U.S. patent application number 10/675469 was filed with the patent office on 2004-04-01 for apparatus for spray-bonding tissue.
This patent application is currently assigned to Eastern Pulp and Paper Corporation, a Massachusetts corporation. Invention is credited to Brown, Michael, Lichtenberg, Ralph B., Taylor, Eric C., Torras, Joseph H. SR..
Application Number | 20040060664 10/675469 |
Document ID | / |
Family ID | 24518664 |
Filed Date | 2004-04-01 |
United States Patent
Application |
20040060664 |
Kind Code |
A1 |
Lichtenberg, Ralph B. ; et
al. |
April 1, 2004 |
Apparatus for spray-bonding tissue
Abstract
Multi-ply tissue product is bonded by an adhesive spray whose
position is controlled so that the web path distance between the
spray application and the location where the webs are forced
together permits sprayed adhesive to partially but not completely
set during travel over that web path distance at operating web
speeds. Typically, the web path distance between the nozzle and the
location is more than 140 inches. The webs are positioned one in
back of the other and each is unwound onto its own carrier roll,
with the spray positioned between the carrier rolls.
Inventors: |
Lichtenberg, Ralph B.;
(Lincoln, ME) ; Torras, Joseph H. SR.; (Shelburne,
MA) ; Taylor, Eric C.; (Lincoln, ME) ; Brown,
Michael; (Lincoln, ME) |
Correspondence
Address: |
FISH & RICHARDSON PC
225 FRANKLIN ST
BOSTON
MA
02110
US
|
Assignee: |
Eastern Pulp and Paper Corporation,
a Massachusetts corporation
|
Family ID: |
24518664 |
Appl. No.: |
10/675469 |
Filed: |
September 30, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10675469 |
Sep 30, 2003 |
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09649775 |
Aug 29, 2000 |
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6635134 |
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09649775 |
Aug 29, 2000 |
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08628386 |
Apr 5, 1996 |
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6136422 |
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Current U.S.
Class: |
156/549 |
Current CPC
Class: |
B32B 2309/14 20130101;
B32B 2309/72 20130101; B32B 2041/06 20130101; Y10T 428/27 20150115;
B32B 29/00 20130101; B32B 38/1875 20130101; B32B 2317/12 20130101;
Y10T 428/31993 20150401; Y10T 428/31982 20150401; D21F 11/14
20130101; B32B 2555/00 20130101; D21F 11/04 20130101; B32B 29/005
20130101; B32B 37/1284 20130101; Y10T 156/1727 20150115; B32B 7/12
20130101 |
Class at
Publication: |
156/549 |
International
Class: |
B32B 031/04 |
Claims
What is claimed is:
1. Apparatus for producing a multi-ply, adhesively bonded tissue
intermediate product, the apparatus comprising: A. a rear reel
stand and a rear carrier roll above the rear stand, forming the
beginning of an upper web path; B. a forward reel stand and a
forward carrier roll above the forward stand, forming the beginning
of a lower web path, the upper web path converging with the lower
web path at the forward carrier roll; C. an adhesive applicator
system for applying adhesive to the bottom of tissue moving in the
upper web path, the adhesive applicator system comprising: i. an
array of spray nozzles positioned at a spray location below and
generally transverse to the upper tissue path, and oriented to
spray generally upward, toward the bottom surface of the upper
tissue, the first location being between the rear and the forward
carrier rolls; ii. an adhesive conduit connected to provide a flow
of adhesive to the spray nozzles, and iii. a pressurized gas
conduit connected to provide a flow of gas to the spray nozzles to
atomize adhesive flow through the spray nozzles, D. a pair of nip
rolls positioned downstream from the spray head array and the
forward carrier roll, the nip rolls being in both the upper and
lower tissue paths, the nip rolls forming a nip for compressing the
upper and the lower tissue together E. a winder downstream of the
nip for winding up bonded tissue product, the winder being designed
to have a running speed within a predetermined range, the nip being
spaced apart from the spray location at least 230 inches, to permit
sprayed adhesive to partially but not completely set during travel
over that web path distance at speeds in the predetermined
range.
