U.S. patent application number 11/071506 was filed with the patent office on 2005-07-07 for photocatalytically-active, self-cleaning aqueous coating compositions and methods.
Invention is credited to Andrews, John.
Application Number | 20050147759 11/071506 |
Document ID | / |
Family ID | 32654981 |
Filed Date | 2005-07-07 |
United States Patent
Application |
20050147759 |
Kind Code |
A1 |
Andrews, John |
July 7, 2005 |
Photocatalytically-active, self-cleaning aqueous coating
compositions and methods
Abstract
Method for producing novel photochemically-active metal
oxide-containing aqueous compositions such as TiO.sub.2
compositions coated or sprayed and dried under ambient conditions
to form novel photochemically-active, colorless coatings having
strong wetability and adhesion to clear substrates such as window
glass. Preferably the present compositions include a suitable
wetting agent or combination of agents to improve the wetability of
the Titanium peroxide-containing amorphous film, allowing thinner
films to be readily applied. Also the inclusion of an acrylic
aliphatic urethane polymer can replace wholly or partially the
titanium peroxide sol and provide additional film forming and
wetability properties. The acrylic urethane polymer reduces or
eliminates the amount of titanyl peroxide that is required and
thereby reduces or eliminates the yellow color.
Inventors: |
Andrews, John; (Madison,
CT) |
Correspondence
Address: |
PERMAN & GREEN
425 POST ROAD
FAIRFIELD
CT
06824
US
|
Family ID: |
32654981 |
Appl. No.: |
11/071506 |
Filed: |
March 3, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11071506 |
Mar 3, 2005 |
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10334229 |
Dec 31, 2002 |
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6884752 |
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Current U.S.
Class: |
427/372.2 |
Current CPC
Class: |
Y10T 428/252 20150115;
Y10T 428/2991 20150115; B01J 35/0013 20130101; C09D 5/1618
20130101; B82Y 30/00 20130101; C08G 18/0823 20130101; C09D 7/61
20180101; Y10T 428/12611 20150115; C08G 18/8048 20130101; C09D
175/04 20130101; B01J 35/004 20130101; C09D 5/00 20130101; Y10T
428/12535 20150115; Y10T 428/12806 20150115; Y10T 428/31504
20150401; C09D 7/67 20180101; B01J 21/063 20130101 |
Class at
Publication: |
427/372.2 |
International
Class: |
B05D 003/02 |
Claims
1-14. (canceled)
15. A process for producing a thin, colorless, water-insoluble
coating on a substrate comprising (a) producing an aqueous
composition containing a metal peroxide; (b) adding a water-soluble
polymeric agent to the solution of step a), where the quantity of
the water-soluble polymeric agent comprises from about 9 to about
55 percent by weight based on the total dry weight of the metal
peroxide and water-soluble polymeric agent; c) coating the
substrate with the solution of step b) at a temperature below
100.degree. C.; and d) drying the coated substrate at a temperature
below 100.degree. C.
16. The process of claim 15 where the metal peroxide is a titanium
peroxide sol.
17. The process of claim 15 where the water-soluble polymeric agent
comprises a polyethylene oxide silane wetting agent.
18. The process of claim 15 where the water-soluble polymeric agent
comprises an acrylic aliphatic urethane polymer.
19. The process of claim 15 where the process further comprises
adding a bis cyclohexyl methane diamine chain extension agent to
the composition of step b) when the water-soluble polymeric agent
is a polyurethane/polyurea.
20. The process of claim 15 where the water soluble polymeric agent
comprises the reaction product of a water-soluble aliphatic
diisocyanate and a tertiary amine.
21. The process of claim 20 where the aliphatic diisocyanate
comprises the reaction product of dimethyl propionic acid and
isophorone diisocyanate.
22. The process of claim 15 where the substrate is coated under
ambient conditions.
23. The process of claim 15 where the coated substrate is dried
under ambient conditions.
24. A process for producing a self-cleaning,
photocatalytically-active, thin, colorless, water-insoluble coating
on a substrate comprising (a) producing an aqueous composition
containing a metal peroxide and photochemically-active metal oxide
particles having a size within the range of about 6 to 10
nanometers, some of which are dissolved in the composition; (b)
adding a water-soluble polymeric agent to the composition of step
a), where the quantity of the water-soluble polymeric agent
comprises from about 5 to about 50 percent by weight based on the
total dry weight of the components of the composition; c) coating
the substrate with the solution of step b) at a temperature below
100.degree. C.; and d) drying the coated substrate at a temperature
below 100.degree. C.
