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Description  |
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DESCRIPTION
Technical Field
This invention relates to soft absorbent imprinted paper, and a method of
manufacturing such paper. Imprinted paper is paper which has had a pattern
impressed on it in a papermaking machine by biasing a patterned member
(such as an imprinting fabric) against another member (such as a back up
roll or Yankee dryer drum) while an embryonic paper web is passed
therebetween prior to the final drying of the paper web.
CROSS-REFERENCE TO RELATED APPLICATION
Reference is made to Ser. No. 019,028, filed even date by the same
applicant, entitled "Papermaking Clothing Having A Surface Comprising A
Bilaterally Staggered Array of Wicker-Basket-Like Cavities.
Background Art
A soft, absorbent, wet-laid imprinted creped paper which is characterized
by alternately spaced unbroken ridges of uncompressed fibers and troughs
of compressed fibers, which ridges and troughs extend in the
cross-machine-direction (hereinafter CD) is disclosed in U.S. Pat. No.
3,301,746 which issued Jan. 31, 1967 to L. H. Sanford et al., as well as a
process for making such paper. The Sanford et al. patent expressly
discloses the use of imprinting fabrics which may be of square or diagonal
weave, as well as twilled and semi-twilled fabrics.
Another soft, absorbent, wet-laid imprinted creped paper which is
characterized by discrete CD aligned uncompressed zones or pillows is
disclosed in U.S. Pat. No. 3,974,025 which issued Aug. 10, 1976 to Peter
G. Ayers, and a process for making such paper is disclosed in U.S. Pat.
No. 3,905,863 which issued Sept. 16, 1975 to Peter G. Ayers. These patents
disclose imprinting the paper with an imprinting pattern from the back
side of a semitwill woven imprinting fabric which has been heat-set and
abraded to provide flat-faced knuckles.
As compared to the paper characterized by unbroken uncompressed CD ridges
of Sandord et al., and the paper characterized by CD aligned uncompressed
zones of Ayers, the paper provided by the present invention is
characterized by an array of uncompressed zones of fibers which are
disposed in staggered relation in both the CD and the machine direction
(hereinafter MD), and which zones are perimetrically enclosed by
picket-like lineaments comprising regions of compressed fibers; that is,
by discontinuous rather than unbroken or continuous lines of compression.
An absorbent pad of air-laid fibers which is pattern densified essentially
only by means of compression to provide a bilaterally staggered array of
generally circular uncompressed tufts is disclosed in U.S. Pat. No.
3,908,659 which issued Sept. 30, 1975 to Bernard Martin Wehrmeyer et al.
As compared to this dry-laid structure having continuous lines of
compression, the paper of the present invention is wet-laid, and has
discontinuous lines/lineaments of compression/imprinting which are
imparted to the paper prior to its final drying. The paper of the present
invention may also be creped after being imprinted and dried.
A fragmentary view of a 5-shed satin weave fabric having a
non-numerically-consecutive warp pick sequence (1, 4, 2, 5, 3) is shown in
FIG. 3-7, page 22, of the book titled Papermachine Felts and Fabrics,
copyrighted by Albany International Corporation, 1976; Library of Congress
Cat. Card No. 76-41647. Also, wet-end fabrics (commonly referred to as
"wires" albeit comprising thermoplastic filaments rather than metal wire)
of this weave are commercially available from Appleton Wire Works Corp.,
Appleton, Wisconsin. However, the book reference does not suggest the use
of such a woven fabric as an imprinting fabric and, therefore, does not
teach the use of such a fabric to achieve a particular objective with
respect to the structure of a paper sheet imprinted thereby. Moreover, it
is believed that the commercially available wet-end fabrics of this weave
have not been heat-set to provide warp and shute knuckles (top-surface
crossovers) in the same plane, or to provide subtop-surface crossovers
which are spaced below the plane defined by the coplanar/monoplanar
knuckles. The coplanar knuckles are hereinafter referred to as
top-surface-plane crossovers and, in combination with the sub-top-surface
crossovers, are very important with respect to imprinting fabrics which
can be used to manufacture paper embodying the present invention.
U.S. Pat. No. 3,473,576 which issued Oct. 21, 1969 to J. S. Amneus teaches
the weaving and heat treating of polyester fabrics to provide coplanar
warp and shute knuckles having equal heights.