2. Apparatus for producing a multi-ply, adhesively bonded tissue
intermediate product, the apparatus comprising: A. a rear reel
stand and a rear carrier roll above the rear stand, forming the
beginning of an upper web path; B. a forward reel stand and a
forward carrier roll above the forward stand, forming the beginning
of a lower web path, the upper web path converging with the lower
web path at the forward carrier roll; C. an adhesive applicator
system for applying adhesive to the bottom of tissue moving in the
upper web path, the adhesive applicator system comprising: i. an
array of spray nozzles positioned at a spray location below and
generally transverse to the upper tissue path, and oriented to
spray generally upward, toward the bottom surface of the upper
tissue, the first location being between the rear and the forward
carrier rolls; ii. an adhesive conduit connected to provide a flow
of adhesive to the spray nozzles, and iii. a pressurized gas
conduit connected to provide a flow of gas to the spray nozzles to
atomize adhesive flow through the spray nozzles, D. a pair of nip
rolls positioned downstream from the spray head array and the
forward carrier roll, the nip rolls being in both the upper and
lower tissue paths, the nip rolls forming a nip for compressing the
upper and the lower tissue together E. a winder downstream of the
nip for winding up bonded tissue product, the winder being designed
to have a running speed within a predetermined range, and F. a lift
mechanism attached to said array of spray nozzles to move said
array between a rest position spaced from the upper web path and a
an operative position for delivering adhesive to web moving in the
upper web path.
3. The apparatus of claim 1 or claim 2 further comprising: A. a
source of adhesive providing a flow of adhesive to the adhesive
conduit; B. a source of pressurized gas providing a flow of gas to
the gas conduit; C. a sensor for sensing the speed of travel of at
least one of the tissue webs, the sensor providing a web speed
signal to a signal processor; D. an adhesive flow control system
for controlling the flow of adhesive to the spray heads responsive
to web speed, the adhesive flow control system including an
adhesive flow monitor and an adhesive flow controller connected the
signal processor; the signal processor providing signals to the
adhesive flow controller responsive to the web speed signal and the
flow monitor signal, whereby spray rate is varied in response to
web travel rate.
4. The apparatus of claim 3 further comprising at least one
intermediate reel stand and intermediate carrier roll, forming the
beginning of an intermediate web path, the intermediate carrier
roll being positioned between the rear and the forward carrier
rolls.
5. The apparatus of claim 4 in which the array of spray nozzles is
a rear array of spray nozzles positioned at least 230 inches from
the nip, and the apparatus further comprises a front array of spray
heads positioned at a front sprayer location below and generally
transverse to the intermediate web path, and oriented to spray
generally upward, toward the bottom surface of the intermediate
tissue.
6. The apparatus of claim 1 or claim 2 characterized in that the
predetermined speed range is a first predetermined range, and the
apparatus is positioned to receive webs from web-forming equipment
which includes a dryer and a winder operating at a speed within a
second predetermined range, the first predetermined range being
fast enough to process the output of the web-forming equipment
substantially without backlog or slowing of that equipment.
7. The apparatus of claim 1 or claim 2 in which the adhesive flow
control system includes circuitry to control the amount of adhesive
flow supplied to the nozzles substantially proportional to the web
travel speed, so as to provide a substantially constant overall
ratio of dry adhesive per unit area of web at different web
speeds.
8. The apparatus of claim 7 in which the adhesive flow control
system comprises circuitry to establish at least two phases, a
running phase and a transition phase, the web speed changing during
the transition phase to or from the running phase the transition
phase being substantially slower than the running phase, and the
amount of liquid adhesive delivered per minute is substantially
proportional to the web speed during both the running phase and the
transitional phase.
9. The apparatus of claim 8 in which the signal processor controls
the pressure or flow of nozzle atomizing air in response to web
speed change between the running and the transition phase.
10. The apparatus of claim 1 or claim 2 comprising multiple nozzles
at the first location, the nozzles being positioned in a shower
housing which includes a damper that is movable from a first damper
orientation that prevents nozzle spray from reaching the moving web
and a second damper orientation in which spray reaches moving
web.
11. The apparatus of claim I or claim 2 further comprising a nozzle
purger including a flush water conduit connected to provide flush
water to the adheseive flow conduit and to the nozzle.
12. The apparatus of 11 further in which the nozzle purger further
comprises a pressurized gas conduit connected via a purge valve
between a source of pressurized gas and the flush water conduit,
the purge valve being controlled by a controller to shut the valve
when flush water is flowing to the nozzle and then to introduce
said pressurized gas when flush water flow is complete, thereby
purging liquid from the adhesive conduit and from the nozzle.
13. The apparatus of claim 12 in which a single source of
pressurized gas provides gas flow both for atomizing the adhesive
and for purging liquid.
14. The apparatus of 13 further in which the pressurized gas is
pressurized air.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional application of U.S.
application Ser. No. 09/649,775, filed Aug. 29, 2000 (issued as
U.S. , on ,) which in turn was a divisional application of U.S.
application Ser. No. 08/628,386, filed on Apr. 5, 1996 (issued as
U.S. Pat. No. 6,136,422, on Oct. 24, 2000). This application claims
priority to, and incorporates by reference the entirety of, both of
the above U.S. patent applications.
TECHNICAL FIELD
[0002] This invention is in the general field of multi-ply tissue
products as well as methods and apparatus for bonding tissue plies
to make such products.
