WO2025166534A1

WO2025166534A1 - Two-component adhesive composition

Info

Publication number: WO2025166534A1
Application number: PCT/CN2024/076278
Authority: WO
Inventors: Xiaolian HU; Yinzhong Guo; Qiangqiang YAN; Yanbin FAN; Chenyan BAI; Xiaomei Song; Qi Gao; Colin Li Pi Shan
Original assignee: Dow Global Technologies LLC
Current assignee: Dow Global Technologies LLC
Priority date: 2024-02-06
Filing date: 2024-02-06
Publication date: 2025-08-14
Anticipated expiration: 2026-08-06

Abstract

A two-component adhesive composition contains (A) a polyol component comprising: (al) a specific oxime-containing diol, where the oxime-containing diol in the polyol component (A) is present in an amount to provide a molar concentration of hydroxy groups in the oxime-containing diol, relative to total moles of hydroxy groups in the polyol component (A), in a range of from 40 mole percent to 90 mole percent; and (a2) a polyol selected from the group consisting of a polyester polyol, a polyether polyol, castor oil, a polyhydric alcohol, and combinations thereof; and (B) an isocyanate component comprising an isocyanate prepolymer that is the reaction product of reactants comprising: (b1) a polyisocyanate; and (b2) a polyol selected from the group consisting of a polyester polyol, a polyether polyol, castor oil, and combinations thereof.

Description

TWO-COMPONENT ADHESIVE COMPOSITION

FIELD

The present invention is a two-component adhesive composition, particularly suitable for use as adhesives for laminates.

INTRODUCTION

Adhesive compositions are useful for a wide variety of purposes. For instance, adhesive compositions are used to bond together substrates such as polyethylenes, polypropylenes, polyesters, polyamides, metals, papers, or cellophane to form composite films, i.e., laminates. The use of adhesives in different laminating end-use applications is generally known. For example, flexible packaging laminating adhesives are applied between laminating films for packaging of foodstuffs, pharmaceuticals, and industrial consumables.

In recent years, the desire to reduce or avoid microplastic pollution has driven the packaging demand for reusable, recyclable, or compostable packaging. Mechanical recycling currently accounts for the majority of plastics recycling. Laminates for flexible packaging typically include multilayer polymer films and/or foils bonded together, and additional materials such as inks and adhesives, with each layer serving different functions in protecting the package contents. Different types of polymer materials in the laminated multilayer structure may not be compatible with each other when melted down, which usually makes it impossible to directly mechanical recycling of flexible packaging after using. Conventional laminating adhesives can provide sufficient and durable bond strength such that the obtained laminated multilayer structures are non-separable, which, however, makes it difficult to separate the multilayer films so as to recycle them individually. Moreover, it is a challenge to remove the inks from the recycled materials. Thus, it would be attractive in flexible packaging mechanical recycling to develop a new laminating adhesive that is debondable under mild conditions that are practical in the industry, thereby rendering the adhesive less effective under mechanical agitation and solution treatment.

It is therefore desirable to discover an adhesive composition particularly suitable for laminating adhesives that provide enough bond strength between multilayers of laminates during the packaging application yet are debondable when subject to certain treatments to facilitate separation of different layers of the laminates during recycling process.

SUMMARY

The present invention solves the problem of discovering a novel two-component adhesive composition comprising two components: a polyol component as a component (A) that comprises a specific oxime-containing diol (a1) and a polyol (a2) , and an isocyanate component as a component (B) . The adhesive composition, upon curing, forms a cured product (also referred to as “polyurethane adhesive” ) . The polyurethane adhesive can provide an acceptable bond strength (also referred to as “initial bond strength” ) for laminates comprising such adhesive, e.g., affording the bond strength of at least 4.0 newtons per 15 millimeters (N/15mm) for laminates based on polyamide and polyethylene (PE) films or at least 2.0 N/15mm for laminates based on polyethylene terephthalate (PET) and PE films. In the meanwhile, these laminates are debondable when subject to mild conditions (e.g., treated with an aqueous alkali solution described herein below) , as indicated by a decrease in bond strength of the laminate of at least 60%. Bond strength properties can be measured according to the Bond Strength Test described in the Examples section below. The present invention also relates to a novel method of debonding such laminate, which may lead to separation (also known as “delamination” ) of different layers of the laminate, so that each type of layer can be recycled separately using existing mechanical recycling equipment and process.

In a first aspect, the present invention provides a two-component adhesive composition, comprising:

(A) a polyol component comprising:

(a1) an oxime-containing diol having the structure of formula (I) :

where R₁ and R₂ are each independently H, an alkyl group having from 1 to 30 carbon atoms, or an aryl group having from 6 to 30 carbon atoms; and R is a single carbon-carbon bond, an alkylene group having from 1 to 30 carbon atoms, or an arylene group having from 6 to 30 carbon atoms; or R, R₁, and R₂ together are bonded to form a cyclic ring having from 4 to 12 carbon atoms;

wherein the oxime-containing diol in the polyol component (A) is present in an amount to provide a molar concentration of hydroxy groups in the oxime-containing diol, relative to total moles of hydroxy groups in the polyol component (A) , in a range of from 40 to 90 mole percent; and

(a2) a polyol selected from the group consisting of a polyester polyol, a polyether polyol, castor oil, a polyhydric alcohol, and combinations thereof; and

(B) an isocyanate component comprising an isocyanate prepolymer that is the reaction product of reactants comprising: (b1) a polyisocyanate; and (b2) a polyol selected from the group consisting of a polyester polyol, a polyether polyol, castor oil, and combinations thereof.

In a second aspect, the present invention provides a laminate comprising a first substrate, a second substrate, and an adhesive layer residing between the first and second substrates, wherein the adhesive layer is a cured product of the two-component adhesive composition of the first aspect.

In a third aspect, the present invention provides a method of making a laminate. The method comprises the steps of: I) applying the two-component adhesive composition of first aspect to a surface of a first substrate; II) bringing the two-component adhesive composition on the surface of the first substrate into contact with a surface of a second substrate; and III) curing, or allowing to cure, the two-component adhesive composition; thereby forming the laminate.

In a fourth aspect, the present invention relates to a process for debonding the laminate of the second aspect. The process comprises: treating the laminate with an aqueous alkali solution, wherein the aqueous alkali solution comprises water, an inorganic base, and a cosolvent selected from an alcohol, an ester, an ether, a ketone, or mixtures thereof.

In a fifth aspect, the present invention is an article comprising the laminate of the second aspect.

DETAILED DESCRIPTION

Test methods refer to the most recent test method as of the priority date of this document when a date is not indicated with the test method number. References to test methods contain both a reference to the testing society and the test method number. The following test method abbreviations and identifiers apply herein: ASTM refers to ASTM International methods.

Products identified by their tradename refer to the compositions available under those tradenames on the priority date of this document.

“And/or” means “and, or as an alternative” . All ranges include endpoints unless otherwise indicated.

A “polyol” herein refers to a compound having an average of more than one hydroxyl group (OH) per molecule. A polyol with exactly two hydroxyl groups is a “diol. ” A polyol with exactly three hydroxy groups is a “triol. ”

Designations of the type C_x-C_y refers to having from x to y number of carbon atoms.

The two-component adhesive composition (also referred to as “adhesive composition” ) of the present invention comprises the component (A) a polyol component, and the component (B) an isocyanate component.

