Patent Grant
8240915
The present invention relates to a bag and method of making the bag, wherein the bag is sealable by a heat activated adhesive.
U.S. Pat. No. 3,380,646 discloses a container of thermally weldable, plastic material and a method of producing the container by welding together multiple strips or sheets of plastic material to form a container having a welded closed, bottom part of the container. An open top of the container is collapsed and flattened to provide a pinch closed top.
U.S. Pat. No. 5,048,692 discloses a bag folded one or more times to form a primary closure. A flap seal extends across the folded configuration. A string underneath the flap seal is used to tear open the flap seal and permit the bag to unfold. A zipper closure provides a secondary enclosure.
US 2007/0292053 A1 discloses a bag of paper material and a paper tape coated with a hot melt adhesive, wherein the tape is folded to adhere the hot melt adhesive against a front panel of the paper bag to provide a glued paper-to-paper section. The tape substitutes for a stepped end of a multi-wall paper bag. The stepped end provides a sealing flap coated with hot melt adhesive, wherein the sealing flap can be folded over and sealed to the front panel of the paper bag.
A bag of polymeric material has a first panel and a second panel forming a pinch closed bag end therebetween, a first layer of heat activated adhesive material on a portion of the first panel having a heat activated first adhesive layer to form an adhesive-to adhesive seal with a heat activated second adhesive layer on a portion of the second panel, the first adhesive layer and the second adhesive layer having respective melt temperatures below the softening point temperature of the polymeric material.
An embodiment of a bag is foldable on itself to form a folded first panel and to form an adhesive-to-adhesive seal of the first adhesive layer on the folded first panel.
An embodiment of a bag has the second adhesive layer on the foldable sealing flap portion.
An embodiment of a bag has a second panel longer than a first panel wherein the second layer of heat activated adhesive material is on a portion of the second panel that is longer than the first panel.
A method of making a bag includes, forming a pinch closed bag end between a first panel and a second panel, applying a heat activated first adhesive layer on a portion of the first panel, applying a heat activated second adhesive layer on a portion of the second panel, wherein heat activation temperatures of the first adhesive layer and the second adhesive layer are below the softening point temperature of the polymeric material, and after filling the bag with contents activating the first adhesive layer and the second adhesive layer by applying heat at a temperature below the softening point temperature of the polymeric material, and pinch closing the end of the bag to urge the adhesive layers into contact and to form an adhesive-to-adhesive seal.
An embodiment of the method includes, folding the bag to fold the first panel on itself to urge the second adhesive layer into contact with the first adhesive layer on the first panel of the bag and form an adhesive-to-adhesive seal.
Another embodiment of the method includes, folding a flap portion of the second panel over the first panel to urge the second adhesive layer into contact with the first adhesive layer on the first panel of the bag and form an adhesive-to-adhesive seal.
Embodiments of the invention will now be described by way of example with reference to the accompanying drawings.
Bags to be used for bulk packaging of granular or finely ground materials, such as nutrients including, but not limited to, whole and ground grains, seeds, dry pet food, chemical fertilizers, other bulk food and non-food products, and growing plant treatments, must be durable to resist material degradation, abrasion, puncture, contamination and leakage of contents, and must withstand a drop test while sealed and filled with contents weighing up to about 50 pounds, and even up to about 80 pounds. Moreover, such bags are typically disposed of after use, which requires an inexpensive and light-weight construction that is environmentally friendly, may be recyclable, and reduces waste in the supply chain from production, use of the bag, to disposal in either a recycling stream or landfill.
Currently, multi-walled paper and polymer layer bags, consisting of multiple paper layers and layers of polymer film, are heavy, expensive to produce and ship, easy to tear and puncture, and create waste in the supply chain. Multi-wall paper/polymer layer bags, traditionally used to package bulk products, are not recyclable and add significant amounts of materials to landfills. This invention overcomes many of the significant drawbacks of multi-wall paper/polymer layer bags, by offering a lighter weight bag that is less expensive, more durable and tear-resistant, resulting in significantly reduced waste in the supply chain, and is 100% recyclable in a suitable recycling stream. Moreover, this invention can function essentially in the same way on existing bag filling and sealing equipment to perfect a pinch-sealed bag filled with product.
