Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Processes of preparing a desired or intentional composition...
Reexamination Certificate
2000-04-27
2003-05-13
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Processes of preparing a desired or intentional composition...
C524S366000, C525S240000, C526S351000
Reexamination Certificate
active
06562886
ABSTRACT:
TECHNICAL FIELD
The present invention relates to propylene-based resins and propylene-based polymer compositions, and also to films and laminates made of them.
More precisely, the invention relates to propylene-based polymers and propylene-based polymer compositions, and also to films, for example, those for wrapping or packaging edibles, as well as laminates, fibers, sheets and moldings made of them, and they have the advantages of good low-temperature heat-sealability, well-balanced toughness and heat-sealability which no one has heretofore experienced in the art, as well as improved anti-blocking properties, improved slip characteristics and improved moldability.
BACKGROUND ART
Polypropylene has good physical properties, as being tough and resistant to heat, and is inexpensive. Therefore, it is a general-purpose resin having many applications in various fields.
For example, as having the advantages of high transparency, high toughness, good heat resistance and little water absorption, polypropylene is used for cast films such as biaxially-oriented films, laminate films, etc. In particular, films of a crystalline propylene-based polymer are widely used as wrapping or packaging films, as having the advantages of high toughness, high transparency and good moisture-proofness.
In general, the films are formed into bags through heat-sealing. After having been filled with objects, the bags are closed by again heat-sealing their open ends.
The recent tendency in the art is toward high-speed production lines for fabricating bags and packages so as to improve the productivity. To meet the requirement, it is desired to improve the quality of films. For example, a plurality of resins having different properties are layered, and the resulting multi-layered films are being widely used. Of such multi-layered films, the resin film to be the outermost layer is specifically desired to have good physical properties of low-temperature heat-sealability (this is for facilitating high-speed production lines for fabricating bags and packages), slip characteristics (these are for attaining smooth re-winding of films), and anti-blocking properties.
In other fields of sheets and non-woven fabrics except the films as above, it is also desired to lower the temperature for layer lamination.
As compared with ethylene-based polymers, propylene-based polymers may have a larger degree of supercooling necessary for the start of their crystallization, and therefore have a lower crystallization temperature (Tc) when their melting point (Tm) is on the same level as that of ethylene-based polymers. This is more noticeable for propylene-based copolymers and polymers with lower stereospecificity, a shaving lower crystallinity. As a result, propylene-based polymers are often difficult to mold, and, in addition, their resin characteristics are poor. In particular, their transparency is low, the heat-sealing temperature (HST) for them is high, and their elasticity and impact resistance are poor. Especially for film applications, propylene-based polymers are often confronted with many problems. For example, with propylene-based polymers being required to have low-temperature heat-sealability comparable to that of linear low-density polyethylene, the problems are that the polymers often fail to be formed into good films, in particular, the films formed often fail to be smoothly released from chill rolls, the edges of the films are unstable, and the films are readily scratched by sweeper rolls. Therefore, to obtain films, fibers, sheets and moldings of the polymers having good low-temperature heat-sealability, the problems with the polymers as above must be solved.
Heretofore, a method of copolymerizing propylene homopolymers with a small amount a comonomer of ethylene, 1-butene or the like has been proposed for improving the low-temperature heat-sealability of films of the polymers. In the method, however, a large amount of ethylene or 1-butene must be copolymerized with the polymers in order to secure satisfactory low-temperature heat-sealability of the polymers. If so, the polymers shall contain a large amount of sticky side products, and, as a result, their anti-blocking properties are greatly worsened, and, in addition, the side products bleed out of the films of the polymers whereby the films are seen whitish and their appearances are not good. After all, the films of the polymers are not on the practicable level. What is more, the crystallinity of the polymers is low, and the films of the polymers could not be tough. Further, the moldability of the polymers is poor, and the anti-blocking properties of the films of the polymers are poor.
To solve the problem, tried is a method of removing the sticky component from the polymers by dissolving it in an inert solvent. In this method, however, even the low-temperature-melting crystalline component that contributes to the low-temperature heat-sealability of the polymers is inevitably removed from the polymers. At present, after all, the low-temperature heat-sealability of the polymers could not be still improved to a satisfactory degree even in the method.
On the other hand, tried is another method of copolymerizing propylene homopolymers with some &agr;-olefin other than ethylene or 1-butene, for example, with 1-hexene, 1-octene, 4-methyl-1-pentene or the like. According to the prior art technology, however, resins obtained all have an extremely broad compositional distribution, and it is difficult to improve their anti-blocking properties, toughness and moldability up to the practicable level.
Conventional propylene-based polymers obtained in the presence of a known Ziegler catalyst have a broad molecular weight distribution and a broad compositional distribution, and are not homogeneous. Therefore, the high-crystalline component in the polymers could readily form crystalline nuclei, and, as a result, the degree of supercooling necessary for the start of their crystallization is not so large and the moldability of the polymers is not so much lowered. However, as their composition is not homogeneous, the polymers have poor physical properties. In particular, as containing a sticky component and a high-crystalline component, the polymers could not exhibit good physical properties intrinsic to resins.
Recently, single-site metallocene catalysts have been developed. Polypropylene obtained in the presence of such a metallocene catalyst has a homogeneous composition and contains a reduced amount of a sticky component and a high-crystalline component that may worsen the physical properties of the polymer. Therefore, the physical properties of the polymer are better than those of the other polymers produced in the presence of any other conventional catalyst. However, as the polymer has a homogeneous composition, the degree of supercooling for it is enlarged and the moldability of the polymer is lowered.
A method of using the propylene-based polymer obtained in the presence of a metallocene catalyst, as a heat-sealability improver for the propylene-based polymer obtained in the presence of a conventional Ziegler catalyst has been proposed (Japanese Patent Laid-Open Nos. 173016/1990, 112682/1993, 112683/1993). The method is effective in some degree for improving the balance of the heat-sealability and the toughness of the polymer films, but could not still solve the problem with the polymer composition in point of the balance between the moldability of the polymer composition and the physical properties of the polymer films.
In that situation, the present invention is to further improve the heat-sealability of polypropylene films, without interfering with the intrinsic good properties of the films, to such a degree that the improved heat-sealability of the films is comparable to that of linear low-density polyethylene films. Specifically, the object of the invention is to provide propylene-based polymers and propylene-based polymer compositions, and also their films including those for wrapping and packaging edibles, as well as their fibers, sheets, non-woven fabrics and other
Funabashi Hideo
Minami Yutaka
Mogi Yasuhiro
Okamoto Takuji
Ota Tsuyoshi
Harlan R.
Idemistsu Petrochemical Co., Ltd.
Wu David W.
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