RS58221B1 - Sealable container and processes for making a sealable container and a sealed container - Google Patents

Description

Description

This invention relates to containers suitable for the packaging, storage, transport and/or display of products, such as for example fresh food products or medical products, as well as to methods of making such containers.

The use of plastic containers for packaging, storage, transportation and display of fresh food is well known. Such containers can be hermetically sealed with a lid in the form of a film in order to protect the food inside the container from the environment. Additionally, the atmosphere within such containers may be altered to thereby extend the shelf life and/or appearance of fresh food within the container.

Transparent plastic containers can be made from polyethylene terephthalate (PET). The application of PET material allows obtaining a product with high transparency and allows the user to clearly see the contents of the container. (Recycled PET material can also be used, the use of which provides environmental and, sometimes, economic improvements.) However, as explained above, it is preferable that the hermetic closure of transparent plastic containers is done by means of a film, where it is difficult to attach the film to the PET material, while the joint between the PET material and the film is particularly sensitive to contamination.

Document WO 2009/121834 relates to a multilayer film containing a pressure-sensitive adhesive intended for resealable packages. This document specifically relates to the application of soluble acrylate polymers for the production of contact adhesive layers in resealable packaging. The packaging can be made of any material, for example glass, paper, metal, plastic or composite materials.

The well-known solution to the previously described problem is based on the production of containers made of PET coated with a layer of polyethylene (PE) and with a central layer made of ethylene vinyl acetate (EVA). PE provides a surface to which the lid film is easily bonded, enabling the production of hermetically sealed containers. In a typical case, the PET layer is significantly thicker than the EVA and PE layers, and the PET/EVA/PE product can be obtained by co-extrusion, lamination, extrusion with coating or some other suitable technique. Although containers with high transparency are obtained from PET/EVA/PE products, EVA and PE have different refractive indices compared to PET, so that the PET/EVA/PE product has a slightly lower transparency compared to the PET product without a coating layer. In addition, the use of EVA and PE leads to additional costs for two key reasons: first, since the production of the laminate or co-extruded layer incurs its own cost, and second, since, as shown below, internal rework of factory molds and "skeletal waste" are conditioned by the presence of EVA and PE on an otherwise clean PET production line. Therefore, compared to a PET product, a PET/EVA/PE product has poorer transparency characteristics, is more expensive, has poorer recycling characteristics, and is less suitable for use in a production facility.

The use of PET/EVA/PE products also implies the existence of environmental consequences. During the production of PET/EVA/PE containers by the thermoforming process, multiple containers are formed from large and often continuous sheets made of PET/EVA/PE material, while individual containers are then cut from these large sheets. Waste material is created from those parts of large leaves that are not used to make individual containers. This waste material, which is also known as "skeletal waste", contains a mixture of PET, EVA and PE which, when recycled, forms a product of reduced transparency that cannot be used to make transparent plastic containers. Since clear plastic containers are preferred over opaque and "cloudy" plastic containers, recycling waste is not economical.

An alternative way to produce the food containers described above involves the application of the plastic injection process. In that case, during thermo-forming, the above-described skeletal waste does not occur, but there is no simple and cost-effective way of forming a PE layer on the surface of the container that will allow it to be easily connected to the cover film.

Accordingly, it is an object of the present invention to provide containers that will overcome some or all of the previously described problems.

According to the first aspect of the invention, there is provided a container that can be hermetically closed, and which contains a base and a continuous side wall that is placed substantially orthogonal to the base from which it rises and that has a flange that is formed along the circumference of the upper, viewed according to the orientation during application, the edge of the continuous side wall, where the adhesive layer is located on the upper, also according to the orientation during application, the flange of the circumference so that the film from which the lid is made can be connect with a flange running along the circumference of the wall to form a hermetically sealed space between the base, the continuous side wall and the cover film. The adhesive layer located on the upper surface of the circumference flange does not extend to the vertical surfaces of the continuous side wall and does not extend to the base.

The term "adhesive" as used herein is used to describe any material that allows the film, from which the cover is made, to adhere and bond to a flange running along the circumference of a continuous wall. The adhesive may be a traditional adhesive, may be a PE or PE co-polymer based material or indeed some other suitable material discretely applied to the circumferential flange.