The polyol component (A) useful in the present invention comprises: (a1) a specific oxime-containing diol described herein below, and (a2) a polyol selected from the group consisting of a polyester polyol, a polyether polyol, castor oil, a polyhydric alcohol that is other than the specific oxime-containing diol, and combinations thereof.

The polyol component (A) comprises (a1) one or more oxime-containing diol having the structure of formula (I) :

where R₁ and R₂ are each independently H (ahydrogen atom) , an alkyl group having from 1 to 30 carbon atoms, or an aryl group having from 6 to 30 carbon atoms; and R is a single carbon-carbon bond, an alkylene group having from 1 to 30 carbon atoms, or an arylene group having from 6 to 30 carbon atoms; or

R, R₁, and R₂ together are bonded to form a cyclic ring having from 4 to 10 carbon atoms, desirably, 5, 6, 7, or 8 carbon atoms. R₁ and R₂ may be the same or different. Desirably, R₁ and R₂ are the same.

“Alkyl” means a cyclic, branched, or unbranched, saturated monovalent hydrocarbon group. “Monovalent hydrocarbon group” means a univalent group made up of hydrogen and carbon atoms. The alkyl groups suitable for R₁ and R₂ may have from 1 to 30 carbon atoms, from 1 to 24 carbon atoms, from 1 to 12 carbon atoms, from 1 to 8 carbon atoms, or from 1 to 6 carbon atoms. Suitable alkyl groups for R₁ and R₂ may include, for example, methyl, ethyl, propyl (e.g., iso-propyl and/or n-propyl) , butyl (e.g., isobutyl, n-butyl, tert-butyl, and/or sec-butyl) , pentyl (e.g., isopentyl, neopentyl, and/or tert-pentyl) , hexyl, as well as branched saturated hydrocarbon groups of 6 carbon atoms, cyclopentyl, cyclohexyl, or dimethyl cyclohexyl. Each R₁ and R₂ independently can be an alkyl group. Desirably, R₁ and R₂ are each independently H or methyl, more desirably, methyl. “Aryl” means a group containing a cyclic, fully unsaturated, hydrocarbon group. The aryl groups suitable for R₁ and R₂ may have from 6 to 30, from 6 to 24, from 6 to 18, or from 6 to 12 carbon atoms. R₁ and R₂ may be each independently phenyl, tolyl, xylyl, naphthyl, benzyl, or dimethyl phenyl, desirably, phenyl.

“Alkylene” means a divalent group by removing one hydrogen atom from an alkyl group such as the alkyl group descried above. “Arylene” means a divalent group by removing one hydrogen atom from an aryl group such as the aryl group described above. When R is a single carbon-carbon bond, the oxime-containing diol is represented by the following structure:

where R₁ and R₂ are as described above.

Desirably, R is a single carbon-carbon bond or an alkylene group having from 1 to 24 carbon atoms, and can be from 1 to 12, from 1 to 8, or from 1 to 6 caron atoms. Particularly, R may be a single carbon-carbon bond, -CH₂-, -CH₂-CH₂-, -CH₂-CH₂-CH₂, or Desirably, R is a single carbon-carbon bond or -CH₂-.

If R, R₁, and R₂ together are bonded (i.e., connected) to form a cyclic ring, such cyclic ring can be aliphatic or aromatic. The cyclic ring may be unsubstituted or substituted, desirably, the cyclic ring is substituted by an alkyl group having 1 to 6 carbon atoms. Specific examples of such oxime-containing diols include:

or mixtures thereof.

Suitable oxime-containing diols may include any one or any combination of more than one of the following oxime-containing diols:

Desirably, the oxime-containing diol comprises, or can consist of,

The oxime-containing diol is typically dissolved in a solvent before incorporated into the adhesive composition, for example, in the polyol component (A) . The solvent can be any protonic or non-protonic solvent that is capable of dissolving the oxime-containing diol, including, for example, ethyl acetate, isobutyl ketone, or mixtures thereof.

The oxime-containing diol in the polyol component (A) is present in an amount sufficient to provide a molar concentration of hydroxyl groups in the oxime-containing diol, relative to the total moles of hydroxyl groups in the polyol component (A) , in a range of from 40 to 90 mole percent (mol%) , and can be 45 mol%or more, 48 mol%or more, 50 mol%or more, 52 mol%or more, 54 mol%or more, 56 mol%or more, 58 mol%or more, 60 mol%or more, 65 mol%or more, even 70 mol%or more while at the same time is 90 mol%or less, and can be 89 mol%or less, 88 mol%or less, 86 mol%or less, 85 mol%or less, 84 mol%or less, 82 mol%or less, or even 80 mol%or less, desirably from 48 to 85 mol%, more desirably from 50 to 80 mol%.

The polyol component (A) useful in the present invention also comprises (a2) a polyol that is different from the oxime-containing diol described above and is selected from the group consisting of a polyester polyol, a polyether polyol, castor oil, a polyhydric alcohol that is other than the oxime-containing diol described above, and combinations thereof.

The polyether polyol and polyester polyol useful in the present invention typically independently have a molecular weight of from 400 to 5,000 g/mol, and can be 500 g/mol or more, 600 g/mol or more, 800 g/mol or more, 1, 100 g/mol or more, 1, 500 g/more or more, even 2,000 g/mol or more while at the same time is 5,000 g/mol or less, and can be 4, 500 g/mol or less, 4,000 g/mol or less, 3, 500 g/mol or less, 3,000 g/mol or less, or even 2,000 g/mol or less, desirably from 400 to 2,000 g/mol, more desirably from 800 to 2,000 g/mol. Molecular weight herein refers to the weight average molecular weight (M_w) and can be measured by gel permeation chromatography (GPC) or calculated by (56100*f) /OHV, where f represents an average number of hydroxyl groups per molecule of the polyol (also referred as “OH functionality” ) , and OHV represents hydroxyl value of the polyol in the units of milligrams potassium hydroxide per gram sample (mg KOH/g) as determined by ASTM D4274-21.

The polyol (a2) in the polyol component (A) may comprise or be free of one or more polyester polyols. An ester is a compound that contains an ester linkage having the structure: in which both of the open bonds are connected to carbon atoms. A polyester is a compound that contains three or more ester linkages per molecule. A compound that is both a polyester and a polyol is a polyester polyol. An aliphatic polyester polyol is a polyester polyol that contains no aromatic ring in its molecule. An aromatic polyester polyol is a polyester polyol that contains one or more aromatic rings in its molecule. Suitable polyester polyols may include, for example, aliphatic polyester polyols such as polycaprolactone polyols or polyols made from aliphatic diacids and aliphatic diols and triols, aromatic polyester polyols made from phthalic acid or anhydride reacting with diols or triols, or mixtures thereof. The polyester polyol may have an average hydroxyl functionality of from 1.8 to 3.0 or from 2.0 to 3.0. “Average hydroxyl functionality” herein refers to the average number of hydroxyl groups per molecule, i.e., total moles of OH groups divided by total moles of polyols.

