U.S. patent application number 10/013875 was filed with the patent office on 2002-10-10 for thermally bonded fabrics and method of making same.
This patent application is currently assigned to The Dow Chemical Company. Invention is credited to Maugans, Rexford A..
Application Number | 20020144384 10/013875 |
Document ID | / |
Family ID | 22965435 |
Filed Date | 2002-10-10 |
United States Patent
Application |
20020144384 |
Kind Code |
A1 |
Maugans, Rexford A. |
October 10, 2002 |
Thermally bonded fabrics and method of making same
Abstract
A method for producing a nonwoven fabric comprises passing a
fiber web through a pair of rollers to obtain a thermally bonded
fabric with a high percentage of bond areas. The high percentage of
bond areas is formed by an engraved pattern on at least one of the
rollers. The engraved pattern has a high percentage of bond point
areas and wide bond point angles. The nonwoven fabric has increased
tensile strength, elongation, abrasion resistance, flexural
rigidity, and/or softness.
Inventors: |
Maugans, Rexford A.; (Lake
Jackson, TX) |
Correspondence
Address: |
JENKENS & GILCHRIST, A PROFESSIONAL CORPORATION
1100 LOUISIANA
SUITE 1800
HOUSTON
TX
77002-5214
US
|
Assignee: |
The Dow Chemical Company
|
Family ID: |
22965435 |
Appl. No.: |
10/013875 |
Filed: |
December 11, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60254747 |
Dec 11, 2000 |
|
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Current U.S.
Class: |
28/116 |
Current CPC
Class: |
D04H 3/14 20130101; D04H
1/544 20130101 |
Class at
Publication: |
28/116 |
International
Class: |
D04H 001/44 |
Claims
What is claimed is:
1. A method of making a non-woven fabric, comprising: passing a
fiber web through a pair of rolls to obtain a thermally bonded
fabric with a high percentage of bond areas, wherein the high
percentage of bond areas is formed by an engraved pattern on one of
the rolls, and the engraved pattern has a high percentage of bond
point areas.
2. The method of claim 1, wherein the engraved pattern has a high
percentage of bond point area and a wide bond point angle.
3. The method of claim 1, wherein the percentage of bond areas is
at least about 16 percent.
4. The method of claim 1, wherein the percentage of bond areas is
at least about 20 percent.
5. The method of claim 1, wherein the percentage of bond areas is
at least about 24 percent.
6. The method of claim 2, wherein the bond point angle is about
20.degree. or higher.
7. The method of claim 2, wherein the bond point angle is about
35.degree. or higher.
8. The method of claim 2, wherein the bond point angle is about
37.degree. or higher.
9. The method of claim 2, wherein the bond point angle is about
42.degree. or higher.
10. The method of claim 2, wherein the bond point angle is about
46.degree. or higher.
11. The method of claim 1, wherein the engraved pattern has at
least about 1.55.times.10.sup.5 bond points per square meter.
12. The method of claim 1, wherein the engraved pattern has at
least about 2.31.times.10.sup.5 bond points per square.
13. The method of claim 1, wherein the engraved pattern has at
least about 3.1.times.10.sup.5 bond points per square meter.
14. The method of claim 1, wherein the engraved pattern has at
least about 3.44.times.10.sup.5 bond points per square meter.
15. The method of claim 1, wherein the engraved pattern has at
least about 4.6.times.10.sup.5 bond points per square meter.
16. The method of claim 1, wherein the engraved pattern has at
least about 4.65.times.10.sup.5 bond points per square meter.
17. The method of claim 1, 4, 7, or 14, wherein the fiber web
comprises polyethylene.
18. The method of claim 17, wherein the polyethylene is a
homopolymer of ethylene.
19. The method of claim 17, wherein the polyethylene is a copolymer
of ethylene and a comonomer.
20. The method of claim 17, wherein the polyethylene is obtained in
the presence of a metallocene catalyst.
21. The method of claim 17, wherein the polyethylene is obtained in
the presence of a constrained geometry catalyst.
22. The method of claim 17, wherein the polyethylene is obtained in
the presence of a single site catalyst.
23. A non-woven fabric comprising a polymer, wherein the fabric is
characterized by a high percentage of bond areas and a high
abrasion resistance.
24. The non-woven thermal bonding fabric of claim 23, wherein the
polymer is polyethylene.
25. The method of claim 23, wherein the percentage of bond areas is
at least about 16 percent.
26. The method of claim 23, wherein the percentage of bond areas is
at least about 20 percent.
27. The method of claim 23, wherein the percentage of bond areas is
at least about 24 percent.
28. A fabric made by the method, comprising: passing a fiber web
through a pair of rolls to obtain a thermally bonded fabric with a
high percentage of bond areas, wherein the high percentage of bond
areas is formed by an engraved pattern on one of the rolls, and the
engraved pattern has a high percentage of bond point areas.
29. The fabric of claim 28, wherein the engraved pattern has a wide
bond point angle.
30. The fabric of claim 28, wherein the percentage of bond areas is
at least about 16 percent.
31. The fabric of claim 28, wherein the percentage of bond areas is
at least about 20 percent.
32. The fabric of claim 28, wherein the percentage of bond areas is
at least about 24 percent.
33. The fabric of claim 29, wherein the bond point angle is about
20 degrees or higher.
34. The fabric of claim 29, wherein the bond point angle is about
35 degrees or higher.
35. The fabric of claim 29, wherein the bond point angle is about
37 degrees or higher.
36. The fabric of claim 29, wherein the bond point angle is about
42 degrees or higher.
37. The fabric of claim 29, wherein the bond point angle is about
46 degrees or higher.
38. The fabric of claim 28, wherein the engraved pattern has at
least about 1.55.times.10.sup.5 bond points per square meter.
39. The fabric of claim 28, wherein the engraved pattern has at
least about 2.31.times.10.sup.5 bond points per square meter.
40. The fabric of claim 28, wherein the engraved pattern has at
least 3.1.times.10.sup.5 bond points per square meter.
41. The fabric of claim 28, wherein the engraved pattern has at
least about 3.44.times.10.sup.5 bond points per square meter.
42. The fabric of claim 28, wherein the engraved pattern has at
least about 4.6.times.10.sup.5 bond points per square meter.
43. The fabric of claim 28, wherein the engraved pattern has at
least about 4.65.times.10.sup.5 bond points per square meter.
44. The fabric of claim 28, 31, 34, or 41, wherein the fiber web
comprises polyethylene.
45. The fabric of claim 43, wherein the polyethylene is a
homopolymer of ethylene.
46. The fabric of claim 43, wherein the polyethylene is a copolymer
of ethylene and a comonomer.
47. The fabric of claim 43, wherein the polyethylene is obtained in
the presence of a metallocene catalyst.
48. The fabric of claim 43, wherein the polyethylene is obtained in
the presence of a constrained geometry catalyst.
49. The fabric of claim 43, wherein the polyethylene is obtained in
the presence of a single site catalyst.
50. A method of making a non-woven polyethylene fabric, comprising:
passing a polyethylene fiber web through a pair of rolls to obtain
a thermally bonded fabric with at least 20 percent of bond areas,
wherein the bond areas is formed by an engraved pattern on one of
the rolls, and the engraved pattern has at least about
3.1.times.10.sup.5 bond points per square meter.
51. The method of claim 50, wherein the engraved pattern has a bond
point angle of about 20.degree. or higher.
52. The method of claim 51, wherein the bond point angle is about
35.degree. or higher.
53. The method of claim 51, wherein the bond point angle is about
37.degree. or higher.
54. The method of claim 51, wherein the bond point angle is about
42.degree. or higher.
55. The method of claim 51, wherein the bond point angle is about
46.degree. or higher.
56. The method of claim 50, wherein the engraved pattern has at
least about 3.44.times.10.sup.5 bond points per square meter.
57. The method of claim 50, wherein the percentage of bond areas is
at least about 24 percent.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application claims priority to U.S. provisional
application serial No. 60/254,747 filed on Dec. 11, 2000, which is
incorporated by reference herein in its entirety.
STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT
[0002] Not applicable.
REFERENCE TO MICROFICHE APPENDIX
[0003] Not applicable.
FIELD OF THE INVENTION
[0004] This invention relates to nonwoven fabrics formed from
polyolefin polymers and methods of making the fabrics.
BACKGROUND OF THE INVENTION
[0005] Fabrics made from fibers include both woven and nonwoven
fabrics. Nonwoven fabrics are used for sanitary and medical uses
including hospital gowns, diaper linings, and sanitary wipes. Many
processes for producing bonded nonwoven fabrics exist. For example,
one can apply heat and pressure for bonding at limited areas of a
nonwoven web by passing it through the nip between heated calender
rolls either or both of which may have patterns of lands and
depressions on their surfaces. During such a bonding process,
depending on the types of fibers making up the nonwoven web, the
bonded regions may be formed autogenously, i.e., the fibers of the
web are melt fused at least in the pattern areas, or with the
addition of an adhesive. The advantages of thermally bonded
nonwoven fabrics include low energy costs and speed of
production.
[0006] Nonwoven fabrics also can be made by a number of other
methods, e.g., spunlacing or hydrodynamically entangling (as
disclosed in U.S. Pat. No. 3,485,706 and U.S. Pat. No. 4,939,016);
by carding and thermally bonding staple fibers; by spunbonding
continuous fibers in one continuous operation; or by melt blowing
fibers into fabric and subsequently calendering or thermally
bonding the resultant web.
[0007] Various properties of nonwoven fabrics determine the
suitability of nonwoven fabrics for different applications.
Nonwoven fabrics can be engineered to have different combinations
of properties to suit different needs. Variable properties of
nonwoven fabrics include liquid handling properties such as
wettability, distribution, and absorbency, strength properties such
as tensile strength and tear strength, softness properties,
durability properties such as abrasion resistance, and aesthetic
properties.
[0008] Polypropylene has been the primary polymer for nonwovens
because of its cost, high strength, and processability. However,
polypropylene nonwovens generally do not have a soft, cotton-like
feel. As such, polyethylene nonwovens have gained interest.
Polyethylenes produce softer fabrics but may have relatively low
tensile strength and abrasion resistance.
[0009] Although nonwoven fabric properties such as liquid handling
properties, strength properties, softness properties and durability
properties, are normally of primary importance in designing
nonwoven fabrics, the appearance and feel of nonwoven fabrics are
often critical to the success of a nonwoven fabric product. The
appearance and feel of nonwoven fabrics is particularly important
for nonwoven fabrics which form exposed portions of products. For
example, it is often desirable that the outer covers of nonwoven
fabric products have a cloth-like feel and a pleasing decorative
design.
[0010] Despite the advances in the art described above, there is
still a need for improved nonwoven fabrics and methods of their
manufacture. In particular, there is a need for nonwoven fabrics
with improved: tensile strength, elongation, abrasion resistance
and softness as defined by fabric flexural rigidity.
