WO1995020487A1 - Adhesive composition - Google Patents

Abstract

The present invention relates to a coextrudable adhesive composition consisting essentially of (A) about 15 to 89 wt % modified polypropylene; (B) about 5 to 50 wt % ethylene copolymer having from about 2 to 10 wt % copolymerized olefin; (C) about 5 to 50 wt % elastomeric ethylene copolymer; and (D) about 1 to 30 wt % tackifier. Also disclosed is a multi-layer structure comprising at least one structural layer, on barrier layer, and at least one layer of the above described adhesive composition used as a bonding layer.

Description

TITLE

ADHESIVE COMPOSITION FIELD OF TFIE INVENTION

The present invention relates to a coextrudable adhesive composition suitable for bonding composite structures of structural layers and barrier layers.

BACKGROUND OF THE INVENTION

Many commercial packaging applications employ composite structures of multiple layers of thermoplastic polymers. Such composite structures often include structural layers and barrier layers. Typically, the structural layers are nonpolar, such as polyolefin, and the barrier layers are polar, such as ethylene/vinyl alcohol copolymer and nylon. To prevent delamination, an adhesive, sometimes referred to as a tie layer, is used.

Composite strucutres are often made by extrusion processes. In such processes, the adhesive is applied to the substrate layers in the molten state. In common variations of these processes, one or more substrate layers are also extruded in the molten state. When adjacent layers are simultaneously extruded from melt, the process is called coextrusion.

Adhesives containing polypropylene are sometimes used to bond nonpolar substrates. Generally, however, polypropylene adhesive compositions are not well-suited for bonding to polar substrates. Moreover, polyproylene adhesives known in the are bond only moderately to nonpolar polymers when applied by extrusion processes. It is desireable to provide extrudable adhesive compositions which provide superior adhesive strength and which are particularly well suited as adhesives for bonding polyolefin substrates to polar substrates.

DISCUSSION OF PRIOR ART

U.S. Pat. No. 4,942,096 discloses blends of polypropylene, polypropylene grafted with a radical polymerizable unsaturated compound, a LLDPE, and rubber. This blend is useful as an adhesive. The patent does not disclose the use of tackifying resins to improve adhesive performance.

U.S. Pat. No. 4,774,144 discloses adhesive blends especially suitable for adhesion to polypropylene and gas barrier materials comprising a mixture of an adhesion promoting amount of high molecular weight low density polyethylene, a non-elastomeric copolymer of polypropylene and a polymerzable ethylenically unsaturated carboxylic acid or derivative, and a non-elastomeric ethylene/propylene copolymer. Specifically stated is that there be no elastomeric component. Thus, it differs from the present invention in that it does not contain an elastomeric component or taclάfying resin. U.S. Pat. No. 4, 198,327 discloses a composition having improved adhesion to solid materials which comprises a modified crystalline polyolefin having grafted there to a monomer such as unsaturated carboxylic acids and their derivatives and a hydrocarbon elastomer. It duffers from the present invention in that it does not include a low density polyethylene component and a tackifying resin. U.S. Pat No. 3,868,433 discloses thermoplastic adhesive compositions such as hot melts which are improved by the inclusion of acid or acid derivative grafted polyolefins and a hydrocarbon elastomer. These compositions may also contain a low density polyethylene component.

SUMMARY OF THE INVENTION

According to the present invention there is provided an adhesive composition consisting essentially of:

(A) about 15 to 80 wt% modified polypropylene;

(B) about 5 to 50 wt% crystalline ethylene copolymer having from about 2 to about 10 wt% copolymerized α-olefin;

(C) about 5 to 50 wt% elastomeric ethylene copolymer having at least 30% copolymerized α-olefin;

(D) about 1 to 30 wt% tackifier which does not contain ester functionality. There is also provided a multilayer structure comprising at least one structural layer, at least one barrier layer, and at least one layer of the above described adhesive composition used as a bonding layer. Such structures exhibit desirable combinations of structural strength barrier properties, with excellent adhesion between the layers.

DETAILED DESCRIPTION OF

THE PREFERRED EMBODIMENT AND BEST MODE

Overview

The adhesive composition of the present invention is a blend consisting of a modified polyproylene component,; a crystalline ethylene polymer component; an elastomeric ethylene copolymer component and a tackifier component. Such composition is extrudable and can be applied to substrates in various coextrusion or thermal lamination processes. It provides superior adhesion perferable for bonding thermoplastic polymer substrates such as polyolefins to barrier polymer films such as for example, nylon or ethylene/vinyl alcohol copolymer (EVOH).

Each component will be discussed separately, followed by a discussion of combinations of these components. Finally, methods and uses of the adhesive compositions of the present invention will be discussed. Modified Polypropylene Component

The modified polypropylene component of the present invention is polypropylene having cyclic carboxylic anhydride functionality, such as for example, maleic anhydride and vinyl succinic anhydride functionality. The modified polypropylene can be prepared by copolymerizing propylene with carboxylic anhydride comonomer or by polymerizing propylene in the present of dicarboxylic acid comonomer followed by dehydration and ring closure to form the anhydride. Alternatively, carboxylic anhydride can be grafted onto polypropylene or dicarboxylic acid can be grafted onto polypropylene then dehydrated to form anhydride. Typical carboxylic anhydride and dicarboxylic acid comonomers include maleic anhydride and citraconic acid.

