Laminates and packaging containers for frozen food

Abstract

The laminate of the present invention comprises an inner layer and a pair of outer layers laminated on both sides of the inner layer. The inner layer contains an inorganic filler and a first thermoplastic resin. The outer layer contains a second thermoplastic resin. The inorganic filler contains calcium carbonate particles. The content of the inorganic filler in the laminate exceeds 50% by mass. The first thermoplastic resin and the second thermoplastic resin each satisfy specific conditions. The combined content of the first thermoplastic resin, the second thermoplastic resin, and the third thermoplastic resin satisfying the specific conditions in the first thermoplastic resin and the second thermoplastic resin exceeds 90% by mass.

Description

Technical Field

[0001] This invention relates to laminates and packaging containers for frozen foods. Background Technology

[0002] In recent years, with the increasing demand for frozen foods, the demand for containers for holding frozen foods and packaging for wrapping frozen foods (hereinafter, sometimes collectively referred to as "packaging containers for frozen foods") has also increased. Packaging containers for frozen foods can be obtained, for example, by processing sheet materials (hereinafter, sometimes referred to as "material sheets") containing thermoplastic resins (e.g., polyethylene resin, polypropylene resin, and polystyrene resin).

[0003] From the perspective of improving the operability of frozen foods during manufacturing and cooking, packaging containers for frozen foods must have appropriate rigidity. Furthermore, during distribution, frozen foods are subject to vibration during transport or accidental drops by consumers or distributors. Therefore, packaging containers for frozen foods must possess the property of not easily breaking under impact at low temperatures (e.g., around -20°C) (hereinafter sometimes referred to as "cold shock resistance"). Moreover, due to increased environmental awareness in recent years, packaging containers for frozen foods are increasingly required to be environmentally friendly. In view of the above, the material sheets used as packaging containers for frozen foods are also required to have excellent rigidity and cold shock resistance, and minimal environmental impact. Additionally, the aforementioned material sheets naturally also require excellent processability.

[0004] To address the above requirements, for example, a material sheet with a three-layer structure, in which a small amount of inorganic filler (talc, etc.), block polypropylene resin, and polyethylene resin are mixed in the middle layer (e.g., Patent Document 1). The material sheet described in Patent Document 1 exhibits excellent cold impact resistance.

[0005] [Patent Documents]

[0006] Patent Document 1: Japanese Patent Application Publication No. 2021-37748 Summary of the Invention

[0007] However, through research, the inventors discovered that the material sheet described in Patent Document 1 cannot fully satisfy the requirements for processability, cold shock resistance, and rigidity. Furthermore, the material sheet described in Patent Document 1 is primarily composed of resin, thus having a significant environmental impact.

[0008] The present invention was made in view of the above-mentioned problems, and its object is to provide a laminate and a packaging container for frozen food formed from the laminate, the laminate having excellent processability, cold shock resistance and rigidity and low environmental impact.

[0009] The laminate of the present invention comprises an inner layer and a pair of outer layers laminated on both sides of the inner layer. The inner layer contains an inorganic filler and a first thermoplastic resin. The outer layer contains a second thermoplastic resin. The inorganic filler contains calcium carbonate particles. The inorganic filler in the laminate contains more than 50% by mass. The first thermoplastic resin and the second thermoplastic resin each satisfy condition A or B below. The combined content of the first thermoplastic resin, the second thermoplastic resin, and the third thermoplastic resin in both the first and second thermoplastic resins exceeds 90% by mass.

[0010] A: Contains a density of 0.942 g / cm³ 3 Above 0.970g / cm 3 The first polyethylene resin having a polydispersity (Mw / Mn) of 2.0 or more and 10.0 or less.

[0011] B: Contains a density of 0.942 g / cm³ 3 Above 0.970g / cm 3 The following are second-generation polyethylene resins with a polydispersity (Mw / Mn) greater than 10.0 and less than 50.0 and a density of 0.850 g / cm³. 3 Above and less than 0.930 g / cm 3 The third polyethylene resin, relative to the total mass of the second polyethylene resin and the third polyethylene resin, has a mass ratio of 5% to 30% by mass.

[0012] The packaging container for frozen food of the present invention is formed by processing and molding the above-mentioned laminate.

[0013] [Invention Effects]

[0014] The laminate of the present invention has excellent processability, cold shock resistance, and rigidity, and has a low environmental impact. The packaging container for frozen food of the present invention has excellent cold shock resistance and rigidity, and has a low environmental impact. Attached Figure Description

[0015] Figure 1 This is an example cross-sectional view of the structure of the laminate of the present invention. Detailed Implementation

[0016] The embodiments of the present invention will be described below. However, the present invention is not limited to these embodiments, and appropriate modifications can be made within the scope of the present invention before implementation. Unless otherwise stated, each material described in the embodiments of the present invention may be used individually or in combination with two or more materials.

[0017] In this specification, the density of polyethylene resin refers to the value measured according to JIS (Japanese Industrial Standard) K7112:1999. Polyethylene resin refers to a resin formed from monomers whose main component is ethylene (for example, monomers in which ethylene accounts for 80% by mass or more).

[0018] The molecular weight (weight-average molecular weight and number-average molecular weight) of the resin refers to the value measured by the following high-temperature GPC (volume exclusion chromatography).

