DE69417964T2 - THROUGH MICROWAVE HEATABLE DISPENSER FOR MELTABLE ADHESIVES - Google Patents

Description

AREA OF EXPERTISE

The present invention relates to improvements in the design and construction of an apparatus for dispensing microwave-heatable hot melt adhesives and other heat-sensitive materials. The apparatus comprises a dispenser which is heated by microwaves and from which a material is subsequently dispensed. The dispenser is specifically designed to convert microwave energy into heat and to transfer the heat to the material to be dispensed in a more efficient and/or safer manner. The dispenser is particularly suitable for heating and dispensing a material (e.g., a hot melt adhesive) which can change from a solid state or a high viscosity state to a low viscosity state when heated above a predetermined threshold temperature, while allowing dispensing of the material when it is in the low viscosity state.

BACKGROUND OF THE INVENTION

Traditionally, hot melt adhesive was applied using hot melt adhesive applicators (glue guns). These glue guns were designed to be connected to a wall socket by a power cord and a plug to continuously supply electric current to the glue gun, thereby melting the adhesive in the glue gun. This meant that the application range of the glue gun was determined by the length of the power cord connecting the glue gun to the wall socket. Furthermore, the cord sometimes represented a material obstacle around which the user had to move when using the glue gun.

To solve these problems, a cordless glue gun was developed. A cordless glue gun is a glue gun that can be separated from its power source so that it can function without a power cord. When designing a cordless glue gun, great attention must be paid to the holding device for the gun. The holding device must conveniently hold the glue gun and allow the glue gun to be supplied with electrical energy (heated) while it is on the holding device. In addition, the holding device and the glue gun must be designed in such a way that the glue gun can be easily detached from the holding device and the power source when one wants to use the glue gun. For these purposes, the holding device includes a base for transmitting electrical energy to the glue gun and a release mechanism that allows the glue gun to be separated from the base when it is removed from the holding device.

Despite the improvements that a cordless glue gun has over a traditional glue gun, a cordless glue gun still has disadvantages. Although the cordless glue gun does not require a constant electrical power, it must first be electrically heated while on the holder, and interim electrical heating may be required to keep the hot melt glue in a low viscosity state. In addition, both the traditional glue gun and the cordless glue gun require hot melt glue sticks or other forms of glue supply to be inserted into the glue gun. Therefore, it is necessary to purchase the hot melt glue separately from the glue gun itself and to handle the hot melt glue before each use of the glue gun. Furthermore, both the conventional glue gun and the cordless glue gun are bulky, relatively expensive to purchase, they require a relatively long preheating time before the glue can be dispensed, and a relatively long cooling time before they can be put away.

A significant improvement and innovation in the dispensing of heat sensitive materials, particularly hot melt adhesives, is disclosed in US-A-5 188256, which was published after the priority date of the present application. Specifically, US-A-5 188 256 discloses a dispenser for heat sensitive materials comprising a first material which, when heated above a predetermined temperature, changes from a solid or high viscosity state to a low viscosity state, a second material which can be used to be heated above a predetermined temperature when exposed to microwave energy for at least a predetermined time, a container containing the first and second materials, and an outlet through which the first material can be dispensed from the container when in the low viscosity state. In the specific embodiment described therein, a hot melt adhesive is contained in a container whose inner surface has been coated with a microwave susceptor material.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 is a schematic diagram of a dispenser and a cover therefor constructed according to the principles of this invention.

Fig. 2 is a cross-sectional view of the dispenser and a cover of Fig. 1, perpendicular to the plane axis of the cover.

Fig. 3 is a cross-sectional view of the dispenser and the cover therefor, similar to that in Fig. 2, additionally with a third material between the first material and the second material in the dispenser.

Fig. 4 is a cross-sectional view of the dispenser of Fig. 2 along line A-A.

Figure 5 is a schematic diagram of a partially assembled dispenser and cover therefor constructed in accordance with an additional embodiment of the present invention.

Fig. 6 is a cross-sectional side view of the dispenser and cover therefor of Fig. 5, with the dispenser and cover fully assembled.

Fig. 7 is an enlarged fragmentary cross-sectional side view of the dispenser and cover of Fig. 6.

Figure 8 is a cross-sectional side view of a dispenser and cover similar to that shown in Figure 6, but showing the dispenser as constructed in accordance with an additional embodiment of the present invention.

Fig. 9 is a cross-sectional plan view of the dispenser of Fig. 8 taken along line 16-16.

Fig. 10 is a cross-sectional plan view of the dispenser of Fig. 8, but showing a pair of ribs extending radially inwardly along opposite sides of the formed tube.

Fig. 11 is a cross-sectional side view of a dispenser and a cover similar to that shown in Fig. 8, but showing a heating pin located within the dispenser.

Fig. 12 is a cross-sectional plan view of the dispenser of Fig. 11 taken along line 18-18.

SUMMARY OF THE INVENTION

The present invention relates to new improvements and developments of the hot melt adhesive dispenser of US-A-5,188,256. More particularly, the present invention relates to modifications and developments of a microwaveable hot melt adhesive dispenser which provide more efficient and, from a consumer standpoint, safer use. In general, the dispensing device of the present invention is designed to be compact and portable for ease of use. Accordingly, it is generally a hand-held dispenser. However, larger embodiments are also included for potential industrial use.

