EP1102805A1

EP1102805A1 - Oriented, propylene polymer film with improved oxygen barrier property

Info

Publication number: EP1102805A1
Application number: EP00900759A
Authority: EP
Inventors: Anthony J. De Nicola, Jr.; Tinh N. Nguyen; Lin-Chen Yu
Original assignee: Basell Technology Co BV
Current assignee: Basell Poliolefine Italia SRL
Priority date: 1999-01-29
Filing date: 2000-01-24
Publication date: 2001-05-30
Also published as: CA2326808A1; NO20004874D0; WO2000044815A1; NO20004874L; KR20010072562A; ID26404A; CN1293690A; PL343282A1; AU3068800A; BR0004531A; TR200002823T1; JP2002535466A

Abstract

Disclosed is oriented, propylene polymer film, the oxygen barrier property of which is substantially improved. The improvement is achieved by incorporating in the propylene polymer composition from which the film is made grafted copolymer material comprising predominantely crystalline, propylene polymer material, the polymer or polymers of which have grafts of polymerized monomer material of a group that includes styrene, p-alkylstyrenes, acrylic acid, alkacrylic acids, alkyl alkacrylates, acrylonitrile and, with or without ethylene, vinyl acetate.

Description

TITLE OF THE INVENTION

Oriented, Propylene Polymer Film With Improved Oxygen Barrier Property

CROSS-REFERENCE TO RELATED APPLICATIONS

Not Applicable

STATEMENT REGARDING FEDERALLY SPONSORED RESEARCH OR DEVELOPMENT

Not Applicable

FIELD OF INVENTION

This invention resides in the chemical arts. It relates to film formed from polymers of propylene.

BACKGROUND OF INVENTION

Predominately crystalline homopolymer of propylene, the polypropylene of commerce, has achieved tonnage use in many applications. One of them is the manufacture of film, especially biaxially oriented film used in the packaging of, for example, snack foods such as potato chips and the like. Indeed, such film has become known as "BOPP" film. Polypropylene film, while having advantageous properties, for example, chemical resistance and excellent barrier to moisture, is not a good barrier to oxygen; oxygen transmission through the film is too high for many packaging film uses. This problem of oxygen barrier property also exists in the case of films formed from predominately crystalline, random copolymers of propylene and other l-olefins such as ethylene and 1- butene. Efforts to solve this problem have included laminating the film with film of another synthetic resin having a good oxygen barrier property, and incorporating additives such as, for example, so-called hard resin, in the propylene polymer composition from which the film is formed. For one reason or another, such efforts have not been entirely satisfactory. BRIEF SUMMARY OF THE INVENTION

This invention is based on the discovery that melt blending with predominantly crystalline polypropylene a graft copolymer of predominantly crystalline polypropylene and certain polymerized monomer material gives a composition that in the form of biaxially oriented film is a good barrier to oxygen transmission. However, the invention is broader than this discovery.

The invention, in summary, broadly comprises oriented film formed from a melt blend consisting essentially of

(1) propylene polymer material selected from the group consisting of predominantly crystalline polypropylene and predominantly crystalline copolymers and terpolymers of propylene and 1-olefin material selected from the group consisting of ethylene and the butenes, which copolymers and terpolymers have more than 50 mole % propylene units; and

(2) graft copolymer material selected from the group consisting of graft copolymers of (a) propylene polymer material selected from the group consisting of predominantly crystalline polypropylene and predominantly crystalline copolymers and terpolymers of propylene and 1-olefin material selected from the group consisting of ethylene and the butenes, which copolymers and terpolymers have more than 50 mole % propylene units, and (b) polymerized monomer material selected from the group of monomers consisting of styrene, p-alkylstyrenes, acrylic acid, alkacrylic acids, alkyl acrylates, alkyl alkacrylates, acrylonitrile, and vinyl acetate with or without ethylene, the alkyls in these monomers with alkyl substituents having one-four carbons, the concentration of the graft copolymer material being such that the rate of oxygen transmission through the film is substantially less than if no graft copolymer material were present.

