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Coatings Technology Handbook, Third Edition

19.5 Die Adjustment as It Relates to Manifold Design

Precise coating weight control depends on the stability of the total system and on operator experience.
Die performance will be at its best when a balance of pressure and flow is reached at the lip area. This
balance is hard to define; changes in materials and rate will affect it. We can best describe this through
the voice of an operator when he talks about the die being “jumpy or nervous” in one case and “lazy or
unresponsive” in the other. In the case of the “jumpy” adjusting die, the pressure balance is too high;
with the “lazy” one, pressure is too low. We will refer to this performance parameter as the operating
window. When a die must be profiled excessively to improve end flow, the operating window will vary
across the die; therefore, the die adjusting characteristics will differ (e.g., jumpy center, lazy ends). This
effect is magnified in automatic control. When a die is set up at 0.010 in. opening in the center and 0.020
in. at ends to achieve balanced flow, a 3% change in opening at the ends is 0.0006 in., and in the center
it is a 0.0003 in. change. As we develop more dynamic computer programs to respond faster or to
predetermine a target point, uniform die response becomes very important.

19.6 Coat Weight Adjustment

Base coat weight is controlled by pump and line speed. Transverse area coat weight is a function of the
lip gap adjustment. It is important to remember that the pump will always deliver a given amount of
fluid to the web. When the operator adjusts the lip, material is not taken away — it is only moved from
one place to another. This difference between roll or knife coating and slot die coating is often overlooked
by the operator.


Slot Die Coating for Low Viscosity Fluids

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2. The angle of contact depends on lip profile, die-to-roll gap, roll hardness, roll diameter, lip step
difference, lip profile, and material spreading tendency. It is impossible to predict this angle without
all these factors and in-depth experience.
3. Reduced contact pressure is necessary to reduce roll and die lip damage.
4. Because roll deflection is very hard and expensive to eliminate, a die that can be deflected or bent
to conform to roll variance is required if roll deflection is a problem. It is common to use a steel
roll backing up the elastomer roll to lessen the deflection problem, and with heated adhesives to
help cool the elastomer roll.
5.
for the best and most reproducible coating surface.

19.10.2 Lip Profiling

Lip shape and the relative position of the lead and trailing wipers to each other are of utmost importance
in today’s coating technology.
In some cases, using today’s high technology coatings, a uniform and proper level of wiping action is
required to produce satisfactory coating. As a result of the shear thinning characteristics in today’s more
difficult adhesives, proper profiling and angle to attack will produce a smooth and even coating. Any
variance in lip profile will create differential wiping, causing an uneven appearance. Because, with modern
coating heads, uniform distribution is not a function of the lip face, we can confine the lip face to a
single function — namely, creating a proper environment at lay-down.
No hard data are available on lip face design as the interrelation between roll diameter, roll hardness,
line speed, substrate, lip design, and adhesive viscosity characteristics come into play. There seem to be
two technical camps. One group adheres to the flat, fixed wiping lip, with a differential step between the

and hydraulic soft stop cushions is used. A micro stop correction adjustment with dial indicator
or LVDT should be provided for each end.

Item 4 in Figure 19.10

: This “Y” adjustment is provided for roll axis position alignment.

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Angle of attack of the die to roll must be pivoted around the pivot point indicated in Figure 19.8
series of design specifications indicated in Figure 19.10 and explained in Section 19.9.4.
that mounting position A in Figure 19.9 is the most advantageous, and position B is the least.

Slot Die Coating for Low Viscosity Fluids

19

-11

arrangement, with indicator markings in degrees. Note that the angle of attack movement is
centered at the die lip (coating contact) point.

19.10.5 Die-to-Roll Positioning

Flexibility and repeatability are primary requirements. Difficult adhesives, speeds, and substrates will
require different setup positions, and the ability to vary the die-to-web position easily with exact repeat-
ability is of prime importance. The support frame must allow in/out movement and angle of attack
adjustment (see Figure 19.10).
In/out adjustment will have two functions: (a) fast movement with 5 to 8 in. (130 to 200 mm) of
travel, allowing lip cleaning; and (b) micro in/out to fine-tune roll-to-lot gap distance. This adjustment

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Item 5 in Figure 19.10: This is an angle of attack positioning adjusted through a rack-and-pinion gear
unaltered. Angle of attack adjustment must pivot about the point indicated in Figure 19.8.

