JP7663382B2 - Method for producing extruded styrene resin foam - Google Patents

Description

The present invention relates to a method for producing extruded styrene-based resin foam.

Styrenic resin extrusion foams are generally produced continuously by heating and melting a styrenic resin composition using an extruder or the like, then adding a blowing agent under high pressure conditions, cooling to a specified resin temperature, and then extruding the mixture into a low pressure region.

Styrene-based resin extruded foams are used, for example, as insulation for structures due to their good workability and insulating properties. In recent years, there has been an increasing demand for energy conservation in homes and buildings, and there is a demand for technological development of foams with higher insulating properties than ever before.

Methods for producing highly insulating foams include a manufacturing method in which graphite or titanium oxide is added in a specified range as a heat radiation suppressant (see, for example, Patent Document 1), and a manufacturing method for extruded styrene resin foams that uses environmentally friendly fluorinated olefins (hydrofluoroolefins and hydrochlorofluoroolefins) with an ozone depletion potential of zero and a small global warming potential as a foaming agent, or alkyl chlorides such as methyl chloride and ethyl chloride (see, for example, Patent Documents 2 to 4).

JP 2013-221110 A Special Publication No. 2008-546892 JP 2019-189811 A JP 2019-108416 A

The present inventors have newly discovered that when graphite is used as a material for styrene-based resin extruded foam, adding the graphite in the form of a master batch may result in the generation of foreign matter.

Therefore, the present invention aims to provide a method for producing extruded styrene resin foam that can suppress the generation of foreign matter.

In order to solve the above problems, the present inventors have conducted intensive research and have found that the generation of foreign matter in a foam can be suppressed by adding a specific component to a graphite master batch, thereby completing the present invention. The present invention includes the following aspects.
<1> A method for producing an extruded styrenic resin foam, comprising: melt-kneading a styrenic resin, a graphite masterbatch, and a blowing agent, wherein the graphite masterbatch contains graphite and a polyhydric alcohol fatty acid ester.
<2> The method for producing an extruded styrene-based resin foam according to <1>, wherein a ratio (MFRg/MFRr) of a melt mass flow rate (MFRg) of the graphite masterbatch measured under conditions of a test temperature of 200°C and a load of 5 kg according to Method A of JIS K7210-1 (2014) to a melt mass flow rate (MFRr) of the styrene-based resin measured under conditions of a test temperature of 200°C and a load of 5 kg according to Method A of JIS K7210-1 (2014) is 0.20 or more.
<3> The method for producing an extruded styrene resin foam according to <1> or <2>, wherein the polyhydric alcohol fatty acid ester is contained in an amount of 1.0% by weight or more based on 100% by weight of the graphite masterbatch.
<4> The method for producing an extruded styrene resin foam according to any one of <1> to <3>, wherein the polyhydric alcohol fatty acid ester includes a glycerin fatty acid ester.
<5> The method for producing an extruded styrene resin foam according to <4>, wherein the glycerol fatty acid ester is at least one selected from the group consisting of lauric acid monoglyceride, lauric acid diglyceride, lauric acid triglyceride, palmitic acid monoglyceride, palmitic acid diglyceride, palmitic acid triglyceride, stearic acid monoglyceride, stearic acid diglyceride, stearic acid triglyceride, and stearic acid tetraglyceride.
<6> The method for producing an extruded styrene resin foam according to any one of <1> to <5>, wherein the graphite is contained in an amount of 40% by weight or more based on 100% by weight of the graphite masterbatch.
<7> The method for producing an extruded styrenic resin foam according to any one of <1> to <6>, wherein a ratio (MFRg/MFRr) of a melt mass flow rate (MFRg) of the graphite masterbatch measured under conditions of a test temperature of 200°C and a load of 5 kg according to Method A of JIS K7210-1 (2014) to a melt mass flow rate (MFRr) of the styrenic resin measured under conditions of a test temperature of 200°C and a load of 5 kg according to Method A of JIS K7210-1 (2014) is 0.50 or more, and the foaming agent contains an alkyl chloride.
<8> The method for producing an extruded styrene-based resin foam according to any one of <1> to <7>, wherein the extruded styrene-based resin foam has a thermal conductivity of 0.0244 W/mK or less.
<9> The method for producing an extruded styrene resin foam according to any one of <1> to <8>, wherein the extruded styrene resin foam has an apparent density of 20 to 60 kg/ ^m3 .
<10> The method for producing an extruded styrene resin foam according to any one of <1> to <9>, wherein the extruded styrene resin foam has a thickness of 10 mm or more and 150 mm or less.

According to one embodiment of the present invention, the generation of foreign matter in extruded styrene-based resin foam is suppressed.

One embodiment of the present invention is described below, but the present invention is not limited to this. The present invention is not limited to each configuration described below, and various modifications are possible within the scope of the claims, and embodiments and examples obtained by appropriately combining the technical means disclosed in different embodiments and examples are also included in the technical scope of the present invention. In addition, all academic literature and patent documents described in this specification are incorporated herein by reference. In addition, unless otherwise specified in this specification, "A to B" representing a numerical range is intended to mean "greater than or equal to A and less than or equal to B."

[1. Extruded styrene resin foam]
A method for producing an extruded styrenic resin foam according to one embodiment of the present invention comprises a step of adding a foaming agent to a melt of a graphite-containing styrenic resin composition to prepare a foamable molten material, and is characterized in that a graphite masterbatch containing graphite and a polyhydric alcohol fatty acid ester is used.

In general, graphite is added in the form of a master batch to facilitate mixing of the graphite into the molten resin. However, when graphite is used as a material for the styrene-based resin extrusion foam and the graphite is added in the form of a master batch, foreign matter may be generated in the styrene-based resin extrusion foam depending on the type and blending of the styrene-based resin and the foaming agent. The inventors investigated and analyzed the foreign matter and found that the foreign matter originated from the graphite master batch. As a result of the investigation by the inventors, by including a polyhydric alcohol fatty acid ester in the graphite master batch, the generation of foreign matter in the styrene-based resin extrusion foam can be stably suppressed regardless of the type and blending of the styrene-based resin and the foaming agent. This is presumably because the MFR of the graphite master batch is adjusted by including a polyhydric alcohol fatty acid ester in the graphite master batch, the MFR of the styrene-based resin and the graphite master batch are properly balanced, the kneadability of the styrene-based resin and the graphite master batch is improved, and the remaining of unmelted matter is suppressed.

(1-1. Styrene-based resin)
In one embodiment of the present invention, the styrene-based resin extrusion foam uses a styrene-based resin as a base resin. The styrene-based resin used in one embodiment of the present invention is not particularly limited, and includes (i) a homopolymer of a styrene-based monomer such as styrene, methylstyrene, ethylstyrene, isopropylstyrene, dimethylstyrene, bromostyrene, chlorostyrene, vinyltoluene, vinylxylene, or a copolymer consisting of a combination of two or more monomers, and (ii) a copolymer obtained by copolymerizing the styrene-based monomer with one or more other copolymerizable monomers such as divinylbenzene, butadiene, acrylic acid, methacrylic acid, methyl acrylate, methyl methacrylate, acrylonitrile, maleic anhydride, and itaconic anhydride. The other copolymerizable monomer can be used in an amount that does not reduce the physical properties such as the compressive strength of the styrene-based resin extrusion foam produced. In addition, the styrene-based resin used in one embodiment of the present invention is not limited to a homopolymer or copolymer of the styrene-based monomer, and may be a blend of a homopolymer or copolymer of the styrene-based monomer and a homopolymer or copolymer of the other monomer. For example, the styrene-based resin used in one embodiment of the present invention may be a blend of a homopolymer or copolymer of the styrene-based monomer and a diene-based rubber-reinforced polystyrene or an acrylic rubber-reinforced polystyrene. Furthermore, the styrene-based resin used in one embodiment of the present invention may be a styrene-based resin having a branched structure for the purpose of adjusting MFR, melt viscosity during molding, melt tension, etc. These may be used alone, or two or more types different in copolymerization components, molecular weights, molecular weight distributions, branched structures, and/or MFR may be mixed and used.

