U.S. patent application number 10/516197 was filed with the patent office on 2006-04-13 for ceramic molded body comprising a photocatalytic coating and method for production the same.
This patent application is currently assigned to Erlus Aktiengesellschaft. Invention is credited to Friederike Bauer, Eduard Gast, Axel Thierauf.
Application Number | 20060078712 10/516197 |
Document ID | / |
Family ID | 29432479 |
Filed Date | 2006-04-13 |
United States Patent
Application |
20060078712 |
Kind Code |
A1 |
Thierauf; Axel ; et
al. |
April 13, 2006 |
Ceramic molded body comprising a photocatalytic coating and method
for production the same
Abstract
The invention relates to a ceramic moulded body consisting of an
oxide ceramic base material and comprising a surface which
self-cleans by means of water-sprinkling or percolation. Said
moulded body has a porous, oxide ceramic coating which is
photocatalytically active and has a specific surface of between
approximately 25 m.sup.2/g and approximately 200 m.sup.2/g,
preferably between approximately 40 m.sup.2/g and approximately 150
m.sup.2/g. The invention also relates to a method for producing one
such ceramic moulded body.
Inventors: |
Thierauf; Axel;
(Mallersdorf-Pfaffenberg, DE) ; Gast; Eduard;
(Kraiburg, DE) ; Bauer; Friederike;
(Bernhardswald, DE) |
Correspondence
Address: |
SYNNESTVEDT LECHNER & WOODBRIDGE LLP
P O BOX 592
PRINCETON
NJ
08542-0592
US
|
Assignee: |
Erlus Aktiengesellschaft
106 Haupstr.
Neufahrn
DE
84088
|
Family ID: |
29432479 |
Appl. No.: |
10/516197 |
Filed: |
May 28, 2003 |
PCT Filed: |
May 28, 2003 |
PCT NO: |
PCT/DE03/01743 |
371 Date: |
September 12, 2005 |
Current U.S.
Class: |
428/143 |
Current CPC
Class: |
Y10T 428/24372 20150115;
B01J 35/1014 20130101; C04B 2103/65 20130101; C04B 33/00 20130101;
C04B 41/4539 20130101; Y10T 428/249967 20150401; C04B 41/87
20130101; C04B 41/009 20130101; C04B 41/4539 20130101; B01J 35/004
20130101; B01J 35/10 20130101; C04B 41/52 20130101; C04B 41/89
20130101; C04B 2111/00586 20130101; C04B 2111/2061 20130101; C04B
41/009 20130101; C04B 41/52 20130101; C04B 41/52 20130101; B01J
35/1019 20130101; C04B 41/5041 20130101; Y10T 428/249969 20150401;
C04B 41/5041 20130101; C04B 41/5027 20130101; C04B 41/5041
20130101 |
Class at
Publication: |
428/143 |
International
Class: |
E01F 9/04 20060101
E01F009/04 |
Foreign Application Data
Date |
Code |
Application Number |
May 29, 2002 |
DE |
102 24 110.4 |
Claims
1. A ceramic molded body, more specifically a roof tile, tile,
clinker brick or facade wall, of oxide-ceramic base material with a
surface which is self-cleaning upon spraying or sprinkling with
water, characterized in that the molded body has a porous
oxide-ceramic coating, wherein the coating is photocatalytically
active and contains TiO.sub.2 and has a specific surface area in a
range of between 25 mg.sup.2/g, and 200 m.sup.2/g, preferably
between 40 m.sup.2/g and 150 m.sup.2/g, wherein the TiO.sub.2 is
produced by flame hydrolysis of TiCl.sub.4 as highly disperse
TiO.sub.2.
2. A ceramic molded body as set forth in claim 1 characterized in
that the coating has a specific surface area in a range of between
40 m.sup.2/g and 100 m.sup.2/g.
3. A ceramic molded body as set forth in claim 1, characterized in
that the mean layer thickness of the coating is in a range of
between 50 nm and about 50 .mu.m, preferably 100 nm and 10
.mu.m.
4. A ceramic molded body as set forth in claim 1, characterized in
that arranged between the oxide-ceramic base material and the
photocatalytically active, porous, oxide-ceramic coating is at
least one layer with raised portions, the oxide-ceramic base
material has raised portions and/or the photocatalytically active,
porous, oxide-ceramic coating is in the form of a layer with raised
portions.
