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solids radiation curable silicone release coatings, which

are used for pressure-sensitive adhesive labels and other

products. The transfer roll coater is a direct roll coater.

The rubber-covered applicator roll is run 5–25 times faster

than the transfer roll, and this decreases the amount of

coating transferred to the substrate by that factor.

Reverse Roll Coaters. The main feature of the reverse

roll coater is that the applicator roll rotates in the direc-

tion opposite to the web travel (therefore, reverse roll) and

transfers the coating by wiping. These coaters are versa-

tile machines. Among the advantages of reverse roll coat-

ing are (a) the possibility to handle a wide range of coating

thickness and viscosities and (b) greater weight of coat-

ings. Solids in the range of 10% (w/w) are typical. More-

over, the reverse roll coating leads to a more thorough and

uniform deposition of the wet coating and a smoother dry

coating as well. In addition, this kind of equipment can

work at higher line speeds than the direct system, achiev-

ing excellent results while handling weak webs. Solvent

solutions, aqueous coatings, and less frequently hot melts

are coated on these machines. Reverse roll coaters are

expensive; rolls must be accurately machined. These coat-

ers are available in several designs: Feed location may be

varied from nip to pan; three or four rolls may be used. In

the case of a nip-fed coater as shown in Figure 7, the

coating is delivered to the nip between metering and

applicator rolls, and dams are used to contain the coating.

A gap set between these two accurately machined rolls

determines the amount of coating carried by the applica-

tor roll. The web usually runs faster than the applicator

roll, and the amount of coating deposited depends on the

ratio between the speed of these two rolls (wipe ratio) as

well as on the gap between metering and applicator rolls.

Gravure Coaters. These machines are inexpensive and

highly reliable, but limited to the coating thickness and

viscosity that can be handled. The main advantage of this

system is related to the possibility of controlling

Figure 2. Coating splitting.

Figure 3. Squeeze coater.

Metering

roll

Applicato

roll

Carrier

roll

Figure 4. Direct roll sheet coater.

Figure 5. Kiss-roll coater.

Matering

roll

Transfer

roll

Rubber

applicator roll

Steel

backup roll

Figure 6. Transfer coater.

288 COATING EQUIPMENT

accurately the amount of substance applied on the web

(i.e. the thickness of dry coatings) as well as its homo-

geneity. It is agreed that gravure coating represents the

most uniform and reproducible system to coat moving web

of material. An engraved chrome-plated (sometimes cera-

mic coated) copper roll is wetted with the coating, excess is

removed by a doctor knife (scraper) (Figure 8), and the

coating remaining in the engraved cells below the roll

surface is transferred to the web at the gravure roll/

backup roll nip (Figure 9). Three engraving patterns are

commonly used for coating purposes: pyramidal, quadran-

gular (truncated pyramid), and tri-helical. The amount of

coating depends on the liquid volume retained in the

cells—that is, on the cell depth and their density, referred

to as screen or ruling (the number of cells per unit length).

The coarser the screen, the larger the diameter and depth

of cells and the higher the deposit. It is important that

the amount of coating entrapped in the depressions of the

gravure roll remains constant over the life of the roll,

guaranteeing a virtual constant uniformity during the

whole production process. The ﬂuid viscosity must be

sufﬁciently low to allow the transfer of the coating from

the cells to the web at nip pressure. Thickness typically

ranges between 3 and 25 mm, even if lower values (0.5 mm)

can be easily obtained. In the direct gravure arrangement

(Figure 9), the engraved roll contacts the web directly. In

offset gravure the coating is ﬁrst transferred to a rubber-

covered roll and then transferred to the web. In this case,

it should be important to use a covering elastomer resis-

tant to solvents eventually present in the coating solution.

Offset gravure allows the use of higher nip pressure and

is therefore more suitable for coating rough-surface

substrates. It also allows the coating to level on the roll

surface before its transfer to the web. Different matrices,

substances, and formulations can be used as coatings to be

applied through this system. Latexes, solvent-based coat-

ings, water-based coatings, hot melts, and reactive (cur-

ing) coatings are the most frequently employed. Gravure

coating is widely used for various decorative and func-

tional lightweight coatings on plastic ﬁlms, paper, and

other packaging substrates. The same technique is suita-

ble for printing, wherein coating deposition takes place

only to limited areas of the substrate. In this case, a given

roll delivers a ﬁxed amount of coating; that is, it deposits

noncontinuous coating.

The most recent machines are able to handle different

substrates continuously—that is, without arresting the

whole plant in order to substitute the coated roll with

another one. Hence, the coating application can take place

by replacing automatically online the just-coated web with

a new one previously mounted on the machine (Figure 10).

