that the
oxide constitutes 10-60% by weight of the non-volatiles. According
to the patentees, this coating composition is suitable for the
pretreatment of solid surfaces such as metals generally, including
steel, titanium, copper, zinc and, particularly aluminum, to
improve adhesion properties of the pretreated surface to
subsequently applied coatings, such as paint, varnish, lacquer; or
of adhesive, either in the presence or absence of a lubricant.
[0012] U.S. Pat. No. 5,882,543 describes methods and compositions
for dehydrating, passivating and coating HVAC (heating, ventilating
and air conditioning) systems. The compositions include an
organometalloid and/or organometallic compound, which reacts with
water in the system. The sealing function of these compositions is
apparently obtained by introducing the composition to the fluid
enclosure and upon exiting from an opening, the composition (i.e.,
organometallic) reacts with atmospheric moisture to seal the
opening.
[0013] U.S. Pat. No. 5,954,869 discloses an antimicrobial coating
from water-stabilized organosilanes obtained by mixing an
organosilane having one or more hydrolyzable groups, with a polyol
containing at least two hydroxyl groups. This patent includes a
broad disclosure of potential applications and end uses, e.g.,
column 4, lines 35-53; columns 23-25.
[0014] U.S. Pat. No. 5,959,014 relates to organosilane coatings
purported to have extended shelf life. Organosilane of formula
R.sub.nSiX.sub.4-n (n=0-3; R=non-hydrolyzable group; X=hydrolyzable
group) is reacted with a polyol containing at least three hydroxyl
groups, wherein at least any two of the at least three hydroxyl
groups are separated by at least three intervening atoms.
[0015] U.S. Pat. No. 5,929,159, to J. Schutt and A. Gedeon, and
commonly assigned with the present application, describes an
oligomeric coating composition in the form of an aqueous
composition comprising a dispersion of divalent metal cations
(especially, Ca, Mn, Cu and Zn divalent ions) in lower aliphatic
alcohol-water solution of the partial condensate of at least one
silanol (at least about 70 wt. % of which was methyltrimethoxy
silane), and acid, in amount to provide a pH in the range of from
about 2.5 to about 6.2, the amount of the divalent metal cations
being from about 1.2 to about 2.4 millimoles, per molar equivalent
of the partial condensate, calculated as methyl silane sesquioxide.
It is also described to provide a coating composition as a two part
formulation, the first part being an acidic aqueous dispersion of
divalent metal cation, having a pH of from about 2.2 to about 2.8;
and the second part a non-aqueous composition comprising at least
one trialkoxy silane; with at least one of the first and second
parts comprising a volatile organic solvent. The corrosion
resistant coatings may be provided as aqueous-alcoholic dispersions
of the partial condensate of monomethyl silanol (obtained by
hydrolysis of monomethyl alkoxysilane) alone or in admixture with
minor amounts of other silanol, e.g., phenyltrimethoxysilanol,
gamma-glycidyloxy silanol, and the like, wherein the reaction is
catalyzed by divalent metal ions, e.g., Ca.sup.+2, typically from
alkaline earth metal oxides. When these coating are applied to,
e.g., boat hulls, such as aluminum hulls, they are highly effective
in preventing corrosion from salt water for extended periods.
[0016] Thus, this patent indicates that the patented coating
compositions are suitable for application to various types of
substrates, but especially, marine surfaces, such as aluminum boat
hulls, to render the surface corrosion resistant in a salt water
environment. Other representative potential applications and
substrates for the patented silane based coating compositions
mentioned in the Schutt and Gedeon patent include coatings for
concrete/rock, wherein the coating can penetrate the porous
materials, due to its low viscosity and active nature;
metals/plastics, wherein the coating is preferably applied to very
clean surfaces but will itself clean the pores in the metal or
plastic and exhume the contamination which generally rises to the
surface of the coating.
[0017] The compositions of the Schutt, et al patent are oligomeric
coatings using a variety of siloxane bond forming monomers as
described. Subsequent modifications of the compositions of the U.S.
Pat. No. 5,929,159 patent have been developed by John Schutt and
are described, for example, in copending provisional applications
Serial Nos. 60/185,367 and 60/185,354, both filed on Feb. 28, 2000,
and Serial No. 60/236,158, filed Sep. 25, 2000. Basically, these
provisional applications disclose formulations for
silane/siloxane/silanol oligomeric compositions, both solvent
(non-aqueous) and water (aqueous) based, which effectively bond to
many different metallic and non-metallic surfaces by means of
siloxy (--Si--O--) bonds.
[0018] The compositions disclosed by the U.S. Pat. No. 5,929,159
patent and provisional applications can cure under ambient
conditions and are catalyzed using, for example, acid, alkali, and
metal alkoxide, catalysts. They may contain organic additives
forming hydrogen bonds of greater energy than those formed with
water. Protection of metallic surfaces occur because bonds of
greater covalency are created which are more robust than dipole or
dispersion forces.
SUMMARY OF THE INVENTION
[0019] It has now been discovered that the coating compositions of
U.S. Pat. No. 5,929,159, and subsequently developed formulations,
as described in the aforementioned three provisional applications,
Ser. No. 60/185,354, 60/185,367, and 60/236,158, the entire
disclosures of which are incorporated herein, in their entireties,
by reference thereto, are very highly effective in providing
strongly adherent, corrosion resistant coatings for heat exchange
systems, including, especially, air conditioning units and other
HVAC systems, and the individual components thereof. Although not
wishing to be bound by any particular theory of operation, it is
believed that the effectiveness of these siloxy bond forming
coating compositions arises, at least in part, from the oligomeric
nature of these compositions. The low molecular weight of the
oligomeric components and the low viscosity of the composition,
enables them to penetrate the defect surface structure found in all
surfaces, with the option of creating dendritic-like networks over
a surface. In particular, scanning electron microphotographs show
that compositions as described herein penetrate defects having
nanometer dimensions while forming films on the order of millionths
of an inch in depth.
[0020] These compositions may be applied not only to coat new heat
exchange systems and component parts thereof, e.g., coils,
condensers and the like, but also may be applied in situ to
existing heat exchange systems and component parts, even when the
system or individual parts thereof are corroded.
[0021] Accordingly, the present invention provides a method for
improving heat exchange (thermal) efficiency of heat transfer
surfaces and corrosion protection for heat transfer surfaces and
heat transfer systems and component parts thereof by coating the
heat transfer surfaces alone or the entire heat transfer system or
component parts thereof, with a low viscosity, penetrating,
reactive, curable, film-forming, silane-based, coating composition
and curing the composition to thereby form an at least
substantially continuous glass-like coating on the coated surface,
the coating extending into voids and defects which may be present
in the surface, whereby a thermally conductive corrosion protective
layer is provided on the heat transfer surface, and any other
coated surfaces.
[0022] In one embodiment, the present invention provides a method
for improving efficiency of heat transfer from a heat transfer
medium flowing in heat transfer contact with a heat transfer
surface of a thermally conductive component of a heat transfer
system across the heat transfer surface.
[0023] In a particularly preferred embodiment of the invention, the
coating composition is applied to at least the heat exchange
surfaces of a fin and tube heat exchange system.
[0024] In the preferred embodiment of the invention, the coating
composition is an aqueous or non-aqueous oligomeric silane coating
composition formed by admixing (a) at least one silane of the
formula (1)
R.sup.1.sub.nSi(OR.sup.2).sub.4-n (1)
[0025] where R.sup.1 represents a lower alkyl group, a
C.sub.6-C.sub.8 aryl or a functional group including at least one
of vinyl, acrylic, amino, mercapto, or vinyl chloride functional
groups;
[0026] (b) silane condensation catalyst, and
[0027] (c) lower alkanol solvent, and optionally, one or more
of
[0028] (d) colloidal aluminum hydroxide;
[0029] (e) metal alcoholate of formula (2):
M(OR.sup.3).sub.m (2)
[0030] where M is a metal of valence 2, 3 or 4, or mixture of two
or more such metals;
[0031] R represents a lower alkyl group; and,
[0032] m represents a number or 2, 3 or 4;
[0033] (f) a silica component selected from the group consisting of
alkali metal silicate, ethyl orthosilicate, ethyl polysilicate, and
colloidal silica dispersed in lower alkanol;
[0034] (g) color forming silanol condensation catalyst;
[0035] (h) epoxysilane; and,
[0036] (i) ultrafine titanium dioxide ultraviolet light
absorber.
