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

Подождите немного. Документ загружается.

cracking, failure on drop test, and even pinholing;

thick sections can act as heatsinks after the bottle is

molded, and the uneven cooling and shrinkage can

lead to bottle distortion. In the case of product that

will cool or outgas after the container is sealed, there

is a potential for distortion due to negative or

positive pressure. This can require special molded-

in structures, expansion areas, or controlled wall

thickness to minimize these effects. The preciseness

of wall thickness guidelines should be determined by

how critical it is for performance of the bottle.

4. Bottle Stability Is Critical. This is especially true for

many of the tall, thin (depth) bottles frequently used

in consumer products to maximize shelf impression.

In injection blow molding, the height of the pushup

(the center of the base of the bottle) can be adjusted.

The center of the bottle base must be high enough to

not ‘‘belly out’’ for a full or empty bottle, or the

bottom of the bottle will be a round surface. Various

aids to stability include molding bottom rings (ra-

diused or with a ﬂat land area) or feet (three or four).

It is a good idea to put a slight depression in the

vicinity of the parting line so that a slightly raised

parting line will not contribute to instability. The

best solution depends on the bottle’s general shape

and center of gravity and on the controls available in

the molding process.

5. Embossed or Debossed Decorations. These include

logos, which can be a free or inexpensive way to add

information to the bottle. However, care should be

taken to avoid thin spots, undercuts, or sharp edges.

6. Information that Is Frequently Molded into the

Bottom of the Bottle. This includes material identi-

ﬁcation symbol (recycling logo, legally required to be

on the bottle in several states), mold and cavity

number (for quality checks and troubleshooting),

and a molder or company logo. Placement should

be planned ahead of time, especially because this

may affect bottle stability. These should generally

not touch or cross the parting line.

7. The Bottle Sealing Area Should Be Closely Speciﬁed.

For standard continuous thread closures, lined or

unlined, the land seal area at the top of the con-

tainer is critical. It needs to be ﬂat, horizontal, and

free of dips or nicks. If the ﬂat surface is going to be

angled, care should be taken to specify a continuous

surface that will create a seal. A minimum land

width (ﬂat neck thickness at the top) can be speci-

ﬁed. If a valve seal closure is to be used, the

circumference inside the ﬁnish where it meets the

valve is critical.

8. Anticipate Pressure Differentials. Special product,

ﬁlling, and distribution circumstances can lead to

pressure differentials between the inside and out-

side of the ﬁlled and sealed container over the course

of product life. Examples of this include hot ﬁll,

product outgassing, product migration through

walls causing suckback, and changes in external

pressure and temperature during distribution, sto-

rage, and handling. Flexible panels or more ﬂexible

materials will not prevent dimensional change, but

can prevent damage to the container and allow it

to be aesthetically acceptable. Variations in wall

thickness support ribs, and stiffer materials can

strengthen containers against dimensional changes

to some extent. Depending on the product, one- or

two-way valves can be added to the closure or inner

seal.

9. Labeling and Decoration. These are a major con-

sideration in bottle design. A label panel must be ﬂat

or have a surface that curves in only one direction.

Many label areas are recessed or provide top and

bottom ‘‘bumpers’’ to protect the label against scuff-

ing during normal handling and distribution. The

maximum label area is determined by a combination

of the tolerances of the label placement equipment,

the label dimensions, and the usable label panel

dimensions. The additive tolerances need to be sub-

tracted from the speciﬁed label panel size. Major

labeling or decoration methods include the follow-

ing: (a) In-line labeling (ﬁlling line)—labels (gener-

ally pressure-sensitive or plain-paper and glue) are

applied on the ﬁlling line; (b) postmold labeling—

labels (generally pressure-sensitive or heat-trans-

fer) are applied soon after the bottle is molded

(further shrinkage in the bottle, particularly over

the next 24 hours, must be taken into account); (c)

in-mold labeling—labels (either plastic or paper) are

applied inside the mold during the molding process

(bottle versus label shrinkage must be designed into

the bottle tooling, especially for paper labels); and

(d) direct application to bottle—instead of applying a

label, the container is decorated by printing or silk

screening directly onto the bottle.

HDPE or PP bottles usually require ﬂame treatment prior

to decoration or labeling. Round bottles may need a

rotational guide in the bottom to help control them during

either process. (See also Labels and labeling machinery.)

Industry Standards

in any purchased

item, speciﬁcations and tolerances

should be set up between the customer and the supplier.

However, the designer is greatly aided by industry stan-

dards. Currently, ASTM publishes D2911-94(2005) Stan-

dard Speciﬁcation for Dimensions and Tolerances for

Plastic Bottles with standard screw closure neck ﬁnish

dimensions, threads, and tolerances, and tolerances for

various ranges of bottle capacity (up to 5 gallons) and body

dimensions. These standards are modiﬁed on an ongoing

basis and should regularly be checked for updates. In

addition to dimensional standards, there are procedures

for stress crack resistance, crush strength, drop impact

and additional tests (3). The existence of standard ﬁnishes

greatly facilitates the interchangeability of various stock

and custom closures that might be available. The standard

tolerances also provide a good starting point for speciﬁca-

tions. The designer might wish to tighten some of these

tolerances as required, but should be prepared to work

158 BOTTLE DESIGN, PLASTIC

closely with any vendors ahead of time to ensure manu-

facturing capability.

A typical dimensioned bottle is shown in Figure 2.

