Adhesive for bag sealing application
Packaging bags having preapplied thereon a reactivatable adhesive.
The invention relates to a packaging system, and more particularly to a packaging bag having a reactivatable adhesive pre-applied to at least a portion thereof, more particularly a closable bag ending thereof.
BACKGROUND OF THE INVENTIONHot melt adhesives are widely used in various commercial applications including packaging applications, such as cardboard case sealing and carton and bag closing operations. Such hot melt adhesives are applied to a substrate while in its molten state and cooled to harden the adhesive layer.
In the conventional processes for the packaging of food and consumer goods, a packaging container is first filled with the goods, then a hot melt adhesive is applied, e.g., to the end flaps of the boxes, bag or other packaging material, on the packaging line and compression is exerted to seal the container. While this process works reasonably well, it requires the packaging company to devote a tremendous amount of time and attention to adhesive-related issues, including adhesive selection, processing, trouble-shooting, inventory, and maintenance of adhesive application equipment.
Re-activation or heat sealing of pre-applied adhesives is known and has been practiced in the art. Heat sealed closures and seams are commonly used in the manufacture of bags, whereby adhesive is coated on the inside of the bag seam or closure flap and subsequently sandwiched under intense heat and pressure using heated platens or bars. This direct application of heat and pressure renders the adhesive molten, after which a bond is formed. This application benefits from the ability to apply steady direct pressure to ensure intimate contact and sufficient wetting of the adhesive layer to the substrate. This process cannot be used for applications where high heat and/or pressure required for closing is not available or desirable. While focused hot air has been used in the reactivation of pre-applied adhesives used in sealing/closing operations, this method requires extremely large amounts of energy and can result in undesired heating of the packaging material, the packaged contents, the surrounding area and equipment. Moreover, line speed is slow.
A need continues to exist in the art for a packaging system that can advantageously be used in bag closing operations whereby the bag to be filled and sealed is provided to the packager with adhesive already applied to the bag and later, during the packaging process, re-activated in order to close or seal the bag. The current invention addresses this need.
SUMMARY OF THE INVENTIONThe invention provides a packaging bag comprising a reactivatable adhesive. A particular embodiment of the invention is directed to bags that have a top and/or bottom bag ending, wherein at least one bag ending has preapplied thereon a reactivatable adhesive composition. Included are flat, folded packaging bags having applied on at least one substrate surface thereof an adhesive capable of being activated upon exposure to short durations of radiant energy.
The hot melt adhesive composition used in the practice of the invention comprises an effective amount of an energy-absorbing ingredient such that upon exposure of the adhesive to radiant energy, the adhesive is activated. The energy-absorbing ingredient selected for use may be dissolved and/or dispersed within the adhesive composition. Organic dyes and pigments are particularly useful energy-absorbing ingredients for use in the practice of the invention. Adhesives comprising carbon black and NIR absorbing dyes are particularly preferred for use in the practice of the invention. Upon exposure to radiant energy, the adhesive melts to the extent that it is capable of bonding the substrate surface to a second substrate surface.
A particular preferred embodiment comprises packaging bag wherein a reactivatable adhesive comprising a near infrared energy absorbing ingredient is used at one or both ends of the bag and/or on the side seam.
Another embodiment of the invention is directed to a method of packaging items such as food and consumer goods, and packaged items. Examples of goods that can be packaged include food, pharmaceuticals, cosmetics, breakfast cereals, beverage containers, bakery items, dry foods (e.g., dog food), produce, household products, paper products, soaps and detergents, candy, popcorn, wet food, frozen food, diapers, light bulbs and the like.
In the practice of the invention, an item is packaged in to a bag by forming filling and sealing a bag having a reactivatable adhesive preapplied to at least one predetermined portion thereof. In one embodiment, the adhesive is located on a closable end flap region.
BRIEF DESCRIPTION OF THE DRAWING FIGURES Drawing
The invention encompasses bags having a closable end and an opposite closed or open end, and bags in which both ends of the bag are closable. Any type of packaging bag can be manufactured in accordance with the invention. Both flat tube style bags and bags having gussets may be manufactured in accordance with the invention. Also encompassed are block bottom and satchel bottom bags. Bags of the invention may constitute a secondary package (e.g., sealed bag within a cereal box) and/or be the primary package (e.g., flour, dog food).
