CA1083281A - Aqueous compositions comprising phenolic resin and crosslinking agent - Google Patents

Abstract

AQUEOUS COMPOSITIONS COMPRISING
PHENOLIC RESIN AND CROSSLINKING AGENT

Abstract Storage-stable, heat-reactive aqueous. compositions prising at least one novolak phenolic resin, at least one formaldehyde polymer, and water, wherein said formaldehyde polymer is present in an amount sufficient to crosslink said novolak resin, are useful for direct bonding of natural and synthetic resins to rigid and non-rigid substrates and as primers for rubber-to-metal adhesives. The herein-described aqueous adhesive systems can have incorporated therein con-ventional additives such as fillers and the like.

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Description

This invention relates to aqueous resinous compositions.
More particularly, the invention relates to storage-stable, heat-reactive phenolic compositions suitable for use as an adhesive or pximer in bonding natural and synthetic elastomers to rigid and non-rigid substrates.
The use of adhesive systems for bonding natural and synthetic elastomers to the same or different elastomers, as well as to non-rigid and other rigid substrates, including metals, natural and synthetic organic and inorganic fibers, and the like is well-known. To meet the operational requirements imposed by commercial considerations in bonding elastomers to rigid and non-rigid substrates, there have been developed any number of adhesive formulations which have enjoyed some measure of commercial success with no single formulation being the panacea which provides opti-mum resu~ts in all bonding applications.
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the general case. adhesives for bonding elaistomeric materials to rigid substrates are organic solvent-based, i. e., the adhesive ingredients, including film-forming adjuncts, are dissolved in or dispersed into organic l;solvents. Solvent-baised adhesives are employed to a lesser extent for bonding 5 j el~stomeric materials to non-rigid substrates, particularly synthetic fiber substrates. Although generally exemplary for bonding with respect to elasto-, meric materials, solvent-based adhesive systems do have several drawbacks.
' One of the more serious drawbacks is the high cost of the solvent systems, , which quite often cannot be reclaimed without prohibitively costly recovery 10 1' systems. The increasing scarcity of petroleum from which the solvents are ¦~ derived, and the apparent continued escalation in cost of petroleum stocks promises even higher costs for solvent-based adhesive systems. A further ¦~ drawback with sol~Tent-based adhesives is the plethora of federal, state, and local legislation in the areas of environmental safety, occupational safety and ,, j, , ' 15 1I consumer product safety. While the latter two areas apply to adhesive systems 1~ generally, the field of environmental protection regulations are directed ; primarily to sol~ent-based adhesives since they are concerned with re- j ,;
strlctions on the type and quantity of emissions to the atmosphere. 1, Il Q!lite obviously, water-based adhesive compositians, i. e., the ad-20 hesive ingredients are soluble in or dispersed into water, appear less '' susceptible to conflict with environmental protection regulations than solvent-'; based systems. Water-based adhesive systems are known, but their use has . been principally in applications wherein at least one substrate is porous or can absorb water, and which are not so hydrophobic as to interfere with or 25 1 inhibit coalescence of the adhesive film former. Because of ~he economic and ernrironmental ~vantages which are promised ~y water-borne systems,

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there is bein~ expended a significant effort by the adhesive industry to develop water-based adhesives which can approach the performance of solvent-based adhesives.
Generally, solvent-based adhesive systems which are in most demand by industry in elastomer-bonding applications are characterized by an extended shelf-stability, i.e. they can be stored for indefinite periods without undue gelation or loss of adhesive capabillty; have good layover stability, i.e.
parts can be coated with wet adhesive, dried and stored for indefinite periods without substantial loss of adhesion proper-ties; and the adhesive is heat-reactive, i.e. the active adhesive mzterials remain substantially inert until the bonded assembly is brought to the temperature at which bonding is to be effected.
Adhesive compositions meeting these criteria and which also afford an adhesive bond which is resistant to adverse environmental conditions are especially advantageous.
While water-based adhesive systems have been proposed which can provide adequate adhesion, such systems are generally deficient with respect to stability. For example, even the best of the known water-based systems must be used within about two weeks after being prepared before gelation and/or less of adhe-sive capability occurs. There remains a need for water-based adhesive compositions which are stable for extended periods of time, retain their strength during storage, and otherwise exhibit ` adhesive characteristics comparable to commercial solvent-based adhesive systems.
In accordance with the present invention, there are ; provided storage-stable, heat-reactive, water-based adhesive compositions comprising at least one phenolic resin, an effective ~ 30 amount of at least one methylene-donor crosslinking agent and - water.

