Patent Description:
This section provides background information which is not necessarily prior art to the inventive concepts associated with the present disclosure.

Hot melt adhesives are solid at room temperature but, upon application of heat, they melt to a liquid or fluid state in which form they are applied to a substrate. On cooling, the adhesive regains its solid form. The hard phase(s) formed upon cooling of the adhesive imparts all of the cohesion strength, toughness, creep and heat resistance to the final adhesive. Hot melt adhesives are generally thermoplastic and can be repeatedly heated to a fluid state and cooled to a solid state. Naturally, the thermoplastic nature limits the upper temperature at which such adhesives can be used.

A different class of hot melt adhesives is reactive hot melt adhesives. Reactive hot melt adhesives are also solid at room temperature but, upon application of heat, they melt to a liquid or fluid state in which form they are applied to a substrate. Reactive hot melt adhesives start out as thermoplastic materials that can be repeatedly heated to a molten state and cooled to a solid state. Reactive polyurethane-based hot melt adhesives are described in <CIT>, <CIT>, <CIT>, <CIT> and <CIT>. However, when exposed to appropriate conditions the reactive hot melt adhesive crosslinks and cures to an irreversible solid form. One class of reactive hot melt adhesives are polyurethane hot melt adhesives. Polyurethane hot melt adhesives comprise isocyanate terminated polyurethane prepolymers such as those obtained by reacting polyols with an excess of isocyanates. The polyurethane prepolymers cure through the diffusion of moisture from the atmosphere or the substrates into the adhesive, and subsequent reaction of that moisture with isocyanate moieties on the prepolymer backbone. The final adhesive product is a crosslinked material polymerized primarily through urea groups and urethane groups. Once the adhesive has crosslinked it is no longer thermoplastic and cannot be heated to a fluid state without destruction of the adhesive.

Green strength refers to initial adhesive strength of the adhesive after application of the molten adhesive to a substrate and before final full curing. High green strength is desirable as it allows bonded parts to be held together by the adhesive without further clamps or fasteners. Open time refers to the length of time after application of the molten hot melt adhesive during which a part can be bonded to the adhesive. Open time should be sufficiently long to allow the bonding substrates to be assembled together, and repositioned, if needed.

Once the structure has been assembled a high green strength is desirable to allow the bonded structures to move to the next operation. High final strength is especially advantageous in certain reactive hot melt adhesive end use applications, such as panel lamination and product assembly.

Conventional polyurethane hot melt adhesives are applied at temperatures of <NUM> to <NUM> or more. The viscosity of a conventional polyurethane hot melt adhesive at about <NUM> or less will be very high, for example <NUM>,<NUM> cps or more. Since hot melt application equipment for flat lamination is designed to work with molten hot melt adhesives having a viscosity of approximately <NUM>,<NUM> cps or less it is difficult or impossible to apply conventional polyurethane hot melt adhesives at temperatures of <NUM> or less. Thus, conventional polyurethane hot melt adhesives cannot be used for some applications at temperatures of <NUM> or less.

There are substrates such as vinyl films that are damaged by exposure to hot melt adhesives applied at temperatures of <NUM>. Thus, conventional polyurethane hot melt adhesives cannot be used to bond these low melting substrates.

This section provides a general summary of the disclosure and is not a comprehensive disclosure of its full scope or all features, aspects or objectives.

The present disclosure provides a moisture curable, polyurethane, hot melt adhesive comprising:.

In at least one embodiment the present disclosure provides a moisture reactive polyurethane hot melt adhesive composition having an application temperature of less than <NUM> and preferably <NUM> to <NUM>.

In at least one embodiment the present disclosure provides a moisture reactive polyurethane hot melt adhesive composition having an application temperature of <NUM> to <NUM>, a green strength of <NUM> kPa (<NUM> psi) or more and a maximum viscosity of <NUM>,<NUM> cps at <NUM>. In some embodiments the disclosure provides a moisture reactive polyurethane hot melt adhesive composition has a maximum viscosity of <NUM>,<NUM> cps or <NUM>,<NUM> cps or <NUM>,<NUM> cps or <NUM>,<NUM> cps or <NUM>,<NUM> cps at <NUM>.

