CA1127061A - Process for preparing retort-proof laminates for packing foodstuffs - Google Patents

Abstract

ABSTRACT OF THE DISCLOSURE
A process for preparing a retort-proof laminate for packing foodstuffs which comprises laminating an aluminum foil or sheet with at least one polyolefin film selected from the group consisting of high-density polyethylene, poly-propylene, ethylene-propylene copolymers and polybutene films using as an adhesive a specific polyolefin resin in melted state prepared by using together (A) at least one member selected from the group consisting of high-density polyethylene, polypropylene, ethylene-propylene copolymers and polybutene, (B) maleic anhydride and (C) aluminum hydroxide.

Description

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This invention ~elates to a process for preparing a retort-proo~ material, particularly laminate, for packing foodstuffs. More particularly, it relates to a process for preparing a retort-proof packaging laminate using a polyo~efin resin as an adhesive in a coating or sheet form thereby enabling the laminate to be produced at a high lamination speed and t~
retain excellent bond strength even after being heated in a retort, the polyole~in resin being produced by using together maleic anhydride, aluminum hydroxide and polyolefin selected from the group consisting of high-density polyethylene, polypropylene, ethylene-propylene copolymers and polybutene.
With the recent diversification and upgrading of dietary life as well as the recent use of pre-cooked food-stuffs, foodstuff packaging laminates have been in remarkably increased demand and various such ones are being used. In particular, there is an increased demand for foodstuff pack-aging laminates which enable foodstuffs packed therein to be sterilized at high temperatures, such packed and sterilized foodstuffs being called "retort foodstuffs" for convenience sake.
It is generally required that foodstuff packaging laminates having the following basic properties: (1) they must not be toxic and are hygienically satisfactory since they have many opportunities to contact directly with foodstuffs,

(2) they are satisfactorily impermeable to gases or the like to permit foodstuffs packed therein to keep their flavour and taste unchanged for a long time (such impermeability being hereinafter sometimes referred - '' , l~Z~7~6~

to as "barrier propertyn), (3) they have ~ati~factory light-intercepting property to pre~ent foodstuf~s packed therein ~rom degradakion and denaturalizatio~ due to radiation o~ ulbravlolet light or the like~ (4) the~ ha~e high mechanical strength and ~atisfaotory impact ~tre~eth~
(5) they are highly rssist~nt to water and chemlcals ~uch as acids and alkalies and (6) they ha~e good heat ~ealability and may be thermally b~nded under pre~sure in a ~ery short timeO In addition~ (7) they are re~ulred to have good heat resistance and (8) required not to degrade ~n bond strength and the like when foodstuffs packed therein are subjected to sterilization in a retort (for example, they mu~t not degrade in properties ~hen contacted with water, acids~ alkalies~ oil~ or the like at high temperatur0~) ~ince they are to be sub~ected to hi~h--temperature sterllizatian at usually lOQv 140C for several ten seconds to several ten minutes.
It is difficult bhat plastic ~ilms or the like alone will meet such ~evere requirements; thu~ composite films or the like are used as foodstuff pscklng material~.
The component~ of the composite mater~als for ~acki~
~oodstuff~ include polyolefin, polyamide, polye~ter and aluminum and~ i~ many case~, combinations of a~ aluml~u~
foil or sheet having particularly excellunt barrier property with a hygienlcally ascellent polyole~in film ar~ used as retort-proo~ packing or packaging materlal~
for foodstuffs. Alu~inu~ foil~ ar~ genera~ly used ~or lamination with poly~ter ~lms or the llke. A~o~g polyole~in ~ilm~ are preferred high~den~ity polyethyle~e~

3 polypropylene, ethylene-propyle~e Gopolrmer~ and - 3 .

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polyb~tene ae retort-proof packlng materials for foodsturf~
becauae of their heat resi~tance.
~ oodstuff packaging laminate~ are requlr0d ko be ~uch as follows. When they are manu~actured industrinlly~
(1) they may be obtalned at a high productio~ ~peed ~thab i~g they may be bo~lded together in 0.5 to sever~l ~econdo)3 (2~ they have high bond or adhesio~ ~trength be~or~ ~nd after being heated in a retort even when they have been bonded together at a high speed9 and they will not decrea~o in bond strength durin~ storage after they are packed with foodstuffs and heated in a retort and (3) they will not produce any extracts or material~ which raise problems às to sanitation.
Tha operation of lamination for producing ordinary foodstu~f packagi~g lam~nates is co~ducted at a lami~atio~
speed o~ 50 - 100 m/min. and it is desirable that the retort-proo~ laminates for packing ~oodstuf~ be pro~uced by la~inatio~ at such a lamination speed as abo~e.
It is generally known that high-den~ity ~ polyethylene, polypropylene~ ~thylene-propylene copolymer~
polybutene ~nd other polyolefins are useful a~ ~ood~tuff packing materials because o~ excellence in sanitatio~ and the like~ howe~er9 they are not easily used because of hlgh cry~tallinity and non~polarity thereby exhibiti~g hardly any adhesiveness to other material3. To eliminata these drawbaoks~ the abo~s pol~ol~fi~s are sub~ect~d to ohemical and phy~ical treatments or tr~ated by the - radiat~on of ultraviolet light~ electronic beam~ or t~e like. More particularly~ ~1) chemical treatme~t~ o~ the 3 polyolefins with aulphuric acid-chromate or the li~ are : - 4 -. ~

certainly e~fective if they aro con~cted at elsvQt0d temperature~, however, these treatments ~re not efflclcntly conducted 3inc~ they are of wet type and corrode the reaction apparatuses used duo to bhe u~e of an AC~d or acids~ Therefore, these treatment~ are ~ow co~ducted only for basio studies in attempts to lmprove the adhesiveness of polyolefins. (2) Copolymers of polyolsrins ~ith a ~-ethylenically ~nsaturated carboxylic acids (such as acrylic acid~ methacryllc acid and malaic anhydride) as well as esters there~f~ are tsied to be ~sed as an adhesive in a ¢oating or film form for bonding polyole~in to other - matarials. In this caset however, either only a very low bond strength is obtained or a time ls t~ken te heat ~nd dry and a pressure is needed even ~ a satisfactory bond strength be obtained a~d9 further, primers are used i~
many cases to accelerate adheslon. ~(3) Coro~a dischar~e-treated polyolefin ~ilm~ are widely used or i~du~trial - p~rpose~ but, in thi~ case, the improvement ln bond strength is limitad and an adhesive is additio~lly use~.
As mentloned above, there are carried out few industrlal proce~ses for modi~ying or re~orming polyolefin itself to make it highly adhesive~ In truth, polyurethane resins a~d the like are widely used as adhesives i~ ca~es where ~ highly secure bond is ~ecessary between polyolefin ~il~s and other materials.
Ho~ever~ polyurethane resins are said t~ have the following di advantages~ it ~s probable that the u~re~cted ~isocyanate and polyol as well as low polymer~
remaining in the polyurethane resins are tra~sferred to 3 th~ foodstuffs packed 1~ the packing materlals ~herei~

the polyurethane resins are used, thereby raising sanitary problems. (2) It takes about one week at ambient temperature or at least one day at 50 - 60C to obtain, by aging, a practically useful bond between packing materials i~ they are metallic or plastic (resinous) films. (3) Foanting is caused in an adhesive used between polyolefin and other material for bonding them together, thereby producing non~uniform bond strength throughout the bonded portion and depreciating the commercial value of ~he resulting product. Although the polyurethane resins have the aforesaid disadvantages, they are now still used since no other materials useful as an adhesive - for polyolefin are now not available. Thus, there have bPen sought polyolefin resin packing materials which are free of sanitary problems and produce satisfactory bond strength by a short-time treatment or foodstuff packing materials in which are used polyolefin resin-containing adhesives capable of ef-fecting a secure bond therewith between polyolefin and other material.
It is also known that polyolefin resins incorporated with a metal compound are used in laminating the materials to-gether in the field of building or construction materials or packaging materials. In addition, the following metal ion-crosslinked polyolefin resins are considered as a kind of `~ thermoplastic resin (ionomer) wherein the long-chain molecules are connected to each other by means of ion linkage. Structur-ally, the ion linkages between the long-chain molecules are ~- produced with aid of the monovalent or polyvalent metal cations and the carboxyl groups of the long chain molecules.