[0037] The coating composition is applied to at least a portion of
a heat transfer surface and the applied coating composition is
allowed to cure to form a highly corrosion resistant and strongly
adherent coating. This coating is effective to fill micropores and
crevices in the heat transfer surface to effectively increase the
area available for heat transfer.
[0038] Similarly, the present invention provides a method for
increasing the contact area between first and second heat transfer
surfaces in thermal contact with each other, thereby improving the
heat transfer efficiency across the thermally contacting heat
transfer surfaces. The method according to this embodiment
comprises applying to the thermally contacting heat transfer
surface of at least one of the first and second heat transfer
surfaces, a low viscosity, penetrating, curable, reactive,
film-forming, coating composition and curing the composition to
thereby form an at least substantially continuous glass-like
coating on the heat transfer surface, the coating extending into
voids and defects which may be present in said heat transfer
surface, whereby a thermally conductive corrosion protective layer
is provided on the heat transfer surface.
[0039] Here again, the preferred coating composition is an aqueous
or non-aqueous oligomeric silane coating composition formed by
admixing (a) at least one silane of the formula (1)
R.sup.1.sub.nSi(OR.sup.2).sub.4-n (1)
[0040] where R.sup.1 represents a lower alkyl group, a
C.sub.6-C.sub.8 aryl or a functional group including at least one
of vinyl, acrylic, amino, mercapto, or vinyl chloride functional
groups;
[0041] (b) silane condensation catalyst, and
[0042] (c) lower alkanol solvent, and optionally, one or more
of
[0043] (d) colloidal aluminum hydroxide;
[0044] (e) metal alcoholate of formula (2):
M(OR.sup.3).sub.m (2)
[0045] where M is a metal of valence 2, 3 or 4, or mixture of two
or more such metals;
[0046] R represents a lower alkyl group; and,
[0047] m represents a number or 2, 3 or 4;
[0048] (f) a silica component selected from the group consisting of
alkali metal silicate, ethyl orthosilicate, ethyl polysilicate, and
colloidal silica dispersed in lower alkanol;
[0049] (g) color forming silanol condensation catalyst;
[0050] (h) epoxysilane;
[0051] (i) ultrafine titanium dioxide ultraviolet light
absorber;
[0052] (j) water; and
[0053] (k) co-solvent.
[0054] In a particularly preferred embodiment, the efficiency of
heat exchange apparatus of the type wherein a metal-to-metal
contact is present wherein a metal heat transfer surface is swaged
or force fit to a metal heat transfer fluid conveyance is improved
by applying to the metal to metal contact a low viscosity,
penetrating, curable, reactive, film-forming, coating composition
and curing the composition to thereby form an at least
substantially continuous glass-like coating on said heat transfer
surface, said coating extending into voids and defects which may be
present in said heat transfer surface, whereby a thermally
conductive corrosion protective layer is provided on said heat
transfer surface. Preferably, the above described aqueous or
non-aqueous oligomeric silane coating composition containing the
silane of formula (1), silane condensation catalyst and solvent,
and one or more optional ingredients, is applied to the interface
of the metal-to-metal contact portions, whereby the oligomeric
coating composition will displace gasses and liquids in the
interface; and allowing the coating composition to cure to a film
thickness of from about 5 to about 150 millionths of an inch, while
also filling microvacancies in the metal surfaces at the
metal-to-metal contact interface.
[0055] The present invention also provides the coated heat exchange
surfaces and heat exchange systems and component parts, especially,
fin and tube heat exchange systems.
DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS
[0056] The coating compositions used in the present invention may
generally be characterized as low molecular weight oligomeric
silane based coatings. As used in this context the term "silane" is
intended to include not only silanes but also silanols and
siloxanes and the low molecular weight partial condensation
products thereof. The term "low molecular weight" is intended to
refer to the general absence of large or bulky organic molecules or
moieties as part of the silane components, namely, wherein the
organic substituents are generally limited to lower alkyl groups,
especially alkyl groups containing from 1 to 4 carbon atoms,
especially, 1 to 3 carbon atoms, including, in particular, methyl,
ethyl, n-propyl and iso-propyl groups, and aryl groups of no more
than about 8 carbon atoms, especially, no more than about 6 carbon
atoms, such as, for example, phenyl, benzyl, and phenethyl.
[0057] Still further, the coating compositions of this invention
are characterized by low viscosity to facilitate the penetration
into the microcrevices and microvoids present on the heat transfer
surface. As used herein, "low viscosity" is taken to mean the
ability to penetrate into micron and submicron size voids in metal
surfaces. Typically, the coating compositions of the present
invention are characterized by a coating viscosity, measured using
a No. 2 (#2) Zahn Cup, of from about 4 to about 10 seconds,
especially, from about 5 to about 8 seconds, measured at room
temperature (approximately 18.degree. C.).
[0058] The present invention also provides improved heat transfer
systems coated with the subject silane based anticorrosion coating
compositions as described herein. In particular, the invention
coating compositions may be applied as protective coatings for new
or refurbished heat transfer systems and components as well as
applied in situ to used, corroded or rusted heat transfer systems
and component parts thereof to significantly improve performance
and increase the useful life of the treated systems and component
parts.
[0059] The compositions according to this invention are able to
readily penetrate into extremely small spaces and crevices,
including down to nanometer inclusions in the indices of the metal
substrates used to manufacture heat exchange systems and component
parts. As compared to conventional organic coatings, including
known silane based coating compositions, the compositions of the
present invention are characterized by low cohesive forces and, as
a result, tend to wick into such small micro-spaces due to their
active chemical nature. Thus, for example, organic coatings,
including acrylics, polyurethanes, epoxies and phenolics, will not
naturally wick into the small (e.g., micro-voids) metal contact
irregularities, even when applied by E-coating (electrocoating)
techniques. While it has been suggested in the art to mix some
silane/siloxane compounds with acrylics, acrylic urethanes, organic
acids and epoxides, however, these known formulations are not able
to take advantage of the small active molecules which characterize
the present compositions, which are capable of wicking into
extremely small voids in and between thermal contact surfaces.
[0060] The coating compositions used in the present invention are
capable of filling small nanometer size voids under driving forces
of capillary action and Helmoltz free energy, displacing gasses
and/or reacting with water or other chemicals. The ability of the
coating compositions of this invention to migrate and penetrate
capillary structures releasing Helmoltz free energy allows them to
displace molecules bonded by means of secondary and tertiary
valence forces and provide protection by forming micron range
thickness coatings, on the order of from about 5 to about 150
millionths of an inch. These driving forces even allow such
penetration to occur under the high pressures, e.g., 2000 p.s.i.,
present injoints of such heat exchangers. Accordingly, the coating
of the present invention are highly effective for increasing the
efficiency of heat exchangers by providing parallel thermal paths
between metal contact of, for example, heat dispersing fins and
tubing or piping carrying fluids or gases for absorption or
dispersion of heat.
[0061] The preferred low viscosity, penetrating, active coating
compositions used in the present invention are silane based coating
compositions, and may be may be aqueous or non-aqueous. Preferred
coating compositions are formed by admixing (a) at least one silane
of formula (1)
R.sup.1.sub.nSi(OR.sup.2).sub.4-m (1)
[0062] where R.sup.1 represents a lower alkyl group, a
C.sub.6-C.sub.8 aryl group or a functional group including at least
one of vinyl, acrylic, amino, mercapto, or vinyl chloride
functional groups; with (b) a silane condensation catalyst, which
may be, for example, an acid, a base, or mixed acid-base. The
silane(s) and catalyst are contacted in a low viscosity solvent,
typically a lower alkanol solvent, such as ethanol, isopropanol,
and the like. One or more additional reactive or functional
ingredients may be included in the composition.
[0063] Representative examples of suitable oligomeric silane
coating compositions useful in the present invention have been
described in my above-identified patent and co-pending provisional
applications and are described briefly below.
