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

Подождите немного. Документ загружается.

much higher rate. In our example, if the product could

withstand a stopping rate of 30G, it could theoretically be

stopped within a minimum stopping distance of 1 in. We

will go on to see that by using cushions, it will actually be

necessary to use much thicker cushions than the 1 in. that

is the minimum stopping distance. This is due to the

limited compressibility of cushions, 50–80% maximum,

and to the nonconstant zero to peak–vs–constant peak

deceleration rate.

Shock refers to the maximum rate of acceleration that

is experienced during an impact often resulting from a

free-fall drop. Obviously a packaged product may experi-

ence mechanical shocks resulting from several other

events. A common event in shipping may be the impact

shock received by a package when another packaged is

dropped onto it. Or, it may result from being hit with a

diverter on a conveyor belt during an automated sorting

process. Whenever there is a sudden rate of change of

velocity, an event called a shock occurs.

MEASURING IMPACT SHOCKS

Measuring shock levels requires the use of instrumenta-

tion and the understanding of what the instrumentation is

presenting. Although mechanical shock recorders

have been used in the past, they have been almost to-

tally replaced with electronic instrumentation when-

ever accurate measurements of shocks are desired. Most

shock-measuring devices rely on the use of accelerometer

transducers. The accelerometers change the measured

characteristics into electronic signals that can be dis-

played, analyzed, and recorded. Acceleration levels are

presented as voltage proportional to the acceleration due

to gravity. Usually this is in the range of 1–100 mV/g.

The voltages are the result of the transducers converting

the forces generated during an impact shock into an

electronic signal. Since F = ma (force = mass accelera-

tion), and the mass in the transducer remains constant,

the measured force is directly proportional to the accel-

eration being experienced.

Accelerometer transducers typically are either piezo-

electric or piezoresistive designs. Piezoelectric acceler-

ometers rely on crystalline elements that generate an

electronic signal when subjected to an applied force.

Both accelerometer designs have their advantages and

limitations, but it is sufﬁcient to say that they are the most

common means of obtaining records of acceleration levels

experienced during impact shocks.

This discussion does not address the signal condition-

ing, power supplies, ﬁltering, and calibration necessary to

obtain records of shock acceleration levels. However, once

the signals are obtained, they are often displayed as a

function of time and are referred to as shock signatures,

shock pulses,orwaveforms.

SHOCK WAVEFORM ANALYSIS

Figure 1 shows a typical acceleration shock waveform

resulting from an impact. We can discuss and characterize

components of the recorded shock waveform. The ﬁrst

observation is that of the peak G level or the maximum

acceleration experienced during the shock event. Since the

entire recording is that of the acceleration levels, we must

determine at what point to take a reading, and since it is

usually the maximum faired acceleration that is of con-

cern, that is what is most often used to deﬁne the shock

acceleration level. Care must be taken when recording

shock acceleration levels to ensure that any ﬁltering used

to clarify the shock signature does not adversely effect the

peak G level recorded.

The second observation is that of the time over which

the event occurred referred to as the shock pulse duration.

By convention, the duration of a shock pulse is measured

from points where the acceleration/time record is at a level

of 10% of the peak G level. This is done because of the

difﬁculty of precisely determining when the waveform

actually crosses the baseline to start and stop the

duration-time measurements. Shock pulse durations ty-

pically measured in package drop tests range from 2 to

50 ms.

Additional data that can be derived from an analysis of

the shock waveform is the velocity change that occurs

during the shock event. The velocity change is propor-

tional to the area under the acceleration time curve. It is,

in fact, the integral of the acceleration with respect to the

time over the total duration of the shock pulse. The

velocity change is the sum of the impact velocity from a

package’s fall plus the rebound velocity resulting from the

impact energy stored in the cushion system being re-

turned in the form of rebound motion.

The shape of a shock waveform can be very instructive

as to the type of impact that has occurred as shaped by the

cushion system’s performance (see Figure 2). The wave-

shape of an elastic cushion acting as a linear spring will

Figure 1. Standard pulse interpretation.

Figure 2. Typical shock waveform shapes.

1108 SHOCK

have a haversine, often referred to as a half-sine, wave-

shape. A nonrebounding cushion such as some corrugated

pads may exhibit a waveform that can be described as a

terminal peak sawtooth waveform on the basis of its visual

shape. The acceleration (deceleration) reaches a peak

when the object comes to rest with no rebound energy to

create a rebound velocity. Another waveform shape that

occurs during package testing is the trapezoidal waveform

in which the acceleration reaches a peak G level that

continues for a period of time as the cushion continues to

crush. These trapezoidal waveforms are most often cre-

ated by honeycomb or cylindrical cushion structures being

crushed or in foam-in-place systems where the cushioning

is provided as the material is being frangibly torn rather

than compressed.