5. A ceramic molded body as set forth in claim 4 characterized in
that the raised portions are formed by particulate material fixed
to the oxide-ceramic base material.
6. A ceramic molded body as set forth in claim 5 characterized in
that the particulate material is temperature-resistant ground
material preferably selected from the group which consists of
ground rock, fire clay, clay, minerals, ceramic powder such as SiC,
glass, glass chamotte and mixtures thereof.
7. A ceramic molded body as set forth in claim 5 or claim 6
characterized in that the size of the particles and/or the raised
portions is or are in a range of up to 1500 nm, preferably of
between 50 nm and 700 nm, further preferably between 50 nm and 200
nm.
8. A ceramic molded body as set forth in claim 1, characterized in
that the photocatalytically active, porous, oxide-ceramic coating
includes additionally photocatalytically active, oxide-ceramic
materials selected from the group which consists of
Al.sub.2O.sub.3, SiO.sub.2 and mixtures thereof.
9. A ceramic molded body as set forth in claim 1, characterized in
that the oxide-ceramic base material of the molded body includes
photocatalytically active, oxide-ceramic materials selected from
the group which consists of TiO.sub.2, Al.sub.2O.sub.3, SiO.sub.2
and mixtures thereof.
10. A ceramic molded body as set forth in claim 1, characterized in
that the photocatalytically active, oxide-ceramic material has an
average particle size in the range of between 5 nm and 100 nm,
preferably between 10 nm and 50 nm.
11. A ceramic molded body as set forth in claim 1, characterized in
that the TiO.sub.2 contained in the photocatalytically active,
porous, oxide-ceramic coating and/or in the oxide-ceramic base
material is present at least in part and preferably in respect of
at least 40% by weight with respect to the total amount of
TiO.sub.2, in the anatase structure.
12. A ceramic molded body as set forth in claim 1, characterized in
that the TiO.sub.2 contained in the photocatalytically active,
porous, oxide-ceramic coating and/or in the oxide-ceramic base
material is present in respect of at least 70% by weight with
respect to the total amount of TiO.sub.2, in the anatase
structure.
13. A ceramic molded body as set forth in claim 1, characterized in
that the TiO.sub.2 is present in a mixture comprising 70% by weight
of anatase and 30% by weight of rutile.
14. A ceramic molded body as set forth in claim 1, characterized in
that the coating has a superhydrophobic surface, wherein the
superhydrophobic surface has a contact or edge angle of at least
140.degree. for water.
15. A ceramic molded body as set forth in claim 14 characterized in
that the superhydrophobic surface of the coating is produced using
Ormoceres, polysiloxane, alkylsilane and/or fluorosilane,
preferably in combination with SiO.sub.2.
16. A ceramic molded body as set forth in one of claims 14 and 15
characterized in that the superhydrophobic surface of the coating
has raised portions.
17. A ceramic molded body as set forth in claim 16 characterized in
that the raised portions of the superhydrophobic surface are
produced using particulate material.
18. A process for the production of a ceramic molded body, more
specifically a roof tile, tile, clinker brick or facade wall, of
oxide-ceramic base material with a surface which is self-cleaning
upon spraying or sprinkling with water, wherein the molded body has
a photocatalytically active, porous, oxide-ceramic
TiO.sub.2-containing coating with a specific surface area in a
range of between 25 m.sup.2/g and 200 m.sup.2/g, preferably 40
m.sup.2/g and 150 m.sup.2/g, wherein the process includes the
following steps: (a) mixing photocatalytically active,
oxide-ceramic powder which contains TiO.sub.2, wherein the
TiO.sub.2 is produced by flame hydrolysis of TiCl.sub.4 as highly
disperse TiO.sub.2, adjusting agent and/or adhesive and a liquid
phase to afford a suspension, (b) applying the suspension produced
in step (a) to the oxide-ceramic base material to produce a layer,
and (c) hardening the layer afforded in step (b) to produce a
photocatalytically active, porous, oxide-ceramic coating.
19. A process as set forth in claim 18 characterized in that at
least one layer with raised portions is applied to the
oxide-ceramic base material in a preceding step and the suspension
produced in step (a) is applied to the oxide-ceramic base material
provided with a layer with raised portions and subsequently
hardened in step (c).
