Plastic composite barrier structures

Abstract

Composite moisture and oxygen barrier structures in the form of films, sheets, tubes, and bottles are described which are composed of foils of high density polyethylene and foils of polar oxygen barrier resins adhered to each other with a coextruded bonding resin composition composed of blends of predominantly high density polyethylene containing low levels of a grafted unsaturated dicarboxylic acid anhydride and linear low density polyethylenes which are copolymers of ethylene with either octene-1 or butene-1. The preferred dicarboxylic acid anhydride is maleic anhydride. The oxygen barrier resins are preferably ethylene/vinyl alcohol copolymers or amorphous polycarboxylamides from condensation polymerization of aliphatic diamines and aromatic dicarboxylic acids.

Description

BACKGROUND OF THE INVENTION

A variety of plastic composite structures have been proposed in the past in which a polar, oxygen barrier resin is adhered to a modified polyolefin resin, frequently a polyethylene resin, which has been chemically modified by grafting varying amounts of an unsaturated carboxylic acid or an unsaturated carboxylic acid anhydride, frequently a dicarboxylic acid anhydride, at various levels to the polyethylene backbone by methods known in the art. In some cases a polyethylene is bonded to a polar oxygen barrier resin with an adhesive which is a modified polyolefin containing various levels of grafted carboxylic acid or dicarboxylic acid anhydride and usually also an amorphous olefin rubber, such as ethylene-propylene diene rubbers, ethylene propylene copolymers, or linear low density polyethylenes which provide toughening and improve adhesion to polar substrates. Generally it has not been possible to obtain both good adhesion of the polyolefin resin to the polar resin and high moisture vapor barrier properties in the polyolefin resin. It is known that high density polyethylene which has a high crystallinity provides better moisture barrier properties than low density polyethylene or linear low density polyethylene or ethylene/propylene rubbers but there have been problems in obtaining adequate adhesion of high density polyethylene or modified high density polyethylene to polar oxygen barrier resins. Frequently the unsaturated carboxylic anhydride employed has been chi-methylbicyclo(2.2.1)hept-5-ene-2,3-dicarboxylic acid anhydride or maleic anhydride, but many other anhydrides have been disclosed in other patents. Illustrative of these types of composite structures known in the art are shown in U.S. Pat. No. 4,087,587, Shida et al., U.S. Pat. No. 4,198,327, Matsumoto et al., U.S. Pat. No. 4,230,830, Tanny et al., U.S. Pat. No. 4,409,364, Schmukler et al., U.S. Pat. No. 4,460,646, Inoue et al., U.S. Pat. No. 4,487,885, Adur et al., and U.S. Pat. No. 4,510,286, Liu. Most commonly, these patents disclose composite structures involving carboxylic acid grafted ethylene polymers or a carboxylic acid grafted polypropylene adhered to crystalline polycarboxylamide such as nylon-6. In some cases, adhesion to superior oxygen barrier materials such as EVOH (ethylene vinyl alcohol copolymer) are described.

U.S. Pat. No. 4,416,944, Adur describes composite structures of modified polyethylene and polypropylene adhered to oxygen barriers such as EVOH or nylon and also shows adhesion to high density polyethylene of modified polyolefin compositions comprising high density polyethylene having a density in the range of 0.94-0.97 g/cc, high density polyethylene grafted to chi-methylbicyclo(2.2.1)hept-5-ene-2,3-dicarboxylic acid anhydride at a level of 1.5 weight percent together with a polypropylene resin and a linear low density polyethylene resin having a density in the range of 0.91-0.94 g/cc. The total amount of high density polyethylene ethylene in the adhesive composition is stated to be in the range of 20-60% by weight in the examples.

