ES2910656T3 - Sealable container, sealed container and methods for manufacturing the same - Google Patents

Abstract

A sealable container, comprising: a base and a continuous sidewall extending substantially perpendicular to the base with a peripheral rim formed along the upper edge, in use, of the continuous sidewall, wherein the The base and continuous sidewall are transparent and consist essentially of polyethylene terephthalate (PET), in which a layer of adhesive is located on an upper surface, in use, of the peripheral rim so that a cover film can be applied. be sealed to the peripheral rim to create a sealed space between the base, the continuous sidewall and the lid film, wherein said layer of adhesive does not extend onto the vertical surfaces, in use, of the continuous sidewall and does not extend on the base, characterized in that the container further comprises at least one disengagement recess, free of adhesive, adjacent to a corner of the container, and an disengagement area, free of adhesive, which extends p partially or completely along the inner periphery of the rim, wherein the distance between the top surface of the disengagement zone and the base of the tray is shorter than the distance between the top surface of the rim and the base, in in which the at least one recess is located in the disengagement area.

Description

DESCRIPTION

Sealable container, sealed container and methods for manufacturing the same

This invention relates to containers suitable for use in the packaging, storage, transportation and/or display of a product, such as a fresh food product or a medical product, and to methods of making such containers.

The use of plastic containers for packaging, storing, transporting and presenting fresh foods is known. These containers can be sealed with a lid film to protect the food inside the container from the surrounding environment. Additionally, the atmosphere within such containers can be modified to improve the shelf life and/or appearance of the fresh foods within the container.

Clear plastic containers can be made from polyethylene terephthalate (PET). The use of PET provides a highly transparent product that allows the user to easily see the contents of the container. (Recycled PET can also be used, which offers environmental and sometimes economic benefits.) However, as explained above, it is desirable to seal transparent plastic containers with a lidding film, but it is difficult to bond a lidding film to PET, and the sealing of a lidding film to PET is particularly sensitive to contamination.

WO 2009/121834 relates to a multilayer film comprising a pressure sensitive adhesive for use with reclosable packaging. This document specifically relates to the use of meltable acrylate polymers to produce pressure sensitive adhesive layers in resealable packaging.

GB 1,432,219 relates to a container made of crystallized polyethylene terephthalate capable of withstanding heat to cook its contents. An adhesive is applied to the rim of the tray to minimize exposure to the contents of the container.

EP0440550 relates to a method in which a heat-sealable material is placed in the vicinity of the opening of a container when producing said container or when sealing a cover thereon.

A known solution to the problem indicated above consists in making the containers of PET coated with a layer of polyethylene (PE) and an intermediate layer of ethylene vinyl acetate (EVA). PE provides a surface to which a lidding film is easily attached, thus facilitating the production of sealed containers. Typically, PET is substantially thicker than the EVA and PE layers, and the PET/EVA/PE product can be produced by coextrusion, lamination, extrusion coating, or any other suitable technique. Although the PET/EVA/PE product produces highly transparent containers, EVA and PE have different refractive indices with respect to PET, and thus the PET/EVA/PE product is slightly less transparent than a pEt product. uncoated. Furthermore, the use of EVA and PE carries extra costs for two key reasons; firstly because the laminated or coextruded layer has an intrinsic cost and secondly because, as described below, in-house reprocessing of factory trays and “process residues” is impaired by the presence of EVA and PE in an otherwise pure PET stream. Therefore, compared to a PET product, the PET/EVA/PE product is less transparent, more expensive, less recyclable, and less easy to use in the manufacturing plant.

There are also environmental consequences of using a PET/EVA/PE product. During the manufacture of PET/EVA/PE containers by thermoforming, multiple containers are formed from large and often continuous sheets of PET/EVA/PE material, and individual containers are cut from these large sheets. Residual material is formed from those parts of the large leaves that are not used in the individual containers. This residual material, known as “process residue”, contains a mix of PET, EVA and PE, which when recycled forms a cloudy product that cannot be used to form clear plastic containers. Since clear plastic containers are more desirable than opaque plastic containers, it is not economical to recycle waste.

An alternative way to manufacture food trays as described above is by injection moulding. Then there is no process waste as described above for thermoforming, but there is also no easy and cost-effective way to apply the PE layer to the tray that facilitates easy sealing to a top film.

