CA1050872A - Paperboard laminate - Google Patents

Abstract

PAPERBOARD LAMINATE

Abstract of the Disclosure An improved paperboard laminate for containers for bulk packaging liquids, syrups and pastes, which includes a layer of a high strength polymer film and which also may in-clude a layer of aluminum foil.

Description

Back~r und of the Invention ~ his is a divisional of Canadian Application Sexial No. 222,437, filed March 18, 1975.
This invention relates to coated, paperboard containers and in particular to containers for pac~aging and storing mate-rials which are prone to lea~ from tpe c~3ntainers,,or, to damage the paper~oard by seeping through minor cuts and imperfections in ~he coating on the paperboard.
, 15 Paperboard containers for a great ~ariety of oods and beverages have become widely known and utilized. For example, containers such as those disclosed in U.S. patent

2,7~0,095 h~ve been employed for hoIding,perishable foods for relatively short periods of time, on the order of about two weeks.
Such containers have found wide applicability for beverages, such as milk an~ orange juice. Typically, su~h containers have been assembled from a paperboard blank, coated on ~oth sides with one or more layers of a protective, ther~oplastic material, such as polye~nylene. Such containers have provided substantial advaD-tages in both economy,and convenience for producers as well as consumers.
However, the use of such containers ~ver an extended period of time with certain penetrative fill products has raised c~rtain significant problems. One problem ~as involved the relative lac~ of durability of such containers when holding liquias an~ syrups for longer than a few weeks.

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The fluid contents o such containers have usually tended to "wick" or seep through damaged areas of or defects in the thermoplastic coating into the paperboard ba'se stock.
This seepage of fluid through the inside, thermoplastic coating into the paperboard has tended ~o weaken the con-tainers and to cause them to.ultimately :Leak or rupture.
It has been found that wicking occurs principally at certain sites, inside the containers. Usually, such sites are .~.I.here the~paperboard material has been score~, olded and/or flexed in forming blanks for cQntainers,.
folding the blanks along the score lines to form the con-tainers, or in fillinq, closing or storin~ the containers.
In the case o~ some diett soft drink syru-ps, it has been noted that almost any damage to the coating material on the inside surface of the containers can result i~ rapid and disastrous penetration of the paperboard base stock by the ~: syrup;. Obviously, this problem is particul rl~ a~gravated when the containers are stored fox a relatively long period of time, since exposuxe of even small areas of the paper- ~.
board base stock, such as may occur through tiny pin holes : in the thermoplastic coating, can, over a long pexiod of ~ ~:time, ~ause the wicking of the fill product into sub~ ~ -stantial portions of the paperboard base stock and the resulting failuxe of the containers. -`
In addition to the problem of the durability of paperboard containers for liquids, another obvious problem -has been the relative lac~ of adeguate protection for ~he quality of the material pac~aged in such containers over ' ,. . .~, ,, ' - :
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a relatively long period of time. Typically, a substantial loss of quality has been encountered when utilizing conven-tional paperboard containers for holding liquid materials for more than about two weeks. This has been due primarily to th~ inadequacy of conventional thermoplastic coating materials as barriers-against the loss of aromatic oils and other ingredients vital to the flavor of varlous sub- -~
stances. Loss of quality has also been attributed to the fact that conventio~al thermoplastic coatings are relatively ;
- 1~ inadequate barriers against penetration by gases such ~s `~ oxyyen. ~ -In order to overcome such proble~s ~n paperboard container~r coated laminates of paperboard and aluminum ~oil have been utilized. Seet for example, U.S. patent no.

