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Most applications require transparency, but Aclar ﬁlm

can be metallized with aluminum. Corona-treated ﬁlm can

be printed with polyamide-based inks (see Inks). Best

results are obtained if the ﬁlm is corona-treated in-line

prior to printing.

PROPERTIES

Aclar ﬁlm can be sterilized with steam and with ethylene

oxide (ETO) systems. Radiation sterilization of Aclar

ﬁlm in the cobalt-60 dosage range of 2.5–5 10

rad (2.5–

5 10

Gy) have been tested. Tests at 1 10

rad

(1 10

Gy) (2) indicate that little or no property loss occurs

at that dosage (see Radiation, Effects of). Aclar ﬁlms have

outstanding barrier properties to water vapor and to other

gases (see Barrier Polymers). Properties at a wide variety

of temperatures can be determined by a method that is

described in Ref. (3). Table 1 compares transmission rates

of Aclar ﬁlms with a number of other ﬁlms.

Aclar ﬁlm is inert to acids, bases, strong oxidizing

agents, and most organic chemicals. It exhibits excellent

dimensional stability in inorganics, including water, salt

solutions, strong acids, and bases. Some polar organics,

especially hot polar solvents, diffuse into Aclar ﬁlm and

act as a plasticizer. These solvents cause it to become more

ﬂexible and sometimes hazy. There are no known solvents

that dissolve the ﬁlm at temperatures up to 2501 (1201C).

Mechanical properties are usually not an important factor

in packaging applications because the important mechan-

ical properties are those of the laminates. Aclar ﬁlms are

not particularly strong or tough, but they have outstand-

ing abrasion resistance, important in clean-room packa-

ging of military hardware.

APPLICATIONS

Aclar ﬁlm is used in military, pharmaceutical, electrical/

electronic, and aircraft/aerospace component applications.

It serves as a key component of a transparent laminated

barrier construction that meets the requirements of the

MIL-F-22191, Type I speciﬁcation (see Military Packa-

ging). This laminate is used for packaging moisture-

sensitive military hardware. Aclar also passes the liquid

oxygen (LOx) compatibility impact test under NASA

speciﬁcation MSFC-106A. It is used for packaging compo-

nents designed for service in liquid oxygen and other

oxidizers used in spacecraft applications. Gas sampling

bags made of Aclar are used on the Space Station (4).

The major commercial applications are in packaging

moisture-sensitive drugs. Aclar Flex 380 exhibits 10 times

the barrier protection of other ﬁlms. It can reduce medical

errors and streamline operations by streamlining quality

control, product inspection, labeling, and product identiﬁ-

cation (1). Laminates are used for rigid and semirigid

blister packs, lidding, unit-dose packages, and aseptic

peel-packs. They are also used in medical applications—

for example, as an overwrap for plastic containers for

biomedical specimens and/or pathology specimens. This

application requires a ﬁlm that is sterilizable by heat and

ETO and that does not absorb or denature biological

ﬂuids. Aclar ﬁlm laminates are used in oxygen-rich en-

vironments for packaging items in liquid nitrogen (4).

SAFETY CONSIDERATIONS

Aclar ﬁlm is inert and nontoxic and safe to handle at

ordinary temperatures. It is thermally stable for up to one

hour at temperatures as high as 4461F (2301C). It can be

processed for a few seconds at temperatures as high as

5541F (2901C), provided that the machine is ventilated

with an exhaust fan. Vacuum forming is typically done at

3741F (1901C) with exhaust-fan ventilation. If Aclar ﬁlm is

continuously processed at temperatures above 4461F

(2301C), the processing machinery should be equipped

with ventilating equipment or the work should be per-

formed in an exhaust hood. The ﬁlm should not be

disposed of by burning. Exposed to ﬂame, it degrades to

ﬂuorochlorocarbon gases, some of which are toxic. In the

presence of oxygen and oleﬁns or polyoleﬁns, it may form

HF and/or HCl when exposed to ﬂame. These acids are

toxic if inhaled and are corrosive to metals (5).

BIBLIOGRAPHY

‘‘Film, Fluoropolymer’’ in M. Bakker, ed., The Wiley Encyclopedia

of Packaging Technology, 1st edition, A. B. Robertson and K. R.

Habermann, John Wiley & Sons, New York, 1986, pp. 311–313;

2nd edition, A. J. Brody and K. S. Marsh, eds., 1977, pp. 403–

405.

Cited Publications

1. ‘‘Aclar Homopolymers, www.honeywell.com, accessed August

2008.

2. King, Broadway, and Pallinchak, ‘‘The Effect of Nuclear Radia-

tion on Elastomeric and Plastic Components and Materials,’’

Report 21, Addendum AD 264890, Radiation Effects Informa-

tion Center (now defunct), Battelle Memorial Institute, Na-

tional Technical Information Series of the Department of

Commerce, August 31, 1964.

