WO2020112034A2

WO2020112034A2 - Susceptor film structure for packaging used with microwave ovens and packaging comprising the said susceptor film structure

Info

Publication number: WO2020112034A2
Application number: PCT/TH2019/000058
Authority: WO
Inventors: Adisak VORAKUNPINIJ; Pimumpai LEELAWAT; Juthamas MAHAJAROENSIRI; Jureeporn NANTARAGSA; Ratchaneewan CHERCHALART
Original assignee: Scg Packaging Public Co Ltd
Current assignee: Scg Packaging Public Co Ltd
Priority date: 2018-11-27
Filing date: 2019-11-08
Publication date: 2020-06-04
Anticipated expiration: 2021-05-27
Also published as: WO2020112034A3

Abstract

This invention is related to susceptor film structure for packaging used with microwave ovens which comprises at least one metalized film layer laminated to at least one polymer substrate layer characterized in that the said polymer substrate layer has the structure containing a number of voids in the range of 8 to 30 percent by volume and the thickness of film structure in the range of 75 to 150 micrometers and also related to packaging for use with microwave ovens which comprises at least one metalized film layer laminated to at least one polymer substrate layer characterized in that the said polymer substrate layer has the structure containing a number of voids in the range of 8 to 30 percent by volume and the thickness of film structure in the range of 75 to 150 micrometers.

Description

SUSCEPTOR FILM STRUCTURE FOR PACKAGING USED WITH MICROWAVE OVENS AND PACKAGING COMPRISING THE SAID SUSCEPTOR

FILM STRUCTURE

FIELD OF INVENTION

Engineering in relation to susceptor film structure for packaging used with microwave ovens and packaging comprising the said susceptor film structure

BACKGROUND OF INVENTION

At present, consumers prefer to use microwave ovens to heat or to cook foods. This leads to more convenience, particularly, for use with ready-to-eat foods which requires less time to heat when compared to the time required for fresh cooking. In this regard, heating food in a microwave oven is considered as a closed system which normally makes food being dry from vaporized moisture then food becomes crispy such as baked breads and pies. However, condensed water inside a microwave rewets the surface of such foods thereby reducing the intended crispiness.

Therefore, there are attempts in developing food packaging for use with microwave ovens with the intention to solve the issues where the food texture becomes too dried or too wet. These include the development of packaging that allows microwaves to partially penetrate to foods and the partial heat can still be accumulated at the surface of packaging. The said heat will transfer to food texture thereby making the texture dried, not soggy, and crispier.

One type of packaging preferred for development with the aforementioned objectives includes packaging having a structure or composition of susceptor film which comprises a substrate layer, generally made from paper, and a metalized film layer such as polyethylene terephthalate. The said packaging may have holes positioned partially on the packaging used to allow steam to vaporize from the packaging or have material layers which can absorb moisture from the food being heated in the microwave ovens.

Examples of the inventions regarding the development of susceptor film structures or packaging having susceptor film structures are as per the following:

The PCT application, publication number W02010/033561 A2, disclosed the structure of paper packaging used for heating dough bakery products in microwave ovens. The box and the wall parts of the said packaging were made from susceptor which is microwave interactive material having the thickness of 100 angstroms and optical density of approximately 0.15 to 0.35. The said packaging structure made from paper has a disadvantage in which the packaging is not firmly closed to the food. When heating the food, the heat may not be uniformly distributed and there may be certain areas that are not crispy or brown when compared to other areas.

U. S. patent No. 5,177,332 disclosed wrapping material having a layered structure for wrapping food to be heated in microwave ovens in order to make the food crispy and the food surface brown. The wrapping materials contained heat-stable and heat-resistance film layers. Both layers could be made from polyethylene terephthalate. The thickness of each layer started from

26 micrometers and the shrinkage of material layers in any direction was not more than around 20 percent This invention does not disclose the specific range of material thickness suitable for use.

