CA2005073C - Composites of paper and plastic film, corrugated paperboard incorporating said composites and methods of making - Google Patents

Abstract

Composites of paper and bioriented plastic film, preferably polyester, are made by passing into and through the nip of a pair of nip rolls a web of paperboard and a web of plastic film, with a layer of molten polymer impregnating and bonding agent extruded into the nip between the webs on the entry side of the nip. The process involves relatively controlling one or more of the speed of the webs, the temperature of the molten polymer, the pressure or spacing of the rolls at the nip, and the rate of extrusion, relative to the porosity and surface characteristics of the paper web such that a substantial portion of the molten polymer impregnates partially into and becomes part of the paper web and a substantial portion lies outwardly of the surface of the paper web and solidifies to form a new surface to which the film is bonded and an which it is supported clear of the paper surface. The product as collected from the nip rolls is a composite comprising paper partially impregnated with solidified polymer, a contiguous layer of solidified polymer having the new surface outwardly of the paper surface, and the plastic film bonded to the new surface. The film may be reverse printed with high quality graphics which are retained in the composite. Various treatments of the film and the paper enhance the characteristics of the composite. The composite is highly resistant to separation or checking when scored and formed into container blanks, and can be combined with a single faced corrugated board in the "double-backer" part of a conventional corrugating machine as the double face liner without adversely affecting the film, its graphics, or the impregnating and bonding polymer. Principal uses are in packaging, point-of-purchase displays, wall panels, and the like.

Description

~~t~'~'~
COhIPpSITES OF Pl~PER A1ND PLP,STIC FILtdl, CORRUGATED
PAPERDOARn Tt~CORPORATTNC SATD CON1P0~2TE$, AIeTD METHODS OF I~IAK~NG
Field o~ the Inyention S 'his invention relates to composites of paper and plastic film, to corrugated pt~perboard inG~rporating such a composite as a liner adhered to the corrugated medium, and to methods of making the composites and the corrugated paperboard. The invention is ~rartiaular~.y useful in the packaging field in the form of containers, but it finds advantageous utility in the fabrication of ether productr~, such as point-af-purchase displays, wall panels, past~rs, and the like, where a combination of the unique structural features of the invention and high quality graphics is desired. The invention is particularly felt, to Satisfy a long-øelt need in the area of falling cartons for packaging, whether as primary packaging or secondary packaging, in composite form ar ag a liner for corrugated paperboard. Although the composite of iaaper and plastic film is highly useful and advantageous in itself, it is a particularly important characteristic of the composite that it can with stand the conditions in the "double beaker" part of a conventional corrugating machine such that it can be combined with a single faced corrugated board to form a double faced Corrugated beard witha~.tt material deterioration of the oomprasite, which, tQ my knowledge, has previously been considered impossible as a practical matter, important char$cteristics of the aam-posite alone or as incorporated in corrugated paperboard include scuff and scratch resistance, strength, stretch resistance, tear resistance, separation resistance, resistance to "checking" (axacking in a scare lin~) an the forming p~ blanks for folding cartons, surface smoothness and gloss, graphics quality and durability, fragrance barrier quality, and moisture barrier quality,

