U.S. patent application number 10/853750 was filed with the patent office on 2005-12-15 for adhesive for bag sealing application.
Invention is credited to McCormick, Demetrius T., Nowicki, James W..
Application Number | 20050276938 10/853750 |
Document ID | / |
Family ID | 34971035 |
Filed Date | 2005-12-15 |
United States Patent
Application |
20050276938 |
Kind Code |
A1 |
McCormick, Demetrius T. ; et
al. |
December 15, 2005 |
Adhesive for bag sealing application
Abstract
Packaging bags having preapplied thereon a reactivatable
adhesive.
Inventors: |
McCormick, Demetrius T.;
(Belle Mead, NJ) ; Nowicki, James W.; (Hopewell,
NJ) |
Correspondence
Address: |
Cynthia L. Foulke
NATIONAL STARCH AND CHEMICAL COMPANY
P.O. Box 6500
Bridgewater
NJ
08807-0500
US
|
Family ID: |
34971035 |
Appl. No.: |
10/853750 |
Filed: |
May 25, 2004 |
Current U.S.
Class: |
428/34.3 ;
53/477 |
Current CPC
Class: |
B65D 33/22 20130101;
Y10T 428/1307 20150115; C09J 5/06 20130101 |
Class at
Publication: |
428/034.3 ;
053/477 |
International
Class: |
B65B 051/10 |
Claims
1. A packaging bag having preapplied to at least a portion thereof
a reactivatable adhesive, wherein the reactivatable adhesive
comprises an effective amount of an energy-absorbing ingredient
such that upon exposure of the adhesive to radiant energy having a
wavelength of from about 400 nm to about 100,000 nm the adhesive is
activated, said process comprising exposing the applied adhesive
with radiant energy having a wavelength of from about 400 nm to
about 100,000 nm for a time sufficient to melt the adhesive,
bringing one of said substrates in contact with the melted adhesive
on the other substrate, and allowing the adhesive to solidify
thereby bonding the first substrate to the second substrate.
2. The bag of claim 1 wherein the adhesive is activated upon
exposure to radiant energy having a wavelength of from about 700 nm
to about 5000 nm.
3. The bag of claim 1 wherein the preapplied adhesive is exposed to
said radiant energy for a period of time of less than about 5
seconds.
4. The bag of claim 1 wherein the preapplied adhesive is exposed to
said radiant energy for a period of time of less than about 2
seconds.
5. The bag of claim 1 comprising at least one closable bag ending,
said adhesive being present on said bag ending.
6. The bag of claim 5 wherein the bag is made of coated paper.
7. The bag of claim 5 comprising a plastic liner bag.
8. The bag of claim 1 wherein the adhesive preapplied to said bag
comprises an organic dye.
9. The bag of claim 1 wherein the adhesive preapplied to said bag
comprises a pigment.
10. The bag of claim 9 wherein the adhesive comprises carbon
black.
11. The bag of claim 1 wherein the reactivatable adhesive is a
thermoplastic adhesive.
12. The bag of claim 1 wherein the reactivatable adhesive is a hot
melt adhesive.
13. A process of packaging an article by forming, filling and
sealing a packaging bag that has had applied to at least a portion
thereof a reactivatable adhesive, wherein said process comprising
forming and/or sealing a packaging bag by exposing the applied
reactivatable adhesive to radiant energy for a time sufficient to
reactivate the adhesive, said radiant energy having a peak
wavelength of from about 400 nm to about 100,000 nm.
14. The process of claim 1 wherein the adhesive is activated upon
exposure to radiant energy having a wavelength of from about 700 nm
to about 5000 nm.
15. The process bag of claim 1 wherein the preapplied adhesive is
exposed to said radiant energy for a period of time of less than
about 2 seconds.
16. The process of claim 13 wherein the adhesive preapplied to said
bag comprises an organic dye.
17. The process of claim 13 wherein the adhesive preapplied to said
bag comprises a pigment.
