Manufacturing method for extruded polystyrene resin foam board

Abstract

To provide a method for manufacturing a polystyrene-based resin extrusion foam plate which can maintain low thermal conductivity over a long period of time, is excellent in manufacturing stability and has good appearance.SOLUTION: A method for manufacturing a polystyrene-based resin extrusion foam plate having apparent density of 20 kg / m3 or more and 50 kg / m3 or less includes a step of extrusion foaming a foamable molten resin composition obtained by kneading a base material resin containing a polystyrene-based resin as a main component, a flame retardant and a physical foaming agent, and molding the molten resin composition into a plate shape, wherein the physical foaming agent contains a foaming agent A composed of 1,1,1,4,4,4-hexafluoro-2-butene, a foaming agent B composed of dialkyl ether having 1 to 3 carbon atoms, and a foaming agent C composed of water and / or aliphatic alcohol having 1 to 5 carbon atoms, the total addition amount of the physical foaming agent is 0.9 mol or more and 1.8 mol or less with respect to 1 kg of the base material resin, an addition amount of the foaming agent A is 0.2 mol or more with respect to 1 kg of the base material resin, an addition amount of the foaming agent B is 0.05 mol or more and 0.8 mol or less with respect to 1 kg of the base material resin, an addition amount of the foaming agent C is 0.1 mol or more and 0.7 mol or less with respect to 1 kg of the base material resin, and the total of the addition amount of the foaming agent A and the addition amount of the foaming B with respect to 100 mol% of the total addition amount of the physical foaming agent is 50 mol% or more.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing an extruded polystyrene resin foam board, and more particularly to a method for producing an extruded polystyrene resin foam board that can be suitably used as a heat insulating material for walls, floors, roofs, etc. of buildings. [Background technology]

[0002] Extruded polystyrene resin foam boards (hereinafter simply referred to as "foam boards") are widely used as building insulation materials due to their excellent thermal insulation properties and mechanical strength. Such foam boards are generally produced by heating and melting polystyrene resin in an extruder, then injecting and kneading a physical blowing agent into the resulting melt to obtain a foamable molten resin mixture, which is then extruded into a low-pressure region through a flat die or the like attached to the tip of the extruder to foam, and then molding the mixture into a board using a molding tool.

[0003] In recent years, there has been an increasing demand for energy conservation in homes, buildings, and the like, creating a growing demand for extruded polystyrene resin foam boards with excellent thermal insulation properties. One method for producing extruded polystyrene resin foam boards with excellent thermal insulation properties is to use a blowing agent made of a hydrofluoroolefin (hereinafter simply referred to as "HFO") such as 1,3,3,3-tetrafluoropropene or 1-chloro-3,3,3-trifluoropropene (see, for example, Patent Documents 1 and 2). These HFOs are non-flammable and have low thermal conductivity, making it possible to impart high thermal insulation properties. Furthermore, they are environmentally friendly blowing agents because they have very low ozone depletion potential and global warming potential.

[0004] In Patent Documents 1 and 2, 1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz) is used as the HFO, either alone or in combination with other blowing agents. The HFO-1336mzz used in Patent Documents 1 and 2 is excellent in maintaining the thermal conductivity of the foam board low over a long period of time (long-term low thermal conductivity). Therefore, there is a need for the production of foam boards that can maintain low thermal conductivity by using HFO-1336mzz as a blowing agent. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Special Publication No. 2010-522808 [Patent Document 2] Special Publication No. 2019-515112 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when manufacturing foam boards, if an excessive amount of HFO-1336mzz is added in an attempt to maintain a lower thermal conductivity, problems arise in that the foaming agent separates from the resin, deteriorating moldability, and when HFO-1336mzz is used in combination with other foaming agents, moldability can also deteriorate depending on the blending ratio.As described above, when HFO-1336mzz is used, manufacturing stability is poor, and there is a possibility that a foam board with a good appearance cannot be obtained.

[0007] The present invention has been made in view of the above background, and aims to provide a method for producing a polystyrene-based resin foam board that can maintain low thermal conductivity for a long period of time, has excellent production stability, and has a good appearance. [Means for solving the problem]

[0008] According to the present invention, there is provided the following method for producing an extruded polystyrene resin foam board.

[0009] [1] A foaming method for producing a foamable molten resin composition having an apparent density of 20 kg / m, which comprises a step of extruding and foaming a foamable molten resin composition obtained by kneading a base resin mainly composed of a polystyrene resin, a flame retardant, and a physical foaming agent, and molding the extrudate into a plate. 3 More than 50kg / m 3 The following method for producing an extruded polystyrene resin foam board: the physical blowing agent comprises blowing agent A consisting of 1,1,1,4,4,4-hexafluoro-2-butene, blowing agent B consisting of a dialkyl ether having 1 to 3 carbon atoms, and blowing agent C consisting of water and / or an aliphatic alcohol having 1 to 5 carbon atoms; the total amount of the physical foaming agent added is 0.9 mol or more and 1.8 mol or less per 1 kg of the base resin; The amount of the foaming agent A added is 0.2 mol or more per 1 kg of the base resin, the amount of the foaming agent B added is 0.05 mol or more and 0.8 mol or less per 1 kg of the base resin, the amount of foaming agent C added is 0.1 mol or more and 0.7 mol or less per 1 kg of base resin, A method for producing an extruded polystyrene resin foam board, characterized in that the total amount of foaming agent A and foaming agent B added is 50 mol % or more relative to 100 mol % of the total amount of the physical foaming agents added.

[0010] [2] The method for producing an extruded polystyrene resin foam board according to the invention [1], wherein the amount of the foaming agent A added is 0.2 mol or more and 0.7 mol or less per kg of the base resin.

[0011] [3] The method for producing an extruded polystyrene resin foam board according to the invention [1] or [2], characterized in that the molar ratio of the amount of the foaming agent B to the amount of the foaming agent C (foaming agent B:foaming agent C) is 25:75 to 90:10.