As described above, transparent plastic containers are considered preferable to opaque plastic containers, so that the continuous side wall and base can be transparent. A suitable material for making the transparent base and the transparent continuous wall is PET, so that the base and the continuous sidewall essentially consist of PET.

Adhesives suitable for use in the present invention include adhesives based on polymeric substrates such as hot melt adhesives. The thickness of the adhesive layer may vary. The inventors determined that a thickness of 20 µm to 100 µm is effective, and that a thickness of 50 µm is the most effective.

Hermetically sealed containers of the present invention can be hermetically sealed to produce hermetically sealed containers. Therefore, according to another aspect of the present invention, hermetically sealed containers have a lid in the form of a film which is connected to the container in the manner described above.

The atmosphere within the hermetically sealed container may be altered to extend the shelf life and/or appearance of the product packaged within the hermetically sealed container. Modified Atmosphere Packaging (MAP) may contain increased levels of oxygen or other gases. For example, when packing red meat, the modified atmosphere can contain an increased level of oxygen, for example the proportion of oxygen increased from 25% to 90%, and preferably to 80%. Alternatively, MAP may contain increased levels of carbon dioxide, as is the case with poultry meat packaging. These are just examples; there is a wide variety of commercially available gas mixtures that are used with a wide range of food and non-food products. There are also significant commercial quantities of controlled atmosphere packaging where the gas mixture within the hermetically sealed package is initially air, but where the product consumes and also generates gases, so that the atmosphere becomes altered due to carefully designed and selected film and container materials. This is known as Controlled Atmosphere Packaging (CAP). For the effectiveness of CAP and MAP packaging, it is crucial to achieve a reliable and effective seal between the film lid and the container, which can be effective despite contamination on the junction side.

Films for the production of covers that are suitable for use in the production of hermetically sealed containers according to the present invention include polypropylene (PP) and/or PE. These materials act as a sealing layer of a multilayer film that can be formed by co-extrusion or lamination. Other layers in the multi-layer structure can be selected to have special characteristics, such as strength, elasticity, gas and/or water vapor barrier, shrinkage characteristics and UV protection. The thickness of the layer for gluing the cover in the form of a film can be different. The inventors determined that an adhesive layer thickness of 15 µm to 50 µm is effective, and that a thickness of 20 µm is the most effective. The total thickness of the cover in the form of a film is typically from 20 µm to 60 µm.

According to the third aspect of the present invention, there is provided a process for making the hermetically sealed container described above, where the process includes:

a) providing a vessel comprising a base and a continuous side wall rising from the base and comprising a flange extending along the circumference of the upper edge of the continuous side wall; and

b) applying a layer of adhesive to the upper surface of the circumferential flange to produce a container that can be sealed hermetically.

The vessel may be corona/arc or plasma treated between steps a) and b) to improve adhesive adhesion to the circumferential flange.

A layer of adhesive can be applied to the upper surface of the circumferential flange using a roller, such as a silicone roller, or a heated copper roller. Alternatively, the adhesive layer can be applied by spraying, using a hot melt gun or using some printing technique.

The inventors have determined that supporting the container during the application of the adhesive layer helps to transfer an even thickness of adhesive to the flange along the circumference. More specifically, the inventors have found that providing support to the flange along the circumference helps produce a superior hermetically sealed container.

The process of making a container that can be hermetically closed according to the subject invention can be realized as a continuous process. For example, the containers can be delivered to the production line continuously for the continuous application of the adhesive layer. The process of making a hermetically sealed container according to the invention can also be realized as a batch process. Alternatively, the process of making a container that can be hermetically closed according to the subject invention can be realized as a combination of continuous and batch process steps. For example, containers may be supplied by performing a batch process step, while the application of an adhesive layer may be performed as a continuous process step.

According to the fourth aspect of the present invention, there is provided a method of making the hermetically sealed container described above, where the method includes:

a) providing a hermetically sealed container prepared according to the container manufacturing process described above;

b) applying a layer of cover film to the flange along the circumference of the container; and

c) applying pressure to the flange along the circumference of the container in order to connect the film from which the cover is made to the container.

In order to unite the film of the lid with the layer of glue applied to the flange carried along the circumference and, in this way, to effect a hermetic closure of the vessel, pressure is used. Preferably, simultaneously with the application of pressure, it also acts thermally, i.e. with an elevated temperature.