3. N. Vanderkooi and M. Ridell, Mater. Eng. 58 (March 1977).

4. ‘‘Aclar Films, Copolymers 22/33,’’ www.texastechnologies.com/

aclar, accessed August 2008.

5. Aclar Homopolymer Films, Material Safety Data Sheet,

www.honeywell.com, January 2004.

FILM, HIGH-DENSITY POLYETHYLENE

R. H. NURSE

J. S. SIEBENALLER

American Hoechst Corporation

Updated by Staff

INTRODUCTION

High-density polyethylene, (HDPE) ﬁlm has been used for

a variety of specialty applications since the mid-1950s, but

468 FILM, HIGH-DENSITY POLYETHYLENE

it was not until the 1970s that signiﬁcant growth began.

Today polyethylene is the third largest resin commodity

after poly(vinyl chloride) and polypropylene (1). Plants

using Ziegler and chromium catalysts to make ﬁlm re-

ported production of 450 thousand tons/year. Japan and

Asia use twice as much ﬁlm as the United States and

Western Europe (1). Much of this ﬁlm is used for grocery

sacks and merchandise bags and a few other nonpacka-

ging applications. HDPE ﬁlm is also used for a variety of

packaging uses that require the unique property proﬁle

that HDPE ﬁlms provide.

In packaging applications, HDPE ﬁlms compete with

LDPE and LDPE/LLDPE blends, cast PP (see also Film,

Non-oriented Polypropylene), and oriented PP (see Film,

Oriented Polypropylene). These polyoleﬁn ﬁlms have

many properties in common, but with some signiﬁcant

differences in degree. Typical HDPE ﬁlm properties are

shown in Table 1.

HDPE, by virtue of its higher density, exhibits higher

tensile strength, lower WVTR, and greater stiffness than

LDPE or LLDPE/LDPE blends. PP ﬁlms can offer higher

tensile strength because of a higher degree of crystallinity

and the ability to be biaxially oriented. PP ﬁlms also have

excellent optical properties due to ﬁne crystal structure

and biaxial orientation behavior. LDPE and LLDPE/

LDPE blends exhibit good clarity due to their lower degree

of crystallinity. HDPE is the most opaque of the three

polyoleﬁn types. This is an advantage if opacity is desired,

because a relatively low amount of pigment is required to

achieve that opacity (see Colorants). LLDPE and LLDPE/

LDPE blends exhibit higher tendency to elongation under

load because of their lower crystallinity and, hence, lower

tensile modulus. This property is useful in stretch-wrap

applications (see Films, Stretch), but it is a disadvantage if

low elongation is required (as in handled grocery sacks). It

is important to recognize, however, that the properties of

all polyoleﬁn ﬁlms can be tailored during polymerization

or through the use of blends or coextrusions.

PACKAGING APPLICATIONS

Two of the most important applications for HDPE ﬁlm are

retail grocery sacks and merchandise bags. HDPE ﬁlms

have replaced large quantities of glassine for packaging

cereals, crackers, and snack foods. In these applications,

clarity is not desirable, and the translucency or opacity of

HDPE ﬁlms is an advantage. They are used in conjunction

with bag-in-box vertical form/ﬁll/seal equipment (see Bag-

in-Box, Dry Product; Form/Fill/Seal, Vertical). Rubber-

modiﬁed HDPE ﬁlm is used for medical overwraps.

HDPE ﬁlms are also used to produce shipping sacks.

Heavy-gauge coextrusions of HDPE with low-density

polyethylene are used for all-plastic shipping sacks (see

Bags, Heavy-Duty Plastic), and thin-gauge HDPE ﬁlms

are used as moisture-barrier plies in multiwall bags (see

Bags, Multiwall). Very thin embossed HDPE ﬁlm is also

used as a replacement for tissue paper; and without

embossing, it is used as an inner wrap for delicatessen

products. HDPE ﬁlm is also used for foods that are heated

in the package (boil-in-bag items) (2).

FILM POLYMERS

Three principal polymer properties can be adjusted to tailor

the performance of HDPE ﬁlms (see Polyethylene, High-

Density). Density plays the most signiﬁcant role as a

measure of the degree of polymer crystallinity. Crystallinity

has a direct inﬂuence on tensile strength, WVTR, hardness ,

opacity, and coefﬁcient of friction. HDPE ﬁlm resins are

0.941–0.965 g/cm

, depending on comonomer type and

Table 1. Typical Properties of High-Density Polyethylene Film, 1 mil (25.4 lm)

Property ASTM Test Method HDPE-HMW (Blown) HDPE-MMW (Blown)

Speciﬁc gravity D1505 0.950 0.950

Yield, in.

