Patent Application
20110179754
The present invention relates to self-venting packaging, in particular to a method wherein a self-venting valve with a weakening stress point is provided after the filling process on ordinary packaging without a specific limitation in valve location.
The present invention is more precisely related to a method for the production of a self-venting plastic packaging for heating a food item in a microwave oven.
One of the current market trends in packaging is convenience, which is driven by the growing number of single household consumers who, for various reasons, do not want to cook any more, and the demand on ready meals that just have to be reheated is therefore constantly growing. Such ready meals are often packed in trays with a lid or in pouches.
Microwave heating is the preferred way to reheat the meals. To avoid bursting when the hermetically packed product is heated, conventional trays or pouches have to be at least partially opened or for example perforated to allow the steam to escape when the meal becomes hot and the contained water transforms to vapour.
Several valve systems integrated in the packaging (in the laminate, add-ons or additional seals) have been developed, which allows to heat for instance vegetables or ready-meals just by putting them in the microwave oven. These systems have advantages like a steam cooking effect, less humidity loss or an indication that the product is hot by the opening noise of the valve. But those systems require a particular packaging structure or packaging process.
WO 2004/048225 describes a valve system that is integrated in the laminate and opens in a non-destructive way via steam pressure building up in the pack during heating. This specific structure is obviously more expensive than an ordinary packaging.
US 2005/0276885 discloses a microwavable food item packed in a self-venting packaging where a rupturable seal is placed at various locations along the aperture. This document does not explain how the sterilisation problem can be solved without using counter-pressure, which is difficult to manage in an autoclave, in order to avoid the rupture of the rupturable seal during the sterilisation process.
EP 1 067 058 describes a steam valve on a stand-up pouch that is an additional seal with a hole in the middle. The seal is placed to the pouch in such a way that it can still be filled after the valve has been sealed. In this document, the valve is performed before it is filled to avoid seal problems due to inside contamination with content.
GB 2414226A and JP 2005187079 describe a similar valve which is an additional seal. In opposition to EP 1 067 058, the seal strength is lower and opens by peeling between the two sealing layers.
JP 2006095708 shows a 4-side sealed pouch with an additional lap seal which opens by peeling as well.
Although self-venting packs for chilled or frozen food are already well established, only very few ready-meals that are typically sterilised in an autoclave have been introduced in the market. In general, the opening pressure of the valve has to be significantly lower than the burst pressure of the pack under the same conditions, otherwise the pack would break.
To obtain a shelf-stable and safe product (commercial sterile), the temperature in an autoclave is typically higher than 121° C. (Buchner N.: Verpackung von Lebensmitteln, Berlin: Springer, 1999). To avoid that the flexible packs expand and even burst during the heat treatment, an appropriate counter-pressure has to be applied. As the water-vapour pressure in an autoclave is changing during the sterilisation cycle (heating-up, sterilisation at constant temperature and cooling), the counter-pressure has to be adjusted to avoid the blowing up and collapsing of the packs as much as possible to prevent any damage (Campden & Chorleywood Food Research Association Group: Guidelines on good manufacturing practice for heat processed flexible packaging, Guidelines No. 50, Chipping Campden: 2006).
Beside pressure control, the right filling—not too much air and/or product—as well as an appropriate positioning of the packs in the retort trays is essential as this can create uncontrolled overpressure inside the packs.
Another thermal process to produce shelf-stable products is pasteurization which is a heat treatment below 100° C. without counter pressure (Buchner N.; Verpackung von Lebensmitteln, Berlin: Springer, 1999). For some products, e.g. in case of pH<4.5, this treatment is sufficient to achieve a shelf-stable product. During heat treatment, the packed product and the air in the pack expand according to their coefficient of expansion. Depending on the amount of air and product in the pack, this expansion can open a valve applied on the pack. This is especially relevant for rigid or semi-rigid trays with a lid as there is no additional space in the pack which allows a compensation of the expansion. Typically the bottom of such trays can turn outward in case there is a pressure build up in the pack and it moves back when the tray is cooled down. Valves on such trays would not withstand the generated inside pressure.
In the light of the previous explanations, it becomes clear that there is a real need for a packaging method of microwavable food items, capable of self-venting via a rupturable weak point when heated up in a microwave oven, where the rupturable weak point is performed on the packaging after the filling and the heat treatment step of the method.
In the following description, the expression “ultrasonic seal valve” is used to describe a rupturable valve seal comprising an inside-inside seal performed by ultrasound seal technology.
