Package for direct contact with food

Abstract

The present invention relates to a package for direct contact with food, and further relates to a method for preparing such a package. Further aspects of the invention relate to the use of such a package. The package according to the present invention better maintains the taste of food in the package.

Description

[0001] The present invention relates to a packaging for direct contact with food, and the present invention further relates to a method for preparing such a packaging. A further aspect of the present invention relates to the use of such a packaging.

[0002] Packagings for direct contact with food (especially those made of plastics) are well known in the art. For example, EP2835051A1 discloses a packaging for food having antifungal properties, which comprises a packaging made of polyethylene terephthalate (PET), wherein an antifungal agent is included in its surface. Besides PET, due to the balance of mechanical properties and its wide availability, such a packaging is also widely made of polypropylene. The polypropylene may be peroxide-shifted to improve the versatility of the production plant. However, a packaging made of polypropylene (especially peroxide-shifted polypropylene) may have a negative impact on the flavor of the food in contact with the packaging. For example, the flavor of the food may be reduced and a "plastic" taste may develop, which gives consumers a perception that the food is contaminated. Means for improving this aspect are also disclosed in the art. For example, US20050129812A1 discloses a method for transferring an odor-eliminating compound to a product, the method comprising the steps of: producing a packaging having an interior; placing a source of the odor-eliminating compound in the interior; and bringing the product into contact with the source. Therefore, there is still a need in the industry for a packaging for direct contact with food, which has little or no impact on the taste of the food in the packaging, in other words, which especially does not maintain or preserve the taste of the food in the packaging by using an absorbent.

[0003] This need is met by a packaging for direct contact with food comprising polypropylene, wherein the melt flow rate (MFR) of the polypropylene, as measured according to ISO1133-1:2011 (230 °C, 2.16 kg), is in the range of 15 - 100 g / 10 min, wherein the production method of the polypropylene comprises:

[0004] - a peroxide-shifting step, wherein the product of the peroxide-shifting step is in pellet form, and

[0005] - a venting step, wherein the polypropylene in pellet form obtained in the peroxide-shifting step is vented in a purge gas, wherein the duration of the venting step is at least 24 hours, wherein the temperature of the purge gas is at least 100 °C, wherein the throughput of the purge gas is at least 15 standard cubic meters per hour per cubic meter of the polypropylene in pellet form, wherein a standard cubic meter of purge gas is a cubic meter of purge gas at a temperature of 23 °C and a pressure of 1 standard atmosphere, and wherein the cubic meter of the polypropylene in pellet form is calculated by dividing the mass of the polypropylene in pellet form by the bulk density of the polypropylene in pellet form.

[0006] The inventors of the present invention have surprisingly found that the packaging according to the present invention maintains well the taste of the food in the packaging.

[0007] Polypropylene

[0008] The polypropylene according to the present invention has a melt flow rate (MFR) in the range of 15 - 100 g / 10 min, preferably 35 - 90 g / 10 min, more preferably 53 - 85 g / 10 min, as measured according to ISO 1133 - 1:2011 (230 °C, 2.16 kg).

[0009] The polypropylene according to the present invention can be a propylene homopolymer, a random propylene copolymer or a multiphase propylene copolymer. Preferably, the polypropylene is a multiphase propylene copolymer.

[0010] Preferably, the multiphase propylene copolymer contains 13 - 20% by weight of an ethylene - propylene copolymer based on the total amount of the multiphase propylene copolymer. Preferably, the amount of the structural part derived from ethylene is in the range of 25 - 55% by weight, preferably 35 - 52% by weight, based on the total amount of the ethylene - propylene copolymer.

[0011] Preferably, the multiphase propylene copolymer further contains a propylene homopolymer matrix, wherein the amount of the propylene homopolymer matrix is in the range of 80 - 87% by weight based on the total amount of the multiphase propylene copolymer.

[0012] In a preferred embodiment, the sum of the propylene homopolymer matrix and the ethylene - propylene copolymer is 100% by weight based on the multiphase propylene copolymer.

