Expanded polystyrene resin particles, pre-expanded particles thereof, and foamed molded articles

Abstract

To provide expandable polystyrenic resin particles which enable provision of a novel expanded molding that is excellent in dimensional stability at 95°C, has high heat insulation properties and flame retardant performance, and has a small content of VOC.SOLUTION: Expandable polystyrenic resin particles contain a resin composition containing a base material resin, a bromine-based flame retardant, and graphite, wherein the base material resin contains a styrenic copolymer resin containing a styrenic monomer unit as a constitutional unit, the resin composition has a glass transition point of 105°C or higher and 125°C or lower, and a content of the styrene monomer is less than 0.03 wt.%.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to expandable polystyrene resin particles, pre-expanded particles, and foamed molded articles.

Background Art

[0002] As heat insulating materials such as hot water storage tanks, roof heat insulating materials, and pipe heat insulating materials, polystyrene-based foamed molded articles are sometimes used because of their light weight and ease of assembly. In these applications, high heat insulation performance is required, and dimensional stability when used for a long time in a high-temperature environment is also required. Therefore, a polystyrene-based foamed molded article with improved heat resistance by copolymerization or the like is used. In addition, flame retardant performance is required from the viewpoint of preventing fires, and a low emission amount of organic volatile components (VOCs) such as styrene monomer is required in terms of environmental response.

[0003] For example, in Patent Document 1, expandable polystyrene resin particles that can obtain a foamed molded article excellent in heat resistance and flame retardancy are provided by kneading a styrene-methacrylic acid copolymer resin with a flame retardant and a foaming agent in an extruder and granulating. Further, in Patent Document 2, expandable polystyrene resin particles with a small amount of styrene monomer are provided, which can obtain a foamed molded article having dimensional stability and flame retardant performance at 95°C with a styrene-alpha-methylstyrene-acrylonitrile copolymer.

[0004] Although these foamed molded articles have excellent heat resistance, in recent years, the requirements for heat insulation performance of heat insulating materials have been increasing further, and it is necessary to further improve the heat insulation performance.

[0005] On the other hand, as in Patent Document 3, it has been found that expandable polystyrene resin particles with improved heat insulation can be obtained by introducing a carbon-based radiation inhibitor such as graphite. Although the heat insulation property is improved by introducing such a carbon-based radiation inhibitor, there has been no expandable polystyrene resin particle that can achieve both dimensional stability at high temperatures and excellent heat insulation property because the heat resistance of the base resin is insufficient.

Prior Art Documents

[0006] [Patent Document 1] Japanese Patent Publication No. 2011-93952 [Patent Document 2] Japanese Patent Publication No. 2015-151486 [Patent Document 3] Japanese Patent Publication No. 2020-33481 [Overview of the project] [Problems that the invention aims to solve]

[0007] One aspect of the present invention provides foamed polystyrene resin particles, pre-foamed particles, a foamed molded article, and an insulating material for a hot water storage tank, which can provide a novel foamed molded article that has excellent dimensional stability at 95°C, high heat insulation and flame retardancy, and low VOC content. [Means for solving the problem]

[0008] As a result of diligent research to solve the above problems, the inventors have found that the above problems can be solved by using a styrene-based resin having a glass transition temperature of 105°C to 120°C, and by introducing a brominated flame retardant and graphite.

