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the melt right up to the gates by use of a sprue heater,

manifold heaters, and nozzle heaters. Past the gates, the

melt ﬂows into the cavities. As the molten plastic solidiﬁes

during cooling, the parts typically shrink 1–2% of their

diameter, causing them to adhere to the cores. When the

mold opens, parts are ejected from the cores and drop

between the mold halves.

Runner System. There are basically two types of runner

systems: cold and hot. In cold runner systems, the melt in

the ﬂow channels between the nozzle and the gates is

allowed to cool and solidify during each cycle and must be

ejected along with the parts before the next cycle begins.

Cold runner systems are simpler to design and are less

expensive than hot runner systems. A disadvantage is that

the plastic of the cold runner must be reprocessed or

scrapped, which adds costs and environmental concerns.

The introduction of scrap material to virgin resin can

adversely affect process repeatability and part quality.

Also, the cold runner can signiﬁcantly slow the cycle at

which the mold operates, since the cold runner must be

cooled before ejection. For these reasons, hot runner sys-

tems have been extensively used in packaging applications.

To ensure consistent quality, the hot runner system

should be balanced so that it supplies melt to each cavity

at the same pressure and temperature. Flow balance is

maximized by ensuring that each ﬂow channel from the

nozzle to the cavity gates has an equal length and an equal

number of turns. True balance can only be achieved

through engineering of the hot runner system with the

use of material software to help identify problamatic areas

of ﬂow through computer simulation. This allows the

engineer to test out various processing and design scenar-

iors before any manufacturing commmences. In cases

where the material characteristics or part requirements

inhibit an engineered approach, artiﬁcially balanced sys-

tems can use sequence controls and shut-offs to control the

material ﬂow. Temperature balance is achieved through

uniform heating and insulation. Hot runner molds with up

to 128 cavities operate reliably with this balanced ap-

proach. The hot runner system should also have manifold

ﬂow channels with smooth, radiused corners to reduce

friction and pressure drop. As a result, there should be no

dead spots where plastic can be trapped and degrade.

Cooling. Cooling time is a key variable in the total

molding cycle. To decrease cooling time and thus increase

productivity, gun drilled cooling channels are located near

the molding surface. High coolant ﬂow rates are necessary

to achieve high heat-transfer rates. In addition, metals

with excellent heat-conductivity properties such as be-

ryllium copper can be used for inserts to improve heat

transfer where high heat is generated, such as around the

gates. Beryllium copper has approximately 10 times the

coefﬁcient of thermal conductivity of steel. With a well-

designed cooling system, typical thin-walled packaging

parts can be cooled rapidly. Total cycle times as short as

1.5 s are now possible. It is also important for the cooling

system to maintain the cores and cavities at approxi-

mately the same temperature. This prevents excessive

wear between interlocking faces due to differences in

thermal expansion between the mold halves.

Traditionally, gun drilling of channels has been used to

allow for water ﬂow around the cores and cavities. As

demands have increased for increased productivity, re-

duced cycle times, improved part quality, and reduced

mold maintenance, new mold cooling technologies have

emerging.

A proven approach has been the use of evaporative

cooling technology to simplify the design and manufactur-

ing requirements of mold cooling by replacing gun-drilled

water lines. Evaporative cooling is achieved through a

‘‘cooling chamber’’ or water pocket that completely envel-

ops mold cooling surfaces. The water chamber ensures

even heat distribution without the engineering compro-

mise often associated with gun drilling. Using heat ex-

changers, evaporative cooling condenses the water, which

in turn is recycled throughout the sealed chamber. The

turbulent ﬂow of the water reduces any buildup of sludge

within the chamber that may impede mold cooling. To

reduce or eliminate corrosion issues, air is removed from

the cooling chamber prior to production. Use of a mold

temperature controller automatically senses and adjusts

water ﬂow to regulate heat levels during processing. The

advantages of evaporative cooling are both environmental

(reduced waster water, reduced energy costs) and design-

oriented (reduced engineering costs, reduced manufactur-

ing costs, simpliﬁed mold construction), resulting in

improved reliability. See Figures 4 and 5 for a detailed

view of evaporative versus gun-drilled cooling.

Part Ejection. There are two basic methods of part ejec-

tion: mechanical and air. Mechanical ejection commonly

uses stripper rings or pins surrounding each mold core, or a

moving core cap to physically push the parts off the cores.

The stripper rings can be activated by hydraulic cylinders

Table 1. Classiﬁcation of Molds

Lifetime Cycles Deﬁnition SPI Classiﬁcation Estimated Build Time (weeks)

Greater than 1 MM Super high production 101 12–20

Less than 1 MM Medium production 102 8–12

Less than 500 M Low production 103 6–8

Less than 100 M Low production 104 6–8

Less than 500 Low production 105 5–6

Low cavity high cycles Pilot mold (class 101) PM 8–12

Less than 500 Prototype PT o6

Source: Courtes y of TecMar Group.

588 INJECTION MOLDING FOR PACKAGING APPLICATIONS

attached to the machine platen, air cylinders in the mold,

or a mechanical linkage tied to the motion of the machine

platen. Air ejection uses blasts of air to loosen and blow the

parts off the cores. Air ejection is the more popular method

because it involves fewer moving parts and, hence, less

maintenance. The mold can also be more compact.