U. S. patent no. 9,073,689 disclosed the microwave interactive structure comprising support film laminated to the polymer film via tie layer, susceptor film, and adhesive layer. There was an addition of a blowing agent in the tie layer for creating an air space in the said layer when heated susceptor packaging in a microwave oven Because moisture in the supporting layer being heated and evaporated by susceptor and causing the gas in the adhesive layer. However, the said air space created in the tie layer may affect and reduce the strength of the adhesions between layers thereby leading to the delamination of each layer.

It has been seen that the above example inventions do not intend to develop susceptor film structures that can be effectively used and still maintain the good external appearance of film susceptor. Specifically, when reheated food in a microwave oven, the foods obtained from the procedure are crispy with suitable browning surfaces, not soggy or soaked wet. Moreover, the susceptor film has less shrinkage after heated in a microwave oven.

SUMMARY OF THE INVENTION

Therefore, the objective of this invention is to provide susceptor film structure for packaging to be used with microwave ovens and packaging comprising the said susceptor film structure that can solve the issue of non-closed contact with food and the loss of crispiness of the food surface when heated in microwave ovens. The susceptor film structures according to this invention are firmly closed to the food surface. This allows consistent heat transfer thereby making food surfaces uniformly crispy, making the texture dried, and not soggy or soaked wet.

The other obj ective of this invention is to provide the susceptor film structure having good dimensional stability without distortion or shrinkage or being shortened when used with microwave ovens. More specifically, the size of susceptor film structure does not change or slightly changes without affecting the external appearance of the said film or causing the same to be unacceptable. The ability to maintain the dimension of susceptor film structure leads to have the good appetizing packaging having the said film structure even when used with microwave ovens. Thus, this will promote the products’ image, create customer satisfaction and enhance the increasing sale volume.

One aspect of this invention is related to susceptor film structure for packaging used with microwave ovens comprising at least one metalized film layer laminated to at least one polymer substrate layer characterized in that the said polymer substrate layer has the structure containing a number of voids in the range of 8 to 30 percent by volume and the thickness of film structure in the range of 75 to 150 micrometers.

The other aspect of this invention is related to packaging used with microwave ovens comprising at least one metalized film layer laminated to at least one polymer substrate layer characterized in that the said polymer substrate layer has the structure containing a number of voids in the range of 8 to 30 percent by volume and the thickness of film structure in the range of 75 to 150 micrometers.

Susceptor film structure and packaging according to this invention can be used with various types of food products such as bakery or baked dough product or ready-to-eat food which require a dried crispy food texture without soggy or soaking wet when reheated in microwave ovens.

BRIEF DESCRIPTIONS OF THE DRAWINGS

Figure 1 shows the cross- sectional view of the example of susceptor film structure according to one embodiment of this invention.

Figure 2 shows the cross- sectional view of the example of susceptor film structure according to the other embodiment of this invention.

Figure 3 shows the shrinkage of the example of susceptor film structure after being heated with a microwave oven.

Figure 4 shows graph demonstrating the shrinkage of susceptor film structure according to one embodiment of this invention and the comparative examples. DETAILED DESCRIPTIONS OF THE PREFERRED EMBODIMENTS

The interpretations in relation to any characteristics as shown herein cover the applications of the same to the other characteristics of this invention except otherwise specified.

Any technical terms and scientific terms as used herein are defined based on the understandings of the persons skilled in the arts except otherwise specified.

Throughout this invention, the words“approximate” are used to indicate that any values shown or appeared herein may vary or deviate in which such variations or deviations are caused by equipment errors or the methods used for determining various values.

The terms“consisting’,“comprising’,“having’ and“including’ are open-ended verbs such as any method“consisting’,_“comprising’,“having’ and_“including_’ one component or a plurality of components or one step or multiple steps. This is not limited to one or multiple components or steps and also include components or steps that are not specified.

Any equipment, apparatus, method, material, or chemical substance described herein, except otherwise specified, means equipment, apparatus, method or material or chemical substance commonly used or operated by persons skilled in the arts.