3,365,111. The aluminum foil, when bonded to the papcrboard, has been found to enhance the ~urability of the result~ing containers by inhibi-ting the liquid or syrup GOntent6 from-penetrating the pap~rboard base stock. More importantly, ~ the aluminum foil has served as~an effective barrier against-`~ 20 both the inflow and outflow o~ gases and liguids~ thereby ~ minimizing the deterioration of the contents of the con- i~
,~ :; , , tainers over ~rolonged periods.
Aluminum ~oil-paperboard laminates have not, however, been entirely satisactory for some fill pEoducts.
;: 25 The containers made from such la~inates have still been :: :
prone to wicking thr~ugh score cuts, breaks or de~ects in the thermoplastic material and aluminum foil into the paper-board base stoc~;, particularly over eY~tended periods o~ time.
Although the amount of wic}:ing has been reduced wi~h such ~;~ 30 lami~ates, t~c ~rQbLem has continued to be a si~nificant one ~.

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when the containers have been used for some fill products over periods of about two months or more.
The problem of seepage through score cuts, breaks or defects in the thermoplastic coatin~ and the aluminum foil has been a particularly serious problem at the corners of paper- ~ ;
board containers. At the corners, the paper.board laminates have - been particularly susceptible to the effectc; of scoring and folding operations to form the containers, clS well as the effects ~ `
of flexing the contain~rs during the filling, conveying and packing of the containers. In this regard, it has been foun~
that the aluminum foil is almost invariably crushed or cracked during the scoring and folding of the paperboara blanks, rendering the containers susceptible to the deleterious effects of fluid leakage into the paperboard base stock.
There has been an unfilled need therefore for a ~;
paperboard laminate material having improved abuse resistance, particularly resistance to the effects of scoring, folding and ;
~: flexing, and which also possesses barrier properties for main-taining the quality of the containers' contents over relatively extended periods of time.
Summary of the Invention In accordance with the invention of the present 1:
divisional in one aspect there is provided a thermoplastic- ¦:
coated, paperboard container, suitable for liquids, pastes ¦~
and syrups, an improved paperboard laminate material which comprises a first layer rf a thermop~astic ma~erial, a layer j~
: of a paperboard base stock, bonded to said first thermoplastic layer; a layer of a polymer film bonded to said layer of a ~.;. .
paperboard base stock, said polymer film having a tensile strength at the yield point greater than about 4000 p.s.i. and an elongation at fracture greater than ab~ut 200%; and a second ~:
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layer of a thermoplastic material, bonded to said layer of a polymer film.

By the impro~ed laminate of this appl;cation, a material is provided having imp~oved strength, durability., resistance to cuts, crac~s and pin holes, as well as improved barrier properties. This laminate is also adapted to be cut and scored on conventional process equipment into blanks for paperboard containers. The lamina~e is therefore well suited for use in inexpensive, disposable, coated, paperboard con-tainers t~ substantially reduce the tendency of the containersto fail, due to the wicking of their contents over extended periods of time.

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Fiyure 1 is a schematic~ cross-sectional view of a laminate i~ ac~ordance with an em~odiment of this inven~
~ion. .
Figure 2 i5 a scllematic, cross-sectiona- view of ;~
a second embodiment of a laminate in accordance with this :
inYentiOn~ ~ich incl.udes an aluminum fQil lay.~r.

2~Detailed Description of the Invention :
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~; . Shown in Figure 1 is a multi-layer laminate 10 which comprises a first layer of a thermoplas~ic materi~l 11; a layer of a paperboard base stoc~ 12; a ~aminatLng ` layer 1~; a layer of a high strength poly~er ilm 14; and :~a second layex of ~ thermoplastic mat~rial 15. The irst ther~opIastic layer 11 is bondea to one ~urfac~ of ~ie papcrb~ard base sto~k 12, and the laminating l~yer 13 is ' 5 . ~:

. j.. .. .. ., . ,, , -bonded to the other surface of the paperboard base stock 12. The laminating layer 13 is also bonded to one surface of the layer of a polymer film 14, and the secon~ ~hermo~
plastic layer 15 is bonded to the other surface o the layer of a polymer film 14.
In the laminate o~ this invention, the ~irst .
thermoplastic layer 11 and the second thermoplastic layer 15 can be ~ormed.from any. thermoplastic material conven-tionally utilized on~the inner or outer surface~s o coated, . 10 pap.erb.oard. containers.. Among the thermoplastic materials :~
which can be utilized are the polyolefins, such as are dis- .:
closed.in U.S. patent no. 3,423,341, e.g., poly~thylene and polypropylene; the ethylene-acrylic acid copolymers, such as are described in U.S. patent 3,423,231; and the Surlyn ;
ionic copolymers, such as are disclosed in U.S. patent 3,791,915. The preferred thermoplastic materials for-the -.
first a~d second thermoplastic layers 1.1 and 1~ are the . polyolefins, particularly low density polyethylene. In this laminate, the thickness of ~he firs~ ther~oplastic layer 1} ~ :
and of the second thermoplastic layer 15 is not critical, and ~.
.~ any thickness greater than about .0005 inches, sufficient to enable a heat-sealed bond to be formed between the two layers, can be ~uitably utilized. Preferably, the thickness of the . first and second thermoplastic layers 11 and 15 is from about 25 .0005 inches to about .0020 inches. A particularly preferred thickness for the first thermoplastic layer, as an outside :-~ coating for a container, is about .00075 in~h~s, and a par- : : ~ .
. ticulariy preferred thic~ness for the second tl~ermoplastic .; layer, as an inside coatinq for a con~ainer, is a~out .0015 3~ inches.

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~L(31~()872 In this laminate, any conventional, high stren~th polymer ~ilm having a tensile strength at the yield point of greater than about 4,000 p.s.i. and an elongation at fracture of greater than about 200% can be utili~ed for the polymer film layer 14. Among the materials which can be suitably utilized for forming the polymer film layer 14 are the syn-thetic linear polyamides, i.e., the nylons, preferably nylon-6, nylon-6,6, nylon-6,10 and copolymers of these nylons. Mate-rials which can also be suitably u~ilized for forming the polymer film layer 14 are polytetramethylene terephthalate and polycyclohexylenedimethylene terephthalate, available from Eastman Chemical Products Co., Kingsport, Tennessee, under the `-trade designations PTMT and PCDT; respectively. The preferred materials for the polymer film layer 14 are the nylons, es-pecially the nylons coated on a sur~ace with an additional gas barrier material, such as saran, i,e~, polyvinylidene chloride. ~ particularly preferred nylon is a saran coated nylon 6 film,--available-unde~-the trade name Capran 7-OK*from All;ed Chemical Corporation, ~lorristown, New Jersey.
The polymer film layer 14 can be treated, if desired, to promote its adhesion to the laminating layer 13 or to the second thermoplastic layer 15. In the laminate 10, the selection of the treatment to promote adhesion and the amount of treatment utilized are not critical. ~hen the polymer film layer 14 i5 a nylon film, adhesion can be pro-moted by applying to a surface of the film an adhesion primer, i~
such as the polyalkylene imines or the urethane based materials disclosed in U.S. patent no. 3,570,748, in an amount sufficient to assure that the nylon film layer is bonded to the secon~