18. The process of claim 17 wherein the comprises carbon black.
19. The bag of claim 13 wherein the reactivatable adhesive is a
thermoplastic adhesive.
20. The bag of claim 13 wherein the reactivatable adhesive is a hot
melt adhesive.
Description
FIELD OF THE INVENTION
[0001] The invention relates to a packaging system, and more
particularly to a packaging bag having a reactivatable adhesive
pre-applied to at least a portion thereof, more particularly a
closable bag ending thereof.
BACKGROUND OF THE INVENTION
[0002] Hot melt adhesives are widely used in various commercial
applications including packaging applications, such as cardboard
case sealing and carton and bag closing operations. Such hot melt
adhesives are applied to a substrate while in its molten state and
cooled to harden the adhesive layer.
[0003] In the conventional processes for the packaging of food and
consumer goods, a packaging container is first filled with the
goods, then a hot melt adhesive is applied, e.g., to the end flaps
of the boxes, bag or other packaging material, on the packaging
line and compression is exerted to seal the container. While this
process works reasonably well, it requires the packaging company to
devote a tremendous amount of time and attention to
adhesive-related issues, including adhesive selection, processing,
trouble-shooting, inventory, and maintenance of adhesive
application equipment.
[0004] Re-activation or heat sealing of pre-applied adhesives is
known and has been practiced in the art. Heat sealed closures and
seams are commonly used in the manufacture of bags, whereby
adhesive is coated on the inside of the bag seam or closure flap
and subsequently sandwiched under intense heat and pressure using
heated platens or bars. This direct application of heat and
pressure renders the adhesive molten, after which a bond is formed.
This application benefits from the ability to apply steady direct
pressure to ensure intimate contact and sufficient wetting of the
adhesive layer to the substrate. This process cannot be used for
applications where high heat and/or pressure required for closing
is not available or desirable. While focused hot air has been used
in the reactivation of pre-applied adhesives used in
sealing/closing operations, this method requires extremely large
amounts of energy and can result in undesired heating of the
packaging material, the packaged contents, the surrounding area and
equipment. Moreover, line speed is slow.
[0005] A need continues to exist in the art for a packaging system
that can advantageously be used in bag closing operations whereby
the bag to be filled and sealed is provided to the packager with
adhesive already applied to the bag and later, during the packaging
process, re-activated in order to close or seal the bag. The
current invention addresses this need.
SUMMARY OF THE INVENTION
[0006] The invention provides a packaging bag comprising a
reactivatable adhesive. A particular embodiment of the invention is
directed to bags that have a top and/or bottom bag ending, wherein
at least one bag ending has preapplied thereon a reactivatable
adhesive composition. Included are flat, folded packaging bags
having applied on at least one substrate surface thereof an
adhesive capable of being activated upon exposure to short
durations of radiant energy.
[0007] The hot melt adhesive composition used in the practice of
the invention comprises an effective amount of an energy-absorbing
ingredient such that upon exposure of the adhesive to radiant
energy, the adhesive is activated. The energy-absorbing ingredient
selected for use may be dissolved and/or dispersed within the
adhesive composition. Organic dyes and pigments are particularly
useful energy-absorbing ingredients for use in the practice of the
invention. Adhesives comprising carbon black and NIR absorbing dyes
are particularly preferred for use in the practice of the
invention. Upon exposure to radiant energy, the adhesive melts to
the extent that it is capable of bonding the substrate surface to a
second substrate surface.
[0008] A particular preferred embodiment comprises packaging bag
wherein a reactivatable adhesive comprising a near infrared energy
absorbing ingredient is used at one or both ends of the bag and/or
on the side seam.
[0009] Another embodiment of the invention is directed to a method
of packaging items such as food and consumer goods, and packaged
items. Examples of goods that can be packaged include food,
pharmaceuticals, cosmetics, breakfast cereals, beverage containers,
bakery items, dry foods (e.g., dog food), produce, household
products, paper products, soaps and detergents, candy, popcorn, wet
food, frozen food, diapers, light bulbs and the like.
