CA2154497A1 - Production technique for blocks of hot melt adhesives - Google Patents

Abstract

In a process for the packaging of molten hot melt adhesive in a film cavity wherein the adhesive is filled into the cavity at a temperature above the melting point of the film and wherein the film cavity is in direct contact with a liquid or gaseous heat sink the improvement which comprises using as the film a heat sealable film at least a portion of which is water soluble.

Description

- 2154~7 This invention relates to a method for packaging hot melt adhesives compositions and to the resulting packaged adhesive compositions.
Hot melt adhesives which are generally applied while in the molten or liquid state are solid at room te",pe,dlure. Typically, these adhesives are provided in the form of blocks; however, because of the nature of these n,dle(ials there are p,.~l-. "s asso~ ed with handling and packaging them. The solid adhesive blocks not only stick or adhere to hands or mechan'~-' handling devices and to each other, but they also pick up dirt and other contaminants. Additionally, certain a~r' ~ ' -ns require high tack fommulations which result in blocks that will deform or cold flow unless suppo, led during shipment.
The need and advanldges for providing tackless or non-blocking hot melt adhesives are appar~:nt and various ways of acco"lpl ~'ning this have been developed.
Japanese Patent 48-103635 published Dece",t,er 26, 1973, cl: ~vloses a granular adhesive which is tacky at room tt:---pe-dture and coated or enveloped with a non-tacky hot ,.,o't~ ' 'o material that is the same type or is miscible or mixable with it.
French Patent 2,544,654 published October 26, 1984, ~lisclQses forrning a ~d~,kless hot melt by adding molten hot melt to a mold containing a preformed support layer having a transfer film thereon which is co"",dl;ble with the hot melt.
U.S. Patent Nos. 4,748,796 issued June 12, 1988, and 4,755,245 issued July 5, 1988, disclose fomming a protective coating for an adhesive material by ele~t,usldlically coating a mo!d or cavity with a powder screen and then pouring hot melt into the mold.

215 4~97 French Patent 2,601,616 published October 22, 1988, ~ oses forming blocks of hot melt pressure sensitive adhesives by casting the pressure sensitive adhesive into molds plt:co~led by spraying with a film of non self-sticking hot melt material thereby forming a fusible non-tacky veil around the pressure sensitive block.
5In German Patent 22 48 046 the hot melt adhesive is squeeze-cut into pillow-shaped pieces;
the pieces 5''hsequently cooled and s-' ' qe~
Still other patents teach coating or wrapping the formed hot melt block with various types of plastic films. Thus, German patents DE 31 38 222 and 32 34 065 disclose coating the circumference of elongdled hot melt portions with a thin polyolefin film. German patent 36 25 358 to Hausdorf teaches 10wrapping the solid hot melt block in a thellllopl~lic, especially copolyamide film with a melting point of 120C to 150C, while EP app' ~ 'icn 0 469 564 and WO 94/01330, both to Rouyer et al. Ilis~loses v"i~p: ,g the solidified hot melt in a plastic or biodegl_de ''- polymeric packaging material.
All the latter methods have provided some degree of improvement in the pack~g ng and handling of hot melt adhesives however they have suffered by virtue of either the need to unwrap or otherwise 15u"pachdge the hot melt or, in the cases of coated hot melts which are added directly to the melting pots, by virtue of the contamination resulting from the build up over time of large quantities of the pa-,hdyi"g ",d~e~;als in the melt pot and app"~ equipment.
In order to overcome the disadvallt~ges inherent in the methods of the prior art, U.S. Patent 5,401,455, issued March 28, 1995, d;,~,loses the finding that when the hot melt adhesive is poured in 20its molten state into a mold or cavity lined with plastic pa '~_ ,9 film and then allowed to solidify, the adhesive is fused to some extent into the film, resulting in a non-blocking adhesive pachage which will melt faster in the melt pot and will not cause a sub~ idl build-up of undesi-~' 'e plastic residue even after extended periods of time.
Since the melting point of the plastic film should be compa,~' 'e to, and p~:r~rably lower than, 25the melting point of the hot melt adl ,esivc in order to provide for s~ ory melting in the melt pot which does not have a source of agitation, it is necessary that the lined mold be in direct contact with a heat 21S~97 sink so as to remove excess heat from the film as quickly as possible and thereby prevent melting, buming or charring of the plastic film wrap.
An improvement on that method is described in U.S. Patent 5,373,682, issued December 20, 1994. According to that e" b" ' ~e~l, the molten adhesive is directly pumped or poured into a cy; ~lical plastic-tube, the cylindrical tube being in di-ect contact with the heat sin~ The resultant adhesive pa~,hdge is thus provided in a readily handleable cartridge form which may be produced in a continuous line ope,dlion and which a~ 'i'icnally plossesses all the ad~,a"t~ges ofthe easily p,uc s s ~'e non-blocking adhesive package of the parent a~ n.
While the methods desc~ ed in the cope~ " ~9 ~r~ ~ 'iOl~ have proved useful for packaging and re-melting of most hot melt adhesive formulations, there remain some:,, ' "- 15, for eAdlll, 'e for non-pressure sensitive adhesives, where ~ FP'-l9 during storage and shipping is unnecess~-y. There are also other eFF'ic "^ns where even sma~l amounts of unmelted film may create pr~bl? ,~s in the melt tank.
lt is ll,e,~ desirable in a limited number of ~"~ inns to provide hot melt adhesive po,li~ns in the convenient size and shape produced by the p,~cesses of the copending ap~ n but without any extemal pacl~ _ ,9 film.