[0013] Processes for the production of polypropylene typically start with a polymerization step, such as a multi-stage polymerization, such as bulk polymerization, gas phase polymerization, slurry polymerization, solution polymerization or any combination thereof. Any conventional catalyst system can be used, such as Ziegler-Natta or metallocene. Such polymerization steps and catalysts are described, for example, in WO06 / 010414; Polypropylene and other Polyolefins, by Ser van der Ven, Studies in Polymer Science 7, Elsevier 1990; WO06 / 010414, US4399054 and US4472524. Preferably, the process for the production of polypropylene includes a polymerization step before a peroxide conversion step and a venting step, wherein the polymerization step is carried out in the presence of a Ziegler-Natta catalyst. Preferably, the Ziegler-Natta catalyst of the present invention does not contain phthalates, for example, the catalyst comprises a compound of a transition metal of Groups 4 to 6 of the IUPAC, a Group 2 metal compound and an internal donor, wherein the internal donor is a compound selected from optionally substituted malonates, maleates, succinates, glutarates, cyclohexene-1,2-dicarboxylates, citraconates, benzoates and their derivatives and / or mixtures. Preferably, the Ziegler-Natta catalyst comprises a citraconate.

[0014] The process for the production of polypropylene includes a peroxide conversion step, wherein the product of the peroxide conversion step is in the form of pellets.

[0015] The peroxide conversion step is widely used to increase the MFR of polypropylene. The peroxide conversion step is typically carried out in an extruder by adding a peroxide, which initiates a free radical chain reaction at an elevated temperature, resulting in β-scission of polypropylene molecules. Examples of suitable peroxides include organic peroxides having a decomposition half-life of less than 1 minute at the average process temperature during extrusion. Suitable organic peroxides include, but are not limited to, dialkyl peroxides, such as dicumyl peroxide, peroxyketals, peroxycarbonates, diacyl peroxides, peroxy esters and diperoxycarbonates. Specific examples of these include benzoyl peroxide, dichlorobenzoyl peroxide, dicumyl peroxide, di-tert-butyl peroxide, 2,5-dimethyl-2,5-di(peroxybenzoato)-3-hexene, 1,4-bis(tert-butylperoxyisopropyl)benzene, lauroyl peroxide, tert-butyl peracetate, a,a'-bis(tert-butylperoxy)diisopropylbenzene ( 802), 2,5 - dimethyl - 2,5 - bis(tert - butylperoxy) - 3 - hexene, 2,5 - dimethyl - 2,5 - bis(tert - butylperoxy) - hexane, tert - butyl perbenzoate, tert - butyl perphenylacetate, tert - butyl per - sec - octoate, tert - butyl perpivalate, cumyl perpivalate, cumene hydroperoxide, diisopropylbenzene hydroperoxide, 1,3 - bis(tert - butylperoxy - isopropyl)benzene, dicumyl peroxide, tert - butyl peroxyisopropyl carbonate and any combination thereof. Preferably, a dialkyl peroxide is used in the process according to the invention. More preferably, the peroxide is a,a’ - bis - (tert - butylperoxy)diisopropylbenzene, 2,5 - dimethyl - 2,5 - bis(tert - butylperoxy) - hexane or 3,6,9 - triethyl - 3,6,9 - trimethyl - 1,4,7 - triperoxynonane. Preferably, the peroxide is selected from the group of non - aromatic peroxides.

[0016] Preferably, the peroxide conversion step has a conversion ratio of at least 1.5, where the conversion ratio is the ratio between the MFR of the polypropylene and the MFR of the polypropylene before the conversion, where the MFR is determined according to ISO 1133 - 1:2011 (230 °C, 2.16 kg). Preferably, the conversion ratio is at most 20, preferably at most 15.

[0017] The bulk density of the polypropylene in pellet form, as determined by ISO 60:1977, is preferably in the range of 465 - 777 kg / m 3 and preferably in the range of 512 - 653 kg / m 3 of the range.

[0018] The process for producing polypropylene further includes a venting step, in which the polypropylene in pellet form obtained in the peroxide conversion step is vented in a purge gas, where the duration of the venting step is at least 24 hours, where the temperature of the purge gas is at least 100 °C, where the throughput of the purge gas is at least 15, preferably at least 20, preferably at least 25, more preferably at least 30 standard cubic meters per hour per cubic meter of the polypropylene in pellet form, where a standard cubic meter of purge gas is a cubic meter of purge gas at a temperature of 23 °C and a pressure of 1 standard atmosphere, and where the cubic meter of the polypropylene in pellet form is calculated by dividing the mass of the polypropylene in pellet form by the bulk density of the polypropylene in pellet form.

[0019] Preferably, the venting step is carried out in a container, and the pressure inside the container is preferably in the range of 0.95 - 1.51 standard atmospheres, more preferably in the range of 1.01 - 1.22 standard atmospheres. The pressure inside the container can be measured, for example, by a sensor placed in the container.

