Mixed adhesive

Abstract

The present application discloses a heat sensitive mixed adhesive comprising an adhesive base and thermo-conductive carbon content material.

Description

MIXED ADHESIVEFIELD AND BACKGROUND OF THE INVENTION

[0001] The present invention relates to a composite material. The composite material comprises at least one layer of a substrate such as textiles, leather synthetics, or thermoplastics that binds to at least another layer of a substrate using the inventive adhesive. The present invention also relates to methods of making the composite.

[0002] Many boots and shoes have an upper formed from a flexible sheet material such as imitation leather or real leather, with the base of the upper mounted on a sole molded from a polymer plastic or rubber material. The use of synthetic materials in the manufacture of soles for boots and shoes is already well established. PVC, polyurethane, EVA and thermoplastic rubber have all been used to fulfill this purpose. These synthetic materials have suitable functional properties and are aesthetically pleasing as well as being comfortable. Rubber, however, is particularly sought after because of its durability, its resistance to hydrolysis and bacterial attack and its thermal resistance.

[0003] During the production process the upper is typically formed around a forming last in a first manufacturing step and then the sole is injection molded onto a base (i.e. insole) of the upper in a second manufacturing step. The forming last provides a template for the three-dimensional size and shape of the upper. Accordingly, the first step involves mainly shaping and stitching the upper. There is generally no heating involved in this step as the last can be made from a variety of materials, including non-thermally conductive material. Wood and metal have traditionally been used, and more recently plastic.

[0004] The second manufacturing step in the conventionally practiced production process involves injection molding of the outsole onto the base of the upper. As mentioned above, several synthetic materials have been known to be used for the outsole. Rubber, however, is seen as being particularly attractive as outsole and so-called twin density midsoles are particularly desirable because they provide a tough outsole and a resilient midsole. Twin density soles therefore provide a durable wear surface at the outsole while maintaining cushioned comfort for the wearer with the resilient midsole.

[0005] Heating process can be employed in making an upper but this is done in flat format before shaping against the shoe last. And, if the sole is made with several different components heating processes may be required prior to contacting the upper.

[0006] In another conventional method, the sole (midsole and outsole) is made separately and independently from the upper and glued later with the upper. The insole is another separate componentmade also independently and manually inserted into the assembled shoe where the upper is bonded with the sole. Further, in another conventional method, the lasted upper is inserted into a mold, and then a liquified PU is injected into the mold to the bottom of the shoe thus making the sole. Yet, this method is not frequently used (called Desma injection) as the foam is limited to polyurethane compound.

[0007] It would therefore be highly desirable to provide a method of integrating the production process steps of creating a composite material such as footwear that would clearly streamline the production process and reduce production costs.SUMMARY OF THE INVENTION

[0008] In one aspect, the invention is directed to a heat sensitive mixed adhesive comprising an adhesive base and thermo-conductive carbon content material. The thermo-conductive carbon content material may be graphite powder. The graphite powder may be present in at least 0.00001 to 0.0002 per cent by weight. The thermo-conductive carbon content material may be graphene. The graphene may be present in an amount from 0.005% to 0.5% graphene by weight. The adhesive base may be liquid water-based.

[0009] In another aspect, the invention is directed to a substrate coated with or comprising the heat sensitive mixed adhesive mentioned above. The substrate may be a component of a shoe. The substrate may be a midsole. The substrate may be an upper. The substrate may be an outsole.

[0010] In another aspect, the invention is directed to a method of obtaining permanently bonded substrates comprising applying the mixed adhesive described above to either first substrate or second substrate that are desired to be permanently bonded so as to form an assembly, and heating the assembly to form permanently bonded substrates. The substrate may be natural or synthetic fabric, natural or synthetic leather, mesh, flexible or pliable plastic, latex, silicone, rubber material, synthetic fiber or composite, EVA foam, olefin or polyolefin foam, PU foam, urethane -based foam, thermoplastic foam, elastomer, or combination thereof. The heating may be via microwave irradiation, infrared, convection, conduction using heat platens or heat presses. The duration for microwave heating may be from about 5 to 300 seconds. The first substrate may be a shoe sole and second substrate may be a shoe upper.

[0011] In another aspect, the invention is directed to a shoe assembly in which the adhesive described above may be applied between shoe sole and bottom of an upper. The sole may be composed of leather or rubber. The adhesive base of the mixed adhesive may be water-based.

[0012] In another aspect, the invention is directed to a method of fusing upper or a component of upper of a shoe to a sole or a component of a sole, comprising the steps of: contacting a pre-formed sole to the bottom of a pre-formed upper, wherein either or both of the pre-formed sole or the preformed upper is applied with the mixed adhesive described above so as to form a shoe assembly; and heating the shoe assembly resulting in activating the mixed adhesive, whereupon pemianent bond is established between the shoe upper and the sole. A non-woven fabric may be placed between the sole and upper. The shoe may be an athletic shoe.