Accor~ , to an aspect of the present invention, a process for the p~ ~ng of molten hot melt a&esive in a film cavity is provided wherein the a&esive is filled into the cavity at a lule above the m~ltir~ point of the film and ~.,.e~ the plastic film cavity is in direct contact with a liquid or gaseous heat sink the ~prvv~melll which co~ .. ;~,s using.as the film, a heat sealable film at least a portion of wllich is water soluble.
According to an embodiment of the invention the water soluble portion of the film co~ .ses polyvinyl alcohol, modified starch or cellulose. Accol~ding to an embodiment of the invention the entire surface of the film co..~l.. ;~; polyvinyl alcohol.
- Accol~ g to a~ ,l embodiment of the present invention the cavity cG.~ es a cylindrical tube of the heat sealable film. In a pIc~;llcd embodiment molten hot melt a&esive is filled into the cavity at a molten viscosity of l,OOO cps. to 200,000 cps.

~_ 215~497 , .

We have now found that when a heat s- '-' 'o film, at least a portion of which is water soluble, is utilized as the film, the molten adhesive can be effectively pa-,hdged using the procedures described previously. The water soluble film or portion thereof will then be slowly d;ssolved in a water bath, after which the resultant adhesive mass will be fully s.,''J'fied and may be packaged directly or may be s~hsequently coated with anti-stick ",dlerial~ using III~UIods conventional in the art The method of the present invention is ada~t ''e to the pac~ 9 of virtually any type of hot melt adhesive co"lposiuon. As eAdll, 'es the method disclosed herein may be used to pachage hot melt adhesives p~pal~d from polymers and copolymers of synthetic resins, rubbers, polyethylene, poly~n~ pjlene, polyurethane, acrylics, vinyl acetate, ethylene vinyl acetate and polyvinyl alcohol. More specific ~Adlll, 'S include hot melt adhesives pl~:pal~d from the r ":.~i.ly.