U.S. Pat. No. 3,573,164 which issued Mar. 30, 1971 to N. D. Friedberg and
Charles L. Wosaba II discloses abrading high portions of filament
crossovers to provide flat-faced knuckles as shown in their FIGS. 3 and 4.
Such flat-faced knuckles are incorporated in the heat-set imprinting
fabrics disclosed in the Ayers' patents discussed hereinabove.
The phrase warp-pick-sequence as used above and hereinbelow relates to the
sequence of manipulating the longitudinally extending warp filaments in a
loom to weave a fabric as the shuttle is traversed back and forth laying
the shute filaments. If, as in all of the plan-view figures of fabric
pieces included in this application, the warps are cyclically numbered
from left to right so that they are numbered in sets of 1 through n for an
n shed fabric (e.g.: warps 62-1 through 62-5 for the 5-shed, n=5 fabric
shown in FIG. 7), then a warp-pick-sequence refers to the order of
displacing the warps downwardly (into the paper as shown in FIG. 7) so
that the next shute filament passes over the picked warp and under the
other warps. Referring to FIG. 7, shute 63-1 was laid while all warps
designated 62-1 were picked, and while all warps designated 62-2 through
62-5 were not picked. Thus, shute 63-1 passes over warps 62-1 and under
warps 62-2 through 62-5 as shown in FIG. 7. Then, warps 62-1 are released
and warps 62-3 are picked prior to passing the shuttle to lay shute 63-2.
In the same manner, warps 62-5 are picked prior to laying shute 63-3;
warps 62-2 are picked prior to laying shute 63-4; and warps 62-4 are
picked prior to laying shute 63-5. Thus, using only the suffix digits of
the warp and shute designators, the warp-pick-sequence to weave fabric 60,
FIG. 7, is 1, 3, 5, 2, 4 to lay in shutes 1 through 5, respectively. This
is a non-numerically-consecutive warp-pick-sequence as distinguished from
the numerically-consecutive warp-pick-sequence manifest in fabrics 80,
FIG. 11, and 90, FIG. 12, which fabrics have warp-pick-sequences of 1, 2,
3 and 1, 2, 3, 4, 5, respectively. Fabrics woven with
non-numerically-consecutive warp-pick-sequences are amenable to being
stressed and heat treated to provide coplanar warp and shute crossovers
and some recessed sub-top-surface crossovers as described more fully
hereinafter whereas fabrics woven with numerically consecutive
warp-pick-sequences have no such sub-top-surface (recessed) crossovers.
Also, opposite hand weaves having substantially similar properties can be
formed through the use of a complimentary warp-pick-sequence. For
instance, the compliment of 1, 3, 5, 2, 4 is 1, 4, 2, 5, 3. Alternatively,
the compliment (opposite hand weave) can in fact be achieved by numbering
the warps from right to left rather than left to right. That is, a fabric
having its warps cyclically numbered -1 through -5 from left to right and
woven with a warp-pick-sequence of 1, 3, 5, 2, 4 is the complimentary
opposite hand weave of a fabric having its warps cyclically numbered -1
through -5 from right to left and woven with the same warp-pick-sequence
of 1, 3, 5, 2, 4.
As compared to the background art, the present invention provides a soft,
absorbent wet-laid sheet of paper which is characterized by an array of
uncompressed zones which zones are staggered in both the machine direction
and the cross-machine direction, and which zones are perimetrically
enclosed by imprinting imparted picket-like discontinuous lineaments. When
creped, this paper provides relatively high bulk; an improved CD:MD
stretch ratio; reduced CD flexural rigidity which is believed to impute an
increased subjectively ascertainable softness impression; and improved
burst to total tensile strength ratio.
DISCLOSURE OF THE INVENTION
In accordance with one aspect of the present invention, there is provided a
soft, absorbent paper sheet which is characterized by an array of
uncompressed zones, which zones are staggered in both the machine
direction (MD) and the cross-machine-direction (CD), and which zones are
perimetrically enclosed by imprinting imparted picket-like-discontinuous
lineaments. The preferred density of the zones is from about 15 to about
3,000 zones per square inch (about 2 to about 450 zones per square
centimeter). When creped, this paper provides relatively high bulk; an
improved CD:MD stretch ratio; reduced CD flexural rigidity which is
believed to impute an increased subjectively ascertainable softness
impression; and improved burst to total tensile strength ratio. This paper
may be made by the process comprising the steps of imprinting the paper
with a suitably patterned imprinting member prior to the final drying of
an embryonic paper web coursing through a papermaking machine, and by
creping the imprinted paper after it has been dried to the desired degree
of dryness for the finished paper.
