Method for manufacturing polystyrene resin extruded foam boards

Abstract

To provide a manufacturing method of a polystyrene-based resin extrusion foam plate which has good foamability and manufacturing stability and low thermal conductivity even when inorganic radiation suppression powder is added thereto, in the case of using a foaming agent containing 1-chloro-2,3,3,3-tetrafluoropropene.SOLUTION: An addition amount of inorganic radiation suppression powder is 1 pts.mass or more and 10 pts.mass or less with respect to 100 pts.mass of a base material resin, a physical foaming agent contains a foaming agent (a) composed of 1-chloro-2,3,3,3-tetrafluoropropene and a foaming agent (b) composed of dialkyl ether having a 1-3C alkyl chain, with respect to 1 kg of the base material resin, an addition amount of the foaming agent (a) is 0.5 mol or more and 1.1 mol or less, and an addition amount of the foaming agent (b) is 0.2 mol or more, a total addition amount of the physical foaming agent is 0.8 mol or more and 2 mol or less, and a total ratio of the addition amount of the foaming agent (a) and the addition amount of the foaming agent (b) in the physical foaming agent is 70 mass% or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing polystyrene resin extruded foam boards, and more specifically, to a method for manufacturing polystyrene resin extruded foam boards that can be suitably used as thermal insulation materials for walls, floors, roofs, etc., of buildings. [Background technology]

[0002] Polystyrene resin extruded foam boards (hereinafter also simply referred to as "extruded foam boards") are widely used as thermal insulation materials due to their excellent thermal insulation properties and mechanical strength. Such sheet-shaped extruded foam boards are generally manufactured by heating and melting a polystyrene resin in an extruder, then injecting and kneading a physical foaming agent into the resulting molten material to obtain a foamable molten resin mixture, which is then extruded into a low-pressure range through a flat die attached to the tip of the extruder to foam it, and then molded into a sheet shape using a molding tool.

[0003] In recent years, there has been a growing demand for energy conservation in homes and buildings, and the demand for extruded foam boards, which offer excellent thermal insulation, is increasing. To improve the thermal insulation properties of extruded foam boards, it is necessary to lower their thermal conductivity.

[0004] Therefore, as one method for manufacturing extruded foam boards with excellent heat insulation properties, the use of 1-chloro-3,3,3-trifluoropropene, a type of hydrofluoroolefin, as a blowing agent is being considered. 1-chloro-3,3,3-trifluoropropene is soluble in polystyrene resins and possesses foaming properties, enabling the production of low apparent density extruded foam boards. Furthermore, 1-chloro-3,3,3-trifluoropropene is non-flammable, has low thermal conductivity and excellent heat insulation properties, and remains in the foam board for extended periods, thus providing long-term heat insulation. In addition, 1-chloro-3,3,3-trifluoropropene has a very low ozone depletion potential and global warming potential, making it an environmentally friendly blowing agent.

[0005] For example, Patent Documents 1 and 2 disclose extruded foam boards using 1-chloro-2,3,3,3-tetrafluoropropene (HFO-1224yd).

[0006] Furthermore, Patent Documents 1 and 2 disclose the use of radiation suppressants such as graphite. By adding radiation suppressants, heat transfer due to infrared radiation is suppressed, making it possible to further reduce the thermal conductivity of extruded foam boards. [Prior art documents] [Patent Documents]

[0007] [Patent Document 1] Japanese Patent Publication No. 2022-044963 [Patent Document 2] Japanese Patent Publication No. 2022-032685 [Overview of the project] [Problems that the invention aims to solve]

[0008] However, in configurations using a foaming agent containing HFO-1224yd, as described in Patent Documents 1 and 2, when a radiation suppressor is added, depending on the amount of HFO-1224yd added, there is a risk that the bubbles may become finer, resulting in poor foaming properties or poor manufacturing stability. Considering these circumstances, the present invention aims to provide a manufacturing method for producing polystyrene resin extruded foam boards that have good foaming properties and manufacturing stability, and low thermal conductivity, even when an inorganic radiation suppressor powder is added, when using a foaming agent containing HFO-1224yd. [Means for solving the problem]

[0009] According to the present invention, a method for manufacturing polystyrene resin extruded foam boards in the forms shown in [1] to [4] below is provided.

[0010] [1] A method for manufacturing polystyrene resin extruded foam board includes a step of extruding and foaming a foamed resin molten composition, which is made by kneading a base resin mainly composed of polystyrene resin, inorganic radiation suppression powder, flame retardant, physical blowing agent and foam modifier, and forming it into a board shape using a molding tool, with an apparent density of 20 to 50 kg / m³. 3 A method for producing a polystyrene resin extruded foam board, characterized in that the amount of inorganic radiation suppression powder added is 1 part by mass or more and 10 parts by mass or less per 100 parts by mass of the base resin, the total amount of physical blowing agent added is 0.8 mol or more and 2 mol or less per 1 kg of base resin, the physical blowing agent comprises a blowing agent (a) consisting of 1-chloro-2,3,3,3-tetrafluoropropene and a blowing agent (b) consisting of a dialkyl ether having 1 to 3 carbon atoms in the alkyl chain, the amount of blowing agent (a) added is 0.5 mol or more and 1.1 mol or less per 1 kg of base resin, the amount of blowing agent (b) added is 0.2 mol or more per 1 kg of base resin, and the total ratio of the amount of blowing agent (a) and the amount of blowing agent (b) added in the physical blowing agent is 70% by mass or more.

[0011] The method for producing polystyrene resin extruded foam board according to [2][1] is characterized in that the molar ratio (a:b) of the amount of foaming agent (a) added to the amount of foaming agent (b) added is 50:50 to 90:10.