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Solvent-based adhesive systems comprising at least one heat-reactive phenolic resole resin have been employed for bond-ing elastomers to metal substrates, and as primers for elastomer adhesives. Resole resins can be emulsified in water to afford aqueous adhesive systems havinggood adhesion; unfortunately, the stability of such thermosetting resoles in water is limited to a few weeks at ambient temperatures. There have been proposed aqeuous adhesive systems comprising phenolic novolak resins and common curatives such as hexamethylenetetramine and formaldehyde.
Such novolak systems afford results which are quite promising with respect to one or more of adhesion, environmental resistance, and stability; unfortunately, they are generally deficient with respect to at least one of these parameters and thus are con-sidered unsatisfactory for commercial use. In contrast to such known adhesive systems, the water-based adhesive compositions of this invention have an indefinite shelf-stability at ambient temperatures and cure at elevated temperatures, i.e. they are heat-reactive, to afford adhesive bonds comparable to solvent-based adhesive systems with respect to adhesion and environmental resistance. In addition, the compositions have highly desirable film properties, are resistant to sweep and flow and can be used as a single-coat adhesive or a primer (in combination with a cover-coat elastomer adhesive) for bonding vulcanizable natural and synthetic rubbers to rigid and non-rigid substrates.
The phenolic resins which are suitable for use in the practice of the invention are selected from the group consisting of thermoplastic phenol-aldehyde condensates which are commonly called phenolic novolak resins. Such resins are prepared according to well-known methods by condensing phenolic compounds and aldehydes, usually under acidic to neutral conditions, with the phenolic material being present in the reaction mixture in n)ore than stoichiometric amounts. Also included within the purview of novolak resins are the reaction products obtained by further condensing a formed resole resin with additional phenolic com-pound. For more detailed information regarding novolak resins, including methods of preparation, see Carswell "Phenoplasts", Interscience Publishers, Inc., New York, N.Y., (1947), which treatise is herein incorporated by reference. Suitable novolak resins inciude resinous oils as well as pulverulent solids.
Novolak resins are permanently fusible and are not converted to an infusible, crosslinked state by the application of heat alone.
Novolak resins can be converted to an infusible state by the addition thereto of a crosslinki~g agent such as a methylene donor.
In forming the phenolic novolak resins which are employed in the practice of this invention, there can be utilized a variety of phenolic compounds, i.e. both monohydroxy and poly-hydroxy phenols, including such compounds having at least one aromatic nucleus, and substituted derivatives thereof, and including mixtures of such phenolic compounds. Among the sub-stituent groups which can be attached to the nucleus of the phenolic compound are alkyl, alkoxy, amino, halogen and the like.
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Representative phenolic compounds include, without being limited ~- thereto, phenol, p-t-butylphenol, p-phenylphenol, p-chlorophenol, ~
p-alkoxyphenol, o-cresol, m-cresol, o-chlorophenol, m-bromophenol, ~ ~ -2-ethylphenol, amyl phenol, nonyl phenol, cashew nut shell liquid, resorcinol, orcinol, phloroglucinol, pyrocatechol, pyrogallol, salicylic acid, bis-phenol A, bis-phenol S, and the like, Partic-ularly preferred novolak resins are obtained when the phenolic precursors comprise:
a) 100 mol percent of at least one polyhydroxy phenol such as resorcinol, phloroglucinol, pyrogallol and the like, with ,,: :. . . ,....... .. .: .
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~083281 resorcinol being particularly preferred;
b) from about 50 to about 98, preferably about 60 to about 98, mol percent of at least one polyhydroxy phenol and from about 50 to about 2, preferably about 40 to about 2, mol percent of at least one monohydric phenol, the nucleus of which is not substituted with a hydrocarbon radical, i.e. a radical containing only carbon and hydrogen atoms, although the nucleus can be substituted with groups such as alkoxy, amino, halogen, and the like;
c) from about 10 to about 98, preferably about 50 to about 98 mol percent of at least one polyhydroxy phenol and from about 90 to about 2, preferably about 50 to about 2, mol percent of at least one monohydric phenol, the nucleus of which is sub-stituted with at least one alkyl group having from 1 to 22 car-bon atoms; and d) 100 mol percent of at least one monohydric phenol, the nucleus of which is substituted with at least one alkyl group having from 1 to 22 carbon atoms; said mol percents being based on total mols of phenolic compound. When forming modified novolak ~ 20 resins by reacting a preformed phenolic resol or phenolic novolak - with additional phenolic compound, it is preferred that such : additional phenolic compound be selected from the group consisting of polyhydroxy phenols and monohydroxy phenols, the nucleus of which is substituted with at least one alkyl group having from 1 to 22 carbon atoms.
Representative aldehydes which can be condensed with phenolic compounds to form novolak resins include, without being limited thereto, formaldehyde, acetaldehyde, propionaldehyde, ; isobutyraldehyde, 2-ethylbu~raldehyde, 2-methylpentaldehyde, 2-ethylhexaldehyde, as well as compounds which decompose to formal-dehyde, such as paraformaldehyde, trioxane, furfural, hexamethyl-enetetramine, acetals which liberate formaldehyde on heating benzaldehyde, and the like.