Obviously, to avoid the stop of the coating line, the

different rolls must have the same width and have to be

coated with the same matrix. The ﬁnal result will be the

increased line speed in the coating process and the

enhancement of the output.

Calender Coaters. The calendering process involves

squeezing a polymeric material between steel rolls into a

Dams

Applicator roll

Backing roll

Metering roll

Figure 7. Nip-fed reverse roll coater.

Figure 8. Gravure coater showing the doctor blade supported by

two pistons. (Courtesy of Metalvuoto Spa, Roncello, Italy.)

Idler rolls

Smoothing bar

Engraved cylinder

Pan

Doctor blade

Impression roll

Figure 9. Direct gravure coater.

COATING EQUIPMENT 289

thin sheet. The formed sheet may be then laminated to a

substrate. Rubber and PVC are most often used for

calender processing. Calendering is rarely used for man-

ufacturing packaging materials.

Knife and Bar Coaters

Knife and bar coaters are metering devices that remove

excess coating and allow only a predetermined amount to

pass through.

Knife-over-Roll Coaters. Knife-over-roll is a useful in-

expensive method for the application of coating, having

both high viscosity and heavy weights. As a result, it is

primarily used to coat paper and textiles. A knife-over-roll

coater consists of a knife placed against a roll. The knife

may be either straight-edged or ‘‘J’’-shaped, depending on

the speciﬁc application. The coating weight is adjusted by

setting a gap between the roll and the knife. An excess

coating is delivered to the bank before the knife, and the

desired amount is metered by the gap. An accurately

machined steel roll and knife are used (Figure 11). In

another version of a knife-over-roll coater, a rubber-cov-

ered roll is used and the coating weight is determined by

the gap and rubber hardness (its capability to deform

because of hydraulic pressure).

Other Knife Coaters. Knife coaters are used in many

other conﬁgurations: ﬂoating knife, knife-over-blanket,

knife-over-channel, and inverted knife. These methods

are used more frequently in the textile industry.

Blade Coating. Flexible-blade coating is the dominant

process for applying pigment coating over paper and

board. Clay coatings give a smooth and printable surface.

Blade coating processes are suitable for high-speed appli-

cation such as required in paper converting. The coating

head consists of a coating applicator, such as roll or

fountain, which applies an excess of coating to the paper.

The excess coating is removed by a blade (Figure 12).

Figure 10. Two rolls simultaneously placed on the

same coating line. Roll 2 (working) will be automati-

cally substituted by roll 1 (not working). (Courtesy of

Metalvuoto Spa, Roncello, Italy.)

Figure 11. Knife-over-roll coater.

Pape

Coating color

Applicator roll

Blade

Backing roll

Figure 12. Blade coater.

290 COATING EQUIPMENT

Several modiﬁcations of blade coaters are available em-

ploying different blade designs, different methods of ap-

plying and regulating blade pressure, and different ways

of applying the coating to the paper. Machines capable of

applying coating to both sides of the web are available.

The air-knife system consists of a head with a narrow

slot emitting a ribbon of pressurized air through nearly

the width of the web being coated. In air-knife coating an

excess of material is applied to the web surface usually by

a kiss-roll applicator or by spraying as a wet matrix to be

dried as quickly as possible. The excess is removed by the

air knife, wherein pressurized air is forced into the head

and is accelerated at the slotted nozzle. The escaping air-

stream impinges on the coated web and removes excess

coating (Figure 13). Air-knife coaters provide an even

thickness of the coating rather than a ﬂat-surfaced coat-

ing. It is the preferred method for coating paper, although

in the recent years it is being replaced by more developed

blade coaters for paper-coating applications.

Wirewound-Rod Coater. A wirewound-rod coater (Meyer

rod) is a simple metering device widely used in applying

lightweight coatings over ﬁlm and paper packaging mate-

rials. The coating is ﬁrstly applied by an applicator, usually

a kiss roll, and then uniformly spread by a rod wound

spirally with stainless-steel wire; ﬁnally, the excess of

coating is removed by the scraping action of the rod.