[0019] Measuring device: HLC-8321GPC / HT manufactured by Tosoh Corporation

[0020] GPC column: TSKgel (Japanese registered trademark) GMHHR-H(20)HT manufactured by Tosoh Corporation.

[0021] Rinse solution: 1,2,4-Trichlorobenzene (TCB)

[0022] Column temperature: 140℃

[0023] Detector: Differential refractometer (RI)

[0024] Flow rate: 1 mL / min

[0025] Injection volume: 300μL

[0026] Standard sample: Standard polystyrene (converted to the Q value of polyethylene)

[0027] <First Embodiment: Laminated Component>

[0028] The laminate according to the first embodiment of the present invention comprises an inner layer and a pair of outer layers laminated on both sides of the inner layer. The inner layer contains an inorganic filler and a first thermoplastic resin. The outer layer contains a second thermoplastic resin. The inorganic filler contains calcium carbonate particles. The content of the inorganic filler in the laminate exceeds 50% by mass. The first thermoplastic resin and the second thermoplastic resin each satisfy condition A or B below.

[0029] A: Contains a density of 0.942 g / cm³ 3 Above 0.970g / cm 3 The first polyethylene resin having a polydispersity (Mw / Mn) of 2.0 or more and 10.0 or less.

[0030] B: Contains a density of 0.942 g / cm³ 3 Above 0.970g / cm 3 The following are second-generation polyethylene resins with a polydispersity (Mw / Mn) greater than 10.0 and less than 50.0 and a density of 0.850 g / cm³. 3 Above and less than 0.930 g / cm 3The mass ratio of the third polyethylene resin to the total mass of the second and third polyethylene resins is more than 5% by mass and less than 30% by mass.

[0031] Below, the density is 0.942 g / cm³. 3 Above 0.970g / cm 3 The following polyethylene resin is sometimes referred to as "high-density polyethylene resin," with a density of 0.850 g / cm³. 3 Above and less than 0.930 g / cm 3 Polyethylene resin is sometimes referred to as "low-density polyethylene resin".

[0032] The laminate of the present invention can be used as a material for packaging containers, for example. The laminate of the present invention is suitable as a material for food packaging containers (especially for frozen foods). Specifically, packaging containers can be formed by processing the laminate of the present invention into a desired shape. Methods for processing the laminate of the present invention include, for example, vacuum forming, pressure forming, and plastic forming.

[0033] Hereinafter, the laminate of the present invention will be described in detail with reference to the accompanying drawings. Figure 1 This is a cross-sectional view of a laminate 1, which is an example of a laminate of the present invention. The laminate 1 includes an inner layer 2 and a pair of outer layers 3 laminated on both sides of the inner layer 2. As described above, the laminate of the present invention has been described in detail with reference to the accompanying drawings. However, the structure of the laminate of the present invention is not limited to... Figure 1 The structure of the laminate 1 shown is illustrated. For example, the laminate of the present invention may also have other layers in addition to the inner layer and an outer layer. Other layers may include, for example, a protective layer that covers the outer layer.

[0034] The laminate of the present invention satisfies the above-described structure, thus exhibiting excellent processability, cold shock resistance, and rigidity, while having a minimal environmental impact. The reasons for these effects are speculated as follows: The laminate of the present invention contains inorganic fillers and thermoplastic resin. The inorganic filler content in the laminate of the present invention exceeds 50% by mass. The resin content in the laminate of the present invention is low, resulting in relatively low carbon dioxide emissions during incineration, thus minimizing environmental impact. Furthermore, under Japan's "Container and Packaging Recycling Law," packaging containers are classified according to the material with the highest mass percentage. Therefore, certain packaging containers (e.g., glass containers, paper packaging containers, PET plastic bottles, and plastic packaging containers) are obligated to be recycled. In contrast, the packaging container formed by the laminate of the present invention has the highest mass percentage of inorganic fillers, and therefore does not fall under the category of specific packaging containers subject to recycling obligations. Moreover, as mentioned above, the packaging container formed by the laminate of the present invention emits relatively low amounts of carbon dioxide during incineration. Therefore, the packaging container formed by the laminate of the present invention can be disposed of as either combustible or non-combustible waste, resulting in low disposal costs.

[0035] In this context, inorganic fillers act as fillers, thus material sheets containing a small amount of inorganic fillers and thermoplastic resin often exhibit excellent cold impact resistance and rigidity. However, when the material sheet contains a large amount of inorganic fillers and thermoplastic resin, the thermoplastic resin often loses its strength and its function as a binding resin at low temperatures, leading to a decrease in cold impact resistance. Through in-depth research, the inventors have discovered that by using thermoplastic resins that meet specific conditions, even material sheets with a large amount of inorganic fillers can exhibit sufficient cold impact resistance.

[0036] Specifically, in the laminate of the present invention, the inner layer contains inorganic fillers and a first thermoplastic resin, while the outer layer contains a second thermoplastic resin. Both the first and second thermoplastic resins contain high-density polyethylene resin. High-density polyethylene resin exhibits excellent strength and rigidity at room temperature, and also excellent cold resistance. Among them, the high-density polyethylene resin with a lower polydispersity (Mw / Mn) (the first polyethylene resin) can fully exert its excellent strength and function as a binding resin at low temperatures. Therefore, the high-density polyethylene resin with a lower polydispersity (Mw / Mn) is suitable as both the first and second thermoplastic resins (condition A).