[0010] In the practice of the invention, an item is packaged in to
a bag by forming filling and sealing a bag having a reactivatable
adhesive preapplied to at least one predetermined portion thereof.
In one embodiment, the adhesive is located on a closable end flap
region.
BRIEF DESCRIPTION OF THE DRAWING FIGURES
[0011] Drawing FIGS. 1-3 illustrate packaging bag closure regions
having adhesive pre-applied thereto.
DETAILED DESCRIPTION OF THE INVENTION
[0012] The invention encompasses bags having a closable end and an
opposite closed or open end, and bags in which both ends of the bag
are closable. Any type of packaging bag can be manufactured in
accordance with the invention. Both flat tube style bags and bags
having gussets may be manufactured in accordance with the
invention. Also encompassed are block bottom and satchel bottom
bags. Bags of the invention may constitute a secondary package
(e.g., sealed bag within a cereal box) and/or be the primary
package (e.g., flour, dog food).
[0013] The packaging material of the invention is typically a paper
product, but is not limited thereto. Paper products are defined
herein as any article of manufacture, at least a portion of which
comprises paper. The paper product may be made totally of paper or
partially of paper. The invention encompasses products made of
either single (e.g., paper or plastic) or multiple layers (e.g., a
paper laminate, a plastic/paper laminate, a plastic laminate).
[0014] In one embodiment, the bag comprises front and back panels
and inwardly extending first and second gusseted side panels. The
front and back panels and the first and second gusseted side panels
each have an exterior surface and an interior surface collectively
defining an interior region, a top end and a bottom end. Each of
the front and back panel means and the first and second gusseted
side panel means of the bag means may, if desired, comprise an
inner ply of substantially grease proof paper material and an outer
ply of paper material.
[0015] Each of the top ends of the front and back panel means and
the first and second gusseted side panel means are operably
sealable to one another before or after filling. The bottom ends
will typically be operably configured to form a substantially
sealed bottom region through adhesive attachment.
[0016] In the practice of the invention, the bag closure means
comprises adhesive that is operably positioned adjacent to the top
end of the interior surfaces of the front and back panel means and
the corresponding adjacent portions of the first and second flaps
of the first and second gusseted side panel means.
[0017] The adhesive and sealing method of the invention is
particularly well suited for bags comprising an inner liner bag
made of plastic or other meltable material. Such inner liner bags
are used for purpose of sift proofing the bag and/or to prevent
moisture ingress during shipping and storage. Bags of this type are
conventional used in the packaging of, for example, powdered milk.
When heat sealing bags that comprise an inner liner, such as PET
liner, application of heat fuses the PET inner liner resulting in a
bag that is partially unfillable.
[0018] In addition, the process of the invention, while useful in
the sealing of pinch bottom bag endings, may be used in any bag
ending configuration, resulting in bags that are more uniform in
shape and more stackable.
[0019] The adhesive formulations of the invention may be
pre-applied in a continuous or discontinuous, e.g., as evenly
spaced beads or dots, manner depending on surface area and coating
weight desired. Particular patterns may be used to optimize
substrate/adhesive contact. Depending on the adhesive, the bead
size, thickness, distance apart and pattern will vary. The adhesive
may be pre-applied to the substrate by any method known in the art,
and include, without limitation roll coating, painting,
dry-brushing, dip coating spraying, slot-coating, swirl spraying,
printing (e.g., ink jet printing), flexographic, extrusion,
atomized spraying, gravure (pattern wheel transfer), electrostatic,
vapor deposition, fiberization and/or screen printing. The method
of pre-application to the substrate is not critical to the practice
of the invention.