BRIEF DESCRIPTION OF THE DRAWINGS
While the claims hereof particularly point out and distinctly claim the
subject matter of the present invention, it is believed the invention will
be better understood in view of the following detailed description of the
invention taken in conjunction with the accompanying drawings in which
corresponding features of the several views are identically designated,
and in which:
FIG. 1 is an enlarged photographic view of the fabric imprinted side of a
fragmentary piece of imprinted creped paper embodying the present
invention.
FIG. 2 is a photographic view similar to FIG. 1 except the degree of
enlargement is less for FIG. 2 than FIG. 1.
FIG. 3 is a photographic view of the opposite side (the dryer drum side) of
the paper shown in FIG. 2.
FIG. 4 is a photographic view of the fabric imprinted side of a fragmentary
piece of prior art imprinted creped paper in which view the degree of
enlargement is the same as for FIGS. 2 and 3.
FIG. 5 is a photographic view of the opposite side (the dryer drum side) of
the fragmentary piece of prior art imprinted creped paper shown in FIG. 4
and in which view the degree of enlargement is the same as for FIG. 4.
FIG. 6 is a side elevational, reduced scale fragmentary portion of a
somewhat schematic papermaking machine for manufacturing paper embodying
the present invention.
FIG. 7 is an enlarged scale fragmentary view of an imprinting fabric for
imprinting an embryonic paper sheet according to the present invention.
FIGS. 8 and 9 are fragmentary sectional views taken along lines 8--8 and
9--9, respectively, of FIG. 7.
FIG. 10 is an enlarged scale fragmentary view of a sheet of paper which has
had printed on it the knuckle pattern of the imprinting fabric shown in
FIG. 7.
FIG. 11 is an enlarged scale fragmentary view of a prior art imprinting
fabric.
FIG. 12 is an enlarged scale fragmentary view of a five shed satin weave
imprinting fabric of the type woven by consecutively picking warps during
the weaving of the fabric.
FIGS. 13 through 16 are enlarged scale fragmentary views of alternate
embodiment satin weave imprinting fabrics for use in manufacturing paper
embodying the present invention.
FIGS. 17, and 20 through 22 are enlarged scale fragmentary views of
alternate embodiment hybrid weave imprinting fabrics for use in
manufacturing paper embodying the present invention.
FIGS. 18 and 19 are sectional views taken along line 18--18 and 19--19,
respectively, of FIG. 17.
DETAILED DESCRIPTION OF THE INVENTION
Referring now to the Figures in which like features are identically
designated, FIG. 1 is an enlarged photographic view of the fabric
imprinted side of a fragmentary piece of imprinted creped paper 40
embodying the present invention. As shown in FIG. 1, paper sheet 40 is
characterized by an array of uncompressed zones 42 which zones are
disposed in staggered relation in both the machine direction (MD) and the
cross-machine direction (CD), and which zones 42 are individually
perimetrically enclosed by imprinting imparted picket-like discontinuous
lineaments which lineaments are discussed more fully hereinafter in
conjunction with FIG. 7. However, as viewed in FIG. 1, the picket-like
lineaments are zones of compacted fibers, which combine corporately to
form the dark shaded areas of FIG. 1. These areas can be viewed as
defining two sets of lines of compression: a first set of parallel lines
of compression which extend in the direction indicated by arrow 44 and
inclined upwardly to the right at angle 45 from the CD direction; and a
second set of generally parallel, sinuous lines of compression which
extend in the general direction indicated by arrow 46 and are inclined
upwardly to the left at angle 47 from the CD direction. Thus, as indicated
by angles 45 and 47, neither set of the lines of compression extend in
either the machine direction or the cross-machine direction. In general,
it is believed this geometry precipitates diminished flexural rigidity in
the CD direction as compared to comparable paper embossed with sets of CD
and/or MD lines of compression.
