by: Eric Finson and Stephen L. Kaplan
In almost every industry, the nature of a material's
surface can drastically affect a product's success. The reasons
can be quite different, varying from purely aesthetic to functional.
This is particularly true for packaging applications. To the consumer
at the point of purchase a package must appear attractive and
clean as well as preserve its contents. Obtaining the appropriate
balance of structural, aesthetic, and functional (barrier) properties
often requires compounding specific additives into the bulk material
or combining several separate materials into a composite structure.
The type of specialty additives often used as bulk treatments
may include but are not limited to antistats, antiblocks, slip
modifiers, plasticizers, fillers, and stabilizers for UV, oxygen,
and heat. The operations or procedures used to take various raw
materials and fashion them into packaging structures is often
referred to as "converting." A surface treatment is
frequently employed as part of the conversion process to alter
the surface characteristics of the specific material being used.
Typical surface treatment processes include altering the wettability
of a substrate, improving the bondability of an applied material
or the elimination of accumulated static charge. Surface treatment
technologies can play a key role in the preparation of surfaces
of the most commonly used packaging substrates such as paper,
plastic, foil, or metal/inorganic depositions for subsequent processing
steps. In many cases, packaging producers are required to select
specially formulated and expensive materials (eg, printing inks,
adhesives, polymer films, or structures) to ensure satisfactory
performance. The alternative to this scenario is to choose a material
or combination of materials for their bulk properties and then
modify their surfaces to achieve appropriate performance attributes.
Surface treatments can allow the necessary modifications to packaging
material surfaces without altering their bulk properties so that
individual or multilaminate composite packaging structures can
meet or exceed end use requirements.
Achieving adequate adhesion to polymers is a recurring
and difficult problem throughout the packaging industry. Historically,
various surface treatments have been used to improve the adhesion
of coatings to plastics, including flame and corona, mechanical
abrasion, solvent cleaning or swelling followed by wet chemical
etching, or the application of specialized coatings in the form
of chemical primers. Also, high energy density treatments (1)
such as ultraviolet (uv) radiation, electron-beam and cold-gas-plasma
methods have gained greater acceptance on a larger scale for substrate
surface modification. They provide a medium rich in reactive species,
such as energetic photons, electrons, free radicals, and ions,
which, in turn, interact with the polymer surface, changing its
chemistry and/or morphology. These processes can be readily adopted
to modify surface properties of webs, films, and rigid containers,
which are commonly incorporated into packaging structures. The
available surface treatment technologies are summarized in Table
or wet blasting, hand or machine sanding
applicable only forlow production volumes, must deal with
immersion, spraying or vapor degreasing
disposal and environmental concerns (i.e, emissions)
environmental systems impact, high volume capacity, and relatively
etching with acids or bases
brushing, rinsing, spraying
issues due to the use of corrosive, toxic materials and hazardous-waste
application of poly ethyleneamine, polyurethanes, acrylates,
chlorinated polymers, nitrocellulose, or shellac
specific equipment, and different primers are necessary for
specific end-use requirements.
for flat films or three-dimensional configurations
hazard, limited to some
extent to thermally insensitivematerials.
for both conductive and dielectric substrates
primarily to films and webs
for film or three dimensional applications can use ac, dc,
or microwave frequency
and cost effective; non toxic materials or disposal issues;
can be effective in numerous different configurations
distinct parts in batch systems.
only in batch format and requires longer residence times
for webs and films only
being developed for commercial-scale applications
exposure to elemental fluorine can be batch or continuous
equipment required for delivery and monitoring fluorine.
be in the form of charge dissipation or charge neutralization
can be simple through complex and expensive, depending on
Among conventional surface treatment techniques, mechanical abrasion
serves only to increase the surface area of the material by "roughening"
the exposed areas prior to coating or adhesive bonding. Mechanical
abrasion can be achieved through dry blasting, wet blasting or
hand/machine sanding. These processes can be very operator. sensitive,
labor-intensive, dirty, and difficult to perform on the high-production
volumes normally associated with packaging applications. To remove
particulates or residues, a solvent wash usually follows mechanical
abrasion. In many cases, the spent abrasive materials fall under
the classification of hazardous substances and must be disposed
Liquid cleaning can be very useful for removing gross contamination.