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Coatings Technology Handbook, Third Edition

19.10.8 Die-to-Roll Gap Setup

The distance from die to roll or substrate is, in general, determined by web thickness and the viscosity
of the fluid to be applied. The more clearance that can be maintained, the less damage there may be due
to positioning or start-up mistakes.
We suggest, as a rule of thumb, that a clearance equal to the substrate thickness be set between
substrate and infeed lip face. This distance may be less for materials of very low viscosity or for hard
roll to lip face.

19.11 Backup Roll Design

Processors and equipment manufacturers alike would like to utilize steel backup rolls to improve
runout (T.I.R.) and to mitigate heat transfer problems. In some cases on lab or narrow production
systems, steel rolls have been successful. In most cases, however, steel rolls are not as forgiving as an
elastomer roll and therefore have not yet been accepted for production. We expect this to change as
the technology matures.
Elastomer rolls have improved over the past several years to allow the precise roll-to-lip conformation
absolutely required for proximity coating. When specifying an elastomer roll, the following items must
be carefully considered:


5% control, assuming the total system
has reached some stability, will be 10 to 20 min, and

±

3% control in 15 to 30 min.

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to smooth materials. Make sure the gap is from web to lip face, as shown earlier (Figure 19.6), not from
bolt arrangements (see Figure 19.12). Minor disagreements exist on details, but total overall performance

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Coatings Technology Handbook, Third Edition

Thickness variations are converted to lip opening correction by increasing or decreasing power to the
individual lip bolt control blocks to trim variations to a minimum.
The key to the transverse thickness control is a microprocessor-based controller that is tied into the
conventional computer control system.
On ambient operation dies, care must be taken to isolate the heat from the Autoflex bolts from the
die body.

19.12.2 Die-to-Roll Position Adjustment System

The ability to repeat the original roll-to-die setup position is critical during start-ups and normal web
splice coating interruption.

complete system, including pump filters and piping.
Purging is the easiest and most common method; but extreme care is necessary to streamline all flow
areas to eliminate dead areas.
The opening and cleaning of a die can be an easy 30 min experience or a 3 to 4 day nightmare. Slot
die designs differ greatly; some are simple two-piece designs, while others have complex assemblies.
It is common to have a dual pumping and piping system, allowing quick changeover from one coating
to the next, cleanup then taking place after the line is up and running.

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In many applications, a rake-type device may be used for stripe coating (Figure 19.14A). This device

20

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20

Extrusion Coating with
Acid Copolymers and

Lonomers

20.1 Product Considerations

20-

1
20.2 End-Use Considerations


Resins with acid contents of 3 to 15% are currently available on the market. The effects of increasing
acid content are as follows:
• Better foil adhesion
• Better hot tack

Donald L. Brebner

E. I. du Pont de Nemours &
Company

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Foil Adhesion • Heat Seal Characteristics
Melt Temperatures • Other Considerations
properties markedly superior to those of conventional polyethylenes. Figure 20.1 shows the structure of
Ionomers (Figure 20.2) are derived from acid copolymers by partial neutralization of the carboxyl
intramolecular hydrogen bonding, as illustrated in Figure 20.3. The forces involved in hydrogen bonding

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Coatings Technology Handbook, Third Edition

Hot tack strength is the ability of a heat seal to remain together when a force is applied while it is still
in the molten state. This is a critical property in vertical form-fill-seal applications, in which the product
is loaded immediately after the seal is made. It is also critical in any high speed packaging operation in
which the package is exposed to some form of abuse before the seal has cooled.
One method of measuring hot tack strength is the Du Pont spring test. A series of springs of different
thicknesses and widths at the narrowest point provides varying levels of spring tension (Figure 20.5).

