WO1999055753A1

WO1999055753A1 - Cure on demand adhesives for assembling shoe soles

Info

Publication number: WO1999055753A1
Application number: PCT/US1999/009103
Authority: WO
Inventors: Leonardo C. Lopez; Dwight K. Hoffman; Michael Janssen
Original assignee: The Dow Chemical Company
Priority date: 1998-04-27
Filing date: 1999-04-27
Publication date: 1999-11-04
Also published as: AU3966999A

Abstract

The invention is an adhesive composition comprising a) a polymer having a flexible backbone and a reactive moiety capable of cross-linking, b) a catalyst for cross-linking of the reactive moiety, a curing agent for the reactive moiety, or a mixture thereof; wherein the catalyst, curing agent or a mixture thereof is encapsulated in a thermoplastic or crystalline polymer. In yet another embodiment, the invention is a process for binding two substrates together which comprises contacting the two substrates such that an adhesive as described herein is located between the two substrates and exposing the substrates and adhesive to sufficient heat to cause the encapsulating material to release the catalyst, curing agent, or both so as to contact the catalyst and/or curing agent with the polymer, and exposing the adhesive to curing conditions.

Description

CURE ON DEMAND ADHESIVES FOR ASSEMBLING SHOE SOLES

This application claims the benefit of U.S. Provisional Application No. 60/083,128 filed on April 27, 1998.

This application relates to a polyurethane curing agent or cross-linking agent encapsulated in a thermoplastic or crystalline polymer. This application relates to a cure on demand adhesive composition for assembling shoe soles to the upper part of the shoe. The application further refers to a process for bonding shoe soles to the upper portion of shoes.

Many mass produced shoes are manufactured by bonding the upper shoe to the shoe sole with an adhesive. Generally, a portion of adhesive is applied to the part of the shoe sole which will be bonded to the upper shoe. At the same time, the adhesive is applied to the portion of the upper shoe which will be contacted with the shoe sole. The adhesive is typically carried in an organic solvent and the upper shoe and shoe sole are exposed to a heat source for a few minutes to cause the solvent to volatilize and later to activate curing of the adhesive and assemble the shoe.

This process exposes the workers to volatile solvents and releases volatile solvents to the atmosphere.

Aqueous dispersions of adhesives are utilized to resolve the issues related to workers exposure to solvents and solvent release to the atmosphere. Such adhesives require longer drying times because water has a higher heat of evaporation than the typical organic solvents used in solvent based adhesives. This makes the assembly process less efficient.

Hot melt adhesives have also been designed to substitute solvent based adhesives. Hot melt adhesives are applied at high temperature (above 100²C) and require special application equipment not present in the current infrastructure.

Further, in many cases, curing agents are added to the adhesives to improve their performance. In these cases, the adhesives cure within a short period of time (2 hours). This results in the need to renew the adhesive every two hours during operations to prevent the loss of adhesive performance. In turn, this generates a waste stream that contributes to the operating costs. Further, some adhesives cure rapidly and can cure completely before the shoe parts are assembled which causes waste in the assembly process.

What is needed is a cure on demand adhesive for bonding shoe soles to shoe uppers which is stable when exposed to atmospheric conditions which can be activated quickly, and preferably in less than 10 minutes, has adequate green strength to hold the shoe parts together while the adhesive completes cure. What is needed are adhesive components which facilitate the preparation of such an adhesive. What is further needed is a process for bonding shoe soles to shoe uppers without the use of a solvent based adhesive. What is further needed is a shoe which has its parts bonded together with such an adhesive.

In one embodiment, the invention is a composition comprising a polyurethane cross-linking agent or curing agent encapsulated in a thermoplastic or a crystalline polymer having a transition point at from 40°C to 100°C. Preferably, the polyurethane cross-linking agent or curing agent is not extractable from the encapsulating agent at ambient conditions during the first extraction after preparation of the encapsulated curing agent or cross-linking agent. The cross-linking agent or curing agent preferably does not volatilize under conditions at which the curing agent or cross-linking agent is encapsulated in the polymer.

In another embodiment, the invention is an adhesive composition comprising

α a) polyurethane prepolymer having free isocyanate moieties, and

b) a polyurethane cross-linking agent or curing agent encapsulated in a thermoplastic or a crystalline polymer having a transition point at from 40°C to 100°C.

In yet another embodiment, the invention is a process for binding two substrates together which comprises contacting the two substrates such that an adhesive as described herein is located between the two substrates and exposing the substrates and adhesive to sufficient heat to cause the encapsulating material to release the cross-linking agent or curing agent so as to contact the cross-linking agent or curing agent with the polyurethane prepolymer, and exposing the adhesive to curing conditions and contacting the activated adhesive covered substrates. In a preferred embodiment, one substrate is a shoe sole and the other is a shoe upper. A shoe comprising a shoe sole comprising an elastomeric polymer, leather, or composite; a shoe upper; and a cured adhesive composition according to this invention located between the sole and upper.

The cure on demand adhesive of the invention exhibits sufficient stability when exposed to atmospheric conditions such that it will not cure for a period of 2 days or more. Furthermore, the adhesive of the invention can be activated relatively quickly and preferably in less than 10 minutes. The adhesive of the invention demonstrates adequate green strength to hold the shoe together until the adhesive further cures. The encapsulated curing agent of the invention facilitates the desired performance of the adhesive composition of the invention.

