Manufacturing method of foamed sheets

Abstract

To provide a method for producing a foam sheet which can obtain a foam sheet having good moldability while reducing a content of inorganic powder, and can obtain a foam sheet which suppresses occurrence of yellow discoloration, even if it produces a foam sheet using a polystyrene-based resin containing a recycled raw material derived from the produced foam sheet, and a foam sheet.SOLUTION: A method for producing a foam sheet by extruding and foaming a foamable resin molten material obtained by kneading a polystyrene-based resin and a physical foaming agent, wherein the physical foaming agent contains hydrocarbon having 3 to 5 carbon atoms and / or dialkyl ether whose alkyl group has 1 to 3 carbon atoms, and nitrogen, the total of the addition amount of the hydrocarbon and / or the dialkyl ether and the addition amount of the nitrogen is 0.2 mol% or more and 1.2 mol or less per 1 kg of the foamable resin molten material, the addition amount of the nitrogen is 0.01 mol% or more and 0.20 mol% or less per 1 kg of the foamable resin molten material, and a ratio of the addition amount of the nitrogen to the addition amount of the hydrocarbon and / or the dialkyl ether is 0.03 or more and 0.4 or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] This invention relates to a method for manufacturing foamed sheets. In the law To relate to. [Background technology]

[0002] Resin foam sheets are used as thermoforming foam sheets and the like due to their excellent lightness and moldability. For example, molded products obtained by thermoforming foam sheets using polystyrene resin as the base resin (sometimes referred to as polystyrene resin foam sheets) are used in a wide range of applications such as lunch boxes, bowls, cups, and other containers.

[0003] As a method for manufacturing polystyrene resin foam sheets, for example, a method is known in which polystyrene resin and a physical foaming agent are supplied to an extruder to form a foamable resin molten material, and the foamable resin molten material is extruded to produce a foam sheet (for example, Patent Document 1). When carrying out such a method for manufacturing foam sheets, inorganic powder is usually added in order to obtain a foam sheet having the desired cellular structure. The inorganic powder functions as a cellular modifier. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2015-145486 [Overview of the project] [Problems that the invention aims to solve]

[0005] In the manufacture of polystyrene foam sheets, from the perspective of reducing environmental impact, recycled raw materials derived from foam sheets, such as scraps generated during the manufacturing process or during the thermoforming process, are sometimes reused as polystyrene resin to form the foam sheets.

[0006] In the case of a foamed sheet manufactured by the method as shown in Patent Document 1, usually, the inorganic powder described above and the dispersant added to disperse the inorganic powder well in the resin remain in the foamed sheet. When a recycled raw material is formed from such a foamed sheet in which an inorganic powder or the like remains and reused for the production of a foamed sheet, depending on the amount of the recycled raw material used, yellowing or the like may occur in the foamed sheet containing the recycled raw material, and the quality of the foamed sheet may deteriorate. In this regard, it is conceivable to reduce the blending amount of the inorganic powder and the dispersant contained in the foamed sheet serving as the recycled raw material. However, generally, when the inorganic powder and the dispersant added to the foamed sheet are reduced, there is a possibility that a desired foamed sheet cannot be obtained.

[0007] An object of the present invention is to obtain a good foamed sheet while reducing the blending amount of an inorganic powder, and to obtain a recycled raw material-containing foamed sheet in which the occurrence of yellowing is suppressed even when a foamed sheet (sometimes referred to as a recycled raw material-containing foamed sheet) is manufactured using a polystyrene-based resin containing a recycled raw material derived from the manufactured foamed sheet. Law It is to provide.

Means for Solving the Problems

[0008] The present invention has the gist of the invention shown in the following (1) to ( 5 ).

[0009] (1) A method for producing a foamed sheet by extrusion foaming a foamed resin melt obtained by kneading a polystyrene-based resin and a physical foaming agent, The physical foaming agent contains a hydrocarbon having 3 to 5 carbon atoms and / or a dialkyl ether having 1 to 3 carbon atoms in the alkyl group and nitrogen, The total of the addition amount of the hydrocarbon and / or the dialkyl ether and the addition amount of the nitrogen is 0.2 mol or more and 1.2 mol or less per 1 kg of the foamed resin melt, The addition amount of the nitrogen is 0.01 mol or more and 0.20 mol or less per 1 kg of the foamed resin melt, and The ratio of the addition amount of the nitrogen to the addition amount of the hydrocarbon and / or the dialkyl ether is 0.03 or more and 0.4 or less, the foaming resin melt does not contain an inorganic powder, or the foaming resin melt contains the inorganic powder and the compounding amount of the inorganic powder is 0.2 parts by mass or less with respect to 100 parts by mass of the polystyrene resin, A method for producing a foamed sheet. (2) The foaming resin melt does not contain a fatty acid metal salt, or the foaming resin melt contains the fatty acid metal salt and the compounding amount of the dispersant is 0.02 parts by mass or less with respect to 100 parts by mass of the polystyrene resin, The method for producing a foamed sheet according to (1) above. (3) The apparent density of the foamed sheet is 40 kg / m , ,

[0011] , or more and 200 kg / m 3 or less, The method for producing a foamed sheet according to (1) or (2) above. <> (4) The average cell diameter of the foamed sheet is 0.08 mm or more and 0.5 mm or less. The method for producing a foamed sheet according to any one of (1) to (3) above. (5) A method for producing a foamed sheet by extruding and foaming a foaming resin melt obtained by kneading a polystyrene resin containing a recycled raw material derived from a foamed sheet produced by the method for producing a foamed sheet according to any one of (1) to (4) above and a physical foaming agent.

Advantages of the Invention

[0010] According to the present invention, a good foamed sheet can be obtained while reducing the compounding amount of the inorganic powder, and even when a foamed sheet is produced using a polystyrene resin containing a recycled raw material derived from the produced foamed sheet, a recycled raw material-containing foamed sheet in which the occurrence of yellowing is suppressed can be obtained. Law It can be provided.

Embodiments for Carrying Out the Invention

[0011] Embodiments of the present invention will be described below in the following order: 1. Method for manufacturing a foamed sheet, 2. Foamed sheet, and 3. Method for manufacturing a foamed sheet using recycled raw materials derived from the foamed sheet.

[0012] However, the present invention is not limited to the embodiments described below.

[0013] [1. Method for manufacturing foamed sheets] [1-1 Structure] The present invention relates to a method for producing a foamed sheet, which involves extruding a foamable resin molten material obtained by kneading a polystyrene resin and a physical foaming agent to produce a polystyrene resin foamed sheet (hereinafter referred to as a foamed sheet) (a so-called extrusion foaming method). In describing the structure of the foamed sheet production method, the explanation will continue using the case where the foamable resin molten material does not contain inorganic powder and dispersant as an example. However, this does not exclude the possibility that residual components such as inorganic powder may be present in the foamed sheet, as will be described later. Nor does it exclude the case where the foamed resin molten material contains inorganic powder and dispersant within a predetermined range. The fact that the polystyrene resin foamed sheet is referred to as a foamed sheet and that the production method for the foamed sheet according to the present invention is an extrusion foaming method applies to both the foamed sheet described later and the method for producing a foamed sheet using polystyrene resin containing recycled raw materials derived from the produced foamed sheet.

[0014] The extrusion foaming method can be used to manufacture general extruded foam sheets using manufacturing equipment. The manufacturing equipment includes extruders connected in series (a first extruder upstream and a second extruder downstream) and a die located downstream of the second extruder. It is preferable that an annular die is used. The following description will use a manufacturing equipment in which an annular die is located downstream of the second extruder as an example. The manufacturing equipment preferably includes a cooling cylinder (mandrel) downstream of the annular die for cooling the cylindrical foam sheet, and a cutter for cutting open the extruded and cooled cylindrical foam sheet. It is also preferable that the manufacturing equipment includes a winding machine for taking the foam sheet into a roll. The upstream and downstream sides are determined based on the transfer direction of the polystyrene resin, which is the base resin of the foam sheet. Furthermore, the manufacturing equipment shown here is merely an example and is not limited to this.

