Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – At least one aryl ring which is part of a fused or bridged...
Reexamination Certificate
2000-01-19
2002-06-11
Moore, Margaret G. (Department: 1712)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
At least one aryl ring which is part of a fused or bridged...
C106S287100, C106S287160, C427S387000, C428S447000
Reexamination Certificate
active
06403689
ABSTRACT:
The present invention relates to dispersions of particles of photocatalytic titanium dioxide which are capable of being used to treat substrates.
It is known that titanium dioxide makes possible, by its photocatalytic activity, the degradation of organic or biorganic molecules.
If this photocatalytic titanium dioxide is deposited on a support, the surface of this support becomes oxidizing and dirty marks, in particular of organic origin, which are deposited there are destroyed by photooxidation. The surface is said to be self-cleaning.
The deposition of titanium dioxide at the surface of the substrate can be carried out from dispersions of titanium dioxide particles. Use is preferably made of dispersions of particles exhibiting a small size, in particular a nanoparticle size, so as to obtain translucent surfaces, in contrast to micrometric titanium dioxide, which gives white surfaces.
The treated surfaces can be glass, plastics, building materials (mortars, concretes, terracottas), ceramics, stones, paper or wood.
The deposit of titanium dioxide on these supports must adhere strongly to the support for the treated surfaces to be able to be installed and in order for them to retain their self-cleaning properties over time. It is also necessary for the binder which allows the particles to adhere to the support not to be sensitive to the photocatalysis of the titanium dioxide particles.
With this aim, several processes have been employed which provide various types of binders which allow the particles to be adhesively bonded to the substrate.
A first process consists in depositing dispersions of titanium dioxide particles comprising the precursor of a binder on the substrate under hot conditions. For example, provision has been made to use dispersions of titanium dioxide particles and of organometallic binders of titanate or silicate type. The particles are then held in a film of silica or titanium dioxide (this principle is disclosed, for example, in WO 97/10185). This inorganic binder exhibits the advantage of not being photodegradable.
A second process consists in depositing dispersions of titanium dioxide particles comprising an organic binder on the substrate under cold conditions. One problem is that this binder must not degrade under the effect of the photocatalytic properties of the titanium dioxide particles. To achieve this, provision has been made, for example, to choose the binder from silicones.
However, although the silicone binders provided do not degrade on contact with the photocatalytic particles, it is observed that they do not always result in a homogeneous, hard and adherent coating: very often, the coatings obtained can be removed by simple rubbing with the finger.
One aim of the present invention is therefore to provide dispersions of titanium dioxide particles and of a non-photodegradable binder which can be used to form photocatalytic coatings at the substrate surface under cold conditions.
Another aim of the present invention is to provide such dispersions, the use of which results in homogeneous, hard and adherent coatings.
With these aims, the invention relates to a dispersion of particles of photocatalytic titanium dioxide, in which dispersion the liquid phase comprises at least one crosslinking catalyst and at least one polyorganosiloxane, either of formula (I):
M
&agr;
D
&bgr;
Q
&dgr;
(O
1/2
R
i
)
&egr;
,
or of formula (II):
M
&agr;
D
&bgr;
T
&ggr;
(O
1/2
R
i
)
&egr;
,
as defined hereinbelow.
With these aims, the invention also relates to the use of this dispersion to treat substrates.
The dispersions according to the invention exhibit the advantage of being chemically neutral and of not interacting with the substrates on which they are deposited.
They also exhibit the advantage of employing inexpensive binders.
In addition, they make it possible, under certain conditions of use, to result in transparent or translucent coatings.
