Note: Descriptions are shown in the official language in which they were submitted.
DEVI~E FOR CQATING FREE-FLOWING MEDIA
ONTO A MOVING WEB
The invention relates to apparatus for0 applying a free-flowing medium onto a web of material
paxticularly to apparatus for applying a
liquid coating onto a web moving through a roll gap
defined by two rotatably mounted rolls disposed with
their axes parallel to one another and including an5 application unit cooperating which each roll for
applying a free-flowing media onto a lateral surface of
the roll.
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Reference is made herein to 5erman ~ ~ -
Offenlegungsschrift 34 17 487 ~corresponding to G~ 2 -~
15~ 370 published November 13, 1985) which discloses
devices for applying free-flowing media onto a web of
paper. Devices of this type can be disposed within or5 outside a paper manufacturing machine. The liquid to
be applied to a paper web being conveyed through such a
device can be, for example, a sizing suspension with
which the paper web i9 impregnated; that is, the sizing
suspen3ion substantially penetrates the paper web. -~
However, the liquid can also be a coating composition
~uch as various pigment suspensions which form a
covering layer on a paper web. The known method~ for
applying and distributing a coating composition on a
paper web often result in the formation of a covering
35 layer which is not uniformly closed. The-optical -~
appearance of such a covering layer may be described as
the "orange-peel effect. n
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It is an object of the invention to obviate or mitigate
one or more of the problems described above. In
S particular, it is an object of the invention to provide
an apparatus for coating free-flowing media onto a
paper web in such a way that the problem of an
undesirable orange peel effect of the liquid film on
the paper web is substantially avoided. Thus, coated
}0 papers with a uniform surface can be produced.
According to the invention, an apparatus for
applying a liquid coating onto a web of material
includes two rotatably mounted rolls disposed with
their axes parallel to one another and defining a roll
gap through which a web may be conveyed. The apparatus
further includes an application unit cooperating with
each roll for applying a free-flowing medium onto a
lateral surface of the roll. In an open area of the
apparatus, downstream from the roll gap with respect to
the direction of travel of a web being conveyed through
the apparatus, at lea~t one spreading device is -
provided and is disposed on a side of the web. The - -
spreading device substantially contacts a width of the ~-
web. ~- -
The spreading device or devices according to
the invention cause spreading by rubbing a coating --~ -
composition, while still in the free-flowing state, as
a rssult of the relative velocity between the web on
the one hand and the working ~urface of the spreading
30 device which is in contact with the web, 90 that a -~
clo~ed and largely uniformly coated web surface is i
achieved. This may be accomplished by one or more of
following: a rotating movement of the spreading
device; an oscillating movement of the device around
its own longitudinal axis; an oscillating movement of
the device transverse to the direction of movement of a
web being conveyed through the apparatus; and/or a
longitudinal oscillating movement with respect to the
direction of movèment of the web (i.e. with respect to
the length of the web).
Preferred embodiments of the present invention
will now be described by way of example only, with reference
to the attached Figures wherein:
Fig. 1 i9 a schematic sectional view of an
apparatus according to the invention.
Fig. 2a i8 a schematic sectional view showing
a second embodiment of an apparatus according to the
invention.
Fig. 2b is a schematic sectional view showing
a third embodiment of an apparatus according to the
invention.
Fig. 3a is a schematic sectional view showing ~ ;
a fourth embodiment of an apparatu~ according to the
invention.
Fig. 3b is a schematic sectional view showing ~ -
a fifth embodiment of an apparatus according to the
invention. -
Fig. 4 is a schematic sectional view showing ~-
a sixth embodiment of an apparatus according to the
invention.
Fig. 5a is a par~ial cross-sectional view of
a spreading device according to the invention taken --
along line V-V of Fig. 4.
Fig. 5b is a partial cross-sectional view of
a second embodiment of a spreading device according tO
the invention.
Fig. 5c is a partial cross-sectional view of
a third embodiment of a spreading device according to
the invention.
Fig. 6a is a partial top plan view of a
spreading device according to the invention referenced
by the arrow VI in Fig. 4.
Fig. 6b is a partial top plan view of a
~econd embodiment of a spreading device according to
the invention.
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Fig. 6c i9 a partial top plan view of a third
embodiment of a spreading device according to the
invention.
Fig. 1 shows an apparatus according to the
invention which includes a two-roll press defining a
roll gap for applying a coating on one side of a moving
paper web, with a spreading device disposed downstream
the roll gap.
