CA2037453A1 - Cellular contact adhesive films with improved bond strength - Google Patents

Abstract

ABSTRACT

An aqueous contact adhesive composition comprising an aqueous adhesive copolymer emulsion, the adhesive composition having a durometer measured on the type A scale by ASTM D2240 of at least 20, and a blowing agent. The aqueous contact adhesive composition is applied as a coaling to a surface of each of two substrates, then foamed, and substantially dried to provide a dry cellular adhesive coating. The adhesive-coated surfaces are then joined. The preferred contact adhesive composition comprises a vinyl acetate/ethylene/-N-methylolacrylamide copolymer emulsion.

Description

203~453 CELLULAR CONTACT ADH SIVE FILMS HAVING IMPROVED BOND STRENGTH

TECHNICAL FIELD
The present 1nventlon relates to aqueous contact adhes1ves and a method for bond1ng two substrates together us1ng such contact adhesives.

BACKGROUND OF THE INVENTION
Contact adhes1ves d1ffer from other adhesives, such as pressure sensltlve adhes1ves, in that the adhes1ves are applied to both substrates to be ~o1ned and then dr1ed. These adhes1ves are characterized by a bonding range or open t1me , i.e., the per10d after the adhes~ve 1s dry during wh~ch adhes1ve coated substrates can be successfully ~o1ned and bonded.
; Contact adhes1ves are used to manufacture decorative laminates.
-~ 10 Env1ronmental regulat10ns requ~re a reduct~on ln solvent emissions in the decorat1ve lamlnate ~ndustry. Solvent based neoprene contact adhes1ves, the lndustry standard, are a pr1mary source of these em~sslons. Attempts have been made to reduce solvent volat11es through the use of aqueous : contact adhes1ves. Such aqueous adhes1ves have been only marg1nally ;15 successful. Also, most of the aqueous adhes1ves do not provide the same bond strength as solvent-based systems.
U.S. 3,565,247 d~scloses a pressure sensit1ve adhes1ve tape, the adhes1ve layer of wh1ch 1s a foam.
U.S. 4,415,615 dlscloses a cellular pressure sens1tlve adhesive membrane compr1s1ng 15-85~ vo1ds that does not collapse after being br~efly -compressed. The adhes1ve product is preferably made by the steps of ;(l) froth1ng a composit10n wh1ch is polymerizable to a pressure ;sens1t1ve adhes1ve state, (2) coat1ng the froth onto a back1ng, and (3) polymerizing the coated froth in-situ to a pressure sens1tive adhes~ve state.
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~037~53 GB 2 135 903 discloses a foamed pressure sensitive adhesive layer having a stable foam structure prepared by mixing a gas comprising oxygen with an aqueous dispers~on comprising an unsaturated polyester a pressure sensitive adhesive component and an accelerator comprising an organic compound effective for oxidative curing of the polyester. The formulations are preferably frothed with air.
U.S. 4 561 918 discloses foaming a v~nyl acetate-ethylene copolymer based adhesive to extend the adhesive and thereafter applying it to the tips of the medium flutes subsequent to the corrugation of the medium. A liner is then applied to the glued medium to produce a single faced corrugated product.
U.S. 4 713 263 discloses a foamable storage-stable flocking adhesive prepared from an aqueous emulsion of a vinyl acetate/ethylenelN-methylol i comonomer copolymer.
: 15 SUMMARY OF THE INVENTION
The present invention provides a water-based contact adhesive composition which demonstrates improved bond strength and comprises an aqueous medium containing an adhesive component preferably having a 20 durometer measured on the type A scale by ASTM D2240 of at least 20 and a :~ blowing agent. The durometer value is determined from a dry film of the unfoamed adhesive component which comprises an emulsion polymer and all other add~tives of the contact adhesive excludlng the blowing agent.
Another embodiment of the inventlon provides a method for laminating 25 two substrates which comprises applying a coating of the water-based contact adhes~ve to a surface of each of the substrates foaming the aqueous adhesive coatings drying the foamed coatings to provide dry cellular adhesive coatings and joining the adhesive-coated surfaces of the substrates preferably under application of pressure.
The invention allows the formulation of aqueous contact adhesives having bond strength superior to that obtained with such aqueous adhesives not having a cellular structure. It also allows aqueous contact adhesives to more closely approach the performance characteristics of solvent-based contact adhesives.