The method for modifying polypropylene can be any of the processes which are well known in the art. For example, modification can be carried out in the melt without a solvent, or in solution or dispersion. Melt modification can be done using a heated extruded, a Brabender® or Banbury® mixer or other shear intensive mixer customarily used to blend polymers, including kneaders and roll mills. Modification may be carried out in the presence of a radical initiator such as a suitable organic peroxide, organic perester, or organic hydroperoxide. Alternatively, anhydride may be thermally grafted onto the polypropylene by heating and shearing the reactants in the essentially complete absence of catalyst. Processes for such reactions are well known in the art.

The amount of copolymerized or grafted anhydride, hereafter collectively referred to as "grafted anhydride", in the modified polypropylene component is not particularly limiting and amy be as low as about 0.03 weight percent or as much as about 5 percent or even more, based on the weight of the modified polypropylene. The amount of grafted anhydride in the adhesive S95/01077

composition, however, is important and perferably should be between about 0.03 and about 0.5 weight percent of the total adhesive composition.

The modified polypropylene is blended with unmodified polypropylene, that is, polypropylene which does not contain anhydride functionality. The unmodified polypropylene can be a copolymer or a blend of polypropylene homopolymer with a copolymer of propylene which contains a minor proportion, usually less than 25 weight percent, of a second olefin, such as ethylene or butene-1 , or a blend of propylene homopolymer with propylene copolymer. Such unmodified polypropylene is referred variously as, for example, isotactic polypropylene, crystalline polypropylene and stereoregular polypropylene. Suitable unmodified polypropylene preferably has a melt flow of from 0.5 to 40 g/10 min. The relative amounts of unmodified polypropylene and modified polypropylene is not critical; provided, however, that the proportions are chosen such that the amount of grafted anhydride is preferably between about 0.03 and 0.5 weight percent of the total composition.

The molecular weight range of the modified polypropylene component (determined by light scattering) is in the range of about 1,000 to about 250,000, more preferably about 10,000 to about 75,000. The modified polypropylene component should have a melt flow, determined by ASTM standard D1238 at 230° C, in the range of about 0.01-100 dg/min, and perferable 0.05-20 dg/min. Crystalline Ethylene Polymer Component

The ethylene polymer component suitable for use in the present invention is partially crystalline and can be a medium density polyethylene (MDPE) or low density polyethylene (LDPE) homopolymer of ethylene and is preferably a linear low density polyethylene (LLDPE) ethylene/α-olefin copolymer.

The LDPE or MDPE ethylene homopolymer generally has a density in the range of 0.92 to 0.94 g/cm³ and a melt flow in the range of about 0.5-10 dg/min. The LLDPE genreally has a density of about 0.88-0.92. Melt flow of LLDPE is generally in the range of about 0.5-10 dg/min. The LLDPE is a copolymer prepared by copolymerization of ethylene with preferably up to about 10 percent of an α- olefin of preferably 4-18 carbon atoms, and most preferably 1-butene, 1-hexene, 1- octene or 4-methyle-l-propene. The LLDPE can include copolymers having two or more α-olefins. A representative example is ethylene/ 1-butene/ 1-hexene terpolymer. Elastomeric Ethylene Copolymer Component

The elastomeric ethylene copolymer component preferably is a substantially amorphous copolymer of ethylene and an α-olefin comonomer. Preferably, the α-olefin comonomer contains 3-18 carbon atoms. Such copolymers are sometimes known as soft polymers; that is they have a low flexural modulus. These copolymers typically behave like rubber to the extent that they deform considerably under stress and return to substantially original shape after removal of the stress.

Representative elastomeric ethylene copolymers include ethylene/propylene copolymer and ethylene/ 1-butene copolymer. Suitable elastomeric ethylene copolymers include ethylene/α-olefin terpolymers wherein the third comonomer is a non-conjugated diolefin, such as: dicyclopentadiene, 1 ,4- hexadiene, ethylidene norbornene, vinyl norbornene, methylene norbornene, 1 ,6- octadiene, 5-methyl-l,4-hexadiene, 3,7-dimethyl-l,6-octadiene; 3,7-dimethyl-l ,7- octadiene, 1 ,4-cyclohexadiene; 1 ,5-cyclooctadiene; 1,5-cyclododecadiene; tetrahydroindene; methyltetrahydroindene; dicyclopentadiene; bicyclo-(2,2,l)- hepta-2,5diene; 5-methylene-2-norbornene(NMB), 5-ethylidene-2-norbornene (ENB), 5-(4-cyclopentenyl)-2-norbornene; and 5-cyclohexylidene-2-norbornene. Conjugated diolefin comonomers are not particularly useful because they tend to react to produced unacceptably highly branched or crosslinked molecules during preparation of the adhesive composition. The most widely known elastomeric ethylene copolymers, and one of the preferred copolymers of this invention, is EPDM, a copolymer of ethylene, 20-75 weight percent propylene, and 2-8 weight percent 1 ,4-hexadiene. The elastomeric component of the current invention may also be introduced by using what is generally called a rubber modified or impact propylene homopolymer or copolymer.