BACKGROUND
[0003] Various tissue products are made by laminating multiple
layers of tissue. These layers or plies must be bonded to prevent
them from delaminating or floating apart when they are converted
into the final product or when they are used by the consumer.
[0004] Ply bonding of the individual tissue sheets into multi-ply
layers is usually achieved by embossing them on converting
equipment without applying adhesive. In this process, two or more
tissue webs are simultaneously unwound and fed through a nip formed
between male and female embossing rolls to emboss or crimp the webs
and thereby bond them together. Often in making such products as
napkins, the webs are embossed only around the perimeter of areas
that will be cut into the individual napkins.
[0005] In a different process, tissue plies may be adhered using a
chemical adhesive rather than by embossing. For example, Bjork U.S.
Pat. No. 5,466,318 discloses a process for laminating webs using a
water-based adhesive.
[0006] Controlling ply bonding is important and difficult.
Inadequate, excessive or inconsistent ply bonding can jam complex,
high-speed machinery, generate high waste, and provide unacceptable
product. The strength of bonding by embossing (without adhesive)
may vary depending, among other things, on water content or dryness
of tissue webs, and on ambient air humidity. While bonding by
embossing sometimes can be improved by increasing the pressure on
the embossing rolls, such pressure can wear out the embossing rolls
more quickly, particularly the female roll, which is usually a
softer roll made of composite material onto which a pattern is
impressed by the opposing, male, engraved metal roll. In addition,
the journals and bearings of both embossing rolls can also wear out
prematurely if subjected to increased pressure over a prolonged
period.
[0007] The use of adhesives can avoid some of the problems of
embossing, but adhesives also cause problems, such as "through
bonding" or "blocking", in which adjacent laminates bond to one
another, and, prevent unwinding of the laminate product from its
roll. Non-uniformity of bonding also causes problems, such as
wrinkling of the tissue and bad printing.
[0008] As noted, the bonding process may be part of the overall
process for making the final multi-ply product. For example,
multi-ply tissue products, particularly napkins, may be printed,
e.g., by a letterpress or a flexographic process. In a typical
letterpress printing process, a multi-ply web is first embossed,
and then the central unembossed area of individual napkins is
printed. In an alternative flexographic printing process, unbonded
webs may be first run through a flexographic printing tower and
then crimped with an embossing nip.
[0009] While the invention has broader application, we refer
specifically to certain markets, particularly high quality napkins
such as the party goods, food service, and other specialty napkin
markets. These markets may require cloth-like character and feel,
high wet strength, and the ability to be decorated with high
quality printing. Increasingly, these markets have expressed
preference for quality and complexity provided by flexographic
printing.
[0010] It can be difficult to achieve cloth-like character and feel
while also achieving satisfactory bonding of two or more plies of
tissue to make one sheet of napkin tissue that will not come apart
either when used by the consumer or when subjected to flexographic
printing. The napkin must not de-ply, it must stay in one piece
like a cloth napkin would. However, the use of adhesives and other
additives to develop the resistance to ply separation tends to make
the product stiff and destroy the cloth-like feel.
[0011] Another product requirement in this field is the need of
strength while wet, which can be critically important to high
quality paper napkins. Non-wet strength napkins may pull apart when
subjected to moisture, such as spilled liquid or a wet glass,
rendering then unsatisfactory for the high quality markets.
Chemicals normally employed to impart wet strength (e.g., urea,
phenol-formaldehyde) can reduce ply bond-strength, which is already
problematic, and can make the napkin stiffer.
[0012] With regard to decorated or printed napkins, certain napkin
machines (e.g., those made by Servotec and Hoberna), which use
flexographic printing have stringent ply requirements. As noted,
these flexographic machines print the napkin first and emboss it
afterwards, in contrast with letterpress napkin machines, which
first emboss the edges of the napkin so that the plies of tissue
are crimped together, after which the napkin is printed. In the
flexographic process, it is critical that the plies be held
together without embossing while the napkin is being printed.
Floating plies as the tissue enters the printing stage result in
jams and high waste together with machine downtime. In addition,
the application of the ink causes the top layer of the tissue to
expand if the plies are not well bonded, resulting in wrinkling,
badly printed napkins, and extremely high costs from waste.
[0013] These problems are sometimes addressed by the use of much
heavier napkin tissue (as has been done in Europe where some of the
flexographic machines were introduced). Heavier tissue is more
expensive.
