Note: Descriptions are shown in the official language in which they were submitted.
O
ARRANGEMENT FOR WEB COATING
The invention relates to an arrangement for one-sided or two-
sided coating of a basically upwardly moving web, for instance
a paper web~ by means of providing an excess supply of coating
S substance onto the web and evening of the coating substance
sticking thereto by pulling the web through a coating nip
formed by a flexible coating blade and a back-up member.
In web coating arrangements, in which the web is pulled
upwards through a nip formed by evening blades, the qpreading
ND of coating substance on the web usually takes part below the
nip by means of a spreading apparatus. In a known arrangement
the spreading apparatus comprises two rolls forming a nip
through which the web i~ pulled. The coating substance is
supplied onto the roll , wherefrom it is transferred and
spread onto the web. At high wsb speeds, one difficulty is due
to web slip in the spreading nip, which causes uneven coating
substance transPer to the web. On the other hand 3 the nip may
be tightened in order to avoid web slip. This, however, often
causes web ruptures a~ a consequence of the inertia of the
aO masBive spreading rolls, which unable~ them to follow fast web
speed changes. Another known coater construction comprises
spreading nozsles in 11eu of the spreading rolls. Also with
this arrangement it is difficult to spread coatirg substance
uniformly on the web.
A common feature of both these known constructions is that, in
the spreading phase, a portion of the coating substance i5
removed from the web. This excess amount has to be pumped back
to the spreading point, and this forms an extra, uneconomical
S step of the proces3. Further, an additional recycling circuit
has to be provided for recycling the coating sub~tance scraped
off by the evening blades. This complicates the construction
and encreases the manufacturing c03ts.
The object of the invention is to provide a web coating ar-
/ rangement, in which the spreading of the coating substance,
also at high web ~peeds, is carried out in a reliable and
economical way and with a homogeneous and even result. An
arrangement acoording to the invention has low manufaoturing
costs and the amount of recycled coating substance is
lS minimized. Thi~ results in an improved coating economy. Also
the coating ~ubqtance scraped off from the web by the coating
nip blades, iq collected for reusa without any pumping action
The invention is charaoterized in that a ooating chamber is
formed, inoluding means for qupplying ooating 3ubstano0
~0 thereto, said coating chamber being open against said web and
having at its bottom, at a conqiderable distance from said
coating nip, a narrow slot through which the web is moved
basically without any contact with the edges of said slot,
the substance supply to said chamber and the width of said
lot being so adapted to the speed of said web and to the
coating substance viscosity, that only a small amount of coating
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substance ~lows downwards through the slot during normal
operation of the arrangement
The web is in direct contact with the coating substance in the
coating chamber. The moving web then carries away coating
substance, which contributes to a firm adherance of coating
substance all over the web surface. The excess coating
substance scraped off by the coating blade is, even at high
web speeds, collected in the coating chamber for immediate
reuse without any pumping mean~. Since only a small amount of
~ coating substance passes through the bottom 510t downwards, a
column of coating substance is formed in the coating chamber.
This provide~ a large and uniform contact between the web and
the coating substance. Moreover, the construction is econo-
mical as a re~ult of the very small amount of coating
~S substance passing down below the coating chamber. When the
viscosity o~ the substance is optimized relatively to the web
speed, no coating substance at all will ~low down below the
chamber. Naturally, no pumping means will then be needed for
recycling coating substance.
ao The coa-ting substance level in the coating chamber can easily
be adjusted by means of an over~low edge or duct being
preferably vertically adjustable. The construction can bs
~urther improved by limiting the width of the slot to at the
most 5 cm, pre~erably at the most 1 cm. Then a coating
2 S substance ~low downwards through the slot is easily prevented
also at low web speeds.
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The coating can favourably be carried out with a coating
substance having a dynamic viscosity higher than 1 mPas.
Thereby, the use of, for instance, water soluble sizing
components requires just small amounts of water, which
3 reduces the need for web drying, thus improving the economy of
the process.
The coating substance which has possibly flown down through
the bottom slot is preferably collected in a tank or trough
below the slot. Naturally, also the coating substance flow
~0 coming from the level regulating means of the coating chamber
can be collected in the same tark or trough.
A favourable embodiment of the invention is obtained by making
the angle between the web and the flexible blade in the
coating nip smaller thar. 40. This mak0s the mounting of the
/~ blade easier and decreases the risk of web damages. Another
favourable embodiment of the invention uses a roll as a back-
up member in the coating nip. The roll rotates with a speed at
least approximately corresponding to the web speed. This
embodiment is very suitabley for example, when the web is
aO simultaneuosly ~ubject to size press coating and pigment
coating. The ~ame device can easlly be used for normal one-
side coating, also. The arrangement is applicable for low and
high web speeds as well.
