US20140037876A1

US20140037876A1 - Hot melt adhesives for multilayer structure enclosures

Info

Publication number: US20140037876A1
Application number: US14/048,304
Authority: US
Inventors: Christine Esangbedo; Patrick Hayes
Original assignee: Henkel US IP LLC
Current assignee: Henkel Corp; Henkel US IP LLC
Priority date: 2011-04-08
Filing date: 2013-10-08
Publication date: 2014-02-06
Also published as: EP2694608A4; BR112013025523A2; CN103459534A; WO2012138689A3; WO2012138689A2; KR20140012707A; EP2694608A2; JP2014517851A

Abstract

The invention provides enclosure adhesives, methods of using the adhesives to bond for enclosing a multilayer structure and to articles of manufacture comprising the adhesives. The multilayer structure is a laminant of at least one composite film and at least one Kraft paper substrates. It has been discovered that an adhesive that comprises (a) a mixture of 1:1 to 5:2 of a metallocene catalyzed polyolefin copolymer with a density greater than or equal to 0.880 g/cm³to a metallocene catalyzed polyolefin copolymer with a density less than 0.880 g/cm³; (b) a compatible tackifier; and (c) a compatible wax, has high adhesion to both Kraft and composite film with low blocking properties.

Description

FIELD OF THE INVENTION

The present invention relates to adhesives for multilayer structure enclosures, more specifically to bond Kraft paper and composite films in pinch bottom bags.

BACKGROUND OF THE INVENTION

Pinch bottom bags are manufactured from multilayer plies or structure, which are laminated plies of composite film(s), Kraft paper(s) and optionally plastic liner(s). The multilayer structures are fabricated to form a tube, and then pinched, whereby one end of the tube is enclosed by folding over the end as a flap and then sealing the flap with an adhesive. In another configuration, the tube is enclosed by tucking or folding a sufficient amount of the sides of the bag inwardly and folding over the flap and then sealing the flaps with the adhesive. The opposite end of the individual bags is left open, to be closed and sealed later by, for example, the customer after filling.
An adhesive can be pre-applied onto the remaining open-end, and this adhesive can be reactivated after filling the bag and then fully sealed. Like the above pinching processes, the remaining end is sealed as a folded flap with the reactivated adhesive.
A great advantage of the pinch bottom bags is that empty bags are flat and many empty bags may be stacked into a relatively small space. This reduces the costs of shipping many empty bags from the manufacturer to the user. However, because the empty bags are stacked, stored and shipped, and often subjected to wide temperature range in storage area, the pre-applied adhesives can prematurely adhere to adjacent stacked bags, a phenomenon known as “blocking.” Blocking can cause the bags to stick to each other and causes problems at the customer processing stage. At this stage, bags must separate easily for the machinery to pick only one bag at a time for filling.
Pinch bottom bags are very useful for holding bulk quantities of material. The bags are well suited to holding bulk dry materials such as granulated products. The bags are easily filled, and easily sealed. Once sealed, the bags are durable and typically avoid sifting or leakage. In contrast to bags that are sewn closed bags, pinch bottom bag closures substantially eliminate the risk of air, water, and insects reaching the filled goods.
Developments in polymer technology have allowed for a new generation of composite film substrates of the multilayer structure. The composite film substrates are made from various chemistry including nylon, polyolefin, polyester, and the like. Because the film substrates are different in composition and structure than Kraft paper, an adhesive that can bind the composite substrates together with low blocking is desirable.
US 20100158418 discloses an acrylic based waterborne adhesive and a polyurethane dispersion adhesives, which requires a drying system to evaporate the water and dry the adhesive layer.
US 20090159192 discloses pinch bottom bags with polypropylene based hot melt adhesive on polypropylene film. The adhesive is applied at a temperature to partially melt the polypropylene film together for better mechanical properties and adhesion.
There continues to be a need in the art for multilayer enclosure hot melt adhesives with desirable adhesion and low blocking properties with robust reactivation temperature window. The current invention addresses this need.

