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

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7. R. F. Ellis, ‘‘Plastic Pallets Eliminate Product Damage in

Storage,’’ Modern Mater. Handling Mag. 39(8), 87 (June 8,

1984).

8. ‘‘Molded Plastic Pallets Solve Odor Transfer Problem,’’ Food

Processing Magazine, 46(3), 108 (March 1985).

PAPER

Updated by Staff

INTRODUCTION

There is no strict distinction between paper and paper-

board, particularly in view of the tremendous variation in

density possible with current technology. Generally, struc-

tures less than 0.012 in. thick (12 ‘‘points’’ or 305 mm) are

considered paper regardless of weight per unit area.

Except for the use of paper as an overwrap for folding

cartons, most packaging papers are used in ﬂexible

applications.

A large number of grades of paper and board are

available for packaging and are employed for many dif-

ferent purposes. Packaging paper grades range from

simple wrapping paper (made from mixed recovered pa-

per) to kraft paper and are predominately supplied in

rolls. They are made from virign pulps (sulﬁte/kraft pulp),

from recycled ﬁbers, or from mixtures of chemical pulp

and recycled ﬁbers. These grades are used in the produc-

tion of bags, beer mats, carrier bags, and gift wrapping

paper for example.

For the foodstuff sector, special types of paper and

board are produced which must fulﬁll the requirements

of the food laws. These papers are used in the nonfood

sector—for example, as coating papers. The possibilities of

combination with each other and with other materials,

such as plastics, are numerous. In this way, special pack-

ing materials can be produced for most packaging pur-

poses (1).

The primary intermediate product used to make paper

is wood pulp. The properties of an individual paper or

paperboard are extremely dependent on the properties of

the pulps used. Pulp preparation from deciduous (hard-

wood) or conifer (softwood) species may be done by me-

chanical, chemical, or hybrid processes (2, 3). These

hardwood or softwood pulps may be used unbleached, or

they can be bleached to varying degrees by a diversity of

techniques.

Mechanical pulps produce papers that are character-

ized by relatively high bulk, low strength, and moderate to

low cost (4). Their use in packaging is very limited.

The kraft (sulfate) pulping process, introduced about

100 years ago, dominates the chemical pulping industry:

Yields are higher, pulps are stronger, and process chemi-

cals more completely and economically recovered than

with any other process. Although the sulﬁte processes

were extremely prominent 75–125 years ago, their chemi-

cals are difﬁcult to recover, the resultant pulps are sig-

niﬁcantly weaker than those produced by the kraft

process, and they produce no unique paper properties.

Unbleached pulps are generally stronger, stiffer, and more

coarse than their bleached counterparts, but papers made

of white, comfortable ﬁbers are used in many more

applications. General treatments of pulping and bleaching

are provided in references (5–8).

The standard ream basis for packaging papers in the

United States is 500 sheets cut to a size of 24 36 in.

(61 91.5 cm) (3000 ft

or 279 m

). On this basis, packa-

ging papers normally weigh 18–90 lb/ream (8.2–40.8 kg/

ream), but some specialty applications require weights as

low as 10 lb (4.5 kg) or as high as 200 lb (90.7 kg)/ream. At

any given basis weight, density may typically be 0.08–

0.16 lb/in.

(2.2–4.4 g/cm

), providing a very wide range of

thickness and strength properties.

The two most general classiﬁcations of packaging

papers are coarse and ﬁne. Coarse (kraft) packaging

papers are almost always made of unbleached kraft soft-

wood pulps. Fine papers, generally made of bleached pulp,

are typically used in applications demanding printing,

writing, and special functional properties such as barriers

to liquid and/or gaseous penetrates.

KRAFT PAPERS

In order to meet the high strength requirements, kraft

papers consist of primary or a mixture of primary and

secondary ﬁbers of kraft pulp. They are used mainly for

packaging purposes.

Kraft papers, produced by the kraft process, derive

their name from the German word for ‘‘strong.’’ Kraft

paper is made from at least 80% sulfate wood pulp. It is

typically a coarse paper with exceptional strength. Some-

times made with a rough ﬁnish to keep bags from sliding

off piles, these papers are often made on a fourdrinier

machine and then either machine-ﬁnished with a calen-

dar stack or machine-glazed by using a Yankee dryer

(5, 6). The surface of these papers is acceptable for printing

by letterpress, ﬂexography, and offset processes (see Print-

ing). In addition to wrapping applications, kraft papers are

used for multiwall bags and shipping sacks (see Bags,

multiwall), grocers’ sacks, envelopes, gummed sealing

tape (see Tape, gummed), butcher wraps, freezer wraps,

tire wraps, and specialty bags and wrappings that require

economy and strength. Paper for grocery bags and fast food

bags must have a high resistance to tearing. The ﬁber of

choice is softwood kraft, which may be bleached or

unbleached (9). Many papers formerly manufactured

from sulﬁte pulps, especially those of tissue weight, are

now manufactured with kraft pulps. Unbleached ‘‘sulﬁte’’

papers are used for products such as oil cans (intermediate

liner) and single-service food packages.

Extensible kraft papers have satisﬁed a special niche in

the packaging industry. Although creped papers have long

served both decorative and functional roles, other papers

capable of absorbing energy at sudden rates of strain have

908 PAPER

become increasingly important in uses such as shipping

sacks. Conventional creping is performed either at the wet

press section of a paper machine (wet crepe) or on a

Yankee dryer (dry crepe). Dry creping is most commonly

used to generate qualities such as softness and absor-

bency; wet creping is a technique for making tough,

ﬂexible papers capable of absorbing tensile energy. A

secondary creping operation rewets a dry sheet, and it

may be done in-line on the paper machine or as an

independent manufacturing process. Whereas a standard

kraft paper might have a stretch (before breaking) of

3–6%, creped papers generally may be stretched

35–200% of their original length before breaking. Manu-

facturers of creped, extensible, and other coarse (kraft)

papers may be found in reference (10).

