U.S. patent application number 11/059713 was filed with the patent office on 2005-08-04 for glass, ceramic and metal substrates with a self-cleaning surface, method of making them and their use.
This patent application is currently assigned to Ferro GmbH. Invention is credited to Baumann, Martin, Fritsche, Klaus-Dieter, Korbelarz, Dagmar, Ludwig, Stephan, Poth, Lutz.
Application Number | 20050170098 11/059713 |
Document ID | / |
Family ID | 7637408 |
Filed Date | 2005-08-04 |
United States Patent
Application |
20050170098 |
Kind Code |
A1 |
Baumann, Martin ; et
al. |
August 4, 2005 |
Glass, ceramic and metal substrates with a self-cleaning surface,
method of making them and their use
Abstract
The invention relates to glass, ceramic and metal substrates
with at least one self-cleaning surface, comprising a layer with a
micro-rough surface structure that is arranged on the substrate and
made at least partly hydrophobic. The layer contains a glass flux
and structure-forming particles with a mean particle diameter
within the 0.1 to 50 .mu.m range; the glass flux and
structure-forming particles are present in a volume ratio within
the 0.1 to 5 range, and the micro-rough surface structure has a
ratio of mean profile height to mean distance between adjacent
profile tips within the 0.3 to 10 range. To produce the subject of
the invention the substrate is coated with a composition containing
a glass flux and structure-forming particles, and the layer is
burnt in and made hydrophobic.
Inventors: |
Baumann, Martin; (Bad
Vilbel, DE) ; Fritsche, Klaus-Dieter; (Colditz,
DE) ; Korbelarz, Dagmar; (Hanau, DE) ; Ludwig,
Stephan; (Neuberg, DE) ; Poth, Lutz;
(Rossdorf, DE) |
Correspondence
Address: |
RANKIN, HILL, PORTER & CLARK, LLP
925 EUCLID AVENUE, SUITE 700
CLEVELAND
OH
44115-1405
US
|
Assignee: |
Ferro GmbH
Frankfurt am Main
DE
|
Family ID: |
7637408 |
Appl. No.: |
11/059713 |
Filed: |
February 16, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11059713 |
Feb 16, 2005 |
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10239066 |
Jan 16, 2003 |
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6872441 |
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10239066 |
Jan 16, 2003 |
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PCT/EP01/02790 |
Mar 13, 2001 |
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Current U.S.
Class: |
427/372.2 ;
427/402 |
Current CPC
Class: |
C03C 2217/465 20130101;
C04B 41/52 20130101; Y10T 428/24364 20150115; B08B 17/065 20130101;
C03C 2217/475 20130101; C23C 24/10 20130101; C23C 30/00 20130101;
C03C 2217/452 20130101; C03C 17/009 20130101; Y10T 428/31612
20150401; C04B 41/52 20130101; C04B 41/89 20130101; Y10T 428/24355
20150115; C03C 17/42 20130101; B08B 17/06 20130101; Y10T 428/31663
20150401; C23C 24/08 20130101; C04B 41/5024 20130101; C03C 2217/77
20130101; C04B 41/5022 20130101; C04B 41/4539 20130101; C04B
2103/54 20130101; C04B 41/522 20130101; C04B 41/5022 20130101; C04B
41/4933 20130101; C04B 41/4511 20130101; C04B 33/00 20130101; Y10T
428/24479 20150115; C04B 41/52 20130101; C04B 41/009 20130101; C04B
41/52 20130101; C04B 41/009 20130101 |
Class at
Publication: |
427/372.2 ;
427/402 |
International
Class: |
B05D 003/02 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 1, 2000 |
DE |
10016485.4 |
Claims
What is claimed is:
1. A method of making a substrate with a self-cleaning surface
having a hydrophobic, micro-rough layer comprising the steps of:
(a) coating the substrate with a composition containing a glass
frit which forms a glass flux and structure-forming particles with
a mean particle diameter within the range of from 0.1 to 50 .mu.m,
the composition containing glass frit and structure-forming
particles in a volume ratio within the range of 0.1 to 5; (b)
burning in the substrate at a temperature above the deformation
temperature of the glass frit thereby forming a burnt-in layer; and
(c) making the burnt-in layer at least partially hydrophobic by
applying an agent to make it hydrophobic.