[0020] Reactivation, as this term is used herein, refers to an
adhesive that resides on at least a portion of at least one
substrate to be bonded. In the context of a hot melt adhesive, the
adhesive has been applied to a substrate in the molten state and
allowed to cool, i.e., solidify, thereon. The adhesive present on
the substrate is thereafter reactivated or heated to a molten
state, brought in contact with a second substrate and allowed to
cool or solidify, thereby bonding the two substrates together. The
application of the adhesive onto a substrate for later activation
or "reactivation" is referred to herein, and in the art as a
"pre-applied" adhesive.
[0021] The reactivation efficiency of an adhesive refers to the
ability of the adhesive to reactive, e.g., become molten in a short
period of time. Reactivation efficiency will depend on the power of
the device and the distance of the energy source from the adhesive.
Reactivation time depends on receptivity of the adhesive, which
depends on the energy absorbing ingredient, the coating weight or
thickness of the adhesive and the energy flux density that the
radiant source can supply to the adhesive (e.g., intensity per unit
area). Energy flux density refers to the distance, focal point,
power and intensity of the lamp or power source.
[0022] Preferably, the reactivatable adhesives are formulated to
reactivate to a temperature of at least about 200.degree. F., more
preferably to a temperature of at least about 250.degree. F. upon
exposure of less than about 1200 watts/sq inch of near infrared
energy for a period of less that about 10 seconds, more preferably
less than about 5 seconds, even more preferably less than about 2
seconds.
[0023] The adhesive compositions applied to the packaging substrate
contain an energy absorbing ingredient that increases the
absorption and reduces the transmission of radiant energy that
creates a temperature distribution within the adhesive that
optimizes performance. The adhesives have improved re-activation
and performance properties after irradiation. The adhesives of the
invention reactivate on exposure to short durations of radiant
energy and provide superior on-line performance and set speed that
allows for quicker production speeds.
[0024] The improved re-activation and performance may preferable be
achieved by incorporating into an adhesive an energy-absorbing
ingredient. Energy-absorbing ingredients include those dyes,
pigments, fillers, polymers, resins, and/or other ingredients that
are capable of absorbing energy and provide an optimal balance of
absorption, reflection, transmission and conduction.
[0025] It has been discovered that when a suitable energy-absorbing
ingredient is added to a conventional adhesive, reactivation upon
short duration of radiant energy can be achieved. Energy-absorbing
ingredients contemplated for use in the practice of the invention
are commercially available and include, but are not limited to
dyes, pigments and fillers. Examples include carbon black,
graphite, Solvent Red
(2',3-dimethyl-4-(2-hydroxy-naphthylazo)azo-benzene), Solvent
Green, dyes such as Forest Green and Royal Blue masterbatch dye
available from Clariant, cyanine-based dyes, oxides such as such as
titanium dioxide, and metals such as antimony,
tetrakis)dialkylaminophenyl)aminium dyes, cyanine dyes, squarylium
dyes and the like.
[0026] Pigments, such as carbon black and graphite, are particulate
in nature and will usually have somewhat of a spherical shape with
average particle sizes in the range of about 0.01 to about 7
microns. Pigment particles aggregate, so aggregate size will be
larger. The pigment aggregate size in hot melt adhesives will
preferably be smaller than about 500 microns. Aggregate sizes of
less than about 100 microns are preferred, more preferably smaller
than about 50 microns.
[0027] A wide variety of organic NIR triggers are described in the
literature and are available for use in the practice of the
invention. Such compounds include cyanine, metal complexes,
quinone, azo, radical multiphenylmethane, perylene, aromatic
annulenes, fluorenylium. Such triggers possess various absorption
characteristics. For example, halogen substituted
1,4,5,8-tetraanilioanthraquinones have excellent transmittance in
the vicinity of 860 nm and can absorb NIR in other ranges. Another
example is squaraine, which is characterized by intense narrow
absorption bands at relatively long wavelength. Also specifically
designed phthalocyanine compounds have been demonstrated exhibiting
high transmittance to visible light and offering high efficient cut
of near infrared.
