U.S. patent application number 10/235197 was filed with the patent office on 2003-02-06 for single-ply embossed absorbent paper products.
Invention is credited to Gracyalny, Dale T., Kershaw, Thomas N..
Application Number | 20030026950 10/235197 |
Document ID | / |
Family ID | 26861101 |
Filed Date | 2003-02-06 |
United States Patent
Application |
20030026950 |
Kind Code |
A1 |
Kershaw, Thomas N. ; et
al. |
February 6, 2003 |
Single-ply embossed absorbent paper products
Abstract
The invention relates to embossing single-ply paper products,
for example, paper towels, tissue and napkins, in which an improved
embossing arrangement is used which is particularly suitable for
paper products which have been processed so as to impart
undulations whose axes extend in a principal undulatory direction,
typically in the machine direction. The absorbent sheet typically
further includes undulations which extend in the cross (transverse
direction) of the web such that the absorbent sheet has a biaxially
undulatory structure. The undulations may be formed by the use of
an undulatory creping blade. Defined parameters accommodate: the
distance at which the undulations are spaced, the total surface
area of the design (embossing) elements, the width and length of
the embossing elements and the aspect ratio of the elements, as
well as the angular orientation of the embossing elements with
respect to the undulations.
Inventors: |
Kershaw, Thomas N.; (Neenah,
WI) ; Gracyalny, Dale T.; (Appleton, WI) |
Correspondence
Address: |
Ferrells, PLLC
P.O. Box 312
Clifton
VA
20124-1706
US
|
Family ID: |
26861101 |
Appl. No.: |
10/235197 |
Filed: |
September 5, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10235197 |
Sep 5, 2002 |
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09709185 |
Nov 9, 2000 |
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6455129 |
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60165080 |
Nov 12, 1999 |
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Current U.S.
Class: |
428/152 ;
428/156; 428/174; 604/380 |
Current CPC
Class: |
B31F 1/122 20130101;
B31F 2201/0738 20130101; B31F 2201/0756 20130101; B31F 2201/072
20130101; Y10T 156/1016 20150115; Y10T 428/24479 20150115; B31F
1/07 20130101; Y10T 156/1023 20150115; Y10T 428/24446 20150115;
Y10T 428/24455 20150115; B31F 2201/0758 20130101; Y10T 428/24694
20150115; B31F 2201/0735 20130101; B31F 1/145 20130101; B31F
2201/0784 20130101; Y10T 428/24628 20150115; B31F 2201/0728
20130101 |
Class at
Publication: |
428/152 ;
428/174; 428/156; 604/380 |
International
Class: |
B32B 003/00; A61F
013/15 |
Claims
What is claimed is:
1. A single-ply absorbent sheet provided with primary undulations
extending along a principal undulatory axis of said sheet, said
primary undulations being laterally spaced apart a distance, S,
said single-ply absorbent sheet being provided with an emboss
pattern comprising a plurality of design elements wherein up to
about 50 percent of the surface area of said absorbent sheet is
embossed, characterized in that each design element of said emboss
pattern has a characteristic emboss element lateral width, W, and a
characteristic emboss element, length, L, along a direction L' and
wherein the ratio of W:S for each design element is from about 1 to
about 4.
2. The single-ply absorbent sheet according to claim 1, wherein the
ratio of W:S for each design element is from about 1.5 to about
3.
3. The single-ply absorbent sheet according to claim 1, wherein the
aspect ratio, L:W for each design element is at least about
1.1.
4. The single-ply absorbent sheet according to claim 1, wherein the
aspect ratio, L:W for each design element is at least about
1.2.
5. The single-ply absorbent sheet according to claim 1, wherein the
aspect ratio, L:W for each design element is from about 1.1 to
about 4.
6. The single-ply absorbent sheet according to claim 1, wherein the
aspect ratio, L:W for each design element is from about 1.2 to
about 2.5.
7. The single-ply absorbent towel according to claim 1, wherein
said direction, L', makes an angle .theta. of less than about 45
degrees with the principal undulatory axis of said sheet.
8. The single-ply absorbent sheet according to claim 7, wherein
said direction, L', makes an angle .theta. of less than about 30
degrees with the principal undulatory axis of said sheet.
9. The single-ply absorbent sheet according to claim 1, wherein the
aspect ratio, L:W for each design element is about 1.
10. The single-ply absorbent sheet according to claim 1, wherein
said sheet is provided with secondary undulations substantially
perpendicular to said primary undulations such that said sheet is a
biaxially undulatory sheet with secondary undulations extending
along a secondary undulatory axis of said sheet.
11. The single-ply absorbent sheet according to claim 10, wherein
said sheet has from about 10 to about 50 primary undulations per
inch extending along said principal undulatory axis and from about
10 to about 150 secondary undulations per inch extending along said
secondary undulatory axis of said sheet.
12. The single-ply absorbent sheet according to claim 11, wherein
said sheet has from about 12 to about 25 primary undulations
extending along said principal undulatory axis of said sheet.
13. The single-ply absorbent sheet according to claim 10, wherein
said secondary undulations have a frequency greater than that of
said primary undulations.
14. The single-ply absorbent sheet according to claim 1, wherein
said sheet is a creped sheet and wherein said primary undulations
extend in the machine direction of said sheet and are
longitudinally extending undulations.
15. The single-ply absorbent sheet according to claim 14, wherein
said sheet has from about 10 to about 150 crepe bars per inch
extending in the cross-direction of said sheet.
16. The single-ply absorbent sheet according to claim 15, prepared
with an undulatory creping blade operative to form said
longitudinally extending undulations.
17. The single-ply absorbent sheet according to claim 16, wherein
said sheet has from about 10 to about 50 longitudinally extending
undulations per inch.
18. The single-ply absorbent sheet according to claim 17, wherein
said sheet has from about 12 to about 25 longitudinally extending
undulations per inch.
19. The single-ply absorbent sheet according to claim 16, wherein
the crepe bars have a frequency greater than that of the
longitudinally extending undulations.
20. The single-ply absorbent sheet according to claim 19, wherein
the frequency of the crepe bars is from about 2 to about 6 times
the frequency of said longitudinally extending undulations.
21. The single-ply absorbent sheet according to claim 20, wherein
the frequency of the crepe bars is from about 2 to about 4 times
the frequency of said longitudinally extending undulations.