All the components and/or methods disclosed and claimed in this invention are intended to cover the characteristics of the invention obtained through actions, operations, modifications, or any changes of variables obtained without significant difference when compared to the experiments according to this invention and such characteristics cause the same effects as those of this invention. Based on the opinions of the persons skilled in the arts, even if there is no specific identification in the claims, the equivalents or resemblances of this invention including the slight modifications or changes that are clearly obvious to persons skilled in the arts should be considered to fall within the objectives, scopes, and concepts of this invention.

Definitions

The term“structure having a number of voids_” used herein refers to the characteristic of polymer substrate having a number of voids which cover a plurality of cavity, pore, porous infiltrated in the polymer texture. Such voids may have the same or different shapes or patterns without limitation. Such voids may also be connected or separated without connections.

The description in more detail regarding this invention will now be provided with reference to the experiments without any limitation to the scope of invention. One aspect of this invention is related to susceptor film structure for packaging used with microwave ovens comprising at least one metalized film layer laminated to at least one polymer substrate layer characterized in that the said polymer substrate layer has the structure containing a number of voids in the range of 8 to 30 percent by volume and the thickness of film structure in the range of 75 to 150 micrometers.

Susceptor film structure according to this invention has a number of voids in the range of 8 to 30 percent by volume. This provides good effects to the property of susceptor films when the said films are used for packaging. Such effects include the ability to maintain dimension when heated in microwave ovens without too much shrinkage or distorting or damaged when heated. In this regard, a number of optimum voids in the polymer substrate structure affects the thermal resistance and strength properties of the susceptor film structure; more specifically, in the case that the polymer substrate does not have the structure containing a number of voids, when heated, the said susceptor film structure will shrink to the extent that the shrinkage is too much and the package cannot be acceptable. In the same manner, polymer substrate having a number of voids that is too low such as less than 8 percent by volume, will not affect the original strength or provide a slight increase to the original strength of susceptor polymer structure thereby making the susceptor film structure shrink and unable to maintain the shape when used at high levels of heat. Such film structure therefore cannot be used as intended. Also, in the case that a number of voids in the polymer substrate structure is too high, for example, more than 30 percent by the volume, it will reduce the strength of susceptor film structure and easily cause a poor bonding and delamination, particularly, when a number of voids in the polymer substrate structure is significantly high such as more than 50 percent by volume. This will significantly reduce the strength of susceptor film structure. The susceptor film structure will become cracking, easily debonding, and not able to support the weight of products or corresponding force caused by the said products intended to be contained and heated.

Susceptor film structure according to this invention has the suitable unrestrained linear shrinkage in the machine direction (MD) in the range of 1.2 to 3.0 percent and in the transverse direction (TD) in the range of 1.2 to 2.2 percent when measured at the temperature of 140 to 160 degree Celsius for 30 minutes according to ASTM D 2732-96. Suitable polymer substrate layer according to this invention has thermal shrinkage in the machine direction (MD) less than 1.5 percent and in the transverse direction (TD) less than 1.2 percent when measured at 150 degree Celsius for 30 minutes according to ASTM D 2732-96.

Susceptor film structure may comprise at least one skin layer laminated to polymer substrate layer wherein the said skin layer has the thickness in the range of 2 to 10 micrometers, preferably, 4 to 9 micrometers. In this regard, the skin layer may be performed with the addition of additives, corona treatment, or plasma treatment.

Preferably, polymer substrate layer and skin layer are made of polyethylene terephthalate.

According to this invention, metalized film layer has the optical density in the range of 0.2 to 0.4, preferably 0.3 to 0.4 and has unrestrained linear shrinkage in the machine direction

(MD) less than 2.2 percent and in the transverse direction (TD) less than 0.4 percent when measured at 150 degree Celsius for 30 minutes according to ASTM D1204.

Metalized film layer comprises films metalized with metal selectable from aluminum, chromium, copper, iron, magnesium, nickel, stainless steel, tin, titanium, tungsten, nickel- chromium-molybdenum alloy with niobium, oxide metal or combination thereof

Preferably, metalized film layer is biaxial oriented polyethylene terephthalate metalized with aluminum.