In at least one embodiment the hot melt adhesive composition further comprises an additive selected from at least one of an additional filler, a plasticizer, a catalyst, a colorant, a rheology modifier, a flame retardant, an UV pigment, a nanofiber, a defoamer, a tackifier, a curing catalyst, an anti-oxidant, an adhesion promoter, a stabilizer, a thixotropic agent, nucleating agent, moisture scavenger, additional resins and mixtures thereof.

In at least one embodiment the hot melt adhesive composition has an open time in the range of <NUM> minute to less than <NUM> minutes. In a typical embodiment the hot melt adhesive composition has an open time in the range of <NUM> minute to less than <NUM> minutes.

In one embodiment the disclosure comprises an article of manufacture comprising an uncured or cured moisture reactive polyurethane hot melt adhesive composition as disclosed above.

In one embodiment the disclosure comprises cured reaction products of a moisture reactive polyurethane hot melt adhesive composition as disclosed above.

In one embodiment the disclosure is a method of bonding two substrates comprising applying a moisture reactive polyurethane hot melt adhesive composition as disclosed above at a temperature of about <NUM> to about <NUM> to one or more substrates and disposing the substrates into contact with the applied adhesive.

The disclosed compounds include any and all isomers and steroisomers. In general, unless otherwise explicitly stated the disclosed materials and processes may be alternately formulated to comprise, consist of, or consist essentially of, any appropriate components, moieties or steps herein disclosed. The disclosed materials and processes may additionally, or alternatively, be formulated so as to be devoid, or substantially free, of any components, materials, ingredients, adjuvants, moieties, species and steps used in the prior art compositions or that are otherwise not necessary to the achievement of the function and/or objective of the present disclosure.

The word "about" or "approximately" as used herein in connection with a numerical value refer to the numerical value ± <NUM>%, preferably ± <NUM>% and more preferably ± <NUM>% or less. These and other features and advantages of this disclosure will become more apparent to those skilled in the art from the detailed description of a preferred embodiment.

Unless specifically noted, throughout the present specification and claims the term molecular weight when referring to a polymer refers to the polymer's number average molecular weight (Mn). The number average molecular weight Mn can be calculated based on end group analysis (OH numbers according to DIN EN ISO <NUM>, free NCO content according to EN ISO <NUM>) or can be determined by gel permeation chromatography according to DIN <NUM> with THF as the eluent. If not stated otherwise, all given molecular weights are those determined by gel permeation chromatography.

Unless otherwise specified weight % or wt. % is based on weight of the moisture reactive polyurethane hot melt adhesive composition.

An adhesive's open time refers to the time during which an adhesive can bond to a material.

An adhesive's green strength refers to the initial holding strength prior to full chemical cure. In one variation green strength more particularly refers to the strength developed within <NUM> minutes after bonding a lauan board to a vinyl foil using the disclosed hot melt adhesive composition. In another variation green strength more particularly refers to the strength developed within <NUM> minutes after bonding an Azdel board to a vinyl foil using the disclosed hot melt adhesive composition. Below this level of initial strength, the green strength is generally insufficient for the bonded layers to withstand in-line finishing operations without exhibiting some debonding or delamination. Azdel is a product of Azdel Onboard in the U.

The present disclosure is directed toward providing reactive polyurethane hot melt adhesives that have some or all of the following properties. An application temperature in the range of <NUM> to <NUM>. A maximum viscosity of <NUM>,<NUM> cps at <NUM>. An open time of <NUM> minutes or less. A green strength of <NUM> kPa or more (<NUM> or more pounds per square inch (psi)), and preferably greater than <NUM> kPa (<NUM> pound per square inch), measured <NUM> minutes after application from the operating temperature. A final cured mechanical strength of at least <NUM> kPa (<NUM> psi) and preferably greater than <NUM> kPa (<NUM> psi).

In one embodiment the moisture reactive polyurethane hot melt adhesive composition is prepared from a combination comprising an amorphous polyester polyol, a crystalline polyester polyol, a polyether polyol, a diisocyanate, one of a polyisocyanate having a functionality greater than <NUM> or a thermoplastic polyurethane having hydroxyl functionality, a catalyst and optionally one or more additives.

