Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Including a second component containing structurally defined...
Reexamination Certificate
2001-06-21
2003-06-24
Chen, Vivian (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Including a second component containing structurally defined...
C428S323000, C428S480000, C428S910000, C525S437000, C525S444000
Reexamination Certificate
active
06582813
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a biaxially oriented polyester film, more particularly to a laminated biaxially oriented polyester film which has easy tearability in at least one direction, excels in antistatic properties, and is useful as a packaging material for foods such as confectionary, pickles, retort pouch foods, etc., pharmaceuticals and such.
Since biaxially oriented polyester films represented by polyethylene terephthalate film are excellent in mechanical properties, electrical properties, chemical resistance, dimensional stability, etc., they are used as base for a variety of commercial products in many fields of industry such as information recording materials, capacitors, packaging materials, printing plates, insulators, photographic films, etc. In the recent years, polyester films have been popularly used as various types of packaging film, and amid the growing recognition of importance of environmental problems, it is expected that the scope of their use will be further expanded in view of their capability to prevent environmental pollution at the time of waste disposal.
The packaging polyester films find their way into many uses, and they are needed in various fields of industry such as foods, electric and electronic parts, machinery, equipment, building materials, chemicals, etc.
Various types of packing or wrapping bags utilizing plastic films, particularly those made by laminating a biaxially oriented plastic film and a sealant film, are popularly used for packaging foods, medicines and sundry goods, but these packages have the problem that when it is tried to rip them open, they may not be ripped up smoothly and linearly, causing a possibility of scattering the contents and consequent soiling of the user's clothes when the packages are opened.
The packages using a plastic film having antistatic properties are also commonly used for packaging or wrapping powders, but these packages also involve the problems; some of them are bad in tearability by hand while others might be torn up in the wrong direction to cause scattering of the contents.
As a result of the present inventors' earnest study to solve the above problems, it has been found that a film having a layer with a specific sea island structure and also possessing a specific surface resistance can solve the above problems.
The present invention has been attained on the basis of the above finding.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a laminated polyester packaging film which can be ripped open with ease and linearly with no fear of causing scattering of the contents and also capable of preventing adhesion of powders.
To attain the above aim, in the first aspect of the present invention, there is provided a biaxially oriented polyester film having at least one layer of a sea island structure which satisfies the following formulae (1) and (2) at the same time, said film having a specific surface resistance of not more than 1×10
15
&OHgr;:
50≦
X/Y
(1)
5≦N≦200 (2)
wherein X is the mean value of length (&mgr;m) of the islands in the longitudinal direction of the film; Y is the mean value of length (&mgr;m) of the islands in the width direction of the film; and N is the number (per &mgr;m
2
) of the islands existing in the section of the film in its width direction.
DETAILED DESCRIPTION OF THE INVENTION
The invention will be described in detail below.
The “polyesters” referred in the present invention are the polymers having ester groups obtained from polycondensation of dicarboxylic acids and diols or hydroxycarboxylic acids. Examples of the dicarboxylic acids usable for the said polycondensation include terephthalic acid, succinic acid, isophthalic acid, adipic acid, azelaic acid, sebacic acid, dodecanoic diacid, 2,6-naphthalenedicarboxylic acid, and 1,4-cyclohexanedicarboxylic acid. Examples of the diols include ethylene glycol, 1,3-propanediol, 1,6-hexanediol, 1,4-butanediol, diethylene glycol, triethylene glycol, neopentyl glycol, 1,4-cyclohexanedimethanol and polyethylene glycol. Examples of the hydroxycarboxylic acids include p-hydroxybenzoic acid and 6-hydroxy-2-naphthoic acid.
Typical examples of such polymers are polyethylene terephthalate and polybutylene terephthalate. These polymers may be homopolymers or ones obtained by copolymerizing a third component.
Polyester D used in the present invention is a polyester obtained from a polycondensation reaction of a polyester B comprising a dicarboxylic acid and a glycol and a dehydrated condensate C mainly comprising a glycol. It is preferably one obtained from a polycondensation reaction of a polyester B comprising a dicarboxylic acid containing not less than 50 mol % of an aromatic dicarboxylic acid and a glycol containing not less than 50 mol % of a C
3
-C
10
glycol and a dehydrated condensate C mainly comprising a C
3
-C
10
glycol. Its preparation method, however, is not specified. Examples of the polyester B include polyethylene terephthalate, polypropylene terephthalate and polybutylene terephthalate. Examples of the dehydrated condensate C include polyethylene glycol, polytrimethylene glycol and polytetramethylene glycol.
The film of the present invention is a biaxially stretched film in view of high strength and excellent dimensional stability.
In order to prevent adhesion of the contents to the package, the film of the present invention needs to have antistatic properties. For this purpose, the polyester film of the present invention has a specific surface resistance of not more than 1×10
15
&OHgr;, preferably not more than 5×10
12
&OHgr;, more preferably not more than 5×10
11
&OHgr;. When the specific surface resistance of the film is more than 1×10
15
&OHgr;, the material contained in the package, especially powder, tends to adhere to the package.
As methods for affording antistatic properties to the film, there is exemplified a method in which an antistatic agent is incorporated in the film or the film is coated with an antistatic agent.
It is possible to use any type of antistatic agent as far as it is capable of reducing specific surface resistance. Examples of such antistatic agent include glycerin fatty acid esters, polyoxyethylene alkyl ethers, polyoxyethylene alkylphenyl ethers, alkyl diethanolamines, hydroxyalkyl monoethanolamines, polyoxyethylene alkylamines, alkyl diethanolamides, alkyl sulfonates, alkylbenzenesulfonates, alkyl phosphates, tetraalkylammonium salts, alkylbetains, alkylimidazoliumbetains and the like. Of these antistatic agents, alkyl sulfonates are preferred.
In the film of the present invention, the mixing ratio (by weight) of polyester D/polyester A falls within the range of 30/70 to 5/95, preferably 25/75 to 10/90, more preferably 20/80 to 10/90. When the ratio of polyester D exceeds 30% by weight, there is a tendency for the film to lower in mechanical strength and/or to increase in thickness unevenness, which may make the film impracticable.
Polyester D used in the present invention is preferably a melt mixed product of a polyester B and a dehydrated condensate C with its repeating units comprising mainly a C
3
-C
10
glycol, in which the polyester B/dehydrated condensate C mixing ratio preferably falls within the range of 55/45 to 98/2, more preferably 5/95 to 30/70, especially 10/90 to 25/75. When the ratio of dehydrated condensate C is less than 2% by weight, insular dispersion of polyester D in polyester A matrix may not take place to badly deteriorate linear tearability of the film. On the other hand, when the ratio of the said condensate exceeds 45% by weight, the obtained film may be reduced in mechanical strength.
For affording easy and linear tearability to the film, it is necessary to effect insular dispersion of polyester D in at least one layer of the film, and the state of such insular dispersion of polyester D needs to satisfy the following formulae (1) and (2) at the same time:
50≦
X/Y
(1)
5≦N≦200 (2)
wherein X is the
Miki Takatoshi
Okumura Hiroteru
Chen Vivian
Conlin David G.
Edwards & Angell LLP
Hazzard Lisa S.
Mitsubishi Polyester Film Corporation
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