[0012] [4] The method for producing an extruded polystyrene resin foam board according to any one of the inventions [1] to [3], wherein the blowing agent C is 60 to 95 mol % of water and 5 to 40 mol % of an aliphatic alcohol having 1 to 5 carbon atoms (provided that the total of water and the aliphatic alcohol having 1 to 5 carbon atoms is 100 mol %).

[0013] [5] The method for producing an extruded polystyrene resin foam board according to any one of the above [1] to [4] inventions, characterized in that the thickness of the extruded polystyrene resin foam board is 20 mm or more. [Effects of the Invention]

[0014] According to the manufacturing method of the present invention, it is possible to provide a method for manufacturing a polystyrene resin foam board that can maintain low thermal conductivity for a long period of time, has excellent manufacturing stability, and has a good appearance. DETAILED DESCRIPTION OF THE INVENTION

[0015] The method for producing an extruded polystyrene resin foam board of the present invention will be described in detail below. The method for producing an extruded polystyrene resin foam board of the present invention includes a step of extruding and foaming an expandable resin composition obtained by kneading a base resin mainly composed of a polystyrene resin, a flame retardant, and a physical blowing agent, and forming the composition into a board. 3 More than 50kg / m 3 The following is a method for producing an extruded polystyrene resin foam board.

[0016] Specifically, a base resin consisting of a polystyrene resin and other resins added as needed, a flame retardant, and other additives added as needed are melted and kneaded under heating in an extruder, a physical foaming agent is injected into the resulting molten mixture and further kneaded to form a foamable resin melt, which is adjusted to an appropriate temperature for foaming and extruded from the high-pressure extruder into a low-pressure region through a flat die to foam, and a forming tool such as a forming mold (for example, a shaping device (hereinafter also referred to as a guider) consisting of two upper and lower plates of polytetrafluoroethylene resin or the like arranged parallel to each other or so as to gradually expand from the entrance toward the exit) or a forming roll is placed at the exit of the flat die, and the extruded foam composition is molded into a plate by passing through the forming tool.

[0017] In the present invention, by using a physical blowing agent containing specific components (1,1,1,4,4,4-hexafluoro-2-butene, a dialkyl ether having 1 to 3 carbon atoms, water and / or an aliphatic alcohol having 1 to 5 carbon atoms) in specific amounts as described below, it is possible to obtain a foamed board that can maintain low thermal conductivity for a long period of time, has excellent production stability, and has a good appearance.

[0018] <Base resin> (Polystyrene resin) Examples of polystyrene-based resins used in the production method of the present invention include polystyrene (general-purpose polystyrene: GPPS), and one or more selected from the group consisting of styrene-methyl acrylate copolymers, styrene-ethyl acrylate copolymers, styrene-methyl methacrylate copolymers, styrene-ethyl methacrylate copolymers, styrene-acrylic acid copolymers, styrene-methacrylic acid copolymers, styrene-maleic anhydride copolymers, styrene-polyphenylene ether copolymers, styrene-acrylonitrile copolymers, styrene-methylstyrene copolymers, styrene-dimethylstyrene copolymers, styrene-ethylstyrene copolymers, and styrene-diethylstyrene copolymers, each containing 50 mol% or more of styrene unit components. Among these, polystyrene is preferred. The polystyrene-based resin may also contain unit components derived from branching agents such as polyfunctional monomers and polyfunctional macromonomers. The content of styrene unit components in the copolymer is preferably 60 mol% or more, more preferably 80 mol% or more, and even more preferably 90 mol% or more.

[0019] The melt viscosity of the polystyrene resin used in the production method of the present invention is preferably 500 to 3000 Pa·s, more preferably 1000 to 2500 Pa·s, and even more preferably 1200 to 2300 Pa·s, in order to provide excellent foaming and moldability. In this specification, the melt viscosity is measured based on JIS K7199:1999 at a temperature of 200°C and a shear rate of 100 sec -1 The values ​​were measured under the following conditions.

[0020] (Other polymers) The base resin may contain polymers other than the polystyrene-based resins as long as the objectives and effects of the present invention are achieved. Examples of other polymers include thermoplastic resins such as polyethylene-based resins (a mixture of one or more selected from the group consisting of ethylene homopolymers and ethylene-based copolymers having an ethylene unit content of 50 mol% or more), polypropylene-based resins (a mixture of one or more selected from the group consisting of propylene homopolymers and propylene-based copolymers having an ethylene unit content of 50 mol% or more), polyphenylene ether-based resins, polymethyl methacrylate, and amorphous polyethylene terephthalate-based resins (heat of fusion of less than 5 J / g, as measured by heat flux differential scanning calorimetry in accordance with JIS K7122-1987), as well as thermoplastic elastomers such as styrene-butadiene-styrene block copolymers, styrene-isoprene-styrene block copolymers, hydrogenated styrene-butadiene-styrene block copolymers, hydrogenated styrene-isoprene-styrene block copolymers, and styrene-ethylene copolymers. These other polymers may be blended within a range that does not impair the objectives and effects of the present invention.

[0021] In the production method of the present invention, a base resin containing a polystyrene-based resin as a main component means that 50% by mass or more of the base resin is a polystyrene-based resin, preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more.

[0022] <Physical foaming agent> The physical blowing agent used in the present invention contains, as essential components, blowing agent A consisting of 1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz), blowing agent B consisting of a dialkyl ether having 1 to 3 carbon atoms, and blowing agent C consisting of water and / or an aliphatic alcohol having 1 to 5 carbon atoms.

[0023] (Blowing agent A) Among hydrofluoroolefins, blowing agent A, 1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz), has moderate solubility in polystyrene resins and excellent retention within the foam, allowing for the production of foam boards with excellent low thermal conductivity over a long period of time. Furthermore, its non-flammability reduces the risk of ignition due to static electricity during foam board production. Furthermore, it has a low ozone depletion potential and a very low global warming potential, making it a blowing agent with a low environmental impact.

