Patent Description:
The invention relates to one-component adhesive compositions that are storage-stable and cure at elevated temperatures.

Epoxy-functional compositions have long been known as building blocks for making epoxy resins. Reaction products of bisphenols and epichlorohydrin, for instance, are mainstays of the epoxy resin industry and have been sold for years as EPON® resins (Hexion Specialty Chemicals). Epoxy resins react with "hardeners" or other crosslinkers --usually polyamines, polycarboxylic acids, or polythiols--to give cured, high polymers for adhesives and other end-use applications. A challenge with most epoxy-based products is in making products having desirable flexibility at low cost while preserving other important properties. Most epoxy-based products have relatively high glass-transition temperatures (Tg > <NUM>) and low ultimate elongations (< <NUM>%).

Recently, we developed new classes of polyether/polyester-epoxide polymers ("polyether PEEPs" and "polyester PEEPs"; see <CIT> and <CIT>, respectively). The polyether PEEPs are reaction products of a polyepoxide compound and a polyol composition comprising a polyether polyol. The polyether polyols have a hydroxyl value within the range of <NUM> to <NUM> KOH/g and an average hydroxyl functionality within the range of <NUM> to <NUM>. The polyester PEEPs are reaction products of a polyepoxide compound and a polyester polyol composition. The polyester polyol has a hydroxyl value within the range of <NUM> to <NUM> KOH/g and an average hydroxyl functionality within the range of <NUM> to <NUM>. The polyester-epoxide compositions retain many of the benefits of traditional epoxy resin-based products, but they have increased elongation and lower Tg. Both varieties of PEEP compositions are useful for coatings, elastomers, adhesives, sealants, and other valuable products and can be made without reliance on polyamines or polyisocyanates.

While the PEEP systems described previously are principally useful as two-component ("<NUM>") systems (i.e., the reaction occurs at room temperature or somewhat elevated temperature when or soon after two reactive components are combined), some practical applications, particularly adhesives, require a one-component ("<NUM>") system in which all of the reactants, including a heat-activated catalyst, can be stored together in one mixture without reacting until a reaction is needed.

Structural adhesives based on room temperature-cured or heat-cured epoxies are known. Polyamides, amidoamines, or aliphatic/aromatic amines are typical curing agents. In some cases, these products have poor resilience, low elongation, and/or low lap shear strength.

Structural adhesives are needed for high-strength, load-bearing applications to replace or supplement mechanical fasteners or welds. For metal, this translates to a lap shear strength greater than <NUM> psi, and for other substrates, strengths greater than <NUM> psi at bond failure. Relevant markets for structural adhesives include transportation, electronics, and building/construction, and these needs are now usually met with <NUM> epoxy or <NUM> urethane systems. Low-VOC, isocyanate-free, polyamine crosslinker-free alternatives to these systems are needed.

The industry would benefit from the availability of storage-stable, one-component epoxy-based products, particularly ones useful as structural adhesives. Desirably, the products would offer improved resilience and greater lap shear strength compared with a conventional epoxy <NUM> system. Preferably, the products could be made using commercially available or readily made starting materials, conventional equipment, and commonly used heat-cure conditions. Ideally, epoxy-based structural adhesives with excellent physical and mechanical properties could be realized without using polyisocyanates or polyamine curatives.

The invention relates to a process for making a one-component (<NUM>) adhesive. The process comprises reacting a mixture comprising a polyepoxide compound, a polyol composition, and a heat-activated Lewis acid catalyst. The heat-activated Lewis acid catalyst is adapted to melt, dissolve, or dissociate to generate a species capable of catalyzing a reaction between an epoxide group of the epoxide compound and a hydroxyl group of the polyol at temperatures greater than <NUM>. The polyepoxide compound has an equivalent weight within the range of <NUM> to <NUM>/eq. The polyol composition comprises: (i) a polyester polyol having a hydroxyl value within the range of <NUM> to <NUM> KOH/g, an average hydroxyl functionality within the range of <NUM> to <NUM>, and an acid number less than <NUM> KOH/g; or (ii) a polyether polyol having a hydroxyl value within the range of <NUM> to <NUM> KOH/g and an average hydroxyl functionality within the range of <NUM> to <NUM>; or (iii) a combination of (i) and (ii). The components are reacted at temperature within the range of <NUM> to <NUM> for a time effective to cure the adhesive.

