Coatings Technology Handbook Episode 1 Part 7 pptx

22

-4

Coatings Technology Handbook, Third Edition

For example, to apply 30 g/m

2

dry of an acrylic or polyurethane binder (50% solids), simply adjust
the wet application weight on the foam processor at 60 g/m

2

.
End uses include velour backcoatings, automotive backcoatings, mattress ticking, fixation of pile on
pile fabrics, flame retardant and cigarette-proof coatings, imitation suede, and antislip coatings.

22.4 Advantages

1. Because substrate, screen, and counterpressure rollers have the same speed, coating is done without
tension and friction. Thus, virtually all substrates can be processed on this system, including
knitted fabrics, velours, nonwovens, and shift-sensitive materials, such as skiwear, mattress ticking,
and Lycra fabrics.
2. The user has penetration control: penetration into the substrate can be completely avoided or, if
desired, controlled.
3. Thanks to the low system content, the coating method is clean, and fast changes are possible.
4. Coatings are exactly reproducible. As parameters, squeegee pressure, squeegee setting, mesh num-

ber, and viscosity can be measured and read off, and any given coating can easily be repeated.
5. Chemical savings (up to 20% of the coating weight) are realized in two ways: (a) through accurately
controllable application and because the screen follows the web structure exactly (thus, the textile
character is maintained, and an excess of paste, such as occurs with knife coating, is avoided); and
(b) through great accuracy, in left/right and longitudinal directions, of the application amount.
6. Application is both tensionless and frictionless.
7. By means of the closed system, the user has total process control.
8. The knife coating option can be attached above the whisper blade roller, mentioned earlier.
This knife coating (see Figure 22.3) can be used as a knife-on-air system for paste or unstable foam
coatings and in the knife-over-roll coater made for foam applications. In both cases, the apparatus is
fitted with a paste or foam distribution system over the full working width. In this way, it is possible to
apply colored coatings with a totally even appearance.

FIGURE 22.3

Adaptation of screen coater for knife coating.
6
1
5
5

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© 2006 by Taylor & Francis Group, LLC
The schematic diagram of a rotary screen coating line is shown in Figure 22.4.

23

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23

Screen Printing

23.1 Introduction

23-

1
23.2 Geometry of the Printing Screen

23-

2

The Rotary Screen

23.3 The Stencil

23-

3
23.4 Dynamics of the Squeegee

23-

3
23.5 Coating Transfer

23-

4
23.6 Converting the Applied Coating

23-

4
23.7 Conclusion

23-

4
References

23-

4

23.1 Introduction

The screen printing process is markedly different from most imaging processes generally associated with
the graphic arts. First, the printing plate is actually porous, formed by a woven mesh of synthetic fabric
threads or metal wire (or in at least one case, by a nonwoven, electroformed metal matrix), which is then
combined with a selective masking material, commonly called a stencil. Because the coating material
flows under pressure into and through this mesh or matrix before being deposited onto a substrate, the
resulting coating has a thickness far greater than that of a material printed onto the substrate by offset
lithography, gravure, flexography, xerography, or ink-jet printing.
For this and other reasons, the screen printing process has many practical applications in industrial
manufacturing areas in which other printing media have few or none.
to a rigid framework of aluminum or steel. In most applications, this framework forms a rectangular
plane. However, variations are possible, including the cylindrical screen, which is affixed and sealed at

both ends. In the case of mesh, whether of synthetic polyester monofilaments or stainless steel wire,
tension is applied simultaneously in opposing directions to obtain a semirigid planar surface. This
stretched printing screen then performs three distinct functions: (a) meters the fluid coating (or ink)
that flows through it under pressure, (b) provides a surface for shearing the viscous columns of coating
material that form during transfer to the substrate, and (c) provide support for the imaging elements
(the stencil).
Ink or coating transfer is initiated by the imposition of pressure on the screen by means of a
flexible plastic blade, the squeegee. Because of the flexibility of the blade material and its physical
profile, a hydraulic action is caused by force exerted in two directions. The blade presses into the
screen, and its inherent flexibility enables it to be put into direct contact with the substrate, thus
effecting ink transfer. The blade also sweeps in a horizontal direction, thus applying the ink or coating
as it moves, and causing the columns of material to shear as the printing screen rebounds after the
squeegee has passed.