Seasoned package designers can often interpret what

may be happening to a product in a cushioned package by

analyzing the shock waveform observed during an impact

(see Figure 3). A symmetrical half-sine waveform typically

indicates that the static stress loading of the product on

the cushion is in the optimum range for maximum cush-

ioning. A waveform approaching a terminal peak sawtooth

shock pulse with a sharp rise near that end compared with

the beginning of the waveform may show that the product

is bottoming out the cushion; the static stress loading may

be too high for the cushion or the thickness of the cushion

insufﬁcient. A waveform showing a high spike at the

beginning of the shock pulse may be indicating that the

cushion is too stiff for the static stress loading being

applied by the product. It may be like a diver making a

belly ﬂop smack on the water. The thickness of the cushion

in this instance is immaterial since none of it is initially

deﬂecting on impact.

CHARACTERIZING PROTECTIVE CUSHIONS

Cushioning materials used to protect products from

shocks are normally characterized by their shock-trans-

mitting attributes. ‘‘Cushion curve’’ data present the

average level of the peak G level experienced on a simu-

lated product dropped from a given height onto the given

thickness of cushion (see Figure 4).

The static stress of the product on the cushion, ex-

pressed in psi, is then varied to determine the optimum

loading range for the cushion. These data are derived

empirically through an extensive series of drop tests

during which the variables of drop height, cushion

thickness, and loading (in psi) are systematically

changed. The cushion-curve data thus presented can

then be used as a starting point for predicting the

effectiveness of a given cushioning material for a needed

application.

From the cushion curve, the peak transmitted shock

level is noted for given drop heights. When the maximum

acceleration fragility of a product is compared with the

cushion curves for the speciﬁed environmental drop

height, both the minimum cushion thickness and opti-

mum static stress loading can be determined. This pro-

vides the initial information for developing protective

package systems for products.

THE DAMAGING EFFECT OF SHOCKS

The use of fragility testing is the most common means of

determining a product’s resistance to mechanical shocks.

The process of fragility testing is described in much

greater detail elsewhere in this Encyclopedia (see Testing,

product fragility). The result of product fragility testing is

the characterization of a product in terms of its resistance

to mechanical shocks.

For a product to be damaged from mechanical shock,

two conditions must occur simultaneously. The ﬁrst is

that the mechanical shock must have sufﬁcient energy

to cause damage. The second required condition is that

the energy be imparted to the product at a rate exceeding

the product’s ability to absorb the energy without break-

ing. The ﬁrst condition is expressed as the velocity-

change side of the damage boundary; the second condition,

as the acceleration side of the damage boundary (see

Figure 5).

The velocity-change side of the damage boundary

curve is an expression of how much energy is required to

damage a product. This is directly related to the velocity

Figure 3. Cushion static stress loading concerns.

Figure 4. Dynamic cushioning curves.

SHOCK 1109

change or area under an acceleration-time shock-wave-

form record. Again, the predominant source of velocity in

package shocks result from drops. Even if the peak accel-

eration level were very high, if the pulse duration were

very short, the resulting velocity change might provide

insufﬁcient energy to damage a product. The product, in

effect, does not respond to the high-intensity shock be-

cause the duration and energy input are too limited to

cause any damage. It is similar to how the human eye can

withstand the high intensity of a ﬂash from a camera for a

very short duration of time since the light does not have

time to cause the eye to respond adversely.

The acceleration side of the damage boundary curve is

of concern only with the prior condition, in which sufﬁ-

cient velocity change has been met, and is thus then a

question of how fast the velocity change is being im-

parted to the product. A familiar analogy is that of an

automobile in a crash. If the speed is slow, usually less

than 5 mph (mi/h), no signiﬁcant damage will occur

because it is below the velocity-change damage boundary.

However, if the automobile is moving much faster, say,

50 mph, sufﬁcient energy is present and damage will

certainly occur if the automobile is driven into a brick

wall, causing the energy to be dissipated at a very high

rate (acceleration level) when it comes to a sudden stop.

If the same automobile traveling 50 mph is impacted into

yellow safety barrels placed in front of the brick wall, the

stop rate may be signiﬁcantly less, resulting from the

added stopping time, so that no signiﬁcant damage

occurs (see Figure 6). It should be apparent that without

seat belts and airbags, people in a vehicle will continue

moving at the 50-mph speed and not beneﬁting from the

yellow barrier cushions stopping the automobile at a

much lower rate.

Although both damage-boundary parameters—velocity

change and acceleration—are critical in deﬁning a pro-

duct’s fragility, the velocity-change side of the damage

boundary is often considered to be sufﬁciently low for

normally cushioned products, so that it will be exceeded

during normal handling conditions. For that reason, often

only the acceleration side of the damage boundary is

referred to when one discusses the fragility of a product.

