Polyolefin Composition and the Use Thereof

The present invention provides a polyolefin resin composition insuring excellent oxygen barrier property.

Polyolefin resins, such as polyethylene and polypropylene, have good moldability and give shaped articles (or moldings) excellent in appearance, moisture resistance, mechanical properties and so forth and, as such, have found application in many uses such as film, sheet, container material, textile fiber and so on.

However, polyolefin resins are rather poor in gas barrier property, in particular oxygen barrier property, and therefore it is substantially impossible to use them by themselves as packaging materials for foodstuffs readily susceptible to oxidation and oxidative denaturation.

Therefore, if said resins could be provided with oxygen barrier property by some or other means, they would be of still more increased utility value.

A measure taken therefor comprises laminating a layer of some other resin having good oxygen barrier property to a polyolefin resin layer or blending such other resin with a polyolefin resin. However, either method has both merits and demerits, physical properties obtainable thereby being not always satisfactory.

The inventors of the present invention also attempted to improve the oxygen barrier property of polyolefin resins by admixing therewith a saponified ethylene-vinyl actate copolymer which has particularly good oxygen barrier property. In some instance, however, such excellent physical properties of polyolefin resins as stretchability and flexibility were sacrificed. Fully satisfactory results have never been obtained as yet.

The intensive research undertaken by the inventors of the present invention revealed that the above-mentioned objects are accomplished or, in other words, the desired oxygen barrier property can be obtained without any impairment of the stretchability or flexibility intrinsic of polyolefins, by providing a polyolefin resin composition which comprises

(A) 50 to 99.5 weight % of a polyolefin resin,

(B) 0.4 to 50 weight % of a saponified ethylenevinyl acetate copolymer, and

(C) 0.1 to 15 weight % of a graft polymer obtainable by grafting an ethylenically unsaturated carboxylic acid or a derivative thereof to a polyolefin resin and reacting the adduct with a polyamide oligomer or polyamide, which composition satisfies the relation: M.sub.2 /M.sub.1 =not less than 1.5 wherein M.sub.2 and M.sub.1 are the melt flow rates of (B) and (A), respectively, under a load of 2160 g at 210 C. The present invention is predicated on the above finding.

The present invention will hereinafter be described in detail, with emphasis placed on the above composition and particularly on uses therefor.

With regard to the polyolefin resin (A), there may be mentioned linear low-density, low-density and high-density polyethylenes, ionomers, ethylene-propylene copolymer, crystalline polypropylene, polybutene, ethylene-vinyl acetate copolymer, ethyleneacrylate ester copolymers, and so on. Particularly, linear low-density, low-density or high-density polyethylene, and isotactic polypropylene are of practical importance.

With regard to the above component (A), its melt flow rate (hereinafter referred to briefly as M.sub.1.) as determined at 210.degree. C. and under a load of 2160 g according to JIS K-6760 is in the range of 0.05 to 100 g/10 minutes and preferably 0.5 to 20 g/10 minutes.

The saponified ethylene-vinyl acetate copolymer (B) to be employed in accordance with the present invention is a copolymer with an ethylene content of 20 to 60 mole %, preferably 25 to 55 mole %, with a degree of saponification of its vinyl acetate component being not less than 95 mole %.

With an ethylene content less than 20 mole %, the oxygen barrier property under high-humidity conditions is not as high as desired, while an ethylene content in excess of 60 mole % leads to decreases in oxygen barrier property, printability and other physical properties. When the degree of saponification or hydrolysis is less than 95 mole %, the oxygen barrier property and moisture resistance are sacrificed.

It should be understood that this saponified copolymer may contain small proportions of other comonomer ingredients including .alpha.-olefins such as propylene, isobutene, .alpha.-octene, .alpha.-dodecene, .alpha.-octadecene, etc., unsaturated carboxylic acids or salts thereof, partial alkyl esters, complete alkyl esters, nitriles, amides and anhydrides of such acids, and unsaturated sulfonic acids or salts thereof.