Table 1 describes a typical container’s dimensions and

their importance. The sample given is a standard contin-

uous thread ﬁnish container, which uses a standard

screw-on/screw-off closure that is common on many con-

sumer bottles.

Materials and Colorants

Critical criteria for selection of bottle materials include

the following:

1. Cost and availability—should be calculated by the

bottle, not just the pound.

2. Environmental—recyclability and availability of

recycled material, toxicity or biodegradability.

3. Clarity or opacity.

4. Stiffness or squeezability.

5. Water or moisture vapor transmission rate (WVTR

or MVTR).

6. Gas permeability.

7. Chemical resistance to type of chemicals required.

8. Temperature range.

9. Impact strength.

10. Environmental stress—crack resistance (ESCR)

Materials generally used for bottles in the United States

include high-density polyethylene (HDPE), polypropylene

(PP), low-density polyethylene (LDPE), linear low-density

polyethylene (LLDPE), polyvinyl chloride (PVC), poly-

ethylene terephthalate (PET), and polystyrene (PS). Of

these, HDPE and PET make up the great majority of

Figure 2. Typical dimensions of a

plastic bottle. Bottle and ﬁnish no-

menclature. T, diameter of thread;

E, diameter of root of thread; I,

diameter of inside; S, distance of

thread start to top of ﬁnish; and H,

height of ﬁnish.

Table 1. Bottle Dimensions

Dimension Description Purpose

T Thread outer diameter Cap ﬁt and torque control.

E Diameter between threads Cap ﬁt and torque control.

H Height from shoulder to top of ﬁnish Bottom of closure must clear shoulder at maximum torque

for proper sealing. The maximum minus minimum H

(DH) should also be speciﬁed to limit neck ‘‘cocking,’’

which will also adversely affect the seal.

S Height from top of thread to top of ﬁnish Thread engagement.

I Inside diameter of ﬁnish Minimum is for ﬁlling tube clearance only. Custom detail

should be added for placement of special ﬁtments.

Ovality T

max

T

min

or other area Ovality in the ﬁnish can affect closure ﬁt, torque control, or

ﬁtment integrity and ﬁt. Speciﬁcation should be based on

requirements and manufacturing capabilities.

Land width Sealing width on top of ﬁnish Cap seal and torque control. Speciﬁcation should be based

on requirements and manufacturing capabilities.

Overﬂow capacity Volumetric capacity of bottle to top Consistent ﬁlling of bottle with proper amount of product

and correct aesthetic ﬁll height.

Overall dimensions Height, width, and depth at maximum point Proper machinability on ﬁlling line and ﬁt in secondary

packaging. Additional dimensions are speciﬁed in article

drawing.

Weight Weight of empty bottle Cost control, to ensure sufﬁcient material, and ﬁll weight

control.

Wall thickness Thickness of wall at minimum and speciﬁed points Thin spots can lead to drop failure or stress crack. Wall

thickness should be speciﬁed at the absolute minimum

found on the bottle (this can vary as to location) and at

other critical locations if necessary.

BOTTLE DESIGN, PLASTIC 159

containers by number and weight. Other materials, in-

cluding engineering plastics such as polycarbonate, are

used for special applications. Individual material proper-

ties can be found in detail under their separate articles.

Many materials can have their properties signiﬁcantly

modiﬁed by additives such as plasticizers, ﬁllers, impact

modiﬁers, antistatic agents, and UV (ultraviolet radiation)

inhibitors. Copolymers and multilayer coextrusions can

further enhance a material.

Colorants are added to provide color and/or opacity to

the material. Pigments, an opacity agent (such as tita-

nium dioxide), and a compatible base material are com-

pounded and added to the regular plastic during the

molding process. The colorant loading, wall thickness of

the plastic, and color and opacity of the product all affect

the ﬁnal aesthetics of the ﬁlled bottle (see Colorants,

plastic).

Different materials and to some extent different color-

ants all affect the shrinkage and ﬁnal performance of a

bottle. This must be taken into consideration for testing

and qualiﬁcation.

Computer Utilization in the Design Process

The computer is an integral part of the bottle design

process, and new ways of using it are being added con-

tinuously. Uses include:

Speciﬁcations. Bottle speciﬁcations are computerized

at both the customer and supplier level.

Computer-Aided Design/Manufacturing (CAD/CAM).

Bottle drawings are performed on CAD systems, with

improved opportunity for analysis and exploration of

options and variables. Mold makers frequently use a

CAM system for production of the mold. Some forms

of rapid prototyping can also be performed.

Analysis and Data Recording. Test data can be both

directly recorded and analyzed on the computer.

Sophisticated engineering programs, such as ﬁnite-

element analysis, can be used to compute and visua-

lize stresses at various points.

Pallet Loads. Several programs, such as those pro-

duced by CAPE (4) or TOPS (5), allow quick calcula-

tions of ﬁnished pallet options based on bottle sizes.

This allows for pallet load optimization at the initial

design stage.

In addition, there is various software to do everything

from evaluating heat transfer in mold design to visualiz-

ing product placement on the supermarket shelf.

PROTOTYPING AND TESTING

Once the bottle is designed and unit-cavity samples have

been produced in the proper materials, a testing program

must be initiated. A testing protocol should be established

that checks bottles against both their speciﬁcations and

the requirement list that was generated.