[0009] That is, one embodiment of the present invention includes the following configuration. [1] These are foamed polystyrene resin particles containing a resin composition comprising a base resin, a brominated flame retardant, and graphite. The base resin includes a styrene copolymer resin containing styrene monomer units as constituent units. The resin composition has a glass transition temperature of 105°C or higher and 125°C or lower. Expandable polystyrene resin particles having a styrene monomer content of less than 0.03% by weight. [2] The styrene copolymer resin comprises styrene monomer units and acrylic monomer units as constituent units. [1] foamable polystyrene resin particles, wherein the content of a styrene resin composed solely of styrene monomer units as constituent units is less than 20 parts by weight per 100 parts by weight of the resin composition. [3] Expandable polystyrene resin particles according to [1] to [2], wherein the ratio (L / D) of the length in the long axis direction (L) to the length in the short axis direction (D) of the particle shape is 0.8 or greater. [4] [1] to [3] are foamed polystyrene resin particles, wherein the weight-average molecular weight of the base resin is between 180,000 and 250,000. [5] Expandable polystyrene resin particles [1] to [4], wherein the brominated flame retardant content is 2 parts by weight or more and 4 parts by weight or less per 100 parts by weight of the base resin. [6] Foamed polystyrene resin particles having a graphite content of 2 parts by weight or more and 8 parts by weight or less per 100 parts by weight of the base resin [1] to [5]. [7] [1] to [6] are foamed polystyrene resin particles, wherein the foamed polystyrene resin particles are pre-foamed 50 times, and the average chord length of the bubbles (cells) in the molded foamed product is 20 μm or more and 150 μm or less. [8] When foamed polystyrene resin particles are pre-foamed 50 times and molded into a foamed molded article, the foamed polystyrene resin particles [1] to [7] satisfy the following (a), (b), and (c). (a) The dimensional change rate after heating at 95°C for 168 hours is less than 2%. (b) The thermal conductivity is 0.033 W / mK or less. (c) The minimum oxygen index is 26 or higher. [9] Pre-foamed particles obtained by pre-foaming the foamed polystyrene resin particles [1] to [8].

[10] A foamed molded body obtained by molding the pre-foamed particles of [9].

[11]

[10] Insulation material for hot water storage tanks comprising a foamed molded body. [Effects of the Invention]

[0010] According to one aspect of the present invention, it is possible to provide foamed polystyrene resin particles, pre-foamed particles, a foamed molded article, and an insulating material for a hot water storage tank, which can provide a novel foamed molded article that has excellent dimensional stability at 95°C, high heat insulation and flame retardancy, and low VOC content. [Modes for carrying out the invention]

[0011] Embodiments of the present invention will be described in detail below. However, the present invention is not limited thereto, and various modifications are possible within the scope described. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments and examples are also included within the technical scope of the present invention. In this specification, unless otherwise specified, "A~B" representing a numerical range means "A or greater (including A and greater than A), B or less (including B and less than B)." The foamed polystyrene resin particles of the present invention are foamed polystyrene resin particles comprising a resin composition containing a base resin, a brominated flame retardant, and graphite. The base resin contains a styrene copolymer resin containing styrene monomer units as constituent units, the glass transition temperature of the resin composition is 105°C to 125°C, and it contains less than 0.03% by weight of styrene monomers. Because the foamed polystyrene resin particles of the present invention have the above configuration, they provide a novel foamed molded article with excellent dimensional stability at 95°C, high heat insulation and flame retardancy, and low VOC content.

[0012] The base resin constituting the foamed polystyrene resin particles of the present invention mainly contains styrene monomers and includes a styrene copolymer resin containing styrene monomer units as constituent units. In this specification, the "styrene monomer unit" is a constituent unit derived from a styrene monomer. Examples of the styrene monomer include styrene (sometimes referred to as styrene monomer), α-methylstyrene, paramethylstyrene, t-butylstyrene, and chlorostyrene.

[0013] The resin composition contained in the foamed polystyrene resin particles of the present invention has a glass transition temperature of 105°C or higher and 125°C or lower. In order to achieve both foam molding properties and dimensional stability as a heat insulating material, the glass transition temperature is preferably 105°C or higher and 120°C or lower, more preferably 108°C or higher and 118°C or lower. If the glass transition temperature of the resin composition is less than 105°C, sufficient dimensional stability during use at high temperatures cannot be obtained. If it exceeds 125°C, the heat resistance becomes too high and it is difficult to obtain the expansion ratio during pre-foaming.