Fluid cleaning techniques for polymer surfaces fall into three
main categories: hand wiping, solvent cleaning, and water-based
washing. Hand wiping can be done with a variety of solvents, combination
of solvents, or an aqueous solution of various chemicals. This
process is very labor-intensive and is usually only employed in
situations with low production volumes. Hand wiping can result
in inconsistencies in quality due to either human error or the
redeposition of soils onto the surfaces being cleaned from contaminated
rags used in the process. Surface treatment by solvent cleaning
is most beneficial in those cases where swelling of the polymer
surface, due to solvent absorption, results in a rougher morphology
that can improve the adhesion of coatings without adversely affecting
the substrate's mechanical properties. The process uses inexpensive
equipment and works reasonably well in many cases such as in the
surface preparation of molded polymer parts for subsequent paint
adhesive, or coating application. Solvent treatment processes
can be conducted through wiping, immersion, spraying, or vapor
degreasing. Typically, high-vapor-pressure organic solvents (alcohols,
ketones, toluene, etc), chlorinated hydrocarbon solvents (eg,
Freons, or 1,1,1-trichloroethane) or low-vapor-pressure organic
solvents (terpenes, isoparaffins, lactates, esters, etc) are used
in these processes (2). The major drawbacks of the technology
are the environmental and process hazards associated with the
use of large quantities of volatile chemicals, to the extent that
any savings in equipment cost are usually offset by the increased
cost of obligatory environmental controls. Also, solvent-based
surface treatment has limited utility when a distinct change in
the chemical nature of the substrate surface is desired. Water-based
cleaning processes operate with relatively low costs, have low
environmental impact, and are well suited for high production
volumes. An industrial power washer usually consists of an overhead
or floor conveyor with parts mounted on racks that pass through
various spray stages. Most systems are composed of seven separate
functions: precleaning, cleaning, rinsing, conditioner or rinse
aid, deionized water rinsing, air blow off, and oven drying (3).
However, for most commercial applications this technology requires
capital investment for new equipment.
Generally, chemical or acid etching is more
effective in improving adhesion to polymers than liquid cleaning
or solvent swelling. These processes cause specific chemical changes
to the substrate surface, allowing greater chemical and physical
interactions to adhesives or coatings. Some common examples of
chemical etching processes for various polymer materials are listed
in Table 2 (4). The chemical treatment of polyolefins in many
cases incorporates the use of chromic-sulfuric acid mixtures (5).
Previous studies have shown that for LDPE and HDPE severe roughening
of the surface occurs. The effect of such treatments on polypropylene
depends strongly on the prior thermal history of the polymer,
and higher etch rates have been observed in areas of low crystallinity.
