Yam, Kit L. (ed.). The Wiley encyclopedia of packaging technology

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Maintaining Consistent Stretch Levels

To measure the degree of stretch your ﬁlm achieves, you

need only three tools: a stretch wheel, a tape measure, and

knowledge of a simple mathematical formula.

A stretch wheel is 10 in. in circumference, rotates on an

axis, and is held in place by a handle. Jutting out from this

wheel is an ink mark that makes a black mark every 10 in.

on a roll of unstretched stretch ﬁlm when the wheel is

allowed to rotate freely against the ﬁlm.

To measure exactly how much a sheet of ﬁlm has

stretched, roll your wheel horizontally against the outer

layer of ﬁlm while it is on the spindle of the machine.

Make sure that at least four black marks have been made.

Initiate the wrap cycle so that the ﬁlm is stretched.

Measure the distance between the marks. (Note: Make

sure that you measure the marks that do not cross

corners, but are on the ﬂat side of the pallet.)

Now, using your mathematical formula, subtract 10 in.

from your measured distance and multiply that difference

Figure 8. Black specks—degraded polymer or other ﬁlm imper-

fections caused by a foreign material. Not a common problem.

Gives appearance of poor ﬁlm quality.

Figure 9. Roll telescoping—the sliding of inner layers of the ﬁlm

in a roll or the core out of a roll, increasing roll width and making

the roll unusable. This is typically caused by tackiﬁer levels and

winding conditions.

Figure 10. Feathered edges—extension of a layer or layers of

ﬁlm past the end of a ﬁlm roll. Caused if the ﬁlm wanders back

and forth during winding. If these loose edges fold over, they may

cause spiral tears during ﬁlm unwinding.

Figure 11. Scalloped edges—sawtooth-appearing ﬁlm edges

caused by poor slitting. Can cause web failure from edges.

Figure 12. Gauge bands—hard or soft rings on a roll of ﬁlm,

caused by gauge (thickness) variations in the ﬁlm. Normally,

gauge bands do not result in any wrapper failure. If a failure does

occur, it will come from a wrinkle in the band area. It will appear

as a slit starting between the prestretch rolls.

Figure 13. Tails–overwind—material that is disrupted by the

automatic index or transfer of the winder. During the transfer

from a full roll to any empty core, the web tends to draw in and

wrinkle. This allows additional air to be trapped and results in a

disrupted ﬁlm appearance.

508 FILM, STRETCH

by 10. The answer is the percentage of stretch that ﬁlm

has endured.

Example: After a sheet of ﬁlm has been stretched, the

distance between the two black wheel marks reads 27 in.

Subtract 10 from this number (2710 = 17), and then

multiply 17 by 10 (17 10 = 170). (Answer: The ﬁlm was

stretched 170%.)

FILM PROBLEMS

There are some problems that can occur when using

stretch ﬁlm. As seen in the preceding section (‘‘Inspecting

and Handling Stretch Film’’), some of these problems are

manufacturer-related and some are shipping related.

Stretch-ﬁlm problems can also stem from equipment con-

ditions, wrapping speeds, and operator ignorance. How-

ever, as long as you know how to identify these problems,

most have correctives.

This section focuses on how to spot common stretch-

ﬁlm problems and what you can do to rectify them when

they arise. Stretch ﬁlm failures and solutions will be

covered under

. Film breaks

. Film ‘‘tails’’

. Tackiﬁer buildup

Film Breaks

There are three common ﬁlm breaks that can be identiﬁed

by the way the stretch ﬁlm tears. These breaks and the

solutions required to repair them are described in the

following list.

Edge. An edge tear starts at the top or bottom of a roll

and tears in a diagonal direction. It is usually caused

by a nick in the ﬁlm edge. To ﬁx the problem, simply

unwind the ﬁlm until the imperfection is gone. (See

Figure 14.)

Ultimate Break. An ultimate break is a straight-line

break with pointed edges. The break occurs when

the ﬁlm has been prestretched beyond its limits. To

avoid this type of break, reduce the percentage of

prestretch on your machine. (See Figure 15.)

Gel. A gel is a V-shaped break in the ﬁlm caused by

resin imperfection or some other manufacturing

problem. Before replacing this roll of ﬁlm, ﬁrst try

to correct the problem by lowering the F2 and/

or prestretch percentage on your machine. (See

Figure 16.)

Figure 14. Film break at edge.

Figure 15. Ultimate break.

Figure 16. Gel or V-shaped break.

FILM, STRETCH 509

Film ‘‘Tails’’

A stretch-ﬁlm ‘‘tail’’ is a loose end piece of stretch ﬁlm that

hangs off a wrapped pallet.

Tails loosen or fall down on wrapped pallets if cling is

too low or there is too much dust on the ﬁlm. But tails

occur primarily because ﬁlm is cut off under tension. To

avoid creating tails, the ﬁnal wrap should be made with a

reduced stretch percentage and lowered F2 so that the

ﬁlm elasticity does not pull the tail free of the load.

