WO2024163128A9

WO2024163128A9 - Recyclable solventless adhesive

Info

Publication number: WO2024163128A9
Application number: PCT/US2024/010500
Authority: WO
Inventors: Yinzhong Guo; Gavin Lu; Qichun Wan; Hongyun XU
Original assignee: Dow Global Technologies Llc; Dow Silicones Corporation
Priority date: 2023-01-30
Filing date: 2024-01-05
Publication date: 2024-11-07
Also published as: WO2024163128A1

Abstract

Currently disclosed is a solvent free laminating adhesive composition comprising (a) a polyurethane prepolymer composition wherein the NCO% of the prepolymer is less than 10% comprising the reaction product of: (i) at least 20 wt.% aromatic isocyanate based on the weight of the prepolymer composition, (ii) no more than 10 wt.% of natural oil polyol based on the weight of the prepolymer composition, and (iii) at least 60% wt.% of polypropylene glycols based on the weight of the prepolymer composition; and (b) a hydroxyl functional coreactant composition comprising: (i) 80 to 100 wt.% natural oil polyol based on the weight of the coreactant composition, (ii) 0 to 20 wt.% hydrophobic polyether polyols based on the weight of the coreactant composition, and (iii) 0 to 2 wt.% phosphate adhesion promoter based on the weight of the coreactant composition; wherein the solvent free laminating adhesive composition is directly mechanically recyclable for polyolefin laminates. A laminate produced using the disclosed adhesive is also disclosed.

Description

RECYCLABLE SOLVENTLESS ADHESIVE

TECHNICAL FIELD

The current disclosure relates to solvent free laminating adhesives. More particularly, the current disclosure relates to solvent free laminating adhesives with improved mechanical recyclability.

INTRODUCTION

Polyurethane based adhesives are widely used in the packaging industry for flexible packages, including flexible food packaging. Solvent based polyurethane adhesives are applied via gravure or flexographic application systems while solvent free systems are applied using five roller application systems. If the flexible package is to be used for a food product, bond strength and sealing condition resistance are imperative.

Traditional flexible package design is based on lamination of functional layers such as polyethylene terephthalate (PET), bi-axially oriented polypropylene (BOPP), metalized PET oriented polypropylene (OPP), aluminum foils, and nylon/polyimide with a sealable layer such as low density polyethylene (LDPE), or cast polypropylene (CPP). Since there is no economically practical and technically efficient process of multi-layer separation and then individual film recycling, traditional flexible packages are non-recyclable. Traditionally used laminating adhesives have included either acrylic-based or polyurethane-based adhesives. Combinations of different polyolefin films laminated with such traditional adhesives are challenging to recycle due to chemical differences between the laminating adhesive and the film's polyolefin backbone, along with the highly crosslinked nature of the adhesive, which results in the non-compatibility of the adhesives with the polyolefin film material.

Thus, a need exists for an adhesive that enables fully recyclable laminate structures with all the beneficial properties described above, namely good performance and enablement of recyclable packaging.

SUMMARY OF DISCLOSURE

Currently disclosed is a solvent free laminating adhesive composition comprising (a) a polyurethane prepolymer composition wherein the NCO% of the prepolymer is less than 10% comprising the reaction product of: (i) at least 20 wt.% aromatic isocyanate based on the

1

SUBSTITUTE SHEET (RULE 26) weight of the prepolymer composition, (ii) no more than 10 wt.% of natural oil polyol based on the weight of the prepolymer composition, and (iii) at least 60% wt.% of polypropylene glycols based on the weight of the prepolymer composition; and (b) a hydroxyl functional coreactant composition comprising: (i) 80 to 100 wt.% natural oil polyol based on the weight of the coreactant composition, (ii) 0 to 20 wt.% hydrophobic polyether polyols based on the weight of the coreactant composition, and (iii) 0 to 2 wt.% phosphate adhesion promoter based on the weight of the coreactant composition; wherein the solvent free laminating adhesive composition is directly mechanically recyclable for polyolefin laminates. A laminate produced using the disclosed adhesive is also disclosed.

DETAILED DESCRIPTION

The terms "comprising," "including," "having," and their derivatives, are not intended to exclude the presence of any additional component, step or procedure, whether or not the same is specifically disclosed. In order to avoid any doubt, all compositions claimed through use of the term "comprising" may include any additional additive, adjuvant, or compound, whether polymeric or otherwise, unless stated to the contrary. In contrast, the term, "consisting essentially of" excludes from the scope of any succeeding recitation any other component, step or procedure, excepting those that are not essential to operability. The term "consisting of" excludes any component, step or procedure not specifically delineated or listed.

The numerical ranges disclosed herein include all values from, and including, the lower and upper value. For ranges containing explicit values (e.g., a range from 1, to 2, or 3 5, 6, or 7), any subrange between any two explicit values is included (e.g., the range 1 to 7 above includes subranges 1 to 2; 2 to 6; 5 to 7; 3 to 7; 5 to 6; etc.).

The term "composition" refers to a mixture of materials which comprise the composition, as well as reaction products and decomposition products formed from the materials of the composition.

An "isocyanate" is a chemical that contains at least one isocyanate group in its structure. An isocyanate group is represented by the formula: — N=C=O or abbreviated as "NCO". An isocyanate that contains more than one, or at least two, isocyanate groups is a "polyisocyanate." An isocyanate that has two isocyanate groups is a diisocyanate and an isocyanate that has three isocyanate groups is a triisocyanate, etc. An isocyanate may be aromatic or aliphatic.