The expression “inside-inside seal” or “inside against inside” is related to the seal of the inner layers of a packaging container, which are those layers in contact or potentially in contact with the food item (see
In the present invention “inside-inside seal” should be understood as a seal between the inside layer of a first panel (deep drawn tray) and an inside layer of a second panel (lid), said first and second panels being sealed together to form a self-venting packaging with a food item inside. The word “inside” means the side of the panel potentially in contact with the food item. Such an inside-inside (inside against inside) seals performed by ultrasound seal technology reduces the global thickness of the two superposed layer (see
The present invention aims to overcome the drawbacks of the prior art and provides a method for the manufacturing of an ultrasonic seal valve on ordinary filled packaging without particular valve positioning and configuration and with minimal constraints for the location of such a valve.
The present invention provides more precisely a self-venting packaging for use in heating a food item in a microwave oven, said packaging comprising a rupturable valve seal (3), said rupturable valve seal comprising an inside-inside seal performed by ultrasound seal technology, called “ultrasonic seal valve”.
The present invention discloses a method for the production of a self-venting packaging for use in heating a food item in a microwave oven, said packaging comprising a rupturable valve seal (3), said rupturable valve seal comprising an inside-inside seal, creating a weak point on said packaging, suitable to break in case of overpressure inside the packaging, said method comprising the following subsequent steps:
Particular embodiments of the present invention comprise at least one or an appropriate combination of the following features:
The safest way to prevent a damage or opening of a self-venting overpressure valve during heat treatment is to apply the valve after the heat treatment process. As already described, most valves are constructed as additional seals.
Nevertheless, after processing and filling the packaging, the inner sealing layer is heavily contaminated by the content. Additionally, in case of sterilisation and because of the high temperatures and contact with the content, the sealing properties can change. Product ingredients of the content can migrate into the sealing layer. This is the reason why usual sealing methods do not allow the production of a reliable valve seal after filling of the packaging.
A very special sealing method is ultrasonic sealing. An advantage of this technology is that it is possible to perform inside-inside seals of packaging through contaminations.
Several tests have demonstrated that the ultrasonic sealing method allows reproducible valve seals even after the sterilisation process, which was a surprise.
Apart from being able to avoid any interference with the sterilisation process, since the valve seal is performed after the sterilisation process, another advantage is that there is no limitation for the valve position which would be given if the packaging's with valve have to be filled.
By using a PS Dialog 1000 ultrasonic sealing unit (Herrmann Ultraschalltechnik), a valve seal as shown in
The laminate used for this pouch was a PETP-AlOx 12 μm/OPA 15 μm/PP 70 μm produced from aluminium oxide coated 12 μm polyester (Camclear 800) adhesive laminated (Adcote 811 with Cat F) to a 15 μm biaxially oriented polyamide (Biaxis 15) again adhesive laminated (Adcote 811/Cat F) to a 70 μm polypropylene film (Groflex 0969.000) (see layer structure of
The pouch was heated in a microwave oven at a power of 700 W. After about 1 minute and 30 seconds, the pouch started to expand and the valve opened by fracture of the laminate.
A valve seal as shown in
The pouch was heated in a microwave oven at a power of 700 W. After around 1 minute and 30 seconds the pouch started to expand and the valve opened by fracture of the laminate.
A valve seal as shown in
The pouch was heated in a microwave oven at a power of 700 W. After around 1 minute and 30 seconds, the pouch started to expand and the valve opened by fracture of the laminate.
A valve seal as shown in
The pouch was heated laying flat in a microwave oven at a power of 700 W. After around 1 minute and 15 seconds, the pouch started to expand and the valve opened by fracture of the laminate.
A valve seal as shown in
The tray was heated in a microwave oven at a power of 700 W. After around 1 minute, the tray started to expand and the valve opened by rupture of the valve seal.
The present invention shows a method allowing the production of a packaging with a steam valve after filling, and possibly after heat treatment, with limited constraint of the positioning of said valve. The described invention can also be used for semi-rigid or rigid trays and cups with a flexible lidding film by using a simple ultrasonic seal equipment rendering the complexity of add-on valve processing lines or structurally complex packaging useless.
The present invention is based on European patent application N° 08447040.0, of which priority is claimed and which is incorporated herein by reference.
| Number | Date | Country | Kind |
|---|---|---|---|
| 08447040.0 | Aug 2008 | EP | regional |
| Filing Document | Filing Date | Country | Kind | 371c Date |
|---|---|---|---|---|
| PCT/EP09/57912 | 6/24/2009 | WO | 00 | 4/18/2011 |
