Food packaging material and manufacturing method thereof

Abstract

The invention discloses a food packaging material and a manufacturing method thereof. The food packaging material comprises a casting polypropylene layer, a heat-resistant surface layer and a middle layer, wherein the middle layer is arranged between the heat-resistant surface layer and the casting polypropylene layer. The casting polypropylene layer is made of a first propylene copolymer, the heat-resistant surface layer is made of a propylene homopolymer and petroleum resin, and the middle layer is made of a second propylene copolymer. The melting point of the heat-resistant surface layer is higher than that of the casting polypropylene layer, and the melting point of the casting polypropylene layer is higher than that of the middle layer. The food packaging material can have the convenience of direct recovery and good physical characteristics.

Description

Technical Field

[0001] The present application relates to a food packaging material and a manufacturing method thereof, and in particular to a food packaging material suitable for heat-sealed packaging or vacuum packaging and a manufacturing method thereof. Background Art

[0002] Currently, most food packaging materials on the market are made from a combination of multiple materials, such as polyester, aluminum foil, and polypropylene. Due to these material differences, food packaging cannot be directly recycled, resulting in a large amount of disposable waste and raising environmental concerns.

[0003] When laminating different materials, adhesive is often required. The adhesive coating step not only complicates the manufacturing process, but the solvents used in the adhesive can also pollute the environment. In the long term, this type of food packaging material appears to be detrimental to environmental protection.

[0004] On the other hand, although single-material food packaging materials have the advantage of being directly recyclable and reusable, their physical properties are usually inferior to those of food packaging materials composed of multiple materials.

[0005] Therefore, how to manufacture food packaging materials composed of a single material while maintaining good physical properties through improvements in materials and structures has become one of the important issues that this industry wants to solve. Summary of the Invention

[0006] The technical problem to be solved by this application is to provide a food packaging material and a manufacturing method thereof in view of the deficiencies in the prior art.

[0007] To solve the above-mentioned technical problems, one of the technical solutions adopted by the present invention is to provide a food packaging material. The food packaging material includes a cast polypropylene layer, a heat-resistant surface layer, and an intermediate layer, wherein the intermediate layer is disposed between the heat-resistant surface layer and the cast polypropylene layer. The cast polypropylene layer is made of a first propylene copolymer, the heat-resistant surface layer is made of a propylene homopolymer and a petroleum resin, and the intermediate layer is made of a second propylene copolymer. The melting point of the heat-resistant surface layer is higher than that of the cast polypropylene layer, and the melting point of the cast polypropylene layer is higher than that of the intermediate layer.

[0008] Furthermore, the melting point of the propylene homopolymer is 160°C to 170°C.

[0009] Furthermore, the first propylene copolymer has a melting point of 145°C to 159°C.

[0010] Furthermore, the second propylene copolymer has a melting point of 125°C to 140°C.

[0011] Furthermore, in the heat-resistant surface layer, with the total weight of propylene homopolymer, petroleum resin and inorganic filler being 100 weight percent, the content of propylene homopolymer is 87 weight percent to 94 weight percent, and the content of petroleum resin is 1.5 weight percent to 5 weight percent.

[0012] Furthermore, based on the total weight of the first propylene copolymer being 100 weight percent, the first propylene copolymer is polymerized from 90 weight percent to 99.99 weight percent of propylene monomer and from 0.01 weight percent to 10 weight percent of ethylene monomer.

[0013] Furthermore, based on the total weight of the second propylene copolymer being 100 weight percent, the second propylene copolymer is polymerized from 70 weight percent to 85 weight percent of propylene monomer and from 15 weight percent to 30 weight percent of ethylene monomer.

[0014] Furthermore, the petroleum resin is a hydrogenated petroleum resin having 5 or 10 carbon atoms.

[0015] Furthermore, the petroleum resin is an aromatic copolymer hydrogenated petroleum resin produced by reacting a hydrogenated petroleum resin having 5 or 10 carbon atoms with an aromatic group.

[0016] Furthermore, the hydrogenated petroleum resin having a carbon number of 5 or 10 is piperylene hydrogenated resin or dicyclopentadiene hydrogenated resin.

