Synthetic resins or natural rubbers -- part of the class 520 ser – Synthetic resins – Mixing of two or more solid polymers; mixing of solid...
Reexamination Certificate
2001-07-11
2003-09-23
Mullis, Jeffrey (Department: 1711)
Synthetic resins or natural rubbers -- part of the class 520 ser
Synthetic resins
Mixing of two or more solid polymers; mixing of solid...
C525S089000, C525S095000
Reexamination Certificate
active
06624247
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Filed of the Invention
The present invention relates to a polypropylene-based film excellent in low temperature heat sealability and transparency.
2. Description of Related Arts
Polypropylene resins are excellent in transparency, heat-resistance, food hygiene and the like, and therefore, widely utilized in such fields as films, sheets and the like. Recently, with increase in bag production speed in fields of food wrapping and the like, materials having low temperature heat sealability are desired. For giving a polypropylene low temperature heat sealability, for example, JP2882237B discloses a copolymer excellent in low temperature heat sealability in which the comonomer content is increased with a Ziegler-Natta catalyst. However, in the method of lowering a seal temperature by increasing comonomer content, when the comonomer content increases over a certain limit, the rigidity decreases and, the solvent extraction amount increases to lead to reduction in food hygiene, therefore, further improvements have been required to solve these problems.
Further, the polypropylene random copolymer having excellent low temperature heat sealability, disclosed in JP2882237B, has insufficient impact resistance.
Therefore, there is desired further improvement of low temperature heat sealability without lowering in food hygiene or impact resistance.
Further, JP09-324022A discloses a polypropylene block copolymer having increased comonomer content by a multi-stage polymerization, and having excellent transparency, flexibility, impact resistance at low temperature and food hygiene. However, further improvement of the material in low temperature heat sealability, is required.
SUMMARY OF THE INVENTION
The present inventors have intensively studied and resultantly found that the above-mentioned object can be attained by a polypropylene-based resin film composed of a resin composition which comprises a polypropylene-based random copolymer and a polypropylene-based block copolymer having a specific content of 20° C. xylene-soluble component and a specific comonomer concentration in 20° C. xylene-soluble component and in which the temperature showing a heat seal strength of a film obtained by film formation of the resin composition has a specific relation with the temperatures showing a heat seal strength of films obtained by film formation of these polypropylene-based random copolymer and polypropylene-based block copolymer, leading to completion of the present invention.
It is usually believed that the temperature showing heat seal strength of a film obtained by using two kinds of polymers having different temperatures showing heat seal strength of a film is between the temperatures showing heat seal strength of these polymers, and the present invention is based on such a finding that, by using a composition composed of a polymer satisfying the requirements of the present invention, a film having lower temperature showing heat seal strength than temperatures showing heat seal strength of respective polymers can be obtained.
An object of the present invention is to provide a polypropylene-based resin film excellent in low temperature heat sealability and transparency.
Another object of the present invention is to provide a polypropylene-based resin film excellent in food hygiene in addition to a low temperature heat sealability and transparency.
Further, another object of the present invention is to provide a polypropylene-based resin film excellent in impact resistance in addition to a low temperature heat sealability and transparency.
Still further, another object of the present invention is to provide a polypropylene-based multi-layer film, comprising at least one layer of the above-mentioned polypropylene-based film.
Other objects and advantages of the present invention will be apparent from the following descriptions.
The present invention relates to a polypropylene-based resin film composed of a resin composition (C) comprising:
40 to 95% by weight of a propylene-based copolymer (A) selected from the group consisting of a propylene-based random copolymer (i) of propylene with ethylene and/or &agr;-olefins having 4 or more carbon atoms, and a propylene-based copolymer (ii) composed of 1 to 30% by weight of a copolymer component (a) having a content of &agr;-olefins having 4 or more carbon atoms of 1 molt and less than 15 molt and an ethylene content of 5 molt or less, obtained by polymerizing propylene, an &agr;-olefin having 4 or more carbon atoms and further optionally ethylene in a first step; and 70 to 99% by weight of a copolymer component (b) having a content of &agr;-olefins having 4 or more carbon atoms of 15 to 30 molt and an ethylene content of 5 molt or less, obtained by polymerizing propylene, an &agr;-olefin having 4 or more carbon atoms and further optionally ethylene in a second step or later steps; and
5 to 60% by weight of a polypropylene-based block copolymer (B) having a content of 20° C. xylene-soluble component (hereinafter, sometimes referred to as “CXS component”) of 5.0% by weight or more, wherein the 20° C. xylene-soluble component is a copolymer of propylene with ethylene and/or an &agr;-olefin having 4 or more carbon atoms, having a content of an ethylene unit derived from ethylene and/or an &agr;-olefin unit derived from the &agr;-olefin of 14 to 35 molt, wherein the heat seal temperature showing a seal strength of 300 g of the film of the resin composition is lower by 3° C. or more than those of respective films of the polypropylene copolymer (A) and the polypropylene-based block copolymer (B), and a multi-layer film comprising the film.
The present invention will be illustrated in detail below.
DETAILED DESCRIPTION OF THE INVENTION
The propylene-based random copolymer (i) used in the present invention is a random copolymer obtained by randomly copolymerizing propylene with at least one comonomer selected from the group consisting of ethylene and &agr;-olefins having 4 or more of carbon atoms, preferably 4 to 20 carbon atoms.
Examples of the &agr;-olefin 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-buene, 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 are exemplified, and preferable are 1-butene, 1-pentene, 1-hexene and 1-octene, further preferable are 1-butene and 1-hexene from the standpoints of copolymerization property and economy and the like.
Examples of the propylene-based random copolymer (i) include, 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, and a propylene-ethylene random copolymer, propylene-1-butene random copolymer and propylene-ethylene-1-butene random copolymer are preferable.
When the propylene-based random copolymer (i) is a random copolymer of propylene with ethylene, the ethylene unit content is preferably from 5.5 to 10.0 mol %, more preferably from 6.5 to 9.0 mol % from the standpoint of the amount of solvent-extracting components, namely, food hygiene.
When the propylene-based random copolymer (i) used in the present invention is a random copolymer of propylene with an &agr;-olefin, the &agr;-olefin unit content is preferably from 11.5 to 25.0 mol %, more preferably from 14.0 to 20.0 mol % from the standpoint of low temperature heat sealability or stable production of the random copolymer.
When the propylene-based random copolymer (i) used in the present invention is a copolymer of propylene, ethylene and the &agr;-olefin, the total content of ethylene unit and &agr;-olefin unit
Kishiro Shigeki
Kume Takanori
Shiratani Eisuke
LandOfFree
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