Tackiﬁer Buildup

Tackiﬁer, the most common of which is PIB, is an additive

responsible for giving blown stretch ﬁlm its cling. Over

time, tackifying agents will build up on machine rollers. If

allowed to accumulate, tackiﬁer residue can cause stretch

ﬁlm to stick to the rollers and to itself.

To avoid this scenario, machine rollers should be

cleaned on a regular basis. It is advised that a mild

detergent (isopropyl alcohol makes a good cleaner),

warm water, and a nonabrasive cloth be used for this

purpose because of the sensitivity of the machine rollers.

ENVIRONMENTAL EFFECTS ON FILM

The strength and protection stretch ﬁlm affords the

packages it wraps has made it the unitizing material of

choice among thousands of businesses worldwide. But this

is not to say that stretch ﬁlm is without its limitations.

There are certain environmental and physical conditions

that can impair regular stretch ﬁlm’s performance. This

section reveals what these conditions are so that you can

avoid them and get the most out of your stretch ﬁlm. The

topics discussed are

. Outside storage

. Static discharge

. The effect of temperature on ﬁlm

. The effect of dust and grit on ﬁlm

. Stacking pallets

Outside Storage

Regular stretch ﬁlm is not designed for prolonged outside

storage. Stretch ﬁlm is subject to photodegradation from

the ultraviolet rays in normal sunlight, which substan-

tially weakens the ﬁlm.

If wrapped pallets are to be stored outside for more

than several weeks, they should be covered. Otherwise, for

prolonged outdoor applications, specially formulated ul-

traviolet-irradiation (UVI)-stabilized ﬁlms should be used.

With UVI ﬁlm, UV protection is optimized when used in

conjunction with opaque tinting.

Static Discharge

Stretch ﬁlms will support a static discharge and, there-

fore, should not be used in explosion-prone environments.

Since stretch ﬁlm can induce a static charge, electronic

devices packaged in stretch ﬁlm run the risk of suffering

damage. Static buildup, however, can be dissipated

through use of Christmas garland or static eliminators.

Effect of Temperature on Film

Generally, higher temperatures make ﬁlm softer and

easier to deform. Lower temperatures make ﬁlm stiffer

and harder to stretch and deform. At higher temperatures,

where ﬁlm is softer, machine-direction tensile strength,

tensile yield, puncture force, and transverse-direction tear

resistance all decrease. Machine-direction ultimate elon-

gation increases.

At lower temperatures, the opposite is true. Machine-

direction tensile strength, tensile yield, puncture force,

and transverse direction tear all increase. Machine-direc-

tion elongation decreases. If temperature plays a role in

your stretch-ﬁlm requirements, contact your packaging

sales professional, who can recommend ﬁlms that are best

suited for your particular needs.

Effect of Dust and Grit on Film

Dust has an adverse effect on ﬁlm, causing it to lose its

cling. In high-dust and high-grit environments, debris can

build up on the prestretch and metal rollers and cause

failures in ﬁlm performance. As mentioned earlier in this

section, the debris that collects on the rollers is often the

result of a buildup of tackifying agents. PIB, the most

common cling additive, can accumulate over time, causing

the ﬁlm to wrap and/or sharp objects to be embedded in

the rubber rollers. Therefore, it is of utmost importance to

keep the rollers clean and free of buildup.

Stacking Pallets

Too much pressure may be placed on pallets by stacking

them too high. Two is the recommended limit.

GLOSSARY OF TERMS

Antiblock. Substances added into plastic materials that

retard or prevent ﬁlm layers from sticking together.

Blowup ratio. The ratio of ‘‘bubble’’ or ‘‘tube’’ diameter

to extrusion die diameter. A primary consideration in

determination of transverse-directional (TD) shrinkage

and a partial determinant of machine-directional (MD)

shrinkage.

Blown ﬁlm. Film that is fabricated by continuously

pumping the polymer through a circular oriﬁce (die).

Once through the die, this polymer is then drawn upward

and ﬁlled with air, creating a tube. The volume of air

contained within the tube stretches the tube out to the

desired width and, in conjunction with rate at which it is

being pulled away from the die, the desired thickness is

created.

Caliper

. The thickness of

a ﬁlm or bag, normally ex-

pressed in mils or as ‘‘gauge’’ (0.9 mil = 90 gauge = 0.0009

in.).

Cast ﬁlm. Film that is fabricated by continuously

pumping the polymer through a straight slot oriﬁce

(die), then chilling this hot sheet of plastic immediately

510 FILM, STRETCH

afterward by contact with a colled roll. Film width is

determined by the length of the slot. Thickness is deter-

mined by how fast the casting roll pulls the plastic away

from the slot (or die).

Cling. The characteristic of stretch ﬁlm that makes it

stick to itself or other clean objects.

Coefﬁcient of friction. A dimensionless numerical

representation of the ease with which two objects or

surfaces will slide against each other. Low numbers slide

easily. Total range due to the test deﬁnition is 0–1.