SUMMARY OF THE INVENTION
[0011] Embodiments of the invention meet the above need by one or
more of the following aspects of the invention. In one aspect, the
invention relates to a method for producing a nonwoven fabric with
increased tensile strength, elongation, abrasion resistance,
flexural rigidity, and/or softness. The method comprises passing a
fiber web through a pair of rollers to obtain a thermally bonded
fabric with a high percentage of bond areas. The high percentage of
bond areas is formed by an engraved pattern on at least one of the
rollers. The engraved pattern has a high percentage of bond point
areas and/or wide bond point angles.
[0012] In some embodiments, the percentage of bond areas of the
fabric is at least about 16 percent, at least about 20 percent, or
at least about 24 percent. The bond point angel is about 20.degree.
or higher, about 35.degree. or higher, about 37.degree. or higher,
about 42.degree. or higher, or about 46.degree. or higher. The
engrave pattern has at least about 1.55.times.10.sup.5 bond points
per square meter, at least about 2.31.times.10.sup.5 bond points
per square, at least about 3.1.times.10.sup.5 bond points per
square meter, at least about 3.44.times.10.sup.5 bond points per
square meter, at least about 4.6.times.10.sup.5 bond points per
square meter, or at least about 4.65.times.10.sup.5 bond points per
square meter. The fiber web may comprise polyethylene, which may be
a homopolymer of ethylene or a copolymer of ethylene and a
comonomer. The polyethylene may be obtained in the presence of a
single site catalyst, such as a metallocene catalyst or a
constrained geometry catalyst.
[0013] In another aspect, the invention relates to a non-woven
fabric made by the method described herein. The non-woven fabric
comprises a polymer and is characterized by a high percentage of
bond area and a high abrasion resistance. In some embodiments, the
polymer is polyethylene, which may be a homopolymer of ethylene or
a copolymer of ethylene and a comonomer. The polyethylene may be
obtained in the presence of a single site catalyst, such as a
metallocene catalyst or a constrained geometry catalyst. In other
embodiments, the percentage of bond areas of the fabric is at least
about 16 percent, at least about 20 percent, or at least about 24
percent.
[0014] Various aspects of the invention and advantages provided by
the embodiments of the invention are apparent with the following
description.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] FIG. 1 is a simplified diagram of a process for producing
fabrics for use in embodiments of the invention.
[0016] FIG. 2A is a fragmentary elevation view of the embossing
roll illustrating one arrangement of the bond points.
[0017] FIG. 2B is a simplified view of a nonwoven fabric produced
from the process of FIG. 1 and the engraved roll of FIG. 2A.
[0018] FIGS. 3A-3I are schematics of bond patterns for use in
embodiments of the invention on an arbitrary scale.
[0019] FIGS. 4A-4I are micrographs of nonwoven fabrics produced
from the bond patterns in FIGS. 3A-3I for PE1 resin used in Example
1.
[0020] FIG. 5 is a graph of normalized peak loads vs. temperature
for fabrics produced from the bond patterns in FIGS. 3A-3I for PE1
resin.
[0021] FIG. 6 is a graph of percent elongation vs. temperature for
fabrics produced from the bond patterns in FIGS. 3A-3I for PE2
resin used in Example 1.
[0022] FIG. 7 is a graph of typical stress-strain curves for three
fabrics produced in Example 1.
[0023] FIG. 8 is a graph of abrasion resistance vs. temperature for
fabrics produced from the bond patterns in FIGS. 3A-3I for PE1
resin.
[0024] FIG. 9 is a graph of flexural rigidity vs. temperature for
fabrics produced from the bond patterns in FIGS. 3A-3I for PE1
resin.
[0025] FIGS. 10A-10I are scanning electron microscope micrographs,
at 80.times. magnification, of bond points of nonwoven fabrics
produced from bond patterns in FIGS. 3A-3I for PE1 resin.
[0026] FIGS. 11A-11C are scanning electron microscope micrographs
of tensile test fracture sites of nonwoven fabrics produced from
bond patterns in FIGS. 3A-3I for various resins.
[0027] FIGS. 12A-12B are scanning electron microscope micrographs
of abraded bond sites of nonwoven fabrics produced from bond
patterns in FIGS. 3A-3I for various resins.
DESCRIPTION OF EMBODIMENTS OF THE INVENTION
[0028] Embodiments of the invention provide a method for producing
a non-woven fabric by thermal bonding. The fabric has a high
percentage of bond areas which are produced by passing a fiber web
through a pair of rolls, with at least one of the rolls having an
engraved pattern with a high percentage of bond point areas along
with wide bond point angles. The term "nonwoven" as used herein
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 term "bonding" as
used herein refers to the application of force or pressure
(separate from or in addition to that required or used to draw
fibers to less than or equal to 50 denier) to fuse molten or
softened fibers together. In some embodiments, the bond strength is
greater than or equal to about 1,500 grams results. The term
"thermal bonding" is used herein refers to the reheating of fibers
and the application of force or pressure (separate from or in
addition to that required or used to draw fibers to less than or
equal to 50 denier) to effect the melting (or softening) and fusing
of fibers. In some embodiments, the bond strength is greater than
or equal to about 2,000 grams results. Operations that draw and
fuse fibers together in a single or simultaneous operation or prior
to any take-up roll (for example, a godet), for example,
spunbonding, are not considered to be a thermal bonding
operation.
[0029] A thermal bonding process for producing a non-woven fabric
is illustrated in FIG. 1. Such a process or variations thereof is
described, for example, in the following U.S. Pat. Nos.: 5,888,438;
5,851,935; 5,733,646; 5,654,088; 55,629,080; 5,494,736; 4,770,925;
4,635,073; 4,631,933; 4,564,553; 4,315,965, which are incorporated
by reference herein in their entirety. All such disclosed processes
may be utilized in embodiments of the invention with or without
modifications.
[0030] Referring to FIG. 1, a web forming system 10, such as a
carding system, is employed to initially form a fibrous web 12. The
fibers are aligned predominantly in the machine direction of web
formation, as indicated by arrow 13. Alternatively, a spunbond
system could be used to produce more random orientation of the
fibers. The web 12 may be directed through a preheating station 14.
The preheated web is then passed to the pressure nip of a bonding
station provided by opposed rolls 20 and 22. The roll 20 is a metal
engraved roll and is heated to a temperature near the melting point
of the fibers. The backup roll (i.e., smooth roll) 22 is heated in
a controlled manner to a temperature near the melting point of the
fibers, preferably below the stick point of such fibers. In some
embodiments, the engraved pattern comprises circles, although other
shapes, such as ovals, squares, and rectangulars, may be used.
[0031] The engraved roll as illustrated in FIG. 2A contains areas,
bond points, that are in intimate, compressed contact with a flat
roll. These areas induce melting and create bond areas. The size of
these areas determines the number of fibers bonded at a single
point and also the total area of the fabric that contains
non-fibrous integrity. The number of fibers connected at one bond
point can influence its overall strength, but also can contribute
to its overall stiffness. There are three factors of an engraved
pattern that effect the overall properties of a nonwoven fabric.
They include bond area, bond point or side-wall angle, and the
concentration of bond points usually stated as points per square
unit area.
[0032] The engraved pattern on the roll is produced via bond
points. These points extend from the engraved roll and when in
contact with the flat roll, produce a bonded area. Generally the
bond points produce a pattern on the nonwoven fabric, such as seen
in FIG. 2B. The bond points of an engraved pattern are generally
expressed in terms of bond points per square area. In a preferred
embodiment, the engraved pattern has about 1.55.times.10.sup.5 bond
points per square meter (100 bond points per square inch),
preferably about 2.31.times.10.sup.5 bond points per square meter
(149 bond points per square inch), more preferably about
3.10.times.10.sup.5 bond points per square meter (200 bond points
per square inch), or about 3.44.times.10.sup.5 bond points per
square meter (222 bond points per square inch), or about
4.60.times.10.sup.5 bond points per square meter (297 bond points
per square inch), or about 4.65.times.10.sup.5 bond points per
square meter (300 bond points per square inch). Higher bond points
per square meter such as 5.42.times.10.sup.5, 6.20.times.10.sup.5,
7.75.times.10.sup.5, 9.30.times.10.sup.5, or more, (per square
inch, such as 350, 400, 500, 600, or more) also may be
feasible.
[0033] The bond point is made up of a bond point angle and bond
area. Referring to FIGS. 3A-I, various bond point patterns of
different bond point angles and bond areas are shown. Bond point
angle refers to the angle at which the bond point extends from the
engraved roll. The bond point angle is about 20 degrees or higher,
preferably about 35 degrees or higher, more preferably about 37
degrees or higher, most preferably about 42 degrees or higher, and
still most preferably about 46 degrees or higher. FIG. 3A is for
bond pattern 1 having a 46.degree. angle, 20 percent bond area,
3.44.times.10.sup.5 pts/m.sup.2 (222 pts/in.sup.2), base width of
1.7.times.10.sup.-3 m (0.067 inch), base height of
4.32.times.10.sup.-4 m (0.017 inch), and a point width of
7.62.times.10.sup.-4 m (0.03 inch). FIG. 3B is for bond pattern 2
having a 20.degree. angle, 16 percent bond area,
3.44.times.10.sup.5 pts/m.sup.2 (222 pts/in.sup.2), base width of
1.7.times.10.sup.-3 m (0.067 inch), base height of
4.32.times.10.sup.-4 m (0.017 inch), and a point width of
6.86.times.10.sup.-4 m (0.027 inch). FIG. 3C is for bond pattern 3
having a 20.degree. angle, 24 percent bond area,
3.44.times.10.sup.5 pts/m.sup.2 (222 pts/in.sup.2), base width of
1.7.times.10.sup.-3 m (0.067 inch), base height of
4.32.times.10.sup.-4 m (0.017 inch), and a point width of
8.38.times.10.sup.-4 m (0.033 inch). FIG. 3D is for bond pattern 4
having a 20.degree. angle, 20 percent bond area,
2.31.times.10.sup.5 pts/m.sup.2 (149 pts/in.sup.2), base width of
1.7.times.10.sup.-3 m (0.067 inch), base height of
4.32.times.10.sup.-4 m (0.017 inch), and a point width of
9.30.times.10.sup.-4 m (0.0366 inch). FIG. 3E is for bond pattern 5
having a 20.degree. angle, 20 percent bond area,
4.60.times.10.sup.5 pts/m.sup.2 (297 pts/in.sup.2), base width of
1.7.times.10.sup.-3 m (0.067 inch), base height of
4.32.times.10.sup.-4 m (0.017 inch), and a point width of
6.60.times.10.sup.-4 m (0.026 inch). FIG. 3F is for bond pattern 6
having a 42.degree. angle, 16 percent bond area,
3.44.times.10.sup.5 pts/m.sup.2 (222 pts/in.sup.2), base width of
1.7.times.10.sup.-3 m (0.067 inch), base height of
4.32.times.10.sup.-4 m (0.017 inch), and a point width of
6.86.times.10.sup.-4 m (0.027 inch). FIG. 3G is for bond pattern 7
having a 37.degree. angle, 24 percent bond area,
3.44.times.10.sup.5 pts/m.sup.2 (222 pts/in.sup.2), base width of
1.7.times.10.sup.-3 m (0.067 inch), base height of
4.32.times.10.sup.-4 m (0.017 inch), and a point width of
8.38.times.10.sup.-4 m (0.033 inch). FIG. 3H is for bond pattern 8
having a 46.degree. angle, 20 percent bond area,
2.31.times.10.sup.5 pts/m.sup.2 (149 pts/in.sup.2), base width of
1.7.times.10.sup.-3 m (0.067 inch), base height of
4.32.times.10.sup.-4 m (0.017 inch), and a point width of
9.3.times.10.sup.-4 m (0.0366 inch). FIG. 3I is for bond pattern 9
having a 35.degree. angle, 20 percent bond area,
4.60.times.10.sup.5 pts/m.sup.2 (297 pts/in.sup.2), base width of
1.7.times.10.sup.-3 m (0.067 inch), base height of
4.32.times.10.sup.-4 m (0.017 inch), and a point width of
6.60.times.10.sup.-4 m (0.026 inch).