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The compositions and uses of co~entlonal )~l~ rc~
ihnnwlvr~ are disclosed in literature a~ indicated below~
In USP 3,264,274, R. W. Ree~ disclo~e~ ionic copolymera obt~ined by reacting a copolymer o~ an a-olo~ln and an ethyl~nically unRaturated monocarbo~ylic acid w~th a mono~alent to trivalent metal ion and al~o dlsclo~s~
ion crosslin~d~copolymers obtained by reacting a copolymer of an a-olefin and an ethylenically unsaturated dicar~oxylic acid with a monovalent metal ion. In addition, in the same USP specific~tion, he t~aches that th~ io~-cros~link0d copolymers are useful a~ adhesive~ and they may be laminated on paper, metal foil~ and plastios and also teaches that it is inappropriate to react the copolymer of ~-olefin and a,~-ethylenically unsaturated dicarbo~ylic acid ~ith the poly~alent metal ion.
In Japanese Pa.tent Gazette No. 19238/77~
K, Shirayama et al tcach that a resin eompoqition is u~eful as an adhesive in forming laminates o~ polyole~i~
with a metal~ the resin composition being prepared by react~ng a crystalline polyolefin with an unsaturated aliphatic carboxylic acid and~or a~hydridc thareof a~
well as with the oxide and~or sulphate o~ a metal of Groups IIa, IIIa and I~b of the Periodic Table a~ a temperature higher than the melting point of ths pclyolefi~.
In Japanese Patent Laying-Ope~ Ga~ette No. 37494/7~ ~. Shirayama et al di6close a polyol~fin composition prepared by reacti~g polyolefin ~i~h an un3aturated aliphatic carboxylic acid and/cr anhydride thereof as well as ~rith the hydroxide or alcoholate o~
3 a metal of Groups Ia, IIa, IIIa and IVb of the Period~c ~ 7 ~

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Table at a temperature higher than the melting point Or the polyole~in~ and they also disolose that the polyole~in composition ~o prepared exhibit particularly e~cellent adhe~ion to polyole~in moldings, ~luminu~, iron~ copper~
zinc and the like and teach that the compo~ition may be used as an adheslYe in laminating a synthetic resin with a metal.
In Japanese Patent Gazette No. 17971/729 I. Ai~i~a et al disclose a proces~ ~or a feasible thermopla~tic monoolefin polymer by reacting a the~moplastic monoolefin polymer with (a) a radically po}ymeri~able carboxylic acid~ (b) a radical initiator and (c) the oxide, ~ydro~ide or carbonate of lithiu~
potassium~ sodium~ magneslum~ calclum, zi~c, aluminum or ~ilicon~ at an elevated tempera~ure in the presence Qr . ~ abse~ce of a solve~t or medium. The feasible thermoplastic - monoole~in polymer so obtained may be used in the product~o~
of injectio~ molded articles, vacuum molded articles and the like without a decrea~e in impact strength and creep characteristlcs.
In Japanese Patent Laying-Open ~azette ~o. 27580/74, I~ Iwami et al dl~close laminates 1~ which the metal ~nd the ethylene-copolymer interpose a metal~
co~taining copolymer therebetween, the ethyle~ic copoly~er being a copolymer of ethylene~ an a,~ ethylenically un~aturated carboxylic acid, an a~-ethylenically unsaturated carboxylic acid ~etal salt and, i~ desir~de an a,~-ethyle~icallr unsaturated carbo~ylic acid ~ster.
The laminates 80 disclosed are used in communication 3 cables.

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~t7~1 In Japanese Patent Laying-Open Gazetta No~ 7~583/73, T. Fujimoto e-t al teach packing materials which are steriliz-able at a high temperature under pressure and have a~ the inner layer a film prepared from a composition consisting of high-density polyethylene and ionomer. Th~ Gazette also teaches that Surlyn (trade mark: ionomer produced by E~I.
Du Pont) may be used as a retort-proof packing material for foodstuffs. However, the lonomer-incorporated film is lam-inated by means of dry lamination using an urethane type ad-hesive.
It is not known in any event that polyolefin resins prepared by using together a heat-resistant polyolefin, maleic anhydride and aluminum hydroxide, are very useful in the pro-duction of retort-proof packing materials for foodstuffs and have excellent adhesiveness and capability of being treated at a high speed.
~; The primary object of this invention is to provide ,:~
- a process for preparing retort-proof, foodstuff packaging laminates which may be produced at an excellently high pro-duction speed and may have excellent bond strength even after being heated in a retort, using as an adhesive a polyolefin resin (hereinafter sometimes referred to as a "specific polyolefin resin") prepared by using heat-resistant polyolefin, maleic anhydride and aluminum hydroxide together in laminating an aluminum foil with a film of polyolefin such as high-density -polyethylene, polypropylene, an ethylene-propylene copolymer . .
or polybutene.
The present inventors have found that specific _g_ 6~

polyolefin resins prepared ~rom heat~resistant polyole~in, maleic anhydride and aluminum hydroxide in combination are very effective in the production of retort-proof, foodstu~f packaging laminates. On the other hand, when a polyuretharle adhesive is used, the lamination might be conducte~ at a somewhat high lamination speed but the aging of the laminates 'is necessary after the lamination whereby as compared with the present invention it takes a considerable time to obtain packaging laminates which will exhibit satisfactory bond strength when used. Such high-speed lamination and post-retort (this term being intended to mean "after heating in a retort" throughout the specification') high bond strength will not be obtained by the use o~ polyolefin resins, which are other than the specific ones used in this invention, prepared '15 by reacting polyolefin with maleic anhydride, by using to-gether polyolefin, an ~, ~-ethylenically unsaturated car-. boxylic acid other than maleic anhydride and aluminum hydroxide - or by using together polyolefin, maleic anhydride and a metal compound other than aluminum hydroxide.
The polyolefin (A) which may be used in the invention is a heat-resistant polyole~in and includes high-density poly-ethylene produced by low pressure polymerization, an ethylene-propylene copolymer produced by low pressure polymerization, high-density p~lyethylene produced by medium pressure poly-merization, an ethylene-propylene copolymer produced by medium pressure polymerization, a highly crystalline polymer such as isotactic or syndiotactic polypropylene, or a low crystalline polymer such as atactic polypropylene.

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Polybutene of any crystallinity may also be used irrespective of the fact that it varies in crystallinity from low to high depending on its tacticity. Ethylene-propylene copolymers may further be used, whether they are random ones or block one~;
however, propylene-rich copolymers are preferred since the ethylene-propylene copolymers are required to be heat re~is-tant. Each or both of these olefins (ethylene and propylene) may be polymerized with a third copolymerizable component to produce a copolymer or terpolymer which may also be used and preferably selected depending on the purpose for which it is used.
- The ~ ethylenically unsaturated carboxylic acid used in the present invention is maleic anhydride (B). As compared with other ~, ~-ethylenically unsaturated carboxylic acids, maleic anhydride may easily graft copolymerized with : the polyolefin (A). Further, the specific polyolefin resins obtained from the thus produced graft copolymer may be used in the preparation of the packaging laminates having excellent post-retort adhesiveness.
Maleic anhydride (B) is used in amounts of 0.01 -30 parts by wei~ht per 100 parts by weight of the polyolefin (A). The use of maleic anhydride in an amount of less than 0.01 part by weight will result in the production of a poly-olefin resin which when contained as a retort-proof adhesive in a laminate packing an edible oil, acetic acid or the li~e therein, will not enable the laminate to have excellent post-retort bond strength, whil~ the use of maleic anhydride ln an amount of more than 30 parts by weight will not axhi~it ~urther increa~ed bond strength when u~ed as an adhesive.
The metal compound (C) used in the pre~enk in~ention i8 aluminum hydroxide . The compound (a ) 19 u~ed ~n an amount of 0.05 - 10 parts br welght per 1~0 pa~te by weight Or the hea~-resistant polyolefin (A~ 7 this resulting in the production of a specific polyolefin resin which will - exhibit high bond 4trength whe~ subjected to heatin~ for 003 - 5 ~econds and will not decrease in bo~d strength with the lapse of time a~ter a retort teRt~ The use of less than 0.05% by weight of the metal compound (C) will make it difficult for the resulting speci~ic polyol~fin resin to ha~e high bond strength by being heat treated for a short time as indicated above~ while the u~e o~
more than 10 parbY by weight of the compound ~C) w~
~ot exhibit increased bond strength when heat treated ', and will allow the resulting polyolefin resin to foam when heated and melted thereby rendering it impos~ible to coat the r~sin uniformly on a sub trate.
A hlgh-speed operation may be attalned by u~in~ ¦
aluminum hydroxide as tha metal compound~
The specific polyolefin resin ~n which alwmi.~u~
hydro~ide is used) may be me~t laminated seeurely on an aluminum foil or sheet at 180 - 220C ~or abou~ one se¢ondO ', An exampl~ of ~n industrial prooess ~or prepar~g r~tort-prG~f, foodsturf packagi~g laminate~ i~ a~ follow~s A ~peci~ic polyolefln resin in molten otate is 3 extruded into betwee~ an aluminum foil and a heat-re~i~t~

t~

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polyolefin film, and the whole is passed through between heating rolls for heat treatment thereof to prepare a retort-proof foodstuff packaging laminate, in this case, the use o~
the specific polyolefin resin enables such packaging laminates to be produced at a high production speed.
If metal compounds other than aluminum hydroxide, such as aluminum oxide, aluminum sulphate, aluminum acetate, sodium hydroxide, calcium hydroxide, iron hydroxides and zinc hydroxide, be used in the production of a polyolefin resin then the thus produced polyolefin resin after heat treated, will not exhibit satisfactory post-retort bond strength even if it exhibit satisfactory pre-retort (this term being intended to mean "before heating in a retort" throughout the specification) bond strength.
Such heat-treated polyolefin resins are disadvan-tageous in that they will not exhibit satisfactory bond strength when tested under severe retort conditions and will decrease in bond strength when they are used in producing a ~` packaging laminate and the thus produced laminate is subjected to a long-term preservation test after packing some material in the laminate.
Some metal compounds other than aluminum hydroxide, which have been reacted with the compounds (~) and (B) to produce a polyolefin resin, will enable the thus produced polyolefin resin to have satisfactory post-retort bond strength if the resin is heat treated for a lon~ time, how-ever, they will not if the resin is heat treated for a short time, this being very i~

