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

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CALCULATING MAXIMUM INSTANTANEOUS

DELIVERY RATE

The acronym MIDR (maximum instantaneous delivery

rate) is used interchangeably with IPDR (instantaneous

pump delivery rate). MIDR is the amount of adhesive that

a pump would need to supply if its associated guns were

ﬁred continuously for a speciﬁed period of time. Useful

units for measuring MIDR are pounds per hour (lb/h) and

grams per minute (g/min).

To calculate the MIDR for a speciﬁc application, follow

the steps in the example below. Refer to Figure 18 for a

visual description of the physical parameters used in the

calculation.

Given

1. Four beads per ﬂap, top and bottom sealing, for a

total of 16 beads per case.

2. Case length of 16 in. (41 cm).

3. Production rate of 20 cases per min at 100% machine

efﬁciency.

4. Bead length of 4 in. (10 cm), 1 in. (2.5 cm) from case

end, with a 6-in. (15-cm) gap between beads.

5. Eight-in. (20-cm) gaps between cases.

6. Adhesive ‘‘mileage’’ of 700 lineal ft lbf (949 J).

‘‘Mileage’’ is a function of bead size and the speciﬁc

gravity of the adhesive. The 700 lineal ft lbf used above is

based on a 3/32-in. (2.4 mm) half-round bead (standard-

size packaging bead) and melt density of 0.82 g/cm

(melt

density of standard packaging adhesive). Adhesives of this

type yield approximately 30 in.

/lb (1 cm

/g).

Calculation

1. Determine the total bead length in in./h (cm/h) and

convert to ft/h (m/h).

ð20 cases=minÞð4 in:=beadÞð16 beads=caseÞ

ð60 min=hÞ¼76; 800 in:=h ð195; 000 cm=hÞ

ð76; 800 in:=hÞð1 ft=12 in:Þ¼6400 ft =h ð1950 m=hÞ

2. Determine the adhesive consumption rate at 100%

machine efﬁciency using total bead length per hour

and adhesive mileage:

ð6400 ft=hÞð1 lb=700 ftÞð1 g=1:54 mÞ

¼ 9:14 lb=h ð4:15 kg=hÞ

Determine duty cycle

using length of bead during

machine cycle and machine cycle (length between

case leading edges).

8-in: bead length

24-in: cycle length

¼ 0:333

4. Determine the MIDR using the inverse of the duty

cycle and the adhesive consumption rate from step 2.

0:333

ð9:14 lb=hÞ¼27:42 lb=h ð207 g=minÞMIDR

Figure 18. Calculating the MIDR for

a speciﬁc application. Dimensions are

given in inches (millimeters in

parentheses).

18 ADHESIVE APPLICATORS

This example demonstrates the difference between the

delivery rate and the adhesive consumption rate. When

the guns are ﬁring, the pump is delivering adhesive at a

rate of 27.42 lb/h. This is the MIDR. Speed reducers are

rated and selected according to the MIDR they can

provide. This ﬁgure should not be confused with the

consumption rate, because the consumption rate is an

average measure of consumption that includes the time

when adhesive demand is zero.

Several equations may prove helpful in some

applications:

Bead Length, Line Speed, and Duration

5 bead lengthðin:ÞðcmÞ

line speedðft=minÞðcm=sÞ

¼ durationðsÞ

line speedðft= min Þðcm=sÞdurationðsÞ

¼ bead lengthðin:ÞðcmÞ

bead lengthðin:ÞðcmÞ5

durationðsÞ

¼ line speedðft=minÞðcm=sÞ

BIBLIOGRAPHY

‘‘Adhesive Applicators’’ in D. H. Shumaker and C. H. Sholl, The

Wiley Encyclopedia of Packaging Technology, 1st edition, Wiley,

New York P&A Division, Nordson Corporation, 1986, pp. 4–14.

General References

G. L. Schneberger, Adhesives in Manufacturing, Marcel Dekker,

New York, 1983.

‘‘Deﬁnitions of Terms Relating to Adhesives and Sealants.’’ Adhes.

Age (May 31, 1983).

I. Kaye, ‘‘Adhesives, Cold, Water-Borne;’’ T. Quinn, ‘‘Adhesives,

Hot Melt;’’ and C. Scholl, ‘‘Adhesives Applicating, Hot Melt’’ in

The Packaging Encyclopedia 1984, Vol. 29, No. 4, Cahners

Publishing, Boston, MA, 1984.

1981 Hot Melt Adhesives and Coatings, Technical Association of the

Pulp and P aper Industry, Norcross, GA, 1981 (Short course notes

presented at the T APPI Conference, San Diego, July 1–3, 1981.)

‘‘Calculating Maximum Instantaneous Delivery Rate,’’ Compo-

nents Catalog, P&A Division, Nordson Corporation, Norcross,

GA, 1984, p. A2.

ADHESIVES

IRVING KAYE

National Starch and Chemical

Company, Murray Hill,

New Jersey

Updated by Staff

INTRODUCTION

The packaging industry represents a signiﬁcant market

for adhesives materials. Some applications include

coatings, which act as adhesive layers for bonding to other

forms of packaging, such as labels or tapes, or are used in

the actual assembly of a carton, or to prepare a laminate.

Adhesives make up more than 80% of the adhesive and

sealants market. In 2002, the global market was about

16.7 million tons and was expected to rise about 3–4% per

year. In the United States, the market was estimated to be

8.89 million tons in 2004; as a comparison, the market in

1999 was 6.89 million tons (1).

The principal uses of adhesves include: the forming and

sealing of corrugated cases and folding cartons; the form-

ing and sealing of bags; the winding of tubes for cores,

composite cans, and ﬁber drums; the labeling of bottles,

jars, drums, and cases; the lamination of paper to paper,

paperboard, and foil; and the lamination of plastic ﬁlms

for ﬂexible packaging. The markets for packaging materi-

als are diverse, mainly concerned with food, beverage,

medical, and heavy-duty industrial applications, each of

which can bring stringent performance requirements and

impose harsh environments under which the adhesive

layer is expected to function.

There is a strong movement to replace solvents and

solvent-based adhesives in both the United States and

Europe, in order to minimize volatile organic emissions.

This has led to a growth in water-based and hot-melt

adhesives at the expense of solvented types. Also, there

has been a strong interest in recyclable adhesives based

on requirements for recycled paper content in the United

States and Europe. There is a desire to develop single

material packaging to facilitate recycling and minimize

sorting. A problem is that adhesive residues left in board

can produce difﬁculties in the subsequent handling of the

regenerated material. Under consideration is the use of

bioadhesives to assist in the material breakdown (2).