SPECIALTY BOTTLE REQUIREMENTS

A number of specialty bottles have distinctive require-

ments. Some of these include:

Roll-On. A round ball is inserted in the ﬁnish; rolling

the ball against a surface (clothes, parts of the

body) dispenses a liquid. The ball is held in place

between two rings in the ﬁnish. The most common

method of sealing is to torque the cap so that it

pushes the ball down tightly against the lower ring

(Figure 3).

Plug. A small oriﬁce plug is placed into the ﬁnish so

that product dispensing can be controlled (eye or

nose drops, creams). The plug must be inserted

without crushing the bottle body or neck ﬁnish and

yet be difﬁcult to remove. Controlled dimensions or

retention rings are some of the solutions.

Drain-Back Closures. These ﬁtments provide pour

spouts and matching caps for detergents and fabric

softeners. The drain-back section is sometimes

Figure 3. Typical special rollon ﬁnish.

160 BOTTLE DESIGN, PLASTIC

placed inside the ﬁnish similar to a plug, but fre-

quently before ﬁlling.

Child-Resistant Closure (CRC). There are a number

of different types of these closures on the market,

generally requiring special ﬁnishes. The popular

‘‘push and turn’’ instruction requires sufﬁcient H

dimension to allow the cap to be pushed down for

thread engagement. The ‘‘line up the arrows’’ in-

struction requires a ring with an interruption under

the arrow. Protocol testing includes both closures

and containers (see Child-resistant packaging).

Nonremovable Closure. Some dispensing closures are

designed to prevent removal. One design has ratch-

ets that can easily be overridden for tightening but

prevent loosening (see Closures, bottle and jar).

Tamper Band. Many products (drugs and foods) have

tamper bands to show tamper evidence. The band

must be able to anchor itself to something on the

bottle—a ring is sometimes added to the outside

under the ﬁnish area (see Bands, shrink; Tamper-

evident packaging).

ENVIRONMENTAL CONCERNS

Whether driven by legislation, consumer preference, or

the desire to be a good corporate citizen, today’s packager

has to take environmental concerns into account when

producing a package. A new plastic bottle presents a

special challenge and opportunity. The following is a brief

look at plastic bottles and the ways of handling solid waste

other than the landﬁll:

1. Reduce. The preferred way of handling the pro-

blem—creating less waste in the ﬁrst place—has

another major advantage. The less plastic we use,

the more money we save. This can be accomplished

through optimizing structural design, eliminating

oversizing, and taking advantage of the best materi-

als for the job.

2. Reuse. Although returnable bottles may seem like

an obvious answer, this is not necessarily the case:

‘‘to withstand the process of return and reﬁll, a

reﬁllable container must be about twice as heavy

as a one-way container of the same material.’’ This

adds impact to energy usage and eventual disposal

also (6). However, a number of consumer products,

notably detergents and cleaning products, are sold

in bottles that the consumer reﬁlls without having to

undergo this process. The reﬁll packages are de-

signed with less plastic and frills, or are made of

lighterweight or more easily crushable materials.

3. Recycle (Recyclable). Everything can be recycled by

somebody, somehow, somewhere. However, unless a

substantial percentage of the bottles can realisti-

cally be recycled in the near future, this doesn’t

mean too much. Although the percentages of bottles

that are recycled or could be from programs in

place changes constantly, the bulk of recycling is

with PET (mostly soda bottles, although some areas

have added capabilities to accept other bottles) or

HDPE (mostly homopolymer milk bottles, although

some areas now accept other containers including

copolymer detergent bottles). Plastic containers can

be recycled into plastic lumber, piping, or even

carpet liner as well as packaging containers. The

recycling rate for plastic containers has been esti-

mated at 24.3% for 2005, based on pounds of resin

sold (7). To aid in potential recycling, as well as

comply with the law in most states, a material

identiﬁcation logo, such as the SPI resin identiﬁca-

tion code, (8) should be added to all containers.

4. Recycle (Recycled). The relatively high cost of col-

lecting, sorting, cleaning, and processing good-qual-

ity post-consumer HDPE generally makes it more

expensive pound for pound than virgin resin. As the

process becomes more efﬁcient and if the cost of

virgin continues to climb, this may change. Because

of the unpredictability of the color and properties of

much regrind, it is frequently used as a middle layer

in a multilayer coextruded bottle or as a small

percentage in a dark bottle holding nonaggressive

product. Food and drug primary packages may not

be permitted to use reground plastic directly,

although repolymerization or special considerations

can be investigated.

5. Incineration and Conversion to Energy. Plastics

produce heat when burned, which, in turn, can be

converted to other forms of energy. The presence of

heavy metals (such as lead or cadmium used in some

colorants) in a bottle will leave toxic waste residue.

Several states have outlawed the use of these mate-

rials, and it is critical to avoid them. Older incin-

erators may also have a problem with chloride

containing materials such as PVC (9).

BIBLIOGRAPHY

1. R. J. Kelsey, Packaging in Today’s Society, St. Regis Paper

Company, 1978, p. 69.

2. S. Levy and J. H. DuBois, Plastic Product Design Engineering

Handbook, Van Nostrand Reinhold, New York, 1977, pp. 169–

170.

3. ASTM International Web information. Available at http://

www.astm.org/cgi-bin/SoftCart.exe/COMMIT/SUBCOMMIT/

D2020.htm?L+mystore+vvra4003+1173846722. Accessed May

30, 2007.

4. CAPE Systems, Inc. Web information. Available at http://

capesystems.com. Accessed May 30, 2007.

5. TOPS Engineering Corporation, Web information. Available at

http://www.topseng.com/. Accessed May 30, 2007.