25. The process of claim 24 where the metal peroxide is titanyl
peroxide.
26. The process of claim 24 where the water-soluble polymeric agent
comprises a polyethylene oxide silane wetting agent.
27. The process of claim 24 where the water-soluble polymeric agent
comprises an acrylic aliphatic urethane polymer.
28. The process of claim 24 where the process further comprises
adding a bis cyclohexyl methane diamine chain extension agent to
the composition of step b) when the water-soluble polymeric agent
is a polyurethane/polyurea.
29. The process of claim 24 where the water soluble polymeric agent
comprises the reaction product of a water-soluble aliphatic
diisocyanate and a tertiary amine.
30. The process of claim 24 where the aliphatic diisocyanate
comprises an adduct, the reaction product of dimethyl propionic
acid and isophorone diisocyanate.
31. The process of claim 24 where the substrate is coated under
ambient conditions.
32. The process of claim 24 where the coated substrate is dried
under ambient conditions.
33. The process of claim 24 where the metal oxide particles are
selected from TiO.sub.2, ZnO, SrTiO.sub.3, CdO, In.sub.20.sub.3,
BaTiO.sub.3, K.sub.2NbO.sub.3, Fe.sub.20.sub.3, Ta.sub.20.sub.5,
WO.sub.3, SaO.sub.2, Bi.sub.2O.sub.3, NiO, Cu.sub.2O, SiO.sub.2,
RuO.sub.2, CeO.sub.2.
34. The process of claim 24 where the metal oxide particles are
selected from TiO.sub.2 and ZrO.sub.2.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] The present invention relates to photocatalytically active
(PCA) coating compositions containing a photocatalytically active
oxide of a transition metal (MO) or (MO.sub.2) such as titanium
dioxide (TiO.sub.2) or zirconium oxide (Zr0.sub.2) catalyst for
producing clear self-cleaning coatings, such as for glass windows,
which react with and decompose organic compounds or pollutants,
deposited thereon from the environment, under the effects of
exposure to sunlight, particularly the ultraviolet radiation
contained therein. The organic pollutants are decomposed to simple
inorganic compounds such as CO.sub.2, H.sub.20 and various mineral
acids, which re-enter the atmosphere and/or wash away under the
effects of heat, wind and/or rain, so that the coatings are
self-cleaning with an efficiency which is dependent upon the degree
of photocatalytic activity of the MO.sub.2 catalyst, which is
directly proportional to the total surface area of the MO.sub.2
particles to which the pollutants are exposed.
[0003] 2. State of the Art
[0004] It is well known that when a metal oxide, such as anatase
Ti0.sub.2 powder, is illuminated by ultraviolet light with a
wavelength below about 390 nm, electrons in the valence band are
excited to the conduction band leaving behind positive-charged
holes which are reactive with absorbed water vapor hydroxide ions,
resulting in the formation of positive-charged hydroxyl radicals,
(OH).sup.+. The hydroxyl radicals are strong oxidizing radicals
which can react with and strip electrons from the organic
pollutants to produce simpler, non-offensive products such as
CO.sub.2 and H.sub.2O, or HCL if halogen pollutants are
involved.
[0005] One commercially-available TiO.sub.2 powder photocatalyst is
Degussa P25, a 70:30% anatase/rutile mixture with a BET surface
area of 55.+-.15 m.sup.2g.sup.-1 and crystalline sizes of 0.1 nm in
30 nm aggregates. It forms an aqueous suspension in dilute alcohol
which forms a chalky catalytic coating on glass. Reference is made
to the article titled "Photocatalytic Degradation Of A Gaseous
Organic Pollutant" by Yu et al., published in. the Journal of
Chemical Education, Vol. 25, No. 6, June 1998.
[0006] It is desirable to produce a TiO.sub.2 composition which can
be applied to surfaces such as window glass and dried under ambient
conditions to form clear, self-cleaning photocatalytic coatings.
