Adhesive bonding and miscellaneous chemical manufacture – Methods – Surface bonding and/or assembly therefor
Reexamination Certificate
2003-02-21
2004-11-30
Sells, James (Department: 1734)
Adhesive bonding and miscellaneous chemical manufacture
Methods
Surface bonding and/or assembly therefor
C156S073100, C156S251000, C156S269000, C156S308400, C156S515000, C156S580200
Reexamination Certificate
active
06824632
ABSTRACT:
TECHNICAL FIELD
In a general manner, the present invention concerns operations for sealing and cutting at least two superimposed flexible sheets.
BACKGROUND OF THE INVENTION
In this field, documents EP 333390 and GB-A-952581 disclose ultrasonic sealing devices between an anvil and a sonotrode oscillating at ultrasonic frequency, of at least two superimposed sheets made out of plastic material, which move continuously along a specific line.
The ultrasonic sealing devices described in these aforesaid documents have, as a common feature, an interstice for passing through two superimposed sheets to be sealed, formed between the opposite surfaces of the sonotrode and the anvil, which has a section that decreases and then increases between its input and outlet.
According to EP 333390, this configuration for the section of the passage interstice is exclusively done so that the force applied by the device to the surfaces to be sealed is homogenous along the whole length of the sealing interstice.
But nothing indicates that the configuration in EP 333390 allows the width of the seal lines to be reduced in an appreciable manner.
Moreover, the device in EP 333390 is not intended for cutting the sheets to be sealed. Instead, it is made clear that for applications of the device described in this document any cutting or perforation of the materials to be sealed is to be avoided.
Nevertheless, it has already been mentioned that it would be desirable to combine a cutting operation with the sealing of the sheets, in particular in the widespread case where one wishes to carry out, at the same time:
A cut to make the sheets of the pouch from the films that are fed through in a continuous manner.
And the sealing of the edges of the folded sheet, or the superimposed sheets, in order to make the pouch.
Thus, the device in EP 333390 does not allow the objectives of manufacturers as described above to be met in a satisfactory manner (significant reduction in the width of the seal, while at the same time allowing a high production rate and ensuring very good mechanical strength and leak tightness, as well as making it possible for a cutting operation to be carried out simultaneously with the sealing).
The same holds for the device in GB-A-952581.
In fact, quite to the contrary, as regards the width of the seal line, it is pointed out that the device described in this document is intended to maintain the seal line relatively large, by increasing the width of the contact zone between the sheets to be sealed and the device (the width of the seal line is, in the case of the device in GB-A-952581 always less than the width of the contact zone between the sheets and the device).
Furthermore, this document does not mention the possibility of carrying out a cutting operation on the sheets to be sealed.
Furthermore, EP 498 364 discloses a sealing/cutting device for sheets fed through in a continuous manner.
In this device, a cutting blade is placed downstream of the sealing sonotrode along the sheet feed direction. The sonotrode and the blade constitute two separate elements that are used, respectively, for sealing and cutting operations.
A disadvantage linked to this type of configuration is that it is very tricky obtaining a thin seal line: the cutting blade positioned downstream of the sonotrode has in fact to act on the middle of the seal line.
The seal line therefore has to be wide enough to ensure that the cutting blade does indeed act on the middle region of said line.
Besides, it is pointed out in EP 498 364 that the reduction in the width of the seal lines is not at all an objective intended for the device in this document; on the contrary, “seal lines that are wider than those obtained by conventional methods” are sought (c.f. col. 4 1. 52-54 of this document).
Furthermore, a further disadvantage of the device in EP 498 364 is that it is tricky to obtain very good symmetry in the cutting profile of the sheet; in other words, obtaining the same width of cut along both sides of the seal line. This disadvantage also derives from the fact that the seal and the cut are carried out in a sequential manner, and not simultaneously. This can lead to production irregularities.
Finally, documents exist that disclose ultrasonic devices to carry out not only sealing but also cutting of films. An example of this type of device may be found, for example, in FR 2 665 683.
However, the device described in this document does not allow films fed through in a continuous manner to be processed, and so the throughput rate is limited by the discontinuous character of the process. Furthermore, no mention is made in this document of the width of the seal lines.
BRIEF SUMMARY OF THE INVENTION
More specifically, according to a first aspect, the invention concerns a type of device that comprises a sonotrode and an anvil arranged opposite each other so that their facing surfaces form an interstice for passing through the sheets to be sealed, with an inlet section and an outlet section, the sonotrode vibrating at high frequencies to emit ultrasonic waves.
The invention also concerns, according to a second aspect, a sealing and/or cutting method employing the aforesaid device, where said method may be used to seal and if appropriate cut two flexible films or sheets.
More specifically, the advantageous applications of the method according to the invention concern:
sealing and if appropriate also cutting the two lateral edges of flexible packages using the aforesaid type of device;
sealing a packaging as described above using the aforesaid type of device.
It also concerns a flexible package produced specifically according to the aforesaid methods.
Such a package may be made from single-layer or multi-layer plastic films.
An advantageous but not limitative application of the invention is the manufacture of flexible pouches or sachets containing foodstuffs, for example animal foodstuffs, where said pouches or sachets are generally intended to be hermetically sealed and heat treated after being filled and sealed (in the text that follows, both the terms “package” and “pouch” will be used indiscriminately to designate flexible packages).
Once filled, these pouches may be sterilized by heating under pressure in a humid atmosphere.
In order to be able to withstand this type of heat treatment, they are made from one or several film(s) with a specific structure.
More specifically, they are generally manufactured from one or several film(s), each film comprising an upper layer and lower layer intended to form the external and internal faces of said packages made out of plastic material, and a central layer, sandwiched between said upper and lower layers, made out of light metal.
Even more precisely, the films from which these packages are manufactured may have the following characteristics:
the upper layer is generally a layer of polyethylene terephthalate, combined or not with a layer of polyamide;
the central layer comprises a gas tight barrier material, in particular aluminium, and the internal layer is a layer of polypropylene combined or not with a layer of polyamide;
between each layer, a spread coat adhesive is provided that allows the different layers to be bonded together;
moreover, the layer of polyethylene terephthalate may be printed on its internal face in order to decorate the exterior of said pouch. In fact, the layer of polyethylene terephthalate is generally used as a printing support and determines the exterior appearance of the pouch;
the central layer of aluminium forms a gas tight barrier, particularly to oxygen and water vapor, in order to isolate from the exterior the materials contained within the pouch;
the polyamide layer constitutes an anti-perforation layer when this is required, depending on the subsequent applications of the pouch, and the polypropylene layer acts as a scaling agent for making the pouch, and provides the general mechanical strength of the pouch and ensures leak tightness at the level of the seals of said pouch.
Such pouches may contain solids, moist solids, liquids or even a combination of solid
Blanchard Daniel
Faul Patrick
Fulbright & Jaworski LLP
Mars Incorporated
Sells James
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