Satas D., Tracton A.A. (ed.). Coatings Technology Handbook
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172
MCINTYRE
t
END CAP
ULTIPLE WIDTH INNER
SUPPLY ROLL
MULTIPLE SUPPLY
PORTS
AND ROTARY UNION
Figure
12
Cross
section
of
a porous roll applicator.
POROUS
ROLL
A
METERED
SUPPLY
A
APPLl
CATlNG
ROLL
A
APPLICATING
ROLL
B
METERED
SUPPLY
B
POROUS
ROLL
B
Figure
13
Two side coating with porous
rolls.
POROUS
ROLL
COATER
173
The porous roll system also can be configured to handle multiple coating materials
within the same applicator.
A
cross section of the applicator is illustrated (Fig. 12) to
show the different chambers within which the multiple fluids are supplied. This feature
permits the converter to coat different materials simultaneously, yet from the same applica-
tor. Special tape products that require different release levels on the same web material
can utilize this concept.
For
example, a pattern of 25 g/25 mm release can be applied on
the left-hand side of the sheet, whereas a
100
g
release coating can be applied in the center
or
adjacent location on the same sheet. Products such as double-sided, release-coated webs
used in transfer tapes can be coated easily by utilizing two separate porous roll coating
systems, located on either side of the web, as shown in Figure 13.
W
or
EB
curing
equipment is incorporated for cross-linking the coatings as dictated for completing the
final products.
The porous roll system also allows for obtaining high release levels, such as 100,
200, and
400
g/25 mm, by using a two-component silicone system. This concept utilizes
two porous
rolls
that are in direct contact with a single rubber coated applicating roll (Fig.
14).
Component
A
is supplied through porous roll
B.
Component
A
represents the base
silicone coating material, whereas component
B
is the diluent. The objective is to intermix
the diluent into the base silicone. The proportional ratio
of
A
to
B
determines the fluid
release level. This concept is experimental at this stage, but tests have indicated that the
two-component system is an alternative process for obtaining future “dial-in” release
levels.
A
schematic diagram of a laboratory coater is shown in Figure
15,
and diagrams
of production-size units are shown in Figures
16-1
8.
T
COMPONENT
0
COMPONENT
A
HOPPER
MATERIAL B
DISPLACEMENT
POSITIVE
ETERING PUMP
(SINGLE
DIS-
CHARGE)
/
WE0 REFERENCE PICKUPTO
SYNCHRONIZE PUMP SPEEDS
TO
WEB SPEED
\
LAMINATING ROLL
Figure
14
Application
of
two
component silicone system.
\-
A
0
4
m
0
1
74
175
176
MCINTYRE
U
177
This Page Intentionally Left Blank
Rotary Screen Coating
1
.O
INTRODUCTION
Not long after the introduction of multicolor printing machines, the one-color printing
unit was also introduced. which through the years has found its way to a wide range of
application areas such as wall cover printing, production
of
hard floor covering, technical
coatings, artificial leather production, and last but not least as a one-color printing machine.
2.0
EQUIPMENT
Screen coating equipment (Fig.
1)
consists of the following.
The screen. which is a seamless, perforated, nickel sleeve. The degree
of
perforation
is expressed
in
the
so-called mesh number, indicating the number of holes per
linear inch.
The squeegee. which is mounted
in
the screen and serves as supply and distribution
pipe
of
the paste. The squeegee blade, which is mounted to this pipe, pushes the
paste out through the wall
of
the screen.
The whisper blade, which smooths the applied coating layer.
The amount of coating to be applied is determined by four factors:
The choice of mesh number.
The squeegee pressure: that is, the angle formed between squeegee blade and screen.
The viscosity
of
the paste.
The squeegee setting with regard to the counter pressure roller.
The smaller this angle, the higher the add-on.
179
180
GOOSSENS
"
Figure
1
Screen coater.
1:
web;
2:
squeegee;
3:
screen;
4:
whisper
blade;
5:
doctor blade.
3.0
PRODUCTS
The coatings that can be applied by rotary screen are discussed in Sections
3.1-3.4.
3.1
Pattern-Type Coatings
In view of the quantities required for pattern-type coatings and flock glue application,
frequent use is made of
125
and
40
mesh screens with a repeat size of
25
in.
(64
cm).
End uses include women's fashions, wall-covering curtains, and partial chintz rain-
wear.
3.2
Dot Coating
Two types of screen are available to accommodate dot coatings:
for
regular dot coating,
the dots are arranged in diagonal rows; for computer dot coating (CP). the dots are arranged
at random.
For regular dot coating, the
17,25,
and
30
mesh screens find the widest application
and the CP
30,
CP
40,
and CP
46
(where
30,40,
and
46
designate the number of perforations
per square centimeter), are the most frequently used CP screens.
Because of the need to apply an oscillating squeegee on the outside surface of the
screen (only used for dot-coating applications), which has been designated to suit
64
cm
repeat screens, dot coating can be effected with
64
cm repeat screens only.
End uses for dot coatings include fusible interlinings (woven and nonwoven) and
printbonding of nonwoven materials.
Advantages of screen coating compared to traditional coating by means of an en-
graved roller are as follows.
Screen costs are considerably lower than the cost of an engraved roller.
The time for exchanging screens is extremely short
(-
10
min).
The application amount is easy to control.
Light-sensitive nonwovens
(20
g/m')
or
knitted fabrics can be processed without
problems thanks to the frictionless application system.
ROTARY
SCREEN COATING
181
Figure
2
Foam
coater.
1:
web;
2:
squeegee;
3:
screen;
4:
whisper blade;
5:
doctor blade.
There is no penetration, resulting in effective use of paste and a good controllable
The constant paste supply ensures precise level control by means
of
a past processor.
A
new development is the application
of
foam-dot
coating,
in which the foam is
applied with the so-called closed system (see Fig. 2). The foam, which has been made in
the foam processor, is applied directly on the substrate via a “closed” squeegee, as shown
(Fig. 2). The foam processor will be adjusted for the application weight wet.
For example, suppose we have a polyamide paste with 33% solids.
To
apply a dot
coating with 10 g/m2 dry add-on, the foam processor is adjusted for 30 g/m2 wet add-on.
3.3
Overall Paste Coatings
Fine or thin coatings, in a range
of
5-25 g/m2 of
dry
application weight. Sorters used are
80 mesh 12% open area,
100
mesh
SP
(special) 20% open area and 125 mesh
SP
12%
open area, 130 pm thickness (indication only).
End uses include anoraks, skiwear, sportswear, rainwear, umbrellas, pressure-sensi-
tive coatings (medical), and shift-fast coatings.
Medium coatings, in a range of
15-50
g/m2 of dry application weight. Screen used
are
60
mesh
LR
(long run)
14%
open area, 125 pm thick and
40
mesh
LR
20% open
area,
130
pm thickness.
End uses include roller blinds, aluminum-coated curtains, bag material, and ironing
bar covers.
Heavy past coatings, having a
dry
application weight of
50-
130 g/mz are frequently
applied with the
40
mesh
HX
(hexagonal) screen with
30%
open area and
300
pm thick-
ness.
End uses include vertical blinds, flame-retardant coatings on upholstery and technical
coatings, and table cloths.
Screens for paste coating always have a
64
cm (25 in.) repeat size.
The squeegee blade is 28
mm
X
0.2 mm.
hand.