[0017] Furthermore, the thickness of the middle layer is 18 microns to 20 microns, the thickness of the cast polypropylene layer is 50 microns to 70 microns, and the thickness of the heat-resistant surface layer is 20 microns to 30 microns.

[0018] In order to solve the above-mentioned technical problems, another technical solution adopted by the present invention is to provide a method for manufacturing food packaging materials. The method for manufacturing food packaging materials includes: performing a casting process to generate a cast polypropylene layer; performing a biaxial stretching process to generate a laminated structure; and arranging the cast polypropylene layer on the laminated structure to obtain the food packaging material. The laminated structure includes an intermediate layer and a heat-resistant surface layer, and the cast polypropylene layer is in contact with the intermediate layer. The material of the cast polypropylene layer includes a first propylene copolymer. The material of the intermediate layer includes a second propylene copolymer. The material of the heat-resistant surface layer includes a propylene homopolymer, a petroleum resin, and an inorganic filler. The melting point of the heat-resistant surface layer is higher than the melting point of the cast polypropylene layer, and the melting point of the cast polypropylene layer is higher than the melting point of the intermediate layer.

[0019] One of the beneficial effects of the present invention is that the food packaging material and its manufacturing method provided by the present invention can achieve both the convenience of direct recycling and good physical properties through the technical solutions of "the material of the heat-resistant surface layer includes propylene homopolymer, petroleum resin and inorganic filler" and "the melting point of the heat-resistant surface layer is higher than the melting point of the cast polypropylene layer, and the melting point of the cast polypropylene layer is higher than the melting point of the intermediate layer."

[0020] In order to further understand the features and technical content of this application, please refer to the following detailed description and drawings of this application. However, the drawings provided are only for reference and explanation and are not used to limit this application. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 Schematic side view of the food packaging material of the present invention. DETAILED DESCRIPTION

[0022] The following is an explanation of the implementation methods of the "food packaging material and its manufacturing method" disclosed in the present invention through specific examples. Those skilled in the art can understand the advantages and effects of the present invention from the contents disclosed in this specification. The present invention can be implemented or applied through other different specific embodiments, and the details in this specification can also be modified and changed based on different viewpoints and applications without deviating from the concept of the present invention. In addition, the drawings of the present invention are only simple schematic illustrations and are not depicted according to actual dimensions. It is stated in advance. The following implementation methods will further explain the relevant technical content of the present invention in detail, but the disclosed content is not intended to limit the scope of protection of the present invention. In addition, the term "or" used in this article may include any one or more combinations of the associated listed items depending on the actual situation.

[0023] In order to overcome the shortcoming that existing food packaging materials cannot be directly recycled and reused due to the complexity of the material types, the present invention develops a food packaging material made of a single material.

[0024] The food packaging material of the present invention is mainly composed of polypropylene. Even though it has the characteristics of a single material, the food packaging material of the present invention can still have excellent physical properties (high tensile strength, low shrinkage, and high heat resistance).

[0025] To achieve excellent physical properties, the food packaging material of the present invention has a multi-layer structure. The design concept is to sandwich a layer with a lower melting point between two layers with higher melting points, thereby improving the heat resistance of the food packaging material while maintaining flexibility.

[0026] Furthermore, the two outer layers have different melting points (the difference in melting points can be 5°C to 25°C). This allows the food packaging material to function as a heat-sealable material, allowing heat sealing to occur at appropriate temperatures. Therefore, the food packaging material of the present invention has a wider range of packaging applications and can replace existing food packaging materials that are not directly recyclable.

[0027] In order to adjust different properties based on the same material, the present invention adjusts the types and proportions of monomers or blends other components to make the layers have different melting point ranges in order to obtain ideal properties.

[0028] See also Figure 1 As shown, the food packaging material 1 of the present invention has a three-layer structure. The food packaging material 1 includes a cast polypropylene layer 10, a heat-resistant surface layer 20, and an intermediate layer 30. The intermediate layer 30 is provided between the cast polypropylene layer 10 and the heat-resistant surface layer 20.

[0029] In the exemplary embodiment, the cast polypropylene layer 10 is secured to the intermediate layer 30 by adhesive, and the heat-resistant surface layer 20 and the intermediate layer 30 are integrally formed, but the present invention is not limited thereto. The specific manufacturing steps for the cast polypropylene layer 10, the heat-resistant surface layer 20, and the intermediate layer 30 will be described later.