[0015] (Formation of foamed resin molten material) In the manufacturing method for foamed sheets, a polystyrene resin and a physical blowing agent are kneaded together. At this time, a foamed resin molten material is formed. In the manufacturing apparatus described above, the polystyrene resin is supplied to the first extruder on the upstream side, and then the physical blowing agent is injected under pressure. Then, the polystyrene resin and the physical blowing agent are kneaded together inside the first and second extruders, and a foamed resin molten material is formed.

[0016] (Extruded foaming) The foamed resin molten material is transferred from the upstream first extruder to the downstream second extruder, where its temperature is adjusted. The foamed resin molten material is then extruded into atmospheric pressure through an annular die in the second extruder, forming a cylindrical foam. The cylindrical foam is taken up along a mandrel and cooled. Subsequently, the cylindrical foam is cut open along its extrusion direction by a cutter, unfolded into a sheet, and then wound into a roll by a winding machine. In this way, a foamed sheet is manufactured by extruding and foaming the foamed resin molten material.

[0017] The resulting foamed sheet may be used as is, or it may be used as a molded product. A molded product refers to a molded body obtained by shaping the foamed sheet into a predetermined shape, and specific examples include containers and the like.

[0018] (Polystyrene resin) The polystyrene resin used in the method for manufacturing foamed sheets is not particularly limited, as long as it is a resin that can be used for applications involving polystyrene resin foams. In this specification, polystyrene resin refers to a resin containing 50% by mass or more of styrene monomer component units. Examples of polystyrene resins include polymers such as polystyrene, rubber-modified polystyrene (impact-resistant polystyrene), styrene-α-methylstyrene copolymer, styrene-acrylic acid copolymer, styrene-methacrylic acid copolymer, styrene-maleic anhydride copolymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, and styrene-acrylonitrile copolymer, as well as mixtures of polystyrene and polyphenylene ether. Among these, polystyrene is preferred as the polystyrene resin. The concept of polystyrene resin includes cases where one of the above-mentioned polymers or mixtures is used (alone), and cases where two or more of the above-mentioned polymers or mixtures are used in combination.

[0019] (Foaming agent) Physical blowing agents are preferably used as blowing agents in the manufacturing method of foamed sheets. Physical blowing agents preferably contain hydrocarbons and / or dialkyl ethers. From the viewpoint of solubility in resins, volatility from foamed sheets, ease of manufacturing desired foamed sheets by extrusion foaming, and ease of obtaining foamed sheets with excellent thermoformability, hydrocarbons having 3 to 5 carbon atoms are preferred. Specifically, examples of hydrocarbons having 3 to 5 carbon atoms include propane, n-butane, isobutane, n-pentane, and isopentane. Among these, n-butane and / or isobutane are preferred as hydrocarbons. Note that hydrocarbons having 3 to 5 carbon atoms used as physical blowing agents are sometimes simply referred to as hydrocarbons.

[0020] As for dialkyl ethers, from the same viewpoint as for hydrocarbons, and from the viewpoint of easily obtaining molded products that do not expand (tertiary foaming) when molded products containing food etc. are heated in a microwave oven, etc., it is preferable to use dialkyl ethers in which the alkyl group has 1 to 3 carbon atoms. Specifically, diethyl ether, dimethyl ether, and ethyl methyl ether can be given as examples of dialkyl ethers in which the alkyl group has 1 to 3 carbon atoms. Among these, dimethyl ether is preferred as the dialkyl ether. Note that dialkyl ethers in which the alkyl group has 1 to 3 carbon atoms used as physical foaming agents are sometimes simply referred to as dialkyl ethers.

[0021] From the viewpoint of easily producing the desired foamed sheet by extrusion foaming and easily obtaining a foamed sheet with excellent thermoformability, it is preferable to use hydrocarbons as physical blowing agents. Furthermore, from the viewpoint of improving extrusion foaming properties and thermoformability while easily suppressing tertiary foaming of the molded article, it is preferable to use hydrocarbons and dialkyl ethers in combination as physical blowing agents.

[0022] (nitrogen) The physical blowing agent contains nitrogen. Nitrogen is thought to function as a blowing agent by separating from the molten polystyrene resin during extrusion foaming and forming a cellular structure within the polystyrene resin. Furthermore, although the detailed mechanism of its function is not clear, as will be described later, nitrogen is thought to also function as a so-called bubble regulator, effectively enhancing the blowing agent function of the hydrocarbons and / or dialkyl ethers used as physical blowing agents. As will be described later, a bubble regulator is an additive that controls the foaming of the resin by the physical blowing agent and adjusts the state of the cellular structure by forming bubble nuclei. Therefore, in the method for manufacturing foamed sheets of the present invention, nitrogen is thought to have both a function as a blowing agent and a function of extruding a bubble regulator. Adding nitrogen as a physical blowing agent is thought to affect the bubble regulator effect and extrusion foaming properties during extrusion foaming.

[0023] Furthermore, the timing of nitrogen addition is not particularly limited as long as the intended objectives of the present invention can be achieved. For example, nitrogen may be added together with hydrocarbons and / or dialkyl ethers, or it may be added at a different timing than that of hydrocarbons and / or dialkyl ethers.

[0024] To the extent that the intended objectives of the present invention can be achieved, other physical blowing agents other than the hydrocarbons, dialkyl ethers, and nitrogen mentioned above may be used in combination. Furthermore, nitrogen may be added alone or in a mixed state. An example of adding nitrogen in a mixed state is the addition of air.

[0025] (Amount of physical foaming agent added) In the method for manufacturing foamed sheets, the total amount of added hydrocarbons and / or dialkyl ethers and nitrogen (referred to as the total amount of physical blowing agents) is 0.2 mol or more and 1.2 mol or less per 1 kg of foamed resin molten material. If the total amount of physical blowing agents is too low, foaming by extrusion foaming will be insufficient, and it may be difficult to obtain a foamed sheet with the desired foaming ratio. From the viewpoint of stably manufacturing foamed sheets with low apparent density, the total amount of physical blowing agents is preferably 0.3 mol or more, more preferably 0.4 mol or more, and even more preferably 0.5 mol or more per 1 kg of foamed resin molten material.

[0026] If the total amount of physical blowing agent added is too high, it becomes difficult to control the foaming ratio and bubble structure, which may make it difficult to obtain the desired foamed sheet, or the thermoformability of the resulting foamed sheet may decrease. From the viewpoint of stably producing foamed sheets with excellent appearance and thermoformability, the total amount of physical blowing agent added is preferably 1.1 mol or less per 1 kg of foamed resin molten material, and more preferably 1.0 mol or less.

[0027] Furthermore, when the physical blowing agent contains hydrocarbons and dialkyl ethers, in order to stably produce the desired foamed sheet by extrusion foaming, and to more stably produce molded bodies that do not expand (tertiary foaming) when heated in a microwave oven or the like when containing food, the ratio of the amount of hydrocarbons added to the amount of dialkyl ethers added (hydrocarbons:dialkyl ethers) is preferably 6:4 to 9:1, and more preferably 7:3 to 8:2. Note that the above ratio of hydrocarbons to dialkyl ethers is a molar ratio.