2. The method according to claim 1 wherein the composition
containing the glass frit which forms a glass flux and
structure-forming particles is applied to the substrate in the form
of a printable paste by a direct or indirect printing process.
3. The method according to claim 1, wherein the composition
containing the glass frit which forms a glass flux and
structure-forming particles is applied to the substrate
electrostatically in the form of a mixture of powders.
4. The method according to claim 1, wherein the burnt-in layer has
a micro-rough surface structure having a ratio of mean profile
height to mean distance between adjacent profile tips within the
0.3 to 10 range.
5. The method according to claim 4, wherein the substrate is
selected from the group consisting of glass, porcelain, vitrified
clay, stoneware, clinker and brick substrates.
6. The method according to claim 4, wherein the volume ratio of
glass flux to structure-forming particles is within the range of
from 0.2 to 2.
7. The method according to claim 4, wherein the micro-rough surface
structure has an aspect ratio within the range of from 1 to 5.
8. The method according to claim 4, wherein the structure-forming
particles have a mean diameter within the range of from 0.5 to 15
.mu.m.
9. The method according to claim 4, wherein the structure-forming
particles are idiomorphic.
10. The method according to claim 4, wherein the layer that makes
the burnt-in layer hydrophobic is based on a fluoroalkyl
alkoxysilane or a fluoroalkyl alkoxysiloxane.
11. A method of making a substrate with at least one self-cleaning
surface that is at least partially hydrophobic, comprising the
steps of: (a) coating the substrate with a composition containing a
glass frit which forms a glass flux and structure-forming particles
having a bimodal size distribution, wherein a first portion of the
structure-forming particles has a mean particle diameter within the
range of from 0.2 to 3 .mu.m and a second portion of the
structure-forming particles has a mean particle diameter within the
range of from 3 to 15 .mu.m, and the glass frit and
structure-forming particles are present in a volume ratio within
the range of 0.1 to 5; (b) burning in the substrate at a
temperature above the deformation temperature of the glass frit
thereby forming a burnt-in layer having a micro-rough surface
structure having a ratio of mean profile height to mean distance
between adjacent profile tips within the 0.3 to 10 range; and (c)
making the burnt-in layer at least partially hydrophobic by
applying an agent to make it hydrophobic.
12. The method according to claim 11, wherein the second portion of
the structure-forming particles has a mean diameter of 5 to 10
.mu.m.
13. The method according to claim 11, wherein the glass flux and
structure-forming particles are present in a volume ratio within
the 0.2 to 2 range.
14. The method according to claim 11, wherein the micro-rough
surface structure has a ratio of mean profile height to mean
distance between adjacent profile tips within the 1 to 5 range.
15. The method according to claim 11, wherein the burnt-in layer is
made at least partially hydrophobic by application of a substance
selected from the group consisting of fluroalkyl alkoxysilane,
fluoroalkyl alkoxysiloxane, and partly fluorinated vinyl
polymer.
16. The method according to claim 11, wherein the substrate is
selected from the group consisting of metal, glass, porcelain,
vitrified clay, stoneware, clinker and brick substrates.
17. The method according to claim 11, wherein the volume ratio of
glass flux to structure-forming particles is within the range of
from 0.3 to 1.
18. The method according to claim 11, wherein the micro-rough
surface structure has an aspect ratio within the range of from 1 to
2.
19. The method according to claim 11, wherein the structure-forming
particles have a mean diameter within the range of from 1 to 2
.mu.m.
20. The method according to claim 11, wherein the structure-forming
particles are idiomorphic.
21. A method of making a glass, ceramic or metal substrate with at
least one self-cleaning surface that is at least partially
hydrophobic, comprising the steps of: (a) coating the substrate
with a composition containing a glass frit which forms a glass flux
and structure-forming particles having a bimodal size distribution,
wherein a first portion of the structure-forming particles has a
mean particle diameter within the range of from 0.2 to 3 .mu.m and
a second portion of the structure-forming particles has a mean
particle diameter within the range of from 5 to 10 .mu.m, and the
glass frit and structure-forming particles are present in a volume
ratio within the range of 0.2 to 2; (b) burning in the substrate at
a temperature above the deformation temperature of the glass frit
thereby forming a burnt-in layer having a micro-rough surface
structure having a ratio of mean profile height to mean distance
between adjacent profile tips within the 0.3 to 10 range; and (c)
making the burnt-in layer at least partially hydrophobic by
applying an agent to make it hydrophobic.
