Method for manufacturing polystyrene resin extruded foam boards

Abstract

To provide a method for producing polystyrene resin extruded foam boards that suppresses the refinement of air bubbles in the extruded foam board, and also produces an extruded foam board with excellent heat insulation properties and suppressed shrinkage, even when 1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz) is added as a physical blowing agent. [Solution] The physical blowing agent contains 1,1,1,4,4,4-hexafluoro-2-butene, pentane, and butane, wherein the amount of 1,1,1,4,4,4-hexafluoro-2-butene added is 0.1 mol or more and 1.8 mol or less per 1 kg of base resin, the ratio of the amount of pentane added to the amount of 1,1,1,4,4,4-hexafluoro-2-butene added is 0.20 or more, and the amount of butane added is 0.08 mol or more per 1 kg of base resin.

Description

[Technical Field]

[0001] This invention relates to a method for producing polystyrene resin extruded foam boards. [Background technology]

[0002] Extruded polystyrene foam boards (hereinafter also simply referred to as "extruded foam boards") are widely used as building insulation materials due to their excellent heat insulation properties and mechanical strength. Extruded foam boards are generally manufactured by heating and melting polystyrene resin in an extruder, then injecting and kneading a physical blowing agent into the resulting molten material to obtain a foamable molten resin composition. This composition is then extruded into a low-pressure area (usually atmospheric pressure) through a flat die attached to the tip of the extruder to foam it, and then molded into a board shape using a molding tool.

[0003] Furthermore, one known method for manufacturing extruded foam boards with excellent heat insulation properties is to use a physical blowing agent containing hydrofluoroolefins (hereinafter also simply referred to as "HFO") such as 1,3,3,3-tetrafluoropropene (HFO-1234ze), 1-chloro-3,3,3-trifluoropropene (HCFO-1233zd), and 1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz).

[0004] Furthermore, among HFOs, 1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz) is superior to other HFOs in its ability to maintain a low thermal conductivity in extruded foam boards over a long period of time. For example, Patent Document 1 describes a method for producing polystyrene resin extruded foam boards using 1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz) and a saturated hydrocarbon having 3 to 5 carbon atoms as physical blowing agents. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2023-085796 [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] However, when 1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz) is added during the manufacturing of extruded foam boards, a problem has been found where the bubbles in the extruded foam board tend to become finer depending on the manufacturing conditions, such as the amount added. When the bubbles formed in extruded foam boards become finer, various problems arise, such as an increase in thermal conductivity in the initial stages after manufacturing (a decrease in thermal insulation), inability to obtain extruded foam boards with the desired apparent density, and, in particular, increased cracking of the widthwise edges of the extruded foam boards when manufactured under conditions where the blow ratio (i.e., the ratio of the width of the extruded foam board to be obtained to the width of the flat die exit) is large.

[0007] Furthermore, it was found that when 1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz) is added during the manufacturing of extruded foam boards, depending on the composition of the physical blowing agent, for example, it can cause shrinkage of the extruded foam board.

[0008] The present invention has been made in view of the above circumstances, and aims to provide a method for producing polystyrene resin extruded foam boards that suppresses the refinement of bubbles in the extruded foam board, and also produces an extruded foam board with excellent heat insulation properties and suppressed shrinkage, even when 1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz) is added as a physical blowing agent. [Means for solving the problem]

[0009] To solve the above problems, the following method for manufacturing polystyrene resin extruded foam boards is provided.

[0010] [1] A method for producing a polystyrene resin extruded foam board having an apparent density of 20 kg / m³ or more and 50 kg / m³ or less and a cross-sectional area perpendicular to the extrusion direction of 100 cm² or more, comprising the step of extruding a foamable molten resin composition containing a base resin containing a polystyrene resin and a physical blowing agent and forming it into a board shape with a molding tool, The physical blowing agent comprises 1,1,1,4,4,4-hexafluoro-2-butene, pentane, and butane. The amount of 1,1,1,4,4,4-hexafluoro-2-butene added is 0.1 mol or more and 1.8 mol or less per 1 kg of the base resin. The ratio of the amount of pentane added to the amount of 1,1,1,4,4,4-hexafluoro-2-butene added is 0.20 or more. A method for producing polystyrene resin extruded foam board, wherein the amount of butane added is 0.08 mol or more per 1 kg of the base resin. [2] A method for producing the polystyrene resin extruded foam board according to [1], wherein the amount of pentane added is 0.05 ml or more and 0.8 ml or less per 1 kg of the base resin. [3] A method for producing the polystyrene resin extruded foam board according to [1] or [2], wherein the physical blowing agent contains water and / or alcohol, and the amount of water and / or alcohol added is 0.01 ml or more and 0.5 ml or less per 1 kg of the base resin. [4] A method for producing a polystyrene resin extruded foam board according to any of [1] to [3], wherein the ratio of the amount of pentane added to the total amount of pentane and butane added is 0.15 or more and 0.85 or less. [5] A method for producing a polystyrene resin extruded foam board according to any of [1] to [4] above, wherein cyclopentane is used as the pentane. [6] A method for producing polystyrene resin extruded foam board according to any of [1] to [5], wherein the amount of 1,1,1,4,4,4-hexafluoro-2-butene added is greater than 0.6 mol and less than or equal to 1.8 mol per 1 kg of the base resin. [7] The method for manufacturing a polystyrene-based resin extruded foam board according to any one of [1] to [6], wherein the total addition amount of the physical foaming agent is 0.7 mol or more and 2.3 mol or less per 1 kg of the base resin. [8] The method for manufacturing a polystyrene-based resin extruded foam board according to any one of [1] to [7], wherein graphite is added to the foamable molten resin composition in an amount of 0.5 parts by mass or more and 5 parts by mass or less per 100 parts by mass of the base resin.

Advantages of the Invention

[0011] The method for manufacturing a polystyrene-based resin extruded foam board of the present invention can obtain an extruded foam board with suppressed fining of bubbles, excellent heat insulation properties, and suppressed shrinkage even when 1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz) is added as a physical foaming agent.

Embodiments for Carrying out the Invention

[0012] Hereinafter, an embodiment of the method for manufacturing a polystyrene-based resin extruded foam board of the present invention will be described.

