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stopping the ﬁnal draw at an appropriate point, a ﬂange is

left on the can, but as with all metal-forming operations,

the eared and irregular collar has to be subsequently

trimmed. Prior to this, the can bottom, or base, has to be

proﬁled, or paneled (see Figure 8) so as to withstand

processing requirements. All these operations are usually

carried out on multilane, multistage transfer press. Set-

ups have to be coherent with regard to their production

capacity. Each follow-up machine should have a capacity

of 0.5% to 1% in excess of the foregoing one, and controlled

infeed should ensure that no jams occur at stops and

starts of the infeed whereas the machines should not be

stopped. However, because of the critical nature of the die-

trimming operation, separate machines that employ dif-

ferent principles can be used, such as rotary trimmers.

When simultaneously drawing and ironing, it is conveni-

ent to draw the body right through the die to achieve

thickness control in the ﬂange area. In this case, the body

is trimmed and ﬂanged in conventional D&I equipment.

For taller cans, the walls may then be beaded in the usual

machine.

Variants in metal forming equipment are the Metal Box

rotary press line (12) (Figure 13) and the Standun op-

posed-action press. The latter features a split blankholder

with separate pressure controls, which is claimed to

permit greater draw reductions and provide control of

wall thickness through stretching rather than ironing,

which is said to be less severe on the coating. Equipment

of various origins are on the market for small to high

production. More intelligently designed lines are engi-

neered together by canmaking experts on proven presses,

machines, and reliable toolings. Figure 8 represents such

a setup.

COATING

With the exception of three-piece cans for certain pro-

ducts, organic protective coatings are applied to both in-

and/or outside surfaces of the cans. Internally, they pro-

vide a protective barrier between the product and the

metal, whereas externally they may protect from atmo-

spheric corrosion. Outside decoration provides product

identity as well as protection especially if inks are pro-

tected by an overvarnish. Coatings are applied ‘‘wet,’’ i.e.,

the resins are suspended in a carrier for ease of applica-

tion and allowed to coalesce, ﬂow out, or extend for proper

ﬁlm forming. The coating is then baked, stoved, or cured,

according to countries of origin, ﬁrst to remove the carrier,

which may be an organic solvent or a mixture, predomi-

nantly water (waterbased lacquers) and then to polymer-

ize (cure) the resins. The methods of application are in

general commercial use: roller coating in case of sheet

stock or on the outside of two-piece cans and spraying on

the inside of formed bodies. Spraying is predominantly

used for the inside of two-piece D&I cans, but DRD cans

are sometimes sprayed as well. Certain categories of

three-piece cans are sprayed for carbonated beverages or

Figure 13. Rotary press DRD line. 1, Infeed conveyor (for stack of coated sheets); 2, lubricator; 3, sheet feeder, 4, cupping press,; 5 ﬁrst

redraw press; 6, second redraw press; 7, trimming and base forming press; 8, can sampling chute; 9, can conveyor (a tester is usually

inserted here); 10, electrical controls, includes press synchronization; 11, pallet feed; 12, palletizer; 13, layer pads; and 14, master control

station. Courtesy of Metal Box Ltd.

738 METAL CANS, FABRICATION

red fruit cans; the spray is a top coat applied on body-

making and side seam striping, and the material has been

roller coated. Alternative methods of application and

curing are available, such as electrophoretic deposition.

This method is also used widely for repair-coating Easy-

Opening-Ends after conversion, i.e., scoring, riveting, and

securing the pull tab. Drying and/or curing (polymerizing)

are normally carried out by forced convection using hot

air. To a lesser extent, inks and some lacquers are cured by

ultraviolet (UV) radiation, electron-beam curing, infrared,

or high-frequency energy. The most diffused nonconven-

tional inks and lacquers are ultraviolet curing products,

and they permit applications of virtually solvent-free

‘‘wet’’ coatings by conventional means. It requires

the use of specially selected materials amenable to this

form of polymerization, which demand care in storage and

handling and complete polymerization, in the interest of

health and safety. Its attraction lies in the absence of

solvents in difﬁcult environmental situations and extre-

mely short curing times coupled with relatively low en-

ergy demand. It is thus used for high-speed operations or

where space is limited, as for instance between two or

more print color applications (‘‘Interdeck Drying’’).

Powder Coating. When resins are applied ‘‘dry’’ in the

form of ﬁne powder, powder coating is directed in many

cases by creating an electrostatic ﬁeld, which charges the

powder particles on the negative pole for being deposited

by the positive pole; the latter is the element of the can, or

the entire can body, which has to be powder coated.

