WO1992009503A1

WO1992009503A1 - Microwave hot melt adhesive package and dispenser

Info

Publication number: WO1992009503A1
Application number: PCT/US1991/008661
Authority: WO
Inventors: Joseph F. Garvey; Deelynn Johnson; Mark E. Schwartz; James E. Toonen
Original assignee: Minnesota Mining And Manufacturing Company
Priority date: 1990-11-29
Filing date: 1991-11-19
Publication date: 1992-06-11
Also published as: JPH06503536A; CA2095118A1; EP0558655A1

Abstract

A microwave package (10) is provided containing a quantity of hot melt adhesive (14) including cements, coatings, and sealants, having a melt temperature range which is capable of being changed from a substantially solid state to a flowable state when subjected to microwave energy. The hot melt adhesive (14) may be of the type which is activatable without microwave susceptors, i.e., of a water retaining type, or may be of a type including microwave susceptors (34). The package preferably comprises a flexible pouch (12) defining a chamber within which the hot melt adhesive is received. The receptable includes a layer of microwave transparent material (16) for defining the chamber (13). A dispensing means (24) is provided as part of the pouch for permitting the hot melt adhesive to be dispensed from the pouch by squeezing the flexible pouch when the hot melt adhesive is microwave heated to its flowable state. Also, the package advantageously includes an insulating means (30) for facilitating the handling of the package and the dispensing of hot melt adhesive from the package when the hot melt adhesive is microwave heated to its flowable state.

Description

MICRO AVE HOT MELT ADHESIVE PACKAGE AND DISPENSER

TECHNICAL FIELD

The present invention relates to heat activated hot melt adhesives, including cements, coatings or sealants, within microwavable packages, 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 from its substantially solid state, which occurs at room temperatures, to a flowable state, which occurs only after the hot melt adhesive is sufficiently heated above the melting point of the hot melt adhesive. Once such an adhesive is melted to its flowable state, the adhesive can be applied by many known techniques to a surface of a substrate to be adhered to another, and thereafter, as the temperature of the adhesive decreases, 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 the items could be separated at that time.

Another manner of activating some hot melt adhesives, that is changing the state of the adhesive from its substantially solid state to a flowable state, is to subject these 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 the hot melt adhesive above its melting temperature to its flowable state. A major factor of microwavable hot melt adhesives that permits such hot melt adhesives to be changed to their flowable state in a microwave oven is the relatively low melt temperature coπuaon of such hot melt adhesives. Thus, as lower melt temperature hot melt adhesives are developed, they become candidates for microwave activated 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 sufficient amount of 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 adhesive.

If the hot melt adhesive to be microwave activated does not inherently contain a high enough residual water content, it is also known to mix a component of a highly hygroscopic water retaining additive in the hot 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 of the hot melt adhesive can be affected thereby changing the heat up rate of the hot melt adhesive. This disadvantageously 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 activatable, 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 meant 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 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 Hell ann et al., issued March 6, 1990. Disclosed as an electrically conductive substance is carbon which may be in the form of carbon fibers, graphites, carbon blacks or carbon black pigments. As binders for the hot melt adhesive, disclosed are thermoplastic polymers or plastics or synthetic resins.

The microwave activatable hot melt adhesive of Hellmann et al. is disclosed to be used 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, after being laid on a foundation surface, by microwaves directed from a microwave generator while pressure is applied to the material. In an alternative embodiment, the hot melt adhesive takes the form of a self-supporting sheet. This hot melt adhesive sheet itself can be used independently of any previous association with a material to be stuck. The use of the self-supporting sheet of hot melt adhesive encompasses positioning the sheet or a portion thereof between items to be adhered together then subsequently subjecting the composite to microwave energy in conjuntion with an application pressure. No specific techniques 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 flowable state. The hot melt adhesive is only described as being heated to its flowable state by microwave energy subsequent to the positioning thereof between the materials to be adhered to one another.