There are many types of packaging adhesives, fre-

quently for the same end-use applications, with the choice

dictated by cost, productivity factors, the particular sub-

strates involved, special end-use requirements, and envir-

onmental considerations (see also Adhesives, extrudable).

To help clarify this complex picture involving many dif-

ferent chemical types, it is useful to classify packaging

adhesives into three physical forms: water-based solutions

and dispersions, solvent-based systems, and solvent-free

100% solids and hot melts.

WATER-BASED SYSTEMS

This is the oldest—and still, by far, the largest-volume—

class of adhesive used in packaging. These adhesives

share the general advantages of ease and safety of hand-

ling, energy efﬁciency, low cost, and high strength. Water-

based adhesives can be further divided into two cate-

gories, natural and synthetic.

Natural Water-Based Adhesives

The earliest packaging adhesives were based on naturally

derived materials—indeed, almost all were until the

1940s—and they still constitute a large segment of the

market. However, they have seen their gradual replacement

ADHESIVES 19

in many applications. Starch and dextrin have been re-

placed by synthetic poly(vinyl acetate) emulsions. However,

starch-based adhesives are still being investigated (3).

Starch. The largest class of natural adhesives is based

on starch; in the United States, this means corn starch.

Some potato starch is used in Europe primarily because of

economics, since they are heavily subsidized. Adhesives

are produced from raw ﬂour or starch, but more frequently

the starch molecule is broken down into smaller chain

segments by acid hydrolysis. Depending on the conditions

of that reaction, the resulting material can be a ﬂuidity or

thin-boiling starch or a dextrin. These can then be further

compounded with alkaline tackiﬁers such as borate salts,

sodium silicate, or sodium hydroxide, with added plastici-

zers or ﬁllers.

A principal use of starch adhesives is in the manufac-

ture of corrugated board for shipping cases. The standard

process involves suspending ungelatinized cornstarch in a

thin carrier-starch cook as a vehicle. When the bond line is

subjected to heat and pressure, the cornstarch gelatinizes

almost instantly, forming a bond between the ﬂutes and

the linerboard at very high rates of production. Additives

are usually used to improve adhesion, lower gel tempera-

ture, increase water resistance, and further increase

speed of bond formation.

Other important uses of modiﬁed starches and dextrins

are in the sealing of cases and cartons, winding of spiral or

convolute tubes, seaming and forming of bags, and adher-

ing the seams on can labels. Glass bottles are frequently

labeled with a special class of alkaline-treated starch

adhesive called a ‘‘jelly gum.’’ These have the special tacky,

cohesive consistency required on some moderate-speed

bottle labeling equipment. Specially modiﬁed starches

based on genetically bred high-amylose strains are also

used as primary ingredients in the remoistening adhesive

on gummed tape used for box sealing.

There are many strong points to recommend starch-

based adhesives. They are regarded as very easy to

handle, clean-machining, easy to clean up, and, above

all, inexpensive. Starch has excellent adhesion to paper;

and, being nonthermoplastic, it has outstanding heat

resistance. Starch also has a green, environmentally

friendly image, being ‘‘natural’’ and based on a renewable

resource. The negatives are the relatively slow rate of

bond formation, the limited adhesion to coatings and

plastics, and poor water resistance.

Protein. Another class of natural adhesives is based on

animal or plant protein. Proteins are highly susceptible to

changes in their structure through changes in pH, the

process of denaturation, and breakdown in molecular

weight to effect solubilization.

Soybeans. Soybeans are important sources of both pro-

teins and trigylceride oils. Proteins for adhesives are

obtained from harvested soybeans by extracting and

pressing out the oils and then heating. Soy in combination

with blood or casein seems to exhibit the most water

resistance. Protein-based adhesives are of interest to the

medical industry; however, blood contamination is an

issue (1). Considerable work is being done in this area.

Stable adhesives from urea-denatured soy ﬂour have been

reported (4).

Animal Glue. This is one of the earliest types of adhe-

sive. It is derived from collagen extracted from animal

skin and bone by alkaline hydrolysis. When used as a

heated colloidal suspension in water, animal glues have an

unusual level of hot tack and long, gummy tack range.

However, because of ﬂuctuating availability and cost,

along with the development of improved synthetics, there

are only two signiﬁcant uses of animal glue in packaging:

(1) as a preferred ingredient in the remoistening adhesive

on reinforced gummed tape use for box sealing and (2)as

the standard adhesive used in forming rigid setup boxes.

Casein. This is produced by the acidiﬁcation of skimmed

cow’s milk. The precipitated curds thus produced form the

basis of casein adhesives. There is a lack of suppliers of

casein in the United States. The main sources for casein are

Australia, New Zealand, and Poland, but it is also produced

in Argentina and the Scandinavian countries.

There are two packaging applications where casein is

used in large volume. One is in adhesives for labeling glass

bottles, particularly on newer high-speed labelers where

they outperform starch-based adhesives. They are espe-

cially favored for beer bottles, where casein provides the

resistance to cold-water immersion required by brewers,

together with removability in alkaline wash when the

bottles are returned. The second use is as an ingredient in

adhesives used to laminate aluminum foil to paper. Com-

bined with synthetic elastomers such as polychloroprene

or styrene-butadiene lattices, casein provides a unique

balance of adhesion and heat resistance (5).

Natural Rubber Latex. This is extracted from the rubber

tree, Hevea brasiliensis, and is available in several varia-

tions of concentration and stabilization. One major use in

packaging is as a principal ingredient in adhesives for

laminating polyethylene ﬁlm to paper, as in the construc-

tion of multiwall bags. Natural rubber latex also ﬁnds use

in a variety of self-seal applications, since it is the only

adhesive system that will form bonds only to itself with

pressure. This property is used in self-seal candy wraps

(where it is called cold-seal) and in press-to-seal cases, as

well as on envelopes.

Synthetic Water-Based Adhesives

Synthetic

water-based adhesives

are the most broadly

used class of adhesives in general packaging. Almost all

are resin emulsions, speciﬁcally poly(vinyl acetate) emul-

sion, which is a stable suspension of poly(vinyl acetate)

particles in water. These systems usually contain water-

soluble protective colloids such as poly(vinyl alcohol) or 2-

hydroxyethyl cellulose ether and may be further com-

pounded by the addition of plasticizers, ﬁllers, solvents,

defoamers, and preservatives.

These emulsions are supplied in liquid form (the ubi-

quitous ‘‘white glue’’) in a range of consistencies from thin

milky ﬂuids to thick, nonﬂowing pastes. They are used in a

20 ADHESIVES

broad range of packaging applications, to form, seal, or

label cases, cartons, tubes, bags, and bottles. In most of

these uses they have replaced natural adhesives because

of their greater versatility. They can be compounded to

have a broad range of adhesion not only to paper and glass

but also to most plastics and metals. They can be rendered

very water-insensitive for immersion resistance, or very

water-sensitive to promote ease of cleanup and good

machining. They are the fastest-setting class of water-

based adhesives, facilitating increased production speeds.

