Note: Descriptions are shown in the official language in which they were submitted.
W092/09503 ~ pcr~us()1/o866l .
1--
MICROWAVE HOT MELrr ADHESIVE PACKAGE AND DISPENSER
TECHNICAL FIELD
The present invention relates to heat activated
hot melt adheçives, including cements, coatings or
seala~ts, within microwavable ~lackages, and in particular
to hot melt adhesives that are microwave activatable
combined with a microwave package from which the hot melt
adhesive can be safely dispensed in a flowable state after
heating in a microwave oven.
BACKGROUND OF THE INVENTION
Many different types of hot melt adhesives are
well known in the art, of which the vast majority are heat
activated by raising the temperature thereof by convection
heating. By activation, it is meant the changing of the hot
melt adhesive by heating ~rom its substantially solid ~.
state, which occurs at room temperatures, to a flowable
state, which occurs only a~ter the hot melt a~hesive is
suf~iciently heated above the melting point of the hot melt
adhesive. Once such an adhesive is melted to its flowabl~
tate, the adhesive can be applied by many known techniques
to a surface o~ a substrate to be adhered to another, and
thereafter, as the temperature of the adhesive decreases,
Z5 the items are bonded together indefinitely. In most cases,
the adhesive could once again be heated to a temperature in
excess of its melting temperature and th~ items oould be
separated at that time.
Another manner of activating some hot melt
adhesives, that is changing the state of the adhesive ~rom
its substantially solid state to a flowable state, is to
sub~ect ~hese hot melt adhesives to microwave energy. The
microwave energy acts on the hot melt adhesive in
accordance with known microwave heating principles to raise
the temperature of th`e hot melt adhesive above its melking
temperature to its flowable state. A major factor of
microwavable hot melt adhesive.s that permits such hot melt
adhesives to be changed to their ~lowable state in a
microwave oven is the relatively low melt temperature
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W~92/09503 ~ t)l1 ~ P~/lJ~l/0~661
1~
MICROWAVE HOT MELT ADHESIVE PACKAGE AND DISPENSER
TEC~HNICAL F:[:ELD
The present invention relates to heat activated
hot melt adhesives, including cements, coatings or
sealants, within microwavable packages, and in partic~lar
to hot melt adhesives that are microwave activatable
combined with a microwave package from which the hot melt
adhesive can be safely dispensed in a flowable state after
heating in a microwave oven.
BACKGROUND OF THE INVENTION
Many different types o f hot melt adhesives are
well known in the art, of which the vast majority are heat
activated by raising the temperature thereof by convection
heating. By activation, it is meant the changing of the hot
melt adhesive by heating from its substantially solid
state, which occurs at room temperatures, to a flowable :-
state, which occurs only a~ter the hot melt adhesive is
suf~iciently heatad above the melting point o~ the hot melt
adhesive. Once such an adhesive is melted to its flowable
state, the adhesive can be applied by mahy known techniques
to a surface of a substrate to be adhered to another, and
thereafter, as the temperature of thP adhesive decreases,
25 the items are bonded together inde~initely. In most cases, ~ :
the adhesive could once again be heated to a temperature in
excess of its melting temperature and the items could be
separated at that time.
Another ma~ner of activating some hot melt
adhesives, that is changing the state of the adhesive ~rom
its substantially solid 5tate to a flowable state, is to
subject these hot rnelt adhesives to microwave energy. The
micxowave ene:rgy acts on the hot melt adhesive in
accordance with ~nown microwave heating prinoiples to raise
the temperatu:re of the hot melt adhesive above its melting
temperatUre to its flowable stat~ A major factor of
microwavable hot melt adhesives that permits such hot melt
adhesives to be changed to the.ir flowable state in a
microwave oven is the relatively low melt temperature
W0~2/~9503 PC~ S9l/0
2~
co~mon of such hot melt adhesives. Thus, ~s lower melt
temperature hot melt adhesives are developed, they become
candidates for microwave acti~ated hot melt adhesives.
However, in order for a low temperature hot melt adhesive
to be microwave activatable, the hot melt adhesive must
have an inherent property which renders it microwave
activatable or must be able to be modified by the addition
of other components which are microwave activatable.
Inherent microwave activatable hot melt
adhesives are those of the type having a su~icient amount
o~ residual water retained in the hot melt adhesive in
solid state. The activatability of such water molecule
containing hot melt adhesives by microwaves is due to the
dielectric properties of the water molecules. Moreover, the
rate of melting of the hot melt adhesive depends on the
amount of residual water in the hot melt adhesivs.
If the hot melt adhesive to be misrowave
activated does not inherently contain a high enough
residual water content, it is also known to mix a component
of a highly hygroccopic water retaining additive in the Aot
melt adhesive. The obvious disadvantage here is that the
additive remains in the adhesive after adhesion and can
reduce the bond strength of the hot melt adhesive.
Moreover, as ambient conditions change such as temperature
and/or humidity, the water component oP the hot melt
adhesive can be affec~ed thereby changing the heat up rate
o~ the hot melt adhesive. This disadvantageou~ly makes it
difficult to predict the heat up time for the hot melt
adhesive since the heat up rates are not constant.
Another manner of rendering a hot melt adhesive
microwave actiYatable, is to mix a component of a microwave
susceptor within the hot melt adhesive. By the term
"microwave susceptor", as used throughout this application,
it is ~eant a microwave interactive material capable of
absorbing microwave energy and converting the microwave
energy to sensible heat. In particular, if the material of
the microwave susceptor has a proper electrical
conductivity, voltages are produced in the material by the
incident microwave energy, giving rise to eddy currents
.
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wo92/os5n3 ~ ~ ~ 3 1 1 ~ Pcr/us~i/
--3--
thereby resulting in resistive heating. An example of a
microwave activatable hot melt adhesive utilizing
electrically conductive substances mixed within hot melt
adhesives is described in U.S. Patent No. 4,906,497 to
Hellmann et al~, issued March 6, 1990. Disclosed as an
electrically conductive substance is carbon which may be ir
the form of carbon fibers, ~raphites, carbon blacks or
carbon black pigments. As binders for the hot melt
adhesive, disclosed are thermoplastic polymers or plastics
or synthetic resins.