It is important that the elastomeric ethylene copolymer component be substantially amorphous. Because crystallinity generally increases as the relative amount of copolymerized ethylene increases, it is preferred that the elastomeric ethylene copolymer contain about 20-80 wt%, and more preferably about 30-50, wt% copolymerized α-olefin. Elastomeric ethylene copolymers that are terpolymers should contain about 20-75 wt% copolymerized α-olefin and about 2-8 wt % copolymerized diene with the balance being copolymerized ethylene. The molecular weight of the elastomeric ethylene copolymer can vary over a wide range. It is believed that the weight average molecular weight could be about 2,000-12,000,000, preferably about 10,000-1 ,000,000 and most preferably about 20,000-750,000.

Tackifier

The tackifier is selected from any of a large number of well known tackifiers. Typically tackifires for use in this invention have a Ring & Ball softening point, determined in accordance with ASTM standard E28, of about 80- 125°C. Representative tackifiers included, for example, polyterpenes obtained by polymerization and/or copolymerization of terpene hydrocarbons such as the alicyclic, monocyclic, and bicyclic monoterpenes and their mixtures, including allo-ocimene, carene, isomerized pinene, pinene, dipentene, terpinene, terpinolene, limonene, terpentine, and various other terpenes; olefins, and mixed olefins such as polyisobutylenes and ataclic polypropylenes; cycloaliphatic hydrogenated olefins; aliphatic and aromatic hydrocarbon resins; polydienes such as dicyclopentadiene; poly(vinyl aromatics) such as α-methyl and styrene-vinyltoluene; and miscellaneous resins such as terpene phenolic and coumarone- indenes; rosin esters; and hydrogenated rosin esters. Illustrative of commerically available tackifiers are, for example, polyterpenes available under the trade designations PICCOLYTE and NYREZ; polymerized 5-carbon diolefins available under the trade designation ESCOREZ; poly(vinyl aromatics) available under the trade designation REGALREZ. Specific representative examples of hydrocarbon tackifiers include REGALREZ 1 139, a hydrogenated styrene-based polymer, made by Hercules, having a softening point of about 139°C; and ESCOREZ 7105, a polymer having a softening point of about 20° C, from Exxon Chemical. Other Additives

The term "consisting essentially" is used herein to mean that additives other than the principal components may be present, usually in small amounts, in the adhesive composition; provided that such additives do not detract from the performance of the invention. A variety of materials are commonly used and known in the adhesive art, such as, for example, antioxidants, surface modifiers, stabilizers, fillers, extenders, waxes, foaming agents, and crosslinking agents.

Antioxidants generally protect the stability of the adhesive when subjected to heat, or during long term storage in bulk form. Suitable antioxidants include typical hindered phenols such as for example, butylated hydroxytolunes (BHT), ETHYL 330 and IRGANOX 1010, believed to be tetrakis-methylene-(3,5- di-t-butyl-4-hydroxyhydrocinnamate)methane, as well as phosphites.

Surface modifiers, such as for example, amide slip agents, such as stearamide, and silica can be used to advantage in adhesive compositions of this invention.

Certain additives customarily employed in adhesive formulations may interfere with the bonding ability of compositions of this invention. The practioner of ordinary skill will be able to determine the negative effect of a potential additive with minimum experimentation. Adhesive Composition

The adhesive composition of the present invention is a blend consisting essentially of about 15 to about 90 wt %, preferably about 30 to about 60 wt%, modified polypropylene; about 5 to about 50 wt%, preferably about 15 to about 25 wt%, partially crystalline ethylene polymer comprising from about 2 to about 10 wt% copolymerized α-olefin; about 5 to about 50 wt%, preferably about 10 to about 30 wt%, elastomeric ethylene copolymer; and about 1 to about 30 wt%, preferably about 5 to about 15 wt%, tackifier. Each of the principal components can be a blend of suitable polymers selected from those available for that component.

Adhesive performance of the composition generally improves with increasing concentration of anhydride funtionality. However, excessive levels of anhydride tends to lower melt strength thereby making the adhesive less suitable for application by coextrusion processes. Accordingly, the anhydride graft concentration in the composition is preferably about 0.03 to 0.5 wt%, and more preferably, about 0.07-0.11 wt%. The melt flow of the adhesive blend should be from about 0.5 to about

40, preferably from about 1 to about 30, and most preferably from about 1 to about 20. Melt flow is an important property because it determines the viscosity of the blend and thus affects fluidity of the blend during extrusion. The desired melt flow can be obtained by selecting principal components of suitable molecular weights. The practitioner of ordinary skill will be able to obtain the desired melt flow with minimum experimentation. The composition is prepared by blending the above described components by any suitable means, including solvent mixing. Melt blending of the ingredients is preferred. The blended composition can be processed directly as an adhesive, for example by melt coating processes, or it can be isolated by known methods, such as underwater melt cutting followed by drying or by sheeting and chopping to produce a pelletized product for subsequent use.