22. The single-ply absorbent sheet according to claim 14, wherein
the emboss pattern does not substantially alter the cross-direction
stretch of the absorbent sheet from which the embossed absorbent
sheet was prepared.
23. The single-ply absorbent sheet according to claim 22, wherein
the cross-direction stretch of said sheet is from about 0.2 to
about 0.8 times the machine direction stretch of said sheet.
24. The single-ply absorbent sheet according to claim 23, wherein
the cross-direction stretch of said sheet is from about 0.35 to
about 0.8 times the machine direction stretch of said sheet.
25. The single-ply absorbent sheet according to claim 1, wherein
the distance between design elements, D, is greater than S.
26. The single-ply absorbent sheet according to claim 25, wherein D
is from about 1.5 to about 3 times S.
27. The single-ply absorbent sheet according to claim 1, wherein
said design elements have an emboss depth of from about 15 to about
30 mils.
28. The single-ply absorbent sheet according to claim 1, wherein
from about 10 to about 25 percent of the surface area of said sheet
is embossed.
29. The single-ply absorbent sheet according to claim 1, wherein
said sheet is a tissue product having a basis weight of from about
5 to about 25 pounds per 3,000 square foot ream.
30. The single-ply absorbent sheet according to claim 1, wherein
said sheet is a towel product having a basis weight of from about
10 to about 40 pounds per 3,000 square foot ream.
31. The single-ply absorbent sheet according to claim 1 prepared
utilizing recycle furnish.
32. A single-ply sheet provided with primary undulations extending
along a principal axis of said sheet, said primary undulations
being laterally spaced apart a distance, S, said single-ply
absorbent sheet being further provided with an emboss pattern
comprising a plurality of embossments of width, W, and length, L,
wherein the lengths are along a direction, L', and wherein said
embossments cover no more than about fifty percent of the area of
said absorbent sheet, and wherein further the embossments are
spaced apart from each other at a distance, D, with the proviso
that at least one of the ratios of W:S and D:S is from about 1 to
about 4.
33. The single-ply absorbent sheet according to claim 32, wherein
at least one of the ratios of W:S and D:S is from about 1.5 to
about 3.5.
34. The single-ply absorbent sheet according to claim 32, wherein
said embossments cover no more than about 25 percent of the surface
area of said sheet.
35. The single-ply absorbent sheet according to claim 32 wherein
the ratio of cross-direction stretch to machine direction stretch
is from about 0.2 to about 0.8.
36. The single-ply absorbent sheet according to claim 35, wherein
the ratio of the cross-direction stretch to the machine direction
stretch is from about 0.35 to about 0.8.
37. The single-ply absorbent sheet according to claim 32, wherein
said principal undulatory axis is along the machine direction of
said sheet.
38. The single-ply embossed sheet according to claim 32, wherein
said primary undulations are non-compacted relative to the other
portions of the sheet.
39. A method of making a single-ply absorbent sheet comprising:
preparing a web comprising cellulosic furnish; drying the web to
form said absorbent sheet; providing said sheet with primary
undulations extending along a principal undulatory axis of the
absorbent sheet, said undulations being spaced apart a distance, S;
and embossing the sheet with an emboss pattern comprising a
plurality of design elements wherein up to about 50 percent of the
surface area of said sheet is embossed, characterized in that each
design element of said emboss pattern has a characteristic emboss
element width, W, and a characteristic emboss length, L, along a
direction, L', and wherein the ratio of W:S for each design element
is from about 1 to about 4.
40. The method according to claim 39, wherein said sheet is dried
to a consistency of at least 90 percent prior to being
embossed.
41. The method according to claim 39, wherein said sheet is
embossed at a consistency of less than about 90 percent.
42. The method according to claim 39, wherein said absorbent sheet
is provided with said primary undulations by way of wet shaping
said sheet on a fabric.
43. The method according to claim 42, wherein said step of wet
shaping said sheet on a fabric is carried out at a consistency of
between about 30 and about 85 percent.
44. The method according to claim 39, wherein said sheet is a
biaxially undulatory sheet with secondary undulations extending in
a direction substantially perpendicular to said principal
undulatory axis.
45. The method according to claim 44, wherein said sheet includes
applying said sheet to a Yankee dryer and wherein said sheet is
creped from said Yankee dryer.
46. The method according to claim 39, wherein the ratio of W:S for
each design element is from about 1.5 to about 3.
47. The method according to claim 39, wherein the aspect ratio, L:W
for each design element is at least about 1.1.
48. The method according to claim 39, wherein the aspect ratio, L:W
for each design element is at least about 1.2.
49. The method according to claim 47, wherein the aspect ratio, L:W
for each design element is from about 1.1 to about 4.
50. The method according to claim 39, wherein the aspect ratio, L:W
for each design element is from about 1.2 to about 2.5.
51. The method according to claim 39, wherein said direction, L',
makes an angle .theta. of less than about 45 degrees with the
machine direction of said sheet.
52. The method according to claim 51, wherein said direction, L',
makes an angle .theta. of less than about 30 degrees with the
machine direction of said sheet.
53. The method according to claim 39, wherein the aspect ratio, L:W
for each design element is about 1.
54. A method of making a single-ply embossed absorbent sheet
comprising: preparing a web comprising cellulosic furnish; applying
said web to a Yankee dryer; creping said web from said Yankee dryer
with an undulatory creping blade at a consistency of between about
40 and about 98 percent, such that said creped sheet is provided
with crepe bars extending laterally in the cross-direction and
undulations extending longitudinally in the machine direction, said
undulations being spaced apart a distance, S; and embossing said
sheet with an emboss pattern comprising a plurality of design
elements wherein up to about 50 percent of the surface area of said
absorbent sheet is embossed, characterized in that each design
element of said emboss pattern has a characteristic emboss element
lateral width, W, and a characteristic emboss element, length, L,
along a direction L' and wherein the ratio of W:S for each design
element is from about 1 to about 4.
55. The method according to claim 54, wherein said step of
embossing said absorbent sheet comprises passing said sheet through
a nip defined by a pair of matched embossing rolls.
56. The method according to claim 55, wherein said matched
embossing rolls are rigid embossing rolls.
57. The method according to claim 56, wherein said rigid embossing
rolls are steel embossing rolls.
58. The method according to claim 55, wherein said matched
embossing rolls include a rigid roll and a yielding roll.