Figure 20.6 shows how the spring is located inside the sample. The sample is heat sealed for 3 sec at a
Figure 20.7 shows the hot tack characteristics of an ionomer and acid copolymers of equivalent acid

21

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21

Porous Roll Coater

21.1 Introduction

21-

1
21.2 Extrusion Porous Roll System

21-

1

21.1 Introduction

Recent progress had been made in silicone-coated products that are curable by electron beam (EB) and
products, in which the release levels range between 25 and 50 g per 25 mm wide strip, typical viscosities
of the materials tested are in the range of 500 to 1000 cp at room temperature. These silicone products
are manufactured by Th. Goldschmidt, in West Germany, and Lord Corporation, in Pennsylvania, and
other companies. The UV products are either one-part premixed/ready-to-use materials, or two-com-
ponent products that require nitrogen inerting to overcome surface smear and to achieve a complete

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Development • Details and Disadvantages
ultraviolet (UV). Advantages of UV and EB converting processes are shown in Table 21.1. Of these new
process is shown in Figure 21.1. The UV lamps used for curing are rated at 300 W/in. (120 W/cm per
approximately 2 megarads (Mrad). A schematic diagram of an EB processor is shown in Figure 21.2.
adjacent to a slow speed “nozzle roll” (see Figure 21.3). The fluid is coated onto the “nozzle roll” and
similar effect (see Figure 21.4). This phenomenon is associated with fluids that have poor flow properties
Figure 21.5. The actual coat weight applied in either case is influenced by the web substrate material,

Porous Roll Coater

21

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FIGURE 21.6

Porous roll coater.

FIGURE 21.7

Diagram of a porous roll.

FIGURE 21.8

Rotary screen printer.
Web
Laminating
Roll

Single Width
Rotary Screen Cylinder
Interior Doctor Blade
Printing
Fluid Ink

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Coatings Technology Handbook, Third Edition

porous roll having larger openings, depending on flow properties. The larger porous openings will
minimize the fluid backpressure and allow for consistent coat weights at various machine speeds.
The porous roll surface can be sealed for printing of fluids in patterns, as shown in Figure 21.10. This
means that special coating patterns required in flexible packaging products, business forms, envelopes,
tapes, and labels can utilize curable silicone coatings in the final converting process, rather than having
pre-silicone-printed web materials.
The porous roll system can also be configured to handle multiple coating materials within the same
within which the multiple fluids are supplied. This feature permits the converter to coat different materials
simultaneously, yet from the same applicator. 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

FIGURE 21.9

Displacement
Metering Pump
(Single
Discharge)
Supply A
Supply B
Hopper
Filter
Digital
Pump Drive
Digital
Pump Drive
Porous Roll A
Porous Roll B
Rotary Union
Applicating Roll
Web Reference Pickup to
Synchronize Pump Speeds
to Web Speed
Laminating Roll
3-Way
Valve
3-Way
Valve
Web
Return A
Return B
Material A
Hopper
Material B

Laminating Web
Wide Band Extrusion Nozzle
1" (2.54 cm) min. to 6" (15.2 cm) Std.
for Both Paper and Film Coating
Web Positioning Mechanisms
for Both Paper and Film Coating
S Loop Positive Web Drive Roll
Variable speeds up to 38 fpm (11.6 mpm)
Rewind Roll
8" (20.3 cm ) dia. max.
Unwind Roll
(Web to be coated)
8" (20.3 cm ) dia. max.
Hopper Blanket
Temperature Control

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Coatings Technology Handbook, Third Edition

FIGURE 21.15

A coating line with a porous roll coater.
Coating Applicator, Hot Melt/eb Curables
(a) Extrusion Coating (Paper/Film)

U V Blower Module
U V Module
Control Console
U V Silicone
Delivery System
U V Power Supply
Corona Power Supply
HMHT-IMP
Hot Melt Adhesive
Delivery System
Dual Turret
Rewind/Slitter
Module
Hot Melt
Control
Console
CL-300 Series
Coater Laminator (171 mm–340 mm)
with Web Drive Controls
Turnbar Module
U V Silicone Coating Module
with Edge Guide Applicator,
Chill Roll and U V Lamps
Corona
Treatment Module

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22

cover printing, production of hard floor covering, technical coatings, artificial leather production, and
last but not least, as a one-color printing machine.

22.2 Equipment

•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 the 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 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 smaller
this angle, the higher the add-on.)
•The viscosity of the paste
•The squeegee setting with regard to the counter-pressure roller

22.3 Products

The coatings that can be applied by rotary screen are discussed in Sections 22.3.1 through 22.3.4.

F. A. Goossens

Stork Brabant

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Pattern-Type Coatings • Dot Coating • Overall Paste Coatings •
Introduction 22-1