The pressure applied to the flange along the circumference of the vessel and the time during which this pressure is applied can be variable. The inventors found that a pressure of 206.84 kPa to 1,241.06 kPa (30 psi to 180 psi) and a time period of 0.5 seconds to 5 seconds were effective, and that a pressure of 758.42 kPa (110 psi) and a period of 1 second was the most effective.

The temperature applied to the circumferential flange may also be variable. The inventors found that a temperature of 105°C to 170°C is effective, and that a temperature of 150°C is the most effective.

The flange along the circumference of the container can be acted upon only by pressure or both by pressure and thermally by any process suitable for hermetically joining the film from which the cover is made with the container that can be hermetically closed.

As is the case with the process of making a container that can be hermetically sealed, the process of making a hermetically sealed container according to the subject invention can be realized as a continuous process. For example, hermetically sealed containers may be delivered to the production line for application of the container sealing film and thermal action to the peripheral flange. The process of making a hermetically sealed container according to the subject invention can also be realized as a batch process. Alternatively, the process of making a hermetically sealed container according to the subject invention can be realized as a combination of continuous and batch process steps.

The process of making a hermetically sealed container can be performed after the container that can be hermetically sealed has been made and after the product has been placed in it, or the process of making a hermetically sealed container can be carried out independently of the process of making a container that can be hermetically closed.

The invention will be further described with reference to the drawings and drawings in which:

Figure 1 represents a cross-section of a shallow container according to the known state of the art;

Sika 2 is a flow chart of a typical known thermoforming process;

Figure 3 shows a perspective view of a shallow container according to the invention; Fig. 4 shows a cross-section of a shallow container according to the invention; Figure 5 is a flowchart of the thermoforming process according to the invention;

Fig. 6 schematically shows a partial view of the flange of a shallow container according to the known state of the art;

Figures 7A to 7E schematically show partial views of shallow containers according to the invention;

Figures 8A, 8B and 8C schematically show top, side and front views of a shallow pan according to the invention, including the modified nested pan separation feature;

Figure 9A is a schematic view of a prior art shallow dish nested within a similar shallow dish; and

Figure 9B is a schematic view of a shallow dish according to the invention that includes an altered feature of separating dishes nested in other similar shallow dishes.

Figure 1 shows a cross-section of a container 1' according to the existing state of the art, which contains a base 2' with ribs 6', side walls 3' with a flange 4' running along the circumference. The container 1' is made of PET and has a thickness of, for example, 400 to 500 µm. the surface of the container is coated with a PE film with a thickness of, for example, 30 to 50 µm. In a typical case, a shallow container contains one gram of PE (ie 5.8% by weight) and 16.8 grams of PET (94.2% by weight).

Figure 2 is a simplified illustration of the thermoforming process in the production of PET/PE containers, in which PET in the form of flakes and pellets is introduced into the system for the production of shallow containers. Flakes and pellets are melted into sheets which are then covered with a layer of PE film. The leaves are then shaped into shallow containers. About 6% of PET/PE waste is generated when extruding shallow containers.

At this stage, the extruded shallow containers are attached to each other by means of a web 7 which is cut to obtain individual shallow containers with a return flange. The process of separating containers produces about 40% of the waste generated from the net. Finally, about 2% of the waste from shallow dishes is generated when ironing the shallow dishes at the end of the process. Extrusion waste, mesh waste and ironing waste are contaminated due to the presence of PE and cannot be recycled for the production of transparent products. Based on the production of 100,000,000 shallow containers, this represents a total of about 888 tonnes of waste per year (ie 148 tonnes per year of waste generated during extrusion, 705 tonnes per year of web waste and 35 tonnes per year from ironing).

Figure 3 shows a container 1 that can be hermetically sealed according to the invention comprising a base 2 and a continuous side wall 3 rising from the base 1. A flange 4 is formed along the circumference of the upper edge of the continuous side wall 3. A layer of adhesive 5 is located on the upper surface of the flange 4 carried along the circumference in such a way that the cover film (not shown) can be hermetically joined to the flange. In this way, a hermetically sealed space can be formed between the base 1, the continuous side wall 3 and the closing film.