Alignment. The proper alignment of core and cavity is

critical in thin-wall molding. Slight misalignment leads to

preferential ﬁlling of the thicker part of the cavity, which

causes a pressure imbalance around the core and cavity,

thus further shifting the core. The overall result is uneven

wall thickness in the molded part. In extreme cases, it can

result in (a) incomplete ﬁlling of the cavity (i.e., a short

shot) and (b) rejected parts. To achieve satisfactory part

quality, center-to-center alignment of the core and cavity

within 70.2 mil (70.005 mm) may be necessary.

There are different methods of aligning the cores and

cavities of packaging molds. One common method is a

stripper ring that uses tapers on the stripper ring to align

the core and cavity. This popular method of alignment has

disadvantages for thin-wall molding, where alignment

forces cause relatively rapid wear of the stripper rings.

Since the stripper rings form part of the molding surface,

excessive wear in this area reduces part quality. To avoid a

drop in part quality, frequent mold maintenance is re-

quired. Wear is not critical if the locking rings are not part

of the molding surface. Either air or mechanical ejection

can be used with this approach.

The ﬂoating-core method is a more recent design that is

suitable for some packaging applications. The cores and

locking rings are not rigidly ﬁxed to the core plate, but are

allowed to ﬂoat to more easily align themselves with the

cavities. Easier alignment results in less wear on the

aligning tapers. This method can also be used with either

air or mechanical ejection.

Mold Materials. High-quality mold materials are of the

utmost importance. Most mold components are made of

through-hardened high-quality tool steel. Hardness

ranges from RC 49–51 (Rockwell C scale) for the cores

and cavities to RC 30 for the mold plates. Only periodic

rebuilding of wear items, such as stripper rings and

leaderpin bushings, is required.

Stack Molds. A two-level stack mold typically has iden-

tical sets of cores and cavities on each mold face, which are

then stacked together back-to-back. In the case of a family

stack mold, the cores and cavities differ between the two

faces, allowing similar or matched pieces (compact-disk

jewel case, ﬂoppy-disk shell, etc.) to be produced during

each cycle . Use of a stack mold almost doubles the produc-

tivity of a machine. F or these reasons, stack molds are

increasingly popular. Three- and four-level stack molds

have recently been introduced for thin-wall lids and contain-

ers to further increase machine productivity (see Figure 6).

THE THERMOPLASTIC INJECTION MOLDING MACHINE

A thermoplastic injection molding machine for Packaging

Applications can be described in seven parts:

1. The machine control and control architecture

2. The power plant

3. The injection unit

4. The clamp unit

5. The ejector mechanism

6. The base unit

7. Features speciﬁc to packaging applications

There are many different conﬁgurations of horizontal

clamp machines based on how they are powered. Hori-

zontal clamp machine varieties include:

. Hydraulic-operated machines with hydraulically dri-

ven clamps

Heat

exchanger

Cooling

water

Evacuated

chamber

Water/foam

Water

Figure 4. Evaporative cooling. (Photo courtesy of Ritemp Pty.

Ltd.)

Water

lines

Hot

spots

Cooled

spots

Figure 5. Gun-drilled cooling. (Photo courtesy of Ritemp Pty.

Ltd.)

INJECTION MOLDING FOR PACKAGING APPLICATIONS 589

. Hydraulic-operated machines with toggle-driven

clamps

. All-electric machines (only with toggle clamp)

. Hybrid machines utilizing hydraulic clamp and elec-

tric screw drive (see Figure 7)

Add to the above the vertical clamp design and there are

quite a lot of models to choose from depending on the

molding application. This article will address the horizon-

tal machine group that is most common for packaging

applications.

The Machine Control and Control Architecture

The injection molding machine performs all functions to

operate a mold in a fully automatic way. The machine

control and the control architecture sets the way in which

all machine devices perform together in the operation of

the mold. There are various control architectures, depend-

ing on the manufacturer. Modern control solutions center

on ‘‘bus-type’’ controls that provide fully digital control

operation of smart devices like smart pumps, smart val-

ving, and digital transducers (see Figure 8). ‘‘Smart’’

means that devices carry their own electronics on-board

to communicate with the central industrial PC-based

controller. Wiring and overall machine complexity is

drastically reduced over traditional ‘‘analogue’’ not-smart

device control architectures. Diagnostics and maintenance

too is greatly simpliﬁed. The machine control carries all

the software programs of sequences and ﬁnite machine

control in the operation of the mold. Screen pages are

separated into their speciﬁc functions such as clamp,

injection, and ejection phases. Controls are intuitive and

user friendly.

The Power Plant

The power plant is very important to the effective and

efﬁcient operation of the injection molding machine (see

Figure 9). Modern trends toward the All-Electric machine

conﬁguration is telling of the great need to reduce power

consumption and energy costs associated with injection

molding. The all-electric design, although more expensive

than its fully hydraulic machine counterpart, allows for

great power savings. Typically, as much as or more than

50% power savings is attributed to the All-electric design

versus hydraulic machine designs. Digital Bus-Type con-

trol architectures (even in hydraulic clamp/injection ma-

chines) as well provide energy savings due to the

Figure 6. A three-level, 12-cavity mold for 5-qt containers

utilizing a patented modular mold change feature. (Photo

courtesy of Top Grade Molds.)