[0012] In the method for producing polystyrene resin extruded foam board according to [3] [1] or [2], the inorganic radiation suppression powder contains graphite, and the amount of graphite added is 0.3 parts by mass or more and 3 parts by mass or less per 100 parts by mass of the base resin.

[0013] In a method for producing polystyrene resin extruded foam board according to any of [4], [1] to [3], the foam regulator contains talc, and the ratio of the amount of graphite added to the amount of talc added is 3 or more and 30 or less. [Effects of the Invention]

[0014] According to the manufacturing method of the present invention, when a foaming agent containing 1-chloro-2,3,3,3-tetrafluoropropene is used, even if an inorganic radiation suppressing powder is added, the foaming property and manufacturing stability are good, and it is possible to provide a polystyrene-based resin extruded foam board having a low thermal conductivity.

Embodiments for Carrying Out the Invention

[0015] The manufacturing method of the present invention includes a step of extruding and foaming a foaming resin melt composition obtained by kneading a base resin mainly composed of a polystyrene-based resin, an inorganic radiation suppressing powder, a flame retardant, a physical foaming agent, and a cell regulator, and molding it into a plate shape by a molding tool (hereinafter referred to as the "molding step"), and has an apparent density of 20 to 50 kg / m 3 This is a method for manufacturing a polystyrene-based resin extruded foam board (hereinafter also simply referred to as an "extruded foam board").

[0016] Specifically, in the molding step according to the present invention, first, a physical foaming agent is press-fitted into a melt-kneaded product obtained by melting and kneading a base resin mainly composed of a polystyrene-based resin, an inorganic radiation suppressing powder, a flame retardant, and other additives blended as necessary in an extruder under heating, and further kneaded to obtain a foaming resin melt composition. Next, the foaming resin melt composition is adjusted to a proper foaming temperature, extruded from a high-pressure extruder through a flat die into a low-pressure region to be foamed, and passed through a molding tool (for example, a mold or a molding roll) arranged at the outlet of the flat die, whereby a plate-shaped extruded foam board is molded. The mold is, for example, a mold (a guide) composed of two upper and lower plates of polytetrafluoroethylene resin or the like installed in parallel or gently expanding from the inlet to the outlet direction.

[0017] <Base Resin> [1] Polystyrene-based resin Examples of the polystyrene resin used in the production method of the present invention include, for example, polystyrene, styrene-methyl acrylate copolymer containing 50 mol% or more of styrene unit component, 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. One or more selected from these can be exemplified. Among these, polystyrene can be preferably used. In addition, polystyrene may contain unit components by a branching agent such as a polyfunctional monomer or a polyfunctional macromonomer in addition to the styrene unit component. The content of the styrene component unit in the above copolymer is preferably 60 mol% or more, more preferably 80 mol% or more, and still more preferably 90 mol% or more.

[0018] The base resin may contain an amorphous polyethylene terephthalate copolymer in order to enhance the heat insulation property of the extruded foam board. In the amorphous polyethylene terephthalate copolymer, the heat of fusion accompanying the melting of the resin based on JIS K7122 is less than 5 J / g. The heat of fusion is measured based on the DSC curve obtained using a heat flux differential scanning calorimeter, adopting "when measuring the heat of fusion after performing a certain heat treatment" described in JIS K7122 (1987) (the heating rate and the cooling rate in the state adjustment of the test piece are both 10 °C / min).

[0019] Also, since the melt viscosity of the polystyrene resin used in the production method of the present invention is excellent in foamability and production stability, it is preferably 500 to 3000 Pa·s, more preferably 1000 to 2500 Pa·s, and still more preferably 1500 to 2300 Pa·s under the conditions of 200 °C and a shear rate of 100 sec -1 -1.

[0020] [2] Other polymers The base resin may include polymers other than polystyrene resins and amorphous polyethylene terephthalate copolymers, to the extent that the objectives and effects of the present invention are achieved. Other polymers include thermoplastic resins such as 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, and polymethyl methacrylate, as well as thermoplastic elastomers such as styrene-butadiene-styrene block copolymers, styrene-isoprene-styrene block copolymers, styrene-butadiene-styrene block copolymer hydrogenated products, styrene-isoprene-styrene block copolymer hydrogenated products, and styrene-ethylene copolymers.

[0021] In the manufacturing method of the present invention, the base resin mainly composed of polystyrene resin means that 50% by mass or more of the base resin is polystyrene resin, 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 is polystyrene resin.

[0022] <Physical foaming agent> The physical blowing agent used in the present invention contains, as essential components, a blowing agent (a) consisting of 1-chloro-2,3,3,3-tetrafluoropropene (hereinafter also referred to as "HFO-1224yd") and a blowing agent (b) consisting of a saturated hydrocarbon having 3 to 5 carbon atoms.

[0023] [1] Foaming agent (a) HFO-1224yd, a foaming agent (a), has moderate solubility and excellent foaming properties in polystyrene resins, making it easier to manufacture low-apparent-density extruded foam boards. Furthermore, because HFO-1224yd is non-flammable, it can reduce the risk of ignition due to static electricity during the manufacturing of extruded foam boards. In addition, HFO-1224yd has a low ozone depletion potential and a very low global warming potential, thus having a small impact on the environment.

[0024] [2] Foaming agent (b) Examples of dialkyl ethers having 1 to 3 carbon atoms in the alkyl chain, which are the foaming agent (b), include dimethyl ether, diethyl ether, dipropyl ether, and ethyl methyl ether, and these can be used alone or in combination of two or more. From the viewpoint of improving manufacturing stability, dimethyl ether can be preferably used among these.

[0025] By using foaming agent (b) in combination with foaming agent (a), it is possible to manufacture extruded foam boards that maintain excellent low thermal conductivity over a long period of time while exhibiting superior foaming properties and manufacturing stability.