[0064] I. an aqueous coating composition comprising a dispersion of
divalent metal cations in lower aliphatic alcohol-water solution of
the partial condensate of at least one silanol of the formula
RSi(OH).sub.3, wherein R is a radical selected from the group
consisting of lower alkyl, or C.sub.6-C.sub.8 aryl or a functional
group including at least one of vinyl, acrylic, amino, mercapto, or
vinyl chloride functional groups (e.g., 3,3,3-trifluoropropyl,
.gamma.-glycidyloxypropyl, and .gamma.-methacryloxypropyl), at
least about 70 percent by weight of the silanol being
CH.sub.3Si(OH).sub.3, acid in amount to provide a pH in the range
of from about 2.5 to about 6.2, said divalent metal cations being
present in an amount of from about 1.2 millimoles to about 2.4
millimoles, per molar equivalent of the partial condensate,
calculated as methyl silane sesquioxide;
[0065] II. an aqueous coating composition formed by admixing
[0066] (A) at least one silane of the formula (1)
R.sup.1Si(OR.sup.2).sub.3 (1)
[0067] wherein
[0068] R.sup.1 is a lower alkyl group, a C.sub.6-C.sub.8 aryl group
or an N-(2-aminoethyl)-3-aminopropyl group, and
[0069] R.sup.2 is a lower alkyl group;
[0070] (B) an acid component selected from the group consisting of
water-soluble organic acids, H.sub.3BO.sub.3 and H.sub.3PO.sub.3;
and
[0071] (D) water;
[0072] III. a non-aqueous coating composition formed by
admixing
[0073] (A) at least one silane of formula (1)
R.sup.1.sub.nSi(OR.sup.2).sub.4-n (1)
[0074] wherein R.sup.1 represents lower alkyl, C.sub.6-C.sub.8
aryl, 3,3,3-trifluoropropyl, .gamma.-glycidyloxypropyl,
.gamma.-(meth)acryloxyp- ropyl, N-(2-aminoethyl)-3-aminopropyl, or
aminopropyl group;
[0075] R.sup.3 represents lower alkyl group; and
[0076] n is a number of 1 to 2; and
[0077] (E) (i) vinyltriacetoxysilane, (ii) colloidal aluminum
hydroxide; and/or (iii) at least one metal alcoholate of formula
(2)
M(OR.sup.3).sub.m (2)
[0078] wherein M represents a metal of valence m,
[0079] R.sup.3 represents lower alkyl group; and
[0080] m is a number of 2, 3 or 4;
[0081] IV. a non-aqueous coating composition formed by admixing
[0082] (A) at least one silane of formula (1)
R.sup.1.sub.nSi(OR.sup.2).sub.4-n (1)
[0083] wherein R.sup.1 represents lower alkyl, C.sub.6-C.sub.8
aryl, 3,3,3-trifluoropropyl, .gamma.-glycidyloxypropyl,
.gamma.-(meth)acryloxyp- ropyl, N-(2-aminoethyl)-3-aminopropyl, or
aminopropyl group;
[0084] R.sup.2 represents lower alkyl or acetyl group; and
[0085] n is a number of 1 to 2;
[0086] (B) boric acid, optionally dissolved in lower alkanol;
[0087] (E) (i) vinyltriacetoxysilane, (ii) colloidal aluminum
hydroxide; and/or (iii) at least one metal alcoholate of formula
(2)
M(OR.sup.3).sub.m (2)
[0088] wherein M represents a metal of valence m,
[0089] R.sup.3 represents lower alkyl group
[0090] m is an number of 2, 3 or 4; and,
[0091] (F) silica component selected from the group consisting of
ethyl ortho-silicate, ethyl polysilicate and colloidal silica,
dispersed in lower alkanol;
[0092] V. a non-aqueous coating composition formed by admixing
[0093] (A) at least one silane of formula (1)
R.sup.1.sub.nSi(OR.sup.2).sub.4-n (1)
[0094] wherein R.sup.1 represents lower alkyl, C.sub.6-C.sub.8
aryl, 3,3,3-trifluoropropyl, .gamma.-(meth)acryloxypropyl,
N-(2-aminoethyl)-3-aminopropyl, or aminopropyl group;
[0095] R.sup.2 represents lower alkyl or acetyl group; and
[0096] n is a number of 1 to 2,
[0097] (A') .gamma.-glycidyloxypropyltrimethoxysilane;
[0098] (B) boric acid, optionally dissolved in lower alkanol;
[0099] (E) (i) vinyltriacetoxysilane, (ii) colloidal aluminum
hydroxide; and/or (iii) at least one metal alcoholate of formula
(2)
M(OR.sup.3).sub.m (2)
[0100] wherein M represents a metal of valence m,
[0101] R.sup.3 represents lower alkyl group
[0102] m is an number of 2, 3 or 4;
[0103] VI. an aqueous coating composition formed by admixing
[0104] (A) at least one silane of formula (1)
R.sup.1.sub.nSi(OR.sup.2).sub.4-n (1)
[0105] wherein R.sup.1 represents lower alkyl, C.sub.6-C.sub.8
aryl, or a functional group containing at least one of vinyl,
acrylic, amino, mercapto, or vinyl chloride functional group;
and
[0106] R.sup.2 is a lower alkyl group;
[0107] (B) acid component comprising a member selected from the
group consisting of water-soluble organic acids, H.sub.3BO.sub.3
and H.sub.3PO.sub.3; and
[0108] (D) water;
[0109] VII. an aqueous coating composition formed by admixing
[0110] (A) at least one silane of formula (1)
R.sup.1.sub.nSi(OR.sup.2).sub.4-n (1)
[0111] wherein R.sup.1 represents lower alkyl, C.sub.6-C.sub.8
aryl, or a functional group containing at least one of vinyl,
acrylic, amino, mercapto, or vinyl chloride functional group;
and
[0112] R.sup.2 is a lower alkyl group;
[0113] (C) alkali component; and
[0114] (D) water;
[0115] VIII. an aqueous coating composition formed by admixing
[0116] (A) at least one silane of the formula (1)
R.sup.1Si(OR.sup.2).sub.3 (1)
[0117] wherein
[0118] R.sup.1 represents lower alkyl group, C.sub.6-C.sub.8 aryl
group or a bifunctional silane containing vinyl, acrylic, amino, or
vinyl chloride functional group; and
[0119] R.sup.2 is a lower all group;
[0120] (E) (ii) colloidal aluminum hydroxide, (iii) metal
alcoholate of the formula (2)
M(OR.sup.3).sub.m (2)
[0121] wherein
[0122] M is a metal of valence m,
[0123] R.sup.3 is a lower alkyl group,
[0124] m is an integer of 3 or 4, or (iii) mixture of (ii) and
(iii); and
[0125] (D) water;
[0126] IX. an aqueous coating composition formed by admixing
[0127] (A) at least one silane of the formula (1)
R.sup.1Si(OR.sup.2).sub.3 (1)
[0128] wherein
[0129] R.sup.1 represents lower alkyl group, C.sub.6-C.sub.8 aryl
group or a bifunctional silane containing vinyl, acrylic, amino, or
vinyl chloride functional group; and
[0130] R.sup.2 is a lower alkyl group;
[0131] (D) water;
[0132] (G) chromium acetate hydroxide; and
[0133] (H) lower alkanol;
[0134] X. an aqueous coating composition formed by admixing
[0135] (A) at least one silane of the formula (1)
R.sup.1Si(OR.sup.2).sub.3 (1)
[0136] wherein
[0137] R.sup.1 represents lower alkyl group, C.sub.6-C.sub.8 aryl
group or a functional group including at least one of vinyl,
acrylic, amino, mercapto, or vinyl chloride functional group;
and
[0138] R.sup.2 is a lower alkyl group;
[0139] (D) water;
[0140] (E) (ii) colloidal aluminum hydroxide, (iii) metal
alcoholate of the formula (2)
M(OR.sup.3).sub.m (2)
[0141] wherein
[0142] M is a metal of valence m,
[0143] R.sup.3 is a lower alkyl group,
[0144] m is an integer of 3 or 4, or (iii) mixture of (ii) and
(iii);
[0145] (F) alkali metal silicate, which may be hydrolyzed; and
[0146] (H) lower alkanol.