The adhesive composition of the invention contains a polyurethane prepolymer having free isocyanate moieties. Preferably the free reactive isocyanate content of the prepolymer is 1.5 percent or greater, more preferably 2.5 percent or greater and most preferably 3.5 percent or greater. Preferably the free reactive isocyanate content of the prepolymer is 25 percent or less, more preferably 20 percent or less and most preferably 15 percent or less. Polyurethane prepolymers useful in this invention include those disclosed in Bhat et. al., U.S. Patent 5,672,652 at column 2, line 35 to column 5, line 20. Such prepolymers are prepared by reacting a polyisocyanate with a polyol. Preferable polyisocyanates are disclosed in Bhat. More preferably the polyisocyanate is toluene diisocyanate (commonly referred to as TDI), diphenylmethane diisocyanate (commonly referred to as MDI) and polymeric and oligomeric derivatives thereof. The most preferred isocyante is TDI.

Polyols which may be used to prepare the polyurethane prepolymers are well-known to those skilled in the art. Bhat et al., U. S. Patent 5,672,652, see column 4, lines 5 to 60,(the entire disclosure is incorporated herein by reference) discloses the preferred polyols useful in preparing the polyurethane prepolymers. The polyols are prepared by reacting an initiator, a compound having one or more active hydrogen atoms, with an alkylene oxide in the presence of a suitable catalyst under appropriate conditions for the alkylene oxide to react with one or more active hydrogen moieties of the initiator so as to add a series of ether units to the initiator thereby preparing a polyol. Initiators which are useful in this invention are well-known to those skilled in the art. Preferable initiator compounds which are employed to prepare the polyols are compounds having 1 to 8 active hydrogens, preferably 2 to 8, more preferably 2 to 4, most preferably 2 to 3 active hydrogens. Preferable initiator compounds include, for example, alcohols, glycols, low molecular weight polyols, glycerin, trimethylol propane, pentaerythritol, glycosides, sugars, ethylene diamine, and diethylenetriamine. Particularly suitable glycols include, for example, ethylene glycol, 1 ,2-propylene glycol, 1 ,3-propylene glycol, 1 ,2-butylene glycol, 1 ,3-butylene glycol, 1 ,4-butylene glycol, 1 ,2-pentylene glycol, 1 ,3-pentylene glycol, 1 ,4-pentylene glycol, 1 ,5-pentylene glycol, 1 ,6-pentylene glycol, neopentyl glycol and various hexane diols, and mixtures thereof. Alkylene oxides useful include ethylene oxide, propylene oxide, 1 ,2- butylene oxide, 2,3-butylene oxide, or mixtures thereof. Most preferred alkylene oxides are ethylene oxide and propylene oxide with propylene oxide most preferred. Combinations of the above mentioned alkylene oxides may be used in random or block polymers.

The polyurethane prepolymer is present in the adhesive composition in sufficient amount such that the adhesive is capable of bonding two substrates together such as one or more of leather, an elastomeric material, glass, wood, metal, plastic, a composite, fabric and fiberglass, and preferably bonds elastomeric polymers, leather or composite materials commonly used for shoe soles to leather or other elastomeric materials. More preferably the polyurethane prepolymer is present in an amount of 50 percent by weight or greater based on the weight of the adhesive, even more preferably 60 percent by weight or greater and most preferably 70 percent by weight or greater. More preferably the polyurethane prepolymer is present in an amount of 99 percent by weight or less based on the weight of the adhesive and most preferably 90 percent by weight or less.

The adhesive composition further comprises a cross-linking agent or a curing agent for the polyurethane prepolymer, hereinafter collectively active agent. Such active agent is encapsulated in a crystalline or thermoplastic polymer as the encapsulating agent (or encapsulating material).

The active agent may be any cross-linking agent or curing agent or mixture thereof that dissolves in or forms a heterogeneous slurry with the encapsulating material. Preferably the active agent is soluble in the encapsulating material. The active agent may either be a liquid or a solid at room temperature but it is preferably a liquid at room temperature. The melting point of the active agent may be greater than, less than, or equal to the melting point of the encapsulating material. Preferably the active agent does not volatilize or degrade under the temperatures of encapsulation process.

The cross-linkers utilized in this invention include any cross-linker which is known and which has an equivalent weight of 200 or less. Cross-linkers as used herein

4 refers to compounds which are also commonly referred to as chain extenders. Such cross- linkers are low molecular weight compounds having two active hydrogen atoms which react with isocyanate moieties. Preferred cross-linkers are C₃ to C₁₀ alkylene diols and cyclo alkylene diols, hydroquinone di(beta-hydroxyl ethyl)ether and ethoxylated bisphenol A. 4.4'- Methylene bis(2-chloroaniline); 4,4'-Methylenebis(3-chloro-2,6-diethylaniline); 3,5- dimethylthio-2,4-toluenediamine/3,5-dimethylthio-2,6-toluenediamine; trimethylene glycol di- p-aminobenzoate; 1 ,4' bis(B-hydroxyethoxy)benzene; hydroquinone di-(2-hydroxyethyl) ether; 1 ,4' cyclo-hexane dimethyl; ethoxylated bisphenol A.

Examples of C₃-C₁₀ alkylene diols are 1 ,4-butanediol, 1 ,6-hexanediol, 2-ethyl- 1 ,3-hexanediol, 2,2,4-trimethyl-1 ,3-pentanediol and 2-butyl-2-ethyl-1 ,3-propanediol.