With regard to (B), its melt flow rate (MFR; hereinafter referred to as M.sub.2) as determined at 210.degree. C. and under a load of 2160 g according to JIS K6760 is in the range of 0.1 to 150 g/10 minutes and preferably 5 to 100 g/10 minutes.

It is essential in the preparation of the composition of the invention that (A) and (B) be used in an M.sub.2 /M.sub.1 ratio of at least 1.5, preferably 2 to 100 and, for still better results, 3 to 50.

With an M.sub.2 /M.sub.1 ratio less than 1.5, (B) is not dispersed in (A), the matrix component, in a lamellar fashion but dispersed as globular or nozzle-shaped particles so that the desired effect cannot be fully attained.

For improving the compatibility between (A) and (B), incorporation of (C) is essential in the practice of the invention.

The component (C) is a graft polymer obtainable by grafting an ethylenically unsaturated carboxylic acid or a derivative thereof to a polyolefin resin and reacting this carboxylic acid or derivative thereof with a polyamide oligomer or polyamide.

This graft polymer can be produced by dissolving or suspending a polyolefin resin in an appropriate solvent or putting it in a molten state, activating the polyolefin resin chain with a peroxide or diazo initiator, grafting an ethylenically unsaturated carboxylic acid or a derivative thereof thereto to give a polymer and mixing this polymer with a polyamide oligomer or polyamide in molten state.

For this reaction, Brabender machine, Buss blender, single-screw extruder, Werner and Pfleiderer twinscrew extruder or the like is employed.

The degree of polymerization of the polyolefin resin to be employed is about 350 to 45,000 and preferably about 500 to 10,000. The melt flow rate (230.degree. C., load 2160 g; the same applies hereinafter) is about 0.1 to 50 g/10 minutes for all practical purposes.

The reaction ratio of the polyolefin resin to the ethylenically unsaturated carboxylic acid or a derivative thereof is 100/0.05 through 100/10 and preferably 100/0.5 through 100/3 as expressed on the weight basis.

If the ratio is 100/less than 0.05, the improving effect on compatibility will not be sufficient. On the other hand, if the ratio is 100/more than 10, the viscosity will be too high for practical molding.

The degree of polymerization of said polyamide oligomer is 5 to 80, preferably not less than 15, and the degree of polymerization of said polyamide is 80 to 1000, preferably not more than 500, for all practical purposes and the reaction ratio is 0.01 to 1 mole and preferably 0.05 to 0.9 mole per mole of the carboxyl group.

As examples of the polyolefin resin, there may be mentioned linear low-density, low-density or high-density polyethylene, ionomers, ethylene-propylene copolymer, crystalline polypropylene, polybutene, ethylene-vinyl acetate copolymer, ethylene-acrylic ester copolymer and so on. Important for practical purposes are linear low-density polyethylene, low-density polyethylene, medium-density polyethylene high-density polyethylene, ethylene-propylene copolymer, ethylene-vinyl acetate copolymer and crystalline polypropylene.

The ethylenically unsaturated carboxylic acid or derivative thereof to be grafted to such a trunk polymer includes, among others, unsaturated carboxylic acids such as acrylic acid, methacrylic acid, crotonic acid, maleic acid, fumaric acid and itaconic acid and the corresponding anhydrides or half esters.

The polyamide oligomer or polyamide can be prepared by the known methods such as addition polymerization of a lactam, polycondensation of an aminocarboxylic acid, polycondensation of a diamine with a dicarboxylic acid, and so on.