59. The method according to claim 58, wherein said rigid roll is a
steel embossing roll and said yielding embossing roll is a rubber
embossing roll.
60. The method according to claim 54, wherein the ratio of W:S for
each design element is from about 1.5 to about 3.
61. The method according to claim 54, wherein the aspect ratio, L:W
for each design element is at least about 1.1.
62. The method according to claim 54, wherein the aspect ratio, L:W
for each design element is at least about 1.2.
63. The method according to claim 61, wherein the aspect ratio, L:W
for each design element is from about 1.1 to about 4.
64. The method according to claim 54, wherein the aspect ratio, L:W
for each design element is from about 1.2 to about 2.5.
65. The method according to claim 54, wherein said direction, L',
makes an angle .theta. of less than about 45 degrees with the
machine direction of said sheet.
66. The method according to claim 65, wherein said direction, L',
makes an angle .theta. of less than about 30 degrees with the
machine direction of said sheet.
67. The method according to claim 54, wherein the aspect ratio, L:W
for each design element is about 1.
68. The method according to claim 54, wherein said sheet has from
about 10 to about 150 crepe bars per inch extending in the
cross-direction of said sheet.
69. The method according to claim 68, wherein said sheet has from
about 10 to about 50 longitudinally extending undulations per
inch.
70. The method according to claim 69, wherein said sheet has from
about 12 to about 25 longitudinally extending undulations per
inch.
71. The method according to claim 54, wherein the crepe bars have a
frequency greater than that of the longitudinally extending
undulations.
72. The method according to claim 71, wherein the frequency of the
crepe bars is from about 2 to about 6 times the frequency of said
longitudinally extending undulations.
73. The method according to claim 72, wherein the frequency of the
crepe bars is from about 2 to about 4 times the frequency of said
longitudinally extending undulations.
74. The method according to claim 54, wherein the emboss pattern
does not substantially alter the cross-direction stretch of the
absorbent sheet from which the embossed absorbent sheet was
prepared.
75. The method according to claim 54, wherein the cross-direction
stretch of said sheet is from about 0.2 to about 0.8 times the
machine direction stretch of said sheet.
76. The method according to claim 75, wherein the cross-direction
stretch of said sheet is from about 0.35 to about 0.8 times the
machine direction stretch of said sheet.
77. The method according to claim 54, wherein the distance between
design elements, D, is greater than S.
78. The method according to claim 77, wherein D is from about 1.5
to about 3 times S.
79. The method according to claim 54, wherein said design elements
have an emboss depth of from about 15 to about 30 mils.
80. The method according to claim 54, wherein from about 10 to
about 25 percent of the surface area of said sheet is embossed.
81. The method according to claim 54, wherein said sheet is a
tissue product having a basis weight of from about 5 to about 25
pounds per 3,000 square foot ream.
82. The method according to claim 54, wherein said sheet is a towel
product having a basis weight of from about 10 to about 40 pounds
per 3,000 square foot ream.
83. The method according to claim 54, wherein said cellulosic
furnish comprises recycle furnish.
84. The method according to claim 54, wherein said cellulosic
furnish comprises non-cellulosic material.
85. The method according to claim 54, wherein said cellulosic
furnish comprises synthetic fiber.
Description
CLAIM FOR PRIORITY
[0001] This application claims the benefit of the filing date of
U.S. Provisional Patent Application Serial No. 60/165,080, filed
Nov. 12, 1999.
TECHNICAL FIELD
[0002] The invention relates to embossed absorbent paper products,
for example, paper towels, tissue and napkins, in which an improved
embossing arrangement is used which is particularly suitable for
embossing single-ply paper products which have been processed so as
to include undulations in the sheet.
BACKGROUND OF THE INVENTION
[0003] Absorbent paper products, such as paper towels, napkins and
toilet tissue are widely used on a daily basis for a variety of
household needs. These products are commonly produced by depositing
cellulosic fibers suspended in water on a moving foraminous support
to form a nascent web, removing water from the nascent web,
adhering the dewatered web to a heated cylindrical Yankee dryer,
and then removing the web from the Yankee with a creping blade
which, in conventional processes, imparts crepe bars, ridges or
undulations whose axes extend generally transversely across the
sheet (the cross-direction). Products produced in this conventional
fashion may often be considered lacking in bulk, appearance and
softness and so require additional processing after creping,
particularly when produced using conventional wet pressing
technology. Absorbent sheet produced using the through air drying
techniques normally have sufficient bulk but may have an
unattractive appearance or undesirable stiffness.
[0004] To overcome these deficiencies, an overall pattern is
imparted to the web during the forming and drying process by use of
a patterned fabric having designs to enhance appearance. Further,
through air dried tissues can be deficient in surface smoothness
and softness unless strategies such as calendering, embossing,
chemical softeners and stratification of low coarseness fibers on
the tissue's outer layers are employed in addition to creping.
[0005] Conventional absorbent paper products produced by wet
pressing are almost universally subjected to various
post-processing treatments after creping to impart softness and
bulk. Commonly such tissues are subjected to various combinations
of both calendering and embossing to bring the softness and bulk
parameters into acceptable ranges for premium quality products.
Calendering adversely affects bulk and may raise tensile modulus,
which is inversely related to tissue softness. Embossing increases
product caliper (bulk) and can reduce modulus, but lowers strength
and can have a deleterious effect on surface softness. Accordingly,
it can be appreciated that these processes can have adverse effects
on strength, appearance, surface smoothness and particularly
thickness perception since there is a fundamental conflict between
bulk and calendering.
[0006] In U.S. Pat. Nos. 5,656,134; 5,685,954; and 5,885,415 to
Marinack et al. (hereinafter the Marinack et al. patents), the
disclosure of which is incorporated by reference as if fully set
forth herein) it was shown that paper products having highly
desirable bulk, appearance (including reflectivity) and softness
characteristics, can be produced by a process similar to
conventional processes, particularly conventional wet pressing, by
replacing the conventional creping blade with an undulatory creping
blade having a multiplicity of serrulated creping sections
presenting differentiated creping and rake angles to the sheet.
Further, in addition to imparting desirable initial characteristics
directly to the sheet, the process of the Marinack et al. patents
produces a sheet which is more capable of withstanding calendering
without excessive degradation than a conventional wet pressed
tissue web.