The dispensing concept of the present invention is particularly suitable for converting materials, particularly hot melt materials, from a solid state or a high viscosity state to a liquid state or a low viscosity state when heated above a predetermined threshold temperature. Hot melt materials that can be used in the practice of the present invention include, for example, hot melt adhesives, food products (i.e., candy, chocolate, etc.), solder, wax, and oil. The present invention can also be used for dispensing and reaction initiation of heat-sensitive reactive materials. Specifically, such heat-sensitive materials include materials that harden or polymerize when exposed to a predetermined temperature for a set time. Such heat-sensitive materials include, for example, heat-curing resins selected from the group consisting of epoxies, polyesters, polyurethanes, polybutadienes, cyanate esters, bismaleimides, polyimides, phenolic resins, alkyd resins, amino resins and silicones. The invention is particularly suitable for dispensing hot melt adhesives and will be discussed largely in this context.

The present invention provides an apparatus for dispensing heat sensitive materials comprising a container having a first material therein and which may either comprise or contain a second material, and an outlet through which the first material may be dispensed following exposure to microwave energy to the apparatus, the first material being such that when heated to a predetermined temperature it is converted from either a solid state or a high viscosity state to a liquid state or a low viscosity state, or is activated to initiate polymerization or curing of the first material, and the second material being designed to be heated to at least the predetermined temperature when exposed to microwave energy for at least a predetermined time, and the second material being in a heat transfer relationship with the first material, characterized in that the second material is not dispersed within the first material, and the second material comprises a ferromagnetic material having a Curie temperature minimum at least equal to the predetermined temperature and a Curie temperature maximum that is lower than the temperature at which the first material will boil or be adversely affected by heat generated by the second material, and that is lower than the ignition temperature of either the first material or the container. The preferred ferromagnetic materials include ferrites, spinels and spinel ferrites. Particularly preferred ferromagnetic materials are those that have predominantly magnetic heating properties most preferably those which have substantially no electrical or resistance heating properties.

According to one embodiment of the present invention, the container, or at least the inner surface of the container, comprises the second material. In particular, this embodiment relates to a molded elongate container having a longitudinal axis, the container including at least one rib on its inner surface which is parallel to and extends inwardly along the longitudinal axis. The container may be molded from a high temperature polymer material having the second material deposited thereon either in particulate form or as a film. Alternatively, the container itself may comprise the second material, the container being molded from a high temperature polymer material having dispersed therein a particulate material which in turn is adapted to heat up when exposed to microwave energy. In this alternative, the polymer material must be selected to have sufficient heat transfer properties to conduct the heat generated by the dispersed particles to the first material contained in the container. The preferred embodiment of this embodiment includes two ribs on opposing inner surfaces of the container. The presence of the ribs extending from the inner surface of the container into the first material accelerates and assists in heating the first material.

Another embodiment according to the practice of the present invention includes as the second material a heating rod having a longitudinal axis parallel to the longitudinal axis of the container. The heating rod may be enclosed by or embedded in the first material. Preferably, the heating rod has a sufficient length and shape to provide a large surface area for contact with the first material. Generally, the heating rod will extend almost the full length of the longitudinal axis of the container. Alternatively, the heating rod will extend through at least substantially all of the first material. This embodiment is particularly effective because all of the radiant energy is transferred from the heating rod to the first material. In addition, this allows the first material to be heated from the inside out so that heating of the outer surface of the container is minimal. Of course, the heating rod could also be used in conjunction with a container which, or whose inner surface, is also made of the second material. Such an embodiment would provide for very rapid heating of the first material because heating of the first material would occur from both directions.

Yet another embodiment in accordance with the practice of the present invention involves the use of an insulating jacket that substantially encloses or encases the dispenser. The insulating jacket may comprise a portion of the container or may comprise a reusable sleeve into which or from which the container is inserted or withdrawn. In the former case, when all of the material in the container has been dispensed, the entire device consisting of the dispenser and the jacket is discarded. In the latter case, when all of the material has been dispensed from the dispenser, the dispenser is withdrawn from the sleeve and a new dispenser is inserted so that the sleeve can be reused.

According to this embodiment of the invention, it is preferred that the insulating jacket comprises at least one layer of an insulating material, preferably at least one layer of a polymer foam. Alternatively, the insulating jacket may comprise several layers, including an outer layer, one of which, but preferably not the outer layer, consists of a glass fiber mat.

The use of an insulating jacket essentially provides an outer surface that is cool to the touch and can be handled by the consumer while allowing the first material to heat sufficiently to change from its solid state or high viscosity state to its liquid state or low viscosity state or to reach the temperature at which polymerization or curing is initiated.

Further features and advantages of the present invention will become apparent from the following detailed description and the accompanying drawings, which form a part hereof.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Generally, the present invention in its broadest sense relates to improvements and variations in a device for dispensing a heat-sensitive material, the device comprising:

(i) a first material which, when heated to a predetermined temperature, is converted from either a solid state or a high viscosity state to a liquid state or a low viscosity state or is activated so as to initiate polymerization or curing of the first material;

(ii) a second material adapted to heat to at least the predetermined temperature when exposed to microwave energy for at least a predetermined time, the second material also being in a heat transfer relationship with the first material;

(iii) a container in which the first material is located and which can either comprise or contain the second material; and

(iv) an outlet through which the first material is delivered following exposition of microwaves to the device.

According to the invention, the second material comprises a ferromagnetic material having a Curie temperature minimum that is at least equal to the predetermined temperature and a Curie temperature maximum that is lower than the temperature at which the first material will boil or be adversely affected by the heat generated by the second material and that is lower than the ignition temperature of both the first material and the container.