, d~sadvantageou~ from the view-point of operational spe0d.
I~ other words~ the operatio~al speed will have to be decreased in the case with a metal oompound o~her t~an t aluminum hydroxide i~ in this c~se the ~ame bond ~trongbh as obtainable iu the case with aluminum hydroxid0 i~
desired and, further, the heat treatment for a long tlmo may adverse effect~ (such as degradation and denatural~æatlo~) o~ the polyolefi~ resin depending on the ~ind Or th~ ¦
starting polyolefin (A).
In the 9y~the8i9 Df a specific polyolefi~ resln 5 ) ~

according to the present invention by~G~Y~ky~ the compounds (A) 9 (B) and (C) together, a third co~ponent such a~ polybutadiene may be used. In this case, the third compon~nt sel~cted must be such that it ha~ no adverse e~fects on the hrgie~ic aspect, heat reslstance, adhesiveness and the like of the resulti~g specific resi~O
The ~pecific polyolefin resi~ used in the present ~nventio~ may be prepar~d by a few methods comprising heating, mixin~ and other steps. The ~ preferable methods are as illu~trated below.
(1) A method comprising adding the compound (C) to a heated mixture o~ the oompounds ~A~ a~d (2~ A method comp~isi~g addin~ the compou~d (B) to a heated mi~ture o~ the compounds (~ a~d ~C)~
(3) A method comprising adding a heated mi2t~ro of the compounds (B) and ~C) to the comp~d i~
heated ~tate, and

(4) A method comprislng mi~lng the compounds (~

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(~) and (C) togeth0r and heating tho resulting mlxtura.
The order in whlch the compQund~ tA) ~ ~nd ~C) are added and ml~d i9 ~ot l~mlted to th0 abov0) ant, in addition to these adding and mixing, r0ac~ions i~
which other enorgy souroes are used ~ay be employ~d.
. By using any one o~ the aforesaid method~ thc specific polyolef~n resins accordin~ to the prcR~nt invention may ba easily obtained. Further, the afore~aid ~our methods ~ay be carried out using sufficient heat to melt the compounds or using a solve~t to di~solve the compounds thsrei~.
For exampls~ the method (1) using sufficlent heat ~o melt the compound~, comprises melt ~ixing the heat-re~istant polyolefin ~) with maleic anhydr~de (B) at a temperature 10 - 100G hlgher than the ~oftening pol~t of the polyolefin (A) by the use of heating roll~
or an extruder and then incorporating th~ re~ultin~
melted mixture with aluminum hydroxide (C~ to obtai~ a ~pecific polyolefin resin. In the above method~ the melt mixing may usually be effected for 5 - 90 minutes~
and the aluminum hydroxide (C) may preferably b~ ~l~e (less tha~ about 1 ~ for example~ in particle size f~r ad~ition a~ it i~, howe~er~ the compound (C) havin~ a larger particle ~ize should ba mi~ed with the other ~ compound~ by a ~uitabl~ ~ean~ to ob$a~n a uniform ~ix~ure~
On the other.hand~ the aforesald methods U~ing a 601vent are advantageou~ in cases where the unreacted materials are remo~ed ~nd tha coloration o~ the product 3 re~in to be obtained ~hould be avoidedO The solve~t~

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used herein generally include aromatlc hydrocarbons ~uch ,~r~de ~ ~I r I
as toluene, xylene and Solvesso tproduced by ~90 Company).
~i For ex~mple~ the polyolc~in (A) and m~lslo ~nhydrlde (~) ln respeoti~e prcdetermlned amount~ aro ~corporated w~th xylena and then graft copolymerized in the preoenc~ o~
benzoyl peroxide (BP0).
In a ca~e where the compounds (A) and (B~ are to be mixed together~ maleic anhydrida (B) may be wholly added at a time to the compound (A) or ma~ be dropwlse added thereto. The latter is advantageous in that by-products will be produced in le8g amounts and the sp0cific polyolefin resin to be ~inally obtained will have more satisfactory adhesivenessO Tha mixing under heat may ba effected a$ 130 - 134C for 30 minutes to 3 hours~ It is desirable that the gra~t copolymer of the compounds (A) and (B) be washed thoroughly.
The graft copolymer is then incorporated with aluminum hydroxide (C) and haated for 15 - 60 mi~utesO
. It is desirable in this case that the aluminum hydroxlde (C) be swollen with, and dispersed int a small amount o~
methanol~ acetone, water or the like to form a dispersion which is then mixed uni~ormly with a solution of th~
resin (graft copolymer~.
The specific polyolefin resin is stric~ly r~quired $o be hyg~enically safa for use a6 an adhcsiv~
in foodstuff packaging lamina*es. Thu5, it i~ desirable that a specific polyolefi~ resin to be obtained be washed thoroughly ~Jith acetone, methyl ethyl ketone~ ethyl aeetate or the like during and after its synthe~i~. Tha specific 3 polyolefi~ reRin 60 obtain~d has hy~ienic safe-ty and , .

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excellent adhesiveness.
As previously stated, lOQ parts by weigh~ of the polyolefin (~) 0.01 - 30 parts by weight of maleic anhydride (B) and 0.05 - 10 parts by weight of aluminum hydroxide were used together to obtain the specific polyolein resin on which about 0.01 - 1% by weight of maleic anhydri~e (B) i~s graft copolymerized, it is desirable that the unreacted maleic anhydride and low molecular weight, maleic anhydride homo-polymers be removed thoroughly since they have otherwise ad-verse effects on the hygienic aspect and adhesiveness of the product resin. In addition, the whole of aluminum hydro-xide (C) used is not necessarily crosslinked with the grafted ` - maleic anhydride. In other words, the aluminum hydroxide may partly or wholly be dispersed in, or reacted (cross-linked or coordinate bond) with the graft copolymer.
~ The specific polyolefin resins so produced may be ,` used in the following various manners. They may be dis-solved or dispersed in xylene, Solvesso (produced by Esso Company), kerosene or other organic solvents, water alone, or a mixed solvent prior to their use; they may be extruded onto a substrate by the use of an extruder to coat the sub-strate therewith, they may be formed to films which are then laminated on a substrate or inserted between two substrates, they may be coated on a substrate to form a coating which is ~5 then laminated with another substrate, or they may be formed to films which are each laminated on a film and then laminated with another substrate; they may be coated in powder form.
The specific polyolefin resins are used as an adhesive layer or in the form of a plastic film.
; 30 The retort-proof, foodstuff packaging laminates /

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o~ the present invention con~i~t as~entially of (1) an ~luminum foil or ~h~et, (2) a high-density poly~thylene film, polypropylene ~llm, ethylene-propyl~ne oopolymer film or polybutene fllm and (3) tha ~pecl~ic polyolerln resin according to the presen~ inventio~ as an adhe~ive in a coating or sheet ~orm. The laminate~ a~e illu~trated by aluminum foil (outer layer~/~pecific polyolefin resin/polypropylene (inner layer), aluminum foil (outer layer~/~pecific polyole~in resin/high-de~sity polyethylene . 10 film (inner layer)~ polyamide film (outer l~yer~/aluminum foil/specific polyolefin resîn/polypropylene film (inner layer), polyamlde film ~outer layer~/aluminum foil/~pecific polyolefin resin/high-density polyethylene film (inner layer), polyester film ~outer layer)/alumi~um ~oll/~pecific polyolefin re~in/polypropylene film (lnner layer~, polyester ~ilm (outer l~yer)~alumlnum foil/~peoific polyolefin resin~high-density polyethylene (inner layer)~
- polye~t~r ~ilm (outer layer)~alumi~um foil/~peciflo polyolefin resinJethylene-prop~lene copolymer ~ilm (inner layer), polye~ter film (outer film)/aluminum foil/specifio polyolefln resin/p~lybutene film (lnner film), and polyester film (outer layer)/aluminum foil/~pecl~ic polyolefin resin/polrpropylene s~spensio~ coati~ (inner layer).
Foodstuf~ packaging laminates using there~n th~
~pecific polyolefin film according to the present in~e~tion include retort-proof ~oft packaging laminates ~ompri~
at least one plastic film and an alwminum foil and retort-proof rigid packaglng laminate~ com~risi~g a~
3 aluminum ~heet or the like. T~e pre ent in~entio~ is 7~6~

