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

Подождите немного. Документ загружается.

tempered steels and their aerosol canmaking used are

illustrated in Table 1.

The thickness and temper of aerosol canmaking plate

must meet certain general guidelines. However, there are

considerable variations between canmakers, regarding

selection. The data presented in Table 2 can be considered

as indicative only.

The plate for aerosol can bodies begins with multistage

hot rolling, down to a thickness of about 0.10–0.06-in. (2.5–

1.5 mm). The plate is then cold-rolled (temperature below

B5001C) into a thickness range of B0.0014–0.0065 in.

(0.036–0.017 mm). It is then annealed. This produces

‘‘CR,’’ or cold-reduced plate of the desired temper. CR

plate is still widely used in can bodies. To make ‘‘DR,’’ or

Table 1. Tempers of Electrotinplated Steel (USA)

Temper Number Hardness Range

Aerosol Canmaking Applications

1 46–53 No longer used

2 50–56 Not used for aerosol cans

3 53–60 Sometimes used for can domes

4 58–64 Used for can bodies and commonly used for can domes

4-CA 54–68 No longer used for aerosols

5 62–68 Some slight use for can bodies

5-CA

62–68 Used for can bases; some bodies

6 67–73 Now obsolete for aerosols

DR-7 72–76 Minor use for can bodies

DR-8 N/A Used for most can bodies

DR-9 N/A Not used

DR-10 N/A Not used

5-CA is the successor to the ‘‘TU’’ plate of 1950–1985.

Rockwell tester; R30 T range. Not applicable to DR-8, DR-9, and DR-10 plates, since the hardened ball pierces the tough, stiff plate before forming a

depression. The preferred method for testing DR plate is by tensile strength. DR-9 and DR-10 are used for three-piece steel beer and beverage cans. Some

aerosol testing is in progress. Tempers are inapplicable to impact-extruded and impact-extruded drawn-and-ironed shells.

Table 2. Thickness and Temper for Tinplate Used for Aerosol Cans

Weight per Base Box, lb (kg)

Average Thickness, in.

(mm)

Typical Temper

Designation

Typical Application

Component Can Diameter (mm)

55 (25) 0.0061 (0.155) DR-8 Body 202 (54)

65 (29) 0.0072 (0.183) DR-8 Body 207.5 (62.7)

70 (32) 0.0077 (0.196) DR-8 Body 211 (68.3)

70 (32) 0.0077 (0.196) T-5 Body 202 (54)

75 (34) 0.0083 (0.211) DR-8 Body 300 (76.2)

75 (34) 0.0083 (0.211) DR-8 or T-5 Body, DOT Speciﬁcation

202, 207.5, 211 (54, 62.7,

68.3)

80 (36) 0.0088 (0.224) DR-8 Body 300 (76.2)

85 (39) 0.0094 (0.239) DR-8 Body, DOT Speciﬁcation

202, 207.5, 211 (54, 62.7,

68.3)

Body, DOT Speciﬁcation

300 (76.2)

90 (41) 0.0099 (0.251) T-5 Body, including DOT

Speciﬁcation 2P

300 (76.2)

107 (49) 0.0118 (0.300) T-5 Bottoms 113, 202 (30, 54)

112 (51) 0.0123 (0.312) T-5 Bottoms 207.5 (62.7)

112 (51) 0.0123 (0.312) T-3 Domes 202 (54)

118 (54) 0.0130 (0.330) DT-2 Domes 207.5 (62.7)

123 (56) 0.0135 (0.343) T-5 Bottoms 211 (68.3)

128 (58) 0.0141 (0.358) T-3 Domes 211 (68.3)

128 (58) 0.0141 (0.358) T-5 Bottoms, including DOT

Speciﬁcation 2P

211 (68.3)

Bottoms 300 (76.2)

135 (61) 0.0149 (0.378) DT-2 Domes, including DOT

Speciﬁcation 2P

300 (76.2)

Domes, including DOT

Speciﬁcations 2P and 2Q

211 (68.3)

135 (61) 0.0149 (0.378) T-5 Bottoms, including DOT

Speciﬁcation 2P

300 (76.2)

202 ¼ 2

in: (54-mm) dia, etc.

1018 PRESSURE CONTAINERS

double (cold)-reduced plate, one starts with CR plate that

is B0.018–0.013-in. thick. Having annealed it, the stock is

again cold-reduced, up to 50% in one pass, to produce

tinplate with a thickness range of B0.0094–0.0065-in.

This corresponds to 85–60-lb DR tinplate—the gauges

normally used in can-body constructions. The advantages

of DR plate are that B10–12% less weight can be used,

compared to CR plates, while retaining the same strength.

The lower apparent cost is offset by the higher manufac-

turing cost of the plate (since another operation is in-

volved), a very slightly higher scrap rate, and sometimes a

bit more variability in the double seams.

DIMENSIONS

The size of tinplate aerosol cans is still described as the

diameter across the double seams, multiplied by the

height from the base to the top of the top double seam.

These designations nearly always have three digits, un-

less the can is extremely tall. The ﬁrst is the inch value,

and the next two are the number of

in: increments

added. Thus the over-the-seams diameter of a standard

(non-necked-in) 202-diameter three-piece can would be

2.125-in. This corresponds to 53.99 mm, but this can be

misleading, since the International Organization for Stan-

dardization (ISO) utilizes the inside diameter of the can

for ‘‘can diameter,’’ and in this case their ﬁgure (expressed

to the nearest millimeter) is 52 mm.