Reference is made to articles by H. Ichinose et al. in the Journal
Of The Ceramic Society Of Japan, titled "Synthesis Of
Peroxo-Modified Anatase Sol From Peroxo-Titanic Acid Solution",
Vol. 104, pages 914-917 (1996), and "Photocatalytic Activities Of
Coating Films Prepared From Peroxotitanic Acid Solution-Derived
Anatase Sols", Vol. 104, No. 8, pages 715-718 (1996). These
articles describe a process to put small amounts (0.85% to 1.7%) of
various forms or shapes (polymorphs) of titanium dioxide
(Ti0.sub.2) into aqueous solution by reaction with hydrogen
peroxide. These solutions are called titanium
peroxidases-Ti0(00H)2. The amorphous titanium dioxide is the
ingredient that results in the film-forming and adhesive
characteristics of the product. The mixture is composed of equal
weights of the amorphous and anatase (crystalline) forms of
titanium dioxide, is soluble in water in up to about 2% by weight
of the composition and can be applied at ambient conditions.
[0007] U.S. Pat. Nos. 6,107,241 (Ogata et al.) and 6,429,169 (H.
Ichinose) disclose an anatase titanium oxide sol having a pH of 7.5
to 9.5 and a particle size of 8-20 nm which is a yellow suspension
made by adding aqueous ammonia or sodium hydroxide to a titanium
salt solution, such as titanium tetrachloride, washing and
separating the formed titanium hydroxide, treating the formed
titanium hydroxide with aqueous hydrogen peroxide solution, and
heating the formed stable amorphous titanium peroxide sol having a
concentration of about 2.9%, a pH of 6.0 to 7.0 and a particle size
of 8 to 20 nm and a yellow transparent color to a temperature of
100.degree. C. or higher to form an anatase titanium oxide sol. The
anatase titanium oxide sol can thereafter be heated to 250.degree.
C. or higher to convert it to anatase titanium dioxide.
[0008] The amorphous titanium peroxide sol has good bonding
strength but poor wetability for substrates and is not
photocatalytic and is yellowish in color. The anatase titanium
formed by heating the amorphous titanium peroxide sol to elevated
temperatures is photocatalytic. Therefore mixtures of the amorphous
titanium peroxide sol and the anatase titanium oxide sol are made
to provide a mixed sol coating composition to which may be added
more photocatalyst, such as titanium dioxide in sub-10 nanometer
particle size powder form, and other inert additives such as
inorganic and organic binder materials, which are clear and
compatible with the peroxotitanic sol so as not to alter the pH or
the clarity of the solution. Even small amounts of Ti0.sub.2 or
other ingredients having particle sizes about about 10 nanometers
will render the composition opaque and unsatisfactory for use as
self-cleaning coatings on glass or other transparent substrates.
The coating must be applied in the form of several layers or dips
to provide adequate bonding but the end result is that the
yellowish color of each layer is intensified to produce an
unsatisfactory appearance on window glass. Multiple layers are
necessary because the peroxide-forming film is very hydrophobic so
that the coating composition does not have good wetting properties
for glass and tends to bead on glass, leaving "holidays" or
uncoated areas and requiring multiple overlayers.
[0009] A process of producing both an amorphous titanium peroxide
solution in water and also anatase particles in the range of 6 to
10 nanometers is described in U.S. Pat. Nos. 6,107,241 and
6,429,169. The amorphous titanyl peroxide forms an insoluble film
when the peroxide breaks down or reacts with water. This serves as
a carrier for the anatase particles.
[0010] The application of the film independently, or with the
particles embedded, when applied to glass, plastic or metal has the
following problems.
[0011] 1. The film former is very hydrophobic and does not wet out
to form a continuous film. A heavy amount or thick layer of the
composition is required to form a continuous film or covering . The
surface tension or the peroxide-containing film is to some degree
overcome by the added thickness and weight of the film. The time
and labor for such application makes the use of the product
impractical.
[0012] 2. The film is formed with difficulty, and is yellowish in
color due to the presence of the titanyl peroxide remaining and
unreacted. This is aggravated if the weight and thickness of film
is increased to overcome the surface tension of the titanyl
peroxide solution to form a continuous coating on the
substrate.