[0147] XI. a non-metallic aqueous coating composition formed by
admixing
[0148] (A) at least one silane of the formula (1)
R.sup.1Si(OR.sup.2).sub.3 (1)
[0149] wherein
[0150] R.sup.1 represents lower alkyl group, C.sub.6-C.sub.8 aryl
group or a functional group including at least one of vinyl,
acrylic, amino, mercapto, or vinyl chloride functional group;
and
[0151] R.sup.2 is a lower alkyl group;
[0152] (A") 3-(2-aminoethylamino)propyltrimethoxysilane or
3-aminopropyltrimethoxysilane;
[0153] (D) water;
[0154] (H) lower alkanol; and
[0155] (I) epoxide silane;
[0156] XII. an aqueous coating composition formed by admixing
[0157] (A) at least one silane of the formula (1)
R.sup.1Si(OR.sup.2).sub.3 (1)
[0158] wherein
[0159] R.sup.1 represents lower alkyl group, C.sub.6-C.sub.8 aryl
group or a functional group including at least one of vinyl,
acrylic, amino, mercapto, or vinyl chloride functional group;
and
[0160] R.sup.2 is a lower alkyl group;
[0161] (B) boric acid;
[0162] (C) at least one alkali component comprising an hydroxide or
carbonate of divalent metal;
[0163] (D) water;
[0164] (H) lower alkanol, and
[0165] (J) ethyl polysiloxane.
[0166] As examples of silanes of formula (1), wherein R.sup.1 is an
alkyl group or aryl group, mention may be made of, for example,
methyltimethoxysilane, ethyltrimethoxysilane, ethyltriethoxysilane,
n-propyltrimethoxysilane, n-propyltriethoxysilane,
isopropyltrimethoxy silane, n-butyltrimethoxy silane,
isobutyltrimethoxy silane, phenyltrimethoxy silane, preferably
methyltrimethoxy silane. In the case where R.sup.1 is a functional
group, mention may be made, for example, of
N-(2-aminoethyl)-3-aminopropyltrimethoxy silane,
3-mercaptopropyltrimetho- xy silane, 3-mercaptopropyltriethoxy
silane, 3-aminopropyltriethoxy silane, 3-(meth)acryloxypropyl
trimethoxy silane, 3-(meth)acryloxypropylt- riethoxy silane,
n-phenylaminopropyltrimethoxy silane, vinyltriethyoxy silane,
vinyltrimethoxy silane, allyltrimethoxy silane, and any of the
aminosilane catalysts, described herein below.
[0167] As used herein, the expression "functional group" is
intended to include any group, other than hydroxyl, (including
alkoxy, aryloxy, etc.), which is hydrolyzable to provide, in situ,
a reactive group (e.g., reactive hydrogen) which will react, in
other than a condensation reaction, with the substrate (e.g.,
metal), itself, or other reactive components in or from the coating
composition.
[0168] The functional groups, in addition to the hydroxyl group (by
hydrolysis of the (OR.sup.2) groups), tend to form
three-dimensional or cross-linked structure, as well known in the
art.
[0169] Moreover, in the various embodiments of the invention, it is
often preferred to use mixtures of two or more silane compounds of
formula (1). Mixtures of at least phenyltrimethoxysilane and
methyltrimethoxysilane are often especially preferred.
[0170] Generally, total amounts of silane compounds of formula (1)
will fall within the range of from about 40 to about 90 percent by
weight, preferably from about 50 to about 85 percent by weight,
based on the total weight of silanes, catalyst(s) and
solvent(s).
[0171] In addition to silane compound(s) of formula (1), the
composition may additionally include a bistrifunctional
aminosilane, such as represented by the following formula (4):
X[R.sup.1Si(OR.sup.2).sub.3].sub.2 (4)
[0172] where R.sup.1 and R.sup.2 are as defined above, and X
represents an amino group (--NH) or keto group 1
[0173] as a basic catalyst, not requiring acid stabilization. As a
representative example of aminosilane or ketosilane catalyst
according to formula (4), mention may be made of, for example,
bis(trimethoxypropylsil- ane) amine, bis(trimethoxyethylsilane)
amine, di(trimethoxybutylsilane) ketone, di(trimethoxypropylsilane)
ketone, and the like. The silane compounds of formula (4) function
as a less active basic catalyst, not requiring acidic passivation.
Minor amounts, usually from about 1 to about 10 parts, preferably,
from about 2 to about 8 parts, of compound of formula (4) per 100
parts of silane compound(s) of formula (1) provide satisfactory
results.
[0174] The silane condensation catalyst (b) may be, for example, a
base or alkali component. As examples, an inorganic base, such as,
for example, calcium hydroxide, aluminum hydroxide or zinc
hydroxide, or mixture thereof; or an organic base component, such
as, for example, aminosilane, may be mentioned.
[0175] The amount of the base catalyst is generally, up to about
2%, such as, for example, from about 0.1 to 2.0%, by weight of the
composition, especially, from about 0.2 to 1.6%.
[0176] The silane condensation catalyst (b) may also be, for
example, an acid. As examples of the acid catalyst component (b),
mention may be made of lower alkanoic acids, such as, for example,
formic acid, acetic acid, propanoic acid, butyric acid, and
inorganic acids, such as, for example, boric acid (H.sub.3BO.sub.3)
or ortho-phosphorous acid (H.sub.3PO.sub.3), preferably acetic
acid, boric acid or ortho-phosphorous acid, most preferably, for
reasons of economy and safety, acetic acid. The acid may be added
as free acid or as inorganic salt thereof, such as alkali metal
(e.g., sodium), alkaline earth metal (e.g., calcium), or ammonium
salt.
[0177] Generally, total amounts of the inorganic acid component
will fall within the range of from about 0.3 to about 4 percent by
weight, preferably from about 0.5 to about 3%, preferably, from
about 0.5 to about 2.5 percent by weight, based on the total weight
of silanes, acid component and water. For acetic acid, the
preferred range is from about 0.1 to about 1.0 percent, preferably,
from about 0.2 to about 0.7 percent, by weight, based on the total
weight of the composition.
[0178] Of course, one or more other silanol condensation catalysts,
as well known in the art, may be used in place of or in addition to
the acid and/or base catalyst.
[0179] As examples of organic solvents (c), mention may be made of
lower alkanol, e.g., C.sub.2-C.sub.4 alkanols, preferably
isopropanol.
[0180] Generally, total amounts of organic solvent, such as, lower
alkanol, will fall within a range of from 10 to about 50 percent by
weight, preferably from 15 to about 40 percent by weight, based on
the total weight of silane(s), acid component and/or base component
and water. In some cases, however, substantially higher amounts may
be convenient, especially where, for example, the coating
compositions are applied, usually by spraying, to preexisting HVAC
systems, such as, for example, evaporators, or other structures
wherein ready access to component parts and/or to metal-metal heat
transfer junctions, may be inhibited due to tight fits, etc.
[0181] Where it is deemed to be advantageous or necessary to
provide especially dilute coating compositions, for example,
amounts of alcohol solvent from about 40 to about 90% by weight, or
more, especially, from about 50 or 60% by weight or higher, based
on the total composition, it is often advantageous, to provide a
portion of the solvent as a separate component to be added to the
remainder of the composition after mixing of the silane(s) and
silane condensation catalyst(s). In such case, the system may be
provided as a two or three "pot" system, e.g., silane compound(s)
in one pot, catalyst(s) in a second pot, a portion of alcohol
solvent, e.g., isopropanol, with one or both of the first and
second pots, and the remainder of the alcohol and/or water solvent
in a third pot.
[0182] The coating compositions of this invention may be
non-aqueous or aqueous. When water, as component (j), is present,
the total amount of water will generally fall within the range of
from about 10 to about 60 percent by weight, preferably from about
10 to about 45 percent by weight, based on the total weight of (a)
silane(s), (b) catalyst component(s), (c) organic solvent, (j)
water, (k) co-solvent.
[0183] Some or all of the water may be provided by the acid and/or
base component, when the base or acid component is supplied as an
aqueous solution, e.g., 5% aqueous solution of ortho-phosphorous
acid or saturated aqueous solution of boric acid (about 6% by
weight of H.sub.3BO.sub.3).
[0184] Since the presence of metallic and other impurities may have
an adverse effect on the properties of the resulting coatings,
preferably, water, when used, is distilled or deionized water.