[0034] Bonded areas and unbonded areas make up the nonwoven fabric.
Bonded areas may be defined as the percentage of the surface area
of the nonwoven fabric that is covered by a bond produced by the
bond point The bond area in embodiments of the invention is
preferably at least 16 percent, more preferably at least 20 percent
and most preferably at least 24 percent, 30 percent, 35 percent, 40
percent, 45 percent, 50 percent or more.
[0035] Fiber and Nonwoven Fabric Fabrication
[0036] A web forming system generally includes processes for
producing fibers which can be thermally bonded to form fabrics
include dry laid, wet laid, and polymer laid or any other
processes. In some embodiments, the fibers are produced by
spunbond, meltblown or carded staple processes. These processes are
further described in the following United States Patents, which are
hereby incorporated by reference in their entirety: U.S. Pat. Nos.
3,338,992; 3,341,394; 3,276,944; 3,502,538; 3,978,185; and
4,644,045. In general, the spunbond process uses a high powered
vacuum chamber to increase the velocity of the fibers in order to
decrease the fiber's diameters to produce a continuous fiber. The
meltblown process blows air down from above and uses surface forces
to drag the fibers to higher velocities to produce very low denier
non-continuous fibers.
[0037] Conventional spunbond processes are described in U.S. Pat.
Nos. 3,825,379; 4,813,864; 4,405,297; 4,208,366; and 4,334,340 all
of which are incorporated by reference herein in their entirety.
The spunbonding process is one which is well known in the art of
fabric production. Generally, continuous fibers are extruded, laid
on an endless belt, and then bonded to each other, and often times
to a second layer such as a melt blown layer, often by a heated
calendar roll, or addition of a binder. An overview of spunbonding
may be obtained from L. C. Wadsworth and B. C. Goswami, Nonwoven
Fabrics: "Spunbonded and Melt Blown Processes" proceedings Eight
Annual Nonwovens Workshop, Jul. 30-Aug. 3, 1990, sponsored by The
Textiles and Nonwovens Development Center (hereinafter "TANDEC"),
University of Tennessee, Knoxville, Tenn.
[0038] The term "meltblown" is used herein 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.
[0039] The term "spunbond" is used herein 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.
[0040] Nonwovens can be produced by numerous methods. Most methods
include substantially the same basic procedures: (1) material
selection; (2) web formation; (3) web consolidation; and (4) web
finishing. Material selection provides the properties suitable for
the application. The web is formed from fibers of the selected
materials. The web is then bonded to form a fabric and the fabric
is finished to produce the final product for cutting and
folding.
[0041] The diameter of the fiber affects properties of the fabric
including strength and flexural rigidity. 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 (i.e., microfiber)
generally refers to fiber having a diameter not greater than about
100 micrometers. For the fibers disclosed herein, the diameter can
be widely varied, with little impact upon the fiber's elasticity.
However, 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. One can
convert the fiber diameter in denier to meter according to the
equation: 1 fiber diameter ( meter ) = 11.89 .times. 10 - 6 .times.
fiberdiamter ( denier ) fiberdensity ( g / cc ) .
[0042] Other fiber properties that influence the fabric's final
properties include the fiber's orientation, crystallinity, diameter
and cooling rates. The strength of the bond is a limiting factor in
nonwoven fabric strength. Lower fiber orientation allows for
greater amounts of melting during bonding, causing stronger bonding
regions. In addition, high amounts of orientation induced by
drawing a polymer causes high amounts of shrinkage during thermal
bonding making processability difficult.
[0043] Crystalline portions of a fiber are particularly of interest
to the thermal bonding process due to the melting that occurs. The
degree of melting and flow significantly impacts the bond strength.
Less stable crystals melt first; followed by the more stable or
oriented crystals if enough heat is transferred to the polymer.
Because of the short duration of heat transfer to the bond area,
only a fraction of the crystals melt.
[0044] After the web has been loosely formed, the individual fibers
need to be bonded together. Web consolidation provides strength and
rigidity to the fabric. Ways to consolidate the web include
mechanical, chemical, and thermal bonding. Mechanical consolidation
is accomplished by entangling fibers at various points in the web,
including needle punching, stitch bonding, spunlacing, or any other
mechanical consolidation process. Chemical bonding involves
spraying or saturating the web with an adhesive such as latex.
Thermal bonding of the web is a common bonding technique and
include point-calender, ultrasonic and radian-heat bonding. In some
embodiments, point-calender bonding is used and comprises passing
the web through two heated rolls that are in intimate contact. One
roll is male-patterned engraved and the other is a flat roll. The
fibers melt and flow over one another. Upon cooling, the fabric is
formed.
[0045] As a web of fibers is pulled into calender there are many
thermomechanical processes of different magnitudes that occur.
These processes include: conductive heat transfer; heat of
deformation; flow of melted polymer; diffusion; and the Clapeyron
effect.
[0046] Conductive heat transfer is transported across the steel
roll, fabric interface. The amount of heat transferred by
conduction is proportional to the temperature of the steel rolls
and the amount of time the web spends under the bond pin (roll
speed). Also adding heat to the system is the heat of deformation.
Due to high pressures between the steel rolls, the web is formed
into a different shape very quickly and mechanical work is done on
the system. This mechanical work is transferred to heat. These two
forms of heat raise the temperature of the web between the rolls
and is highest under the bond pin. An equation assuming that all of
the mechanical work transfers to heat is given by:
[F(s)ds]=V.rho.C.sub.p.DELTA.T+f.DELTA.H.sub.f.chi..DELTA.V
[0047] where F(s)ds is the force exerted on the web over a distance
ds, a is the fraction of mechanical work converted to heat, V is
the volume of the web, .chi. is the crystallinity, and f is the
fraction of crystals that melt. The first term on the right side is
the amount of heat used to increase the temperature and the second
term describes the amount of heat that melts the polymer
crystals.
[0048] When the temperature reaches its melting point, the high
pressure under the pins causes the melt to flow outside to an area
of lower pressure. Also while in the molten state, the polymer
self-diffuses. Upon exiting the calender, the melt solidifies and
mechanically locks the fibers at the bond point. These two
phenomena fuse together several fibers at a bond point and turn the
web into a fabric. The diffusion penetration distance for polymers
during the bonding process is almost negligible. The penetration
distance is given by:
R=[t(2.times.D)].sup.1/2
[0049] where R is the penetration distance, t is the time, and D is
the self-diffusion coefficient. In general, most polymers have a
diffusion coefficient of a magnitude of 10.sup.-15 and spend 10 to
40 milliseconds under the bond pins. Using these rough numbers it
is calculated that the penetration distance is only between 45
.ANG. and 100 .ANG.. Considering most fibers used in thermal
bonding are about 20 microns in diameter, the fibers only diffuse
0.00000225 percent of their total diameter. Therefore, the
mechanical interlocking of the polymer melt around the fibers in
the bonding area is likely to be the dominating force holding the
fibers together at the bond point.
[0050] The increased pressure under the bond pins leads to an
increase in melting temperature otherwise known as the Clapeyron
Effect. The effect of pressure increases the melting point of
polypropylene 38 K/kbar or 0.38.degree. C./Mpa. Using a typical
pressure under the bond pin, polypropylene's melting point
increases about 10.degree. C. Polyethylene's melting temperature
increases only about 5.degree. C. under typical bonding
pressures.
[0051] Several factors of the point-bond hot calendering process
affect final fabric properties including temperature, pressure,
speed, roll diameter and engraved pattern. The choice of
temperature is mainly a function of the material, but it should be
noted that the total energy transfer to the web is a function of
temperature, pressure, roll diameter, and line speed. If the
temperature is chosen too low, then the web is under-bonded and the
fabric strength tends to be weak. If the roll temperature is too
high then the web is over-bonded and the resulting fabric is too
stiff or the web completely melts and sticks to the roll.
[0052] The effect of pressure applied to the fabric is small, but
not negligible. At low pressures, the bonding of the web is poor
and strength is, therefore, poor. As pressure increases, the fabric
strength is a function of both bonding temperature and pressure. At
very high pressure, though, the fabric strength reaches a maximum
and then begins to decrease with increasing pressure. Below this
pressure the strength increases continuously up to the melting
point of the polymer.
[0053] The speed and diameter of the bond roll affect the total
time of heat transfer to the web. Larger bond roll diameters allow
for more intimate contact with the heated rolls than do smaller
rolls. Hence there is more heat transferred to the web. In the same
manner, slow spinning rolls have more contact time then fast
spinning rolls.
[0054] The amount of time a fabric spends in the nip (intimate
contact region) may be expressed as:
t=AC.sub.O.sup.1/2R.sup.1/2V.sup.-1
[0055] t=time
[0056] R=radius of bond roll
[0057] V=velocity of bond roll 2 A = C O - C N C O + C R - C N C
O
[0058] where C.sub.O is the original web thickness, C.sub.N is the
thickness between the bond rolls, and C.sub.R is the thickness
after compression in the bond roll.
[0059] The shape of the fiber is not limited and can be any
suitable shape. For example, typical fiber have a circular cross
sectional shape, but sometimes fibers have different shapes, such
as a trilobal shape, or a flat (i.e., "ribbon" like) shape.
[0060] After a thermally bonded fabric has eluded from the bond
pins, cooling and solidifying of the bond regions occurs. The
quench rate of the fabric and more specifically the bonding region
may have an impact on the final fabric properties.
[0061] Important fabric properties include strength, elongation,
peak load, abrasion and flexural rigidity. The strength or tenacity
and elongation of a nonwoven fabric is important to both post
production processes and the consumer. The more strength and
elasticity a fabric has, the faster it can be combined with other
materials into a final consumer product. Another property of a
nonwoven fabric is its ability to resist abrasion. When an abrasive
surface is applied to a nonwoven fabric, fibers are pulled from the
surface and cause fuzz or pilling to form on the surface. As such,
high abrasion resistance is desirable for nonwoven fabrics. Still
another important property of a material that is worn by humans and
placed against the skin is its stiffness. This property can be
measured by flexural rigidity or handfeel evaluations.
