Stock material or miscellaneous articles – Web or sheet containing structurally defined element or... – Physical dimension specified
Reexamination Certificate
2002-07-01
2004-06-08
Jackson, Monique R. (Department: 1773)
Stock material or miscellaneous articles
Web or sheet containing structurally defined element or...
Physical dimension specified
C428S337000, C428S532000
Reexamination Certificate
active
06746762
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a film selectively permeable to carbon dioxide gas derived from a specified natural raw material and to a food packaging film comprising the same. More particularly, the present invention relates to a film selectively permeable to carbon dioxide gas which comprises chitosan that is basic polysaccharide and in which the ratio of the carbon dioxide gas transmission (CO
2
TR) to the oxygen gas transmission (O
2
TR), (CO
2
TR/O
2
TR), is high, is highly safe from the standpoint of food hygiene, is insoluble in water, and is suitable for packaging fermented foods and vegetables, cut flowers and the like, and to a food packaging film comprising the same.
BACKGROUND ART
In the field of food packaging, technologies related to films that are selectively permeable to carbon dioxide gas include, for example, a molded article for packaging food, which comprises a composition composed of a polyvinyl alcohol resin and at least one compound which is selected from the group consisting of an alkylene glycol monomer, a hydroxy acid monomer and polymers thereof and which has a ratio of the solubility of carbon dioxide to the solubility of oxygen gas being 30 or more as disclosed in JP-A-5-222215. This publication describes that the films obtained from the molded article are suitable for packaging those foods which generate much carbon dioxide gas, and disfavor contact of oxygen, for example, cheese products, coffee beans and so forth. JP-A-9-316208 describes that a film obtained by heat-treatment of a reaction mixture of a polyacrylic acid and an aliphatic diamine has a resistance to water and has a ratio of the permeability to carbon dioxide gas to the permeability to oxygen gas of 15 or higher. Further, JP-A-11-538 describes that a film that comprises a polymer having a polyamine structure has a high ratio of the carbon dioxide gas transmission to the oxygen gas transmission.
For such a material having selective gas permeability, a progress has been made in the development of applications in particular as food packaging materials, and there have been demanded packaging materials in view of satisfying the safety from the standpoint of food hygiene.
An object of the present invention is to provide in an economical way a film which is insoluble in water, is highly safe from the standpoint of food hygiene, and has such selective gas permeability that the ratio of the carbon dioxide gas transmission to the oxygen gas transmission is high.
DISCLOSURE OF THE INVENTION
The inventors of the present invention have found that a film, which comprises a specified chitosan, has a high ratio of the carbon dioxide gas transmission to the oxygen gas transmission and can solve such problems, thus achieving the present invention.
Therefore, the present invention provides a film selectively permeable to carbon dioxide gas, which comprises a chitosan having a degree of deacetylation of 70 mol % or higher and in which the ratio of the carbon dioxide gas transmission (CO
2
TR) to the oxygen gas transmission (O
2
TR), (CO
2
TR/O
2
TR), is 15 or higher. The present invention provides a film selectively permeable to carbon dioxide gas comprising a laminate film including at least three layers composed of an outer layer, an intermediate layer and an inner layer, in which the outer layer and the inner layer comprise a thermoplastic resin and the intermediate layer comprises a film according to the above-mentioned invention, and in which the ratio (CO
2
TR/O
2
TR) as the laminate film is 10 or higher. Further, the present invention provides a film selectively permeable to carbon dioxide gas according to the above-mentioned invention, in which the film composed of chitosan in the intermediate layer has a thickness of 0.2 to 50 &mgr;m. Further, the present invention provides a food packaging film which comprises a film selectively permeable to carbon dioxide gas according to the above-mentioned invention, in which the food is coffee, cheeses, bean pastes, pickles, root crops, mushrooms, leaf-stem crops, fruit vegetables, or fruits.
