EP0700338A1

EP0700338A1 - Flexible multilayered composite

Info

Publication number: EP0700338A1
Application number: EP95911416A
Authority: EP
Inventors: John Patrick Grayson
Original assignee: BP Chemicals Ltd
Current assignee: BP Chemicals Ltd
Priority date: 1994-03-28
Filing date: 1995-03-17
Publication date: 1996-03-13
Also published as: AU1899295A; WO1995026268A1; GB9406106D0

Abstract

This invention relates to a multi-layer composite comprising at least one sequence of layers comprising a heterosphasic polypropylene (co)polymer layer/tie-layer/EVOH/tie-layer/polyolefin layer characterised in that the heterophasic polypropylene (co)polymer layer comprises a homopolymer of propylene or a co-polymer of propylene with ethylene and/or an alpha-olefin. These composites have (a) low permeability to oxygen and other gases; (b) good heat sealability for conversion of the composites into bags or other containers; (c) a very high degree of flexibility thereby allowing collapse of the bag when the contents thereof are dispensed; and (d) excellent flex-crack resistance which enable them to retain performance integrity.

Description

Flexible multllayered composite

This invention relates to a novel multi-layered composite comprising a plurality of polymer layers and having good flexibility and high fiex-crack resistance.

Composites comprising several polymers are well known. In view of the limited ability of virgin polymeric layers to adhere to each other it is customary to introduce intervening tie layers having adhesive properties between the virgin polymers. Such tie layers may comprise grafting of maleic anhydride or acrylate ester polymers on to one surface of a polyolefin film and then applying thereon a further layer of a virgin polymer or a metallic layer in order to produce the desired composite. Such composites have found uses in various industries including the production of protective garments, canning of food products, the so called 'bag-in-box' containers and barrier films for oxygen, gasoline or other industries where toxic or hazardous emissions have to be contained. Such composites have also been used to produce a flexible vapour containment liner (hereafter "VCL") for a fuel tank system in order to minimise the risk of accidental ignition and to control emissions from such tanks whether eg they be used in automotive vehicles, aircraft or in oil tankers. Most of these prior art laminates have been made from a layer of a hydrolysate of an ethylene-vinyl acetate copolymer, ie ethylene-vinyl alcohol copolymer (hereafter "EVOH"), sandwiched between layers of a polyolefin which may be polyethylene or polypropylene, optionally using a tie layer in between the polyolefin and the EVOH layers to improve adhesion thereof. However, in the composites used hitherto, the primary problem has been their relatively low flex-crack resistance which causes them to lose their performance integrity. This loss of performance is particularly undesirable if the composite is used for storing liquids, especially consumable liquids.

It has now been found that by modifying the nature of and the components in the composites, an improved product having a very high degree of flexibility and flex-crack resistance can be produced which has all the desirable properties including its ability to be used as a container for liquids such as eg wine, fruit juice, UHT milk, tomato concentrate, post-mix syrup, fruit pulps, as intermediate bulk 'bag-in-box' containers where a 'bag' forms the interior lining of a rigid or flexible container of upto 1000 litres volume, a liner for sacks etc., as a feed for form fill seal packaging machines for making eg pouches and for medical uses such as eg in colostomy bags.

Accordingly, the present invention is a multi-layer composite comprising at least one sequence of layers comprising a heterophasic polypropylene (co)polymer layer/tie-layer/EVOH/tie-layer/polyolefin layer characterised in that the heterophasic polypropylene (co)polymer layer comprises a homopolymer of propylene or a co-polymer of propylene with ethylene and/or an alpha-olefin.

By the expression "composite" as used herein and throughout the specification is meant a product prepared either by lamination of several layers and/or by coextrusion of a number of components in order to give the desired product. In defining the composite, the various components are referred to herein as "layers" for convenience, whether or not they have been laminated.

In the composite defined above, the expression "EVOH" signifies an ethylene-vinyl alcohol copolymer which may be derived by the hydrolysis of an ethylene-vinyl acetate copolymer.