BRIEF SUMMARY OF THE INVENTION

The invention provides novel adhesives, methods of using the adhesives to bond multilayer enclosures, and articles of manufacture comprising the adhesives. In one embodiment, the adhesive comprises:
(A) a mixture of a metallocene catalyzed polyolefin copolymer;
(B) a compatible tackifier;
(C) a compatible wax; and
wherein the mixture (A) has a ratio of 1:1 to 5:2 of a metallocene catalyzed polyolefin copolymer with a density less than 0.880 g/cm³and a metallocene catalyzed polyolefin copolymer with a density greater than or equal to 0.880 g/cm³. It has been discovered that the above enclosure adhesive has high adhesion and low block properties to Kraft paper and composite films.
In a further embodiment, the adhesive further comprises additives, including radiation curable agents, blooming agents, antioxidant, defoamer and colorants.
Yet another embodiment is directed to the process of sealing the pinch bottom bags comprising:
(i) applying the aforementioned adhesive onto both open end flaps of a pre-formed tube, wherein the pre-formed tube is a multilayer ply, which comprises a composite film, Kraft paper and optionally a plastic liner;
(ii) folding over a sufficient amount of one flap to seal one end, whereby the adhesive seals one end of the tube;
(iii) cooling the remaining adhesive to room temperature;
(iv) reactivating the remaining adhesive with heat; and
(v) folding over a sufficient amount of the remaining flap to seal the remaining end, whereby the reactivated adhesive seals the remaining end.
Another aspect of the invention is directed to an article manufactured with the aforementioned enclosure adhesive. Articles of manufacture encompassed by the invention include multilayer bags, pinch bottom bags, case and carton, and the like.

BRIEF SUMMARY OF THE FIGURES

FIG. 1 is a diagram illustrating the adhesion test performed on composite film substrates.

FIG. 2 is graph of a modulus curve measured in Rheometrics Dynamic Mechanical Analyzer.

