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

Подождите немного. Документ загружается.

as well as vertical compression sections suited to overhead

case-conveyor systems (see the Conveyors article). The

selection of a wrap-around versus a premade case machine

requires close scrutiny of the particular application

requirements including type of case, potential board sav-

ings, machine cost, ﬂoor space, case rate, size case, and

so on.

TRAY FORMER/LOADER

The concept of replacing a corrugated case with a shrink-

wrapped tray was developed as part of an ongoing effort to

reduce packaging material costs. The tray former/loader

(see Figure 8) with a shrink wrap is ideally suited for

those products, e.g., cans and bottles, that do not require

the complete product protection provided by a full case.

Corrugated trays that are 1–2 in. (2.5–5.1 cm) high are

preferred, but there are a host of different tray designs

suited to the product, distribution, display, and so on.

Many machine alternatives are available, including equip-

ment to make a tray and present it to a vertical or drop-

load caser. There are also integrated systems that extract

a blank from the magazine, fold up two or three sides of

the blank, index to the load area (where the product is

deposited horizontally or vertically), and transfer, folding

remaining panels, and gluing to form the ﬁnal tray. At this

point, the ﬁlled and sealed tray is indexed into a shrink-

wrapping machine (see the Wrapping, shrink article)

where ﬁlm (see the Films, shrink article) is completely

wrapped and shrunk around the complete load. The ﬁlm

unitizes and holds the product in the tray and provides

protection from the external environment. The cost for the

corrugated tray and shrink ﬁlm is considerably less than a

full corrugated case, but consideration must be given to

product protection and warehouse stacking strengths

because now the product must bear the full vertical

load, warehouse identiﬁcation, and so on. Tray rates for

intermittent-motion machines are approximately 30/min,

whereas continuous-motion machines can run in excess of

70/min.

OTHER CONCEPTS

The case-loading ﬁeld is extremely broad, and many

other different types of machines are available for sp

ecial markets and applications too numerous to describe

in detail. For example, there is automatic case-opening/

bottom-gluing machinery that presents an opened case

with the bottom ﬂaps glued for the manual loading of large

or irregular-shaped items. This same equipment can also

present an opened/glued case to a vertical or drop-load

caser, increasing the operating speeds of hand-packed

lines. Automatic case openers are available that bring a

case down vertically over the accumulated product and

then fold and seal the ﬂaps or that lift the acculated

product vertically up through the bottom of a corrugated

case, folding and sealing ﬂaps accordingly. There are case

loaders that role the product into the case and manual

machines that are used for handling irregular-shaped

products in a wrap-around blank. All these variations

and concepts are necessary in providing the unique ma-

chinery to meet the changing markets and products of

today.

BIBLIOGRAPHY

General References

The PMMI 1984–1985 Packaging Machinery Directory, Packaging

Machinery Manufacturers Institute, Washington, DC.

S. Sacharow, A Guide to Packaging Machinery, Harcourt-Brace

Jovanovich, New York, 1980.

CAST, POLYPROPYLENE

ELDRIDGE M. MOUNT

EMMOUNT Technologies,

Canandaigua, New York

Cast polypropylene ﬁlm is made primarily by the chill-roll

cast ﬁlm process using multilayer coextrusion systems

(Figure 1). Other methods can also be used to produce cast

polypropylene ﬁlm such as slot die extrusion into a water

bath or a tubular water quench processes. However, these

have been largely superseded by the cast ﬁlm process due

to the higher productivities and superior ﬁlm ﬂatness

possible with the chill roll process. Because cast polypro-

pylene ﬁlm does not go through the solid-state orientation

process (see Film, oriented polypropylene), the barrier

properties, low temperature durability, and mechanical

strength are not as well developed as in mono- or biaxially

oriented polypropylene ﬁlm. Typical cast polypropylene

ﬁlms are desired for their increased temperature resis-

tance, high clarity, and gloss compared to typical cast or

blown polyethylene ﬁlms. Other desirable properties of

the cast polypropylene is the ﬁlms stiffness, oil and grease

resistance, and heat sealing properties when used as a

sealant layer in a lamination to paper, cellophane, or-

iented polyester, or oriented PP. Barrier properties of cast

polypropylene may be signiﬁcantly enhanced by vacuum

metalization allowing the ﬁlm to compete directly with

oriented metalized ﬁlms in laminations.

Figure 8. Tray former/loader.

248 CAST, POLYPROPYLENE

A typical product design of a 1 side corona treated,

three layer cast PP ﬁlm is shown in Figure 2. Depending

on the desired ﬁlm surface properties, the ﬁlms can have

the same or different outer skin polymers to give coex-

truded ﬁlms with A/B/A, B/B/A or A/B/C structures.

Product designs of this type are alone or for inner sealing

webs in laminations, where the treated surface is the

lamination surface. Suitability of the ﬁlms for metaliza-

tion of the treated surface will depend on the type and

level of migratory and particulate additives added to the

ﬁlm.

Typically, the ﬁlm design of Figure 2 would have 500–

3000 ppm of a migratory slip additive, such as erucamide,

added to the skins and the core of the ﬁlm to reduce the

ﬁlm coefﬁcient of friction (COF). The outer skins will also

have 2000–6000 ppm of a mineral antiblock particle such

as amorphous silica (of 1.5–8-micron average diameter)

added to aid in blocking resistance, COF control, ﬁlm

winding, and packaging machine performance. Metaliza-

tion grade ﬁlms would be produced without any migratory

or particulate additives in the treated (metalization) sur-

face and a reduced level of migratory additives in the core

layer.

