Gas separation: apparatus – Apparatus for selective diffusion of gases – Membrane to degasify liquid
Reexamination Certificate
2000-09-27
2002-05-28
Foelak, Morton (Department: 1711)
Gas separation: apparatus
Apparatus for selective diffusion of gases
Membrane to degasify liquid
C096S012000, C428S315900, C521S134000
Reexamination Certificate
active
06395071
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to a film having excellent capability of preserving freshness of contents. More specifically, it relates to a film preferably used for packaging fresh produce, having good anti-bacterial performance and proper degree of permeability for each gases: mainly water vapor, oxygen and ethylene.
(2) Description of the Related Art
Recently plastic films are widely used for packaging food, textiles and others. Especially, among polyolefin films, polypropylene film drawn at least in one direction (hereafter sometimes referred to as “drawn PP film”) is used for many ways as a packaging material because of excellent transparency, and further, providing good printability, bag making processability and filling workability due to its high mechanical strength.
A drawn PP film, in general, tends to become less permeable to gases such as water vapor and oxygen because its density goes higher as the order of molecular orientation increases by drawing. Consequently, when an item like fresh produce is packaged by such a film, its freshness goes worse because of insufficient supply of oxygen to the packaged produce from the outside of the packaging material. Also it often occurs that the packaged fresh produce rot through propagation of microbes existing in air or attached to the packaged item like fresh produce thus losing commercial value.
Also it is said that fresh produce lose its commercial value typically if more than 5% of contained water is exhaled.
Therefore it is also necessary to suppress the amount of water vaporizing outwards through the packaging material from the packaged fresh produce.
However, on the other hand, over humidification or dewing inside the package can be another cause of rotting of packaged fresh produce.
Additionally a film used for packaging material of fresh produce with low permeability of ethylene gas results in such a problem that it accelerates over-ripening or rotting of the fresh produce due to accumulation of ethylene gas generated by the fresh produce themselves.
Currently drawn PP films circulating as the packaging material for fresh produce are actually unable to properly adjust the amount of water vapor permeation from inside to outside of the packaging material but inhibiting dew formation by incorporating a anti-fogging agent into the film, or unable to properly adjust the permeating amount of gases such as water vapor, oxygen and carbon dioxide but physically perforated through the film in the course of packaging fresh procedure to supplement gas permeability.
SUMMARY OF THE INVENTION
The present invention is a breathing film which contains at least one layer obtained by processing a propylene resin composition comprising crystalline propylene polymer(A) and propylene/&agr;-olefin random copolymer(B) having 45 to 85% by weight of propylene unit based on the weight of copolymer(B); a film having anti-bacterial agent coated thereon or included therein; in which said composition comprises 10 to 60% by weight of propylene/&agr;-olefin random copolymer(B) based on the total weight of polymer(A) and copolymer(B) and the ratio [&eegr;]
B
/[&eegr;]
A
of intrinsic viscosity [&eegr;]
B
of propylene/&agr;-olefin random copolymer(B) and intrinsic viscosity [&eegr;]
A
of crystalline propylene polymer(A) being 0.3 to 1.2; and (1) water vapor permeability [T
H2O
] (according to JIS Z 0208), (2) oxygen gas permeability [T
O2
] (according to JIS K 7126-A), and (3) ethylene gas permeability [T
ethylene
] (according to JIS K 7126-A) are each in the range described below.
(1) [T
H2O
]=9 to 50 (unit:g/m
2
·24 h)
(2) [T
O2
]=600 to 12500 (unit:nmol/m
2
·s·100 kPa)
(3) [T
ethylene
]=600 to 22500 (unit:nmol/m
2
·s·100 kPa)
DESCRIPTION OF PREFERRED EMBODIMENTS
One object of the present invention is to provide a film capable of properly adjusting the permeability of gases influencing the freshness of packaged items when used for packaging material and especially to provide a film suitable as the packaging material for fresh produce.
Also another object is to provide a film capable of properly adjusting the permeability of gases influencing the freshness of packaged items when used for packaging material together with having anti-bacterial performance and especially to provide a film suitable as the packaging material for fresh produce.
Furthermore, another object is to provide a film capable of adjusting the permeability of water vapor, oxygen and ethylene gas each to a level properly preserving freshness of packaged items without perforating process conventionally performed when used for packaging material and capable of maintaining good transparency, gloss and mechanical strength originally possessed by PP film and to provide a film suitable especially for packaging material for fresh produce.
The present inventors, after enthusiastic efforts of study to achieve the above-mentioned objects, found out that a film using specific propylene resin composition and having anti-bacterial agent coated thereon or included therein has good gas permeability and anti-bacterial performance and is preferable especially as a film for packaging fresh produce and completed the present invention.
The breathing film of the present invention has water vapor permeability of 9 to 50 g/m
2
·24 h, preferably in the range of 10 to 45 g/m
2
·24 h. When water vapor permeability of the film is lower than 9 g/m
2
·24 h, rotting of fresh produce is apt to be accelerated due to over humidity if used this film as a packaging material for such fresh produce. On the other hand, when said water vapor permeability exceeds 50 g/m
2
·24 h, fresh produce especially vegetables are apt to be dried up to death.
Oxygen permeability of the breathing film of the present invention is 600 to 12500 nmol/m
2
·s·100 kPa, preferably in the range of 1000 to 9000 nmol/m
2
·s·100 kPa. When oxygen permeability of the film is lower than 600 nmol/m
2
·s·100 kPa, respiration level of fresh produce decreases due to insufficient supply of oxygen to the packaged fresh produce from outside of packaging and the fresh produce are apt to lose freshness. On the other hand, when said oxygen permeability exceeds 12500 nmol/m
2
·s·100 kPa, increase of water vapor permeability is accompanied up to the undesirable level.
Ethylene gas permeability of the breathing film of the present invention is 600 to 22500 nmol/m
2
·s·100 kPa, preferably in the range of 600 to 15000 nmol/m
2
·s·100 kPa. When ethylene permeability is lower than 600 nmol/m
2
·s·100 kPa, over-ripening or rotting of fresh produce is likely to be accelerated. On the other hand, ethylene gas permeability exceeds 22500 nmol/m
2
·s·100 kPa, water vapor permeability is accompanied up to the undesirable level.
Thickness of the breathing film of the present invention is preferably in the range of 10 to 100 &mgr;m from the viewpoint of film making processability, workability (packaging fitness) and so on. When film thickness is thinner than 10 &mgr;m, it is difficult to make film of uniform thickness. When film thickness is heavier than 100 &mgr;m, gas permeability lowers.
Also the breathing film of the present invention has anti-bacterial agent coated thereon or included therein. When the anti-bacterial agent is included in the film, it is preferable for the anti-bacterial agent to exist near the surface of film from the point of efficient anti-bacterial action. When film thickness is heavier than 100 &mgr;m, concentration of anti-bacterial agent existing near the surface of film lowers.
Therefore film thickness is preferably in the range of 15 to 70 &mgr;m because of good preservation of freshness of fresh produce and elevated efficiency of anti-bacterial action.
The crystalline propylene polymer(A) constituting propylene resin composition used in the present invention is preferably homopolymer of propylene or propylene/&agr;-olefin random copolymer having higher than 90% by weight
Nakashima Takanori
Nakata Shinji
Niijima Kentaro
Shiraishi Yasuhiro
Chisso Corporation
Foelak Morton
Leydig , Voit & Mayer, Ltd.
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