applicable preferably to the preparation of the retort-proof ~oft packaging laminates which are required to ha~e high bond strength under more savere conditio~s and, in ~act, it makes the preparation oE such e~cellent ~o~b packaging laminates po~sible, In addit.ion, it iB desirable for the packa~ing laminates from the ~iew-point of adhesivene~s that polypropylene film~ ethylene-propylene copolymer film~
and polybute~e films be used as the componen~ films of the laminate in a case wher0 the speclfic polyolefin resin is polypropylene, while hi~h-denaity polyet~ylene films be u~ed as the compo~ent films in a case whare the ~pe~i~ic polyolefin resin i~ highdensity polyethyleneO
The component materials used in the present invention may be lami~ated together i~ the following variou~ manners. As an.example of laminatlon, an aluminum foil or sheat is coated with the sp2cific polyolefi~ resin in melted state and then laminated on the polyolefin re~i~
layer with a heat-re~i~tant polyolefin film. In thl~
laminatio~ of the heat-resistant polyole~in fllm~ ig is not a}ways necessar~ to melt the speci~ic polyolefi~
resin. As another example of lamination~ the speci~lc polyolefin re~in i~ laminated with a heat-resistant polyolefin film and then melt laminated o~ the ~el~ed resin ~ide with an aluminum foil or sheet. ~ a ~urther example~ the 8peci~ic polyolefin resin is lnterposed betwee~ a heat~resista~t polyolefin film and an alumi~um foil or ~heet, after ~hich the three are laminated together at a time.
Packaging laminates ha~in~ high bond ~tre~gth .

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are not obtained only by coating or sUperpo9ing the speciflc polyolefln resln on an alwninum ~oil or ~heet~
in a~y la~ination method, therefore, a aompo6ibe o~ an aluminum ~oil or shQet and the ~p~cl~lc polyole~in re~in coated or superposed thereon or a composit0 of ~n alum~num foil or she~t~ a heat-realstant polyole~ln fllm and th0 specific polyolefin resin interpo~ed therebetween subjected to heat treatment to ~elt the speci~ic re~i~
thereby to increa~e the bond ~trength of the reoultlng l~minate.. The term ~'composite" used herein is întendsd to mean "component materials ~such as an aluminu~ foil or ~heet, pla~tic film~ a specific polyole~in resin and thè
like) ~ust superposed one upon another and not ecurely laminated with each other because of no heat treatment".
.: 15 The heat treatment may be effected by contac~ with heating roll~ or heating plates~ by`the radiation of i~ra-red light or by the use o~ a heatlng ~urn~ce.
In a case where such a composite is obtained by the u~a of an extruder or the like~ it i3 effecti~e from the view-point of operatio~ and heat efficiency to heat troat the composite i~mediately after it i~ obtainedO
The heat treatment with heat~ng rolls or plate~
is mors effective since it makes pos~ible a high-spesd operation, that is ~ a short-time melt adhe~ion a~d also since such haating roll~ or plates ma~ be easily inobrporated 1~ an industrial manu~acturing systein. F`urther, heati~ng by contact with the heating roll~ or plate~ i~ excellellt in heat efficiency and may be eas:Lly kept co~starlt ~l~ereby advarse effacts caused by ~ riatio~l of temperature may be 3 eliminatad. The contact with the heat:Lng roll~; or plates ~ 20 -i8 to m~ce the ~pecific polyolefi~ rasin malt ~dhere to the othar componen-t material. The composite is contacted with the he~tin~ device at the speci~lc polyole~ln ro~i~
~ide or the other compon~nt material, preferably ~t thc aluminum foil or ~heet~ In a method for contacti~ the heating de~ice with the speci~ic polyole~in re~i~, since this re~in is softened or melted~ care must be taken 90 that the ~pecific polyolefin res~n be not trans~erred to the heating rolls or plates. In the practlce of the 10 present inventio~, it is not always necessary to melt tha specific polyolefin resin perfectly although the term ~melt~ is used in the descrlptio~ of lamination i~ the specificatlon. The heating roll~ or plates are preferably o~ rotation type or moving-around type 7 however, they may be of fixed type. ~hey may be cylindrical, semi-cylindrical~ flat or of curved surface in shap~ however~
they are not particularly limited in shape and are onl~ so shaped that they contact with the compo~ent materials (including ths specific polyolefin rssin) ~or a nece~sarr 20 period of time. The preferable heating roll~ are rotata~le and cylindrical ones. Ths heating rolls may be rotated by a drivi~g source, by frictlonal contact with the compo~e~t material~ or by a trackless belt system.
l`he heating rolls or plates may be heated by a 25 hot medium~ an electric heater, i~lduction heatin~, flame or the like . There may be u~ed any heating qourc~s whi ::h heats ~he heating rolls or pla-tes 50 that the~ surface thereof i s kept at a fixed suitable temperature ~ The surface temperature of the heating roll~ or plates ~ay 3 vary dependlng mainly on the kind of the gpecific l~Z7~6~

polyolefin resin, line velocity and contact time, The sur-face temperature may be about 150 to 220C for the specific polyolefin resin in which the polyolefin unit is derived from high-density polyethylene or polybutene and it may be about 180 to 250C for the resin in which the polyolein unit is derived from polypropylene or ethylene-propylene copolymers.
The heating rolls or plates may be made of any satisfactorily heat-resistant material, preferabl~ a metal, and they may also be made of a metal/heat-resistant polymer laminate. In cases where the specific polyolefin resin or other component materials are likely to be partly transferred to the heating rolls or plates, it is preferable that the sur-face of the rolls or plates be a Teflon (trade mark)-treated one.
The methods by which the heating rolls or plates contact with the component materials of laminates to be prepared, will be explained hereinbelow by reference to the accompanying drawing in which:
FigsO 1 - 4 are each a cross-sectional view showing an embodiment of the present invention;
Fig. 5 is a cross-sectional view showing a sandwich lamination obtained by extruding a specific polyole~in resin into between an aluminum foil and a polyolefin film;
Fig. 6 is a cross-sectional view showing melt ad-hesion and infra-red light radiation, and Fig. 7 is a cross-sectional view showing heating by an electric heater.
Figs 1 and 4 show a method using a heating roll -~2-6~L

Fig. 2 a method uqing a heating plate, Fig. 3 a method u~ing a belt type heatlng plate. Numeral 1 indi¢ats~
an aluminum foil or sheet (There may also be used an aluminum foil or sh0e t laminated with a poly0ster res!n or the like although it is not ~hown in the accompanying drawing~), a heat reslstant polyolefin film i~ indlcated at 2, a spe~ific polyolefin resin at 3, a device to coat or laminate the speciflc polyolefln resin at 4, a heating roll or plate at 5, a heating source at 6 and ~ rubber roll at 7. Th~ heating source 6 ls shown in ~ig. 1, a heating medium in the roll in Figs. 3, 5 and 6, flame in F~g. 2 and an electric heater in Fig. 4.
Rapid heating may be effected by the us0 of the heating roll or plate 5 because Or heat conduction. This is an e~icient heating method~ If neces~ary, the heating roll or plate 5 capable of rapid heating9 the lnfra-red light radiation de~ice and a heating ~urnace 8 may be u~ed in combination. The infra-red light radiation de~ice andJor the heating furnaoe 8 may be used simul-taneously with, or after, the use of the heating roll or plate 8 in melting and adhesion. The combined use o~ the heating roll or plate 59 the in~ra-red light radiation device and/or the heating furnace 8 is effectiv~ in for~ing a specific polyolefin r0sin c~ating in a large thickne~0 Figs. 6 and 7 are each a cross-sectional view, and ~ig, 6 shows a method using the heating roll 5 and the infra-red light radiation device 8 i~ comb~nation for ~elting and adhe~ionO Fig. 7 shows a method u~ing ~he heating ~urnace 8 lm~ediately after the us~ o~ the 3 heating belt 5 for melting and adhesionL. Fig. 6 shows ,-, .

~.~LZ7Q6~

an effective method for formin~ a ~pacific polyole~i~
resin in a large thicXness, while it is more difficult to obt~n qecure adhesion by the use o~ cDn~entlo~al methods~
The heat treatment has been explained mainly re~erring to the heating roll or plate in the dra~irlg~
howeYer) it may be effected by the u8e of the in~ra-rad light radiation alone or the heating ~urnace alone~
The present invention will be better ~nderstood by the following E~amples wherein parts a~d perce~tage~
are by weigh$ unle39 ~therwise ~peci~ied.