Five-layer product designs add considerable ﬂexibility to

the ability to tailor ﬁlm properties by both layer polymer

selection and ﬁlm layer additive control. Figure 3 shows a

product design for optimizing the effectiveness and cost of

expensive ﬁlm additives such as antiblock particles. In this

design, the antiblock particles are conﬁned to the outer-

most thin surface layers to enhance their effectiveness and

decrease the overall additive concentration in the ﬁlm. This

reduces the cost of the ﬁlm by reducing the consumption of

additive concentrates and helps improve ﬁlm clarity by

lowering ﬁlm haze induced by the particles. The potential

number of product designs possible with ﬁve or more layers

is enormous and greatly aids in the production of products

focused for various end uses while enhancing product

properties.

Cast polypropylene ﬁlms are being used in both packa-

ging and nonpackaging applications. In the packaging

area, the majority of applications are food-related. In

food packaging, the cast polypropylene ﬁlm accounts

for a major share of the candy twist wrap application,

because cast polypropylene ﬁlm is particularly suitable for

newer high-speed twist wrap machines. In cheese-wrap-

ping applications, polypropylene/low-density polyethylene

(PP/LDPE) coextruded ﬁlm is used because of improved

moisture barrier and ﬁlm stiffness supplied by the cast

polypropylene layer compared to single-layer LDPE.

Cast polypropylene ﬁlm lamination using a high-

strength outer web for snack-food packaging are widely

used in Asian markets and represents a large potential

market in North America, particularly in applications and

laminations using metalized polypropylene ﬁlms. In the

metalized laminations, the cast polypropylene is meta-

lized and represents the addition of a high-barrier sealant

to the lamination. In addition, the use of the metalized

cast polypropylene in laminations permits the use

of reverse-printed outer webs giving improved graphics

and print durability when compared to laminations of

surface printed metalized ﬁlms to LDPE sealants. In

laminations that do not require the low-temperature

durability and mechanical strength of metalized oriented

polypropylene ﬁlms, cast polypropylene ﬁlm can offer an

improved heat sealing capability readily producing her-

metic seals, a distinct advantage in some applications and

markets.

Other applications include tapes, labels, diaper compo-

nents, photograph holder, page protectors, medical

Extruder

Core

Skin

Coextrusion

adapter

Die

Air knife

Chilled

casting

roll

Film trim

Vacuum

box

Thickness

monitor

Trim knife

Winding

station

Tension

control

Corona

treater

Skin

Figure 1. Three-layer cast-ﬁlm line.

Corona treated surface

10%-25% random copolymer PP outer layer

80% to 50% homopolymer PP core

10%-25% random copolymer PP outer layer

Figure 2. Typical three-layer cast PP ﬁlm product design.

Corona treated surface

2%-5% random copolymer PP outer layer + Antiblock particle

8%-20% random copolymer or homopolymer PP intermediate layer

80% to 50% homopolymer PP core

8%-20% random copolymer or homopolymer PP intermediate layer

2%-5% random copolymer PP outer layer+ Antiblock particle

Figure 3. Possible ﬁve-layer cast PP ﬁlm product design to

optimize additive addition.

CAST, POLYPROPYLENE 249

packaging, and textile packaging. The advantages for

using cast polypropylene ﬁlm in textile packaging are

faster bag production rates and better contact clarity

and gloss for PP compared to LDPE. The use of cast

polypropylene ﬁlm for medical packaging is a potential

growth area, due to PP’s higher temperature resistance in

steam sterilization. Cast polypropylene ﬁlm laminated

with high-temperature-resistant outer web is particularly

suitable for retort pouch applications due to the high-

temperature resistance for cast polypropylene ﬁlm in the

retort process. This is also an advantage in microwavable

cook in bags emerging in the market. Cast multilayer

polypropylene ﬁlms are being used for industrial stretch

ﬁlm applications. In the stretch ﬁlm application, the use of

multilayer coextrusion of PP with PE resins is being used

(1, 2) to increase the toughness of the stretch ﬁlms.

FILM FABRICATION

Cast polypropylene ﬁlm is commonly made by chill roll

casting drum process. Today three- to ﬁve-layer cast lines

of 6000-mm widths running at speeds of 350 m/min

producing rolls of up to 1.2-M diameter are available.

Typical extrusion melt temperatures are from 4801Fto

5201F. Screw designs are varied but will tend toward

longer L/Ds and barrier designs typical of PP extrusion.

Today many new cast polypropylene ﬁlm products are

made by the coextrusion process using a multilayer feed-

block–single cavity die combination, or a multicavity ﬂat

die or a combination of a feedblock and a multicavity die.

Film product design complexity is increasing as the use of

microlayer ﬁlms is increasing due to claimed physical and

barrier property advantages.

Once melted and formed in the coextrusion system, the

polypropylene extrudate emerges out of the ﬂat die and is

immediately quenched on the chill roll with an air knife or

vacuum box. This melt pinning forces the extrudate into

intimate contact with the chill roll (see Figure 1). Increas-

ing the chill-roll temperature and/or increasing chill-roll

takeoff speed normally improves ﬁlm stiffness but de-

creases optical clarity. After the quenching station, there

is an edge trimming station to slit off the thickened edges

formed as the melt is drawn from the die. Then, a ﬁlm-

thickness monitoring device, typically with a b-radiation

source, is repetitively moved across the ﬁlm on a rigid

650

600

550

500

Film 1% secant modulus (MPa)

450

400

0 7 14 21 28

s after extrusion

1% secant modulus CPP vs. days from extrusion

25 micron Cast copolymer PP film

Figure 4. Plot of 1% secant modulus as a function of

time from extrusion of a 25-micron cast ﬁlm of PP

random copolymer. (Redrawn from reference 4.)