Blending of the components can be accomplished in batch or continuous mixing equipment well known in the art to provide uniform polymer blends. Such equipment includes, for example, Banbury, Brabender or equivalent intensive batch mixers, and continuous processors such as the Farrel continuous mixer and single or twin-screw extruders. Ingredients are charged to the mixing equipment in routine fashion.

Typically, all the ingredients are charged to the mixer prior to blending. Preblending can be used to facilitate uniform distribution of each component in the adhesive composition in order to obtain optimum properties. If desired, the portions of principal components can be precompounded as "masterbatches" in a suitable mixing device. These "masterbatches" can then be compounded together and with other components and additives to produce the adhesive composition. Generally, changes in the sequence of addition of ingredients have not been found to be significant, provided that the adhesive mixture is thoroughly fluxed to attain uniformity.

The composition should be prepared by blending the cmponents at a temperature above the highest melting temperature of any poymeric component present, but below the temperature at which any of the components degrade substantially. Typically, blending is performed at temperatutes in the range from about 180°C to about 230°C. Blending should be carried out until the composition is substantially homogeneous; however, it is not critical that all of the components be dispersed on a microscale. More specifically, some components may be incompatible to the extent that dispersed particles up to about 10 μm are present; however, there is sufficient macroscopic compatibility to provide good physical properties of the composition as a whole.

The adhesive composition generally provides excellent adhesion as an extrudable adhesive for bonding a composite of a nonpolar, structural layer to a polar, barrier layer. The combination of processability and barrier properties provided by such composite structures make them useful in applications such as packaging and disposable containers. Nonpolar, strucutral layer materials include polyolefins such as polyethylene, polypropylene and polybutylene. Polar, barrier layer materials typically include, for example, EVOI I, polyamide, polyester, polyvinyl chloride and polycarbonate. The resulting composite structures generally provide excellent thermoforming properties. Compositions of this invention can be used as extrudable adhesives in such processes as coextrusion coating, coextrusion laminating and coextrusion cast film, coextrusion blow molding, and coextrusion sheet/thermoforming.

EXAMPLES This inventions is now illustrated by representative examples of certain preferred embodiments thereof, where all parts, proportions, and percentages are by weight, unless otherwise indicated. All units of weight and measure other than SI units have been converted to SI units. The following abbreviations are used hereafter:

B butylene C CXXAA coextrudable adhesive

E ethylene

H 1 ,4-hexadiene

O octene

LLDPE linear low density polyethylene

MAN maleic anhydride

MI Melt Index, dg/min, according to ASTM standard D-1238 at 190°C and 2160 g weight.

MFR Melt Flow, dg/min, according to ASTM standard D-1238 at 230° and 2160g weight M MVV Mooney viscosity at 121 °C (ML at 121°C (250°F)

P propylene

PP polypropylene

The term "% man in CXA" refers to the total level of MAN functionality calculated from the total of all the MAN-containing moieties in the adhesive formulation. Materials used in the examples are identified in Table I. TABLE I - MATERIALS USED

Code Trade Designation Description

Rl 2% E/98% P copolymer MFR = 5 R2 3% E/97% P copolymer; MFR = 5 R3 4% E/96% P copolymer; MFR = 5 R4 4% E/96% P copolymer; MFR = 7 R5 PP homopolymer; MFR = 4 R6 PP homopolymer; MFR = 37

LLDPE with 6.8% copolymerized butene; R7 density = 0.918 gm/cc

R8 72% E/21% P/7% H terpolymer; MV = 26 R9 70% E/23% P/7% H terpolymer; MV = 46

LLDPE; 89% E 5% B/6% O; RIO

Ml=1.8, Density=0.910 gm/cc

LLDPE; 82% E/13% B/ 5% P;

Rll

MI=12, density= 0.895 gm/cc

LLDPE; 83% E/17% B;

R13

MI=2.5, Density=0.885 gm/cc

LLDPE; 85% E/15% B;

R15

MI=0..8, Density=0.885 gm/cc

Hydrogenated aromatic CQ tackifier; softening

Tl "Arkon" P125 (Arakawa Chemical Co.) point 125°C

T2 "Escorez" 1102 (Exxon Chemical Co.) Aliphatic petroleum hydrocarbon resin T3 "Escorez" 7105 (Exxon Chemical Co.) Aromatic petroleum hydrocarbon resin T4 "Escorez" 7312 (Exxon Chemical Co.) Aromatic petroleum hydrocarbon resin T5 "Foral" 105 (Hercules Chemical Co.) Pentaerythritol ester of hydrogenated rosin T6 "Nirez" 2019 (Arizona Chemical Co.) High terpene level, terpenephenolic tackifier T7 "Nirez" V02040 (Arizona Chemical Co.) terpene phenolic resin T8 "Piccolyte" Cl 15 (Hercules Chemical Co.) Terpene hydrocarbon tackifier Aliphatic hydrocarbon tackifier; T9 "Piccotac" 95 (Hercules Chemical Co.) 95°C softening point Aliphatic hydrocarbon tackifier;

T10 "Piccotac" B (Hercules Chemical Co.) °C softening point

T 11 "Regalite" Rl 25 (Hercules Chemical Co.)