Fig. 4 shows a cross-section of a container 1 according to the present invention, where the container is hermetically sealed and comprises a base 2 and a continuous side wall 3 rising from the base 1. The container is made of PET and has a thickness of, for example, 400 to 500 µm. The flange 4 is carried along the upper edge of the circumference of the continuous side wall 3 and may contain a return flange. The container is not covered with a layer of PE film as in Figure 2, but an adhesive film 5 is applied to the upper surface of the flange 4 carried out along the circumference so that the closing film can be connected to the flange. The thickness of the adhesive film is preferably approximately 50 µm. The ribs 6 are made in the part of the base 2 in order to strengthen the base of the shallow bowl.

Figure 5 represents a simplified illustration of the thermoforming process for the production of PET containers according to the subject of the invention, where PET in the form of flakes and pellets is introduced into the system for the production of shallow containers. Flakes and pellets are first melted into pure PET sheets. The process according to the present invention therefore, after extruding the PET sheets, produces a waste that can be recycled to obtain a transparent product, since the waste is essentially free of glue or PE. The shallow containers are then formed in PET sheets, and then glue is applied to the flange using the glue applicator 8, while the shallow containers are ironed and separated. Mesh waste is also essentially free of glue and can be recycled and fed back into the process. At the end of the production line, waste from shallow containers containing PET and glue is produced. In this way, the mentioned procedure produces significantly less waste that is contaminated by the presence of glue or PE, and which is consequently more cost-effective because it enables the production of transparent products from aggregated recycled waste. Again, using the example of the production of 100,000,000 shallow containers we can predict the same 888 tons of aggregated waste, but of which only 35 tons are threatened by PE/glue. This waste can be reused in the extrusion process without incurring a penalty on container transparency, or worst, separated for products (eg colored products) where transparency is not important.

As explained above, it is difficult to attach the lid film to PET surfaces, so a previously proposed solution was to coat the entire top surface of the container with a PE layer and a center layer of EVA, since the PE layer provides a surface to which the lid film is easily attached. However, the containers thus obtained were heavier and less suitable for recycling compared to PET containers due to the presence of additional layers.

In the container according to the present invention, the layer of adhesive is located on the upper surface of the flange made along the circumference, so that subsequently and if necessary the lid in the form of a film could be connected to the peripheral flange to form a hermetically sealed space between the base, the continuous side wall and the film of the lid. In this way, no modifications were made to the film for closing the container from the top side (which is a conventional film for closing the containers used in the subject industry), but changes were made only to the container. Other solutions would require expensive and complex changes to the cover and/or container. The resulting container has better characteristics when it comes to recycling, and in this way shallow containers can be obtained that are up to 3% lighter compared to shallow containers according to the existing state of the art.

A further advantage of the present invention is that the layer of adhesive located on the upper surface of the flange is a means of visually identifying the presence of the bonding layer before the actual hermetic closure of the container, since the adhesive surface is visually different from the PET surface. Additionally, after hermetically sealing, the adhesive layer provides a means to visually check the integrity of the joint by forming an adhesive "strip" that can be seen through the cover film.

When shallow vessels are stacked and thus nested within each other, they are often difficult to separate due to the blocking characteristics of PET (ie, the tendency of PET surfaces to adhere well to other PET surfaces). Figure 6 schematically represents an angle of a known shallow dish design. Due to the design of the bowl, the flange is wider at the corners than along the sides of the bowl. With known containers, this additional area can be used to create a separation feature to help separate nested containers. This is achieved by forming an indentation in the shallow vessel where the indentation rests on the top flange of the nested vessel. The location of the bearing alternates so that it does not correspond to the vessel on which it rests.

According to the subject invention, the upper surface of the flange along the circumference is coated with glue. Some adhesives have low adhesion strength at room temperatures; however, as the temperature increases, so does the level of adhesion. The result of this will be locking (or partial bonding) of the vessels together as the underside of the separation recess (upper) vessel contacts the upper flange of the nested (lower) vessel.

In order to address this problem, the shallow container according to the present invention contains at least one indentation for separating the nested containers located in the separation area, where this area is released relative to the upper surface of the flange, i.e. it is placed lower than the level of the flange by a distance of preferably 1 mm. The free area extends partially (for example in the form of sickles adjacent to the corners of the container) or completely (that is, both adjacent to the corners of the container and along the sides of the container) along the inner circumference of the flange so that when the glue is applied to the shallow container, the upper surface, the free area is not covered with glue. For example, in Figures 7A, 7B and 7C, the clearance area is located at the corners of the sickle-shaped container, while the recess for separating the containers is located in the clearance area. In Figures 7D, 7E and 7F (and also in Figures 8A, 8B and 8C) the free area extends along the entire inner circumference of the flange, so that the shallow vessel comprises an outer adhesive-coated flange and an inner flange without adhesive.

