Thermoforming sheet and molded container

Abstract

To provide a thermoforming sheet and a molded container that have an excellent elastic modulus, use a small amount of resin, and have impact resistance in a freezing environment such as -30°C.SOLUTION: There is provided a thermoforming sheet (1) having a base layer (2) containing an inorganic filler and a polypropylene-based resin, in which the base layer (2) contains an inorganic filler containing talc and calcium carbonate in an amount of 20 to 30 mass% relative to the base layer (2), a mass composition ratio of the talc to the calcium carbonate is 50 / 50 to 75 / 25, an amount of the talc is 12 to 18 mass% of the base layer (2), an average particle diameter (D50) of the talc is 3 to 7 μm, the polypropylene resin is mainly composed of block polypropylene, and has a tensile modulus of elasticity in at least one of MD and TD of 1500 MPa or more, and a DuPont 50% breaking energy at a test temperature (-30°C) of 1.5 J or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a thermoforming sheet having a base layer containing an inorganic filler and a polypropylene-based resin, and to a molded container. The molded container can be used as a food packaging container, and can contribute to various environmental load reductions, such as reducing plastic usage and food waste. [Background technology]

[0002] Containers made by thermoforming a thermoforming sheet made of polypropylene resin using vacuum or compressed air are used as containers for selling boxed lunches and prepared meals at supermarkets and convenience stores. Because these molded containers have the heat and oil resistance inherent to the polypropylene resin, they are often used as packaging containers for hamburger steaks or spaghetti, which consumers can microwave after purchase.

[0003] In recent years, the issue of plastic waste has been attracting social attention from the perspective of reducing environmental impact. As a result, reducing the amount of plastic used in plastic containers has become one of the challenges. Recently, there has also been an increase in demand for frozen foods in the food packaging container field. Frozen foods can be stored for long periods, can be used in the amount needed when needed, and produce less food waste, so they are expected to be a way to combat food loss.

[0004] Patent Document 1 below discloses a thermoforming sheet used for food packaging containers used at temperatures below zero. The thermoforming sheet is characterized by containing a propylene-ethylene block copolymer that meets specific requirements. Examples of the thermoforming sheet include a thermoforming sheet made of the propylene-ethylene block copolymer.

[0005] However, although propylene-ethylene block copolymer (block polypropylene) has excellent impact resistance in a refrigerated environment, it has a low modulus of elasticity. Therefore, when using block polypropylene alone, the sheet thickness must be increased to achieve the required bending rigidity, making it difficult to reduce the amount of plastic used.

[0006] Patent Document 2 below discloses a thermoforming resin sheet and a container that are said to have excellent rigidity, heat resistance, and cold resistance. The thermoforming resin sheet is a sheet containing high-density polyethylene, block polypropylene, homopolypropylene, and an inorganic filler. In the examples, a DuPont impact test result at -30°C of 0.50 to 0.56 (J) is disclosed. However, from the perspective of consumer safety, there is a recent demand for further improvement in the impact resistance of frozen food containers during transportation. [Prior art documents] [Patent documents]

[0007] [Patent Document 1] Japanese Patent Application Laid-Open No. 2009-185240 [Patent Document 2] Japanese Patent Publication No. 2022-087445 Summary of the Invention [Problem to be solved by the invention]

[0008] The problem to be solved by the present invention is to provide a thermoforming sheet and a molded container that have an excellent elastic modulus, require a small amount of resin, and are impact resistant in a freezing environment such as -30°C. [Means for solving the problem]

[0009] The present invention has been made to solve the above-mentioned problems, and the thermoforming sheet of the present invention is a thermoforming sheet having a base layer containing an inorganic filler and a polypropylene-based resin, the base layer containing 20 to 30 mass% of an inorganic filler containing talc and calcium carbonate, the mass composition ratio of talc to calcium carbonate is 50 / 50 to 75 / 25, and the talc accounts for 12 to 18 mass% of the base layer, the average particle size (D50) of the talc is 3 to 7 μm, the polypropylene-based resin is mainly composed of block polypropylene, at least one of the tensile modulus of elasticity in MD and TD is 1500 MPa or more, and the DuPont 50% fracture energy at a test temperature (-30°C) is 1.5 J or more.

[0010] The thermoforming sheet according to the present invention has a base layer containing an inorganic filler, a polypropylene-based resin, and biomass high-density polyethylene, and the base layer contains 20 to 30 mass% of an inorganic filler containing talc and calcium carbonate, with the mass composition ratio of talc to calcium carbonate being 50 / 50 to 75 / 25, and the talc accounts for 12 to 18 mass% of the base layer, the average particle size (D50) of the talc being 3 to 7 μm, the polypropylene-based resin being primarily composed of block polypropylene, and at least one of the tensile moduli in MD and TD being 1500 MPa or more, and the DuPont 50% fracture energy at a test temperature (-30°C) being 1.5 J or more.