[0028] Preferred energy-absorbing ingredients for use in the
practice of the invention are broad band near IR absorbers such as
Epolight 1125 (Epolene, Inc), SDA6248 (H.W. Sands Corp.), SDA2072
(H.W. Sands Corp.) and carbon black. Carbon black can be purchased
from Cabot under trade name of Monarch, Regal, Black Pearl, and
Elftex, or Degussa (FW series), or from Columbian Chemical Company
(Raven Series). Carbon black can be manufactured by different
methods such as the furnace black method, the gas (channel) black
method, and the lamp black method. The key parameters affecting the
radian energy absorption of carbon black prepared by these various
methods are average primary particle size, surface chemistry and
aggregate structure.
[0029] Energy absorbing ingredients for use in the practice of the
invention will typically have an absorption in the range of from
about 400 nm to about 100,000 nM, more preferably from about 700 nm
to about 10,000 nm, even more preferably from about 750 nm to about
5000 nm.
[0030] Suitable energy-absorbing ingredients for use in
reactivatable adhesives of the invention may be identified by
blending a desired adhesive with a chosen additive of various
particle size and various amounts. Any conventional method of
blending the energy-absorbing ingredient with the adhesive such as
through use of a paddle mixer or high shear mixer such as Ross M
E-100LC extruder, as would be apparent to the skilled practitioner,
may be used to prepare the adhesive compositions of the invention.
The starting adhesive and the adhesive containing the
energy-absorbing ingredient then are compared by heating samples of
each with a light from a radiant heat source. The samples are
tested for reactivation efficiency and bonding performance, as
described in detailed in the Examples. Reactivation efficiency is
the ability the adhesive to become molten in a short period of
time. Suitable additives are those that reactivate quickly and
exhibit acceptable bond strength. Preferred are thermoplastic
adhesives which, when pre-applied to a substrate, re-activates with
a short duration of exposure to radiant energy, preferably less
that about 10 seconds, more preferably less than about 5 seconds,
and provides acceptable bond force after a short period of
compression or cooling, preferably a period of less that about 30
seconds, more preferably less than about 15 seconds.
[0031] Included in the practice of the invention are adhesives
comprising absorber coated fillers and encapsulated absorbers. For
example, the adhesive may comprise a cureative encapsulated within
a shell comprising a NIR absorbing agent. Exposure to NIR energy
melts the capsule thereby expelling the curing agent and allowing
for cure of the adhesive.
[0032] The term tubular, as in a tubular package or tubular
packaging capsule is not limited to a cylindrical shaped package
but encompasses rectangular shaped packages as well as triangular,
hexagonal, pentagonal, octagonal and the like shaped packaging.
Packaging containers can have a rectangular, circular, square or
other shaped cross-section.
[0033] In accordance with the practice of the invention, the
converter, in addition to applying adhesive to the side seal
location, applies to at least one predetermined location an amount
of adhesive sufficient to seal the bag ending. The adhesive applied
to the bag ending comprises an energy-absorbing ingredient. By
including an energy-absorbing ingredient, the absorption,
reflection and transmission characteristics of the adhesive
composition is tailored so as to optimize the composition's
re-activation and subsequent bond formation. The adhesive is
applied to the substrate and, depending on the type of adhesive
applied, allowed to dry or solidify. Such adhesives are capable of
reactivating upon short duration of exposure to radiant energy,
preferably less that about 10 seconds, more preferably less than
about 5 seconds, even more preferably less than about 2 seconds,
and provides acceptable bond force after a short period of
compression or cooling, preferably a period of less that about 30
seconds, more preferably less than about 15 seconds.
[0034] Thus, the flat folded configuration supplied to the packager
has all the adhesive elements required to seal the container and
the packager can avoid applying adhesive in the packaging line and
avoid the problems associated with such application. The bag ending
may be sealed prior to filling or after filling as desired by the
packager and/or dictated by the type of material to be packaged in
the bag of the invention.