They are low in odor, taste, color, and toxicity and have

excellent long-term aging stability. They are tough, with

an excellent balance of heat and cold resistance. The

equipment used to apply them is relatively simple and

inexpensive to purchase and to operate. Finally, they are

economical and reasonably stable in cost.

The utility of these emulsion systems has broadened in

recent years with the greater use of copolymers of vinyl

acetate. Copolymerizing vinyl acetate with ethylene or

acrylic esters in particular has greatly improved the adhe-

sion capabilities of these emulsions, particularly where

adhesion to plastics or high-gloss coatings is required. For

example, crosslinking acrylic–vinyl acetate copolymer emul-

sions have replaced polyurethane solution systems for

laminating plastic ﬁlms for snack packages. The largest

areas of use for vinyl emulsions, however, are in case and

carton sealing, forming the manufacturers joint on cases

and cartons , and the spiral winding of composite cans.

All acrylic emulsion pressure-sensitive adhesives have to

a signiﬁcant degree replaced acrylic or rubber solution

products in the manufacture of pressure-sensitive labels.

The development of wa ter-based acrylics eliminates a

source of solvent vapors. The development of pressure-

sensitive adhesives compared to other tapes is convenience

of use. There are no storage problems , and no mixing or

activation is necessary. No waiting is involved. Often the

bond is reversible. Disadvantages are that adhesive

strength is low and they are not suitable for rough surfaces .

Polyurethane dispersions have found acceptance in

medium-performance ﬂexible packaging applications la-

minating plastic ﬁlms together where some chemical

resistance is required.

The use of other synthetic water-based systems is quite

minor and specialized. Some synthetic rubber dispersions

are used in ﬁlm adhesives and, in conjunction with casein,

for the lamination of aluminum foil to paper. There is

some use of tackiﬁed rubber dispersions as pressure-

sensitive masses on tapes and labels replacing solvent-

based rubber–resin systems.

Sodium silicate was once widely used in many paper

packaging applications, ranging from corrugating to case

sealing, but today the primary use of silicate adhesives is in

tube winding, especially in the convolute winding of large

drums or cores where it produces a high degree of stiffness.

SOLIDS/HOT-MELT ADHESIVES

Hot melts are the fastest-growing important class of

adhesives in packaging. Most of their volume goes into

high-speed large-volume case and carton sealing. Hot

melts can be deﬁned as 100% solids adhesives based on

thermoplastic polymers, which are applied heated in the

molten state and set to form a bond on cooling and

solidiﬁcation. Their chief attraction is the extremely rapid

rate of bond formation, which can translate into high

production rates on a packaging line.

The backbone of any hot melt is a thermoplastic poly-

mer. Although almost any thermoplastic can be used, and

most have been, the most widely used material by far is the

copolymer of ethylene and vinyl acetate (EVA). These

copolymers have an excellent balance of molten stability,

adhesion, and toughness over a broad temperature range,

as well as compatibility with many modiﬁers. The EVA

polymers are further compounded with waxes and tackify-

ing resins to convert them into useful adhesives. The

function of the wax is to lower viscosity and control set

speed. Parafﬁn, microcrystalline, and synthetic waxes are

used, depending on the required speed, ﬂexibility, and heat

resistance. The tackifying resins also function to control

viscosity, as well as wetting and adhesion. These are

usually low-molecular-weight polymers based on aliphatic

or aromatic hydrocarbons, rosins, rosin esters, terpenes,

styrene or phenol derivatives, or any of these in combina-

tion. The formulations always include stabilizers and anti-

oxidants to prevent premature viscosity change and char or

gel formation that could lead to equipment stoppage.

Two variations on traditional EVA hot melts have

recently become commercially signiﬁcant. First, the re-

cent availability of very low-molecular-weight EVA copo-

lymers has made possible EVA hot melt that can be run at

much lower temperatures, 2501F (1211C), rather than the

traditional 3501F (1771C). This allows for much safer

running conditions as well as energy savings. Second, an

analog of EVA, ethylene-butyl acrylate, has been intro-

duced as the backbone polymer in some packaging hot

melts (6), providing advantages in both adhesion and in

heat and cold resistance. Decrease in the application

temperature has lessened safety concerns associated

with this type of adhesive (1).

Another class of hot melts used in packaging is based

lower-molecular-weight polyethylene,

compounded

with natural or synthetic polyterpene tackiﬁers. These

lack the broader adhesion capabilities of the EVA-based

hot melts as well as their broader temperature resistance

capabilities. However, they are economical and are ade-

quate for many paper bonding constructions, and they ﬁnd

application in case sealing and bag seaming and sealing.

A third type of hot melt is based on amorphous-poly a-

oleﬁn (APAO) polymers. Originally these were based on

amorphous polypropylene, which was widely available as

the byproduct of the polymerization of isotactic polypropy-

lene plastics. As a byproduct, it was inexpensive, but it

suffered from low strength and was limited to applications

such as lamination of paper to paper to produce water-

resistant wrapping material on two-ply reinforced ship-

ping tape. Improvements in polypropylene polymerization

catalysts have almost eliminated this byproduct, but sev-

eral producers noted the market and began producing on-

purpose APAO polymers, albeit at somewhat higher costs.

Another recent class of hot melt is based on thermo-

plastic elastomers: block copolymers of styrene and

ADHESIVES 21

butadiene or isoprene. These ﬁnd primary application in

hot-melt pressure-sensitive adhesives for tapes and labels

replacing solvent-borne rubber systems. More recently,

their broad adhesion and low temperature and impact

resistance are ﬁnding use such as (a) the attachment of

polyethylene-base cups to polyester soft-drink bottles (7)

and (b) the sealing of ﬁlm laminated frozen-food cartons.

Pressure-sensitive adhesives from high-molecular-weight

block copolymers having a high diblock copolymer are

suitable for PVC ﬁlm labels and decals (8).

Even more specialized applications use hot melts based

on polyamides or polyesters when speciﬁc chemical- or

heat-resistance requirements have to be met, but their

high cost and relatively poor molten stability have pre-

cluded their widespread use to date.

The most recent and highest-performance hot-melt tech-

nology is moisture curing polyurethane hot melts, but these

have been limited to higher-requirement product assembly

applications and have found few uses in packaging.