A typical manufacturing production line provides apparatus to fill the bags with contents, and further provides apparatus to close the bag in a simple manner by pinch closing, and further provides equipment to seal the pinch closed bag. Bags of traditional construction can be close by sewing or alternatively, sealed with a hot melt sealant instead of sewing. Such bags of traditional construction include multi-wall bags fabricated of paper and polymeric film laminates. The bag construction must allow quick filling of the bag with contents and thereafter must allow closing and sealing the bag.
The traditional bag construction has layers of polymer laminated with a paper layer or layers. Sealing of the traditional bags after filling is accomplished by re-melting a hot melt adhesive and/or meltable polymer layer at an elevated temperature while the paper resists damage to the bag construction. The high flash point inherent to paper is relied upon to withstand the application of heat at an elevated temperature and thereby to protect the bag from damage due to the heat and temperature. Further, a thin polyethylene, PE, polymer coating on the paper surface can melt or soften together with the hot melt adhesive to adhere to the paper and form a secure seal. Existing end-user production line equipment applies hot air onto the bag to melt and activate the hot melt adhesive and/or meltable polymer layer, following the bag filling operation. The heat must be applied at a temperature that melts the hot melt adhesive, and further, to at least partially melt the polymer coating on the paper surface, while relying on the paper to withstand the heat and temperature, and to prevent bag weakening or burning due the heat and temperature. However, a major drawback of the multi-wall paper and polymer laminates is that they are composite materials not capable of recycling as either paper or plastic as a single material classification. Further, the multi-wall laminates of the traditional bag are not compostable, and consequently remain in one piece in landfills. Further, the multi-wall laminates are heavy, and add unnecessary shipping costs.
In an end-user's manufacturing production line, apparatus is provided to fill the bags with contents through an open end of the bag, followed by closing and sealing the filled bag. Traditional production lines have employed stitching equipment to sew the bags shut. Alternative production lines have heated air jets to apply heat at an elevated temperature to melt and activate pre-applied hot melt adhesives that have been pre-applied to traditional bags of thick multiwall paper and polymer film laminate construction. Thereafter, a closure mechanism closes the bags in an advantageous manner simply by pinch closing the open ends. The closure mechanism applies pressure on the bags to close and hold the bags closed while the hot melt adhesive adheres to the closed bag and until the adhesive cools and hardens.
The heat must be applied at a temperature that melts the hot melt adhesive, and further, which can melt portions of the polymer coating on the paper surface, while relying on the paper to withstand the heat and temperature, and prevent weakening or burning due the heat and temperature. The traditional bags have a construction of thick multi-wall paper and polymer film laminates. The one or more, thick paper layers of the traditional bags withstand the heat applied at elevated temperatures without weakening the bag strength and without burning the paper. Further, a laminated film coating of polyethylene, PE, on the paper surface partially melts while in contact with the melted, hot melt adhesive to form a heat seal with the adhesive.
The embodiments of the invention provide a sustainable solution to the long existing need for bags that replace traditional bags of multi-wall paper and polymer laminates, and yet can withstand the application of heat and temperature to seal the bags, which continue to be prevalent in existing production equipment.
Accordingly, there has been a long existing need for a bag fabricated of structural components capable of being recycled or resulting in less landfill material compared to traditional bags, and capable of being sealed by existing production equipment to avoid expensive replacement of existing production line equipment. Accordingly, to replace the existing structural components of a laminated paper and polymer bag with an improved bag, the improved bag must be heat sealed by existing production equipment while withstanding the application of heat and/or pressure to melt the adhesive and seal the bag. Moreover, there has been a long existing need to eliminate a paper and polymer laminate as one of the structural components of the bag, which is incapable of recycling and/or degradation in a land fill, and which add significantly higher weight and quantities of materials in a landfill.