This is technically insufﬁcient; however, it is a signiﬁcant

improvement over working without any product fragility

data.

It is next to impossible to determine the fragility of

products through observations or even calculations. It is

essential to conduct fragility testing to assess the fragility

of any given product. However, there are certain cate-

gories of products that because of the severity of their use

environments, they typically have fragility levels

that reach a minimum stated acceleration fragility level.

Table 1 lists the typical minimum fragility levels of

products found in these categories. Stated again, without

testing, one cannot know the fragility of a product. How-

ever, it may be sufﬁcient to test only to a minimum-

assurance fragility level. In other words, it may be

sufﬁcient to subject a product only to a minimum accep-

table acceleration shock level to ensure that it at least

withstands the minimum assurance level. This then be-

comes the basis for developing protective packaging.

One critical issue must be addressed when discussing

the shock fragility of a product. That is the manner in

which the force of a mechanical shock is imparted into a

product. As an example, the acceleration portion of a

damage boundary for a fresh chicken egg is 35–50G,

depending on how it is impacted on the side or end of

the egg. This is based on testing and imparting the shock

Figure 5. Typical damage boundary curve.

Figure 6. Effects of impact velocity and cushioning on damage in

an automobile impact.

Table 1. Benchmark Fragility Levels of Products

G Factor Classiﬁcation Examples

15–25 Extremely fragile Precision instruments, ﬁrst-generation computer hard drives

25–40 Fragile Benchtop and ﬂoor-standing instrumentation and electronics

40–60 Stable Cash registers, ofﬁce equipment, desktop computers

60–85 Durable Television sets, appliances, printers

85–110 Rugged Machinery, durable appliances, power supplies, video monitors

110 Portable Laptop computers, optical readers

150 Handheld Calculators, telephones, microphones, radios

1110 SHOCK

using a ﬂat impact surface. If, on the other hand, the shock

is imparted to the fresh egg using a surface conforming to

the shape of the egg, the acceleration fragility level

exceeds 150G. The same holds true for many products.

How the cushions transmit shock into the products, on

corners, edges, or ﬂat surfaces, can signiﬁcantly effect the

critical fragility of the product.

Product-fragility tests must be conducted with an eye

toward the ﬁnal package cushion conﬁguration that will

be used. It almost makes one wonder what comes ﬁrst, the

cushion or the egg.

SUMMARY

In summary, shock occurs usually as the result of stopping

a fall. Shocks are characterized by their duration, peak

acceleration, velocity change, and waveshape. Waveshapes

are the signatures of shock events that can be analyzed to

characterize impacts and to analyze protective cushioning.

Protective cushions are characterized as cushion curves

that depict the cushion’s transmitted peak acceleration

levels for given drop heights and cushion thicknesses.

Product-fragility testing measures the product’s resistance

to shocks deﬁning in terms of both velocity sensitivity and

resistance to peak acceleration shock levels. The use and

analysis of shocks provide the measurements essential to

engineer products and packages that can withstand their

shock-generating environments.

BIBLIOGRAPHY

General References

ASTM D1586, Method of Test for Dynamic Properties of Package

Cushioning Materials, American Society for Testing and

Materials, 1996.

ASTM D3332, Standard Test Methods for Mechanical-Shock

Fragility of Products, Using Shock Machines, American

Society for Testing and Materials, 1996.

ASTM D4003, Standard Test Methods for Programmable Hori-

zontal Impact Test for Shipping Containers and Systems,

American Society for Testing and Materials, 1996.

ASTM D4168, Standard Test Methods for Transmitted Shock

Characteristics of Foam-in-Place Cushioning Materials, Amer-

ican Society for Testing and Materials, 1996.

ASTM D5276, Standard Test Method for Drop Test of Loaded

Containers by Free Fall, American Society for Testing and

Materials, 1996.

ASTM D5487, Standard Test Method for Simulated Drop of

Loaded Containers by Shock Machines, American Society for

Testing and Materials, 1996.

ASTM D5277, Standard Test Method for Performing Programmed

Horizontal Impacts Using an Inclined Impact Tester, Amer-

ican Society for Testing and Materials, 1996.

C. M. Harris and C. E. Crede, Shock and Vibration Handbook,

Editions 1–4, McGraw-Hill, New York, 1961.

International Electrotechnical Commission, Basic Environmental

Testing Procedures, Part 2: Tests-Test Ea: Shock, Publication

68-2-27, 2nd ed., 1972.

R. D. Newton, Fragility Assessment Theory and Test Procedure,

Monterey Research Laboratory, Inc., Monterey, CA, 1968.

SKIN PACKAGING

BURT SPOTTISWODE

DuPont P&IP

Wilmington, Delaware

The innovative, technological developments in skin packa-

ging over the past several years have opened up a whole

new arena for this packaging concept. The major develop-

ments that have been made in skin packaging are

better quality skin board [solid bleached sulfate (SBS)

and recycled] and improved printing techniques. Now,

with the new specialized printing equipment that provides

higher resolution [133 dots per inch (dpi)], you can

obtain beautiful-looking graphics with great sales appeal.