20. A process as set forth in claim 19 characterized in that
particulate material is additionally added in step (a).
21. A process as set forth in claim 18 or claim 19 characterized in
that the raised portions are formed by fixing particulate material
on the oxide-ceramic base material.
22. A process as set forth in claim 20 characterized in that the
particulate material is temperature-resistant ground material
preferably selected from the group which consists of ground rock,
fire clay, clay, minerals, ceramic powder such as SiC, glass, glass
chamotte and mixtures thereof.
23. A process as set forth in claim 20, characterized in that the
mean particle size of the particulate material is in a range of up
to 1500 nm, preferably between 50 nm and 700 nm, further preferably
between 50 nm and 200 nm.
24. A process as set forth in claim 18, characterized in that
adjusting agent used in step (a) is an organic viscosity
regulator.
25. A process as set forth in claim 24 characterized in that
carboxymethylcellulose is used as the organic viscosity
regulator.
26. A process as set forth in claim 18, characterized in that
adhesive used in step (a) is polysiloxane.
27. A process as set forth in claim 18, characterized in that water
is used as the liquid phase in step (a).
28. A process as set forth in claim 18, characterized in that the
adhesion between the catalytically active coating and the
oxide-ceramic base material is improved by a procedure whereby the
photocatalytically active, porous, oxide-ceramic coating produced
in step (c) is irradiated with laser light or NIR or UV light.
29. A process as set forth in claim 18, characterized in that the
photocatalytically active, oxide-ceramic powder used in step (a)
additionally includes materials selected from the group which
consists of Al.sub.2O.sub.3, SiO.sub.2 and mixtures thereof.
30. A process as set forth in claim 18, characterized in that
contained in the oxide-ceramic base material of the molded body are
photocatalytically active, oxide-ceramic materials selected from
the group which consists of TiO.sub.2, Al.sub.2O.sub.3, SiO.sub.2
and mixtures thereof.
31. A process as set forth in claim 18, characterized in that the
photocatalytically active, oxide-ceramic powder used in step (a)
includes particles in the range of between 5 nm and 100 nm,
preferably between 10 nm and 50 nm.
32. A process as set forth in claim 18, characterized in that the
TiO.sub.2 contained in the photocatalytically active, oxide-ceramic
powder and/or in the oxide-ceramic base material is present at
least in part and preferably in respect of at least 40% by weight
with respect to the total amount of TiO.sub.2 in the anatase
structure.
33. A process as set forth in claim 18, characterized in that the
TiO.sub.2 contained in the photocatalytically active, oxide-ceramic
powder and/or in the oxide-ceramic base material is present in
respect of at least 70% by weight with respect to the total amount
of TiO.sub.2 in the anatase structure.
34. A process as set forth in claim 18, characterized in that the
TiO.sub.2 contained in the photocatalytically active, oxide-ceramic
powder and/or in the oxide-ceramic base material is present in a
mixture comprising 70% by weight of anatase and 30% by weight of
rutile.
35. A process as set forth in claim 18, characterized in that the
layer produced in step (b) is hardened in step (c) by drying at a
temperature of up to 300.degree. C. and/or by calcining at a
temperature of more than 300.degree. C. to 1100.degree. C.
36. A process as set forth in claim 35 characterized in that the
layer produced in step (b) is at least partially pre-dried prior to
the calcining operation in step (c) by evaporation of the liquid
phase.
37. A process as set forth in claim 18, characterized in that the
coating hardened in step (c) is hydrophobised to provide a
superhydrophobic surface, wherein the superhydrophobic surface has
a contact or edge angle of at least 140.degree. for water.
38. A process as set forth in claim 18, characterized in that a
hydrophobising agent is additionally added in step (a) and the
coating produced in step (b) is hardened in step (c) by drying at a
temperature of up to 300.degree. C.
39. A process as set forth in claim 37 or claim 38 characterized in
that an inorganic-organic hybrid molecule, preferably a
polysiloxane solution is used for hydrophobisation.
40. A process as set forth in claim 37 or claim 38 characterized in
that Ormoceres, alkylsilane and/or fluorosilane, preferably in a
mixture with SiO.sub.2, is used for the hydrophobisation
operation.
