US2657187A

US2657187A - Dilute alkali dispersible hot melt bookbinding adhesives

Info

Publication number: US2657187A
Application number: US131908A
Authority: US
Inventors: Evans John Lloyd; Micucci Dominic Donald
Original assignee: EI Du Pont de Nemours and Co
Current assignee: EIDP Inc
Priority date: 1949-12-08
Filing date: 1949-12-08
Publication date: 1953-10-27
Anticipated expiration: 1970-10-27
Also published as: FR1036600A; BE499917A; CH300599A; GB689715A

Description

Patented Oct. 27, 1953 STATE-S PATENT ()FFICE DILUTE' ALKALI' DISPERSIBLE- HOT M'ELT BOOKBINDING ADHESIVES John Lloyd Evans; South River, and Dominic Donald-Micucci; New Brunswick, N; .12, assign-- ors't'o E". I." an Pont'de Nemours & Company, Wilmington, Dela, a. corporation. of Delaware No. Drawing; ApplicationDecember 8', 1949,.

' Serial No. 131,908.

7 Claims; 260'-30'.8).

This invention relates to improvements inthe In applicationSeriaLNo...593.,099, filed May'li0,

1945, having. a. common.assignee...withltliis invention is. described. a novel. process of! binding." the page edges-of. books, magazines: and similar articles; of,-.manufacture= with solvent-free; hotemelt vinyl resin adhesive compositions whichtpermits dispensing with theeconventional step of stitching.-;With .cord-1orstapling associated-with conventionalglue-binding That hot-melt process has mettwithrsig-nificanta trade acceptance because of the; permissible; speed-up; of" the binding opera-'- tions as aresultof the'qui'ck-setting ofhot melt" adhesivesw in. comparison with: theslow setting; aqueousglues; liurthermore;;. a superior adhesively-- bound-- volume is.- obtainedin comparisonwith; the; glue, bound; product; reinforced with stitching or-w-ith vcrash-which is subj eat to deteriorationwvith age andby; mold, moisture and loss of? plasticity; Significant economyaccompanied the'adopt-ionrot the; new process as a result of the increased rate: of; output; elimination of stitching or stapling steps and reductiongins storage space normally required because of conventional practice .of providing interrupted schedules for setting. upthe glue. sented by a precise'schedule becauseatmospheric.

humidity conditions influence the rate at which It: is not profitabl'e tolconsume the serapwfor its.

fuel; value-and: therefore-the trimmings are 7 sold ass scrapz paper: and: eventually reused in some Scrap-paper iagsadectaccording tonestablished standards and.

form of. processed: paper "products;

priced: accordin'glyzrv Scrap containing: substane: tialsrforeigncmatter is saleable. only; atI-low prices:

Trimmingsscentainingtconsiderable vinyliiresin'v adhesive arezparticularlyt objectionable: as paper scrap because the adhesive is Water insolublean'd. cannot he-dispersed bwconventional means used irr de=inl ingz operations andf-processes associated The with paper manufacture and conversion. undispersed adhesive particles; unlesssubstantially-removed; lead to spots orblemishes inthe final paperproduct: These adhesive particles also clogthefeltingiscreens of the papermachine;

thereby preventing proper felting of the pulp Setting up of the glue is notreprer slurry andconsequently cause holes in final paper sheet; Adhesive particles are'furtlier deposited on theliot cylinder drying rollswhere their ad hesiveness may be sufliciently great to cause tear-- ing of the felted paper -web as it passes over the drying rolls.

As more and more-hot-melt bookbind-ing adhesive is," used; greater tonnage ofcatalogs; telephone directories; magazines and pocketbooks having the synthetic plastic adhesive incorporatedgtherein willfindgitsway into the-scrap; market: and subsequently into. the; paper; mills:

Therefore, disposal of adhesive contaminated" waste paper presents a seriousproblem;

Itis an. object of this inventionto modify the bookbinding polymeric organic hot melt.adhe.--

sives I to remedy the. above mentioned, conditions in reference to. wastepapen disposal \byrendering the. adhesive:dispersiblerin, aqueous dilute: alkali solutions-normally. used? in conventional. process.- ing of. paper scrap... Anotherobject is tomodify thecomposition-onthe polymeric adhesive chem ically. to-provide susceptibilityto dispersion in.