Traditional multi-wall paper and polymer laminate bags each have about 275 grams of paper and 50 grams of polypropylene polymer, and a carbon footprint of about 11 as a measure of carbon emissions. Lighter weight bags of about 150 grams results from embodiments of the invention with fewer raw materials than those used in making the traditional bags, and result in a substantially reduced carbon footprint of about 5.
According to embodiments of the invention, woven bags are fabricated entirely of a recyclable polypropylene, and with structural components including a tubular woven (mesh) bag laminated inside of a non-porous polymeric film of a single layer or of laminated layers. The bags are fabricated entirely of a recyclable polypropylene material that is recyclable and may be compostable due to having resin additives such as metallocene, and further that is free of recycled or contaminated polymers of unknown chemistry and unknown material mixtures. Moreover, the bags according to embodiments of the invention are less heavy and are more resistant to abrasion, tearing and puncture, and are reusable compared with traditional multi-wall paper and polymer laminates that are susceptible to abrasion and damage. The bags according to embodiments of the invention reduce waste due to shipping costs, damaged bag contents and increased shelf life of the contents.
The embodiments of the invention fulfill a long existing need for lighter weight, strong bags having structural components that eliminate traditional non-recyclable paper-polymer laminates, and moreover, that are durable for reuse, and are degradable by composting in a landfill and are recyclable as a single material. Moreover, the recyclable and/or compostable bags include water soluble adhesive materials as structural components of the bags. Embodiments of the adhesive materials can be pre-applied while soluble in water, a nontoxic solvent. The adhesive materials are applied onto opposed surfaces of the bags, followed by curing by exposure to radiant or entrained heat, electron beam, EB, radiation, air or other curing medium and/or to evaporate the nontoxic dispersion for environmentally safe removal from the activatable adhesive components of the dispersion mixture that attain a non-adhesive hardened state, which is non-reactive to water or humidity, and is nontoxic by incidental contact with nutrients being filled in the bags. An opposite end of each of the bags has a pinch bottom or alternatively, a flat bottom configuration that is closed and sealed by sewing, or by an adhesive preferably a nontoxic adhesive or by plastic welding or by a material including, but not limited to polymeric, paper or nonwoven tape. The bags are folded flat for shipment to another manufacturing facility where the bags are filled with contents and closed and sealed.
The adhesive materials to seal the bag are activatable to a melted adhesive state using existing production line equipment that apply heat at a temperature sufficiently below the softening point temperature Tg of the polymeric structural components of the bag, and to melt the adhesive materials to an adhesive state without damaging the other structural components of the bag.
While a traditional multi-wall paper/polymer layer bag can be sealed with a re-melted hot melt adhesive, these hot melt adhesives are not suitable for sealing polymeric bags, which typically are comprised of one or more polymeric layers of recyclable polypropylene, or a recyclable and/or compostable polypropylene woven bag and an outer polymeric layer or laminate of two or more polymeric layers of recyclable polypropylene or other polymer material, but not including either paper or an outer layer, which is not heat-sealable on traditional bag manufacturing production equipment. The heat required to activate a hot melt adhesive to an adhesive state would be detrimental to a polymer woven bag and would destroy the structural integrity of the bag. A traditional multi-wall paper/polymer layer bag can be sealed with a hot melt adhesive, whereas on a polymeric bag the heat applied by existing end-user equipment to reactivate or re-melt a hot melt adhesive would further heat the polymer material of the bag above its softening point Tg temperature causing the polymer material to soften, lose tensile strength or even undergo plastic deformation. Accordingly, typical known hot melt adhesives are not suitable for forming a seal on a polymeric bag.
The first panel 106 and the second panel 108 are joined along their side edges along sides 110 of the bag 100. An end 122 of the bag is open through which contents can be introduced into the bag 100. The end 122 is adapted to be pinch closed between end edges of the first panel 106 and the second panel 108. The panels 106, 108 are joined along their side edges and end edges by plastic welding of the edges or by an adhesive. Alternatively the bag 100 is tubular, and the panels 106, 108 are defined by making folds or creases in the bag 100. An opposite end 124 of the bag 100 is closed by being sewn, taped, glued or plastic welded. Advantageously, the bag 100 is fabricated entirely of compostable polypropylene, PP.