Coextrusion. Fabrication of a multilayer ﬁlm by

pumping the various materials through separate extru-

ders and then merging the extrudates into a common die

assembly. These die assemblies are constructed to main-

tain distinct material layers with fusion occurring at the

boundaries, due to the pressures and temperature of the

extrudates.

Copolymer. A plastic or polymeric whose chemical

composition consists of more than one basic hydrocarbon

type. The materials are chemically bonded and remain in

combination, thus inﬂuencing the performance by their

own distinct characteristics.

Crosslinked PE. A polyethylene that has been speciﬁ-

cally treated by chemical or physical means to cause

intrachain bonding.

Crystallization. The formation of distinct, ordered, and

repeated molecular groups. Polyethylene forms varying

amounts of crystalline structure depending on process

conditions and original molecular makeup. The remaining

portion is amorphous (which is the antonym of crystal-

line). Ice is crystalline; water is amorphous.

Dart drop. A method of measuring a ﬁlm?s impact

strength or dynamic toughness. A hemispherical shaped,

weighted ‘‘dart’’ is dropped onto a ﬁlm sample. The weight

at which 50% of the samples are punctured is considered

the WF

reading.

Die. A device used in extrusion processes to shape the

extrudate. Circular dies are used for blown products, and

slot dies are used for cast products.

Drawdown ratio. Commonly expressed as the ratio of

the width of the extrusion die oriﬁce to the thickness of a

particular ﬁlm. Frequently, however, and more correctly, it

is a ratio involving die oriﬁce, blowup ratio, and ﬁnal ﬁlm

thickness as follows: die gap/(ﬁlm gauge blowup ratio).

Eldastic recovery. The ability of a material to return to

its original shape or size after having been deformed or

subjected to strain.

Elmendorf tear. A testing method used to quantify a

material?s resistance to tearing forces. Generally, a sam-

ple is slit (initiated tear), then the force required to tear

apart the sample is measured and given as the tear value.

Elongation at break. The strain or deformation re-

quired to break a sample. Generally expressed as a

percentage by dividing the strain (distance) at which a

sample breaks by the original sample length.

EVA. Abbreviation (acronym) for the copolymer ethy-

lene vinyl acetate. Small percentages (1–18%) of vinyl

acetate monomers are frequently polymerized with ethy-

lene to provide greater extensibility or greater low-

temperature strength or to improve sealability.

Extrudate. Molten polymer.

Extrusion. The process of feeding, melting, and pump-

ing a material such that a desired shape or conﬁguration

can be created. It is a continuous process and utilizes a

device similar to a meat grinder.

Film yield. Generally expressed as the square inches of

a ﬁlm (area) that weighs one pound if the ﬁlm is 1 mil

(0.001 in.) thick. Coverage is on a per pound (lb

1

) basis.

This should not be confused with yield point, yield

strength, or tensile yield, which are strength measure-

ments. Polyethylene yields 30,000 in.

/lb at 1 mil.

Gauge. Used as a synonym for ﬁlm thickness or ﬁlm

caliper. Sometimes expressed as 80- or 100-gauge, which

equates to 0.8 or 1 mil, respectively, or 0.008 or 0.001 in.,

respectively.

Gauge band. A conformation irregularity found in rolls

of material. A thick area in a ﬁlm will produce a raised or

elevated ring in a ﬁnished roll of product. Conversely, a

thin area will result in a soft ring in a ﬁnished roll.

Gloss. The shine or sparkle of a surface. In LDPE ﬁlm,

gloss is described as the amount of light reﬂected from the

surface. Standard technique places a light source and a

receiver at 451 angles from the surface. The number value

produced is roughly the percentage of light reﬂected from

the source into the receiver.

Haze. The lack of ﬁlm transparency. It can be induced

by process considerations, inherently due to molecular

conﬁgurations or created by pigmentation. It is measured

by determination of the percentages of light not trans-

mitted through a ﬁlm sample.

Homopolymer. a plastic resin or polymer whose entire

chemical molecular structure is of a single hydrocarbon

group. It is made by feeding a single monomer to the

reactor.

Impact strength. The ability of an object or material to

resist rapidly applied destructive forces. Refer to ‘‘Dart

drop.’’

LDPE. Low-density polyethylene—any polyethylene

homopolymer whose density is between 0.913 and

0.925 g/cm

(g/mL).

Modulus. Short for modulus of elasticity, which is a

numerical value reﬂecting a material’s resistance to de-

formation. A ﬁlm with a high modulus is hard to stretch or

elongate.

Monomer. The incremental or elemental chemical ele-

ments before polymerization. Ethylene is a monomer.

Neckdown. The ‘‘narrowing’’ tendency of a ﬁlm when it

is being stretched or pulled. Occurs when ﬁlm is stretched

in the machine direction, resulting in decreased trans-

verse direction width.

Opaque. Film that is impervious to light: 100% haze

level.