The invention relates first of all to a dispersion of particles of photocatalytic titanium dioxide, in which dispersion the liquid phase comprises at least one polyorganosiloxane:
either of mean formula (I):
M
&agr;
D
&bgr;
Q
&dgr;
(O
1/2
R
1
)
&egr;
,
in which:
M=R
ii
3
SiO
1/2
D=R
ii
2
SiO
2/2
Q=SiO
4/2
with R
ii
, which are identical or different, representing either a linear or branched alkyl radical having from 1 to 8 carbon atoms or a substituted or unsubstituted aryl group having from 6 to 12 carbon atoms or an aralkyl, alkaryl, aryloxyalkyl or alkoxyaryl group in which the aryl group comprises from 6 to 12 carbon atoms, which atoms can optionally be substituted by at least one linear or branched alkyl or alkoxy group having from 1 to 4 carbon atoms, and in which the alkyl or alkoxy group has from 1 to 4 carbon atoms and is linear or branched,
&agr;, &bgr; and &dgr; respectively represent the molar fractions of the silicon atoms of the M, D and Q units, with &agr;+&bgr;+&dgr;=1, and:
&agr;≦0.10, preferably &agr;≦0.010,
&bgr;≦0.85,
&dgr;≧0.10,
R
i
, which are identical or different, represent an alkyl group having from 1 to 4 carbon atoms,
&egr; represents the mean number of O
1/2
R
i
units per silicon atom,
or of mean formula (II):
M
&agr;
D
&bgr;
T
&ggr;
(O
1/2
R
i
)
&egr;
,
in which:
M, D, R
i
and &egr; have the above meanings and
T=R
ii
SiO
3/2
, with R
ii
having the same meaning as above,
&agr;, &bgr; and &ggr; respectively represent the molar fractions of the silicon atoms of the M, D and T units, with &agr;+&bgr;+&ggr;=1, and:
&agr;≦0.20, preferably &agr;≦0.010,
&bgr;≦0.60,
&ggr;≧0.30.
Preferably, the polyorganosiloxane of the dispersion has the formula (I) or (II) and R
i
is an ethyl or methyl group. On average, the polyorganosiloxane can also exhibit silanol ends (R
i
=H), the said ends not representing more than 20% of all the ends.
According to a first preferred alternative form, the dispersion according to the invention comprises a polyorganosiloxane of formula (II) in which:
for each unit T=R
ii
SiO
3/2
, R
ii
is a methyl,
for each unit D=R
ii
2
SiO
2/2
, one R
ii
substituent is a methyl and the other R
ii
substituent is an octyl,
&bgr; has a value of at most 0.10,
&ggr; has a value of at least 0.70.
According to a second preferred alternative form, the dispersion according to the invention comprises a polyorganosiloxane of formula (II) in which:
for each unit T=R
ii
SiO
3/2
, R
ii
is a methyl,
for each unit D=R
ii
2
SiO
2/2
, the two R
ii
substituents are methyls,
&bgr; has a value of at most 0.30,
&ggr; has a value of at least 0.70.
According to a third preferred alternative form, the dispersion according to the invention comprises a polyorganosiloxane of formula (II) in which:
for each unit T=R
ii
SiO
3/2
, R
ii
is a propyl,
for each unit D=R
ii
2
SiO
2/2
, the two R
ii
substituents are methyls,
&bgr; has a value of at most 0.40,
&ggr; has a value of at least 0.40.
The dispersions according to the invention can also comprise a crosslinking catalyst. The latter can be chosen from organic titanium compounds (for example, alkyl titanates) or organic tin compounds (for example, dialkyltin dicarboxylate).
Alkyl titanates are preferred.
The use of this catalyst is recommended for the use of the dispersion during the treatment of glass substrates.
The liquid phase of the dispersion according to the invention may comprise only a polyorganosiloxane as defined above or else may also comprise a solvent.
The solvent of the liquid phase of the dispersion according to the invention can be aqueous or organic.
It is generally an organic solvent. The solvent can be chosen from the solvents for the silicone polymers used, such as, for example, D4 (octamethylcyclotetrasiloxane) or other volatile siloxanes, white spirit, C
1
-C
8
alcohols, or aliphatic or aromatic hydrocarbons, such as cyclohexane or alkanes.
The choice of the solvent is made according to its compatibility with the polyorganosiloxane. It is thus possible to vary the transparency of the final
Cardinaud Denis
Lehaut Corinne
Moore Margaret G.
Rhodia Chimie
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