203745i3 In one parttcular embodiment of the invention the contact adhesive comprises an aqueous vinyl acetate/ethylene/N-methylolacrylamide (VAE/NMA) copolymer emulsion with or without a blowing agent. The use of such emulsions as contact adhesives affords unexpectedly superior bond strength in the resulting laminated substrates.
The most preferred contact adhesive composition comprises a VAE/NMA
copolymer emulslon a blowing agent colloidal silica and an acid catalyst.
These contact adhesives provide bonds demonstrating improved high temperature resistance.
,`' 10 DETAILED ~ESCRIPTION OF THE INVENTION
- The water-based contact adhesive compositlQns comprise an aqueous medium containing 30 to 80 wtX adhes~ve component preferably having a durometer greater than about 20 desirably greater than about 30. Any of a number of adhesive polymer emulsions well known in the art and based upon for example vlnyl acetate-ethylene acrylic styrene-acrylic styrene-butadlene or neoprene polymers may be used in the adhesive component - of the cellular adhesive coating.
The preferred aqueous adhesive copolymer emulsion for use in the foamable contact adhesive compos~t~on is a vinyl acetate-ethylene (VAE) copolymer emulsion containing 40 to 65 wt% solids. The copolymer would comprise vinyl acetate 5 to 40 wt~ preferably 15 to 30 wt% ethylene and 0 to 10 wtX other copolymerizable monomers. Des~rable contact adhesive compositions containing such VAE emulsions also contain up to 30 wt%
plasticizer and may also contain 0-20 wtX phenolic or polyester thermosetting resin. Such VAE emulsions and contact adhesive compositions are disclosed in Application Ser. No. 07/382 828 filed 19 July 1989 which is ; hereby incorporated by reference.
- ~ An especially preferred VAE copolymer emulsion is one in which the copolymer contains about 1-7 wtX copolymerized N-methylolacrylamide (NMA).
Methods to prepare VAE/NMA copolymer emulsions are well known and U.S.
Patents 4 713 263 and 3 370 680 may be cited as illustrative. VAE/NMA
~ copolymers having Tg s ranging from -30 to 30C preferably -16 to +5C may - be used. Foamed VAE/NMA contact adhesives are superior in strength to . , , ` .

2037~5:~

conventional aqueous neoprene adhesives. The most preferred foamable, aqueous contact adhesive comprlses an adhes~ve component of a VAEtNMA
copolymer emulsion, and 0-20 wt% plasticizer, 0.1-30 wtX colloidal silica, and 0-5 wtX acid catalyst, based on copolymer.
Most surpris~ngly, nonfoamable VAEINMA contact adhesives (no blowing agent) yield greater bond strengths than comparable VAE s not containing NMA. Such nonfoamable aqueous contact adhesives would comprise VAE/NMA
copolymer emulsion, and 0-20 wtX plasticizer and 0-5 wt% acid catalyst, based on copolymer.
As suitable plasticizers there may be used materials wh~ch a worker in the art may know as belng a tackifier or a softening agent so long as it is the functional equivalent of a plastic~zer for the purpose of this invention.
Suitable plastlcizers are of the usual type and well known to those in the art, namely, substantially non-violatile solvents for the polymer and lS compatible therewith in the emulsion system. Examples of such plasticizersinclude dibutyl phthalate, ethyl butyl phthalate, butyl benzyl phthalate, aryl sulfonamides such as N-ethyl o and p-toluenesulfonamide. polymeric ester plast1cizers, polyglycol ethers of phenols, such as nonylphenoxy poly(ethyleneoxy) ethanols and the like. Preferred amounts of plasticizer in the composition are 0-lO wt%.
Fillers of known utility such as clay, calcium carbonate, mica, feldspar, and the like are suitable.
Since acid catalysts accelerate the crosslinking of NMA, a suitable catalyst such as ammonium chlor~de, ammon~um sulfamate, citric acid or 2s salicylic acid should be used. In fact, almost any acid soluble in the aqueous or plasticizer phase may be used. Preferred amounts of acid catalyst in the composition are 0.5-2 wtX.
The cellular structure may be obtained by mechanically frothing the aqueous adhesive composition prior to coating, in which case the blowing agent is air, addition of a physical blowing agent such as, for example, a halocarbon or a hydrocarbon, or addition of a chemical blowing agent such as, for example, sulfonyl hydrazide. These blowing agents may be actlvated by evaporation at room temperature as ~n the case for the halocarbon or .