aqueous. dilute-alkalisolution. Aiurther. object is to. bind the edges. of. pages of books, catalogs and: the like... without stitching'or stapling using.

avinyl acetate copolymer,hotmelt adhesive composition. which is. dispersible: inaqueous dilute alkali; Stillanothen object istoprovidea book,

catalog; or; similar articlaadhesively bound,. with.

out reinforcement. Withstitchingor, staples, by meansofa vinyl: acetate oopolymeradhesive com.- positionsapplied in.-hotmelt'.condition,-. said ad.-

hesives being durableand-zresistantto. Water butv which. may: be dispersed. in. aqueous: dilute alkali to facilitateuseof paper. trimmings contaminated therewith, and. volumesv subsequently disposed of asst-rap papers These; objects .are accomplished by means; of. a hot, melt; adhesive composition which consists.

essentially of a.- coplymer. of vinyl acetate and crotonicacid. preferably the polymerization productof, 9,0. to;=-98:-. parts-vinyl acetatee-and 19. to 2. parts, of crotonicz. acid that is dispersible: in

- aqueous dilute. alkalisolution, and. methylated Adhesive compositions,- forum-- diaryl: sulfone.. lated with these vinyl acetatevcrotonic'.acid co-- polymersand methylated; cliaryl: sulfone- :will .de-

posit an adhesive film which hastfree: carboxylic:

anal to 2f'part's"off'a* methylateddi'arylsulfone. havmgat least one methyl" substituent' on each' aryl group for each part of copolymer. A minor portion of conventional compatible plasticizer, more than 10% of the adhesive composition ma be included in the composition for modification of flexibility. The term liquefying softener is used herein to describe softeners, which alter the properties of the vinyl acetate-crotonic acid copolymer from a thermoplastic resinous material having a gradual softening point to a composite blend having a sharply defined melting range as measured by the ball and ring method, said hot melt composition above its melting point rapidly becoming very liquid and capable of wetting and being adsorbed by the paper edges destined to become the backbone of the book.

The following examples are given by way of illustration only and no limitations are intended thereby except as, indicated in the appended claims.

Example 1 \The following components were charged into a polymerization kettle equipped with means for agitation, reflux and temperature control.

Parts Dixylylsulfone 220 Vinyl acetate monomer 300 Crotonic acid 14 Polymerization initiator 0.9

A suitable polymerization initiator is ma azo his (isobutyronitrile) The mixture was constantly agitated at about 95 R. P. M. for the stirrer and the temperature raised to 70 C. and as the polymerization commenced the temperature increased gradually during about six hours to a temperature plateau at about 94 C. under slow reflux without altering the external source of heat, the temperature increase resulting from the conversion monomers to copolymer. 0.25 part of additional azonitrile polymerization initiator was charged into the kettle and polymerization continued under moderate to fast reflux for five additional hours during which time the temperature increased to a new plateau of about 105 C. Polymerization was then stopped by addition of 0.5 part of Ionol inhibitor, which is a Shell Chemical Company proprietary antioxidant. Ionol is described as one of the trialkyl-substituted hindered phenols having antioxidant properties,

each of the said alkyl groups containing not more than 4 carbon atoms. More specifically, it is identified as 2,6 di-tertiary butyl 4 methyl phenol having a molecular weight of 220.3 and a melting point of 70 C. The unpolymerized vinyl acetate was removed by vacuum distillation at 50 mm. of mercury until the temperature of the melt reached 160 C. 86.8 parts of vinyl acetate were recovered as the distillate and the recovered product was 440 parts leaving an unaccountable loss of about 8 parts which apparently was vinyl acetate.

The product was calculated as having the following composition:

Per cent Dixylyl sulfone 50.0 Vinyl acetate/crotonic acid copo1ymer 49.9 Ionol inhibitor 0.1

The copolymer is estimated to consist of 93.6 parts vinyl acetate and 6.4 parts crotonic acid.

