JP2024063688A - Thermoplastic resin extrusion foam board - Google Patents

Abstract

[Problem] To provide a method for producing an extruded thermoplastic resin foam plate having good flame retardancy and excellent long-term heat insulation. [Solution] An extruded thermoplastic resin foam plate contains a base resin containing a styrene-acrylonitrile copolymer and a flame retardant, has an apparent density of 20 kg/m3 to 50 kg/m3, a cross-sectional area perpendicular to the extrusion direction of 100 cm2 or more, and a thickness of 20 mm to 150 mm, in which the total amount (Ch+Cc) of a content Ch of hydrofluoroolefins per 1 kg of the extruded thermoplastic resin foam plate and a content Cc (including 0) of aliphatic saturated hydrocarbons having 3 to 5 carbon atoms per 1 kg of the extruded thermoplastic resin foam plate, as measured by gas chromatography using a test piece conditioned by the following method (1), is 0.5 mol or more and 1.3 mol or less, and the ratio [Ch/(Ch+Cc)] of the content Ch to the total amount (Ch+Cc) is greater than 0.5. Method (1): A test piece with no molded skin, measuring 500 mm in length, 200 mm in width, and 5 mm in thickness, is cut out from a thermoplastic resin extruded foam plate, and the test piece is conditioned by being left to stand for 37 days in an atmosphere with a temperature of 23°C and a humidity of 50%. [Selected figure] None

Description

The present invention relates to an extruded thermoplastic resin foam board, specifically, an extruded thermoplastic resin foam board that can be suitably used as an insulating material for the walls, floors, roofs, etc. of buildings.

Extruded thermoplastic resin foam boards (hereinafter simply referred to as "extruded foam boards") are widely used as building insulation materials due to their excellent thermal insulation and mechanical strength. Extruded foam boards are generally produced by heating and melting a thermoplastic resin such as polystyrene in an extruder, then injecting a physical foaming agent into the resulting melt and kneading it to obtain a foamable molten resin kneaded product, which is extruded into a low-pressure area through a flat die or the like attached to the tip of the extruder to foam it, and then forming it into a board shape using a molding tool.

In recent years, there has been an increasing demand for energy conservation in houses and buildings, and extruded foam boards with excellent flame retardancy and thermal insulation are in demand. One method for producing extruded foam boards with excellent thermal insulation is to use various hydrofluoroolefins (hereinafter simply referred to as "HFOs") as physical foaming agents. HFOs are non-flammable foaming agents, and can impart high thermal insulation to extruded foam boards. Furthermore, they are environmentally friendly foaming agents because they have very low ozone depletion potential and global warming potential.

Also, attempts have been made to use styrene-acrylonitrile copolymer as the base resin for extruded foam boards. For example, Patent Document 1 discloses the production of extruded foam boards using styrene-acrylonitrile copolymer as the base resin and 1,3,3,3-tetrafluoropropene (HFO-1234ze) as the HFO.

JP 2019-94472 A

However, with the technology of Patent Document 1, HFOs are unlikely to remain in the extruded foam board, and the HFO content in the extruded foam board may decrease significantly over a long period of time after production. In other words, there is room for improvement in terms of improving long-term thermal insulation. In consideration of the above circumstances, the present invention provides an extruded thermoplastic resin foam board that has good flame retardancy and excellent long-term thermal insulation.

According to the present invention, the following extruded thermoplastic resin foam board is provided.

[1] An extruded thermoplastic resin foam plate comprising a base resin containing a styrene-acrylonitrile copolymer and a flame retardant, having an apparent density of 20 kg/ ^m3 to 50 kg/ ^m3 , a cross-sectional area perpendicular to the extrusion direction of ¹⁰⁰ cm2 or more, and a thickness of 20 mm to 150 mm, wherein the total amount (Ch+Cc) of the hydrofluoroolefin content Ch per 1 kg of the extruded thermoplastic resin foam plate and the aliphatic saturated hydrocarbon content Cc (including 0) having 3 to 5 carbon atoms per 1 kg of the extruded thermoplastic resin foam plate, as measured by gas chromatography using a test piece conditioned by the following method (1), is 0.5 mol or more and 1.3 mol or less, and the ratio [Ch/(Ch+Cc)] of the content Ch to the total amount (Ch+Cc) is more than 0.5. Method (1): A test piece having a length of 500 mm, a width of 200 mm, and a thickness of 5 mm and no molded skin was cut out from an extruded thermoplastic resin foam plate, and the test piece was conditioned by leaving it to stand in an atmosphere having a temperature of 23° C. and a humidity of 50% for 37 days.

[2] In the extruded thermoplastic resin foam board of [1], the molecular weight of the hydrofluoroolefin is 110 or more.

[3] In the extruded thermoplastic resin foam board of [1] or [2], the hydrofluoroolefin is at least one selected from the group consisting of 1-chloro-2,3,3,3-tetrafluoropropene, 1-chloro-3,3,3-trifluoropropene, and 1,1,1,4,4,4-hexafluoro-2-butene.

[4] In the extruded thermoplastic resin foam board described in any one of [1] to [3] above, the hydrofluoroolefin is 1-chloro-2,3,3,3-tetrafluoropropene.

[5] In the extruded thermoplastic resin foam board described in any one of [1] to [4] above, the content Cc of aliphatic saturated hydrocarbons having 3 to 5 carbon atoms per 1 kg of the extruded thermoplastic resin foam board is 0.1 mol or more and 0.6 mol or less.

[6] In the extruded thermoplastic resin foam plate described in any one of [1] to [5] above, the average bubble diameter in the thickness direction of the extruded thermoplastic resin foam plate is 50 μm or more and 300 μm or less.

[7] In the extruded thermoplastic resin foam board described in any one of [1] to [6] above, the content of the acrylonitrile component derived from the styrene-acrylonitrile copolymer in the base resin is 20% by mass or more and 40% by mass or less.

[8] In the extruded thermoplastic resin foam board described in any one of [1] to [7] above, the flame retardant contains a brominated styrene-butadiene copolymer, and the amount of the brominated styrene-butadiene copolymer is 0.5 parts by mass or more and 8 parts by mass or less per 100 parts by weight of the base resin.

[9] In the extruded thermoplastic resin foam board of [8], the flame retardant further contains a brominated bisphenol, the amount of the brominated bisphenol is 0.1 to 1 part by mass per 100 parts by mass of the base resin, and the ratio of the amount of the brominated bisphenol to the amount of the brominated styrene-butadiene copolymer is 0.05 to 0.3.

The extruded foam board of the present invention has good flame retardancy and excellent long-term insulation properties.

<Extruded thermoplastic resin foam board>
The extruded thermoplastic resin foam board (hereinafter, also referred to as "extruded foam board") according to the present invention will be described below. The extruded foam board of the present invention contains a base resin, a physical foaming agent, and a flame retardant, has an apparent density of 20 kg/ ^m3 or more and 50 kg/ ^m3 or less, a cross-sectional area perpendicular to the extrusion direction of ¹⁰⁰ cm2 or more, and a thickness of 20 mm or more and 150 mm or less.

The extruded foam board according to the present invention is generally manufactured as follows. For example, additives such as a flame retardant and a bubble regulator are added to a base resin, which is then fed to an extruder, heated, melted, and kneaded. Next, a physical foaming agent is pressed into the extruder and further kneaded to form a foamable molten resin composition, which is then extruded from a high-pressure region to a low-pressure region (usually into the atmosphere) to cause foaming. The resulting foam is then shaped into a plate using a shaping device (such as a guider) connected to the die outlet of the extruder, to produce an extruded thermoplastic resin foam board. As the shaping device, for example, a device consisting of a pair of upper and lower polytetrafluoroethylene plates is used. The manufacturing method for the extruded foam board will be described in detail later.

[Base resin]
The extruded foam board of the present invention contains a styrene-acrylonitrile copolymer as a base resin. Specifically, the base resin preferably contains 50% by mass or more of the styrene-acrylonitrile copolymer, more preferably 60% by mass or more, even more preferably 70% by mass or more, still more preferably 80% by mass or more, particularly preferably 90% by mass or more, and most preferably 100% by mass, i.e., the base resin is substantially composed of only the styrene-acrylonitrile copolymer.

Styrene-acrylonitrile copolymer is a copolymer of styrene and acrylonitrile. The styrene-acrylonitrile copolymer may contain one type, or may contain two or more types with different copolymerization ratios of styrene and acrylonitrile.