Usually, the wire-wound rod is rotated counter to the

rotation of the web, allowing a more precise control of the

process. Moreover, the rod is rotated to help dislodge any

particles that might become trapped between the wire and

the web and to ensure uniform wear of the wire. The rod

wipes the surface clean, except what escapes through the

spaces between the wires. The thickness of the wet coating

can be easily established by selecting the diameter of the

wire winding on the rod. In particular, the following

equation can be taken into consideration for this purpose:

K ¼ D 0:5 



¼ 0:1073ðDÞ

where K and D are, respectively, the thickness of the wet

coating and the diameter of the wire, expressed in the same

units. As it can be seen, K is practically 10 times less than

D. It means that, for instance, a wire 125 mm in diameter

will spread a wet coating 12.5 mm thick. In some cases a rod

wound with two wires could be used, with the second one of

lesser diameter than the ﬁrst. This allows us to spread

coatings thicker (about 500 mm) than those obtained by

using a single wire and to provide for coatings that ﬂatten

out faster. Wire rod coating is particularly useful to lay

down thin layers of PVDC latex to paper. In general, paper

should not be extensible, to avoid the fact that the tension

developed to hold the web tightly against the rod coater will

stretch the extensible ﬁlm (such as a polyoleﬁn) enough to

jeopardize the process. On the contrary, stiff plastic ﬁlms

like PET as well as cellophane, papers, and paperboards are

suitable to be worked in rod coaters.

Hot Melt Coating

Hot melting coating concerns the application of molten

polymers characterized by an intermediate molecular

weight. It can be considered as a variation of extrusion

coating. Both processes use a heated coating material to be

applied onto a moving web. The major difference is linked

to the viscosities, much lower for the hot melting coating.

Another further difference concerns the magnitude of

pressure applied during deposition of the coating. In

fact, hot melts are applied with little pressure. Different

materials can be used in the hot melting process, such as

waxes, resins, and thermoplastics of low molecular weight.

However, blends of polyoleﬁns and poly(ethylene-vinyl

acetate) with resins and waxes represent the majority of

applications in food packaging. In particular, these hot

melts are widely used to obtain (a) heavy coatings to

wrapping cases for waterprooﬁng and (b) lighter layers

to food cartons for frozen foods. Typical hot melt coating

methods include: slot-oriﬁce coating, curtain coating, and

roll coating.

Slot-Oriﬁce Coating. In the slot-oriﬁce coating, the

coating is forced through a narrow slot extending

the full width of the web. The slot die is designed to give

a uniform coating thickness across the width. A slot-oriﬁce

coater is widely used for manufacturing hot-melt

Applicator

Air knife

Excess-coating

collector

Figure 13. Air-knife coater.

COATING EQUIPMENT 291

pressure-sensitive adhesive packaging tapes (13) and for

applying waterproof coatings over paper. It also found

applications in aqueous emulsion coating. A slot oriﬁce

coater is shown in Figure 14.

Curtain Coating. Curtain coating is similar to slot-or-

iﬁce coating, except that the liquid curtain coming from

the die is allowed to drop down some distance to the

material to be coated. The slot width is adjustable and

the ﬂow is regulated by the slot width, by the liquid level

(in weir-type coaters), or by pressure and pump speed in

enclosed-head coaters, as well as by the distance between

the slot and the coated material, which determines the

acceleration of the curtain. This technique is used for

heavier coatings. In the packaging area, curtain coating

may be employed to deposit a hot wax coating over

corrugated board.

Roll Coating. Both direct and reverse roll methods can

be used for the application of hot melt coatings to the

substrate. Moreover, the rolls used for spreading the

coatings can be either smooth or engraved.

The application of the hot coatings usually takes place

at speeds ranging from 100 to 500 m min

1

at coating

weights of 3 to 600 g m

2

SATURATORS

The saturation or impregnation process is used to treat

paper and paperboard with a polymeric binder to improve

the web’s strength, barrier properties as packaging mate-

rial, and resistance to water and grease. The process

consists of immersion of the web into a coating bath, or

applying an excess of coating on both sides and then

squeezing or scraping to remove the excess. The coating

may penetrate the web or most of it may remain on the

surface, depending on the product needs.

Saturating machines consist of a web-immersion sec-

tion and a metering section. Several saturating arrange-

ments are used. Figure 15 shows a conventional sawtooth

saturator followed by squeeze-roll metering. Other types

of metering arrangements are inﬂatable bars, bar scra-

pers, doctor blades, and similar devices.

DRYING

Coatings applied as solutions or emulsions must be dried

in order to remove the liquid vehicle. Heat and mass

transfer take place simultaneously during the drying

process. Different methods are used in commercial prac-

tice, including convection drying with heated air; hot air

impingement; infrared; conduction heating; and radio-

frequency heating.

In the convection drying method, the wet web is passed

through a tunnel oven heated by a ﬂux of hot air forced in

the same direction (sometimes in the opposite direction) as

the web.

Impingement drying consists of a forced air ﬂux able to

dry the wet web more rapidly than convection drying. This

is because the method exploits the increased heat transfer

achieved by blowing rapidly heated air over the web

surface.

Infrared drying is carried out by using a heating source

emitting infrared rays. Indeed, infrared radiation is

usually used in combination with convection and impinge-

ment drying, to raise quickly surface temperatures and

hence to increase the efﬁciency of the solvent removal by

forced air.