Low molecular weight hydrogenated styrene

T12 "Regalrez" 1128 (Hercules Chemical Co.) polymer

Low molecular weight hydrogenated styrene

T 13 "Regalrez" 1 139 (Hercules Chemical Co.) polymer

T14 "Superester" W125 (Arakawa Chemical Co.) Modified rosin gum glyceryl ester

T 15 "Zonarez" 71 15 (Arizona Chemical Co.) Polyterpene resin

T16 "Duraflex" DP8310 (Shell Chemical Co.) 6% E/94% B isotactic copolymer

T 17 "Duraflex" DP8510 (Shell Chemical Co.) 6% E/94% B isotactic copolymer Adhesive compositions were prepared and evaluated according to the following procedures. Procedure for Blown-film Extrusion:

Ingredients of the adhesive composition, including 0.1 % IRGANOX®1010, hindered phenolic antioxidant product of Ciba-Geigy, were dry blended by tumbling in a polyethylene bag. The blend was melt-mixed at 210°C to 230°C in a 28 mm or 30 mm twin-screw extruder equipped with avacuum port then extruded as strand and pelletized.

The adhesive composition was coextruded between a layer of polypropylene and a layer of ethylene/vinyl alcohol copolymer (EVOH) which contained 32 mole percent vinyl alcohol comonomer. Blown film coextrusion operating conditions are shown in Table II. Line speed was 0.102 m/s. The multilayer structure thus produced had finished layer thicknesses of 0.05mm/0.125 mm/0.025 mm polypropylene/adhesive/EVOH.

TABLE II - BLOWN FILM COEXTRUSION CONDITIONS

Resin Polvpropvlene Adhesive EVOH

Extruder Conditions

Diameter, mm 25.4 25.4 25.4

Length/Diam. 30/1 24/1 24/1

Compress. Ratio 3.5:1 3:1 3.5:1

Rear Temp, °C 200 200 190

Center Temp °C 210 215 210

Front Temp, °C 225 230 230

Clamp Temp °C 230 —

Adapter Temp °C 230 230 230

Die Temp, °C 230 230 230

Screw speed, rad s 8.4 2.1 4.5

Back Press, Mpa 20.7 13.8 13.8

Melt Temp., °C 230 215 225

Film Thickness,mm 0.05 0.0125 0.025

Peel strength of each multi-layer structure was measured according to ASTM standard D1876 using a "T" configuration, 2.54 cm wide sample strips, crosshead speed of 4.23 mm/s, full scale load of 0.89 kg/cm, and minimum displacement of 5 cm. Thermoformed Sheet

Sheet samples were prepared on a Sano coextrusion line for solid phase pressure forming. Typical sheet strucutre and typical dimensions were 0.65 mm polypropylene/0.06 mm adhesive compositon 0.1 1 mm EVOH/0.06 mm adhesive composition/0.65 mm polypropylene. Respective melt temperatures of coextrusion were 240/230/205/230/235°C.

Clyindrical containers were thermoformed at the draw ratios and temperatures shown in Table III. Peel strength was measured on 25 mm wide strips were cut lengthwise in a circumferential direction parallel to the bottom, about 10- 15 mm above the bottom to avoid thin cross-sections. Samples were separated at the outside adhesive/EVOH interface and subjected to "T" peel testing, in the same manner as for blown film samples, but with a crosshead speed of 0.5 mm/s. Results fo the average of five samples tested at each conditons were reported.

Adhesive compositions and test results are shown in Table III.

TABLE HI - EXAMPLES

Component Component Component Component

"A" "B" "C" "D" Properties

POLYPROPYLENES Partially

Ciystalline Elastomeric

PP#1 PP#2 Modified PP PE PE Tackifier

%MA Peel N in 230°C 1 WK

Ex. # Comments Grade % Grade % % CXA Grade % Grade % Grade % MFR (gm/cm)

