Stock material or miscellaneous articles – Composite – Of silicon containing
Reexamination Certificate
2001-07-03
2003-11-25
Dawson, Robert (Department: 1712)
Stock material or miscellaneous articles
Composite
Of silicon containing
C427S299000, C427S387000, C427S372200, C524S261000, C524S266000, C524S368000, C524S588000, C524S609000, C525S100000, C525S101000
Reexamination Certificate
active
06652976
ABSTRACT:
BACKGROUND
The invention relates to conductive, highly abrasion-resistant coatings on mouldings, including at least one conductive layer and at least one highly abrasion-resistant layer and a process for their production and their use.
Conductive coatings based on polyethylene dioxythiophene (PEDT) already have a broad area of application, e.g, anti-static finishes for photographic films. Numerous processes have described how such conductive coatings can be produced. Basically, either the PEDT, which is mixed with a binder, is applied or a multi-layered structure is chosen which has the advantage that binder and PEDT do not have to be compatible (miscible).
Conductive and scratch-resistant multi-layered structures for coating picture tubes are described in WO 96/05606. Scratch-resistant layers, for example silicon dioxide obtained by hydrolysis and condensation of tetraethyl orthosilicate, are applied to a conductive PEDT layer, the layer thickness being limited to 50 to 250 nm. Alternatively, production of scratch-resistant layers from inorganic-organic hybrid materials is described, which layers can be applied to the conductive layer in a layer thickness of 10 &mgr;m and greater. These hybrid materials are based on trialkoxysilanes of Formula R′—Si(OR)
3
, wherein R′ represents a polymerisable group. The multi-layered structures described in WO 96/05606 have several fundamental disadvantages however:
After applying one of the described scratch-resistant layers, a notable level of conductivity can no longer be measured on the surface of the multi-layered structure.
Although a good level of scratch resistance is found (ascertained by determining the lead pencil hardness), the abrasion resistance of the coatings is poor.
High curing temperatures, 160° C. in the examples.
Antistatic multi-layered structures, in which the top (scratch-resistant) layer must also exhibit a certain level of conductivity, or multi-layered structures with vitreous abrasion resistance cannot therefore be produced. Furthermore, curing temperatures of 160° C. cannot be used for coating the majority of plastics materials (softening).
Conductive coatings for transparent substrates, such as plastics materials or glass for example, must retain their optical properties undiminished under mechanical load and must therefore have high resistance to abrasion. In WO 98/25274, mixtures are described which produce conductive coatings with good adhesion and with improved scratch resistance and transmittance of visible light. These mixtures consist of a binder based on polyfunctional organosil(ox)anes and a conductive organic polymer which are known from WO 98/25274 and EP-A 0 947 520. The described binders are wherein they contain heterometals such as boron or aluminium and exhibit particularly good abrasion resistance.
In EP-A 0 947 520 it is stated that these binders react sensitively to the addition of water, so by adding PEDT for example, in the conventional form supplied (Baytron® P, approximately 1.3% dispersion of PEDT and polystyrene sulphonate in water), the processing time of these mixtures is significantly reduced. Furthermore, the addition of PEDT to the binder often leads to a loss in abrasion resistance which can clearly be seen even with highly abrasion resistant coatings.
The object of the present invention was therefore to provide conductive surfaces provided with abrasion-resistant coatings, during the production of which the above-mentioned disadvantages are avoided.
Surprisingly it has now been found that a multi-layered structure on a substrate (moulding) including at least one conductive layer and at least one highly abrasion-resistant layer still has a measurable level of electrical conductivity on the surface of a moulding even though the top, highly abrasion resistant layer is a good electrical insulator.
SUMMARY
The invention relates to a conductive and highly abrasion-resistant coating. The coating comprises (a) a first layer comprising an electrically conductive polymer, and (b) a second layer comprising a highly abrasion-resistant layer of a polyfunctional organosil(ox)ane, wherein the coating is on a substrate of a multi-layer structure. The invention also relates to a method for making and using such a coating. These and other features, aspects, and advantages of the present invention will become better understood with reference to the following description and appended claims.
DESCRIPTION
The present invention therefore relates to conductive and highly abrasion-resistant coatings on a substrate as a result of a multi-layered structure, wherein an electrically conductive polymer is applied in a first layer and a highly abrasion-resistant layer of polyfunctional organosil(ox)anes is applied in a second layer.
The mouldings coated according to the invention have a measurable level of electrical conductivity on the surface even though the highly abrasion-resistant layer is a good insulator. The abrasion resistance of the multi-layered structure according to the invention (in the Taber abraser test) is similar to that of glass and curing can advantageously take place at temperatures lower than 160° C.
The present invention also relates to a process for producing conductive and highly abrasion-resistant coatings, wherein a conductive layer is applied wet chemically in a first stage and a highly abrasion-resistant layer is subsequently applied in a second stage.
Highly abrasion-resistant coatings in the context of the invention are those which exhibit scattered light on the scratch mark (determined in accordance with ASTM D 1003) in the Taber abraser scratch test (determined according to ASTM D 1044, 1,000 cycles, 500 g load per wheel, CS-10-F stones) of less than 20%, preferably less than 10%, particularly preferably less than 5%. In comparison, commercially available Makrolon®, for example, exhibits scattered light of more than 30% on the scratch mark even after 100 cycles in the Taber abraser test. Glass exhibits scattered light of approximately 1 to 3% after 1,000 cycles in the Taber abraser test.
Polyfunctional organosil(ox)anes in the context of the invention are linear, branched or cyclic monomeric organosil(ox)anes which have at least two silicon atoms with hydrolysable and/or condensation crosslinking groups, wherein the silicon atoms are connected to one another in each case by means of a linking constructional unit with at least one carbon atom. Examples of polyfunctional organosil(ox)anes are found inter alia in EP-A 0 947 520. Production of aluminium- and boron-containing sol-gel condensates from which coatings with particularly high abrasion resistance can be obtained is also described therein.
Sol-gel materials based on cyclic carbosiloxanes of Formula (I)
in which
m is 3 to 6, and preferably m is 3 or 4,
o is 2 to 10, and preferably o is 2 and
a is 1 to 3,
R
1
is C
1
-C
6
-alkyl, C
6
-C
14
-aryl, preferably R
1
is methyl, ethyl, isopropyl and when a is 1 R
1
can also represent hydrogen, furthermore when
R
2
is C
1
-C
6
-alkyl, C
6
-C
14
-aryl, preferably R
2
is methyl and
R
3
is C
1
-C
6
-alkyl, C
6
-C
14
-aryl, preferably R
3
is methyl, ethyl and particularly preferably R
3
is methyl,
are used to produce highly abrasion-resistant coatings which, in addition to their high mechanical strength, also exhibit good weathering resistance.
As described in WO 98/52992 and in U.S. Pat. No. 6,005,131, the cyclic carbosiloxanes are co-condensed with tetraalkoxysilanes, organotrialkoxysilanes and/or nanoparticles, the presence of aluminium or boron alkoxides enhancing the abrasion resistance of the coatings produced from the condensates as shown in EP-A 0 947 520.
Conductive coatings in the context of the invention exhibit a surface resistance of 0.1 to 10
12
&OHgr;/□.
Preparations of polythiophenes as they are described in DE-OS 42 11 459, EP-A 339 340 and EP-A 440 957 are preferably used as conductive layers. They contain polythiophene salts of the polythiophene
m+
An
m−
({circumflex over (=)} polyanion) type, wherein the polythiophene ca
Guntermann Udo
Mager Michael
Wussow Klaus
Dawson Robert
Keehan Christopher M.
Matz Gary F.
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