DETAILED DESCRIPTION OF THE INVENTION

All documents cited herein are incorporated in their entireties by reference.
In one embodiment, the composite film adhesive comprises:
(A) a mixture of a metallocene catalyzed polyolefin copolymer;
(B) a compatible tackifier;
(C) a compatible wax; and
wherein the mixture (A) has a ratio of 1:1 to 5:2 of a metallocene catalyzed polyolefin copolymer with a density less than 0.880 g/cm³and a metallocene catalyzed polyolefin copolymer with a density greater than or equal to 0.880 g/cm³.
The term “polymer or copolymer” as used herein, refers to a single (co)polymer or a blend of different (co)polymers produced by metallocene catalysis polymerization. The polymer component includes block and/or random copolymer. The copolymers are any polymers that have at least two monomers. Typical monomers are ethylene, propylene, butene and octenes. These copolymers typically have narrow molecular weight distributions and are available from various manufactures under the trade name Infuse (Dow Chemicals), Engage (Dow Chemical), Versify (Dow Chemical), Vistamaxx (Exxon Mobil), Exact (Exxon Mobil), Tafiner (Mitsui Petrochemical) and LMPO (Idemmitsu).
In one embodiment, the metallocene catalyzed polyolefin copolymer is a copolymer of ethylene and at least one comonomer selected from C_3-10alpha-olefins. In one particular embodiment, the copolymer is ethylene-octene.
The polymer component of the composite film adhesive is a mixture of a low and a high density polymer, or a mixture of a low crystalline polymer and a high crystalline polymer. It is widely known in the art that as the density of the polymer increases, the crystallinity of the polymer also increases. The ratio of the low to high density metallocene catalyzed polyolefin copolymer polymers range from 1:1 to 5:2. In another embodiment, the ratio of the low to high density metallocene catalyzed polyolefin copolymer polymers ranges from 1:1 to 2:1. The low density polymer is a metallocene catalyzed polyolefin copolymer with a density less than 0.880 g/cm³. The low density polymer can be purchased from Dow under the trade name Affinity. The high density polymer is a metallocene catalyzed polyolefin copolymer with a density greater than or equal to 0.880 g/cm³. The high density polymer can be purchased from Dow under the trade name Engage.
In another embodiment, the polymer is mixture of ethylene vinyl acetate polymers. The polymer mixture has a ratio of 1:1 to 5:2 of an ethylene vinyl acetate polymer with a vinyl acetate content greater than or equal to 28% and an ethylene vinyl acetate polymer with a vinyl acetate content less than 28%. In another embodiment, polymer mixture has a ratio of 1:1 to 2:1 of an ethylene vinyl acetate polymer with a vinyl acetate content greater than or equal to 28% and an ethylene vinyl acetate polymer with a vinyl acetate content less than 28%.
The composite film adhesive further comprises a compatible tackifier with a ring and ball softening point, typically measured in accordance with ASTM E28-58T, less than 120° C. Tackifiers that stays can combine with the polymer, without phase separating, is considered as compatible tackifier.
Useful tackifying resins may include any compatible resin or mixtures thereof such as natural and modified rosins including, for example, as gum rosin, wood rosin, tall oil rosin, distilled rosin, hydrogenated rosin, dimerized rosin, resinates, and polymerized rosin; glycerol and pentaerythritol esters of natural and modified rosins, including, for example as the glycerol ester of pale, wood rosin, the glycerol ester of hydrogenated rosin, the glycerol ester of polymerized rosin, the pentaerythritol ester of hydrogenated rosin, and the phenolic-modified pentaerythritol ester of rosin; copolymers and terpolymers of natured terpenes, including, for example, styrene/terpene and alpha methyl styrene/terpene; polyterpene resins; phenolic modified terpene resins and hydrogenated derivatives thereof including, for example, the resin product resulting from the condensation, in an acidic medium, of a bicyclic terpene and a phenol; aliphatic petroleum hydrocarbon resins; aromatic petroleum hydrocarbon resins and the hydrogenated derivatives thereof; and alicyclic petroleum hydrocarbon resins and the hydrogenated derivatives thereof, having a softening point, as determined by ASTM method E28-58T, of less than 120° C. Examples of hydrogenated aliphatic tackifiers particularly suitable include Eastotac C-100L, C-100R, C-100W, C-115L, C-115R, C-115W, H-100E, H-100L, H-100R, H-100W, H-115E, H-115L, H-115R, H-115W, Regalite C6100, Regalite C6100L, Regalite R1010. Regalite R1090, Regalite R1100, Regalite R1100CG, Regalite R7100, Regalite R9100, Regalite S1100, Regalite S5090, Regalite S5100 from Eastman Chemical Company; Escorez 5300, Escorez 5380, Escorez 5400, Escorez 5415, Escorez 5600, Escorez 5615, and Escorez 5690 from Exxon Mobil Chemicals, Arkon P115, Arkon P100, Arkon P90, Arkon M115, Arkon M100, Arkon M90 from Arakawa, and the like. Also included are the cyclic or acyclic C₅resins and aromatic modified acyclic or cyclic resins. Examples of commercially available rosins and rosin derivatives that could be used to practice the invention include SYLVALITE RE 100L, RE 110L, and SYLVARES RE 115 available from Arizona Chemical; Dertocal 140 from DRT; Limed Rosin No. 1,GB-120, and Pencel C from Arakawa Chemical. Examples of commercially available phenolic modified terpene resins are Sylvares TP 2040 HM and Sylvares TP 300, both available from Arizona Chemical.
Non-limiting examples include aliphatic olefin derived resins such as those available from Exxon under trade name and the Escorez series. Eastotac series from Eastman are also useful in the adhesive.