DETAILED DESCRIPTION OF THE INVENTION

The propylene polymer material in one general embodiment of the blend from which the oriented film of this invention is formed is composed of only one propylene polymer of the recited group. In another general embodiment it is composed of more than one such polymer. All of the members of the group from which the propylene polymer material is selected, and processes for making them, are generally known.

The graft copolymer material in one general embodiment of the blend from which the oriented film of this invention is formed is composed of only one graft copolymer of the recited group. In another general embodiment it is composed of more than one such grafted polymer. In more specific embodiments of these general embodiments, the grafted, polymerized monomer material comprises only one grafted, polymerized monomer. In other, more specific embodiments of these general embodiments, the grafted, polymerized monomer material comprises more than one grafted, polymerized monomer. The members of the group of graft copolymers, and processes for making them, are generally known.

Examples of such processes are a radiation process such as that disclosed in EP 519, 341, issued August 14,1996, and a peroxide process such as that disclosed in the same patent. The relevant disclosures of this patent are incorporated herein by reference.

In both processes, and especially in the peroxide process, a significant amount (as much as 80 weight % of the graft copolymer product remaining after removal of unreacted monomer material) of the propylene polymer material is not grafted. Hence, in some embodiments the graft copolymer product furnishes not only the graft copolymer material component, but all of the propylene polymer material component of the blend. However, in most embodiments the graft copolymer product supplies only part of the propylene product material.

Also, in both processes, and especially in the peroxide process, non-grafted polymerized monomer material is formed. The quantity of such can be as much as 50% by weight of the graft copolymer material product of the process in each case. However, the presence of such in the melt blend generally can be tolerated. In general, satisfactory results are obtained with the concentration of the graft copolymer material in the blend being about 10-90 weight % of the propylene polymer material.

In addition to the essential components, that is, the propylene polymer material and the graft copolymer material, most embodiments of the melt blend comprise at conventional concentrations stabilizer material selected from the group consisting of antioxidants, heat stabilizers, ultraviolet light inhibitors, and the like. Moreover, embodiments of the melt blend can comprise at conventional concentrations other additives, for example, nucleating agent material, filler material, extender material, colorant material, antacid material, mechanical property improver material (for example, a polyolefin type rubber such as ethylene-octene copolymer rubber), and the like.

The melt blend and the oriented film thereof are made by conventional ways and means.

While most embodiments of the oriented film of this invention are in biaxial orientation, film of monoaxial orientation is within the broader concepts of this invention.

The best mode now contemplated of carrying out the invention is depicted by Examples 1-23 set forth in the following tables. These Examples illustrate specific embodiments of the oriented film of this invention, their compositions, and typical data including oxygen transmission data obtained in physical testing of them.

These data were obtained in work in which oriented film samples of the formulations set forth in the following tables were made, and the physical properties indicated in the tables were measured. In that work grafted copolymer products were made by the peroxide process. The starting propylene polymer material for such products consisted of a propylene homopolymer resin (polymer + conventional stabilizer material, added at the time of production of the polymer, at a concentration intended to stabilize the polymer until it is compounded for use) commercially available from Montell USA Inc. as KPO10. Typical properties of this resin include: spherical particles; melt flow rate = 10 dg/min at 230oC and 2.16Kg; porosity = 0.44 cc/g; and room temperature xylene insoluble fraction: 96.5 wt%.

The monomer material used to make the various grafted polymers were these mixtures: methyl methacrylate and methyl acrylate, methyl methacrylate and methacrylic acid, and methyl methacrylate and acrylonitrile. The concentration of the methyl acrylate in these mixtures was 5 mole %.

The peroxide was t-butyl peroxy-2-ethyl hexanoate. It was used while in solution (50 wt%) in mineral spirits. The solution is commercially available from Elf Atochem North America, Inc., as Lupersol PMS.

