CA1250720A

CA1250720A - Multiple layer flexible sheet structure

Info

Publication number: CA1250720A
Application number: CA000474755A
Authority: CA
Inventors: Dwight D. Redding
Original assignee: American National Can Co
Current assignee: Rexam Beverage Can Co
Priority date: 1984-05-29
Filing date: 1985-02-20
Publication date: 1989-03-07
Also published as: GR81234B; CN85104868A; EP0164232B2; DK164651B; FI843929A0; DK476584A; IL75297A; DE3573912D1; NO845223L; CN1006208B; KR920004801B1; ES295415Y; DK476584D0; AU579124B2; AR242741A1; EP0164232A2; EP0164232B1; ES543562A0; DK164651C; HK12191A

Abstract

MULTI-LAYER SHEET STRUCTURE, METHOD OF MAKING SAME AND
CONTAINERS MADE THEREFROM

Abstract of the Disclosure A multi-layer paperless sheet structure having an oriented sub-structure is provided for making tubular containers for packaging dentrifice and other products. The sheet structure comprises a unique combination of polymer layers, including a uniaxially ori-ented polymer (polypropylene or high density polyethylene) layer.
The sheet structure has two exterior heat sealable surfaces for forming the tubular containers by lap heat seal and the resulting containers exhibit improved strength and deadfold retention pro-perties. A method is also provided for forming the sheet struc-ture with its oriented substructure,

Description

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The presellt invention yenerally relates to rnulti-~layer flexible sheet structures and to containers made there-from. In one aspect, this invention is concerned with a paper-less multi-layer flexible sheet structure, including an oriented substructure, for use in making flexible tubes of the type com-monly employed for packaging and dispensing paste-type products.
In other aspects this invention is directed to such multi-layer sheet structures, including a uniaxially oriented substructure, and to containers and tubes made therefrom.
Metal foils have long been used for making containers and tubes for packaging and dispensing various products, includ-ing paste-type products. Such containers and tubes have fre-quently been made from a single foil layer. However, containers and tubes rnade from metal foil have had several disadvantages compared to containers made of plastic. ~etal tubes tend to dent and deform more readily, crack with a moderate amount of flexure and they are more expensive.

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More recently, a large share o~ the tube market has been taken by flexible sheet structure materials having a multiplicity of polymeric layers. Typically, such tubes have an inner heat sealable layer, an outer heat sealable layer, and a barrier layer interposed therebetween. Additional layers may be used in con-ventional structures to provide other properties or qualities.

Layers of a non-polymeric nature, such as paper and thin metal foils, may also be included in these sheet materials to provide specialized performance functions. It is known, for example, to provide a ~ayer of thin aluminum foil as a high quality barrier layer. When foil is used, it is common practice to use a highly adherent polymer to adhere the foil to its adja-cent layers. While such structures have had some success in the commercial market place, they have exhibited certain disadvantages which have limited their use.

Certain products are particularly hard to hold because of their chemical activity in attacking the inner tube layers and particularly the aluminum foil layer. This problem has been addressed by using chemically-resistant polymers as the tube interior layer to protect the foil. In order to alleviate this problem, commonly assigned, copending application serial number 306,675 discloses the Use of linear low density polyethylene as the innner sealant layer of the tube.

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It is also known to provide a layer of paper for imparting dimensional stability, which is particularly important for printing, and which also provides an aesthetically pleasing and aseptically clean appearing white background. The lnclusion of a paper layer also improves the deadfold retention properties of the tube.

Tube fallure is generally attributed to their rough handl~ng during shipment, as a result of which the tube sidewall splits, allowing the contents to ooze out. It has been observed that the paper layer in the laminate is the weakest part of the structure and once it begins to fail, the entire tube is weakened and breaks.

The ability of a tube to withstand rough handling is related to its ability to withstand "drop test", hereinafter also described as "tube drop test", in which a tube filled with pro-duct is repeatedly dropped until it fails. All tubes shipped in commerce may be expected to be sub~ected to rough handling, essentially independent of the product contained therein, and are thus sub~ect to handling stresses as encountered in the tube drop test. Economical construction of tubes which are consistently capable of passing the tube drop test has remained a problem.
This problem has been addressed by using a reinforcing layer of a biaxially oriented polypropylene in the interior of the sheet structure, as described in said commonly assigned U.S. Patent No.
4,418,841 issued December 6, 1983. The structure disclosed in said U.S. Patent, however, contains paper, and while certain improvements in strength are realized in such structures, it is desirabl~ to provide other structures which afford the dimen-sional stability and economy of such paper-containing structures, and which also have increased strength and other improved attributes.

Improvement in preventing chemical attack by the pro-duct in the container is described in commonly assigned Canadian ~.
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Patent No. 1,201,050 issued August 19, 1986, in which a poly acrylic acid chrome complex primer is used between the foil and the ethylene acrylic acid copolymer on -the sealant side of the foil.

The present invention provides a dimensionally stable multi-layer structure without a paper layer.

The present invention also provides such paper-free, multi-layer laminates for making tubes which are resistant to chemical attack by products of the type packaged in dispensing containers.

The present invention further provides containers and tubes having acceptable deadfold and crease retention properties.

The present invention provides a unique multi-layer laminate sheet structure, including an oriented substructure, which can be formed lnto containers and tubes for packaging vari-ous products. Due to the uniqueness of this multi-layer laminate structure, the resulting containers are resistant to chemical attack by the packaged ingredients, exhibit acceptable deadfold crease retention properties and can withstand rough handling dur-ing shipment without failure due to cracks.

In one embodiment of the invention, the sheet structure comprises, in order, a first heat sealable layer on a first one of two exterior surfaces, a first adhesive layer of ethylene acrylic acid copolymer, and a layer of metal foil. A second adhesive layer of ethylene-acrylic acid copolymer adheres the ,..~.