In some aspects, the heat-activated Lewis acid catalyst is a complex of boron trifluoride and a primary aliphatic amine such as ethylamine.

The invention includes one-component adhesives, especially structural adhesives used by the construction and transportation industries, made by the process described above.

In other aspects, the invention includes heat-curable, one-component adhesive mixtures. These mixtures are curable at temperatures within the range of <NUM> to <NUM> and comprise the polyepoxide, polyols, and heat-activated Lewis acid catalyst described above.

We found that one-component adhesives having excellent lap shear strength and flexibility can be made by including a heat-activated Lewis acid catalyst in a PEEP system. The one-component PEEP compositions complement the <NUM> systems curable at room temperature or elevated temperature that we described earlier. The <NUM> systems are desirable for fully formulated products intended to be stored before use, such as the structural adhesives used for construction and automotive applications. Compared with conventional epoxy <NUM> compositions, the <NUM> PEEP compositions offer improved room temperature lap shear strength, better resilience, and higher elongation. The inventive <NUM> systems deliver a desirable balance of physical and mechanical properties while avoiding polyisocyanates or polyamine crosslinkers.

In one aspect, the invention relates to a process for making a one-component (<NUM>) adhesive by reacting a polyepoxide compound and a composition comprising a polyol in the presence of a heat-activated Lewis acid catalyst.

Suitable polyepoxide compounds have two or more epoxide groups per molecule and an equivalent weight within the range of <NUM> to <NUM>/eq. , or in some aspects <NUM> to <NUM>/eq. or <NUM> to <NUM>/eq.

In preferred aspects, the polyepoxide compounds have an average of <NUM> to <NUM> epoxide groups per molecule ("average epoxide functionality"). In some aspects, the average epoxide functionality is from <NUM> to <NUM>, <NUM> to <NUM>, or about <NUM>.

Some suitable polyepoxide compounds are commercially available, while others are readily synthesized from the reaction of epichlorohydrin and a suitable polyol or polyamine precursor, preferably from epichlorohydrin and an aromatic or cycloaliphatic polyol or polyamine.

In some aspects, the polyepoxide compound is a reaction product of a bisphenol (e.g., bisphenol A, bisphenol AP, bisphenol BP, bisphenol C, bisphenol F, bisphenol S, bisphenol Z, or the like) and epichlorohydrin. In other aspects, the polyepoxide compound is the reaction product of a hydrogenated bisphenol and epichlorohydrin. In other words, in some cases the polyepoxide compound is a "diglycidyl ether" of the bisphenol or hydrogenated bisphenol. Many of these materials are commercially available. For instance, suitable polyepoxide compounds include the EPON® <NUM> series of epoxy resins (products of Hexion Specialty Chemicals), mostly from bisphenol A or bisphenol F, such as EPON® resins <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, and the like. Suitable bisphenol F-based resins also include EPALLOY® <NUM>, EPALLOY® <NUM>, and EPALLOY® <NUM>, products of CVC Thermoset Specialties. EPON® <NUM> and EPALLOY® <NUM> resins are particularly preferred.

Suitable epoxide compounds include bisphenol diglycidyl ethers in which the aromatic rings have been hydrogenated, such as EPALLOY® <NUM> and EPALLOY® <NUM>, or modified with alkyl or functional groups, such as EPALLOY® <NUM>. Suitable polyepoxide compounds include di-, tri-, or tetrafunctional aromatic polyepoxides such as resorcinol diglycidyl ether (available as ERISYS™ RDGE from CVC Thermoset Specialties), the triglycidyl ether of tris(hydroxyphenyl)ethane (available, for instance, as EPALLOY® <NUM>), and the tetraglycidyl ether of m-xylenediamine (available as ERISYS™ GA <NUM>). Suitable polyepoxide compounds also include aromatic and cycloaliphatic glycidyl esters, such as the diglycidyl ester of isophthalic acid, phthalic acid, or terephthalic acid and hydrogenated versions thereof, such as hexahydrophthalic acid diglycidyl ester (available, for instance, as EPALLOY® <NUM>).