[0062] Fiber-Forming Polymers
[0063] Any fiber-forming polymers, especially those which can be
thermally bonded, may be used in embodiments of the invention. For
example, suitable polymers include, but are not limited to,
.alpha.-olefin homopolymers and interpolymers comprising
polypropylene, propylene/C.sub.4-C.sub.20 .alpha.-olefin
copolymers, polyethylene, and ethylene/C.sub.3-C.sub.20
.alpha.-olefin copolymers, the interpolymers can be either
heterogeneous ethylene/.alpha.-olefin interpolymers or homogeneous
ethylene/.alpha.-olefin interpolymers, including the substantially
linear ethylene/.alpha.-olefin interpolymers. Also included are
aliphatic .alpha.-olefins having from 2 to 20 carbon atoms and
containing polar groups. Suitable aliphatic .alpha.-olefin monomers
which introduce polar groups into the polymer include, for example,
ethylenically unsaturated nitriles such as acrylonitrile,
methacrylonitrile, ethacrylonitrile, etc.; ethylenically
unsaturated anhydrides such as maleic anhydride; ethylenically
unsaturated amides such as acrylamide, methacrylamide etc.;
ethylenically unsaturated carboxylic acids (both mono- and
difunctional) such as acrylic acid and methacrylic acid, etc.;
esters (especially lower, e.g. C.sub.1-C.sub.6, alkyl esters) of
ethylenically unsaturated carboxylic acids such as methyl
methacrylate, ethyl acrylate, hydroxyethylacrylate, n-butyl
acrylate or methacrylate, 2-ethyl-hexylacrylate, or ethylene-vinyl
acetate copolymers etc.; ethylenically unsaturated dicarboxylic
acid imides such as N-alkyl or N-aryl maleimides such as N-phenyl
maleimide, etc. Preferably such monomers containing polar groups
are acrylic acid, vinyl acetate, maleic anhydride and
acrylonitrile. Halogen groups which can be included in the polymers
from aliphatic .alpha.-olefin monomers include fluorine, chlorine
and bromine; preferably such polymers are chlorinated polyethylenes
(CPEs). Polymers, such as polyester and nylon, also may be
used.
[0064] Heterogeneous interpolymers are differentiated from the
homogeneous interpolymers in that in the latter, substantially all
of the interpolymer molecules have the same ethylene/comonomer
ratio within that interpolymer, whereas heterogeneous interpolymers
are those in which the interpolymer molecules do not have the same
ethylene/comonomer ratio. The term "broad composition distribution"
used herein describes the comonomer distribution for heterogeneous
interpolymers and means that the heterogeneous interpolymers have a
"linear" fraction and that the heterogeneous interpolymers have
multiple melting peaks (i.e., exhibit at least two distinct melting
peaks) by DSC. The heterogeneous interpolymers have a degree of
branching less than or equal to 2 methyls/1000 carbons in about 10
percent (by weight) or more, preferably more than about 15 percent
(by weight), and especially more than about 20 percent (by weight).
The heterogeneous interpolymers also have a degree of branching
equal to or greater than 25 methyls/1000 carbons in about 25
percent or less (by weight), preferably less than about 15 percent
(by weight), and especially less than about 10 percent (by
weight).
[0065] The heterogeneous polymer component can be an .alpha.-olefin
homopolymer preferably polyethylene or polypropylene, or,
preferably, an interpolymer of ethylene with at least one
C.sub.3-C.sub.20 .alpha.-olefin and/or C.sub.4-C.sub.18 dienes.
Heterogeneous copolymers of ethylene, and propylene, 1-butene,
1-hexene, 4-methyl-1-pentene and 1-octene are especially
preferred.
[0066] Linear low density polyethylene (LLDPE) is produced in
either a solution or a fluid bed process. The polymerization is
catalytic. Ziegler Natta and single-site metallocene catalyst
systems have been used to produce LLDPE. The resulting polymers are
characterized by an essentially linear backbone. Density is
controlled by the level of comonomer incorporation into the
otherwise linear polymer backbone. Various alpha-olefins are
typically copolymerized with ethylene in producing LLDPE. The
alpha-olefins which preferably have four to eight carbon atoms, are
present in the polymer in an amount up to about 10 percent by
weight. The most typical comonomers are butene, hexene,
4-methyl-1-pentene, and octene. The comonomer influences the
density of the polymer. Density ranges for LLDPE are relatively
broad, typically from 0.87-0.95 g/cc (ASTM D-792).
[0067] Linear low density polyethylene melt index is also
controlled by the introduction of a chain terminator, such as
hydrogen or a hydrogen donator. The melt index, measured according
to ASTM D-1238 Condition 190.degree. C./2.16 kg (formerly known as
"Condition E" and also known as "I.sub.2"), for a linear low
density polyethylene can range broadly from about 0.1 to about 150
g/10 min. For purposes of the present invention, the LLDPE should
have a melt index of greater than 10, and preferably 15 or greater
for spunbonded filaments. Particularly preferred are LLDPE polymers
having a density of 0.90 to 0.945 g/cc and a melt index of greater
than 25.
[0068] Examples of suitable commercially available linear low
density polyethylene polymers include the linear low density
polyethylene polymers available from Dow Chemical Company, such as
the ASPUNTM series of fibergrade resins, Dow LLDPE 2500 (55 MI,
0.923 density), Dow LLDPE Type 6808A (36MI, 0.940 density), and the
EXACTTM series of linear low density polyethylene polymers from
Exxon Chemical Company, such as EXACT.TM. 2003 (31 MI, density
0.921).
[0069] The homogeneous polymer component can be an .alpha.-olefin
homopolymer preferably polyethylene or polypropylene, or,
preferably, an interpolymer of ethylene with at least one
C.sub.3-C.sub.20 .alpha.-olefin and/or C.sub.4-Cl.sub.8 dienes.
Homogeneous copolymers of ethylene, and propylene, 1-butene,
1-hexene, 4-methyl-1-pentene and 1-octene are especially
preferred.
[0070] The relatively recent introduction of metallocene-based
catalysts for ethylene/.alpha.-olefin polymerization has resulted
in the production of new ethylene interpolymers known as
homogeneous interpolymers.
[0071] The homogeneous interpolymers useful for forming fibers
described herein have homogeneous branching distributions. That is,
the polymers are those in which the comonomer is randomly
distributed within a given interpolymer molecule and wherein
substantially all of the interpolymer molecules have the same
ethylene/comonomer ratio within that interpolymer. The homogeneity
of the polymers is typically described by the SCBDI (Short Chain
Branch Distribution Index) or CDBI (Composition Distribution Branch
Index) and is defined as the weight percent of the polymer
molecules having a comonomer content within 50 percent of the
median total molar comonomer content. The CDBI of a polymer is
readily calculated from data obtained from techniques known in the
art, such as, for example, temperature rising elution fractionation
(abbreviated herein as "TREF") as described, for example, in Wild
et al, Journal of Polymer Science, Poly. Phys. Ed., Vol. 20, p. 441
(1982), in U.S. Pat. No. 4,798,081, or as is described in U.S. Pat.
No. 5,008,204, the disclosure of which is incorporated herein by
reference. The technique for calculating CDBI is described in U.S.
Pat. No. 5,322,728 and in U.S. Pat. No. 5,246,783 or in U.S. Pat.
No. 5,089,321 the disclosures of all of which are incorporated
herein by reference. The SCBDI or CDBI for the homogeneous
interpolymers used in the present invention is preferably greater
than about 30 percent, especially greater than about 50 percent, 70
percent or 90 percent.
[0072] The homogeneous interpolymers used in this invention
essentially lack a measurable "high density" fraction as measured
by the TREF technique (i.e., the homogeneous
ethylene/.alpha.-olefin interpolymers do not contain a polymer
fraction with a degree of branching less than or equal to 2
methyls/1000 carbons). The homogeneous interpolymers also do not
contain any highly short chain branched fraction (i.e., they do not
contain a polymer fraction with a degree of branching equal to or
more than 30 methyls/1000 carbons).
[0073] The substantially linear ethylene/.alpha.-olefin polymers
and interpolymers are also homogeneous interpolymers but are
further herein defined as in U.S. Pat. No. 5,272,236, and in U.S.
Pat. No. 5,272,872, the entire contents of which are incorporated
by reference. Such polymers are unique however due to their
excellent processability and unique rheological properties and high
melt elasticity and resistance to melt fracture. These polymers can
be successfully prepared in a continuous polymerization process
using the constrained geometry metallocene catalyst systems.
[0074] The term "substantially linear" ethylene/.alpha.-olefin
interpolymer means that the polymer backbone is substituted with
about 0.01 long chain branches/1000 carbons to about 3 long chain
branches/1000 carbons, more preferably from about 0.01 long chain
branches/1000 carbons to about 1 long chain branches/1000 carbons,
and especially from about 0.05 long chain branches/1000 carbons to
about 1 long chain branches/1000 carbons.
[0075] Long chain branching is defined herein as a chain length of
at least one carbon more than two carbons less than the total
number of carbons in the comonomer, for example, the long chain
branch of an ethylene/octene substantially linear ethylene
interpolymer is at least seven (7) carbons in length (i.e., 8
carbons less 2 equals 6 carbons plus one equals seven carbons long
chain branch length). The long chain branch can be as long as about
the same length as the length of the polymer back-bone. Long chain
branching is determined by using .sup.13C nuclear magnetic
resonance (NMR) spectroscopy and is quantified using the method of
Randall (Rev. Macromol. Chem. Phys., C29 (2&3), p. 285-297),
the disclosure of which is incorporated herein by reference. Long
chain branching, of course, is to be distinguished from short chain
branches which result solely from incorporation of the comonomer,
so for example the short chain branch of an ethylene/octene
substantially linear polymer is six carbons in length, while the
long chain branch for that same polymer is at least seven carbons
in length.
[0076] Additional suitable polymers are disclosed in the following
U.S. Pat. No.: 6,316,549; 6,281,289; 6,248,851; 6,194,532;
6,190,768; 6,140,442; 6,037,048; 5,603,888; 5,185,199, and
5,133,917, all of which are incorporated by reference herein in
their entirety.
[0077] Examples of commercial fiber-forming polyethylene include
ASPUN.TM. 6806A (melt index: 105.0 g/10min.; density: 0.930 g/cc),
ASPUN.TM. 6842A (melt index: 30.0 g/10 min.; density: 0.955 g/cc),
ASPUN.TM. 681A (melt index: 27.0 g/10min.; density: 0.941 g/cc),
ASPUN.TM. 6830A (melt index: 18.0 g/10min.; density: 0.930 g/cc),
ASPUN.TM. 6831A (melt index: 150.0 g/10min.; density: 0.930 g/cc),
and ASPUN.TM. 8635A (melt index: 17.0 g/10min.; density: 0.950
g/cc), all available from The Dow Chemical Company, Midland, Mich.
These linear low density polyethylene may be blended with a
homogeneous substantially linear ethylene polymer, such as
AFFINITY.TM. resin from The Dow Chemical Company.
