Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02720568 2012-09-20
=
Vig)2009/123229
PCMUS2009/039398
METHOD FOR APPLYING A PRESSURE SENSITIVE SHRINK LABEL TO AN ART/CLE
Technical Field
This invention relates to pressure sensitive shrink labels. More specifically,
o the invention relates to pressure sensitive labels that have superior
conformability to
containers having complex shapes and methods for applying such labels.
Background
It is common practice to apply labels to containers or bottles to provide
information such as the supplier of the container or the contents of the
container.
Such containers and bottles are available in a wide variety of shapes and
sizes for
holding many different types of materials such as detergents, chemicals,
personal
care products, motor oil, beverages, etc.
Polymeric film materials and film facestocks have been described for use as
labels in various fields. Polymeric labels are increasingly desired for many
applications, particularly clear polymeric labels since they provide a no-
label look to
decorated glass and plastic containers. Paper labels block the visibility of
the
container and/or the contents in the container. Clear polymeric labels enhance
the
visual aesthetics of the container, and therefore the product, and are growing
much
faster than paper labels in the package decoration market as consumer product
companies are continuously trying to upgrade the appearance of their products.
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Polymeric film labels also have superior mechanical properties, such as
tensile
strength and abrasion resistance.
Traditional pressure sensitive adhesive (PSA) labels often have difficulty
adhering smoothly to containers having curved surfaces and/or complex shapes
without wrinkling, darting or lifting on the curved surfaces. The label size
of typical
PSA labels is limited to no larger than 1/4 inch away from the edge
(beginning) of
curvature of a container or article. Shrink sleeve labels have typically been
used on
these types of compound containers. Labeling operations are carried out using
processes and methods that require the formation of a tube or sleeve of the
heat
shrink film that is placed over the container and heated in order to shrink
the film to
conform to the size and shape of the container. Alternatively, the containers
are
completely wrapped with a shrink label using a process wherein the shrink film
is
applied to the container directly from a continuous roll of film material and
then heat
is applied to conform the wrapped label to the container. However, label
defects can
occur during labeling operations of simple or compound shaped bottles during
application or in post application processes. These misapplied labels result
in high
scrap or extra processing steps that can be costly.
The present invention provides a pressure sensitive adhesive label that can
be applied to containers and articles on complex shapes and compound curves
with
less material required and less cost than for shrink sleeve or shrink wrap
labels. In
addition, the labels of the present invention enable the user to expand the
billboard
or graphics region of traditional pressure sensitive labels on containers and
articles
having complex shapes and/or compound curves.
Summary
A label for application on a curved or nonplanar surface comprising a heat
shrink film and a pressure sensitive adhesive is provided. In one embodiment,
there
is provided a pressure sensitive adhesive label for application on a surface
having at
least one compound curve, the label comprising: a heat shrinkable film having
an
inner surface and outer surface, and a machine direction and a transverse
direction,
the film having an ultimate shrinkage S in at least one direction of at least
10% at
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90 C, wherein the shrinkage in the other direction is S + 20%; and a layer of
pressure sensitive adhesive on the inner surface of the heat shrinkable film.
The
shrink film has moderate and balanced shrink in both the machine direction and
the
transverse direction. In one embodiment, the film has an ultimate shrinkage S
in at
least one direction of at least 10% at 90 C, and the shrinkage in the other
direction is
S + 10%. The label may further include a release liner removal adhered to the
adhesive layer.
There is also provided an article bearing a label comprising: an article
having
a surface comprising at least one compound curve; and a pressure sensitive
label
comprising a heat shrinkable film having an inner surface and outer surface,
and a
layer of pressure sensitive adhesive on the inner surface of the heat
shrinkable film,
wherein the label is applied to at least one compound curve.
A method of applying a label to an article wherein the article has a surface
having at least one compound curve is provided. The method comprises: (a)
providing an article having a surface comprising at least one compound curve;
(b)
providing a label comprising (i) a heat shrinkable film having an inner
surface and
outer surface and (ii) a layer of pressure sensitive adhesive on the inner
surface of
the heat shrinkable film, wherein the label has a central portion and a
peripheral
portion; (c) contacting the adhesive layer of the central portion of the label
with the
article; (d) applying pressure to the label in an outward direction from the
central
portion to the peripheral portion, wherein at least a portion of the label is
applied to
at least one compound curve of the article; and (e) applying heat to at least
a portion
of the label to shrink at least that portion of the label and adhere the label
to the
article. After or during the application of heat, the label may be further
compressed
or wiped down to fully adhere the label to the article and eliminate any
remaining
defects in the label.
In one aspect of the invention, there is provided a method of applying a label
to an article, the method including the steps of providing an article having a
surface
comprising at least one compound curve; providing a label comprising (i) a
heat
shrinkable film having an inner surface and an outer surface; and (ii) a layer
of
pressure sensitive adhesive on the inner surface of the heat shrinkable film,
wherein
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the label has a first edge and a contact region; contacting the adhesive layer
in the
contact region of the label with the article; and applying heat and pressure
simultaneously to the label in a direction from the contact region to the
first edge
such that the first edge of the label adheres to the article and the label
shrinks to
conform to the compound curve of the article, wherein the heat and pressure
are
applied by at least one hot air knife assembly comprising a source of heated
air, a
flow control mechanism and one or more hot air knife slots.
In one embodiment, the label includes a center and a second edge opposite
the first edge, and the contact region is proximate to or in the center of the
label. In
lo another embodiment, the label includes a second edge opposite the first
edge and
the contact region is proximate to the second edge of the label.
Heat and pressure may be applied to the label by a hot air knife assembly
that includes at least two hot air knife slots that rotate outwardly from the
center of
the label to the first and second edges to adhere the label to the article.
In one embodiment of the method of the present invention, a first hot air
knife
slot applies heat and pressure to the center of the label outwardly to the
first edge of
the label, and a second hot air knife slot applies heat and pressure to the
center of
the label outwardly to the second edge of the label. The article may be
rotated
about 1800 prior to the application of heat and pressure by the second hot air
knife
slot to the label.
Brief Description of Drawings
FIG. 1 illustrates a front view of a container to which the label of the
present
invention has been applied as compared to prior art pressure sensitive labels.
FIG. 2A to 2D illustrates the labeled container before and after the
application
of heat to the label.
FIG. 3A to 3D illustrate embodiments of containers having complex shapes
and compound curves to which the label of the present invention is applied.
FIG 4A and 4B illustrate front views of embodiments of containers having
irregular surfaces.
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FIG. 5 is a three dimensional view of a portion of a labeled article having a
compound curve.
FIGS. 6A-6D schematically illustrate the process of applying the label to an
article having a compound curve.
FIGS. 7A and 7B schematically illustrate an embodiment of the process of
applying a label to an article wherein a walking beam is used.
FIGS. 8A and 8B are schematic views of an air knife assembly for
simultaneously applying heat and pressure to a label.
FIGS. 9A-9E are schematic views of a process for applying a label to an
lo article using multiple air knife slots.
Detailed Description
Pressure sensitive adhesive labels are provided that can improve the
appearance of labeled containers and articles by conforming to the contours of
the
container or article and by providing an enlarged billboard appearance. End
users
and product designers must currently alter their designs to accommodate the
limitations of traditional product decorating technologies. The labels of the
present
invention provide the designers with more freedom in product designs to create
more shelf appeal and to carry more information.
Containers and articles with compound curves typically have to be fully
wrapped with shrink film in order to label or decorate the article. The labels
of the
present invention are capable of expanding the label over complex curves
without
having to fully wrap the article. This partial label coverage impacts the
product cost
as well as the product appearance. Typical pressure sensitive labels cannot be
applied to containers and articles without undesirable darting and wrinkling
of the
label. "Darting" is defined as the accumulation of excess label material that
rises up
away from the article to which the label is applied.
The labels of the present invention provide significant processing advantages
over traditional shrink labels. For example, the pressure sensitive shrink
labels of
the present invention allow for more traditional printing and secondary
processes
such as foils and hot stamping. Where typical shrink labels must be subsurface
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printed, the labels of the present invention can be surface printed, which
enhances
the color quality, sharpness and texture of the printed image. The label film
may be
printed by water flexographic, UV flexographic, UV letterpress, UV screen,
solvent
gravure and hot foil stamp.
