Plastic and nonmetallic article shaping or treating: processes – Direct application of fluid pressure differential to... – Including application of internal fluid pressure to hollow...
Reexamination Certificate
2000-08-01
2004-05-11
McDowell, Suzanne E. (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Direct application of fluid pressure differential to...
Including application of internal fluid pressure to hollow...
C428S035700, C264S537000
Reexamination Certificate
active
06733717
ABSTRACT:
The present invention relates to injection stretch blow molded containers made from olefin polymers, comprising homopolymers of propylene or copolymers of propylene with other C
2
-C
10
-alk-1-enes, which are obtainable by polymerizing the corresponding monomers with metallocene catalysts. The invention also relates to processes for producing injection stretch blow molded containers from olefin polymers and to the use of olefin polymers for producing injection stretch blow molded containers.
Due to their excellent resistance to heat and chemicals, exceptionally good stiffness and toughness, and also their cost-effectiveness, containers and bottles made from olefin polymers are widely used, for example as packaging for food and drink, household items or cosmetics, and in the medical sector. Injection stretch blow molding (ISBM) has been developed in order to obtain containers of adequate transparency.
Injection stretch blow molding has been known for quite some time. U.S. Pat. No. 4,357,288 teaches a process in which initially a parison is injection molded from a crystalline polypropylene at a temperature which is only slightly higher than the lowest temperature at which a clear melt is obtained, and the parison is then cooled until it hardens. The parison is then heated again to a temperature just below the amorphous flow temperature and stretch blow molded.
EP-A 151 741 describes a process which includes three steps for producing containers from propylene polymers, in which initially a parison is injection molded. The significant step is then that this is preblown in a specific temperature range; only after this has been done is it stretch blow molded. Suitable polymers are propylene copolymers with a comonomer content of from 1 to 6% by weight and a melt flow rate of from 4 to 50 g/10 min. This text also teaches that amounts of up to 1% by weight of nucleating agents, such as dibenzylidenesorbitol or a derivative thereof, may be added to the polymers to improve transparency.
EP-A 309 138 relates to a process for producing containers from propylene copolymers which uses propylene-ethylene copolymers with an ethylene content of from 0.5 to 8% by weight and having a melt flow rate of greater than 50 g/min. The preblowing step is not essential as long as the parison produced by injection molding in the first step is in a partially molten state when it is transferred into the stretch blow molding apparatus. However, the extent to which it is molten must not be so great that it deforms when removed from the injection mold. This implies that a thin skin of a crystalline material must have formed both on the inner surface and on the outer surface of the parison, and the area between these must remain in a partially crystalline or partially amorphous state, in order that the desired properties are obtained in the end product.
The polymers used in this process are obtained by peroxidic degradation. This on the one hand increases the melt flow rate and on the other hand lowers the molar mass distribution, expressed, for example, by the ratio M
w
/M
n
. This brings about a shortening of cycle times. However, the peroxidic degradation also increases the content of soluble fractions and impairs mechanical properties.
H. Heyn, in Kunststoffe 84, 1994, pages 1415-1418 describes a two-step injection stretch blow molding process in which polypropylene parisons which have been separately injection molded are processed after they have been heated once again, to give hollow articles.
A feature common to the known injection stretch blow molding processes for producing transparent containers is that precisely specified, narrow temperature ranges must be maintained during the production process. In particular for propylene homopolymers, this temperature window is so small that it is not possible to ensure problem-free production of containers or of other items when operating continuously, since even small deviations from one of the specified temperatures give products with significantly impaired properties. Although the use of propylene copolymers widens the temperature window to some extent, it is still not sufficient to give completely problem-free container production. In addition, the copolymerization raises the content of soluble fractions and impairs stiffness.
It is an object of the present invention to set aside the disadvantages described and in particular to provide containers which have excellent transparency combined with good mechanical properties and small contents of soluble fractions, and which can be produced by a process which has a wide temperature window and permits short cycle times.
We have found that this object is achieved by means of injection stretch blow molded containers made from olefin polymers, comprising homopolymers of propylene or copolymers of propylene with other C
2
-C
10
-alk-1-enes, which can be obtained by polymerizing the corresponding monomers with metallocene catalysts, processes for producing injection stretch blow molded containers from olefin polymers and the use of olefin polymers for producing injection stretch blow molded containers.
For the purposes of the invention, olefin polymers are homo- or copolymers of linear or branched &agr; olefins, in particular of C
2
-C
10
-alk-1-enes, such as ethylene, propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene or 4-methyl-1-pentene, or mixtures of these &agr;-olefins. Preference is given to homo- or copolymers of ethylene or of propylene, where the proportion of ethylene or of propylene in the copolymers is at least 50 mol %. Among the copolymers of ethylene, preference is given to those which comprise, as other monomers, propylene, 1-butene, 1-hexene or 1-octene, or mixtures of these. The copolymers of propylene are in particular those which comprise, as other monomers, ethylene or 1-butene, or mixtures of these. The propylene copolymers may comprise the other &agr; olefins incorporated randomly. They may also take the form of block copolymers or impact copolymers. Preferred polymers of propylene are propylene homopolymers and random propylene copolymers. Olefin polymers of this type are known per se or may be prepared by known methods by polymerizing with conventional Ziegler-Natta catalysts or with metallocene catalysts.
The olefin polymers of which the novel injection stretch blow molded containers are composed comprise propylene polymers, which are obtainable by polymerizing the corresponding monomers with metallocene catalysts. The proportion of the propylene polymers which are obtainable with metallocene catalysts is generally at least 40% by weight, preferably at least 70% by weight and in particular at least 90% by weight, based on the olefin polymers. In a very particularly preferred embodiment, the olefin polymers are obtained by homopolymerization of propylene or copolymerization of propylene with other C
2
-C
10
-alk-1-enes with metallocene catalysts.
The propylene polymers which are obtainable with metallocene catalysts are propylene homopolymers or copolymers made from propylene and another C
2
-C
10
-alk-1-ene or more than one other C
2
-C
10
-alk-1-ene, preferably selected from the class consisting of ethylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, 1-decene and 4-methyl-1-pentene, or are mixtures of these polymers, in which case the mixing ratios are not critical. The copolymers of propylene used are generally random copolymers.
For the purposes of the invention, metallocene catalysts are substances which are generally obtained by combining a transition metal compound or more than one transition metal compound, preferably of titanium, of zirconium or of hafnium, and comprising at least one ligand which, in the broadest sense, is a derivative of the cyclopentadienyl ligand, with an activator, also called cocatalyst or metallocenium-ion-forming compound, and generally have activity for polymerizing the monomers described. Examples of such catalysts are described in EP-A 545 303, EP-A 576 970 and EP-A 582 194. Metallocene catalysts which are
Bidell Wolfgang
Fischer David
Jones Peter John Vaughan
Kersting Meinolf
Langhauser Franz
Basell Polyolefine GmbH
Keil & Weinkauf
McDowell Suzanne E.
LandOfFree
Injection stretch-blow molded containers made of olefin... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Injection stretch-blow molded containers made of olefin..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Injection stretch-blow molded containers made of olefin... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3229875