The microwave activa~able hot melt adhesive of
Hellmann et al. is disclosed to be use~ in two forms.
First, as a coating to be applied to the back of a material
such as a floor covering which is microwave activated,
a~ter being laid on a foundation surface, by microwaves
directed ~rom a microwave generator while pressure is
applied to the material~ In an alter~ative embodiment, the
hot melt adhesive takes the form of a sel~osupporting
sheet. This hot melt adhesive sheet itsel~ can be used
independently of any previou~ association with a material
to be stuck. The use ~of the self-supporting sheet of hot
melt adhesive encompasses positionin~ the sheet or a
portion thereof between items to be adhered together then
subse~uently subjecting the composite to microwave energy
in conjuntion with an application pressure. No specific
techni~ues are described or needed for handling the
Hellmann et al. microwave activatable hot melt adhesive in
a flowable state since it is not contemplated to dispense
the hot melt adhesive when in its ~lowable state. The hot
melt adhesive is only described as being heated to its
flowable state by microwave eneryy subsequent to the
positioning thereof between the matQrials to be adhered to
one another.
Another type of microwave susceptor particles
suitable ~or use in a hot melt adhesive is disclosed in
copending commonly owned U.S. application Serial No.
07/588,591, filed September 26, 1990 to Chamberlain et al.
which is a continuation-in-part of U.5. application Serial
No. 335,044, ~iled April 7, 1989. These ~icrowave susceptor
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WO9~/Og5~3 P~T/~Sgl/0~661
~àll~
--4--
particles comprise non-susceptor particulate substra!:es
shap~d to be spherical, spheroidal, ellipsoidal, grannular,
acicular, plates or flakes which are coated with
electrically conductive susceptor material. Disclosed
electrically conductive materia:Ls include metals, metal
oxides, nitrides, carbides, silicides, borides and
phosphides. The microbubbles or fla~es can then be admixed
within hot melt adhesives to be activated within a
microwave oven.
Moreover, known prior art microwave activatable
hot melt adhesives, whether of the water co~taining or
microwave susceptor mixture types, are limited in thsir use
because of the difficulty in handling a hot melt adhesive
in its activated flowable state. The hot melt adhesives
become extremely sticky and messy in their flowable state
rendering them difficult to handle for application to any
substrate. Presently, the application of flowable hot melt
adhesives to a substrate is primarily done with glue guns
that melt and dispense the hot melt adhesives concurrently.
Such glue guns increase complexity and costs associated
with the adhesive application and make it inconvenient for
household tasks requiring only small amounts of adhesive.
Furthermore, flowable hot melt adhesives must be heated to
a degree (in excess of 200F) making them dangerous to
handle in a users hands due to the risk of burning one's
hands. This becomes increasingly dangerous because of the
difficult tasX of completely melting the hot melt adhesive.
To overcome this dif~iculty, the hot melt adhesive is often
overheated at portions thereof in order to fully change the
hot melt adhesive ~rom a substantially solid state to a
useable flowable state.
. In t:his regard, it is hard to predict exactly
how a microwave hot melt adhesive will heat in a microwave
oven so as to c:hange to its flowable state. This was not a
problem of the Hellmann et al. prior art microwave
adhesives because the hot melt adhesives were only
subjected to microwaves and heated thereby once positioned
at the point of adherence. Even if a material coa ted with
such a hot melt adhesive was subjected to microwave energy
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wo 92/09~n3 ~ V ~ ~i 1. 1 3 P~l/US91/08661
. 5
prior to its ultimate position, there would be no handling
problem since the hot melt adhesive has been alre.ady
appli~d to at least one substrate which can be safely
handled.
Prior activity dealing with the handling of and
dispensing of microwave heated material has been limited to
the handling and dispensing of ~oodstuffs. Ever since the
common acceptance of household microwave ovens for food
heating, innumerable efforts have b~en made to refine
microwave cooking and to uniformly haat such microwavable
foodstuffs. Such efforts have included positioning means
for locating or moving a foodstuff specifically within a
microwave oven, packages including microwavs susceptor
layers, packages with shielding portions of the foodstuffs,
and the shaping or locating particular portions of the
foodstuffs relative to one anothex. Efforts have also
concentrated on the ability of certain ~oods to absorb
microwave energy as a result of the inherent properties
thereof. One of the biggest problems associated with
microwave cooking of ~ood is that th@ edges or thinner
portions of foods generally heat much quicker than ~he
central portions or the thicker portions. Thus, the
aforementioned efforts to re~ine microwave cooking v~ry
often are directed to attempting to concentrate more of the
microwave energy on the central or thicker slower heating
portions than on the edges or ~hinner faster heating
portions.
A microwavable food package for heating and
dispensing of sauces, cheese and the like comprised of a
laminated ~lexible material shaped into a pouch having an
insulating layer is disclosed in commonly owned copending
U.S. application Serial No. 415,99g, Piled October 2, 1989
to Garvey et al. The disclosed pouches are designed
specifically t:o optimize the microwave cooking of these
~oodstuffs ancl to permit dispensing thereof.
In complete contrast to microwave cooking of
~oodstuf~s, the applicants of the present invention have
discovered tha~ hot melt adhesives when subjectPd to
microwave energy heat in an opposite manner. Specifically,
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wos2/osso3 ~ U~ g -6- PCT/US')1/08661
the more central portions and the relatively thicker
portions of ~he hot melt adhesive tend to heat more quickly
than the edges or thinner portions thereof. Thus, known
techniques for microwave food cooking are not helpful in
determining and designing optimum heating configurations
for microwave activatiable hot melt adhesives.
