Patent Application
20120225227
The present invention relates in general to films, and more particularly, to multi-layer high temperature films, and liners and bags formed from such films. Embodiments of the present invention are particularly well suited, but in no way limited, to food cooking applications, such as meat cooking bag applications.
Current commercially available copolyester thermoplastic elastomers (e.g., COPE or TPE-E) materials that are suitable for meat cooking bag applications can be safely used at cooking temperatures up to 350 degree F. Degradation of materials occurs over time at higher cooking temperatures. Bags made from these resins may be FDA certified, may be tough (i.e., resistant to tear), may have low meat adhesion, and may be heat sealable. Limitations for bags made from these resins are: (a) high gas permeability (e.g., bags can't hold a vacuum); and (b) missed market segments where temperatures up to 400 degree F. are required.
Cooking bags may also be made from biaxially oriented PET film (also referred to as polyester homopolymer film) (e.g., Mylar® from DuPont). This material may hold up to 400 degree F. cooking temperatures, may hold a vacuum, and may be FDA certified. However, limitations of bags made from these materials include: weaknesses, including poor resistance to tear; and difficult sealability.
A recent development is the discovery of a higher heat resistant copolyester thermoplastic elastomer (e.g., Arnitel® by DSM) that is suitable for 400 degree F. cooking. It possesses the attributes listed above, except for its high gas permeability which prevents its use where food is to be stored under vacuum.
At present, there is an unsatisfied market segment that requires a multi-layer film and cooking bag having the following attributes:
suitable for 400 degree F.;
FDA certified for 400 degree F. food cooking use;
good toughness and tear resistance;
low adhesion to meat (bag won't stick to meat upon cooking);
easy to heat seal with strong seal strengths;
hold a vacuum for extended time periods.
Embodiments of the present invention address and overcome the above shortcomings and drawbacks, by providing multi-layer high temperature films that: are suitable for 400 degree F.; are FDA certified for 400 degree F. food cooking use; have good toughness and tear resistance; have low adhesion to meat; are easy to heat seal with strong seal strength; and are capable of holding a vacuum for extended time periods. This technology is particularly well-suited for, but by no means limited to, food service applications including for example, high temperature cooking of meats. Embodiments of the present invention also include liners, such as pan liners, made from such multi-layer high temperature films. Further embodiments of the present invention are directed to high temperature cooking bags comprised of multi-layer high temperature films that are capable of fully satisfying all of the above needs and requirements.
According to one embodiment of the invention, a three layer film structure is disclosed. The three layer film structure comprises: a straight crystalline polyethylene terephthalate (PET) film; an amorphous polyethylene terephthalate (APET) layer; and a higher heat resistant copolyester thermoplastic elastomer (COPE) layer. The APET layer is located between and connects the COPE layer and the PET layer. In one embodiment, the APET layer is a co-extruded APET layer and the COPE layer is an extrusion coated COPE layer.
According to one aspect of the invention, the first layer of copolyester thermoplastic elastomer (COPE) film is melt extrusion coated onto the second layer of amorphous polyethylene terephthalate (APET) film.
According to another aspect of the invention, the straight crystalline polyethylene terephthalate (PET) layer and the amorphous polyethylene terephthalate (APET) layer comprise a co-extruded, biaxially oriented, polyester homopolymer film. In some embodiments, the heat resistant copolyester thermoplastic elastomer (COPE) layer is melt extrusion coated onto the amorphous polyethylene terephthalate (APET) side of the co-extruded, biaxially oriented, polyester homopolymer film, thereby forming a three layer film.
According to another embodiment of the invention, a five layer film structure is disclosed. The five layer film structure comprises: a clear PET film, a co-extruded APET layer; an extrusion coated higher heat resistant COPE layer; a co-extruded APET layer; and a clear PET film. This exemplary five layer film structure may comprise: a middle layer comprising a copolyester thermoplastic elastomer (COPE) film; a first intermediate layer comprising an amorphous polyethylene terephthalate (APET) film, a first side of the first intermediate layer connected to a first side of the middle layer; a first outer layer comprising a straight crystalline polyethylene terephthalate (PET) film, a first side of the first outer layer connected to a second side of the first intermediate layer; a second intermediate layer comprising an amorphous polyethylene terephthalate (APET) film, a first side of the second intermediate layer connected to a second side of the middle layer; and a second outer layer comprising a straight crystalline polyethylene terephthalate (PET) film, a first side of the second outer layer connected to a second side of the second intermediate layer.