BLEACHED PAPER

Packaging applications that place a higher priority on

printing, writing, and special functional properties than

on economy and strength generally utilize bleached pa-

pers. The pulps used to manufacture bleached papers are

relatively white, bright, and soft, and they are also

receptive to special chemicals necessary to develop many

functional properties. Although generically not as strong

as unbleached kraft papers, bleached papers can be man-

ufactured to meet simultaneous requirements of both

strength and printability. Their whiteness enhances print

quality and generates a perception of cleanliness and

quality. The aesthetic appeal of bleached packaging pa-

pers may be augmented by clay coating one side (C1S) or

both sides (C2S). The increasing demand for a combina-

tion of functional performance and top-quality graphics

favors the C1S manufacturer who can satisfy the variety

of challenges of this market.

VEGETABLE PARCHMENT

Vegetable parchment is a highly waterproof, greaseproof,

boilproof paper of high purity. It is used in the packaging

of fats in combination with aluminum foil or a plastic

coating. Silicon-coated parchment paper has a wide range

of applications—for example, in antiadhesive papers (1).

The process for producing parchment paper was devel-

oped in the 1850s, making it one of the grandfathers of

special packaging papers. By soaking an absorbent paper

in concentrated sulfuric acid, the cellulosic ﬁbers are

swollen tremendously and partially dissolved. In this state

the plasticized ﬁbers close their pores, ﬁll in voids in the

ﬁber network, and thus produce intimate contact for

extensive hydrogen bonding. Rinsing with water causes

reprecipitation and network consolidation, resulting in a

paper that is stronger wet than dry, lint-free, odor-free,

taste-free, and resistant to grease and oils. By combining

parchment’s natural tensile toughness with extensibility

imparted by wet creping, paper with great shock-absorb-

ing capability can be produced. Special ﬁnishing processes

provide qualities ranging from rough to smooth, brittle to

soft, and sticky to releasable. Parchment was ﬁrst used for

wrapping fatty substances like butter; but this versatile

paper is now also used whenever food is prepared, frozen,

packaged, or displayed, as well as when tough, lint-free,

chemically pure surfaces are needed for special packages.

GREASEPROOF AND GLASSINE

Because cellulose is hydrophilic, it is a good substrate to

use for resisting penetration of hydrophobic liquids. As

noted above, vegetable parchment performs well as a

greaseproof paper because it is essentially pore-free and

composed of a hydrophilic material. ‘‘Greaseproof’’ paper

is a substrate manufactured to also have an essentially

pore-free consolidation; but mechanical reﬁning (‘‘bufﬁng’’

or cutting) is used in its production instead of swelling

with concentrated sulfuric acid. Reﬁning ﬁbrillates,

breaks, and swells the cellulose ﬁbers to permit consolida-

tion of a web with many interstitial spaces ﬁlled in.

Glassine paper is produced by further treating ‘‘grease-

proof’’ paper with a supercalendar operation. The super-

calendar step involves moist high temperatures (steam),

pressure (several hundred pounds per lineal inch or

B100 kg/cm), and differential hardness (one roll typically

cotton or soft rubber, the other roll hard rubber or metal)

to polish the surface. Supercalendering a greaseproof

paper generates such intimate interﬁber hydrogen bond-

ing that the refractive index of the glassine paper ap-

proaches the 1.02 value of amorphous cellulose. This

indicates that very few pores or other ﬁber–air interfaces

exist for scattering light or allowing liquid penetration.

High transparency is achieved by intensive supercalen-

dering. The paper is frequently colored. This paper is

used, for example, for wrapping chocolates or for packing

high-quality preserves.

Greaseproof and glassine papers are frequently plasti-

cized to further increase their toughness. They have a

reputation of running well on high-speed packaging lines,

and they have served well for odor and aroma barriers.

Like other ﬂexible-packaging papers, they can be chemi-

cally modiﬁed to enhance functional properties (e.g., wet

strength, adhesion, release). When waxed, they are stan-

dard materials for primary food pouches used to package

dry cereals, potato chips, dehydrated soups, cake and

frosting mixes, bakery goods, candy and ice cream confec-

tions, coffee, sugar, pet food, and so on. In addition to their

protective functions, these papers heat-seal easily when

waxed and reclose well. Greaseproof paper is neither

waterproof nor boilproof.

WATER-, GREASE-, AND OIL-RESISTANT PAPERS

The distinction between greaseproof papers and grease-

resistant papers is a fairly subtle one, involving an under-

standing of the methods of penetration of liquids into

surfaces. Because the primary mechanisms involve capil-

lary penetration and/or wetting, it is appropriate to con-

sider the severity of the packaging requirement. The

requirement

may be for

minimal staining by grease, oil,

or water under negligible pressure; or it may be for

PAPER 909

absolute resistance to any penetration of the liquid over

long periods of time and/or under substantial pressure;

or it may lie between these extremes. Parchment, glassine,

and greaseproof papers offer decreasing protection from

grease and oil at the more restrictive end of the spectrum.

As noted above, their resistance is generated by the lack

of capillaries and the oleophobic nature of cellulose.

Greaseproof paper can be made resistant to grease pri-

marily by a beating process and by the addition of

auxiliary agents (1).

A consideration in designing primary packages is the

economics of using the various barriers available for the

job. A bag for a single-service consumable (e.g., French-

fried potatoes) may require resistance to staining for

only several minutes. A lubricating oil package, on the

other hand, may require a stain-free barrier for several

months. Imparting sufﬁcient resistance to liquid penetra-

tion to meet the requirements of the less demanding

applications can be done very economically with chemical

treatments. If grease and/or oil penetration is the only

concern, moderate resistance (package life of minutes

to days) can be developed using waxes (see Waxes) and

other low-surface-energy materials such as ﬂuorocarbons.