[0185] According to a particularly preferred embodiment of the
present invention, the coating compositions may include metal
catalysts which additionally provide a tint or coloration to the
resulting coating. Chromium acetate hydroxide is especially useful
in this regard, serving as a basic catalyst which provides a bluish
tint to the resulting coating. This feature may be especially
useful, for example, in connection with providing corrosion
resistant coatings to HVAC systems having large surface areas
and/or difficultly accessible regions, where visibility of the
applied coating can assure total coverage of the areas to be coated
while avoiding wasting coating by excessive applications over
already coated surfaces.
[0186] Other basic metal catalysts providing a colorant function
include, for example, iron acetate, iron acetate hydroxide,
chromium acetate, and the like. Other metal compounds such as
compounds of antimony, lead, barium, etc., also form colored
products, but tend to be more toxic and, therefore, less useful for
general purposes.
[0187] The present coating composition may be formed by mixing the
above-noted components and allowing them to react. A suitable
reaction time is typically 4 to 12 hours, if no colloidal aluminum
hydroxide and/or metal alcoholate is present. Shorter reaction
times may be obtained in the presence of colloidal aluminum
hydroxide and/or metal alcoholate.
[0188] For ease of handling, the coating composition may be
provided as a two or three container system, e.g., the silane
component and any silicate component, if present, being provided in
a first container and all other components being provided in a
second or second and third container. Water, when included in the
composition, may be provided separately from the other components.
The contents of the two or three (or more) containers may be mixed
shortly prior to use and allowed to react for an appropriate
reaction time, as noted above.
[0189] While general and preferred ranges of amount for the
film-forming, catalytic and solvent components have been described
above, it will be recognized by those skilled in the art, that
these amounts may be increased or decreased as necessity demands
and that the optimum amounts for any particular end use application
may be determined by the desired performance and HVAC system to be
coated, including type of system and location. In this regard, for
example, when the amount of catalyst is reduced, the time to
achieve freedom from tack will increase. Similarly, when the amount
of the catalyst(s) is (are) increased, this may lead to increased
rates of cracking, loss of adhesion and performance loss of the
resulting coating.
[0190] The compositions of this embodiment may further include one
or more additional additives for functional and/or esthetics
effects, such as, for example, (d) colloidal aluminum hydroxide,
(e) metal alcoholate, (f) silica and/or silicates, (g) color
forming silanol condensation catalyst, (h) epoxide silane, (i)
ultraviolet absorber, (j) water, (k) cosolvent, and the like.
[0191] The above-noted optional ingredients may be used singly or
in any combination in the coating composition of this
invention.
[0192] As examples of silicate component (f), mention may be made
of ethyl or methyl orthosilicate or ethyl polysilicate. These
silicates may be hydrolyzed, for example, from about 28% to about
52% silica. Especially preferred in this regard is
tetraethylsilicate (TEOS) (often referred to simply as ethyl
silicate) which has been subjected to controlled hydrolysis,
providing a mixture of TEOS and, from about 20% to about 60%
polydiethoxysilane oligomers. For example, a 50% hydrolysis product
may be referred to herein as "polydiethoxysilane (50%)."
[0193] Generally, total amounts of silicate component, when used,
will fall within the range of from 0 to about 45 percent by weight,
preferably from 0 to about 25 percent by weight, based on the total
weight of silanes, acid component and water.
[0194] As example of (k) co-solvent, mention may be made, for
example, of mono-lower alkyl ether of alkylene (e.g., ethylene)
glycol, such as, mono-C.sub.1-C.sub.6-alkyl ethers of ethylene
glycol, for example, monomethyl ether, monoethyl ether, monopropyl
ether, monobutylether, monopentylether or monohexylether,
preferably monoethyl ether of ethylene glycol. Other known and
conventional co-solvents may also be used, for example, acetone,
ketones (e.g., methylethylketone, ethers (e.g., ethylether), esters
(e.g., ethyl acetate), and the like. The co-solvents should also
have low viscosity, e.g., lower than that of water, preferably,
less than about 8 centipoise.
[0195] Generally, total amounts of the mono-lower alkyl ether of
ethylene glycol or other co-solvent, when used, will fall within
the range of from 0 to about 15 percent by weight, preferably from
0 to about 6 percent by weight, based on the total weight of
silanes, acid component and water. However, in the event that one
of the low viscosity solvents, e.g., methylethylketone, is used as
the main solvent, the same amounts as discussed above for the
preferred alcohol solvents, may be used.
[0196] As an example of (i) ultra-violet light absorber, mention
may be made of titanium dioxide in finely powdered form, e.g.,
having an average particle diameter of about 20 nm. Other inorganic
or organic ultra-violet light absorbers may be utilized in so far
as they do not interfere with the objects of this invention.
[0197] Generally, total amounts of the ultra-violet light absorber,
when used, will fall within the range of from 0 to about 10 percent
by weight, preferably from 0 to about 5 percent by weight, based on
the total weight of silanes, acid component and water.
[0198] Metal catalysts, such as, for example (d) colloidal aluminum
hydroxide, and/or (e) metal alcoholates, such as those represented
by the following formula (2):
M(OR.sup.3).sub.m (2)
[0199] where M is a metal of valence m (namely, from Groups IIIA,
IVA, IIB or IVB of the periodic table of the elements), e.g.,
boron, titanium, aluminum, indium, yttrium, cerium, lanthanum,
silicon, tin, hafnium, etc. and R.sup.3 is a lower alkyl group,
e.g., C.sub.1-C.sub.6 straight or branched chain alkyl group,
preferably C.sub.2-C.sub.4 alkyl group, most preferably, isopropyl,
isobutyl or n-butyl; and m is an integer of 3 or 4, may also be
used. Boron, aluminum and titanium are especially preferred as
metal M because the alkoxides of these metals are more readily
commercially available, and tend to be non-toxic).
[0200] As specific examples of the metal alcoholates of formula
(2), mention may be made of titanium alcoholates of C.sub.2-C.sub.4
alkanols, e.g., titanium tetraisopropoxide and titanium
tetrabutoxide.
[0201] In addition, double metal alcoholates of, for example, AlTi,
AlZr, AlY, MgAl, MgTi, MgZr, etc., may also be used.
[0202] The presence of the trivalent and tetravalent metal ions are
especially useful for coating compositions applied to steel since
they tend to form insoluble (water and alkali) iron silicates,
whereas the products of divalent metals, tend to be soluble.
[0203] Generally, total amounts of the colloidal aluminum hydroxide
and/or metal alcoholate, when used, will fall within the range of
from 0 to about 2.5 percent by weight, preferably from 0 to about 1
percent by weight, based on the total weight of (a) silane(s), (b)
acid and/or base component(s) and solvent(s).
[0204] Within the above general proportions, and based on the
weight of the entire composition, the amount (parts by weight) of
the individual classes of ingredients, will usually fall within the
following ranges: silane component (a) from about 15 to about 25
parts, preferably, as a mixture of from about 15 to about 20 parts
of methyltrimethoxysilane and from about 1 to about 5 parts of
phenyltrimethoxysilane;
[0205] base component condensation catalyst (b), when present, from
about 0.1 to 3 parts, preferably from about0.2 to 2.5 parts; acid
component condensation catalyst (b), when present, from about 0.2
to about 0.8 part: solvent. e.g.. isopropyl alcohol, to provide the
appropriate viscosity, generally, from about 5 to about 60 parts.
preferably, from about 10 to about 40 parts: water (j), when
present, from about 2.5 parts by weight to about 40 parts: silicate
component (f), when used, from 0 to about 15 parts by weight:
mono-lower alkyl ether of ethylene glycol and/or other co-solvent
(k), when used, from 0 to about 3 parts; ultra-violet light
absorber (i), when used, from 0 to about 2 parts by weight:
colloidal aluminum hydroxide and/or the metal alcoholate, when
used, from 0 to about 0.5 part by weight.
[0206] Furthermore, the above general and preferred amounts of the
respective ingredients apply equally to the various embodiments
I-XII, of the coating compositions, as identified above.
[0207] Moreover, on some occasions it has been observed that the
activity of the coating compositions is so high that when applied
too thickly, a random distribution of lumps, presumably due to
gelling, may form. Such lumps, if present, can serve as corrosion
initiation centers. Accordingly, one skilled in the art will
recognize that the coating compositions according to this invention
should preferably be applied in the minimum amount necessary to
substantially completely coat the surface to be protected. Coating
thicknesses of less than 1 mil. preferably, less than about 0.5
mil, are usually satisfactory.