[0013] In another aspect, the invention is directed to a method of fusing upper of a shoe to a sole, comprising the steps of:

[0014] making an upper around a shoe last;

[0015] contacting a pre-formed sole with bottom of the upper, wherein either or both of the preformed sole or the upper is applied on surface of contact the mixed adhesive described above to form a shoe assembly;

[0016] heating the shoe assembly, resulting in the activation of the mixed adhesive; and

[0017] optionally allowing the shoe upper and sole to cool down, whereupon permanent bond is established between the pre-formed sole and the upper. A non-woven fabric may be placed between the sole and upper. The shoe may be a boot, athletic shoe, or walking shoe.

[0018] In another aspect, the invention is directed to a method of fusing upper of a shoe to a sole, comprising the steps of:

[0019] making an upper around a forming last;

[0020] removing the fomiing last from the upper;

[0021] contacting a pre-formed sole with bottom of the upper, wherein either or both of the preformed sole or the upper is applied on surface of contact with the mixed adhesive of described above to form a shoe assembly;

[0022] heating the shoe assembly, resulting in the activation of the mixed adhesive; and

[0023] optionally allowing the shoe upper and sole to cool down, whereupon permanent bond is established between the pre-formed sole and the upper. A non-woven fabric is placed between the sole and upper. The shoe may be a boot, athletic shoe, or walking shoe.

[0024] In another aspect, the present invention is directed to an apparatus comprising the mixed adhesive described above.

[0025] In another aspect, the present invention is directed to a method of de-bonding a composite comprising at least two substrate materials comprising: obtaining a composite bonded with mixedadhesive; applying heat to the composite; and separating the substrate material from each other. A heat source may be microwave radiation.

[0026] In yet another aspect, the invention is directed to making the upper itself by using the mixed adhesive to bond various components to make the full finished upper. Likewise, the soles, both the midsole and outsole may be made separately as they incorporate components that are required to be bonded together to make the finished soles. Thus, the mixed adhesive may be used to bond all manner of materials together, including making the upper separately as the finished product, soles separately as the finished product, and bonding the finished upper and finished soles together.

[0027] These and other objects of the invention will be more fully understood from the following description of the invention, the referenced drawings attached hereto and the claims appended hereto.BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The present invention will become more fully understood from the detailed description given herein below, and the accompanying drawings which are given by way of illustration only, and thus are not limitative of the present invention, and wherein;

[0029] FIGURE 1 shows an exploded view of conventionally made shoes.

[0030] FIGURE 2 shows an exploded view of conventionally made shoes.

[0031] FIGURE 3 shows a conventionally made shoe upper.

[0032] FIGURE 4 shows an exploded view of conventionally made shoes.

[0033] FIGURE 5 shows insertion of a sockliner into conventionally made shoe upper-midsoleoutsole assembly.DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS OF THE INVENTION

[0034] In the present application, “a” and “an” are used to refer to both single and a plurality of objects.

[0035] As used herein, a “sole” refers to an outsole or midsole.

[0036] As used herein, “activating” heat sensitive mixed adhesive that is present between substrates refers to causing the substrates to be permanently bonded together.

[0037] As used herein, “adhesive” refers to any glue or cement, adhesive film, heat or microwave or radio-wave activated adhesive, two-sided adhesive film, and the like. It is understood that any of these or other methods for permanently bonding a substrate to another substrate may be used. In onepreferred aspect, the adhesive may be water-based. It is preferred that the adhesive is in liquid form when the thermo-conductive carbon content material is mixed into the adhesive and applied.

[0038] As used herein, “thermo-conductive carbon content material” refers to a catalyst used to elevate heat in the adhesive. This includes carbon in powder format, small enough so as to be able to be well-disbursed in the adhesive, which is preferably water-based adhesive. Carbon particles absorb energy quickly and slowly dissipate the heat throughout the adhesive evenly and consistently. Graphite, graphene platelets, graphene oxide, carbon nanotube, silver oxide, are examples of such material.

[0039] As used herein, “mixed adhesive” or “heat sensitive mixed adhesive” refers to an adhesive to which is mixed in thermo-conductive carbon content material. A thermo-conductive carbon content material such as graphite powder may be mixed directly into the liquid water-based adhesive such a liquid PU while stirring. Alternatively, the powder may be premixed with a certain amount of glue such as 10 percent of glue such that a high concentration solution is made. The premixed solution may be added to the rest of the 90 percent of the base adhesive solution. Preferably, the mixed adhesive is in liquid form. When liquid form of adhesive or mixed adhesive is used, the application method may include any manner of applying such liquid to a substrate such as by brushing, spraying, using a roller, silk screening, and so on.

[0040] As used herein, “mixed adhesive bonded composite” refers to a composite material that is formed by fusing at least two substrates together with the inventive adhesive mixed with thermo- conductive carbon content material such as graphite or graphene. This is distinguished from ordinary use of the word “composite”, which may be a combination of substrates without using the inventive mixed adhesive.