[0037] On the other hand, high-density polyethylene resin (second polyethylene resin) with a high polydispersity ratio (Mw / Mn) is difficult to maintain its strength and function as a bonding resin at low temperatures, and therefore is not suitable as a first or second thermoplastic resin alone. However, by adding low-density polyethylene resin (third polyethylene resin) to high-density polyethylene resin with a high polydispersity ratio (Mw / Mn) to form a mixed resin, excellent adhesive strength is achieved at low temperatures. Therefore, the aforementioned mixed resin can adequately maintain excellent strength and function as a bonding resin at low temperatures. However, when too much low-density polyethylene resin is added to the aforementioned mixed resin, its rigidity at room temperature tends to decrease. Therefore, a mixed resin containing both high-density polyethylene resin with a high polydispersity ratio (Mw / Mn) and low-density polyethylene resin in a specific mixing ratio is suitable for use as a first or second thermoplastic resin (condition B).

[0038] In summary, in the laminate of the present invention, by satisfying conditions A or B for the first thermoplastic resin and the second thermoplastic resin, excellent cold impact resistance and rigidity can be achieved.

[0039] Furthermore, the laminate of the present invention has a three-layer structure comprising an inner layer and an outer layer. Material sheets containing a large amount of inorganic filler often have poorer processability (especially ductility) compared to material sheets without inorganic fillers. Specifically, when a material sheet containing a large amount of inorganic filler is stretched at a high ratio (e.g., about 4 times), it sometimes cannot be stretched sufficiently, resulting in holes. In contrast, in the laminate of the present invention, the inner layer is covered by an outer layer. Since the outer layer does not contain a large amount of inorganic filler like the inner layer, it has excellent ductility. Therefore, when the laminate of the present invention is stretched at a high ratio, even if the inner layer is not stretched sufficiently, the outer layer will be stretched sufficiently, thus reducing the likelihood of holes forming throughout the laminate.

[0040] Furthermore, in the laminate of the present invention, the inorganic filler acts as a filler, thus exhibiting excellent heat resistance. Therefore, the laminate of the present invention can be used, for example, as a food packaging container for microwave heating. Also, in the laminate of the present invention, the surface (outer layer) is a layer with resin as the main component, thus exhibiting excellent acid resistance. Therefore, the laminate of the present invention can be used, for example, as a food packaging container for contact with acidic foods (dried plums, lemons, etc.).

[0041] The overall thickness of the laminate of the present invention is preferably 200 μm to 1000 μm, more preferably 250 μm to 800 μm. When the overall thickness of the laminate of the present invention is 200 μm or more, the cold shock resistance of the laminate of the present invention can be further improved. When the overall thickness of the laminate of the present invention is 1000 μm or less, the packaging container formed by the laminate of the present invention can be made lighter.

[0042] [Inner layer]

[0043] The inner layer is a layer containing inorganic fillers and a first thermoplastic resin. In the inner layer, the first thermoplastic resin functions as a binding resin.

[0044] The thickness of the inner layer is preferably 150 μm to 800 μm, more preferably 220 μm to 700 μm. When the thickness of the inner layer is 150 μm or more, the cold shock resistance of the laminate of the present invention can be further improved. When the thickness of the inner layer is 800 μm or less, the processability of the laminate of the present invention can be further improved.

[0045] (Inorganic packing)

[0046] Inorganic fillers contain calcium carbonate particles. The purity of these calcium carbonate particles varies greatly depending on their source. Specifically, most calcium carbonate particles used as inorganic fillers are obtained by directly granulating calcium carbonate ore obtained from mineral resources without refining. Therefore, the purity of the calcium carbonate particles varies significantly depending on the origin. For example, some producing areas have low-purity calcium carbonate particles containing approximately 70% by mass. On the other hand, high-purity calcium carbonate particles obtained through chemical synthesis are also available for food and pharmaceutical use.

[0047] The laminate of the present invention preferably contains calcium carbonate particles of the highest possible purity. Specifically, the calcium carbonate content in the calcium carbonate particles is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 97% by mass or more. The higher the purity of the calcium carbonate particles, the higher the environmental safety. When the calcium carbonate content in the calcium carbonate particles is 90% by mass or more, the environmental impact can be further reduced.

[0048] The maximum particle size of the calcium carbonate particles is preferably 20 μm or less. However, voids may exist at the interface between the calcium carbonate particles and the first thermoplastic resin in the inner layer. Regarding the laminate of the present invention, the fewer such voids in the inner layer, the better the processability. It can be determined that the larger the particle size of the calcium carbonate particles, the easier it is for such voids to form. Therefore, by making the maximum particle size of the calcium carbonate particles 20 μm or less, the formation of voids at the interface between the calcium carbonate particles and the first thermoplastic resin can be suppressed. As a result, the processability of the laminate of the present invention can be further improved.