Briefly, paper sheet 40, FIG. 1, was made as a two layer web from two
furnishes: a first furnish which formed the fabric imprinted layer of the
finished paper and a second furnish which formed the other layer of the
finished paper; the layer which contacted the Yankee drying drum of the
papermaking machine, FIG. 6. The first furnish comprised about 9 pounds
per 3000 square feet of relatively long fiber northern softwood (spruce
and/or pine) kraft such as Grand Prairie Charmin Prime available from
Procter & Gamble Cellulose, Limited of Canada. The second furnish
comprised an admixture of about 5 pounds per 3000 square feet of
relatively short fiber mercerized southern softwood kraft such as HPZ
manufactured by The Buckeye Cellulose Corporation, and about 5 pounds per
3000 square feet of relatively short fiber southern hardwood kraft which
had been post bleach extracted with cold caustic solution. A suitable
southern hardwood kraft is known as Natchez-98 which is available from
International Paper Company. After formation, layering, and initial
dewatering, the embryonic paper web 40a was transferred from an upstream
wire or fabric 50 to a drying-imprinting fabric 73 of the type shown in
FIG. 7 and having a mesh count of 24.times.20 filaments per inch, and
described more fully hereinafter. The fiber consistency at transfer was
about 25 to about 30 percent. The embryonic web 40a was then transferred
to a Yankee dryer drum 70 at a fiber consistency of about 70 to about 80
percent. Imprinting was effected at the point of transfer to the Yankee
through the use of a pressure roll 71 as generally indicated in FIG. 6.
Final drying was effected on the Yankee dryer drum 70, and the paper sheet
was creped and removed from the Yankee by the action of doctor blade 72.
FIG. 2 is a photographic view similar to FIG. 1 except the degree of
enlargement is less for FIG. 2 than FIG. 1, and the fragmentary piece of
paper 40 is therefore commensurately larger.
FIG. 3 is a photographic view of the opposite side (Yankee dryer drum side)
of the paper 40 shown in FIG. 2. FIGS. 2 and 3 have the same degree of
enlargement and are included for the purpose of side-by-side comparisons
with similar views of a piece of prior art paper 41 shown in FIGS. 4 and
5.
FIG. 4 is a photographic view of the fabric imprinted side of a fragmentary
piece of prior art imprinted creped paper 41 in which view the degree of
enlargement is the same as in FIGS. 2 and 3. FIG. 5 is a photographic view
of the opposite side (Yankee dryer drum side) of the fragmentary piece of
prior art imprinted creped paper 41 shown in FIG. 4. This paper was
described hereinbefore in conjunction with discussing U.S. Pat. No.
3,974,025 which is titled "Absorbent Paper Having Imprinted Thereon a
Semi-Twill, Fabric Knuckle Pattern Prior to Final Drying".
When the paper 40, FIGS. 2 and 3, is compared in side-by-side relation with
corresponding views of prior art paper 41 shown in FIGS. 4 and 5, it is
quite apparent that the prior art paper 41 is characterized by
cross-machine-direction lines of compression 44a, whereas the paper 40 is
devoid of such cross-machine-direction lines of compression. Rather, it is
apparent from these figures that the paper sheet 40 of the present
invention is characterized by uncompressed zones 42 which are in staggered
relation in both the CD and the MD directions, whereas the prior art paper
41 as seen in FIG. 4 is characterized by uncompressed zones 42a which are
aligned in the cross-machine direction.
FIG. 6 is a fragmentary side elevational view of a somewhat schematic
papermaking machine 49 for manufacturing paper embodying the present
invention. The papermaking machine 49 is shown fragmentarily because it is
believed that the wet-end geometry of the machine is not critical to the
present invention. However, in addition to the earlier brief description
of the papermachine 49, the other members of the machine which are shown
include vacuum dewatering boxes 51, transfer means 52 which includes air
jet 53 and vacuum box 54, blow through pre-dryer means 55, fabric cleaning
showers 56, fabric dewatering box 57, turning rolls 58, and adhesive
applicator 59. The functions and operations of these members are believed
to be well known to persons skilled in the papermaking machine art, and
similar apparatus is disclosed in U.S. Pat. No. 3,301,746 which was
referenced hereinbefore.
FIG. 7 is a fragmentary plan view of an imprinting fabric 60 having four
(4) oval-shape planchets 61 disposed thereon. Fabric 60 comprises
monofilament thermoplastic warps and shutes; preferably a polyester
thermoplastic material. The warps and shutes of fabric 60 are designated
MD-warp filaments 62 and CD-shute filaments 63 which are woven into a
5-shed satin weave using a non-numerically-consecutive 1, 3, 5, 2, 4 warp
pick sequence. After being woven, fabric 60 is heat treated under tension
to heat set the filaments in the complimentary serpentine configurations
shown in the fragmentary sectional views taken along lines 8--8 and 9--9
of FIG. 7, and which views are identified as FIGS. 8 and 9, respectively.