The open end 122 is adapted for being closed and sealed after the bag 100 has been filled with contents, as will now be discussed. A structural component of the first panel 106 includes a first adhesive layer 600 on a portion of the first panel 106. A structural component of the second panel 108 includes a second or further adhesive layer 602 on a portion of the second panel 108. According to an embodiment of the invention, the adhesive layer 600 and the further adhesive layer 602 are applied simultaneously. According to another embodiment of the invention, the adhesive layer 600 and the further adhesive layer 602 can be the same material applied simultaneously or, alternatively, applied separately.
An embodiment of the method of making the bag 100 of
In
Further, in
The bag 100 is foldable along a fold line 206 extending across the bag 100, wherein the fold line 206 extends across the first panel 106 between a panel first section 202 adjacent to a panel second section 204. The bag 100 is foldable without creasing, or alternatively is foldable along a crease formed along the fold line 206 by a creasing apparatus. The first adhesive layer 600 is applied on the first section 202 of the first panel 106, and on the second section 204 of the first panel 106, and on the exposed portions 118, 120 of the side gussets 110 exposed by the stepped or step cut construction. The adhesive layers 600, 602 are dried similarly as described above.
In
According to embodiments of the invention, an adhesive material was required to be developed to provide a first adhesive layer 600 of heat activated adhesive material on a portion of the bag 100. The same or another adhesive material was required to be developed to provide a second adhesive layer 602 of heat activated adhesive material on another portion of the bag 100, wherein heat activation temperatures of the first adhesive layer 600 and the second adhesive layer 602 are below the softening point temperature of the polymeric material of the bag 100, and wherein the adhesive layer 600 can be urged into contact with the further adhesive layer 602 and form an adhesive-to-adhesive seal to close and seal the bag 100 at its end 122. Sealing was advantageously to be performed by using existing end-user production line equipment for applying controlled temperature heat to activate the adhesive layers 600, 602 to adhesive states. A soluble adhesive was developed, wherein the adhesive layer 600 and the adhesive layer 602 comprise an adhesive material soluble in an air dryable solvent. For example, the adhesive layer 600 and the further adhesive layer 602 comprise adhesive material or materials soluble in water and air dried to dimensionally stable, non-adhesive states impervious to water or water vapor.
The adhesive layer 600 and the further adhesive layer 602 comprise respective adhesive materials having a melt temperature below 300° F., which is below the softening point temperature Tg of the polymeric materials in the layers 102, 104 of the bag 100. Further, each of the adhesive layer 600 and the further adhesive layer 602 comprise adhesive materials dried in air, at a temperature below the temperature required to activate to adhesive states.
Then, the embodiments of the bag 100 are prepared for storage and shipment. The end 122 of the bag 100 is pinch closed by closing the first panel 106 and the second panel 108 against each other at their end edges adjacent the open end 122. The end 122 of the bag 100 is folded flat while remaining unsealed, and the bag 100 is folded flat for storage and shipment to another manufacturing facility wherein the end 122 of the bag 100 is opened, the bag 100 is unfolded and expanded from the flat configuration, and the bag is filled with contents. Then, the end 122 is closed and sealed. The adhesive layers 600, 602 are activated to an adhesive state by applying heat at a heat activation temperature below the heat activation temperatures of standard or traditional hot melt adhesives or solvent based adhesives that can seal traditional paper and polymer laminated bags without damaging the paper layers, but which exceed the softening point temperature Tg of polymeric bags 100 fabricated without paper layers. The standard or traditional hot melt adhesives cannot be combined with polypropylene bags 100 because the temperatures needed to activate the adhesives are destructive to the PP material structure.