2 ~tl~t~ s aackc~xound Tt is known in the packaging and other arts to form a packaging material in the farm of a laminate of paper and plasf.ic film secured together by an adhesive. for instance, particularly in the field o:~ flea~ible packaging, various films have been laminaf.ed to paper with various adhesives, of which polyethylene is one exempla. ~'or instance, T am aware that a flexible packaging mate vial has bean made by laminating ".Mylar" polyester f i1m to pro-to duct of E. T. Dupont ~eNamours & Co, hnc., Ydilmington, Delaware, U. S. A.> to thin high-quality paper using a polyethylene adhesive. I am also aware of pear p. S.
patent No. 4,254,173 issued March 3, 1981, which proposes a secondary contain~;r packaging material te.g., a six-pa~ek can or bottle wrap) comprising a paper material laminated to a plastic film. The patent discloses various films, including polyester, vari~rus papers such as kraf~t paper of various weights, and various adhesives, including polyethylene, to bond the film to the paper. xt is disclosed in this patent $nd generally known otherwise .hat. the film can be reverse printed with graphics prior to lamination. To my knowledge, all prior proposals have used the adhering agent only as an adhesive and, thus, have used only that amount necessary to achieve adhesion of the two laminated components. I do not find in the prior art any recognition or appreciation of the possibi-lity of using the adhering agent not just as an adhesive but rather as an impregnant and surface enhancer go as to achieve the Characteristics and advantages of the present inv~entton.
It is a basic purpose of the present invention to provid~a an improved composite of paper or paperboard and plastic film in which the adhering agent is used not merely as an adhesive, but rather as an impregnating and bonding agent and as an enhancer of the paper sur~ac~ by essentially farming a new surface. ~y operating under con-ditions which ensure substantial impregnation of the adhering agent into the paper, but with a substantial part overlying the surface of the paper and firmly adhering to the plastic film, Z obtain a product which is highly resistant to separation, which enhanoes and protests the graphics quality of reverse printed film or a painted paper surface, which will withstand the rigors of the double-backer portion of a conventional corrugating l0 machine, which minimizes the norms? adverse effects of scoring, cutting, folding, etc., in the formation of a carton, and which generally is a new and improved product capable of many uses.
features and As ects of the" Invention In making a composite of paper and plastic film in accordance with my invention, a web of paper arid a web of plastic film are passed into and through the nip of a pair of nip rolls, and a layer of molten polymer impregnating and bonding agent is extruded into the nip between the webs an the entry side of the nip, One ar mare of the speed of the webs, the temperature of the molten polymer, the pressure or spacing of the rolls at the nip, and the rate of extrusion is or are controlled relative to the porosity and surface characteristics of the paper web such that a substantial portion of the molten polymer impreg-nates partially into and becomes part a~ the paper wsb, and a substantial portion lies outwardly of the surface o~
the paper web and solidifies to farm an enhanced surface, which is essentially a new surface, to which the film is bonded and on which it is supported clear of the paper surface. there is collected Pram the nip rolls a com-posite comprising paper partially impregnated with solidp ified polymer, a contiguous layer of solidified polymer having the new surface outwardly of the paper surface, and tho plastic film banded to the new surface. In one pre-. 4 ~~~ a(~'~~~
ferred practice of the invention, the inner surface of this ~ilm is reverse printed with desired graphics by any a~
several printing processes. Howavar, the .fnvent~,on also provides improvements where the printing is done on the surface of the paper web itself, since the printed paper surface is protested against scufffng of the print, and hence less ink can be used. ~referak~ly the molten polymer comprises polyethylene, the film is biori$nted, and the paper is kraft paper. A particularly preferred film is bioriented polyester. Adherence of the Components in the resulting composite is such that peeling essentially is not possible, in that the fibers of the paper will separate before the solidified polymer or the film will peel from the paper. As mentioned above, one of the most important and, indeed, surprising features of the com-posite is that it can be passed through the doub3,e-back~r portion of a conventional corrugating machine to form the outside liner of a double-faced corrugated paperboard, which typically involves movement of the exposed face of the film along a hot plate section maintained at tem-peratures up to about 350°F. Equally as important and surprising is the ability of either the composite ar the corrugated paperboard of which it forms the outer 7,iner surface to withstand the rigors of formation into folding carton blanks and folded cartons with little ax no separa-tion, "checking", etc. The graphics quality which Gan be obtained and maintained in thQ end prpduct is believed to be decidedly suparior.
While the Eoregaing sets forth some of the basin features and aspects of the invention, subsidiary features and aspeots of varying degrees of importance will bra brought out in ar apparent from th~ ensuing description and illustration of preferred embodiments.
Brief Description of the brawinr~s Figure 1 is a diagrammatic illustration of apparatus ~~~~~'r ~
and steps involved in praeticirig preferred embodiments of the invention, including the fabrication of the composite arid optional incorporation of the composite in a double-faced carrugated paperboard;
h'igure 2 is a schematic ~ectian (not to scale) of t,ha preferred embodiment of the composite; and Figure 3 is a schematic section of a double-faced corrugated paperboard in which the composite is incor-porated as the double face liner.
Deseriptipn of the Preferred Embodiments Referring to Figure 2 of the drawings, a composite of the invention is shown at 1. The composite includes a paperboard substrate 4, a reverse printed plastic film a, and an impregnating and bonding polymer 3. As shown, the Z5 polymer has been Caused to partially impregnate the paper 4 so as to farm a substantial thickness of impregnated paper 6. tit the same time, a substantial portian of the polymer 3 lies outwardly of the paper surface and essen-tially forms a new and enhanced s~urfaee relative to that of the paper, the reverse printed film 2 being supported an and firmly adhered to the new enhanced surface provided by the polymer 3. The impregnation depth of the polymer into the paper is indicated. at 5. Tha composite. 1 differs markedly from the prior art of which r am aware because of the degree of impregnation of the polymer into the paper and the extent to which the new enhanced surface provided by the polymer lies outwardly of the paper surface so as to prevent or at least minimixe surface characteristics of the paper z~ffecting the reverse printed film 2. zn the conventional prior art laminates of which I am aware, the conventional adhesive does not impregnate the paper at least to any substantial extent, and 'the fibrous character of the paper surface adversely affects the appearance of the film. This latter characteristic of the prior art aan be and probably has been alleviated to some extent by ~~~~'~~
using a high quality clay-coated paper as the substrate.
I~iawever, clay-coated paper is expensive and still would not provide the enhanced surface provided by the overlying polymer in accordance with the present invention. Also, play-coated paper is relatively less porous than conven-tional kraft paper such that it can be more difficult to obtain the desired impregnation of the polymer. Htithout substantial impregnation, together with the overlying polymer, the product simply would not withstand the rigors of folding car~.on formation while provida.ng a high quality, commercially viable end product. I~or would it withstand the conditions in the Bauble-backer portion of a conventional corrugated board making machine.
Figure 2 illustrates a double-faced corrugated paper-board structure which is conventional apart from the incorporation of the composite of the invention as the double face l.lner, as Shawn at 10. The otherwise conven-tional corrugated paperboard structure 7 comprises a corrugated medium 9 and a single face liner 8. While Figure 3 illustrates only one corrugated medium 9 and one single face liner 8, the combination of which is typically known as single faced corrugated board, it will be understood that there are known in the art corrugated paperboard structures consisting of two, three or mare single faced boards glued to each other, the single face liner of one single faced board being glued to the corru-gated medium of another single face liner so as to form a built-up structure, For instance, such a combination of three single faced boards is ty~aiaally referred to as tripls walk. beard. xt is to be understood, therefore, that the present invention encompasse$ alno such built-up structures in which the composite 10 forms the outer liner, such a built-up structure being exemplified by p~,C-turing Figure 3 as including one, two or mare additional single faced boards above and adhered to single face liner (~~r f~
6 or to the correspandinan'~e ace liner of a further single faced board.
Referring now to Figure 1, there is illustrated in the upper part of the figure a diagrammatic representation of apparatus for and the process of making the compcasite of paper and plastic film. collector rolls are shown at 20 and 22 to reflect the fact that various parts o~ the process may be formed at different times and in different locations, although the process could be continuous. From the point represented by the second Collector roll 22, the completed composite can be passed to apparatus, schemat-ically indicated at 23, for formation into a package or blank or any other form, typically involving cutting, scoring, slitting, etc. Alternatively, the completed com-posits 1 can be passed to a corrugated board making machine for incorporation as the outside liner of a double faced corrugated board. Thus, the lower part o~ the figure, connected by the broken line, illustrates a typi-cal "double backer" part of a conventional corrugated board making machine as shown in, for example Griffith et al U. 6. ,patent 3,39,901 dated March 25, 19f9. From this "double backer" part of the machine, the double faced corrugated board is passed to a conventional cutting or blank forming station shown at 38 where it may be cut into sheets, formed into container blanks, etc.
As shown in the upper part of the figure, paper material, typically conventional kraft paper or paper-board, is led from a roll 1.1 through a flame treatment station 12 where the inner surface (the upper surface as viewed in Figure 1) is flamed by a gas burner or burners to burn off' loose fibers and reduce the water content.
xhis has two e.fE~:cts. First, it provides a better paper surface by burning off loose fibers, dust, atc. Second, by reducing the moisture content, it aidt~ in the latex impregnation of the rnalten polymer into the paper since the molten polymer sees to replace the driven-off moisture, The flame treatment is controlled so as not to drive off all the mois~.ure, or tea mush moisture, par-ticularly from the opposite face of the paperboard, since S otherwise the opposite face mould be so dry as to re-attract moisture later and cause unwanted curling.
aasica3ly, the important point is to slightly lower and control the moisture content an the inner face so as to facilitate the desired later impregnation of the molten ~.0 polymer.
From the flame treatment station 12 the paper is passed to a primer application station 12a where the upper surface of the paper is primered (e. g., by a roller appli-cator) with a primer that facilitates and enhances 15 penetration of the molten polymer into the paper when the molten polymer is extruded into the nip of the nip rolls at the combining station. Thus, the primer acts in the nature of a flux for the molten polymer. Such primers axe known in the extrusion casting art, and a typical primer 20 usable in the preferred process of the present invention ig marketed in the fnited states by Morton.ChemiCal Company under the brand name or trademark "Adcote."
From the primer a~ppiication station 12a, the paper 4 passes into the nip between a pair of nip rolls 13 and 19 25 where it is combined with the plastic film and molten polymer 3 which is extruded iota the nip from extrudex 15 at a high temperature. As shown, nip roll 13 is pref-erably a vacuum rail, which is simply a re~ll having its surface covered with very small holes, the interior of the 30 roll being connected to vacuum or suction such that the paper 4 on the surface o~ the roll 13 can be gubje.cted to a controllable suction to assist or control penetration of the molten polymer into the porous paper. The use of a vacuum roll is not Critical to the invention, but it can 35 provide an added measure of control or enhancement of impregnation. Correspondingly, nip roll 14 is illustrated as a chill roll to quickly set or harden the molten polymer