X03~453 through thermal decomposition. For the purposes of this invention both the evaporation of the physical blowing agent and the thermal decomposition of the chemtcal blowing agent are considered as thermal activatlon.
The amount of blowing agent may be 1-30 wt% based on dry adhesive component preferably 3-20 wtX. Illustrative of suitable chemical blowing agents would be the following thermally activated materials: sulfonyl hydrazides diazoaminobenzene azobis(isobutyronitrile) dinitroso pentamethylene tetramine azodicarbonamide sulfonyl semicarbazides inorganic carbonates and inorganic b~carbonates. Also room temperature activated blowing agents may involve the reaction of an acid on inorganic carbonate or bicarbonate or the catalytic decomposition of hydrogen peroxide or its reaction with a reducing agent. Suitable physical blowing agents would include pentane trichlorofluoromethane trichlorotrifluoroethane and l~ke materials having a heat of vaporization of <300 Joules/g a swell index of <500X in the polymer and a botling point of <50C.
The foamable contact adhesive compositions accordlng to the invention may also contain other components like silica foam nucleators and stabilizers such as surfactants and thickeners.
The addition of colloidal silica to VAE~NMA emulsions in amounts ranging from 0.1 to 15 wtX (solids) provides a foamable aqueous contact adhesive having surpris~ngly improved high temperature reslstance ~; particularly in the presence of acid catalyst. Suitable silica would be any free non-aggregated particles having a smaller partlcle s~ze than fumed silica or silica formed by other processes such as colloidal silica marketed by DuPont under the trademark LUDOX AM.
The foamable contact adhesive composition can be applied to any substrate surface and will firmly bond such materials as leather wood metals particle board Formica and Wilsonart brand plastic laminates fabrics unglazed ceramics wallboards and carpet to themselves and to each other.
A coat~ng of the aqueous contact adhesive is applied to a surface of each of the substrates to be joined. The aqueous adhesive coat~ngs are ; foamed by thermal activation of the blowing agent or the aqueous adhesive compostt~on is foamed as lt ls applled uslng a foaming applicator as is well known in the art. The foamed coat~ngs are then dried to provide dry cellular coat~ngs and the adhesive-coated surfaces of the substrates are ~o~ned together, preferably under pressure.
The VAE/NMA-containlng contact adheslves can be used on the above lam~natlng process without the need of the foaming step.
In the followlng examples, the cellular contact adheslves were tested ln a hlgh pressure lamlnate (HPL) to partlcle board constructlon. Coat welghts glven ln the Table are dry weight of adhesive per slde. Laminatlon temperature refers to the temperature at which the two coated surfaces were mated. The peel test was performed across a bond length of 3 inches at a crosshead speed of 2 lnch/mln. The dlsc adhesion test was performed by cuttlng a 2.25 inch (4 in2) dlsc through the HPL without damaglng the partlcle board and bondlng a steel dlsc to the surface of the HPL wlth epoxy. The HPL cutout is pulled ln a tensile mode at 2 inch/min.

EXAMPLE l In thls example, Alrflex 465 vinyl acetate-ethylene copolymer emulslon was m~xed wlth 4.8 parts by welght ammsnlum b~carbonate, based on the wet emulslon. Thls adheslve composltlon was applled to HPL and partlcle board surfaces with a palnt roller at 4g/ftZ dry and then drled for 2 mlnutes at 300F. The drylng at elevated temperature caused the adheslve composltlon to foam and, upon drylng, yleld a cellular structure. The adheslve coated HPL and partlcle board surfaces were then lam~nated w~th a 30 pound roller.
Table l Lamination Peel Temp Edae Peel (~ounds) Temp (F) (F) A-465*A-465 with 4.8 ~arts NH4HC03_ 30 70o 70 3 28 300 l80 21 30 * Alrflex 465 VAE copolymer emulslon (66% sollds) avallable from Air Products and Chemlcals, Inc.

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It can be seen from the data ~n Table 1 that laminates prepared us~ng the Airflex 465 copolymer emuls~on contain~ng the ammonium b~carbonate blow~ng `:agent provided surprisingly superior edge peel compared to laminates prepared using solely Airflex 465 copolymer emuls~on.

