Note: Descriptions are shown in the official language in which they were submitted.
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For the coating of cardboard it has been demons~rated to be
favorable to only dose the second application coat by means of
the grooves of a rotary doctor provided with peripheral
grooving, without acting on the coat with another smoothing
element. With proper ad~ustment of the consistency of the
coating substance, a sufficient spreading is accompli~hed,
making an additional smoothing unneces~a~y, which might be
as60ciated with scrape-off disadvantages.
Accordingly, in one of its aspects the present invention
provides a process for coating a running web of paper or
cardboard, compri~ing:
providing at least one rotatable roll having a chell
surface for the support of the web during ~ first coating
process;
providing at least one rotatable roll for the support of
the web during a second coating proce~s;
applying by way of a rotary doctor to the ~hell 6urface of
the rotatable roll of the first coating process a ~mall dosed
quantity of a first coating substance, the rotary doctor having
closely adjacent fine peripheral groGves or helical grooves,
the first coating substance having a 601id or pigment substance
content, the ~olid substance content being maximally 70%;
passing the web through a press ~ap formed between a
backing roll and the rvtatable roll of the first coating
process wherein the dosed quantity of the first coating
substance i~ pressed on the web as it passes through the press
gap so that at least a thin layer of the first coating
~ubstance cover~ the web, specifically with regard to the solid
or pigment content; and
applying a second coating ~ubstance to the web durin~ the
6econd coating proce~s, at least the 6econd coating subs~ance
being do~d and applied direotly on the web, wher~in the ~econd
coating substance i~ applied in direct 6uccession to the first
layer ~ne upon the other while the fir~t layer i~ ~till ~oist.
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In another of its aspects, the present invention
provides a process for coating a running web of paper or
cardboard, comprising:
providing at least one rotatable roll having a ~hell
surface for ~he support of the w~b during ~ fir~t coating
process;
providing at least one rotatzble roll for the support of
the web during a second coating process;
applyin~ by way of a doctor blade to ~he ~hell ~urface of
the rotatable roll of the first coating process a small dosed
guantity of a first coating sub~tance, the iirst coating
subs~ance haviny a solid or pi~ment ~ubs~ance contant, the
solid substance content being maximally 70%;
passing the web through a pres~ gap formed between a
backing roll and ~he rotatable roll of the first coating
procesg wherei~l thç~ dosed quantity of th& firBt ~oating
substance is pressed on the web a~ it pas~es through the press
gap so that at least a thin layer of the irs t coating
substance covers the web, specifically with regard to the solid
or pigment content; and
applying a second coatirlg 6ubstance to the web during the
second coating process, at least the second coating substance
being dosed and applied directly on the web, wherein the second
coating substance i8 applied in direct succes3ion to the first
lay~r one upon the other whilQ the first layer i8 still moist.
In yet another of its aspects, the present invention
provides a device for coating a runnin~ web, comprising~
at least one rotatable roll having a shell surface for th~
support of ~he web during a first coating proce~s;
a backing roll situated generally axially parallel to and
in clo~ely spaced relationship to -the roll ~upporti~g the web
durin~ the first coating proce~s ~o that a press gap i~ formed
therebetween;
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first applicator means for applying to the ahell surface of
the roll of the fir~t ~oating process a 6mall dosed quantity of
a first coating ~ubstance, the first applicator mean~ including
a nozzle chamber having a discharge end near the roll shell
~urface through which the fir6t coating ~ubstance i~ passed,
the first applicator means further including a holder and a
rotary doctor arranged at the discharge end, the rotary
doct~r having closely adjacent fine peripheral groove~ or
helical grooves, the fir~t coating substance having a ~olid ~r
pigment ~ubstance content, the ~olid sub~tance content being
maximally 70%;
means for passing the web through the pre~ gap wherein
the do~ed quantity of the first coating ~ubsta~ce i~ pres&ed on
the we~ so that at least a thin layer of the fir~t coating
~ubstance covers the web, 6pecifically with regard to the ~olid
or pigment content;
second applicator means for applying a layer of a seCond
coating substance directly on .the web during a ~econd coating
process, the ~econd layer being applied in direct ~uccession to
the first layer one upon the other while the fir~t lay~r i8
~till moistl the 6econd applicator means including a nozzle
chamber having a dischar~e end through which the sacond coating
substance i~ pas6ed, th~ 6econd applicator means further
including a holder and a rotary doctor arran~ed at the
di4charge end near the surf~ce to ~e ~oated.