[0026] [3] Other foaming agents (c) In addition to blowing agent (a) and blowing agent (b), the present invention may use one or more other blowing agents (c) selected from water, carbon dioxide, alkyl chloride, aliphatic alcohols having 1 to 5 carbon atoms, saturated hydrocarbons having 3 to 5 carbon atoms, and hydrofluoroolefins having 3 or 4 carbon atoms other than HFO-1224yd.

[0027] By using foaming agent (c) in combination with foaming agents (a) and (b), the foaming ratio of the resulting extruded foam board can be improved, making it easier to obtain an extruded foam board with a low apparent density and good appearance.

[0028] Water and carbon dioxide are released early from the extruded foam board, reducing the environmental burden and allowing the dimensions of the resulting extruded foam board to stabilize quickly.

[0029] Examples of alkyl chlorides include methyl chloride and ethyl chloride. Alkyl chlorides facilitate foaming of polystyrene resins, and when used in combination with foaming agents (a) and (b), extruded foam boards with the desired apparent density can be obtained. Furthermore, alkyl chlorides have a fast permeation rate through polystyrene resins and dissipate quickly after the production of the extruded foam boards, thus allowing the dimensions of the resulting extruded foam boards to stabilize quickly.

[0030] Aliphatic alcohols with 1 to 5 carbon atoms do not deplete the ozone layer or contribute to global warming, and because they dissipate quickly from extruded foam boards, they can stabilize the shape of the extruded foam boards early. When used in combination with blowing agents (a) and (b), aliphatic alcohols can contribute to obtaining extruded foam boards with low apparent density (high foaming ratio).

[0031] 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 from the viewpoint of environmental and human safety.

[0032] Examples of saturated hydrocarbons having 3 to 5 carbon atoms include propane, n-butane, isobutane (2-methylpropane), n-pentane, isopentane (2-methylbutane), cyclobutane, neopentane (2,2-dimethylpropane), and cyclopentane. Two or more of these can also be used in combination. Among these, isobutane can be preferably used.

[0033] In addition to the blowing agent (a) HFO-1224yd, other hydrofluoroolefins having 3 or 4 carbon atoms can be used, such as trans-1,3,3,3-tetrafluoropropene (trans-HFO-1234ze), cis-1,3,3,3-tetrafluoropropene (cis-HFO-1234ze), 2,3,3,3-tetrafluoropropene (HFO-1234yf), and 1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz). These hydrofluoroolefins also include hydrochlorofluoroolefins partially substituted with chloride ions. These blowing agents can be used individually or in combination of two or more.

[0034] When using a foaming agent (c), it is preferable that the foaming agent (c) is one or more selected from water, carbon dioxide, alkyl chloride, and aliphatic alcohols having 1 to 5 carbon atoms, from the viewpoint of dissipating quickly from the extruded foam board and stabilizing the dimensions of the resulting extruded foam board quickly, and it is more preferable that the foaming agent (c) is one or more selected from water, carbon dioxide, and aliphatic alcohols having 1 to 5 carbon atoms.

[0035] <Amount of foaming agent added> The total amount of physical blowing agent added is 0.8 mol or more and 2 mol or less per 1 kg of base resin. If the amount of physical blowing agent added is too little, the apparent density of the resulting extruded foam board will be high, and it may not be possible to obtain an extruded foam board with the desired low apparent density. On the other hand, if the amount of physical blowing agent added is too much, the apparent density will be too low, the strength of the resulting extruded foam board will decrease, making it unsuitable for use as insulation material for building materials, or numerous gas spots may occur, resulting in a poor appearance of the resulting extruded foam board. For these reasons, the total amount of physical blowing agent added is preferably 1 mol or more, more preferably 1.1 mol or more, and preferably 1.8 mol or less, more preferably 1.5 mol or less.

[0036] The amount of foaming agent (a) added is 0.5 mol or more and 1.1 mol or less per 1 kg of base resin. If the amount of foaming agent (a) added is too small, it may not be possible to maintain a low thermal conductivity in the extruded foam board. From this viewpoint, it is preferable that the amount of foaming agent (a) added is 0.6 mol or more per 1 kg of base resin, and more preferably 0.7 mol or more per 1 kg of base resin. On the other hand, if the amount of foaming agent (a) added is too large, many gas spots may be generated, and the appearance of the resulting extruded foam board may deteriorate. From this viewpoint, it is preferable that the amount of foaming agent (a) added is 1.0 mol or less per 1 kg of base resin, and more preferably 0.9 mol or less per 1 kg of base resin.

[0037] Furthermore, if the production of extruded foam boards is difficult under conditions where a large amount of foaming agent (a) is added, the production of extruded foam boards can be facilitated by using high-kneading type screws, such as screws with a large ratio of axial length to screw diameter or twin-screw screws, as needed.

[0038] The amount of foaming agent (b) added is 0.2 mol or more per 1 kg of base resin. If the amount of foaming agent (b) added is too little, there is a risk of reduced surface smoothness and the occurrence of gas spots. From this viewpoint, it is preferable that the amount of foaming agent (b) added is 0.3 mol or more per 1 kg of base resin, and more preferably 0.4 mol or more per 1 kg of base resin. On the other hand, from the viewpoint of suppressing ignition during molding immediately after extrusion foaming and maintaining excellent manufacturing stability, it is preferable that the amount of foaming agent (b) added is 0.8 mol or less per 1 kg of base resin, more preferably 0.7 mol or less per 1 kg of base resin, and even more preferably 0.6 mol or less per 1 kg of base resin.