Also useful are aromatic hydrocarbon resins that are C₉aromatic/aliphatic olefin-derived and available from Sartomer and Cray Valley under the trade name Norsolene and from Rutgers series of TK aromatic hydrocarbon resins. Norsolene 1100 is a low molecular weight thermoplastic hydrocarbon polymer commercially available from Cray Valley.
Alpha methyl styrene such as Kristalex F115, 1120 and 5140 from Eastman Chemicals, Sylvares SA series with a ring and ball softening point less than 120° C. from Arizona chemicals are also useful as tackifiers in the invention. Mixtures of two or more described tackifying resins may be required for some formulations.
Small quantities of alkyl phenolic tackifiers can be blended with additional tackifier agents detailed above to improve the high temperature performance of these adhesives. Alkyl phenolics added in less than 20 wt % of the total weight of the adhesive are compatible and in the proper combination increase high temperature adhesive performance. Alkyl phenolics are commercially available from Arakawa Chemical under the Tamanol trade name and in several product lines from Schenectady International.
Preferred tackifiers are a mixture of aliphatic hydrocarbon resins and pentaerythritol esters of natural and modified rosins.
In one embodiment, the tackifier is typically present at about 15 to about 60 wt %, more preferably from 20 to about 55 wt %, based on the total weight of the adhesive.
The adhesives of the invention further comprise a wax. A wax is considered to be different than a polymer due to its lower molecular weight and lower viscosity.
Waxes suitable for use in the composite film adhesives have a viscosity of 20-10,000 cps at 140° C. (Brookfield visocometer, spindle 27, room temperature). Exemplary waxes include paraffin waxes, microcrystalline waxes, polyethylene waxes, polypropylene waxes, by-product polyethylene waxes, Fischer-Tropsch waxes, oxidized Fischer-Tropsch waxes and functionalized waxes. Functionalized waxes include acid or anhydride grafted onto polyethylene and polypropylene. Preferred functionalized waxes include ethylene maleic anhydride copolymers and propylene maleic anhydride copolymers. The functionalized waxes have a bound saponification number of about 2-90 mg KOH/g.
In the adhesive, the wax component will typically be present in amounts of 10 to about 30 wt %.
The composite film adhesives of the present invention may desirably also contain at least one stabilizer and/or at least one antioxidant. These compounds are added to protect the adhesive from degradation caused by reaction with oxygen induced by heat, light, or residual catalyst from the raw materials such as the tackifying resin.
Among the applicable stabilizers or antioxidants included herein are high molecular weight hindered phenols and multifunctional phenols such as sulfur and phosphorous-containing phenol. Hindered phenols are well known to those skilled in the art and may be characterized as phenolic compounds which also contain sterically bulky radicals in close proximity to the phenolic hydroxyl group thereof. In particular, tertiary butyl groups generally are substituted onto the benzene ring in at least one of the ortho positions relative to the phenolic hydroxyl group. The presence of these sterically bulky substituted radicals in the vicinity of the hydroxyl group serves to retard its stretching frequency, and correspondingly, its reactivity; this hindrance thus providing the phenolic compound with its stabilizing properties. Representative hindered phenols include; 1,3,5-trimethyl-2,4,6-tris-(3,5-di-tert-butyl-4-hydroxybenzyl)-benzene; pentaerythrityl tetrakis-3(3,5-d i-tert-butyl-4-hydroxyphenyl)-propionate; n-octadecyl-3(3,5-di-tert-butyl-4-hydroxyphenyl)-propionate; 4,4′-methylenebis(2,6-tert-butyl-phenol); 4,4′-thiobis(6-tert-butyl-o-cresol); 2,6-di-tertbutylphenol; 6-(4-hydroxyphenoxy)-2,4-bis(n-octyl-thio)-1,3,5 triazine; di-n-octylthio)ethyl 3,5-di-tert-butyl-4-hydroxy-benzoate; and sorbitol hexa[3-(3,5-d i-tert-butyl-4-hydroxy-phenyl)-propionate].
Such antioxidants are commercially available from BASF and include IRGANOX® 565, 1010, 1076 and 1726 which are hindered phenols. These are primary antioxidants which act as radical scavengers and may be used alone or in combination with other antioxidants such as phosphite antioxidants like IRGAFOS® 168 available from Ciba Specialty Chemicals. Phosphite catalysts are considered secondary catalysts and are not generally used alone. These are primarily used as peroxide decomposers. Other available catalysts are CYANOX® LTDP available from Cytec Industries and ETHANOX® 330 available from Albemarle Corp. Many such antioxidants are available either to be used alone or in combination with other such antioxidants. These compounds are added to the hot melts in small amounts, typically less than about 10 wt %, and have no effect on other physical properties. Other compounds that could be added that also do not affect physical properties are pigments which add color, or fluorescing agents, to mention only a couple. Additives like these are known to those skilled in the art.
Depending on the contemplated end uses of the adhesives, other additives such as radiation curable agents, blooming agents, pigments, dyestuffs, colorants, defoamer and fillers conventionally added to hot melt adhesives may be incorporated in minor amounts, i.e., up to about 10% by weight, into the formulations of the present invention.
The adhesive compositions of the present invention are prepared by blending the components in a melt at a temperature about 175° C. to form a homogeneous blend. Various methods of blending are known in the art and any method that produces a homogeneous blend. The blend is then cooled and may be formed into pellets or blocks for storage or shipping. These pre-formed adhesives can then be reheated to apply onto composite film substrates. The pre-formed adhesive can also be pre-applied for later reactivation. The reactivation means include heat and/or radiation.