More preferably, susceptor film structure comprises at least one adhesive layer which adheres metalized film layer and polymer substrate layer together and/or adheres each polymer substrate layer together and/or adheres each metalized film layer together.

Adhesive layer according to this invention is the water-based acrylic emulsion adhesive, water- based acrylic pressure sensitive adhesive, or polyurethane adhesive.

In a more specific embodiment according to this invention, adhesive layer is a water-based acrylic emulsion adhesive or polyurethane in which the weight of each layer is in the range of 2 to 30 grams per square meter. For the adhesive layer which is the water-based acrylic pressure sensitive adhesive, the weight of each layer is in the range of 10 to 25 grams per square meter.

Susceptor film structure according to this invention is, preferably, susceptor film structure for food packaging used with microwave ovens and food that contains water in the range of 35 to 65 percent by weight. Figures 1 and 2 show the examples of the arrangement of susceptor film structure according to this invention. Figure 1 shows the examples of susceptor films structure according to the first embodiment which comprises skin layer 1 laminated to polymer substrate layer 2 having a number of voids 3, adhesive layer 4 and metalized film layer 5 laminated to metal layer 51 metalized on polymer film surface 52.

Figure 2 shows the examples of susceptor film structure according to second embodiment which comprises two polymer substrate layers 2, each laminated to surface layer 1 and having adhesive layer 4 positioned between said surface layer 1 and metalized layer 5 comprising metal layer 51 which is metalized on surface of polymer film 52 with the adhesive layer 4 arranged between surface layer 1 and metalized layer 5 for adhering two layers together.

The second embodiment is related to the packaging for use with microwave oven which comprises susceptor film structure having the special characteristics as described above.

Packaging according to this invention contains a seal with a steam venting port to release steam occurred during warming or heating using microwave ovens or forming as a sleeve with the opening port or opening ends to release steam occurred during warming or heating using microwave ovens.

Packaging according to this invention can be used with food products and various bakery or dough baked products that require crispy foods surface and textures that are drier and not soggy after being heated in microwave ovens. The examples of such products include cooked foods such as chicken nuggets and bakery, breads, pies, pastry. More specifically, this invention is suitable for food having water in the amount of 35 to 65 percent by weight.

The experiment examples

The experiment was conducted to compare the performances of susceptor film structures in respect to quality of food after being heated in microwave ovens.

In the experiment, the food samples were obtained from 4 sales sources in which the amount of water is indicated in the Table 1.

Table 1

Additionally, in the study of the effects in relation to various variables including type and amount of adhesive, level of optical density of metalized film layer, structure of polymer substrate layer having a number of voids and thickness including the arrangement of each layer being components of susceptor film structure, the experiment was conducted using the sample metalized film layer made of biaxial oriented polyethylene terephthalate which was metalized with aluminum and skin layer and polymer substrate layer which were made of polyethylene terephthalate.

The study of types of suitable adhesive

The study was conducted by laminating the sample metalized film sheet having the thickness of 12 micrometers to the sample polymer substrate sheets having the thickness of 50 and 75 micrometers using various types of adhesives and heating the same with microwave ovens using the power of 850 watts for 120-180 seconds. This is to compare the physical characteristics that can be observed from the said samples. The results of the experiment are shown in Table 2.

Table 2

From the experiment, it was found that the adhesive being polyurethane (sample No. 2), water based acrylic emulsion adhesive (sample No. 3) and water-based acrylic pressure sensitive adhesive ₍sample No. 4) were the suitable adhesives as they were able to provide good adhesion between the metalized film and the polymer substrate layer, even after being heated by microwave ovens.

The study of suitable optical density of metalized film layer

The study was conducted by laminating the sample metalized film sheet having various levels of optical densities to the substrate layer being polyethylene terephthalate using water based acrylic emulsion adhesive. Thereafter, the sample sheets prepared were used for wrapping bread coated with butter on both surfaces and the said wrap was heated by a microwave oven using the power of 850 watts for 75 seconds. The results of the experiment are shown in Table 3.