After being heat set, fabric 60 is subjected to an abrading means to
provide elongate flat-faced crossovers (knuckles) 64 on the MD-warp
filaments 62, and oval-shape flat-faced crossovers (knuckles) 65 on the
CD-shute filaments 63. The flat-faced crossovers 64 and 65 are coplanar
(alternatively referred to as monoplanar) and are alternately corporately
designated top-surface-plane crossovers. That is, the flat faces of
crossovers 64 and 65 define the top surface plane 66, FIGS. 8 and 9, of
fabric 60. The remainder of fabric 60 is disposed below plane 66 and
includes sub-top-surface crossovers (knuckles) 67. Thus, as shown in FIGS.
7 and 9, sub-top-surface crossovers 67 are disposed in sub-arrays of
side-by-side pairs and, as shown in FIG. 7, each pair of sub-top-surface
crossovers 67 are generally perimetrically enclosed by adjacent portions
of four MD-warp crossovers 64 and two CD-shute crossovers 65. Each such
network of crossovers and the intermediate spans of filaments form, in the
nature of wicker-like baskets, concave depressions or cavities in which
zones of an embryonic paper web can be accommodated without substantial
compression or compaction while the top-surface crossovers 64 and 65 are
imprinted on the embryonic paper web. In this manner, the uncompressed
zones 42 of paper 40 are defined by discontinuous picket-like lineaments
wherein the fibers of the paper are alternately compacted and not
compacted. The planchets 61 are provided in FIG. 7 to indicate the
plan-view shape of the above described wicker-basket-like cavities.
Parenthetically, as used herein, the term "satin weave" is defined as a
weave of n-shed wherein each filament of one set of filaments (e.g., warps
or shutes) alternately crosses over one and under n-1 filaments of the
other set of filaments (e.g., shutes or warps), and each filament of the
other set of filaments alternately passes under one and over n-1 filaments
of the first set of filaments. As illustrated in FIG. 12, fabric 90 is a
five-shed satin weave which has been woven using a 1, 2, 3, 4, 5
warp-pick-sequence. Fabric 90 comprises sets of warp filaments 83-1
through 83-5, and shute filaments 84-1 through 84-5. The warps have
elongate flat-faced knuckles 85 and the shutes have oval-shape flat-faced
knuckles 86 which knuckles are coplanar. The wicker-basket-like cavities
of fabric 90 are covered by planchets 61y. These cavities span two warp
filaments and no shute filaments; and this fabric has no sub-top-surface
knuckles comparable to, for instance, knuckles 67 of fabric 60, FIG. 7 as
described more fully above. By way of contrast, the cavities of fabric 60,
FIG. 7, span two warp filaments and one shute filament as indicated by
planchets 61a through 61d which span two side-by-side sub-top-surface
knuckles 195. Thus, the five-shed satin weave fabric 90
(numerically-consecutive warp-pick-sequence), FIG. 12, has no
sub-top-surface crossovers whereas the five-shed satin weave fabric 60
(non-numerically-consecutive warp-pick-sequence), FIG. 7 has
sub-top-surface crossovers 67.
Still referring to FIG. 7, the grouping of four planchets 61 clearly shows
that the array of uncompressed zones 42 of a paper sheet 40 imprinted by
fabric 60 are sufficiently closely spaced that the machine-direction span
MDS of each zone (a reference zone) spans the machine-direction length L
of the space intermediate a longitudinally spaced pair of zones which pair
is disposed laterally adjacent the reference zone, and the array of zones
are sufficiently closely spaced that the cross-machine-direction span CDS
of each zone spans the cross-machine-direction width W of the space
intermediate a laterally spaced pair of zones which pair is disposed
longitudinally adjacent the reference zone. To illustrate these spatial
relations, planchets 61a and 61c, FIG. 7, are a pair of longitudinally
spaced planchets which are disposed laterally adjacent planchet 61b, and
planchets 61b and 61c are a pair of laterally spaced planchets which are
disposed longitudinally adjacent both planchet 61a and 61d. This degree of
overlapping of the zones tends to obviate MD and CD tearing of such
imprinted paper, and such an overlapped array is hereby designated a fully
overlapped bilaterally staggered array.