Figure 15. Sawtooth saturator.

Web path

Driven, rubber-covered, backing roll

Die orifice and metering blade adjustments

Die

Die positioning adjustment

relative to web

Angular attitude adjustment of die

Pneumatic raise/lower loading cylinders

Drip tray

Figure 14. Hot-melt slot-oriﬁce coater. (Courtesy of

Black Clawson Co.)

292 COATING EQUIPMENT

Conduction drying is obtained by the direct contact of

the web with a heated surface. The ﬁnal dried substrate

(paper, paperboard, pulp, and laminations of porous webs)

is generally obtained very quickly, usually using heated

rotating cylinders.

Radio frequency (or dielectric heating) is a powerful

drying method especially for heavy coatings and water-

based systems.

Drying is a fundamental step in the coating process.

Incomplete or partial drying could lead to serious pro-

blems affecting the further converting phases, such as

bubble formation between layers, haziness, and separa-

tion of layers, among others. It is also to avoid the over-

drying a web.

The drying equipment also has a means of vapor

removal and recirculating and heat-exchange equipment

to conserve energy. Figure 16 schematically shows the

airﬂow in a convection dryer. If a coating from a solution

in an organic solvent is used, the solvent vapor must

be removed from the exhaust in order to satisfy the

environmental laws and to decrease solvent costs. Solvent

adsorption on activated carbon, incineration, or condensa-

tion in an inert-gas dryer are used. Drying equipment (see

also Figures 17 and 18) may be subdivided according to

the heat-transfer mechanism or according to web hand-

ling as listed in Table 2.

Extruded, hot-melt, and wax coatings do not require

drying and are solidiﬁed by chilling. Such coating ma-

chines require considerably less space than do the coating

lines with drying ovens.

Some coatings are applied as reactive monomers or

polymer/oligomer/monomer blends and may be cured by

either ultraviolet or electron-beam irradiation. Such irra-

diation units are incorporated into the coating line.

WEB HANDLING

Coating machines may apply the coating or the adhesive

to the packaging material supplied as a continuous web on

Supply

fan

Makeup

air

Combustion

air

Exhaust

fan

Dryer nozzle section

Heater

Figure 16. Airﬂow in a convection oven.

Figure 17. Coating line, with the extensive overhead convection

dryer system. (Courtesy of Metalvuoto Spa, Roncello, Italy.)

Figure 18. In-line infrared drying equipment (enlightened part).

Note the engraved chrome-plated roll partially covered by the

metallic pan. (Courtesy of Metalvuoto Spa, Roncello, Italy.)

COATING EQUIPMENT 293

a roll, and the ﬁnished product is rewound after comple-

tion of the operation (see Roll Handling). Unwind and

rewind stands, web-carrying equipment, and web controls

and other accessories are used (14). Controls are needed to

track the web properly on the machine and may consist of

tension-sensing devices and means of controlling the

tension and of edge-sensing devices and means of keeping

the web centered on the coating machine. Many packaging

materials are coated as sheet, requiring sheet-feeding and

sheet-handling devices. There is less of a choice between

various coating heads for sheet coating.

BIBLIOGRAPHY

1. D. Satas, Web Processing and Converting Technology and

Equipment, Van Nostrand Reinhold, New York, 1984.

2. H. L. Weiss, Coating and Laminating Machines, Converting

Technology Co., Milwaukee, WI, 1977.

3. G. L. Booth, Coating Equipment and Processes, Lockwood

Publishing, New York, 1970.

4. E. D. Cohen and E. B. Gutoff, Modern Coating and Drying

Technology, VCH Publishers, New York, 1992.

5. W. E. Brown, Plastics in Food Packaging: Properties, Design,

and Fabrication, Marcel, Dekker, New York, 1992.

6. S. E. M. Selke, J. D. Culter and R. J. Hernandez, Plastics

Packaging: Properties, Processing, Applications, and Regula-

tions, 2nd edition, Hanser Carl, Munich, 2004.

7. G. L. Robertson, Food Packaging: Principles and Practice,

Marcel, Dekker, New York, 1993.

8. A. A. Tracton, Coatings Technology Handbook, Taylor &

Francis, Boca Raton, FL, 2006.

9. R. Ryntz and P. Yaneff, Coatings of Polymers and Plastics,

Marcel, Dekker, New York, 2003.

10. M. J. Forrest, Coatings and Inks for Food Contact Materials,

Rapra Review Report, Vol. 16, No. 6, Report 186, 2007.

11. ASTM, Standard Test Method for Wetting Tension of Poly-

ethylene and Polypropylene Films, D 2578-84, Book of Stan-

dard, 08.03, Plastics, American Society for Testing and

Materials, Philadelphia, 1988.