SUMMARY OF THE IN~ENTION
The present invention provides the combination
of a microwave activatable hot melt adhesive with a
microwavable package for handling and dispensing hot melt
adhesive in its heated flowable state for application to
any selected substrate. Hot melt adhesives encompass
cements, sealants, coatings and the like which are heat
activated and dispensed onto substrates or in between
substrate~ to be affixed together. Such hot melt adhesives
can be advantageously dispensed in accordance with the
specific quantity needed for a particular application, and
small o~ large amounts can be actiYated by choosing a
properly sized package dep~nding on the need. The packages
can also be advantageously reused if only a portion of the
hot melt adhesive is previously used by simply reheating
the package with the remaining hot melt adhesive within a
~icrowave oven. Moreover, the present invention is
speci~ically amenable to use in a conventional household
microwave oven, although industrial uses are also
contemplated. The packages further can be safely handled
without risk of burning a user's hands, and provides quick
and easy heating and dispensing of hot melt adhesive
suitable for a particular use. Moreover, the package
enhances the heating of the hot melt adhesive to more
uniformly heat the hot melt adhesive and more completely
convert the hot: melt adhesive from its solid state to a
readily useable flowable state.
According to the present invention, a microwave
transparent package is provided containing a quantity of
hot melt adhesive having a sufficiently low temperature
melt range which is capable of being changed from a
substantially solid state to a flowable state when
,
.
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WOg2/09503 ~ ~`J a 1 1~ PcT/US'~1/0~61
~7~
subjected to microwave energy. The hot melt adhesive may be
of the type which is activatable without microwave
susceptors, i.e., of the water retaining type, or may be of
the type including microwave susceptors. Preferably,
microwave susceptors mixed within a hot melt adhesive are
utilized. The package comprises a receptacle defininy a
chamber within which the hot melt adhesive is received. The
~ receptacle includes a layer of microwave transparent
material for defining the chamber. A dispensing means is
provided as part of the receptacle for permitting the hot
melt adhesive to be dispensed fxom the receptacle when the
- hot melt adhesive is microwave heated to its flowable
state. Preferably, the microwave transparent layer and thus
the receptacle are flexible such that the hot melt adhesive
lS is dispensed by squeezing such a flexible ~eceptacle. Also,
the package advantageously includes an insulating means for
facilitating the handling of the package and the dispensing
o~ hot melt adhesive ~rom the package when the hot melt
adhesive is microwave heated to its ~lowable s ate.
Preferably, the insulating means comprises a layer of
flexible thermal insulating material provided adj~cent to
; the layer of flexible microwave transparent material over
at least a portion o~ the f lexible receptacle such that the
flexible receptacle can be safely grasped and squeez~d
without burning the user.
The microwave transparent package containing the
quantity of hot melt adhesive can be made in a variety o~
forms which enhance the uniform heating of the hot ~elt
adhesiv~ in a microwave oven. In a ~`irst embodiment, a low
profile pouch is provided which is constructed o~ a
~lexible layer of polymeric microwave transparent film
laminated with a layer of insulating material~ The package
can be advantageously heat sealed into form. A corner of
the pouch extends from the pouch to provide a dispensin~
means which is opened by cutting or tearing the corner of
the pouch from the pouch. The low pxofile and the
combination of the insulating layer help ensure
sub~tantially complete melting of a hot melt adhesive
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W092/0~S03 ~ 8 PCT/U~91/08~61
within a microwave oven without unreasonable overheating of
portions o~ the hot melt adheisive.
In another embodiment, a similarly constructed
heat sealed laminated pouch isi provided as a low profile
pouch which is divided into wlng portions. Once the low
profile package is heated in a microwave oven and the hot
melt adhesive is changed to itis flowable state, the wing
portions are folded against one another, the dispensing
means is opened, and the hot melt adhesive is dispensed for
use. In yet another embodiment, the pouch containing the
hot melt adhesive can be further placed within a moisture
barrier sealed bag. Such a combination bag or pouch ii3
beneficial when a moisture curing hot melt adhesive is
- . provided within the insulated pouch. In this case, once the
outer ~oisture barrier pouch is opened, the insulated pouch
with the moisture activated hot melt adhesive can be
microwave heated to its flowable state and used. The hot
melt adhesive then sets as a normal hot melt adhesive
- ~ollowed by moisture curing (cross-linking).
~: 20
BRIEF_pESCR~IPTION OF THE DRAWINGS
The present invention will be ~urther described
below with reference to the accompanying drawings, wher~in
plural embodiments in accordance with the present invention
are illustrated and described, in which,
Figure l is a top view of a microwave
activatable pouch with hot melt adhesive in accordance with
. the present invention;
Figure 2 is a longitudinal cross sectional view
taken along line 2-2 in Figure l;
Figure 3 is a partial cross-sectional view taken
along line 3-3 in Figure l rotated clockwise by 90;
Figure 4 i5 another embodiment o~ a microwave
activatable pouch with hot melt adhesive formed in
accordance with the present invention;
Figure 5 is a partial cross-sectional view taken
along line 5-5 i.n Figure 4 with the dispensing means
closed;
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W~92/0~03 ~ PC~/VS~l/086fil
_9_
Figure 6 is a similar cross~sectional view as
that of Figure 5 taken along line 5 5 in Figure ~ with the
dispensing means opened;
: Figure 7 is a partial cross sectional vi~w taken
along line 7-7 in Figure 5;
Figure 8 is a side view of the microwave
activatable pouch and hot melt adhesive of Fiyure 5 when
the hot melt adhesive is activated to itC flowable stat2;
Figure 9 is a perspective view showing the
-10 dispensing of hot melt adhesive ~rom the pouch of Figure 5;
Figure 10 is a perspective view of yet another
embodiment of a microwave activatable pouch with hot melt
adhesive combined with an outer barrier bag in accordance
with the present invention;
Figure 11 is a perspective view illustrating the
the dispensing of hot melt adhesive from another pouch
similar to that of Figure l;
Figure 12 is a graphical representation
comparing the temperature achieved at the center of various
pouches to the time the pouches are subjected to microwave
energy with varying percentages by volume o~ microwave
susceptor material within the hot melt adhesi~e;
Figure 13 is a graphical representation
comparing ~empQratUre at multiple points within a pouch
having 20% susceptor material by volume to time;
Figure 14 is a graphical representation
comparing temperature at multiple points of a block of hot
melt adhesive with 10~ volume susceptor mate.rial and
without an insulating bag to time; and
Figure 15 is a graphical representation similar
: to Figure 14 wherein the block o~ hot melt adhesive was
heated within an insulated ba~.