Curing agent, as used herein, is a compound which cross-links a polyurethane prepolymer. Typically such a curing agent contains three or more active hydrogen atoms. Curing agents for polyurethanes are well-known in the art. Preferred curing agents are polyols, as described herein, which have three or more hydroxyl moieties and polyamines having more than three active hydrogen atoms, hydrogen atoms bound to an amine nitrogen. Preferred are low molecular weight polyols such as glycerin, trimethylolpropane, pentaerythritol, glycosides,and sugars. Preferred polyamines are primary amines, with cyclo aliphatic polyamines and sterically hindered aromatic polyamines preferred. More preferred curing agents are dialkyl toluene diamines, such as diethyl toluene diamine.

Preferably the active agent and encapsulating agent are chosen such that the active agent can be encapsulated within the encapsulating agent at a temperature at which the active agent does not volatilize. The use of an encapsulating agent that the active agent is soluble in reduces the volatility of the active agent and enhances the formation of the desired particles. "Does not volatilize" herein means that under the conditions of the encapsulated active agent particle formation the formed particle does not exhibit substantial extraction of the active agent at ambient conditions during the first extraction after particle formation. Preferably the active agent has a low partial pressure under particle formation conditions. Active agents exhibit enhanced solubility in encapsulating agents having a polar nature, such as, for example, polyester, polyamides, and side chain crystalline polymers. Careful selection of the encapsulating material is warranted under this circumstance.

The encapsulating agent is a crystalline or thermoplastic polymer which exhibits a transition point of 40°C or greater, more preferably 45°C or greater, even more

5 preferably 60°C or greater. Preferably such crystalline or thermoplastic polymer has a transition point of 100°C and most preferably 70°C. Transition point, as used herein, refers to the point at which the thermoplastic or crystalline polymer undergoes a change which results in the release of the active agent such that the active agent can come into contact with the polyurethane prepolymer. One transition point is where the thermoplastic or crystalline polymer melts and releases the active agent. Another transition point is where the thermoplastic or crystalline polymer changes sufficient to allow the active agent to permeate out of the particles or through the thermoplastic or crystalline polymer. It is preferable that the thermoplastic or crystalline polymeric moiety should cross over the transition point, for instance melt, over a relatively small temperature range so that release of the active agent can occur quickly.

Preferable thermoplastic polymers include styrenics, styrene-acrylonitriles, low molecular weight chlorinated polyethylenes, soluble cellulosics, acrylics, such as those based on methyl methacrylate or cycloaliphatic acrylates.

Crystalline polymers useful herein include polymers in which the crystallinity results exclusively or predominantly from the polymer backbone, e.g. polymers of α-olefins containing 2 to 12, preferably 2 to 8, carbon atoms, for example polymers of monomers having the formula CH₂=CHR, where R is hydrogen, methyl, propyl, butyl, pentyl, 4- methylpentyl, hexyl or heptyl, as well as other polymers such as polyesters, polyamides, and polyalkylene oxides, for example polytetrahydrofuran. A crystallinity such that the DSC heat of fusion is at least 10 J/g, particularly at least 20 J/g, is preferred. The steric nature of the polymeric moiety can also be significant in determining the availability of the active moiety.

Preferably the crystalline polymer is a polyolefin, polyester, polyamide, phenoxy thermoplastics, polylactic acid, polyalkylene glycol, polyhydroxy alkanoates, polyether or a side chain crystalline polymer. More preferably the crystalline polymer is polyethylene, polypropylene, polyethylene glycol or a side chain crystalline polymer. Even more preferred crystalline polymers are polyethylene, polyethylene glycol or a side chain crystalline polymer, with side chain acrylate polymers being most preferred.

The side chain crystalline (SCC) polymers can be derived from a single polymer or from a mixture of polymers, and the polymer can be a homopolymer, or a copolymer of two or more comonomers, including random copolymers, graft copolymers, block copolymers and thermoplastic elastomers. The SCC polymer may be derived from one or more acrylic, methacrylic, olefinic, epoxy, vinyl, ester-containing, amide-containing or ether-containing monomers. The preferred SCC polymeric moieties are described in detail below.

SCC polymer moieties which can be used in this invention include moieties derived from known SCC polymers, for example polymers derived from one or more monomers such as substituted and unsubstituted acrylates, methacrylates, fluoroacrylates, vinyl esters, acrylamides, methacrylamides, maleimides, α-olefins, p-alkyl styrenes, alkylvinyl ethers, alkylethylene oxides, alkyl phosphazenes and amino acids; polyisocyanates; polyurethanes; polysilanes; polysiloxanes; and polyethers; all of such polymers containing long chain crystalline groups. Suitable SCC polymers are described, for example in J. Poly. Sci. 60,19 (1962), J. Poly. Sci. (Polymer Chemistry) 7, 3053 (1969), 9, 1835, 3349, 3351 , 3367, 10, 1657, 3347, 18, 2197, 19,1871 , J. Poly. Sci. Poly-Physics Ed. 18,. 2197 (1980), J. Poly. Sci. Macromol. Rev. 8, 117 (1974), Macromolecules 12, 94 (1979), 13, 12, 15, 18, 2141 , 19, 61 1 , JACS 75,3326 (1953), 76; 6280, Polymer J 17, 991 (1985); and Poly. Sci. USSR 21, 241 (1979).