[0014] In addition, the foamed polystyrene resin particles of the present invention contain less than 0.03% by weight of styrene monomer. The monomer component contained therein tends to volatilize from the foamed molded article obtained by foaming the foamed polystyrene resin particles. Therefore, since the amount of styrene monomer remaining in the foamed polystyrene resin particles is less than 0.03% by weight, the amount of styrene monomer contained in the foamed molded article formed by foaming the foamed polystyrene resin particles, that is, the VOC content can be suppressed. As a result, the amount of VOC released from the foamed molded article can be reduced. The amount of styrene monomer contained in the foamed polystyrene resin particles is preferably as small as possible. For example, it is preferably 0.02% by weight or less, more preferably 0.015% by weight or less, and still more preferably 0.01% by weight or less. According to the above configuration, the VOC content of the obtained foamed molded article can be further reduced. The content of the styrene monomer can be reduced by appropriately setting the conditions during melt extrusion in the production process of the foamed polystyrene resin particles and suppressing the decomposition of the resin component into the monomer. As appropriate extrusion conditions, for example, it is preferable to set the temperature during melt extrusion to 230°C or lower because it is easy to suppress the decomposition.

[0015] In the foamed polystyrene resin particles of the present invention, the styrene-based copolymer resin contained in the base resin contains an acrylic monomer unit in addition to the styrene-based monomer unit as a structural unit. In the present specification, the "acrylic monomer unit" is a structural unit derived from an acrylic monomer. Examples of the acrylic monomer include acrylic acid, methacrylic acid, methyl acrylate, methyl methacrylate, butyl acrylate, 2-ethylhexyl acrylate, acrylonitrile, and the like. In order to easily adjust the glass transition point of the resin composition, it is preferable that the base resin contains a styrene-based copolymer resin obtained by copolymerizing acrylic acid, methacrylic acid, or acrylonitrile with a styrene-based monomer. As the copolymer component, acrylic acid and methacrylic acid are preferable from the viewpoint of being less likely to generate toxic gases during combustion.

[0016] Furthermore, in the resin composition, it is preferable that the content of styrene-based resin, which consists solely of styrene-based monomer units as constituent units, is less than 20 parts by weight per 100 parts by weight of the resin composition. If the proportion of styrene-based resin in the resin composition is high, the glass transition temperature of the resin composition tends to be below 105°C, and the heat resistance tends to deteriorate. In this specification, "styrene-based copolymer resin" refers to a resin consisting of a copolymer of a styrene-based monomer and a monomer copolymerizable with a styrene-based monomer, and "styrene-based resin" refers to a resin consisting of styrene-based monomers, that is, a resin consisting of a homopolymer of styrene-based monomers.

[0017] The foamed polystyrene resin particles of the present invention require the inclusion of a brominated flame retardant in the resin composition to impart flame retardancy. Examples of brominated flame retardants include halogenated aliphatic hydrocarbon compounds such as hexabromocyclododecane, tetrabromobutane, and hexabromocyclohexane; brominated phenols such as tetrabromobisphenol A, tetrabromobisphenol F, and 2,4,6-tribromophenol; tetrabromobisphenol A-bis(2,3-dibromopropyl ether); and tetrabromobisphenol A-bis(2,3-dibromo-2-methyl ether). Examples of brominated phenol derivatives such as propyl ether, tetrabromobisphenol A-diglycidyl ether, 2,2-bis[4'(2",3"-dibromoalkoxy)-3',5'-dibromophenyl]-propane, brominated styrene-butadiene block copolymer, brominated random styrene-butadiene copolymer, and brominated styrene-butadiene graph copolymer, as well as brominated butadiene-vinyl aromatic hydrocarbon copolymers (for example, EMERALD3000 from Chemtura, or disclosed in Japanese Patent Publication No. 2009-516019). These flame retardants may be used individually or in mixtures of two or more. The content (amount added) of the brominated flame retardant is preferably 2 to 4 parts by weight per 100 parts by weight of the base resin, and more preferably 2.5 to 3 parts by weight. If the amount is less than 2 parts by weight, the flame retardant performance is difficult to exhibit, and if it exceeds 4 parts by weight, the dimensional stability of the base resin tends to decrease.