12. T. W. Sprecher, ‘‘Testing Corona Treatments’’, Paper, Film and

Foil Converter 57(11), 114, 1983.

13. D. Satas, Handbook of Pressure Sensitive Adhesive Technol-

ogy, Van Nostrand Reinhold, New York, 1982.

14. D. R. Roisum, The Mechanics of Winding, TAPPI Press,

Atlanta, 1994.

CODE, BAR

HENRI BARTHEL

GS1 Global Ofﬁce, Brussels,

Belgium

A bar code may be deﬁned as a series of bars and spaces

arranged according to the encodation rules of a particular

speciﬁcation in order to represent data. Its purpose is to

represent information in a form that is machine-readable.

Bar codes are read by scanning devices that are pro-

grammed to analyze the structure of the bars and spaces

and transmit the encoded data in electronic format. These

data can then be stored on a ﬁle or transmitted to a

computer for processing.

Techniques other than bar codes achieve the same

objective: capturing automatically data encoded using a

particular technology. These include optical character

recognition, magnetic stripe, and radio-frequency identi-

ﬁcation. The concept of encoding and reading data auto-

matically is called automatic data capture (ADC).

BENEFITS OF BAR CODES

The main beneﬁts of bar codes are speed and accuracy.

Capturing data automatically by reading a bar code can be

done in a fraction of a second, much faster than manual

key entry. It is commonly agreed that an operator doing

key entry makes one error for every 300 characters typed.

Reading bar codes makes data capture almost error-free.

The error rate depends on the type of bar code and

equipment being used, but usually it is lower than one

error per 1,000,000 readings.

BAR-CODE SYMBOLOGIES

A bar-code symbology is a set of rules describing the way

bar and spaces have to be organized to encode data

characters.

Since the invention of the bar code concept in the

United States in the late 1950s, hundreds of bar-code

symbologies have been developed, but only a few of them

are actually being used on a large scale.

Typically, a symbology is qualiﬁed as being discrete or

continuous. In a discrete symbology, the spaces between

symbol characters do not contain information because

each character begins and ends with a bar. In a continuous

symbology, there is no intercharacter gap; that is, the ﬁnal

element of one symbol character abuts the ﬁrst element of

the next symbol character, and all the elements carry data

contiguously. The most popular bar-code symbologies are

brieﬂy described below.

Code 39 was launched in 1975. It is widely used for

industrial applications. Code 39 is a discrete, variable-

length symbology encoding the 36 numeric and uppercase

alpha characters (A–Z, 0–9) and seven special characters:

space, dollar sign ($), percent (%), plus (+), minus (–), dot

(.), and slash (/). A symbol character is composed of nine

Table 2. Drying Equipment

Heat Transfer Web Handling

Convection dryers

Parallel air ﬂow Idler-supported

Impingement air Conveyer dryers

Through dryers U-type dryers

Infrared radiation dryers Arch dryers

Near infrared (electric) Tenter frame dryers

Far infrared (electric or gas) Floater dryers

Conduction dryers

Hot roll dryers

An arch dryer including winding, coating, and laminating stations is

shown in Figure 16.

294 CODE, BAR

elements, ﬁve bars and four spaces. An element is either

wide or narrow. There are three wide elements and six

narrow elements in a symbol character. A Code 39 symbol

begins with a start character and ends with a stop

character. It can be read from the right to the left and

from the left to the right.

Interleaved two of ﬁve (abbreviated ITF) has been found

to be well adapted to the materials and printing conditions

frequently used on ﬁberboard cases. It is a continuous

symbology encoding only numeric digits. A pair of digits is

represented by ﬁve bars and ﬁve spaces. One of the pair is

represented by the dark bars and the other by the light

bars, and the dark and light bars are interleaved. Because

the digits are represented in pairs, the symbol can only

encode even number of digits. In addition to the digit

characters, there are two auxiliary characters used as

guard bars at the beginning and at the end of the digit

representation. The symbol is designed to be read bi-

directionally by ﬁxed or portable scanners.

Code 128 was introduced in 1981 in response to the

need for a compact alphanumeric code symbol that could

be used to encode complex data. The fundamental require-

ment called for a symbology capable of being printed by

existing data-processing printers. Code 128 uniquely ad-

dresses this need with the most compact, complete, alpha-

numeric linear symbology available. In addition, Code 128

has been designed with geometric features to improve

scanner reading performance and to be self-checking.