[0049] In addition, the maximum particle size of calcium carbonate particles can be measured using the following method. First, using an electron microscope, the particle size (long axis) of the calcium carbonate particles is measured at five randomly selected locations (field of view: 100 μm × 100 μm) from the inner layer cross-section. Then, the maximum measured particle size of the calcium carbonate particles is taken as the maximum particle size of the calcium carbonate particles.

[0050] Calcium carbonate particles can also undergo surface treatment. Examples of surface treatments include silane coupling agent treatment and metal soap treatment (e.g., calcium stearate treatment). By surface treating the calcium carbonate particles, voids at the interface between the calcium carbonate particles and the first thermoplastic resin can be suppressed. As a result, the processability of the laminate of the present invention can be further improved.

[0051] The inorganic filler content in the inner layer is preferably 53% by mass or more and 70% by mass or less, more preferably 55% by mass or more and 60% by mass or less. When the inorganic filler content in the inner layer is 53% by mass or more, the cold shock resistance of the laminate of the present invention can be further improved. When the inorganic filler content in the inner layer is 70% by mass or less, the ductility of the inner layer can be improved.

[0052] The inorganic filler content in the laminate of the present invention exceeds 50% by mass, preferably exceeds 50% by mass and is 60% by mass or less, more preferably exceeds 50% by mass and is 55% by mass or less. By making the inorganic filler content in the laminate of the present invention exceed 50% by mass, the heat resistance of the laminate of the present invention can be improved. Furthermore, the packaging container formed from the laminate of the present invention is not subject to the recycling obligations stipulated by the Japanese Container and Packaging Recycling Law. Moreover, the carbon dioxide emissions of the laminate of the present invention during incineration can be reduced. In addition, inorganic fillers are generally cheaper than resins; therefore, by using more inorganic fillers, the material cost of the laminate of the present invention can be reduced. By making the inorganic filler content in the laminate of the present invention 60% by mass or less, the processability of the laminate of the present invention can be further improved.

[0053] The inner layer may also contain other inorganic fillers besides calcium carbonate particles. Examples of other inorganic fillers include: calcium sulfate particles, barium sulfate particles, kaolin particles, mica particles, zinc oxide particles, dolomite particles, glass fiber, hollow glass microspheres, silica particles, chalk particles, talc, pigment particles, titanium dioxide particles, silica particles, bentonite, clay, diatomaceous earth, and zeolite. Compared to other inorganic fillers, calcium carbonate particles are inexpensive and readily available, making them a preferred choice.

[0054] The proportion of calcium carbonate particles in the inorganic filler is preferably 90% by mass or more, and more preferably 100% by mass.

[0055] (First thermoplastic resin)

[0056] The first thermoplastic resin contained in the inner layer satisfies either condition A or B below.

[0057] A: Contains a density of 0.942 g / cm³ 3 Above 0.970g / cm 3 The first polyethylene resin having a polydispersity (Mw / Mn) of 2.0 or more and 10.0 or less.

[0058] B: Contains a density of 0.942 g / cm³ 3 Above 0.970g / cm 3 The following are second-generation polyethylene resins with a polydispersity (Mw / Mn) greater than 10.0 and less than 50.0 and a density of 0.850 g / cm³. 3 Above and less than 0.930 g / cm 3 The mass ratio of the third polyethylene resin to the total mass of the second and third polyethylene resins is more than 5% by mass and less than 30% by mass.

[0059] The first type of polyethylene resin is a high-density polyethylene resin with a relatively low polydispersity (Mw / Mn). The density of the first type of polyethylene resin is 0.942 g / cm³. 3 Above 0.970g / cm 3 The preferred value is 0.950 g / cm³. 3 Above 0.960g / cm 3 The polydispersity (Mw / Mn) of the first polyethylene resin is 2.0 to 10.0, preferably 6.0 to 9.0. The weight-average molecular weight (Mw) of the first polyethylene resin is preferably 100,000 to 1,000,000, more preferably 250,000 to 500,000. The number-average molecular weight (Mn) of the first polyethylene resin is preferably 10,000 to 400,000, more preferably 30,000 to 60,000. By keeping the various physical properties of the first polyethylene resin within the above-mentioned numerical ranges, the cold shock resistance and rigidity of the laminate of the present invention can be improved.

[0060] When the first thermoplastic resin satisfies condition A, the first thermoplastic resin may contain only the first polyethylene resin, but it is preferable to further contain a third polyethylene resin. When the first thermoplastic resin contains both the first and third polyethylene resins, the mass ratio of the third polyethylene resin relative to the total mass of the first and third polyethylene resins is preferably 5% by mass or more and 30% by mass or less, more preferably 15% by mass or more and 25% by mass or less. When the above ratio is 5% by mass or more, the cold shock resistance of the laminate of the present invention can be further improved. When the above ratio is 30% by mass or less, the rigidity of the laminate of the present invention can be further improved.