Another type of microwave susceptor particles suitable for 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.S. application Serial No. 335,044, filed April , 1989. These microwave susceptor particles comprise non-susceptor particulate substrates shaped to be spherical, spheroidal, ellipsoidal,, grannular, acicular, plates or flakes which are coated with electrically conductive susceptor material. Disclosed electrically conductive materials include metals, metal oxides, nitrides, carbides, suicides, borides and phosphides. The microbubbles or flakes 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 containing or microwave susceptor mixture types, are limited in their 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 200°F) 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 task of completely melting the hot melt adhesive. To overcome this difficulty, the hot melt adhesive is often overheated at portions thereof in order to fully change the hot melt adhesive from a substantially solid state to a useable flowable state.

In this regard, it is hard to predict exactly how a microwave hot melt adhesive will heat in a microwave oven so as to change 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 coated with such a hot melt adhesive was subjected to microwave energy prior to its ultimate position, there would be no handling problem since the hot melt adhesive has been already applied 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 foodstuffs. Ever since the common acceptance of household microwave ovens for food heating, innumerable efforts have been made to refine microwave cooking and to uniformly heat such microwavable foodstuffs. Such efforts have included positioning means for locating or moving a foodstuff specifically within a microwave oven, packages including microwave susceptor layers, packages with shielding portions of the foodstuffs, and the shaping or locating particular portions of the foodstuffs relative to one another. Efforts have also concentrated on the ability of certain foods to absorb microwave energy as a result of the inherent properties thereof. One of the biggest problems associated with microwave cooking of food is that the edges or thinner portions of foods generally heat much quicker than the central portions or the thicker portions. Thus, the aforementioned efforts to refine microwave cooking very 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 thinner faster heating portions.

A microwavable food package for heating and dispensing of sauces, cheese and the like comprised of a laminated flexible material shaped into a pouch having an insulating layer is disclosed in commonly owned copending U.S. application Serial No. 415,999, filed October 2, 1989 to Garvey et al. The disclosed pouches are designed specifically to optimize the microwave cooking of these foodstuffs and to permit dispensing thereof.

In complete contrast to microwave cooking of foodstuffs, the applicants of the present invention have discovered that hot melt adhesives when subjected to microwave energy heat in an opposite manner. Specifically, the more central portions and the relatively thicker portions of the 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 INVENTION

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 substrates 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 or large amounts can be activated by choosing a properly sized package depending 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 microwave oven. Moreover, the present invention is specifically 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 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 defining 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 from 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 is dispensed by squeezing such a flexible receptacle. Also, the package advantageously includes an insulating means for facilitating the handling of the package and the dispensing of hot melt adhesive from the package when the hot melt adhesive is microwave heated to its flowable state. Preferably, the insulating means comprises a layer of flexible thermal insulating material provided adjacent to the layer of flexible microwave transparent material over at least a portion of the flexible receptacle such that the flexible receptacle can be safely grasped and squeezed without burning the user.

The microwave transparent package containing the quantity of hot melt adhesive can be made in a variety of forms which enhance the uniform heating of the hot melt adhesive in a microwave oven. In a first embodiment, a low profile pouch is provided which is constructed of a flexible 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 dispensing means which is opened by cutting or tearing the corner of the pouch from the pouch. The low profile and the combination of the insulating layer help ensure substantially complete melting of a hot melt adhesive within a microwave oven without unreasonable overheating of portions of the hot melt adhesive.

In another embodiment, a similarly constructed heat sealed laminated pouch is provided as a low profile pouch which is divided into wing portions. Once the low profile package is heated in a microwave oven and the hot melt adhesive is changed to its 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 is beneficial when a moisture curing hot melt adhesive is provided within the insulated pouch. In this case, once the outer moisture 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 followed by moisture curing (cross-linking) .