The pressure sensitive labels comprise (a) a heat shrinkable polymeric film
having an inner surface and an outer surface and a machine direction and a
transverse direction; and (b) a layer of pressure sensitive adhesive on the
inner
surface of the heat shrinkable film. The shrinkage of the heat shrinkable
polymeric
film is balanced in the machine direction and the transverse direction. In at
least one
lo
direction, the ultimate shrinkage (S) is at least 10% at 90 C and in the other
direction, the shrinkage is S + 20%. As an illustration of balanced shrinkage,
if the
shrinkage in the machine direction is 40% at 105 C, then the shrinkage in the
transverse direction is 40% + 20%, or within the range of 20% to 60% at 105 C.
In
one embodiment, the ultimate shrinkage (S) is at least 10% at 90 C and in the
other
direction, the shrinkage is S + 10%. As used herein, the term "ultimate
shrinkage"
means the maximum shrinkage the film is capable of achieving at a particular
shrink
temperature, as measured by ASTM Method D 1204.
The labels are not provided as a shrink sleeve or tube that encapsulates the
entire article or as a shrink wrap label that wraps around the article and
forms a
seam wherein the ends of the label meet. The present labels may be provided in
a
variety of shapes to suit the article or container to which they are applied,
giving the
container designer greater latitude in container configuration and label
design than
with traditional pressure sensitive labels or with shrink wrap or shrink
sleeve labels.
The labels may be cut into the desired shape by any known method, including,
for
example, die cutting and laser cutting. In one embodiment, the label is die
cut to a
specific configuration that compensates for the shrinkage of the label and the
shape
of the article to which it is applied.
Because the label is conformable, the billboard or graphics area of the
labeled container can be extended further onto the container edges and onto
compound curved areas of the container. The label may be 10% to 30% larger
than
a standard PSA label. As used herein, the term "compound curve" means a
surface
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having no direction for which there is no curvature. For example, the surface
of a
sphere or the surface of an ellipsoid has curvature in every direction, and
therefore
has compound curves. A cylinder, on the other hand, has a surface for which
there
is at least one direction for which there is no curvature. Thus, a simple
cylinder does
not have compound curves.
FIG. 1 illustrates the expanded billboard area of the pressure sensitive
shrink
label of the present invention. Bottle 10 has pressure sensitive shrink label
12
adhered thereto. The dashed line 14 indicates the outer boundary of standard
pressure sensitive labels. A standard (i.e., non-shrink) pressure sensitive
label
lo cannot extend onto the areas of the bottle having the compound curves 16
(the area
between the inner dashed line and the outer solid line). When label 12 is
initially
applied to the bottle 10, darts and pleats may form near the perimeter of the
label in
the areas of the bottle having compound curves 16.
Once the pressure sensitive label is applied to the container, heat is applied
as needed to eliminate any label application defects such as darts, edge lift
and
wrinkles. In one embodiment, pressure and/or wipe down may be used in addition
to the application of heat to eliminate any defects.
Referring to FIGS. 2A ¨ 2D, the present label and method for applying the
label are illustrated. In FIGS. 2A and 2B, a label 12 that includes a shrink
film
having a continuous layer of pressure sensitive adhesive applied thereto is
applied
to a container 10 having compound curves around the circumference of the
container, and then wiped down. No heat is applied to the label. The label 12
extends onto the compound curves 16 where darts 18 are formed near the
perimeter
20 of the label. FIGS. 20 and 2D show the labeled container of FIGS. 2A ¨ 2B
after
heat is applied to the label. The darts 18 have been eliminated and the label
12
conforms to the compound curves of the container 10 near the label perimeter
20
without any defects.
The article or container to which the label is applied can be provided in a
variety of forms or shapes. Non-limiting examples of suitable articles include
containers with and without closures, trays, lids, toys, appliances, etc. The
article or
container may be made of any conventional polymer, glass, or metal such as
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aluminum. Examples of suitable polymeric materials include high
density
polyethylene (HDPE), low density polyethylene (LDPE), polyethylene
terephthalate
(PET), polypropylene (PP), polyvinyl chloride, polycarbonate, nylon,
fluorinated
ethylene propylene, polystyrene, etc. The article or container can be made by
a
number of various processes known in the art, such as blow molding, injection
molding, thermoforming, rotational molding and the like.
Useful containers include, for example, a bottle having a closure on the top
of
the bottle, an upside down bottle having a closure on the bottom of the
bottle, a
bottle with a pump dispenser or a foaming dispenser, a tube with a closure and
a
bottle with a closure.
The container or article may have a transparent appearance. In one
embodiment, the container or article has a translucent appearance. The
translucent
appearance can be achieved by, for example, treatments of the transparent
container or article, the addition of ingredients such as dyes and pearlescent
agents
to base polymers, the use of polypropylene and/or polyethylene that are mixed
with
clarifying agents. The treatments include, for example, spray coating,
sandblasting,
and mold surface treatment.
The container or article may include aesthetic features, including, for
example, textures, embossing, lenticular lens, colors, holograms, frosted or
matte
color, etc. The surface of the container or article may be treated prior to
application
of the label. For example, the surface of the container or article may be
flame
treated or a primer coating may be applied.
FIGS. 3A, 3B and 30 each illustrate a container having a complex shape and
compound curves. FIG. 3A is a front view of a container 30a having a
symmetrical,
spherical shape wherein the container has a tapered concave area 32 at the top
and
a wider convex area 33 toward the bottom. Typically, a shrink sleeve would be
used
to provide a functional label for this container. With the present invention,
a
pressure sensitive shrink label 31 can be smoothly applied to container 30a
without
the appearance of label defects. FIG. 3B is a front view of a container 30b
having
an asymmetrical shape wherein one side of the container has both a concave
area
34 and a convex area 35 and the opposing side curves in a substantially
similar
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manner along the length of the container. The conventional method of labeling
container 30b would be to apply a shrink sleeve label to conform to the
complex
shape of the container. A pressure sensitive shrink label 31 can be applied to
the
container 30b to provide sufficient billboard area with much less label
material. FIG.
30 is a front view of a container 30c that is an upside down bottle having a
closure
36 at the bottom and label 31 applied to the front surface. Fig. 3D is a side
view of
container 30c. The areas 37 within the dashed lines indicate the outer
boundaries of
standard pressure sensitive labels that can be applied to the container. The
complex shape of this container requires two separate standard pressure
sensitive
lo labels to decorate the container, as the application of one continuous
standard
pressure sensitive label would result in the formation of darts and pleat
defects.
Pressure sensitive shrink label 31 can cover a much larger area, which
provides
more design options for the product designer.
FIGS. 4A and 4B each illustrate a container having an irregular surface. FIG.
4A is a front view of a container 40a having raised ridges 42 along one side
of the
container. The opposing side of the container has a smooth surface. FIG. 4B is
a
front view of a container 40b having circumferentially recessed rings 43 along
the
length of the container. It should be noted that cylindrically shaped articles
having
areas of compound curves such as containers 40a and 40b are not excluded from
the articles claimed herein.
FIG. 5 is a schematic three dimensional view of a portion of a container to
which the label has been applied. The container 50 has surface comprising a
compound curve. Label 52 is applied to the container and covers a portion of
the
compound curved area. Line 54 indicates the outer boundary to which typical
pressure sensitive labels can be applied with out the formation of defects in
the
label. Area 56 indicates the expanded billboard area that is obtainable with
the
present labels without the formation of defects such wrinkles, edge lift or
darts.
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Shrink Film
The polymeric films useful in the label constructions of the present invention
possess balanced shrink properties. The balanced shrink properties allow the
film to
tighten darts and wrinkles initially formed in the label when the label is
applied over
curved surfaces and allow the darts and wrinkles to be wiped down with minimal
graphics distortion of the label. Films having unbalanced shrink, that is,
films having
a high degree of shrink in one direction and low to moderate shrink in the
other
direction are not particularly useful because while darts may be removed in
one
direction, in the other direction the formation of darts is exacerbated.
Useful films
lo
having balanced shrink allow for a wider variety of label shapes to be applied
to a
wider variety of container shapes.