125~)'720 -'oil to a first layer of polyethylelle or ethylene copolymer.
On the opposing surface of the first polyethylene layer is a second layer of polyethylene or ethylene copolymer. The second polyethylene layer is adhered through a first primer to a layer of uniaxially oriented polypropylene having an orientation ratio between about 2/1 and about 6/1 and preferably between 3/1 and 9/1. A third adhesive layer adheres the polypropylene layer to a second heat sealable layer on the second exterior surface of the sheet material. Significantly, the polypropylene layer is within about 1.5 and preferably within about 1 to about 1.5 mil of the second extericr surface of the sheet structure.
1~ a preferred structure of this invention, the second heat sealable la~er, the third adhesive layer, and the pclypropy-l~ne layer, and produced by coextrusion as a three-layerfilm sub-structure, and uniaxially oriented simultaneously, the orientation ratio being between about 2/1 and about 6/1 and pre-ferably between 3/1 and 4/1. In the finished sheet structure the three layer oriented coextruded film is suitably 2.0 - 2.5 mils thick and the polypropylene layer is about 1.0 mil thick.
In order that the sheet material of the invention may be formed into a tubular container, the first and second heat sealable layers must be compatible for heat sealing to each other.
The invention also contemplates providing a flexible dispensing tube made oE the multiple layer sheet structure here-inabove described, with the uniaxially- oriented layers disposed toward the exterior surface of the tube.
The invention also provides a method of making a multiple layer sheet material structure, which comprises first coextruding a three-layer film and uniaxially orienting the film at an orientation ratio of about 2/1 to about 6/1 and preferably between 3/1 and ~/1 to produce an oriented film sub-structure ~ ~ 5 ~Z ~

having three consecutive layers of low density polye-thylene and suitably 0.8 to 1.2 mils, ethylene-methyl acrylate copoly-mer and suitably 0.2 to 3 mils, and polypropylene of about 1 mil. The oriented film is corona treated on the external polypropylene surface, and the treated surface is then primed with polyethylene imine. A previously formed low density polyethylene film suitably having a thickness of 2.75 to 3.25 mils is then extrusion laminated to the treated and primed polypropylene layer, using low density polyethylene suitably of about 1 mil as the extrusion laminant. The previously formed low density polyethylene layer is then extrusion lami-nated to an aluminum foil layer using ethylene-acrylic acid copolymer suitably of 1 mil as the extrusion laminant.
Optionally, the exposed surface of the foil may be primed using a polyacrylic acid based primer.
The foil is finally coextrusion coated with a coex-trudate of ethylene-acrylic acid copolymer and polyethylene or linear low density polyethylene, with the ethylene-acrylic acid copolymer being coated onto the foil.
Thus in another aspect thereof the present invention provides a method of making a paperless multi-layer sheet structure comprising the steps of: (a) coextruding three po]ymeric layers to form a film substructure of said layers and uniaxially orienting said film to an orientation ratio of from about 2/1 to about 6/1, said layers being, consecutively, a polyethylene layer, a first adhesive layer and an orienting polymer layer; (b) priming a surface of said orienting polymer layer with a primer; (c) extrusion laminating a layer of polyethylene to said primed surface of said orienting polymer layer; (d) extrusion lam~nating said polyethylene layer to an aluminum foil layer using a second polymeric adhesive layer as the extrusion laminant, and (e) coextrusion coating said foil ~ :, ~zs~a with a coextruda-te a third adhesive layer and polyethylene to complete the sheet structure. Desirably, said orientation ra-tio is from about 2/1 to about 5/1. Preferably, the method further includes the step of priming said foil with a poly-acrylic acid chrome complex primer prior to coextrusion coat-ing of said foil. Suitably, the method further includes the step of priming said foil with a polyacrylic acid chrome com-plex primer prior to coextrusion coating of said foil. Desir-ably, said orienting pol~mer is polypropylene.
In another aspect thereof the present invention pro-vides a method of making a paperless multi-layer sheet struc-ture comprising the steps: a) coextruding a three-layer film having three consecutive layers of low density polyethylene, ethylene-methyl acrylate copolymer and polypropylene, b) uni-axially orienting the ilm at an orientation ratio of about

2/1 to about 6/1 to produce an oriented film substructure, c) corona treating the external polypropylene surface, d) priming the treated surface with polyethylene amine, e) extrusion lam-inating a low density polyethylene film to the treated and primed polypropylene layer using low density polyethylene as the extrusion laminant, and f) extrusion laminating said low density polyethylene layer to an aluminum foil layer using ethylene-acrylic acid copolymer as the extrusion laminant.
The present invention will be further illustrated by way of the accompanying drawings, in which:
Figure 1 is a cross-sectional view of a multi-layer sheet structure of a preferred embodiment of the invention;
Figure 2 is a cross-sectional vlew of a multi-layer sheet structure in accordance wlth a different embodimen-t of the invention;
Figure 3 is a cross-sectional view of a multi-layer sheet structure illustrating a further embodiment of the nventlon;

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- Figure 4 :is a perspective view of the tube forrning assembly illustrating the manner oE shaping a sheet structure into a tube wherein at least some of the layers of -the sheet struc-tures are oriented in the machine direction;
Figure 5 is a view similar to Figure 4, but wherein at least some of the layers of the multi-layer structure are oriented in the cross machine direction during tube forming operation;

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Figure 6 is a partially cut-away view of a tube formed of a multi-layer sheet structure with orientation in the machine direc-tion;
Fi~ure 7 is a view si~ilar to Figure 6, but with orientation in the cross machine direction, and Figure 8 is another cross-sectional view of a multi layer sheet structure which is the most preferred embodiment of the present invention.

Referring now to the drawings, and first to Figure 1, the multi-layer sheet structure is generally designated as 10. Layers 12 and 20 are both low density polyethylene (LDPE). Layer 22 is pig-mented low density polyethylene. Layer 14 is ethylene-methyl acry-late (EMA) copolymer. Layer 16 is propropylene (PP). Layer 18 is polyethylene imine (PEI~ primer. Layers 24 and 30 are both ethy-lylene-acrylic acid (EAA) copolymer. Layer 26 is aluminum foil.
Layer 28 is a polyacrylic acid chrome complex primer, and Layer 32 is linear low density polyethylene (LLDPE). Thus, the multi-layer sheet structure shown in Figure 1 does not contain paper.
In order to realize the advantages of this invention, the poly-propylene Layer 16 must be uniaxially oriented, with an orienta-tion ratio of frorn about 2/1 to about 6/1 for example 3/1 to 4/1. Additionally, it has been found that unexpected advantages can be realized when the uniaxially oriented polypropylene layer is within 0.2 mil to about 4 mils, preferably about 1 to about 1.5 mils of the surface of the sheet structure forming the out-side of the tube.