In one embodiment of the present invention, it is preferable to use a styrene-based resin having an MFR of 0.1 to 50 g/10 min, because (i) it has excellent moldability during extrusion foam molding, (ii) it is easy to adjust the discharge amount during molding, the thickness, width, apparent density, and closed cell ratio of the obtained styrene-based resin extruded foam to the desired values, (iii) it has excellent foamability (the thickness, width, apparent density, closed cell ratio, and surface properties of the foam are easily adjusted to the desired conditions), (iv) it is possible to obtain a styrene-based resin extruded foam with excellent appearance, and (v) it is possible to obtain a styrene-based resin extruded foam with a good balance of properties (for example, mechanical strength such as compressive strength, bending strength, or bending deflection amount, toughness, etc.). Furthermore, the MFR of the styrene-based resin is more preferably 0.3 to 30 g/10 min, and particularly preferably 0.5 to 25 g/10 min, from the viewpoint of the balance between moldability and foamability and mechanical strength and toughness. However, it is preferable to determine the MFR of the styrene resin in relation to the MFR of the graphite master batch described below. In one embodiment of the present invention, the MFR is measured according to JIS K7210-1 (2014) Method A and test condition H (test temperature 200°C, load 5 kg).

(1-2. Graphite Masterbatch)
In one embodiment of the present invention, the extruded styrene-based resin foam uses graphite as a heat radiation inhibitor to improve heat insulation. Examples include scaly (flake) graphite, clayey graphite, spherical graphite, and artificial graphite. Among these, it is preferable to use graphite whose main component is scaly (flake) graphite because of its high heat radiation inhibitory effect. The graphite preferably has a fixed carbon content of 80% or more, and more preferably 85% or more. By setting the fixed carbon content within the above range, a foam having high heat insulation properties can be obtained.

The average particle size of the graphite is preferably 15 μm or less, more preferably 10 μm or less. By setting the average particle size within the above range, the specific surface area of the graphite increases, and the probability of collision with heat radiation increases, resulting in a higher heat radiation suppression effect. The average particle size refers to the particle size at which the cumulative volume of the total particle volume is 50% (volume average particle size by laser diffraction scattering method) when the particle size distribution is measured and analyzed by a laser diffraction scattering method based on the Mie theory in accordance with ISO13320:2009 and JIS Z8825:2013.

In one embodiment of the present invention, the graphite is used in the form of a master batch. The graphite master batch is a high-concentration dispersion of graphite in a resin, and is preferably prepared so that the styrene resin contains 30 to 70% by weight of graphite, and more preferably 40 to 60% by weight of graphite. As the styrene resin used in the graphite master batch, the styrene resins exemplified in "1-1. Styrene resin" above can be used similarly and are suitable. From the viewpoint of kneadability, the MFR of the styrene resin is preferably 0.5 to 30 g/min. From the viewpoint of kneadability with the base resin, the MFR of the graphite master batch is preferably 0.3 to 30 g/10 min, and more preferably 0.5 to 25 g/10 min. However, it is preferable to determine the MFR of the graphite master batch in relation to the MFR of the styrene resin as follows.

In one embodiment of the present invention, the ratio (MFRg/MFRr) of the melt mass flow rate (MFRg) of the graphite master batch measured under the conditions of JIS K7210-1 (2014) A method test temperature 200°C and load 5 kg to the melt mass flow rate (MFRr) of the styrene resin measured under the conditions of JIS K7210-1 (2014) A method test temperature 200°C and load 5 kg is preferably 0.20 to 5, more preferably 0.21 to 4, and even more preferably 0.22 to 3. By setting the ratio value of the MFR of the base resin and the graphite master batch to a specific value, the generation of foreign matter can be effectively suppressed. In particular, in the case where the foaming agent contains alkyl chloride, foreign matter tends to be generated easily, and adjusting the MFR ratio value (MFRg/MFRr) to 0.50 or more acts more effectively and suppresses the generation of foreign matter.

In one embodiment of the present invention, in order to adjust the MFR of the graphite masterbatch, a polyhydric alcohol fatty acid ester is contained in the graphite masterbatch.
Examples of the polyhydric alcohol fatty acid ester used in one embodiment of the present invention include esters of higher fatty acids having 10 to 24 carbon atoms and polyhydric alcohols such as ethylene glycol, glycerin, 1,2,4-butanetriol, diglycerin, pentaerythritol, sorbitol, erythritol, hexanetriol, etc. These polyhydric alcohol fatty acid esters may be used alone or in combination of two or more kinds.

Among these, glycerin fatty acid esters, particularly mono-, di-, tri-, or tetra-fatty acid esters of glycerin, are preferred in terms of availability, price, etc.

As the glycerol fatty acid ester, it is preferable to use at least one selected from the group consisting of, for example, lauric acid monoglyceride, lauric acid diglyceride, lauric acid triglyceride, palmitic acid monoglyceride, palmitic acid diglyceride, palmitic acid triglyceride, stearic acid monoglyceride, stearic acid diglyceride, stearic acid triglyceride, and stearic acid tetraglyceride.
The amount of the polyhydric alcohol fatty acid ester used in one embodiment of the present invention is adjusted so that it is contained in the graphite masterbatch at 0.5 to 6.0% by weight, more preferably 1.0 to 5.0% by weight, and even more preferably 1.5 to 4.0% by weight. If the amount of the polyhydric alcohol fatty acid ester is less than 0.5% by weight, there is almost no effect in adjusting the MFR, and if it exceeds 6.0% by weight, the processability of the masterbatch decreases.
In the method for producing an extruded styrene resin foam according to one embodiment of the present invention, graphite is used (added) in the form of a graphite masterbatch, but a part of the graphite may be added directly without being in the form of a masterbatch. Adding a part of the graphite directly may be economically advantageous in some cases.

In one embodiment of the present invention, the graphite content in the styrene-based resin extruded foam is preferably 0.5 parts by weight or more and 5.0 parts by weight or less, and more preferably 1.0 parts by weight or more and 3.0 parts by weight or less, per 100 parts by weight of the resin component. If the content is less than 0.5 parts by weight, a sufficient heat radiation suppression effect cannot be obtained. If the content is more than 5.0 parts by weight, the heat radiation suppression effect corresponding to the content cannot be obtained, and there is no cost benefit. The "resin component" referred to here refers to the resin component including the base resin and the resin contained in the graphite master batch.