[0024] (Blowing agent B) Examples of the C1-3 dialkyl ether of the blowing agent B include dimethyl ether, diethyl ether, dipropyl ether, and methyl ethyl ether, which can be used alone or in combination of two or more. From the viewpoint of improving production stability, dimethyl ether is preferably used among these. The C1-3 dialkyl ether means a dialkyl ether having an alkyl chain with 1 to 3 carbon atoms.

[0025] By using a C1-3 dialkyl ether together with Blowing Agent A, it is possible to obtain a method for producing an extruded foam board that maintains excellent low thermal conductivity for a long period of time, has excellent surface smoothness, suppresses the occurrence of gas spots, and is highly stable in production.

[0026] (Foaming agent C) Blowing agent C is at least one of water and an aliphatic alcohol having 1 to 5 carbon atoms. By using blowing agent C together with blowing agent A and blowing agent B, it is possible to more easily obtain an extruded polystyrene resin foam board that satisfies the above-mentioned range of apparent density.

[0027] The water used as the foaming agent C does not destroy the ozone layer or contribute to global warming, and is quickly dissipated from the foam board, allowing the dimensions of the resulting foam board to be quickly stabilized.

[0028] Examples of the aliphatic alcohol having 1 to 5 carbon atoms in the blowing agent C include monohydric alcohols such as methyl alcohol (methanol), ethyl alcohol (ethanol), n-propyl alcohol, isopropyl alcohol, butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, aryl alcohol, crotyl alcohol, propargyl 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. These can be used alone or in combination of two or more. Among these, ethanol is preferred for achieving a better appearance. The ratio of ethanol to 100% by weight of the aliphatic alcohol having 1 to 5 carbon atoms is preferably 60% by weight or more, more preferably 70% by weight or more, and even more preferably 85% by weight or more.

[0029] Like water, aliphatic alcohols having 1 to 5 carbon atoms do not destroy the ozone layer or contribute to global warming, and they quickly dissipate from the foam board, allowing the shape of the foam board to be stabilized quickly.

[0030] In the present invention, blowing agents A, B, and C are used as essential components of the physical blowing agent, but various other blowing agents can be appropriately blended with the physical blowing agent as long as the effects of the present invention are not impaired. Examples of other blowing agents include carbon dioxide, nitrogen, saturated hydrocarbons having 3 to 5 carbon atoms (e.g., isobutane and normal butane), and chlorinated hydrocarbons (e.g., methyl chloride and ethyl chloride), which can be used alone or in combination of two or more.

[0031] <Amount of physical foaming agent added> In the present invention, the total amount of the physical foaming agent added is 0.9 mol to 1.8 mol per kg of base resin. From the viewpoint of obtaining a foamed board that has excellent appearance, a low apparent density, and can maintain low thermal conductivity for a long period of time, the total amount of the physical foaming agent added is preferably 1.0 mol to 1.6 mol, more preferably 1.2 mol to 1.5 mol, per kg of base resin.

[0032] The amount of blowing agent A (1,1,1,4,4,4-hexafluoro-2-butene) added is 0.2 mol or more per kg of base resin. By setting the amount of blowing agent A added within this range, it is possible to maintain low thermal conductivity over a long period of time. From the viewpoint of maintaining low thermal conductivity over a long period of time, the amount of blowing agent A added is preferably 0.3 mol or more per kg of base resin, more preferably 0.4 mol or more, and even more preferably 0.5 mol or more.

[0033] On the other hand, from the viewpoint of improving the mechanical strength of the extruded foam board, such as bending strength and bending fracture deflection, the amount of foaming agent A added is preferably 1.0 mol or less, more preferably 0.8 mol or less, even more preferably 0.7 mol or less, and even more preferably 0.6 mol or less, per kg of base resin.

[0034] In the present invention, in a high-mixing extruder such as a twin screw or screw with a large ratio of axial length to screw diameter, or a tandem extruder in which a first extruder and a second extruder are connected in series, a continuous static mixer may be used at the connection between the first extruder and the second extruder or at the connection between the second extruder and the die, as needed, to facilitate the production of extruded foam plates with excellent appearance even when a large amount of blowing agent A is added.

[0035] If the amount of blowing agent B (dialkyl ether having 1 to 3 carbon atoms) added is too small, there is a risk of reduced surface smoothness and the occurrence of gas spots. Furthermore, since blowing agent B is a flammable gas, if the amount of blowing agent B added is too large, there is a risk of ignition during molding after extrusion foaming and there is a risk of reduced manufacturing stability. Therefore, the amount of blowing agent B added is 0.05 mol to 0.8 mol, preferably 0.1 mol to 0.7 mol, more preferably 0.2 mol to 0.6 mol, and even more preferably 0.3 mol to 0.5 mol, per kg of base resin.

[0036] The total amount of blowing agent C (water and / or aliphatic alcohol having 1 to 5 carbon atoms) added is 0.1 mol to 0.7 mol, preferably 0.2 mol to 0.7 mol, more preferably 0.3 mol to 0.6 mol, and even more preferably 0.4 mol to 0.55 mol, per kg of base resin, from the viewpoints of production stability and good appearance. When the physical blowing agent contains blowing agent C, it becomes easier to maintain an appropriate pressure during extrusion. The amount of blowing agent C added is the sum of the amount of water added and the amount of aliphatic alcohol having 1 to 5 carbon atoms added.

[0037] From the viewpoint of achieving a low apparent density and a good appearance by reducing gas spots, blowing agent C is preferably both water and an aliphatic alcohol having 1 to 5 carbon atoms, more preferably 60 to 95 mol % of water and 5 to 40 mol % of an aliphatic alcohol having 1 to 5 carbon atoms (provided that the total of water and the aliphatic alcohol having 1 to 5 carbon atoms is 100 mol %), and even more preferably 65 to 85 mol % of water and 15 to 35 mol % of an aliphatic alcohol having 1 to 5 carbon atoms.

[0038] From the viewpoint of maintaining production stability and low thermal conductivity over a long period of time, the total amount of blowing agent A (1,1,1,4,4,4-hexafluoro-2-butene) and blowing agent B (dialkyl ether having 1 to 3 carbon atoms) added is 50 mol% or more, preferably 55 mol% or more, relative to the total amount of physical blowing agents added (100 mol%). On the other hand, the upper limit of the total amount of blowing agent A and blowing agent B added is preferably 90 mol%, more preferably 80 mol%, and even more preferably 70 mol%.