[0018] The foamed polystyrene resin particles of the present invention contain graphite as a carbon-based radiant heat transfer inhibitor to provide thermal insulation. The graphite content is preferably 2 to 8 parts by weight, more preferably 3 to 5 parts by weight, and even more preferably 3.5 to 4 parts by weight, per 100 parts by weight of the base resin. If the amount of graphite is less than 2 parts by weight, the thermal insulation is not sufficiently provided, and if it exceeds 8 parts by weight, the bubbles tend to break during pre-foaming and molding, making it difficult to obtain a sufficient foaming ratio and heat resistance.

[0019] The amount of foaming agent added to the foamed polystyrene resin particles in the present invention is 3.0 to 12.0 parts by weight, preferably 6.0 to 9.0 parts by weight, per 100 parts by weight of the base resin.

[0020] If the foaming agent content is less than 3 parts by weight, the foaming force during pre-foaming is low, making it difficult to obtain pre-foamed particles with a suitable foaming ratio for use as insulation material. If the foaming agent content exceeds 12 parts by weight, the flame retardant performance tends to deteriorate due to the foaming agent remaining in the foamed molded product. A good balance between foaming and moldability is achieved when the amount of foaming agent added is 6.0 to 9.0 parts by weight.

[0021] Examples of foaming agents used in the present invention include aliphatic hydrocarbons such as propane, butane, and pentane; alicyclic hydrocarbons such as cyclobutane and cyclopentane; and halogenated hydrocarbons such as methyl chloride, dichlorodifluoromethane, and dichlorotetrafluoroethane. These foaming agents may be used individually or in combination of two or more. Among these foaming agents, the combined use of pentane and butane is preferred because it provides stable foaming power and bubbles (cells). The foamable polystyrene resin particles in the present invention preferably have a particle shape where the ratio of the length in the long axis direction (L) to the length in the short axis direction (D) is L / D = 0.8 or higher, more preferably 0.85 or higher, and even more preferably 0.9 or higher. When the L / D of the foamable polystyrene resin particles is within the above range, the shape of the pre-foamed particles approaches a spherical shape, improving the packing of pre-foamed particles into the mold during the creation of a foamed molded article, and making it easier to obtain a foamed molded article in which pre-foamed particles are filled to the finest details, even in molds with complex shapes.

[0022] In the present invention, the weight-average molecular weight Mw of the foamed polystyrene resin particles is preferably 180,000 to 250,000, and more preferably 200,000 to 220,000.

[0023] When the weight-average molecular weight (Mw) of foamed polystyrene resin particles is less than 180,000, the dimensional stability of the foamed molded article tends to deteriorate. On the other hand, when the weight-average molecular weight (Mw) of foamed polystyrene resin particles exceeds 250,000, the foaming properties tend to decrease. Furthermore, although the weight-average molecular weight (Mw) of foamed polystyrene resin particles is similar to the weight-average molecular weight (Mw) of the raw material resin, depending on the extrusion conditions, when the weight-average molecular weight (Mw) exceeds 250,000, stress is applied to the resin particles during extrusion, resulting in significant deformation after extrusion and making it difficult to obtain stably spherical particles.

[0024] Here, the weight-average molecular weight Mw of the foamed polystyrene resin particles in the present invention is a value measured using gel permeation chromatography (hereinafter sometimes abbreviated as "GPC") under the conditions described later.

[0025] Furthermore, the foamed polystyrene resin particles of the present invention may contain, as needed, heat stabilizers such as hindered amine compounds, phosphorus compounds, and epoxy compounds; processing aids such as sodium stearate, magnesium stearate, calcium stearate, zinc stearate, barium stearate, and liquid paraffin; additives such as phenolic antioxidants, nitrogen stabilizers, sulfur stabilizers, benzotriazoles, and other light-resistant stabilizers; antistatic agents; colorants such as pigments; silica, calcium silicate, and wollastonite. It may also contain foaming aids such as inorganic compounds like t, kaolin, clay, mica, zinc oxide, calcium carbonate, and sodium bicarbonate; methyl methacrylate copolymers; olefin waxes such as polyethylene wax; fatty acid bisamides such as talc, methylene bisstearyl amide, ethylene bisstearyl amide, hexamethylene bispalmitate amide, and ethylene bisoleate amide; nucleating agents such as ethylene-vinyl acetate copolymer resins; and solvents with a boiling point of 200°C or less at atmospheric pressure, such as cyclohexane and ethyl chloride.