0.7

0.6

0.5

Film COF (film to film)

0.4

0.3

0.2

0.1

0 5 10 15

Days after extrusion

20 25 3

COF vs. days from extrusion

25 micron cast film of PP Random copolymer

Figure 5. Plot of ﬁlm-to-ﬁlm coefﬁcient of friction

as a function of time from extrusion of a 25-micron

cast ﬁlm of PP random copolymer. (Redrawn from

reference 4.)

250 CAST, POLYPROPYLENE

track to scan the ﬁlm width and report the transverse-

direction (TD) thickness (gauge) proﬁle. Automatic control

systems then adjust the die opening to control ﬁlm thick-

ness to speciﬁed thickness tolerances. Film thickness

variations of 1–2% are readily achieved.

Between the thickness monitoring station and the ﬁlm

winding station, a corona treatment station is located to

enhance ﬁlm surface energy of the ﬁlm. This is done to

improve the wetability of the ﬁlm surface for better ink

printability, metalization, or lamination adhesion.

Tension control for cast polypropylene ﬁlm winding is

very important due to the relatively low modulus of the

ﬁlm. With very high tension, the ﬁlm tends to stretch as it

is wound in the area of any areas of thicker ﬁlm. These

stretched areas form harder raised bands in the wound

roll which are called a ‘‘gauge band.’’ When such a roll

with hardened gauge bands is unwound for use, it will not

lay ﬂat in the stretched area and will show defects that are

called ‘‘baggy lanes’’ in the ﬁlm. Films with baggy lanes

are unsuitable for subsequent slitting, printing, metaliza-

tion, or lamination. To aid in minimizing gauge bands,

winder oscillation in the transverse direction, of up to 10

cm, can be added to randomize the gauge proﬁle. This can,

in some cases, avoid the buildup of the gauge band and

minimize or eliminate baggy lane formation.

After winding up, the mill rolls normally need post-

treatment (aging) to stabilize the ﬁlm properties. A general

aging condition is 401C for 72 h. This aging is necessary

because polypropylene undergoes a secondary crystalliza-

tion. The secondary crystallization is most pronounced

over a period of 7 days but can continue for up to 21

days. The impact of the secondary crystallization can

be observed as an increase in ﬁlm modulus with time

(Figure 4) (3).

Film surface coefﬁcient of friction (COF) can, and often

must, be modiﬁed with antiblock particles and migratory

slip additives, such as fatty acid amides, to improve

the ﬁlm-handling characteristics on packaging machines.

However, these additives reduce ﬁlm clarity by increasing

ﬁlm internal (particulate additives) and surface (migra-

tory additives) haze. The balance of ﬁlm clarity and

surface COF must be optimized to insure a balance

between appearance and ﬁlm machineability. Coextrusion

technology is used to minimize the level of particulate

additives by limiting them to the ﬁlms outermost surface

layers, maximizing the surface effects while minimizing

the additive effect on clarity. Film COF will decrease with

storage time as the migratory additives diffuse (Bloom) to

the ﬁlm surface (Figure 5) (4) and create a thin layer of

additive on the surface which serves as a surface lubri-

cant. The time required to complete the additive migration

will depend upon the storage temperature and the migra-

tory additive chosen. Migratory slip technology is difﬁcult

to control with any precision and can result in ﬁlms with

too high a COF (low migration) or too low a COF (high

migration). Too high a migration can create a weak

boundary layer on the ﬁlm surface and prevent proper

ink, metal, or adhesive bonding. Too high a migration will

also interfere with ﬁlm optics giving lower gloss and

increased haze.

FILM PROPERTIES

Cast polypropylene ﬁlms can be a monolayer or multi-

layer coextruded ﬁlm to balance barrier, printing, heat

seal, COF, and other properties. Typical properties for cast

polypropylene ﬁlm are shown in Table 1. Oriented poly-

propylene ﬁlm is superior to cast polypropylene ﬁlm in

barrier properties and mechanical strength. However, cast

polypropylene ﬁlm has excellent tear resistance and is

cost effective. Each type of ﬁlm has beneﬁts and disad-

vantages, which must be weighed in determining which

ﬁlm is most appropriate ("ﬁt for use") for a particular

application.

BIBLIOGRAPHY

General References

K. R. Osborn and W. A. Jenkins, Plastic Films, Technomic

Publishing, Lancaster, PA, 1992.

Table 1. Typical Properties for Nonoriented Polypropylene Film (1 mil)

Properties Copolymer Homopolymer ASTM Test Method

Density, g/mL 0.89 0.90 D792

Haze, % 2 2 D1003

Gloss, % 86 86 D2457

Ultimate tensile strength, psi

MD 8600 9200 D882

TD 5200 6300

Elongation, %

MD 500 600 D882

TD 650 650

1% secant modulus, psi

MD 70,000 100,000 D882

TD 70,000 100,000

Heat-seal temperature range, 1F 270–330 330–370

Water-vapor transmission rate, g mil/100 in.

