1. Field of the Invention
This invention relates to a snap zipper, which can be utilized in the fields of food packaging and medical products.
2. Description of the Related Art
Bags with zipper are used in many fields such as those of food packaging and medical products. In a bag with a snap zipper, a strip-like snap zipper comprising a male and a female member is provided on the bag at a sealing portion thereof. Heretofore, various methods of producing bags with snap zippers have been proposed.
Among the proposed methods, there are (1) one, in which a cylindrical film with a male and a female portion of a snap zipper is extrusion formed as a one-piece molding by using extrusion dies, and (2) one, in which a tape with a snap zipper is produced and is thermally fused to a base film for forming a bag body.
In the former method (1), the bag with a snap zipper, which is produced as a one-piece molding from the outset, takes space due to the shape of the snap zipper. Its storage and handling, therefore, are rather inconvenient. In addition, restrictions are imposed on the structure of the base film. Accordingly, the latter method (2) which is free from the above drawbacks has recently become a popular method.
The snap zipper is usually made of low density polyethylene (LDPE) or polypropylene (PP). In many cases, a sealant layer (which forms the innermost layer of the bag body, and to which the snap zipper is fused), is applied to a base film of the same material. For example, with a base film sealant layer of LDPE, the snap zipper is made of the same LDPE.
With a sealant layer of the same material as the snap zipper, the snap zipper can be sealed to the sealant layer without any trouble.
Meanwhile, polyester resins, polyamide resins, ethylene-vinyl-alcohol copolymerization resins, and so forth have excellent heat resistance, retention properties and order gas-barrier, and thus they are used suitably as the material of the sealant layer of the bag body.
However, since a sealant layer of a polyester type resin is a different material from the snap zipper, sufficient adhesion for fusing the snap zipper can not be obtained. Therefore, it has been difficult to use polyester type resins for the sealant layer.