Stock material or miscellaneous articles – Coated or structually defined flake – particle – cell – strand,... – Rod – strand – filament or fiber
Reexamination Certificate
2001-06-21
2003-09-23
Kelly, Cynthia H. (Department: 1774)
Stock material or miscellaneous articles
Coated or structually defined flake, particle, cell, strand,...
Rod, strand, filament or fiber
C428S375000, C526S319000, C174S1100PM
Reexamination Certificate
active
06623855
ABSTRACT:
FIELD OF INVENTION
The present invention relates generally to ethylene-vinyl acetate (“EVA”) copolymers, and more specifically, to EVA copolymer waxes having a unique combination of properties that find advantage in a variety of applications, particularly, as to highly strippable wire sheathing for insulated electrical conductors.
BACKGROUND OF THE INVENTION
Ethylene-vinyl acetate copolymer waxes find use in a wide variety of commercial applications and are of particular interest in the manufacture of coatings and/or films capable of adhering to various substrates. For example, because EVA waxes tend to exhibit relatively strong adhesive properties, such waxes have been added to plastic sheathing compositions to form wire sheaths that adhere with relatively high strength to the wire cores of insulated electrical conductors.
However, in addition to adhering strongly to substrates, it is often both desirable and advantageous in many applications to form coatings and/or films that are readily removable from a substrate with a minimum amount of force. In the wire sheathing industry, for example, it is often desirable to have sheaths which can be readily removed, or “stripped”, to allow easy access to the conductive core for making electrical contact with the wires. See, for example, U.S. Pat. No. 6,013,202, which is incorporated herein by reference.
Unfortunately, as has been long recognized in the art, the use of traditional EVA waxes in wire sheathing applications has been problematic. More particularly, prior EVA waxes tend to form coatings requiring an undesirably high level of force to remove them from substrates. See, for example, U.S. Pat. No. 6,013,202. This is disadvantageous in that applications requiring removal of prior art coatings and films result in an increase in the amount of work required to perform removal applications and the costs associated therewith. Recognizing these and other drawbacks, applicants have developed the present invention, in part, to overcome the drawbacks of the prior art.
SUMMARY OF THE INVENTION
The present invention relates to novel EVA copolymers which find particular use and offer numerous advantages in the manufacture of removable coatings and films, including wire sheathing. For example, the preferred EVA copolymer waxes of the present invention can be added to plastic sheathing compositions used to form sheaths which not only adhere sufficiently to wires, but can also be advantageously removed from the wire core using less force than has been heretofore required to remove traditional wire sheaths. The present invention thus produces products which are capable of reducing the effort associated with making electrical connections in the field and which tend to reduce the costs associated therewith. In addition, the waxes of the present invention can be used as simple “drop-in” replacements for traditional EVA waxes. That is, in certain applications, the present waxes can be readily substituted for traditional EVA waxes in sheathing compositions without the need for modification of existing equipment or requalification of existing products.
According to certain preferred embodiments, the present invention provides an EVA copolymer comprising at least about 10% by weight of at least one moiety derived from vinyl acetate, the copolymer having a polydispersity (“Mw/Mn”) of at least about 6 and a molecular weight (“Mw”) of from about 15,000 to about 40,000.
In certain other preferred embodiments, the present invention provides a substrate coating composition comprising an EVA copolymer comprising at least about 10% by weight of at least one moiety derived from vinyl acetate, the copolymer having a polydispersity (“Mw/Mn”) of at least about 6 and a molecular weight (“Mw”) of from about 15,000 to about 40,000.
The present invention further provides a film comprising an EVA copolymer wax comprising at least about 10% by weight of at least one moiety derived from vinyl acetate, the copolymer having a polydispersity (“Mw/Mn”) of at least about 6 and a molecular weight (“Mw”) of from about 15,000 to about 40,000.
Additionally, the present invention provides an insulated electrical conductor comprising a conductive core and an insulating sheath substantially surrounding the core, said sheath comprising an EVA copolymer wax comprising at least about 10% by weight of moieties derived from vinyl acetate, the copolymer wax having a Mw/Mn of at least about 6 and a Mw of from about 15,000 to about 40,000.
DETAILED DESCRIPTION OF INVENTION AND PREFERRED EMBODIMENTS
The preferred ethylene-vinyl acetate copolymer waxes of the present invention are formed by the copolymerization of ethylene and vinyl acetate monomers. As used herein, the term “wax” refers generally to oligomeric polymer compounds having the following properties: (a) solid at room temperature; (b) low melting point; and (c) insoluble in water. An “EVA copolymer wax” or “EVA wax”, as used herein, refers generally to oligomeric polymer compounds having the aforementioned properties that are prepared via a process comprising the co-polymerization of ethylene monomers and vinyl acetate monomers.
In general, the present copolymer waxes comprise at least 10% by weight of at least one moiety derived from vinyl acetate, based on the total weight of the EVA copolymer. EVA waxes comprising less than about 10 weight % of vinyl acetate typically do not exhibit the unexpected and beneficial properties associated with the polymers of the present invention.
In certain preferred embodiments, the EVA copolymer waxes of the present invention comprise from about 10 to about 40 wt % of at least one moiety derived from vinyl acetate, in more preferred embodiments from about 11 to about 30 wt %, and even more preferably, from about 12 to about 25 wt %.
The number average molecular weight (“Mn”) of the EVA copolymers of the present invention preferably ranges from about 1,500 to about 3,100, as measured using known Gel Permeation Chromatography (“GPC”) methods. More, preferably, the Mn is from about 1,800 to about 2,800, and even more preferably from about 1,900 to about 2,700. Methods for determining Mn, including GPC methods, are known to those of skill in the art.
The weight average molecular weight (“Mw”) of the present EVA copolymers preferably ranges from about 15,000 to about 40,000, as measured using known Gel Permeation Chromatography (“GPC”) methods. More preferably, the Mw is from about 20,000 to about 35,000, and even more preferably from about 25,000 to about 30,000. Methods for determining Mw, including GPC methods, are known to those of skill in the art.
The EVA copolymers of the present invention have a relatively high polydispersity index. As used herein, the term “polydispersity index” refers generally to the ratio of weight average molecular weight to number average molecular weight (“Mw/Mn”) of an EVA copolymer wax. This ratio, as will be understood by those of skill in the art, describes and is related to the molecular weight distribution of a polymer. A higher ratio indicates a broader distribution of molecular weights, while a lower ratio indicates a narrower distribution. Preferably, the copolymers of the present invention have a polydispersity index of at least about 6, more preferably, of from about 7 to about 20, and even more preferably of from about 7 to about 16.
The melt viscosity of the EVA copolymer waxes of the present invention is preferably from about 500 to about 1600 centipoise (“cps”) at 140° C. as measured using a Brookfield Viscometer. Preferably, the melt viscosity is from about 550 to about 1400 cps at 140° C., and even more preferably from about 600 to about 1300 cps at 140° C.
The EVA copolymers of the present invention preferably have a hardness of from about 5 deci-millimeters (“dmm”) to about 30 dmm as measured via ASTM D-5 for petroleum waxes. Preferably, the copolymers have a hardness of from about 6 dmm to about 25 dmm, and more preferably from about 7 dmm to about 25 dmm.
The Mettler drop points of the copolymer waxes of the present invention preferably range from
Gray J. M.
Honeywell International , Inc.
Jacobson Scott D.
Kelly Cynthia H.
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