In three-piece canmaking, it is speciﬁcally the weld and

the weld margin (lacquer-free) area that are coated. The

absence of solvents avoids the otherwise excessive cost

of drying and eliminates the eventual blistering caused

by trapped solvents, which cause porosity or boiling off,

because solvent-based lacquers are applied on too-hot

welds. Curing, which is a simple fusion of the applied

powder layer, is usually done by infrared radiation or high-

frequency induction heating, as hot convected air could

disturb the uncured coating. In many cases, the same

curing ovens are used for powders as well as for lacquers.

Only their length is different, as curing of the different,

products used for side-seam striping need m ore or less

curing time: polyester powder, 8 s; epoxy powders, 10 s;

airspray lacquers, 12 s; airless sprayed lacquers, 14 s; and

roller coated lacquers, 17 s. In case both powder or lacquer

have to be applied, the oven length should ﬁt the longer

curing time. Electrophoretic deposition provides a means

for electrically depositing a resin ﬁlm on a metallic sub-

strate from an acqueous suspension (13). Originally used

at low speed for protecting automobile bodies, it has now

been developed to be applied at can production speeds with

practicable voltage and current demands. Two-piece and

three-piece cans are currently coated on high production

lines on both inside- and/or outside of the bodies. Deco-

rated cans of either type can be washed, without affecting

the prints, and inside coated in the most positive way. A

system of process cells is described in Refs. (14) and (15).

It must be stressed that for food and drink cans, only

the anodic system is applicable. Compared with spray

application, it gives a more even distribution of coating

over the full can wall and base, providing a saving of the

quantity used without sacriﬁcing the required minimum

coating thickness. Its throwing power enables it to coat

regions inaccessible to spray, which is useful for the severe

proﬁles that have to be used to obtain adequate container

strength with a thin plate. The system provides practi-

cally pore-free ﬁlms, and practically near-to-zero milliam-

pere current permeability tests are obtained, even when

particularly severe tests are applied. Electrodeposition

was initially used (American Can Co.) to repair-coat

converted Easy Open ends, thus protecting scores, rivets,

and cut edges of the tabs, as well as other possible

damages to the roller-coated lacquer ﬁlm applied prior to

stamping shells and converting. This equipment is avail-

able on the market as an improved version, which is

offered by CORIMA in Tresigallo/Italy.The thermal trans-

fer of the complete design from printed paper to a plain

coating on the can provides a method of obtaining a high-

quality decoration in two-piece cans if the extra cost is

justiﬁed (16). It is used in the Uunited Kingdom under the

trade name Reprotherm (Metal Box Ltd.) for promotional

designs or single-service beer cans.

COATING EQUIPMENT

Offset Coating. Offset coating is based on the offset

printing principle, whereby a metered quantity of coating

is applied to a rubber or polyurethane covered roller, to be

transferred therefrom to the metal substrate (see Figure

14). In roll coating, metering is accomplished by a series of

steel or rubber rollers that pick up the coating from a

trough and ensure even distribution and weight control

through a combination of relative surface speed and the

pressure or gaps between them. Another method called

gravure coating employs a pattern of cavities etched into a

steel roll, which are ﬁlled as the roll dips into a trough.

The excess is removed, and the precise amount ﬁlling the

cavities is then given up to the transfer roll for offset

application onto the metal substrate.

Rotary Screen Lacquering. A third method is a develop-

ment that uses the old established principles of silk-screen

printing. The screen is in the form of a cylindrical thin,

narrow meshed sieve like metallic screen that is fed

internally with the coating material, which is forced

through the screen by an internal doctor blade onto the

transfer roll. Several patterns govern the shape (cutting

diagrams for blanks and/or ends) and weight of the

applied coating by photomechanic methods.

Roll

Coating. This method is

the most common for

coating in the ﬂat, which is used for both coil and sheets.

In sheet coating, it is possible to cut a pattern (stencil) into

the transfer roll (which would be the blanket cylinder on

an offset press) and coat only the areas to be used for

blanks. In a large-scale operation, this could yield signiﬁ-

cant savings in material, but it requires the sheet to be

accurately registered with the transfer roll. Most of the

present-day coaters are provided with front lays that

METAL CANS, FABRICATION 739

ensure precise registering, and magnetic or vacuum cy-

linders avoid irregular travel of the sheets while being

transferred by the pressure contact between the transfer

roll and the compression cylinder.