In th~s example the base aqueous contact adhesive formulation used comprised 98 parts by weight Alrflex 465 emulsion one part Benzoflex 988 plasticizer and one part by weight Igepal C0 887 surfactant (plast~c~zer).
;10 The base formulation was compared to the same formulation containing 4.8 parts by weight ammon~um b~carbonate blow~ng agent. Laminates were prepared by -:-applying the adhesive compositions with an air spray gun to part~cle board and HPL at 49/ft2 dry. The substrates were then dried for 2 m~nutes at 300F
and laminated with a 30 pound roller at 300F.
.. ,~ 15 Table 2 : Viscosity Peel Temp Edge Peel (pounds) (cDs) (F) w/o Blowing Agentw/4.8 parts NH4~Q3_ :
Again it can be seen that the addition of ammonium bicarbonate as a ;chem~cal blowing agent to the base adhesive compos~tion resulted ~n a marked ~mprovement ln the edge peel values. The adhes~ve composit~ons havtng a viscosity of 1300 cps were achieved through the addition of a thickener.

~-The same base aqueous adhesive composition used in Example 2 was used with and without ammonium bicarbonate blowing agent to prepare partlcle board laminates which were tested for edge peel strength and water resistance by a 24 hour water soak. The lam~nates were prepared by the same procedure of Example 2.

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'-: , : -` 2037~53 Table 3 :` Edge Peel (pounds) 24 HR Water Soak Peel Temp w/4.8 parts w/4.8 parts (F) w/o Blowlna Aaent NH4~ÇQ3_ w/o Blowing Agent NH4HC03_ 70 40 55 poor-fair bond fair-good severe edge lift bond very sllght edge l~ft : Not only did the adhesive compos~t~on conta~ning the blowing agent prov~de ~mproved edge peel strength at both peel temperatures ~t also provided a laminate that demonstrated ~mproved water res~stance.

In this example the same base contact adhesive formulation of Example 2 with and without ammonium bicarbonate blowing agent was used to prepare commercial countertops for evaluation on a Midwest Automat~on post-form~ng 2Q un~t under condit~ons standard ~n the industry. The base contact adhes~vecomposition without the blowing agent was appl~ed at greater than 5g/ft whereas the adhesive composit~on conta~ning the blowing agent was applied in an amount of 4g/ft2.
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Table 4 2 D~sc Adhesion . lbs (% Fiber Tear) Ct. Wt (a/ft ) Front Middle Back w/o Blowing Agent >5 205~0) 85~0) 245~0) w/4.8 parts NH4HC03 4 570~100) 180(5) 345(10 It can be seen from the data in Table 4 that the use of a thermally activated blowing agent to provide a contact adheslve composit~on having a ~ 20;~53 g cellular structure resulted ln the laminate havtng dramatically lmproved adhesion properttes as demonstrated by the disk adhesion test on samples from the front middle and back of the laminate.
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- In this example an aqueous contact adhesive composition based on Airflex 129 emulsion was compared in a commerclal countertop trial using a Mldwest Automatlon post-forming unit with a solvent-based neoprene adhesive. The following aqueous-based adheslve composit~on conta~ning a blow~ng agent was ` prepared:
... ' A-129a 1009 - Benzoflex 988 lOg . NH4HC03 b 4.8g Vlscalex AT66 0.17g a Airflex 129 VAE/(4.8%)NMA copolymer emulsion (52X sollds) avallable from Air Products and Chemicals Inc. Tg -16C
b Thlckener avallable from Allied Collo~ds Inc.
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~ble 5 Ct. Wt. D~sc Adhes~on . pounds (X Flber Tear) Adhesive(g/ft2) Front Mlddle Back Backsplash - Aqueous 2.0 450(40) 240(5) 520(15) 450(20) 2.0 450(30) 150(5) 290(5) 270(5) ~ 2.0 480(80) 270(10) 350(10) 360(10) ,: , ; Solvent 1.5 340(5) 370(10) 450(20) 270(5) Neoprene 1.5 410(10) 380(5) 280(5) 420(10) The data in Table 5 shows that the aqueous A~rflex 129 contact adhesive compositlon upon foam~ng and subsequent drying provided laminates that were substantlally equivalent ln performance in the disk adhesion test to laminates prepared using the ~ndustry standard solvent-based neoprene contact adhesive.

