Stock material or miscellaneous articles – Composite – Of epoxy ether
Reexamination Certificate
2002-01-04
2004-05-18
Tarazano, D. Lawrence (Department: 1773)
Stock material or miscellaneous articles
Composite
Of epoxy ether
C428S414000, C428S419000, C428S522000, C428S520000, C428S447000
Reexamination Certificate
active
06737162
ABSTRACT:
FIELD OF THE INVENTION
The invention concerns a transparent plastics molding and more particularly a molding carrying a heat absorbing coating and a scratch-resistant coating.
SUMMARY OF THE INVENTION
Transparent moldings comprising a polymeric base material and at least one coating formed thereon is disclosed. The coating includes a primer coat that containing an epoxy and/or acrylic resin is disposed on at least one surface of the base material, a heat-absorbing coating which contains a polythiophene compound and a scratch-resistant coating. In an additional embodiment of the invention, the coating contains no primer and the heat absorbing coating contains a polythiophene compound.
BACKGROUND OF THE INVENTION
It is known that coatings which absorb infrared light can be used to reduce the heat-up of plastics and composite glass sheets or panes by solar radiation. Thin coatings of polythiophene or of soluble polythiophene salts have proved particularly effective in this regard.
In order to produce light-absorbing composite glass sheets such as these, aqueous/alcoholic solutions of polythiophenes, mostly in admixture with a silane-based bonding agent, are deposited on a transparent glass sheet and the solvent is evaporated at room temperature. The dry thickness of the coating is about 0.2 &mgr;m. To produce a composite glass sheet, the glass sheet is pressed with a polyvinylbutyral film and a further glass sheet at 145° C./10 bar. Heat-absorbing composite glass sheets are known from DE 42 26 757 A1, for instance.
Moreover, DE 41 29 282 A1 discloses that transparent plastics sheets of polycarbonate or polymethyl methacrylate can be coated with polythiophenes for thermal insulation, and can optionally be provided with an acrylate- or polyurethane-based protective coating. This specification gives an example of a polycarbonate to which a solvent-containing primer based on polyvinyl acetate is first applied, followed by drying of the primer and the application of a solvent-containing coating of 3,4-ethylene dioxythiophene and volatilization of the solvent. The polycarbonate film which is coated in this manner exhibits infrared-absorbing properties.
Whilst the production of heat-absorbing composite glass sheets described above has become a process which is commonly used in industry, the corresponding coating of plastics glass sheets has proved to be extraordinarily difficult in practice. In particular, the known substances for the formation of infrared absorbing coatings, such as the material which is marketed for this purpose by Bayer AG under the trade name Baytron®, cannot be satisfactorily applied on plastics as they can on glass. Both the wetting of the plastics surface by the latter material and the adhesion thereof to the plastics surface are poor, and give unsatisfactory results. Even the polyvinyl acetate-based primer which is described in DE 41 29 282 A1 and which is disposed between a plastics sheet and a polythiophene coating has proved to be unsatisfactory for ensuring uniform wetting and durable bonding of the polythiophene compound to the plastics surface.
The underlying object of the present invention is thus to provide forms of application for known substances which absorb infrared light on plastics such as polycarbonates and poly(meth)acrylates.
DETAILED DESCRIPTION OF THE INVENTION
This object is achieved according to the invention by a transparent plastics molding comprising a polymeric base material (B) and at least one coating which is formed thereon, wherein a primer coat (G) containing an epoxy and/or acrylic resin is disposed on at least one side of the base material (B), on the surface of which primer coat a heat-absorbing coating (Z) is disposed which contains a polythiophene compound, and a scratch-resistant coating (K) is formed over the intermediate coating (Z).
This object is also achieved according to the invention by a transparent plastics molding comprising a polymeric base material (B) and at least one coating formed thereon, characterized in that a heat-absorbing coating (W), which is obtainable by hardening an aqueous dispersion containing an epoxy and/or acrylic resin and a polythiophene compound, is disposed on at least one side of the base material (B), and a scratch-resistant coating (K) is formed over the heat-absorbing coating (W).
Attempts were made to apply Baytron coatings to polycarbonates, using very different primer and outer coatings. However, it became clear that the UV stability and thermal stability of Baytron were unsatisfactory with regard to the aforementioned problems.
It has now been ascertained that heat-absorbing polythiophene compounds can be bonded surprisingly well into acrylic and/or epoxy resin-based systems, and exhibit excellent compatibility therewith. It has also been ascertained that certain scratch-resistant coatings (K), particularly those based on silanes containing polysiloxanes and epoxide groups, are particularly suitable in combination with polythiophene compounds.
In principle, the plastics molding according to the invention may comprise two different types of coating structure. In a first embodiment of the invention, an acrylic and/or epoxy resin-based primer coat (G) is first applied to a plastics substrate (B) and is hardened. Water-based acrylic or epoxy resin systems, i.e. those with little or no solvent content, are preferred in this respect. A heat-absorbing intermediate coating (Z) which contains a polythiophene compound is then applied to said primer coat (G). This coating composition is also present in the form of an aqueous system, i.e. it has little or no solvent content. After drying, a scratch-resistant coating (K) is applied to the heat-absorbing intermediate coating (Z), and protects the underlying coatings, particularly the intermediate coating (Z) which contains the sensitive polythiophene compound, from mechanical damage and UV radiation.
The molding according to the invention which comprises the coating structure described above is distinguished by uniform wettability of the primer coat (G) by the coating composition for the intermediate coating (Z), which contains a polythiophene compound. It is also distinguished by the outstanding adherence of the individual coatings to each other and by its excellent heat-absorbing properties as measured by TSET (Total Solar Energy Transmission).
According to a second embodiment of the invention, the heat-absorbing coating (W) which contains a polythiophene compound is applied directly, i.e. without a prior primer coat, to the plastics substrate (B). For this purpose, a coating composition which contains an epoxy and/or acrylic resin and a polythiophene compound is applied to the plastics substrate (B) and hardened. It is important here that the coating composition is applied as an aqueous system, e.g. as an aqueous dispersion, since it is only in this manner that a uniform distribution of the polythiophene compound in the acrylic or epoxy resin, as well as good wettability, may be attained. The aqueous dispersion should therefore contain as little solvent as possible, preferably none at all. A scratch-resistant coating (K) is subsequently applied to the heat-absorbing coating (W) which is applied and hardened in this manner, in order to protect the underlying coating from mechanical damage and UV radiation.
The molding according to the invention which comprises the coating structure described above is distinguished by outstanding bonding between the plastics substrate (B) and the heat-absorbing coating (W), by a uniform distribution of the polythiophene compound in the heat-absorbing coating (W), and by its outstanding heat-absorbing properties as measured by TSET (Total Solar Energy Transmission).
The individual components which are suitable for producing moldings according to the invention are described in detail below:
Polymeric Base Material (B)
Substances which are particularly suitable as the polymeric base material (B) are thermoplastic materials such as those which are described, for example, in Becker/Braun, Kunststofftaschenbuch, Carl Ha
Bier Peter
Jonas Friedrich
Peters Mark
Bayer Aktiengesellschaft
Gil Joseph C.
Preis Aron
Tarazano D. Lawrence
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