Timothy B. McSweeney

Screen Printing Association
International

DK4036_book.fm Page 1 Monday, April 25, 2005 12:18 PM
© 2006 by Taylor & Francis Group, LLC
The basic process steps are as follows (see also Figure 23.1). The woven mesh (or matrix) is affixed

24

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24

Flexography

24.1 Introduction

24-

1

24.2 Flexo Press Systems

24-

2

24.3 The Most Important Flexo Deck System

24-

5

24.4 Printing Forms or Plates

24-

7

24.5 Print Substrates and Printing Inks

24-

9

24.1 Introduction

Throughout the printing industry, flexography, or flexo, has established its reputation as a quality printing
process bearing comparison with letterpress, gravure, and offset, which have been used industrially for
many years. Today, the whole packaging sector and other areas of the printing industry would be
unthinkable without this highly economical quality printing process. This is attributable primarily to the
high flexibility flexo offers, its qualification for a wide range of materials, the large and variable range of
print repeat lengths, the different press widths available, and the quite extraordinarily high production
speeds. Other advantages include the highly diversified flexo press specifications and the possibility of
using flexo in line with other printing techniques and processing operations.
Finally, the developments and improvements achieved in the field of press engineering, flexo printing
plates, and flexo inks have recently contributed quite decisively to the position the process holds today.

24.1.1 Historical Development of the Aniline and Flexographic
Printing Process

To day’s flexo process is far more than 100 years old. According to historians, extremely primitive aniline
work was produced in the United States as far back as 1860.
The original name of this letterpress process, “aniline printing,” is traceable to the aniline dyes used
in the mid-19th century that were diluted in alcohol and had been used in printing for many years. This
rubber printing process — until 1970, rubber printing plates were used exclusively — was initially
employed for the printing of wrapping papers. The first aniline printing apparatuses are said to have
been used in England and Germany beginning in 1890. From about 1910, some European machine
manufacturers started to supply aniline printers in combination with paper bag machines to permit
printed paper bags to be produced in a single pass. From the early 1920s until approximately 1940, aniline

Richard Neumann

Windmöller & Hölscher

DK4036_book.fm Page 1 Monday, April 25, 2005 12:18 PM
© 2006 by Taylor & Francis Group, LLC
Historical Development of the Aniline and Flexographic
End Printers • Stack Presses • In-Line Systems • Central
Printing Process • The Flexo Process
Impression Machines
Three-Roller System (Fountain Roller Color Deck) •
Rubber and Photopolymer Plate Making • Printing Plate
Two-Roller or Fountainless Printing Deck
Mounting and Proofing
Print Substrates • Flexo Inks

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Coatings Technology Handbook, Third Edition

consist of colorants (dyes or pigments), binding agents (natural resins, artificial resins, or plastics), and
a solvent or solvent blend. Whereas flexo inks used to be based on basic (soluble) dyes, pigment inks are
used primarily today because of more exacting demands on the ink’s fastness. To obtain the desired
properties such as brilliance, adhesion, and qualification for laminating, the correct binding agents and
additives must be selected.
Apart from the aforementioned properties, flexo inks are required to generate a quality end product.
Fast and perfect drying of inks on the substrate during printing is another aspect of paramount impor-
tance, and in this respect, the solvent of the solvent mixture used is the decisive factor.
The drying system involves evaporation of solvents after the ink has been applied to the web. This
drying process is substantially accelerated within the printing press using hot air, which is blown onto
the web, and appropriate exhaust arrangements.