When reference is made here to the first material, the second material and the container, unless otherwise stated, it is intended to mean this general construction.

The first material that can be used in the practice of the present invention can include a variety of materials that are heat sensitive in that they change from a solid or high viscosity state to a liquid or low viscosity state when heated to a predetermined temperature or activated such that polymerization or curing of the first material is initiated upon heating to a predetermined temperature. Materials that satisfy the above properties are often characterized as hot melt materials. Examples of such materials include hot melt adhesives, food products such as candy, chocolate, syrups, jams and the like, solder, wax and oil. The former materials encompassed by the latter characterization include thermosetting resins such as e.g. Epoxides, polyesters, polyurethanes, polybutadienes, cyanate esters, bismaleimides, polyimides, phenolic resins, alkyd resins, amino resins and silicones as well as other thermosetting or thermopolymerizable materials.

When these latter materials are to be dispensed, it is particularly preferred to control the rate of curing or polymerization so as to allow sufficient time for the material to be heated and dispensed for its intended use before it substantially cures or polymerizes.

The present invention is particularly suitable for heating and dispensing hot melt adhesives. In this regard, and for ease and simplicity of discussion, the apparatus and methods of the present invention will be discussed specifically with respect to hot melt adhesives.

A hot melt adhesive suitable for these purposes is manufactured and sold by H.B. Fuller Company under product designation No. 2125. Of course, other hot melt adhesives may be used in the practice of the present invention, including those based on or comprising polyvinyl formal, polyvinyl butyral, ethylene vinyl acetate (EVA), polyethylene (PE), polypropylene (PP), polyamide, polyester, polyesteramide, and copolymers and blends of the above.

The second material, which is in heat transfer relationship with the first material, is capable of being heated above a predetermined temperature when exposed to microwave energy for at least a predetermined time. Typically, these materials are known as susceptors and consist of microwave absorbing particles. Examples of susceptors that can be used in the practice of the present invention are those known for use in microwave cooking. In their simplest embodiment, susceptors comprise microwave absorbing materials which, depending on the particular embodiment or construction of the Device of the present invention may be in particulate form, as dusts or in film form. The susceptor materials, in turn, generally include metals such as iron and stainless steel, metal oxides such as ferrites, spinels and spinel ferrites. Those skilled in the art will also readily recognize other susceptor materials that can be used in the practice of the present invention.

In a specific embodiment of the susceptor, particulate microwave absorbing materials are bonded to or embedded in a high temperature polymer film substrate. The film is used as a layer in the construction of the device. Alternatively, particles of the microwave absorbing material may be dispersed within a high temperature resistant polymer matrix which is then coated on the interior surface of the container or which may form one or more layers of the container. Further, as will be discussed below, the second material may comprise, be adhered to, or dispersed within a structure such as a heating rod, compressible coil, or foam particles which is in turn located within at least a substantial portion of the first material.

As mentioned, one type of susceptor essentially comprises microwave energy absorbing particles adhered to a high temperature polymer film. Susceptors of this type are normally classified by their optical density. Those susceptors suitable for use in accordance with the practice of the present invention generally have an optical density in the range of 0.05 to 2.0. Such films having optical densities at the upper end of this range or higher generally have better reflective properties and poorer absorptive properties so that the generation of heat by the susceptor is very slow, and at extremely high optical densities they are use in the practice of the present invention. Preferably, such film susceptors have optical densities of from 0.10 to 0.35. A commercially available susceptor of this type comprises metal particles supported on a high temperature polyimide film. Such materials are manufactured and sold by National Metalizing Company, Cranbury, NJ. The underlying polyimide film or substrate is manufactured by EI DuPont De Nemours & Company and sold under the trade designation "Kaptan." Other high temperature polyimide films that can be used to make such susceptor films include the polyetherimides manufactured by General Electric Company, Pittsfield, MS and sold under the trade designation "Ultem."

Other high temperature films may also be used as the substrate for the microwave absorbing particles, including various thermoplastic polymers, synthetic resins and the like, including, for example, polyester films. These films too are readily available commercially from a number of suppliers, including the above-mentioned National Metalizing Company. The susceptor films may be used alone or in conjunction with a second, typically a carrier film. In this latter aspect, the susceptor film forms part of a film composite in which the polymer film having the microwave absorbing particles deposited thereon is bonded to a higher temperature resistant or more structurally oriented carrier polymer film. The carrier film may comprise, for example, polyimide films of the type mentioned above, as well as other high temperature materials. The susceptor film is bonded to the carrier film by means of high temperature adhesives, for example, Avery 1184, manufactured and sold by Avery Products Corporation, San Marino, CA. In any case, the reinforcement or carrier layer ensures a stable high temperature ture reinforcement for the outer susceptor film. A specific embodiment of this composite comprises a susceptor film which is a polyester film having microwave absorbing particles deposited thereon, bonded to a microwave transparent polyimide film by means of a high temperature adhesive. This embodiment will be discussed further with reference to the figures.