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thermoplastic layer 15 or to the laminating layer 13.
A preferred method of promoting adhesion of a nylon film layer 14 is by electrostatically treating one or both sur-faces thereof.
In the laminate 10, when the laminating layer 13 ~ ;;
or the second thermoplastic layer 15 or both are polyolefins, ~`~
a nylon film layer 14 is preferably treated to promote adhe~
sion. It is particularly preferred that a barrier coated nylon fil~ layer 14 be electrostatically treated on its uncoated surface and that it be treated with an adhesion primer on its coated surface to assure a~hesion of both sur- ;~
faces to the polyolefin laminating layer 13 and the polyo-lefin second thermoplastic layer 15. A suitable adhesio~
primer for bonding the coated surface of the nylon film ~ ~
layer 14 to the polyolefin second thermoplastic layer 15 or ~ ~i to the polyolefin laminating layer 13 is an ethylene-acrylic acid copolymer, such as is available under the trade name ~ ;
Adcote 50 C12*from Morton Chemical Company of CXicago~ ~ -Illinois. This adhesion primer is preferably applied to the f nylon film layer 14 in an amount of at least 1~4 pound, pre-ferably 1/2 to 1 pound, per 3,000 sq. ft. of paperboard base stock 12. !' ~ ' In the laminate of this application, the thickness of the layer of the high strength polymer film 14 is not critical, and any thic~ness between about .0003 inches and .0015 inches can be s~itably utilized~ Preferably, the j polymer film layer 14 is a nylon having a thickness of about ¦
.0004 to about .0010 inches, particulaxly about .0006 inches.
In the laminate lOj any paperboard base stock `~
conventionally utilized in coated, paperboard containers can .. . _ * Trademark - 8 ;~;

~2 be utilized in the paperboard base stock laye~ 12. Preferably, the paperboara base stoc~ has a basis weight of from about lS0 pounds to about 400 pounds per 3,000 sq. ft. and~a thic~ness of about .010 inches to about 0.030 inches. In a laminate intended for use in a one gallon SiZ2 container, it is especially preferred that a paperboard base stock of about 300 to 335 pounds per 3,000 sy. ft. and of about .024 to about .028 inches thickness be uti-lized, particularly a paperboard base stocX having a weight of about 327 pounds per 3,000 sq. ft. and a thickness of about .026 inches. However, for laminates intended for containers larger or smaller than a one gallon size, paperboard base stocks of greater or lesser weights and thicknesses than the foregoing are especially preferred. For example, in a laminate for a quart size container, a paperboard base stock of about 180 to 250 pounds per 3000 sq. ft. and of about ~013 to about .019 inches thickness is especially preferred.
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In this laminate, the laminating layer 13 ca~ be any conventional material for bonding a layer of a polymer film to a layer of paperboara. ~mong the preferred materials for the 20 laminating layer 13 are the thermoplastic materials, such as j~
the thermoplastic materials described above for the first and secand thermoplastic layers lI and 15, especially the poly-olefins, particularly low density polyethylene. I~owever, if desired, other adhesive materials, such as the two component laminating adhesive available under the tradename ~dcote 503*
from Morton Chemical Co., Chicago, Illinois, c~n be utilized ,~
;- in the layer 13 for laminating the polymer film layer 14 to the paperboard layer 12. The thickness of the lamunating layer : ;
13 is not critical, but rather will depend upon the type of material used in the laminating layer. With the especially * Traaemark ~ : !