41. A process as set forth in claim 37 or 38, characterized in that
particulate material is added to produce a superhydrophobic surface
with raised portions in the hydrophobisation operation.
42. Use of highly disperse TiO.sub.2 produced by flame hydrolysis
of TiO.sub.4 in an oxide-ceramic coating for roof tile, tile,
clinker brick or a facade wall.
Description
[0001] The invention concerns a ceramic molded body of
oxide-ceramic base material with a surface which is self-cleaning
upon spraying or sprinkling with water and a process for the
production thereof.
[0002] EP 0 590 477 B1 discloses a building material which can be
for example an outside wall material or roof material, wherein a
thin metal oxide film with a photocatalytic action is applied on
the surface of the building material. The metal oxide film is
preferably applied by means of sol-gel processes. A titanium
dioxide thin film building material is preferably produced using
titanium dioxide sol. The thin metal oxide film known from EP 0 590
477 B1 has deodorosing anti-mold properties.
[0003] By virtue of its film-like structure the metal oxide film
known from EP 0 590 477 B1 is of a small surface area and
accordingly has a low level of catalytic activity.
[0004] DE 199 11 738 A1 discloses a titanium dioxide photocatalyst
which is doped with Fe.sup.3+ ions and which has a content of
pentavalent ions, which is equimolar or approximately equimolar in
relation to the Fe.sup.3+ ions. The titanium dioxide photocatalyst
known from DE 199 11 738 A1 and doped with Fe.sup.3+ ions is
produced by way of sol-gel processes.
[0005] EP 0 909 747 A1 discloses a process for producing a
self-cleaning property of surfaces, in particular the surface of
roof tiles, upon being sprayed or sprinkled with water. The surface
has hydrophobic raised portions of a height of between 5 and 200
.mu.m in distributed form. To produce those raised portions, a
surface is wetted with a dispersion of powder particles of inert
material in a siloxane solution and the siloxane is then hardened.
The process known from EP 0 909 747 A1 makes it possible to produce
a ceramic body having a surface to which particles of dirt can
cling poorly. The ceramic body known from EP 0 909 747 A1 does not
have any catalytic activity whatsoever.
[0006] WO 01/79141 A1 discloses a further process for producing a
self-cleaning property of a surface and an article produced with
that process. In accordance with that process, a metallorganic
compound of titanium oxide is applied to a surface by means of a
sol-gel process, the surface is dried and then subjected to heat
treatment at elevated temperature. The surface of the titanium
oxide layer can be subsequently hydrophobised.
[0007] The object of the present invention is to provide a molded
body, in particular roof materials, which has an improved
self-cleaning capability and improved stability such as for example
improved resistance to abrasion.
[0008] A further object of the invention is to provide a process
for the production of such an improved ceramic molded body.
[0009] The object of the invention is attained by a ceramic molded
body of oxide-ceramic base material with a surface which is
self-cleaning upon spraying or sprinkling with water, wherein the
molded body has a porous oxide-ceramic coating, wherein the coating
is photocatalytically active and has a specific surface area in a
range of between about 25 mg.sup.2/g and about 200 m.sup.2/g,
preferably between about 40 m.sup.2/g and about 150 m.sup.2/g.
[0010] Preferred developments of the ceramic molded body are set
forth in appendant claims 2 through 18.
[0011] The object of the invention is further attained by a process
for the production of a ceramic molded body of oxide-ceramic base
material with a surface which is self-cleaning upon spraying or
sprinkling with water, wherein the molded body has a
photocatalytically active, porous, oxide-ceramic coating with a
specific surface area in a range of between about 25 m.sup.2/g and
about 200 m.sup.2/g, preferably about 40 m.sup.2/g and about 150
m.sup.2/g, wherein the process includes the following steps:
[0012] (a) mixing photocatalytically active, oxide-ceramic powder,
adjusting agent and/or adhesive and a liquid phase to afford a
suspension,
[0013] (b) applying the suspension produced in step a) to the
oxide-ceramic base material to produce a layer, and
[0014] (c) hardening the layer afforded in step (b) to produce a
photocatalytically active, porous, oxide-ceramic coating.
[0015] Preferred developments of that process are recited in
appendant claims 20 through 43.
[0016] The ceramic molded body produced using the process according
to the invention involves a highly suitable porosity and
stability.