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will be further described below with reference to the accompanying drawings, wherein plural embodiments in accordance with the present invention are illustrated and described, in which,

Figure 1 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 1;

Figure 3 is a partial cross-sectional view taken along line 3-3 in Figure 1 rotated clockwise by 90°;

Figure 4 is another embodiment of 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 in Figure 4 with the dispensing means closed; Figure 6 is a similar cross-sectional view as that of Figure 5 taken along line 5-5 in Figure 4 with the dispensing means opened;

Figure 7 is a partial cross-sectional view taken along line 7-7 in Figure 5;

Figure 8 is a side view of the microwave activatable pouch and hot melt adhesive of Figure 5 when the hot melt adhesive is activated to its flowable state;

Figure 9 is a perspective view showing the dispensing of hot melt adhesive from 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 1;

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 of microwave susceptor material within the hot melt adhesive;

Figure 13 is a graphical representation comparing temperature 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 material and without an insulating bag to time; and Figure 15 is a graphical representation similar to Figure 14 wherein the block of hot melt adhesive was heated within an insulated bag.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS With reference to the attached figures 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 several figures. The microwavable hot melt adhesive package 10 comprises a flexible pouch 12 which defines therein a chamber 13 within which a quantity of microwavable hot melt adhesive 14 is provided. Hot melt adhesives encompass cements, sealants, coatings and the like which are heat activated. The flexible 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 fold 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 is also understood that the upper wall portion 18 could be formed separately from the lower wall portion 20, in which case all edge portions would be joined to one another to fully enclose the chamber 13. It is further 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 25, which is preferably centrally located along the upper wall portion 18' , leaving folds at both longitudinal edges connecting the upper and lower wall portions. This type of pouch is particularly amenable to receiving a generally cylindrically shaped quantity of hot melt adhesive as well as low profile shapes.

The microwave transparent layer 16 is preferably a polymeric film and may be made as a single layer or from multiple layers. In the preferred embodiment of the invention, the microwave transparent layer 16 comprises a polymeric film having two layers (not shown) including an inner layer that is heat sealable to itself and an outer layer that provides strength and support for the heat sealable layer. It is contemplated 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 the 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 16 on the external surface thereof. The insulating layer 30 may consist of a polypropylene foam or preferably a foam blend of polystyrene 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 layer 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 after 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 adhesive 14 above its melt temperature for a longer period of time after microwave heating. Furthermore, the insulating layer 30 helps to uniformly heat the hot melt adhesive 14 within a microwave oven by limiting thermal loss from the hot melt adhesive surfaces during the microwave heating.

In a preferred example of a microwavable hot melt adhesive package 10 according to the present invention, a sheet was constructed by laminating the polyvinylidene chloride (PVDC) side of a 0.00052 inch

(0.013 mm) thick support layer of Scotchpar™ 2708 brand film available from Minnesota Mining and Manufacturing Company of St. Paul, Minnesota to a 0.001 inch (0.025 mm) thick heat sealing layer of CP136 polypropylene film available from the Crown Advanced Film division of James River Corporation of Orange, Texas with Adcote 76T198 adhesive available from Morton Thiokol of Chicago, Illinois (dry weight of 2-3 pounds per 3000 square feet of film) . An insulating layer of 0.0625 inch (1.59 mm) thick polypropylene foam available from Ametek, Inc. of Chadds Ford, Pennsylvania under the trademark "MICROFOAM" was laminated to the exterior of the film previously described when formed into a pouch as shown in Figure 1 with a Swift No. 48803 Brand pressure sensitive adhesive available from the Swift Adhesives Division of Reichhold Chemicals, Inc. of Downer's Grove, Illinois to the outside (polyester) of the pouch film. A 0.00057 inch (0.014 mm) thick layer of Scotchpar™ 86096 brand film may 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, utilizing a similar laminated material as described above is illustrated and described in the commonly owned copending U.S. patent application Serial No. 415,999, filed October 2, 1989 to Garvey et al. The complete disclosure and contents of this copending application Serial No. 415,999, filed October 2 , 1989 are fully incorporated herein by reference. The particular hot melt adhesive 14 provided within the chamber 13 of the flexible pouch 12 is selected due to its ability to be activated in a microwave oven. By the term activated, it is meant to be changed by heat 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 water content within the adhesive whether inherent to the hot melt adhesive or resulting from the addition of a hygroscopic water retaining 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 of the type including microwave susceptor particles mixed therein. Illustrated is a hot melt adhesive 14 including a matrix hot melt adhesive 32 with microwave susceptor particles 34 mixed therein. In the preferred embodiment of the present invention, the hot melt adhesive 14 is provided as a mixture of the microwave susceptor particles 34 retained within the hot melt adhesive matrix 32 because of the resulting relatively high heating rates as compared to microwavable hot melt adhesives without microwave susceptor particles.

