Note: Descriptions are shown in the official language in which they were submitted.
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Express Mail No. RB516880947
PATENT
EXTRUSION COATED SYNTHETIC PRINTING PAPER FOR IN-MOLD
5LABEL COUPON APPLICATIONS
BACKGROU~ OF_THE INVENTION
The present invention relates to a peelable, releasable
label material for use with plastic bottles. More
particularly, the present invention relates to a
polypropylene/low density polyethylene laminate which can be
adhered to a high density polyethylene bottle.
Consumer marketing is a multi-million dollar husiness
today. Pac~aging plays a major role in this area. An
infinite number of today's products are sold in plastic
bottles. The variety of contents for these bottles ranges
from motor oil, to laundry detergent to orange juice. Many
of the bottles are made from high densi~y polyethylene.
20As part of the marketing strategy for these products,
certain manufacturers like to use point of purchase and rebate
coupons. These coupons are attached to the item, typically
a glass or high density polyethylene (HDPE) bottle, peeled off
by the consumer at the point of purchase and redeemed at the
cash register for the value of the coupon. Post mold labeling
is one type of method which has been developed for attaching
these coupons to the bottled consumer products after the
bottles have been produced. One execution of this method
includes the use of multi-layered pressure sensitive paper
labels which are affixed to the bottle by a pressure sensitive
adhesive. The top one or two layers can be clearly peeled off
and redeemed for cents off at the cash register or used for
such things as game pieces for promotional games and
sweepstakes. Examples of pressure sensitive systems are
"Clean Dri" and "Double Dri" labèl constructions from Mid
America Tag and Label a Division of Menasha Corporation of
Neenah, Wisconsin.
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A second method of labeling is to use glue applied labels
which have unglued perforated sections of the label which can
be separated via the perforations and redeemed. Rough
handling, however, can cause the labels to prematurely
separate from the bottle or cause the labels to become ripped
and torn.
A third method of affixing labels is to use a hang tag
around the neck of the bottle. The hang tag can be attached
by a piece of string or by a hole which is die cut into the
tag. Once again such a method of labeling is subject to a
high degree of damage and loss due to the nature of the
construction and affixation.
While all of the above methods of labeling are adapted
for post mold labeled bottles, there is a concerted effort to
label bottles during the molding process because of the
efficiencies which can be obtained by eliminating the step of
labeling the bottle on the filling line. Labeling on the
filling line is normally the slowest most inefficient step in
the filling process. Given the inefficiencies of post mold
label attachment, it would seem apparent to affix the label
during the molding process, i.e., in-mold labeling. To date,
however, a successful system has not been developed which will
allow a label with a point of purchase coupon to be applied
to a plastic bottle by the in-mold labeling process.
In-mold labeling is a process commonly used with bottle
forming process such as blow molding. The blow molding
machines used for producing high density polyethylene (HDPE)
bottles conventionally include an extruder that extrudes a
tube or parison of hot high density polyethylene between open
sections of a mold. Closing of the mold then clamps the
plastic parison and allows air to be blown into the tube such
that the plastic parison assumes the shape of the mold. After
suitable cooling has taken place, the mold sections are opened
to allow ejection of the molded bottle.
In-mold labeling has been developed to provide an
attachment of labels to bottles during the molding process.
This in-mold labeling is performed by inserting a label,
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plastic or paper, within the mold prior to the extrusion of
the hot HDPE parison and subsequent closing of sections of the
mold in preparation of the blowing operation. The subsequent
blowing operation forms the hot HDPE parison around the label
and activates a heat sensitive adhesive, that bonds the label
to the thus formed bottle.
If labels used in the in-mold labeling process are to be
used for in-store redemption and mail-in rebates, they must
be sufficiently adhered to the bottle to prevent loss,
premature release and damage, yet the same labels must be
easily removable from the exterior of the container by the
consumer.
One type of label made for such applications is a
thermoplastic polypropylene film adhered to the bottle with
a water-based ethylene vinyl acetate adhesive. A problem with
such water-based adhesives is their failure due to the water
sensitivity of the adhesive. The water-based ethylene vinyl
acetate adhesive (EVA) has the proper softening point and hot
tack to allow attachment of the label to HDPE bottles during
the blow molding process. Testing by the applicant indicates
that the bond between the thermoplastic polypropylene film and
the adhesive (150-580 g/15 mm)[ 90 peel adhesion test using
an Instron Universal Testing Instrumen~ as described on page
7: lines 30-31 supra] was of the proper magnitude to allow the
label to be cleanly peeled from the surface of the bottle.