[0041] As used herein, “graphite” refers to a crystalline form of the element carbon. It consists of stacked layers of graphene. Graphite occurs naturally and is the most stable form of carbon under standard conditions. Synthetic and natural graphite are consumed on large scale for uses in pencils, lubricants, and electrodes. It is a good conductor of both heat and electricity. Graphite consists of sheets of trigonal planar carbon. The individual layers are called graphene. In each layer, the carbon atoms are arranged in a honeycomb lattice with a bond length of 0.142 nm, and the distance between planes is 0.335 nm. Bonding between layers is relatively weak van der Waals bonds and are often occupied by gases, which allows the graphene-like layers to be easily separated and to glide past each other. Electrical conductivity perpendicular to the layers is consequently about 1000 times lower. Graphite is a strong microwave absorbing material which can sustain high temperatures and providehigh heating rates. Carbon materials such as graphite generate microplasma when they are heated in the presence of microwaves. Graphite is also a good conductor of thermal energy, both electricity and heat. This is due to its molecular structure, which allows electrons to move freely through it. Heating graphite increases the free electrons in graphite products and make the conductivity of graphite better.

[0042] As used herein, “graphite particle” refers to a form of carbon which has the ability to conduct electricity and serve as an industrial lubricant. Many grades of graphite powder including natural microcrystal grade, synthetic conducting grade, natural briquetting grade, natural universal grade, natural high purity, synthetic conducting grade, and nuclear grade; forms include crystalline, mesh, and nickel coated are conventionally available. Standard powder particle sizes average in the range of - 325 mesh, - 100 mesh, 10-50 microns and submicron (< 1 micron). Materials are produced using crystallization, solid state and other ultra-high purification processes such as sublimation. Preferably as used herein, an average particle size is about 10 to 40 microns in diameter. In one aspect, 2-D graphene, which is a flat single layer of carbon atoms arranged in a honeycomb structure, has many of the same mechanical properties as a 3-D graphite, which is a naturally occurring form of carbon made up from a very weak stack of many layers of graphene.

[0043] As used herein, “graphene” refers to an allotrope of carbon consisting of a single layer of atoms arranged in a hexagonal lattice nanostructure. The name is derived from "graphite" and the suffix -ene, reflecting the fact that the graphite allotrope of carbon contains numerous double bonds. Each atom in a graphene sheet is connected to its three nearest neighbors by a-bonds and a delocalized 7t-bond, which contributes to a valence band that extends over the whole sheet. Graphene is a single layer (monolayer) of carbon atoms, tightly bound in a hexagonal honeycomb lattice. It is an allotrope of carbon in the form of a plane of sp2-bonded atoms with a molecular bond length of 0.142 nanometers. Without being bound by theory, it has been hypothesized that the critical points, 22 per cent and 50 per cent relative humidity, are very common conditions in daily life and these points can be easily crossed. Hence, many of the extraordinary properties of graphene could be modified by water in between graphene layers.

[0044] As used herein, “microwave” is a form of electromagnetic radiation with wavelengths ranging from about 30 centimeters to one millimeter corresponding to frequencies between 1000 MHz and 300 GHz respectively. In a particular embodiment, the present invention uses a microwave radiation at a frequency near 2 to 4GHz (7.5 cm to 15 cm), in particular 2.45 GHz (12 cm), causing dielectric heating primarily by absorption of the energy in water. Without being bound by theory, water in the liquid state possesses many molecular interactions that broaden the absorption peak. Watermolecules reacts with microwave radiation generating heat which activates the adhesive resulting in a covalent bonding between the sole and shoe upper.

[0045] As used herein, “reactivate” refers to the process of activating by heating a substrate that had been applied with mixed adhesive such that the mixed adhesive had dried on the substrate.

[0046] As used herein, a "forming last" is used to shape the shoe upper.

[0047] As used herein, a “shoe assembly” is used to refer to a shoe construct on which heat activatable or heat sensitive adhesive has been applied to various substrates on a shoe that are desired to be permanently bonded to each other, such as for example, the bottom of the shoe upper and the sole, in which the substrates are in contact with each other, but where the adhesive has not yet undergone the activation process. In like manner, an “assembly” may be applied to not only shoes, but any structure comprising substrates that are desired to be permanently bonded by applying the inventive mixed adhesive to the substrates.

[0048] As used herein, “strobel” construction refers to a shoe-making technique where the upper of the shoe is stitched directly to the insole, without any lasting board or midsole. This creates a flexible and lightweight shoe that conforms to the shape of the foot, making it an ideal choice for athletic and casual footwear.

[0049] As used herein, “substrate” refers to substrate is natural or synthetic fabric, natural or synthetic leather, mesh, flexible or pliable plastic, latex, silicone, rubber material, synthetic fiber or composite, EVA foam, olefin or polyolefin foam, PU foam, urethane-based foam, thermoplastic foam, elastomer, or combination thereof.

[0050] As used herein, “volumetric bonding” refers to permanent bonding at multiple locations simultaneously when exposed to heat from a heat source. This means that multi-layered bonding and binding hidden areas are possible for bonding simultaneously. An assembly may be made with mixed adhesive applied at different sites where permanent bond is desired and in one heating pass through, the permanent bond has occurred in all areas where mixed adhesive was applied.

[0051] As used herein, “water-based adhesive” refers to adhesives comprising a combination of water, polymers, and additives. They may be used for porous or non-porous substrates. These adhesives may be formulated as solutions and are activated as the water evaporates or is absorbed by the substrate. There are several different chemistries - both natural-based and synthetic-based materials - these include: VAM (vinyl acetate monomer)-based emulsions (VAE (vinyl acetate ethylene) or PVA (polyvinyl acetate) emulsions), acrylic-based emulsions, natural based or bio-based adhesives, natural rubber adhesives, or liquid polyurethane. Water-based adhesives have differentviscosities - defined by application. They range from flowing like water up to more viscos options similar to molasses. Viscosity is measured by centipoise (cPs) - essentially this is the thickness of a water-based adhesive. The higher the cPs, the thicker the substance. Water is measured at 1 cPs, castor oil is 1,000 cPs, and peanut butter is 250,000 cPs.

