Propylenic random copolymer and composition comprising it,...

Details Propylenic random copolymer and composition comprising it,... Propylenic random copolymer and composition comprising it,...

2002-11-22

2004-05-18

Lu, Caixia (Department: 1713)

Stock material or miscellaneous articles

Composite

Of addition polymer from unsaturated monomers

C428S034900, C428S035200, C428S035700, C428S515000, C526S348000, C526S348100

Reexamination Certificate

active

06737171

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a propylenic random copolymer and a composition comprising it, and also to their use. More precisely, it relates to a binary random copolymer of propylene and ethylene, and a composition comprising the copolymer, and also to a film, especially a stretched film and a stretched film laminate comprising the copolymer or composition.
BACKGROUND OF THE INVENTION
Having enveloped the objects to be wrapped or packaged, and heated under heat, shrink film is shrunk to thereby airtightly seal in the objects. With such a property, shrink film is much used in shrink wrapping or packaging, for example, for separately wrapping cupped instant noodles and for packaging a plurality of objects such as notebooks.
For such shrink wrapping or packaging, shrink film of polyvinyl chloride resins is used in the conventional art. The film is advantageous in that it produces good wrapping and packaging with neither wrinkles nor looseness, but is problematic in that it gives harmful hydrogen chloride gas when it is formed from the resins, when it is heat-sealed over the objects to be wrapped or packaged therewith and when it is incinerated. For these reasons, it is desired to produce shrink film from polyolefinic resins that are free from those problems.
As having high stiffness, transparency and moisture-proofness, film of polyolefinic resins, especially that of crystalline propylenic polymers, is much used as wrapping or packaging film. However, for use in shrink wrapping or packaging, film of propylene homopolymers is problematic in that the heat-sealing step for it could not be finished rapidly and the temperature in the heat-shrinking step for it must be high, since the melting point of the film is high.
Given that situation, in order to improve the heat-sealability and the heat-shrinkability of the film of polypropylenic resins in shrink wrapping or packaging, some techniques have heretofore been proposed of copolymerizing propylene with ethylene and other &agr;-olefins to give polyolefinic resins that are favorably usable in shrink wrapping or packaging. For example, one technique is to copolymerize propylene with a large amount of ethylene and other &agr;-olefins to give crystalline propylenic polymers, of which the heat-sealability and heat-shrinkability is said to be improved to such a degree that the film of the polymers is favorably usable in shrink wrapping or packaging. However, since the crystalline propylenic polymers are formed through copolymerization of such a large amount of ethylene and other &agr;-olefins, they shall contain a large amount of unfavorable sticky side products and, in addition, their crystallinity is poor. Therefore, the film of those polymers have low stiffness, poor anti-blocking ability and poor hot-slipping ability, resulting in that it could not be used as shrink film for wrapping or packaging.
In order to remove the sticky components from the crystalline propylenic resins, a method has been tried of processing the resins with inert solvents to dissolve out the components. In this method, however, the crystalline, low-melting-point components are also dissolved out, resulting in that the film of the thus-processed resins could not have good heat-sealability and heat-shrinkability at low temperatures and is unfavorable for shrink wrapping or packaging.
Resins for shrink wrapping or packaging film are required to have other various properties. For example, the necessary properties of those resins include biaxial stretchability in tenter methods and tubular methods, slippability and anti-blocking ability in the re-winding step in the stretching process, and good outward appearance and transparency of film of the resins. In addition to those, the resins must be applicable to large-scaled, high-speed filming machines which are used recently for improving the producibility of film.
SUMMARY OF THE INVENTION
One object of the present invention is to provide a binary random copolymer of propylene and ethylene capable of being sheeted into films that are favorably used as various wrapping and packaging films with good stretchability while having the intrinsic good characteristics of polypropylene films, and to provide a resin composition comprising the copolymer. Another object of the invention is to provide a film and a multi-layered laminate film with good low-temperature heat-sealability that is formed from the copolymer or the resin composition, especially a stretched film and a stretched multi-layered laminate film with good heat-shrinkability.
We, the present inventors have assiduously studied in order to attain the above-mentioned objects of the invention and, as a result, have found that a propylenic random copolymer and its composition having specific characteristics such as those mentioned below are favorably used for those objects, and that films of various forms, such as a single-layered film, a stretched single-layered film, a multi-layered laminate film, and a stretched multi-layered film comprising the copolymer or its composition have good characteristics which could not be found in any conventional polymer films. On the basis of those findings, we have completed the present invention.
Specifically, the invention provides the following:
[1] A propylenic random copolymer of propylene and ethylene, which satisfies the following (1) to (5):
(1) The ethylene unit content (x, wt. %) of the copolymer is from 0.2 to 10 wt. %.
(2) The copolymer has a melt index (MI, g/10 min) of from 0.1 to 4 g/10 min.
(3) The relation between the boiling diethyl ether extraction (E, wt. %) of the copolymer and x satisfies the following (I) or (II):
E≦
0.25
x
+1.1 (0.2≦
x
<6)  (I)
E≦
2.6 (6≦
x
≦10)  (II)
(4) The relation between the melting point (Tm, ° C.) of the copolymer as measured with a differential scanning calorimeter and x satisfies the following (III):
Tm≦
165−5
x
  (III)
(5) The isotactic triad fraction (mm, mol %) in the PPP sequence of the copolymer, as measured in
13
C-NMR, is not smaller than 98.0 mol %.
Preferably, the propylenic random copolymer further satisfies the following (6):
(6) The relation between the melt index (MI, g/10 min) of the copolymer and the time of relaxation (&tgr;, sec) of the copolymer as obtained through frequency dispersion measurement at a frequency &ohgr;0=10
0
rad/sec satisfies the following (IV):
&tgr;≧0.523−0.077 log
MI
  (IV)
[2] A propylenic random copolymer composition comprising from 60 to 95% by weight of the propylenic random copolymer of [1] and from 5 to 40% by weight of a polyolefinic polymer.
[3] A film of the propylenic random copolymer of [1] or the composition of [2]; a stretched film to be prepared by stretching the film; a multi-layered film laminate comprising at least one layer of the propylenic random copolymer or the composition; and a stretched multi-layered film laminate as prepared by stretching the film laminate. Especially, a multi-layered film laminate and a stretched multi-layered laminate film comprising at least one layer of the propylenic random copolymer or its composition, and one or more layers of other thermoplastic resins.
[4] The multi-layered laminate film or stretched multi-layered laminate film of [3], in which the layer of the propylenic random copolymer [1] or its composition [2] is the outermost layer of at least one surface of the film.
PREFERRED MODES OF CARRYING OUT THE INVENTION
Now, the invention is described in detail hereinunder.
The propylenic random copolymer of the invention is prepared through copolymerization of propylene and ethylene, and satisfies the following (1) to (5):
(1) The ethylene unit content (x, wt. %) of the copolymer is from 0.2 to 10 wt. %, preferably from 2 to 6% by weight. If x is smaller than 0.2% by weight, the heat-sealing temperature of the copolymer could not be satisfactorily lowered. If so, in addition, the film of

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