Note: Descriptions are shown in the official language in which they were submitted.
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BACKGROUND OF THE INVENTION
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FIELD OF THE INVENTION
This invention relates to the manufacture of paper
towels and the like. More particularly, it relates to
methods of embossing multi-ply paper sheets.
BRIEF DESCRIPTION OF THE PRIOR ART
It is well known in the papermaking industry that
embossing a paper sheet gives the sheet bulk, a property
that is of particular importance in manufacturing paper
towels because it is associated with softness and absorbency
by the consumer. Bulk is not only important with regard to
the feel of the individual sheets, but also in regard to the
bulkiness of the packaged product. In the case of paper
towels, where the product is packaged in rolls it is
desirable to minimize nesting of the sheets within one
another in order to maintain a larger roll diameter with a
given number of sheets per roll.
In manufacturing multi-ply paper sheets, there are
basically two processes which are well known in the art.
2~ One is a nested process and the other is a pillowed process.
The nested process is illus~rated by U.S. 3,694,300 to Small
and U.S. 3,867,225 to Nystrand and generally involves the
separate embossing of two plies between a rubber roll and a
steel embossing roll, applying an adhesive with a roller to
the protruding embossments of one of the plies, and
combining the two plies together such that the protrusions
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of one ~heet are attached withln the depre~slon~ of the other.
The pillowed procesa i8 similar and i8 illuRtrated by U.S.
3,961,119 to Thomas. ~n this process, however, the plias are
lamlnated together such that the protrusions of one ply are not
aligned wi~hin the depressions of ~he other. In both of the~e
processes, it is necessary to have two rubber/steel nips and an
adhesive applicator of the roller type. These ~ystems are
unnecessarily cumbersome.
The u~e of embos~ed deQigns to improve the ae~thetlc appeal
of the product ls al~o known in the art, as illustrated by U.S.
Des. 262,74~ to Erickson which show~ a shamrock design.
In one aspect the invention resides in a multi-ply paper
sheet, particularly sultable for use as a paper towel, having
first and second sides and an embossed pattern thereon, said
embos~ed pattern compris~ng a background arrangement o~ alter-
nate~ly protruding and depre~sed deflected zones spaced apart by a
subE~tantially undeflected neutral plane. The deflected zone~ are
generally elongated in Qhape having ma~or and minor axis dlmen-
8ion~ wherein the ma~or axl~ is substantially aligned in the
cro~s-machine direction. The depre~sed and protruding deflected
zone~ of the first side correQpond ~o the protruding and
depressQd deflectlve zones, re~pectively, of the ~econd ~lde.
A speci~lc embodlment of the invention resides in a method
for producing paper towels comprising embossing a preattached
multi-ply web with matched steel rolls and imparting to the web a
pattern of alternately protruding and depressed deflected zon~s
~eparated by a sub~tantially undeflected neutral plane. The
matched steel rolls provide more control over bulk forma~ion,
have reduced energy requirements, cause lesser ~tatic build-up,
and last longer than rubber/steel rolls.
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This invention has a primary advantage over prior processes
and products in that it produces a one-sided product (both sheet
sides have similar appearance and feel). It also reduces nesting
which is accomplished by incorporating a design into the back-
ground pattern which has increased unembossed area (neutral
plane) and/or arrangement Or elements within this design on a
dissimilar grid relative to the background pattern. The elements
within the design can also have a diferent size, shape, or
orientation compared to the background pattern, thereby further
reducing the opportunity to nest with the background pattern,
According to another aspect of the invention there is
provided an embossed paper sheet of the creped paper type for
paper towels and tissue. the shee-t having embossments in a
pattern with an evenly spaced background. The embossments have
major axis and minor axis, the major axis of substantially all of
the embossments being substantially aligned in the cross machine
direction.
Suitable embossment shapes include ovals, diamonds, rec-
tangles, etc. as well as unsymmetrical or irregular shapes.
aligning -the major axis in the C.D. direction has been found to
reduce C.D. strength degradation caused by the embossing. For
the purpose herein, "substantial" alignment in the C.D. direc-tion
means within about 10 of the C.D. direction. A iesser degree of
alignment is believed to have relatively minimal benefits.
"Substantially all of the embossments" means at least 80 percent
of the background embossments of the embossing pattern. A lesser
percentage of the embossments having proper alignment also would
result in minimal benefit in terms of reducing strength degrada-
tion.
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BRIEF DESCRIPTION OF TH~ DRAWrNG
Figure 1 i8 a schemat~c view o a process in accordance with
this invention.
Figure 2 i9 a cros~-sectional repr*sentation of the proPile
of a two-ply web in accordance with this invention.
~ igure 3 1B a plan view illustratlng succe~sive curvilinear
rows of background embos~ments.
Figure 4 i~ a plan view o~ a paper shaet in accordance with
thi~3 inventlon, illustratlng alignm~nt of the ma~or axiQ of the
background embossments in the cross-machine direction.