There can also be changes in the polymer surface chemistry after
chromic acid oxidation. Reflection ir spectra (6) show that this
treatment results in the incorporation of oxygen (hydroxyl, carbonyl,
and ester groups) and sulfur (SO3H)-containing functional groups
in the LDPE surface. However, the precise chemical state of a
polymer surface after chemical exposure is dependent on the nature
and thermal history of the polymer, the composition of the etchant
solution, and the time and temperature of the exposure. Often
a process will work well for one material but will not be effective
for another, necessitating specific treatments for each type of
substrate. Also, chemical etching processes must be monitored
closely as overexposure can result in overtreated, discolored,
or damaged materials. In many instances, the etchant materials
used can pose serious safety, hazard, and disposal problems. Although
many of these processes can be effective in treating specific
polymer materials, numerous users are seeking alternatives because
of the concerns for operator safety and the complications of use
(PET & PETG)
hydroxide, 20 pbw
Distilled water, 80 pbw
in hot water and hot-air-dry
Sodium, 2.0 pbw
Tetrahydrofuran, 85.0 pbw
in MEK and toluene, then rinse in distilled water
Distilled water, 7%
Concentrated sulfuric acid, 88%
in distilled water
Distilled water, 9.5%
Concentrated sulfuric acid, 90%
in distilled water
Concentrated sulfuric acid, 95%
in distilled water
Perchloroethylene, 54.0 pbw
p-Toluene sulfuric acid, 2.0 pbw
at 120C for 1 min.; rinse in tap water
Distilled water, 20.0 pbw
off twice with tap water
Chemical primers can provide improved printing and adhesion characteristics
by applying a chemically distinct layer on the substrate. This
is usually accomplished by applying a liquid material in the form
of a thin film and then drying off the solvents to leave a desired
resin coating. Many polymer surfaces in the form supplied by the
manufacturer can generate problems with respect to printability
or the adhesion of decorative or functional coatings. Many packaging
grade polymers are treated for improved adhesion, but chemical
priming can also be used to improve productivity of converting
processes. When primers are used on low-surface-energy substrates
such as polyolefins, printing defects can be greatly reduced and
issues such as screening, mottling, and "fisheyes" can
be virtually eliminated. In the printing industry, press-speed
limitations are seldom a function of solvent retention, but rather
of adequate ink adhesion (7). As press speed increases the effectiveness
of high-energy density treatments decreases. The fact that printing
primers have the same surface tension characteristics at all press
speeds provides a productive advantage as long as there is adequate
drying capacity. As a result, maximum press or laminator speeds
are attainable as long as the primer and subsequent printing inks
can be dried. Unlike corona or flame treatment methods, primed
surfaces tend to remain unaltered and the effect of additive migration
to their surfaces appears to be limited. Primers can fall under
various chemical classes such as polyethyleneimine, polyurethanes,
acrylates, and chlorinated polymers. To prime foil substrates
for printing or other subsequent converting operations, solvent-based
solutions of nitrocellulose and shellac are still used. However,
the trend is toward specific high-performance water-based primers
such as ethylene acrylic acid. The main drawback to chemical priming
is that there is no universal primer and different materials are
needed for specific end-use requirements.
In flame treatment, the polymer surface is passed through a flame
generated by the combustion of a hydrocarbon (typically natural
gas). Flame treatment can be conducted in a variety of configurations
(illustrated in Fig. 1). Usually, containers or polymer webs are
passed through a bank of flame jets at a given speed to provide
the desired properties. In direct flame treatment, the high temperature
(adiabatic flame temperature is approximately 33,000'F) is sufficient
to dissociate nitrogen and oxygen molecules into free atoms (8).
In addition, this high-temperature plasma contains carbon, free
electrons, positively charged oxygen, and other ions and excited
species. Because of this reaction, polar functional groups such
as ether, ester, carbonyl, carboxyl, and hydroxyl are contained
in a flame plasma; these are incorporated into the surface and
affect the electron density of the polymer material. The result
is that the polymer surface is polarized. By changing the polymer
surface from nonpolar to polar, the ink adhesion, laminating,
and metallizing characteristics are enhanced. Also, exposure to
the open flame oxidizes the surface and burns off surface contamination
such as material additives, processing aids, or organic contamination
such as oils or grease (9). It is probable that some of the polymer
chains actually undergo melting, which "locks" their
positions on cooling with respect to the three-dimensional configuration
of the substrate, restricting rotation of the polymer molecules.
Polar functional groups tend to stay in place on the surface,
which can explain why the surface change due to flame treatment
does not decay like that due to corona treatment. This process
is somewhat energy-intensive, and it may be difficult to reach
recessed areas and to evenly treat complex shapes. Also, care
must be taken to prevent thermal damage to sensitive materials
such as thin-walled plastics or film substrates, and higher-energy
output is necessary as production speed or throughput are increased.