[0052] Bonding using mixed adhesives

[0053] In order to fuse a substrate to another substrate the mixed adhesive is coated on one substrate or both and as the mixed adhesive is activated with heat and cooled to create a strong bond. As the substrates are temporarily held together by the adhesive, the substate assembly is subjected to heat in any form such that the adhesive is able bond to the substrates together permanently resulting in “mixed adhesive bonded composite”. In the mixed adhesive bonded composite material, the adhesive used creates such a strong bond that the covalent bonding optimizes tear and shear strength on bonded surfaces, up to material breaking point on most materials. In independent laboratory tests, average tear on conventional EVA bonded to rubber is 8kgf / cm, and rubber bonded to TPU is 10- 25kgf / cm. The bonding strength results are equivalent to the maximum tear strength of the weakest material being joined together. The mixed adhesive when dried becomes a solid thin layer of plastic which acts as a bridge between the material being joined. Separation, delamination or breakage of composite or joined materials occurs at the weakest point towards the applied force direction. And most often, materials that are being joined such as foam or leather surfaces have less tear strength or shear strength than the area joined by the inventive mixed adhesive. In other words, the mixed adhesive bonding is so strong that often the tear does not occur at the adhered joint, rather it is the substrate material that is usually torn first when the assembly is attempted to be torn or sheared.

[0054] It is also seen that multiple layers of bonding are possible. No shrinkage and no yellowing of the composite materials is seen caused by using the mixed adhesive. The mixed adhesive can be applied to any fabric. Simply dry and reactivate. There is no curling or peeling. The present invention also provides for sectional and / or customized multiple area bonding in a single operation or single bonding pass through. Thus, the present invention provides precise, consistent and strong covalent bonding of substrate materials.

[0055] It is to be understood that shoe making is provided herein merely to illustrate an application of the inventive mixed adhesive technology.

[0056] An upper of a shoe is made using a forming last, in which case if it is desired to fuse a sole to the upper, the mixed adhesive may be applied to either or both of the sole or the bottom of the upper, which are then contacted together via the mixed adhesive thus forming an assembly, and the assemblyis then placed on or in an apparatus such that it is exposed to a heat source such as microwave in a microwave oven to heat the mixed adhesive thus activating the mixed adhesive applied on the sole or bottom of the upper.

[0057] On occasion, as an upper is made without necessarily using a forming last, in which case if it is desired to fuse the sole to the upper, the sole can be brought juxtaposed to the bottom of the upper, and a microwave instrument can be used to heat the mixed adhesive applied on the sole or bottom of the upper to make the shoe.

[0058] In another aspect, the present invention is directed to a method of fusing upper of a shoe to a sole, comprising the steps of:

[0059] (i) contacting a pre-formed sole with the bottom of a pre-formed upper, wherein either or both of the pre-formed sole or the pre-formed upper is applied with mixed adhesive on the surface that is desired to be contacted with each other so as to form a permanent bond, thus creating an assembly;

[0060] (ii) heating the assembly, resulting in the activation of the mixed adhesive; and

[0061] (iii) optionally allowing the shoe upper and sole to cool down, whereupon permanent bond is established between them. Preferably, non-woven fabric is placed between the sole and upper. The shoe may be an athletic shoe, but all types of shoes are contemplated by the present invention.

[0062] In another aspect, the present invention is directed to a method of fusing upper of a shoe to a sole, comprising the steps of:

[0063] making an upper around a forming last,

[0064] contacting a pre-formed sole on to bottom of the upper, wherein either or both of the preformed sole or the upper is applied with mixed adhesive on the surface of the pre-formed sole or the upper that are desired to be contacted with each other so as to form a permanent bond thus forming a shoe assembly;

[0065] heating the shoe assembly, resulting in activating the mixed adhesive; and

[0066] optionally allowing the shoe upper and sole to cool down, whereupon permanent bond is established between them. Non-woven fabric may be placed between the sole and upper. The shoe may be a boot, athletic shoe, or walking shoe or any other type of shoe that uses a last to make an upper.

[0067] In another aspect, the present invention is directed to a method of fusing upper of a shoe to a sole, comprising the steps of:

[0068] making an upper around a forming last;

[0069] removing the forming last from the upper;

[0070] contacting a pre-formed sole on to bottom of the upper, wherein either or both of the preformed sole or the upper is covered with mixed adhesive on the surface of the pre-formed sole or the upper that are desired to be contacted with each other so as to form a permanent bond thus forming a shoe assembly;

[0071] heating the shoe assembly, resulting in activating the mixed adhesive; and

[0072] optionally allowing the shoe upper and sole to cool down, whereupon permanent bond is established between them. Non-woven fabric may be placed between the sole and upper. The shoe may be a boot, athletic shoe, or walking shoe or any other type of shoe that uses a last to make an upper.