FIG. 10 is a plan view of a fragmentary sheet of paper 40x which has had
the pattern of flat-face crossovers 64 and 65 of fabric 60, FIG. 7,
printed (but not debossed as by imprinting) thereon. The prints of
crossovers 64 are designated 64x, and the prints of crossovers 65 are
designated 65x. Planchets 61x are indicated on FIG. 10 to illustrate the
plan view shape of the zones of the paper which would not be substantially
compressed by imprinting it with fabric 60. This figure also makes it
clear that sub-top-surface knuckles 67 are indeed below the top surface
plane 66 inasmuch as knuckles 67 did not print on paper 40x, FIG. 10.
Three sample pairs of paper 40, FIGS. 1 through 3, and prior art paper 41,
FIGS. 4 and 5, were run (described below) to illustrate the comparative
benefits of paper 40 with respect to prior art paper 41. Paper 40 was made
using imprinting fabrics of the type designated 60 and shown in FIG. 7,
and the prior art paper 41 was made using imprinting fabrics of the type
shown in FIG. 11 and designated 80. Briefly, fabric 80, FIG. 11, comprises
elongate MD knuckles 81 and oval-shape CD knuckles 82 and provides
cavities for obviating compressed fibers which cavities are indicated by
planchets 61y. As shown by the disposition of the planchets 61y in FIG.
11, paper which has been imprinted by this type fabric has elongate
uncompressed zones which are aligned in the CD direction and staggered in
the MD direction. This fabric 80 and paper 41 are more fully described in
the two Ayers patents referenced hereinbefore. However, fabric 80 has no
sub-top-surface knuckles comparable to sub-top-surface knuckles 67 of
fabric 60. Therefore, the cavities of fabric span no sub-top-surface
knuckles. This distinguishes fabric 80 from fabric 60 as well as all of
the other alternate embodiment fabrics described hereinbelow.
Sample Pair I
These samples of paper sheet 40, FIGS. 1 through 3, embodying the present
invention and prior art paper sheet 41, FIGS. 4 and 5, were imprinted by
fabrics having 24.times.20 (filaments per inch) mesh counts in the MD and
CD directions, respectively. But for the different imprinting fabric
weaves, fabric 60 of FIG. 7, and fabric 80 of FIG. 11, the runs were
substantially identical and made on the same papermaking machine. The
papermaking machine comprised two headboxes and thus created discretely
layered two-layer paper sheets. A first headbox of the fixed roof former
type delivered a first furnish comprising northern softwood kraft (Grand
Prairie Charmin Prime, Procter & Gamble Cellulose, Limited of Canada)
which furnish formed the first layer of an embryonic paper web. The basis
weight of the first layer was about fifty percent (50%) of the total basis
weight of the finished paper sheet. A second headbox delivered a second
furnish to a twin wire former to form the second layer of the paper sheet
after which the first layer was juxtaposed the second to complete the
formation of the embryonic web designated 40a in FIG. 6. The second
furnish comprised a blend of about fifty percent (50%) each of HPZ and
Natchez-98 which were both fully identified hereinbefore. Additionally,
Parez 631-NC (American Cyanamid Corporation), a wet strength additive was
introduced into the first furnish (northern softwood kraft) at the rate
indicated in Table I below.
The first layer was formed on a 78.times.60 (filaments per inch) mesh
S-weave forming wire (Appleton Wire Works), and the second layer was
formed between a 74.times.56 (filaments per inch) mesh M-weave forming
wire (also Appleton Wire Works) and a 78.times.60 (filaments per inch)
mesh S-weave intermediate carrier wire. Parenthetically, an S-weave is a
4-shed satin weave with a numerically consecutive warp-pick-sequence
having the long crossovers oriented in the cross-machine direction; an
M-weave is a 5-shed satin weave with a non-numerically-consecutive
warp-pick-sequence having the long surface crossovers oriented in the
cross-machine direction. The M-weave fabric does not have coplanar warp
and shute knuckles. The second layer was then carried on the intermediate
wire to a position where the first layer was juxtaposed superjacent the
second layer. This completed the formation of the embryonic paper sheet
designated 40a, FIG. 6. The embryonic paper sheet 40a was then transferred
to the appropriate imprinting fabric at a fiber consistency of from about
25 to about 30 percent. The embryonic paper sheets were further dried
using blow through drying (pre-dryer means 55, FIG. 6) to a fiber
consistency at transfer to the Yankee dryer drum 70 of from about 75 to
about 80 percent. Imprinting with the fabrics occurred at the point of
transfer to the Yankee. The paper sheets were dried to their desired end
point dryness on the Yankee and then creped therefrom by doctor blade 72.