In the composites of the present invention, the heterophasic polypropylene (co)poiymer layer is suitably that derived by the copolymerisation of propylene with ethylene and/or an alpha olefin which has 2-8 carbon atoms such as eg (iso)butene, and may optionally contain other monomers such as dienes, eg butadiene, 1 ,4-hexadiene, 1 ,5-hexadiene and a mixture of ethylidene norbornene and diene monomers. Such heterophasic polypropylenes are suitably produced by an extended Spheripol® process of Himont which is the so called "catalloy" process and involves the use of a multi-component catalyst system to produce engineering resins and elastomers. The polymers are believed to behave as a polyolefin 'alloy' and hence the process is known as the catalloy process. Such polymers are usually copolymers of propylene/ethylene/butene made by a two-stage polymerisation process as described in the following published references: EP-A-0472 946, EP-A-0 477 662, EP-A-0 483 675 AND EP-A-0489 284. The processes described in these documents are incorporated herein by reference. Films made from such (co)polymers have a thickness of about 10-80 μm and have a flexural modulus of less than 150, suitably in the range of 20-100. A specific example of such a copolymer is HIFAX® 7029XCP (ex Himont). The olefin copolymer layer may be a blend. Thus, HIFAX®

7029XCP (80% wt/wt) can be blended with Himont EP2S12B (20% wt/wt, ex Himont), a random copolymer of polypropylene and polyethylene. The thickness of this layer in the composite is suitably in the range from 10-80μm, preferably from 20-40μm, eg 30μm. The expression "heterophasic polypropylene (co)polymer" as used herein and throughout the specification signifies that such a polymer may be a homopolymer or a copolymer of propylene.

It is essential that at least one end layer of the composite is of a heterophasic polypropylene (co)polymer. As regards, the olefin polymer layer at the other end (opposite to the heterophasic (co)polymer) of such a composite, such olefin polymer may itself be a homo-polymer or co-polymer of ethylene, propylene or mixtures thereof with one another or with other comonomers such as vinyl acetate, acrylic acid, alkyl acrylates and alkyl methacrylates. Thus, such olefin polymers may be selected from one or more of a heterophasic polypropylene (co)polymer, a polypropylene homopolymer, a polypropylene copolymer, linear low density polyethylene (hereafter "LLDPE"), low density polyethylene (hereafter "LDPE"), high density polyethylene (hereafter "HDPE"), medium density polyethylene (hereafer "MDPE"), very low density polyethylene (hereafter "VLDPE"), ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ionomers such as eg SURLYN® and IOTEK®, ethylene-acrylic acid copolymer, ethylene- methacrylic acid copolymer, a polycarbonate, a polyamide and any blend thereof. A blend of LLDPE containing some octene comonomer and VLDPE is preferred. Particularly preferred is a blend of STAMYLEX® 09016 (ex, DSM, 80% wt/wt) and a conventional LDPE grade LD150BW (ex Exxon, 20% wt/wt).

