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

Подождите немного. Документ загружается.

vehicle ﬂoor when it is moving down and will be left

suspended in the air momentarily, hitting the ﬂoor mo-

ments after. This will cause packages to receive impacts

rather than only the vibration that occurs at the vehicle

ﬂoor. Impacts have acceleration levels (G levels) much

higher than vibrations (impact accelerations can get up

100 g very easily) and are much more likely to cause

damage to products during distribution.

SINUSOIDAL VERSUS RANDOM VIBRATION

Regarding the mode of vibration, there are two ways it can

occur: sinusoidal and random. The displacement of the

mass shown on the spring in Figure 1 characterizes a

sinusoidal motion and it can be expressed mathematically

as a function of the time only. For example, when time

t = 0, the displacement is at its minimum, when t = T/4, the

displacement is zero, and when t = T/2, the displacement is

at its maximum. This pattern repeats itself every interval

of duration T. Vibration encountered in distribution such

as in a truck when it travels on the road is not like the

periodic or sinusoidal vibration of a spring-mass system as

represented in Figure 1; rather, it is complex (10). Vehicles

vibrate at several frequencies simultaneously, with the

displacement, and therefore the acceleration, varying at

each instant and never repeating itself again in the same

pattern. Figure 2 shows an example of a typical random

signal measured on a truck ﬂoor.

Because of this complex characteristic, random vibra-

tion cannot be described in a deterministic manner, i.e.,

one cannot write an equation of acceleration versus time

to describe this motion. Therefore, a statistical technique,

or spectral analysis, is used to study such vibrations and

to interpret the motions of the vehicle (9), which are

covered in the next sections.

VIBRATION MEASUREMENT AND ANALYSIS

Most packaging-dynamics applications use accelerometers

for measuring vibration. Accelerometers are sensors

that produce an electrical output signal proportional to

acceleration. These sensors are rigidly mounted on the

surface of a truck ﬂoor or package item and are connected

to data-recording devices. Manufacturers of acceler-

ometers supply a calibration certiﬁcate with each sensor.

One important information in this certiﬁcate is the accel-

erometer sensitivity (in output units per g). The sensitivity

and the output voltage relate to the acceleration by

Acceleration ¼

voltage output

sensitivity

ð3Þ

For example, consider an accelerometer with a 10 mV/g

sensitivity. If it senses a vibration with peak amplitude

output of 6 mV, the acceleration is 6 mV/(10 mV/g) = 0.6 g.

Accelerometers should be calibrated regularly to ensure

accuracy of results acquired (11).

There are two basic ways to measure and store vibra-

tion data: continuous (or analog) and intermittent (or

digital). The recording equipment deﬁnes the type of

measurement and data storage.

In continuous recording, accelerometers are installed

in strategic places in the vehicle and vibration data are

recorded, without interruption, on a magnetic tape. A

voice channel may be used to record a description of the

events as they occur, such as the crossing of a rail track,

the vehicle speed, or any other occurrence that may be of

value for subsequent data analysis and interpretation.

This technique requires the continuous presence of an

operator, and the instrumentation used can be cumber-

some, occupying as much space in a vehicle as one whole

pallet load. After stored in the magnetic tapes, the accel-

eration recordings are transferred to additional instru-

mentation for analysis, interpretation and use.

Intermittent monitoring has grown substantially in the

last few years with the availability of digital recording and

storage instrumentation. Intermittent recording uses self-

contained recording units to obtain and store acceleration

either at predetermined intervals or above a preset trig-

gering level. Recording units used for intermittent mon-

itoring are usually small and contain a real-time clock and

a battery to provide the operating power. After stored, the

vibration is downloaded to a computer, analyzed, and

summarized for subsequent use.

In random-vibration analysis, the complex signal is

ﬁrst decomposed into component sine waves of various

frequencies either mathematically using Fourier decom-

position (8) or electronically using bandpass ﬁlters. What-

ever the technique used, the complex signal is analyzed

in individual component frequency intervals determined

by the bandwidth. For most packaging applications, the

bandwidth has been traditionally set at 1 Hz.The random

signal of a vehicle vibration has component sine waves

that vary over time but have a zero average, and their

peak amplitudes are distributed normally over time so

that the Gaussian distribution and all its properties may

be used to describe the process.

The acceleration level of any component frequency

analyzed is represented by the power density (PD), which

is calculated as

PDðf Þ¼

i¼1

ðGrms

n BW

ð4Þ

Figure 2. Acceleration versus time in random vibration.

1268 VIBRATION

where PD(f) = power density at the frequency f, n = num-

ber of samples at the frequency f, Grms

= root mean

square acceleration of the ith sample at the frequency f,

BW = bandwidth (normalized to 1 Hz).

A power-spectrum density (PSD) represents the results

of random-vibration analysis. The PSD is a graphic re-

presentation of the vibration intensity at each frequency.

As an example, Figure 3 shows the results, in PSD format,

of vibrations encountered in semitrailers in urban-area

trafﬁc at 60 km/h. This example shows that the single-axle

trailer has an overall higher vibration force than the

double-axle trailer, except for the frequencies in the range

9–22 Hz (12). Notice that the graphs are in a log–log scale

for better clarity at the low-frequency range.

The PSD plots show the component frequencies in the

horizontal axis and an indication of their amplitude in the

vertical axis. High power-density levels at particular fre-

quencies may indicate problems with the vehicle. This

occurs because there are resonant reactions between the

vehicle structure and the road surface in this frequency

range. For example, for both vehicles represented in Figure

3, there are high power-density levels between 2 and 3 Hz.