This hot melt adhesive was found to be thermally stable for 96 hours and longer at 160 C.

without loss of its dilute alkali dispersiblity. By dilute aqueous alkali solutions is meant herein alkalinity of the order of the magnitude of 05% sodium hydroxide or its equivalent.

This hot melt adhesive used to bind books as shall be described later yielded an excellently bound volume having a tough, flexible backbone which was waterproof and resistant to deterioration with age and exposure to atmospheric conditions.

Rather than copolymerization in situ in the "liquefying softener, the monomers may be copolymerized in orthodox solvents and subsequently compounded with the liquefying softener and other desirable components to form the hot melt adhesive composition from which the solvent had been removed by distillation. The following example illustrates this practice.

Example 2 The following composition was charged into an agitated polymerization kettle.

Parts by weight Toluene 124 Vinyl acetate 300 Crotonic acid 14 Polymerization initiator 0.9

A suitable polymerization initiator is azo bis (isobutyronitrile).

This mixture was heated to 70 C. and as polymerization proceeded, the temperature rose to a plateau at about 91 C. 0.25 additional part of initiator were charged into the kettle and polymerization continued until a plateau at about 98 C. was reached while under moderate reflux. 0.5 part of inhibitor was added to arrest the polymerization. 200 parts of molten dixylylsulfone were charged into the kettle and dispersed throughout the polymerized charge. The toluene and unpolymerized vinyl acetate were removed by distillation under vacuum at 50 mm. until the temperature reached 160 C. 176 parts of distillate and about 460 parts of adhesive were recovered. The adhesive was calculated to have the following composition:

Per cent Dixylylsulfone 47.8 Vinyl acetate/crotonic acid copolymer 52. Inhibitor 0.1

The copolymer was estimated to contain about 5.6 parts of crotonic acid and 94.4 parts vinyl acetate.

This hot melt adhesive was equivalent to that of Example 1, exhibiting heat stability for 96 hours and longer at 160 C. without loss of its dispersibility in dilute alkali. Likewise applied in the art of binding books with hot melt adhesives,

it yielded an acceptably bound volume having the characteristics desirable for durable bindings and in addition, the adhesive contaminated trimmings and scrap thereof had full salvage because the adhesive was adequately removed by alkali dispersibility by the orthodox operations.

By further experimentation it has been found that similar hot melt adhesive compositions in which the copolymer contained as little as 2% crotonic acid exhibit adequate dilute alkali dispersibility. The preferred content of crotonic acid is in the range of 2 to 10%, the balance being vinyl acetate. Still higher contents of crotonic acid promote solubility in dilute alkali.

However, .higher contents of this-copolymerizable monomer .leadsto low molecular weightcopolymore and -.exceptionally long polymerization cycles. The resulting low molecular weight copolymers are slacking in toughness, :are soft .and exhibit cold flow, properties which characterize the :copolymer as inadequate for use in hot melt adhesives for bi-nding books. Othenfields of adhesive application may tolerate sacrifice'in these properties andfin'd utility for hot melt adhesives formulated with copolymers rhavinga higher content "than 10f nrotonic zacid coprolturn-miced For :example, such hot melts might he used .ior attachment of Elabe'ls :to glass :and metal containers *where it desirable to subsequently remove .the :label by soaking in very dilute aque ous alkali solutions.

The foregoing examples :show 'a two component hot-melt composition, ithatzis, vinyl acetatecrotonic acid rcopolymer modified :witha Jiguefying softener. It is obvious that such :products may be modified with compatible orthodox-ester plasticizers 'to alter "the physical icharacteristics of the adhesive film. Generally the :use aqf hot melt adhesives for the purpose of binding books limits the acceptable content of such "plastic'izers to 10% based Imthe'total weight :oi'nonvolatile hot melt adhesiim. Di(methyl 'Gel-losolve) 'phthalate and triethyl citrate are particularly useful for ipl'asticizi-ng the vinyl acetate- 90 crotonic acid copolymer adhesive. 'liricresyl phosphate, dicresyl carbitol, butyl'phthallyl butyl 'g'lycollate, ortho-cresyl para-toluene sulfonate and polyethylene glycol di z-ethyl hexoate may also be used. The latter palsticizer shows exceb lent compatibility with polyvinyl acetate, but its compatibility with 'thev inyl acetate-crotonic acid copo'lymer is more limited and in some instances it may not be used to the frill extent-of 10%.

