Field of the Invention
[0001] The invention refers to a peel off device for unwinding a web of material from a
stock or forming roll, especially for high speed unwinding a web of a thin polymer
film or the like.
Background of the Invention
[0002] The problem underlying the present invention arises in the field of continuous production
of e.g. baby or feminine hygiene care products like diapers or sanitary napkins, where
thin polymer films such as a backing sheet or a topsheet have to be peeled off from
a stock roll at a high speed. As production practice shows, such as a polymer web
may tend to adhere to the stock roll for several reasons, such as interlocking phenomena
due to microstructures in the web (e.g. apertures) or adhesion due to the surface
properties of the web material.
[0003] Due to prior use it is known to provide for an idler at the periphery of the stock
roll to support the unwind process of the web from the roll. The web is guided around
the circumference of the idler along an angle of contact of about 90° to 120°, then
running to the so-called unwind dancers which are a balancing means for the web as
concerns instabilities or irregularities in the following in-line production process
of any product. The problem is that due to the interlocking phenomena and/or adhesion
the web nevertheless tends to stick to the roll leading to a phenomenon, already mentioned
above, called "blocking" which occurs whenever a web presents high tendency to stick
to itself during unwinding. This can be caused by surface forces, electrostatic forces
or mechanical interlocking of apertures, adhesive coating etc.
[0004] Said blocking is a severe problem for downstream processes as it introduces sudden
changes of tension, cross-direction tracking issues and wrinkle formation within the
web. In most critical cases a web breakage can occur leading to a complete production
line stop.
[0005] The problems in unwinding a rolled web of material are already addressed in
US 3 368 771 A which discloses a method and an apparatus for unwinding a rolled web of material.
The apparatus comprises two rollers which are in contact with each other and supported
on a rocker arm by means of which a first idler is pivoted onto the stock roll. The
web is led around the flexible surface of the first idler, runs through a gap between
the first and a second idler and then is led away via the second idler. The latter
has a surface with venting passages at the periphery which together with a surface
layer of elastic material on the first idler helps to enable the air between the web
of material and the surface of the roller to escape completely to the side. The overall
object of the prior art apparatus on the one hand is to compensate for the local distortions
that are inherent in a particular web of material and which extend in the longitudinal
direction and are due, for example, to variations in thickness. On the other hand
the air introduced between the web and the rollers is removed owing to a slight contact
pressure between the first and second roller which displaces the film of air which
is drawn between the web of material and the second roller. Important is the fact
that the first idler is in a "out of pressure contact", this means that the stock
roll and the first idler have a space between them or may just touch so long as no
appreciable pressure is exerted by the roller on the stock roll.
[0006] It was found out that with this "pressureless" concept and the two contacting idlers
no significant improvement in avoiding web blocking in modern high speed applications
can be reached.
[0007] FR 2 573 059 A1 discloses a peel off device for unwinding a web of material from a stock roll especially
for high speed unwinding a web of a thin polymer film or the like. This peel off device
comprises a base associated to the roll and a linear guiding device mounted on the
base. On the linear guiding device several rolls are positioned offset to each other
providing for a meandering path of the web between the rolls. Two of the rolls are
driven to unwind the web material from the stock roll.
[0008] The problem of this known construction is the fact that the heavy stock roll has
to be driven indirectly via the traction forces applied by the driven rolls onto the
web. High tension forces could lead to a tearing of the web and thus to a disruption
of the peeling off process.
[0009] It is therefore an object of the invention to provide a peel off device for unwinding
a web material from a stock roll in a reliable and undisturbed manner, avoiding web
blocking to a high extent.
Summary of the Invention
[0010] This object is achieved by a peel off device and method for unwinding a web of material
from a roll as indicated in the claims. In particular a device comprising:
- a base associated to the roll,
- a linear guiding device mounted on the base,
- an idler support linearly guided on the base by the linear guiding device in a direction
towards the roll, and
- a pair of idlers for the web to be unwound wherein
= the idlers are mounted offset with respect to each other on the idler support to
provide for a meandering path of the web between the idlers,
= the axes of rotation of the idlers are parallel to the bearing axis of the roll,
and
= a first one of the idlers is pushed towards the roll so that a contact force is
maintained between the first idler and the surface of the roll while the web is peeled
off the roll
is provided.
