Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Noninterengaged fiber-containing paper-free web or sheet...
Reexamination Certificate
1999-12-02
2003-12-30
Jackson, Monique R. (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Noninterengaged fiber-containing paper-free web or sheet...
C428S297400, C428S298100, C428S323000, C428S327000, C428S500000, C428S910000
Reexamination Certificate
active
06670027
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a uniaxially oriented film formed from a film-forming material comprising a polypropylene-based resin material. More precisely, it relates to a uniaxially oriented polypropylene-based film in which tensile elongation along the transverse direction is improved without degrading transparence.
BACKGROUND ART
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 excellent in cuttability along that direction (straight cuttability). Therefore, they are widely used mainly in the field of food packaging, for example, individual packaging of products likely to break, such as confectionery, individual packaging of rice balls and the like.
While conventional uniaxially oriented polypropylene-based films are excellent in the straight cuttability along the MD direction, however, they are poor in elongation along the perpendicular direction to the MD direction (TD direction), and therefore they are likely to be torn when force is applied along the TD direction. Therefore, the films may be broken when used for packaging of heavy contents.
Further, when the conventional uniaxially oriented polypropylene-based films are torn along the MD direction, they generate fine fibers on their torn surfaces, which may be mixed in foodstuffs and the like.
DESCRIPTION OF THE INVENTION
The object of the present invention is to provide a uniaxially oriented polypropylene-based film in which tensile elongation along the TD direction is improved without degrading transparence of the film, and which generates less fibers when it is torn.
The present inventors earnestly conducted studies in order to achieve the foregoing object. As a result, they found that, in a uniaxially oriented film composed of a polypropylene-based resin material comprising a propylene-&agr;-olefin copolymer dispersed as particles in crystalline polypropylene, the straight cuttability along the MD direction and the tensile elongation along the TD direction could be improved without degrading the transparence by controlling form of the film so that the film should have a specific dispersion state of the copolymer particles in a cross section along the MD direction of the film. Thus, they accomplished the present invention.
That is, the present invention provides a uniaxially oriented polypropylene-based film formed from a film-forming material which comprises a polypropylene-based resin material consisting of 40 to 95% by weight of crystalline polypropylene, and 60 to 5% by weight of propylene-&agr;-olefin copolymer dispersed as particles in the crystalline polypropylene, wherein the particles of the copolymer have an aspect ratio (L/D) of mean dispersed particle length (L) to mean dispersed particle diameter along the film thickness direction (D) of 100 or more in a cross section along the MD direction of the film, and the mean dispersed particle diameter of 0.10 &mgr;m or less.
The present invention also provides a uniaxially oriented polypropylene-based film formed from a film-forming material which comprises a polypropylene-based resin material consisting of 40 to 95% by weight of crystalline polypropylene, and 60 to 5% by weight of propylene-&agr;-olefin copolymer, and has a ratio of MFR of the crystalline polypropylene to that of 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 uniaxially oriented along the MD direction so that the orienting ratio should be 3 to 12 times.
The uniaxially oriented film of the present invention comprises the copolymer particles dispersed elongatedly in a matrix of the crystalline polypropylene in such a manner the particles should have an aspect ratio higher than a certain level, and an oriented film composed of a polyolefin-based resin material having such a dispersion state has been made by the present invention for the first time.
According to the present invention, there can be obtained an oriented film that exhibits good straight cuttability along the MD direction, excellent tensile elongation along the TD direction and high transparence, and does not generate fibers, thanks to such a characteristic in form.
The production method of the film is not particularly limited so long as an oriented film having such a characteristic in form as mentioned above can be provided. However, a uniaxially oriented polypropylene-based film which is composed of a polypropylene-based resin material comprising crystalline polypropylene and propylene-&agr;-olefin copolymer and having a ratio of MFR of the crystalline polypropylene to that of the propylene-&agr;-olefin copolymer of 10 or less, and oriented under a certain condition can have the aforementioned characteristic.
The uniaxially oriented film of the present invention is useful as a film for package, in particular, as a film for packaging heavy contents or for food package.
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 uniaxially 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 or a block 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-1-pentene, 3-methyl-1-pentenel, 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 based on the whole copolymer. When the content of propylene unit exceeds 80%, the desired dispersed state of the copolymer particles (referred to as “copolymer domains” hereinafter) in the matrix of crystalline polypropylene may not be obtained, and hence the improvement of the tensile elongation along the TD direction targeted in the present invention may not be obtained. On the other hand, when it is less than 20%, the copolymer domains are difficult to be formed, and thus the desired performance may not be obtained.
As the &agr;-olefin other than propylene, ethylene, 1-butene, 1-pentene, 1-hexene, 1-octene, 1-decene, 1-dodecene, 4-methyl-1-pentene, 3-methyl-1-pentene and the like can be mentioned. Among these, a propylene-ethylene copolymer containing ethylene as the &agr;-olefin is preferably used because it is beneficial to the production cost.
While MFR of the propylene-&agr;-olefin copolymer used for the present invention is not particularly limited, it is preferably in the range of 0.1-20 g/10 minutes.
More preferably, MFR of the propylene-&agr;-olefin copolymer is preferably selected so that its ratio to MFR of the crystalline
Ishimoto Yuya
Maehara Hiroyuki
Nakashima Takanori
Okayama Chikashi
Saito Noriaki
Chisso Corporation
Jackson Monique R.
Kilpatrick & Stockton LLP
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