Note: Descriptions are shown in the official language in which they were submitted.
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STACK OF SHEETS WITH REPOSITIONABLE ADHESIVE ALTERNATING
BETWEEN OPPOSITE EDGES AND CONTA1NING ONE OR MORE SHEETS
DIFFERENT FROM OTHER SHEETS
Technical Field
The present invention relates to a stack of flexible sheet material and to a
dispenser containing such stack. The stack contains a plurality of sheets with
each
sheet attached to the other by repositionable adhesive and wherein at least
two
sheets are different from each other. The present invention further relates to
a
method for applying coating material to a plurality of sheets of which at
least two
1o sheets are different and to an apparatus for carrying out that method.
Background of the Invention
US 5,417,345 discloses a dispensing device for use in dispensing sheets of
material coated along one edge with a narrow band of readily releasable
pressure-
sensitive adhesive. The dispenser comprises a container having a pair of
sidewalls
15 connected by a top wall which is foamed with a transversely extending
rectangular
opening extending in the direction parallel to the side walls. The sheets are
stacked
within the dispenser such that upon removing the uppermost sheet in the stack
the
adhesive coating along one edge of the sheet adhered to the edge of the next
sheet
in the stack will cause the next sheet in the stack to be withdrawn at that
free edge
2o through the dispensing opening upon withdrawal of the uppermost sheet. A
typical
embodiment disclosed includes a stack of sheets where the adhesive alternates
between two opposite edges of the stack. Further, dispensers such as those
disclosed in this patent are commercially available. However, a stack of
sheets used
therein typically consists of sheets that are all simiiar.
25 There exists now a desire to have one or more sheets in the stacks of such
dispensers to be different from the other sheets in the stack. For example, it
may be
desirable to have sheets of alternating color in the stack or to have one or
more
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sheets in the stack that contain a message, in particular an advertisement or
an
indication that the end of the stack is approaching.
It has however until now not been possible to produce such stacks of sheets
where the adhesive alternates between opposite edges. In particular, a stack
of
sheets as disclosed in US 5,417,345 is typically prepared by coating the
adhesive
stripes to a continuous web of sheet material, for example paper. Such process
does not give the required flexibility needed to produce stacks in which one
or more
sheets are different from the other sheets.
WO 94/19419 discloses a process for coating a plurality of individual sheets
to with adhesive, for example repositionable adhesive. This process allows for
one or
more sheets, different from the other sheets to be inserted during the coating
process thereby allowing to produce a stack of sheets with inserts. However,
the
process disclosed in this patent application is not adapted to produce stacks
of
sheets where the adhesive alternates between opposite edges of the stack and
that
15 can be used in a dispenser such as disclosed in the above US 5,417,345.
Summary of the Invention
The present invention provides a stack of flexible sheet material comprising
a plurality of sheets disposed one on top of another, each sheet having
repositionable adhesive along one edge and being free of adhesive along the
2o opposite edge and the sheets are stacked with the repositionable adhesive
edge of
each sheet disposed along alternate opposite edges to maintain the sheets in
the
stack, characterised in that said stack comprises at least two sheets that are
different
from each other.
The present invention also provides a dispenser comprising a stack of sheets
2s as defined above, said dispenser having wall means enclosing the stack
including a
top wall with a transverse opening through which a portion at the edge free of
adhesive of the uppermost sheet in the stack extends.
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3
The present invention further provides a method for applying coating
- material to sheets, comprising the steps of:
(a) applying coating material to an endless transfer surface;
(b) conveying a plurality of sheets, of which at least two sheets are
different
s from each other, in an overlapped end-to-end relationship to a transfer
location; and
(c) contacting the sheets at the transfer location with the transfer surface
to
transfer the coating material to the sheets thereby obtaining a coated area on
each of
said sheets;
wherein said coating material is applied to said endless transfer surface such
1o that when coating material is transferred to a first and second sheet that
are next to
each other, the coated areas on said first and second sheets are offset
relative to
each other in the direction perpendicular to the direction of conveyance of
the
sheets.
Also provided is an apparatus for applying coating material to a plurality of
15 sheets, the apparatus including a conveyor arrangement for conveying a
plurality of
sheets in overlapped end-to-end relationship to a transfer location;
an endless transfer surface which is movable through the transfer location in
contact with the conveyed sheets;
and a coating means arranged to apply, to the endless transfer surface,
2o coating material for subsequent transfer to sheets to form coated areas
thereon at
the transfer location;
~ wherein said coating means is capable of applying coating material to said
endless transfer surface in such a way that when coating material is
transferred to a
first and second sheet that are next to each other, the coated areas on said
first and
25 second sheets are offset relative to each other in the direction
perpendicular to the
direction of conveyance of the sheets.
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4
Brief Description of the Drawings
Embodiments of the invention will be described, by way of example, with
reference to the accompanying drawings, wherein like structure is referred to
by like
numerals in the several views, and in which:
Figure 1 is a schematic side view of sheet coating apparatus in accordance
with the invention;
Figure 2 is a schematic plan view of the apparatus shown in Figure 1;
Figure 3 is a diagrammatic illustration of the relative positions of sheets at
the entry to a dual coater forming part of the apparatus shown in Fig. 1;
1o Figure 4 is a view of a dual coater forming part of the apparatus shown in
Figure 1;
Figure 5 is a view similar to Figure 4 showing part of the dual coater in
greater detail;
Figure 6 shows a coating material supply system for the dual coater of Figs.