[0039] The total ratio of the amount of blowing agent (a) and the amount of blowing agent (b) added to the physical blowing agent is 70% by mass or more. From the viewpoint of maintaining manufacturing stability and low thermal conductivity over a long period of time, the total ratio of the amount of blowing agent (a) and the amount of blowing agent (b) added is preferably 80% by mass or more, and more preferably 85% by mass or more.

[0040] Furthermore, there is no particular upper limit to the total ratio of the amount of foaming agent (a) added and the amount of foaming agent (b) added; for example, it may be 100% by mass.

[0041] The molar ratio (a:b) of the amount of foaming agent (a) to the amount of foaming agent (b) added is preferably 40:60 to 95:5. From the viewpoint of improving the continuous moldability of the extruded foam board, it is more preferable to have a ratio of 50:50 to 90:10, and even more preferable to have a ratio of 60:40 to 80:20.

[0042] When, in addition to blowing agent (a) and blowing agent (b), one or more blowing agents selected from water, carbon dioxide, alkyl chloride, aliphatic alcohols having 1 to 5 carbon atoms, saturated hydrocarbons having 3 to 5 carbon atoms, and hydrofluoroolefins having 3 or 4 carbon atoms other than HFO-1224yd are added as other blowing agents (c), the amount of each is preferably 0.5 mol or less, more preferably 0.3 mol or less, and even more preferably 0.2 mol or less per 1 kg of base resin.

[0043] <Inorganic radiation suppression powder> In the manufacturing method of the present invention, an inorganic radiation-suppressing powder is blended into the foamed resin molten composition in order to improve heat insulation by suppressing heat transfer due to infrared radiation.

[0044] From the viewpoint of improving thermal insulation without affecting the manufacturing stability of the extruded foam board, the amount of inorganic radiation suppression powder added is preferably 1 to 10 parts by mass, 1.1 to 7 parts by mass, and 1.2 to 5 parts by mass, per 100 parts by mass of the base resin.

[0045] Inorganic radiation suppression powders include, for example, graphite. Examples of graphite include flake graphite, scaly graphite, artificial graphite, and clay-like graphite, and it is preferable to use graphite whose main component is flake graphite. As described later, it is preferable to use graphite as a masterbatch blended at a high concentration in a polystyrene resin. Graphite with a fixed carbon content of 90% or more is preferred because it offers good workability when manufacturing the masterbatch and provides excellent thermal insulation improvement to the resulting extruded foam board. To further enhance the thermal insulation of the extruded foam board, graphite with a fixed carbon content of 93% 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.

[0046] The amount of graphite added is preferably 0.2 parts by mass or more and 4 parts by mass or less per 100 parts by mass of the base resin. When the amount of graphite added is within the above range, the heat insulation performance is improved, and an extruded foam board with the desired low thermal conductivity can be obtained. From the above viewpoint, the amount of graphite added is more preferably 0.3 parts by mass or more and 3 parts by mass or less per 100 parts by mass of the base resin of the extruded foam board, and even more preferably 0.4 parts by mass or more and 2.5 parts by mass or less.

[0047] Furthermore, in the manufacturing method of the present invention, in order to further improve the heat insulation properties, components other than graphite may be included in the extruded foam board as inorganic radiation suppression powder.

[0048] Examples of components other than graphite include one or more selected from metal oxides such as titanium dioxide, metals such as aluminum, ceramics, carbon black, infrared shielding pigments, hydrotalcite, etc. The amount of each of these components blended is preferably 0.5 parts by mass or more and 5 parts by mass or less, and more preferably 1 part by mass or more and 4 parts by mass or less, per 100 parts by mass of the base resin.

[0049] In the method for producing polystyrene resin extruded foam boards containing HFO-1224yd as a foaming agent, the addition of inorganic radiation suppression powder may lead to a reduction in foaming properties due to the miniaturization of bubbles and a decrease in manufacturing stability. This tendency was particularly pronounced when a large amount of HFO-1224yd was added to reduce the thermal conductivity of the extruded foam board. In the present invention, in a configuration in which inorganic radiation suppression powder is added, by using a foaming agent (a) consisting of HFO-1224yd and a foaming agent (b) consisting of a dialkyl ether with 1 to 3 carbon atoms in the alkyl chain in the predetermined proportions described above, it is possible to produce an extruded foam board with good surface properties and manufacturing stability, and low thermal conductivity, despite the addition of inorganic radiation suppression powder. In particular, when the inorganic radiation suppression powder contains graphite, it is possible to produce an extruded foam board with good surface properties and manufacturing stability.

[0050] <Other ingredients> [1] Flame retardant The extruded foam board obtained by the manufacturing method of the present invention is mainly used as an insulating material for building materials, and flame retardancy is imparted by blending a flame retardant into the base resin.

[0051] The flame retardant is not particularly limited, but brominated flame retardants are preferred. 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. One or more of these brominated flame retardants can be used in combination.

[0052] In addition to 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, and hypophosphate compounds can be used in combination.

[0053] Among these flame retardants, it is preferable to use a flame retardant containing one or more of the following: brominated butadiene-styrene copolymer, tetrabromobisphenol A-bis(2,3-dibromopropyl ether), tetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl ether), or tris(2,3-dibromopropyl) isocyanurate, because it can impart high flame retardancy to extruded foam boards. Furthermore, among these, it is even more preferable to use a flame retardant containing a brominated butadiene-styrene copolymer, or a flame retardant using a combination of tetrabromobisphenol A-bis(2,3-dibromopropyl ether) and tetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl ether), because it can impart high flame retardancy to extruded foam boards, does not easily decompose the polystyrene resin during extrusion, and makes it easy to obtain stable extruded foam boards even at low apparent density (high foaming ratio) and large cross-sectional area.