Itis obvious that the adhesive used for'bind- 'ing pages without the reinforcing action or staples or stitched thread to form the backbone of the volume must be "characterizedby greater toughness, flexibility and'freedom'from cold flow than adhesives used for other binding purposes, such as 'for attaching the-cover'to the said backbone. Consequently, "for purposes of economy, the "adhesive ncrmallyused informing the "backbone may be modified with low cost diluentswhen used as a cover adhesive. The following example is representative of a satisfactory cover adhesive which may be used either in combination'with the hot melt "bound backbone or "alone to attach covers to stitchedior stapled volumes.

iEzrample As in Example the vinyl acetate and protonic acid were copolym'erized in 'to'luen'e'and the .liquefying softener added to displace the solvent. The following ingredients were charged into the polymerization kettle with stirrnig:

Parts bywveiglrt Toluene .1 24 Vinyl acetate 3300 Crotonicacid Polymerization initiator 11. 9

Polymerization Was carried out for about TI hours While the temperature increased lfrom 170 to .91 C. Then .25 part of additional polymerization 10 initiator were charged. into the kettle and the temperature increased from 81 .0. J30 .a -,plateau at .97 'C. in about ,five hours. At this temperature, polymerization was arrested :by additionnf .5 part aQJf (Honor). 220 parts of sulione were charged into the hot nosolution and distillation was-commenced under :50 mm. vacuum to displace the toluene and remove the excess vinyl acetate. Distillation was stopped at 160 C., 200 grams of distillate having been recovered. To the solvent free hot melt adhesive remaining in the kettle 'were added parts of idixylyl :sulfone, 103.2 parts of Vinsol resin, M1 parts of Asbestine (a complex hydrated magnesium :silicate of fibrous, icrystal- --'lme structure?) and 154 parts inhibitorifor a final to'tahcharge nor-841.1 parts.

This hot :melt adhesive was found. .to be heat stable for about :96 hours :at 16.0 and adequately retained its sdispiersibility in dilute The product used as an :adhesive for attaching covers was found to be entirely satisfactory :for the purpose. The "use of the diluents, however, contributed "brittleness and detracted from the toughness and flexibility inherent "to the undiluted adhesive making it less desirable as a backbone adhesive.

The examples illustrat the invention using d'ixyly'l su'lfone as the liquefying softener. Other methylated diaryl monosulfones having at least one methyl substituen't on each 'aryl group or mixtures thereof may be substituted i like amount. In addition to the dixylyl sulfone and its isomers, the various isomeric forms of ditolyl sulfone and :xylyl toly'l sulfone are also particularly useful as the lique'fy'ing softener for the hot-melt adhesives of this invention.

Example '3 shows the use of resinous and mineraldiluents. Still other'diluents which are inert, non-volatile and heat stable for periods of 72 hours and longer in the presence of the hot melt composition at C. may be used. Cotton flock, regenerated cellulose flake particles, glass fibers and the like which are generally characterizedby dimensions ofwhich the maximum on the average is about ;12 :inch and the ratio "between'length and diameter or thickness is in the range of 20-100 to 1, may also beused as diluents. Embedded in the applied adhesive, they exhibit reinforcing strength. Obviously due to "matting eifects, the amount of this diluent is limited. 'In the art of binding books and .cover application, it is preferred that the content of this type of diluent does not exceed 7% based on the total adhesive composition.

The solvent used as a polymerization medium has an effect on the molecular weight of the polymer .or copolymer. When tertiary butanoil was used as solvent in place of toluene, .a higher intrinsi viscosity product was obtained. However, in general, these .copolymers have viscosities in the .range of commercially .low viscosity vinyl acetate .pclymers. fIhe copolymerization can also be carried out in 'Ihenzene or .ethyl a1- co'hdl.