[0013] 3. Transparency and clarity of the coating(s) when applied
over glass is impaired due to the thickness required to overcome
the non wettability of the substrate. The refractive index of the
film so produced and the excessive thickness causes moire patterns
and a seemingly rainbow effect when viewed through clear glass.
[0014] The photo-chemically active component is the anatase
polymorph. The peroxytitanic acid polymorph has no photochemical
activity. The photo-chemically active polymorph is derived by
heating the amorphous titanyl peroxide sol at 100 degrees
centigrade temperature for six hours.
[0015] The peroxytitanic acid polymorph has a yellow coloration
that remains in the product even when it is mixed with the titanium
peroxidase. This yellow coloration is objectionable on clear window
glass. However, the solubility of the TiO.sub.2 is related to the
addition of the peroxide; without the peroxide, the TiO.sub.2 does
not go into solution. Consequently, it is highly desirable, and
necessary for many uses, to remove entirely, or to reduce as much
as possible, the yellow coloration, to provide clear, self-cleaning
window coatings.
SUMMARY OF THE INVENTION
[0016] The present invention relates to a novel method for
producing novel photochemically-active metal oxide containing
(MO.sub.2) aqueous compositions which can be coated or sprayed and
dried under ambient conditions to form novel
photochemically-active, colorless coatings having strong wetability
and adhesion to clear substrates such as window glass.
[0017] The metal oxide photocatalysts usable in the present
invention include TiO sub.2, ZnO, SrTiO sub.3, CdS, CdO, CaP, InP,
In sub.2 O sub.3, CaAs, BaTiO sub.3, K sub.2 NbO sub.3, Fe sub.2 O
sub.3, Ta sub.2 O sub.5, WO sub.3, SaO sub.2, Bi sub.2 O sub.3,
NiO, Cu. Sub.2 O, SiC, SiO sub.2, MoS sub.2, MoS sub.3, InPb, RuO
sub.2, CeO sub.2 and the like. Of these, titanium oxide is
preferred. Titanium oxide may be used in the form of particles or
powder, or in the form of a sol.
[0018] The use of a suitable wetting agent or combination of agents
alleviate the non wettability or hydrophobic nature of the Titanium
peroxide-containing amorphous film, allowing thinner films to be
readily applied. This reduces the moire patterns and the yellowing,
as the thinner film has much less yellow nature, and also allows a
faster cure and elimination of the yellow-causing peroxide over
time. A suitable wetting agent is a polyethylene oxide silane in
amounts of 0.01 to 1 percent of the dry weight of the film former
(titanium peroxide sol). This material is commercially available as
Dow Chemicals Silicone Q25211 super wetting agent (a polyethylene
oxide silane).
[0019] The application of an acrylic urethane polymer solution as a
primary coating over glass acts as a barrier to sodium and
potassium ions migrating from the substrate up into the titanium
layer and blocking photocatalysis.
[0020] An acrylic aliphatic urethane polymer can replace wholly or
partially the titanium peroxide sol and provides additional film
forming and wettability properties. The acrylic urethane polymer
reduces or eliminates the amount of titanyl peroxide that is
required and thereby reduces or eliminates the yellow color. The
acrylic urethanes are the film forming counterparts of the titanyl
peroxides that form insoluable films. Also due to the high
oxidation resistance of the polymer, it resists self deterioration
and is compatible with the titanium amorphous film former. Also, it
reduces the moir patterns by both reducing the refractive index of
the coating as well as allowing a thin film to be applied. The
chemical nature of the polymer is as follows:
[0021] An acrylic diol is capped with ethylene oxide. The molecular
weight or hydroxyl number of the formed diol is between 110 and 150
mg KOH per gram solid diol polymer. At this point aliphatic
diisocyanate is added in stoichiometric ratios of between 2 to 3 to
one. The diisocyanate can be isophorone diisocyanate (IPDI Huls
Chemical), or methylene bis cyclohexyl diisocyanate (Mondur W.
Bayer Chemical). Other cyclo aliphatic diisocyantes can also be
used. As the ratio of the diisocyanate increases, the polymer
becomes harder and more chemically resistant. That fact and the use
of the acrylic backbone insure a high degree of oxidation
resistance and chemical resistance. Marine paints for instance are
based on urethane acrylics.