Some examples of hot melt adhesives useable in the insulated pouch 12 of the present invention are: those based on ethylene vinyl acetate (EVA) , polyethylene (PE) , polypropylene (PP) including amorphous polypropylene, polya ide, polyester, polyesteramide, nylon polymers and copolymers, and blends and mixtures of the above. Of these polymers, some can be used with or without microwave susceptor particles mixed therein. For example, some of the ester and nylon polymers will absorb microwave energy without the presence of additional microwave susceptor particles. Specific examples of microwavable hot melt adhesives which absorb microwave energy without microwave susceptor particles are the hot melt adhesive known under the trademark "Jet-Weld" TE-030 Thermoset Adhesive, commercially available from Minnesota Mining and Manufacturing Company of St. Paul, Minnesota and the hot melt adhesive available under the trademark "Macromelt"

6211, commercially available from Henkel Corp. of 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 present invention that can be blended or mixed into the above cited polymers can range from metal to carbon or ferromagnetic particles. The particles may take the form of a powder, as grains, fibers, flakes or the like. Carbon can be provided in the form of carbon fibers, graphites, carbon blacks or carbon black pigments and is widely available in these forms and largely chemically inert. Metalic microwave interactive susceptor materials include aluminum, nickel, antimony, copper, molybdenum, iron, chromium, tin, zinc, silver, gold, and various alloys of these metals in flake, granular or powdered form. Other microwave interactive susceptor materials are also contemplated provided that 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 of microwave susceptor particle suitable for blending in a hot melt adhesive 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 is a continuation-in-part of U.S. application Serial No. 335,044, 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 examples of the microwave susceptor material are disclosed including metals such as, for example, tungsten, zirconium, copper, iron, titanium, chromium, silver, molybdenum, and aluminum, or compounds which have fairly high electrical conductivities such as, for example, metal oxides, nitrides, carbides, suicides, 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. Then, the microwave oven would be turned on for a period of 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 for effective 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 preferably include a notch 38 so that the dispensing means 36 can be more easily torn along the line X illustrated in Figure l. 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 the same line. In the alternative, the user may be simply directed to cut the flexible pouch 12 at or near, the line X for opening the dispenser means 36.

Once the flexible pouch 12 is 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 thereof. 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 of 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 of the packages 10 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* are advantageous in that they can be safely grasped by the fingers of a user so that the hot melt adhesive can be squeezed therefrom 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 pouches; however, it is contemplated that other non-flexible packages could be used if 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 adhesive 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 adhesive 44. Like the Figure 1 embodiment, the flexible pouch 42 is comprised of a microwave transparent layer 46, which may be a single layer or multi-laminate as amplified above. The 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 material 60 is provided adjacent to the microwave transparent layer 46 at the external surface thereof. Once again, it is not necessary that the entire exterior surface of the microwave transparent layer 46 be covered by the insulating layer 60, but it is preferable 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 42 with the insulating material 60, the risk of burning ones fingers is reduced.