The most important solvents are hydrocarbons, alcohols, glycols, esters, and ketones. Recently, water-
soluble pigment inks, once used exclusively in the printing of multiwall paper sacks, gift wrap, corrugated
board, and wallpaper, have been playing an increasingly important role and also have been adopted in
the fields of newspapers and plastic films. The obvious reason for the growing trend to use water-soluble
inks in package printing and for plastic films is the new set of laws calling for reduction of solvent
emissions into the environment.

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© 2006 by Taylor & Francis Group, LLC

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25

Ink-Jet Printing

25.1 Introduction

25-

1
25.2 Continuous Jet Printing

25-

1
25.3 Impulse Jet (Drop-On-Demand) Printing

25-

2
25.4 Ink-Jet Inks

25-

3
Bibliography

25-

4

25.1 Introduction

Ink-jet printing refers to any system in which droplets of ink are ejected onto a printing surface to form
characters, codes, or other graphic patterns. The ink-jet concept dates from the 1860s, when Lord Kelvin
developed the first practical jet for pattern generation. Early commercialization was in the oscillographic
recorder area in the 1950s. Since the 1960s, ink-jet developments have focused on computer output, with
major contributions made by such scientists as Hellmuth Hertz in Europe (Lund Institute, Sweden) and
Richard Sweet (Stanford University) and Steven Zoltan (Brush Instruments) in the United States.
Current commercial products range from printers for direct coding of packages, to high-speed–low-
resolution direct mail printers (from Diconix), to graphic arts quality color plotters (from Iris Graphics),
to graphic arts quality color plotters (from Hewlett Packard). To address this range of applications, several
variants of the technology have been developed. Each approach involves trade-offs among cost, speed,
reliability, and print quality, determined by interactions between hardware and supplies.
Ink-jet printing functions include the following:
•Creation of an ink stream or droplets under pressure
• Ejection of ink from a nozzle orifice

•Control of drop size and uniformity
•Control of which drops reach the paper
• Placement of drops on the recording surface
Control of these processes depends on several design variables, such as nozzle size, firing rates, drop
deflection methods, and ink viscosity. Changing any variable typically requires adjustments to other
system variables, making R&D advances slow and expensive.
Ink-jet printers fall into two basic categories: continuous jet (synchronous) and impulse jet (drop-on-
demand). Most early development took place in the continuous jet arena, but recent emphasis has shifted
to the less complex (and therefore less costly) drop-on-demand approaches.

25.2 Continuous Jet Printing

Continuous ink-jet systems operate by forcing pressurized ink in a cylinder through nozzles in a contin-
uous stream. Nozzle diameters range from 3 to 0.5 mil; the smallest nozzles can require up to 600 psi of
pressure to eject the ink. The ink stream is unstable, breaking into individual droplets either naturally

Naomi Luft Cameron

Datek Information Services

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© 2006 by Taylor & Francis Group, LLC

26

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26

Electrodeposition

of Polymers

26.1 Introduction

26-

1
26.2 Advantages

26-

1
26.3 History

26-

2
26.4 Process

26-

2

26.5 Equipment

26-

3

26.6 Laboratory 5
References

26-

5
Bibliography

26-

6

26.1 Introduction

The electrodeposition of polymers is an extension of painting techniques into the field of plating and,
like plating, is a dip coating process. The art of metal plating utilizes the fact that metal ions, usually
Ni

2+

or Cu

2+

, can be discharged on the cathode to give well-adhering deposits of metallic nickel, copper,
etc. The chemical process of deposition can be described as 1/2 Me

2+

+

1

F

(or 96,500 coulombs) of
electrons gives 1/2 Me

0

. In the case of electrodeposition of ionizable polymers, the deposition reaction
is described as R

3

NH

+

OH

–



+

1

F



→

R

3

N

+

H

2

O or the conversion of water-dispersed, ammonium-type
ions into ammonia-type, water-insoluble polymers known as cathodic deposition. Alternatively, a large
number of installations utilize the anodic deposition process RCOO

–



+

H

+

less 1

F



→

RCOOH. It should
be mentioned that “R” symbolizes any of the widely used polymers (acrylics, epoxies, alkyds, etc.).
The electrodeposition process is defined as the utilization of “synthetic, water dispersed, electrodepos-
itable macro-ions.”