[0011] This two-idler peeling system significantly differentiates the invention from the
known unwinding devices. Firstly, the first idler is maintained in permanent contact
with the surface of the roll while the web is peeled off which helps to maximize and
maintain constant the peel force even at high speed. Secondly, the separate, offset
second idler provides immediate restraining action to prevent the web from passing
underneath the first (peeling) idler without being peeling off. Furthermore, the span
between the two idlers and the next span of the web path can be maintained at a constant
angle.
[0012] Finally, the invention only needs a limited layout space due to the compact construction
elements involved.
[0013] Preferred embodiments are subject matter of the depending claims, the features and
advantages of which are explained in detail in the following description of a preferred
embodiment referring to the accompanying drawing.
Brief description of the drawings
[0014]
Fig. 1 shows a schematic elevation of a peel off device according to the invention
in a first embodiment.
Fig. 2 shows an enlarged partial schematic elevation of a peel off device according
to the invention in a second embodiment.
Detailed description of the drawings
[0015] The first embodiment of a peel off device depicted in Fig. 1 is associated to a stock
roll 1 of material, e.g. a thin plastic web 2. The stock roll 1 is supported on a
driven central reel 3 on which it rotates in the direction R when the web 2 is unwound
and supplied to a production line via common unwind dancers (not shown) after leaving
the second idler 10. The web may then be used in a converting line for example to
be used as topsheet or backsheet in an absorbent article.
[0016] To peel off the web 2 from the stock roll 1 in a reliable manner, a peel off device
4 is provided which comprises a base 5 associated to the stock roll 1, i.e. in the
case shown the beamlike base 5 extends behind the stock roll 1.
[0017] A linear guiding device 6, such as a guiding rail, is mounted on the base 5 in lengthwise
direction. This guiding rail 6 holds the idler support 7 via a guide block 8 which
is linearly guided along the guiding rail 6.
[0018] First and second idlers 9, 10 are mounted offset with respect to each other on the
idler support 7 to provide for a meandering path of the web 2 between the two idlers
9, 10. The idlers can freely rotate in relation to the idler support. The idlers 9,
10 respectively comprise axes of rotation A9 and A10 which are parallel to the bearing
axis A3 of the stock roll reel 3.
[0019] The first idler 9 is kept in surface contact with the circumference 11 of the stock
roll 1 by being pushed towards the stock roll 1 by the idler support 7 to generate
a contact force F between the first idler 9 and the circumference 11 of the stock
roll 1 as the web is peeled off. This force F can be generated by a pneumatic drive
system using a pressurized air cylinder 12 abutting on the base 5 and pushing the
idler support 7 along the guiding rail 6. The contact force F may be desired to be
maintained in a range between 2 N and 5 N, and may be set up to remain approximately
constant during the peeling off process. It may be desirable to use lower force for
particularly soft material, or higher forces relatively sturdy material, so that the
force may also be in the range of between 1 N and 15 N for example .
[0020] When peeling off the web 2 from the stock roll 1 the web 2 is led around the first
idler 9 by a peel off angle of contact which is about 90° because the first idler
is maintained in contact with the surface of the roll (the peel off angle is defined
as the angle between the tangent of the roll at the point of peeling off and the line
tangent with the surface of the first idler guiding the web and passing through the
center of the roll). It is believed that a peel off angle of about 90° maximizes the
peeling force and reduces the risk of breakup of the web.
[0021] Then the web 2 is led to the second idler 10 which is mounted with a fixed offset
with respect the first idler 9. The center to center distance of the two idlers can
be a multiple of the (first) idler diameter, e.g. three to six times the diameter.
The first and second idlers may advantageously be formed by identical pieces to simplify
installation and maintenance but this is not necessary. The angle C between the tangent
of the surface 11 of the roll 1 at the point of contact with the idler 9 and the line
passing through the centers of the first and second idlers is of more than 270° to
provide a meandering path for the web between the idlers. Advantageously, the angle
C may be of from 300° to 360°, more advantageously between 320° to 350°, or more precisely
from 330° to 350°. The two idlers can be advantageously mounted in a fixed position
relative to each other on the idler support so that their distance and angle are advantageously
kept constant during the peel off process.
[0022] A magnetic position tracking system 13 may be incorporated into the guiding rail
6 for detecting the position of the guide block 8 along the guiding roll 6. This serves
to record the position of the guide block 8 and thus of the first idler 9, i.e. this
gives a signal for the current size of the stock roll 1. A magnetic position tracking
system may be advantageous to provide a robust system against natural occurring dust
formation.