A selection of commercially available, standard

(straight-wall) three-piece cans is shown in Table 3.

Several can diameters are now available in the necked-

in style that are not available in the older, straight-wall

can (e.g., 113, 205, and 214). The diameter over the top

double seam is less than the diameter of the can body, and

this has led to a curious nomenclature, where the top-

seam diameter is described, followed by that of the can

body, and then the height over the double seams. For

example, the smallest three-piece tinplate can is described

as a 111/113 214 container, and the largest is a 211/

214 1006 can. The necked-in cans are more aesthetically

pleasing than the standard or straight-wall types. They

are also lighter. Because there are no protruding double

seams, they ﬁt into slightly smaller corrugate or tray/

shrink-wrap shippers. An idea of the diverse necked-in

can sizes can be seen from Table 4.

Construction and Linings. See the article on Aerosol

containers.

PRESSURE RESISTANCE

The 701F pressure range of aerosols is generally about 20–

142 psig (320–1100 kPa), although most fall in the 30- to

100-psig (360- to 791-kPa) range. However, all aerosols

having a capacity of more than 4.00 ﬂ oz (118.2 mL) are

regulated by the DOT Dangerous Goods Transport Tariff.

Cans are divided into four groupings. The ‘‘nonspeciﬁca-

tion’’ can may be used for products having pressures of

r140 psig (9.66 bars) at 1301F (54.41C). They must hold

the product, when heated to 1301F, without leakage or

permanent distortion and must also tolerate a pressure

one and one-half times that high without bursting. This

can probably account for 85% of all steel aerosol-can sales.

The ‘‘DOT Speciﬁcation 2P’’ can may be used with

aerosols having pressures as high as 160 psig (11.03

bars) at 1301F (54.41C), but must satisfy several require-

ments. They must not distort at 160 psig and must not

burst below 240 psig (16.55 bars). They must have a

minimum plate thickness of 0.007-in (0.0178 mm) and be

imprinted with both the words ‘‘DOT-2P’’ and the regis-

tered canmaker’s logo. One can in 25,000 must be pres-

sure-tested to destruction to prove strength. Some

canmakers reduce plate inventories by offering the same

can speciﬁcation for ‘‘nonspeciﬁcation’’ and ‘‘DOT Speciﬁ-

cation 2P’’ containers; they simply omit the imprints and

destructive testing in the case of ‘‘nonspeciﬁcation’’ cans.

The third grouping consists of ‘‘DOT Speciﬁcation 2Q’’

cans. They can be used with products having pressures of

r180 psig (12.41 bars) at 1301F. The cans must tolerate

180 psig without deformation, and they must withstand

270 psig (18.62 bars) without bursting. The minimum

plate thickness is 0.008 in. (0.203 mm). Finished cans

must be imprinted with the word ‘‘DOT-2Q’’ and the

registered logo of the can supplier. One can per 25,000

must be destructively tested, and results must be main-

tained on ﬁle. These cans are about 12–15% heavier than

‘‘nonspeciﬁcation’’ or DOT-2P cans, and their higher prices

reﬂect the added cost of metal. These heavy duty cans

Table 3. Dimensions and Capacities of Standard Three-

Piece Cans

Nominal Size (English) Nominal Size (Metric)

Capacity

(mL)

202 214 52 73 147

202 314 52 98 192

202 406 52 111 226

202 505 52 135 270

202 509 52 141 290

202 700 52 178 367

202 708 52 191 391

207.5 413 57 122 332

207.5 509 57 141 389

207.5 605 57 160 452

207.5 701 57 179 498

207.5 703 57 183 508

207.5 708 57 191 527

207.5 713 57 198 541

211 410 65 117 396

211 503 65 132 438

211 600 65 152 499

211 604 65 159 522

211 607 65 164 539

211 612 65 171 567

211 710

65 194 648

211 713 65 198

657

211 908 65 241 796

211 1008 65 266 872

300 709 73 192 796

Metric measurements are by ISO convention.

Capacities are on a brimfull basis. Subtract about 3 mL for crimped cup

volume.

PRESSURE CONTAINERS 1019

represent 2% of the market. They must carry the DOT 2 Q

words along with the registered logo of the manufacturer.

The ﬁnal grouping is the ‘‘DOT special exemption’’ can.

For the express purpose of approving (a) whipped creams,

(b) HCFC-22, and (c) HFC-134a, the DOT has issued

exemptions allowing certain cans to be shipped with pro-

ducts whose 1301F (54.41C) pressures exceed 180 psig (12.41

bars). The whipped-cream can is a ‘‘DOT Speciﬁcation 2Q’’

container, but ﬁtted with a pressure-relief mechanism

(PRM) on the top of the top double seam, which effectively

prevents the can from bursting at excessive pressures by

venting the contents in a controllable fashion. This can may

hold whipped cream (only) at pressures of r210 psig

(1.55 MPa) at 1301F(54.41C). Such aerosols have a number

of product advantages over those packed at lower internal

pressures. The DOT also considered that these cans are

shipped, stored, and used under refrigeration, making the

chance of heat-generated deformation de minimus.

HCFC-22 (CHClF

) has a pressure of 301 psig

(2.19 MPa) at 1301F (54.41C). It requires a very heavy

can to safely hold it. The Sexton Can Company produces a

two-piece can, with a base-centered pressure-relief attri-

bute that can do so. Here there is no double seam. The ﬁrm

developed various designs that are stamped into the can

base, before it is double-seamed to the shell segment.