Amorphous polyester polyols are polyester polyols that exhibit only a glass transition (Tg) and no substantial melting endotherm or crystallization exotherm in a DSC scan. Preferably at least one amorphous polyester polyol will have a Tg greater than <NUM>. In one variation the moisture reactive polyurethane hot melt adhesive composition will comprise a mixture of at least one amorphous polyester polyol having a Tg greater than <NUM> and at least one amorphous polyester polyol having a Tg of less than <NUM>.

Crystalline and/or semi-crystalline polyester polyols are polyester polyols that exhibit both a glass transition and melting and crystallization peaks in a DSC scan. In some embodiments useful crystalline and semi-crystalline polyester polyols have a melting point Tm of greater than <NUM>. Useful crystalline polyester polyol polymers include the Dynacoll materials available from Evonik Industries, for example Dynacoll <NUM>.

Preferably, the polyester polyols are used at an amorphous polyester polyol : crystalline polyester polyol ratio of <NUM> : <NUM> to <NUM> : <NUM>. Below a <NUM> : <NUM> ratio the initial strength of the resulting adhesive will be too low to be acceptable. Above a <NUM> : <NUM> ratio the viscosity at <NUM> will be too high to be acceptable and the final bond strength will suffer.

Polyisocyanates, which may be used to prepare the present adhesive include f=<NUM> diisocyanates such as alkylene diisocyanates, cycloalkylene diisocyanates, aromatic diisocyanates and aliphatic-aromatic diisocyanates and f><NUM> polyisocyanates. Examples of suitable polyisocyanates for use in the present disclosure include, by way of example and not limitation: methylenebisphenyldiisocyanate (MDI), isophoronediisocyanate (IPDI), hydrogenated methylenebisphenyldiisocyanate (HMDI), toluene diisocyanate (TDI), ethylene diisocyanate, ethylidene diisocyanate, propylene diisocyanate, butylene diisocyanate, trimethylene diisocyanate, hexamethylene diisocyanate, cyclopentylene-<NUM>, <NUM>-diisocyanate, cyclo-hexylene-<NUM>,<NUM>-diisocyanate, cyclohexylene-<NUM>,<NUM>-diisocyanate, <NUM>,<NUM>'-diphenylmethane diisocyanate, <NUM>,<NUM>-diphenylpropane-<NUM>,<NUM>'-diisocyanate, xylylene diisocyanate, <NUM>,<NUM>-naphthylene diisocyanate, <NUM>,<NUM>-naphthylene diisocyanate, m-phenylene diisocyanate, p-phenylene diisocyanate, diphenyl-<NUM>,<NUM>'-diisocyanate, azobenzene-<NUM>,<NUM>'-diisocyanate, diphenylsulphone-<NUM>,<NUM>'-diisocyanate, <NUM>,<NUM>-tolylene diisocyanate, dichlorohexa-methylene diisocyanate, furfurylidene diisocyanate, <NUM>-chlorobenzene-<NUM>,<NUM>-diisocyanate, <NUM>,<NUM>',<NUM>"-triisocyanatotriphenylmethane, <NUM>,<NUM>,<NUM>-triisocyanato-benzene, <NUM>,<NUM>,<NUM>-triisocyanato-toluene, <NUM>,<NUM>'-dimethyldiphenyl-methane-<NUM>,<NUM>',<NUM>,<NUM>-tetratetraisocyanate, and the like. Preferred polyisocyanates include methylenebisphenyl diisocyanate (MDI).

Aromatic polyisocyanates having a functionality greater than <NUM> (f><NUM>) can also be optionally used to prepare the adhesive in some embodiments. Preferably, these aromatic polyisocyanates have an average functionality of <NUM> to <NUM>. Useful aromatic polyisocyanates having a functionality greater than <NUM> include polymeric MDI, such as Rubinate M.