/(lb mil)

/(kg m)]

29,200 [1635] 29,200 [1635]

Haze, % D1003 78 78

Tensile strength, psi (MPa) D882 MD/XD, yield 5200 (35.9)/5000 (34.5) 4600 (31.7)/4400 (30.3)

MD/XD, failure 7500 (51.7)/7000 (48.3) 6500 (44.8)/6100 (43.1)

Elongation, % D882 MD 450 350

XD 500 550

Tensile modulus, 1% secant,

psi (MPa)

MD 125,000 (862) 120,000 (828)

XD 130,000 (897) 125,000 (862)

Tear strength, gf/mil (N/mm) D1922 Propagating, MD/XD 20 (7.7)/150 (57.9) 15 (5.8)/100 (38.6)

Service temperature range,

1F(1C)

200–250 (93–121) 200–250 (93–121)

WVTR, g mil/(100 in.

day)

[cm

mm/(m

day)];

381C, 98% rh

0.8 [0.3] 0.8 [0.3]

COF, face-to-face D1894 0.3 0.3

COF = coefﬁcient of friction; MD, XD = machine, cross-direction.

FILM, HIGH-DENSITY POLYETHYLENE 469

concentration. The most common comonomers are butene

and hexene. As density increases, tensile modulus and

tensile strength increase as well (see Figure 1). The same

is true for ﬁlm hardness and, to some extent, for water-

vapor transmission rate (see Figure 2).

The molecular weight (MW) of the polymer has a

signiﬁcant inﬂuence on toughness and impact strength.

For many years, HDPE ﬁlms were made from medium-

molecular-weight (MMW) or low-molecular-weight (LMW)

polymers, for applications that required only medium-to-

low toughness. The development of high-molecular-weight

(HMW) polymers changed the range of applications avail-

able to HDPE ﬁlms (3). The inﬂuence of MW on ﬁlm

impact strength is signiﬁcant (impact resistance increases

with molecular weight), but the processing of the resin is

critical as well (4).

Molecular-weight distribution (MWD) is the third para-

meter inﬂuencing resin design, because it inﬂuences

processing. Broad-MWD resins are easier to process

than narrow-MWD resins. The ability to process HDPE

at economic speeds and at controlled melt temperatures

requires careful resin design. High-ﬂow LMW ﬁlm resins

can be narrow or medium in MWD and still be extruded at

high output rates without excessive shear that would

degrade the polymer. MMW resins require some careful

control for high-speed extrusion (5). The use of HMW-

HDPE ﬁlm resins requires extreme MWD control to

ensure both acceptable output rates and control of melt

temperatures. Thermal degradation must be avoided to

maintain the long molecular chains necessary to impart

high impact strengths. This MWD has been achieved in

some cases by bimodal polymerization technology. The

polymer chemist has certain secondary design criteria

available to ﬁne-tune the HDPE ﬁlm polymers. These

include special process stabilizers, high-heat stabilizers,

antistatic agents (see Additives, Plastics), different como-

nomer types, and the physical form in which the resins are

supplied (i.e., pellets or coarse powders).

FILM MANUFACTURING

Chromium-based catalysts can be used quite widely for

production of HDPE grades, but some of the best ﬁlms, in

terms of mechanical properties and extrusion rates, are

bimodal resins made from Ziegler catalysts passing

through two or more reaction zones. Most recently, me-

tallocene resins have been used to produce extremely high

clarity resins, despite the high density (6).

HDPE ﬁlms are produced using two principal extrusion

techniques: blown and cast (see Extrusion). The most

common is blown-ﬁlm extrusion, in which 1

 to 6-in:

(3.8 – to 15.2-cm) extruders extrude the resin in tubular

form. The tube is cooled, collapsed to a ﬂat ﬁlm, and either

wound in tubular form or slit and folded. The properties of

blown HDPE ﬁlm are highly dependent on the type of

resins used and the design of the extrusion equipment

employed (6). MMW-HDPE ﬁlms, monolayer or coex-

truded, are generally made with extruders in the

 to 6-in. (6.4– to 15.2-cm) diameter range operating

at relatively low screw speeds yet achieving high output at

moderate melt temperatures. The screw L:D ratio is

normally 25–30 and the barrel design is normally smooth.

These conventional extruders do not allow full

Figure 1. Inﬂuence of density on tensile strength. To convert psi

to MPa, divide by 145.

Figure 2. Inﬂuence of density on WVTR. To convert g mil/(100

in.

d) to g mm/(m

d), multiply by 0.3937.

Figure 3. Effect of neck length on ﬁlm toughness. To convert

ft lbf/in. to J/m, multiply by 53.38 (see ASTM D256).