The nature .of the polymerization initiator-also affects the molecular weight .of the .copolymer. Peroxide initiators, .such as lauroyl peroxide and benzoyl peroxide, and .azonitrile initiators, such as -d'.,rz' .azo-bisiisobutyronitrile) and 0.,11' azo- -bis.(.alpha-gamma dimethyl') (valeronitrile) give copolymers having melocular weights which are satisfactory for hotmelt adhesives and which are dispersible indilute alkali. In general, any polymerization initiator which is satisfactory for the polymerization of vinyl acetate can be used :for the icopolymerization of vinyl acetate and raretonicacid.

it might be :expected that introduction of carhDXyllG groups in th .linear polymer contributes a. alkali solubility and, therefore, an attempt was mad to introduce such a group in a prepolymerized vinyl acetate resin by heating it with phthalic anhydride plus water.

Example 4 100 parts by weight or medium viscosity polyvinyl acetate were intimately mixed with parts of phthalic anhydride and melted at a temperature of about 160 C. and with the kettle equipped with a reflux condenser, 10 parts of water were slowly added with continuous agitation of the charge. After 1 hour heating, distillation of the volatiles was commenced and heating continued for four hours. The distillate consisted of acetic acid and water, indicating that some ester interchang occurred between the vinyl acetate polymer and the phthalic acid. This modified polymer was found to be alkali soluble, at caustic soda concentrations of about 1.9% but not at the a desired concentration of 0.1% and less, preferably about parts of this polymer and 50 parts of a iiquciying softener were meltblended at about 160 C. to form a hot melt adhesive. The product was not heat stab-l as evidenced by gelation and charring. Crosslinking of the polycarboxylic phthalic acid by ester interchange in the vinyl acetate polymer presumably accounted for the gelation.

Attempts to overcome crosslinking by blocking one of the two carboxyl groups of the phthalic acid through the use of acid salts of phthalic acid failed to accomplish the desired. objects. A c0 polymer of vinyl acetate and butyl hydrogen maleate also failed. Similarly, a difuncticnal reactant having both a carboxyl group and an inorganic acid reacting group, for example, metasulfobenaoic acid, failed by gelation. Furthermore, competitive ester interchange between a mixture of phthalic acid and a monocarboxylic fatty acid, such as stearic acid, with the vinyl. acetate polymer failed to produce a modified vinyl ester polymer satisfactory for hot melt adhesive use.

Monofunctional acid reacting olefinic unsaturated materials which satisfactorily copolyinerize with vinyl esters, particularly vinyl acetate were also tried. Acrylic acid and metha'crylic acid polymerized in the presence of vinyl acetate yielded polymer compositions of non-uniform quality, apparently constituting mixtures of homopolyrners and copolymers due to the significant difference in relative reactivities of the vinyl acetate and the acrylic and methacryiic acid in copolymerization.

It was indeed surprising to find that erotonic acid, isomeric with methacrylic acid, yielded uniform copolymcrs with vinyl acetate which are essential to the heat-stable, alkali-dispersible hotmelt adhesive particularly adaptable to the art oi bookbinding.

The adhesives of the present invention may be used. as other hot-melt adhesives in binding books. The basic design of a machine commer" cially used binding books using glue is the bookibinding covering machine described in the Bredenburg U. 5. Patent 1,073,324, granted September 16, 1913. Numerous subsequent patshow modification in the machines and improved steps in the process of binding books involving such machines. Application Serial No. 593,099, filed May 16, 1945, describes modification of the process of binding books and similar articles by substitution of a solvent-free hot melt vinyl acetate adhesive composition for the g ue and elimination of the steps ofstitching or stapling to reinforce the glue binding. Briefly, in commercial practice, the folded signatures subsequently to become pages of the bound vol ume are assembled between fiat metal plates held together under pressure, the position of the gathered signatures being adjusted between the clamping plates to leave about {-6- to /4 inch of page backbone edge exposed after the cutting operation has trimmed oi? the signature folds to reduce the signatures to a plurality of pages. The assembled clamped signatures are then passed. through cutter to remove the said signature folds. The backbone now having a smooth uniform edge is subjected to roughers which serve the purpose or" opening up the fibers at the edges of the pages to make them more receptive to the adhesive composition to provide better keying action by permitting the composition to penetrate into the interstices. Roughing may vary in degree and pattern to produce the desired keying action. The roughened edge is then freed of loose extraneous material by brushing, airblast or vacuum means. Following these propanatory steps, the hot melt adhesive is applied to the backbone edge by means or a conventional applicator roll consisting of a fiat surfaced wheel revolving in and about immerse-o. in a hot melt adhesive, such as described in Examples 1 and 2, maintained at a temperature of about 166 C. An adjustable scraper-doctor blade or metering hot spinner removes the excess adhesive, leaving the desired thickness of film on the backbone. The adhesive application may be single stage or by multiple coats applied by subjecting the baclo bone to a series of adhesive applicators.