The SCC polymer moieties which are preferably used in this invention can be broadly defined as moieties which comprise repeating units of the general formula:

-Y- Cy where Y is an organic radical forming part of the polymer backbone and Cy comprises a crystalline moiety. The crystalline moiety may be connected to the polymer backbone directly or through a divalent organic or inorganic radical, for example an ester, carbonyl, amide, hydrocarbon (for example phenylene), amino, or ether link, or through an ionic salt linkage (for example a carboxyalkyi ammonium, sulfonium or phosphonium ion pair). The radical Cy may be aliphatic or aromatic, for example alkyl of at least 10 carbons, fluoralkyl of at least 6 carbons or p-alkyl styrene wherein the alkyl contains 6 to 28 carbons. The SCC moiety may contain two or more different repeating units of this general formula. The SCC may also contain other repeating units, but the amount of such other units is preferably such that the total weight of the crystalline groups is at least equal to, for example twice, the weight of the remainder of the block.

Preferred SCC moieties comprise side chains containing in total at least 5 times as many carbon atoms as the backbone of the moiety, particularly side chains comprising linear polymethylene moieties containing 12 to 50, especially 14 to 22 carbon atoms, or linear perfluorinated or substantially perfluorinated polymethylene moieties containing 6 to 50 carbon atoms. Polymers containing such side chains can be prepared by polymerizing one or more corresponding linear aliphatic acrylates or methacrylates, or equivalent monomers such as acrylamides or methacrylamides. A number of such monomers are available commercially, either as individual monomers or as mixtures of identified monomers, for example C12A, C14A, C16A, C18A, C22A, a mixture of C18A, C20A and C22A, a mixture of C26A to C40A, fluorinated C8A (AE800 from American Hoechst) and a mixture of fluorinated C8A, C10A and C12A (AE12 from American Hoechst). The polymers can optionally also contain units derived from one or more other comonomers preferably selected from other alkyl, hydroxyalkyl and alkoxyalkyl acrylates, methacrylates (for example glycidal methacrylates); acrylamides and methacrylamides, acrylic and methacrylic acids; acrylamide; methacrylamide; maleic anhydride; and comonomers containing amide groups. Such other co-monomers are generally present in a total amount of less than 50 percent, particularly less than 35 percent, especially less than 25 percent, for example 0 to 15 percent. They may be added to modify the melting point or other physical properties of the polymers. The melting point of a polymer containing such polymethylene side chains is influenced by the number of carbon atoms in the crystalline side chains. For example, homopolymers of C14A, C16A, C18A, C20A, C22A, C30A, C40A and C50A, respectively, typically have melting points of 20, 36, 49, 60, 71 , 76, 96 and 102°C, while the homopolymers of the corresponding n-alkyl methacrylates typically have melting points of 10, 26, 39, 50, 62, 68, 91 and 95°C. Copolymers of such monomers generally have intermediate melting points. Copolymers with other monomers, for example acrylic acid or butyl acrylate, typically have somewhat lower melting points.

Other polymers which can provide SCC moieties for use in this invention include atactic and isotactic polymers of n-alkyl α-olefins (for example the atactic and isotactic polymers of C₁₆ olefin, having T_m's of 30° and 60°C, respectively); polymers of n- alkylglycidyl ethers (for example the polymer of C₁₈ alkyl glycidylether); polymers of n-alkyl vinyl ethers (for example the polymer of C_1β alkylvinylether having a T_m of 55°C; polymers of n-alkyl-α-epoxide having a T_m of 60°C); polymers of n-alkyl oxycarbonylamido- ethylmethacrylates (for example the polymers of C_1β IEMA, C₂₂ IEMA and C₃₀ IEMA having T_m's of 56°, 75° and 79°, respectively); polymers of n-fluoro alkyl acrylates (for example the polymers of C_a hexadecafluoroalkylacrylate, and of a mixture of C_{8 12} alkyl fluoroacrylates having T_m's of 74°C and 88°C, respectively), polymers of n-alkyloxazolines (for example the

8 polymer of C₁₆ alkyl oxazoline having a T_mof 155°C); polymers obtained by reacting an hydroxyalkyl acrylate or methacrylate with an alkyl isocyanate (for example the polymers obtained by reacting hydroxyethyl acrylate with C₁₈or C_2Z alkyl isocyanate and having T_m's of 78° and 85°C, respectively); and polymers obtained by reacting a difunctional isocyanate, a hydroxyalkyl acrylate or methacrylate, and a primary fatty, alcohol (for example the polymers obtained by reacting hexamethyiene diisocyanate, 2-hydroxyethyl acrylate, and C₁₈ or C₂₂ alcohols, and having T_m's of 103°C and 106°C, respectively).

