Foam sheet

Abstract

To provide a foamed sheet capable of obtaining a foamed sheet having good moldability while reducing the content of an inorganic powder, and capable of obtaining a foamed sheet in which the occurrence of yellowing is suppressed even when the foamed sheet is produced using a polystyrene-based resin containing a recycled raw material derived from the produced foamed sheet.SOLUTION: The polystyrene foam sheet has apparent densities of 40kg / m3 or more and 200kg / m3 or less, an average bubble size of the foam sheet of 0. 08mm or more and 0. 5mm or less, and a combustion residue of 0.2 mass% or less (including 0) when the foam sheet is burned.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a foam sheet. [Background technology]

[0002] Resin foam sheets are used as foam sheets for thermoforming, etc., because of their light weight, moldability, etc. For example, molded articles (molded products) obtained by thermoforming foam sheets using polystyrene-based resins as the base resin (sometimes referred to as polystyrene-based resin foam sheets) are used in a wide range of applications, such as various containers, including lunch boxes, rice bowls, and cups.

[0003] As a method for producing a polystyrene-based resin foam sheet, for example, a method is known in which a polystyrene-based resin and a physical foaming agent are supplied to an extruder to form a foamable resin melt, and the foamable resin melt is extruded and foamed to produce a foam sheet (for example, Patent Document 1). When carrying out such a method for producing a foam sheet, an inorganic powder is usually added to obtain a foam sheet having a desired cell structure. The inorganic powder functions as a cell regulator. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2015-145486 Summary of the Invention [Problem to be solved by the invention]

[0005] In the production of polystyrene-based resin foam sheets, from the viewpoint of reducing the environmental load, recycled raw materials derived from foam sheets, such as foam sheet scraps generated during the production of foam sheets and scraps generated during thermoforming of foam sheets, are sometimes reused as polystyrene-based resins to form foam sheets.

[0006] In foam sheets produced by the method described in Patent Document 1, the inorganic powder and the dispersant added to disperse the inorganic powder well in the resin typically remain in the foam sheet. When a recycled raw material is formed from a foam sheet containing such residual inorganic powder and reused in the production of a foam sheet, depending on the amount of recycled raw material used, yellowing or other issues may occur in the foam sheet containing the recycled raw material, potentially resulting in a deterioration in the quality of the foam sheet. To address this issue, it is conceivable to reduce the amounts of inorganic powder and dispersant contained in the foam sheet to be recycled. However, reducing the amounts of inorganic powder and dispersant typically added to foam sheets may result in the failure to obtain the desired foam sheet.

[0007] An object of the present invention is to provide a foam sheet that can provide a good foam sheet while reducing the blending amount of inorganic powder, and can provide a foam sheet containing recycled materials with suppressed yellowing even when the foam sheet (sometimes referred to as a foam sheet containing recycled materials) is produced using a polystyrene-based resin containing recycled materials derived from the produced foam sheet. [Means for solving the problem]

[0008] The present invention is summarized as follows: (1) to (2). (1) Apparent density is 40 kg / m 3 More than 200kg / m 3 A polystyrene-based resin foam sheet as follows: The average cell diameter of the foamed sheet is 0.08 mm or more and 0.5 mm or less, A foamed sheet, wherein the proportion of combustion residue when the foamed sheet is burned is 0.2 mass % or less (including 0). (2) The composition does not contain a fatty acid metal salt, or contains the fatty acid metal salt and the amount of the fatty acid metal salt is 0.02% by mass or less. The foam sheet according to (1) above.

[0009] The present invention may also be the inventions shown in the following (3) and (4). (3) When the foam sheet is used as a recycled raw material, the b* value of the recycled raw material in the L*a*b* color space is 3.6 or less. The foamed sheet according to (1) or (2) above. (4) A foamed sheet containing recycled materials, the foamed sheet containing recycled materials derived from the foamed sheet according to any one of (1) to (3) above. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a foamed sheet that can obtain a good foamed sheet while reducing the blending amount of inorganic powder, and that can obtain a foamed sheet containing recycled materials with suppressed yellowing, even when the foamed sheet is produced using a polystyrene-based resin containing recycled materials derived from the produced foamed sheet. DETAILED DESCRIPTION OF THE INVENTION

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

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

[0013] [1. Foam sheet manufacturing method] [1-1 Configuration] The method for producing a foamed sheet according to the present invention is a method (so-called extrusion foaming method) for producing a polystyrene-based resin foamed sheet (hereinafter referred to as a foamed sheet) by extruding and foaming a foamable resin melt obtained by kneading a polystyrene-based resin and a physical foaming agent. In explaining the configuration of the foamed sheet production method, the explanation will be continued taking as an example a case in which the foamable resin melt does not contain an inorganic powder or a dispersant. However, as will be described later, this does not exclude the presence of residual components such as inorganic powder in the foamed sheet. Furthermore, it does not exclude the case in which the foamable resin melt contains an inorganic powder and a dispersant within a predetermined range. The fact that a polystyrene-based resin foamed sheet is referred to as a foamed sheet and that the method for producing a foamed sheet according to the present invention is an extrusion foaming method also applies to both the foamed sheet described later and the method for producing a foamed sheet using a polystyrene-based resin containing recycled materials derived from the produced foamed sheet.

[0014] The extrusion foaming method can be performed using a typical manufacturing apparatus for producing extruded foam sheets. The manufacturing apparatus can include extruders connected in series (a first extruder on the upstream side and a second extruder on the downstream side) and a die provided downstream of the second extruder. Preferably, an annular die is used as the die. The following description will be given using an example of a manufacturing apparatus equipped with an annular die downstream of the second extruder. The manufacturing apparatus preferably includes a cooling cylinder (mandrel) downstream of the annular die for cooling the cylindrical foam sheet, and a cutter for slicing open the extruded and cooled cylindrical foam sheet. The manufacturing apparatus also preferably includes a winder for winding up the foam sheet in a roll. The upstream and downstream sides are defined based on the direction of travel of the polystyrene resin, which serves as the base resin for the foam sheet. The manufacturing apparatus shown here is merely an example and is not intended to be limiting.