[0035] Radiant energy can be supplied by a number of sources, as
will be apparent to the skilled practitioner. Both coherent and
non-coherent sources may be used. Examples include lasers, a high
pressure xenon arc lamp, a coiled tungsten wire, ceramic radiant
heater, tungsten-halogen lamps and ultrasonic waves. In a preferred
embodiment, radiant energy within the near infra-red (NIR) region
is used. Peak wavelengths of from 400 nm to about 100,000 nm may be
used. More typically, wavelengths of from 700 nm to about 10,000
nm, most typically from about 750 nm to about 5000 nm will be used
in the practice of the invention. Commercial sources of equipment
capably of generating radiant heat required for use in the practice
of the invention include Research Inc. (Eden Prairie, Minn.),
Chromalox (Ogden, Utah), DRI (Clearwater, Fla.), Advent Electric
Inc. (Bridgeport, Pa.), and Glo-Quartz Inc. (Mentor, Ohio).
[0036] It is to be understood that the terms "bottom" and "top" are
relative terms and not terms used to designate the top or bottom of
the finished packaged article.
[0037] The specific source of energy and distance from the surface
to be irradiated will be dictated by the type and amount of
adhesive used. In one embodiment, the energy source is NIR
radiation. It is to be understood that the selection and duration
of the radiant energy used will depend on the energy absorbing
material incorporated into the adhesive located on the container
being sealed.
[0038] In contrast to adhesives applied on the packaging line, and
to conventional heat seal hot melt adhesives, it has been
discovered that adhesive reactivated in accordance with the
invention have improved performance properties. Moreover less
adhesive is required to be used. Bag endings used in the practice
of the invention will typically be coated with from about 0.5 mil
to about 15 mil of adhesive. The adhesive present on the carton
blank reactivates upon exposure to short durations of radiant
energy and provide superior on-line performance and set speed which
allows for quicker production speeds.
[0039] The type of adhesive that can be reactivated in accordance
with the invention is not particularly limiting or critical to the
practice of the invention. Reactivatable adhesives encompassed by
the invention include but are not limited to hot melt adhesives,
waterborne adhesives, solvent borne adhesives, moisture curable
adhesives, ultraviolet curable adhesives, blocked urethane systems,
epoxy based adhesives, and adhesives comprising an encapsulated
cureative or the like. Thermoplastic and hot melt adhesives are
particularly useful when formulated for pre-application and
subsequent later reactivation and are particularly useful for case
and carton sealing. It will be apparent that a thermoplastic
adhesive present on a substrate may be applied to a substrate in
the form of a waterborne emulsion or solution.
[0040] The energy-absorbing ingredient may be added, with stirring,
any time during the preparation of the base adhesive, or following
preparation of the base adhesive. The amount added will depend on
the type of adhesive, the energy-absorbing ingredient used, the
size of the energy-absorbing ingredient and the dissolution or
dispersion properties of the energy-absorbing ingredient. The
additive is added in an amount effective to reactivate the adhesive
upon exposure to short durations (typically less that 10 seconds)
of radiant energy. Typically, the additive will be present in an
amount of about 0.001 to about 10 parts per 100 parts of the
adhesive composition.
[0041] Substrates to be bonded include virgin and recycled kraft,
high and low density kraft, chipboard and various types of treated
and coated kraft and chipboard. Composite materials are also used
for packaging applications such as for the packaging of alcoholic
beverages. These composite materials may include chipboard
laminated to an aluminum foil which is further laminated to film
materials such as polyethylene, mylar, polypropylene,
polyvinylidene chloride, ethylene vinyl acetate and various other
types of films. Additionally, these film materials also may be
bonded directly to chipboard or kraft. The aforementioned
substrates by no means represent an exhaustive list, as a
tremendous variety of substrates, especially composite materials,
find utility in the packaging industry.