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preferred polyolefins, any th.ickness from about .0003 inches to about .0020 inches can be suitably utllized, with about .0010 inches being preferred. Alternatively, if desired, the laminating layer 13 can be dispensed with entirely by extrud~
i~g or otherwise a.pplying. the.polymer film layer 14 directly ~
on *o the surface of the paperboard base ~tock 12. ~ :
. As seen from the above d~scription, all of the layexs of the mul~i-layer lami~ate 10, when considered indi~
vidually, ar~ well know~ ma~erials. However, in combina~ion;
:; 10 the layer of paperboard base stock 12, the p~lymer film layer ~;
14 and the first and second thermoplastic layers 11 ancl 15 combine to provide a laminate having superior strength and ~:~
durability, resistance to cuts, cracks and the formation ~f pin hole~, as well as improved barrier properties, bu~ which 15 i5 nevertheless suitable for cutting and scoring into container -:~ blanks-on ~onventional process e~uipment. Bec~use of-i~ im- -pro~èd.. properties, the laminate 10 is well suited for use in ~ :
containers for holding and storing liquids, syrups and pastes of various comestibles~ such as milk, soft drink concentrates, ~ ~
juices, juice concentrates and mustard, over extended periods -: .
of time. --Shown in Figure 2 is a second embodiment of this .inventio~. The.mul~i-layer laminate 20 in Fig~re 2 comprises:
a first layer of a thermoplastic material 21; a layer ~f.a ~.
paperboard base stock 22; a first laminating layer 23; a layer o~ a high strength polymer film 24; a second laminati~g layer 25; a layer of aluminum foil Z6; and a second layer of a thermoplastic material 27. The first thermoplastic layer :~:
; 21 is bonded to ~ne surface of the paperboard base $tock 22, -; 30 and the first Iaminati~g layer 23 is bonded to ~e other sur-face o~ the paperboard base stock 22. The flrst ama second : , ~, ~5t:~87~
laminating layers 23 and 25 are bonded to the surfaces o~
the polymer film layer 24. The second laminating layer 25, and the second thermoplastic layer ~7 ara bonded ~o the surfaces of the aluminum foil 26 In the laminate 20, in accordanc:e with the second e~bodiment of this invention, the i.rst.~2~ermoplasti,c layer ~ ' 21 and the second thermoplastic layer 27 can be formed from any thermoplastic material conventionally utilized for coating the insi.ae or the ou,.t~side surfa~.es of,.paperboard ,containers The first and second thermoplastic layers 21 and 27 ar~
pre~erably'the same as the first and second thermoplastic ,~
layers 11 and 15 in the multi-layer laminate 10, described above.
The layer of paperboard base stock-22 in the laminate 20 can be any paperboard base stock con~'entionally , utilized in coa~ed, pape~board container-s. Pree~ably, the .i , .
'' paperboard base stoGk 22 i~ th~ m~lti-la~e~ laminate.-20 is the same ~s the paperboard base stock 12 in the multi-layer ~' laminate 10, described above.
The iayer of a high strength polymer film 24 in the laminate 20 can be any conventional polymer film having a ten~
sile st'rength at ~he yield point of greater than about 4000 p.s.i. and an elongation at ,fracture.of greater than about 200~, such as the high strength polymer films described above ~ 25 for the layer 14 of the laminate 1O. The preferred pol~mer :~
.~; films far the layer 24, are the nylon iilms described above in :.-. connection with the polymer film layer 14 in the laminate 10.
In the lamina~e 20, ~he fir~t laminating layer 23 : can be any ~onventional adhesive ma~er~al adapted to bond the ~, ' 30 layer of a polymer ~ilm 24 ~o the l~yer of the paperh~ard base stock 22, and the second laminati~g layer 25 ca:n be any .~ . . ~ .