4 and 5;
Figure 7 is an enlarged view of part of Figure 5.
Figure 8 is an enlarged diagrammatic view illustrating a part of the
apparatus shown in Fig. 1;
Figure 9 shows a component of Figure 8;
2o Figure l0a is a diagrammatic side view of part of an adhesive coater
forming
part of the apparatus shown in Figure 1;
Figure lOb is a diagrammatic view of a gravure roller for use in the adhesive
coater shown in Figure 10a;
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Figure l Oc is a diagrammatic representation of an endless transfer coated
' with adhesive stripes using the gravure roller shown in Figure lOb;
Figure 11 is an enlarged partial view illustrating, diagrammatically, a part
of
Figure 10a;
5 Figure 12 is a partial plan view of a component of Figure 11; and
Figure 13 is a partial plan view of another component of Figure 11.
Figure 14a to 14c schematically depict trimming of a stack of sheets in pads
of desired size and shape.
Detailed Description
1o The flexible sheet material for use in connection with the present
invention
can be any kind of flexible material and includes paper as well as plastic
film
materials such as polyethylene, polypropylene and polyester. Preferably the
flexible
sheet material is paper and the description will be primarily directed thereto
without
however the intention to limit the invention thereto. Preferably, the stack of
flexible
sheet material is a stack of repositionable notes. Preferably, such notes are
coated
on one surface with a primer coating and on the other side with a low adhesion
backsize (LAB). The repositionable adhesive is coated to the surface coated
with
the primer coating. The primer material may be obtained by mixing
approximately
3-7% by weight of the binding agent MOWIOL (Trade Mark) available from
2o Hoechst AG, Frankfurt/Main, Germany and approximately 3-8% by weight of the
pigment AEROSIL (Trade Mark) available from Degussa AG, Frankfurt/Main,
Germany with approximately 90% by weight of water.
The LAB material may be any suitable material including, but not limited to,
acrylate co-polymers, silicone materials, urethanes, and fluoro polymers. For
example, the LAB may be a water-based solution of the material described in EP-
A
0618509, the solution comprising typically from about 5% to about 10% solid
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6
material. Other LAB materials that may be employed include those disclosed in
United States Patent Nos. 5,202,190 and 5,032,460.
The repositionable adhesive is preferably a repositionable microsphere
pressure-sensitive adhesive, for example as described in US-A-5 045 569; 4 495
318; 4 166 152; 3 857 731; 3 691 140; US Re 24906; US 5,571,617 and EP-A-0
439 941.
The sheets in the stack may be of any desired size and shape but are
typically rectangular or square and have a width between 5 cm and 15 cm and a
length between 5 cm and 25 cm. The number of sheets in the stack can vary
widely
l0 but is typically between 10 and 100, preferably between 25 and 50.
The stack of this invention contains at least two sheets that are different
from each other. While they may be different in any kind of respect they are
preferably different in color, printing or kind of material. According to a
particular
embodiment of this invention, the stack contains a majority of sheets that are
similar
and only a few sheets that are different from that majority of sheets.
Typically,
these few sheets may contain messages such as an advertisement or an
indication
that the end of the stack is approaching. Alternatively, the stack comprises
similar
first sheets and similar second sheets and these first and second sheets
differ from
each other in for example color and are alternated throughout the stack.
2o The flexible sheet material in accordance with this invention has a first
major
surface and a second major surface opposite to the first major surface. Along
one
edge of the second major surface there is provided the repositionable adhesive
preferably in the form of a band or stripe, although any other form can be
used as
well such as for example spots of repositionable adhesive. The sheets are
stacked
together with second major surface of one sheet adhering to first major
surface of
the next sheet in the stack and the adhesive coating alternates between two
opposite
edges of the stack. Accordingly, of two consecutive sheets of a stack one
sheet in
the stack will have the repositionable adhesive along a first edge of two
opposite
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edges and will be free of repositionable adhesive along second edge of the two
opposite edges and the next sheet in the stack will be free of repositionable
adhesive
along the first edge and have repositionable adhesive along the second edge.
The stack of flexible sheet material of this invention is typically used in a
dispenser as described above. This adds an element of surprise to commercial
advertisements contained on inserted sheets in the stack because such sheets
only
appear to a user when the previous sheet relative to the inserted sheet is
withdrawn
from the dispenser. Suitable dispensers for use in this invention are
described in
more detail in US 5,417,345.
to Preferred Apparatus and Method for Coating the Flexible Sheet Material
The apparatus shown schematically in Figures 1 and 2 is specifically for use
in the production of repositionable notes from sheets of any suitable
substrate
material, for example, paper, polymeric film or foils and, in particular, for
the
application to individual sheets of a primer material, a low adhesion backsize
(LAB)
is material, and a repositionable adhesive so that the sheets can subsequently
be used
to form repositionable notes. In the following description, it will be
assumed, unless
otherwise noted, that the sheets (which may be pre-printed) are of paper. The
paper
may be any suitable paper, such as the paper utilized to construct the Post-it
brand
repositionable notes available from Minnesota Mining and Manufacturing Company
20 ("3M") of St. Paul, Minnesota.