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

According to a first aspect of the invention, there is provided a sealable container comprising a base and a continuous side wall extending substantially perpendicular to the base with a peripheral rim. formed along the upper edge, in use, of the continuous side wall, in which the base and continuous side wall are transparent and consist essentially of polyethylene terephthalate (PET), in which a layer of adhesive it is located on an upper surface, in use, of the peripheral rim, such that a lid film can be sealed to the peripheral rim to create a sealed space between the base, the continuous sidewall and the lid film. The layer of adhesive located on the upper surface of the peripheral rim does not extend on the vertical surfaces of the continuous side wall and does not extend on the base. The container further comprises an adhesive-free disengagement zone extending partially or completely along the inner periphery of the rim, wherein the distance between the upper surface of the disengagement zone and the base of the tray is shorter than the distance between the top surface of the rim and the base. The container further comprises at least one adhesive-free disengagement recess adjacent to a corner of the container and located in the disengagement area.

The term "adhesive" is used herein to indicate any material that allows adhesion of the lid film to the peripheral rim. The adhesive may be a conventional adhesive, it may be a PE or PE copolymer based material, or indeed any other suitable material applied discreetly to the peripheral rim.

As explained above, clear plastic containers are more desirable than opaque plastic containers, and therefore the base and continuous sidewall may be transparent. A suitable material for making the transparent base and continuous transparent sidewall is PET, therefore the base and continuous sidewall consist essentially of PET, optionally recycled PET.

Adhesives suitable for use in the present invention include adhesives based on a polymeric substrate, such as a hot melt adhesive. The thickness of the adhesive layer can vary. The inventors have found that a thickness of from 20 pm to 100 pm is effective, and a thickness of 50 pm is the most effective.

The sealable containers according to the present invention can be sealed to produce sealed containers. Therefore, according to a second aspect of the present invention, the sealed containers are provided with a lid film sealed to a sealable container as described above.

The atmosphere within the sealed container can be modified to improve the shelf life and/or appearance of the products packaged within the sealed container. Modified Atmosphere Packaging (MAP) may contain high levels of oxygen or other gases. For example, for packaging red meat, the modified atmosphere may contain increased levels of oxygen, such as 25% to 90% oxygen, preferably 80% oxygen. Alternatively, EAM may contain elevated levels of carbon dioxide, such as is used to pack poultry. These are just examples; There are a wide variety of commercially available gas mixtures that are used in a wide variety of food and non-food products. There are also significant commercial volumes of controlled atmosphere packaging where the gas mixture within a sealed package is initially air, but where the product consumes and also generates gases in such a way that the atmosphere is modified by means of air conditioning options. carefully designed and selected film material and container material. This is known as controlled atmosphere packaging (EAC). A reliable and effective seal between the lidding film and the sealable container, which can be effective despite contamination on the seal face, is key to effective EAM and EAC.

Lid films suitable for use in the manufacture of sealed containers according to the present invention may comprise polypropylene (PP) and/or PE. These materials can act as a seal layer in a multilayer film, which can be formed by coextrusion or lamination. The other layers in a multilayer structure may be chosen to impart particular properties, such as strength, elasticity, gas and/or water vapor barrier, shrinkage characteristic, and UV filtering properties. The thickness of the sealing layer of the lidding film can vary. The inventors have found that a stamp layer thickness of from 15 pm to 50 pm is effective, and a thickness of 20 pm is most effective. The total thickness of the lidding film is normally from 20 pm to 60 pm.

According to a third aspect of the present invention, there is provided a method of making a sealable container as described above, wherein the method comprises:

a) providing a container comprising a base and a continuous sidewall rising from the base with a peripheral rim formed along the upper edge of the continuous sidewall, wherein the base and continuous sidewall are transparent and consist essentially of PET, wherein the container further comprises at least one disengagement recess adjacent a corner of the container, and a disengagement zone extending partially or completely along the inner periphery of the rim, wherein the distance between the upper surface of the disengagement zone and the base of the tray is shorter than the distance between the upper surface of the rim and the base, in which the at least one recess is located in the disengagement zone; Y

b) applying a layer of adhesive to an upper surface of the peripheral rim to produce a sealable container, wherein said layer of adhesive does not extend onto the vertical surfaces, in use, of the continuous side wall and does not extend to the base and in which the at least one disengagement recess and the disengagement area are free of adhesive.