For the double-axle vehicle, there is another high power-

density level at just above 10 Hz; for the single-axle

vehicle, a high power density also occurs at 35 Hz.

The PSD plot is interpreted as a ‘‘signature’’ of the

random vibration and is used to statistically represent

vibrations that occur in vehicles. It can be used to deter-

mine the quality of the road or the vehicle, or both. The

PSD plots of vehicles are important in the design of

protective packages to attenuate how products receive

the vibrations that occur in these vehicles. They are also

widely used in the execution of laboratory vibration tests

to simulate the transportation hazards encountered in

these vehicles.

VIBRATION TESTS

In a laboratory, it is typical to perform two types of vibration

tests: sinusoidal and random. Sinusoidal tests are used to

identify resonant frequencies of a product, a packaging

material, or a complete package. Random-vibration tests

are usually performed to test ﬁnished-packages prototypes

and packaging systems (13) but can also be used to test

vibration transmissibility of cushioning materials using a

frequency analysis technique (14).

Sinusoidal vibration tests should deﬁne (a) the upper

and lower frequency of the test, (b) the level to be main-

tained at each frequency, (c) the rate at which frequency will

sweep and whether it is logarithmic or linear, and (d) the

number of sweeps or duration of the test. Random-vibration

tests should deﬁne (a) the PSD to be used, (b) the duration

of test at each PSD, and (c) the level sequences of each PSD.

Both test types are performed using an electrohydraulic

vibration tester mounted on a seismic mass (15), although

mechanical shakers are still widely used, mainly for sinu-

soidal vibration tests with a narrow frequency range.

The purpose of a ﬁnished-package vibration test is to

recreate in the laboratory the damage potential that

the packages would encounter in distribution. These tests

determine how effective a package system can be in

providing product protection (2). ASTM standard D4169

recommends speciﬁc PSDs for each transportation mode

(truck and rail). It also recommends that random-vibra-

tion tests last 3 h (13), although studies have shown that

tests with durations as short as 20 min produce valid

results (16). There is generally a tradeoff between test

severity and test duration (17). Ideally, a test should be

only long enough to impose on the packages events that

have the same damage potentials of the events the test is

supposed to reproduce.

TERMINOLOGY

The application of mechanical vibrations in packaging

involves many terms that may not be familiar to some

readers. For a deﬁnition of common terms used in vibra-

tion, refer to Harris and Crede (18). In addition, more

speciﬁc terminology on distribution packaging may be

found in ASTM standard D996-90a (19).

BIBLIOGRAPHY

1. J. P. Mackson and S. P. Singh, ‘‘The Effect of Temperature

and Vibration on Emulsion Stability of Mayonnaise in Two

Different Package Types.’’ Packag. Technol. Sci. 4, 81–90

(1991).

2. S. P. Singh, G. J. Burgess, and M. Xu, ‘‘Bruising of Apples in

Four Different Packages Using Simulated Truck Vibration,’’

Packag. Technol. Sci. 5, 145–150 (1992).

3. T. D. Gillespie, Heavy Truck Ride, Society of Automotive

Engineers, Warrendale, PA, 1985.

4. J. A. Marcondes, S. P. Singh, and G. J. Burgess, ‘‘Dynamic

Analysis of a Less Than Truckload Shipment,’’ ASME Winter

Annual Meeting, paper 88-WA/EEP-17, Chicago, IL, 1988.

5. S. P. Singh, J. R. Antle, and G. J. Burgess, ‘‘Comparison

Between Lateral, Longitudinal, and Vertical Vibration Levels

in Commercial Truck Shipments, Packag. Technol. Sci. 5, 71–

75 (1992).

6. W. Weaver, Jr., S. P. Timoshenko, and D. H. Young, Vibration

Problems in Engineering, Wiley, New York, 1990.

Figure 3. PSDs comparing vibration in single- and double-axle

trailers (12). (Originally published in IPENZ Transactions.)

VIBRATION 1269

7. R. E. Blake, ‘‘Basic Vibration Theory’’ in C. M. Harris, ed.,

Shock and Vibration Handbook, 3rd edition, McGraw-Hill,

New York, 1988.

8. W. T. Thomson, Theory of Vibration with Applications,

Prentice-Hall, Englewood Cliffs, NJ, 1988.

9. D. E. Newland, An Introduction to Random Vibrations and

Spectral Analysis, 2nd edition, Longman, New York, 1984.

10. S. P. Singh and D. E. Young, ‘‘Measurement and Analysis

Techniques Used to Simulate the Shipping Environments,’’

ASME Winter Annual Meeting, paper 88-WA/EEP-18,

Chicago, IL, 1988.

11. H. Schueneman, ‘‘Calibrating Issues in Packaging Testing,’’

Test Eng. Manage. 57(2), 6–7 (1995).

12. J. A. Marcondes and W. H. Feather, ‘‘Assessment of Vibration

Levels on Truck Shipments’’ in Trans. Inst. Prof. Eng. New

Zealand (Wellington, NZ) 19(1), 22–27 (1992).

13. ASTM, Selected ASTM Standards on Packaging, 4th edition,

ASTM, Philadelphia, PA, 1994.

14. J. A. Marcondes, M. Sek, and V. Roulliard, ‘‘Testing Foamed

Polymeric Materials for Mechanical Protection of Packaged

Goods’’ in Anais do 2nd Congresso Brasileiro de Polimeros,

Volume 2, Sao Paulo, Brazil, 1993, pp. 1126–1128.