[0011] "MD" stands for "Machine Direction" and refers to the direction in which the sheet emerges from the manufacturing machine. "TD" stands for "Transverse Direction" and refers to the width direction of the sheet.

[0012] In particular, it is preferable that the base layer has surface layers made of block polypropylene on both sides thereof. [Effects of the Invention]

[0013] According to the present invention, it is possible to provide a resin having an excellent elastic modulus, using a small amount of resin, and also having impact resistance in a freezing environment such as -30°C. [Brief explanation of the drawings]

[0014] [Figure 1] 1 is a cross-sectional view of a thermoforming sheet according to one embodiment of the present invention. [Figure 2] FIG. 3 is a cross-sectional view of a molded container formed from the thermoforming sheet. DETAILED DESCRIPTION OF THE INVENTION

[0015] An embodiment of the present invention will be described below. This embodiment is an example of how the present invention is implemented, and the present invention is not limited to this embodiment.

[0016] <Thermoforming sheet> <Composite filler> The inorganic filler, which is a component forming the base layer (2), is a composite filler obtained by mixing talc having a specific particle size with calcium carbonate under specific conditions using a high-speed mixer known as a "Henschel mixer" or "super mixer," thereby crushing, mixing, and dispersing the two. The selection of talc and calcium carbonate used in the present invention and the composite method are described in detail below.

[0017] <Talc selection> The talc (5) forming the composite filler (4) may have an average particle size (D50) in the range of 3 to 7 μm. Here, the average particle size (D50) is the median size (D50) measured in accordance with JIS Z 8825:2013 "Particle size analysis - laser diffraction and scattering method." The average particle size (D50) of the talc (5) is preferably 3 to 7 μm, and most preferably 4 to 6 μm.

[0018] Furthermore, talc (5) having an aspect ratio in the range of 20 to 50 can be used. The aspect ratio can be determined by observing talc particles at 30,000 to 100,000 magnifications using an ultra-high resolution field emission scanning electron microscope (for example, Hitachi's "S-4800"), arbitrarily selecting 10 particles whose cross sections can be observed, measuring the thickness and length of each cross section, and calculating each aspect ratio (length / thickness), and then calculating the arithmetic average value.

[0019] To confirm the properties of talc from a thermoforming sheet and a forming container described below, for example, a test piece of an appropriate size, about 80 mm × 80 mm, is cut out from the thermoforming sheet or the forming container, and the test piece is dissolved at high temperature in a high-boiling point solvent such as decalin, and the talc is extracted and dried, and then measured using the method described above.

[0020] <Selection of calcium carbonate> Industrially, calcium carbonate can be classified into heavy calcium carbonate and light calcium carbonate. Heavy calcium carbonate is calcium carbonate obtained by mechanically grinding (dry method, wet method, etc.) natural raw materials (limestone, etc.) whose main component is CaCO3. Light calcium carbonate is calcium carbonate prepared by a synthetic method (chemical precipitation reaction, etc.). Heavy calcium carbonate and / or light calcium carbonate can be used as the calcium carbonate (6) that forms the composite filler (4). Usually, it is preferable to use heavy calcium carbonate.

[0021] The calcium carbonate (6) may have an average particle size of 0.5 to 5 μm, preferably 0.5 to 3 μm, and more preferably 0.5 to 2 μm. The average particle size of the calcium carbonate (6) may be calculated from the specific surface area measured by the air permeability method according to JIS M8511:2014 "Industrial analysis and testing methods for natural graphite."

[0022] <Manufacturing method of composite filler> The composite filler (4) is obtained by mixing, crushing, mixing, and dispersing talc (5) and calcium carbonate (6) under specific conditions using a high-speed mixer such as a "Henschel mixer" or "super mixer."

[0023] The tip speed of the blades (hereinafter sometimes simply referred to as "circumferential speed") is usually used as a parameter for stirring in a high-speed mixer. The composite filler (4) is obtained by stirring talc (5) and calcium carbonate (6) at a peripheral speed of 20 m / s or more, preferably 30 m / s or more, and particularly preferably 40 m / s or more, to crush, mix, and disperse them.

[0024] When raw powders of talc (5) and calcium carbonate (6) are stirred at the above-mentioned peripheral speed, the strong shearing action breaks down secondary agglomerates, and simultaneously, the talc (5) and calcium carbonate (6) exchange positions with each other, resulting in mixing and dispersion. Ultimately, a unique mixture is formed in which calcium carbonate (6) adheres to the surface of the newly formed talc (5) produced by the breakage. This mixture is thought to function as a spacer between the talc (5) and calcium carbonate (6), preventing each from forming secondary agglomerates again. This is thought to be a technical factor that enables the thermoforming sheet (1) and the forming container (10) described later to exhibit the necessary impact resistance in a frozen environment such as -30°C while maintaining an excellent elastic modulus.