The separation indentations of the nested vessels are located in the free area so that when the adhesive is applied to the vessel, the top surface of the separation indentation and the area surrounding the indentation are not coated with a layer of adhesive. In this way, the possibility of mutual locking of the containers is eliminated. The height of the steps can be changed to adjust the distance between the containers. A typical gap is in the region of about 7 mm.

In these designs, the distance between the upper surface of the free area and the base of the container is shorter than the distance between the upper surface of the flange and the base. Preferably, the distance between the upper surface of the flange and the upper surface of the free area is approximately 1 mm. Preferably, the width of the free area is approximately 1 mm. As can be seen from Figures 9A and 9B, the distance between the adhesive-applied flange of the lower container and the adjacent wall of the upper container can typically be increased by approximately 1 mm (eg 0.84 mm for standard containers and 1.71 for containers according to the present invention). The free area is thus desirable as it prevents the first container according to the present invention from sticking to the second nested container due to the distance formed between the adhesive on the upper surface of the flange of the first container and the adjacent wall of the second container.

Examples

Meat containers named "LINPAC rfresh R2-45" were prepared and tested to demonstrate the suitability of the invention for packaging fresh meat using the MAP system.

The containers are manufactured from a 500 µm thick mono-layer of amorphous PET sheet. The molded containers were coated with an adhesive (reference BAM 2041) manufactured by Beardow and Addams (Adhesives) LTD. The adhesive was applied to the container flange using a Diemme Fin roller machine, model SC4. The adhesive was melted under a chrome roller at a temperature of 177°C and applied to the pan flange using a silicone rubber roller at a temperature of 125°C. The coating equipment had a line speed of 10 m/min and the pans were coated in batches of four using an aluminum bracket designed to receive and carry the flange of each pan as they passed under the coating roller. The container is adapted to apply the adhesive in a uniform manner on the flange and form a layer of coating with a thickness of 50 µm, 60 µm, 80 µm and 90 µm. The rest of the container surfaces are exempt from glue contamination.

The containers are hermetically sealed using 35 µm thick commercially available lidding film. The film is manufactured by LINPAC Packaging Limited (reference THB 26110). The containers are filled with an atmosphere containing a gas consisting of 80% oxygen and 20% carbon dioxide using a World Class Packaging, model T200 container sealing machine. When sealing the containers, a number of different sealing conditions were applied with a sealing time range of 1 to 3 seconds, a sealing pressure range of 206.83 kPa to 1,241.06 kPa (30 psi to 180 psi), and a sealing temperature range of 130°C to 170°C. The containers were then stored for a period of 10 days at 4°C to simulate the packaging and supply chain. After that, the residual oxygen content was measured using a HiTec MAP 4050 gas analyzer. No significant loss of oxygen concentration was detected, indicating that the packages were still hermetically sealed and that there were no leaks. Leakage tests were performed at room temperature using the Lippke 4000 Packaging Test System. The test pressure was 50 mBar with a settling period of 30 seconds and a leak detection time of 30 seconds. The packages were again determined to be still hermetically sealed as the observed pressure drop was less than 2 mBar. Burst tests were performed using a Lippke 400 Package Test System. The rate of pressure increase was 5 mBar/s. The failure mode was tearing of the top film, which confirmed that the bond made between the container and the top mesh by the adhesive was good.