[0023] The position tracking system 13 may also be used to detect an anomalous blocking
of the movement of the idler support towards the roll 1. In this case a control unit
(not shown) may give a signal to push the idler support 7 by means of a short burst
of pressurized from the air cylinder 12 in a direction towards the roll 1. In this
connection a force impulse is applicable which exceeds the continuous pushing force
F. The pressure burst may exemplarily generate a force F of 8 N in a time of 0.5 s.
[0024] The dot and dash lines in the drawing show the situation when the stock roll 1 has
decreased in diameter considerably versa the initial state depicted in full lines.
As can be seen, the idler support 7 has moved linearly along the guiding rail 6 thus
moving the idler 9 in a more or less radial direction as concerns the stock roll 1
in synchronism with the diminishing stock on the roll 1. The idler 9 is kept in contact
with the stock roll 1 during the complete unwinding process.
[0025] The second embodiment of the peel off device as it is shown in Fig. 2 again includes
a stock roll 1 of e. g. a thin plastic web 2. The support and drive of the stock roll
1 may be the same as the embodiment of Fig. 1. Also, the peel off device 4' of the
second embodiment comprises a base 5 associated to the stock roll 1, on which a linear
guiding device 6, such as a guiding rail, is mounted in lengthwise direction. This
guiding rail 6 holds the idler support 7', the guide block 8' of which - contrary
to the first embodiment - rotatably supports only the second idler 10.
[0026] The first idler 9 is rotatably supported on the pivoting end 15 of a lever arm 16
which is pivotably mounted on the idler support 7' via a pivot axis A17. The latter
is provided by a rotary pneumatic cylinder 17 which biases the lever arm 16 and thus
the idler 9 towards the surface of the stock roll 1 to generate the contact force
F. The pivot axis A17 of the lever arm 16 is parallel to the axis of rotation A9 of
the idler 9.
[0027] A further difference compared to the embodiment shown in Fig. 1 is the drive of the
roller support 7' with guide block 8'. Whereas in the first embodiment the pressurized
air cylinder 12 biases the roller support 7 and thus guide block 8 towards the roll,
thus creating the contact force F, within the second embodiment the roller support
7' with the guide block 8' are linearly driven along the guiding rail 6 by a stepper
motor 18. By means of this stepper motor 18, the roller support 7' and guide block
8' are basically positioned according to the decreasing roll diameter by tracking
the roller support 7' and guide block 8' to the right referring to Fig. 2.
[0028] Due to the support of the idler 9 on the pivotable lever arm 16, any unroundness
of the stock roll 1 can be compensated, as the lever arm 16 with the idler 9, as having
a relatively low mass, can easily track any deviations of the surface of the stock
roll 1 from the ideal round shape.
[0029] The control of the tracking of the roller support 7' and guide block 8' is provided
by position sensors, e. g. proximity sensors 19, which monitor the the position of
the lever arm 16 within its pivot range P. When the lever arm 16 increasingly pivots
in clockwise direction related to Fig. 2, this is an indication that the stock roll
1 decreases in diameter. Accordingly, the roller support 7' and guide block 8' are
moved to the right, thus pivoting the lever arm 16 in the counterclockwise direction
again until the lever arm 16 on average stands upright and centrally between the pair
of proximity sensors 19.
[0030] To limit the pivot range P of the lever arm 16, a pair of stoppers 20 is provided
on the roller support 7'.
[0031] Summing up the advantages of the embodiment of Fig. 2, both the decreasing roll diameter
and the unroundness of the roll are compensated. Further on, the idler 9 mounted on
the lever arm 16 is well controllable as to the contact force F which is approximately
8 N. The angle of the lever arm stays within a certain operating range which is smaller
than the pivot range P never touching the end positions defined by the stoppers 20.
When the lever arm tends to move outside of this operation range due to the decreasing
roll diameter, the stepper motor 18 will advance the roller support 7' and guide block
8' forward by a certain distance against the stock roll 1.
[0032] The controller of the stepper motor 18 "knows" where the roller support 7' and guide
block 8' are, as it comprises a counter for the moving steps of the motor. Thus, additional
information for the machine control is provided.