[0020] Containers for ventilation purposes typically have an inlet and an outlet for polypropylene in pellet form. Preferably, the inlet for polypropylene in pellet form is located at the top of the container and the outlet for polypropylene in pellet form is located at the bottom of the container. Containers for ventilation purposes typically also have an inlet and an outlet for purge gas. Particularly preferably, the inlet for purge gas is located at the bottom of the container and the outlet for purge gas is located at the top of the container. Such a configuration can result in better ventilation effects.

[0021] The ventilation step can be carried out in a continuous or batch manner. "Continuous" means that the volume of polypropylene in pellet form moves continuously, i.e., without interruption. The "continuous" mode can be accomplished by continuously feeding polypropylene in pellet form into the container and extracting it from the container. "Batch" means feeding a certain amount of polypropylene in pellet form into the container, where the outlet for polypropylene in pellet form is closed. Then both the inlet and the outlet for polypropylene in pellet form are closed and ventilation is started. Finally, the polypropylene in pellet form is extracted from the outlet for polypropylene in pellet form.

[0022] Preferably, the ventilation step is carried out in a batch manner.

[0023] Preferably, the filling rate of the container is in the range of 30 - 95%, preferably in the range of 50 - 93%, more preferably 60 - 90%, where the filling rate of the container is calculated as the ratio between the volume of polypropylene in pellet form and the internal volume of the container.

[0024] Preferably, the duration of the ventilation step is at least 48 hours, more preferably at least 60 hours, even more preferably at least 72 hours. The duration of the ventilation step can be calculated, for example, as the duration during which the polypropylene in pellet form is exposed to the purge gas at at least 100°C.

[0025] Preferably, the temperature of the purge gas is at least 110°C, preferably at least 112°C, and preferably the temperature of the purge gas is in the range of 115 - 130°C. The temperature of the purge gas can be measured, for example, by a temperature sensor located in the inlet for the purge gas, or by a temperature sensor located in the container. It is known to those skilled in the art that the temperature of the purge gas can vary at different positions in the container, especially after freshly feeding the polypropylene in pellet form into the container.

[0026] It is known to those skilled in the art that the ventilation step has no effect on the size or dimensions of the polypropylene in pellet form.

[0027] Packaging

[0028] In a subsequent step, the polypropylene in pellet form is formed into a package, which can be, for example, a bag, a tray or a film. Preferably, the package has a thickness in the range of 0.01 - 0.6 mm, preferably 0.03 - 0.4 mm, and even more preferably 0.04 - 0.2 mm.

[0029] Preferably, the polypropylene in pellet form is injection molded into a package.

[0030] The package according to the invention is for direct contact with food, preferably food for direct consumption, for example the food is fresh fruit, biscuits, soft drinks, etc.

[0031] The invention further relates to a method for preparing a package according to the invention, the method comprising the following steps:

[0032] a) providing polypropylene in pellet form according to the invention;

[0033] b) forming (preferably by injection molding) the polypropylene in pellet form obtained in the venting step into a package.

[0034] In a preferred embodiment, the invention relates to a method for preparing a package, the method comprising the following steps:

[0035] a) providing polypropylene, wherein the melt flow rate (MFR) of the polypropylene, as determined according to ISO 1133 - 1:2011 (230 °C, 2.16 kg), is in the range of 15 - 100 g / 10 min, wherein the production method of the polypropylene comprises:

[0036] - a peroxide conversion step, wherein the product of the peroxide conversion step is in pellet form, and

[0037] - a venting step, wherein the polypropylene in pellet form obtained in the peroxide conversion step is vented in a purge gas, wherein the duration of the venting step is at least 24 hours, wherein the temperature of the purge gas is at least 100 °C, wherein the throughput of the purge gas is at least 15 standard cubic meters per hour per cubic meter of polypropylene in pellet form, wherein a standard cubic meter of purge gas is a cubic meter of purge gas at a temperature of 23 °C and a pressure of 1 standard atmosphere, and wherein the cubic meter of polypropylene in pellet form is calculated by dividing the mass of the polypropylene in pellet form by the bulk density of the polypropylene in pellet form;

[0038] b) forming (preferably by injection molding) the polypropylene in pellet form obtained in the venting step into a package.

[0039] The invention further relates to the use of a package according to the invention containing polypropylene for direct contact with food for maintaining the taste of the food in the package.

