Brushing – scrubbing – and general cleaning – Attachments – Optical-member-attachable cleaner
Reexamination Certificate
1995-11-08
2001-11-06
Graham, Gary K. (Department: 1744)
Brushing, scrubbing, and general cleaning
Attachments
Optical-member-attachable cleaner
C015S245000, C428S325000, C428S331000, C428S336000, C428S422000, C428S447000, C428S451000, C264S130000, C264S241000, C264S255000, C264S340000
Reexamination Certificate
active
06311364
ABSTRACT:
FIELD OF THE INVENTION
This invention relates generally to silicone rubber windshield wipers, and is more particularly concerned with novel wipers having an unique combination of low coefficient of friction and long service life and with a new method for producing them.
BACKGROUND OF THE INVENTION
The windshield wiper has long been an attractive subject for development efforts, particularly to improve operating characteristics and cleaning effectiveness over extended periods. The demand for a better combination of high performance and long service life, however, remains unsatisfied. Incremental gains toward that goal have been made but always at the expense of significant penalty. Recently the trend has been toward the use of new materials of fabrication, silicone rubber attracting considerable attention in spite of its well-known high coefficient of friction characteristic because of its noted durability and utility over a broad range of operating conditions. To bring the silicone rubber friction coefficient down to a reasonable and acceptable level for windshield wiper purposes, others have added various materials in compounding it. Also attempts have been made to coat or cover silicone wiper blades with low friction coefficient materials such as Teflon
T
plastic or other elastomeric tetrafluoroethylene polymer having similar properties. In all instances, however, either the desired friction coefficient was not reached or the service life was considerably less than required because of rapid loss of the covering material.
SUMMARY OF THE INVENTION
This invention, which is based upon my discoveries and new concepts set out below, provides the solution to this long standing problem. Thus, both coefficient of friction and service life requirements can be met consistently. Moreover, this new result does not entail any substantial cost penalty or other offsetting disadvantage.
In making this invention, I discovered that it is possible to gain the low coefficient of friction property of Teflon plastic without sacrificing the long service life of the silicone rubber substrate. This I found on turning away from covering the windshield wiper wiping surface with Teflon plastic films or sheets sprayed or brushed on or adhesively attached, which do not last nearly long enough. Instead I subjected the silicone rubber wiper blade to pressure in a heated mold with Teflon plastic cover material in contact with the wiper. The plastic was sunk or embedded to substantial extent in the surface region of the silicone rubber wiper blade. Surprisingly, this novel product proved to have a coefficient of friction of 0.2, which it retained under conditions of normal use for an acceptably long time.
Following that course, I shortly later conceived the idea of making this new wiper blade by coating the inside wall of the wiper blade mold with the Teflon plastic material. I found that a uniform coating of Teflon plastic can thereby be transferred to the silicone rubber substrate as a coating of essentially uniform thickness embedded to the extent of up to about half its thickness in the silicone rubber blade. Then I found, surprisingly, that consistently good results can be gained by providing a “permanent” elastomeric polytetrafluoroethylene coating to the mold interior surface and then overcoating with Teflon plastic or equivalent and removing the molded silicone rubber windshield wiper blade after the overcoating has been securely bonded to the blade. The separation of the blade product from the mold permanent coating is clean and complete along the coating-overcoating interface and the permanent coating is therefore reusable many times without significant wear or loss of surface quality.
As an alternative the Teflon plastic or other equivalent plastic may be applied by brushing, spraying or otherwise depositing on the silicone rubber substrate prior to placing it in the windshield wiper mold. An important consideration in the practice of this invention is pressure at temperature sufficient to force the Teflon plastic into the surface of the silicone rubber.
It was not at all expected that such a great increase in wear of the plastic cover on a silicone windshield wiper in these various ways, can be gained in this manner. This may result in or involve a chemical reaction between the silicone rubber and the Teflon plastic, but it does not appear that a physical admixture results or accounts for the tenacious adherence of the Teflon plastic in the surface region of the substrate where it exerts its lubricating effect for very much longer than the Teflon plastic covers applied in accordance with the prior art described above. The bonding that results is weld-like in form and effect whatever reason—chemical, physical or both—may be.
Further in accordance with my new concepts involved here, other materials than Teflon plastic and like tetrafluoroethylene polymer elastomers may be used to gain the new advantages and results of this invention. The criteria for selection of such materials are compatibility with the silicone rubber, coefficient of friction matching that of Teflon plastic and tenacious attachment of the coating or covering material in the surface region of the silicone rubber body.
Briefly, then, in its method aspect the present invention comprises the steps of forming a silicone rubber windshield wiper blade, applying a layer of tetrafluoroethylene polymer to the blade and pressing the assembly together and thereby forcing the polymer layer into the blade surface to a depth of at least 0.001 mil. In preferred practice the three steps are carried out simultaneously and the tetrafluoroethylene polymer is provided in the form of a coating on the inside surface of a mold in which the wiper blade is formed.
Likewise stated in essence, a silicone rubber windshield wiper blade of this invention has a basic blade portion to bear against a windshield surface to serve the clearing or cleaning purpose, the basic blade portion carrying a layer of tetrafluoroethylene polymer embedded in its surface region and exposed for wiping contact with a windshield surface.
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Graham Gary K.
Schmeiser Olsen & Watts
Specialty Silicone Products, Inc.
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