Polyisobutylene (PIB). Tackiﬁer additive in blown

ﬁlm that gives it cling.

psi. Abbreviation for pounds per square inch (lb/in.

). A

unifying statistical measurement by which various thick-

ness of material can be tested, equated, and compared

without regard to actual specimen thickness.

Puncture performance. The relative comparison of a

material’s resistance to failures caused by penetration—

for example, how easily your ﬁnger pokes through a ﬁlm

sample.

FILM, STRETCH 511

PVC. Abbreviation for poly(vinyl chloride). In ﬁlm form,

it is used as a meat or produce wrap, as stretch ﬁlm, and

as a high-clarity shrink wrap for consumer or retail

packaging.

Polymer. Means ‘‘many members.’’ A structure gener-

ated by the repetitious joining of many of the same

elementary units. Natural polymers are cotton, wood, or

protein. Synthetic polymers are polyethylene, polystyr-

ene, nylon, and so on.

Polyoleﬁn. Polymers of basic unsaturated hydrocarbon

chains containing at least one double bond (e.g., polyethy-

lene, polypropylene, and polybutene). Not PVC or PVA.

Reactor. The equipment used to transform ethylene gas

to polyethylene.

Stress relaxation. Primarily it is the phenomenon of

force decay as a function of time. It means that the ‘‘rubber

band’’ tying a stretch load together exerts less force as

time passes. This rate of decrease varies greatly with

different polymers. PVC has an early decay that is much

greater and more rapid than that of LDPE.

Stretchability. A combination of factors related to the

ability of a material to be stretched or elongated—for

example, how easily and to what extent a ﬁlm stretches

and whether it will return to its original length.

Tack. An adjective used to describe a ﬁlm’s resistance to

slide against itself or another surface, or its resistance to

separation from itself. Similar terms are surface adhesion

or cohesion, surface seal, wetting of ﬁlm layers, blocking,or

cling.

Tackiﬁers. Chemical substances added to increase the

tack of the parent or base material.

Tear resistance. The resistance of a ﬁlm to be torn.

This is quantiﬁed by Elmendorf tear testing, and is

measured as the force required to propagate an initated

tear in the MD or TD direction.

Tensile ultimate. This is a stress level, measured in

psi, beyond which the specimen will break. It is the

laboratory-measured, maximum stress (applied force)

that the material will withstand. Tensile indicates that

test is conducted with a pulling or tensioning type of

Tensile yield. This is a stress level, measured in psi,

beyond which permanent deformation occurs. ‘‘Tensile’’

indicates that the specimen is pulled or ‘‘tensioned’’ rather

than compressed. Up to this stres or applied force level, a

release of the force will result in the specimen returning to

its original size. Pulling with a higher force will result in

an elongated sample, even after the force is removed.

Tint. A slight coloring that allows light transmission

and relatively good clarity.

Toughness. An overall strength measurement that

takes into account both the amount of pull and the amount

of elongation a sample can withstand. A tough material

will resist breakage by both resisting force and by elongat-

ing. A brittle material (e.g., glass) will resist force, but will

break instead of deforming; hence it has low toughness.

LDPE, which is plastic or tough, both resists and elon-

gates—hence is tougher than glass. The rate of force

application has signiﬁcant effects on toughness, so com-

parisons must include testing data.

Ultimate Strength. Same as ‘‘Tensile ultimate.’’

Wide web. Wrapping with a roll of ﬁlm approximately

the size of the load.

Wrap. One revolution of a machine turntable.

Yield stretch. Same as ‘‘Tensile yield.’’

Zippering. Lack of resistance to tear propagation of an

initiated TD cut or tear. Once the ﬁlm has been torn or cut,

the resulting slit rapidly opens and completes a full-web

break.

FILM, TRANSPARENT GLASS ON PLASTIC

FOOD-PACKAGING MATERIALS

RUSSELL J. HILL

BOC Coating Technology,

Concord, California

INTRODUCTION

Commonly used polymeric packaging materials, such as

polyethylene terephthalate (PET), oriented polypropylene

(OPP), and biaxially oriented nylon (BON), do not have

sufﬁcient oxygen or water-vapor barrier properties for

many packaging applications. To resolve this issue, multi-

layer material structures that incorporate aluminum foil

and polymeric ﬁlms, aluminum metallized ﬁlms, PVDC-

coated ﬁlms, or coextruded EVOH ﬁlms routinely are

applied. However, environmental considerations and the

push toward source reduction have created a market need

for a thin-ﬁlm transparent oxygen or water-vapor barrier

coating that is friendly to the environment and convertible

into usable packaging materials and at the same time

capable of meeting the cost requirements of the food-

packaging industry. The coating should also use a low-

temperature process to coat heat-sensitive polymeric ﬁlms

such as OPP and BON.