SUMMARY
[0014] We have discovered spray bonding processes and apparatus
that provide substantially improved efficiency and process control
of tissue bonding. The resulting adhesively bonded intermediate
product is improved, particularly for use in flexographic printing
applications. The final product may be a paper napkin, a paper
towel, a medical disposable towel, a table cover or other similar
tissue product. The cloth-like feel achieved by the invention is
suitable for a wide range of markets, including not only markets
where softness is important but also markets where a certain amount
of product stiffness is required, such as the markets in which
napkins are forced into plastic wraps containing cutlery (napkins
made and packaged by "Austin-Gordon" or "Gordon"-type machines)
[0015] In particular, the invention provides a well-bonded napkin
product that can be used in converting apparatus, particularly
flexographic printing apparatus. This ply-bonded tissue is
constructed of lighter weight material that is less costly than the
previously used tissue (particularly in Europe), yet the tissue
exhibits printability and a cloth-like feel. Cloth-like character
and feel, high wet strength, printability and low cost are achieved
in a reliably ply-bonded product without the need to emboss before
printing. The result is markedly enhanced ply bonding of the tissue
layers and efficient and high quality printing, without detracting
from the cloth-like character and feel that the use of adhesives
can cause.
[0016] One aspect of the invention generally features a multi-ply
adhesively bonded tissue roll with an extremely limited amount of
waste at the core, which results from the absence of bonding or
poorly controlled bonding during start-up of the bonding process.
The roll comprises a bonded region that extends to within at least
3/4 inch of the core. (This 3/4 inch measurement is made from the
outer diameter of the core, which is typically about 4 inches to
the point in the product at which adhesive bonding begins.)
Adhesive contact between the plies is substantially continuous over
the bonded region of the roll (i.e., at radiuses greater than
3/4"), and the strength throughout the bonded region of the roll is
high, substantially without through bonding in that region. While
bond strengths of at least 100 mg/cm are achieved, in one
particular embodiment, the bond strength is at least 400 mg/cm.
[0017] In another aspect of the invention described below, we have
found that careful process control permits lower adhesive loading
and the use of a pressurized nip to force the webs together without
unacceptable adhesive build-up on the nip rolls, particularly for
two-ply tissue product. Strong two-ply adhesion can be achieved
with lower adhesive loading, thus avoiding problems caused by
inconsistent adhesive loading while at the same time enabling
better control over winding tension (because the nip controls
tension transmitted upstream). Thus, this aspect of the invention
features methods of producing an adhesively bonded two-ply tissue
product by: spraying an adhesive mixture upwardly onto one of the
moving webs from at least one nozzle array positioned in a spray
location below one of the webs; compressing the webs together as
they run through a nip formed by two nip rolls positioned at a
compression point downstream of the spray location; and winding the
bonded two-ply tissue product onto a roll under tension using a
winder which pulls the two-ply product, exerting tension on it. In
this aspect of the invention, it is practical to use a pressurized
nip to force the adhesively bonded webs together. The distance
between the spray location and the nip is selected to permit
sprayed adhesive to partially but not completely set during travel
over that distance at operating web speeds. The webs may be forced
together with nip rollers that have enough pressure to
substantially confine winder tension to the nip-to-winder portion
of the web path, as opposed to transmitting winder tension upstream
to the parent reels (i.e. the reels on which the tissue stock has
been supplied to the bonder), thereby providing improved control
over winder tension. Because the spray location is carefully
controlled, it is possible to use such a nip without unacceptable
adhesive build-up on the nip rolls.
[0018] In the above process, the adhesive is considered to be
partially but not completely set when it has what is known in the
field as "green tack". At that stage, the adhesive is damp to the
touch, but it does not transfer to another surface, so the adhesive
will contact bond, but it will not migrate so far through the
tissue web that it causes through bonding as the bonded webs are
wound into a roll.
[0019] Typically, each tissue web is unwound over its own carrier
roll, and spray nozzle(s) are positioned between the carrier rolls,
particularly adjacent to and downstream of the rear carrier roll.
For example, the web travel distance between the nozzles and the
nip is more than 140 (and even more than 200 but less than 500)
inches.
[0020] In a third aspect, the invention features methods of
producing tissue product with more than 2 (usually 3 or 4) plies.
The method uses at least two spray nozzle arrays, a rear array to
spray the bottom of an upper web and a forward array to spray the
bottom of an intermediate web. The multiple webs are tensioned by a
winder around a compression roll (usually but not necessarily a nip
roll as described above) to compress the webs. The web travel
distance between the two nozzle arrays and the nip roll is
controlled so that adhesive is partially but not completely set
when it reaches the roll. Both nozzle arrays are positioned as
discussed above. Typically the forward nozzle array will be more
than 140 inches (preferably more than 200 inches) from the
compression roll.
[0021] Preferably, webs are run at a speed of well over 1500
feet/min (more preferably 2,300 feet/min or higher), and the dwell
time for adhesive applied to the web is between 0.3 and 1.3
seconds. Dwell time is the period from application of adhesive to
the web until the adhesive treated web reaches the nip.