The above mentioned and other features and objects of this
invention, and the manner of attaining them, will become more
apparent and the invention itself will be fur~r und4rstood by
reference to the following description of ernbodiments of the
in~ention taken in conjunction with the accompanying drawings,
wherein:
Fig. 1 i8 an apparatus for coating a running web of paper
or cardboard in accordance with the present invention;
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Fig. 2 i~ sn alternate embodLment of ~he coating apparatus
of the present invention wherein only two rolls are utilized;
Fig. 3 is another embodiment of the coating apparatus of
the present invention wherein a rotary doctor provided with
peripheral grooving is provided as a dosing element for the
final dosing; and
Fig. 4 is a further embodiment of the present invention
wherein a transfer roll is utilized to apply the coating
substance.
Corresponding reference characters indicate corresponding
parts throughout the several views. The exemplifications set
out herein illustrate a preferred embodime~t of the invention,
in one form thereof, and such exemplifications are not to be
construed as limiting the ~cope of the invention in any manner.
Accordin~ to Fig. 1, the web W runs through a press gap
formed between two rolls 1 and 2. Coordinated with roll 1,
which is provided with a rubberized surface, is an applicator
mechanism that features a nozzle chamber 6 and, on its discharge
end, a rotary doctor 7 provided with peripheral or helical
grooYing and a holder 8 for the latter. The hardness of the
rubber coatin~ of roll 1 may range between 0 and ~00, preferably
between lO and 70, P u.J. The amount of coatins applied in
the f~rst coating layer in the case of cardboard is dimensioned
to be 6 to 40 ml/m2, preferably 12 to 22 ml/m2. The second coat
may be applied using a comparable arranyement with rotary doctor
ll and its holder 12, along with a nozzle chamber 9, but where
the equalizing element may also be a blade or a smooth rotary
doctor at the point lO.
The applicable consistencies, i.e., solid substance
contents, range for the first coat between 5~ and 70% maximum,
and for the second coat between 60 and 70~ maximum. It has been
found to be favorable to provide for the applicator mechanism a
nozzle chamber 6, q on the discharge end of which, near the
surface to be coated, a rotary doctor 7, 11 with its holder 8,
12 is arranged. ~h~s, the advantage here i5, over the airbrush
method, that the process may be performed with a relatively high
consistency overall, but especially for the second coat. The
line pressures in the press gap between the two first rolls 1
and 2 range betwe~n 5 and 60 kN/m, preferably 20 to 40 kN/m.
The setup according to Fig. 2 has only two web
support rolls 21 and 22, with an applicator device of the
described type coordinated with each. This arrangement is
possible in the case of cardboard because it stretches less than
paper due to the moistening in the coater.
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A favorable option in th~ case of cardboard i5 providing on
the leaving end of the nozzle chamber 9 as dosing element for
the second coat (final dosing) a rotary doctor 11 provided with
peripheral grooving and a holder 12~ and to omit a further
smoothing element thereafter. This is illustrated in Fig. 3.
With this setup, a very good coating can be obtained at
relatively sparing use of coating substance.
Illustrated additionally, in Fig. 4, for the second coating
device is a transfer ro]l 17 for the coating substance that may
be used as well. A scraping by means of one of the known dosing
elements is to be provided thereafter.
In a specific application area, in the case of sizing
application for paper, it i5 possible to dose the first coat
also with a blade or a suitable lath, instead of a rotary doctor
provided with grooves, but the action of the blade needs to be
very closely monitored here.
While this invention has been described as having a
preferred design, the present invention can be further modified
within the spirit and scope of this disclosure. This
application is therefore intended to cover any variations, uses,
or adaptations of the invention using its general principles.
Further, this application is intended to cover such departures
from the present disclosure as come within known or customary
practice in the art to whi~h this invention pertains and which
fall within the limits of the appended claims.