[0013] The method for manufacturing a polystyrene-based resin extruded foam board of the present invention includes a step of extruding and foaming a foamable molten resin composition containing a base resin containing a polystyrene-based resin and a physical foaming agent, and forming it into a plate shape by a molding tool, with an apparent density of 20 kg / m 3 or more and 50 kg / m 3 or less, and a vertical cross-sectional area perpendicular to the extrusion direction of 100 cm 2 or more. It is a method for manufacturing a polystyrene-based resin extruded foam board.

[0014] Specifically, a base resin consisting of a polystyrene resin and other resins added as needed, along with flame retardants and other additives added as needed, are melted and kneaded under heating in an extruder. A predetermined physical foaming agent is then injected under pressure into the resulting molten mixture and kneaded further to obtain a foamable molten resin composition. This foamable molten resin composition is adjusted to an appropriate foaming temperature and extruded through a flat die from a high-pressure extruder to a low-pressure region to cause foaming. Molding tools such as a mold (for example, a shaping device consisting of two plates of polytetrafluoroethylene resin, etc., arranged parallel to each other or to gradually expand from the inlet to the outlet (hereinafter also called a guider)) and molding rolls are placed at the outlet of the flat die, and the extruded foamed composition is formed into a plate shape as it passes through these molding tools. In this invention, by setting the amount and proportion of the physical blowing agents 1,1,1,4,4,4-hexafluoro-2-butene, pentane, and butane within a specific range, it is possible to suppress the refinement of bubbles in the extruded foam board, and to obtain an extruded foam board with excellent heat insulation properties and suppressed shrinkage.

[0015] <Base resin> (Polystyrene resin) The base resin mainly consists of a polystyrene resin. Specifically, the polystyrene resin content in the base resin is 50% by mass or more, preferably 60% by mass or more, more preferably 70% by mass or more, even more preferably 80% by mass or more, and particularly preferably 90% by mass or more.

[0016] Examples of polystyrene-based resins include one or more selected from polystyrene, styrene-methyl acrylate copolymer, styrene-ethyl acrylate copolymer, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, styrene-acrylic acid copolymer, styrene-methacrylic acid copolymer, styrene-maleic anhydride copolymer, styrene-polyphenylene ether copolymer, styrene-acrylonitrile copolymer, styrene-methylstyrene copolymer, styrene-dimethylstyrene copolymer, styrene-ethylstyrene copolymer, styrene-diethylstyrene copolymer, etc. Among these, polystyrene, styrene-methyl methacrylate copolymer, styrene-ethyl methacrylate copolymer, and styrene-acrylonitrile copolymer can be preferably used as polystyrene-based resins. In addition to the styrene unit component, polystyrene may also contain unit components formed by branching agents such as polyfunctional monomers and polyfunctional macromonomers. The content of styrene component units in the copolymer is preferably 60 mol% or more, more preferably 70 mol% or more, even more preferably 80 mol% or more, and particularly preferably 90 mol% or more.

[0017] The melt viscosity of the polystyrene resin used in the manufacturing method of the present invention is preferably 500 to 3000 Pa·s, more preferably 1000 to 2500 Pa·s, and even more preferably 1500 to 2300 Pa·s, due to its excellent foaming and moldability. In this specification, the melt viscosity is based on JIS K7199:1999, at a temperature of 200°C and a shear rate of 100 sec. -1 These are values ​​measured under the following conditions.

[0018] (Other polymers) The base resin may include polymers other than polystyrene resins, to the extent that the objectives and effects of the present invention are achieved. From the viewpoint of improving the heat insulation properties of the extruded foam, amorphous polyethylene terephthalate copolymers can be exemplified as other polymers. When amorphous polyethylene terephthalate copolymers are blended as polymers other than polystyrene resins, the amount of amorphous polyethylene terephthalate copolymer blended is preferably 5% by mass or more and 35% by mass or less in the base resin, and more preferably 8% by mass or more and 25% by mass or less.

[0019] In amorphous polyethylene terephthalate copolymers, the heat of fusion associated with the melting of the resin, according to JIS K7122 (1987), is less than 5 J / g. This heat of fusion is measured using a differential scanning calorimetry device, employing the procedure described in JIS K7122 (1987) as "measuring the heat of fusion after a certain heat treatment" (both the heating rate and cooling rate in conditioning the test specimen are 10°C / min). The measurement is based on the DSC curve obtained by raising the temperature of the conditioned test specimen at a heating rate of 10°C / min.

[0020] Examples of polymers other than amorphous polyethylene terephthalate copolymers include polyethylene resins (one or more selected from the group of ethylene homopolymers and ethylene copolymers with an ethylene unit content of 50 mol% or more), polypropylene resins (one or more selected from the group of propylene homopolymers and propylene copolymers with a propylene unit content of 50 mol% or more), polyphenylene ether resins, thermoplastic resins such as polymethyl methacrylate, and thermoplastic elastomers such as styrene-butadiene-styrene block copolymer, styrene-isoprene-styrene block copolymer, styrene-butadiene-styrene block copolymer hydrogenated, styrene-isoprene-styrene block copolymer hydrogenated, and styrene-ethylene copolymer. The amount of these other polymers blended in the base resin is preferably 30% by mass or less, more preferably 10% by mass or less, even more preferably 5% by mass or less, even more preferably 3% by mass or less, and most preferably 0.

[0021] <Physical foaming agent> The physical blowing agent contains 1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz), pentane, and butane. In the method for producing polystyrene resin extruded foam boards of the present invention, by adjusting the amounts of these three types of physical blowing agents to a predetermined range described later, it is possible to suppress the miniaturization of bubbles formed in the extruded foam board, and to obtain an extruded foam board with excellent heat insulation properties and suppressed shrinkage.

[0022] 1,1,1,4,4,4-Hexafluoro-2-butene (HFO-1336mzz) possesses moderate solubility in polystyrene resins and excellent retention within the foam, making it possible to produce extruded foam boards with excellent long-term low thermal conductivity. Furthermore, its non-flammability reduces the risk of ignition due to static electricity during the manufacturing of extruded foam boards. However, as mentioned above, when adding 1,1,1,4,4,4-Hexafluoro-2-butene (HFO-1336mzz), if the amount added is large, the bubbles in the extruded foam board tend to become finer, potentially leading to the various problems described above. In addition, depending on the composition of the physical blowing agent, it may cause shrinkage of the extruded foam board, so measures to improve this are required.