Figure 7. Electric screw drive and hydraulic toggle clamp are

the main features of the machine shown. (Photo courtesy of Negri

Bossi.)

Figure 8. PC-based machine control with CanBus DIGITAL

control architecture. (Photo courtesy of Negri Bossi.)

590 INJECTION MOLDING FOR PACKAGING APPLICATIONS

reduction of machine components required. A ‘‘smart’’

hydraulic pump that controls its own pressure and ﬂow

eliminates the need for a separate hydraulic manifold

block to perform the same function. This reduces not

only energy usage but also the number of components,

allowing for very cost-effective operation.

The Injection Unit. Raw plastic material from the resin

maker is processed by the injection unit of an injection

molding machine. It is the most critical device in the

control of the ﬁnal plastic part’s quality. The process is

organized in sequences of the operation of the injection

unit as follows: injection shot size, speed, injection and

hold pressures, plasticizing recovery rate (melting/shear-

ing rate of the plastic as a function of screw rotational

speed), and backpressure (as a function of the resistance

pressure on the screw to melt the plastic during plastici-

zation). The injection unit also functions to move the

nozzle and apply pressure onto the mold. It does this via

‘‘carriage’’ hydraulic cylinders operating on both sides of

the injection unit (see Figure 10).

Determination of the injection pressure will depend on

the wall thickness of the part (t), the length of ﬂow (L)of

the plastic resin from gate entry into the part to its ﬁnal

stopping point, and the force of injection created by the

injection unit. The higher the L/t ratio (called the aspect

ratio), the greater the injection forces and pressures

required for injection. Typically, thin-walled packaging

applications require injection forces greater than

30,000 psi and very fast plasticizing rates. Most packag-

ing applications hover between 5 and 10 s of cycle time

(even o5-s cycle times) so rapid actions of the injection

unit are vital in meeting this requirement. The type of

injection unit used most commonly is the reciprocating

screw driven rotationally by an electric motor and linear

movement driven by hydraulic cylinders. To reach the

high speeds of injection, hydraulic accumulators (energy

storage devices) are used to instantaneously drive the

cylinders and therefore screw forward. The hydraulic

power plant of the machine is engineered to allow mold

opening and hydraulic ejection during the screw plasticiz-

ing mode. These ‘‘overlapping’’ motions in the sequence

are designed to reduce the cyle time to its minimum,

thereby maximizing machine and mold production output.

Every aspect of machine design is tailored to maximize

production output. Most often it is not the machine which

creates delays in the production of plastic parts. The mold

construction, quality, and the rate of part/mold cooling will

determine the ﬁnal production output. Advances in mold

cooling technology as described in Figure 4 greatly reduce

cycle time and increase part production.

The Clamp Unit

The main purpose of the clamp unit is to hold the mold

closed under the force of plastic injection pressure that is

trying to force the mold open (see Figure 11). Its design

takes into consideration the objective of fast and precise

operation while protecting the mold from damage should a

plastic part get trapped from improper ejection or some

part of the mold somehow interferes with the proper and

complete mold closing sequence. This feature is called

simply ‘‘mold protection.’’

Clamp units come in two different operating types: the

toggle clamp (hydraulic or electrically operated) and the

fully hydraulic clamp. The toggle clamp’s advantages are

its fast operating speed and natural geometric motion of

high-speed acceleration, maximum velocity, controlled

deceleration to ﬁnal mold closing, and sensitivity on

mold protection. The fully hydraulic clamp features

capabilities to mold deep-draw parts such as extra large

Figure 9. The power plant under the injec-

tion unit displays a double smart pump and

motor system on this 700-ton electric–hy-

draulic hybrid machine. The oil tank is

located between the smart pumps. The

guarding is partially removed from the in-

jection unit for this photo. (Photo courtesy of

Negri Bossi.)

Figure 10. The injection unit displayed here shows a stainless

steel purge guard over the heated barrel and hydraulic carriage

cylinders (both sides). (Photo courtesy of Negri Bossi.)

INJECTION MOLDING FOR PACKAGING APPLICATIONS 591

deep-draw containers and is usually engineered into

larger machines.

Clamp rigidity, precise alignment/parallelism, and op-

eration is of prime importance because of the extreme

forces generated to hold the mold closed during injection.

The machine’s stationary platen and moving platen’s

deﬂection is of great concern; as a result, the most

advanced metals, casting methods, and machining pro-

cesses are typically used in their construction in order to

minimize it.

The Ejector Mechanism

Molten thermoplastic resin, when cooled, shrinks onto the

‘‘core’’ of the mold and requires some force to eject it. This

can be done in two ways: (a) via an air blast originating

from the mold itself or (b) this in combination with

mechanical ejector rods operated by the machine which

in turn operate mold ejection surfaces. By their very

nature, packaging applications produce ultra-thin parts.

These ultra-thin parts in a relatively ‘‘warm’’ condition

ﬁxed to the mold core can create a problem during ejec-

tion. The part could deform if only mechanical ejection is

used. Most thin-walled parts take advantage of the mold

air eject feature to break the vacuum created between the

part and the metal surface of the core.