~ ~IP~TION OF TH~ PREFERRED EMBOpIMENTS
With reference to the attached ~igures and
initially to Figures 1-3, a microwavable hot melt adhesive
package 10 is illustrated. It is noted that like numerals
represent like elements throughout each of the s~veral
figures.
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wos2/09503 PCr/VS~l/0~
10~ '
The microwavable hot melt adhesive package lo
comprises a flexible pouch 12 which defines therein a
chamber 13 within which a quanti.ty of microwavable hot melt
adhesive 14 is provided. H~t melk adhesives encompass
cements, sealants, coatings and the like which are heat
activated. The ~lexible pouch 12 is made up of a microwave
transparent layer 16 which includes an upper wall portion
18 and a lower wall portion 20. The term "microwave
transparent", as used throughout this application refers to
materials which allow microwaves to be transmitted
therethrough without a substantial alteration of the
intensity or direction of the microwaves. The upper wall
portion 18 and the lower wall portion 20 are preferably
made from a single flexible sheet of the microwave
transparent layer 16 and are connected to one another by
way of ~old portion 22. The remaining side edges of the
flexible microwave transparent layer 16 are joined and
sealed to one another at edge portions 24, 26 and 28 thus
defining the fully enclosed chamber 13. The edge portions
24, 26 and 28 are preferably joined and sealed by heat
sealing; however, it is contemplated that other joining and
sealing techniques could be utilized including the use of
adhesives or the like. It i5 also understood that the upper
wall portisn 18 could be formed separately ~rom the lower
wall portiGn 20, in which case all edge portions w~uld be
joined to one another to fully enclose the chamber 13. It
is ~urther understood that many other seam configurations
for defining a closed chamber 13 are possible. For example,
referring to Figure 11, a single longitudinal seam 25 could
be provided connected between end seams 27 and 29. This
pouch 12' requires only the single longitudinal seam 2~,
which is preferably centrally located along the upper wall
portion 1~', leaving ~olds at both longitudinal edges
connecting the upper and lower wall port;.ons. This type o~
pouch is particularly amenable to receiving a generally
cylindrically shaped quantity of hot melt adhesive as well
as low pro~ile shapes.
The microwave transparent layer 16 is preferably
a polymerio ~ilm and may be made as a single layer or from
WO 92~09503 ~ PCl/US'~1/08661
multiple layers. In the preferred embodiment of the
invention, the microwave transparent layer 16 co~prises a
polymeric film having two layers (not shown) including an
innex layer that is heat sealable to itself and an ouker
layer that provides strength ancl support ~or the heat
sealable layer. It is contemplat:ed that other layers could
be substituted for or used in conjunction with these layers
depending on the type of hot melt adhesive stored within
the chamber 13 and whether or not that hot melt adhesive is
particularly susceptible to any gas or material such as
moisture, oxygen, or the like. The following is a
non-exclusive list of materials suitable for use in
constructing the heat sealable layer: polypropylene, medium
density polyethylene, ionomers, heat sealable polyesters,
copolyesters, or blends of polyester and copolyester. For
thP support layer, a non-exclusive list of materials is:
polypropylene, polyester and nylon.
The flexible pouch 12 further includes an
insulating means comprising an insulating layer 30 provided
adjacent to the microwave transparent layer 76 on the
external ~ur~ace thereof. The insulating layer 30 may
consist of a polypropylene oam or preferably a ~oam blend
of polystyren~ and polyphenylene oxide which is preferably
adhered to and laminated with the microwave transparent
layer 16. It is understood that other insulating materials
can be used instead of polypropylene foam as long as the
insulative properties can be obtained, and that the
insulating layer 30 can be connected with the microwave
transparent layex 16 by other means such as by thermal.
bonding or coextrusion. Moreover, the insulating layer 30
is preferably heat sealed with the microwave transparent
layer 16 at the edge portions 24, 26 and 28, as seen in
Figures 1 3.
The insulating layer 30 beneficially provides a
flexible pouch 12 which can be safely handled immediately
a~ter the package 10 is heated in a microwave oven.
Moreover, the insulating layer 30 advantageously enhances
the time period during which the hot melt adhesive remains
flowable for use thereof by maintaining the hot melt
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W092/09~03 ~ t~ PC~/US~1/0866i
-12~
adhesive 14 above its melt temperature ~or a longer period
of tim~ after microwave heating. Furthermore, the
insulating layer 30 helps to uniformly heat the hot melt
adhesive 14 within a microwa~e Gven by limiting thermal
loss from the hot melt adhesive surfaces during the
microwave heating.
In a preferred example of a microwaYable hot
melt adhesive package 10 according to the present
invention, a sheet was constructed by laminating the
10 polyvinylidene chloride (PVDC) side of a 0.00052 inch
(O.013 mm) thick support layer oE ScotchparTM 2708 brand
film available ~rom Minnesota Minin~ and Manufacturing
Company of St. Paul, Minnesota to a 0.001 inch (0.025 mm)
thick heat sealing layer of CP135 polypropylene film
available from the Crown Advanced Film division oi James
River Corporation of Orange, Texas with A~cote 76T198
adhesive available from Morton Thiokol of Chicago, Illinois
(dry weight of 2-3 pounds per 3000 square ~eet of film). An
insulating layer of 0.0625 inch (1.59 mm) thick
polypr~pylene oam available from ~metek, Inc. o~ Chadds
Ford, Pennsylvania under the trademark s'NICROFOAMI' was
laminated to the exterior of the film previously des~ribed
when formed into a pouch as shown in ~iyure l with a Swift
No. 48803 Brand pressure sensitive adhesive available from
the Swi~t Adhesives Division of Reichhold Chemicals, Inc.
of Downer's Grove, Illinois to the outside (polyester) of
the pouch ~ilm. A 0.00057 inch (0.014 mm) thick layer of
Scokchpar~M 86096 brand film ~ay be substituted for the
Scotchpar~ 2708 brand film.