22. The method according to claim 21, wherein the structure-forming
particles are selected from the group consisting of SiO.sub.2,
TiO.sub.2, ZrO.sub.2, SnO.sub.2, Al.sub.2O.sub.3, zirconium
silicates and zeolites.
Description
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application is a division of application Ser. No.
10/239,066, filed Jan. 16, 2003, which was a U.S. National Stage
Application of PCT/EP01/02790, filed Mar. 13, 2001, and claims
priority to DE 10016585.4, filed Apr. 1, 2000.
BACKGROUND OF THE INVENTION
[0002] 1. Field of Invention
[0003] The invention relates to glass, ceramic and metal substrates
with at least one structured hydrophobic surface that provides a
good self-cleaning effect. Another subject of the invention is a
method of making said substrates with a self-cleaning surface, the
method comprising forming a structured surface then making it
hydrophobic. A further subject is use of the glass, ceramic and
metal substrates with a surface according to the invention having a
self-cleaning effect.
[0004] 2. Description of Related Art
[0005] It is known that in order to obtain a good self-cleaning
effect a surface needs to have not only good hydrophobic properties
but also a micro-rough surface structure. Both features are present
in nature, for example in the lotus leaf; the surface, formed from
a hydrophobic material, has pyramidal elevations a few micrometers
away from each other. Drops of water substantially come into
contact only with these tips, so the contact area is minute,
resulting in very low adhesion. These relationships and the
theoretical possibility of applying the "lotus effect" to
industrial surfaces are taught by A. A. Abramzon, Khimia i Zhizn
(1982), No. 11, pp. 38-40.
[0006] Without reference to the lotus effect, water-repellent
surfaces are known from U.S. Pat. No. 3,354,022, where the surface
has a micro-rough structure with elevations and depressions and is
formed from a hydrophobic material in particular a
fluorine-containing polymer. In one embodiment a surface with a
self-cleaning effect may be applied to ceramic bricks or to glass
by coating the substrate with a suspension containing glass spheres
with a diameter within the 3-12 .mu.m range and a glass sphere
(diameter 3-12 .mu.m) and a fluorocarbon wax based on a
fluoroalkylethoxy methacrylate polymer. A disadvantage of such
coatings with a self-cleaning effect is their poor resistance to
abrasion. As established by the inventors involved in this patent
application, glass spheres do indeed form a structure but their
self-cleaning effect is only moderate.
[0007] EP 0 909 747 A1 teaches a method of producing self-cleaning
properties in surfaces, particularly roof tiles. The surface has
hydrophobic elevations 5 to 200 .mu.m high. A surface of this type
is formed by applying a dispersion of powder particles of an inert
material in a siloxane solution then letting it harden. As in the
previously assessed method the structure-forming particles are not
fixed on the surface of the substrate in an abrasion-resistant
manner.
[0008] EP 0 772 514 B1 and EP 0 933 388 A2 teach of self-cleaning
surfaces on articles with an artificial surface structure
comprising elevations and depressions, the distance between the
elevations being within the 5 to 200 .mu.m range (EP 0 772 514 B1)
or the 50 nm to 10 .mu.m range (EP 0 933 388 A2) and the height of
the elevations being within the 5 to 100 .mu.m range or the 50 nm
to 10 .mu.m range respectively and the structure being made of
hydrophobic polymers or materials made durably hydrophobic. Methods
suitable for forming the structures are etching and embossing
processes, coating processes for sticking on a structure-forming
powder and shaping processes using appropriately structured female
molds. If the material forming the structure is not itself
hydrophobic the formation of the structure is followed by treatment
to make it hydrophobic, particularly by silanising it. Although
self-cleaning surfaces according to EP 0 772 514 B1 may also be
applied to glazing or roofs the process is very expensive and the
surface forming the structure, like that in the documents assessed
above, has little resistance to abrasion, so the self-cleaning
effect declines rapidly under quite strong mechanical stress.