[0022] Alternatively, to make three- or more ply product, the
number of sprayer locations may be two less than the number of
plies being bound. For example, four moving webs are positioned
vertically to form an upper web, a upper-middle web, a lower-middle
web, and a bottom web respectively, and only two arrays of adhesive
spray nozzles are used: a first array positioned in the rear
location to spray upwardly onto the bottom surface of the
upper-middle web; and a second array positioned in a third location
to spray upwardly onto the bottom of the lower-middle web.
Similarly, the method may be used to make three-ply tissue by
positioning three moving webs as an upper web, a middle web, and a
lower web, respectively, and using only one adhesive nozzle array,
which is positioned in the rear location to spray upwardly onto the
middle web.
[0023] A significant advantage of the method is that it can be used
in series with high-speed tissue-forming equipment, i.e., reels of
tissue webs are provided by forming them on equipment including a
dryer, and winding up the resulting webs, which then are bonded at
a rate which exceeds the rate at which the webs are produced. When
we say that the webs are bonded at a rate which exceeds the rate at
which the webs are produced, we take into account down time at the
beginning of a run for loading reels of freshly made unbonded
tissue and time at the end of a run to unload bonded multi-ply
tissue. We also take into account similar down time for the tissue
production process. Finally, we take into account that at least two
and sometimes three or four tissue webs must be made to produce a
single multi-ply bonded web so that, as a rough approximation and
if all other things were equal, a two-ply bonding process could run
at 1/2 the speed of the tissue manufacturing process without
becoming a bottleneck. In general, the web speed exceeds 1500
feet/min (preferably over 2000 feet/min) during a significant
portion of the bonding process.
[0024] Tissue making relies on management of the creping process,
in which dried tissue is scraped from a heated drying cylinder to
which it has been adhered. Creping is improved generally when the
drying cylinder is hot and the tissue is relatively dry at the
point of creping. The above described bonding process is
advantageous in that it can bond relatively dry webs, without
adding or retaining moisture at the tissue-forming stage to
accommodate the needs of the bonding process.
[0025] Control over the spray process may include controlling the
adhesive mixture flow with respect to web travel speed, for
example, to maintain a substantially constant (+or -20%) overall
rate of addition of dry adhesive per unit area of web at different
speeds (preferably the addition rate is between 5 and 25 (most
preferably between 5 and 20) pounds/million square feet of
multi-ply web). The method may also include controlling the air
pressure used to spray the mixture at different web travel
speeds.
[0026] Typically, the method includes at least two phases, a
running phase and a substantially slower transition phase (e.g.,
starting up or slowing down the winder). The amount of liquid
adhesive delivered per minute is substantially proportional
(.+-.20%) to the web speed during both the running phase and the
transitional phase. The atomizing airflow pressure or flow rate may
also be controlled responsive to changes in web travel rate between
the running and the transition phase.
[0027] Multiple nozzles may be positioned on supports in a shower
housing which includes a drain for over-spray. The shower housing
includes a damper that is movable from a first damper orientation
that prevents nozzle spray from reaching the moving web to a second
damper orientation in which spray reaches moving web. During the
start-up phase, the damper is positioned in the first orientation
so that web is not bonded. The shower housing may be raised from a
an inactive position during idle periods when the web is slowed or
stopped to a second active position. Adhesive may be purged from
the nozzles in a cycle that includes introducing flush water and/or
airflow into the shower nozzle.
[0028] Preferred adhesives are aqueous mixtures, e.g., of
carboxymethyl cellulose; polyvinyl alcohol; or starch. The spraying
process control described above enables the use of higher (for
example at least 13%) solids in the liquid adhesive, which in turn
results in shorter drying times.
[0029] After the adhesive is applied, the webs may be forced
together by a pair of rolls (e.g. calender rolls) that are in
contact as the two webs pass through. For example, these rolls may
be biased together to form a pressure nip. The bonded tissue plies
are then wound up on a winder downstream of the nip, and tension on
the winder is substantially maintained downstream of the nip and is
not substantially communicated upstream of the nip.