The packaging material of the invention is typically a paper product, but is not limited thereto. Paper products are defined herein as any article of manufacture, at least a portion of which comprises paper. The paper product may be made totally of paper or partially of paper. The invention encompasses products made of either single (e.g., paper or plastic) or multiple layers (e.g., a paper laminate, a plastic/paper laminate, a plastic laminate).
In one embodiment, the bag comprises front and back panels and inwardly extending first and second gusseted side panels. The front and back panels and the first and second gusseted side panels each have an exterior surface and an interior surface collectively defining an interior region, a top end and a bottom end. Each of the front and back panel means and the first and second gusseted side panel means of the bag means may, if desired, comprise an inner ply of substantially grease proof paper material and an outer ply of paper material.
Each of the top ends of the front and back panel means and the first and second gusseted side panel means are operably sealable to one another before or after filling. The bottom ends will typically be operably configured to form a substantially sealed bottom region through adhesive attachment.
In the practice of the invention, the bag closure means comprises adhesive that is operably positioned adjacent to the top end of the interior surfaces of the front and back panel means and the corresponding adjacent portions of the first and second flaps of the first and second gusseted side panel means.
The adhesive and sealing method of the invention is particularly well suited for bags comprising an inner liner bag made of plastic or other meltable material. Such inner liner bags are used for purpose of sift proofing the bag and/or to prevent moisture ingress during shipping and storage. Bags of this type are conventional used in the packaging of, for example, powdered milk. When heat sealing bags that comprise an inner liner, such as PET liner, application of heat fuses the PET inner liner resulting in a bag that is partially unfillable.
In addition, the process of the invention, while useful in the sealing of pinch bottom bag endings, may be used in any bag ending configuration, resulting in bags that are more uniform in shape and more stackable.
The adhesive formulations of the invention may be pre-applied in a continuous or discontinuous, e.g., as evenly spaced beads or dots, manner depending on surface area and coating weight desired. Particular patterns may be used to optimize substrate/adhesive contact. Depending on the adhesive, the bead size, thickness, distance apart and pattern will vary. The adhesive may be pre-applied to the substrate by any method known in the art, and include, without limitation roll coating, painting, dry-brushing, dip coating spraying, slot-coating, swirl spraying, printing (e.g., ink jet printing), flexographic, extrusion, atomized spraying, gravure (pattern wheel transfer), electrostatic, vapor deposition, fiberization and/or screen printing. The method of pre-application to the substrate is not critical to the practice of the invention.
Reactivation, as this term is used herein, refers to an adhesive that resides on at least a portion of at least one substrate to be bonded. In the context of a hot melt adhesive, the adhesive has been applied to a substrate in the molten state and allowed to cool, i.e., solidify, thereon. The adhesive present on the substrate is thereafter reactivated or heated to a molten state, brought in contact with a second substrate and allowed to cool or solidify, thereby bonding the two substrates together. The application of the adhesive onto a substrate for later activation or “reactivation” is referred to herein, and in the art as a “pre-applied” adhesive.
The reactivation efficiency of an adhesive refers to the ability of the adhesive to reactive, e.g., become molten in a short period of time. Reactivation efficiency will depend on the power of the device and the distance of the energy source from the adhesive. Reactivation time depends on receptivity of the adhesive, which depends on the energy absorbing ingredient, the coating weight or thickness of the adhesive and the energy flux density that the radiant source can supply to the adhesive (e.g., intensity per unit area). Energy flux density refers to the distance, focal point, power and intensity of the lamp or power source.
Preferably, the reactivatable adhesives are formulated to reactivate to a temperature of at least about 200° F., more preferably to a temperature of at least about 250° F. upon exposure of less than about 1200 watts/sq inch of near infrared energy for a period of less that about 10 seconds, more preferably less than about 5 seconds, even more preferably less than about 2 seconds.
The adhesive compositions applied to the packaging substrate contain an energy absorbing ingredient that increases the absorption and reduces the transmission of radiant energy that creates a temperature distribution within the adhesive that optimizes performance. The adhesives have improved re-activation and performance properties after irradiation. The adhesives of the invention reactivate on exposure to short durations of radiant energy and provide superior on-line performance and set speed that allows for quicker production speeds.