[0078] Examples of commercial fiber-forming polypropylene include
homopolypropylene designated as 5A10 (melt flow rate: 1.4 g/10min.;
flexural modulus: 1585 MPa (230,000 psi)); 5A28 (melt flow rate:
3.0 g/10min.; flexural modulus:: 1585 MPa (230,000 psi)); 5A66V
(melt flow rate: 4.6 g/10min.; flexural modulus: 1654 MPa (240,000
psi)); 5E17V (melt flow rate: 20.0 g/10min.; flexural modulus: 1344
MPa (195,000 psi)); 5E40 (melt flow rate: 9.6 g/10min.; flexural
modulus: 1378 MPa (200,000 psi)); NRD5-1258 (melt flow rate: 100.0
g/10min.; flexural modulus: 1318 MPa (191,300 psi)); NRD5-1465
(melt flow rate: 20.0 g/10min.; flexural modulus: 1344 MPa (195,000
psi)); NRD5-1502 (melt flow rate: 1.6 g/10min.; flexural modulus:
1347 MPa (195,500 psi)); NRD5-1569 (melt flow rate: 4.2 g/10min.;
flexural modulus: 1378 MPa (200,000 psi)); NRD5-1602 (melt flow
rate: 40.0 g/10min.; flexural modulus: 1172 MPa (170,000 psi));
SRD5-1572 (melt flow rate: 38.0 g/10min.; flexural modulus: 1298
MPa (188,400 psi)); SRD5-1258 (melt flow rate: 25.0 g/10min.), and
INSPIRE.TM. resin (melt flow rates ranging from 1.8 to about 25
g/10min.), all available from The Dow Chemical Company. The melt
flow rate is measured according to ASTM D 1238 (230.degree. C./2.16
kg), and flexural modulus according to ASTM D 790A. It should be
understood that resins from other companies, such as Exxon, Bassel,
Mitsui, etc., also may be used.
[0079] Additives such as antioxidants (e.g., hindered phenolics
such as IRGANOX.TM. 1010 or IRGANOX.TM. 1076 supplied by Ciba
Geigy), phosphites (e.g., IRGAFOS.TM. 168 also supplied by Ciba
Geigy), cling additives (e.g., PIB), pigments, colorants, fillers,
and the like, can also be included in the fiber materials disclosed
herein.
[0080] Similarly, the polymers disclosed herein can be admixed with
other polymers to modify characteristics such as elasticity,
processability, strength, thermal bonding, or adhesion, to the
extent that such modification does not adversely affect the desired
properties.
[0081] Some useful materials for modifying the polymers include,
other substantially linear ethylene polymers as well as other
polyolefins, such as high pressure low density ethylene homopolymer
(LDPE), ethylene-vinyl acetate copolymer (EVA), ethylene-carboxylic
acid copolymers, ethylene acrylate copolymers, polybutylene (PB),
ethylene/.alpha.-olefin polymers which includes high density
polyethylene (HDPE), medium density polyethylene, polypropylene,
ethylene-propylene interpolymers, ultra low density polyethylene
(ULDPE), as well as graft-modified polymers involving, for example,
anhydrides and/or dienes, or mixtures thereof.
[0082] Still other polymers suitable for modifying the polymers
include synthetic and natural elastomers and rubbers which are
known to exhibit varying degrees of elasticity. AB and ABA block or
graft copolymers (where A is a thermoplastic endblock such as, for
example, a styrenic moiety and B is an elastomeric midblock
derived, for example, from conjugated dienes or lower alkenes),
chlorinated elastomers and rubbers, ethylene propylene diene
monomer (EDPM) rubbers, ethylene-propylene rubbers, and the like
and mixtures thereof are examples of known prior art elastic
materials contemplated as suitable for modifying the elastic
materials disclosed herein.
[0083] Polypropylene can be blended with a lower melting polymer
such as polyethylene to increase the strength in the bond region.
In the same way LLDPE can be blended with a low melting/low density
polyethylene to produce the same results.
[0084] The initial chemical structure of the polymer used to
produce nonwovens has an affect on the fabric properties. A
polymer's chemical structure impacts the polymer's
density/crystallinity, viscosity, and molecular weight
distribution. Also, addition of two or more polymers to make a
blend can have a significant impact on the nonwoven properties.
Fabric strength increases with increasing molecular weight
distribution. The increase in MWD decreases the orientation of the
fibers in the spinning process, causing greater melting during
calendering.
[0085] The nonwoven fabrics in accordance with embodiments of the
invention have utility in a variety of applications. Suitable
applications include, 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) and 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). The nonwoven fabrics also may
be used in manners taught in the following U.S. Pat. Nos.:
6,316,687; 6,314,959; 6,309,736; 6,286,145; 6,281,289; 6,280,573;
6,248,851; 6,238,767; 6,197,322; 6,194,532; 6,194,517; 6,176,952;
6,146,568; 6,140,442; 6,093,665; 6,028,016; 5,919,177; 5,912,194;
5,900,306; 5,830,810; and 5,798,167, all of which are incorporated
by reference herein in their entirety.
EXAMPLES
[0086] The following examples exemplify some embodiments of the
invention. They do not limit the invention as otherwise described
and claimed herein. All numbers in the examples are approximate
values. In the following examples, various nonwoven fabrics were
characterized by a number of methods. Performance data of these
fabrics were also obtained. Most of the methods or tests were
performed in accordance with an ASTM standard, if applicable, or
known procedures.
[0087] Preparation of Polymer Blends
[0088] A HAAKE twin screw extruder was used to produce polymer
blends. The extruder has the following characteristics:
[0089] 6 heating zones with temperatures of 110.degree. C.,
120.degree. C., 130.degree. C., 135.degree. C., 135.degree. C.,
135.degree. C. respectively.
[0090] Two 18 mm diameter screws.
[0091] L/D=30
[0092] Melt temperature=146.degree. C.
[0093] Die Pressure=2.64.times.10.sup.6 Pa (383 psi)
[0094] Torque=3.44.times.10.sup.7 Pa (5000 psi)
[0095] Speed=200 rpm
[0096] Preparation of Polymer Fibers
[0097] Fibers were produced by extruding the polymer using a one
inch diameter extruder which feeds a gear pump. The gear pump
pushes the material through a spin pack containing a 40 micrometer
(average pore size) sintered flat metal filter and a 108 hole
spinneret. The spinneret holes have a diameter of 400 micrometers
and a land length (i.e., length/diameter or L/D) of 4/1. The gear
pump is operated such that about 0.3 grams of polymer are extruded
through each hole of the spinneret per minute. Melt temperature of
the polymer varies depending upon the molecular weight of the
polymer being spun. Generally the higher the molecular weight, the
higher the melt temperature. Quench air (slightly above room
temperature (about 24.degree. C.) is used to help the melt spun
fibers cool. The quench air is located just below the spinneret and
blows air across the fiber line as it is extruded. The quench air
flow rate is low enough so that it can barely be felt by hand in
the fiber area below the spinneret. The fibers are collected on
godet rolls having a diameter of about 0.152 m (6 inches). The
godet roll's speed is adjustable, but for the experiments
demonstrated herein, the godet's speed is about 1500
revolutions/minute. The godet rolls are located about 3 meters
below the spinneret die. Immediately following the spinning
process, all fibers are cut into fibers of 0.0381 m (1.5 inches) in
length.
[0098] Preparation of Nonwoven Fabrics
[0099] Nonwoven fabric samples were produced on a laboratory
calender equipped with a hardened, chromed engraved steel roll
according to the procedures described herein. An engraved pattern
contains a 20 percent total bonding area and 3.44.times.10.sup.5
bonding points per square meter (222 bonding points per square
inch). FIGS. 3A-3I schematically show various bonding patterns
along with their dimensions that were used in embodiments of the
invention.
[0100] For each pattern design the following procedure was
followed. All fibers were 3 denier. The fibers were then fed into a
carding machine. The fibers were pulled into the RotorRing by a
vacuum and passed through a series of needles. The fibers were then
neatly arranged for future carding by a high speed centrifuge. This
process was repeated for each sample. Next, the fibers were
distributed evenly on a steel tray of dimensions 10 cm by 40 cm a
paper feed card encases the front end of the fiber web. This
produces a web with a basis weight of 33 g/m.sup.2 or 1
oz/yd.sup.2. The fiber web was placed between the moving, heated
calender rolls where the web was thermally bonded into a nonwoven
fabric. The starting bond roll conditions were as follows:
[0101] Top (engraved) roll temperature--from about 110.degree. C.
(230.degree. F.) to about 121.1.degree. C. (250.degree. F.), which
is the temperature described in the figures and tables.
[0102] Bottom (smooth) roll temperature--from about 110.degree. C.
(230.degree. F.) to about 121.1.degree. C. (250.degree. F.), which
is about 4.degree. C. higher than the top roll to avoid sticking to
the top roll.
[0103] Hydraulic pressure--from about 4.82.times.10.sup.6 Pa (700
psi) to about 1.03.times.10.sup.7 Pa (1500 psi).
[0104] Roll Speed/dial setting=from about 3 to about 5 m/min.
[0105] Test Methods
[0106] The fabrics produced contain mostly machine direction
alignment. There is very little cross direction alignment of the
fibers. Characterization of fabrics and fiber orientation were
conducted using the following technique:
[0107] 1. Optical micrographs were obtained from randomly selected
fabrics from this experiment. Both the top of the fabric and the
bottom of the fabric were photographed at 40.times. magnification.
Optical micrographs were also obtained from commercial Spunbond PP
fabric made at TANDEC in the same manner.
[0108] 2. The micrographs were transferred to Scion Imaging
software and divided into four quarters.
[0109] 3. The angles of the fibers in each quarter of the
micrographs were measured with the machine direction being vertical
(0.degree.) and the cross direction being horizontal
(90.degree.).
[0110] Once all fibers were measured, the following equation was
used to quantify the orientation:
F.sub.p=2*avg.(cos.theta.).sup.2-1
[0111] .theta. is the angle of the fiber and F.sub.p is the
orientation parameter is which a value of 0 corresponds to random
orientation and a value of 1 corresponds to perfect alignment in
one direction.
[0112] The tensile strength of each fabric sample was investigated
using an Instron 4501 tensile tester. Line grip jaws were used to
fasten the fabric to the Instron. The "Standard Test Method for
Breaking Force and Elongation of Textile Fabrics" (ASTM D 5035-90)
was used with one exception. The strips were not cut into 0.152 m
(6 inch) strips but into 0.101 m (4 inch) strips.
[0113] A standard abrasion procedure was developed comprising the
following steps using a Taber Abraser model 503 (Rotary
Platform-Double-Head Method) with an 8 compartment sample
holder:
[0114] 1. The fabric was cut into 0.0762.times.0.0762 m (3.times.3
inch) pieces and labeled.
[0115] 2. An adhesive backing was applied to the edges of the
abraded surface to prevent tearing at the edges.
[0116] 3. Samples were weighed individually to 4 decimal
places.
[0117] 4. The samples were placed in the sample holder making sure
not to cause any wrinkles or loose areas. The samples were arranged
with the machine direction pointing at the center of the sample
holder and the engraved pattern side facing up.
[0118] 5. The fabric samples were abraded for a determined amount
of cycles (100) using CO.sub.2 rubber abrasion wheels. Masking tape
made by American Tape was applied to the abraded surface and then
removed in a steady, but quick motion.
[0119] 6. The fabric was again weighed and recorded.
[0120] Any samples that tore or completely degraded during abrasion
were thrown out and deleted from further testing.