[0073] In another aspect, the present invention directed to shoes that are made from the processes described above.

[0074] According to an aspect of the present invention, there is provided a method of making an item of footwear such as a shoe such as athletic footwear or a boot, comprising the steps of:

[0075] forming an upper for the item of footwear on a forming last, the forming last including a body having the general shape of a foot around which the upper of the footwear item is to be formed, the body having a base corresponding in shape to a sole of the foot;

[0076] bonding a pre-formed sole on to the bottom of the pre-formed upper, wherein either or both of the pre-formed sole or the pre-formed upper is applied with mixed adhesive on the surface of the pre-formed sole or the pre- formed upper that are desired to be contacted with each other so as to form a permanent bond in which a shoe assembly is formed; and

[0077] heating the shoe assembly, resulting in activating the mixed adhesive, and whereupon optionally cooling the shoe upper and sole, permanent bond is established between the sole and the upper.

[0078] As mentioned above, the inventive method is directed to fusing a pre-formed sole to an upper using a heating instrument in the manner as described above.

[0079] Preferably, non-woven textile that is made of entangled thin layers of fiber can be laminated as a cheap carrier to bind the sole in particular outsole to the upper. The melting temperature of hot-melt film and the various types of polymers used can be determined using known tables.

[0080] While conventional thermal conduction heating mechanism may be used, induction heat can be used as another mechanism of heating the instrument. This is exemplified in US Patent No. 8,959,690, which is incorporated by reference herein as to the disclosure of induction mechanism ofheating an assembly. Preferably, microwave is used. A microwave oven is preferably used to heat the shoe assembly in which mixed adhesive is applied at the interface of the shoe upper and the sole.

[0081] The present invention is based on the discovery that mixing certain thermo-conductive carbon content material into heat sensitive adhesive results in an adhesive that provides an advantageously strong permanent bond upon heating.

[0082] Footwear production is traditionally a labor and time intensive process, and requires the cutting, stitching, gluing, and assembly of many separate parts and subcomponents. Figure 1 depicts the traditional steps for making footwear by assembling three major components: The shoe upper 1, customarily made of fabric, leather, or other suitable synthetic material; the shock-absorbing midsole 2; and the outsole 3, customarily made of rubber, plastic, leather, or other durable material. The major components may be glued together by applying inventive adhesive on at least one of the surfaces of contact.

[0083] As depicted in Figure 2, shoe upper 1 is customarily made by cutting and assembling numerous subcomponents, and sewing, stitching, and gluing those subcomponents together. The major components may be glued together by applying inventive adhesive on at least one of the surfaces of contact.

[0084] Conventionally, the heel quarter 8 is made by separately cutting and gluing or sewing heel quarter component outer layer 9A to a heel quarter component padding 9B and heel quarter component inner lining 9C. Likewise, the shoe “tongue” component 4 is made by separately cutting and gluing or sewing a tongue outer layer 5A to tongue padding 5B and tongue inner lining 5C. The heel counter 6 is made by cutting and gluing or sewing together heel counter outer layer 7A, heel counter component 7B, and heel counter inner lining 7C. A toe cap component 10A and toe cap reinforcement 10B may be glued or sewn together, and then glued or sewn to shoe vamp 11A. Other subcomponents similarly require assembly, stitching, or gluing of discrete parts or swatches of materials in separate steps. The major components may be glued together by applying inventive adhesive on at least one of the surfaces of contact.

[0085] Conventionally, the various subcomponents must be glued or sewn together to form the shoe upper 1. By way of example only, the toe cap component 10A must be glued or sewn to shoe vamp 11A and to toe cap reinforcement 10B; the shoe vamp 11A must be glued or sewn to front quarter component 11B; the shoe tongue component 4 must be glued or sewn to shoe vamp 11 A; and the heel counter 6 and heel quarter 8 must be glued or stitched to the front quarter component 11B, in separate steps.

[0086] The partially assembled shoe upper 1 is then stitched or glued to innersole board 12, to form shoe upper 1.

[0087] The completed or fully assembled shoe upper 1 is depicted in Figure 3.

[0088] Thereafter, as depicted in Figure 4, shoe upper 1 is stitched or glued to midsole 2, and to outsole 3, with midsole 2 being “sandwiched” between shoe upper 1 and outsole 3.

[0089] Finally, a sockliner 15 shown in Figure 5 is inserted, positioned, or glued to the completed shoe upper-midsole-outsole assembly 14.

[0090] In the conventionally made shoes as above, as the different parts of the shoe are contacted with each other via the inventive mixed adhesive, strong bonds are formed as heat is passed through the assembly. If volumetric bonding is desired, each of the pieces of the shoe may be held together and held in place with the mixed adhesive and irradiated in a microwave oven in which all of the mixed adhesive are activated and the binding of individual parts occurs simultaneously to provide a fully assembled shoe that is covalently bonded where the adhesive were applied.

[0091] Examples of the thermo-conductive carbon content material are without limitation, graphite, graphene platelets, graphene oxide, carbon nanotube, silver oxide. A preferable average size of a graphite particle may be 10-40 microns in diameter. The amount of the graphite particle or graphene mixed into the adhesive may be at least 0.00001 per cent by weight, to about 0.5 per cent by weight depending on the thermo-conductive substance being added, and whether the adhesive is waterbased or not.