[0023] The amount of 1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz) added is between 0.1 mol and 1.8 mol per 1 kg of base resin. If the amount of 1,1,1,4,4,4-hexafluoro-2-butene added is too low, the desired thermal insulation may not be obtained. On the other hand, if the amount of 1,1,1,4,4,4-hexafluoro-2-butene added is too high, the bubbles in the extruded foam may become excessively fine, making it impossible to manufacture the extruded foam. By keeping the amount of 1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz) within the above range, and further satisfying the relationship described later regarding the amounts of pentane and butane added, it is possible to suppress the fineness of the bubbles in the extruded foam, thereby obtaining an extruded foam with excellent thermal insulation and suppressed shrinkage. From this perspective, the amount of 1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz) added is preferably 0.3 mol or more and 1.5 mol or less per 1 kg of base resin, more preferably 0.5 mol or more and 1.4 mol or less, even more preferably 0.6 mol or more and 1.3 mol or less, and particularly preferably more than 0.6 mol and 1.2 mol or less.

[0024] 1,1,1,4,4,4-Hexafluoro-2-butene (HFO-1336mzz) may be in its cis isomer, trans isomer, or a mixture thereof. From the viewpoint of being less likely to separate as a gas from the foaming molten resin composition and more stably improving foam moldability, it is preferable that 1,1,1,4,4,4-Hexafluoro-2-butene (HFO-1336mzz) be in its cis isomer.

[0025] Pentane can be one or more selected from n-pentane, isopentane, neopentane, and cyclopentane. Among these, from the viewpoint of further enhancing the bubble expansion effect and more reliably suppressing the refinement of bubbles in the resulting extruded foam board, it is preferable to use cyclopentane or isopentane as the pentane, and more preferable to use cyclopentane. Also from the same viewpoint, when cyclopentane is used as the pentane, it is preferable that the amount of cyclopentane added is 50% by mass or more, more preferably 60% by mass or more, even more preferably 80% by mass or more, particularly preferably 90% by mass or more, and most preferably 100% by mass.

[0026] The ratio of pentane to 1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz) is 0.20 or higher. When the ratio of pentane to 1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz) is within this range, the refinement of air bubbles in the extruded foam board can be suppressed (it exhibits a bubble expansion effect). Therefore, the various problems associated with the refinement of air bubbles in the extruded foam board described above can be easily avoided. From this viewpoint, the ratio of pentane to 1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz) is preferably 0.25 or higher, more preferably 0.28 or higher, and even more preferably 0.30 or higher. Furthermore, the upper limit of the ratio of pentane to 1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz) may be, for example, 1.0 or less, 0.8 or less, or 0.6 or less, from the viewpoint of ensuring the flame retardancy of the extruded foam board.

[0027] Furthermore, from a similar viewpoint, the amount of pentane added is preferably 0.05 ml to 0.8 ml per 1 kg of base resin, more preferably 0.08 ml to 0.6 ml, and even more preferably 0.1 ml to 0.5 ml.

[0028] Examples of butanes include normal butane, isobutane, and mixed butane, which is a mixture of normal butane and isobutane. Isobutane is particularly preferred because it has a relatively slow gas permeation rate through polystyrene resins, remains in the extruded foam board for a relatively long period of time, and can contribute to reducing thermal conductivity.

[0029] The amount of butane added is 0.08 mol or more per 1 kg of base resin. When the amount of butane added is within this range, the shrinkage of the extruded foam board caused by the combined use of 1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz) and pentane can be suppressed. From this viewpoint, it is preferable that the amount of butane added is 0.1 mol or more per 1 kg of base resin. Furthermore, the upper limit of the amount of butane added may be, for example, 1.0 mol or less, 0.8 mol or less, or 0.6 mol or less per 1 kg of base resin.

[0030] Furthermore, the ratio of the amount of pentane added to the total amount of pentane and butane is preferably 0.15 to 0.85. When the ratio of the amount of pentane added to the total amount of pentane and butane is within this range, it is easier to achieve a better balance between the effect of suppressing the refinement of air bubbles in the extruded foam board and the effect of suppressing the shrinkage of the extruded foam board, resulting in excellent heat insulation and making it easier to obtain an extruded foam board with the desired apparent density.

[0031] From the viewpoint of exhibiting the above-mentioned bubble expansion effect and shrinkage suppression effect, the total amount of pentane and butane per 1 kg of base resin is preferably 0.2 ml or more, more preferably 0.3 ml or more, and even more preferably 0.4 ml or more. On the other hand, from the viewpoint of easily ensuring the flame retardancy of the extruded foam board, it is preferably 1.2 ml or less, more preferably 1.0 ml or less, and even more preferably 0.8 ml or less per 1 kg of base resin.

[0032] The physical blowing agent may include other physical blowing agents besides the 1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz), pentane, and butane mentioned above. Examples of other physical blowing agents include one or more selected from other hydrofluoroolefins other than 1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz), water, carbon dioxide, dialkyl ethers with 1 to 3 carbon atoms in the alkyl chain, and aliphatic alcohols with 1 to 5 carbon atoms.

[0033] Other hydrofluoroolefins besides 1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz) include, for example, 1,3,3,3-tetrafluoropropene (HFO-1234ze), 1-chloro-3,3,3-trifluoropropene (HCFO-1233zd), and 1-chloro-2,3,3,3-tetrafluoropropene (HCFO-1224yd). Furthermore, two or more of these can be used in combination.

[0034] Because water has a low molecular weight and high foaming efficiency, it can lower the apparent density of extruded foam boards. In addition, water reduces the environmental impact and dissipates quickly from the foam board, making it easier to stabilize the dimensions of the resulting foam board quickly.

[0035] Carbon dioxide can be used to achieve a high foaming ratio without hindering the flame retardancy of the resulting extruded foam board. Furthermore, because of the high gas permeability to the base resin, carbon dioxide escapes quickly from the extruded foam board, making it easier to stabilize the dimensions of the foam insulation board early.

[0036] Dialkyl ethers with 1 to 3 carbon atoms in the alkyl chain and aliphatic alcohols with 1 to 5 carbon atoms have a low environmental impact, similar to water, and are released early from extruded foam boards, making it easier to stabilize the shape of the foam boards early.