(1-3. Foaming Agent)
In one embodiment of the present invention, examples of the blowing agent include hydrofluoroolefin and/or hydrochlorofluoroolefin (hereinafter, "hydrofluoroolefin and/or hydrochlorofluoroolefin" may be referred to as "hydro(chloro)fluoroolefin"), saturated hydrocarbons having 3 to 5 carbon atoms, and other blowing agents. From the viewpoint of improving the heat insulating properties of the extruded styrene-based resin foam, it is preferable to use hydro(chloro)fluoroolefin as the blowing agent. These blowing agents may be used alone, or two or more kinds may be used in combination. For example, a saturated hydrocarbon having 3 to 5 carbon atoms and a hydrofluoroolefin may be used in combination.

The hydrofluoroolefin used in one embodiment of the present invention is not particularly limited, but tetrafluoropropene and hexafluorobutene are preferred from the viewpoint of low gas thermal conductivity and safety. Specific examples include trans-1,3,3,3-tetrafluoropropene (trans-HFO-1234ze), cis-1,3,3,3-tetrafluoropropene (cis-HFO-1234ze), 2,3,3,3-tetrafluoropropene (trans-HFO-1234yf), and cis-1,1,1,4,4,4-hexafluoro-2-butene (cis-HFO-1336mzz). The hydrochlorofluoroolefin used in one embodiment of the present invention is not particularly limited, but hydrochlorotrifluoropropene is preferred from the viewpoint of low gas thermal conductivity and safety. Specific examples include trans-1-chloro-3,3,3-trifluoropropene (trans-HCFO-1233zd), and the like. These hydrofluoroolefins and hydrochlorofluoroolefins may be used alone or in combination of two or more.

The amount of hydro(chloro)fluoroolefin added in one embodiment of the present invention is preferably 1.0 to 14.0 parts by weight, more preferably 2.0 to 13.0 parts by weight, and particularly preferably 3.0 to 12.0 parts by weight, per 100 parts by weight of the resin component. When the amount of hydro(chloro)fluoroolefin added is less than 1.0 part by weight per 100 parts by weight of the resin component, the effect of improving the heat insulating properties by hydro(chloro)fluoroolefin tends not to be very promising. On the other hand, when the amount of hydro(chloro)fluoroolefin added is more than 14.0 parts by weight per 100 parts by weight of the resin component, the hydro(chloro)fluoroolefin separates from the resin melt during extrusion foaming, and spot holes (traces where localized lumps of hydro(chloro)fluoroolefin break through the surface of the extruded foam and are released into the outside air) may occur on the surface of the extruded foam, or the closed cell ratio may decrease, resulting in impaired heat insulating properties.

Examples of saturated hydrocarbons having 3 to 5 carbon atoms according to one embodiment of the present invention include propane, n-butane, i-butane, n-pentane, i-pentane, and neopentane. Among these saturated hydrocarbons having 3 to 5 carbon atoms, propane, n-butane, i-butane, or mixtures thereof are preferred from the viewpoint of foamability. Furthermore, from the viewpoint of the thermal insulation properties of the styrene-based resin extruded foam, n-butane, i-butane, or mixtures thereof are preferred, with i-butane being particularly preferred. hereinafter, i-butane is also referred to as "isobutane".

Depending on the desired foam properties such as expansion ratio and flame retardancy, the amount of hydro(chloro)fluoroolefin and/or saturated hydrocarbon having 3 to 5 carbon atoms added may be limited. If the amount added is outside the desired range, extrusion foam moldability may be insufficient. In this case, by further using another foaming agent, a plasticizing effect and/or a co-foaming effect during foam production can be obtained. This allows the extrusion pressure to be reduced, making it possible to stably produce foams.

In the present invention, by using other foaming agents, a plasticizing effect and/or a co-foaming effect can be obtained during foam production, reducing the extrusion pressure and enabling stable production of foams.

Other foaming agents include, for example, ethers such as dimethyl ether, diethyl ether, methyl ethyl ether, isopropyl ether, n-butyl ether, diisopropyl ether, furan, furfural, 2-methylfuran, tetrahydrofuran, and tetrahydropyran; ketones such as dimethyl ketone, methyl ethyl ketone, diethyl ketone, methyl n-propyl ketone, methyl n-butyl ketone, methyl i-butyl ketone, methyl n-amyl ketone, methyl n-hexyl ketone, ethyl n-propyl ketone, and ethyl n-butyl ketone; saturated alcohols having 1 to 4 carbon atoms such as methanol, ethanol, propyl alcohol, i-propyl alcohol, butyl alcohol, i-butyl alcohol, and t-butyl alcohol; carboxylic acid esters such as methyl formate, ethyl formate, propyl formate, butyl formate, amyl formate, methyl propionate, and ethyl propionate; and organic foaming agents such as alkyl halides such as methyl chloride and ethyl chloride. In addition, inorganic foaming agents such as water and carbon dioxide; chemical foaming agents such as azo compounds and tetrazole can also be used. These other foaming agents can be used alone or in combination of two or more.

Among the other blowing agents, from the viewpoints of foaming property and foam moldability, etc., saturated alcohols having 1 to 4 carbon atoms, dimethyl ether, diethyl ether, methyl ethyl ether, methyl chloride, ethyl chloride, etc. are preferred. From the viewpoints of the combustibility of the blowing agent, the flame retardancy or heat insulating property of the foam, etc., water and carbon dioxide are preferred. Among these, dimethyl ether is particularly preferred from the viewpoint of the plasticizing effect. From the viewpoints of cost and the effect of improving heat insulating property by controlling the bubble diameter, water is particularly preferred.
The total amount of the foaming agent according to one embodiment of the present invention is preferably 2 to 20 parts by weight, more preferably 2 to 15 parts by weight, based on 100 parts by weight of the resin component. If the amount of the foaming agent is 2 parts by weight or more, the expansion ratio can be sufficiently increased, so that the properties of the resin foam, such as light weight and heat insulation, can be easily exhibited. If the amount of the foaming agent is 20 parts by weight or less, the occurrence of defects such as voids in the foam can be prevented.
In one embodiment of the present invention, when water is used as a blowing agent, it is preferable to add a water-absorbing substance in order to perform stable extrusion foam molding. Specific examples of water-absorbing substances used in one embodiment of the present invention include water-absorbing polymers such as polyacrylate polymers, starch-acrylic acid graft copolymers, polyvinyl alcohol polymers, vinyl alcohol-acrylate copolymers, ethylene-vinyl alcohol copolymers, acrylonitrile-methyl methacrylate-butadiene copolymers, polyethylene oxide copolymers, and derivatives thereof, as well as fine powders having hydroxyl groups on the surface such as anhydrous silica (silicon oxide) having silanol groups on the surface [for example, AEROSIL manufactured by Nippon Aerosil Co., Ltd. is commercially available]; water-absorbing or water-swelling layered silicates such as smectite and swelling fluoromica, and organically treated products thereof; and porous substances such as zeolite, activated carbon, alumina, silica gel, porous glass, activated clay, diatomaceous earth, and bentonite. The amount of the water-absorbing substance to be added is appropriately adjusted depending on the amount of water to be added, but is preferably 0.01 to 5 parts by weight, and more preferably 0.1 to 3 parts by weight, per 100 parts by weight of the resin component.

(1-4. Flame retardants)
In one embodiment of the present invention, a flame retardant is added to the extruded styrene-based resin foam, thereby imparting flame retardancy to the resulting extruded styrene-based resin foam.