[0007] Accordingly, using a creping technique it is possible to
achieve overall processes which are more forgiving and flexible
than conventional existing processes. In particular, the processes
of Marinack et al. can be used to provide not only desirable
premium products including high softness tissues and towels having
surprisingly high strength accompanied by high bulk and absorbency,
but also to provide surprising combinations of bulk, strength and
absorbency which are desirable for lower grade commercial products.
For example, in commercial (away-from-home) toweling, it is usually
considered important to put quite a long length of toweling on a
relatively small diameter roll. In the past, this has severely
restricted the absorbency of these commercial toweling products as
absorbency suffered severely from the processing used to produce
toweling having limited bulk, or more precisely, the processing
used to increase absorbency also increased bulk to a degree which
was detrimental to the intended application.
[0008] The process and apparatus of the Marinack et al. patents
makes it possible to achieve surprisingly high absorbency in a
relatively non-bulky towel thus providing an important new benefit
to this market segment. Similarly, many webs of the present
invention can be calendered more heavily than many conventional
webs while still retaining bulk and absorbency, making it possible
to provide smoother, and thereby softer feeling, surfaces without
unduly increasing tensile modulus or unduly degrading bulk. On the
other hand, if the primary goal is to save on the cost of raw
materials, the tissue of the present invention can have surprising
bulk at a low basis weight without an excessive sacrifice in
strength or at low percent crepe while maintaining high caliper.
Accordingly, it can be appreciated that the advantages of the
present invention can be manipulated to produce novel products
having many combinations of properties which previously were
impractical.
[0009] The objective of the undulatory creping blade of Marinack et
al. is to work the web more effectively than previous creping
arrangements. That is, the serrulations of the creping blade
operate to contact the web rotating off of the dryer in such a way
that a part of the web contacts the tops of the serrulations while
other parts of the base sheet contact the valleys, thereby forming
undulations in the base sheet. This creping operation effectively
breaks up the hydrogen and mechanical bonds which link the
cellulosic fibers together, thereby producing a smoother, bulkier
and more absorbent sheet, which is well suited for consumer use.
Creping in accordance with the Marinack et al. patents creates a
machine direction oriented shaped sheet which has higher than
normal stretch in directions other than the machine direction, that
is, particularly high cross-direction stretch.
[0010] While the paper products produced with an undulatory creping
blade have commercially desirable properties, additional processing
in the form of embossing can further add to the properties and
appeal of the products. Such embossing can enhance the bulk,
softness and appearance of the products. It has been found that the
proper selection of emboss element spacing, distribution and
orientation can positively impact on the retention or enhancement
of the beneficial properties caused by the creping of the web with
an undulatory blade. Conversely, improper selection of the emboss
element spacing, distribution and orientation can negatively
impact, or cause a complete loss of, the beneficial properties
caused by the creping of the web with an undulatory blade.
[0011] Undulatory blade creping creates a machine direction
oriented shaped sheet which has higher than normal stretch in the
directions other than the machine direction. The present invention
recognizes and takes this three dimensional sheet shape and stretch
into consideration. The application of embossing to the biaxially
undulatory sheet is done in a way that the emboss process provides
the desired modifications to the sheet with controlled extension
and disruption of the localized bonds and fiber shapes imparted by
the undulatory blade creping. In order to determine the parameters
for embossing for sheets processed with an undulatory creping blade
certain test embossings were made: when a relatively large size
Quilt emboss was applied to undulatory blade creped base sheets
made with a number of different blades (tooth spacings being
different) unsatisfactory interference patterns are seen. This is a
direct result of the relative spacing of the local shape and
cross-direction stretch in the sheet to the spacing of the points
of application of the force due to the embossing process. At the
other extreme, when a very busy and tight spacing of emboss
patterns are applied to undulatory blade creped base sheets, most
if not all of, the benefits of the undulatory creping is lost.
[0012] In accordance with the present invention there were
established parameters for embossing webs that have undulations
extending longitudinally along a principal undulatory axis and
optionally include secondary undulations which extend in the cross
(transverse direction) of the web. The parameters must accommodate:
the distance at which the undulations are spaced, the total surface
area of the design (embossing) elements, the width and length of
the embossing elements and the aspect ratio of the elements, and
the angular orientation of the embossing elements with respect to
the undulations.
[0013] It is an object of the present invention to provide
processing to provide single-ply paper products that have improved
appearance, bulk and strength.
[0014] It is another object of the present invention to provide
embossing parameters which are compatible with paper webs that have
been produced with an undulatory structure.
[0015] The embossing parameters of the present invention are
applicable to paper webs having undulations running in either the
machine or cross-directions regardless of the means used to apply
the undulations to the web.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] For a better understanding of the invention reference is
made to the following drawings which are to be taken in conjunction
with the detailed description to follow:
[0017] FIG. 1 illustrates schematically the creping, calendering
and embossing of the paper web in accordance with the present
invention;
[0018] FIGS. 2 and 3 illustrate the front and back of an undulatory
creping blade used to crepe the web to be embossed in accordance
with the embossing parameters of present invention;
[0019] FIG. 4 illustrates the appearance of a biaxially undulatory
web that is to be embossed in accordance with the embossing
parameters of present invention;
[0020] FIGS. 5(a) and 5(b) are photographs of the surface of a
conventional absorbent sheet with an emboss pattern, FIG. 5(a) is a
photograph at 4.times.magnification; while FIG. 5(b) is a
photograph at 6.times.magnification;
[0021] FIGS. 6(a) and 6(b) are photographs of the surface of an
embossed single-ply absorbent sheet produced in accordance with the
present invention, FIG. 6(a) is a photograph at
4.times.magnification, while FIG. 6(b) is a photograph at
6.times.magnification;
[0022] FIGS. 7(a) and 7(b) are photographs at 6.times.magnification
of the surface of an embossed single-ply absorbent sheet produced
in accordance with the present invention, the embossments of FIG.
7(a) were produced by steel to steel embossing rollers, while the
embossments of FIG. 7(b) were produced by steel to rubber embossing
rollers;
[0023] FIGS. 8(a) and 8(b) are photographs of another absorbent
sheet produced in accordance with the present invention, FIG. 8(a)
is a photograph at 6.times.magnification, while FIG. 8(b) is at
4.times.magnification;
[0024] FIG. 9 depicts schematically the orientation of a portion of
a floral design embossing element with respect to the undulations
of the base sheet;
[0025] FIG. 10 is a schematic illustration which depicts in detail
the embossed sheet of FIGS. 6(a) and 6(b);
[0026] FIG. 11 is a schematic illustration which depicts in detail
the embossed sheet of FIGS. 7(a) and 7(b); and
[0027] FIG. 12 is a schematic illustration which depicts in detail
the embossed sheet of FIGS. 8(a) and 8(b).