[0037] Examples of dialkyl ethers having 1 to 3 carbon atoms in the alkyl chain include dimethyl ether, diethyl ether, dipropyl ether, and methyl ethyl ether, among which dimethyl ether can be preferably used. Furthermore, two or more of these can be used in combination.

[0038] Examples of aliphatic alcohols having 1 to 5 carbon atoms include methyl alcohol (methanol), ethyl alcohol (ethanol), n-propyl alcohol, isopropyl alcohol, butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, aryl alcohol, clotyl alcohol, propagyl alcohol, n-amyl alcohol, sec-amyl alcohol, isoamyl alcohol, tert-amyl alcohol, neopentyl alcohol, 3-pentanol, 2-methyl-1-butanol, and 3-methyl-2-butanol. Among these, ethanol can be preferably used. Furthermore, two or more of these can be used in combination.

[0039] Other physical blowing agents preferably include water and / or alcohol (aliphatic alcohols having 1 to 5 carbon atoms), and the amount of water and / or alcohol added is preferably 0.01 ml to 0.5 ml per 1 kg of base resin. In other words, if the physical blowing agent contains both water and alcohol, the total amount of water and alcohol added is preferably 0.01 ml to 0.5 ml per 1 kg of base resin. In the production of extruded foam boards, adding water and / or alcohol as a physical blowing agent within the above range makes it easier to reliably expand the bubbles in the extruded foam board and to suppress the miniaturization of bubbles. From this viewpoint, it is more preferable that the amount of water and / or alcohol added is 0.02 ml to 0.4 ml per 1 kg of base resin.

[0040] Furthermore, if the physical blowing agent contains both water and alcohol, the molar ratio of water to alcohol (water:alcohol) is preferably 65:35 to 85:15, and more preferably 70:30 to 80:20.

[0041] The total amount of physical blowing agent added is preferably 0.7 ml to 2.3 ml per 1 kg of base resin, more preferably 0.9 ml to 2.1 ml, and even more preferably 1.1 ml to 1.9 ml. When the total amount of physical blowing agent added is within this range, it is easier to obtain extruded foam boards with the desired apparent density.

[0042] <Other ingredients> (Flame retardant) Flame retardancy is imparted by incorporating a flame retardant into the base resin. The flame retardant is not particularly limited, but it is preferable to use a brominated flame retardant. Examples of brominated flame retardants include brominated butadiene polymers such as brominated butadiene-styrene copolymers, tetrabromobisphenol-A-bis(2,3-dibromo-2-methylpropyl ether), tetrabromobisphenol-S-bis(2,3-dibromo-2-methylpropyl ether), tetrabromobisphenol-F-bis(2,3-dibromo-2-methylpropyl ether), tetrabromobisphenol-A-bis(2,3-dibromopropyl ether), and tetrabromobisphenol- Examples include brominated bisphenol compounds such as sphenol-S-bis(2,3-dibromopropyl ether) and tetrabromobisphenol-F-bis(2,3-dibromopropyl ether), and brominated isocyanurates such as tris(2,3-dibromopropyl) isocyanurate, mono(2,3,4-tribromobutyl) isocyanurate, di(2,3,4-tribromobutyl) isocyanurate, and tris(2,3,4-tribromobutyl) isocyanurate. Furthermore, one or more of these brominated flame retardants can be used in combination.

[0043] In addition to these brominated flame retardants, nitrogen-containing cyclic compounds such as cresyldi-2,6-xylenyl phosphate, antimony trioxide, antimony pentoxide, ammonium sulfate, zinc stannate, cyanuric acid, pentabromottoluene, isocyanuric acid, triallyl isocyanurate, melamine cyanurate, melamine, melam, melem, silicone compounds, inorganic compounds such as boron oxide, zinc borate, and zinc sulfide, phosphate esters represented by triphenyl phosphate, red phosphorus compounds, ammonium polyphosphate, phosphazene, hypophosphate, and other phosphorus compounds can be used in combination.

[0044] From the viewpoint of imparting a high degree of flame retardancy to the extruded foam board and suppressing a decrease in extruded foamability and mechanical properties, the amount of flame retardant added is preferably 0.1 to 10 parts by mass, and more preferably 1 to 9 parts by mass, per 100 parts by mass of the base resin. Within this range, the flame retardant does not inhibit foamability, and an extruded foam board with a high degree of flame retardancy, such as that specified in the flammability test method A of JIS A9521:2017 for extruded polystyrene foam insulation materials, can be obtained.

[0045] (Flame retardant) To further improve the flame retardancy of extruded foam boards, flame retardant additives can be used in combination with flame retardants. Examples of flame retardant additives include one or more selected from diphenylalkanes and diphenylalkenes such as 2,3-dimethyl-2,3-diphenylbutane, 2,3-diethyl-2,3-diphenylbutane, 3,4-dimethyl-3,4-diphenylhexane, 3,4-diethyl-3,4-diphenylhexane, 2,4-diphenyl-4-methyl-1-pentene, and 2,4-diphenyl-4-ethyl-1-pentene, as well as polyalkylated aromatic compounds such as poly-1,4-diisopropylbenzene. The amount of flame retardant additive is preferably about 0.01 to 1 part by mass, and more preferably 0.05 to 0.5 parts by mass, per 100 parts by mass of the base resin.

[0046] (Radiation suppressant) To further improve the thermal insulation properties of extruded foam boards, graphite can be added to the foamed molten resin composition as a radiation suppressor. Graphite reflects infrared rays, thereby improving the thermal insulation properties of extruded foam boards.

[0047] Examples of graphite include flake graphite, scaly graphite, artificial graphite, and clay-like graphite, with the use of graphite whose main component is flake graphite being preferable. Graphite is preferably used as a masterbatch blended at a high concentration in a polystyrene resin. Graphite with a fixed carbon content of 80% or more is preferable because it offers good workability during masterbatch production and excellent thermal insulation properties of the resulting foam board. Furthermore, to further enhance the thermal insulation properties of the foam board, graphite with a fixed carbon content of 90% or more is more preferable, and graphite with a fixed carbon content of 95% or more is even more preferable. The fixed carbon content of graphite refers to the value measured by the method described in JIS M8511:2014.