[0028] (Percentage of nitrogen added to foamed resin molten material) In the method for producing foamed sheets according to the present invention, the nitrogen addition ratio (referred to as nitrogen addition amount) in the foamed resin molten material is 0.01 mol or more and 0.20 mol or less per 1 kg of foamed resin molten material. If the nitrogen addition amount is too low, foaming does not occur, possibly due to insufficient nitrogen-induced bubble nucleation during extrusion foaming, making it difficult to obtain the desired foamed sheet.

[0029] On the other hand, if the amount of nitrogen added becomes too high, the effect of nitrogen in forming bubble nucleation points tends to become excessively strong, which can lead to the miniaturization of bubbles in the foamed sheet. This can result in corrugations forming in the foamed sheet during extrusion foaming, and the foamed sheet becoming more prone to breakage when taken up, making it difficult to obtain a good quality foamed sheet.

[0030] From the viewpoint of stably producing a foamed sheet having a desired expansion ratio and a good cellular structure, the amount of nitrogen added is preferably 0.02 mol or more, more preferably 0.05 mol or more, and even more preferably 0.08 mol or more per 1 kg of foamed resin molten material. From a similar viewpoint, the amount of nitrogen added is preferably 0.18 mol or less, more preferably 0.15 mol or less, and even more preferably 0.12 mol or less per 1 kg of foamed resin molten material. Furthermore, as will be described later, if the foamed resin molten material contains inorganic powder, from the viewpoint of further improving the controllability of the cellular structure of the foamed sheet, the amount of nitrogen added is preferably 0.15 mol or less, more preferably 0.12 mol or less, and even more preferably 0.10 mol or less per 1 kg of foamed resin molten material.

[0031] (Percentage of nitrogen in physical blowing agents (relative ratio)) In physical blowing agents, the ratio of the amount of nitrogen added (FA2) to the amount of hydrocarbon and / or dialkyl ether added (FA1) (FA2 / FA1) is set to 0.03 or more and 0.4 or less. In this specification, FA2 / FA1 may be referred to as the relative ratio of nitrogen.

[0032] If the relative ratio of nitrogen is excessively high, the effect of nitrogen in forming bubble nucleation points becomes excessively strong, which can lead to the formation of finer bubbles in the foamed sheet. This can easily cause corrugation in the foamed sheet during extrusion foaming, making it difficult to obtain a good quality foamed sheet. Conversely, if the relative ratio of nitrogen is excessively low, the effect of forming bubble nucleation points is insufficient, making foaming during extrusion foaming difficult. Therefore, it can be difficult to obtain a foamed sheet with a low apparent density, which may be the desired result.

[0033] From the viewpoint of easily obtaining foamed sheets with relatively large bubbles and facilitating the stable production of foamed sheets with excellent thermoformability, the upper limit of the relative ratio of nitrogen (FA2 / FA1) is preferably 0.35, more preferably 0.32, and even more preferably 0.30. Furthermore, the lower limit of the relative ratio of nitrogen (FA2 / FA1) is preferably 0.05, more preferably 0.08, and even more preferably 0.1. In addition, as will be described later, when the foaming resin molten material contains inorganic powder, from the viewpoint of further improving the controllability of the bubble structure of the foamed sheet, the upper limit of the relative ratio of nitrogen (FA2 / FA1) is preferably 0.30, more preferably 0.25, and even more preferably 0.20.

[0034] In the method for manufacturing a foamed sheet according to the present invention, a foamed sheet having the basis weight and apparent density described below can be obtained.

[0035] (Basis weight of foamed sheet) The foamed sheet obtained by the foamed sheet manufacturing method according to the present invention has a basis weight of 80 g / m². 2 More than 400g / m 2 The following is preferable. By using the above basis weight, it is possible to stably obtain a molded product that is lightweight, has good thermoformability, and has appropriate rigidity. From the viewpoint of increasing the rigidity of the foamed sheet and the molded product obtained by thermoforming the foamed sheet, the basis weight of the foamed sheet is 100 g / m². 2It is preferably the above, 120 g / m 2 It is more preferably the above. Further, from the viewpoint of enhancing the lightness of the foamed sheet, it is preferably 300 g / m 2 or less, and more preferably 250 g / m 2 or less, and still more preferably 200 g / m 2 or less.

[0036] (Method for measuring the basis weight of the foamed sheet) The basis weight of the foamed sheet is measured as follows. First, in the foamed sheet obtained by the production method of the present invention, 10 locations are selected at equal intervals along the width direction of the foamed sheet (the direction orthogonal to the extrusion direction and the thickness direction of the foamed sheet). Next, at each of the 10 locations, a test piece of 25 mm in length × 25 mm in width (however, the thickness is the thickness of the foamed sheet) is cut out. The mass of each of the obtained test pieces is measured. Then, based on the measured mass and the area of the test piece, the basis weight (mass / area) of each test piece is calculated, and the obtained values are arithmetically averaged. This arithmetically averaged value is defined as the basis weight (g / m 2 ) of the foamed sheet.

[0037] (Apparent density of the foamed sheet) Regarding the foamed sheet obtainable by the production method of the foamed sheet according to the present invention, the apparent density of the foamed sheet is preferably 40 kg / m 3 or more and 200 kg / m 3 or less. By having the above apparent density, a molded body that is lightweight, has good thermoformability, and has appropriate rigidity can be stably obtained. The apparent density of the foamed sheet is preferably 50 kg / m 3 or more, and more preferably 60 kg / m 3 or more. Further, from the viewpoint of enhancing the strength of the molded body formed by thermoforming the foamed sheet, the apparent density of the foamed sheet is preferably 180 kg / m 3 or less, and more preferably 170 kg / m 3 or less, and still more preferably 160 kg / m 3 or less.

[0038] (Method for measuring the apparent density of foamed sheets) The apparent density of the foamed sheet is measured as follows: Using the same method and conditions as described above for measuring the basis weight of the foamed sheet, test specimens are prepared at 10 different locations, and the basis weight is calculated for each specimen. The thickness of the test specimen (thickness of the foamed sheet) is also measured, and the measured basis weight is divided by the thickness of the test specimen (thickness of the foamed sheet). This calculates the density of each specimen, and the resulting values ​​are then given an arithmetic mean. This arithmetic mean value is the apparent density (kg / m³) of the foamed sheet. 3 ) is defined as follows.

[0039] (Width of the foam sheet) Regarding the foam sheet obtained by the foam sheet manufacturing method according to the present invention, the width of the foam sheet is not particularly limited, however, in the foam sheet manufacturing method according to the present invention, it is preferable that the length (sometimes referred to as the sheet width) of the foam sheet in the direction perpendicular to the extrusion direction and the thickness direction of the foam sheet is 500 mm or more. When the sheet width is 500 mm or more, when molded products are manufactured using the foam sheet, many molded products can be molded at once by multi-cavity thermoforming, so the foam sheet has excellent productivity. From this viewpoint, it is more preferable that the sheet width of the foam sheet is 600 mm or more. The upper limit of the foam sheet is not particularly limited, but is generally 2000 mm.

[0040] (Thickness of the foam sheet) The foam sheet obtained by the foam sheet manufacturing method according to the present invention preferably has a thickness of approximately 0.5 mm to 4 mm, and more preferably 1 mm to 3 mm. In this case, it is easier to obtain a molded body that is lightweight, has good thermoformability, and has appropriate rigidity. The thickness of the foam sheet is measured as follows. First, 10 locations are selected at equal intervals along the width direction of the foam sheet. Next, the thickness of the foam sheet is measured at each of the 10 locations, and the arithmetic mean of the measured thicknesses is calculated. This measurement is performed at three randomly selected locations along the extrusion direction, and these arithmetic mean values ​​are taken as the thickness of the foam sheet.