One hundred (10~) parts of polypropylene (M.I. 10), 20 parts of malelc anhydride and 375 parts o~ xylene were added to a l-liter three-necked fla~k providad with a nitrogen inlet 3 thermometer and agita$or.
The resulting mixture was heated t~ 130C ~th agitation in a nitrogen gas atmosphere and *hen in~orporated dropwise with a solution o~ 0.1 part of ben~oyl pero~ide in 40 part~ of xylene over a time pèrio~ of 90 minutes9 after which the whole was heated to 13QC and ~aintalned at thi3 temperature with agltabion for 60 minuteY . The reaction mixture so obtained was cooled to ro~ temperature to obtain a suspension~ The 6uspension ~o obtained wa~
~iltered to remove the ~ylens there~rom 9 washed repeatedly with methyl ethyl ketone until the unr~acted maleic a~hydride-:. and low molecular weight~ maleic anh~drid~
homopolymer~ were hardly appreciated in the methyl ethyl ketone washings by liquid chromatography, thereby to 3 obtain a polypropylene-~aleic a~hydride copolym~r reai~

_ 24 I " ,~
~127~)6~ , :t ~maleic anhydride graft rabiot o.6~) whlch wao then alr dried. Tho copolymer re~in 80 air dried was incorporated with 6.5 parts of aluminum hydroxid0 to ~orm ~ ture , whlch was melted at 180C 1~ an ext~uder ~nd e~rudot ~o obtain a spacifio polyolefin res~n i~ pellet form. ~e speci~ic polyolefin re~in pelleta ~o obtai~ed ~a~ ~truded b~ an extruder (dies temperature, 240C; resin temp~ragure~
210C) onto the aluminum foil sur~ace o~ a 15 ~ thi¢k alu~inum foil/polyester ~ilm la~inate to form thereo~ a 10 ~ thick coati~g of the ~peci~ic polyolefin resinO
After the whole was heat tre~ted at 180C for ~ ~eco~ds~
- a 70 ~ thlck corona discharge-treated polypropylene fil~
: wa~ laminated o~ the speclfic polyolefin resin layer of the whole and the r~sulting lami~ate wa~ then pa-~s~d on r`` 15 ~ heat~ng roll heated to 180C at a velociby o~ 40 m/~9 thereby obtal~lng a packaging laminate.
- The bond ~trength (adhesion strength) bet~oe~
the polypropylene a~d aluminum foil o~ th0 packaging laminate ~o obtained was ab least 1230 g/~5 mm without interlayer separabion although the polypropyleno film was elongated when a 90~ peeling tesb wa~ effeoted a~ a pull relocity of 100 mm/min. Containers or pouches ~era made of th0 thus obtained packaging laminate. Water~ a salad oil/water (1 t 1) mlx~ure~ ~nd a 3% aqueou~ ~olu~io~
0~ acetic acid ~ere enclo~ed respscti~ely i~ the thus mad~
col~tainers and the~ ub~ected to a retort te~t a$ 120O
for 30 mlnute~ wit~ the results being show~ i~ the following Table 1.

~lZ7~!6~

; Table 1 Salad oil/wAter ~ ~g. ~ tl~
Contents Wator (1 1) of aoetic acid ~, , . . , , _ _~ . ~', Poat-retort . . .

5 . bond strength 1220 1140 1020 .
(g/l~mm) ., .
_ . .~ ~
,, .~ :'' , Then~ a 4% aqueous solut~on of acetic ac~d and a BeaSoning for Chinese food (p~oduced br Compa~y A) were packed reapectively in contai~ers or pouche~ made of the, aforesaid packaging laminate and then subiccted to a preservation test at 66C. The a~oresaid seasoning which contained soy~ soyabean oil~ bean paate~ ~ce wine~ garlic,.
ginger and the like, was ~uch that it was to be sub~ected lS to a -~evere retort treatment a~ compared with various other seaso~ings such as currr and meat sauce~ The container ~or tha acetic acid solution was tested ~or it~
`.. ~ bond or adhesio~ atren~th one ~ee~ after the start of t~e te~t and the co~tainer for the ssasoning was tested for it~ bond or adhasion strength two weeks thereafter. The .
results are shown in the following Table 2.
.
, Table 2 . . .
4% acetic Sea~oning for : Contents acid solution Chinese food __~ ~ ,. . .

(1./~ ) ~
:" ' ~, ' ' ~ ' ' ., - 26 _ , . ' .

~Z7~1 .~
Samples of the packaging laminate obtained in Example 1 were subjec~ed to a r~ort ~est at 140C

- ~or 20 minutes with the r0sulbs being ~hown in the ~ollowing Table 3 Table 3 . _ 3~ aqueous Contents l~ater Salad oil/water solution of acetic acid 10 . _ ~_ ,_ , , " __ Post-r0tort bond strength 1040 1250 10~0 (g/15 mm) .... . _ _ ................. , , _ _ .

~rom the above results it was confirmed that the packaging laminate o~ the present inve~tion was satisfactorily resistant t.o the re*ort test at 140C.

The procedure of Example 1 was followed except that a specific polyolefin resin was prepared by reacting m~leic anhydride, ~enzoyl peroxide and al~inum hydroxide at a time in a xylene solution of the polypropylene, to obtain a packaging laminate~ The packaging laminate so obtained was tested in the same ; manner as in Example 1 and approximately the same results as in Exa~ple 1 were obtained.
xample 4 The retort test procedure of Example 1 was followed except that a heat treatment-at 180C for one second was substituted for the heat treatment at 180 C
for 5 seconds with the results being shown in.the following Table 4.
~7 ~27~6~

h ~ _ ~ ~1 0 --~
~n o u~
., ~ ~ ~ ~ O
~ '~ :~
,. r~ O ~ ~ .
~ U~

h a~ O~rl P. ~ d ~d,!4 h ~ ,1 o ~ O
,~ ~ C~ G~
~ td~
_ lH~ _,.
' . ~o~ O
~'~rl O

h h . cu ~: ~ h ~ ~ O
,~ .,. ¢ ~_ h ., ~ O
,~
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`. h O
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a ~P
_ _ _I

h "~
v ~3 ; _! m .

J

' ~2706~

Example 5 The procedure of Example 1 was followed except that the speci~ic polyolefin resin obtained ln Example 1 was used and a heat treatment wa~ carr~ed out by contact with a heating roll having a surface tempera-ture of 220C for each o~ 0.3 and 0.5 seco~ds.
The results are shown in the following Table 5.

',' . ' "''~' ', ' ' .

' : ~ -, - ' ~2'7~

_ h ~ __ _ ~ ~0~ O O

o a) ~ ¢ o o o Q) ~ h o--~1 U~ U

h o ~ O O
;~
~ O O

r~ ~ O
h . .. O O

~ . _ h O O
,~ ,1 ~I
_ . .
,~ . ..
O h O ~oo I Xi~ . r1 ~I
.' ~ ' /
. ~ / ~3 ~

/~ O O
h ~ V ~

7~6 ~ ' '~he procedure o~ Example 1 wa~ ~ollowed except that hlgh-dsn~lty poly~th~len~ (M.I. 6~.o~ or gL propylene-ethylene copol~er (propylene/ethyleAe :~ 95/5 ~ was ~ubstituted for the polypropylene to obtaln a speo:L~io polyolefin r~in. Usin~ each Or the thus obt~lned specirlo polyole~ resin~ the ~ame test a~ ln E:samplo 1 wa~ carried out wlth the result~ being showr~ lch0 ~ollowing 'rable ~.
In the undermentioned laminates a high-density polyethylene film was used in substitution for the polypropylene film when the polyolefin of the specific polyolefin resin used was high density polyethyleneO
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.

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_ _ _ ,, Og,,~ O O
i~ ,_~ rl ~t~

5t _ h .,~ . O N
.. `Z- , . 3: O N
_ _.

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c~ Il, h " o 5 o . ~ ~
v h r~ ~) h O
P, o 1:4 ~ h ~ .