The paper sheets were then drawn away from the doctor blade zone and
reeled to provide an ultimate residual crepe of about 30%. Comparative
data from Sample Pair I are tabulated in Table I. These data were obtained
from comparable populations of data over a range of fabric knuckle areas
(resulting from different degrees of abrading to provide a range of
flat-face knuckle areas), and basis weights. Although the basis weight
ranged from 15.4 to 20.4 pounds per 3000 square feet for paper sheet 40 of
Sample Pair I, the remaining comparative data would be virtually unchanged
if the data points were selectively limited to a basis weight range of
17.0 to 19.3 pounds per 3000 square feet.
SAMPLE PAIR I
TABLE I
______________________________________
SAMPLE PAIR I
Wet Strength Tissue
Prior Art
Paper 40 Paper 41
Imprinting Fabric: Figure No.;
7 11
______________________________________
Mesh (filaments per inch, MD .times. CD)
24 .times. 20
24 .times. 20
Caliper, Mils 26.3 22.8
CD Stretch, % 10.6 8.3
MD Stretch, % 40.1 43.1
CD:MD Stretch Ratio .27 .19
Flexural Rigidity, CD, mg-cm
47.9 69.8
CD Tensile, grams/inch
165 197
MD Tensile, grams/inch
234 336
CD:MD Tensile Ratio 1.4 1.7
Total Tensile (CD + MD Tensiles)
399 533
Burst Strength, grams
169 164
Burst/Total Tensile Strength
.429 .308
Density, gms/cc .043 .050
Nominal Basis Weight, pounds
per 3000 square feet 17.7 17.9
Basis Weight Range, pounds
per 3000 square feet 15.4-20.4 17.7-18.2
Parez 631-NC, usage rate range,
pounds per ton of fibers
10-16 8
Accostrength 98 dry strength
additive, pounds per ton of fibers
0 0
Accostrength 514 potentiating agent,
pounds per ton of fibers
0 0
______________________________________
Sample Pair II
These samples of paper sheet 40, FIGS. 1 through 3, embodying the present
invention and prior art paper sheet 41, FIGS. 4 and 5, were imprinted by
fabrics having 31.times.25 (filaments per inch) mesh counts in the MD and
CD directions, respectively. The runs were substantially the same as made
with respect to Sample Pair I except:
a. The fiber content of the second furnish was wholly southern hardwood
kraft (Natchez-98 identified hereinbefore);
b. The fiber consistencies at the point of imprinting and transfer to the
Yankee dryer drum ranged from about 65 to about 80 percent; and,
c. Specific fabric knuckle areas of twenty and thirty percent were used.
Comparative data are tabulated in Table II below.
SAMPLE PAIR II
TABLE II
______________________________________
SAMPLE PAIR II
Wet Strength Tissue
Prior Art
Paper 40 Paper 41
Imprinting Fabric: Figure No.;
7 11
______________________________________
Mesh (filaments per inch, MD .times. CD)
31 .times. 25
31 .times. 25
Caliper, Mils 18.3 17.6
CD Stretch, % 8.9 8.2
MD Stretch, % 41.2 41.5
CD:MD Stretch Ratio .22 .20
Flexural Rigidity, CD, mg-cm
61.2 73.3
CD Tensile, grams/inch
199 182
MD Tensile, grams/inch
347 346
CD:MD Tensile Ratio 1.7 1.9
Total Tensile (CD + MD Tensiles)
546 528
Burst Strength, grams
151 134
Burst/Total Tensile Strength
.27 .26
Density, gms/cc .063 .067
Nominal Basis Weight, pounds
per 3000 square feet 18.0 18.4
Basis Weight Range, pounds
per 3000 square feet 17.8-18.2 18.0-18.8
Parez 631-NC, usage rate range,
pounds per ton of fibers
6-8 6
Accostrength 98 dry strength
additive, pounds per ton of fibers
0 0
Accostrength 514 potentiating agent,
pounds per ton of fibers
0 0
______________________________________
Sample Pair III
These samples of paper sheet 40, FIGS. 1 through 3, embodying the present
invention and prior art paper sheet 41, FIGS. 4 and 5, were imprinted by
the same fabrics as were Sample Pair II described above. The runs were
substantially the same as made with respect to Sample Pair II except the
sheets were formed as three (3) layer structures rather than two layer
structures through the use of a partitioned fixed roof headbox through
which three furnishes were delivered to a 78.times.60 (filaments per inch)
mesh count S-weave forming wire. The furnishes were provided so that both
outer layers were eucalyptus hardwood kraft (Champion International) and
the center layer was northern softwood kraft identified hereinbefore.