24 h 90% rh/1001F 0.8 0.7 Mocon

Oxygen permeability, C(mL mil)/(100 in.

24 h/atm 231C, 0% rh 240–300 240–300 Mocon

CAST, POLYPROPYLENE 251

J. H. Briston and L. L. Katan, Plastics Films, Longman Scientiﬁc

& Technical, London, 1989.

K. M. Finlayson, Plastic Film Technology, Technomic Publishing,

Lancaster, PA, 1989.

I. Miglaw and E. Pirog, ‘‘Film, Nonoriented Polypropylene’’, in M.

Bakker, ed., The Wiley Encyclopedia of Packaging Technology,

John Wiley & Sons, New York, 1986, pp. 315–317.

Cited References

1. S. Miro and W. L. Harkey, ‘‘Industrial Stretch Films,’’ U.S.

Patent 5,756,219, May 26, 1998.

2. D. Simpson and T. Jones, ‘‘Multilayer Stretch Cling Film,’’ U.S.

Patent 6,265,055, July 24, 2001.

3. Redrawn Figure 1 from I. Miglaw and E. Pirog, ‘‘Film, Non-

oriented Polypropylene’’ in M. Bakker, ed., The Wiley Encyclo-

pedia of Packaging Technology, John Wiley & Sons, Inc., New

York, 1986, p. 316.

4. Redrawn Figure 1 from I. Miglaw and E. Pirog, ‘‘Film, Non-

oriented Polypropylene’’ in M. Bakker, ed., The Wiley Encyclo-

pedia of Packaging Technology, John Wiley & Sons, New York,

1986, p 316.

CELLOPHANE

Updated by Staff

INTRODUCTION

The word cellophane was derived from the ﬁrst syllable

of cellulose and the ﬁnal syllable of diaphane, meaning

transparent. It was invented in the early 1900s in France

and introduced in this country in 1924 by E. I. du Pont de

Nemours & Company, Inc. In the early stages, cellophane

was somewhat of a curiosity that was very expensive, and

its use was limited to the packaging of luxury items.

The growth of cellophane paralleled the growth and

development of the entire ﬂexible-packaging industry,

from printing presses and inks to automatic packaging

machinery. For 30 or more years, the dominant ﬂexible

packaging material was cellophane because it was so well

suited to offer the marketplace a wide variety of charac-

teristics adaptable to product needs at reasonable costs.

The large markets were in the areas of baked goods,

candies, and tobacco products.

The advent of plastic materials such as polyethylene

and polypropylene started the corrosion of cellophane

consumption that resulted in the closing of many cello-

phane plants, due mostly to the higher prices of cellophane.

However, in a new more environmetnally conscious mar-

ket, cellophane may return in popularity. Cellophane is

100% biodegradable and made from a renewable source.

Cellophane is a thin, ﬂexible, transparent material used

worldwide mainly in packaging applications. The primary

raw material used in manufacturing cellophane is ‘‘dissol-

ving’’ wood pulp purchased from wood pulp suppliers. Since

its introduction in 1924, additional types of cellophane

have been introduced to meet changing packaging needs.

The primary markets for cellophanes are the food, phar-

maceutical, and healthcare product markets. In the food

sector, cellophane is used to package nuts, candies, dried

fruits, spices, cake mixes, and greasy or oily products (1).

FEATURES

Cellophane has various attributes that have accounted for

its continued acceptance and ongoing utilization in ﬂex-

ible-packaging applications. These include:

. Dead-Fold. Once shaped in certain packaging appli-

cations, cellophane, unlike plastic ﬁlms, can main-

tain its shape. This is especially true in twist-wrap

applications such as packaging for hard candies.

. Ease in Tearing. Differentiated tensile strength

within cellophane allows for ease in tearing and

opening products that utilize this material for

packaging and for tape.

. Machinability. Cellophane can be cut and sealed

easily and economically. Many competing ﬂexible-

packaging materials require more sophisticated and

expensive packaging equipment to process them. A

method and device for ﬁnishing cellophane packets

has recently appeared in the literature (2).

. Appearance. Cellophane has a high level of gloss and

haze versus certain competing ﬂexible ﬁlms. These

factors are important to customers desiring a pre-

mium appearance for their packaging.

. Resistance to High Temperatures. Cellophane can be

used in temperature ranges above those of many

common plastic ﬁlms, which is critical for hot-ﬁll

applications and for use in shrink tunnels.

. Barrier to Air and Moisture. Cellophane, when

coated with poly(vinylidene chloride) copolymer

(PVdC) or other barrier resins, has increased

strength, seal, and barrier properties. Uncoated

cellophane has good barrier to gases and aroma,

but poor barrier to moisture.

FILM TYPES

Cellophane ﬁlm is produced in various types, which vary

with respect to (1) ﬁlm thickness, (2) ﬁlm width, (3) type

and degree of coating, and (4) combination with other

materials.

1. Film Thickness. Cellophane can be supplied in vary-

ing thickness depending on customers desire for

strength, ﬂexibility, and resistance to air and

moisture.

2. Film Width. The ﬁlms can also be produced in

numerous widths, which are custom cut to speciﬁc

packaging needs.

3. T

ype and Degree of Coating. A large percentage

cellophane products are coated, generally on

both sides of the ﬁlm. These coatings increase the

252 CELLOPHANE

cellophane’s durability and seal qualities. Two of

the major coating materials are poly(vinylidene

chloride) copolymer (PVdC) and nitrocellulose

(NC). PVdC offers more durability and higher moist-

ure and gas barriers than NC. NC-coated ﬁlms are

typically used to package cookies, snacks, cheese,

gum, and cough drops.