[0121] Flexural rigidity was measured according to the design
specifications of ASTM method D 1388-64. A leveling bubble was
placed on the horizontal platform before measurements were taken to
ensure consistency. The length of overhang and the basis weight of
the fabric was then used to calculate flexural rigidity. Although
the cantilever test is a way to easily measure the stiffness of all
fabrics, it is important to be able to correlate the results with
consumer opinion. The feel of a fabric in a persons hand may have
different properties than that found in a mechanical test. In
addition, the surface of the fabric should have a soft feel to the
touch as well.
[0122] All handfeel evaluations were conducted by a panel of 12 who
were chosen to make evaluations on the graininess and stiffness of
the fabrics. All panelists followed the following procedure:
[0123] 1. Each panelist was given 4 anchor samples and their
corresponding number ranging from 1 for the least grainy or least
stiff to 15 for the most stiff or most grainy. The anchors and
their corresponding numbers are given in Table 10.
[0124] 2. The panelist laid the sample flat on the table with the
embossed side of the fabric face up. Their wrist lay on the table
top and their index and middle fingers moved across the entire
surface of the sample. This process was repeated in all four
directions of the sample. Their evaluation rating for graininess
was recorded.
[0125] 3. The panelist laid the sample flat on a table with their
dominant hand on top of the sample. Their fingers were positioned
so the fingers are pointed toward the top of the sample. The sample
was gathered with fingers moving toward their palm while the
opposite hand guided the sample into a cupped hand. The sample is
squeezed and released repeatedly.
[0126] 4. Their evaluation rating was recorded for stiffness.
[0127] All samples were evaluated before a number rating was given
for each. Due to the availability of panelists only a selected set
of samples were tested.
Example 1
[0128] Polyethylene (PE) polymers were obtained from The Dow
Chemical Company. The polyethylene polymers have varying density
and melt indices. A polypropylene (PP) polymer also was obtained
from The Dow Chemical Company. The properties of the polymers are
given in Table 1.
1TABLE 1 Polymers Used in Experiments Melt Index Polymer Grade
Density (g/cc) (g/10 minutes) Melt Point (.degree. C.) PE1 0.955 29
131 PE2 0.941 27 125 PE3 0.950 17 129 PE4 0.870 1 55 PP1 0.910 35
165
[0129] Polyethylene that is representative of PE1 include ASPUN.TM.
6842A available from The Dow Chemical Company, Midland, Mich.
Polyethylene that is representative of PE2 include ASPUN.TM. 6811
available from The Dow Chemical Company, Midland, Mich.
Polyethylene that is representative of PE3 include ASPUN.TM. 6835A
available from The Dow Chemical Company, Midland, Mich.
Polyethylene that is representative of PE4 include AFFINITY.TM.
EG8100 available from The Dow Chemical Company, Midland, Mich.
Polypropylene that is representative of PP1 include H500-35
available from The Dow Chemical Company, Midland, Mich. Four
samples were formulated from the polyethylene polymers. Three
homopolymers and a 95 percent/5 percent blend of PE1 and PE4 were
tested. Compounding for the blend was as described above. 4.75 kg
of PE1 pellets were combined with 0.25 kg of PE4 and placed in the
hopper of the twin screw extruder. After exiting the extruder, the
polymer is pulled through a cooling bath maintained at 5.degree. C.
The solid polymer is then fed into a Berlyn Clay Group chipper
where it is cut into pellets. The polymer was purged for 15 minutes
and pellets were collected for 100 minutes.
[0130] Fibers were produced using the spinning conditions given in
Table 2 and the process described above.
2TABLE 2 Spinning Conditions for Various Fibers Predicted Total
Extruder Godet Godet Fiber Mass of Temp. Speed Speed Diameter
Sample Fiber Polymer (.degree. C.) (rpm) (m/min) (microns) (g) 1
PE1 190 1800 900 21 540 2 PE2 190 1800 900 21 180 3 PE3 190 1800
900 21 180 4 PE1 + PE4 190 1800 900 21 180 5 PP1 230 1800 900 21
180
[0131] Fabrics were produced from the above described processes
using the fibers produced in Table 1 and were coded in the
following manner. A series of three numbers was assigned to each
sample. The first number indicated the polymer used. The second
number indicated the bond pattern number and the third number
indicated the bonding temperature. Refer to Table 2 for reference
to the polymer number and FIGS. 3A-3I for reference to bond pattern
numbers. For convenience, this labeling system is used to identify
samples.
[0132] FIG. 3A is for bond pattern 1 having a 46.degree. angle, 20
percent bond area, 3.44.times.10.sup.5 pts/m2 (222 pts/in.sup.2),
base width of 1.7.times.10.sup.-3 m (0.067 inch), base height of
4.32.times.10.sup.-4 m (0.017 inch), and a point width of
7.62.times.10.sup.-4 m (0.03 inch). FIG. 3B is for bond pattern 2
having a 20.degree.angle, 16 percent bond area, 3.44.times.10.sup.5
pts/m.sup.2 (222 pts/in.sup.2), base width of 1.7.times.10.sup.-3 m
(0.067 inch), base height of 4.32.times.10.sup.-4 m (0.017 inch),
and a point width of 6.86.times.10.sup.-4 m (0.027 inch). FIG. 3C
is for bond pattern 3 having a 20.degree. angle, 24 percent bond
area, 3.44.times.10.sup.5 pts/m.sup.2 (222 pts/in.sup.2), base
width of 1.7.times.10.sup.-3 m (0.067 inch), base height of
4.32.times.10.sup.-4 m (0.017 inch), and a point width of
8.38.times.10.sup.-4 m (0.033 inch). FIG. 3D is for bond pattern 4
having a 20.degree. angle, 20 percent bond area,
2.31.times.10.sup.5 pts/m.sup.2 (149 pts/in.sup.2), base width of
1.7.times.10.sup.-3 m (0.067 inch), base height of
4.32.times.10.sup.-4 m (0.017 inch), and a point width of
9.30.times.10.sup.-4 m (0.0366 inch). FIG. 3E is for bond pattern 5
having a 20.degree. angle, 20 percent bond area,
4.60.times.10.sup.5 pts/m.sup.2 (297 pts/in.sup.2), base width of
1.7.times.10.sup.-3 m (0.067 inch), base height of
4.32.times.10.sup.-4 m (0.017 inch), and a point width of
6.60.times.10.sup.-4 m (0.026 inch). FIG. 3F is for bond pattern 6
having a 42.degree. angle, 16 percent bond area,
3.44.times.10.sup.5 pts/m.sup.2 (222 pts/in.sup.2), base width of
1.7.times.10.sup.-3 m (0.067 inch), base height of
4.32.times.10.sup.-4 m (0.017 inch), and a point width of
6.86.times.10.sup.-4 m (0.027 inch). FIG. 3G is for bond pattern 7
having a 37.degree. angle, 24 percent bond area,
3.44.times.10.sup.5 pts/m.sup.2 (222 pts/in.sup.2), base width of
1.7.times.10.sup.-3 m (0.067 inch), base height of
4.32.times.10.sup.-4 m (0.017 inch), and a point width of
8.38.times.10.sup.-4 m (0.033 inch). FIG. 3H is for bond pattern 8
having a 46.degree. angle, 20 percent bond area,
2.31.times.10.sup.5 pts/m.sup.2 (149 pts/in.sup.2), base width of
1.7.times.10.sup.-3 m (0.067 inch), base height of
4.32.times.10.sup.-4 m (0.017 inch), and a point width of
9.3.times.10.sup.-4 m (0.0366 inch). FIG. 3I is for bond pattern 9
having a 35.degree. angle, 20 percent bond area,
4.60.times.10.sup.5 pts/m.sup.2 (297 pts/in.sup.2), base width of
1.7.times.10.sup.-3 m (0.067 inch), base height of
4.32.times.10.sup.-4 m (0.017 inch), and a point width of
6.60.times.10.sup.-4 m (0.026 inch).
[0133] Next, pieces of fabric were cut for tensile testing,
abrasion testing, and a cantilever test. All samples were cut from
the center due to inconsistency in the fiber web and processing
temperature at the edges.
[0134] The fabrics were visually evaluated. Temperature, pressure
and resin choice had no effect on the visual appearance of the
fabric. Bond roll pattern had a noticeable effect on the fabric's
visual property. FIGS. 4A-4I are micrographs at 20.times.
magnification of nonwovens produced from resin 6824A at
119.4.degree. C. (247.degree. F.) which show the differences in the
fabrics visually. The dark diamond areas are the bond areas of the
fabrics, while the lighter areas are unbonded fibers.
[0135] A comparison of FIGS. 4A, 4F, 4G, 4H and 4I to FIGS. 4B, 4C,
4D, and 4E show that a side wall angle of 20.degree. produces a
smaller bond area than that of patterns that contain a larger side
wall angle. Measurements of the bond site areas of the fabric are
given in Table 3. The data show a greater percent bond area than
the roll pattern that produced the fabric in bond patterns 1, 6, 7
and 8. This is due to the melt flow of polymer from under the bond
pin and also the increased heat transfer due to compaction of
fibers in the void areas between the bond pins. The fibers contain
less free space and heat transfer via conduction is higher. All
patterns containing 20.degree. side wall angles show a fabric
percent bond area less than that of the roll pattern. Shrinkage of
the polymer fibers is a possible cause. During the spinning process
of the fibers, the fibers are solidified under tension in an
oriented state. When the fibers are exposed to the higher
temperatures under the bond pins, the polymer molecules relax back
or shrink to a more stable state.
3TABLE 3 Measured Bond Areas of Nonwoven Samples Temperature
Average percent Resin Pattern .degree. C. (.degree. F.) bond area
PE1 1 119.4 (247) 33.7 PE1 2 119.4 (247) 16.5 PE1 3 119.4 (247)
30.8 PE1 4 119.4 (247) 19.0 PE1 5 119.4 (247) 20.7 PE1 6 119.4
(247) 17.7 PE1 7 119.4 (247) 31.8 PE1 8 119.4 (247) 24.7 PE1 9
119.4 (247) 24.1 PE2 1 116.1 (241) 31.1 PE2 2 116.1 (241) 14.0 PE2
3 116.1 (241) 20.7 PE2 4 116.1 (241) 17.6 PE2 5 116.1 (241) 17.5
PE2 6 116.1 (241) 17.1 PE2 7 116.1 (241) 28.6 PE2 8 116.1 (241)
22.2 PE2 9 116.1 (241) 23.1 PE3 1 119.4 (247) 33.0 PE3 2 119.4
(247) 13.8 PE3 3 119.4 (247) 23.5 PE3 4 119.4 (247) 15.5 PE3 5
119.4 (247) 17.3 PE3 6 119.4 (247) 16.3 PE3 7 119.4 (247) 28.4 PE3
8 119.4 (247) 23.2 PE3 9 119.4 (247) 19.8 95 percent PE1 + 1 119.4
(247) 30.8 5 percent PE4 95 percent PE1 + 2 119.4 (247) 13.4 5
percent PE4 95 percent PE1 + 3 119.4 (247) 19.0 5 percent PE4 95
percent PE1 + 4 119.4 (247) 17.0 5 percent PE4 95 percent PE1 + 5
119.4 (247) 16.5 5 percent PE4 95 percent PE1 + 6 119.4 (247) 15.3
5 percent PE4 95 percent PE1 + 7 119.4 (247) 26.8 5 percent PE4 95
percent PE1 + 8 119.4 (247) 21.8 5 percent PE4 95 percent PE1 + 9
119.4 (247) 20.0 5 percent PE4
[0136] The 20.degree. side wall angle patterns also appear to have
fibers that are less compacted together or a higher porosity. Bond
patterns 4, 5, 7 and 8 have the same percent bond area, but
different concentrations of points per square meter. The distance
between each bond point is greater for the patterns with the lower
concentration of points per square meter.