6. L. Erwin and L. H. Healy, Jr., Packaging and Solid Waste

Management Strategies, American Management Association,

New York, 1990, p. 26.

7. Plastics Division of the American Chemistry Council and the

Association of Postconsumer Plastic Recyclers 2005 National

Post-Consumer Plastics Bottle Recycling Report Web informa-

tion. Available at http://www.plasticsrecycling.org/documents/

2005NationalPost-ConsumerPlasticsBottleRecyclingReportFI-

NAL.pdf. Accessed May 30, 2007.

BOTTLE DESIGN, PLASTIC 161

8. The Society of the Plastics Industry—SPI Resin Identiﬁcation

Code Guide To Correct Use Web information. Available at

http://www.plasticsindustry.org/outreach/recycling/2124.htm.

Accessed May 30, 2007.

9. L. Erwin and L. H. Healy, Jr., Packaging and Solid Waste

Management Strategies, American Management Association,

New York, 1990, p. 37.

General References

R. J. Kelsey, Packaging in Today’s Society, St. Regis Paper

Company, 1978.

S. Levy and J. H. DuBois, Plastic Product Design Engineering

Handbook, Van Nostrand Reinhold, New York, 1977.

The Society of the Plastics Industry—Web site: http://www.plas-

ticsindustry.org/.

ASTM International—Web site: http://www.astm.org/.

The Association of Postconsumer Plastic Recyclers—Web site:

http://www.plasticsrecycling.org.

L. Erwin and L. H. Healy, Jr., Packaging and Solid Waste

Management Strategies, American Management Association,

New York, 1990.

S. Selke, Ph.D., Packaging and the Environment, Technomic

Publishing Inc., Lancaster, PA, 1990.

J. Hanlon, Handbook of Package Engineering, second edition,

Technomic Publishing Co., Lancaster, PA, 1992.

A. Mandel, ‘‘Bottle Design, Plastic’’ in The Wiley Encyclopedia of

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

York, 1997, p.93.

A. Mandel, ‘‘Packaging Beer in Plastic Bottles,’’ Teltech online

article, May 1999.

BOXES, CORRUGATED

GENE A. FOSTER

Middlesex Container Company,

Inc., Milltown, New Jersey

Updated by Staff

INTRODUCTION

Corrugated containers (erroneously termed cardboard

boxes) became the shipping package of preference in the

early 1900s as a replacement for wooden crates. Corru-

gated ﬁberboard packaging is, in terms of tonnage, by far

the most common type of paper and paperboard-based

packaging (1).

The corrugated shipping container and related inner

packaging is multifunctional. Its varied uses include

wrapping, enclosing, protecting, cushioning, indexing,

stacking, and displaying. The basic function of the packa-

ging is to protect the product during distribution until the

product is removed from the package. The growing use of

palletization in warehousing and distribution requires

corrugated boxes with good stackability. Corrugated board

is an appropriate material for obtaining high stackability.

Product containability and cost-effective adaptation to

logistics systems are important issues in corrugated-board

transport design. Today’s packaging is used not only for

protection, but also for promotional and adverstising

support. It is a communication medium carrrying infor-

mation and artwork. Printing quality has been developed

to meet these needs (1).

RAW MATERIALS

Kraft linerboard derives its name from the Swedish word

kraft, meaning strength. It is produced for its facial

stiffness (stackability) and puncture resistance. These

characteristics are achieved through use of soft-wood

ﬁbers that are long and resilient. Linerboard becomes

the facings of corrugated board.

The basic raw material for liner is cellulose ﬁber

extracted from wood chips. The chips are digested in a

cooking liquor to remove lignin and resin, leaving the ﬁber

that is ﬁbrilated to enhance the tendency for the ﬁbers to

mat together. The ﬁbers are pulped with water and spread

onto the screen of a Fourdrinier paper machine. Water is

drained, leaving the mass of ﬁber to form a sheet of paper

that is dried and wound into rolls. Many Fourdrinier

machines are over 20 ft (6 m) wide. Linerboard is graded

by basic weight, which will be explained in the section on

liner grades.

The natural color of pulp is tan or kraft. A small

percentage of the pulp is bleached white in a chlorine

bath and then converted into fully bleached white paper.

Bleached white pulp is also furnished as a topping for

kraft liners to produce mottled white linerboard. Paper

mills sell linerboard to corrugated converting plants in

units of tons.

The medium is the paper rollstock that is converted into

the ﬂuted portion of corrugated board. The medium is also

known as ‘‘nine point’’ because it calipers 0.009 in. It is also

termed ‘‘semichem’’ because the pulp is cooked with che-

micals and then mechanically ground into ﬁbers. The pulp,

like linerboard, is converted into paper on the Fourdrinier

machine; however, pulp for the medium is selected from

hard-wood trees that have short ﬁbers that hold a set better

when they are steamed and ﬂuted on the corrugator.

Technical advances have made possible the use of roots

and recycled containers as percentage additives to medium

stock. Recycled ﬁber from recovered paper and board is a

major source of ﬁber for the corrugating industry.

The universal weight for the medium is 26 lb/1000 ft

(11.7 kg/90 m

); however, minimum quantities (33 and

40 lb) of medium are used to improve ﬂat crush, stacking,

and moisture resistance in ﬁnished board.