The polyolefin layer suitably has the same thickness as that of the heterophasic polypropylene (co)polymer, ie a range of 10-80μm, preferably 20-40μm, eg 30μm. The tie-layer in the composite is the adhesive layer which binds the polyolefin layer or the polyolefin copolymer layer with the layer of EVOH. The tie-layer may be formed by grafting at least one polymerizable ethylenically unsaturated monomer (hereafter "EUM") which is suitably an ethylenically unsaturated carboxylic acid, ester or anhydride on to a material which is the same as the adjacent polyolefinic end layer to form a graft-copolymer. This enables the tie layer to key in and blend into the polyolefin or heterophasic polypropylene (co)polymer end layer as the case may be when preparing the composite. Thus, if the end layer in the composite is of polypropylene, it is preferable for the tie-layer to be a graft copolymer of polypropylene and a polymerizable ethylenically unsaturated monomer. Examples of such polymerizable ethylenically unsatured monomers include maleic acid (hereafter "MA"), maleic anhydride (hereafter "MAH"), acrylic acid (hereafter "AA"), alkyl acrylate esters (hereafter "AAE"), methacrylic acid (hereafter "MAA"), alkyl methacrylate esters (hereafter "AME"), itaconic acid, citraconic acid, mesaconic acid, 4-methyl cyclohex-4-ene-1 ,2-dicarboxylic acid anhydride, bicyclo (2.2.2)oct-5-ene-2,3-dicarboxylic acid anhydride, 1 ,2,3, 4,5,8, 9, 10-octahydronaphthalene-2,3-dicarboxyiic acid anhydride, 2- oxa-1 ,3-diketospiro(4.4)non-7-ene, bicyclo(2.2.1 )hept-5-ene-2,3-dicarboxylic acid anhydride (also known as and sold under the trade name NADIC ANHYDRIDE® by Allied Chemicals Corp and under HIMIC ANHYDRIDE® by Hitachi Chemical Co.), maleopimaric acid, tetrahydrophthalic anhydride, methyl-norbom-5-ene-2,3-dicarboxylic acid anhydride, norbom-5-ene-2,3- dicarboxylic acid anhydride, and other fused ring monomers described in US- A-3 873 643 and US-A-3 882 194. Of these, maleic anhydride, tetrahydrophthalic anhydride and bicyclo(2.2.1 )hept-5-ene-2,3-dicarboxylic acid anhydride are preferred. A typical and preferred example of a tie-layer is the graft copolymer derived from a polyolefin and maleic anhydride and sold as ADMER® grades, especially ADMER® NF 530E and ADMER® AT 851. Conjugated unsaturated esters, in addition to the alkyl acrylates and alkyl methacrylates mentioned above, may also suitably be used for co- grafting. These esters include, eg, dialkyl maleates, dialkyl fumarates, dialkyl itaconates, dialkyl mesaconates, dialkyl citraconates, alkyl crotonates, alkyl tiglates wherein the alkyl group aliphatic, cycloaliphatic, alicyclic or an arlkyl group and suitably has 1-12 carbon atoms. Dibutyl maleate, diethyl fumarate and dimethyl itaconate are particularly preferred. These monomers may be used either alone or in combination with the anhydrides listed above and are suitably applied to at least one side of the adjacent polyolefinic layer. Methods of grafting these monomers on to the polyolefin layer or polyolefin copolymer layer are well known in the art. For instance, methods of grafting MAH to the polyolefin layer are described eg in US-A-2973344 and US-A- 3290415. The grafting may be performed in a solvent by placing the monomer in a solvent followed by irradiation as described in US-A-3290415 with peroxides. Alternatively, the grafting may be carried out, eg in the case of polypropylene, by melt mixing with peroxides. The peroxides that may be used include, eg, t-butyl hydroperoxide, p-menthane hydroperoxide, pinane hydroperoxide and cumene hydroperoxide. Other grafting techniques include extrusion grafting and coating the polyolefin surface with a molten monomer followed by irradiation as described eg in US-A-3290415. These methods are incorporated herein by reference to these prior publications.

The thickness of the tie layer is suitably in the range from 2-1 Oμm, preferably from 3-6μm, eg 5μm.

The EVOH used is suitably of a grade which contains from 25-50 mol% of ethylene, preferably from 29-44 mol% and even more preferably from 32- 38 mol %. Examples of EVOH grades that may be used include inter alia, the so-called EVAL® LCH 101 or EPJ 102B (both ex Kuraray Industries).