In one embodiment, the polymeric film has an ultimate shrinkage (S) as
measured by ASTM procedure D1204 in at least one direction of at least 10% at
90 C and in the other direction, the shrinkage is S + 20%. In another
embodiment,
the film has an ultimate shrinkage (S) in at least one direction of about 10%
to about
50% at 70 C and in the other direction, the shrinkage is S + 20%. In one
embodiment, the ultimate shrinkage (S) is at least 10% at 90 C and in the
other
direction, the shrinkage is S + 10%. The shrink initiation temperature of the
film, in
one embodiment, is in the range of about 60 C to about 80 C.
The shrink film must be thermally shrinkable and yet have sufficient stiffness
to be dispensed using conventional labeling equipment and processes, including
printing, die-cutting and label transfer. The stiffness of the film required
depends on
the size of the label, the speed of application and the labeling equipment
being used.
In one embodiment, the shrink film has a stiffness in the machine direction
(MD) of
at least 5 mN, as measured by the L&W Bending Resistance test. In one
embodiment, the shrink film has a stiffness of at least 10 mN, or at least 20
mN. The
stiffness of the shrink film is important for proper dispensing of labels over
a peel
plate at higher line speeds.
In one embodiment, the die-cut labels are applied to the article or container
in
an automated labeling line process at a line speed of at least 100 units per
minute,
or at least 250 units per minute or at least 500 units per minute.
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In one embodiment, the shrink film has a 2% secant modulus as measured by
ASTM D882 in the machine direction (MD) of about 20,000 to about 400,000 psi,
and in the transverse (or cross) direction (TD) of about 20,000 to about
400,000 psi.
In another embodiment, the 2% secant modulus of the film is about 30,000 to
about
300,000 in the machine direction and about 30,000 to about 300,000 in the
transverse direction. The film may have a lower modulus in the transverse
direction
than in the machine direction so that the label is easily dispensed (MD) while
maintaining sufficiently low modulus in the TD for conformability and/or
squeezability.
lo
The polymeric film may be made by conventional processes. For example,
the film may be produced using a double bubble process, tenter process or may
comprise a blown film.
The shrink film useful in the label may be a single layer construction or a
multilayer construction. The layer or layers of the shrink film may be formed
from a
polymer chosen from polyester, polyolefin, polyvinyl chloride, polystyrene,
polylactic
acid, copolymers and blends thereof.
Polyolefins comprise homopolymers or copolymers of olefins that are aliphatic
hydrocarbons having one or more carbon to carbon double bonds. Olefins include
alkenes that comprise 1-alkenes, also known as alpha-olefins, such as 1-butene
and
internal alkenes having the carbon to carbon double bond on nonterminal carbon
atoms of the carbon chain, such as 2-butene, cyclic olefins having one or more
carbon to carbon double bonds, such as cyclohexene and norbornadiene, and
cyclic
polyenes which are noncyclic aliphatic hydrocarbons having two or more carbon
to
carbon double bonds, such as 1,4-butadiene and isoprene. Polyolefins comprise
alkene homopolymers from a single alkene monomer, such as a polypropylene
homopolymer, alkene copolymers from at least one alkene monomer and one or
more additional olefin monomers where the first listed alkene is the major
constituent
of the copolymer, such as a propylene-ethylene copolymer and a propylene-
ethylene-butadiene copolymer, cyclic olefin homopolymers from a single cyclic
olefin
monomer, and cyclic olefin copolymers from at least one cyclic olefin monomer
and
one or more additional olefin monomers wherein the first listed cyclic olefin
is the
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major constituent of the copolymer, and mixtures of any of the foregoing
olefin
polymers.
In one embodiment, the shrink film is a multilayer film comprising a core
layer
and at least one skin layer. The skin layer may be a printable skin layer. In
one
embodiment, the multilayer shrink film comprises a core and two skin layers,
wherein in at least one skin layer is printable. The multilayer shrink film
may be a
coextruded film.
The film can range in thickness from 0.5-20, or 0.5-12, or 0.5-8, or 1-3 mils.
The difference in the layers of the film can include a difference in
thermoplastic
lo
polymer components, in additive components, in orientation, in thickness, or a
combination thereof. The thickness of the core layer can be 50-95%, or 60-95%
or
70-90% of the thickness of the film. The thickness of a skin layer or of a
combination of two skin layers can be 5-50%, or 5-40% or 10-30% of the
thickness
of the film.
The film can be further treated on one surface or both the upper and lower
surfaces to enhance performance in terms of printability or adhesion to an
adhesive.
The treatment can comprise applying a surface coating such as, for example, a
lacquer, applying a high energy discharge to include a corona discharge to a
surface, applying a flame treatment to a surface, or a combination of any of
the
foregoing treatments. In an embodiment of the invention, the film is treated
on both
surfaces, and in another embodiment the film is treated on one surface with a
corona discharge and is flame treated on the other surface.
The layers of the shrink film may contain pigments, fillers, stabilizers,
light
protective agents or other suitable modifying agents if desired. The film may
also
contain anti-block, slip additives and anti-static agents. Useful anti-block
agents
include inorganic particles, such as clays, talc, calcium carbonate and glass.
Slip
additives useful in the present invention include polysiloxanes, waxes, fatty
amides,
fatty acids, metal soaps and particulate such as silica, synthetic amorphous
silica
and polytetrafluoroethylene powder. Anti-static agents useful in the present
invention include alkali metal sulfonates, polyether-modified
polydiorganosiloxanes,
polyalkylphenylsiloxanes and tertiary amines.
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In one embodiment, the shrink film is microperforated to allow trapped air to
be released from the interface between the label and the article to which it
is
adhered. In another embodiment, the shrink film is permeable to allow fluid to
escape from the adhesive or from the surface of the article to escape. In one
embodiment, vent holes or slits are provided in the shrink film.
Adhesives
A description of useful pressure sensitive adhesives may be found in
Encyclopedia of Polymer Science and Engineering, Vol. 13, Wiley-Interscience
lo Publishers (New York, 1988). Additional description of useful PSAs may
be found
in Polymer Science and Technology, Vol. 1, Interscience Publishers (New York,
1964). Conventional PSAs, including acrylic-based PSAs, rubber-based PSAs and
silicone-based PSAs are useful. The PSA may be a solvent based or may be a
water based adhesive. Hot melt adhesives may also be used. In one embodiment,
the PSA comprises an acrylic emulsion adhesive.
The adhesive and the side of the film to which the adhesive is applied have
sufficient compatibility to enable good adhesive anchorage. In one embodiment,
the
adhesive is chosen so that the labels may be cleanly removed from PET
containers
up to 24 hours after application. The adhesive is also chosen so that the
adhesive
components do not migrate into the film.
In one embodiment, the adhesive may be formed from an acrylic based
polymer. It is contemplated that any acrylic based polymer capable of forming
an
adhesive layer with sufficient tack to adhere to a substrate may function in
the
present invention. In certain embodiments, the acrylic polymers for the
pressure-
sensitive adhesive layers include those formed from polymerization of at least
one
alkyl acrylate monomer containing from about 4 to about 12 carbon atoms in the
alkyl group, and present in an amount from about 35-95% by weight of the
polymer
or copolymer, as disclosed in U.S. Pat. No. 5,264,532. Optionally, the acrylic
based
pressure-sensitive adhesive might be formed from a single polymeric species.
The glass transition temperature of a PSA layer comprising acrylic polymers
can be varied by adjusting the amount of polar, or "hard monomers", in the
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copolymer, as taught by U.S. Pat. No. 5,264,532.
The greater the percentage by weight of hard monomers is an acrylic copolymer,
the
higher the glass transition temperature. Hard monomers contemplated useful for
the
present invention include vinyl esters, carboxylic acids, and methacnilates,
in
concentrations by weight ranging from about zero to about thirty-five percent
by
weight of the polymer.
The PSA can be acrylic based such as those taught in U.S. Pat. No.
5,164,444 (acrylic emulsion), U.S. Pat. No. 5,623,011 (tackified acrylic
emulsion)
and U.S. Pat No. 6,306,982. The adhesive can also be rubber-based such as
those
o taught in U.S. Pat. No. 5,705,551 (rubber hot melt). It can also be
radiation curable
mixture of monomers with initiators and other ingredients such as those taught
in
U.S. Pat No. 5,232,958 (UV cured acrylic) and U.S. Pat. No. 5,232,958 (EB
cured).