[0015] (Formation of foamable resin melt) In the method for producing a foamed sheet, a polystyrene resin and a physical foaming agent are kneaded together to form a foamable resin melt. In the production apparatus described above, the polystyrene resin is supplied to the first extruder on the upstream side, and the physical foaming agent is further injected into the extruder. The polystyrene resin and the physical foaming agent are then kneaded together inside the first extruder and the second extruder to form a foamable resin melt.

[0016] (Extrusion foaming) The foamable resin melt is transferred from the first extruder on the upstream side to the second extruder on the downstream side, and the temperature of the foamable resin melt is adjusted by the second extruder. The foamable resin melt is then extruded into atmospheric pressure from an annular die provided in the second extruder to form a tubular foam. The tubular foam is drawn along a mandrel and cooled. The tubular foam is then cut open along the extrusion direction with a cutter, developed into a sheet, and wound into a roll by a winder. In this manner, the foamable resin melt is extruded and foamed to produce a foam sheet.

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

[0018] (Polystyrene resin) The polystyrene-based resin used in the method for producing a foamed sheet is not particularly limited as long as it is a resin that can be used in applications involving polystyrene-based resin foams. In this specification, polystyrene-based resin refers to a resin containing 50% by mass or more of a styrene-based monomer component unit. Examples of polystyrene-based resins include polymers such as polystyrene, rubber-modified polystyrene (high-impact 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 preferably used as the polystyrene-based resin. The term "polystyrene-based resin" encompasses both the use of the above-mentioned various polymers and mixtures alone and the use of two or more of the above-mentioned various polymers and mixtures in combination.

[0019] (foaming agent) A physical foaming agent is preferably used as the foaming agent in the method for producing a foamed sheet. The physical foaming agent preferably contains a hydrocarbon and / or a dialkyl ether. From the viewpoints of solubility in resins and volatility from foamed sheets, ease of producing a desired foamed sheet by extrusion foaming, and ease of obtaining a foamed sheet with excellent thermoformability, hydrocarbons having 3 to 5 carbon atoms are preferably used as the hydrocarbon. Specific examples of hydrocarbons having 3 to 5 carbon atoms include propane, normal butane, isobutane, normal pentane, and isopentane. Of these, normal butane and / or isobutane are preferably used as the hydrocarbon. Hydrocarbons having 3 to 5 carbon atoms used as physical foaming agents may sometimes be simply referred to as hydrocarbons.

[0020] As the dialkyl ether, it is preferable to use a dialkyl ether having an alkyl group with 1 to 3 carbon atoms, from the same viewpoint as in the case of hydrocarbons, and from the viewpoint of easily obtaining a molded article that is resistant to expansion (tertiary foaming) when a molded article containing food or the like is heated in a microwave oven or the like. Specific examples of dialkyl ethers having an alkyl group with 1 to 3 carbon atoms include diethyl ether, dimethyl ether, and ethyl methyl ether. Of these, it is preferable to use dimethyl ether as the dialkyl ether. Note that a dialkyl ether having an alkyl group with 1 to 3 carbon atoms that is used as a physical foaming agent may be simply referred to as a dialkyl ether.

[0021] From the viewpoints of facilitating the production of a desired foamed sheet by extrusion foaming and of facilitating the production of a foamed sheet with excellent thermoformability, it is preferable to use a hydrocarbon as the physical foaming agent. Furthermore, from the viewpoints of facilitating the suppression of tertiary foaming of a molded article while improving extrusion foamability and thermoformability, it is preferable to use a hydrocarbon and a dialkyl ether in combination as the physical foaming agent.

[0022] (nitrogen) The physical foaming agent contains nitrogen. Nitrogen is thought to function as a foaming agent by separating from the molten polystyrene resin during extrusion foaming and forming a cell structure within the polystyrene resin. Although the detailed mechanism of nitrogen's function is unclear, as will be described later, it is thought that nitrogen can also function as a so-called cell control agent, effectively enabling the hydrocarbon and / or dialkyl ether used as the physical foaming agent to function as a foaming agent. As will be described later, a cell control agent is an additive that has a cell control effect by forming cell nuclei and controls the foaming of the resin by the physical foaming agent, thereby adjusting the state of the cell structure. Therefore, in the method for producing a foamed sheet of the present invention, nitrogen is thought to function both as a foaming agent and to exert a cell control effect. Adding nitrogen as a physical foaming agent is thought to affect the cell control effect and extrusion foamability during extrusion foaming.

[0023] The timing of adding nitrogen is not particularly limited as long as the intended object of the present invention can be achieved. For example, nitrogen may be added together with the hydrocarbon and / or dialkyl ether, or nitrogen may be added at a timing different from that of the hydrocarbon and / or dialkyl ether.

[0024] As long as the intended object of the present invention can be achieved, physical blowing agents other than the above-mentioned hydrocarbons, dialkyl ethers, and nitrogen may be used in combination. 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 producing a foamed sheet, the total amount of the added hydrocarbon and / or dialkyl ether and the added nitrogen (referred to as the total amount of added physical foaming agents) is 0.2 mol or more and 1.2 mol or less per 1 kg of the foamable resin melt. If the total amount of added physical foaming agents is too small, foaming by extrusion foaming may be insufficient, making it difficult to obtain a foamed sheet having the desired expansion ratio. From the viewpoint of stably producing a foamed sheet with a low apparent density, the total amount of added physical foaming 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 the foamable resin melt.

[0026] If the total amount of the physical foaming agents added is too large, it may be difficult to control the expansion ratio and cell structure, making it difficult to obtain a desired foamed sheet, and the thermoformability of the resulting foamed sheet may be reduced. From the viewpoint of stably producing a foamed sheet excellent in appearance and thermoformability, the total amount of the physical foaming agents added is preferably 1.1 mol or less, and more preferably 1.0 mol or less, per kg of the foamable resin melt.

[0027] When the physical foaming agent contains a hydrocarbon and a dialkyl ether, the ratio of the amount of the hydrocarbon to the amount of the dialkyl ether (hydrocarbon:dialkyl ether) is preferably 6:4 to 9:1, more preferably 7:3 to 8:2, from the viewpoints of stably producing a desired foamed sheet by extrusion foaming and stably producing a molded article that is less prone to expansion (tertiary foaming) when a molded article containing food or the like is heated in a microwave oven or the like. The ratio of the hydrocarbon to the dialkyl ether is a molar ratio.