U.S. Pat. No. 4,481,262, Shida et al., describes composite structures adhered to nylon-6 or ethylene vinyl alcohol copolymer in which the hydrocarbon copolymer adhered to it is a composition containing a linear low density polyethylene having carboxylic anhydride grafted to it and blended with a variety of different materials including ethylene vinyl acetate copolymer, ethylene methyl acrylate copolymer, low density polyethylene homopolymers or linear low density copolymers. In the adhesive compositions, the grafted linear low density polyethylene comprises 10% and the other materials 90% of the blend. In the examples ethylene vinyl acetate copolymer or an ethylene acrylate copolymer or an ethylene methyl acrylate copolymer are illustrated as comprising 90% of the adhesive blend but in one example a polyethylene having a density of 0.94 g/cc was substituted for these copolymers and provided some adhesion to nylon.

U.S. Pat. No. 4,460,632, Adur et al., discloses composite structures in which an adhesive polyethylene blend is adhered to substrates such as nylon, nylon-6, polyethylene or ethylene/vinyl alcohol copolymer. The adhesive compositions disclosed are blends of a medium density high pressure, free-radical polyethylene, a linear low density polyethylene and a high density polyethylene graft to a carboxylic anhydride such as chi-methylbicyclo(2.2.1)hept-3-ene-2,3-dicarboxylic anhydride or in one example maleic anhydride. In the adhesive compositions employed in these composites, linear low density polyethylene comprises from 10-90% by weight according to the generic disclosure. The examples show 10% of the grafted high density polyethylene and a total of from 10-90% of the mixture of grafted high density polyethylene and medium density polyethylene. It is shown that the grafted high density polyethylene may contain a very wide range of acid anhydride grafted to it generically stated as from 0.05-30 weight percent.

Another patent of interest is Mito et al., U.S. Pat. No. 4,370,388. This patent discloses adhesive compositions and composite structures made from them. Broadly adhesive structures are disclosed which contain from 97-50 parts by weight of a polyethylene resin having a density in the range of 0.945-0.970 grafted with a dicarboxylic acid anhydride such as maleic anhydride, 3-50 parts by weight of an ethylene/4-methyl-1-pentene copolymer having an ethylene content of 93-99.9 mole percent and 0-20 parts by weight of a rubbery synthetic polymer or copolymer. The patent broadly discloses that the amount of the grafted monomer in the grafted high density polyethylene may range from 0.001-10%, more preferably 0.02-5%. Comparative examples in which the copolymer of ethylene/4-methyl-1-pentene copolymer was replaced with an ethylene/hexene-1 copolymer or an ethylene/propylene copolymer rubber are said to be unsatisfactory. The density of the ethylene/4-methyl-1-pentene copolymer disclosed is from 0.910-0.945 g/cm³ or preferably 0.920-0.93 g/cm³. Primarily two layer composites are contemplated in which, in addition to the adhesive resin, nylon-6, nylon-66 and other similar crystalline nylons as well as a variety of polyesters and saponified copolymers of ethylene/vinyl acetate are contemplated. The only exemplified grafted high density polyethylene employed is one containing 2% by weight of maleic anhydride, a melt index of 7 g/10 min and a density of 0.962 g/cm³.

In all of the above patents the peel strengths disclosed are substantially impossible to relate to each other because they are so dependent upon laminating conditions and unstated percentages of carboxylic anhydride grafted to a polyolefin.

Generally peel strength for coextruded composites are not shown.