Commercially available PSAs are useful in the invention. Examples of these
adhesives include the hot melt PSAs available from H.B. Fuller Company, St.
Paul,
Minn. as HM-1597, HL-2207-X, HL-2115-X, HL-2193-X. Other useful commercially
available PSAs include those available from Century Adhesives Corporation,
Columbus, Ohio. Another useful acrylic PSA comprises a blend of emulsion
polymer
particles with dispersion tackifier particles as generally described in
Example 2 of
U.S. Pat. No. 6,306,982. The polymer is made by emulsion polymerization of 2-
ethylhexyl acrylate, vinyl acetate, clioctyl maleate, and acrylic and
methacrylic
comonomers as described in U.S. Pat. No. 5,164,444 resulting in the latex
particle
size of about 0.2 microns in weight average diameters and a gel content of
about
60%.
A commercial example of a hot melt adhesive is H2187-01, sold by Ato
Findley, Inc., of Wauwatusa, Wis. In addition, rubber based block copolymer
PSAs
described in U.S. Pat. No. 3,239,478 also can be utilized in the adhesive
constructions of the present invention.
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In another embodiment, the pressure-sensitive adhesive comprises rubber
based elastomer materials containing useful rubber based elastomer materials
include linear, branched, grafted, or radial block copolymers represented by
the
diblock structure A--B, the triblock A--B--A, the radial or coupled structures
(A--B),
and combinations of these where A represents a hard thermoplastic phase or
block
which is non-rubbery or glassy or crystalline at room temperature but fluid at
higher
temperatures, and B represents a soft block which is rubbery or elastomeric at
service or room temperature. These thermoplastic elastomers may comprise from
about 75% to about 95% by weight of rubbery segments and from about 5% to
about
25% by weight of non-rubbery segments.
The non-rubbery segments or hard blocks comprise polymers of mono- and
polycyclic aromatic hydrocarbons, and more particularly vinyl-substituted
aromatic
hydrocarbons that may be monocyclic or bicyclic in nature. Rubbery materials
such
as polyisoprene, polybutadiene, and styrene butadiene rubbers may be used to
form
the rubbery block or segment.
Particularly useful rubbery segments include
polydienes and saturated olefin rubbers of ethylene/butylene or
ethylene/propylene
copolymers. The latter rubbers may be obtained from the corresponding
unsaturated
polyalkylene moieties such as polybutadiene and polyisoprene by hydrogenation
thereof.
The block copolymers of vinyl aromatic hydrocarbons and conjugated dienes
that may be utilized include any of those that exhibit elastomeric properties.
The
block copolymers may be diblock, triblock, multiblock, starblock, polyblock or
graftblock copolymers. Throughout this specification, the terms diblock,
triblock,
multiblock, polyblock, and graft or grafted-block with respect to the
structural
features of block copolymers are to be given their normal meaning as defined
in the
literature such as in the Encyclopedia of Polymer Science and Engineering,
Vol. 2,
(1985) John Wiley & Sons, Inc., New York, pp. 325-326, and by J. E. McGrath in
Block Copolymers, Science Technology, Dale J. Meier, Ed., Harwood Academic
Publishers, 1979, at pages 1-5.
Such block copolymers may contain various ratios of conjugated dienes to
vinyl aromatic hydrocarbons including those containing up to about 40% by
weight of
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vinyl aromatic hydrocarbon. Accordingly, multi-block copolymers may be
utilized
which are linear or radial symmetric or asymmetric and which have structures
represented by the formulae A--B, A--B--A, A--B--A--B, B--A--B, (AB)00,2 . BA,
etc.,
wherein A is a polymer block of a vinyl aromatic hydrocarbon or a conjugated
dieneivinyl aromatic hydrocarbon tapered copolymer block, and B is a rubbery
polymer block of a conjugated diene.
The block copolymers may be prepared by any of the well-known block
polymerization or copolymerization procedures including sequential addition of
monomer, incremental addition of monomer, or coupling techniques as
illustrated in,
io for example, U.S. Pat. Nos. 3,251,905; 3,390,207; 3,598,887; and
4,219,627. As
well known, tapered copolymer blocks can be incorporated in the multi-block
copolymers by copolymerizing a mixture of conjugated cliene and vinyl aromatic
hydrocarbon monomers utilizing the difference in their copolymerization
reactivity
rates. Various patents describe the preparation of multi-block copolymers
containing
tapered copolymer blocks including U.S. Pat. Nos. 3,251,905; 3,639,521; and
4,208,356.
Conjugated dienes that may be utilized to prepare the polymers and
copolymers are those containing from 4 to about 10 carbon atoms and more
generally, from 4 to 6 carbon atoms. Examples include from 1,3-butadiene, 2-
methy1-1,3-butadiene(isoprene), 2,3-dimethy1-1,3-butadiene, chloroprene, 1,3-
pentadiene, 1,3-hexadiene, etc. Mixtures of these conjugated dienes also may
be
used.
Examples of vinyl aromatic hydrocarbons which may be utilized to prepare
the copolymers include styrene and the various substituted styrenes such as o-
methylstyrene, p-methylstyrene, p-tert-butylstyrene, 1 ,3-dimethylstyrene,
alpha-
methylstyrene, beta-methylstyrene, p-isopropylstyrene, 2,3-dimethylstyrene, o-
chlorostyrene, p-chlorostyrene, o-bromostyrene, 2-chloro-4-methylstyrene, etc.
Many of the above-described copolymers of conjugated dienes and vinyl
aromatic compounds are commercially available. The number average molecular
weight of the block copolymers, prior to hydrogenation, is from about 20,000
to
about 500,000, or from about 40,000 to about 300,000.
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The average molecular weights of the individual blocks within the copolymers
may vary within certain limits. In most instances, the vinyl aromatic block
will have a
number average molecular weight in the order of about 2000 to about 125,000,
or
between about 4000 and 60,000. The conjugated diene blocks either before or
after
hydrogenation will have number average molecular weights in the order of about
10,000 to about 450,000, or from about 35,000 to 150,000.
Also, prior to hydrogenation, the vinyl content of the conjugated diene
portion
generally is from about 10% to about 80%, or from about 25% to about 65%,
particularly 35% to 55% when it is desired that the modified block copolymer
exhibit
rubbery elasticity. The vinyl content of the block copolymer can be measured
by
means of nuclear magnetic resonance.
Specific examples of diblock copolymers include styrene-butadiene (SB),
styrene-isoprene (SI), and the hydrogenated derivatives thereof. Examples of
triblock polymers include styrene-butadiene-styrene (SBS), styrene-isoprene-
styrene
(S(S), alpha-methylstyrene-butadiene-alpha-methylstyrene, and alpha-
methylstyrene-isoprene alpha-methylstyrene. Examples of commercially available
block copolymers useful as the adhesives in the present invention include
those
available from Kraton Polymers LLC under the KRATON trade name.
Upon hydrogenation of the SBS copolymers comprising a rubbery segment of
a mixture of 1,4 and 1,2 isomers, a styrene-ethylene-butylene styrene (SEBS)
block
copolymer is obtained. Similarly, hydrogenation of an S1S polymer yields a
styrene-
ethylene propylene-styrene (SEPS) block copolymer.
The selective hydrogenation of the block copolymers may be carried out by a
variety of well known processes including hydrogenation in the presence of
such
catalysts as Raney nickel, noble metals such as platinum, palladium, etc., and
soluble transition metal catalysts. Suitable hydrogenation processes which can
be
used are those wherein the diene-containing polymer or copolymer is dissolved
in an
inert hydrocarbon diluent such as cyclohexane and hydrogenated by reaction
with
hydrogen in the presence of a soluble hydrogenation catalyst. Such procedures
are
described in U.S. Pat. Nos. 3,113,986 and 4,226,952.
Such hydrogenation of the block copolymers
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which are carried out in a manner and to extent as to produce selectively
hydrogenated copolymers having a residual unsaturation content in the
polydiene
block of from about 0.5% to about 20% of their original unsaturation content
prior to
hydrogenation.