15. P. J. Vergano and R. F. Testin, ‘‘An Inside Look at Seismic

Mass Design for Vibration Test System,’’ Packag. Technol.

Eng. 3(4), 38–43 (1994).

16. S. P. Singh and J. A. Marcondes, ‘‘Accelerated Lab Simulation

of Truck Transport Environment Using Random Vibration,’’

ASME Winter Annual Meeting, paper 89-WA/EEP-17, San

Francisco, CA, 1989.

17. D. Charles, ‘‘Derivation of Environment Descriptions and

Test Severities from Measured Road Transportation Data,’’

J. Inst. Environ. Sci. 37–42 (Jan./Feb. 1993).

18. C. M. Harris and C. E. Crede, ‘‘Introduction to the Handbook’’

in C. M. Harris, ed., Shock and Vibration Handbook, 3rd

edition, McGraw-Hill, New York, 1988.

19. ASTM, ‘‘D996-90a Standard Terminology of Packaging and

Distribution Environments’’ in Selected ASTM Standards on

Packaging, 4th edition, ASTM, Philadelphia, PA, 1994.

General References

R. K. Brandenburg and J. J.-L. Lee, Fundamentals of Packaging

Dynamics, LAB, Skaneatles, NY, 1991.

R. M. Fiedler, Distribution Packaging Technology, Institute of

Packaging Professionals, Herndon, VA, 1995.

PCB Piezotronics, Vibration and Shock—Sensor Selection Guide,

PCB Piezotronics, Depew, NY, 1993.

C. E. Crede and J. E. Ruzicka, ‘‘Theory of Vibration Isolation’’ in C.

M. Harris, ed., Shock and Vibration Handbook, 3rd edition,

McGraw-Hill, New York, 1988.

K. Unholtz, ‘‘Vibration Testing Machines’’ in C. M. Harris, ed.,

Shock and Vibration Handbook, 3rd edition, McGraw-Hill,

New York, 1988.

J. Curtis, ‘‘Concepts in Vibration Data Analysis’’ in C. M. Harris,

ed., Shock and Vibration Handbook, 3rd edition, McGraw-Hill,

New York, 1988.

1270 VIBRATION

WAXES AND WAX-COATED FOLDING

CARTONS

HARRY KANNRY

GARY LATTO

Dussek-Campbell, Skokie,

Illinois

Updated by Staff

INTRODUCTION

Historically, in the United States, the use of wax-coated

folding cartons to provide proper product protection has

been a popular concept within the food-packaging indus-

try. A wide assortment of refrigerated and frozen-food

entre

es have been packaged in this manner since the

1920s.

However, in the late 1950s, a new concept in the

manner in which the wax coatings were applied to the

folding-carton blank was commercialized. Coupled with

the new, commercialized folding-carton waxers, a large

number of new wax-based folding-carton formulations

emerged. From the 1960s to the present, a large number

of new wax-based folding-carton formulation concepts

have been successfully commercialized and reﬁned in

order to fulﬁll the ever-changing packaging requirements

of the specialty market.

Over the years, wax-based folding carton formulations

have improved to provide the following properties:

1. Adequate protection against loss or gain of moisture

by the food to the ambient environment

2. Effective bond strengths during heat-seal closing

operations on packaging equipment

3. Ability to retain good bonds at low-temperature

storage conditions

4. High initial gloss and excellent gloss retention

5. Adequate scuff and abrasion resistance

6. Adequate slip properties for high-speed handling on

packaging equipment

7. Good grease resistance

8. Tamper-proof closures before sale, yet open easily at

point of use

9. Economical costs commensurate with product

protection

Today, a wide variety of specialty foods are now being

packaged in wax-coated folding cartons. Wax-blend-coated

folding cartons are especially suited for butter, margarine,

ice cream, frozen vegetables, frozen pizzas, frozen shrimp,

and frozen-dinner entre

es, and prepared food specialties,

to mention just a few of the limitless applications.

This article focuses on the past, present, and future

applications of wax-based coated folding cartons. Waxes,

in particular parafﬁn wax, are used in a great many

packaging applications. The folding types include corru-

gated containers and folding cartons; the ﬂexible types

include wrappers, labels, bags, sacks, and pouches; the

rigid types include bottles, jars, drums, and tubes. Accord-

ing to the paper and paperboard industry, container board

is the largest single grade of paper produced and remains

a growing grade. Corrugated containers for shipping

manufactured goods make them one of the largest grade

forms of packaging.

HOT-MELT WAX CARTON COATERS

From the early 1920s to the late 1950s there were two

commercially accepted methods of coating folding carton

blanks with wax: (a) the hot-wax method, which imparted

a limited amount of protection and release to the carton—

the wax coating did not enhance the appearance of the

carton itself and, therefore, had very little shelf appeal;

and (b) the cold-water waxer, which gave added surface

protection and a reasonably glossy ﬁnish that increased

the shelf appeal of the carton.

The coating used for both of these methods, wax, was

initially nothing more than fully reﬁned parafﬁn wax. As

years went by, it was discovered that additives such as

microcrystalline wax and small amounts of low-molecular-

weight polyethylene could be added to the fully reﬁned

parafﬁn wax, slightly increasing the appearance and

protective functional properties of the carton.

The hot-wax method and the cold-water waxer pre-

sented one major problem with the overall wax coating.

With the exception of mechanically locked and tuck car-

tons, and except for those cartons where a dry strip could

be left in the waxing operation, the other cartons had to be

dewaxed before gluing. The dewaxing operation was time-

consuming, very costly, and generated a large volume of

wax waste.