Fluorocarbon technology in papermaking has expanded

from multiwall and consumer bags to labels, coupons, and

carryout food packaging, perishable bakery goods packa-

ging, candy and confection packages, and form-and-ﬁll

packages where edge wicking may be an important

consideration.

In many applications (e.g., carryout food packaging),

resistance to both water and oils must be developed for

adequate performance. The use of rosin-based chemicals

for developing water repellency in paper requires the use

of alum (Al

(SO

)

) or other multivalent cations that

destroy the grease-resisting properties of ﬂuorocarbons.

The simultaneous development of both water and oil

resistance requires (a) the use of oleophobic chemicals

that react with hydroxyl and carboxyl groups on the

cellulose ﬁbers and (b) the use of hydrophobic chemicals

such as ﬂuorocarbons, which have also been modiﬁed

to react with the same cellulose functional groups. Typical

oleopholic chemicals currently in widespread use are

alkylsuccinic anhydrides and alkylketene dimers. The

most successful economic choices are made through

close consultation between the paper manufacturer and

the user, which allows the careful selection of designs for

meeting speciﬁc performance requirements. Grease- and

oil-resistant papers can be made to run well in most any

converting and printing processes.

WAXED PAPERS

Waxed papers are age-old papers that have served the

packaging industry well in applications requiring direct

contact with food for barrier against penetration of liquids

and vapors, as well as heat sealability, lamination, and

even printing. Waxing can be performed in-line with the

paper-manufacturing process, in-line with printing, con-

verting or lamination processes, or as a discrete process. A

great many base papers are suitable for waxing processes,

including (a) greaseproof and glassine papers and (b)

water-resistant papers. Supercalendered base paper is

designed for waxing and frequently contains titanium

dioxidea as ﬁller. This type of paper is used for wrapping

candy. There are two fundamentally different waxing

processes, generating different characteristics for the

ﬁnished sheet (see Waxes). Wet waxing is an operation

in which the wax coating is applied to the surface of the

sheet. Surface wax is desirable for heat sealing and

lamination and is essential for vapor-barrier development.

Dry waxing is performed to absorb wax into the sheet,

leaving a surface that often does not look or feel waxy.

Penetration of wax allows additional surface treatments

for special release applications, or for further lamination.

Absence of the continuous ﬁlm of wax on the surface

characteristic of wet waxed paper also allows the dry

waxed paper to ‘‘breathe’’ moisture, carbon dioxide, and

oxygen.

Waxed papers provide an economical choice for pri-

mary food packaging not only because of their versatility

but also because of their safety as tasteless, odorless,

nontoxic, and relatively inert materials. Their widespread

use in conventional packaging applications includes: de-

licatessen pickup sheets; box liners; cover, scale, and

utility sheets; patty papers; sandwich wraps; and bags,

laminations to other papers and paperboard for food

trays, locker papers, carryout cartons, food pails, baking

cups, folding cartons, cereal liners, and folding carton

overwrap.

SPECIALTY-TREATED PAPERS

Many packaging applications require barrier to sub-

stances other than water, grease, or oil. Most food-packa-

ging applications are well-served with water- and/or oil-

penetration resistance, but a number of products require

more elaborate barriers. Meat-wrapping paper demands

exceptional strength; resistance to grease, moisture, and

blood; easy release with no residual taste or odor; plus

‘‘bloom’’ retention. Freezer paper must remain pliable at

low temperatures and must offer puncture resistance,

moisture-vapor barrier, exceptional seal integrity, and

easy release from frozen or thawed meats. Other products

such as chemicals, drugs, cosmetics, personal-care items,

and industrial products require package functions such as

acid resistance, alkali resistance, alkali solubility, mold

resistance, ﬂame retardation, solvent resistance, organic

polymer adsorption/absorption resistance or afﬁnity, ad-

hesion, release, tarnish or rust inhibition, heat stability,

sterilizability, speciﬁc-ion adsorption, conductivity, resis-

tivity, stiffness, or ﬂexibility. Photographic protective

wrapping paper is a black-dyed chemically neurtral paper

that can be folded without breaking and is suitable for

wrapping photographic ﬁlm. To address the general man-

ufacturing techniques or even the functional property

classiﬁcation of such a variety is beyond the scope of this

publication. Reference (11) provides a general treatment

of some of these products that have transcended proprie-

tary technology.

910 PAPER

WET-STRENGTH PAPERS

Conventional papers are not strong when wet. The most

predominant fraction of paper’s strength is the result of

hydrogen bonding between hydroxyl and carboxyl groups

of adjacent ﬁbers. The removal of water during the

papermaking process generates these bonds, and the

process is reversible. The two strategies for manufactur-

ing strong-when-wet papers are (a) keep the water out of

the paper and (b) introduce additional chemical bonds

between ﬁbers which are not inﬂuenced by the introduc-

tion of water.

As mentioned above, paper that has been parchmen-

tized is actually stronger wet than dry, principally

because of the loss of individual ﬁber identity during the

gelatinized stage of the process. Through advances in

chemical technology, several more economical alternatives

exist for generating wet-strength papers. In general,

the chemicals used to augment the natural hydrogen

bonding are crosslinked during the manufacturing

process. Common chemicals for producing wet-strength

papers include protein, urea, melamine, resorcinol,

and other phenolic or amino resins crosslinked with

formaldehyde, and condensation products of polyalkylene

polyamines with dicarboxylic acids crosslinked with epi-

chlorohydrin (12).

