Package making – Methods – Closing package or filled receptacle
Patent
1995-09-25
1997-11-04
Sipos, John
Package making
Methods
Closing package or filled receptacle
533712, 533742, 533759, B65B 5110
Patent
active
056827326
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an apparatus for sealing and/or joining together thermoplastic materials or materials coated with thermoplastic, preferably packaging materials, by heating and compression of the materials within the sealing zone, with a view to achieving a surface fusion of mutually applied thermoplastic layers for the purpose of obtaining a tight and mechanically durable seal.
BACKGROUND ART
It has long been known within packaging technology to produce packages of thermoplastic materials or materials coated with thermoplastic layers, for example plastic-coated paper or cardboard. The advantage inherent in these materials is that they can be joined together and sealed to one another in a convenient manner by surface fusion of mutually applied thermoplastic layers. By such means, not only is it possible to achieve the result that the packages, which have been formed by folding or other methods, can be maintained in their given shape, but it is also possible to achieve the result that the packages may be given a tight seal which protects the contents in the package and prevents it from leaking out. Seals of this type are most generally realized with the aid of so-called hot jaws which consist of devices which can accommodate between them the materials intended for sealing and compress them under the simultaneous supply of heat so that the desired parts of the compressed and mutually facing plastic layers are caused to fuse together into a tight and mechanically durable seam or joint. The commonly occurring type of such sealing jaws consists of metallic bands or strips disposed on support rails, or metal bodies which are either permanently heated or are heated on each sealing occasion by the passage of an electric current through them. Sealing may either be carried out with the aid of two heated sealing jaws which are urged towards one another on either side of the material which is to be sealed, or also by one heating jaw and a so-called counter jaw whose sole purpose is to constitute a back-up abutment for the heating jaw and cool the material in order that the sealing seam or joint may rapidly be stabilized. The most commonly occurring sealing jaws in modern, automatic packaging machines consist of heat jaws with thin metal bands or strips disposed over an insulating ceramic material provided on a steel rail. At the moment of sealing, the sealing jaws are closed with great compressive force so that between them they accommodate the material which is to be sealed, whereafter a brief current pulse is passed through the above-mentioned metallic strips which are instantaneously heated to high temperature. The heat generated in the metallic strips is transferred to the packaging material and the mutually facing thermoplastic layers are caused to fuse together. The current pulse is discontinued when sufficient quantity of heat has been generated, whereafter the sealing jaws are opened and the sealed material is released.
For production engineering and other reasons, for example those forces which act on the strips because of their elongation on heating, it is difficult, employing thin metal strips, to realize anything other than identical and straight seals. In certain cases, there is however a need to be able to work with curved sealing lines or seals of different strengths or adhesive force along the extent of the seal. It has not in principle been possible to realize this with the aid of prior art technology which utilizes metallic strips but, according to the present invention, these needs may be satisfied.
SUMMARY OF THE INVENTION
The present invention is characterized by two sealing jaws which are disposed to be movable in relation to one another, and are arranged to be capable of accommodating between them the material intended for sealing, at least the one sealing jaw displaying a ceramic part which comprises at least two ceramic materials, of which the one is electrically insulating and the other electrically conductive, and that the electrically conductive cerami
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Kim Gene L.
Sipos John
Tetra Laval Holdings & Finance S.A.
LandOfFree
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