United States Patent: 6,500,540 
    
  
 
 
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      United States Patent 6,500,540 
      Langohr ,   et al. December 31, 2002 

Articles having elevated temperature elasticity made from irradiated and 
crosslinked ethylene polymers and method for making the same 

Abstract
The present invention relates to elastic articles comprising a crosslinked or 
crosslinkable ethylene polymer and a method for making the same. In particular, 
the invention relates to a shaped article (e.g. film or fiber) characterized by 
improved elasticity at elevated temperatures and comprising a substantially 
cured, irradiated, or crosslinked (or curable, irradiated or crosslinkable) 
homogeneously branched ethylene polymer. The improved elastic article of the 
present invention is particularly suitable for use in applications where good 
elasticity must be maintained at elevated temperatures such as, for example, 
personal hygiene items and disposable infection-control garments at body 
temperatures of about 100.degree. F. (38.degree. C.). 

      Inventors: Langohr; Michael F. (Lake Jackson, TX); Bensason; Selim 
      (Houston, TX); Patel; Rajen M. (Lake Jackson, TX); Martin; Jill M. (Lake 
      Jackson, TX); Ho; Thoi H. (Lake Jackson, TX); Schrock; Nancy J. (Lake 
      Jackson, TX) 
      Assignee: The Dow Chemical Company (Midland, MI) 
      Appl. No.: 313740
      Filed: May 18, 1999

      Current U.S. Class:428/364; 428/394; 525/342; 525/343 
      Intern'l Class: D02G 003/00; C08C 019/20
      Field of Search: 525/342,393 428/364,394 

References Cited [Referenced By]

U.S. Patent Documents
      5824718Oct., 1998Penfold et al.522/120. 
      Foreign Patent Documents
      94/25515Nov., 1994WO. 
      95/29197Nov., 1995WO. 
      97/26297Jul., 1997WO. 
      98/26001Jun., 1998WO. 
      99/10395Mar., 1999WO. 

Primary Examiner: Kelly; Cynthia H. 
Assistant Examiner: Gray; J. M. 

Parent Case Text

CROSS-REFERENCE TO RELATED APPLICATION 

This application claims the priority benefit of provisional application number 
60/086059, field May 18, 1998, now abandoned the disclosure of which is 
incorporated herein by reference in its entirety. 

Claims

We claim: 

1. A heat-resistant, shaped, irradiated and crosslinked article free of a silane 
crosslinker, and comprising an ethylene interpolymer of ethylene 
interpolymerized with at least one other monomer and characterized as having: 

a) an interpolymer density of less than 0.89 g/cm.sup.3 or a DSC crystallinity 
at 23.degree. C., as determined using differential scanning calorimetry, of less 
than about 26 weight percent before being shaped, irradiated and crosslinked, 
and 

b) xylene extractables of less than or equal to about 70 weight percent. 

2. The article of claim 1 wherein the ethylene interpolymer is a homogeneously 
branched ethylene polymer. 

3. The article of claim 2, wherein the homogeneously branched ethylene polymer 
is a homogeneously branched linear ethylene polymer. 

4. The article of claim 3, wherein the homogeneously branched linear ethylene 
polymer is characterized as having a single differential scanning calorimetry, 
DSC, melting peak between -30.degree. and 150.degree. C. 

5. The article of claim 2, wherein the homogeneously branched ethylene polymer 
is a substantially linear ethylene polymer characterized as having 

(a) melt flow ratio, I.sub.10 /I.sub.2.gtoreq.5.63, 

(b) a molecular weight distribution, M.sub.w /M.sub.n, as determined by gel 
permeation chromatography and defined by the equation: 

(M.sub.w /M.sub.n).ltoreq.I.sub.10 I.sub.2)-4.63, 

(c) a gas extrusion rheology such that the critical shear rate at onset of 
surface melt fracture for the substantially linear ethylene polymer is at least 
50 percent greater than the critical shear rate at the onset of surface melt 
fracture for a linear ethylene polymer, wherein the substantially linear 
ethylene polymer and the linear ethylene polymer comprise the same comonomer or 
comonomers, the linear ethylene polymer has an I.sub.2 and M.sub.w /M.sub.n 
within ten percent of the substantially linear ethylene polymer and wherein the 
respective critical shear rates of the substantially linear ethylene polymer and 
the linear ethylene polymer are measured at the same melt temperature using a 
gas extrusion rheometer, and 

(d) a single differential scanning calorimetry, DSC, melting peak between 
-30.degree. and 150.degree. C. 

6. A heat-resistant, shaped, irradiated and crosslinked article free of a silane 
crosslinker and comprising an ethylene interpolymer of ethylene interpolymerized 
with at least one other monomer and characterized as having an interpolymer 
density of less than 0.87 g/cm.sup.3 or a DSC crystallinity at 23.degree. C., as 
determined using differential scanning calorimetry, of less than about 12 weight 
percent before being shaped, irradiated and crosslinked. 

7. A heat-resistant, shaped and elastic article free of a silane crosslinker and 
which comprises at least one ethylene interpolymer which has been irradiated and 
crosslinked wherein the interpolymer comprises ethylene interpolymerized with at 
least one other monomer and is characterized as having: 

(a) an interpolymer density of less than or equal to 0.89 g/cm.sup.3 or a DSC 
crystallinity at 23.degree. C., as determined using differential scanning 
calorimetry, of less than about 26 weight percent before being shaped, 
irradiated and crosslinked, 

(b) a percent permanent set of less than 60 at 23.degree. C. and 200 percent 
strain when measured at a 2 mil thickness using an Instron tensiometer after 
being shaped, irradiated and crosslinked, 

(c) a percent stress relaxation of less than or equal 25 at 23.degree. C. and 
200 percent strain when measured at a 2 mil thickness using a Instron 
tensiometer after being shaped, irradiated and crosslinked, and 

(d) a percent stress relaxation of less than or equal 55 at 38.degree. C. and 
200 percent strain when measured at a 2 mil thickness using an Instron 
tensiometer after being shaped, irradiated and crosslinked. 

8. A heat-resistant, shaped, irradiated and crosslinked article free of a silane 
crosslinker, and comprising an ethylene interpolymer of ethylene 
interpolymerized with at least one other monomer and characterized as having: 

a) an interpolymer density of less than 0.89 g/cm.sup.3 or a DSC crystallinity 
at 23.degree. C., as determined using differential scanning calorimetry, of less 
than about 26 weight percent before being shaped, irradiated and crosslinked, 
and 

b) xylene extractables of less than or equal to about 40 weight percent. 

9. A heat-resistant, shaped, irradiated and crosslinked article free of a silane 
crosslinker, and comprising an ethylene interpolymer of ethylene 
interpolymerized with at least one other monomer and characterized as having: 

a) an interpolymer density of less than 0.87 g/cm.sup.3 or a DSC crystallinity 
at 23.degree. C., as determined using differential scanning calorimetry, of less 
than about 12 weight percent before being shaped, irradiated and crosslinked, 
and 

b) xylene extractables of less than or equal to about 70 weight percent. 

10. A heat-resistant, shaped, irradiated and crosslinked article free of a 
silane crosslinker, and comprising an ethylene interpolymer of ethylene 
interpolymerized with at least one other monomer and characterized as having: 

a) an interpolymer density of less than 0.89 g/cm.sup.3 or a DSC crystallinity 
at 23.degree. C., as determined using differential scanning calorimetry, of less 
than about 26 weight percent before being shaped, irradiated and crosslinked, 

b) xylene extractables of less than or equal to about 70 weight percent, and 

c) a heat resistance of greater than 250.degree. C. at both 50 percent and 300 
percent elongation. 

11. The article of any of claims 1-3 and 8-10 in the form of a fiber. 

Description

FIELD OF THE INVENTION 

The present invention relates to a crosslinked, heat resistant elastic article 
having elevated temperature elasticity comprising a cured, irradiated or 
crosslinked ethylene polymer and a method for making a crosslinked, heat 
resistant elastic article. In particular, the invention relates to a shaped 
article (e.g. film or fiber) characterized by heat resistance and improved 
elasticity at elevated temperatures and comprising a substantially cured, 
irradiated, or crosslinked homogeneously branched ethylene polymer. The improved 
elastic article of the present invention is particularly suitable for use in 
applications where good elasticity must be maintained at elevated temperatures 
such as, for example, personal hygiene items and disposable infection-control 
garments at body temperatures of about 100.degree. F. (38.degree. C.). 

BACKGROUND OF THE INVENTION 

Materials with excellent stretchability and elasticity are needed to manufacture 
a variety of disposal and durable articles such as, for example, incontinence 
pads, disposable diapers, training pants, sport apparel and furniture 
upholstery. Stretchability and elasticity are performance attributes which 
function to effectuate a closely conforming fit to the body of the wearer or to 
the frame of the item. It is desirable to maintain the conforming fit during 
repeated use, extensions and retractions at body temperatures. Further, for 
incontinence articles, stretchability and elasticity are particularly desirable 
to ensure comfort and provide security against unwanted leaks. 

Disposable articles are typically elastic composite materials prepared from a 
combination of polymer film, fibers, sheets and absorbent materials as well as a 
combination of fabrication technologies. Whereas the fibers are prepared by well 
known processes such as spun bonding, melt blowing, melt spinning and continuous 
filament wounding techniques, the film and sheet forming processes typically 
involve known extrusion and coextrusion techniques, e.g., blown film, cast film, 
profile extrusion, injection molding, extrusion coating, and extrusion sheeting. 

A material is typically characterized as elastic where it has a high percent 
elastic recovery (i.e., a low percent permanent set) after application of a 
biasing force. Ideally, elastic materials are characterized by a combination of 
three important properties, i.e., a low percent permanent set, a low stress or 
load at strain, and a low percent stress or load relaxation. That is, there 
should be (1) a low stress or load requirement to stretch the material, (2) no 
or low relaxing of the stress or unloading once the material is stretched, and 
(3) complete or high recovery to original dimensions after the stretching, 
biasing or straining is discontinued. 

Lycra (spandex) is a segmented polyurethane elastic material which is known to 
exhibit goodelastic properties. But Lycra tends to be extremely cost prohibitive 
for a many of applications. Also, Lycra like natural rubbers tend to exhibit 
poor environmental resistance to ozone, chlorine and high temperature, 
especially in the presence of moisture. 

Natural rubbers, as discussed by Ferdinand Rodriguez in Principles of Polymer 
Systems, pp. 242-43, McGraw-Hill (1982), the disclosure of which is incorporated 
herein by reference, generally show decreases in elongation to break with 
increase in degree of crosslinking. Furthermore, at high degrees of 
crosslinking, even tenacity at break may decrease for natural rubbers. 

Elastic materials such as films, strips, coating, ribbons and sheet comprising 
at least one substantially linear ethylene polymer are disclosed in U.S. Pat. 
No. 5,472,775 to Obijeski et al., the disclosure of which is incorporated herein 
by reference. But U.S. Pat. No. 5,472,775 does not disclose the performance of 
these materials at elevated temperatures (i.e., at temperatures above room 
temperature). 

WO 94/25647 (Knight et al.), the disclosure of which is incorporated herein by 
reference, discloses elastic fibers and fabrics made from homogeneously branched 
substantially linear ethylene polymers. The fibers are said to posses at least 
50 percent recovery (i.e., less than or equal 50% permanent set) at 100 percent 
strain. But there is no disclosure in WO 94/25647 regarding the elasticity of 
these fibers at elevated temperatures, nor is there any disclosure regarding 
resistance to high temperatures. 

U.S. Pat. No. 5,322,728 to Davey et al., the disclosure of which is incorporated 
herein by reference, discloses elastic fibers comprised of single site catalyzed 
ethylene polymers. But polymers are not cured, irradiated or crosslinked and 
therefore are believed to exhibit poor elevated temperature elasticity. 

WO 95/29197 (Penfold et al.), the disclosure of which is incorporated herein by 
reference, discloses curable, silane-grafted substantially ethylene polymers 
which are useful for use in wire and cable coatings, weather-stripping and 
fibers. WO 95/29197 reports examples which include fibers comprising 
silane-grafted substantially ethylene polymers having densities of 0.868 
g/cm.sup.3 and 0.870 g/cm.sup.3. While example fibers are shown to exhibit 
improved elastic recovery at elevated temperatures, there is no disclosure 
regarding percent stress or load relaxation performance at elevated 
temperatures. 