Rotary-screen coating permits a better deﬁnition of the

pattern in the applicator itself without cutting (or stencil-

ing) the transfer roll, which leaves a sharper, cleaner edge

between coated and uncoated areas. Other advantages

claimed are the ability to apply double the coating, which

could possibly save one pass, i.e., the coating operation

and curing, as well as applying differential coating

weights on adjacent areas of the sheet or on individually

coated spots. Thus, the coating pattern can be identical to

an end-cutting diagram whereon all geometrical losses

(shreds and skeleton) remain uncoated. In this way, the

ﬂange area of any end that receives the sealing compound

can receive a low-weight lacquer ﬁlm, whereas the curl

portion can remain totally unlacquered. There is a twofold

advantage: water-based compound adheres better on un-

coated endstock, and the blank cut in the end-stamping

press is made on a lacquer-free area. Cured resins,

especially when they ‘‘feather,’’ act as emery in end tools,

adhere to the tool parts, and scratch other ends, which

causes downtime for cleaning. The uncoated curl area is

covered by compound, at least to 1/64 in. from the cut edge

of the end and does therefore disappear in the double-

seam end hook.

Roller coating is similarly used, although in reduced

dimensions as compared with sheet coaters, for the out-

side of two-piece cans. For this application, however, the

more precise method of gravure coating is gaining favor.

Decorators operate in a similar fashion (17) but are

considerably more complicated, because they apply four,

and sometimes up to six colors with extreme accuracy of

registration to build up the total picture. Thus, a can

decorator uses the same can-handling system as the

coater, replacing the coating head by a reduced size offset

press printing equipment for each color, all of them four

to six colors, transferred onto one and the same blanket

cylinder, which transfers the total label onto the can

envelope in one rotation of the can. Cans (in the same

way as collapsible tubes) are stripped from the printing

mandrels and are transferred onto the pins of the pin oven

chain for curing.

Spraying. The method normally employed is the airless

spray system, where atomization of the enamel into ﬁne

droplets of appropriate size is achieved by the use of high

pressure on the enamel, about 650–850 psi (45–60 kg/cm

A spray gun consists of a spray nozzle designed to give the

desired spray pattern, a needle valve to cut off the ﬂow

without dripping, and the means to activate the valve at

high speeds, usually a solenoid.

Because the viscosity of the enamel has a decisive

inﬂuence on the spray pattern, discharged quantity and

dripping, it is heated and continuously circulated through

the gun. The quantity of lacquer deposited in the can is

determined by precise timing of the valve. A typical spray

time is approximately 100 ms. In modern practice, the gun

is at a ﬁxed position at the mouth of the can, although

machinery exists for moving it axially inside the can during

spraying. This is called a lancing gun. The can is indexed to

a position in front of the gun and rotated at about 2000 rpm

to ensure an adequate number of rotations while spraying

is in progress. It is practically compulsory to keep rotating

the can on its way from the spray coater to the oven to

Figure 14. Offset coating, showing application to two-piece can bodies. 1, Body infeed; 2, star wheel; 3, mandrel wheel; 4, prespin; 5, offset

cylinder; 6, gravure roll; 7, coating material feed; 8, doctor blade; 9, stabilizer roll; 10, coating material tank, with pump; 11, oven pin chain;

12, mandrel; and 13, metering rolls.

740 METAL CANS, FABRICATION

assist ﬂow out (extension and full wetting for poreless ﬁlm

formation and avoid rundown) and even distribution. The

pattern of coverage and number of coats depend on the type

of product to be packed (beer or carbonated soft drinks), the

can material (steel or aluminum), and the can size (h/d

ratio). Coverage can be total, where one spray covers the

total area, or zonal, where one spray is directed towards the

base and lower side wall of the can, and a second one

covering the upper side wall of the can up to its open end.

Two coats may be applied in consecutive indexing stations

on the same machine (wet on wet) or in separate machines

with intermediate drying (wet on dry).

Internal Side-Seam Protection for Welded Cans. The bare

metal that exists in the weld area must be protected in

many cases. Roller coating, spray, and electrostatic pow-

der coating are used. The applicator is mounted on an

extension of the welding arm through which the coating

material is supplied from a connection ﬁtted before the

can cylinder is formed around it. Roller coating permits a

low-pressure ﬂuid supply, but the lack of space makes the

applicator components extremely small as they must be

contained inside the sometimes small internal can dia-

meter, i.e., 202 cans. Spray application requires a high-

pressure ﬂuid supply. Although good initial coverage can

be achieved, liquid enamel tends to retract from sharp

edges and cause eventual ‘‘splashes,’’ so that high applica-

tion weights are needed for adequate coverage of the cut

edge of the blank. The overspray, which escapes from the

gaps between the cans, poses exhaust problems, especially

in avoiding external contamination through drips. Powder

is ﬂuidized with air for conveyance through the welding

arm and electrostatically charged to achieve deposition on

the welded area. This method undoubtedly provides the

best protection, but it is expensive in material and must be

run carefully in production. Wherever epoxy powders can

be applied instead of polyester ones, the material cost is

substantially reduced.