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0028] The web to be processed according to the present invention
can be made using non-recycled and recycled fibers well known to
the skilled artisan. Preferred fibers are cellulose based fiber and
may include softwood, hardwood, chemical pulp obtained from
softwood and/or hardwood by treatment with sulfate or sulfite
moieties, mechanical pulp obtained by mechanical treatment of
softwood and/or hardwood, recycle fiber, refined fiber and the
like. Papermaking fibers used to form the soft absorbent products
of the present invention may include cellulosic fibers commonly
referred to as wood pulp fibers, liberated in the pulping process
from softwood (gymnosperms or coniferous trees) and hardwoods
(angiosperms or deciduous trees). The particular tree and pulping
process used to liberate the tracheid are not critical to the
success of the present invention. Cellulosic fibers from diverse
material origins may be used to form the web of the present
invention, including non-woody fibers liberated from sabai grass,
rice straw, banana leaves, paper mulberry (i.e. bast fiber), abaca
leaves, pineapple leaves, esparto grass leaves, and fibers from the
genus hesperalae in the family agavaceae. The recycled fibers used
in accordance with the present invention may contain any of the
above fiber sources in different percentages and can be useful in
the present invention. The furnish may include non-cellulosic
components including synthetic fiber if so desired.
[0029] Papermaking fibers can be liberated from their source
material by any one of the number of chemical pulping processes
familiar to the skilled artisan including sulfate, sulfite,
polysulfide, soda pulping, etc. The pulp can be bleached if desired
by chemical means including the use of chlorine, chlorine dioxide,
oxygen, etc. Furthermore, papermaking fibers can be liberated from
source material by any one of a number of mechanical/chemical
pulping processes familiar to anyone experienced in the art
including mechanical pulping, thermomechanical pulping, and
chemithermomechanical pulping. The mechanical pulps can be
bleached, if one wishes, by a number of familiar bleaching schemes
including alkaline peroxide and ozone bleaching.
[0030] Fibers for use according to the present invention can be
obtained from recycling of pre-and post-consumer paper products.
Fiber may be obtained, for example, from the recycling of printers
trims and cuttings, including book and clay coated paper, post
consumer paper including office and curbside paper recycling and
old newspaper. The various collected papers can be recycled using
means common to recycled paper industry. The papers may be sorted
and graded prior to pulping in conventional low-, mid-, and
high-consistency pulpers. In the pulpers the papers are mixed with
water and agitated to break the fibers free from the sheet.
Chemicals common to the industry may be added in this process to
improve the dispersion of the fibers in the slurry and to improve
the reduction of contaminants that may be present. Following
pulping, the slurry is usually passed through various sizes and
types of screens and cleaners to remove the larger solid
contaminants while retaining the fibers. It is during this process
that such waste contaminants as paper clips and plastic residuals
are removed.
[0031] The pulp is then generally washed to remove smaller sized
contaminants consisting primarily of inks, dyes, fines and ash.
This process is generally referred to as deinking. Deinking, in the
modern sense, refers to the process of making useful pulp from
wastepaper while removing an ever-increasing variety of
objectionable, noncellulosic materials. One example of a deinking
process by which fiber for use in the present invention can be
obtained is called floatation. In this process small air bubbles
are introduced into a column of the furnish. As the bubbles rise
they tend to attract small particles of dye and ash. Once upon the
surface of the column of stock they are skimmed off. At this point
the pulp may be relatively clean but is often low in brightness.
Paper made from this stock can have a dingy, gray appearance, not
suitable for near-premium product forms.
[0032] To increase the brightness the furnish (pulp) is often
bleached. Bleaching can be accomplished by a number of means
including, but not limited to, bleaching with chlorine,
hypochlorite, chlorine dioxide, oxygen, peroxide, hydrosulfite, or
any other commonly used bleaching agents. The types and amounts of
bleaching agents depend a great deal on the nature of the
wastepaper being processed and upon the level of desired
brightness. Generally speaking, unbleached waste papers can have
brightness levels between 60 to 80 on the G.E. brightness scale,
depending upon the quality of the paper being recycled. Bleached
waste papers can range between the same levels and may extend up to
about 90, however, this brightness level is dependent upon the
nature of the waste papers used. The particular brightness level
selected will likewise depend on the product desired.
[0033] The creping process is illustrated in FIG. 1. In the
process, a web of single-ply paper tissue sheet 20 is creped from
the surface of a Yankee dryer 22 using an undulatory creping blade
24. Creping blade 24 imparts to the sheet undulations which extend
in the longitudinal direction (machine direction) in addition to
transverse crepe bars as is discussed and illustrated in detail to
follow. Optionally, creped sheet 20 may be calendered by passing it
through the nip of a pair of calender rolls 26a and 26b which
impart smoothness to the sheet while reducing its thickness. After
calendering, the sheet is wound on reel 28. To emboss sheet 20 it
is unwound from reel 28 in a converting operation and passed
through the nip of a pair of embossing rollers 30a, 30b. Thereafter
sheet 20 proceeds to further process steps such as perforating,
cutting the sheet into the widths suitable for end users and
winding of same unto tubes.
[0034] As long as embossing rollers 30 are capable of carrying out
embossing according to the parameters of the present invention,
rollers 30 may be of either the matched or unmatched type and can
be of either steel or rubber. Matched embossing rollers means that
the male embossing elements, carried by one roller, are engraved
first and the female elements carried by the other rollers are
subsequently made from the male elements, or vice versa, so that
both elements are virtually inverse or reciprocal images of each
other within the practicalities of manufacturing tolerances. This
is in contrast to unmatched embossing rollers in which the male and
female embossing elements are not identical in shape, but still are
positioned relative to each other in registry such that they
engage.