[0025] The stirring treatment of talc (5) and calcium carbonate (6) may be carried out in the presence of a surface modifier. Examples of the surface modifier include higher fatty acids or their salts, silane coupling agents, titanate coupling agents, and phosphate esters. When a surface modifier is used, it is preferable to set the temperature of the high-speed mixer's kettle above the melting point of the surface modifier.

[0026] The compositing of talc (5) and calcium carbonate (6) may be completed in a single stirring treatment, or may be performed in two separate treatments: one for crushing talc (5) or calcium carbonate (6), and the other for mixing and dispersing them. For example, talc (5), calcium carbonate (6), and, if necessary, a surface modifier may all be added at the same time, and the compositing may be completed in a single stirring treatment. For example, talc (5) and, if necessary, a surface modifier may be added first, and the talc (5) may be crushed by a primary stirring treatment. Next, calcium carbonate (6) and, if necessary, a surface modifier may be added, and the compositing may be completed by a secondary stirring treatment. For example, calcium carbonate (6) and, if necessary, a surface modifier may be added first, and the calcium carbonate (6) may be crushed by a primary stirring treatment. Next, talc (5) and, if necessary, a surface modifier may be added, and the compositing may be completed by a secondary stirring treatment. For example, two or three high-speed mixers may be prepared, and talc (5) and, if necessary, a surface modifier may be added to a first high-speed mixer to perform disintegration by primary stirring, calcium carbonate (6) and, if necessary, a surface modifier may be added to a second high-speed mixer to perform disintegration by primary stirring, and finally, the respective processed products may be combined in the first high-speed mixer, the second high-speed mixer, or the third high-speed mixer to perform secondary stirring to complete the compounding.

[0027] In the above-mentioned primary stirring treatment, even when talc (5) or calcium carbonate (6) is stirred alone, the peripheral speed of the high-speed mixer is preferably 20 m / s or more, more preferably 30 m / s or more, and particularly preferably 40 m / s or more. Among the above-mentioned methods, the second and fourth exemplified methods in which talc (5) alone is stirred and then stirred for mixing and dispersion with calcium carbonate (6) are preferred. According to these exemplified methods, the talc (5) is sufficiently disintegrated by the stirring treatment of talc (5) alone before being mixed and dispersed with calcium carbonate (6), which is thought to facilitate the development of the above-mentioned "unique mixed form in which calcium carbonate (6) adheres to the surface of talc (5)."

[0028] <Mass composition ratio of talc and calcium carbonate> The mass ratio of the talc (5) to the calcium carbonate (6) in the composite filler (4) can be in the range of 50 / 50 to 75 / 25. When the mass ratio of the talc (5) to the calcium carbonate (6) is in this range, the thermoforming sheet (1) and the molding container (10) described below can exhibit a good balance between an excellent elastic modulus and impact resistance in a freezing environment such as -30°C.

[0029] <Masterbatch of composite fillers, etc.> To facilitate handling in subsequent processes, the composite filler (4) may be made into granulated talc using rosin or the like as a binder. It may also be made into a masterbatch using the polypropylene resin that forms the base layer (2) as the base resin. Alternatively, it may be compounded to form the final base layer formulation. Granulation can be performed using an appropriate manufacturing method, such as a disc pelletizer. Masterbatching and compounding can be performed using an appropriate method, such as a Banbury mixer, an opposed roll, or a single-screw or twin-screw extruder.

[0030] <Amount of composite filler mixed with the base layer> The composite filler (4) can be blended in the range of 20 to 30% by mass with respect to the base layer (2). Even when blended in a concentration of 20 to 30% by mass with respect to the base layer (2), the composite filler (4) can exhibit sufficient impact resistance in a freezing environment such as -30°C while still having an excellent elastic modulus.

[0031] <Final concentration of talc in the base layer> The talc (5) forming the composite filler (4) is preferably contained in the range of 12 to 18% by mass relative to the base layer (2). If the talc (5) is contained in the base layer (2) at less than 12% by mass, the thermoforming sheet (1) and the molding container (10) described below may not have a sufficient elastic modulus. If the talc (5) is contained in the base layer (2) at more than 18% by mass, the impact resistance may not be sufficient in a freezing environment such as -30°C.