083~Z81 order to make the novolak resins including those suitable for use lin the practice of the invention, infusibte, such resins must be further reacted jjwith a methylene donor or a source of methylene bridges or linkages. Among l,the numerous organic compounds which have been employed as methylene 5 d~nors are formaldehyde; compounds which decompose to formaldehyde such ' as paraformaldehyde, s-trioxane, hexamethylene tetramine, anhydroformalde-ilhydeaniline, ethylene diar~ine formaldehyde; methylol derivatives of urea and formaldehyde; acetaldehyde; furfural: and the .ike. These organic compounds l are considered methylene donors in that they effect rapid crosslinking of heat 10 i'fusible novolak resins with methylene or equivalent linkages by the application ' !of heat. While these materials are effective to crosslink the novolak phenolic ¦ resin adhesive systems of the present in~vention, they are ineffective in other ¦!critical areas s~ch as film properties, stability and the like. Thus it is a , critical feature of the present invention tha~ there be employed certain here -15 !inafter defined high molecular weight aldehyde homopolymers and copolymers as the crosslir~ing agent.
The high molecular weig~ aldehyde homopolymers and copolymers ',which must be employed as crosslinking agents in the practice of the present ¦'invention are selected from the group consisting of acetal homopolymers, 20 jacetal copolymers, andpolyoxymethylene ethers having the characteristic structure 1 _ o ( CH2 )n ~ R2 and H0 ~ R3 0 ~ CH2 )n - (R4 0 ~ H;

~, wherein R1 a~d R2 can be the same or different and each is an alkyl group having from 1 to 8, preferably 1 to 4, carbon atoms; R3 and R4 canbe il i 1i - 7 i.

lp83Z81 ,'the same or different and each is an alkylene group having from 2 to 12, preferably 2 to 8, carbon atoms; n is greater than 100. and is prefer~bly in the range from about 200 to about 2000; and x is in the range from 0 to 8 I preferably 1 to 4, with at least one x being equal to at least 1~ The high 5 ,~ olecular weight aldehyde homopolymers and copolymers are further characterized by a melting point of at least 75 C, i. e., they are substan-tially inert with respeet to the novolak resin until heat activate~; and by being substantially completely insoluble in water at ~ temperature below the melting point. The acetal homopolymers and acetal copolymers are well-known articles 10 ,of commerce (Delrin~9acetal homopolymers, E.l.DuPont de Nemours 8~ Co., Inc., and Celcon~9acetal copolymers, Celanese Corporation). The polyoxy-methylene materials are also well-known and can be readily synthesized by ~he action of monoalcohols having from 1 to 8 carbon aton~.~ or dihydroxy glycols and ether glycols on polyoxymethylene glycols in the presence of an , i .
15 acidic catalyst. A representative method of preparing these crosslinking agents ¦~s described in Londergon U.S. Patent No. 2,512,950. A particularly pre-~ferred crosslinking agent for use in the practice of the invention is 1 ~ -polyoxymethylene dimethyl ether.
¦l In forming the water-based adhesive compositions of the present in-20 'vention, the phenolic novolak resin, curing agent, and water will be combined ,In amounts sufficient to afford a shelf-stable, heat-reactive composition com-pr~sing - i) 100 parts by weight of at least one water-soluble or water-dispersiole ; phenolic novol~k resin;
25 1' il) an effective amount, preferably from about 2 to 60, more pre-` ~ferably from ~bout 5 to about 30, parts by weight per 100 parts by wei~ht of novol~c resln, of crosslilqklng agent; and .

iii) water, in an amount sufficient to afford a dis-persion having a total solids content (TSC) based on novolak resin in the range from about 5 to about 75, preferably about 10 to about 60 percent.
The herein-described compositions are water-dilutable, i.e. the individual ingredients are soluble or dispersible in water alone or with the addition of a minor amount of organic solvents which are largely or completely miscible with water, e.g. mono- and di-alkyl ethers of ethylene glycol or diethylene glycol, ethylene glycol, propylene glycol, isopropylene glycol, n-butylene glycol, diacetone alcohol, ketones such as acetone, methyl ethyl ketone, methyl isobutyl ketone, and the like.
The water-dilutable adhesive systems of the invention can optionally contain other well-known additives including plasticizers, fillers, pigments, reinforcing agents and the like, in amounts conventionally employed by those skilled in the adhe-sive arts.