As the flame retardant, a bromine-based flame retardant is preferably used. Specific examples of the bromine-based flame retardant in one embodiment of the present invention include hexabromocyclododecane, tetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl)ether, tetrabromobisphenol A-bis(2,3-dibromopropyl)ether, tris(2,3-dibromopropyl)isocyanurate, and aliphatic bromine-containing polymers such as brominated styrene-butadiene block copolymers. These may be used alone or in a mixture of two or more.

Of these, tetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl)ether, mixed brominated flame retardants consisting of tetrabromobisphenol A-bis(2,3-dibromopropyl)ether, brominated styrene-butadiene block copolymer, and hexabromocyclododecane are preferably used because they have good extrusion operation and do not adversely affect the heat resistance of the foam. These substances may be used alone or as a mixture.

In one embodiment of the present invention, the content of the bromine-based flame retardant in the styrene-based resin extruded foam is preferably 1.0 to 8.0 parts by weight, more preferably 1.5 to 7.0 parts by weight, and even more preferably 2.0 to 6.0 parts by weight, based on 100 parts by weight of the resin component. If the content of the bromine-based flame retardant is less than 1.0 part by weight, it tends to be difficult to obtain good foam properties such as flame retardancy, while if it exceeds 8.0 parts by weight, the stability and surface properties during foam production may be impaired. However, it is more preferable that the content of the flame retardant is appropriately adjusted according to the amount of foaming agent added, the apparent density of the foam, and the type or content of additives having a flame retardant synergistic effect, so that the flame retardancy specified in JIS A 9521 Measurement Method A is obtained.

In one embodiment of the present invention, a radical generator can be used in combination with the styrene-based resin extrusion foam to improve the flame retardant performance. Specific examples of the radical generator include 2,3-dimethyl-2,3-diphenylbutane, poly-1,4-diisopropylbenzene, 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. Peroxides such as dicumyl peroxide are also used. Among them, those that are stable under the resin processing temperature conditions are preferred, specifically 2,3-dimethyl-2,3-diphenylbutane and poly-1,4-diisopropylbenzene, and the preferred amount of the radical generator to be added is 0.05 to 0.5 parts by weight per 100 parts by weight of the resin component.

Furthermore, for the purpose of improving flame retardant performance, in other words as a flame retardant auxiliary, phosphorus-based flame retardants such as phosphate esters and phosphine oxides can be used in combination, as long as the thermal stability performance is not impaired. Examples of phosphate esters include triphenyl phosphate, tris(tributylbromoneopentyl)phosphate, tricresyl phosphate, trixylyleneyl phosphate, cresyl diphenyl phosphate, 2-ethylhexyl diphenyl phosphate, trimethyl phosphate, triethyl phosphate, tributyl phosphate, tris(2-ethylhexyl)phosphate, tris(butoxyethyl)phosphate, and condensed phosphate esters, and triphenyl phosphate and tris(tributylbromoneopentyl)phosphate are particularly preferred. Furthermore, triphenylphosphine oxide is preferred as a phosphine oxide-type phosphorus-based flame retardant. These phosphate esters and phosphine oxides may be used alone or in combination of two or more. The preferred amount of phosphorus-based flame retardant to be added is 0.1 to 2 parts by weight per 100 parts by weight of styrene-based resin.

(1-5. Stabilizers)
In one embodiment of the present invention, a stabilizer for a flame retardant can be used. Specific examples of the stabilizer include, but are not limited to, (i) epoxy compounds such as bisphenol A diglycidyl ether type epoxy resins, cresol novolac type epoxy resins, and phenol novolac type epoxy resins, (ii) polyhydric alcohol esters, which are reaction products of polyhydric alcohols such as pentaerythritol, dipentaerythritol, and tripentaerythritol with monovalent carboxylic acids such as acetic acid and propionic acid, or divalent carboxylic acids such as adipic acid and glutamic acid, and which are mixtures of esters having one or more hydroxyl groups in the molecule and may contain a small amount of the raw material polyhydric alcohol, and (iii) triethylene glycol-bis-3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate, pentaerythritol tetrakis[3-( 3',5'-di-tert-butyl-4'-hydroxyphenyl)propionate] and octadecyl 3-(3,5-di-tert-butyl-4-hydroxyphenyl)propionate, and (iv) phosphite stabilizers such as 3,9-bis(2,4-di-tert-butylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane, 3,9-bis(2,6-di-tert-butyl-4-methylphenoxy)-2,4,8,10-tetraoxa-3,9-diphosphaspiro[5.5]undecane, and tetrakis(2,4-di-tert-butyl-5-methylphenyl)-4,4'-biphenylene diphosphonite), are preferably used since they do not reduce the flame retardant performance of the foam and improve the thermal stability of the foam.

(1-6. Heat radiation suppressant)
In one embodiment of the present invention, in addition to graphite, other heat radiation inhibitors may be used in combination. The heat radiation inhibitor refers to a substance that has the properties of reflecting, scattering, and absorbing light in the near infrared or infrared region. By containing a heat radiation inhibitor, a foam having high thermal insulation properties can be obtained. As the heat radiation inhibitor that can be used in the present invention, in addition to graphite, white particles such as titanium oxide, barium sulfate, zinc oxide, aluminum oxide, and antimony oxide can be used. These may be used alone or in combination of two or more. Among the white particles, titanium oxide or barium sulfate is preferred from the viewpoint of a large radiation suppression effect, and titanium oxide is more preferred. The average particle size of the white particles is not particularly limited, but in consideration of effective reflection of infrared rays and color development to resin, for example, titanium oxide is preferably 0.1 μm to 10 μm, and more preferably 0.15 μm to 5 μm.

In one embodiment of the present invention, the content of white particles in the styrene-based resin extruded foam is preferably 1.0 parts by weight or more and 3.0 parts by weight or less, and more preferably 1.5 parts by weight or more and 2.5 parts by weight or less, per 100 parts by weight of the resin component. Compared to graphite, white particles have a smaller heat radiation suppression effect, and when the content of white particles is less than 1.0 part by weight, there is almost no heat radiation suppression effect even if the white particles are contained. When the content of white particles exceeds 3.0 parts by weight, the heat radiation suppression effect corresponding to the content cannot be obtained, while the flame retardancy of the foam tends to deteriorate.

In one embodiment of the present invention, the total content of the heat radiation inhibitor in the styrene-based resin extrusion foam is preferably 1.0 to 6.0 parts by weight, more preferably 2.0 to 5.0 parts by weight, relative to 100 parts by weight of the resin component resin. If the total content of the heat radiation inhibitor is less than 1.0 part by weight, it is difficult to obtain heat insulation, and on the other hand, as the content of solid additives such as heat radiation inhibitors increases, the number of nucleation points increases, so that the bubbles in the foam become finer and the elongation of the resin itself deteriorates, which tends to make it difficult to impart a beautiful surface to the extrusion foam and to produce a thick extrusion foam. However, if the total content of the heat radiation inhibitor exceeds 6.0 parts by weight, it tends to be particularly difficult to impart a beautiful surface to the extrusion foam and to produce a thick extrusion foam, and further, there is a tendency for extrusion stability and flame retardancy to be impaired.