[0041] (Average bubble diameter of foamed sheet) The average bubble diameter (mm) of the foamed sheet obtained by the manufacturing method of the present invention is preferably 0.08 mm or more and 0.5 mm or less, from the viewpoint of improving the moldability (thermoformability) and appearance of the foamed sheet. Furthermore, from the viewpoint of easily obtaining a foamed sheet with excellent thermoformability in a stable manner, the average bubble diameter of the foamed sheet is preferably 0.10 mm or more, more preferably 0.12 mm or more, and even more preferably 0.15 mm or more. Furthermore, in a molded article obtained by thermoforming a foamed sheet, from the viewpoint of easily forming a smooth surface, easily increasing glossiness, and easily obtaining a molded article with a good appearance in a stable manner, the average bubble diameter of the foamed sheet is preferably 0.4 mm or less, more preferably 0.35 mm or less, even more preferably 0.30 mm or less, and particularly preferably 0.26 mm or less. Note that the average bubble diameter of the foamed sheet represents the average value of the average bubble diameter along the width direction (TD) of the foamed sheet, the average bubble diameter along the extrusion direction (MD) of the foamed sheet, and the average bubble diameter along the thickness direction (VD) of the foamed sheet.

[0042] (Method for measuring the average bubble diameter of foamed sheets) The average bubble diameter (mm) of a foamed sheet is measured as follows: A test specimen is cut from the foamed sheet, approximately in the center (near the center) along the width direction of the sheet. The size of this test specimen is 10 cm in length along the width direction and 10 cm in length along the extrusion direction, and the length in the thickness direction of the test specimen is the thickness of the foamed sheet. In addition, test specimens of similar size to the one cut from the center are cut from both approximately one end and approximately the other end (near the end of each end) along the width direction of the foamed sheet.

[0043] For each cut-out test piece, a magnified photograph of the cross-section perpendicular to the extrusion direction (MD) of the foam sheet (MD direction magnified photograph) is taken. An optical microscope can be used to take the magnified photograph. A specific example of an optical microscope is the digital microscope ("VHX-7000") manufactured by Keyence Corporation. The magnification of the cross-section can be set to, for example, 100 times when taking the magnified photograph of the cross-section. Furthermore, using the same method as for taking the MD direction magnified photograph, a magnified photograph of the cross-section perpendicular to the width direction (TD) of the foam sheet (TD direction magnified photograph) is taken.

[0044] On both the magnified MD-direction and TD-direction photographs, line segments are drawn at equal intervals along the thickness direction of the foam sheet. Based on the images of bubbles intersecting the line segments in both the MD-direction and TD-direction magnified photographs, the maximum bubble diameter in the MD-direction, TD-direction, and VD-direction is measured for each bubble, taking into account the magnification of the magnified photograph. Note that all bubbles that are visually observed to intersect the line segments are selected. The average bubble diameters in the MD-direction, TD-direction, and VD-direction are then calculated by arithmetic mean of the measured bubble diameters in each direction. For example, the average bubble diameter in the TD-direction of the test specimen can be calculated by calculating the arithmetic mean of the bubble diameters measured in the TD-direction for multiple bubbles.

[0045] Then, by calculating the arithmetic mean of the average bubble diameters in the MD, TD, and VD directions for each test specimen, the average bubble diameter of the foamed sheet in the MD, TD, and VD directions is calculated. For example, by calculating the arithmetic mean of the average bubble diameters in the TD direction measured for multiple test specimens, the average bubble diameter in the TD direction of the foamed sheet can be calculated.

[0046] Furthermore, the arithmetic mean of the average bubble diameter in the TD direction, the average bubble diameter in the MD direction, and the average bubble diameter in the VD direction of the foamed sheet is calculated. This calculated value is determined as the average bubble diameter (mm) of the foamed sheet.

[0047] (Closed cell ratio of foamed sheet) The closed-cell ratio of the foamed sheet is preferably 70% or higher. Having a closed-cell ratio within this range allows for good secondary foaming of the foamed sheet during thermoforming of molded articles using the foamed sheet. Furthermore, it ensures the strength and other properties of the molded product obtained by thermoforming the foamed sheet. From this viewpoint, a closed-cell ratio of 80% or higher is more preferable, and 90% or higher is even more preferable.

[0048] (Method for measuring the closed-cell ratio of foamed sheets) A test specimen is prepared by cutting a 25mm x 25mm x sheet thickness (thickness of the extruded foam sheet) piece from approximately the center of the foam sheet. Multiple test specimens are stacked so that the sum of the sheet thicknesses is as close to 20mm as possible. Next, the true volume Vx of the test specimen is measured using a Toshiba Beckman Corporation air-comparative hydrometer 930 or similar device, according to procedure C of ASTM-D2856-70, and the closed-cell ratio S (%) is calculated using the following formula (Equation (1)). The above measurement is performed using five test specimens, and the arithmetic mean is taken as the closed-cell ratio of the foam sheet.

[0049]

number

[0050] however, Vx: True volume of the test specimen measured by the above method (cm³) 3 ) is equivalent to the sum of the volume of the resin constituting the foam sheet and the total volume of the closed-cell portion of the test specimen. Va: The apparent volume (cm³) of the test specimen calculated from the external dimensions of the test specimen used for measurement. 3 ), W: Total mass (g) of the test specimen used for measurement, and ρ: Density of the resin constituting the foam sheet (g / cm³) 3 ), That is the case.

[0051] [1-2 Action and Effects] In the method for manufacturing foamed sheets according to the present invention, nitrogen is used as a physical blowing agent in addition to hydrocarbons and / or dialkyl ethers. Nitrogen is thought to serve both as a blowing agent and a bubble regulator. The reason for this is not entirely clear, but the following is considered possible: During extrusion foaming, nitrogen contained in the foamed resin molten material separates earlier from the molten polystyrene resin compared to hydrocarbons and / or dialkyl ethers, and is thought to form bubble nuclei in the extruded resin that serve as the starting point for bubble formation. Furthermore, as foaming of the foamed resin molten material progresses, the separation of hydrocarbons and / or dialkyl ethers from the resin progresses, and it is thought that the formation and growth of bubbles proceeds starting from the bubble nuclei (or their vicinity) formed by nitrogen.

[0052] Therefore, in the method for manufacturing foamed sheets according to the present invention, since nitrogen can function as a foam regulator, it is possible to manufacture foamed sheets with a desired foaming ratio and foam structure, and good thermoformability, even by suppressing the amount of inorganic powder that has been conventionally added as a foam regulator, or by manufacturing the foamed sheet without adding any inorganic powder.

[0053] Furthermore, as previously mentioned, in the manufacture of foamed sheets, recycled raw materials derived from foamed sheets are sometimes reused as polystyrene resin to form the foamed sheets. In conventional foamed sheets to which inorganic powder is added as a foam regulator, the inorganic powder and dispersants added to properly disperse the inorganic powder in the resin usually remain in the foamed sheet. Therefore, when recycled raw materials are manufactured from conventional foamed sheets to which such inorganic powder remains and reused as raw materials for foamed sheets, depending on the amount of recycled raw materials used, yellowing or other issues may occur in the foamed sheet, potentially degrading the quality of the foamed sheet.

[0054] In the method for manufacturing foamed sheets according to the present invention, the amount of inorganic powder, which has generally been added as a foam regulator, can be suppressed. Therefore, even if a foamed sheet is manufactured using recycled raw materials derived from the foamed sheet obtained in the present invention, a foamed sheet with suppressed yellowing (foamed sheet containing recycled raw materials) can be obtained.

[0055] Furthermore, conventional foamed sheets often contain large amounts of inorganic powder and dispersants added to disperse the inorganic powder within the resin. In addition, the amount of inorganic powder and dispersants added to foamed sheets often varies depending on the application and manufacturing conditions of the foamed sheet. For this reason, when recycled raw materials derived from conventional foamed sheets are reused as polystyrene-based resin to form foamed sheets, it may become difficult to adjust the foamed sheet's magnification and bubble structure (bubble size, bubble distribution, etc.) to the desired range, potentially leading to a decrease in the productivity of the foamed sheets.