In the late 1950s, recognizing the wax coating problem

within the folding carton industry, the Oakland Paper Box

Company developed the Oakland Hi-Gloss Pattern Coater.

The Oakland Hi-Gloss Pattern Coater allowed wax coat-

ings to be applied in any desired pattern, leaving voids in

areas to be glued or printed.

The section where the wax is applied has two rubber-

covered cylinders: One cylinder coats the underside of a

carton blank, while the second waxes the top.

The waxing blanket favored is brass-backed 30–40

durometer neoprene. Like the cutting die or the printing

plates, the blanket must be prepared to the needs of a

speciﬁc carton. Like the cutting die or the printing plate,

the blanket will be saved if repeats of the job are

anticipated.

A rubber waxing blanket is prepared by stretching an

uncut sheet over a cylinder of the same size as the cylinder

on which it will be mounted. A template of the speciﬁc

carton design is cut, and this serves as a pattern for

1271

cutting the blanket. Wherever wax is not to be applied, the

rubber will be cut away. The result is a pad that is

identical to a reverse-printing plate.

With the inception of the Oakland Hi-Gloss Pattern

Coater, other machine manufacturers began to market

similar wax coaters. In the United States, the majority of

the carton coaters in operation are the IPBM GM Carton

Coater and the 88-B Carton Center. The two IPBM wax

coaters are capable of applying wax coating with viscos-

ities approaching 1000 cP at 3001F (148.91C).

The IPBM GM Carton Coater has two coating stations.

The ﬁrst station coats the inside (bottom) surface of the

carton. The second station coats the outside (top) surface.

This arrangement permits the application of different

blends on the inside and outside surfaces, if desired. The

wax coating weights are controlled by adjustment of the

metering roll nip and the reverse or burnishing roll at

each coating station. The second coating station is

equipped with a weir-type curtain feed to ensure uniform

distribution of the wax coating across the applicator roll.

This is particularly important in applying high-viscosity

wax coatings. Silicone rubber back-up rolls are used to

prevent carton blanks sticking to the rolls.

The wax-coated cartons pass through a remelt section

consisting of gas-ﬁred infrared heaters. The temperature

of the gas-ﬁred infrared heaters is typically 2501F

(137.11C), and these heaters are rated at about

500,000 Btu. This exposure to the heat gives a smoother,

more evenly dispersed ﬂow to the wax coating and pro-

duces a high-gloss ﬁnish.

The wax-coated cartons are then passed through a

refrigerated, chilled-water curtain and into a water-

immersion tank. The temperature of the chilled water

must be carefully controlled within a temperature range of

34–401F (1.1–4.41C). The purpose of the chilled water is to

facilitate the setting of the wax coating without disturbing

the surface. This process also enhances the high-gloss

ﬁnish. If the chilled water is at a temperature above

401F (4.41C), the wax coating does not set properly and

will produce a carton with a dull, uneven surface. The

position of the heaters and the distance to the water-

immersion section can be adjusted to obtain the maximum

gloss for the particular wax coating being applied.

The waxed cartons are then passed through a set of

squeeze rolls to remove the excess water. The waxed

cartons are then deposited onto a slow-speed stacker

apron.

The ideal wax-coating weight, per carton side, is ap-

proximately 3 lb/1000 ft

(14.6 g/m

The machines are usually installed with three channels

or lanes that automatically feed the folding carton blanks

through the wax coater. Each single lane is capable of

waxing 15,000 cartons per hour.

HOT-MELT WAX CARTON COATINGS

In the late 1950s, coupled with the development and

commercialization of the ‘‘new’’ folding-carton coaters,

new developments and reﬁnements were also taking place

in the area of ‘‘new’’ hot-melt wax carton-coating

formulations. Specialty wax blends were being researched

and developed for exclusive use with the ‘‘new’’ folding-

carton coaters. The simple formulations are as follows:

1. Straight, fully reﬁned parafﬁn-wax blend

2. Fully reﬁned parafﬁn-wax/microcrystalline wax

blend

3. Fully reﬁned parafﬁn-wax/low molecular weight

polyethylene blend

These gave way to sophisticated blends of carefully

selected petroleum-derived waxes with carefully selected

wax additives. Because of the signiﬁcant changes made in

the area of folding-carton coaters, a new era in formulat-

ing wax-based coatings for this specialty packaging in-

dustry began.

In early 1960, another series of products became com-

mercially available that created an entirely new concept

in hot-melt wax-based coatings. This new series of pro-

ducts were termed copolymers and consisted of various

percentages of ethylene and vinyl acetate, or simply EVA.

Other wax additives that became commercially available

around the time of the EVA copolymers were polyterpene

resins, stabilized ester gums, and a wide product diversi-

ﬁcation of low-molecular-weight and high-molecular-

weight polyethylenes. The commercialization of these

new wax additives gave compounders the tools to manu-

facture an almost limitless number of combinations or

formulations of hot-melt wax-based folding carton

coatings.

On the basis of the requirements of the folding carton

industry, hot-melt wax-based folding-carton coatings are

classiﬁed into the following two categories:

1. Non-heat-sealable folding-carton waxes

2. Heat-sealable folding-carton waxes

Non-heat-sealable folding-carton waxes are usually ap-

plied in a deﬁned pattern onto the folding-carton blank,

leaving unwaxed areas where a hot-meal adhesive (HMA)

is applied to seal the folding carton closed. The wax

coating is applied to both the outside (printed side) and

the inside (unprinted side) of the folding carton.

Heat-sealable folding-carton waxes are applied onto

the entire surface area of the folding carton blank, and

they will seal the folding carton without the use of a HMA.