X03~7453 In this example Composit~ons 1 and 2 as shown Table 6 were prepared using Freon 11 (tr~chlorofiuoromethane) as the blowing agent and evaluated in an HPL
to particle board lam~nate prepared according to the procedure in Example 1.
Compositions 3 and 4 were the same as 1 and 2 respectively but without a blowing agent. The adheslve was dried one hour at room temperature and laminated at room temperature.
Table 6 ComD 1 2 3 4 Benzoflex 988 10 10 10 10 - 15 KCS Clay 10 10 10 10 Freon 11 10 10 --- ---70F Edge Peel (lbs) 36 38 9 14 Compositions 1 and 2 which contained the Freon 11 blowing agent to - provide a cellular adhesive structure upon drying gave vastly improved edge peel performance compared to the same adhesive compositions which do not generate a cellular structure upon drying.

In this example commercially available aqueous neoprene contact adhesives Fastbond 30 and Swift 45656 were evaluated with Freon 11 blowing agent under conditions described in Example 6.

;~)37453 . - 11 -Table 7 - Edge Peel (lb) Fastbond 30 40 Fastbond 30 58 . ~ lO parts Freon ll Sw1ft 45656 40 Sw~ft 45656 62 ~ + lO parts Freon ll ., 10 The add1tion of a blowing agent to the aqueous neoprene contact adhesives : provlde a lam~nate of HPL and part~cle board demonstrat7ng surpris~ngly ~mproved peel strength.

~ Two VAE/NMA copolymer emuls~ons (Alrflex 129 and A~rflex lO9) were : blended wlth a plastlclzer and a~monlum blcarbonate blow~ng agent to provlde ; foamable contact adheslves and compared to solvent-based and water-based neoprene contact adheslves ln hot lamlnat~on. The lam~nate samples were roll coated at 4 g/ft2 dr~ed as shown ~n Table 8 and lamlnated hot dlrectly out of the oven at the temperature lndlcated us~ng a 30 lb roller. The samples were cooled pr~or to testing.
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Z03~S3 Table 8 Drying Edge Peel Disc Adh Adhesive (wet parts~ Conditions (lb) (lb~ Durometer Airflex 129(100) 2 min 302F 98 590 25 Benzoflex 988 (10) 4 m~n 176F 86 NH4HC03 (4.8) .~ A~rflex 109(100) 2 m~n 302F 98 610 - Plasthall BSA (3) 4 min 176F 87 Aquatac 6085(5) NH4HC03 (4.8) Aqueous-based Neoprene 2 m~n 302F 75 310 47 - 4 min 176F 69 Solvent-base Neoprene 2 m~n 302F 62 480 4 min 176F 40 :.
The lam~nates made using the two foamed VAE/NMA-containing contact adheslves demonstrated s1gnificantly superior edge peel strength and disc adhes~on compared to the two neoprene contact adhes~ves.

- EXAMP~E 9 Thls example demonstrates the unexpected ~mprovement ~n high temperature resistance of the laminate prov~ded by the addition of s~lica to a foamable aqueous VAE/NMA contact adhesive. The two aqueous contact adhesive - formulattves contained Freon 113 (trichlorotr~fluoroethane) as the blowing agent. The laminate samples were brush coated at 4g/ft dried one hour at 70F and then laminated at 70F using a 30 lb roller.
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. -' ~ ~03 ~'453 Table 9 . A B
Airflex lO9a 100 100 Plasthall BSA 10 10 --` Igepal C0630 2 0.5 Igepal C0987 2 ---ASP 400 Clay --- 5 Ludox AM Silicab --- 25 Freon 113 8 8 NH4Cl ___ 0.5 :

a VAE/(4.8X)NMA copolymer emulsion available from Air Products and Chemicals Inc. 52% solids Tg 5 0C
b Colloidal silica from DuPont.

:, Dlsc Shear Failure Peel Failure Adhesion Edge PeelTemperature F TemDerature F
Adhesive (lbs) (lbs) Initial 1 week Initial1 we~

8 - 66 >302 >302 257 >284 25Aqueous 230 43 >302 >302 228 257 Neoprene Table 9 shows that the sheer failure temperature and peel failure temperature for the laminate using the silica-containing contact adhesive 8 were greatly lmproved over adhesive A and comparable to aqueous neoprene adhes~ve.

Z0~7453 EXAMPLE lO
This example demonstrates that the incorporation of NMA as a comonomer lnto ~n a VAE copolymer provides a foamable aqueous contact adhesive composition hav~ng vastly improved edge peel. The two contact adhes~ve compositions A and B contained ammon~um bicarbonate as the blowing agent. The laminates were prepared by coating the HPL and the particle board with a paint brush. The adheslve coat~ngs were foamed and dried us~ng a hot a~r gun and cooled to room temperature. ~he substrates were then laminated us~ng a 30 lb roller.