A microwavable food bag suitable for microwave
heating of foodstuffs, such as cheeses, sauces, and the
like, utilizinc~ a similar laminated material as descxibed
above is illustrated and described in the commonly owned
copending U.S. patent application Serial No. 415,999, filed
35 October 2, 1989 to Garvey et al. The co~plete disclosure
and contents oi this copending application Serial No.
415,999, ~ilad October 2, 1989 are fully incorporated
herein by reference.
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W092/09~03 ~ V ~ 1 1 8 PCT/VS~l/08661
-13-
The particular hot melt adhesive 14 provided
within the chamber 13 of the flexible pouch 12 is selected
due ~o its ability to be activated in a microwave oven. By
the term activated, it is meant to be changed by haat from
a substantially solid dry state, which the adhesive assumes
at normal room temperatures, to a flowable state, above the
melt temperature of the hot melt adhesive, such that the
hot melt adhesive 14 can be applied to a substrate. With
reference to the Background section of this application,
such adhesives may inherently be activatable in a
microwave, such as by the ~ater content within the adhesive
whether inherent to the hot melt adhesive or resulting from
the addition of a hygroscopic water retalning additive, or
the hot melt adhesive may be rendered microwavable by the
addition of microwave susceptor particles which are
electrically conductive and which cause or enhance the
heating of the hot melt adhesive sufficiently to transform
the hot melt adhesive to its flowable state.
Referring again to Figures 2 and 3, the chamber
13 is illustrated filled with the hot melt adhesive 14. The
hot melt adhesive 14 can be of either the type of hot melt
adhesive without susceptor particles or o~ thP type
including microwave susceptor particles mixed therein.
Illustrated is a hot melt adhesive 14 includlng a matrix
hot melt adhesive 32 with microwave susceptor particles 34
mixed therein. In the preferred embodiment of the present
invention, th~ hot melt adhesive 14 is provided as a
mixture of the microwave susceptor particles 34 retained
within the hot melt adhesive matrix 32 because o~ the
resulting relatively high heating rates as compared to
microwavable hot melt adhesives without microwave susceptor
particles.
Sol~e examples of hot melt adhesives useable in
ths insulated pouch 12 of the present invention are: those
based on ethy:lelle vinyl acetate (EVA), polyethylene (PE),
polypropylene (PP) including amorphous polypropylene,
polyamide, po:lyester, polyesteramide, nylon polymers and
copolymers, and ~lends and mixtures of the above. Of these
polymers, some can be used with or without microwave
... .
wog~os503 ~ t~ q_ pcr/ussl/o86~l
susceptor particles mixed therein. For example, some of khe
ester and nylon polymer~ will absorb microwave energy
without the presence of additional microwave susceptor
particles. Specific examples of microw~vable hot melt
adhesives which absorb microwave! energy without microwave
~usceptor particles are the hot melt adhesive known under
the trademark "Jet-Weld" TE~030 Thermoset Adhesive,
commercially available rrom Minnesota Mining and
Manufacturing Company of St. Paul, Minnesota and the hot
melt adhesive available under the trademark "Macromelk"
6211, commercially available from Henkel Corp. o~ Chicago,
Illinois. These microwave energy absorbing hot melt
adhesives can also be blended with microwave susceptor
particles to increase the heat rate thereof. The other
non-absorbing hot melt adhesives noted above are rendered
microwave activatable due to the presence therein of the
microwave susceptor particles.
Suitable microwave interactive susceptors
materials for use in the presPnt invention that can be .
blended or mixed into the above cited polymers can range
from metal to carbon or ferxomagnetic particles. The
particles may take the form o a powder, as grains, fibers,
flakes or the like. Carbon ~an be provided in the form o~
carbon fibers, graphites, carbon blacks or carbon black
pigments and is widely available in these forms and largely
chemic~lly inert. Metalic microwave interactive susceptor
materials include aluminum, nickel, antimony, copper,
molybdenum, iron, chromium, tin, zinc, silver, gold, and
various alloys o~ these metals in flake, granular or
powdered form. Other microwave interactive susceptor
materials are also contemplated provided thak they can be
effectively blended within a hot melt adhesive and can
render the hot melt adhesive activatable in a microwave
oven.
Yet another type o~ microwave susceptor particle
suitable for blending in a hot melt adhe6ive is that of the
type described and claimed in copending U.S. application
Serial No. 07/588,591, filed September 26, 1990, entitled
"Microwave Heatable Composites" to Chamberlain et al. which
'' ' ' '
W092/09s03 ~ PC~/US~1/08~.61
-15-
is a continuation in-part of U.S. application Serial No.
335,04~, filed April 7, 1989, both of which are commonly
owned by the assignee of the present invention. The entire
contents of both of the copending application Serial Nos.
588,591, filed September 26, 1990 and 335,044, filed April
7, 1989 are fully incorporated herein by reference.
Briefly, the microwave interactive susceptor particles
comprise non-susceptor particles, such as microbubbles or
flakes, which are coated with a microwave susceptor layer.
Many suitable exampl~s of the microwave susceptor material
are disclosed including metals such as, ~or example,
tungsten, zirconium, copper, iron, titanium, chromium,
silver, moly~denum, and aluminum, or compounds which have
fairly high electrical conductivities such as, for axample,
metal oxides, nitrides, carbides, silicides, borides and
phosphides. Such coated microbubbles or flakes can be
incorporated within the present invention by blending them
within a suitable hot melt adhesive to be received within
the chamber 13 of such a flexible pouch 12.
