MXPA96002321A - Urethane adhesives of cured in humidity quecontienen alfa-butirolact - Google Patents

Abstract

The present invention relates to a method for bonding a first substrate to a second substrate, comprising interposing between the substrates, in the presence of moisture, a moisture curable urethane composition, comprising a urethane resin component comprising polyfunctional isocyanate , the composition has no active hydrogen or a curing agent reactive to the urethane, the composition cures in the presence of moisture at room temperature, the improvement wherein the urethane adhesive composition further contains between about 1 and about 10 parts per hundred parts by weight (phr) of alpha-butyrolactone resin as a humed diffusing agent

Description

ADHESIVES OF URETANQ OF CURED IN HUMIDITY CONTAINING y-BUTI LACTONA The present invention is directed to moisture curing urethane adhesives and, particularly to non-moisture curing uret adhesives containing / -bu i olac tona as a moisture diffusing agent.

BACKGROUND OF THE INVENTION Moisture cure adhesives on the one hand are well known. They are useful as structural adhesives, such as for bonding polymeric foam to wood, glass to metal, and wood to wood, e.g., in the production of I-joists. These co-positions are also useful as sealants and coatings and the term "adhesive" as used herein is intended to include similar wet curing urethane compositions, either as an adhesive or as a sealant or as a coating. Examples of these compositions are found in U.S. Patent Nos. 3,707,521, 3,779,794 4,176,212, the teachings of which are incorporated herein by reference. In a typical bonding process that uses wet curing adhesives on the one hand, a layer of adhesive is applied to a substrate. A thin layer of moisture is applied to the top of the adhesive layer, e.g., by spraying. The agu acts as the curative for the adhesive.

In some cases, a wet-curing adhesive may simply be a functional isocyanate (dual functionality of two or more), be it a monomer, isocyanate short-chain polymer (or oligomer), or monomer / mixture. ol igomer More rarely, however, the wet cure adhesive comprises urethane prepolymers which are short-chain polymers blocked with isocyanate, such as polyesters, polyethers and polyesters / polyesters. The wet curing adhesives of a part n contain an internal crosslinking agent, based on the ag during the crosslinking of the adhesive. However, the adhesive can, and often does, contain a catalyst to move a faster wet cure. The adhesive may be unfilled or may optionally contain filler. The invention is generally directed to the use of -b-thylactone as a moisture diffusing agent in adhesives cured in moisture on the one hand. Because the moisture is applied to a surface of the adhesive, one of the determinants of the curing regime of any moisture curing adhesive is the rate of diffusion of the water towards the adhesive layer. It is found that f-butyrolactone, when mixed at low levels with a moisture-curing urethane adhesive, promotes the diffusion of water to the adhesive layer and thus promotes faster curing.

Summary of the Invention A moisture cured urethane adhesive is added between about 1 and about 10 parts per hundred parts resin (phr) by weight of jf-butyrolactone, preferably no more than about 10 phr, and so more preferred between about 2 and about 3 phr. When a layer of adhesive is applied to a substrate and a layer of moisture applied to the adhesive layer, Y-butyrolactone promotes the diffusion of water to the adhesive layer, thereby reducing the curing time of the adhesive.

Detailed Description of Certain Preferred Modes Hereof, unless otherwise noted, -the percentages are expressed by weight, in parts per hundred resin (phr), relative to the urethane resin. The urethane resin as used herein consists of the total amount of polyisocyanate monomers, polyisocyanate oligomers and polyisocyanate end capped polymers, such as end stop polyethers of plugged polyether polyethers. extreme. To promote moisture cure, it is generally necessary to add at least about 1 phr of -butyrolac tone. Adding more than about 10 phr of jr'-buti rolactone and undesirable because it can result in instability. Generally, no more than about 5 phr are added and better results have been achieved with a-buti rol actona used at about 3 phr.