A "polyisocyanate" is a molecule that contains at least two isocyanate groups.

The term "polymer" refers to a polymeric compound prepared by polymerizing monomers, whether of the same or a different type. The generic term polymer thus embraces the term "homopolymer," usually employed to refer to polymers prepared from only one type of monomer as well as "copolymer" which refers to polymers prepared from two or more different monomers. The term "interpolymer," as used herein, refers to a polymer prepared by the polymerization of at least two different types of monomers. The generic term interpolymer thus includes copolymers, and polymers prepared from more than two different types of monomers, such as terpolymers.

As used herein, a "polyolefin" refers to an olefin-based polymer. As used herein, an "olefin," which may also be referred to as an "alkene," refers to a linear, branched, or cyclic compound including carbon and hydrogen and having at least one double bond. As used herein, when a polymer or copolymer, e.g., the polyolefin elastomer, is referred to as comprising an olefin, the olefin present in the polymer or copolymer is the polymerized form of the olefin.

As used herein, the term "polyethylene" refers to polymers comprising greater than 50% by weight of units which are derived from ethylene monomer, and optionally, one or more comonomers. This may include polyethylene homopolymers or copolymers (meaning units derived from two or more comonomers). Common forms of polyethylene known in the art include Low Density Polyethylene (LDPE); Linear Low Density Polyethylene (LLDPE); Ultra Low Density Polyethylene (ULDPE); Very Low Density Polyethylene (VLDPE); single-site catalyzed Linear Low Density Polyethylene, including both linear and substantially linear low density resins (m-LLDPE); Medium Density Polyethylene (MDPE); and High Density Polyethylene (HDPE).

A "polyether" is a compound containing two or more ether linkages in the same linear chain of atoms.

A "polyester" is a compound containing two or more ester linkages in the same linear chain of atoms. A "polyol" is an organic compound containing multiple hydroxyl (OH) groups. In other words, a polyol contains at least two OH groups. Nonlimiting examples of suitable polyols include diols having two OH groups, triols having three OH groups, and tetraols having four OH groups.

A "polyester polyol" is a compound that contains a polyester and a hydroxyl functional group n the backbone structure of the compound.

A "polyether polyol" is a compound that contains a polyether and a hydroxyl functional group in the backbone structure of the compound.

A "film," including when referring to a "film layer" in a thicker article, unless expressly having the thickness specified, includes any thin, flat, extruded, blown, or cast thermoplastic article having a generally consistent and uniform thickness.

A "polymer film" is a film that is made of a polymer or a mixture of polymers. The composition of a polymer film is typically, 80 percent by weight (wt %) of one or more polymers. Laminate Film Produced Using the Adhesive

The laminate film produced using the adhesive, can comprise a polyolefin/polyolefin structure. The laminate film produced using the adhesive can comprise polyethylene/polyethylene. The laminate film produced using the adhesive can comprise HDPE//LDPE. The polyethylene/polyethylene structure may have a bond strength greater than or equal to 1000 g/25.4mm. The polyolefin/polyolefin structure can have a bond strength of from 1000 to 2500 g/25.4mm. All internal values and subranges are included. For example, the polyethylene/polyethylene substrate layer can have a bond strength of from an upper limit of 3000, 2500, 2400, 2300, 2200, 2100, 2000, 1900, 1800, 1700, 1600, 1500, or 1400 g/25.4mm to a lower limit of 1300, 1400, 1500, 1600, 1700, 1800, 1900, 2000, 2200, 2400 g/25.4mm.

The laminate produced using the adhesive, may comprise a polyolefin/polyolefin structure. The polyolefin/polyolefin structure may comprise a BOPP//BOPP seal structure and have a bond strength of greater than or equal to 230 g/25.4mm. The polyolefin substrate layer may comprise a BOPP//BOPP seal structure and have a bond strength of from 230 to 450 g/25.4mm. All internal values and subranges are included. For example, the polyolefin substrate layer may comprise a BOPP//BOPP seal structure and have a bond strength of from an upper limit of 600, 450, 430, 410, 390, 370, 350, 330, 310, 290, 270, or 250 g/25.4mm to a lower limit of 230, 250, 270, 290, 310, 330, 350, 370, 390, 410, or 430 g/25.4mm.

The laminate produced using the adhesive may have a static or kinetic coefficient of friction (COF) of from 0.150 to 0.400

The polyolefin laminate produced using the adhesive may have a recyclability property of less than or equal to 33%. The laminate produced using the adhesive may have a recyclability property of from 1.5% to 33%. All internal values and subranges are included and disclosed. For example the laminate produced using the adhesive may have a recyclability property of from an upper limit of 25%, 23%, 21%, 19%, 17%, 15%, 13%, 11%, 9%, 7%, 5%, or 3% to a lower limit of 1.5%, 2% 4%, 6%, 8%, 10%, 12%, 14%, 16%, 18%, 20%, 22%, or 24%.

The polyethylene laminate produced using the adhesive may have a melt index after HAAKE compounding of 1.0 to 4.5 g/lOmin at a temperature of 210°C. All internal values and subranges are included. For example, the laminate produced using the adhesive may have a melt index after HAAKE compounding of from an upper limit of 4.5, 4.3, 4.1, 3.9, 3.7, 3.5, 3.3, 3.1, 2.9,

2.7, 2.5, 2.3, 2.1, 1.9, 1.7, 1.5, 1.3, or 1.1 to a lower limit of 1.0, 1.2, 1.4. 1.6, 1.8, 2.0, 2.2, 2.4, 2.6,

2.8, 3.0, 3.2, 3.4, 3.6, 3.8, 4.0, 4.2, or 4.4.