The apparatus has a paper path which receives a succession of paper sheets
(not shown) from a stack in a sheet feeder 1. From the sheet feeder 1, the
sheets
travel along the paper path in the direction indicated by the arrow 100 past a
sheet
inserter 2 (which, as shown in Fig. 2, is located to one side of the paper
path) and
25 then through a dual coater 3, a sheet overlapping station 4, a dryer 5, a
sheet
guiding section 6, and an adhesive coater 7. The control and synchronization
of the
drives of the various stations may be performed by a central electronic
control unit
(not shown), for example a Siemens PLC 135.
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8
As described in greater detail below, when the inserter 2 is not in use,
sheets
leave the feeder 1 in a continuous stream in which, to reduce the space
required
between the feeder 1 and the dual coater 3, the trailing edge of one sheet
overlaps
the leading edge of the subsequent sheet. The sheets are, however, conveyed
separately through the dual coater 3 where they are coated individually on one
side
with a primer material and on the other side with an LAB material. The sheets
emerging from the dual coater 3 are then overlapped once again, in the
overlapping
station 4, forming a pseudo-web in which the trailing edge of one sheet is
overlapped by the leading edge of the subsequent sheet. The pseudo-web is then
1o maintained throughout the remainder of the apparatus although the initial
direction
of overlap, being undesirable for the dryer 5 and unsuitable for the adhesive
coater
7, is reversed when the pseudo-web leaves the overlapping station 4. Following
passage through the dryer 5 (in which the primer and LAB coatings are dried),
the
pseudo-web passes through the guiding section 6 (in which the sheets are side
registered and aligned) and the adhesive coater 7 (in which a plurality of
adhesive
stripes are applied to the sheets, on the side coated with primer material in
the dual
coater 3). The sheets can then be stacked and trimmed as required to form pads
of
repositionable notes. As an alternative, the sheets leaving the dryer 5 can be
stacked
and stored and subsequently re-fed, as a pseudo-web of overlapped sheets, to
the
2o adhesive coater.
The inserter 2, which is not an essential part of the apparatus, can be used
when it is required to insert one or more sheets from another stack into the
stream
of sheets entering the dual coater 3. Alternatively, for making a stack of
this
invention, a stack of uncoated sheets with one or more different sheets
inserted
therein may be fed from sheet feeder 1. The inserter 2 may be as described in
our
GB application serial no. 9603345.1 filed 16.02.96 and entitled "Sheet coating
method and apparatus with sheet insertion".
Operation of the sheet feeder 1 will now be described in greater detail. The
sheet feeder 1 is a rear edge feeder of the type comprising a vertically-
movable table
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9
on which a stack of sheets 11 is located, and a suction head 12 positioned
above
the rear edge of the stack. When the feeder I is in operation, the suction
head 12
lifts the top sheet from the stack 11, by its rear edge, and moves it forwards
(assisted by a jet of air from nozzle 12a) so that the sheet is taken up by
rollers 13
5 and conveyed out of the feeder and onto a conveyor 14. The suction head 12
then
returns and picks up the next sheet which is moved forwards and taken up by
the
rollers 13 while the first sheet is still present between the rollers. In that
way, the
trailing end of each sheet overlaps the leading end of the succeeding sheet as
the
sheets pass between the rollers and are fed onto the conveyor 14. The extent
of the
10 overlap depends on the size of the sheets and the relationship between the
operation
of the suction head 12 and the take-up speed of the rollers 13. As the height
of the
stack 11 decreases, the table 10 moves upwards to maintain the top of the
stack in a
predetermined location relative to the suction head 12.
Sheet feeders of the type just described are available from MABEG
1s Maschinenbau GmbH of Offenbach, Germany, under the trade designation
"41988". It will be appreciated, however, that any other suitable sheet feeder
could
be used.
The sheets from the feeder 1 are carried on the conveyor 14 past the sheet
inserter 2 to a gate 15 at the entry to the dual coater 3. For the purposes of
the
2o present description, it will be assumed that the sheet inserter 2 is not
firnctioning, in
which case the overlapped sheets from the feeder I form a continuous stream on
the
conveyor 14 as illustrated in Fig. 3. As the first sheet 21 arrives at the
gate 15, it is
temporarily halted while the rollers of upper and lower coating stations 16,
17
(described below) within the dual coater 3 rotate to the correct position for
25 transporting and coating the sheet. The gate 15 then opens to allow the
first sheet
21 to enter the dual coater 3, following which the gate closes in advance of
the
arrival of the second sheet 22 and halts the latter until the rollers of the
upper and
lower coating stations 16, 17 have again rotated to the correct position.
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The dual coater 3, which is shown in Fig. 4 and, in greater detail, in Figs. 5
and 6, will now be described. The sheets from the conveyor 14 are picked up by
a
nip roll pair 30 within the dual coater 3 and fed between the upper coating
station
16 and lower coating station 17 (already mentioned) which are located,
respectively, above and below the paper path through the dual coater. As the
sheets
pass through the dual coater the upper station 16 applies a coating of primer
material to one side of each sheet and the lower station 17 simultaneously
applies a
coating of LAB material to the other side of each sheet. The sheets are fed
into the
dual coater 3 in a non-overlapped condition. This exposes all, or a
substantial
to portion, of both major surfaces of the sheets to coating by the LAB and the
primer.
As described below, mechanical means are used to grip and advance the sheets
through the dual coater allowing the primer material and the LAB material to
be
coated over substantially the entire major surfaces of the sheets.