(1-7. Moldability improver)
In one embodiment of the present invention, a polyhydric alcohol fatty acid ester and/or polyethylene glycol may be added as a moldability improver, if necessary, which can impart an attractive surface to the extruded foam and increase the thickness of the extruded foam (i.e., improve the moldability of the extruded foam).

The polyhydric alcohol fatty acid ester used in one embodiment of the present invention includes, for example, esters of higher fatty acids having 10 to 24 carbon atoms with polyhydric alcohols such as ethylene glycol, glycerin, 1,2,4-butanetriol, diglycerin, pentaerythritol, sorbitol, erythritol, and hexanetriol. These polyhydric alcohol fatty acid esters may be used alone or in combination of two or more kinds.

Among these, glycerin fatty acid esters, particularly mono-, di-, tri-, or tetra-fatty acid esters of glycerin, are preferred in terms of availability, price, etc.

As the glycerin fatty acid ester, it is preferable to use at least one selected from the group consisting of, for example, lauric acid monoglyceride, lauric acid diglyceride, lauric acid triglyceride, palmitic acid monoglyceride, palmitic acid diglyceride, palmitic acid triglyceride, stearic acid monoglyceride, stearic acid diglyceride, stearic acid triglyceride, and stearic acid tetraglyceride.

The melting point of the glycerin fatty acid ester used in the present invention is preferably 150°C or less, more preferably 130°C or less, and particularly preferably 110°C. When the melting point of the glycerin fatty acid ester is 150°C or less, it is excellent in handleability, for example, in the dry blending process during the production of extruded foam, and since it exists as a liquid during extrusion foam molding, it can also impart a plasticizing effect to the styrene-based resin during extrusion foam molding, so that a sufficient thickening effect of the extruded styrene-based resin foam can be exhibited. On the other hand, when the melting point is higher than 150°C, it exists as a solid during extrusion foam molding, and it cannot impart a plasticizing effect to the styrene-based resin during extrusion foam molding, so there is a risk that a sufficient thickening effect of the extruded styrene-based resin foam cannot be exhibited.

In the manufacturing method of styrene-based resin extruded foam according to one embodiment of the present invention, the amount of polyhydric alcohol fatty acid ester added is preferably 0.05 parts by weight or more and 5.0 parts by weight or less, more preferably 0.1 parts by weight or more and 3.0 parts by weight or less, and particularly preferably 0.5 parts by weight or more and less than 2.0 parts by weight, per 100 parts by weight of the resin component. If the amount of polyhydric alcohol fatty acid ester added is less than 0.05 parts by weight, the effect of thickening the extruded foam tends to be insufficient. On the other hand, if the amount exceeds 5.0 parts by weight, the excessive amount may impair extrusion, foaming, and molding stability during manufacturing, or may deteriorate various properties such as the heat resistance of the extruded foam.

The average molecular weight of the polyethylene glycol used in one embodiment of the present invention is not particularly limited, but is preferably 1000 to 25000, more preferably 1500 to 20000, and particularly preferably 3000 to 15000. These polyethylene glycols with different average molecular weights may be used alone or in combination of two or more. If the molecular weight of the polyethylene glycol is 1000 to 25000, the freezing point of the polyethylene glycol is higher than room temperature and the polyethylene glycol is in a solid state at room temperature. Depending on the amount used, the polyethylene glycol has excellent handleability in, for example, a dry blending process during the production of an extruded foam, does not bleed out from the inside of the extruded foam to the surface, and has a freezing point lower than the extrusion foam molding temperature, and can impart a plasticizing effect to the styrene-based resin during extrusion foam molding. Therefore, the polyethylene glycol can exert a sufficient surface property imparting effect and a sufficient thickness-imparting effect to the styrene-based resin extruded foam.

In one embodiment of the present invention, the amount of polyethylene glycol added is preferably 0.05 parts by weight to 5.0 parts by weight, more preferably 0.1 parts by weight to 3.0 parts by weight, and particularly preferably 0.2 parts by weight to 1.0 parts by weight, relative to 100 parts by weight of the styrene-based resin. If the amount of polyethylene glycol added is less than 0.05 parts by weight, the surface property imparting effect and the thickness-imparting effect tend to be insufficient. On the other hand, if the amount of polyethylene glycol added is more than 5.0 parts by weight, the amount of polyethylene glycol added is excessive, which may impair the extrudability, foamability, and molding stability during production, or may deteriorate various properties such as the heat resistance of the extruded foam.

In one embodiment of the present invention, when polyethylene glycol and polyhydric alcohol fatty acid ester are used in combination as a moldability improver, the total amount of polyethylene glycol and polyhydric alcohol fatty acid ester is preferably 0.05 parts by weight to 5.0 parts by weight, more preferably 0.1 parts by weight to 3.0 parts by weight, and particularly preferably 0.2 parts by weight to 2.0 parts by weight, relative to 100 parts by weight of the resin component. If the content is less than 0.05 parts by weight, the surface property imparting effect and the thickness-imparting effect tend to be insufficient. On the other hand, if the content is more than 5.0 parts by weight, the content is excessive, which may impair extrudability, foamability, and molding stability during production, or may deteriorate various properties such as the heat resistance of the extruded foam.

(1-8. Other Additives)
In one embodiment of the present invention, further, as necessary, additives such as inorganic compounds such as silica, calcium silicate, wollastonite, kaolin, clay, mica, calcium carbonate, sodium stearate, calcium stearate, magnesium stearate, barium stearate, liquid paraffin, olefin wax, stearylamide compounds, phenol antioxidants, phosphorus stabilizers, nitrogen stabilizers, sulfur stabilizers, light resistance stabilizers such as benzotriazoles and hindered amines, cell size regulators such as talc, flame retardants other than the above, antistatic agents, colorants such as pigments, and plasticizers may be contained in the styrene resin, as long as the effect of one embodiment of the present invention is not impaired. In addition, as necessary, other resins may be used in combination with the styrene resin in the base resin, as long as the effect of one embodiment of the present invention is not impaired.

(1-9. Physical Properties)
The thermal conductivity of the styrene-based resin extruded foam according to one embodiment of the present invention is not particularly limited, but from the viewpoint of thermal insulation considering that the foam functions, for example, as a thermal insulation material for building, or as a thermal insulation material for refrigerators or refrigerated vehicles, the thermal conductivity measured at an average temperature of 23° C. one week after production is preferably 0.0284 W/mK or less, more preferably 0.0244 W/mK or less, and particularly preferably 0.0224 W/mK or less.

The apparent density of the extruded styrene-based resin foam according to one embodiment of the present invention is preferably 20 kg/m3 or more and 60 kg/ ^m3 or less, more preferably 25 kg/m3 or more and 40 kg/ ^m3 or less, from the viewpoints of heat insulation property and light weight, taking into consideration that the foam functions as, for example, a heat insulating material for ^{a building} or a heat insulating material for a refrigerator or a ^refrigerated vehicle.
The thickness of the styrene-based resin extruded foam according to one embodiment of the present invention is preferably 10 mm or more and 150 mm or less, and more preferably 15 mm or more and 120 mm or less, from the viewpoints of insulation properties and light weight, taking into consideration that the foam functions as, for example, an insulation material for a building or an insulation material for a refrigerator or a refrigerated vehicle.

The closed cell ratio of the extruded styrene-based resin foam according to one embodiment of the present invention is preferably 90% or more, and more preferably 95% or more. If the closed cell ratio is less than 90%, the foaming agent will dissipate from the extruded foam prematurely, resulting in reduced thermal insulation.