1~7~6~

Comparative example 1 The polypropylene-maleic anhydride copol~/mer (~ot reacted with aluminum hydroxid0) was coated 1~ a 10 thickness by the use of an extruder in th0 same manner 5 as in Example 1 to obtain a laminate, Samples o~ the , laminate so obtained were heat treated at 180O for one second~ at 180C for 5 seconds and at 220C for ~0 seconds, respectively~ after which the heat treated s~mples were each la~inated on the copolymer coating with a 70~ thick polypropylene film and the whole was then passed at a velocity of 40 m/min. on a heating roll at 180~C to obtain a product laminate. The bo~d strength ~or the polypropylene/aluminum ~oil of each of the product laminates so obtained was not higher than 100 g/15 mm.
Comparative examples 2 - 6 In accordance with the procedure of Comparative example 1, a polyolefin-a,~-ethylenically unsaturated oarboxylic acid copolymer was prepared and there were ~hen prepared polyester film (outer layer~aluminum foil/polyolefi~-a,~-ethylenical}y unsaturated carboxylic acid copolymer/polypropylene film (inn~r layer3 laminates.
Thc lami~ates so prepared were subjected to a retort test at 120 C for 30 minutes with the results being indicated in the following Table 7. The laminates obtained by the heat treatment at 180 C for o~e second or 5 seconds had a pre-retort bond strength of less than 100 g/15 mm.
In Com?arati~e example 6, the laminate used was a polyester film (outer layer)/aluminum foil/high-density polyethylene-maleic anhydride copolymer/high-dcnsity 3 polyethylene film, 3L1;~7~6~
_ ~ . . __ ~
~n ,~ a) ~ ~ o o o o ~ ~ ~ ~ h O I O O o~ ~ ;l ,~ rl _ ~I ~_1 ~1 tU
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_ ~ I~ ~ ;l ,lo-r P~ I>
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h h _ _, ~ ~ ,_1 p~ ~rl , ~o~ . _ _ l ~ .
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a~ , ~ ~ ~ o u~ O O ~ ~
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'J3 h -- 'I 'I 'I
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t~ ~ r~l C~l ,9 t~
_ _ _ .
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,1 h o ~d ,1 ~ ~ ~ ~ U~ ~
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~ o ~1 '~:1 ~ ~1 ~ ~ O ~ ~ O
E3 ~1 ~ ~ ~ ~ 0 5~ bD ~ O
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h I td ~ ~ ~ ,_1 r-l 0 ~ ~ ~1 P ~L O h d h ~t~ ~ O o ~1 ~ ~ ~ ~ ~ca t~ a~ ~
P~ bD - ~ h o ~ ~ ~ ~ ~ ~ _ ~ q~
h ~ ~ ~ h R~ u~
O ~ O O h .q ~ u~ ~ O ~ ~~ ~ 1:~
O ~ ~ ~1 hI h ~ O
V h 1~ 0 ~ I ~ ~ O ~ a~ a:l r~ U~ 1) ~ ~ ~ u~ -~' h $-~
P~ ~ ~ ~ h O O O o ~_ ~ P ~ 1:4 h ,9 u ~a~
The procedure of Ex~mple 1 was followed except that polyolefin resins other than the speci~lu polyole~in resins acoording to the present in~entlon were pr~pared9 5 to obtain la~inates. The laminates BO obtained were tested as in ~xample 1 with the results being shown in th~
following Table 8.
In the above laminates ~ a high~density polyethylene film was used in substitution for the 10 polypropylene film when the polyolefin of the speclfic polyolefin resin was high-density polyethylene.

~Z7~
_ __ ~ _ _ .__ o 1~ ` ~ ~ O )~ u~ O
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a~ h o ~ ~ .~ ~ ~ c~l o o ~ 1 El X ~
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- - - - ~ -t_ p. 1~ V ~ ~~0 U~ It~ O
~1 r~ O ~ ~rlO ~ U~ U~
o h c~ o o o td ~ _ ___ . .
. ~ ~ _ h P, o h ~1 ,1 v ~~ ~ o ~ u~
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O t~ ~ V O td o _, , . ~ _ ._ , ,vl I l rl h P. ~ h~:l O ~ ~) o u~ O
o h a~ o o _ ~ , r-- o~
.
_ _ I ~ rl I ~
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o h ~ h -- h ~ _ P~ p~ ~ H ~ Pl _ _ I ~ ~0 ,_ U~ o oo ,1 ~ P. 10~ ~~i ~ ~oo ~D ~D
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p~ ~ P~
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C~ r~l o ~ 1 rl ~ s~ ~ ri N
o F~, h -- ~-rS h-~l o~ a:l co P~ ~ ~ .~_ ~ _ . _ ~ l l ~ s:~ ~ h ~ O ~ O O
a) r~ O .q~ ~ . ;t O oo ,1 O h ~ ~ -rl ~ ~ ~ ~ n ~ ~ ~ 0~ x-- - - - -__ I O
~ o o o o o h ~ ~ C~ O h a~ ~ O o~ ~ O
~-1 0 ~ ~ ~: ~ ~ N r~ ~ o~ It~
O h O al ~ h ~ rl h rl _ --I
P~ ~ ~ ~
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'I:J O h ~ :1 o o o ~L p. o ~ ~ h ~ ~ td 1:1 .~ ~ 'O _ ~ ~ ~d ~ b~
td a~ q~ o ~ " ~ ~ ~ o h~: ~n _ c~ O
Ql O rl ~ ~I h 5:1 h ~ ~ ,q ~~
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O ~ ~ ~1 ~ O ~ -- t~ p~ ~ I ~ I h 1~ u~
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P~ ~ O Pl L! O ~ O ~ ~D
, _ ~ _ ~

~1~7~6~L

r, In add~tion, the packaging la~inates obta~ned in Compara~ive exampl~ 7 - 20 were kreated ~nd su~aked to th~ same pres~rvatlon te~t as in Example 1 with the rasult that both the conta~ner~ co~taining a 4% aqueou3 solution of acetic acid and those contalning a ~easoning ~or Chinese food produced by Company A caused delami~ation.
The containers or pouches mad~ re~pectlvely of lami~ate~ lncluding magnesium~ and calcium-containlng polyole~n reRi~ caused bli3ter~ when holding therein a 3% aqueou~ solution of acetic acid~ ~he containers made in the Comparative examples e~hibited very low bond strength as shown in Table 9 after having been subjeeted to retort treatment and then a preservation te3t at 40~C
~or 30 days (the pre~ervation test being a very mild one as compared with that in Example 1). Thu~, theYe comparative con~ainer~ ~ailed in the preservation test and~ ~urth~r~ they were inferior in post-retort.bond stre~gth to the container~ o~ tha Example~

, Table 9 ~ ~ ~ ~ 3~ aque~us :i~. . Com- ~ ontent~ Water Salad oil/water solution of parati~e \ ~ aCetiG aoid . example \
__ _ ___ _ ___ 7 310 ~1~ 160 ,~
Bond .
strength _ ~g/lS mm) __ __ 290 2~0 120 .

- 37 ~

3~LZ7~

The procedure of each of Comparative examples 10, 12, 15 and 20 was followed except that a polyolefln reBin W~9 heat treat0d at 180C for one sec4nd ~n ~ub~titution for the heat treatme~t at 180C ~or 5 sesv~d~
to obtain containers which were te~ted ~or bond ~tren~th with the re6ults belng ~hown in the following Table lOo In addition, the containers respeotlvely containing a 4%
aqueous solution of acetio acid and a ~easoning ~or Chine~e food produced by Company A caused delaminatio~
~hen they were sub~ected to the ~me preservation te~t as in E~ample 1.

Table }0 _ . i . ~
\ Contents Pre-retort After retort te~t \ bo~d ~trength ~ . . . .. _ .. . .
Com- \ W t Salad oil/water 3~ aqueous parative\ . a er (1 s 1) solution example \ acid ~____ ___ ____ 620 59o 480 460 ~ ,, , _, . .. _. _ . , . __ . .~~r . ~_ _ ____ ~_ __ r . . .. _ __ __ _ 7~00 610 450 430 ___ ~ ___ _____ ~

The substitution of heat treatment at 180C
: 25 ~or one second for the heat traatment at 180C for 5 second~ exhibited hardly any decrease in bond streRgth ln the Examples and a conslderable decrease in bond strength in the Co~parati~e e~ample~.

3 Po~yolefi~ r~sins (contRi~ing metal3 as ind~cag~d . -1~7~

in Table 11 were prepared and thare were prepared polye~t0rrilm (outer layer)/aluminum foil/polyolefln resin/poly-propylene film (ir~er layer3 packaging lamlnates. Th0 packaging laminates so prepared were sub~ected to a re~ort test at 120C for 30 minutes. Further, containers made of the laminatea were packed respectlvely with a 4% a~ueou~
solution of acetic acid and a sea~oning ~or Chlnas0 ~ood produced by Company A9 were sub~ected to a test for bond strength after a preservation test àt 66C for one week and two wee~s, respectively. The result~ are shown i~
the ~ollowin~ Table 11~

- 39 ~

7~
. __ _ ___ _ _ _ ~ I h ~ rl rl~l O ~ _ ~ X~ ~
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R, t~ ~ 1-l h ~) ~ ~ h I h 1:~ ~: h ~ o E~ ~ h ~ . o ~CI I ~:1 ~ o ~ o 1~ q rl ~; ~ ~ ~ o~ ~ ~ h ~ a o P.~ 1 ~ o o O o ~ O ~ ~ h t~ o Q
~1 C) ~ 1 P~ ~ P~ h ,Q ~ a~ P, :~' ~ ~;2;
~_ _._ _ _ .