The laminate produced using the adhesive may have a molecular weight M_n of from 41,000 to 43,000g after HAAKE compounding. All internal values and subranges are disclosed. For example the laminate produced using the adhesive may have a molecular weight M_n of from 41,000 to 42,000g or 42,000 to 43,000g after HAAKE compounding.

The laminate produced using the adhesive may have a molecular weight M_w of from 165,500g to 172,000g after HAAKE compounding. All internal values and subranges are included. For example, the laminate produced using the adhesive may have a molecular weight M_wof from

165.500 to 168,000g or from 168,000 to 172,000g after HAAKE compounding.

The laminate produced using the adhesive may have a molecular weight M_z of from

457.500 to 480,000g after HAAKE compounding. All internal values and subranges are included. For example, the laminate produced using the adhesive may have a molecular weight M_z of from

457,500 to 465,000g or from 465,000 to 480,000g after HAAKE compounding. The laminate produced using the adhesive may have a molecular weight M_p of from 100,000 to 110,000g after HAAKE compounding. All internal values and subranges are included. For example, the laminate produced using the adhesive may have a molecular weight M_pof from 100,000 to 106,000g or from 106,000 to 110,000g after HAAKE compounding.

The laminate produced using the adhesive may have a PDI (M_w/M_n) of from 4.00 to 4.05 after HAAKE compounding. All internal values and subranges are included. For example, the laminate produced using the adhesive may have a PDI (M_w/M_n) of from 4.00 to 4.02 or from 4.02 to 4.05.

Polyolefin Substrate Layer

The disclosed polyolefin substrate layers are made from an olefin-based polymer. The polyolefin substrate layer may comprise an ethylene-based polymer. Common forms of polyethylene known in the art include, but are not limited to, low density polyethylene (LDPE); linear low density polyethylene (LLDPE); ultra low density polyethylene (ULDPE); very low density polyethylene (VLDPE); single-site catalyzed linear low density including both linear and substantially linear low density resins (m-LLDPE); medium density polyethylene (MDPE); and high density polyethylene (HDPE). For example, the polyolefin substrate layer, can include one or more polyolefin layers such as HDPE, LDPE, LLDPE, MDO PE, BOPE, and mixtures thereof.

Additionally, as described herein, the term "LDPE" may also be referred to as "high pressure ethylene polymer" or "highly branched polyethylene" and is defined to mean that the polymer is partly or entirely homopolymerized or copolymerized in an autoclave or a tubular reactor at pressures above 14,500 psi (100 MPa) with the use of free-radical initiators, such as peroxides (see, e.g., U.S. Patent No. 4,599,392). LDPE resins typically have a density in the range of 0.916 g/cm to 0.940 g/cm.

The term "LLDPE", as described herein, may include resins made using Ziegler Natta catalyst systems as well as resins made using single-site catalysts, including, but not limited to, bis-metallocene catalysts (sometimes referred to as "m-LLDPE"), phosphinimine, and constrained geometry catalysts; and resin made using post-metallocene, molecular catalysts, including, but not limited to, bis(biphenylphenoxy) catalysts (also referred to as polyvalent aryloxyether catalysts). LLDPE includes linear, substantially linear, or heterogeneous ethylene-based copolymers or homopolymers. LLDPEs contain less long chain branching than LDPEs and include the substantially linear ethylene polymers, which are further defined in U.S. Patent No. 5,272,236, 5,278,272, 5,582,923, and 5,733,155; the homogeneously branched ethylene polymers such as those described in U.S. Patent No. 3,645,992; the heterogeneously branched ethylene polymers such as those prepared according to the process disclosed in U.S. Patent No. 4,076,698; and blends thereof (such as those disclosed in U.S. Patent No. 3,914,342 or U.S. Patent No. 5,854,045). The LLDPE resins can be made via gas-phase, solution-phase, or slurry polymerization as well as any combination thereof using any type of reactor or reactor configuration known in the art. The LLDPE resins can be made via gas-phase, solution-phase, or slurry polymerization as well as any combination thereof, using any type of reactor or reactor configuration known in the art.

Additionally, as described herein, the term "HDPE" refers to polyethylenes having densities of about 0.940 g/cm or greater, which are generally prepared with Ziegler-Natta catalysts, chrome catalysts, or even metallocene catalysts. The polyolefin substrate layer can be a multilayer film which includes an outer layer comprising an ethylene-based polymer.

The polyethylene polymer suitable for use in the present disclosure may be commercially available. Suitable commercial polyethylene polymers include but are not limited to: AGILITY™ (e.g, AGILITY™ 1000 , AGILITY™ 1001, and AGILITY ™1021), INNATE™ ST 50, ELITE™ 5940, ELITE™ 5960, DOW™ LDPE 6211, and DOW™ LDPE 7511, all of which are available from The Dow Chemical Company.