[0048] The amount of graphite added is preferably 0.2 to 10 parts by mass per 100 parts by mass of the base resin. When the amount of graphite added is within this range, an extruded foam board with excellent heat insulation properties can be obtained. From this viewpoint, the amount of graphite added is more preferably 0.3 parts by mass or more, and even more preferably 0.5 parts by mass or more, per 100 parts by mass of the base resin. On the other hand, from the viewpoint of maintaining the moldability and flame retardancy of the foam board, the upper limit of the amount of graphite added is preferably 8 parts by mass, and more preferably 5 parts by mass, per 100 parts by mass of the base resin of the foam board.

[0049] On the other hand, when a large amount of graphite is incorporated, the miniaturization of air bubbles in the extruded foam board is promoted, which can lead to the aforementioned problems. In contrast, in the manufacturing method of the present invention, even when graphite is incorporated, by adjusting the amounts of the three physical blowing agents, 1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz), pentane, and butane, within the predetermined range described above, it is possible to suppress shrinkage in the extruded foam board while suppressing the miniaturization of air bubbles in the extruded foam board, thereby obtaining an extruded foam board of the desired shape with excellent heat insulation properties.

[0050] Furthermore, in the manufacturing method of the present invention, in order to further improve the heat insulation properties, the extruded foam board may also contain radiation suppressants other than graphite. Examples of radiation suppressants other than graphite include one or more selected from metal oxides such as titanium oxide, metals such as aluminum, ceramics, carbon black, infrared shielding pigments, hydrotalcite, and the like.

[0051] Furthermore, in the manufacturing method of the present invention, other known additives may be appropriately blended into the base resin as needed. Examples of other additives include foam regulators, colorants such as pigments and dyes, heat stabilizers, fillers, and various other additives.

[0052] (Bubble regulator) In the manufacturing method of the present invention, it is preferable to form a foamable molten resin composition by blending a foam regulator with a base resin. As the foam regulator, inorganic powders such as talc, kaolin, mica, silica, calcium carbonate, barium sulfate, titanium dioxide, clay, aluminum oxide, bentonite, and diatomaceous earth can be used. Among these, talc is preferred because it is easy to adjust the bubble diameter. In particular, talc with a 50% particle size (light transmission centrifugal sedimentation method) of 0.1 to 20 μm is preferred, and talc with a particle size of 0.5 to 15 μm is preferred. The amount of foam regulator added varies depending on the type of regulator, the desired bubble diameter, etc., but when using talc as the foam regulator, 0.1 to 7 parts by mass per 100 parts by mass of base resin is preferred, 0.2 to 5 parts by mass is more preferred, and 0.3 to 3 parts by mass is even more preferred.

[0053] (Heat stabilizer) Heat stabilizers can improve the thermal stability of flame retardants by being blended into raw materials or scraps during the manufacturing of extruded foam boards or when recycling and repelling scraps of extruded foam boards. Examples of heat stabilizers include one or more heat stabilizers selected from bisphenol-type epoxy compounds such as the EPICLON series manufactured by DIC Corporation, novolac-type epoxy compounds, hindered phenol compounds such as (pentaerythritol tetrakis[3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate]), and phosphite compounds such as (bis(2,6-di-t-butyl-4-methylphenyl)pentaerythritol-diphosphite). Preferably, the amount of heat stabilizer blended is 0.1 to 40 parts by mass per 100 parts by mass of the total amount of flame retardant.

[0054] In the manufacturing method of the present invention, a method can be employed in which a predetermined proportion of the flame retardant and other additives are supplied together with the base resin to a supply unit located upstream of the extruder and kneaded in the extruder. Alternatively, a method can be employed in which the flame retardant and other additives are supplied to the molten resin from a supply unit located in the middle of the extruder. Specifically, methods can be employed such as supplying a dry blend of the flame retardant, other additives, and base resin to the extruder and melt-kneading it, supplying a molten mixture obtained by kneading the flame retardant, other additives, and base resin using a kneader or the like to the extruder, or preparing a masterbatch in which a high concentration of the flame retardant and other additives is pre-mixed with the base resin, supplying this to the extruder, and melt-kneading it with the base resin. Particularly from the viewpoint of dispersibility, it is preferable to prepare a flame retardant masterbatch and supply it to the extruder. The flame retardant masterbatch is preferably prepared using a polystyrene-based resin as the base resin, with a melt flow rate of approximately 0.5 to 30 g / 10 min at 200°C and a load of 5 kg, so that the flame retardant is contained in 10 to 95% by mass, more preferably 30 to 90% by mass, and even more preferably 50 to 85% by mass.

[0055] <Physical properties of extruded foam boards> Next, we will describe the polystyrene resin extruded foam board obtained by the manufacturing method of the present invention.

[0056] (Cross-sectional area, dimensions, etc.) The extruded foam board of the present invention is in the form of a board, and its cross-sectional area perpendicular to the extrusion direction is 100 cm². 2 That's all, 200cm 2 It is preferable that the above is true. The upper limit of the cross-sectional area is approximately 1500 cm². 2 In this specification, the cross-sectional area perpendicular to the extrusion direction refers to the area of ​​the cross-section of the extruded foam board that is perpendicular to the extrusion direction.

[0057] The extruded foam board of the present invention is usually manufactured by producing a raw board having a size that is at least one size larger than the desired size, and then cutting the raw board to adjust the width, length, and optionally the thickness.

[0058] In the case of an extruded foam board used as a heat insulating material, its thickness is preferably 20 mm or more, more preferably 30 mm or more, and even more preferably 50 mm or more. On the other hand, the upper limit of the thickness of the extruded foam board is preferably 150 mm, and more preferably 130 mm.

[0059] Also, the width of the extruded foam board is preferably 500 mm or more, more preferably 800 mm or more, and even more preferably 900 mm or more. The upper limit of the width of the extruded foam board may generally be 1500 mm, and preferably may be 1200 mm.

[0060] Incidentally, the cross-sectional area perpendicular to the extrusion direction and the width of the above-mentioned extruded foam board can be adjusted to a larger value by increasing the blow ratio during production. In this case, as described above, when the bubbles are refined, the end portions in the width direction tend to be easily cracked. However, according to the manufacturing method of the extruded foam board of the present invention, since the refinement of the bubbles is suppressed, such problems can be easily avoided, and a larger-sized extruded foam board can be stably manufactured.