The container may be corona treated or plasma treated between steps a) and b) to improve adhesion of the adhesive to the peripheral rim.

The layer of adhesive can be applied to the upper surface of the peripheral rim by a roller, such as a silicone roller or a heated chrome roller. Alternatively, the adhesive layer can be applied by spray coating, by hot melt gun or by printing technique. The inventors have discovered that supporting the container during the application of the adhesive layer helps to transfer a uniform thickness of the adhesive to the peripheral rim. In particular, the inventors have found that supporting the peripheral rim is useful for producing a sealable upper container.

The process for making a sealable container can be operated as a continuous process. For example, the containers can be continuously supplied to a production line for continuous application of the adhesive layer. The process for manufacturing a sealable container according to the present invention can also be operated as a batch process. Alternatively, the process for making a sealable container according to the present invention can be operated as a combination of batch and continuous process steps.

For example, the containers can be supplied by a batch process step and the application of the adhesive layer can function as a continuous process step.

According to a fourth aspect of the present invention, there is provided a method of manufacturing a sealed container as described above, wherein the method comprises:

a) providing a sealable container prepared according to the process for making a sealable container described above;

b) applying a layer of lidding film to the peripheral rim of the sealable container; Y

c) applying pressure to the peripheral rim to seal the lidding film to the sealable container.

Pressure is used to fuse the lidding film with the adhesive layer applied to the peripheral rim and thereby seal the container. Preferably, the heat is applied simultaneously with the pressure. The pressure applied to the peripheral rim and the time over which the pressure is applied can vary. The inventors have found that a pressure of from 206.84 kPa to 1241.06 kPa (30 psi to 180 psi) and a time period of from 0.5 seconds to 5 seconds are effective, and a pressure of 758.42 kPa (110 psi) and a time period of 1 second are the most effective.

The heat applied to the peripheral rim can also vary. The inventors have found that a temperature of from 105°C to 170°C is effective, and a temperature of 150°C is the most effective.

Pressure alone or pressure and heat may be applied to the peripheral rim by any suitable method to seal the lidding film to the sealable container. A sealing shoe matching the shape of the peripheral rim is typically used to seal the lidding film to the sealable container.

As with the process for making a sealable container, the process for making a sealed container according to the present invention can be operated as a continuous process. For example, sealable containers can be supplied to a production line to provide a layer of lidding film and the application of heat to the peripheral rim. The process for manufacturing a sealed container according to the present invention can be operated as a batch process. Alternatively, the process for making a sealed container according to the present invention can be operated as a combination of batch and continuous process steps.

The method of manufacturing a sealed container may be carried out after the sealable container has been manufactured and a product placed inside the sealable container or the method of manufacturing the sealed container may be carried out separately from the process for manufacturing the sealable container.

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

Figure 1 is a cross-sectional view of a prior art tray;

Figure 2 is a flow chart of a typical prior art thermoforming process;

figure 3 shows a perspective view of a tray according to the invention;

Figure 4 is a cross-sectional view of a tray according to the invention;

Figure 5 is a flow diagram of a thermoforming process according to the invention;

Figure 6 is a schematic partial view of a rim of a prior art tray;

Figures 7A to 7E are schematic partial views of trays according to the invention;

Figures 8A, 8B and 8C are schematic top, side and front views of a tray according to the invention, including a modified release feature;

Figure 9A is a schematic view of a prior art tray nested in a similar tray; Y

Figure 9B is a schematic view of a tray according to the invention and including a modified release feature fitted to a similar tray.

Figure 1 shows a cross-sectional view of a prior art container 1' comprising a base 2' with ribs 6', side walls 3' with a peripheral rim 4'. The container 1' is made of PET and has a thickness of, for example, 400-500 µm. The surface of the container is covered with a PE film with a thickness of, for example, 30 to 50 µm. Typically the tray comprises 1 gram PE (ie 5.8% w/w) and 16.8 grams PET (ie 94.2% w/w).