The disclosed polyolefin substrate layers are made from an olefin-based polymer. The polyolefin substrate layer may comprise a propylene-based polymer. Common forms of polypropylene known in the art include, but are not limited to, BOPP and CPP films;

The polyolefin substrate layer used for making the recyclable laminate structures of the present disclosure can include a single layer (monolayer) made of one or more polyolefins, olefinic polymers, or ethylene vinyl acetate (EVA); or ethylene vinyl alcohol (EVOH), or the recyclable laminate structures can include a multilayer structure made of one or more polyolefin layers. The polyolefin substrate layer of the present disclosure may be a multilayer film which contains more than one layer. As described herein, a "multilayer film" means any film having more than one layer. For example, the multilayer film may have two, three, four, five, or more layers. A multilayer film may be described as having the layers designated with letters to assist in describing the film. For example, a two-layer film having two different polyolefin film layers can be designated as A/B; and a three-layer film having a core layer B, and two external layers A and C may be designated as A/B/C. Likewise, a structure having two core layers B and C and two external layers A and D would be designated A/B/C/D. The polyolefin films may be coextruded films with an odd number of layers from 3 to 35, such as from 3 to 11 or from 3 to 7. For example, the polyolefin substrate layer may be a three-layer multilayer film comprised of three layers of polyethylene.

The polyolefin substrate layer can be a multilayer film comprised of one or more layers of HDPE, LLDPE, and LDPE; a PP film a biaxially oriented PP (BOPP) film layer, or a machine-direction oriented PE (MDO PE) or a biaxially oriented PE (BOPE).

The thickness of the polyolefin substrate layer can be, for example, from 8 (pm) to 125 pm, from 20 pm to 100 pm, or from 25 pm to 50 pm.

The polyolefin substrate layer may have a thickness of less than or equal to (<) 1 mm, such as < 900 pm, < 800 pm, < 700 pm, < 600 pm, < 500 pm, < 400 pm, < 300 pm, or even < 200 pm. The polyolefin substrate layer may have a thickness of greater than or equal to (>) 1 pm, > 5 pm, > 10 pm, > 20 pm, > 30 pm, > 40 pm, or even > 50 pm. As is understood by those skilled in the art, in multilayer films, the thicknesses of the different layers can be the same or different; and layer thicknesses may be selected by techniques known to those having skill based on the disclosure herein.

The polyolefin substrate layers can be produced with low density polymers. The polyolefin substrate layer can be polyethylene/polyethylene films or polypropylene/polypropylene films. The polyolefin substrate layer can be blown or co-extruded.

Solvent Free Laminating Adhesive

The solvent free laminating adhesive can have a Hansen Solubility Factor, calculated as described below, less than or equal to 21. The solvent free laminating adhesive can have a Hansen Solubility Factor calculated as described below from 16 to 21. All internal values and subranges are included and disclosed. For example, the solvent free laminating adhesive can have a Hansen Solubility Factor from an upper limit of 21, 20, 19, 18, or 17 to a lower limit of 16, 17, 18, 19 or 20.

It is contemplated that two components, an isocyanate component and a polyol component, are employed in the present disclosure. It is also contemplated that the isocyanate component and the polyol component of the disclosed adhesive composition can be made separately and, if desired, stored until it is desired to use the adhesive composition. The NCO index (mole of NCO functional group to hydroxyl functional group) of the mixed adhesive can be from 1.0 to 1.5, or from 1.1 to 1.3. The mixing ratio of the isocyanate component and a polyol component can be from 100:80 - 100:30 or from 100:70 - 100:40.

The adhesive composition can be directly mechanically recyclable for polyolefin laminates. Polyolefin laminates coated with the adhesive composition should have no more than a 33 change in performance after direct mechanical recycling when compared to the performance of a substrate layer without the adhesive dispersion composition. This is referred to as having a "recyclability property" of 25%. Properties that can be tested to determine a recyclability property include, but are not limited to, the laminate's: (1) mechanical properties (e.g., tensile modulus), and (2) IR absorbance properties. Other properties, such as clarity and gel content, of the films present in the multi-layer laminate structure of the recycled materials can be measured if desired, to further determine the recyclability of the laminate film structure.

The adhesive composition of the present disclosure can include one or more additional optional conventional ingredients or additives including but not limited to, catalysts, tackifiers, plasticizers, rheology modifiers, adhesion promoters, antioxidants, fillers, colorants, pigments, surfactants, polymers (including, for example, thermoplastic resins other than those discussed herein above), dehydrating agents (including, for example, silanes), benzoyl chloride, other polyols (including, for example, fatty polyols), ultraviolet indicators, and combinations of two or more of these.

The adhesive composition may include, for example, an adhesion promoter. Non-limiting examples of suitable adhesion promoters include coupling agents such as a silane coupling agent, a titanate coupling agent, and an aluminate coupling agent; epoxy resin, phosphoric acid, polyphosporic acid, and phosphate esters.

Examples of the silane coupling agent useful in the present disclosure include, but are not limited to, aminosilanes such as y-aminopropyltriethoxysilane, y-aminopropyl-trimethoxysilane, N-P(aminoethyl)-y-aminopropyltri methoxysilane, N-P(aminoethyl)-y-aminopropyltrimethyl dimethoxysilane, and N-phenyl-y-aminopropyltrimethoxysilane; epoxysilanes such as |3-(3,4- epoxycyclohexyl)-ethyltrimethoxysilane, y-glycidoxypropyl-tri methoxysilane, and y-glycidoxypropyltriethoxysilane; vinylsilanes such as vinyl tris(P-methoxyethoxy)silane, vinyltriethoxysilane, vinyltrimethoxysilane, and y-methacryloxypropyltrimethoxysilane; hexamethyldisilazane; y-mercaptopropyl-trimethoxysilane; and mixtures thereof.

Examples of the titanate coupling agent useful in the present disclosure include, but are not limited to, tetraisopropoxy titanium, tetra-n-butoxy titanium, butyl titanate dimer, tetrastearyl titanate, titanium acetylacetonate, titanium lactate, tetraoctyleneglycol titanate, titanium lactate, tetra stearoxy titanium; and mixtures thereof.