Accostrength 98 which is a dry strength additive and Accostrength 514
which is a potentiating agent with respect to Accostrength 98 were added
to the center layer furnish, and Parez 631-NC, a wet strength additive was
added to the outer layer furnish which ultimately became the Yankee dryer
drum side of the paper sheets 40 and 41, FIGS. 3 and 5 respectively, in
order to control lint. Each of the three layers constituted about
one-third of the basis weight of each sample paper sheet. After being
formed on the 78.times.60 forming wire, the embryonic paper sheets were
transferred to the same intermediate carrier wire as Sample Pairs I and
II, and re-transferred to the appropriate imprinting fabric at a fiber
consistency of from about 25 to about 30 percent. The fiber consistency
was increased by blow through predrying to from about 75 to about 80
percent at the point of imprinting and transfer to the Yankee dryer drum.
Residual crepe of 18 percent was provided and the paper sheet was
calendared through a rubber-steel roll calendar stack. Prior to data
sampling, the paper sheet samples were converted into a standard
4.5.times.4.5 inch toilet tissue format. Comparative data are tabulated in
Table III below.
SAMPLE PAIR III
TABLE III
______________________________________
SAMPLE PAIR III
Dry Strength Tissue
Prior Art
Paper 40 Paper 41
Imprinting Fabric: Figure No.;
7 11
______________________________________
Mesh (filaments per inch, MD .times. CD)
31 .times. 25
31 .times. 25
Caliper, Mils 12.1 11.5
CD Stretch, % 7 4
MD Stretch, % 24 21
CD:MD Stretch Ratio .28 .19
Flexural Rigidity, CD, mg-cm
32.5 53.6
CD Tensile, grams/inch
161 182
MD Tensile, grams/inch
190 205
CD:MD Tensile Ratio 1.2 1.1
Total Tensile (CD + MD Tensiles)
351 387
Burst Strength, grams
120 100
Burst/Total Tensile Strength
.34 .26
Density, gms/cc .094 .098
Nominal Basis Weight, pounds
per 3000 square feet 17.9 17.6
Basis Weight Range, pounds
per 3000 square feet 17.7-18.0 17.4-17.9
Parez 631-NC, usage rate range,
pounds per ton of fibers
0 2
Accostrength 98 dry strength
additive, pounds per ton of fibers
1 1
Accostrength 514 potentiating agent,
pounds per ton of fibers
10 10
______________________________________
Referring to the tabulated data, the superiority of paper 40 embodying the
present invention over prior art paper 41 is apparent from the tabulated
data inasmuch as the data from all three sample pairs (Tables 1, 2 and 3)
indicate:
a. Lower density/greater bulk;
b. Decrease CD flexural rigidity;
c. Greater CD:MD stretch ratios; and
d. Greater burst to total tensile strength ratio.
The significance of lower density/greater bulk is believed to be that it
directionally tends to improve absorbency, and subjective (expert panel)
softness perception.
The significance of decreased CD flexural rigidity is believed to be that
softness impression is strongly influenced by the poorest directional
property. That is, if MD rigidity is low and CD rigidity is high as it
typically is because of CD crepe ridges, then CD properties will be
disproportionately adversely influential on softness. Therefore, reducing
CD rigidity as by obviating CD creping ridges without materially affecting
MD rigidity is directionally right to achieve improved softness
impression. This also makes the paper more clothlike inasmuch as it is
more isotropic in its CD versus MD properties.
The significance of improved (greater) CD:MD stretch ratios is believed to
be derived from:
a. Since strength properties in general are governed by the weakest
component, the maximum strength perception at minimum technically
measurable integrated strength will occur when the sheet is isotropic in
strength properties. Those strength properties such as burst, and tensile
energy absorption (or any work/energy absorption type of strength
property) that are functions of stretch will directionally approach
optimization as the CD:MD stretch ratio approaches 1.0;
b. Paper having isotropic stretch more closely simulates woven cloth; and
c. Achieving a relatively high CD:MD stretch ratio will allow the paper to
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