Another embodiment containing the susceptor is one in which the microwave absorbing particles are dispersed in a high temperature thermoplastic matrix. Suitable thermoplastic matrices include the above-mentioned polyesters, polyimides, silicones, and the like. Examples of such susceptor materials filled with microwave absorbing particles include ferrite-filled silicone resins and the like. In general, the amount of particulate microwave absorbing material incorporated into the polymer matrix is that which is sufficient to conduct sufficient heat to the first material in a reasonable period of time. Preferably, the amount of material to be incorporated into the polymer resin matrix can be anywhere from 5 to 50 weight percent, preferably from 10 to 40 weight percent, based on the combined weight of the microwave absorbing material and the polymer matrix resin. Although lower concentrations could be incorporated, such lower concentrations will result in poor heating or heating too slow for commercial viability. At the same time, higher concentrations of the microwave absorbing material may be employed, although such a high concentration may adversely affect the physical properties of the polymer matrix resin and may also result in too rapid a heating rate or the attainment of excessively high temperatures.

The microwave absorbing materials used as or embedded in the susceptor are ferromagnetic materials selected to have a Curie temperature minimum at least equal to the predetermined temperature at which the first material will either be converted from its solid state or its high viscosity state to its liquid state or its low viscosity state or will be activated to initiate polymerization or curing of the first material, and a Curie temperature maximum lower than the temperature at which the first material will boil or be adversely affected by heat generated by the second material and lower than the ignition temperature of any of the materials used in the construction of the device. In their preferred embodiment, these ferromagnetic materials should have a Curie temperature maximum of no more than 10°C above the recommended temperatures for safe use or safe irradiation of the container. Such ferromagnetic materials are desirable in that, depending on their heating properties, they will typically not exceed their Curie temperature. Such ferromagnetic materials preferably include ferrites, spinels, spinel ferrites, among others. Particularly preferred ferromagnetic materials are those which have predominantly magnetic heating properties. Particularly preferred are those which have substantially no electrical or resistive heating properties, most preferably those which are substantially free of electrical or resistive heating properties. In the latter, saturation magnetism and Curie temperature are reached substantially simultaneously so that the material is microwave transparent and heating is stopped. In electrical or resistive heating, on the other hand, no cut-off point exists and thus, depending on the degree of electrical or resistive heating, property in the chosen ferromagnetic material, heating will proceed, albeit at a much slower rate. A non-quantified estimate of the degree of electrical or resistive heating properties of such ferromagnetic materials can be made in part from the electrical interaction or impedance of the ferromagnetic material at the frequency of microwave energy to be used. In general, the lower the electrical interaction, ie, the higher the impedance, the more preferable the material.

The use of such ferromagnetic materials is particularly desirable in applications where the materials used to construct the dispenser, particularly in the container and insulating jacket as discussed below, have ignition points that are not significantly or not significantly higher than the Curie temperature. It is also desirable to use such ferromagnetic materials when the first material is adversely affected by higher temperatures or boils at such higher temperatures. If a hot melt material is to be used as the first material, it is merely desirable to heat the hot melt material to a temperature at which the liquid state or low viscosity state is achieved. At the same time, when a heat sensitive material is the first material, it is also desirable to avoid heating the first material to a temperature that is significantly above the reaction temperature.

Of course, it is recognized that other materials may be added to the susceptor, including, for example, blocking agents such as calcium salts, zinc salts, zinc oxides, etc., which have proven effectiveness in controlling the heat generated by the susceptor material itself.

The first material is located within a container which may include the second material or may also have the second material therein. Generally, the container provides structural definition and integrity for the dispensing device of the present invention. The container itself may include one or more layers of material, depending on the desired construction and materials to be dispensed. Additionally, it is contemplated that the interior surface of the container may be coated with the second material, that the second material may include an intermediate layer sandwiched between two non-susceptor layers, the container may include all of these, or that it may be made entirely of the second material.

Materials suitable for use in making the container depend on the particular design and embodiment which the device of the present invention is to take. For example, if the inner surface of the container is coated with the second material, or the container contains the second material, then the container comprises at least one high temperature resistant material immediately adjacent to the second material or, if the second material is contained in the first material, on the inner surface of the container itself. Such high temperature resistant materials must be microwave transparent to allow microwave energy to reach the second material. If the container comprises multiple layers, including an intermediate layer consisting of the second material, then the outer layer immediately adjacent to the second material must be a microwave transparent high temperature resistant material and is preferably non-heat transferring. At the same time, the inner layer; that is, the layer between the second material and the first material, must be a high temperature resistant heat-conducting material to allow the transfer of heat from the second material to the first material, and is preferably microwave-permeable so that the movement of microwaves through the delivery device is not impeded. Finally, if the container comprises the second material, the container must be made of a high temperature resistant microwave-permeable heat transfer material.

Examples of materials that may be used to make the container include polyimides, high temperature polyesters, modified polyphenylene oxide resins, silicones, and other thermoplastic polymers having the desired properties noted above. The selection of a particular material for use in making the container will depend in part on the temperature required to effect conversion and/or curing of the first material, as well as the likely temperatures reached by the second material during the period that the device is or will be exposed to the microwave energies. Therefore, for example, if the first material is a low temperature hot melt adhesive having a melting point of about 100°C and the design or configuration of the container is such that the maximum recommended heating time is not expected to exceed three minutes, so that the temperature to be reached by the second material is not likely to rise above 150°C, a suitable high temperature material for use in making the container may be one having a melting point of 180°C. At the same time, if a high temperature hot melt material (one having a melting temperature of 250°C) is to be used, a second material reaching correspondingly higher temperatures in combination with a polymer resistant to even higher temperatures will be used for the container. In summary, the choice of material will depend on the proximity of the second material to the container and on the maximum temperatures that this second material is likely to reach. if it is heated for longer than the recommended time. This latter condition is intended for those cases where the consumer is likely to leave the appliance in a microwave oven for longer than the time specified in the instructions and will compensate for overheating which may occur due to hot spots in the microwave oven even if the recommended heating time is observed.