Hot melt application of adhesives are well known to one of skill in the art. The adhesives of the present invention may be applied to a desired 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 application temperature ranges from about 275° F. to 400° F., preferably 300° F. to 375° F. The desirable viscosity ranges of the adhesive is from about 1000 to 50,000 cps at 350° F., preferably up to 35,000 cps, more preferably up to 20,000 cps.
The multilayer structure is made of at least one outer layer of a composite film and at least one Kraft paper inner layer. In some embodiment, a plastic liner is added as the innermost layer. In another embodiment, there are multiple layers of composite film and multiple Kraft paper layers constructed together in various forms to form the multilayer structure. While the multilayer structure contains multiple layers of different components, each of the layers may be different in length. Pinch bottom bags are often constructed with shorter plastic liner, longer Kraft paper and longest composite film. With such construction, the inner portion of the end flaps exposes the Kraft paper, which in turn folds over to bond onto the composite film surface.
The composite film of the multilayer structure is made of, for example, nylon (polyamide); polyolefin such as polyethylene, polypropylene, biaxially oriented polypropylene, polyethylene terephthalate, polyethylene terephthalate polyester, polytrimethylene; polyester; polyvinyl chloride; polystyrene; and the like. The composite film allows for better printability with higher gloss, grease-resistance, moisture-resistance, air-resistance, and durability, e.g., (puncture, tear and scratch resistance).
Kraft paper is typically porous and high elasticity and high tear resistance.
Similar to the composite film, the plastic liner is also made of nylon (polyamide); polyolefin such as polyethylene, polypropylene, biaxially oriented polypropylene, polyethylene terephthalate, polyethylene terephthalate polyester, polytrimethylene; polyester; polyvinyl chloride; polystyrene; and the like. The primary function of the plastic liner is barrier protection from air, grease and moisture.
Each layer of the composite film, Kraft papers and optionally plastic liner are laminated together with a lamination adhesive. The lamination adhesives include solvent-based adhesives and water-based adhesives. The aforementioned enclosure adhesive can also be used as a lamination adhesive.
In another embodiment, the process of sealing the pinch bottom bags comprises:
(i) applying the aforementioned adhesive onto both open end flaps of a pre-formed tube, wherein the pre-formed tube is a multilayer ply made of a composite film, Kraft paper, and optionally a plastic liner;
(ii) folding over a sufficient amount of one flap to seal one end, whereby the adhesive seals one end of the tube;
(iii) cooling the remaining adhesive layer to room temperature;
(iv) reactivating the remaining adhesive with heat; and
(v) folding over a sufficient amount of the remaining open flap to seal the remaining end, whereby the reactivated adhesive seals the remaining end.
In another configuration, the tube is enclosed by tucking or folding a sufficient amount of the sides of the bag inwardly and folding over the flap and then sealing the flaps with the adhesive and/or reactivated adhesive.
Other process steps may also be included, for example, printing the outer surface of the composite film with various information, such as the identity of the product, the manufacturer of the product, and the net weight of the bag after step (iii) of (v). Also, the bags may be filled in the after step (iii).
After sealing one end of the bag, the bags are stacked together and the pre-applied adhesive is exposed to its adjacent bag. It is desirable for the pre-applied adhesive to remain non-blocky and non-tacky during storage and transport, even under various temperature and humidity changes. During the bag filling stage, it is desirable for the bag to separate without much force. Blocking and tackiness of the adhesive will cause the bags to stick together which results in the machinery to pick up more than one bag during the user filling stage.
The adhesive is applied and/or pre-applied to the Kraft paper or to the composite film of the multilayer structure. During the pinching stage, the adhesive bonds the Kraft paper surface to the composite film surface. The Kraft paper surface is porous and has high surface energy, whereas the composite film surface is non-porous and low in surface energy.
The aforementioned adhesive creates a strong bond between the different surfaces of the composite film. In addition, the adhesive is flexible and allows movement of the filled bags, e.g., during storage and transportation, to prevent debonding at the enclosure sites.
Without being bound to any particular theory, high crystalline polymer (crystallinity is directly corrected to density in polymer) is typically formulated for such adhesives in order to achieve non-block performance. However, high crystalline polymer blends tends to poorly adhere to low surface energy surfaces. Surprisingly, the use of high crystalline polymer, even in significant quantity, achieves both desirable non-block and adhesion properties of the adhesive.
Another embodiment is directed to an article manufactured with the aforementioned composite film adhesive. Articles of manufacture encompassed by the invention include bags of different pinch type configurations, case, carton, trays and the like.