470 FILM, HIGH-DENSITY POLYETHYLENE

development of the resin capability in terms of optimum

toughness, but they serve a useful role in providing high

outputs at economic rates for applications which do not

require the full–strength potential of HDPE.

In contrast, other designs for HMW–HDPE ﬁlm extru-

sion are based on forced-feed grooved sections. They oper-

ate at high screw speed, using relatively short (18–21) L:D

ratios. These extruders achieve high output with the mini-

mum residence time required to produce a homogeneous

melt for the subsequent blowing and orientation processes

necessary to develop the optimum toughness and tensile

strength. For HMW ﬁlm it is imperative to use a relatively

long neck length (frost height) (6–10 die diameter) and

high blowup ratio (3–5 die diameter) to achieve balanced

properties. The inﬂuence of these processing parameters

on the optimum toughness of the ﬁlm is illustrated in

Figures 3 and 4.

LMW-HDPE ﬁlms are generally made with cast-ﬁlm

technology, in which free-ﬂowing polymer melts are ex-

truded from ﬂat dies on to substrates or chill rolls. These

polymers do not have the melt strength necessary for the

blown ﬁlm process and their applications are limited.

BIBLIOGRAPHY

R. H. Nurse and J. S. Siebenaller, ‘‘Film, High Density Polyethy-

lene’’ in M. Bakker, ed., The Wiley Encyclopedia of Packaging

Technology, 1st edition., John Wiley & Sons, New York, 1986,

pp. 313–315; 2nd edition, A. J. Brody and K. S. Marsh, eds.,

1997, pp. 405–407.

Cited Publications

1. A. Borruso, ‘‘Polyethylene, High Density’’ in Chemical Econom-

ics Handbook, SRI Consulting, Menlo Park, CA, April 2008.

2. J. C. Brennan and B. P. F. Day, in J. C. Brennan, ed., Food

Processing Handbook, Wiley-VCH, Weinheim, Germany, 2006,

p. 306.

3. A. Brockschmidt, Plast. Technol. 30, 64 (1984).

4. H. R. Seintsch and H. E. Braselmann, ‘‘Further Evaluations of

HMW-HDPE Film Processing and Effects on Film Properties,’’

TAPPI Paper Synthetics Conference, Washington, DC, 1979.

5. H. E. Braselmann and R. E. Barry, ‘‘HMW-MMW HDPE

Extrusion and Fabrication Techniques for Grocery Sacks and

Merchandise Bags,’’ TAPPI 1984 Polymers, Laminations and

Coatings Conference, Boston.

6. E. Benham and M. McDaniel, ‘‘Polyethylene, High Density’’ in

Kirk–Othmer Encyclopedia of Chemical Technology, Vol. 20,

5th edition., Wiley, Hoboken, NJ, 2006.

FILM, ORIENTED POLYESTER

JOHN NEWTON

ICI, Delaware

Updated by Staff

INTRODUCTION

Biaxially oriented polyester ﬁlm is considered a high-

performance ﬁlm. It is used in numerous applications,

including graphic arts, information storage and display,

labels, solar control, membrane touch switches, pressure-

sensitive tapes, hot-stamping foils, photoresists, ﬁber-

glass-reinforced panels, postlamination, ID and smart

cards, and, last but not least, packaging.

World supply of PET ﬁlm continues to expand. The

domestic manufacturers of PET ﬁlm for the merchant

market are DuPont Films (Mylar, Melinex), Mitsubishi

(Hostaphan), Toray Lumirror), Terphane (Terphane), and

3 M (Scotchpar).

FILM MANUFACTURING PROCESS

Polyester is produced by combining ethylene glycol and

either terephthalic acid or dimethyl terephthalate in a

condensation reaction. PET ﬁlm can be either cast or

oriented. The oriented variety can be either blown or

tentered (stentered). Tenter-oriented PET ﬁlm is the

most versatile because the process imparts an improved

combination of physical properties.

In the cast-tentered process, the molten resin is ex-

truded onto a cooled casting drum (see Figure 1). The ﬁlm

is oriented in the machine direction by heating, then

stretching the ﬁlm to three to four times its original

length. The ﬁlm is then heated again in a tenter (a large

oven consisting of several heating zones) and drawn three

to four times in the transverse direction (see Figure 2).

The ﬁlm proceeds to the hottest zone of the oven, where

the now biaxially oriented ﬁlm is heat-set, or annealed.

This prevents the ﬁlm from shrinking back to its original

unstretched shape.

Film processing conditions affect shrinkage, gloss, ten-

sile strength, elongation, and other characteristics. The

ﬁlm can be treated or coated, within the manufacturing

process or afterward, to change or enhance its properties.

Figure 4. Effect of blowup ratio (BUR) on ﬁlm toughness. To

convert ft lbf/in. to J/M, multiply by 53.38.