[0035] The present invention is applicable to uncreped as well as
to both dry and wet creping processes. In a dry creping process,
the moisture content of the web when it contacts undulatory creping
blade 24 is usually in the range of 2 to 8 percent which permits
the web to be calendered and wound on reel 28. In a wet creping
process the consistency of the web contacting undulatory creping
blade 24 is usually in the range of 40 to 75 percent (solids
content). After the creping operation, the drying process is
completed by use of one or more heated dryers through which the web
is wound. These dryers are used to reduce the water content to its
desired final level, usually from 2 to 8 percent. The dried sheet
is then optionally calendered and wound on reel 28.
[0036] FIGS. 2 and 3 illustrate a portion of undulatory creping
blade 24 which extends indefinitely in length, typically exceeding
100 inches in length and often reaching over 26 feet in length to
correspond to the thickness of the Yankee dryer on the larger
modern paper machines. In contrast, the thickness of blade 24
indicated at 25 is usually on the order of fractions of an inch. As
illustrated in FIGS. 2 and 3, an undulatory cutting edge 34 is
defined by serrulations 36 disposed along, and formed in, one edge
of blade 24 so that an undulatory engagement surface 38, engages
Yankee dryer 22 during use. The shape of undulatory cutting edge 34
strongly influences the configuration of the creped web, in that
the peaks and valleys of serrulations 36 form undulations in web 20
whose longitudinal axes lies along the machine direction. The
number of serrulations 36 can range from 10 to 50 per inch
depending upon the desired number of undulations per inch in the
finished web.
[0037] FIG. 4 is a close up illustration of the configuration of
web 20 after it has been creped by the action of an undulatory
creping blade such as that shown in FIGS. 2 and 3, but before being
embossed. Web 20 is characterized by a reticulum of intersecting
crepe bars 39 extending transversely in the cross-direction which
are formed during the creping of web 20 from Yankee dryer 22. As is
seen at right edge shown in FIG. 4, crepe bars 39 form a series of
relatively small undulations 40 whose longitudinal axes extend in
the crossdirection. The action of serrulations 36 of crepe blade 24
form a series of larger undulations 42 whose longitudinal axes
extend in the machine direction, each undulation 42 includes an
upwardly disposed portion (peak) 44 and a downwardly disposed
portion (valley) 46. As is seen at lower edge 48 shown in FIG. 4,
undulations 42 extend in the machine direction and are larger than
undulations 40 formed by creped bars 39 extending in the
cross-direction. Thus, web 20 has undulations running in both the
machine and cross-direction forming a biaxially undulatory web. The
present invention provides embossing parameters which enhance the
desirable properties of the web shown in FIG. 4. It will be
appreciated by one of skill in the art that the absorbent sheet in
accordance with the invention may be provided with an undulatory
structure or a biaxially undulatory structure such as is shown in
FIG. 4 by any suitable technique for making absorbent sheet. One
technique, used in both creped and uncreped through-air drying
processes involves wet-shaping the web or sheet on a fabric. There
is disclosed, for example, a method of forming tissue in U.S. Pat.
No. 5,607,551 to Farington, Jr. et al. wherein the functions of
providing machine direction stretch and cross machine direction
stretch are accomplished by providing a wet end rush transfer and a
particular through air drying fabric design respectively. The
process according to the '551 patent does not include a Yankee
dryer or creping; however, this process may be used to provide
undulatory structures useful in connection with the present
invention. The disclosure of U.S. Pat. No. 5,607,551 is hereby
incorporated by reference. Absorbent sheet with undulatory
structures may also be prepared in the absence of wet-end pressing
or undulatory creping. There is disclosed, for example, in U.S.
Pat. No. 3,994,771 to Morgan, Jr. et al. a sheet provided with an
undulatory pattern by knuckling a thermally pre-dried web onto a
Yankee dryer followed by creping the sheet off the Yankee dryer.
This process may likewise be employed to prepare an undulatory
substrate for embossing in accordance with the present invention.
The disclosure of U.S. Pat. No. 3,994,771 is hereby incorporated by
reference in its entirety into this application.
[0038] There is shown in FIGS. 5(a) and 5(b) a conventional
absorbent sheet with an emboss pattern. The sheet has a generally
smooth finish and does not include undulations extending
longitudinally in the machine direction. FIG. 5(a) is a photograph
at 4.times.magnification of the surface, while FIG. 5(b) is a
photograph at 6.times.magnification of the surface of the sheet.
The embossments cover more than about 50 percent of the surface
area. In FIGS. 5(a) and 5(b), the machine direction is the shorter
(vertical) direction, while the longer dimension (horizontal) is in
the cross-direction of the sheet. FIGS. 6(a) through 8(b) are
similarly oriented as discussed in more detail hereinafter.
[0039] There is shown in FIGS. 6(a) and 6(b) an embossed single-ply
absorbent sheet produced in accordance with the present invention.
FIG. 6(a) is a photograph of a portion of the sheet at
4.times.magnification, while FIG. 6(b) is a photograph of the sheet
at 6.times.magnification. In both cases, the machine direction of
the sheet is in the vertical (shorter) direction of the photograph,
while the cross-direction of the sheet is in the larger
(horizontal) direction. It will be appreciated from the photographs
that the sheet has an undulatory structure in the machine
direction, crepe bars in the cross-direction, as well as a floral
emboss pattern made up of a plurality of design elements.
[0040] The design elements of FIGS. 6(a) and 6(b) can be
characterized as follows: there is an upper circular portion having
an aspect ratio of approximately 0, thus having an angle with the
machine direction of 1; a central stem portion having an aspect
ratio of roughly 3, also having an angular relation to the machine
direction of 0.degree. and a leaf portion having an aspect ratio of
about 1.5, having a characteristic angle with the machine direction
of about 25.degree. to about 35.degree.. As will be appreciated
from the discussion which follows, the sheet may also be described
as having primary undulations extending along a principal
undulatory axis of the sheet (in this case the machine direction),
as well as having secondary undulations substantially perpendicular
to the primary undulations (in this case the cross-direction of the
sheet) such that the sheet is biaxially undulatory. This structure
is conveniently provided by way of an undulatory creping blade as
noted above, but may also be accomplished in connection with wet
shaping or fabric molding.
[0041] There is shown in FIG. 7(a) a photograph of another sheet
produced in accordance with the invention, wherein the photograph
is at 6.times.magnification and there is provided a plurality of
repeating hexagonal embossments in accordance with the invention.