[0030] The cast polypropylene layer 10 is the inner surface of the food packaging material 1 and the surface that primarily contacts the food. In a preferred embodiment, the cast polypropylene layer 10 is formed from a single component, without any other materials or additives. In some applications, the cast polypropylene layer 10 can also serve as a heat-seal layer. Specifically, the melting point of the cast polypropylene layer 10 is lower than that of the heat-resistant surface layer 20. This allows the heat-resistant surface layer 20 to retain its original shape and condition during the heat-sealing process.

[0031] The material of the cast polypropylene layer 10 includes a first propylene copolymer. The melting point of the first propylene copolymer is 145° C. to 159° C., preferably 147° C. to 155° C. The melting point of the first propylene copolymer can be 148° C., 149° C., 150° C., 151° C., 152° C., 153° C., or 154° C. Experimental measurements show that the melt flow index (MI) of the first propylene copolymer is 5 g / 10 min to 10 g / 10 min (under measurement conditions of 230° C. and 2.16 kg).

[0032] The cast polypropylene layer 10 is formed by casting. Since it does not undergo a stretching step, the cast polypropylene layer 10 can have preferable heat resistance and transparency.

[0033] The first propylene copolymer is formed by copolymerizing propylene monomer and ethylene monomer. Taking the total weight of the first propylene copolymer as 100 weight percent, the first propylene copolymer is formed by copolymerizing 90 weight percent to 99.99 weight percent of propylene monomer and 0.01 weight percent to 10 weight percent of ethylene monomer. For example, the content of propylene monomer can be 92wt%, 94wt%, 96 or 98wt%, and the content of ethylene monomer can be 1wt%, 2wt%, 4wt%, 6wt%, 8wt% or 9wt%. During the polymerization process, ethylene monomer will be randomly interspersed between the propylene monomers, which will reduce the crystallinity and melting point of the first propylene copolymer. However, by adding a small amount of ethylene monomer, the toughness, impact resistance, oxidation aging resistance and long-term heat resistance of the first propylene copolymer can be improved.

[0034] The heat-resistant surface layer 20 is the outer surface of the food packaging material 1 and is exposed to the outside world for extended periods of time. Furthermore, the heat-resistant surface layer 20 is the most heat-resistant layer in the food packaging material 1, possessing the highest melting point. Therefore, when the food packaging material 1 is heat-sealed, the heat-sealing temperature must not exceed the melting point of the heat-resistant surface layer 20.

[0035] The material of the heat-resistant surface layer 20 includes propylene homopolymer, petroleum resin and inorganic filler, wherein the propylene homopolymer is the main component (ie, the content is greater than 70 weight percent).

[0036] Compared to propylene copolymers, propylene homopolymers have a more regular molecular arrangement, resulting in a higher melting point. Specifically, the melting point of propylene homopolymers is 160°C to 170°C, preferably 165°C to 168°C. For example, the melting point of the first propylene copolymer may be 166°C or 167°C. Experimental measurements show that the melt index of propylene homopolymers is 2 g / 10 min to 3 g / 10 min (measured at 230°C and 2.16 kg).

[0037] The addition of petroleum resin can enhance the crystallinity of the amorphous phase in the propylene homopolymer, thereby increasing the melting point rigidity of the propylene homopolymer. Preferably, the petroleum resin can be a hydrogenated petroleum resin. Hydrogenated petroleum resin can impart appropriate crystallinity to the propylene homopolymer. Furthermore, hydrogenated petroleum resin can enhance viscosity and reinforcement, improving the mechanical and optical properties of the propylene homopolymer, thereby imparting optimal heat resistance to the heat-resistant surface layer 20.

[0038] For example, the petroleum resin can be a hydrogenated petroleum resin with a carbon number of 5 or 9, such as a hydrogenated piperylene resin or a hydrogenated dicyclopentadiene (DCPD) resin. In some embodiments, the hydrogenated petroleum resin with a carbon number of 5 or 10 can be further reacted with an aromatic component to produce an aromatic copolymer hydrogenated petroleum resin. Aromatic copolymer hydrogenated petroleum resins can provide the heat-resistant surface layer 20 with improved heat resistance.