According to another embodiment of the invention, another five layer film structure is disclosed. This embodiment of the five layer film structure comprises: an extrusion coated higher heat resistant COPE layer; a co-extruded APET layer; a clear PET film, a co-extruded APET layer; and an extrusion coated higher heat resistant COPE layer. This exemplary five layer film structure may comprise: a middle layer comprising a straight crystalline polyethylene terephthalate (PET) film; a first intermediate layer comprising an amorphous polyethylene terephthalate (APET) film, a first side of the first intermediate layer connected to a first side of the middle layer; a first outer layer comprising a copolyester thermoplastic elastomer (COPE) film, a first side of the first outer layer connected to a second side of the first intermediate layer; a second intermediate layer comprising an amorphous polyethylene terephthalate (APET) film, a first side of the second intermediate layer connected to a second side of the middle layer; and a second outer layer comprising a copolyester thermoplastic elastomer (COPE) film, a first side of the second outer layer connected to a second side of the second intermediate layer. This five layer film structure results in a balanced structure that is well suited for heat sealing and facilitates formation of bags having a gusseted bottom.
Additional features and advantages of the invention will be made apparent from the following detailed description of illustrative embodiments that proceeds with reference to the accompanying drawings.
The foregoing and other aspects of the present invention are best understood from the following detailed description when read in connection with the accompanying drawings. For the purpose of illustrating the invention, there is shown in the drawings embodiments that are presently preferred, it being understood, however, that the invention is not limited to the specific instrumentalities disclosed. Included in the drawings are the following Figures:
The above problems in the prior art have motivated the creation of a multi-layer high temperature film having the characteristics of: being suitable for use in 400 degree F. temperature applications; being FDA certified for 400 degree F. food cooking use; having good toughness and tear resistance; exhibiting low adhesion to meat; being easy to heat seal with resultant strong seal strengths; holding a vacuum for extended time periods (low gas permeability). In addition, embodiments of the present invention are directed to liners, such as pan liners, made from such multi-layer high temperature films. Other embodiments are directed to cooking bags made from such multi-layer high temperature films.
As used herein, the following terms have the following meaning. Good toughness and tear resistance means having a Tear Propagation Force greater than about 100 gms-force and Ultimate Tensile Elongation greater than about 50%. Low adhesion to meat means substantially no meat or meat protein visually sticking or adhering to the film after it is stripped away from the meat after cooking at 400 degree F. for two hours or more. Easy to heat seal means the film has at least a 25 degree F. heat seal window, heat seal window being defined as the spread between the lowest temperature and highest temperature at which the film can be heat sealed. Resultant strong seal strengths means greater than about 6.0 lbs-force/in. Holding a vacuum may be measured by heat sealing, for example, a whole chicken under vacuum in a bag formed from a multi-layer film according to embodiments of the invention, and after one month the bag is still under vacuum as determined visually by trying to pull the bag away from the chicken. Extended time periods means about three weeks or more.
In one embodiment, multi-layer, high temperature film 10 comprises: a high heat resistant copolyester thermoplastic elastomer layer 12; and a commercially available co-extruded, biaxially oriented, polyester homopolymer film 14 comprising one layer that is straight crystalline PET layer 18 and another layer that is amorphous PET (APET) 16. The PET and APET layers naturally adhere to each other when coextruded together. In one embodiment, the multi-layer, high temperature film 10 is produced by melt extrusion coating the high heat resistant copolyester thermoplastic elastomer (COPE) layer 12 onto the amorphous PET side 16 of the co-extruded, biaxially oriented, polyester homopolymer film 14, thereby forming a three layer film 10.
Table 1 shows preferred materials and layer thickness ranges for the three layer film embodiment of
2nd Layer
The copolyester thermoplastic elastomer (COPE) layer 12 generally has the characteristics of: high temperature, high heat resistant, 400 degree F. cooking, non-stick to food, FDA certified for food content applications, good toughness, and good sealability. The straight crystalline PET layer 18 generally has characteristics of: good barrier properties that allow the multi-layer film to hold a vacuum, and avoids seal stretch (since the PET layer 18 generally has a melting point about 500 degree F. it does not melt during the heat seal process, whereas the COPE layer 12 has a melting point closer to about 410 degrees F. and melts to form the seal having good adhesion without melting of the PET layer 18).