FILM, ORIENTED POLYESTER 471

FILM PROPERTIES

PET has an outstanding combination of properties that

make it valuable to the converting and packaging indus-

tries. Base PET ﬁlm offers mechanical strength, dimen-

sional stability, moisture resistance, chemical resistance,

clarity, stiffness, and barrier properties. It handles well

and can be printed or laminated (see Table 1). In response

to customer needs, polyester ﬁlm manufacturers have

developed many technologies that change ﬁlm properties

to achieve useful effects (see Table 2).

Thermal

Polyester ﬁlm gains excellent thermal properties through

the heat-set process, allowing it to be processed and used

in a wide range of temperatures. It tolerates temperatures

ranging from 701C to 1501C for several hours or more,

and can withstand even higher temperatures for shorter

time periods, making it suitable for extended drying

ovens, hot stamping, and packaging processes that form,

ﬁll, and seal.

Barrier

Flavor preservation is a major concern in the packaging

industry. Barrier-type ﬁlms constitute 50% of current U.S.

PET ﬁlm consumption. Polyester ﬁlm has demonstrated

an excellent ability to retain ﬂavor and exclude odor from

outside the packaging (see Figures 3 and 4). Metallizing or

coating with PVC can provide greatly increased barrier

properties.

Metallizing. Metallized ﬁlms provide value to food

packagers concerned with package integrity and shelf

life. Metallized materials are decorative and also enhance

properties such as moisture, light and gas barrier, ﬂavor

protection, protection against static electricity, and excel-

lent machineability. Films other than polyester are now

being metallized and used in packaging. However, polye-

ster is still chosen when superior thermal stability and

moisture and oxygen barrier are desired. Increasing the

metal thickness further improves these barriers (see also

Metallizing, vacuum).

PVC. PET can be coated ofﬂine (after the manufactur-

ing process) with poly(vinylidene chloride). PVDC-coated

PET is used in transparent packages to provide good

barrier properties without metallizing. Typical coating

thickness is 0.0001 in. (approximately 2 lb per ream). A

major application for PVC-coated PET is in packaging

processed meats such as hot dogs and luncheon meats.

Flavor Scalping

PET ﬁlm is an excellent ﬂavor and odor barrier for

packaging products that contain strong ﬂavors, smells,

and migratory agents. The sealant that is used in a

package is important if ﬂavor scalping (the loss of ﬂavor

from a product to the laminate or environment) is an

Figure 1. Film processing.

Figure 2. Polyester orientation.

472 FILM, ORIENTED POLYESTER

issue. A coextruded, heat-sealable PET used as the sealant

layer scalps signiﬁcantly less ﬂavor from products than

does a PE sealant or an ionomeric (surlyn) sealant layer

(see Figure 5).

The sealant (in conjunction with the laminate chosen)

can either adsorb the ﬂavor or allow permeation through

the sealant and perhaps the laminate. PET ﬁlm as a

barrier web and coextruded, heat-sealable PET as a

sealant layer each provide superior ﬂavor barriers in

comparison with other packaging ﬁlms and sealants.

SURFACE MODIFICATIONS OF PET FILMS

Corona Treating

Corona treatments use an electrical charge to raise the

surface tension of ﬁlm and enhance its wet-out properties.

Corona treatment more closely matches the energy of the

coating surface to the energy of the substrate surface. This

promotes the polyester ﬁlm’s adhesion to various materi-

als used in different phases of conversion. Corona treating

has been an accepted method for over 30 years. Its use is

limited, however, because the treatment level dissipates

with time.

Pretreatments

Polyester can be pretreated in-line for a variety of surface

properties, making the coating an integral part of the ﬁlm.

With pretreatment, the coating is so thin that it is

virtually invisible. The speciﬁc coating to be used depends

on customer needs and processes, including the inks or

solvents to be used, the processing equipment, and the

demand of the end use. Pretreatments can improve hand-

ling by affecting slip characteristics on one or both sides.

Some pretreats create a ﬁlm surface that is receptive to a

broad range of coatings and inks. Antistat pretreatments

reduce static, which can cause handling problems and

compromise worker safety during processing. Other pre-

treats produce superior metal adhesion for certain end-

use applications.

Coextrusion

Coextrusion is another method for changing ﬁlm proper-

ties. This process involves casting together two or more

Table 1. Typical Properties of Polyester Films

Typical

Property Gauge Values Units Test Methods

Physical Nominal yield 48 42,200 in.