[0054] The amount of flame retardant added is such that it can impart high flame retardancy to the extruded foam board while suppressing a decrease in extruded foaming properties and mechanical properties. For example, it is 0.1 parts by mass or more and 10 parts by mass or less, preferably 1 part by mass or more and 8 parts by mass or less, and more preferably 3 parts by mass or more and 7 parts by mass or less, per 100 parts by mass of the base resin. Within this range, the flame retardant does not inhibit foaming properties, and an extruded foam board with high flame retardancy, such as that specified in the flammability standard for extruded polystyrene foam insulation materials described in "Test Method A" of Annex C of JIS A9521:2022, can be obtained.

[0055] [2] Flame retardant additive In the manufacturing method of the present invention, a flame retardant additive can be used in combination with the above-mentioned flame retardant for the purpose of further improving the flame retardancy of the extruded foam board. 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.

[0056] The amount of flame retardant additive added is, for example, 0.01 parts by mass or more and 1 part by mass or less, preferably 0.05 parts by mass or more and 0.5 parts by mass or less, per 100 parts by mass of the base resin.

[0057] In the 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 or dyes, heat stabilizers, and fillers. The total amount of other additives blended is preferably 50 parts by mass or less per 100 parts by mass of the base resin.

[0058] [3] Bubble regulator In the manufacturing method of the present invention, it is preferable to blend a foaming resin molten composition with a base resin to form a foaming resin molten composition.

[0059] As a foam regulator, one or more inorganic powders such as talc, kaolin, mica, silica, calcium carbonate, barium sulfate, titanium dioxide, clay, aluminum oxide, bentonite, and diatomaceous earth can be used in mixtures. Among these, talc is preferred because it allows for easy adjustment of the bubble diameter and reduces the bubble diameter without impairing flame retardancy. In particular, fine talc with a 50% particle size (by light transmission centrifugal sedimentation method) of 0.1 to 20 μm is preferred, and fine talc with a particle size of 0.5 to 15 μm is preferred.

[0060] The amount of bubble regulator added varies depending on the type of regulator and the desired bubble diameter, but when talc is used as the bubble regulator, for example, it is 0.02 parts by mass or more and 7 parts by mass or less per 100 parts by mass of the base resin, preferably 0.1 parts by mass or more and 5 parts by mass or less, and more preferably 0.2 parts by mass or more and 3 parts by mass or less.

[0061] When talc is included as a foam regulator and graphite is included as an inorganic radiation suppression powder, the ratio of the amount of graphite added to the amount of talc added (graphite / talc) is preferably 1 or more and 70 or less. From the viewpoint of forming uniform bubbles and producing an extruded foam board with excellent thickness uniformity, the ratio of the amount of graphite added to the amount of talc added (graphite / talc) is more preferably 3 or more and 30 or less, and even more preferably 3 or more and 10 or less. If the above range of the ratio of the amount of graphite added to the amount of talc added (graphite / talc) is satisfied, an extruded foam board with excellent thickness uniformity can be produced even when a large amount of foaming agent (a) consisting of HFO-1224yd, such as 0.7 mol or more, is added.

[0062] [4] Heat stabilizers Heat stabilizers can improve the thermal stability of brominated 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 DIC EPICLON series, 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 parts by mass or more and 40 parts by mass or less per 100 parts by mass of the total amount of flame retardant.

[0063] 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 polystyrene resin from a supply unit located in the middle of the extruder. Specifically, a method can be employed in which a dry blend of the flame retardant, other additives and base resin is supplied to the extruder and melt-kneaded; a method can be employed in which the flame retardant, other additives and base resin are kneaded in a kneader or the like and the molten mixture is supplied to the extruder; a method can be employed in which a masterbatch is prepared in advance by blending a high concentration of the flame retardant and other additives into a polystyrene resin, and this is supplied to the extruder and melt-kneaded with the base resin. In particular, 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 with an MFR of approximately 0.5 to 30 g / 10 min as the base resin, so that the masterbatch contains 10 to 95% by mass of the flame retardant, more preferably 30 to 90% by mass, and even more preferably 50 to 85% by mass.

[0064] In the molding process of the manufacturing method of the present invention, as described above, a foamed resin molten composition obtained by melting a base resin, inorganic radiation suppression powder, additives such as a flame retardant, and a physical blowing agent is extruded and foamed under atmospheric pressure and molded into a plate shape using a molding tool to obtain a polystyrene resin extruded foam sheet.

[0065] <Physical properties of foamed boards> Next, we will describe the polystyrene resin extruded foam board obtained by the manufacturing method of the present invention.

[0066] [Cross-sectional area and dimensions] The extruded foam board according to the present invention is in the form of a board. The cross-sectional area perpendicular to the extrusion direction of the extruded foam board is 100 cm². 2 Preferably, it should be 200 cm or more. 2It is more preferable that the above is true. The upper limit of the cross-sectional area perpendicular to the extrusion direction of the extruded foam board is, for example, 1500 cm². 2 The cross-sectional area perpendicular to the extrusion direction refers to the area of ​​the cross-section of the extruded foam board perpendicular to the extrusion direction. Extruded foam boards are usually manufactured by creating a base sheet that is at least one size larger than the desired size, and then cutting the base sheet to adjust the width, length, and sometimes thickness.

[0067] When using extruded foam board as insulation material, the thickness of the extruded foam board is preferably 10 mm to 150 mm, and more preferably 15 mm to 120 mm.

[0068] The width of the extruded foam board is preferably 800 mm or more, and more preferably 900 mm or more. The upper limit of the width of the extruded foam board is, for example, 1200 mm.

[0069] [Apparent Density] The apparent density of extruded foam board is 20-50 kg / m³. 3 The load is preferably 30-45 kg / m³. 3 When the apparent density is within the above range, it has sufficient mechanical strength and excellent lightweight properties, making it suitable for use as, for example, thermal insulation. The apparent density can be determined by cutting a sample from the extruded foam board, measuring its mass, and dividing that mass by its volume.