Table 3

From the experiment in table 3, it was found that the film samples comprising the sample metalized film No. 1 and 2 having the optical densities in the ranges as shown in the table were efficient to generate the crisping and browning surface of bread when heating in a microwave oven

The analysis of a number of voids in the structure of polymer substrate layer

The experiments were conducted to determine a number of optimum voids in the polymer substrate structure by bringing polymer substrate samples according to this invention, then cross- sectional cutting the same and taking an image using scanning electron microscope (SEM) JEOL model JSM-6490LV configured with the magnification level of 1000 times.

Thereafter, the cross-sectional image was used for calculating the void areas by comparing the areas of all the polymer substrate samples. The calculation of the void areas in the polymer substrate was conducted by using the image analysis techniques having the following procedure

• Adjust the color intensities in the image to the same

• Dissect image areas into 5 areas for analyzing the percentage of void area according to Z-direction

• Specify the color intensity level for the void and use Image J software to count the number of all the void areas.

From the aforementioned analysis, it was found that the sample polymer substrate according to this invention had a number of voids in the polymer substrate structure in the range of 10 to 20 percent by volume.

The study of suitable polymer substrate layer

The experiment was conducted to compare the properties in the aspects of food quality and the ability to maintain the dimension of the susceptor film structure or packaging when heated in microwave ovens. The comparisons at various thicknesses of polymer substrate layer were made between the susceptor film structure or packaging comprising polymer substrate layer in the type of polyethylene terephthalate having structure containing a number of voids according to this invention and the susceptor film structure or packaging comprising polymer substrate layer in the type of polyethylene terephthalate without the structure containing a number of voids.

Details of the preparations of susceptor film structure are following:

• Preparing sample susceptor film structure consisted of a metalized film sheet (mPET) having the OD of 0.30-0.38 and the thickness of 12 micrometers laminating to a polymer substrate sheet in the type of polyethylene terephthalate (PET) according to this invention which contains a number of voids (sample No. 1-3 in the Table 5) or the polymer substrate sheet being comparative examples without having a number of voids in the structure (sample No.4 and 5 in the Table 5) by using water-based acrylic emulsion adhesive and drying in the temperature of 100- 110 degree Celsius. Two types of multilayer susceptor film lamination structure are. Type PET//mPET Laminating polymer film substrate layer to the metalized film layer with adhesives

Type PETl//PET2//mPET Laminating the first polymer film substrate layer to the second polymer film substrate layer using adhesives and laminating the second polymer film substrate layer to the metalized film layer with adhesives.

• Using susceptor films structure from above description prepared for wrapping pies in the manner that the metalized film layer was closely attached to pie surface.

Thereafter, heating the same using a microwave oven at the power of 850 watts for 180 seconds and

• Observing the characteristics of pie and surfaces of susceptor film structure, then measuring the obtained dimension

Table 4

From the experiments in the table 4, it was found that the structure of polymer substrate layer having a number of voids and overall thickness according to the ranges specified in this disclosure was able to provide a better ability to the susceptor film structure in maintaining the dimension. More specifically, polymer substrate layer was only slightly shrunk after being heated in microwave ovens. When compared to the polymer substrate layer without voids in the structure, as seen from the sample No. 2, the susceptor film structure comprising polymer substrate layer having a number of voids in the structure and the overall thickness of 75 micrometers were slightly shrunk (as shown in Figure 3b) and the shrinkage was not found in the sample No.3 having the overall thickness of polymer substrate layer of 150 micrometers.