The Base Unit

The importance of this part of the machine’s construction

should not be underestimated. The base unit houses all of

the major components described above. It carries the

weight of these large components and connects them

into one cohesive structure.

The base unit can be engineered in different ways, but

almost all designs center on the ‘‘box tubular steel’’ welded

constuction. This provides the necessary rigidity,

strength, and stage for the operation of all components.

Features Speciﬁc to Packaging Applications

Thus far the machine description has been universal.

Packaging applications demand features of the mold and

machine dedicated to it. The packaging mold has been

described in detail in this article. The packaging machine

needs further clariﬁcation on design features which sepa-

rate it from universal applications. Here is a summary and

description of those features required by packaging

applications:

. Hydraulic Accumulator-Assisted Injection. As de-

scribed earlier in this article, this feature increases

the velocity of injection in order to ﬁll the cavity

completely in a thin-walled mold. Instantaneous

energy is directed to the injection unit to affect

o0.5- to 1.0-s injection times.

. Positive Nozzle Shut-off. This feature allows the

screw to rotate and plasticize resin while the clamp

is opening. It prevents drool out of the nozzle during

screw recovery/plasticizing.

. Independent Plasticizing (Mold Opening During

Plasticizing Phase). This feature allows faster cycle

times of the machine/mold operation.

. Independent Ejector Motion (Mold Opening and Ejec-

tion Simultaneously). This feature also allows fas-

ter cycle times of the machine/mold operation.

. High-Pressure Injection (30,000 psi or Greater). Pres-

sure is the result of restriction to ﬂow. Due to the

thin-wall restriction of the mold, greater forces and

speeds of injection are required to completely ﬁll the

cavity. The forces here are created by the accumula-

tor assisted injection described above. Keeping the

screw size as small as possible also aids in higher

injection pressures (pressure = force/area).

. Barrier Screw for Higher Plasticizing Rates. This

type of screw is sometimes called a ‘‘double-wave’’

screw. The ﬂights of the screw are doubled for

greater shearing capacity and therefore greater

plasticing/melting output. Another beneﬁt is the

greater mixing of the melt which aids in better

part quality and processability. Typically, barrier

screws are best suited for the polyoleﬁn materials

such as polyethylene. A thermoplastic material in

high use for packaging applications.

. High-Flow Check Ring. The objective is to minimize

any restriction to the ﬂow of plastic material. High-

ﬂow check valves located on the tip of the screw do

just that.

. Magnetic Resin Filter under Hopper. Entry points of

the plastic into the mold are very small, in the area of

0.04 in. (1 mm) and smaller. Any foreign matter and

especially metal can damage the mold or get trapped

in the mold, creating ﬂow restrictions. The magnetic

ﬁlter assists in removing these contaminants.

. Air Ejection Valves (for Mold Air-Eject Sequence). As

described earlier in this article, the plastic part

shrinks onto the mold core due to cooling and creates

air-lock that needs

to be broken for safe and

effective ejection of the part.

Figure 11. The clamp unit displayed here shows the moving

platen with T-slots for ease of mold mounting. (Photo courtesy of

Negri Bossi.)

592 INJECTION MOLDING FOR PACKAGING APPLICATIONS

. Hot Runner Temperature Controls. The hot runner

system in the mold requires temperature controls to

affect the heat energy directed to the molten plastic.

. Possible Hot Runner Valve Gate Hydraulic Valve and

Control. Periodically, a type of hot runner system

known as a Valve Gate System is required to posi-

tively shut off the plastic ﬂow directly at the cavity

entry point (gate). This is done by a metal pin in the

ﬂow of the plastic operated by a piston in the mold.

The control of the valve gate piston can be done

pneumatically or hydraulically. The machine would

then be ﬁtted with a pneumatic or hydraulic valve to

activate the valve gate piston.

. Possible Parts Blow-Down after Ejection. Multicav-

ity molds eject parts that fall at the speed of gravity.

In order to quicken the speed of the machine/mold

operation (reduce cycle time), a blast of air directed

downward on the parts can be beneﬁcial in reducing

the time it takes for the parts to clear the mold and

allow it to close unhindered.

. Increase Power Plant Horsepower. In order to supply

the instantaneous power requirements for pack-

aging applications, the machine’s power plant needs

to be engineered accordingly. Pumps, motors, and

valves must be sized properly and integrated with

the machine control architecture to create condi-

tions for ultra-fast and ultra-precise operation.

AUTOMATION FOR INJECTION MOLDING MACHINES

The process of injection molding does not end with the

part being ejected from the machine. Somehow the part

must get from the ejection sequence to the carton box in

which the part will be shipped, or on to a secondary

process such as subassembly with other parts. This pro-

cess is called ‘‘downstream part handling,’’ and there are

many ways to do this. Parts could drop directly into the

shipping box if there are no cosmetic abrasion concerns. It

is certainly the least expensive way without need of any

handling equipment. An operator could manually take

parts off a conveyor belt and stack them into the shipping

box? Or a better, more cost-effective way would be to

automate the process fully and eliminate the need for

costly manual labor while protecting the quality of the

part molded.