[0017] Unlike the sol-gel processes preferably used in the state of
the art for the production of coatings, in accordance with the
invention a suspension of photocatalytically active, oxide-ceramic
powder with further components is applied to an oxide-ceramic base
material. This therefore does not involve producing a film but a
porous structure of large specific surface area.
[0018] The structure produced is a highly porous structure, that is
to say the specific surface area of the catalytically active,
porous, oxide-ceramic coating is in a range of between 25 m.sup.2/g
and 200 m.sup.2/g, further preferably in a range of between about
40 m.sup.2/g and about 150 m.sup.2/g. More preferably the specific
surface area is in a range of between 40 m.sup.2/g and about 100
m.sup.2/g.
[0019] With a specific surface area of about 50 m.sup.2/g a highly
satisfactory catalytic activity in respect of the applied
oxide-ceramic coating is achieved. In that respect the mean layer
thickness of the oxide-ceramic coating is preferably in a range of
between about 50 nm and about 50 .mu.m, further preferably between
about 100 nm and about 10 .mu.m. A highly satisfactory catalytic
activity is obtained with a layer thickness of about 1 .mu.m.
[0020] The photocatalytically active, porous, oxide-ceramic coating
according to the invention provides that mold, fungal and plant
growth, for example moss, algae etc, bacterial contamination etc,
which are deposited on or in the ceramic molded body are
photochemically broken down and removed. The photocatalytic
activity of the porous, oxide-ceramic coating is extremely
advantageously adequate at ambient temperature to oxidise and thus
break down the stated substances and contamination. The oxidised
substances have a reduced adhesion capability and are easily
flushed off the surface of the molded body according to the
invention when subjected to the action of spraying or sprinkling
with water.
[0021] It is assumed that the photocatalytically active coating can
have an oxidative action on the one hand directly on the organic
contamination and impurities. On the other hand it is assumed that
the oxidative effect of the photocatalytically active coating is
effected indirectly by the production of oxygen radicals which
subsequently oxidise and accordingly break down the contaminating
substances or impurities.
[0022] The self-cleaning action of the ceramic molded body
according to the invention can be further enhanced if a surface
structure with raised portions or depressions is arranged under the
photocatalytically active, porous, oxide-ceramic coating and/or if
the photocatalytically active, porous, oxide-ceramic coating itself
has a surface structure with raised portions and recesses.
[0023] It has been found that ceramic surface structures with
raised portions, preferably involving a predetermined distribution
density, have a surprising self-cleaning property. The raised
portions can also be hydrophobised so that the adhesion of
hydrophilic soiling substances or contaminants is further greatly
reduced.
[0024] The raised portions can be formed by the application of
particulate material to the ceramic base material. In that respect
preferably temperature-resistant crushed material is used as the
particulate material, preferably selected from the group which
consists of crushed stone, fire clay, clay, minerals, ceramic
powder such as SiC, glass, glass chamotte, and mixtures
thereof.
[0025] It will be appreciated that TiO.sub.2, Al.sub.2O.sub.3,
SiO.sub.2, and/or Ce.sub.2O.sub.3 can be used as the particulate
material. In that respect particles of a size in a range of up to
1500 nm, preferably between about 50 nm and about 700 nm, have
proven to be highly suitable. In addition a particle size range of
between about 50 nm and about 200 nm is highly preferred.
[0026] It is preferred that the raised portions or recesses are of
heights or depths respectively in a range of up to 1500 nm,
preferably between about 50 nm and about 700 nm, further preferably
between about 50 nm and about 200 nm. In that way the raised
portions can also be formed with the aggregation or agglomeration
of smaller particles.
[0027] In that respect the particulate material can be fixed to the
ceramic base material using adhesives. For example the adhesives
used can be polysiloxanes which on the one hand fix the particulate
material to the surface of the oxide-ceramic base material and on
the other hand provide the produced coating with a superhydrophobic
surface. The adhesive, for example the polysiloxane, is added in
step (a) of the process according to the invention in production of
the suspension.
[0028] If hydrophobisation of the surface of the coating is to be
maintained, in that case the hardening operation in step (c) is not
to be effected at a temperature of more than 300.degree. C. If the
temperature is increased above 300.degree. C., that can involve
thermal decomposition of the polysiloxane and the breakdown of the
superhydrophobic surface on the photocatalytically active, porous,
oxide-ceramic coating.