3 to protect the film, but not so quickly as to adversely affect the desired substantial impregnation of the extremely hot polymer into the paper.
The plastic film entering the nip between the nip rollers starts from a roll 16 of plastic film material. The film is passed through a treatment station 17 where it is subject to corona discharge treatment or chemical etching of its inner surface (the: upper surface as viewed in Figure 1).
In general, the corona treatment might be described as bombardment with electrons to create minute surface crevices and cracks. The chemical etching with a solvent or acid can be considered as giving a somewhat scuffed surface. Either surface treatment has a number of desirable effects. Thus, there is a greater bonding area by virtue of the surface "roughening". It is believed that there is less melting resistance at the peaks of the minute crevices or cracks, such that the later heat of the molten polymer tends to melt these peaks and ;prov:id.e better fusion between the film and the polymer. The reduced melting resistance at the peaks tends to slow dissipation of heat. Furthermore, it is believed that th~~ fi:Lm. treatment has what might be termed a "rip-stop" effect, in that it tends to make the point of least resistance against separation of the composite in the paper itself. Still further, the film treatment is believed to increase the :heat resistance of the film, among other things, and hence permit more latitude on the extrusion temperature of t:he molten polymer. As is already known, the plastic film can be purchased with one or both surfaces already pretreated, and either treated or untreated film can be used in the present invention. Preferably even factory pretreated film .is treated again, either before or after printing, or botz, since treating after printing does not attect the print quality, and such post-printing treatment is believed to enhance the ulti-mate bond.
x~rom the corona or chemical etch station 17, the ~ilm passes to a primer station 18 there any oonvantion~al primer, typical a urethane primer, is applied to the ,inner surface of the film. Various such primers are known in the art far improving the bond between a plastic film and ink. A urethane primer is believed to at~aid or minimize problems which might otherwise occur when the molt~n polymer contacts the printed gilm.
From primer station 18, the film passes to a printing operation 19, which can be any of various printing toch-niques known in the art, such as flaxography, offset and gravure, using solvent-based ax water-based inks.
Although not illustrated in Figure l, the printed film optionally can be primered again after printing, which, as stated previously, can eliminate or minimize the possibility of problems when the molten polymer contacts the ink. Thus far, this additional primering step is not considered critical in preferred embodiments of the inven-tion and, theregor~, can be considered as optional, although probably advantageous under particular con-ditions.
Asi previaugly stated, Ghe reverse printed film can then be passed to a collector roll for Storage, transport, etc. Alternatively, it could be gassed directly from the printing station 19, as well as from the collector roll 20, to a further corona discharge treatment or chemical etch operation .indicated at 21. This further treatment does not a~fgct.the print qualit~r and is believed to fa-cilitate the bond between the molten polymer and the printed film.
The .~ilm then passes into the nip between sip rolls 13 and 19 to b~s combined With the molten polymer 3 from ~d~~~~
extruder 15 and the paper ~, from which nip rolls the aom-posi~.e passes through a further corona discharge treatment or chemical at.ch station 21a f.or treatment of the ou~ker film surface of the composite, and onto a collector roll 22. The molten polymer from the extruder 15 is preferably polyethylene of low density and a melt index between 12 and 15. In general, the lowest density polyethylene that gives a satisfactory result is used. However, whege the composite is intended for use as the outer face of a double faced carrugated board, there should be used the lowest density polyethylene that will withstand the tem-perature and other conditions in the °'double backer" part of the corrugated board making machine.
Conditions are controlled arid varied at the combining station to give the desired product. Thus, imprt~griation of the molten polymer, preferably polyethylene, into the paper is controlled by controlling the temperature o.f the molten polymer and the machine speed, the machine speed being controlled by controlling the speed o:f the take-up or collector roll 22. The thickness of the molten polymer passing into and through the nip is controlled by Controlling the speed of the take-up ar collector roll, and hence the rate of travel of the paper and film through the nip. Additionally, the spacing of the nip rolls can be ~raried. 2n a preferred arrangement, one o~ the nip rolls is spring loaded or pneumatically loaded, and the spring pressure or pneumatic pressure can be controlled.
Tn general, s~lthaugh practically any of the conditions at the combining station could be controlled and varied as needed, including the pressure or Spacing of the nip rolls, the thickness, temperature and viscosity of the molten polymer, the speed of the webs, and the rate of extrusion, generally it suffices to controllably waxy only three conditions, these being the take-up roll speed, the temperature of the molten polymer, and the spring or ~~~i ~
pneumatic pressure on the adjustable nip rolls Theoret-ically it would be possible to vary the ap~E~d by cc~.ntrCOl°
lably varying the speed of the nip rolls, but this would be an unnecessary complication relative to varying the speed of the take-up roll.
The schematically illustrated apparatus for malting the composite should be considered as merely typical, al~khauc~h presently preferred. Tn general, the process of making the composite can be carried out on properly cantralled conventional machinery normally used for merely laminating paper, ar machinery normally used far extrusion coat~.ng paper if modified to additionally handle the film, In the typical practice of the process, the treated and reverse printed film is taken up on collector roll 20, which is thereafter transported to and mounted on the com-bining machinery, appropriately modified as xec~uired. As previously mentioned, this could be conventional machinery for eutrusion coating paper modified to handle and treat th~ pla~tlC f llm a The primary purpose of the corona discharge treatment or chemical etch treatment indicated at 21a is to facili-tate gluing of the outar curfaac of the film to itGelf or same other surface in the fabrication of boxes, con-tainers, etc. Thus, it will be understood that the treat-merit ~t station 21a is of the outer surface of the film part of the composite.
The package/blank forming operation indicated at 23 may be any conv~zntianal operation for forming carton blanks, cartoon, boxe$, containers, or simply cutting the composite into individual sheets far use as desired.
Ta camb~.ne the completed composite as part of a corrugated structure, tha roll of composite can be mounted in a conventional corrugating machine ag the supply xoll for the outside liner of double faced corrugated board, as diagrammatically indicated in the lower part o~ figure l, ~~~'~.~