[0026] As a method for producing the foamed polystyrene resin particles of the present invention, known methods can be employed, but a preferred method involves melt-kneading a base resin containing a styrene copolymer resin with various compounds using an extruder, and then cutting it into particles. Two such methods are described below. Specifically, the first method involves melt-kneading a base resin with a foaming agent, graphite, a brominated flame retardant, and other additives as needed using an extruder, cooling it to a predetermined temperature, extruding it through a die with small holes into a cutter chamber filled with pressurized circulating water, cutting it with a rotary cutter immediately after extrusion, and then cooling and solidifying it with pressurized circulating water to obtain foamed polystyrene resin particles. The second method for producing foamed polystyrene resin particles involves melt-kneading a base resin with a foaming agent, graphite, a brominated flame retardant, and other additives as needed using an extruder, extruding it through a die with small holes, and then cutting it with a cutter to obtain styrene resin particles. The styrene resin particles are then suspended in water in a sealed container, and a foaming agent is supplied to impregnate them to obtain foamed polystyrene resin particles.

[0027] Furthermore, known and commonly used external additives can be applied to the surface of the foamed polystyrene resin particles of the present invention.

[0028] Specific examples of external additives include, for example, fatty acid triglycerides such as triglyceride laurate, triglyceride stearate, and triglyceride linoleate; fatty acid diglycerides such as diglyceride laurate, diglyceride stearate, and diglyceride linoleate; fatty acid monoglycerides such as monoglyceride laurate, monoglyceride stearate, and monoglyceride linoleate; fatty acid metal salts such as zinc stearate, calcium stearate, magnesium stearate, aluminum stearate, zinc laurate, and calcium laurate; silicone oils such as dimethylpolysiloxane and methylphenylpolysiloxane; castor wax; and vegetable oils such as castor oil and olive oil. These external additives may be used individually or in combination of two or more. As for the method of coating (applying) the external additive to the surface of the foamed polystyrene resin particles, known methods can be used, but a preferred coating method is to apply the external additive to the foamed polystyrene resin particles obtained by the above manufacturing method after drying, and then coat them by mixing and stirring.

[0029] Pre-foamed particles in one embodiment of the present invention are obtained by pre-foaming (primary foaming) the above-mentioned foamable polystyrene resin particles.

[0030] As for the pre-foaming method, conventional methods can be employed, such as using a cylindrical pre-foaming device and heating the expandable polystyrene resin particles with a heating medium such as steam to cause foaming. The device used for pre-foaming and the conditions for pre-foaming can be set appropriately according to the composition of the expandable polystyrene resin particles and the desired pre-foaming ratio, and are not particularly limited.

[0031] A foamed molded article in one embodiment of the present invention is obtained by heating and foaming (secondary foaming) the above-mentioned pre-foamed particles.

[0032] As a method for heating and foaming pre-foamed particles, conventional methods such as in-mold foaming molding, in which the pre-foamed particles are filled into a mold and heated by blowing in a heating medium such as steam, can be employed. The equipment used for heating and foaming, and the conditions for heating and foaming, can be set appropriately according to the desired foaming ratio, etc., and are not particularly limited. Foamed molded bodies, especially in-mold foamed molded bodies, are suitable for interlocking heat-insulating materials due to advantages such as the ease with which molded bodies of the desired shape can be produced.

[0033] The average chord length of the bubbles (which may be referred to as cells in this specification) in the foamed molded article obtained by pre-foaming the foamed polystyrene resin particles of the present invention 50 times and molding is preferably 20 μm to 150 μm, more preferably 25 μm to 100 μm, and even more preferably 40 μm to 80 μm. If the average chord length is too small, the surface of the foamed molded article is likely to melt due to heating during molding, and conversely, if it is too large, the fusion properties deteriorate during molding, making it difficult to obtain a good quality foamed molded article. When comparing the first manufacturing method and the second manufacturing method, the foamed molded article using foamed polystyrene resin particles produced by the first manufacturing method tends to have a larger average chord length of bubbles than the foamed molded article using foamed polystyrene resin particles produced by the second manufacturing method.