U.S. Pat. No. 5,324,576 to Reed et al., the disclosure of which is incorporated 
herein by reference, discloses an elastic nonwoven web of microfibers of 
radiation crosslinked ethylene/alpha olefin copolymers, preferably having a 
density less than 0.9 g/cm.sup.3. The examples reported in U.S. Pat. No. 
5,324,576 comprise ethylene polymers having polymer densities greater than or 
equal to 0.871 g/cm.sup.3 which subjected to electron beam radiation. But Reed 
et al. provide no disclosure regarding the elastic performance of these radiated 
polymers at elevated temperatures. 

U.S. Pat. No. 5,525,257 to Kurtz et al., the disclosure of which is incorporated 
herein by reference, discloses that low levels of irradiation of less than 2 
megarads of Ziegler catalyzed linear low density ethylene polymer results in 
improved stretchability and bubble stability without measurable gelation. 

U.S. Pat. No. 4,425,393 to Benedyk et al., the disclosure of which is 
incorporated herein by reference, discloses low modulus fibers having diameters 
in the range of 0.5 to 3 mils (about 1 to about 37 denier). 

Canadian Patent No. 935,598 to Hardy et al., the disclosure of which is 
incorporated herein by reference, discloses elastic fibers comprised of various 
ethylene polymers wherein the fibers are post-drawn (stretched) and crosslinked 
while under tension. 

U.S. Pat. No. 4,957,790 to Warren, the disclosure of which is incorporated 
herein by reference, discloses the use of pro-rad compounds and irradiation to 
prepare heat-shrinkable linear low density polyethylene films having an 
increased orientation rate during fabrication. In the examples provided therein, 
Warren employs Ziegler catalyzed ethylene polymers having densities greater than 
or equal to 0.905 g/cm.sup.3. 

In spite of various disclosures relating to elastic ethylene polymer articles, 
including articles comprising curable, radiated and/or crosslinked ethylene 
polymers, there is a present need for cost-effective elastic articles having 
good heat resistance and elasticity at elevated temperatures, especially at 
human body temperatures of about 100.degree. F. There is also a need for a 
method of making elastic articles having good elasticity at elevated 
temperatures. We have discovered that these and other objects can be completely 
met by the invention herein described. 

SUMMARY OF THE INVENTION 

We have discovered that elastic articles comprising a substantially cured, 
radiated or crosslinked ethylene polymer wherein the polymer is characterized as 
having a polymer density of less than 0.89 g/cm.sup.3, especially less than 0.87 
g/cm.sup.3 and most especially less than or equal to 0.865 g/cm.sup.3 (or a 
differential scanning calorimetry (DSC) crystallinity at 23.degree. C. of less 
than 26weight percent, especially 12 weight percent, and most especially less 
than or equal to 8.5 weight percent). These novel articles exhibit excellent 
elasticity at room temperature and at elevated temperatures. 

The broad aspect of the invention provides a heat resistant, shaped cured, 
irradiated or crosslinked article comprising an ethylene interpolymer of 
ethylene interpolymerized with at least one other monomer and characterized as 
having: 

a) a polymer density of less than 0.89 g/cm.sup.3 or a DSC crystallinity at 
23.degree. C., as determined using differential scanning calorimetry, of less 
than 26 weight percent before being shaped, cured, irradiated or crosslinked and 

b) in meltspun fiber form, a value less than 0.75 for the expression 

Abs[.DELTA.E/E.sub.0 ]+Abs[.DELTA.T/T.sub.0 ] 

where .DELTA.E and .DELTA.T are taken from a stress-strain plot, as determined 
using an Instron tensiometer at 500 mm/minute crosshead speed and 10.2 cm gage 
length and from the average of four replications of five fiber samples; .DELTA.E 
is taken as the difference in percent elongation between the cured, irradiated 
or crosslinked polymer and the uncured, irradiated or uncrosslinked interpolymer 
at a tenacity of 0.4 grams/denier; E.sub.0 is taken as the percent elongation of 
the uncured, irradiated or uncrosslinked interpolymer at a tenacity of 0.4 
grams/denier; .DELTA.T is taken as the difference in tenacity (in grams/denier) 
between the cured, irradiated or crosslinked polymer and the uncured, irradiated 
or uncrosslinked polymer at a percent elongation of 300 percent; T.sub.0 is 
taken as the tenacity (in grams/denier) of the uncured, irradiated or 
uncrosslinked interpolymer at a percent elongation of 300 percent; and Abs 
denotes absolute value. 

Another aspect of the invention is a heat resistant cured, irradiated or 
crosslinked elastic fiber comprising ethylene interpolymerized with at least one 
other monomer wherein the interpolymer is characterized as having: 

a) polymer density of less than 0.89 g/cm.sup.3 or a crystallinity at 23.degree. 
C., as determined using differential scanning calorimetry, of less than 26 
weight percent before being shaped, cured, irradiated or crosslinked and 

b) in meltspun fiber form, a value less than 0.75 for the expression 

Abs[.DELTA.E/E.sub.0 ]+Abs[.DELTA.T/T.sub.0 ] 

where .DELTA.E and .DELTA.T are taken from a stress-strain plot, as determined 
using an Instron tensiometer at 500 mm/minute crosshead speed and 10.2 cm gage 
length and from the average of four replications of five fiber samples; .DELTA.E 
is taken as the difference in percent elongation between the cured, irradiated 
or crosslinked polymer and the uncured, irradiated or uncrosslinked interpolymer 
at a tenacity of 0.4 grams/denier; E.sub.0 is taken as the percent elongation of 
the uncured, irradiated or uncrosslinked interpolymer at a tenacity of 0.4 
grams/denier; .DELTA.T is taken as the difference in tenacity (in grams/denier) 
between the cured, irradiated or crosslinked polymer and the uncured, irradiated 
or uncrosslinked polymer at a percent elongation of 300 percent; T.sub.0 is 
taken as the tenacity (in grams/denier) of the uncured, irradiated or 
uncrosslinked interpolymer at a percent elongation of 300 percent; and Abs 
denotes absolute value. 

A third aspect of the invention is a heat resistant shaped elastic article which 
comprises at least one ethylene interpolymer which has been cured, irradiated or 
crosslinked wherein the interpolymer comprises ethylene interpolymerized with at 
least one other monomer and is characterized as having: 

(a) a polymer density of less than 0.87 g/cm.sup.3 before being shaped, cured, 
irradiated or crosslinked, 

(b) a percent permanent set of less than or equal 25 at 23.degree. C. and 200 
percent strain when measured at a 2 mil thickness using an Instron tensiometer 
after being shaped, cured, irradiated or crosslinked, 

(c) a percent stress relaxation of less than or equal 25 at 23.degree. C. and 
200 percent strain when measured at a 2 mil thickness using a Instron 
tensiometer after being shaped, cured, irradiated or crosslinked, and 

(d) a percent stress relaxation of less than or equal 55 at 38.degree. C. and 
200 percent strain when measured at a 2 mil thickness using an Instron 
tensiometer after. 

A fourth aspect of the invention is a method of making an elastic article 
comprising the steps of 

(a) providing an ethylene interpolymer having a density of less than 0.87 
g/cm.sup.3, 

(b) fabricating the article from the interpolymer, and 

(c) after the fabrication, subjecting the article to heat or ionizing radiation 
or both. 

A fifth aspect of the invention is a method of making an elastic article 
comprising the steps of 

(a) providing an ethylene interpolymer having a density of less than 0.87 
g/cm.sup.3, 

(b) incorporating a pro-rad crosslink additive into the interpolymer, 

(c) fabricating the article from the interpolymer, and 

(d) after fabrication, subjecting the article to heat or ionizing radiation or 
both. 

Preferably, the article is fabricated using an extrusion technique (i.e., the 
method consists of melting the interpolymer). Suitable extrusion techniques 
include, but are not limited to, fiber melt spinning, fiber melt blowing, film 
blowing, cast film, injection molding, or rotomolding technique. Preferably, the 
extrudate, filament, web or part is permitted to cool or is quenched to ambient 
temperature (i.e., permitted to substantially solidify) before the application 
of additional heating or ionizing radiation. 

In a preferred embodiment of the invention, the ethylene polymer is a 
homogeneously branched ethylene polymer, especially a substantially linear 
ethylene polymer. In another preferred embodiment, the ionizing radiation is 
provided by electron beam irradiation. 

We discovered that (unlike natural rubbers) curing, irradiation or crosslinking 
(increased crosslink densities) do not decrease the elongation at break or 
tenacity at break for homogeneously branched ethylene polymers having a polymer 
density of less than 0.89 g/cm.sup.3 and that articles (especially fibers) of 
cured, irradiated or crosslinked-homogeneously branched ethylene polymers 
exhibit substantially improve heat resistance. 

We also discovered that there is a subset of ethylene polymers which provide 
completely unexpected elastic performance results when cured, radiated or 
crosslinked. In particular, we found for the broad range of polymer densities 
above and below 0 0.87 g/cm.sup.3, curing, radiation or crosslinking 
dramatically decrease percent permanent set performance (i.e., improve 
elasticity or elastic recovery) and have no substantial effect on ambient 
percent stress or load relaxation performance. But while tending to adversely 
affect (i.e., increase) or have no effect on percent stress or load relaxation 
at elevated temperatures for polymer having densities equal to or greater than 
0.865 g/cm.sup.3, surprisingly curing, radiation and crosslinking decreases 
(i.e., improves) the elevated temperature percent stress or load relaxation 
performance of ethylene interpolymer having a polymer density less than 0.87 
g/cm.sup.3 or a DSC crystallinity at 23.degree. C. less than 12 weight percent. 
That is, curing, radiating or crosslinking is an effective means for providing 
elastic materials and articles characterized as having excellent elevated 
temperature stress relaxation characteristics. 

Not only is the dramatically different response to irradiation or crosslinking 
surprisingly in itself, these results are surprising for other reasons as well. 
For example, these results are surprising and unexpected because at a density of 
0.87 g/cm.sup.3, ethylene polymers are already substantially amorphous. That is, 
a cross-over or transition in elastic performance attributable to curing, 
radiation or crosslinking would ordinarily be expected to relate to the 
amorphosity of the polymer; but according to hexane extraction data at 
50.degree. C., determined according to the Food and Drug Administration (FDA) 
test method set forth under 21 37 C.F.R. .sctn..sctn.177.1520 (d)(3)(ii), 
ethylene polymers are substantially amorphous at a density of 0.89 g/cm.sup.3 
and below. Given such small differences in amorphosity or crystallinity, 
dramatic elasticity differences in response to irradiation or crosslinking 
simply would not ordinarily be expected. 

Accordingly, the shaped elastic articles of present invention exhibit a unique 
combination of properties such as tenacity at break, elongation, elastic 
recovery, chlorine and aromatic/polar solvent resistance, moisture resistance, 
heat aging and excellent high temperature mechanical performance compared to 
traditional elastic materials, for example, natural rubber and spandex. 

BRIEF DESCRIPTION OF THE DRAWINGS 

FIG. 1 is a plot of percent stress relaxation at 23.degree. C. versus megarads 
of electron beam radiation for Inventive Examples 1 and 2 and comparative runs 
3, 4 and 5. 

FIG. 2 is a plot of percent permanent set at 23.degree. C. versus megarads of 
electron beam radiation for Inventive Examples 1 and 2 and comparative runs 3, 4 
and 5. 

FIG. 3 is a plot of percent stress relaxation at 38.degree. C. versus megarads 
of electron beam radiation for Inventive Example 1 and comparative run 4. 

FIG. 4 is a stress-strain comparison between Inventive Example 6 and comparative 
run 7. 

FIG. 5 is a plot of percent elastic recovery (as percent set elongation) versus 
percent elongation (strain) for Inventive Example 6. 

DETAILED DESCRIPTION OF THE INVENTION 

The term "elastic" as used herein refers to a material having a permanent set 
less than 60 percent, especially less than or equal to 25 percent (i.e. 
especially greater than or equal to 87.5 percent recovery) at 200 percent strain 
and is stretchable to a stretched, biased length at least 150 percent greater 
than its relaxed, unstretched length. Elastic materials are also referred to in 
the art as "elastomers" and "elastomeric". 