The sensitivity of the adhesive and therefore the problem with
the system resides in the fact that such labels will fall off
the bottles when exposed to high moisture conditions as are
encountered during a freeze-thaw cycle. Freezing and thawing
most often occurs when products are shipped and or stored
during the winter or stored in the freezer section of a
grocery store. Typically a large amount of moisture will
condense on a frozen bottle containing product when it is
removed from the freezer or taken from a frozen state and
placed in a room at normal reiative humidity (RH) of
approximately 30 to 90% RH. The condensed moisture on the
outside of the label wicks into the water sensitive adhesive
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from the edge of the label causing the adhesive to fail and
the label to loosen and fall-off the bottle. As a result,
labels which use EVA adhesives are seen to be less than
desirable when used in conjunction with labels involved in the
in-mold labeling process.
Other adhesives are available for attaching thermoplastic
polypropylene film labels to HDPE bottles in the in-mold label
process. Examples are the Adcote~ ethylene vinyl acetate gel
lacquers from Morton International of Woodstock, Illinois.
The problem with these adhesives is that the bond strength
between label material adhesive and the bottle is so high that
the coupon portion of the label can not be cleanly removed
from the bottle. Testing by the applicant indicates that bond
strengths for these adhesives are in the order of 650-800 g/15
mm when using a 90 peel adhesion test. As a result, when
att~mpting to remove such labels, the film tends to delaminate
and tear thereby making the labels unsuitable for redemption.
A third type of adhesive which can be used in the in-
mold labeling process is a low density polyethylene. Oji Yuka
Synthetic Paper Company of Tokyo, Japan has prepared labels
from a thermoplastic polypropylene film (Ximdura~) which is
tie coated either with polyurethane or polyethyleneimine and
extrusion coated with low density polyethylene. The tie coat
serves to firmly bond the LDPE to the Kimdura~ and the LDPE
acts as the adhesive in the in-mold labeling process. While
this material works well for permanent label applications,
this material does not function properly as a coupon label
becau~e the typical 650-900 g/15 mm bond strength between the
Pilm adhesive and bottle is too high. The coupon portion of
the label cannot be cleanly peeled from the bottle because the
film tears and delaminates.
It is therefore the object of the present invention to
provide a label material that will peel cleanly from a bottle
without tearing or delaminating. It is another object of the
present invention to provide a label material which will not
come loose from the bottle until removal is affected by the
consumer.
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It is yet another object of the present invention to
provide a label material which, when peeled, has a bond
~ailure which occurs between the label material and the
adhesive thereby leaving a clean back surface to the label
which can be written on by the consu~er.
It is still a further object of the present inventioh to
provide a label material which can be printed by normal label
printing methods such as flexography, offset lithography or
rotogravure printing.
These and other objects of the present invention will
become more apparent upon a further review of the following
specification and claims.
SUMMARY OF THE INV_ENTION
The present invention relates to a label usable with
plastic bottles and in particular with bottles made with
exterior surfaces of high density polyethylene. The label
itself is a laminate of label stock with an adhesive layer of
low density polyethylene. In a preferred embodiment, the
label stock is polypropylene.
When the label according to the present invention is
attached to a bottle, such as a high density polyethylene
bottle, the release strength between the label and the bottle
should be between about 100 and 580 grams per 15 mm.
Preferably the release strength should be between about 150
and 400 grams per 15 mm. As a result of using such a label
stock, the label/bottle combination should be able to be
cooled to a temperature of at least -10~C for a period of at
least 24 hours and the label should not self-release upon
thawing. Furthermore, when the label is peeled from the
bottle, the majority of adhesive should remain with the bottle
and not with the label stock itself.
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DESCRIPTION OF TH~ PREFERRED EMBO~IMENT
The present invention relates to a releasable label
material suitable for use as a label for containers in general
and most preferably for thermoplastic containers such as high
density polyethylene (HDPE). Materials suitable for bottles
which are blow molded and in-mold labeled are polyesters such
as polyethylene terephthalate (PET), polyvinylchloride, and
polypropylene multi-layer bottles. As described in the
background of the present invention, the label material of the
present invention is best suited for use in the in-mold
labeling process even though other processes are also
contemplated as being within the scope of the present
invention.