3a 2 1 ~ 7 a. rubber polymers such as block copolymers of monovinyl a,u",dtic hydrocarbons and conjugateddiene,e.g.,styrene-butadiene, styrene-but-" ne-styrene, styrene-isoprene-styrene, styrene-ethylene-butylene-styrene and styrene-ethylene propylene-styrene;
b. ethylene-vinyl acetate poly~,,ela~ other ethylene esters and copolymers, e.g., ethylene 5 ",etl,ac~ylate, ethylene n-butyl acrylate and ethylene acrylic acid;
c. polyolefins such as polyethylene and poly~,,u~,ylene;
d. polyvinyl acetate and random copolymers thereof;
e. polyacrylates;
f. polyamides;
9. polyesters;
h. polyvinyl alcohols and copolymers thereof;
i. polyurethanes;
j. polystyrenes;
k. polyepu~ides;
I. graft copoly",e,a of vinyl n,ono"~,(s) and polyalkylene ox'lde polymers; and m. ''hydecontainingresinssuchasphenol-aldehyde,urea-aldehyde,IIIeICA~ c~'~ehyde and the like.
Most often such adl,esives are formulated with tackifying resins in order to improve adhesion and introduce tack into the adl.cs.-e. Such resin indude, among other ",dt~rials, (a) natural and ",~ d 20 resins, (b) polyterpene resins, (c) phen~ ",o lified hyd~uca~l on resins, (d) coumarone-indene resins, (e) aliphatic and 'dl~llldtiC p~t,.' ~ ~n l"rd~-)cd,bon resins, (f) phthdldtt: esters and (g) hyd~gendled hydlu~,d,l,ons, I.~d~ugendled rosins and hydlugel,dled rosin esters.
Desi, ''- opffonal iny,~ r,ts include diluents, e.g., liquid polybutene orpolypropylene, pet,-' ~urn waxes such as paraffn and microcrystalline waxes, polyethylene greases, I"rd,ugend~ed animal, fish and 25 vegetable fats, mineral oil and synthetic waxes as well as hyd,ucd,~on oils such as napl~U, ~n~ or pd,drri".~ mineral oils.