This embodiment is different from the Figure 1 embodiment in that the flexible pouch 42 is divided into wing portions 62 and 64 and includes 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. However, the seam 67 is modified so that a spout 68 is defined within 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 flexible pouch 42. When it is desired to open the spout 68, one must simply remove the sealed portion 70 to open spout 68 to the exterior of the flexible 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 portion 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 adhesives suitable for use and activation within a microwave oven with or without susceptor particles. In the 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 particles described above as disclosed in the U.S. application Serial Nos. 588,591, filed September 26, 1990 and 335,044, filed April 7, 1989 and incorporated by reference herein.

In use of the microwavable hot melt adhesive package 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 44 is raised in temperature, whether by its own inherent characteristics or by the addition of microwave susceptor particles, sufficiently 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 downwardly about the centrally located 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 wing portions 62 and 64 against one another thereby forcing the hot melt adhesive 44 from the flexible pouch 42.

Yet another embodiment in accordance with the present invention is illustrated in Figure 10, wherein a microwavable hot melt adhesive 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 while ensuring that moisture does not affect the quality 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 "Jet-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 sealed. It is also contemplated that other types of barrier materials 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 pouch 82 on the floor of a microwave oven, the moisture barrier bag 84 must initially be removed. In this regard, it is preferable that the moisture barrier bag 84 be removed as soon as practicable just prior to microwave heating of the flexible pouch 82 with the hot melt adhesive therein. This is because as soon as the barrier is 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 adhesive that occurs during cooling after the hot melt adhesive is applied.

Referring now to Figure 12, a graphical representation is made showing the temperature in degrees 5 Fahrenheit to time (heat rate) of a variety of pouches formed in accordance with the present invention, each containing 40 grams of hot melt adhesive with different percentage loading by volume of microwave susceptor particles blended within the hot melt adhesive. The 10. temperature was measured by a probe centrally located within the hot melt adhesive of each pouch. In all of the samples tested that are represented in Figures 12-15, the susceptor particles loaded within the hot melt adhesive were glass microbubbles coated with tungsten as the 5 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 12-15 0 were generated using a 700 watt home microwave oven. The samples were placed at the center of the floor of the microwave oven and elevated 2 inches off the floor of the oven when exposed to microwave energy.

Line A shows the rate of heating of a pouch 5 containing hot melt adhesive loaded to 5% by volume with microwave susceptor particles. Line B shows the heating rate of a similar pouch with a similar quantity of hot melt adhesive having a 10% loading of microwave susceptor particles by volume. As can be clearly seen, the 10% loaded 0 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 5 time savings associated with the increased microwave susceptor loading. Line D represents the heating rate of a similar pouch loaded with 30% by volume microwave susceptor particles. Again, a time reduction is achieved for obtaining a comparable temperature, but the amount of time savings is somewhat lessened. Line E represents yet another similar pouch loaded with 40% by volume of microwave susceptor 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 achieve 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 volume of the hot melt adhesive with microwave susceptor particles. Thus, it is preferable to maintain the percentage loading by volume of microwave susceptor particles in the hot melt adhesive between 0% and 50%, and more preferably between 10% and 30%. This is not to say that higher loading of microwave susceptor particles cannot be done, even above 50%, but the potential harm of having additional non-adhesive material may outweigh the need 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 obtain similar heating rates.

Referring now to Figure 13, a graphical representation is illustrated showing the rate of temperature increase of three differently located temperature monitoring probes within a pouch designed in accordance 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 center probe located at the center of the hot melt adhesive. Line H represents the temperature sensed over time of a probe located half way between the center probe and an edge of the hot melt adhesive. 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 uniform 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. Thus, when dealing with the microwave heating of a hot melt adhesive, it is important to understand and design for a quicker heating at the center of the adhesive with a slower heating at the edges thereof. Thus, it is preferable to limit edges and thin portions and to maximize the thicker but even portions. A rectangular slab has been 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 cylinders and the like, have also performed satisfactorily.