[0061] The second type of polyethylene resin is a high-density polyethylene resin with a relatively high polydispersity (Mw / Mn). The density of the second type of polyethylene resin is 0.942 g / cm³. 3 Above 0.970g / cm 3 The preferred value is 0.950 g / cm³. 3 Above 0.960g / cm 3 The polydispersity (Mw / Mn) of the second polyethylene resin is greater than 10.0 and less than 50.0, preferably more than 15.0 and less than 25.0. The weight-average molecular weight (Mw) of the second polyethylene resin is preferably more than 100,000 and less than 2,000,000, more preferably more than 250,000 and less than 800,000. The number-average molecular weight (Mn) of the second polyethylene resin is preferably more than 5,000 and less than 100,000, more preferably more than 10,000 and less than 30,000. By keeping the various physical properties of the second polyethylene resin within the above-mentioned numerical ranges, the cold shock resistance and rigidity of the laminate of the present invention can be improved.

[0062] Examples of third-party polyethylene resins include: low-density polyethylene resins with branched structures (e.g., density 0.910 g / cm³). 3 Above and less than 0.930 g / cm 3 ) and linear low-density polyethylene resin (e.g., density 0.850 g / cm³) 3 Above and less than 0.930 g / cm 3 ).

[0063] The density of the third type of polyethylene resin is 0.850 g / cm³. 3 Above and less than 0.930 g / cm 3 The preferred value is 0.870 g / cm³. 3 Above and less than 0.930 g / cm 3 By ensuring that the density of the third polyethylene resin is within the aforementioned numerical range, the cold impact resistance and rigidity of the laminate of the present invention can be improved.

[0064] When the first thermoplastic resin satisfies condition B, the mass ratio of the third polyethylene resin to the total mass of the second and third polyethylene resins is 5% by mass or more and 30% by mass or less, more preferably 8% by mass or more and 22% by mass or less. When the above ratio is 5% by mass or more, the cold shock resistance of the laminate of the present invention can be improved. When the above ratio is 30% by mass or less, the rigidity of the laminate of the present invention can be improved.

[0065] If the content of the first thermoplastic resin is relatively low, the first thermoplastic resin may further contain resins other than the first polyethylene resin, the second polyethylene resin, and the third polyethylene resin. Examples of other resins include: polyolefin resins (e.g., polypropylene and medium-density polyethylene), ABS resin, polyamide resin, polystyrene resin, and polyester resins (e.g., polyethylene terephthalate resin and polybutylene terephthalate resin). The content of other resins in the first thermoplastic resin is preferably 10% by mass or less, more preferably 0% by mass. In other words, the total content of the first polyethylene resin, the second polyethylene resin, and the third polyethylene resin in the first thermoplastic resin is preferably more than 90% by mass, more preferably 100% by mass.

[0066] (Other additives)

[0067] The inner layer may further contain additives other than inorganic fillers. Other additives include, for example, coupling agents, lubricants, filler dispersants, antistatic agents, antioxidants, heat stabilizers, ultraviolet absorbers, and weather stabilizers.

[0068] As described above, the inner layer contains a high proportion of inorganic fillers. Therefore, it is preferable that the inner layer contains a filler dispersant as an additional additive. By including a filler dispersant in the inner layer, the dispersibility of the inorganic filler can be improved. Examples of filler dispersants include metal soaps (e.g., calcium stearate and magnesium stearate). When the inner layer contains other additives, the proportion of these other additives is preferably 0.5% by mass or more and 5% by mass or less.

[0069] [Outer layer]

[0070] The outer layer is a layer containing a second thermoplastic resin. The thickness ratio of each outer layer relative to the overall thickness of the laminate of the present invention is preferably 2.0% to 20.0%, more preferably 3.0% to 10.0%. When the thickness ratio of the outer layer is 2.0% or more, the processability of the laminate of the present invention can be further improved. When the thickness ratio of the outer layer is 20.0% or less, the content ratio of inorganic fillers in the laminate of the present invention can be easily adjusted to exceed 50% by mass. Furthermore, the thicknesses of the two pairs of outer layers can be the same or different.

[0071] The thickness of each of the outer layers is preferably 5 μm or more and 80 μm or less, more preferably 10 μm or more and 50 μm or less. When the thickness of the outer layer is 5 μm or more, the processability of the laminate of the present invention can be further improved. When the thickness of the outer layer is 80 μm or less, the content ratio of inorganic filler in the laminate of the present invention can be easily adjusted to exceed 50% by mass.

[0072] (Second thermoplastic resin)

[0073] The second thermoplastic resin contained in the outer layer satisfies condition A or B above. The specific composition of the second thermoplastic resin contained in the outer layer, and the specific composition of the first, second, and third polyethylene resins contained within the second thermoplastic resin, can, for example, be the same as the first, second, and third thermoplastic resins in the inner layer. Furthermore, in the laminate of the present invention, the first and second thermoplastic resins preferably have the same composition.

[0074] The second thermoplastic resin in the outer layer preferably contains 90% by mass or more, more preferably 95% by mass or more. The total content of the first polyethylene resin, the second polyethylene resin, and the third polyethylene resin in the second thermoplastic resin preferably exceeds 90% by mass, more preferably 100% by mass.

[0075] The outer layer is preferably free of inorganic fillers, but may contain a small amount of inorganic fillers. The proportion of inorganic fillers in the outer layer is preferably 5% by mass or less, more preferably 0% by mass.