Embodiments of the adhesive layers 600, 602 comprise, an aqueous dispersion of an adhesive material or a water based adhesive materials applied in liquid form and air dried or cured to a stable, non-adhesive state when air dried to ambient temperature. Further embodiments of the adhesive layers 600, 602 each are an acrylic based waterborne adhesive or a polyurethane dispersion adhesive, or a butyl, synthetic or natural rubber adhesive. Other embodiments of the adhesive layers 600, 602 include a polyurethane adhesive dispersed in water (PUD). A preferred embodiment is made up of 35 percent solids. It is applied at 1.75 grams/bag wet, assuming an 18″ wide bag, across the 3″ sealing area. The viscosity is adjusted to correspond with the mass flow rate of the preferred embodiments of an applicator apparatus and method, for example, a slot die applicator applying a stripe of the adhesive layers each of a viscosity of 800-1000 centipoises and a coating weight sufficient to form an adhesive-to-adhesive seal that will withstand bag tests to be described herein.
An embodiment of the adhesive layers 600, 602 for pinch sealing of PP woven bags 100 is comprised of synthetic polymer or co-polymer emulsions that are water- or solvent-based, including without limitation polyurethane dispersion adhesives, vinyls, acrylics, or other polymer or co-polymer emulsions, or may include natural or synthetic rubber-based adhesives, which are applied wet solubilized and then dried to a hardened state impervious to water and water vapor. Known application apparatus to use on a production line includes, but is not limited to spray applicators, wheels, or a slot die applicators. The adhesive layers 600, 602 form an adhesive-to-adhesive seal when activated to adhesive states by heat applied by a hot air jet or other thermal source at an elevated temperature up to about and less than about 300 degrees F. which is below the melting point temperature of the polymeric, polyolefin films and/or PP woven materials of the bag panels 106, 108 and the bag gussets 110 when present. Such adhesive layers 600, 602 provide adequate bond and adhesion to polyolefin films and/or PP woven materials, are FDA approved for non-direct food contact, and provide adequate sheer, peel and bond strengths to meet bag testing parameters to be described herein.
Two adhesive layers 600, 602 in particular are an acrylic based waterborne adhesive and a polyurethane dispersion adhesive. Each has an adhesive state activation temperature below 300° F., and below the softening point temperature Tg of the polymeric layers 102, 104 made of compostable polypropylene, for example.
An embodiment of the adhesive layers 600, 602 includes: a polyurethane adhesive dispersion of 35% solids in water, with a viscosity adjusted for application to the bags, for example, a viscosity of approximately or about 800-1000 centipoises for application by a slot die applicator, or less than about 800 centipoises for application by a spray applicator. The viscosity is varied or adjusted to obtain an optimum mass flow rate and attain a desired coating weight as need for application by a specific form of applicator. Adhesive 1623-63A, is available commercially from Bostik, Inc. Wauwatosa, Wis. 53226, USA, wherein the adhesives per se form no part of the present invention separate from being a structural component of the bags disclosed herein. The embodiments of adhesive layers 660, 602 as a structural component of the bags includes 1.75 grams adhesive material per bag applied wet, solubilized in water, assuming an 18 inch wide bag and a 3 inches wide stripe of adhesive on the bag, which is equivalent to 0.6 grams per bag dry or about 10.6 lbs per ream dry weight coating. Once the adhesive layers 600, 602 are applied, they must pass under a drying system to evaporate the water and dry the adhesive layers to a stable state impervious to water, water vapor and ambient temperatures.
The bag 100 includes heat sealable material or materials on a low melt temperature, woven and solid polyolefin films. The suitable adhesive material or materials are applied to the bag surfaces as a solution or emulsion, and are air dried at temperatures below their heat activation temperatures to evaporate the volatiles of solvent or water and solidify. The solid adhesive materials are not moisture or pressure sensitive to activate to an adhesive state, and thereby avoid contamination of the bag contents during bag filling.
One suitable adhesive material for heat sealing polyolefin films of the bag 100 comprises a water based emulsion of triethylamine adhesive commercially available as AQUAGRIP® l9566F, manufactured by Bostik, Inc., 11320 Watertown Plank Road, Wauwatosa, Wis. 53226 USA. The water based emulsion comprises triethylamine Cas #121-44-8 Percent 0.5-1.5 which can be absorbed through the skin.