A ~uitable back-up member for the coating nip can be formed as
a plate extending vertically upwards slightly above the
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coating nip and downwards to or past the bottom level of the
collection tank or trough. The width of the plate should
correspond to or exceed the web width. By this meanq the web
is simply and firmly supported at its one side and the nip
S back-up member as well as the slot limiting member are formed
by one single member.
In an arrangement according to the invention, the members
located at the opposite sides of the web may be fully or
partly identical. For two-sided coating a coating chamber can
J4 be arranged at both sides of the web, preferably at the same
vertical level. These chambers may be supplied with the same
kind or with different kinds of coating substance. In the
latter case, the slot widths and liquid level positions at
both sides may be considerably different.
.
ls In order to obtain an uniform coating result, the arrangement
can be provided with a load member applying an adjustable
pressure on the fle~ible coating blade, as known per se.
In the following, the invention will be described more in
detail with reference to the attached drawing, in which
0 - Figure 1 i9 a schematical perspective view of an arrange-
ment according to the invention,
- Figure 2 shows a sectional side view of a first embodiment
of the invention,
- Figure 3 shows a sectional slde view of a second embodiment
of the invention,
- Figure 4 shows a sectional side view of a third embodiment
of the invention,
- Figure 5 shows a sectional side view of a fourth embodiment
of the invention.
In the drawing, reference numeral 1 indicates a moving web,
which is pulled through a coating nip 4 formed between a
flexible blade 2 and a back-up member 3. The running direc-
/0 tion of the web is indicated by an arrow. A narrow slot 5 isformed below nip 4. Slot 5 is ~ormed between a slot limiting
member 6 and the edge 11 of an adjustable slot width regulator
10. The slot width is infinitely variable up to a~maximum of
preferably 5 cm. Back-up member 3 and limiting member 6 may be
~S separate or combined to a single member, which may be a roll9
a flexible or a rigid plate or a fixed web guide member. A
coating chamber 7 is formed above slot 5. This chamber is
limited by the web 1, the flexible blade 2, a back wall 8 and
side walls 8a. A ~upport plate 9 is connected to slot width
a~ regulator 10, which is movably suspended so as to allow
adjustment of the width of slot 5. For example, width
regulator 10 may be provided with threaded members so
arranged, that turning of the members causes adjustment of the
width of slot 5.
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Coating substance 16 is supplied to chamber 7 through a supply
duct 13. A collecting tank 12, open against web 1, i9
arranged below slok 5. The small amounts of coating substance
flown through slot 5 and collected in tank 12 are recycled to
3 chamber 7 through an outlet duct 14, which via pumping means
(not shown) is connected to ~upply duct 13. Chamber 7 is
provided with means for regulating the level of coating
~ubstanoe contained therein. For example, coating sub~tance
may flow over edge ~c of side wall 8a into tank 12. The edge
8c is preferably vertically adjustable.
The embodiment of Figure 3 includes a roll 15, which at the
same time forms the back up member for flexible blade 2 and
the limiting member for slot 5. Roll 15 is rotated in the
running direction of web 1.
1s The embodiment acoording to Figure 4, basically symmetric
relative to vertical web 1, is used for two-sided coating. It
is, however, not necessary to use a ~ymmetrical coating
arrangement. If 7 for instance, different coating ~ub tances
with different vi~cosity are supplied to chambers 7 at
~0 opposite sides of the web, the slot regulating edges 11 may be
at different distances from web 1.
Collecting tank 12 is suspended at coating chamber wall 8.
Tank 12 can al~o be formed in one piece with wall 8 by pro~
viding the latter with a long, downwards extending portion
bent at its lower edge towards web 1 to form a trough. The
trough or tank 12 may extend outside the qide edge~ of web 1.
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The back-up member of coating nip 4 and the limiting member of
slot 5 may be combined into a single, mainly rigid web guiding
plate 17, as shown in Figure 5.
The invention is not limited to the embodiments described, but
S several modif.ications thereof are feasible within the ~cope of
the claims. For example, slot width regulator 10 can be
rotatably attached to the inside of ~ide wall 8. The axis of
rotation should then be parallel to slot 5 and excentric with
re~pect to slot width regulator 10.