Examples of the epoxy resin useful in the present disclosure include, but are not limited to, a variety of readily available epoxy resins such as bisphenol A-epichlorohydrin (epi-bis) type epoxy resin, novolak type epoxy resin, 0-methylepichlorohydrin type epoxy resin, cyclic oxirane type epoxy resin, glycidyl ether type epoxy resin, glycidyl ester type epoxy resin, polyglycol ether type epoxy resin, glycol ether type epoxy resin, epoxidation fatty acid ester type epoxy resin, polycarboxylic acid ester type epoxy resin, aminoglycidyl type epoxy resin, resorcin type epoxy resin; and mixtures thereof.

The adhesion promoter can be a phosphate ester compound or an epoxy silane ((3- glycidyloxypropyl)-trimethoxysilane). Phosphoric acid can be incorporated in the polyol component while epoxy silane can be incorporated in the isocyanate component. Both epoxy silane and phosphoric acid can be incorporated in the polyol component.

The amount of optional components when used can be from 0 wt % to 15 wt %, from 0.01 wt % to 10 wt % or from 0.1 wt % to 5 wt % based on the total amount of components in the adhesive composition. Adhesive Polyurethane Prepolymer

The isocyanates in the isocyanate component can be, for example, an isocyanate monomer, a polyisocyanate (e.g. dimers, trimers, etc.) an isocyanate prepolymer, and mixtures of two or more of the preceding. A "polyisocyanate" is any compound that contains two or more isocyanate groups.

The polyurethane prepolymer composition can comprise at least 20 wt.% aromatic isocyanate based on the weight of the prepolymer. The polyurethane prepolymer composition can comprise 20 to 50 wt.% based on the weight of the prepolymer composition. All internal values and subranges are disclosed. For example, the polyurethane prepolymer composition can comprise from an upper limit of 50, 45, 40, 35, 30, or 25 wt.% to a lower limit of 20, 25, 30, 35, 40, or 45 wt.% based on the weight of the prepolymer composition.

The aromatic-based isocyanates useful in the present disclosure can include, for example, one or more polyisocyanate compounds including, but are not limited to, for example 1,3- and 1,4-phenylene diisocyanate; 1,5-naphthylene diisocyanate; 2,4'-diphenylmethane diisocyanate (2,4'-MDI); 4,4'-diphenylmethane diisocyanate (4,4'-MDI); 2,2'-diphenylmethane diisocyanate (2,2'-MDI), 3,3'-dimethyl-4,4'-biphenyldiisocyanate (TODI) and isomers thereof; polymeric isocyanates; and mixtures of two or more thereof.

Exemplary of some of the commercial aromatic-based components useful in the present disclosure can include, but not limited to, for example, ISONATE™ 125 M, ISONATE™ 143L, ISONATE™ 50OP, ADCOTTE™ L76-204, COREACTANT CT™, and CATALYST F™, available from The Dow Chemical Company; DESMODUR™ E 2200/76, available from The Covestro Company; and mixtures thereof.

The polyurethane prepolymer composition can comprise no more than 10 wt.% natural oil polyol based on the weight of the prepolymer composition. The polyurethane prepolymer can comprise from 0.1 to 10 wt.% based on the weight of the prepolymer composition. All internal values and subranges are disclosed. For example, the polyurethane prepolymer can comprise from an upper limit of 10, 9.5, 9.0, 8.5, 8.0, 7.5, 7.0, 6.5, 6.0, 5.5, 5.0, 4.5, 4.0, 3.5, 3.0, 2.5, 2.0, 1.5, 1.0, or 0.05 to a lower limit of 0.1, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5, 4.0, 4.5, 5.0, 5.5, 6.0, 6.5, 7.0, 7.5, 8.0, 8.5, 9.0, or 9.5 wt.% based on the weight of the prepolymer composition. Examples of natural oils that are suitable for use in the current disclosure include but are not limited to castor oil, rape seed, and palm kernel oil.

The polyurethane prepolymer composition can comprise at least 60 wt.% of polypropylene glycols based on the weight of the prepolymer composition. The polyurethane prepolymer composition can comprise from 60 to 80 wt.% of polypropylene glycol based on the weight of the prepolymer. All internal values and subranges are included. For example, the polyurethane prepolymer composition can comprise from an upper limit of 80, 75, 70, or 65 wt.% to a lower limit of 60, 65, 70, or 75 wt.% of polypropylene glycol.

The NCO% of the prepolymer can be less than or equal to 12% based on the weight of the prepolymer. The NCO% of the prepolymer can be from 1 to 12%. All internal values and subranges are disclosed. For example, the NCO% of the prepolymer can be from an upper limit of 12, 9, 8, 7, 6, 5, 4, 3, or 2% to a lower limit of 1, 2, 3, 4, 5, 6, 7, 8, 9 or 10%.

Adhesive Hydroxyl Functional Coreactant

The adhesive hydroxyl functional coreactant can comprise 80 to 100% natural oil polyol based on the weight of the coreactant composition. All internal values and subranges are disclosed. For example, the adhesive hydroxyl functional coreactant can comprise from an upper limit of 100, 95, 90, or 85% to a lower limit of 80, 85, 90, or 95% natural oil polyol based on the weight of the coreactant composition. Examples of natural oils that are suitable for use in the current disclosure include, but are not limited to, castor, rape seed, and palm kernel oil.