Adhesives

Contemporary corrugator adhesives are starch-based with

additives and are selected for their ﬂow, tack, absorbtion,

evaporation, and set qualities. Specialty additives may be

blended with the base adhesive to improve wet strength

and moisture resistance. Borax is added because it causes

the starch to become a more highly branched polymer chain

with higher viscosity and tack (1). Modern corrugators use

162 BOXES, CORRUGATED

as little as 2 lb (0.9 kg) of adhesive per 1000 ft

(90 m

)to

combine single-wall board. Fingerless single-facers have

eliminated the old problem of adhesive buildup lines (ﬁnger

lines) in the ﬁnished product. The manufacture of corru-

gator adhesive is highly technical and is controlled through

a series of extreme speciﬁcations.

Joint adhesives can be plastic based hot melts or

starch-based cold melts. Both are used successfully to

produce high-speed manufacturer’s joint closure (see

Adhesives).

Inks

Are a product of earth elements and chemical formula-

tions. The base carrier for modern ﬂexographic printing

inks is water laced with additives designed to enhance

drying speed, produce image clarity, inhibit smearing, and

eliminate spotting or blotching. Inks must be carefully

scrutinized for their pH factor because acidic inks differ in

performance from base inks. For example, basic inks tend

to smear. Ready-to-run inks are supplied to the corrugated

printers in drums of 50-lb (22.5-kg) pails. In-house ink

kitchens afford the converting plant the ﬂexibility of

mixing raw materials delivered from the ink manufac-

turers into custom batches in which the corrugated prin-

ters can control tones, viscosities, additive selections, and

many other custom characteristics that will enhance the

ﬁnal printed image (see Inks).

The industry’s modern ink kitchens use the Pantone

Matching System (PMS) Service. An endless range of

available ink colors has been opened up. The color of the

print is measured by the CIE system.

Printing Plates

Modern printing plates are supplied to the corrugator

mounted on poly backing, ready to be locked into the

press. The industry has moved from a rather slow, meth-

odical art form to a highly technical and efﬁcient producer.

The engraved rubber plate (die) has been replaced by a

photopolymer plate that is rapidly produced through a

series of computer imaging, and photoprocessing. The

photopolymer plate is presently subject to ultraviolet

(UV) deterioration; however, chemical suppliers of the

base poly material will solve this problem soon.

Cutting Dies

Corrugated products with scores or slots with angles other

than 901 must be die-cut. Cutting dies are produced for the

purpose by imposing an image onto a plywood sheet,

jigsawing or laser-cutting the imaged lines, and ﬁlling

the eradicated space with a cutting knife or scoring rule as

desired. The dies are made on curved or ﬂat plywood,

depending on the style of diecutter to be used. Stripping

forms accompany cutting dies if they are to be used on

automatic equipment.

Labels

High-graphics products incorporate the use of labels in

conjunction with or in lieu of printing. Labels are supplied

to the corrugated converters by label manufacturers.

Typical speciﬁcations requested for labels are number of

printed colors, paper basis weight, stock color, ﬁnish, and

grade. Labels are adhered to the corrugated stock manu-

ally, semiautomatically, or fully automatically.

Additives

Finished corrugated blanks may be treated by many

additives or coatings to improve water repellency, scuff

resistance, and petrochemical resistance. Waxes and poly-

mers are favored additives.

BOARD CONSTRUCTION

Corrugated board is a sandwich of one or more linerboard

sheets adhered to a ﬂuted medium. Single-face construc-

tion incorporates one linerboard adhered to the medium.

Double-face, better known as single-wall, has a linerboard

adhered to both sides of the medium. Additional media

and linerboards yield double-wall and triple-wall (see

Figure 1).

Combinations of linerboard grades and ﬂute conﬁgura-

tions are used to generate the many variations of corru-

gated board. Liner weights are increased to improve board

bursting and stacking strength, and ﬂutes are modiﬁed to

accommodate various compression, stack, and printing

Figure 1. Various examples of corrugation.

BOXES, CORRUGATED 163

features. Two important requirements of corrugated board

are ﬂat crush and stacking strength. Flat crush measures

the pounds per square inch (psi) resistance to pressure

applied at a 901 angle to a horizontal sheet, thus establish-

ing the rigidity of the ﬂute structure. This property is

changed by varying the ﬂute outline and linear density. It

can also be revised by changing the basis weight of the

ﬂuted medium. Flat crush supplies the internal resistance

to squeezing forces such as feed rollers in presses and

gluers. It also supplies resistance to gravitational forces

imposed upon bottom sheets in stacks and bottom cartons

in units.

Stacking strength measures the ability of a vertical

panel to resist bowing, buckling, or collapsing from pres-

sure exerted in line with that panel. This is regulated by

varying the linerboard weights, changing ﬂute heights, or

both. Stacking strength is probably the most sought-after

characteristic in corrugated cartons.

Flutes

Flutes are most essential to the characteristic of corru-

gated board. They supply the rigidity to the board that

imparts strength with minimal weight and density. Flut-

ing makes the product economical. Flutes are designed by

height (thickness) and density (number per linear foot).

Higher ﬂutes produces a physically stronger columnar

stack in line with the ﬂutes. Denser ﬂutes—that is, ﬂutes

that present more images per linear foot—produce more

resistance across the ﬂutes. C is the most used ﬂute size,

followed by B and E. The C ﬂute is considered a compro-

mise between A and B. Other, minimally used ﬂutes

include J (jumbo), which is larger than the others, as the

name suggests; S ﬂute; and F ﬂute, which is the lowest

ﬂute height.