BRIEF SUMMARY OF THE INVENTION
[0009] The object of the invention is to indicate substrates of
glass, a ceramic material or metal with a structured and
hydrophobic surface having a good self-cleaning effect. A further
object is that the structured surface should have higher abrasion
resistance than known surfaces in which structure-forming particles
were fixed to the surface by means of an organic polymer. A further
object of the invention is that substrates with the self-cleaning
surface according to the invention should be obtainable by a simple
method. It should be possible to carry out the structure-forming
method using stages in the process and industrial apparatus normal
for surface treatment, such as decoration, of said substrates.
[0010] It has been found that the above objects and other objects
revealed in the following description can be achieved, in that a
substrate of glass, a ceramic material or metal is coated with a
composition containing a material producing a glass flux such as a
glass frit and structure-forming particles, and the coated
substrate is fired at a temperature adapted to the substrate and
the material forming the glass flux then made hydrophobic, the
substrate being made hydrophobic preferably using a
fluoroalkylsilane or fluoroalkylsiloxane.
[0011] The subject of the invention is accordingly a glass, ceramic
or metal substrate with at least one self-cleaning surface
comprising a layer with a micro-rough surface structure which is
arranged on the substrate and made at least partly hydrophobic,
characterized in that the layer contains a glass flux and
structure-forming particles with a mean particle diameter within
the 0.1 to 50 .mu.m range, the glass flux and structure-forming
particles are present in a volume ratio within the 0.1 to 5 range,
and the micro-rough surface structure has a ratio of mean profile
height to mean distance between adjacent profile tips within the
0.3 to 10 range.
[0012] The foregoing and other features of the invention are
hereinafter more fully described and particularly pointed out in
the claims, the following description setting forth in detail
certain illustrative embodiments of the invention, these being
indicative, however, of but a few of the various ways in which the
principles of the present invention may be employed.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] FIG. 1 is a scanning electron microscope photograph of a
self-cleaning surface according to the invention.
DETAILED DESCRIPTION OF THE INVENTION
[0014] The substrates in question are ones that are resistant to
ceramic burning under temperature conditions adapted to the
substrate. They are accordingly glass of any chemical composition
including glass-ceramics, any ceramic materials such as bricks,
clinker, architecturally applied ceramics, stoneware, vitrified
clay, hard and soft porcelain, oxide and special ceramics and
metals, in particular steels. The substrates may also be coated
with colored slip, glazed or enameled before the self-cleaning
surface is applied.
[0015] The term "self-cleaning surface" is used in the same sense
as in prior art. The surface is virtually unwettable by water and
preferably by other liquids, so rapid drop formation becomes
possible and dirt particles deposited are washed away in a simple
manner with the drops running down. Substrates with a self-cleaning
surface produced according to the invention are substantially dry
when water has run off the surface.
[0016] The self-cleaning surface has a micro-rough structure, i.e.
a structure with elevations and depressions in a geometrical or
random, preferably random arrangement. The elevations and
depressions are distributed substantially over the whole
self-cleaning surface. There may be a simple structure of
elevations and depressions; alternatively the micro-roughness may
comprise a coarse structure and a fine structure, with the
elevations and depressions of the fine structure located on a
coarse structure (=superstructure) having depressions and
elevations. A surface with a coarse and a fine structure has been
found to allow a particularly good self-cleaning effect.
[0017] The mean profile height of the surface roughness is normally
within the 0.2 to 10 .mu.m range although values outside those
limits are not excluded. Roughness with a profile height within the
range from approx. 1 .mu.m to approximately 10 .mu.m is preferred.
If the surface has both a coarse and a fine structure the mean
profile height of the fine structure is generally within the range
from 0.2 to approx. 4 .mu.m, particularly 0.5 to 3 .mu.m and that
of the coarse structure within the range from 1 to 10 .mu.m but
above the height of the fine structure.
[0018] A feature of the surface structure that is important for a
good self-cleaning effect is the ratio of the mean profile height
to the mean distance between adjacent profile tips. This aspect
ratio is desirably within the 0.3 to 10 range, preferably within
the 1 to 5 range and particularly preferably within the 1 to 2
range. Said aspect ratios apply to both the coarse and the fine
structure.