These designs are often in the form of about 3351 degrees

of a circle, perhaps 10 mm in diamter. The tinplate is both

thinned and work-hardened there so that when the base

buckles under excessive contents pressure, the stamped

area will fracture and lean outward so that the product

can safely escape.

No exemptions have been made for aluminum cans

because their bottoms are too variable in thickness to

permit a relief mechanism to be incorporated.

The United States is virtually alone in requiring mini-

mum plate thicknesses for speciﬁcation aerosol cans. Some

nations, such as Mexico, have no pressure regulations. The

European Union members use the 12-, 15- , and 18-bar

can. For example, the 18-bar can may be used to contain

aerosols having pressure to 12 bars at 501C and must not

burst below 18 bars (261 psig). For many products, this

pressure limit is equivalent to 13.9 bars at 54.41C (202 psig

at 1301F), although the can has a lower burst pressure

than the DOT Speciﬁcation 2Q. This permits the 18-bar

can to hold such products as HFC-134a, which in the

United States would require a DOT exemption. Currently,

the United Nations is asking the U.S. DOT to revise their

criteria to match those of Europe and Japan, among others.

In Europe, the Federation of Aerosol Associations is peti-

tioning the EU to establish a 2-bar extra-strength can,

which would be useful for the improvement of formulations

pressurized with nitrogen or compressed air.

ALUMINUM CANS

Aluminum cans have been available since at least 1948.

Historically, they have almost always been of one-piece

(monobloc) construction, and this is the only type cur-

rently made in North America—although one ﬁrm in

Europe still makes a two-piece specialty can by attaching

an aluminum or tinplate dome to a suitably ﬂanged

aluminum shell section.

United States aluminum can suppliers as of 2007 are

CCL Container Company and the Exal Corporation. Some

pharmaceutical marketers make their own very small

cans—and some are imported.

While the smallest commercial tinplate can is

35 97 mm (86 mL), aluminum cans are made in sizes

down to about 3 mL. At the other end of the size spectrum,

the largest aluminum aerosols are about 66 275 mm

(890 mL).

The essentials of the aluminum canmaking process

involve taking a round slug (billet, or puck) and extruding

it into a ‘‘cup’’ of essentially the same diameter, using a 25-

to 50-ton ram. The top is trimmed to a ﬁxed length, after

which the metal is cleaned and enameled—normally in-

side and outside. The top is then die-formed into a dome

and curl (or bead). The curl engages the aerosol valve—all

‘‘one-in’’ (1-in.) valves and most of the smaller, ferrule-type

valves. The very small 13- and 15-mm-diameter cans may

use noncurl ﬁnishes.

Table 4. Dimensions and Capacities of Necked-in Three-

Piece Cans

Nominal Size (English) Nominal Size (Metric) Capacity (mL)

111/113  43/45 

214 73 106

312 95 140

410 117 175

508 140 209

608 165 247

200/202  50/52 

214 73 145

314 98 190

406 111 224

509 141 288

514 149 303

700 178 365

708 191 389

711 195 398

202/205  52/57 

410 117 272

604 159 388

607 164 401

701 179 428

704 184 445

710 194 486

802 206 522

805 211 536

207.5/211  60/65 

410 117 395

413 122 419

604 159 518

612 171 563

710 194 647

713 198 671

211/214  65/67 

315 100 346

413 122 480

714 200 766

804 210 802

1006 263 999

1020 PRESSURE CONTAINERS

Aluminum cans have no seams, and thus the linings

can be applied more effectively than on tinplates. Many

formulas, such as the popular mousse types, may be

commercially packed in aluminum without corrosion,

whereas they almost always severely attack lined tinplate

cans. The permeation of water-based solutions through

aluminum-can linings is on the order of 0.1–1.0% as fast as

in the case of double-lined and striped tinplate structures.

The smooth-wall construction of aluminum aerosol

cans permits the insertion of plastic, ﬂoating-type pistons,

so that certain products can be kept ‘‘nonaerated.’’ This is

important for the popular gel-type (postfoaming) shaving

creams and the recently test-marketed toothpaste option,

as well as dozens of other product types. In time, as one-

and two-piece tinplate cans continue their development,

some of this market may go to such containers.

GLASS AND PLASTIC

Historically, glass and plastic-coated glass aereosols have

been restricted for use as containers for colognes, per-

fumes, and pharmaceutical liquids. Unfortunately, the

ﬂammable and bursting hazards, plus cost and a relative

lack of aesthetics, have transferred most of their market to

plain-glass bottles (nonpressurized) containing pump-ac-

tion valves. Then, too, some of their pharmaceutical base

has moved over to aluminum aerosols. As a result, the

glass and plastic-coated glass market is currently very

small, and only a few ﬁllers participate.

There has been a lot of interest in the potential of

certain plastics as aerosol containers. For most of this

time, DOT regulations greatly limited such developments,

since they would not permit the shipment of nonmetallic

aerosols having capacities greater than 4 ﬂ oz (118.2 mL).

Meanwhile, products such as furniture polish, cleaning

preparations, and even hair sprays have been successfully

marketed in Europe and parts of South America—using

biaxially oriented PET plastic. Aside from some minor

concerns about distortion at temperatures over B1221F

(501C), this clear plastic seems almost ideal. Special bases

and shrink-label attributes were needed to hide the often

unappealing aerosol formulation, but these were minor

concerns. Currently, the DOT has canceled their regula-

tions to (a) permit plastic aerosols to be shipped and (b)

reduce hot-water bath testing requirements.