EAN/UPC was developed in the late 1960s when

researches were conducted in the United States to im-

prove the efﬁciency of checkout operations in retail

stores. EAN/UPC is a continuous symbology encoding

ﬁxed-length numeric digits. Several variants exist, known

as EAN-13, UPC-A, EAN-8, and UPC-E. In addition, the

symbology enables to encode two small symbols encoding

two and ﬁve digits. These are called add-ons because the

information they contain supplement the main symbols. A

symbol character is composed of seven modules, two bars,

and two spaces. A bar or a space is composed of one to four

modules. An EAN/UPC symbol begins and ends with a

guard pattern. In the EAN-13, UPC-A, and EAN-8 ver-

sion, a center pattern separates the symbol into segments

that can be read separately by a decoding equipment, thus

making the symbol omnidirectionally readable. The EAN/

UPC symbology is widely used to encode the identiﬁcation

number of consumer products.

The symbologies described above are all linear symbol-

ogies. The symbol is always formed of a single row of

symbol characters. Since the early 1990s, two-dimensional

symbologies have been developed. Some are qualiﬁed as

multirow symbologies consisting of two or more vertically

adjacent rows of symbol characters. Others are known as

matrix symbologies, which take the form of a two-dimen-

sional graphic that is decoded in its entirety and not row

by row. Two-dimensional symbologies can encode a large

amount of data in a small amount of space.

PDF417 is a two-dimensional, stacked bar-code sym-

bology. In PDF417, the basic data unit or minimum

segment containing interpretable data is called a code-

word. Every codeword in the symbol is the exact same

physical length, and each codeword can be divided into 17

equal modules. Within every codeword, there are four bars

and four spaces. The minimum number of modules of any

bar or space is one; the maximum is six. The PDF417

symbology deﬁnes 929 distinct codewords and supports 12

modes. Each mode speciﬁes the meaning of the codewords.

The standard modes are Extended Alpha Numeric Com-

paction Mode, Binary/ASCII Plus Mode, and Numeric

Mode. The number of data characters that can be encoded

in a PDF417 symbol depends on the mode being used. In

the extended alphanumeric compaction mode, the max-

imum number of ASCII characters per symbol is 1850. In

numeric mode, a symbol can encode a maximum of 2725

digits.

Data Matrix is a two-dimensional matrix symbology

that is made up of nominally square modules arranged

within a perimeter ﬁnder pattern. Each Data Matrix

symbol consists of data regions that contain nominally

square modules set out in a regular array. The data region,

or set of data regions and alignment patterns, is sur-

rounded by a ﬁnder pattern, and this is in turn sur-

rounded on all four sides by a quiet zone border. The

number of data characters per symbol is up to 2335

alphanumeric characters or 3116 numeric only characters.

Data Matrix Symbols are read by two-dimensional ima-

ging scanners or vision systems. Most other scanners

that are not two-dimensional imagers cannot read Data

Matrix. Data Matrix Symbols are designed for use with

applications that involve imaging scanners throughout

the supply chain.

DATA CONTENT

The purpose of bar-code applications is to capture data

automatically and to process these data in computer

applications. Rules are therefore required to specify the

way data should be encoded in a symbol. Similarly, when

reading a bar code, there must be a way to know accu-

rately what data have been captured. Three methods exist

to specify the rules of encoding and decoding data in bar-

code symbols:

1. The ﬁrst method is to establish a one-to-one relation-

ship between the symbology and the data content.

this case, a

particular symbology is exclusively

reserved to carry certain types of data. The EAN/

UPC symbology is an example of this method. EAN/

UPC bar codes always carry a number that is a

unique identiﬁer of the item on which the bar code is

afﬁxed.

2. The second method is based on conventions deﬁned

either by a party for its own applications or estab-

lished on the basis of mutual agreements between

two or more parties. The conventions describe the

symbology to be used and speciﬁc rules indicating

the way data elements are to be encoded. This

method is appropriate only in internal or closed

applications, because the rules are relevant only to

the parties agreeing to follow the convention.

3. The third method is based on the concept of data

identiﬁers, which are preﬁxes used to deﬁne data

CODE, BAR 295

ﬁelds. Each preﬁx uniquely identiﬁes the meaning

and the format of the data ﬁeld following it. Two sets

of identiﬁers have been standardized and are used

in many bar-code applications.

In the late 1980s, a body called FACT (Federation of

Automated Coding Technologies) was formed in the Uni-

ted States to examine existing standards and to produce

materials that would permit coexistence of standards

from all industries. A dictionary of FACT data identiﬁers

has been put together and was formally approved as an

American National Standard by the American National

Standards Institute (ANSI) in 1991. On December 31,

1992, the FACT organization was dissolved. Prior to its

dissolution, the Subcommittee 8 of Accredited Standards

Committee (ASC) MH10 agreed to continue the mainte-

nance of data identiﬁers. ANSI MH10 identiﬁers are

composed of one alpha character preceded by up to three

digits. These data identiﬁers usually have to be comple-

mented by industry guidelines providing additional clar-

iﬁcations regarding the deﬁnition and format of the data

ﬁelds.