[0028] (Ratio of nitrogen added to foamable resin melt) In the method for producing a foamed sheet according to the present invention, the proportion of nitrogen added to the foamable resin melt (referred to as the nitrogen addition amount) is 0.01 mol to 0.20 mol per kg of the foamable resin melt. If the nitrogen addition amount is too small, foaming does not occur, possibly due to an insufficient effect of nitrogen on the formation of bubble nuclei during extrusion foaming, making it difficult to obtain the desired foamed sheet.

[0029] On the other hand, if the amount of nitrogen added is too large, the effect of nitrogen in forming bubble nuclei becomes excessively strong, which may result in the formation of finer bubbles in the foamed sheet, which may lead to the formation of corrugated foamed sheets during extrusion foaming and to the breakage of the foamed sheet when it is taken up, making it difficult to obtain a good foamed sheet.

[0030] From the viewpoint of stably producing a foamed sheet having a desired expansion ratio and a good cell 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 the foamable resin melt. From the same 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 the foamable resin melt. Furthermore, when the foamable resin melt contains an inorganic powder as described below, from the viewpoint of further improving the controllability of the cell 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 the foamable resin melt.

[0031] (Ratio of nitrogen in physical foaming agent (relative ratio)) In the physical blowing agent, the ratio (FA2 / FA1) of the amount of nitrogen added (FA2) to the amount of hydrocarbon and / or dialkyl ether added (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 proportion of nitrogen is too high, the bubble nucleation effect of nitrogen may be too strong, which may lead to finer bubbles in the foamed sheet. This may result in corrugation of the foamed sheet during extrusion foaming, making it difficult to obtain a good foamed sheet. On the other hand, if the relative proportion of nitrogen is too low, the bubble nucleation effect may be insufficient, which may lead to poor foaming during extrusion foaming. This may result in difficulty in obtaining a desired foamed sheet with a low apparent density.

[0033] From the viewpoints of easily obtaining a foamed sheet having bubbles with a relatively large diameter and stably producing a foamed sheet with excellent thermoformability, the upper limit of the relative nitrogen ratio (FA2 / FA1) is preferably 0.35, more preferably 0.32, and even more preferably 0.30. The lower limit of the relative nitrogen ratio (FA2 / FA1) is preferably 0.05, preferably 0.08, and even more preferably 0.1. When the foamable resin melt contains an inorganic powder as described below, the upper limit of the relative nitrogen ratio (FA2 / FA1) is preferably 0.30, more preferably 0.25, and even more preferably 0.20, from the viewpoint of further enhancing the controllability of the cell structure of the foamed sheet.

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

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

[0036] (Method for measuring the basis weight of foam sheets) The basis weight of a foam sheet is measured as follows. First, ten equally spaced locations are selected in the width direction of the foam sheet obtained by the manufacturing method of the present invention (the direction perpendicular to the extrusion direction of the foam sheet and the thickness direction of the foam sheet). Next, test pieces measuring 25 mm in length and 25 mm in width (where the thickness is the thickness of the foam sheet) are cut out from each of the ten locations. The mass of each of the obtained test pieces is measured. Then, the basis weight (mass / area) of each test piece is calculated based on the measured mass and the area of ​​the test piece, and the obtained values ​​are arithmetically averaged. This arithmetically averaged value is the basis weight (g / m2) of the foam sheet. 2 ) is defined as

[0037] (Apparent density of foam sheet) The foamed sheet obtainable by the foamed sheet manufacturing method according to the present invention has an apparent density of 40 kg / m 3 More than 200kg / m 3 The apparent density of the foamed sheet is preferably 50 kg / m or less. By having the apparent density in the above range, it is possible to stably obtain a molded product that is lightweight, has good thermoformability, and has appropriate rigidity. The apparent density of the foamed sheet is preferably 50 kg / m or less. 3 It is preferable that the saturation is 60 kg / m or more. 3 From the viewpoint of increasing the strength of a molded article obtained by thermoforming the foamed sheet, the apparent density of the foamed sheet is more preferably 180 kg / m or more. 3 It is preferable that the saturation is 170 kg / m or less. 3 More preferably, it is 160 kg / m or less. 3 It is even more preferable that:

[0038] (Method for measuring apparent density of foam sheet) The apparent density of a foam sheet is measured as follows. Using the same method and conditions as in the method for measuring the basis weight of a foam sheet described above, test specimens are prepared at each of the 10 positions, and the basis weight of each test specimen is calculated. The thickness of the test specimen (thickness of the foam sheet) is measured, and the measured basis weight is divided by the thickness of the test specimen (thickness of the foam sheet). This calculates the density of each test specimen, and the obtained values ​​are arithmetically averaged. This arithmetically averaged value is the apparent density (kg / m) of the foam sheet. 3 ) is defined as

[0039] (Foam sheet width) The width of the foam sheet obtainable by the foam sheet manufacturing method of the present invention is not particularly limited. However, in the foam sheet manufacturing method of the present invention, the length of the foam sheet in the direction perpendicular to the extrusion direction and the thickness direction of the foam sheet (sometimes referred to as the sheet width) is preferably 500 mm or more. When the sheet width is 500 mm or more, when a molded product is produced using the foam sheet, many molded products can be molded at once by multi-cavity thermoforming, and the foam sheet has excellent productivity. From this perspective, the sheet width of the foam sheet is more preferably 600 mm or more. The upper limit of the foam sheet is not particularly limited, but is generally 2000 mm.

[0040] (Thickness of foam sheet) The thickness of the foam sheet obtainable by the foam sheet manufacturing method of the present invention is preferably approximately 0.5 mm to 4 mm, more preferably 1 mm to 3 mm. In this case, a molded product that is lightweight, has good thermoformability, and has appropriate rigidity is easily obtained. The thickness of the foam sheet is measured as follows: First, 10 equally spaced locations are selected 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 the arithmetic mean of these measurements is defined as the thickness of the foam sheet.

[0041] (Average bubble diameter of foam sheet) The average cell diameter (mm) of the foamed sheet obtained by the production method of the present invention is preferably 0.08 mm or more and 0.5 mm or less from the viewpoints of improving the moldability (thermoformability) and appearance of the foamed sheet. Furthermore, from the viewpoint of easily and consistently obtaining a foamed sheet with excellent thermoformability, the average cell 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, from the viewpoints of easily forming a smooth surface and increasing gloss in a molded product obtained by thermoforming the foamed sheet, and easily and consistently obtaining a molded product with good appearance, the average cell 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. The average cell diameter of the foamed sheet refers to the average of the average cell diameter along the transverse direction (TD) of the foamed sheet, the average cell diameter along the extrusion direction (MD) of the foamed sheet, and the average cell diameter along the thickness direction (VD) of the foamed sheet.