Example

Samples listed in Table 1 were prepared by using techniques known in the art. The components to each adhesive samples are listed in the Table. An exemplary procedure involved placing approximately half of the total tackifier in a jacketed mixing kettle, which is equipped with rotors, and raising the temperature to a range from about 100° C. to 200° C. When the tackifier melted, stirring was initiated and the rest of the components were added until a homogeneous mass was obtained.
High density polymer 1 is a metallocene catalyzed polyolefin with a density of 0.885 g/cm³measured in accordance with ASTM D 792.
High density polymer 2 is a metallocene catalyzed polyolefin with a density of 0.902 g/cm³measured in accordance with ASTM D 792.
Low density polymer is a metallocene catalyzed polyolefin with a density of 0.870 g/cm³measured in accordance with ASTM D 792.
Wax 1 is a polyethylene wax, with a Brookfield viscosity of <50 cps at 140° C.
Wax 2 is a maleic anhydride grafted polyethylene wax (SAP 25 mg KOH/g, Brookfield viscosity of 1700 cps at 140° C.).
Tackifier 1 is a Hydrogenated C5 aliphatic hydrocarbon tackifier with a Ring and Ball softening point (ASTM E 28) of 100° C.
Tackifier 2 is Hydrogenated C5 aliphatic hydrocarbon tackifier with a Ring and Ball softening point (ASTM E 28) of 115° C.
Tackifier 3 is a pentaerythritol ester of rosin tackifier with a softening point of 100° C.
Tackifier 4 is a pentaerythritol ester of rosin tackifier with a softening point of 110° C.
Anti-oxidant is a hindered phenol antioxidant.