[0039] The molar ratio (blowing agent B:blowing agent C) of the amount of blowing agent B (dialkyl ether having 1 to 3 carbon atoms) to the amount of blowing agent C (water and / or aliphatic alcohol having 1 to 5 carbon atoms) added is preferably 15:85 to 95:5. From the viewpoints of further improving production stability and maintaining low thermal conductivity over a long period of time, the molar ratio (blowing agent B:blowing agent C) is more preferably 25:75 to 90:10, and even more preferably 25:75 to 75:25.

[0040] In the present invention, by setting the total amount of the physical foaming agent, the amount of foaming agent A, the amount of foaming agent B, the amount of foaming agent C, and the ratio of the amount of foaming agent A to the amount of foaming agent B within the above-mentioned specific ranges, it is possible to maintain low thermal conductivity for a long period of time and to obtain a foamed board with good manufacturing stability and appearance (surface smoothness and gas spots).

[0041] <Other ingredients> (Flame retardant) The foam board obtained by the manufacturing method of the present invention is mainly used as a heat insulating material for building materials, and flame retardancy is imparted by blending a flame retardant with the base resin. The flame retardant used in the present invention is not particularly limited, but it is preferable to use a brominated flame retardant. Examples of the brominated flame retardant 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), tetrabromobisphenol-B-bis(2,3-dibromopropyl ether), tetrabromobisphenol-C-bis(2,3-dibromopropyl ether), tetrabromobisphenol-D ... Examples include brominated bisphenol compounds such as tetrabromobisphenol-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. These brominated flame retardants can be used alone or in combination.

[0042] In addition to these bromine-based flame retardants, nitrogen-containing cyclic compounds such as cresyl di-2,6-xylenyl phosphate, antimony trioxide, diantimony pentoxide, ammonium sulfate, zinc stannate, cyanuric acid, pentabromotoluene, isocyanuric acid, triallyl isocyanurate, melamine cyanurate, melamine, melam, and melem; inorganic compounds such as silicone compounds, boron oxide, zinc borate, and zinc sulfide; and phosphorus compounds such as phosphate esters represented by triphenyl phosphate, red phosphorus, ammonium polyphosphate, phosphazene, and hypophosphites.

[0043] Among these flame retardants, it is more preferable to use a flame retardant containing a combination of tetrabromobisphenol A-bis(2,3-dibromopropyl ether) and tetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl ether), or a flame retardant containing a brominated butadiene-styrene copolymer, because these can impart high flame retardancy, are less likely to decompose the polystyrene resin during extrusion, and make it easier to stably obtain foamed boards even when the foamed board has a low apparent density (high expansion ratio) and a large cross-sectional area.

[0044] The amount of flame retardant added is preferably 0.1 to 10 parts by mass, more preferably 1 to 9 parts by mass, and even more preferably 1.5 to 7 parts by mass, per 100 parts by mass of the base resin, because this allows the foam board to have high flame retardancy while suppressing deterioration in extrusion foamability and mechanical properties. Within this range, the flame retardant does not inhibit foamability, and a foam board can be obtained that exhibits high flame retardancy, as specified in "Test Method A" for extruded polystyrene foam insulation, which is defined in JIS A9521:2022, Test Methods for Flammability of Foamed Plastic Insulation Materials.

[0045] (Flame retardant synergist) In the method of the present invention, a flame retardant synergist can be used in combination with the flame retardant to further improve the flame retardancy of the foam board. Examples of the flame retardant synergist 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, and polyalkylated aromatic compounds such as poly-1,4-diisopropylbenzene. The amount of the flame retardant synergist added is generally 0.01 to 1 part by mass, more preferably 0.05 to 0.5 parts by mass, per 100 parts by mass of the base resin.

[0046] (Radiation suppressant) In the manufacturing method of the present invention, graphite can be blended into the foamable resin composition as a radiation suppressor to improve the heat insulating property of the foam board by reflecting infrared rays.

[0047] Examples of graphite include flake graphite, scaly graphite, artificial graphite, and amorphous graphite, and it is preferable to use graphite whose main component is flake graphite. As described below, graphite is preferably used as a masterbatch in which it is blended at a high concentration with a polystyrene-based resin. Graphite with a fixed carbon content of 80% or more is preferred because it provides good workability when producing the masterbatch and is effective in improving the thermal insulation of the resulting foam board. Furthermore, to further improve the thermal insulation of the foam board, graphite with a fixed carbon content of 90% or more is more preferred, and graphite with a fixed carbon content of 95% or more is even more preferred. The fixed carbon content of the graphite refers to a value measured by the method described in JIS M8511:2014.

[0048] When graphite is added, 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 added is within this range, the heat insulating properties are improved, and a foam board with the desired low thermal conductivity can be obtained. From this perspective, the amount of graphite added is more preferably 0.3 parts by mass or more, and even more preferably 0.4 parts by mass or more, per 100 parts by mass of the base resin of the foam board. On the other hand, from the perspective of maintaining the flame retardancy of the foam board, the upper limit of the amount of graphite added is more preferably 5 parts by mass, even more preferably 3 parts by mass, and particularly preferably 1 part by mass, per 100 parts by mass of the base resin of the foam board.

[0049] In addition, in the manufacturing method of the present invention, a radiation suppressor other than the graphite can be incorporated into the foam board to further improve heat insulation. Examples of radiation suppressors other than graphite include one or more selected from metal oxides such as titanium oxide, metals such as aluminum, ceramics, carbon black, graphite, infrared-shielding pigments, and hydrotalcite. Among these, titanium oxide is preferably used. The amount of radiation suppressor other than graphite added is generally 0.5 to 5 parts by mass, more preferably 1 to 4 parts by mass, per 100 parts by mass of the base resin.