[0061] (Apparent density) The apparent density of the extruded foam board of the present invention is 20 kg / m 3 or more and 50 kg / m 3 or less, more preferably 25 kg / m 3 or more and 45 kg / m 3 or less, and even more preferably 30 kg / m 3 or more and 40 kg / m 3 or less. When the apparent density is within this range, it has sufficient mechanical strength and can be suitably used as a heat insulating material with excellent lightness.

[0062] (Closed cell ratio) The closed-cell ratio of the extruded foam board is preferably 85% or higher, more preferably 90% or higher, and even more preferably 95% or higher. When the closed-cell ratio is within this range, the foaming agent is more likely to remain in the cells, allowing the high thermal insulation performance of the extruded foam board to be maintained over a long period of time. Furthermore, it is possible to produce an extruded foam board with excellent mechanical strength, such as compressive strength.

[0063] In this specification, the closed-cell ratio of extruded foam board is determined using the true volume Vx of the extruded foam board (cut sample) measured using the following formula (1), and the closed-cell ratio S (%) is calculated using the average value for N=3. This is done by placing a cut sample without a molded surface, cut to a size of 25 mm × 25 mm × 20 mm from the extruded foam board, into a sample cup for measurement. However, if the thickness is thin and a cut sample of 20 mm in the thickness direction cannot be cut, for example, two cut samples of size 25 mm × 25 mm × 10 mm may be placed simultaneously into the sample cup for measurement.

[0064] S(%)=(Vx-W / ρ)×100 / (V A -W / ρ) (1) Vx: True volume (cm³) of the cut sample measured by the above method. 3 (This corresponds to the sum of the volume of resin constituting the cut sample of the extruded foam board and the total volume of the closed-cell portions within the cut sample.) V A : The apparent volume (cm³) of the cut sample calculated from the external dimensions of the cut sample used for measurement. 3 ) W: Total weight of the cut sample used for measurement (g) ρ: Density of the resin constituting the extruded foam board (g / cm³) 3 )

[0065] (Bubble structure: Average bubble diameter in the thickness direction) The average cell diameter in the thickness direction of the extruded foam board is preferably 80 to 250 μm, and more preferably 100 to 220 μm. When the average cell diameter is within this range, the extruded foam board has high thermal insulation properties and excellent mechanical strength.

[0066] The method for measuring the average bubble diameter in the thickness direction of extruded foam board is as follows: The average bubble diameter in the thickness direction can be obtained by taking magnified photographs at three locations: the center and near both ends of the cross-section perpendicular to the width direction of the extruded foam board. The magnification is adjusted within a range of 50 to 200 times so that the number of cells in the photograph is approximately 200 to 1500. On each photograph, the maximum diameter of individual bubbles in the thickness direction is measured using the image processing software WinROOF2021 manufactured by Mitani Corporation, and the average of these values ​​is calculated by taking the arithmetic mean of each value.

[0067] (Bubble structure: Bubble deformation rate) The extruded foam board preferably has a cell deformation ratio of 0.7 to 1.5. The cell deformation ratio is calculated by taking the average cell diameter in the thickness direction, obtained by the measurement method described above, measuring the maximum diameter of each cell in the width direction using WinROOF2021 image processing software manufactured by Mitani Corporation on magnified photographs of the cells, taking the arithmetic mean of these values ​​to obtain the average cell diameter in the width direction, and then dividing the average cell diameter in the thickness direction by the average cell diameter in the width direction. The smaller the cell deformation ratio is than 1, the flatter the cell; the larger the cell deformation ratio is than 1, the more elongated the cell. When the cell deformation ratio is within the above range, the extruded foam board has excellent mechanical strength and higher thermal insulation properties. The lower limit of the cell deformation ratio is more preferably 0.8 and even more preferably 1.0 from the viewpoint of compressive strength and dimensional stability of the extruded foam board. The upper limit of the cell deformation ratio is more preferably 1.4 and even more preferably 1.3 from the viewpoint of improving thermal insulation properties.

[0068] (Thermal conductivity) The extruded foam board obtained by the manufacturing method of the present invention has a particularly low thermal conductivity in the initial period after manufacturing. For example, the thermal conductivity of the extruded foam board one day after manufacturing (at 23°C) is, for example, 0.0240 W / m·K or less, preferably 0.0230 W / (m·K) or less, more preferably W / (m·K) or less, even more preferably 0.0220 W / (m·K) or less, and particularly preferably 0.0210 W / (m·K) or less. The thermal conductivity is measured by cutting a test piece measuring 200 mm in length, 200 mm in width, and of any thickness without a surface layer from the extruded foam board immediately after manufacturing, storing it for 24 hours in an atmosphere at 23°C and 50% humidity, and measuring it based on the flat plate heat flow meter method (two heat flow meters, high temperature side 38°C, low temperature side 8°C, average temperature 23°C) described in JIS A1412-2:1999. [Examples]

[0069] The method for manufacturing polystyrene resin extruded foam boards of the present invention will be described in detail below with reference to examples, but the method for manufacturing polystyrene resin extruded foam boards of the present invention is not limited in any way to the following examples.

[0070] In the examples and comparative examples, the following apparatus and raw materials were used.

[0071] An extrusion apparatus was used in which a first extruder with an inner diameter of 115 mm and a second extruder with an inner diameter of 180 mm were connected in series, a physical foaming agent injection port was provided near the end of the first extruder, and a flat die with a resin discharge port (die lip) with a rectangular cross-section of 1 mm gap x 150 mm width was connected to the outlet of the second extruder. In addition, a molding device (guider) consisting of a pair of upper and lower plates made of polytetrafluoroethylene resin installed horizontally at approximately constant intervals was attached to the resin outlet of the second extruder.