Ring burner for round-bottle treatment; burner arrangement for treatment of
round plastic bottles.
In the case of corona treatment, the surface is exposed to a discharge
between a grounded and powered electrode at high voltage. A low-frequency
(typically 10-20 kHz) generator and step up transformer usually
provide the high voltage to the electrode. In each half-cycle
the applied voltage (20 kV peak) increases until it exceeds the
threshold value for electrical breakdown of the air gap, causing
the atoms and molecules to become ionized and creating an atmospheric
plasma discharge. The voltage eventually peaks and falls below
the conducting threshold. Each cycle consists of two such events
involving current flow in each direction. In continuous operation
the discharge appears to be a random series of faint sparks in
a blue-purple glow (uv radiation). The point discharge generated
across the pair of electrodes ionizes the gas present in the gap,
which subsequently induces changes in the chemistry of the surface.
Researchers (10) have demonstrated through derivatization reactions
that carbonyl, enol, and carboxylic acid groups are formed on
polyolefin materials after corona treatment. The most likely mechanism
is free-radical in nature. The corona discharge contains ions,
electrons, excited neutrals (atoms and molecules, and photons.
All of these have sufficient energy to cause bond cleavage in
the polymer surface. The resulting polymer chain radicals react
extremely rapidly with 02.. Chain scission is involved in the
formation of many of these groups, leading to a progressive reduction
in the average molecular weight and finally to the production
of CO, CO2, and H2O. In addition to oxidative degradation, there
will also be direct degradation by ion-induced sputtering. These
changes can have dramatic effects on the surface energy and functionality
of polymer materials. Both dielectric polymer and conductive substrates
can be treated with this method as illustrated in Figure 2. With
nonconducting polymer films, the grounded roller is covered with
a dielectric insulating material and a linear electrode is used.
However, with conductive metallic substrates, the process is simply
reversed by using a rotating electrode covered with a dielectric
insulating material to prevent short-circuiting to ground. In
either case, the electrode is always connected to a source of
high voltage power, and the roller always remains grounded. However,
the corona is a shower of arcs or sparks and each discharge point
has the capability of causing localized damage and is difficult
to apply consistently on three-dimensional components or structures.
With corona treatment the effect on many materials is reported
to be short-lived. This can represent a problem in some packaging
applications where treatment stability is important.
Corona discharge treaters
with segmented electrodes; driven electrode rolls.
This process consists of exposing a polymer to a low-temperature,
low-pressure glow discharge (ie, a plasma). The resulting plasma
is a partially ionized gas consisting of large concentrations
of excited atomic, molecular, ionic, and free-radical species.
Excitation of the gas molecules is accomplished by subjecting
the gas, which is enclosed in a vacuum chamber, to an electric
field, typically at radio frequency (rf). Free electrons gain
energy from the imposed rf electric field, colliding with neutral
gas molecules and transferring energy, dissociating the molecules
to form numerous reactive species. It is the interaction of these
excited species with solid surfaces placed in the plasma that
results in the chemical and physical modification of the material
surface (see Fig. 3).
The effect of a plasma on a given material is determined
by the chemistry of the reactions between the surface and the
reactive species present in the plasma. At the low exposure energies
typically used for surface treatment, the plasma surface interactions
only change the surface of the material; the effects are confined
to a region only several molecular layers deep and do not change
the bulk properties of the substrate. The resulting surface changes
depend on the composition of the surface and the gas used. Gases,
or mixtures of gases, used for plasma treatment of polymers can
include air, nitrogen, argon, oxygen, nitrous oxide, helium, tetrafluoromethane,
water vapor, carbon dioxide, methane, or ammonia. Each gas produces
a unique plasma composition and results in different surface properties.