[0056] In the method for producing foamed sheets according to the present invention, the amount of inorganic powder, which has generally been added as a foam regulator, can be suppressed. Therefore, even when recycled raw materials derived from the foamed sheets obtained in the present invention are used as raw materials for foamed sheets, it becomes easy to obtain foamed sheets that achieve the desired foam structure (i.e., stabilize the quality of foamed sheets using polystyrene resin containing recycled raw materials).

[0057] Furthermore, when conventional foam sheets are used as recycled raw materials, the recycled raw material-containing foam sheets contain inorganic powder. Conventional foam sheets and recycled raw material-containing foam sheets are processed into molded products such as containers by thermoforming, for example. In this process, the foam sheets may be formed in a state where many containers are connected together by thermoforming of multiple cavities. In order to separate these containers into individual containers, the connecting parts between adjacent containers are cut (melted) with a heating wire (such as a nichrome wire). At this time, it has been pointed out that inorganic powder contained in the foam sheet may adhere to the heating wire, contaminating it and potentially leading to a decrease in the cutting function of the heating wire.

[0058] In this regard, according to the present invention, since nitrogen can also perform the function of conventional inorganic powders (function as a foam regulator), the foamed sheet can be made without dispersants or inorganic powders, or even if it contains dispersants or inorganic powders, the amount of dispersants or inorganic powders can be reduced compared to conventional foamed sheets. For this reason, according to the present invention, it is possible to obtain a foamed sheet that can suppress the deterioration of the cutting function of the heating element.

[0059] [1-3 Regarding residual components and combustion residue] As described above, in the method for manufacturing foamed sheets of the present invention, the resulting foamed sheet does not need to contain residual components such as inorganic powder derived from the foam regulator, but the manufactured foamed sheet may contain residual components within a predetermined range. When inorganic powder is included in the residual components, nitrogen and inorganic powder are used in combination in the foaming resin molten material.

[0060] (Residual component) In the foamed sheet of the present invention, residual components derived from inorganic powders and dispersants may be present. Residual components refer to components remaining in the foamed sheet from the raw materials used in the manufacture of the foamed sheet, excluding the resin component and the foaming agent. Examples of residual components include various additives such as foam regulators and dispersants, and specifically, inorganic powders having the function of a foam regulator as described later can be exemplified. Specific examples of inorganic powders include talc, calcium carbonate, barium sulfate, silica, titanium dioxide, clay, and aluminum oxide. Among these, talc can be preferably used as the inorganic powder added as a foam regulator. When using an inorganic powder containing talc, from the viewpoint of enhancing the foam regulation effect, the average particle size of the talc is preferably 0.1 μm or more and 15 μm or less, and more preferably 0.5 μm or more and 10 μm or less. Furthermore, from the viewpoint of being able to disperse the talc well without adding a large amount of dispersant, the average particle size of the talc is preferably 2 μm or more, more preferably 3 μm or more, and even more preferably 5 μm or more.

[0061] The above average particle diameter can be measured by laser diffraction scattering. Specifically, the average particle diameter is the particle diameter corresponding to 50% of the cumulative volume in the volume-based particle size distribution measured by laser diffraction scattering (D 50 This means that the above average particle diameter refers to the diameter of a virtual sphere having the same volume as the particles corresponding to 50% of the cumulative volume.

[0062] (Amount of inorganic powders used) When inorganic powder is added to a foamed resin molten material, the amount of inorganic powder added is preferably 0.2 parts by mass or less per 100 parts by mass of the polystyrene resin. If the amount of inorganic powder is too high, it may cause contamination of the heating element during the manufacture of the molded product, or impair the stabilization of the quality of the foamed sheet when the foamed sheet is used as a recycled material.

[0063] When inorganic powder is blended into a foamed resin molten material, from the viewpoint of enhancing the quality stabilization effect of foamed sheets using recycled foamed sheets as raw materials, and from the viewpoint of further suppressing contamination of heating elements during the manufacture of molded products, the amount of inorganic powder blended is preferably 0.15 parts by mass or less, more preferably 0.12 parts by mass or less, and even more preferably 0.10 parts by mass or less, per 100 parts by mass of the polystyrene-based resin.

[0064] Furthermore, when inorganic powder is blended into the foaming resin molten material, from the viewpoint of enhancing the effects of the inorganic powder described later (effect of facilitating control of foaming ratio (facilitating control of bubble diameter)), the amount of inorganic powder blended is preferably 0.02 parts by mass or more, preferably 0.03 parts by mass or more, and more preferably 0.05 parts by mass or more, per 100 parts by mass of polystyrene resin. Note that the amount of inorganic powder contained in the foamed sheet usually corresponds to the amount of inorganic powder added during the manufacturing of the foamed sheet.

[0065] (Combustion residue of foamed sheets) From the viewpoint of improving the quality stabilization effect of foamed sheets using recycled foamed sheets as raw materials, it is preferable that the proportion of combustion residue when the foamed sheets are burned is 0.2% by mass or less (including 0). The combustion residue mainly consists of components derived from inorganic powders. From the viewpoint of further enhancing this effect, it is preferable that the proportion of combustion residue when the foamed sheets are burned is 0.15% by mass or less, more preferably 0.12% by mass or less, and even more preferably 0.10% by mass or less.

[0066] The proportion of combustion residue can be determined from the mass of the combustion residue of the foamed sheet measured as follows: A crucible containing a predetermined amount (e.g., 5g) of foamed sheet is heated in an electric furnace set to an ambient temperature of 600°C for 1 hour. After heating, the mass of the residue (combustion residue) remaining in the crucible is measured. By dividing the measured mass of combustion residue by the mass of the foamed sheet used in the measurement and expressing it as a percentage, the proportion of combustion residue when the foamed sheet is burned can be determined. In addition, for measurement, a test piece may be prepared by cutting the foamed sheet so that a predetermined amount of foamed sheet fits into the crucible, and the measurement may be performed using this test piece.

[0067] (Effects of using nitrogen and inorganic powder in combination with foamed resin molten material) When manufacturing foamed sheets with a desired foaming ratio and bubble diameter, it is preferable to strictly control the amount of nitrogen added in order to utilize nitrogen alone as a foam regulator. In this regard, if inorganic powder is included in the foaming resin molten material in an amount that does not significantly impair the effects of the present invention, then nitrogen and inorganic powder are used together as components that exert the function of a foam regulator, and the controllability of the amount of nitrogen added to obtain the desired foamed sheet can be improved. This is because the degree of increase in the foaming ratio with increasing inorganic powder is more gradual than the degree of increase with increasing nitrogen. Therefore, it is easier to manufacture foamed sheets by controlling the foaming ratio by adjusting the amount of inorganic powder rather than by adjusting the amount of nitrogen added. For example, when obtaining a foamed sheet with a foaming ratio of about 12 times, by adding enough nitrogen during manufacturing to produce a foamed sheet with a foaming ratio of 11 to less than 12 times, and then adjusting the amount of inorganic powder to adjust the foaming ratio to about 12 times, a foamed sheet with a foaming ratio of about 12 times can be stably obtained. Therefore, when inorganic powder is included in the foamed resin molten material within a predetermined range, it becomes possible to more easily adjust the foaming ratio and bubble diameter of the foamed sheet while suppressing the risk that the inorganic powder will significantly impair the effects of the present invention.

[0068] [1-4 Regarding dispersants] In the manufacturing method of the present invention, the foamed resin molten material does not need to contain a dispersant, but it may contain a dispersant within a predetermined blending range. As mentioned above, the dispersant is usually included together with the inorganic powder when the foamed resin molten material contains inorganic powder.