[0050] In the method of the present invention, other known additives may be appropriately blended with the base resin as needed, such as cell regulators, colorants such as pigments and dyes, heat stabilizers, and fillers.

[0051] (Foam adjuster) In the manufacturing method of the present invention, a foamable resin composition is preferably formed by blending a cell regulator with the base resin. Examples of the cell regulator include inorganic powders such as talc, kaolin, mica, silica, calcium carbonate, barium sulfate, titanium oxide, clay, aluminum oxide, bentonite, and diatomaceous earth. Among these, talc is preferred because it is easy to adjust the cell size and can easily reduce the cell size without impairing flame retardancy. Fine talc with a 50% particle size (measured by centrifugal sedimentation using light transmission) of 0.1 to 20 μm is particularly preferred, with talc of 0.5 to 15 μm being particularly preferred. The amount of cell regulator added varies depending on the type of regulator, the desired cell size, and other factors. When talc is used as a cell regulator, the amount is preferably 0.1 to 7 parts by weight, more preferably 0.2 to 5 parts by weight, and even more preferably 0.3 to 3 parts by weight per 100 parts by weight of the base resin.

[0052] (heat stabilizer) The thermal stabilizer can be incorporated into raw materials or waste materials during foam board production or when recycling and repelletizing foam board waste materials, thereby improving the thermal stability of the brominated flame retardant. Examples of the thermal stabilizer include one or more selected from bisphenol-type epoxy compounds and novolac-type epoxy compounds, such as those in the EPICLON series manufactured by DIC Corporation; 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. The amount of the thermal stabilizer added is preferably 0.1 to 40 parts by mass per 100 parts by mass of the total amount of flame retardant.

[0053] In the manufacturing method of the present invention, a method for blending a flame retardant or other additives into a base resin can be employed, for example, by feeding a predetermined proportion of the flame retardant or other additives together with the base resin into a feeder provided upstream of the extruder and kneading them in the extruder. Alternatively, a method can be employed in which the flame retardant or other additives are fed into a molten resin from a feeder provided midway through the extruder. Specifically, a method can be employed in which a dry blend of the flame retardant, other additives, and base resin is fed into 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 a melt-kneaded mixture is fed into the extruder; or a method can be employed in which a masterbatch is prepared by blending a high concentration of the flame retardant or other additives into the base resin, and the masterbatch is fed into the extruder and melt-kneaded with the base resin. Particularly from the viewpoint of dispersibility, it is preferable to prepare a flame retardant masterbatch and feed it into the extruder. The flame retardant masterbatch is prepared by using a polystyrene resin as the base resin having a melt flow rate of approximately 0.5 to 30 g / 10 min at 200°C under a load of 5 kg, and adjusting the masterbatch so that the flame retardant content is 10 to 95 mass %, more preferably 30 to 90 mass %, and even more preferably 50 to 85 mass %.

[0054] <Physical properties of foam board> Next, the extruded polystyrene resin foam board obtained by the production method of the present invention will be described.

[0055] (Apparent density) The apparent density of the foam board of the present invention is 20 kg / m 3 More than 50kg / m 3 or less, preferably 25 kg / m 3 More than 45kg / m 3 More preferably, it is 30 kg / m or less. 3 More than 40kg / m 3 When the apparent density is within the above range, the material has sufficient mechanical strength and is suitable for use as a lightweight heat insulating material.

[0056] (closed cell ratio) The closed cell ratio of the foam board is preferably 85% or more, more preferably 90% or more, and even more preferably 93% or more. If the closed cell ratio is within this range, the blowing agent is more likely to remain in the cells, and the high thermal insulation performance of the foam board can be maintained for a long period of time.

[0057] The closed cell percentage of the extruded foam board in this specification is measured in accordance with Procedure C of ASTM-D2856-70 using a Toshiba Beckman Co., Ltd. air comparison hydrometer, Model 930. (A cut sample, without a molded skin, cut into 25 mm x 25 mm x 20 mm pieces from the foam board is placed in a sample cup for measurement. However, if the foam board is too thin to cut a 20 mm cut sample in the thickness direction, for example, two cut samples each measuring 25 mm x 25 mm x 10 mm may be placed in the sample cup at the same time for measurement.) The true volume Vx of the extruded foam board (cut sample) is used to calculate the closed cell percentage S (%) using the following formula (1), and the average value is calculated for N = 3.

[0058] S(%)=(Vx-W / ρ)×100 / (V A -W / ρ) (1) Vx: The true volume (cm) of the cut sample measured by the above method 3) (This corresponds to the sum of the volume of the resin that makes up a cut sample of the extruded foam board and the total volume of the air bubbles in the closed cell portion of the cut sample.) V A : Apparent volume (cm) of the cut sample calculated from the outer 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 that makes up the extruded foam board (g / cm 3 )

[0059] (Thermal conductivity after 7 days) The foam board of the present invention preferably has a thermal conductivity of 0.028 W / m·K or less, and more preferably 0.025 W / m·K or less, 7 days after production.

[0060] (Thermal conductivity after 300 days) Furthermore, the thermal conductivity 300 days after production is preferably 0.032 W / m·K or less, and more preferably 0.027 W / m·K or less.

[0061] The thermal conductivity can be measured based on the heat flow meter method described in JIS A1412-2:1999 (symmetrical construction of one test piece, high temperature side 38°C, low temperature side 8°C, average temperature 23°C).

[0062] (Bending failure deflection) The flexural deflection of the foamed plate of the present invention is preferably 10 mm or more, more preferably 20 mm or more, and even more preferably 30 mm or more. The flexural deflection is the deflection at which the test piece breaks.

[0063] (bending strength) In the foamed board of the present invention, the bending strength (maximum bending stress) is 40 N / cm 2 It is preferable that the resistance is 50N / cm or more. 2 More preferably, it is 55N / cm or more. 2 More preferably, it is equal to or greater than this.