The upper coating station 16 comprises a metering roller 31 and a coating
1s roller 32, located above the path of the sheets of paper through the dual
coater. The
coating roller 32 cooperates with a coating drum 33 of the lower coating
station 17
which also comprises a metering roller 34 and a transfer roller 35, all
located below
the paper path through the dual coater. The coating drum 33 has a cut-out
portion
36 of rectangular cross-section (shown in greater detail in Figure 7) which
contains
2o a conventional sheet gripper 37 (shown closed in Figure 7) for grasping
sheets from
the feed nip 30. In addition, the drum is covered, around less than half its
circumference, with a blanket 38 (not shown in Figure 4) whereby, as described
below, the coating roller 32 and coating drum 33 form a coating nip only when
the
blanket is located directly adjacent the coating roller 32. As described
below, the
25 upper coating station 16 provides substantially full surface roll coating
of primer
material on the upper surface of the sheets, and the lower coating station 17
provides substantially full surface roll coating of LAB material on the lower
surface
of the sheets. In each case, the portions engaged with the grippers (as
described
herein) are not coated.
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11
In the upper coating station, a trough 39 for the printer material is formed
by the surfaces of the metering and coating rollers 31, 32 adjacent the nip
between
the rollers and on the upper side thereof together with two opposed end wails
(not
shown) which engage in grooves (not shown) adjacent the ends of the rollers.
As
the rollers 31, 32 rotate, the primer material forms a film on the coating
roller 32
and is transferred to a sheet passing underneath the roller.
The thickness of the primer film on the coating roller 32, and hence the
amount of primer coated onto a sheet, is dependent on the viscosity of the
primer
and on the pressure between the metering and coating rollers 31, 32 and, for a
given
to primer, can be adjusted by moving the metering roller towards or away from
the
coating roller and by adjusting its speed. The trough 39 is supplied with
primer by
nozzles 40 (see also Figure 6) which receive the primer from a tank 41 by
means of
a pump 42. The trough 39 also has overflow outlets 43 through which excess
primer is returned to the tank.
In the lower coating station 17, a trough 44 for LAB material is similarly
formed between the metering roller 34 and the transfer roller 35. As in the
upper
station, the coating material forms a film on the transfer roller, the
thickness of
which can be adjusted by moving the metering roller 34 towards or away from
the
transfer roller 35 and by adjusting its speed, thereby controlling the amount
of LAB
2o material that passes from the transfer roller to the blanket covering 38 on
the
coating drum 33 (but not on to the remainder of the drum, which the transfer
roller
35 does not contact).
In a similar manner to the trough 39 in the upper coating station 16, the
trough 44 is supplied with LAB material by respective nozzles 45 (see also
Figure
6) which receive the LAB material from a respective tank 46 by means of a pump
47. The trough 44 has overflow outlets 48 through which excess LAB material is
returned to the tank 46. As the blanket-covered part of the drum 33 moves
around
adjacent the coating roller 32 of the upper station, a sheet that is incoming
from the
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12
feed nip 30 of the dual coater 3 will be picked-up by the gripper 37 in the
drum and
carried through the coating nip between the roller 32 and the blanket 38 on
the
drum 33 and, as the sheet passes through the nip, it will be coated on one
side with
the LAB material. Sheet strippers (not shown) are located on the downstream
sides
of the coating roller and the coating drum to ensure that sheets do not wrap
around
either the roller or the drum but are fed out to the overlapping station 4.
The next
sheet from the feed roll nip 30 will be picked up and carried between the
coating
roller 32 and the coating drum 33 when the blanket covering once again moves
around adjacent the roller 32, operation of the gate 15 being timed to ensure
that a
to sheet is picked up on every rotation of the drum. In the event that no
sheet is
waiting at the gate 15 (as a result, for example, of a mis-feed at the feeder
1 or the
inserter 2), that fact is detected by a photocell (not shown) at the gate, and
the
roller 32 is moved away from the drum 33 to prevent any mixing of the primer
and
LAB materials.
It will be appreciated that the coating in the dual coater 3 is discontinuous
because it occurs only when the blanket covering 38 on the coating drum 33 is
adjacent the coating roller 32 (i.e. when a sheet is passing through the
coating nip).
A typical coating weight for the LAB material on the sheets is from about 0.5
gsm
to about 12.0 gsm and the coating weight of the primer material would be
matched
2o to that to ensure that the coated sheets remain flat. Because the primer
and the LAB
materials are applied to the paper sheets simultaneously in the coating
station and
are preferably selected to have appropriately selected characteristics, such
as
viscosity, % solids, and coating weights, the risk that the sheets will curl
or wrinkle
is substantially eliminated. As an alternative, a dual coater which does not
apply the
primer and LAB coatings simultaneously could be used although with a loss of
benefits associated with simultaneous coating. For example, the primer coating
station 16 could be located prior to the LAB coating station 17, in which case
the
coating roller 32 and the coating drum 33 would each require respective
counter-
pressure roller.
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I3
The blanket covering 38 on the coating drum 33 can be of any suitable type,
but is preferably formed from a rubber or any other suitable elastomeric
material.
The blanket 38 is secured by adhesive to a sheet of support material 38A which
is
capable of being wrapped around and releasably-secured to the drum 33. The
support sheet 38A may, for example, be a plastics material such as that
available
under the trade designation "Mylar", and the blanket 38 may be secured to the
support sheet by a neoprene glue such as that available, under the trade
designation
"1236", from Minnesota Mining and Manufacturing Company of St. Paul,
Minnesota, U.S.A. The support sheet 38A is releasably secured to the drum 33,
for
to example by screws. In that way, the blanket 38 can be easily removed from
the
drum and replaced when necessary. If the blanket 38 is secured to the support
sheet
38A while the latter is laid out flat, it is preferred that a flexible
adhesive should be
used to secure the blanket. The flexibility of the adhesive is less important
if the
blanket 38 is secured to the support sheet after the latter has been attached
to the
drum 33. Any suitable adhesive can be used to secure the elastomeric blanket
38 to
the support sheet provided, in particular, that it will ensure that the
corners of the
blanket do not lift away from the support sheet during the coating process.
