Thermoforming resin sheets and molded products

Abstract

To provide a resin sheet for thermoforming which has a large content of an inorganic substance and is excellent in mechanical characteristics and cold resistance, and a molded article obtained by molding the sheet.SOLUTION: A resin sheet for thermoforming has a base layer containing an inorganic substance and a thermoplastic resin, wherein a mass ratio of the inorganic substance to the thermoplastic resin is 80:20 to 50:50, the thermoplastic resin contains a polypropylene-based resin and a polyethylene-based resin, the polyethylene-based resin contains a high density polyethylene-based resin having a flow rate ratio measured according to JIS K 7210 of 10-13, and a blending amount of the high density polyethylene is 5 wt.% or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a thermoforming resin sheet having a high inorganic content and excellent mechanical properties and cold resistance, and to a molded article obtained by molding the sheet. [Background technology]

[0002] Traditionally, thermoplastic resins have been widely used for various molded products, such as food and beverage containers, due to their excellent physical properties. However, in recent years, the issue of plastic waste has attracted social attention. To address this issue, efforts have been made to reduce the amount of thermoplastic resin used by mixing inorganic fillers into the thermoplastic resin at high concentrations.

[0003] However, mixing a high concentration of inorganic filler into a thermoplastic resin tends to reduce the mechanical properties and impact strength of the thermoplastic resin. Regarding this point, Patent Document 1 discloses that by blending a specific amount of a specific elastomer component with low-density polyethylene in a propylene resin composition filled with a large amount of inorganic powder, it is possible to significantly improve impact resistance without substantially impairing strength. Furthermore, Patent Document 2 discloses a blow-molded article that contains an inorganic filler and polypropylene and high-density polyethylene with specific physical properties, and that exhibits a good balance between rigidity and impact properties.

[0004] Furthermore, in the past, heat resistance during microwave heating has been emphasized for resin containers used to store food for cooking. However, in recent years, in order to reduce food waste, foods cooked in microwave ovens are generally stored and transported at frozen temperatures. As the use of food and beverage containers at frozen or chilled temperatures has increased, food and beverage containers are also required to have cold resistance so that they do not crack when subjected to external impact even at low temperatures. Patent Document 3 discloses that the cold impact strength of a laminate is improved by laminating a composition consisting of a polypropylene-based polymer, an ethylene-based polymer, and a nucleating agent. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent No. 6892185 [Patent Document 2] Patent No. 5913285 [Patent Document 3] Patent No. 6480472 Summary of the Invention [Problem to be solved by the invention]

[0006] As described above, resin sheets are required to have excellent mechanical properties and also excellent cold resistance, despite the large amount of inorganic material blended therein. However, Patent Document 1 does not mention any technical knowledge regarding the cold resistance of resin sheets blended with a large amount of inorganic material. Furthermore, Patent Document 2 contains an inorganic filler in an amount of 50 wt % or less relative to the total weight, and, like Patent Document 1, does not mention any technical knowledge regarding the cold resistance of resin sheets.

[0007] Furthermore, Patent Document 3 discloses that high density ethylene polymers have poor cold impact strength, and indicates that resin sheets using high-density polyethylene (HZ5000H) have poor cold impact strength compared to resin sheets blended with linear low-density PE or ethylene elastomer.

[0008] An object of the present invention is to provide a thermoforming resin sheet having a high inorganic content and excellent mechanical properties and cold resistance, and a molded article obtained by molding the sheet. [Means for solving the problem]

[0009] The thermoforming resin sheet of the present invention has a base layer containing an inorganic material and a thermoplastic resin, wherein the mass ratio of the inorganic material to the thermoplastic resin is 80:20 to 50:50, the thermoplastic resin includes a polypropylene (PP)-based resin and a polyethylene (PE)-based resin, the PE-based resin includes a high-density PE-based resin having a flow rate (FR) ratio measured in accordance with JIS K7210 in the range of 10 to 13, and the blending amount of the high-density PE is 5% by weight or more.

[0010] The molded article of the present invention is characterized in that it is obtained by thermoforming the thermoforming resin sheet of the present invention. [Effects of the Invention]

[0011] The thermoforming resin sheet and molded article of the present invention have excellent mechanical properties and cold resistance despite the high inorganic content. Therefore, they are suitable for use as food and beverage containers stored and transported at freezing temperatures. Furthermore, the high inorganic content allows for a reduction in the amount of resin used, which reduces the heat generated when burned compared to when the resin is used alone, thereby contributing to a reduction in environmental impact. DETAILED DESCRIPTION OF THE INVENTION

[0012] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following describes an embodiment of the present invention. The embodiment is an example of implementing the present invention, and the present invention is not limited to the embodiment.