Automation can take on many different forms. It can

start right at the mold with specialized mold chutes

designed to carry the parts to another station that

packs them into boxes. It could be various robotic equip-

ment such as three-axis or six-axis robots programmed

for sequenced action (see Figure 12). These robots

could stage a secondary process where parts are wrapped

or stacked or printed or any other process required.

Automation can perform quality control procedures

such as weighing, inspecting, dimensioning, and so on.

Indeed, every approach to automating plastic-molded

part production is a creative process, and the choices

available are extensive, impressive, and worthy of

investigation.

MONITORING AND SERVICING THE MACHINERY

Every second of production downtime costs money and

valuable resources in a molding company. There is a great

need to diagnose and monitor the machine operation

including visual imagery from wherever the production

manager is located, be it in the plant or out of town on

business or even at home in critical situations. It is

identically vital that the machine maker’s service techni-

cian access real-time machine data and visual imagery

from wherever they are in the name of responsive service

and uptime for their customer, the molder.

Internet technology has made the above scenario pos-

sible. Real-time data on the machine process is now

available via secure networks with access to any internet

location worldwide. This 21st-century technology is revo-

lutionizing the service, monitoring, and control of injection

molding machines. It makes the job of servicing machines

easier, faster, and better like never before. Problems get

diagnosed immediately via the internet through secure

levels of access. The manpower, tools, and parts needed to

make the ﬁx are prepared ahead of the travel to the

machine’s location. The jobs are done effectively, efﬁ-

ciently, and at minimum cost to the service company

and/or molder, depending on cause. For the ﬁrst time in

the evolution of the injection molding machine, the custo-

mer and machine maker have the power over every aspect

of machine operation in realtime. One system made by a

well-known machine maker also allows real-time changes

to be made to machine parameters/settings remotely via

any internet location worldwide. This is by far the most

powerful service tool ever devised for injection molding

machines. See Figure 13 for a graphical explanation of a

unique remote teleservice system that works with a

Figure 12. Floor-mounted 6-axis articulating robot. Models also

come in platen-mounted designs. End of arm tooling not shown.

(Photo courtesy of KUKA Robotics.)

INJECTION MOLDING FOR PACKAGING APPLICATIONS 593

patented wireless communication system between ma-

chine and central PC.

BIBLIOGRAPHY

F. Johannaber, Injection Molding Machines—A User’s Guide, Carl

Hanser Verlag, Munich, 1985.

H. Rees, Understanding Injection Molding Technology, Carl Hanser

Verlag, Munich, 1994.

B. James, Ritemp Pty. LTD, Australia, An Introduction to the

Latest Development in Mold Cooling Technology, Gardner

Publications, New York, 2006.

T. Schwenk, Process and Design Technologies, Building a Better

Injection Mold, 2007.

R. Carter, Injection Molding, Wiley Encyclopedia, New York, 1997.

Contributors

R. Carter, Injection Molding, Wiley Encylopedia, 1997 (written

portions of the section entitled ‘‘The Thermoplastic Injection

Mould’’).

W. Stoddard, TecMar Group, Georgetown, Ontario, Canada (writ-

ten portions of the section entitled ‘‘The Thermoplastic Injec-

tion Mould’’ and the graphics: Chart 1, Figure 3: Evaporative

Cooling and Figure 4: Gun Drilled Cooling).

Top Grade Molds, Mississauga, Ontario, Canada (Figures 2, 3,

and 6).

KUKA Robotics, Clinton Township, Michigan, USA (Figure 12).

Negri Bossi Inc., Mississauga, Ontario, Canada (Figures 1, 7, 8, 9,

10, 11, and 13)

INKS

R. W. BASSEMIR

A. J. BEAN

Sun Chemical Corporation

INTRODUCTION

Printing ink is a mixture of coloring matter dispersed or

dissolved in a vehicle or carrier, which forms a ﬂuid or

paste that can be printed on a substrate and dried.

Printing inks are used to decorate the exterior of virtually

every package and substrate used in packaging. Since

there are various substrates, a number of different print-

ing methods are required to satisfy the needs of this entire

market (1). In general, the inks required may be subdi-

vided into two classes: liquid inks and paste inks. The

liquid inks include those printed by the ﬂexographic,

rotogravure, and screen process methods; the paste inks

include those printed by lithographic offset, letterset, and

letterpress (see Decorating; Printing).

Basically, all printing inks consist of a colorant (see

Colorants), which is usually a pigment but may be a dye,

and a vehicle that acts as a binder for the colorant and a

ﬁlm former. Vehicles generally consist of a resin or poly-

mer and a liquid dispersant, which may be a solvent, oil,

or monomer. Many other additives are used to provide

some speciﬁc property or function to the ink or ink ﬁlm.

Approximate viscosities and ﬁlm thicknesses used in

different printing processes are given in Table 1. The

four key properties of ink are drying, rheology, color, and

end use.