[0064] The flexural deflection and flexural strength can be measured in accordance with JIS K7221-2:2006. Seven days after production, extruded foam plates are cut into test specimens with dimensions of 250 mm in length, 75 mm in width, and 25 mm in thickness, free of the molded skin. Three test specimens are cut out so that the length is aligned with the extrusion direction of the extruded foam and the midpoint in the width direction, and three test specimens are cut out so that the length is aligned with the width direction of the extruded foam and the midpoint in the width direction is the center of the length. These test specimens are used for testing with a pressure wedge and support base tip radius of 10 mm, a support distance of 200 mm, and a test speed of 20 mm / min. The flexural strength and flexural deflection can be calculated by arithmetically averaging the measured values ​​for each test specimen.

[0065] (cross-sectional area, dimensions, etc.) The foamed board of the present invention is in the form of a plate, and its cross-sectional area perpendicular to the extrusion direction is 100 cm 2 It is preferable that the length is 200cm or more. 2 The upper limit of the cross-sectional area is approximately 1500 cm 2 In this specification, the cross-sectional area perpendicular to the extrusion direction refers to the area of ​​a cross section perpendicular to the extrusion direction of the foam board.

[0066] The foam board of the present invention is usually produced by preparing a base plate one size larger than the desired size, and then cutting the base plate to adjust the width, length, and in some cases the thickness.

[0067] However, if the width of the base plate fluctuates significantly during production and becomes narrower than specified, it becomes impossible to obtain a foamed board of the specified size, resulting in a poor yield. Furthermore, in the production of foamed boards, the lower the apparent density and the larger the cross-sectional area, the more difficult it tends to be to expand. The production method of the present invention has excellent production stability, making it possible to stably produce foamed boards with good appearance, even when producing foamed boards with large thicknesses and cross-sectional areas. Extruded foamed boards with a good foaming state and excellent surface smoothness can be suitably used as foamed boards with a molded skin without cutting the surface in the thickness direction.

[0068] In the case of a foam board used as a thermal 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 is generally about 150 mm. Since the present invention includes a step of extruding and foaming a foamable molten resin composition into a plate, foam boards can be produced stably even when the thickness is large.

[0069] The width is preferably 800 mm or more, more preferably 900 mm or more, with the upper limit being approximately 1200 mm.

[0070] (Bubble structure: average bubble diameter in thickness direction) The average cell diameter in the thickness direction of the foam board is preferably 50 to 200 μm, more preferably 70 to 170 μm, and even more preferably 80 to 150 μm. When the average cell diameter is within the above range, the foam board has even higher heat insulation properties and superior mechanical strength.

[0071] The average bubble diameter in the thickness direction is measured as follows: Enlarged photographs are taken at three locations, near the center and both ends of a cross section perpendicular to the width direction of a foamed board, with the magnification adjusted to a range of about 50 to 200 times so that the number of cells in the photograph is about 200 to 500. The maximum diameter of each bubble in the thickness direction is measured in each photograph using image processing software NS2K-pro manufactured by Nano System Co., Ltd., and the average of these values ​​is calculated.

[0072] (Bubble structure: bubble deformation rate) Furthermore, the foam board preferably has a cell deformation ratio of 0.7 to 1.5. The cell deformation ratio is calculated by dividing the average cell diameter in the thickness direction determined by the above-described measurement method by the average cell diameter in the width direction of an enlarged photograph of the cells, measuring the maximum diameter of each cell in the width direction using image processing software NS2K-pro manufactured by Nano System Co., Ltd., and arithmetically averaging these values ​​to determine the average cell diameter in the width direction. The smaller the cell deformation ratio is below 1, the flatter the cells are, and the larger the cell deformation ratio is above 1, the more elongated the cells are. Having a cell deformation ratio within the above range results in a foam board with excellent mechanical strength and higher thermal insulation. From the viewpoint of dimensional stability of the foam board, the lower limit of the cell deformation ratio is more preferably 0.8. Furthermore, from the viewpoint of improved thermal insulation, the upper limit of the cell deformation ratio is more preferably 1.1, and even more preferably 1.05. [Example]

[0073] The present invention will be described in more detail below with reference to examples, although the present invention is not limited to these examples.

[0074] In the examples and comparative examples, the following devices and raw materials were used.

[0075] The extrusion equipment used consisted of a first highly mixed extruder with an inner diameter of 115 mm and a second extruder with an inner diameter of 180 mm connected in series, a physical foaming agent injection port near the end of the first extruder, and a flat die equipped with a resin outlet (die lip) with a rectangular cross section measuring 1 mm and a width of 440 mm, connected to the outlet of the second extruder. A molding device (guider) consisting of a pair of upper and lower polytetrafluoroethylene resin plates placed horizontally at an approximately fixed interval was attached to the resin outlet of the second extruder.

[0076] (1) Base resin (1-1) Polystyrene resin: DIC Corporation polystyrene "HP600ANJ", melt viscosity (200 ° C, 100 sec -1 )1400 Pa·s The melt viscosity was measured using a Capillograph 1D (manufactured by Toyo Seiki Seisakusho Co., Ltd.) flow property measuring device at a temperature of 200°C and a shear rate of 100 sec -1 The values ​​were measured under the following conditions.

[0077] (2) Flame retardants (2-1) A flame retardant masterbatch (GR-134BG manufactured by Dai-ichi Kogyo Seiyaku Co., Ltd.) containing a mixed flame retardant of 60% by mass of tetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl ether): Dai-ichi Kogyo Seiyaku "SR-130" / 40% by mass of tetrabromobisphenol A-bis(2,3-dibromopropyl ether): Dai-ichi Kogyo Seiyaku "SR-720" was used, and the masterbatch was added so as to obtain the flame retardant amounts shown in Tables 1 and 2.

[0078] (3) Foam adjuster Talc (manufactured by Matsumura Sangyo Co., Ltd., product name "High Filler #12", particle size (d50) 7.5 μm)

[0079] (4) Radiation suppressants (4-1) Graphite (Graphite: manufactured by Resino Color Kogyo Co., Ltd., product name: SBF-T-1683, flake graphite powder, average particle size 17 μm, 40% masterbatch) (4-2) Titanium oxide (manufactured by Nikko Bix Co., Ltd.)