.: -In forming the adhesive compositions of the invention, it is preferred that the novolak phenolic resin be dissolved in water, or, if water-insoluble, dispersed into water, preferably to form an emulsion, employing conventional practices. The remain-ing ingredients can be admixed into the aqueous novolak composi-tion in any order and by any conventional means so as to provide a final homogeneous solution or dispersion of adhesive materials in the carrier water. If is preferred that solid insoluble mat-erials be finely ground to preferably afford a colloidal adhesive composition. The resulting one-package water-based compositions are storage-stable at ambient temperatures, have excellent pot~
life, and heat-activated, i.e, are cured or hardened by heating at an elevated temperature. The compositions also exhibit excellent layover qualities, i.e. the compositions can be applied to a substrate, allowed to _ g _ ,:
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10t33281 dry and ren ~in in storage in their dry and uncured state ~or an ei~ended time, and then cured with the aid of heat.
At the time of use, the adhesive compositions of this invention can be . applied to either or both of the surfaces to be adhesively joined in any con-5 jventional ma~,ner, by calendaring or brushing, allowed to dry and then , cured or hardened by heating to an elevated temperature, such as a tem-i perature range normally employed in vulcanizing natural aIld synthetic rubbers, ~nd preferably in the range of about 135 C to about 235 C.
- Ij The adhesive systems of the invention are useful for direct bonding of 10 1 natural and synthetic rubbers to a variety of rigid and non-rigid substrates, ~ including metals, natural and synthetic organic and inorganic fibers, and the 1, , e. The herein-described adhesive systems are useful as well as priming ¦l compositions for treating such rigid and non-rigid substrates in combination with both sol~ent-based and water-based rtlbber adhesives. In addition, the adhesive systems of this invention can be combined with latices such as vinyl i pyridine rubber to form R~L-type adhesives for bonding fabric-to-rubber and which afford effective adhesive bonds and also afford significantly increased working time. ID addition to the unexpectedly good storage stability, the ~ compositions of this lnvention exhibit desirable film properties; are highly 20 ` resistant to sweep and flowwhen employed either as a one-pac~ primary '~ ' !! ~, . ad~sive, e. g., direct rubber-to-metal bonding, or as a primex composition ~ as p t ~f a two-pack, i. e., primer coat-rubber adhesive coat, system; and - ' are highly rssistaIlt to ad~erse environmental conditions.

; ~ . The fo}lowing e.~mples are provided to illustr~te the im~ention. All ~ 25 j pa~ts and percent ~ges are by weight unless otherwise indicated.
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EXAMPLE i Into a reactor equipped with a mixing device are charged 300 parts of dry methanol and 702 parts paraformaldeh~de. The mixture is heated to 70C and there is added a solution of 0.7 parts sodium hydroxide in 10 parts dry methanol. To the reaction mixture there is added 264 parts concentrated sulfuric acid. The temperature is maintained below ~0C during this addition. The reaction mixture is cooled to room temperature; washed with aqueous sodium hydroxide; and heated for two hours at 60C. The solid product is recovered by filtration, washed with aqueous sodium hydroxide, and again heated for two hours at 60C. The reaction mixture is filtered and the solid polyoxymethlene dimethyl ether product is washed with water until the formaldehyde odor is sub~
stantially eliminated.
EXAMPLE II
A novolak phenolic resin is prepared by reacting 13.21 ; moles resorcinol, 0.2 moles p-nonylphenol and 8.0 moles formalin (37% sol'n.) in the presence of a catalytic amount of hexamethyl-enetetramine at 90C. The resulting resin is dispersed in water with sodium caseinate at 31% N.V. An adhesive composition is prepared by dispersing into the thus-prepared novolak resin emul-sion 25 parts by weight per 100 parts by weight of novolak resin of y - polyoxymethylene dimethyl ether prepared according to the procedure of Example I. The adhesive composition is employed to ` bond to non-primed, grit-blasted steel a sulfur-vulcanizable !~ acrylonitrile-butadiene elastomer stock. The assembly is cured at 154C for 40 minutes. Peel adhesion, boiling water resistance ! and hot oil resistance tests are performed. Peel adhesion tests ` are effected according to ASTM D-429, method B modi~ied to 45.

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1~183Z81 ~Boiling water resistance is me~sured by immersing test samples in boiling water for 2 hours. Failure is determined by peeling rubber from metal With ~pliers immediately after removal from the water. This test is more severe than standard tests which cools the sample to ambient temperature before 5 l peeling. Hot oil resistance is determined by immersing test samples in ASTM #1 reference oil for 70 hrs. at 144 C, cooling the sample to ambient l . . I
;temperature, wiping the sample free of oil and peeling rubber from ~etal with pliers. In each instance, rubber-tearing bonds (100 R) are obtained. The icomposition iS equally as effective after being aged for 6 weeks at 51 C

10 , (1250 F). Substantially no change in appearance or viscosity of the com-Ipositions is noted after storage for six months at 51 C.
i When paraformaldehyde is substituted for~-polyoxymethylene dimethyl ¦ethex in the above-described adhesive the resulting composition gels upon 'standing overnight.

¦1 A phenolic solutlon is prepared by d-~sol~ing 100 parts by weight resorcinol-formaldehyde novolak phenolic resin (SRF-1501a, Schenectady l~ Chemicals, Inc. ) in 295 parts distilled water containing 12. 5 parts con-llcentrated ammonium hydroxide solution. Into the phenolic solution there is 20 , ùlspersed 25 parts ~-polyoxymethylene dimethyl ether to afford an aqueous I adhesive composition. The adhesive CompoSition is employed to bond non-¦ primed,grit-blasted steel to acrylonitfile-butadiene elastomer stock. The bonded assembly iS cured at 154 C for 40 minutes. Peel adhesion and boiling ! water resistance tests are performed according to the procedure of Exarnple 25 ',II withthe following results:

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': , ' ' , iO83Z81 Peel strength, Ib./in. 120 Peel adhesion, failure 95 R
Boiling water resistance 95 R
a - believed to be the trimeric methyleneamino acrylonitrile~atalyzed condensation product of resorcinol and formaldehyde.