As seen in the lower part of Figure l, which shows a typi-cal., prior art, double backer operation. single faced corrugated board 24, consisting of a web of corrugated medium 2~a having a coextensive web of liner 2~4b banded to tips of the corrugations on one side thereof, is trained over a preheater drum 25, The single face 24, after having its temperature raised tp perhaps 150-200°F by the preheater drum 25, is then passed aver an adhesive appli~-cator 26 and into the combining section generally indi-lU sated at 2?. The composite l, constituting a web of outside liner, as also trained aver a preheater drum 28 and 'hence into the combining section 2? where it is pressed against the adhesive covered flute tips of the single faced board. Qf course, the paper face of the ce~m-polite is the upper faoe as viewed in the lower part of Figure 1, such that the corrugated medium 2~a is pressed against the paper face of the composite 1. The combining section consists, basically, of two parts: a hot plate seotion 29 and a draw section 38. Feat is applied in the hot plate section by a series of steam heated chests 31 having their upper portions aligned to provide a heated, substantially continuous surface. An endless belt 32, trained about a pair of dr~.ven rollers 33 and having a series of smaller rollers 39 bearing on its lower reach, serves to press the single .faxed board 24 and composite 1 toward the steam chest 31. A second belt 35, trained about driven roll~ars 36 and pressure rollers 3?, cooper-ates with the downstream portion of the halt 32 to grip the assembled single faced board and composite outside liner 1 and draw them through the double backer apparatus.
The Completed double faced board is then passed to an appropriate operation station indicated at 38 far cutting, box blank farming, or whatever operation i.s desired.
Apart from the incorporation of the navel composite as the outside liner, the lower portion of Figure 1 may be (~~~~'~~3 m regarded as conventional, and, indeed, this is one of ~.he great advantages of the invention in that this is the first ,instance of which I am aware in which a double faced corrugated board can be made an a aonvent.ional double backer corrugating machine while providing an outside liner having the fea~.ures and chmxacteristics of the com-posite of the present invention. Thus, the invention pro.-vides not only a new anti advantageous composite of paper and plastic film useful in itself, but also provides a 14 composite which can successfully withstand the conditions involved in passing through the double backer part of a conventional double faced board corrugating machine as the outside liner.
Tn the finished composite, adherence of the original components is such that they are essentially inseparable, that is, peeling is practically impossible. The weakest point against separation is in the unimpreg.nat.ed part of ttie paper, and the fibers of ache paper will separate before the molten polymer, preferably polyethylene, will ~0 peel from th$ paper, and typically before the plastic film will peel from the polyethylene impregnant and bonding agent. It is indeed surprising that the composite can gt~
'through a double backer corrugator with no ar little damage t.o the film ar the polyethylene impregnant and bonding agent, considering that ths~ heat plates of the carruga~a~r r,ypically involve temperaturQa of up to 350°F, a temperature at which regular adhesi~res will not stand up and, indeed, a temperature at which it is believed that the polyethylene of conventional "pdly mounted~~ laminates will not stand up. Furthermore, polyethylene being moisture resistant, the new aomposit~a with impregnated polyethylene is highly resi,~tant to separation even when ~~ t V
Successful runs of the composite have bean made in a ILangston $7" X8 corrugator, 1865 moc~s~l, the heat, table in off'~~~~'~~
the double backer being at a temperature o~ appro~tim~ately 340. The composite should run well in similar conven-tional machines under normal, commercial operating con--ditions or, perhaps in same instances, with minimial 5 deviations from normal commercial operating conditions.
It is difficult to attribute the ability o~ the composite to successfully pass through a double backer corrugator to any particular feature or features. However, a tentative theory is that the substantial amount of polyethylene 10 ism~3s~~,;aLly aW l.muMiAy mc~emt ~r~sent in rwhe compOSite softens slightly in passing over the: hot plate, so as to act a$ a cushion and reduce or eliminate scuffing of the film as it drags over the hot plate. Also, it may be that the paper and the substantial amount of polyethylene 15 impregnated therein act as a heaf~ sink to prevent -excessivo softening or bubbling of the polyethylene overlying the paper and forming the new or ~anhanced sur-face to which the film is bonded.
In the making of the camposi~te, conditions should be controlled such that in the completed composite there generally is at least about. 0.5 rnil of polyethylene be-tween the reverse printed film and the surface of the paper. This generally ensures that paper fibers, with or without the preferred flame treatment operation, do not contact the inner surface of the film. In general, in th~
extracted composite the polyethylene should be generally 'uniform over the area of the composite in amount of at least about .five pounds per thousand square feat of cpm-posite, with preferably at least about thre~ pounds of polyethylene per thousand square feet being generally uni-formly present between the prinf.ed film and the surface of the paper to form the new and enhanced surface. Where the paper is of the order of forty-two pound (forty-two pounds per thousand square feet) liner board, the preferred mini-mum total polyethylene is at least about six pounds per '~(lt)~~'~~