[0208] Heat exchange devices often use a swaged metal to metal
joint from fin to tube/pipe, made by hydraulically or physically
expanding the tube/pipe to force intimate metal to metal contact
for heat transfer from fin to joint. However, whether or not
exacerbated by imperfections in the expansion techniques/equipment,
or/and as a result of corrosion, the presence of micro-voids are
inherent in such metal to metal contact. In accordance with the
present invention, these micro-voids are filled by the new
chemically active coating compositions described herein, thereby
providing more efficient parallel heat paths as well as corrosion
protection, not heretofore possible. Accordingly, the efficiencies
of both new and used heat exchange apparatus is significantly
increased while extending the useful service life of the apparatus.
However, it is noted that the relative increases in efficiency are
substantially higher for older and corroded systems, often on the
order of 20% to 60% or even 80% or more improvements in
efficiencies and reduction in operating costs, as compared to more
modest, but substantial improvements, on the order of from about 1
to 4%. or higher, for new (e.g.. OEM) HVAC systems and/or
components. At the same time, however, by applying the coatings of
the present invention to new or old HVAC systems and/or component
parts, long term reductions in maintenance requirements and
associated costs are achievable.
[0209] Organic coatings, such as epoxies, have a thermal
conductivity generally about one hundredth the thermal conductivity
of a metal-to-metal contact surface. Even with metal or other
conductive fillers, which tend to have a short life from corrosion
from molecular level water permeation, organic coatings are two
orders of magnitude less conductive than metal-to-metal contact.
Silicone or glass-like coatings formed according to the present
invention, on the other hand, are generally less than 5 to 10 times
less conductive than the metal-to-metal contact. However, the
significant and unique ability of these coatings to penetrate
metal-to-metal nano-voids created by the irregular microsurface
profile of metals allows the coatings to fill a significant amount
of void space in such metal-to-metal joint (e.g., fin-tube/pipe)
and, while providing less conductivity, and offers a significant,
parallel path for thermal conductivity.
[0210] Therefore, even for a corroded metal-to-metal thermal joint,
e.g., a fin and tube structure, a significant improvement in
thermal transfer efficiency will be achieved.
[0211] Often, electrolytes will react with metals or crystallize
with such a thermal joint and create salts, other crystalline
corrosion structures, or corrosion by-products that expand as they
are formed with pressures as high as 2000 pounds per square inch.
This causes the amount of contact in a metal to metal heat transfer
joint, as described herein, to have less contact then when
manufactured, or in some cases, virtually no direct contact due to
air or corrosion by-products remaining between metal surfaces.
[0212] This problem is substantially completely avoided by the
present invention since the subject coating compositions, in
addition to displacing gasses, form bonds to the corrosion
products, including chemical bonds to oxides, medium to strong
hydrogen bonds to electrolytes, thereby dissolving the corrosion
products, and/or encapsulating/filling and providing parallel
thermal path(s) around the corrosion products. As a result, heat
exchangers otherwise operating at low efficiencies due to
corrosion, joint expansion and the like, will undergo a significant
and substantial improvement in thermal conductivity as a result of
the coating treatment according to this invention.
[0213] Again, while not wishing to be bound by any theory of
operation, it is believed that the effectiveness of the instant
classes of silane/siloxane coating compositions arises from the
ability of such coatings to form dendritic interfacial linkages
that effect their performance in thin layers, normally about 5 to
about 150 millionths of an inch.
[0214] Therefore, notwithstanding low thermal conductivities of the
silane coatings, per se, due to the extremely thin nature of the
deposited coatings, only an insignificant and negligible thermal
loss occurs, in contrast to the thermal transfer gains by the
parallel path for heat exchange.
[0215] Moreover, for new/original manufactured and/or refurbished
exchangers, a 10 to 40% increase in surface conducting area is
achieved by application of the present coatings (with thermal
conductivities 5 to 10 times less than metal-to-metal contact) in a
metal-to-metal joint. This will, therefore, produce an overall
cooling/power reduction efficiency increase of usually from about 1
to about 10%.
[0216] The overall corrosion protection provided according to this
invention, either within the metal-to-metal joint, which is
effectively filled and rendered unavailable for penetration of
electrolytes or other corrosive gases or chemicals; or on other
heat transfer surfaces in contact with air, water, or conductive
structure or media/chemical or conveyance (e.g., tube, pipe,
conductive metal sink, etc.) for fluid or gases passed through the
exchanger; are all protected with a double corrosion protection not
offered by normal organic coatings. The instant coating
compositions are effective, for example, in eliminating "white
rusting" problems resulting from growth of zinc oxide on brass or
other zinc-containing metals or alloys. In the present invention,
the zinc and zinc oxide will be effectively brought into the
polymeric matrix coating to not only eliminate further growth of
the zinc oxide but enhancing the strengthening of the coating.
[0217] Coatings formed using the subject oligomeric silane based
coating compositions, applied to metal surfaces and wiped off until
only the areas of bonding remains, 5 to 20 millionths of an inch,
form coated metal surfaces able to pass 700 to 1000 hours in as
ASTM B-117 salt spray test. If the coating is allowed to grow the
dendritic glass structures to about 150 millionths of an inch the
combination of the bond and glasslike coating growth enables the
coated metal surface to pass 4000 to 6000 hours in the same ASTM
test.
[0218] Thus, a double protection is afforded the heat exchangers
treated in accordance with the present invention.
[0219] The present invention may be applied to any type of heat
exchange system and the component parts thereof. For example,
mention may be made of evaporator and condensing coils in HVAC
systems, radiators for dispelling or absorbing heat, exchangers
with dissimilar or similar metals, refrigeration exchangers, and
the like. A particularly preferred type of heat exchange system is
the fin and tube type. Heat exchangers coated according to the
present invention will maintain high efficiencies, equivalent or
superior to new, uncoated exchangers, due to exclusion of
electrolytes that would normally form corrosion products in metal
contact areas, thereby retarding corrosion due to the dual surface
chemical bond and coating structure formed on surfaces and in small
inclusions in joints, not accessible with previously known coating
materials.
[0220] The anticorrosion silane-based oligomeric coating
compositions of this invention may be applied to confer protection
on all heat transfer surfaces that come into contact with air,
water, or conductive structure or media/chemicals, including,
conveyances (e.g., tubes, pipes, conductive metal sinks, etc.) for
liquid or gasses passing through the exchanger. For example, the
present invention may be applied to coat new or used heat
exchangers and all other components of air-conditioners and
chillers, and other refrigeration devices, including cabinets,
components, compressors, tubing, piping, grills, fans, motors,
external electrical conduits, coated and uncoated wiring, switch
boxes, and the associated nuts, bolts, and other connectors.
[0221] The coating compositions of this invention may be applied to
new or used/corroded heat exchangers, made of similar or dissimilar
metals, wherein heat transfer fluids or gasses flow in tubing,
piping, or other forms of heat conveyance, which are swaged or
expanded (e.g., force fit metal joints) to metal to metal contact
with other heat exchanger surfaces, and cooled by, for example,
air, water, conductive metal heat sink, etc., to increase
efficiency of heat transfer of the heat exchanger by improving the
metal to metal joint transfer by increasing the contact area
between the similar or dissimilar metals. As a result of the
improved efficiency, energy costs for running the coated units,
e.g., air-conditioning condenser; condenser/chiller; will be
substantially lowered.
[0222] The coated substrates of the HVAC systems and/or component
parts, whether new or used/corroded, by virtue of the chemical
bonding and silica or siloxane bonding, with the additional
dendritic linkages, producing a glass-like structural formation
over the chemical bond area, reduces the available chemical
activity on the coated surfaces/interfaces of the metal or metal to
metal, to thereby provide a "double" protection. This protection is
provided on all heat transfer surfaces in contact with air, water,
or conductive structure or media/chemicals; as well as on the
conveyances (tubes, pipes, conductive metal sinks, etc.) for fluid
or gases which pass through the exchanger.