Preferred SCC polymer moieties used in this invention comprise 30 to 100 percent preferably 40 to 100 percent, of units derived from at least one monomer selected from alkyl acrylates, alkyl methacrylates, N-alkyl acrylamides, N-alkyl methacrylamides, alkyl oxazolines, alkyl vinyl ethers, alkyl vinyl esters, α-olefins, alkyl 1 ,2-epoxides and alkyl glycidyl ethers in which the alkyl groups are n-alkyl groups containing 12 to 50 carbon atoms, and the corresponding fluoroalkyl monomers in which the thermoalkyl groups are n- fluoroalkyi groups containing 6 to 50 carbon atoms; 0 to 20 percent of units derived from at least one monomer selected from alkyl acrylates, alkyl methacrylates, N-alkyl acrylamides, alkyl vinyl ethers, and alkyl vinyl esters in which the alkyl groups are n-alkyl groups containing 4 to 12 carbon atoms; and 0 to 15 percent of units derived from at least one polar monomer selected from acrylic acid, methacrylic acid, itaconic acid, acrylamide, methacrylamide, acrylonitrile, methacrylonitrile, vinyl acetate and N-vinyl pyrrolidone. Such SCC moieties may also contain units derived from other monomers to change compatibility with the matrix, or to raise the modulus of a reaction product containing the modifying agent; such monomers include styrene, vinyl acetate, and mono acrylic functional polystyrene.

The number average molecular weight of the SCC polymer moiety is preferably less than 200,000, more preferably less than 100,000, particularly less than 50,000, more particularly 1 ,000 to 20,000. The molecular weight of the SCC polymer moiety can be adjusted (for example through choice of the reaction conditions and addition of chain transfer agents) so as to optimize the reactivity of attached moieties without substantial change in T .

The encapsulated active agent may be prepared by the following procedures: a) dispersing or dissolving the active agent in the encapsulating material at a temperature sufficient to melt the encapsulating material and preferably, not so high that the active agent volatilizes; b) forming droplets of active agent interspersed with the encapsulating material and c) cooling the droplets to solidify the encapsulated material. Optionally, the process

9 may further comprise d) contacting the droplets with a solvent that dissolves the active agent but does not dissolve the encapsulating material, so as to remove active agent from the surface of the encapsulating material. It is preferable to avoid this last step. This process is described in U.S. Patent 5,601 ,761.

The concentration of active agent in the particles is preferably 1 weight percent, or greater, more preferably 20 weight percent or greater and most preferably 25 weight percent or greater. The concentration of active agent in the particles is preferably 70 weight percent or less, more preferably 65 weight percent or less, even more preferably 50 weight percent or less, and most preferably 45 weight percent or less based on the total weight of active agent and encapsulating material.

In performing this process, the temperature of the process is selected such that the encapsulating agent is in a molten or liquid form and has a suitable viscosity for the processing technique used, such as a rotating disk. Further, the temperature and other process conditions should be chosen that the active agent is not volatile. Generally, not volatile or low volatility as used herein means the active agent has a low partial pressure. One skilled in the art can readily determine appropriate conditions and components and acceptable volatility levels. In performing this process, it is preferable that the temperature at which the active agent is contacted with the encapsulating material is 40°C or greater, more preferably 45°C or greater, most preferably 70°C or greater and preferably 200°C or less and most preferably 180°C or less. In order to successfully prepare the desired particles, it is preferable that the mixture prepared have a viscosity which is suitable for use with a rotating disk. Preferably the viscosity is 500 centipoise or less, more preferably 100 centipoise or less and most preferably 50 centipoise or less. In order to achieve the desired viscosity, it may be useful to add a solvent or plasticizer to the mixture. In a preferred embodiment of this process, the active agent dissolves in the molten polymer. It is believed that this provides for better dispersion and distribution. The active agent is preferably mixed with an encapsulating agent in the molten state at a temperature at which the active agent or a mixture thereof is not volatile. Under these circumstances, the particle prepared will not exhibit significant extraction of the active agent at ambient temperatures. This results in a very stable encapsulated active agent and a very stable adhesive formulation prepared from such active agent. Preferably the temperature of the disk upon which the molten mixture is poured is 75°C or greater, more preferably 100°C or greater and most preferably 125°C or greater and is preferably 250°C or less, more preferably 200°C or less and most preferably

180°C or less. Preferably the disk is rotating at 500 rpm or greater, more preferably 1 ,000

10 rpm or greater and most preferably 5,000 rpm or greater. The upper limit on the revolutions per minute used for the rotating disk is based on practicality.

In one preferred embodiment, the encapsulated active agent preferably exhibits a shell of crystalline polymer about a mixture of polymer having dispersed therein an active agent. The crystal structure of this shell layer is different than the crystal structure of the encapsulating agent crystal structure at the interior of the particle. There is no significant active agent in the shell at and near the surface of the particle. It is believed that this shell layer at and near the surface prevents the extraction of the active agent by solvent. The presence of this layer is indicated by the active agent not being extractable in a significant amount when the particles are contacted with a solvent for the active agent. The ability of the particle to resist extraction of the active agent using a solvent is an indication that the encapsulated active agent will be stable in a formulation at ambient temperatures, meaning significant amounts of the active agent will not come into contact with the curable composition and initiate cure at ambient temperatures. In one preferred embodiment, it is believed that the encapsulated active agent of the invention preferably has a shell of crystalline polymer which has a crystal structure which is somewhat different than the structure of the polymer on the interior of the particle. Preferably, the active agent is not significantly extractable from the particles of active agent in encapsulating agent. By not significantly extractable is meant that there is no need to wash the surface of the particle with a solvent to make the particle stable in the adhesive formulation. Preferably, not substantially extractable means 10 percent or less of the active agent based on the amount of active agent in the encapsulated active agent, more preferably 5 percent or less, even more preferably 1 percent or less, even more preferably 0.5 percent by weight or less and most preferably 0.1 percent by weight or less, of the active agent contained in the particle is extracted by a solvent or plasticizer when the particles are contacted with the solvent or plasticizer for the active agent. In some embodiments, the amount of active agent extracted is below the detection limits of the analytical techniques used to measure for the active agent Preferably the particles have a particle size of 3000 microns or less, more preferably 300 microns or less and most preferably 150 microns or less. It is believed that a narrow particle size distribution enhances the performance of the particles of the invention in the intended uses. Preferably the particles demonstrate a narrow particle size distribution. Narrow particle size distribution means herein that there are not a significant amount of particles with a size greater than 5 times the median particle size of the particles, and more preferably 2 times the median particle size. Particle size as used herein can be measured by laser scattering particle size analysis. The active agent in the encapsulating