In some aspects, the polyepoxide compound is an aliphatic diglycidyl ether, particularly aliphatic diglycidyl ethers having average epoxide functionalities of at least <NUM>, preferably at least <NUM>. Suitable aliphatic diglycidyl ethers include, for example, <NUM>,<NUM>-butanediol diglycidyl ether, <NUM>,<NUM>-cyclohexanediol diglycidyl ether, neopentyl glycol diglycidyl ether, ethylene glycol diglycidyl ether, <NUM>-methyl-<NUM>,<NUM>-propanediol diglycidyl ether, <NUM>,<NUM>-hexanediol diglycidyl ether, dipropylene glycol diglycidyl ether, glycerol triglycidyl ether, trimethylolpropane triglycidyl ether, pentaerythritol tetraglycidyl ether, and the like, and mixtures thereof. Suitable polyepoxide compounds of this type are easily made by reacting the polyols with excess epichlorohydrin, many are commercially available from CVC Thermoset Specialties under the ERISYS™ mark or from other suppliers.

Mixtures of various types of polyepoxide compounds can be used. In preferred aspects, the polyepoxide compound comprises at least <NUM> wt. %, at least <NUM> wt. %, or at least <NUM> wt. %, of an aromatic polyepoxide compound, a cycloaliphatic polyepoxide compound, or a combination thereof.

The polyepoxide compound is used in an amount such that the ratio of epoxy equivalents of the polyepoxide compound to hydroxyl equivalents of the polyol composition (also described herein as the "epoxy/OH eq. ratio") is within the range of <NUM>:<NUM> to <NUM>:<NUM>. In other aspects, the ratio of epoxy to hydroxyl equivalents will range from <NUM>:<NUM> to <NUM>:<NUM>, from <NUM>:<NUM> to <NUM>:<NUM>, or from <NUM>:<NUM> to <NUM>:<NUM>. The "epoxy/OH index" or "index" referred to herein is the epoxy/OH eq. ratio multiplied by <NUM>.

The amount of polyepoxide compound used can vary and will depend on many factors, including the nature of the polyepoxide compound, the nature of the polyol composition, the desired stoichiometry, and other factors. In general, however, the amount of polyepoxide compound will be within the range of <NUM> to <NUM> wt. %, <NUM> to <NUM> wt. %, or <NUM> to <NUM> wt. %, based on the amount of PEEP composition.

The <NUM> PEEP compositions are reaction products of the polyepoxide compound described above and a polyol composition. In a preferred aspect, the polyol composition comprises a polyester polyol, especially an aromatic polyester polyol.

Suitable polyester polyols are well known and include aromatic and aliphatic polyester polyols. These polyols are terminated with hydroxyl groups and generally have low acid numbers (i.e., below <NUM> KOH/g). Suitable polyester polyols are readily synthesized by condensation polymerization of dicarboxylic acids, esters, or anhydrides with low molecular weight diols, polyols, or their mixtures. Suitable dicarboxylic acids, esters, or anhydrides include, for example, phthalic anhydride, isophthalic acid, terephthalic acid, dimethyl terephthalate, trimellitic anhydride, maleic anhydride, succinic anhydride, succinic acid, dimethyl succinate, diethyl adipate, glutaric acid, adipic acid, sebacic acid, suberic acid, and the like, and combinations thereof. Suitable diols and polyols useful for making polyester polyols include, for example, ethylene glycol, propylene glycol, <NUM>-methyl-<NUM>,<NUM>-propanediol, <NUM>,<NUM>-butanediol, <NUM>,<NUM>-hexanediol, diethylene glycol, dipropylene glycol, triethylene glycol, tripropylene glycol, neopentyl glycol, <NUM>,<NUM>-cyclohexanedimethanol, glycerin, trimethylolpropane, trimethylolethane, pentaerythritol, and the like, and combinations thereof.

Many suitable polyester polyols for use herein are commercially available from Stepan Company and other polyol suppliers. Examples include the STEPANPOL® PS-, PC-, PD-, PH-, PHN-, PN-, and AA- series polyols, products of Stepan. Particular examples include STEPANPOL® PS-<NUM>, STEPANPOL® PS-<NUM>, STEPANPOL® PS-<NUM>, STEPANPOL® PC-<NUM>-<NUM>, and STEPANPOL® PC-<NUM>-<NUM> (aromatic polyester polyols) and STEPANPOL® AA-<NUM>, STEPANPOL® PS-<NUM>-<NUM>, STEPANPOL® PC-1011P-<NUM>, STEPANPOL® PC-<NUM>-<NUM>, STEPANPOL® PC-<NUM>-<NUM>, STEPANPOL® PC-<NUM>-<NUM>, and STEPANPOL® PC-<NUM>-<NUM> (aliphatic polyester polyols). Other commercially available products include TERATE® and TERRIN™ polyols from INVISTA, TEROL® polyols from Huntsman, LUPRAPHEN® polyols from BASF, DESMOPHEN® polyols from Covestro, FOMREZ® polyols from Chemtura, and DIEXTER™ polyols from Coim.