The wax coating is applied to both the outside (printed

side) and the inside (unprinted side of the folding carton).

The use of a heat-sealable folding-carton coating is ad-

vantageous because the gluing operation is eliminated.

As the folding-carton industry developed, it became

apparent that only four wax-based folding-carton coatings

were necessary to fulﬁll the requirements of the industry.

The wax-based coating product line consisted of the

following:

1. Non-heat-sealable folding-carton waxes

a. One economical coating

b. One general-purpose coating

c. One heavy-duty coating

1272 WAXES AND WAX-COATED FOLDING CARTONS

2. Heat-sealable folding-carton wax

a. One premium heat-sealable coating

The selection of the proper folding carton coating

depends on the physical speciﬁcations of the formulation

as well as the functional properties that the formulation

must impart to the folding carton. Functional properties

such as gloss, creased vapor barrier, grease resistance,

scuff resistance, freezer-burn resistance, and heat seal-

ability are some of the points to be considered in the

section of the proper folding-carton coating. In most

instances, the folding-carton coating must be nonﬂaking,

exhibit no ruboff, and exhibit a high antiblock character-

istic. These three properties are important when the

waxed folding carton is processed through the folder/gluer.

The wax coating cannot build up on the runners of the

folder/gluer. When the wax coating builds up on the

runners of the folder/gluer, subsequent waxed folding

cartons stick and jam on the runners. The folder/gluer

must then be shut down and cleaned (see also Sealing,

heat).

The economical non-heat-sealable folding-carton coat-

ing provides minimal functional properties. The econom-

ical formulation is used in applications of generic folding

cartons where minimum functional properties are re-

quired and the low cost of the wax coating is an important

consideration. With a hot-melt wax carton coater contain-

ing two separate wax-coating stations, the economical

formulation can be used on the inside (unprinted) of the

folding carton, while the general-purpose formulation or

the heavy-duty formulation can be used on the outside

(printed) of the folding carton. This procedure is used for

monetary consideration.

The general-purpose non-heat-sealable folding-carton

coating offers improved functional properties over the

economical coating. The general-purpose coating may be

used on the outside (printed) area of the folding carton as

well as the inside (unprinted) area of the folding carton.

The heavy-duty non-heat-sealable folding-carton coat-

ing imparts the optimum appearance, protection, and

functional properties of the non-heat-sealable coatings.

The heavy-duty coating may be used on the outside

(printed) area of the folding carton as well as the inside

(unprinted) area of the folding carton.

The premium heat-sealable folding-carton coating

imparts the optimum appearance, protection, and func-

tional properties to the folding and will seal the folding

carton closed without the use of a HMA. This product will

give a ﬁber-tearing seal over a wide range of sealing

temperatures.

An additional consideration for all four products is that

all ingredients and ﬁnal products must fully comply with

FDA (Federal Drug Administration) regulation as suitable

for use in food packaging. The regulation cited most often

is Paragraph 21, CFR 176.170 for ‘‘components of paper

and paper-board in contact with aqueous and fatty foods.’’

With the new generation of hot-melt wax-based coat-

ings and the commercialization of the new generation of

hot-melt carton coaters, the folding-carton industry was

well on its way to establishing itself as a strong specialty

market within the food-package industry.

CURRENT USE

Many changes have occurred in the folding-carton indus-

try since its modern conception in the early 1960s. A

newer variety of boardstock required newer blends of

wax coatings. At present, the most widely used of the

petroleum waxes is parafﬁn wax, also called macrocrystal-

line wax. More than 50 companies produce petroluem

waxes worldwide (1). It is extremely unreactive at normal

temperatures. It remains cost-effective as a moisture and

gas barrier. It can also be blended with microcrystalline

wax or combined with polyethylene or ethyl vinyl acetate

(EVA) to improve performance. The use of reﬁned grades

of petroleum wax are regulated by the FDA (21 CFR

172.886 and 21 CFR 178.3710) (2).

Petroleum waxes are now used to coat corrugated board

as well. The most common methods used for applying wax

are saturating or cascading and curtain coating. In satur-

ating or cascading, a thick layer of wax is ﬂushed or

sprayed onto the ﬁnished board. The board will pick up

40–50% of its weight in wax. The wax is normally low

melting. In curtain coating, the corrugated board is al-

lowed to pass horizonatally through falling wax. The

coating formulations contain parafﬁn wax, microcrystal-

line wax, and additves such as EVA copolymers, tackiﬁer

resins, and antioxidants. EVA increases the viscosity to

produce a stable curtain. Tackiﬁers increase ﬂexibility and

antioxidants prevent the formation of odor and discolora-

tion (3).

Folding cartons are made from heavy paper or pape-

board. The carton is printed, folded into the basic carton

shape, sealed and glued, and shipped to the user. The

carton usually goes into an automatic ﬁlling line where it

is popped open and ﬁlled with product. Waxing allows the

board to sustain ply separation without splitting or failing

when bent back.

FUTURE OUTLOOK

The current awareness of the environmental impact of

products has consumers and manufacturers re-evaluating

their existing materials. This is true for the packaging

industry because much of its end product requires

disposal.

Petroleum waxes have many properties that make it a

barrier to gases and vapors. This is very desirable for the

actual packaging, but makes it very difﬁcult to recycle.

Closed-loop

recycling of paper

products is called repulp-

ing. Packaging containing petroleum waxes requires spe-

cial handling at recycling mills. The most severe problem

is that the waxes combine with other contaminants, and

clog the wires and felts of the paper machine, forming

‘‘stickies.’’ Waxes can also delay the deﬁbering in the

pulper. Most existing plants are not equipped to remove

the contaminants (4).