All hot melts share the same basic advantages, based

on their mechanism of bond formation by simple cooling

and solidiﬁcation. They are the fastest-setting class of

adhesive—indeed, preset before both substrates can be

wet is the most frequent cause of poor bonds with hot

melts. Because of the wide range of polymers and modi-

ﬁers used, they can be formulated to adhere to almost any

surface. With no solvent or vehicle to remove, they are

generally safe and environmentally preferred. They are

excellent at gap ﬁlling, since a relatively large mass of

material can ‘‘freeze’’ in place, thus joining poorly mated

surfaces with wide dimensional tolerances.

However, all hot melts share the same weakness, which

is the rapid falloff in strength at elevated temperatures.

They also have a tendency to damage substrates that

cannot withstand their application temperature (1). Prop-

erly formulated hot melts can be suitable for almost all

packaging applications, but they are not appropriate for

very hot-ﬁll or bake-and-serve applications.

SOLVENT-BASED ADHESIVES

Solvent-based adhesives, which are by far the smallest,

and most rapidly declining, of the three classes of adhesive

used in packaging, ﬁnd use in specialized applications

where water-based or hot-melt systems do not meet the

technical requirements.

Rubber–resin solutions are still used as pressure-sen-

sitive adhesives for labels and tapes. However, factors of

cost, safety, productivity, and, above all, compliance with

clean-air laws have led to a strong movement toward

water-based or soilds/hot-melt alternatives. Such alterna-

tives are available to meet most requirements and most

knowledgeable observers predict an almost total disap-

pearance of rubber–resin solvent-based pressure sensi-

tives for packaging tapes and labels in the near future.

Solvented polyurethane adhesives are widely used in

ﬂexible packaging for the lamination of plastic ﬁlms.

These multilayer ﬁlm constructions ﬁnd application in

bags, pouches, wraps for snack foods, meat and cheese

packs, and boil-in-bag food pouches. They have the ideal

properties of adhesion, toughness, ﬂexibility, clarity, and

resistance to heat required in this area. However, here,

too, alternative systems are being introduced to eliminate

the costs, hazards, and regulatory problems associated

with solvent-based systems. Crosslinking waterborne ac-

rylic polymers have gained acceptance in the large snack

food laminating market for constructions such as potato

chip bags. Polyurethane dispersions and (100% solids)

‘‘warm melt’’ systems are starting to ﬁnd use in some of

the more demanding food packaging applications.

Solvent-based ethylene–vinyl acetate systems found

use in some heat-seal constructions, such as the thermal

strip on form–ﬁll–seal pouches, or on lidding stock for

plastic food containers such as creamers or jelly packs.

BIBLIOGRAPHY

I. Kaye, ‘‘Adhesives’’ in The Wiley Encyclopedia of Packaging, 2nd

edition, John Wiley & Sons, New York, 1997, pp. 23–25.

Cited Publications

1. E. M. Yorkgitis, ‘‘Adhesives’’ in Kirk–Othmer Encyclopedia of

Chemical Technology, 5th edition, Vol. 1, John Wiley & Sons,

Hoboken, NJ, 2004.

2. R. J. Ashley, ‘‘Packaging Industry’’ in D. E. Packham, ed.,

Handbook of Adhesion, 2nd edition, John Wiley & Sons,

Chichester, UK, 2005.

3. S. Peltonen and H. Mikkonen, U.S. Patent 7,264,666 (to Valtion

tecknillen tutkimuskeskus, Finland), September 4, 2007.

4. J. M. Wescott and M. J. Birkeland, U.S. Patent Application

20080021187, January 24, 2008.

5. W. B. Kinney, U.S. Patent 2,754,240, (to Borden Company),

July 10, 1956.

6. F. Brady and T. Kauffman, U.S. Patent 4,816,306 (to National

Starch and Chemical Company), March 28, 1989.

7. T. Taylor and P. Puletti, U.S. Patent 4,212,10 (to National

Starch and Chemical Company), July 15, 1980.

8. D. J. St. Clair and co-workers, U.S. Patent 7,297,741 (to Kraton

Polymrs U.S. LLC), November 20, 2007.

General References

I. Skeist, ed., Handbook of Adhesives, 3rd edition, Van Nostrand

Reinhold, New York, 1990.

K. Booth, ed., Industrial Packaging Adhesives, CRC Press, Boca

Raton, FL, 1990.

D. E. Packham, ed., Handbook of Adhesion, 2nd edition, John

Wiley & Sons, Chichester, UK, 2005.

ADHESIVES, EXTRUDABLE

STEPHEN R. TANNY

DuPont Polymers,

Wilmington, Delaware

In its broadest deﬁnition, extrudable adhesives are poly-

meric resins that can be processed by standard extrusion

22 ADHESIVES, EXTRUDABLE

processes and are useful for bonding together various

substrates. In practice, extrudable adhesives are com-

monly polyoleﬁn materials useful in processes such as

blown and cast ﬁlm, blow molding, and extrusion coating.

OVERVIEW

The variety of polymeric materials available to both

the industrial user and the consumer and are useful as

adhesives include several materials almost equal to the

number of polymer types themselves (see also Adhesives).

Adhesives are developed from such polymers as poly-

vinyl acetate, polyvinyl alcohol, polyamides, polyesters,

and many others. Adhesives can be applied as solvent

solutions, aqueous dispersions, pastes, spray coatings,

tapes, and thermally activated ﬁlms. One special subset

of adhesives, called extrudable adhesives, are different in

that, in their application, they are applied in an extrusion

process, in which they are melted, conveyed, and inserted

between the substrates that are to be bonded together.

Although there are many adhesive application methods

that require the melting of a polymeric adhesive, extrud-

able adhesives are distinguished from other adhesive

types used in processes such as powder coating, ﬂame

spraying, and the thermal lamination of adhesive ﬁlms

and webs. As a second distinction, extrudable adhesives

are also distinguished from hot-melt adhesives that

generally require a resin viscosity unsuitable for tradi-

tional extrusion processes. Thus, extrudable adhesives

are those materials speciﬁcally designed to function in

processes such as coextrusion blown and cast ﬁlm, mono-

layer and coextrusion coating and lamination, coextrusion

cast sheet, coextrusion blow molding, and coextrusion

tubing.

TYPES OF EXTRUDABLE ADHESIVE

Extrudable adhesives are most often polyoleﬁn-based

compositions. The most common use of these polyoleﬁn

extrudable adhesives is as a speciﬁc layer in a multilayer

coextrusion. Coextrusion is a technique that allows the

creation of a plastic composite, in a single operation, which

combines the beneﬁts of a number of different materials.

The plastic composite may be, for example, a packaging

ﬁlm that combines the properties of an oxygen-barrier

resin with a heat-sealable layer on one side and an abuse-

resistant layer on the other side. The purpose of the

extrudable adhesive is to bond the diverse plastic materi-

als in the construction that would not, under ordinary

circumstances, bond with each other. The polyoleﬁn ad-

hesive is designed to bond with similar polyoleﬁns by a

diffusion process. That is, during the extrusion process,

the molten extrudable adhesive resin comes in contact

with the molten polyoleﬁn. Their molecules diffuse to-

gether creating a strong bond between the materials (1).

