Stock material or miscellaneous articles – Structurally defined web or sheet – Including aperture
Reexamination Certificate
1995-07-10
2001-03-27
Sweet, Mark D. (Department: 1501)
Stock material or miscellaneous articles
Structurally defined web or sheet
Including aperture
C428S208000, C428S208000, C428S208000, C428S208000, C428S208000
Reexamination Certificate
active
06207251
ABSTRACT:
BACKGROUND OF THE INVENTION
A. Field of the Invention
This invention describes a particle-loaded fibrillated polytetrafluoroethylene web with a reinforcing screen or scrim at least partially embedded therein. Compared to an unreinforced web, this reinforced web can resist a much greater pressure drop across it without deforming and displays greater strength against various mechanical stresses.
B. Description of Related Art
Particle-loaded, non-woven, fibrous articles wherein the non-woven fibrous web can be compressed, fused, melt-extruded, air-laid, spunbonded, mechanically pressed, or derived from phase separation processes have been disclosed as useful in separation science. Web products of non-woven webs having dispersed therein sorbent particulate have been disclosed to be useful as, for example, respirators, protective garments, fluid-retaining articles, wipes for oil and/or water, and chromatographic and separation articles. Coated, inorganic oxide particles have also been enmeshed in such webs. Such webs with enmeshed particles which are covalently reactive with ligands (including biologically-active materials) have also been recently developed.
Numerous examples of PTFE filled with or entrapping particulate material are known in many fields. Many applications for PTFE filled with electroconductive materials are known. These include circuit boards, oil leak sensors, electrical insulators, semipermeable webs, and various types of electrodes. Other such combinations have been used as gasket or sealing materials and wet friction materials. Still others have been used to produce high-strength PTFE films and webs with applications as structural elements and electronic components. Where the particulate has catalytic properties, this type of combination provides a form which can be conveniently handled. U.S. Pat. No. 4,153,661 discloses various particulate distributed in a matrix of entangled PTFE fibrils as being useful in, among other things, electronic insulators and semipermeable webs.
Numerous combinations of PTFE and metals in which the metal is not entrapped within a PTFE matrix are also known. These include PTFE webs completely or partially coated with metal and metal matrices with a network of fibrillated PTFE in the pores thereof. PTFE powder with metal filler has been used (in paste form) as a battery electrode and as a self-lubricating layer coated on bronze bearings. PTFE films coated onto metal films and plates are also known.
Methods of preparing fibrillated PTFE webs have been described in, for example, U.S. Pat. Nos. 4,153,661, 4,460,642, and 5,071,610.
The physical properties of such particle-loaded fibrillated PTFE webs are somewhat limited, however. They do not resist high pressure drops without deforming and have limited strength against mechanical stresses created by, for example, fluid flow, tensile force, mechanical impact, and abrasion.
SUMMARY OF THE INVENTION
In one aspect, the present invention provides a composite article, preferably a separation science medium, comprising a fibrillated polytetrafluoroethylene (PTFE) web having particulate entrapped therein and, at least partially embedded in the web, means for reinforcing the web. Preferably, this reinforcing means is a screen or scrim. The web, the reinforcing means, and the overall article are all liquid permeable.
In another aspect, the present invention provides a method for making this article comprising the steps of providing a fibrillated PTFE web with particulate entapped therein and pressure bonding to the web a means for reinforcing the web so that the reinforcing means is at least partially embedded in the web.
Unless otherwise indicated, the following definitions apply in this application:
“screen” means a reinforcing material with a regular geometric pattern of threads which can be polymeric, glass, metallic, etc.;
“scrim” means a non-woven web the fibers of which are not in a regular geometric pattern and which can be polymeric, glass, metallic, etc.; and
“partially embedded” (when used in connection with a reinforcing means) means the reinforcing means is (a) at least partially depressed in the web to which it has been pressure bonded so that the reinforced web, when viewed from an edge, shows only up to 95%, preferably up to 90%, more preferably up to 75%, and most preferably up to 50%, of the reinforcing means and (b) at least partially mechanically entangled with the web.
Embedding a reinforcing means in a fibrillated PTFE web provides the web with mechanical strength and resistance to deformation when a pressure drop is applied across it. Use of such a reinforcing means also allows the web to be formed into configurations that were previously difficult, if not impossible to achieve. For example, such reinforced webs can be pleated, whereas unreinforced webs suffer catastrophic damage when pleating is attempted.
The reinforcing means used in the composite article of the present invention is at least somewhat porous, preferably very porous (i.e., at least 50% voids), so as not to greatly interfere with the porosity of the fibrillated PTFE web. This reinforcing means is at least partially embedded in the fibrillated PTFE web. The PTFE fibrils appear to actually attach to or become mechanically entangled with the reinforcing means. This is further illustrated by reference to the drawings described below.
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Balsimo William V.
White Lloyd R.
Burleson David G.
Griswold Gary L.
Kirn Walter N.
Minnesota Mining and Manufacturing Company
Sweet Mark D.
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