Also, the new advances in the separation of the colors

allow you to print just about anything on a skin board.

Improvements in printing, along with the advance-

ments made in skin equipment and the development of

new high-performance skin packaging ﬁlms, has helped

to greatly expand the market opportunities for skin

packaging.

As the proliferation of mass merchandising outlets

and self-serve retailing continues to expand, the growth

of skin packaging will continue because of its merchan-

dising appeal to both the consumer and retailer. Today,

manufacturers are striving for a cost-effective eye-ap-

pealing package that sets their product apart from

competition and enhances the product. They are looking

for packaging that will put new life into old products to

gain additional market share. A package that offers

product visibility and creates impulse sales to help

make the buying decision easier. Skin packaging provides

all this and in addition has the merchandising advantage

of being peggable.

There are two market opportunities for skin packaging:

retail and industrial. For the retail visual-carded packa-

ging market, skin packages are typically merchandised by

hanging them on a peg. This enhances space use in that

the package requires less shelf space and provides better

use of the space allocated by offering ‘‘more facings’’ and

‘‘good vertical display.’’ Skin packaging is a cost-effective

alternative to other visual carded packaging, i.e., blister

packaging, clam-shells, foldover blisters, and Stretch Pak,

because it requires no tooling in that the product itself

becomes the mold over which the ﬁlm is drawn down and

around by vacuum.

Industrial skin packaging differs from visual carded

packaging in that its primary purpose is to protect

products in transit. Products as divergent as computer

tapes, lamps, service repair kits, fans, and tabletops

may be skin packaged instead of using die-cut corru-

gated, foam-in-place, foam peanuts, and other stabilizing

or dunnage materials. Industrial skin packaging offers

high throughputs and full visibility to check for tamper-

ing or missing components and allows quick identiﬁca-

tion, usually at signiﬁcant cost reduction. It also

considerably reduces the amount of waste that has to

be disposed of and is therefore more environmentally

friendly.

SKIN PACKAGING 1111

SKIN-PACKAGING MATERIALS AND EQUIPMENT

Skin packaging involves placing a product on a substrate

material such as paperboard or corrugated board (see

Figure 1). When the ﬁlm is heated to the proper softening

temperature, it is draped over the product and the sub-

strate material and a vacuum draws the ﬁlm down and

around the product and into the pores of the board to make

a secure and attractive-looking package.

A skin package has four components: the plastic ﬁlm, a

heat-seal coating, printing ink, and a paperboard or

corrugated substrate card. The product itself becomes

the mold over, which the heated plastic ﬁlm is drawn

down and around. This is one of the major differences

between blister and skin packaging, in that in blister

packaging you have to form a blister that requires a

mold, for not only the thermoforming machine but also

the blister packaging machine if you are buying preformed

blisters.

Skin packaging begins with a sturdy card made of high-

porosity paperboard or corrugated paperboard. After

printing the board, which, with the developments in

printing technology and the higher-quality skin board

available today, you can now get beautiful four- to

six-color graphics, is coated with a heat-seal dispersion

coating. Today, most printers use an ethylene vinyl acetate

(EVA) water-based coating. The product is placed on to the

board, and then the product and board are moved onto the

platen. The plastic ﬁlm is held tightly in place by a

clamping frame, directly below the heater, which is lo-

cated above the platen.

At the beginning of the packaging cycle, the product is

usually loaded onto a printed, coated skin board that is

then moved onto the platen of the machine to be skinned.

The plastic ﬁlm that is held in the frame above the product

on the skin board is heated to the proper softening

temperature and is then lowered over the product and

the skin board. As the frame is being lowered, the vacuum

system is energized, and as the ﬁlm is draped over the

product and the board, the vacuum pulls the ﬁlm tightly

around the product and into the pores of the skin board,

making a tight, attractive-looking package. The hot ﬁlm

instantly activates the coating on the board, and when a

milky white coating is used, it becomes crystal clear when

coming in contact with the hot ﬁlm. The paperboard card

with the product skinned to it is then moved to the die

cutter, which die-cuts it into individual packages (see

Figure 2).

Plastic Film. One of the least expensive components of

the total package, the ﬁlm is one of the most important. It

is the ﬁlm that holds the product on the board. The ﬁlm

also reinforces the board and provides a glossy surface for

enhanced graphics. The ﬁlm of DuPont Surlyn ionomer

resin is the most widely used ﬁlm in the retail visual

carded packaging market with some low-density polyethy-

lene (LDPE) and EVA coextruded ﬁlms used for the low-

end retail market. The ﬁlm of Surlyn is a tough clear ﬁlm

and enhances the graphics and appearance of the package

to help create impulse sales. It has excellent abrasion

resistance and also has a low shrink force, which elim-

inates any unsightly board curl. Polyethylene (PE) is used

Figure 1. A typical skin package.