[0019] The micro-rough surface structure is formed from particles
anchored in a glass flux and/or particle aggregates bonded together
by glass flux. The glass flux is thus the binder for the
structure-forming particles and gives the surface structure
considerably higher abrasion resistance than was possible using
known resins. The layer forming a micro-rough surface structure
substantially comprises a glass flux and the structure-forming
particles. A fraction of the particles may be completely enveloped
in glass flux but another fraction, namely the fraction forming the
structure, projects out of the flux. In addition to the glass flux
and structure-forming particles the micro-rough layer may contain
other constituents, for example pigments to give the system a
decorative appearance or metallic powders providing electrical
conductivity. Said categories of material may themselves be a
component of the structure-forming particles.
[0020] The layer with the micro-rough surface structure located on
the substrate contains glass flux and structure-forming particles
in a volume ratio desirably within the 0.1 to 5 range, preferably
within the 0.2 to 2 range and particularly preferably within the
0.3 to 1 range. As the proportion of glass flux increases, given
the same particle spectrum, the degree of roughness and thus the
effectiveness is diminished.
[0021] Conversely if the quantity of glass flux is too small,
abrasion-proof fixing of the structure-forming particles on the
substrate surface can no longer be guaranteed. The volume ratio of
glass flux to structure-forming particles that is particularly
suitable for the intended purpose also depends to a certain extent
on the particle spectrum of the structure-forming particles. The
optimum ratio can be determined by carrying out simple tests.
[0022] The mean particle diameter of the structure-forming
particles may be within a range from 0.1 to 50 .mu.m, although it
is preferably within the range from 0.2 to 20 .mu.m and
particularly preferably within the range from 0.5 to 15 .mu.m. As
the mean particle diameter of the structure-forming particles and
the thickness of the micro-rough layer increase the layer becomes
more opaque. A layer with the above-mentioned preferred bimodal
structure (fine structure on a superstructure) contains a spectrum
of structure-forming particles with an adequate proportion of fine
particles, preferably within the range from 0.2 to 3 .mu.m, and an
adequate proportion of coarse particles of a diameter within the
range from 3 to 15 .mu.m, particularly from 5 to 10 .mu.m.
[0023] The particles used to form the micro-rough structure are
those with a melting point above the firing temperature and thus
above the deformation point of the glass flux. Particularly
effective surface structures can be obtained when the
structure-forming particles are idiomorphic, i.e. when they have
pronounced edges and faces. Although particles with a rather
spherical morphology or even glass spheres enable a micro-rough
surface structure to be formed, its self-cleaning effect is only
moderate or unsatisfactory.
[0024] Any products may be present as structure-forming particles;
their melting point is above the firing temperature and the
structure is preferably idiomorphic. Some examples of
structure-forming particles are oxides and silicates such as
zirconium silicates, zeolites, SiO.sub.2, TiO.sub.2, ZrO.sub.2,
SnO.sub.2 and Al.sub.2O.sub.3.
[0025] The glass flux may be of very different compositions.
Numerous glass compositions are known to those having skill in the
art that have a deformation range from approximately 500.degree. C.
to over 1000.degree. C. Glass compositions of the flux for a
micro-rough surface structure on glass understandably have a
deformation temperature below that of the glass substrate.
Micro-rough surface structures on for example ceramic substrates
generally have a substantially higher deformation point.
[0026] The thickness of the micro-rough layer is variable,
generally within the range from 5 to 100 .mu.m, preferably from 10
to 20 .mu.m. The given thickness covers the height of the layer
including the mean profile height of the elevations.
[0027] The surface of the micro-rough layer is at least partly made
hydrophobic, especially the tips of the elevations. However the
whole surface is preferably made hydrophobic.
[0028] This is done substantially by a very thin coating, for
example 1 to 10 nm thick, which adheres firmly to the surface below
it. The adhesion results from the coating material forming a film
after application. Preferred agents for making the surface
hydrophobic are chemically bonded to the substrate for example by a
Si--O--Si bridge. Such bridges result from the reaction of a
silanol group of a silicate substrate with an alkoxysilane or
alkoxysiloxane. Preferred substrates according to the invention
with a self-cleaning surface have a coating, often only very few
atomic layers thick, based on an alkyltrialkoxysilane and
preferably a longer-chain fluoroalkyl trialkoxysilane or oligomers
of those silanes.