The two-roll press shown in Fig. 1 includes
rotatably mounted rolls 1 and 2, the axes of which are
disposed parallel to one another. Together, the rolls
1 and 2 define a roll gap 3 for passage of a paper web
4 therethrough. The rolls 1 and 2 are driven in
opposite directions. ~pplication unit~ 5 and 6 are
di3posed at a outer or lateral side of the rolls 1 and
2, respectively (i.e. each application unit is located
at a lateral side of the roll where the surface of the
roll moves from the bottom to the top of the roll when
the roll is rotating). Each application unit applies a -
free-flowing medium onto the lateral surface of the
re~pective roll and the free-flowing medium is
subsequently depoqited onto the paper web 4. The
application device 5 applies a coating onto the roll 1
and the application device 6 applies sizing onto the
roll 2. The paper web 4 is guided from the top o~ the
apparatus (and the rolls 1 and 2) toward the bottom
thereof through the roll gap 3. In areas 7 and 8 which
the roll gap 3 forms with the paper web 4, a film of
the free-flowing medium is applied onto the paper web 4
along the surface of the rolls 1 and/or 2. As a result
of guiding the paper web 4 from top to bottom through
the roll gap 3, the coating composition is applied onto
the paper web 4 in a desired thickness.
Subsequent to the application of the free-
flowing media onto the paper web 4, in a relatively
unobstructed or open area of the apparatu~ immediately
downstream of the roll gap (with respect to the
direction of conveyance of a paper web) generally
~~ designated 9, a spreading device 10 is mounted on the
apparatus so as to be disposed on a side of the paper
web 4 upon which the coating composition was applied by
the roll 1. The spreading device 10 i9 a rotationally
symmetrical body (i.e. the spreading device 10 is
symmetrical about an axis thereof) and more
particularly may be a spreader roll 10. The spreader
roll 10 is pres~ed against the paper web 4 coated with
the coating composition, using a certain pressure. The
10 spreader roll 10 is rotatably mounted and is driven. -~
The spreader roll 10 rotates about its axis in the
direction of movement of the paper web 4 or in the
opposite direction thereof and, with the aid of another
drive (not shown) the spreader roll 10 performs ~;~
oscillating movements transverse to the direction of
movement of the paper web 4.
The paper web 4 is then introduced to further
working devices via a deflecting device, which is shown -~
here as a deflecting roll 11. ~-
Overall, there are various spreading device -
driving possibilities. The main differentiating -~
characteristics between these driving possibilities are
the direction of rotation of the spreader roll 10 with
respect to the direction of movement of the paper web 4
and the relative velocity between the spreader roll
circumference and the paper web 4.
If the ~preader roll 10 rotates in the
direction of movement of the web 4 and the relative
velocity between the spreader roll circumference and
the paper web 4 i8 equal to zero, then a spreading
effect can be accomplished only under the following
conditions:
(1~ when the spreader roll 10 performs
oscillating movements oriented longitudinally with
respect to the length of the paper web 4;
(2) when the spreader roll 10 performs
oscillating movements transverse to the length of the
paper web 4; and
(3) when the spreader roll 10 performs a
combination of transverse and longitudinal movement
with respect to the paper web 4.
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If the rotational velocity of the sp.eader
roll 10 i9 not equal to the velocity of conveyance of
the paper web 4, that i9, the relative velocity between ;
the spreader roll periphery and the paper web is not
equal to zero, a corresponding spreading effect is
achieved mainly by the rotational movement of the
spreader roll 10. The spreading effect is enhanced by
additional oscillation of the spreader roll 10. A
superimposition of spreader roll rotation and
oscillating movement with respect to the paper web 4
makes it possible to provide spreading of a coating in
the direction of movement of the paper web 4 and
transversely to this direction of movement. If the
spreader roll 10 only rotates, spreading-of a coating
is provided in the direction of movement of the paper
web 4.
In summary, the following possibilities arise
when a spreader roll 10 is rotated in the direction of
movement of the paper web 4 and there is a relative
velocity between the spreader roll periphery and the
paper web:
~ 1) the spreader roll 10 performs only a
pure rotational movement;
(2) the spreader roll lO also perform~
oscillating movements transverse to the length of the
paper web 4;
(3) the spreader roll 10 additionally
performs a longitudinaL oscillating movement with
respect to the movement of the paper web 4 (i.e.
corresponding to the length of the paper web);
(4) the ~preader roll 10 performs a
combination of longitudinal and transverse movement
with respect to the direction of movement of the paper
web 4.