[0069] (Dispersant) Dispersants have the function of improving the dispersibility of inorganic powders when a polystyrene resin and inorganic powders are kneaded together to form a state in which the inorganic powders are dispersed in the resin. Examples of dispersants include fatty acid metal salts. Examples of fatty acid metal salts include salts of fatty acids (higher fatty acids) having 12 to 30 carbon atoms and metals, and more specifically, examples include stearate metal salts, laurate metal salts, and palmitate metal salts. Examples of metals that make up fatty acid metal salts include zinc, magnesium, calcium, barium, and aluminum. When a dispersant contains a fatty acid metal salt, the proportion of the fatty acid metal salt in the dispersant is preferably 50% by mass or more, preferably 60% by mass or more, more preferably 80% by mass or more, and particularly preferably 90% by mass or more.

[0070] (Amount of dispersant) The amount of dispersant (fatty acid metal salt) contained in the foamed resin molten material is preferably 0.02 parts by mass or less (including 0) per 100 parts by mass of polystyrene resin. By setting the amount of dispersant within the above range, it is possible to manufacture foamed sheets having the desired foaming ratio and bubble diameter, and when manufacturing foamed sheets using recycled raw materials derived from foamed sheets, the yellowing of the resulting foamed sheets can be suppressed more stably. From this viewpoint, when the foamed resin molten material contains a dispersant, the amount of dispersant is preferably 0.015 parts by mass or less, preferably 0.012 parts by mass or less, more preferably 0.010 parts by mass or less, and even more preferably 0.008 parts by mass or less per 100 parts by mass of polystyrene resin. Furthermore, from the viewpoint of further suppressing the yellowing of the resulting foamed sheets, it is particularly preferable that the foamed resin molten material does not contain a dispersant (i.e., the amount of dispersant is 0). Furthermore, from the same viewpoint as above, it is preferable that the resulting foamed sheet either does not contain a dispersant (fatty acid metal salt), or contains the dispersant (fatty acid metal salt) and the amount of the dispersant is 0.02% by mass or less. In addition, if the foamed sheet contains the dispersant, the amount of the dispersant is preferably 0.015% by mass or less, preferably 0.012% by mass or less, more preferably 0.010% by mass or less, and even more preferably 0.008% by mass or less. The amount of dispersant contained in the foamed sheet generally corresponds to the amount of dispersant added during the manufacturing of the foamed sheet.

[0071] [2 Foam Sheets] The foamed sheet according to the present invention is obtained by extruding a foamed resin molten material, which is made by kneading a polystyrene resin and a physical foaming agent, and has an apparent density of 40 kg / m³. 3 More than 200kg / m 3The following applies. The physical blowing agent contains a hydrocarbon with 3 to 5 carbon atoms and / or a dialkyl ether with 1 to 3 carbon atoms in the alkyl group, and nitrogen. Preferably, the foamed sheet has an average bubble diameter of 0.08 mm or more and 0.5 mm or less. The foamed sheet according to the present invention is a polystyrene resin foamed sheet manufactured using the method described in [1 Method for Manufacturing a Foamed Sheet] above. Therefore, regarding the foamed sheet according to the present invention, the components such as the polystyrene resin and physical blowing agent are the same as those described in [1 Method for Manufacturing a Foamed Sheet] above, so their explanation is omitted.

[0072] As mentioned above, the foamed sheet may be free of residual components, or it may contain residual components. Furthermore, in the foamed sheet according to the present invention, it is preferable that the proportion of combustion residue when the foamed sheet is burned is 0.2% by mass or less (including 0). In the foamed sheet according to the present invention, if the foamed sheet contains a fatty acid metal salt as a dispersant, it is preferable that the amount of fatty acid metal salt blended in the foamed sheet is 0.02% by mass or less.

[0073] The foamed sheet according to the present invention can suppress the risk of yellowing occurring in foamed sheets using the foamed sheet according to the present invention as a recycled material. The foamed sheet according to the present invention can stabilize the quality of foamed sheets using the foamed sheet according to the present invention as a recycled material. Furthermore, the foamed sheet according to the present invention can suppress the deterioration of the cutting function of heating wires used in the process of manufacturing molded products using the foamed sheet according to the present invention.

[0074] [3. Method for manufacturing foamed sheets using recycled materials derived from foamed sheets] Next, we will explain a method for manufacturing foamed sheets using recycled materials derived from foamed sheets (hereinafter sometimes referred to as the method for manufacturing foamed sheets containing recycled materials).

[0075] The method for producing a foamed sheet containing recycled materials involves kneading a polystyrene resin containing recycled materials with a physical foaming agent to produce a foamed resin molten product, which is then extruded to produce the foamed sheet. The extrusion foaming method described in [1 Method for producing a foamed sheet] can be suitably employed.

[0076] The method for manufacturing a foamed sheet containing recycled materials may be the same as that described in [1. Method for Manufacturing a Foamed Sheet], except that the polystyrene resin contains recycled materials and the foamed sheet produced is a foamed sheet containing recycled materials. Therefore, the explanation of physical blowing agents (hydrocarbons, diethyl ether, and nitrogen), etc., is omitted. Furthermore, the steps for extruding and foaming the foamable resin molten material obtained by kneading the polystyrene resin and physical blowing agent are the same as those described in [1. Method for Manufacturing a Foamed Sheet], so the explanation is omitted.

[0077] (Polystyrene resin) Polystyrene resin contains recycled materials. Polystyrene resin may be a mixture of recycled materials and non-recycled materials, or it may be composed entirely of recycled materials. From the viewpoint of enabling efficient recycling through the use of recycled materials, the proportion of recycled materials in the polystyrene resin is preferably 5% or more, more preferably 10% or more, even more preferably 20% or more, and even more preferably 30% or more. Furthermore, from the viewpoint of improving the production stability of foamed sheets, the proportion of recycled materials in the polystyrene resin is preferably 80% or less, more preferably 70% or less, even more preferably 60% or less, and even more preferably 50% or less. Non-recycled materials are the same as those described in [1 Method for Manufacturing Foamed Sheets], so their description is omitted.

[0078] (Recycled materials) Recycled raw materials are raw materials derived from foamed sheets. Specifically, recycled raw materials refer to raw materials manufactured from foamed sheets produced by the foamed sheet manufacturing method of the present invention, scraps generated during the production of such foamed sheets, scraps generated during the thermoforming of such foamed sheets, etc.

[0079] (Method of manufacturing recycled materials) Recycled raw materials are manufactured, for example, by supplying materials such as scraps of foamed sheets to an extruder, melting and kneading the materials inside the extruder to form a molten resin, and then extruding the molten resin from the extruder and pelletizing it into a predetermined shape. However, this is just one example of a method for manufacturing recycled raw materials, and the method of manufacturing recycled raw materials is not limited to this method.

[0080] (Recycled material-containing foamed sheet) According to the method for manufacturing a foamed sheet containing recycled materials, the apparent density of the polystyrene-based resin foamed sheet is 40 kg / m³. 3 More than 200kg / m 3 The following foamed sheets can be obtained. The explanation of various physical properties such as apparent density of the polystyrene resin foamed sheet obtained by the method for producing a foamed sheet containing recycled materials is the same as that of the foamed sheet obtained in [1 Method for producing a foamed sheet], so the explanation is omitted.

[0081] (Mechanism of Action and Effects) According to the method for manufacturing a foamed sheet containing recycled raw materials, since the foamed sheet is manufactured using recycled raw materials derived from the foamed sheet obtained by the method for manufacturing a foamed sheet according to the present invention, as explained in [1 Method for manufacturing a foamed sheet] above, it is possible to obtain a foamed sheet in which the occurrence of yellowing is suppressed, and it is also easy to stabilize the quality of the foamed sheet using recycled raw materials.

