Stock material or miscellaneous articles – Composite – Of polyamidoester
Reexamination Certificate
2000-07-19
2003-05-27
Sergent, Rabon (Department: 1711)
Stock material or miscellaneous articles
Composite
Of polyamidoester
C428S425100, C428S425500, C428S425800, C428S425900, C524S442000, C524S591000, C524S839000, C524S840000, C528S044000, C528S085000
Reexamination Certificate
active
06569533
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a gas barrier polyurethane resin which is useful as a film, a sheet, or a molding material excellent in gas barrier properties against water vapor, oxygen, aromatics, and others, and in adhesion to a base film, and to a gas barrier film using the same.
BACKGROUND OF THE INVENTION
Gas barrier films and packaging materials using the same are already well known. Of these, although aluminum foil is known to have the most excellent oxygen gas barrier properties, it cannot be used as it is but for special uses, for its pinhole resistance is too weak. Therefore, the aluminum foil is mostly used as an intermediate layer of a laminated film. The gas barrier properties of the laminated film are far excellent, but the film is opaque and therefore an object contained therein cannot be observed therethrough, hence difficulty in judging whether the film has surely been heat-sealed or not.
As the oxygen gas barrier film, films of polyvinylidene chlorides or vinylidene chloride copolymers (hereinafter referred to simply as PVDC) and PVDC-coated films are well known. Particularly, PVDC-coated films are known as laminated films with excellent barrier properties against oxygen gases and water vapor. PVDC hardly absorbs moisture and can exhibit its good gas barrier properties even under conditions of high humidity. Therefore, a variety of base films, on which a layer of PVDC is coated, can be employed regardless of their moisture permeability. Examples of the base film include biaxially stretched films of polypropylene, nylon, or of polyethylene terephthalate, and cellophane. Taking advantage of their gas barrier properties, these laminated films are utilized for wrapping or packing of a variety of foods, regardless of their being dry or moisture-laden. These packaging materials, after being used, are disposed as non-industrial, domestic wastes from homes. These wastes when incinerated give off toxic and hazardous gases and, what is worse, are causes of highly carcinogenic chlorine-containing organic compounds generated upon incineration at low temperatures. For such reasons, transition to the use of other materials has strongly been desired. However, the reality is that alternatives with performance and cost-performance equivalent to those of PVDC are not yet found.
For example, as the oxygen-gas barrier film, a polyvinyl alcohol (PVA)-series film is also well known. Only if the degree of its moisture absorption is low does the PVA film show extraordinarily excellent gas barrier properties against oxygen. However, the PVA film is originally high in moisture absorption, and its gas barrier properties against oxygen are immediately deteriorated upon exposure to an environment with a relative humidity of 70% or higher. Therefore, the PVA film has been considered to be lacking in practicality. For improving the moisture absorption of PVA, there has been proposed a copolymerization of PVA with ethylene into ethylene.vinyl alcohol copolymer (EVOH), a polycondensation with alkoxysilane by the sol-gel method [Japanese Patent Application Laid-Open No. 345841/1992 (JP-A-4-345841)], and a modification of part of the alcohol of PVA to make it water-resistant. However, none of the methods provides resins with satisfactory performance.
Moreover, although there have been suggested that a polyamide film obtained by reacting an aliphatic dicarboxylic acid with 4,4′-methylene bis(phenylisocyanate) shows excellent gas barrier properties and thermal resistance [Japanese Patent Application Laid-Open No. 252631/1989 (JP-A-1-252631)] and that a polyallyl alcohol-containing aqueous dispersion for gas barrier coating and a multilayered structure having a layer made therefrom exhibit excellent gas barrier properties and transparency [Japanese Patent Application Laid-Open No. 140072/1998 (JP-A-10-140072)], they are still unsatisfactory in their gas barrier properties under conditions of high humidity and water resistance.
There have been produced films with high oxygen-gas barrier properties, which are made by depositing an inorganic oxide such as silicon oxide [Japanese Patent Publication No. 12953/1978 (JP-B-53-12953)] and aluminium oxide [Japanese Patent Application Laid-Open No. 179935/1987 (JP-A-62-179935)] on a film. Since such inorganic oxide-made film is fabricated through a physical or chemical deposition process, the base film thereof itself is required to be deposition-durable, and therefore only to a limited variety of base film materials can be adopted. In addition, as these films are made of inorganic oxides, they are inferior in flexibility and tend to crack in the course of their secondary processing, possibly resulting in the degradation of the gas barrier properties.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a polyurethane resin that shows extraordinarily excellent gas barrier properties against water vapor, oxygen, aromatics, etc., and a film containing the same.
Another object of the present invention is to provide a polyurethane resin which exhibits significantly good gas barrier properties particularly even under conditions of high humidity, and a film containing the same.
Still another object of the present invention is to provide a polyurethane resin having no fear of contaminating the environment and excellent in water-resistance and adhesion to a base film, and a film containing the same.
The inventors of the present invention made intensive and extensive studies to solve the above-mentioned problems, and finally found that a film material having remarkably good gas barrier properties and no fear of contaminating the environment can be obtained by using a polyurethane resin having specific urethane group and urea group concentrations. The present invention was accomplished based on the above findings.
That is, in the gas barrier polyurethane resin of the present invention, the total concentration of the urethane group and the urea group is not less than 15% by weight. The gas barrier properties of the polyurethane resin are excellent and its oxygen permeability is, at a thickness of 25 &mgr;m, 50 ml/m
2
·atm·day or less. In addition, the humidity-dependency of the polyurethane resin is low, and the ratio of the oxygen permeability at 50% RH relative to that at 90% RH is about 1/1 to 1/2. The repeating unit of the polyurethane resin may contain a hydrocarbon ring as a unit (e.g., a ring derived from an aromatic or alicyclic compound).
Such polyurethane resin can be prepared from, e.g., an aromatic, aliphatic araliphatic, or alicyclic diisocyanate as its diisocyanate component, and a C
2-8
alkylene glycol as its diol component. Examples of the diisocyanate component are any isomers of xylylene diisocyanate and hydrogenated xylylene diisocyanate. The proportion of the hydrocarbon ring in the repeating unit of the polyurethane resin is about 10 to 70% by weight. Into the gas barrier polyurethane resin may be added a silane coupling agent, a layered inorganic compound, and others. Regarding what form the gas barrier polyurethane resin is in, it may be in the form of an aqueous dispersion. Moreover, the layered inorganic compound may be a water-swellable one.
The present invention also includes a gas barrier film comprising a resin layer containing the above polyurethane resin. This film may be a single-layered gas barrier film, such as a single-layered film formed from the aforementioned polyurethane resin, or may be a gas barrier composite film comprising a base film layer and a resin layer at least comprising the aforementioned polyurethane resin. In the composite film, at least one side of the base film may be provided with an inorganic layer.
DETAILED DESCRIPTION OF THE INVENTION
The polyurethane resin of the present invention can be obtained by a urethanizing reaction of a diisocyanate component and a diol component (if necessary, a diol component and a diamine component).
[Diisocyanate Component]
Examples of the diisocyanate component include
Shiraki Hiroyuki
Tawa Tsutomu
Uchida Takashi
Mitsui Takeda Chemicals Inc.
Sergent Rabon
Wenderoth , Lind & Ponack, L.L.P.
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