For example, during heat sealing the multi-layer film may be folded such that the COPE layer 12 is in contact with the COPE layer 12 on the inside of the fold, and the PET layer 18 is on the outside of the folded film. Then, a heat seal may be applied to the exterior layer—i.e., the PET layer 18—which transmits the heat through the film and causes the two COPE layers 12 to melt together and heat seal (while the PET layer 18 having a higher melting point does not melt). This helps avoid stretching in the seal and helps ensure a good/strong seal.
The amorphous PET 16 layer serves to bond the COPE layer 12 and the PET layer 18. The amorphous PET 16 layer has a broad softening range around 400 degree F. (e.g., non-crystalline in a temperature range below and above 400 degree F.), which prevents this layer from being used on its own as the outside layer of a heat sealed film.
Table 2 shows alternative compositions and layer thickness ranges for alternative embodiments of a three layer high temperature film similar to the embodiment of
2nd Layer
After exiting the die system 34, the COPE layer 12 feeds into opposing nip rollers 36, 38. As shown, the nip rollers may include an upper nip roller 36 and a lower nip roller 38. In the illustrated embodiment, the upper nip roller 36 rotates clockwise (arrow 36a) and the lower nip roller 38 rotates counterclockwise (arrow 38a). The nip rollers 36, 38 may be heated nip rollers.
As shown in
As shown, a heating device 40 may be positioned proximate the upper nip roller 36 to heat the polyester homopolymer film 14 and its co-extruded APET layer 16. The heating device 40 may include an IR heating lamp.
As shown in
Conventional corona discharge equipment may be used including, for example, a high-frequency power generator, a high-voltage transformer, a stationary electrode, and a treater ground roll. The corona treatment system 42 converts standard utility electrical power into higher frequency power which is then supplied to the treater station. The treater station applies this power through ceramic or metal electrodes over an air gap onto the film surface.
In some embodiment, the surface treatment system 42 may include ozone treatment to improve the bonding characteristics of the films. For example, adhesion between the polymer films—i.e., the COPE layer 12 and the APET layer 16—may be enhanced by treating the surface of the films with ozone before the two films are brought together. Other embodiments may include a surface treatment system 42 having both corona and ozone treatment.
Alternatively, the multi-layer high temperature film may be formed using co-extrusion techniques.
The multi-layer film structure of
Table 3 shows preferred materials and layer thickness ranges for the five layer film embodiment of
Table 4 shows alternative compositions and layer thickness ranges for alternative embodiments of a five layer high temperature film similar to the embodiment of
The embodiment illustrated in
Table 5 shows preferred materials and layer thickness ranges for the five layer film embodiment of
Table 6 shows alternative compositions and layer thickness ranges for alternative embodiments of a five layer high temperature film similar to the embodiment of
Embodiments of the present invention are directed to bags made from such multi-layer high temperature films illustrated and described with reference to
In some embodiments, the bottom of the bag may be formed having a gusset 58. In some embodiments, the sides of the bag may be formed into a gusset (not shown). The gusset 58 may be formed using heat seal techniques.
In addition, embodiments of the present invention are directed to liners made from such multi-layer high temperature films illustrated and described with reference to
Working example of one embodiment of a new extrusion coated multi-layer film:
An exemplary three layer film was produced by melt extrusion coating a high heat resistant copolyester thermoplastic elastomer (COPE) (e.g., Arnitel® X06111) onto an amorphous PET (APET) side of a co-extruded, biaxially oriented, polyester homopolymer film comprising one layer that is straight crystalline PET and another layer that is APET (e.g., Mylar® 850H film). In this example, the Arnitel® X06111 layer was an approximately 1.92 mils in thickness and the Mylar® 850H was an approximately 0.48 mil film, which produced a three layer structure having a total film thickness of approximately 2.4 mils. See e.g.,
Experimental Results for Exemplary Cooking Bag Trials:
Bag Preparation and Cooking Procedures:
Several cooking bags were prepared using a new extrusion coated three layer film structure, as described above with reference to
Cooking Results:
The cooked chickens browned appropriately and the bags did not show any signs of deterioration due to cooking at oven temperatures between 400 degree F. and 410 degree F. for approximately 2 hours. There was no meat adhesion onto the bag surfaces. The seals were still strong and no leaks were observed. Also, there was no delamination between any of the layers of the multi-layered film.