Figure 2 is a simplified illustration of a thermoforming process for the manufacture of PET/PE containers in which pEt in the form of flakes and granules is introduced into the system to produce the trays. The flakes and granules are melted down to sheets which are covered with a PE film. The sheets are then molded into trays. Approximately 6% of the PET/PE waste is obtained from the extrusion of the trays.

At this stage the extruded trays are joined together by a band 7 which is cut to produce individual trays with a return lip. This separation procedure produces approximately 40% web waste. Finally, approximately 2% tray waste is produced in the act of trimming the trays at the end of the process. Extrusion slag, web slag and tray slag are contaminated with PE and cannot be recycled to produce transparent products. Based on the production of 100,000,000 trays, this represents a total of approximately 888 tonnes of waste per year (i.e. 148 tonnes per year of extrusion waste, 705 tonnes per year of web waste and 35 tonnes per year of waste). of tray).

Figure 3 shows a sealable container 1 according to the invention comprising a base 2 and a continuous side wall 3 rising from the base 1. A peripheral rim 4 is formed along the upper edge of the side wall 3 keep going. A layer 5 of adhesive is located on an upper surface of the peripheral rim 4 so that a cover film (not shown) can be sealed to the rim. In this way, a sealed space can be created between the base 1, the continuous side wall 3 and the lid film.

Figure 4 shows a cross-sectional view of a sealable container 1 according to the invention comprising 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, 400-500 |im. A peripheral rim 4 is formed along the upper edge of the continuous side wall 3 and may comprise a return rim. The container is not covered with a PE film as in Figure 2, but instead an adhesive film 5 is applied on an upper surface of the peripheral rim 4, so that a lid film can be sealed to the rim. The thickness of the adhesive film is preferably about 50 µm. Ribs 6 are located on base 2 to strengthen the base of the tray.

Figure 5 is a simplified illustration of a thermoforming process for the manufacture of PET containers according to the present invention in which PET in the form of flakes and granules is introduced into the system to produce the trays. The flakes and granules are first melted down to give pure PET sheets. Therefore, a process according to the present invention produces residues after the extrusion of PET that can be recycled to produce a transparent product, since the residues are substantially free of adhesive or PE. Trays are then formed in the PET sheet and then subsequently the adhesive is applied onto the rim using an adhesive applicator 8 and the trays are trimmed and separated. The web waste is also substantially free of adhesive and can be recycled into the process. At the end of the production line, tray waste comprising PET and adhesive is produced. Accordingly, the claimed process produces substantially less adhesive or PE contaminated waste and is therefore more cost effective as it allows the production of transparent products from the aggregated recycled waste. Again, using the example of the production of 100,000,000 trays, we can predict the same 888 tons of waste added, but only 35 tons are affected with PE/adhesive. This can be re-admitted into the extrusion process without the existing disadvantages in terms of transparency, or in the worst case, segregated and used for products. (eg colored products) where transparency is not important.

As explained above, it is difficult to bond a lidding film to PET surfaces and a solution proposed in the past was to coat the entire top surface of the container with a layer of PE and an intermediate layer of EVA, as PE provides a surface to which a lid film is easily attached. However, the resulting trays were heavier and less recyclable than the PET trays due to the presence of the additional layers.

In the container of the present invention, a layer of adhesive is located on an upper surface of the peripheral rim such that, at a later stage, when necessary, a lidding film can be sealed to the peripheral rim to create a sealed space between the base, the continuous sidewall and the lid film. Consequently, no changes are made to the top sealing film (which may be a conventional lidding film as used in the industry) and only the container is modified. Other solutions would require expensive and complex modifications to the lid and/or tray. The resulting container has better recyclability and trays can be obtained that are up to 3% lighter than prior art trays.

An additional advantage of the present invention is that the adhesive layer located on the top surface of the rim provides a means to visually identify the presence of a seal layer prior to sealing, because the adhesive surface is visually different from the surface of the seal. pEt. Furthermore, after sealing, the layer of adhesive provides a means to visually verify the integrity of the seal by forming a "strip" of adhesive that is visible through the lidding film.