In suitable polyol compositions, the polyester polyol will have a hydroxyl value within the range of <NUM> to <NUM> KOH/g. In some aspects, the polyester polyol will have a hydroxyl value within the range of <NUM> to <NUM> KOH/g, or within the range of <NUM> to <NUM> KOH/g.

The polyester polyols will have average hydroxyl functionalities within the range of <NUM> to <NUM>. In some aspects, the polyester polyol will have an average hydroxyl functionality within the range of <NUM> to <NUM> or <NUM> to <NUM>.

The polyester polyols have mostly hydroxyl end groups, not carboxylic acid end groups, and consequently will have low acid numbers, i.e., less than <NUM> KOH/g. In some aspects, the polyester polyols will have acid numbers less than <NUM> KOH/g, less than <NUM> KOH/g, or less than <NUM> KOH/g.

In some aspects, the polyol composition comprises a polyether polyol, especially a high-functionality polyether polyol. Suitable polyether polyols have average hydroxyl functionalities within the range of <NUM> to <NUM>, from <NUM> to <NUM>, or from <NUM> to <NUM>. These polyols are readily synthesized by ring-opening polymerization of propylene oxide, ethylene oxide, butylene oxides, tetrahydrofuran, or mixtures thereof, in the presence of suitable hydroxy- and/or amine-functional initiators. In some cases, the reactions are catalyzed by bases (e.g., KOH), transition metal catalysts (e.g., double metal cyanide catalysts), Lewis acids (e.g., BF<NUM> catalysts) or the like. A variety of diols, triols, and higher functionality starters can be used alone or in combination provided that the average hydroxyl functionality of the polyol is between <NUM> and <NUM>. In some aspects, sucrose, sorbitol, or another high-functionality starter is used alone or in combination with a diol (e.g., ethylene glycol, diethylene glycol), triol (e.g., glycerin, trimethylolpropane, triethanolamine), or amine starter (e.g., ethylene diamine) to achieve a high targeted functionality within the range of <NUM> to <NUM>.

Many suitable polyether polyols having average hydroxyl functionalities within the range of <NUM> to <NUM>, particularly polyethers initiated by triol and higher functionality starters, are commercially available from Dow Chemical, Covestro, Huntsman, Carpenter, and other suppliers.

Examples of the high-functionality (<NUM> to <NUM>) polyols include the MULTRANOL® products from Covestro (e.g., MULTRANOL® <NUM>, MULTRANOL® <NUM>, MULTRANOL® <NUM>, MULTRANOL® <NUM>, MULTRANOL® <NUM>, MULTRANOL® <NUM>, MULTRANOL® <NUM>, MULTRANOL® <NUM>, MULTRANOL® <NUM>, and MULTRANOL® <NUM>), the CARPOL® products from Carpenter (CARPOL® GSP-<NUM>, CARPOL® GSP-<NUM>, CARPOL® GSP-<NUM>, CARPOL® SP-<NUM>, CARPOL® SPA-<NUM>, CARPOL® SPA-<NUM>, CARPOL® EDAP-<NUM>, and CARPOL® EDAP-<NUM>), the VORANOL® products from Dow Chemical (VORANOL® <NUM>, VORANOL® <NUM>, and VORANOL® <NUM>), and the JEFFOL® products from Huntsman (JEFFOL® S-<NUM>, JEFFOL® SA-<NUM>, JEFFOL® SD-<NUM>, JEFFOL® SD-<NUM>, JEFFOL® SG-<NUM>, and JEFFOL® SG-<NUM>).

In suitable polyol compositions, the polyether polyol will have a hydroxyl value within the range of <NUM> to <NUM> KOH/g. In some aspects, the polyether polyol will have a hydroxyl value within the range of <NUM> to <NUM> KOH/g, or within the range of <NUM> to <NUM> KOH/g.