The moisture reactive polyurethane hot melt adhesive composition combination comprises polyether polyols including linear and branched polyethers having hydroxyl groups. Examples of the polyether polyol may include a polyoxyalkylene polyol such as polyethylene glycol, polypropylene glycol, polybutylene glycol and the like. Further, a homopolymer and a copolymer of the polyoxyalkylene polyols may also be employed. Particularly preferable copolymers of the polyoxyalkylene polyols may include an adduct of at least one compound selected from the group ethylene glycol, propylene glycol, diethylene glycol, dipropylene glycol, triethylene glycol, <NUM>-ethylhexanediol-<NUM>,<NUM>, glycerin, <NUM>,<NUM>,<NUM>-hexane triol, trimethylol propane, trimethylol ethane, tris(hydroxyphenyl)propane, triethanolamine, triisopropanolamine, ethylenediamine and ethanolamine. Most preferably the polyether polyol comprises a polypropylene glycol. Typically, the polyether polyol has a number average molecular weight of greater than <NUM> Daltons with a preferred range of <NUM> to <NUM> Daltons. The polyether polyol may comprise a mixture of different polyether polyols.

The adhesive can optionally include a catalyst. Some useful catalysts include, for example <NUM>,<NUM>'-dimorpholinodiethylether, triethylenediamine, dibutyltin dilaurate and stannous octoate. In some variations the adhesive free of organometallic catalysts. A preferred catalyst is <NUM>,<NUM>'-dimorpholinodiethylether.

The adhesive formulation can optionally include one or more of a variety of known hot melt adhesive additives such as filler; additional resins such as reactive acrylic polymer, nonreactive acrylic polymer, EVA, amorphous polyalphaolefin; plasticizer; colorant; rheology modifier; flame retardant; UV pigment; nanofiber; defoamer; tackifier; anti-oxidant; adhesion promoter; stabilizer; a thixotropic agent such as fumed silica; and the like. Conventional additives that are compatible with a composition according to this invention may simply be determined by combining a potential additive with the composition and determining if they are compatible. An additive is compatible if it is homogenous within the product at room temperature and at the use temperature.

Examples of useful fillers for use in the present disclosure include inorganic materials such as calcium carbonate, kaolin and dolomite. Calcium carbonate has been referred to as a non-fossil fuel based, sustainable, renewable material. Other examples of suitable fillers can be found in <NPL>and <NPL>.

Reactive acrylic polymers comprise moieties that are reactive with other materials. Examples of useful reactive acrylic polymers include Elvacite <NUM> and Elvacite <NUM>.

Nonreactive acrylic polymers are free of moieties that are reactive with other materials. Examples of useful nonreactive acrylic polymers include Elvacite <NUM> and Elvacite <NUM>.

Tackifiers useful in the adhesive composition are not limited. Examples of useful materials for the optional tackifier include aliphatically modified C<NUM>-C<NUM> hydrocarbons such as Novares TK <NUM>, Norsolene A-<NUM>, Henghe HH2-<NUM>; alpha methyl styrene based tackifiers such Kristalex <NUM>; rosin ester tackifiers such as Sylvalite RE <NUM>; terpene phenolic tackifiers such as Sylvarez TP2040 and mixtures thereof.

Examples of useful adhesion promoters include silane based adhesion promoters such as Silquest A-link, Dynasylan AMEO and Dynasylan AMMO.

In the Table below the components of some embodiments of the presently disclosed adhesive composition are presented. The amounts are the percentage by weight of that component based on the total adhesive weight.

The hot melt adhesives according to the present disclosure can be prepared by as follows. Add functional polyols, other polymers or resins (for example, thermoplastic urethane polymer, acrylic resin) into a reactor. Optionally add defoamer, filler, plasticizer or other non-reactive additives into the reactor. Mix the components at an elevated temperature until homogeneous. Dehydrate the mixture, for example by maintaining at an elevated temperature and under vacuum. To the dehydrated mixture add the diisocyanate (f=<NUM>) with mixing, under vacuum and at a temperature of about <NUM> to <NUM> and allow the reaction to proceed until for <NUM> hour or until a desired viscosity and NCO content are reached. Subsequently, add the polyisocyanate (f><NUM>), if desired, catalyst, pigment, colorant, stabilizer, adhesion promoter and mix under vacuum for about <NUM> to <NUM> hour. Pack the final adhesive product into a container under an inert atmosphere to exclude moisture.