BEST MODE FOR CARRYING OUT THE INVENTION
Chitosan can be obtained by deacetylating chitin, which exists widely in nature, for example, as a component constituting shells of lobsters and crabs, in a concentrated alkali. Fully deacetylated chitin is a basic polysaccharide having two hydroxyl groups and one amino group in the constitutional unit molecule thereof. Free chitosan does not dissolve in water and organic solvents but forms a salt in the presence of an inorganic acid such as hydrochloric acid or organic acid such as acetic acid, propionic acid, oxalic acid, butyric acid, lactic acid, tartaric acid, succinic acid, or citric acid to give an acid salt solution. As for the chitosan used in the present invention, one that has a molecular weight of 10,000 to 1,000,000, and further 10,000 to 500,000 and a viscosity of 1 to 20,000 cp (1 to 20,000 mPa·s), and further 1 to 2,000 cp (1 to 2,000 mPa·s) is preferred in consideration of coating properties as shown in the examples described hereinbelow. The degree of deacetylation of chitosan is 70 mol % or higher, preferably 80 mol % or higher. It is desirable that the viscosity of chitosan is 3 to 2,000 cP (3 to 2,000 mPa·s) for preparing solutions. Note that chitosan having a degree of deacetylation of below 70 mol % obtained by treating chitin in a concentrated alkali does not dissolve in acetic acid and cannot form films.
When using chitosan, it is handled in the form of the aforementioned chitosan acid salt solutions in consideration of ease of handling. Among these, acetic acid salt and lactic acid salt are preferred in consideration of price and safety of foods. In the chitosan acid salt solutions, hydrophilic organic solvents, for example, alcohols such as methanol, ethanol and isopropanol and ketones may be used as diluents. Further, when coating a chitosan acid salt solution on a substrate, in cases where the chitosan acid salt solution is difficult to coat on the surface of the substrate and thus being repelled, use of the diluent or of a small amount of surfactant will make the coating easy.
To obtain a film selectively permeable to carbon dioxide gas comprising chitosan according to the present invention, the above-mentioned chitosan acid salt solution is coated on a substrate in the form of a film, sheet, plate or the like and is dried (for example, at 30 to 150° C., for 1 second to 30 hours) together with the substrate film to obtain a dry coating of chitosan acid salt. That is, the film is molded by a solvent casting method in which a chitosan acid salt solution is cast on a support (substrate) such as a metal plate, a glass plate or a plastic film and dried to form a coating, an extrusion method in which an aqueous chitosan acid salt solution of a high concentration is cast through a small slit of an extruder in the form of a film under a discharge pressure and the wet film is dried on a rotary drum or a belt, a method in which after coating the aqueous solution on a plastic film, the coated film is dried by heating or the like method. In this way, a dry chitosan acid salt coating is obtained. Of those film-forming methods, in particular, the solvent casting method (casting method, coating method) is preferably used since molded films (dry coatings) having excellent transparency can be easily obtained.
The chitosan acid salt coating is water-soluble. A film comprising water-insoluble chitosan is obtained by treating the dry coating with an alkaline aqueous solution, for example dipping it in an aqueous sodium hydroxide solution (for example, dipping it in an aqueous 1 N sodium hydroxide solution for 0.5 seconds to 48 hours), and then washing it with water (for example, in tap water for 1 second to 1 hour) to obtain a film made of chitosan which is insoluble in water. By drying this film (for example, at 30 to 200° C. for 0.5 seconds to 1 hour), the film of the present invention can be obtained.
Here, to obtain a chitosan acid salt solution, 0.1 to 10 mass parts, preferably 0.2 to 5 mass
Hosoda Tomonori
Kawaguchi Katsumi
Oba Hiroyuki
Saika Toru
Jackson Monique R.
Kureha Chemical Industry Co. Ltd.
Nixon & Vanderhye PC
LandOfFree
Film selectively permeable to carbon dioxide gas and food... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Film selectively permeable to carbon dioxide gas and food..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Film selectively permeable to carbon dioxide gas and food... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3338754