Examples of the starting materials for said polyamide oligomer or polyamide are various lactams such as .epsilon.-caprolactam, enantholactam, caprylolactam, laurolactam, .alpha.-pyrrolidone, .alpha.-piperidone, etc., .alpha.-amino acids such as 6-aminocaproic acid, 7-aminoheptanoic acid, 9-aminononanoic acid, 11-aminoundecanoic acid, etc., dibasic acids such as adipic acid, glutaric acid, pimellic acid, suberic acid, azelaic acid, sebacic acid, undecadioic acid, dodecadioic acid, hexadecadioic acid, hexadecenedioic acid, eicosadioic acid, eicosadienedioic acid, diglycolic acid, 2,2,4-trimethyladipic acid, xylylenedicarboxylic acid, 1,4-cyclohexanedicarboxylic acid, terephthalic acid, isophthalic acid, etc., and diamines such as hexamethylenediamine, tetramethylenediamine, nonamethylenediamine, undecamethylenediamine, dodecamethylenediamine, 2,2,4- (or 2,4,4-)trimethylhexamethylenediamine, bis(4,4'-aminocyclohexyl)methane, metaxylylenediamine and so on. For molecular weight control, a monoamine such as laurylamine or oleylamine can also be used in an appropriate amount.

In the composition of the present invention, the proportion of (A) should be 50 to 99.5 weight % and preferably 60 to 95 weight %, that of (B) should be 0.4 to 50 weight % and preferably 4.5 to 35 weight %, and that of (C) should be 0.1 to 15 weight % and preferably 0.5 to 10 weight %.

When the proportion of (A) is less than 50 weight % or that of (B) is over 50 weight %, the moldability, in particular stretchability, is adversely affected. Conversely when the proportion of (A) is over 99.5 weight % or that of (B) is less than 0.4 weight %, the oxygen barrier property-improving effect is insufficient.

When the proportion of (C) is less than 0.1 weight the compatibility between (A) and (B) is poor and the oxygen barrier property-improving effect is also poor. Conversely when the proportion of (C) exceeds 15 weight %, long-run moldability is adversely affected.

While the composition according to the present invention is useful for a variety of applications such as shaped articles, adhesives, coatings and so on, it is most useful for molding purposes and can be molded into pellets, film, sheet, containers, fibers, bars, pipe and other shaped articles by the melt-kneading technique. Such products can be crushed (for reclaiming) or pelleted for re-melt-molding.

For melt-molding of the composition, extrusion molding (e.g. T-die extrusion, inflation molding, blow molding, melt spinning or contour extrusion) and injection molding are mostly employed. The melt-molding temperature is selected in many cases from the range of 160 to 290.degree. C. In addition to the above techniques, two-color molding and injection-blow molding techniques may also be employed and shaped articles with good dimensional tolerances can be manufactured.

In the molding process, it is of course possible to use two or more different saponified ethylene-vinyl acetate copolymers varying in ethylene content and/or in the degree of saponification in combination. In melt-molding, it is also possible to incorporate suitable amounts of additives such as a plasticizer (for example, a polyhydric alcohol), stabilizer, surfactant, crosslinking agent (for example, an epoxy compound, polyvalent metal salt, inorganic or organic polybasic acid or salt thereof), filler, colorant, reinforcing fiber (for example, glass fiber, carbon fiber, etc.}and so on. It is also possible to incorporate a further thermoplastic resin in a suitable proportion. Such thermoplastic resin includes, among others, various polyolefins other then (A), modified polyolefins obtainable by graft-modification of such polyolefins with unsaturated carboxylic acids or derivatives thereof, polyamides, polyvinyl chloride, polyvinylidene chloride, polyesters, polystyrene, polyacrylonitrile, polyurethanes, polyacetal, polycarbonates, melt-moldable polyvinyl alcohol resin and so on.

As mentioned hereinbefore, the composition of the present invention is not only used for the manufacture of a single-layer article solely composed of the composition but also used often as a laminated article including at least one layer of the composition. The layer of the composition of the present invention shows a characteristically high bonding affinity for the layer material to be laminated therewith.