[0039] Inorganic fillers are added to prevent adhesion during the manufacturing process, which can affect the quality of the layers. The inorganic filler can be silica, for example, silica with a particle size of 2 to 15 microns. In an exemplary embodiment, a mixture of two inorganic filler particle sizes can be used, for example, silica with a particle size of 1 to 3 microns and silica with a particle size of 3.1 to 5 microns.

[0040] In an exemplary embodiment, based on the total weight of the propylene homopolymer, petroleum resin, and inorganic filler being 100 weight percent, the content of the propylene homopolymer is 87 to 94 weight percent, the content of the petroleum resin is 1.5 to 5 weight percent, and the content of the inorganic filler is 0.03 to 0.15 weight percent. For example, the content of the propylene homopolymer may be 88 weight percent, 89 weight percent, 90 weight percent, 91 weight percent, 92 weight percent, or 93 weight percent.

[0041] The intermediate layer 30 acts as a flexible, soft layer within the food packaging material 1, enhancing its usability. Intermediate layer 30 is sandwiched between the cast polypropylene layer 10 and the heat-resistant surface layer 20. It has the lowest melting point within the food packaging material 1. Specifically, the melting point of the heat-resistant surface layer 20 is higher than that of the cast polypropylene layer 10, which in turn has a higher melting point than that of the intermediate layer 30.

[0042] The material of the middle layer 30 includes the second propylene copolymer and may optionally include an inorganic filler, wherein the second propylene copolymer is a main component (ie, the content is greater than 70 weight percent).

[0043] The melting point of the second propylene copolymer is 125° C. to 140° C., preferably 130° C. to 133° C. The melting point of the second propylene copolymer may be 131° C. or 132° C. According to experimental measurements, the melt index of the first propylene copolymer is 5 g / 10 min to 7 g / 10 min (measured at 230° C. and 2.16 kg).

[0044] The second propylene copolymer is formed by copolymerizing propylene monomer and ethylene monomer. Taking the total weight of the second propylene copolymer as 100 weight percent, the second propylene copolymer is formed by copolymerizing 70 weight percent to 85 weight percent of propylene monomer and 15 weight percent to 30 weight percent (wt%) of ethylene monomer. For example, the content of propylene monomer can be 72wt%, 74wt%, 76wt%, 78wt%, 80wt%, 82wt% or 84wt%, and the content of ethylene monomer can be 16wt%, 18wt%, 20wt%, 22wt%, 24wt%, 26wt% or 28wt%.

[0045] In short, by adjusting the type and structure of micromolecules, the polypropylene material can have different melting points, thereby controlling the properties of the layer. The melting point of the propylene homopolymer is higher than that of the first propylene copolymer, which in turn has a higher melting point than the second propylene copolymer. Therefore, the melting point of the heat-resistant surface layer 20 can be higher than that of the cast polypropylene layer 10, which in turn can be higher than that of the intermediate layer 30.

[0046] For ease of use and packaging functionality, the thickness of the cast polypropylene layer 10 can be adjusted to be greater than the thickness of the heat-resistant surface layer 20, and the thickness of the heat-resistant surface layer 20 can be adjusted to be greater than the thickness of the intermediate layer 30. In a preferred embodiment, the thickness of the intermediate layer is 18 to 20 microns, the thickness of the cast polypropylene layer is 50 to 70 microns, and the thickness of the heat-resistant surface layer is 20 to 30 microns.

[0047] The manufacturing method of the food packaging material of the present invention comprises the following steps. The first propylene copolymer can be used to perform a casting process to obtain a cast polypropylene film (CPP film). In the casting process, the first propylene copolymer is first melted by an extruder and then extruded through a T-shaped die. The molten first propylene copolymer is generated into a sheet on a steadily rotating roller drum and, after cooling and shaping, the cast polypropylene layer can be obtained.

[0048] The aforementioned propylene homopolymer, petroleum resin, and inorganic filler are mixed to form a heat-resistant surface layer material. The aforementioned second propylene copolymer and inorganic filler are mixed to form an intermediate layer material. Next, the heat-resistant surface layer material and the intermediate layer material are respectively fed into the feed port of a biaxial stretching machine. After melt extrusion and stretching, a laminated structure can be obtained. The laminated structure is formed by integrally forming the heat-resistant surface layer and the intermediate layer. In other words, the heat-resistant surface layer and the intermediate layer are both biaxially oriented polypropylene film (BOPP film). In terms of the actual product, no obvious interface can be observed between the heat-resistant surface layer and the intermediate layer, but there are indeed differences in composition.