The polyester polyol useful in the present invention can be a polycondensate of (i) a diol (and optionally, a polyol having a functionality higher than 2 such as triols and/or tetraols) , and (ii) a dicarboxylic acid (and optionally, an additional polycarboxylic acid (e.g., a tricarboxylic acid and/or tetracarboxylic acid) or a hydroxycarboxylic acid) or a lactone. The diol herein may include a compound represented by the general formula HO- (CH₂) _z-OH, where z is an integer from 2 to 16 or from 3 to 6, where one hydrogen atom of a methylene unit may also be replaced by an alkyl group having from 1 to 4 carbon atoms. Suitable diols may be selected from the group consisting of ethylene glycol, butylene glycol, diethylene glycol, triethylene glycol, polyalkylene glycols such as polyethylene glycol, 1, 2-propanediol, 1, 3-propanediol, 1, 3-butanediol, 1, 4-butanediol, 1, 6-hexanediol, neopentyl glycol, and mixtures thereof. The dicarboxylic acid can be an aliphatic acid, an aromatic acid, or mixtures thereof. As used herein, the term “acid” also includes any anhydrides of said acid. Desirably, the aliphatic acid and/or the aromatic acid are saturated. Suitable examples of aromatic acids include phthalic acid, isophthalic acid, terephthalic acid, and tetrahydrophthalic acid. Suitable aliphatic acids include hexahydrophthalic acid, cyclohexane dicarboxylic acid, adipic acid, azelaic acid, sebacic acid, glutaric acid, tetrachlorophthalic acid, maleic acid, fumaric acid, itaconic acid, malonic acid, suberic acid, 2-methyl succinic acid, 3, 3-diethyl glutaric acid, 2, 2-dimethyl succinic acid, trimellitic acid, or mixtures thereof. Desirably, the dicarboxylic acid is selected from adipic acid, sebacic acid, azelic acid, or mixtures thereof. Exemplary lactones include ε-caprolactone, methyl-ε-caprolactone, β-propiolactone, γ-butyrolactone, or mixtures thereof. The polyol having a functionality of greater than 2 may include, for example, trimethylolpropane, glycerol, erythritol, pentaerythritol, trimethylolbenzene or trishydroxyethyl isocyanurates, or mixtures thereof; and can be optionally included to prepare a polyester polyol with a functionality greater than 2.

The polyester polyol in the polyol component (A) may be present in an amount to provide a molar concentration of hydroxy groups in the polyester polyol in a range of from zero to 60 mol%, and can be zero or more, 5 mol%or more, 10 mol%or more, 15 mol%or more, 20 mol%or more, 25 mol%or more, 30 mol%or more, 35 mol%or more, even 40 mol%or more while at the same time is 60 mol%or less, and can be 55 mol%or less, 50 mol%or less, or even 45 mol%or less, alternatively, 0 to 50 mol%, alternatively, from 20 to 40 mol%, based on the total moles of hydroxy groups in the polyol component (A) .

The polyol (a2) in the polyol component (A) may comprise or be free of one or more polyether polyols. A “polyether polyol” is a polyol that contains three or more ether linkages per molecule. The polyether polyol may have an average hydroxyl functionality of from 1.8 to 6.0, and can be 2.0 or more, greater than 2.0, 2.1 or more, 2.2 or more, 2.3 or more, 2.4 or more, even 2.5 or more while at the same time is 6.0 or less, and can be 4.0 or less, 3.9 or less, 3.8 or less, 3.7 or less, 3.6 or less, 3.5 or less, 3.4 or less, 3.2 or less, 3.1 or less, 3.0 or less, 2.9 or less, 2.8 or less, or even 2.7 or less, desirably from 2.0 to 4.0.

The polyether polyol useful in the present invention can be the ring open polymerization products of ethylene oxide, propylene oxide, tetrahydrofuran, butylene oxide, or mixtures thereof; co-addition and grafted products thereof; polyether polyols obtained by condensation of polyhydric alcohols; or mixtures thereof. The polyether polyols may be initiated with, for example, water or polyhydric alcohols (such as dihydric to pentahydric alcohols or dialkylene glycols) including, for example, ethanediol, 1, 2-and 1, 3-propanediol, diethylene glycol, dipropylene glycol, 1, 4-butanediol, 1,6-hexanediol, glycerol, trimethylolpropane, pentaerythritol, sorbitol, and sucrose or blends thereof; linear and cyclic amine compounds which may also contain a tertiary amine such as ethanoldiamine, triethanoldiamine, and various isomers of toluene diamine, methyldiphenylamine, aminoethylpiperazine, ethylenediamine, N-methyl-1, 2-ethanediamine, N-methyl-1, 3-propanediamine, N, N-dimethyl-1, 3-diaminopropane, N, N-dimethylethanolamine, diethylene triamine, bis-3-aminopropyl methylamine, aniline, aminoethyl ethanolamine, 3, 3-diamino-N-methylpropylamine, N, N-dimethyldipropylenetriamine, aminopropyl-imidazole, or mixtures thereof; or a combination of at least two of them. Examples of suitable polyether polyols include polypropylene glycol ( “PPG” ) , polyethylene glycol ( “PEG” ) , polybutylene glycol, polytetramethylene ether glycol ( “PTMEG” ) , propylene oxide/ethylene oxide copolymer polyols, ethylene oxide-capped polyether polyols, or mixtures thereof.

The polyether polyol useful in the present invention may have an average hydroxy number of from 20 to 500 mg KOH/g or from 50 to 400 mg KOH/g, according to ASTM D4274-21. The polyether polyol may have an average equivalent weight of from 140 to 6,000, and can be 140 or more, 200 or more, 300 or more, 400 or more, even 500 or more while at the same time is 6,000 or less, and can be 4,000 or less, 3,000 or less, 2,000 or less, or even 1,000 or less. Equivalent weight is the weight of a polyol per reactive site. Equivalent weight is calculated by 56000/ (OH number in mg KOH/g) .

Suitable examples of commercially available polyether polyols include VORANOL^TM CP450, VORANOL^TM 1010L, VORANOL^TM CP 1050 and VORANOL^TM W2104 polyether polyols all available from The Dow Chemical Company (VORANOL is a trademark of The Dow Chemical Company) .

The polyether polyol may be present in the polyol component (A) in an amount to provide a molar concentration of hydroxy groups in the polyether polyol in a range of from zero to 60 mol%, and can be zero or more, 5 mol%or more, 10 mol%or more, 15 mol%or more, 20 mol%or more, 25 mol%or more, 30 mol%or more, 35 mol%or more, even 40 mol%or more while at the same time is 60 mol%or less, and can be 55 mol%or less, 50 mol%or less, or even 45 mol%or less, alternatively, from zero to 50 mol%, alternatively, from 20 to 40 mol%, based on the total moles of hydroxy groups in the polyol component.

The polyol (a2) in the polyol component (A) may comprise or be free of castor oil. The castor oil may have an average hydroxy functionality of from 2.0 to 4.0, and can be 2.1 or more, 2.2 or more, 2.5 or more, 2.6 or more, even 2.7 or more while at the same time is 4.0 or less, and can be 3.8 or less, 3.5 or less, 3.2 or less, 3.0 or less, 2.8 or less, or even 2.7 or less, desirably, from 2.5 to 2.8. The castor oil may be present in the polyol component (A) in amount to provide a molar concentration of hydroxy groups in the castor oil in a range of from zero to 60 mol%, and can be zero or more, 5 mol%or more, 10 mol%or more, 15 mol%or more, 20 mol%or more, 25 mol%or more, 30 mol%or more, 35 mol%or more, even 40 mol%or more while at the same time is 60 mol%or less, and can be 55 mol%or less, 50 mol%or less, or even 45 mol%or less, alternatively, 0 to 40 mol%, alternatively, from 10 to 30 mol%, based on the total moles of hydroxy groups in the polyol component (A) .