Following the requirements of their membership, EAN

International and UCC jointly developed a system of

application identiﬁers, permitting the encodation of a

wide range of information. EAN International and UCC

merged into one single global organisation called GS1 in

early 2005. The GS1 system is characterized by the

management of a unique identiﬁcation scheme for pro-

ducts, services, and locations, by a clear and unambiguous

deﬁnition of data elements and by the strict recommenda-

tion of protected symbologies, offering a high level of

security.

When considering the use of data identiﬁers for their

bar-coding applications, users should consider the follow-

ing guidelines:

. Made-to-Order Products. When the products are

manufactured for and shipped to individual custo-

mers operating in a speciﬁc industry sector, the ANSI

MH10 data identiﬁer set can be suitable.

. Products for General Distribution. When products

are traded with more than one customer and possibly

with more than one industry sector, the GS1 applica-

tion identiﬁer set should be used.

APPLICATIONS

The bar-coding technology has gained wide acceptance in

numerous applications. Today, virtually all packages,

from the smallest units intended for sale to a consumer

to the biggest transport units, bear one or several bar

codes carrying their identiﬁcation number and other data

relevant to the parties shipping, carrying, or receiving

goods.

Scanning at retail point of sale is a major application

using bar-code technology. Millions of stores around the

world have implemented scanning systems relying on the

GS1 identiﬁcation number and the associated EAN/UPC

bar-code symbol. Scanning at point of sale enables us to

automatically register the sales through price-lookup ﬁles.

It also opens up the opportunity to implement a wide

range of applications such as inventory management,

automatic reordering, and sales analysis.

A rapidly growing ﬁeld of applications using bar-coding

technologies lies within the supply chains. Goods ready for

shipment by a supplier are packed, and each package is

numbered and bar-coded with a unique number. Before

the physical delivery of the merchandise, the supplier

sends an electronic message to the delivery point, advising

about the arrival of the goods. This electronic message

contains the unique identiﬁcation number of each package

and the description of its contents. When processed by the

receiver, the electronic message is matched against the

original purchase order and stored in a computer data-

base. When goods arrive, a bar-code reading device scans

the unique number identifying the goods, and the compu-

ter makes the link with the information previously stored.

The system is then able to show what has to be delivered,

and the actual delivery can be checked. Inventories can

then be updated automatically, because the information is

already available in electronic form.

PRINTING BAR CODES

Virtually any printing technology can be used to print bar

codes, provided that it is accurate enough to achieve the

right level of required quality. The printing processes fall

into two categories: commercial and on-site. The choice

between these two approaches is determined by the

nature of the information to be encoded and the number

of codes to be printed. Typically, if the information is static

(e.g., the identiﬁcation number of a product to be placed on

a package) and if the number of codes to be printed is

large, the traditional commercial method using ﬁlm mas-

ters is appropriate. If the information is variable (i.e.,

different for each item or short series of items or if the

quantity required is small), then on-site printing pro-

cesses should be used.

The commercial printing techniques use a master im-

age of the bar code on the printing plate. Film masters are

very accurate and are available on the market from

commercial companies. The printing process itself gener-

ally generates a print gain due to the ink viscosity, the

pressure of the printing plate, or the type of substrate

being printed. This print gain can be evaluated and

compensated in the ﬁlm master itself by reducing the

size of the bars. The party ordering the ﬁlm, the ﬁlm

master supplier, and the printer must work closely to-

gether to achieve a quality bar code.

The

on-site printing techniques

may use a piece of

hardware acting as graphics controller between the com-

puter and the printer. They may also use ‘‘intelligent’’

printers incorporating the controller equipment. Finally,

software is commercially available to generate the picture

of the bar code and send it to a printer. The printing

systems may be based on character-by-character impact,

on serial dot-matrix, or on linear-array technologies. The

choice of the appropriate technology depends on many

parameters linked to the application requirements.

296 CODE, BAR

READING BAR CODES

Many types of devices are commercially available to read

bar codes. They all illuminate the symbol and analyze the

resulting reﬂectance. Areas of high reﬂectance are inter-

preted as spaces, while areas of low reﬂectance do represent

bars. The reﬂected pattern of bars and space is converted to

an electric signal that is then digitized. The decoder assigns

a binary value to the signal and forms a complete message.

The message is checked by the decoder’s software and

transformed into data according to the appropriate decod-

ing algorithm relevant to the symbology being read.