A coating drum as shown in Fig. 7 is also described in our GB application
serial no. 9603366.7 filed 16.02.96 and entitled "Sheet coating apparatus
including
2o a coating roller".
As an alternative, the blanket covering 38 on the coating drum 33 may be a
DuPont "CYRELL" polyurethane blanket available from E.I. DuPont de Nemours
ofWilmington, Delaware, U.S.A.
On the exit side of the coating nip 32, 33, is the sheet overlapping station 4
in which a gripper unit 50 is positioned to take sheets as they emerge from
the
coating nip and deposit them on a conveyor 5 i (not shown in Figure 5). The
gripper
unit 50, which is conventional, comprises sheet grippers 52 carried on an
endless
chain 53 the movement of which is synchronized with the sheet feed so that a
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14
gripper 52 is positioned to receive each sheet that leaves the coating nip. A
blower
54, located below the paper path on the exit side of the coating nip, provides
a
cushion of air to support the sheets as they are being carried by the sheet
grippers
52. The blower 54 incorporates a heater (not shown) which serves to dry the
LAB
coating on the sheet to some extent, to prevent the sheets from sticking to
the
conveyor. The conveyor 51 is run at a slower speed than the chain 53 of the
gripper
unit so that each sheet is deposited on the conveyor with the leading edge of
the
sheet lying on top of the trailing edge of the preceding sheet, forming a
pseudo-web
of sheets. Typically (but not essentially), the extent of the overlap is from
about 1
to centimeter (cm) to about 2 cm. The conveyor 51 is a vacuum conveyor
connected
to a source SS of low pressure so that the sheets are positively held on the
conveyor
and the overlapped relationship between them is maintained.
The dual coater 3 together with the sheet overlapping station 4 may be
based on the "GULLA SPEED GS GS 8000" coater available from Billhofer
Maschinenfabrik GmbH of Nurnberg, Germany.
From the output end of the conveyor 51, the sheets move to a further
vacuum conveyor 56 (Fig. 1) which carries the sheets through the dryer 5
(described in greater detail below). Between the conveyors 51, 56, the sheets
pass
through an arrangement which reverses the direction in which the sheets are
overlapped. That arrangement, which includes a blower 60 shown in Fig. 4, is
illustrated diagrammatically in Figs. 8 and 9. In addition to the blower 60
(which is
located between the conveyors 51, 56 and below the paper path) the arrangement
includes a stationary vacuum cylinder 61 with closed ends 62 which is located
above the paper path and slightly downstream of the blower. The portion of the
vacuum cylinder 61 directed towards the blower 60 is formed with a plurality
of
apertures 63, shown in Fig. 9, the remainder of the cylinder being closed. In
use,
the interior of the cylinder is connected by a line 67, through one of the
closed ends
62, to a source of vacuum 66. Typically, the cylinder 61 has a diameter of
about 15
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cm and the apertures 63 (of which there are three rows, spaced at 30 mm) have
a
diameter of 6 mm and are spaced at 30 mm within the rows.
The arrangement shown in Fig. 8 functions as follows. Operation of the
blower 60 is timed so that a discrete jet of air is directed at the overlap
between
5 each pair of successive sheets 64, 65 (i.e. when a sheet 64 has begun to
move onto
the conveyor 56 and the sheet 65 has begun to move off the conveyor S 1 ),
causing
the trailing end of the sheet 64 and the leading end of the sheet 65 to lift
up as
shown in dotted lines in Fig. 8. The trailing end of the sheet 64 will then
come
under the influence of the vacuum within the cylinder 61, acting through the
1o apertures 63, and will be pulled towards the cylinder where it will be held
while the
leading end of the sheet 65 falls back onto the paper path. The sheet 65 now
continues to move forwards onto the conveyor 56 which, at the same time, pulls
the
trailing end of the sheet 64 away from the cylinder 61 and back onto the paper
path
although now located above, rather than below, the leading end of the sheet
65.
15 It will be appreciated that, because the vacuum within the cylinder 61 does
not influence the sheets while they are lying flat on the conveyors 51, 56,
the
vacuum can be applied constantly. The vacuum should be applied at a level
sufficient to ensure that it can attract and hold the trailing end of a sheet
(such as
sheet 64 in Fig. 9) but not so great that the sheet cannot be removed by the
2o forwards movement of the conveyor 56. If desired, a plate 68 can be located
above
the cylinder 61 and the blower 60, for example as shown in Fig. 8, to direct
the jet
of air from the blower towards the cylinder.
Any other suitable arrangement could be used for changing the direction of
overlap of the sheets between the conveyors 51 and 56 including, for example,
an
air knife alone or an equivalent mechanical arrangement, for example similar
to that
described in GB-A-2 166 717 but with a loss of benefits associated with the
arrangement of Fig. 8.