thousand square feet of composite, with a preferred range being about nine pounds to faux~.een pounds per thousand sguare feet of composite. Preferably the extruded molten golymer, preferabJ.y polyethylene, passes into the nip at a rate corresponding to a cantinucrus thicknesb of at least about. one mil relative to the speed of the webs, and advantageously this continuous thickness should be at least about. 1.5 mils. As previously mentioned, impregna-tion of the polyethylene or other polymer into the paper z~lay be controlled by controlling the temperature of the molten polye~.hylene and the machine speed. In general, decreasing the temperature of the polyethylene decreases impregnation. Therefore, the polyethylene Chould be kept at a high temperature, typically about 600°F or higher.
If clay coated paperboard is used in the process, it is gene~cally necessary xa use a very high temperature.for the polyethylene so as to ensure migration through the clay coating and impregnation into the paperboard. The clay coated paperboard, even though it has an improved surface relative to uncoated kraft paper, generally should be flame treated abouf, the same as uncoated kraft paper, but possibly slightly less. If using clay coated paperboard, it is important not to drive off too much moisturs, part-cularly from the opposite face of the paperboard, since otherwise the oppo$ite face will reattract moisture and caue~c~ curling, possibly mare so than for uncoated kraft.
While usable j.n the invention, play coated paperboard is npt preferred because of its expense, one feature of the invention Y~eing the provision of a high quality product from a low grade ar relatively inexpensive papex ar paper-board. It. is also to be noted that in general machine finished paper does nit work as well as plain kraft paper a1' ~s~lper15cW1'd. This i~ helidvdc3 tc.~ be l~c:r~u~a ma411ine finished paper has a polished surface, and is not suf-ficiently paraus far the most advantageous practice of the ~~SCI'~3 la invention. In genera,, natural kraft paper, unbleached and uncoafed, works well in the practice of the invention, rn general, the printing of the film will involv~
continuous cover prin~,ing where high quality graphics are desired, although this is not critical to the invention for some uses where high quality graphics are not nosded or where only the structural features are desired. How-ever, as a variant of the invention as previously described, high dual3.ty graphics could be obtained by printing the film without continuous print cover, that is, with some unprinted areas, The film so printed then could be extrusion mounted on metallized film, which then would be combined with paperboard to form a composite as pre-viously described. The metallized surface of the metallized film should be toward the paperboard.
F~part from the packaging field, a principal use of the composite is in the manufacture of wall paneling by laminating the composite to wallboard such as particle board or plywood, the paper surface being laminated to the wallboard. The composite far such use is made in th~ same general manner previously described, except that a lighter weight of paper can be used in the composite, such as ten pound or twelve pound kraft paper. This results in a scuff resistant panel of high graphics quality. Where high gloss is undesired, delust~red film such as delustered "Mylar" film may beg used. Alternatively, polypropylene film could be used. The f3.lcn need not be, but preferably is, biariented since this produces a better duality product, and avoids fabrication problems that might arise because of the re~la~tive~.y less stability of unor~.ented film.
An outstanding characteristic of th$ Composites of the invention relative to conventional laminates is its resistance ~.o separation, "checking," cranking, etc. when being scored to farm box blanks, for instance, or when .. 12/17/99 12:53 FAX 232 5831 SEABY-ASSOCIATES 0 002/002 being folded into completed boxes or ether containers.
Scoring involves substantial compression in a small area, and in many laminates can result in separation or delamination, which does not occur with composites in accordance with the present invention. The reason for this is difficult to pen down to a particular feature, but it is believed to result from a combination of the substantial impregnation of the polyethylene into the paper and the overall cushioning effect provided by the impregnated and unimpregnated polyethylene. No doubt the preferred bioriented polyester film contributes to this also_ In general, containers of which the composite of the invention forms the outer surface have a smooth, high-gloss surface that will not separate or ~tcheck~~ in the corners after scoring.
Cartons or boxes made from the composite per se or in its corrugated form not only provide high strength and resistance to crushing, but also are moisture proof or resistant and retain fragrance, characteristics which axe extremely important in primazy container packaging for products such as laundry detergents, soap, etc.
The paper or paperboard used in the composite of the present invention generally may be any paper suitable for folding cartons or corrugated board or as a substrate for laminating to a backing such as wallboard. The preferred paper is kraft paper of a weight known as liner board or paperboard. As is well-known in the art, kraft paper is paper produced by a chemical cooking process using sodium hydroxide and sodium sulfide, and there are many different types of kraft paper manufactured with various additives and treatments for various applications. Natural kraft paper generally refers to kraft paper which has not been bleached or dyed. Of course, paper itself refers to a web of cellulosic fibers in sheet form- The invention can also make good use of reprocessed paper, that is, not ~~)~~'~' virgin kraft paper. In general, the heaviest paper pres-ently contemplated as useful in the invention is twenty-two point kraft liner board having a weight of about ninety pounds per thout~and square feet. The fi.erm "pointy' as generally used in the industry and herein, means a thickness of one-thousandth of an inch for each point.
For composites to be incorporated in a corrugated struc-ture, a preferred paper is natural kraft paper (unbleached and uneoated), twen~.y-six pounds per thousand square feet or heavier, and ct~mmonly about nine point. ~ther useful paperboard far corrugated structure incorporation is twenty-three pound paper, with t.hirty--three pound to forty-two pound paper being also typically useful, ~'or some uses of the composite itself as secondary packaging, fifty pound, nine point kraft would be a typical example.
In general, one should use the least expensive and lowest grade paper that results in a composite having the necessary characteristics for the particular project, Th~ much preferred film for use in the composite of the invention is bioriented polyester such as bupont's "mylar" film, which is a strong, tough, clear plastic film made principally from polyethylene terephthalate and used widely in packaging, particularly flexible packaging.
Polypropylene might ba ust~d where les6 scuff resistance is needed, but the polypropylene and polyethylene impregnant and bonding anent preferably should be cross-linked by radiation aff.er formation of the composite, Radiation cross~~.inking itself is well-known in the art, The pres-ently preferred "Mylar" film in one-half mil (forty-eight-gauge ) . 4dhere ~Ghe composite is t,o be used in a corrugated structure, the film should be a bioriented film of high heat resistance sufficient to successfully ga through the double-backer part of a cc~nven~.ianal corruga-tor having a heat plate or table operating at about be-tween 250° and 350°.
The preferred impregnating and bonding agent is polyethylene, typically a low density polyethylene having a 5 melt index between twelve and fifteen. For use in a composite to be incorporated in a corrugated structure, one should generally use t:he lowest density polyethylene that will successfully go through the double-backer part of a conventional corrugated board making machine. Examples of 10 suitable polyethylene resins are Eastman 1390, of 0.915 density and melt index of fifteen, manufactured by a subsidiary of Eastman Kodak company. Another example is DuPont's "Alathon" 1570, a low density polyethylene resin known for use in flexible packaging.
15 As previously stated, the molten polyethylene preferably is extruded at 600°F or higher, but this should be varied as needed to achieve the desired substantial impregnation into the paper. In general, the extrusion temperatures used are substantially higher than would be 20 necessary merely to adhere two components together in a conventional laminating process, the higher temperatures facilitating the impregnation. As an example, if the molten polyethylene is of 1.5 mils continuous thickness out of the extruder, conditions should be maintained such that at least about one-half mil will penetrate and impregnate into the liner board.
As a typical example of making a composite for use as the outside liner fo:r a double-faced corrugated board, one could use one-half m:il bioriented polyester film (typically "Mylar"), twenty-three pound paper, and at least one mil thickness of polyethylene out of the extruder and through the nip. As another typical example, the composite would involve forty-eight gauge (one-half mil) bioriented polyester film, a minimum of 1.5 mils thickness polyethylene out of the extruder <~nd through the nip (of which at least one-half mil should penetrate and impregnate the liner board), the polyethylene being extruded between about 600°

