Stock material or miscellaneous articles – Web or sheet containing structurally defined element or...
Reexamination Certificate
2002-03-18
2004-03-02
Acquah, Samuel A. (Department: 1711)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
C525S185000, C525S191000, C525S240000, C525S242000, C264S210100, C264S210700
Reexamination Certificate
active
06699574
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a polypropylene-based resin composition for stretched film, a process for producing this resin composition, and a stretched film. More particularly, the present invention relates to a polypropylene-based resin composition for stretched film, having transparency and anti-blocking property maintained at practical levels and excellent rigidity and stretching processability, and small heat shrinkage percentage, to a process for producing said resin composition, and to a stretched film made of the resin composition.
2. Description of Related Arts
Polypropylene-based stretched films are widely used as packaging materials, and there are conventionally known methods of mixing polypropylenes having different physical properties for improving the physical properties and stretching processability of a polypropylene-based stretched film.
For example, methods of mixing polypropylenes having different molecular weights are known, and JP58-173141A discloses a method for producing a polypropylene-based resin composition enabling the production of a stretched material excellent in extrusion moldability and stretching property for extrusion stretching, comprising producing a propylene homopolymer or random copolymer having a melt flow index of 0.02 to 5 g/10 minutes and a propylene homopolymer or random copolymer having a melt flow index of 50 to 1000 g/10 minutes by means of polymerization.
Further, JP06-248133A discloses a propylene-based composition rich in extrusion moldability and excellent in balance between rigidity and impact resistance, composed of a polypropylene of high molecular weight having an intrinsic viscosity of 1.0 or more and an meso pentad fraction of 0.90 or more and a highly stereoregular polypropylene of relatively low molecular weight having an intrinsic viscosity of 0.1 to 0.8 and an meso pentad fraction of 0.93 or more, and.
However, for use as stretched films of the propylene-based resin compositions mentioned above, improvement of rigidity, heat shrinkage percentage and stretching processability has been desired.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a polypropylene-based resin composition for stretched film, having a transparency and anti-blocking property maintained at a practical level, excellent rigidity and stretching processability, small heat shrinkage percentage, a process for producing said resin composition, and a stretched film made of the same.
Namely, the present invention relates to a polypropylene-based resin composition for stretched film, comprising:
20 to 98 parts by weight of a propylene-based polymer(A) having an intrinsic viscosity [&eegr;]
A
measured intetralinat 135° C. of 1.8 to 8 dl/g and a melting temperature Tm
A
measured by a differential scanning calorimeter (herein-after, referred to as “DSC”) of 140 to 165° C., and
2 to 80 parts by weight of a propylene-based polymer B having an intrinsic viscosity [&eegr;]
B
measured in tetralin at 135° C. of 0.8 to 1.7 dl/g and a melting temperature Tm
B
measured by DSC of 150 to 170° C., wherein the ratio of the melting temperature Tm
A
of the propylene-based polymer(A) to the melting temperature Tm
B
of the propylene-based polymer(B) (Tm
A
/Tm
B
) is less than 1, the ratio of the intrinsic viscosity [&eegr;]
A
of the propylene-based polymer(A) to the intrinsic viscosity [&eegr;]
B
of the propylene-based polymer(B) ([&eegr;]
A
/[&eegr;]
B
) is more than 1 and less than 10 (1<[&eegr;]
A
/[&eegr;]
B
<10), and the melt flow rate is from 0.1 to 20 g/10 minutes; a process for producing said resin composition; and a stretching film made of the same.
The present invention will be described in detail below.
DETAILED DESCRIPTION OF THE INVENTION
The propylene-based polymer(A) used in the present invention is a propylene homopolymer or a propylene-based random copolymer. As the propylene-based random copolymer, propylene-based random copolymers obtained by copolymerizing propylene with ethylene and/or at least one comonomer selected from &agr;-olefins having 4 to 20 carbon atoms are mentioned.