Higher (less dense) ﬂutes in addition to stacking

strength provide softer cushion characteristics, while

lower (more dense) ﬂutes provide greater ﬂat crush

resistance, smoother print surfaces, and crisper score

lines. Flutes are often used in combinations such as BC

double wall, which provides an overlap of required

characteristics. B and C ﬂutes are the most com-

monly produced ﬂutes, and E is considered sparingly.

Flute selection is determined by shipper needs. A fragile-

decorations shipper would choose C ﬂute for its stacking

strength and cushioning qualities. A canned beverage

ﬁller would choose B ﬂute for its end-to-end compres-

sion attributes; and a point-of-purchase display designer

would select E ﬂute for its superior printing surface. (See

Table 1.)

MULLEN VERSUS EDGE CRUSH

Carrier regulating agencies require a board upgrade to

accommodate increased loads and increased box sizes

analogous to the idea that a 3/4-in. (19-mm) plywood sheet

is stronger than a 1/4-in. (6.35-mm) sheet. Paper mills

fulﬁll this requirements by producing various-weight liner

grades, corrugated converters combine board using proper

heavier grades to accommodate the need for stronger

containers.

Liner Grades

The universally accepted test for corrugated board has

been the Mullen test (TAPPI test method T-810), which

measures the resistance of the board to withstand a

puncturing pressure measured in pounds per square

inch (psi) or metric kilopascals (kPa). Linerboard grades

have been manufactured to meet speciﬁc Mullen require-

ments. Increased Mullen demands increased linerboard

strength, which is accomplished by increasing the mass of

the linerboard measured in pounds per thousand square

feet (lb/1000 ft

) (kg/90 m

A major modiﬁcation to containerboard was initiated in

the 1980s, when paper mills developed a process that

enhanced linerboard material, giving it an ability to with-

stand crush or compression examinations at lower basis

weights. Table 2 compares STFI crush performance of

standard to high-performance liners. Note the improved

STFI in high-performance liner.

The product high-performance linerboard provides a

serious potential for user satisfaction and improved eco-

nomics. New linerboard concepts prompted the corrugated

industry trade associations to sponsor proposals to truck-

and rail-carrier committees to consider classiﬁcations

recognizing edge crush as a test criteria. Proponents for

the new test methods argued that edge crush is more

customer-oriented and that it permits more latitude for

manufacturers to design and supply boxes that meet

customer performance criteria. Rules committees of truck

and rail carriers accepted the proposals, and in 1991 they

approved the edge-crush test (ECT) as an alternative test

method for containerboard.

Edge-crush Test

This measures the resistance of the containerboard to

edgewise compression. Ring-crush and STFI tests mea-

sure the resistance of the linerboard and medium. These

tests are performed to give the linerboard and corru-

gated manufacturers relative material comparisons. The

Table 1. Standard U.S. Corrugated Flutes

Flute Designation Flutes per Linear Foot Flutes per Linear Meter Flute Thickness, in. (mm) Flutes per Cross Section

A ﬂute 3373 108710 3/16 (4.8)

B ﬂute 4773 154710 1/8 (3.2)

C ﬂute 3973 128710 5/32 (4.0)

E ﬂute 9074 295713 1/16 (1.6)

Corrugator equipment manufacturer’s single-face ﬂute roll dimension may vary slightly to accommodate user preference.

164 BOXES, CORRUGATED

edge-crush test includes the value of the medium’s resis-

tance to compression as well as the linerboard. It should

be noted that these tests can, and are, performed on

standard weight liners as well as on high-performance

liners (see Edge-crush concept).

Medium Grades

General industrial principle requires use of the same

medium weight (26 lb/1000 ft

) (11.7 kg/90 m

) for all board

grades; that is, liner weights change to generate increas-

ing board tests, but the medium remains the same. There

are some approved exceptions that call for upgrading

medium to improve ﬂat crush and moisture resistance.

Two upgraded medium weights are 33 and 40 lb.

REGULATIONS

Freight carriers and government agencies control the

regulations for the container industry. The major regula-

tion is encompassed in Rule 41 (Uniform Freight Classi-

ﬁcation) established by the National Railroad Freight

Committee (2). This regulation is closely paralled by

Item 222 (National Motor Freight Carriers). Table 3 out-

lines minimum standards. Triple-wall and solid-ﬁber stan-

dards have not been included in this chart.

Rules prescribed by these agencies outline require-

ments that determine proper liner weights and manufac-

turing speciﬁcations. All corrugated boxes made to

conform to the regulations carry a printed certiﬁcate

identifying the boxmaker and appropriate board grade

as shown in Figure 2. Note the apparent difference

between the burst-test and the edge-crush certiﬁcates.

Table 2. STFI Crush Performance of Standard to High-

Performance Liners

Liner Basis Weight STFI

lb/1000 ft

(kg/90 m

) lb/in. width (kg/cm width)

26 11.8 12 13.9

33 14.9 15 17.4

38 17.2 17 19.7

42 19.0 19 22.0

69 31.2 29 33.6

90 40.7 38 44.0

Medium-Performance Liner

26 11.8 11 12.8

33 14.9 15 17.4

40 18.0 19 22.0

High-Performance Liner

35 15.8 20.3 23.6

45 20.3 27.5 31.9

57 25.8 33.7 39.1

72 32.6 45.0 52.2

Table 3. Minimum Standards for Construction of Corrugated Boxes

Table A Table B

Maximum Weight of

Box and Contents, lb

(kg)