[0029] FIG. 1 shows a scanning electron microscope photograph of a
self-cleaning surface according to the invention, where the
substrate is glass and the structure-forming particles are a
zeolite of the Pentasil type (ZSM 5) bonded to the substrate by a
glass flux. The volume ratio of zeolite to glass flux is 1 to 1; a
printing paste containing zeolite and glass frit in said volume
ratio has been applied to the substrate by screen printing and
burnt in at 650.degree. C. The surface thus produced had an
extremely good self-cleaning effect and high abrasion
resistance.
[0030] Substrates according to the invention with a self-cleaning
surface can be produced by a method comprising applying a
hydrophobic, micro-rough layer to the substrate and characterized
by the steps of coating the substrate with a composition containing
a glass frit which forms a glass flux and structure-forming
particles with a mean particle diameter within the 0.1 to 50 .mu.m
range, the composition containing glass frit and structure-forming
particles in a volume ratio within the 0.1 to 5 range, burning in
the layer at a temperature above the deformation temperature of the
glass frit, and making the burnt-in layer at least partly
hydrophobic by applying an agent to make it hydrophobic.
[0031] The choice of material, the structure and the spectrum of
structure-forming particles used in the composition forming the
layer can be found in the above description. The same applies to
the volume ratio of glass frit forming glass flux to
structure-forming particles to be used; glass flux and glass frit
have the same volume, so the said ratio is also the same. The glass
frit forming the glass flux may be one frit or a mixture of
different glass frits. In addition to the one or more glass frits
and the structure-forming particles the composition may also
contain one or more inorganic pigments and/or metallic powders such
as silver for conductivity purposes and/or processing aids to
improve the preparation of the composition and/or its application
to the substrate to be coated.
[0032] To produce a metallic substrate with a self-cleaning surface
it is desirable to select the usual glass frits for making enamels
on metallic substrates. It may be desirable, in order to improve
adhesion, first to provide the metallic substrate with a base
enamel and only then to apply the composition for forming a layer
with a micro-rough surface structure to the enamel.
[0033] The composition to be used for forming the micro-rough layer
may be applied in a known manner to at least one surface of the
substrate to be coated. Suitable methods of doing so are direct and
indirect printing processes including screen printing and pad
transfer printing processes, also dipping and spraying methods and
electrostatic coating processes.
[0034] To enable the layer-forming composition to be applied in a
normal printing process the composition contains, in addition to
the above-mentioned inorganic constituents, a liquid printing
medium in which the inorganic constituents are made into a paste.
Aqueous and/or organic or organic-aqueous media may be used,
containing one or more organic binders and possibly normal
processing aids such as viscosity regulators in addition to one or
more solvents. Appropriate media are those known in the art for
producing printing pastes for making ceramic decorations which are
burnt-in in a decorative baking process.
[0035] In an alternative embodiment the layer-forming composition
is applied to the substrate to be coated by a known electrostatic
coating process. For this purpose the composition should desirably
also contain a few percent of a thermoplastic material, in
particular 1 to 8% by weight of a polyethylene wax, and the
substrate should be heated to a temperature above the deformation
point of the thermoplastic material before or immediately after the
electrostatic coating. Details of electrostatic coating of glass
and ceramic materials can be found in WO 94/26679 and WO
98/58889.
[0036] Application of the layer-forming composition to the
substrate is followed by normal baking. At a temperature above the
deformation point of at least one glass frit, the frit fuses
together into a glass flux. The structure-forming particles near
the surface surprisingly form the required micro-rough surface
structure with the aspect ratio claimed. The particles located at
the surface are securely anchored in the glass flux.
[0037] In a further embodiment the micro-rough layer is printed by
means of a printing paste containing a glass frit which forms a
glass flux, and the structure-forming particles are applied to the
still moist printing surface for example by powdering or dripping
on, possibly followed by partial pressing of the particles into the
printed surface. The substrate thus treated is then burnt and made
hydrophobic in a known manner.
[0038] After the baking at least part of the micro-rough surface,
particularly the tips of the elevations, preferably the whole
surface is made hydrophobic. The agents for making the surface
hydrophobic are products normally used in the art. They are either
polymers with that action or preferably monomeric or oligomeric
compounds containing a fairly long-chain alkyl or preferably
fluoroalkyl radical with that action and also a functional group
whereby the compounds with a hydrophobising action can be
cross-linked and thus form a film and/or whereby a reaction with
functional groups at the surface of the micro-rough layer is
enabled.