VALVES

An estimated 95% of the U.S. aerosol valves are currently

manufactured by three large ﬁrms: Precision Valve Cor-

poration (PVC, Yonkers, NY), SeaquistPerfect Dispensing

(Division of the Aptar Group) (S/P) (Cary, IL), and Summit

Packaging Systems, Inc. (Manchester, NH). There are

smaller domestic ﬁrms such as the Clayton Corporation

(St. Louis, MO) and Newman-Green, Inc. (Addison, IL). A

few marketers make their own valves, including some of

the drug houses that ﬁll metered-dose inhalant (MDI)

aerosols. Two European-based international valve suppli-

ers have now established sales and technical service

ofﬁces in the U.S., but produce there valves elsewhere.

They are Coster Tecnologie Speciali, s.p.a. (Milan, Italy)

and the Lindal Packaging Group (Germany). The Emson

Research, Inc. ﬁrm, now owned by S/P, specializes in the

production of the ferrule-type valves, including the meter-

spray types. The Majesty Valve Company (China) is said

to be setting up a sales ofﬁce facility in the United States.

The world’s largest valve-maker is PVC, with about 24

plants in 18 countries. They produce about 4 109 valves

per year, or about 34% of the world’s production. Both S/P

and Summit are also international.

COMPONENTS

Modern valves consist of six to seven components:

Actuator (sprayhead or foam spout)

Valve stem

Stem gasket

Body (housing or spring cup)

Spring

Mounting cup

Dip tube

These will vary according to the type of valve. Perhaps the

simplest valves are the Clayton and ReddiWhip types,

which consist of a very large spout (or stem), a large

rubber gasket, and a mounting cup. Since these valves

have no dip tube, the can must be inverted before pressing

the stem sideways to extrude the product.

In the Newman–Green and other ‘‘female’’ valves the

actuator and stem are molded on one piece of plastic (see

Figure 1). There is a terminal oriﬁce, often provided by a

nylon insert, and a stem oriﬁce that consists of slots in the

hollow sidewall of the stem section. This design has

several advantages. One basic valve can be tested with

up to about 100 actuator/stem combinations, which is

convenient for formulators trying to get the most desirable

delivery rate and spray pattern. Also, if the valve plugs,

the actuator/stem can easily be pulled upward and sepa-

rated from the rest of the valve, so that it can be washed

free of such things as paint pigments, starch powders, and

possibly any extraneous textiles, cardboard ﬁbers, or other

detritus. The valve can then be reassembled.

Stems

Most valves have separate stem components. The stem

ranges from about 3.18 to 3.96 mm (0.125’’ to 0.156’’) in

outside diameter; and it protrudes different distances

from the top of the mounting cup pedestal, which sur-

rounds the lower half. Depressing the stem will serve to

operate most valves, but a particular type of stem may be

pressed sideways to gain the same effect. Such valves are

commonly

called tilt-action or

toggle action. Note that

‘‘Toggle Action’’ is a registered trademark of the Seasquist-

Perfect Dispensing ﬁrm. These valves have several ad-

vantages. The large slanted ﬁnger-pad on the actuator

provides good spray directionality, even if one operates the

PRESSURE CONTAINERS 1021

valve in poor lighting conditions, or in the case of poor

eyesight. The button also requires only about 0.6 kg

(1.32 lb) of ﬁnger force to operate, whereas the vertical

sprays may require as much as 3 kg. (6.6 lb). This feature

makes the valve popular with beauticians and others who

must operate it frequently. The valve is somewhat sensi-

tive to formulations that contain solids or which have

solvents able to swell the components unduly. In such

cases the vertical valves may be preferred.

The vertical-acting (reciprocating or up-down) ‘‘male’’

aerosol valve is the most popular type. It is relatively

simple and trouble-free. The valve can be ﬁtted with a

variety of large spray-heads, spray domes, or spouts, each

with comfortable ﬁnger pads, and these aesthetically

pleasing ﬁtments are a major factor in its relative popu-

larity. When the stem is pressed downward sufﬁciently,

the stem oriﬁce, normally above or against the stem

gasket, slides to a position below the stem gasket, thus

opening a small hole through with the pressurized product

can pass up the dip tube, through the valve body, past the

stem oriﬁce and into the actuator, from which it then is

delivered as either a gas, spray, foam, gel or liquid stream.

Most often, it is as a spray. Figure 2 is an exploded view of

the two most popular valve designs. Male valves are

characterized by having stems that are separate from

the actuators. Figures 3 and 4 give a more detailed view

of these valves.

Body/Spring

The valve body, or housing, contains a SS-302 spring that

acts to close off the valve when the ﬁnger pressure is

released. This is a major safety feature. It may also carry a

tailpiece oriﬁce and often a vapor-tap oriﬁce. The tailpiece

oriﬁce is often not an oriﬁce at all, but instead a 1.57- to

2.03-mm (0.062- to 0.080-in.) hole in the end of the dip

tube to protrude into the head space, then only gas will be

emitted. A number of corrective steps have been taken,

over the years, to resolve this problem. The ﬁrst was to

place a directional dot (typically using a black ‘‘Magic

Marker’’) on the crown of the mounting cup, to indicate

the curvature of the dip tube, and then align the actuator

to it. In that way the end of the dip tube would always be

in the lowest position when the can is tilted (see Figure 5).

Another method was to use a so-called ‘‘Jumbo dip tube,’’

where the typically 7.25 mm (0.285 in.) inside diameter dip

0.297 ± 0.010 in.

(7.54 ± 0.25 mm)

0.064 ± 0.015 in.

(1.63 ± 0.38 mm)

0.0260 ± 0.015 in.