In one embodiment, the conjugated diene portion of the block copolymer is at
least 90% saturated and more often at least 95% saturated while the vinyl
aromatic
portion is not significantly hydrogenated. Particularly useful hydrogenated
block
copolymers are hydrogenated products of the block copolymers of styrene--
isoprene-styrene such as a styrene-(ethylene/propylene)-styrene block polymer.
lo When a polystyrene-polybutadiene-polystyrene block copolymer is
hydrogenated, it
is desirable that the 1,2-polybutadiene to 1,4-polybutadiene ratio in the
polymer is
from about 30:70 to about 70:30. When such a block copolymer is hydrogenated,
the
resulting product resembles a regular copolymer block of ethylene and 1-butene
(EB). As noted above, when the conjugated diene employed as isoprene, the
resulting hydrogenated product resembles a regular copolymer block of ethylene
and propylene (EP).
A number of selectively hydrogenated block copolymers are available
commercially from Kraton Polymers under the general trade designation "Kraton
G."
One example is Kraton G1652 which is a hydrogenated SBS triblock comprising
about 30% by weight of styrene end blocks and a midblock which is a copolymer
of
ethylene and 1-butene (EB). A lower molecular weight version of G1652 is
available
under the designation Kraton G1650. Kraton G1651 is another SEBS block
copolymer which contains about 33% by weight of styrene. Kraton G1657 is an
SEBS diblock copolymer which contains about 13%w styrene. This styrene content
is lower than the styrene content in Kraton G1650 and Kraton G1652.
In another embodiment, the selectively hydrogenated block copolymer is of
the formula:
B(AB)OAp
wherein n=0 or 1; o is 1 to 100; p is 0 or 1; each B prior to hydrogenation is
predominantly a polymerized conjugated diene hydrocarbon block having a number
average molecular weight of about 20,000 to about 450,000; each A is
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predominantly a polymerized vinyl aromatic hydrocarbon block having a number
average molecular weight of from about 2000 to about 115,000; the blocks of A
constituting about 5% to about 95% by weight of the copolymer; and the
unsaturation of the block B is less than about 10% of the original
unsaturation. In
other embodiments, the unsaturation of block B is reduced upon hydrogenation
to
less than 5% of its original value, and the average unsaturation of the
hydrogenated
block copolymer is reduced to less than 20% of its original value.
The block copolymers may also include functionalized polymers such as may
be obtained by reacting an alpha, beta-olefinically unsaturated monocarboxylic
or
dicarboxylic acid reagent onto selectively hydrogenated block copolymers of
vinyl
aromatic hydrocarbons and conjugated dienes as described above. The reaction
of
the carboxylic acid reagent in the graft block copolymer can be effected in
solutions
or by a melt process in the presence of a free radical initiator.
The preparation of various selectively hydrogenated block copolymers of
conjugated dienes and vinyl aromatic hydrocarbons which have been grafted with
a
carboxylic acid reagent is described in a number of patents including U.S.
Pat. Nos,
4,578,429; 4,657,970; and 4,795,782, and the disclosures of these patents
relating
to grafted selectively hydrogenated block copolymers of conjugated dienes and
vinyl
aromatic compounds.
U.S. Pat. No. 4,795,782 describes and gives examples
of the preparation of the grafted block copolymers by the solution process and
the
melt process. U.S. Pat. No. 4,578,429 contains an example of grafting of
Kraton
G1652 (SEBS) polymer with maleic anhydride with 2,5-dimethy1-2,5-di(t-
butylperoxy)
hexane by a melt reaction in a twin screw extruder.
Examples of commercially available maleated selectively hydrogenated
copolymers of styrene and butadiene include Kraton FG1901X, FG1921X, and
FG1924X, often referred to as maleated selectively hydrogenated SEBS
copolymers. FG1901X contains about 1.7%w bound functionality as succinic
anhydride and about 28%w of styrene. FG1921X contains about 1%w of bound
functionality as succinic anhydride and 29%w of styrene. FG1924X contains
about
13% styrene and about 1% bound functionality as suc,cinic anhydride.
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Useful block copolymers also are available from Nippon Zeon Co., 2-1,
Marunochi, Chiyoda-ku, Tokyo, Japan. For example, Quintac 3530 is available
from
Nippon Zeon and is believed to be a linear styrene-isoprene-styrene block
copolymer.
Unsaturated elastomeric polymers and other polymers and copolymers which
are not inherently tacky can be rendered tacky when compounded with an
external
tackifier. Tackifiers, are generally hydrocarbon resins, wood resins, rosins,
rosin
derivatives, and the like, which when present in concentrations ranging from
about
40% to about 90% by weight of the total adhesive composition, or from about
45% to
about 85% by weight, impart pressure-sensitive adhesive characteristics to the
elastomeric polymer adhesive formulation. Compositions containing less than
about
40% by weight of tackifier additive do not generally show sufficient
"quickstick," or
initial adhesion, to function as a pressure-sensitive adhesive, and therefore
are not
inherently tacky. Compositions with too high a concentration of tackifying
additive,
on the other hand, generally show too little cohesive strength to work
properly in
most intended use applications of constructions made in accordance with the
instant
invention.
It is contemplated that any tackifier known by those of skill in the art to be
compatible with elastomeric polymer compositions may be used with the present
embodiment of the invention. One such tackifier, found useful is Wingtak 10, a
synthetic polyterpene resin that is liquid at room temperature, and sold by
the
Goodyear Tire and Rubber Company of Akron, Ohio. Wingtak 95 is a synthetic
tackifier resin also available from Goodyear that comprises predominantly a
polymer
derived from piperylene and isoprene. Other suitable tackifying additives may
include Escorez 1310, an aliphatic hydrocarbon resin, and Escorez 2596, a C5 -
C9
(aromatic modified aliphatic) resin, both manufactured by Exxon of Irving,
Tex. Of
course, as can be appreciated by those of skill in the art, a variety of
different
tackifying additives may be used to practice the present invention.
In addition to the tackifiers, other additives may be included in the PSAs to
impart desired properties. For example, plasticizers may be included, and they
are
known to decrease the glass transition temperature of an adhesive composition
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containing elastomeric polymers. An example of a useful plasticizer is
Shellflex 371,
a naphthenic processing oil available from Shell Lubricants of Texas.
Antioxidants
also may be included on the adhesive compositions. Suitable antioxidants
include
Irgafos 168 and Irganox 565 available from Ciba-Geigy, Hawthorne, N.Y. Cutting
agents such as waxes and surfactants also may be included in the adhesives.
The pressure sensitive adhesive may be applied from a solvent, emulsion or
suspension, or as a hot melt. The adhesive may be applied to the inner surface
of
the shrink film by any known method. For example, the adhesive may be applied
by
die coating curtain coating, spraying, dipping, rolling, gravure or
flexographic
lo techniques. The adhesive may be applied to the shrink film in a
continuous layer, a
discontinuous layer or in a pattern. The pattern coated adhesive layer
substantially
covers the entire inner surface of the film. As used herein, "substantially
covers" is
intended to mean the pattern in continuous over the film surface, and is not
intended
to include adhesive applied only in a strip along the leading or trailing
edges of the
film or as a "spot weld" on the film.
In one embodiment, an adhesive deadener is applied to portions of the
adhesive layer to allow the label to adhere to complex shaped articles. In one
embodiment, non-adhesive material such as ink dots or microbeads are applied
to at
least a portion of the adhesive surface to allow the adhesive layer to slide
on the
surface of the article as the label is being applied and/or to allow air
trapped at the
interface between the label and the article to escape.
A single layer of adhesive may be used or multiple adhesive layers may be
used. Depending on the shrink film used and the article or container to which
the
label is to be applied, it may be desirable to use a first adhesive layer
adjacent to the
shrink film and a second adhesive layer having a different composition on the
surface to be applied to the article or container for sufficient tack, peel
strength and
shear strength.
In one embodiment, the pressure sensitive adhesive has sufficient shear or
cohesive strength to prevent excessive shrink-back of the label where adhered
to
the article upon the action of heat after placement of the label on the
article,
sufficient peel strength to prevent the film from label from lifting from the
article and
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sufficient tack or grab to enable adequate attachment of the label to the
article
during the labeling operation. In one embodiment, the adhesive moves with the
label as the shrink film shrinks upon the application of heat. In another
embodiment,
the adhesive holds the label in position so that as the shrink film shrinks,
the label
does not move.