In the manufacture of a laminated product according to the invention, in which a different material is laminated to one side or either side of a layer of the composition of the invention, the following laminating methods, for instance, can be employed. Thus, the method which comprises melt-extruding a thermoplastic resin onto a film or sheet of the composition of the invention, the method which comprises melt-extruding the composition of the invention onto a substrate made of a thermoplastic resin or some other material, the method which comprises co-extruding the composition of the invention and a different thermoplastic resin, and the method in which a film or sheet of the composition of the invention is laminated to a film or sheet of a different material with a known adhesive such as an organotitanium compound, an isocyanate compound or a polyester compound can be mentioned.

As mating resins for co-extrusion, there may be mentioned linear low-density polyethylene, low-density polyethylene, medium density polyethylene, high-density polyethylene, ethylene-vinyl acetate copolymer, ion-omers, ethylene-propylene copolymers, ethylene-acrylic ester copolymers, polypropylene, propylene-.alpha.-olefin (C.sub.4-20 .alpha.-olefin) copolymers, homo- or copolymers of olefins such as polybutene, polypentene, etc., and polyolefin resins in a broad sense as obtainable by modifying such homopolymers or copolymers of olefins by grafting of an unsaturated carboxylic acid or an ester thereof, polyesters, polyamides, copolymerized polyamides, polyvinyl chloride, polyvinylidene chloride, acrylic resins, styrenic resins, vinyl ester resin, polyester elastomers, polyurethane elastomers, chlorinated polyethylene, chlorinated polypropylene and so on. A saponified ethylene-vinyl acetate copolymer can also be co-extruded.

When a film or sheet or the like shaped article is prepared from the composition of the invention and, then, extrusion-coated with a different material or laminated to a film or sheet of a different material with an adhesive, said different material is not limited to said thermoplastic resins but may be virtually any other material (such as paper, metal foil, uniaxially or biaxially oriented plastic film or sheet, woven fabric, nonwoven fabric, metal filament, wood and so on).

The laminar structure of said laminated product is optional. Thus, a layer of the composition of the invention being designated as A (A.sub.1, A.sub.2, . . . ) and a layer of a different material, e.g. a thermoplastic resin, being designated as B (B.sub.1, B.sub.2, . . . ), not only a two-layer structure of A/B but a variety of other combinations such as B/A/B, A/B/A, A.sub.1 /A.sub.2 /B, A/B.sub.1 /B.sub.2, B/A/B, B.sub.2 /B.sub.1 /A/B.sub.1 /B.sub.2, etc. can be employed for a film, sheet or bottle, for instance. In the case of a filament, a bimetal-type, core (A)--sheath (B), core (B)--sheath (A), eccentric core-sheath and other combinations of A and B can be adopted.

For co-extrusion, A may be bended with B or vice versa, or for improved interlayer adhesion, a suitable resin may be incorporated in at least one of A and B.

The laminated product may be optionally configured. Thus, film, sheet, tape, bottle, pipe, filament, or modified cross-section extrudate may be mentioned.

The laminated product may, if necessary, be further subjected to a variety of processings, such as heat treatment, cooling, rolling, printing, dry lamination, solution- or melt-coating, bag production, deep-drawing, box-making, tubing, splitting and so on.

The aforementioned shaped articles and laminated products, in particular in the form of films or sheets, can be improved in physical properties by stretching or drafting, if required.

In the present invention, the composition is melt-molded into a film material. The thickness of such film is virtually optional and may range from a few microns to several hundred microns. The term `film` as used in this specification means a film in the broad sense of the term, thus including a sheet, tape, tube, container and so on.

The film obtained in the above manner is conditioned for absorption of moisture or drying, if necessary, and then stretched.

This stretching may be uniaxial or biaxial. The effects of the invention are better materialized when the stretching ratio or draft is as high as possible. In the case of uniaxial stretching, the stretching ratio is preferably at least 1.5 times and, for still better results, not less than 2 times. In the case of biaxial stretching, the stretching ratio is preferably not less than 1.5 times, more desirably not less than 2 times and, for still better results, not less than 4 times on the area basis.