The goal of the scaleup process for the QLF transparent

barrier coating was to design and manufacture equipment

to provide SiO

-coated material that is environmentally

friendly, recyclable, microwavable, crystal-clear in trans-

parency, excellent in adhesion to the substrate, and able to

allow metal detection. In addition, the coating must with-

stand mechanical stress and the high temperatures gen-

erated during extrusion lamination and heat seal. It

should be printable, able to run at a high speed on

standard converting equipment, and be cost-competitive

compared with existing barrier materials. For commercial

success, the coating process must be capable of producing

high throughputs to meet the low coating cost demands of

the packaging industry.

WHY PLASMA-ENHANCED CHEMICAL VAPOR

DEPOSITION (PECVD)?

Coatings of SiO

can be produced by several methods that

include sputtering, evaporation, and PECVD.

512 FILM, TRANSPARENT GLASS ON PLASTIC FOOD-PACKAGING MATERIALS

Extensive R&D programs have been completed to in-

vestigate each technology to determine the most effective

method for creating a SiO

coating to meet scaleup process

goals. At the same time, a prototype machine was built

capable of coating rolls 660 mm wide to prove the produc-

tion and economic viability of whichever process was

chosen. This system had the capability to use all three

technologies. Table 1 shows the results of the study that

led to the focus on the PECVD process. Sputtering was

disqualiﬁed early, because of large power requirements

and low deposition rate. The process was not economical

for food packaging.

In contrast, the main advantage of evaporation was the

potential to run at very high line speeds, comparable with

those speeds used in vacuum metallizing of aluminum.

This potential has not been realized. SiO cannot be

evaporated at as high a rate as aluminum. If it is

evaporated at a power level to give the same rate as

aluminum, then molten SiO is spattered onto the ﬁlm,

which causes holes in the ﬁlm. Also, the thickness of the

coating needed to gain a suitable barrier is much greater

than that for aluminum metallizing (1500–3000 A

vs.

200 A

On the basis of the coating work carried out, the

PECVD process showed much more promise than eva-

poration in terms of economics and coating performance.

The economics for the PECVD process are better than

those for evaporation, because the vacuum requirements

are less stringent, which means that the time to change

rolls should be less; the power requirement per unit area

is less; cooling requirements are less; raw material is

inexpensive and available; source usage is higher, mainly

because of patented equipment design; and coating thick-

ness is less.

SCALEUP OF MANUFACTURING SYSTEMS

The SiOx deposition process described is a low-pressure,

low-frequency, and low-temperature PECVD process that

uses a mixture of helium, oxygen, and the organosilicon

compound hexamethyldisiloxane (HMDSO), as shown in

Figure 1. The plasma source uses a multipole magnetic

ﬁeld to conﬁne the plasma to obtain enhanced deposition

rates at low pressures. The resulting silicon oxide is the

QLF barrier coating.

The three coaters used in the course of the maufactur-

ing scaleup effort are shown schematically in Figure 2.

The QLF coating was initially developed in a small

research roll coater. Because of technical risks and the

capital cost required to build a 1.5- or 2-m-wide vacuum

roll coater, the strategy involved incremental steps in

scaling up the coating process from a web width and speed

of 0.3 m wide at 0.3 m/min, to 0.66 m wide at 100 m/min,

then 1.5 m at W100 m/min and ﬁnally to 2 m at W100 m/

min. The challenge to incrementally increase the web

width and speed was recognized because of the need to

develop hardware capable of running under the process

conditions required to achieve the target barrier perfor-

mances and line speeds. BOC coating technology (BOCCT)

has systematically scaled up the process using statisti-

cally designed experiments that optimized the parameters

through different treatment conditions as well as the use

Table 1. Comparison of Glass-Coating Technologies

Feature Sputtering Evaporation PECVD

Vacuum (torr) 10

3

(proc.) 10

6

2

6

(base) 10

6

2

Power (kw) Thousands Hundreds Tens

Process temperature High High Low

Source Si + O

SiO/SiO

Monomer

Source cost High High/medium Low

Source utilization Roughly 40% Roughly 25% W50%

Coating thickness 400–500 A

1500–3000 A

150–300 A

Film color Yellow Yellow Clear

Coating bond Mechanical Mechanical Chemical

Barrier (unlaminated) Medium Medium High

Figure 1. Proprietary plasma-enhanced chemical vapor

deposition.

FILM, TRANSPARENT GLASS ON PLASTIC FOOD-PACKAGING MATERIALS 513

of previous experience from other vacuum coating

machines.

The ﬁrst scaleup phase was completed in a develop-

ment coater that can mechanically handle 0.66-m-wide

webs at speeds from 0.1 to 150 m/min. The second scaleup

phase was conducted in a production-scale coater that can

handle 1.5-m-wide webs at speeds from 10 to 300 m/min

(Figure 3). The process scaleup in this coater was com-

pleted using HMDSO as the monomer. The third scaleup

phase is a production coater that can handle 2-m-wide

webs at speeds from 30 to 300 m/min (Figure 4). This is a

modular design production coater with three isolated

process zones that provide ﬂexibility for pretreatment

and/or posttreatment or for deposition with different

chemistries.