Finally, the outlet through which the first material is to be dispensed is preferably in the form of a nozzle. However, depending on the specific shape of the dispenser as a whole, other outlet shapes may be suitable. Preferably, the second material is also located in the nozzle or outlet. In this case, the nozzle, which may be integral with the container or an independent component attached to the container, may comprise a polymeric material in which the susceptor material is dispersed. Alternatively, the nozzle may be coated with the susceptor material or with a film susceptor. The purpose of incorporating the susceptor in the nozzle is to prevent heat loss in the first material as it is dispensed through the nozzle. Otherwise, such heat loss may result in solidification and clogging of the outlet.

In use, the dispenser described above is placed in the microwave oven or exposed to a microwave energy source for a predetermined time sufficient at a given frequency of microwave energy to cause the conversion of the first material from a solid state or a high viscosity state to a liquid state or a low viscosity state, or to activate the reactive components comprising the first material to initiate its polymerization or curing. This dispenser is suitable for use in conventional household microwave ovens with a wattage from 400 watts to 800 watts and higher and a frequency of about 2.5 GHz. Of course, the dispenser could also be used in commercial or industrial microwave ovens, which typically have a wattage of more than 900 watts and a frequency of about 10 KHz to 100 GHz, with the same result but in a shorter time. When the dispensing device has been heated for a sufficiently long time, the dispenser is removed from the oven and the materials dispensed therefrom to the desired application site. Dispensing is usually effected by squeezing or compressing the container so that the first material is forced through the outlet. Accordingly, it is generally preferred to select low or medium modulus, i.e. readily compressible materials for use in the construction of the device. Likewise, although not specifically required, such materials are resilient in that once pressure is removed from the container surface, the container returns to its original or substantially its original configuration and shape. Such an elastic property will enable the first material in the nozzle part to be sucked back into the main body of the container.

In its most preferred embodiment, the dispensing device of the present invention also comprises an insulating jacket which, as described above, substantially encloses the dispensing device. This insulating jacket is microwave transparent and comprises at least one layer of an insulating material. Particularly preferred are insulating jackets which comprise two or more layers, at least one of which is an insulating material. In one embodiment, the insulating jacket may comprise one or more layers with insulating properties and an outer layer without insulating properties. Accordingly, the outer layer may be made of any suitable polymeric material, paper or cardboard and the like on which the desired label, the desired te packaging color and the like. Suitable insulating layers include, for example, a foamed or expanded polymeric material such as polyethylene foam, polypropylene foam, modified polyphenylene oxide foam, polystyrene foam, etc. Other suitable insulating materials include, for example, fiberglass, a fiberglass mat, injection molded high temperature fiberglass-filled plastic, low thermal conductivity silicones, and the like. When the thermally insulating jacket comprises multiple layers, it is contemplated and preferred that the jacket include at least one intermediate insulating layer formed from a material such as a nonwoven fiberglass, a fiberglass mat, or a foamed polymer. In general, it is preferred that the insulating layer be made from flexible, pliable materials capable of withstanding high temperatures, for example, about 260°C (500°F), during the time that the dispenser is to be heated in the microwave oven.

The use of the insulating jacket serves a dual purpose and benefit. First, the insulating jacket provides a cool-to-the-touch surface so that the consumer can easily remove the dispenser from the microwave oven by hand without fear of burning their hand. Additionally, the insulating jacket serves to store heat generated by the second material in the container and thus in the first material since the insulating jacket is substantially non-heat-conductive. Consequently, the use of such insulating jackets provides for much longer periods of use following removal of the dispenser from the microwave energy source. In one embodiment, it is preferred that the insulating jacket surround the entire dispenser except for the very top of the outlet or dispensing nozzle. This will also serve to store heat in the nozzle portion as well.

In one embodiment of this aspect of the present invention, the insulating jacket may adhere to or comprise the outer layers of the container for the dispenser. If so, then the entire dispenser is discarded when the first material has been fully dispensed. In another (and preferred) embodiment, the insulating jacket comprises a sleeve into which the dispenser is inserted for use as described above and from which it is removed and discarded after the first material has been fully dispensed. This embodiment allows the sleeve to be reused, thereby minimizing cost and waste of raw materials.

Regardless of which embodiment is used, it is essential that the insulating jacket is microwave-permeable and constructed of sufficiently flexible and pliable materials so that the delivery of the first material is not disturbed following irradiation of the delivery device with microwave energy.

To aid in fully understanding the scope and nature of the present invention, Applicants will now describe several specific embodiments of the apparatus of the present invention with reference to the accompanying figures.

Fig. 1 illustrates a perspective view of a dispensing unit 10 according to an embodiment of the practice of the present invention. The dispensing unit 10 includes a dispenser 12 and a cover 14 therefor. The cover 14 serves as both a cool-to-the-touch dispensing tool and a stand for the dispenser and includes a pair of side members 30 and 32 and a central member 34 therebetween. The side members 30 and 32 and the central member 34 are integrally molded and each have between the side members and the central member is an integrally formed hinge structure 36. Preferably, the cover 14 includes an opening 38 extending through the central member 34, through each hinge structure 36, and through the upper portion of each of the side members 30 and 32. The opening 38 is sized to allow the nozzle 24 of the dispenser 12 to pass therethrough.