The term "nonelastic" as used herein means the material or article is not 
elastic as defined herein (i.e. the martial or article has a percent permanent 
set greater than 25). 

Elastic materials and articles include, the cured, radiated or crosslinked 
article, ethylene interpolymer itself or both as well as, but not limited to, a 
fiber, film, strip, tape, ribbon, sheet, coating, molding and the like comprised 
of the cured, radiated or crosslinked ethylene interpolymer. Preferred elastic 
articles are fiber and film. 

The term "radiated" or "irradiated" as used herein means the ethylene polymer, 
the shaped ethylene interpolymer or the article comprised of the ethylene 
polymer was subjected to at least 3 megarads (or the equivalent thereof) of 
radiation dose whether or not there was a measurable decrease in percent xylene 
extractables (i.e., increase in insoluble gel). That is, substantial 
crosslinking may not result from the irradiation. 

The terms "crosslinked" and "substantially crosslinked" as used herein mean the 
ethylene polymer, the shaped ethylene interpolymer or the article comprised of 
the ethylene polymer is characterized as having xylene extractables of less than 
or equal to 70 weight percent (that is, greater than or equal to 30 weight 
percent gel content), preferably greater than or equal to 40 weight percent 
(that is, greater than or equal to 60 weight percent gel content), where xylene 
extractables (and gel content) are determined in accordance with ASTM D-2765. 

The terms "cured" and "substantially cured" as used herein means the ethylene 
interpolymer, the shaped ethylene interpolymer or the article comprised of the 
ethylene interpolymer was subjected or exposed to a treatment which induced 
crosslinking. As used herein, the terms relate to ethylene interpolymers 
comprising a grafted silane. 

The terms "curable" and "crosslinkable" as used herein mean the ethylene 
interpolymer, the shaped ethylene interpolymer or the article comprised of the 
ethylene interpolymer is not crosslinked and has not been subjected or exposed 
to treatment which induces crosslinking although the ethylene interpolymer, the 
shaped ethylene interpolymer or the article comprised of the ethylene 
interpolymer comprises additive(s) or functionality which will effectuate 
crosslinking upon subjection or exposure to such treatment. 

In the practice of the present invention, curing, irradiation or crosslinking 
can be accomplished by any means known in the art, including, but not limited 
to, electron-beam irradiation, beta irradiation, gamma irradiation, corona 
irradiation, peroxides, allyl compounds and UV radiation with or without 
crosslinking catalyst. Electron-beam irradiation is preferred. 

Suitable electron-beam irradiation equipment is available from Energy Services, 
Inc. Wilmington, Mass. with capabilities of at least 100 KeV and at least 5 Kw. 

The term "pro-rad additive" as used herein means a compound which is not 
activated during normal fabrication or processing of the ethylene interpolymer, 
however can be activated by the application of temperatures (heat) substantial 
above normal fabrication or processing temperatures or ionizing energy (or both) 
to effectuate some measurable gelation or preferably, substantial crosslinking. 

The term "homofil" as used herein refers to fiber which has a single polymer 
region or domain and does not have any other distinct polymer regions (as do 
bicomponent fibers). 

The term "meltblown" is used herein in the conventional sense to refer to fibers 
formed by extruding a molten thermoplastic polymer composition through a 
plurality of fine, usually circular, die capillaries as molten threads or 
filaments into converging high velocity gas streams (e.g. air) which function to 
attenuate the threads or filaments to reduced diameters. Thereafter, the 
filaments or threads are carried by the high velocity gas streams and deposited 
on a collecting surface to form a web of randomly dispersed meltblown fibers 
with average diameters generally smaller than 10 microns. 

The term "spunbond" is used herein in the conventional sense to refer to fibers 
formed by extruding a molten thermoplastic polymer composition as filaments 
through a plurality of fine, usually circular, die capillaries of a spinneret 
with the diameter of the extruded filaments then being rapidly reduced and 
thereafter depositing the filaments onto a collecting surface to form a web of 
randomly dispersed spunbond fibers with average diameters generally between 
about 7 and about 30 microns. 

The term "nonwoven" as used herein and in the conventional sense means a web or 
fabric having a structure of individual fibers or threads which are randomly 
interlaid, but not in an identifiable manner as is the case for a knitted 
fabric. The elastic fiber of the present invention can be employed to prepare 
nonwoven fabrics as well as composition structures comprises elastic nonwoven 
fabric in combination with nonelastic materials. 

The term "conjugated" refers to fibers which have been formed from at least two 
polymers extruded from separate extruders but meltblown or spun together to form 
one fiber. Conjugated fibers are sometimes referred to in the art as 
multicomponent or bicomponent fibers. The polymers are usually different from 
each other although conjugated fibers may be monocomponent fibers. The polymers 
are arranged in substantially constantly positioned distinct zones across the 
cross-section of the conjugated fibers and extend continuously along the length 
of the conjugated fibers. The configuration of conjugated fibers can be, for 
example, a sheath/core arrangement (wherein one polymer is surrounded by 
another), a side by side arrangement, a pie arrangement or an "islands-in-the 
sea" arrangement. Conjugated fibers are described in U.S. Pat. No. 5,108,820 to 
Kaneko et al.; U.S. Pat. No. 5,336,552 to Strack et al.; and U.S. Pat. No. 
5,382,400 to Pike et al., the disclosures of all of which are incorporated 
herein by reference. The elastic fiber of the present invention can be in a 
conjugated configuration, for example, as a core or sheath, or both. 

The ethylene interpolymer to be irradiated, cured or crosslinked has a density 
at 23.degree. C. less than 0.89 g/cm.sup.3, preferably less than 0.87 
g/cm.sup.3, more preferably less than or equal to 0.865 g/cm.sup.3, especially 
in the range of about 0.865 g/cm.sup.3 to about 0.855 g/cm.sup.3, as measured in 
accordance with ASTM D792. At densities higher than 0.89 g/cm.sup.3 the desired 
improved high temperature elastic performance (especially, low percent stress or 
load relaxation) is not obtained. Densities less than about 0.855 g/cm.sup.3 are 
not preferred due to their low tenacity, very low melting point and pre-cross 
ink handing problems (blocking and tackiness). 

Preferably, the ethylene interpolymer is characterized as having a DSC 
crystallinity of less than 26 weight percent, preferably less than 12 weight 
percent, more preferably less than or equal to 8.5 weight percent, and most 
preferably less than or equal 6 percent. 

Preferably, the ethylene interpolymer is characterized as having a melt index 
(I.sub.2) less than 50, more preferably less than 10 g/10 minutes, as determined 
in accordance with ASTM D-1238, Condition 190.degree. C./2.16 kilogram (kg). 

In meltspun fiber form, the irradiated, cured or crosslinked ethylene polymer of 
the present invention generally has a value less than 0.75, preferably less than 
0.6, more preferably less than 0.5 for the expression: 

Abs[.DELTA.E/E.sub.0 ]+Abs[.DELTA.T/T.sub.0 ] 

The irradiated, cured or crosslinked ethylene polymer of the present invention 
(and articles made therefrom) is characterized as having a percent permanent set 
of less than 60 at 23.degree. C., preferably less than or equal 25 at 23.degree. 
C., more preferably less than or equal to 20 and most preferably less than or 
equal to 15 at 23.degree. C. and 38.degree. C. and 200 percent strain when 
measured at a 2 mil thickness using an Instron tensiometer; or preferably a 
percent set elongation of less than or equal to 25, more preferably 20, most 
preferably 15 at 23.degree. C. and 100 percent strain. 

The irradiated, cured or crosslinked ethylene polymer of the present invention 
(and articles made therefrom) is characterized as having a percent stress 
relaxation of less than or equal 25 at 23.degree. C. and 200 percent strain and 
less than or equal to 55, preferably less than or equal to 50, more preferably 
less than or equal to 30, most preferably less than or equal to 20 at 38.degree. 
C. and 200 percent strain when measured at a 2 mil thickness using a Instron 
tensiometer. 

Irradiation may be accomplished by the use of high energy, ionizing electrons, 
ultra violet rays, X-rays, gamma rays, beta particles and the like and 
combination thereof. Preferably, electrons are employed up to 70 megarads 
dosages. The irradiation source can be any electron beam generator operating in 
a range of about 150 kilovolts to about 6 megavolts with a power output capable 
of supplying the desired dosage. The voltage can be adjusted to appropriate 
levels which may be, for example, 100,000, 300,000, 1,000,000 or 2,000,000 or 
3,000,000 or 6,000,000 or higher or lower. Many other apparatus for irradiating 
polymeric materials are known in the art. The irradiation is usually carried out 
at a dosage between about 3 megarads to about 35 megarads, preferably between 
about 8 to about 20 megarads. Further, the irradiation can be carried out 
conveniently at room temperature, although higher and lower temperatures, for 
example 0.degree. C. to about 60.degree. C., may also be employed. Preferably, 
the irradiation is carried out after shaping or fabrication of the article. 
Also, in a preferred embodiment, the ethylene interpolymer which has been 
incorporated with a pro-rad additive is irradiated with electron beam radiation 
at about 8 to about 20 megarads. 

Crosslinking can be promoted with a crosslinking catalyst, and any catalyst that 
will provide this function can be used. Suitable catalysts generally include 
organic bases, carboxylic acids, and organometallic compounds including organic 
titanates and complexes or carboxylates of lead, cobalt, iron, nickel, zinc and 
tin. Dibutyltindilaurate, dioctyltinmaleate, dibutyltindiacetate, 
dibutyltindioctoate, stannous acetate, stannous octoate, lead naphthenate, zinc 
caprylate, cobalt naphthenate; and the like. Tin carboxylate, especially 
dibutyltindilaurate and dioctyltinmaleate, are particularly effective for this 
invention. The catalyst (or mixture of catalysts) is present in a catalytic 
amount, typically between about 0.015 and about 0.035 phr. 

Representative pro-rad additives include, but are not limited to, azo compounds, 
organic peroxides and polyfunctional vinyl or allyl compounds such as, for 
example,. triallyl cyanurate, triallyl isocyanurate, pentaerthritol 
tetramethacrylate, glutaraldehyde, ethylene glycol dimethacrylate, diallyl 
maleate, dipropargyl maleate, dipropargyl monoallyl cyanurate, dicumyl peroxide, 
di-tert-butyl peroxide, t-butyl perbenzoate, benzoyl peroxide, cumene 
hydroperoxide, t-butyl peroctoate, methyl ethyl ketone peroxide, 
2,5-dimethyl-2,5-di(t-butyl peroxy)hexane, lauryl peroxide, tert-butyl 
peracetate, azobisisobutyl nitrite and the like and combination thereof. 
Preferred pro-rad additives for use in the present invention are compounds which 
have poly-functional (i.e. at least two) moieties such as C.dbd.C, C.dbd.N or 
C.dbd.O. 

At least one pro-rad additive can be introduced to the ethylene interpolymer by 
any method known in the art. However, preferably the pro-rad additive(s) is 
introduced via a masterbatch concentrate comprising the same or different base 
resin as the ethylene interpolymer. Preferably ,the pro-rad additive 
concentration for the masterbatch is relatively high e.g., about 25 weight 
percent (based on the total weight of the concentrate). 

The at least one pro-rad additive is introduced to the ethylene polymer in any 
effective amount. Preferably, the at least one pro-rad additive introduction 
amount is from about 0.001 to about 5 weight percent, more preferably from about 
0.005 to about 2.5 weight percent and most preferably from about 0.015 to about 
1 weight percent (based on the total weight of the ethylene interpolymer. 

The term "polymer", as used herein, refers to a polymeric compound prepared by 
polymerizing monomers, whether of the same or a different type. As used herein, 
generic term "polymer" embraces the terms "homopolymer," "copolymer," 
"terpolymer" as well as "interpolymer." 

The term "interpolymer", as used herein refers to polymers prepared by the 
polymerization of at least two different types of monomers. As used herein the 
generic term "interpolymer" includes the term "copolymers" (which is usually 
employed to refer to polymers prepared from two different monomers) as well as 
the term "terpolymers" (which is usually employed to refer to polymers prepared 
from three different types of monomers). 