The average bubble diameter in the thickness direction of the styrene-based resin extruded foam according to one embodiment of the present invention is preferably 0.05 mm or more and 0.5 mm or less, more preferably 0.05 mm or more and 0.4 mm or less, and particularly preferably 0.05 mm or more and 0.3 mm or less. In general, the smaller the average bubble diameter, the shorter the distance between the bubble walls of the foam, so that the range of movement of the bubbles of the extruded foam when shaping the extruded foam during extrusion foaming is narrow, making deformation difficult, and it tends to be difficult to impart a beautiful surface to the extruded foam and to achieve a thick extruded foam. If the average bubble diameter in the thickness direction of the styrene-based resin extruded foam is smaller than 0.05 mm, it becomes particularly difficult to impart a beautiful surface to the extruded foam and to achieve a thick extruded foam. On the other hand, if the average bubble diameter in the thickness direction of the styrene-based resin extruded foam exceeds 0.5 mm, there is a risk that sufficient heat insulation cannot be obtained.

The average cell diameter of the styrene-based resin extruded foam according to one embodiment of the present invention can be evaluated using a microscope (DIGITAL MICROSCOPE VHX-900, manufactured by KEYENCE CORPORATION) as described below.

The obtained styrene resin extrusion foam was observed from the extrusion direction at a total of three vertical cross sections in the thickness direction center, namely, the center in the width direction and a location 150 mm from one end in the width direction to the opposite end (the same location for both ends in the width direction), using the microscope, and a 100x magnified photograph was taken. Similarly, the three vertical cross sections in the thickness direction center of the width direction were observed from the width direction using the microscope, and a 100x magnified photograph was taken. Three 2 mm straight lines were drawn in the thickness direction of the magnified photograph (three lines for each observation point and each observation direction), and the number a of bubbles in contact with the straight lines was measured. From the measured number a of bubbles, the average bubble diameter A in the thickness direction for each observation point was calculated using the following formula (1). The average value of the three points (two directions at each point) was taken as the average bubble diameter A (average value) in the thickness direction of the styrene resin extrusion foam.

Average bubble diameter A (mm) in the thickness direction at each observation point = 2 x 3 / number of bubbles a
...(1).

The obtained styrene-based resin extruded foam was observed from the width direction using the microscope at three locations in the center of the thickness direction, namely, the center of the width direction and a location 150 mm from one end of the width direction to the opposite end (the same location for both ends of the width direction), and a vertical cross section in the extrusion direction was taken from the width direction. A 100x magnified photograph was taken. Three 2 mm straight lines were drawn in the extrusion direction of the enlarged photograph (three lines for each observation location), and the number b of bubbles in contact with the lines was measured. From the measured number b of bubbles, the average bubble diameter B in the extrusion direction for each observation location was calculated using the following formula (2). The average value of the three locations was taken as the average bubble diameter B (average value) in the extrusion direction of the styrene-based resin extruded foam.

Average bubble diameter B (mm) in the extrusion direction at each observation point = 2 x 3 / number of bubbles b
...(2).

The obtained styrene-based resin extruded foam was observed with the microscope from the extrusion direction at three locations in the width direction center and at a location 150 mm from one end in the width direction to the opposite end (the same location for both ends in the width direction), and a vertical cross section in the width direction at the center of the thickness direction was taken. A 100x magnification photograph was taken. Three 2 mm straight lines were drawn at random in the width direction of the enlarged photograph (three lines for each observation location), and the number c of bubbles in contact with the lines was measured. From the measured number c of bubbles, the average bubble diameter C in the width direction for each observation location was calculated using the following formula (3). The average value of the three locations was taken as the average bubble diameter C (average value) in the width direction of the styrene-based resin extruded foam.

Average bubble diameter C (mm) in the width direction at each observation point = 2 x 3 / number of bubbles c
...(3).

The bubble deformation ratio of the styrene-based resin extruded foam according to one embodiment of the present invention is preferably 0.7 to 2.0, more preferably 0.8 to 1.5, and even more preferably 0.8 to 1.2. If the bubble deformation ratio is less than 0.7, the compressive strength is low, and the extruded foam may not have a strength suitable for the intended use. In addition, the bubbles tend to return to a spherical shape, which tends to result in poor dimensional (shape) retention of the extruded foam. On the other hand, if the bubble deformation ratio exceeds 2.0, the number of bubbles in the thickness direction of the extruded foam is reduced, which reduces the effect of improving the insulation due to the bubble shape.

The cell deformation rate of the extruded styrene resin foam according to one embodiment of the present invention can be calculated from the average cell diameter described above using the following formula (4).

Bubble deformation rate (unitless) = A (average value) / {[B (average value) + C (average value)] / 2} ... (4).

The thickness of the styrene-based resin extruded foam according to one embodiment of the present invention is preferably 10 mm or more and 150 mm or less, more preferably 20 mm or more and 130 mm or less, and particularly preferably 30 mm or more and 120 mm or less, from the viewpoints of insulation, bending strength, and compressive strength, taking into consideration the functioning of the foam as, for example, a thermal insulation material for buildings, or a thermal insulation material for refrigerators or refrigerated vehicles.

As described in the examples and comparative examples of the present invention, the styrene-based resin extruded foam may be shaped by extrusion foaming, and then both surfaces of a plane perpendicular to the thickness direction may be cut to a depth of about 5 mm on each side in the thickness direction to obtain the product thickness. However, unless otherwise specified, the thickness of the styrene-based resin extruded foam according to one embodiment of the present invention refers to the uncut thickness after extrusion foaming to give the shape.

Thus, one embodiment of the present invention makes it possible to easily obtain an extruded styrene resin foam that has excellent heat insulation and flame retardancy, a beautiful appearance, and a sufficient thickness suitable for use.

2. Method for producing extruded styrene resin foam
The configurations already explained in [1. Extruded styrene resin foam] are used by reference, and the explanation thereof will be omitted here.

As an example of a method for producing a styrene-based resin extrusion foam, the following method can be mentioned. First, the styrene-based resin and, if necessary, the various additives described above are supplied to the heat-melting section of an extruder having a die slit section (in other words, the resin composition is supplied to the heat-melting section of the extruder). At this time, a foaming agent can be mixed into the resin composition under high pressure conditions at any stage (for example, during or after the resin composition is heated and melted). This is the melting process.

Then, the foamable molten material obtained in the melting process is cooled to a temperature suitable for extrusion foaming, and the fluid gel is extruded through the die slit into a low-pressure region (e.g., an atmospheric pressure region) to form a styrene-based resin extruded foam. This completes the foaming process.

In the melting process, methods of blending various additives with styrene resin include, for example, a method of adding various additives to styrene resin and mixing by dry blending; a method of adding various additives to molten styrene resin from a supply section installed in the middle of the extruder; a method of preparing a master batch in which various additives are incorporated into styrene resin at high concentrations using an extruder, kneader, Banbury mixer, rolls, etc., and mixing the master batch with styrene resin by dry blending; and a method of feeding various additives to the extruder using a feeding facility separate from the styrene resin. However, in the present invention, graphite is added as a master batch.