[0042] (Method for measuring the average cell diameter of foamed sheets) The average cell diameter (mm) of a foam sheet is measured as follows. A test piece is cut out of a foam sheet from approximately the center (near the center) in the width direction of the foam sheet. The size of the test piece is 10 cm in length along the width direction and 10 cm in length along the extrusion direction, and the length of the test piece in the thickness direction is the thickness of the foam sheet. In addition, test pieces of the same size as the test piece cut out near the center are cut out of the foam sheet from both approximately one end and approximately the other end (near the end of each of both ends) in the width direction of the foam sheet.

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

[0044] On each of the MD and TD enlarged photographs, lines are drawn at equal intervals along the thickness direction of the foam sheet. Based on the images of bubbles intersecting the lines in each of the MD and TD enlarged photographs, the maximum cell diameters along the MD, TD, and VD directions are measured for each bubble, taking into account the magnification of the enlarged photograph. Note that all bubbles that intersect with the lines are selected as bubbles that the examiner visually recognizes as intersecting with the lines. The average cell diameters in the MD, TD, and VD directions are then calculated by arithmetically averaging the cell diameters measured for each bubble along the MD, TD, and VD directions. For example, the average cell diameter in the TD direction of a test specimen can be calculated by calculating the arithmetic mean of the cell diameters measured along the TD direction for multiple bubbles.

[0045] Then, the average cell diameters of the foamed sheet in the MD, TD, and VD directions are calculated by calculating the arithmetic mean values ​​of the average cell diameters in the MD, TD, and VD directions calculated for each test piece. For example, the average cell diameter in the TD direction of the foamed sheet is calculated by calculating the arithmetic mean value of the average cell diameters in the TD direction measured for a plurality of test pieces.

[0046] Furthermore, the arithmetic mean values ​​of the average cell diameter in the TD direction, the average cell diameter in the MD direction, and the average cell diameter in the VD direction of the foamed sheet are calculated, and the calculated values ​​are defined as the average cell diameter (mm) of the foamed sheet.

[0047] (Closed cell ratio of foam sheet) The closed cell ratio of the foam sheet is preferably 70% or more. When the closed cell ratio of the foam sheet is within the above range, the secondary foaming property of the foam sheet can be improved when the foam sheet is thermoformed into a molded article. Furthermore, the strength of the molded article obtained by thermoforming the foam sheet can be ensured. From this viewpoint, the closed cell ratio of the foam sheet is more preferably 80% or more, and even more preferably 90% or more.

[0048] (Method for measuring the closed cell ratio of foam sheets) A test piece measuring 25 mm x 25 mm x sheet thickness (thickness of extruded foam sheet) is prepared by cutting the foam sheet from approximately the center. Multiple test pieces are stacked so that the total thickness of the sheets is as close to 20 mm as possible. Next, the true volume Vx of the test piece is measured using an air comparison hydrometer such as the Model 930 manufactured by Toshiba Beckman Corporation according to Procedure C of ASTM-D2856-70, and the closed cell percentage S (%) is calculated using the following formula (Equation (1)). The above measurement is performed on five test pieces, and the arithmetic average value is the closed cell percentage of the foam sheet.

[0049]

number

[0050] however, Vx: The true volume (cm) of the test piece measured by the above method 3 ) which corresponds to the sum of the volume of the resin constituting the foam sheet and the total volume of the closed cell portion in the test piece. Va: Apparent volume (cm) of the test specimen calculated from the outer dimensions of the test specimen used in the measurement 3 ), W: total mass (g) of the test specimens used in the measurement, and ρ: Density of the resin that makes up the foam sheet (g / cm 3 ), is.

[0051] [1-2 Actions and Effects] In the method for producing a foamed sheet according to the present invention, nitrogen is used as a physical foaming agent in addition to hydrocarbons and / or dialkyl ethers. It is believed that nitrogen functions both as a foaming agent and as a cell control agent. The reason for this is unclear, but the following is thought to be the case. During extrusion foaming, nitrogen contained in the foamable resin melt is thought to separate from the molten polystyrene resin earlier than hydrocarbons and / or dialkyl ethers, forming bubble nuclei that serve as the starting points for bubble formation in the extruded resin. Furthermore, as foaming of the foamable resin melt progresses, separation of the hydrocarbons and / or dialkyl ethers from the resin progresses, which is thought to promote bubble formation and growth starting from the bubble nuclei (or their vicinity) formed by nitrogen.

[0052] Therefore, in the method for producing a foamed sheet according to the present invention, nitrogen can function as a cell regulator, so that a foamed sheet having a desired expansion ratio and cell structure and good thermoformability can be obtained even when the amount of inorganic powder, which has conventionally been added as a cell regulator, is reduced or no inorganic powder is added.

[0053] As described above, in the production of foam sheets, recycled raw materials derived from foam sheets are sometimes reused as polystyrene-based resins for forming foam sheets. In conventional foam sheets to which inorganic powders are added as cell control agents, the inorganic powders and dispersants added to disperse the inorganic powders well in the resin usually remain in the foam sheets. Therefore, when recycled raw materials are produced from conventional foam sheets containing such residual inorganic powders and reused as raw materials for foam sheets, depending on the amount of recycled raw materials used, yellowing or other changes may occur in the foam sheets, potentially resulting in a deterioration in the quality of the foam sheets.

[0054] In the method for producing a foamed sheet according to the present invention, the amount of inorganic powder that has generally been added as a cell adjusting agent can be reduced. Therefore, even when a foamed sheet is produced using recycled raw materials derived from the foamed sheet obtained according to the present invention, a foamed sheet (recycled raw material-containing foamed sheet) in which yellowing is suppressed can be obtained.