The heat shrinkable film may include other layers in addition to the monolayer
or multilayer heat shrinkable polymeric film. In one embodiment, a metalized
coating
of a thin metal film is deposited on the surface of the polymeric film. The
heat
shrinkable film may also include a print layer on the polymer film. The print
layer
-to may be positioned between the heat shrink layer and the adhesive layer,
or the print
layer may be on the outer surface of the shrink layer. In one embodiment, the
film is
reverse printed with a design, image or text so that the print side of the
skin is in
direct contact with the container to which the film is applied. In this
embodiment, the
film is transparent.
The labels of the present invention may also contain a layer of an ink-
receptive composition that enhances the printability of the polymeric shrink
layer or
metal layer if present, and the quality of the print layer thus obtained. A
variety of
such compositions are known in the art, and these compositions generally
include a
binder and a pigment, such as silica or talc, dispersed in the binder. The
presence of
the pigment decreases the drying time of some inks. Such ink-receptive
compositions are described in U.S. Pat. No. 6,153,288 (Shih et al).
The print layer may be an ink or graphics layer, and the print layer may be a
mono-colored or multi-colored print layer depending on the printed message
and/or
the intended pictorial design. These include variable imprinted data such as
serial
numbers, bar codes, trademarks, etc. The thickness of the print layer is
typically in
the range of about 0.5 to about 10 microns, and in one embodiment about 1 to
about
5 microns, and in another embodiment about 3 microns. The inks used in the
print
layer include commercially available water-based, solvent-based or radiation-
curable
inks. Examples of these inks include Sun Sheen (a product of Sun Chemical
identified as an alcohol dilutable polyamide ink), Suntex MP (a product of Sun
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Chemical identified as a solvent-based ink formulated for surface printing
acrylic
coated substrates, PVDC coated substrates and polyolefin films), X-Cel (a
product of
Water Ink Technologies identified as a water-based film ink for printing film
substrates), Uvilith AR-109 Rubine Red (a product of Daw Ink identified as a
UV ink)
and CLA91598F (a product of Sun Chemical identified as a multibond black
solvent-
based ink).
In one embodiment, the print layer comprises a polyester/vinyl ink, a
polyamide ink, an acrylic ink and/or a polyester ink. The print layer may be
formed
in the conventional manner by, for example, gravure, flexographic or UV
lo
flexographic printing or the like, an ink composition comprising a resin of
the type
described above, a suitable pigment or dye and one or more suitable volatile
solvents onto one or more desired areas of the film. After application of the
ink
composition, the volatile solvent component(s) of the ink composition
evaporate(s),
leaving only the non-volatile ink components to form the print layer.
The adhesion of the ink to the surface of the polymeric shrink film or metal
layer if present can be improved, if necessary, by techniques well known to
those
skilled in the art. For example, as mentioned above, an ink primer or other
ink
adhesion promoter can be applied to the metal layer or the polymeric film
layer
before application of the ink. Alternatively the surface of the polymeric film
can be
corona treated or flame treated to improve the adhesion of the ink to the
polymeric
film layer.
Useful ink primers may be transparent or opaque and the primers may be
solvent based or water-based. In one embodiment, the primers are radiation
curable
(e.g., UV). The ink primer may comprise a lacquer and a diluent. The lacquer
may
be comprised of one or more polyolefins, polyamides, polyesters, polyester
copolymers, polyurethanes, polysulfones, polyvinylidine chloride, styrene-
maleic
anhydride copolymers, styrene-acrylonitrile copolymers, ionomers based on
sodium
or zinc salts or ethylene methacrylic acid, polymethyl methacrylates, acrylic
polymers and copolymers, polycarbonates, polyacrylonitriles, ethylene-vinyl
acetate
copolymers, and mixtures of two or more thereof. Examples of the diluents that
can
be used include alcohols such as ethanol, isopropanol and butanol; esters such
as
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ethyl acetate, propyl acetate and butyl acetate; aromatic hydrocarbons such as
toluene and xylene; ketones such as acetone and methyl ethyl ketone; aliphatic
hydrocarbons such as heptane; and mixtures thereof. The ratio of lacquer to
diluent
is dependent on the viscosity required for application of the ink primer, the
selection
of such viscosity being within the skill of the art. The ink primer layer may
have a
thickness of from about 1 to about 4 microns or from about 1.5 to about 3
microns.
A transparent polymer protective topcoat or overcoat layer may be present in
the labels of the invention. The protective topcoat or overcoat layer provide
desirable
properties to the label before and after the label is affixed to a substrate
such as a
lo container. The presence of a transparent topcoat layer over the print
layer may, in
some embodiments provide additional properties such as antistatic properties
stiffness and/or weatherability, and the topcoat may protect the print layer
from, e.g.,
weather, sun, abrasion, moisture, water, etc. The transparent topcoat layer
can
enhance the properties of the underlying print layer to provide a glossier and
richer
image. The protective transparent protective layer may also be designed to be
abrasion resistant, radiation resistant (e.g, UV), chemically resistant,
thermally
resistant thereby protecting the label and, particularly the print layer from
degradation from such causes. The protective overcoat may also contain
antistatic
agents, or anti-block agents to provide for easier handling when the labels
are being
applied to containers at high speeds. The protective layer may be applied to
the
print layer by techniques known to those skilled in the art. The polymer film
may be
deposited from a solution, applied as a preformed film (laminated to the print
layer),
etc.
When a transparent topcoat or overcoat layer is present, it may have a single
layer or a multilayered structure. The thickness of the protective layer is
generally in
the range of about 12.5 to about 125 microns, and in one embodiment about 25
to
about 75 microns. Examples of the topcoat layers are described in U.S. Pat.
No.
6,106,982 which is incorporated herein by reference.
The protective layer may comprise polyolefins, thermoplastic polymers of
ethylene and propylene, polyesters, polyurethanes, polyacryls, polymethacryls,
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epoxy, vinyl acetate homopolymers, co- or terpolymers, ionomers, and mixtures
thereof.
The transparent protective layer may contain UV light absorbers and/or other
light stabilizers. Among the UV light absorbers that are useful are the
hindered
amine absorbers available from Ciba Specialty Chemical under the trade
designations "Tinuvin". The light stabilizers that can be used include the
hindered
amine light stabilizers available from Ciba Specialty Chemical under the trade
designations Tinuvin 111, Tinuvin 123, (bis-(1-octyloxy-2,2,6,6-tetramethy1-4-
piperidinyl) sebacate; Tinuvin 622, (a dimethyl succinate polymer with 4-
hydroxy-
2,2,6,6-tetramethy1-1-piperidniethanol); Tinuvin 770 (bis-(2,2,6,6-tetramethy1-
4-
piperidiny1)-sebacate); and Tinuvin 783. Additional light stabilizers include
the
hindered amine light stabilizers available from Ciba Specialty Chemical under
the
trade designation "Chemassorb", especially Chemassorb 119 and Chemassorb 944.
The concentration of the UV light absorber and/or light stabilizer is in the
range of up
to about 2.5% by weight, and in one embodiment about 0.05% to about 1% by
weight.
The transparent protective layer may contain an antioxidant. Any antioxidant
useful in making thermoplastic films can be used. These include the hindered
phenols and the organo phosphites. Examples include those available from Ciba
Specialty Chemical under the trade designations Irganox 1010, Irganox 1076 or
Irgafos 168. The concentration of the antioxidant in the thermoplastic film
composition may be in the range of up to about 2.5% by weight, and in one
embodiment about 0.05`)/0 to about 1`)/0 by weight.
A release liner may be adhered to the adhesive layer to protect the adhesive
layer during transport, storage and handling prior to application of the label
to a
substrate. The liner allows for efficient handling of an array of individual
labels after
the labels are die cut and the matrix is stripped from the layer of facestock
material
and up to the point where the individual labels are dispensed in sequence on a
labeling line. The release liner may have an embossed surface and/or have non-
adhesive material, such as microbeads or printed ink dots, applied to the
surface of
the liner.
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Process
The process of applying the labels to articles or containers involves non-
traditional operations and equipment. The process begins with traditional
dispensing
equipment that separates the label from the release liner via a peel plate or
tip that
presents the label with exposed adhesive to the container or article to be
decorated.