[0076] [Manufacturing Method]

[0077] The laminated part of the present invention is manufactured, for example, by the well-known multi-layer T-die method. Specifically, an inner layer forming material (a material containing a first thermoplastic resin and an inorganic filler) and an outer layer forming material (a material containing a second thermoplastic resin) are first prepared. Then, the inner layer forming material and the outer layer forming material are extruded separately from different extruders, and the laminated part of the present invention can be obtained by laminating them inside a T-die. However, the method for manufacturing the laminated part of the present invention is not limited to the multi-layer T-die method.

[0078] <Second Embodiment: Food Packaging Container>

[0079] The frozen food packaging container according to the second embodiment of the present invention is formed by processing the laminated part according to the first embodiment. The frozen food packaging container of the present invention can be used, for example, as a bento box, food bag, tray, plate, cup, and cup lid. Because the frozen food packaging container of the present invention is formed by processing the laminated part according to the first embodiment, it has excellent cold shock resistance and rigidity and has a relatively small environmental impact.

[0080] The frozen food packaging container of the present invention has the same layer structure as the laminate according to the first embodiment. However, compared with the laminate according to the first embodiment, the frozen food packaging container of the present invention can also change the thickness of each layer by stretching during processing. For example, different parts of the frozen food packaging container of the present invention may have different thicknesses. In this case, the thickness ratio of the thickest part to the thinnest part of the frozen food packaging container of the present invention is preferably 2.0 times to 4.5 times and more preferably 3.5 times to 4.5 times and less.

[0081]

Example

[0082] The present invention will be further described below through embodiments. However, the present invention is not limited to the embodiments.

[0083] [Material]

[0084] First, the materials used in the embodiments will be described.

[0085] CaCO3: Calcium carbonate particles, maximum particle size approximately 20 μm

[0086] Talc: Average particle size 12μm

[0087] HDPE-A: High-density polyethylene resin (manufactured by KEIYO POLYETHYLENE CO.,LTD., "B5803"); Mw: 380,000; Mn: 19,000; Mw / Mn: 20.0; Density: 0.957 g / cm³ 3

[0088] HDPE-B: High-density polyethylene resin (manufactured by KEIYO POLYETHYLENE CO.,LTD. as "E8040"); Mw: 370,000; Mn: 47,000; Mw / Mn: 7.9; Density: 0.957 g / cm³ 3

[0089] PP: Block polypropylene resin (Prime Polymer Co., Ltd. manufactures "E702MG")

[0090] LDPE: Low-density polyethylene resin with a branched structure (manufactured by Japan Polyethylene Corporation, "LF128"), density: 0.922 g / cm³ 3

[0091] LLDPE-A: Linear low-density polyethylene resin (manufactured by Japan Polyethylene Corporation, "KS240T"), density: 0.880 g / cm³ 3

[0092] LLDPE-B: Linear low-density polyethylene resin (manufactured by Prime Polymer Co., Ltd. as "SP1520"), density: 0.912 g / cm³ 3

[0093] In the above materials, HDPE-A is the second polyethylene resin. HDPE-B is the first polyethylene resin. LDPE, LLDPE-A, and LLDPE-B are the third polyethylene resins. Hereinafter, HDPE-A, HDPE-B, and PP are sometimes collectively referred to as matrix resins. LDPE, LLDPE-A, and LLDPE-B are sometimes collectively referred to as additive resins.

[0094] [Example 1]

[0095] The following materials are mixed using a twin-screw mixer and then sliced ​​to obtain masterbatches for inner layer and outer layer formation.

[0096] Materials used for forming the inner layer: CaCO3 (58 parts by mass), HDPE-A (38 parts by mass), and LLDPE-A (4 parts by mass).

[0097] Materials used for outer layer formation: HDPE-A (90 parts by weight) and LLDPE-A (10 parts by weight)

[0098] Furthermore, both the inner layer forming material and the outer layer forming material contain a first thermoplastic resin and a second thermoplastic resin. Each of the first and second thermoplastic resins contains a second polyethylene resin (HDPE-A) and a third polyethylene resin (LLDPE-A). In both the first and second thermoplastic resins, the mass ratio of the third polyethylene resin (LLDPE-A) relative to the total mass of the second polyethylene resin (HDPE-A) and the third polyethylene resin (LLDPE-A) is 10% by mass. As described above, the first and second thermoplastic resins satisfy condition B.

[0099] A laminate is formed using a multi-layer T-die method, comprising an inner layer and a pair of outer layers laminated on both sides of the inner layer. The inner layer is formed using the aforementioned material for forming the inner layer. Each of the outer layers is formed using the aforementioned material for forming the outer layer. The overall thickness of the laminate is 300 μm. The thickness of the inner layer is 270 μm (90% of the overall thickness of the laminate). Each of the outer layers is 15 μm (5% of the overall thickness of the laminate). The inorganic filler content in the laminate is 52% by mass. This is used as the laminate of Example 1.

[0100] [Examples 2-6 and Comparative Examples 1-9]

[0101] Except for changing the composition of the inner layer forming material and the outer layer forming material as shown in Tables 1 and 2 below, laminates of Examples 2 to 6 and Comparative Examples 1 to 9 were formed according to the method of laminate of Example 1.

[0102] [Comparative Example 10]

[0103] The following materials are mixed using a twin-screw mixer and then sliced ​​to obtain a masterbatch for single-layer forming.