BIBLIOGRAPHY

1. Brit. Pat. 621,629 (June 16, 1949), J. Keller.

2. U.S. Pat. 760,921 (May 24, 1904), J. J. Rigby (to E. W. Bliss

Company).

3. U.S. Pat. 2,355,079 (Aug. 8, 1944), L. L. Jones (to American

Can Company).

4. Brit. Pat. 1,574,421 (Sept. 10, 1980), J. T. Franek and E. W.

Morgan (to Metal Box Ltd.).

5. Brit. Pat. 910,206 (Nov. 14, 1962), Soudronic AG.

6. Fr. Pat. 2,338,766 (Aug. 19,1977), E. E. V. V. Saurin and E. V.

Gariglio.

7. Brit. Pat. 1,256,044 (Dec. 12, 1971), E. Paramonoff and H.

Dunkin (to Standun Inc.).

8. U.S. Pat. 3,270,544 (Sept. 6, 1966), E. G. Maeder and G. Kraus

(to Reynolds Metals Company).

9. U.S. Pat. 3,704,619 (Dec. 5, 1972), E. Paramonoff (to Standun

Inc.).

10. Brit. Pat. 1,534,716 (Dec. 6, 1978), J. T. Franek and P. H.

Doncaster (to Metal Box Ltd).

11. Brit. Pat. 2,083,382B (Mar. 24, 1982), J. B. Abbott and E. O.

Kohn (to Metal Box Ltd.).

12. Brit. Pat. 1,509,905 (May 4, 1978), J. T. Franek and P.

Porucznik (to Metal Box Ltd.).

13. Brit. Pat. 455, 810 (Oct. 28, 1936), C. G. Sumner, W. Clayton,

G. F. Morse, and R. I. Johnson (to Crosse & Blackwell Ltd.).

14. U.S. Pat. 3,922,213 (Nov. 25, 1975), D. A. Smith, S. C. Smith,

and J. J. Davidson (to Aluminum Company of America).

15. Brit. Pat. 1,604,035 (Dec. 2, 1981), T. P. Murphy, G. Bell, and

F. Fidler (to Metal Box Ltd.).

16. Brit. Pat. 2,101,530A (Jan. 19, 1983), L. A. Jenkins and T. A.

Turner (to Metal Box Ltd.).

17. Brit. Pat. 1,468,904 (Mar. 30, 1977), (to Van Vlaanderen

Container Machinery Inc.).

General References

A. L. Stuchbery, ‘‘Engineering and Canmaking,’’ Proceedings of

the Institution of Mechanical Engineers, 180, 1, 167–1193

(1965–1966).

J. T. Winship, Am. Machinist, Special Rep. No. 721, 155 (Apr.

1980). Explains how metal containers are made.

The Metal Can, Open University, Milton Keynes, UK 1979, 52 pp.

C. Langewis, Technical Paper MF80–908, Society of Manufactur-

ing Engineers, Detroit, MI, 1980.

E. Morgan, Tinplate and Modern Canmaking Technology, Perga-

mon Press, London, UK, 1985. Contains a broad summary of

printing processes.

W. A. H. Collier in Proceedings of Cold Processing of Steel, The

Iron and Steel Institute and the Staffordshire Iron and Steel

Institute, Bilston, UK, Oct. 1971 and Mar. 1972, pp. 70–77.

Describes drawing, forming, and joining of steel containers.

J. D. Mastrovich, Lubrication 61, 17 (Apr./June 1975). Describes

aluminum can manufacture.

Proceedings of 1st International Tinplate Conference, Interna-

tional Tin Research Council, London, Oct. 1976. Full set of

papers and discussions issued in book form which provide the

best source of reference for can-making technology. Papers

include: G. F. Norman, ‘‘Welding of Tinplate Containers—An

Alternative to Soldering,’’ Paper 20, pp. 239–248; J. Siewert

and M. Sodeik, ‘‘Seamless Food Cans Made of Tinplate,’’ Paper

13, pp. 154–164; and W. Panknin, ‘‘Principles of Drawing and

Wall Ironing for the Manufacture of Two-Piece Tinplate Cans,’’

Paper 17, pp. 200–214.