In example 1, for the susceptor film structure comprising polymer substrate layer having a number of voids in the structure and thickness of 50 micrometers, substantial shrinkages were observed (as shown in Figure 3a). In samples No. 4 and 5, for the susceptor film structure comprising polymer substrate layer without voids in the structure, substantial and significant shrinkages were observed (as shown in Figure 3 c as per example No.5 in table 4) respectively. The study of heat conduction and thermal resistivity of susceptor film structure

The study of heat conduction and thermal resistivity of the three samples of the susceptor film structures was conducted according to the table 5

Table 5

The unrestrained linear shrinkages of the sample susceptor films according to the table 5 were measured both in the machine direction (MD) and the transverse direction (TD) at the temperatures between 140-160 degree Celsius and the experimental results are shown in the table 6 and the figure 4a, 4b.

Table 6

From the experiments as per table 6 and figure 4, it was found that, from the temperature of 150 degree Celsius, susceptor film using polymer substrate without voids in the structure (sample No. 3) was significantly shrunk at the level higher than the polymer substrate film having a number of voids (samples No.1 and 2) which are the sample susceptor films according to this invention. BEST MODE

As disclosed in the detailed descriptions of the preferred embodiments.

Claims

1. Susceptor film structure for packaging used with microwave ovens comprising at least one metalized film layer laminated to at least one polymer substrate layer characterized in that the said polymer substrate layer has the structure containing a number of voids in the range of 8 to 30 percent by volume and having the overall thickness of film structure in the range of 75 to 150 micrometers.

2. Susceptor film structure according to claim 1 wherein unrestrained linear shrinkage in the machine direction ₍MD) is in the range of 1.2 to 3.0 percent and in the transverse direction

₍TD) is in the range of 1.2 to 2.2 percent when measured at the temperature of 140 to 160 degree Celsius for 30 minutes.

3. Susceptor film structure according to claim 1 wherein thermal shrinkage of the polymer substrate layer in the machine direction (MD) is less than 1.5 percent and in the transverse direction (TD) is less than 1.2 percent when measured at the temperature of 150 degree Celsius for 30 minutes.

4. Susceptor film structure according to claim 1 wherein the said structure further comprises at least one skin layer laminated to the polymer substrate layer.

5. Susceptor film structure according to claim 4 wherein the skin layer has the thickness in the range of 2 to 10 micrometers, preferably 4 to 9 micrometers.

6. Susceptor film structure according to claim 4 or 5 wherein the skin layer is performed with the addition of additives, corona treatment or plasma treatment.

7. Susceptor film structure according to any of the claims 1, 3, to 6 wherein the polymer substrate layer and the skin layer are made of polyethylene terephthalate.

8. Susceptor film structure according to claim 1 wherein the optical density of the metalized film layer is in the range of 0.2 to 0.4, preferably 0.3 to 0.4.

9. Susceptor film structure according to claims 1 or 8 wherein unrestrained linear shrinkage of the metalized film layer in the machine direction (MD) is less than 2.2 percent and in the transverse direction (TD) is less than 0.4 percent when measured at the temperature of 150 degree Celsius for 30 minutes.

10. Susceptor film structure according to any of claims 1, 8, or 9 wherein the metalized film layer comprises films metalized with metal selectable from aluminum, chromium, copper, iron, magnesium, nickel, stainless steel, tin, titanium, tungsten, nickel- chromium- molybdenum alloy with niobium, oxide metal or combination thereof.

11. Susceptor film structure according to any of claims 1 , 8, to 10 wherein the metallized film layer is biaxial oriented polyethylene terephthalate metalized with aluminum.

12. Susceptor film structure according to claim 1 wherein the said structure further comprises at least one adhesive layer which adheres metalized film layer and polymer substrate layer together and/ or adheres each polymer substrate layer together and or adheres each metalized film layer together.

13. Susceptor film structure according to claim 12 wherein adhesive is water-based acrylic emulsion adhesive, water- based acrylic pressure sensitive adhesive, or polyurethane adhesive.

14. Susceptor film structure according to claim 13 wherein the weight of each water-based acrylic emulsion adhesive layer is in the range of 2 to 30 grams per square meter.

15. Susceptor film structure according to claim 13 wherein the weight of each water-based acrylic pressure sensitive adhesive layer is in the range of 10 to 25 grams per square meter.