For example, the surface energy can be increased very quickly
and effectively by plasma-induced oxidation, nitration, hydrolyzation,
or amination. Depending on the chemistry of the polymer and the
source gases, substitution of molecular moieties into the surface
can make polymers either wettable or totally non-wettable. The
specific type of substituted atoms or groups determines the specific
surface potential. For any gas composition, three competing surface
processes simultaneously alter the plastic, with the extent of
each depending on the chemistry and process variables: ablation,
crosslinking, and activation (11). Ablation is similar to an evaporation
process. In this process, the bombardment of the polymer surface
by energetic particles (ie, free radicals, electrons, and ions)
and radiation breaks the covalent bonds of the polymer backbone,
resulting in lower-molecular-weight polymer chains. As long molecular
components become shorter, the volatile oligomer and monomer byproducts
boil off (ablate) and are swept away with the vacuum-pump exhaust.
Crosslinking is done with an inert process gas (argon or helium).
The bond breaking occurs on the polymer surface, but since there
are no free-radical scavengers, it can form a bond with a nearby
free radical on a different chain (crosslink). Activation is a
process where surface polymer functional groups are replaced with
different atoms or chemical groups from the plasma. As with ablation,
surface exposure to energetic species abstracts hydrogen or breaks
the backbone of the polymer, creating free radicals. In addition,
plasma contains very high-energy uv radiation. This uv energy
creates additional similar free radicals on the polymer surface.
Free radicals, which are thermodynamically unstable, quickly react
with the polymer backbone itself or with other free-radical species
present at the surface to form stable covalently bonded atoms
or more complex groups.
Figure 4 illustrates the components of a typical
plasma surface-treatment system. In a conventional plasma process,
the chamber is evacuated to a specified pressure using a mechanical
vacuum pump and gas is introduced into it through flow controllers.
Once the gas flow has stabilized and the desired operating pressure
has been reached, the rf power is applied to the electrodes and
the gas is ionized. A capacitance-matching network tunes the chamber
impedance to a constant load. During normal operation, gas is
being continually introduced into the chamber and the unreacted
species and byproducts are continuously evacuated. The chamber
thus operates in a steady state. Cold-gas plasma offers the engineer
a means of reengineering the polymer surface and introducing the
desired functional groups in a controlled and reproducible manner.
The nature of plasma surface modification lends itself to precise
control and process repeatability. In a majority of applications,
plasma surface treatment employs innocuous gases that allow the
engineer or scientist to radically modify the surface while maintaining
workplace and environmental cleanliness and safety (12). The treatment
effect can be very long-lived and can be applied to a variety
of configurations such as webs of plastic films or three dimensional
of a typical plasma surface-treatment system.
Cold-gas-plasma processes can also be used to apply
transparent thin-film silicon oxide-based gas-barrier depositions
for flexible-packaging applications. Common polymer packaging
films such as polyethylene terephthalate (PET) and biaixially
oriented polypropylene (OPP) can be used as substrates for plasma-deposition
processes. A common process involves the plasma decomposition
of 1,1,3,3-tetramethyldisiloxane (TMDSO) or hexamethyldisiloxane
(HMDSO) in a helium and oxygen plasma to form a gas and vapor
barrier layer of SiO2 (Fig. 5). The process has been successfully
commercialized into production equipment that can accommodate
1.5 meter web widths and run up to 100 m/min. (13). The resulting
barrier films can then be processed through typical converting
steps to form transparent high-barrier flexible packaging. This
approach can improve the shelf life of packaged foods or products
and offer an alternative to conventional packaging gas-barrier
SiO2 plasma deposition process.
Ultraviolet/ozone. For this process, the polymer
surface is exposed to both uv light and ozone to increase the
number of oxygen functional groups incorporated into the material.