1 1 material on a weight basis can be 70 percent by weight or less, more preferably 65 percent by weight or less, even more preferably 50 percent by weight or less and most preferably 45 percent by weight or less based on the total weight of active agent and encapsulating agent. Preferably the loading level is 1 percent or greater, more preferably 20 percent by weight or greater and most preferably 25 percent by weight or greater based on the weight of the active agent and the encapsulating agent. Preferably the loading level is 70 percent or less, more preferably 60 percent by weight or less and most preferably 50 percent by weight or less based on the weight of the active agent and the encapsulating agent.

In one embodiment, active agents can be encapsulated in a side chain crystalline polymer as described hereinbefore. In another embodiment, the side chain crystalline polymers are heated above their melting point to a molten state and the active agent is dissolved in the side chain crystalline polymer. The mixture is then cooled resulting in the polymer crystallizing and causing phase separation of the catalyst rich regions to form microparticulates. This mass is then mechanically ground. In some embodiments, the adhesive formulations made using these encapsulated active agents are not stable without further processing of the particles. In some embodiments, it is necessary to wash the particles with a solvent for the active agent to remove them from the surface area of the particles. This process may be per ormed as described in Hoffman et al., U.S. Patent 5,601 ,761.

The adhesive formulation of the invention contains a sufficient amount of encapsulated active agent particles to effectuate curing or cross-linking of the adhesive composition when exposed to the necessary conditions for curing or cross-linking. Preferably the adhesive composition contains 1 percent by weight or greater of encapsulated active agent particles, more preferably 5 percent by weight or greater and most preferably 10 percent by weight or greater. The adhesive formulation of the invention preferably contains 40 percent by weight or less of encapsulated active agent particles, more preferably 35 percent by weight or less of the particles and most preferably 30 percent by weight or less of the particles.

The adhesive formulation may contain other additives commonly used in adhesive formulations as known to those skilled in the art.

Preferably the adhesive formulation contains a fatty acid which acts as an activator for the curing of the polyurethane prepolymer. Preferably the fatty acid is oleic acid. The fatty acid is present in a concentration sufficient to activate the curing reaction

12 and to achieve the desired curing rate. The fatty acid is present preferably in an amount of 0.05 percent by weight of the adhesive composition or greater, more preferably 0.2 percent by weight or greater and most preferably 0.5 percent by weight or greater. Preferably the fatty acid is present in an amount of 5 percent by weight of the adhesive composition or less, more preferably 3 percent by weight or less and most preferably 2 percent by weight or less.

In another preferred embodiment, the adhesive composition contains a swelling agent for the elastomeric polymer out of which the substrate, for instance shoe sole, is made from. Any swelling agent known to one skilled in the art for the specified elastomeric polymer may be used. Preferred swelling agents are the tetra alkyl ureas such as tetra ethyl urea. The swelling agent is present preferably in an amount of 0.5 percent by weight of the adhesive composition or greater, more preferably 2 percent by weight or greater and most preferably 5 percent by weight or greater. Preferably the swelling agent is present in an amount of 30 percent by weight of the adhesive composition or less, more preferably 20 percent by weight or less and most preferably 15 percent by weight or less.

The adhesive of the invention may be formulated with fillers known in the prior art for use in adhesive compositions. By the addition of such materials, physical properties such as viscosity, flow rates, and sag can be modified. However, to prevent premature hydrolysis of the moisture sensitive groups of the polyurethane prepolymer, fillers should be thoroughly dried before admixture therewith.

Optional components of the adhesive of the invention include reinforcing fillers. Such fillers are well-known to those skilled in the art and include carbon black, titanium dioxide, calcium carbonate, surface treated silicas, titanium oxide, fumed silica, and talc. Preferred reinforcing fillers comprise carbon black. In one embodiment, more than one reinforcing filler may be used, of which one is carbon black, and a sufficient amount of carbon black is used to provide the desired black color to the adhesive. The reinforcing fillers are used in sufficient amount to increase the strength of the adhesive and to provide thixotropic properties to the adhesive. Preferably the reinforcing filler is present in an amount of 1 part by weight of the adhesive composition or greater, more preferably 15 parts by weight or greater and most preferably 17 parts by weight or greater. Preferably the reinforcing filler is present in an amount of 40 parts by weight of the adhesive composition or less, more preferably 25 parts by weight or less and most preferably 23 parts by weight or less.