(6.60 ± 0.38 mm)

0.140 ± 0.007 in.

(3.56 ± 0.18 mm)

0.305-in. max dia

(7.75-mm)

Spring

Spring cup

1.278-in. dia

(32.46-mm)

0.513-in. (13.0-mm) max

0.440 in. (11.2 mm)

0.442-in. dia

(11.23-mm)

Various

terminal

orifices

Actuator

Mounting

cup

Cup

gasket

Lathe-cut

Cup gaske

Dimples

Circular

orifice

diameter

Vapor-tap

orifice

Body

Dip tube

Body orifice

1.013-in. (25.73-mm) equiv. dia

circumscribin

3 dimples

0.991-in. dia

(25.2-mm)

0.370 in.

(9.40 mm)

Figure 1. Cross section of female valve.

1022 PRESSURE CONTAINERS

tube could hold up to about 8 g of product. In this case the

can could be inverted and operated for several seconds

before the dip tube emptied and gas began to come out.

This is a preferred option for disinfectant bathroom

cleaners.

Another method is the ‘‘Spray Any Way’’ valve, where

a 1.00-mm (0.039-in.) stainless steel ball is placed in a

tiny runway. When the can is inverted the ball travels to

the opposite end of the runway and seals off the oriﬁce

served by the dip tube, while opening one at the valve

body. Liquid product then ﬂows directly into the valve

body, allowing the aerosol to function normally. This

unit is an accessory that attaches to (or is made a part

of) the valve body. The cost of the valve is increased

accordingly.

The ﬁnal approach is to use a compartmentalized

aerosol package. In this case, one can select one of three

versions: a piston can, a bag-on-can, and a bag-on-valve.

Most generally, the propellant is separated from the

product, being gassed into the ‘‘exo-space’’—under the

piston, or around the bags—so the product is continually

squeezed and emerges as such when the valve is operated.

Products of this type include cheese spreads, caulking

compounds, and sunscreens. In some cases a small

amount of low-pressure gas (typically 90% isopentane

and 10% isobutane) is pre-mixed with a gelled aerosol

product. When these products are used, the gel emerges

through a foam-type spout. It is generally both clear and

tinted blue or green. Upon stirring with the ﬁngertip, the

positive yield point of the gel is reduced so that the

dispersed propellant can form a nice white puff of foam.

This type of product has now captured the bulk of the

shave cream market, with sales of over 200 106 cans per

year in the United States during 2006.

Mounting Caps

The vast majority of aerosol valves are supplied in nom-

inal ‘‘one-inch’’ (25.4-mm) mounting cups. These cups are

designed to ﬁt into the nominal ‘‘one-inch’’ hole of aerosol

cans. A crimping operation is then used to hermetically

seal the valve cup to the can. An elastomeric gasket is

required in order to obtain good sealing, since metal-to-

metal interfaces will always leak. In the past, the industry

used a ‘‘Flowed-In’’ neoprene gasket, but this has almost

totally disappeared worldwide, in favor of alternative

gaskets. There are now three gasket choices: the 1.0- to

1.15-mm (0.039- to 0.045-in.) thick lathe-cut gasket, of

buna, neoprene, or butyl rubber; the 0.356-mm (0.014-in.)

thick PE-Sleeve; and the 0.203-mm (0.008-in.)-thick PP-

laminate. The last two gaskets must ﬁt between the

vertical wall of the valve cup and the can bead, which

means that the metal valve cups must be downsized

accordingly. If the typical wall diameter of a valve with a

PE-Sleeve is to be 25.25 mm (0.994 in.), then the mounting

cup itself must be 24.54 mm.(0.966 in.).

Mounting cups are made of different proﬁles (ﬂat,

conical, and cone-conical) and from different metals (tin-

plate, heavier tinplate, and aluminum), according to spe-

ciﬁc requirements that relate to product pressure,

corrosion aspects, and so on. The usual tinplate-mounting

cup is about 0.267 mm (0.0105 in.) thick, while those of the

softer aluminum metal are about 0.406 mm (0.0160 in.)

thick. The heavy-duty, thicker tinplates are reserved for

high-pressure aerosol formulations, including most of

those based on U.S.DOT exemptions. Mounting cups

with ﬂat bottoms often distort slightly, becoming more

conical, during the hot water-bathing of aerosols during

production, when pressures usually get into the 8.27- to

12.41-bar (120- to 180-psig) range. This sometimes poses a

problem, where a plastic ﬁtment, such as a large spray-

head or spout, may have to ﬁt onto both the mounting cup

(for attachment) and the stem (for actuation). The conical

valve cups do not deform appreciably in this manner and

are generally preferred. In fact, some valve-makers no

longer offer the ﬂat-bottomed mounting cups.

The hermetic seal between valve cup and can is accom-

plished by the use of a crimping machine. They are usually

rotary devices, where an eight-segment collet descends to

a precise depth, after which a mandrel spreads the eight

tines to a precise circumscribing diameter. This action

compresses the gasketing material and creates the seal.

For the popular combination of a tinplate aerosol can and

a tinplate valve with a PP-laminate, the preferred crimp-

ing dimensions are: diameter 27.27 mm (1.074 in.) and

depth 4.65 mm (0.183 in.). These will vary slightly, accord-

ing to the type of can and valve cup. The usual tolerance is

only 70.13 mm (0.005 in.) and the range for a given can

should not exceed 0.178 mm (0.007 in.).