[0092] While any type of heat may be applied to the adhesive to effectively cause permanent bond, Applicant has discovered that microwave heating is preferable and economical. In particular, a conventional food microwave oven may be employed for about 5 to 300 seconds set on maximum power to cause the mixed adhesive to be effective to cause permanent bonding between the contacting substrates. Regular infrared (IR) oven is a “conduction” type of heat transfer. “Convection” heat transfer can be used as well. A combination of conduction and convection heat transfer can be used to perform the present invention. However, “radiation” by microwave is preferred to practice the present invention in particular as it relates to volumetric bonding.

[0093] Utilizing a microwave radiation-reactive adhesive mixed with thermo-conductive carbon material such as graphene, graphite, silver oxide, and so on allows for volumetric bonding, which enables hidden or multiple layered materials to be bonded simultaneously and only where the mixed adhesive has been applied. As microwave radiation causes water molecules to generate heat, the carbon atoms within the glue stores the energy thus accelerating and prolonging the heating duration,resulting in optimal covalent bonding, saving energy and streamlining steps in the shoe making process, in particular the gluing phase.

[0094] Microwave heating time would require a consideration of the following:

[0095] 1) power (W)

[0096] 2) size and type of microwave

[0097] 3) Frequency. 2.4Ghz is the most used in household microwave) and higher frequencies are used on industrial microwaves.

[0098] 4) Volume of products being heated.

[0099] A household microwave was used with 800 Watts / 2.4 GHz, heating a 1 / 2 pair of lasted upper and EVA midsole and rubber outsole. The optimal heating duration was obtained when heated between 5 - 300 seconds, preferably, 90-120 seconds. However, as discussed above, the duration needed to sufficiently heat the coated adhesive surface depends on the volume and area of the coated surface, the overall direct exposure to the radiation and the power of the radiation.

[0100] While the shoe upper binding to a sole is discussed and exemplified herein, the inventive mixed adhesive may be applied on any substrate on any object that is desired to be glued together. In other words, the mixed adhesive may be applied to multiple substrates, not only in shoe assembly but in any structure that requires permanent bonding between substrates by the step of forming an assembly using the mixed adhesive and heating the assembly preferably with microwave radiation. In particular, while it is possible to have one surface of the substrate be treated and its binding partner substrate not treated with the mixed adhesive to achieve a strong permanent bond, it is preferred that both substrates be treated with the mixed adhesive.

[0101] The shoe may be made of different types of materials, such as natural or synthetic fabric, natural or synthetic leather, mesh, flexible or pliable plastic, latex, silicone, other rubber material, synthetic fiber or composite, or any combination of the foregoing, which may optionally impart different degree of breathability, stretchability, shock absorption, weight, and structural integrity to the assembly. Optionally, the shoe may also be made of sheets of EVA foam, olefin or polyolefin foam, PU foam, urethane-based foam, thermoplastic foam, elastomer, or other material with suitable shock absorbing characteristics, suitably rigidity, or resistant to puncture or abrasion, and the like, including a combination of any such materials.

[0102] Debonding or thermal separation of assemblies glued with mixed adhesive

[0103] Recycling materials is a big challenge in society today as the products that are desired to be recycled are made with all sorts of materials and they need to be separated in order to be recyclableand or to be reusable. The inventive method allows for separating the substrate components that have been bonded using the inventive mixed adhesive. The substrates to be de-bonded may include parts of shoes, apparel or bags and so forth. Microwave may be used to separate the bonded areas by melting the adhesive so that the parts can be easily separated for recycling. Mixed adhesive can bond as well as de-bond provided that enough energy is induced for the adhesive to melt. The substrates may be separated while the adhesive is still hot and in melted stage. The mixed adhesive heats up very quickly within about two minutes, and most in less than a minute in a consumer grade microwave thus melting the previously bonded surfaces. This method of debonding allows for cost efficient and easily adoptable method to recycle or reuse these materials. The separated substrates may be recycled or reused by bonding to a different substrate. For instance, a used sole may be exchanged for a new one, or fully recycle by material type. Without being bound by theory, radiation energy such as microwave works best for debonding because energy is generated from within the adhesive thus heating the thermo-conductive carbon content material in the adhesive, leading to quick melt of the adhesive and less damage to the substrate, whereas convection, conduction, and induction heat require generating heat from outside spreading inward, thus debonding would not occur without destroying the substrate from exposure to heat.

[0104] Advantages of using the inventive mixed adhesive

[0105] Summarizing some of the benefits of using the inventive mixed adhesive may be as follows: Precise and consistent and controlled strong covalent bonding between the surfaces is achieved. Primers may be optionally used, provided the bonding surfaces are free of dirt or oxidation. Buffing bonding surfaces is recommended to ensure covalent bond. Reactivation of adhesive is allows for time delayed bonding. For instance, bonding surfaces may be coated with adhesive, dried and stored for a lengthy period of time (+30 days), then reactivated without re-application of adhesives on one of the surfaces. For example, midsoles can be coated, dried and stored away for activation by heat later when it is desired to assemble the shoes. Also, allowing for prolonging work time on each shoe to bond the surfaces together provides margin of error is reduced.