Cl Comparative Example R3 67.3 R5 10 2.75 0.11 R7 20 — — — — 4.5 89

C2 Comparative Example R3 67.1 R5 10 2.90 0.11 R7 20 — — — — 4.7 32

C3 Comparative Example R3 67.1 R5 10 2.89 0.11 R7 20 — — — — 4.5 34

C4 Comparative Example R3 42.1 — 2.93 0.11 R7 12.5 R9 30 T5 12.5 1.8 14

C5 Comparative Example R3 44.6 — 2.93 0.11 R7 25 R9 15 T14 12.5 2.7 1.8

C6 Comparative Example R3 42.1 — 2.93 0.11 R7 12.5 R9 30 T14 12.5 1.8 5.4

1 R3 44.6 — 2.93 0.11 R7 25 R8 15 T16 12.5 3.0 223

2 R3 22.1 — 2.93 0.11 R7 25 R8 30 T16 20 2.1 195

3 R3 42.1 — 2.93 0.11 R7 12.5 R8 30 T17 12.5 3.3 305

4 R3 22.1 — 2.93 0.11 R7 25 R8 30 T17 20 3.8 198

5 R3 43.1 — 1.87 0.07 R7 15 R9 30 Tl 10 1.9 268

_X1 6 Example #5 with 0.09% MAN R3 42.6 — 2.40 0.09 R7 15 R9 30 Tl 10 2.0 296 cr 7 Example #5 with 0.11 % MAN R3 42.1 — 2.93 0.11 R7 15 R9 30 Tl 10 2.1 311 rπ 8 Duplicate of Example #7 R3 42.1 — 2.93 0.11 R7 15 R9 30 Tl 10 1.6 354

?\-> c- 9 Duplicate of Example #7 R3 42.1 — 2.94 0.11 R7 15 R9 30 Tl 10 1.8 171

9-C1 Example #9 without Tactifier R3 52.1 - 2.94 0.11 R7 15 R9 30 — — 1.5 163

9-C2 Example #9 without elastomeric polyethylene R3 72.1 - 2.94 0.11 R7 15 — — Tl 10 6.8 16

9-C3 Example #9 without crystalline polyethylene R3 57.1 - 2.94 0.11 - — R9 30 Tl 10 3.0 100

10 Example #9 with Homopropylene R5 R3 32.1 R5 10 2.93 0.11 R7 15 R9 30 Tl 10 2.0 268

11 Example #9 with Homopropylene R6 R3 32.1 R6 10 2.93 0.11 R7 15 R9 30 Tl 10 2.4 266

12 R3 44.6 — 2.93 0.11 R7 25 R9 15 T2 12.5 3.0 238

13 R3 42.1 - 2.93 0.11 R7 12.5 R9 30 T2 12.5 2.2 236

14 R3 44.6 - 2.93 0.11 R7 25 R9 15 T3 12.5 3.0 170

15 R3 22.1 — 2.93 0.11 R7 25 R9 30 T3 20 1.4 141

16 R3 44.6 - 2.93 0.11 R7 25 R9 15 T4 12.5 2.9 166

17 R3 42.1 — 2.93 0.11 R7 12.5 R9 30 T4 12.5 2.0 188

18 R3 42.1 — 2.93 0.11 R7 12.5 R8 30 T6 12.5 3.5 238

19 R3 17.1 - 2.93 0.11 R7 1 25 R8 30 T6 25 4.7 263

20 R3 42.1 — 2.93 0.11 R7 12.5 R8 30 T7 12.5 3.5 180

21 R3 17.1 — 2.93 0.11 R7 25 R8 30 T7 25 4.6 71 cr

XXI 22 R3 42.1 — 2.93 0.11 R7 12.5 R9 30 T8 12.5 2.4 202 CO -H 23 R3 44.6 — 2.93 0.11 R7 25 R9 15 T8 12.5 3.6 214

24 R3 46 R5 10 2.37 0.09 R7 20.8 R8 12.5 T9 8.33 4.1 245 cr

-4 25 Duplicate of Example #24 R3 46 R5 10 2.36 0.09 R7 21 R8 13 T9 8.3 4.6 255 m 25-C1 Example #25 without tackifier R3 54.3 R5 10 2.36 0.09 R7 21 R8 13 — — 3.4 163 o

_x: ----- 25-C2 Example #25 witout elastomeric polyethylene R3 58.5 R5 10 2.36 0.09 R7 21 — — T9 8.3 6.2 14

IT . •--- rn 25-C3 Example #25 without ciystalline polyethylene R3 66.8 R5 10 2.36 0.09 — — R8 12.5 T9 8.3 6.3 21 — 1 26 R3 46.4 R5 10 1.97 0.075 R7 20.8 R8 12.5 T9 8.3 4.3 205

27 Example #26 at higher Resin R8 R3 42.5 R5 10 1.97 0.075 R7 12.5 R8 23 T9 10 4.0 223 cr i — 28 R3 42.1 — 2.93 0.11 R7 12.5 R9 30 T9 12.5 2.3 318 rπ ro 29 R3 43.1 — 1.87 0.07 R7 12.5 R9 30 T9 12.5 2.2 214 -o 30 Example #29 at 0.09% MAN in CXA R3 42.6 — 2.40 0.09 R7 12.5 R9 30 T9 12.5 2.2 300

