Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
1999-09-02
2001-12-04
Thibodeau, Paul (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C428S910000, C525S240000
Reexamination Certificate
active
06326080
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a biaxially oriented film formed from a film-forming material comprising a polypropylene-based resin material. More precisely, it relates to a biaxially oriented polypropylene-based film having straight tearing property along the longitudinal direction.
BACKGROUND ART
Oriented films formed from polypropylene-based resin materials are used as various package films. For example, uniaxially oriented polypropylene-based films have a property that they are likely to be torn along the film-flowing direction during the film production, i.e., the longitudinal direction called machine direction (MD direction), and thus they are easily cut straight along that direction (straight cuttability). Therefore, they are widely used mainly in the field of food packaging.
While uniaxially oriented films comprising polypropylene-based resin materials are excellent in the straight cuttability along the MD direction, however, they are poor in the strength along the direction perpendicular to the MD direction (TD direction), and therefore they may be broken when used for packaging heavy contents.
As a film for packaging heavy contents having straight cuttability and improved strength along the TD direction, there have been known those produced by a method utilizing polypropylene formulated with polybutene (Japanese Patent Unexamined Publication No. 7-156264). While this method improves the strength along the TD direction, however, it cannot afford straight cuttability along the MD direction at a sufficient level. In addition, it suffers a problem concerning the cost, because it utilizes a large amount of expensive polybutene.
DESCRIPTION OF THE INVENTION
The object of the present invention is to provide a biaxially oriented polypropylene-based film that is excellent in straight cuttability along the MD direction and strength along the TD direction, and is economically advantageous.
The present inventors earnestly conducted studies in order to achieve the foregoing object, and as a result, they found that a biaxially oriented film of a polypropylene-based resin material comprising a copolymer of propylene and another &agr;-olefin dispersed as particles in crystalline polypropylene wherein the film is formed so that the dispersed particles of the copolymer should have a mean diameter of 0.1 &mgr;m or less along the TD direction exhibits excellent straight cuttability along the MD direction. Thus, they accomplished the present invention.
That is, the present invention provides a biaxially oriented polypropylene-based film formed from a film-forming material which comprises a polypropylene-based resin material consisting of 40 to 88% by weight of crystalline polypropylene, and 60 to 12% by weight of propylene-&agr;-olefin copolymer dispersed as particles in the crystalline polypropylene, wherein the particles of the copolymer have a mean dispersed particle diameter of 0.1 &mgr;m or less along the TD direction.
The present invention also provides a biaxially oriented polypropylene-based film formed from a film-forming material which comprises a polypropylene-based resin material consisting of 40 to 88% by weight of crystalline polypropylene, and 60 to 12% by weight of propylene-&agr;-olefin copolymer, wherein a ratio of birefringences along the MD direction and the TD direction (birefringence along the MD direction/birefringence along the TD direction) and a ratio of orienting ratios for the MD direction and the TD direction (orienting ratio for the MD direction/orienting ratio for the TD direction) of the film satisfy the following equation (I):
Y≧X−
0.1 (
I
)
wherein X represents the ratio of orienting ratios, and Y represents the ratio of birefringences.
The present invention also provides a biaxially oriented polypropylene-based film formed from a film-forming material which comprises a polypropylene-based resin material consisting of 40 to 88% by weight of crystalline polypropylene, and 60 to 12% by weight of propylene-&agr;-olefin copolymer, wherein a ratio of birefringences along the MD direction and the TD direction (birefringence along the MD direction/birefringence along the TD direction) of the film is 0.6 or more.
The present invention further provides a biaxially oriented polypropylene-based film formed from a film-forming material which comprises a polypropylene-based resin material consisting of 40 to 88% by weight of crystalline polypropylene, and 60 to 12% by weight of propylene-&agr;-olefin copolymer, and having a ratio of MFRs of the crystalline polypropylene and the propylene-&agr;-olefin copolymer (MFR of the crystalline polypropylene/MFR of the propylene-&agr;-olefin copolymer) of 10 or less, wherein the film is biaxially oriented so that a ratio of orienting ratios for the MD direction and the TD direction (orienting ratio for the MD direction/orienting ratio for the TD direction) should be 0.3 to 1.6.
The biaxially oriented film of the present invention comprises the fine copolymer particles dispersed in a matrix of the crystalline polypropylene, and such a oriented film having such a dispersion structure composed of a polyolefin-based resin material has been made by the present invention for the first time. In the biaxially oriented film of the present invention, the ratio of birefringences along the MD direction and the TD direction satisfies the certain condition.
The present invention is based on the finding that such characteristics as mentioned above can provide a oriented film that is excellent in the straight cuttability along the MD direction and strength along the TD direction, and exhibits high transparency and good economy. While the production method therefor is not particularly limited so long as a oriented film having such characteristics can be obtained, a biaxially oriented polypropylene-based film which is composed of a polypropylene-based resin material having a ratio of MFRs of the crystalline polypropylene and the propylene-&agr;-olefin copolymer of 10 or less, and oriented under the certain conditions can have the aforementioned characteristics.
The biaxially oriented film of the present invention is useful as a film for package, in particular, as a film for packaging heavy contents.
Preferred embodiments;of the present invention will be explained hereinafter.
(1) Polypropylene-based Resin Material of the Present Invention
The film-forming material for forming the biaxially oriented film of the present invention comprises a polypropylene-based resin material that consists of crystalline polypropylene and propylene-&agr;-olefin copolymer, the copolymer being dispersed as particles in the crystalline polypropylene (the copolymer is dispersed as domains in a matrix of the crystalline polypropylene).
(i) Crystalline Polypropylene
The crystalline polypropylene used for the present invention is a crystalline polymer comprising principally of propylene units, and preferably comprises 90% by weight or more of the propylene units based on the whole polymer. Specifically, it may be a homopolymer of propylene, or it may be a random copolymer comprising 90% by weight or more of propylene units and less than 10% by weight of &agr;-olefin. When it is a copolymer, the &agr;-olefin may include ethylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 4-methyl-l-pentene, 3-methyl-1-pentene, and the like. It is preferable in view of the production cost to use a propylene homopolymer or propylene-ethylene copolymer having a propylene unit content of 90% by weight or more.
The melt flow rate (abbreviated as “MFR” hereinafter) of the crystalline polypropylene is preferably in the range of 0.1-50 g/10 minutes in view of the stability upon film-forming.
(ii) Propylene-&agr;-olefin Copolymer
The propylene-&agr;-olefin copolymer used for the present invention is a random copolymer of propylene and an &agr;-olefin other than propylene. The content of propylene unit is preferably in the range of 20-80% by weight, more preferably 20-75% by weight, particularly preferably 20-70% by weight of the whole co
Ishimoto Yuya
Nakashima Takanori
Okayama Chikashi
Saito Noriaki
Shiraishi Yasuhiro
Chisso Corporation
Kilpatrick & Stockton LLP
Tarazano D. Lawrence
Thibodeau Paul
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