/lb

Tensile strength MD 48 32,000 psi ASTM DB82A

TD 39,000

Elongation at break MD 48 110 % ASTM D882A

TD 70

Coefﬁcient of friction (in/out) Dynamic 48 0.4 ASTM D1894

Static 0.5

Density 48 1.40 g/cc

Optical Total luminous transmission 48 88.5 % ASTM D1003

Gardner haze 48 3.6 % ASTM D1003

Thermal Typical shrinkage MD 48 3.6 % Unrestrained at

3741F for 5 minTD 4.0

Barrier MVTR 48 2.8 g/100 in.

ASTM F372

Unmetallized (24 h at 1001F and 90% rh)

Gas permeability (24 h at 771F and

75% rh at 1 atm)

48 O

6.0 1.6

31.0

cc/100 in.

ASTM D1434

Metallized MVTR (24 h at 1001F and 90% rh 48 0.05 g/100 in.

ASTM F372

Table 2. Technologies Available that Affect Film

Properties

Technology Film Properties Affected

Manufacturing process Tensile strength

Flatness

Shrinkage

Abrasion resistance

Roll formation

Polymer modiﬁcation (e.g., additives

or alloying)

Gloss

Clarity

Surface roughness

Slip

Abrasion resistance

Flexcrack

Adhesion

Heat seal

Barrier

Surface modiﬁcations (e.g., treating

or coating)

Adhesion

Slip

Barrier

Heat seal

Coextrusion Adhesion

Slip

Heat seal

Barrier

Surface roughness

Gloss

FILM, ORIENTED POLYESTER 473

layers of polyester ﬁlm to produce desired surface proper-

ties (see Figure 6). For instance, one layer of clear ﬁlm can

be coextruded with a layer of matte ﬁlm, or a ﬁlm that

handles well can be coextruded with a layer of heat-

sealing polyester, or resins of different colors can be

coextruded. The ﬁrst commercially available coextruded

PET ﬁlm imparted gloss and resisted glass ﬁber bloom

when used as a construction material for pool enclosures

and glazing. Today, one of the major applications for

coextruded PET is metallized snack-food laminations,

where it provides an absence of microcracking, a broad

seal range, temperature resistance, excellent barrier prop-

erties, and improved handling.

Other Surface Modiﬁcations

Techniques for producing high-barrier transparent coat-

ings have been available for many years. However, they

were not economically viable. Sputtering techniques using

indium tin oxide and aluminum oxide have produced ﬁlms

with oxygen transmission rates equal to those of metalliz-

ing. More recently, plasma treatments using silicon oxide

products have also yielded barrier properties equal to

metallized polyester (see Figures 3 and 4).

TYPES AND APPLICATIONS

Flexible packaging is a large and ever-changing source of

demand for oriented PET ﬁlm. Applications continue to

grow as manufacturers change processes and properties to

meet customer needs. In the past, polyester was consid-

ered the premier packaging material because of its unique

characteristics. However, many companies continued to

look for more economical ways of packaging. In many

cases, they were able to maintain product integrity while

using a less expensive package.

Figure 3. Barrier comparison. (Base substrates are 1 mil/metallic substrates 48 g unless noted otherwise.)

474 FILM, ORIENTED POLYESTER

In this day of downsizing and consolidation, however,

companies are investing in equipment that allows them to

run faster and use fewer people, and polyester is regaining

its cost-competitiveness. To run equipment at full poten-

tial, polyester is preferred by converters because of its

excellent ability to maintain registration (temperature

stability) and because of its outstanding uniformity across

the web and from point to point. The companies that use

these converted products are also looking to reduce their

costs by running faster. At one time, candy bars were

wrapped at a rate of 100 per minute; today they exceed

400 per minute. Companies using polyester for packaging

can obtain these higher speeds without distortion.

Coffee

Coffee has long been packaged in metallized polyester

structures for the fractional pack market. Typically, it has

been used for restaurants and ofﬁces. PET in conjunction

with aluminum foil and metallizing has taken a substan-

tial portion of the coffee-packaging market previously held

by metal cans. The brick-pack concept offers better eco-

nomics and reduced shelf space.

Boil-in-Bag

Boil-in-bag applications typically use a 0.5-mil PET ﬁlm

with 2-mil medium-density PE adhesive lamination. A

two-part adhesive system is used. The PET ﬁlm is neces-

sary for good dimensional stability in fabricating and

sealing the pouch. It also provides heat-dimensional sta-

bility during the boiling operation (1).

Figure 5. Percent of ﬂavor compound retained. This graph in-

dicates the percentage of ﬂavor compound retained in orange-

ﬂavored Kool-Aid powder. Ethyl butyrate, myrcene, and limonene

are the three key ﬂavor components in the orange-ﬂavored

powder drink mix. The laminate structures were paper/poly/foil/

PE, paper/poly/foil/ionomer (surlyn), and paper/poly/metallized

heat-sealable PET.

Figure 6. Coextrusion.