[0042] By modifying the placement of adhesive on the substrate
(e.g., top or bottom end flap, vertical side section), the size or
surface area, the shape and/or pattern of the adhesive applied to
the substrate, packaging may be designed to control the amount of
force required to open a sealed package, i.e., control the ease of
opening. Thus packaging can be designed that is child proof or,
alternatively, geriatrically friendly (i.e., easy open). The
adhesive formulations of the invention may be pre-applied in a
continuous or discontinuous, e.g., as evenly spaced beads or dots,
manner depending on surface area and coating weight desired.
Particular patterns may be used to optimize substrate/adhesive
contact. Depending on the adhesive, the bead size, thickness,
distance apart and pattern will vary.
[0043] Drawing FIGS. 1-3 illustrates non-limiting embodiments of
packaging bags encompassed by the invention.
[0044] FIG. 1 is a diagram of a bag end closure having front and
back regions and two side regions. In FIG. 1, a PET inner bag is
adhesively tacked to the inner surface of the back region of the
bag (1). Adhesive is preapplied to the outer surface of the side
regions (2 and 3), shown folded, and to the inner surface of the
front region (4). Following reactivation of the adhesive, the back
region and front region are folded along the crease lines 5 and 6
respectively, to seal the bag ending.
[0045] FIG. 2 illustrates the bag of FIG. 1 following folding of
the back region along crease line 5.
[0046] FIG. 3 shows another type of bag closure, commonly referred
to as a pinch bottom bag ending, having adhesive preapplied to the
inner surface of the back (rear) flap of the bag. Following
reactivation, the flap is folding along the crease line 7 to seal
the bag ending.
[0047] The invention is further illustrated by the following
non-limiting examples.
EXAMPLES
[0048] Reactivation efficiency and bonding performance of various
hot melt adhesives were determined as follows:
[0049] Near Infrared (NIR) Reactivation Test
[0050] Adhesives were cast into films of 2 inch long, 1 inch wide,
and 2 mm thick. The film was placed underneath a halogen tungsten
lamp (250 W/120 V) of 35 mm long. The lamp was located in an
aluminum reflector and the distance between the lamp filament and
the adhesive top surface was kept constant (24.5 mm). The input
voltage of the lamp was precisely controlled so that the power of
the lamp was 140 W. The adhesive film was heated by the lamp for 20
seconds and the surface temperature of the adhesive film was
continuously measured using an infrared thermal probe. The surface
temperature (temperature after 20 second irradiation, beginning
temperature of 70.degree. F.) reported in the tables below are the
average of six samples tested for each formulation.
[0051] Bond Strength Test
[0052] Adhesives in a bead shape were pre-coated on corrugated
paperboard at the coating weight of 1.5 g/m. The bead cross-section
had a dimension of 2 mm.times.2 mm. The pre-applied adhesive beads
were cooled down to room temperature and then were subjected to NIR
radiation for various periods of time. NIR radiant energy was
emitted by a 240 W halogen tungsten lamp, which was placed in an
aluminum reflector. The distance of the lamp filament and the
adhesive bead was precisely controlled as 10.5 mm. After being
radiated, the adhesive bead was exposed to air for 3.5 seconds and
then another corrugated substrate (2".times.2") was placed on the
top of the adhesive bead to form a bond. The bond was pressed at 1
kgf/cm.sup.2 for a certain period of time and then was pulled
apart. The resulting bond force, adhesive bead flatness, and the
percentage of fiber tear were recorded. The bead flatness measured
the deform-ability and flow-ability (i.e., the level of
reactivation) of the hot melt adhesive under the test
condition.
Example 1
[0053] This example illustrates the influence of the concentration
of the energy-absorbing ingredient on the reactivation efficiency
and bonding performance.