Referring now to Figures 14 and 15 together, Figure 14 illustrates the heating rate of a relatively thick block of 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 thickness of 1 inch. As represented by Figure 15, a similar thick block dimensioned the same as above and loaded with the same percentage by volume of microwave susceptor particles was heated in a microwave oven with the block of adhesive provided in an insulated pouch designed in accordance with the present invention. The lines K, L and M in Figure 14 represent the 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. When comparing Figures 14 and 15, the first apparent result from 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 of 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 prefitted pouch can be supplied with the quantity of hot melt adhesive by pouring the hot melt adhesive into the pouch while in its flowable state. This minimizes air spaces forming between the pouch and the hot melt adhesive. Then, once allowed to set, the subsequent package can be microwave heated with greater uniformity across the hot melt adhesive. Alternately, vacuum packaging techniques could be utilized in order to substantially eliminate air from the package 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. the present invention provides a convenient means for dispensing hot melt adhesive, can be 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, sealants 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, octagonal, 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 described by the language of the appended claims.

Claims

CLAIMS :

1. A microwavable package at least partially microwave transparent containing a quantity of hot melt adhesive having a melt temperature range capable of being changed from a substantially solid state to a flowable state when subjected to microwave energy, said package comprising a receptacle including a layer of microwave transparent material defining a chamber within which said hot melt adhesive is received, dispensing means for permitting said hot melt adhesive to be dispensed from said receptacle when said hot melt adhesive is microwave heated to its flowable state, and thermal insulating means for facilitating handling of said package and dispensing said hot melt adhesive when said hot melt adhesive is microwave heated to its flowable state.

2. The microwave package of claim 1, wherein said insulating means comprising a layer of thermal insulating material provided adjacent to said layer of microwave transparent material over at least a portion of said receptacle.

3. The microwave package of claim 2, wherein said receptacle is comprised of a flexible layer of microwave transparent material, and said layer of insulating material is flexible and adhered to said flexible layer of microwave transparent material, whereby said hot melt adhesive is dispensed when in its flowable state by squeezing said receptacle.

4. The microwave package of claim 3, wherein said receptacle is a pouch having an upper portion and a lower portion of said flexible layer of microwave transparent material connected at at least one edge by a fold portion of said flexible layer of microwave transparent material, said upper and lower portions being adhered to one another along the remaining edges thereof to define said chamber which receives said hot melt adhesive. and said layer of insulating material is disposed to cover the entire external surface of said layer of microwave transparent material.

5. The microwave package of claim 4, wherein said dispensing means comprises an extended corner portion of said pouch which is to be removed from the pouch for dispensing of the hot melt adhesive therefrom when in its flowable state.

6. The microwave package of claim 5, wherein said dispensing means further comprises a line of weakening dividing said corner portion from the rest of said pouch to facilitate easy opening of said pouch.

7. The microwave package of claim 4, wherein said dispensing means comprises an intermediate seam located along said upper portion of said layer of flexible microwave transparent material and a spout formed in said intermediate seam having a sealed portion which is to be removed from said pouch to open said spout, said intermediate seam and said spout dividing said pouch into two wing portions which can be forced against one another when said hot melt adhesive is in its flowable state to force said hot melt adhesive through said spout for dispensing.

8. The microwave package of claim 7, wherein said dispensing means further comprises a line of weakening dividing said sealed portion from the rest of said pouch to facilitate easy opening of said pouch.

9. The microwave package of claim 4, further comprising a sealed barrier bag within which said pouch containing said hot melt adhesive is received, wherein said barrier bag is to be removed before said pouch is impinged by microwave energy.

10. The microwave package of claim 9, wherein said barrier bag is made of a moisture barrier material and said hot melt adhesive comprises a moisture sensitive hot melt adhesive.

11. The microwave package of claim 1, wherein said hot melt adhesive is selected from a group based on ethylene vinyl acetate, polyethylene, polypropylene, amorphous polypropylene, polyamide, polyester, polyesteramide, and nylon polymers and copolymers and mixtures of the above.

12. The microwave package of claim 11, wherein said hot melt adhesive further comprises microwave susceptor particles mixed within said hot melt adhesive.