" ~s~o In order to impart beneficial and highly desirable propertieC
to containers made fro~ the multi-layer sheet structures of this invention, it is important that the polypropylene layer be uni-axially oriented and that this layer be disp~sed at a certain S distance from the outer surface of the container. Thus, the poly~
propylene Layer 16 is uniaxially oriented to the desired orienta-tion ratio and thereafter laminated, such as by extrusion lamina-tion, to the LDPE Layer 12 using the EMA adhesive layer as the extrusion laminant to form a film substructure made of Layers 12, 14 and 16. Or, as it is often more convenient, the Layers 12, 14 and 16 are coextruded to form the film substructure of these three layers, and thereafter this film is uniaxially oriented to obtain the desired orientation ratio of the polypropylene layer.
Regardless of how the film substructure is formed, the poly-propylene layer is corona treated and primed with PEI primer Laye 18 before extrusion laminating to the LDPE Layer 20 of the sub-structure made of the Layers 20, 22, 24, 26, 28 and 32. The latter substructure may also be found separately as a film which is then extrusion laminated to the film substructure of Layers 12, 14 and 16, usin~ the PEI Layer 18 as the extrusion laminant, as aforesaid.

The advantages resulting from the inclusion of a uniaxially oriented polypropylene layer are realized both wnen this layer is oriented in the machine direction (MD~ or cross-mac'nine direction (CMD), i.e., at 90 degrees relative to the MD.

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Whether the PP layer is oriented in the ~ or C~, in gen-eral, beneficial results are realized when the orientation ratio is from about 2:1 to about 6:1, preferably from about 3:1 to about S:l.
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~ ile PP is the polymer of choice of Layer 16, this layer may, if desired, be replaced with oriented high density poly-ethylene (HDPE), a blend of PP and HDPE, or with nylon.

In addition to using a layer of uniaxially oriented PP, it is also important that this layer be within certain critical dis-tance from the outer surface of the container. Thus, it has been found that most beneficial results are realized when the PP layer is disposed within about 0.2 to about 4 mils, preferably within about 1 to about 1.5 mils of the outer surface of the tube.

Also, while Figure 1 depicts a film substructure of the Layers 12, 14 and 16, the present invention also contemplates a film substructure made of the PP Layer 16 and EMA Layer 14 without the LDPE Layer 12. In such film the PP Layer 16 is either coated with, or is extrusion laminated to the EMA Layer 14.

The inclusion of uniaxially oriented PP layer in the multi-layer sheet structure of this invention as herein described im-parts several highly advantageous properties to the tubes madeof such structure. These advantages include greater stability for printing and withstanding subsequent processing operations;
increased strength and, surprisingly, improved deadfold charac-teristics.

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Referring now to Figure 2, the overall sheet structure is generally designated as 110. The several layers in this sheet structure are designated by 100 series rsference numerals corre-sponding to the two digit reference numerals of like layers serv-ing the same or similar functions as the layers in Figure 1.Thus, for example, Layers 12 and 112 are both LDPE serving as the outermost layers of their respective sheet structures, and they are heat sealable. Similar comparisons apply to the remainlng layers of Figure 2 except for Layers 114 and 119. Layer 114 is maleic anhydride modified polypropylene adhesive used instead of the EMA Layer 14 in Figure 1, and Layer 119 is an ink layer or coating used for printing artwork on the PP layer.

In Figure 3, the overall sheet structure is designated as 210. The several layers in this Figure are designated by 200 series corresponding to the two digit reference numerals of like layers serving the same or similar functions as the layers in Flgure 1. Thus, Layers 212, 214 and 216 represent, respectively, rJDpE~ EMA and PP forming a film sub-structure as aforesaid.
Layer 218 is PEI; Layers 220 and 232 are both LDPE; Layers 224 and 230 are both EMA; Layer 226 is aluminum foil; and Layer 232 is LDPE.

In order to form the tubular body of a typical dlspens-ing container, reference may be had to Figure 4 which shows an apparatus for continuously forming tubing from flat stock. Such apparatus is illustrated and described in commonly assigned United States Patent No. 3,540,g59, issued to J.H. Conner on November 17, 1970. Thus, as shown in Figure 4, the strip of the multi-layer sheet structure of the present invention, designated as W, is fed through a guide roller 301 onto a worklng piece or mandrel 303 which is enclosed in a shaping block 305. During its travel, the strip W is progressively folded around the mandrel 303 and joined together as a lap seam L by a heated pressure roller 307. The arrows A, B and C in Figures 4 indicate the direction of orientation of the strip W, i.e., in the machine ~ ~ S ~ ~ 2 direction (MD).

Figure 5 illustrates the method of forming tubing from a strip of the multi-layer sheet structure of the present inven-tlon, designated as Wl wherein the direction of orientation is inthe cross machine direction (CMD). The apparatus employed in Figures 4 and 5 are otherwise the same and the various parts of the apparatus are designated with the same reference numeral fol-lowed by the reference letter A for simplicity.

In Figure 5, the strip Wl fed through the apparatus with its direction of orientation at about 90 degrees relative to the flow direction as shown by the arrows D, E and F. Hence, in the resulting tubing, the sheet structure will be oriented in the CMD.
Figures 6 and 7 illustrate tubular containers, gener-ally designated as 401 and 501, respectively. The arrows A, B
and C in Figure 4 and D, E and F in Figure 6 shows the direction of orientation of the uniaxially oriented layers in the struc-ture.