4. Combination with Other Materials. Cellophane

ﬁlm can be laminated to other ﬁlms such as biaxially

oriented polypropylene (BOPP) or metallized polye-

ster ﬁlm. These products offer enhanced qualities

of both cellophane and the particular reinforcement

material that is used. The end result is a ﬂexible ﬁlm

that has excellent resistance to breakage and a high-

quality appearance. Reinforced cellophane is used

primarily to package pretzels, popcorn, chips, nuts,

meats and cheeses.

PHYSICAL PROPERTIES

The physical properties of cellophane are closely related

for all the ﬁlm types. They are differentiated according to

coatings, reinforcing structures, and thicknesses. All of

them are clear with the exception of two of the reinforced

structures: metallized polyester and white opaque poly-

propylene core.

The nitrocellulose-coated ﬁlms range from 16,000 to

18,000 psi (lb/in.

) tensile strength in machine direction

and 8000–9000 psi in transverse direction. Elongation is

15–25% in machine direction and 30–45% in the trans-

verse direction. The heat-sealable coatings have a wide

sealing range, usually requiring temperatures of 225–

3501F, depending on machine speed and pressure.

Water-vapor transmission rate (WVTR) for the

moisture-proof ﬁlm types averages about 0.5/100 in.

per

h, and the breathable types range between 30 and

50. Oxygen permeability averages about 2 mL/(100 in.

)

(24 h) (atm) for most two-side-coated nitrocellulose ﬁlm

types.

The PVdC- or saran-coated ﬁlms utilize very similar

and in some cases identical cellulose base sheets; but as

previously described, the PVdC coating results in im-

proved keeping characteristics.

Machine direction (MD) and transverse direction (TD)

tensile strengths and elongations are roughly equivalent

to the nitrocellulose-coated ﬁlms. PVdC-coated ﬁlms ex-

hibit superior gas barrier properties to nitrocellulose

coated ﬁlms. Where the average oxygen barrier for nitro-

cellulose is about 2 mL/100 in. per h, the PVdC-coated

ﬁlms are about 0.5. Coefﬁcient of friction is about 0.30–

0.35 for both PVdC- and NC-coated ﬁlms.

The third major type of cellophane ﬁlm is plain,

uncoated ﬁlm. This ﬁlm is used most widely in produ-

cing pressure-sensitive tapes and also for applications

where high-quality printing is desired. This uncoated

ﬁlm prints most easily with almost any ﬂexographic

printing ink. The reason for this wide range of ink

receptivity is that the surface being uncoated readily

absorbs liquids.

CELLOPHANE PRODUCTION

Cellophane is a regenerated cellulose ﬁlm derived from

chemically puriﬁed wood pulp known in the trade as

‘‘dissolving pulp.’’ Cellulose, the primary repeating mole-

cule of regenerated cellulose ﬁlm, is shown below:

Cellulose

The cellophane production process involves ﬁve major

steps: (1) soaking of the wood pulp in sodium hydroxide

solution for several hours to form alkali cellulose; (2)

polymerization of the alkali cellulose, under controlled

conditions; (3) reaction of the alkali cellulose with carbon

disulﬁde to form an alkali-soluble sodium xanthate; (4)

formation of viscose by dissolving sodium xanthate in a

solution of sodium hydroxide; and (5) extrusion of the

viscose through a slit die into a water/sulfuric acid/sodium

sulfate coagulating bath. After the regeneration of the

cellulose, the process is completed by neutralizing, wash-

ing, and drying the ﬁlm (3).

ENVIRONMENTAL ASPECTS

Packaging accounts for 30% of all solid waste by weight.

The increasing cost of disposing solid waste has forced

the adoption of new methods of packaging that promote

recycling and degradability. Cellophane is made from

cellulose, a component of plants and trees. Trees are

farmed and harvested. No rainforest or old growth trees

are used in the production of cellophane. Cellophane is

100% biodegradable. When buried, uncoated cellophane

degrades in 28–60 days, coated cellophane degrades in 80–

120 days. In comparison, the other packaging materials

such as poly(vinyl chloride), polyethylene, poly(ethyl ter-

ephthalate), and polypropylene show no signs of degrada-

tion over long periods of time (1). Nevertheless, the

polluting effects of carbon disulﬁde and other byproducts

produced during the production of cellophane should also

be considered.

BIBLIOGRAPHY

B. Jenkins, ‘‘Cellophane’’ in A. J. Brody and K. S. Marsh, eds., The

Wiley Encyclopedia of Packaging Technology, 2nd edition,

Wiley, New York, 1997, pp. 194–197.

Cited Publications

1. ‘‘Cellophane, ‘‘Pak-sel Corporation, Portland, OR, www.pak-

sel.com, accessed February 2008.

2. S. Boriani and S. Negrini, U.S. Patent 7,131,247 (to G. D.

Societa per Azioni), November 7, 2006.

CELLOPHANE 253

3. J. N. BeMiller, ‘‘Carbohydrates’’ in Kirk–Othmer Encyclopedia

of Chemical Technology, 5th edition, Wiley, Hoboken, NJ, 2004,

p. 716.