The polyol (a2) in the polyol component (A) may comprise or be free of one or more polyhydric alcohols that are other than the oxime-containing diol described above. The polyhydric alcohol typically has a molecular weight less than 400 g/mol. The polyhydric alcohol may contain from 2 to 6 hydroxyl groups. The polyhydric alcohol may include a C₂-C₁₆ aliphatic polyhydric alcohol, a C₆-C₁₅ cycloaliphatic polyhydric alcohol, or mixtures thereof. Desirably, the polyhydric alcohol is a linear and/or branched diol having the structure represented by general formula of HO-(CH₂) _y-OH, where y is an integer from 1 to 16 or an integer from 2 to 9. Examples of suitable polyhydric alcohols include ethylene glycol, 1, 2-propanediol, 1, 3-propanediol, 1, 2-butanediol, 1, 3-butanediol, 1, 4-butanediol, 1, 5-pentanediol, neopentylglycol, bis (hydroxy-methyl) cyclohexanes such as 1, 4-bis (hydroxymethyl) cyclohexane, 2-methylpropane-1, 3-diol, methylpentanediols, diethylene glycol, triethylene glycol, tetraethylene glycol, dipropylene glycol, dibutylene glycol, or mixtures thereof.

The polyhydric alcohol may be present in the polyol component (A) in an amount to provide a molar concentration of hydroxy groups in the polyhydric alcohol, in a range of from zero to 60 mol%, and can be zero or more, 5 mol%or more, 10 mol%or more, 15 mol%or more, 20 mol%or more, 25 mol%or more, 30 mol%or more, 35 mol%or more, even 40 mol%or more while at the same time is 60 mol%or less, and can be 55 mol%or less, 50 mol%or less, or even 45 mol%or less, alternatively, from zero to 50 mol%, alternatively, from 20 to 50 mol%, based on the total moles of hydroxy groups in the polyol component (A) .

The adhesive composition of the present invention also comprises the component (B) isocyanate component. The isocyanate component (B) comprises: an isocyanate prepolymer that is the reaction product of reactants (hereinafter referred to as “prepolymer reactants” ) comprising: (b1) a polyisocyanate; (b2) a polyol selected from the group consisting of a polyester polyol, a polyether polyol, castor oil, and combinations thereof; and optionally, (b3) the oxime-containing diol having the structure of formula (I) described above. The oxime-containing diol (b3) can be as described above in the polyol component (A) section. The oxime-containing diol in the prepolymer reactants can be the same or different from the oxime-containing diol in the polyol component (A) .

A “polyisocyanate” refers to any compound that contains two or more isocyanate (NCO) groups. A polyisocyanate that contains exactly two isocyanate groups is a diisocyanate. The polyisocyanate may comprise a monomeric diisocyanate, a polymeric isocyanate, an isocyanate prepolymer, or mixtures thereof. The polyisocyanates can be aromatic, aliphatic, araliphatic or cycloaliphatic polyisocyanates, or mixtures thereof. Preferred polyisocyanates are aromatic polyisocyanates. An “aromatic polyisocyanate” refers to a polyisocyanate that contains one or more aromatic rings. An “aliphatic polyisocyanate” refers to a polyisocyanate containing no aromatic rings.

The isocyanate prepolymer in the isocyanate component (B) may have an isocyanate group (NCO) content of 4 to 20 wt%or more, and can be 4 wt%or more, 6 wt%or more, 8 wt%or more, even 10 wt%or more while at the same time is 20 wt%or less, and can be 19 wt%or less, 18 wt%or less, 17 wt%or less, 16 wt%or less, or even 15 wt%or less. The NCO content herein refers to the weight percentages of NCO groups relative to the isocyanate prepolymer weight, as measured according to ASTM D2572.

The isocyanate prepolymer can be prepared by prepolymer reactants comprising the polyol (b2) , and optionally, the oxime-containing diol (b3) , and a stoichiometric excess of the polyisocyanate (b1) . The polyisocyanate (b1) useful for preparing the isocyanate prepolymer may be selected from the group consisting of aromatic polyisocyanates, aliphatic polyisocyanates, and combinations thereof. The polyisocyanate (b1) may have an average NCO functionality of 2.0 or more, and can be from 2.0 to 7.0, from 2.0 to 5.0, or from 2.0 to 3.0. Suitable aromatic polyisocyanates may include, for example, monomeric diisocyanates including isomers of methylene diphenyl dipolyisocyanate (MDI) such as 4, 4′-MDI, 2, 4′-MDI and 2, 2′-MDI, 1, 3-and 1, 4-phenylene diisocyanate, isomers of toluene-dipolyisocyanate (TDI) such as 2, 4-TDI, 2, 6-TDI, 3, 3′-Dimethyl-4, 4′-Biphenyldiisocyanate (TODI) , isomers of naphthalene-dipolyisocyanate (NDI) such as 1, 5-NDI, xylene dipolyisocyanate (XDI) ; polymeric derivatives thereof, such as dimers of the above monomeric diisocyanatesdi and/or trimers of the above monomeric diisocyanates; and combinations thereof. Suitable aliphatic polyisocyanates may include, for example, monomeric diisocyanates including hexamethylene diisocyanate (HDI) , cyclohexane diisocyanate, methylcyclohexane diisocyanate, ethylcyclohexane diisocyanate, propylcyclohexane diisocyanate, methyldiethylcyclohexane diisocyanate, propane diisocyanate, butane diisocyanate, pentane diisocyanate, hexane diisocyanate, heptane diisocyanate, octane diisocyanate, nonane diisocyanate, nonane triisocyanate, such as 4-isocyanatomethyl-1, 8-octane diisocyanate (TIN) , decane di-and triisocyanate, undecane di-and triisocyanate and dodecane di-and triisocyanate, isophorone diisocyanate (IPDI) , diisocyanatodicyclohexylmethane (H₁₂MDI) , 2-methylpentane diisocyanate (MPDI) , 2, 2, 4-trimethylhexamethylene diisocyanate/2, 4, 4-trimethylhexamethylene diisocyanate (TMDI) , and norbornane diisocyanate (NBDI) ; polymeric derivatives thereof, such as dimers of the above monomeric diisocyanates and/or trimers of the above monomeric diisocyanates; and combinations thereof. Desirably, the polyisocyanate (b1) comprises, or can consist of, an aromatic polyisocyanate such as MDI. Particularly, a mixture of 2, 4′-MDI and 4, 4′-MDI can be used.

The amount of the polyisocyanate (b1) for preparing the isocyanate prepolymer may be, based on the weight of the isocyanate prepolymer, in a range of from 20 to 70 wt%, and can be 22 wt%or more, 24 wt%or more, 25 wt%or more, 30 wt%or more, 35 wt%or more, 40 wt%or more, 45 wt%or more, even 50 wt%or more while at the same time is 70 wt%or less, and can be 68 wt%or less, 66 wt%or less, 65 wt%or less, 64 wt%or less, 62 wt%or less, 60 wt%or less, 55 wt%or less, 50 wt%or less, 45 wt%or less, or even 40 wt%or less, alternatively from 20 to 40 wt%, alternatively from 45 to 65 wt%, alternatively from 50 to 60 wt%.