[0055] Furthermore, in conventional foam sheets, a large amount of inorganic powder and a dispersant added to disperse the inorganic powder in the resin remain in the foam sheet. In addition, the amounts of inorganic powder and dispersant added to the foam sheet often vary depending on the application and manufacturing conditions of the foam sheet. Therefore, when recycled raw materials derived from conventional foam sheets are reused as polystyrene-based resins to form foam sheets, it may be difficult to adjust the expansion ratio and cell structure (cell size, cell distribution, etc.) of the foam sheet to the desired range, which may result in a decrease in productivity of the foam sheet.

[0056] In the method for producing a foamed sheet according to the present invention, the amount of inorganic powder, which has generally been added as a cell adjusting agent, can be reduced. Therefore, even when recycled raw materials derived from the foamed sheet obtained according to the present invention are used as the raw material for the foamed sheet, it is easy to obtain a foamed sheet having a desired cell structure (i.e., it is easy to stabilize the quality of a foamed sheet made from a polystyrene-based resin containing recycled raw materials).

[0057] Furthermore, when a conventional foam sheet is used as a recycled raw material, the recycled-raw-material-containing foam sheet contains inorganic powder. Conventional foam sheets and recycled-raw-material-containing foam sheets are processed into molded products such as containers, for example, by thermoforming. In this process, the foam sheet may be molded into a multi-cavity thermoforming process to form a multiplicity of connected containers. To separate these containers into individual containers, the connecting portions between adjacent containers are cut (fused) with an electric heating wire (such as a nichrome wire). It has been pointed out that the inorganic powder contained in the foam sheet may adhere to the electric heating wire, contaminating it and potentially reducing its cutting function.

[0058] In this regard, according to the present invention, nitrogen can also perform the function of conventional inorganic powders (function as a bubble adjuster), so the foamed sheet can be in a state where no dispersant or inorganic powder is contained, or even if a dispersant or inorganic powder is contained, the content of the dispersant or inorganic powder can be reduced compared to conventional foamed sheets. Therefore, according to the present invention, a foamed sheet can be obtained that can suppress the deterioration of the cutting function of the heating wire.

[0059] [1-3 Residual components and combustion residues] As described above, in the foam sheet manufacturing method of the present invention, the foam sheet obtained may be free of residual components such as inorganic powder derived from the cell control agent, but the foam sheet may contain residual components within a predetermined range. When the residual components contain inorganic powder, nitrogen and the inorganic powder are used in combination in the foamable resin melt.

[0060] (Residual component) The foam sheet of the present invention may contain residual components derived from inorganic powders or dispersants. Residual components refer to the components remaining in the foam sheet, excluding the resin component and the foaming agent, from the raw materials used in producing the foam sheet. Examples of residual components include various additives such as cell regulators and dispersants. Specific examples include inorganic powders that function as cell regulators, as described below. Specific examples of inorganic powders include talc, calcium carbonate, barium sulfate, silica, titanium oxide, clay, and aluminum oxide. Among these, talc is preferably used as the inorganic powder added as a cell regulator. When using an inorganic powder containing talc, the average particle diameter of the talc is preferably 0.1 μm to 15 μm, and more preferably 0.5 μm to 10 μm, from the viewpoint of enhancing the cell-regulating effect. Furthermore, from the viewpoint of being able to disperse the talc well without adding a large amount of dispersant, the average particle diameter 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 average particle size can be measured by a laser diffraction scattering method. Specifically, the average particle size is the particle size (D ) corresponding to 50% of the cumulative volume in the volume-based particle size distribution measured by the laser diffraction scattering method. 50 The average particle size means the diameter of a hypothetical sphere having the same volume as the volume of particles corresponding to 50% of the cumulative volume.

[0062] (Amount of inorganic powder blended) When an inorganic powder is blended into the foamable resin melt, the blending amount of the inorganic powder is preferably 0.2 parts by mass or less per 100 parts by mass of the polystyrene-based resin. If the amount of inorganic powder is too large, there is a risk of contamination of the heating wire during the production of a molded product or of the quality stability of a foamed sheet when the foamed sheet is used as a recycled raw material.

[0063] When an inorganic powder is blended into the foamable resin melt, the blending amount of the inorganic powder 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, from the viewpoint of enhancing the effect of stabilizing the quality of foamed sheets when foamed sheets are used as recycled raw materials and from the viewpoint of further suppressing contamination of electric heating wires during the production of molded products.

[0064] Furthermore, when an inorganic powder is blended into the foamable resin melt, from the viewpoint of easily enhancing the effect of the inorganic powder described below (the effect of facilitating control of the expansion ratio (facilitating control of the cell diameter)), the blending amount of the inorganic powder is preferably 0.02 parts by mass or more, 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 the polystyrene-based resin. The amount of inorganic powder contained in the foamed sheet usually corresponds to the blending amount of inorganic powder added during the production of the foamed sheet.

[0065] (Combustion residue of foam sheet) From the viewpoint of enhancing the effect of stabilizing the quality of foamed sheets when the foamed sheet is used as a recycled raw material, the proportion of combustion residue when the foamed sheet is combusted is preferably 0.2% by mass or less (including 0). The combustion residue is mainly a component derived from inorganic powder. From the viewpoint of further enhancing this effect, the proportion of combustion residue when the foamed sheet is combusted is preferably 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 foam sheet measured as follows. A crucible containing a predetermined amount (e.g., 5 g) of foam sheet is heated for 1 hour in an electric furnace with the ambient temperature set to 600°C. After heating, the mass of the residue (combustion residue) remaining in the crucible is measured. The measured mass of the combustion residue is divided by the mass of the foam sheet used in the measurement and expressed as a percentage, thereby determining the proportion of combustion residue when the foam sheet is combusted. Note that the measurement may be performed using a test piece prepared by cutting the foam sheet so that a predetermined amount of foam sheet can fit in the crucible.

