Coating processes – With pretreatment of the base – Heating or drying pretreatment
Reexamination Certificate
2002-07-19
2004-01-27
Cameron, Erma (Department: 1762)
Coating processes
With pretreatment of the base
Heating or drying pretreatment
C427S393500, C427S412100, C528S045000
Reexamination Certificate
active
06682779
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a water-based coating composition for elastomers which is suitable as a friction-reducing coating on elastomeric moldings. More particularly, the invention relates to water-based polyurethane compositions which establish a low coefficient of friction after application to typical elastomeric sealing profiles.
2. Description of the Related Art
There are a number of industrial applications which require elastomers that have to meet a number of requirements. This applies in particular to the sealing of window channels for moving glass parts and glass guide rails for glass windows in vehicles, especially motor vehicles. The elastomers are expected to show high heat resistance and weathering resistance under various climatic conditions. The surface of the elastomers is expected to have a very low friction coefficient, particularly for holding and guiding moving glass windows. The surfaces of the elastomer profiles on which the moving glass slides are normally coated with a film which has improved surface slip towards glass compared with the uncoated elastomer. There are various known processes for improving the surface slip of this coating.
DE-A-3335150 describes a polyurethane coating with beads or other particles embedded in the binder, the beads or other particles being larger than the layer thickness of the binder. These so-called “spacers” may be particles of glass, aluminium, polypropylene or polyvinyl chloride. A basic disadvantage of this procedure is that the peak and trough structure of the spacer-containing paint does not provide for optimal sealing so that unwelcome noise-creating drafts are able to penetrate. Another disadvantage is that the surface of the elastomer profiles thus coated is neither smooth nor glossy to the eye, but instead looks like emery cloth.
Another process which is described in U.S. Pat. No. 4,572,872 and U.S. Pat. No. 4,572,871 comprises adding silicones or fluororesins to a friction-reducing paint. Paints such as these have the disadvantage that, under extreme weather conditions, such as heat cold, wind and rain, to which the elastomer profile is normally exposed, the added silicones and fluororesins are depleted which results in a reduction in the surface slip of the elastomer profile towards glass and is therefore unwelcome. Another disadvantage is that the silicones are oils which are known to act as release agents. By reason of their characteristic properties, such release agents are dispersed relatively easily and can lead to difficulties, for example at the assembly stage, such as in the bonding and painting of bodywork parts. Accordingly, the use of silicone oils which have not been firmly bound is not welcomed by car manufacturers.
DE-A-3503479 proposes a coating composition containing a polyurethane prepolymer obtained by reacting a hydroxyl-terminated polyester polyol with an organic diisocyanate in a molar NCO:OH ratio of 0.6:1 to 0.95:1, a castor oil polyol and an isocyanate-terminated urethane prepolymer as a friction-reducing film. This coating composition is said also to contain a fluorocarbon resin, a liquid silicone oil and a small quantity of fillers and/or pigments. The coating composition is used in the form of a solution of the binder components in an organic solvent. There is no indication as to whether this binder system can be made up as a single-component system or multicomponent system for the user.
EP-A-655488 describes a urethane-resin-based coating composition for reducing friction which comprises a polyurethane paint containing a polyol and an isocyanate hardener and a polymeric powder of 11-nylon and/or 12-nylon with a melting point below the vulcanization temperature and a solubility parameter greater by at least 0.5 than the solubility parameter of the urethane paint. The polymeric powder is said to have a mean diameter of 5 to 500 &mgr;m. Again, there is no indication as to whether the coating compositions in question can be formulated as storage-stable one-component systems.
U.S. Pat. No. 5,558,741 describes a process for the production of a window sealing profile in which the elastomeric sealing profile is extruded and the surface of the elastomeric sealing profile is then exposed for 0.5 to 60 seconds to a UV radiation of about 0.2 to 40 joules. The surface thus treated is then coated with a friction-reducing coating consisting of a resin binder and a lubricating pigment. Fluorocarbon polymers, such as PTFE, and silicone lubricants are mentioned as preferred lubricants. The binder is not described in detail, but is merely said to be obtainable from Acheson Industries Inc. under the name of “EMRALON”.
DE-A-19608057 describes a water-dilutable sealing strip coating comprising a two- or three-component system containing a silicone emulsion base, a composition based on a polyurethane dispersion which extends the life of the bath and a crosslinker composition based on a silicone-like or non-silicone-like organic epoxy resin which preferably also contains an organic solvent.
DE-A-19520278 describes one- or two-component urethane paints for coating elastomers containing polyurethane prepolymers with on average two or more isocyanate groups per molecule which are prepared by mixing alcohols having a functionality of two or higher with an excess of isocyanate compounds having a functionality of two or higher and solvent and which contain an extremely large quantity of a compound containing iron oxide for improving surface slip.
EP-A-0375923 describes moisture-curing one-component polyurethane paints for coating elastomers containing polyurethane prepolymers with on average two or more isocyanate groups per molecule which are prepared by mixing alcohols having a functionality of two or higher with an excess of isocyanate compounds having a functionality of two or higher and solvents, reactive polysiloxanes and reactive surfactants being used for improving surface slip. The surfactants are compounds containing a perfluorinated alkyl group with 6 to 12 carbon atoms and a non-fluorinated hydrophilic group with a group reactive to isocyanate-terminated paint ingredients. The paints in question may preferably contain other auxiliaries such as, for example, retarders, accelerators, stabilizers and pigments. However, they may only be applied as very thin films.
The problem addressed by the present invention was to provide one-component water-based coating compositions for coating elastomers which would enable the elastomer profile to be satisfactorily coated and, at the same time, would establish a very low coefficient of friction. In addition, the coatings would show improved abrasion resistance and media resistance in relation to the prior art.
The solution to this problem is defined in the claims and consists essentially in the provision of a suitable polyurethane paint composition containing an effective agent for improving surface slip behavior.
BRIEF SUMMARY OF THE INVENTION
Accordingly, the present invention relates to water-based one-component polyurethane paint compositions for coating elastomers which contain at least one aqueous polyurethane dispersion, a compound containing blocked isocyanate groups, an agent for improving surface slip (friction coefficient), at least one wetting and flow control agent and optionally typical coupling agents, dyes and/or pigments.
The present invention also relates to a process for improving the surface slip of elastomer surfaces, characterized by the following key steps:
optionally cleaning the elastomer surface,
optionally applying a layer of coupling agent to the elastomer surface,
coating the elastomer surface with a composition containing at least one aqueous polyurethane dispersion, a compound containing blocked isocyanate groups, an agent for improving surface slip, at least one wetting and flow control agent and other auxiliaries and additives, coating being carried out by dipping the elastomer profiles in or spraying them with the composition,
drying the elastomer profile for 0.5 to 15 minutes
Hemel Richard
Wefringhaus Rainer
Cameron Erma
Harper Stephen D.
Henkel Kommanditgesellschaft auf Aktien
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