Moisture cure urethane compositions are based on polyisocyanates. The polyisocyanates that can be used include aromatic, aliphatic and cycloalphaic polyisocyanates and combinations thereof. Exemplary examples are diisocyanates such as phenylene diisocyanate, 2,4-toiuene isocyanate, 2,6-toluene diisocyanate, mixture of 2,4-toluene diisocyanate and 2,6-toluene diisocyanate, Isocyanate of hexa eti-wood, tetramethyl diisocyanate, 1,4-cyclohexane di-cyanate, hexahydrotoluene diisocyanate, 1,5-naphtha-1,3-diisocyanate, diisocyanate, d-1-methoxy-2, 4-phenyl, diisocyanate. of 4,4 '-difeni l-methane, 4,4'-bi nylene diisocyanate, 3, 3' -diioethoxy-4,4'-biphenium diisocyanate, 3,3-dimeti 1-4,4 'diisocyanate -bifeni lo and 3, 3 'diisocyanate -dimeti 1-4,4 diphenyl-methane; triisocyanates such as 4,4 ', 4"-trifeni-imethane tri-isocyanate, polymethylene polyphenylene and 2,4,6-toluene tri-isocyanate, and tetraisocyanates such as 4-tetraisocyanate; , 4 '-dimeti 1-2,2' -5, 5 '-difeni lmetan Toluene diisocyanate, 4,4'-diphenyl-methane diisocyanate (MDI) and polyisocyanate are particularly useful due to their availability and property. polymethylene poi ifeni log Polymethylene polyphenylene cyanate is a product that results from the phosgenation of a condensation product of ani-na-for maldehyde, sometimes called "raw MDI" containing typically between 40 and 60 % by weight of MDI and between 60 and 40% by weight of oligomeric MDI, typically oligomers of 2-5 units.

Although polyisocyanates, such as crude MDI, can be used alone as moisture curing urethane adhesives, it is more common for the adhesive to include builder prepolymers formed by reacting polyisocyanates, such as those described above, with polyols. , including polyol monomers and / or polyhydroxy functional polymers, such as OH-functional ethers, polyesters, polyester / polyols and mixtures thereof. To provide moisture cure the ratio of NCO to OH must be at least greater than 1: 1 and more generally an NC0 / 0H ratio of at least 1.1: 1 is reacted. There is no upper limit on the NC0 / 0H ratio that can be used, because, as noted above, pure polyisocyanate can function as a moisture curing adhesive. However, when a polyisocyanate and functional hydroxyl polymer are reacted to form urethane prepo, the ratio of NC0 / 0H is typically not greater than about 10: 1. An excess of NC0 / 0H means that an adhesive composition contains some polyisocyanate, mole and / or unreacted oligomer. The functional hydroxyl polymers may be straight or branched chain, the degree of rmification being determined by the amount of monomer having a functionality greater than 2 used to form the prepolymers. The polyols used in the invention may vary in molecular weight (average in weight) from about 250 to about 8000.

The polyethers which form urethane prepolymers Othi in the invention can be prepared by the reaction of alkylene oxide with a polyhydric alcohol. The a-kylene oxides which can be used in the preparation of the polyether materials useful in the present invention include ethylene oxide, propylene oxide, isomeric normal butyiene oxides, hexylene oxide, octylene oxide, dodecene oxide, methoxy and other oxides of alkoxy propylene, styrene oxide and xenic acid. The halogenated alkylene oxides can also be used, such as epichlorohydrin, epiiodohydrin, epibro or hydride, 3, 3-dichloropropylene oxide, 3-chloro-1,2-epoxypropane, 3-chloro-1, 2-epoxy butane, 1-chloro-2,3-epoxy butane, 3,4-dichloro-1,2-epoxybutane, 1,4-dichloro-2, 3-epoxybutane, 1-chloro-2,3-epoxybuta and e, e, e-trichloropropyl oxide. Mixtures of any of the above alkylene oxides can also be used. The polyhydric alcohols which can be reacted with the alkylene oxides to prepare the hydroxyl functional polyethers which can be employed in the invention include but are not limited to ethylene glycol, propylene glycol, butomeric butylene glycols, 1,5-pentanediol, , 6-hexanediol, glyceroi trimetiolpropane, 1, 2, 6-hexantriol, pentaeri tri-toi, sorbitol, sucrose-alphamethyl glycoside and mixtures thereof. The polyhydroxy functional alcohols can be driven with polycarboxylic acids (or their anhydrides when applicable) to form hydroxyl-terminated polyesters which are then end capped with optional polyisocyanates to form polyester-based urethane prepolymers useful in the invention. . Examples of these polycarboxylic acids useful for forming polyesters according to the invention include but are not limited to, adipic acid, maleic acid, trimellitic anhydride, phthalic acid, tetrahydrophthalic acid, hexahydrophthoic acid, sebacic acid, terephthalic acid, isophthalic acid, 1,3- and 1,4-cyclohexane-dicarboxylic acids and mixtures of the same. Likewise, the urethane prepolymer can be a polyther / polyether, which has both ester and ether linkages and is endcapped with a polyisocyanate. Or a mixture of polyester, polyether and / or polyester or polyesters can be reacted with polyisocyanate to form the prepolymers of moisture-cured adhesive. The urethane moisture curing adhesive need not contain a catalyst, but may contain up to about 0.1 phr of a catalyst, such as a tertiary amine catalyst or a tin catalyst, e.g., dibutyltin dilaurate. If a catalyst is used, it is typically used at a level of at least 0.005 phr. The use of ^ -buti olactone as a moisture diffusing agent to effect a faster cure may have the advantage of achieving in a particular formulation a similar cure in time with relatively low catalyzed level of cost.

