US 20090173041 A1
A device for sealing packages comprises a sealing bar (1, 2). It is the object of the present invention to provide a sealing bar which solves the problems of lacking evenness of the sealing bar due to manufacturing tolerances. Advantageously, the quality of the sealing seam shall be enhanced. This object is solved by a compressible, heat conducting material (5) provided on the sealing bar (1, 2).
18. A device for sealing of packages, comprising a first sealing bar having a sealing face and a compressible, heat conducting material provided on the sealing bar at the sealing face.
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30. A method of sealing packages, said method comprising: pressing a first sealing bar to a counter-bearing; and providing a compressible, heat conducting material on the first sealing bar.
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The present invention refers to a device and method of sealing packages.
For instance, in the field of packages for medical aseptic goods, validation of the packaging processes is required by the qualification department. The validation is to ensure that the process having the same parameters always leads to the same result. Among other things, this pertains to the packaging machine itself. One component to be validated is the sealing bar. In order to assure the reproducibility of a sealing seam, the real process parameters of sealing time, sealing pressure and sealing temperature must agree with the input requirements.
In a prepared concept of pulse sealing, where a wire is heated by an electric current pulse, the validation of the sealing time is possible just like that. Moreover, the sealing pressure can also be indirectly measured via a diaphragm exerting the pressure. However, the sealing temperature can not be adjusted. The sealing temperature results from the sealing time, the remaining heat of the previous sealing operation, the ambient temperature, the electric resistance of the wire and the applied voltage. Direct presetting of the sealing temperature is not possible, since the small mass of the wire and the shortness of the sealing time do neither allow a measurement of the heating process nor a feedback control thereof. Therefore, sealing methods have been developed, which can be validated.
In such a thermo-controlled (TC) method, a solid aluminium profile is continuously heated. The significant higher mass and the thermal buffer capacity being involved therewith can feedback control the sealing temperature with sufficient accuracy due to time mitigation. For common package material of high quality, which is manually inserted into the machine without crinkles, this method creates acceptable sealing results. Using cheaper package materials, sealing by means of a continuously heated sealing bar will be difficult due to the limited time frame of the process. If the product shall be packed by an automatic conveyor belt chamber machine, for instance, unavoidable crinkles in the sealing area result in a package which is not properly sealed. Since the heat must pass through all web layers during sealing on one side, either the upper layers get too hot and flow away or the lower layers are insufficiently heated, whereby the crinkles are not sealed through.
An obvious solution as also used by the pulse sealing method is the use of a second sealing bar. The poach is heated both above and below.
The realization of a reliable device for sealing above and below is, however, difficult with two sealing bars of aluminium, for instance. The sealing bars must be accurately aligned to each other to be flush with each other when webs having a thickness of 100 μm or less are used, since the sealing pressure is not uniformly applied. In addition to the thermal deformation during operation, the sealing bars are formed concave or convex caused by the manufacture thereof so that gaps of 0.1 to 0.3 mm are created. This is not allowable in particular during sealing medical products.
It is the object of the present invention to provide a sealing bar which solves the above-mentioned problems caused by manufacturing tolerances. Advantageously, the quality of the sealing seam shall be improved.
This object is solved by the device according to claim 1. The object is also solved by the method according to claim 12. Further developments of the invention are indicated in the respective dependent claims.
By means of the sealing bar according to the invention, the manufacturing tolerances and the thermal deformations can be compensated for during the sealing operation by a metal meshwork provided at the sealing face. In addition to the desired flexibility for compensating for tolerances and tilting, the metallic material enables good heat conduction for optimum sealing. For instance, this is indispensable and required by law, respectively, for medical products to be packed. Since manufacturing of sealing bars does not need high demands in dimensional accuracy due to the following integration of the metal meshwork, the manufacturing of the sealing bars is considerably cheaper.
Further features and advantages of the invention are disclosed in the description of embodiments together with the enclosed drawings. In the Figures show:
In the following, a first preferred embodiment of the present invention is described with reference to the figures on the basis of an example of a chamber machine.
In the enlarged view of
The metal meshwork 5 can compensate for a plurality of form deviations and, hence, continuously provides a constant sealing pressure for ensuring the optimum quality of the sealing seams. It can be used in a woven form, for instance, i.e. with longitudinal and transverse fibres. Moreover, other embodiments such as fabric like steel wool are conceivable.
With reference to the
The present invention is not limited to the use of the metal meshwork. Instead of it, the use of other heat conducting materials such as specifically adapted plastics having heat conducting fillers or ceramics with good heat conductance such as aluminium nitride are conceivable.
The sealing bars are not limited to the T-shaped cross-sectional form. Any forms and shapes such as rectangle or triangular forms of the sealing bars are conceivable.
Instead of a Teflon strip on the sealing bar, other components having anti-adhesive materials are conceivable. Instead of a strip, which is glued on the ceiling bar, other fixing mechanism such as rivets or clips are conceivable.
The invention is not limited to the use in chamber machines, either. The device according to the present invention can be incorporated in any packaging machine such as a deep drawing machine, a thermo former or a chamber machine, where a sealing operation is carried out.
The individual features of the disclosed embodiment can be freely combined with each other.