In order to realize increased strength and improved deadfold retention properties in the multi-layer sheet struc-tures, and in .,~ "

lZ5L)720the containers made therefrom, the oriented PP layer must be disposed within about 0.2 to about 4 mils, preferably within about 1 to 1.5 mil of the surface of the sheet structure. Since Layer 12 functions as a heat seal layer in forming the lap seal on the tube sidewall, it should, as a practical matter, be suffi-ciently thick to consistently form a heat seal. Layer 14, then, should be as thin as possible while still fulfillin~ it adhesive function for adhering ~ayers 12 and 16 to each other. In prac-tice, the Layer 12 is from about 0.8 mil to about 1.2 mils thick, and the Layer 14 is from about 0.2 to about 0.3 mils thick While PEI is shown as a Layer 18, it will be appreciated that, in its use as a primer, it is a thin coating and is shown as a layer for illustration purposes only. Li~ewise, Layer 2~ is also applied as a thin coating e~en though it is shown as a layer for illustration. Layer 22 is usually a pre-formed film of pig-mented white LDPE, and is typically about 2.75 to about 3.25 mils thick. I,ayer 20 (LDPE) is conventionally used as an extrusion laminant to join Layers 22 and 16, and is typically about 1.0 mil thick.

Layer 24 is conventionally used as an extrusion laminant to join Layer 22 to the foil of Layer 26. The foil is advantageously between about 0.25 and about 0.7 mil thick, depending on the anti-cipated product and its use. The foil may be extrusion coateddirectly with a relatively thick layer of about 2.0 mils of EAA
and about 1.2 mils of LDPE as in Figure 3. Alternatively, as in Figures 1 and 2, the foil may first be primed with polyacrylic acid chrome complex primer (Layers 28 and 128). With the foil ~2~i~72(:~

thus primed, the primer provides a certain degree of resistance to chemical attack. In these structures, the thickness of the expensive EAA layer may be reduced to that required to perform its adhesive function, namely about 0.5 mil. The outer sealant layer of LLDPE is about 2.0 mils.

Tubes made with the sheet structures of this invention show improved strength in surviving drop tests described hereinafter.
Suprisingly, they also show increased deadfold retention.

The following examples serve to illustrate the present invention.

Example 1 LDPE, EMA, and PP are cast coextruded using three extruders feeding into a coextrusion die, and formed into a three-layer coextruded film. The coextruded film is uniaxially oriented at an orientation ratio of 3.2/1 to form an oriented three-layer substructure 2.0 mils thick, with the following thicknesses:

0.8 mil LDPE
0.2 mil EMA
1.0 mil PP

The PP surface is corona treated and primed with PEI primer.
The PP surface is then extrusion laminated to a previously formed 2.75 mil film of pigmented LDPE, using 1.0 mil LDPE as the ex-trusion laminant, to make a five-layer substructure excluding the primer. The 2.75 mil LDPE surface layer is then extrusion lami-nated to a 0.7 mil aluminum foil, using 1.0 mil EAA as the ex-lZ5{)7~0 trusion laminant. The opposite side of the foil is then primed with polyacrylic acid chrome c~mplex primer and coextrusi~n coated with 0.5 mil EAA and 2.05 mils LLDPE, with the EAA against the foil, and the LLDPE layer forming the second outer surface the completed sheet structure. The first outer surface is the LDPE in the unaxially oriented three-layer substructure.

Example 2 Another sheet structure is made using the same method and materials as in Example 1, but with some different layer thick-nesses. The three-layer oriented substructure is 2.5 mils thick, as follows:

1.2 mils LDPE
0.3 mil EMA
1.0 mil PP
The other differences are using 0.25 mil foil and 2.0 mil LLDPE.

Example 3 Another sheet structure is made as in Example 2 using the sa~e method and materials, except that the three-layer oriented substructure is two mils thick, as follows:

0.8 mil LDPE
0.2 mil Admer -1.0 mil PP

Admer is maleic anhydride modified polypropylene-based adhesive il;~SV720 polymer. After the PP layer is corona treated and primed, it is printed with ink before being extrusion laminated to the LDPE
layer, which in this case is 3.25 mils thick.
. ., Example 4 Another sheet structure is made as in Example 3 USillg the same method.and ~aterials, except that in the three-layer orientec substructure, 0.2 mil EMA is substituted for 0.2 mil Admer and the ink is omitted. The extrusion laminant LDPE layer corres-ponding to Layer 220 in Figure 3 is 0.8 mil. The polyacrylic acid chrome complex primer is omitted; and the final three layers are:

.25 mil foil 2.0 mlls EAA
1.2 mils LDPE

Table 1 shows the complete structures of Exa~ples 1-4 along with structures of comparative Examples A, B and C which are not within the scope of this invention. Comparative Example A is paperless, but does not contain a uniaxially oriented layer.
Comparative Example B contains a uniaxially oriented PP layer, but it is substantially farther than l.S mils from the surface of the sheet structure. Comparative Example C is a conventional sheet structure used commercially to make toothpaste tubes.

EX. 1 X. 2 0.3 mil LDPE* 1.2 mi~ LDPE-~
O.2 mil EMA* 0.3 mil EMA~
1.0 mil PP* 1.0 mil PP~
Primer Primer 1.0 mil LDPE 1.0 mil LDPE
2.75 mils white LDPE 2.75 mils white LDPE
1.0 mil EAA 1.0 mil EAA
0.7 mil foil 0.25 mil foil Primer Primer O.5 mil EAA 0.5 mil EAA
2.05 mils LLDPE 2.0 mils LLDPE
10.0 mils Total 10.0 mils Total EX. 3 EX. 4 0.8 mil LDPE~ 0.8 mil LDPE:~
0.2 mil Admer* 0.2 rnil E~*
1.0 rlnil PP^- 1.0 mil PP*
Primer . Primer Ink 0.8 mil LDPE
1.0 mil LDPE 3.25 mils white LDPE
lS 3.25 mils white L~PE 1.0 mil EAA
1.0 mil EAA 0.25 mil foil 0.25 mil foil 2.0 mils EAA
Primer 1.2 mils LDPE
0.5 mil EAA 10.0 mils Total 2 0 mils LLDPE
10.0 mils Total Comp. Ex. A Comp. Ex. B Comp. Ex. C
2.5 mils LDPE 2.5 mils LDPE 1.5 mils LDPE
0.5 mils LDPE 1.25 mils LDPE Ink

