Note: Descriptions are shown in the official language in which they were submitted.
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Title: Labelled, returnable plastic crate.
BACKGROUND OF THE INVENTTnN
The present invention is directed to a returnable
plastic crate provided with at least one ink only label, to
a process for applying an ink only label to a polymeric
surface and to a system for using returnable crates.
More in particular the present invention is
directed to a technique for labelling returnable plastic
crates and more specifically to a technique for applying
decorative promotional and/or informational labels to
plastic crates. Still more particularly, the invention is
directed to a technique for using a label composite which
applies only the inks of the graphics to a polymeric
substrate, a method for applying the label inks to the
crate, a method of strengthening of same through a post
coating encapsulation of the inks in conjunction with a post
treatment, and finally the ability to remove the composite
ink label without altering the crate, i.e. without
destructive treatment of the substrate surface, so that it
can be relabelled.
Plastic crates are presently labelled in one of
three different ways. The predominant method is to silk
screen a non-removable permanent image prior to end user
use. Such labels offer a highly durable finish with 2 or 3
color availability to promote enclosed product at the
consumer level. This technique offers limited colors, lacks
the improved graphics that other labelling techniques offer,
is not flexible in its ability to have graphic changes to
meet market strategies leading to large inventories of
obsolete units, tends to show signs of wear after only four
(4) trips (typical crate life expected at 60 return trips)
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and is relatively expensive as compared to other label
techniques.
A second way encompasses glueing printed paper
labels to the plastic crates at the time of filling and
sealing. This type of label offers an almost unlimited art
potential. However, this type of label offers little
resistance to label damage from handling and exposure to
moisture and will not survive the washing procedures
required of a returnable container thereby requiring
relabelling.
A third, and more recently developed crate
labelling technique, is that of applying a thin pressure
sensitive label. This is a widely used method but has
limited service life, it is difficult to remove when desired
and is comparatively expensive.
The need for the returnable crate is a direct
result of industry preference and government legislation
with regard to returnable (refillable) containers in various
parts in the world in lieu of one way packaging. In this
type of recycling environment a whole new market has been
created for the handling of packaged beverage containers.
This is presently true of both refillable PET and glass
bottle containers. Certain countries, Europe in particular,
have invested large sums of money in the creation of
distribution systems that rely heavily on the returnable
crate concept.
Typically the only product presentation in such a
recycling (refillable) market is that which can be printed
on the exterior of the crate. Due to handling, space and
storage considerations the only marketing, name brand,
promotional, UPC code or other informational presentation is
that which is printed on the exterior of the crate. The
reason is that typically the crates are stacked at
commercial outlets such as grocery stores with only the side
and end panels showing. As such, the presentations on the
said panels of the crates are the only distinguishing
features from one product to another.
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In the use of returnable crates it would be very
interesting to be able to use one uniform crate for various
different products or brands. However, this is only possible
if there exists an easy and inexpensive method of providing
an image or imprint on the crate, which is also easily
removed after the crate is returned to the bottling line for
refilling.
On the other hand, it is important that the label,
image or imprint on the crate is durable, especially during
transport and storage, more importantly is durable even when
subjected to humid conditions.
Accordingly, embodiments of the present invention may
advantageously provide a returnable plastic crate having an
imprint, label or image on at least one of its surfaces, which
is durable, scratch, wear, weather and moisture resistant during
use, but which is easily removable during crate washing upon
return to the factory.
Embodiments of the present invention may
advantageously offer a method of labelling plastic containers
such as beverage bottle crates.
Embodiments of the present invention may
advantageously provide a method to label the plastic container
at the time of beverage bottle loading so that the label is
indicative of the special contents.
Embodiments of the present invention may
advantageously include a label on the plastic container that is
impervious to all handling contact and ambient storage
conditions both outdoor and indoor.
Embodiments of the present invention may
advantageously include a label, if desired, be readily and
completely removed in the standard crate washer used when the
plastic container is returned to the beverage plant for
refilling.
Embodiments of the present invention may
advantageously include a label where the properties of the label
with respect to removing it can be controlled, so that the label
will not be removed or damaged in standard crate washing
operations, but only under specific, more severe crate washing
operations.
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It is an object of the present invention that the
labels incorporate a full range of graphics, from a simple
one color up to a full photographic reproduction.