[0137] An analysis of the fabric weight is shown in Table 4. Due to
the variation in the carding process and the handling of fiber
webs, thin spots appear in the fabric. Variability in thickness can
have a strong impact on mechanical properties. The weight of one
square inch samples within a fabric has very low variability.
4TABLE 4 Analysis of Fabric Weight Between and Within Samples Resin
Pattern Average Weight (g) PE1 1 0.021 PE1 2 0.023 PE1 3 0.023 PE1
4 0.020 PE1 5 0.019
[0138] FIGS. 4A-4I are micrographs of varying bond patterns of PE1
resin at 119.4.degree. C. (247.degree. F.) that were also used to
evaluate fiber orientation. A study of the figures show most of the
fibers arranged in one direction (up and down). This is the machine
direction (MD) of the fibers. Most spunbond and meltdown fabrics
contain more of a random arrangement of fibers so that the fabric
contains cross direction (CD) strength as well as machine direction
strength. An evaluation of randomly selected fabrics showed that
fabric orientation (f.sub.p) values for a commercial spunbond
fabric were much lower than that of the samples produced and tested
in these examples. The commercial spunbond fabric was made from
polypropylene at TANDEC. The results are given in Table 5. The
f.sub.p values at the bottom of the fabric are higher than that of
the top meaning the fibers are more aligned in the machine
direction on the bottom. The bond pins on the top pushes the fibers
into a more random state while the bottom fibers bonded against a
flat roll maintain the alignment of the web.
5TABLE 5 Data Collected from Orientation of Fibers Measurement
Fabric f.sub.p (1) f.sub.p (2) f.sub.p (3) Average f.sub.p PE (Top)
0.56 0.54 0.53 0.54 PE (Bottom) 0.7 0.82 0.69 0.74 Spunbond PP 0.22
0.19 0.25 0.22 Spunbond PP 0.16 0.18 0.22 0.19
[0139] Tables 6 through 9 show various properties of the nonwoven
fabrics for each polymer fiber tested using various bond patterns
at various temperatures. A series of three numbers was assigned to
each sample. The first number indicates the polymer used. The
second number indicates the bond pattern number and the third
number indicates the bonding temperature in .degree. F. Refer to
Table 2 for reference to the polymer number and FIGS. 3A-3I for
reference to bond pattern numbers. For convenience, this labeling
system is used to identify samples. For example, 1-1-116.1 stands
for fabric made of PE1 resin using bond pattern 1 (FIG. 3A) at a
bonding temperature of 116.1.degree. C. (241.degree. F.). Tensile
properties of all samples were measured for peak load and
elongation at break using an Instron 4501 and procedure ASTM D
5035-90 as previously described. Due to variability between fabrics
produced at the same conditions 6 tensile samples were tested. The
average abrasion (ABR) observed at each of the processing
conditions is listed. For flexural rigidity (FR), each fabric was
measured for length of overhang along with its basis weight to
determine FR according to ASTM D 1388-64 as described above. The
average FR measured of each resin with each processing condition is
listed.
6TABLE 6 Data for Resin PE1 Avg. percent Normalized Avg. Avg.
Abrasion Avg. FR Sample Elongation Peak Load (g) (mg/cm.sup.2)
(mg*cm) 1-1-116.1 43.17 1974 0.76 29.1 1-1-117.7 52.20 2026 0.71
33.8 1-1-119.4 70.00 2161 0.55 45.9 1-2-116.1 16.77 920 1.02 17.6
1-2-117.7 17.40 882 1.01 20.3 1-2-119.4 31.61 1186 0.83 22.0
1-2-116.1 17.00 927 0.77 30.4 1-3-117.7 20.06 1032 0.71 28.8
1-3-119.4 27.81 1330 0.53 33.6 1-4-116.1 20.73 956 1.08 17.8
1-4-117.7 19.66 915 0.92 19.6 1-4-119.4 27.64 1141 0.64 19.6
1-5-116.1 9369 806 0.99 17.9 1-5-117.7 0.89 25.3 1-5-119.4 19.37
1073 0.66 32.4 1-6-116.1 32.08 1253 0.93 28.4 1-6-117.7 49.86 1393
0.89 38.4 1-6-119.4 76.48 1619 0.75 50.8 1-7-116.1 41.15 1511 0.72
48.0 1-7-117.7 52.51 1821 0.66 51.4 1-7-119.4 93.13 2149 0.54 70.1
1-8-116.1 48.27 1517 0.97 41.4 1-8-117.7 75.35 1666 0.83 46.2
1-8-119.4 70.34 1865 0.61 56.0 1-9-116.1 24.08 1193 0.94 45.7
1-9-117.7 28.04 1335 0.85 55.6 1-9-119.4 53.75 1493 0.64 85.2
[0140]
7TABLE 7 Data for Resin PE2 Avg. percent Normalized Avg. Avg.
Abrasion Avg. FR Sample Elongation Peak Load (g) (mg/cm.sup.2)
(mg*cm) 2-1-112.7 24.62 1646 0.94 31.8 2-1-114.4 31.54 1912 0.80
43.3 2-1-116.1 45.24 2075 0.68 66.2 2-2-112.7 49.30 1228 1.20 30.1
2-2-114.4 60.96 1336 0.92 36.7 2-2-116.1 36.26 1188 0.75 50.3
2-3-112.7 63.42 1370 1.00 35.9 2-3-114.4 62.79 1544 0.74 41.8
2-3-116.1 33.12 1336 0.59 55.1 2-4-112.7 81.15 1482 1.06 20.2
2-4-114.4 90.96 1525 0.78 24.2 2-4-116.1 39.15 1316 0.65 35.9
2-5-112.7 54.37 1409 0.97 35.0 2-5-114.4 64.09 1508 0.84 40.1
2-5-116.1 19.75 1344 0.61 51.5 2-6-112.7 74.57 1530 1.06 39.6
2-6-114.4 56.29 1438 0.93 52.8 2-6-116.1 38.05 1057 0.75 57.4
2-7-112.7 68.12 1583 0.96 43.0 2-7-114.4 64.24 1743 0.78 54.3
2-7-116.1 50.48 1858 0.58 72.5 2-8-112.7 95.53 1594 1.04 35.5
2-8-114.4 91.61 1617 0.75 40.3 2-8-116.1 33.78 1122 0.65 48.6
2-9-112.7 60.33 1685 0.95 54.6 2-9-114.4 78.11 1705 0.83 54.1
2-9-116.1 73.58 1950 0.61 60.8
[0141]
8TABLE 8 Data for Resin PE3 Avg. percent Normalized Avg. Avg.
Abrasion Avg. FR Sample Elongation Peak Load (g) (mg/cm.sup.2) (mg*
cm) 3-1-116.1 17.74 1447 0.92 40.0 3-1-117.7 21.50 1702 0.61 41.0
3-1-119.4 27.82 1919 0.55 46.3 3-2-116.1 13.53 1242 1.09 41.4
3-2-117.7 23.23 1785 0.97 40.1 3-2-119.4 32.40 1992 0.79 46.0
3-2-116.1 21.65 1922 0.89 36.8 3-3-117.7 28.69 2021 0.62 44.8
3-3-119.4 40.03 2274 0.56 44.9 3-4-116.1 22.66 1721 1.06 27.7
3-4-117.7 26.83 1845 0.89 38.7 3-4-119.4 38.57 2035 0.69 42.1
3-5-116.1 12.33 1248 1.05 28.8 3-5-117.7 16.31 1582 0.87 35.4
3-5-119.4 28.89 1975 0.70 40.3 3-6-116.1 18.79 1138 1.03 60.4
3-6-117.7 28.29 1677 0.88 88.4 3-6-119.4 41.52 1980 0.80 98.0
3-7-116.1 24.87 1597 0.94 82.9 3-7-117.7 41.28 1879 0.66 90.1
3-7-119.4 51.97 2376 0.55 125.5 3-8-116.1 26.63 1255 0.97 74.1
3-8-117.7 43.24 1806 0.81 79.9 3-8-119.4 36.78 2017 0.68 88.4
3-9-116.1 16.56 904 0.90 80.7 3-9-117.7 16.83 1279 0.84 103.7
3-9-119.4 20.26 1456 0.65 116.4
[0142]
9TABLE 9 Data for Resin Containing 95 percent PE1 and 5 percent PE4
Avg. percent Normalized Avg. Avg. Abrasion Avg.FR Sample Elongation
Peak Load (g) (mg/cm.sup.2) (mg*cm) 4-1-116.1 54.03 2065 0.96 22.9
4-1-117.7 81.32 2288 0.75 35.8 4-1-119.4 31.72 1988 0.50 39.0
4-2-116.1 20.23 1322 1.09 32.6 4-2-117.7 33.20 1659 1.00 42.0
4-2-119.4 33.48 1676 0.72 53.4 4-2-116.1 27.46 1485 0.95 35.3
4-3-117.7 36.27 1735 0.71 32.6 4-3-119.4 51.98 2192 0.53 49.0
4-4-116.1 27.59 1452 1.33 26.5 4-4-117.7 39.67 1756 1.05 30.3
4-4-119.4 42.27 1928 0.77 29.4 4-5-116.1 19.75 1344 1.28 31.0
4-5-117.7 34.79 1800 1.03 47.7 4-5-119.4 41.19 2017 0.70 48.7
4-6-116.1 34.41 1590 0.97 56.9 4-6-117.7 60.42 1812 0.84 71.0
4-6-119.4 28.85 1589 0.63 91.0 4-7-116.1 49.89 1920 0.93 67.9
4-7-117.7 75.67 2241 0.73 82.0 4-7-119.4 32.57 1861 0.48 102.7
4-8-116.1 54.02 1862 0.99 46.5 4-8-117.7 45.77 2076 0.85 62.4
4-8-119.4 46.92 1884 0.64 77.9 4-9-116.1 29.05 1362 1.03 67.7
4-9-117.7 53.70 1737 0.85 80.7 4-9-119.4 57.83 1862 0.58 109.6
[0143] Peak load values ranged from 800 g to as high as 2400 g.
These values are much less than a typical PP sample. Using pattern
2 at 136.6.degree. C. (278.degree. F.), PP1 produces a peak load of
4875 g. In general, the normalized peak load increases with an
increase in temperature, bond area, and bond angle. For resin PE2
and the blend of 95 percent PE1 and 5 percent PE4 the peak load
decreased when increasing the temperature from 114.4.degree. C.