13 Among optional materials in the adhesive composition are clays. Preferred clays useful in the invention include kaolin, surface treated kaolin, calcined kaolin, aluminum silicates and surface treated anhydrous aluminum silicates. The clays can be used in any form which facilitate formulation of a pumpable adhesive. Preferably the clay is in the form of pulverized powder, spray dried beads or finely ground particles. Clays may be used in an amount of 0 part by weight of the adhesive composition or greater, more preferably 1 part by weight or greater and even more preferably 6 parts by weight or greater. Preferably the clays are used in an amount of 20 parts by weight or less of the adhesive composition and more preferably 10 parts by weight or less.

The adhesive composition of this invention may further comprise plasticizers so as to modify the rheological properties to a desired consistency. Such materials should be free of water, inert to reactive groups and compatible with a polymer. Suitable plasticizers are well-known in the art and preferable plasticizers include alkyl phthalates such as dioctylphthalate or dibutylphthalate, partially hydrogenated terpene commercially available as "HB-40", trioctyl phosphate, epoxy plasticizers, toluene-sulfamide, chloroparaffins, adipic acid esters, castor oil, toluenexyleneimethylpyrolidinone and alkyl naphthalenes. The amount of plasticizer in the adhesive composition is that amount which gives the desired rheological properties and which is sufficient to disperse the encapsulated catalyst, curative or mixture thereof in the system. The amounts disclosed herein include those amounts added during preparation of the prepolymer and during compounding of the adhesive. Preferably plasticizers are used in the adhesive composition in an amount of 0 part by weight or greater based on the weight of the adhesive composition, more preferably 5 parts by weight or greater and most preferably 10 parts by weight or greater. The plasticizer is preferably used in an amount of 45 parts by weight or less based on the total amount of the adhesive composition and more preferably 40 parts by weight or less.

The adhesive of this invention may further comprise stabilizers which function to protect the adhesive composition from moisture, thereby inhibiting advancement and preventing premature cross-linking of the isocyanates of the prepolymers in the adhesive formulation. Included among such stabilizers are diethyl malonate and alkyl phenol alkylates. Such stabilizers are preferably used in an amount of 0.1 part by weight or greater based on the total weight of the adhesive composition, preferably 0.5 part by weight or greater and more preferably 0.8 part by weight or greater. Such stabilizers are used in an amount of 5.0 parts by weight or less based on the weight of the adhesive composition, more preferably 2.0 parts by weight or less and most preferably 1.4 parts by weight or less.

14 Optionally, the adhesive composition may further comprise a thixotrope. Such thixotropes are well-known to those skilled in the art and include alumina, limestone, talc, zinc oxides, sulfur oxides, calcium carbonate, perlite, slate flour, salt (NaCI),and cyclodextrin. The thixotrope may be added to the adhesive of the composition in a sufficient amount to give the desired rheological properties. Preferably the thixotrope is present in an amount of 0 part by weight or greater based on the weight of the adhesive composition, preferably 1 part by weight or greater. Preferably the optional thixotrope is present in an amount of 10 parts by weight or less based on the weight of the adhesive composition and more preferably 2 parts by weight or less.

Other components commonly used in adhesive compositions may be used in the adhesive composition of this invention. Such materials are well-known to those skilled in the art and may include ultraviolet stabilizers and antioxidants.

As used herein, all parts by weight relative to the components of the adhesive composition are based on 100 total parts by weight of the adhesive composition.

The adhesive composition of this invention may be formulated by blending the components together using means well-known in the art. Generally the components are blended in a suitable mixer. Such blending is preferably conducted in an inert atmosphere in the absence of oxygen and atmospheric moisture to prevent premature reaction. It may be advantageous to add any plasticizers to the reaction mixture for preparing the polymer such as an isocyanate containing prepolymer so that such mixture may be easily mixed and handled. Alternatively, the plasticizers can be added during blending of all the components.

The encapsulated active agent particles can be blended or mixed into the adhesive formulation using different processes at different stages of production. The encapsulated active agent particles can be blended into the prepolymer after it has been synthesized. This prepolymer, with the blended encapsulated active agent particles, is then used for compounding into the adhesive. The encapsulated active agent particles can also be blended into the adhesive directly after the compounding stage. Once the mixing and wetting cycle of the fillers is complete within the mixing or blending apparatus, the encapsulated active agent particles are added so as to achieve a good dispersion. The encapsulated active agent particles can be coextruded either dry or in a slurry with the prepolymer directly into the package during the filling and packaging stage.

15 The adhesive composition of the invention is used to bond two substrates together. The adhesive composition is applied to each substrate and then exposed to sufficient heat to cause the encapsulating agent to pass through its transition point and release the active agent to thereby initiate cure of the polyurethane prepolymer. Heat may be applied to the adhesive by means of convection heat, infrared or microwave heating

In a preferred embodiment, the first substrate is a shoe sole and the second substrate is a shoe upper. Preferably the shoe sole is an elastomeric polymer, leather, or a composite. Preferred elastomeric polymers include polyurethanes, thermoplastic rubbers, styrenic block copolymers, polychloroprene, and natural rubber. Preferred elastomeric polymers are polyurethanes.

Preferably the adhesive formulation has a Brookfield viscosity of 500 cps or greater and more preferably 1000 cps and preferably 50,000 cps or less and most preferably 32,000 cps or less.

