Stock material or miscellaneous articles – Structurally defined web or sheet – Physical dimension specified
Patent
1991-03-18
1993-06-22
Thibodeau, Paul J.
Stock material or miscellaneous articles
Structurally defined web or sheet
Physical dimension specified
426106, 426118, 426404, 426415, 428 355, 428 357, 428 365, 4283155, 428329, 428331, 428523, 428702, B32B 702
Patent
active
052215717
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates to a plastic film packaging material that contains a uniform dispersion of porous powder. The film can be used to preserve fruits, vegetables and cut flowers by controlling the concentrations of oxygen, carbon dioxide, ethylene and humidity surrounding the produce.
PRIOR ART
It is well known that all fruits, vegetables and cut flowers age and deteriorate after harvesting. This deterioration occurs via several mechanisms and the most important of these are dehydration where moisture is lost from the produce, internal biological changes where starches are converted into sugars, attach by bacteria and attack by fungi.
Various methods are used to reduce the rate of deterioration. The main one is cooling the produce to as low a temperature as possible without causing chilling injury. This reduces the rate at which bacteria and fungi multiply and reduces the metabolic rate of the produce. Cooling generally involves the use of refrigeration in one form or another which tends to dehydrate the produce unless additional humidification equipment is installed with the refrigeration. This is generally not done and is quite difficult to do on domestic refrigerators.
An improvement on cooling the produce is to cool the produce and modify the atmosphere surrounding it. This technique is commonly called Controlled Atmosphere storage when applied to bulk storage of produce and is widely practiced in the storage of apples. Typically, the oxygen concentration surrounding the produce is reduced from 21% to between 0.5% and 2% and the carbon dioxide concentration is increased from 0.03% to 1 to 10%. When applied to the wrapping of produce with a film, the technique is called Modified Atmosphere packaging.
Compared with cooling alone, CA storage and MA packaging usually improve the storage life of produce because firstly, the modified atmosphere slows down the rate of respiration via chemical signals and secondly, the modified atmosphere reduces the rate of bacteria and fungi growth.
Many films and bags have been developed to improve the storage life of produce. The simplest of these is a plain polyethylene (PE) bag which is cheap to manufacture and does not contaminate the produce. Plain PE films and bags have low gas permeabilities and suffer from excess condensation of water inside the bag which promotes decay by bacteria and fungal attack. The produce stored within a polyethylene bag is alive and respires by consuming oxygen and giving off carbon dioxide.
A major problem with storing produce in a plain PE bag is the fact that oxygen within the bag can go below 0.5% and the produce can go into anaerobic decay. Alternatively, the carbon dioxide concentration can increase to levels that injure the produce well before the oxygen concentration gets to dangerously low levels. Plain polyethylene bags are not permeable enough for the long term storage of most produce.
Some films overcome this permeability problem by having small holes punched into the film. This is generally satisfactory for humidity control but is unsatisfactory to maintain a CA or MA environment around the produce because the permeability is too high.
Microporous films have been developed which provide a good permeability characteristic, but these films are opaque and do not permit visual inspection of the produce without opening the bag and detrimentally disturbing the modified atmosphere.
Chigami et al, U.S. Pat. No. 4,840,823 disclose that the addition of a naturally porous silica CRISBAL in polyethylene improves the storage life of fruits and vegetables. The CRISBAL is hydrophillic and absorbs water, ethylene, carbon dioxide and other gases. A favourable atmosphere is provided around the produce by gas absorption into the CRISBAL rather than by modifications to the polyethylene permeability. The main problem with this film is that to ensure reasonable film clarity, processability into bags and tear strength, only 3 wt % to 5 wt % of CRISBAL is added to polyethylene vs up to 50 wt % detailed in the patent. With
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patent: 3088844 (1963-05-01), Hungerford et al.
patent: 3790402 (1974-02-01), Eastes
patent: 4423080 (1983-12-01), Bedrosian et al.
patent: 4840823 (1989-06-01), Chigami et al.
patent: 4937115 (1990-06-01), Leatherman
patent: 4939030 (1990-07-01), Tsuji et al.
Cammiss Mark A.
Russo Gaetano
Ausdel Pty. Ltd.
Le Hoa T.
Thibodeau Paul J.
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