The polyol (b2) for preparing the isocyanate prepolymer is selected from the group consisting of a polyester polyol, a polyether polyol, castor oil, and combinations thereof.

The polyol (b2) for preparing the isocyanate prepolymer may comprise or be free of one or more polyester polyols. The polyester polyols suitable for the polyol (b2) may include the polyester polyol described above for the polyol (a2) in the polyol component (A) section above. The amount of the polyester polyol for preparing the isocyanate prepolymer may be, based on the weight of the isocyanate prepolymer, in a range of from zero to 50 wt%, and can be zero or more, 2 wt%or more, 5 wt%or more, 8 wt%or more, 10 wt%or more, 12 wt%or more, 14 wt%or more, even 15 wt%or more while at the same time is 50 wt%or less, and can be 45 wt%or less, 40 wt%or less, 35 wt%or less, 30 wt%or less, 28 wt%or less, 26 wt%or less, 25 wt%or less, 24 wt%or less, 22 wt%or less, 20 wt%or less, 18 wt%or less, or even 15 wt%or less, alternatively from 5 to 35 wt%, alternatively from 10 to 35 wt%, alternatively from 10 to 20 wt%.

The polyol (b2) for preparing the isocyanate prepolymer may comprise or be free of one or more polyether polyols. The polyether polyols suitable for the polyol (b2) may include the polyether polyols described above for the polyol (a2) in the polyol component (A) section above.

The amount of the polyether polyol for preparing the isocyanate prepolymer may be, based on the weight of the isocyanate prepolymer, in a range of from zero to 50 wt%, and can be 2 wt%or more, 5 wt%or more, 8 wt%or more, 10 wt%or more, even 15 wt%or more while at the same time is 50 wt%or less, and can be 45 wt%or less, 40 wt%or less, 35 wt%or less, 30 wt%or less, 25 wt%or less, or even 20 wt%or less, alternatively, from 10 to 50 wt%, alternatively, from 15 to 25 wt%, alternatively from 35 to 50 wt%.

The polyol (b2) for preparing the isocyanate prepolymer may comprise or be free of castor oil. The castor oil useful for the polyol (b2) may include castor oil described above for the polyol (a2) in the polyol component (A) section above. The amount of castor oil may be, based on the weight of the isocyanate prepolymer, in a range of from zero to 30 wt%, and can be 0.1 wt%or more, 0.5 wt%or more, 1 wt%or more, 2 wt%or more, 5 wt%or more, 8 wt%or more, even 10 wt%or more while at the same time is 30 wt%or less, and can be 28 wt%or less, 25 wt%or less, 22 wt%or less, 20 wt%or less, or even 15 wt%or less, desirably from 5 to 30 wt%, more desirably from 10 to 15 wt%.

The total amount of the polyol (b2) (i.e., the combined amounts of the polyester polyol, the polyether polyol, and castor oil, if used) for preparing the isocyanate prepolymer can be, based on the weight of the isocyanate prepolymer, in a range of from 30 to 80 wt%, and can be 30 wt%or more, 32 wt%or more, 34 wt%or more, 35 wt%or more, 36 wt%or more, 38 wt%or more, 40 wt%or more, 45 wt%or more, 50 wt%or more, 55 wt%or more, even 60 wt%or more while at the same time is 80 wt%or less, and can be 78 wt%or less, 76 wt%or less, 75 wt%or less, 70 wt%or less, 65 wt%or less, 60 wt%or less, 55 wt%or less, or even 50 wt%or less, alternatively, from 60 to 80 wt%, alternatively, from 35 to 55 wt%, alternatively, from 40 to 50 wt%.

The polyol (b2) for preparing the isocyanate prepolymer may be a mixture of the polyether polyol and castor oil, or a mixture of the polyether polyol and the polyester polyol.

The polyol (b2) may comprise, or can consist of, from 10 to 30 wt%of the polyether polyol and 5 to 30 wt%of castor oil, based on the weight of the isocyanate prepolymer. Desirably, the isocyanate prepolymer is the reaction product of reactants comprising, based on the weight of the isocyanate prepolymer, from 40 to 70 wt%of the polyisocyanate (b1) , from 10 to 30 wt%of the polyether polyol, and from 5 to 30 wt%of castor oil.

The polyol (b2) may comprise, or can consist of, from 15 to 40 wt%of the polyester polyol and from 10 to 65 wt%of the polyether polyol, based on the weight of the isocyanate prepolymer. Desirably, the isocyanate prepolymer is the reaction product of reactants comprising, based on the weight of the isocyanate prepolymer, from 20 to 50 wt%of the polyisocyanate (b1) , from 15 to 40 wt%of the polyester polyol, and from 10 to 65 wt%of the polyether polyol.

The prepolymer reactants for preparing the isocyanate prepolymer may comprise or be free of (b3) the oxime-containing diol as described in the polyol component (A) section above, such as The amount of the oxime-containing diol (b3) in the prepolymer reactants may be in a range of from zero to 30 wt%, and can be 20 wt%or less, 10 wt%or less, or from zero to 5 wt%, based on the weight of the isocyanate prepolymer.

The weight ratio of the isocyanate component (B) to the polyol component (A) in the adhesive composition of the present invention may be in a range of from 100: 5 to 80: 100, and can be 100: 6 or lower, 100: 10 or lower, 100: 20 or lower, 100: 30 or lower, 100: 40 or lower while at the same time 80: 100 or higher, and can be 90: 100 or higher, 100: 100 or higher, 100: 70 or higher, 100: 60 or higher, or even 100: 50 or higher, alternatively from 100: 5 to 100: 70, alternatively from 100: 5 to 100: 50; alternatively from 100: 30 to 100: 100, alternatively from 100: 40 to 100: 80.

Alternatively, the polyol component (A) and the isocyanate component (B) can be present in amounts sufficient to provide a molar ratio of total isocyanate groups in the isocyanate component (B) to total hydroxyl groups in the polyol component (A) in a range of from 1: 1 to 3: 1, and can be 1.05: 1 or higher, 1.1: 1 or higher, 1.2: 1 or higher, 1.5: 1 or higher, even 1.8: 1 or higher while at the same time is 3: 1 or lower, and can be 2.8: 1 or lower, 2.5: 1 or lower, 2.2: 1 or lower, 2.0: 1 or lower, or even 1.8: 1 or lower, desirably from 1: 1 to 2: 1, more desirably from 1.2: 1 to 1.8: 1.

The adhesive composition of the present invention may comprise or be free of a solvent. Suitable solvents may include, for example, acetone, methyl ethyl ketone, toluene, 1, 3-dioxolane, ethanol, isopropanol, those described above used for dissolving the oxime-containing diol such as ethyl acetate, or mixture thereof. Desirably, the solvent is ethyl acetate. The solvent may be present in the polyol component (A) and/or the isocyanate component (B) . The total amount of the solvent can be, based on the total weight of the adhesive composition, in a range of from zero to 80 wt%, and can be 5 wt%or more, 10 wt%or more, even 15 wt%or more while at the same time is 80 wt%or less, and can be 75 wt%or less, or even 70 wt%or less, desirably from 15 to 70 wt%.