[0013] (1) Thermoforming resin sheet The thermoforming resin sheet according to this embodiment (hereinafter referred to as "the sheet") has a base layer containing an inorganic material and a thermoplastic resin.

[0014] The type, components, and shape of the inorganic material are not particularly limited. Specific examples of the inorganic material include inorganic fillers intended to improve the physical properties (e.g., impact resistance or heat resistance) of the resin sheet. The inorganic material may be a single material or a combination of two or more materials. Specific examples of the inorganic filler include talc, calcium carbonate, silica, diatomaceous earth, alumina, titanium oxide, magnesium oxide, aluminum hydroxide, magnesium hydroxide, calcium silicate, glass beads, bentonite, glass flakes, glass fiber, carbon fiber, aluminum powder, molybdenum sulfide, boron fiber, potassium titanate, calcium titanate, hydrotalcite, carbon fiber, pumice powder, mica, calcium phosphate, and aluminum phosphate. Calcium carbonate and talc are inexpensive and easily available, and calcium carbonate is preferred because it has better impact resistance than talc.

[0015] The thermoplastic resin includes a PP-based resin and a PE-based resin. There are no particular limitations on the structure and properties of the PP-based resin and the PE-based resin. The PP-based resin and the PE-based resin may be a homopolymer or a copolymer with other monomers. The PP-based resin may be a single type or two or more types. The PE-based resin may also be a single type or two or more types. Furthermore, the PP-based resin and the PE-based resin may have an MFR value of 0.2 to 2.0 g / 10 min or 0.3 to 1.0 g / 10 min, for example. In this document, the MFR values ​​are values ​​measured according to the method of JIS K7210, for polypropylene-based resins at a measurement temperature of 230°C and a load of 2.16 kg, and for polyethylene-based resins at a measurement temperature of 190°C and a load of 2.16 kg.

[0016] Specific examples of the PP-based resin include homo-PP (propylene homopolymer) and copolymers of propylene and α-olefins (e.g., ethylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, and 1-decene).Specific examples of the PE-based resin include homo-PE (ethylene homopolymer; low-density polyethylene, high-density polyethylene, etc.) and copolymers of ethylene and α-olefins (e.g., propylene, 1-butene, 1-pentene, 1-hexene, 1-heptene, 1-octene, 1-nonene, and 1-decene) (however, the PP-based resin and the PE-based resin are different resins).

[0017] The PE resin contains high-density PE having an FR ratio measured in accordance with JIS K7210 in the range of 10 to 13. The PE resin may consist solely of the high-density PE, or may contain other PE resins. The sheet preferably contains the high-density PE, since this improves the cold resistance of the resin sheet and molded articles. Here, "high-density PE" refers to a PE having a density of 0.94 g / cm. 3 or more, preferably 0.942 to 0.970 g / cm 3 This is PE.

[0018] The amount of the high-density PE blended is 5% by weight or more, preferably 10% by weight or more, based on the total weight of the sheet. The upper limit of the amount of the high-density PE blended can be set as appropriate, as long as the mass ratio of the inorganic material to the thermoplastic resin satisfies the requirement of 80:20 to 50:50. The upper limit of the amount of the high-density PE blended can be, for example, 40% by weight, 35% by weight, or 30% by weight, based on the total weight of the sheet.

[0019] There are no particular limitations on the blending ratio of the PP-based resin and the PE-based resin in the thermoplastic resin. The total ratio of the PP-based resin and the PE-based resin in 100% by mass of the thermoplastic resin is usually 50 to 100% by mass. The lower limit of this ratio can be 55, 60, 65, or 70% by mass. The upper limit of this ratio can be 95, 90, 85, or 80% by mass. Furthermore, there are no particular limitations on the mass ratio of the PP-based resin and the PE-based resin. The mass ratio can usually be (1 to 3):1.

[0020] The thermoplastic resin may consist of only the PP-based resin and the PE-based resin, or may contain other thermoplastic resins.