~2 The polypropylene-maleic anhydrlde copolymer (maleic ~nhydride gra~t ratio~ o.6~) obtai~ed 1~ Exam~le 1 were reacted with 6.5 part~ of aluminum hydroxlde 1 xylene at 130 C for one hour to obtaln a speoifio polyolefin resin. The polyolefin resin 90 obtained was washed~ dried~ dispersed ~n xylene (~olid matters 15%) and coated on the same aluminum foil as in Example 1 to form a 5~ thick coating which was then dried at 180~C
for 5 second~. The speoific polyolefin re3in-coated alumi~um ~oil was lami~ated on the resin coating with a 70 ~ thick coron~ discharge-treated polypropylene f~lm and then passed at ~ ~elocity o~ 40 m/min. over a heating roll at 180C. The packaging laminates 80 obtained ~howed a polypropylene ~ilm/aluminum ~oil bond stren~th of at least 1150 g/15 mm when subjected to a pc~ling test.
The packaging laminate~ were made i~to container~
which were packed respectivel~ with water~ salad oil/water (1 : 1) and a 3% aqueous ~olution of acetic acid and the~
sub~ected to a retort test at 120C for 30 minute~.
Thereafter, the packaging laminates of the te~ted containers were measured for bond strength with the re~ults being ~ndicated i~ the ~ollowin~ Table 12.

2S Table 12 tur ~ t-r (1 s 1) acetic ac~d _ __ _ POBt -retort bond strength 1190 1090 1040 (~ _ ~; 41 -~LlZ7~6~

E~ample 10 The qpeclfic polyole~in resin pellet~ obtalnéd in Example 1 were made into 70 ~ thick ~llms at 190C b~
t~e U9e of an inflatlon extruder~ The ~llm uo ~ade ~ao laid on a 15 ~ thick aluminum foil and heated undor pressure on a heatin~ roll at 180C ~or 3 seoond~ to obtain a specific polyolefin resin~aluminum foil lami~ate~
The laminat~ sc obtained was tested for bond strength and ~ound to ha~e a bond strength of 1160 g/15 m~ The lamlnate was made into containers which were pa~ked resp~tively with water, salad oil/water (1 s 1) ~nd a 3% aqueou~
solution of acetic acid ~nd then subjected to a retort test at 140C for 20 minute~ After the retort test~ th~
tested containers were measured for bond strength with the result that they axhiblted 1120 ~/15 mm~ 1010 g/15 mm ~nd 1050 g/15 mm~ respectively. The said container~ s~hibitod - ~atis~actor~ re~ults when sub~ected to thc same pre~er~atlo~
te~t a~ in Example 1 Example 11 T~e speci~ic polyolefin resin obtainad in Example 1 ~as melt extruded in a 10 ~ thickness into between a 15 ~ thick aluminum fo~l/polyestar laminata and a 70 ~ thick polypropylene film by the use of an extruder a~d then ~andwich laminated by such a method as show~ i~
~ 25 Flg. 5 thereby to obtain a packaging lamlnate.` The lami~atio~
: was effected at a lamination speed sf 60 m/minq by contact~.~g the to-be-laminated material~ with a heating roll hav~ng - ~ surfacs temperature of 220C for one second. The packi~e lami~ate thus obtained exhibited satisfaetor~ la~i~ate 3 ~trength~ po~t-retort bond strength ~nd prese~r~t~on -- ' .

~27~

te~t re~ults as in E~ample 1~

The specif~c polyolefln re~in obtained ln Example 1 and polypropylene were co-oxtrud~d to obtai~
a lamlnate of a 10 ~ thick specific polyolefin re~in with a 50~ thick polypropylene. Then~ the thu~ ob~ained laminate was laid on a 15 ~ thick aluminum roil/polyest0r laminate with the specific polyolefin resin sidc facing to the aluminum foil side~ and the whols wa~ then contacted with a heatlng roll having a surface temperature o~ 220C for one second thereby to produce a packagin~
laminate. The laminate so produced a~hibited 3ati6factorr bond ~trength as in E~ample 1.

The spe¢ific polyolefin resin/polypropyle~e laminate ~btained in Exa~ple 12 was lald on a 100 ~
thick aluminum sheet with ths polyolefln resin 3ide facing to the aluminum sheet~ and the whole was contac*~d ~ith a heating plate having a surface temperature vf 250 C for 3 Reconds thereby to obtai~ a packaglng laminate. The packaging laminate so obtained wa3 te~ted as in Example 1 with the ~esults bei~g indicated i~
Table 13.

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~lZ7~6~L

omparati~e example 2~
A propylene-acrylic acid copolymer (acryllc acid contents 3 mol~) WQS incorpor~ted with 0~3 mol Or ~luminum hydroxid~ in di~persion in me~hanol per mo!
of the acrylic acld, and the whole wa~ mixed together on a kneading roll ~190C) for 30 minutes. T~e maltod mixture so obtained was disper~ed in xylene and coated in a 5~ thickness on a 30 ~ thick aluminum ~oil. The thus ~oated alumi~um foil WQ~ conta¢ted at the aluminu~
~0 foil slde with a heating roll at 190 C ~rotat~g at 10 r.p~.). Then~ a 70~ thick polypropylene fllm was applied to the polyolefin resin ~ide at 180C to form a laminate~ The bond strength between the aluminum foil and the polypropylene f3lm was 1030 g/15 mm. The laminates 15 ~ obtained were ~ubjected to retort test ~n the ~a~e manner as in Example 1 ~nd the results are qhow~
Table 14.

. Table 14 _____ . . . ~
Contents Water Salad oll/water 3~ aqueous (1 : 1) acetlc acid _--_ _ Post-retort bo~d strength 960 1210 990 ~ ) ,,, __ The ~ame preservatio~ te~t as ln E~ample 1 was made on tha l~minates with the resuit that they were fo~d unsati~factory for practical use a~ ~hown i~

Table 15 '~
~ 45 -:

llZ7~6 r~bl~ 15 . ~ . . . , . , _ 4~ aqueous solution Seasoning ~or Chine~e Content~ of acebic acid ~ood produced by Company A
__ _ ~ond strength U~1amiAAt~ ~5 .. E~ ' One hu~dred (100) part~ of polypropylene~ 0.4 10 partB of maleic anhydrid~ and 0.1 part o~ benzoyl pero~ide were melt kneaded on a heating roll at 185C for 10 mi~ute~O After the end o~ melt ~neading, the material~' were extsacted thoroughly with acetone to remo~e t~e unreacted maleic anhydride and low molecular wei~ht/
maleic anhydride homopolymers to obtain a polypropylene-maleic anhydride copolymer. The copolymer so obtai~ed wa~ incorporated with aluminum hydro~ide in a~ ~mount Or 1.5 partq per 10~ parts o~ the polypropylene to for~ a mi~ture which was blended on a Henschel mixer.
The blend so obtained was melt blended and extruded by an extruder at 180C. Th~ speci~ic polyol~fin resin pellet~ thus obtalned were extrusion coated a~ a~
adhesi~e in a 10 ~ thickness on a 15 ~ ~hick aluminum ~oil (a lamlnate of al~minum foil/polyester) by the use of an extruder (dies temperature: 235~C) to ~orm a re~in/aluminum laminate~ Immediatel~ after the coatl~g~
: the thus ~ormed laminate was contacted on the reverse ~polye~ter) side with a heating roll ~sur~ace temperature~
lBOC) for one ~econd as indicated in ~lg. 1~ to heat 3 (~eat treatm~nt correspo~ding to 60 m/min.) the lami~ato .

, :~ , .

3L~Z7Q~

thereby enabl~ ng the ~urface-coated ~peoific polyole~n re~ln to adhere to the aluminum foil securely.
Further~ ~ 70~ thick polypropylene ~1~ w~
l~id on the speoific polyolefin re~in coabln~ Qnd tho whole was pa~ed on a heating roll (sur~aco temperaturo~
180C) at a travelling velooity of 60 m/min~ In the t~u~
obtained packing laminate, the bond strength o~ the polypropylene ~ilm/aluminum foil was te3ted and ~ound to be as high as 1020 g/15 mmO The p~ckaging laminate was made into containers which were packed ~espectively with water, salQd oil/water (1 ; 1) a~d a 3% aqueou~ 801utio~
of acetic acid and then qub~ected to a retort te~t ~t `- 120C ~or 30 minutes. A~ter the retort test~ thv packaging laminates were te~ted for bond qtrength with the results boing shown in the following Table 1~.

"
Table 16 ~_ __ . ContentqNater Salad oil/water solution o~
(1 : 1) acetic acid _ _.__ __ Poat-r~tort bond strength 1040 1110 99 ~5--~

Furthermore, the packagl~g lamlnates ~ere qub~ected to the same preservatlon teat as i~ Example 1 with the results bei~g shown i~ ~able 17.