[0040] In a preferred embodiment, the present invention relates to the use of a polypropylene-containing packaging for direct contact with food for maintaining the taste of the food in the packaging, wherein the melt flow rate (MFR) of the polypropylene, as measured according to ISO 1133-1:2011 (230 °C, 2.16 kg), is in the range of 15 - 100 g / 10 min, and wherein the production method of the polypropylene comprises:

[0041] - a peroxide conversion step, wherein the product of the peroxide conversion step is in the form of pellets, and

[0042] - a venting step, wherein the polypropylene in pellet form obtained in the peroxide conversion step is vented in a purge gas, wherein the duration of the venting step is at least 24 hours, wherein the temperature of the purge gas is at least 100 °C, wherein the throughput of the purge gas is at least 15 standard cubic meters per hour per cubic meter of the polypropylene in pellet form, wherein a standard cubic meter of purge gas is a cubic meter of purge gas at a temperature of 23 °C and a pressure of 1 standard atmosphere, and wherein the cubic meter of the polypropylene in pellet form is calculated by dividing the mass of the polypropylene in pellet form by the bulk density of the polypropylene in pellet form.

[0043] To avoid any confusion, the polypropylene in pellet form according to the present invention has the same meaning as the polypropylene in pellet form according to the present invention.

[0044] Experiment

[0045] Material

[0046] PP1 is a multiphase propylene copolymer, grade name FPC70, commercially available from SABIC. PP1 has an MFR of 70 g / 10 min as measured according to ISO 1133-1:2011 at 230 °C and 2.16 kg. The production method of PP1 includes a peroxide conversion step. PP1 is in pellet form and has a bulk density of 534 kg / m 3 as determined by ISO 60:1977.

[0047] Venting operation

[0048] Container: A container is used for the venting operation. The container is substantially in the form of an upright cylinder in the vertical direction. The container has an inlet for the polypropylene and an outlet for the purge gas at the top, and a discharge point for the polypropylene and an inlet for the purge gas at the bottom.

[0049] Operation: The aeration operation of PP1 is carried out in batches. 40 tons of PP1 is fed into a container and maintained in the container for 48 h for aeration. The ratio between the overall volume of PP1 and the internal volume of the container is 0.75. Air is used as the purge gas, and the throughput is 2400 Nm 3 / hr, where Nm 3 is standard cubic meter, which means the cubic meter of purge gas at room temperature (23 °C) and a pressure of 1 atmosphere (i.e., ambient pressure). Before entering the container, the air is heated to 115 °C, as measured by a thermocouple placed in the air. After 48 hours of aeration, PP1 is discharged from the discharge point for measurement.

[0050] Measurement

[0051] Taste transfer is carried out via a triangle test by evaluating whether there is a perceivable taste transfer from PP1 (aerated or non-aerated) to the food simulant to identify the effect of the aeration step on taste.

[0052] The reference sample is 180 ml of distilled water (as the food simulant) placed in a glass beaker;

[0053] Samples with PP1 (aerated or non-aerated) are prepared by placing 9.75 g of PP1 in 180 ml of distilled water in the first glass beaker. Since PP1 has a lower density than water, a second glass beaker is placed in the first glass beaker to submerge PP1 in the distilled water.

[0054] All samples are stored at 70 °C for 3 hours. Then all samples are placed at room temperature (23 °C) for 1 hour.

[0055] A triangle test is carried out according to ISO 4120:2021 with 6 well-trained panelists (6 Ph.D.s in flavor chemistry) to identify whether there is a perceivable difference between the taste of the reference sample and the taste of the samples with PP1 (aerated or non-aerated). The panelists conduct a retronasal (sipping and swallowing) assessment of the sample taste. The detailed measurement procedure is explained in Chapter 7 of ISO 4120:2021. The triangle test results are shown in Table 1:

[0056] Table 1

[0057]

[0058] According to Table 1, it is evident that there is a perceivable difference between the taste of the reference (distilled water in glass) and the taste of the sample with non-vented PP1 (distilled water in contact with non-vented PP1), with a confidence level of 99% (α risk = 0.01). In contrast, no difference can be identified between the taste of the reference and the taste of the sample with vented PP1. This indicates that the venting operation of PP1 is effective in maintaining the taste of the water in contact with PP1.

Claims

1. A packaging containing polypropylene for direct contact with food, wherein the melt flow rate (MFR) of the polypropylene is in the range of 15 - 100 g / 10 min as determined according to ISO 1133-1:2011 (230 °C, 2.16 kg), and the production method of the polypropylene includes: - A peroxide conversion step, wherein the product of the peroxide conversion step is in the form of pellets, and - A venting step, wherein the polypropylene in the form of pellets obtained in the peroxide conversion step is vented in a purge gas, the duration of the venting step is at least 24 hours, the temperature of the purge gas is at least 100 °C, the throughput of the purge gas is at least 15 standard cubic meters per hour per cubic meter of the polypropylene in the form of pellets, a standard cubic meter of purge gas being a cubic meter of purge gas at a temperature of 23 °C and a pressure of 1 standard atmosphere, and the cubic meters of the polypropylene in the form of pellets being calculated by dividing the mass of the polypropylene in the form of pellets by the bulk density of the polypropylene in the form of pellets.