(238.degree. F.) to 116.1.degree. C. (241.degree. F.) for PE2 and
from 117.7.degree. C. (244.degree. F.) to 119.4.degree. C.
(247.degree. F.) for the blend. This may be contributed to a change
in the fracture mechanism. The pairwise comparison of samples shows
that a 24 percent bond area has a higher peak load than the 16
percent bond area. As shown earlier, the bond angle has a dramatic
effect on the actual bond area on the samples. FIG. 5 is a graph of
normalized peak load versus temperature of PE2 resin at different
temperatures and using various bond patterns. The peak load was
linearly normalized to a basis weight of 33 g/m.sup.2(1
oz/yd.sup.2) because peak load is a strong function of basis
weight.
[0144] FIG. 6 is a graph of percent elongation versus temperature
for resin PE2 at different temperatures using various bond
patterns. The elongation of PE nonwovens ranged from 10 percent to
as high as 95 percent. Using pattern 2 at 136.6.degree. C.
(278.degree. F.), the elongation of PP only reached 31 percent and
37 percent was the highest value reached at any process condition.
A decrease in the concentration of bond points increases the
elongation significantly. In fact, resin PE2 almost doubled its
elongation at 114.4.degree. C. (238.degree. F.) with a decrease in
concentration of bond points from 4.60.times.10.sup.5 pts./m.sup.2
to 2.31.times.10.sup.5 pts./m.sup.2 (297 pts./in.sup.2 to 149
pts./in..sup.2). The exception to this is resin of 95 percent PE1
and 5 percent PE4 which does not show a large difference in
elongation with decreasing concentration of bond points. This can
be explained by the highly elastic property of PE4 that could be
more significant than the effect of the bond pattern. Temperature
control is important. A 1.6.degree. C. (3.degree. F.) difference in
temperature can have as much as a 100 percent decrease in
elongation.
[0145] Three examples of typical stress-strain curves for resin PE1
are given in FIG. 7. The samples were manufactured using PE1 resin
using bond pattern 3 at temperatures of 116.1.degree. C.
(241.degree. F.), 117.7.degree. C. (244.degree. F.), and
119.4.degree. C. (247.degree. F.). As the temperature increases so
does the peak load. At the highest temperature of 119.4.degree. C.
(247.degree. F.), the elongation of the fabric decreases. Also the
initial modulus of the fabric produced at 119.4.degree. C.
(247.degree. F.) is higher than those produced at lower
temperatures. This is typical of all the fabric samples.
[0146] FIG. 8 is a typical graph of abrasion versus temperature for
resin PE1. In general, the data show that elongation is a function
of all processing variables. An increase in bond area and bond
angle which are interrelated increases the elongation of the
fabric. In general the abrasion resistance is mostly a function of
temperature, although significant differences can be seen between
bond patterns. This may be explained by its fracture mechanism. As
the surface is abraded, the fibers are pulled from the bond points.
Because of the fracture mechanism for abrasion, the amount of fuzz
on the surface depends on bond strength more than the size of the
bond. The values for abrasion ranged from 0.48 mg/cm.sup.2 to
greater than 1 mg/cm.sup.2. A PP sample using bond pattern 2 at
136.6.degree. C. (278.degree. F.) has an abrasion value of 0.15
mg/cm.sup.2, over 3 times less than that of PE.
[0147] A plot of flexural rigidity ("FR") vs. temperature is shown
as FIG. 9 for resin PE2. This is a typical plot and represents the
trends found in the other resins. A high length of overhang
indicates a stiff fabric. Also, a high basis weight contributes to
an increase in stiffness since the fabric supports a larger weight
as it hangs over the edge. An average of the fabric's overhang with
the engraved roll side facing up and facing down was considered the
total overhang for an individual piece of fabric. An average of
each was taken. This is thought to better represent the overall
stiffness of the fabric since the fabric bends in both directions
during wear. Four measurements were taken for each sample in this
manner.
[0148] It is observed that bond patterns 6-9 with larger bond
angles have higher values than patterns 2-5 with 20.degree. bond
angles. The flexural rigidity of all the PE samples ranged from the
low twenties to a high of 125 mg*cm for sample 3-7-119.4. These
values are relatively low, considering a typical PP fabric has a FR
value of over 200 mg*cm. Resin PE2 showed the least stiffness when
compared to other resins of the same processing conditions. This is
likely due to the low density of the polymer. The highest FR values
were obtained by PE3 and can be attributed to a higher polymer
density. The addition of PE4 to PE1 produced a higher FR values. It
is likely due to an increase in melting in the bond area and/or
shrinkage of the fibers and fabric. Concerning the bond pattern, it
is shown that low bond areas, low side wall angles, and low bond
point concentrations produce the lowest values of FR. It should be
noted that low bond areas, side wall angles, and bond point
concentrations can affect other properties, i.e., abrasion.
Therefore, due to PE's low modulus, the FR value may not be as
important as other properties.
[0149] The effect that bond roll patterns have on the stiffness
(ST) of the fabric and the graininess (GR) of the surface was
evaluated by the handfeel test. 12 panelists rated the two
properties on a scale of 1 to 15. Anchors (used as a baseline) were
provided as listed in Table 10. Resin PE1 processed at
119.4.degree. C. (247.degree. F.) on each bond pattern were used as
samples. Table 11 summarizes the averages of the two hand ratings
for each bond pattern.
10TABLE 10 Anchor Materials and their Corresponding Value Test Type
Anchor Material Anchor Number Grainy Bleached mercerized cotton
poplin 2.1 Grainy Army carded cotton sateen 4.9 bleached Grainy
Cotton momie fabric 9.5 Grainy Cotton duck greige 13.6 Stiffness
Polyester/cotton 50/50 single knit 1.3 Stiffness Bleached
mercerized cotton print 4.7 cloth Stiffness Bleached mercerized
cotton poplin 8.5 Stiffness Cotton organdy 14.0
[0150]
11TABLE 11 Data Collected for Hand Survey Sample Stiffness Grainy
1-1-119.4 2.5 5.6 1-2-119.4 0.9 2.9 1-3-119.4 1.8 3.9 1-4-119.4 1.6
4.0 1-5-119.4 1.1 2.8 1-6-119.4 1.7 3.5 1-7-119.4 3.0 5.4 1-8-119.4
1.5 4.0 1-9-119.4 2.5 4.9 5-2-140 5.3 6.4
[0151] Scanning Electron Microscopy (SEM) was used to analyze the
effects of processing conditions on the nonwoven surface, bond
perimeter, cross section and failure mechanism. It has been shown
that processing conditions effect the feel and the strength of the
fabric. This section discusses the relationship between the fabric
surface and its properties and also identifies the fracture
mechanisms as a function of processing conditions.
[0152] Arial views and cross-section views were obtained using the
following procedure:
[0153] 1. The cross-section of the fabric was cut by placing it
between two pieces of paper and placing the sample into liquid
nitrogen for about 1 min, followed by cutting with a razor blade
perpendicular to the machine direction.
[0154] 2. The sample was placed on a stage with conductive tape and
the edges were lined with conductive graphite paint.
[0155] 3. A Denton Vacuum Hi-Res 100 high-resolution chromium
sputtering system was used to coat the fabric with 100-120
Angstroms thick film.
[0156] 4. The sample was placed in the sample compartment and the
compartment was evacuated to 1.3.times.10.sup.-5 Pa (10.sup.-7
torr).
[0157] 5. 5 kEV was used out of the 20 kEV available due to
problems with charge buildup on the fabric surface.
[0158] 6. Micrographs were obtained at various magnifications.
[0159] 7. Scion imaging software was used to view and measure the
micrograph images.
[0160] All tested samples were micrographed at a low magnification
of between 60.times. and 100.times. focusing on the bond point.
Since there was no noticeable surface difference between
temperatures, all pictures were taken of samples at 1.6.degree. C.
(3.degree. F.) below their stick point. This temperature is
119.4.degree. C. (247.degree. F.) for all samples except for resin
PE2 which was at 119.4.degree. C. ( 247.degree. F.). All nine bond
patterns made from resin PE1 are shown in FIGS. 10A-10J. All bond
points contain a large flat surface in the middle that raises up
toward the edge. Patterns 1, 6, 7 and 8 all contain a large side
wall angle. The effect of this is not nearly as noticeable with the
PE1 resin as it is in the other resins, probably due to its high
melt index. The patterns with the small side wall angle produce a
bond that contains a smaller flat area and, geometrically, a more
rounded bond point. Because the shape of the bond point produced
with a 20 degree side wall angle is rounded and covers less surface
area as shown previously, then the space between each bond point is
larger. This larger space gives the fabric its softer feel due to
the increase in exposure area of the fibers. This correlates well
with the handfeel evaluation data. Conversely, the small bond point
surface coverage produces less entangled fibers and decreased the
fabric strength. This was seen previously in tensile data.
[0161] One effect of processing conditions on the nonwoven fabric
is its failure mechanism during destructive testing such as tensile
and abrasion testing. Three types of failure can occur. The fibers
can pull out of the bond sight, break at the bond perimeter, or
break away from the bond. SEM micrographs were also used to
identify the failure mechanism for selected nonwoven samples. FIGS.
11A-C shows examples of the failure mechanisms during tensile
failure. Notice that most processing conditions cause the
polyethylene fabric to fail by the fibers pulling away from a weak
bond point. In some cases at higher temperatures it was evident
that the bonds were strong enough to cause fiber breakage at the
bond perimeter. The addition of 5 percent the PE4 resin to the PE1
resin increased the bond strength enough at 119.4.degree. C.
(247.degree. F.) to cause some fibers to break at the bond
perimeter. There was evidence of two fracture mechanisms at this
point including fibers pulling away from the bond and fibers
breaking at the perimeter.
[0162] An analysis of failure mechanisms caused by abrasion showed
no sign of failure by breaking at the bond perimeter. FIGS. 12A-B
show two examples of a fractured bond point caused by abrasion. The
thin ribbon-like strips are remnants of the previously thermally
bonded point. Even those samples that failed in tensile tests by
brittle fiber failure at the bond perimeter did not show the same
fracture mechanism. After abrasion the fabric failed by destruction
of the bond point. This phenomena may explain why abrasion
resistance does not reach a peak value and then decrease as the
processing temperature is increased as does the tenacity and
elongation. The abrasion resistance is dependent only on the bond
strength.
[0163] As demonstrated above, embodiments of the invention provide
a nonwoven fabric which has relatively increased tensile strength,
elongation, abrasion resistance, flexural rigidity, and/or
softness. Additional characteristics and advantages provided by
embodiments of the invention are apparent to those skilled in the
art.
[0164] While the invention has been described with reference to a
limited number of embodiments, variations and modifications
therefrom exist. For example, the fabric composition need not be a
mixture within the compositions given above. It can comprise any
amount of components, so long as the properties desired in the
fabric composition are met. It should be noted that the application
of the fabric composition is not limited to sanitary articles; it
can be used in any environment which requires a thermally bonded
nonwoven fabric. The appended claims intend to cover all such
variations and modifications as falling within the scope of the
invention.
* * * * *