The thickness of the EVOH layer is suitably in the range from 2-25μm, preferably from 4-1 Oμm, eg 6μm. Thus, the thickness of each of the layers in the composite is suitably in the following range: Polypropylene copolymer : 10-80μm, preferably 20-50μm eg 30μm

Each tie layer: 2-1 Oμm, preferably 4-6μm eg 5μm

EVOH layer: 2-25μm, preferably 4-1 Oμm eg 6μm

Polyolefin blend: 10-80μm, preferably 20~40μm eg 30μm

Within the ranges specified above, it is preferable that the total thickness of the composite is from 35-180μm, preferably from 60-1 OOμm, typically 80μm.

Where the composite is produced by co-extrusion, this is suitably carried out within an overall average temperature in the range from 170-260° C. Within this range the polyolefin layers, ie both the heterophasic polypropylene (co)polymer layer and the olefin blend layer at the opposite end are suitably maintained at 180-220°C, the EVOH layer at 180-220°C, and the tie layer at upto 250°C.

Where the composite is produced by the standard procedure of lamination of various layers, this is suitably carried out by conventional lamination or film casting techniques.

Where the composite is prepared by combining more than one sequence of heterophasic polypropylene (co)polymer layer/tie- layer/EVOH/tie-layer/polyolefin layer, the adhesive used to combine such sequences is suitably a polyurethane adhesive. Additional examples of such adhesives that may be used include a polyester/polyurethane adhesive or a polyether/polyurethane adhesive. The composite preferably has at least two such sequences and the grades of any of the generic components in each sequence may be same or different.

A feature of the composites of the present invention is that they have: a. low permeability to oxygen and other gases; b. good heat sealability for conversion of the composites into bags or other containers; c. a very high degree of flexibility thereby allowing collapse of the bag when the contents thereof are dispensed; and d. excellent flex-crack resistance which enable them to retain performance integrity.

The composites of the present invention and the use thereof as a 'bag- in-box' type container is illustrated with respect to the following Example: EXAMPLE: Several types of laminates prepared by co-extrusion of various components (shown below) into a 5-layer tubular blown film using a BARMAG four-component five-layer extruder) were tested for their flex crack resistance and other physical properties. The materials used for preparing the various coextruded films are identified below in Table 1 : TABLE 1

Material (Grade) Abbreviation used Commercial Source

Dowlex*5056 NG LLDPE Dow

Admer* NF 530E Tie layer Mitsui

EVAL LCH 101 BD EVOH-38% Kuraray

EVAL F 101 BZ EVOH-32% Kuraray

Hifax^* 7029XCP "Catalloy" Resin Himont

EP2S12B PP/PE random copolymer Himont

Maxithen^* 7051 PP slip masterbatch Gabriel Chemie

Stamylex* 09016 VLDPE DSM

PZ904 PE slip masterbatch BP

*Registered Trade Mark

Other abbreviations used in respect of the composites of the present invention and the films for comparative purposes are shown below in Table 2:

TABLE 2

Abbreviation Remarks

LLDPE Linear low density polyethylene

COF Coefficient of friction

MD Machine direction

TD Transverse direction

PP Polypropylene

PE Polyethylene

FF Film failure

OTR Oxygen transmission rate

RH Relative humidity

VLDPE Very low density polyethylene

EVOH Ethylene-vinyl alcohol copolymer

Tensiles Yield Tensile Strength at yield

Tensiles Break Tensile Strength at break The various composite films tested are identified by reference Nos. and each of these had the following composition with respect to the various layers in the composite as shown in Tables 3 and 4 below:

TABLE 3 Layers in Film EWT 13664 CD:

*Registered Trade Mark

PPH§ - parts per hundred of the component of said layer

TABLE 4 Layers in Film EWT 13664 E,F:

eg stered ra e ar

PPH§ - parts per hundred of the component of said layer The flex crack resistance of the composites described above was tested using an internal BP standard test reference No. PFB STM 029 and involved the following procedure:

Using an A4 metal template samples of the composite film were cut out with the longest side in the transverse film direction. The following number of samples were tested:

2 samples of <650 mm film width and

4 samples of >650 mm width Each of the samples were fitted to the circular discs on a Gelbo flex tester using jubilee clips ensuring that the film was well secured and not twisted. The samples were then flexed for at least 1000 flexes (unless otherwise stated). After the stated number of flexes, the sample was removed and placed on top of a flat piece of white A4 paper. A solution containing a blue die was then washed over the film surface using a cotton wool pad. The white paper was then inspected for any blue spots thereon which would signify pinholing of the film as a consequence of the flex testing. When all the samples had been tested, the results were tabulated and expressed as the number of pinholes/number of flexes (see Tabls 5 below).