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16
Returning to Figure i, the pseudo-web of sheets now moves out of the sheet
overlapping station 4 and into the dryer 5 in which moisture is removed from
the
primer and LAB coatings. The dryer 5 is preferably a radio-frequency dryer,
for
example a particularly adapted version of the Model No. SP 890 GF"C"-AG
manufactured by Proctor Strayfield Ltd. of Berkshire, England. The dryer 5 is
provided with a control unit (not shown) which adjusts the power of the dryer
in
accordance with the line speed of the apparatus. That control unit may, for
example,
be a Siemens PLC 55 95U interconnected with the central electronic control
unit of
the whole apparatus. The overlapped sheets move through the dryer 5
continuously
on the endless belt 56 and are dried at a rate which attenuates the tendency
of the
sheets to curl but which ensures that they emerge substantially dry. The use
of a
radio-frequency dryer is not essential and the overlapped sheets could,
instead, be
dried using infra-red heating or hot air. Alternatively, the endless belt 56
could be
heated to dry the sheets. However, radio-frequency drying is preferred for its
simplicity and lower energy consumption.
Although it is preferable to change the direction of sheet overlap before the
sheets enter the dryer 5 (as described above) because it is then less likely
that the
sheets will lift away from the belt 56, it is possible to defer that operation
until the
sheets have been dried. In that case, the apparatus shown in Fig. 8 would be
located
2o at the outlet of the dryer 5.
Downstream of the dryer 5, the overlapped sheets move through the guiding
section 6 in which they are side registered and aligned with each other in
preparation for advancement to the adhesive coater 7. In the adhesive coater
7, the
overlapped sheets pass through a transfer station 70 (see also Figure l0a)
where
they contact an endless transfer belt 71 to which an adhesive coating has
previously
been applied in the form of spots or a plurality of stripes extending
longitudinally of
the belt.
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17
The transfer belt 71 is trained around rollers 72, at least one of which is
driven so that the belt advances in the direction of the arrow 73. As the
transfer belt
71 moves (at the same rate of advance as the overlapped sheets), it passes a
coating
mechanism 74, a dryer 75 and the transfer station 70, each of which will be
s described in greater detail below. Preferably, the adhesive is dried at
least partially
(i.e. the moisture content is reduced to a desired level), in the dryer 75,
before being
transferred to the overlapped sheets at the transfer station 70. For instance,
the
moisture content of the water-based adhesive may be approximately 50% - 80%
prior to drying and 0% - 50% after drying. Preferably, substantially all of
the
to moisture is removed during the drying process.
The coating mechanism 74 applies repositionable adhesive to the transfer
surface 76 of the transfer belt 71. The coating mechanism may, for example,
use a
rotating grawre roller 77 to apply the adhesive. The grawre roller 77 (Figure
10a,
i Ob) contacts, and extends across the width of, the transfer belt 71 and has
at least a
15 first (770) and a second (771 ) grawres formed in its surface. The first
770 and
second 771 grawres extend around only part of the circumference of the grawre
roller 77 and they are radially and axially offset relative to each other such
that at
desired locations repositionable adhesive is applied on the transfer belt. The
grawres 770, 771 are preferably in the form of a band in which the
repositionable
2o adhesive is applied in the form of stripes of adhesive or the grawre can be
in the
form of a circle or ellipse so that a spot of repositionable adhesive is
applied.
Preferably, the transfer belt 71 also includes a synchronisation means 711
such that the coating of the repositionable adhesive on the transfer belt 71
can be
started at a predefined position (see figure lOc). For example, transfer belt
71 may
25 have a marking for example in the form of a vertical stripe extending
across the
transfer belt 71 or a marking area, for example a square along one edge. Such
marking can then be used to position the grawre roller 77 at this part of the
transfer
belt 71 such that the grawre roller 77 is contacted with the transfer belt 71
between
the first 770 and second 771 grawres when coating to the transfer belt is
started.
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18
To aid in correctly positioning the gravure rolled 77 relative to the
synchronisation
means 711 on the transfer belt, the gravure roller 77 may also include a
synchronisation means (not shown) for example in the form of a mark.
Positioning
the gravure roller 77 at the start of coating then results in a coating on the
transfer
belt 71 as illustrated in Figure lOc.
As shown in Figure l Oc, when the gravure roller 77 is contacted (not
shown) between the first 770 and second 771 gravure bands at the
synchronisation
means 711 on the transfer belt 71 and then makes a half turn while maintaining
contact between the gravure roller 77 and the transfer belt 71, adhesive is
applied
to from first gravure bands 770 to the transfer belt 71. Turning the grawre
roller 77
further while in contact with the transfer belt 71 to complete a full turn,
will apply
repositionable adhesive from second gravure bands 771 to the transfer belt.
Because first 770 and second 771 gravure bands only extend around part of the
circumference of the gravure roller and are radially and axially offset
relative to
each other, the adhesive coatings from first 770 and second 771 gravure bands
resulting on the transfer belt 71 are transversally offset and are
discontinuous.
Preferably, the length of the discontinuity in the adhesive stripes
corresponds to at
least the length of the sheets in their direction of conveyance. Accordingly,
if the
start of a sheet is synchronised with the start of an adhesive stripe,
adhesive stripes
2o resulting from first 770 and second 771 gravures will be applied
alternatingly to the
sheets.