16. Susceptor film structure according to any of claims 1 to 15 for food packaging used with microwave ovens wherein foods containing water component in the amount of 35 to 65 percent by weight.

17. Packaging for use with microwave oven comprising the susceptor film structure according to any of claim 1 to 16.

18. Packaging for use with microwave ovens according to claim 17 wherein said packaging contains a seal with an opening port for releasing steam occurred during heating in microwave ovens.

19. Packaging for use with microwave ovens according to claim 17 wherein said packaging comprises a sleeve with the opening port and/or opening ends for releasing steam occurred during heating in microwave ovens.

20. Packaging for use with microwave ovens comprising the susceptor film structure comprising at least one metalized film layer laminated with at least one polymer substrate layer characterized in that the said polymer substrate layer has the structure containing a number of voids in the range of 8 to 30 percent by volume and having the overall thickness of film structure in the range of 75 to 150 micrometers.

21. Packaging according to claim 20 wherein the susceptor film structure has the machine direction (MD) unrestrained linear shrinkage in the range of 1.2 to 3.0 percent and the transverse direction (TD) unrestrained linear shrinkage in the range of 1.2 to 2.2 percent when measured at the temperature of 140 to 160 degree Celsius for 30 minutes.

22. Packaging according to claim 20 wherein thermal shrinkage of the polymer substrate layer in the machine direction (MD) is less than 1.5 percent and in the transverse direction (TD) is less than 1.2 percent when measured at the temperature of 150 degree Celsius for 30 minutes.

23. Packaging according to claim 20 wherein the said packaging further comprises at least one skin layer laminated to the polymer substrate layer.

24. Packaging according to claim 23 wherein the skin layer has the thickness in the range of 2 to 10 micrometers, preferably 4 to 9 micrometers.

25. Packaging according to claim 23 or 24 wherein the skin layer is performed with the addition of additives, corona treatment or plasma treatment.

26. Packaging according to any of the claims 20, 22 to 25 wherein the polymer substrate layer and the skin layer are made of polyethylene terephthalate.

27. Packaging according to claim 20 wherein the optical density of the metalized film layer is in the range of 0.2 to 0.4, preferably 0.3 to 0.4.

28. Packaging according to claim 20 or 27 wherein unrestrained linear shrinkage of the metalized film layer in the machine direction (MD) is less than 2.2 percent and in the transverse direction (TD) is less than 0.4 percent when measured at the temperature of 150 degree Celsius for 30 minutes.

29. Packaging according to any of claims 20, 27, to 28 wherein the metalized film layer comprises films metalized with metal selectable from aluminum, chromium, copper, iron, magnesium, nickel, stainless steel, tin, titanium, tungsten, nickel-chromium-molybdenum alloy with niobium, oxide metal or combination thereof.

30. Packaging according to any of claims 20, 27, to 29 wherein the metallized film layer is biaxial oriented polyethylene terephthalate metalized with aluminum.

31. Packaging according to claim 20 wherein the said packaging further comprises at least one adhesive layer which adheres metalized film layer and polymer substrate layer together and/or adheres each polymer substrate layer together and or adheres each metalized film layer together.

32. Packaging according to claim 31 wherein adhesive is water based acrylic emulsion adhesive, water based acrylic pressure sensitive adhesive or polyurethane adhesive.

33. Packaging according to claim 32 wherein the weight of each water-based acrylic emulsion adhesive layer is in the range of 2 to 30 grams per square meter.

34. Packaging according to claim 32 wherein the weight of each water-based acrylic pressure sensitive adhesive layer is in the range of 10 to 25 grams per square meter.

35. Packaging according any of claims 20 to 34 wherein said packaging is used for foods containing water component in the amount of 35 to 65 percent by weight.

36. Packaging according to any of the claims 20 to 35 wherein said packaging contain a seal with an opening port for releasing steam occurred during heating in microwave ovens.

37. Packaging according to any of the claims 20 to 35 wherein said packaging comprises a sleeve with the opening port and or opening ends for releasing steam occurred during heating in microwave ovens.