TABLE 1

Adhesive Composition

Exam-	Exam-	Exam-	Exam-	Comp.
ple 1	ple 2	ple 3	ple 4	Example A

High density	20	0	0	0	0
polymer 1
High density	0	20	15	15	0
polymer 2
Low density	19.5	19.5	24.5	29.5	39.5
polymer
Wax
1	10	10	0	0	10
Wax 2	10	10	20	20	10
Tackifier 1	0	0	20	15	0
Tackifier 2	20	20	0	0	20
Tackifier 3	0	0	20	20	0
Tackifier 4	20	20			20
Anti-oxidant	0.5	0.5	0.5	0.5	0.5

Table 2 lists the performance properties of the samples listed in Table 1 and a polyamide based adhesive, Comparative Sample B, purchased from Arizona Chemical Company under the name of Unirez 2638.
Viscosity was measured at 350° F. using a standard Brookfield viscometer, spindle 27.
To test the adhesion, as illustrated in FIG. 1, (i) the adhesive (300) was applied onto the Kraft paper (200) at 350° F. with 6 mil thickness at 1″×1″ area on a 1″×3″ strip of Kraft paper; (ii) immediately mated 1″×1″ area of a 1″×3″ nylon (100) (Dartek® Cast Nylon 6,6 Films, Exopack) strip onto the applied adhesive and rubbed with hand to adhere; (iii) aged at room temperature (or 20° F. or 130° F. overnight) for about 8 hours; and (iv) pried the two strips apart by hand at the nylon corner (400). The adhesion is reported on a scale of 1-5, where 5 has the highest strength.
1. delaminates readily, without much force
2. bond is intact, but comes apart with force
3. difficult to separate but not substrate failure
4. difficult to separate and substrate failure, i.e., film distortion or delamination impossible to separate and results in fiber tear
Blocking, tack, fiber tear and residue was measured by (i) coating the adhesive onto a 2″×2″ Kraft substrate with 10 mil thickness at 350° F.; (ii) cooling the adhesive; (iii) stacking 4 coated Kraft paper, facing in the same direction, placing a 3.75 pound weight on top of the stack; (iv) heating the entire stack with weight in a 140° F. for 24 hours; (v) removing the stack from the oven and weight; (vi) immediately separating the 4 coated Kraft paper from each other to indicate the results.
Blocking notes the degree of how the squares were bound (stuck) together. “None” indicates that none of the 4 squares were bound together; “low” indicates 1-2 of the 4 squares were bound together, and “heavy” indicates that all 4 squares were bound together.
Tack indicates the degree of tackiness observed during separation of the squares. “None” indicates that the squares were easily separated by hand, “moderate” indicates that some force was necessary for separation by hand, and “heavy” indicates force beyond hand pulling was necessary to separate the squares.
Fiber tear indicates whether any fibers tore during hand separation.
Residue indicates whether some of the adhesive transferred to its adjacent square.

TABLE 2

Performance for the Composite Film Adhesives

				Comp.	Comp.
Example 1	Example 2	Example 3	Example 4	Example A	Example B

Viscosity	7175	7250	6650	9000	2300
(cps)
Adhesion	2	2	5	5	2	3
RT
Adhesion
			4	3		3
20 F.
Adhesion
			4	5		3
130 F.
Blocking	none	none	none	none	yes	none
Tack	heavy	moderate	moderate	moderate	heavy	low
Fiber Tear	none	none	none	none	yes	none
Residue	some	none	none	none	yes	none

FIG. 2 is graph of elastic (G′) modulus of Example 4 and Comparative Sample B. A Rheometrics Dynamic Mechanical Analyzer (Model RDA 700 and Rhios software version 4.3.2) was used to obtain the elastic (G′) modulus. Each sample was loaded onto 8 mm diameter parallel plates separated by a gap of about 2 mm. The sample was cooled to about −30° C., and was subjected to a temperature ramp of 5° C. intervals with a soak time of 10 seconds, all under nitrogen. The frequency was maintained at 10 rad/s. The initial strain at the start of the test was 0.05% (at the outer edge of the plates). An auto-strain option in the software was used to maintain an accurately measurable torque throughout the test. The option was configured such that the maximum applied strain allowed by the software was 80%. The auto-strain program adjusted the strain at each temperature increment if warranted using the following procedure. If the torque was below 200 g-cm the strain was increased by 25% of the current value. If the torque was above 1200 g-cm it was decreased by 25% of the current value. At torques between 200 and 1200 g-cm no change in strain was made at that temperature increment.
The modulus-temperature curves of Example 4 and Comparative Example B are shown in FIG. 2. Comparative Example B flows at about 110° C. and Example 4 flows at about 70° C., and therefore, Example 4 has better wet-out on substrates than Comparative Example B. This demonstrates that the inventive adhesive has a more robust reactivation temperature than the polyamide based adhesive.
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