This approach can be useful in the surface modification of three
dimensional parts. The process has been used on polypropylene
and polyester substrates and has shown rapid and reproducible
uptake of surface oxygen functional groups (14). The attachment
of oxygen groups greatly changes the surface energy and chemistry,
which can lead to improved adhesion of functional and decorative
coatings. Most of the initial process development has been targeted
at the treatment of three-dimensional plastic components, These
are suspended or tumbled inside a reaction chamber at room temperature
and pressure and exposed simultaneously to uv (mercury-source)
light and various concentrations of ozone (O3) gas. After 5 min.
of exposure, oxygen functional groups can be attached to as many
as 30% carbon atoms on the outermost surface of polypropylene.
The stability of this treatment is usually quite good. For example,
relatively little change in the receding contact angle occurs
on the treated surface of polypropylene after aging in air for
a period of 28 days.
This is a relatively new high speed process in which thin highly
uniform acrylate coatings are applied to the polymer surface in
order to smooth the surface of polymer film substrates so that
subsequent depositions are more defect-free. This process involves
feeding acrylate monomeric fluids into an ultrasonic atomizer
connected to an evaporator in a reaction chamber at reduced pressure.
The acrylate material is atomized into a mist that contacts the
hot walls of the evaporator, where it is transformed into a gas.
The molecular vapor that results exits through a slit in the evaporator
nozzle and is condensed on a substrate moving in front of the
nozzle. This thin liquid is then irradiated with a low-voltage
electron gun and the coating is transformed into a hard, tough
thin-film coating. The process is claimed to be compatible with
various vacuum coating processes such as sputtering, evaporation,
or plasma deposition; and can in principle be conducted in series
with other deposition processes within the same reaction vessel.
The presence of this coating has been shown (15) to greatly improve
the coating uniformity of aluminum metallized barrier depositions
on both oriented polypropylene and polyester packaging films.
Consequently, the oxygen- and water-vapor barrier properties are
improved. This can have an impact in numerous applications for
extending the shelf life of packaged products, The improvement
in barrier can be attributed to three factors:
1. The coating forms a smooth layer on the polymer
surface, eliminating any surface irregularities.
2. The coating has very good temperature stability
which provides a thermally stable platform on which to apply a
3. The acrylate surface is more chemically polar
than many polymer films, and the density of the resulting film
is higher. Barrier layers composed of metals and inorganic oxides
tend to grow more readily on a polar substrate than on a nonpolar
The fluorination process involves exposing polymeric webs continuously
to fluorine gas (F2) diluted with an inert gas (eg, nitrogen)
inside a reaction chamber (16). This process can greatly increase
the surface energy of polymer materials such that excellent adherence
can be attained to other materials such as lacquers and adhesive
agents. Diatomic fluorine, an almost colorless gas, is one of
the strongest oxidizing agents; it reacts with almost all organic
and inorganic substances (except nitrogen and other inert gases).
Fluorine's great reactivity is due to the interaction of the low
dissociation energy of the molecule and the very strong bonds
it forms with other atoms. Electron spectroscopy for chemical
analysis (ESCA) data indicate that the activation of polymer surfaces
using this process results from the partial fluorination of the
hydrocarbon structure of the polymer molecules. An additional
application would be the fluorination of high-density polyethylene
gasoline tanks to provide hydrocarbon barrier. Fluorine is routinely
transported in its liquid state and is commercially available
because of use in the nuclear industry for the refinement of fuels.
The safeguards used for this technology are similar to safety
measures used and approved for ozone generation. Compared with
other pretreatment processes, surface fluorination not only has
a wide spectrum of applications but also doesn't require the use
of electrical equipment such as corona or plasma treatment. Surfaces
treated with fluorine exhibit long-lasting, if not irreversible,
changes. This can be very important in practical applications
in industry, since subsequent converting processes don't have
to immediately follow the surface activation.