Proceedings of 2nd International Tinplate Conference, Interna-

tional Tin Research Council, London, Oct. 1980. Papers in-

clude G. Schaerer, ‘‘Food and Beverage Can Manufacture,’’

Paper 17, pp. 176–186.

Proceedings of 3rd International Tinplate Conference, Interna-

tional Tin Research Council, London, Oct. 1984. Papers in-

clude W. Panknin, ‘‘New Developments in Welding Can

Bodies;’’ G. Schaerer, ‘‘Soudronic Welding Techniques—A Pro-

moter for the Tinplate Container;’’ and R. Pearson, ‘‘Side Seam

Protection of Welded Cans.’’

Developments in the Drawing of Metals, Conference organized by

The Metals Society, London, UK, May 1983. Section on deep

drawing and stretch forming, pp. 76–125. Papers include P. D.

C. Roges and G. Rothwell, ‘‘DWI Canmaking: The Effect of

Tinplate and Aluminum Properties,’’ E. O. Kohn, ‘‘The Use of

Spinning for Re-forming Ultra-thin Walled Tubular Contain-

ers;’’ and three papers on aspects of deep drawing.

A. M. Coles and C. J. Evans, Tin and Its Uses, International Tin

Research Institute, Hertfordshire, UK, No. 139, 1984, pp. 1–5.

METAL CANS, FABRICATION 741

F. L. Church, Mod. Metals 37, 18 (July 1981).

N. T. Williams, D. E. Thomas, and K. Wood, Metal Constr. 9, 157

(Apr. 1977); 9, 202 (May 1977).

A. G. Maeder, Aerosol Age 18, 12 (Nov. 1973). Still the best ﬁrst

introduction to the subject.

D. Campion, Sheet Metal Ind. 57, 111 (Feb. 1980); 57, 330 (Apr.

1980); 57, 563 (June 1980); 57, 830 (Sept. 1980).

S. Karpel, Tin Int. 54, 208 (June 1981).

Metal Decorating and Coating, Annual Convention of National

Metal Decorators Association (NMDA), October, annual. Re-

viewed in Modern Metals.

E. A. Gamble, J. Oil Colour Chem. 10, 283 (1983).

METALLIZING, VACUUM

ROBERT BAKISH

Bakish Materials Corporation,

Englewood, New Jersey

INTRODUCTION

Vacuum metallizing, which is a physical vapor-deposition

(PVD) process, produces coatings by thermal evaporation

of metals under conditions that permit and enhance this

deposition on a wide range of substrates. It is a process for

the manufacture of a great variety of products, which

include a diversity of polymeric webs of interest to the

packaging industry.

The key here is the thermal evaporation of metals.

Changes in needs and demand for new products have also

led to the application of this process for coating of these

webs with a variety of ceramics.

The control of the evaporation process and the evapor-

ant depends on the thermal source, the properties of the

evaporant, the vessel from which one evaporates, the

manner of holding and supplying of the evaporant, and

last but not least, the prevailing process pressure and/or

environment.

In the equipment where this coating is performed, i.e.,

the vacuum metallizers, variables such as geometry,

distance between the evaporant source and web, and

presence or absence of chill rolls, which is a system

component that determines the substrate temperature

and coating velocity, all affect the properties of the coating.

Although sputter technology, which is another PVD

process, could also be considered and in fact is a vacuum

metallizing process, it is not referred to here. The process

is considerably slower, and its high costs truly eliminate it

from consideration in production of coatings for the packa-

ging industry that this encyclopedia serves.

THERMAL SOURCES

Today, three basic heat sources are used in vacuum

metallizing: resistance heating, induction heating, and

electron-beam heating.

Resistance Heating. Source development began with

resistance heating using refractory metals. The successful

resistance source is an electrical conductor with resistivity

that allows it to reach the evaporation temperature with

reasonable current ﬂow. This material must have a higher

melting point and lower vapor pressure than the evapor-

ant. It also must be chemically inert to the evaporant, and

it certainly should not form by-products that could de-

grade the properties of the ﬁlms produced. The source

should be so designed to be able to contain the evaporant.

The ease of handling and advantageous cost should also

be integral characteristics of this source. The refractory

metals—tungsten, molybdenum, and tantalum—have

these characteristics, although tungsten is by far the

preferred source. A range of conﬁgurations for braided

wires to refractory metal boat sources is to be found in

service. Usually when complexly shaped containers are

needed, one will use tantalum. Resistance-heated wire

sources and refractory metal boats sources are shown in

Figure 1 (1). The refractory metal resistance source re-

mains in use in small installations, but when we speak of

industrial applications, the intermetallic boat is now the

mainstay. Initial success with resistance-heated ceramic

boats were recorded in the 1960s (2).