[0106] The inventive process also saves electricity / energy by at least 30% by simply shortening the duration of the heating time compared with using conventional base adhesive alone. And further energy savings by a combination of increased oven temperature, duration, and size.

[0107] Advantages of using microwave radiation with mixed adhesive

[0108] Using radiation energy to bond surfaces, in particular in complexly layered composites or assemblies, inventive method provides volumetric bonding, meaning multi-layered bonding andbinding hidden areas. An assembly may be made with mixed adhesive applied at different sites where permanent bond is desired and in one heating pass through, the permanent bond is formed in all areas where mixed adhesive was applied. In one aspect, 3D volumetric bonding also means that the product is temporarily assembled in the final shape by joining, securing by jigs, wrapping, or using shoe last and so on. The mixed adhesive is activated by applying radiation in multiple areas of the shoe that is temporarily pre-assembled having hidden and exposed surfaces. This side steps the process of having to go through multiple passes of binding in order to separately bind areas of an assembly of a shoe. The 3D volumetric process allows for a single pass radiation to make permanent shape the temporarily pre-assembled product.

[0109] It is understood that all thermal energy transferring methods work utilizing the mixed adhesive. However, microwave irradiation method is the only method that works efficiently to bond hidden or unexposed surfaces without heat damaging the materials that are not coated with the adhesive. Without being bound by theory, microwave irradiation is understood to penetrate the substrate materials and heat energy is generated from the mixed adhesive areas, thus causing the melting of the mixed adhesive forming the bond in the adhesive coated area.

[0110] The present invention is not to be limited in scope by the specific embodiments described herein. Indeed, various modifications of the invention in addition to those described herein will become apparent to theose skilled in the art from the foregoing description and accompanying figures. Such modifications are intended to fall within the scope of the appended claims. The following examples are offered by way of illustration of the present invention, and not by way of limitation.

[0111] EXAMPLES

[0112] Example 1 -

[0113] By example, 100 mg of graphite particle was mixed in 1 kg of base adhesive of waterbased liquid polyurethane adhesive thus forming mixed adhesive, and applied by brushing the mixed adhesive on a sole made of EVA foam. Several rubber strips were contacted with the sole on which was applied the mixed adhesive thus constructing an assembly. The assembly was placed into a conventional food microwave oven and irradiated for 15 seconds at full power wattage, causing a permanent bond between the sole and the rubber strips such that the bond was stronger than if the base adhesive had been applied instead of the mixed adhesive.

[0114] Example ! -

[0115] The shoe last and upper (lasted upper) are held together throughout the entire gluing process with the sole using the mixed adhesive of Example 1 applied on the surface of contact; the assembly is pneumatically pressed and put into a cooler. Then the shoe last is extracted. The shoe last determines the shape of the shoe so it needs to be inserted and taken out only after the entire shoe making process is finished.

[0116] Example 3 -

[0117] Types of shoe constructions: 1) Board lasting: a board is placed on the bottom of the shoe last and upper is folded over the board and glued. 2) Strobel lasting - strobel, slip, force, or California lasting is the most common shoe construction for casual and athletic shoes. Once the upper is complete, a “sock” or bottom material is added to “close” the upper. This material is non-stretch and is marked so the assembler can keep the upper straight on the last.

[0118] Example 4 - Volumetric bonding.

[0119] A. Certain rubber pieces are desired to be permanently bound on the midsole, and the rubber outsole and lasted upper is desired to be permanently bonded to the midsole. These various bonding can occur simultaneously with microwave radiation if the areas to be bonded are applied with the mixed adhesive of Example 1.

[0120] B Several pieces of EVA foam are stacked on top of each other wherein the mixed adhesive of Example 1 is applied between the pieces of EVA foam. The stack is microwaved for 60 seconds in household microwave oven. It is then placed in a freezer for 5 minutes to let it cure. Excellent and permanent bonding of all of the pieces on the stack are seen.

[0121] C. Several pieces of EVA foam are applied with the mixed adhesive of Example 1, and are contacted with midsole, thermal cured with microwave for 60 seconds, and cooled. Excellent permanent bonding is seen.

[0122] D. EVA midsole is contacted with six pieces of EVA foam in various regions. An outsole is also applied with the mixed adhesive of Example 1 and contacted the midsole. The mixed adhesive is applied onto contacted substrates. The assembly is microwaved in a household microwave oven for 60 seconds, and cooled.

[0123] E. A combination of substrates made of rubber, TPU, PU, EVA are contacted together after applying the mixed adhesive of Example 1 and are microwaved in a household microwave oven, and cooled. Strong bond was observed.

[0124] F. In bonding using microwave, the lasted upper and sole are put together into the microwave. Both bottom of lasted upper and inside of sole (bonding substrate) were coated withgraphite infused water-based PU adhesive, and heated for 60 seconds in a household microwave oven and cooled.

[0125] In volumetric bonding, infrared heating is not effective because activation by IR heating requires the coated surface to be exposed to absorb and transfer heat. In contrast, microwave heating of the adhesive is not dependent on open exposure to the heat. Therefore, where the mixed adhesive of Example 1 was applied microwave radiation was able to heat and activate it.