[0032] <Polypropylene resin> The polypropylene resin forming the base layer (2) is mainly composed of block polypropylene (hereinafter sometimes referred to as "block polypropylene (8)"). Here, "mainly composed of block polypropylene (8)" means that the polypropylene resin forming the base layer (2) contains 50% by mass or more of block polypropylene (8). There are no particular limitations on the grade of the block polypropylene (8). For example, an extrusion-molding grade can be suitably used, and one having an MFR of 0.1 to 10, preferably 0.1 to 5, more preferably 0.1 to 1 can be used. In this document, the MFR of the polypropylene resin is measured at 230°C and 2.16 kg in accordance with JIS K7210-1.

[0033] Examples of polypropylene resins other than the block polypropylene (8) include homopolypropylene, random polypropylene, etc. When the polypropylene resin contains polypropylene resins other than the block polypropylene (8), they may be contained alone or in combination.

[0034] <Thermoplastic resin components other than polypropylene-based resin> The base layer (2) may contain a thermoplastic resin other than the polypropylene-based resin. There are no particular limitations on the thermoplastic resin other than the polypropylene-based resin. For example, a polyethylene-based resin may be used. Examples of polyethylene-based resins include HDPE, LDPE, and LLDPE. Among these, HDPE is preferably used and may be blended in an amount of 10 to 20% by mass relative to the base layer (2). HDPE can impart drawdown resistance during thermoforming of the thermoforming sheet (1).

[0035] These polyethylene resins may also be biopolyethylene resins derived from biomass such as sugarcane or corn. The use of biopolyethylene resins can further reduce the environmental impact. The biopolyethylene resins may be used alone or in combination with petrochemically derived polyethylene resins.

[0036] The biomass ratio of the biopolyethylene resin, i.e., the ratio of plant-derived carbon atoms to the total carbon atoms, is preferably 90% or more, particularly 95% or more. The biomass ratio can be measured, for example, in accordance with ASTM D6866.

[0037] <Additives, etc.> The base layer (2) may contain additives, etc. There are no limitations on the additives, etc. Examples include nucleating agents. The type of nucleating agent is not particularly limited, and examples include nonitol-based nucleating agents, sorbitol-based nucleating agents, and phosphate ester-based nucleating agents.

[0038] Examples of the additives other than the nucleating agent include colorants and additives used in known thermoplastic resin sheets, such as ultraviolet absorbers, fluorescent brighteners, antistatic agents, antifogging agents, lubricants, antiblocking agents, flow improvers, plasticizers, dispersants, and antibacterial agents.

[0039] <Layer structure of thermoforming sheet> The thermoforming sheet (1) only needs to have one base layer (2), and may have a single-layer structure with only the base layer (2), or a multi-layer structure with multiple base layers (2). When there are multiple base layers (2), they may each have the same composition or different compositions.

[0040] The thermoforming sheet (1) may have layers other than the base layer (2). The other layers may be coextruded layers coextruded together with the base layer (2), or may be film layers laminated on the sheet having the base layer (2). There may be multiple coextruded layers or film layers, or the sheet may have both a coextruded layer and a film layer.

[0041] There are no particular limitations on the type of resin used in the coextrusion layer. Examples include polyethylene resins, polypropylene resins, ethylene-propylene copolymers, ethylene-α-olefin copolymers, polystyrene resins, polyester resins, gas barrier resins (ethylene-vinyl alcohol copolymers, polyamide resins, etc.), and adhesive resins (modified polyethylene, modified polypropylene, etc.). These resins may be used alone or in combination.

[0042] When the film layer is used, the type of film is not particularly limited. Examples include polypropylene resin films, polyethylene resin films, polyester resin films, polyamide resin films, printed films (films printed for decorative purposes), and gas barrier films (single-layer or multi-layer films having at least one layer with gas barrier properties). These films may be used alone, or multiple films may be laminated together.

[0043] An example of the other layer is surface layers (3, 3') formed on both sides of the base layer (2), as shown in Figure 1. Examples of thermoplastic resins constituting the surface layers (3, 3') include polypropylene-based resins and polyethylene-based resins, with polypropylene-based resins being preferred, and block polypropylene being particularly preferred.

[0044] When a block polypropylene is used as the thermoplastic resin forming the surface layers (3, 3'), the block polypropylene does not need to be the same as the block polypropylene (8) forming the base layer (2), and for example, a block polypropylene having a higher MFR than the block polypropylene (8) contained in the base layer (2) can be used. For example, when the MFR of the block polypropylene (8) is 0.1 to 5, a block polypropylene having an MFR of 5 to 20 can be used to form the surface layers (3, 3').

[0045] There is no particular limitation on the thickness of the thermoforming sheet (1), which may be 0.1 to 3 mm, preferably 0.2 to 2 mm, and more preferably 0.3 to 1 mm.

[0046] When the thermoforming sheet (1) has the other layers, there are no particular limitations on the mass proportion of the base layer (2) relative to the entire thermoforming sheet (1), and it can be, for example, 50 mass% or more, preferably 80 mass% or more, and more preferably 90 mass% or more.