The content of acrylonitrile components derived from the styrene-acrylonitrile copolymer in the base resin is, for example, 10% by mass or more and 40% by mass or less.

From the viewpoint of further increasing the residual property of the hydrofluoroolefin in the extruded foam board, the content of the acrylonitrile component derived from the styrene-acrylonitrile copolymer in the base resin is preferably 15% by mass or more, and more preferably 20% by mass or more.

To further improve the surface properties of the resulting extruded foam board, the content of the acrylonitrile component in the base resin is preferably 35% by mass or less, and more preferably 30% by mass or less.

When two or more types of styrene-acrylonitrile copolymers with different acrylonitrile contents are used, the content of the acrylonitrile component derived from the styrene-acrylonitrile copolymer in the entire base resin is calculated according to the content (mass%) of each styrene-acrylonitrile copolymer in the base resin and the content (mass%) of the acrylonitrile component in each styrene-acrylonitrile copolymer. For example, when the base resin is composed of 40 mass% of styrene-acrylonitrile copolymer with an acrylonitrile component content of 50 mass% and 60 mass% of styrene-acrylonitrile copolymer with an acrylonitrile component content of 20 mass%, the content of the acrylonitrile component derived from the styrene-acrylonitrile copolymer in the base resin is 40 mass% x 0.5 + 60 mass% x 0.2 = 32 mass%.

The content of acrylonitrile in styrene-acrylonitrile copolymers can be determined by pyrolysis gas chromatography analysis.

The base resin according to the present invention may contain other polymers besides styrene-acrylonitrile copolymers, within the scope in which the object and effect of the present invention are achieved. Examples of other polymers include thermoplastic resins such as polystyrene resins, polypropylene resins, polyester resins, polyolefin resins, polyphenylene ether resins, and polymethyl methacrylate, 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. However, the content of other polymers is preferably less than 30% by mass in the base resin (100% by mass), more preferably 20% by mass or less, even more preferably 10% by mass or less, particularly preferably 5% by mass or less, and most preferably 0% by mass, i.e., the base resin contains only styrene-acrylonitrile copolymers as polymer components.

The melt viscosity of the base resin used in the extruded foam board of the present invention is preferably 500 Pa·s or more and 4000 Pa·s or less, more preferably 1000 Pa·s or more and 3700 Pa·s or less, and even more preferably 1200 Pa·s or more and 3000 Pa·s or less, in order to provide excellent foamability and moldability. In this specification, the melt viscosity is a value measured according to JIS K7199:1999 at a temperature of 200°C and a shear rate of 100 sec ^-1 .

[Physical foaming agent]
The physical blowing agent used in the present invention includes hydrofluoroolefin (hereinafter also referred to as "HFO"). Hydrofluoroolefin (HFO) refers to a fluorine-containing hydrocarbon having a structure in which at least a hydrogen atom and a fluorine atom are bonded to a carbon skeleton having an unsaturated bond. For example, hydrofluoroolefin may have a structure in which a hydrogen atom and a fluorine atom are bonded to a carbon skeleton having an unsaturated bond. In addition, a chlorine atom may be bonded to the carbon skeleton of hydrofluoroolefin in addition to a hydrogen atom and a fluorine atom. That is, the hydrofluoroolefin in this specification is a concept including hydrochlorofluoroolefin (HCFO) having a structure in which a hydrogen atom, a fluorine atom and a chlorine atom are bonded to a carbon skeleton having an unsaturated bond.

HFOs include one or more selected from 1,3,3,3-tetrafluoropropene (hereinafter also referred to as "HFO-1234ze"), 1-chloro-3,3,3-trifluoropropene (hereinafter also referred to as "HFO-1233zd"), 1-chloro-2,3,3,3-tetrafluoropropene (hereinafter also referred to as "HFO-1224yd"), 2,3,3,3-tetrafluoropropene (hereinafter also referred to as "HFO-1234yf"), 1,1,1,4,4,4-hexafluoro-2-butene (hereinafter also referred to as "HFO-1336mzz"), and the like. Hydrofluoroolefins have an ozone depletion potential of zero, a very small global warming potential, low thermal conductivity in the gaseous state, and are non-flammable.

In particular, it is preferable to include an HFO with a molecular weight of 110 or more as a physical foaming agent. By including an HFO with a molecular weight of 110 or more, the HFO is more likely to remain in the extruded foam board having a styrene-acrylonitrile copolymer as the base resin, compared to when an HFO with a molecular weight of less than 110 is included, and the long-term heat insulation of the extruded foam board can be improved. When two or more HFOs with different molecular weights are included, it is preferable that the proportion of HFOs with a molecular weight of 110 or more in 100 mol % of HFO is 60 mol % or more, more preferably 80 mol % or more, and even more preferable that it is 100 mol %, that is, only HFOs with a molecular weight of 110 or more are included.

Furthermore, since HFOs are more likely to remain in an extruded foam board having a styrene-acrylonitrile copolymer as the base resin, and the extruded foam board can have good long-term heat insulation, it is more preferable that the HFO contains one or more selected from the group consisting of 1-chloro-2,3,3,3-tetrafluoropropene (HFO-1224yd), 1-chloro-3,3,3-trifluoropropene (HFO-1233zd), and 1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz). Among these, it is preferable that the HFO is HFO-1224yd. By containing HFO-1224yd as the HFO, even when the HFO content Ch per kg of the extruded foam board described below is relatively large, for example, 0.5 mol or more, the effect of suppressing a decrease in the heat resistance of the extruded foam board is achieved.

The HFO content Ch per 1 kg of extruded foam board is, for example, 0.25 mol or more, and 0.3 mol or more. By keeping the content Ch within the above range, the long-term insulation properties of the extruded foam board are improved.

In order to more reliably increase the long-term thermal conductivity of the extruded foam board, the HFO content Ch per 1 kg of the extruded foam board is preferably 0.5 mol or more, more preferably 0.55 mol or more, and even more preferably 0.6 mol or more. When producing the extruded foam board according to the present invention, for example, by blending the above-mentioned base resin with a predetermined amount of HFO, it is possible to retain the above-mentioned high content of HFO in the obtained extruded foam board.

On the other hand, from the viewpoint of more reliably preventing the occurrence of gas spots that deteriorate the appearance of the extruded foam board and the deterioration of heat resistance, the HFO content Ch per 1 kg of the extruded foam board is preferably 1.3 mol or less, 1.1 mol or less, and more preferably 1.0 mol or less.

The physical foaming agent may contain other physical foaming agents besides HFOs, as long as the purpose and effect of the present invention are not impaired.

Other examples of physical blowing agents include water, alcohol, aliphatic saturated hydrocarbons with 3 to 5 carbon atoms, dialkyl ethers with 1 to 3 carbon atoms (e.g., dimethyl ether and diethyl ether), and carbon dioxide.

From the viewpoint of increasing the compressive strength of the resulting extruded foam board, it is preferable to use an aliphatic saturated hydrocarbon having 3 to 5 carbon atoms among the other physical foaming agents exemplified above. As the aliphatic saturated hydrocarbon having 3 to 5 carbon atoms, for example, one or a mixture of two or more selected from propane, normal butane, isobutane (2-methylpropane), normal pentane, isopentane (2-methylbutane), cyclobutane, neopentane (2,2-dimethylpropane), cyclopentane, etc. can be used. Among these, isobutane can be preferably used.

The content Cc of aliphatic saturated hydrocarbons having 3 to 5 carbon atoms per 1 kg of extruded foam board is, for example, preferably 0.1 mol to 0.6 mol, and more preferably 0.2 mol to 0.5 mol. When the content Cc of aliphatic saturated hydrocarbons having 3 to 5 carbon atoms is within the above range, the compressive strength of the extruded foam board can be improved.

The total amount (Ch+Cc) of the hydrofluoroolefin content Ch per 1 kg of extruded foam board and the aliphatic saturated hydrocarbon content Cc with 3 to 5 carbon atoms per 1 kg of extruded foam board is 0.5 mol or more and 1.3 mol or less, and the ratio of the content Ch to the total amount (Ch+Cc) [Ch/(Ch+Cc)] is more than 0.5. When the total amount (Ch+Cc) and the ratio [Ch/(Ch+Cc)] are within the above range, the long-term heat insulation of the extruded foam board is good.

In the extruded foam board of the present invention, the content Cc of one or more hydrocarbons selected from aliphatic saturated hydrocarbons having 3 to 5 carbon atoms may be 0. In this case, the total amount (Ch+Cc) corresponds to the content Ch, and the ratio [Ch/(Ch+Cc)] is 1.