[0070] [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 93% or higher. When the closed-cell ratio is within the above range, the foaming agent (a) and foaming agent (b) tend 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.

[0071] The closed cell ratio of the extruded foam board is measured using a Toshiba Beckman air comparison pycnometer model 930 in accordance with procedure C of ASTM-D2856-70 (A cut sample without a formed skin, cut from the extruded foam board to a size of 25 mm × 25 mm × 20 mm, is placed in a sample cup for measurement. However, if the thickness is too thin and a 20 mm cut sample cannot be cut out in the thickness direction, for example, two cut samples with a size of 25 mm × 25 mm × 10 mm can be placed in the sample cup simultaneously for measurement.). Using the true volume Vx of the extruded foam board (cut sample), the closed cell ratio S (%) is calculated by the following formula (1) and obtained as the average value with N = 3.

[0072] S (%) = (Vx - W / ρ) × 100 / (V A - W / ρ) ··· (1) Vx: True volume of the cut sample (cm 3 )(Equivalent to the sum of the volume of the resin constituting the cut sample of the extruded foam board and the total volume of the air bubbles in the closed cell part within the cut sample.) V A : Apparent volume of the cut sample calculated from the outer dimensions of the cut sample used for measurement (cm 3 ) W: Total weight of the cut sample used for measurement (g) ρ: Density of the resin constituting the extruded foam board (g / cm 3 )

[0073] [Thermal conductivity] (After 7 days) The thermal conductivity of the extruded foam board 7 days after production is preferably 0.025 W / m·K or less, more preferably 0.023 W / m·K or less, and even more preferably 0.021 W / m·K or less. (After 100 days) The thermal conductivity of the extruded foam board 100 days after production is preferably 0.027 W / m·K or less, more preferably 0.026 W / m·K or less, and even more preferably 0.025 W / m·K or less. (After 300 days) The thermal conductivity of the extruded foam board 300 days after manufacturing is preferably 0.030 W / m·K or less, more preferably 0.028 W / m·K or less, and even more preferably 0.026 W / m·K or less.

[0074] The thermal conductivity of extruded foam board can be measured based on the heat flow meter method described in JIS A1412-2:1999 (single test specimen, symmetrical configuration, high temperature side 38°C, low temperature side 8°C, average temperature 23°C). The specific measurement method will be explained in the examples.

[0075] The long-term thermal conductivity (after 100 and 300 days) of extruded foam boards is measured on samples that have undergone accelerated testing as described in Test Method A of the accelerated test for long-term changes in thermal resistance, in accordance with JIS A1486:2014. According to this method, for example, the thermal conductivity measured 16 days after manufacture on a sample of 25 mm thick extruded foam board sliced ​​to a thickness of 10 mm corresponds to the thermal conductivity of the extruded foam board approximately 100 days after manufacture, and the thermal conductivity measured 48 days after manufacture corresponds to the thermal conductivity of the extruded foam board approximately 300 days after manufacture.

[0076] [Average bubble diameter] The average cell diameter of the extruded foam board is preferably 65 μm to 200 μm, more preferably 78 μm to 190 μm, and even more preferably 85 μm to 180 μm. Having the average cell diameter within this range further improves thermal insulation and mechanical strength.

[0077] The average bubble diameter of an extruded foam board is determined by cutting the extruded foam board perpendicular to the width and thickness directions, and calculating the average bubble diameter equivalent to a circle at the center of the cut cross-section. To calculate the average bubble diameter, an enlarged photograph is taken of the cross-section, specifying a range of 1.5 mm in the thickness direction x 1.5 mm in the width direction, with the center of the width and thickness directions as the center. The area of ​​each bubble is measured on the photograph using the image processing software NS2K-pro manufactured by Nano System Co., Ltd., the obtained area of ​​each bubble is converted to represent a circle, the diameter of that converted circle is determined, and these values ​​are arithmetically averaged to calculate the average bubble diameter. [Examples]

[0078] The present invention will be described in more detail below with reference to examples. However, the present invention is not limited in any way by these examples.

[0079] In Examples 1-9 and Comparative Examples 1-6, the following apparatus and raw materials were used.

[0080] 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 440 mm width was connected to the outlet of the second extruder. In addition, a molding tool (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.

[0081] (1) Base resin Polystyrene resin (abbreviated as PS): DIC Corporation's polystyrene "HP780AN", melt viscosity (temperature 200℃, shear rate 100s) -1 ) = 1950 Pa·s

[0082] (2) Flame retardants GR-134BG: A flame retardant masterbatch (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) containing a mixed flame retardant of [Tetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl ether): Daiichi Kogyo Seiyaku "SR-130"] / [Tetrabromobisphenol A-bis(2,3-dibromopropyl ether): Daiichi Kogyo Seiyaku "SR-720"] = 60% / 40% by mass. E3000: Brominated butadiene-styrene block copolymer (Emerald innovation 3000, manufactured by Lanxess K.K.)

[0083] (3) Bubble regulator Talc: (Manufactured by Matsumura Sangyo Co., Ltd., product name "High Filler #12", particle size (d50) 7.5 μm)

[0084] (4) Inorganic radiation suppression powder Graphite: (Manufactured by Resino Color Industries Co., Ltd., Product name: SBF-T-1683, flake-shaped graphite powder, average particle size 17 μm, 40% masterbatch) Titanium dioxide: (JR-405 manufactured by Teika Co., Ltd., primary particle size (d50) = 0.2 μm)

[0085] (5) Physical foaming agents 1-Chloro-2,3,3,3-tetrafluoropropene (abbreviation 1224yd): Manufactured by Honeywell Japan. Dimethyl ether (DME): Manufactured by Mitsubishi Gas Chemical Company Alcohol (ethanol / isopropyl alcohol / 1-propanol = 90% by weight / 6% by weight / 4% by weight): Manufactured by Yamaichi Chemical Industry Co., Ltd. water Isobutane (abbreviated as Bu): Manufactured by Mitsui Chemicals, Inc.