Figure 4. Barrier comparison. (All substrates are 48 g unless noted otherwise.)

FILM, ORIENTED POLYESTER 475

Bag-in-Box

Typical structures are polyethylene/metallized PET/poly-

ethylene. Metallized PET is used because of good oxygen-

and moisture-barrier properties and resistance to ﬂavor

scalping. Wine was the ﬁrst application for this type of

structure. Today it is also used for bulk packaging of

condiments such as ketchup and mustard, as well as for

foods such as tomato sauce (see Bag-in-box-liquid product).

Retort

The term retort refers to the process of sterilizing (cook-

ing) a product after it is already packaged. A typical

structure contains PET/aluminum foil/high-temperature

adhesive/cast polypropylene (as a sealant layer) or PET-

aluminum foil/HDPE (2). This type of packaged provides

ﬂavor that is closer to fresh vegetables in comparison with

canned vegetables.

Dual Ovenable Lidding

PET is typically used as a lid to cover frozen single-serve

dinners packaged in CPET trays. PET ﬁlm can withstand

the temperature differential of the freezer-to-oven transi-

tion, for both convection and microwave ovens. This

market has a unique requirement: The ﬁlm must seal to

the tray, but must be peelable after heating.

Standup Pouches

The conversion from rigid containers to standup pouches in

the United States has begun. Although the new packaging

is touted for source reduction, the conversion will be driven

by economics. The cost of producing, transporting, and

storing unﬁlled ﬂat pouches is less than that of rigid

containers. Also, the pouches easily accept high-end gra-

phics to create bolder, brighter packages on the shelf. These

structures are typically thicker laminates (5–7 mil) to pro-

vide the stiffness necessary to stand on the shelf. PET, when

reverse-printed on the outside of these packages, provides

the thermal stability necessary to heat-seal through the

thickness of the laminates (see Standup pouches).

Medical Applications

Oriented polyester ﬁlm is ideal for packaging of medical

and surgical devices because of its clarity (visibility) and

temperature stability during sterilization. Untreated

polyester has no migratory products. The PET ﬁlm is

combined with special paper and spun-bonded polyoleﬁn,

which allow gases to permeate both ways and restrict

unwanted bacteria. Ethylene oxide is the preferred ster-

ilization method today. Other techniques include steam

and gamma radiation. The properties of polyester ﬁlm are

not affected at the highest levels of g radiation. Sheets are

also used to make X-ray ﬁlm and test strips (3).

Shrinkable PET

Historically, both tamper-evident sleeves and labels have

been made of vinyl. Over the last few years, Europe has

begun to insist on products other than vinyl because of

environmental concerns. Now being offered in Europe is a

polyester that provides 50% shrink in the transverse

direction and 5% in the machine direction.

Hot-Stamping Foils

The preferred substrate for hot-stamping foil has, for

many years, been polyester ﬁlm. The typical thickness is

48 gauge. Most of the ﬁlm used is heat-stabilized to allow

for better quality in processing and reproduction. In the

normal hot-stamping process, heat and pressure are ap-

plied to produce a decorative image. Metallic hot-stamping

foils are used to decorate boxes and bottles for the

cosmetics and personal-care industries. A pigmented

stamping foil is used to code or date products.

Holograms

In the past, holograms were used primarily as security

devices on credit cards. Polyester was initially chosen as a

substrate for use in this application because of its high-

temperature stability and dimensional stability, along

with its ability to be produced in thin gauges (48 gauge).

The ability to use continuous processes with wider ﬁlm

widths has led packagers to begin incorporating holo-

grams into packaging. New polyester ﬁlms are being

developed that allow holograms to be produced at faster

speeds without coating (see also Holography).

Labels

The label industry uses many substrates, including paper,

PVC, styrene, polypropylene, and polyester. Polyester

plays many roles in this industry. It is sometimes used

as a base stock that receives printing or bar codes. It can

also be used as a protective cover lay or as a release liner.

It is available either in transparent or white. The ease

with which polyester can be metallized makes it suitable

for high-quality decorative applications such as personal-

care products, cosmetics, and pharmaceuticals.

ENVIRONMENTAL CONCERNS

PET ﬁlm has a number of opportunities to stand out

against other ﬂexible-packaging ﬁlms as more and more

environmental pressure is placed on the packaging in-

dustry. Polyester is a good environmental choice because it

is inherently more recyclable than other plastics and

because of its capacity for including recycled content.

The biggest impact on the environment comes from

reducing the amount of overall material used in packa-

ging. Source reduction is driven by economic forces as

well. Rigid containers (glass, metal cans, rigid plastics,

etc.) are being converted to ﬂexible standup pouches

where possible. Flexible standup pouches can reduce the

amount of packaging material by 70–80% when compared

to a rigid container. Empty pouches occupy 70–90% less

landﬁll volume. Rigid containers (plastic, cardboard, etc.)

are also being source-reduced to the minimum technical

requirements for their particular product.