The improved re-activation and performance may preferable be achieved by incorporating into an adhesive an energy-absorbing ingredient. Energy-absorbing ingredients include those dyes, pigments, fillers, polymers, resins, and/or other ingredients that are capable of absorbing energy and provide an optimal balance of absorption, reflection, transmission and conduction.
It has been discovered that when a suitable energy-absorbing ingredient is added to a conventional adhesive, reactivation upon short duration of radiant energy can be achieved. Energy-absorbing ingredients contemplated for use in the practice of the invention are commercially available and include, but are not limited to dyes, pigments and fillers. Examples include carbon black, graphite, Solvent Red (2′,3-dimethyl-4-(2-hydroxy-naphthylazo)azo-benzene), Solvent Green, dyes such as Forest Green and Royal Blue masterbatch dye available from Clariant, cyanine-based dyes, oxides such as such as titanium dioxide, and metals such as antimony, tetrakis)dialkylaminophenyl)aminium dyes, cyanine dyes, squarylium dyes and the like.
Pigments, such as carbon black and graphite, are particulate in nature and will usually have somewhat of a spherical shape with average particle sizes in the range of about 0.01 to about 7 microns. Pigment particles aggregate, so aggregate size will be larger. The pigment aggregate size in hot melt adhesives will preferably be smaller than about 500 microns. Aggregate sizes of less than about 100 microns are preferred, more preferably smaller than about 50 microns.
A wide variety of organic NIR triggers are described in the literature and are available for use in the practice of the invention. Such compounds include cyanine, metal complexes, quinone, azo, radical multiphenylmethane, perylene, aromatic annulenes, fluorenylium. Such triggers possess various absorption characteristics. For example, halogen substituted 1,4,5,8-tetraanilioanthraquinones have excellent transmittance in the vicinity of 860 nm and can absorb NIR in other ranges. Another example is squaraine, which is characterized by intense narrow absorption bands at relatively long wavelength. Also specifically designed phthalocyanine compounds have been demonstrated exhibiting high transmittance to visible light and offering high efficient cut of near infrared.
Preferred energy-absorbing ingredients for use in the practice of the invention are broad band near IR absorbers such as Epolight 1125 (Epolene, Inc), SDA6248 (H.W. Sands Corp.), SDA2072 (H.W. Sands Corp.) and carbon black. Carbon black can be purchased from Cabot under trade name of Monarch, Regal, Black Pearl, and Elftex, or Degussa (FW series), or from Columbian Chemical Company (Raven Series). Carbon black can be manufactured by different methods such as the furnace black method, the gas (channel) black method, and the lamp black method. The key parameters affecting the radian energy absorption of carbon black prepared by these various methods are average primary particle size, surface chemistry and aggregate structure.
Energy absorbing ingredients for use in the practice of the invention will typically have an absorption in the range of from about 400 nm to about 100,000 nM, more preferably from about 700 nm to about 10,000 nm, even more preferably from about 750 nm to about 5000 nm.
Suitable energy-absorbing ingredients for use in reactivatable adhesives of the invention may be identified by blending a desired adhesive with a chosen additive of various particle size and various amounts. Any conventional method of blending the energy-absorbing ingredient with the adhesive such as through use of a paddle mixer or high shear mixer such as Ross M E-100LC extruder, as would be apparent to the skilled practitioner, may be used to prepare the adhesive compositions of the invention. The starting adhesive and the adhesive containing the energy-absorbing ingredient then are compared by heating samples of each with a light from a radiant heat source. The samples are tested for reactivation efficiency and bonding performance, as described in detailed in the Examples. Reactivation efficiency is the ability the adhesive to become molten in a short period of time. Suitable additives are those that reactivate quickly and exhibit acceptable bond strength. Preferred are thermoplastic adhesives which, when pre-applied to a substrate, re-activates with a short duration of exposure to radiant energy, preferably less that about 10 seconds, more preferably less than about 5 seconds, and provides acceptable bond force after a short period of compression or cooling, preferably a period of less that about 30 seconds, more preferably less than about 15 seconds.
Included in the practice of the invention are adhesives comprising absorber coated fillers and encapsulated absorbers. For example, the adhesive may comprise a cureative encapsulated within a shell comprising a NIR absorbing agent. Exposure to NIR energy melts the capsule thereby expelling the curing agent and allowing for cure of the adhesive.