[0049] Next, a cast polypropylene layer is placed on the laminate structure, and the cast polypropylene layer is brought into contact with the intermediate layer to produce the food packaging material of the present invention. Since the cast polypropylene layer and the laminate structure are both formed, they can be fixed by polyolefin adhesive, but the present invention is not limited thereto.

[0050] In an exemplary embodiment, the polyolefin adhesive is prepared from polyolefin particles, a modifier, a hardener, and a mixed solvent. The polyolefin particles may be made of a propylene random copolymer. The modifier may be selected from the group consisting of maleic anhydride, methyl tetrahydrophthalic anhydride (MTHPA), 3,4,5,6-tetrahydrophthalic anhydride, 1,2,3,6-tetrahydrophthalic anhydride (THPA), methylhexahydrophthalic anhydride (MHHPA), methyl nadic anhydride (MNA), and 2,3-naphthalenedicarboxylic anhydride. The hardener may be a polyisocyanate hardener, such as: ultra N3300, ultra N3600 or a combination thereof. The mixed solvent may comprise a non-polar solvent and a polar solvent, with the mass ratio of the non-polar solvent to the polar solvent being 4:1 to 3:2. The non-polar solvent may be methylcyclohexane, cyclohexane, n-hexane, or a combination thereof. The polar solvent may be methyl ethyl ketone, ethyl acetate, methyl isobutyl ketone, n-propyl acetate, or a combination thereof. Preferably, the non-polar solvent is methylcyclohexane, and the polar solvent is methyl ethyl ketone, ethyl acetate, or a mixture thereof.

[0051] It is worth noting that the order of generating the cast polypropylene layer and generating the laminated structure is not limited to the above, and the laminated structure may be generated first and then the cast polypropylene layer may be generated.

[0052] To measure the properties of the food packaging materials of the present invention, Example 1 and Comparative Examples 1 and 2 were prepared according to the above steps. The material compositions of the resulting layers are listed in Table 1. The differences between the Examples and Comparative Examples lie in the composition of the heat-resistant surface layer. Specifically, Comparative Example 1 did not contain a stiffening agent masterbatch, while Comparative Example 2 did not contain a stiffening agent masterbatch, and neither did it use a propylene homopolymer as the main component.

[0053] To ensure uniform mixing of the materials, petroleum resin (hardening agent masterbatch) and inorganic filler (anti-sticking agent masterbatch) can be added via masterbatch. Specifically, the hydrogenated petroleum resin (a hydrogenated petroleum resin produced by copolymerization of dicyclopentadiene and aromatics) content in the hardening agent masterbatch is 30 to 50 weight percent, and the silica content in the anti-sticking agent masterbatch is 3 to 5 weight percent. Table 1 shows the amount of masterbatch added; the specific petroleum resin or inorganic filler content can be calculated.

[0054] To demonstrate the excellent properties of the food packaging material of the present invention, the tensile strength of the food packaging material was measured according to the ASTM D-638 standard test method. The food packaging material was subjected to static temperatures of 120°C and 150°C for three minutes, and its shrinkage relative to its original size was measured. Two sheets of food packaging material were heat-sealed at 180°C and a pressure of 0.2 MPa for one second. The seal strength was then measured using a tensile testing machine at a speed of 300 m / min. The temperature at which the food packaging material began to stick due to heat was recorded to assess its heat resistance. The test results are listed in Table 1.

[0055] Table 1

[0056]

[0057]

[0058] The results in Table 1 indicate that the food packaging material of the present invention possesses superior tensile strength, making it a viable alternative to currently available food packaging materials. Furthermore, it offers the advantage of direct recyclability. Furthermore, the food packaging material of the present invention exhibits low shrinkage and excellent heat resistance (high sticking temperature), maintaining its original dimensions at 120°C and shrinking only slightly at 150°C. These excellent properties enable the food packaging material of the present invention to have a wider range of applications, particularly in heat-sealed packaging and vacuum packaging.

