Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2000-08-23
2002-12-03
Wu, David W. (Department: 1713)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Polymers from only ethylenic monomers or processes of...
C526S348200, C526S348500, C526S348600
Reexamination Certificate
active
06489426
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a propylene base polymer and a film comprising the same. More specifically, the present invention relates to a polypropylene film which is excellent in antistatic performance and also relates to a film which has a high rigidity and excellent metallizability, and a propylene base polymer which can provide the same.
BACKGROUND ART
A polypropylene film has excellent rigidity, transparency and gloss and therefore is widely used as a packaging material.
However, a polypropylene film has a high electrical insulating property and is liable to be statically charged, so that various problems are brought about in practical uses. When a polypropylene film is given an antistatic performance by adding an antistatic agent, a large amount of the antistatic agent has to be added in order to obtain the satisfactory performance, and this has caused the problems that the antistatic agent bleeds out on the film surface with time. Further, it is tried to lower a crystallinity of polypropylene to thereby improve an antistatic performance of an antistatic agent added. However, there has been occurred the problem that while the antistatic performance is raised, the resulting polypropylene film is reduced in a rigidity.
And a polypropylene film has an excellent rigidity, transparency and gloss and therefore is widely used as a wrapping material. In general, a polypropylene film has a gas permeability, so that a polypropylene film which is deposited on a surface thereof with metal its used for uses in which a gas barrier property is required such as a food packaging material. However, there is the problem that deposited metal layer is easily peeled off because of a lower adhesiveness between the polypropylene film surface and deposited metal. Publicly known is a technique in which in order to improve a peeling strength of deposited metal, the polypropylene film surface is subjected to corona treatment and/or flame treatment and then metal is deposited. However, these techniques are unsatisfactory for improving the peeling strength, and therefore practical demand allows further improvement in the peeling strength to be desired.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a polypropylene film which is excellent in an antistatic performance and has a high rigidity and a propylene base polymer which can provide the same. Specifically, an object of the present invention is to provide a polypropylene film which has satisfactory antistatic performance in practical use, by adding a small amount of an antistatic agent as compared with those of conventional polypropylenes, which is provided with more excellent antistatic performance than ever by adding the same amount of an antistatic agent as ever and which has a high rigidity, and a propylene base polymer which can provide the same.
Another object of the present invention is to provide a polypropylene film which has a high rigidity and a good metallizability and a propylene base polymer which is suited for producing the above described polypropylene film. In particular, an object of the present invention is to provide a propylene base polymer which is excellent in a film processability and has a good aluminum-depositing property and which is excellent in a rigidity and a polypropylene film comprising the above described propylene base polymer.
The present inventors have made extensive research in order to solve the problems described above. As a result, we have found that a propylene base polymer in which the respective characteristics of an isotactic pentad fraction, a melt flow rate, weight average molecular weights of solubles of 0° C. or lower, 50° C. or lower and 90° C. or lower obtained by a cross fractionation chromatography, boiling pentane extractables and boiling heptane extractables fall in specific ranges, has the anticipated performance, and the film prepared by using polypropylene composition obtained by adding an antistatic agent to the propylene base polymer has excellent antistatic performance and the film prepared by using the propylene base polymer has an excellent metallizability and a high rigidity. And we have achieved the present invention based on the above findings.
The present invention consists in the following items.
1. A propylene base polymer having the following characteristics (1) to (5):
(1) it is a propylene homopolymer or a propylene-olefin copolymer of propylene with at least one olefin selected from ethylene and &agr;-olefins having 4 or more carbon atoms, wherein a propylene content in this copolymer is 98% by weight or more,
(2) a melt flow rate (MRF: 230° C., 21.18N) falls in a range of 0.5 to 20 dg/min,
(3) an isotactic pentad fraction [mmmm] falls in a range of 0.89 to 0.95,
(4) boiling pentane extractables (C5-Ext) are 0.5% by weight or more; boiling heptane extractables (C7-Ext) are 5% by weight or less; and (C5-Ext) and (C7-Ext) reside in a relation of (C7-Ext)>3.5 (C5-Ext), and
(5) solubles of 0° C. or lower obtained by a cross fractionation chromatography have a weight average molecular weight of 7×10
4
or more, and solubles of 50° C. or lower have a weight average molecular weight of 6×10
4
or more.
2. A propylene base polymer according to item 1, further having the following characteristics (6) and (7):
(6) existential ratio of a meso dyad and a racemic dyad in the pentad comply with a two-site model based on Bernoullian statistics, wherein a statistical parameter &agr; falls in a range of 0.989≦&agr;≦0.995, and
(7) solubles of 90° C. or lower obtained by a cross fractionation chromatography have a weight average molecular weight of 6×10
4
or more.
3. A film prepared by using polypropylene composition obtained by adding an antistatic agent to the propylene base polymer as described in item 1.
4. A film prepared by using the propylene base polymer as described in item 2, which the film has an excellent metallizability.
DETAILED DESCRIPTION OF PREFERRED EMBODIMENT
The present invention shall specifically be explained below.
The propylene base polymer of the present invention is a homopolymer of propylene or a copolymer of propylene with at least one olefin selected from ethylene and &agr;-olefins having 4 or more carbon atoms. When the propylene base polymer is a copolymer, a propylene content in the copolymer is 98% by weight or more, preferably 98.5% by weight or more and more preferably 99% by weight or more. Use of such propylene base polymer that a propylene content in the copolymer is less than 98% by weight is liable to provide a film having an unsatisfactory rigidity.
The propylene base polymer of the present invention has a melt flow rate (MRF: 230° C., 21.18N) falling in a range of 0.5 to 20 dg/min, preferably 1 to 15 dg/min. The polymer having an MFR falling in the range described above provides a film which has excellent in an antistatic performance and metallizability and has a high rigidity.
In the propylene base polymer of the present invention, an isotactic pentad fraction [mmmm] which is an index of a stereoregularity of propylene base polymer falls in a range of 0.89≦[mmmm] 0.95, more preferably 0.90≦[mmmm]≦0.94. The [mmmm] is determined according to a method described in A. Zambelli et al., Macromolecules Volume 8, pp. 687 to 689 (1975). If the [mmmm] is less than 0.89, the antistatic performance is elevated, but the rigidity of the resulting film is reduced. On the other hand, if the [mmmm] exceeds 0.95, the film has a high rigidity, but the antistatic effect is reduced. In this case, the antistatic effect and the antistatic performance mean a surface resistivity of a film blended with an antistatic agent, and the smaller the surface resistivity is, the larger the antistatic effect is, and the more excellent the antistatic performance is.
And also, if the [mmmm] is less than 0.89, the metallizability of the film is elevated but the rigidity of the film is reduced. On the other hand, if the [mmm
Ando Yuji
Kawamoto Naoshi
Minamizawa Hisanobu
Nakata Shinji
Ohno Katsuhiko
Cheung William
Chisso Corporation
McDermott & Will & Emery
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