The application of a. priming coat may precede the application of the principal hot melt adhesive. The primer is generally identical with the solvent-free, hot melt adhesive except it is cut with a volatile solvent which reduces the viscous hot melt to a very thin, penetrating liquid. The use of the primer necessitates provision of adequate means of substantially removing the volatile component of the applied primer prior to application of the hot melt. Obviously, since dilute alkali dispersibility is the object of the invention, it is pertinent that the deposited primer, like the principal adhesive, be characterized by that property.

As an alternativ to priming the backbone of the book with a solution type primer, an aqueous dispersion of polyvinyl acetate containing a smal percentage of polyvinyl alcohol as the dispersing and stabilizing agent may be used as a primer. Apparently the polyvinyl alcohol promotes redispersibility of the deposited primer in aqueous media, although a hot-melt adhesive formulated with vinyl acetate polymer is inadequate y dispersible in dilute aqueous alkali solutions.

While the applied hot melt adhesive film is still in a substantial fluid condition an open mesh fabric or crash may be embedded therein to reinforce the backbone if such strengthening of the volume is desired. Finally the cover is attached following application of any of the solvent-free hot melt, heat-stable, alkali dispersible adhesives described herein. Example 3 which contains economical diluents is representative of a solvent free hot melt adhesive entirely satisfactory for cover application. The covering machine often is separate from the main bookbinding machine which provides the means of converting the signatures to an uncovered volume having an adhesively bound backbone. Consequently, the covering operation using a hot melt adhesive may be employed in covering magazines, pocketbooks,

pamphlets, catalogs, etc. in which the signatures are held together with staples or stitched cord with or without the presence of conventional adhesives.

The trimming operations in the process of binding books, magazines and the like result in waste paper scrap contaminated with adhesive. When this'adhesive is a conventional proteinaceous glue, the disintegration processes used by the paper converters in consuming the scrap cause the glue to disperse or dissolve, thereby providing a means of separation of substantially all of the adhesive to the extent that the ultimate product is unaffected by the small content of adhesive that may have been retained. When the adhesive is an orthodox resinous or elastomeric composition formulated with water insoluble polymers, the paper manufacturer using the waste paper encounters difficulty in using the scrap because the adhesive is not adequately and substantially dispersed and removed.

The waste paper and scrap contaminated with the adhesives of this invention formulated essentially with a copolymer consisting of the polymerization product of 90 to 98 parts vinyl acetate and 10 to 2 parts of crotonic acid and a compatible liquefying softener present no problem to the paper converter inasmuch as the adhesive is solubilized or dispersed in aqueous dilute alkali solution containing .05% sodium hydroxide, although dispersion in .01% caustic has been obtained by lengthening the contact time.

The trim or adhesive contaminated waste paper is generally consumed by paper mills in the manufacture of new paper. In some mills, as high as 80% of the furnish is Waste paper with 20% being virgin pulp and the waste paper generally being magazine stock. Such operations involve repulping and de-inking steps which are described briefiy to indicate that alkaline conditions adequate for dispersion of the adhesives of this invention exist in current practices. Repulping or defibering of the waste paper is carried out in a breaker beater or hydrapulper where the waste paper is subject to mechanical action at a consistency of paper and 95% water. During this mechanical operation, chemicals such as alkali, wetting agents, etc. are added for the purpose of de-inking the stock. De-inking is generally carried out at elevated temperatures in the range of110 F. to about 180 F.