The hot melt adhesives according to the present disclosure can be applied in a variety of manners including by spraying, roller coating, via a slot die, extruding and as a bead. The disclosed hot melt adhesive is stable during storage provided moisture is excluded. The disclosed hot melt adhesive has a commercially acceptable pot life in the molten state during application. It can be applied to a range of substrates including metals, wood, plastics, glass and textiles.

The invention also provides a method for bonding articles together which comprises applying the reactive hot melt adhesive composition of the disclosure in a liquid melt form to a first article, bringing a second article in contact with the composition applied to the first article, allowing the adhesive to cool and solidify and subjecting the applied composition to conditions which will allow the composition to fully cure to a composition having an irreversible solid form, said conditions comprising moisture. The composition is typically distributed and stored in its solid form and stored in the absence of moisture to prevent curing during storage. The composition is heated to a molten form prior to application and applied in the molten form. Typical application temperatures are in the range of from about <NUM>° C to about <NUM>° C and more typically about <NUM> to about <NUM>. Thus, this disclosure includes reactive polyurethane hot melt adhesive compositions in both its uncured, room temperature solid form, as it is typically stored and distributed and its molten form after it has been melted just prior to its application and in its irreversibly solid form after curing.

After application, to adhere articles together, the reactive hot melt adhesive composition is subjected to conditions that will allow it to solidify and cure to a composition that has an irreversible solid form. Solidification or setting occurs when the liquid melt begins to cool from its application temperature to room temperature. This provides green strength. Curing, i.e. chain extending, to a composition that has an irreversible solid form, takes place in the presence of ambient moisture. This provides final or cured strength.

In some embodiment the disclosed reactive hot melt adhesive provides one or more advantages over conventional reactive hot melt adhesives. The disclosed hot melt adhesive can be applied at <NUM> - <NUM> while conventional reactive hot melt adhesives are generally applied above <NUM>, for example above <NUM>. The disclosed hot melt adhesive has a maximum viscosity of <NUM>,<NUM> cps at <NUM>. In some embodiments the disclosure provides a moisture reactive polyurethane hot melt adhesive composition has a maximum viscosity of <NUM>,<NUM> cps or <NUM>,<NUM> cps or <NUM>,<NUM> cps or <NUM>,<NUM> cps or <NUM>,<NUM> cps at <NUM>. These low viscosities at <NUM> allow use in commercial application equipment at this temperature. Conventional reactive hot melt adhesives have a viscosity of <NUM>,<NUM> - <NUM>,<NUM> cps or more at <NUM>, a viscosity too high for use in commercial application equipment to achieve a desired low coating weight. The disclosed hot melt adhesive when heated to <NUM> to <NUM> can be applied at a coating weight of <NUM>/m<NUM> (<NUM> grams per square foot (gsf)) or less. Conventional reactive hot melt adhesives cannot be applied at a coating weight of about <NUM>/m<NUM> (<NUM> gsf) when used at a temperature of <NUM> to <NUM>. The disclosed hot melt adhesive provides significant green strength of at least <NUM> kPa (<NUM> psi), and more preferably at least <NUM> kPa (<NUM> psi), <NUM> minutes after application of <NUM>/m<NUM> (<NUM> gsf) or less, more preferably application of <NUM>/m<NUM> (<NUM> gsf) or less. Other low temperature hot melt adhesives require substantially higher coating weights to increase their green strength. The disclosed hot melt adhesive has similar cured strength to conventional reactive hot melt adhesives.

The following components, in Table <NUM>, were utilized in the examples that follow.

Viscosity was measured using a Brookfield viscosimeter at <NUM> using a number <NUM> spindle and <NUM> rpm.

%NCO was measured by the conventional titration method.

Bond strength was measured at room temperature using a <NUM>° peel test at a rate of <NUM> (<NUM> inches) per minute. Samples were prepared and aged for either <NUM> minutes (short term bond strength or green strength) or <NUM> hours (long term bond strength or cured bond strength) before testing. Samples were tested by pulling at <NUM>° to the bond line.

Open time was measured by drawing a <NUM> (<NUM> mil) film of adhesive and pressing strips of Kraft paper onto the adhesive in intervals of <NUM>-<NUM> seconds. After <NUM>, or when the adhesive is hardened, the paper strips are pulled off the adhesive. Paper strips applied after the open time will have less than <NUM>% fiber tear.