The conventional tests of wet-strength papers are for

tensile, tear, and burst strength, because these are the

most useful indicators of use requirements. The degree of

wet strength is expressed as a percentage of original dry

strength, and is referred to as the percent of strength

retention. The typical range for sack or pouch papers is

15–30%. Wet strength may also be generated in a variety

of permanence levels, so that the product will either

remain tough-when-wet, or eventually disintegrate with

soaking time or application of force.

ABSORBENT PAPERS

Papers designed for absorption of speciﬁc ﬂuids are an

important part of the packaging industry. Although they

are a member of the class of ‘‘specialty-treated papers,’’

they are distinctive enough to warrant separate discus-

sion. Typically at the low end of the strength spectrum,

absorbent papers must not only be exceptionally porous,

they must also have surface modiﬁcations to render

afﬁnity to the target liquid. When that liquid is aqueous,

they must generally also have a deﬁnitive level of wet

strength. Providing the special afﬁnity to a given liquid is

often a proprietary technology involving chemicals that

are substantive to cellulose and to the target liquid. This

special class of papers currently services industries ran-

ging from fresh-food packaging to industrial-products

packaging.

TISSUE PAPERS

Tissues form a special group of ﬁne packaging papers

because of their versatile performance. Tissue is made of

either virgin or recycled ﬁber. Always fairly thin, tissues

range from semitransparent to totally opaque. They can

be waxed or treated with any of the specialty treatments

(e.g., edible oils, for fruit wrapping, antitarnish metal

protection), or they can be used ‘‘as is’’ for applications

ranging from intermediate lamination steps in composite-

container construction (see Cans, composite) to gift wrap-

ping. They may be made exceptionally weak for softness,

or surprisingly tough in all directions. Tissue papers are

generally either machine-ﬁnished (MF) or machine-glazed

(MG). Machine ﬁnishing involves calendering between

rolls that are usually constructed of highly polished steel

that are hydraulically loaded to squeeze and polish both

sides of the paper to similar levels of smoothness. Machine

glazing of papers produces a smooth glazed side and a

rough back side. The special ﬁnish is the result of drying

the paper with 60–70% moisture on a Yankee dryer

[diameter 6–18 ft (1.8–5.5 m)] with a mirrorlike surface.

This glazing process produces a very smooth surface for

printing, adhesion, release, or wet waxing. A physical

fusion takes place with the surface ﬁbers, producing a

physical barrier similar to a cast ﬁlm. MG papers may

also be machine-ﬁnished to improve the smoothness

on both sides or to produce intermediate rolls which

process better through subsequent converting steps. A

great many applications for tissue paper today utilize

special treatments for adhesion or release in an inter-

mediate package-manufacturing process where the pa-

per’s light weight and thinness make it an economical

carrier for more costly substances (see Multilayer-ﬂexible

packaging).

COATED PAPERS

Coated papers is a term generally reserved for papers

acting as a base for aqueous mixtures of clay and/or

other mineral pigments with natural and/or synthetic

polymers as pigment binders. The term does not typically

refer to papers that have been extrusion- or solvent-coated

with organics or plastics, or surface-treated with specialty

treatments listed above for functional improvements.

Aqueous coatings of paper are performed primarily for

market appeal where graphics are important. Coated

papers are consumed not only for labels and multiwall

bags, but also for lamination or combination with other

functional materials in composite structures. Coated pa-

pers are often coated on one side. Coated papers can be

designed for printing by any process from letterpress

to ink jet (see Code marking and imprinting). They

can also be painted, bronzed, and punched. They are

waterpoof and alkali-resistant to prevent the detachment

of labels in washing machines. They are used, for example,

as wrapping paper for chocolates, cigarettes, and soap.

Coated packaging papers are bleached kraft papers

having a one-sided matt or glossy coat and are suited for

the production of bags and carrier bags. Packaging lami-

nates based on cardboard and paper have been reported

(13, 14). The most-valued grades are typically produced

in discrete manufacturing processes that vary widely

(5,

6, 8). Detail

of coating technology state of the art are

PAPER 911

contained in annual TAPPI Coating Conference Proceed-

ings (15).

NONWOVENS

Nonwovens are materials used as cloth substitutes, made

entirely or partially from cellulosic ﬁbers. As an industry,

nonwovens is dynamic and growing in medical, health-

care, industrial, food-processing, and consumer- and

household-products areas. Differentiated from classical

paper, which is formed in water and consolidated with

interﬁber hydrogen bonds, nonwoven-manufacturing

technologies include resin and thermally bonded carded

web process, melt-blown process, and an air-laid process

(16) (see Nonwovens).

BIBLIOGRAPHY

M. Sikora, ‘‘Paper’’ in The Wiley Encyclopedia of Packaging

Technology, 1st edition, James River Corporation, Speciality

Packaging Papers Group, pp. 497–500; in 2nd edition, pp. 714–

717.

Cited Publications

1. O. Tillma, in H. Holik, ed., Handbook of Paper and Board,

Wiley-VCH. Weinheim, 2006, Chapter 11.

2. S. A. Rydholm, Pulping Processes, Wiley-Interscience, New

York, 1965.

3. M. G. Halpern, ed., Pulp Mill Processes, Developments Since

1977, Noyes Data Corp., Park Ridge, NJ, 1981.

4. D. R. Allen, ed., Uncoated Groundwood Papers, Miller Free-

man Publications, San Francisco, CA, 1984.

5. J. P. Casey, ed., Pulp and Paper Chemistry and Tech-

nology, 3rd edition, Vols. I–IV, Wiley-Interscience, New York,

1980.

6. R. G. MacDonald, ed., Pulp and Paper Manufacture, 2nd

edition, Vols. I–III, McGraw-Hill, New York, 1969.

7. Pulp Technology and Treatment for Paper, Miller Freeman

Publications, Inc, San Francisco, CA, 1979.

8. M. J. Kocurek and C. F. B. Stevens, eds., Pulp and Paper

Manufacture, 3rd edition, Joint Textbook Committee of The

Paper Industry, Atlanta, GA, 1984.