and 640°F and being of low to medium density, and twenty-six pound low density kraft paper of nine point thickness. An alternative paper could be thirty-three pound to forty-two pound kraft paper. A:~ an example of a composite for use in secondary packaging, such as a "six-pack" or "twelve-pack"
for cans or bottles, there could be used sixteen point, fifty pound kraft paper, forty-eight gauge bioriented polyester film, and two mils continuous thickness of polyethylene out of the extruder and through the nip.
Although the illustrated embodiment involves reverse printing of the film, and this technique generally will be used where the highest. quality graphics are desired, it is to be understood that the invention is advantageous also where the printing is~ done on the paper surface, that is, printing the paperboard or liner board instead of the film.
A principal advantage of the invention in such embodiments is that the printing on the paper is well protected against scuffing, and hence :less ink can be used. In typical paperboard printing, it is necessary to lay down a fairly heavy coat of ink to allow for scuffing and the like. With the printed paperboard. well protected by the polyethylene and the film in the present invention, this is not a problem. Thus, one can use less ink while achieving better quality printing, using, for example, a 120 line screen. In general, where t:he paperboard is to be printed, it is preferred to use clay coated kraft paper or solid bleached sulfate kraft paper or paperboard or linerboard, typically known in the art as SBS kraft linerboard. Both products have an improved surface relative to untreated kraft paper.
In such embodiments of the invention, not only is there an advantage in the initial printing of the paperboard and in the protection of this printing, but there is also an advantage in appearance arising from the smoothness of the film supported o:~ the new or enhanced polyethylene surface, such that the characteristics of the paper do not carry through to the film arid hence there is improved film gloss where desired.
As mentioned previously, it is known in the art to laminate paper and polyester film, including bioriented polyester film, using a polyethylene adhesive, in, for instance, flexible packaging. It is also known in the art to produce a laminate of polyester and paperboard by coextruding polyester and polyethylene adhesive onto paperboard which has been pretreated by flame priming, the polyethylene adhesive layer being thinner than the one-half mil polyester outer layer, as described in Thompson U.S.
Patent No. 4,455,184, issued June 19, 1984. Kozlowski U.S.
Patent No. 4,064,302 relates to flexible, semi-rigid fabricating material, and mentions "Mylar", among others, bonded to paper or paperboard by an adhesive coating of thermoplastic polyethylene. The previously mentioned Peer U.S. Patent No. 4,254,173 discloses a secondary container packaging material for' use in six-pack can wraps, etc.
comprising a laminate of a paper material laminated to a plastic film, which paper may be natural kraft paper among others, which film may be polyethylene terephthalate, among others, the film being reverse printed, a mentioned adhesive being a polyethylene resin, among others. However, these known or proposed products do not respond to the structural and appearance features of the present invention and are all believed to be distinctly different from the present invention.
In the fore!~oing, I have described and illustrated the inventive concepts with reference to illustrative and presently preferred embodiments of my invention. However, the scope and substance of my invention are as set forth in the ensuing claims as interpreted in the light of the foregoing description and illustrations, and it is ~Q~~~~