The cover 14 is preferably formed of a relatively rigid, heat insulating composite material. An example of a suitable material for a cover is a composite formed by laminating 1.59 to 2.38 mm (1/16 to 3/32 inch) polypropylene foam and/or polyethylene foam to a bleached 0.25 to 0.51 mm (0.01 to 0.02 inch) thick hardwood kraft paper. In general, the cover enables the dispenser to be held in an upright position when the cover is placed on a surface in an inverted "V" position. The hinge structure 36 allows the side members 30 and 32 to be subjected to opposing forces and, when squeezed, compresses the dispenser 12, thereby dispensing the first material contained within the dispenser through outlet 24.

Figures 2 and 3 illustrate cross-sectional views of two alternative embodiments of the dispenser, wherein the first material 18, which is the material to be dispensed, is contained in the container 22, the inner surface of which is coated with a layer of the second material 20. The second material 20 comprises a susceptor film, for example a high temperature polyimide film, with metal particles deposited thereon. In general, it is preferred to maintain an air space 25 above the first material 18 to allow the first material to expand when heated. This is particularly important in the event that the dispensing unit is exposed to microwave energy for too long and the first material begins to boil.

Figure 3 illustrates a similar embodiment in which the container 22 is formed from a multilayer composite comprising an outer layer 23, an intermediate layer 20 of second material and an inner layer 40. In this example, the second material or susceptor film is sandwiched between the microwave-transparent outer layer 23 and a thermally conductive and preferably microwave-transparent inner layer 40. As in the embodiment shown in Figure 2, the second material may comprise a polyimide film with metal particles deposited thereon. The outer layer 23 and the inner layer 40 may be made of the same material, for example, high temperature thermoplastics such as polyimides, polyesters, silicones and the like. Multilayer configurations are particularly desirable when the first material 18 is a food product that, for health reasons, cannot come into contact with the material contained in the susceptor layer 20 or the outer layer 23. Similarly, the use of the inner layer 40 may be important when the first material 18 is a reactive material that is adversely affected by the components contained in the susceptor layer 20 or the outer layer 23.

Figure 4 illustrates a cross-section of the dispenser 12 shown in Figure 2, taken along line A-A. Again, this embodiment shows the container 22 enclosing both the susceptor layer 20 and the first material 18.

Figures 5 and 6 illustrate another embodiment of a dispensing unit 50 constructed in accordance with the practice of the present invention. The dispensing unit 50 includes a dispenser 52 and an insulating jacket 54 therefor. The dispenser 52 includes a first material 58 to be dispensed, a second material 60 in heat transfer relationship with the first material 58, and an outlet 61 through which the first material 58 can be dispensed. The second material 60 comprises a susceptor adapted to be heated above a predetermined temperature when exposed to microwaves for at least a predetermined time. The susceptor comprises microwave absorbing particles deposited on a thin (48 gauge) microwave transparent polymer film, e.g., polyester film. In one embodiment, the susceptor 60 is bonded to a second microwave transparent inner film 62, e.g., a polyimide film, using a high temperature adhesive (e.g., Avery 1184). This inner film 62 provides a stable high temperature reinforcement for the outer susceptor film 60. The composite film comprising the susceptor 60 and the microwave transparent inner film 62 is then spirally wrapped around the first material 58 to form a container, such as a tube, with the susceptor 60 on the outer surface of the tube. In this embodiment, it is generally preferred that the upper edge of the composite film overlap and adhere to the lower edge of the following turn of the composite film. This aspect is particularly well shown in Figure 7.

In an alternative embodiment of this embodiment, the inner microwave transparent film 62 may first be spirally wrapped around the first material 58, and then the susceptor 60 may be widthwise wrapped or folded around the entire length of the inner microwave transparent film to form a container. In this case, the susceptor does not overlap at the edges and the formation of "hot spots" along the dispenser is avoided. Furthermore, the susceptor particles may be deposited directly on the outer surface of the outer microwave transparent film 62, and this single Foil may then be spirally wrapped around the first material 58 into a tube to form a container. In any event, when a composite foil is constructed, a high temperature adhesive is applied to bond the susceptor foil 60 to the inner microwave transparent foil 62. Furthermore, if there is any overlap of the composite structure in building the container, this high temperature adhesive is also applied between such overlapping edges to firmly bond the foils together.

As shown in Figures 5-7, the thus formed dispenser 52 is then enclosed in an insulating jacket 54 which includes one or more layers of thermally insulating material and which allows the user to grasp the dispensing unit 50 and remove it from the microwave oven. For example, in the particular embodiment illustrated, the insulating jacket 54 comprises an outer insulating jacket 70, an intermediate insulating layer 72, and an inner insulating layer 74. The outer insulating jacket 70 may include grooves and ridges (not shown) to facilitate heat dissipation and access by a user, and is preferably formed from a flexible, thermally insulating material, such as a polyethylene, polypropylene, polyimide, or polystyrene foam. Of course, other materials having flexible, resilient, insulating capabilities may be used. The inner insulating layer 74 and the intermediate insulating layer 72 may also be formed from flexible, resilient, thermally insulating materials. For example, the inner insulating material 74 may be formed in the form of a tube made of fiberglass mat, fiberglass, fiberglass-filled injection molded high temperature thermoplastic, or molded silicone. Similarly, the intermediate insulation 72 may be formed of material such as nonwoven fiberglass and other insulating materials. In addition, as mentioned above, any one or any of the layers of the insulating jacket may consist of a non-insulating material, as long as at least one layer comprises an insulating material.