[0223] In this regard, by filling the microvoids and macrovoids
within the metal to metal joints, the metal becomes unavailable for
penetration of electrolytes or corrosive gases or chemicals.
[0224] In addition, in view of the hydrophobic nature of the
applied coatings, the coated surfaces will stay cleaner for longer
periods of time, thereby affording significant and substantial
savings in maintenance costs.
[0225] Moreover, in accordance with a particular feature of the
present invention, even when corrosion protection is not of
paramount importance, the coated HVAC systems and component parts
according to the present invention are characterized by being
non-adherent to various types of soiling agents and to microbial
growths. Accordingly, the coated articles of the present invention
have the additional advantage of requiring less frequent
maintenance (e.g., cleaning) and, since they do not promote growth
of microorganisms, e.g., fungi, mold spores, yeast, bacteria, and
the like, are advantageous for use in protecting HVAC systems used
to heat/cool occupied structures, e.g., offices, factories, and the
like. That is, since growth of microorganisms is inhibited, when
the HVAC systems and component parts thereof, e.g., evaporators,
flow ducts, and the like, are treated in accordance with the
present invention, subsequent introduction of microorganisms into
the structures which are heated/cooled by the coated systems is
greatly inhibited or prevented.
[0226] The invention will now be illustrated by the following
non-limiting examples. It is understood that these examples are
given by way of illustration only and without intent to limit the
invention thereto.
Referential Example 1A
[0227] Calcium hydroxide (1 millimole) is added to 20 part water
containing 0.3 grams glacial acetic acid. The initial pH is about
4.2. The acetic acid catalyst and the calcium hydroxide should
react to form calcium acetate. In a separate container 20 parts of
methyltrimethoxysilane is mixed with 20 parts isopropyl alcohol.
While the silane alcohol mixture is being stirred, the aqueous
solution is slowly added. The composition is allowed to react for
about 3 hours. The resulting mixture (oligomeric coating
composition) has a viscosity of about 8 seconds, using a #2 Zahn
cup, and is ready for application. The solids level of the
composition is about 16%, based on sesquioxide content.
Referential Example 1B
[0228] The procedure of Referential Example 1A is repeated except
that the 20 parts of methyltrimethoxysilane is added to 40 parts of
isopropyl alcohol.
Referential Example 2
[0229] The procedure of Referential Example 1 is repeated, except
that the amount of calcium hydroxide is changed from 1 millimole to
0.7 millimole.
Referential Example 3
[0230] The procedure of Referential Example 1 is repeated, except
that the amount of calcium hydroxide is changed from 1 millimole to
about 2.4 millimoles.
Referential Example 4
[0231] The procedure of Referential Example 1 is repeated, except
that in place of calcium hydroxide, an equivalent amount of calcium
oxide is used.
Referential Example 5
[0232] The procedure of Referential Example 1 is repeated, except
that in place of calcium hydroxide, an equivalent amount of
magnesium hydroxide is used.
Referential Example 6
[0233] The procedure of Referential Example 1 is repeated, except
that in place of calcium hydroxide, an equivalent amount of zinc
oxide is used.
Referential Example 7
[0234] The procedure of Referential Example 1 is repeated, except
that in place of calcium hydroxide, a mixture of calcium hydroxide
and zinc oxide is used.
Referential Example 8
[0235] The procedure of Referential Example 1 is repeated, except
that, 0.4 parts 20 nanometer TiO.sub.2, and 0.15 parts of
hydroxybenzoylphenone, are added to the coating composition.
Referential Example 9
[0236] The procedure of Referential Example 1 is repeated, except
that instead of using 20 parts of methyltrimethoxysilane and 20
parts isopropyl alcohol, a mixture of 18 parts
methyltrimethoxysilane,2.5 parts .gamma.-glycidyloxypropylsilane
and 1.9 parts phenyltrimethoxysilane and 20 parts isopropyl alcohol
is used.
Referential Example 10
[0237] In a first container containing 20 parts isopropyl alcohol,
methyltrimethoxysilane, phenyltrimethoxysilane and
propyltrimethoxysilane are mixed in amounts of 15 parts, 1 part and
5 parts, respectively. In a second container,
aminoethylaminopropyl-trimethoxysilane
{N-(2-aminoethyl)-3-amino-propyltrimethoxysilane}, water, acetic
acid, and titanium dioxide (average particle size, 22 nm), are
mixed in amounts of 0.2 part, 13 parts, 0.4 part, and 0.2 part,
respectively. After combining the contents of the two containers,
the resulting mixture is allowed at least four hours to homogenize.
Faster homogenization will be achieved by using a mechanical shaker
or stirrer.
Referential Example 11
[0238] In a first container containing 10 parts isopropyl alcohol,
phenyltrimethoxysilane, methyltrimethoxysilane and
tetrabutoxytitanate are mixed in amounts of 5 parts, 15 parts and
0.3, 0.4, 0.5 or 0.6 part, respectively. In a second container,
isopropyl alcohol and an aqueous 3% boric acid solution are mixed
in amounts of 13 parts and 13 parts, respectively. After combining
the contents of the two containers, the resulting mixture is ready
for application after about three hours.
Referential Example 12
[0239] 10 parts of a 3% boric acid solution are placed in a first
container. 20 parts of methyltrimethoxysilane, 10 parts of
isopropyl alcohol and 0.5 part of tetrabutoxy titanate are mixed in
a second container. The contents of the two containers are mixed
together and allowed to react to form a coating composition.
Referential Example 13
[0240] 20 parts of methyltrimethoxysilane, 10 parts of isopropyl
alcohol and 0.2 parts of magnesium ethoxide are mixed until the
solution becomes homogeneous. To this solution a base catalyst (a
saturated solution of a mixture of calcium hydroxide, calcium
carbonate and magnesium carbonate, diluted with 2 parts water), is
added. The resulting formulation is allowed to react for about 1
hour.
Referential Example 14
[0241] After thoroughly mixing 20 parts methyltrimethoxysilane with
10 parts isopropyl alcohol,0.2 parts of
aminoethylaminopropyltrimethoxysilan- e is added to the resulting
silane-alcohol mixture, and again thoroughly mixed. Then 6 parts of
water is added to the resulting mixture and, after standing for 90
minutes, the composition is ready for use.
Referential Example 15
[0242] 20 parts of methyltrimethoxysilane and 20 parts isopropyl
alcohol are mixed and the resulting mixture is combined with 0.25
parts of aluminum isopropoxide under stirring until the aluminum
isopropoxide is partially dissolved. To this mixture 6 parts water
is added. After stirring for about one hour, the mixture is ready
to be applied.
Referential Example 16
[0243] This example shows the use of a double metal alkoxide
catalyst for the silane coating composition. A uniform solution,
obtained by mixing 15 parts methyltrimethoxysilane, 5 parts
phenyltrimethoxysilane, 20 parts isopropyl alcohol, and 2 parts
polydiethoxysiloxane (.about.50% solids) is catalyzed with 6 parts
of an alcoholic (isopropyl alcohol) solution of a double alkoxide
of aluminum and titanium. The resulting mixture is allowed to react
for about 4 hours using six parts water.
Referential Example 17
[0244] To a mixture formed by combining 20 parts
methyltrimethoxysilane, 20 parts isopropyl alcohol, and 2 parts
polydiethoxysiloxane (.about.52% solids), there is added a catalyst
containing 0.6 parts boron ethoxide and 0.2 parts aluminum
isopropoxide. After the solids are dissolved, water (6 parts) is
added to complete the catalysis. The resulting mixture is allowed
to stand (react) for about 1 hour.
Referential Example 18
[0245] 20 parts methyltrimethoxysilane, and 20 parts isopropyl
alcohol, are mixed with 0.2 parts of
aminoethylaminopropyltrimethoxysilane (as hydrolysis catalyst).
After thoroughly mixing with 6 parts water, the mixture is allowed
to react (hydrolyze) for 45 minutes. Then, the mixture is combined
with 0.3 parts phenyltrimethoxysilane predispersed in 10 parts
isopropyl alcohol. After about 1 hour, the composition is ready to
be applied.