In each Example 100 parts (all parts are by weight) of the resin were introduced into a mechanically agitated reactor, the interior of the reactor was inerted by nitrogen flushing, and the reactor contents were heated to and maintained at reaction temperature. Then, 95 parts of monomer material per 100 parts of resin were introduced into the reactor at the rate per minute of 1 part of monomer material per 100 parts of resin, while at the same time the peroxide solution was introduced into the reactor at a rate equivalent to 1 mole of peroxide per 100 moles of monomer material being introduced. After introduction of the monomer material and the peroxide solution were completed, and while continuing agitation of the reactor contents, they were maintained at 125oC for 30 minutes, and then the temperature was raised to 140oC for 1.5-2.0 hours while purging with nitrogen residual monomer material from the graft copolymer product particles.

A sample of the composition of each Example, the formulation of which is set forth in the tables, was prepared by admixing graft copolymer particles with particles of a broad molecular weight distribution polypropylene resin ("BMWD PP"), and additional stabilizer material. The resin is commercially available from Montell USA Inc. as KM210. Typical properties of this resin include: Mw/Mn >6; melt flow rate = 1.1 g/min at 230oC and 2.16Kg; and room temperature xylene insoluble fraction = 97.8 wt%. The quantity of BMWD PP in the sample was such as to give the Effective Add Level of the total polymerized monomer material (both that which was grafted to the KPO10 polymer, and that which was not grafted to the KP010 polymer) reported for the Example in the following tables. The stabilizer material in all examples comprised a conventional-for-film antacid and a conventional-for-film phenolic antioxidant at a 1:4 wt ratio. In Example 5, however, the stabilizer material comprised a different, but conventional-for-film, antacid, a different, but conventional-for-film, phenolic antioxidant, and a conventional-for-film, phosphite type stabilizer at approximately a 1 :1 :1 wt ratio. While the different composition of the stabilizer material in Example 5 is believed not to have skewed the results, it is reported here for accuracy. In this regard, because the stabilizer material is not at the heart of the invention, it is not considered necessary to enable the best mode to be practiced to identify specifically the stabilizer material components, as long as the chemical types of the components are disclosed.

Each sample was melt extruded from either a 34 mm co-rotating, intermeshing Leistritz LSM twin screw extruder at a barrel temperature of 240oC, a screw speed of 250 rpm, and a throughput rate of 13.6 kg/hr, or a 40mm co-rotating, intermeshing Werner & Pfleiderer ZSK twin screw extruder at a barrel temperature of 210oC, a screw speed of 500 rpm, and a throughput rate of 73 kg/hr. The thus extruded sample was cast at 250oC into a 25 mil (635aem) thick sheet which was quenched on a water-cooled chill roll.

Subsequently, all four sides of a 2 in (5.1 cm) by 2 in (5.1 cm) specimen of the sheet were clamped on a TM Long stretcher, and after being heated to a temperature of 140-160oC the specimen was stretched biaxially by the machine at the stretch rate of 9000% per min to a stretch ratio of 6:1 in both directions. The thickness of the thus obtained biaxially oriented film specimen was approximately 1 mil (25-em).

All film specimens thus obtained were aged at 23oC and 50% relative humidity for at least two weeks. Thereafter the following physical properties were measured by the indicated methods.

Tensile Strength, Young's Modulus and ASTM D882

Elongation-@-break Oxygen transmission rate ("OTR") ASTM D3985-81

(at 23.3oC and dry condition) [The OTR is expressed as "cc x mil/m2/24hrs",

(equivalent to "cc x 25∑em /m2/24hrs").] Haze and clarity Measured with a Byk Gardner

YK Haze-Guard meter The following tables set forth the composition of the oriented film of each Example, and the data obtained in measuring the physical properties thereof. These data were obtained on samples made at different times. In the case of multiple samples of a composition made at different times there were normal variations in the physical measurement data. These were averaged and the averages are reported in the tables along with the number of values averaged as indicated in the "No. of Data Points" lines. Further, the first table includes for comparison the data obtained on a commercial, film grade, polypropylene resin (polypropylene + conventional stabilizer material).