[0082] Next, we will continue the explanation using examples. [Examples]

[0083] (Polystyrene resin and physical foaming agent) As a polystyrene resin, we use general polystyrene manufactured by PS Japan Co., Ltd. (product name GX154) (density 1050 kg / m³). 3 A solution (MFR 1.6g / 10min, glass transition temperature 122°C) was prepared. Isobutane, dimethyl ether, and nitrogen were prepared as physical blowing agents.

[0084] (Bubble regulator) A masterbatch containing inorganic powder and a dispersant was prepared as a foam regulator (referred to as "foam regulator" in Table 1 for convenience). This masterbatch uses polystyrene resin as the base resin, and contains 40% by mass of inorganic powder and 2.5% by mass of dispersant. The inorganic powder is talc (particle size (D) 50 The particle size of the talc is 7.5 μm, and the dispersant is magnesium stearate. The particle size of the talc was measured using the volume-based particle size distribution method by laser analytical diffraction scattering using a Shimadzu Corporation SALD-2100 laser diffraction particle size distribution analyzer, and the particle size corresponding to 50% of the cumulative volume (D 50 This was calculated by determining ( ).

[0085] In the examples and comparative examples described later, in which the foamed resin molten material contains inorganic powder and a dispersant (Examples 3, 4, 6, and 8, and Comparative Example 5), the foamed resin molten material was prepared by adding inorganic powder and a dispersant using the masterbatch described above.

[0086] (manufacturing equipment) A manufacturing apparatus for producing foamed sheets was prepared. The apparatus consisted of a tandem extruder with two extruders connected in series: a first extruder (65 mm diameter) and a second extruder (90 mm diameter) (the upstream extruder was called the first extruder, and the downstream extruder was called the second extruder); an annular die (outlet diameter 60 mm) located on the discharge side of the second extruder; a cooling cylinder (mandrel) (diameter 212 mm) located downstream of the annular die; a cutter that cuts open the cylindrical foam cooled by the mandrel; and a winding machine that winds up the foamed sheet cut open by the cutter.

[0087] Examples 1, 2, 5, 7 and 9 For each of Examples 1, 2, 5, 7, and 9, polystyrene resin was supplied to the first extruder and heated and kneaded at approximately 220°C. Furthermore, for each of Examples 1, 2, 5, 7, and 9, the amount of physicoblasting agent shown in Table 1 was injected into the molten resin of the first extruder. Regarding the timing of injection of the physicoblasting agent, nitrogen (nitrogen gas) was injected simultaneously with the other physicoblasting agents (isobutane and / or dimethyl ether). In Table 1, the amount of physicoblasting agent added (mol / kg) indicates the amount of substance (mol) of physicoblasting agent added per 1 kg of foaming resin molten material. Also in Table 1, the physicoblasting agent other than nitrogen (isobutane and / or dimethyl ether) is denoted as A, and nitrogen as B. The total amount of A and B added is recorded in the total amount column, and the ratio of the amount of B added to the amount of A set to 1 is recorded in the B / A column.

[0088] The molten resin containing the physical foaming agent, formed by the first extruder, was transferred from the first extruder to a second extruder connected downstream of the first extruder. The second extruder then adjusted the resin temperature of the molten resin to approximately 159°C. In this way, a foaming resin molten product was formed.

[0089] The molten foaming resin from the second extruder was extruded from the annular die of the second extruder under atmospheric pressure at a discharge rate of 50 kg per hour (50 kg / h). This formed a tubular foam. The extruded tubular foam was then taken up along the outer surface of a mandrel, with a blow ratio of 3.5, while adjusting the take-up speed (e.g., winding speed on the winding machine) to achieve a basis weight approximately as shown in Table 2. As the tubular foam moved during take-up, it was cut open with a cutter along the extrusion direction to produce a foamed sheet with a sheet width of approximately 670 mm. The foamed sheet was then wound into a roll using a winding machine.

[0090] The thickness, basis weight, apparent density, and closed-cell ratio of the obtained foamed sheets were measured. The percentage of combustion residue when the foamed sheets were burned was also measured. The previously described methods were used for each measurement. The results are shown in Table 2.

[0091] The combustion residue was measured as follows: A Yamato Scientific Muffle Furnace MF28 was used as the electric furnace. Approximately 5g of foam sheet was taken as a test specimen, its mass was measured, and it was cut into pieces that would fit into the crucible. A cut foam sheet was placed in a ceramic crucible, and the crucible containing the foam sheet was heated for 1 hour in an electric furnace set to an ambient temperature of 600°C. After heating, the mass of the crucible containing the residue (combustion residue) was measured, and the mass of the combustion residue was determined by subtracting the mass of the crucible from this mass. The proportion of the combustion residue when the foam sheet was burned was determined by dividing the measured mass of the combustion residue by the mass of the foam sheet used in the measurement and expressing it as a percentage.

[0092] Furthermore, for the foamed sheets, the average bubble diameter in the extrusion direction (MD), the width direction (TD), and the thickness direction (VD) were measured. The average bubble diameter of the foamed sheet was calculated based on the average bubble diameters in the MD, TD, and VD directions. The results are shown in Table 2. In Table 2, the average bubble diameters in the MD, TD, VD, and foamed sheets are listed in the MD, TD, VD, and Average columns, respectively, within the Average Bubble Diameter column.

[0093] Furthermore, yellowing tests and heating element contamination tests were conducted using the obtained foamed sheets. The results are shown in Table 2.

[0094] (Yellowing test) The yellowing test is a test to evaluate the degree of yellowing of recycled raw materials when recycled raw materials are produced using the obtained foamed sheets.

[0095] The yellowing test was conducted as follows. The foamed sheets obtained in the examples were melted in an extruder for producing recycled materials and repelled to produce recycled materials. In the repelling of the foamed sheets, first, the obtained foamed sheets were crushed to a size that could be fed into the extruder, and the crushed material was fed into a single-screw extruder with an inner diameter of 65 mm and melted and kneaded at a maximum temperature of 230 °C to form a molten resin. Next, the molten resin was extruded from the extruder in a strand shape at a discharge rate of 20 kg / hr, and the extruded resin was cut into pellets to produce recycled materials. Next, the recycled materials were hot-pressed to produce test pieces (solid sheets) with a thickness of 1 mm.

[0096] The prepared test specimens were subjected to L-scale colorimeter analysis using a spectrocolor meter (Nippon Denshoku: Spectro Color Meter SE2000). * a * b * The (color space) was identified.

[0097] (Evaluation of the ability to suppress yellowing) b obtained in the yellowing degree test * The ability to suppress yellowing was evaluated based on the value of b. * The value of b represents the color in the yellow direction, * A higher value indicates that yellowing has occurred. Furthermore, if the recycled material is prone to yellowing, the foamed sheet obtained using that recycled material will also be more susceptible to yellowing.

[0098] From the perspective of being a recycled material that can further suppress the yellowing of the resulting foamed sheet, b * The value of is preferably 3.6 or less, more preferably 3.4 or less, and even more preferably 3.0 or less. Each example (Examples 1 to 9) is better than Comparative Example 5. * The values ​​were small, and all of them were 3.6 or less.

[0099] (Heating wire contamination test) The test for contamination of the heating element was conducted as follows: Fifty of the obtained foam sheets were stacked to form a laminate, and the laminate was cut along the entire width of the foam sheets. The cutting process was carried out by cutting the laminate along the thickness direction with a heating element (nichrome wire) heated by electricity.