SUMMARY OF THE INVENTION

The present invention is directed to coextruded composite structures in the form of foils, sheets, tubes or blown bottles and other containers which provide both excellent oxygen barrier properties and excellent moisture barrier properties. The oxygen barrier properties are provided by a polar resin selected from the group consisting of ethylene/vinyl alcohol copolymers prepared by saponification or hydrolysis of corresponding ethylene/vinyl acetate copolymers, polyvinyl alcohol, and polycarboxylamides. Moisture barrier properties are provided by a foil of high density polyethylene and by an adhesive composition consisting essentially of a blend of from 70-90 weight percent of a high density linear polyethylene having a melt index of from 0.1-8.0 g/10 min and a density in the range of from above 0.950 to 0.970 g/cm³ and containing sufficient of a modified linear high density polyethylene having a density in the range of 0.950 to 0.970 g cm³ and a melt index in the range of from 0.1 to 8.0 g/10 min having from .[∅7-14 mole 0.091 0.028 0.089 0.08 I10 #x2205;170 Ex 1 HDPEA LLDPEB 20 H 9.5 0.095 0.099 0.020 0.112 0.58 I10 Ex 2 HDPEA LLDPEB 20 P 18.3 0.165 0.102 0.020 0.112 0.51 I76 Ex 3 HDPEA LLDPEB 20 P 14.6 0.131 0.102 0.020 0.112 0.47 I76 Ex 4 HDPEA LLDPEB 12 P 18.3 0.165 0.102 0.020 0.107 0.40 I76 Ex 5 HDPEA LLDPEB 12 P 14.6 0.131 0.099 0.023 0.117 0.34 I76 Ex 6 HDPEB LLDPEB 20 E 20.0 0.120 0.102 0.020 0.107 0.72 I10 Ex 7 HDPEB LLDPEB 20 D 24.0 0.120 0.086 0.016 0.117 0.68 I10 Ex 8 HDPEB LLDPEB 20 H 12.0 0.120 0.086 0.019 0.117 0.71 I10 Ex 9 HDPEB LLDPEB 20 D 24.0 0.120 0.107 0.021 0.132 0.44 I10 __________________________________________________________________________

TABLE III
__________________________________________________________________________
EXAMPLES 10-17 AND COMPARATIVE EXAMPLES 2-6
Patent
HDPE  LLDPE LLDPE
Graft
Graft
CAL   EVOH F
CXA   HDPE  Peel
Anti
Example
Type  Type  %    Code
%   % Maleic
mm Thick
mm Thick
mm Thick
kg/cm
Oxidant
__________________________________________________________________________
Comp 2
HDPEA LLDPEA
5    P   14.6
0.131 0.066 0.025 0.140 0.25
I10
Comp 3
HDPEA NONE  0    P   21.9
0.197 0.076 0.018 0.142 0.22
I10
Comp 4
HDPEA LLDPEB
5    P   14.6
0.131 0.071 0.025 0.122 0.21
I10
Comp 5
HDPEA NONE  0    P   14.6
0.131 0.089 0.023 0.122 0.16
I10
Comp 6
HDPEA LLDPEB
20   S   14.6
0.161 0.071 0.020 0.117 0.12
I10
Ex 10
HDPEA LLDPEB
30   P   14.6
0.131 0.069 0.015 0.122 0.89
I10
Ex 11
HDPEA LLDPEB
10   P   14.6
0.131 0.097 0.020 0.137 0.29
I10
Ex 12
HDPEA LLDPEB
20   P   14.6
0.131 0.071 0.018 0.130 0.51
I10
Ex 13
HDPEA LLDPEA
30   P   14.6
0.131 0.076 0.023 0.124 0.50
I10
Ex 14
HDPEA LLDPEB
20   P   7.3 0.066 0.081 0.020 0.122 0.45
I10
Ex 15
HDPEA LLDPEB
20   P   21.9
0.197 0.071 0.020 0.112 0.45
I10
Ex 16
HDPEA LLDPEA
20   P   14.6
0.131 0.084 0.020 0.145 0.40
I10
Ex 17
HDPEA LLDPEA
10   P   14.6
0.131 0.086 0.020 0.107 0.38
I10
__________________________________________________________________________

TABLE IV
__________________________________________________________________________
EXAMPLES 18-22 AND COMPARATIVE EXAMPLES 7-9
EXAMPLES 19-22 AND COMPARATIVE EXAMPLES 1-9 AND 21
HDPE  LLDPE LDPE
Graft
Graft
CAL %
EVOH F
CXA   HDPE   Peel
Anti
Example
Type  Type  %   Code %   Maleic
mm Thick
mm Thick
mm Thick
kg/cm
Oxidant
__________________________________________________________________________
Comp 7
NONE  LLDPEA
85.4
P    14.6
0.131
0.086  0.021 0.112  0.47
I10
Comp 8
HDPEA LLDPEB
30.0
P    3.3 0.030
0.091  0.021 0.112  0.06
I10
Comp 9
HDPEA LLDPEB
30.0
P    5.6 0.050
0.097  0.020 0.127  0.20
I10
Ex 18
HDPEA LLDPEA
20.0
P    14.6
0.131
0.102  0.020 0.127  0.36
I10
Ex 19
HDPEA LLDPEB
20.0
D    22.0
0.110
0.107  0.020 0.142  0.56
I10
Ex 20
HDPEA LLDPEB
30.0
P    14.6
0.131
0.086  0.020 0.127  0.78
I10
Ex 21
HDPEA LLDPEB
45.0
P    14.6
0.131
0.081  0.020 0.142  0.78
I10
Comp 21
Ex 22
HDPEA LLDPEB
20.0
P    14.6
0.131
0.102  0.018 0.142  0.64
I10
__________________________________________________________________________