The adhesive composition of the present invention may comprise or be free of any one or any combination of more than one of the following additives: pigments, adhesion promoters, plasticizers, stabilizers such as ultraviolet stabilizers, flame retardants, and antioxidants. These additives may be present in the polyol component (A) and/or the isocyanate component (B) at a total concentration of from zero to 10 wt%, from 0.1 to 5 wt%, or from 0.5 to 1 wt%, based on the total weight of the adhesive composition.

The present invention also provides a process for preparing the two-component adhesive composition described above. Such process comprises admixing the polyol component (A) and the isocyanate component (B) . Mixing in the process for preparing the adhesive composition can be conducted by conventional means, for example, through cold-blending process, typically at room temperature (23±2 degrees Celsius (℃) ) . The polyol component (A) and isocyanate component (B) can be made separately and, if desired, stored until it is desired to use the adhesive composition. The two components are reactive with one another and when contacted or mixed upon application have adhesive properties and undergo a curing reaction (e.g., reaction between the isocyanate groups and the hydroxyl groups, forming urethane links) , where the reaction product of the two components is a cured product that is capable of bonding certain substrates together. The adhesive composition, upon curing, forms the cured product, i.e., a polyurethane (PU) adhesive. The adhesive composition is useful for adhering a wide variety of polymer materials, particularly, polymer films described herein below.

The adhesive composition of the present invention is suitable for use in flexible packaging applications, such as food packaging or non-food packaging applications. The adhesive made from the adhesive composition (i.e., upon curing) is debondable when subject to treatment under mild conditions such as an aqueous alkali solution (described herein below) , thereby enabling mechanical recycling of flexible packaging using existing recycling process.

The adhesive composition of the present invention is particularly suitable for use as laminating adhesives in laminate applications. The present invention also provides a laminate comprising a first substrate, a second substrate, and an adhesive layer residing between the first and second substrates, where the adhesive layer is the cured product of the adhesive composition described above. The adhesive layer is typically in contact with the first and second substrates, such as the first and second substrates are bonded via the adhesive layer. The first and second substrates can be the same or different. Suitable substates may include, for example, polymer films, metalized polymer films, or combinations thereof. Desirably, the first and second substrate are films, particularly, polymer films. The polymer films optionally have a surface on which an image is printed with ink. The ink may be in contact with the adhesive composition. Suitable polymers for the first substrate and the second substrate may include, for example, polyolefins such as polyethylenes and polypropylenes, polyolefin copolymers, polycarbonates, polyesters, and polyamides (also known as “nylons” ) . Polyolefins are homopolymers and copolymers of olefin monomers, which are hydrocarbon molecules containing one or more carbon-carbon double bond. Polyolefin copolymers are copolymers of one or more olefin monomer with one or more vinyl acetate, acrylate monomers, and methacrylate monomers. Suitable first and second substrates may include, for example, polyethylene terephthalate (PET) films, polyamide films, polyethylene (PE) films, polypropylene (PP) films, metalized PET film, metalized PP films, and metalized PE films. Desirably, the first and/or second substrates include PE films, PET films, nylon films, or combinations thereof. More desirably, the first and second substrates are PE and nylon films. Alternatively, the first and second substrates are PE and PET films. Alternatively, the first and/or second substrates are each independently metal-coated films of the polymers described above, such as those coated with aluminum oxide, silicon oxide, and combinations thereof. The surface of the first and/or second substrate can be optionally surface treated prior to application of the adhesive composition of the present invention. Any known surface treatment means which increase the number of polar groups present on the surface of the substrates such as plastics may be used, including corona discharge, and plasma treatment. The laminate may comprise three or more layers of the polymer films and the metalized polymer films described above, which can be the same or different, and the adhesive described above residing between and adhered to the film layers.

The laminate of the present invention can be made by a method comprising: I) applying the adhesive composition to a surface of the first substrate; II) bringing the adhesive composition on the surface of the first substrate into contact with a surface of the second substrate, and III) curing, or allowing to cure, the adhesive composition; thereby forming the laminate.

In step I) , the adhesive composition can be applied to at least a portion of the surface of the first substrate, which can be conducted at ambient temperature (for example, from 23 to 35 ℃) . The coating weight of the adhesive composition to the first substate typically ranges from 0.8 to 5.0 grams per square meter (g/m²) , from 1 to 4.0 g/m², or from 1.5 to 3.0 g/m².

In step II) , bringing the adhesive composition on the surface of the first substrate into contact with the surface of the second substrate can be conducted by laminating the coated first substrate with the second substrate such that the adhesive composition resides therebetween, typically using conventional laminating equipment (such as Hot Roll Laminator from ChemInstruments) under conventional conditions. Laminating temperatures may be adjusted according to the substate materials being laminated, for example, 70 ℃ or lower, and can be 60 ℃ or lower, 55 ℃ or lower, 40 ℃ or lower, even room temperature. Before contacting the second substrate, the adhesive composition on the first substrate obtained from step I) may be allowed for a period of time sufficient to dry, for example, from 0.01 to 3 minutes, from 0.1 to 3 minutes, or from 0.1 to 2 minutes, at temperatures typically ranging from room temperature to less than 100 ℃, and can be from 60 to 100 ℃, from 80 to 95 ℃ depending on lamination methods.

Curing, or allowing to cure, the adhesive composition (e.g., in step III) can be conducted at ambient temperature or elevated temperatures to speed up the curing reaction between the polyol component (A) and the isocyanate component (B) , without degradation of either the substrates (e.g., films) or the adhesive composition, e.g., at room temperature or higher, and can be 35 ℃ or higher, 40 ℃ or higher, 50 ℃ or higher, and can be 60 ℃ or lower, desirably from 40 to 50 ℃. The curing of the adhesive composition may be further accelerated by applying convection heat, infrared irradiation, induction heating, microwave heating, and/or enhancing the amount of moisture in the atmosphere such as by using a humidity chamber.

The method of making the laminate of the present invention may comprise one or more step of applying pressure. For example, pressure may be applied after contacting the adhesive composition with the surface of the second substrate. Desirably, the first substrate and second substrate are run through a device for applying external pressure to the first and second substrates, which may be helpful to facilitate different layers of the resultant laminate to closely contact and/or adhere with each other. Applying pressure may be conducted at conventional equipment, for example, by passing the laminate between rollers such as nip rollers. The step of applying pressure may be conducted at room temperature or at elevated temperatures such as those described in the step III) above to speed up the curing reaction.

The laminate of the present invention or the laminate prepared by the method described above is suitable for use in an article. The article, particularly, a flexible food packaging article, comprises such laminate. The adhesive composition of the present invention, upon curing, forms the adhesive that provides a laminate comprising nylon and PE films as the first and second substrates with a bond strength of at least 4.0 N/15mm. The adhesive is also debondable when treated under mild conditions described herein below, as indicated by at least 60%decrease in bond strength of the laminate after treatment, which facilitates easy debonding of the laminate. Bond strength properties may be measured according to the Bond Strength Test described in the Examples section below. Particularly, the laminate of the present invention can be delaminated under mild conditions, that is, the first and second substrates of the laminate are detached or separated from each other by themselves.