3.25 rnils white LDPE 2.0 mils PP~ 2.0 mils white LDPE
1.O mil EAA 1.5 mil white EAA 1. 6 mils paper 0.25 mil foil 0.25 mil foil 0.7 mil LDPE
Primer Primer 3.3 mils EAA
0.5 mil EAA O.S mil EAA 0.7 mil foil 2.0 mils LLDPE 2.0 mils LLDPE 2.0 mils EM
10.0 mils Total 10.0 mils Total 1.2 mils LDPE
13.0 mils Total `:;Uniaxially oriented layer " ~'~5~)~Z() Portions of the sheet structures of Examples l, 2 and 3 and comparative Examples A, B and ~ were made into dispensing tubes in known manner as described in the aforementioned, com~only assigned United States Patent No. 3,540,959. .Thus, the tubes were formed by forming a longitudinal lap seam by heat sealing technique to form tubes of l-ll/32 inches in diameter. The tubes were then cut to length and heads were injection molded into one end, including the use of conventional inserts, and capped. The tubes were filled with product and the ends sealed. The filled tubes were then subjected to testing to demonstrate their desired properties.

Drop Tests lS In a head drop test performed with tubes filled with tooth-paste, a tube was dropped on its capped head from a height of

4 feet onto a hard surface. The same tube was repeatedly dropped until it failed, with a maximum of ll drops per tube, 3 tubes per variable.
In evaluating the tubes according to the drop tests, each drop was counted as one point, and the points for each example were averaged to obtain a representative score for each example.
Table 2 shows that tubes made with sheet structures of this in-vention are physically as strong as tubes from comparative Ex-a~ples A and B, and much stronger than tubes from comparative xample C. - 18 -. - .

lZ5~7;Z0 Deadfold Tests In using a tube filled with product such as a tube of tooth-paste, it is desirable to be able to flatten.the tube as the pro-duct i5 used, making subsequent dispensing easier Thus thedeadfold characteristics of a tube sheet structure material pre-dict the ability of that tube to stay flat. This characteristic is specificall)~ important when testing the fold on the side of the sheet structure that simulates the fold when a tube is flattened; namely folding onto itself that surface that would form the inside of the tube, such as Layer 32 in Figure 1.

In performing the deadfold test, a Inetal weight is used to establish the fold. The metal weight is a rectangular rod 1 inch square and 15 inches long, weighing 4 pounds. Each test specimen of the sheet structure is 4 inches long and 1 inch wide. The strip is placed on a flat surface and bent over across its 1 inch width without creasing it. The weight is then placed squarely and gently across the bent strip so that it folds it down flat and remains squarely on the folded strip. After 30 seconds the weight is removed and the sample is tipped on its edge. 30 seconds after the weight is removed a protractor is used to read the angle. Table 2 shows that deadfold retention for structures of this invention is better than deadfold retention of comparative Examples A and B and, in the case of Example 1 is nearly as good as comparative Example C.

5'~J720 _ _ Caliper Drop .Deadfold Example (mils) Stren~th Retention 1 10.0 11 23 2 10.0 10 54 3 10.0 9 34~
Comp A 10.0 11 104 Comp B ~0.0 8 76 Comp C 13.0 1 22 To put the data into perspective, some basic overall com-parisons need to be pointed out. The commercial structure of comparative Example C has good deadfold, poor drop strength, and is 30% thicker than the other examples, and is more costly.

Comparative Examples A and B h~ve good drop strengths and are comparatively less expensive, but have poor deadfold retention.
The examples of the invention have good drop strength, are relatively inexpensive, and approach the commercial structure in deadfold characteristics.

As indicated hereinabove the strength and deadfold charac-teristics of the sheet structure materials of this invention are believed to be attributable to the uniaxial orientation of the PP
layer in combination with its proper positioning in the structure.
Thus it is anticipated that similar results will be obtained with similar structures wherein only the PP layer is oriented or wherein the PP and the LDPE layer such as Layer 12 in ~igure 1 are oriented.

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As it was previously mentioned, the advantages of the present invention will also be realized when the PP layer, or the film substructure of PP, EMA and LDPE (Figure 1), or their equivalent layers in Figures 2 and 3, are oriented in the cross machine di-S rection (CMD). T~lus, two tubes of similar dimensions (1-11/32" x 7-7/16") from two multi-layer sheet structures, both having layers as shown in Figure 1 as follows:

Example 5 0.7 mil ~DPE*
0.3 mil EMA^
2.0 mils PP*
PEI ~rimer 0.75 mil LDPE
2.75 white LDPE
0.75 mil E M
0.25 ~il foil Polyacrylic Acid Chrome Complex (Primer) O.S mil EAA
2.0 mils LLDPE
10.0 mils * oriented The tubes were formed by the method described in the aforementionec United States Patent l~o. 3,540,959. The PP layer in one of the sheet structures was oriented in the MD, and in the other sheet structure, the PP layer was oriented in the CMD. The tubes were filled with Crest BSM toothpaste, headed, including a urea insert, and capped. Five tubes of each type (MD and CMD) were dropped on their heads from a height of four feet. In the case of the MD
oriented tubes, all five failed during the first drop, with four tubes failing along the sea~, and one failing in the body. In the case of the CMD oriented tubes, four of the five tubes survived 10 drops, but one failed at the sea~ and head bond on the first drop.