[0047] <Method of manufacturing the thermoforming sheet> There are no particular limitations on the method for producing the thermoforming sheet (1). For example, it can be produced by an extrusion molding method using a T-die method (hereinafter referred to as the "T-die method"). When a multilayer is to be formed, a co-extrusion method can be adopted. Taking FIG. 1 as an example, a composition for forming the base layer (2) is melt-kneaded in a main extruder, and a composition for forming the surface layers (3, 3') is melt-kneaded in a sub-extruder, and the melt-kneaded mixtures are joined in a multi-manifold type multilayer die or a feed block type multilayer die to produce a multilayer sheet.

[0048] The method for supplying the various raw materials forming the base layer (2) to the extruder is not particularly limited, and examples thereof include the following: a method in which the composite filler (4) and the polypropylene-based resin pellets, etc. are blended in advance in a mixer or tumbler to form the final composition of the base layer (2), and the mixture is then charged into a single charging tank (hereinafter referred to as the "hopper") and fed to the extruder for melt-kneading; a method in which the composite filler (4) and the polypropylene-based resin pellets, etc. are charged into separate hoppers and fed to the extruder by a multi-point feed system to form the final composition of the base layer (2), and melt-kneaded; a method in which compound pellets composed of the composite filler (4) and the polypropylene-based resin, etc., blended to form the final composition of the base layer (2), are prepared, and then charged into a hopper and fed to the extruder for melt-kneading; a method in which a masterbatch of the composite filler (4) using the polypropylene-based resin as the base resin is prepared, and then blended with the polypropylene-based resin, etc., to form the final composition, or fed to the extruder by a multi-point feed system to melt-knead.

[0049] There are no limitations on the method for laminating films such as decorative films and gas barrier films. For example, a method in which a single-layer or multilayer sheet having at least one base layer (2) is extruded by the T-die method and a film is laminated by the so-called extrusion lamination method can be used. Alternatively, after a single-layer or multilayer sheet having at least one base layer (2) is produced by the T-die method, a film such as a decorative printed film or a gas barrier film can be laminated in a separate step, optionally via an adhesive layer.

[0050] <Molded container> A cross-sectional schematic diagram of a molded container according to this embodiment is shown in Figure 2. The molded container (10) can be obtained by thermoforming a thermoforming sheet (1). There are no particular limitations on the specific thermoforming method, and known thermoforming methods such as hot platen forming, vacuum forming, pressure forming, vacuum pressure forming, and double-sided vacuum forming can be used. There are no particular limitations on the molding conditions, and they can be determined appropriately as needed.

[0051] The layer structure and thickness of the formed container 10 are substantially the same as those of the thermoforming sheet 1 from which the formed container is made. In the performance evaluation described below, the thermoforming sheet 1 and the formed container 10 provide substantially the same evaluation results.

[0052] The shape and dimensions of the forming container 10 are not particularly limited and can be set appropriately. Specific examples of the forming container 10 include a container body having a body and a bottom formed at one end of the body, and an opening at the other end of the body. In the present invention, the forming container is not limited to the container body, and may also be a lid or an inner container.

[0053] There is no particular limitation on the specific use of the molded container 10. For example, it can be used as a packaging container for food.

[0054] <Mechanical properties of thermoforming sheets and molded containers> The thermoforming sheet (1) and the formed container (10) have the following mechanical properties:

[0055] <Tensile modulus> The thermoforming sheet (1) and the forming container (10) preferably have a tensile modulus of at least 1500 MPa in at least one of the MD or TD directions of the sheet, measured at a room temperature of 23°C in accordance with JIS K7127:1999 "Plastics - Test methods for tensile properties - Part 3: Test conditions for films and sheets." If the tensile modulus is 1500 MPa or more in at least one of the MD or TD directions, the sheet can exhibit sufficient bending rigidity from room temperature to a freezer environment such as -30°C, and even after the forming container containing the contents is removed from the microwave.

[0056] When measuring the tensile modulus from the forming container (10), it can be measured by cutting a test piece from the flat bottom of the forming container (10). The MD and TD of the test piece taken from the forming container (10) can be treated as the same as the MD and TD of the thermoforming sheet (1) before forming. If the MD and TD cannot be determined from the forming container (10), the direction in which the tensile modulus of the test piece taken from the forming container (10) is maximum can be taken as MD, and the direction perpendicular to that can be taken as TD. Test conditions and the like will be described in detail in the Examples section.