[0029] It will be appreciated that other adhesives, preferably of
organic nature, such as for example carboxymethylcelluloses, can
also be used.
[0030] When calcining the ceramic molded body which is usually
effected in a range of between more than 300.degree. C. and about
1100.degree. C., the particulate material used for producing raised
portions is subjected to the action of a temperature which results
in superficial softening of the particle surfaces so that a
sinter-like join is produced between the particulate material and
the oxide-ceramic base material. In that respect it is for example
also possible to add fluxing agents which reduce the sintering
temperature.
[0031] The man skilled in the art is aware from EP 0 909 747, EP 00
115 701 and EP 1 095 023 of various possible ways of fixing
particulate material on a ceramic surface. The contents of EP 0 909
747, EP 00 115 701 and EP 1 095 923 are hereby incorporated by
reference thereto.
[0032] Preferably, the photocatalytically active, porous,
oxide-ceramic coating is formed by using photocatalytically active,
oxide-ceramic materials selected from the group consisting of
TiO.sub.2, Al.sub.2O.sub.3, SiO.sub.2, Ce.sub.2O.sub.3 and mixtures
thereof.
[0033] In accordance with a further preferred embodiment the
above-mentioned photocatalytically active, oxide-ceramic materials
may also be contained in the oxide-ceramic base body.
[0034] In accordance with a preferred embodiment the
photocatalytically active, oxide-ceramic material in the coating
and/or in the oxide-ceramic base material includes TiO.sub.2 or
Al.sub.2O.sub.3, optionally in combination with further
oxide-ceramic materials. For example mixtures of titanium dioxide
and silicon dioxide, titanium dioxide and aluminum dioxide,
aluminum dioxide and silicon dioxide and also titanium dioxide,
aluminum oxide and silicon dioxide have been found to be highly
suitable.
[0035] In that respect preferably titanium dioxide with an anatase
structure is used as the titanium dioxide. The aluminum oxide used
is preferably aluminum oxide C which is to be allocated
crystallographically to the .delta.-group and has a strong
oxidation-catalytic effect.
[0036] A suitable aluminum oxide C can be obtained from Degussa AG,
Germany. For example AEROSIL COK 84, a mixture of 84% AEROSIL 200
and 16% aluminum oxide C has proven to be very usable in the
present invention.
[0037] When using TiO.sub.2 in the oxide-ceramic coating it is
preferable that the TiO.sub.2 is present at least in part in the
anatase structure, preferably in respect of at least 40% by weight,
preferably in respect of at least 70% by weight, further preferably
in respect of at least 80% by weight, with respect to the total
amount of TiO.sub.2.
[0038] TiO.sub.2 which is present in a mixture of about 70-85% by
weight anatase and about 30-15% by weight rutile has proven to be
highly suitable.
[0039] Preferably the TiO.sub.2 used in the present invention is
obtained by flame hydrolysis of TiCl.sub.4 in the form of highly
disperse TiO.sub.2 which preferably has a particle size of between
about 15 nm and 30 nm, preferably 21 nm.
[0040] By way of example, it is possible to use for that purpose
the titanium dioxide which can be obtained under the name titanium
dioxide P25 from Degussa AG, Germany and which comprises a
proportion of 70% anatase form and 30% rutile. Extremely
advantageously titanium dioxide in the anatase form absorbs UV
light at wavelengths of less than 385 nm. Rutile absorbs UV light
at a wavelength of less than 415 nm.
[0041] In accordance with a preferred development the ceramic
molded body according to the invention has a superhydrophobic
surface.
[0042] It has been found that the self-cleaning property of the
surface can be markedly improved if the photocatalytically active,
porous, oxide-ceramic coating is provided with a superhydrophobic
surface. The oxidised organic soiling substances are still more
easily flushed away from the surface by spraying or sprinkling with
water.
[0043] In accordance with the invention the term superhydrophobic
surface is used to denote a surface with an edge angle of at least
140.degree. for water. The edge angle can be determined in
conventional manner at a drop of water of a volume of 15 .mu.l,
which is put on to a surface.
[0044] Preferably the edge angle is at least 150.degree., further
preferably 160.degree., still further preferably at least
170.degree..