From the viewpoint of suppressing an increase in the thermal conductivity of the extruded foam board over a long period of time and further improving the thermal insulation, the total amount (Ch + Cc) is preferably 0.52 mol or more per 1 kg of the extruded foam board, more preferably 0.55 mol or more, and even more preferably 0.6 mol or more.

From the viewpoint of more reliably suppressing the risk of the occurrence of numerous gas spots in the resulting extruded foam board, which would deteriorate the appearance of the extruded foam board, and the risk of the heat resistance of the extruded foam board being reduced, the total amount (Ch+Cc) is preferably 1.1 mol or less, more preferably 1.0 mol or less, and even more preferably 0.8 mol or less, per kg of the extruded foam board.

From the viewpoint of more reliably preventing the thermal conductivity of the extruded foam board from increasing over a long period of time and from the viewpoint of obtaining a higher level of flame retardancy, the ratio [Ch/(Ch+Cc)] is preferably 0.55 or more, more preferably 0.6 or more, even more preferably 0.75 or more, and particularly preferably 0.9 or more, and most preferably 1, i.e., does not contain one or more hydrocarbons selected from aliphatic saturated hydrocarbons having 3 to 5 carbon atoms.

In this specification, the content of physical blowing agents (HFOs, aliphatic saturated hydrocarbons) in the extruded foam board is a value measured by the following method using a gas chromatograph. Specifically, a test piece with no molded skin, measuring 500 mm in length, 200 mm in width, and 5 mm in thickness, is cut from the center of the extruded foam board, and the test piece is conditioned by standing in an atmosphere at a temperature of 23°C and a humidity of 50% for 37 days. In this specification, this conditioning method is referred to as method (1). A sample weighing 1 g is cut from the test piece conditioned by method (1), and the content of HFOs and aliphatic saturated hydrocarbons in the extruded foam board is measured by gas chromatographic analysis. The content of physical blowing agents obtained in a 37-day accelerated test with a test piece thickness of 5 mm corresponds to the content of physical blowing agents about 10 years after the manufacture of an extruded foam board with a thickness of 50 mm.

Gas chromatographic analysis is performed as follows. The above sample is precisely weighed and placed in a lidded sample bottle containing 50 mL of toluene (containing approximately 0.02 g of precisely weighed cyclopentane as an internal standard), and the bottle is immediately capped. The sample is then thoroughly stirred to dissolve the physical foaming agent in the sample in the toluene to prepare a measurement sample. Approximately 2 μL of this solution is then taken with a microsyringe and injected into the gas chromatograph to obtain a chromatogram.

The measurement conditions for the gas chromatograph are as follows.
Equipment used: Shimadzu Corporation GC-14B
Column: Shimadzu GC-14B glass column manufactured by Shinwa Kako Co., Ltd. Packed column: Glass column, length 4.1 m x inner diameter 3.2 mm
Stationary phase: Silicone DC550 20%
Support: Chromosorb W AW DMCS (60/80 mesh)
Column temperature: 40°C
Detector: FID
Carrier gas: Nitrogen Carrier gas flow rate: 50 mL/min
Inlet temperature: 200°C
Detector temperature: 200°C
From the resulting gas chromatogram, the peak area of each physical blowing agent component is read, and the HFO content and isobutane content are calculated using the calibration curves of the internal standard and the relative sensitivity of each blowing agent component.

The measurement of the content (residual amount) of the physical foaming agent described above is preferably performed on the extruded foam board immediately after production (for example, within 24 hours after production). The content of the physical foaming agent does not fluctuate significantly within a range of, for example, 10 years ± 1 year after production. Therefore, the content of the physical foaming agent may be measured by the above method for extruded foam boards regardless of the time that has passed since production.

In the present invention, as described above, a specific resin having an acrylonitrile content adjusted within a predetermined range is used as a base resin, and HFO is blended as a physical foaming agent to produce an extruded foam plate, so that the amount of HFO remaining in the resulting extruded foam plate is maintained high for a long period of time. In other words, the extruded foam plate is characterized by a high residual HFO ratio Rh. The residual HFO ratio Rh in the extruded foam plate is expressed by the following formula (1):
Rh = Ch / Bh × 100 (1)

Here, Bh is the amount of HFO (mol/kg) blended per 1 kg of the resulting extruded foam board during production of the extruded foam board, and Ch is the content of HFO (mol/kg) per 1 kg of the extruded foam board, which is a value determined by the accelerated test using the above-mentioned method (1). In the extruded foam board obtained by the present invention, the residual rate Rh of HFO in the extruded foam board is preferably 65% or more, more preferably 70% or more, and even more preferably 75% or more. There is no particular upper limit for the residual rate Rh of HFO in the extruded foam board, but it is generally about 90%.

When the physical foaming agent contains one or more hydrocarbons selected from aliphatic saturated hydrocarbons having 3 to 5 carbon atoms, the ratio (Rh/Rc) of the residual rate Rh of HFO in the extruded foam plate to the residual rate Rc of one or more hydrocarbons selected from aliphatic saturated hydrocarbons having 3 to 5 carbon atoms in the extruded foam plate is preferably 0.8 or more, more preferably 0.85 or more, and even more preferably 0.9 or more. The residual rate Rc of one or more hydrocarbons selected from aliphatic saturated hydrocarbons having 3 to 5 carbon atoms in the extruded foam plate is expressed by the following formula (2).
Rc = Cc / Bc × 100 (2)

Here, Bc is the amount (mol/kg) of one or more hydrocarbons selected from aliphatic saturated hydrocarbons having 3 to 5 carbon atoms that are blended during the production of the extruded foam board per 1 kg of the resulting extruded foam board, and Cc is the content (mol/kg) of one or more hydrocarbons selected from aliphatic saturated hydrocarbons having 3 to 5 carbon atoms per 1 kg of the extruded foam board, and is a value determined by the accelerated test using the method (1) described above.

[Radiation suppressant]
The extruded foam board of the present invention may contain graphite as a radiation suppressant in order to improve the heat insulating property. By containing graphite as a radiation suppressant, the effect of improving the heat insulating property can be enhanced.

Examples of graphite include flake graphite, scaly graphite, artificial graphite, and earthy graphite, and it is preferable to use graphite whose main component is flake graphite. Graphite is preferably added as a master batch mixed at a high concentration with a base resin. Graphite with a fixed carbon content of 80% or more is preferable because it has good workability when producing a master batch and has an excellent effect of improving the insulation of the resulting extruded foam board. In addition, in order to further improve the insulation of the extruded foam board, graphite with a fixed carbon content of 90% or more is more preferable, and graphite with a fixed carbon content of 95% or more is even more preferable. The upper limit of the fixed carbon content is approximately 100%. The fixed carbon content of graphite refers to a value measured by a method conforming to JIS M8511:2014.

When graphite is contained, the content of graphite is, for example, 0.1 parts by mass or more and 5 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 radiation suppression effect of graphite is more easily exhibited. In addition, it is possible to suppress an excessive decrease in the apparent density of the extruded foam board and a deterioration in the surface condition. From the viewpoint of more reliably exhibiting the above effects, it is more preferable that the amount of graphite added is 0.3 parts by mass or more per 100 parts by mass of the base resin, and even more preferable that it is 0.5 parts by mass or more. On the other hand, the upper limit of the amount of graphite added is more preferably 3 parts by mass or more and even more preferably 1 part by mass per 100 parts by mass of the base resin.

The extruded foam board of the present invention may contain a radiation suppressor other than graphite to further improve the 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, infrared shielding pigments, hydrotalcite, etc. Among these, titanium oxide is preferably used. The content of the radiation suppressor other than graphite is, for example, 0.5 parts by mass or more and 5 parts by mass or less, and preferably 1 part by mass or more and 4 parts by mass or less, relative to 100 parts by mass of the base resin.

[Flame retardants]
The extruded foam board of the present invention is used mainly as a heat insulating material for building materials, and flame retardancy is imparted to the board by the inclusion of a flame retardant in the base resin.

The amount of flame retardant blended is preferably 0.5 to 8 parts by mass, more preferably 2 to 7 parts by mass, and even more preferably 2.5 to 6 parts by mass, per 100 parts by mass of the base resin, since it can impart a high level of flame retardancy to the extruded foam board and also suppress deterioration in foamability and mechanical properties. If the amount of flame retardant blended is within the above range, the flame retardant will not inhibit foamability, and an extruded foam board can be obtained that has a high level of flame retardancy, such as the flammability standard for extruded polystyrene foam insulation described in "Test Method A" in the flammability test method of JIS A9521:2017.