Table lO

Adhesive Aa Ba 15 Airflex 465 89 __ Airflex lZ9 -- 9l Benzoflex 988 lO 9 Igepal C0 887 l --NH4HC03 4.8 4.8 a wet we~ghts Coating Wt. 70F Edge Peel Adhesive (dry g/ft2) ~lb.) A 2.l l3 2.5 lO
3.l 20 4.0 38 B 2.1 28 - 2.6 30 3.0 46 4.1 56 `:
' It can be seen from the data in Table lO that the VAE/NMA copolymer emulsion-containlng contact adhesive B provided lam~nates w~th surprisingly superior edge peel strength compared to lam~nates made w~th contact adhesive A
at approximately equal coat weights.

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;~037453 ; -- 15 -EXA~PLE 11 This example also demonstrates the surprising improvement in high temperature res~stance of a laminate resulting from the addition of colloidal silica to an acld catalyzed foamable aqueous VAE/NMA contact adhesive. The compositions of adhesives A-F are shown ~n Table 11 in parts by weight wet.
The HPL to particle board laminate samples were brush coated at 4g/ft dried for one hour at 70F and then lam~nated at 70F. The edge peel failure test was performed across a 3 inch wide laminate starting at 68F and rising 18F/10 min. The shear test was performed at 302F on a one square inch sample with a 1 kg weight.
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Table ll Adhesive A B C D E F
Airflex 109 100 100 100 100 Airflex 465 - - - - 100 100 Colloidal Sillca - - 25 25 - 25 Plasticlzer 10 10 10 10 10 10 Salicyl~c Acid - 0.5 - 0.5 Freon 113 10 10 10 10 10 10 Peel Failure Temperature (F) 273 293 290 >392 270 243 Shear Resistance At 302F (hrs) 0.1 0.1 >22 >22 .
Durometer - 30 65 64 35 Including colloidal silica in a plasticized foamable aqueous VAE/NMA
adhesive containing acid catalyst (Adhesive D) resulted in a marked increase in peel failure temperature and high temperature shear resistance. The addition of colloidal silica without an acid catalyst (Adhesive C) although still giving improved high temperature shear resistance relative to adhesives without collo~dal s~lica (Adhesives A and B), did not show the superior peel fa~lure temperature performance of Adhesive D. Adding colloidal silica to a plasticized aqueous VAE adhesive did not afford such improvements, and ~n fact, the peel fa~lure temperature decreased.

This example shows that a VAEtMNA copolymer emulsion can be used as a unfoamed aqueous contact adhesive to prepare lam~nates having surpr~stngly good bond strength.
A~rflex 129 VAE/NMA emuls~on and Airflex 465 VAE emulsion, both neat and plastic~zed, were roll coated onto HPL and part~cle board at 49/ft2 dry weight. The substrates were dr~ed for 2 min. at 302F and joined together at the ~ndicated temperature.

Table 12 Lam~nated Lam~nated 302F _ At 70F
Adhes~ve 70F Peel 180F Peel 24 hrs. Soak 70F Peel Airflex 129 52 24 - 30 ad~. to 1300 cps Airflex 465 39 22 - 5 1450 cps A~rflex 129 (loo)a72,70 19,19 no edge lift 40,41 Benzoflex 988 (10) excellent bond Airflex 129 (100)67,63 20,19 - 32,40 BenzofleX 988 (5) Airflex 465 (983 41,46 21,19 severe edge 4,9 Benzoflex 988 (10) lift, poor bond Igepal C0 887 (1) a part by we~ght, wet 0;~7453 - 17 _ `:
Both the plasticized and unplasticized nonfoamable aqueous VAE/NMA
adhesives compared to their VAE counterparts showed improved 70F peel while the 180F peels were comparable for laminates made at 302F. The plasticized VAE/NMA adhesive provided a 302F laminate showing excellent water resistance compared to the VAE version. For laminates made at 70F the VAE/NMA
containing adhesives were vastly superior in 70F peel.
- The present invent~on allows the formulation of aqueous contact adhesives with improved bond strength. This is achieved by taking advantage of higher modulus polymers which normally do not form a good contact bond due to the~r poor flow characteristics and foaming the aqueous emulsions of the polymers.
The cellular structure makes even a h~gh modulus adhesive film more deformable and enhances the formatlon of a contact bond.
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STATEMENT OF INDUSTRIAL APPLICATION
The present invention prov~des improved aqueous-based contact adhesive compositions and a method for making laminates having improved bond strength.