31 R3 46 R5 10 2.37 0.09 R10 20.8 R8 12.5 T9 8.3 5.6 230

32 R3 42.5 R5 10 1.98 0.075 R10 12.5 R8 23 T9 10 4.9 164

33 R3 56 — 2.40 0.09 R1I 20.8 R8 12.5 T9 8.3 10.0 107

34 R3 56 — 2.40 0.09 R12 20.8 R8 12.5 T9 8.3 5.8 159

35 R3 56 — 2.40 0.09 R13 20.8 R8 12.5 T9 8.3 4.7 132

36 R2 44.6 R5 10 2.89 0.11 R7 12.5 R8 25 T10 5 3.3 227

37 R4 56 — 2.37 0.09 R7 20.8 R9 12.5 T10 8.3 5.3 175

38 R3 46 R5 10 2.37 0.09 R7 20.8 R8 12.5 T10 8.3 6.0 307

39 R4 43.5 R6 10 2.37 0.09 R7 20.8 R8 15 T10 8.3 7.0 304

40 Rl 39.6 R5 10 2.89 0.11 R7 12.5 R8 25 T10 10 4.2 163

41 Tackifier Tl 1 in Example #7 R3 42.1 — 2.89 0.11 R7 15 R9 30 Ti l 10 1.7 232

42 R3 42.1 — 2.93 0.11 R7 12.5 R9 30 T12 12.5 2.3 359

43 R3 44.6 - 2.93 0.11 R7 25 R9 15 T12 12.5 3.0 236

TABLE m - EXAMPLES

44 R3 44.6 — 2.93 0.11 R7 25 R9 15 T13 12.5 3.2 282

45 R3 17.1 — 2.93 0.11 R7 25 R9 30 T13 25 2.9 66

CO 46 R3 42.1 — 2.93 0.11 R7 12.5 R8 30 T15 12.5 3.6 136

CO 47 R3 44.6 — 2.93 0.11 R7 25 R8 15 T15 12.5 4.3 246 CO

48 R3 17.1 — 2.93 0.11 R7 25 R8 30 T15 25 4.7 216

49 R3 44.6 - 2.93 0.11 R7 25 R8 15 T15 12.5 4.3 246 ϋi

CO re m m cr ro

DISCUSSION OF EXAMPLES

Blown Film Evaluation

The examples shown in Table III are sorted according to Component "D", the tackifier. The best performing formulations are those containing aliphatic hydrocarbon resins such as RIO or hydrogenated aromatic tackifiers such as Tl , T7, and T8 (Component "D"), and a high level of either the ethylene/a-olefin copolymer (Component "B") or the elastomeric ethylene copolymer (Component "C"). Tackifiers which are more polar, such as T3, T4, T7, and T13, all give poorer peel performance. In comparison, tackifiers T5 and T 14, which contain ester groups, give very poor adhesive properties (comparative examples C4 to C6). Comparative examples Cl, C2, and C3 indicate the poor performance exhibited by adhesive formulations which do not contain elastomeric component "C" and tackifier component "D". Tackifier Tl allows good peel performance to be achieved even at low polypropylene graft levels (Examples 6 and 7). Never-the-less, all four components of the present invention are still needed for a good balance of properties. This is demonstrated by examples 9-C1 to -C3. Eliminating tackifier Tl in this particular formulation esults only in a slight decrease in peel strength compared to the control (Example 9 vs. 9-C1). The effect of the tackifier loss is minimized by having a relatively high level of elastomeric component "C". In contrast, eliminating either the elastomeric polyethylene or the partially crystalline polyethylene results is a much greater degradation of adhesive performance. Similar trends are observed for Examples 25-C1 to -C3. However, as there is less elastomeric polyethylene to start with, eliminating tackifier T9 results in a much greater loss in peel strength. These results indicate the synergistic interactions between the elastomer and tackifier in these adhesive formulations.

Reproducibility relative to adhesion performance in indicated by comparing Examples 7, 8, and 9 and Examples 24 and 25. Of the two sets of results, only Example 8 is not comparable to its replicates. However, this sample was prepared using a blown film die configuration which has a shorter contact time between the three hot films as they are extruded through the die. Shorter contact times are known to give reduced adhesion between films in a multi-layer laminate structure. Those skilled in the art will recognize that altering composition merely to maximize peel strength can have negative effects on other properties. These include:

Increasing the level of elastomer increases peel strength and improves low temperature performance, but decreases melt flow, increases extractables (reduced solvent resistance), and decreases film clarity. As the elastomeric component is frequently the most expensive ingredient, cost is also increased.

Increasing tackifier level may actually reduce peel strength if there is poor compatibility between the tackifier and the balance of the formulation components, as well as increase melt flow, decrease low temperature performance, decrease performance in thermoforming applications, increase color, and harm organoleptic properties. Depending upon the relative cost of the tackifier the cost of the formulation may be increased.

Evaluation of Thermoformed Sheet

Results of evaluation of thermoformed sheet are shown in Table IV. Included were comparative examples, Cl and C2, which contain no tackifier and elastomer. The peel strengths for blown film constructions are those as shown for these formulations in Table III.