EXA~LE IV
A novolak resin prepared by reacting 1.425 moles resorcinol, 0.027 moles cashew nut shell liquid and 1. 206 moles formalin (37% solution) in the presence of a cal~Llytic amount of he~Lmethylenetetr~mine. The resulting 10 resin is dispersed with sodium caseinate at 28. 7~c N. V. . The novolak resindispersion is formulated into an aqueous adhesive system havin~ the following composition Parts bY Weiçrht Novolak resin dispersion 379. 2 ~r-Polyo~ymethylene dimethyl ether 19 Silica 25 . 7 Titanium dioxide 18 Carbon black 3. 9 Anionic surfactant ~Tamol 850, Rohm & ~laas Co. ) 2.52 Water (to 25. 8% total solids content) The thus-prepared aqueous adhesive composition is employed as a single-coat adhesive to bond to non-primed, grit-blasted steel a sulfur vul-canizable acrylonitrile-butadiene elastomer (NBR) and as a metal primer coat for the bonding of natural and synthetic elastomers to metal (steel) with 25 a commercially available solvent-based covercement. The results are reported below:
Peel,Peel Adhesion, BoilingW~ter Elastomer Covercement Ibs.~ln. Failure 2 hrs.

Naturat rubberChemlok~9220a 48 100 R 95 R
SBR Chemlok'9 220 124 100 R ---` NBR b 90 100 R ---Natural rubber b 51 100 R 90 R
NBR c 67 100 R 100 R
35 ~Trademark, Lord Corporation, Erie, Pennsylvania a - heat relctive hllogen~ted rubber solventbased ;ldhesive, Hughsoh Chemic~ls, a division of Lord Corporation.
b - control adhesive system: Chemlok 205 primer (solvenl-b~sed he~t reactive phenolic resole primer, Hughson Cherr~icals) with Chemlok 220 rubber adhesive covercement.
c - control adhesive system: Chemlok 205, no primer coat.

The data demonstrate the utility of the herein-described aqueous adhesive sys~tems as a primary one-coat adhesive and as a primer for rubber-to-metal adhesive applications. The data ~rther demonstrate the bond capability of the aqueous adhesives of the invention is substantially equivalent to commercial solvent-based rubber-to-metal adhesive systems.
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EXAMPLE V
Cashew nut shell liquid and resorcinol are reacted with formaldehyde in the presence of a catalytic amount of hexamethylenetetramine at a phenolic: -formaldehyde molar ratio of 1. 70 to afford a phenolic novolak resin (6. 7%
cashew nut shell l~iquid/93. 3% resorcinol). The resin is emulsified with sodiumcaseinate to afford an emulsion having a total solids content, based on novolak resin, of 40%.
Aqueous adhesive compositions are formulated from the thus-prepared resin as follows:
Composision A B
Novolak resln 90 80 ~ -Polyoxymethylene dimethyl ether 10 20 Water (to ~0 TSC, based on novolak resin) The adhesive compositions are employed to bond a sulfur-vulcanizable acrylonitrile-butadiene rubber stoc~ to non-primed, grit-blasted steel. The adhesive-bonded assemblies are cured at 154 C for 40 minutes~ Peel adhesion, bolling water resist~nce and hot oil resistance tests are performed according to the procedure of Example II. The results are reported in the following table:

Peel Adhesion Adhesivelb./in. Failure Boiling WaterHot Oil Chemlock 205 67 100 R 100 R 100 R

The data demonstrate that the aqueous adhesives of the inven-tion afford a bonding capacity at least equivalent to commercial soivent-based rubber-to-metal adhesives.
EXAMPLE VI
Resorcinol and nonyl phenol are reacted with formalde-hyde in the presence of a catalytic amount of hexamethylene-tetramine at a total phenol:formaldehyde molar ratio of 1.7:1 to afford a novolak cocondensate resin (97 mol. ~ resorcinol/3 mol. % nonylphenol). The solid resin is washed to remove formal-~ dehyde odor. The wet resin is dried under vacuum. The dry '~ resin is dispersed in water with sodium caseinate at 40% N.V.
' to afford Emulsion A.
Resorcinol and cashew nut shell liquid are reacted .
with formaldehyde in the presence of a catalytic amount ofhexamethylenetetramine at a total phenol:formaldehyde molar ratio of 1.7:1 to afford a novolak cocondensate resin (96.8 mol. % resorcinol/3.2 mol. % cashew nut shell liquid). The - resin is washed to remove formaldehyde odor. The wet resin is divided into equal portions and one portion is dried under , vacuum. The wet and dry resin portions are separately dispersed ; in water with sodium caseinate at 40% N.V. to afford Emulsions B and C, respectively.