Synchronisation of the start of a sheet with the start of adhesive stripes may
be accomplished by detecting the position of the transfer belt 71 and the
start of a
sheet. This can for example be done by a contrast cell detecting the
synchronisation
means 711 on the transfer belt 71 and by having a black stripe at the start of
each
sheet which might also be detected by a contrast cell. The detection of the
position
of the transfer belt 71 and start of a sheet may then be used to adjust the
speed of
the transfer belt 71 and/or speed of conveyance of the sheets to obtain proper
synchronisation.
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The adhesive which is to be applied to the transfer belt 71 by the gravure
roller 77 is supplied by a pump 78 from a tank 79 to a trough 80 at the
coating
mechanism 74. A metering roller 81 dips into the adhesive in the trough and,
as it
rotates, the metering roller picks up adhesive which it then transfers to the
reverse
rotating gravure roller 77 and in particular, to the gravures. One or more
doctor
blades (such as at 82) engage the gravure roller 77 to remove any excess
adhesive
and ensure that all the adhesive on the gravure roller is contained only
within the
cells of the gravures, thereby ensuring that the adhesive will be transferred
in stripes
or spots to the transfer belt 71.
to The transfer belt 71 with the adhesive stripes then passes through the
dryer
75 (Figure 1) in which the adhesive stripes are dried at least partially (i.e.
ranging
from 0% - 50%). This is done to improve the adherence of the adhesive to the
sheets. The dryer 75 is preferably a radio-frequency dryer, for example a
particularly adapted version of the Model No. SPW 12-73 manufactured by
Proctor
Strayfield Ltd. of Berkshire, England operated, typically, at about 27 MHz, or
alternatively, at about 30 MHz. The dryer is about 2.5 m long in the direction
of
travel of the belt and has an exhaust (not shown) through which the interior
of the
dryer is vented with the aid of a fan 84. The dryer is provided with a control
unit
(not shown) which adjusts the power of the dryer in accordance with the line
speed
of the coating apparatus. That control unit may, for example, be a Siemens PLC
55-
95U interconnected with the central electronic control unit of the whole
apparatus.
A radio-frequency dryer requires that the material of the transfer belt 71 be
non-reactive (i.e. transparent or otherwise not affected by the radio
frequency
radiation to a degree that adversely affects the operation of the method and
apparatus of the present invention) to radio frequency radiation. This
arrangement
offers the advantage that the adhesive is dried without the transfer belt
being
significantly heated, thereby eliminating any heat transfer from the belt to
the
coating mechanism 74 and then to the adhesive which could cause the adhesive
to
coagulate before it has been applied to the transfer belt 71. A radio-
frequency dryer
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also offers the advantages of comparative simplicity and lower energy
consumption.
Further, the transfer belt 71 requires no prolonged pre-heating to a
particular
operating temperature and the adhesive is released readily from the belt for
transfer
to the sheets at the coating station.
Preferably, the transfer belt 71 comprises a fibre glass fabric base layer,
approximately 0.1 mm thick, coated on each side with a layer of silicone
rubber
approximately 0.15 mm thick.
However, it will be understood that other forms of transfer belt can be used
that are incompatible with a radio frequency dryer (i.e. are not transparent
or inert
to radio frequency radiation) although with a loss of benefits associated with
a belt
that is non-reactive. For example, the transfer belt may comprise a metal
substrate
with a coating of silicone rubber on each side. Other types of dryers that may
be
employed include, for example, an infra-red heater, or a hot air dryer.
However, if
the dryer causes the transfer belt 71 (and then the coating mechanism 74) to
become
15 heated it may be necessary to cool the adhesive and the transfer belt to
reduce the
risk of the adhesive coagulating.
At the transfer station 70, the adhesive-coated transfer belt 71 passes
through a transfer nip 85 comprising a transfer roller 90 and an idler counter
pressure roller 91. The overlapped sheets 86 from the guiding section 6 of the
2o apparatus are also directed through the transfer nip 85, as already
mentioned, and
are supported by the counter-pressure roller 91 against the transfer roller 90
and
consequently against the transfer belt 71 so that adhesive is transferred from
the belt
to the sheets.
The counter-pressure roller 91 at the transfer nip 85 is provided with a
plurality of spaced circumferential grooves 92 (Fig. 11 ), and a plurality of
fingers 93
are provided immediately downstream of the roller 90 to engage in those
grooves.
The fingers 93 ensure that the overlapped sheets 86 continue to travel with
transfer
belt 71 after the sheets have left the transfer nip 85 and do not wrap around
the
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21
counter-pressure roller 91. The sheets 86 are removed from the transfer belt
71,
downstream of the fingers 93, by a detachment conveyor in the form of a vacuum
belt 95 which, as described below, also serves to transport the sheets to the
paper
path exit 96 of the apparatus (Fig. l0a). The removal of the sheets from the
transfer
belt 71 is facilitated by the direction in which the sheets overlap (i.e. by
the fact that
the leading edge of each sheet is overlapped by the trailing edge of the
preceding
sheet).
An additional roller 97 is provided to engage the inside of the transfer belt
71 downstream of the beginning of the vacuum belt 95 and is positioned to
ensure
to that the transfer belt is initially (i.e. prior to the roller 97) inclined
at a small angle
(of about 1 to 3 degrees) to the vacuum belt and then (i.e. after the roller
97) at a
much greater angle (of about 3 to 6 degrees). Typically, the angle at which
the
transfer belt 71 is inclined to the vacuum belt 95 is initially about two or
three
degrees for a distance of about SO mm while the vacuum belt functions to
remove
sheets from the transfer belt, and then increases to about five degrees to
increase the
separation between the transfer belt and the sheets. The roller 97 is movable,
as
indicated by the arrow 97a, to enable the angles between the transfer belt 71
and the
vacuum belt 95 to be adjusted.