II. Apparatus
[0030] The above method is practiced using apparatus that
includes:
[0031] A. a rear reel stand and a rear carrier roll above the rear
stand, forming the beginning of an upper web path;
[0032] B. a forward reel stand and a forward carrier roll above the
forward stand, forming the beginning of a lower web path, the upper
web path converging with the lower web path at the forward carrier
roll;
[0033] C. an adhesive applicator system for applying adhesive to
the bottom of tissue moving in the upper web path, the adhesive
applicator system comprising:
[0034] i. an array of spray nozzles positioned at a spray location
below and generally transverse to the upper tissue path, and
oriented to spray generally upward, toward the bottom surface of
the upper tissue, the first location being between the rear and the
forward carrier rolls;
[0035] ii. an air pressure source connected to provide air to the
spray nozzles
[0036] iii. an adhesive source connected to provide a flow of
adhesive to the spray nozzles, and
[0037] D. a pair of nip rolls positioned downstream from the spray
head array and the forward carrier roll, the nip rolls being in
both the upper and lower tissue paths, the nip rolls forming a nip
for compressing the upper and the lower tissue together
[0038] E. a winder downstream of the nip for winding up bonded
tissue product, the winder being designed to have a running speed
within a predetermined range, the nip being spaced apart from the
spray location at least 230 inches, to permit sprayed adhesive to
partially but not completely set during travel over that distance
at speeds in the predetermined range.
[0039] The location of the array of spray heads is controlled as
described above. For example, the nip is spaced apart from the
first (rear) location by at least 200 inches to permit sprayed
adhesive to partially but not completely set during travel over
that distance. Specifically, the array is located between the rear
and the forward carrier rolls.
[0040] The apparatus may also include: A. an adhesive pump
providing a flow of adhesive to the spray heads; B. an air pump
providing air pressure to the spray heads; C. a sensor for sensing
the speed of travel of at least one of the tissue webs, which
provides a web speed signal to a signal processor; and D. an
adhesive flow control system for controlling the flow of adhesive
to the spray heads; the adhesive flow control system includes a
flow rate monitor, a signal processor which receives a signal from
the monitor and provides signals to an adhesive flow motor,
responsive to the web speed signal, so that the adhesive delivery
rate is varied in response to web travel rate.
[0041] When more than two tissue webs are being bound, the
apparatus includes at least one intermediate reel stand and
intermediate carrier roll, forming the beginning of an intermediate
web path, the intermediate carrier roll being positioned between
the rear and the forward carrier rolls. The apparatus may also
include additional arrays of spray heads positioned at a second
(forward) location below and generally transverse to the
intermediate web path, and oriented to spray generally upward,
toward the bottom surface of the intermediate tissue.
[0042] The apparatus can operate fast enough to process the output
of the web-forming equipment substantially without backlog or
slowing of that equipment.
[0043] A signal processor includes circuitry to control the amount
of adhesive flow supplied to the nozzles substantially proportional
to the web travel speed, so as to provide a substantially constant
overall ratio of dry adhesive per unit area of web at different web
speeds. The controller also includes circuitry to establish the
other method controls described above, such as the controls on
adhesive flow, airflow damper position, and shower housing
position. The controller also controls a purge cycle in which flush
water and/or airflow is directed into the nozzle.
[0044] As noted, the above process and apparatus use tissue that is
very dry without need for further modification. The process avoids
the need to emboss as a bonding process. The process permits
effective use of high speed tissue forming machinery. The process
improves utilization and reduces waste, particularly waste from
discarding the beginning and end of rolls due to improper adhesive
loading at transition speeds.
[0045] The details of one or more embodiments of the invention are
set forth in the accompanying drawings and the description below.
Other features, objects, and advantages of the invention will be
apparent from the description and drawings, and from the
claims.
DESCRIPTION OF DRAWINGS
[0046] FIG. 1 is a diagram showing apparatus for spray bonding two
moving tissue webs.
[0047] FIG. 2 is a chart of a operating sequences during a process
for spray bonding moving tissue webs.
[0048] FIGS. 3A through 3C are top, front and side views,
respectively, of a shower housing.
[0049] FIG. 4 is a diagram of the valves and supply conduits for
the housing of FIGS. 3A-3C.
[0050] FIG. 5 is a sectional view of a nozzle.
[0051] FIG. 6 is a diagram of controls for the apparatus of FIG.
1.
[0052] FIG. 7 shows an alternative embodiment for producing
four-ply tissue.
[0053] Like reference symbols in the various drawings indicate like
elements.
DETAILED DESCRIPTION
[0054] In FIG. 1, individual tissue webs 10 and 20 are spray bonded
on ply bonder 40 to form a two-ply tissue product 30. Bonder 40
includes two reel stands 42 and 44 suitable to receive webs as they
are produced by tissue forming apparatus (not shown).
[0055] Webs 10 and 20 are unwound from the reel stands and threaded
over carrier rolls 46 and 48 to roll 49 and from there to calender
rolls 50 and 52 and winder 54.
[0056] A shower assembly 60 is positioned between carrier rolls 46
and 48, beneath, and across the width of (i.e. transverse to the
movement of), web 10. Shower assembly 60 (shown in greater detail
in FIGS. 3A-3C) includes a row of nozzles (shown in FIG. 4)
positioned in a rectangular housing 64, which extends across the
width of the web (about 112 inches) and the housing section (FIG.