The polyol compositions can include polycarbonate polyols or other kinds of polyols in addition to the polyester polyol and/or polyether polyol. In general, the polyol composition comprises at least <NUM> mole %, in some aspects at least <NUM> mole % or at least <NUM> mole %, of one or more polyester or polyether polyols. In some aspects, the polyol composition will consist of or consist essentially of one or more polyester polyols. In other aspects, the polyol composition will consist of or consist essentially of one or more polyether polyols.

The amount of polyester polyol and/or polyether polyol composition used can vary and will depend on many factors, including the nature of the polyepoxide compound, the nature of the polyol composition, the desired stoichiometry, and other factors. In general, however, the amount of polyol composition will be within the range of <NUM> to <NUM> wt. %, <NUM> to <NUM> wt. %, or <NUM> to <NUM> wt. %, based on the amount of PEEP composition.

Suitable heat-activated Lewis acid catalysts include an electron pair acceptor such as aluminum chloride, aluminum bromide, zinc chloride, boron trichloride, boron trifluoride, tin tetrachloride, antimony pentachloride, and the like, with boron trifluoride as especially preferred.

The electron pair acceptor is bonded or strongly associated with an electron donor such that under ambient or warm conditions, the Lewis acid is essentially unreactive as a catalyst for hydroxyl-epoxide reactions. Suitable electron donors include primary and secondary amines, which strongly associate with many Lewis acids, including boron trifluoride, under these conditions.

The catalyst is "heat-activated," i.e., it melts, dissolves, or dissociates to generate a species capable of catalyzing a reaction between an epoxide group of an epoxide compound and a hydroxyl group of a polyol at temperatures greater than <NUM>.

Complexes of boron trifluoride and primary or secondary aliphatic or aromatic amines are preferred and many are commercially available from Laborchemie Apolda GmbH and other suppliers. Thus, suitable BF<NUM>-amine catalysts include complexes of boron trifluoride with ethylamine, di-n-butylamine, isopropylamine, piperidine, isophorone diamine, N-methylcyclohexylamine, benzylamine, aniline, N-methylaniline, and <NUM>,<NUM>-dimethylaniline. Complexes of BF<NUM> with primary aliphatic amines, particularly ethylamine ("monoethylamine," "MEA") are preferred. In some cases, the BF<NUM>-amine catalysts are supplied (or can be supplied) as mixtures with a polyol such as polyethylene glycols, polyester polyols, or other polyols.

The amount of heat-activated Lewis acid catalyst needed will depend on the nature of the epoxy compound, the nature of the polyol composition, the epoxy/hydroxyl index, the curing temperature, the particular catalyst used, and other factors. Generally, however, the amount used will be within the range of <NUM> to <NUM> wt. %, <NUM> to <NUM> wt. %, or <NUM> to <NUM> wt. % based on the amount of PEEP composition.

A one-component system comprising a mixture of the polyepoxide compound and the composition comprising a polyol are reacted in the presence of a heat-activated Lewis acid catalyst at temperature within the range of <NUM> to <NUM>, or from <NUM> to <NUM>, or from <NUM> to <NUM>, for a time effective to cure the adhesive. Cure times depend on the curing temperature, catalyst level, epoxy/hydroxyl index, the desired working time, and other factors. Typically, however, cure times are within the range of several minutes to an hour, such as <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> minutes. As shown in Table <NUM>, choosing a <NUM> curing temperature can give fully cured adhesives in as little as <NUM> minutes.

The reaction of the polyepoxide compound and the polyol composition provides a polyester-epoxide or polyether-epoxide polymer ("PEEP") adhesive composition. The PEEP compositions are distinguishable from conventional epoxy adhesives in having a unique balance of properties.

For instance, the inventive adhesive compositions will have a relatively low glass-transition temperature (Tg), as measured by differential scanning calorimetry (DSC), within the range -<NUM> to <NUM>. In some aspects, the Tg of the PEEP composition will be within the range of <NUM> to <NUM>, or within the range of <NUM> to <NUM>, or within the range of <NUM> to <NUM>.

When compared with conventional epoxy adhesives, the inventive adhesive compositions have increased ultimate elongations (i.e., "elongation at break," hereinafter simply "elongation"). In some aspects, the PEEP compositions will have elongations (as measured by ASTM D412, Method A) of at least <NUM>%, at least <NUM>%, at least <NUM>%. In other aspects, the PEEP compositions will have elongations within the range of <NUM>% to <NUM>% or from <NUM>% to <NUM>%.