The flame retardant used in the present invention is not particularly limited, but it is preferable to use a brominated flame retardant. Examples of brominated flame retardants include brominated butadiene polymers such as brominated styrene-butadiene 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-S-bis One or more selected from the following may be used in combination: brominated bisphenol compounds represented by tetrabromobisphenol-F-bis(2,3-dibromopropyl ether), tetrabromobisphenol-F-bis(2,3-dibromopropyl ether), brominated isocyanurates represented by tris(2,3-dibromopropyl)isocyanurate, mono(2,3,4-tribromobutyl)isocyanurate, di(2,3,4-tribromobutyl)isocyanurate, and tris(2,3,4-tribromobutyl)isocyanurate. From the viewpoint of improving flame retardancy, it is preferable that the flame retardant is a brominated styrene-butadiene copolymer among these. In particular, it is preferable that the main component of the flame retardant is a brominated styrene-butadiene copolymer. The main component of the flame retardant is a brominated styrene-butadiene copolymer, which means that the content of the brominated styrene-butadiene copolymer in the flame retardant is 50% by mass or more, preferably 70% by mass or more, more preferably 80% by mass or more, and even more preferably 90% by mass or more. The upper limit of the content of the brominated styrene-butadiene copolymer in the flame retardant is not particularly limited, and may be 100% by mass.

From the viewpoint of improving flame retardancy, the amount of brominated styrene-butadiene copolymer is preferably 0.5 parts by mass or more and 8 parts by mass or less, more preferably 1 part by mass or more and 6 parts by mass or less, and even more preferably 2 parts by mass or more and 5 parts by mass or less, per 100 parts by mass of the base resin.

In an extruded foam board using a styrene-acrylonitrile copolymer as the base resin, if a brominated styrene-butadiene copolymer is used as the flame retardant, the desired flame retardancy may not be achieved. In the extruded foam board of the present invention, as described above, good flame retardancy can be achieved even when a brominated styrene-butadiene copolymer is used as the flame retardant. The reason for this is unclear, but one possible reason is that a relatively large amount of hydrofluoroolefin is included as a physical foaming agent.

Furthermore, from the viewpoint of more stable expression of flame retardancy when a brominated styrene-butadiene copolymer is used as the flame retardant, it is preferable to contain a brominated bisphenol-based flame retardant such as tetrabromobisphenol A-bis(2,3-dibromopropyl ether) or tetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl ether) in addition to the brominated styrene-butadiene copolymer. In consideration of the above circumstances, it is preferable that the flame retardant contains a brominated styrene-butadiene copolymer and a brominated bisphenol.

From the viewpoint of improving flame retardancy without impairing moldability, the amount of brominated bisphenol flame retardant is preferably 0.1 to 1 part by mass, more preferably 0.2 to less than 1 part by mass, and even more preferably 0.3 to 0.9 parts by mass. From the same viewpoint, the ratio of the brominated bisphenol content to the brominated styrene-butadiene copolymer content (brominated bisphenol content/brominated styrene-butadiene copolymer content) is preferably 0.05 to 0.3, more preferably 0.1 to 0.25.

In addition to the bromine-based flame retardants, one or more compounds selected from the following may be used in combination: 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, melem, and other nitrogen-containing cyclic compounds; silicone-based compounds; inorganic compounds such as boron oxide, zinc borate, and zinc sulfide; phosphoric acid esters such as triphenyl phosphate, red phosphorus, ammonium polyphosphate, phosphazene, hypophosphites, and other phosphorus-based compounds.

[Flame retardant synergist]
In addition, the extruded foam board of the present invention may contain a flame retardant auxiliary in combination with the flame retardant for the purpose of further improving the flame retardancy. Examples of the flame retardant auxiliary 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 auxiliary is, for example, 0.01 parts by mass or more and 1 part by mass or less, and preferably 0.05 parts by mass or more and 0.5 parts by mass or less, relative to 100 parts by mass of the base resin.

The extruded foam board of the present invention may contain other additives known in the base resin as necessary. Examples of other additives include cell regulators, colorants such as pigments and dyes, heat stabilizers, and fillers.

[Foam regulator]
In the extruded foam board of the present invention, it is preferable to include a bubble regulator. As the bubble regulator, inorganic powders such as talc, kaolin, mica, silica, calcium carbonate, barium sulfate, titanium oxide, clay, aluminum oxide, bentonite, and diatomaceous earth can be used. Among them, talc is preferable because it is easy to adjust the bubble diameter and easy to reduce the bubble diameter without inhibiting flame retardancy, and fine talc with a 50% particle size (light transmission centrifugal sedimentation method) of 0.1 μm to 20 μm is particularly preferable, and fine talc with a 50% particle size (light transmission centrifugal sedimentation method) of 0.5 μm to 15 μm is preferable. The amount of the bubble regulator to be added varies depending on the type of regulator, the target bubble diameter, etc., but when talc is used as the bubble regulator, the content of talc is preferably 0.1 parts by mass to 7 parts by mass per 100 parts by mass of the base resin, more preferably 0.2 parts by mass to 5 parts by mass, and even more preferably 0.3 parts by mass to 3 parts by mass.

[Heat stabilizer]
The heat stabilizer can improve the thermal stability of the bromine-based flame retardant by blending it with the raw material or scraps when producing an extruded foam board or when recycling and repelletizing scraps of an extruded foam board. Examples of the heat stabilizer include one or more heat stabilizers selected from bisphenol-type epoxy compounds and novolac-type epoxy compounds such as 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 heat stabilizer added is preferably 0.1 parts by mass or more and 40 parts by mass or less with respect to 100 parts by mass of the total amount of the flame retardant.

[Apparent density]
The apparent density of the extruded foam board according to the present invention is, for example, 20 kg/m ³ to 50 kg/m ³ , preferably 20 kg/m ³ to 45 kg/m ³ , and more preferably 25 kg/m ³ to 40 kg/m ³ . When the apparent density is within the above range, the foam board has sufficient mechanical strength and is suitable for use as a heat insulating material having excellent light weight.

The apparent density was measured in accordance with JIS K6767 (1999). Rectangular samples measuring 50 mm long x 50 mm wide x 50 mm thick were cut from three locations, namely the widthwise center and both widthwise ends, of each extruded foam plate, and the apparent density of each sample was measured. The arithmetic mean of the measurements at the three locations was used as the apparent density.

[Closed bubble ratio]
The closed cell ratio of the extruded foam board is, for example, 85% or more, preferably 90% or more, and more preferably 93% or more. If the closed cell ratio is within the above range, the foaming agent is more likely to remain in the bubbles, and the extruded foam board can maintain high thermal insulation properties for a long period of time.

The closed cell ratio 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 type specific gravity meter Model 930 (a cut sample without a molded skin cut to a size of 25 mm x 25 mm x 20 mm is placed in a sample cup for measurement. However, if the thickness is too thin to cut a 20 mm cut sample in the thickness direction, for example, two cut samples of a size of 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 ratio S (%) using the following formula (3), and the average value of N = 3 is obtained.

S(%)=(Vx-W/ρ)×100/( _VA -W/ρ) (3)
Vx: true volume (cm ³ ) of the cut sample measured by the above method (corresponding 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 portion of the cut sample).
V _A : Apparent volume (cm ³ ) of the cut sample calculated from the outer dimensions of the cut sample used in the measurement
W: total mass (g) of cut sample used for measurement
ρ: density of the resin constituting the extruded foam board (g/cm ³ )

[Average bubble diameter in thickness direction]
The average bubble diameter in the thickness direction of the extruded foam plate is preferably 50 μm or more, more preferably 80 μm or more, from the viewpoint of further suppressing the emission of hydrofluoroolefin from the extruded foam plate. On the other hand, from the viewpoint of suppressing radiative heat transfer and further enhancing heat insulation, the average bubble diameter in the thickness direction is preferably 300 μm or less, more preferably 200 μm or less, and even more preferably 150 μm or less.

The method for measuring the average bubble diameter in the thickness direction is as follows. The average bubble diameter in the thickness direction is determined by taking enlarged photographs of three locations, the center and both ends of the cross section perpendicular to the width direction of the extruded foam board, adjusting the magnification to a range of 50x to 200x so that the number of cells in the photograph is approximately 200 to 500, measuring the maximum diameter of each bubble in the thickness direction on each photograph using image processing software NS2K-pro manufactured by Nano Systems Co., Ltd., and taking the arithmetic average of these values.

