Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
2002-02-19
2003-07-29
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Composite
Of silicon containing
C524S379000, C524S588000, C528S035000, C528S037000
Reexamination Certificate
active
06599635
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to inorganic coating compositions based on cyclic carbosiloxanes, inorganic polycondensates and &agr;,&ohgr;-functional linear oligosiloxanes, and also to a process for production thereof and to the use thereof and to a non-stick coating so obtained.
Inorganic coatings based on siloxane have been state of the art for a long time and are valued in many fields on account of their properties. Silicone-resin lacquers, which are substantially composed of randomly distributed T, D and M units and, in part, also of Q units, are produced from the corresponding chlorosilanes with the aid of direct or indirect hydrolysis. The step of hydrolysis of the silanes to form oligosiloxanes is followed by the step of condensation to form organopolysiloxane resins, so-called “bodying”. The production processes are described, for example, in W. Noll, Chemie und Technologie der Silicone, VCH-Verlag, 1968 and in Chemie in Unserer Zeit, 23, (1989), 86-99. The technology and properties of silicone resins are also summarised therein. Hard, mechanically loadable though brittle coatings can be produced, in particular, with pure methyl-silicone resins. In order to obtain the final properties, silicone-resin lacquers have to be baked at temperatures from 180 to 230° C.
In contrast with the production of silicone resin, in the case of the sol-gel process an oligosiloxane sol is produced by hydrolysis and polycondensation of alkoxysilanes without subsequent “bodying”. In comparison with silicone resins, the sols have a much larger number of reactive SiOH or SiOR groups and possess a higher crosslinkage density by virtue of a higher proportion of Q units. Sol-gel coating systems have the known positive properties of the silicon resins, such as high thermal stability, resistance to solvents and to many liquids in daily use, non-stick action and resistance to weathering. By reason of their higher reactivity and crosslinkage density, sol-gel coatings can be cured at lower temperatures from about 80° C. to about 130° C., and they surpass silicone-resin lacquers in hardness and mechanical stability.
The disadvantage of condensation-crosslinking sol-gel coating systems is their lower solids content or, to be more exact, their high VOC content. The solids content of sol-gel lacquers lies, as a rule, between 10 and 50 wt. %, generally around a maximum of 30 wt. %. However, the reduction of volatile organic compounds (VOC) is being demanded to an increasing extent by the coating industry. A further disadvantage of the existing sol-gel coating systems is their tendency to crack by reason of low flexibility. They can therefore only be applied in slight layer thicknesses of a few &mgr;m. In addition, for many applications, such as for example for providing protection against graffiti on buildings, large vehicles and rail vehicles, it would be advantageous if inorganic sol-gel systems obtained their properties already in the course of curing at room temperature.
A demand therefore exists for inorganic sol-gel systems without the disadvantages stated above but with the stated advantages.
The state of the art consists in varying the flexibility and hardness of sol-gel lacquers within certain limits via the type and the quantitative ratios of the silanes and additives that are employed for producing the coating composition. In U.S. Pat. No. 4,624,870 methyltrialkoxysilane is hydrolysed with colloidal SiO
2
. The properties are controlled via the ratio of CH
3
SiO
3/2
units to SiO
2
units. U.S. Pat. Nos. 3,986,997, 4,027,073 and EP-A 358 011 describe the (co)hydrolysis of organofunctional alkyltrialkoxysilanes such as methyltrialkoxysilane, glycidyloxypropyltrialkoxysilane or methacryloxypropyltrialkoxysilane and tetraethoxysilane (TEOS) as well as, optionally, inorganic nanoparticles. With these systems the properties can be controlled via the type and proportion of the organofunctional silanes with respect to the overall composition. In U.S. Pat. No. 4,324,712 the tendency of the coating composition to crack is reduced by addition of 0.5 to 5% of a linear functional oligosiloxane to the (co)hydrolysate formed from alkyltrialkoxysilane and colloidal SiO
2
. In PCT patents 8/52992 and 94/06807 multifunctional, preferably cyclic, organosiloxanes are employed for the modification of inorganic coatings.