13. The microwave package of claim 12, wherein said microwave susceptor particles are comprised of microbubbles coated with a microwave susceptor material selected from a metal or metal oxide, and said coated microbubbles are present in said hot melt adhesive in the range of between 0% and 50% by volume.

14. The microwave package of claim 13, wherein said coated microbubbles are provided in said hot melt adhesive in the range of between 10% - 30% by volume.

15. The microwave package of claim 1, wherein said hot melt adhesive is provided within said receptacle so that air voids are substantially eliminated between said hot melt adhesive and said receptacle over substantially the external surface of said hot melt adhesive.

16. A microwave transparent package containing a quantity of hot melt adhesive having a melt temperature range capable of being changed from a substantially solid state to a flowable state when subjected to microwave energy, said package comprising a flexible receptacle including a layer of microwave transparent material defining a chamber within which said hot melt adhesive is received, dispensing means for permitting said hot melt adhesive to be dispensed from said flexible receptacle when said hot melt adhesive is microwave heated to its flowable state and said flexible receptacle is squeezed, and insulating means for facilitating handling of said package and dispensing said hot melt adhesive when said hot melt adhesive is microwave heated to its flowable state, said insulating means comprising a layer of flexible thermal insulating material provided adjacent to said layer of microwave transparent material over at least a portion of said flexible receptacle.

17. The microwave package of claim 16, wherein said receptacle is a pouch having an upper portion and a lower portion of said flexible layer of microwave transparent material connected at at least one edge by a fold portion of said flexible layer of microwave transparent material, said upper and lower portions being joined to one another along the remaining edges thereof to define said chamber which receives said hot melt adhesive, and said layer of insulating material is disposed to cover the entire external surface of said layer of microwave transparent material.

18. The microwave package of claim 17, wherein said dispensing means comprises an extended corner portion of said pouch which is to be removed from the pouch for dispensing of the hot melt adhesive therefrom when in its flowable state, and said dispensing means further comprises a line of weakening-dividing said corner portion from the rest of said pouch to facilitate easy opening of said pouch.

19. The microwave package of claim 17, wherein said dispensing means comprises an intermediate seam located along said upper portion of said layer of flexible microwave transparent material and a spout formed in said intermediate seam having a sealed portion which is to be removed from said pouch to open said spout, said intermediate seam and said spout dividing said pouch into two wing portions which can be forced against one another when said hot melt adhesive is in its flowable state to force said hot melt adhesive through said spout for dispensing, and said dispensing means further comprises a line of weakening dividing said sealed portion from the rest of said pouch to facilitate easy opening of said pouch.

20. The microwave package of claim 17, further comprising a sealed barrier bag within which said pouch containing said hot melt adhesive is received, wherein said barrier bag is to be removed before said pouch is impinged by microwave energy, and said barrier bag is made of a moisture barrier material and said hot melt adhesive comprises a moisture sensitive hot melt adhesive.

21. The microwave package of claim 16, wherein said hot melt adhesive is selected from a group based on ethylene vinyl acetate, polyethylene, polypropylene, amorphous polypropylene, polyamide, polyester, polyesteramide, and nylon polymers and copolymers and mixtures of the above.

22. The microwave package of claim 21, wherein said hot melt adhesive further comprises microwave susceptor particles mixed within said hot melt adhesive.

23. The microwave package of claim 22, wherein said microwave susceptor particles are comprised of microbubbles coated with a microwave susceptor material selected from a metal or metal oxide, and said coated microbubbles are present in said hot melt adhesive in the range of between 0% and 50% by volume.

24. The microwave package of claim 23, wherein said microwave susceptor particles are provided in said hot melt adhesive in the range of between 10% - 30% by volume.

25. The microwave package of claim 16, wherein said hot melt adhesive is provided within said receptacle so that air voids are substantially elminated between said hot melt adhesive and said receptacle over substantially the external surface of said hot melt adhesive.