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It ~ust be noted that the thickness of the PP layer in the tubes formed in Example 5 was 2~0 mils compared to a thickness of 1.0 mil in Examples 1-4. The increased PP thickness in Ex-ample 5 requires better control of the seaming conditions, par-ticularly in case of tubes made with multi-layer sheet structure oriented in the MD. As shown in Example 5, however, increased thickness of PP layer is less disadvantageous in case of CMD ori-ented tubes.
In general, it is preferable that the thickness of the PP
layer be less than about 2 mils, otherwise the seaming conditions during formation of the tubes must be more carefully controlled.
Thus, in practice, optimum thickness of the PP layer is about 1 mil.
In the most preferred embodiment of the invention, high density polyethylene may be substituted for polypropylene. This embodi-ment is illustrated in Figure 8.
Referring to Figure 8, the layer 812 is low density polyethylen~
and layer 814 is high density polyethylene. The remaining layers are as follows: layer 818 is polyethylene imine (PEI) primer;
layer 820 is low density polyethylene; layer 822 is pigmented low density polyethylene; layer 824 is ethylene-acrylic acid copolymer layer 826 is aluminum foil; layer 828 is polyacrylic acid chrome com?lex primer; layer 830 is ethylene-acrylic acid copoly~er, and layer ~32 is linear low density polyethylene (LLDPE).
It will be noted from Figure 8 that the structure shown therein is similar to the structure of Figure 1, except that the polypro-pylene layer 1~ and the ethylene-methyl acrylate layer 14 of the structure of Figure 1 have been replaced wi~h a single layer of high density polyethylene.

` ~ 7~) As in the embodiment illustrating the use of uniaxially orientec polypropylene, the high density polyethylene is also uniaxially oriented, either in the machine direction (MD) or in the cross-machine direction (C~). The sheet structure illustrated in Figure 8 is otherwise formed in the same manner as hèreinbefore described in connection with the other embodiments of this invention When usin~ high density polyethylene as in the embodiment shown in Figure 8, its orientation ratio can be at least about 3/1, and i preferably about 4/1 to about 8/1. Also, the high density poly-ethylene layer should be placed at about the same distance fromthe surface as in the case o using polypropylene.
Examples 6 and 7 illustrate a sheet structure having the severa layers depicted in Figure 8.

lSExample 6 1.05 mils LDPE
1.6 mils HDPE
PEI Primer 1.3 mils LDPE
2.25 mils Pigmented LDPE
1.1 mils EAA
0.7 mil foil 20Polyacrylic Acid chrome complex (Primer) 0.5 mil EAA
2.0 mils LLDPE

Example 7 25The sheet structure in this example is similar to Example 6 except that an ink layer is interposed on one or both sides of the hi~h density polyethylene layer.
The multi-layer sheet structure shown in Examples 6 and 7 ex-hibit improved properties similar to the multi-layer sheet structu using uniaxially oriented polypropylene as hereinbefore described.

l . ~2S~

Those skilled in the art will see certain polymer substitutions which may be made without detracting from the overall performance of the sheet structure, depending on the intended use. The two outer layers of the structure, for example, may be made of other heat sealable polymers, so long as they are co~patible for heat sealing purposes. Depending on the polymer selected for the outer layer as at 12, an alternate adhesive polymer may be selected for Layer 14. Also, higher density polyethylene, or ethylene copolymer s may, in some cases, be advantageously used instead of LDPE in the interior layers of the sheet structure, as in Layers 20 and 22.
Likewise, any graphics, or other ink printing could be done at an alternate layer surface.

Claims

THE EMBODIMENTS OF THE INVENTION IN WHICH AN EXCLUSIVE
PROPERTY OR PRIVILEGE IS CLAIMED ARE DEFINED AS FOLLOWS:

1. A multi-layer sheet structure having two exterior heat sealable layers, comprising, in order:
(a) a first heat sealable layer on one of said exterior surfaces;
(b) a first adhesive layer;
(c) a layer of metal foil;
(d) a second adhesive layer;
(e) a first layer of polyethylene or ethylene copolymer;
(f) a second layer of polyethylene or ethylene copolymer (g) a first primer;
(h) a layer of oriented polymer selected from the group;
consisting of polypropylene, polyethylene, ethylene copolymer, polyethylene-polypropylene blend, nylon and polyester having an orientation ratio of about 2/1 to about 6/1;
(i) a third adhesive layer; and (j) a second heat sealable layer on the second of said exterior surfaces.
Wherein said oriented polymer layer is disposed from about 0.2 to about 4.0 mils of said second exterior surface.

2. A multi-layer sheet structure as in claim 1, wherein said oriented polymer is uniaxially oriented in the machine direction.

3. A multi-layer sheet structure as in claim 1, wherein said orienting polymer is uniaxially oriented in the cross machine direction.

4. A multi-layer sheet structure as in claim 1, wherein the orientation ratio of the oriented polymer is from about 3/1 to about 5/1.

5. A multi-layer sheet structure as in claim 2, wherein the orientation ratio of the oriented polymer is from about 3/1 to about 5/1.

6. A multi-layer sheet structure as in claim 3, wherein the orientation ratio of the oriented polymer is from about 3/1 to about 5/1.

7. A multi-layer sheet structure as in claim 1, wherein said oriented polymer layer is disposed from about 1 to about 1.5 mils of said second exterior surface.

8. A multi-layer sheet structure as in claim 2, wherein said oriented polymer layer is disposed from about 1 to about 1.5 mils of said second exterior surface.

9. A multi-layer sheet structure as in claim 3, wherein said oriented polymer layer is disposed from about 1 to about 1.5 mils of said second exterior surface.

10. A multi-layer sheet structure as in claim 4, wherein said oriented polymer layer is disposed from about 1 to about 1.5 mils of said second exterior surface.

11. A multi-layer sheet structure as in claim 5, wherein said oriented polymer layer is disposed from about 1 to about 1.5 mils of said second exterior surface.

12. A multi-layer sheet structure as in claim 6, wherein said oriented polymer layer is disposed from about 1 to about 1.5 mils of said second exterior surface.

13. A multi-layer sheet structure as in claim 1, 2 or 3, wherein said oriented polymer is made of polypropylene.

14. A multi-layer sheet structure as in claim 1, 2 or 3, wherein said second heat sealable layer is uniaxially ori-ented.

15. A multi-layer sheet structure as in claim 1, 2 or 3, wherein said second heat sealable layer is heat sealable to said first head sealable layer.