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Il 1083'~81 il The thus prepared emulsions are employed to prep~re aqueous ad-I hesive compositions according to the following recipes:
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Adh~sive I II III
I Emulsion A lOOa _ _ !,Emulsion B _ 1OOa ! E~ulsion c ~ ~ lOOa ¦IY~Polyoxymethylene dimethyl ether 25 25 25 Water b b b a = parts by weight of novolak resin.
10 t,b - w~ter in an amount sufficient to provide 45C~c TSC.
The thus prepared adhesive compositions are employed to bond ¦ sulfur-vulcanizable acrylonitrile-butadiene elastomer stock to untreated and treated cold rolled steel. The bonded assemblies are cured at 154 C for 40 1 mlnutes. Peel adhesion and environmental resistance (immersion in boiling ll water for two h~urs, immersion in hot oil for 70 hours at 149 C, and ex-¦Iposure to 5% sodium chloride spray at 100~o relative humidity) tests are performed. The results are reported in the following table.

, TABLE
~, Peel Adhesion, Room Temperature Pull SurfaceAdhesive Treatment I II m Chemlok 205 ,;
j~ lb/in Failure Ib/inFailure Ib/in Failure Ib/in Failure ¦I None 84 40R 24 7R 30 8R 150 99R
! Solvent-wiped, I
; grit-blasted 124 100R 125 g8R 104100R 120 10ûR
iiPh~sphatized 124 100R 118 96R 117 96R 104 100R ' ' , . ~ 11 ~ .
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l083Z81 ¦ Environmental Resict,mce A. Solvent-wiped, grit-blasted steel Hot Oil ReIerence Water,R.T. Salt Spray AdhesiveMil-L-23699Mil-L-7808 Fuel B 1 wk.100 hrs.
~ 100 R 100 R 100 R 100 R 92 R
i II 100 R 100 R 100 R 100 R 92 R
;III 100 R 100 R 100 R 67 R 80 R
Chemlok 205 100 R 100 R 87 R 100 R 70 R

3. Phosphatized Steel . Hot Oil Reference Water, R. T. Salt Spray ¦ Adhesive Mil-L-236g9Mil-L-7808 Fuel B 1 wk. 100 hrs.
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, II 100 R 100 R 93 R 97 R 96 R
,III 100 R 100 R 37 R 98 R 100 R
lS j, Control 100 R 100 R 97 R .100 R 100 R

¦1 The data`demonstrate the excellent adhesion and environmental iresistance afforded by the aqueous systems of the invention. As is generally 'the case, bonding is enhanced when the substrate is cleaned or otherwise ,treated prior to app~ying the adhesive.
EXAMPLE VII
¦. A cashew nut shell liquid/resorcinol/formaldehyde novolak resin is ~prep~red and emulsified according to the procedure of Example V. An aqueous `
adhesive composition is prepared by dispersing into the resin emulsion 25 , parts r-polyoxymethylene dimethyl ether per 100 parts novolak resin. The ` initial pH of the adhesive system is 6. 4. The pH of aliquot portions is ad-justed to 6. 6, 6. 8, 7. 0, 7. 2, 7. 4, 7. 8 and 8. 0 with concentr~ted sodium hydroxide solution. The resulting adhesives are utilized to h~nd solvent-wiped, grit-blasted steel to acrylonitrile-butadiene elastomer stock. The results are reported in the following t~ble:

q _ Adhesion Failure _ lb/in 6.~ 100 99 R
6.8 132 SB 100 R
1 7.0 100 100 R
j 7.2 103 99 R
¦ 7.4 101 100 R
7. 6 123 100 R
l; 7.8 99 100 R
! 8.0 90 80 R
1 - i ii The data indicate that excellent bond results are obtained over a wide ,jrange of pH of the aqueous adhesive systems. Generally, the pH will not ex-¦ ceed about 7. 9, and is preferably in the range of about 6. 2-7. 7, most I preferably about 6. 4-70.
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EXAMFLE VlrI
~¦ Cashewnut shell liquid, resorcinol and formaldehyde are reacted ,according to the procedure of Example V to afford novolak resins comprising i6. 7 mol percent cashew nut shell liquid and 93. 7 mol percent resorcinol having varied phenol: formatdehyde ratios. The resins are divided into aliquot 20 portions, and emulsified with sodium caseinate according to the procedure of Example V. Prior to emulsification, certain of the aliquot portions are i dehydrated. Aqueous adhesive compositions are prepared from each portion ¦accordlng to the procedure of Example VII. The compositions are employed ~o bond sulfur-vulcanizable acrylonitrile-butadiene elastomer to solvent-wiped, , 25 ; grit-btasted steel. The results are reported in the following table:
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' 1 i ,i ii , ,Novolak Resin Room Temperature PullBoiling ~Fa Dehydrat~d Ib/inFailure Water ¦1.61 No 98 98 R 95 R
I 1.. ;1 Yes 113 100 R 100 R
~ 1.94 No 105 80 R
. ~ 4 Yes 107 57 R 100 R
11~ 70 No 126 100 R 100 R
¦ 1. 70 Yes 125 100 R 100 R

la = Total phenolic:formaldehyde ratio .