The term tubular, as in a tubular package or tubular packaging capsule is not limited to a cylindrical shaped package but encompasses rectangular shaped packages as well as triangular, hexagonal, pentagonal, octagonal and the like shaped packaging. Packaging containers can have a rectangular, circular, square or other shaped cross-section.
In accordance with the practice of the invention, the converter, in addition to applying adhesive to the side seal location, applies to at least one predetermined location an amount of adhesive sufficient to seal the bag ending. The adhesive applied to the bag ending comprises an energy-absorbing ingredient. By including an energy-absorbing ingredient, the absorption, reflection and transmission characteristics of the adhesive composition is tailored so as to optimize the composition's re-activation and subsequent bond formation. The adhesive is applied to the substrate and, depending on the type of adhesive applied, allowed to dry or solidify. Such adhesives are capable of reactivating upon short duration of exposure to radiant energy, preferably less that about 10 seconds, more preferably less than about 5 seconds, even more preferably less than about 2 seconds, and provides acceptable bond force after a short period of compression or cooling, preferably a period of less that about 30 seconds, more preferably less than about 15 seconds.
Thus, the flat folded configuration supplied to the packager has all the adhesive elements required to seal the container and the packager can avoid applying adhesive in the packaging line and avoid the problems associated with such application. The bag ending may be sealed prior to filling or after filling as desired by the packager and/or dictated by the type of material to be packaged in the bag of the invention.
Radiant energy can be supplied by a number of sources, as will be apparent to the skilled practitioner. Both coherent and non-coherent sources may be used. Examples include lasers, a high pressure xenon arc lamp, a coiled tungsten wire, ceramic radiant heater, tungsten-halogen lamps and ultrasonic waves. In a preferred embodiment, radiant energy within the near infra-red (NIR) region is used. Peak wavelengths of from 400 nm to about 100,000 nm may be used. More typically, wavelengths of from 700 nm to about 10,000 nm, most typically from about 750 nm to about 5000 nm will be used in the practice of the invention. Commercial sources of equipment capably of generating radiant heat required for use in the practice of the invention include Research Inc. (Eden Prairie, Minn.), Chromalox (Ogden, Utah), DRI (Clearwater, Fla.), Advent Electric Inc. (Bridgeport, Pa.), and Glo-Quartz Inc. (Mentor, Ohio).
It is to be understood that the terms “bottom” and “top” are relative terms and not terms used to designate the top or bottom of the finished packaged article.
The specific source of energy and distance from the surface to be irradiated will be dictated by the type and amount of adhesive used. In one embodiment, the energy source is NIR radiation. It is to be understood that the selection and duration of the radiant energy used will depend on the energy absorbing material incorporated into the adhesive located on the container being sealed.
In contrast to adhesives applied on the packaging line, and to conventional heat seal hot melt adhesives, it has been discovered that adhesive reactivated in accordance with the invention have improved performance properties. Moreover less adhesive is required to be used. Bag endings used in the practice of the invention will typically be coated with from about 0.5 mil to about 15 mil of adhesive. The adhesive present on the carton blank reactivates upon exposure to short durations of radiant energy and provide superior on-line performance and set speed which allows for quicker production speeds.
The type of adhesive that can be reactivated in accordance with the invention is not particularly limiting or critical to the practice of the invention. Reactivatable adhesives encompassed by the invention include but are not limited to hot melt adhesives, waterborne adhesives, solvent borne adhesives, moisture curable adhesives, ultraviolet curable adhesives, blocked urethane systems, epoxy based adhesives, and adhesives comprising an encapsulated cureative or the like. Thermoplastic and hot melt adhesives are particularly useful when formulated for pre-application and subsequent later reactivation and are particularly useful for case and carton sealing. It will be apparent that a thermoplastic adhesive present on a substrate may be applied to a substrate in the form of a waterborne emulsion or solution.
The energy-absorbing ingredient may be added, with stirring, any time during the preparation of the base adhesive, or following preparation of the base adhesive. The amount added will depend on the type of adhesive, the energy-absorbing ingredient used, the size of the energy-absorbing ingredient and the dissolution or dispersion properties of the energy-absorbing ingredient. The additive is added in an amount effective to reactivate the adhesive upon exposure to short durations (typically less that 10 seconds) of radiant energy. Typically, the additive will be present in an amount of about 0.001 to about 10 parts per 100 parts of the adhesive composition.