TABLE V
______________________________________
EXAMPLES 23-30 & COMPARATIVE EXAMPLES 10-25
MVT
g mm/
Patent Base      LLDPE     LLDPE  Graft  M2 /
Example
Resin     Type      %      Code   24 HR
______________________________________
Comp 10
HDPEA                            0.138
Comp 11
HDPEA                            0.104
Comp 12
LLDPEA                           0.273
Comp 13
LLDPEA                           0.276
Ex 23  HDPEA     LLDPEA    9      D     0.132
Comp 14
HDPEA     LLDPEA    24     S     0.162
Comp 15
HDPEA     LLDPEA    20           0.145
Ex 24  HDPEA     LLDPEA    20     G     0.158
Ex 25  HDPEA     LLDPEA    20     G     0.154
Ex 26  HDPEA     LLDPEA    20     D     0.160
Ex 27  HDPEA     LLDPEA    20     D     0.162
Ex 28  HDPEA     LLDPEB    8      G     0.139
Ex 29  HDPEA     LLDPEB    12     G     0.152
Ex 30  HDPEA     LLDPEB    20     G     0.160
______________________________________

It is to be understood that the absolute values of the peel strengths set out in the above Examples are dependent upon the conditions under which the coextruded composite film structures were made, upon the method and rate of testing the peel strength and the thicknesses of the individual foils making up the composite film structure and therefore cannot readily be compared with peel strengths of such composite structures made under other conditions.

EXAMPLES 31-42

The composite film structures of Examples 31-42 were prepared in the same fashion as described for the composite film structures of Example 1-30. However, in these Examples the composition of the bonding resin was varied by varying the type of LLDPE as shown in Table VI.

In Table VI the heading "Structure Type" refers to the type of HDPE used as the moisture barrier foil in the composite film structure. The heading "Bar Type" TM refers to the type of EVOH employed.

TABLE VI
__________________________________________________________________________
EXAMPLES 31-42
HDPE
Patent
HDPE LLDPE LLDPE
Graft
Graft
CAL %
EVOH  CXA mm
mm   Bar
Struct
Peel
Example
Type Type  %    Code
%   Maleic
mm Thick
Thick Thick
Type
Type kg/cm
__________________________________________________________________________
Ex 31
HDPEA
LLDPEB
20   P   6.1 .[∅099
0.094 0.023 0.152
F  HDPEA
0.91
#x2205;055
Ex 32
HDPEA
LLDPEB
20   P   12.2
.[∅050
0.117 0.025 0.163
F  HDPEA
1.16
#x2205;110
Ex 33
HDPEA
LLDPEC
20   P   12.2
.[∅055
0.127 0.025 0.163
F  HDPEA
0.77
#x2205;110
Ex 34
HDPEA
LLDPED
20   P   12.2
0.110
0.132 0.028 0.168
F  HDPEA
0.65
Ex 35
HDPEA
LLDPEE
20   P   12.2
0.110
0.117 0.028 0.163
F  HDPEA
0.28
Ex 36
HDPEA
LLDPEE
28   P   12.2
0.110
0.086 0.023 0.173
F  HDPEA
0.71
Ex 37
HDPEA
LLDPEF
20   P   12.2
0.110
0.107 0.025 0.152
F  HDPEA
0.75
Ex 38
HDPEA
LLDPEF
28   P   12.2
0.110
0.097 0.025 0.152
F  HDPEA
1.07
Ex 39
HDPEA
LLDPEG
20   P   12.2
0.110
0.112 0.025 0.152
F  HDPEA
0.88
Ex 40
HDPEA
LLDPEG
28   P   12.2
0.110
0.094 0.025 0.157
F  HDPEA
0.93
Ex 41
HDPEB
LLDPEB
20   P   12.2
0.110
0.091 0.025 0.107
E  HDPEB
0.54
Ex 42
HDPEB
LLDPEB
20   P   12.2
0.110
0.069 0.020 0.086
E  HDPEB
0.87
__________________________________________________________________________