The adhesive hydroxyl functional coreactant composition can comprise 0 to 20 wt.% of hydrophobic polyether polyols based on the weight of the coreactant composition. All internal values and subranges are included. For example, the adhesive hydroxyl functional coreactant can comprise from an upper limit of 20, 15, 10, or 5 to a lower limit of 0, 5, 10, or 15 wt% hydrophobic polyether polyols based on the weight of the coreactant composition. Suitable hydrophobic polyether polyols include but are not limited to polypropylene glycol, polyl,2- butylene glycol, or polyl,2-pentylene glycol.

Suitable commercial examples include, but are not limited to, VORANOL™ CP 450, and Vorapel T5001. The adhesive hydroxyl functional coreactant composition can comprise 0 to 2 wt.% phosphate adhesion promoter based on the weight of the coreactant composition. All internal values and subranges are included. For example, the coreactant composition can comprise from an upper limit of 2, 1.8, 1.6, 1.4, 1.2, 1.0, 0.8, 0.6, 0.4, or 0.2 wt.% to a lower limit of 0, 0.2, 0.4, 0.6, 0.8, 1.0, 1.2, 1.4, 1.6, or 1.8 wt.% phosphate adhesion promoter based on the weight of the coreactant composition. Suitable commercial examples include but are not limited to MOR- FREE™ 88-138 available from DOW™ Chemical.

Formation Of The Adhesive And The Laminate

The solvent free laminating adhesive composition can be produced through mixing, admixing, blending, or any other process known in the art the polyurethane prepolymer composition, comprising the reaction product of at least 20 wt.% aromatic isocyanate based on the weight of the prepolymer composition, no more than 10 wt.% natural oil polyol based on the weight of the prepolymer composition, and at least 60 wt.% of polypropylene glycol based on the weight of the prepolymer composition wherein the NCO% of the prepolymer is less than 10% with a hydroxyl functional coreactant composition, in the ratios described above, comprising 80 to 100 wt.% natural oil polyol based on the weight of the coreactant composition, 0 to 20 wt.% hydrophobic polyether polyol based on the weight of the coreactant composition, and 0 to 2 wt.% phosphate adhesion promoter based on the weight of the coreactant composition; wherein the solvent free laminating adhesive thus produced is directly mechanically recyclable for polyolefin laminates.

In general the polyurethane prepolymer composition and the hydroxyl functional coreactant composition can be prepared separately from one another and the components can be stored in separate containers. Optional additives may be present in either the polyurethane prepolymer composition or the hydroxyl functional coreactant composition or both. A suitable container for the storage of each component can be, for example, a drum, a hobbock, a bag, a bucket, a can, a jar, a bottle, a cartridge or a tube. The two components can be mixed with one another prior to application of the adhesive composition or the two components can be mixed only during the application. The application of the adhesive to the surface of at least one substrate can be carried out by conventional means such as by using a roll coater, a doctor blade, or extrusion equipment and process. The adhesive composition can be applied at a level, in grams of dry composition per square meter, of 1 or greater in one embodiment and 2 or greater in another embodiment. The adhesive composition can be applied at a level, in grams of dry composition per square meter, of 7 or less in one embodiment and 5 or less in another embodiment.

Another embodiment of the present invention is directed to a process for bonding at least a first substrate to at least a second substrate including the steps of: (a) mixing the polyurethane prepolymer composition and the hydroxyl functional coreactant composition as described above to form the adhesive, (b) applying the adhesive of step (a) to at least one of the substrate surfaces to be bonded and (c) contacting (or joining) together the first and second substrates to be bonded with the adhesive.

The recyclable laminate structures of the present disclosure can be used, for example, in packaging applications for manufacturing various packaging materials and products. Nonlimiting examples of uses for the disclosed recyclable laminate structures include: bulk packaging of food grains/pulses, packaging of seeds, packaging of lentils and cereals, packaging of fertilizer, packaging of oilseed, packaging of sugar, packaging of salt, packaging of pharmaceuticals, packaging of other food stuff, and personal care items such as bath salts, detergent pods and the like. The recyclable laminate structures may also be used as a wrapper for baby wipes, feminine hygiene products, cereal bars, protein bars, cheese and confectionary products.

TEST METHODS

Hansen Solubility Calculation

The calculation of Hansen's solubility parameter (HSP), the arithmetic distance (R_a), the geometric distance ( Rb), and the aliphatic carbon ratio (ACR) of polyurethane adhesive or coating compositions is described in the filing titled "SYSTEMS, METHODS, AND NON- TRANSITORY COMPUTER-READABLE MEDIUM OF PREDICTING A COMPATIBILITY OF AN ADHESIVE OR COATING COMPOSITION AND POLYOLEFIN POLYMERS". Briefly, the model works as follows. For each component in an adhesive composition, the number of moles of functional groups are calculated. [The functional groups are specified in Table 7.12 of D.W. van Krevelen's book "Properties of Polymers" 4th ed., Completely Revised Edition, available from Elsevier: Amsterdam, 2009, ebook ISBN : 9780080915104.)

Then, values of group contributions are calculated, including the molar attraction function (Ft), the polar component (F_p), the molar volume (V), the Lydersen correction for solvents (AT), and the Lydersen correction for polymers(AT^(p)), or combinations thereof, of each ingredient on the list. All numerical values and equations are in FIG. 4 of the filing titled "SYSTEMS, METHODS, AND NON-TRANSITORY COMPUTER-READABLE MEDIUM OF PREDICTING A COMPATIBILITY OF AN ADHESIVE OR COATING COMPOSITION AND POLYOLEFIN POLYMERS". Finally, the HSP, R_a, and Rb are calculated.