If the spreader roll 10 rotates in a
direction opposite to the direction of movement of the -`
paper web 4, a spreading effect can be achieved by the ~;~
rotation of the spreader roll 10 alone, longitudinally
with respect to the length of the paper web 4 and its
40 direction of movement. Additional oscillation of the -
spreader roll 10 transverse to the directior. of
movement of the paper web 4 further promotes the
spreading effect. Oscillating movements of the
spreader roll 10 which are longitudinal with respect to
the direction of movement of the paper web 4 and a
combination of longitudinal and transverse movement of
the roll 10 with respect to the paper web 4 are
possible. ~;
If the spreader roll 10 is rotatably mounted
and is not driven, the roll 10 can be entrained by the
10 paper web 4 due to the paper web velocity. It may ~ ~ ~
therefore be necessary to equip the apparatus with a ~ -
further device which brakes the spreader roll 10 in
order to achieve a spreading effect on the paper web 4. -~
Additionally, it is also expedient to provide the
15 spreader roll 10 with a drive which allows the roll 10 ~ -
to perform oscillating movements transversely to the
direction of movement of the paper web 4 in order to
provide good spreading effect over the entire plane of
the surface of the paper web 4.
The surface of the spreader roll 10 can be
smooth or contoured. Another possibility is to use a
spreader roll having a wire wound therearound. Smooth
spreader rolls are preferably provided with a finish,
such as a chromium (Cr) coating material (or several
coating materials) which repels the liquid coating
being applied to the paper web. The spreader roll
finish could be made from any of a variety of materials
which are resistant to wear, for example, Teflon~ (Du
Pont), rubber, polyurethane or ceramic. The diameter
of the spreader roll 10 is preferably about 100 to
about 400 mm.
Fig. 2a shows an apparatus according to the ~ ;
invention which is analogous to the apparatus shown in
Fig. 1 and includes a two-roll press having rolls la
35 and 2a defining a roll gap for applying coating onto ;~
both sides of a paper web 4a, with rods on both sides
of the paper web utilized as spreading devices and
further includes a downstream smooth deflecting roll.
The axes of the rolls la and 2a are arranged parallel
to one another, are rotatably mounted and define a roll
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gap 3a for passage of the paper web 4a. The two rolls -~
la and 2a are driven in opposite directions.
Application units 5a and 6a for applying a
free-flowing medium onto the rolls are arranged on the
sides of the rolls la and 2a, respectively, near a part
of each roll circumference which travels from the ~ ~
bottom toward the top of the respective roll. The ~ -
paper web 4a is guided from the top to the bottom of
the rolls la and 2a through the roll gap 3a. In
regions 7a and 8a, which form the roll gap 3a with the
paper web 4a, a film of free-flowing medium i9 applied
onto the paper web 4a.
The elements la - 9a illustrated in Fig. 2a
are substantially identical in structure and function
to the elements 1 - 9, respectively, described herein
with respect to Fig. 1. However, both of the
application units 5a and 6a apply a coating onto a
surface of the rolls la and 2a, respectively. As a
result of guiding the paper web 4a from top to bottom
through the roll gap 3a, a coating composition i~
applied onto both sides of the paper web 4a in a
desired thickne g.
In a downstream section 9a of the apparatus
shown in Fig. 2a, spreading devices illustrated as
spreading rods lOa are disposed on both sides of the
paper web 4a to spread the coating composition thereon.
The spreading rods lOa have a symmetry similar to the
devices 10 described with respect to Fig. 1. The
surface of each rod lOa can be smooth and each rod
preferably has a diameter of between about 10 mm and
about 30 mm. Each rod lOa may have a wire wrapped
therearound to provide a contoured rod surface.
The rods; lOa do not rotate. In order to
achieve good spreading effect, additional drive ~-
35 possibiIities are provided (not shown in Fig. 2a) in ~ -
order to achieve oscillating movements around the rod
axis, as well as longitudinally or transversely with ~ -
respect to the direction of movement of the paper web
4a. A combination of longitudinal and transverse
movement of each rod lOa relative to the paper web 4a
may also be provided.
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'~ According to the invention it is also
possible to replace the rods lOa located on either side
of the paper web 4a with the driven spreader rolls 10
described with respect to Fig. 1. -~
Preferably, the spreading rods lOa are ~ -
arranged on both sides of the paper web in such a way
that the rods lOa are evenly displaced with respect to
one another in the direction of movement of the paper
web 4a. In particular, the axis of a fir3t spreading
device lOa may be di~posed in a first plane
perpendicular to a tangent of the web 4a conveyed about
the first spreading device lOa and the axis of the
second spreading device lOa is disposed in a ~econd
plane perpendicular to a tangent of the web 4a conveyed
about the second spreading device lOa, with the first
and second planes being parallel.
Downstream the rods lOa, the paper web 4a is
guided further by contact with a deflection roll lla.
To avoid contact of a still wet or moist coated paper
web 4a with the deflection roll lla a drying apparatus
(not shown) may be provided between the deflection roll
lla and the spreading device lOa.