The present invention also relates to a process for debonding the laminate (hereinafter also referred to as “debonding process” ) . The process comprises the step of treating the laminate with an aqueous alkali solution. “Debonding” means a decrease in bond strength of the laminate after treated by the aqueous alkali solution being at least 60%, desirably at least 70%, more desirably at least 90%, as compared to the bond strength of the laminate before (without) treatment (i.e., initial bond strength) . Desirably, the debonding process results in delamination of the laminate. The aqueous alkali solution may comprise water, an inorganic base, and a cosolvent selected from an alcohol, an ester, an ether, a ketone, or mixtures thereof. Suitable cosolvents may include, for example, ethanol, isopropanol, acetone, 1-butanol, t-butyl alcohol, or mixtures thereof. The cosolvent may be present, based on the total volume of the aqueous alkali solution, at a volume concentration of from 3 to 80 volume percent (vol%) , from 10 to 60 vol%, or from 30 to 50 vol%. Suitable inorganic bases may comprise, for example, sodium carbonate, sodium hydroxide, potassium carbonate, potassium hydroxide, sodium bicarbonate, potassium bicarbonate, or mixtures thereof. The concentration of the aqueous alkali solution is typically in a range of from 1 to 20 wt%and can be from 3 to 15 wt%or from 5 to 10 wt%, desirably less than 10 wt%, based on the total weight of the aqueous alkali solution. Temperatures for treating the laminate may vary depending on the amount of time for treating, for example, in a range of from 10 to 100 ℃, from 20 to 80 ℃, or lower than 60 ℃, even at room temperature. Thus, the treatment can be conducted under mild conditions, such as using the aqueous alkali solution at temperatures up to 60 ℃. Time for treating the laminate depending on the treating temperatures as long as the laminate can be debonded, for example, 1 to 12 hours or 3 to 8 hours, typically under stirring. After treating in step a) , different layers of the laminate, such as the first and the second substrates, are easily detached from each other such that they can be recycled separately via conventional mechanically recycling process. The debonding process may include mechanical shearing during the aqueous alkali solution treatment such as mechanical agitation, e.g., treating the laminate with the aqueous alkali solution under mechanical shearing.

The present invention also relates to a process for recycling the laminate. The process may comprise first debonding the laminate as described in step a) above, and then subject to mechanical recycling.

EXAMPLES

Some embodiments of the invention will now be described in, but not limited to, the following Examples, wherein all parts and percentages are by weight unless otherwise specified. The following materials are used in the examples:

MOR-FREE^TM 706A Prepolymer, available from The Dow Chemical Company, is an isocyanate-terminated polyurethane prepolymer.

MOR-FREE^TM C79 Coreactant, available from The Dow Chemical Company, is a hydroxy-terminated polyol component and is a blend of materials comprising a polyether polyol and castor oil.

Isopropanol (IPA) , ethyl acetate (EA) , sodium carbonate (Na₂CO₃) (an inorganic base) , 1, 4-butanediol (BDO) (apolyhydric alcohol) , and dimethylglyoxime (DMGO) (an oxime-containing diol) are all commercially available from Sinopharm Chemical Reagent Co., Ltd. of China.

Prepolymer B, an isocyanate-terminated polyurethane prepolymer, was synthesized below.

Synthesis of Prepolymer B:

Polyether polyols (12 wt%VORANOL^TM 222-056 Polyol, 30 wt%VORANOL^TM 3010 Polyol, 2 wt%methoxy polyethylene glycol (Mw=1000 g/mol) available from Haian Petrochemical, and 2 wt%polyethylene glycol (Mw=1000 g/mol) available from The Dow Chemical Company) and a polyester polyol (30 wt%SONGSTAR^TM SS-208) were charged into a 500 ml three neck flask and dehydrated at 115 ℃ under 76 mmHg pressure for one hour, then the dehydrated polyol mixture was naturally cooled down to 60 ℃. Benzoyl chloride was added into the obtained dehydrated polyol mixture under nitrogen (N₂) flow protection and mechanical stirring. After 10 minutes, 24 wt%methylenediphenyl diisocyanate (MDI) was poured into the polyol mixture, the exothermic reaction increased the reaction temperature gradually to 75 ℃, then the reaction was maintained at 75 ℃ for 2-3 hour. The obtained product (Prepolymer B) was packaged with a plastic bottle and stored hermetically under N₂ protection. The w%values are based on the total weight of reactants for preparing the Prepolymer B (i.e., the combined weights of the polyether polyols, the polyester polyol, and MDI) .

VORANOL^TM 222-056 Polyol (apolyether polyol with a M_w of 2000 g/mol) and VORANOL^TM 3010 Polyol (apolyether polyol with a M_w of 3000 g/mol) are both available from The Dow Chemical Company.

SONGSTAR^TM SS-208 Polyol, available from Songwon Industrial Group, is a polyester polyol with a M_w of 2000 g/mol.

Inventive Examples (IEs) 1-3 and Comparative Examples (CEs) 1-6 Adhesive Compositions

Formulations for adhesive compositions are in Table 1, with the amount of each ingredient reported in grams (g) . Ingredients listed in Table 1, including an isocyanate-terminated polyurethane prepolymer (Prepolymer B or MOR-FREE^TM 706A Prepolymer) , a polyol and/or polyhydric alcohol (MOR-FREE^TM C79 Coreactant or BDO) , ethyl acetate, and if present, oxime-containing diol DMGO were mixed in a magnetic mixer to give adhesive compositions. The obtained adhesive compositions were then used for making laminates. Each adhesive composition was first diluted with ethyl acetate to a solids content of 30 wt%, subjected to reduced pressure in a vacuum oven to remove air bubbles for 30 minutes, and then coated on a nylon film with #8 rod with a coat weight of around 1.6-3.2 grams per square meter (g/m²) . The coated film was placed in an oven, dried at 80 ℃ for 2 minutes, and then taken out and laminated with a polyethylene (PE) film on a lamination machine (Hot Roll Laminator from ChemInstruments) at a laminating temperature of 60 ℃, a speed of 3 revolutions per minute (rpm) and a pressure of 4 bars. The films are available from Dongguan Tianrun Packaging Technology Co., Ltd. of China. The obtained laminated multilayer films (also referred to as “laminates” ) were dried in an oven at 50 ℃ for 1 day. Some laminate samples were directly evaluated for bond strength, denoted as “Initial Bond Strength” , according to the Bond Strength Test described below. Other laminate samples were further treated under different degradation conditions listed in Tables 1 and 2 and then evaluated for bond strength after treatment, denoted as “final bond strength” , according to the Bond Strength Test described below.

Treatment under degradation conditions was conducted as below:

A laminate sample with a size of 200 millimeters (mm) x 15 mm was immersed into an alkali solution with or without a cosolvent such as IPA specified in Tables 1 and 2, and then maintained at 50 ℃ for 3 hours with stirring at 200 rpm. The sample after treatment was then taken out for characterization of bond strength ( “final bond strength” ) .

Notably, some samples after the treatment were delaminated by themselves, i.e., nylon film and PE film of the samples were detached or separated from each other by themselves, so final bond strength of these samples was not measured, thus reporting as “delaminated” . When calculating decrease percentage in bond strength of these delaminated samples, final bond strength ＜ 0.1 N/15mm was used for the calculation.

Bond Strength Test

Laminate samples were cut into 15 mm width strips for T-peel test under 250 millimeters per minute (mm/min) crosshead speed using a 5940 Series Single Column Tabletop System available from Instron Corporation (Instron 5943 machine) . During the test, the tail of each strip was pulled slightly by fingers to make sure the tail remained 90 degrees to the peeling direction. Three strips for each sample were tested and the average value was calculated. Results were in the unit of N/15mm. Decrease percentage in bond strength ( “%bond strength decrease” ) is calculated by:

[ (Initial bond strength –final bond strength) ] /Initial bond strength x 100%.