[0039] The micro-rough surface may be made hydrophobic by applying
a lacquer or by polymerizing monomers on the surface. Some suitable
polymeric lacquers are solutions or dispersions for example of
polyvinylidene fluoride.
[0040] As an alternative to the use of fluorine-containing silanes
and siloxanes, the surface may be made hydrophobic by plasma
polymerisation of fully or partly fluorinated vinyl compounds.
[0041] It is particularly desirable for the surface to be made
hydrophobic using reactive alkyl or preferably fluoroalkyl silanes
and oligomeric alkyl or fluoroalkyl siloxanes. The silanes or
siloxanes preferably contain one or more alkoxy groups such as
ethoxy groups as the reactive group. The agent for making the
surface hydrophobic may be cross-linked and also chemically bound
to a silicate surface containing silanol groups by these alkoxy
groups. Particularly preferred silanising agents are
tridecafluoroctyltriethoxy silane and oligomers thereof
(Dynasilanes.RTM. produced by Sivento Chemie Rheinfelden GmbH).
Products of this type may be applied to the surface to be made
hydrophobic in the form of dilute organic, in particular alcoholic,
aqueous-organic and aqueous solutions for example by dipping,
spraying or painting.
[0042] When a solution containing a fluorine-containing silane or
siloxane has been applied to it, the substrate is dried and
hardened preferably at a temperature up to 500.degree. C., for
example for 10-15 minutes at 250.degree. C. to 300.degree. C. or 1
minute at about 500.degree. C. or 30-60 minutes at about
150.degree. C. The optimum thermal post-treatment for maximum
abrasion resistance is at a temperature in the range from
200.degree. C. to 300.degree. C.
[0043] By using dilute solutions of said silanes or siloxanes
chemically and mechanically very resistant layers only a few nm
thick are obtained, which are 2- and 3-dimensional siloxane
networks.
[0044] Hydrophobic layers which can be obtained by using reactive
fluoroalkyl silanes or siloxanes are characterized by equally good
hydrophobic and oleophobic properties, so even substrates according
to the invention which are soiled with hydrophobic dirt particles
can easily be cleaned with water.
[0045] Substrates with a self-cleaning surface according to the
invention may be used wherever the surface (a) is exposed to a
constant danger of soiling and (b) must be cleanable in an
extremely simple manner with water. Glass substrates with a
self-cleaning surface according to the invention can appropriately
be used for glazing vehicles and trains and for glass bricks.
Ceramic substrates with a self-cleaning surface according to the
invention are suitable for use as a building material such as roof
tiles, clinker and floor tiles.
[0046] The advantages of the invention are that self-cleaning
surfaces of glass, ceramic and metal substrates are easily
accessible and have a good self-cleaning effect. The
structure-forming layer has high abrasion resistance. Preferred
surfaces have "super-hydrophobic properties", causing water drops
to run down them almost without friction. In addition to surfaces
where a self-cleaning effect is important, substrates with a
structured surface made hydrophobic according to the invention are
also suitable for chemical engineering apparatus such as coated
pipes and heat exchanger plates.
[0047] The following examples are intended only to illustrate the
invention and should not be construed as imposing limitations upon
the claims.
EXAMPLE 1
[0048] General information on the production of substrates with a
self-cleaning surface follows. Details such as the products used,
relative quantities and baking conditions to obtain the structured
surface and conditions to make it hydrophobic can be found in the
Tables.
[0049] Direct printing: Glass frit and structure-forming particles
were made into a paste in a known manner with a printing medium
which can be diluted with water (No. 80858 from dmc.sup.2 AG) or a
purely organic one (No. 80820 from dmc.sup.2 AG), and the printing
paste was applied to the substrate by screen printing.
[0050] Indirect printing: Glass frit and structure-forming
particles were made into a paste with a screen printing oil (No.
80820 from dmc.sup.2 AG). The printing method was screen printing
on transfer paper; after drying a covering film was formed. The
printed image was applied in known manner to the substrate to be
decorated.