Figure 2. (a) Product and backing are moved onto the vacuum platen of skin-packaging machine and ﬁlm is heated; (b) heated ﬁlm is

draped over product and backing; (c) vacuum suction draws ﬁlm around product and backing, creating a skin-tight package; (d) ﬁnished

board is moved out of the machine.

1112 SKIN PACKAGING

primarily for the industrial skin-packaging market where

optical properties are not as important as in the retail

visual carded packaging market. PE is not as clear as ﬁlm

of Surlyn and requires more heat and dwell time. It

shrinks more of the cooling cycle and has a higher shrink

force than ﬁlm of Surlyn, which causes board curl. It is a

tough ﬁlm and adheres well to primed paperboard and

corrugated. PE is less expensive but requires a heat-cycle

time that is twice that of Surlyn; therefore, Surlyn can be

more cost effective because of the increase in productivity.

The ﬁlm gauge that is needed will depend on the weight

of the product, the draw required, and the abuse that the

package is likely to encounter. It is recommended that the

ﬁlm be corona treated to a level of 42 dyn to further

improve the adhesion of the ﬁlm to the board. If the ﬁlm is

surface-treated on one side, then the roll label should

designate which side is treated. The treated side should be

down to come in contact with the board.

Primer. Most skin-packaging ﬁlms (Surlyn, LDPE, etc.)

do not exhibit good natural adhesion to ink or board.

Printed and unprinted boards are, therefore, coated with

heat-sealable primers to provide strong, long-term adhe-

sion of the ﬁlm to the ink/board surface.

EVA ﬁlms and coextruded ﬁlms containing EVA have

good initial board/ink adhesion. However, actual package

failures have demonstrated that EVA to ink/board bonds

will deteriorate with time. The deterioration is accelerated

by high ambient temperatures (like those usually experi-

enced during shipping).

Primers are generally aqueous EVA-based dispersions

speciﬁcally formulated to provide a good bond between the

ﬁlm and board. The primers soak into the board ﬁbers and

porous inks. This maximizes mechanical and chemical

adhesion between the ﬁlm, ink, and board.

Application of Primer. The manufacturers of dispersion

coatings can supply speciﬁc recommendations for applying

their primers to achieve a good ﬁber tear bond between

the ﬁlm and the board. The general properties of commer-

cially available dispersions are described in Table 1.

Dry coatings are applied commercially with a gravure

cylinder. The applied coating should be of the proper

weight and one that will not seal the surface of the sheet.

Too light a coating will result in poor adhesion. Too heavy

a coating will block the pores in the board and ink. This

will cause poor evacuation and ﬁlm forming.

Board Priming. Board priming is usually done most

economically by a company setup to print and coat the

boards in one operation.

Ink. It is important to use the correct compatible heat-

resistant ink to ensure good adhesion to the board (see the

Inks article). Using the wrong inks or the wrong board/

ink/primer combinations can interfere with the ink’s

adhesion to the board because of one or more of the

following chemical or physical problems:

Chemical Incompatibility. A primer-to-ink bond fail-

ure can occur if the ink and primer are chemically

incompatible.

Unstable Pigment, Vehicle, or Binder. An ink cohesive

failure will occur if the pigment, vehicle, or binder is

not stable under heat.

High Board Porosity. The ink may fail to adhere to the

board if the ink has a low binder and vehicle:pig-

ment ratio and the board is very porous. The binder

and vehicle are absorbed into the board, and the

poorly bound pigment remains on the surface. This

phenomenon is known as ‘‘chalking.’’

Ink/Board Incompatibility. The ink may not bond to

the board if the ink and board are incompatible. This

is often caused by contaminated board.

Ink/Primer Incompatibility. A primer-to-ink bond

failure will occur when the ink contains lubricants,

waxes, or oils incompatible with the primer.

When starting a new job, it is important that preproduc-

tion ink evaluation tests be made before any board is

printed in large quantities. This is a simple precaution to

assure that the ink system is compatible with board and

ﬁlm. This test consists of having proofs prepared by the

printer with the ink and board intended for use. Sample

skin packages should be prepared with these proofs,

checking for proper evacuation of air and adhesion.

Paperboard. Three types of board are used for skin

packaging:

. Fourdrinier board (solid bleached sulfate)

. White lined recycled board

. Corrugated board

The board must be compatible with the ink and primer

system, be porous enough to permit a vacuum to be drawn

through it, and be strong enough to hold and display the

product (see the Paperboard article).