[0034] The foamed polystyrene resin particles of the present invention, when pre-foamed 50 times and molded into a foamed molded body, preferably have a dimensional change rate of less than 2% when heated at 95°C for 168 hours, a thermal conductivity of 0.033 W / mK or less, and a minimum oxygen index of 26 or higher. Within the above range, when used as an insulating material, it is lightweight, easy to assemble, has excellent cost-quality, is resistant to deformation even when the temperature rises, and possesses excellent heat insulation and flame retardancy, making it suitable as an insulating material for parts with complex shapes exposed to high temperatures, such as hot water storage tanks.

[0035] The foamed molded article of the present invention can be used as insulation material for hot water storage tanks, roof insulation material, and pipe insulation material, but it is particularly suitable as insulation material for hot water storage tanks because it has excellent dimensional stability, high heat insulation and flame retardancy, and low VOC content. [Examples]

[0036] The present invention will be described in more detail below with reference to examples and comparative examples, but the present invention is not limited to these examples. The measurement and evaluation methods were carried out as follows. <Measurement of glass transition temperature of resin composition> Styrene-based resin particles, which are resin particles before impregnation with a foaming agent, were sealed in an open-type aluminum pan. Using a differential scanning calorimeter (Hitachi High-Tech Science DSC7000X), nitrogen gas was flowed at 40 ml / min, and the pan was heated from 40°C to 150°C at a rate of 10°C / min. The point of maximum endothermic heat (peak of endothermic heat) was defined as the glass transition point of the resin composition. <Measurement of residual styrene monomers in expanded polystyrene resin particles> 0.25 g of foamed polystyrene resin particles were dissolved in 20 cc of methylene chloride (internal standard cyclopentanol), and the amount of residual styrene monomer (residual styrene) contained in the foamed resin particles was quantified from a calibration curve using gas chromatography (Shimadzu GC-14B, column: 3 m, packing material: PEG-20M 25%, column temperature: 110°C, carrier gas: helium). The sample was deemed acceptable if the total value was less than 0.03% by weight relative to the foamed resin particles.

[0037] <Weight-average molecular weight measurement of foamed polystyrene resin particles> To obtain the resulting foamed polystyrene resin particles, 0.02 g of the foamed polystyrene resin particles was dissolved in 20 ml of tetrahydrofuran (hereinafter sometimes abbreviated as "THF"). Then, GPC measurements were performed using a gel permeation chromatograph (GPC) under the following conditions to obtain a GPC measurement chart, weight-average molecular weight (Mw), and number-average molecular weight (Mn). The obtained values ​​are relative values ​​in terms of polystyrene. Measurement device: Tosoh Corporation, high-speed GPC device HLC-8220 Columns used: Tosoh Corporation, SuperHZM-H x 2, SuperH-RC x 2 Column temperature: 40°C, Mobile phase: THF (tetrahydrofuran) Flow rate: 0.35ml / min, injection volume: 10μl Detector: RI.

[0038] <Measurement of the shape (L / D) of expanded polystyrene resin particles> For expanded polystyrene resin particles, the length in the long axis direction (L) and the length in the short axis direction (D) were measured using calipers, and the L / D ratio was calculated. The L / D ratio was measured for N=5 particles, and the average value was calculated. The expanded polystyrene resin particles for which the L / D ratio was measured were selected at random from the obtained expanded polystyrene resin particles.

[0039] <Preparation of pre-foamed particles> The obtained expandable polystyrene resin particles were placed into a pressurized pre-foaming machine (BHP-110, manufactured by Daikai Kogyo Co., Ltd.) equipped with a stirrer. Using steam as the heating medium, the mixture was heated at a vapor pressure of 0.09 MPa to induce pre-foaming (primary foaming), resulting in pre-foamed particles with a bulk ratio (apparent ratio) of 50 times.

