Stock material or miscellaneous articles – Hollow or container type article – Flexible food casing
Reexamination Certificate
1999-06-22
2002-07-09
Kiliman, Leszek (Department: 1773)
Stock material or miscellaneous articles
Hollow or container type article
Flexible food casing
C428S035200, C428S348000, C428S474400, C428S474700, C428S474900, C428S475800, C428S476300
Reexamination Certificate
active
06416832
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a single-layer or multi-layer packaging film or sheet having a layer of a polyamide resin composition, and more particularly to packaging films or sheets which are well balanced among properties such as formability, heat shrinkability, gas barrier properties, softness and suitability for automatic packaging machines equipped with a sealing mechanism such as a high-frequency sealer.
The packaging films or sheets according to the present invention are particularly suitable for use as casing films, pillow packaging films or sheets and deep-draw packaging films or sheets for filling and packaging fluid or semifluid foods such as sausage and solid foods such as processed meat and ham.
BACKGROUND OF THE INVENTION
In recent years, remarkable technical innovation has been made in the field of food packaging, and packaging materials most suitable for packaging, preservation, shipment and the like of various foods have been always demanded. The development of an automatic packaging system has been advanced with a view toward increasing production and reducing cost, and so the packaging materials are required to have excellent suitability for automatic packaging machines.
Single-layer or multi-layer films or sheets formed of various kinds of synthetic resins are generally used in the fields of casing films, pillow packaging films or sheets and deep-draw packaging films or sheets for filling and packaging fluid or semifluid foods, for example, processed livestock products such as sausage, processed marine products such as fish meat sausage, and processed farm products and cooked products such as devil's-tongue jelly and sweet rice jelly, and solid products such as processed meat products and ham. For example, films formed of a resin composition composed of nylon and a polyolefin resin, or multi-layer laminated films composed of a nylon layer and a polyolefin resin layer are often used in the field of the casing films.
Of these films, a multi-layer laminated film composed of a nylon layer and a polyethylene layer (hereinafter referred to as “Ny/PE film”) has good heat sealing property and gas barrier properties and is hence widely used. However, this Ny/PE film has involved a problem that it is lacking in softness. In addition, to the Ny/PE film, may be applied fin sealing (sealing surfaces being both the polyethylene layer) in which the polyethylene layer is used as sealing layers, but can not be applied the so-called overlap sealing (the sealing surfaces being the nylon layer and polyethylene layer). Therefore, the Ny/PE film can not be applied to any automatic filling and packaging machine equipped with an envelope-seam type sealing mechanism.
Several proposals have been made for polyamide resin compositions satisfying various properties as a casing film by a single layer. For example, in Japanese Patent Application Laid-Open No. 122732/1992, has been proposed a casing film formed from a mixture of nylon 6, and an aromatic copolyamide (hereinafter referred to as “nylon 6I/6T”) composed of a polycondensate of hexamethylenediamine with terephthalic acid and isophthalic acid. However, this casing film has involved difficulty in stably conducting blow stretching when this casing film is produced by blown-film extrusion, because the internal stress of a tubular parison upon the blow stretching is high, so that the air pressure within a blown bubble becomes high, and bubble break often occurs. In addition, this casing film has also involved a problem that when the casing film is filled with sausage in accordance with a method known per se in the art, boiled and then cooled, the wrinkles occur on the surface of the product, and the dimensions of the product become unstable. Further, the casing film has high stiffness, so that working properties such as shirring and ease of filling are deteriorated.
When an aromatic nylon (hereinafter referred to as “nylon MXD6”) composed of adipic acid and m-xylylene-diamine is used in place of the nylon 6I/6T in the polyamide resin compositions, the above-described tendency becomes more pronounced. A film or sheet obtained by blown-film extrusion using the nylon MXD6 involves difficulty in deep drawing it because when it is deep drawn, elongation of the film or sheet becomes uneven at portions corresponding to parts of from corners of the bottom to side walls of a deep-draw mold.
OBJECTS AND SUMMARY OF THE INVENTION
It is an object of the present invention to provide a single-layer or multi-layer packaging film or sheet having excellent formability, heat shrinkability, gas barrier properties and softness.
Another object of the present invention is to provide a single-layer or multi-layer packaging film or sheet which has excellent ease of filling, causes no wrinkle and has excellent dimensional stability when it is used as a casing film.
A further object of the present invention is to provide a single-layer or multi-layer packaging film or sheet which has such excellent properties as described above and is suitable for use as a casing film, a pillow packaging film or sheet, or a deep-draw packaging film or sheet for packaging fluid or semifluid food, or solid food.
The present inventors have carried out an extensive investigation with a view toward overcoming the above-described problems involved in the prior art. As a result, it has been found that when a polyamide resin composition comprising a specific copolymer nylon is used for a single-layer or multi-layer packaging film or sheet having a layer formed of a polyamide resin composition, the above objects can be achieved.
The packaging films or sheets according to the present invention may be used in the form of a single-layer film or sheet, but may be used in the form of a multi-layer film or sheet by laminating it on other layers such as a polyolefin resin layer, as desired. The single-layer films composed of a layer of the polyamide resin composition according to the present invention or the multi-layer films having the layer of the polyamide resin composition as a surface layer have excellent suitability for automatic packaging machines equipped with a high-frequency sealing mechanism and may also be ultrasonically sealed.
The packaging films or sheets according to the present invention can be suitably used as heat shrinkable films, in particular, casing films when they are formed into oriented films. A multi-layer film or sheet obtained by laminating a polyolefin resin layer on the layer of the polyamide resin composition can be heat sealed by using the polyolefin resin layer as a sealing surface. A single-layer or multi-layer tubular film or sheet obtained by blown-film extrusion can be used as a casing film as it is. Non-oriented packaging films or sheets according to the present invention have excellent suitability for automatic packaging machines and deep drawing property and are suitable for use as films or sheets for pillow packaging (i.e., flow-pack) and deep-draw packaging (i.e., thermo-forming).
The present invention has been led to completion on the basis of these findings.
According to the present invention, there is thus provided a single-layer or multi-layer packaging film or sheet having at least one layer formed of a polyamide resin composition, wherein the layer formed of the polyamide resin composition is a layer (A) formed of a polyamide resin composition comprising a copolymer nylon (c) composed of an aliphatic nylon (co)polymer component (1) and an aromatic nylon (copolymer component (2) in a proportion of at least 5 wt.%.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Copolymer nylon (c):
In the present invention, as a polyamide resin composition for forming the polyamide resin composition layer (A), is used a polyamide resin composition comprising a copolymer nylon (c) composed of an aliphatic nylon (co)polymer component (1) and an aromatic nylon (co)polymer component (2) in a proportion of at least 5 wt. %.
Examples of the aliphatic nylon (co)polymer component (1) include nylon 6, nylon 11, nylon 12, nylon 66, nylo
Ishii Hitoshi
Tsukamoto Hajime
Uehara Tsutomu
Dinsmore & Shohl LLP
Kiliman Leszek
Kureha Kagaku Kogyo K.K.
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