fnten~ed that the claims ~e construed as inclining ~lter°
native embodiments, except insn~ax as limited by the prier ~~t o

Claims (34)

I Claim:

1. A method of making a composite of paper and plastic film, comprising passing into and through the nip of a pair of nip rolls a web of paper and a web of plastic film, extruding a molten plastic impregnating and bonding agent into the nip between said webs of a thickness such that the combined thicknesses of the molten plastic, the paper web and the plastic film web passing into the nip are greater than the least dimension of said nip, the porosity of the paper, the pressure of the nip rolls, and the thickness, temperature and vicsosity of said molten plastic being such that part of said molten plastic agent impregnates partially into and becomes part of said paper web and a substantial part of the plastic agent extends outwardly of the paper web surface and forms a new solidified surface on which the plastic film is supported and to which it is firmly banded, and extracting from the nip rolls a composite consisting of paper at least partially impregnated with the plastic impregnating and bonding agent so as to be inseparable therefrom without destruction of the paper, the new surface of the solidified plastic overlying the paper surface, and the plastic film web supported on and bonded to the new surface of solidified plastic clear of the paper web surface, the thickness of the composite being less than the combined thicknesses of the paper web, the extruded layer of molten plastic passing into the nip, and the plastic film web.

2. A method as claimed in Claim 1 wherein the inner surface of said plastic film is provided with a decorative surface, coat before passing into said nip.

3. A method as claimed in claim 2 wherein the inner surface of said plastic film is printed before passing into said nip.

4. A method as claimed in Claim 3 wherein said molten plastic impregnating and bonding agent is polyethylene, said plastic film is bioriented polyester film, and said paper is uncoated kraft paper.

5. A method as claimed in Claim 4 wherein the extruded layer of molten polyethylene passing into the nip is of substantially greater thickness than said bioriented polyester film and substantially less thickness than said paper web.

6. A method as claimed in Claim 5, wherein a double-faced corrugated paperboard is formed from said composite and a corrugated medium of single-faced corrugated paperboard having flute tips on one side of said medium further comprising adhering the paper surface of said composite to the flute tips on one side of the medium so as to form said double-faced corrugated paperboard.