Referring to FIGS. 6A to 6D, the label 62, which has a central portion 61 and
a
peripheral portion 63 surrounding the central portion and having an outer
boundary
defined by the label edges, is contacted to the container 60 initially by
applying
pressure to the label in the central portion. Having the initial tack point(s)
64 located
in a more central portion of the label rather than on the leading edge or
peripheral
portion of the label facilitates a more even distribution of any darts or
wrinkles
formed between the leading and trailing edges of the applied label. This in
turn
facilitates removal of the darts or wrinkles with the application of heat.
For those articles having both compound curves and relatively planar regions,
the label may be initially contacted with the container not on a compound
curve, but
closer to or within a relatively planar area of the container surface.
In one embodiment, the label is pre-heated to soften the shrink film and/or
activate the adhesive layer.
Pressure is applied to the transferred label with a series of brushes,
rollers,
wipers, squeegees, pneumatic rollers, or walking beam in a center outward
direction,
as indicated by arrows 65, to obtain intimate contact between the label and
the
container or article. This process is referred to herein as "wipe down" of the
label.
The center to edge wiping motion forces any air trapped beneath the label to
the
outer edges, as indicated by arrows 66, and creates smaller, more evenly
distributed
darts at the edges of the label. As the label covers the complex curves of the
article,
excess label material accumulates in the form of darts, pleats, channeling,
bubbling
and other application defects generally in the peripheral portion of the
label. Heat is
applied to at least a portion of the label to fully and smoothly adhere the
label to the
container as shown in FIG. 6D.
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In one embodiment, pressure is applied to the label using a walking beam
system equipped with a foam roller or foam covered beam. The foam roller or
beam
applies downward pressure in the longitudinal direction to the central region
of the
label and then proceeds to the outer edges of the label, directing any air
trapped
under the label and the pleats, wrinkles and/or other defects to the outer
edges of
the label. This embodiment is illustrated in FIG. 7, wherein container 70
having label
71 applied thereto, is positioned on lower foam block 72a of a walking beam.
Upper
foam block 72b applies downward pressure onto label 71 on container 70 to push
air
from under the central portion of the label to the periphery of the label as
label and
container are compressed between the foam blocks of the walking beam.
Once the label is applied and initial wipe down is completed, the excess label
material darts and defects are eliminated by heating at least a portion the
label to
shrink the darts and/or wrinkles. The label may be heated via passage through
a
heat tunnel, forced air, steam tunnel, direct contact heat pads or forms. In
one
embodiment, the label is heated to a temperature of at least 40 C. In one
embodiment, the label is heated to at least 60 C, or at least 70 C, or at
least 80 C.
A subsequent wipe down of the label may be performed to eliminate any
remaining darts or wrinkles in the label. Pressure is again applied to the
label in a
center outward direction to the label. The second wipe down can be performed
by a
series of rollers, wipers, squeegees, brushes, pneumatic rollers or a walking
beam.
The subsequent wipe down may be performed concurrently with the application of
heat to the label, or subsequent to the application of heat.
When applying the label to an article or container, the label may be initially
tacked to the article by applying pressure in a contact region of the label,
and then
applying pressure across the label in a direction to a first edge of the
label. The
contact region may be in the center of the label or may be proximate to a
second
edge of the label opposite to the first edge. For example, initial contact may
be
made in the center of the label and then pressure is applied in an outward
direction
to the edges or periphery of the label. Alternatively, initial contact may be
made
near one edge of the label and then pressure applied across the label to the
opposite edge of the label. When applying the label to the article or
container, it is
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desirable to move the excess label material, i.e., the darts or wrinkles, to
at least one
label edge. The excess material is typically moved in the direction of the
compound
curve(s), where the heat applied to the label will shrink the label and allow
it to
conform to the compound curve and eliminate any darts or wrinkles formed. Heat
and pressure may be applied to the label simultaneously.
In one embodiment of the invention, the method of applying a label to an
article includes the steps of: providing an article having a surface including
at least
one compound curve; providing a label including (i) a heat shrinkable film
having an
inner surface and an outer surface; and (ii) a layer of pressure sensitive
adhesive on
the inner surface of the heat shrinkable film, wherein the label has a first
edge and a
contact region; contacting the adhesive layer in the contact region with the
article;
and applying heat and pressure simultaneously to the label in a direction from
the
contact region to the first edge such that the first edge of the label adheres
to article
and the label shrinks to conform to the compound curve of the article, wherein
the
heat and pressure are applied by at least one hot air knife assembly including
a
source of heated air, a flow control mechanism and one or more hot air knife
slots.
The contact region may be located in or near the center of the label.
Alternatively,
the contact region may be proximate to a second edge of the label opposite the
first
edge.
FIG. 8 illustrates an embodiment of the invention wherein a hot air knife
assembly is used to apply the label to the article or container. A label may
be
applied to one or both sides of the container. For the sake of simplicity of
illustration,
a label is applied only to one surface of the container of FIG. 8. The hot air
knife
assembly includes a source of hot air, a flow control mechanism and one or
more
hot air knife slots. As shown in FIG. 8A, two hot air knife slots 84a, 84b
direct hot air
at a high velocity to the center region 83c of the label 82. The label 82 is
first
applied to the center region 83c of the container 81 with a standard peel-tip
dispensing process (not shown) with the leading edge (first edge 83a) and
trailing
edge (second edge 83b) not tacked down. The container with the label tacked
thereto is transported to the air knife assembly via a conveyor. Depending on
the
size and configuration of the container, additional hot air knife slots and/or
hot air
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assemblies may be used to apply heat and pressure to the label. As shown in
FIG.
8B, the hot air knifes 84a, 84b are rotated outwardly to direct hot air from
the center
region of the label 83c to the first edge 83a and second edge 83b of the label
82. As
the hot air is forced against the label 82, the air between the label and the
container
81 is pushed to the edges 83a, 83b of the label to smooth the label and
eliminate or
reduce air bubbles under the label. The hot air directed at the label 82
softens the
label and shrinks the label. The simultaneous application of heat and pressure
from
the air knife slots 84a, 84b to the label forces the label 82 to conform to
the surface
of the container 81, including the compound curve(s) of the container. An
optional
subsequent heating step may be used to further shrink the label. An advantage
of
this method is that there is no direct contact with the label so that surface
imperfections are not likely to be imparted to the label. An advantage is the
ability to
obtain high speed processing due to the excellent heat transfer to the label
and the
continuous heat recovery of the air knife assembly. This method may be used to
apply labels to a variety of container and article shapes without the need for
re-
tooling.
FIG. 9 illustrates an embodiment wherein multiple air knife slots and/or air
knife assemblies are used to apply a label to a container or article in a
sequence of
steps. A label may be applied to one or both sides of the container. For the
sake of
simplicity of illustration, a label is applied only to one surface of the
container of FIG.
9. The hot air knife assembly includes a source of hot air, a flow control
mechanism
and one or more hot air knife slots. In an initial stage shown in 9A, a hot
air knife
slot 94 directs hot air at a high velocity to the center region 93c of the
label 92. The
label 92 is first applied to the center region 93c of the container 91 with a
standard
peel-tip dispensing process (not shown) with the leading edge (first edge 93a)
and
trailing edge (second edge 93b) not tacked down. The container with the label
tacked thereto is transported to the air knife assembly via a conveyor. As
shown in
9B, as the container 91 is transported by conveyor past the air knife slot 94,
hot air is
forced against the label 92 to the first edge 93a of the label, heating the
label and
causing it to conform to the surface of the container 91, while second edge
93b not
conformed and/or tacked down. The container is then rotated about 1800 as
shown
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in 90. As shown in 9D, the container 91 with the label 92 adhered thereto is
then
transported to a second hot air slot 95 that forces hot air against the label
92 from
the center 93c to the second edge 93b of the label, heating the label and
causing it
to conform to the surface of the container 91 as shown in 9E. Depending on the
size
and configuration of the container, additional hot air knife slots and/or hot
air
assemblies may be used to apply heat and pressure to the label. An optional
subsequent heating step may be used to further shrink the label.
The labeled article of the present invention may be used in a variety of
applications, including, but not limited to personal care products, household
chemical products, food and beverages, toys, electronics, pharmaceuticals,
health
care products, industrial products and appliances.
EXAMPLES
The following examples are intended only to illustrate methods and
embodiments in accordance with the invention, and as such should not be
construed
as imposing limitations upon the claims.