CHANGEOVER OF PACKAGING LINES

JOHN R. HENRY

In the part, one popular soft drink was available in a

single ﬂavor, bottle and size. Changeovers were unknown.

That same product today is available in over 100 varia-

tions. The company went from no changeovers to multiple

daily changeovers. Most companies are in the same boat.

They face more frequent and more changeovers as product

variations proliferate. This trend is expected to increase

into the future. Changeover is a key issue in the operation

of almost every packaging line today.

This article will deﬁne and describe changeover and

changeover time. It will also provide a roadmap and

techniques to improve the quality of changeover while

reducing the time lost to it.

Caution: While it is important to reduce changeover

times, this must never be done by taking shortcuts that

can jeopardize the safety of people, plant, or product.

CHANGEOVER

The words changeover and setup are often used inter-

changeably. This is a mistake because setup is only one

component part of changeover. Changeover is deﬁned as

follows:

Changeover is the total process of converting a machine

or line from running one product to another.

Note: Changeover can and often does take place on a

single machine. In most instances it involves several ma-

chines that operate together to form a packaging or produc-

tion line. The term ‘‘line’’ is used in this article for simplicity.

The key word in this deﬁnition of changeover is ‘‘total.’’

Changeover must include every task necessary for the

conversion. Some of the tasks that may not be readily

apparent are material handling to ensure that excess

components, materials, and scrap are removed and dis-

posed of. Documentation and line clearance are part of

changeover as well. All of these tasks must be done

correctly at the correct time.

It cannot be overemphasized that the changeover pro-

cess includes everything.

As with many large concepts, it can help to subdivide

changeover. One way to consider changeover is to break it

down into the ‘‘three ups’’: clean-up, setup, and start-up.

CLEAN-UP

Clean-up is the process of removing all product, material,

components, and contaminants from the line. In some

cases, this is very simple. A line ﬁlling hardware

components into bags may require no cleaning at all other

than removal of the previous nuts and bolts. In other

cases, clean-up may be complex and time-consuming. The

machinery in a sterile pharmaceutical ﬁlling line may

need to be completely disassembled, washed, autoclaved,

and tested for residual contamination in the laboratory.

Meanwhile, the entire ﬁlling room will be washed from

ﬂoor to ceiling, sterilized, inspected, and tested. Copious

amounts of documentation are usually involved and must

be considered part of changeover.

These examples represent extremes of clean-up. Most

instances will fall in between.

SET-UP

Setup is the process of changing the line to accommodate

the next product. It is mostly, but not only, the resetting of

the machinery to the next product. This may be done via

adjustment of machine components. An example is raising

or lowering the turret on a capper to accommodate a

different bottle size.

Different products may also be accommodated by the

use of ‘‘changeparts’’ (Figure 1; also see Changeparts).

Changeparts are product-speciﬁc machine parts. They

should normally be designed to mount in a single, speciﬁc,

ﬁxed position with no adjustment in order to minimize

variability in the setup. No tools should be required for

mounting or dismounting.

Virtually all machines will have some settings made by

changeparts and other settings made by adjustment.

There is some disagreement about the relative preferabil-

ity of changeparts versus adjustment. Some feel that

emphasis should be on package-speciﬁc changeparts

with no adjustment, whereas others feel that all machine

components should be adjustable. There is some merit to

both sides. Eliminating the need to make adjustments not

only saves time, it eliminates the possibility that the

adjustment will be made imprecisely or improperly. On

the other hand, changeparts can be expensive, especially if

there are many package sizes. The nonadjustability of

changeparts can be a liability as well as a beneﬁt. If

components are at the high or low range of their speciﬁca-

tion, it is impossible to adjust the changeparts to accom-

modate them.

Setup may also include a number of tasks not directly

related to machinery:

. Bring all the materials, including product, for the

next run to the line.

Figure 1. Typical changepart set.

254 CHANGEOVER OF PACKAGING LINES

. Charge machines with product, components, and

materials.

. Test the setup for correct ﬁll volumes, label place-

ment, and cap torque.

. Document the setup.

. Inspect the line and approve for production.

Once the ﬁnal approval to run is obtained, the line

must be brought up to speed. This is usually relatively

brief and involves ﬁlling the line with production. In some

cases, this must be done at a slow speed. Some bottles may

have a tendency to fall down without other bottles nearby

to support them. Some machine infeeds, timing screws,

or starwheels may require manual assistance to get the

initial products into them. Once the line has been fully

charged and initially brought up to speed, setup is

concluded.

START-UP

Start-up is sometimes called ‘‘run-up’’ or ‘‘ramp-up.’’ It is

the period of time between the end of setup and when the

line begins operating at normal speed and efﬁciency.

Start-up is characterized by frequent product jams, ﬁne-

tuning of machine adjustments, damaged product, and

false rejection of good product, as well as nonrejection of

bad product, line stoppages, and other abnormal condi-

tions. In some plants, start-up time is negligible. In others,

it takes longer than the rest of changeover combined. A

few plants run entire production lots without ever getting

out of start-up mode.

The cause of start-up can be described with one word:

variability.

Variability comes in two forms. The most obvious in

many cases is variability of the setup and occasionally

clean-up. A too-frequent tendency in changeover is to

perform an approximate setup and then ﬁne-tune by trial

and error once the line is running. One cause of this

practice is the absence of the knowledge or tools to

perform a precise setup. Each mechanic will have a

different technique of setting up a machine. They will

have different opinions about how tight a carton should

be held in the cartoner lugs. They will guess at machine

speeds (if tachometers are not provided) differently. An-

other cause is inadequate training and supervision. It

must be noted that meaningful training is impossible if

the proper setup speciﬁcations and tools are not available

in the ﬁrst place.