Finally, in the embodiment shown in Figures 5-7, the dispensing unit 50 also includes a nozzle 52 having an outlet 61 through which the first material 58 can be dispensed, and a stand 76 that holds the dispensing unit 50 in an upright position (the nozzle pointing upward) while the dispenser is being heated in a microwave oven or not in use. The stand 76 may be separately molded from other heat-resistant materials, such as polypropylene. Alternatively, the stand 76 may be removably connected to the insulating jacket 54, such as by a hinge or threaded connection (not shown), to allow replacement dispensers 52 to be inserted into the bottom of the insulating jacket 54 for reuse.

Again, with hot melt adhesive, it is considered important to keep nozzle 61 unoccluded so that hot melt adhesive can be easily applied to an object after the adhesive has been heated and to avoid pressure buildup within dispenser 52. Keeping dispenser 52 in an upright position prevents hot melt adhesive from dripping out of the dispenser during heating. However, outer insulating layer 70 may be made slightly higher than intermediate insulating layer 72 so that any hot melt adhesive dripping out of nozzle 61 is caught in the intermediate insulating layer and prevented from dripping down onto the outer surface of the cover.

Another embodiment of the dispensing unit 50 made according to the practice of the present invention is shown in Figs. 8 and 9. Here, the dispensing unit 50 comprises an insulating man tel 54 in which the dispensing unit 52 is contained. As described above, the insulating jacket 54 may comprise a plurality of insulating layers 70 and 72. The dispenser 52 comprises a container 63 in which the first material 58 is contained and a stopper 81 at the end. In one embodiment, the inner surface of the container 63 may be coated with a susceptor material 65. Alternatively and preferably, the container 63 comprises a high temperature thermoplastic resin in which the second material is dispersed. In this case, if desired, an intermediate layer 65 comprising a high temperature thermally conductive polymer film 65 may serve as a chemical barrier between the container 63 and the first material 58. Alternatively, no such intermediate layer may be used.

Fig. 9 shows a cross-section of the dispensing unit 50 of Fig. 8 along line 16-16. Again, this drawing illustrates the first material 58 contained within the container 63, which in turn is surrounded by an inner insulating layer 72 and an outer insulating layer 70. Once the dispensing unit has been heated in a microwave oven for a sufficient time to cause the conversion or activation of the first material 58, one merely applies pressure to the dispensing unit to force the dispensing of the first material 58 through the outlet 61.

The container 63 for the dispenser 52 made in accordance with this embodiment of the present invention is preferably a resilient, flexible thermoplastic or silicone rubber. When the container 63 also includes the susceptor for the hot melt dispenser 52, the microwave absorbing particles are dispersed within the polymer matrix of which the container 63 is made. Examples of materials suitable for this purpose include ferrite-filled silicone.

A more efficient and faster acting embodiment of the dispensing unit 50 shown in Figures 8 and 9 is of the type shown in Figure 10. Specifically, Figure 10 shows a cross-section of a dispensing unit 50 similar to that shown in Figure 8 except that it includes two ribs 64 extending from the inner surface of the container 63 and running along the inside of the container in a direction parallel to the longitudinal axis of the container. As with the previous embodiment, a susceptor material 65 may be deposited on the surface of the ribs 64 as well as on the inner surface of the container 63. Alternatively, the container 63 and ribs 64 may be made of a second material comprising a polymer matrix in which the microwave absorbing particles are dispersed. Again, dispensing of the first material 58 from the dispenser 52 through outlet 61 is effected by applying pressure to the outer surface of the insulating cover 54 substantially as shown by the arrows in Fig. 10. The use of radially opposed ribs in the construction of this embodiment of the dispenser 52 enables maximum dispensing of the first material 58.

The improved efficiency in heating the first material 58 resulting from the use of the fins 64 is evident from the results shown in Table 1. Specifically, Table 1 shows heating rates for a dispenser made using the standard tube configuration of Figures 8 and 9 and the finned tube configuration of Figure 10 with two different types of ferrite susceptors. Each dispenser was injection molded from an injection molding grade silicone rubber available from Ronsil Rubber incorporating 40% by weight of the identified ferrite material. The silicone tube was coated with a standard EVA hot melt adhesive and heat-seamed at its end to prevent escape of the hot melt adhesive during heating. The dispensers were then exposed to microwave energy and the internal temperature of the hot melt adhesive was recorded over time using a probe. TABLE 1

¹ P.T. FCX 3242 from Powder Technology, Valparaiso, CA, a Mn/Zn modified ferrite with a magnetic saturation of 5000 Gauss and a Curie temperature of 240ºC.

² Fair-Rite 77 from Fair-Rite Products, Wall Kill, NY, a Mn/Zn modified ferrite with a magnetic saturation of 4600 Gauss and a Curie temperature of 200ºC.

+ Maximum adhesive temperature.