3C) is about 9.times.11 inches. Housing 64 (shown for clarity in
FIGS. 3A-3C without nozzles) includes several features described in
greater detail below. Axle 66 extends across the width of the
housing, and it controls rotation of a baffle plate (or "flapper")
68. A trailing lip 70 extends from the rear (trailing) edge of
housing 64. Side ports 72 are provided for air adhesive conduits
(shown in FIG. 4) which supply nozzles 62.
[0057] FIG. 4 shows an array of 12 nozzles 62 spaced about 8.75
inches center-to-center. Generally, the number of nozzles is
selected to provide 200% coverage--i.e., any given point on the web
generally receives output from two nozzles. As described in greater
detail below, each nozzle is connected to a liquid adhesive supply
63, and atomizing air supply 65 and a control air supply 67.
[0058] A representative nozzle 62 is shown in FIG. 5. The nozzle
comprises a control chamber 74 which drives a shut-off and
clean-out pin 76 to shut off or open orifice 78. Adhesive is
supplied from one side port 80, and air is supplied from an
atomizing air port 82 on the other side of the nozzle. The pressure
in chamber 74 overcomes the spring bias, driving pin 76 rearwardly
and opening orifice 78. Generally, the nozzle produces a fine flat
fan spray with a fairly wide spray angle (thus reducing the number
of nozzles needed). The wider the spray angle, the fewer nozzles
that are required, thus reducing costs and generally stabilizing
and maximizing adhesive flow in any single nozzle.
[0059] FIG. 6 is a diagrammatic representation of the systems that
supply and control the equipment described above.
[0060] Shower assembly 60 and supply conduit 63 are connected to
adhesive reservoir 102 and supply pump 103 via supply conduit 104,
which includes filter 105 and valve 120. Pump 103 is a positive
displacement pump, driven by a variable speed motor to control
adhesive flow. A magnetic flow meter 107 monitors flow in conduit
104. Valves 120 and 121 as a pair can be set to direct adhesive
flow to conduit 63 (valve 120 open and 121 shut) or to return loop
123 which returns adhesive to supply 102 when valve 121 is open and
120 is shut.
[0061] The shower assembly is connected to atomizing air supply
conduit 65 (introduced through both sides of housing 60) from air
supply 106. Atomizing airflow is controlled by supply valve
109.
[0062] Nozzle control air is provided via conduit 67, and is
controlled by pneumatic valve 134, which is supplied by air supply
106.
[0063] Flapper control arm 69 is connected to pneumatic controller
71, which is supplied from via air supply conduit 106. Flush water
supply 91 is connected to atomizing air supply conduit 65 via
control valve 115 and check valve 117. Shower housing assembly lift
mechanism 108 is controlled by pneumatic valve 131 which is
pressurized by air supply 106 via conduit 133.
[0064] Quick purge valve 140 opens the atomizing air conduit 65 to
purge any liquid in it at the end of the purge cycle described
below.
[0065] A computer (signal processor) 100 is separately connected to
adhesive supply pump 103 and to air supply valve 109. Computer 100
is also connected to control the speed of pump 103 responsive to
signals it receives from: a) flow meter 107; b) operator input of
the adhesive flow set point; and c) winder speed. Computer 100 is
also connected to other components as described above and shown in
the figures.
[0066] A system of compressed air supply 106 supports the number of
operations described above, e.g., it provides pressure and volume
to operate the spray nozzles and various system components
described below. The compressed air capacity required will vary
depending on the needs of a particular system. Generally, a source
on the order of 40 CFM at 80 psi is adequate.
[0067] Computer 100 reads the winder speed (WS), the adhesive flow
(AF) and any control modes supplied by operator input 113. From
these values, computer 100 calculates the required adhesive flow
(AF), so that AF=K.times.WS.times.SP, where WS is the winder speed;
SP is an operator supplied set point for the adhesive
loading--i.e., dry weight of adhesive per area of web. The set
point for making a two-ply product typically will be on the order
of 5-25 (more preferably 5-20) pounds of dry adhesive per million
square feet of web. When three-ply tissue is made with two showers,
each shower is set in the above range. Where a single shower is
used to bond three plies, the adhesive spray must penetrate the
middle layer to bond both the upper and lower layer. In that event,
the set point for that shower is higher (e.g. in the range of 30-35
pounds/million square feet). "K" is a proportionality constant that
takes into account the width of the winder, the density of adhesive
mixture (gallons of mixture per unit of dry adhesive weight) and
that reconciles and scales units used.