Abbreviations in the tables, and their meanings, are:

"AN" means acrylonitrile.

"MAA" means methacrylic acid. "MeAc" means methyl acrylate.

"PP" means polypropylene. "PP-g-PMMA" means the graft copolymer product that consists essentially of polypropylene grafted with polymerized methyl methacrylate and polymerized methyl acrylate.

"PP-g-PMMA/ AN" means the graft copolymer product that consists essentially of polypropylene grafted with polymerized methyl methacrylate and polymerized acrylonitrile.

"PP-g-PMMA/MAA" means the graft copolymer product that consists essentially of polypropylene grafted with polymerized methyl methacrylate and polymerized methacrylic acid.

"na" means not available.

1J The data of the above tables demonstrate the outstanding oxygen barrier properties of the oriented film of this invention.

Other embodiments and features of advantage of this invention will become readily apparent to those exercising ordinary skill in the art after reading the foregoing disclosures. Such embodiments are within the spirit and scope of the claimed subject matter unless expressly excluded therefrom by claim language or by not being within the doctrine of equivalents.

DEFINITIONS

The term "film" as used in this specification means a sheet, the thickness of which is 10 mils (254 -em) or less.

The expression "consisting essentially of in this specification excludes an unrecited substance at a concentration sufficient to substantially adversely affect the essential properties and characteristics of the composition of matter being defined, while permitting the presence of one or more unrecited substances at a concentration or concentrations insufficient to substantially adversely affect said essential properties and characteristics.

Claims

1. Oriented film formed from a melt blend consisting essentially of

(1) propylene polymer material selected from the group consisting of predominately crystalline polypropylene and predominately crystalline copolymers and terpolymers of propylene and 1-olefin material selected from the group consisting of ethylene and the butenes, which copolymers and terpolymers have more than 50 mole % propylene units; and

(2) graft copolymer material selected from the group consisting of graft copolymers of

(a) propylene polymer material selected from the group consisting of predominately crystalline polypropylene and predominately crystalline copolymers and terpolymers of propylene and 1-olefin material selected from the group consisting of ethylene and the butenes, which copolymers and terpolymers have more than 50 mole % propylene units, and

(b) polymerized monomer material selected from the group of monomers consisting of styrene, p-alkylstyrenes, acrylic acid, alkacrylic acids, alkyl acrylates, alkyl alkacrylates, acrylonitrile and, with or without ethylene, vinyl acetate, the alkyls in these monomers with alkyl substituents having one-four carbons, the concentration of the graft copolymer material being such that the rate of oxygen transmission through the film is substantially less than if no graft copolymer material were present.

2. Film according to claim 1, in which the concentration of said graft copolymer material in said blend is about 10-90 weight % of the propylene polymer material.

3. Film according to claim 2 in which said blend comprises non-grafted polymerized monomer material at about 1-50 weight % of the blend.

4. Film according to claim 3 in which said propylene polymer material consists essentially of predominately crystalline polypropylene.

5. Film according to claim 4 in which said grafted copolymer material consists essentially of predominately crystalline polypropylene grafted with polymerized alkyl alkacrylate and alkyl acrylate.

6. Film according to claim 5 in which said alkyl alkacrylate is methyl methacrylate, and said alkyl acrylate is methyl acrylate.

7. Film according to claim 5 in which said predominately crystalline polypropylene also is grafted with polymerized alkacrylic acid and alkyl alkacrylate.

8. Film according to claim 7 in which said alkacrylic acid is methacrylic acid, and said alkyl alkacrylate is methyl methacrylate.

9. Film according to claim 5 in which said predominately crystalline polypropylene also is grafted with polymerized acrylonitrile.