[0021] The mass ratio of the inorganic material to the thermoplastic resin is 80:20 to 50:50. When the mass ratio is within this range, deterioration in mechanical properties and impact strength due to blending a high concentration of inorganic material is suppressed, and the amount of resin can be reduced, which results in suppressing the amount of heat generated during combustion and reducing the environmental load, which is preferable.

[0022] The layer structure of the present sheet is not particularly limited. The present sheet may have a single-layer structure consisting of only the base layer, or may be a laminated sheet having the base layer and one or more other layers. When there are two or more other layers, the other layers may be the same layer or may be layers of different types or physical properties. There is no particular limit to the type of the other layer. Specific examples of the other layer include a laminate film layer with decorative printing on the surface, a gas barrier layer, and an adhesive layer that bonds layers together.

[0023] Specific examples of the laminate sheet include a laminate sheet having a polyolefin (PO) layer laminated on one or both sides of the base layer. The PO layer may be laminated directly on the surface of the base layer, or may be laminated on the surface side of the base layer via another layer such as an adhesive layer.

[0024] The type and structure of the PO resin constituting the PO layer are not particularly limited. The PO resin may be a homopolymer, a copolymer of two or more olefins, or a copolymer of an olefin and another monomer. Furthermore, the polyolefin resin may be, for example, a PO resin having an MFR value of 1.0 to 3.0 g / 10 min or 1.5 to 3.0 g / 10 min, particularly a homo PP resin having an MFR value within the above range.

[0025] When a PP-based resin or a PE-based resin is used as the PO-based resin, it may be the same resin as the PP-based resin or the PE-based resin contained in the base layer, or it may be a resin with different properties, for example, a resin with a different MFR. For example, the PO-based resin may be a PP-based resin or a PE-based resin with a higher MFR than the PP-based resin or the PE-based resin contained in the base layer. More specifically, for example, a PP-based resin or a PE-based resin with an MFR of 2.0 or more may be used as the PO-based resin, and a PP-based resin or a PE-based resin with an MFR of 1.0 or less may be used as the PE-based resin and / or the PE-based resin contained in the base layer.

[0026] Specific examples of the PO resin include PE resins (e.g., high-density polyethylene and low-density polyethylene), PP resins, polystyrene resins, and copolymers of ethylene or propylene with other monomers (e.g., propylene-ethylene copolymer resins and ethylene-vinyl acetate copolymer resins).The PO resins may be used alone or in combination of two or more.

[0027] The PO layer may be made of only the PO-based resin, or may contain other resins.

[0028] The method for producing the laminate sheet is not limited. The laminate sheet can be produced by common lamination molding methods such as coextrusion, injection molding, and hot molding. Any single-screw or twin-screw extruder can be used for the coextrusion method. The coextrusion method is not limited to a specific method, as long as the base layer and the other layers are laminated in a molten state immediately before being extruded through a die. Specific examples of the coextrusion method include a multi-manifold method in which the raw materials for the base layer and the other layers are melt-kneaded in an extruder and then laminated in a die. The die can be any of a T-die, a coat hanger type, or an annular die. In the coextrusion method, the resin laminate sheet extruded from the die is cooled and solidified by a known method, such as a polishing roll, an air knife, or a mandrel. It is then wound on a winder or cut to a predetermined size by a cutter.

[0029] The specific shape of the sheet is not particularly limited and can be determined appropriately as needed. Therefore, the term "sheet" also includes a film-like shape. The thickness of the sheet can be, for example, 0.1 to 3 mm, or 0.3 to 2 mm.

[0030] The present sheet may contain other components as needed, as long as the moldability and cold resistance are not significantly impaired. Examples of the other components include additives commonly used in resin sheets, such as flame retardants, ultraviolet absorbers, fluorescent brighteners, antistatic agents, antifogging agents, lubricants, antiblocking agents, flow improvers, plasticizers, dispersants, and antibacterial agents. When the present sheet is a laminate sheet, the other components may be contained in all or any of the layers constituting the laminate sheet.

[0031] There are no particular limitations on the specific uses of the present sheet, but as will be described later, the present sheet can be used to obtain molded articles such as containers by various molding methods.

[0032] (2) Molded products The molded article according to this embodiment (hereinafter referred to as "the molded article") can be obtained by thermoforming the sheet. Examples of such molding include thermoforming. There are no particular limitations on the specific method of thermoforming, and known thermoforming methods such as hot platen molding, vacuum molding, pressure forming, vacuum pressure forming, double-sided vacuum forming, plug molding, or press molding can be used. There are also no particular limitations on the thermoforming conditions. The molding conditions can be appropriately determined as needed.