[0067] (Effect of using nitrogen and inorganic powder in combination with foamable resin melt) When producing a foamed sheet having a desired expansion ratio and cell diameter, it is preferable to strictly control the amount of nitrogen added so that nitrogen alone can function as a cell regulator. In this regard, if the foamable resin melt contains an inorganic powder to an extent that does not significantly impair the effects of the present invention, nitrogen and the inorganic powder are used in combination as components that function as a cell regulator, thereby improving the controllability of the amount of nitrogen added to obtain a desired foamed sheet. This is because the rate of increase in expansion ratio with an increase in the amount of inorganic powder added is more gradual than the rate of increase in expansion ratio with an increase in the amount of nitrogen added. Therefore, controlling the expansion ratio by adjusting the amount of inorganic powder added is easier to produce a foamed sheet than by adjusting the amount of nitrogen added. For example, to obtain a foamed sheet with an expansion ratio of approximately 12 times, nitrogen is added during production in an amount that will produce a foamed sheet with an expansion ratio of less than 11 to 12 times, and the amount of inorganic powder is adjusted to obtain an expansion ratio of approximately 12 times. This allows for consistent production of a foamed sheet with an expansion ratio of approximately 12 times. Therefore, when the foamable resin melt contains inorganic powder within a predetermined range, it becomes possible to more easily adjust the expansion ratio and cell 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 About dispersants] In the production method of the present invention, the foamable resin melt may not contain a dispersant, but may contain a dispersant within a predetermined blending amount. As described above, when the foamable resin melt contains an inorganic powder, the dispersant is usually contained together with the inorganic powder.

[0069] (dispersant) The dispersant functions to enhance the dispersibility of the inorganic powder when kneading the polystyrene resin with the inorganic powder to form a state in which the inorganic powder is dispersed in the resin. Examples of dispersants include fatty acid metal salts. Examples of fatty acid metal salts include salts of metals with fatty acids (higher fatty acids) having 12 to 30 carbon atoms. More specific examples include metal stearates, metal laurates, and metal palmitates. Examples of metals constituting fatty acid metal salts include zinc, magnesium, calcium, barium, and aluminum. When the 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, more preferably 60% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more.

[0070] (Amount of dispersant blended) The amount of dispersant (fatty acid metal salt) contained in the foamable resin melt is preferably 0.02 parts by mass or less (including 0) per 100 parts by mass of the polystyrene-based resin. By setting the amount of dispersant in this range, a foam sheet having a desired expansion ratio and cell diameter can be produced, and when a foam sheet is produced using recycled raw materials derived from a foam sheet, yellowing of the resulting foam sheet can be more stably suppressed. From this perspective, when the foamable resin melt contains a dispersant, the amount of dispersant is preferably 0.015 parts by mass or less, more 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 the polystyrene-based resin. From the perspective of further suppressing yellowing of the resulting foam sheet, it is particularly preferred that the foamable resin melt does not contain a dispersant (i.e., the amount of dispersant is 0). From the same viewpoint as above, it is preferable that the resulting foam sheet 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. When the foam sheet contains the dispersant, the amount of the dispersant is preferably 0.015% by mass or less, more 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 foam sheet roughly corresponds to the amount of dispersant added during the production of the foam sheet.

[0071] [2 Foam Sheet] The foamed sheet according to the present invention is produced by extrusion foaming a foamable resin melt obtained by kneading a polystyrene resin and a physical foaming agent, and has an apparent density of 40 kg / m. 3 More than 200kg / m 3The physical foaming agent contains a hydrocarbon having 3 to 5 carbon atoms and / or a dialkyl ether in which the alkyl group has 1 to 3 carbon atoms, and nitrogen. The foamed sheet preferably has an average cell diameter of 0.08 mm or more and 0.5 mm or less. The foamed sheet of the present invention is a polystyrene-based resin foamed sheet produced by the method described in [1. Method for producing a foamed sheet] above. Therefore, the components of the foamed sheet of the present invention, such as the polystyrene-based resin and the physical foaming agent, are the same as those described in [1. Method for producing a foamed sheet] above, and therefore further description will be omitted.

[0072] As described above, the foam sheet may contain no residual components, or may contain residual components. Furthermore, the foam sheet according to the present invention preferably has a combustion residue of 0.2% by mass or less (including 0) when the foam sheet is combusted. When the foam sheet according to the present invention contains a fatty acid metal salt as a dispersant, the amount of the fatty acid metal salt in the foam sheet is preferably 0.02% by mass or less.

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

[0074] [3. Manufacturing method of foam sheets using recycled materials derived from foam sheets] Next, a method for producing a foam sheet using recycled materials derived from a foam sheet (hereinafter, sometimes referred to as a method for producing a foam sheet containing recycled materials) will be described.

[0075] The method for producing a foamed sheet containing recycled raw materials is a method for producing a foamed sheet by extruding and foaming a foamable resin melt obtained by kneading a polystyrene-based resin containing recycled raw materials with a physical foaming agent, and the extrusion foaming method as described in [1. Method for producing foamed sheet] can be suitably employed.

[0076] The method for producing a recycled material-containing foam sheet may be the same as that described in [1. Method for producing a foam sheet], except that the polystyrene resin contains recycled materials and the foam sheet produced is a recycled material-containing foam sheet, and therefore a description of physical foaming agents (hydrocarbons, diethyl ether, and nitrogen) will be omitted. Furthermore, each step of extrusion-foaming a foamable resin melt obtained by kneading a polystyrene resin and a physical foaming agent is similar to that described in [1. Method for producing a foam sheet], and therefore a description thereof will be omitted.

[0077] (Polystyrene resin) The polystyrene-based resin contains recycled raw materials. The polystyrene-based resin may be a mixture of recycled and non-recycled raw materials (non-recycled raw materials), or may be composed entirely of recycled raw materials. From the viewpoint of enabling efficient recycling through the use of recycled raw materials, the proportion of recycled raw materials in the polystyrene-based 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 foam sheets, the proportion of recycled raw materials in the polystyrene-based resin is preferably 80% or less, more preferably 70% or less, even more preferably 60% or less, and even more preferably 50% or less. The non-recycled raw materials are the same as those for the polystyrene-based resin described in [1. Foam Sheet Manufacturing Method], and therefore will not be described here.

[0078] (recycled materials) The recycled raw material is a raw material derived from a foam sheet. Specifically, the recycled raw material refers to a raw material produced from a foam sheet produced by the foam sheet production method of the present invention, scraps generated during the production of such foam sheets, scraps generated during the thermoforming of such foam sheets, etc.

[0079] (Manufacturing method of recycled materials) The recycled raw material is produced, for example, by feeding a material such as a foam sheet scrap into an extruder, melting and kneading the material inside the extruder to form a resin melt, and then extruding the resin melt from the extruder and pelletizing it into a predetermined shape, etc. However, this is just one example of a method for producing recycled raw materials, and the method for producing recycled raw materials is not limited to this method.