The effectiveness of the crimping operation is checked

during hot water -bathing, after the can has passed through

the gasser and been pressurized. If bubbles of gas are seen

through the hot water, the can is extracted and discarded.

Actually, cans leaking gas at rates of less than about 12 g

per year produce gas bubbles so infrequently in the hot

water bath that they are not detected by the operator.

Vertical male type Tilt-action type

Figure 2. Exploded view of aerosol valve components.

PRESSURE CONTAINERS 1023

Dip Tube

The aerosol valve will generally have a dip tube, unless

the can is designed to be used in the inverted position,

such as whipped creams and the various mousse products.

Also, for compartmentalized aerosols, there is no need for

a dip tube, since the product is squeezed up against the

valve regardless of can position.

Dip tubes come in essentially three sizes: capillaries,

regular, and ‘‘jumbo.’’ The capillary tubes are inserted into

the valve body tailpiece, while the larger tubes are

stretched over the body tailpiece. Some tailpieces are

designed with encircling barbs, which look like ﬁsh hooks

in cross section. They hold the polyethylene dip tubes so

ﬁrmly that they stretch before they can be pulled off. This

feature is used most frequently for those high-solvent

aerosols (such as paints) that tend to swell dip tubes so

that their connection with the valve body is loosened. On

the other hand, the capillary dip tubes, which are gen-

erally made from either polypropylene (PP) of an alloy,

such as PE/PP, tend to swell more than the nylon or delrin

valve bodies when in contact with strong solvents. This

makes their connection even tighter. Capillary dip tubes

are now often used for products such as air fresheners and

water-based insecticides, which form large layers of pro-

pellant (top) and concentrate (bottom) upon standing for a

few minutes. If a regular diameter dip tube were to be

used, when the can is shaken just before use, the main

product would be redispersed, but that in the dip tube

would tend to remain layered. In such cases the ﬁrst

product out of the aerosol would be the propellant, fol-

lowed by the concentrate and then followed by the disper-

sion of both. The very small internal volume of the

capillary tube minimizes this effect, and the valve gen-

erally also has a vapor tap oriﬁce, which serves to help

spray the tiny bit of concentrate. Also, the vapor-tap

allows the contents in the dip tube to drop back down to

the liquid level in the aerosol, after it is used. This further

reduces the layering problem, so that it is never noticed by

the consumer.

Actuator

The ﬁnal valve component is the actuator. It is often the

most critical. Originally, all actuators were small and had

either straight bore, outward ﬂaring, or inward ﬂaring

Stem

Stem orifice

High-retention stem

0.260 ± 0.015 in.

(6.60 ± 0.38 mm)

0.441 ± 0.010 in. dia

(11.2 ± 0.25 mm)

0.135 ± 0.007 in.

(3.43 ± 0.18 mm)

0.074 ± 0.015 in.

(1.88 ± 0.38 mm)

0.234 ± 0.020 in.

(5.94 ± 0.51 mm)

Valve cup

Typical gasket

Dimples

Stem gasket

Spring

Body

Vapor tap orifice

Body orifice

Dip tube

1.278-in. dia

(

32.46-mm

)

0.993-in. dia

(25.2-mm)

0.965-in. dia

(24.5-mm)

0.370-in. max dia

(9.39-mm)

0.355 in.

(9.02 mm)

0.536 in.

(13.6 mm)

0.130-in. dia

(3.30-mm)

Various

terminal

orifices

0.455 in. dia

(11.6 mm)

0.395-in. dia

(9.91-mm)

Actuator

0.450 in.

(11.4 mm)

Figure 3. Aerosol valve: ‘‘one-inch’’ cup, vertical action, ‘‘male’’ type.

1024 PRESSURE CONTAINERS

(reverse taper) oriﬁce designs in various diameters. While

these are still available, many are now of the mechanical

break-up (MB-U) design. These ﬁrst came to the market in

1953, on cans of BonAmi Glass Cleaner. They utilize the

swirling action caused by directing the liquid product

through (typically) four tangential channels that feed a

central straight-taper or reverse-taper terminal oriﬁce.

Most aerosol emerge from cans at speeds of about

6.1–9.2 m/s. (20–30 ft/s), so it follows that the product

revolutions per minute within the terminal oriﬁce is

extremely high. The centrifugal force is correspondingly

high in the emerging stream, which causes it to break up

into a spray. By controlling the length of the terminal

oriﬁce (land), its diameter, and other aspects, sprays can

be created with varying conical shapes, delivery rates, and

other features. Mechanical break-up valves are usually

made by adding an insert disc to the main structure of the

actuator. The discs are of nylon and ﬁt very snugly into the

actuator opening. This is the only way to provide the

necessary channels and swirl chamber. For spray unifor-

mity, all the key dimensions must be produced with a high

degree of precision.

Another type of actuator is the foam or gel spout. This

usually consists of a single large terminal oriﬁce, but in

some cases an attractive grid may be utilized. The usual

foam spout is operated by pressing downward, although

there are some that must be pressed sideways. They are

always larger than the simple spray actuators.

In recent years there has been a major transition from

small spray-heads and foam actuators to large ﬁtments

that incorporate these components. The ﬁtment may cover

the entire valve cup, or even the entire top of the dispenser.

Quite often they make the inclusion of a cover, or hood,

unnecessary. This is a plus for the consumer, who need no

longer remove and reapply the cover each time the product

is used. There is another marketing aspect. Consumers are

still somewhat reluctant to purchase aerosols, probably

harking back to the ‘‘CFC/ozone’’ issue of the mid-1970s,

and all the bad press that accompanied it. Recently, 61% of

survey responders said they would rather buy a non-

aerosol, if it was just as good as the aerosol. Marketers

have found that consumers tend to identify aerosols by

their characteristic valve cups and perhaps the top contour

0.193 ± 0.020 in.