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conventional adhesive material adapted to bond the layer of aluminum foil 26 to the polymer film layer 24. Preferably, the first laminating layer 23 is the same material as the laminating layer 13 in the laminate 10, described above, 5 especially the polyolefins, particularly polyethylene. The second laminating Iayer 25 is aIso pre~erlably the same mate~
rial as the laminating layer 13 in the laminate 10, especially :~
a polyolefin, particularly polyethylene. Alternatively, if^: ~ ;
desired, either one or both of the first and second laminating layers may be eliminatea entirely by extruding or otherwi~e applying the-polymer film laye~ 24 dire~tly Qn to a surface of one or both of the paper~oaEd base stock 22 and alu~inw~
. oil 26. `~
The layer of aluminum foil 26 in the multi-layer 1~ laminate 20 Gan be of any thickness co~ntionally utilized in paperboard containers, such as are described in U.S.. patent 3,365,111. .Preferably, th-.e. al~uninum ~ii has. a ~hic~ness of. :
from about-.00025 to.about o O~ chè~, e3pecially a thick~
ness of about .00035 inches. -.

; 20 As seen from the ab~ve, all of the layers.. of the - laminate 20 of the second embodiment of this invention, eon- .
sidered individually, are conventional materials. However, in combination, the layer of paperboard ~ase stoc~ 22, the layer of a high strengt-h ~olymer ilm 24; the layer of the 25 aluminum foil ~6 and the first and second layers Qf ther~o-plastic materials 21 and 27 provide a laminate material 20 ::
having superior streng~h and durability/ resistancè *o cuts, .
crac~s and pin holes, as well as superior barrier properties-with regard to penetra-tion by Iiquids and gases, bu~ which ~s:n~verthe~ess su~ta~l~ f~r cutti~g ~ sc~i~g ~nt~-~on- .
tai~ blanks.o~ cou~*i~L pr~u~; eqnLp~e~ Because of ~: its superior propert~es, the laminate 20 is ~ery well suited - ;~ ' .. ~. , .
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8~2 for use in containers ~or holding and storing liguids, syrups and pastes of var~ous comestibles, such as juicest soft drink syrups, particularly diet soft drink syrups, juic~ concen- .
. tratcs and the like. .
In the laminates of this invention, it is considered :
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that-the particular arrangement and nwmber of layers described '~
above are preferred but not critical and t.hat different arrange~
; ments and additional layers may be suitably utilized, aepending . .
on the purpose for w~hich'`the laminate is to be employed. ~or example, it is preferred that the ~ayer of a pol~ner film 14 ;
be-positioned interiorly of the la~er of the paperboarcl base stock 12 in a container made o l~ninate 10. However, if- desired, the polymer film layer 14 can also be locatea exte~riorly of the paperboard base stock 12 or, alternatively, :.
I5 polymer film la~ers can be provided both interiorly and ex- ;
teriorly of the paperboard base stock in a.container. Like- '.`
wise, in the laminate 20, it is preferre~ that the. lay.er of ;~
aluminum foil 26 be located interiorly'of the layer of a polymer film 24 ana that both the polymer film layer and the aluminum 2~ foil layer be located interiorly of the layer of paperboard base' ;
stock 2Z in a container. However, i~.desired, either the poly '- `~
mer ~ilm layer 24 or the layer of aluminum ~oil 26 or bo~h may be located exteriorly o~ the layer of paperboard' ~ase sto¢k 22 `' :~;
~' or layers of a polymer film and aluminum foil may be located both interiorly and exteriorly of the layer of paperboard base stock in a container constructed from the laminate 20.
' ` , ? .: ` ' It is also considered tha~ the invention and many '~
'l of its attendant advantages will be obvious from the fore-. going description and that it will be likewise apparent that v~rious changes may be-made in the o~ constructiQ~ and : arrangement of the parts without departing from the spirit ~; ' ` ` " '~
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ana scope of the invention or sacrificing all of i~s material : advantages, the form herein~efore describe~ being merely pre-ferred embodiments thereof.
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Claims (6)

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

1. In a thermoplastic-coated, paperboard container, suitable for liquids, pastes and syrups, an improved paperboard laminate material which comprises:
a first layer of a thermoplastic material;
a layer of a paperboard base stock, bonded to said first thermoplastic layer;
a layer of a polymer film bonded to said layer of a paperboard base stock, said polymer film having tensile strength at the yield point greater than about 4000 p.s.i. and an elongation at fracture greater than about 200%; and a second layer of a thermoplastic material, bonded to said layer of a polymer film.

2. The container of claim 1 wherein said polymer film is a nylon film.

3. The container of claim 2 wherein first and said second layers of thermoplastic material have a thick-ness about .0005 to about .0020 inches; said nylon film has a thickness of about .0004 to about .0010 inches; and said paperboard base stock has a thickness of about .010 to about .030 inches and a basis weight of about 150 to about 400 pounds/3000 sq. ft.

4. The container of claim 1 wherein said im-proved paperboard laminate material includes a layer of aluminum foil.

5. The container of claim 3 wherein said improved paperboard laminate includes a layer of aluminum foil, having a thickness of about .00025 to about .001 inches, between said layer of a nylon film and said second layer of a thermoplastic material.

6. The container of claim 2 wherein said nylon film is a nylon-6 coated on a surface with saran.