The term "homogeneously branched ethylene polymer" is used herein in the 
conventional sense to refer to an ethylene interpolymer in which the comonomer 
is randomly distributed within a given polymer molecule and wherein 
substantially all of the polymer molecules have the same ethylene to comonomer 
molar ratio. The term refers to an ethylene interpolymer that are manufactured 
using so-called homogeneous or single-site catalyst systems known in the art 
such Ziegler vanadium, hafnium and zirconium catalyst systems and metallocene 
catalyst systems e.g., a constrained geometry catalyst systems which is further 
described herein below. 

Homogeneously branched ethylene polymers for use in the present invention can be 
also described as having less than 15 weight percent, preferably less 10 weight 
percent, more preferably less than 5 and most preferably zero (0) weight percent 
of the polymer with a degree of short chain branching less than or equal to 10 
methyls/1000 carbons. That is, the polymer contains no measurable high density 
polymer fraction (e.g., there is no fraction having a density of equal to or 
greater than 0.94 g/cm.sup.3), as determined, for example, using a temperature 
rising elution fractionation (TREF) technique and infrared or 13C nuclear 
magnetic resonance (NMR) analysis. 

Preferably, the homogeneously branched ethylene polymer is characterized as 
having a narrow, essentially single melting TREF profile/curve and essentially 
lacking a measurable high density polymer portion, as determined using a 
temperature rising elution fractionation technique (abbreviated herein as 
"TREF"). 

The composition distribution of an ethylene interpolymer can be readily 
determined from TREF as described, for example, by Wild et al., Journal of 
Polymer Science, Poly. Phys. Ed., Vol. 20, p. 441 (1982), or in U.S. Pat. Nos. 
4,798,081; 5,008,204; or by L. D. Cady, "The Role of Comonomer Type and 
Distribution in LLDPE Product Performance," SPE Regional Technical Conference, 
Quaker Square Hilton, Akron, Ohio, Oct. 1-2, pp. 107-119 (1985), the disclosures 
of all which are incorporated herein by reference. 

The composition (monomer) distribution of the interpolymer can also be 
determined using .sup.13 C NMR analysis in accordance with techniques described 
in U.S. Pat. No. 5,292,845; U.S. Pat. No. 4,798,081; U.S. Pat. No. 5,089,321 and 
by J. C. Randall, Rev. Macromol. Chem. Phys., C29, pp. 201-317 (1989), the 
disclosures of all of which are incorporated herein by reference. 

In analytical temperature rising elution fractionation analysis (as described in 
U.S. Pat. No. 4,798,081 and abbreviated herein as "ATREF"), the film or 
composition to be analyzed is dissolved in a suitable hot solvent (e.g., 
trichlorobenzene) and allowed to crystallized in a column containing an inert 
support (stainless steel shot) by slowly reducing the temperature. The column is 
equipped with both a refractive index detector and a differential viscometer 
(DV) detector. An ATREF-DV chromatogram curve is then generated by eluting the 
crystallized polymer sample from the column by slowly increasing the temperature 
of the eluting solvent (trichlorobenzene). The ATREF curve is also frequently 
called the short chain branching distribution (SCBD) or composition distribution 
(CD) curve, since it indicates how evenly the comonomer (e.g., octene) is 
distributed throughout the sample in that as elution temperature decreases, 
comonomer content increases. The refractive index detector provides the short 
chain distribution information and the differential viscometer detector provides 
an estimate of the viscosity average molecular weight. The composition 
distribution and other compositional information can also be determined using 
crystallization analysis fractionation such as the CRYSTAF fractionalysis 
package available commercially from Polymer Char, Valencia, Spain. 

Preferred homogeneously branched ethylene polymers (such as, but not limited to, 
substantially linear ethylene polymers) have a single melting peak between -30 
and 150.degree. C., as determined using differential scanning calorimetry (DSC), 
as opposed to traditional Ziegler polymerized heterogeneously branched ethylene 
polymers (e.g., LLDPE and ULDPE or VLDPE) which have two or more melting points. 

The single melting peak is determined using a differential scanning calorimeter 
standardized with indium and deionized water. The method involves about 5-7 mg 
sample sizes, a "first heat" to about 180.degree. C. which is held for 4 
minutes, a cool down at 10.degree. C./min. to -30.degree. C. which is held for 3 
minutes, and heat up at 10.degree. C./min. to 150.degree. C. to provide a 
"second heat" heat flow vs. temperature curve from which the melting peak(s) is 
obtained. Total heat of fusion of the polymer is calculated from the area under 
the curve. 

The homogeneously branched ethylene polymers for use in the invention can be 
either a substantially linear ethylene polymer or a homogeneously branched 
linear ethylene polymer. 

The term "linear" as used herein means that the ethylene polymer does not have 
long chain branching. That is, the polymer chains comprising the bulk linear 
ethylene polymer have an absence of long chain branching, as in the case of 
traditional linear low density polyethylene polymers or linear high density 
polyethylene polymers made using Ziegler polymerization processes (e.g., U.S. 
Pat. No. 4,076,698 (Anderson et al.)), sometimes called heterogeneous polymers. 
The term "linear" does not refer to bulk high pressure branched polyethylene, 
ethylene/vinyl acetate copolymers, or ethylene/vinyl alcohol copolymers which 
are known to those skilled in the art to have numerous long chain branches. 

The term "homogeneously branched linear ethylene polymer" refers to polymers 
having a narrow short chain branching distribution and an absence of long chain 
branching. Such "linear" uniformly branched or homogeneous polymers include 
those made as described in U.S. Pat. No. 3,645,992 (Elston) and those made using 
so-called single site catalysts in a batch reactor having relatively high 
ethylene concentrations (as described in U.S. Pat. No. 5,026,798 (Canich) or in 
U.S. Pat. No. 5,055,438 (Canich)) or those made using constrained geometry 
catalysts in a batch reactor also having relatively high olefin concentrations 
(as described in U.S. Pat. No. 5,064,802 (Stevens et al.) or in EP 0 416 815 A2 
(Stevens et al.)). 

Typically, homogeneously branched linear ethylene polymers are 
ethylene/.alpha.-olefin interpolymers, wherein the .alpha.-olefin is at least 
one C.sub.3 -C.sub.20 .alpha.-olefin (e.g., propylene, 1-butene, 1-pentene, 
4-methyl-1-pentene, 1-hexene, 1-octene and the like) and preferably the at least 
one C.sub.3 -C.sub.20 .alpha.-olefin is 1-butene, 1-hexene or 1-octene. Most 
preferably, the ethylene/.alpha.-olefin interpolymer is a copolymer of ethylene 
and a C.sub.3 -C.sub.20 .alpha.-olefin, and especially an ethylene/C.sub.4 
-C.sub.8 .alpha.-olefin copolymer such as an ethylene/1-octene copolymer, 
ethylene/1-butene copolymer, ethylene/1-pentene copolymer or ethylene/1-hexene 
copolymer. 

Suitable homogeneously branched linear ethylene polymers for use in the 
invention are sold under the designation of TAFMER by Mitsui Chemical 
Corporation and under the designations of EXACT and EXCEED resins by Exxon 
Chemical Company. 

The term "substantially linear ethylene polymer" as used herein means that the 
bulk ethylene polymer is substituted, on average, with about 0.01 long chain 
branches/1000 total carbons to about 3 long chain branches/1000 total carbons 
(wherein "total carbons" includes both backbone and branch carbons). Preferred 
polymers are substituted with about 0.01 long chain branches/1000 total carbons 
to about 1 long chain branches/1000 total carbons, more preferably from about 
0.05 long chain branches/1000 total carbons to about 1 long chain branched/1000 
total carbons, and especially from about 0.3 long chain branches/1000 total 
carbons to about 1 long chain branches/1000 total carbons. 

As used herein, the term "backbone" refers to a discrete molecule, and the term 
"polymer" or "bulk polymer" refers, in the conventional sense, to the polymer as 
formed in a reactor. For the polymer to be a "substantially linear ethylene 
polymer", the polymer must have at least enough molecules with long chain 
branching such that the average long chain branching in the bulk polymer is at 
least an average of from about 0.01/1000 total carbons to about 3 long chain 
branches/1000 total carbons. 

The term "bulk polymer" as used herein means the polymer which results from the 
polymerization process as a mixture of polymer molecules and, for substantially 
linear ethylene polymers, includes molecules having an absence of long chain 
branching as well as molecules having long chain branching. Thus a "bulk 
polymer" includes all molecules formed during polymerization. It is understood 
that, for the substantially linear polymers, not all molecules have long chain 
branching, but a sufficient amount do such that the average long chain branching 
content of the bulk polymer positively affects the melt rheology (i.e., the 
shear viscosity and melt fracture properties) as described herein below and 
elsewhere in the literature. 

Long chain branching (LCB) is defined herein as a chain length of at least one 
(1) carbon less than the number of carbons in the comonomer, whereas short chain 
branching (SCB) is defined herein as a chain length of the same number of 
carbons in the residue of the comonomer after it is incorporated into the 
polymer molecule backbone. For example, a substantially linear ethylene/1-octene 
polymer has backbones with long chain branches of at least seven (7) carbons in 
length, but it also has short chain branches of only six (6) carbons in length. 

Long chain branching can be distinguished from short chain branching by using 
.sup.13 C nuclear magnetic resonance (NMR) spectroscopy and to a limited extent, 
e.g. for ethylene homopolymers, it can be quantified using the method of 
Randall, (Rev. Macromol.Chem. Phys., C29 (2&3), p. 285-297 (1989)), the 
disclosure of which is incorporated herein by reference. However as a practical 
matter, current .sup.13 C. nuclear magnetic resonance spectroscopy cannot 
determine the length of a long chain branch in excess of about six (6) carbon 
atoms and as such, this analytical technique cannot distinguish between a seven 
(7) carbon branch and a seventy (70) carbon branch. The long chain branch can be 
as long as about the same length as the length of the polymer backbone. 

Although conventional .sup.13 C nuclear magnetic resonance spectroscopy cannot 
determine the length of a long chain branch in excess of six carbon atoms, there 
are other known techniques useful for quantifying or determining the presence of 
long chain branches in ethylene polymers, including ethylene/1-octene 
interpolymers. For example, U.S. Pat. No. 4,500,648, incorporated herein by 
reference, teaches that long chain branching frequency (LCB) can be represented 
by the equation LCB=b/M.sub.w wherein b is the weight average number of long 
chain branches per molecule and M.sub.w is the weight average molecular weight. 
The molecular weight averages and the long chain branching characteristics are 
determined by gel permeation chromatography and intrinsic viscosity methods, 
respectively. 

Two other useful methods for quantifying or determining the presence of long 
chain branches in ethylene polymers, including ethylene/1-octene interpolymers 
are gel permeation chromatography coupled with a low angle laser light 
scattering detector (GPC-LALLS) and gel permeation chromatography coupled with a 
differential viscometer detector (GPC-DV). The use of these techniques for long 
chain branch detection and the underlying theories have been well documented in 
the literature. See, e.g., Zimm, G. H. and Stockmayer, W. H., J. Chem. Phys., 
17, 1301 (1949) and Rudin, A., Modern Methods of Polymer Characterization, John 
Wiley & Sons, New York (1991) pp. 103-112, the disclosures of both of which are 
incorporated by reference. 

A. Willem deGroot and P. Steve Chum, both of The Dow Chemical Company, at the 
Oct. 4, 1994 conference of the Federation of Analytical Chemistry and 
Spectroscopy Society (FACSS) in St. Louis, Mo., presented data demonstrating 
that GPC-DV is indeed a useful technique for quantifying the presence of long 
chain branches in substantially linear ethylene polymers. In particular, deGroot 
and Chum found that the level of long chain branches in substantially linear 
ethylene homopolymer samples measured using the Zimm-Stockmayer equation 
correlated well with the level of long chain branches measured using .sup.13 C. 
NMR. 

Further, deGroot and Chum found that the presence of octene does not change the 
hydrodynamic volume of the polyethylene samples in solution and, as such, one 
can account for the molecular weight increase attributable to octene short chain 
branches by knowing the mole percent octene in the sample. By deconvoluting the 
contribution to molecular weight increase attributable to 1-octene short chain 
branches, deGroot and Chum showed that GPC-DV may be used to quantify the level 
of long chain branches in substantially linear ethylene/octene copolymers. 