10 ' The data demonstrate that excellent adhesion can be obtained over a ¦!wide phenolic:formaldehyde ratio range and, although the best results are , obtained with dehydrated resins, wet resins also provide excellent adhesive ¦¦bonds, Generally, the phenolic:formaldehyde ratio will be in the range of

4:1, and is most preferably in the range of 1, 4-2:1. No advantage has 15 . iibeen seen at ratios above 4:1.
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¦ ~ EXAMPLE IX
~I Several novolak resins were prepared and emulsified following the ijprocedure of Example V; with certain of the resins being dehydrated prior to Ijemulsification. The emulsions are employed to formulate aqueous adhesive 20 systems according to the procedure of Example VII. The adhesives are employed to bondsulfur-vulcanizable acrylonitrile-butadiene elastomer to solvent-wiped, grit-blasted steel and to phosphatized steel. The results are . . , reported in the following table: ` ¦
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~ 1083281 ¦ Adhesive System A B C D E F G H
¦ Novolak resin j composition I Phenolic portion,

5 , Mo1%
j Cashew nut shell I liquid 6.7 6.7 3.1 3.1 3.1 3.2 j~ Nonyl phenol 3 6 I! o-cresol 15 j Resorcinol 93.3 93.3 85 97 94 96.9 96.9 96.9 96.8 i Phenolic:formaldehyde 1.70 1.51 1.70 1.70 1.70 1.70 1.70 1.70 1.70 Dehydrated Yes Yes Yes No No No No No Yes Adhesive composition, I pH 6.11 6.02 6.19 6.41 6.39 6. 396.26 6.42 6.95 ~oom temperature pull Grit-blasted steel ! Peel adhesion,lb/in 98 85 96 120 114 116 86 97 95 i Failure 8~R 99R 99R 99R 100R 92R 90R 100R 100R
I Phosphatized steel 20Peel adhesion 108 115 115 115 115 110 102 104 97 Failure 91R 94R 98R 98R 97R 97R 92R 86R 97R

~I The data demonstrate the excellent ~rersatility with respect to com- ¦
¦I positional formulation afforded by the adhesive systems of the invention.

1. A novolak resin is prepared by reacting 1.425 moles resorcinol, 0.028 ¦I moles cashew nut shell llquid and 1.10 moles formaldehyde at 90 C in the , presence of a catalytic amount of hexamethylenetetramine according to the 1, procedure of Example II. The resulting resin is emulsified in water with !~ sodium caseinate at 28.8 total solids content. The resin emultion is employcd 30 to formulate an aqueous tire cord dip adhesive having the following com-I position: ' I

PBW

Styrene-butadiene-vinyl pyridine latexa 6obb Novolak resin emulsion 36 y-Polyoxymethylene dimethyl ether 25 Water, to 32.1% TSC

a = Goodrite 2828 emulsion, B.F. Goodrich Chemical Company.
b = PBW resin solids.
The adhesive is used to bond sulfur-vulcanizable SBR
elastomer stock to nylon with the following results:
Peel adhesion, lbs/in. 65-70 After the adhesive is aged six weeks at 52C, the bond-ing of ssR elastomer stock to nylon is repeated with the follow-ing result:
Peel adhesion, lbs/in. 88-96.
A similar tire cord dip adhesive employing resorcinol and hexamethylene-tetramine affords substantially the same re-sults t_70 lbs/in. peel adhesion) when freshly prepared; however such an adhesive is substantially gelled after two weeks aging at 52C.
EXAMPLE XI
.
Several aqueous adhesive systems are prepared from novolak phenolic resins and the following methylene donors:
; . : .
hexamethylenetetramine, formaldehyde, paraformaldehyde, trioxane, trimethylol phenol, methyl aziridinyl phosphine oxide, trimethylol cyanurate, tris (hydroxymethyl)nitromethane, hexamethylene diamine carbamate, hydroxymethyl diacetone acrylamide, poly-tN-methylol acrylamide), polytvinyl pyrollidone), polythydroxymethyl diacetone acrylamide), adduct of 2-amino-2-methyl-1-propan 1 and formalde-hyde, adduct of tris (hydroxymethyl) aminomethane and formalde-hyde, triethylene melamine, methoxy methyl melamine, dimethylol-ethylene urea, hexamethoxymethyl melamine, dihydroxydimethylol ethylene urea, butylated dimethylo;ethylene urea, urea-formal-dehyde condensate, ethylene-urea-. . . .

formaldehyde condensate and melamine-formaldehyde condensate.
In no instance is there obtained a satisfactory combination of properties including adhesion, environmental resistance, film properties and system stability.
From the foregoing examples, it can be appreciated that a versatile, storage-stable, heat-convertible water-based composition has been developed which is effective as a single-coat primary adhesive and as well as part of a two-pack primer-covercoat adhesive system. It can also be appreciated that all combinations of ingredients do not serve with equal effective~
ness and that each combination may require adjustment to reach optimum performance.
EXAMPLE XII
Emulsion A of Example VI is employed to prepare aqueous adhesive compositions according to the following receipes:
Adhesive XII-A XII-B

Emulsion A lb lOOa Polyacetal 25 y-Polyoxymethylene dialkyl ether - 25d Water c a = Formaldehyde-ethylene oxide copolymer (Celcon ~ M-90, Celanese Corporation).
b = y-Polyoxymethylene isopropyl methyl ether.
c = Water in an amount sufficient to provide 25% TSC.
d = Water in an amount sufficient to provide 45% TSC.