1

26.2 Advantages

Metal ions, typically 1/2 Ni

2+

, show an electrical equivalent weight 1/2 Ni

2+

equal to approximately 29.5
g, while the polymeric ions typically used for electrodeposition exhibit a gram equivalent weight (GEW)

of approximately 1600. Thus, 1

F

plates out of 30 g of nickel and deposits 1600 g of macroions. If we

George E. F. Brewer*

George E. F. Brewer Coating
Consultants

* Deceased.

DK4036_book.fm Page 1 Monday, April 25, 2005 12:18 PM
© 2006 by Taylor & Francis Group, LLC
Throwing Power • Maintaining a Steady State • Rupture Voltage
Conveyors • Metal Preparation • Tank Enclosures • Dip Tanks •
Wate r • Bake or Cure
Rectifiers • Counterelectrodes • Agitation • Temperature
Control • Ultrafilter • Paint Filters • Paint Makeup • Deionized

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27

Electroless Plating

27.1 Introduction

27-

1
27.2 Plating Systems

27-

2
27.3 Electroless Plating Solutions

27-

3

27.4 Practical Applications

27-

4
27.5

27.6 Stability of Plating Solutions

27-

7
27.7 Electroless Plating

27-

7

27.8 Properties of Chemically Deposited Metal Coatings

27-

10
References

27-

11

27.1 Introduction

In electroless plating, metallic coatings are formed as a result of a chemical reaction between the reducing
agent present in the solution and metal ions. The metallic phase that appears in such reactions may be
obtained either in the bulk of the solution or as a precipitate in the form of a film on a solid surface.
Localization of the chemical process on a particular surface requires that the surface must serve as a
catalyst. If the catalyst is a reduction product (metal) itself, autocatalysis is ensured, and in this case, it
is possible to deposit a coating, in principle, of unlimited thickness. Such autocatalytic reactions constitute
the essence of practical processes of electroless plating. For this reason, these plating processes are
sometimes called autocatalytic.
Electroless plating may include metal plating techniques in which the metal is obtained as a result of
the decomposition reaction of a particular compound; for example, aluminum coatings are deposited
during decomposition of complex aluminum hydrides in organic solvents. However, such methods are
rare, and their practical significance is not great.
In a wider sense, electroless plating also includes other metal deposition processes from solutions in
which an external electrical current is not used, such as immersion, and contact plating methods in which

another more negative (active) metal is used as a reducing agent. However, such methods have a limited
application; they are not suitable for metallization of dielectric materials, and the reactions taking place
are not catalytic. Therefore, they usually are not classified as electroless plating.
Electroless plating now is widely used in modifying the surface of various materials, such as noncon-
ductors, semiconductors, and metals. Among the methods of applying metallic coatings, it is exceeded
in volume only by electroplating techniques, and it is almost equal to vacuum metallization.
Electroless plating methods have some advantages over similar electrochemical methods. These are as
follows:

A. Vakelis

Lithuanian Academy of Sciences

DK4036_book.fm Page 1 Monday, April 25, 2005 12:18 PM
© 2006 by Taylor & Francis Group, LLC
Deposition Rate • Solution Life • Reducing Agent Efficiency
Copper Deposition • Nickel Plating • Cobalt, Iron, and Tin
Factor • Solution Sensitivity to Activation
Plating • Deposition of Precious Metals • Deposition of Metal
Mechanisms of Autocatalytic Metal Ion Reduction
27-5
Alloys