As can be seen from Table VI, Examples 38, 39 and 40, LLDPE made from ethylene/butene-1 copolymer is equally effective as ethylene/octene-1 copolymer for this component.

COMPARATIVE EXAMPLES 43, 44 AND EXAMPLE 45

Examples 43, 44 and 45 illustrate the preparation of blown bottles having a composite structure; Example 45 has the composite structure of this invention. Comparative Examples 43 and 44 illustrate other composite structure bottles where adhesion was not satisfactory. The preparation of these bottles involved coextrusion of a parison having high density polyethylene on the outside and an amorphous polycarboxylamide prepared from the condensation product of hexamethylenediamine and a mixture of 30% terephthalic acid and 70% isophthalic acid on the inside, with melt extrudable bonding compositions between the two layers.

The conditions for extruding the parisons and blowing the bottles for Example 45 were as follows:

The amorphous polycarboxylamide was extruded from a 50 mm single screw extruder whose set temperatures was 221.C to 227 C except for the feed section which was 93 C. The HDPE was fed from 50 mm single screw extruder with 17°C to 193°C barrel temperature except for the feed section which was at approximately 66°C The extruder for the coextrudable adhesive was a 38 mm single screw extruder. Barrel temperatures were 177.C to 232.C except for the feed section which was set at approximately 66.C. These extruders formed the multilayer parison with the polyamide on the inside and the HDPE on the outside. The parison was blown into 32 oz Boston round cylindrical bottles with a weight of 40±0.3 g. The HDPE layer of the bottle was 0.36 to 0.41 mm thick, the adhesive layer was 0.05 to 0.08 mm thick and the copolyamide layer was 0.08 to 0.10 mm thick. The cycle time per bottle was 14 seconds.

The parisons were blown into a mold which provided 32 oz. Boston round cylindrical plastic bottles having a weight of 40±3 g. The HDPE used as outer layer of the composite structure of the bottle was HDPEC. HDPEC is a high density linear ethylene. The polycarboxylamide layer provides excellent oxygen barrier properties while the HDPE layer provides excellent moisture vapor barrier properties. In Example 45, the middle layer of the bonding resin composition provided both excellent adhesion and high MVT resistance. Similar conditions were used to prepare the composite bottles of Comparison Examples 43 and 44. In Comparison Examples 43 and 44, the bonding resins were ethylene/vinyl acetate copolymer blended with EPDM rubber having maleic anhydride grafted to it and which failed to give the high peel strength provided by a bonding resin composition of the present invention. The compositions of Examples 43, 44 and 45 are set out in Table VII.

The peel strengths in the machine direction (MD) and the transverse direction (TD) were measured by cutting one inch wide strips in those two directions from the blown bottles and then measured as described for the peel strength measurements in Examples 1-42.