Claims (23)

PATENT REQUESTS 1. A vessel comprising a base and a continuous side wall rising substantially at right angles from the base and containing a flange extending along the circumference of its upper edge, as viewed from the orientation of the vessel during use, forms a shallow vessel, wherein the base and continuous sidewall consist essentially of polyethylene terephthalate (PET) where the layer of adhesive is located on the upper, according to the orientation during use, surface of the flange carried out along the circumference and where said layer of adhesive does not extend to the vertical, during application, surfaces of the continuous side wall and does not extend to the base wherein the container further comprises a lid film connectable to a flange extending along the circumference of the side wall of the container to form a hermetically sealed space between the base, the continuous side wall and the lid film; and wherein the cover film is a multi-layer film comprising a bonding layer and wherein the bonding layer comprises polypropylene (PP) and/or PE; wherein the vessel further comprises at least one recess for separating nested vessels located in the vessel separation area, wherein the vessel separation area is free relative to the upper surface of the flange and extends partially or fully along the inner circumference of the flange, so that when the adhesive layer is applied to the shallow vessel, the upper surface of the free vessel separation area is not coated. 2. A container according to Claim 1, wherein the base and the continuous side wall are transparent. 3. A container according to Claim 2, wherein the base and continuous sidewall consist essentially of recycled PET. 4. Container according to Claim 1, 2 or 3, wherein the adhesive is based on a polymer substrate or polyethylene (PE) or a material based on PE co-polymers. 5. Container according to any of the preceding Claims, where the thickness of the adhesive layer is from 20 µm to 100 µm, preferably 50 µm. 6. A container according to any one of the preceding Claims, wherein the distance between the top surface of the container separation area and the base of the shallow container is shorter than the distance between the top surface of the flange and the base. 7. A container according to any of the preceding Claims, wherein a cover film is adhered thereto. 8. A container according to Claim 7, wherein the atmosphere within the hermetically sealed container is altered or controlled. 9. The vessel of claim 8, wherein the altered atmosphere contains increased levels of oxygen or carbon dioxide. 10. A vessel according to any of the preceding Claims, wherein the thickness of the lid film bonding layer is from 15 µm to 50 µm, preferably 20 µm. 11. A container according to any one of the preceding Claims, wherein the thickness of the cover film is from 20 µm to 60 µm. 12. The process of making a vessel according to any of Claims 1 to 6, where the process contains: a) providing a container comprising a base and a continuous sidewall rising from the base and having a flange formed along the upper, in-use orientation, edge of its circumference, thereby forming a shallow container, wherein said base and sidewall consist essentially of polyethylene terephthalate (PET), and with at least one nested container separation depression formed in the separation region, where the separation region is free relative to the top surface flanges and extending partially or fully along the inner circumference of the flange, i b) applying a layer of glue to the upper, according to the orientation during use, surface of the flange carried along the circumference to produce a container that can be hermetically closed, so that the layer of glue does not extend to the vertical, according to the orientation during use, surfaces of the continuous side wall and does not extend to the base; so that when the adhesive layer is applied to the shallow dish, the upper surface of the free area for separating the nested dishes is not coated. c) providing a multi-layer lid film comprising a bonding layer and wherein the bonding layer comprises polypropylene (PP) and/or PE. 13. The method according to Claim 12, wherein the vessel is treated by means of an electric arc or plasma between performing steps a) and b). 14. The method according to Claim 12 or 13, where a layer of glue is applied to the upper surface of the flange along the circumference by means of a roller, by spraying, by means of a melting gun or by some printing technique. 15. The method of Claim 14, wherein the roller is a silicon roller or a heated chrome roller. 16. The method according to any of Claims 12 to 15, where during the application of the adhesive layer, the flange along the circumference is carried or supported. 17. The process according to any one of Claims 12 to 16, wherein the process is a continuous process. 18. A process for making a container according to any of Claims 7 to 11, where the process includes: a) providing a vessel prepared according to any one of Claims 12 to 17; b) applying the cover film to the flange along the circumference of the container; and c) acting by pressing on a circumferential flange to adhere the lid film to the container. 19. The method of Claim 18, wherein the circumferential flange is subjected to a pressure of 206.84 kPa to 1241.06 kPa (30 psi to 180 psi) for a time period of 0.5 s to 5 s, and preferably 758.42 kPa (110 psi) for a period of 1 second. 20. The method according to Claim 18 or 19, where simultaneously with the pressure, thermal is also applied. 21. The method according to Claim 20, where the flange made along the circumference is treated with a temperature of 105°C to 170°C, and preferably with a temperature of 150°C. 22. A method according to any one of Claims 18 to 21, wherein for joining the lid film for a container that can be sealed hermetically, a joining horseshoe is used, the shape of which corresponds to the shape of the flange. 23. The process according to any one of Claims 18 to 22, wherein the process is a continuous process.