Electrostatic discharge treatment. Plastic, as
opposed to metal, substrates make good electrical insulators because
they are electrically nonconductive and possess high electrical
resistivity. The higher the surface resistivity, the lower the
surface conductivity. However, those plastic insulating materials
that have high dielectric constants can generate and store static
electricity. Static electricity is generated when two materials
in intimate contact are separated by a frictional force causing
electrons to be preferentially stripped from one surface and transferred
to the other surface. This causes the electron-rich and electron-deficient
surfaces to assume positive and negative charges and this surface
polarization results in the generation of static electricity.
Unless this charge is dissipated, the static buildup can cause
the attraction of dust, lint, sparks, materials-handling problems,
shocks, and difficulty in wetting or adhering.
Packaging substrates made from polyethylene, polypropylene,
polyester, polystyrene, and other dielectric materials at some
time during their manufacture are usually subjected to at least
one of the many available static control techniques. These fall
into two separate categories: charge dissipation and charge neutralization.
With electrically conductive materials, dissipation of static
charge can he accomplished by simply grounding the charged material.
However, this is difficult with nonconducting materials such as
polymer films, so one approach is to humidify the work area so
that the exposed surface absorbs a thin layer of water that conducts
the charge to ground. An alternative method is to shield the surface
with antistatic organic compounds. Most antistatic agents fall
under the following types: nonionic ethoxylated alkylamine, anionic
aliphatic sulfonate/phosphates, and cationic quaternary ammonium
compounds (17). Antistats can be applied topically or blended,
and their purpose is to retard static buildup and also to rapidly
discharge any accumulated charge.
Another approach to static elimination is to neutralize
the accumulated charge using devices capable of ionizing the surrounding
air. This works by exposing electrically neutral atoms in air
to an applied electric field of voltage high enough to create
positively and negatively charged ions. Because of the bipolar
nature of the ionized air, the static charge on a material can
be neutralized by the oppositely charged ions present in the surrounding
air. Basically, there are three types of air-ionizing devices
available: nonpowered, powered, and self-powered. The nonpowered
induction type of static eliminator consists of brass brushes
mounted on ground straps that come in light contact with the charged
material, causing the surrounding air to ionize. Electrically
powered static eliminators are powered with a low-amperage high
voltage power supply for the ionization of the air. Radioactive
self-powered units are similar to electrical static eliminators
in design and construction except for the source of power. Radioactive
devices are self-propagating, usually consisting of a low-energy
source of an alpha-emitting radioisotope such as polonium-210
(210Po). The alpha radiation interacts spontaneously with the
air molecules, producing ionization of the surrounding environment.
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2. R. S. Gallagher, "Manual Cleaning Relies
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5. D. Briggs, "Surface Treatments for Polyolefins"
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6. H. A. Willis and V. J. 1. Zichy in D. T. Clark
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Sept. 1995, pp. 37-61.
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Proceedings for the Society of Vacuum Coaters, Chicago, 1995.
12. S. L. Kaplan, and W. P. Hansen, "Plasma-the
Environmentally Safe Method to Prepare Plastics and Composites
for Adhesive Bonding and Painting," paper presented at SAMPE
Environmental Symposium, San Diego, May 1991.
13. E. Finson, and J. Felts, "Transparent
Si02 Barrier Coatings: Conversion and Production Status,"
TAPPI J. 79(l), 161-165 (Jan. 1995).
14. N. S. Mcintyre and M. J. Walzak, "New
UV/Ozone Treatment Improves Adhesiveness of Polymer Surfaces,"
Modern Plast., 79-81 (March 1995).
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Characteristics of Evaporated Acrylate Coatings" in 37th
Annual Technical Conference Proceedings /br the Society of Vacuum
Canters, Boston, MA, 1994,
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Handbook, Marcel Dekker, New York, 1991, Chapt. 31, pp. 303-339.
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of Packaging Materials," Am. Lab., 81-89 (Nov. 1983).
The Wiley Encyclopedia of Packaging
Technology, Second Edition, Edited by Aaron L. Brody and Kenneth
S. Marsh - ISBN 0-471-063975-5 © 1997 by John Wiley & Sons,