DeGroot and Chum also showed that a plot of Log(I.sub.2, melt index) as a 
function of Log(GPC Weight Average Molecular Weight) as determined by GPC-DV 
illustrates that the long chain branching aspects (but not the extent of long 
branching) of substantially linear ethylene polymers are comparable to that of 
high pressure, highly branched low density polyethylene (LDPE) and are clearly 
distinct from ethylene polymers produced using Ziegler-type catalysts such as 
titanium complexes and ordinary homogeneous catalysts such as hafnium and 
vanadium complexes. 

For substantially linear ethylene polymers, the empirical effect of the presence 
of long chain branching is manifested as enhanced rheological properties which 
are quantified and expressed in terms of gas extrusion rheometry (GER) results 
and/or melt flow, I.sub.10 /I.sub.2, increases. 

The substantially linear ethylene polymers used in the present invention are a 
unique class of compounds that are further defined in U.S. Pat. No. 5,272,236, 
application number 07/776,130, filed Oct. 15, 1991; U.S. Pat. No. 5,278,272, 
application number 07/939,281, filed Sep. 2, 1992; and U.S. Pat. No. 5,665,800, 
application number 08/730,766, filed Oct. 16, 1996, each of which is 
incorporated herein by reference. 

Substantially linear ethylene polymers differ significantly from the class of 
polymers conventionally known as homogeneously branched linear ethylene polymers 
described above and, for example, by Elston in U.S. Pat. No. 3,645,992. As an 
important distinction, substantially linear ethylene polymers do not have a 
linear polymer backbone in the conventional sense of the term "linear" as is the 
case for homogeneously branched linear ethylene polymers. 

Substantially linear ethylene polymers also differ significantly from the class 
of polymers known conventionally as heterogeneously branched traditional Ziegler 
polymerized linear ethylene interpolymers (for example, ultra low density 
polyethylene, linear low density polyethylene or high density polyethylene made, 
for example, using the technique disclosed by Anderson et al. in U.S. Pat. No. 
4,076,698, in that substantially linear ethylene interpolymers are homogeneously 
branched polymers. Further, substantially linear ethylene polymers also differ 
from the class of heterogeneously branched ethylene polymers in that 
substantially linear ethylene polymers are characterized as essentially lacking 
a measurable high density or crystalline polymer fraction as determined using a 
temperature rising elution fractionation technique. 

The homogeneously branched substantially linear ethylene polymers for use in the 
present invention is characterized as having 

(a) melt flow ratio, I.sub.10 /I.sub.2.ltoreq.5.63, 

(b) a molecular weight distribution, M.sub.w /M.sub.n, as determined by gel 
permeation chromatography and defined by the equation: 

(M.sub.w /M.sub.n).ltoreq.(I.sub.10 /I.sub.2)-4.63, 

(c) a gas extrusion rheology such that the critical shear rate at onset of 
surface melt fracture for the substantially linear ethylene polymer is at least 
50 percent greater than the critical shear rate at the onset of surface melt 
fracture for a linear ethylene polymer, wherein the substantially linear 
ethylene polymer and the linear ethylene polymer comprise the same comonomer or 
comonomers, the linear ethylene polymer has an I.sub.2 and M.sub.w /M.sub.n 
within ten percent of the substantially linear ethylene polymer and wherein the 
respective critical shear rates of the substantially linear ethylene polymer and 
the linear ethylene polymer are measured at the same melt temperature using a 
gas extrusion rheometer, 

(d) a single differential scanning calorimetry, DSC, melting peak between 
-30.degree. and 150.degree. C., and 

(e) a density less than or equal to 0.865 g/cm.sup.3. 

Determination of the critical shear rate and critical shear stress in regards to 
melt fracture as well as other rheology properties such as "Theological 
processing index" (PI), is performed using a gas extrusion rheometer (GER). The 
gas extrusion rheometer is described by M. Shida, R. N. Shroff and L. V. Cancio 
in Polymer Engineering Science, Vol. 17, No. 11, p. 770 (1977) and in Rheometers 
for Molten Plastics by John Dealy, published by Van Nostrand Reinhold Co. (1982) 
on pp. 97-99, the disclosures of both of which are incorporated herein by 
reference. 

The processing index (PI) is measured at a temperature of 190.degree. C., at 
nitrogen pressure of 2500 psig using a 0.0296 inch (752 micrometers) diameter 
(preferably a 0.0143 inch diameter die for high flow polymers, e.g. 50-100 
I.sub.2 melt index or greater), 20:1 L/D die having an entrance angle of 
180.degree.. The GER processing index is calculated in millipoise units from the 
following equation: 

PI=2.15.times.10.sup.6 dyne/cm.sup.2 /(1000.times.shear rate), 

where: 2.15.times.10.sup.6 dyne/cm.sup.2 is the shear stress at 2500 psi, and 
the shear rate is the shear rate at the wall as represented by the following 
equation: 

32 Q'/(60 sec/min)(0.745)(Diameter.times.2.54 cm/in).sup.3, 

where: 

Q' is the extrusion rate (gms/min), 

0.745 is the melt density of polyethylene (gm/cm.sup.3), and 

Diameter is the orifice diameter of the capillary (inches). 

The PI is the apparent viscosity of a material measured at apparent shear stress 
of 2.15.times.10.sup.6 dyne/cm.sup.2. 

For substantially linear ethylene polymers, the PI is less than or equal to 70 
percent of that of a conventional linear ethylene polymer having an I.sub.2, 
M.sub.w /M.sub.n and density each within ten percent of the substantially linear 
ethylene polymer. 

An apparent shear stress vs. apparent shear rate plot is used to identify the 
melt fracture phenomena over a range of nitrogen pressures from 5250 to 500 psig 
using the die or GER test apparatus previously described. According to 
Ramamurthy in Journal of Rheology, 30(2), 337-357, 1986, above a certain 
critical flow rate, the observed extrudate irregularities may be broadly 
classified into two main types: surface melt fracture and gross melt fracture. 

Surface melt fracture occurs under apparently steady flow conditions and ranges 
in detail from loss of specular gloss to the more severe form of "sharkskin". In 
this disclosure, the onset of surface melt fracture is characterized at the 
beginning of losing extrudate gloss at which the surface roughness of extrudate 
can only be detected by 40.times.magnification. The critical shear rate at onset 
of surface melt fracture for the substantially linear ethylene polymers is at 
least 50 percent greater than the critical shear rate at the onset of surface 
melt fracture of a linear ethylene polymer having about the same I.sub.2 and 
M.sub.w /M.sub.n. Preferably, the critical shear stress at onset of surface melt 
fracture for the substantially linear ethylene polymers of the invention is 
greater than about 2.8.times.10.sup.6 dyne/cm.sup.2. 

Gross melt fracture occurs at unsteady flow conditions and ranges in detail from 
regular (alternating rough and smooth, helical, etc.) to random distortions. For 
commercial acceptability, (e.g., in blown film products), surface defects should 
be minimal, if not absent. The critical shear rate at onset of surface melt 
fracture (OSMF) and critical shear stress at onset of gross melt fracture (OGMF) 
will be used herein based on the changes of surface roughness and configurations 
of the extrudates extruded by a GER. For the substantially linear ethylene 
polymers used in the invention, the critical shear stress at onset of gross melt 
fracture is preferably greater than about 4.times.10.sup.6 dyne/cm.sup.2. 

For the processing index determination and for the GER melt fracture 
determination, substantially linear ethylene polymers are tested without 
inorganic fillers and do not have more than 20 ppm aluminum catalyst residue. 
Preferably, however, for the processing index and melt fracture tests, 
substantially linear ethylene polymers do contain antioxidants such as phenols, 
hindered phenols, phosphites or phosphonites, preferably a combination of a 
phenol or hindered phenol and a phosphite or a phosphonite. 

The molecular weight distributions of ethylene polymers are determined by gel 
permeation chromatography (GPC) on a Waters 150 C high temperature 
chromatographic unit equipped with a differential refractometer and three 
columns of mixed porosity. The columns are supplied by Polymer Laboratories and 
are commonly packed with pore sizes of 10.sup.3, 10.sup.4, 10.sup.5 and 10.sup.6 
.ANG.. The solvent is 1,2,4-trichlorobenzene, from which about 0.3 percent by 
weight solutions of the samples are prepared for injection. The flow rate is 
about 1.0 milliliters/minute, unit operating temperature is about 140.degree. C. 
and the injection size is about 100 microliters. 

The molecular weight determination with respect to the polymer backbone is 
deduced by using narrow molecular weight distribution polystyrene standards 
(from Polymer Laboratories) in conjunction with their elution volumes. The 
equivalent polyethylene molecular weights are determined by using appropriate 
Mark-Houwink coefficients for polyethylene and polystyrene (as described by 
Williams and Ward in Journal of Polymer Science, Polymer Letters, Vol. 6, p. 
621, 1968, the disclosure of which is incorporated herein by reference) to 
derive the following equation: 

M.sub.polyethylene =a*(M.sub.polystyrene).sup.b 

In this equation, a=0.4316 and b=1.0. Weight average molecular weight, M.sub.w, 
is calculated in the usual manner according to the following formula: M.sub.j 
=(.SIGMA.w.sub.i (M.sub.i.sup.j)).sup.j Where w.sub.i is the weight fraction of 
the molecules with molecular weight M.sub.i eluting from the GPC column in 
fraction i and j=1 when calculating M.sub.w, and j=-1 when calculating M.sub.n. 

For the at least one homogeneously branched ethylene polymer used in the present 
invention, the M.sub.w /M.sub.n is preferably less than 3.5, more preferably 
less than 3.0, most preferably less than 2.5, and especially in the range of 
from about 1.5 to about 2.5 and most especially in the range from about 1.8 to 
about 2.3. 

Substantially linear ethylene polymers are known to have excellent 
processability, despite having a relatively narrow molecular weight distribution 
(that is, the M.sub.w /M.sub.n ratio is typically less than about 3.5). 
Surprisingly, unlike homogeneously and heterogeneously branched linear ethylene 
polymers, the melt flow ratio I.sub.10 /I.sub.2 of substantially linear ethylene 
polymers can be varied essentially independently of the molecular weight 
distribution, M.sub.w /M.sub.n. Accordingly, especially when good extrusion 
processability is desired, the preferred ethylene polymer for use in the present 
invention is a homogeneously branched substantially linear ethylene 
interpolymer. 

Suitable constrained geometry catalysts for use manufacturing substantially 
linear ethylene polymers include constrained geometry catalysts as disclosed in 
U.S. application Ser. No. 07/545,403, filed Jul. 3, 1990 (pending); U.S. Pat. 
No. 5,132,380 (application Ser. No. 07/758,654); U.S. Pat. No. 5,064,802 
(application Ser. No. 07/547,728); U.S. Pat. No. 5,470,993 (application Ser. No. 
08/241,523); U.S. Pat. No. 5,453,410 (application Ser. No. 08/108,693); U.S. 
Pat. No. 5,371,696 (application Ser. No. 08/08,003); U.S. Pat. No. 5,532,394 
(application Ser. No. 08/295,768); U.S. Pat. No. 5,494,874 (application Ser. No. 
08/294,469); and U.S. Pat. No. 5,189,192 (application Ser. No. 07/647,111), the 
teachings of all of which are incorporated herein by reference. 

Suitable catalyst complexes may also be prepared according to the teachings of 
WO 93/08199, and the patents issuing therefrom, all of which are incorporated 
herein by reference. Further, the monocyclopentadienyl transition metal olefin 
polymerization catalysts taught in U.S. Pat. No. 5,026,798, which is 
incorporated herein by reference, are also believed to be suitable for use in 
preparing the polymers of the present invention, so long as the polymerization 
conditions substantially conform to those described in U.S. Pat. No. 5,272,236; 
U.S. Pat. No. 5,278,272 and U.S. Pat. No. 5,665,800, especially with strict 
attention to the requirement of continuous polymerization. Such polymerization 
methods are also described in PCT/US 92/08812 (filed Oct. 15, 1992). 