The International Group, Inc., a world leader in reﬁn-

ing and marketing of petroleum waxes, is working with

paper and equipment suppliers to develop new products

that improve pulpability and to modify technologies to

better handle contaminants (5). The industry is now

WAXES AND WAX-COATED FOLDING CARTONS 1273

developing wax alternatives, many of which have become

commercial.

BIBLIOGRAPHY

H. Kannry and G. Latto, ‘‘Waxes’’ in A. J. Brody and K. S. Marsh,

eds., The Wiley Encyclopedia of Packing Technology, 2nd

edition, Wiley, Hoboken, NJ, 1997, pp. 962–964.

Cited Publications

1. M. Malveda, M. Blagoev, and M Yoneyama, ‘‘Waxes’’ in Che-

mical Economics Handbook, SRI Consulting, Menlo Park, CA,

2006.

2. C. Leray, ‘‘Waxes’’ in the Kirk–Othmer Encyclopedia of Chemi-

cal Technology, Vol. 26, 5th edition, Wiley, Hoboken, NJ, 2007,

pp. 203–226.

3. ‘‘Corrugated Waxes’’, The International Group, Inc., 2006,

www.igiwax.com.

4. ‘‘Environmental Awareness’’, The International Group, Inc.,

2006, www.igiwax.com/.

5. ‘‘Wax Alternatives,’’ Corrugated Packaging, www.corrugate-

d.org/, accessed April 2008.

General References

I. N. Davie, ‘‘Compostability of Petroleum Wax Based Coatings,’’

TAPPI J. February 167–170 (1993).

R. J. Hamilton, ed., Waxes: Chemistry, Molecular Biology, and

Function, Oily Press, Dublin, 1995.

WRAPPING MACHINERY, STRETCH-FILM

EDWIN HO

OSI Industries

Lisle, Illinois

HISTORICAL OVERVIEW

The stretch-wrapper industry is over 30 years old in 2008.

In 1976 there were only four or ﬁve manufacturers

producing a wide-web model used to wrap standard-height

pallet loads with a large 60-in. roll of stretch ﬁlm. Soon

after that the demand to wrap variable pallet load heights

produced the spiral model, which used a smaller 20-in. roll

of stretch ﬁlm. Unlike the large roll of ﬁlm, which was

stationary when wrapping the entire pallet load, the

smaller 20-in. roll traveled up and down on a motorized

carriage, wrapping the entire load in a crisscross fashion.

The spiral wrapper offered the primary advantage of

wrapping a wide variety of load heights at minimal cost

and dramatically reduced the use of the wideweb model.

Today the spiral wrapper (Figure 1), in both semiauto-

matic and fully automatic formats, represents approxi-

mately 90% of all wrapper production. Wrapper

manufacturers in the United States now number over

20, ranging from small producers of lower-cost models to

major producers offering a complete line of wrapper

models to accommodate virtually every stretch-wrap ap-

plication known.

THE DEMAND FOR STRETCH WRAPPERS

Prior to the energy crisis of 1974, the use of shrink ﬁlm to

unitize pallet loads of product was an increasingly popular

packaging medium. The costly and excessive use of heat

energy (gas, electric, or propane) to shrink ﬁlm, however,

along with the rising cost/availability of shrink resins,

placed industry of all types in a cost-prohibitive situation.

Another unitizing method, using strapping (steel, ny-

lon, polyethylene, or polypropylene) to unitize pallet loads,

was recognized as labor-intensive; and an average pallet

load could take up to 7 min to strap, depending on the

nature of the product and the acceptable strapping pat-

tern desired.

Still other unitizing mediums such as pressure-

sensitive tape, twine, or spot adhesives did not provide

inherent protection from the elements and would tend to

loosen while in transit.

Stretch ﬁlm offered a lower cost advantage of being

applied by equipment that used only ‘‘on/off’’ electricity as

a source of power and could be applied by a semiautomatic

stretch wrapper. Signiﬁcantly less labor time was involved

and an average size product load could be wrapped in less

than 2 min. As a result, many of the initial products

Figure 1. A semiautomatic, spiral wrapper (IPM 55UTS30F)

equipped with Uni-Tension power prestretch. For unitizing up

to 35 pallet loads per hour.

1274 WRAPPING MACHINERY, STRETCH-FILM

stretch-wrapped were packaged in multiwall paper bags,

polyethylene bags, or cartons. The following is a list of

very early stretch ﬁlm product applications:

Product

Kitty (cat) litter

Dog and cat food

Detergent

Chemicals

Printed forms

Injection-molded bottles

Mortar mix

Concrete block and brick

Potting soil and mulch

Seed

Canned and jarred food

Liquids in polyethylene/

glass bottles

Shipped in

Multiwall paper bags

Multiwall paper bags and

cartons

Corrugated cartons

Multiwall paper bags and

steel drums

Corrugated cartons

Multiwall paper bags

Strapped (steel)

Polyethylene bags

Corrugated cartons

Corrugated cartons or

trays

It should be noted that, even in 30 years later, these

products are still being shipped on pallets and in some

cases corrugated slip sheet via the stretch-wrap medium.