[0086] Examples 1-9 and Comparative Examples 1-6 were manufactured as follows.

[0087] The base resin, inorganic radiation suppression powder, and foam regulator shown in Table 1, along with the flame retardant masterbatch, were supplied to the first extruder, heated to 200°C and kneaded, and the physical blowing agent was supplied from the physical blowing agent injection port provided in the first extruder at the amounts shown in Table 1 and the respective blowing agent injection pressures, and further kneaded to form a foamable resin molten product.

[0088] Next, the obtained foamed resin molten material is transferred to a second extruder to adjust the resin temperature, then extruded into a guider at a discharge rate of 400 kg / hr, and molded into a plate shape by passing it through the guider while foaming to produce a 30 mm thick foamed base plate. Furthermore, the width and length of the base plate are adjusted by cutting, and the molded skin on both sides is evenly cut to produce a rectangular polystyrene foamed board without a molded skin (width: 910 mm, length: 1820 mm, thickness: 25 mm, cross-sectional area perpendicular to the extrusion direction: 227.5 cm²). 2 They manufactured ).

[0089] [Table 1]

[0090] For the extruded foam boards obtained in Examples 1-9 and Comparative Examples 1-6, the closed-cell ratio, apparent density, thermal conductivity (after 7 days, 100 days, and 300 days), and average cell ratio were measured using the following methods. Then, flammability, thickness uniformity, surface quality, and continuous moldability were evaluated as follows. Note that the closed-cell ratio and average cell diameter are indicators for evaluating the foaming properties of the extruded foam board. Thickness uniformity, surface quality, and continuous moldability are evaluated to understand the manufacturing stability of the extruded foam board.

[0091] [Apparent Density] The apparent density of the extruded foam board was determined as follows: Rectangular parallelepiped samples measuring 50 mm (length) x 50 mm (width) x 25 mm (thickness) were cut from the center and near both ends of the obtained extruded foam board in the width direction, and their masses were measured. The apparent density of each sample was calculated by dividing the mass by the volume, and the arithmetic mean of these was taken as the apparent density.

[0092] [Closed cell ratio] The closed-cell ratio of the foam board was determined using the following formula (1), with 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.

[0093] Specifically, cut samples were taken from three locations in the width direction of the extruded foam board: the center and near both ends. Each cut sample was used as a measurement sample, and the closed-cell ratio was measured for each sample. The arithmetic mean of the closed-cell ratios from the three locations was then calculated. The cut samples used were pieces cut from the extruded foam board to a size of 25 mm (length) x 25 mm (width) x 25 mm (thickness).

[0094] S(%)=(Vx-W / ρ)×100 / (Va-W / ρ)···(1) In equation (1), Vx, Va, W, and ρ are as follows: Vx: True volume of the cut sample (cm³) 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 )

[0095] [Thermal conductivity after 7 days of manufacture] A test specimen measuring 200 mm (length) x 200 mm (width) x 25 mm (thickness) was cut from the center of the width direction of the extruded foam board immediately after manufacturing. This test specimen was stored in a constant temperature and humidity chamber at 23°C and 50% relative humidity. Seven days after manufacturing, the thermal conductivity was measured according to 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.

[0096] [Thermal conductivity 100 days and 300 days after manufacture] The thermal conductivity values ​​100 and 300 days after manufacture were obtained by measuring the thermal conductivity of extruded foam boards subjected to test method A of the accelerated long-term change test for thermal resistance, in accordance with JIS A1486:2014. Specifically, a rectangular parallelepiped measuring 200mm (length) x 200mm (width) x 25mm (thickness) was cut from the center of the width direction of an extruded foam board immediately after manufacturing. Further, test pieces measuring 200mm (length) x 200mm (width) x 10mm (thickness) were cut by evenly trimming both sides. These test pieces were stored in a constant temperature and humidity chamber at 23°C and 50% relative humidity. The thermal conductivity was measured using test pieces 16 days after manufacturing (corresponding to 100 days after manufacturing of a 25mm thick extruded foam board) and 48 days after manufacturing (corresponding to 300 days after manufacturing of a 25mm thick extruded foam board) 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).

[0097] [Average bubble diameter] The average bubble diameter was determined by cutting the extruded foam board perpendicular to the width and thickness directions, and calculating the average bubble diameter equivalent to a circle at the center of the cut cross-section. To calculate the average bubble diameter, an enlarged photograph was obtained specifying a range of 1.5 mm in the thickness direction × 1.5 mm in the width direction, with the center of the width and thickness directions being the center of the above cross-section. On each photograph, the area of ​​each bubble was measured using the image processing software NS2K-pro manufactured by Nano System Co., Ltd. The obtained area of ​​each bubble was converted to represent a circle, and the diameter of that converted circle was determined. The average bubble diameter was then calculated by arithmetic mean of these values.

[0098] [Flammable] Immediately after manufacturing, extruded foam boards were stored in a constant temperature and humidity chamber at 23°C and 50% relative humidity. Four weeks after manufacturing, five test pieces were randomly cut from the extruded foam boards (N=5), and their flammability was measured according to "Test Method A" specified in Annex C of JIS A9521:2022. The flame retardancy was then evaluated according to the following criteria. ◎: The average burning time of the 5 test specimens is 3 seconds or less. ×: The average burning time of the 5 test specimens exceeds 3 seconds.