[0080] (5) Physical foaming agents (a) HFO-1336mzz: Mitsui Chemours Fluoroproducts (b) Dimethyl ether: manufactured by Mitsubishi Gas Chemical Company, Inc. (c1) water (c2) Alcohol (ethanol / isopropyl alcohol / 1-propanol = 90% by weight / 6% by weight / 4% by weight): manufactured by Yamaichi Chemical Industry Co., Ltd. Carbon dioxide: manufactured by Showa Carbonic Acid Co., Ltd.

[0081] Examples 1 to 9, Comparative Examples 1 to 5 The types and amounts of base resin, flame retardant masterbatch, and cell control agent shown in Table 1 (Examples 1 to 9) and Table 2 (Comparative Examples 1 to 5) were fed into a first extruder, heated to 200°C, and kneaded. The types and amounts of physical blowing agents shown in Tables 1 and 2 were fed through a physical blowing agent inlet provided in the first extruder, and further kneaded to form a foamable resin melt. The resulting foamable resin melt was then transferred to a second extruder to adjust the resin temperature, and then extruded into a guider at a discharge rate of 400 kg / hr. The melt was passed through the guider while foaming and molded (shaped) into a plate to produce a 30 mm thick base plate. The width and length of the base plate were adjusted by cutting, and the molding skins on both sides were evenly cut to produce a rectangular parallelepiped polystyrene resin foam plate (width: 910 mm, length: 1820 mm, thickness: 25 mm, cross-sectional area perpendicular to the extrusion direction: 227.5 cm) without a molding skin. 2 In Example 4, ethanol (reagent ethanol (99.5) grade 1, manufactured by Kanto Chemical Co., Inc.) was used as (c2) alcohol.

[0082] [Table 1]

[0083] [Table 2]

[0084] The foamed boards obtained under the conditions of the Examples and Comparative Examples were measured for cell structure (average cell diameter in the thickness direction, cell deformation rate), thickness, apparent density, closed cell ratio, and thermal conductivity (after 7 days and 300 days) using the following methods, and flammability, bending fracture deflection, bending strength (maximum bending stress), manufacturing stability, and appearance (surface smoothness, gas spots) were evaluated according to the following criteria. The results are shown in Tables 1 and 2.

[0085] (Bubble structure: average bubble diameter in thickness direction) The average bubble diameter in the thickness direction was determined as follows: Enlarged photographs were taken at 100x magnification at three locations, the center and both ends, of the cross section perpendicular to the width direction of the foamed plate. The maximum diameter of each bubble in the thickness direction was measured using image processing software NS2K-pro (manufactured by Nano System Co., Ltd.), and the arithmetic mean of these values ​​was calculated.

[0086] (Bubble structure: bubble deformation rate) The bubble deformation ratio was determined in the same manner as in the method for measuring the bubble diameter in the thickness direction described above. For an enlarged photograph of the bubbles, the maximum diameter of each bubble in the width direction was measured using the image processing software NS2K-pro manufactured by Nano System Co., Ltd., and the average bubble diameter in the width direction was calculated by arithmetically averaging these values, and then dividing the average bubble diameter in the thickness direction by the average bubble diameter in the width direction.

[0087] (Thickness) The foamed plate was measured at three positions that divided the plate into four equal parts in the width direction, and the measured values ​​were averaged to obtain the thickness.

[0088] (Apparent density) The apparent density of the foam board was determined as follows: rectangular parallelepiped samples, each 50 mm long x 50 mm wide x 20 mm thick, were cut out from the center and both ends of the foam board at a position that divided the foam board into two equal parts in the length direction, and the masses were measured. The apparent density of each sample was calculated by dividing the mass by the volume, and the arithmetic average of the masses was used as the apparent density.

[0089] (closed cell ratio) The closed cell ratio of the foam board was calculated from the above formula (1) using the true volume Vx of the foam board measured using an air comparison hydrometer (Toshiba Beckman Co., Ltd., air comparison hydrometer, model: 930) in accordance with procedure C of ASTM-D2856-70.

[0090] (Thermal conductivity: 7 days after manufacture) Test pieces measuring 200 mm long x 200 mm wide x 20 mm thick were cut out from the center of the width direction of the foamed board immediately after production, and the test pieces were stored in a constant temperature and humidity room at a temperature of 23°C and a relative humidity of 50%. Seven days after production, the thermal conductivity of each test piece was measured using the flat plate heat flow meter method described in JIS A1412-2 (1999) (two heat flow meter system, high temperature side 38°C, low temperature side 8°C, average temperature 23°C).

[0091] (Thermal conductivity: 300 days after manufacture) The thermal conductivity 300 days after manufacture was measured on extruded foam boards subjected to Test Method A of the Long-Term Accelerated Test for Thermal Resistance in accordance with JIS A1486:2014. Specifically, a rectangular parallelepiped (200 mm x 200 mm x 25 mm) was cut from the center of the width of the extruded foam board immediately after manufacture, and then uniformly scraped from both sides to cut test pieces (200 mm x 200 mm x 10 mm). These test pieces were stored in a constant temperature and humidity chamber at 23°C and 50% relative humidity. The thermal conductivity of the test pieces 48 days after manufacture (equivalent to 300 days after manufacture of a 25 mm-thick extruded foam board) was measured using the flat plate heat flow meter method (two heat flow meters, high temperature 38°C, low temperature 8°C, average temperature 23°C) described in JIS A1412-2 (1999).