As was the case for the blown film results, the rubber modified and tackified adhesive formulations shown much superior peel strengths in thermoformed sheet relative to Comparative Example 1 and 2. The superior performance is maintained throughout four different forming temperatures and two draw ratios.

TABLE IV PROPERTIES OF THERMOFORMED SHEET

Example Example Example Example Example Example Example

Composition Cl #9 C2 #28 #30 #31 #49

Resin R3 (Co-PP) 67.1% 42.1% 67.1% 46% 46.4% 42.6% 42.1%

Resin R5 (Homo-PP) 10% — 10% 10% 10% 10% —

Resin R7 Polyethylene 20% 15% 20% 20.8% 20.8% 12.5% 15%

MAN-graftedPP 2.9% 2.9% 2.9% 2.4% 2% 2% 2.9%

Resin R8 Elastomer — — — 12.5% 13% 23% —

Resin R9 Elastomer — 30% — — — — 30%

Tackifier Tl — 10% — — — — —

Co c-r Tackifier T9 — — — 8.3% 8.3% 10% —

CO Tackifier Tl 1 — — — — — — 10% CO Anhydride Content 0.11% 0.11% 0.11% 0.09% 0.75% 0.75% 0.11% cr MFR @230°C 4.5 2.1 4.5 4.1 4.3 4.0 1.7

Blown Film

•rn oo Peel Strength (gm/cm) 34 311 34 245 205 223 232 -x rπ Thermoformed Sheet @ L Draw Ratio @1:1 Draw Ratio rπ Forming Temp, °C (°F) 132 (270) 132 (270) 150 (300) 150 (300) 150 (300) 150 (300) 150 (300) ro Peel Strength (gm/cm) 30 186 46 152 130 177 129 c i —r @1:1 Draw Ratio m cr» Forming Temp, °C (°F) 145 (290) 145 (290)

Peel Strength (gm/cm) 36 261

@1:1 Draw Ratio

Forming Temp, °C (°F) 155 (310) 155 (310)

Peel Strength (gm/cm) 68 377

I @3.27.i Draw Ratio

Forming Temp, °C (°F) f 132 (270) 132 (270)

Peel Strength (gm/cm) | 1 1 84

Claims

WHAT IS CLAIMED IS:

1. A coextrudable adhesive composition consisting essentially of:

(A) About 15 to 90 wt % of a blend of polypropylene with polypropylene containing a cyclic carboxylic anhydride grafted to a level of from 0.03 to 5 wt %;

(B) About 5 to 50 wt % crystalline ethylene copolymer having about from 2 to 10 wt % copolymerized a-olefin;

(C) About 5 to 50 wt % elastomeric ethylene copolymer having at least 20 wt % copolymerized a-olefin; and (D) About 1 to 30 wt % tackifier which does not conain ester functionality.

2. The coextrudable adhesive composition of Claim 1 wherein the composition of component (A) is a blend of unmodified polypropylene homopolymer or polypropylene copolymer and a polypropylene homopolymer or copolymer modified to contain a cyclic carboxylic anhydride functionality.

3. The coextrudable adhesive composition of Claim 1 wherein the composition of component (B) is selected from a medium density polyethylene, low density polyethylene homopolymer, and a linear low density ethylene/a-olefin copolymer.

4. The coextrudable adhesive composition of Claim 1 wherein the composition of component (C) is a substantially amorphous copolymer of ethylene and one or two a-olefin comonomers.

5. The coextrudable adhesive composition of Claim 1 wherein the cyclic carboxylic acid functionality in the modified polypropylene is itaconic anhydride, maleic anhydride, succinic anhydride, citraconic anhydride, and dimethyl maleic anhydride.

6. The coextrudable adhesive composition of Claim 1 wherein the cyclic carboxylic acid functionality in the modified polypropylene is maleic anhydride.

7. The composition of Claim 2 wherein the level of cyclic carboxylic anhydride functionality is as low as 0.03 wt % to as much as 10 wt % or more.

8. The coextrudable adhesive composition of Claim 1 wherein the amount of cyclic carboxylic anhydride functionality is between about 0.03 to about 0.5 wt%.

9. The coextrudable adhesive composition of Claim 2 wherein the composition of the unmodified polypropylene component is a blend of polypropylene homopolymer or copolymer with a rubber modified propylene homopolymer or copolymer.

10. The coextrudable adhesive composition of Claim 1 wherein the tackifier component (D) is selected from the group consisting of ethylene/butene copolymer, an hydrogenated aromatic Cα. resin, an aromatic petroleum hydrocarbon resin, a terpene phenolic resin, or an aliphatic hydrocarbon resin.

1 1. A laminated structure comprising at least three layers of:

(1) A polypropylene layer,

(2) A layer composed of the coextrudable adhesive composition of Claim 1 , and

(3) A polar barrier layer of an ethylene/vinyl alcohol copolymer.