[0080] (Foam sheet containing recycled materials) According to the method for producing a foamed sheet containing recycled materials, a polystyrene-based resin foamed sheet having an apparent density of 40 kg / m 3 More than 200kg / m 3 The following foamed sheet can be obtained. The explanation of the 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 omitted here because it is the same as that of the foamed sheet obtained by [1. Method for producing a foamed sheet].

[0081] (Action and effect) According to the method for producing a foam sheet containing recycled raw materials, a foam sheet is produced using recycled raw materials derived from a foam sheet obtained by the method for producing a foam sheet according to the present invention. Therefore, as described in [1. Method for producing a foam sheet] above, a foam sheet with reduced yellowing can be obtained, and the quality of a foam sheet produced using recycled raw materials can be easily stabilized.

[0082] Next, the explanation will be continued using an example. [Example]

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

[0084] (Foam adjuster) A masterbatch containing an inorganic powder and a dispersant was prepared as a cell control agent (referred to as cell control agent 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 was talc (particle diameter (D 50 The particle size of the talc was measured by measuring the volumetric particle size distribution using a laser diffraction scattering method using a laser diffraction particle size distribution analyzer SALD-2100 manufactured by Shimadzu Corporation, and the particle size (D ) corresponding to 50% of the cumulative volume was used. 50 ) was calculated.

[0085] Among the examples and comparative examples described below, in the examples in which inorganic powder and dispersant were contained in the foamable resin melt (Examples 3, 4, 6 and 8, Comparative Example 5), the above masterbatch was used to form a state in which inorganic powder and dispersant were added to the foamable resin melt.

[0086] (manufacturing equipment) A manufacturing apparatus for producing a foam sheet was prepared. The manufacturing apparatus was equipped with a tandem extruder in which two extruders, a first extruder (65 mm diameter) and a second extruder (90 mm diameter) (where the upstream extruder is referred to as the first extruder and the downstream extruder is referred to as the second extruder), were connected in series, an annular die (exit diameter 60 mm) provided at the discharge port 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 winder that winds up the foam sheet cut open by the cutter.

[0087] Examples 1, 2, 5, 7 and 9 In each of Examples 1, 2, 5, 7, and 9, a polystyrene-based resin was supplied to a first extruder and heated and kneaded at approximately 220°C. Furthermore, in each of Examples 1, 2, 5, 7, and 9, a physical foaming agent was injected into the molten resin in the first extruder in the amount shown in Table 1. Regarding the timing of the injection of the physical foaming agent, nitrogen (nitrogen gas) was injected simultaneously with the physical foaming agents other than nitrogen (isobutane and / or dimethyl ether). In Table 1, the amount of physical foaming agent added (mol / kg) indicates the amount of physical foaming agent (mol) added per kg of the foamable resin melt. In Table 1, the physical foaming agents other than nitrogen (isobutane and / or dimethyl ether) are designated A and nitrogen is designated B. The total amount of A and B is listed in the Total Amount column, and the ratio of the amount of B added when the amount of A is set to 1 is listed 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, and the resin temperature of the molten resin was adjusted to about 159°C by the second extruder. In this way, a foamable resin melt was formed.

[0089] The foamable resin melt was extruded from the annular die of the second extruder under atmospheric pressure at an hourly output of 50 kg (50 kg / h). This produced a tubular foam. The extruded tubular foam was then pulled along the outer surface of a mandrel at a blow ratio of 3.5, while adjusting the take-up speed (e.g., the take-up speed of a winder) to obtain a basis weight approximately equal to that shown in Table 2. As the tubular foam moved during the take-up, it was cut open along the extrusion direction with a cutter, producing a foam sheet with a sheet width of approximately 670 mm. The foam sheet was then wound into a roll on a winder.

[0090] The thickness, basis weight, apparent density, and closed cell content of the resulting foamed sheet were measured. The foamed sheet was also combusted to measure the proportion of combustion residue. The respective measurement methods were as described above. The respective 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 5 g of foam sheet was collected as a test piece for measurement, its mass was measured, and the piece was cut to fit into a crucible. The 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 with the ambient temperature set to 600°C. After heating, the mass of the crucible containing the residue (combustion residue) was measured, and the mass of the combustion residue was measured by subtracting the mass of the crucible from this mass. The measured mass of the combustion residue was divided by the mass of the foam sheet used in the measurement and expressed as a percentage to determine the proportion of combustion residue when the foam sheet was combusted.

[0092] The foamed sheet was also measured for the average cell diameter in the extrusion direction (MD), the average cell diameter in the width direction (TD), and the average cell diameter in the thickness direction (VD). The average cell diameter of the foamed sheet was calculated based on the average cell diameter in MD, the average cell diameter in TD, and the average cell diameter in VD. The results are shown in Table 2. In Table 2, the average cell diameter in MD, the average cell diameter in TD, the average cell diameter in VD, and the average cell diameter of the foamed sheet are listed in the MD, TD, VD, and average columns of the average cell diameter column, respectively.

[0093] Furthermore, the resulting foamed sheet was subjected to a yellowing test and an electric heating wire staining test, and the results are shown in Table 2.

[0094] (Yellowing test) The yellowing test is a test for evaluating the degree of yellowing of recycled raw materials when the resulting foamed sheet is used to produce recycled raw materials.

[0095] The yellowing test was performed as follows. The foamed sheet obtained in each example was melted in an extruder for producing recycled materials and re-pelletized to produce recycled materials. In re-pelletizing the foamed sheet, the obtained foamed sheet was first crushed to a size that could be fed to the extruder, and the crushed material was fed to a single-screw extruder with an inner diameter of 65 mm and melt-kneaded at a maximum temperature of 230°C to form a molten resin. Next, the molten resin was extruded in the form of strands from the extruder 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 L*a*b* (color space) of the prepared test pieces was determined using a spectrocolorimeter (Spectro Color Meter SE2000, manufactured by Nippon Denshoku).

[0097] (Evaluation of yellowing prevention) The yellowing suppression was evaluated based on the b* value obtained in the yellowing test. The b* value indicates a yellowish color, and the larger the b* value, the more yellowing occurs. Furthermore, if recycled raw materials are prone to yellowing, the foamed sheet obtained using the recycled raw materials will also be prone to yellowing.