Thus, the demand for stretch ﬁlm continues to grow with

over 2.2 billion pounds being produced annually in the

United States. The demand for stretch ﬁlm is projected to

rise 4.7% annually for the next few years. It is estimated

that more than 40,000 stretch wrappers are sold annually

in the United States as this type of machinery continues to

replace conventional packaging methods. In addition,

virtually every type of product shipped today in a carton,

paper/polyethylene bags, drums, or polyethylene contain-

ers is being stretch-wrapped. Products having been con-

sidered marginal as a stretch-wrap application are now

being packaged or unitized with stretch ﬁlm. Some of the

once considered marginal product applications are as

follows:

Aluminum/steel coils

Tires

Engine castings

Expanded styrofoam

sheets

Doors

Coils of copper tubing

Batteries

Signatures

Perishable foods (produce

and meat)

Windows

Furniture

File cabinets

Frozen ﬁsh in ice

Frozen foods

Recycled rubber in

polyethylene bags

Hazardous chemicals and

powders

PRESTRETCHING FILM

Wrapping a pallet product load with stretch ﬁlm is gen-

erally accomplished by ﬁrst placing the load on the turn-

table of the stretch wrapper. The turntable is activated,

and rotates and draws ﬁlm from the supply roll.

Originally, ﬁlm stretch was created by the ﬁlm roll being

gradually retarded from turning while the load pulled the

ﬁlm from the roll. Retarding the ﬁlm roll was affected by

an electromagnetic brake ﬁxed to the ﬁlm core or through

a series of rollers bars. The effective maximum stretch,

however, was no more than 120% and in most cases

averaged 50–60%. Higher percentages of stretch would

generally cause product cartons to crush and could even

pull the load from the turntable unless otherwise held in

place by an optional top compression platen (electric or

air-operated).

Prestretching ﬁlm, however, became instantly popular

in the late 1970s as moderate-to high-volume shippers

took advantage of the higher ﬁlm yields offered by im-

proved stretch ﬁlms coming into the marketplace. These

improved ﬁlms utilized linear low-density polyethylene

(LLDPE) resins either alone or combined with ethyl vinyl

acetate (EVA) to enhance puncture resistance, reduce

tear propagation, and extend ﬁlm yield up to 400%. The

prestretch method of stretching such ﬁlms was found

to reduce stretch ﬁlm cost per pallet load by 20–45% as

sophisticated prestretch machine assemblies became part

of an upscale trend in stretch wrappers in the 1980s.

Unlike a stretch wrapper equipped with brake tension,

a prestretch assembly stretches the ﬁlm at the machine by

routing the stretch ﬁlm between two powered rollers prior

to its application to the load. Because the two powered

rollers are moving mechanically or electrically at different

speeds, the ﬁlm stretches between the rollers.

The percentage of stretch that can be attained through

a ﬁxed-ratio or variable-prestretch assembly can reach

300%

with the appropriate

ﬁlm quality and gauge. Com-

mon or the most desirable level of prestretch is 200–225%,

which allows for maximum ﬁlm recovery (holding force) at

an economical level of ﬁlm usage. Excessive prestretch can

cause stretch ﬁlm to thin, reduce puncture/abrasive re-

sistance, and diminish the ‘‘cling’’ or self-adhering prop-

erty of the ﬁlm. Without a reasonable amount of ‘‘cling,’’

the trailing segment of the ﬁlm wrap (pressed against the

side of the load at the end of the wrap cycle) can release

itself allowing the wrapped load to partially unwrap.

Another advantage of prestretch is that most manu-

facturers have a method to apply tension of the ﬁlm to the

load immediately after the prestretch process occurs.

Generally, an adjustable spring or air operated dancer

bar is utilized to regulate ﬁlm tension to the product load.

One such system is the patented IPM Uni-Tension system

(Figure 2), which provides constant and consistent ﬁlm

tension (adjustable) to the product load. As a result, many

product loads, which could normally not be stretch-

wrapped without the use of a top stabilizer platen, can

be wrapped with power prestretch. Examples of these

types of loads are as follows:

Mixed-Product Loads

Partial-pallet loads

Tall-pallet loads

Empty drums

Empty plastic bottles

Load weights of 150–500 lb

WRAPPING MACHINERY, STRETCH-FILM 1275

Prestretch is preferred by many volume shippers be-

cause it reduces the amount of stretch ﬁlm received by

their customers. Although stretch ﬁlm is recyclable, pre-

stretch minimizes the ﬁlm disposal process.

WRAPPER MODELS AVAILABLE

The stretch-wrapper industry has come a long way since

the original wide-web machine was introduced. The sin-

gle-turntable wide-web machine (using a 45- to 80-in. ﬁlm

roll size) has been expanded to at least several additional

models to include wide web prestretch. The spiral wrapper

model has evolved into multiple models designed to ac-

commodate a wide variety of applications and user pre-

ferences. The following is a list of the most popular models

currently available—also noted is the average production

rate for which that model would be applicable:

Wrapper Model

Hand wrapper

Power turntable with hand

wrapper

Powered-turntable machine

with manually operated

ﬁlm carriage (has me-

chanical powered

carriage)

Semiautomatic, powered-

turntable machine with

adjustable programmable

controls for number of

wraps, speeds of turnta-

ble, ﬁlm carriage, etc.,

and brake tension

Semiautomatic, powered-

turntable machine with

adjustable programmable

controls for number of

wraps, speeds of turnta-

ble, ﬁlm carriage, etc.,

and ﬁxed-ratio powered

prestretch

Production Rate

0–10 pallets/day

r20 pallets/day

r35 pallets/h

(Note: These powered-turntable machines are available in

a high-platform turntable design (for forklift use only) or a

low-proﬁle design with a loading ramp for hand/electric

pallet jack and forklift use. These machines are also

available in wide-web or spiral-type models.).