By specifying board density and the weights of any

coatings to be used, you can ensure acceptable porosity for

your skin board, specify the nature of any coatings or

treatments to ensure compatibility of the board with inks

and primers, and ensure that the board is strong enough

for the application by specifying board type and thick-

ness. The strength of the board is enhanced by the

skin-packaging ﬁlm used. Film of Surlyn, with its

superior strength, will produce a stronger package than

Table 1. Properties of Aqueous Dispersions of Skin

Packaging

Solids (weight %) 40–50

Viscosity 500–100 mPa

pH 9.5–10

Odor None

Appearance unfused Clear or milky white

Appearance fused Colorless

Dilution Water as required

Flammability Nonﬂammable

Drying 130–2301F (55–1101C), variable

SKIN PACKAGING 1113

competitive skin packaging ﬁlms, so you may sometimes

be able to specify a slightly thinner board gauge.

SBS Board. Solid bleached sulfate board for skin packa-

ging is available in four calipers: 0.020, 0.024, 0.026, and

0.028. The speciﬁcations for a SBS board that will be

acceptable in skin packaging are as follows:

Density. The density should be low enough to produce a

board porosity that will allow a suitable vacuum to be

drawn through the skin card. This porosity can be at-

tained with a density that is equal to or less than 1.9 kg/

mm) (9.8 lb/1000 ft

-point).

Finish. A soft ﬁnish is recommended for SBS board.

Brightness. The board should have a brightness of 80 or

better (General Electric (GE) brightness scale). The prin-

ter may have to adjust the inks used to accommodate

variations in board tint.

Sizing. Waxes, lubricants, release agents, and surface

treatments are not recommended for this board and

should be avoided.

Clay Coating. Clay coating is not recommended. If a

clay coating is used, then the coating weight should be less

than 0.49 kg/100 m

(1.0 lb/1000 ft

Clay Binders. Clay binders must be heat stable. Protein

binders are acceptable. Styrene latex binders should be

avoided.

WHITE LINED RECYCLED BOARD

Density. White lined recycled board for skin packaging

is available in ﬁve standard calipers: 0.028, 0.032, 0.036,

0.042, and 0.054.

The density of white lined recycled board should be low

enough to produce a board porosity that will allow a

suitable vacuum to be drawn through the card. This

porosity can be attained with a density that is equal to

or less than 2.1 kg/(m

mm) (11.1 lb/1000 ft

-point). A

denser board will require perforations.

Finish. A number 2 or number 3 ﬁnish is preferred,

although number 4 may be acceptable (according to box-

board standards of the National Paperboard Association).

Finish refers to density and surface; higher numbers are

smoother and more dense.

Brightness. The board should have a brightness of 72 or

better (GE brightness). Printers may have to adjust their

inks to accommodate variations in board tint.

Gross Ink Treatment. Gross ink treatment is not recom-

mended for white lined recycled board. If gross ink is used,

then the treatment should not contain any release agents

or wax-based material.

Binders. No wax or styrene binders should be used on

white lined recycled board.

Clay Coating. Clay coating is not recommended for

white lined recycled board. If a clay coating is used, then

the coating weight should be less than 0.49 kg/100 m

(1.0 lb/1000 ft

Clay Binders. Clay binders must be heat stable. Protein

binders are acceptable. Styrene latex binders should be

avoided.

CORRUGATED BOARD

Density. Nearly all common corrugated boards are

porous enough to permit skin packaging. Normal bleached

facing and unbleached facing made from 90-lb liner are

satisfactory. The time required to permit 100 mL of air to

pass through the board, as measured with a Gurley

densometer (TAPPI method T460 OS75), should be less

than 100 s. Laminated facings should generally be

avoided. All ﬂutings are acceptable; types B, C, and E

are the most popular for skin packaging.

Finish. If a printed label is applied to the corrugated

board, then all the considerations that apply to a solid

bleached sulfate board should apply to the label. The

adhesive used to bond the label to the board should not

form a continuous ﬁlm as this will destroy board porosity.

Pressure-sensitive-type adhesives should be avoided. Con-

verted starch adhesives are acceptable.

Sizing. Waxes, lubricants, release agents, and most

surface treatments are not recommended for this board

and should be avoided. A normal starch calender coating

is acceptable.

Clay Coating. Clay coating is not recommended for

corrugated board. If a clay coating is used, then the

coating weight should be less than 0.49 kg/100 m

(1.0

lb/1000 ft

Clay Binders. Clay binders must be heat-stable. Protein

binders are acceptable. Styrene latex binders should be

avoided.