Finally it is also an object that the method be
simple and low cost.
SUMMARY OF THE INVENTION
These and other objects are achieved by the
returnable plastic crate according to the present invention,
which is provided on at least one surface with an ink only
label that is removable by caustic washing, said label being
adhered to said at least one surface of said crate by an
activated adhesive layer.
In this respect the term "ink only label" is used
to define a label that does not have a paper or plastic
backing, but which comprises an image layer of ink, which is
directly applied to a surface. Quite often the surface
remains at least partly visible through the image layer. An
ink only label may conveniently be applied to a surface by
image transfer, using a reverse printed label.
The label to be used in accordance with the
present invention is essentially based on an ink image
without a backing material. The ink image is adhered to the
surface of the crate by an adhesive, and the surface of the
image may be protected by a protective layer.
The present invention provides a distinct
improvement over the prior art systems, which were based on
paper or plastic labels. In order to remove these labels
expensive high pressure equipment was necessary, especially
in case labels were required on adjacent sides of the crate.
Removal of the labels through simple soaking, as in the
present invention, is virtually impossible. Further the
residues of the labels have a tendency to clog the crate
washing equipment.
The system of the present invention is less
expensive and environmentally more friendly, as the residues
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of the ink only label are easily recovered from the soaking
water and recycled.
The present invention also provides the
possibility to use the label for scanning possibilities, for
5 example by including a UPC (bar) code therein, which code
may be used to define the recipient, the contents or any
other information that is suitable. The system also allows
the producer to reduce the stock of crates, as it is no
longer necessary to keep stock crates of all brands or
types. The system according to the present invention makes
it possible for a producer to have only one type of crate
for each type of material, for example bottle, irrespective
of the brand of the material. This makes it possible to
reduce the stock of crates tremendously. Of course the
reduction would be even greater if the whole industry in a
country or continent would decide to use the system.
In such a case many different producers (bottlers)
of beverage containers would share common crates, and yet
maintain individual market identification via the present
invention. At the same time an improved, user friendly and
costs effective recycling system would be perfected. Such a
system could be utilized on a national or even a multi
national level.
According to a preferred embodiment a transparent
protective coating is present on top of the ink only label.
This coating improves the resistance of the label against
environmental influences. Generally the material of the
protective coating is compatible with the material of the
ink. More preferably all materials, adhesive, ink and
protective coating are based on acrylate polymers. In order
to improve the durability of the label further, it may be
advantageous that after application of the label (and the
coating) one or more treatments are given. These treatments
provide a coalescence of the materials of the various
layers, resulting in improved service life, however, without
deteriorating the wash-off behaviour.
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By careful selection of the composition of the
label, the use of a protective coating and the nature of the
post treatment, it is possible to steer the properties of
the label, especially with respect to the behavior during
crate washing. More specifically, it is possible to design
the system in such a way, that the label is removed during
standard crate washing. This means that after each return to
the beverage filling plant, the label is removed and a new,
optionally different, label may be applied. On the other
hand, the label may be made so durable that it will not be
remaxved or damaged during standard crate washing, but only
in case a specific, severe washing operation is used. In
this way the label is not permanent, however it has all the
advantages of a permanent imprint, for example a silk
screen, without the disadvantages thereof, such as the high
costs thereof in terms of investments and energy
requirements, inflexibility and low number of colors.
The selection of the adhesive to be used in
adhering the label image to the crate surface will at least
partly depend on the intended service life of the label,
one-way or multiple trip use. Of course the adhesive must
remain removable during crate washing. The adhesive must
have been activated prior to or during application of the
image to the crate. An easy and generally preferred method
of applying the image is through the use of heat activatable
adhesives, that have been applied to the image in the form
of a reverse printed label. Other methods include the use of
adhesives that can be activated through radiation,
chemicals, electron-beam, micro-wave, UV and the like. It is
also possible to use adhesives that can be activated through
photo initiation, humidity, enzymatic action, pressure or
ultra-sonic treatment.
It is preferred to use adhesives that are
activated either by heat or by pressure. The latter case
also encompasses adhesives, which require pressure to remain
adhered, although they may have some tackiness without
pressure.
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The adhesive is preferably present on the back
side of the image before it is applied to the crate surface.