Referential Example 19
[0246] Twenty (20 ) parts methyltrimethoxysilane, 5 parts
phenyltrimethoxysilane and 20 parts isopropyl alcohol are combined
and thoroughly mixed. To this mixture is first added 0.2 parts of
boric acid followed by addition of 4 parts of polydiethoxysiloxane
(50%). After the boric acid is dissolved, 0.6 parts tetrabutoxy
titanate and then 6.5 parts water are added. By adding the water
slowly, premature hydrolysis of the tetrabutoxy titanate may be
prevented. After about one hour, 1.6 parts of a 0.5%
solution-suspension of calcium hydroxide in isopropyl alcohol is
added and the mixture is allowed to react for at least one hour and
is then ready for application.
Referential Example 20
[0247] To a container containing 10 parts of polydiethoxysiloxane
(.about.50%) is added 20 parts of isopropyl alcohol and 0.2 parts
of aluminum isopropoxide, followed by 5 parts of
phenyltrimethoxysilane. The mixture is stirred until it becomes
clear. At that time, while continuing stirring, 2.3 parts of water
are added, followed by 5 parts of phenyltrimethoxysilane. After
stirring for about 3 hours, the mixture may be applied.
Referential Example 21
[0248] To a container containing 10 parts of polydiethoxysiloxane
(approx. 50%) is added, while stirring, 20 parts of isopropyl
alcohol and 0.1 part of boric acid. Stirring is continued until the
solution becomes clear. Then, 0.2 parts of titanium tetrabutoxy
oxide are added. The mixture is stirred for about 3 hours. Then,
2.3 parts of water are added, while stirring, followed by 5 parts
of phenyltrimethoxysilane. After stirring for an additional about 3
hours, the solution may be applied.
Referential Example 22
[0249] 200 parts methyltrimethoxysilane and 100 parts isopropyl
alcohol are mixed in a first container (Container A). Separately,
in Container B, 40 parts of a saturated solution of calcium
hydroxide is diluted with 20 parts of water before the diluted
solution is added to Container A.
[0250] In Container C, 6.2 parts boric acid is dissolved in 96.8
parts of isopropyl alcohol and is then combined after cooling
begins, with the contents of Container A (to which the contents of
Container B has been added).
[0251] After about three days, the resulting mixture forms a
sprayable or wipable coating composition.
Referential Example 23
[0252] 20 parts each of methyltrimethoxysilane and isopropyl
alcohol are mixed in a first container, Container A. Then, 0.3 part
of boric acid is added, followed by addition of 0.2 to 0.3 part of
tetrabutyl titanate to assist in the solubilization of the boric
acid catalyst. Finally, 10 to 20 parts of water are slowly added
since the reaction is exothermic. After a few minutes, the mixture
will warm up and is ready to be applied.
Referential Example 24
[0253] In a first container, isopropyl alcohol,
methyltrimethoxysilane, phenyltrimethoxysilane and
isobutyltrimethoxysilane are mixed in amounts of 10 parts, 15 parts
by weight, 1 part by weight and 5 parts by weight, respectively. In
a second container, N-(2-aminoethyl)-3-aminopropyltrimet-
hoxysilane, water, acetic acid, ethylene glycol monoethyl ether and
titanium dioxide are mixed in amounts of 0.2 part by weight, 13
parts by weight, 0.4 part by weight, 3 parts by weight and 0.2 part
by weight, respectively. After combining the contents of the two
containers, the resulting mixture is allowed at least four hours to
homogenize. The so-formed liquid mixture is ready to be
applied.
Referential Example 25
[0254] 5 parts by weight of phenyltrimethoxysilane are added to a
container containing 15 parts by weight of methyltrimethoxysilane.
While mixing, 0.3 part by weight of tetrabutoxytitanate are added,
along with 15 parts by weight of ethyl polysilicate, which has been
hydrolyzed to 40% silica, and 15 parts by weight of isopropyl
alcohol. After mixing, 13 parts by weight of an aqueous 6% boric
acid solution are added and, after waiting eight hours, the
resulting mixture is ready to be applied.
Referential Example 26
[0255] 5 parts by weight of phenyltrimethoxysilane and 2 parts by
weight of .gamma.-glycidyloxypropyltrimethoxysilane are added to a
vessel containing 15 parts by weight of methyltrimethoxysilane and
mixed. While mixing, 0.4 part by weight of tetraisopropyoxytitanate
in 20 parts isopropyl alcohol is added. The resulting nonaqueous
composition is ready to be applied.
Referential Example 27
[0256] To a vessel containing 15 parts by weight of
methyltrimethoxysilane and 15 parts isopropyl alcohol, there is
added, while stirring, 5 parts by weight of phenyltrimethoxysilane.
To the resulting mixture, while continuing stirring, 0.2 part by
weight of tetrabutoxytitanate is added, followed by 4 parts by
weight of ethyl polysilicate (hydrolyzed to 40% silica), and 0.2
part by weight of vinyltriacetoxysilane. The resulting composition
is ready to be applied.
Referential Example 28
[0257] This formulation illustrates a coating composition which is
shown formulated as a three container system (i.e., water;
silane/alcohol; catalyst).
[0258] In one container a mixture of 20 parts of
methyltrimethoxysilane and 20 parts isopropyl alcohol is provided.
While the silane-alcohol mixture is being stirred, 20 parts water
is added. After thoroughly mixing, 1 part of an amine stabilized
titanium catalyst (e.g., Tyzor.TM. 131, from E. I. duPont de
Nemours), is further added. The composition is allowed to react for
about 4 hours and is ready for application. In this system, the
alcohol prevents formation of a two-phase mixture.
[0259] In any of the above formulations, the amount of alcohol or
other diluent can be increased at will, e.g., to reduce the solids
loading level, improve sprayability or flowability, or otherwise,
if necessary, further increase phase stability.
EXAMPLE 1
[0260] Both new and existing (corroded) air-conditioning units (The
Trane Company, Jacksonville, Fla.), located in a Jacksonville
Electric Authority sewage treatment plant were treated with a
coating composition according to the above Referential Example 1,
or were left untreated. The coating compositions were applied,
after the units were thoroughly washed, one to three times, with
soapy water, rinsed and dried, using hand held pump sprayers. The
applied coatings, before beginning to gel, may be wiped with a
cloth or sponge to remove excess or pooled coating composition.
[0261] In this location, all metal surfaces and parts of the units
are normally reduced to inoperable condition by gases (e.g., flue
gases) and corrosive chemicals after as little as two months
operation, and in general, after only 4 to 6 months, on average.
Power usage was monitored by either Florida Power and Light or by
Jacksonville Electric Authority.
[0262] Thermal cooling changes were monitored by The Trane Company.
Improvements for highly corroded units were as high as 84%.
Improvements for new units ranged from 1 to 10%. Moreover, the
units treated according to this invention were examined by an
independent laboratory and found to have only superficial corrosion
after more than 22 months. It is also observed that the coated
units stay cleaner longer than the uncoated units and are more
easily cleaned.
[0263] Similar results will be obtained using the coating
compositions of other Referential Examples given above.
EXAMPLE 2
[0264] Air conditioning units in the U.S. Naval Facility at NS
Mayport, Jacksonville, Fla. were tested with the coating
composition as prepared in the above Referential Example 8. In this
case, the entire unit, including the external electrical boxes,
cabinets, screws, valves, cooling fins, wires. etc., was coated
with the invention coating composition. The units are first
thoroughly washed with soapy water, rinsed and dried, before the
coating is applied. The application can be achieved using any type
of manual sprayer, or with a mechanical sprayer. For comparison,
units were either coated with conventional organic coatings, were
overcoated on the organically coated units with a coating
composition according to this invention, were coated directly on
the untreated unit or were not coated. The units coated with the
silane coating compositions of the present invention were
substantially corrosion free after more than one years service. In
contrast, the organically treated unit and the untreated unit
underwent substantial corrosion in as little as two months.
[0265] Similar results may be obtained using coating compositions
of other representative compositions of the above Representative
Examples.
Example 3
[0266] By applying the coating composition of Referential Example
1B to the evaporator of an HVAC unit located on the outside of an
apartment building or office building, the coated evaporator is
able to prevent growth or collection of fungal spores and bacteria,
thereby preventing future transport of the undesirable
microorganisms into the building through the HVAC system. Similar
results can be achieved with other representative coating
compositions described in the above Referential Examples or
elsewhere within the above disclosure.
* * * * *