[0054] A sample (Sample A) of an EVA, paraffin wax, and hydrocarbon
tackifier-based hot melt adhesive available from National Starch
& Chemical Company (Cool-Lok.RTM. 34-2125) was compared to
adhesive samples (Samples B-F) to which various amounts of carbon
black (Regal 400, Cabot) had been added. Samples B-E were prepared
by fully blending the adhesive and Regal 400 using a paddle mixer
and all Samples had the same level of dispersion quality. The
increase in adhesive temperature that occurred during the NIR
reactivation test (described above) was determined and is reported
in Table 1. In the Bond Strength Test, the adhesive bead was
radiated for 0.3 seconds, and the bond was pressed for 15 seconds.
Results (bond force, % bead flatness and % fiber tear) are reported
in Table 1.
1 TABLE 1 Sample Sample Sample Sample Sample Sample A B C D E F
Additive Regal 0 0.1 0.3 0.5 0.75 1.5 400 Concentration (wt %)
Radiation Time 0.3 0.3 0.3 0.3 0.3 0.3 (S) Compression 15 15 15 15
15 15 Time (S) Adhesive 125 200 250 282 293 306 Surface Temperature
(.degree. F.) Bond Strength <1 2-4 >6 >5 2-4 <1 (KgF)
Bead Flatness 0 50 100 100 25 25 (%) Fiber Tear (%) 0 1-25 75-100
50-75 1-25 1-25
Example 2
[0055] This example illustrates the utility of various NIR
absorbing dyes as the energy-absorbing ingredient in providing
short reactivation time and high bond strength. These dyes were
dissolved homogeneously into the base hot melt adhesive (Cool-Lok
34-2125) and absorbed impinging radiant energy, most preferably
ranging from 400 nm to 5000 nm in wavelength. Epolight 1125 is a
green dye available from Epolight, near IR-1050 and near IR-1048
are dyes available from Aldrich, Inc. The samples were prepared by
uniformly blending the adhesive and dye with a paddle mixer. The
influence of NIR absorbing dyes on reactivation efficiency is shown
in Table 2.
2 TABLE 2 Sample G Sample H Sample I Epolight 1125 (wt %) 0.5 near
IR-1050 (wt %) 0.5 near IR-1048 (wt %) 0.5 Radiation Time (S) 0.3
0.3 0.3 Compression Time (S) 15 15 15 Surface Temperature (.degree.
F.) 245 245 241 Bond Strength (KgF) >6 >6 >6 Bead Flatness
100 100 100 Fiber Tear 100 75-100 75-100
Example 3
[0056] A construct comprising two PET layers sandwiched between
paper layers were used as substrate material. To one of the
substrate surfaces, Cool-Lok 34-212 modified to contain 0.2 wt %
Epolight 1125 was applied and allowed to solidify. 24 hours later
the adhesive was reactivated using a 3200 watt broad band emitter
as the source of near-IR light. The size of the energy source was
22 inches long, 4 inches deep, and 1.5 inches in width. A second
substrate was pressed onto the surface of the reactivated
adhesive.
[0057] Table 3 shows reactivation at different speeds. Tables 4 and
5 show reactivation at different power levels. In each case,
reactivation occurred without fusion the PET layers.
3TABLE 3 Lamp Power Speed (ft/min) Fiber Tear 10 60 50% 10 90 100%
10 120 80% 10 131 80% 10 143 70%
[0058]
4TABLE 4 Lamp Power Speed (ft/min) Fiber Tear 90 90 100% 80 90 100%
70 90 80% 60 90 60% 50 90 10%
[0059]
5TABLE 5 Lamp Power Speed (ft/min) Fiber Tear 90 120 80% 80 120 60%
70 120 60% 60 120 0%
[0060] Many modifications and variations of this invention can be
made without departing from its spirit and scope, as will be
apparent to those skilled in the art. The specific embodiments
described herein are offered by way of example only, and the
invention is to be limited only by the terms of the appended
claims, along with the full scope of equivalents to which such
claims are entitled.
* * * * *