[0100] (Evaluation of the ability to suppress heating element contamination) The effectiveness of suppressing heating element contamination was evaluated by observing whether or not inorganic powder was adhering to the heating element after the cutting treatment. The degree of heating element contamination was evaluated as follows:

[0101] ○ (Good): No inorganic powder was observed adhering to the heating element. × (Defective): Inorganic powder is found adhering to the heating element.

[0102] Comparative Examples 1 to 4 For each of Comparative Examples 1 to 4, the same method as in Example 1 was followed. However, the physical blowing agent was injected into the first extruder under pressure in the amounts shown in the respective columns for Comparative Examples 1 to 4 in Table 1.

[0103] In Comparative Examples 1 and 2, no cellular structure was formed in the polyethylene resin when extruded from the manufacturing equipment (no foamed state was formed), and therefore, foamed sheets could not be obtained. For this reason, the thickness, basis weight, apparent density, closed-cell ratio, and average cell diameter of the foamed sheets were not measured. Furthermore, yellowing tests and heating element contamination tests were not performed.

[0104] In Comparative Examples 3 and 4, the bubbles formed in the polyethylene resin during extrusion from the manufacturing equipment became excessively fine, making it impossible to take up the foamed sheet, and consequently, no foamed sheet could be obtained. Therefore, the thickness, basis weight, apparent density, closed-cell ratio, and average cell diameter of the foamed sheet were not measured. Furthermore, yellowing tests and heating element contamination tests were not performed.

[0105] Examples 3, 4, 6, and 8, Comparative Example 5 For each of Examples 3, 4, 6, and 8, and Comparative Example 5, a foamed sheet was obtained using the same method as in Example 1, except that instead of supplying polystyrene resin to the first extruder, a masterbatch containing polystyrene resin, inorganic powder, and a dispersant was supplied to the first extruder. In Table 1, the respective amounts of inorganic powder and dispersant correspond to the respective amounts (parts by mass) of inorganic powder and dispersant blended per 100 parts by mass of polystyrene resin.

[0106] The thickness, basis weight, apparent density, and closed-cell ratio of the obtained foamed sheets were measured using the same method as in Example 1. Also, similar to Example 1, the percentage of combustion residue when the foamed sheets were burned was measured. For the foamed sheets, the average cell diameter in the extrusion direction (MD), the width direction (TD), and the thickness direction (VD) were measured using the same method as in Example 1, and the average cell diameter of the foamed sheet was calculated. The results are shown in Table 2.

[0107] Furthermore, using the obtained foamed sheets, yellowing tests and heating element contamination tests were conducted using the same methods and evaluation criteria as in Example 1. The results are shown in Table 2.

[0108] [Table 1]

[0109] [Table 2]

[0110] The manufacturing method and examples of the present invention described above are merely examples, and the present invention is not limited thereto.

[0111] The present invention has been described, but it can be configured as follows. (A1) A method for producing a foamed sheet by extruding a foamed resin molten material obtained by kneading a polystyrene resin and a physical foaming agent, The physical blowing agent comprises a hydrocarbon having 3 to 5 carbon atoms and / or a dialkyl ether having 1 to 3 carbon atoms, and nitrogen. The sum of the amount of hydrocarbon and / or dialkyl ether added and the amount of nitrogen added is 0.2 mol or more and 1.2 mol or less per 1 kg of the foamed resin molten material. The amount of nitrogen added is 0.01 mol or more and 0.20 mol or less per 1 kg of the foamed resin molten material, and The ratio of the amount of nitrogen added to the amount of hydrocarbon and / or dialkyl ether added is 0.03 or more and 0.4 or less, characterized in that A method for manufacturing foamed sheets. (A2) The foamed resin molten material does not contain inorganic powder, or the foamed resin molten material contains inorganic powder, and the amount of inorganic powder is 0.2 parts by mass or less per 100 parts by mass of the polystyrene resin. A method for manufacturing the foamed sheet described in (A1) above. (A3) The foamed resin molten material does not contain a fatty acid metal salt, or the foamed resin molten material contains the fatty acid metal salt, and the amount of the fatty acid metal salt is 0.02 parts by mass or less per 100 parts by mass of the polystyrene resin. A method for manufacturing a foamed sheet as described in (A1) or (A2) above. (A4) The apparent density of the aforementioned foam sheet is 40 kg / m³ 3 More than 200kg / m 3 The method for manufacturing a foamed sheet as described in any one of (A1) to (A3) above, which is as follows: (A5) The average bubble diameter of the foamed sheet is 0.08 mm or more and 0.5 mm or less. A method for manufacturing a foamed sheet as described in any one of (A1) to (A4) above. (A6) A method for producing a foamed sheet by extruding a foamed resin molten material obtained by kneading a polystyrene resin containing recycled raw materials derived from a foamed sheet produced by any one of the foamed sheet manufacturing methods described in (A1) to (A5) above with a physical blowing agent. (A7) It is made by extruding a foamed resin molten material, which is obtained by kneading a polystyrene resin and a physical foaming agent, and has an apparent density of 40 kg / m³. 3 More than 200kg / m 3 The foam sheet is as follows: The physical blowing agent comprises a hydrocarbon having 3 to 5 carbon atoms and / or a dialkyl ether having 1 to 3 carbon atoms, and nitrogen. The average bubble diameter of the foamed sheet is 0.08 mm or more and 0.5 mm or less. The percentage of combustion residue when the aforementioned foamed sheet is burned is 0.2% by mass or less (including 0). Foam sheet. (A8) It does not contain fatty acid metal salts, or it contains the fatty acid metal salts, and the amount of the fatty acid metal salts is 0.02% by mass or less. The foam sheet described in (A7) above. (A9) The thickness of the foam sheet is between 1 mm and 3 mm. The foam sheet described in (A7) or (A8) above. (A10) The basis weight of the foamed sheet is 80 g / m². 2 More than 400g / m 2 The following is: A foam sheet as described in any one of the above (A7) to (A9).

Claims

1. A method for producing a foamed sheet by extruding a foamed resin molten material obtained by kneading a polystyrene resin and a physical foaming agent, The physical blowing agent comprises a hydrocarbon having 3 to 5 carbon atoms and / or a dialkyl ether having 1 to 3 carbon atoms, and nitrogen. The sum of the amount of hydrocarbon and / or dialkyl ether added and the amount of nitrogen added is 0.2 mol or more and 1.2 mol or less per 1 kg of the foamed resin molten material. The amount of nitrogen added is 0.01 mol or more and 0.20 mol or less per 1 kg of the foamed resin molten material, and The ratio of the amount of nitrogen added to the amount of hydrocarbon and / or dialkyl ether added is 0.03 or more and 0.4 or less. A method for producing a foamed sheet, characterized in that the foamed resin molten material does not contain inorganic powder, or the foamed resin molten material contains inorganic powder, and the amount of inorganic powder is 0.2 parts by mass or less per 100 parts by mass of the polystyrene resin.

2. The method for producing a foamed sheet according to claim 1, wherein the foamed resin molten material does not contain a fatty acid metal salt, or the foamed resin molten material contains the fatty acid metal salt, and the amount of the fatty acid metal salt is 0.02 parts by mass or less per 100 parts by mass of the polystyrene resin.

3. The apparent density of the aforementioned foam sheet is 40 kg / m³ ３ More than 200kg / m ３ The method for manufacturing a foamed sheet according to claim 1 or 2, which is as follows:

4. A method for manufacturing a foamed sheet according to any one of claims 1 to 3, wherein the average bubble diameter of the foamed sheet is 0.08 mm or more and 0.5 mm or less.

5. A method for producing a foamed sheet by extruding and foaming a foamable resin molten material obtained by kneading a polystyrene resin containing recycled raw materials derived from a foamed sheet produced by the method for producing a foamed sheet according to any one of claims 1 to 4 with a physical foaming agent.

Images