However, it is also possible to apply the adhesive to the
crate prior to transferring the image. Another possibility
is the use of inks in the image that have the adhesive
incorporated therein.
The protective layer, if used, may be applied
after the image has been transferred to the crate, for
example using a conventional roller coater. In the
alternative the protective layer may be part of the image
material as it is transferred
The present invention also provides for a method
of applying an ink only label to a polymeric surface, more
in particular to a crate surface.
The method of the present invention comprises in
its broadest form:
- providing the surface, preferably moving at a uniform
rate,
- presenting a reverse printed label on a substrate,
separable from its substrate and preferably over printed
with an activatable adhesive, and
- transferring the label ink to the polymeric surface.
The label is applied to the polymeric surface
which has preferably been surface treated and temperature
stabilized. The label is applied by transferring the ink
from its film substrate utilizing a roller, a pad, a doctor
blade or an air knife. Preferably a heated roller is used
under pressure. As indicated previously, the adhesive may
either be present on the label or may be on the polymeric
surface. The adhesive has to be activated prior to or during
transfer. depending on the type of adhesive, the activation
method will differ. The skilled person will be aware which
type of activation will be required. In case of a pressure
sensitive adhesive, pressure will be applied during
transfer. If a heat activatable adhesive is used, it is
preferred to preheat the polymeric surface, optionally in
combination with a heated transfer system, such as a roller. -
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In a preferred embodiment a heat activatable
adhesive is used, in combination with a heat-pretreatment of
the polymeric surface. As the heat activated adhesive
printed over the ink becomes tacky, the ink is released from
the film substrate and adheres to the plastic surface.
The labels may be supplied on a roll, from which
the images are transferred to the substrate, optionally in
combination with a cutting operation. It is also possible to
provide a stack of separate labels, using a suitable
application device.
Depending on the requirements on the image it may
be preferred to have a protective coating on top thereof.
This coating may have been applied as part of the reverse
printed 1'.abel during image transfer. In a preferred
embodiment the protective coating is applied after image
transfer, for example by the use of a roller coater.
In that situation, the transfer surface is coated
with a thin layer of protective coating, such as an acrylic
wax. Subsequently a post treatment, preferably one or more
heat treatments are given. With this treatment the label
materials coalesce and without being bound thereto, it is
assumed that the durable bond obtained thereby is affected
through inter diffusion of the adhesive and plastic surface.
In case the image has to be more durable, for
example for multi-trip use, it is preferred to use either a
more durable coating, such as a urethane, and/or a
prolonged, more severe post treatment.
It is well-known that polymeric materials and
especially high density polyethylene in particular, are
difficult materials to bond with adhesives. This invention
describes a specific method of surface treatment to ensure
adhesive bonding that is fast and economical.
An important discovery described in the invention
is the coalescing of the label materials and surface coating
by exposing the labelled area to very high temperatures for
a few seconds to increase durability and resistance to
moisture. This process alters the label composite from a
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series of adhered layers which are easily dissociated with
immersion in water for 2 or more hours to a coalesced matrix
of label adhesive, label inks and outer coating. During the
heating the adhesive material inter diffuses with the
plastic surface. The simultaneous coalescing and inter
diffusion of this preferred embodiment of the invention
result in a very durable label matrix. Resistance to water
immersion can be varied from a few hours to several weeks by
varying the time of exposure and the resultant temperature.
it should be noted, that the resistance to water
immersion of an untreated label according to the invention
may be sufficient as it never completely loses its bonding
with the polymeric surface. The bonding only weakens; drying
restores the bonding strength to its original value.
Having achieved the required label durability, it
is also necessary to remove the label after it has served
its purpose of identifying the contents of the container
prior to consumption. The empty plastic containers and
beverage bottles are returned to the beverage plant for
refilling. The plastic containers are washed. During this
wash the label must either be completely removed, or remain
on the surface undamaged, depending on the situation (one-
way or multi-trip).
In the former case, the heat treated adhesive used
to bond the ink matrix, while durable in water, breaks down
in the washing solution, preferably hot caustic, enabling
the label and adhesive to be completely removed. The label
residue is filtered out of the caustic solution. In the
latter case the label is only removed when the washing
conditions are changed to remove the label, for example by
using a prolonged soaking and/or a stronger caustic
solution, optionally in combination with the use of high
pressure jets (liquid or gas).