[0072] <1> Base resin • Styrene-methyl methacrylate copolymer (MS): Manufactured by Toyo Styrene Co., Ltd., product name MS200NT, melt viscosity (200℃, 100sec) -1 )1980Pa·s, density 1075kg / m 3 • Polystyrene resin (PS): DIC Corporation's polystyrene "HP600ANJ", melt viscosity (200℃, 100sec) -1 )1424Pa·s, density 1050kg / m 3 )

[0073] <2> Physical foaming agent • cis-1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz(Z)): Manufactured by Mitsui Chemours Fluoroproducts, Inc. • 1-Chloro-3,3,3-trifluoropropene (HCFO-1233zd): Manufactured by Honeywell Japan. Isobutane (i-Bu) • Cyclopentane (c-Pe) • Isopentane (i-Pe) ·water ·ethanol

[0074] <3> Flame retardant Brominated butadiene-styrene block copolymer (Emerald innovation 3000 (E3000) manufactured by Lanxess K.K.)

[0075] <4> Bubble regulator Talc (manufactured by Matsumura Sangyo Co., Ltd., product name "High Filler #12", particle size (d50) 7.5 μm)

[0076] <5> Radiation suppressant Graphite (manufactured by Nippon Graphite Co., Ltd., product name CP-N, average particle size 13 μm (catalog value), flaky graphite)

[0077] [Examples 1-8, Comparative Examples 1-11] The base resin, flame retardant, and foam regulator were supplied to the first extruder, heated to 200°C and kneaded, and the type and amount of physical blowing agent shown in Table 1 (amount of substance per 1 kg of base resin: mol / kg) was supplied from the physical blowing agent inlet provided in the first extruder and kneaded further to form a foamable molten resin composition. Next, the obtained foamable molten resin composition was transferred to the second extruder, and after adjusting the resin temperature to the temperature shown in Table 1, it was extruded into a guider at a discharge rate of 300 kg / hr, and molded into a plate shape by passing it through the guider while foaming to obtain a base plate of extruded foam board with a thickness of 60 mm. After that, the molded skin on both sides of the base plate was evenly cut to form a plate-shaped extruded foam board (width: 400 mm, length: 1820 mm, thickness: 50 mm, area of ​​the cross-section perpendicular to the extrusion direction: 200 cm²). 2 ) was manufactured. For Example 4 and Comparative Example 7, a radiation suppressant was further added as an additive.

[0078] For the extruded foam boards obtained under the conditions of the examples and comparative examples, the apparent density, foaming ratio, closed cell ratio, average cell diameter in the thickness direction, cell deformation rate, and thermal conductivity (after 1 day) were measured by the following method.

[0079] [Apparent Density] Apparent density was measured in accordance with JIS K6767 (1999). Rectangular samples measuring 50 mm (length) x 50 mm (width) x 50 mm (thickness) were cut from three locations (the center in the width direction and near both ends in the width direction) of each extruded foam board (immediately after manufacturing and one day after manufacturing). The apparent density was measured for each sample, and the arithmetic mean of the three measured values ​​was taken as the apparent density.

[0080] [Expansion ratio] The foaming ratio of extruded foam board is determined by the density of the base resin [kg / m³]. 3 ] is the apparent density of the extruded foam board [kg / m³ 3 The expansion ratio was determined by dividing by [ ]. The expansion ratio was determined for extruded foam boards immediately after manufacturing and one day after manufacturing, respectively.

[0081] [Closed cell ratio] The closed-cell ratio of the extruded foam board was determined from equation (1) above, using the true volume Vx of the extruded foam board, measured using an air-comparative hydrometer (Toshiba Beckmann Corporation, air-comparative hydrometer, model: 930), according to procedure C of ASTM-D2856-70.

[0082] [Average bubble diameter in the thickness direction] The average bubble diameter in the thickness direction was determined by the following method: Magnified photographs were taken at three locations in the vertical cross-section of the obtained extruded foam board, specifically near the center and both ends, with the magnification adjusted to 100x. The maximum diameter of each bubble in the thickness direction was measured in each photograph using WinROOF2021, an image processing software manufactured by Mitani Corporation, and the average bubble diameter in the thickness direction was determined by arithmetic mean of these values.

[0083] [Bubble deformation rate] The bubble deformation rate was determined in the same manner as the method for measuring the bubble diameter in the thickness direction described above. This was done by measuring the maximum diameter in the width direction of each bubble using WinROOF2021 image processing software manufactured by Mitani Corporation on magnified photographs of the bubbles, calculating the average bubble diameter in the width direction by taking the arithmetic mean of these values, and then dividing the average bubble diameter in the thickness direction by the average bubble diameter in the width direction.

[0084] [Thermal conductivity: 1 day after manufacturing] A test piece measuring 200 mm (length) x 200 mm (width) x 10 mm (thickness) was cut from the center of the width direction of the extruded foam board immediately after manufacturing. This test piece was stored for 24 hours in a constant temperature and humidity chamber at 23°C and 50% relative humidity, and the thermal conductivity of each piece was measured based on the flat plate heat flow meter method (two heat flow meters, high temperature side 38°C, low temperature side 8°C, average temperature 23°C) described in JIS A1412-2 (1999).

[0085] [Table 1]

[0086] Examples 1-8 contain 1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz) in an amount of 0.1 mol to 1.8 mol per 1 kg of base resin, with a ratio of pentane to 1,1,1,4,4,4-hexafluoro-2-butene of 0.20 or higher, and a butane of 0.08 mol or higher per 1 kg of base resin. The extruded foam boards obtained with the foaming agent compositions of Examples 1-8 had an average cell diameter in the thickness direction that was 20 μm or larger than that obtained with the foaming agent compositions of the respective comparative examples, confirming that the cell diameter expansion effect was achieved. Furthermore, the extruded foam boards obtained with the foaming agent compositions of Examples 1-8 did not have a significantly higher thermal conductivity compared to the extruded foam boards obtained with the foaming agent compositions of the respective comparative examples, confirming that the thermal conductivity was low in the initial period after manufacturing. Furthermore, the extruded foam boards obtained with the foaming agent compositions of Examples 1-8 showed a change in foaming ratio of -2.0% or more ((foaming ratio one day after manufacturing - foaming ratio on the day of manufacturing) / foaming ratio on the day of manufacturing × 100), which is calculated from the difference between the foaming ratio measured on the day of manufacturing and the foaming ratio measured one day after manufacturing. This confirmed that the shrinkage of the extruded foam boards was suppressed.