[0059] [Beneficial Effects of Embodiments]

[0060] One of the beneficial effects of the present invention is that the food packaging material and its manufacturing method provided by the present invention can achieve both the convenience of direct recycling and good physical properties through the technical solutions of "the material of the heat-resistant surface layer includes propylene homopolymer, petroleum resin and inorganic filler" and "the melting point of the heat-resistant surface layer is higher than the melting point of the cast polypropylene layer, and the melting point of the cast polypropylene layer is higher than the melting point of the intermediate layer."

[0061] The contents disclosed above are only preferred feasible embodiments of the present application and do not limit the scope of protection of the claims of the present application. Therefore, all equivalent technical changes made using the contents of the present application specification and drawings are included in the scope of protection of the claims of the present application.

Claims

1. A food packaging material, characterized in that: The food packaging material comprises: a cast polypropylene layer, wherein the material of the cast polypropylene layer comprises a first propylene copolymer; a heat-resistant surface layer, wherein the material of the heat-resistant surface layer comprises propylene homopolymer and petroleum resin; and an intermediate layer, the intermediate layer being disposed between the heat-resistant surface layer and the cast polypropylene layer, the material of the intermediate layer comprising a second propylene copolymer; The melting point of the heat-resistant surface layer is higher than the melting point of the cast polypropylene layer, and the melting point of the cast polypropylene layer is higher than the melting point of the intermediate layer.

2. The food packaging material according to claim 1, characterized in that The melting point of the propylene homopolymer is 160°C to 170°C.

3. The food packaging material according to claim 1, characterized in that The first propylene copolymer has a melting point of 145°C to 159°C.

4. The food packaging material according to claim 1, characterized in that The second propylene copolymer has a melting point of 125°C to 140°C.

5. The food packaging material according to claim 1, characterized in that In the heat-resistant surface layer, with the total weight of the propylene homopolymer, the petroleum resin and the inorganic filler being 100 weight percent, the content of the propylene homopolymer is 87 weight percent to 94 weight percent, and the content of the petroleum resin is 1.5 weight percent to 5 weight percent.

6. The food packaging material according to claim 1, characterized in that Taking the total weight of the first propylene copolymer as 100 weight percent, the first propylene copolymer is polymerized from 90 weight percent to 99.99 weight percent of propylene monomer and 0.01 weight percent to 10 weight percent of ethylene monomer.

7. The food packaging material according to claim 1, characterized in that Based on the total weight of the second propylene copolymer being 100 weight percent, the second propylene copolymer is polymerized from 70 weight percent to 85 weight percent of propylene monomer and from 15 weight percent to 30 weight percent of ethylene monomer.

8. The food packaging material according to claim 1, characterized in that The petroleum resin is a hydrogenated petroleum resin having 5 or 10 carbon atoms.

9. The food packaging material according to claim 1, characterized in that The petroleum resin is an aromatic copolymer hydrogenated petroleum resin produced by reacting a hydrogenated petroleum resin having 5 or 10 carbon atoms with an aromatic.

10. The food packaging material according to claim 8 or 9, characterized in that: The hydrogenated petroleum resin having 5 or 10 carbon atoms is piperylene hydrogenated resin or dicyclopentadiene hydrogenated resin.

11. The food packaging material according to claim 1, characterized in that The thickness of the middle layer is 18 to 20 microns, the thickness of the cast polypropylene layer is 50 to 70 microns, and the thickness of the heat-resistant surface layer is 20 to 30 microns.

12. A method for manufacturing a food packaging material, characterized in that: The manufacturing method comprises: Performing a casting procedure to generate a cast polypropylene layer; wherein the material of the cast polypropylene layer includes a first propylene copolymer; Performing a biaxial stretching process to generate a laminated structure; wherein the laminated structure includes an intermediate layer and a heat-resistant surface layer, the intermediate layer is made of a second propylene copolymer, and the heat-resistant surface layer is made of a propylene homopolymer and a petroleum resin; and Disposing the cast polypropylene layer on the laminate structure to produce a food packaging material; wherein the cast polypropylene layer is in contact with the intermediate layer; The melting point of the heat-resistant surface layer is higher than the melting point of the cast polypropylene layer, and the melting point of the cast polypropylene layer is higher than the melting point of the intermediate layer.

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