9. M. A. Hubble, ‘‘Paper,’’ in Kirk-Othmer Encyclopedia of Che-

mical Technology, Vol. 18, 5th edition, Wiley Interscience,

Hoboken, NJ, 2006.

10. Walden’s ABC Guide, www.pulpandpaper.net.

11. R. H. Mosher and D. S. Davis, Industrial & Specialty

Papers, Vols. 1–4, Chemical Publishing Co., 1970–1974,

1969–1973, Vol. 1 (Technology), 1968, Vol. 2 (Manufacture),

1968; Vol. 3 (Applications), 1969; Vol. 4 (Product Develop-

ment), 1970.

12. G. A. Keim, U.S. Patent No. 2,926,154, (to Hercules Powder

Company) February 23, 1960.

13. K. Magnusson, U.S. Patent Application 20050260366, Novem-

ber 24, 2005.

14. P. Frisk, K. Ono, and H. Agita, U.S. Patent No. 7, 201,971,

April 10, 2007.

15. A. F. Turbak, Introduction to Nonwovens, TAPPI, Atlanta,

GA, 1998.

16. Proceedings of PLACE: Polymers, Laminates, Adhesives,

Coatings, and Extrusions Conference, annual publication of

TAPPI Press, Atlanta, GA.

General References

B. Wirtzfeld, ed., The Paper Yearbook, Harcourt Brace Jovanovich,

New York, comprehensive listing of typical uses.

The Competitive Grade Finder, 18th edition, Grade Finders Inc.,

Bala-Cynwyd, PA, 1984.

J. Hube, ed., Kline Guide to the Paper Industry, 4th edition, C. H.

Kline, Fairﬁeld, NJ, 1980.

API annual Statistics of Paper and Paperboard for relative

shipment and sales volume.

The Dictionary of Paper, 4th edition, American Paper Institute,

Inc., New York.

B. Toale, The Art of Papermaking, Davis Publications, Worcester,

MA, 1986; concise but fairly comprehensive treatment of

historical techniques for making contemporary decorative

papers

I. P.

Leif, An International Sourcebook of Paper History, Archer

Dawson, Hamden, CT, 1978.

H. F. Rance, ed., Handbook of Paper Science, Elsevier Scientiﬁc

Publishing; New York, 1982, Vol. 1, Raw Materials and

Processing, Vol. 2, Structure and Properties.

R. P. Singh, ed., The Bleaching of Pulp, 3rd edition, TAPPI Press,

Atlanta, 1979.

G. R. Hutton, ed., Phillips Paper Trade Directory-Mills

of the World, Derek G. Muggleton Publishers, Kent, UK,

1985.

PAPER, SYNTHETIC

TAMERICA PRODUCTS

Chino, California

Updated by Staff

INTRODUCTION

Synthetic plastic paper is a calendered plastic sheet that is

a unique mixture of clay (calcium carbonate) and poly-

propylene resin. This formulation makes it feel, look,

print, and fabricate like paper, but with the durability

and tear resistance of plastic. White opaque with a ﬁne

matte ﬁnish, it is a single-layered substrate that offers

superior ink adhesion and has excellent bonding charac-

teristics. It is easily printable (no pretreatment). Hop-Syn

G2 synthetic paper is designed for printing high-quality

heavy-gauge polypropylene and designated for packaging

applications. Hop Industries, the maker of the Hop-Syn

line, has reported an increase in sales of its products from

its initial sales in 1997 of $22.9  10

to $45.2  10

2006 (1).

912 PAPER, SYNTHETIC

PROPERTIES

Temperature, Abrasion, Moisture, and Tear Resistance

Synthetic paper is dimensionally stable and can withstand

temperatures ranging from 601F to +2001F. Under any of

the above conditions, it is resistant to cracking, abrasion,

shrinking, or any distortion in color or sheet size. It is

scuff-resistant and weather-resistant and has high opa-

city for two-sided printing.

It is 100% waterproof and will not be affected by

moisture or humidity and offers superior tear resistance

over paper.

Printability

Hop-Syn brand synthetic paper (trademark of HIC Indus-

tries Corporation, formerly Tamerica) is formulated with

antistatic agents and offers a porous printing surface

good layﬂat and a very close gauge tolerance suitable for

high-speed printing. Its antistatic surface eliminates dou-

ble-fed sheets when printing, folding, and stacking. Sui-

table commerical printing methods include ﬂexography,

rotary gravure, offset lithography, thermal transfer, ro-

tary letterpress, and screen (1).

Its porous surface allows ink to be absorbed under-

neath its surface, preventing the printed image from being

damaged by scufﬁng or scratching; this makes it easily

washable with a damp cloth when removing stains such as

grease, oil, foods, soft drinks, soaps, and/or detergents.

USES

Since synthetic paper is manufactured in a variety of

gauge thicknesses from 0.0031 to 0.020 in both sheet

and roll form, it has many new uses. Popular applications

include displays, boxes, tags, labels, maps, charts, li-

censes, credit cards, menus, posters, signs, banners, ca-

lenders, greeting cards, and shopping bags. However, this

is only a small sample of applications.

ENVIRONMENTAL CONSIDERATIONS

Synthetic paper (in this case Hop-Syn) is made from

polypropylene resin and clay (calcium carbonate). These

are nontoxic materials that contain no chlorine or other

halogens, producing neither dioxins, hydrochloric acids, or

other highly toxic materials. It recycles as a plastic, does

not drip when burned, emits no toxic fumes, and leaves a

clean ash when incinerated and can be easily recycled in

the manufacturing process.

BIBLIOGRAPHY

Tamerica Products, ‘‘Paper, Synthetic,’’ in The Wiley Encyclopedia

of Packaging, 2nd edition, John Wiley & Sons, New York, 1997,

p. 722.