Acceptable initial bond strength is at least 4 N/15mm for nylon/PE laminates and acceptable decrease percentage in bond strength is at least 60%.

Table 1 gives the formulations and characterization results of Prepolymer B/BDO based adhesive systems (with or without DMGO) . PU adhesives made from IE1 and IE2 adhesive compositions contained specific amounts of the oxime-containing diol (e.g., ≥ 50 mol%of DMGO) . Laminates comprising such PU adhesives made from IE1 and IE2 demonstrated significant decrease in bond strength between nylon and PE layers (≥ 70%decrease) when treated under mild degradation conditions (e.g., 10%Na₂CO₃/IPA aqueous solution) , thus leading to delamination of nylon and PE in multilayer packaging films. In contrast, CE1 and CE2 adhesive compositions that do not contain specific amounts of the oxime-containing diol showed no or insufficient decrease in the bond strength even when treated under the same conditions as IE1 and IE2. As compared to the combination of an aqueous solution of Na₂CO₃ and a cosolvent such as IPA, only use of the aqueous solution of Na₂CO₃ or the aqueous solution of IPA didn’t effectively trigger the degradation of PU adhesives made from CE3 and CE4 compositions.

Table 2 gives formulations and characterization results of MORE-FREE^TM 706A Prepolymer/MORE-FREE^TM C79 Coreactant based adhesive systems (with or without DMGO) . The adhesive made from IE3 composition with 50 mol%of the oxime-containing diol such as DMGO also demonstrated significant decrease in bond strength between nylon and PE layers (≥ 70%decrease) under mild degradation conditions (e.g., Na₂CO₃/IPA aqueous solution) . In contrast, CE5 and CE6 adhesive compositions that do not contain specific amounts of the specified oxime-containing diol showed insufficient decrease in the bond strength when treated under the same conditions as IE3. In summary, the obtained laminates made from IEs 1-3 showed at least 60%decrease in the bond strength after treated with the specified aqueous alkali solution, which indicates these laminates were detachable under mild degradation conditions.

Table 1

Table 2

“Solids content” refers to the solids content of an adhesive composition sample, as determined according to ASTM D2369, by weighing a certain amount of a sample, denoted as “m₁” , placing the sample in an oven at 150 ℃ for 2 hours, and then weighing the remaining solids, denoted as “m₂” . Then the solids content is calculated by [m₂/m₁ x 100%] .

“mol%of DMGO” refers to molar percentage of hydroxy groups in DMGO in the polyol component (A) relative to the total moles of the hydroxy groups in the polyol component (A) .

“V (water) /V (IPA) ” means a mixture of water and IPA at a specified volume ratio of water to IPA.

“V (10%Na₂CO₃) /V (IPA) ” means a mixture of an aqueous solution of Na₂CO₃ (10 wt%) with IPA at a specified volume ratio of the NaCO₃ aqueous solution to IPA.

“10%Na₂CO₃” represents an aqueous solution of Na₂CO₃ (10 wt%) .

“%Bond strength decrease” is calculated by [ (Initial bond strength –final bond strength) ] /Initial bond strength x 100%.

Claims

A two-component adhesive composition, comprising:

(A) a polyol component comprising:

(a1) an oxime-containing diol having the structure of formula (I) :

where R₁ and R₂ are each independently H, an alkyl group having from 1 to 30 carbon atoms, or an aryl group having from 6 to 30 carbon atoms; and R is a single carbon-carbon bond, an alkylene group having from 1 to 30 carbon atoms, or an arylene group having from 6 to 30 carbon atoms; or R, R₁, and R₂ together are bonded to form a cyclic ring having from 4 to 12 carbon atoms;

wherein the oxime-containing diol in the polyol component (A) is present in an amount to provide a molar concentration of hydroxy groups in the oxime-containing diol, relative to total moles of hydroxy groups in the polyol component (A) , in a range of from 40 to 90 mole percent; and

(a2) a polyol selected from the group consisting of a polyester polyol, a polyether polyol, castor oil, a polyhydric alcohol, and combinations thereof; and

(B) an isocyanate component comprising an isocyanate prepolymer that is the reaction product of reactants comprising: (b1) a polyisocyanate; and (b2) a polyol selected from the group consisting of a polyester polyol, a polyether polyol, castor oil, and combinations thereof.
The two-component adhesive composition of claim 1, where, in formula (I) , R₁ and R₂are each independently an alkyl group having 1 to 6 carbon atoms, and R is a single carbon-carbon bond or an alkylene group having from 1 to 6 carbon atoms.
The two-component adhesive composition of claim 1, wherein the oxime-containing diol is selected from the group consisting of:
and mixtures thereof.
The two-component adhesive composition of claim 1, wherein the oxime-containing diol comprises
The two-component adhesive composition of any one of claims 1-4, wherein the molar concentration of hydroxy groups in the oxime-containing diol in the polyol component (A) is in a range of from 50 mole percent to 80 mole percent, based on the total moles of hydroxy groups in the polyol component (A) .
The two-component adhesive composition of any one of claims 1-5, wherein the reactants for preparing the isocyanate prepolymer also comprise the oxime-containing diol.
The two-component adhesive composition of any one of claims 1-6, wherein the molar ratio of total isocyanate groups in the isocyanate component (B) to total hydroxy groups in the polyol component (A) is in a range of from 1: 1 to 3: 1.
The two-component adhesive composition of any one of claims 1-7, wherein the polyol (b2) in the reactants is a mixture of the polyester polyol and the polyether polyol, or a mixture of the polyether polyol and castor oil.
The two-component adhesive composition of any one of claims 1-7, wherein the isocyanate prepolymer is the reaction product of reactants comprising, based on the weight of the isocyanate prepolymer, from 40 to 70 weight percent of the polyisocyanate, from 10 to 30 weight percent of the polyether polyol, and from 5 to 30 weight percent of castor oil.
The two-component adhesive composition of any one of claims 1-7, wherein the isocyanate prepolymer is the reaction product of reactants comprising, based on the weight of the isocyanate prepolymer, from 20 to 50 weight percent of the polyisocyanate, from 15 to 40 weight percent of polyester polyol, and from 10 to 65 weight percent of the polyether polyol.
A laminate comprising a first substrate, a second substrate, and an adhesive layer residing between the first and second substrates, wherein the adhesive layer is a cured product of the two-component adhesive composition of any one of claims 1-10.
A method of making a laminate, comprising the steps of:

I) applying the two-component adhesive composition of any one of claims 1-10 to a surface of a first substrate;

II) bringing the two-component adhesive composition on the surface of the first substrate into contact with a surface of a second substrate; and

III) curing, or allowing to cure, the two-component adhesive composition; thereby forming the laminate.
A process for debonding the laminate of claim 11, comprising:

treating the laminate with an aqueous alkali solution, wherein the aqueous alkali solution comprises water, an inorganic base, and a cosolvent selected from an alcohol, an ester, an ether, a ketone, or mixtures thereof.
The process of claim 13, wherein the cosolvent is selected from the group consisting of ethanol, isopropanol, acetone, 1-butanol, t-butyl alcohol, and mixtures thereof.
An article comprising the laminate of claim 11.