Alternative methods for removing the images
without a destructive treatment of the substrate (polymeric)
surface comprise chemical removal (solvents), ultra sonic,
sub-cooling, heating, brushing, enzymatic treatment, vacuum
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treatment, peeling and radiation, such as UV. Combinations
of various methods are of course also possible.
It may be desirable that the processing equipment
be arranged so that the plastic containers are labelled in-
5 line during the normal progression through the beverage
facility, so that the crate label matches the bottle
contents.
DESCRIPTION OF THE DRAWINGS
Figure 1 Heat Transfer Label
Figure 2 Surface Treatment and Temperature Stabilization
Figure 3 Label Application and Ink Transfer
Figure 4, Coating Application 15 Figure 5 Post Treatment
Figure 6 Specific embodiment of image transfer process
Figures
7A and 7B Graphs of Crate Speed and Roller Temperature
relationship
DET I=ED DESCRIPTION OF THE INVENTION
The preferred embodiment of the label and
application according to the present invention will be
described first with references to Figure 1 which shows the
plastic container (1) and the label positioned for
application. The label is printed on a film substrate (10)
which may be any thin film, but in the case described is
polypropylene of 2 mils thickness. (14) is an acrylic
coating which may or may not be employed, depending on the
type and source of the film available. (12) is a release
material which coats the film. In the case of the invention
it is silicone which is applied at the time of film
manufacture. (20) represents all the printed ink material.
Depending on the label graphics and opacity requirements the
ink materials may be as many as five (5) different colors in
one or more layers, some of which may overlay another.
(30) and (40) represent two (2) layers of adhesive to
indicate the build up of adhesive from 0.5 to 1.5 pounds per
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ream, depending on the labelled surface uniformity and
rigidity of the container being labelled.
Upon application, all of the printed materials are
transferred from the silicone release coated film substrate.
The printed ink materials are vinyl or acrylic resin based,
colored with temperature and ultra violet stable pigments.
In the case of white ink, titanium dioxide is the pigment of
choice. Pigment particle size ranges from three (3) to five
(5) pm. The printed adhesive is a urethane modified acrylic
with an initial tack temperature of 175 F (80 C). This
initial tack temperature is very important to the plastic
labelling process because it determines the required plastic
surface temperature at the time of transfer. With the
particular plastic container being labelled, there is no
support of the inside surface, hence it is desired to
maintain the plastic below 200 F (93 C) to avoid distortion
of the surface by reaching its point of deformation during
the label transfer.
The label application method will now be described
in the order of progression. Figure 2 shows the technique of
surface treatment and temperature stabilization. For
adhesion of two polymeric materials to occur, many factors
must be considered such as cleanliness, pressure,
temperature, contact time, surface roughness, movement
during bonding and adhesive film thickness. An additional
important consideration is the critical surface tension. The
commonly accepted method of measuring the critical surface
tension is with a Dyne solution, which is well known. For
most adhesive applications the critical surface tension of
polyethylene is 31 Dynes per centimetre. A series of tests
were performed which demonstrated for best adhesion of the
adhesive previously described to the polyethylene surface, a
treatment level of 60 to 70 Dynes per centimetre was
necessary. Further testing of commercially available
equipment showed that flame treatment optimized both capital
cost, operating cost and time required to achieve the
required critical surface treatment.
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For the adhesive to achieve and maintain tack
quickly it is necessary to heat the polyethylene container
before the label adhesive is in contact with it. To avoid
deforming the container, it is desirable not to heat the
surface over 200 F (93 C). As the surface temperature
leaving the flame treatment is approximately 125 F (52 C),
it is necessary to heat the surface approximately 75 F
(24 C). Here again, many options are available for heating.
Hot air, additional flame heaters, gas fired infra-red
panels and electric ceramic panels were all tested and found
to be either too slow or difficult to control. It was found
that an electrically heated flat fused quartz emitter plate
with zonal band control for localized label transfer would
provide maximum free air transmission of infra-red energy
without the effects of ambient environmental factors. With
an emissivity of 0.9 for polyethylene a desired temperature
of between 1650 F (900 C) to 1725 F (940 C) will emit the
most efficient wavelength (2.5 to 3.2 E.tm) of infra-red
energy for peak absorption. The unit tested was rated at
60 watts per square inch. The time to heat the polyethylene
surface the necessary 75 F (24 C) was 4.5 seconds at a
distance from the emitter plate of 2.5 centimetres.