[Bubble deformation rate]
Further, in the extruded foam board, the bubble deformation ratio is preferably 0.7 or more and 1.5 or less. The bubble deformation ratio is a value calculated by measuring the maximum diameter of each bubble in the width direction using the image processing software NS2K-pro manufactured by Nano System Co., Ltd., as well as the average bubble diameter in the thickness direction, for an enlarged photograph of the bubbles, and calculating the average bubble diameter in the width direction by arithmetically averaging the values, and dividing the average bubble diameter in the thickness direction by the average bubble diameter in the width direction. The smaller the bubble deformation ratio is than 1, the flatter the bubbles are, and the larger it is than 1, the longer the bubbles are. By having the bubble deformation ratio within the above range, the extruded foam board has excellent mechanical strength and higher thermal insulation. In addition, the shrinkage of the extruded foam board is more easily suppressed, and the extruded foam board has better dimensional stability. The lower limit of the bubble deformation ratio is more preferably 0.8 from the viewpoint of dimensional stability of the extruded foam board. In addition, the upper limit of the bubble deformation ratio is more preferably 1.3, and even more preferably 1.2, from the viewpoint of the effect of improving thermal insulation.

[Shape, cross-sectional area and dimensions]
The extruded foam plate of the present invention is in the form of a plate. The cross-sectional area perpendicular to the extrusion direction of the extruded foam plate is ¹⁰⁰ cm2 or more, preferably ²⁰⁰ cm2 or more, more preferably ³⁰⁰ cm2 or more, and even more preferably ⁴⁰⁰ cm2 or more. The upper limit of the cross-sectional area perpendicular to the extrusion direction is about 1500 ^cm2 . In this specification, the cross-sectional area perpendicular to the extrusion direction refers to the area of the cross section of the extruded foam plate perpendicular to the extrusion direction.

When an extruded foam board is used as a heat insulating material, the thickness of the extruded foam board is preferably 20 mm or more, more preferably 30 mm or more, and even more preferably 50 mm or more. On the other hand, the upper limit of the thickness of the extruded foam board is generally about 150 mm.

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 approximately 1200 mm.

[Thermal conductivity]
The thermal conductivity of the extruded foam board is, for example, 0.028 W/m·K or less, preferably 0.027 W/m·K or less, and more preferably 0.026 W/m·K or less. The method for measuring the thermal conductivity in the present invention is as follows.

The thermal conductivity of the present invention is measured by the following method, which conforms to the accelerated test described in ISO 11561, except for changing the thickness of the test piece. This standard uses an accelerated test to determine the long-term change in thermal conductivity due to the diffusion of the foaming agent from an extruded foam board. Specifically, it is as follows. First, a test piece is obtained from the extruded foam board by the following method (method (1)). A test piece without a molded skin, measuring 500 mm in length x 200 mm in width x 5 mm in thickness, is cut out from the center of the extruded foam board, and the test piece is left to stand in an atmosphere at a temperature of 23°C and a humidity of 50% for 37 days to condition it. Then, the thermal conductivity is measured using the test piece obtained by the above method based on the flat plate heat flow meter method described in JIS A1412-2:1999 (two heat flow meter method, high temperature side 38°C, low temperature side 8°C, average temperature 23°C).

In the accelerated test described in ISO 11561, the thickness of the test piece is 6 mm or more, but in the present invention, the thickness of the test piece was set to 5 mm for convenience. The thermal conductivity obtained in the 37-day accelerated test with the test piece thickness of 5 mm corresponds to the thermal conductivity of an extruded foam board with a thickness of 50 mm, for example, about 10 years after its manufacture.

[Dimensional change rate]
The dimensional change rate of the extruded foam plate after heating for 22 hours in an atmosphere at 75 ° C. is preferably within ± 1%, for example. Specifically, when the dimension of the extruded foam plate after heating for 22 hours in an atmosphere at 75 ° C. is Da, and the dimension of the extruded foam plate before heating is Db, the dimensional change rate of the extruded foam plate after heating [(Da-Db)/Db x 100] is within ± 1%. In each of the thickness direction, width direction, and length direction, the dimensional change rate when the extruded foam plate is heated for 22 hours in an atmosphere at 75 ° C. is preferably within ± 1%. The dimensional change rate means the dimensional change rate due to shrinkage and expansion caused by heating. If the dimensional change rate of the extruded foam plate at 75 ° C. is within the above range, it can be said that the heat resistance is particularly good. The dimensional change rate of the extruded foam plate at 75 ° C. is more preferably within ± 0.8%.

The dimensional change rate can be measured by the following method. Specifically, the extruded foam board is first left to stand in an environment at 23°C for 12 hours. After standing, a test piece without a skin surface is cut out from the extruded foam board with dimensions of 25 mm in thickness direction, 100 mm in extrusion direction, and 100 mm in width direction. The dimensions Db of the cut test piece in each direction (VD, MD, TD) are measured. VD is the thickness direction, MD is the extrusion direction, and TD is the width direction. The test piece is then placed in an oven adjusted to a predetermined temperature (75°C), and after 22 hours, the test piece is removed and the dimensions Da of each direction (VD, MD, TD) are measured. Then, the dimensional change rate [(Da-Db)/Db x 100] in each direction is calculated. The largest value among the obtained dimensional change rates in each direction is taken as the dimensional change rate of the extruded foam board after heating for 22 hours in an atmosphere of 75°C.

<Method of manufacturing extruded thermoplastic resin foam board>
An example of the method for producing an extruded thermoplastic resin foam plate of the present invention will be described in detail below. The method for producing an extruded thermoplastic resin foam plate of the present invention (hereinafter, simply referred to as "extruded foam plate") includes, for example, a step of extruding and foaming a foamable molten resin composition containing a base resin, a flame retardant, and a physical foaming agent, and molding the composition into a plate shape using a molding tool, and is a method for producing an extruded thermoplastic resin foam plate having an apparent density of 20 kg/ ^m3 or more and 50 kg/ ^m3 or less, a cross-sectional area perpendicular to the extrusion direction of ¹⁰⁰ cm2 or more, and a thickness of 20 mm or more and 150 mm or less. However, the method for producing an extruded thermoplastic resin foam plate of the present invention is not limited to the following examples.

In summary, the manufacturing method of the present invention involves, for example, adding additives such as a flame retardant and a bubble regulator to a base resin, feeding the base resin into an extruder, and heating and kneading the base resin. Next, a physical foaming agent is pressed into the extruder and further kneaded to form a foamable molten resin composition, which is then extruded from a high-pressure region to a low-pressure region (usually into the atmosphere) to cause foaming. The resulting foam is then shaped into a plate using a shaping device (such as a guider) connected to the die outlet of the extruder, to produce a thermoplastic resin extrusion foam plate. As the shaping device, for example, a device consisting of a pair of upper and lower polytetrafluoroethylene plates is used. As the base resin, the above-mentioned materials can be used.

[Physical foaming agent]
The physical foaming agent used in the present invention can be the one described above. The amount Ah of HFO per 1 kg of base resin is, for example, 0.4 mol or more and 1.3 mol or less. By setting the amount Ah of HFO within the above range, the amount Ch of HFO remaining in the obtained extruded foam board can be further increased. As a result, an extruded foam board with excellent long-term heat insulation can be obtained.

In order to further improve the long-term insulation properties of the resulting extruded foam board, the compounding amount Ah is preferably 0.45 mol or more, more preferably 0.5 mol or more, even more preferably 0.6 mol or more, and particularly preferably 0.7 mol or more.

On the other hand, from the viewpoint of more reliably suppressing the risk of the occurrence of numerous gas spots that would deteriorate the appearance of the extruded foam board and the risk of a decrease in heat resistance, the compounding amount Ah is preferably 1.1 mol or less, more preferably 1.0 mol or less, and even more preferably 0.9 mol or less.

The proportion of HFO in the total amount of physical foaming agent (100 mol%) is, for example, 25 mol% or more, preferably 30 mol% or more, more preferably 40 mol% or more, even more preferably 50 mol% or more, and particularly preferably 55 mol% or more, from the viewpoint of improving heat insulation. The upper limit of the amount of HFO in the total amount of physical foaming agent (100 mol%) may be 100 mol%, but from the viewpoint of more reliably suppressing gas spots, it is preferably 80 mol%, more preferably 70 mol%.

The physical foaming agent may contain other physical foaming agents besides HFOs, as long as the purpose and effect of the present invention are not impaired.