When the HSP of the polyurethane adhesive or coating composition is lower than or equal to 22.7 and the ACR of the polyurethane adhesive or coating composition is greater than or equal to 6.9, for adhesive or coating composition based on chemistries other than polyurethanesthe HSP and ACR values may be different.

When the arithmetic distance (R_a) is lower than or equal to 12 and the ACR of the polyurethane adhesive or coating composition is greater than or equal to 6.9, for adhesive or coating composition based on chemistries other than polyurethanes the ACR and R_a values may be different.

When the geometric distance (Rb) is lower than or equal to 6 and the ACR of the adhesive or coating composition is greater than or equal to 6.9, for adhesive or coating composition based on chemistries other than polyurethanes the ACR and Rb values may be different.

T-peel bond strength

An Instron Tensile Tester with a 200 N loading cell is used to test three 1-inch strips per laminate at a rate of lOinch/min. The high and mean strength are recorded together along with the failure mode. In case of film tear and stretch the high value is reported and in other failure modes the average T-peel bond strength is reported. Typical failure modes include: AF- Adhesive failure (adhesive with primary) AT- Adhesive transfer (adhesive with secondary) AS- Adhesive split (cohesive failure of adhesive) FT- Film Tear (substrate stretch or failure)

T- Tunnel

Boil In Bag Test

A 9 inch x 11 inch cured laminate is folded over to form a double layer such that the PE film of one layer is in contact with the PE film of the other layer. The edges are then trimmed with a paper cutter to obtain a folded piece about 5 inch x 7 inches in size. The edges are then heat sealed to form a pouch with an interior size of 4 inch x 6 inches and the pouches filled with 100 mL of 1/1/1 sauce blend equal parts by weight of catsup, vinegar, and vegetable oil through the open edge. The pouch is then sealed in a mannerthat minimizes airentrapment and carefully immersed in boiling water for thirty or sixty minutes. After boiling the extent of tunneling, delamination or leakage is compared with marked pre-existing flaws. The bags are then emptied and at least three 1 inch strips are cut from the pouches and T-peel bond strength is measured as soon as possible.

COF

The COF of the laminated films is tested after 21 days of cure time using a TMI COF tester in a 25°C and 50% humidity control room according to ASTM D1894

Primary Aromatic Amine (PAA)

Primary aromatic amines ("PAA") decay of the laminated structure is tested after samples are cured at 25 °C, 50 % RH for 2 or 3days. A cured laminate structure is folded over to form a double layer such that the polyethylene film of one layer is in contact with the polyethylene film of the other layer. The edges are then trimmed with a paper cutter to obtain a folded piece about 6.5 inches x 7 inches. The edges are then heat sealed to form a pouch with an interior size of 5.5 inches x 5.6 inches. The pouches are then filled with 100 mL of 3 % acetic acid. These pouches are extracted at 70 °C in the air circulation oven for a period of 2 hr. After quench cooling of the pouches in cold tap water, the test solution is allowed to equilibrate at room temperature, and the 100 mL test solution is transferred into a beaker. The amount of primary aromatic amines extracted to 3 % acetic acid solution is determined by utilizing a classical colorimetric method.

Recyclability

Recyclability is evaluated by comparing the mechanical properties of the adhesive containing laminated structure with films containing no adhesive after a HAAKE compounding process and compresion to a sheet as described below. Mechanical property variation within ± 25% between the experimental and control samples is defined as recyclable.

The Haake compounding process comprises mixing and compressing sheet molding of the film (either laminated or control) in a RS5000 equipped with a Haake Rheomix 3000 mixer with 25% GF Teflon bushings and Cam style rotors. The mixer is attached to a RS5000 torque rheometer drive unit, controlled by System 5 PC based control/data acquisition software designed to operate the RS5000 drive.

Film samples are melt blended in the heated mixer at 160°C for PE laminated material, and at 190°C for BOPP laminated material for 20-25 minutes. Mixing speed is at max 5-20 rpm with a nitrogen purge block to limit sulfur oxidation. Once melt blending is completed the sample is quickly removed and cooled in the chilled platens of a carver hydraulic press at 20000 psi for about 3 minutes.

Compressed sheet samples are prepared with 15-16 grams of Haake remolded sample in a 188°C carver press with a 4.5"x4.5"x0.035 chase. For the first 3 minutes the sample is heated in the upper platens of the Carver press, then it is moved to the lower platens and cooled, for 3 minutes, to 20°C. Bubbles are preferably avoided and a width of 1/8" or smaller is desirable.

The mechanical properties of both the control and inventive samples were tested on an Instron tensile tester according to ASTMD1708. Results are reported in Table 11 and 12 below.

Melt Flow Rate

ASTM standard D1238 method B with a Tinius Olsen Plastometer MP993 with a 9.55 mm diameter and 162 mm long cylinder in an HHD ASTM lab is used to test the melt flow rate. A 9.55 mm diameter die with a 2.0955 mm center bore diameter and a 8mm length is used with a 9.474 in diameter piston. At least 2.8 grams of sample is used. A 2.16kg weighted piston is used to measure the polymer flow at 190°C for PE samples and 210°C for BOPP samples with a thermostatically controlled heated steel cylinder.