Cited Publications

1. ‘‘Quality, Dedication, Integrity,’’ Hop Industries Corp., Lynd-

hurst, NJ, www.hopindustries.com, accessed July 2008.

PAPERBOARD

B. W. ATTWOOD

St. Annes Paper and

Paperboard Developments Ltd.

Updated by Staff

INTRODUCTION

Paperboard, often called simply ‘‘board,’’ is one of the major

raw materials used in packaging. The term includes box-

board, chipboard, containerboard, and solid ﬁber. Its appli-

cation covers a wide range of uses from simple cartons

(see Cartons, folding) to complex containers used for

liquids. It can also be converted into drums for bulk

packaging of chemicals or combined with other materials

to produce containers large and strong enough for the

protection of large, heavy, and often fragile items during

transport. In addition to product-protection requirements,

paperboard must often have at least one smooth surface

capable of accepting high-quality print (see Printing).

Paperboard is widely used because it meets the following

criteria for successful packaging, namely to: contain the

product; protect goods from mechanical damage; preserve

products from deterioration; inform the consumer; and

provide visual impact through graphical and structural

design (1).

TERMINOLOGY

‘‘Paper’’ is the general term for a wide range of matted or

felted webs of vegetable ﬁber (mostly wood) that have been

formed on a screen from a water suspension. The general

term can be subdivided into paper (see Paper) and paper-

board. There is no rigid line of demarcation between paper

and board, and board is often deﬁned as a stiff and thick

paper. ISO standards state that paper with a basis weight

(grammage) generally above 250 g/m

(B51 lb/1000 ft

)

shall be known as paperboard, or ‘‘board.’’ The deﬁnition

becomes less clear because in some parts of the world,

board is classed as such when its caliper (thickness)

exceeds 300 mm(B12 mil) [in the United Kingdom, 250 mm

(B10 mil)]. There are exceptions to the above: Blotting

papers and drawing papers thicker than 300 mmare

classiﬁed as paper; and corrugating medium, linerboard,

and chipboard less than 300 mm are classiﬁed as

paperboard.

It is also not possible to strictly deﬁne paperboard by its

structure or by the type of machine used to produce it. For

example, paperboard can have either a single- or multi-ply

structure and can be formed on a fourdrinier-wire part, a

PAPERBOARD 913

single or a series of cylinder molds, or a series of modern

formers, or sometimes by means of a combination of one or

more of the above (see diagrams and related text). For a

small part of the market, paperboard is produced by

laminating sheets of paper together. In that case, the

product is solid ﬁber (see Boxes, solid ﬁber).

The following terms are in general use in paperboard

manufacturing and associated converting industries:

Basis Weight. This is the weight of a known area—for

example, g/m

(grammage) or (lb/1000 ft

), the

weight in pounds of a ream (usually 500 sheets) of

paperboard cut to its ‘‘basic size.’’

Caliper (Thickness). The thickness of the sheet ex-

pressed in micrometers (mm), or thousandths of an

inch (mil or points) (mil = 25.4 mm).

Size of a Sheet. The width and length of a sheet of

paperboard. The width, always expressed ﬁrst, is

the dimension cut at right angles to the direction of

the sheet. Length is the dimension cut in the ma-

chine direction. For example, 20  30 in. means 20

in. (50.8 cm) cut across the machine by 30 in.

(76.2 cm) cut in the direction of the machine. The

ﬁrst dimension is often termed the cross-direction

and the second dimension the machine direction.

Structure. The composition of the web (see Figure 1).

Ply. A ﬁbrous layer of homogeneous composition.

Topside. The side of the web opposite to the wire side

is the normal paper deﬁnition for this term. In the

case of paperboard, topside can also mean liner side,

generally the better-quality face of the web. Some

grades of paperboard are known as double-lined, in

which case the two faces of the web are both of high

quality.

Liner. A ply of good-quality ﬁber (usually white), on

the topside.

Underliner. The layer (ply) of ﬁber between the ex-

ternal layer (topside/liner) and the middle.

Middle. The layer (ply) of ﬁber between the two

external layers or between the underliner and an

external layer.

Backs. The outside layer (ply) of ﬁber directly oppo-

site to the liner layer.

Duplex (or Biplex). This is a board consisting essen-

tially of two layers of different furnish.

Triplex. This is a board consisting essentially of three

different furnish layers (external furnish layers may

have the same composition).

Multiplex. This is a board with more than three

furnish layers. Two or more of the layers can have

the same composition. Also known as a multilayer

board.

Furnish. The constitution of the various materials

that are blended in the stock suspension from which

the paperboard plies are made. The main constitu-

ents are the ﬁbrous material (pulp or secondary

ﬁber), sizing agent, ﬁllers, and dyes.

STRUCTURE AND PROPERTIES

The structure of a typical multiply paperboard (see Figure 1)

consists mainly of cellulose ﬁbers. The most common source

is mechanical and chemical pulps derived from wood. Sec-

ondary ﬁbers are used widely in the cheaper grades. Other

sources of cellulose ﬁber are occasionally used such as straw

and esparto.

Examination of the structure shows that it consists of a

compact network of the ﬁbers bonded together by mechan-

ical entanglement and chemical links. This structure can

be a thick single homogeneous ply or, as is more often the

case, of two to eight thinner plies. The multiply construc-

tion allows different types of ﬁbers to be used for the

different plies. Improved ﬁber economy is achieved by

selected distribution of the ﬁber types through the web

(e.g., by using cheaper ﬁbers for the inner layers). Im-

proved characteristics are obtained by using the correct

selection of ﬁber for the individual layers (e.g., stronger

ﬁbers for the outer plies). A typical example of a multi-ply

construction is a type of paperboard known as whitelined

chip. The top ply (liner) is made of bleached chemical wood

pulp, which provides surface strength, good appearance,

and printing properties. For the other plies, secondary

ﬁber is used.