Other examples of physical blowing agents include water, alcohol, aliphatic saturated hydrocarbons with 3 to 5 carbon atoms, dialkyl ethers with 1 to 3 carbon atoms (e.g., dimethyl ether and diethyl ether), and carbon dioxide.

From the viewpoint of increasing the compressive strength of the extruded foam board, it is preferable to use an aliphatic saturated hydrocarbon having 3 to 5 carbon atoms among the other physical foaming agents exemplified above. As the aliphatic saturated hydrocarbon having 3 to 5 carbon atoms, for example, one or a mixture of two or more selected from propane, normal butane, isobutane (2-methylpropane), normal pentane, isopentane (2-methylbutane), cyclobutane, neopentane (2,2-dimethylpropane), cyclopentane, etc. can be used. Among these, isobutane can be preferably used.

The amount Ac of the aliphatic saturated hydrocarbon having 3 to 5 carbon atoms per 1 kg of the base resin is, for example, preferably 0.1 mol or more and 0.6 mol or less, and more preferably 0.2 mol or more and 0.5 mol or less. By keeping the amount Ac within the above range, the compressive strength of the extruded foam board can be increased.

It is preferable that the sum (Ah+Ac) of the amount Ah of HFO per 1 kg of base resin and the amount Ac of the aliphatic saturated hydrocarbon with 3 to 5 carbon atoms per 1 kg of base resin is 0.5 mol or more, and that the ratio [Ah/(Ah+Ac)] of the amount Ah to the total (Ah+Ac) is greater than 0.5. By having the total amount (Ah+Ac) and the ratio [Ah/(Ah+Ac)] within the above range, the long-term heat insulation of the resulting extruded foam board can be improved.

From the viewpoint of further improving the thermal insulation properties of the extruded foam board, the total amount (Ah+Ac) is preferably 0.6 mol or more, and more preferably 0.7 mol or more, per 1 kg of base resin.

On the other hand, from the viewpoint of more reliably preventing the occurrence of numerous gas spots that would deteriorate the appearance of the extruded foam board and more reliably preventing the heat resistance of the extruded foam board from decreasing, the total amount (Ah+Ac) is preferably 1.3 mol or less, more preferably 1.1 mol or less, and even more preferably 1.0 mol or less, per 1 kg of base resin.

From the viewpoint of improving the long-term heat insulation and flame retardancy of the extruded foam board, the ratio [Ah/(Ah+Ac)] is preferably 0.55 or more, more preferably 0.65 or more, and even more preferably 0.75 or more. The upper limit of the ratio [Ah/(Ah+Ac)] is 1.0.

From the viewpoint of suppressing gas spots and improving the appearance of the extruded foam board, it is preferable to use water and/or alcohol (i.e., one or both of water and alcohol) among the other physical foaming agents mentioned above, and it is even more preferable to use both water and alcohol.

When both water and alcohol are used, there are no restrictions on the mixing ratio of the two, but water:alcohol = 90 mol%:10 mol%-50 mol%:50 mol% is preferred, and 80 mol%:20 mol%-60 mol%:40 mol% is more preferred.

As the alcohol, aliphatic alcohols having 1 to 5 carbon atoms are preferred. Examples include 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, 3-methyl-2-butanol, etc., which can be used alone or in combination of two or more. From the viewpoint of improving the appearance of the extruded foam board, ethanol is preferably used among these.

The ratio of the amount of water and/or alcohol per kg of base resin to the amount of HFO Ah per kg of base resin [(amount of water and/or alcohol)/amount of HFO] is, for example, 0.3 to 2.5. From the viewpoint of improving the surface condition of the extruded foam board, [(amount of water and/or alcohol)/amount of HFO] is preferably 0.4 to 2, more preferably 0.5 to 1.5, and even more preferably 0.6 to 1.2. The amount of water and/or alcohol is preferably 0.2 mol or more, more preferably 0.3 mol or more, and even more preferably 0.4 mol or more per kg of base resin. The upper limit of the amount of water and/or alcohol is, for example, 0.8 mol per kg of base resin.

From the viewpoint of more reliably exerting the effect of suppressing gas spots and improving the appearance of the extruded foam board, the amount of water and/or alcohol to be blended is preferably 0.2 mol or more, more preferably 0.3 mol or more, even more preferably 0.4 mol or more, and particularly preferably 0.5 mol or more, per 1 kg of base resin. The upper limit of the amount of water and/or alcohol to be blended is, for example, 0.8 mol per 1 kg of base resin. The amount of water to be blended is, for example, 0.1 mol or more and 0.6 mol or less, preferably 0.3 mol or more and 0.5 mol or less, per 1 kg of base resin. It is preferably 0.05 mol or more and 0.3 mol or less, and more preferably 0.1 mol or more and 0.2 mol or less.

The total amount of physical foaming agent is preferably, for example, 0.8 mol or more and 1.8 mol or less per 1 kg of base resin. From the viewpoint of more easily obtaining an extruded foam board with a desired apparent density, the total amount of physical foaming agent is preferably 1.0 mol or more per 1 kg of base resin. On the other hand, from the viewpoint of further suppressing the occurrence of gas spots due to separation of the foaming agent from the extruded foam board, the total amount of physical foaming agent is preferably 1.6 mol or less per 1 kg of base resin.

[Radiation suppressant]
In the production method of the present invention, various additives such as the above-mentioned radiation suppressant, flame retardant, flame retardant assistant, and heat stabilizer can be used.

In addition, in the manufacturing method of the present invention, other known additives can be appropriately blended with the base resin as necessary. Examples of other additives include various additives such as cell regulators, colorants such as pigments and dyes, heat stabilizers, and fillers.

In the manufacturing method of the present invention, the method of blending the flame retardant and other additives into the base resin can be a method of feeding a predetermined ratio of the flame retardant and other additives together with the base resin to a feed section provided upstream of the extruder and kneading them in the extruder. Alternatively, a method of feeding the flame retardant and other additives into the molten resin from a feed section provided midway through the extruder can also be used.

Specifically, a method of feeding a dry blend of the flame retardant, other additives, and base resin to an extruder and melt-kneading it, a method of feeding a melt-kneaded product obtained by kneading the flame retardant, other additives, and base resin using a kneader or the like to an extruder, a method of preparing a master batch in which a high concentration of the flame retardant and other additives is blended with the base resin in advance, feeding this to an extruder and melt-kneading it with the base resin, and the like can be adopted. In particular, from the viewpoint of dispersibility, it is preferable to adopt a method of preparing a flame retardant master batch and feeding it to an extruder. The flame retardant master batch is preferably prepared by using a base resin having a melt flow rate of about 0.5 to 30 g/10 min at 200°C and a load of 5 kg as the base resin, and adjusting it so that the flame retardant is contained in the master batch by 10 to 95 mass%, more preferably by adjusting it to contain 30 to 90 mass%, and even more preferably by adjusting it to contain 50 to 85 mass%.

The present invention will be described in detail below with reference to examples. However, the present invention is not limited to the contents of the examples.

In the examples and comparative examples, the following extrusion equipment and raw materials were used for production.

[Extrusion device]
An extrusion device was used in which a first extruder with an inner diameter of 180 mm and a second extruder with an inner diameter of 225 mm were connected in series, an inlet for a physical foaming agent was provided near the end of the first extruder, and a flat die equipped with a resin outlet (die lip) with a rectangular cross section with a gap of 2.5 mm and a width of 400 mm was connected to the outlet of the second extruder. A shaping device (guider) consisting of a pair of upper and lower polytetrafluoroethylene resin plates was attached to the resin outlet of the flat die so that the upper and lower resin plates were parallel to each other.

<1> Base resin Details of the base resin used are shown in Table 1. The melt viscosity of the thermoplastic resin in Table 1 was measured by the following method using a Capillograph 1D manufactured by Toyo Seiki Seisakusho Co., Ltd. A capillary with a hole diameter of 1.0 mm and a length of 10.0 mm was attached to the tip of a cylinder with a cylinder diameter of 9.55 mm and a length of 350 mm, and the cylinder and capillary were heated to 200°C, after which a measurement sample (resin pellets) was filled in the cylinder and sufficiently melted by preheating for 4 minutes, and the melt viscosity of the resin was measured under the condition of a shear rate of 100 sec-1.