(4.90 ± 0.51 mm)

0.565 in. (14.35 mm)

[0.607 in. (15.42 mm) crimped]

0.455-in. dia

(11.56-mm)

5°

0.577 in.

(14.66 mm)

Toggle

Valve stem

Valve cap

Typical cup

gasket

Stem

gasket

Pedestal

Valve seat

Housing

Dip tube

Tailpiece orifice

Figure 4. Aerosol valve: ‘‘one-inch’’ cup,

toggle-action type.

Directional dot

Spray

target

Foam

spout

Foam

target

(Palm)

Dip

tube

Remaining

product

Incorrect

curvature

Figure 5. The importance of directional dot on the crown of the

valve cup.

PRESSURE CONTAINERS 1025

of three-piece tinplate cans. By the use of large ﬁtments,

designed to cover up these attributes, the aerosol no longer

appears mildly offensive to some consumers. As a corollary,

since the press condemned ‘‘spray cans,’’ most consumers

think cans that produce foams and gels are not aerosols.

The aerosol valve is a component of almost inﬁnite

variability, when one considers all the parts and all the

variations of these parts. One valve executive calculated

that his company could theoretically produce over

150,000,000 variables, not counting a diversity of dip

tube lengths. Fifty years ago, valves were of very low

quality and almost twice as costly as they are today. Now,

valves are produced with so many online control checks

and manual inspections that their quality is unsurpassed

by any other aerosol chemical or component. They have an

enormous breadth and versatility. For example, their de-

livery rates can be adjusted from 0.24 to 160.00 g/s. Particle

sizes can range from mean diameters of about 2.3 to

125 mm. They certainly do their part in making the aerosol

packaging form the basis for ﬁnely tuned, reliable products.

BIBLIOGRAPHY

General References

M. A. Johnsen, The Aerosol Handbook, 2nd edition, Wayne E.

Dorland Co., Mendham, NJ, 1982.

The Aerosol Guide, 8th edition, The Chemical Specialties Manu-

facturer’s Association, Inc. (CSMA), Washington, DC, 1995; a

10th edition as a CD will be published in 2009.

W. Tauscher, Aerosol Technology (Handbook of Aerosol-Packa-

ging), Melcher Verlag GmbH., Heidelberg/Munich, Germany,

1996 (English edition).

J. J. Sciarra and L. Stoller, The Science and Technology of Aerosol

Packaging, John Wiley & Sons, New York, 1974.

PRINTING: GRAVURE AND FLEXOGRAPHIC

ARTHUR J. TAGGI

DuPont Printing and

Publishing, Wilmington,

Delaware

PETER A. WALKER

Consultant

DuPont Printing and

Publishing, Wilmington,

Delaware

The four main printing processes are as follows: (1)

planography or lithography, (2) intaglio or gravure, (3)

porous or screen, and (4) relief (ﬂexography or letterpress).

In general, the process of printing involves generating two

physically different areas, the printing or image area and

the nonprinting, or nonimage, area. In relief printing,

whether ﬂexographic or letterpress, the image or printing

area is raised above the nonprinting area. Ink is applied to

the raised surface, which is brought into direct contact

with the substrate on which the print is to appear. The

ﬂexographic relief printing process is used to print on a

variety of paper and plastic packaging materials as well as

for some magazines and newspapers, labels, and business

forms. Water-based or solvent inks are used.

The most typical method of intaglio printing is the

gravure process, which uses a nonprinting area that is at

a common surface level while the printing area is recessed,

which consists of wells etched or engraved, usually to

different depths. Solvent inks are transferred to the print-

ing surface, and a metal doctor blade is used to remove

excess ink from the nonprinting surface. Ink is transferred

directly to the substrate. Gravure printing is used to print

long-run magazines, cartons, bags, labels and gift wraps,

as well as plastic laminates, ﬂoor coverings, and even

textiles. Other types of intaglio printing, such as steel

plate or copper-plate printing, use metal plates that are

hand- or machine-engraved or chemically etched to pro-

duce the lines and characters of the printed piece.

Direct printing refers to the transfer of the image directly

from the image carrier to the paper. Most letterpress and

gravure printing are done by this method. In indirect or

offset printing, the image is transferred from the image

carrier to an intermediate rubber-covered blanket cylinder,

from which it is transferred to the paper. Letterpress and

gravure can also be printed by the offset method.

Images are deﬁned for these printing processes in a

number of different ways. The images are produced on a

support by chemical, mechanical, or increasingly by electro-

nic imaging means. As of this writing (c.a., 1996), the

greatest number of plates and images are made by photo-

mechanical methods. These systems are characterized by

photographic images and light-sensitive coatings that, by

using chemical etching or other treatments, lead to the

formation of a printing surface. Increasingly, however, this

printing surface is produced directly by electronic imaging

without the traditional photographic intermediates.

Although four types of commonly used printing exist,

gravure and ﬂexographic printing are widely used in

packaging printing. These methods are considered in

more detail in the remainder of this article.

GRAVURE

The gravure printing process, sometimes called rotogravure,

uses a recessed-image plate cylinder to transfer the ima ge

to the substrate. The plate cylinder can be either chemically

etched or mechanically engraved to generate the image

cells. The volume of these cells determines the darkness

or lightness of the image. If an area is darker, then the cells

are larger; if the area is lighter, then the cells are smaller.