2. The packaging according to claim 1, wherein the MFR of the polypropylene is in the range of 35 - 90 g / 10 min, preferably 53 - 85 g / 10, as determined according to ISO 1133-1:2011 (230 °C, 2.16 kg).

3. The packaging according to any one of the preceding claims, wherein the duration of the venting step is at least 48 hours.

4. The packaging according to any one of the preceding claims, wherein the temperature of the purge gas is at least 110 °C, preferably at least 112 °C.

5. The packaging according to any one of the preceding claims, wherein the throughput of the purge gas is at least 20, preferably at least 25, more preferably at least 30 standard cubic meters per hour per cubic meter of the polypropylene in the form of pellets.

6. The packaging according to any one of the preceding claims, wherein the bulk density of the polypropylene in pellet form, determined by ISO 60:1977, is in the range of 465 - 777 kg / m 3 and preferably in the range of 512 - 653 kg / m 3 .

7. The packaging according to any one of the preceding claims, wherein the polypropylene is a multiphase propylene copolymer, preferably the multiphase propylene copolymer contains 13 - 20 wt% of an ethylene-propylene copolymer.

8. The packaging according to any one of the preceding claims, wherein the peroxide conversion step has a conversion ratio of at least 1.5, the conversion ratio being the ratio between the MFR of the polypropylene and the MFR of the polypropylene before conversion, and the MFR being determined according to ISO 1133-1:2011 (230 °C, 2.16 kg).

9. The packaging according to any one of the preceding claims, wherein the food is for direct consumption.

10. The packaging according to any one of the preceding claims, wherein the venting step is carried out in a container, and the pressure inside the container is preferably in the range of 0.95 - 1.51 standard atmospheres, more preferably in the range of 1.01 - 1.22 standard atmospheres.

11. The package according to any one of the preceding claims, wherein the method for producing the polypropylene comprises a polymerization step before the peroxide conversion step and the venting step, and wherein the polymerization step is carried out in the presence of a Ziegler-Natta catalyst.

12. The package according to claim 11, wherein the Ziegler-Natta catalyst comprises citraconate.

13. A method for producing a package according to any one of the preceding claims, the method comprising the steps of: a) providing polypropylene, wherein the melt flow rate (MFR) of the polypropylene, as measured according to ISO 1133-1:2011 (230 °C, 2.16 kg), is in the range of 15 - 100 g / 10 min, and wherein the method for producing the polypropylene comprises: - a peroxide conversion step, wherein the product of the peroxide conversion step is in the form of pellets, and - a venting step, wherein the polypropylene in the form of pellets obtained in the peroxide conversion step is vented in a purge gas, wherein the duration of the venting step is at least 24 hours, wherein the temperature of the purge gas is at least 100 °C, wherein the throughput of the purge gas is at least 15 standard cubic meters per hour per cubic meter of the polypropylene in the form of pellets, wherein a standard cubic meter of purge gas is a cubic meter of purge gas at a temperature of 23 °C and a pressure of 1 standard atmosphere, and wherein the cubic meter of the polypropylene in the form of pellets is calculated by dividing the mass of the polypropylene in the form of pellets by the bulk density of the polypropylene in the form of pellets; b) shaping the polypropylene in the form of pellets obtained in the venting step into a package.

14. The method according to claim 13, wherein step b) is carried out by injection molding.

15. Use of a package containing polypropylene for direct contact with food for maintaining the taste of the food in the package, wherein the melt flow rate (MFR) of the polypropylene, as measured according to ISO 1133-1:2011 (230 °C, 2.16 kg), is in the range of 15 - 100 g / 10 min, and wherein the method for producing the polypropylene comprises: - a peroxide conversion step, wherein the product of the peroxide conversion step is in the form of pellets, and - a venting step, wherein the polypropylene in the form of pellets obtained in the peroxide conversion step is vented in a purge gas, wherein the duration of the venting step is at least 24 hours, wherein the temperature of the purge gas is at least 100 °C, wherein the throughput of the purge gas is at least 15 standard cubic meters per hour per cubic meter of the polypropylene in the form of pellets, wherein a standard cubic meter of purge gas is a cubic meter of purge gas at a temperature of 23 °C and a pressure of 1 standard atmosphere, and wherein the cubic meter of the polypropylene in the form of pellets is calculated by dividing the mass of the polypropylene in the form of pellets by the bulk density of the polypropylene in the form of pellets.

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