[0126] Example 5 - Delayed bonding

[0127] The substrates that are desired to be bonded may be treated with the mixed adhesive of Example 1 and heated with for instance infrared heating independent of each other, and soon after finishing the heating process, they are contacted with each other and held together, and are allowed to cure. There is allowance duration where two coated surfaces need to be joined before the glue gets cold. This is one of the advantages of the mixed adhesive that it keeps the coated surface hot longer than regular glue, thus increasing the duration for the surfaces to be temporarily joined together.

[0128] The shoe last and upper (lasted upper) were held together throughout the entire gluing process. The sole of the lasted upper was applied with the mixed adhesive of Example 1, and outer was also applied with mixed adhesive. Each was heated separately. After heating the lasted upper and outsole separately they were brought together and held together to make an assembly; the assembly was pneumatically pressed and put into a cooler. Then the shoe last was extracted. The shoe last determines the shape of the shoe so it needs to be inserted and taken out only after entire shoe making process is finished.

[0129] Example 6 - Reactivation

[0130] It is possible to apply the mixed adhesive to a substrate and allow it to dry, store and activate (reactivate) later. For example, a coated midsole may be applied and dried and it is not sticky. Adhesive turns clear after drying. It is later brought out and heated and the mixed adhesive is activated.

[0131] Example 7 - Debonding

[0132] A fully assembled athletic shoe in which the upper and outer sole were bonded together by applying the mixed adhesive of Example 1 on either or both substrates of the contact surfaces of the outer sole and the upper, which was cooled and was in wearable condition was lightly sprayed with water and microwaved in a consumer grade microwave for one and a half minutes. Water was sprayed on the shoe assembly in order to prevent any possible burning. The upper and outer sole were separated manually by hand by grabbing the outer sole and the upper and pulling them apart as the adhesive hadmelted without heat damaging the substrate material. A plier was also used to grab the outer sole, such that the separating occurred along the surface of the adhesion.

[0133] The present invention is not to be limited in scope by the specific embodiments described herein. Indeed, various modifications of the invention in addition to those described herein will become apparent to those skilled in the art from the foregoing description and accompanying figures. Such modifications are intended to fall within the scope of the appended claims. The following examples are offered by way of illustration of the present invention, and not by way of limitation.

[0134] Those skilled in the art will recognize, or be able to ascertain using no more than routine experimentation, many equivalents to the specific embodiments of the invention specifically described herein. Such equivalents are intended to be encompassed in the scope of the claims.

Claims

What is claimed is:

1. A heat sensitive mixed adhesive comprising an adhesive base and thermo-conductive carbon content material.

2. The heat sensitive mixed adhesive of claim 1, wherein the thermo-conductive carbon content material is graphite powder.

3. The heat sensitive mixed adhesive of claim 2, wherein the graphite powder is present in at least 0.00001 to 0.0002 per cent by weight.

4. The heat sensitive mixed adhesive of claim 1, wherein the thermo-conductive carbon content material is graphene.

5. The heat sensitive mixed adhesive of claim 4, wherein the adhesive comprises 0.005% to 0.5% graphene by weight.

6. The heat sensitive mixed adhesive of claim 1, wherein the adhesive base is liquid water-based.

7. A substrate comprising the heat sensitive mixed adhesive of claim 1.

8. The substrate of claim 7, is a component of a shoe.

9. The substrate of claim 8, wherein the substrate is a midsole or a component of the midsole.

10. The substrate of claim 8, wherein the substrate is an upper or a component of the upper.

11. The substrate of claim 8, wherein substrate is an outsole or a component of the outsole.

12. A method of obtaining permanently bonded substrates comprising applying the mixed adhesive of claim 1 to either first substrate or second substrate that are desired to be permanently bonded so as to form an assembly, and heating the assembly to form permanently bonded substrates.

13. The method of claim 12, wherein the substrate is natural or synthetic fabric, natural or synthetic leather, mesh, flexible or pliable plastic, latex, silicone, rubber material, synthetic fiber or composite, EVA foam, olefin or polyolefin foam, PU foam, urethane-based foam, thermoplastic foam, elastomer, or combination thereof.

14. The method of claim 12, wherein the heating is via microwave irradiation, infrared, convection, conduction using heat platens or heat presses.

15. The method of claim 12, wherein the first substrate is a sole and second substrate is a shoe upper.

16. A shoe assembly in which the adhesive of claim 1 is applied between sole and bottom of an upper.

17. The shoe assembly of claim 16, wherein sole is composed of leather or rubber.

18. A method of fusing upper of a shoe to a sole, comprising the steps of: contacting a pre-formed sole to the bottom of a pre-formed upper, wherein either or both of the pre-formed sole or the pre-formed upper is applied with the mixed adhesive of claim 1 so as to form a shoe assembly; heating the shoe assembly resulting in activating the mixed adhesive, whereupon permanent bond is established between the shoe upper and the sole.

19. A method of de-bonding a composite comprising at least two substrate materials comprising: obtaining a composite bonded with mixed adhesive of claim 1; applying heat to the composite; and separating the substrate material from each other.

20. The method of claim 19, wherein the source of heat is microwave radiation.

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