The gravure market can be considered to comprise

three approximately equal segments that are as follows:

publications, packaging, and specialty printing. In pub-

lications, gravure retains a signiﬁcant proportion of the

long-run magazine market. In packaging printing, in

which paperboard and repeat-run cartons are encoun-

tered, gravure is the ideal process. The cylinder lasts

virtually forever, and color consistency is high. The ﬁnal

third of the gravure market is specialty printing of such

items as wallpaper, gift wrap, and ﬂoor coverings.

1026 PRINTING: GRAVURE AND FLEXOGRAPHIC

The fundamental strengths of gravure are that the

process provides consistent color throughout long print

runs, and, because of its ability to apply heavy ink cover-

age, can be used to print high-quality work or to print on a

lower grade of paper than offset lithography while main-

taining acceptable print quality.

In contrast, the primary process disadvantages of

gravure are long lead time, high cost of manufacture for

gravure cylinders, generally long press make-ready times,

and environmental hazards associated with the use of

solvent-based inks. These disadvantages need to be elimi-

nated if the technique is to remain competitive.

The gravure printing process is based around an inking

system that is extremely simple, which provides a high

degree of consistency, particularly with regard to color

printing. This consistency is difﬁcult to match using other

printing techniques. The system, shown in Figure 1, uses

a liquid ink that has traditionally been solvent-based,

although environmental pressures have also resulted in

the development of aqueous-based inks . The environmental

concerns associated with the use of toxic and ﬂammable

solvent inks are being addressed by ink manufacturers,

who are working on the development of water-based

products.

The gravure cylinder sits in the ink fountain and is

squeegeed off with a doctor blade as it rotates. The impres-

sion cylinder is covered with a resilient rubber composition,

which presses the paper into contact with the ink in the tiny

cells of the printing surface . The image is thus transferred

directly from the gravure cylinder to the substrate. Fre-

quently, an electrostatic assist is used to help the ink

transfer from the gravure cylinder to the substrate (1).

Gravure inks are composed of pigment, resin binder,

and—most frequently—a volatile solvent. The ink is quite

ﬂuid and dries entirely by evaporation. In multicolor

printing, where two or more gravure units operate in

tandem, each color dries before the next is printed. This

process is seen as a particular advantage for gravure over,

for example, offset, where the placing of wet ink on wet ink

can lead to inferior print quality. The wet ink on dry and

the simple ink train, together with a long-run-length

capability, have led to the belief that gravure sets the

standard for high-quality printing.

Traditionally, a gravure cylinder was prepared chemi-

cally by using a chemical-etch process. Since the early

1970s, electromechanical engraving, in which a diamond

stylus cuts the cells into cylinders, has become the pre-

ferred approach (2). Newer approaches include laser- and

electron-beam engraving.

In gravure, all elements within the image are screened.

This screening is in contrast to ﬂexographic and litho-

graphic plates, which can contain true solids as well as

halftones.

In the chemical process for preparing gravure cylin-

ders, a light-sensitive ﬁlm, typically gelatin that contains

dichromate salts and carbon black, is exposed ﬁrst

through a gravure screen to establish the cell pattern,

then through a continuous-tone photographic negative,

which hardens the carbon tissue in the light exposed areas

in proportion to the amount of light that passed through

the negative. The exposed tissue is attached to a fresh

copper-plated surface of a gravure cylinder. The unex-

posed gelatin is washed out, and the cylinder placed in a

chemical etching bath that dissolves away the copper

layer in proportion to the thickness of the remaining

hardened gelatin layer, thus creating the ink-carrying

cells. Since the cell pattern is established using a screen

pattern, all cells are the same area, but vary in depth. The

surface of the etched cylinder is then chrome-plated to

impart wear resistance. Gravure cylinders can be recycled

many times by removing the copper layer and replating.

In the case of electromechanically engraved cylinders,

an electronic scanner reads the density of the photo-

graphic negative pixel by pixel, and translates the density

into an electromechanical impulse that drives a diamond

stylus into the soft copper layer of a cylinder. The com-

pleted cylinder is then chrome-plated and is ready for use.

Because of the shape of the diamond stylus, the cells

produced vary both in depth and area depending on how

far into the copper surface the stylus is driven (3).

Electromechanical engraving avoids all the complexity,

hazards, and toxic wastes involved with using chemical

etching techniques, at the cost of increased capital invest-

ment in the engraving equipment. Electromechanical

engraving is a slow process, but this is offset by the ability

to use digital data, which better ﬁts a modern electronic

prepress workﬂow. Newer systems drive the engraving

stylus (or multiple styli for improved efﬁciency) directly

with digital data from an electronic prepress system, or

engrave a cylinder using a high-power laser (4).

FLEXOGRAPHY

Flexography is a variation of letterpress printing used

mainly for packaging applications. It is characterized by

the use of an elastomeric printing plate, fast-drying inks,

and an inkmetering (anilox) roll system. The principal

advantages of ﬂexography are reﬂected in the markets in

which it is most often used. Flexo’ s ability to print on a wide

range of substrates, which include plastic ﬁlms, foils , coated

and uncoated paper, paperboard, and corrugated board,

make it ideal for many packaging uses as well as for printing

continuous patterns, such as w allpaper and gift wrap.

Other advantages include low cost and short cycle time,

the ability to change cylinder diameters to reduce

stock waste, precise ink transfer with minimum on-press

Figure 1. Gravure printing system.

PRINTING: GRAVURE AND FLEXOGRAPHIC 1027