16. A flexible dispensing tube made of a unitary multi-sheet structure having two exterior heat sealable layers, com-prising, consecutively, from the inside to the outside: (a) a first heat sealable layer; (b) a first adhesive layer; (c) a layer of metal foil; (d) a second adhesive layer; (e) a first layer of polyethylene or ethylene copolymer; (f) a second layer of polyethylene or ethylene copolymer; (g) a first primer; (h) a layer of oriented polymer selected from the group consisting of polypropylene, polyethylene, ethylene copolymer, polyethylene-polypropylene blend, nylon and polyester having an orientation ratio of about 2/1 to about 6/1; (i) a third adhesive layer; and (j) a second heat sealable layer on the second one of said exterior surfaces;
Wherein said uniaxially oriented polymer layer is disposed from about 0.2 to about 4.0 mils of said second exterior surfaces said multi-layer sheet structure being formed into a general-ly cylindrical shape tube having lap seal between said first and second heat sealable layer.

17. A flexible dispensing tube as in claim 16, wherein said oriented polymer is uniaxially oriented in the machine direction.

18. A flexible dispensing tube as in claim 16, wherein said oriented polymer is uniaxially oriented in the cross machine direction.

19. A flexible dispensing tube as in claim 16, wherein the orientation ratio of the oriented polymer is from about 3/1 to about 5/1.

20. A flexible dispensing tube as in claim 17, wherein the orientation ratio of the oriented polymer is from about 3/1 to about 5/1.

21. A flexible dispensing tube as in claim 18,wherein the orientation ratio of the oriented polymer is from about 3/1 to about 5/1.

22. A flexible dispensing tube as in claim 16, wherein said oriented polymer layer is disposed from about 1 to about 1.5 mils of said second exterior surface.

23. A flexible dispensing tube as in claim 17, wherein said oriented polymer is disposed from about 1 to about 1.5 mils of said second exterior surface.

24. A flexible dispensing tube as in claim 18, wherein said oriented polymer is disposed from about 1 to about 1.5 mils of said second exterior surface.

25. A flexible dispensing tube as in claim 19, wherein said oriented polymer is disposed from about 1 to about 1.5 mils of said second exterior surface.

26. A flexible dispensing tube as in claim 20, wherein said oriented polymer is disposed from about 1 to about 1.5 mils of said second exterior surface.

27. A flexible dispensing tube as in claim 21, wherein said oriented polymer is disposed from about 1 to about 1.5 mils of said second exterior surface.

28. A flexible dispensing tube as in 16, 17 or 18, wherein said oriented polymer is polypropylene.

29. A flexible dispensing tube as in claim 16, 17 or 18, wherein said second heat sealable layer is uniaxially ori-ented.

30. A flexible dispensing tube as in claim 16, 17 or 18, wherein said second heat sealable layer is heat sealable to said first heat sealable layer.

31. A method of making a paperless multi-layer sheet structure comprising the steps of: (a) coextruding three poly-meric layers to form a film substructure of said layers and uni-axially orienting said film to an orientation ratio of from about 2/1 to about 6/1, said layers being, consecutively, a polyethy-lene layer, a first adhesive layer and an orienting polymer layer; (b) priming a surface of said orienting polymer layer with a primer; (c) extrusion laminating a layer of polyethylene to said primed surface of said orienting polymer layer; (d) extru-sion laminating said polyethylene layer to an aluminum foil layer using a second polymeric adhesive layer as the extrusion lami-nant, and (e) coextrusion coating said foil with a coextrudate of a third adhesive layer and polyethylene to complete the sheet structure.

32. A method as in claim 31, wherein said orientation ratio is from about 2/1 to about 5/1.

33. A method as in claim 31, further including the step of priming said foil with a polyacrylic acid chrome complex primer prior to coextrusion coating of said foil.

34. A method as in claim 32, further including the step of priming said foil with a polyacrylic acid chrome complex primer prior to coextrusion coating of said foil.

35. A method as in claim 31, 32 or 33, wherein said orienting polymer is polypropylene.

36. A paperless laminated sheet structure having mult-iple layers of thermoplastic polymers including a layer of uniax-ially oriented polymer having an orientation ratio of about 2/1 to about 6/1.

37. A paperless laminated sheet structure as in claim 36, wherein said oriented layer is selected from the group con-sisting of polypropylene, polyethylene, ethylene copolymer, polyethylen-polypropylene blend, nylon and polyester.

38. A paperless laminated sheet structure having mult-iple layers comprising, in order: (a) a first heat sealable layer; (b) a first adhesive layer; (c) a layer of metal foil; (d) a second adhesive layer; (e) a first layer of polyethylene or ethylene copolymer; (f) a second layer of polyethylene or ethy-lene copolymer; (g) a primer; (h) a layer of uniaxially oriented high density polyethylene having an orientation ratio of at least about 3/1, and (i) a second heat sealable layer.

39. A paperless laminated sheet structure as in claim 38, wherein the orientation ratio of said high density polyethy-lene is from about 4/1 to about 8/1.

40. A paperless laminated sheet structure as in claim 38 or 39, wherein said first heat sealable layer and said second heat sealable layer is each low density polyethylene.

41. A multiple layer sheet structure having two exter-ior surface layers and a plurality of interior layers, compris-ing, in order: (a) a first heat sealable layer on a first one of said exterior surfaces; (b) a first adhesive layer of ethy-lene acrylic acid copolymer; (c) a layer of metal foil; (d) a second adhesive layer of ethylene acrylic acid copolymer; (e) a first layer of polyethylene or ethylene copolymer; (f) a second layer of polyethylene or ethylene copolymer; (g) a first primer;
(h) a layer of uniaxially oriented polypropylene, the orientation ratio being between 3/1 and 4/1; (i) a third adhesive layer;
and (j) a second heat sealable layer on the second one of said exterior surfaces; said layer of uniaxially oriented polypropy-lene being within 1.5 mils of said second exterior surface.

42. A multiple layer sheet structure as in claim 41, wherein said second heat sealable layer is uniaxially oriented.

43. A multiple layer sheet structure as in claim 41, wherein said second heat sealable layer, said third adhesive layer and said polypropylene layer are produced by coextrusion as a three layer film and uniaxially oriented simultaneously as a three layer film, the orientation ratio being between 3/1 and 4/1.