It is of extreme importance that the individual plies of

multilayer paperboard are bonded together. If the bonding

is poor, the structure can break up, with resultant dete-

rioration in strength during subsequent processing and

use. The level of bonding achieved, which must meet

certain requirements, is dependent on having the right

balance of mechanical entanglement and chemical bond-

ing. If, for example, a paperboard sheet is subjected to

continuous folding (e.g., the hinged lid of a cigarette

carton) and the bonding level is too high, cracking at the

hinge will occur.

PHYSICAL CHARACTERISTICS

Mechanical Properties

Because paperboard has the same type of ﬁbrous structure

as paper, the strength-to-weight relationship is of the

same order as that for paper. Because of its extra thick-

ness and the bonding between the plies, it normally has

considerably greater ﬂexural rigidity (stiffness). The

choice of furnish for the individual plies inﬂuences the

Figure 1. Structure of a typical multi-ply paper-

board.

914 PAPERBOARD

stiffness characteristics: Increased stiffness is obtained by

increasing the strength of the outer plies by using a

stronger pulp. During the converting of paperboard, it is

often necessary to fold the sheet, and because of the

thickness of the paperboard, large internal forces are

generated. These can cause structural damage to the

outer layers (cracking). In order to carry out the folding

operation with minimum damage to the outer layers, the

ply bonding is broken down locally by a creasing operation

before the paperboard is folded. A paperboard sheet has

grain characteristics similar to those of paper, with the

sheet being strongest in the machine direction.

Optical Properties

Paperboard is normally opaque by virtue of its thickness,

and only the color (whiteness, etc.) and occasionally the

gloss of its outside plies are important. For a multi-ply

paperboard with a white liner on darker underplies (e.g.,

when wastepaper is used), liner-ply opacity is important

in order to maintain the white appearance of the liner

surface. If a dark waste paper is used, an underply

(underliner), consisting either of a lighter colored waste

paper or a mechanical pulp furnish, is applied. This

reduces the showthrough of the dark waste layer and

improves the whiteness of the liner surface.

Absorptive Properties

The surface of paperboard is often required to have

characteristics suitable for printing. To obtain these char-

acteristics the surface layers are sized in ways similar to

those used for paper. Paperboard, however, must often be

glued during the manufacture of cartons, and for this the

surfaces must be absorbent. In a typical case, the back

surface has higher absorption characteristics than the

liner ply, thus allowing the back ply to absorb some

moisture during the gluing operation. Like paper, paper-

board changes dimensions if it absorbs moisture. The

degree of change depends on many factors such as type

of ﬁber, condition of ﬁber, and structure of the ﬁbrous

network. This effect of dimensional change with change of

moisture content presents many problems during convert-

ing operations such as printing. For example, in lithogra-

phy and laminating (see Laminating), serious dimensional

change can cause print misregister or curling of the

paperboard web.

PAPERBOARD MANUFACTURE

The methods of ﬁber treatment (beating, reﬁning, clean-

ing, etc.) are essentially the same as those used in

manufacturing paper grades. After the sheet has been

formed, the methods used for removing excess water and

ﬁnishing the web (pressing, drying, calendering, etc.) are

also essentially the same as those in the manufacture of

paper. The main difference is found at the forming section

of the machine, where the web is formed.

Sources of Fiber

The choice is between virgin, or primary, ﬁber derived

from logs of wood, and recovered, or secondary ﬁber

derived from waste paper and paperboard. About 55% of

ﬁber used is virgin ﬁber and the remainder is from

recovered ﬁber. It must be noted that ﬁbers from all

sources are not universally interchangeable with respect

to the paperboard products that can be made from them.

Some ﬁbers are not not recoverable and some that are

recovered are not suitable for recycling. Fiber cannot e

recyled indeﬁnitely.

Forming Methods

The following are the main forming methods used in the

manufacture of paperboard:

. Single-ply paperboard: mainly Fourdrinier.

. Multi-ply paperboard:

1. Fourdrinier with secondary head boxes.

2. Rotary formers (multiples and using multilayer

formers).

3. Twin wire formers (multiples and using multi-

layer ﬂow boxes).

4. Combination of the above.

Fourdrinier Machine

The forming section of a Fourdrinier machine is made up

of two essential parts: the ﬂow box and the drainage table.

The operation of both parts can inﬂuence the structure of

the resulting paperboard web. It is normally the aim to

deliver the ﬁber suspension, well-dispersed, to the moving

screen at approximately the same velocity as the screen.

The concentration going to the screen for paperboard

generally ranges within 0.4–1.2%, depending on the fur-

nish and product requirements (Figure 2).

On early machines and some still used today, prelimin-

ary dewatering takes place at the table rolls. The action of

each table roll can be considered as a pump, with drainage

being induced by the suction on the downstream side of

each table roll, so that the drainage ﬂow is intermittent. A

positive-pressure pulse exists on the upstream side of each

table roll, so water is forced up through the screen and the

deposited mat. This mechanism has considerable inﬂu-

ence on web structure. The magnitude of the positive and

negative pulses depends on table roll diameter and screen

speed.