Let us now look at these. Boron nitride (3) with a ﬁller

of aluminum nitride, which permits the materials to be

shaped in virtually any desired shape, seems to have wide

acceptance for boats. This material has zero resistance

when cold and an increasing resistance as the tempera-

ture increases.

As a result, sophisticated controls of the heat input are

needed for these boats. Three-phase boats that consist of

boron nitride, aluminum nitride, and titanium diborate

are also used. Here, the A1N is added for its thermal

conductivity and electrical resistivity properties. These

boats operate at voltages of the order of 20 V with pro-

grammable current input that limits the power to the boat

when it is cold to avoid cracking. There is a variety of ideas

for the most efﬁcient way to power the boats; two of these

are shown in Figure 2 (4). Figure 2(a), which shows a

Figure 1. Resistance-heated wire sources (top); refractory metal

boat source (bottom).

742 METALLIZING, VACUUM

system where a single transformer is used to power all

boats, has two main disadvantages. The ﬁrst is that there

is a voltage drop from the ﬁrst to the last boat, which

makes it virtually impossible to control the individual

boats. The alternative approach, which is shown in Figure

2(b), is the more common and preferred method used. It

permits individual boat control, which makes possible

setting of uniform heating despite resistivity changes

caused by aging of the boats.

In addition, the design of boats clamping must be

properly engineered to permit good electrical contact and

avoid mechanical stresses caused by thermal expansion.

Various designs are possible. The size of the evaporation

boats is dependent on the individual machine, and a wide

range of opinions are related to boat size. Boats are

habitually wire fed with a wide variety of feed drives to

be found in the ﬁeld. Overall resistance heating is rapid

and provides efﬁcient deposition rates. This source also

has lower outgassing rate. The choice of boat material is

determined for each installation based on machine para-

meters, operation experiences, and end-product require-

ments. Boat life varies extensively. Table 1 (5) shows some

of the factors that inﬂuence it.

Induction Heating. Induction heating is the second heat

source used here. Although in the past it used to be a very

popular source, it seems that U.S. and European produ-

cers of metallizers have abandoned it in favor of resistance

heating. Their reason for the move in this direction was

their feeling, based on experience, that this source was

difﬁcult to operate, that it could not be feed continuously,

and that it had unfavorable economics.

By contrast, it seems that ULVAC, the premiere Japa-

nese metallizing equipment producer, has remained loyal

to induction heating (6) for its metallizers. ULVAC feels

strongly about it, listing the advantages in Table 2 (7).

Electron-Beam Heating. In electron-beam heating, the

heat generated is a result of an energy conversion process.

Here, the kinetic energy of the highly accelerated elec-

trons is converted to heat on impact with the workplace.

The electron gun is a device that generates electrons and,

after columniating them, directs them to the workplace.

Electron-beam heating has no upper limit, which makes it

possible to evaporate virtually any material. Today, trans-

verse and axial electron guns are to be found in metalliz-

ing systems. The transverse guns generate the electron

beam, and after a 2701 bending direct it to the workpiece.

The reason for this path is mandated by the need to

maintain the area where the electrons are generated

free of the high-density material vapors that habitually

are found on top of the evaporant and that can and will

defocus the beam reducing its efﬁciency. The axial guns

generate the beam and axially directs them to the

workpiece.

Figure 2. Two modes of powering resistance boats.

Table 1. Some Factors Inﬂuencing Boat Life

Electrical contact

Initial heating

Initial wetting of the cavity

Operating temperature

Utilization of cavity area

Vacuum level

Number of cycles (length of rolls)

Purity of aluminum wire

Correct resistivity

Age of unused boats

Cooling of boats

Boat defects

Operator controllable.

Figure 3. A 100-kW von Ardenne Anlagentechnik gun and

parameters.

Table 2. Advantages of Induction Heating

Constant evaporation rate

Stable control on thickness uniformity using multiple evaporation

source

No splaches; pinhole-free ﬁlm can be coated

Automatic control of evaporation rate is easy and simple to

operate

Aluminum purity can be 3N, instead of 4N or 5N

Aluminum blocks used can be easily available (10–300 g/piece)

Cheap running cost of evaporation source

Crucible life is long, and can be used for more than 40 batches

Simple evaporation source mechanism

Dense evaporated ﬁlm structure

Higher yield of evaporation source: 95–98% for crucible and 90–

93% for boat

METALLIZING, VACUUM 743

With these guns, the beam is magnetically deﬂected to

effect desired coverage of the evaporant ﬁlled crucible. A

typical axial gun is given in Figure 3. It can produce a

beam that, by suitable deﬂection, can cover the crucible

containing the evaporant with virtually any desired con-

ﬁguration. This includes the beam in a line conﬁguration

that was ﬁrst introduced in 1984 (8), which makes possible

the generation of a uniform vapor curtain (see Figure 4).