<2> Flame retardant Brominated styrene-butadiene copolymer (manufactured by LANXESS AG: "Emerald innovation 3000")
Brominated bisphenol (Suzuhiro Chemical Co., Ltd.: FCP-680, tetrabromobisphenol A-bis(2,3-dibromopropyl ether))

<3> Foam adjuster: Talc (manufactured by Matsumura Sangyo Co., Ltd.: High Filler #12, particle size (d50) 7.5 μm)

<4> Radiation suppressant: Graphite (manufactured by Nippon Graphite Industry Co., Ltd.: CP-N (flake graphite), primary particle size (d50) = 13.5 μm, fixed carbon content 99%)

<5> Physical foaming agent: Hydrofluoroolefin (HFO)
1-Chloro-3,3,3-trifluoropropene (HFO-1224yd): manufactured by AGC 1-Chloro-3,3,3-trifluoropropene (HFO-1233zd): manufactured by Honeywell Trans-1,3,3,3-tetrafluoropropene (HFO-1234ze): manufactured by Honeywell Cis-1,1,1,4,4,4-hexafluoro-2-butene (HFO-1336mzz): manufactured by Mitsui-Chemours Fluoroproducts, Isobutane (i-Bu)
・Water ・Ethanol (EtOH)
Dimethyl ether (DME)

The base resin, flame retardant and cell regulator shown in Table 2 were fed to the first extruder, heated to 200°C and kneaded, and the physical foaming agent shown in Table 2 was fed from the physical foaming agent inlet provided in the first extruder, and further kneaded to form a foamable resin melt. Next, the obtained foamable resin melt was transferred to the second extruder to adjust the resin temperature, and then extruded into a guider at a discharge rate of 700 kg/hr, and passed through the guider while foaming to form (shape) a plate-like shape to obtain a base plate of an extruded foam plate with a thickness of 55 mm. Then, the molded skins on both sides of the base plate were evenly cut to produce a plate-like extruded foam plate (width: 910 mm, length: 2000 mm, thickness: 50 mm, cross-sectional area perpendicular to the extrusion direction: 455 cm ² ). The extruded foam plate after production was left at rest at a temperature of 23°C and 50% RH for 24 hours, and was subjected to the following evaluations of <1> to <10>.

The extruded foam board obtained was evaluated for the following items <1> to <10>. Table 2 shows the evaluation results for items <1> to <10>.

<1> Apparent density The apparent density was measured in accordance with JIS K6767 (1999). Rectangular samples measuring 50 mm long x 50 mm wide x 50 mm thick were cut out from three locations, namely, the center and both ends in the width direction, of each extruded foam plate, and the apparent density of each sample was measured. The arithmetic mean of the measurements at the three locations was taken as the apparent density.

<2> Closed cell ratio The closed cell ratio of the extruded foam plate was calculated from the true volume Vx of the extruded foam plate measured using an air comparison type specific gravity meter (manufactured by Toshiba Beckman Co., Ltd., air comparison type specific gravity meter, model: 930) according to procedure C of ASTM-D2856-70, using the following formula (3) similar to that described above. The average value of N=3 was taken as the closed cell ratio.

S(%)=(Vx-W/ρ)×100/( _VA -W/ρ) (3)
Vx: true volume (cm ³ ) of the cut sample measured by the above method (corresponding 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 portion of the cut sample).
V _A : Apparent volume (cm ³ ) of the cut sample calculated from the outer dimensions of the cut sample used in the measurement
W: total mass (g) of cut sample used for measurement
ρ: density of the resin constituting the extruded foam board (g/cm ³ )

<3> Average bubble diameter in the thickness direction The average bubble diameter in the thickness direction was determined as follows: Enlarged photographs were taken at 100x magnification at three locations, namely, the center and both ends of the cross section perpendicular to the width direction of the obtained extruded foam plate, and the maximum diameter of each bubble in the thickness direction was measured on each photograph using image processing software NS2K-pro manufactured by Nano System Co., Ltd., and the average of these values was calculated.

<4> Bubble Deformation Ratio The bubble deformation ratio was determined in the same manner as in the measurement of the bubble diameter in the thickness direction, by measuring the maximum diameter of each bubble in the width direction on an enlarged photograph of the bubbles using image processing software NS2K-pro manufactured by Nano System Co., Ltd., and calculating the arithmetic average of these values to determine the average bubble diameter in the width direction, and then dividing the average bubble diameter in the thickness direction by the average bubble diameter in the width direction.

<5> Content of physical blowing agent (HFO, isobutane) (Ch, Cc)
The HFO content Ch per 1 kg of the extruded foam plate and the isobutane content Cc per 1 kg of the extruded foam plate were determined. The content Ch and the content Cc were determined by a method using a gas chromatograph as follows.

Specifically, a test piece with no molded skin, measuring 500 mm in length, 200 mm in width, and 5 mm in thickness, was cut from the center of the extruded foam plate, and the test piece was conditioned by being left at rest for 37 days in an atmosphere with a temperature of 23°C and a humidity of 50% (i.e., method (1)). Five samples weighing approximately 1 g were cut out from the test piece. The samples were selected at five points at 20 mm intervals along the length direction near the center of the width direction of the test piece, and a sample weighing 1 g was cut out from each point with the same thickness (i.e., 5 mm). A gas chromatographic analysis was performed to measure the content of HFO and aliphatic saturated hydrocarbons in the extruded foam plate. The measured content was converted into units to determine the content of HFO and isobutane per 1 kg of the extruded foam plate (mol/kg). The arithmetic average values of the HFO and isobutane contents (mol/kg) per 1 kg of extruded foam board obtained from the five samples were taken as the HFO content Ch (mol/kg) per 1 kg of extruded foam board and the isobutane content Cc (mol/kg) per 1 kg of extruded foam board.

Gas chromatographic analysis was performed as follows. The above sample was precisely weighed and placed in a lidded sample bottle containing 50 mL of toluene (containing approximately 0.02 g of precisely weighed cyclopentane as an internal standard), and the bottle was immediately capped. The sample was then thoroughly stirred to dissolve the physical foaming agent in the sample in the toluene to prepare a measurement sample. Approximately 2 μL of this solution was taken with a microsyringe and injected into the gas chromatograph to obtain a chromatogram.

The measurement conditions for the gas chromatograph are as follows.
Equipment used: Shimadzu Corporation GC-14B
Column: Shimadzu GC-14B glass column manufactured by Shinwa Kako Co., Ltd. Packed column: Glass column, length 4.1 m x inner diameter 3.2 mm
Stationary phase: Silicone DC550 20%
Support: Chromosorb W AW DMCS (60/80 mesh)
Column temperature: 40°C
Detector: FID
Carrier gas: Nitrogen Carrier gas flow rate: 50 mL/min
Inlet temperature: 200°C
Detector temperature: 200°C
From the resulting gas chromatogram, the peak area of each physical blowing agent component was read, and the HFO content and isobutane content were calculated using the calibration curves of the internal standard and the relative sensitivity of each blowing agent component.

The residual HFO rate Rh was calculated from the HFO content Ch per kg of extruded foam board using the following formula (4). Specifically, the residual HFO rate Rh was calculated by dividing the HFO content Ch per kg of extruded foam board by the HFO blending amount Bh per kg of extruded foam board added during the production of the extruded foam board, and multiplying the result by 100 to convert it into a percentage. Similarly, the residual isobutane rate Rc was calculated from the aliphatic saturated hydrocarbon content Cc per kg of extruded foam board using the following formula (5).
Rh = Ch / Bh × 100 (4)
Rc = Cc / Bc × 100 (5)

<6> Thermal insulation The thermal insulation was evaluated by measuring the thermal conductivity of the extruded foam board. The thermal conductivity of the extruded foam board was measured in accordance with the accelerated test described in ISO 11561, except for changing the thickness of the test piece. This standard determines the long-term change in thermal conductivity due to the diffusion of the foaming agent from the extruded foam board by an accelerated test. Specifically, it is as follows. A test piece without a molded skin, measuring 500 mm in length x 200 mm in width x 5 mm in thickness, is cut out from the center of the extruded foam board, and the test piece is conditioned by being left at rest for 37 days in an atmosphere at a temperature of 23°C and a humidity of 50%. The thermal conductivity is measured using the test piece based on the flat plate heat flow meter method (two heat flow meter plates, high temperature side 38°C, low temperature side 8°C, average temperature 23°C) described in JIS A1412-2:1999.