The thus-prepared adhesive compositions are employed to bond sulfur-vulcanizable acrylonitrile-butadiene elastomer stock to solvent-wiped, grit-blasted, cold-rolled steel. The bonded assembIies are cured at 154 for 40 minutes. Peel adhe-sion tests are performed with the following results:

~' , 1083281 Peel Adhesion, Room Temperature Pull Adhesive Ib. /in. Failure _ XII-A 9¢ 80 R
~I-B 116 100 R

The data demonstrate that high molecular weight polyacetals and Y-poly-¦¦ oxymethylene dialkyl ethers are ef~ective in affording excellent adhesive Il systems in accordance with the invention.
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Claims (15)

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

1. A heat-reactive water-based adhesive composition comprising: (a) at least one water-dispersible novolak phenolic resin; (b) an effective amount of at least one methylene donor selected from the group consisting of acetal homopolymers and acetal copolymers having an average degree of polymerization greater than 200 and gamma-polyoxymethylene ethers having the characteristics structure R1 - 0 -(CH20)n-R2 wherein R1 and R2 can be the same or different and each is an alkyl radical having from 1 to 8 carbon atoms and n is at least 100; and (c) water, the amount of water being sufficient to afford an aqueous dispersion having a total solids content, based on novolak resin, in the range from about 5 to 75 percent.

2. A heat-reactive water-based adhesive composition comprising (a) at least one at least water-dispersible novolak phenolic resin; (b) an effective amount of at least one methylene donor selected from the group consisting of gamma-polyoxymethyl-ene ethers having the characteristic structure R1 - 0 -(CH2 0)n-R2 wherein R1 and R2 can be the same or different and each is an alkyl radical having from 1 to 8 carbon atoms, and n is at least 100; and (c) water, the amount of water being sufficient to afford an aqueous dispersion having a total solids content, based on novolak resin, in the range from 5 to about 75 percent.

3. A composition according to claim 2, wherein the amount of methylene donor is in the range from about 2 to about 60 parts by weight per 100 parts by weight of novolak resin.

4. A composition according to claim 3, wherein each of R1 and R2 is methyl.

5. A composition according to claim 2, wherein said novolak resin is selected from the group consisting of (a) novolak resins wherein the phenolic precursor comprises 100 mole percent of at least one polyhydroxy phenol; (b) novolak resins wherein the phenolic precursor comprises about 50 to about 98 mole percent of at least one polyhydroxy phenol and about 50 to about 2 mole percent of at least one monohydric phenol, the nucleus of which monohydric phenol is not substituted with a hydrocarbon radical; (c) novolak resins where the phenolic precursor comprises about 10 to about 98 mole percent of at least one polyhydric phenol and about 90 to about 2 mole percent of at least one monohydric phenol, the nucleus of which monohydric phenol is substituted with at least one alkyl group having from 1 to 22 carbon atoms; (d) novolak resins wherein the phenolic precursor comprises 100 mole percent of at least one monohydric phenol, the nucleus of which is substituted with at least one alkyl group having from 1 to 22 carbon atoms; (e) modified novolak resins formed by reacting a preformed phenolic resole resin with additional phenolic precursor, said mole percents being based on total moles of phenolic precursor.

6. A composition according to claim 5, wherein said phenolic precursor comprises 100 mole percent resorcinol.

7. A composition according to claim 5, wherein the amount of said methylene donor is in the range from about 2 to about 60 parts by weight per 100 parts by weight of novolak resin.

8. A composition according to claim 7, wherein each of R1 and R2 is methyl.

9. A composition according to claim 7, wherein the ratio of phenol:aldehyde is in the range of about 1.4-4:1.

10. A composition according to claim 5, wherein said phenolic precursor comprises about 50-98 mole percent resorcinol and about 50-2 mole percent cashew nut shell liquid, and the ratio of phenol:aldehyde is in the range of about 1.4-4:1.

11. A composition according to claim 10, wherein each of R1 and R2 is methyl.

12. A composition according to claim 5, wherein the phenolic precursor comprises about 50-98 mole percent resorcinol and about 50-2 mole percent nonyl phenol; and the ratio of phenol:aldehyde is in the range of about 1.4-4:1.

13. A composition according to claim 12, wherein each of R1 and R2 is methyl.

14. A composition according to claim 3, wherein said novolak resin comprises cashew nut shell liquid modified phenolic resole.

15. A composition according to claim 7, wherein said novolak resin comprises the trimeric methylene amino acrylonitrie-catalyzed condensation product of resorcinol and formaldehyde.