[0068] Computer 100 also is programmed with routines to
[0069] 1. start, stop and control the speed of the adhesive feed
pumps;
[0070] 2. start, stop and regulate atomizing air;
[0071] 3. turn control air on and off;
[0072] 4. open and close the flapper;
[0073] 5. raise and lower the shower box;
[0074] 6. toggle adhesive diverting valves;
[0075] 7. flush the shower by,
[0076] i. starting and stopping flush water,
[0077] ii. opening and closing the quick purge valve,
[0078] iii. starting and stopping the atomizing air;
[0079] The operation of the above-described equipment will be
better understood with reference to the following operating
sequences diagrammed in FIG. 2. Overall operation can be divided
into a start-up cycle, a normal running mode, and a shutdown cycle.
The operator may select manual or automatic operation. At rest
(col. 1), the winder is off, a run interlock is open, the adhesive
flow is off, the atomizing air is off, the shower housing is in the
lower, inactive position, the flapper is closed, the control air is
off, valves in the adhesive flow loop are set to recycle adhesive
to the supply (i.e., valve 120 is closed and valve 121 is open),
flush water is closed, and purge air is closed.
[0080] In automatic operation, the computer begins start up with a
threading mode (col. 2) by turning the winder on to a slow,
threading speed, and turning on the pump to begin adhesive flow
(with valve 121 remaining open and valve 120 remaining closed). The
computer then enters a mode in which the web is running (col. 3) by
closing the run interlock, turning on the atomizing air valve 107,
and moving the shower housing and the flapper into operating
positions. Once the web running status is achieved, there are two
two-second speed-up checks (cols. 4 and 5) as the winder speed is
increased. Control air is turned on between these two checks.
[0081] Immediately after the second speed check, diverter valve 121
is closed and supply valve 120 is opened to start adhesive flow to
the nozzles. The apparatus is then in its normal running mode (col.
6).
[0082] Shut-down includes several phases, and it may be initiated
manually or automatically as the winder slows and a low speed
threshold (e.g. <100 feet/min) is reached.
[0083] In shut down, atomizing air is ramped down with the winder,
and then both are turned off. The run interlock is opened, and
adhesive flow is diverted by closing valve 120 and opening valve
121. The shower housing is lowered and the flapper is closed.
Nozzle control air pressure is also shut off.
[0084] A nozzle wash cycle is achieved by introducing flush water
into the atomizing air conduit 65. A nozzle air purge cycle (col.
9) is achieved by turning off flush water, and starting atomizing
air flowing through the nozzles. Atomizing airflow is increased for
the final purge (col. 10) by opening quick purge valve 140 at the
far end of the nozzle housing. When the atomizing air and quick
purge valve 140 are turned off, the system is at rest (col.
12).
[0085] A flush mode as described above can be instituted manually
whenever the shower is in auto mode and the winder is not running.
The water valve will stay open for as long as 15 minutes (compared
to the 15 seconds in the auto mode).
[0086] A manual mode permits each of the control functions to be
operated manually and independently.
[0087] Bond strength of the product may be tested according to a
standardized protocol. For example, small strips of bonded product
(typically about 2.5 inches wide) are subjected to known force to
determine the amount of force required to separate the tissue
layers. In general, for flexographic product applications, the bond
strength should exceed 100 mg/cm. Preferably the median value of
the bond strength should be over 400 mg/cm. If necessary, the
measured force for separating a given strip may be doubled using
two strips, and obtaining a value for separating both strips.
[0088] Because the product is bonded with a carefully controlled
adhesive spray, the adhesive is substantially continuous and
uniform, even when analyzed at a detailed level. For example, when
a starch or PVA adhesive applied by the above spray is evaluated
using a standard iodine visualizing procedure (e.g., spraying a
0.01N I.sub.2 solution on the tissue from a standard pump sprayer),
color development indicative of adhesive shows very little
non-uniformity, and what non-uniformity exists is generally random,
at least over areas greater than 1 mm.sup.2. In contrast, adhesive
applied by a textured roll will show a regular uniform matrix of
starch dots over areas up to 1 cm.sup.2.
[0089] Other embodiments are within the following claims. For
example, in FIG. 7, each of four reel stands 301-304 is occupied,
and one of carrier rolls 305-308 is included to carry web from each
of the respective rolls.
[0090] Only two shower assemblies 309 and 310 are positioned
between carrier rolls 301 and 302, and between 302 and 303,
respectively. No shower is necessary or desirable between carrier
rolls 303 and 304. Instead, the adhesive load from shower 309 is
increased to provide sufficient adhesive to bond webs 303 and
304.
[0091] In an alternative embodiment (not shown) three-ply tissue
may be manufactured by omitting the roll on stand 301. Shower
assembly 310 is optional in that configuration.
[0092] A number of embodiments of the invention have been
described. Nevertheless, it will be understood that various
modifications may be made without departing from the spirit and
scope of the invention. Accordingly, other embodiments are within
the scope of the following claims.
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