Variability can come from the product. The same liquid

products may vary in characteristics such as density or

foaminess from lot to lot. This may be impossible to predict

in advance. If so, it means that the ﬁller can never be

completely set until actual product can be ﬁlled.

Packaging components and materials can vary. If

hot melt glue comes from two different suppliers, or

even two different plants of the same supplier, it may

run differently depending on the source. This can prevent

the glue system from being ﬁnally set until it is in

production.

Paper products such as labels, cartons, and cases may

vary in physical dimensions or they may vary in stiffness,

depending on humidity levels during manufacture, trans-

port, and storage. Again, this variability prevents a proper

setup from being performed.

There is little that can be done on the packaging ﬂoor to

avoid these problems. If the set-up is not under good

control, it is often difﬁcult to determine whether the

startup is caused by variability of setup or variability of

materials. If the changeover process, particularly setup, is

brought under control, it becomes easier to focus on the

material variability issues. If the amount of time lost

due to material issues can be documented, it may be

possible to justify obtaining better-quality materials with

less variation.

The traditional deﬁnition of quality is usually ex-

pressed along the lines of ‘‘meets speciﬁcations’’ or ‘‘within

tolerance.’’ John S. McConnell does not think that is

enough. In his book Safer than a Known Way (1) he

deﬁnes quality as ‘‘absence of variation.’’ It is consistency,

not simply conformance to the range of a speciﬁcation,

which is required for success. This is as true of changeover

as it is of any other process.

Start-up ends when the line is running at normal speed

and efﬁciency.

Clean-up and setup can be simpliﬁed and shortened

but can seldom be completely eliminated. Start-up exists

because of variation; and, if variation can be eliminated,

start-up will be eliminated as well. Total elimination will

almost never be achieved in the real world. That does

not make it any less worthy a goal to continuously strive

for.

CHANGEOVER TIME

Changeover time is the key metric usually associated with

changeover. It is deﬁned as follows:

Changeover time is the total elapsed time between the

last unit of good production of the previous product run, at

full line efﬁciency, and the ﬁrst unit of good production, at

full line efﬁciency, of the succeeding product run.

Changeover time may be more compactly deﬁned as

‘‘elapsed time between good products’’, provided that it is

understood by all that this incorporates the normal speed

and efﬁciency criteria of the full deﬁnition.

In some cases, a line must be slowed down before

production actually stops. A liquid ﬁller may, as the

reservoir

runs down, need

more time to complete a ﬁll

cycle. This time of slower-than-normal production is called

purgeout. It is when the line slows down or stops running

at ‘‘full speed and efﬁciency’’ that the changeover clock

must start. Likewise, the clock on changeover time cannot

be stopped until the start-up is over. Marking the begin-

ning of changeover time is generally fairly easy and

obvious. Marking the end can be trickier.

One way is with a SCADA or other automated system

that can display a graph of line performance. When the

graph ﬂattens, indicating a normal steady state, start-up

is over.

CHANGEOVER OF PACKAGING LINES 255

Electronic counting displays that calculate and average

line speeds over periods of time (5–15 minutes) can also

provide good visual indication of when start-up has ended.

When the extended average speed achieves target, start-

up and changeover is complete.

Another technique is to end the start-up period when

the line has run for 15 continuous minutes without

stoppage or reject.

Still another technique does not measure start-up time

directly but does give an indirect measure of how well the

changeover has been done. This technique calculates how

much product would normally be produced in 15 minutes

(or some other period). Once the line has been fully

charged and enters the start-up phase, the length of

time it takes to produce that quantity of product is

measured. As an example, a line may run at three cases

per minute as measured at the discharge of the case

packer. In 15 minutes of normal operation, the line should

produce 45 cases.

If 45 cases are produced in the ﬁrst 15 minutes, change-

over has been done perfectly. If it takes 30 minutes to

produce the ﬁrst 45 cases, this indicates that time was lost

due to start-up.

Graphing the time to the ﬁrst 45 cases will provide a

relative indication of how well changeovers are being

performed.

This may not be as good a technique as direct measure-

ment. However, it is simple and provides a good illustra-

tion of trends in start-up times.

The key is that start-up must be measured. If change-

over time is deﬁned only by clean-up and setup, because

they are easy to measure, there will be a tendency to

perform these more quickly and imprecisely at the

expense of extending start-up and overall changeover time.

It is the elapsed time that is important to the change-

over time metric, not the total labor hours used. Labor

time is relatively inexpensive, measured in tens of dollars

per hour. Line downtime is very expensive and measured

in hundreds, thousands, or even tens of thousands of

dollars per hour. The goal of changeover must be to get

the line up and running again in the shortest possible

amount of time.

CHANGEOVER COST

Downtime from changeover is expensive. Many plants do

not even know how expensive because they have never

calculated the cost. Some plants that have calculated it

count the cost in hundreds of dollars per hour. Most

plants that have calculated it ﬁnd it to be thousands of

dollars per hour. These calculations need to be done, and

they need to be done by the ﬁnance department. It needs

to be calculated because management needs to know

its costs. It needs to be calculated to enable cost-beneﬁt

analysis for improvement. It needs to be calculated by

the ﬁnance department, rather than the engineering or

packaging department, because only calculations by ﬁ-

nance are ‘‘ofﬁcial’’ and readily accepted throughout the

company.