,-, `' . .. ,... ~ ~ ' :. ' ' , ' ~ ' ~

: ` :

- 47 ~

7(~1 Table 17 __ __ 4~ aqueous Soasonlng for Chine~e Co~tents 301ution of food produoed by acetic acid Company A
__ _ _ _ _ 5B~nd tr~n~tb 960 ___ ~a!~ ' The packaging laminate obtained in E~ampl0 14 was made into contain~r~ which were packed respectively with the following materials as shown in Tab~e 18 and then ~ubjected tD a retorg te~t at 135C ~or 20 minutes;
The re6ults are a~ shown in Table 18, Table 18 Con~e~ Water ~ d ~ t~ solution of ~1 s 1) ac~tic acid . -... ___ Post-retort .
bond strength 1010 980 960 20 ~ w~ _ ~rom the abovs results it was confirmed that the ~pecific polyolefin re~in according to the pre~ent ~vention was satisfactorily resistant to t~e retort test at 135~C~ `
~ ' ., The re~i~ extrusion coated laminates ~re~i ~ aluminu~
laminates~ obtained in Exampl0 14 were re~pect~ve}y he~t treated as shown in Table 19 a~d then each laminated w~th 3 a 70 ~ thick polypropylene film to obtal~ pac~a~in~

.

~ ~Z7at~

laminates. The packaging lamlnate~ wers each made into contalners w~ich were p~ck~d respectively with the materials ~hown ln Table 19, subjeoted to a retort be~t at 120C for 30 minutes a~d then test~d for bond strengthO The ré3ults are as ~hown in Table 19.

Table 19 ~_ Post-retort bond strength Heat treating(g/15n~) ~ condition~_ ~__ _~ __~__~_ _ __ __ __ __ __ __ lv Salad o~l/water 3% aqueous ~olution (~ : 1) of acet~c acid 160 (C) 20 (sec) 1190 1180 ~ ~ ..., ..._. ~ .., ~
180, 5 1110 9~0 200, 3 1140 1110 __ 22~, ~ ~220 I-7 A~ is ~een from the above result~ the packaging laminate containing the resin/aluminum laminate previously heat treated at 200C for 3 soco~ds exhibited hl~ bo~d strength.

In the same manner as ~n ~ample 14~ ~pec~ic polyol~in resins were prepared under the ~arious condition~ s~own in Table 20~ The packaging la~i~ate~
obtained were a laminate of polyester film (outer layer)/aluminum foil~specific polyol~fin resln/polypropyle~
~ilm (inner layer) and subjected to 8 retor~ te~t at l~O~C
3~ ~or 30 minutes with the results being 6hown in Table 20~
' . . ~ ~9 _ .

7~6~L

In the abo~e pack~ging laminates~ a polyethylene film wa~ u~ed as the inner layer in substitut~on ~or the pol~-propylene film when the polyole~in o~ the ~peol~lc polyole~in resln was polyethylene, ~Z7Q61 ,-, .~ _ _ - ~ _ "~
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o ~t:: ~ ~ 1:: ~ h h ~ h g ~J ~0~~ ~_ ~ t o ~~ ~t: ~ h P.p, O o . .. . __ _ __ __ ~27 ~a~2 The polypropylene-maleic anhydride copolymer as obtained in Example 1~ was incorporated with 1. ~ part~
of aluminum hydroxide and xylerlc ~solid matters 17 wt.%) and heated to 130C for 60 minuta~ aPter whlch the requlting mixture was coated in a thicknes~ o~ about 5 on a 15 ,~ thick aluminum ~oil ( alwD~ num/polyester laminate). The thuR-coated alumin~m foil was heat treated at 180C ~or 5 second3~ a 70 ~ thick polypropyl0~0 ~ilm was laid thereon and the whole wa~ passed at a ~elooity of 60 m/min on a heating roll at 180C to produce a packaging laminate. rrh0 thus produced packaging laminate was confirmed to have high bond strength of 1160 g/15 mm between the polypropylene ~ilm ~nd aluminum foil. Fur$her~
15 the packaging laminate was made into co~tainers which were packed respecti~ely with salad oll/water t1 s 1) and a 3%
aqueou~ ~olution of acetio acid and then sub~ected to a retort test at 120C for 30 minutes with the result they exhibited bond ~trengths of 1140 and 1020 g/15 mm. They al~s er~ibited satisfactory result~ i~ thv same pre~er~at~o~
test as mentioned before.

~L~ .
One hundred ~100) parts of polypropylene (M.I. g 10), 16 parts o~ malelc anhydride~ 10 parts o~
l~Z-polybutadiene (n~ber average molecular ~aights 150,000) and 375 parts of xylene ~ere charged i~to ~
l-llter three necked ~lask ~itted with a nitr~ge~ gas ~nletg thermometer and stirrer to form a mixtura wh~ch was heated to 130~C with stirring in a nitro~en ga~
3 atmosphere to obtain a reactio~ mixture9 To the ,.

o 53 _ ~Z7~6~

thus-obtained reaction mixture wa~ dropw~se ~dded a ~olution of 1.5 parts of benzo~l peroxld~ i~ 40 part~
of xylene over a time period o~ 90 minutes. ~hereafter~
the reaction mixture contlnued to be heated to 130C
~ith ~tirring for 30 minutes ~nd was then cool~d to room temperatur~ to obtain a ~uspen~ion. The ~uspa~sio~ ~o obtained was filtered to remove therefrom the xyle~e and repeatedly washed with acetone until the unreaated maleio anhydride and low molecular weight~ maleic anhydride homopolymers ~ere hardly appreciated in th0 acetone wa~hings to obtain a powdery resin. The powde~y resin was air dried9 a~ain dissolYed ln xylene~ incorporated with 1.0 part o~ aluminum hydroxide and heated to 130C
with 3tirring for 30 minute~ in a nitrogen atmosphere to obta~l a specific polyolefin resin. After the e~d Or ths heating, the resin so obtained was applied i~ an about 5 ~ thickness to a 15 ~ a7uminum ~oil (aluminum/polyester laminate~ while it wa~ hot. The re~in-applle~ aluminu~
~oil was heated to 180C for 5 ~eoonds, a 70 ~ thick polypropylene film was laid t~eraon, ~nd the whole wa~
pa~sed at a velocity o~ 20 m/min (two ~econd~ co~tact) on a heating roll at 180C to obtain a packagi~g 12minataO
The polypropylene ~ilm/aluminum foil o~ the packaging laminate e~Yhibited a high bo~d ~trength of 1360 ~ 15 ~m wh~n a 90 peeling test wa~ effected at a pull veloclty o~ 100 mm/min3 The packaglng laminate was made i~to containers which were pa¢ked respectlYei~ with the material3 indicated in Table 21 aQd then subjeoted re3pectlvely to a retort test a~ 120C ~or 30 minuta~

3 and a preservatio~ test at 66~co The me~sursm~t of , ~4 ~3 o~ bond 3tr~ngth was ~0cted as pre~riou~ly me:~tioned~
The re~ults ar~ a~ Yhown in Table . 21.

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Furthermore~ some of the packaging laminate~
using there~n the polyolefin resin a~ an adhe~ve in the Examples and Comparative exa~ples were tested ~or thelr hy~ienic properties with the result~ being ~hown in the follo~ing Table 22. Two measure~l~ents were ef~0ctod for each of the tests as show~in Table 22.

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~ 57 , ~Z~6~

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~7~6~L i As ls secn Erom Tab~o 22~ th0 specl~lo poly~le~in resins according to tho preson-t lnvontlon are oxcellerl~ in hygienic propertios as compared with the urethane typ0 adhesi~e and are also suitablo ~or use~ to whiah hygienic considerations should be gi~en.

~ 5~ ~

Claims (5)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A process for preparing a retort-proof laminate for packing foodstuffs which comprises laminating an aluminum foil or sheet with at least one polyolefin film selected from the group consisting of high-density polyethylene, polypropylene, ethylene propylene copolymers and polybutene films using as an adhesive a specific polyolefin resin in melted state pre-pared by using together (A) at least one member selected from the group consisting of high-density polyethylene, polypro-pylene, ethylene-propylene copolymers and polybutene, (B) maleic anhydride and (C) aluminum hydroxide.

2. A process according to claim 1, wherein the specific polyolefin resin is prepared by using together 100 parts by weight of the compound (A), 0.01 - 30 parts by weight of the compound (B) and 0.05 - 10 parts by weight of the compound (C).

3. A process according to claim 1, wherein the compound (A) is graft copolymerized with the compound (B) to form a graft copolymer, the thus formed copolymer is washed and the copolymer so washed is incorporated under heat with the com-pound (C).

4. A process according to claim 1, 2 or 3, wherein the specific polyolefin resin is laid on the aluminum foil or sheet, the two materials are contacted with a heating roll or plate having a surface temperature of 150° - 250°C to melt bond them together thereby producing a resin-coated aluminum foil or sheet, and the thus produced resin-coated aluminum foil or sheet is then laminated on the resin side with the at least one member selected from the group consisting of high-density polyethylene, polypropylene, ethylene-propylene copolymer and polybutene films.

5. A process according to claim 1, 2 or 3, wherein the specific polyolefin resin is extruded into between the alum-inum foil or sheet and the at least one member selected from the group consisting of high-density polyethylene, poly-propylene, ethylene-propylene copolymer and polybutene films by the use of an extruder to obtain a composite, and the thus-obtained composite is contacted with a heating roll or plate having a surface temperature of 150° - 250°C thereby to obtain the retort-proof laminate.