The heating temperature in the heat melting section is equal to or higher than the temperature at which the styrene resin used melts. The heating temperature is preferably a temperature at which molecular deterioration of the resin due to the influence of additives and the like is suppressed as much as possible (for example, about 150°C to 260°C). The melt kneading time in the heat melting section cannot be uniquely defined because it differs depending on the amount of styrene resin extruded per unit time and/or the type of extruder used as the melt kneading section, and can be appropriately set as the time required for the styrene resin, the foaming agent, and the additives to be uniformly dispersed and mixed.

As the melt-kneading section, any mechanism used in normal extrusion foaming can be used without particular limitations, such as a screw-type extruder.

There are no particular limitations on the pressure at which the foaming agent is added or injected, as long as it is higher than the internal pressure of the extruder, etc.

In the foaming process, an example of a method for extrusion foaming is a method in which the above-mentioned fluid gel is released from a high-pressure region to a low-pressure region through a die slit section having a straight slit-shaped opening used for extrusion molding. In this way, an extruded foam is obtained. Note that there are no particular limitations on the shape of the die slit section, and various die slit sections in this technical field can be used.

The styrene-based resin extruded foam may be molded into a plate-shaped foam, i.e., an extruded foam plate. For example, the extruded foam obtained as described above can be molded into a plate-shaped foam with a large cross-sectional area using a molding die installed in close contact with or in contact with a slit die and a molding roll installed adjacent to the downstream side of the molding die. The desired cross-sectional shape, surface properties, and foam quality can be obtained by adjusting the flow surface shape of the molding die and the die temperature.

The following describes examples of the present invention, but the present invention is not limited to these.

[Raw materials]
The raw materials used in the examples and comparative examples are as follows.

Styrene-based resin: Polystyrene A [manufactured by PS Japan Co., Ltd., 680; MFR 7.0 g/10 min]
Polystyrene B [Toyo Styrene Co., Ltd., G120; MFR 21 g/10 min]
Polystyrene C [PS Japan Co., Ltd., G9401; MFR 2.1 g/10 min]
Styrene-acrylonitrile copolymer [Denka AS GR-AT-5S, manufactured by Denka Co., Ltd.; acrylonitrile content 25% by weight, MFR 8.0 g/10 min]
Thermal radiation suppressant - graphite [Marutoyo Foundry Manufacturing Co., Ltd., M-885; flake graphite, average particle size 5.5 μm, fixed carbon content 89%]
Flame retardant: A mixed bromine-based flame retardant consisting of tetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl)ether and tetrabromobisphenol A-bis(2,3-dibromopropyl)ether [GR-125P, manufactured by Daiichi Kogyo Seiyaku Co., Ltd.]
Flame retardant synergist: Triphenylphosphine oxide [Sumitomo Shoji Chemicals]
Stabilizer: Bisphenol A glycidyl ether [ADEKA Corporation, EP-13]
Dipentaerythritol-adipic acid reaction mixture [Ajinomoto Fine-Techno Co., Ltd., Plainlyzer ST210]
Triethylene glycol-bis-3-(3-tert-butyl-4-hydroxy-5-methylphenyl)propionate [Songwon Japan Co., Ltd., Sonnox 2450FF]
Other additives: Talc [Talc Powder PK-Z, manufactured by Hayashi Kasei Co., Ltd.]
Calcium stearate [Sakai Chemical Industry Co., Ltd., SC-P]
Bentonite [Hojun Co., Ltd., Bengelbright 11K]
Silica [Evonik Degussa Japan Co., Ltd., Carplex BS-304F]
Stearic acid monoglyceride [Rikemal S-100P, manufactured by Riken Vitamin Co., Ltd.]
Ethylene bis stearic acid amide [NOF Corporation, Alflow H-50S]
○ Foaming agent: HFO-1234ze [manufactured by Honeywell Japan Co., Ltd.]
- Dimethyl ether [Iwatani Corporation]
Ethyl chloride [Nippon Specialty Chemical Industry Co., Ltd.]
- Isobutane [Mitsui Chemicals, Inc.]
・Water [Settsu City, Osaka Prefecture tap water]

[Measurement method]
In the examples and comparative examples, various parameters were measured and evaluated according to the following measurement methods.

(1) MFR of styrene resin and graphite masterbatch
The MFR of the raw material styrene-based resin and the obtained graphite masterbatch was measured using a semi-automatic melt tester [manufactured by Yasuda Seiki Seisakusho Co., Ltd., 120HA] in accordance with JIS K7210-1 (2014) Method A (test temperature 200°C, load 5.00 kg).

(2) Thickness of extruded styrene resin foam (before cutting)
The thickness of the extruded foam plate having a cross section of 60 mm thick x 1000 mm wide obtained in [Preparation of extruded foam] described later was measured at three points in total, namely, the center in the width direction and a point 150 mm from one end in the width direction to the opposite end (the same point on both ends in the width direction) using a vernier caliper [Mitutoyo Corporation, M-type standard vernier caliper N30]. The average value of the three points was regarded as the thickness of the extruded styrene resin foam.

(3) Apparent density (kg/ ^m3 )
The weight of the resulting extruded styrene resin foam was measured, and its length (in the extrusion direction), width and thickness were also measured.

From the measured weight and each dimension, the apparent density of the extruded styrene resin foam was calculated based on the following formula: Then, the unit of the apparent density was converted into kg/ ^m3 .
Apparent density (g/cm ³ )=foam weight (g)/foam volume (cm ³ ).

(4) Closed cell ratio Test pieces measuring 40 mm thick x 25 mm long (in the extrusion direction) x 25 mm wide were cut out from three locations of the obtained extruded styrene-based resin foam: the widthwise center, a location 150 mm from one end in the widthwise direction toward the opposite end, and a location 150 mm from the other end in the widthwise direction toward the opposite end. Using the test pieces, measurements were performed according to procedure C of ASTM-D2856-70, and the closed cell ratio of each test piece was calculated according to the following formula. The average value of the closed cell ratios at the three locations was taken as the closed cell ratio of the extruded styrene-based resin foam.
Closed cell ratio (%) = (V1-W/ρ) x 100/(V2-W/ρ)
Here, V1 (cm ³ ) is the true volume (excluding the volume of the portion that is not an independent cell) of the test piece measured using an air comparison type specific gravity meter [Tokyo Science Co., Ltd., air comparison type specific gravity meter, Model 1000]. V2 (cm ³ ) is the apparent volume calculated from the outer dimensions of the test piece measured using a caliper [M-type standard vernier caliper N30, Mitutoyo Corporation]. W (g) is the total weight of the test piece. In addition, ρ (g/cm ³ ) is the density of the styrene-based resin that constitutes the extruded foam, which was set to 1.05 (g/cm ³ ).

(5) Average Cell Diameter and Cell Deformation Rate The average cell diameter of the obtained styrene-based resin extruded foam was measured using a microscope [DIGITAL MICROSCOPE VHX-900, manufactured by KEYENCE CORPORATION] as described above, and the cell deformation rate was calculated from the measured average cell diameter.

