Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Polymers from only ethylenic monomers or processes of...
Reexamination Certificate
2001-10-23
2003-06-24
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...
C526S348000, C526S348100, C526S351000
Reexamination Certificate
active
06583254
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a propylene-based polymer and a stretched film prepared therefrom. More specifically, the present invention relates to a propylene-based polymer which provides a stretched film excellent in rigidity, heat resistance and stretchability when formed into a film, and a stretched film prepared therefrom.
2. Description of Related Art
Stretched polypropylene films are widely used as a wrapping material by utilizing their excellent transparency, gloss, rigidity, heat resistance, water vapor barrier property and the like. In stretched polypropylene films, a highly crystalline propylene homopolymer obtained by using a highly stereoregular polymerization catalyst is used for improving the physical properties of the film such as rigidity and the like. However, a highly crystalline propylene homopolymer has a poor stretchability and has a defect that deterioration in film appearance, film cracking and the like tend to occur in stretching. Therefore, use of a propylene copolymer obtained by copolymerizing a small amount of ethylene or 1-butene is known, for improving the stretchability of a highly crystalline polypropylene homopolymer.
For example, JP59-135209A discloses a propylene copolymer in which the ethylene content is 0.1 to 2.0 mol % and the isotactic value satisfies a specific range, and a stretched polypropylene film excellent in stretchability, rigidity, transparency, impact resistance and heat shrinkage resistance obtained by using the above-mentioned copolymer.
Further, JP59-149909A discloses a propylene copolymer in which the 1-butene content is 0.1 to 2.5 mol% and the isotactic value satisfies a specific range, and a stretched polypropylene film excellent in stretchability, impact resistance, heat shrinkage resistance, transparency and rigidity obtained by using the above-mentioned copolymer.
However, these known stretched polypropylene films have insufficient stretchability due to small comonomer content, and even if the comonomer content is increased, the isotactic value of a propylene sequences decreases remarkably and balance of stretchability, rigidity and heat resistance is insufficient, only by increase in the comonomer content. Thus, further improvements have been required even in conventionally known methods, regarding a propylene-based polymer manifesting excellent rigidity, heat resistance and stretchability when used in a film, and a stretched film obtained by using this polymer.
SUMMARY OF THE INVENTION
The present inventors have intensively studied in view of the above-mentioned situations, and resultantly found that the present invention can solve the above-mentioned problems, leading to completion of the present invention.
An object of the present invention is to provide a propylene-based polymer which gives a stretched film excellent in rigidity, heat resistance and stretchability when used in a film, and a stretched film prepared from the same.
Namely, the present invention relates to a propylene-based polymer having a melt flow rate measured according to JIS K7210 of 1.0 to 20 g/10 min. and a melting point Tm (° C.) measured by using a differential scanning calorimeter (DSC) of 147 to 159° C., in which the half width HW (° C.) of the melting peak measured by using a differential scanning calorimeter (DSC) and the melting point Tm (° C.) satisfy the relation: HW≦(188−Tm)/5, and a stretched film prepared from the propylene-based polymer.
The present invention will be illustrated specifically below.
DETAILED DESCRIPTION OF THE INVENTION
The propylene-based polymer of the present invention preferably has a melt flow rate (g/10 min.) of 1.0 to 20 g/10 min., more preferably 1.0 to 10 g/min. When the melt flow rate is less than 1.0 g/10 min., the flowability in extrusion processing may be insufficient, and when over 20 g/10 min., the stretching property may be insufficient.
The propylene-based polymer of the present invention has a melting point Tm (° C.) measured by using a differential scanning calorimeter (DSC) of 147 to 159° C. It is preferably 150 to 158° C., more preferably 152 to 157° C. When the melting point Tm (° C.) is less than 147° C., the rigidity of a stretched film may be insufficient, and when over 159° C., the stretching property of a film may deteriorate.
In the propylene-based polymer of the present invention, the half width HW (° C.) of the melting peak measured by using a differential scanning calorimeter (DSC) and the melting point Tm (° C.) satisfy the relation: HW≦(188−Tm)/5, preferably the relation: HW≦(184−Tm)/5, more preferably the relation: HW≦(182−Tm)/5. When the half width HW (° C.) and the melting point Tm (° C.) manifest the relation: HW>(188−Tm)/5, a stretched film may not have excellent stretchability and excellent rigidity at the same time.
The propylene-based polymer of the present invention preferably includes a propylene homopolymer and a propylene-based random copolymer. A propylene-based random copolymer is preferable.
The propylene-based random copolymer of the present invention is a random copolymer obtained by copolymerizing propylene with at least one comonomer selected from ethylene and &agr;-olefins having 4 to 20 carbon atoms.
Specific examples of the &agr;-olefins having 4 to 20 carbon atoms include 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, diethyl-1-butene, 1-nonene, 1-decene, 1-undecene, 1-dodecene and the like. Preferably, 1-butene, 1-pentene, 1-hexene and 1-octene can be used, and further preferably, 1-butene and 1-hexene can be used.
As the propylene-based random copolymer of the present invention, for example, a propylene-ethylene random copolymer, propylene-1-butene random copolymer, propylene-1-hexene random copolymer, propylene-ethylene-1-butene random copolymer, propylene-ethylene-1-hexene random copolymer and the like are listed, preferably, a propylene-1-butene random copolymer is exemplified.
When the propylene-based random copolymer of the present invention is a propylene-ethylene random copolymer, the content of units derived from ethylene (herein-after, referred to as “ethylene content”) is preferably 2.1 to 4.0 mol %, more preferably 2.2 to 3.0 mol %, from the standpoint of balance of rigidity, heat resistance and stretchability.
When the propylene-based random copolymer of the present invention is a propylene-&agr;-olefin random copolymer, the content of units derived from the &agr;-olefin (herein-after, referred to as “&agr;-olefin content”) is preferably 2.6 to 10 mol %, more preferably 3.0 to 8.0 mol %, from the standpoint of balance of rigidity, heat resistance and stretchability.
When the propylene-based random copolymer of the present invention is a propylene-ethylene-&agr;-olefin copolymer, the total amount of the ethylene content and the &agr;-olefin content is preferably 2.6 to 10 mol %, more preferably 3.0 to 8.0 mol %, from the standpoint of balance of rigidity, heat resistance and stretchability.
The producing method of the propylene-based polymer of the present invention is not particularly limited. However, the propylene-based polymer of the present invention can be preferably produced using a known polymerization catalyst system formed from (a) a solid catalyst component containing magnesium, titanium, halogen and an electron donor as essential components, (b) an organoaluminum compound, and (c) an electron donor component, for example, a catalyst system described in U.S. Pat. Nos. 4,983,561, 5,608,018, or 6,187,883, or the like, and adjusting appropriately polymerization conditions so that the propylene-based polymer of the present invent
Tsuji Mitsuji
Yada Kenichiro
Yunoki Syunji
Birch Stewart Kolasch & Birch, LLP.
Rabago R.
Sumitomo Chemical Company Limited
Wu David W.
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