When using electron-beam heating, one must ensure

that virtually no secondary electrons impinge on the

polymeric web; unless this is accomplished, their thermal

load will lead to severe damage and even complete

destruction of the web. Figure 5 shows 1000-mm crucible

and magnetic trap for an electron-beam line evaporator in

a roll-coating plant. Note, in electron-beam heating, that

the evaporant, depending on its nature, is evaporated

either from a cold crucible (i.e., water-cooled copper) or

from a hot crucible vessel that can be made of a variety of

ceramic materials. The speciﬁc selection is based on

compatibility with evaporant. Table 3 shows a theoretical

comparison between resistance and electron-beam heat-

ing for aluminum coating (9). As you can observe from this

table, the electron-beam heating, although more expen-

sive, is notably simpler.

From the heat sources, only electron-beam heating can

be used for direct evaporation of ceramics. The electron

beam can also be used for a deposition process referred to

as plasma-activated reactive evaporation of aluminum

(10). The geometry of the process is shown in Figure 6

(10). This process can be carried out equally well with a

resistance-heated boat evaporator. Table 4 (10) shows

maximum rates obtained by reactive evaporation. We

Figure 4. Evaporation line of an electron-beam line evaporator for 1000-mm web width.

744 METALLIZING, VACUUM

are likely to observe considerably more reactive evapora-

tion applications in the future. Reference should also be

made to Table 5 for the advantages and limitations of the

electron-beam evaporation (11).

METALLIZING EQUIPMENT

As with equipment to carry out any other process, so with

metallizing equipment the details of the system are

governed by the process to be used, and the product that

it must produce. Once details are ﬁxed, the ability to carry

out the process in the system depends on the competence

and the skill of the equipment producer. By saying this,

one could say that the estimated 500 metallizers operating

in the world today are, in fact, 500 different pieces of

equipment. The estimate of their production is given in

Figure 7 (12). Although in the true sense of the word this

might be correct, I will only refer to a few typical systems.

The metallizers, or roll coaters, if you will, accomplish a

wide range of tasks far and beyond the needs of the

packaging industry, which is the largest consumer of

Table 3. Comparative Theoretical Evaluations between EB and Resistance Heating

General assumptions

1000-mm coating width

400-A Al layer

10-ms

1

coating speed

12-mm PET

645/1000-mm roll diameter

3-shift operation

85% machine availability

Resistance-heated boats EB

Cost calculation basis

Number of boats/crucible 11 1

Price per boat ($) 35 400

Boat/crucible lifetime (h) 17 100

Pumpdown time/conditioning (min) 5 20 (15)

Vent time (min) 5 20 (5)

Investment costs (percent) 100 112 (120)

Resistance-heated boats EB EB with crucible lock chamber

Coating proﬁtability 645-mm roll diameter

Annual productivity (tons/yr) 1502 1141 1402

Coating costs ($/kg) 0.47 0.62

0.53

0.57

0.50

1000-mm roll diameter

Annual productivity (tons/yr) 2093 1799 2036

Coating costs ($/kg) 0.37 0.45

0.43

0.40

0.38

With crucible lock chamber.

EB evaporator with 50% higher Al consumption.

EB evaporator with same Al efﬁciency as intermetallic boats. The calculation shows that in case of aluminum coating of PET, the EB-coating costs are

deﬁnitely higher mainly because the inherently higher possible evaporation speed of the EB evaporator cannot be used.

Figure 6. Schematic of the aluminum oxide deposition process

by plasma-activated reactive evaporation of aluminum.

Figure 5. 1000-mm crucible and magnetic traps in a roll-coating

plant.

METALLIZING, VACUUM 745

polymer ﬁlms coated with aluminum. It is thus appro-

priate to refer to Table 6 (13), which refers to most, if not

all, products that can be made in metallizers. However,

many of these are actually products of sputter technology.

Increased productivity and lower costs have been the

engine driving this technology since its introduction. They

have been responsible for (a) the widening of the metalli-

zers, with ability to coat today’s widths, exceeding 125 in.;

(b) the increases in coating speed, today getting ready to

exceed 3000 ft/min; and (c) numerous quantum leaps from

the manual controls of yesterday, to fully computer-con-

trolled systems of today (14), including the use of artiﬁcial

intelligence (AI) techniques to provide real-time process

control and troubleshooting advice (15).