Here again, the machine direction of the sheet is the vertical
(shorter) side of the photograph, while the cross-direction of the
sheet is the longer (horizontal) side of the photograph. The sheet
of FIG. 7(a) was produced with matched steel embossing rolls. Two
features to note in connection with the sheet of FIG. 7(a) are: (1)
the embossments have relatively "soft" edges due to local
elongation and the longitudinal undulations are offset laterally by
the embossments.
[0042] Yet another sheet of the present invention is shown in FIG.
7(b) which is also a photograph at 6.times.magnification of a sheet
in accordance with the present invention. The machine direction is,
here again, in the shorter (vertical) direction of the photograph
and the cross-direction is along the longer (or horizontal) side of
the photograph, as mounted. The sheet of FIG. 7(b) is, in most
aspects, similar to the sheet of FIG. 7(a); however, the edges of
the embossments are sharp. The sheet of FIG. 7(b) was made by way
of rubber to steel embossing. Here again, the embossments are
operative to laterally displace the vertical or machine direction
undulations due to movement allowed by cross-direction stretch.
[0043] Still yet another absorbent sheet produced in accordance
with the present invention appears in the photographs of FIGS. 8(a)
and 8(b). FIG. 8(a) is a photograph at 6.times.magnification, while
FIG. 8(b) is a photograph of the sheet of FIG. 8(a) at
4.times.magnification. In both cases, the machine direction is
along the shorter edge of the photograph, with the cross-direction
being perpendicular thereto. The embossments are arranged in a
plurality of diamond-like arrays, repeating over the surface of the
sheet. The individual embossments have an aspect ratio of about 1.5
and one spaced at a distance of about 1.5 times the separation
distance between longitudinal undulations as further described
below.
[0044] FIG. 9 depicts schematically a portion of a floral design
element 50 such as a petal shown on FIGS. 6(a) and 6(b) including a
first elongate embossment 52 opposing a second elongate embossment
54. The embossments are provided on a base sheet indicated
generally at 56 provided with a plurality of undulations 58, 60, 62
which repeat over the surface of sheet 56. The undulations extend
in the machine direction 64 of the sheet.
[0045] Design element 50 has a characteristic maximum width, 66,
also labeled W in the figure and a characteristic maximum length,
L, indicated at 68. The aspect ratio, L:W, is characteristically
from about 1 to about 4. Length, L, is disposed about a direction,
L', indicated at 70 which is at an angle, .theta., shown at 72,
with the machine direction (MD) 64.
[0046] Longitudinal undulations such as undulations 58-62 cover the
base sheet in a repeating pattern typically with a frequency of
from about 1 to about 50 undulations per inch with from about 12 to
about 25 undulations per inch being more typical. The undulations
are thus spaced at a plurality of crest to crest distances, S1, S2,
S3, indicated at 74, 76, 78 typically in some embodiments at
slightly more than a millimeter; 1.5 millimeters or so also being
typical. S1, S2 and S3 may be the same in the case of uniform
spacing, or may differ if so desired. In the case of non-uniform
spacing, the respective distances may be averaged when compared
with emboss distances and design element widths.
[0047] While embossments 52, 54 may define a design element of an
embossing pattern applied in accordance with the present invention,
the design elements may also be in the form of embossed shapes,
such as hexagons, diamonds, square, ovals, rectangular structures
and the like which are uniformly repeating over the surface of the
sheet or are provided in clusters. Most preferably, the emboss
design elements have an aspect ratio, L:W, greater than 1 and are
aligned in the machine direction such that .theta. is 0.
[0048] The invention is further exemplified and described with
reference to FIGS. 10 through 12.
[0049] FIG. 10 depicts the embossed sheet of FIGS. 6(a) and 6(b).
The sheet 80 has a plurality of longitudinal undulations 82, 84, 86
and so forth extending in the machine direction 88. A flower design
element 90 is essentially circular, having an aspect ratio of 1 and
making an angle .theta. with the machine direction 88 of 0. The
central stem design element 92 also extends along the machine
direction (.theta.=0.degree.) and has an aspect ratio of roughly 3.
A leaf design element, 94, has an aspect ratio of roughly 1.5 and
makes an angle .theta. with the machine direction of between about
25.degree. and 35.degree.. It should also be noted that sheet 80 is
a creped sheet having repeating crepe bars 96, 98, 100 and so forth
in the cross-direction. The longitudinal undulations have a
frequency of about 20 undulations per inch, while the frequency of
the crepe bars is much higher.
[0050] There is shown in FIG. 11 embossed sheet of FIGS. 7(a) and
(7b) indicated at 102. Sheet 102 has a plurality of design elements
in the form of embossed hexagons 104, 106, 108 and so forth which
repeat over the surface of the sheet as shown. Longitudinal
undulations are provided at a frequency of about 20 undulations per
inch. Interestingly, some of the undulations, such as longitudinal
undulations 110 conform to a serpentine shape in the machine
direction due to the embossments. This is believed due to the
property of relative high cross-direction stretch of the inventive
embossed sheets. Thus, the design elements may be continuously
embossed shapes such as hexagons.
[0051] FIG. 12 shows the sheet of FIGS. 8(a) and 8(b) at 112.
Hence, the emboss pattern of the invention is embodied in
diamond-like clusters 114 of elongate embossments 116 having a
collective aspect ratio of about 1. Individual embossments 116 have
an aspect ratio of 1.5 and a width, W, of about 1 mm. The
longitudinal undulations are spaced at 20 per inch, thus having a
spacing, S, of about 1.3 mm. The individual embossments are spaced
at a distance, D, of about 1.4 mm. Thus, the ratio of D:S is about
1 or more.
[0052] There is thus provided in accordance with the present
invention a single-ply absorbent sheet provided with primary
undulations extending along a principal undulatory axis of the
sheet, the primary undulations being laterally spaced apart a
distance, S, while the single-ply absorbent sheet is provided with
an emboss pattern comprising a plurality of design elements wherein
up to about 50 percent of the surface area of said absorbent sheet
is embossed. The sheet is characterized in that each design element
of the emboss pattern has a characteristic emboss element lateral
width, W, and a characteristic emboss element, length, L, along a
direction L' and wherein the ratio of W:S for each design element
is from about 1 to about 4. More typically, the ratio of W:S for
each design element is from about 1.5 to about 3, and usually the
aspect ratio, L:W for each design element is at least about 1.1. An
aspect ratio, L:W for each design element is at least about 1.2 is
preferred in some cases, but may be from about 1.1 to about 4, or
from about 1.2 to about 2.5.