[0099] [Uniformity of thickness] Thickness uniformity was evaluated based on the following criteria for the cut surfaces obtained by cutting the original sheet perpendicular to the width and thickness directions. ◎: The variation in the thickness of the original plate (maximum value - minimum value) is less than 3 mm. ○: The variation in the thickness of the original plate (maximum value - minimum value) is 3 mm or more and less than 5 mm. ×: The variation in the thickness of the original plate (maximum value - minimum value) is 5 mm or more.

[0100] [Superficiality] The surface quality of the top, bottom, and side surfaces of the base plate and the extruded foam board was evaluated visually according to the following criteria. ◎: The top, bottom, and side surfaces of the base plate and the extruded foam board were in excellent condition. ○: Although roughness and spots occasionally occurred on the top, bottom, or sides of the original board, the top, bottom, and sides of the extruded foam board were in excellent condition. △: Roughness and spots occurred on the top, bottom, or sides of the original sheet, and even after cutting the original sheet, roughness and spots occasionally remained on the top, bottom, or sides of the extruded foam board. ×: The original board had roughness and numerous spots on its top, bottom, or sides, and even after cutting the original board, many roughness and spots remained on the top, bottom, or sides of the extruded foam board.

[0101] [Continuous moldability] Continuous moldability was evaluated visually according to the following criteria. ◎: No variation was observed in the width of the original plate, and it was possible to manufacture it continuously and stably. ○: Although there was some variation in the width of the original plate, continuous manufacturing was possible. ×: It was difficult to mold the raw material, making continuous production difficult.

[0102] As can be seen from Table 1, good quality extruded foam boards were not obtained in Comparative Examples 1 to 6. Furthermore, for Comparative Examples 1 to 5, since they were not particularly good, the closed-cell ratio, apparent density, thermal conductivity, average cell diameter, and flammability (except for Comparative Examples 4 and 5) were not evaluated. The specific evaluations for Comparative Examples 1 to 6 are as follows.

[0103] In Comparative Example 1, dimethyl ether was not added, and the amount of 1-chloro-2,3,3,3-tetrafluoropropene added was greater than 1.1 mol, resulting in poor thickness uniformity, surface quality, and continuous moldability.

[0104] In Comparative Example 2, the content of 1-chloro-2,3,3,3-tetrafluoropropene was less than 0.5 mol, which resulted in a relatively higher amount of dimethyl ether added, and consequently, the uniformity of thickness and the ability to continuously mold were reduced.

[0105] In Comparative Example 3, the use of water and alcohol instead of dimethyl ether resulted in a decrease in thickness uniformity, surface quality, and continuous moldability.

[0106] In Comparative Example 4, although there were no problems with flammability or thickness uniformity, the amount of dimethyl ether added was less than 0.2 mol, and furthermore, the total proportion of 1-chloro-2,3,3,3-tetrafluoropropene and dimethyl ether in the physical blowing agent was less than 70% by mass, resulting in poor surface properties and continuous moldability.

[0107] In Comparative Example 5, although there were no problems with flammability or thickness uniformity, the total proportion of 1-chloro-2,3,3,3-tetrafluoropropene and dimethyl ether in the physical blowing agent was less than 70% by mass, resulting in poor surface quality and continuous moldability.

[0108] In Comparative Example 6, although there were no problems with the closed-cell ratio, apparent density, thermal conductivity, average cell diameter, flammability, thickness uniformity, and continuous moldability, the surface quality deteriorated because the amount of dimethyl ether added was less than 0.2 mol.

[0109] In contrast, Examples 1-9 exhibited low thermal conductivity, excellent foaming properties (closed cell ratio, average cell diameter), and good manufacturing stability (thickness uniformity, surface quality, and continuous moldability). Furthermore, Examples 1-9 also showed good flammability and apparent density.

Claims

1. The process includes a step of extruding and foaming a foamed resin molten composition, which is made by kneading a base resin mainly composed of polystyrene resin, inorganic radiation suppression powder, flame retardant, physical foaming agent, and foam modifier, and then molding it into a sheet shape using a molding tool, with an apparent density of 20 to 50 kg / m³. ３ A method for producing polystyrene resin extruded foam board, A method for producing polystyrene resin extruded foam board, characterized in that the amount of inorganic radiation suppression powder added is 1 part by mass or more and 10 parts by mass or less per 100 parts by mass of the base resin, the total amount of the physical blowing agent added is 0.8 mol or more and 2 mol or less per 1 kg of base resin, the physical blowing agent comprises a blowing agent (a) consisting of 1-chloro-2,3,3,3-tetrafluoropropene and a blowing agent (b) consisting of a dialkyl ether having 1 to 3 carbon atoms in the alkyl chain, the amount of blowing agent (a) added is 0.5 mol or more and 1.1 mol or less per 1 kg of base resin, the amount of blowing agent (b) added is 0.2 mol or more per 1 kg of base resin, and the total ratio of the amount of blowing agent (a) and the amount of blowing agent (b) added in the physical blowing agent is 70% by mass or more.

2. The method for producing polystyrene resin extruded foam board according to claim 1, characterized in that the mol ratio (a:b) of the amount of foaming agent (a) added to the amount of foaming agent (b) added is 50:50 to 90:

10.

3. The method for producing a polystyrene resin extruded foam board according to claim 1 or 2, characterized in that the inorganic radiation suppression powder contains graphite, and the amount of graphite added is 0.3 parts by mass or more and 3 parts by mass or less per 100 parts by mass of the base resin.

4. The method for producing polystyrene resin extruded foam board according to claim 3, characterized in that the foam regulator contains talc, and the ratio of the amount of graphite added to the amount of talc added is 3 or more and 30 or less.

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