LIQUID INKS

Flexographic Ink

Flexographic printing utilizes a rubber or plastic printing

plate and is essentially a typographic process, printing

from a raised area. The inks used are very low in viscosity

(see Table 1) and dry rapidly because of their relatively

high volatility. Since the printing press used has a very

simple ink distribution system, these volatile inks do not

cause problems in drying on the inking rollers. The

thickness of the ink ﬁlm is controlled by the depth of

engraving used on the anilox inking roller. The commer-

cial speeds used for this type of printing range from 500 to

1000 ft/min (152–305 m/min). Flexographic ink accounts

for more than half of the ink utilized in decorative

packaging.

Flexographic inks may be subdivided into two general

classes: solvent-based and water-based. The volatile sol-

vents selected for the formulation must be chosen with

care, since they are in constant contact with the plate

elastomer. It is important to screen these ink solvents with

the plate and roller elastomers to ensure that no swelling

Figure 13. A graphical representation of a remote teleservice system utilizing patented wireless connectivity between machine and

central PC. Real-time monitoring, diagnostics, and real-time machine control changes can be made remotely via any internet location

worldwide. (Graphic courtesy of Negri Bossi.)

594 INKS

or attack of the surface takes place. In most cases, alcohols

are the material of choice for solvent-based ﬂexographic

inks, with additions of lower esters and small amounts of

hydrocarbons. These are used as needed to achieve solu-

bility of the vehicle resin and proper drying of the ink ﬁlm

at press speed. Solvent blends are required to achieve the

best balance of viscosity, volatility, and substrate wetting

and must also take into account EPA (Environmental

Protection Agency) requirements.

Water-based inks have increased in popularity because

of air pollution concerns and are being used in increasing

amounts for both absorbent and nonabsorbent substrates.

The solvent used in these inks is usually not 100% water.

They may contain as much as 20% of an alcohol to increase

drying speed, supress foaming, and increase resin compat-

ibility. The wetting of plastic substrates is also greatly aided

by the lower surface tension of the alcohol–water mixture.

The resins and polymers used in the ﬂexo-ink vehicles

cover a wide range of chemistry and are selected to

achieve adhesion to various substrates or to confer resis-

tance properties to the dried ink ﬁlm. A number of resin

classes and the substrates upon which they are generally

used are shown in Table 2. Note that the water-based

vehicles are listed in a separate portion of the table, since

they are generally emulsions or colloidal dispersions

rather than true solutions.

A generic formulation for an aqueous ﬂexographic ink

(components amounts are in %, w/w) is as follows: pigment

dispersion, 35–50; emulsion vehicle, 25–35; solution

vehicle, 10–20; amine neutralizer, 0.5–1.5; wax emulsion

compound, 2–5; wax powder, 0–2; surfactant, 1–1.5; cross-

linking additive, 0–2; silica additive, 2–5; corrosion inhi-

bitor, 0–1; defoamer, 0–1, other additives, 0.25–0.5 (2).

Gravure Ink

Gravure printing utilizes an etched or engraved cylinder to

transfer ink directly onto the substrate. Because of the

mechanics of ﬁlling the very small cells, the viscosity of

gravure inks must be relatively low (see Table 1). This is

also required in order to transfer ink from the engraved

cells at high speeds. The rotogravure press uses a simple

inking system, where ink is applied directly to the gravure

cylinder and excess ink is scraped off with a doctor blade.

The ink-ﬁlm thickness is determined by both the depth of

engraving and the area of the cells, because these two

factors determine the volume of ink transferred. Commer-

cial speeds vary from 800 to 1500 ft/min (244–457 m/min) or

more. Gravure ink is the second-largest category of packa-

ging inks. Together with ﬂexographic ink, these two liquid

inks account for more than 80% of all packaging ink.

Rotogravure inks can also be classiﬁed as solvent-based

or water-based types. The solvent-based inks are not as

restricted by plate compatibility problems as are the

ﬂexographic inks because the plate is metal and resistant

to nearly all solvents. Since a wider variety of solvents

can be utilized in manufacturing a rotogravure ink, a

much wider range of resin types and resin molecular

Table 1. Ink Viscosity and Film Thickness by Process

Process Viscosity, Poise (Pa  s) Printed Film Thickness (mm)

Lithography 50–500 (5–50) 1–2

Letterpress 20–200 (2–20) 3–5

Flexography 0.1–1 (0.01–0.1) 6–8

Gravure 0.1–0.5 (0.01–0.05) 8–12

Letterset 30–300 (3–30) 1.5–3

Screen 1–100 (0.1–10) 20–100

Table 2. Liquid Ink Applications for Packaging: Flexographic and Gravure

Paper/paperboard Foil PE PP Vinyl PET Cellophane

Solvent Ink Systems

NC–maleic X X X X X

NC–polyamide X X X X X

NC–acrylic X X X

NC–urethane XX

NC–melamine X X

Chlorinated rubber X X

Vinyl X X

Acrylic X X X X X

ASP–acrylic X X

CAP–acrylic X X

Styrene X

Water Ink Systems

Acrylic emulsion X X X X X X X

Maleic resin dispersion X X

Styrene–maleic anhydride resins X X X X

NC, Nitrocellulose; ASP, alcohol-soluble propionate; CAP, cellulose acetate propionate.