Before use consult the Material Safety Data Sheet (MSDS) for Material Name: L9566F prepared and distributed pursuant to the Federal Hazard Communication Standard: 29 C.F.R. 1910.1200. The MSDS discloses the following:
Adhesive layers 600, 602 are applied on one or both bag panels 106, 108 across an area of width ranging from ½ inch to 6 inches across the entire or part of a bag panel 106, 108. The bag 100 is filled with contents through the open end 122 of the bag 100 where one or both panels 106, 108 have heat activated adhesive layers 600, 602 applied across the width of the open end 122 of the bag 100, wherein the first panel 106 and the second panel 108 are left unsealed to form an open bag end 122 through which bag contents are filled. Following a filling process, the panels forming an adhesive-to-adhesive seal, layer contact; the open bag end is then processed through a convention hot air or heat sealing apparatus, and the application of heat is at a temperature below the softening point temperature of the polymeric material to re-melt the first layer of adhesive material and the second layer of adhesive material preferably before making contact with each other, or alternatively, while in contact with each other.
After filling an embodiment of the bag 100 with contents on a manufacturing production line, the bag 100 is passed through a pinch sealing unit, not shown, that blows hot air onto the adhesive layers 600, 602 to activate the adhesive layers 600, 602 to adhesive states.
In the embodiment of
Similarly, in the embodiment of
Similarly, in the embodiment of
An embodiment of structural components of a polymeric woven bag 100 includes a polymeric outer layer 104, an inner polymeric woven bag layer 102 laminated to or adhesively adhered to the outer layer 104, a first panel 106 and a second panel 108 and an open end 122 of the bag 100 to be pinched closed between the first panel 106 and the second panel 108 after filling the bag 100 with contents, a structural component of a portion of the first panel 106 having a heat activated first adhesive layer 600 on a portion of the first panel to form an adhesive-to adhesive seal by contact with a heat activated adhesive layer 660 on a structural component of a portion 108 or 502 of the second panel 108, wherein the first adhesive layer 600 and the second adhesive layer 602 have respective heat activation temperatures below the softening point temperature of the polymeric material, and wherein the first adhesive layer 660 and the second adhesive layer 602 are dried and are water impervious, and wherein after filling the bag 100 with contents through the end 122 the first adhesive layer 600 and the second adhesive layer 602 are activatable to adhesive states by an application of heat at a temperature below the softening point temperature of the polymeric materials of the bag 100 to form the adhesive-to-adhesive seal.
Another embodiment of the structural components include a foldable flap portion 502 having a portion of the second adhesive layer 602 thereon to form the adhesive-to-adhesive seal.
The structural components must pass the following tests without tearing the first panel 106 or the second panel 106 or an embodiment of the sealing flap 502, and without opening the adhesive-to-adhesive seal between the first adhesive layer 600 and the second adhesive layer 602.
Bag Closure Test Requirements: 7 Point Drop Test
Creep Test
Peel and Sheer Data
Grease Resistance
1. 20 lbs. of pet food with a minimum of 20% fat content hung or suspend in an environmental chamber with the weight of the product against the sealed end being evaluated;
2. Suspension for at minimum, 72 hours at 140° F. at 70% relative humidity or other period adequate to test shelf-life and requirements suitable for the pet food market
Another embodiment of a suitable adhesive material for heat sealing polyolefin films of the bag 100 comprises a liquid state, acrylated epoxy based adhesive commercially available as the product name, VERSA-WELD™ 70-7879 adhesive material manufactured by Henkel Corporation P.O. Box 6500; 10 Finderline Avenue, Bridgewater, N.J. 08807 USA, wherein the adhesives per se form no part of the present invention separate from being a structural component of the bags disclosed herein.
VERSA-WELD™ 70-7879 adhesive material has a suggested running range of 162.78-190.55° C. (325-375° F.) designed for pre-application to polyethylene foam, and designed for application by slot (die) and roll coaters for high-viscosity hot melts.