[0057] <DuPont 50% breaking energy (-30℃)> The thermoforming sheet (1) and the formed container (10) preferably have a DuPont 50% breaking energy of 1.5 J or more, measured in a frozen environment at -30°C. If the value is greater than this, the formed container (10) can exhibit sufficient impact resistance to withstand transportation and other conditions when used as a packaging container for frozen foods. Here, "DuPont 50% breaking energy" refers to a value measured and calculated using a DuPont measuring device in accordance with JIS K 5600-5-3:1999 "General test methods for paints - Part 5: Mechanical properties of coatings - Section 3: Falling weight resistance" in accordance with JIS K 7124 "Plastic films and sheets - Free-falling dart impact test method - Part 1: Staircase method." The test conditions and other details are described in detail in the Examples section. [Example]

[0058] The present invention will be specifically described below with reference to examples. The present invention is not limited to the embodiments shown in the examples. The embodiments of the present invention can be modified in various ways within the scope of the present invention depending on the purpose, application, etc.

[0059] In the following tables, etc., polypropylene may be abbreviated as "PP," block polypropylene as "B-PP," homopolypropylene as "H-PP," calcium carbonate as "calcium carbonate," biomass high-density polyethylene as "bio-HDPE," and DuPont 50% breaking energy as "DuPont E50."

[0060] <Production and Evaluation of Examples and Comparative Examples> <Raw materials used> The following raw materials were used. MFR was measured in accordance with JIS K7210-1:2014, JIS K6921-2:2018, and JIS K6922-1:2018. Average particle size was measured using the laser diffraction method in accordance with JIS Z8825:2013.

[0061] <Talc (A)> Nippon Talc "RA-3" (average particle size 5 μm, aspect ratio 35) <Talc (H)> Nippon Talc "SG-95" (average particle size 2 μm, aspect ratio 15) <Talc (I)> Nippon Talc "P-8" (average particle size 3 μm, aspect ratio 20) <Talc (J)> Nippon Talc "P-2" (average particle size 7 μm, aspect ratio 30) <Talc (K)> Nippon Talc "K-1" (average particle size 8 μm, aspect ratio 20) <Calcium carbonate (C)> Nitto Powder "NCC#1010" (heavy calcium carbonate, average particle size 1.1 μm, surface treated)

[0062] <Block polypropylene (D)> (for base layer) SanAllomer "CS182M" (MFR 0.4 (test conditions: 230°C, 2.16 kg)) <Homopolypropylene> (for base layer) SanAllomer "PS201A" (MFR 0.5 (test conditions: 230°C, 2.16 kg)) <High density polyethylene> (for base layer) "Novatec HD HB530" manufactured by Japan Polyethylene Corporation (MFR 0.3 (test conditions: 190°C, 2.16 kg)) <Biomass high-density polyethylene> (for base layer) Braskem "SGM9450F" (MFR 0.3 (test conditions: 190°C, 5 kg), bio-based carbon content 96% (ASTM D6866 compliant)) <Block polypropylene (E)> (for surface layer) Prime Polymer "J715M" (MFR 9.0 (test conditions: 230°C, 2.16 kg))

[0063] [Example 1] <Preparation of composite filler> 1500 g of talc (A) and appropriate amounts of calcium stearate and a nonionic surfactant as surface modifiers were added to a Henschel mixer ("FM20C / I", capacity 20 L, manufactured by Mitsui Mining Co., Ltd. (now Nippon Coke Company)), and the mixture was stirred for 1 minute at a kettle temperature of 140°C and a peripheral speed of 40 m / s to crush and surface-treat the talc (A).

[0064] Next, 500 g of heavy calcium carbonate (C) was added, and the mixture was stirred for 1 minute at a kettle temperature of 140°C and a peripheral speed of 40 m / s to obtain a composite filler (F-1) consisting of talc (A) and heavy calcium carbonate (C).

[0065] Next, 8000 g of resin pellets of block polypropylene (D) were added so as to obtain the composition shown in the table, and the mixture was stirred for 30 seconds at a kettle temperature of 140° C. and a peripheral speed of 40 m / s to obtain a mixture.

[0066] <Preparation of Compounds Containing Composite Fillers and Polypropylene Resins> The mixture of the composite filler (F-1) and block polypropylene (D) prepared above was melt-kneaded in an extrusion granulator (manufactured by The Japan Steel Works, Ltd., "TEX30XSST-31.5AW-2V", φ30 mm, L / D: 31.5) to obtain compound pellets (G-1). The temperature setting of the extrusion granulator from the cylinder to the die head was 230 to 240°C.