The machine models listed above continue to withstand

the test of time, being the most popular and often manu-

factured with the following most common options to

enhance the stretch-wrapping process, increase the pro-

duction rate, or improve operator efﬁciency:

. Photoelectric height sensor (for semiautomatic spiral

models)—located on the ﬁlm carriage to automati-

cally seek the top of the pallet load, halt the ﬁlm

carriage, and permit the top wrap cycle to occur.

. Mast extension to permit pallet loads in excess of 85

in. in height to be wrapped.

. Top-compression platen (electric or air-operated)—

exerts an adjustable amount of stabilizing pressure

on the top of a lightweight or unstable product load.

. Additional turntable (dual-turntable model)—in-

creases production rate by 33%.

. Conveyorized turntable (gravity roller)—for in-line

capability; that is, machine is installed into existing

or new gravity roller production line.

. Pit mount—machine is installed into the ﬂoor with

turntable virtually ﬂush with ﬂoor; enhances use of

pallet jacks.

. Scale—5,000- to 10,000-lb capacity scale integrated

with and under the wrapper turntable eliminates

double

handling of pallet

loads.

FULLY AUTOMATIC CONVEYORIZED MODELS

Shippers with moderate to high production (15–85

pallets/h) have generated an increased demand for fully

automatic stretch wrappers. The most popular fully auto-

matic has a powered conveyorized turntable for in-line

powered-conveyor systems or for multiple forklift opera-

tions. Unlike a semiautomatic wrapper, the fully auto-

matic wrapper eliminates the operator, who necessarily

would ﬁrst attach the stretch ﬁlm to the load and then

press a

START button. At the completion of the wrap cycle,

the operator would cut the ﬁlm and adhere the trailing

edge of the ﬁlm to the side of the load. The automatic,

however, operates through an electric programmable logic

controller (or microprocessor) and a series of electronic

photoelectric load sensors. The stretch ﬁlm is held in a

mechanical clamp between load wrap cycles and is cut and

brush-wiped onto the pallet load automatically at the

completion of the wrap cycle.

A fully automatic wrapper equipped with a power infeed

and discharge conveyor can be integrated with an auto-

matic load palletizer (which feeds loads to the wrapper).

This same system can be used effectively by having a

Figure 2. Powered prestretch.

1276 WRAPPING MACHINERY, STRETCH-FILM

forklift operator set a load on the power infeed conveyor

and then activate that conveyor with an overhead remote

pendant control. As that load would feed into the wrapper

module, the forklift operator would drive over to the

discharge conveyor section to remove a completely wrapped

load and place it into storage or a shipping vehicle. Auto-

matics are generally equipped with a prestretch assembly

for maximum utilization of the stretch ﬁlm.

Common optional equipment to enhance higher-speed,

fully automatic systems are as follows:

. Top-compression platen exerts an adjustable amount

of stabilizing pressure on the top of a lightweight or

unstable product load.

. Automatic top-sheet dispenser that automatically

places a 2- to 3-mil polyethylene top sheet on top of

the pallet load prior to the load being conveyed to the

wrapping module. A top sheet is usually desirable to

prevent the elements from damaging the product.

. The 901 index turntable is used primarily to direct

the discharge of the pallet load 901 from which it was

accepted onto the machine. This option is usually

desired if there is a ﬂoor-space restriction.

. Mast extension to permit pallet loads in excess of

85 in. in height to be wrapped.

OTHER WRAPPER MODELS

In recent years, new stretch-wrapper designs have been

created by different manufacturers to accommodate either

the end user’s speciﬁc product application or existing

packaging line. One such model is the increasingly popu-

lar overhead rotary-arm-type stretch wrapper (Figure 3).

With this model, the product load does not rotate on a

turntable. The load sits on the ﬂoor or on conveyor, and the

roll of stretch ﬁlm travels on the overhead arm around the

load wrapping it in a spiral fashion. The ﬁlm stretch

delivery system can be either the brake tension type or

the powered prestretch type.

The overhead rotary-arm-type machine is advanta-

geous for wrapping pallet loads when

. Loads are extremely heavy.

. The product on the pallet is subject to damage if

rotated.

. Loads are unstable and not easily moved by forklift,

pallet jack, or conveyor.

. Washdown is required—that is for use in poultry

plants or facilities where the machinery and general

work areas must be washed down periodically for

sanitation reasons.

The overhead-arm-type machine is currently manufac-

tured as a wall- or ﬂoor-mounted semiautomatic or can be

upgraded and incorporated into a fully automatic con-

veyorized system for high-production use.

The semiautomatic robotic wrapper is a battery-oper-

ated, wheeled vehicle with a vertical mast and ﬁlm-stretch

delivery system. This wrapper is placed next to a product

load and, when activated, travels around the perimeter of

the load while the ﬁlm carriage travels up and down

stretch wrapping the load. A sensing device signals the

wrapper to turn as it senses the corner of the load. This

type of wrapper has been used to wrap longer-than-

average product loads and requires ample ﬂoor space in

which to operate.

Orbit stretch wrapping has become a popular method

to stretch wrap large ﬂat panels such as ofﬁce dividers,

locker-room partitions, and so on, in which the panel is

conveyorized through a large ringlike assembly and a 10-

to 30-in. roll of stretch ﬁlm travels in a vertical plane with

a circular motion around the entire panel wrapping it as it

moves through the ring on the conveyor.

Figure 3. A semiautomatic overhead rotary-arm-type stretch

wrapper.

WRAPPING MACHINERY, STRETCH-FILM 1277