Modern practice is to replace the table rolls by sta-

tionary foils. These units generate less intense suction

pulses than table rolls, and the length of the drainage zone

can be considerably extended. These foils are often closely

spaced along the Fourdrinier forming table so that there is

a gain in available drainage. Further down the Four-

drinier table, when concentration is 3–4%, suction ﬂat

boxes are used to continue the drainage at a rate con-

trolled by the level of vacuum in the box. It should be

noted that ﬂat vacuum boxes can be used at the initial

drainage

zone, and today

a unit is often used that in effect

is a combination of foil sections in a vacuum enclosure

PAPERBOARD 915

(wet-suction box). When producing heavyweight papers

and boards, because drainage is more difﬁcult, it is usual

to use additional vacuum boxes. This can lead to excessive

drag on the screen, resulting in higher power require-

ments and excessive wear of suction box tops and screen,

and may even lead to screen stalling. For the production of

multi-ply paperboard, such as linerboard, a secondary

ﬂow box is often used. A base ply is formed ﬁrst and after

sufﬁcient dewatering has taken place a second ply is

applied by means of the secondary ﬂow box. The asso-

ciated ﬁbrous suspension is then drained through the base

ply, and dewatering is carried out essentially by ﬂat

vacuum boxes with thickening as the main mechanism.

Rotary Forming Devices

In these units the forming screen is in the form of a drum

and the ﬁbrous suspension is fed to the screen by various

methods ranging from (a) simply immersing the rotating

screen in a chamber (vat) containing the ﬁbrous suspen-

sion to (b) the use of a type of ﬂow box.

Cylinder Mold Machines. There are two basic types:

Uniﬂow and Contra Flow. In the Uniﬂow machine, the

ﬁbrous suspension is fed into the vat at the ingoing face of

the cylinder mold (forming screen); in the Contra Flow, the

suspension enters at the emerging face (see Figure 3).

The draining forces are low, typically 1–5 in. of water

static head difference. The mechanism of forming is com-

plex; and because of the low-drainage forces, considerable

washoff of the fragile newly formed web followed by

redeposition takes place in the forming area. The forming

zone is obviously too long with continual washing off and

redepositioning taking place so that the overall mat

deposition is inefﬁcient. Various modiﬁcations have taken

place in attempts to overcome this problem. Further

development has led to a variation known as the rotary

former.

Roll Formers. Figure 4 shows a typical rotary former. It

is easy to see that it consists essentially of a cylinder-

forming screen with an associated type of ﬂox box.

The forming length has been considerably decreased,

and the drainage forces can be far higher than is the

case with the previously described cylinder mold units

(Figure 4).

The cylindrical screen can be of relatively simple con-

struction relying on a pressure force in the forming zone

to assist drainage or it can be in the form of a suction

roll using a series of vacuum boxes to further assist

dewatering. Compared to cylinder molds, roll formers

have several advantages:

1. They can develop and tolerate higher levels of

turbulence in the initial forming zone because the

drainage zone is enclosed, whereas the initial form-

ing zone in a cylinder-mold machine starts at a free

surface.

2. High pressure in the free suspension and the possi-

bility of using suction on the underside of the forming

screen permit a much higher rate of drainage.

3. The rotary former has a more uniform metering of

the ﬁbrous suspension onto the forming screen.

Although both types of rotary forming devices can be used

to produce paper, the greatest application by far is the

manufacture of multi-ply board. A number of the units are

operated in series, progressively building up a multi-ply

web.

Figure 2. Fourdrinier forming.

Figure 3. Cylinder-mold forming.

916 PAPERBOARD

Twin-wire Formers

The third basic method used for paper and paperboard

forming is a relative newcomer, invented in the 1950s

and called the twin-wire method. In this technique the

paper web is formed between two forming screens.

The idea dates back to the nineteenth century, but it

was only in the 1950s that serious development took place,

taking advantage of improved ancillary equipment. The

process became a commercial reality and a viable conten-

der in some applications. Figure 5 shows a typical twin-

wire forming unit, in this case the basic Inverform

concept, a UK invention and the ﬁrst commercial twin-

wire system.

In all twin-wire formers, the ﬁbrous suspension is fed

into the gap between two converging forming screens by

means of a ﬂow box where dewatering and associated web

forming takes place. The action related to web structuring

in the forming zone is still not fully understood but

with regard to dewatering, the twin-wire concept offers

the opportunity to carry out symmetrical drainage of

the ﬁbrous suspension from both sides. This allows a

symmetrically structured web to be formed and provides

the opportunity to greatly increase the dewatering poten-

tial. Dewatering is assisted by the use of deﬂectors, which

press into the forming screens, and/or vacuum boxes

operating on one or both forming screens. A further

beneﬁt of the twin wire concept is the absence of a free

surface in the forming zone. Wire hs been repalced by

plastic netting.

In general terms, multi-ply webs are produced by (a)

separately forming the individual plies and then combin-

ing them together; (b) forming onto an existing ply or

plies, to form more plies; (c) using multilayer (stratiﬁed)

ﬂow boxes; or (d) a combination of a–c.

Examples of multi-ply arrangements in use today are

shown in Figures 6 and 7.

Machine Finishing

The surface of the paperboard web can be treated during

the manufacturing process by various means according

to the characteristics required of the ﬁnished product. It is

not unusual to use as part of the drying process an M.G.

(Yankee) cylinder, which imparts a smooth surface to one

side of the web without too much densiﬁcation of the web

taking place. In the drier section, there is often a size press

where chemicals can be added to the surfaces of the web in

order to impart certain characteristics (e.g., hard sizing or

barrier properties). Paperboard machines often have coat-

ers ‘‘in line’’ with the operation at which one or more

layers of coating medium can be applied. At the end of the

manufacturing process, right before the windup, one or

more stacks of calenders are installed. A stack of calenders

consists of a number of horizontal cast iron rolls set one

above each other. As the web of paperboard passes

through the nips, the calenders increase the smoothness

and gloss of the surface of the web.

TYPES OF PAPERBOARD

The simplest types of paperboard are single-ply thick

papers used for many nonpackaging purposes (e.g., index

board for card-ﬁling systems and display mounting). They

have a degree of stiffness and an acceptable appearance

(e.g., a uniform surface). This type of paperboard can also

Figure 5. An Inverform (Beloit) twin-

wire forming section.

Figure 4. A cylinder former.

PAPERBOARD 917