[0104] Materials for single-layer formation: talc (15 parts by weight) and PP (85 parts by weight)

[0105] A single-layer material plate was formed using the T-die method. The thickness of the single-layer material plate was 300 μm. The inorganic filler content in the single-layer material plate was 15% by mass. This was used as the single-layer body for Comparative Example 10.

[0106] [Comparative Example 11]

[0107] The following materials are mixed using a twin-screw mixer and then sliced ​​to obtain a masterbatch for single-layer forming.

[0108] Material for single-layer formation: PP (100 parts by weight)

[0109] A single-layer material plate was formed using the T-die method. The thickness of the single-layer material plate was 300 μm. The inorganic filler content in the single-layer material plate was 0% by mass. This was used as the single-layer body for Comparative Example 11.

[0110] In addition, Comparative Examples 10 and 11 are single-layer bodies whose composition is similar to that of the material plates used in the packaging containers for frozen foods in the prior art.

[0111] In Tables 1 and 2 below, "parts" indicates parts by mass. The "ratio" of added resin indicates the mass ratio of added resin to the total mass of the thermoplastic resin. "A" and "B" in the "conditions" section of the thermoplastic resin each indicate that condition A or B is satisfied. "-" in the "conditions" section of the thermoplastic resin indicates that neither condition A nor condition B is satisfied.

[0112] Table 1

[0113]

[0114] Table 2

[0115]

[0116] <Evaluation>

[0117] The cold shock resistance, rigidity, and environmental friendliness (degree of environmental impact) of the laminates (or monolayers) of Examples 1-6 and Comparative Examples 1-11 were evaluated using the following methods. The evaluation results are shown in Table 3 below.

[0118] [Cold Shock Resistance]

[0119] For the laminated components (or monolayers) used as evaluation objects, the 50% breaking energy was measured using an impact testing machine ("DuPont Drop Impact Testing Machine with Cryogenic Bath No. 603-L" manufactured by MYS-TESTER Company Limited) according to JIS (Japanese Industrial Standard) K7211-1:2006. First, the evaluation object was cut into 50mm × 50mm rectangles to create test pieces. Next, a constant-mass hammer was repeatedly dropped from multiple heights onto multiple test pieces, and the energy at which 50% of the test pieces broke (50% breaking energy) was measured. The measurement conditions were a hammer mass of 200g and a measurement temperature of -20°C (low-temperature environment). In this test, the cold shock resistance of the evaluation object can be numerically determined in the form of 50% breaking energy [J]. Specifically, the higher the 50% breaking energy of the evaluation object, the higher its cold shock resistance.

[0120] The cold shock resistance of the evaluated object is determined according to the following criteria.

[0121] A (Qualified): 50% destructive energy is above 0.50J.

[0122] B (Unacceptable): 50% destructive energy less than 0.50J

[0123] [rigidity]

[0124] For the laminated components (or monolayers) used as the evaluation objects, tensile testing was performed using a tensile testing machine (INTESCOco.,ltd., "Type 201X Testing Machine") according to JIS (Japanese Industrial Standard) K7161-1:2014. First, the evaluation object was cut into a "test piece type 5" (JIS (Japanese Industrial Standard) K7127:2009) shape (dumbbell shape). The two ends of the obtained test piece were clamped using the chuck of the tensile testing machine, and the tensile test was performed under conditions of a chuck spacing of 80 mm and a tensile speed of 20 mm / min. The dimensions of the test piece after the test were measured, and the tensile modulus of the test piece was calculated. In this test, the rigidity of the evaluation object can be numerically determined in the form of tensile modulus [MPa]. Specifically, the higher the tensile modulus of the evaluation object, the higher its rigidity.

[0125] The rigidity of the evaluation object is determined according to the following criteria.

[0126] A (Qualified): Tensile modulus is above 1500MPa

[0127] B (Unacceptable): Tensile modulus less than 1500 MPa

[0128] [Environmentally friendly]

[0129] The environmental friendliness of the laminate (or monolayer) being evaluated is determined based on the material composition of the evaluated object according to the following criteria.

[0130] A (Qualified): The resin content is less than 50% by mass.

[0131] B (Unqualified): The resin content is 50% or more by mass.

[0132] Table 3

[0133]

[0134] The laminates of Examples 1-6 comprise an inner layer and a pair of outer layers laminated on both sides of the inner layer. The inner layer contains an inorganic filler and a first thermoplastic resin. The outer layer contains a second thermoplastic resin. The inorganic filler contains calcium carbonate particles. The proportion of inorganic filler in the laminate exceeds 50% by mass. The first and second thermoplastic resins each satisfy condition A or B above. The laminates of Examples 1-6 exhibit excellent cold shock resistance and rigidity, and have minimal environmental impact. Furthermore, the laminates of Examples 1-6 have a three-layer structure consisting of an outer layer with excellent ductility covering the inner layer, thus demonstrating excellent processability.

[0135] On the other hand, in the laminate of Comparative Example 1, the first thermoplastic resin and the second thermoplastic resin contain only the second polyethylene resin. It can be determined that the second polyethylene resin is difficult to maintain its strength and function as a bonding resin at low temperatures. Therefore, the cold shock resistance of the laminate of Comparative Example 1 is unqualified.