PET ﬁlm can also accommodate postconsumer recycled

(PCR) feedstock within its manufacturing process. The

476 FILM, ORIENTED POLYESTER

feedstock can be mechanically recycled, which requires a

relatively pure PET feedstock. Mechanically recycled PET

soda bottles can create a feedstock pure enough for FDA

compliance. The feedstock can also be chemically recycled

by either methanolysis or glycolysis process and can

remain in FDA compliance. PCR feedstock is more expen-

sive than virgin PET resin because of the additional

processing involved (see also Recycling).

PEN FILMS

Opportunities in the packaging market were created by the

introduction of PEN ﬁlm and resin for bottles. PEN [poly

(ethylene naphthalate)] is a member of the polyester family

with a higher glass-transition temperature that delivers

improved performance characteristics. The most important

is its barrier properties. Teonex is the world’s ﬁrst PEN

ﬁlm developed by Teijin DuPont ﬁlms. Compared to PET,

PEN provides approximately ﬁve times the barrier for

carbon dioxide, oxygen, or water-vapor transmission (see

Figure 7). PEN also provides superior performance at

higher temperatures when compared to PET. When used

as a resin for rigid-container packaging, PEN allows them

to be hot-ﬁllable and both returnable and rewashable. As a

ﬁlm, PEN provides 25% greater stiffness, allowing thinner

designs and greater barriers simultaneously (4).

BIBLIOGRAPHY

J. Newton, ‘‘Film, Oriented Polyester’’ in A. J. Brody and K. S.

Marsh, eds., The Wiley Encyclopedia of Packaging, 2nd edition,

John Wiley & Sons, New York, 1997, pp. 408–415.

Cited Publications

1. J. G. Brennan and B. P. F. Day, ‘‘Packaging’’ in J. G. Brennan,

ed., Food Processing Handbook, Wiley-VCH, Weinheim, 2006.

2. M. J. Kirwan and J. W. Strawbridge, ‘‘Plastics in Food Packa-

ging’’ in R. Coles, D. McDowell, and M. J. Kirwan, eds., Food

Packaging Technology, Blackwell Publishing, Oxford, 2003.

3. ‘‘Mylar Film and Polyester Film’’ Graﬁx Plastics, www.

graﬁxplastics.com/mylar, accessed October 2008.

4. Teonex, product outline, Teijin DuPont Films, www.

teijindupontﬁlms.jp, accessed October 2008.

FILM, ORIENTED POLYPROPYLENE

ELDRIDGE MOUNT

EMMOUNT Technologies,

Fairport, New York

Oriented polypropylene ﬁlm was made commercially for

the ﬁrst time by Montecatini of Italy in the late 1950s.

Shortly after Imperial Chemical Industries (ICI) of the

United Kingdom entered into OPP ﬁlm production, Kor-

dite (the predecessor of ExxonMobil’s Commercial Films

Division), Hercules, Olin, and DuPont started production

in the early 1960s. Through the mid-1980s, OPP manu-

facturing equipment was engineered using in house ex-

pertise at the ﬁrst 10–20 OPP manufacturers, but today

orientation equipment suppliers supply the engineering

expertise supplying turnkey lines around the world as the

demand for OPP ﬁlms continues to grow. Orienting lines

are typically 6–8 M in width with 4–10 M lines in opera-

tion. Line speeds range from a low of 200 M/min (for older

machines), to 500 M/min (for a modern orienter).

In 2000, world demand stood at about 2,801,000 tonnes

and was in balance with annual capacity followed by a 5-

year period of excess capacity which is just now coming

back into balance with capacity at a world-wide demand of

approximately 5,000,000 tonnes (1, 2). Market growth of

approximately 5–6% is expected for the next 10 years with

world–wide capacity growing to approximately 9,000,000

tonnes by the year 2015. This assumes the continued

shutdown of older slower and narrower lines which are

rapidly becoming obsolete based upon their economics as

well as aspects of their machine design. Growth of OPP

markets is driven by technological product innovations,

geographic expansion, and population growth as the per

capita consumption of OPP increases with economic de-

velopment. In the last 10 years, capacity growth has been

primarily in the Far Eastern markets (China and India) as

well as in Latin America and Central and Eastern Europe.

Production capacity has been decreasing in North Amer-

ica, Japan, and, to a small extent, Western Europe. Also, a

great deal of consolidation has been taking place in the

market, with several manufacturers being absorbed by

other companies.

As of 2007, there were reported to be 195 producers and

516 orienting machines (2).

Figure 7. PEN ﬁlms.

FILM, ORIENTED POLYPROPYLENE 477