Machinery. Skin-packaging equipment is available in a

wide range of models and sizes. The most inexpensive

manual models will provide only the basic requirements

needed to skin package a product. A manual system will

normally run at speeds of 2–3 cycles per minute. The

number of packages produced per minute on these sys-

tems will depend on the skin-board size and the number of

individual cards that can be cut out of the board. The

standard skin-board sizes are 18 in. 24 in., 24 in. 30

in., 30 in. 36 in., and 36 in. 36 in.; however, there are

skin-board sizes available up to 30 in. 96 in. Depending

on the size of the package, you can normally get 10–12

individual packages out of an 18-in. 24-in. skin

board. Semiautomatic and fully automatic systems can

1114 SKIN PACKAGING

run at 5–12 or more cycles per minute depending on the

sophistication of the machine.

The heating system on a skin machine is mounted

above the platen, and a radiant-heat source is used to

soften the ﬁlm. The source of radiant heat is usually a

series of electric resistance rods, wire coils, or quartz

infrared heat lamps. A diffuse reﬂecting surface directs

all available radiation toward the ﬁlm and platen and

avoids the formation of hot spots.

The vacuum system is connected to the base of the

platen and is capable of drawing through the substrate

board during the vacuum cycle. There are two types of

vacuum systems: turbine and positive displacement. The

turbine system is the least expensive and is generally used

on the manual and inexpensive skin models. This system

has a turbine blower (like the type used in commercial

vacuum cleaning equipment) and can draw a large volume

of air at a relatively low vacuum pressure. This system

works most effectively with board that has good porosity.

The positive displacement vacuum system consists of a

pump and a surge tank that can evacuate the air between

the ﬁlm and the board rapidly with a strong force. This

system is used for the faster, more sophisticated skin

machines. In some cases, a dual-vacuum system (turbine

and positive displacement) is needed, such as for high-

proﬁle and odd-shaped products and for board with poor

porosity. It is sometimes worthwhile to purchase both

systems if you have a wide range of products to package.

A roller-type or hydraulic die cutter cuts the skin-

packaged board into individual packages and die cuts

the hanger hole used to hang the card on a hook. Stainless

steel or polypropylene is an acceptable cutting surface.

High-speed fully automatic skin packaging systems can

meet the packaging speed requirements of today’s packa-

ging applications while solving the concerns traditionally

associated with skin packaging. They come equipped

with smooth acceleration ‘‘no roll’’ product infeed,

adjustable high/low vacuum controls, quick changeover

(o5 min), automatic card feeding, ease of loading with

templates, and automatic off-load boxing systems to meet

industry’s high-volume, just-in-time (JIT) production re-

quirements. The new quiet hydraulic die cutters come

equipped with in-press die-saver sensor systems to elim-

inate product damage. Automatic product placement sys-

tems are also available today for high-speed automatic

packaging.

Applications. A wide variety of applications are being

skin packaged today, although not all products are suita-

ble for skin packaging. The product’s shape and composi-

tion will usually determine whether it can be skin

packaged successfully.

For example, ﬂimsy products that would be crushed by

the force of the vacuum or articles that would stick to the

skin-packaging ﬁlm should not be skin packaged. How-

ever, in the past where you could not package round or

unstable ferrous metal parts, i.e., ball bearings, because of

the difﬁculty of maintaining the product on the card prior

to ﬁlm contact, today you can with moving magnetic

plates. You can also package parts that protrude through

the back of the card.

The weight and conﬁguration of the product will

usually determine the strength of the board and the gauge

of the ﬁlm that is needed. Heavy, high-proﬁle items will

require stronger board and heavier-gauge ﬁlm.

Skin packaging for the retail visual carded display

market offers several beneﬁts for the packager, retailer,

and consumer. The packaging operation is quick and

uniform, the ﬁlm’s clarity and sparkle enhance the pro-

duct, and the display method spurs impulse buying be-

cause of product visibility and the attractive colorful

graphics.

SLITTING AND REWINDING MACHINE

R. W. YOUNG

John Dusenberry Co.

Randolph, New Jersey

Flexible plastic packaging materials generally do not have

perfectly ﬂat surfaces. The material in a parent roll

contains stretch lanes and varies in gauge by about

1–5% across the web width. Slitting and rewinding such

rolls requires equipment that can control the rewinding

speed of each slit roll independently (1). The rewinding

process is complicated even more by air entrainment into

the coils of the rewinding rolls, which separates the outer

convolutions and allows them to slip laterally. Winding

difﬁculty caused by this phenomenon increases when

handling high-slip ﬁlms or ﬁlms with smooth surfaces.

The primary aim of every slitter design is to provide

apparatus to deal selectively or generally with one or

more of the diverse products presented to it. All designs

are based on center winding (1), surface winding (2), or a

combination of both.

CENTER WINDING

Center Winder (Duplex Winder). The most widely used

and versatile slitter is a duplex stagger center winder or

two-bar winder (see Figure 1). The web tension at the

unwind of the machine is isolated from the rewind section

by driven rollers in the slitting section of the machine.