The polyoleﬁn extrudable adhesive is designed to bond

with other polymeric materials, such as oxygen-barrier

resins like polyamides and ethylene vinyl alcohol, through

a chemical reaction between a functional group on the

adhesive and a functional group on the barrier resin.

Often, the functional group on the extrudable adhesive

can be chosen for bonding to speciﬁc materials of interest.

Many types of extrudable adhesive exist. Polyethylene

can be considered to be an extrudable adhesive. Com-

monly, polyethylene is used in extrusion lamination of

paper to aluminum foil. The polyethylene is extruded at

very high temperatures. The melt is oxidized by contact

with air creating polar functionality on the surface of the

melt. This process provides chemical bonding to the

aluminum oxide on the surface of the foil (2). The low

viscosity of the melt and its polar nature allows for good

wetting on the paper and for encapsulation of the indivi-

dual ﬁbers. Co-polymers of ethylene and vinyl acetate also

are useful extrudable adhesives and capable of bonding

polyethylene to polyvinyl chloride. However, the most

sophisticated extrudable adhesives are polyoleﬁns with

either acid or anhydride functionality. Acids and anhy-

drides are particularly reactive and can create strong

bonds to several different materials in extrusion pro-

cesses. Examples of acid-modiﬁed polyoleﬁns are the co-

polymers of ethylene with acrylic acid or methacrylic acid.

Variations include the partially neutralized acid co-poly-

mers with metal ions referred to as ionomers or terpoly-

mers of ethylene, an acid and an acrylate such as methyl

acrylate or isobutyl acrylate. Acid-containing extrudable

adhesives are widely used to bond with aluminum foil (3,

4). Examples of anhydride modiﬁed polyoleﬁns include

terpolymers of ethylene, maleic anhydride, and acrylates

such as ethyl acrylate or butyl acrylate and the anhydride

grafted polyoleﬁns.

The anhydride grafted polyoleﬁns are created by com-

bining the polyoleﬁn with an anhydride, most commonly

maleic anhydride. The anhydride is added to the poly-

oleﬁn with a free-radical initiator in a solvent or the melt.

This addition allows for the attachment of the highly

reactive anhydride to polyoleﬁns, such as high-density

polyethylene, linear low-density polyethylene, polypropy-

lene, ethylene vinyl acetate copolymers, or ethylene pro-

pylene rubbers. Although the polar functionality of the

anhydride and the polyoleﬁn backbone are the necessary

ingredients for the extrudable adhesive to function, al-

most all commercially available extrudable adhesives are

formulated with other polymers. Formulations of anhy-

dride modiﬁed extrudable adhesives will generally contain

two or three basic components. Two-component extrudable

adhesives will contain the anhydride graft blended into a

second, or matrix polyoleﬁn (5). The purpose of the second

polyoleﬁn is to lower the overall cost of the adhesive and to

control the viscosity, modulus, tensile, thermal, and other

properties of the adhesive. The three-component formula-

tion will contain the anhydride graft, the matrix polyole-

ﬁn, and a modiﬁer (6). The purpose of the modiﬁer is to

enhance the peel strength characteristics of the bonded

composite. In most cases, the efﬁciency of the extrudable

adhesive is judged by peeling the bonded composite apart

in a ‘‘T’’ peel mode. The modiﬁer affects the peel strength

characteristics of the adhesive by dissipating the force at

the interface where the composite is being peeled apart.

The

result of this

process is the necessity for more work to

peel apart the bonded composite (7). These extrudable

ADHESIVES, EXTRUDABLE 23

adhesives also can have other additives, such as antiox-

idants, slip agents, or resin tackiﬁers.

Although the formulation of an extrudable adhesive is

very important to its utility, many other factors also affect

how well an extrudable adhesive will bond different ma-

terials together. How the extrudable adhesive is processed,

its thickness, and whether the bonded composite is or-

iented, shaped, or exposed to aggressive environmental

conditions can affect the performance of the adhesive (8, 9).

COMMERCIAL OFFERINGS

Many producers of extrudable adhesives around the world

exist. Some of these producers will produce only a few

types of extrudable adhesive. Others have a broader

product line. Some manufacturers market their adhesives

internationally; others only market regionally, to speciﬁc

market areas, or for use in speciﬁc applications. Manu-

facturers of acid copolymers include Dow Chemical Com-

pany as Primacor and E. I. DuPont de Nemours as Nucrel.

DuPont also manufactures acid terpolymers. Ethylene

terpolymers of anhydride with acrylate are produced by

Atochem under the name Lotader. DuPont manufactures

extrudable adhesives based on anhydride graft technology

under the name Bynel. Quantum Chemical Company also

makes and sells extrudable adhesives under the name

Plexar. Other manufacturers include Mitsui Petrochem-

ical Company with Admer, Morton International with

Tymor, Atochem with Orevac, and DSM with Yparex.

EXTRUDABLE ADHESIVE APPLICATIONS

Extrudable adhesives are used primarily in coextrusion

processes (see Coextrusion). The major market area is food

packaging. Examples include the coextrusion coating of an

oxygen-barrier material, extrudable adhesive, and poly-

oleﬁn onto paperboard to create high-barrier, nonscalping

fruit juice cartons. Oxygen barriers, extrudable adhesives,

and ionomers are coextruded by either cast-ﬁlm or blown-

ﬁlm processes to produce packaging ﬁlms for hot dogs,

bacon, and other processed meats. A third example is the

coextrusion blow molding of polyoleﬁn, extrudable adhe-

sive, and oxygen barrier to produce high-barrier ketchup

bottles. Extrudable adhesives also are used in applications

that do not involve the packaging of foods. Extrudable

adhesives are used to bond high-density polyethylene

to ethylene vinyl alcohol in a coextrusion blow-molding

process to produce automotive gas tanks (see Blow mold-

ing). Extrudable adhesives also are used to bond cross-

linked polyethylene to ethylene vinyl alcohol through a

coextrusion crosshead tubing process to make radiant hot-

water heating pipes.