According to the measured thermal conductivity, the thermal insulation was evaluated according to the following criteria.
A: 0.026 W/m.K or less B: 0.026 W/m or more but less than 0.027 W/m.K C: 0.027 W/m.K or more

<7> Appearance Appearance was evaluated by visually observing gas spots (excessively large bubbles having a diameter of 2 mm or more observed on the surface and cross section due to separation of the foaming agent generated during extrusion foaming) in the obtained base plate. The evaluation criteria for appearance are as follows.
◎: Almost no gas spots were observed on the surface of the original plate and on a cross section perpendicular to the extrusion direction. ◯: A few gas spots were observed on the surface of the original plate and on a cross section perpendicular to the extrusion direction. ×: Many gas spots were observed on the surface of the original plate and on a cross section perpendicular to the extrusion direction.

<8> Heat resistance Heat resistance was evaluated by measuring the dimensional change rate after heating the extruded foam board for 22 hours at each of several temperatures (55, 60, 65, 70, 75, and 80° C.). The dimensional change rate was measured specifically as follows.

First, the extruded foam plate was left to stand for 12 hours in an environment of 23°C. After standing, a test piece without a skin surface was cut out from the extruded foam plate with dimensions of 25 mm in thickness direction, 100 mm in extrusion direction, and 100 mm in width direction. The dimensions Db of the cut out test piece in each direction (VD, MD, TD) were measured. VD is the thickness direction, MD is the extrusion direction, and TD is the width direction. The test piece was then placed in an oven adjusted to 55°C, and after 22 hours, the test piece was taken out and the dimensions Da of each direction (VD, MD, TD) were measured. The dimensional change rate in each direction for the dimension Da of the test piece after heating relative to the dimension Db of the test piece before heating was calculated by [(Da-Db)/Db×100]. The largest value of the dimensional change rate in each direction obtained was taken as the dimensional change rate at 55°C. This method was repeated at temperatures of 60°C, 65°C, 70°C, 75°C, and 80°C, and the dimensional change rate was determined at each temperature. The "Heat resistance" column in the table lists the maximum temperature at which the dimensional change rate was within ±1%.

<9> Flame retardancy (oxygen index)
Flame retardancy was evaluated by the oxygen index. Specifically, the oxygen index was measured in accordance with the flame retardancy test method for polymeric materials by the oxygen index method described in JIS K7201-2 (2007). A plurality of test pieces were cut out from the center of the width direction of the extruded foam board to a size of 10 mm wide x 150 mm long x 10 mm thick, and were conditioned at a temperature of 23 degrees and a relative humidity of 50% for 168 hours. A flame retardancy tester (ON-1D type manufactured by Suga Test Instruments Co., Ltd.) was used as the measuring device. The type of heat source of the igniter was liquefied petroleum gas (LPG), the ignition procedure was method A, and the test piece was made to stand on its own in a predetermined position in the tester. Depending on the measured oxygen index, the flame retardancy was evaluated according to the following criteria, and shown in the "Flame retardancy" column in the table.
◯: Oxygen index is over 28 ×: Oxygen index is 28 or less

(Flammability test)
In addition, the following flammability test was conducted on the examples with the above oxygen index evaluation of "◯" and confirmed to pass. Specifically, the flammability test was conducted on the extruded foam boards 7 days after production in accordance with the measurement method A of the flammability test method of JIS A9521:2017. For the measurement, five test pieces were randomly cut from one extruded foam board, and those that met the following criteria were deemed to pass.
Pass: The average flame-out time for five test pieces is within 3 seconds, no residual dust is present, and no combustion occurs beyond the flammability limit line.
All of the examples in which the oxygen index was evaluated as "good" passed the flammability test.

<10> Compressive strength For Example 1, Example 2, Comparative Example 1, Comparative Example 2, Comparative Example 3, and Comparative Example 4, the compressive strength of the obtained extruded foam board was measured. Specifically, in accordance with JIS K7181 (2011), the compression strength was measured using a Tensilon universal material testing machine manufactured by A&D Co., Ltd., by the following method. A test piece (50 mm in the extrusion direction x 50 mm in the width direction x 25 mm in thickness [excluding the skin layer]) cut out from the center of the extruded foam board was compressed by 10% at a speed of 10 mm/min to obtain a stress-strain curve. The stress at 10% compression was read from the obtained stress-strain curve, and divided by the compressed area of the test piece to obtain the 10% compression strength. The above measurements were performed in the three directions of the extrusion direction, width direction, and thickness direction of the extruded foam board, and the arithmetic average value was taken as the compression strength.

The compressive strength of the extruded foam boards was 30.6 N/cm ² for Example 1, 25.5 N/cm ² for Example 2, 24.5 N/cm ² for Comparative Example 1, 25.4 N/cm ² for Comparative Example 2, 23.9 N/cm ² for Comparative Example 3, and 22.4 N/cm ² for Comparative Example 4.

As can be seen from Table 2, Examples 1 to 9 are examples in which a styrene-acrylonitrile copolymer is used as the base resin, the total amount (Ch+Cc) of the hydrofluoroolefin content Ch and the content Cc of one or more hydrocarbons selected from aliphatic saturated hydrocarbons having 3 to 5 carbon atoms is 0.5 mol or more and 1.3 mol or less, and the ratio [Ch/(Ch+Cc)] of the content Ch to the total amount (Ch+Cc) is more than 0.5. It was confirmed that Examples 1 to 9 exhibited high flame retardancy and excellent long-term heat insulation. Examples 1 to 6, which contained 1-chloro-2,3,3,3-tetrafluoropropene as the hydrofluoroolefin, also had excellent heat resistance. In Comparative Examples 1 to 7, in which at least one of the total amount (Ch+Cc) and [Ch/(Ch+Cc)] did not satisfy the numerical range of the present invention, it was not possible to improve both heat insulation and flame retardancy.

Claims (9)

An extruded thermoplastic resin foam plate containing a base resin including a styrene-acrylonitrile copolymer and a flame retardant, the plate having an apparent density of 20 kg/ ^m3 or more and 50 kg/ ^m3 or less, a cross-sectional area perpendicular to the extrusion direction of ¹⁰⁰ cm2 or more, and a thickness of 20 mm or more and 150 mm or less,
the total amount (Ch+Cc) of the hydrofluoroolefin content Ch per 1 kg of the extruded thermoplastic resin foam plate and the aliphatic saturated hydrocarbon content Cc (including 0) having 3 to 5 carbon atoms per 1 kg of the extruded thermoplastic resin foam plate, as measured by gas chromatography using a test piece conditioned by the following method (1), is 0.5 mol or more and 1.3 mol or less, and the ratio [Ch/(Ch+Cc)] of the content Ch to the total amount (Ch+Cc) is more than 0.5;
Thermoplastic resin extruded foam board.
Method (1): A test piece having a length of 500 mm, a width of 200 mm, and a thickness of 5 mm and no molded skin was cut out from an extruded thermoplastic resin foam plate, and the test piece was conditioned by leaving it to stand in an atmosphere having a temperature of 23° C. and a humidity of 50% for 37 days. The molecular weight of the hydrofluoroolefin is 110 or more.
The extruded thermoplastic resin foam board according to claim 1. The hydrofluoroolefin is at least one selected from the group consisting of 1-chloro-2,3,3,3-tetrafluoropropene, 1-chloro-3,3,3-trifluoropropene, and 1,1,1,4,4,4-hexafluoro-2-butene;
The extruded thermoplastic resin foam board according to claim 1. The hydrofluoroolefin is 1-chloro-2,3,3,3-tetrafluoropropene;
The extruded thermoplastic resin foam board according to claim 1. The content Cc of aliphatic saturated hydrocarbons having 3 to 5 carbon atoms per 1 kg of the extruded thermoplastic resin foam board is 0.1 mol or more and 0.6 mol or less.
The extruded thermoplastic resin foam board according to claim 1. The average bubble diameter in the thickness direction of the thermoplastic resin extruded foam plate is 50 μm or more and 300 μm or less.
The extruded thermoplastic resin foam board according to claim 1. The content of the acrylonitrile component derived from the styrene-acrylonitrile copolymer in the base resin is 20% by mass or more and 40% by mass or less.
The extruded thermoplastic resin foam board according to claim 1. the flame retardant contains a brominated styrene-butadiene copolymer, and the amount of the brominated styrene-butadiene copolymer blended is 0.5 parts by mass or more and 8 parts by mass or less per 100 parts by weight of the base resin;
The extruded thermoplastic resin foam board according to claim 1. the flame retardant further contains a brominated bisphenol, the amount of the brominated bisphenol is 0.1 parts by mass or more and 1 part by mass or less per 100 parts by mass of the base resin, and the ratio of the amount of the brominated bisphenol to the amount of the brominated styrene-butadiene copolymer is 0.05 or more and 0.3 or less;
The extruded thermoplastic resin foam board according to claim 8.