Let us now look at schematics of few of the large variety

of web coaters built over the years for the purpose of

illustrating the equipment that operates in industry.

Figure 8 (16) shows a cross section of a coater representing

smaller type machines. In this schematic, electron-beam

heating is indicated, although resistance heating for such

systems is much more common. Figure 9 (17) shows a

schematic of a coater, and Figure 10 (17) show its internal

rolls assembly; note both electron-beam- and induction-

heated sources. Figures 11 (18) and 12 (19) show cross

sections typical of a high-speed, large machine. All these

Table 4. Maximum Evaporation Rates and Theoretically Derived Deposition Rates for Reactive Aluminum Evaporation

Boat Evaporator

per 100 mm (1 boat) per 1000 mm (10 boats)

EB Line Evaporator per

1000 mm

Maximum evaporation

rate (Al)

min

12 (cavity 30 cm

) 120 E200

Derived deposition rate

(Al)

2400 (200 nm/s per 1 g/min) 2400 E4000

Derived deposition rate

(Al

)

75%–150% of Al deposition rate depending on the location of O

inlet

Limitation for Al

evaporation rate

Size of boats (max. 0.4 g/min

per cm

cavity)

Number of boats per 1000 mm

(10 boats per row)

Splashing (max. 2 g/min

per cm

)

Precondition: No other limitation for deposition rate.

Table 5. Advantages and Limitations of EB Evaporation

Advantages Limitations

High deposition rates for metals and

dielectrics

Low source efﬁciency

Multisource control

Direct deposition of oxides, ﬂuorides,

sulﬁdes, and magnetic materials

Source inventory

Thermal load to

substrate

Coating material change over ﬂexibility Source orientation

Figure 7. Estimates of worldwide 1993 metallizing production

capacity.

Table 6. Present and Future Applications of Roll Coaters

Application Products

Gold and silver yarns Obi(sash), sash clip, bag, tie, sandals, curtain, towel, shawl, socks, slippers, embroidery, table cloth,

lace, stage costome, tatami brim, etc.

Ornaments Interior decorations, Christmas-tree decorations, nameplate, case, ballom, cosmetic package, etc.

Stamp foils Pencil, book cover, postcard, label, Christmas card, poster, cigarette package, picture frame, lighter,

cassete case, kimono, kimono sash, etc.

Packages Medicines, confectionary, rice, cigarette, food, etc.

Building materials Parasol, sunshade, greenhouse shade, interior wall, heat-insulation wall, solar ﬁlm, ﬁreﬁghter’s suite,

curtain, space suit, etc.

Farming materials Reﬂective sheet, beach mat, cooler bag, scarecrow, etc.

Reﬂection sheet Trafﬁc sign, number plate, mirror, guidance sign (airplane), etc.

Food package Lunchbox, tableware, etc.

High added value products Magnetic tape, copying ﬁlm (substitute of copy drum), aerial photograph ﬁlm, optical ﬁlter, multilayer

ﬂexible circuit board with polyimide, etc.

Precision capacitor Logic circuit (communication device, personal computers, etc); bypass capacitor (TV, radio, VCR, etc).

Phase advance capacitors High industrial power unit, etc; low power—washing machine, motor, Pachinko machine, home

bakery, ﬂuorescent lamp.

746 METALLIZING, VACUUM

are referred to as batch or semicontinuous coaters. The

production cycle of these machines habitually consists of

four steps as follows: (a) precoating, (pumpdown), (b)

coating, (c) venting, and (d) recharging. These steps vary

from machine to machine. Figure 13 (20) shows an exam-

ple of such a cycle. One could look at it as somewhat

representative of batch systems. However, one should note

that there is considerable variation in the production cycle

from machine to machine.

To increase productivity, air-to-air machines have been

built. The producer of one of these (21) claims that output

here can be increased up to 50% in relation to a batch-type

machine. Figures 14 (20) and 15 (21) show schematics of

air-to-air metallizers. The costs of the equipment, however,

are notably increased. Although a limited number of air-to-

air machines serve the packaging ﬁeld, this type of in-

stallation remains primarily the province of metal strip

coaters. To round up the discussion on metallizers,

one should examine a couple of 1995 vintage systems

serving the packaging and related industries. Figure 16

(left—machine; right—schematic) shows the Leybold

Figure 9. Schematic of a coater.

Figure 8. Outline of a vacuum roll coater typical of smaller

machines.

Figure 10. Internal roll assembly of water shown in Figure 9.

METALLIZING, VACUUM 747