The foregoing catalysts may be further described as comprising a metal 
coordination complex comprising a metal of groups 3-10 or the Lanthanide series 
of the Periodic Table of the Elements and a delocalize .beta.-bonded moiety 
substituted with a constrain-inducing moiety, said complex having a constrained 
geometry about the metal atom such that the angle at the metal between the 
centroid of the delocalized, substituted pi-bonded moiety and the center of at 
least one remaining substituent is less than such angle in a similar complex 
containing a similar pi-bonded moiety lacking in such constrain-inducing 
substituent, and provided further that for such complexes comprising more than 
one delocalized, substituted pi-bonded moiety, only one thereof for each metal 
atom of the complex is a cyclic, delocalized, substituted pi-bonded moiety. The 
catalyst further comprises an activating cocatalyst. 

Suitable cocatalysts for use herein include polymeric or oligomeric 
aluminoxanes, especially methyl aluminoxane, as well as inert, compatible, 
noncoordinating, ion forming compounds. So-called modified methyl aluminoxane 
(MMAO) is also suitable for use as a cocatalyst. One technique for preparing 
such modified aluminoxane is disclosed in U.S. Pat. No. 5,041,584, the 
disclosure of which is incorporated herein by reference. Aluminoxanes can also 
be made as disclosed in U.S. Pat. No. 5,218,071; U.S. Pat. No. 5,086,024; U.S. 
Pat. No. 5,041,585; U.S. Pat. No. 5,041,583; U.S. Pat. No. 5,015,749; U.S. Pat. 
No. 4,960,878; and U.S. Pat. No. 4,544,762, the disclosures of all of which are 
incorporated herein by reference. 

Aluminoxanes, including modified methyl aluminoxanes, when used in the 
polymerization, are preferably used such that the catalyst residue remaining in 
the (finishe 

d) polymer is preferably in the range of from about 0 to about 20 ppm aluminum, 
especially from about 0 to about 10 ppm aluminum, and more preferably from about 
0 to about 5 ppm aluminum. In order to measure the bulk polymer properties (e.g. 
PI or melt fracture), aqueous HCl is used to extract the aluminoxane from the 
polymer. Preferred cocatalysts, however, are inert, noncoordinating, boron 
compounds such as those described in EP 520732, the disclosure of which is 
incorporated herein by reference. 

Substantially linear ethylene are produced via a continuous (as opposed to a 
batch) controlled polymerization process using at least one reactor (e.g., as 
disclosed in WO 93/07187, WO 93/07188, and WO 93/07189, the disclosure of each 
of which is incorporated herein by reference), but can also be produced using 
multiple reactors (e.g., using a multiple reactor configuration as described in 
U.S. Pat. No. 3,914,342, the disclosure of which is incorporated herein by 
reference) at a polymerization temperature and pressure sufficient to produce 
the interpolymers having the desired properties. The multiple reactors can be 
operated in series or in parallel, with at least one constrained geometry 
catalyst employed in at least one of the reactors. 

Substantially linear ethylene polymers can be prepared via the continuous 
solution, slurry, or gas phase polymerization in the presence of a constrained 
geometry catalyst, such as the method disclosed in EP 416,815-A, the disclosure 
of which is incorporated herein by reference. The polymerization can generally 
be performed in any reactor system known in the art including, but not limited 
to, a tank reactor(s), a sphere reactor(s), a recycling loop reactor(s) or 
combinations thereof and the like, any reactor or all reactors operated 
partially or completely adiabatically, nonadiabatically or a combination of both 
and the like. Preferably, a continuous loop-reactor solution polymerization 
process is used to manufacture the substantially linear ethylene polymer used in 
the present invention. 

In general, the continuous polymerization required to manufacture substantially 
linear ethylene polymers may be accomplished at conditions well known in the 
prior art for Ziegler-Natta or Kaminsky-Sinn type polymerization reactions, that 
is, temperatures from 0 to 250.degree. C. and pressures from atmospheric to 1000 
atmospheres (100 MPa). Suspension, solution, slurry, gas phase or other process 
conditions may be employed if desired. 

A support may be employed in the polymerization, but preferably the catalysts 
are used in a homogeneous (i.e., soluble) manner. It will, of course, be 
appreciated that the active catalyst system forms in situ if the catalyst and 
the cocatalyst components thereof are added directly to the polymerization 
process and a suitable solvent or diluent, including condensed monomer, is used 
in said polymerization process. It is, however, preferred to form the active 
catalyst in a separate step in a suitable solvent prior to adding the same to 
the polymerization mixture. 

The substantially linear ethylene polymers used in the present invention are 
interpolymers of ethylene with at least one C.sub.3 -C.sub.20 .alpha.-olefin 
and/or C.sub.4 -C.sub.18 diolefin. Copolymers of ethylene and an .alpha.-olefin 
of C.sub.3 -C.sub.20 carbon atoms are especially preferred. The term 
"interpolymer" as discussed above is used herein to indicate a copolymer, or a 
terpolymer, or the like, where, at least one other comonomer is polymerized with 
ethylene or propylene to make the interpolymer. 

Suitable unsaturated comonomers useful for polymerizing with ethylene include, 
for example, ethylenically unsaturated monomers, conjugated or non-conjugated 
dienes, polyenes, etc. Examples of such comonomers include C.sub.3 -C.sub.20 
.alpha.-olefins such as propylene, isobutylene, 1-butene, 1-hexene, 1-pentene, 
4-methyl-1-pentene, 1-heptene, 1-octene, 1-nonene, 1-decene, and the like. 
Preferred comonomers include propylene, 1-butene, 1-pentene, 1-hexene, 
4-methyl-1-pentene, 1-heptene, and 1-octene, and 1-octene is especially 
preferred. Other suitable monomers include styrene, halo- or alkyl-substituted 
styrenes, vinylbenzocyclobutane, 1,4-hexadiene, 1,7-octadiene, and naphthenics 
(e.g., cyclopentene, cyclohexene and cyclooctene). 

The ethylene interpolymer can be blended with other polymers. Suitable polymers 
for blending with the ethylene interpolymer are commercially available from a 
variety of suppliers and include, but are not limited, an ethylene polymer 
(e.g., low density polyethylene, ultra or very low density polyethylene, medium 
density polyethylene, linear low density polyethylene, high density 
polyethylene, homogeneously branched linear ethylene polymer, substantially 
linear ethylene polymer, polystyrene, ethylene styrene interpolymer, ethylene 
vinyl acetate interpolymer, ethylene acrylic acid interpolymer, ethylene ethyl 
acetate interpolymer, ethylene methacrylic acid interpolymer, ethylene 
methacrylic acid ionomer, and the like), polycarbonate, polystyrene, 
polypropylene (e.g., homopolymer polypropylene, polypropylene copolymer, random 
block polypropylene interpolymer and the like), thermoplastic polyurethane, 
polyamide, polylactic acid interpolymer, thermoplastic block polymer (e.g. 
styrene butadiene copolymer, styrene butadiene styrene triblock copolymer, 
styrene ethylene-butylene styrene triblock copolymer and the like), polyether 
block copolymer (e.g., PEBAX), copolyester polymer, polyester/polyether block 
polymers (e.g., HYTREL), ethylene carbon monoxide interpolymer (e.g., 
ethylene/carbon monoxide (ECO), copolymer, ethylene/acrylic acid/carbon monoxide 
(EAACO) terpolymer, ethylene/methacrylic acid/carbon monoxide (EMAACO) 
terpolymer, ethylene/vinyl acetate/carbon monoxide (EVACO) terpolymer and 
styrene/carbon monoxide (SCO)), polyethylene terephthalate (PET), chlorinated 
polyethylene, and the like and mixtures thereof. 

In one preferred embodiment, the ethylene interpolymer is blended with a 
polypropylene resins. Suitable polypropylene polymers for use in the invention, 
including random block propylene ethylene polymers, are available from a number 
of manufacturers, such as, for example, Montell Polyolefins and Exxon Chemical 
Company. At Exxon, suitable polypropylene polymers are supplied under the 
designations ESCORENE and ACHIEVE. 

Suitable poly lactic acid (PLA) polymers for use in the invention are well known 
in the literature (e.g., see D. M. Bigg et al., "Effect of Copolymer Ratio on 
the Crystallinity and Properties of Polylactic Acid Copolymers", ANTEC, '96, pp. 
2028-2039; WO 90/01521; EP 0 515203A; and EP 0 748846A2, the disclosures of each 
of which are incorporated herein by reference). Suitable poly lactic acid 
polymers are supplied commercially by Cargill Dow under the designation EcoPLA. 

Suitable thermoplastic polyurethane for use in the invention are commercially 
available from The Dow Chemical Company under the designation PELLATHANE. 

Suitable polyolefin carbon monoxide interpolymers can be manufactured using well 
known high pressure free-radical polymerization methods. However, they may also 
be manufactured using traditional Ziegler-Natta catalysis and even with the use 
of so-called homogeneous catalyst systems such as those described and referenced 
herein above. 

Suitable free-radical initiated high pressure carbonyl containing ethylene 
polymers such as ethylene acrylic acid interpolymers can be manufactured by any 
technique known in the art including the methods taught by Thomson and Waples in 
U.S. Pat. No. 3,520,861 and by McKinney et al. in U.S. Pat. Nos. 4,988,781; 
4,599,392; and 5,384,373, the disclosures of which are incorporated herein by 
reference. 

Suitable ethylene vinyl acetate interpolymers for use in the invention are 
commercially available from various suppliers, including Exxon Chemical Company 
and Du Pont Chemical Company. 

Suitable ethylene/alkyl acrylate interpolymers are commercially available from 
various suppliers. Suitable ethylene/acrylic acid interpolymers are commercially 
available from The Dow Chemical Company under the designation PRIMACOR. Suitable 
ethylene/methacrylic acid interpolymers are commercially available from Du Pont 
Chemical Company under the designation NUCREL. 

Chlorinated polyethylene (CPE), especially chlorinated substantially linear 
ethylene polymers, can be prepared by chlorinating polyethylene in accordance 
with well known techniques. Preferably, chlorinated polyethylene comprises equal 
to or greater than 30 weight percent chlorine. Suitable chlorinated 
polyethylenes for use in the invention are commercially supplied by The Dow 
Chemical Company under the designation TYRIN. 

Additives e.g., Irgafos.RTM. 168 or Irganox.RTM. 1010 supplied by Ciba Geigy 
Corp., may be added to the ethylene polymer protect against undo degradation 
during shaping or fabrication operation and/or to better control the extent of 
grafting or crosslinking (i.e., inhibit excessive gelation). In-process 
additives, e.g. calcium stearate, water, fluoropolymers, etc., may also be used 
for purposes such as for the deactivation of residual catalyst and/or improved 
processability. 

The ethylene interpolymer can be filled or unfilled. If filled, then the amount 
of filler present should not exceed an amount that would adversely affect 
elevated temperature elasticity. Typically, the amount of filler present is 
between 20 and 80, preferably between 50 and 70, weight percent (wt percent) 
based on the total weight of the interpolymer. Representative fillers include 
kaolin clay, magnesium hydroxide, silica, calcium carbonate. In a preferred 
embodiment, in which a filler is present, the filler is coated with a material 
that will prevent or retard any tendency that the filler might otherwise have to 
interfere with the crosslinking reactions. Stearic acid is illustrative of such 
a filler coating. 

The elastic ethylene interpolymer and elastic article of the invention have 
utility in a variety of applications. Suitable applications include, for 
example, but are not limited to, disposable personal hygiene products (e.g. 
training pants, diapers, absorbent underpants, incontinence products, feminine 
hygiene items and the like); disposable garments (e.g. industrial apparel, 
coveralls, head coverings, underpants, pants, shirts, gloves, socks and the 
like); infection control/clean room products (e.g. surgical gowns and drapes, 
face masks, head coverings, surgical caps and hood, shoe coverings, boot 
slippers, wound dressings, bandages, sterilization wraps, wipers, lab coats, 
coverall, pants, aprons, jackets, bedding items and sheets and the like) and 
sports apparel. 

Various homofil fibers can be made from the elastic ethylene interpolymer of the 
present invention, including staple fibers, spunbond fibers or melt blown fibers 
(using, e.g., systems as disclosed in U.S. Pat. No. 4,340,563 (Appel et al.), 
U.S. Pat. No. 4,663,220 (Wisneski et al.), U.S. Pat. No. 4,668,566 (Braun), or 
U.S. Pat. No. 4,322,027 (Reba), all of which are incorporated herein by 
reference), and gel spun fibers (e.g., the system disclosed in U.S. Pat. No. 
4,413,110 (Kavesh et al.), incorporated herein by reference)). Staple fibers can 
be melt spun (i.e., they can be extruded into the final fiber diameter directly 
without additional drawing), or they can be melt spun into a higher diameter and 
subsequently hot or cold drawn to the desired diameter using conventional fiber 
drawing techniques. 