The films were also subjected to an oxygen transmission test (OTR) and the test was carried out using a Mocon Ox-Tran 100 Twin tester.

The results of physical testing and the physical properties of these coextruded film composites are tabulated in Table 5 below along with a comparison of these properties with those of a conventional composite HY- BAR® Grade BB 202/80 (ex BP Chemicals Ltd) of the structure type LLDPE/EVOH-32%/LLDPE which had a width of 815 mm and a thickness in each case of 80μm.

TABLE 5

*Average per sheet

§ - Delamination occurred

A further comparison of physical properties was carried out between the conventional composite HY-BAR® Grade BB202/80 (width 2 x 600) and the EWT's 13664/D and 13664/E using a film of width 1200 mm. The results of this comparison are tabulated in Table 6 below: TABLE 6

' verage per sheet

Samples of EWT 13664D and 13664E were compared with HY-BAR® Grade BB 202/100 for pinholing by vibration testing followed by evaluation for oxygen transmission rate (OTR)of each of the samples. The pinholing tests were carried out by subjecting bags of the respective samples filled with water to vibration for 20 minutes. For evidence of pinholing the bags so vibrated were subjected to OTR measurement Mocon Ox-tran 100 twin tester referred to above in the front, back and spout areas of the bag which are normally the worst area for flex damage. The OTR measurement was carried out and measured as cc/m²/day at 23°C at 60% relative humidity. The OTR of the unflexed samples in each case under these conditions was 0.8 cc/m²/day. The results of these tests are tabulated in Table 7 below:

TABLE 7

Sample Used Bag No. of Pinholes OTR No.

Front Back Front Back Spou t

BB 202/100 1 9 6 0.98 2.1 2.2

2 6 6 44.9

3 14 6 2.3

Mean 9.7 6 16.5

EWT 13664D 4 7 1 2.2 1.8

5 6 6 1.9 8.3

6 5 2 5.2

Mean 6 3 5.1

EWT 13664E 7 2 3 0.93 13.4

8 2 2 2.0 3.4

9 2 4 6.4

Mean 2 3 7.7

From the above results it can be seen that the composite films of the present invention, when compared with conventional films, show a. a much better flex-crack resistance (as shown by the Gelbo test); b. a lower stiffness (as shown by the tensile properties and Secant Modulus); and c. a greater resistance to pinholing and therefore reduced OTR.

Claims

Claims:

1. A multi-layer composite comprising at least one sequence of layers comprising a heterophasic polypropylene (co)polymer layer/tie- layer/EVOH/tie-layer/polyolefin layer characterised in that the heterophasic polypropylene (co)polymer layer comprises a homopolymer of propylene or a co-polymer of propylene with ethylene and/or an alpha-olefin.

2. A composite according to Claim 1 wherein the heterophasic polypropylene (co)polymer layer is derived by the copolymerisation of propylene with ethylene and/or an α-olefin which has 2-8 carbon atoms and optionally contains other diene monomers.

3. A composite according to Claim 1 or 2 wherein the α-olefin is an n- butene or isobutene and the optional diene monomer is selected from the group consisting of butadiene, 1 ,4-hexadiene, 1 ,5-hexadiene and a mixture of ethylidene norbornene and diene monomers.

4. A composite according to any one of the preceding Claims wherein the heterophasic polypropylene is a copolymer of propylene/ethylene/butene.