The adhesive compositions can include additives such as fillers, pigments, flame retardants, viscosity modifiers, reactive diluents, adhesion promoters, moisture scavengers, plasticizers, flexibilizers, and the like. The type and amount of additive used will depend on the requirements of the specific adhesive application.

In some aspects, the adhesive compositions normally will have increased resilience compared with conventional epoxy adhesives as reflected by higher total energy absorption ("T. ") values as determined hereinbelow. values will typically range from <NUM> to <NUM> lb. <NUM>, <NUM> to <NUM> lb. <NUM>, or <NUM> to <NUM> lb. The units are commonly written as "lb.

The following examples merely illustrate the invention; the skilled person will recognize many variations that are within the scope of the claims.

Note: Hydroxyl values, functionalities, molecular weights, and viscosities are nominal or approximate values.

EPON® <NUM> (Hexion Specialty Chemicals): a liquid bisphenol A diglycidyl ether-based epoxy resin. Viscosity: <NUM>,<NUM> cP at <NUM>.

EPALLOY® <NUM> (CVC Thermoset Specialties): an epoxy phenol novolac resin. Viscosity: <NUM>-<NUM> cP at <NUM>.

STEPANPOL® PC-1028P-<NUM> (Stepan Company): aromatic polyester polyol from <NUM>,<NUM>-hexandiol and phthalic anhydride. OH value: <NUM> KOH/g. Functionality: <NUM>.

IPA-HDO polyol: aromatic polyester polyol from isophthalic acid and <NUM>,<NUM>-hexanediol. OH value: <NUM> KOH/g. Functionality: <NUM>.

AA-BDO polyol: aliphatic polyester polyol from adipic acid and <NUM>,<NUM>-butanediol. OH value: <NUM> KOH/g. Functionality: <NUM>.

STEPANPOL® PS-<NUM>-<NUM> (Stepan): aliphatic polyester polyol, OH value: <NUM>-<NUM> KOH/g. Functionality: <NUM>.

STEPANPOL® PC-1011P-<NUM> (Stepan): aliphatic polyester polyol, OH value: <NUM>-<NUM> KOH/g. Functionality: <NUM>.

VORANOL® <NUM> (Dow): glycerin/sucrose-initiated polyether polyol. Functionality: <NUM>.

MULTRANOL® <NUM> (Covestro): sucrose-based polyol, OH value: <NUM>-<NUM> KOH/g.

MULTRANOL® <NUM> (Covestro): sucrose-based polyol, OH value: <NUM>-<NUM> KOH/g, molecular weight <NUM>.

CARPOL® PGP-<NUM> (Carpenter): polypropylene glycol, mol.

Isophthalic acid (<NUM>) and <NUM>,<NUM>-hexanediol (<NUM>) are charged to a flask equipped with an overhead stirrer, stir shaft, thermocouple, nitrogen sparge tube, and distillation head. The contents are heated to <NUM> under nitrogen. During the condensation reaction, titanium tetrabutoxide (<NUM>) is added, and the reaction continues until the acid value of the polyol product is less than <NUM> KOH/g. Hydroxyl value: <NUM> KOH/g. Acid value: <NUM> KOH/g.

Adipic acid (<NUM>) and <NUM>,<NUM>-butanediol (<NUM>) are charged to a flask equipped with an overhead stirrer, stir shaft, thermocouple, nitrogen sparge tube, and distillation head. The contents are heated under nitrogen to <NUM>, then gradually to <NUM>. When the acid value reaches <NUM> KOH/g, tin(II) chloride (<NUM>) is added, and heating continues until the acid value of the product is less than <NUM> KOH/g. The measured hydroxyl number is <NUM> KOH/g. Additional <NUM>,<NUM>-butanediol (<NUM>) is added, and the mixture is digested at <NUM> for <NUM>. Hydroxyl value: <NUM> KOH/g. Acid value: <NUM> KOH/g.

Control formulations are prepared by mixing the appropriate amount (see Table <NUM>) of epoxy resin (EPON® <NUM> resin, product of Hexion, or EPALLOY® <NUM>, product of CVC Thermoset Specialties) with boron trifluoride-ethylamine complex (BF<NUM>-MEA) in a glass jar. The BF<NUM>-MEA is added to the epoxy resin, and the mixture is heated to <NUM> to <NUM> with occasional stirring with a metal spatula. When the mixture becomes homogeneous, it is allowed to cool to room temperature and is then used for lap shear and mechanical testing.