[0087] It was confirmed that the extruded foam board obtained with the foaming agent composition of Comparative Example 1, which did not contain pentane, had smaller bubble diameters compared to the extruded foam board obtained with the foaming agent compositions of Examples 1-3.

[0088] In Comparative Example 2, which contained pentane but no butane, the extruded foam board obtained with the foaming agent composition of Comparative Example 1 (the blank) showed an enlarged bubble diameter, but significant shrinkage of the extruded foam board was observed.

[0089] In Comparative Example 3, where the ratio of pentane to 1,1,1,4,4,4-hexafluoro-2-butene added was less than 0.20, the extruded foam board showed almost no difference in bubble diameter compared to the extruded foam board obtained with the blank Comparative Example 1's foaming agent composition, confirming that the bubble diameter expansion effect was insufficient.

[0090] Comparative Example 4 is an example in which the amount of ethanol and water was increased without adding pentane in an attempt to enlarge the bubble diameter. When the resin temperature was adjusted to achieve an apparent density equivalent to that of the blank Comparative Example 1 using the foaming agent composition of Comparative Example 4, the extruded foam obtained showed almost no difference in bubble diameter compared to the extruded foam obtained using the foaming agent composition of the blank Comparative Example 1, confirming that the effect of enlarging the bubble diameter was insufficient.

[0091] In the foaming agent composition of Comparative Example 4, the extruded foam board of Comparative Example 5, obtained without adjusting the resin temperature, appeared to have an effect of expanding the bubble diameter compared to the extruded foam board obtained with the foaming agent composition of Comparative Example 1 (which served as the blank). However, it was confirmed that this was simply due to a decrease in apparent density, and that the initial thermal conductivity after manufacturing was higher.

[0092] The extruded foam board obtained with the foaming agent composition of Comparative Example 6, in which HCFO-1233zd was added without the addition of pentane, had smaller bubble diameters compared to the extruded foam board obtained with the foaming agent composition of Comparative Example 1, which served as the blank. This confirmed that the bubble diameter enlargement effect was not achieved.

[0093] The extruded foam board obtained with the foaming agent composition of Comparative Example 7, which did not contain pentane, was found to have smaller bubble diameters compared to the extruded foam board obtained with the foaming agent composition of Example 4. Note that graphite was added as a radiation suppressant in these examples.

[0094] Comparative Example 8, in which the ratio of pentane added to 1,1,1,4,4,4-hexafluoro-2-butene added was less than 0.20, was found to have smaller bubble diameters compared to the extruded foam board obtained with the foaming agent composition of Example 5.

[0095] In Comparative Example 9, where pentane was sufficiently added but butane was not, the extruded foam board obtained with the foaming agent composition of Comparative Example 8 (the blank) showed enlarged bubble diameters, but significant shrinkage of the extruded foam board was observed. Note that Examples 5, Comparative Example 8, and Comparative Example 9 are examples in which a particularly large amount of 1,1,1,4,4,4-hexafluoro-2-butene was added as the foaming agent.

[0096] The extruded foam board obtained with the foaming agent composition of Comparative Example 10, which did not contain pentane, was found to have smaller bubble diameters compared to the extruded foam board obtained with the foaming agent composition of Example 6. Note that polystyrene was used as the base resin in these examples.

[0097] Comparative Example 11, in which the ratio of pentane added to 1,1,1,4,4,4-hexafluoro-2-butene added was less than 0.20, showed smaller bubble diameters compared to the extruded foam board obtained with the blank blowing agent composition of Comparative Example 8. Furthermore, a comparison of Comparative Example 11 and Example 7 showed that the ratio of pentane added to 1,1,1,4,4,4-hexafluoro-2-butene added is more important than the absolute amount of pentane for the bubble expansion effect.

[0098] As described above, the method for manufacturing polystyrene resin extruded foam boards of the present invention suppresses the miniaturization of air bubbles in the extruded foam board, resulting in an extruded foam board with excellent heat insulation properties and suppressed shrinkage.

Claims

1. The process includes extruding and foaming a foamable molten resin composition containing a base resin including a polystyrene resin and a physical foaming agent, and then molding it into a sheet using a molding tool, with an apparent density of 20 kg / m³. ３ More than 50kg / m ３ Below, the cross-sectional area perpendicular to the extrusion direction is 100 cm². ２ The above is a method for producing polystyrene resin extruded foam boards, The physical blowing agent comprises 1,1,1,4,4,4-hexafluoro-2-butene, pentane, and butane. The amount of 1,1,1,4,4,4-hexafluoro-2-butene added is 0.1 mol or more and 1.8 mol or less per 1 kg of the base resin. The ratio of the amount of pentane added to the amount of 1,1,1,4,4,4-hexafluoro-2-butene added is 0.20 or more. A method for producing polystyrene resin extruded foam board, wherein the amount of butane added is 0.08 mol or more per 1 kg of the base resin.

2. The method for producing a polystyrene resin extruded foam board according to claim 1, wherein the amount of pentane added is 0.05 mol or more and 0.8 mol or less per 1 kg of the base resin.

3. A method for producing a polystyrene resin extruded foam board according to claim 1 or 2, wherein the physical blowing agent contains water and / or alcohol, and the amount of water and / or alcohol added is 0.01 mol or more and 0.5 mol or less per 1 kg of the base resin.

4. A method for producing a polystyrene resin extruded foam board according to claim 1 or 2, wherein the ratio of the amount of pentane added to the total amount of pentane and butane added is 0.15 or more and 0.85 or less.

5. A method for producing a polystyrene resin extruded foam board according to claim 1 or 2, wherein cyclopentane is used as the pentane.

6. A method for producing a polystyrene resin extruded foam board according to claim 1 or 2, wherein the amount of 1,1,1,4,4,4-hexafluoro-2-butene added is greater than 0.6 mol and less than or equal to 1.8 mol per 1 kg of the base resin.

7. A method for producing a polystyrene resin extruded foam board according to claim 1 or 2, wherein the total amount of the physical blowing agent added is 0.7 mol or more and 2.3 mol or less per 1 kg of the base resin.

8. A method for producing a polystyrene resin extruded foam board according to claim 1 or 2, wherein graphite is added to the foamable molten resin composition in an amount of 0.5 parts by mass or more and 5 parts by mass or less per 100 parts by mass of the base resin.

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