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Claims (20)

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. In an aqueous contact adhesive composition comprising an aqueous polymer emulsion the improvement which comprises an adhesive component which has a durometer measured on the type A scale by ASTM D 2240 of at least 20, and 1-30 wt% (based on dry adhesive component) blowing agent.

2. The adhesive composition of Claim 1 in which the polymer is a vinyl acetate-ethylene, acrylic, styrene-acrylic, styrene-butadiene or neoprene polymer.

3. The adhesive composition of Claim 1 in which the polymer is a vinyl acetate-ethylene copolymer.

4. The adhesive composition of Claim 1 in which the adhesive component has a durometer of at least 30.

5. The adhesive composition of Claim 1 in which the blowing agent is ammonium bicarbonate, trichlorofluoromethane or trichlorotrifluoroethane.

6. The adhesive composition of Claim 3 which also contains up to 30 wt%
plasticizer.

7. In an aqueous contact adhesive composition comprising an aqueous polymer emulsion the improvement which comprises an adhesive component comprising a vinyl acetate-ethylene copolymer which is 5 to 40 wt% ethylene and 0-10 wt% other copolymerizable monomers and having a durometer measured on the type A scale by ASTM D2240 of at least 20 and 1-30 wt%, based on dry adhesive component, blowing agent.

8. The adhesive composition of Claim 7 in which the blowing agent is a material having a heat of vaporization of <300 Joules/g, a swell index of <500% in the polymer and a boiling point of <50°C.

9. The adhesive composition of Claim 7 in which the copolymer contains 1-7 wt% N-methylolacrylamide and has a Tg of -30 to +30°C.

10. The adhesive composition of Claim 9 which also contains 0-20 wt%
plasticizer and 0-5 wt% acid catalyst.

11. The adhesive composition of Claim 7 in which the blowing agent is trichlorofluoromethane or trichlorofluoroethane.

12. The adhesive composition of Claim 7 in which the blowing agent is ammonium bicarbonate.

13. The adhesive composition of Claim 10 in which the blowing agent is trichlorofluoromethane or trichlorofluoroethane.

14. The adhesive composition of Claim 10 in which the blowing agent is ammonium bicarbonate.

15. In a method for laminating two substrates using an aqueous-based copolymer contact adhesive composition the improvement which comprises applying a coating of the contact adhesive composition of Claim 1 to a surface of each of the substrates, foaming the adhesive composition, drying the foamedcoating to provide a dry cellular adhesive coating and joining the adhesive-coated surfaces of the substrates.

16. In a method of laminating two substrates using an aqueous-based copolymer contact adhesive composition, the improvement which comprises applying a coating of the contact adhesive composition of Claim 2 to a surface of each of the substrates, foaming the adhesive composition, drying the foamed coating to provide a dry cellular adhesive coating and joining the adhesive-coated surfaces of the substrates.

17. In a method of laminating two substrates using an aqueous-based copolymer contact adhesive composition, the improvement which comprises applying a coating of the contact adhesive composition of Claim 5 to a surface of each of the substrates, foaming the adhesive composition, drying the foamedcoating to provide a dry cellular adhesive coating and joining the adhesive-coated surfaces of the substrates.

18. In a method of laminating two substrates using an aqueous-based copolymer contact adhesive composition, the improvement which comprises applying a coating of the contact adhesive composition of Claim 7 to a surface of each of the substrates, foaming the adhesive composition, drying the foamed coating to provide a dry cellular adhesive coating and joining the adhesive-coated surfaces of the substrates.

19. In a method of laminating two substrates using an aqueous-based copolymer contact adhesive composition, the improvement which comprises applying a coating of the contact adhesive composition of Claim 13 to a surface of each of the substrates, foaming the adhesive composition, drying the foamed coating to provide a dry cellular adhesive coating and joining the adhesive-coated surfaces of the substrates.

20. In a method of laminating two substrates using an aqueous-based copolymer contact adhesive composition, the improvement which comprises applying a coating of the contact adhesive composition of Claim 14 to a surface of each of the substrates, foaming the adhesive composition, drying the foamed coating to provide a dry cellular adhesive coating and joining the adhesive-coated surfaces of the substrates.