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weights can be utilized in achieving the desired ink

properties. This means that gravure inks for packaging

can be tailored for good adhesion to the widest selection of

substrates. Historically, there are 10 gravure inks cate-

gorized by the binders or solvents used: A, aliphatic

hydrocarbons; B, aromatic hydrocarbons; C, nitrocellu-

lose; D, polyamide resins; E, SS, nitrocellulose; M, poly-

styrene; T, chlorinated rubber; V, vinyls; W, water-based;

and X, miscellaneous. Many of these classiﬁcations are

blurring as blends of these materials are becoming more

common (1).

The resins and polymers used in packaging gravure

vehicles cover a wide range of chemistries and are chosen

to achieve adhesion to various substrates or to confer

speciﬁc properties to the ﬁnished ink ﬁlm. These are listed

in Table 2.

Approximately 50% of all ﬂexographic inks use water

as their primary solvent and diluent. Water-based gravure

inks are used widely for printing paper and paperboard

substrates, and their use for nonpaper substrates is

growing because of concern about air pollution. The for-

mulation of these inks is very similar to those used in

water-based ﬂexography and the polymers are also very

similar. These are listed in a separate section of Table 2.

Main advantages of water inks include excellent press

stability, printing quality, heat resistance, absence of ﬁre

hazard, and convenience of water for reduction and wash-

up. The main disadvantage of water inks is the increased

energy required for drying due to the high latent heat of

water. A signiﬁcant problem that can occur with water-

based inks in gravure is the drying of the vehicle polymer

or resin in the engraved cells. This can occur during

shutdowns of the press. Some of these materials are not

readily resoluble once they have dried because they are

usually emulsions or colloidal dispersions in water. To

assist in the drying of water-based inks, the gravure

cylinders are usually engraved or etched with shallower

cells. A thinner ink ﬁlm is applied, which contains less

water to evaporate. This also means, however, that the

amount of pigment in the press-ready ink must be higher

in concentration to achieve the same relative printing

density as the solvent-based ink.

Uses. Type C inks are the dominant group used in

packaging gravure. Type C is used for printing on foil,

paper, cellophane, paperboard, coated and uncoated paper,

glassine, acetate, and metallized paper. Type A and B are

used for gift wrapping paper. Type D inks have excellent

adhesion to many plastic ﬁlms. This type ink is used in

foil, paper, and paperboard. Type E includes a wide variety

of inks and lacquers and some dye inks. They are often

used on paper and paperboard, some grades of cellophane

shellac, or nitrocellulose primed foil pouch stock glassine

and other coated speciality products. Type T inks show

extremely good resistance to alcohol and soap. They are

considered high-quality inks. Type W gravure inks, pri-

mers, and lacquers are used to comply with VOC emission

standards. Water inks are primarily used in packaging

gravure on board and paper. Type V inks are used for

printing vinyl ﬁlms and Saran (1).

Screen Ink

Screen printing, which accounts for a relatively small

percentage of ink used in the packaging market, is used

on low-volume specialty items or where very thick ﬁlms

are desired (see Table 1). Screen ink is included in the

liquid-ink section because of its paintlike rheology and

chemistry.

Screen inks are applied by squeegeeing the ink through

a stencil screen with a rubber blade. The inks must have

adequate ﬂow to pass through the screen, but must also

have enough body to resist dripping and stringing when

the screen is lifted. For many years this was a hand-

printing operation, but has now become largely mecha-

nized due to the development of rotary screen technology

which allows screen units be inserted in-line with other

printing technologies on web-fed combination presses. The

two largest classiﬁcations of screen inks are solvent types

and plastisol types, although water-based, radiation-cur-

ing, and two-part catalytic systems are also available.

Substrates need not be ﬂat, because oval and round forms

can be printed.

Lamination Inks

These inks must not interfere with the bond that is formed

when two or more ﬁlms are bonded together to obtain a

structure that provides more resistance than is found in a

single ﬁlm. Laminations are used in candy and food

wrappers. Resins used for this ink cannot exhibit any

tendency to retain solvent because this would contaminate

the product. In addition to polyamides, these inks contain

modiﬁers such as polyethylene resins, plasticizers, and

wax. Laminations are usually reverse-printed and end up

sandwiched between ﬁlms. Water-based inks are being

tested for their functionality and ability to meet U.S. EPA

emission standards.

PASTE INKS

Offset Lithographic Ink

Lithographic printing uses a planographic plate in which

the ink-receptive image is chemically differentiated from

the nonimage area. Since these plates are constantly

wetted with a dampening solution, the inks must resist

the chemicals contained in these solutions without chang-

ing in their printing characteristics. The thickness of the

ink ﬁlm in this process is 1–2 mm, which is the thinnest

ﬁlm in any commercial process. Because of this, the

colorant concentrations in lithographic inks are generally

higher

than those found

in inks for other processes.

Lithographic inks generally have relatively high viscos-

ities due to the ink-distribution systems used on the press

equipment for this process. It is also common to ﬁnd a

gelled consistency in the body of these inks because of the

need to obtain high printing resolution and faithful re-

production of the plate image. Image quality of half-tone

reproduction is extremely high.

Sheetfed Offset Lithography. A large segment of com-

mercial prinitng is done on sheet-fed presses almost

596 INKS

entirely by the litho process. Inks for these presses are

based on vehicles containing phenolic-modiﬁed, maleic-

modiﬁed, or unmodiﬁed rosin-ester resins dissolved in

vegetable-drying oils and diluted with hydrocarbon resins.