'-. 215~g7 Other optional additives may include stabilizers alllioxiddlll:~ co!ard"l:, and fillers. The selection of components and amounts as well as the prepa,dlion thereof are well known in the art and described in the literature.
The heat s,e- - e water soluble film into which the molten adhesive is poured may be any film which will ~ , its integrity during filling but will suhsequently dissolve in water. Suitable materials include polyvinyl alcohol n,odi~ied sld~d~es cellulose films and the like. Polyvinyl alcohol hlms are the most preferred Rather than using the water soluble material as the entire hlm substrate in accordance with an alternative embodiment of the invention it is p~s- 'E that the film include a non-water soluble portion with the water soluble portion serving only as the vehicle to effect dissolution and separdtion of the film from the adhesive mass during the water cooling. In the case of hlms which comprise more than one material it is only necessary that the portion of the film which will provide the longitudinal lapped seal around the adhesive mass during the filling ope,dtion be heat see It may also be desi, e in the case of pressure sensitive adhesives to use a co",posite water soluble film la" Idted to a non-soluble coating the latter remaining on the adhesive mass and providing a cori",dtil)le tackless coating after d . ~ ution of the water soluble film. For eAdlllr ~ pressure sensitive masses may be so pachaged by using a lamination of an ethylene vinyl acetate coating on the polyvinyl alcohol film.
The tl, k.,ess of the film utilked generally varies between about 0.1 mil to 5 mil pl~ldbly 0.5 mil to 4 mil. The tl, k.,ess of the particular film also varies depending upon the te",perdlure at which the molten adhesive is pumped or poured into the plastic film cylinder. The particular viscosity at which the adl,e:,;ve can be introduced into the plastic film cylinder will vary depen~ ,9 on a variety of factors induding the pumping capacity of the pump the strength of then plastic film and the like. Visco~i~ies in the range of 1 000 to 200 000 cps pr~f~.dbly 2 000 to 100 000 may be utilized. I IuJ elcr we have found that the most p,t:fer~ed viscosity of the adhesive which is to be pa l~aged in accordance with the invention is b~tv een 10 000 and 50 000 cps. It will be l~coylli~ed that the l~",pe,dture at which an adhesive ~r"pos;tion will exhibit this viscosity range will vary from one adhesive to another. In the case of adhesives which obtain their viscosity within the tenlpe,dlure range of 110 to 130C, film thicknesses of about 1.25 mil are preferred; while for adhesives which exhibit this viscosity at temperatures of 130 to 150C, films of about 1.5 mil are plt:f~ d.
The heat sink may colllplise any means which will effectively and rapidly remove o~ absorb the 5 excess heat from the entire surface of the film which is in contad with the molten hot melt adhesive colll~.osition so as to prevent the lelll~eldlure of the film from exceeding its melting point even though the molten hot melt adhesive temperature is higher than the film melting temperature. Suitable heat sinks are provided by spraying the surface of the cylindrical plastic tube with cooled water or other ~rligel~lll means such as chilled glycol, liquid or g~seous nitrogen, colllpl~:ssed carbon dioxide or the like. The spraying may be accomr' hed, for exdr,l, 'e, using a series of spray nozzles aimed at the mandrel or a water or cooling ring or series of rings may be positioned around the mandrel so as to provide a curtain or ca~cade of water or r~:rliger~lll around the entire circumference of the cylinder.
As ~liscussed above, the molten adhesive is generally poured or pumped into the film cylinder at a tel I Ipera~ure at which the molten adhesive exhibits a viscosity of 1,000 to 200,000, pr~re, ~tly 10,000 to 50,000 cps. This lellq~er~lure will generally vary from about 110 to about 150C depending upon the particular adllesive. Since the adhesive is pumped or poured continuously through the mandrel into the film cylinder, it is possible to void and then cut the continuous filled tube into individual callridges at virtually any desired length. In general, the individual cal ll idges are produced in a variety of sizes ranging from about three inches to 18 inches in length and varying in weight, depending upon length, from about 20 0.5 to five pounds.
After filling, the adhesive cdll~idges, either individually orin a connected series, are further cooled in a water bath to ambient t~lllpelal-Jre so as to dissolve the film and solidify the adhesive. Depending upon the water soluble material used in the film, the film may begin to sepdldt~ from the adhesive and dissolve within about fifteen minutes after being placed in the water bath in which case any residual film 25 remaining after cooling can be removed by placing the adhesive cdlllidge in water of about 60C prior to bulk packaging. Some films may not be soluble in the cold water bath and, in such cases, when -- ` 215~497 removal of the plastic film is desired the s ' ~ ed packages are submerged in room temperature of slightly heated water until ~iss~ tion of the film occurs. In either case any residual amounts of film which remain may be readîly removed by passing the pa._hdges through a series of rotating brushes or using other scrubbing me.;l,ani;",ls. In the e",bodil"enl wherein the film co",prises a non-water soluble 5 component the It:fll_ ,9 film may be readily removed from the chilled water bath and may if desired be recycled. This emba 'i ~e~l has the additional advantage in that less of the water soluble polymer is present in the water bath thus pr~!an~' ,g the useful life thereof and producing less dissolved matter in the water when it is d:~rosed of. The pa- l~ges are then dried either under ambient condilions or using hot air knives or the like.
In the case of non-pressure sensitive adhesives the resultant ii~dividually packaged hot melt adhesive cd,llidges can be stored handled and used directly. In the case of pressure sensitive adhesives the s 'i~'i'ied adhesive ca,llidge may be treated with an anti-stick agent such for eAc",l~'e as by dipping or spraying with molten wax or other non-tacky cor"pdlible coating.
The resultant hot melt adhesive ~,l,idge may be pa._kaged in a conbiner to reduce its exposure 15 to the env;.on",enl moisture or other contaminants. The container or other v~"~pp ,gs would then be removed by conventional procedures prior to utilkation of the hot melt adhesive.
A prer~"ed e",L~ ' "ent of the method of the invention described herein is illustrated in Figure 1. In the Figure the water soluble film (1) is passed through a series of idler rollers (2) which smoothes the film and controls the tension across the web. The film is then ll"~aded into a film folder (3) which 20 folds the film and forms a lap seal around a one to four inch d;d",~ler fill pipe or mandrel (4). The lap seal is sealed with hot air (5) induction sealing or ultrasonic welding and then may be further sprayed with cooling air to set the seal.
After the seal has set the tubular film is carried along the exterior of the fill pipe p~rerdbly using a series of spreader rings (6) film guide(s) (7) and drive wheels (8) until it reaches the end of the fill 25 pipe at which point the molten hot melt adhesive pumped from a remote holding container through the mandrel enters the cylindrical tube (9). If desired in order to maintain the desired molten viscosity the 2151~97 .