In order to use the flexible pouches 12 and 12'
of Figures 1-3 and 11, a user would simply place the lower
wall portion 20 side of the flexible pouch 12 or 12'
containing the quantity of hot melt adhesive 14 therein
flat on the floor of a microwave oven. ~hen, the microwave
oven would be turned on for a period o~ time required to
completely transform the dry substantially solid hot melt
adhesive 14 into a flowable state by the impinging
microwave energy. See below for more details of specific
time periods required for achieving the temperatures ~or
e~fective microwave heating. Next, the flexible pouch 12
would be opened at a dispensing means 36 provided at an
extension of a corner portion of the flexible pouch 12. The
dispenser means 36 may also prefarably include a notch 38
so that the dispensing means 36 can be more easily torn
along the line X illustrated in Figure 1. The notch 38
could be provided at one or both of the edge portions 24 or
26. Moreover, a perforation or other line of weakening
could be provided extending along the line X for easy
opening. Additionally, a tear strip could be included along
.
W092/09503 ~ 8 Pcr/us~i/o86G1
-16-
the same line. In the alternative, the user may be simply
dir~cted to cut the flexib]~ po~lch 12 at or near the line X
for opening the dispenser means 36.
Once the flexible pouch 12 i5 opened at the
dispenser means 36, the flowable hot melt adhesive 14 can
be expelled from the chamber 13 and the hot melt adhesive
14 can be applied to any substrate for affixation thereo.
As seen in Figure 11, the hot melt adhesive 14 is
illustrated in the process of being applied to a substrate
S by squeezing the flexible pouch 12 ! by the fingers o~ a
user's hand. Once the hot melt adhesive is applied, the
package 10' may be discarded if the hot melt adhesive is
used up or may be saved for future reuse.
Preferably, the dimensions o~ the packages lo
are such as to encourage single use applications. For
household uses, a variety of pouches could be provided for
doing a variety of tasks. Such flexible pouches 12 and 12'
ar~ advantageous in that they can be safely grasped by the
fingers of a user so that the hot melt adhesive can be
squeezed there~rom while the insulating layer 30 protects
the user from the temperature of hot melt adhesive which
would typically be in the range of between 200 and 250 F
or higher. Moreover, since the pouches are flexible, the
hot melt adhesive can be readily dispensed by simply
squeezing the pouchesi however, it is contemplated that
o her non-flexible packag~s could be used i~ provided with
a means to force or pressurize the hot melt adhesive out of
the package. one specific example (not shown) would be a
syringe type arrangement which may or may not be insulated
from which hot melt adhesi~e could be expelled after
microwave heating thereof.
Another embodiment of a microwavable hot melt
adhesive package 40 is illustrated in Figures 4-9. The
microwavable hot melt adhesive package 40 comprises a
flexible pouch 42 defining a chamber 43 therein for
receiving and retaining a quantity of hot melt adhesi~e 44.
Like the Figure 1 embodiment, the flexible pouch ~2 is
comprised of a microwave kransparent layer 46, which may be
a single layer or multi-laminate as amplified above. The
..... - . ~ . . .. . . . . .. .. . .
W092/09503 h~t')t~ 118 pcr/us~l/o8fi
-17-
microwave transparent layer 46 also includes an upper wall
portion 48 and a lower wall portion 50. The upper and lower
wall portions 48 and 50, respectively, are connected
together at opposite transverse edges by fold portions 52
and 54 and at the other opposite edges at edge portions 56
and 58 by heat sealing, adhesive or the like.
A layer of insulating matPrial 60 is provided
adjacent to the microwave transparent layer 46 at the
external surface thereof. Once again, it is not necessary
~0 that the entire exterior surface o~ the microwave
transparent layer 46 be covered by the insulating layer 60,
but it is pre~erable in order to enhance the microwave
heating of the hot melt adhesive 44 and to maintain the hot
melt adhesive in its flowable state for longer application.
Moreover, by covering the entire pouch ~2 with the
insulating material 60, the risk of burning ones fingers is
reduced.
This embodiment is di~ferent from the Figure
embodiment in that the ~lexible pouch 42 is divided into
wing portions 62 and 64 and includ~s a centrally disposed
dispensing means 66. The dispensing means 66 is made along
the upper wall portion 48 at the point where a centrally
located seam 67 is provided. Howev~r, the seam 67 is
~odi~ied so that a spout 68 is de~ined withln the seam 67
leaving a sealed portion 70 which closes the spout 68 from
the exterior until opened. The spout 68 can be arranged
vertically as illustrated in Figure 5 with the sealed
portion 70 closing the chamber 43 and spout 68 from the
exterior of the ~lexible pouch 42. When it is desired to
open the spout 68, one must simply remove ths sealed
portion 70 to open spout 6~ to the exterio~ of the ~lexible
pouch 42. This can be done as described above by including
a notch at 72, by providing perforations or a line of
weakening along line Y, or by simply cutting away the
sealed portion 70 by cutting along the line Y. An open
spout 68 with the sealed portio~ 70 removed is illustrated
in Figure 6.
The hot melt adhesive 44 as illustrated in
Figures 5-7 can comprise any of the aforementioned hot melt
, . : ...... - ., , , . . ., . : , ; . :
~ - .. :, .,: : . ., . : .
,. . : .: :::, :, , :., - , . .: ., . :: , , : . :
.. -. . - ...... . .. .
wo92/ngso3 ~ PCr/V~1/0~61
adhesives suitable for use a~d activation within a
microwave oven with or without susceptor particles. In th~
preferred embodiment, the hot melt adhesive 44 comprises a
matrix 74 of hot melt adhesive within which is blended or
mixed a quantity by volume of microwave susceptor particles
76. The microwave susceptor particles 76 are preferably
made in accordance with the susceptor partlcles described
above as disclosed in the U.S. application Serial Nos .
588,591, filed September 26, 1990 and 335,044, filed April
10 7, 1989 and incorporated hy reference herein.
In use of the microwavabla hot melt adhesive
pacXage 40, the flexible pouch 42 is placed flat with the
lower wall portion 50 down on the floor of a microwave
oven. Then, the flexible pouch 42 containing the quantity
of hot melt adhesive 44 is impinged with microwave energy
upon activation of the microwave oven. As a result, the hot
melt adhesive 4a is raised in temperature, whether by its
own inherent characteristics or by the addition of
micr4wave susceptor particles, su~iciently to a degree
above the melt temperature of the hot melt adhesive 44. The
microwave heating is conducted until substantially the
entire quantity of hot melt adhesive 44 is melted. Again,
- see below for more details of specific time periods
required for effective microwave heating.