BARRIER PERFORMANCE

The unlaminated oxygen transmission properties achieved

to date for PET and OPA are listed in Figure 5 and 6. A

typical oxygen transmission rate (OTR) for uncoated PET is

115 cm

/(m

24 h). With QLF coating applied at a speed of

100 m/min, the OTR is reduced to 1.1 cm

/(m

24 h). In-

creasing the line speeds to 200 m/min will result in an OTR

reading of 2 cm

/(m

24 h). The opportunity for high bar-

rier performance on other substrates is also possible.

Production rolls of OPA with QLF coating run at line speeds

of 300 m/min demonstrate an OTR of 7 cm

/(m

24 h).

These results represent the ﬂexibility a roll coater can

offer. Whether a customer is targeting a high or medium

Figure 2. Flex-1, Flex-3, and Flex-4 schematic.

Figure 3. Flex-3: production-scale QLF roll coater.

Figure 4. Flex-4: production-scale QLF roll coater.

514 FILM, TRANSPARENT GLASS ON PLASTIC FOOD-PACKAGING MATERIALS

barrier application, a roll coater can satisfy their

requirements.

Initially, the technology was focused on an effort to

optimize the oxygen barrier primarily for liquid packa-

ging. Continued development was targeted toward up-

grading and optimizing the process for water vapor

(WVTR) as well. As indicated in Figure 7, the WVTR for

PET with QLF coating has been reduced from a level of

5.6 g/(m

24 h) in August 1995 to 1.4 g/(m

24 h) in De-

cember 1995. Development efforts are now focused on

increasing line speeds and on introducing a range of

different substrates to the PECVD process. (See also

Barrier Polymers.)

CONVERTING

Successful large-scale acceptability of QLF-coated materi-

als is dependent on the ease of convertibility as well as on

their cost and barrier properties. Extensive research has

been dedicated to determining how ‘‘robust’’ QLF coatings

are in varying converting processes. Because of the strong

chemical bond that exists between QLF coatings and PET,

converting results have been encouraging. Several packa-

ging converters have successfully adhesive- and extru-

sion-laminated QLF-coated PET, which maintain barrier

properties and achieve excellent bond-strength results.

Good ink adhesion also was achieved directly on the QLF-

coating surface. BOCCT can supply a recommended list of

inks and adhesives on request.

Gelbo ﬂexing, which is a test commonly used to simu-

late stresses encountered in ﬁnished-packaged shelf life in

the marketplace, is also being investigated. Earlier papers

(1,2) already have reported that the ﬁnished-packaging

structures with the QLF coating survived the tests when

properly laminated.

COMMERCIALIZATION OF QLF BARRIER COATING

The transparent oxide barrier market has been plagued

by high cost and/or difﬁculties in converting or printing on

the barrier coating surface without losing the barrier

properties. One of the most crucial success factors in the

transparent high-barrier market is the ability to provide a

better, or comparable, material at a lower cost. QLF

coatings are not only the most ‘‘robust’’ transparent oxide

coatings available in the marketplace—they also provide

the most competitive economics.

Today, BOCCT roll coaters are built to offer the con-

verter or ﬁlm manufacturer the ﬂexibility to target both

the medium-barrier and the high-barrier markets. De-

pending on the barrier level one is looking to achieve, QLF

coating costs can range fromo$0.03 to o$0.045/m

. These

costs will continue to lower as more advances in line

speeds and barriers are achieved.

The use of commercial size coaters to improve the QLF

coating performance is continuing. QLF coatings are FDA

approved, provide a better barrier than polyvinylidene

chloride (PVDC) coatings, and are insensitive to humidity

changes as opposed to ethylene vinyl alcohol (EVOH).

Replacement of these coatings on substrates such as

PET and BON are the initial targets for large-scale

commercialization of QLF coatings.

CONCLUSION

QLF barrier coatings have been scaled up from a 0.3-

m-wide web laboratory coater at a line speed of 0.3 m/min

to a 2-m-wide web production coater capable of 300 m/min.

BOCCT is committed to continued improvements in both

line speeds and barrier performance. Currently, technol-

ogy-driven converters and ﬁlm manufacturers are forming

partnerships with BOCCT to make QLF coatings a com-

mercial reality.

Figure 5. OTR of 12-mm PET with QLF coating.

Figure 7. WVTR of 12-mm PET with QLF coating.

Figure 6. OTR of 15-mm OPA with QLF coating.

FILM, TRANSPARENT GLASS ON PLASTIC FOOD-PACKAGING MATERIALS 515

QLF coatings applied to PET substrates can now per-

form with barriers and line speeds that exceed even the

most demanding expectations of the packaging industry.

Meeting the demand in the packaging industry for an

environmentally friendly, transparent barrier coating is

the goal of BOCCT.

BIBLIOGRAPHY

1. E. Finson and J. Felts, ‘‘Transparent SiO

Barrier Coatings:

Conversion and Production Status,’’ TAPPI J. 78, (1995).