In a representative case the paper was repulped at a consistency of 4.5% and for de-inking the temperature was raised to 170 F., with a 6.0% sodium silicate and 1.4% sodium peroxide, on the basis of dry weight paper, being added as the de-inking chemicals. The processing cycle was three hours.

In another instance, 6000 pounds of dry paper were hydropulped at 3 consistency followed by a 45 minute de-inking cycle at 180 F. in the presence of 200 pounds of soda ash and 100 pounds dry caustic soda.

In these instances, the alkalinity is in excess of the .05% suggested as the most suitable concentration for dispersing the hot melt adhesive.

Still another mill de-inked at 5% consistency at a temperature of 120 F. for a cycle ranging from 20 minutes to 2 hours using 1% caustic soda based on the dry paper. This caustic concentration is about .05%. V

These mills which experienced serious difficulty in using waste paper contaminated with polyvinyl acetate to the extent that such type of scrap would not be purchased had no difficulty in using scrap contaminated with an equivalent adhesive in which the vinyl acetate-crotonic acid copolymer of this invention was substituted for polyvinyl acetate in the formulation.

A distinct advance in the art of bookbinding, particularly in the art of binding books, magazines, catalogs and the like with a solvent-free, hot melt polymeric resinous adhesive has been made by the use of adhesives comprises essentially of a copolymer consisting of the polymerization product of to 98 parts by weight of vinyl acetate and 10 to 2 parts of crotonic acid and a liquefying softener, the latter being present preferably in the range of /2 to 2 parts for each part of copolymer. The use of the said hot melt adhesives characterized by dispersibility or solubility in aqueous dilute alkali at concentrations as low as .01% NaOH equivalent, preferably about .05% serves to eliminate a serious disposal problem in reference to use of waste paper contaminated with hot melt polymeric adhesive which heretofor was not dispersible during conventional waste paper processing. These advantages were economically accomplished without sacrifice in desirable characteristics of the adhesive, such as toughness, flexibility and freedom from cold fiow.

It is apparent that many widely different embodiments of this invention may be made without departing from the spirit and scope thereof, and therefore, it is not intended to be limited except as indicated in the appended claims.

We claim:

1. A hot melt adhesive which is dispersible in a .05% aqueous alkali solution which comprises one part of a copolymer of from 90 to 98 parts of vinyl acetate and 10 to 2 parts of crotonic acid; and from to 2 parts of a liquefying softener consisting essentially of a methylated diaryl sulfone having at least one but not more than two methyl substituents on each aryl group.

2. The composition of claim 1 which contains less than about 10% of a compatible solvent plasticizer.

3. The composition of claim 1 in which the liquefying softener is dixylyl sulfone.

4. The composition of claim 1 in which the liquefying softener is ditolyl sulfone.

5. The composition of claim 1 in which the liquefying softener is tolyl Xylyl sulfone.

6. The composition of claim 1 in which the liquefying softener is a mixture of isomeric methylated diaryl sulfones.

7. The adhesive of claim 1 which contains a polymerization inhibitor.

JOHN LLOYD EVANS. DOMINIC DONALD MICUCCI.

References Cited in the file of this patent UNITED STATES PATENTS Number Name Date 1,659,401 Kirschbrauin Feb. 14, 1928 1,819,159 Gale Aug. 18, 1931 2,127,400 Gibbs Aug. 16, 1938 2,249,545 Swan July 15, 1941 2,263,598 Sarck et a1 Nov. 25, 1941 2,310,725 Widder et a1 Feb. 9, 1943 2,390,695 Dean et a1 Dec. 11, 1945

Claims

1. A HOT MELT ADHESIVE WHICH IS DISPERSIBLE IN A .05% AQUEOUS ALKALI SOLUTION WHICH COMPRISES ONE PART OF A COPOLYMER OF FROM 90 TO 98 PARTS OF VINYL ACETATE AND 10 TO 2 PARTS OF CROTONIC ACID; AND FROM 1/2 TO 2 PARTS OF A LIQUEFYING SOFTENER CONSISTING ESSENTIALY OF A METHYLATED DIARYL SULFONE HAVING AT LEAST ONE BUT NOT MORE THAN TWO METHYL SUBSTITUENTS ON EACH ARYL GROUP.