<NUM> PEEP formulations are prepared by mixing in a glass jar the appropriate amounts of polyol and BF<NUM>-MEA needed to achieve a targeted index (see Tables A and <NUM>-<NUM>). The BF<NUM>-MEA is added to the polyol, and the mixture is heated to <NUM> to <NUM>, with occasional stirring with a metal spatula. When the mixture becomes homogeneous, it is allowed to cool to room temperature. The polyol/catalyst blend is then mixed with the appropriate amount of epoxy resin, and physical/mechanical properties of cured adhesive products made from this mixture are subsequently evaluated.

The procedure of ASTM D-<NUM> is generally followed. Samples of the mixtures described above are applied to a <NUM>" x <NUM>" area of a cold-rolled steel (CRS) coupon (Q-Panel® RS-<NUM>; <NUM>" x <NUM>" x <NUM>", product of Q-Lab Corp. The coupons are wiped with acetone prior to use. For the <NUM> lap shear testing, a hole is drilled into one of the coupons prior to bonding. After the mixture is applied to one of the coupons, the coated portion is sprinkled with <NUM>-mil glass beads to provide even substrate spacing. A second test coupon is placed on top of the first coupon to form a <NUM>-in<NUM> overlap section sandwiching the liquid adhesive. A binder clip is affixed across the overlap area, and excess adhesive is removed. Samples are heated at <NUM>, <NUM>, or <NUM> for curing times of <NUM>, <NUM>, <NUM>, <NUM>, <NUM>, or <NUM> minutes. Three to five samples are produced and tested under identical conditions, and the results are averaged. The samples are allowed to cool to room temperature and are placed in a <NUM>/<NUM>% relative humidity room for <NUM> hour prior to adhesive strength testing. Results of these tests appear in Tables <NUM>-<NUM>, <NUM>, and <NUM>.

Plaques used for mechanical property measurements are produced by pouring about <NUM> of <NUM> PEEP reaction mixture into <NUM>" x <NUM>" x <NUM>" preheated molds (coated with mold release). The <NUM> PEEP systems are heated to <NUM> for <NUM> to <NUM>. to ensure cure. Plaques are removed from the mold while still warm and are allowed to cool to room temperature. The <NUM> PEEP test dogbone samples are prepared using a die punch (<NUM>" x <NUM>"). Due to the brittleness of the epoxy comparative systems and the inherent difficulty to cut samples, a dogbone shaped mold is employed for these samples. This mold is heated to <NUM> for <NUM> to ensure cure. All samples are conditioned at <NUM> and <NUM>% relative humidity for <NUM> prior to physical testing.

Lap shear strength is measured using an Instron universal testing machine (MTS ReNew™ system) and TestWorks® <NUM> software. The binder clip is removed and the non-adhered ends of the metal coupon strips are secured in Instron <NUM> kN metal test grips (model # <NUM>-<NUM>) affixed to the testing apparatus. The assembly is then pulled in the tensile direction at <NUM> in/min until overlap bond failure occurs. The peak stress at failure is measured and averaged for each polymer system.

Peak stress, modulus, and elongation are determined generally in accord with ASTM D412-<NUM>.

Total energy absorbed ("T. ") is calculated by the universal testing machine software (Testworks <NUM>) and obtained by normalizing the area under the stress-strain curve by the surface area of the central test portion (tapered portion) of the dogbone sample. The area under the stress-strain curve is calculated from the product of the total force (pounds) required to produce extension of the sample up to breakage (inches). For each sample, the surface area is <NUM> in. Total energy absorbed is a measurement that allows for comparison of the relative toughness of each sample tested. The units of T. <NUM> (or lb.

Hardness of cured polymer samples is determined using a Type A durometer (Pacific Transducer, Model <NUM>) according to ASTM <NUM>-<NUM>. The dogbone samples described earlier are used.

Mechanical properties and hardness measurements are performed at <NUM> ± <NUM> and <NUM>% relative humidity.

Glass-transition temperatures (Tg) are determined using a TA Instruments Discovery Series differential scanning calorimeter and Trios (V3. <NUM>) software from TA Instruments. Samples are prepared by trimming a <NUM>-<NUM> piece from the cast adhesive plaques. The sample is accurately weighed, crimped in the test pan, and placed in the sample holder of the instrument along with a reference pan. The sample is cooled to - <NUM> and then warmed from -<NUM> to <NUM> at <NUM> per minute. The <NUM> polyester-epoxide polymer samples exhibited a strong Tg signal with a midpoint generally within the range of <NUM> to <NUM>.