Maximum Outside

Dimensions, Length,

Width, and Depth

Added Inches (cm)

Minimum Bursting

Test, Single-Wall,

Double-Wall, psi (See

Note 1) (MPa)

Minimum Combined

Weight of Facings,

Including Center

Facing(s) of Double-

Wall, lb/1000 ft

(g/m

)

Minimum ECT, lb/in.,

Width (See Note 2) (kg/

cm width)

Single-Wall Corrugated Fiberboard Boxes

20 (9) 40 (102) 125 (0.862) 52 (254) 23 (26.3)

35 (16) 50 (127) 150 (1.034) 66 (322) 26 (29.7)

50 (22) 60 (152) 175 (1.206) 75 (366) 29 (33.1)

65 (29) 75 (190) 200 (1.379) 84 (410) 32 (36.5)

80 (36) 85 (216) 250 (1.723) 111 (542) 40 (45.7)

95 (43) 95 (241) 275 (1.896) 138 (674) 44 (50.3)

120 (54) 105 (267) 350 (2.412) 180 (879) 55 (62.8)

Double-Wall Corrugated Fiberboard Boxes

80 (36) 85 (216) 200 (1.379) 92 (449) 42 (48)

100 (45) 95 (241) 275 (1.896) 110 (537) 48 (54.9)

120 (54) 105 (267) 350 (2.412) 126 (615) 51 (58.2)

140 (63) 110 (279) 400 (7.757) 180 (878) 61 (69.6)

160 (72) 115 (292) 500 (3.445) 222 (1084) 71 (81.1)

180 (81) 120 (305) 600 (4.135) 270 (1318) 82 (93.6)

Note 1—Burst test: (a) Tests to determine compliance with the bursting test requirements of Table A must be conducted in accordance with Technical

Association of Pulp and Paper Industry (TAPPI), Ofﬁcial Test Method T-810; (b) a minimum of six bursts must be made three from each side of the board, and

only one burst test will be permitted to fall below the speciﬁed minimum value. Board failing to pass the foregoing test will be accepted if in a retest consisting

of 24 bursts (12 from each side of the board), not more than four burst tests fall below the speciﬁed minimum value. Note 2—Edge-crush test: (a) Tests to

determine compliance with the edge crush requirements of Table B must be conducted in accordance with Technical Association of Pulp and Paper Industry

(TAPPI), Ofﬁcial Test Method T-811; (b) a minimum of six tests must be made and only one test is permitted to fall below the speciﬁed minimum value, and

that one test cannot fall below the speciﬁed minimum value by more than 10%. Board failing to pass the forgoing will be accepted if in a retest consisting of 24

tests, not more than four tests fall below the speciﬁed minimum value, and none of those tests fall below the speciﬁed minimum value by more than 10%.

BOXES, CORRUGATED 165

Several other regulatory agencies are included depend-

ing on shipper requirements, including

Department of Transportation—Code of Federal Regu-

lations No. 49 (Transportation)-Pointing speciﬁcally

at hazardous materials

International Air Transport Authority (IATA)—con-

cerned with air transport

International Maritime Authority—water cargo

United Parcel Service (UPS)—ground deliveries of

o150 lb

U.S. Postal Service—Domestic Mail Manual

CONVERTING OPERATIONS

Corrugated ﬁberboard boxes are manufactured in a cor-

rugated board plant or in a sheet feeder plant. The

corrugated board plant consists of the corrugator, which

produces ﬂat sheets of corrugated ﬁberboard, and the

converting equipment where the corrugated sheet is con-

verted into corrugated board boxes by printing, cutting,

scoring, and gluing. Sheet feeder plants are smaller

factories that convert board into packaging for shorter

run length orders, for quick deliveries, and for a local

market.

Contemporary box plants vary widely in size and

capability. A small sheet plant may ship one truckload of

cartons per day while the megacontainer plant will ship 50

truckloads per day. Corrugated requirements are so di-

verse that a wide variety of company sizes is a desirable

asset to the industry.

Corrugator

This is the major piece of equipment in a box plant. The

machine converts mill-supplied roll stock (linerboard and

medium) into ﬂat sheets. It varies from 50 to 100 in. plus

(12.7–25.4 m) in width, and most are over 300 ft (91.5 m)

long. Wide computer-managed corrugators operating at

speeds of up to 1000 lineal feet per minute are capable of

producing four truckloads of corrugated board per hour.

The single-facer (wet end) of the corrugator converts

the medium into ﬂuted paper and adheres it to the

inside liner of the corrugated sandwich. Next, a double

backer roll is applied as the outside liner, and ﬁnally the

sandwich is run over dryer plates and delivered to the dry

end. Cross-corrugation scores may be applied and the

board is trimmed into two-dimensional blanks in prepara-

tion for delivery to the plant for further conversion into

a box.

Scheduling (trimming) a corrugator requires skill and

training because variations of liner combinations, quan-

tity requests, and blank dimensions are endless. Modern

computer-trimmed corrugators are capable of producing

several hundred setups per day.

Printer-Slotters

These machines print, slot, and score ﬂat banks in pre-

paration for folding and joining into ﬁnished boxes. Sized

blanks are delivered from the corrugator prescored for ﬂap

and depth dimension. The operator, generally one of a two-

or three-worker crew, sets scoring and slotting heads at

proper dimensions to cut required length, width, and joint

dimensions into the carton. The operator then hangs the

premounted printing plates on the print cylinders, ﬁlls the

ink wells with desired colors, and begins production.