- The label material of the present invention includes a
label stock which has been extrusion coated on one side with
an adhesive layer of low density polyethylene (LDPE). LDPE
is a highly chain-branched polyethylene polymer produced by
polymerizing ethylene under high pressure. Low density
polyethylene can contain a variety of short and long chain
branches and usually has densities ranging from about O.910
to about 0.940 grams per cubic centimeter (g/cm3). Melt flow
indices for LDPE using ASTM standard Dl238-88 can range from
about 0.15 to 15.0 grams per 10 minutes (g/10 min.) when
measured at l90-C under a load of 2.16 kilograms (kg). The
LDPE can be applied at a coating rate of about 9.32 to about
23.3 g/m2 with the preferred range being 11.7-18.4 g/m2.
This correlates to a coating thickness of approximately 10 to
25 microns.
The label stock itself can be any one of a number of
materials well known to be used as label stock, however, a
preferred material is a thermoplastic polyolefin film. Note
that whatever label stock which is chosen should be compatible
with the coating of LDPE. In particular, the label stock used
in the example below is a thermo~lastic polypropylene film
which has been biaxially oriented. When using such a
polypropylene film, it will generally have a density between
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about 0.17 and 1.02 grams per cubic centimeter (g/cm3). The
caliper of the label stock generally will be between about 60
microns and about lS0 microns and preferably between 60
microns and 95 microns. Basis weights for the label stock
will range between about 50 g/m2 and about 116 g/m2 and
preferably will be from 60 g/m2 to 82 g/m2. Several examples
will now follow which will further demonstrate the present
invention and its attributes.
EXAMPLE 1
A 76 cm wide web of polypropylene film (Kimdura~ KPK-80
from Kimberly-Clark Corporation of Neenah, Wisconsin) having
a caliper of 80 microns, a basis weight of 81 g/m2 and a
density of 1.02 g/cm3 was extrusion coated on one side with
11.7 g/m2 low density polyethylene (LDPE). The extrusion
equipment included a Hexco 8.9 cm single screen extruder with
a 24 to 1 L/D (length to diameter ratio), an EDI 91 cm die and
a Gloucester Engineering Company, Inc. laminator with a steel
chill roll and a silicone rubber back up roll. The LDPE
(Petrothene 1014 from Quantum Chemical Corporation of
Cincinnati, Ohio) had a density of 0.918 g/m3 and a melt flow
index of 7.0 g/10 min. No tie coat or precorona treatment was
applied to the label stock prior to coating with the LDPE.
To extrude the LDPE onto the polypropylene label stock the
LDPE was heated to 316~C.
The LDPE coated polypropylene label stock was printed
with a label pattern on the surface opposite the LDPE label
coating by rotogravure and then die cut into label shapes.
The labels were then applied to HDPE bottles by the in-mold
labeling process on a wheel type blow molding machine by
Continental Plastic Containers, 2375 Touhy Avenue, Elk Grove
Village, Illinois 60007.
The labeled bottles were tested for label bond strength
and for moisture resistance by a freeze thaw cycle test. To
determine bond strength the label panels were cut from the
bottle and the panels were then cut into lS mm wide strips
L s t~ 7 s
using a standard sample cutter. One end of the label was then
peeled back on itself approximately 15 mm. The peeled end of
the label film was placed in one jaw of an Instron Universal
Testing Instrument(model 1122, Instron Corporation, Canton,
MA 02021) and the other end of the bottle panel, opposite the
peeled end, was placed in the other jaw. The sample to be
peeled was held horizontally so the jaws peeled the label film
from the bottle at so from the horizontal. Settings from the
Instron were as follows:
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Cross head speed - 30 cm/min.
Span - 2.54 cm
Scale - 2 kg full scale
Chart speed - 15 cm/min.
Three test samples were run and yielded peel strengths of
250g/15 mm, 240g/15 mm and 220 g/15 mm. The average of the
three tests was 237g/15 mm.
To conduct the freeze/thaw test, bottles with labels were
filled with warm water at 50C and placed in a freezer at -
10C for 17 hours at which time the water was frozen. The
bottles were then removed from the freezer and placed in a
room at 23'C and 50~ relative humidity for six hours until the
water was thawed. While a large amount of water condensed on
the outside of the bottles, after thawing none of the bottles
lost their labels and the bond strength using the previously
described 90- peel adhesion was 180 g/15 mm after thawing.