[0067] <Preparation of thermoforming sheets> A multilayer sheet with compound pellets (G-1) as the base layer was produced using a sheet extruder equipped with a feedblock-type multilayer die (Plastic Engineering Research Institute "SBTN32-S2-36-L" (main extruder (twin screw, φ32, L / D: 36), sub-extruder (single screw, φ32, L / D: 32)). Compound pellets (G-1) were fed into the main extruder, and block polypropylene (E) for the surface layer was fed into the sub-extruder. The discharge rates of the main extruder and sub-extruder were adjusted to 95% by mass:5% by mass, and a two-kind, three-layer multilayer sheet with a layer structure of (E) / (G-1) / (E) was obtained. The temperatures set for the extruder, etc., from the cylinder to the die head were 230 to 240°C. The take-up speed of the take-up rolls, etc., was adjusted to a sheet thickness of 0.42 mm. The temperatures set for the take-up rolls, etc., were 40°C / 50°C / 30°C for the first roll, second roll, and third roll (from the die side), in that order.

[0068] <Production of molded container> Using the thermoforming sheet prepared above, a rectangular container measuring 200 mm long x 150 mm short x 45 mm deep was produced using a vacuum-compressed air thermoforming machine for prototypes (Kinki Machinery Industry Co., Ltd., "KFM-C60P-D7K016"). The sheet was molded so that the MD direction was parallel to the long sides. The molding conditions were as follows: the sheet was softened by holding it for 15 seconds in a heating furnace set at an upper heater temperature of 300°C and a lower heater temperature of 300°C, and then shaped in a mold set at a mold temperature of 30°C.

[0069] <Evaluation of thermoforming sheets and molded containers> The thermoforming sheets and molded containers prepared as described above were subjected to the following various evaluations. The evaluation results of the examples and comparative examples are shown in the tables below.

[0070] [Table 1]

[0071] [Table 2]

[0072] <Tensile modulus> The tensile modulus was measured at room temperature of 23°C in accordance with JIS K7127:1999 "Plastics - Test methods for tensile properties - Part 3: Test conditions for films and sheets." Equipment used: Shimadzu Corporation "AUTOGRAPH AGS-X" Test piece: Width 25mm x Length 150mm (rectangular) Test temperature: 23°C (ambient temperature) Test speed: 1mm / min Chuck distance: 100mm Tensile modulus is calculated from the slope of the SS curve at strains of 0.005% to 0.25%. Number of tests: 5 for each of MD and TD (Table 2 shows the average values ​​for each).

[0073] <DuPont 50% breaking energy (-30℃)> Measurements were carried out in accordance with JISK7124 "Plastic films and sheets - Impact test method using free-falling dart method - Part 1: Staircase method" using a DuPont measuring device in JISK5600-5-3:1999 "General test methods for paints - Part 5: Mechanical properties of coatings - Section 3: Resistance to falling weights." Measurements were carried out in a frozen environment at -30°C. Testing equipment: Yasuda Seiki "DuPont Impact Tester No. 517" Test piece: 50mm x 50mm Test temperature: -30°C (in a large freezer; test specimens are conditioned for 24 hours before measurement) · Weight: 300g ·Strike core: φ10mm - Method for determining 50% fracture energy: Measurement was performed using the staircase method, in which a weight of a fixed mass is used and the drop energy is adjusted by changing the height (based on the staircase method in JIS K7211-1:2006 "Plastics - Puncture impact test methods for rigid plastics - Part 1: Non-instrumented impact tests"). Number of Tests: After testing 20 test pieces, count the total number of broken test pieces (N). If N is 10 at this point, the test is terminated. If N is greater than 10, increase the number of test pieces and repeat the test until the number of non-broken pieces reaches 10. If N is less than 10, increase the number of test pieces and repeat the test until N reaches 10.

[0074] <Amount of deflection of molded container after heating in the microwave> The contents were placed in the molded container, a separately prepared lid was placed on top, and the container was heated in a microwave oven. After the container was removed from the microwave, the short side of the container was clamped 60 mm in the long side direction and the downward displacement (deflection) of the bottom of the container before and after the microwave removal was measured. Test container: rectangular container with long side 200 mm x short side 150 mm x depth 45 mm Heating time: 600W x 5 minutes 30 seconds Contents: 250g frozen pasta Evaluation criteria: Deflection of 10mm or less (◎), Deflection of more than 10mm but less than 15mm (〇), Deflection of more than 15mm (×). The target criteria are ◎ and 〇.

[0075] <Free fall test (-30℃)> In accordance with JIS Z0200:2023 "Packaged Goods - General Rules for Performance Test Methods," a free-fall test was conducted on molded containers in a -30°C frozen environment. The contents were placed in a molded container, a separately prepared lid was placed on top, and eight of these were placed in a cardboard case. The cardboard case containing the eight filled molded containers was then allowed to free-fall from a specified height, and the molded containers were visually inspected for cracks. Test container: rectangular container with long side 200 mm x short side 150 mm x depth 45 mm Contents: 250g frozen pasta Cardboard case: Large enough to hold a total of eight molded containers with lids, two on each side, with no gaps between them. Test temperature: -30°C (in a large freezer; measured after conditioning the contents in a cardboard case for 24 hours) Number of drops: 10 (1 corner + 3 edges + 6 faces) Drop height: 40cm (Level 4 height when the case contains 10kg or less of material) Evaluation method: The number of molded containers with cracks was counted. The target standard was to have no molded containers with cracks.