Elastic staple fibers of the present invention herein can also be used as 
bonding fibers, especially where the inventive elastic fibers have a lower 
melting point than the surrounding matrix fibers. In a bonding fiber 
application, the bonding fiber is typically blended with other matrix fibers and 
the entire structure is subjected to heat, where the bonding fiber melts and 
bonds the surrounding matrix fiber. Typical matrix fibers which benefit from use 
of the inventive elastic fibers disclosed herein include, but are not limited 
to, poly(ethylene terephthalate) fibers, cotton fibers, nylon fibers, 
polypropylene fibers, heterogeneously branched polyethylene fibers, 
homogeneously branched ethylene polymer fibers, linear polyethylene homopolymer 
fibers and the like and combinations thereof. The diameter of the matrix fiber 
can vary depending upon the end use application. 

Bicomponent fibers can also be made from the novel homogeneously branched 
substantially linear ethylene polymers. Such bicomponent fibers have the elastic 
ethylene interpolymer of the present invention in at least one portion of the 
fiber. For example, in a sheath/core bicomponent fiber (i.e., one in which the 
sheath concentrically surrounds the core), the elastic ethylene interpolymer can 
be in either the sheath or the core. Different elastic ethylene interpolymers of 
the present invention can also be used independently as the sheath and the core 
in the same fiber, preferably where both components are elastic and especially 
where the sheath component has a lower melting point than the core component. 
Other types of bicomponent fibers are within the scope of the invention as well, 
and include such structures as side-by-side conjugated fibers (e.g., fibers 
having separate regions of polymers, wherein the elastic ethylene interpolymer 
of the present invention comprises at least a portion of the fiber's surface). 

The shape of the fiber is not limited. For example, typical fiber has a circular 
cross-sectional shape, but sometimes fibers have different shapes, such as a 
trilobal shape, or a flat (i.e., "ribbon" like) shape. The elastic fiber 
disclosed herein is not limited by the shape of the fiber. 

The heat resistant elastic fiber of the present invention can be used with other 
fibers such as PET, Nylon, cotton, etc. to make elastic fabrics. As an added 
advantage, the heat (and moisture) resistance of the elastic fiber of present 
invention can enable polyester PET fibers to be dyed at ordinary PET dyeing 
conditions. The other commonly used elastic fibers, especially spandex, can only 
be used at less severe PET dyeing conditions to prevent degradation of 
properties. 

Fiber diameter can be measured and reported in a variety of fashions. Generally, 
fiber diameter is measured in denier per filament. Denier is a textile term 
which is defined as the grams of the fiber per 9000 meters of that fiber's 
length. Monofilament generally refers to an extruded strand having a denier per 
filament greater than 15, usually greater than 30. Fine denier fiber generally 
refers to fiber having a denier of about 15 or less. Microdenier (aka 
microfiber) generally refers to fiber having a diameter not greater than about 
100 micrometers. For the inventive elastic fibers disclosed herein, the diameter 
can be widely varied, with little impact upon the fiber's elasticity. But the 
fiber denier can be adjusted to suit the capabilities of the finished article 
and as such, would preferably be: from about 0.5 to about 30 denier/filament for 
melt blown; from about 1 to about 30 denier/filament for spunbond; and from 
about 1 to about 20,000 denier/filament for continuous wound filament. 
Nonetheless, preferably, the nominal denier is greater than 37, more preferably 
greater than or equal to 55 and most preferably greater than or equal to 65. 
These preference are due to the fact that typically durable apparel employ 
fibers with deniers greater than or equal to about 40. 

Fabrics made from the inventive elastic fibers disclosed herein include both 
woven and nonwoven fabrics. Nonwoven fabrics can be made variously, including 
spunlaced (or hydrodynamically entangled) fabrics as disclosed in U.S. Pat. No. 
3,485,706 (Evans) and U.S. Pat. No. 4,939,016 (Radwanski et al.), the 
disclosures of which are incorporated herein by reference; by carding and 
thermally bonding staple fibers; by spunbonding continuous fibers in one 
continuous operation; or by melt blowing fibers into-fabric and subsequently 
calandering or thermally bonding the resultant web. These various nonwoven 
fabric manufacturing techniques are well known to those skilled in the art and 
the disclosure is not limited to any particular method. Other structures made 
from such fibers are also included within the scope of the invention, including 
e.g., blends of these novel fibers with other fibers (e.g., poly(ethylene 
terephthalate) (PET) or cotton). 

Fabricated articles which can be made using the inventive elastic fibers and 
fabrics disclosed herein include elastic composite articles (e.g., diapers) that 
have elastic portions. For example, elastic portions are typically constructed 
into diaper waist band portions to prevent the diaper from falling and leg band 
portions to prevent leakage (as shown in U.S. Pat. No. 4,381,781 (Sciaraffa), 
the disclosure of which is incorporated herein by reference). Often, the elastic 
portions promote better form fitting and/or fastening systems for a good 
combination of comfort and reliability. The inventive elastic fibers and fabrics 
disclosed herein can also produce Structures which combine elasticity with 
breathability. For example, the inventive elastic fibers, fabrics and/or films 
of the present invention many be incorporated into the structures disclosed in 
U.S. Pat. No. 6,176,952, the disclosure of which is incorporated herein by 
reference. 

The inventive elastic fibers and fabrics disclosed herein can also be used in 
various structures as described in U.S. Pat. No. 2,957,512 (Wade), the 
disclosure of which is incorporated herein by reference. For example, layer 50 
of the structure described in U.S. Pat. No. '512 (i.e., the elastic component) 
can be replaced with the inventive elastic fibers and fabrics, especially where 
flat, pleated, creped, crimped, etc., nonelastic materials are made into elastic 
structures. Attachment of the inventive elastic fibers and/or fabric disclosed 
herein to nonelastic fibers, fabrics or other structures can be done by melt 
bonding or with adhesives. Gathered or shirred elastic structures can be 
produced from the inventive elastic fibers and/or fabrics disclosed herein and 
nonelastic components by pleating the non-elastic component (as described in 
U.S. Pat. No. '512) prior to attachment, pre-stretching the elastic component 
prior to attachment, or heat shrinking the elastic component after attachment. 

The inventive elastic fibers described herein also can be used in a spunlaced 
(or hydrodynamically entangle 

d) process to make novel structures. For example, U.S. Pat. No. 4,801,482 
(Goggans), the disclosure of which is incorporated herein by reference, 
discloses an elastic sheet (12) which can now be made with the novel elastic 
fibers/fabric described herein. 

Continuous elastic filaments as described herein could also be used in woven 
applications where high resilience is desired. 

The inventive elastic fibers and fabrics disclosed herein with adjust in the 
interpolymer melt index and/or degree of crosslinking or extent or radiation 
also have adjustable tenacity and retractive force. Such capabilities and 
characteristics enable extensive design flexibility, for example, to provide for 
variable retractive force in the same garment, if needed, as described for 
example in U.S. Pat. No. 5,196,000 (Clear et al.), the disclosure of which is 
incorporated herein by reference. 

U.S. Pat. No. 5,037,416 (Allen et al.), the disclosure of which is incorporated 
herein by reference, describes the advantages of a form fitting top sheet by 
using elastic ribbons (see member 19 of U.S. Pat. '416). The inventive elastic 
fibers could serve the function of member 19 of U.S. Pat. '416, or could be used 
in fabric form to provide the desired elasticity. 

Composites that utilize very high molecular weight linear polyethylene or 
copolymer polyethylene also benefit from the inventive elastic fibers disclosed 
herein. For example, the inventive elastic fibers have a low melting point (with 
the melting point of the polymer essentially linearly related to the polymer 
density), such that in a blend of inventive elastic fibers disclosed herein and 
very high molecular weight polyethylene fibers (e.g., Spectra.TM. fibers made by 
Allied Chemical) as described in U.S. Pat. No. 4,584,347 (Harpell et al.), the 
disclosure of which is incorporated herein by reference, the lower melting 
elastic fibers bond the high molecular weight polyethylene fibers without 
melting the high molecular weight fibers, thus preserving the high strength and 
integrity of the high molecular weight fiber. 

In U.S. Pat. No. 4,981,747 (Morman), the inventive elastic fibers and/or fabrics 
disclosed herein can be substituted for elastic sheet 122, which forms a 
composite elastic material including a reversibly necked material. 

The inventive elastic fibers disclosed herein can also be a melt blown elastic 
component, as described in reference 6 of the drawings of U.S. Pat. No. 
4,879,170 (Radwanski), the disclosure of which is incorporated herein by 
reference. U.S. Pat. No. '170 generally describes elastic co-form material and 
manufacturing processes. 

Elastic panels can also be made from the inventive elastic fibers and fabrics 
disclosedherein, and can be used, for example, as members 18, 20, 14, and/or 26 
of U.S. Pat. No. 4,940,464 (Van Gompel), the disclosure of which is incorporated 
herein by reference. The inventive elastic fibers and fabrics described herein 
can also be used as elastic components of composite side panels (e.g., layer 86 
of U.S. Pat. '464). 

The elastic ethylene polymer can also be shaped or fabricated into elastic 
films, coatings, sheets, strips, tapes, ribbons and the like. The elastic film, 
coating and sheet of the present invention may be fabricated by any method known 
in the art, including blown bubble processes (e.g., simple bubble as well as 
biaxial orientation techniques such trapped bubble, double bubble and tenter 
framing), cast extrusion, injection molding processes, thermoforming processes, 
extrusion coating processes, profile extrusion, and sheet extrusion processes. 
Simple blown bubble film processes are described, for example, in The 
Encyclopedia of Chemical Technology, Kirk-Othmer, Third Edition, John Wiley & 
Sons, New York, 1981, Vol. 16, pp. 416-417 and Vol. 18, pp. 191-192. The cast 
extrusion method is described, for example, in Modern Plastics Mid-October 1989 
Encyclopedia Issue, Volume 66, Number 11, pages 256 to 257. Injection molding, 
thermoforming, extrusion coating, profile extrusion, and sheet extrusion 
processes are described, for example, in Plastics Materials and Processes, 
Seymour S. Schwartz and Sidney H. Goodman, Van Nostrand Reinhold Company, New 
York, 1982, pp. 527-563, pp. 632-647, and pp. 596-602. 

The elastic strips, tapes and ribbons of the present invention can be prepared 
by any known method, including the direct extrusion processing or by 
post-extrusion slitting, cutting or stamping techniques. Profile extrusion is an 
example of a primary extrusion process that is particularly suited to the 
preparation of tapes, bands, ribbons and the like. 

The elastic materials of the present invention can also be rendered pervious or 
"breathable" by any method well known in the art including by apperturing, 
slitting, microperforating, mixing with fibers or foams, incorporating fillers 
and stretching or combinations thereof. Examples of such methods include, U.S. 
Pat. No. 3,156,242 by Crowe, Jr., U.S. Pat. No. 3,881,489 by Hartwell, U.S. Pat. 
No. 3,989,867 by Sisson and U.S. Pat. No. 5,085,654 by Buell, the disclosures of 
all of which are incorporate herein by reference. 

Fabricated articles which can be made using the inventive elastic articles 
disclosed herein include composite fabric articles (e.g., disposable 
incontinence garments and diapers) that are comprised of one or more elastic 
component or portion. The inventive elastic articles disclosed herein can also 
produce fabric composite structures which combine elasticity with breathability 
by utilizing a technique that renders the elastic material pervious or 
"breathable" such as suggested by Lippert et al. in U.S. Pat. No. 4,861,652 and 
indicated above. 

The inventive elastic articles disclosed herein can also be used in various 
structures as described in U.S. Pat. No. 2,957,512 (Wade), the disclosure of 
which is incorporated herein by reference. For example, layer 50 of the 
structure described in U.S. Pat. '512 (i.e., the elastic component) can be 
replaced with the novel elastic materials, especially where flat, pleated, 
creped, etc., nonelastic materials are made into elastic or semi-elastic 
structures. Attachment of the novel elastic materials to nonelastic or 
less-elastic materials can be done with heat bonding or with adhesives. Gathered 
or shirred elastic composite materials can be produced from the new elastic 
material described herein and nonelastic components by pleating the non-elastic 
component (as described in U.S. Pat. '512) prior to attachment, prestretching 
the elastic component prior to attachment, or heat shrinking the elastic 
component after attachment. 