[0033] Features described in relation to one embodiment may of course be used with the apparatus
or method of another embodiment unless they are mutually excluding.
[0034] The dimensions and values disclosed herein are not to be understood as being strictly
limited to the exact numerical values recited. Instead, unless otherwise specified,
each such dimension is intended to mean both the recited value and functionally equivalent
range surrounding that value. For example, a dimension disclosed as "40 mm" is intended
to mean "about 40 mm".
1. Peel off device (4) for unwinding a web of material (2) from a stock roll (1), especially
for high speed unwinding a web of a thin polymer film or the like, comprising
- a base (5) associated to the roll (1),
- a linear guiding device (6) mounted on the base (5),
- an idler support (7) linearly guided on the base (5) in a direction towards the
roll (1), and
- a pair of idlers (9, 10) for the web (2) to be unwound, wherein
= the idlers (9, 10) are mounted offset with respect to each other on the idler support
(7) to provide for a meandering path of the web between the idlers (9, 10),
= the axes of rotation (A9, A10) of the idlers (9, 10) are parallel to the bearing
axis (A3) of the roll (1), and
= a first (9) one of the idlers (9, 10) is pushed towards the roll (1) so that a contact
force (F) is maintained between the first idler (9) and the surface (11) of the roll
while the web is peeled off the roll (1).
2. Peel off device according to claim 1, wherein the idler support (7) pushes the first
idler (9) towards the roll (1) to generate the contact force.
3. Peel off device according to claim 1 or 2, wherein the idler support (7) is powered
by a pneumatic drive system (12).
4. Peel off device according to claim 1 or 2, wherein the idler support (7) is guided
along the guiding device (6) by means of a stepper motor (18).
5. Peel off device according to any of the preceding claims, wherein the contact force
(F) between the first idler (9) and the surface of the roll (1) has a value of from
between 2 N and 5 N in a direction towards the roll (1).
6. Peel off device according to one of the preceding claims, comprising a position tracking
system (13) for the position of the idler support (7).
7. Peel off device according to one of the preceding claims, wherein the linear guiding
device is a guiding rail (6).
8. Peel off device according to one of the preceding claims, wherein the angle (C) between
the tangent of the surface (11) of the roll (1) at the point of contact with the first
idler (9) and the line passing through the centers of the first and second idlers
is of from 300° to 360°, preferably from 320° to 350°, more preferably from 330° to
350°.
9. Peel off device according to any one of the preceding claims, wherein the idler support
(7) can be pushed by a force impulse exceeding the continuous contact force (F) in
a direction towards the roll (1) in case of blocking of the normal movement of the
idler support.
10. Peel off device according to one of the preceding claims, wherein the first idler
(9) is supported on a lever arm (16), which is pivotably mounted on the idler support
(7) and biased towards the roll (1) to generate the contact force (F).
11. Peel off device according to claim 10, wherein the pivot axis (A17) of the lever arm
(16) is parallel to the axis of rotation (A9) of the idler (9).
12. Peel off device according to claims 10 or 11, comprising a rotary pneumatic cylinder
(17) mounted on the idler support (7) for biasing the lever arm (16) and first idler
(9) towards the roll (1).
13. Peel off device according to at least one of the claims 10 to 12, comprising position
sensors (19) for the pivot position of the lever arm (16).
14. A method for unwinding a web of material (2) from a stock roll (1), especially for
high speed unwinding of a web of a thin polymer film or the like, comprising the steps
of
- providing a peel off device comprising a base (5) associated to the roll (1), a
linear guiding device (6) mounted on the base (5), an idler support (7) linearly guided
on the base (5) in a direction towards the roll (1), and a pair of idlers (9, 10)
for the web (2) to be unwound, wherein the idlers (9, 10) are mounted offset with
respect to each other on the idler support (7) to provide for a meandering path of
the web between the idlers (9, 10), the axes of rotation (A9, A10) of the idlers (9,
10) being parallel to the bearing axis (A3) of the roll (1), and
- pushing the first idler (9) towards the roll (1) so that a contact force (F) is
maintained between the first idler (9) and the surface (11) of the roll while the
web (2) is peeled off the roll (1).
15. A method for the continuous converting a web of material (2) from a stock roll (1)
into an absorbent article, for example wherein the web is converted as a topsheet
or backsheet in the absorbent article, wherein the web is unwound according to the
method of the preceding claim.