Before use of the VERSA-WELD™ 70-7879 hot melt adhesive consult the Material Safety Data Sheet (MSDS) for Product Number 70-7879, IDH #1218687 prepared and distributed pursuant to the Federal Hazard Communication Standard: 29 C.F.R. 1910.1200. The MSDS discloses the following:
1. A hot melt adhesive chemical family having components:
2. Typical Physical Properties: Solid mixture; tan solid color; Odor slight; Viscosity 21,000 cps@ 176.67° C. (350° F.); Specific gravity 0.98; Bulk density 970.594 kg/m2 (8.1 lb/gal).
3. Insoluble in water
4. Boiling Point>(500° F.); Flashpoint>(500° F.). Storage temperatures 6.67-37.78° C. (20-100° F.).
5. Non-combustible fire and explosion hazard.
6. Hazard categories, distillates, petroleum, hydrogenated heavy naphthenic, ACGIH exposure limits 5.000 MG/M3 TLV-TWA (oil mist) only generated by spraying or use at elevated temperatures, OSHA exposure limits 5.000 MG/M3 TWA (oil mist) only generated by spraying or use at elevated temperatures.
7. No hazardous polymerization.
8. Stable under normal conditions.
9. Hazardous combustion products may include carbon monoxide, carbon dioxide and unknown hydrocarbons.
10. Skin exposure to hot melt adhesive material may cause thermal burns.
11. HMIS® Hazard Rating, a registered trademark of the National Paint and Coatings Association (NPCA); Health 0/2, Flammability 1; Reactivity 0. The adhesive material includes an air dryable solvent, and as used at elevated temperature can cause thermal burns and forms vapors and/or aerosols at elevated temperature that may be irritating to eyes and respiratory tract.
Polypropylene has a melting point temperature of ˜160° C. (320° F.), as determined by differential scanning calorimetry (DSC). The softening point temperature of polypropylene is below its melting point temperature. Thus, a polypropylene bag 100 can be heated to a temperature below its softening point temperature without causing heat damage of the polypropylene material.
Respective embodiments of hot melt adhesive materials disclosed herein are applied to a bag 100 according to a process now to be described. Respective embodiments of the adhesive materials are heated to respective, recommended melt flow temperatures to obtain a liquid flow state. The melt flow temperature for an adhesive material to attain a liquid flow state can be greater than the melt temperature of a polymeric bag 100. Typically, the adhesive material is heated to attain a liquid flow state, to flow through an adhesive applicator apparatus. The adhesive material is heated to at least its melt flow temperature to flow as a liquid through an applicator apparatus. According to an embodiment of the invention, the adhesive material flows as a liquid through a spray applicator constituting a swirl gun applicator, which is capable of applying a thin coating of adhesive material, rather than a thicker bead of adhesive material. The adhesive material cools rapidly to a lower temperature below the melt temperature of polypropylene while being discharged from the applicator and applied by the applicator as a distributed thin coating onto the polypropylene surface of a bag 100. The discharged adhesive material cools rapidly due to its mass as a thin coating, which loses its thermal units of heat energy due to cooling in ambient air and due to heat transfer to the polypropylene. The thermal units of heat transfer to the polypropylene is insufficient to raise the temperature of the polypropylene to its softening point temperature. The adhesive material becomes more viscous at the lower temperature, and nonetheless retains a melt adhesive state to adhere to the polypropylene. The melt state adhesive forms the adhesive layers 600, 602 while at a temperature below the softening point temperature of the polymeric bag 100, which avoids heat damage to the bag 100. The adhesive layers 600, 602 solidify by being dried, to drive off solvent and to cool to ambient temperature. The adhesive layers 600, 602 formed by application of a water based emulsion solidify by being dried. The adhesive layers 600, 602 are rendered non-adhesive to the touch. The embodiments of adhesive material constituting the adhesive layers 600, 602 are non-adhesive at elevated ambient temperatures within a confined space in a truck or warehouse. Preferred embodiments of the solidified adhesive layers 600, 602 are insoluble in water including water vapor. The adhesive layers 600, 602 remain non-adhesive unless and until heated or re-heated to a melt state. The bag 100 is then folded flat for shipping and handling. The bag 100 is available for sale and purchase, for a purchaser to fill the big 100 with contents, followed by closing and sealing the bag 100 to avoid bag leakage and contamination of the contents.