The adhesive is applied to the substrates by any known means known in the art. Preferably the adhesive is brushed or rolled onto the substrates. Thereafter the adhesive is activated by exposing the substrate with the adhesive applied thereto to a temperature at which the encapsulating agent undergoes transition to release the curing agent or cross-linking agent. The adhesive is preferably heated to a temperature of 40°C or greater, preferably 45°C or greater, and most preferably 70°C or greater and preferably 100°C or less and most preferably 80°C or less. It is preferable that the time period over which the heat activation takes place is as short as possible. This is to reduce the amount of heating equipment and floor space necessary for activating the adhesive. Preferably the time period necessary for activation is less than 10 minutes, more preferably less than 7 minutes, and most preferably less than 5 minutes. In most practical applications, heating time required will be greater than 30 seconds and more preferably greater than 60 seconds. The heating temperature should be selected so as not to cause the polymer in the adhesive composition to degrade thereby comprising the properties of the finely cured system. Once the adhesive is activated, the substrates are contacted along the portion of each to which the adhesive is applied to bond the substrates together. Thereafter the adhesive is allowed to finally cure. This usually takes 12 hours or greater time and preferably 24 hours or greater, and preferably 72 hours or less and more preferably 50 hours or less.

16 The adhesive of this invention is stable for about 2 days when exposed to atmospheric conditions, in particular what is meant by stable for 2 days is that the_adhesive remains curable and has not cured completely.

The following examples are provided to more fully illustrate the invention, and are not intended to limit the scope of the claim. Unless otherwise stated, all parts and percentages are by weight.

Example 1

A 20 weight percent solution of diethyltoluene diamine was encapsulated in a C₂₂ polyacrylate based side chain crystalline homopolymer. The solution was prepared at 130°C, which is above the melting point of the homopolymer. The solution was fed at a rate of 130 grams per minute onto the surface of a rotating disk, rotating at a rotation speed of 15,000 revolutions per minute. The molten solution formed particles upon hitting the rotating disk which expelled them into an ambient temperature collection area. The final product was a powdery solid having a particle size ranging from 20-100 microns

Example 2

Ten grams of Isonate^* M636 polyurethane based prepolymer having free isocyanate groups prepared from TDI and 2000 equivalent weight polyethylene oxide polyol which contains a low amount of residual monomeric TDI(^*Trademark of The Dow Chemical Company) were blended with 0.74 gram of diethyltoluene diamine. Hand mixing was continued through the gel point which was reached after 7 to 8 minutes.

Example 3

71 .49 Grams of Isonate M636 polyurethane prepolymer were blended with 25.16 grams of diethyltoluene diamine encapsulated as described in Example 1 . The viscosity of the formulation was measured utilizing a Brookfield HBTDV II digital viscometer. The initial viscosity was 30.6 x 10³ centipoise. The viscosity doubled in 7 days.

Example 4

68.81 Grams of Isonate M636 polyurethane prepolymer were blended with

24.22 grams of diethyltoluenediamine encapsulated by the process of Example 1 , 13.76 grams of tetraethylurea and 0.83 gram of oleic acid. A 1.5 percent by weight solution of trichloroisocyanuric acid was prepared in ethyl acetate. Plates of natural rubber sole

17 material, 30 mm x 100 mm in size, were immersed in this solution for 30 seconds. Samples were dried for 60 minutes at room temperature. After drying, the substrates were immersed in a 25 percent by volume ethanol solution in water for 30 seconds. This was followed by a 1 hour drying stage at room temperature. The adhesive formulation was applied to the treated natural rubber substrates. The samples were heated in an oven at 70°C for seven minutes and assembled. The peel strength after four days of cure at room temperature was 2.5 N/mm.

Claims

1 . A composition comprising a polyurethane cross-linking agent or curing agent encapsulated in a thermoplastic or a crystalline polymer having a transition point at from 40┬░C to 100┬░C wherein the cross-linking or curing agent are not extractable from the encapsulated curing agent or cross-linking agent in the first extraction after encapsulation under ambient conditions.

2 . A composition according to Claim 1 wherein the cross-linking agent or curing agent does not volatilize under conditions at which the curing agent or cross-linking agent is encapsulated in the polymer.

3 . A composition according to Claim 2 wherein the cross-linking agent or curing agent is a primary amine.

4 . A composition according to Claim 3 wherein the polymer is a crystalline polymer.

5 . A composition according to Claim 4 wherein the primary amine is cycloaliphatic or sterically hindered aromatic amine.

6 . An adhesive composition comprising

a) a polyurethane prepolymer having free isocyanate moieties, and

b) a polyurethane cross-linking agent or curing agent encapsulated in a thermoplastic or a crystalline polymer as claimed in any one of Claims 1 to 5 having a transition point at from 40┬░C to 100┬░C.

7 . An adhesive composition according to Claim 6 which further comprises a fatty acid.

8 . An adhesive composition according to Claim 7 further comprising a swelling agent for an elastomeric polymer.

9 . A process for binding two substrates together which comprises contacting the two substrates such that an adhesive according to any one of Claims 6 to 8 is located between the two substrates and exposing the substrates and adhesive to sufficient heat to cause the encapsulating agent to release the cross-linking agent or curing

19 agent so as to contact the cross-linking agent or curing agent, the polyurethane prepolymer, and exposing the adhesive to curing conditions.

10 . A shoe comprising a shoe sole comprising an elastomeric polymer, a shoe upper and a cured adhesive composition according to any one of Claims 6 to 8 located between the sole and upper.

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