Bottle closures made of polyolefins

Details Bottle closures made of polyolefins Bottle closures made of polyolefins

2000-10-16

2003-06-03

Seidleck, James J. (Department: 1711)

Synthetic resins or natural rubbers -- part of the class 520 ser

Synthetic resins

Mixing of two or more solid polymers; mixing of solid...

C525S191000, C525S217000, C525S232000, C428S035700, C428S500000, C524S500000, C524S502000, C524S515000

Reexamination Certificate

active

06573334

ABSTRACT:

The present invention relates to bottle closures made of olefin polymer resins. In particular, it relates to screw caps for bottles.
The use of thermoplastic olefin polymer resins for the production of bottle closures is in itself known. In particular, the use of a propylene homopolymer and high density polyethylene is already known.
Bottle closures made of the said polymers are widely employed, for example, in beverage industries through out the world. However, their use is limited because of the fact that bottles with the said closures cannot be subjected to heat treatments at high temperatures, such as severe pasteurising cycles at 80-90° C. Pasteurisable polyolefin closures are disclosed in GB patent specification 1,387,556. According to the disclosure of the said GB patent specification, the bottle closures are capable of withstanding temperatures of up to 75° C.
The need of pasteurising beverages in bottles at higher temperatures is now felt. Examples of beverages that could be pasteurised are soft drinks, in particular cider, fruit juices and some carbonated drinks. It is now desirable to carry out the pasteurisation cycles approximately at a temperature higher than 75° C., generally from about 77 to 88° C. The pasteurisation time is normally from 10 to 50 minutes, more typically 10-30 minutes.
Because of the low mechanical properties, in particular in terms of heat and creep resistance, of the olefin polymers until now employed, the said closures do not withstand the high pressure of the content inside the bottle during the pasteurising cycle. Consequently, gas and liquid tend to escape during the pasteurisation cycle and closures may even blow-off from the bottles.
Surprisingly, it has now been found that bottle closures made of particular polypropylenes can be subjected to heat treatments at high temperatures, in particular pasteurisation cycles. Hence, the bottle closures of the present invention are capable of withstanding heat treatments, in particular pasteurisation, at said high temperature without shortcomings. In particular the problem of brittleness is overcome. Hence, it is now possible to pasteurise bottles with the propylene polymer closures of the present invention at temperatures higher than 75° C. and for a time relatively long (e.g. 10-75 minutes) without the problems encountered with the closures of polypropylene used until now.
In addition to the above, the bottle closures of the present invention do not undergo any deformation at high temperatures.
Moreover, the types of polymers selected for producing the bottle closures of the present invention are suited for use in contact with food and beverages.
Hence, an object of the present invention is a bottle closure comprising or substantially made of an olefin polymer composition (A) comprising:
1) 90-100% by weight, preferably 92-98, more preferably 94-98, of a crystalline propylene homopolymer or random copolymer thereof with a comonomer selected from ethylene and a C
4
-C
10
&agr;-olefin; said polymers containing at least 94% by weight, preferably at least 96% of a fraction insoluble in xylene at room temperature (Polymer (1)); and
2) 0-10% by weight, preferably 2-8%, more preferably 2-6%, of an elastomeric copolymer of ethylene with propylene or a C
4
-C
10
&agr;-olefin or mixtures thereof and, optionally, from 0.5 to 10% by weight of a diene, the said elastomeric copolymer containing from 40% to 85% in moles of ethylene (Polymer (2));
provided that when the amount of Polymer (2) is 0% by weight, Polymer (1) is selected from the above said random copolymers.
Polymer composition (A) typically has a flexural elastic modulus (FM) value at 23° C. at least of 1620 MPa, preferably from 1650 to 2500 MPa; a value of the strength at yield at 23° C. at least of 33 MPa, preferably up to 45 MPa; and an IZOD impact resistance value at 0° C. at least of 2.5 kJ/m