TABLE VII
__________________________________________________________________________
COEXTRUDED COMPOSITE STRUCTURE BOTTLES
Peel Strength
Patent
HDPE  LLDPE LLDPE
Graft
Graft
CAL  PCA** CXA    HDPE  kg/mm
Example
Type  Type  %    Code
Wt. %
% Maleic
mm Thick
mm Thick
mm Thick
MD  TD
__________________________________________________________________________
Comp.
(1)   --    --   T   10   0.2  0.08-0.10
0.05-0.08
0.36-0.41
0.18
0.30
Ex 43
Comp.
(2)   --    --   T   5    0.1  0.08-0.10
0.05-0.08
0.36-0.41
0.16
0.16
Ex 44
Ex 45
HDPEC LLDPEB
20%  P   14   0.126
0.08-0.10
0.05-0.08
0.36-0.41
CNS*
CNS*
__________________________________________________________________________
*CNS = Could not separate.
**PLA = Amorphous polycarboxylamide. 70/30 6I/6T.
(1) Copolymer of ethylene with 18% vinyl acetate having a melt index of
2.5 g/10 min.
(2) Copolymer of ethylene with 9.5% vinyl acetate having a melt index of
0.8 g/10 min.

A further test was made on the bottles of Examples 43 and 45. In this test the bottles were filled four-fifths of the way to the top with a mixture of 80% xylenes and 20% cyclohexanol. The bottles were stoppered and placed in an oven at 60°C and the peel strength measured after various exposure times up to 100 hours. Table VIII sets out peel strength data for these bottles. It is evident that the bottle of Example 45 was particularly outstanding in that even after 100 hours of this test the HDPE and polycarboxylamide layers could not be separated.

TABLE VIII
______________________________________
PEEL STRENGTH AFTER EXPOSURE OF
80% XYLENE/20% CYCLOHEXAMINE AT 60°C
Peel Strength (MD)
Exposure Time
kg/mm
hours        Comp. Example 43
Example 45
______________________________________
0            0.18          CNS*
8            0.12          CNS
24           0.08          CNS
100          0.17          CNS
______________________________________
*CNS = could not be separated.

Depending upon the intended use of the coextruded bottle, the amorphous polycarboxylamide layer can form either the inside or the outside layer of the composite structure bottle of Example 45; this can be accomplished by extruding the parison with the polycarboxylamide on the outside and the HDPE on the inside with the bonding resin between and then blowing the parison into the mold. Similarly, other oxygen barrier resins can be substituted for the amorphous polycarboxylamide of Example 45. If desired, multiple layer composite bottles can be made in accord with the invention, for example by extruding a parison with HDPE on both the inside and the outside with an oxygen barrier resin in between which is adhered on both sides of the HDPE with layers of an extrudable bonding resin of this invention when the parison is blown into the bottle.

Claims

1. A melt-extrudable bonding resin composition capable of adhering nonpolar high density linear polyethylene in the form of foils, sheets, tubes or blown bottles to polar oxygen barrier resins in the form, respectively, of foils, sheets, tubes or blown bottles which exhibits a combination of resistance to separation of said nonpolar high density polyethylene from said polar oxygen barrier resins and low moisture vapor transmission, said bonding resin composition consisting essentially of a blend of from 70 to 90 weight percent of composition (i) and from 10 to 30 weight percent of composition (ii) wherein composition (i) is composed of a blend of high density linear polyethylene having a melt index in the range of 0.1 to 8.0 g/10 min and a density in the range of from above 0.950 to 0.970 g/cm³ and sufficient of a high density linear polyethylene having a melt index in the range of 0.1 to 8.0 g/10 min and a density in the range of 0.950 to 0.970 g/cm³ having from .[∅7-14 mole #x2205;5 to 1 weight percent of maleic anhydride grafted to said high density linear polyethylene to provide from .[∅245-1.05 mole #x2205;055 to 0.2 weight percent of said grafted maleic anhydride in said composition (i), wherein composition (ii) is a linear low density polyethylene selected from the group consisting of linear copolymers of ethylene with butene-1 and linear copolymers of ethylene with octene-1 having a density in the range of 0.912 to 0.930 g/cm³ and a melt index in the range of 0.5 to 3.35 g/10 min.

2. The bonding resin of claim 1 in which composition (i) comprises 80 to 90 weight percent and composition (ii) comprises 10 to 20 weight percent of the bonding resin.

3. The bonding resin of claim 2 in which the linear low density polyethylene of composition (ii) is a copolymer of ethylene and octene-1.

4. The bonding resin of claim 2 in which the linear low density polyethylene of composition (ii) is a copolymer of ethylene and butene-1.