When the trays are nested together, it is often difficult to separate them due to the blocking properties of PET (ie the tendency of PET surfaces to adhere to other PET surfaces). Figure 6 is a schematic view of a corner of a known tray design. Due to the design of the tray, the rim is wider at the corners than along the sides of the tray. In known trays, this additional area can be used to create a disengagement feature to facilitate separation of nested trays. This is achieved by forming a recess in the tray, this recess being on the top rim of the nested tray. The location of the recess alternates in a sequence, so it does not match the tray it fits against.

In the present invention, the upper surface of the peripheral rim is coated with an adhesive. Some adhesives have low tack at room temperature; however, as the temperature increases, the level of stickiness also increases. The result of this would be the interlocking (or partial sticking together) of the trays, since the underside of the disengagement recess of one (upper) tray comes into contact with the upper rim of its nested (lower) tray.

To address this problem, the tray of the present invention comprises at least one disengagement recess located in a disengagement zone. The disengagement zone is recessed relative to the upper surface of the rim, ie it is configured lower than the rim level by a distance of preferably 1 mm. The recessed area extends partially (i.e., as crescents adjacent to the tray corners) or completely (i.e., both adjacent to the tray corners and along the tray sides) along the inner periphery of the rim, so that when the adhesive material is applied to the tray, the upper surface of the recessed area is not covered. For example, in figures 7A, 7B and 7C, the recessed area is located in the corners of the tray in the shape of a crescent and the disengagement recess is located in the recessed area. In figures 7D, 7E and 7F (and also in figures 8A, 8B and 8C), the recessed area extends along the entire inner periphery of the rim, so that the tray comprises an outer peripheral rim coated with adhesive. and an inner peripheral rim, devoid of adhesive.

The breakout recesses are located in the recessed area so that when the adhesive material is applied to the tray, the top surface of the breakout recess and the area surrounding the recess are not covered. As such, the possibility of trays blocking each other is eliminated. The height of the step can be modified to adjust the gap between the trays. A typical gap is about 7 mm.

In these embodiments, the distance between the top surface of the recessed area and the base of the tray is shorter than the distance between the top surface of the rim and the base. Preferably, the distance between the upper surface of the rim and the upper surface of the recessed area is about 1 mm. Preferably, the width of the recessed area is about 1 mm. As can be seen in Figures 9A and 9B, the distance between the adhesive coated rim of a lower tray and the adjacent wall of an upper tray can typically be increased by approximately 1mm (for example, 0.84mm for conventional trays and 1mm for conventional trays). .71 for trays according to the present invention). The recessed area is therefore advantageous in that it prevents a first tray of the present invention from sticking to the nested second tray due to the distance created between the adhesive on the top surface of the first tray rim and the adjacent wall of the tray. the second tray.

examples

LINPAC rfresh R2-45 meat trays were prepared and tested to demonstrate the suitability of the invention for packaging fresh meat using an EAM system.

The trays were made from a 500 µm thick monolayer of amorphous PET sheet. The formed trays were coated with an adhesive (reference BAM 2041) supplied by Beardow and Adams (Adhesives) Ltd. The adhesive was applied to the rim of the tray using a Diemme Fin model SC4 roller gluer. The adhesive was cast against a 177°C chrome roller and applied to the tray rim through a 125°C silicone rubber roller. The coating equipment had a line speed of 10m/min and the trays were coated in batches of four using an aluminum carrier designed to support the rim of each tray as it passed under the coating roller. The equipment was set to apply the adhesive evenly to the rim at coating thicknesses of 50 µm, 60 µm, 80 µm and 90 µm. All other tray surfaces were free of adhesive contamination.

The trays were sealed using a commercially available 35 µm thick lidding film. This was supplied by LINPAC Packaging Limited (reference THB 267110). The trays were filled with an atmosphere of 80% oxygen and 20% carbon dioxide gas using a World Class Packaging model T200 tray sealing machine. A variety of sealing conditions were used with sealing times from 1 to 3 seconds, sealing pressures from 30 psi to 180 psi (206.84 kPa to 1241.06 kPa) at and seal bar temperatures from 130°C up to 170°C.