2. E. Finson, and R. J. Hill, ‘‘Glass-Coated Packaging Films

Ready for Commercialization,’’ Packag. Technol. Eng., 36

(1995).

FLEXIBLE INTERMEDIATE BULK CONTAINERS

BRUCE CUTHBERTSON

Flexible Intermediate Bulk

Container Association

Updated by Staff

INTRODUCTION

Flexible intermediate bulk containers are deﬁned as an

intermediate bulk container, having a body made of

ﬂexible fabric, which (1) cannot be handled manually

when ﬁlled, (2) is intended for the shipment of solid

material in powder, ﬂake, or granular form, (3) does not

require further packaging, and (4) is designed to be lifted

from the top by means of integral, permanently attached

devices (lift loops or straps) (1).

Flexible intermediate bulk containers (FIBCs), also

known as ‘‘big bags,’’ ‘‘bulk bags,’’ and ‘‘bulk sacks,’’ were

ﬁrst manufactured in the late 1950s or early 1960s. There

is some controversy as to where the ﬁrst FIBCs were

made; however, it is known that FIBCs were made in the

United States, Europe, and Japan during the time period

mentioned above. The ﬁrst FIBCs were constructed with

heavy-duty PVC-coated nylon or polyester where the cut

sheets are welded together to form the FIBC. These FIBCs

were made with integrated lift slings around the con-

tainer, or were attached to a specially made pallet, or were

manufactured a metal lifting device that the container sat

on. These handling devices allowed the container to be

ﬁlled from the top and discharged from the bottom.

The initial cost of these heavy-duty containers is high;

therefore, they are designed to be reused many times in a

closed-circuit system, where problems of control logistics,

prevention of contamination, cleaning, and liability for

loss or damage can be agreed on by the shipper and

receiver of the product.

Flexible intermediate bulk containers manufactured

with polyoleﬁn fabrics were experimented with in Eng-

land, Japan, Canada, and the United States all at about

the same time in the late 1960s to the early 1970s. It was

the development of these high-strength light-weight fab-

rics (i.e., polypropylene) that spurned the growth of the

ﬂexible bulk bags that is universally used today.

The rapid growth in Europe in the manufacture of

FIBCs occurred in the mid-1970s during the oil crisis.

The oil-producing countries building program required

large quantities of cement. The demand for cement was

shipped in FIBCs at the rate of 30,000–50,000 metric tons

per week from Northern Europe, Spain, and Italy to the

Middle East.

The demand for bulk bags in the United States grew

slower than in Europe until 1984, when the U.S. Depart-

ment of Transportation (DOT) agreed to grant exemptions

for the shipment of hazardous products in FIBCs. Perfor-

mance standards for FIBCs were established and issued

by the Chemical Packaging Committee of the Packaging

Institute, USA under T-4102-85. These standards were

used to obtain exemptions until DOT included ﬂexible

containers with the other types of IBCs in the regulation

HM181-E for hazardous products.

DESIGN

The ﬂexible bulk container offers many features that are

unique to this package. It can be folded ﬂat and baled for

shipment to the user. The weight of a bulk bag to ship one

metric ton of product weighs 8–10 lb, offering a low pack-

age:product weight ratio. The cost of FIBCs is competitive

with other forms of packaging because it is usually utilized

without pallets. They are easy to store and handle in

warehouses with standard equipment. When shipping by

boat, the FIBCs are gang-loaded with up to 14 bulk bags on

a spreader bar, and they are shipped as break bulk.

The standard diameter of FIBCs is 45–48 in., designed

to ﬁt two across in a truck or a shipping container. Special

conﬁgured containers are made to meet speciﬁc require-

ments of the container user.

FIBCs generally are manufactured to meet speciﬁc

requirements of the container users. The height of the

container, the diameter and length of the spouts, coated or

uncoated fabric, and whether a polyethylene liner is

necessary will be speciﬁed according to the type of product

that will be shipped.

USES

Modern FIBICs transport over 0.25 10

t of goods per

year. They are used to store and move a variety of products

such as cereals, powdered chemicals, ﬂour, and animal

feeds. With a capacity of of up to 3 m

and load capability

of 0.5–2 t, FIBCs are highly cost effective, easily recycl-

able, and ideal for free-ﬂowing granules, powders, pellets,

and ﬂakes (2).

When hazardous products are shipped in FBCs, the UN

mark for the product must be printed on the container

body. In the United States the manufacturer of the con-

tainer is self-certifying and marks the container according

to the regulations HM 181E. All other countries require

the container manufacturer to submit containers to third-

party testing for certiﬁcation.

516 FLEXIBLE INTERMEDIATE BULK CONTAINERS

FIBCs containing nonhazardous or nonregulated pro-

duct when shipped export from the United States must

have performance testing certiﬁcation if destined for a

country that require performance standards for bulk bags.

The following regulation numbers apply for perfor-

mance standards for containers with regulated products:

United States, HM 181E; United Nations, Chapter 16;

England, B.S. 6939; Canada, CGSB 43.146.