Fixed-beam readers depend on external motion to read

the symbol. This can be provided by an operator moving

the reader across the symbol or by providing movement to

the symbol in front of the reader. A low-cost popular

reading device is the handheld contact scanner. It requires

an operator to move the reader smoothly over the symbol.

Moving-beam readers use a mirrored moving surface to

provide the illumination. The light source appears as a

continuous line of light. The most common moving-beam

readers in use are generally referred to as laser scanners.

Imaging devices are also used to read bar codes. They

operate similarly to a camera. The reﬂected image of the

bar code is projected onto photodiodes composed of many

photodetectors. The photodetectors are sampled by a

microprocessor and produce a video signal that is then

decoded.

The choice of a reading device is dictated by many

parameters linked to the application and to economic

criteria.

BIBLIOGRAPHY

1. GS1 General Speciﬁcations, available from GS1, avenue

Louise 326, B-1050 Brussels, Belgium.

2. C. K. Harmon, Lines of Communication, Bar Code and Data

Collection Technology for the 90s, Helmers Publishing, Dublin,

NH, 1994.

3. R. C. Palmer, The Bar Code Book, Reading, Printing and

Speciﬁcation of Bar Code Symbols, Helmers Publishing, Du-

blin, NH, 1991.

4. W. H. Erdei, Bar Codes, Design, Printing & Quality Control,

McGraw-Hill, Interamericana de Mexico, 1993.

COEXTRUSION FOR SEMIRIGID PACKAGING

This article pertains to a ﬂat, semirigid coextruded sheet,

which is a minimum of 0.010 in. (0.25 mm) thick (see

Coextrusion machinery, ﬂat). These coextruded sheet

structures are thermoformed to produce high-barrier

plastic packages (see Barrier polymers; Thermoforming).

A similar concept is used to produce high-barrier plastic

bottles, except the bottles are formed from coextruded

multilayer tubes instead of a ﬂat sheet (see Blow molding).

The production of coextrusions for semirigid packaging

was made possible by technology developed in the late

1960s and early 1970s (1, 2). Utilization of this technology

was initially limited to ‘‘simple’’ structures, such as two-

layer systems (a general-purpose polystyrene cap layer on

a high-impact polystyrene base layer) for drink cups.

Commercialization of high-barrier coextrusions occurred

in the 1970s in Europe and Japan. Large-scale commercial

barrier coextrusion applications did not surface in

the United States until the 1980s. For the purposes of

this discussion, barrier materials are deﬁned as those that

exhibit an oxygen transmission rate of less than

0.2 cm

mil/(100 in

day atm) [0.777 c

mm/(m

d kPa)]

(see Barrier polymers). Other techniques that can be used

to produce multilayer barrier structures are coating and

lamination (see Coating equipment; Laminating). Some

advantages coextrusion offers versus these other two

methods are thicker barrier layer capability, single-pass

production, barrier layer sandwiched between cap layers,

and generally lower cost. The potential markets for

packages formed from these high-barrier coextrusions

include both low- and high-acid food products sterilized

by aseptic, hot-ﬁll, or retort methods. These markets

obviously represent a signiﬁcant opportunity for barrier

coextrusions.

BARRIER MATERIALS

On the basis of the barrier deﬁnition above, only two

commercially available thermoplastic resins can be con-

sidered as barrier resin candidates for these extrusions:

ethylene–vinyl alcohol (EVOH) (see Ethylene–vinyl alco-

hol) and poly(vinylidene chloride) (PVDC) (see Vinylidene

chloride copolymers). The barrier properties of speciﬁc

grades of these two materials are listed in Table 1. The

resins identiﬁed in the table are currently the highest

barrier, commercially available, coextrudable resins of

their respective polymer classes. Other formulations of

both resin types are available offering certain property

and processing improvements at the sacriﬁce of barrier

properties.

The most signiﬁcant technical issue concerning the use

of EVOH as a barrier material is its moisture sensitivity.

The material is hygroscopic, and its barrier properties are

reduced as it absorbs moisture. The importance of this

property to the food packager is dependent on the ster-

ilization process, food type packaged, and the package

storage conditions. The most severe conditions are en-

countered during retort processing (see Canning, food).

Special consideration to coextrusion structure design and

postretorting conditions may be required to achieve the

desired oxygen barrier for packages produced from EVOH

coextrusions (3).

PVDC is not moisture sensitive and does not exhibit the

deterioration of barrier properties shown by EVOH. The

challenges associated with using heat-sensitive PVDC are

faced by the coextruded sheet producer. Equipment and

process design are critical to the production of coextru-

sions containing PVDC. Concern relating to the reuse of

scrap generated in the production of coextrusions based on

COEXTRUSION FOR SEMIRIGID PACKAGING 297