[0076] [Examples 2 to 18 and Comparative Examples 1 to 8] Thermoforming sheets and molded containers were produced in the same manner as in Example 1, except that the base layer compositions shown in the table were used, and various evaluations were carried out.

[0077] Comparative Example 9 A thermoforming sheet and a molded container were produced in the same manner as in Example 1, except that the block polypropylene (D) was directly supplied to the main extruder of the sheet extruder so as to form a base layer consisting of block polypropylene (D) alone, and various evaluations were performed.

[0078] [Comparative Examples 10 and 11] A thermoforming sheet and a molded container were produced and various evaluations were carried out in the same manner as in Example 1, except that only talc (A) was used as the inorganic filler component and compound pellets were produced to have the base layer composition shown in the table. Note that talc (A) was subjected to a stirring treatment in the Henschel mixer under the same conditions as in Example 1, and was then crushed and surface-treated.

[0079] [Examples 19 to 22 and Comparative Examples 12 to 15] Thermoforming sheets and molded containers were produced and various evaluations were performed in the same manner as in Example 1, except that talc (H), (I), (J), and (K) with different average particle sizes were used instead of talc (A) to achieve the base layer composition shown in the table.

[0080] <Evaluation results> [Examples 1 to 22] In Examples 1 to 22, the tensile modulus in at least one of the MD and TD directions was 1500 MPa or more, and the DuPont 50% breaking energy at -30°C was 1.5 J or more.

[0081] [Comparative Example 1] In Comparative Example 1, the tensile modulus of elasticity in both MD and TD did not reach 1500 MPa.

[0082] Comparative Example 2 In Comparative Example 2, the DuPont 50% breaking energy at -30°C was less than 1.5J.

[0083] [Comparative Examples 3 to 5] In Comparative Examples 3 to 5, the DuPont 50% breaking energy at -30°C was less than 1.5J.

[0084] [Comparative Examples 6 to 8] In Comparative Examples 6 to 8, the tensile modulus of elasticity in both MD and TD did not reach 1500 MPa.

[0085] Comparative Example 9 In Comparative Example 9, the tensile modulus in both MD and TD did not reach 1500 MPa.

[0086] [Comparative Examples 10 and 11] In Comparative Examples 10 and 11, the DuPont 50% fracture energy at -30°C was less than 1.5 J.

[0087] [Comparative Examples 12 and 14] In Comparative Examples 12 and 14, the tensile modulus of elasticity in both MD and TD did not reach 1500 MPa.

[0088] [Comparative Examples 13 and 15] In Comparative Examples 13 and 15, the DuPont 50% fracture energy at -30°C was less than 1.5 J. [Explanation of symbols]

[0089] 1 sheet 2 Base layer 3 Surface layer 3' surface layer 10 Molded container

Claims

1. A thermoforming sheet having a base layer containing an inorganic filler and a polypropylene-based resin, The base layer contains an inorganic filler containing talc and calcium carbonate in an amount of 20 to 30% by mass relative to the base layer, The mass composition ratio of talc to calcium carbonate is 50 / 50 to 75 / 25, and the talc content is 12 to 18 mass% with respect to the base layer; The average particle size (D50) of the talc is 3 to 7 μm. Polypropylene resin is mainly composed of block polypropylene, At least one of the tensile modulus in MD and TD is 1500 MPa or more, A thermoforming sheet having a DuPont 50% breaking energy of 1.5 J or more at a test temperature (-30°C).

2. 2. The thermoforming sheet according to claim 1, which has surface layers made of block polypropylene on both sides of the base layer.

3. A thermoforming sheet having a base layer containing an inorganic filler, a polypropylene-based resin, and a biomass high-density polyethylene, The base layer contains an inorganic filler containing talc and calcium carbonate in an amount of 20 to 30% by mass relative to the base layer, The mass composition ratio of talc to calcium carbonate is 50 / 50 to 75 / 25, and the talc content is 12 to 18 mass% with respect to the base layer; The average particle size (D50) of the talc is 3 to 7 μm. Polypropylene resin is mainly composed of block polypropylene, At least one of the tensile modulus in MD and TD is 1500 MPa or more, A thermoforming sheet having a DuPont 50% breaking energy of 1.5 J or more at a test temperature (-30°C).

4. 4. The thermoforming sheet according to claim 3, which has surface layers made of block polypropylene on both sides of the base layer.

5. A molded container obtained by molding the thermoforming sheet according to any one of claims 1 to 4.

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