DETAILED DESCRIPTION OF T~E DRAWING
Directing attention to Figure 1, the invention will be
described ln mora detail. Figure 1 i8 a schematic
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view illustrating the manner in which the paper sheets of
this invention are produced. Separate rolls 1 and 2 feed
web~ to be attached between nip rolls 4 and 5. At least one
of the webs is provided with an adhesive, preferably in the
form of a spray 3, as shown. In the nip the two webs are
bonded together to form a preattached sheet 6. Although not
shown, the preattached sheet 6 can be wound up on a hardroll
to be subsequently used as a feed roll for the embossing
step to permit flexibility due to varying production speeds~
The preattached sheet is then directed between matched steel
embossing rolls 7 and 8 wherein the desired embossing
pattern is imparted to the preattached sheet resulting in
the embossed sheet 9. It will be appreciated that the
manner in which the preattached sheet is formed is not to be
considered as limiting the scope of the invention. For
example, the multi-ply sheet can be formed by folding a
single web and cutting off the fold to produce a two-ply
sheet, rather than supplying each ply from a separate roll
as shown in Figure 1. In addition, a sheet containing more
than two plies can also be embossed in accordance with this
invention, as long as the plies are sufficiently bonded
together, either mechanically or with adhesive, to maintain
the integrity of the sheet through the embossing process.
This is necessarv because the embossing process does not
provide sufficient ply attachment, it being an object of the
process not to damage the sheet by punching through the
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sheet with the embossing rolls which, if it occurred, would
provide some degree of ply attachment in and of itself.
Figure 2 illustrates a cross-section of a portion
of the embossed sheet 9 of Figure 1. Shown are the
protruding deflected zones 10, the depressed deflected zones
11, and the substantially undeflected neutral plane 12 of
the 2-ply sheet. In a preferred embodiment, the height of
the protrusions 10 and the depth of the depressions 11 is
about .01~ inch. The deflected zones, when viewed from the
top or bottom of the sheet, are oval in shape and have a
length (major axis) of about 0.075 inch and a width (minor
axis) of about 0.035 inch. The width of the neutral plane
12, i.e. the distance between deflected zones 10 and 11, is
about 0.035 inch or greater. It is pre~erred that the
spacing of the deflected zones be at least as great as the
dimension of the minor axis in those instances when the
deflected ~ones are generally elongate in shape~ If the
deflected zones are generally circular in shape, the spacing
is pre~erably at least as great as the diameter. It will be
appreciated that the precise spacing and shape of the
deflected areas can vary depending upon the strength and
aesthetic requirements of the sheet. Also shown by Figure 2
is the corresponding relationship between the protrusions
and depressions on one side of the sheet relative to the
depressi~ns and protrusions on the other side of the sheet.
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Figure 3 i~ a plan view lllustrating an intermittent
shamrock embos~ing pattern~ The black ovals represent protruding
deflected zones and the white oval~ repre~ent depres~ed deflected
zones. The whi~e background area represents the sub~tantlally
undeflected neutral plane. As shown, the oval-shaped de~lect~d
zones are arranged to ~orm a background pattern comprising
succes3ive curvilinear row~ of alternately protruding and
depre3~ed deflected ~ones spaced apart by the neutral plane. The
background pattern need not be curvilinear, but ~uch a patt2rn 1
advantageous in tha~ lt a~proximate~ a random pa~tern and reduce~
the tendency of the sheets to nest when wound up into rolls.
In addition, the intermittent shamrock pattern al80 reduces
the nesting tendency. AB previou~ly mentloned, rcduced ne~in~
improves the bulky ~eel of the rolled product~ As sho~m the
shamrock pattern i~ es~entlally a neutral plane pattern contain-
ing oval-shaped protruding and depressed zones having their ma~or
axi~ alignsd in a directlon different from that of the oval~ in
the background pattern. This ~urther aids in retarding ne~ting.
Figure 4 ~llu~trate~ an embossing de~ign of the present
invention and i8 different than that shown in Flgure 3 in that
the ma~or axis o~ the background ovals has been rotat~d 90,
parallel to the cross-machine directlon of the webs compri~ing
the ~heet. This
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orientation has been found to decrease the cross-machine
direction strength degradation due to embossing.
EXAMPLE
In making a two-ply embossed towel, two softrolls
containing suitable single-ply webs were produced on a paper
machine using typical paper industry equipment and
practices. The softrolls were unwound and the two
single-ply base sheets were plied together by spraying a
polyvinyl acetate adhesive between them and passing them
between press rolls having a loading of about 20-40 pli.
The polyvinyl acetate adhesives had a solids content of
about 15-30 weight percen~. Typically, about 7-15 lbs. of
adhesive solids per ton of base sheet are used for a base
sheet having a finished basis weight of 10-14 lbs./2880 ft.2
per ply. The resulting two-ply sheet was rewound into a
hardroll at speeds of about 2500-4500 feet per minute.
The two-ply hardrolls were converted into a
finished product using standard paper towel converting
equipment, excepting the embossing rolls. The two-ply sheet
was unwound and passed between matched-steel embossing rolls
at speeds of about 1300-1800 feet per minute. The embossing
rolls had a diameter of about 14-16 inches and a width of
about 99 inches. The embossing rolls were mated in the same
position in which they were matched-steel engraved and were
of the design shown in Figure 4. The embossing rolls were
set at about 0.007-0.020 inches off bottom clearance and
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adjusted for no steel-to-steel contactO Ply attachment of
the final product therefore resulted from the adhesive
rather than the embossing.
The dimensions of the oval embossing pattern
elements were as follows: major axis of oval (0.070 inch1;
minor axis of oval (0.035 inch); M.D. direction
element-to-element spacing 10.065 inch); C.D. direction
element-to-element spacing (0.048 inch); and element depth
(0.050 inch)~ ~hese dimensions can vary about + lO percent
across the pattern.
The embossed sheet was then passed through a
printing operation, perforated, and wound into finished logs
having the desired sheet count. The logs were then cut into
segments of the desired width and wrapped.
It will be appreciated that the specific designs
shown for purposes of illustration are not to be construed
as limiting the scope of this invention as defined by the
following claims.
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