In addition to the bond strength and freeze/thaw testing,
labeled bottles were also peeled by hand as would happen
during actual consumer use. Labels could be cleanly peeled
from the HDPE bottles leaving the LDPE adhesive on the bottles
thereby making it possible to write on the labels.
Furthermore, when the labels were peeled from the bottles they
did not tear or delaminate.
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EXAMPLE 2
A 84 cm wide roll of KPK-80 Rimdura~ polypropylene label
stock was extrusion coated with 13 microns of low density
polyethylene extrusion resin (Petrothane 1014, melt flow index
7.0g/10 min., density 0.918 g/cm3) at a temperature of 316C.
No tie coat or precorona treatment was applied to the KimduraX
film befcre extrusion coating. Labels were die cut from this
low density polyethylene adhesive polypropylene label film
laminate. They were applied to HDPE bottles using an in-mold
labeling process by Graham Container Corporation, York, PA on
a wheel type blow molding machine manufactured by the same
company.
A label panel was cut from one of the bottles and the
bond strength tested at 579 g/ls mm by 90 peel on an Instron
using a 15 mm wide strip. Instron settings were as follows:
Cross head speed - 30 cm/min.
Span - 2.54 cm
Scale - 2 kg full scale
Chart speed - 15 cm/min.
One bottle was filled with warm water at 47-C and frozen
in a freezer at -10-C for 23 hours. It was taken from the
freezer and placed in a room at 22'C and 50% RH for 24 hours.
A large amount of moisture collected on the surface of the
bottle and label as it thawed. After 24 hours the bottle had
warmed to room temperature and the label was still firmly
attached to the bottle. The bond strength was 480 g/15 mm
using the previously described 90- peel adhesion test. The
label could be cleanly removed from the bottle.
EXAMPLE 3
Labels prepared by the Oji-Yuka Synthetic Paper Company
of Tokyo, Japan from a thermoplastic polypropylene film
~Kimdura~) which was tie coated either with polyurethane or
polyethyleneimine and extrusion coated with low density
polyethylene w~re evaluated. The tie coat served to firmly
bond the LDPE to the ~imdura~, in fact, firmly enough that the
label could not be removed from the bottle without tearing and
delaminating after in-mold labeling.
The present invention provides a labèl material which is
extrusion coated with low density polyethylane without prior
use of a tie coat or corona treatment. This provides a label
material that will peel cleanly from a bottle without tearing
or delaminating. It is desirable to be able to test the bond
strength of the extrusion coated low density polyethylene to
the label film material before in-mold labeling to determine
if this bond strength is in a range which will allow it to
peel cleanly from the bottle after in-mold labeling.
Consequently, Dennison Standard Paper Testing Waxes (series
No. 39-330 from Dennison Manufacturing company, Framingham,
Mass., using ASTM Method D2482-86T) was used to measure the
bond strength of the LDPE adhesive film to the Kimdura~ label
film. The Dennison waxes are a numbered series of waxes with
graded adhesive powers used to test bond strength of coatings
to web materials. Higher numbers indicate stronger bonding.
A 8 1/2" x 11" sheet of Kimdura0 KPK-80 extrusion coated
with 11.7 g/m2 of low density polyethylene (Petro-theme 1014
from Quantum Chemical Corporation of Cincinnati, Ohio) was
tested by placing waxes, which had been heated until the end
was molten, firmly on the LDPE surface of the sample. Waxes
having ratings of 5 through 3 were used. After cooling, the
wax was pulled from the sample with a quick jerk. Bond
strength was determined by finding the wax numbers between
which the coated surface was not disrupted and where it became
detached. In this case, the LDPE did not pick with a #5 wax
and did pick with a #6 wax. For Oji-Yuka LDPE coated Kimdura~
label material, the LDPE coating did not pick with a #8 wax
but did pick with a #9 wax.
Thus for a coupon application the LDPE extrusion coating
should have a bond strength corresponding to a wax pick of at
least a #5 wax to ensure good bonding to the bottle but a bond
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strength below that corresponding to a #8 wax to ensure a
clean peel from the bottle.
Having thus described the invention in detail it should
be apparent that various modifications and changes can be made
in the present invention without departing from the spirit and
scope of the following claims.