Figure 3 illustreLes the method of label
application whereby the printed ink materials are
transferred from the polypropylene film substrate to the
polyethylene surface utilizing the tactile characteristics
of the heat activated adhesive to overcome the bond of the
ink layer 14 to the corona treated silicone coating 12. The
factors that influence transfer are time to contact,
temperature during contact and film tension during contact
particularly tension on the film after ink release. Pressure
roll diameter is also a factor but not a variable. For this
application the roll diameters are 38 mm. The rollers were
made of silicone rubber over a steel core, with rubber
durometer ranging from 50 Shore A to 80 Shore A. It should
be noted that distortion (flattening) of the rubber roller
is less at the higher durometer, consequently the contact
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area is less and the transfer pressure is greater. This is
important at the higher line speeds where contact time is
minimized. Thus a crate moving 18.3 meters per minute (60
feet per minute) past a roller of 38 mm diameter will have a
contact time of 1 millisecond per.l degree of roller
rotation where there is no roller distortion.
Roller pressure is provided by an air cylinder
activated by a conventional solenoid valve which in turn is
operated by two (2) proximity switches, one to advance the
roller and the other to retract. Other means, such as
mechanical linkage are obvious and will not be listed here.
The pressure is distributed across the length of the cylinder
and for this particular ink, transfer ranges from 12 to
17 kilograms per centimetre of roller length. See Figure 7A.
Thus the invention results in the film being
advanced at exactly the same rate as the crate is moving
past the roller by virtue of the heat activated adhesive
adhering to the high energy crate surface. The pressure
roller, which rotates freely, maintains the same tangential
speed as the linear speed of the film and crate. Thus the
ink is transferred completely and without distortion.
For purposes of fast and complete adhesion the
pressure roller is molded to a hollow core. Suspended within'
the hollow core is a resistance heater operated through a
controller. The heating element, rated at 500 W, will
maintain the roller surface at any predetermined
temperature. For purposes of the invention, the roller
surface temperature range between 250 F and 370 F.(120 C and
190 C). See Figure 7B.
Many silicone coated polymer films may be used for
the printed substrate, High temperature films such as
polyester may be operated in continuous contact with the
heated roller. Low temperature films such as polypropylene
must be prevented from contacting the heated roller during
pauses in the labelling operation. To accomplish this, film
guides are used to support the film when the roller is
retracted. The guides are mounted to maintain a clearance of
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approximately 13 mm between the guides and the labelled
surface. At the same_time the roller is retracted
approximately 13 mm behind the film. By maintaining those
clearances, stretching and distortion of the film such as
polypropylene is avoided. High temperature films would not
require the guides.
It has also been discovered that film tension,
especially on the film exit side of the roller, is important
to complete ink transfer. Through trials, it was found a
continuous tension of approximately 2.5 kilograms is useful.
This i.s achieved through a spring loaded dancer arm and
roller.
Conventional nip rollers and stepping motor are
used to advance the film to the next label and position it
accurately, using a printed mark to trigger an optical
scanning device.
Protection of the ink against scratching by casual
handling as well as insuring its weatherability when
subjected to outdoor storage is achieved with the
application of an acrylic based wax water emulsion as shown
in figure 4. This is applied by a roll applicator which is
supplied from a wet roller with a controlled amount of
coating. Control is achieved with a doctor blade. The
coating extends well past the edges of the ink pattern and
seals the edges from intrusive moisture.
The final processing step is to coalesce the
layers of the coating, label ink, and adhesive and also to
inter diffuse the adhesive layer with the polyethylene
substrate as shown in figure 5. This discovery was made
through extensive trials of many heating systems. As flame
treatment was discovered to be the best technique that would
provide the required surface energy for label adhesion, so
it was discovered that flame treatment of the label and
coating composite was the best technique that would develop
the required water immersion durability without sacrificing
mechanical properties or altering the visual characteristics
of the applied label, or distorting the polypropylene crate.
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In figure 6 the presently developed best mode of
application of the invention is shown.
It will be appreciated that further modifications
could be made to the embodiment disclosed above, while still
5 obtaining many of the advantages and without departing from
the spirit and scope of the invention as defined in the
appended claims.