A final further embodiment of the apparatus of the present invention is shown in Figures 11 and 12. Specifically, this embodiment shows a dispensing unit 50 in which the second material or susceptor comprises a heating rod 80 surrounded by or embedded in the first material 58. The heating rod 80 may comprise a substrate coated with the second material, or the heating rod 80 may be made of the second material, in which case the heating rod is made of a polymeric material in which a susceptor material is dispersed. Figure 12 shows a cross-section of the dispensing unit 50 of Figure 11 along line 18-18. According to this embodiment, the container 63 may be made of a thermoplastic material or a silicone rubber in which additional amounts of the second material may or may not be dispersed. Furthermore, this embodiment also contemplates that the inner surface of the container 63 may be coated with a layer of the second material. Generally, however, the presence of the second material is only necessary in the heating rod 80. When the dispensing unit 50 is in this configuration, the heating of the first material 58 takes place from the inside out. This type of heating further reduces the temperature that reaches the outside of the container 63. In this regard, it is possible for the container 63 to be made of a microwave-transparent, heat-insulating material. Such an embodiment may make the use of the insulating sleeve 54 unnecessary.

As with the embodiment shown in Fig. 8, the dispensing unit 50 further includes a stand 76 that can be removably connected to the insulating jacket 54.

Claims (29)

1. Apparatus for dispensing heat-sensitive materials, comprising a container (52) having a first material (58) therein and which may either comprise or contain a second material (60), and an outlet (61) through which the first material may be dispensed following exposure to microwave energy on the apparatus, the first material being such that when heated to a predetermined temperature it is either converted from a solid state or a high viscosity state to a liquid state or a low viscosity state or is activated to initiate polymerization or curing of the first material, the second material being designed to be heated to at least the predetermined temperature when exposed to microwave energy for at least a predetermined time, the second material being in a heat transfer relationship with the first material, characterized in that the second material (60) is not dispersed within the first material (58) and the second material is a ferromagnetic material having a Curie temperature minimum that is at least equal to the predetermined temperature and a Curie temperature maximum that is lower than the temperature at which the first material will boil or be adversely affected by heat generated by the second material and that is lower than the ignition temperature of either the first material or the container. 2. The device of claim 1, wherein the first material is a hot melt adhesive, a food product, a solder, a wax or an oil. 3. The device of claim 1, wherein the first material is a hot melt adhesive. 4. The device of claim 1, wherein the first material is a heat activated polymerizable composition selected from epoxies, polyesters, polyurethanes, polybutadienes, cyanate esters, bismaleimides, polyimides, phenolic resins, alkyd resins, amino resins and silicones. 5. Apparatus according to any one of claims 1 to 4, wherein the second material comprises a ferromagnetic microwave absorbing susceptor material which may be in particulate, atomized or film form. 6. Device according to any one of claims 1 to 5, wherein the second material comprises a high temperature polymer film on which a ferromagnetic microwave absorbing susceptor material is deposited. 7. Device according to any one of claims 1 to 5, wherein the second material comprises a ferromagnetic microwave absorbing susceptor material in the form of particles dispersed within a high temperature polymer material. 8. Device according to claim 6 or 7, wherein the high temperature polymer material is selected from polyimides, high temperature polyesters, modified polyphenylene oxides and silicones. 9. Device according to any one of claims 5 to 8, wherein the microwave absorbing susceptor material is selected from metals and metal oxides. 10. The device of claim 9, wherein the microwave absorbing susceptor material is a metal oxide in particulate form selected from ferrites, spinels and spinel ferrites. 11. Device according to claim 9 or 10, wherein the microwave absorbing susceptor material is a ferromagnetic material with predominantly magnetic heating properties. 12. The apparatus of claim 9, wherein the microwave absorbing susceptor material is a particulate metal selected from the group consisting of aluminum particles, iron particles, and stainless steel particles. 13. Device according to any one of claims 1 to 12, wherein the second material is in the form of a heating rod (80) or a compressible coil embedded or enclosed in the first material (58). 14. Apparatus according to any one of claims 1 to 12, wherein the second material comprises the container. 15. The device of claim 14, wherein the second material comprises a silicone having dispersed therein a ferromagnetic microwave absorbing susceptor. 16. Device according to any one of claims 1 to 12, wherein the second material is between the first material and the container. 17. The device of claim 16, wherein the second material is present as a coating on the inner surface of the container. 18. Apparatus according to any one of claims 1 to 17, wherein the container is substantially tubular with a longitudinal axis and includes at least one rib (64) on its inner surface which is parallel to the longitudinal axis of the tube and extends inwardly. 19. The device of claim 18, wherein the container has two ribs, one rib being located on each of the opposite inner surfaces of the container. 20. Apparatus according to any one of claims 1 to 19, wherein the outlet includes a nozzle and the second material is also within said nozzle. 21. Device according to any one of claims 1 to 20, further comprising an inner layer (62) of a high temperature resistant thermally conductive material located between said first material and said second material. 22. Device according to any one of claims 1 to 21, further comprising a lid (14). 23. A device according to claim 22, wherein the lid comprises a heat insulating material and enables the device to remain in an upright position. 24. Apparatus according to any one of claims 1 to 21, further comprising a microwave-transparent insulating jacket (54) substantially enveloping the container. 25. The device of claim 24, wherein the insulating jacket comprises at least one layer of an insulating material. 26. Device according to claim 25, wherein the insulating material is a polymer foam. 27. A device according to any one of claims 24 to 26, wherein the insulating jacket comprises at least two layers, including an outer layer, one of which, but not the outer layer, is either of glass fiber or glass fiber mat. 28. Device according to any one of claims 24 to 27, in which the insulating jacket forms a reusable sleeve into which or from which the container is inserted or withdrawn. 29. A device according to any one of claims 24 to 28, wherein the insulating jacket comprises a non-insulating outer layer.