[0033] The specific uses of the present molded article are not particularly limited. Examples of such uses include containers such as packaging containers, for example, containers for food and beverages. As the containers for food and beverages, particularly containers for food and beverages that are heated and cooked together with the container, for example, food containers for microwave heating, are preferred. Furthermore, since the present sheet has excellent low-temperature impact strength as described above, the packaging containers for food and beverages are preferably packaging containers for food and beverages that are stored or transported at low temperatures.

[0034] The shape and dimensions of the molded product are not particularly limited and can be set as appropriate. When the molded product is a container, a specific example of the shape of the container is a container having a body and a bottom formed at one end of the body, and an opening at the other end of the body. The opening may further have a flange. Note that the "container" includes not only the entire container but also a part of the container. For example, the "container" includes not only the container body but also the container lid. Therefore, the "container" may be only the container body or only the container lid. [Example]

[0035] The present invention will be specifically described below with reference to examples. Note that 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.

[0036] (1) Manufacturing of resin sheets The following ingredients were used as raw materials. (A) Calcium carbonate: heavy calcium carbonate (average particle size 1.5 μm) (B) PP resin <For surface layer> (B-1) Homo PP: manufactured by Japan Polypropylene Corporation, grade name "FY6C" (MFR 2.4g / 10min) <For base layer> (B-2) Homo PP: manufactured by Japan Polypropylene Corporation, grade name "EA9" (MFR 0.5g / 10min) (B-3) Block PP: Made by Japan Polypropylene Corporation, grade name "EC9GD" (MFR 0.5g / 10min) (C)PE resin (C-1) High-density PE: Keiyo Polyethylene Co., Ltd., Grade "E8040" (MFR: 0.35g / 10min, FR ratio: 11.4) (C-2) High-density PE: Keiyo Polyethylene Co., Ltd. Grade "B5803" (MFR: 0.3g / 10min, FR ratio: 20.0)

[0037] The MFR values ​​of (C-1) and (C-2) were measured under the following conditions in accordance with JIS K7210. The FR ratios of (C-1) and (C-2) were calculated by dividing the MFR value under condition 2 by the MFR value under condition 1. Condition 1: MFR value measured at 190°C under a load of 2.16 kg (unit: g / 10 min) Condition 2: MFR value measured at 190°C under a load of 10.0 kg (unit: g / 10 min)

[0038] <Examples 1 to 6 and Comparative Examples 1 to 6> A base layer composition was prepared by blending (A) calcium carbonate, (B-2) homo PP, (B-3) block PP, and (C) high-density polyethylene in the proportions shown in Table 1. The composition was dry-blended in an extruder and then fed into a hopper. The melt-mixed resin was extruded to obtain resin sheets (single layer) of Examples 1 to 6 and Comparative Examples 1 to 6 (thickness: 0.40 mm).

[0039] <Examples 7 to 12 and Comparative Examples 7 to 12> A base layer composition was prepared by blending (A) calcium carbonate, (B-2) homo-PP, (B-3) block PP, and (C) high-density polyethylene in the proportions shown in Table 2. The (B-1) homo-PP used for the surface layer and the base layer composition were dry-blended in their respective extruders, then fed into hoppers. The melt-mixed resins were co-extruded to obtain resin sheets of Examples 7 to 12 and Comparative Examples 7 to 12 (thickness: 0.40 mm, layer structure: surface layer / base layer / surface layer, layer ratio: 2 / 96 / 2). Specifically, a twin-screw extruder was used for the base layer, and a single-screw extruder was used for the surface layer. The extruded materials merged in a feed block, then discharged through a T-die and cooled on a cooling roll, thereby forming and laminating the base layer and surface layer.

[0040] (2) Performance evaluation of resin sheets The performance of the resin sheets of the Examples and Comparative Examples was evaluated by the following methods, and the results are shown in Table 1 (single layer) and Table 2 (laminate).

[0041] (A) DuPont impact strength Test pieces measuring 50 mm long x 50 mm wide were prepared, and the 50% breaking energy E50 (J) of these test pieces was measured using a DuPont impact tester manufactured by Mize Testing Machinery Co., Ltd. in accordance with JIS K7124.