Next, the spout 68 with sealed portion 70 is
arranged vertically and the dispensing means 66 is opened
by cutting or tearing away the sealed portion 70 at or near
line Y leaving spout 68 open. It is noted that at this time
the pouch can be easily handled because of the insulating
layer 60 protecting the user from burning their fingertips.
Once the flexible pouch 42 is opened at spout 68, the wing
portions 62 and 64 are folded downw~rdly about the
centrally locat:ed spout 68, as seen in Figure 8. Then, as
illustrated in Figure 9, the hot melt adhesive 44 can be
dispensed to a substrate S by the user squeezing the winy
portions 62 and 64 against one another thereby forcing the
hot melt adhesive ~4 from the flexible pouch 42.
Yet anothex embodiment in accordance with the
pre~ent invention is illustrated in Figure 10, wherein a
WV92/0~03 P~T/U~;/08661
~ u ~
--19--
microwavable hot melt adhesiv~ package 80 is provided
including a flexible pouch 82 containing a quantity of hot
melt adhesive therein (not shown) and a sealed moisture
barrier bag 84. The flexible pouch 82 is illustrated as
being similar to the flexible pouch 12 of Figure 1, but it
is understood that any of the above mentioned pouches could
be used. The moisture barrier bag 84 is provided to seal
the flexible pouch 82 therein whil~ ensuring that moisture
does not affect the ~uality of hot melt adhesive within the
flexible pouch 82. This is particularly important when the
hot melt adhesive within the flexible pouch 82 is a
moisture curing hot melt adhesive, such as that available
under the trademark "~et-Weld" TE-030 Thermoset Adhesive
from 3M. The moisture barrier bag 84 can be constructed of
any known material suitable for preventing the passage of
moisture therethrough of which a foil bag is preferred.
Moreover, a desiccant material can be provided between the
moisture barrier bag 84 and the flexible pouch 82 for
absorbing any moisture present within the moisture barrier
bag 84 when it is sealedO It is also contemplated that
other types o~ barrier material~ could be used as a single
layer or laminate for the barrier bag 84 depending on any
particular susceptibility of the microwavable hot melt
adhesive within the pouch 82.
The use of the microwavable hot melt adhesive
package 80 is similar to the use of the packages 10 and 40
enumerated above, except that prior to placing the flexible
poucih 82 on the ~loor of a microwave oven, the moisture
barrier bag 84 must initially be removed. In this regard,
it is preferable that the moisture barrier bag R4 be
removed as soon as practicable just prior to microwave
heating of the flexible pouch 82 with the hot melt adhPsive
therein. This i5 because as soon as the barrier i9 removed,
the hot melt adhesive immediately begins reacting with
moisture within the ambient air which results in a cross
linking of the polymer of the hot melt adhesive. As well
known, this cross-linking is beneficially known as
secondary setting of the hot melt adhesive which takes
place in addition to the normal setting of the hot melt
. ~ . , , . , . - . . ~ .. . .
, ~ :. , .. :, .. ... . .
w0~2/0~503 ~ ~ Y-~L ~ S P~T/U~91/086f~1
~20-- ~
adhesive that occurs durin~ cooling after the hot melt
adhesive is applied.
Referring now to Figure 12, a graphical
representation is made showing the temperature in degrees
Fahrenheit to time (heat rate) oi~ a variety of pouches
formed in accordance with the present invention, each
containing 40 grams of hot melt adhesive with di~ferent
percentage loading by volume of microwave susceptor
particles blended within the hot melt adhesive~ The
temperature was measured by a probe centrally located
within the hot melt adhesive of each pouch. In all o~` the
samples tested that are represented in Fiqures 12-15, the
susceptor particles loaded within the hot melt adheisive
were glass microbubbles coated with tungsten as the
microwave susceptor material. The hot melt adhesive
consisted of the hot melt adhesive available under the
trademark "Jet-melt" 3760 available from Minnesota Mining
and Manufacturing Company, St. Paul, Minnesota.
All of the curves illustrated in Figures 12-l~
were generated using a 700 watt home microwave oven. The
samples were placed at ths center of the floor of the
microwave oven and elevated 2 inches of~ the floor of the
oven when exposed to microwave energy.
Line A shows the rate of heating of a pouch
containing hot melt adhesive loaded to 5% by volume with
microwave susceptor particles. ~ine B shows the heating
rate of a similar pouch with a similar ~uantity of hot melt
adhesive having a 10% loading of microwave susceptor
particles by volume. As can be clearly seen, the 10% loaded
pouch achieves approximately the same temperature as the 5%
loaded pouch at slightly less than half of the time. Line C
represents the rate of heating of a similar pouch with hot ~ :
melt adhesive loaded with 20% by volume of microwave
susceptor particles. Once again, there is a significant
time savings associated with the increased microwave
su~ceptor loadi11g. Line D represents the heating rate of a
similar pouch loaded with 30% by volume microwave susceptor
particles. Again, a time reduction is achieved ~or
obtaining a comparable temperature, but the amount of time
. ~ . . :: ,, , . : ,
WO92/n9so3 PCr/US~l/0~661
21-
savings is somewhat lessened. Llne E represents yet another
similar pouch loaded with 40~ by volume of microwave
suscepkor particles. In this case, no substantial
additional time savings was observed by the 10% increase of
susceptor particle loading. Likewise, line F which
represents a 50% by volume loading of microwave susceptor
particles was not observed to significantly achi~ve a time
savings over the 30% by volume loaded pouch represented by
line D.