Also state of the art is the hydrophobic and/or oleophobic modification of the previously described coating compositions by addition of fluorine-containing components, fluorine-containing alkoxysilanes being preferred. Such coatings are distinguished by good non-stick properties and are described, for example, in DE-A 41 18 184 and in WO 99/03941.
However, all the condensation-crosslinking sol-gel systems known in accordance with the state of the art exhibit at least one of the disadvantages stated at the outset, ruling out extended use in many fields.
The object of the present invention was therefore to make available an inorganic solgel coating that does not exhibit the disadvantages described previously. A further object of the invention consisted in making available a suitable process for production of the coating composition according to the invention.
The invention is based on the surprising observation that coating compositions that achieve the object underlying the invention can be obtained through the combination of cyclic carbosilanes and/or carbosiloxanes, inorganic polycondensates and &agr;,&ohgr;-functional linear oligosiloxanes.
SUMMARY OF THE INVENTION
The invention consequently provides coating compositions containing
I) a multifunctional carbosilane and/or carbosiloxane of the general formula (I)
W[(CH
2
)
m
SiR
1
n
X
(3−n)
]
p
(I)
and/or the (partial) condensation product thereof with
R
1
C
1
-C
18
alkyl and/or C
6
-C
20
aryl, where R
1
within the molecule may be the same or different,
X a residue selected from the group consisting of OH, C
1
-C
4
alkoxy, C
6
-C
20
aryloxy, C
1
-C
6
acyloxy, preferably OH, methoxy or ethoxy,
n 0 to 2
m 2 to 6
p integer≧2 and
W either a linear, cyclic or branched silane or siloxane,
II) a polycondensation product of one or more hydrolysable compounds of the general formula (II)
R
2
a
M(Y)
(b)
(II)
with
M Si, B, Al, Ti, Zr, V, Zn, preferably Si
R
2
the same or different non-hydrolysable C
1
-C
14
alkyl residues or C
6
-C
20
aryl residues, which may be replaced by at least one member of the group consisting of O, N, S, P,
Y a hydrolysable group, preferably C
1
-C
8
alkoxy or C
2
-C
8
acyloxy, C
1
-C
2
alkoxy being quite particularly preferred,
a 0 to 3, preferably 0 or 1
b 1 to 4, where a+b is equal to 3 or 4
and a solids content of at least 40 wt. %, preferably of at least 50 wt. %, in an OH-functional solvent,
(III) an &agr;,&ohgr;-functional linear oligosiloxane of the general formula (III)
with
Z hydroxy or C
1
-C
4
alkoxy
R
3
C
1
-C
18
alkyl or alkenyl, where R
3
within the molecule may be the same or different,
c 1 to 60, preferably 3 to 25,
IV) catalysts selected from the group consisting of the acidic, basic or metallic catalysts, preferably from the group consisting of the acids such as hydrochloric acid, sulfuric acid, p-toluenesulfonic acid, trifluoroacetic acid, trifluoromethanesulfonic acid, acetic acid or formic acid,
as well as, optionally,
V) inorganic fillers and/or inorganic nanoparticles, as well as
VI) conventional auxiliary substances pertaining to coating technology.
DETAILED DESCRIPTION OF THE INVENTION
The coating composition according to the invention exhibits a solvent content of at most 50 wt. %, preferably of at most 40 wt. %. It can be applied in flawless manner in dry-layer thicknesses of clearly more than 30 &mgr;m and cures at room temperature. The cured films are transparent and flexible. They are hydrophobic and possess good non-stick properties.
Suitable multifunctional carbosilanes and/or carbosiloxanes of the general formula (I) in the sense of the invention are silanes of the general formula (IV)
R
4
4
Mechtel Markus
Mundstock Holger
Pütz Wolfgang
Schmalstieg Lutz
Sonntag Michael
Bayer Aktiengesellschaft
Dawson Robert
Gil Joseph C.
Roy Thomas W.
Zimmer Marc S
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