[0098] From the viewpoint of making the resulting foamed sheet a recycled raw material that can further suppress yellowing, the b* value is preferably 3.6 or less, more preferably 3.4 or less, and even more preferably 3.0 or less. Each of the Examples (Examples 1 to 9) had a smaller b* value than Comparative Example 5, and all of them satisfied the requirement of 3.6 or less.

[0099] (Electric heating wire contamination test) The test for the degree of contamination by an electric heating wire was carried out as follows. 50 of the obtained foamed sheets were stacked to form a laminate, and the laminate was cut across the entire width of the foamed sheet. The cutting was carried out by cutting the laminate in the thickness direction with an electric heating wire (nichrome wire) that was heated by passing electricity through it.

[0100] (Evaluation of the suppression of heating wire contamination) The evaluation of the ability to suppress contamination of the heating wire was carried out by observing whether or not adhesion of inorganic powder to the heating wire was observed after the cutting process. The degree of contamination of the heating wire was evaluated as follows.

[0101] ◯ (Good): No adhesion of inorganic powder to the heating wire is observed. × (bad): Adhesion of inorganic powder was observed on the heating wire.

[0102] Comparative Examples 1 to 4 For each of Comparative Examples 1 to 4, the same method as in Example 1 was carried out, except that the physical foaming agent was injected into the first extruder in the amount shown in each column of Comparative Examples 1 to 4 in Table 1.

[0103] In Comparative Examples 1 and 2, a cellular structure was not formed in the polyethylene resin when it was extruded from the production apparatus (a foamed state was not formed), and a foamed sheet could not be obtained. Therefore, the thickness, basis weight, apparent density, closed cell ratio, and average cell diameter of the foamed sheet were not measured. In addition, the yellowing test and the electric heating wire contamination test were not performed.

[0104] In Comparative Examples 3 and 4, the cells formed in the polyethylene resin during extrusion from the production equipment were excessively miniaturized, making it impossible to collect the foamed sheet. As a result, no foamed sheet was obtained. Therefore, the thickness, basis weight, apparent density, closed cell ratio, and average cell diameter of the foamed sheet were not measured. In addition, the yellowing test and the electric heating wire contamination test were not performed.

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

[0106] The thickness, basis weight, apparent density, and closed cell content of the resulting foamed sheet were measured using the same methods as in Example 1. The foamed sheet was combusted and the proportion of combustion residue was measured using the same methods as in Example 1. The average cell diameter in the extrusion direction (MD), width direction (TD), and thickness direction (VD) of the foamed sheet were measured using the same methods as in Example 1, and the average cell diameter of the foamed sheet was calculated. The results are shown in Table 2.

[0107] The resulting foamed sheet was subjected to a yellowing test and a heating wire staining test 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 the embodiment of the present invention described above are merely examples, and the present invention is not limited to these.

[0111] The present invention has been described above, but the present invention can be configured as follows. (A1) A method for producing a foamed sheet by extruding and foaming a foamable resin melt obtained by kneading a polystyrene-based resin and a physical foaming agent, comprising: the physical blowing agent contains a hydrocarbon having 3 to 5 carbon atoms and / or a dialkyl ether having an alkyl group having 1 to 3 carbon atoms, and nitrogen; the total amount of the hydrocarbon and / or the dialkyl ether and the nitrogen is 0.2 mol or more and 1.2 mol or less per 1 kg of the foamable resin melt, The amount of nitrogen added is 0.01 mol or more and 0.20 mol or less per 1 kg of the foamable resin melt, 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 foam sheet. (A2) the foamable resin melt does not contain inorganic powder, or the foamable resin melt contains the inorganic powder, and the blending amount of the inorganic powder is 0.2 parts by mass or less relative to 100 parts by mass of the polystyrene-based resin; A method for producing a foamed sheet according to (A1) above. (A3) the foamable resin melt does not contain a fatty acid metal salt, or the foamable resin melt contains the fatty acid metal salt, and the amount of the fatty acid metal salt blended is 0.02 parts by mass or less relative to 100 parts by mass of the polystyrene-based resin; A method for producing a foamed sheet according to (A1) or (A2) above. (A4) The apparent density of the foamed sheet is 40 kg / m 3 More than 200kg / m 3 The method for producing a foamed sheet according to any one of the above (A1) to (A3), 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 producing a foamed sheet according to any one of the above (A1) to (A4). (A6) A method for producing a foamed sheet, comprising extruding and foaming a foamable resin melt obtained by kneading a polystyrene-based resin containing recycled raw materials derived from a foamed sheet produced by the method for producing a foamed sheet according to any one of the above (A1) to (A5) with a physical foaming agent. (A7) Apparent density 40kg / m 3 More than 200kg / m 3 A polystyrene-based resin foam sheet as follows: The average cell diameter of the foamed sheet is 0.08 mm or more and 0.5 mm or less, A foamed sheet, wherein the proportion of combustion residue when the foamed sheet is burned is 0.2 mass % or less (including 0). (A8) The composition does not contain a fatty acid metal salt, or contains the fatty acid metal salt and the amount of the fatty acid metal salt is 0.02 mass% or less. The foam sheet according to (A7) above. (A9) The thickness of the foam sheet is 1 mm or more and 3 mm or less. The foam sheet according to (A7) or (A8) above. (A10) The foam sheet has a basis weight of 80 g / m 2 More than 400g / m 2 Below is the The foam sheet according to any one of (A7) to (A9) above. (A11) When the foam sheet is used as a recycled raw material, the b* value of the recycled raw material in the L*a*b* color space is 3.6 or less. The foam sheet according to any one of the above (A7) to (A10). (A12) A recycled material-containing foam sheet containing recycled materials derived from the foam sheet according to any one of (A7) to (A11).

Claims

1. Apparent density 40 kg / m ３ More than 200kg / m ３ A polystyrene-based resin foam sheet as follows: The foamed sheet has an average cell diameter of 0.08 mm or more and 0.5 mm or less, A foamed sheet, wherein the proportion of combustion residue when the foamed sheet is combusted is 0.2 mass % or less (including 0).

2. The composition does not contain a fatty acid metal salt, or contains the fatty acid metal salt and the amount of the fatty acid metal salt is 0.02 mass% or less. The foamed sheet according to claim 1 .

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