The vacuum belt 95 is connected to a source of low pressure in vacuum box
99 and is apertured as indicated at 98 in Fig. 13, so that reduced pressure is
applied
through the belt to sheets on the surface of the belt. The reduced pressure
applied
through the vacuum belt 95 is comparatively strong over the initial part of
the run
of the belt, where the relative inclination of the transfer belt 71 is
smallest, and then
decreases when the relative inclination of the transfer belt increases. To
that end, a
compartment 101 is formed within the vacuum box 99 and is connected, through
port 102, to a source of comparatively strongly-reduced pressure while the
remainder of the vacuum box is connected, through ports 103, to a source of
more
moderately-reduced pressure. In addition, the reduced pressure in compartment
101
is applied to the belt 95 through comparatively large openings 104 in the
surface of
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22
the vacuum box 99 while the reduced pressure in the remainder of the vacuum
box
is applied through more restricted openings 105. The reduced pressure applied
through the openings 104 is su~ciently high to detach the sheets from the
transfer
belt 71 without damaging them and it then decreases over the remainder of the
vacuum box 99 to a level sufficient to maintain the detached sheets on the
vacuum
belt, again without damaging them (in this case, for example, by being marked
by
the apertures 98) so that they can be transported to the paper path outlet 96.
For
example, a reduced pressure in the range of from 350 to S50 mm H20 (typically
400 mm H20) may be applied over the initial part of the run of the belt 75,
with a
l0 reduced pressure in the range of from 150 to 200 mm Hz0 being applied over
the
remainder of the run. In each case, the degree of reduced pressure that can be
applied is limited by the need to avoid damage to the sheets and will vary
depending
on the nature of the sheet material. Once detached from the vacuum belt 95,
the
sheets may be stacked and trimmed to form pads of repositionable notes, for
example those available under the trademark "Post-it" available from the
Minnesota Mining and Manufacturing Company ("3M") of St. Paul, Minnesota.
The vacuum belt 95 need not be a single belt that extends over the width of
the
vacuum box 99 but could comprise a plurality of narrower belts arranged side-
by-
side.
2o Figures 14a to 14c schematically illustrate the trimming process. Thus, a
stack of sheets 200 from a coating apparatus shown in figure 1 will typically
comprise backing sheets 201, first sheets 203 and second sheets 204 different
from
the first sheets 203 with repositional adhesive 202 coated to the back of
sheets 203
and 204. As shown in figure 14b, the stack 200 is then cut by means of knifes
205
along lines 206 such that individual stacks result wherein the repositionable
adhesive alternates between two opposite edges of the stack. A thus resulting
stack
may then be further trimmed along a direction perpendicular thereto to obtain
a
desired size and shape of the stack (figure 14c).
f
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23
Although the above description refers to the sheets as being paper, they
could (as already mentioned) be formed of other materials, for example
polymeric
films as previously described. When the sheets are paper, they are preferably
fed
through the apparatus with the "machine direction" of the paper sheets aligned
with
s the machine process direction; in that way, the tendency of the sheets to
curl or
wrinkle can be further attenuated.
Papers of different weights and textures can be used if desired. For example,
the described apparatus is readily adaptable to handle for example, sheets of
A4 size
or sheets of A2 size. Likewise, the apparatus is able to handle sheets of a
1o comparatively high weight (e.g. 250 gsm) and also sheets of a lower weight
(e.g. 80
gsm).
If the sheets supplied to the dual coater 3 are pre-printed, the above-
described method results in the LAB coating material being applied over the
printed
matter on the sheets. The LAB coating then serves to protect the printed
matter,
15 especially against removal by the adhesive on an adjacent sheet when the
sheets are
subsequently stacked and cut to form pads of repositionable notes. The
protection
offered by the LAB coating enables the use of stronger adhesives on printed
notes
to be considered. Of course, printed matter may also be applied to the sheets
after
the dual coater 3, whether or not pre-printed, using any conventional printing
20 operatoon.
Although the sheet removal arrangement of Fig. 1 Oa has been described
above as forming part of an adhesive coater, it will be appreciated that it
could be
used in other circumstances when it is required to apply a coating material to
sheets
using an endless-transfer.
25 It will also be appreciated that various modifications may be made to the
overall configuration of the apparatus shown in Fig. 1 without affecting the
operation of the adhesive coater 7 (and, in particular, the sheet removal
arrangement). For example, the overlapping station 4 could be omitted and the
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24
sheets could be fed directly from the dual coater 3 to the dryer. In that
case, the
sheets can be overlapped just before they are fed into the adhesive coater 7.
Such an
arrangement is described in our GB application Serial no. 9603281.8 filed
16.2.96
and entitled "Method and apparatus for coating sheets on both sides with water-
s based material", which also describes how sheets from the dryer may be
collected
and stacked and subsequently re-fed, as a pseudo-web of overlapped sheets to
the
adhesive coater.
Furthermore, although desirable, it is not essential for sheets to be fed into
the dual coater 3 in a non-overlapped condition. They could, for example, be
fed
to into and through the dual coater as a pseudo-web of overlapped sheets as
described
in the above identified WO 94/19419. In that case, the sheet overlapping
station 4
of Fig. 1 (including the apparatus of Fig. 8 for changing the direction of
overlap) is
not required.