2
, preferably up to 20 kJ/m
2
.
The said polymer composition (A) has approximately a VICAT value of at least 150° C., preferably 155° C., up to 160° C.
The methods for measuring the above properties and xylene-insoluble fraction are described hereinbelow.
Preferably Polymer (1) is a propylene homopolymer. When copolymers are used as Polymer (1), preferred are copolymers of propylene with a comonomer selected from ethylene, 1-butene, 1-pentene, 1-hexene, 4-methyl-1-pentene and 1-octene. Ethylene and butene-1 are the most preferred comonomers. The comonomer content normally ranges from 0.5 to 6% by weight, preferably 2 to 5%.
The MFRL value of polymer composition (A) is typically from 0.3 to 100 g/10 min, preferably 0.7-30 g/10 min, more preferably 1-15 g/10 min.
A suitable example of the above Polymer (1) is a crystalline propylene polymer with a broad molecular weight distribution (hereinafter referred to as Polymer (I)) in terms of the {overscore (M)}
w
/{overscore (M)}
n
ratio. The propylene homopolymer is preferred.
Typically Polymer (I) has {overscore (M)}
w
/{overscore (M)}
n
values from 5 to 60, preferably from 5 to 30. The intrinsic viscosity [&eegr;] values of Polymer (I) determined in tetrahydronaphthalene at 135° C. may vary from 1.2 to 7 dl/g, for example.
Suitable examples of Polymer (I) are those containing 10-65% by weight of a high molecular weight fraction (fraction (i)) and 35-60% by weight of a low molecular weight fraction (fraction (ii)) as described in European patent application 573862.
Polymer (2) is preferably selected from ethylene/propylene copolymers, ethylene/butene-1 copolymers, ethylene/propylene/C
4
-C
10
&agr;-olefin copolymers containing from 5 to 15% in moles of the &agr;-olefin.
Preferably Polymer (2) comprises from 0 to 40% by weight of a fraction insoluble in xylene at room temperature.
Polymer (2) may be added in the pure state or as a mixture with crystalline polyolefins. The said mixture can replace Polymer (2) totally or partially. Suitable examples of said mixtures are thermoplastic elastomeric olefin polymer compositions. Accordingly, an object of the present invention is also a bottle closure comprising a blend of said Polymer (I) and a thermoplastic elastomeric olefin polymer composition comprising the following components (percentage by weight):
a) 70-97%, preferably 78-97%, of a propylene homopolymer containing more than 90%, preferably more than 94%, of a fraction insoluble in xylene at room temperature, or a crystalline propylene copolymer with ethylene or a C
4
-C
10
&agr;-olefin or a mixture thereof, containing over 85% by weight of propylene; the copolymer containing at least 85% by weight of a fraction insoluble in xylene at room temperature;
b) 0-10%, preferably 1-10%, of a crystalline copolymer containing ethylene, insoluble in xylene at room temperature; and
c) 3-20%, preferably 3-12%, of an amorphous copolymer of ethylene with propylene and/or a C
4
-C
10
1-olefin and, optionally, from 1 to 10% of a diene, soluble in xylene at room temperature, and containing from 20 to 75% of ethylene.
In this case the previously said Polymer (2) is constituted by the sum of components (b) and (c).
Preferably said blend comprises 30-80% by weight of Polymer (I) and 20-70% by weight of the thermoplastic elastomeric olefin polymer composition with respect to the blend, more preferably 40-60% by weight of polymer (I) and 60-40% by weight of the thermoplastic elastomeric olefin polymer composition.
In the preferred both Polymer (I) and component (a) of the thermoplastic elastomeric olefin polymer composition are propylene homopolymers and the total ethylene content is 4% by weight or less.
In the present application the room temperature means a temperature of about 25° C.
Typically the thermoplastic elastomeric olefin polymer composition used in the present invention has a flexural elastic modulus value at 23° C. from 1300 to 1600 MPa.
Examples of dienes useful in the preparation of component (c) are 1,4-hexadiene, 1,5-hexadiene, dicyclopentadiene, ethylidene norbornene, 1,6-octadiene and vinyl norbornene. Ethylidene norbornene is preferred.
Examples of C
4
-C
10
&agr;-olefins useful in the preparat

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