The selection of the proper extrudable adhesive for any

particular application may be a complex problem. The ﬁrst

consideration is always the materials that need to be

bonded together. The adhesive must be able to bond with

these materials. When bonding a polyoleﬁn with an oxy-

gen barrier, such as ethylene vinyl alcohol or polyamide,

extrudable adhesives with anhydride functionality are

usually the adhesive of choice. The type of anhydride

modiﬁed polyoleﬁn will depend on the polyoleﬁn being

co-extruded with the barrier. For example, if polyamide is

being co-extruded with polyethylene, an anhydride-mod-

iﬁed polyethylene or anhydride modiﬁed ethylene vinyl

acetate will be the resin best able to perform in the

application. If polypropylene is coextruded with polya-

mide, then an anhydride modiﬁed polypropylene will be

chosen. Second, the adhesive must be processable in the

equipment that the converter intends to use. This may

mean choosing a resin with a relatively lower viscosity for

coating applications and a relatively higher viscosity for

blow-molding applications. If the bonded composite is

going to see a speciﬁc environment, such as oil or grease,

then it should be resistant to that product. If the compo-

site will be exposed to either very high or very low

temperatures, then the adhesive must be functional at

those temperatures. Finally, some extrudable adhesive

resins may have to have a speciﬁc regulatory compliance

depending on the application for the bonded composite.

Most manufacturers of these extrudable adhesives are

prepared to help the converter select the best adhesive

for their application.

REFERENCES

1. L. Lee, Fundamentals of Adhesion, Plenum Press, New York,

1992.

2. A. Stralin and T. Hjertberg, J. Adhes. Sci. Technol. 7, 1211–

1229 (1993).

3. M. Finlayson and B. Shah, ‘‘The Inﬂuence of Surface Acidity

and Basicity on Adhesion of (Ethylene-co-acrylic acid) to

Aluminum’’ in Acid–Base Interactions: Relevance to Adhesion

Science and Technology, VSP BV, Utrecht, 1991, pp. 303–311.

4. G. Hoh, S. Sadik, and J. Gates, ‘‘1989 Polymers’’ in Proc.

Laminations and Coatings Conf., 1989, Tappi, Atlanta, GA,

pp. 361–366.

5. U.S. Patent 4,230,830 (Oct. 28, 1980), S. Tanny and P. Blatz (to

DuPont).

6. U.S. Patent 4,198,327 (April 15, 1980), H. Matsumoto and H.

Niimi (to Mitsui Petrochemical Industries, Ltd.).

7. S. Wu, Polymer Interface and Adhesion, Marcel Dekker, New

York, 1982.

8. B. Morris, Tappi J. 75, 107–110 (1992).

9. B. Morris, Eng. Plast. 6, 96–107 (1993).

AEROSOL CONTAINERS

MONTFORT JOHNSEN

Montfort A. Johnsen &

Associates, Ltd., Danville,

Illinois

The ﬁrst aerosol cans were heavy steel ‘‘bombs,’’ consisting

of two shells about 0.090 in. (2.3 mm) thick, brazed to-

gether at the lateral centerline. They were known at least

since the early work of Eric A. Rotheim (Oslo, Norway,

24 AEROSOL CONTAINERS

1931) and gained fame during 1943–1945 as insecticides

for U.S. troops ﬁghting in such places as Guadalcanal and

other South Paciﬁc areas. After the war, these products

were made available to the public, but acceptance was

very poor, due to the high initial expense and the aspect of

having to return the emptied unit for reﬁlling. It was

obvious that a lightweight, disposable can was needed.

In 1946–1947, Harry E. Peterson developed such a can

in the laboratories of the Continental Can Corporation in

Chicago. It consisted of a 2.68-in.-diameter solder side

seamed can body, to which were seamed a pair of concave

end sections. The top section, assembled to the body by the

canmaker, carried a small valve, soldered at the center-

line. The can was designed to be ﬁlled upside-down with

highly refrigerated (451For431C) aerosol concentrates

and propellants, after which the end was double-seamed

to the body. The ﬁnal unit stood 4.8 in. tall and had a

capacity of about 12.2 ﬂuid oz (361 mL). In an almost

concurrent but independent development, Earl Graham of

Crown Cork & Seal Company developed a higher-strength

modiﬁcation of the ‘‘Crowntainer’’ beer can. This was a

two-piece container. The base was double-seamed onto

a drawn steel shell that contained a soldered valve.

The early valves were manufactured by Bridgeport Brass

Company, Continental Can Corporation, and many other

ﬁrms. Most were outrageously costly and inefﬁcient.

Slightly later, pioneers such as Robert Alplanalp (Preci-

sion Valve Corp.) and Edward Green, Sr. (Newman-Green,

Inc.) patented more efﬁcient types.

A major innovation occurred about 1951, when Crown

Cork & Seal Company engineers developed the ‘‘1-in.’’

(‘‘25.4-mm’’) hole, along with a corresponding valve cup.

The cup could carry the valve components within the

central pedestal (except for actuator and dip tube), and

it could be crimped (swaged) onto the curl or bead that

surrounded the ‘‘one-inch’’ (‘‘1-in.’’) hole. This secondary

plug-type closure rather quickly displaced the soldered

valve units, the last of which were ﬁlled during October

1953. The Continental Can Company developed a can

dome—called a ‘‘cone’’ in the United Kingdom—to provide

the needed ‘‘1-in.’’ hole, while at the same time enlarging

their can somewhat and making it taller.

The budding aerosol industry had to make do with

these two nominal 12-oz cans until 1953, when the 2.12-

in.-diameter can size was developed as a nominal 6-oz

container.

At the insistance of a fast-growing industry, the two can

companies introduced some additional can heights. They

were joined in 1955 by the American Can Company, who

entered the market with their ‘‘Regency’’ line of 2.47-in.-

diameter cans in four heights. The National Can Corpora-

tion followed soon afterward.

The impact extrusion technology for drawing alumi-

num beer and beverage cans was well developed by the

1950s. The Peerless Tube Company produced aerosol units

as early as 1952 and perhaps even earlier. The American

Can Company made a unique two-piece aluminum can

(Mira-Spray and Mira-Flo) in just two 6-oz sizes. Other

very early entrants were Victor Tube, White Metal, and

Hunter-Douglas Corporation (see also Cans, aluminum;

Cans, fabrication).

Glass aerosols were made, ﬁrst by the Wheaton Glass

Company (Mays Landing, NJ) about 1953 and then by

Ball Brothers and several other ﬁrms. The valve was

incorporated into a ferrule by Risdon Manufacturing

Corporation, Emson Research, Inc., and Precision Valve

Corporation, and the ferrule was sealed to the glass ﬁnish

by means of clinching—a method then also used to seal

metal caps on beer bottles.

During 1954, Wheaton developed a method for encas-

ing their bottles in a heavy skin of PVC. The plastic

envelope helped the bottle withstand minor falls to hard

surfaces, but if breakage should occur, it contained the

glass shards and kept them from ﬂying outward and

possibly injuring persons nearby. Later on, a bonded ﬁlm

was developed and made an unofﬁcial industry standard

on glass bottles of W1-oz (30-mL) capacity.