The conclusion based on the above is that indeed
the increased microwave susceptor particle loading greatly
reduces the amount of time necessary that a pouch must be
impinged by microwave energy to achieve a sufficient
temperature for melting the hot melt adhesive in a
microwave oven. Additionally, this information also shows
that beyond approximately 30~ loading by volume of the
specific microwave susceptor particles, no significant time
savings is appreciated by higher percentage loading by
volum~ of the hot melt adhe~ive with microwave susceptor
particles. Thus, it is prePerable to maintain the
percentage loading by volume of microwave suscep or
particles in the hot melt adhesive between 0% and 50%, and
more preferably between 10% and 30%. This i5 not to say
that higher loading o microwave susceptor particles cannot
be done, even above 50~, ~ut the potential harm of having
additional non-adhesive material may outweigh the n~ed for
additional slight time savings. However, the efficiency of
the microwave susceptor particles in converting microwave
energy to heat must be considered as a function :in volume
loading. If lower efficiency microwave susceptor particles
are used, a higher loading is needed to obtaln similar
heating rates.
Re~erring now to Figure 13, a graphical
representation is illustrated showing the rate of
temperature inc:rease of three di~erently located
temperatur~ monitoring probes within a pouch designed in
acc~rdance with the present invention containing a hot melt
adhesive loaded with 20% by volume of microwave susceptor
particles. Line G represents the heat rate sensed by a
.
., .,, , : ,
. ~ : . ~ . : . .
W~/0~503 ~ 2~- PCI/U~91/0~661
center probe located at the center of the hot melt
adhesive. Line H represents the temperature sensed over
time of a probe located hal~ way between the center probe
and an edge of the hot melt adhe~sive. As observed, the
center of the hot melt adhesive and the point midway
between the center and an edge of the hot melt adhesive
were heated at substantially identical rates. Line J
represents the temperature sensed over time by a probe
located at the edge of the hot melt adhesive. This shows
that the edges of a substantially uni~orm thickness slab of
hot melt adhesive are heated at a rate substantially slower
than at the center or midpoint of the same slab. This
evidence is directly contrary to the measured heating
characteristics generally associated with microwaved foods.
Typically, when microwave cooking foods, the edges are seen
to heat most quickly with the center heating slower. ~hus,
when dealing with the microwave heating of a hot melt
adhesive, it i5 important to undexstand and design for a
quicker heati~g at the cen~er of the adhesive with a slower
heating at the edges thereof. Thus, it is pre~erable to
limit edges and thin portions and to maximize the thickPr
but even portions. A rectan~ulax slab has heen found to be
particularly advantageous in that edges are limited while a
uniform thickness can be maintained. Moreover, such
rectangular slabs fit easily within the insulated
microwavable packages of the present invention. Other
shapes, such as ~ylinders and the like, have also per~ormed
satis~actorily.
Referring now to Figures 14 and 15 together,
Figure 14 illustrates the heating rate o~ a relatively
thick block o~ microwave susceptor loaded hot melt adhesive
without an insulating pouch. The block had a width of 1.5
inches a length of 4 inches and a thicXness of ~ inch. As
represented by Figure 15, a simi].ar thick block dimensioned
the same as above and loaded with the same percentage by
volume o~ microwave susceptor particles was heated in a
microwave oven with the block of adhesive provided in an
insulated pouch designed in accordance with the prqsent
invention. The lines K, L and M in Figure 14 represent the
- :, . : : ~ . :
W092/09~03 ~J~ PCT/US9l/0866l
~23-
temperature over time of center, midway and edge probes,
respectively. In Figure 15, lines N, O and P represent the
temperature over time sensed by center, midway and edge
probes, respectively, as well. ~Jhen comparing Figures 14
and 15, the first apparent resu].t fro~ heating the thick
block in an insulated bag is that the edges are heated more
uniformly with the center and midpoints. In this regard,
compare lines P and M. Additionally, it is noted that the
probes in general sensed temperatures that increase
somewhat quicker when the block was provided in the
insulated bag. Thus, the insulated bag not only assists in
the rate o~ heating of the block of hot melt adhesive in
general, it more importantly reduces thermal losses which
increasingly occur near and at the edges of the hot melt
adhesive block.
Furthermore, it has been found that by
eliminating air spaces surrounding the hot melt adhesive
within the pouch, the results are even better. To achieve
this, a pre~itted pouch can be supplied with the quantity
of hot melt adhesive by pouring the hot melt adhesive into
the pouch while in its flowable statP. This minimizes air
spaces forming between the pouch and the hot melt adhesive.
Then, once allowed to set, the subsequent package can be
microwav2 heated with greater uniformity across the hot
melt adhesive. Alternately, vacuum packaging techniques
could be utilized in order to 5ubstantially eliminate air
from the pacXage when filled with the hot melt adhesive.
The present invention, as described above,
provides a microwavable hot melt adhesive package having
thermal insulation for ease of handling, dispensing and
promoting even heating. The present invention is
particularly applicable to use in the home wherein it is
desirable to heat and use relatively small quantities of
hot melt adhesive. However, it is just as understandable
that the present invention could be used in an industrial
setting. In this regard, larger tubes or pouches of hot
melt adhesive could be used with the consideration that the
hot melt adhesive could be impinged with industrial
microwave generators having greater wattages In any case,
"
: .- : . : , ::. ; ~ . :
; . , .. ; .. . . . .
W092/09503 PCT/US91/086~1
? 1 1 ~3
-2~-
the present invention provides a converlient means for
dispensing hot melt adhesive, can b~ directly or indirectly
handled by a user, is easy to manufacture, and
advantageously has a low cost construction. Furthermore,
such insulated packages can be microwave heated, handled
and loaded within other mechanical or pressurization
devices which squeeze the packages for dispensing of the
contents therefrom. Other heat activated cements, sQalants
and coatings are within the scope of hot melt adhesives and
may include, for example, window caulking, machine
gasketing, protective (mar-resistant) strips and the like.
Finally, the shape of the package and/or pouch may be
varied as desired in accordance with the above principles
to be round, triangular, octa~onal, cylindrical or the
like. Thus, the scope of the present invention should not
be limited to the structures described by the plural
embodiments of this application, but only by the structures
dPscribed by the language of the appended claims.
,
,. . ~ , .,: .
,