[0045] The photocatalytically active, porous, oxide-ceramic coating
can be hydrophobised using Ormoceres, polysiloxane, alkylsilane
and/or fluorosilane.
[0046] Preferably a mixture of SiO.sub.2 and fluorosilane is
applied, thereby producing a superhydrophobic surface. That
hydrophobising effect or the provision of a superhydrophobic
surface is extremely advantageous for the self-cleaning property of
the molded body according to the invention.
[0047] In accordance with a further preferred embodiment the
superhydrophobic surface has raised portions. Those raised portions
can be produced when applying the hydrophobising agent by a
procedure whereby particulate material is added to the
hydrophobising agent and that mixture is subsequently applied to
the photocatalytically active, porous, oxide-ceramic coating.
[0048] When the surface is hydrophobised with the above-specified
hydrophobising agents, the temperature may not be raised above
300.degree. C. as that can then involve thermal decomposition,
which has already been mentioned above, of the hydrophobising
agents.
[0049] Therefore in accordance with the invention hardening is
effected by calcining only when no hydrophobic surface has yet been
applied to the photocatalytically active, porous, oxide-ceramic
coating. If polysiloxane were used as an adhesive and subsequently
the molded body were hardened by calcining, the surface usually has
to be hydrophobised once again if a hydrophobic surface is to be
afforded on the photocatalytically active, porous, oxide-ceramic
coating.
[0050] Preferably the ceramic molded body is in the form of a roof
tile, a tile, a clinker brick or a facade wall.
[0051] In the production according to the invention of a ceramic
molded body the photocatalytically active, oxide-ceramic powder
used in step (a) is preferably in a nano-disperse form. In that
respect the particle size range of the oxide-ceramic powder in a
range of between 5 nm and about 100 nm, further preferably between
about 10 nm and about 50 nm, has proven to be highly suitable.
[0052] To produce the ceramic molded body according to the
invention a preferably homogenous suspension is produced from
oxide-ceramic powder, adjusting agent and/or adhesive and a liquid
phase, by mixing. That suspension can be applied in a desired layer
thickness to the oxide-ceramic base material.
[0053] The suspension may be applied to the oxide-ceramic base
material for example by pouring, brushing, spraying, flinging and
so forth. It will be appreciated that the oxide-ceramic base
material can also be dipped into the suspension.
[0054] Preferably the suspension is applied in such a layer
thickness that, after the drying and/or calcining operation, the
result obtained is a ceramic molded body with a photocatalytically
active, porous, oxide-ceramic coating in a thickness of between 50
nm and about 50 .mu.m, preferably between about 100 nm and about 10
.mu.m.
[0055] The layer thickness of the undried suspension is usually in
a range of between about 0.5 .mu.m and about 100 .mu.m.
[0056] The oxide-ceramic base material may be a green body
(uncalcined ceramic material) or a pre-calcined or calcined ceramic
material.
[0057] Preferably organic viscosity regulators, for example
carboxymethylcellulose, are used as the adjusting agent. Those
viscosity regulators impart a suitable viscosity to the suspension
so that it can be reliably applied to the ceramic base material in
the desired layer thickness. Extremely advantageously, the organic
adjusting agent, preferably the carboxymethylcellulose, burns when
the operation of hardening the layer is effected by calcining in a
temperature range of between more than 300.degree. C. and about
1100.degree. C. Due to burning of the organic adjusting agent, the
formation of a porous structure in the photocatalytically active,
porous, oxide-ceramic coating is favored. In that situation the
organic adjusting agent preferably burns completely and preferably
without residue, forming a porous structure.
[0058] Calcination of the layer produced in step (b) can be
effected on the one hand by calcining the molded body in a
calcining furnace or in a calcining chamber at a temperature of
more than 300.degree. C. to about 1100.degree. C. In addition the
calcining operation is preferably effected in a temperature range
of between about 700.degree. C. and about 1100.degree. C.
[0059] The drying operation is effected at a substantially lower
temperature than the calcining operation. Drying is usually
effected in a temperature range of between 50.degree. C. and
300.degree. C., preferably between 80.degree. C. and 100.degree. C.
In that temperature range an applied superhydrophobic coating is
not broken down or destroyed.