5. A composite according to any one of the preceding Claims 2-4 wherein films made from the heterophasic polypropylene (co)polymers have a thickness of about 10-80 μm and have a flexural modulus of less than 150.

6. A composite according to any one of the preceding Claims wherein at least one end layer of the composite is of a heterophasic polypropylene

(co)polymer.

7. A composite according to any one of the preceding Claims wherein the olefin polymer layer at the other end (opposite to the heterophasic (co)polymer) of the composite is itself a homo-polymer or co-polymer of ethylene, propylene or mixtures thereof with one another or with other comonomers selected from the group consisting of vinyl acetate, acrylic acid, alkyl acrylates and alkyl methacrylates.

8. A composite according to Claim 7 wherein the olefin polymer is selected from the group consisting of one or more of a heterophasic polypropylene (co)polymer, a polypropylene homopolymer, a polypropylene copolymer, linear low density polyethylene (hereafter "LLDPE"), low density polyethylene (hereafter "LDPE"), high density polyethylene (hereafter "HDPE"), medium density polyethylene (hereafer "MDPE"), very low density polyethylene (hereafter "VLDPE"), ethylene-vinyl acetate copolymer, ethylene-ethyl acrylate copolymer, ionomers, ethylene-acrylic acid copolymer, ethylene-methacrylic acid copolymer, a polycarbonate, a polyamide and any blend thereof.

9. A composite according to Claim 7 or 8 wherein the olefin polymer is a blend of LLDPE, containing some octene comonomer and VLDPE.

10. A composite according to any one of the preceding Claims wherein the olefin polymer layer has the same thickness as that of the heterophasic polypropylene (co)polymer.

11. A composite acccording to any one of the preceding Claims wherein the tie-layer is formed by grafting at least one polymerizable ethylenically unsaturated monomer (hereafter "EUM") on to a material which is the same as the adjacent polyolefinic end layer to form a graft-copolymer.

12. A composite according to Claim 11 wherein the adjacent polyolefinic end layer is of polyethylene or a heterophasic polypropylene (co)polymer and the tie-layer is a graft copolymer of polyethylene or the heterophasic polypropylene (co)polymer and a polymerizable ethylenically unsaturated monomer.

13. A composite according to any one of the preceding Claims wherein the thickness of the tie-layer is from 2-1 Oμm.

14. A composite according to any one of the preceding Claims wherein the EVOH is of a grade which contains from 25-50 mol% of ethylene.

15. A composite according to any one of the preceding Claims wherein the thickness of the EVOH layer is from 2-25μm.

16. A composite according to any one of the preceding Claims wherein the thickness of each of the layers in said composite is in the following range: Polypropylene copolymer : 10-80μm, preferably 20-50μm eg 30μm Each tie layer: 2-1 Oμm, preferably 4-6μm eg 5μm

EVOH layer: 2-25μm, preferably 4-1 Oμm eg 6μm

Polyolefin blend: 10-80μm, preferably 20-40μm eg 30μm

17. A composite according to any one of the preceding Claims wherein the total thickness of the composite is from 35-180μm, preferably from 60-1 OOμm, typically 80μm.

18. A composite according to any one of the preceding Claims wherein said composite comprises more than one sequence of heterophasic polypropylene (co)polymer layer/tie-layer/EVOH/tie-layer/polyolefin layer and said sequences are combined together using a polyurethane adhesive.

19. A process for producing a composite claimed in any one of the preceding Claims said process comprising coextruding the component layers of the composite within an overall average temperature in the range from 170 to 260°C whereby the polyolefin layers, inclusive of the heterophasic polypropylene (co)polymer layer and the olefin blend layer at the opposite ends are maintained at 180 to 220°C, the EVOH layer is maintained at 180 to 220°C, and the tie layer is maintained at up to 250°C.

20. A process for producing a composite claimed in any one of the preceding Claims 1-18 said process comprising bringing together the component layers in the right sequence by lamination or film casting techniques.