All of the tested systems demonstrate cohesive failure, i.e., the adhesive splits, and adhesive residue remains on both metal coupons.

Overall, the results in Tables <NUM>-<NUM>, <NUM>, and <NUM> show that greater concentrations of catalyst, higher index (ratio of epoxy to hydroxyl equivalents), and higher curing temperatures generally promote more rapid development of lap shear adhesive strength, which can be expected. Room temperature lap shear strength of systems based only on EPON® <NUM> and catalyst provide a maximum lap shear strength of about <NUM> psi under optimum conditions. In contrast, the inventive <NUM> PEEP systems based on aromatic polyester polyols reach lap shear strengths of about <NUM> psi, or roughly double that of the EPON® <NUM>-only comparative examples. A similar dramatic improvement is seen in each of Tables <NUM>-<NUM> when comparing epoxies made using only EPALLOY® <NUM> (Comparative Example <NUM>) with a <NUM> PEEP system incorporating EPALLOY® <NUM> (Example <NUM>). There was no way to predict these outcomes in advance of making and testing the samples.

As shown in Table <NUM>, when the lap shear tests are performed at <NUM> instead of room temperature, the results are variable. Overall, adhesive strength of the <NUM> PEEP systems based on aromatic polyester polyols is reduced, which might be expected based on the relatively low Tg values of these <NUM> PEEP compositions (see Table <NUM>).

In addition to the lower Tg values, plaques made from the <NUM> PEEP adhesive systems based on aromatic polyester polyols generally demonstrate higher tensile strength (peak stress), higher elongation, and greater resilience (as evidenced by higher TEA values) when compared with the EPON® <NUM>-only or EPALLOY® <NUM>-only comparative compositions (Table <NUM>).

The results in Table <NUM> demonstrate that the PEEP formulation and curing conditions can be tailored to provide products having a desirably wide range of strength and flexibility properties. For instance, products can be made with high peak stress and stiffness at modest elongation (see Table <NUM>, Examples <NUM>-4D) or at somewhat lower peak stress and stiffness with much higher elongation (Table <NUM>, Examples <NUM> and <NUM>).

Results with aliphatic polyester polyols appear in Tables <NUM> and <NUM>. As shown in Table <NUM>, excellent lap shears develop within <NUM>. at a cure temperature of <NUM> or within <NUM>. at a cure temperature of <NUM>. Curing at <NUM> extends working time, with properties well developed at <NUM>. The cast adhesive results in Table <NUM> suggest that a single aliphatic polyester polyol can deliver different attributes that depend on index and curing conditions. For example, a more flexible product can be made by reducing index or reducing the cure temperature (see Examples 14A, 14B, and <NUM>).

With polyether polyols, higher functionalities provide desirable crosslinking and development of acceptable lap shear properties. Table <NUM> shows faster development of lap shear strength at higher cure temperatures and overall better properties when compared with the epoxy-only systems (Comparative Examples <NUM> and <NUM>). Table <NUM> again underscores the need for adequate hydroxyl functionality. High stiffness can be retained while improving elongation when a polyether polyol is included with the epoxy resin.

Claim 1:
A process for making a one-component (<NUM>) adhesive, the process comprising reacting a mixture which comprises:
(a) a polyepoxide compound having an equivalent weight within the range of <NUM> to <NUM>/eq.;
(b) a composition comprising:
(i) a polyester polyol having a hydroxyl value within the range of <NUM> to <NUM> KOH/g, an average hydroxyl functionality within the range of <NUM> to <NUM>, and an acid number less than <NUM> KOH/g; or
(ii) a polyether polyol having a hydroxyl value within the range of <NUM> to <NUM> KOH/g and an average hydroxyl functionality within the range of <NUM> to <NUM>; or
(iii) a combination of (i) and (ii);
and
(c) a heat-activated Lewis acid catalyst, wherein the heat-activated Lewis acid catalyst is adapted to melt, dissolve, or dissociate to generate a species capable of catalyzing a reaction between an epoxide group of the epoxide compound and a hydroxyl group of the polyol at temperatures greater than <NUM>;
at a temperature within the range of <NUM> to <NUM> for a time effective to cure the adhesive.