[0136] In the laminate of Comparative Example 2, both the first and second thermoplastic resins contain only block polypropylene resin. It can be determined that block polypropylene resin is unlikely to maintain its strength and function as a bonding resin at low temperatures. Therefore, the cold shock resistance of the laminate of Comparative Example 2 is unqualified.

[0137] In the laminates of Comparative Examples 3-7, the first thermoplastic resin and the second thermoplastic resin contain block polypropylene resin and either a second polyethylene resin or a third polyethylene resin in various mixing ratios. It can be determined that even when used with various additive resins, the block polypropylene resin is unlikely to maintain its strength and function as a bonding resin at low temperatures. Therefore, the cold shock resistance of the laminates of Comparative Examples 3-7 is unqualified.

[0138] In the laminate of Comparative Example 8, the first and second thermoplastic resins contain block polypropylene resin and a large amount of third polyethylene resin. The block polypropylene resin, by being used in conjunction with the large amount of third polyethylene resin, maintains its strength at low temperatures and functions as a bonding resin. On the other hand, it can be determined that the rigidity of the thermoplastic resin containing the large amount of third polyethylene resin will decrease. Therefore, the rigidity of the laminate of Comparative Example 8 is unacceptable.

[0139] In the laminate of Comparative Example 9, the first thermoplastic resin and the second thermoplastic resin contain a second polyethylene resin and a large amount of a third polyethylene resin. The second polyethylene resin, by being used in conjunction with the large amount of the third polyethylene resin, maintains its strength at low temperatures and functions as a bonding resin. On the other hand, it can be determined that the rigidity of the thermoplastic resin containing the large amount of the third polyethylene resin will decrease. Therefore, the rigidity of the laminate of Comparative Example 9 is unqualified.

[0140] In the monolayer of Comparative Example 10, the thermoplastic resin contains block polypropylene resin and a small amount of talc. The cold impact resistance and rigidity of the monolayer of Comparative Example 10 are satisfactory; however, since resin is the main component, its environmental friendliness is unsatisfactory.

[0141] In the monolayer of Comparative Example 11, the thermoplastic resin contained only block polypropylene resin. It can be determined that block polypropylene alone cannot provide sufficient rigidity. Therefore, the rigidity of the monolayer of Comparative Example 11 is unqualified. Furthermore, since the monolayer of Comparative Example 11 is primarily composed of resin, its environmental friendliness is unqualified.

[0142] The results above demonstrate that the laminate of the present invention exhibits excellent processability, cold shock resistance, and rigidity, while having a minimal environmental impact. In particular, it can be determined that the laminate of the present invention, while having a minimal environmental impact, still demonstrates cold shock resistance and rigidity equal to or greater than that of the material sheets used in prior art frozen food packaging containers (Comparative Examples 10 and 11). Furthermore, the frozen food packaging container of the present invention is formed by processing the aforementioned laminate, thus demonstrating excellent cold shock resistance and rigidity, and a minimal environmental impact.

[0143] [Industry Availability]

[0144] The laminate of the present invention can be used as a material for packaging containers. The packaging containers for frozen foods of the present invention can be used in the sale of frozen foods.

Claims

1. A laminate comprising an inner layer and a pair of outer layers laminated on both sides of the inner layer, characterized in that, The inner layer contains inorganic fillers and a first thermoplastic resin. The outer layer contains a second thermoplastic resin. The inorganic filler contains calcium carbonate particles. According to JIS K7211-1:2006, the 50% failure energy of the laminate, measured at a weight of 200g and a testing temperature of -20℃, is above 0.50J. The inorganic filler in the laminate contains more than 50% by mass. The first thermoplastic resin and the second thermoplastic resin each satisfy either condition A or B below. The total mass of the first polyethylene resin, the second polyethylene resin, and the third polyethylene resin contained in the first thermoplastic resin is 100% by mass relative to the total mass of the first thermoplastic resin. The total mass of the first polyethylene resin, the second polyethylene resin, and the third polyethylene resin contained in the second thermoplastic resin is 100% by mass relative to the total mass of the second thermoplastic resin. A: Contains a substance with a density of 0.942 g / cm³. 3 Above 0.970g / cm 3 The following are first polyethylene resins with a Mw / Mn ratio of 2.0 or higher and 10.0 or lower; B: Contains a substance with a density of 0.942 g / cm³ 3 Above 0.970g / cm 3 The following are second-generation polyethylene resins with Mw / Mn ratios exceeding 10.0 and below 50.0 and a density of 0.850 g / cm³. 3 Above and less than 0.930 g / cm 3 The third polyethylene resin, relative to the total mass of the second polyethylene resin and the third polyethylene resin, has a mass ratio of 5% to 30% by mass.

2. The laminate according to claim 1, characterized in that, The overall thickness of the laminate is between 200 μm and 1000 μm.

3. The laminate according to claim 1, characterized in that, The thickness ratio of each outer layer relative to the overall thickness of the laminate is 2.0% to 20.0%.

4. The laminate according to claim 1, characterized in that, The inorganic filler in the inner layer contains more than 53% by mass and less than 70% by mass.

5. A packaging container for frozen food, It is formed by processing and molding the laminate as described in claim 1.

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