[0051] Electrostatic application: Glass frit and structure-forming
particles mixed with Siloxane H68 (Weinstock & Siebert) were
treated (first mixed then tempered) to raise the specific
resistance of the powder to >10.sup.14 .OMEGA.m. The powder
mixture of the glass frit thus siliconised and structure-forming
particles was applied using an electrostatic gun at 90 kV.
[0052] The coatings applied to the substrate by direct or indirect
printing or electrostatically were burnt-in in a known manner;
heating-up time 200 K/h, T.sub.max and holding time are given in
the Table.
[0053] The substrate was 4 mm float glass in all the examples.
[0054] The glass frits were a low melting point glass frit with a
high Pb content, a d.sub.50 value of 3.3 .mu.m and a d.sub.90 value
of 10 .mu.m (No. 10022 from dmc.sup.2 AG), another glass frit (No.
10157 from dmc.sup.2 AG) and a glass frit for electrostatic glazing
(VNR 9316 F) with a d.sub.50 value of 3.7 .mu.m and a d.sub.90
value of 6.8 .mu.m.
[0055] The structure-forming particles used were zirconium dye
pigments, namely zirconium iron rose (FK 27357 from dmc.sup.2 AG),
and a hydrophobic zeolite of the Pentasil type (Wessalith.RTM.
DAZ).
[0056] The structured burnt-in surface was made hydrophobic using a
fluoroalkyl silane formulation, namely Dynasilan.RTM.) F8262
(Degussa-Huls AG) (a solution of tridecafluoroctyltriethoxy silane
in ethanol). The solution was poured over the surface then hardened
at an elevated temperature.
[0057] The self-cleaning effect was evaluated by a test with drops
of water running down a slightly inclined surface:
[0058] +++ very good, ++ good, + moderate, .smallcircle. poor
[0059] Tables 1a and 1b below give the detailed conditions and
results.
1TABLE 1a 1 2 3 4 5 6 Glass frit* 10022 10022 10022 10022 10022
10022 Structure-forming FK 22389 FK 22389 FK 22389 FK 27357 FK
27357 FK 27357 particles Glass frit/particles 50:50 80:20 50:50
50:50 50:50 50:50 (volume ratio) Printing medium* 80858 80858 80820
80858 80820 80820 (ratio of frit + particles: 10:3 10:3 10:10 10:6
10:10 10:10 medium) Application method direct direct indirect
direct direct direct Screen fabric 100 180 100 100 180 100 Baking
condition: 560/4 560/4 560/4 560/4 560/4 660/4 (.degree. C./min)
Making 150.degree. C./60 min 150.degree. C./60 min 150.degree.
C./60 min 300.degree. C./60 min 300.degree. C./60 min 300.degree.
C./60 min hydrophobic/hardening conditions Drop of water running
+++ + +++ +++ ++ ++ down effect *Numbers given are product numbers
of commercially available products of dmc.sup.2 AG.
[0060]
2 TABLE 1b 7 8 9 10 11 Glass frit* 10157 10022 10022 10022 VNR
9316F Structure-forming FK 22389 DAZ DAZ DAZ ** particles Glass
frit/particles 50:50 50:50 50:50 50:50 -- (volume ratio) Printing
medium* 80858 80858 80858 -- 80858 (ratio of frit + particles: 10:6
10:7 10:7 -- 10:8 medium) Application method direct direct direct
electrostatic direct Screen fabric 100 100 180 -- 100 Baking
condition: 560/4 560/4 560/4 650/4 630/4 (.degree. C./min) Making
150.degree. C./60 min 150.degree. C./60 min 150.degree. C./60 min
150.degree. C./60 min 150.degree. C./60 min hydrophobic/hardening
conditions Drop of water running ++ ++ ++ ++ .largecircle. down
effect *Numbers given are product numbers of commercially available
products of dmc.sup.2 AG; **The glass frit fuses incompletely and
is thus structure-forming; surface like matt glass; micro-structure
differs from that in Examples 1-10, in that the elevations are
rounded.
[0061] Additional advantages and modifications will readily occur
to those skilled in the art. Therefore, the invention in its
broader aspects is not limited to the specific details and
illustrative examples shown and described herein. Accordingly,
various modifications may be made without departing from the spirit
or scope of the general inventive concept as defined by the
appended claims and their equivalents.
* * * * *