Samples were prepared by roll coating adhesive to one or both substrates and pressing or nipping the coated substrates together.

The following Table lists comparative samples. Amounts are in weight percent (wt.

Samples were made by coating each of the above samples at about <NUM> on both test substrates, contacting the coated surfaces of the test substrates and holding the contacted surfaces together for <NUM> minutes or <NUM> hours. Coating weights were <NUM> - <NUM>/m<NUM> (<NUM> - <NUM> grams per square foot (gsf)) on the vinyl foil and <NUM> - <NUM>/m<NUM> (<NUM> - <NUM> grams per square foot) on the board. The vinyl foil is a commercially available <NUM> to <NUM> (<NUM> to <NUM> mil) thick product. The board is commercially available Lauan plywood or Azdel board. Sample sizes for vinyl foil and board were <NUM> by <NUM> (<NUM> inch by <NUM> inches) and adhesive was applied to the entire <NUM> by <NUM> (<NUM> inch by <NUM> inch) surface. Results are shown in the following Table.

The following Table lists moisture reactive polyurethane hot melt adhesive composition samples. Amounts are in weight percent (wt.

Samples were made by coating each of the above samples at about <NUM> on test substrates, contacting the coated surfaces of the test substrates and holding the contacted surfaces together for <NUM> minutes or <NUM> hours. Coating weights were <NUM> - <NUM>/m<NUM> (<NUM> - <NUM> grams per square foot (gsf)) on the vinyl foil and <NUM> - <NUM>/m<NUM> (<NUM> - <NUM> grams per square foot) on the board. Results are shown in the following Table.

As shown in results composition E7 with only f=<NUM> diisocyanate (no f><NUM> polyisocyanate or thermoplastic urethane) provided acceptable green and cured strength on Lauan to vinyl foil bonding and acceptable cured strength on Azdel board to vinyl foil bonding. Composition E7 did not have acceptable green strength for Azdel board to vinyl foil bonding. Composition E5 comprised f=<NUM> diisocyanate and f><NUM> polyisocyanate but no thermoplastic urethane. Composition E6 comprised f=<NUM> diisocyanate and thermoplastic urethane but no f><NUM> polyisocyanate. Compositions E5 and E6 provided improved green and cured strength on Lauan to foil bonding compared to composition E7 and marginal green and cured strength on Azdel board to vinyl foil bonding for some applications. Composition E4 comprised all of f=<NUM> diisocyanate; f><NUM> polyisocyanate and thermoplastic urethane. The surprisingly improved strengths of this composition across all materials and cure levels indicate an unexpected synergy from using all of f=<NUM> isocyanate; f><NUM> polyisocyanate and thermoplastic urethane.

Claim 1:
A moisture curable, polyurethane, hot melt adhesive comprising:
an isocyanate functional prepolymer that is the reaction product of a mixture comprising:
<NUM> to <NUM> wt. % of an amorphous polyester polyol having a Tg greater than <NUM>;
<NUM> to <NUM> wt. % of at least one crystalline polyester polyol, wherein the crystalline polyester polyol has a melting point in the range of <NUM> to <NUM>;
wherein the weight ratio of crystalline polyester polyol : amorphous polyester polyol is in the range of <NUM> : <NUM> to <NUM> : <NUM>, and preferably is <NUM>:<NUM>;
<NUM> to <NUM> wt. % of a diisocyanate;
<NUM> to <NUM> wt. % of at least one polyether polyol;
a catalyst;
either <NUM> to <NUM> wt. % of a polyisocyanate having a functionality greater than <NUM> or <NUM> to <NUM> wt. % of a thermoplastic polyurethane having hydroxyl functionality;
optionally one or more additives;
wherein the hot melt adhesive has a green strength determined by the method provided in the description of at least <NUM> kPa (<NUM> psi), and more preferably at least <NUM> kPa (<NUM> psi), <NUM> minutes after application of the hot melt adhesive to a substrate at a temperature of <NUM> to <NUM> and a coating weight of <NUM>/m<NUM> (<NUM> gsf) or less, more preferably application of <NUM>/m<NUM> (<NUM> gsf) or less.