RF-sealable pillow pouch

Details RF-sealable pillow pouch RF-sealable pillow pouch

1999-04-15

2003-06-03

Pyon, Harold (Department: 1772)

Stock material or miscellaneous articles

Structurally defined web or sheet

Physical dimension specified

C428S349000, C428S518000, C428S035700

Reexamination Certificate

active

06572959

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention refers to an RF-sealable pillow pouch of a thermoplastic material particularly suitable for packaging flowable products and to a method of packaging said product in a vertical form-fill-seal machine using an RF sealable, thermoplastic material.
Flowable products, such as powders, liquid and pasty materials, e.g. detergents, liquid soaps, household cleaning products, bleaches, etc., are currently packaged in so called pillow pouches made of PVC. These pillow pouches are typically used as monodose packages or as refill cartridges that are opened and poured in a re-usable rigid or semi-rigid container as desired.
The machine that makes and fills packages in a single operation is called a vertical form-fill-seal (VFFS) machine. Said machine forms pouches from a web of flat flexible film while filling them with the product. The film is fed from a roll to a device that forms it into a tube of a suitable diameter around the product filling tube. The two film edges are then sealed together, longitudinally, either with a lap seal or with a fin seal. As the tube moves down the machine, two horizontal sealing bars come together to form a transverse seal which becomes the bottom of the pouch. At that point, a measured amount of product is allowed to flow through the product filling tube and into the just formed pouch. By the time filling is complete, the top of the pouch has traveled down to the sealing bar location, where the bars once again meet to simultaneously create the top seal and the bottom seal of the next pouch above. Alternatively, it is also possible to manufacture the pillow pouches in two separate steps, where the first step is the production of the pouches by any conventional system and the second one is the pouch filling In a vertical machine followed by the sealing of the pouch mouth.
Pillow pouches are characterized in that at least one of the transverse sealing is a melt cut sealing. The melt cut sealing Is a sealing carried out with heating while at the same time the film is pressed and cut. The sealing bars are therefore equipped with a knie which cuts through the seal to separate the filled pouch from the machine. To give the appearance of a pillow, as the name does suggest, once the pouch is filled with the metered volume of flowable product, generally of the liquid or pasty product, air or a suitable gas is injected before the transverse sealing bars are pressed together.
Working with PVC at least the transverse sealing system in these VFFS machines is based on dielectric heating or RF heating. In this system high frequency electric current is passed through the film by the sealing bars. When the film contains polar molecules, as in the case of PVC, these molecules oscillate under the influence of the current and this molecular agitation is converted to heat sufficient to melt the film in the seal area.
The advantages of “pillow pouches” are obvious: reduced volume, reduced consumption and waste of plastic material, lower cost, etc.
However the use of PVC, that up to now has been considered the polymer of choice for this application, presents many drawbacks.
First of all PVC has no gas-barrier and moisture-barrier characteristics. Volatile components, e.g. perfumes, aromas, etc., can easily escape through the packaging material, thus reducing the content thereof in the packaged product and, when these components have an unpleasant smell, e. g. in case of bleaches, imparting said smell to the whole package. Water also can evaporate through the PVC layer thus reducing the volume of the packaged product and increasing the concentration of the non volatile components therein.
Secondly, PVC generally contains a high level of plasticizers. Said plasticizers do easily migrate Into the packaged product with a consequent package integrity problem. The mechanical properties of PVC films in fact are determined by the level of plasticizers: a decrease In the amount of plasticizers due to their migration into the packaged product will increase the stiffness and brittleness of PVC thus reducing its mechanical (puncture, abuse) resistance.
A third disadvantage of the use of thick PVC films is the amount of chlorine containing polymer that needs to be disposed of.
PVC replacement in the manufacture of pillow pouches for the packaging of flowable products has been widely described in the patent literature.
Of interest is EP-B-477,025 that describes the use of a multilayer film having a barrier layer of a thermoplastic material, preferably an LLDPE or a composite of a polyethylene layer and a polyamide or EVOH layer, and on at least one side thereof a layer of an RF-sealable polymer, e.g. EVA with a high VA content According to EP-B-77,025, the problem created by the low RF-sensitivity of the thermoplastic barrier materials is overcome by the use of sealing layers of EVA with a high VA content and a low, controlled, content of additives, while the problem of sticking that derives from the use of such a sealing layer is overcome by the use of structures with a matted surface. These structures do not contain chlorine and have moisture barrier properties, however they do not overcome the other drawbacks connected with the use of PVC as for instance the structures described In EP-B-477,025 do not have odour-barrier properties or only to a limited extent While in fact polyethylene and polyamide have no or moderate odor barrier properties, EVOH is very sensitive to moisture and its odor barrier properties, that are satisfactory under dry conditions, are drastically reduced after exposure to a moistured environment. Furthermore, owing to the low RF-sensitivity of these barrier materials, and depending on their thickness, the seal strength of the RF-seal may sometimes be unsatisfactory in spite of the high VA content of the EVA sealing layer. Finally, with these structures an additional step in the film manufacturing process is required to provide the matted surface, what adds an extra-cost to the film.
Also of Interest is EP-A-471,607 that describes RF-sealable thermoplastic films particularly suitable for packaging gas-emitting flowable products. Said films comprise a core polyolefin layer and EVA sealing layers and are characterized by an oxygen transmission rate (OTR) of at least about 600 cm
3
/m
2
.d.atm. This high OTR is required, according to EP-A-471,607, because in packaging gas-emitting products, such as bleaches, a gas, typically oxygen, is evolved during storage and should be allowed to be dissipated through the pouch wall to avoid that pressure builds up into the pouch and the pouch seal breaks.
Also the structure described in EP-A-471,607 does not contain chlorine and has moisture barrier properties but it has no odor barrier properties. Furthermore, also in this case, the presence of a thick core layer of polyolefin material with a low RF sensitivity affects the RF sealability of the overall structure. It is probably due to the low seal strength of the thus obtained RF-seal that such a high OTR is needed to avoid breaking of the seal.
It has now been found that It Is possible to solve the above problems in a satisfactory way by using, as PVC replacement in the manufacture of said pillow pouches, a film comprising an RF-sealable outer layer of ethylene-vinyl acetate copolymer with from about 14 to about 28 wt. % of VA and a layer of PVDC.
The use of such a film as a PVC replacement offers many advantages as the RF-seal will have a good seal strength because the presence of a PVDC layer improves the sealability of the overall structure; it has also been found that the presence of a PVDC layer imparts to the pouch the desired balance of stiffness and flexibility so that films 75-150 &mgr;m thick can be run in the commercial VFFS machines giving a better performance than conventional 200-250 &mgr;m thick PVC films, and thus drastically reducing the amount of plastic material per package which needs to be disposed of after use; the amount of chlorine containing polymer is highly reduced as the PVDC layer will be only few micron

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