Urethane adhesives that are moisture cured are generally free of solvent and, therefore, do not have substantially volatile components. The -butiro! Actone has a boiling point of 210 ° C and does not evaporate to any significant degree during curing, which usually oc- cur at ambient temperatures up to about 55 ° C. Rather, the -butyrolactone remains in the cured adhesive and served as an asthmatic function. The moisture curing urethane may be unfilled but may contain fillers up to about 50 p. Examples of fillers include silicas, clays, talcs, carbon black, and titanium dioxide. Also, other known additives such as antioxidants and UV absorbers can be added in lower amounts. The invention will now be described in more detail through a specific example.

Example A 100% non-volatile material (RVM) of 1 part, moisture-curing urethane product was formed from Crude MDI (50 per cent by weight), a polypropylene oxide of Pm of 200 (35% by weight) and polyester diol of Pm of 1000 (15% by weight). The NC0 / 0H ratio used was 5.5: 1. The reactants were combined, under stirring, in a glass-lined reactor, calcined at 80 ° C and maintained for three hours. The reaction product was then cooled to 50 ° C and degassed in vacuo. Then dibutyltin dilaurate was added. (0.07% phr). The agitation and vacuum degassing was continued until the mixture reached 30 sec. C; leugo was discharged into clean dry containers. Various levels of -butyrolactone were added to this adhesive. A cure rate was determined by spraying a wet film of 0.00508 millimeters toward a clean piece of glass plate. The glass plate with the applied adhesive was then placed on a normal piece of equine designed exclusively to check the cure of reactive urethane to moisture. The machine is equipped with a slide that moved at a constant speed. The equipment was maintained at a temperature maintained at a constant temperature and humidity (24 + 19C / 50 + 2% RPH). The plate is placed on the slide and a digital timer is started. A fixed stainless steel stylet is directed down to the wet adhesive pallet and as the slide moves, it is dragged through the wet film. As the adhesive cures, the stylet begins to mount on top of the cured adhesive. The transition point from uncured to cured adhesive film is manifested by an arrowhead shaped end tip. The curing time is determined by the ratio of the distance to the end point, to the total length traveled, by the total time elapsed.

Effect of y-butyrolactone (GBL) on Cured Urethane Cure by Moisture of 1 Part, 100% NVM GBL (phr) Curing Regime (min 0.0 140 1.0 95

Claims (4)

CLAIMS:

1. - In a moisture curable urethane adhesive composition comprising a urethane resin component comprising optional polyisocyanate, the composition having neither active nor curative urethane reagent, curing the composition in the presence of humidity at ambient temperatures. the improvement wherein the urethane adhesive composition furthermore ranges from about 1 to about 10 phr in weight of y-butyrolactone as a moisture diffusion bond.

2. An adhesive composition according to claim 1, containing between about 1 and about 5 phr in weight of -butyrolactone.

3. An adhesive composition according to claim 1, containing between about 2 and about 3 phr in weight of) -butyrolactone.

4. A moisture curable urethane additive composition according to claim 1, wherein the urethane adhesive composition is a reaction product of a polyacrylate is cyanate with a hydroxyl-terminated polymer selected from the group consisting of it consists of polyether, polyester / polyester ether and mixtures thereof, the reaction product having an NCO / OH ratio of between about 1. and about 10: 1.