As to the stretching technique that can be employed, there may be mentioned roll stretching, tenter stretching, tubular stretching and stretching blow processes, as well as high-draft deep drawing or vacuum molding. In the case of biaxial stretching, whichever of concurrent biaxial stretching and serial biaxial stretching can be adopted.

The stretching temperature is selected from the range of about 40.degree. to 150.degree. C.

After completion of stretching, the product is thermally set. This thermal setting can be effected by the well-known technique. Thus, with the stretched film being held in taut condition, it is heat-treated at a temperature of 50.degree. to 160.degree. C., preferably at 80.degree. to 160.degree. C. for about 2 to 600 seconds.

The resulting oriented film can be subjected to a variety of processings such as cooling, rolling, printing, dry lamination, solution- or melt-coating, bag-making, deep-drawing, box-making, tubing, splitting and so on.

The film, sheet or container obtainable from the composition of the present invention is useful for packaging foodstuffs, pharmaceutical products, industrial chemicals, agrochemical products add so on.

The composition according to the invention which comprises (A), (B) and (C) can have markedly improved oxygen barrier property while retaining those excellent molding characteristics and physical properties (stretchability, flexibility, etc.) which are inherent to polyolefins.

The following examples are further illustrative of the composition of the present invention. In the following description, all parts and % are by weight unless otherwise indicated.

Pellets of the composition of (A), (B) and (C) were mixed in a Henschel mixer and fed to a T-die extrusion machine for melt-kneading and extrusion from the T-die to produce a 30 .mu.-thick film. (In the evaluation of stretchability, a 180 .mu.-thick film was used.)

The extrusion molding conditions were as follows.

Extruder: 40 mm-dia. extruder

Screw Full-flight type, L/D =28, CR =3

Extrusion temperature (.degree.C.): C.sub.1 /C.sub.2 /C /H/D.sub.1 /D.sub.2 =170/200/220/220/220/210/210

RPM of screw: 30 rpm or 85 rpm

The data on the film are presented in Table 1.

Oxygen permeability: Determined with a MOCON Oxtran 10/50.

Stretchability: Evaluated in terms of uneven stretching in concurrent biaxial stretching (5.times.5 times) at 90.degree. C.

Impact strength: Determined with a film impact tester, impact head diameter 1 inch, 20.degree. C..times.65% RH

Inner layer (I): Low-density polyethylene (MFR: 16 g/10 minutes, 190.degree. C./2160 g)

Adhesive layers (II) and (IV): Maleic anhydride-modified ethylene-vinyl acetate copolymer (MFR: 2 g/10 minutes, 190.degree. C./2160 g)

Intermediate layer (III): The composition comprising (A), (B) and (C) according to the invention

Outer layer (V): Low-density polyethylene (MFR: 16 g/10 minutes, 190.degree. C./2160 g)

Using the above resin materials, a five-layer laminate of the construction and film thicknesses (.mu.) (I)/(II)/(III)/(IV)/(V)=20/5/60/5/20 was fabricated under the following conditions.

Extrusion machines

60 mm-dia. extruder (for inner layer)

40 mm-dia. extruder (for intermediate layer)

40 mm-dia. extruder (for adhesive layers)

60 mm-dia. extruder (for outer layer)

Screw: All full-flight type, L/D =30, compression ratio 2.8.

RPM of screw:

50 rpm for inner layer

40 rpm for intermediate layer

40 rpm for adhesive layers

50 rpm for outer layer

Die:

A T-die with a 5-layer combining adapter

Die width: 300 mm

Extrusion temperature:

The results are set forth in Table 2.

Using the following graft polymer, a four-layer laminate was produced in the same manner as Examples 1 through 10. The results are set forth in Table 3.

A five-layer laminate was produced in the same manner as Examples 11 through 15. The results are set forth in Table 4.