The packaging process also underwent dramatic

changes. Several equipment suppliers are now specialized

in the manufacture of aerosol ﬁlling and packaging equip-

ment. As aerosol volume grew, higher speed lines were

needed. Even double-indexing, two-lane-in-line equip-

ment could not produce more than 125 cans/minute.

Reengineering resulted in a production rate of 216 cans/

minute. This rate was important to contract ﬁllers because

it related directly to competitivety and proﬁtability. Today,

very complex rotary machines are available with rated

capacities of 480 cans/minute.

In recent history, the aerosol industry has had to

contend with many obstacles: the ban on the popular

CFC propellants, the global warming potential of various

propellants, and, in 2007, legislation that curtails the use

of volatile organic chemicals (see Propellants, aerosol).

CAN-MAKING TECHNOLOGY

Tinplate

The three-piece tinplate can still command about 82% of

the U.S. aerosol market. This translates to 3.65 109

cans

in 2006.

Tinplate,

in a number of thicknesses of steel and tin, is

routinely delivered to the can-making plant in the form of

large rolls typically 39.4 in. (1 m) wide and 48 in. (1.22 m)

in diameter. A roll may weigh 15,000 lb (6800 kg) and

contain about 4.5 mi (7.25 km) of tinplate, depending on

the thickness. After sending the roll through a straigh-

tener, a slitter cuts it into sheets best suited for making

can bodies with a minimum of waste. At the same time, a

scroll cutter produces strips from which dome and base

section circles can be cut—again with a minimum of waste

(see also Cans, steel).

The body sheets are ﬁrst lined with epoxy–phenolics or

other materials, baked in huge ovens, and then litho-

graphed. At this point the individual can bodies are cut

apart. A bare metal fringe is allocated for the area to be

welded. The WIMA or other type of bodymaker acts to roll

up the can body and tackweld it every inch or two to hold it

in place with just the right lapover. After this the welding

process produces either a ‘‘standard’’ or ‘‘full’’ (tin-free)

weld line. Weld nuggets (B31 in.

1

) form the basic

AEROSOL CONTAINERS 25

structure. While still extremely hot, the overlap thickness

is reduced by heavy compression to only B1.4 times the

average plate thickness. The cylindrical can body is then

ﬂanged top and bottom for a ‘‘standard’’ or straight-wall

can, or is both necked-in and ﬂanged for the ‘‘necked-in’’

containers. The latter have several advantages and are

increasingly popular.

Meanwhile, can domes and bases are being formed in

multistage presses. They either are used directly or are

‘‘sleeved’’ into long paper tubes for later fabrication. Quite

often, one large plant will make sleeve packs of can ends,

for shipment to satellite locations where the assembly

process is undertaken. The same is true for can bodies,

which can be easily shipped in the ﬂat to other facilities.

The ﬁnal can is assembled using double seamers that

typically operate at about 350 cans/minute. As a rule, the

ﬁnished cans are then tested using a large wheel-like

device that pumps a signiﬁcant air pressure into each one

and then checks for pressure leakage, if any. Such cans are

automatically shunted aside and scrapped. Finally, the

cans are tiered onto pallets of about 40-in. 44-in. size,

strapped, plastic shrink-wrapped, and warehoused for

delivery to ﬁllers.

A recent innovation in tinplate can manufacturing is

simply known as shaping. It was developed in the 1970s.

The process consists of placing a cylindrical can in a metal

mold and then pressurizing it with about 1 160 psig (80 bars)

of nitrogen (or puriﬁed compressed air) to create a can with

the shape of the mol d. This process remained dormant for

20 years, to some extent because the process was expensive.

The method has been improved upon and is now commer -

cialized. Today a relatively large number of aerosol cans are

shaped, especially those made of aluminum. One reason for

shaping relates to the increasing duplication of U.S . product

labels by ﬁrms in foreign countries . The use of shaped cans

has corrected the problem for now since forgien can-makers

do not have the technology. As an example, the WD-40

Company has collected 380 cans of foreign-made specialty

lubricants, many of which have patterned their labels and

product claims on WD-40 aerosols, They have now changed

to shaped cans.

Another innovation dating back to the 1970s involves

the development of a compartmentalized tinplate aerosol.

The initial product consisted of a 52-mm 149-mm aerosol

can into which a ﬂuted collapsible polyethylene bag was

inserted before the base section was attached. The tubular

chimney of the bag protruded through the nominal 1-in.

can opening and then it was gently heated and ﬂared

around the can bead. The aeosol ﬁller poured the concen-

trate into the bag, almost ﬁlling it but leaving a little space

for the insertion of the valve. After the valve was crimped

into place, isobutane was added through the bottom hole

and into the space between the can and the bag. With the

isobutane exerting a constant squeezing pressure in the

bag of the concentrate, the product would be dispensed

when the valve was actuated regardless of the can posi-

tion. In this fashion the dispenser could extrude such

products as honey, jellies, ointments, and so on. This

process was expensive and languished until S. C. Johnson

& Sons, Inc. developed a unique gelled shave cream

concentrate that contained 2–3% of a weak propellent

blend. When the mixture was dispensed into the hand

and touched with the ﬁngertips, the consumers had the

pleasing experience of generating their own foam. The

company patented their invention and marketed it under

the ‘‘Edge’’ brand. By 2006, the compartmentalized shave

creams captured over 62% of the market despite their

higher price.

Aluminum

Aluminum cans, which constituted about a 18% of the U.S.

market in 2006 (and growing), are made quite differently.

Pure (99.70%) aluminum slugs or pucks are lubricated

with zinc stearate in a tumbler and are then conveyed to

an extruder, where they are formed into a ‘‘cup.’’ The cup

may be drawn and ironed (draw–ironed), in some ad-

vanced operations, to obtain a more uniform wall thick-

ness and lighter structure. After trimming and vigorous

cleaning, the lining and exterior decoration coatings are

applied. The top is then formed in a number of stages (the

number increasing with can diameter) and ﬁnally convo-

luted into either an outside or inside curl conﬁguration.

The outside curl is more common. Both have different

advantages. Curl machining is sometimes done to smooth

the curl surface of larger-diameter cans. Finally, they are

strapped into typically 96-pack hexagon shapes and

loaded onto 40-in. 44-in. wood pallets. After strapping

and shrink-wrapping, they are ready for delivery. Table 1

gives some details on aluminum aerosol cans.

Table 1. General Information on Aluminum Aerosol Cans

. Most common diameters: 22, 25,35, 38, 45,50, 55, 59, and 66 mm.

. Largest size is 66 235 mm. Overﬂow capacity is 709 mL. (Typical use: Saline rinsing solution—sterile.)

. The 22- and 35-mm cans require valves with 20-mm-diameter ferrules.