The trays were stored for 10 days at 4°C to simulate the packaging supply chain. Residual oxygen was then measured using a HiTec MAP 4050 gas analyzer. No significant loss in oxygen concentration was observed, indicating that the packages were leak-free. Leak tests were carried out at room temperature using a Lippke 4000 container testing system. The leak test pressure was 50 mBar with a settling period of 30 seconds and a leak detection time of 30 seconds. The containers were again shown to be leak-free as the observed pressure drop was <2 mBar. Burst tests were carried out using the Lippke 4000 container testing system. The pressure rise rate was 5 mBar/second. The failure mode was failure of the top web film which showed that the adhesive bond between the tray and the top web was good.

Claims (12)

Yo. A sealable container, comprising: a base and a continuous sidewall extending substantially perpendicular to the base with a peripheral rim formed along the upper edge, in use, of the continuous sidewall, wherein the base and continuous sidewall are transparent and consist essentially of polyethylene terephthalate (PET), wherein a layer of adhesive is located on an upper surface, in use, of the peripheral rim such that a lid film can be sealed to the peripheral rim to create a sealed space between the base, the continuous sidewall and the lid film , wherein said layer of adhesive does not extend on the vertical surfaces, in use, of the continuous side wall and does not extend on the base, characterized in that the container further comprises at least one adhesive-free disengagement recess adjacent a corner of the container and an adhesive-free disengagement zone extending partially or completely along the inner periphery of the rim, in which the distance between the upper surface of the disengagement area and the base of the tray is shorter than the distance between the upper surface of the rim and the base, in which the at least one recess is located in the area of disengagement A sealable container according to claim 1, wherein the sealable container is thermoformed. 3. A sealable container according to claim 1, wherein the PET is recycled PET. A sealable container according to any preceding claim, wherein the adhesive is an adhesive based on a polymeric substrate or a material based on polyethylene (PE) or PE copolymer. 5. A sealable container according to any preceding claim, wherein the thickness of the adhesive layer is from 20 µm to 100 µm. A sealed container comprising a sealable container according to any one of claims 1 to 5 and a lid film sealed thereto. 7. A sealed container according to claim 6, wherein the atmosphere within the sealed container has been modified or controlled. 8. A sealed container according to claim 7, wherein the modified atmosphere contains increased levels of oxygen or carbon dioxide. 9. A sealed container according to any of claims 6 to 8, wherein the lid film is a multilayer film comprising a seal layer and the seal layer comprises polypropylene (PP) and/or PE. A sealed container according to claim 9, wherein the thickness of the seal layer is from 15 µm to 50 µm. 11. A sealed container according to any of claims 6 to 10, wherein the thickness of the lidding film is from 20 µm to 60 µm. 12. A method of making a sealable container according to any of claims 1 to 5, wherein the method comprises: a) providing a container comprising a base and a continuous sidewall rising from the base with a peripheral rim formed along the upper edge, in use, of the continuous sidewall, wherein the base and sidewall continuous are transparent and consist essentially of PET, wherein the container further comprises at least one disengagement recess adjacent to a corner of the container, and a disengagement zone extending partially or completely along the inner periphery of the rim, in which the distance between the upper surface of the disengagement area and the base of the tray is shorter than the distance between the upper surface of the rim and the base, in which the at least one recess is located in the area of disengagement; Y b) applying a layer of adhesive to an upper surface, in use, of the peripheral rim to produce a sealable container, wherein said layer of adhesive does not extend over the vertical surfaces, in use, of the side wall continuous and not extending to the base and in which the at least one disengagement recess and the disengagement area are free of adhesive. A method according to claim 12, wherein the adhesive layer is applied to an upper surface of the peripheral rim by roller, spray coating, hot melt gun or printing technique. A method of manufacturing a sealed container according to any of claims 6 to 11, wherein the method comprises: a) providing a sealable container prepared according to claim 12; b) applying a layer of lidding film to the peripheral rim of the sealable container; and c) applying pressure to the peripheral rim to seal the lidding film to the sealable container. A method according to claim 14, wherein the pressure is applied to the peripheral rim at a pressure of from 206.84 kPa to 1241.06 kPa (from 30 psi to 180 psi) for a period of time of from 0.5 seconds up to 5 seconds, preferably 758.42 kPa (110 psi) for 1 second. A method according to claim 14 or 15, in which heat is applied to the peripheral rim simultaneously with pressure, at a temperature of from 105°C to 170°C, preferably at a temperature of 150°C.