EXAMPLES

Materials used are listed in Table 1 below. All commercial samples are available from DOW Inc. Table 1: Materials

Prepolymer Synthesis

Experimental prepolymer compositions 1, 2, and 3 (PP 1, PP 2, and PP 3) are shown in Table 2 below. A 3L triple mouths flask was dried and purged with N2 and connected with a condenser, an overhead mixer, a thermocouple temperature controller, and a nitrogen bubbler. The given amount of ISONATE™ 125M isocyanate and/or ISONATE™ 50 OP MDI is charged and the given amount of VORANOL™ 220-56N and then castor oil or the modified castor oil POLYCIN™ GR-50 are loaded into the reactor under mixing. After N2 is bubbled through the reactor for a couple minutes, the reactor is heated gradually to 78°C and then maintained at this temperature for two hours as the reaction proceeded. After two hours the product was dumped into a glass bottle and characterized as shown in Table 3.

Table 2: Inventive prepolymer (PP) formulations

Table 3: Prepared prepolymer properties

Coreactant inventive compositions 1 and 2 (CC 1, and CC 2) are listed in table 4 below.

These compositions were mixed by a high speed mixer for 1800rpm for 1 min.

Table 4: Coreactant compositions

An example calculation of HSP, R_a, and Rb is given in the filing titled "SYSTEMS, METHODS, AND NON-TRANSITORY COMPUTER-READABLE MEDIUM OF PREDICTING A COMPATIBILITY OF AN ADHESIVE OR COATING COMPOSITION AND POLYOLEFIN POLYMERS" with Dow's polyurethane adhesive "ADCOTE® 102E/Coreactant CT" at a mix ratio of 100:5.2.

The solubility parameters calculated as described above are shown in table 5 below. Table 5: Calculated Hansen Solubility Parameters

Laminated samples were prepared using a Nordmeccanica LaboCombi pilot laminator. The disclosed formulation was first applied to an HDPE or BOPP primary film followed by lamination with a LDPE GF-19 or BOPP seal secondary film. The coating weight was maintained within the application range of typical solventless laminating adhesives; specifically 1.0-1.2 Ibs/ream. The formed laminate was cured in a control room (25°C, 50%RH). Bond strength was tested after 1, 7, 14, and 28 days as shown in the tables below on HDPE//LDPE, and BOPP//BOPP-Seal structures. Table 6: Adhesive performance in an HDPE//LDPE structure (g/25.4mm)

Table 7: Adhesive performance BOPP//BOPP-seal structure (g/25.4mm)

Table 8: 7 day COF impact of the adhesive on HDPE and LDPE films in laminated structures

Table 9: 7 day COF impact of the adhesives on BOPP and BOPP-seal films in the laminated structure

Table 10: PAA decay results for IE 3 in HDPE//GF-19 and BOPP//BOPP seal structures

Recyclability

Recyclability is evaluated by comparing the mechanical properties of the adhesive containing laminated structure with films containing no adhesive after a HAAKE compounding process and the compressed sheet made as described below. Mechanical property variation within ± 25% between the experimental and control samples is defined as recyclable.

The mechanical properties of both the control and inventive samples were tested on an Instron tensile tester according to ASTMD1708. Results are reported in Table 11 and 12 below. Table 11: Recyclability of HDPE//LDPE films using comparative and inventive samples

*control sample, mechanical property change defined as "0", other samples change comparing the control. Table 12: Recyclability of BOPP laminated material using inventive and comparative samples

*control sample, mechanical property change defined as "0", other samples change comparing the control.

Melt flow rate is measured as described in testing procedures above. Results are reported in Table 13 below.

Table 13: Melt index of laminated samples after HAAKE compounding process

The molecular weight of the BOPP samples before and after HAAKE compounding is measured as described above in testing procedures. Results are reported in table 14 below. Table 14: Molecular weight of the BOPP/BOPP laminated samples after HAAKE compounding process (Dalton)

Claims

What is claimed is:

1. A solvent free laminating adhesive composition comprising: a. a polyurethane prepolymer composition comprising the reaction product of: i. at least 20 wt.% aromatic isocyanate based on the weight of the prepolymer composition, ii. no more than 10 wt.% natural oil polyol based on the weight of the prepolymer composition, and iii. at least 60 wt.% of polypropylene glycols based on the weight of the prepolymer composition wherein the NCO% of the prepolymer is less than 10%; b. a hydroxyl functional coreactant composition comprising: i. 80 to 100 wt.% natural oil polyol based on the weight of the coreactant composition, ii. 0 to 20 wt.% hydrophobic polyether polyol based on the weight of the coreactant composition, and iii. 0 to 2 wt.% phosphate adhesion promoter based on the weight of the coreactant composition; wherein the solvent free laminating adhesive composition is directly mechanically recyclable for polyolefin laminates.

2. The solvent free laminating adhesive composition of any preceding claim wherein the Hansen Solubility Parameters, calculated as disclosed in the specification, is less than 21.

3. The polyurethane prepolymer composition of any preceding claim wherein the aromatic isocyanate comprises 20 to 50 wt.% based on the weight of the prepolymer composition.

4. The polyurethane prepolymer composition of any preceding claim wherein the propylene glycol comprises 60 to 80 wt.% based on the weight of the prepolymer composition.

5. The polyurethane prepolymer composition of any preceding claim wherein the NCO is from 5 to 10%.

6. The solvent free laminating adhesive composition of any preceding claim wherein the Hansen Solubility Parameters, calculated as disclosed in the specification, are from 16 to 21.

7. The polyurethane prepolymer of any preceding claim wherein the natural oil polyol comprises 0.1 to 10 wt.% based on the weight of the prepolymer composition.

8. A laminate produced using the adhesive of any preceding claim.