I/We claim:

1. A composite adhesive comprising:

a) a mixture of a metallocene catalyzed polyolefin copolymer;

b) a tackifier;

c) a wax; and

wherein the mixture is a combination of a metallocene catalyzed polyolefin copolymer with a density less than 0.880 g/cm³and a metallocene catalyzed polyolefin copolymer with a greater than or equal to than 0.880 g/cm³.

2. The composite adhesive of claim 1 wherein the mixture has a ratio of 1:1 to 5:2 of the lower density to higher density polyolefin copolymer.

3. The composite adhesive of claim 1 wherein the copolymer comprises an ethylene comonomer.

4. The composite adhesive of claim 3 wherein the copolymer further comprises a C₂-C₁₀alpha olefin comonomer.

5. The composite adhesive of claim 4 wherein the C₂-C₁₀alpha olefin comonomer is an ethylene-octene comonomer and mixtures thereof.

6. The composite adhesive of claim 1 wherein the tackifier has a softening point less than about 110° C.

7. The composite adhesive of claim 6 wherein the tackifier is natural and modified rosins, rosin ester, synthetic hydrocarbon resins, copolymers and terpolymers of natured terpenes, including, aliphatic and aromatic petroleum hydrocarbon resins; cyclic or acyclic C₅resins, aromatic modified acyclic and cyclic resins, or mixtures thereof.

8. The composite adhesive of claim 7 wherein the plasticizer is a mixture of cyclic or acyclic C₅resins with rosin ester.

9. The composite adhesive of claim 1 wherein the wax has a viscosity of about 20 to about 10,000 cps at 140° C.

10. The composite adhesive of claim 9 wherein the wax is a maleic anhydride grafted polyethylene or polypropylene with a saponification number of about 2 to about 90 mg KOH/g.

11. The composite adhesive of claim 1 further comprising a radiation curable agents, antioxidant, blooming agents, defoamer, colorants, and mixtures thereof.

12. A composite adhesive comprising:

a) a mixture of an ethylene vinyl acetate polymer;

b) a tackifier;

c) a wax; and

wherein the mixture has a ratio of 1:1 to 5:2 of an ethylene vinyl acetate polymer with a vinyl acetate content greater than or equal to 28% and an ethylene vinyl acetate polymer with a vinyl acetate content less than 28%.

13. An article comprising the adhesive of claim 1.

14. The article of claim 13 which is a multilayer ply.

15. The article of claim 14 which is a pinch bottom bag.

16. The article of claim 15 comprising at least one composite film, at least one Kraft paper ply, and optionally a plastic liner.

17. The article of claim 15 wherein the composite film is selected from the group consisting of nylon, polyethylene, polypropylene, polyester, and mixture thereof.

18. A process of sealing a pinch bottom bags comprising:

(i) applying the adhesive of claim 1 onto both open end flaps of a pre-formed tube, wherein the pre-formed tube comprises a composite film, Kraft paper and optionally a plastic liner;

(ii) folding over a sufficient amount of one flap to seal one end, whereby the adhesive seals one end of the tube; and

(iii) cooling the remaining adhesive layer to room temperature.

19. The process of claim 15 further comprising:

(iv) reactivating the remaining adhesive with heat; and

(v) folding over a sufficient amount of the remaining flap to seal the remaining end,

whereby the reactivated adhesive seals the remaining end.