Changeover costs can be divided into two broad cate-

gories, tangible and intangible:

Tangible costs are those for which it is relatively easy to

calculate a monetary value. They include lost production

output, lost capacity, direct labor, and lot size and inven-

tory effects. Not all will apply in all plants, and different

factors will differ in importance from plant to plant. The

plant that is operating at 100% capacity will value lost

output differently from the plant operating at 75% capa-

city. For one, the sale of the unproduced product is lost and

gone forever. For the other, the lost production can be

made up, perhaps with overtime, and may not represent

lost sales.

Intangible costs are those costs that are difﬁcult or

impossible to value in monetary terms. Perhaps the most

important is responsiveness to customers. If extended

changeover times inhibit meeting a customer’s changing

demands, there is certainly a cost for that even if it is not

easily measured.

If unnecessary time is lost on changeover, this allows

less time for maintenance and forces the team to work

harder to produce. This causes stress on machines and on

people. The time consumed by lengthy changeover also

reduces the time available to develop and implement

improvement ideas.

In addition to the costs mentioned above, different

plants and industries may have other costs not shown.

However measured, changeover time is expensive. Re-

ducing it is critical to any company’s long-term strategic

health.

REDUCING CHANGEOVER TIME

The ﬁrst thing to realize about reducing changeover time

is that it requires participation by everyone in the com-

pany, not just the packaging team (Figure 2).

The primary effort must come from them, it is true, but

if they reduce line changeover from two hours to one and

quality still takes two hours to sign off the line clearance,

nothing has been gained. Marketing/package design must

be involved. Sometimes minor changes in product design

can have a major impact on changeover time. If families

of bottles are chosen with common footprints, varying

height for volumes, changeover times can be reduced

signiﬁcantly.

Human resources may need to review and modify job

descriptions. Engineering must provide various services

as well as reviewing improvements before they are put

into practice. The safety department must make sure that

safety is never jeopardized, and so on. There is no depart-

ment that does not have some role to play.

It should go without saying that top management

support is vital. They must provide moral support by

making changeover reduction a priority. They must also

provide

material support as

necessary. Without manage-

ment support, no changeover program can succeed. With

it, it cannot fail.

256 CHANGEOVER OF PACKAGING LINES

CHANGEOVER TIME REDUCTION

Changeover reduction can be accomplished using a four-

step process expressed by the acronym ESEE (pronounced

easy). ESEE stands for eliminate, simplify, externalize,

exactly. The acronym establishes the priority order of the

four steps, but these are not set in stone. It might be that

changeover can be eliminated by package redesign. This

may be a good idea but a long-term project. While changing

the package, beneﬁts from simplifying, externalizing, or

making measurable changeover tasks must not be ignored.

ELIMINATE

It makes no sense to improve something that does not need

to be changed at all. The ﬁrst step in reducing changeover

time is to identify those tasks that can be eliminated.

One common task is the application of shipper labels to

a corrugated case. In many instances, the label is placed in

the center of the case. This satisﬁes the natural human

urge toward symmetry, but it is hardly necessary for

identiﬁcation or, in most cases, for aesthetics. If the label

is centered on the case, it means that each time the case

size changes, the labeler must be reset.

It may be possible to relocate the label to a common

position, relative to the lower leading corner of the case. If

this can be done, it eliminates any need to reset the labeler

during changeover.

A pouching machine has a cutoff arm controlled by a

cam. This arm and cam must be adjusted for three pouch

sizes. The original 3/4-in.-wide cam was replaced with a

custom-madecamofthesameproﬁlebut3in.wide.The

additional width eliminated the need to reposition the cam

during changeover. This eliminated the need for a mechanic,

allowing the length to be changed, toollessly, by an operator.

This freed the mechanic to perform more valuable tasks.

Some larger machines may require ladders for access

to some adjustments. Time will be spent looking for the

ladders. Worse, instead of using ladders, a chair may be

used, creating a safety hazard. Ladders, platforms or step

plates incorporated into the machine eliminate the need to

fetch ladders.

Electronics can eliminate changeover tasks. Tradition-

ally packaging machines have been built with a single,

relatively large motor (Figure 3).

This would power the various machine functions we

connected through an often elaborate system of shafts,

belts, chains, and gears. Changeover involves physically

adjusting timings or changing gear sets for the next size.

Some newer packaging machines replace the linkages

from the main motor with smaller servo motors at the

point of use. These are controlled and operating para-

meters are changed, via software. Many of the physical

adjustments have been eliminated.

Cleaning can be eliminated or greatly reduced by mod-

ifying machines to eliminate areas that catch dust and dirt.

Instead of mounting a ﬁller on a closed cabinet that must

be cleaned internally, it may be mounted on an open frame

constructed of tubular stainless steel. If this is not possible,

at the very least the cabinet should be thoroughly sealed to

minimize or eliminate the need to clean inside.

SIMPLIFY

All changeover tasks that cannot be eliminated must be

simpliﬁed to the maximum degree possible. Simpliﬁcation

Top

management

Champion

Packaging

Manufacturing

Quality

Marketing/

package

engineeting

Materials/

purchasing

Validation

Planning

and

scheduling

Finance

Human

resources

Engineering/

maintenance

Lean

changeover

team

Figure 2. Lean changeover team members.

CHANGEOVER OF PACKAGING LINES 257