44. A multiple layer sheet structure as in claim 41, wherein said first and second heat sealable layers are compatible for being heat sealed to each other.

45. A multiple layer sheet structure as in claim 43, wherein said first and second heat sealable layers are compatible for being heat sealed to each other.

46. A multiple layer sheet structure as in claim 45, and including ink printing on said first primer and between said first primer and said second layer of polyethylene or ethy-lene copolymer.

47. A multiple layer sheet structure as in claim 45, and including a second primer between said metal foil and said first adhesive layer.

48. A multiple layer sheet structure as in claim 46, and including a second primer between said metal foil and said first adhesive layer.

49. A multiple layer sheet structure as in claim 48, wherein said three layer oriented coextruded film is 2.0 - 2.5 mils thick and said polypropylene layer is about 1.0 mil thick.

50. A flexible dispensing tube made of a unitary mul-tiple layer sheet material, said sheet material having two exter-ior surface layers and a plurality of interior layers, said sheet material comprising consecutive layers, from the inside of the tube outwardly; (a) a first heat sealable layer; (b) a first adhesive layer of ethylene acrylic acid copolymer; (c) a layer of metal foil; (d) a second adhesive layer of ethylene acrylic acid copolymer; (e) a first layer of polyethylene or ethylene copolymer; (f) a second layer of polyethylene or ethylene copoly-mer; (g) a first primer; (h) a layer of uniaxially oriented poly-propylene, the orientation ratio being between 3/1 and 4/1, the orientation direction running the length of said tube; (i) a third adhesive layer; and (j) a second heat sealable layer on the second one of said exterior surfaces of said sheet material, and forming the exterior surface layer of the tube; said sheet material being formed into a generally cylindrical shape and having a lap heat seal between said first and second heat seal-able surfaces, said layer of uniaxially oriented polypropylene being within 1.5 mils of the exterior surface of the tube.

51. A flexible dispensing tube as in claim 50, wherein said uniaxially oriented polypropylene layer is within 1 mil of the exterior surface of the tube.

52. A flexible dispensing tube as in claim 50, wherein said second heat sealable layer, said third adhesive layer and said polypropylene layer are all uniaxially oriented, the orienta-tion ratio being between 3/1 and 4/1, and the orientation direction running the length of the tube.

53. A multiple layer sheet structure having two exter-ior surface layers and a plurality of interior layers, compris-ing in order: (a) a first heat sealable layer of linear low density polyethylene on a first one of said exterior surfaces;
(b) a first adhesive layer of ethylene acrylic acid copolymer;
(c) a polyacrylic acid-based primer; (d) a layer of metal foil;
(e) a second adhesive layer of ethylene acrylic acid copolymer;
(f) a first layer of low density polyethylene; (g) a second layer of low density polyethylene; (h) a polyethylene imine primer;
(i) a layer of uniaxially oriented polypropylene; (j) an adhesive layer of uniaxially oriented ethylene methyl acrylate; and (k) a layer of uniaxially oriented low density polyethylene on the second one of said exterior surfaces; the stretch ratios of said polypropylene layer, said ethylene methyl acrylate layer and said third layer of low density polyethylene all being the same, and being between 3/1 and 4/l; said polypropylene layer being within 1.5 mils of said second surface.

54. A multiple layer sheet structure as in claim 53, wherein the thickness of the overall sheet structure is about 10 mils.

55. A multiple layer sheet structure as in claim 53, wherein said third low density polyethylene layer is about 1.2 mils thick, said ethylene methyl acrylate layer is about 0.3 mil thick, and said polypropylene layer is about 1.0 mil thick, the overall sheet structure being about 10 mils thick.

56. A multiple layer sheet structure as in claim 53, wherein said third low density polyethylene layer is about 0.8 mil thick, said ethylene methyl acrylate layer is about 0.2 mil thick, and said polypropylene layer is about 1.0 mil thick, the overall sheet structure being about 10 mils thick.

57. A method of making a multiple layer sheet material comprising the steps of: (a) coextruding a three layer film and uniaxially orienting it at an orientation ratio of 3/1 and 4/1 to produce an oriented film having three consecutive layers of 0.8 - 1.2 mils low density polyethylene, 0.2 to 0.3 mil ethy-lene methyl acrylate, and about 1.0 mil polypropylene; b) corona treating the polypropylene surface of said oriented three-layer film; c) priming the polypropylene surface of said oriented three-layer film with polyethylene imine; d) extru-sion laminating a previously formed low density polyethylene film, having a thickness of about 2.75 to 3.25 mils to said treated and primed polypropylene layer, using about 1.0 mil of low density polyethylene as the extrusion laminant; e) extru-sion laminating said 2.75 to 3.25 mil low density polyethylene layer to an aluminum foil layer using about 1.0 mil of ethy-lene acrylic acid copolymer as the extrusion laminant; and f) coextrusion coating said foil with a coextrudate of ethylene acrylic acid copolymer and polyethylene or linear low density polyethylene, said ethylene acrylic acid copolymer being coated onto said foil; the overall thickness of said sheet ma-terial being about 10 mils.

58. A method as in claim 57, and including the step of priming said foil with a polyacrylic acid chrome complex primer before coextrusion coating said foil.

59. A method of making a paperless multi-layer sheet structure comprising the steps: a) coextruding a three-layer film having three consecutive layers of low density polyethy-lene, ethylene-methyl acrylate copolymer and polypropylene, b) uniaxially orienting the film at an orientation ratio of about 2/1 to about 6/1 to produce an oriented film substructure, c) corona treating the external polypropylene surface, d) priming the treated surface with polyethylene amine, 2) extrusion lam-inating a low density polyethylene film to the treated and primed polypropylene layer using low density polyethylene as the extrusion laminant, f) extrusion laminating said low den-sity polyethylene layer to an aluminum foil layer using ethy-lene-acrylic acid copolymer as the extrusion laminant.

60. A method according to claim 59 wherein said foil is primed using a polyacrylic acid based primer.