Special acrylic resins have been developed for use in

quickset inks, and they offer nonskinning properties and

excellent press stability. This process is widely used for

printing on packaging board, paper, metal, and plastic

sheets. The use of the offset blanket permits excellent

reproduction even on surfaces that are not entirely ﬂat

owing to the compressibility of the blanket material. The

inks used for most conventional sheetfed printing are

dried by an oxidative process and may also be accelerated

by the use of infrared radiation. These inks set rapidly in a

matter of seconds, but are not truly dry for several hours.

In the case of metal, the inks are usually reactive only at

high temperatures of Z3001F(Z1491C), which are

achieved by passing the metal sheets through a heated

oven after removal from the press.

Drying of sheet-fed lithographic inks can be done with

ultraviolet radiation, which is applied by means of high-

powered mercury arc lamps immediately after printing.

This process is widely used in the production of packaging

that must be die cut and ﬁnished in-line, such as cartons

for cosmetics and alcoholic beverages. Ultraviolet drying of

the ink offers signiﬁcant energy savings in metal decorat-

ing where it replaces long, energy-consuming ovens.

Web Offset Lithography. In web offset, the same litho-

graphic principles that are used in sheet-fed lithography

are applied to the printing of the substrate in the form of a

web. The web of the substrate is fed into the printing press

for decoration from a large roll. The printed substrate,

upon exiting the press, must be dried immediately so that

the ﬁnished product can either be rewound, sheeted, or

ﬁnished in-line. The most common method to dry the

printed ink immediately is the utilization of a high-tem-

perature oven that employs recirculated hot air at a

temperature of about 250–3501F(121–1771C). For this

reason, the handling of plastic substrates is generally not

possible because of the distortion of the substrates at these

high temperatures. Drying inks with ultraviolet or electron

beam radiation allows the printing of temperature-sensi-

tive substrates. Generally, web offset printing in packaging

is conﬁned to paper and board printing. However, drying

technology utilizing radiation curing promises to offer the

packaging market the advantages of high-speed printing,

the quality of offset lithography, and the lower cost of offset

plates compared to gravure cylinders. Typical speeds for

web offset printing are 800–1200 ft/min (244–366 m/min).

Letterset Ink

This printing process, formerly known as dry offset, is a

combination of letterpress and offset in that the printing

plate uses raised images, but the printing on the substrate

is accomplished with a rubber blanket. Therefore, the inks

used in letterset generally have the viscosity and body of a

letterpress ink. The predominant use of letterset printing

in packaging is for the decoration of two-piece metal cans

(see Metal cans, fabrication). Plastic preformed tubs and

containers are also printed utilizing the letterset process on

a mandrel press. Two-piece can printing is accomplished on

special presses that produce at the rate of 1200 cans per

minute with up to ﬁve colors and a clear varnish. The inks

for beverage cans are generally dried by heat.

Ultraviolet drying is used by several metal-decorating

printers, primarily for beer cans. Ultraviolet is widely

used for curing plastic containers where thermal sensitiv-

ity is a serious problem and heat curing cannot be used.

The metal-decorating ovens used for thermal curing have

recently gone to short cycles that use temperatures of

6001F (3161C) for only a few seconds to cure the inks.

These inks are used primarily for ecological reasons (3).

Letterpress Inks

These inks are used primarily for printing corrugated

packaging (see Boxes, corrugated), although small

amounts are still used for folding-carton and multiwall-

bag (see Bags, paper) printing. Since letterpress uses

raised images, the inks are fairly heavy in body (Table

1), and the primary mechanism for drying is oxidative or

absorptive. The inks are generally formulated in a manner

similar to sheet-fed offset inks but with a slightly lower

viscosity. This printing method has been losing market

share to the other printing processes for a number of years

because of high preparatory and labor costs. This is

particularly true in corrugated printing, which is going

primarily to water-based ﬂexography.

ENVIRONMENTAL CONCERNS

Speciality inks are a sector of the chemical industry.

Federal regulations fall under the auspices of the United

States Environmental Protecion Agency and the Depart-

ment

of Labor and

to a lesser degree the Food and Drug

Administration. Some states and voluntary guidelines

also impact ink.

In general, environmental concerns affect various in-

dustries involved with ink. These include the converting

industry that uses inks to produce packaging and printed

matter of all types and even extends to issues related to

the ultimate end-user companies whose printed or pack-

aged products are often distributed around the world.

Common environmental aims such as reducing air

pollution, use of renewable resources rather than crude-

oil based chemistries, biodegradable inks and coatings,

and the pressure to recycle waste materials back into the

raw materials supply impact the printing ink industry.

Over the past 20 years, new ink products have been

developed and will continue to be developed in response

to environmental issues.

The United States has been among the most highly

regulated countries in the world. Beginning in the 1970s

and continuing through the 1990s, there was a persistent

ﬂow of regulations governing not only printing processes

but also the use and disposal of printed matter. A clear

historical account of the effect of antipollution laws and

the ink industry can be traced. Since the late 1980s,

Canadian, Asian, and European markets have had a

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