These rollers positively control web speed, opposing any

overdraw by the rewind. For most applications, the re-

winding is done on differential-rewind (slip-core) man-

drels to maintain suitable rewind tension on each slit roll

despite stretch lanes in the web and unequal diameter

buildup caused by gauge bands commonly found in

plastic webs (1). Individual riding rollers forced against

each of the rewinding rolls minimize air entrainment

into the rewinding roll. For winding paper products, the

riding roller also has a surface-winding effect that in-

creases roll hardness without using excessive rewind

tension (3).

These machines are suitable for handling web widths

up to about 80 in. (2032 mm), rewind diameters up to

SLITTING AND REWINDING MACHINE 1115

24 in. (610 mm), and web speeds of r 1500 ft/min (B460 m/

min). They are especially suited for narrow-width slitting.

The productivity of machines with removable rewind

mandrels can be increased by using two pairs of mandrels

so that the slitting operation can continue while the

alternative pair is being serviced. Removable mandrels

commonly require two operators or one operator and a

hoist for handling into and out of the machine. Machines

equipped with nonremovable cantilevered mandrels per-

mit one operator to remove the slit rolls, recore, and

restart winding quickly without mandrel handling (see

Figure 2). The choice of systems depends on the size and

number of slit rolls per setup. Maximum production is

achieved by mounting cantilevered mandrels into two-

station turrets (see Figure 3). With automatic cutoff and

restart of web around the core, these machines can slit

and rewind a web emerging from an extruder on a

continuous basis.

Individual-Rewind-Arm (IRA) Surface-Center Winders.

IRA-winder design is based on both center- and surface-

winding principles (see Figure 4). The design stresses the

ability to control the surface-contact force and rewind

torque of each rewinding roll individually. Each rewind

core is supported by chucks (one or both driven by a

torque-controlled motor) supported on pivoted arms ar-

ranged in stagger-wind fashion on each side of a winding

drum. The handling of rewind mandrels is eliminated (1).

The contact force between the rewind roll and the winding

drum is exerted by air cylinders controlled manually or by

microprocessors. For better control of roll hardness, this

force can be programmed as a function of rewind diameter

and web speed.

These machines are suited for processing webs in

excess of 80 in. (2032 mm) in width and for winding in

excess of 24-in. (610-mm) diameter. Maximum design web

speed is about 2000 ft/min (610 m/min). Actual production

operating speed is frequently limited to r1200 ft/min (365

m/min) because of web properties, vibration of the

Figure 1. Center winder (duplex winder) illustrating stagger differential winding principle.

Figure 2. Center winder with cantilevered rewind mandrels and

integral unwind station.

Figure 3. Center winder with cantilevered rewind mandrels

mounted in turrets for continuous differential winding.

1116 SLITTING AND REWINDING MACHINE

rewound roll (4), parent-roll eccentricity, or off-machine

roll-handling backup (see the Roll handling article). Doff-

ing of the rewound rolls can be done in sets with overhead

hoist and special ‘‘grabbing’’ devices. Recent designs fea-

ture rotating rewind arm support beams, allowing the

rewound rolls to be lowered and released directly onto low-

bed, wheeled dollies. This is called dofﬁng to the ﬂoor (see

Figure 5).

IRA Center Winders. This winder is similar to the IRA

discussed above except that an individual contact roller,

supported by a pair of pivoted arms, contacts the rewound

roll in place of a full-width winding drum (see Figure 6).

The contact roller is urged against the rewound roll by air

cylinders. The winding tension is developed by a rewind

motor driving each core. The primary function of the

contact roller is to minimize air entrainment. Sensors

detect the buildup of the rewind roll, which causes the

rewind arms to move outward and maintain a relatively

ﬁxed position of the contact roller. This winding method is

more responsive to the control of stretch lanes in the web

and signiﬁcantly reduces the roll vibration sometimes

associated with high-speed surface winders (4). For best

results, the contact force and rewind torque must be

programmed by microprocessors as a function of web

speed and rewind diameter, thereby giving the desired

hardness and uniformity in the rewound roll at web

speeds upward of 2000 ft/min (610 m/min). These ma-

chines also feature dofﬁng to the ﬂoor.

SURFACE WINDERS

Many versions and sizes of slitting equipment employ the

surface-winding principle (2, 5). For a detailed discussion

of larger-size rewinders, see Ref. (6). The machine most

widely used for general converting is the two-drum winder

with riding roll (see Figure 7). It is commonly used for

slitting plain paper and paperboard, as well as many

printed, coated, and laminated paper products.

Figure 4. IRA surface-center winder.

Figure 5. IRA surface-center winder with dofﬁng to ﬂoor.

Figure 6. IRA center winder with riding roll and dofﬁng to ﬂoor.

Figure 7. Two-drum surface winder with kiss-shear slitting.

SLITTING AND REWINDING MACHINE 1117