Example 1:
A pressure sensitive shrink label is constructed from a 3 mil thick low
density
polyethylene multilayer shrink film designated CorrTuff from Sealed Air. The
film is
coated with an acrylic emulsion adhesive S692N from Avery Dennison. The
adhesive is carried on a paper Glassine BG-40 silicone coated release liner.
The
label is oversized, having the dimensions of approximately 5 x 3.5 inches,
which is
20% greater than the industry standard recommended label size for the bottle
to
which the label is applied.
A 15 oz Johnson & Johnson Baby Lotion bottle having compound curves is
filled with water, capped and processed through a Label-Aire 9000 series
labeler at
100 bottles per minute (BPM). The labeler has dual-feed screws with matched
speed top and lower belts with Label-Aire 2115-CD labeler heads with high
torque
stepper motor drive. The labels are pressed down with a walking beam type wipe
down apparatus providing straight out, center outward forces to direct the
trapped air
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beneath the label and resultant dart/pleat defects to the edge of the label.
The
oversized label as applied to the bottle initially results in unacceptable
small darts
and pleat defects around the perimeter of the label. The labeled bottle is
then
processed through a Leister hot forced air, conveyor wipe down system at 100
bpm.
High velocity 260 C hot air heats the bottle and label to 50 C, shrinking and
taking
up the excess label material darts and pleats down to the bottle surface. The
label is
wiped down with a walking beam for good label contact. The darts shrink and
are
easily wiped flat after application of heat.
The finished labeled bottle with larger label area and larger graphics content
lo is smoothly wiped down without the darts, pleats, ridges or wrinkle
defects present in
typical pressure sensitive oversized labels. The darts do not return upon
aging.
Table 1 below shows the properties of the label components.
Example 2:
In accordance with the process described in Example 1, a pressure sensitive
shrink label constructed from a 2 mil thick polypropylene multilayer shrink
film
designated CZPA 200 from Innovia is applied to the bottle having compound
curves.
After initial wipe down, medium sized darts are formed. High velocity hot air
heats
the bottle and label to 100 C. The darts shrink and are easily wiped flat
after
application of heat. The darts do not return after aging.
Example 3:
In accordance with the process described in Example 1, a pressure sensitive
shrink label constructed from a 2 mil thick polylactic acid single layer
shrink film
designated EARTHFIRST PLA from Plastic Suppliers is applied to the bottle
having
compound curves. After initial wipe down, medium sized darts are formed. High
velocity hot air heats the bottle and label to 70 C. The darts shrink and are
easily
wiped flat after application of heat. The darts do not return after aging.
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Comparative Example 4:
In accordance with the process described in Example 1, a pressure sensitive
shrink label constructed from a 2 mil thick machine direction oriented
polypropylene
single layer roll-on-shrink-on film from Avery Dennison is applied to the
bottle having
compound curves. High velocity hot air heats the bottle and label to 70 C. The
darts formed at the top and bottom of the label shrink upon application of
heat and
are easily wiped down, while the darts formed at the leading and trailing
edges
remain. The removed darts do not return upon aging.
lo Comparative Example 5:
In accordance with the process described in Example 1, a pressure sensitive
shrink label constructed from a 1.9 mil thick transverse direction oriented
polyvinyl
chloride single layer film designated Penta Label from Kloeckner is applied to
the
bottle having compound curves. High velocity hot air heats the bottle and
label to
60 C. The darts formed at the leading and trailing edges of the label shrink
upon
application of heat and are easily wiped down, while the darts formed at the
top and
bottom of the label remain. The removed darts do not return upon aging.
Comparative Example 6:
In accordance with the process described in Example 1, a pressure sensitive
shrink label constructed from a 2 mil thick transverse direction oriented
glycol
modified polyethylene terephthalate (PETG) single layer film designated Fusion
1775E from Mitsubishi is applied to the bottle having compound curves. High
velocity hot air heats the bottle and label to 50 C. The darts formed at the
leading
and trailing edges of the label shrink upon application of heat and are easily
wiped
down, while the darts formed at the top and bottom of the label remain. The
removed
darts do not return upon aging.
Comparative Example 7:
In accordance with the process described in Example 1, a pressure sensitive
shrink label constructed from a 1.4 mil thick machine direction oriented
polyvinyl
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chloride single layer film designated MF-L243/01 from Kloechner is applied to
the
bottle having compound curves. High velocity hot air heats the bottle and
label to
60 C. The film does not conform to the container. Initial wipe down is poor
with
many darts formed in all directions. The darts and ridges remain after the
application of heat and a second wipe down. The film exhibits excessive shrink
back.
Comparative Example 8:
In accordance with the process described in Example 1, a pressure sensitive
lo shrink label constructed from a 2.0 mil thick polypropylene multilayer
film designated
BTNY from Vifan is applied to the bottle having compound curves. High velocity
hot
air heats the bottle and label to 100 C. The darts formed do not shrink
completely at
high temperature and do not entirely wipe down flat. The darts return upon
aging.
Comparative Example 9:
In accordance with the process described in Example 1, a pressure sensitive
shrink label constructed from a 3.4 mil thick medium density polyethylene
(MDPE)
multilayer film designated PE 85 from Charter Films is applied to the bottle
having
compound curves. High velocity hot air heats the bottle and label to 100 C.
The
darts formed do not shrink completely at high temperature and do not entirely
wipe
down flat. The darts return upon aging.
33
Table 1
o
L&W
t-.)
Film Ult Tensile
Modulus Shrink: Shrink: =
Ex. Grade Polymer Process Suppliers Gauge
Stiffness Adhesive Liner =
(mN)
1--,
1 CorrTuff LDPE single layer double Sealed
3.0 10,000 MD 30,000 MD 26 MD 40% (106C) 49%
(106C) S692N BG40 .6.
bubble Air 20,000 CD 30,000
CD 24 CD 70% (120C) 69% (120C) glassine t-.)
2 CZPA 200 PP multi-layer double Innovia 2.0
20,000 MD 100,000 24 MD 10% (106C) 0% (106C) S692N 1.2 mil
bubble 22,000 CD MD
18 CD 14% (120C) 10% (120C) PET
130,000
CD
3 EARTHFIRST Poly single layer blown Plastic
2.0 8,000 MD 300,000 44 MD 7% (106C) 12%
(106C) S692N 1.2 mil
PLA Lactic Suppliers 8,000 CD MD
60 CD 8% (120C) 14% (120C) PET
Acid
300,000
CD
n
Comp. Med Shrink PP single layer MDO Avery
2.0_ 200,000 30 MD 14% (106C) 0%
(106C) S692N 1.2 mil 0
4 ROSO Film PPD MD
26 CD 23% (120C) 0% (120C) PET I.)
-.3
123,000 I.)
0
CD
in
c7,
.6. Comp. Penta Label 2.0 PVC single layer TDO Kloeckner 1.9
7,200 MD 52 MD 4% (106C) 56% (106C)
S692N BG40 co
I.)
mil OT-M276/41, 16,900 CD 36 CD
glassine o
H
71/9400, GLGL
0
1
Comp. Fusion 2.0 mil PETG single layer TDO Mitsubishi 2.0
7,250 MD 70 MD 6% (106C) 66% (106C)
S692N BG40 H
0
1
6 1775E 29,000 CD
30 CD glassine 0
Comp. MF-L243/01 PVC single layer MDO
Kloechner 1.4_ 220,000 _ 41% (106C) 0% (106C)
S3506 1.2 mil a,
7 WHT 03/402-B MD
45% (120C) +3% (120C) PET
150,000
CD
Comp. BTNY PP multi-layer tenter Vifan 2.0
40,000 MD ¨ 35 MD 2% (106C) 0% (106C) 5692N
BG40
8 20,000 CD
65 CD 2% (120C) 2% (120C) glassine
Comp. PE 85 MDPE multi-layer
blown Charter 3.4 3,000 MD 75,000 MD 40 MD 0%
(106C) 0% (106C) 5692N BG40 Iv
9 Films 3,500 CD 60,000
CD 50 CD 4% (120C) 0% (120C) glassine n
,-i
cp
t..)
=
=
'a
oe
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While the invention has been explained in relation to its preferred
embodiments, it is to be understood that various modifications thereof will
become
apparent to those skilled in the art upon reading the specification.
Therefore, it is to
be under stood that the invention disclosed herein is intended to cover such
modifications as fall within the scope of the appended claims.