[0053] The direction, L', makes an angle .theta. of less than about
45 degrees with the principle undulatory axis of the sheet in
preferred cases while instances wherein L', makes an angle .theta.
of less than about 30 degrees with the principal undulatory axis of
the sheet are preferred. An aspect ratio, L:W for each design
element of about 1 is preferred in some embodiments.
[0054] In biaxially undulatory embodiments the sheet is provided
with secondary undulations substantially perpendicular to the
primary undulations such that the secondary undulations extend
along a secondary undulatory axis of the sheet. In such cases, the
sheet may have from about 10 to about 50 primary undulations per
inch extending along the principal undulatory axis and from about
10 to about 150 secondary undulations per inch extending along the
secondary undulatory axis of said sheet. In particularly preferred
embodiments, the sheet has from about 12 to about 25 primary
undulations extending along the principal undulatory axis of the
sheet.
[0055] Typically, the secondary undulations have a frequency
greater than that of said primary undulations and the sheet is a
creped sheet wherein the primary undulations extend in the machine
direction of the sheet and are longitudinally extending
undulations. The sheet may have from about 10 to about 150 crepe
bars per inch extending in the cross-direction of the sheet, and
may be prepared with an undulatory creping blade operative to form
the longitudinally extending undulations. Here, also, the sheet has
from about 10 to about 50 longitudinally extending undulations per
inch, and more typically, from about 12 to about 25 longitudinally
extending undulations per inch. The crepe bars likewise have a
frequency greater than that of the longitudinally extending
undulations; generally with a frequency of the crepe bars from
about 2 to about 6 times the frequency of the longitudinally
extending undulations. More typically, the frequency of the crepe
bars is from about 2 to about 4 times the frequency of the
longitudinally extending undulations. Preferably, the emboss
pattern does not substantially alter the cross-direction stretch of
the absorbent sheet from which the embossed absorbent sheet was
prepared. Preferably, the cross-direction stretch of the sheet is
from about 0.2 to about 0.8 times the machine direction stretch of
the sheet, whereas a cross-direction stretch of the sheet from
about 0.35 to about 0.8 times the machine direction stretch of said
sheet is more preferred.
[0056] The distance between design elements, D, is greater
generally than S, typically from about 1.5 to about 3 times S. The
design elements have an emboss depth of from about 15 to about 30
mils in many cases and from about 10 to about 25 percent of the
surface area of the sheet is embossed.
[0057] The absorbent sheet may be a tissue product having a basis
weight of from about 5 to about 25 pounds per 3,000 square foot
ream, or a towel product having a basis weight of from about 10 to
about 40 pounds per 3,000 square foot ream. In any case, the sheet
may be prepared utilizing recycle furnish.
[0058] In another aspect of the present invention there is provided
a single-ply sheet provided with primary undulations extending
along a principal axis of the sheet, the primary undulations is
laterally spaced apart a distance, S, and the single-ply absorbent
sheet being further provided with an emboss pattern comprising a
plurality of embossments of width, W, and length, L, wherein the
lengths are along a direction, L', and wherein the embossments
cover no more than about fifty percent of the area of said
absorbent sheet. The embossments are spaced apart from each other
at a distance, D, with the proviso that at least one of the ratios
of W:S and D:S is from about 1 to about 4. More typically, at least
one of the ratios of W:S and D:S is from about 1.5 to about 3.5,
and the embossments cover no more than about 25 percent of the
surface area of the sheet. The ratio of cross-direction stretch to
machine direction stretch is from about 0.2 to about 0.8, whereas
from about 0.35 to about 0.8 is more typical. In preferred
embodiments, the principal undulatory axis is along the machine
direction of said sheet, and the primary undulations are
non-compacted relative to the other portions of the sheet.
[0059] In still yet another aspect of the present invention, there
is provided a method of making a single-ply absorbent sheet
comprising: preparing a web comprising cellulosic furnish; drying
the web to form the absorbent sheet; providing the sheet with
primary undulations extending along a principal undulatory axis of
the absorbent sheet, the undulations being spaced apart a distance,
S; and embossing the sheet with an emboss pattern comprising a
plurality of design elements wherein up to about 50 percent of the
surface area of the sheet is embossed, characterized in that each
design element of the emboss pattern has a characteristic emboss
element width, W, and a characteristic emboss length, L, along a
direction, L', and wherein the ratio of W:S for each design element
is from about 1 to about 4. In most cases, the sheet is dried to a
consistency of at least 90 percent prior to being embossed;
however, the sheet may be embossed at a consistency of less than
about 90 percent. The absorbent sheet may be provided with the
primary undulations by way of wet shaping the sheet on a fabric at
a consistency of between about 30 and about 85 percent.
Furthermore, the sheet may be a biaxially undulatory sheet with
secondary undulations extending in a direction substantially
perpendicular to the principal undulatory axis. In preferred
embodiments, the process includes applying the sheet to a Yankee
dryer and creping the sheet from the Yankee dryer.
[0060] Another method for making a single-ply embossed absorbent
sheet in accordance with the present invention comprises: preparing
a web comprising cellulosic furnish; applying the web to a Yankee
dryer; creping the web from the Yankee dryer with an undulatory
creping blade at a consistency of between about 40 and about 98
percent, such that the creped sheet is provided with crepe bars
extending laterally in the cross-direction and undulations
extending longitudinally in the machine direction, the undulations
being spaced apart a distance, S; and embossing the sheet with an
emboss pattern comprising a plurality of design elements wherein up
to about 50 percent of the surface area of the absorbent sheet is
embossed, characterized in that each design element of the emboss
pattern has a characteristic emboss element lateral width, W, and a
characteristic emboss element, length, L, along a direction, L',
and wherein the ratio of W:S for each design element is from about
1 to about 4. Typically, the step of embossing the absorbent sheet
comprises passing said sheet through a nip defined by a pair of
matched embossing rolls. The matched embossing rolls may be rigid
embossing rolls, such as steel rolls, or may include a rigid roll
and a yielding roll. A yielding roll may be a rubber embossing roll
prepared by laser engraving.
[0061] The invention has been described with respect to preferred
embodiments. However, as those skilled in the art will recognize,
modifications and variations in the specific details which have
been described and illustrated may be resorted to without departing
from the spirit and scope of the invention as defined in the
appended claims.
* * * * *