The recovery after heat shrinking can be further enhanced by effectuating a high 
degree of orientation into the inventive elastic articles during fabrication. 
Significant orientation can be accomplished by the utilization of various known 
techniques such as high blow-up blown film fabrication, tenter framing of cast 
films and "double bubble" or "trapped bubble" blown film fabrication. 

The inventive elastic articles described herein can also be used make other 
novel structures. For example, U.S. Pat. No. 4,801,482 (Goggans), the disclosure 
of which is incorporated herein by reference, discloses an elastic sheet (12) 
which can now be made with the inventive elastic articles described herein. 

The inventive elastic articles described herein can also be used to make 
breathable portion or breathable elastic composite materials. For example, U.S. 
Pat. No. 5,085,654 (Buell) discloses a leg band (15) with a breathable portion 
45, a breathable topsheet (26), a breathable backsheet (25), elastic elements 
(31 and 64), a breathable element (54), and a breathable sub-element (96) all or 
any combination of which can now be made with the inventive elastic articles 
disclosed herein in either pervious or impervious forms. 

U.S. Pat. No. 5,037,416 (Allen et al.), the disclosure of which is incorporated 
herein by reference, describes the advantages of a form fitting top sheet by 
using elastic ribbons (member 12) and an elastic backsheet (member 16). Pervious 
inventive elastic articles described herein could serve the function of member 
12 and impervious elastics materials of this invention could function as member 
16, or disclosed elastic materials could be used in an elastic composite fabric 
form. 

In U.S. Pat. No. 4,981,747 (Morman), the inventive elastic articles disclosed 
herein can be substituted for elastic sheets 12, 122 and 232 to construct an 
elastic composite material which includes a reversibly necked material. 

Elastic panels, elements, portions or the like can also be made from the 
inventive elastic articles disclosed herein, and can be used, for example, as 
members 18,20, 24, and/or 26 of U.S. Pat. No. 4,940,464 (Van Gompel), the 
disclosure of which is incorporated herein by reference. The inventive elastic 
articles described herein can also be used, for example, as elastic composite 
side panels (e.g., layer) or as elastic ribbons 42 and/or 44. 

The following examples are provided to further illustrate and illuminate the 
present invention but are not intended to limit the invention to the specific 
embodiments set forth. 

EXAMPLES 

In an evaluation to determine the elastic performance of various ethylene 
polymers in response to irradiation or crosslinking, five different ethylene 
interpolymers were subjected to varying degrees of electron beam radiation and 
their elastic properties as 2 mil cast films were measured at room temperature. 
The polymer densities and the melt indexes of the ethylene polymers are shown in 
Table 1. All of the polymers were homogeneously branched ethylene/1-octene 
interpolymers supplied commercially by Dupont Dow Elastomers, Ltd. and 
manufactured using a constrained geometry catalyst system. However, DDE 8190 
also contained via blending 4-5 weight percent polypropylene. The densities for 
the various polymer were determined in accordance with ASTM D-792 and the melt 
indexes were determined in accordance with ASTM D-1238 condition 190.degree. 
C./2.16 kilograms. 

        TABLE 1
                   Density     Melt Index
        Polymer (g/cm.sup.3)  (g/10 minutes)     Designation
           A        0.863           0.5        ENGAGE EG 8180
           B        0.859           1.0           DDE 8190
           C        0.870           1.0        ENGAGE EG 8100
           D        0.870           5.0        ENGAGE EG 8200
           E        0.870          10           XU-58380.00

2 mil cast films of each polymer listed in Table 1 were fabricated using 
conventional cast film extrusion equipment at melt temperatures of 
430.degree.-500.degree. F. After film fabrication, the cast films were electron 
beam radiated at various dosage using equipment similar to that described in 
U.S. Pat. No. 5,324,576, the disclosure of which is incorporated herein by 
reference. The elastic properties (stress-strain data) for the various films was 
determined using an Instron tensiometer set at 10 inch/minute, except as 
otherwise indicated. 

For the permanent set determinations at 23.degree. C., the gage length was 2 
inches and the crosshead speed was 10 inches/minute. The test consisted of 
pulling the film sample to 200% strain (elongation) and holding it for 30 
seconds, then returning the crosshead to the starting point and holding it for 
60 seconds, and then pulling the sample to determine the point where the load 
initially rises above zero. The percent permanent set was taken as the percent 
strain at which the load rose above zero. The test was a one cycle test which 
was run in duplicate. 

For percent stress or load relaxation determination at 23.degree. C., the gage 
length was 2 inches and the crosshead speed was 10 inches/minute. This test 
consisted of pulling the film sample to 200% strain (elongation) and holding it 
for 30 seconds. The stress at initially at 200% strain was taken as the maximum 
stress and the stress after the 30 second holding period was taken as the 
minimum stress. The percent stress or load relaxation was run in duplicate and 
was calculated from the following equation: ##EQU1## 

Table 2 reports the elastic property (stress-strain) data as as the permanent 
set and stress relaxation data for the various film samples. 

Data in Table 2 was plotted and shown in FIG. 1 and 2. FIG. 1 indicates that 
electron beam radiation up to 8-12 megarads has no substantial affect on the 
percent stress relaxation performance of the various polymers. Conversely, FIG. 
2 shows that irradiation has a dramatic affect on the percent permanent set 
performance of the ethylene polymers. However, FIG. 2 (like FIG. 1 and the 
results shown in WO 95/29197) shows no particular distinction between the 
various polymers as the polymer density dominated the percent permanent set 
response and radiation affected the various polymer equally. 

In another evaluation, 2 mil cast films of Resin A and Resin D were subjected to 
varying dosages of electron beam radiation and evaluated to determine their 
respective percent stress or load relaxation performances at 38.degree. C. This 
test was performed as described above, except the temperature was 38.degree. C. 
instead of 23.degree. C. and the sample was held at 200% strain for 1 hour 
instead for 30 seconds. Table 3 shows the results for this evaluation and FIG. 3 
plots the results using the average of duplicative samples as well as a 
four-datapoint average for Resin D at 5 and 8 megarads of electron beam 
radiation. 

                      TABLE 2
                        *    Inventive Ex. 1     *    Inventive Ex. 2
     Comparative Ex. 3*
    Resin               A     A      A      A     B     B     B     B     C
     C     C     C
    e-Beam,megarad      0     3      5      8     0     3     5     8     0
     3     5     8
    100% Strain Load,  232   242    254    259   191   170   211   214   330
     315   318   327
    g/inch
    200% Strain Load,  269   290    318    354   226   211   235   238   409
     384   380   395
    g/inch
    % Strain @ Break   762   651    785    491  1109   896   973   860   667
     676   697   410
    % Permanent Set @  21     9     10     22    17    11    7.5   6.6   41
     28    20    23
    200% Strain
    % Stress           19    18     16     19    20    17    19    20    22
     20    25    21
    Relaxation @
    200% Strain
    % Xylene           NA   98.7   91.04  68.2   NA   99.6  99.1  99.6   NA
     99.6  99.8  73.9
    Extractive
                                                Comparative Ex. 4*
     Comparative Ex. 5*
                             Resin               D     D     D     D     E
     E     E     E
                             e-Beam,megarad      0     5     8    12     0
     5     8    12
                             100% Strain Load,  331   328   329   397   327
     325   303   317
                             g/inch
                             200% Strain Load,  387   357   423   379   367
     430   382   385
                             g/inch
                             % Strain @ Break   812   780   883   784   909
     869   809   773
                             % Permanent Set @  42    24    35    22    50
     24    24    26
                             200% Strain
                             % Stress           23    18    23    19    23
     23    22    21
                             Relaxation @
                             200% Strain
                             % Xylene           NA   99.7  99.3  81.5   NA
     99.6  99.4  77.5
                             Extractive
    *not an example of the invention; provided for comparative purposes only.
       TABLE 3
           E-Beam         Maximum      Minimum      % Stress
          megarads      Stress, psi   Stress, psi    Relaxation
           Resin D
        (Comp. Ex. 4)
              0             192          127          33.9
              0             181          125          30.9
              5             235          112          52.3
              5             230          108          53.0
              8             231          132          42.9
              8             245          136          44.5
             12             250          120          52.0
             12             227          115          49.3
           Resin A
        (Inv. Ex. 1)
              0             126           55          56.3
              0             120           53          55.8
              3             120           57          52.5
              3             134           59          56.0
              5             134           64          52.2
              5             142           69          51.4
              8             137           70          48.9
              8             145           78          46.2

The data in Table 3 and FIG. 3 show surprisingly the irradiation can 
substantially reduce the elevated temperature percent stress relaxation 
performance of ethylene interpolymers having densities less than 0.87 g/cm.sup.3 
and conversely, show irradiation has no affect or increase the elevated 
temperature stress relaxation performance of ethylene interpolymers 
characterized as having densities greater than 0.87 g/cm.sup.3. Table data in 
Table 3 also show that the minimum stress of ethylene interpolymers 
characterized as having densities less than 0.87 g/cm.sup.3 desirably increases 
at higher dosage level. Extrapolation of FIG. 3 indicates that at an electron 
beam radiation dosage level of about 20 megarads, such interpolymer will exhibit 
a percent stress relaxation at 38.degree. C. of less than 20. 

In another evaluation, a homogeneously branched ethylene polymer was evaluated 
to determine its elongation-tenacity stability upon crosslinking. The 
homogeneously branched ethylene polymer selected for this evaluation was a 
substantially linear ethylene/1-octene interpolymer supplied by The Dow Chemical 
Company under the designation AFFINITY.TM. EG8200. This interpolymer has 5 
I.sub.2 melt index and a 0.87 g/cc density. The interpolymer also contained 200 
ppm IRGANOX.TM. 1010, 2000 ppm Chimassorb 944 (both supplied by Ciba-Geigy 
Corporation) and 800 ppm Standostab PEPQ.TM. (supplied by Sandox Chemicals). The 
polymer was meltspun into monofilament fibers of nominal 70-75 denier at 
Alex-James Corporation and wound onto spools. Subsequently, some of the spools 
were electron-beam irradiated at 32 Mrad dosage. The stress-strain properties 
(tenacity and percent elongation) of both crosslinked fibers (Inventive Example 
6) and uncrosslinked fibers (comparative run 7) are shown in the FIG. 4. 

FIG. 4 shows surprisingly the tenacity at break and percent elongation at break 
for Inventive Example 6 was not substantially reduced as a result of a high 
degree of crosslinking (about 60-65 percent weight gel content). For the 
expression 

Abs[.DELTA.E/E.sub.0 ]+Abs[.DELTA.T/T.sub.0 ] 

Inventive Example 6 had a value of 0.46. 

FIG. 5 which shows the elastic recovery (percent permanent set) results for 
Inventive Example 6 indicates this fiber exhibited adequate elastic recovery at 
percent elongations less than 100 percent as it would be used in a fabric form. 

In another evaluation, the heat resistance of fibers was evaluated by exposing 
the fibers to elevated temperatures in a strained state. This test determines 
the survival probability of fibers subject to heat setting and ironing. Because 
fiber in the fabric is in extended state, this test was conducted with fibers 
were tested in strained form. 

Two strains, 50 percent and 300 percent, were used in the test. The exposure to 
heat was 1 min, hence the test measures resistance to heat shock. Fibers were 
stretched to the desired extension in a lab stretcher and exposed to heat by 
inserting the stretcher in a temperature-equilibrated forced-air oven for 1 
minute. The oven temperature was increased at 5.degree. C. increments using new 
samples for each test until fiber fracture occurred for at least two repeats. 
The temperature where fracture occurred was recorded for each strain. 

In this test, the heat resistance for comparative run 7 fiber was about 
80.degree. C. at 50 percent elongation and 70.degree. C. at 300 percent 
elongation. Conversely, the heat resistance of Inventive Example 6 was 
dramatically improved. That is, for Inventive Example 6, the heat resistance was 
greater than 250.degree. C. at both 50 percent and 300 percent elongation. 

* * * * *