[0042] (B) Flexural modulus (MPa) Measurements were performed using Shimadzu Corporation's Autograph AGS-X under the conditions of a support distance of 30 mm and a bending speed of 20 mm / min in accordance with JIS (Japanese Industrial Standards) K7171. Measurements were performed at 23°C in accordance with JIS-K7203.

[0043] (C) Tensile modulus (MPa) Measurements were made using Shimadzu Corporation's Autograph AGS-X at a speed of 1 mm / min in accordance with JIS (Japanese Industrial Standards) K7127. Measurements were made at 23°C in accordance with JIS-K7203.

[0044] (3) Manufacturing method of container Using a vacuum pressure molding device (manufactured by Asano Laboratory), the resin sheets of the examples and comparative examples were thermoformed by vacuum pressure molding to produce containers (long side 232 mm x short side 195 mm x depth 34 mm) with a bottom formed at one end of the body and an opening at the other end.

[0045] (4) Container performance evaluation The performance of the containers manufactured from the resin sheets of the Examples and Comparative Examples was evaluated by the following methods, and the results are shown in Table 1 (single layer) and Table 2 (laminate).

[0046] (A) Container waist strength Using Orientec's "Tensilon Universal Testing Machine RTC-1310A," the container was clamped in an upright position along its short side, and the entire long side wall of the container was compressed 18 mm in the width direction at a compression speed of 400 mm / min, and the maximum stress (g) at this time was taken as the stiffness.

[0047] (B) Container falls and breaks A 400 g weight was placed in the container, and a separately thermoformed rectangular lid (232 mm long x 195 mm short x 17 mm deep) was placed over the container. The container was then stored for 24 hours at the set temperatures shown in Tables 1 and 2. After that, the container was dropped from a height of 1 m (n=20) in the same atmosphere, and the containers were visually inspected for cracks and the number of broken containers was counted.

[0048] (C) Heat resistance test Using Yamato's Fine Oven DH62, the container body was placed upside down, a 170g weight was placed on top of it, and the container was stored for 1 minute at the set temperatures shown in Tables 1 and 2, after which the degree of deformation of the container was visually confirmed. "〇": No deformation "△": Slightly warped "×": Transform

[0049] [Table 1]

[0050] [Table 2]

[0051] As can be seen from Table 1, the resin sheets of Examples 1 and 2, in which the FR ratio of the high-density PE falls within the range of the present invention, exhibited good flexural and tensile moduli despite containing a large amount of inorganic material (60 wt%). They also exhibited superior impact strength compared to Comparative Examples 1 and 2, in which the FR ratio of the high-density PE fell outside the range. The impact strengths of Examples 1 and 2 were greater than those of Comparative Examples 1 and 2 at both 23°C and -20°C. Furthermore, in a container drop test, the containers of Examples 1 and 2 did not crack after storage at -20°C, whereas the containers of Comparative Examples 1 and 2 did crack. These results indicate that Examples 1 and 2 have excellent cold resistance. Similar results were also obtained for Examples 3 and 4 and Examples 5 and 6, in which the blending amount of (B) PP-based resin was increased.

[0052] As can be seen from Table 2, Examples 7 to 12, which are laminates, also showed results similar to those of Examples 1 and 2.

Claims

1. a base layer including an inorganic filler and a thermoplastic resin; the mass ratio of the inorganic filler to the thermoplastic resin is 80:20 to 50:50; the thermoplastic resin includes a polypropylene-based resin and a polyethylene-based resin, The polyethylene resin comprises a high-density polyethylene having a flow rate ratio measured in accordance with JIS K7210 (MFR value (unit: g / 10 min) measured at 190°C under a load of 10.0 kg / MFR value (unit: g / 10 min) measured at 190°C under a load of 2.16 kg) in the range of 10 to 13 and a density of 0.94 g / cm 3 or more; A thermoforming resin sheet, characterized in that the blending amount of the high-density polyethylene is 5% by weight or more.

2. 2. The thermoforming resin sheet according to claim 1, wherein the mass ratio of the polypropylene-based resin to the polyethylene-based resin is (3 to 1):

1.

3. 3. The thermoforming resin sheet according to claim 1, wherein the inorganic filler contains calcium carbonate.

4. 4. The thermoforming resin sheet according to claim 1, further comprising a polyolefin layer laminated on one or both sides of the base layer.

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

6. The molded article according to claim 5, wherein the molded article is a container for food or drink.

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