Examples of the &agr;-olefin having 4 to 20 carbon atoms include, for example, 1-butene, 2-methyl-1-propene, 1-pentene, 2-methyl-1-butene, 3-methyl-1-butene, 1-hexene, 2-ethyl-1-butene, 2,3-dimethyl-1-butene, 2-methyl-1-pentene, 3-methyl-1-pentene, 4-methyl-1-pentene, 3,3-dimethyl-1-butene, 1-heptene, methyl-1-hexene, dimethyl-1-pentene, ethyl-1-pentene, trimethyl-1-butene, methylethyl-1-butene, 1-octene, methyl-1-pentene, ethyl-1-hexene, dimethyl-1-hexene, propyl-1-heptene, methylethyl-1-heptene, trimethyl-1-pentene, propyl-1-pentene, dimethyl-1-butene, 1-nonene, 1-decene, 1-undecene, 1-dodecene and the like, preferably 1-butene, 1-pentene, 1-hexene and 1-octene, and more preferably 1-butene and 1-hexene.
As the propylene-based random copolymer(A), for example, a propylene-ethylene random copolymer, propylene-&agr;-olefin random copolymer and the like are listed. Examples of the propylene-&agr;-olefin random copolymer include, for example, a propylene-1-butene random copolymer, propylene-1-hexene random copolymer, propylene-1-octene random copolymer, propylene-ethylene-1-butene random copolymer, propylene-ethylene-1-hexene random copolymer, propylene-ethylene-1-octene random copolymer and the like, and preferably a propylene-ethylene random copolymer, propylene-1-butene random copolymer, propylene-1-hexene random copolymer, propylene-ethylene-1-butene random copolymer and propylene-ethylene-1-hexene random copolymer.
When the propylene-based random copolymer(A) is a propylene-ethylene random copolymer, the ethylene content is preferably 4% by weight or less, more preferably 3.5% by weight or less, further preferably 3% by weight or less, from the standpoint of the rigidity of the resulting polypropylene-based stretched film.
When the propylene-based random copolymer(A) is a propylene-&agr;-olefin random copolymer, the &agr;-olefin content is preferably 15% by weight or less, more preferably 12% by weight or less, further preferably 8% by weight or less, from the standpoint of the rigidity of the resulting polypropylene-based stretched film.
When the propylene-based random copolymer(A) is a propylene-ethylene-&agr;-olefin random copolymer, the total content of ethylene and &agr;-olefin is preferably 15% by weight or less, more preferably 12% by weight or less, further preferably 8% by weight or less, from the standpoint of the rigidity of the resulting polypropylene-based stretched film.
The intrinsic viscosity [&eegr;] measured in tetralin at 135° C. of the propylene-based polymer(A) used in the present invention is from 1.8 to 8 dl/g, preferably 1.9 to 6 dl/g. When the intrinsic viscosity [&eegr;] of the propylene-based polymer(A) is less than 1.8 dl/g, the stretching processability of the resulting polypropylene-based resin composition may deteriorate, and when over 8 dl/g, the flowability in extrusion processing of the resulting polypropylene-based resin composition may deteriorate, and granule structures may tend to generate.
The melting temperature Tm measured by DSC of the propylene-based polymer A used in the present invention is from 140 to 165° C., more preferably from 143 to 164° C., further preferably from 147 to 163° C. When the melting temperature Tm of the propylene-based polymer(A) is less than 140° C., the rigidity of the resulting polypropylene-based stretched film may be deficient, and when over 165° C., the stretching processability of the polypropylene-based resin composition for stretched film may deteriorate. Herein, the melting temperature Tm is determined from the peak temperature of a melting curve measured by DSC.
The meso-pentad fraction of the propylene-based polymer (A) used in the present invention is preferably from 0.7 to 0.99, more preferably from 0.8 to 0.98, from the standpoint of the rigidity of the resulting polypropylene-based stretched film.
The 2
Ebara Takeshi
Obata Yoichi
Yunoki Shunji
Acquah Samuel A.
Sumitomo Chemical Company Limited
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