[0092] (flammability) Immediately after production, the foam boards were stored in a constant temperature and humidity room at a temperature of 23°C and a relative humidity of 50%. Four weeks after production, five test pieces (N=5) were randomly cut out from the foam boards. Flammability was measured based on "Test Method A" specified in JIS A9521:2022, a test method for flammability in foam plastic insulation materials, and the flame retardancy of the foam boards was evaluated according to the following criteria. ○: The average burning time of the five test specimens is 3 seconds or less ×: The average burning time of the five test specimens exceeds 3 seconds (not applicable)

[0093] (manufacturing stability) The manufacturing stability was evaluated according to the following criteria. ◎: Continuous and stable extrusion molding into a plate shape is possible during extrusion foaming. Good: Although some sticking occurred during extrusion foaming, stable extrusion molding into a plate was possible. △: Sometimes snagging occurred during extrusion foaming, but extrusion molding into a plate was possible ×: Stuckness frequently occurs during extrusion foaming, making it difficult to extrude into a plate shape

[0094] (Appearance: surface smoothness) The surface smoothness of the base plate and the extruded foam plate was visually evaluated according to the following criteria: The base plate was a foam plate with a molded skin that was one size larger than the desired size, and the extruded foam plate was a foam plate that had been cut to adjust the width, length, and sometimes the thickness, and had the molded skin removed. ◎: The surfaces of the base plate and extruded foam plate are extremely good ○: The surface of the base plate is occasionally rough, but the surface of the extruded foam plate is extremely good. △: Roughness rarely occurs on the surface of the extruded foam board ×: A lot of roughness occurs on the surface of the extruded foam board

[0095] (Exterior: Gas spot) Gas spots (excessively large bubbles observed on the surface and cross section of the foam board due to separation of the blowing agent generated during extrusion foaming) were evaluated according to the following criteria. ◎: No spot holes are found on the original plate or extruded foam plate ○: Most of the original plate had no spot holes, and the extruded foam plate had no spot holes at all. △: Spot holes are observed in some parts of the extruded foam plate. ×: Multiple spot holes were observed in the extruded foam plate, and a good foam plate was not obtained.

[0096] From the results of the above measurements and evaluations, it was confirmed that Examples 1 to 9, which contained 1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz) (blowing agent A) as a physical blowing agent, a dialkyl ether having 1 to 3 carbon atoms (blowing agent B), and water and / or an aliphatic alcohol having 1 to 5 carbon atoms (blowing agent C) under the conditions of the present invention, were excellent in all of the apparent density, closed cell content, thermal conductivity of the foamed board (after 7 days and 300 days), bending properties (flexural deflection at break, bending strength), manufacturing stability, and appearance (surface smoothness, gas spots).

[0097] Furthermore, it was confirmed from Examples 1 to 5 that higher production stability was achieved when the molar ratio of blowing agent B to blowing agent C was 25:75 to 75:25. Furthermore, a comparison of Example 3 with Examples 6 and 9 confirmed that the use of both water and an aliphatic alcohol having 1 to 5 carbon atoms as blowing agent C further suppressed the occurrence of gas spots. A comparison of Examples 1 to 5 with Examples 7 and 8 confirmed that the flexural strength was further improved when the amount of blowing agent A added was 0.7 mol or less per kg of base resin.

[0098] In contrast to Examples 1 to 9, Comparative Examples 1 to 5 were unable to improve the cell structure, apparent density, closed cell ratio, thermal conductivity of the foamed board, bending properties, manufacturing stability, and appearance. Specifically, these are as follows:

[0099] In Comparative Example 1, no dialkyl ether having 1 to 3 carbon atoms (blowing agent B) was used. As a result, a foamed board could be produced, but the foaming ability was poor and the manufacturing stability and appearance were also poor. In Comparative Example 2, the amount of foaming agent A added was set higher than the conditions of the present invention. As a result, foaming was unstable in Comparative Example 2, making it difficult to produce a foamed board. In Comparative Example 3, no foaming agent C was used. As a result, it was difficult to produce a foamed board in Comparative Example 3. In Comparative Example 4, carbon dioxide was used instead of foaming agent C. As a result, the cells in Comparative Example 4 were too fine, making it difficult to produce a foamed board. In Comparative Example 5, the amount of foaming agent B added was set lower than the conditions of the present invention. As a result, a foamed board could be produced in Comparative Example 5, but the foaming ability was poor and the manufacturing stability and appearance were also poor.

Claims

1. The method includes a step of extruding and foaming a foamable molten resin composition obtained by kneading a base resin mainly composed of a polystyrene-based resin, a flame retardant, and a physical foaming agent, and molding the extrudate into a plate. ３ More than 50kg / m ３ The following method for producing an extruded polystyrene resin foam board: the physical blowing agent comprises a blowing agent A consisting of 1,1,1,4,4,4-hexafluoro-2-butene, a blowing agent B consisting of a dialkyl ether having 1 to 3 carbon atoms, and a blowing agent C consisting of water and / or an aliphatic alcohol having 1 to 5 carbon atoms; the total amount of the physical foaming agent added is 0.9 mol or more and 1.8 mol or less per 1 kg of the base resin, The amount of the foaming agent A added is 0.2 mol or more per 1 kg of the base resin, the amount of the foaming agent B added is 0.05 mol or more and 0.8 mol or less per 1 kg of the base resin, the amount of the foaming agent C added is 0.1 mol or more and 0.7 mol or less per 1 kg of the base resin, A method for producing an extruded polystyrene resin foam board, characterized in that the total amount of foaming agent A and foaming agent B added is 50 mol % or more relative to 100 mol % of the total amount of the physical foaming agents added.

2. A method for producing a polystyrene-based resin extruded foam board as described in claim 1, characterized in that the polystyrene-based resin is polystyrene.

3. 3. The method for producing an extruded polystyrene resin foam board according to claim 1, wherein the amount of the foaming agent A added is 0.2 mol or more and 0.7 mol or less per 1 kg of the base resin.

4. The method for producing an extruded polystyrene resin foam board according to claim 1 or 2, characterized in that the molar ratio of the amount of foaming agent B to the amount of foaming agent C (foaming agent B:foaming agent C) is 25:75 to 90:

10.

5. The method for producing an extruded polystyrene resin foam board according to claim 1 or 2, wherein the blowing agent C is 60-95 mol % of water and 5-40 mol % of aliphatic alcohol having 1-5 carbon atoms (provided that the total of water and aliphatic alcohol having 1-5 carbon atoms is 100 mol %).

6. 3. The method for producing an extruded polystyrene foam board according to claim 1, wherein the thickness of the extruded polystyrene foam board is 20 mm or more.

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