BIBLIOGRAPHY

1. B. Cuthbertson, ‘‘Flexible Intermediate Bulk Containers’’ in

A. J. Brody and K. S. Marsh, eds., The Wiley Encyclopedia of

Packging Technology, 2nd edition, John Wiley & Sons, New

York, 1997, pp. 448–449.

Cited Publications

1. Flexible Intermediate Bulk Container Association,

www.ﬂexintcontainerassoc.com/index html, September 2008.

2. J. J. Wooster, ‘‘Packaging Flexible’’ in Mark Encyclopedia of

Polymer Science and Technology, Vol. 3, John Wiley & Sons,

Hoboken, NJ, 2003, p. 361.

FOAM, EXTRUDED POLYSTYRENE

PHILLIP A. WAGNER

The Dow Chemical Company,

Midland, Michigan

Updated by Staff

INTRODUCTION

Polystyrene foam sheet is a reduced-density sheet made

from polystyrene by the extrusion process. Produced in

many forms, it is most easily classiﬁed by its density and

thickness. This article deals with a sheet that has densities

of 3–12 lb/ft

(0.05–0.19 g/cm

) and thickness 0.012–0.250

in. (0.3–6.35 mm). Foamed thermoplastics provide excel-

lent insulating properties because of their low thermal

conductivity, good shape retention, and good resistance to

moisture pickup (1).

The ﬁrst extruded foam sheet was produced in 1958 by

extruding expandable polystyrene beads. In the early

1960s, the direct-gas-injection extrusion technology was

developed and is by far the most widely used system today.

In the late 1980s and early 1990s, there was a decrease in

the volumes of foam produced due to the environmental

issues related to the blowing agents being used and

disposal of the foam. The use of new and more ecologically

acceptable blowing agents and increased recycling of the

products has reduced these concerns. Most of the foam is

used for disposable packaging such as meat and produce

trays, egg cartons, containers and trays for carryout

meals, and disposable dinnerware. It is also used for drink

cups, bottle labels, miscellaneous cushion packaging, and

applications where it is laminated to paper or ﬁlms. A

large percentage of all foam sheet produced is thermo-

formed to manufacture the ﬁnished product. When it is

laminated with paper, it is usually fabricated by die

cutting and scoring to produce folding containers.

PRODUCTION

There are four direct gas injection processes to produce

polystyrene foam sheet. All four have the same objectives:

to melt the polymer, uniformly mix in the blowing agent

and nucleator, cool the melt, and allow the mix to expand

into a biaxially oriented sheet. The four processes employ

large-diameter or long L/D extruders, twin screw extru-

ders, the Winstead system using a single screw extruder

and its cooling system, and the two single-screw extruder

tandem system. Of these processes, the tandem system is

most successful and widely used (see Figure 1).

The tandem extruder system utilizes two single-screw

extruders: a primary extruder for melting, mixing, and

feeding the extrudate to a secondary extruder for cooling

and additional mixing of the extrudate prior to exiting an

annular die. Most tandem systems use 4.5-in. (11.4-cm)

primary extruders and 6-in. (15.2-cm) secondary extru-

ders with output rates of 500–1200 lb/h (227–544 kg/h). As

producers strived for higher output rates, 6-in. (15.2-cm)

primary and 8-in. (20.3-cm) secondary extruders with

output rates of 900–2000 lb/h (408–909 kg/h) have become

more popular. Tandem foam lines are supplied by several

extruder manufacturers (see also Extrusion).

In addition to the rather unique extrusion system, the

die–mandrel–takeoff system must be carefully designed. As

mentioned above, an annular die is generally used because

of the three-dimensional expansion of the foam. The foam

is drawn over a cooling sizing mandrel to cool the foam and

provide the desired sheet width. Blowup ratios and the die

diameter:mandrel diameter ratio must be calculated ac-

cording to the density and desired orientation of the foam

to be produced. Ratios of 3:1 to 4.5:1 are common. This

tubular sheet is slit into the required widths as it is drawn

off the mandrel and is then wound into rolls.

RAW MATERIALS

The ingredients required to produce foam sheet are resin,

nucleator, and blowing agent. The resin is normally a

high-heat general-purpose polystyrene such as Dow

Styron 685D. Nucleators, such as talc or a citric acid–

sodium bicarbonate mixture, are added to provide foaming

sites to obtain the desired cell size and uniformity. The

chlorinated ﬂuorocarbons formerly used as blowing agents

have been replaced with more environmentally friendly

substitutes, such as HCFCs (HFC-152a) or low-molecular-

weight hydrocarbons such as butane or isopentane, carbon

dioxide, and blends of these blowing agents (1). The

blowing agent is dissolved and held in solution by the

pressure in the extruder (2). The blowing agent is injected

into the primary extruder approximately two-thirds of the

way up the barrel. This is accomplished by the use of a

positive-displacement volumetric pump. The amount and

FOAM, EXTRUDED POLYSTYRENE 517