. Since aluminum cans are nonmagnetic, most production lines have ‘‘puckers’’ and ‘‘de-puckers.’’ The pucks must be ordered for each can

diameter.

. Aluminum cans of 45- to 66-mm diameters must use valve with ‘‘lathe-cut’’ rubber cup gaskets, generally Buna-N. (With over 10% DME,

use butyl or cholorbutyl.)

. The 38 97 mm is (more or less) standard for laboratory samples. (Fills can be 2 oz.)

. Tare weights in a lot of aluminum cans are quite constant as compared to tinplate or steel.

. Aluminum can corrosion can create hydrogen, but very rarely. This overpressurizes the can.

. The passivity range for aluminum is about pH = 4.3 to 8.2 (251C).

26 AEROSOL CONTAINERS

Other

Very small numbers of cans are made by other methods.

The Sexton Can Company produces one-piece steel cans

by an extrusion process. For larger diameters, they ex-

trude a steel shell, and then double-seam a can bottom to

it. The company is able to make very strong cans by this

process, able to withstand pressures up to 650 psig (lb/in.

gauge) (45 bars). They are used to pack such higher-

pressure products as HCFC-22 refrigerant, which gener-

ates 302 psig at 1301F (21 bars at 54.41C). A special permit

from the U.S. DOT (Department of Transportation) is

required for such high pressures. As part of the develop-

ment process, Sexton learned how to produce these cans

with a bottom indentation, able to open at about 425 psig

(30 bars) and thus long before heating could cause burst-

ing. The oriﬁce lets the product come out with a fair degree

of control; otherwise, the dispenser might eventually burst

with the brissance and concussive effects of a grenade.

TINPLATE OPTIONS

The electrotinplated steel sheet stock from the tin mill is

available in a modest variety of plate thicknesses and tin

coating weights. The steel for aerosol cans will typically be

B0.007–0.015 in. (0.18–0.38 mm) thick, according to in-

tended use. The thinnest plate is used for bodies of small

(45 to 52-mm)-diameter cans. The bodies of larger cans

(57–76 mm in diameter) will typically be made from 75

to 85-lb ETP, which is a can-making term for stock of

B0.0083–0.0094 in. (0.21–0.24 mm) thick. Tops and bot-

toms require still heavier plate, to prevent premature

buckling (eversion) and subsequent unwrapping of the

top or bottom double seam, leading to a burst event. End

sections of the smaller cans typically use 112-lb ETP, or

plate that is 0.0123 in. (0.31 mm) thick. The largest-dia-

meter aerosol can is a nominal 3.00-in. (76-mm) size and

requires 135-lb ETP, or 0.015-in. (0.38-mm)-thick plate.

Valve cups are almost always made of 95-lb ETP [e.g.,

0.0105-in. (0.266-mm) plate].

Since aluminum is notably softer and more deformable

than steel, these cans are extruded to have thicker metal.

The thickness must be increased as diameters are made

larger. The thinnest part of a typical 52-mm-diameter

aluminum aerosol can will be about 25% up on the body

wall, measuring about 0.017 in. (0.43 mm). The base

of the largest aluminum can (66 mm) may easily get to

0.080 in. (2.0 mm). Aluminum valve cups average 0.016 in.

(0.41 mm) thick.

In the past, tinplate could be ordered with very heavy tin

coatings: up to 1.35 lb of total tin weight per basis box area

of 31,360 in.

on each side. This is equivalent to a tin coating

of 15.1 g/m

on each side. But today, with economic con-

siderations forcing lower inventories , plus improvements in

the tinplating process, it is rare to see tinplate of greater

than 0.50 lb—that is, 5.6 g/m

per side. Some tinplates are

made with the so-called ‘‘kiss of tin’’ (0.05-lb ETP) having a

nominal coating weight of only 0.56 g/m

per side. The

thickness then averages only 0.00000303 in. (0.077 mm) per

side. The dark gray color of the steel and F eSn

alloy layer

can be easily seen through this ultrathin coating.

With electrotinplating methods it has been possible to

obtain differentially coated tinplates; that is, plate having

coatings of different thickness on each side. For example,

D50/25-lb ETP (more accurately noted as D0.50/0.25-lb

ETP) will carry 0.25 lb of tin on one face and 0.125 lb of tin

on the other (5.6 + 2.8 g/m

). This type of plate is generally

used with the heavier tin-coated area turned toward the

aerosol product, to provide corrosion protection.

Linings

Over half of all tinplate aerosol cans and virtually 100% of

all aluminum cans have organic linings. Single linings

are the most common, but double linings and (for a few

tinplate can bodies) even triple linings can be ordered. A

variety of lining materials are used. The most common are

the epoxyphenolics, used for about 70% of tinplate cans

and around 78% of aluminum cans. Other options include

the vinyl organosols, polyamideimide (PAM), and now the

polyimideimide (PIM). The PAM and PIM coatings are

relatively costly and often more difﬁcult to apply, espe-

cially on tinplate. They are extremely resistant to permea-

tion. Finally, there are the pigmented epoxyphenolics and

the vinyls. The latter do not adhere well to metal sub-

strates, and are used as a second or top coating, when

extra performance is needed. They are unaffected by

water, but quickly dissolved by methylene chloride, oxy-

genated solvents, and certain other solvents.

Corrosion inhibitors should be considered whenever

aqueous solutions or dispersions are packed in tinplate.

Typical inhibitors include sodium nitrite, sodium benzo-

ate, and various amines.

Can decorations are a very valuable sales tool. They

must always be the correct color and not affected by body

contouring, consumer use or product spillages. The lining

is often critical as a means of assuring product purity and

dispenser shelf life. Table 2 gives data on the surface

coatings (or linings) process for aluminum aerosol cans.

Size

The can-making industry has strived for uniform dimen-

sions of cans, both from different plants of a given supplier

and between suppliers. This acts to save ﬁllers from

making time-consuming adjustments to crimping and

gassing machines when moving from one lot of cans

to the next. The CSMA (Aerosol Division) Commercial

Standards Committee has now developed about 13 key

dimensions and their tolerances for tinplate cans—both

standard and necked-in—and about 10 more for alumi-

num cans (see Figures 1 and 2).

The smallest tinplate can is 112 214 (45 72 mm)

size, holding 101 mL. Aluminum aerosol cans are known

in sizes down to 13 26 mm and posibly smaller. The 13-

mm size is used for such products as metered dose

inhalants (MDIs), breath fresheners, and pepper sprays

(which attach to key chains). These tiny aerosols require a

13-mm ferrule-type aerosol valve.

The terminolgy used to designate tinplate can sizes

is never used for aluminum aerosol cans, which are

always described in the metric system. For tinplate, the

AEROSOL CONTAINERS 27