[0022] The use of small amounts of dimethylol propionic acid and
subsequent salt formation allow the urethane acrylic to go into
water solution. Chain extension agents typically include ethylene
glycol. The use of methylene, bis cyclohexyl diamine forms
particularly hard and oxidation resistant films for this purpose
when used as a carrier for the anatase particles.
[0023] The use of a peroxide mechanism of controlled degradation is
not explicitly mentioned in prior art. Once the peroxide is formed
of the MO.sub.2 (Ti0.sub.2) metal oxide and the mineral is put in a
sol state and if soluble in water the following process is
available for nano production.
[0024] By heating at 100 degrees Celsius the peroxide begins to
break down. The MO.sub.2 units thus are allowed to combine in their
natural crystalline states. As in the case of titanium dioxide,
anatase particles are formed in the range of 6 to 10 nanometers. To
achieve such a small range by grinding is not believed to be
possible at this time. At below 40 nanometers the Ti0.sub.2 will
reanneal or recombine due to the heat generated and the pressure of
grinding. Also the distribution of particles, quantity versus
numbers of particles present, contains 1 to 1/2% of very large
agglomerations of particles. This prevents transparency in the case
of TiO.sub.2.
[0025] The following examples are illustrative of the preparation
of compositions suitable for the application of colorless
self-cleaning coatings to glass, metal and other substrates.
EXAMPLE 1
[0026]
1 Material Dry weight Wet weight Titanyl peroxide sol 1.00 100 Nano
anatase particles 1.00 100 Polyethylene oxide silane 0.10 10.0
EXAMPLE 2
[0027]
2 Titanyl peroxide sol 1.00 100 Nano anatase particles 1.0 100
Urethane acrylic copolymer 1.0 2.857 Polyethylene oxide silane .20
2.0
EXAMPLE 3
[0028]
3 Nano anatase particles 1.00 100 Diisocyanate 1.00 2.00 (DMPA and
IPDI adduct) Polyethylene oxide silane 0.10 10.0 Tertiary amine
catalyst .10 .10 (polycat 41 air products)
EXAMPLE 4
[0029]
4 Nano anatase particles 2.00 200 DMPA IPDI adduct 1.0 2.0
Polyethylene oxide silane 0.10 10.0 Urethane acrylic polymer 1.0
2.857 Polycat 41 .10 .10
EXAMPLE 5
[0030]
5 Nano anatase particles 2.0 200 DMPA IPDI adduct 1.0 2.0
Polyethylene oxide silane .10 10.0 Polycat 41 (tertiary amine) .10
.10
EXAMPLE 6
[0031]
6 Nano anatase particles 1.0 100 Titanyl peroxide sol 0.5 50
Polyethylene oxide silane 0.10 10 Urethane acrylic polymer 0.5
1.4285
EXAMPLE 7
[0032]
7 Nano anatase particles 1.0 100 Titanyl peroxide sol .5 50
Polyethylene oxide silane .10 10 DMPA IPDI adduct .5 1.0 Polycat 41
.10 .10
[0033] The DMPI adduct is the reaction product of one mol of
dimethyl propionic acid and two mols of isophorone diisocyanate. It
is a water-soluble, stable cross-linking agent. The adduct is
aliphatic and will not yellow. It is water soluble. The isocyanate
is stable for a usable period of time in the water so that it can
react in several ways. One would be the eventual reaction with
water of the isocyanate to form an amine which would immediately
react with isocyanate to form a film.
[0034] Polycat 41 is a tertiary amine catalyst which trimerizes the
isocyanate to form a hard film which is compatible with the anatase
sol particles to form an active photocatalytic film. Trimerization
produces optically clear films which have a greater optical
transmission of visible light than polyurethane polymers by
themselves.
[0035] The present invention relates preferably to the use of all
photochemically-active transition elements designated by MO.sub.2,
M being the transitional metal, and 0.sub.2 is the oxide thereof,
most preferably T.sub.10.sub.2 and 2r0.sub.2.
[0036] It should be understood that the foregoing description is
only illustrative of the invention. Various alternatives and
modifications can be devised by those skilled in the art without
departing from the invention. Accordingly, the present invention is
intended to embrace all such alternatives, modifications and
variances which fall within the scope of the appended claims.
* * * * *