(6) Thermal Conductivity According to JIS A 9521, a test piece having a thickness of 50 mm, a length (extrusion direction) of 300 mm, and a width of 300 mm was cut out from a styrene-based resin extruded foam, and the thermal conductivity was measured at an average temperature of 23° C. using a thermal conductivity measuring device [Eiko Seiki Co., Ltd., HC-074]. Specifically, after the production of the styrene-based resin extruded foam, a test piece having the above dimensions was cut out, and the test piece was allowed to stand under the conditions of standard temperature condition class 3 (23° C.±5° C.) and standard humidity condition class 3 (50 ^{+20, -10} % R.H.) specified in JIS K 7100, and then the thermal conductivity was measured one week (7 days) after the production of the styrene-based resin extruded foam.

(7) JIS Flammability According to JIS A 9521, a test piece having a thickness of 10 mm, a length (in the extrusion direction) of 200 mm, and a width of 25 mm was used to evaluate the flammability according to the following criteria. The produced styrene-based resin extruded foam was cut into a test piece having the above dimensions, and the test piece was left to stand under the conditions of standard temperature condition Class 3 (23°C ± 5°C) and standard humidity condition Class 3 (50 ^{+ 20, -10} % R.H.) specified in JIS K 7100. One week after the production of the styrene-based resin extruded foam (after 7 days), the flammability was evaluated using the test piece.
○: Meets the criteria of "flame goes out within 3 seconds, there is no residual fuel, and the fire does not burn beyond the flammability limit indicator line."
×: Does not meet the above criteria.

(8) Foreign matter A foam board having a thickness of 50 mm, a width of 910 mm, and a length (in the extrusion direction) of 1820 mm was cut out from the obtained styrene-based resin extruded foam, and then cut into 30 test pieces having a thickness of 10 mm, a width of 910 mm, and a length of about 300 mm (in the extrusion direction). The surfaces of the test pieces were visually inspected and evaluated for foreign matter according to the following criteria.
○: No foreign matter (unfoamed portion) with a diameter of 2 mm or more was observed. ×: Foreign matter (unfoamed portion) with a diameter of 2 mm or more was observed.

[Examples and Comparative Examples]
Example 1
[Preparation of graphite master batch]
Into a Banbury mixer, 48 weight percent of polystyrene [manufactured by PS Japan Co., Ltd., 680; MFR 7.0 g/10 min], 50 weight percent of graphite [manufactured by Marutoyo Foundry Manufacturing Co., Ltd., M-885], and 2.0 weight percent of stearic acid monoglyceride [manufactured by Riken Vitamin Co., Ltd., Rikemar S-100P] were charged, and melt-kneaded for 20 minutes without heating or cooling under a load of 5 kgf/cm ^2. At this time, the resin temperature was measured and found to be 190°C. The strand-shaped resin, which was supplied to a ruder and extruded at a discharge rate of 250 kg/hr through a die having a small hole attached to the tip, was cooled and solidified in a water tank at 30°C, and then cut to obtain a master batch. The MFR of the obtained graphite master batch is shown in Table 1.

[Preparation of resin mixture]
The materials shown in Table 1 (materials other than the foaming agent) were dry-blended in the composition shown in Table 1 to obtain a resin mixture.

[Preparation of extruded foam]
The obtained resin composition was supplied at about 800 kg/hr to an extruder in which a single screw extruder (first extruder) with a diameter of 150 mm, a single screw extruder (second extruder) with a diameter of 200 mm, and a cooler were connected in series.

The resin composition fed to the first extruder was heated to 250°C to melt or plasticize it, and then kneaded to obtain a resin composition, and a foaming agent was injected into the resin composition near the tip of the first extruder.

Then, in the second extruder and cooler connected to the first extruder, the temperature of the resin composition was cooled to the resin temperature shown in Table 1, and the resin composition was extruded and foamed into the atmosphere at the foaming pressure shown in Table 1 through a die (slit die) with a rectangular cross section and the thickness shown in Table 1, which was installed at the tip of the cooler. Then, an extruded foam board with a cross-sectional shape of 60 mm thick x 1000 mm wide was obtained using a molding die installed in close contact with the die and a molding roll installed downstream of it. The evaluation results of the obtained foam are shown in Table 1.

(Examples 2 to 6)
A graphite master batch and an extruded foam were obtained in the same manner as in Example 1, except that the formulation and production conditions were changed as shown in Table 1. The physical properties of the obtained extruded foam are shown in Table 1.

(Comparative Examples 1 to 3)
A graphite master batch and an extruded foam were obtained in the same manner as in Example 1, except that the formulation and production conditions were changed as shown in Table 2. The physical properties of the obtained extruded foam are shown in Table 2.

As shown in Table 1, no foreign matter was found in the foam in Examples 1 to 6. On the other hand, as shown in Table 2, foreign matter was found in Comparative Examples 1 to 3.

The styrene-based resin extruded foam according to one embodiment of the present invention can be used, for example, as a heat insulating material, a sound absorbing material, a core material for vacuum insulation materials, a cushioning material, and a filler material.

Claims (9)

A method for producing an extruded styrene-based resin foam, comprising melt-kneading a styrene-based resin, a graphite master batch, and a foaming agent,
the graphite masterbatch comprises graphite and a polyhydric alcohol fatty acid ester;
The polyhydric alcohol fatty acid ester is contained in an amount of 0.5 to 6.0% by weight based on 100% by weight of the graphite masterbatch . The method for producing an extruded styrene-based resin foam according to claim 1, wherein the ratio (MFRg/MFRr) of the melt mass flow rate (MFRg) of the graphite master batch measured at a test temperature of 200°C and a load of 5 kg according to JIS K7210-1 (2014) Method A to the melt mass flow rate (MFRr) of the styrene-based resin measured at a test temperature of 200°C and a load of 5 kg according to JIS K7210-1 (2014) Method A is 0.20 or more. The method for producing an extruded styrene resin foam according to claim 1 or 2 , wherein the polyhydric alcohol fatty acid ester comprises a glycerin fatty acid ester. 4. The method for producing an extruded styrene resin foam according to claim 3, wherein the glycerol fatty acid ester is at least one selected from the group consisting of lauric acid monoglyceride, lauric acid diglyceride, lauric acid triglyceride, palmitic acid monoglyceride, palmitic acid diglyceride, palmitic acid triglyceride, stearic acid monoglyceride , stearic acid diglyceride, and stearic acid triglyceride. The method for producing an extruded styrene resin foam according to any one of claims 1 to 4 , wherein the graphite is contained in an amount of 40% by weight or more based on 100% by weight of the graphite masterbatch. a ratio (MFRg/MFRr) of a melt mass flow rate (MFRg) of the graphite masterbatch measured under conditions of a test temperature of 200° C. and a load of 5 kg in accordance with Method A of JIS K7210-1 (2014) to a melt mass flow rate (MFRr) of the styrene-based resin measured under conditions of a test temperature of 200° C. and a load of 5 kg in accordance with Method A of JIS K7210-1 (2014) is 0.50 or more,
The method for producing an extruded styrene resin foam according to any one of claims 1 to 5 , wherein the foaming agent contains an alkyl chloride. The method for producing an extruded styrene resin foam according to any one of claims 1 to 6 , wherein the extruded styrene resin foam has a thermal conductivity of 0.0244 W/mK or less. The method for producing an extruded styrene-based resin foam according to any one of claims 1 to 7 , wherein the extruded styrene-based resin foam has an apparent density of 20 to 60 kg/ ^m3 . The method for producing an extruded styrene resin foam according to any one of claims 1 to 8 , wherein the extruded styrene resin foam has a thickness of 10 mm or more and 150 mm or less.