An alternative-spreading device orientation
according to the~invention is shown in Fig. 2b. The
elements lb - 9b, and llb, of the apparatus shown in
Fig. 2b are identical in structure, function and
orientation to elements la - 9a, and lla, respectively,
described herein with re~pect to Fig. 2a. Spreading ~-
devices lOb shown in Fig. 2b are identical in function
and structure to the spreading devices lOa described
herein with respect to Fig. 2a. However, the axes of
the spreading devices lOb shown in Fig. 2b are disposed
in a common plane perpendicular to the direction of
movement of the web 4b conveyed between the spreading
35 devices lOb. ~-
Fig. 3a shows a modified two-roll press -
according to the invention similar to what i described
herein with respect to Fig. 2a having first and second
rolls defining a roll gap for applying coating onto
both sides of a paper web with spreading devices
arranged on both sides of the paper web and including
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an air-cushioned deflection device and a subsequent
infrared drying device.
Elements lc - lOc of the apparatus shown in
Fig. 3a are identical in structure, function and
orientation to elements la - lOa, respectively,
described herein with respect to Fig. 2a. The
spreading device~ or rods lOc can be designed as rods
described with respect to Figs. 2a and 2b or as driven
spreader rolls as described with respect to Fig. 1.
having the drive possibilities already described with
respect thereto.
The apparatus shown in Fig. 3a is equipped
with an air-cushion deflecting device llc so that the
paper web 4c i~ deflected without contact to a
deflection roll or any other element of the device.
The advantage of this is that paper webs which still
contain moist coating can be deflected with a
deflecting device without direct contact with the side
of the paper web that still contains moist coating and
thus prior intermediate drying is not required. Then
the paper web 4c i~ dried u~ing an infrared device 12c.
Another possibility of subsequent drying is
shown in Fig. 3b. An apparatus according to the
invention shown in Fig. 3b includes a two-roll press --
defining a roll gap for applying coating onto both
sides of a paper web with spreading devices disposed on
both sides of the paper web, an air-cushioned
deflection device and a sub~equent infrared and
suspension drying device.
The elements ld - 12d of the apparatus shown
in Fig. 3b are identical in structure, function and
orientation to the elements lc - 12c, respectively, -
described herein with respect to Fig. 3a.
Additionally, the apparatus shown in Fig. 3b includes a
suspension dryer 13 downstream of the infrared drying
device 12d.
The two-roll press shown in Fig. 4
corresponds in construction and function essentially to
the embodiment shown in Fig. 2 and includes first and
second roll~ defining a roll gap for applying coating
onto both sides of a paper web with rods arranged on
both sides of the paper web, spreading devices each
having a convex working surface for contacting a coated
paper web and a downstream smooth deflecting roll.
The elements le - 9e of the apparatus shown
in Fig. 4 are identical in structuxe, function and
orientation to the elements la - 9a, respectively,
described herein with respect to Fig. 2a. Rods lOe
which are u3ed as spreading devices have convex working
surfaces lOf as viewed from the sides thereof. The
rods lOe are also known as ~hydrobar shoes. n
The radius of curvature of the working
surface lOf of a rod lOe i9 preferably chosen to be
larger than the radius of the rod lOe so that the
effective working sur~ace of the spreading device is
enlarged.
Hydrobar shoes having a working surface lOf
can be stationary or can be equipped with an additional
drive (not shown) to produce oscillating movements
transverse to the direction of movement of the paper
web 4e.
The surface lOf of a hydrobar shoe can be --
smooth or contoured as shown in Figs. 5a - 5c and 6a -
6c. Preferably, the contoured profile does not extend
over the entire working surface lOf of the hydrobar -
shoe, but only throughout a first ascending curved
portion in the direction of movement of the paper web
4e. The subsequent de~cending part of the shoe is
preferably smooth. AS a result, an initially uneven
coating compo~ition covering the paper web will first
be roughened and then uniformly spread by such a
working surface lOf. Then the paper web 4e is
introduced, for example, to a subsequent drying device
or devices via a deflecting device lle.
Figs. 5a, 5b and 5c show possibilitie~ for
35 the design of the hydrobar shoe surface contour. The ~ -
profile of the working surface shown in Fig. 5a i9
wavy. Figs. 5b and 5c show the possibility of using a
tooth profile and a rack profile, respectively. ~-
Figs. 6a, 6b and 6c show various po33ible
profile contours from a top view of the surface lOf of
the hydrobar shoe lCe. Parallel profile contours,
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-~ profile contours with a slope and profile contours with
alternating slopes can be provided.
The selection of the spreading device or
devices according to the invention to be used, their
number (e.g. the possibilities of connecting spreading
devices one after another on the 3ame side of the paper
web), and the possibilities of operation are chosen for
a each specific application and according to the effect
to be achieved.
The foregoing detailed description is given
for clearness of understanding only, an no unnecessary
limitations should be understood therefrom, as
modifications within the scope of the invention will be
apparent to those skilled in the art.