These machines are referred to by the number of colors

they are capable of printing in one pass plus cylinder

diameter and machine width. Small-dimension machines

are obviously better suited for producing small boxes, and

so on. A majority of presses today are two-color; however,

presses in up to six colors are available.

Corrugated printer-slotters are letterpress printers;

however, most current equipment is a ﬂexographic varia-

tion that incorporates the use of an analox roller with

water-base inks versus the old doctor and impression

rollers with oil-based ink. Flexographic printing offers

many advantages over letterpress, including operating

speed, clarity, registration, trapping, drying, and cleanup.

Printer-slotters employing ﬂexographic printing can pro-

duce an average size-box (e.g., a 24/12-oz beverage box) at

approximately 15,000 per hour.

Figure 2. Boxmaker certiﬁcate.

166 BOXES, CORRUGATED

Flexofolder-Gluer

The Flexofolder-Gluer (FFG) incorporates the addition of

an automatic folder–gluer system with the printing unit,

which permits the completion of most cartons on one

machine. The equipment has been available since the

1960s, when ﬂexographic printing with high-speed drying

made it possible for cartons to be folded immediately after

printing without smearing. These machines may also be

equipped with automatic bundeling and unitizing sys-

tems. The most advanced FFG can run up to speeds of

26,000 boxes per hour. Boxes can be produced for any

application.

Folder–Gluers

These are designed to ﬁnish boxes in a straight line or

right angle. Both are extremely efﬁcient at folding panels

and applying adhesive to produce ﬁnished cartons that

require minimum or no ﬁnal sealing. Predecorated,

slotted, and or die-cut blanks are belt fed through the

folding sections; glue is applied at required spots; and

ﬁnished cartons are stacked at the ﬁnish end. Most

equipment is designed to accept a wide variety of sizes

both in the machine direction and across the machine.

Die Cutters

Die cutters are required for all parts that are scored or

slotted other than 901 or in line with press direction.

Intricate die cut interior parts and box designs are a

very common part of the industry.

Flatbed die cutters are designed to produce accurate

products. They vary from small hand-fed machines that

are limited in speed to the operators performance (about

500 blanks per hour) to high-performance automatic

equipment that include multicolor printing selections.

Flatbed cutting dies are reasonably priced. The process

for ﬂatbed die cutting closely resembles cookie cutting.

The die board is locked into a chase that holds it in a ﬁrm

position. Corrugated board is registered under the die;

and the machine is closed, striking the die impression into

the board.

Rotary die cutters are best used to produce parts at

high speeds. They are not as accurate as ﬂatbed machines;

however, they can be designed to accept large blanks.

Rotary cutting rule is inserted into curved plywood and

then locked onto the die-cutting cylinder. An impression is

made into the board when a blank is passed between the

cut die cylinder and an opposing thick polyblanketed

impression cylinder.

Slitters

Slitters have a series of wide rotating shafts to which

scoring and slitting collars (heads) are attached. These

heads can be moved by the operator to change dimensions.

Most slitters are manually fed; however, some are

equipped with automatic feed sections. Slitters are used

to reduce large sheets to smaller blank dimensions, add

scores to existing blanks, and prepare small runs for

further processing. Slitters are very versatile machines.

Small sheet plants may be totally equipped with a slitter a

printer–slotter and a taper.

Partition Slotters

These machines slot corrugated pads in preparation for

assembly into partitions.

Partition Assemblers

These machines automatically assemble slotted racks into

cell-divided partitions for use in separating delicate parts

such as glass bottles.

Tapers

These machines apply tape fed from rolls onto prefolded

cartons to form a manufacturer’s joint. Standard tape

widths are 2 in. (5.08 cm) or 3 in. (7.62 cm). Tapers are

handfed semiautomatic or hopper-fed automatic. The

machine is an economical piece of equipment that can be

adjusted and set very quickly. Taped joints represent a

minimal amount of todays production because of their

relatively slow production speeds and higher costs com-

pared with glued joints. Glued joints also perform better in

regulatory transit tests.

Stitchers

These devices apply staples cut from a roll and are driven

into the joints of prefolded boxes. Stitched joints have

limited use in today’s market; they are used mostly with

government-grade boards and specialty wet-strength

containers.

Coaters

These machines are operated at box plants or, in many

cases, at specialty plants that process coatings on ﬁnished

containers. These specialty plants function as a separate

entity to the corrugated industry; that is, they seek custo-

mers for their process, mostly from the ﬁsh, poulty, and

produce industries; purchase ﬁnished containers from cor-

rugated converters; and add the required coatings (waxes

and plastics) to the containers. The industry specializes in

wet-strength and moisture-barrier containers.

Curtain coaters feed box blanks under a curtain of

liquid coating (molten poly) that coats one side of the

blank and passes it to a drying section. Some coaters are

capable of ﬂipping the blank to deposit a coating on both

sides. Cascaders pour wax coatings onto ﬁnished contain-

ers. Wax dippers immerse ﬁnished containers into tanks of

molten wax and then hang them to dry. The process looks

very much like your local laundry.

Laminators

Litholaminators have

become an important

adjunct to the

high-graphics corrugated producer. This equipment rolls

adhesive onto a printed litholabel, registers the label

under the substrate, drops the substrate onto the label,

and rolls the combined stock to achieve 100% adhesion

and eliminate air bubbles. Litholaminators are designed

to feed ﬂat banks, including joined (knocked-down) boxes.

BOXES, CORRUGATED 167