Substrates to be bonded include virgin and recycled kraft, high and low density kraft, chipboard and various types of treated and coated kraft and chipboard. Composite materials are also used for packaging applications such as for the packaging of alcoholic beverages. These composite materials may include chipboard laminated to an aluminum foil which is further laminated to film materials such as polyethylene, mylar, polypropylene, polyvinylidene chloride, ethylene vinyl acetate and various other types of films. Additionally, these film materials also may be bonded directly to chipboard or kraft. The aforementioned substrates by no means represent an exhaustive list, as a tremendous variety of substrates, especially composite materials, find utility in the packaging industry.
By modifying the placement of adhesive on the substrate (e.g., top or bottom end flap, vertical side section), the size or surface area, the shape and/or pattern of the adhesive applied to the substrate, packaging may be designed to control the amount of force required to open a sealed package, i.e., control the ease of opening. Thus packaging can be designed that is child proof or, alternatively, geriatrically friendly (i.e., easy open). The adhesive formulations of the invention may be pre-applied in a continuous or discontinuous, e.g., as evenly spaced beads or dots, manner depending on surface area and coating weight desired. Particular patterns may be used to optimize substrate/adhesive contact. Depending on the adhesive, the bead size, thickness, distance apart and pattern will vary.
Drawing
The invention is further illustrated by the following non-limiting examples.
EXAMPLESReactivation efficiency and bonding performance of various hot melt adhesives were determined as follows:
Near Infrared (NIR) Reactivation Test
Adhesives were cast into films of 2 inch long, 1 inch wide, and 2 mm thick. The film was placed underneath a halogen tungsten lamp (250 W/120 V) of 35 mm long. The lamp was located in an aluminum reflector and the distance between the lamp filament and the adhesive top surface was kept constant (24.5 mm). The input voltage of the lamp was precisely controlled so that the power of the lamp was 140 W. The adhesive film was heated by the lamp for 20 seconds and the surface temperature of the adhesive film was continuously measured using an infrared thermal probe. The surface temperature (temperature after 20 second irradiation, beginning temperature of 70° F.) reported in the tables below are the average of six samples tested for each formulation.
Bond Strength Test
Adhesives in a bead shape were pre-coated on corrugated paperboard at the coating weight of 1.5 g/m. The bead cross-section had a dimension of 2 mm×2 mm. The pre-applied adhesive beads were cooled down to room temperature and then were subjected to NIR radiation for various periods of time. NIR radiant energy was emitted by a 240 W halogen tungsten lamp, which was placed in an aluminum reflector. The distance of the lamp filament and the adhesive bead was precisely controlled as 10.5 mm. After being radiated, the adhesive bead was exposed to air for 3.5 seconds and then another corrugated substrate (2″×2″) was placed on the top of the adhesive bead to form a bond. The bond was pressed at 1 kgf/cm2 for a certain period of time and then was pulled apart. The resulting bond force, adhesive bead flatness, and the percentage of fiber tear were recorded. The bead flatness measured the deform-ability and flow-ability (i.e., the level of reactivation) of the hot melt adhesive under the test condition.
Example 1This example illustrates the influence of the concentration of the energy-absorbing ingredient on the reactivation efficiency and bonding performance.
A sample (Sample A) of an EVA, paraffin wax, and hydrocarbon tackifier-based hot melt adhesive available from National Starch & Chemical Company (Cool-Lok® 34-2125) was compared to adhesive samples (Samples B-F) to which various amounts of carbon black (Regal 400, Cabot) had been added. Samples B-E were prepared by fully blending the adhesive and Regal 400 using a paddle mixer and all Samples had the same level of dispersion quality. The increase in adhesive temperature that occurred during the NIR reactivation test (described above) was determined and is reported in Table 1. In the Bond Strength Test, the adhesive bead was radiated for 0.3 seconds, and the bond was pressed for 15 seconds. Results (bond force, % bead flatness and % fiber tear) are reported in Table 1.