hll pipe may be insulated or jacketed as with double walls and filled with inlet and outlet ports (10) through which heated water, steam or mixtures thereof may be circulated, so as to prevent premature cooling of the molten adhesive in the mandrel and melting of the plastic film on the mandrel. The double wall construction also ~ s con~r'~' ~ deaning and purging of the mandrel after the filling operation is completed.
During filling, the tubular package is in contact with cooling water (11) or other refrigerant medium. This water contact may be acco,l, ' hed using a series of water 3ets positioned around the circumference of the cylind-ical tube. Altematively, a water or cooling ring (12) or series of water or cooling rings may be positioned around the mandrel. It will be recognized that while the term "spraying with coolant" is utilked herein, the invention also cort~"lpldles carrying out the entire filling opeldlion in a cooled env;.onllælll as in the pl~:sence of liquid nitrogen.
Suhsequently, the adhesive filled tube is passed through voider rolls (13) which crimp or pinch the continuous filled cylinder into smaller cd,(,idge sked seyllæn(s and which are set so as to assure the proper Cdl Uidge length. Spraying with coolant is continued through additional spray nozles (14) until the pa-,hage is sufficiently cooled so that the pa~ ged adhesive forms a self-seal formed at the voided porbons. The cdlt,idge pa~ ges may then be cut at the voided area using conventional means, e.g., "e.,han - ' scissor (15), laser cutter, water jet or a heated knife or wire and subsequently cooled to room telllpe.d(ure in a water bath. Altematively, the voided but uncut call,idge segments, still attached in serial form may be cooled and cut Uleredrl~r.
As cliscussed above, the film may be dissolved in the cooling water bath itself or may be subsequently dissolved in a sepaldle water bath prior to final pa-,h~ 9.

~ 215~497 ` While the invention has been specifically described with respect to the continuous hlling of adhesive cartridges claimed in U.S.-ar~ n Serial No. 07/993,890, it is equally adapt ''e to the method described in pending f~rP'~ n Serial No. 07/883,994, wherein a mold, preferably a mesh screen mold, is lined with the water soluble film and the molten adhesive poured therein all the while ,l ,la;" ,9 the mold in contact with a heat sink.
In accordance with the latter embodiment, the mold into which the the""oplaalic film is placed and into which the molten adhesive is to be poured may comprise any rigid, self-supporting material The molds are generally forrned from rigid plastic, e.g., acrylonitrile/butadiene/styrene polymers or polypropylene orfrom metallic s(Jbslldles. Since it is desirable to keep the film in direct contact with the water bath after filling, the use of pe,tu,dled or otherwise apertured molds is desired. A particularly preferred mold is formed from steel mesh. The size of the mold varies according to the size of the desired hot melt adhesive block. In general each mold is app,uxi",dl~ly 3" x 3" x 11" in di",ension and often a series of molds are formed from one contiguous plastic m -'lulosic or metal sheet.

Fur~er details of the pl~,f~l~d çmbotlimP.nt~ of the invention are ;llustrated in the follo~nng F,Y~mples. The Exarnples are p~so~ d for the ~ ose of illusl~ation of the invention and are not intPn-lP, i to be l;...;l;~ of the invention as defined in the appended claims.