7. A method as claimed in Claim 6, wherein said double-faced corrugated paperboard is formed on the double-facer combining section of a corrugating machine having a hot plate section wherein said composite is adhered to flute tips of said corrugated medium by adhesively applying the paper surface of the composite to the flute tips of a single-faced corrugated paperboard in said double-facer combining section of a corrugating machine such that the composite forms the outside liner of a double-faced corrugated paperboard and the surface of the solidified plastic overlaying the paper surface of the 25a composite moves along the hot plate section in passing through the machine.

8. A method as claimed in Claim 7 wherein said double-faced corrugated paperboard is subsequently subjected to one or more of cutting, scoring, slotting and slitting to form container blanks.

9. A method as claimed in Claim 4 further comprising flame treating the inner surface of said paper before passing into said nip so as to remove some of the loose or protruding fibers and lower the water content so as to provide a smoother paper surface, enhance impregnation by the molten polyethylene to replace the lowered water content, and minimize the risk of paper surface fibers extending to the new plastic surface.

10. A method as claimed in Claim 4 wherein said extruded molten polyethylene is extruded into said nip at a temperature of approximately 600°F, and the nip roll contacted by the film is a chill roll.

11. A method as claimed in Claim 10 wherein said polyester film is pretreated on its inner surface by a pretreatment selected from corona treatment and chemical etching.

12. A method as claimed in Claim 10 wherein the inner surface of the film is treated with a urethane primer before printing.

13. A method as claimed in Claim 4 wherein the materials and operating conditions are such that in the extracted composite there is at least about 0.5 mil of polyethylene between said printed film and the surface of the paper.

14. A method as claimed in Claim 4 wherein the operating conditions are such that in the extracted composite the polyethylene is generally uniform over the area of the composite in an amount of at least about five pounds per thousand square feet.

15. A method as claimed in Claim 14 wherein in the extracted composite at least about three pounds of polyethylene per thousand square feet is generally uniformly present between said printed film and the main surface of the paper,

16. In a corrugated paperboard structure comprising at least one corrugated intermediate member and two substantially flat outer liners adhesively secured to flute tips of corrugations of an intermediate member, the improvement wherein one of said outer liners comprises a composite comprising a substrate of paper, a solidified plastic impregnating and bonding agent impregnated partially into the paper substrate from one face thereof and overlying the surface of said one face and forming a plastic surface outwardly of the surface of said one face of the paper, and a bioriented plastic film supported on and bonded to said plastic surface, said paper substrate having its other face adhesively secured to flute tips of said corrugations such that said film forms the outer surface of said one liner.

17. A corrugated paperboard structure as claimed in Claim 16 wherein said film is transparent and reverse printed on its inner face.

18. A corrugated paperboard structure as claimed in Claim 17 wherein said solidified plastic is polyethylene, and said bioriented plastic film is polyester.

19. A corrugated paperboard structure as claimed in Claim 18 wherein said corrugated paperboard structure is a container blank.

20. A composite of paper and plastic film comprising a substrate of paper, a solidified plastic impregnating and bonding agent partially impregnated into and forming part of the paper substrate and overlying one surface of the paper and forming a new surface outwardly of the paper surface, and a bioriented polymer film supported on and bonded directly to said new surface of solidified plastic clear of said paper surface.

21. A composite as claimed in Claim 20 wherein said film is reverse printed on its inner surface.

22. A composite as claimed in Claim 21 wherein said solidified plastic impregnating and bonding agent is polyethylene and said film is bioriented polyester film.

23. A composite as claimed in Claim 22 wherein said composite is a cut-and-scored blank for forming into a container,

24. A method of making a composite of paper and film comprising passing into and through the nip of a pair of nip rolls a web of paper and a web of plastic film;
extruding a layer of molten polymer impregnating and bonding agent into the nip between the webs on the entry side of the nip; relatively controlling one or mare of the speed of the webs, the temperature of the molten polymer, the pressure or spacing of the rolls at the nip, and the rate of extrusion, relative to the porosity and surface characteristics of the paper web such that a substantial portion of the molten polymer impregnates partially into and becomes part of the paper web and a substantial portion lies outwardly of the surface of the paper web and solidifies to form a new surface to which the film is bonded and on which it is supported clear of the paper surface; and collecting from the nip rolls a composite comprising paper partially impregnated with solidified polymer, a contiguous layer of solidified polymer having said new surface outwardly of the paper surface, and the plastic film bonded to said new surface.

25. A method as claimed in Claim 24 wherein the inner surface of said film is reverse printed.

26. A method as claimed in Claim 25 wherein said molten polymer comprises polyethylene, said film is bioriented, and said paper is kraft paper.

27. A method as claimed in Claim 26 wherein said film is bioriented polyester.

28. A method as claimed in Claim 25 wherein the reverse printed film is pretreated on its inner surface by a pretreatment selected from corona treatment and chemical etching.

29. A method as claimed in Claim 24 wherein said film is pretreated on its inner surface by a pretreatment selected from corona treatment and chemical etching,

30. A method as claimed in Claim 24 wherein the nip ro21 adjacent said paper web is a vacuum roll imposing suction on said paper web, and the nip roll adjacent said plastic film web is a chill roll.

31. A method as claimed in Claim 24 wherein the operating conditions are such that the extruded molten polymer passes into the nip at a rate corresponding to a continuous thickness of at least about 1 mil.

32. A method as claimed in Claim 31 wherein said continuous thickness is at least about 1.5 mils.

33. A method as claimed in Claim 31 wherein the operating conditions are such that the solidified polymer lying outwardly of said surface of the paper web is of at least about 0.5 mil thickness.

34. A product made by the process of Claim 24.