This example illustrates the utility of various NIR absorbing dyes as the energy-absorbing ingredient in providing short reactivation time and high bond strength. These dyes were dissolved homogeneously into the base hot melt adhesive (Cool-Lok 34-2125) and absorbed impinging radiant energy, most preferably ranging from 400 nm to 5000 nm in wavelength. Epolight 1125 is a green dye available from Epolight, near IR-1050 and near IR-1048 are dyes available from Aldrich, Inc. The samples were prepared by uniformly blending the adhesive and dye with a paddle mixer. The influence of NIR absorbing dyes on reactivation efficiency is shown in Table 2.
A construct comprising two PET layers sandwiched between paper layers were used as substrate material. To one of the substrate surfaces, Cool-Lok 34-212 modified to contain 0.2 wt % Epolight 1125 was applied and allowed to solidify. 24 hours later the adhesive was reactivated using a 3200 watt broad band emitter as the source of near-IR light. The size of the energy source was 22 inches long, 4 inches deep, and 1.5 inches in width. A second substrate was pressed onto the surface of the reactivated adhesive.
Table 3 shows reactivation at different speeds. Tables 4 and 5 show reactivation at different power levels. In each case, reactivation occurred without fusion the PET layers.
Many modifications and variations of this invention can be made without departing from its spirit and scope, as will be apparent to those skilled in the art. The specific embodiments described herein are offered by way of example only, and the invention is to be limited only by the terms of the appended claims, along with the full scope of equivalents to which such claims are entitled.
Claims
1. A packaging bag having preapplied to at least a portion thereof a reactivatable adhesive, wherein the reactivatable adhesive comprises an effective amount of an energy-absorbing ingredient such that upon exposure of the adhesive to radiant energy having a wavelength of from about 400 nm to about 100,000 nm the adhesive is activated, said process comprising exposing the applied adhesive with radiant energy having a wavelength of from about 400 nm to about 100,000 nm for a time sufficient to melt the adhesive, bringing one of said substrates in contact with the melted adhesive on the other substrate, and allowing the adhesive to solidify thereby bonding the first substrate to the second substrate.
2. The bag of claim 1 wherein the adhesive is activated upon exposure to radiant energy having a wavelength of from about 700 nm to about 5000 nm.
3. The bag of claim 1 wherein the preapplied adhesive is exposed to said radiant energy for a period of time of less than about 5 seconds.
4. The bag of claim 1 wherein the preapplied adhesive is exposed to said radiant energy for a period of time of less than about 2 seconds.
5. The bag of claim 1 comprising at least one closable bag ending, said adhesive being present on said bag ending.
6. The bag of claim 5 wherein the bag is made of coated paper.
7. The bag of claim 5 comprising a plastic liner bag.
8. The bag of claim 1 wherein the adhesive preapplied to said bag comprises an organic dye.
9. The bag of claim 1 wherein the adhesive preapplied to said bag comprises a pigment.
10. The bag of claim 9 wherein the adhesive comprises carbon black.
11. The bag of claim 1 wherein the reactivatable adhesive is a thermoplastic adhesive.
12. The bag of claim 1 wherein the reactivatable adhesive is a hot melt adhesive.
13. A process of packaging an article by forming, filling and sealing a packaging bag that has had applied to at least a portion thereof a reactivatable adhesive, wherein said process comprising forming and/or sealing a packaging bag by exposing the applied reactivatable adhesive to radiant energy for a time sufficient to reactivate the adhesive, said radiant energy having a peak wavelength of from about 400 nm to about 100,000 nm.
14. The process of claim 1 wherein the adhesive is activated upon exposure to radiant energy having a wavelength of from about 700 nm to about 5000 nm.
15. The process bag of claim 1 wherein the preapplied adhesive is exposed to said radiant energy for a period of time of less than about 2 seconds.
16. The process of claim 13 wherein the adhesive preapplied to said bag comprises an organic dye.
17. The process of claim 13 wherein the adhesive preapplied to said bag comprises a pigment.
18. The process of claim 17 wherein the comprises carbon black.
19. The bag of claim 13 wherein the reactivatable adhesive is a thermoplastic adhesive.
20. The bag of claim 13 wherein the reactivatable adhesive is a hot melt adhesive.
Type: Application
Filed: May 25, 2004
Publication Date: Dec 15, 2005
Inventors: Demetrius McCormick (Belle Mead, NJ), James Nowicki (Hopewell, NJ)
Application Number: 10/853,750