Physical Testing Results on Films:
As illustrated in the Table of
As also shown in the Table of
Still further, the new extrusion coated three layer film structure exhibits excellent seal strength properties and is easy to seal over a broad seal temperature window. The sealability and seal strength properties of the new extrusion coated three layer film are similar to the mono-layer Arnitel® X06111 film.
Importance of Heat Activated Layer on Polyester Film:
All attempts to extrusion coat a high heat resistant copolyester thermoplastic elastomer (e.g., Arnitel® X06111) onto mono-layer biaxially oriented, polyester homopolymer film (e.g. Mylar® 800) were unsuccessful. The extrusion coated layer easily delaminated from the Mylar® layer when a sealed bag, made from the two layer film structure, was stressed. All of the following attempts at improving the adhesion between the two layers failed to show any improvement in preventing delamination:
Successful results were obtained, however, when the extrusion coating substrate included a co-extruded, biaxially oriented, polyester homopolymer film; where one layer is straight crystalline PET and the other layer is amorphous PET. In one embodiment, Arnitel® X06111 was melt extrusion coated onto the amorphous PET side of the Mylar® 850H film. The resulting three layer structure did not delaminate when subjected to cooking and bag burst tests.
Further, it was discovered that application of IR heating to the Mylar® film surface and using a relatively high melt temperature (e.g., around 530 degree F.) for the Arnitel® X06111 further improved the adhesion between this substrate and the Arnitel® X06111 and was sufficient to obtain excellent adhesion between the layers.
The fact that the individual layers of this multi-layer film (e.g., COPE layer 12 and amorphous PET 16) did not delaminate during high temperature applications was somewhat unexpected. The inventors believe that this phenomenon is a result of one or more of the following. It is believed that the amorphous polyester layer 16, being very, very, very thin, helps avoid delamination because thin layers usually have higher surface energies than thicker layers. When one is trying to bond two layers together, usually one of the two layers is as thin as possible, resulting in a stronger adhesion between the two. It is also believed that loading up the temperature of the extrusion coating as hot as possible leads to improved bonding between layers; for example, one or more of: heating the nip rolls, preheating the layer of amorphous material with an infra-red lamp, etc. It is also believed that in an oven, amorphous polyester layer 16 softens up and become somewhat fluid, but since this is such a thin layer, since it's so viscous, there is still adhesion even though it's melted. Another explanation is the surface tension between the adjacent layers. Still another explanation is that during the heat extrusion process, the materials of the two layers merged into one another forming a slightly different polymer.
Use of a bio-based material, such as Arnitel® X06111, as the high heat resistant copolyester thermoplastic elastomer provides further benefits. It is believed that this application discloses the first use of a bio-based material, for example, a based material polymerized from rapeseed (canola oil) for use in an “ovenable cooking” environment (e.g., 400 degree F. or higher). The reason for this is that most bio-based materials can not withstand 400 degree F., and also most cannot achieve FDA approval for food contact at 400 degree F. Therefore, identification and use of the specific grades of bio-based high heat resistant copolyester thermoplastic elastomer, such as Arnitel, for formation of multi-layer high temperature films, pan liners, and oven bags is another novel feature of the present invention. The properties and characteristics of a Bio-based COPE are very similar to a petroleum based COPE.
In accordance with embodiments of the present invention, the multi-layer, high temperature film, and cooking bags produced from such films, provide the following additional advantages and benefits:
Although the invention has been described with reference to exemplary embodiments, it is not limited thereto. Those skilled in the art will appreciate that numerous changes and modifications may be made to the preferred embodiments of the invention and that such changes and modifications may be made without departing from the true spirit of the invention. It is therefore intended that the appended claims cover be construed to all such equivalent variations as fall within the true spirit and scope of the invention.
This application claims the benefit of U.S. Provisional Application Ser. No. 61/448,776, filed Mar. 3, 2011, entitled “Multi-Layer High Temperature Films, Liners, and Cooking Bags,” which is incorporated herein by reference in its entirety.
| Number | Date | Country | |
|---|---|---|---|
| 61448776 | Mar 2011 | US |