After filling the bag 100 with contents through the open end of the bag 100, the adhesive layers 600, 602 are activated to respective melt adhesive states by heating to an elevated temperature. Unexpectedly the adhesive layers 600, 602 activate to adhesive states by heating them to an elevated temperature below the softening point temperature of polypropylene, and without heating the adhesive layers 600, 602 to their melt flow state temperatures recommended by the manufacturers. Instead, the adhesive layers 600, 602 are activated to respective melt adhesive states, by heating at least to temperatures at which melt occurs, near their softening point temperatures, as distinguished from the higher melt flow state temperatures recommended by their manufacturers. A softening point temperature of the respective layers 600, 602 is construed to mean an elevated temperature level at which the respective adhesive layers 600, 602 soften without melt occurring. A softening point temperature of polypropylene is construed to mean an elevated temperature at which polypropylene softens without melt occurring. The adhesive layers 600, 602 are heated to a temperature sufficient to activate the adhesive layers 600, 602 to melt adhesive states, which is sufficient for them to form an adhesive-to-adhesive seal at a temperature unexpectedly below the liquid flow temperature of the adhesive materials themselves, and which maintains the adhesive layers 600, 602 in viscous adhesive states and prevents them from undergoing excessive liquid flow by avoiding being heated to their liquid flow temperatures. For example, the adhesive layers 600, 602 are heated by blowing hot air at an air pressure of about 703-1055 gm/cm2 (10-15 lb/inch2) and at a temperature range of about 110-137.78° C. (230-280° F.), which is below their liquid flow temperature ranges.
The open end of the bag 100 is pinched closed while the adhesive layers 600, 602 engage against each other in melt adhesive states. According to an embodiment of a bag sealing process, the adhesive layers 600, 602 are heated to their melt adhesive states, and the open end of the bag 100 is pinch closed to engage the adhesive layers 600, 602 against each other while in melt adhesive states. According to an alternative embodiment of a bag sealing process, the open end of the bag 100 is pinch closed, and the adhesive layers 600, 602 engage each other while they are heated to their melt adhesive states.
Upon cooling to ambient temperature, the engaged adhesive layers 600, 602 solidify and become non-adhesive to the touch. Preferably the adhesive layers 600, 602 become insoluble in water including water vapor. The adhesive layers 600, 602 form an adhesive-to-adhesive seal to seal the pinch closed end of the bag 100 in a manner sufficient to withstand repeated, seven-point drop tests and to prevent bag leakage and contamination of contents.
This description of the exemplary embodiments is intended to be read in connection with the accompanying drawings, which are to be considered part of the entire written description. In the description, relative terms such as “lower,” “upper,” “horizontal,” “vertical,”, “above,” “below,” “up,” “down,” “top” and “bottom” as well as derivative thereof (e.g., “horizontally,” “downwardly,” “upwardly,” etc.) should be construed to refer to the orientation as then described or as shown in the drawing under discussion. These relative terms are for convenience of description and do not require that the apparatus be constructed or operated in a particular orientation. Terms concerning attachments, coupling and the like, such as “connected” and “interconnected,” refer to a relationship wherein structures are secured or attached to one another either directly or indirectly through intervening structures, as well as both movable or rigid attachments or relationships, unless expressly described otherwise.
Patents and patent applications referred to herein are hereby incorporated by reference in their entireties. Although the invention has been described in terms of exemplary embodiments, it is not limited thereto. Rather, the appended claims should be construed broadly, to include other variants and embodiments of the invention, which may be made by those skilled in the art without departing from the scope and range of equivalents of the invention.
This application is a Continuation-in-Part of U.S. patent application Ser. No. 12/508,710 filed Jul. 24, 2009 (E4919-00154), and claims the benefit of U.S. Provisional Patent Application No. 61/180,271 filed May 21, 2009 (E4919-00147) and the benefit of U.S. Provisional Patent Application No. 61/139,994 filed Dec. 22, 2008 (E4919-00144).
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