A conve~ltiohal pressure sensitilc hot melt adhesive co",position suitable for dispcs.''e ar F ' - 'i~ ns was p~ ~:pared using a ta ,hilied and pl ~ ; ed blend of ethylene vinyl acetate copobmer and wax.
A continuous supported cylindrical tube was formed by vnat~,~ ,g a plastic film co~prising a 1.2 mil p olyvinyl alcohol film around a 1.5 inch d;d",t:ler insulated mandrel or fill pipe. After the lap seam was formed, it was sealed using hot air and then set by spraying with ambient l~llq)eldlure air.
The molten hot melt adhesive, at a viscosity of 10,û00-15,000 cps. (120-130C) was pumped therein through a nozle while the entire surface of the film was sprayed with chilled water (5-1 0C). The filled tubes were voided at lengths of 6 inches and then cut to form individual cartridges. The resultant ca,l,idges were allowed to cool in a chilled water bath until they had co"., '~t ~y s 3 '~e~l The resultant cd,l-idges were lldllat~ d to a hot water bath (about 65C.) where the film was dii,solved and the blocks then removed, dried and packed in dp~JIuplidle shipping co"l~ 1e,a.

., The procedure of Example 1 was repeated to package a pressure sensitive hot melt adhesive composition suitable for can/bottle labelling app'i~ ns.
After transfer to the hot water bath, the film was d;ssolved, the adhesive removed, dried and then 5 passed to a tank COIlbdi~ 9 a molten COlllr ~ !e wax material. The block was dipped into the tank, the surplus material allowed to run off, dried and packed to the shipping container. The outer coating thus fommed a non-tacky wax coating co"lF "' !e with the adhesive.

The procedure of Example I may also be repeated using film which consi~ts of low density 10 polyethylene film with a strip of polyvinyl alcohol film adhered to one side wherein the polyvinyl alcohol strip co",prises about 20% of the surface area of the film. After, ~;~ sn'ution of the polyvinyl alcohol portion of the film, the remaining low density polyethylene may be readily peeled off the caill idge.
Testing of the resultant ca,l,i~ges indicates that the adhesive properties of the adhesive blocks are ~"drr~l~d by the filling and pac~ "9 process. Similar results would also be obtained when 15 packaging other hot melt adhesive forrnulations.
Although prGrG~ d embo~ x of the invention have been described herein, it w~ll be lm-l.orstood by those skilled in the art that variations, modifications, and equ;valents may be made thereto wi~ ul departing from the sp~r~t of the invention or the scope of the appended claims.

Claims (13)

1. In a process for the packaging of molten hot melt adhesive in a film cavity wherein the adhesive is filled into the cavity at a temperature above the melting point of the film and wherein the plastic film cavity is in direct contact with a liquid or gaseous heat sink the improvement which comprises using as the film a heat sealable film at least a portion of which is water soluble.

2. The process of Claim 1 wherein the water soluble portion of the film comprises polyvinyl alcohol modified starch or cellulose.

3. The process of Claim 2 wherein the water soluble portion of the film comprises polyvinyl alcohol.

4. The process of Claim 1 wherein the entire surface of the film comprises polyvinyl alcohol.

5. The process of Claim 1 wherein the film comprises a lamination of a water soluble film laminated to a non-soluble coating.

6. The process of Claim 5 wherein the film comprises an ethylene vinyl acetate coating on a polyvinyl alcohol film.

7. The process of Claim 1 wherein the cavity comprises a cylindrical tube of the heat sealable film.

8. The process of Claim 1 wherein the molten hot melt adhesive is filled into the cavity at a molten viscosity of 1 000 cps. to 200 000 cps.

9. The process of Claim 1 wherein the film is present in an amount of 0.2 to 1.0% by weight of the adhesive mass.

10. The process of Claim 1 wherein the hot melt adhesive is non-pressure sensitive.

11. The process of Claim 1 wherein the hot melt adhesive is pressure sensitive and wherein the adhesive mass, after dissolution and removal of the water soluble film is coated with a compatible non-tacky coating material.

12. The process of Claim 1 wherein the molten adhesive is poured into the film cylinder at a temperature of 110-130°C. and wherein the thickness of the film is 1.25 mil.

13. The process of Claim 1 wherein the molten adhesive is poured into the film cylinder at a temperature of 130-150°C and wherein the thickness of the film is 1.5 mil.