[0060] When using adhesive there is preferably added to the
suspension polysiloxane which promotes adhesion of the
oxide-ceramic powder to the oxide-ceramic base material. Besides
its adhesive effect polysiloxane also results in hydrophobisation
of the structure. In addition addition of adhesive such as for
example polysiloxane also produces an increase in the viscosity of
the suspension produced in step (a) of the process according to the
invention. Accordingly an adjusting agent does not necessarily have
to be added when adding adhesive to the suspension in step (a). The
viscosity which is adjusted using adhesive can be sufficient so
that in step (b) the suspension can be applied to the oxide-ceramic
base material, to form a layer.
[0061] The liquid phase used is preferably water.
[0062] In a further configuration of the process particulate
material can also be added to the suspension produced in step (a).
In this alternative configuration of the process, the raised
portions which are advantageous in regard to the self-cleaning
effect of the surface and also the catalytically active, porous,
oxide-ceramic coating are produced in one step.
[0063] In a ceramic molded body produced in accordance with this
alternative configuration of the process, there is then not a
separate layer structure consisting of a layer with raised portions
and, arranged thereover, catalytically active, porous,
oxide-ceramic coating. Rather, the raised portions produced using
particulate material and the photocatalytically active,
oxide-ceramic components are present in substantially mutually
juxtaposed relationship or intimately mixed with each other.
[0064] Optionally a hydrophobising agent can then also be added to
that suspension so that superhydrophobisation of the oxide-ceramic
surface is effected in the same step in the process. In this
alternative form of the process the hardening operation can then be
effected only by drying so that no thermal decomposition of the
superhydrophobic surface occurs.
[0065] It will be appreciated that it is also possible firstly for
the above-mentioned particulate material to be applied to the
oxide-ceramic base material to produce raised portions and for it
to be fixed to the surface of the ceramic base material by means of
adhesive and/or sintering, for that surface which is prepared in
that way and which has raised portions to be provided with a
photocatalytically active, porous, oxide-ceramic coating using the
process according to the invention, and for a superhydrophobic
surface optionally to be subsequently produced on the
photocatalytically active coating.
[0066] The hydrophobising agents used are preferably
inorganic-organic hybrid molecules such as for example siloxanes,
in particular polysiloxanes. In addition Ormoceres, alkylsilanes
and/or fluorosilanes have proven to be suitable as the
hydrophobising agents.
[0067] The hydrophobising agents can be applied by a suitable
process, for example spraying, pouring, flinging, sprinkling etc.
For example, firstly a hydrophobising solution or suspension can be
produced using a preferably aqueous liquid phase. Optionally
particulate materials can also be added to that hydrophobising
solution or suspension if raised portions are to be produced in the
superhydrophobic surface. That hydrophobising solution or
suspension can then be applied in the above-described conventional
manner.
[0068] The term superhydrophobic surface is used in accordance with
the invention to denote a superhydrophobic layer, wherein the edge
angle for water is at least 140.degree., preferably 160.degree.,
further preferably 170.degree..
[0069] In addition, a pre-drying step can also be carried out after
application of the suspension produced in step (a) to the
oxide-ceramic base material, prior to the calcining operation. In
that pre-drying step the liquid phase, preferably water, can be
removed by evaporation. That can be effected for example by
heating, for example in a circulating air furnace or a radiant
furnace. It will be appreciated that it is also possible to use
other drying processes, for example using microwave technology.
[0070] The pre-drying step has proven to be advantageous in order
to avoid cracking or tearing of the layer produced from the
suspension, in the calcining operation.
[0071] After the calcining operation a superhydrophobic surface can
then be applied in the above-described manner.
[0072] In a preferred embodiment, after the calcining step and the
optionally implemented hydrophobising operation, it is possible to
carry out a post-treatment of the photocatalytically active,
porous, oxide-ceramic coating produced. The post-treatment is
effected by irradiation with laser light, or NIR or UV light. That
post-treatment can improve the adhesion between the
photocatalytically active coating and the oxide-ceramic base
material.
[0073] It has been found that the ceramic molded body according to
the invention, besides an improved self-cleaning property, also has
improved mechanical stability. There is the very great advantage
that the catalytically active, porous, oxide-ceramic coating with a
possibly superhydrophobic surface adheres very firmly and reliably
to the ceramic base material. Thus when that coating is applied for
example to roof tiles it is not destroyed or abraded when a person
walks on the roof.
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