[0040] <Preparation of foamed molded products> Using a molding machine (Daisen Co., Ltd., KR-57), pre-foamed particles, pre-expanded 50 times using the method described above, were filled into a flat plate-shaped mold measuring 450 mm in length, 300 mm in width, and 25 mm in thickness. Using steam (water vapor) as the heating medium, the blown steam pressure was set to 0.07 MPa, and in-mold foam molding was performed under the following molding conditions: cracking of 1 mm, mold heating for 2 seconds, heating on one side for 6 seconds, heating on the other side for 4 seconds, heating on both sides for 8 seconds, supplemental heating for 5 seconds, water cooling for 5 seconds, air cooling for 5 seconds, and vacuum cooling for 120 seconds, to obtain a box-shaped foamed molded body. The obtained foamed molded body was dried at room temperature for 24 hours, and the following evaluation was performed. The density of the obtained molded body was 0.20 kg / m3.

[0041] <Evaluation of moldability> The appearance of the foamed molded product was evaluated and determined as follows. ○: The molded surface shows no shrinkage or melting, and the surface of the molded body has few gaps between foam particles, resulting in a smooth surface. △: There is no shrinkage or melting of the molded surface, but the gaps between foam particles on the molded surface are large. ×: Shrinkage and melting are observed on the surface of the molded product.

[0042] <Measurement of the average chord length of air bubbles (cells) in foamed molded products> The resulting foamed molded body was cut with a slicer, and images were created by magnifying the cut surface 30 times using a scanning electron microscope (JEOL, JSM-6060LV). The observation conditions for the scanning electron microscope are as follows: Pressurized voltage: 18kV, working distance: 18mm, vacuum level: SEI, spot size: 35. Next, draw a 60mm long straight line on the image, count the number of bubbles located on this line, and use the following calculation formula. Average chord length [μm] = (60 × 1000 / image magnification) / number of bubbles Based on this, the average chord length of the bubbles in the foamed molded product was calculated.

[0043] <Dimensional change rate of foamed molded material at 95°C> A foamed molded body with a 50x expansion ratio was dried at 60°C for 24 hours. Then, the molded body was cut to a length of 150 mm, a width of 150 mm, and a thickness of 20 (t) mm. The initial dimensions (A) were determined by measuring the length and width at three points each. Next, the body was left in a 95°C dryer for 168 hours, and the same measurements were performed afterward to determine the dimensions (B). The dimensional change rate was calculated using the following formula, and the results were determined as follows. Dimensional change rate (%) = ((A) - (B)) / (A) × 100 ◎: Dimensional change rate is less than 1% ○: Dimensional change rate is 1% or more but less than 2% ×: Dimensional change rate is 2% or more

[0044] <Thermal conductivity of foamed molded material> A test specimen measuring 300 mm in length, 300 mm in width, and 25 mm in height, with a double-sided skin layer, was cut from the center of the foamed molded body, avoiding the mold's feeder holes and release pin marks. The test specimen was left to stand at 60°C for 48 hours, and then at 23°C for 24 hours. After that, the thermal conductivity was measured using a thermal conductivity measuring device (HC-074, manufactured by Eiko Seiki Co., Ltd.) in accordance with JIS A1412-2:1999 using the heat flow meter method at an average temperature of 23°C and a temperature difference of 20°C.

[0045] <Flame retardancy of foamed molded materials> The self-extinguishing properties and minimum oxygen index of the foamed molded material were measured, and if both passed, the material was deemed flame-retardant. • Self-extinguishing properties of foamed molded materials The foamed molded body was left to stand at a temperature of 60°C for 48 hours, and then at a temperature of 23°C for another 24 hours. After this, it was evaluated according to the measurement method A of JIS A9511 (Foamed Plastic Insulation Material), and a fire extinguishing time of 3 seconds or less was considered acceptable. • Minimum oxygen index [LOI] of foamed molded material After the foamed molded body was left to stand at 60°C for 48 hours, and then at 23°C for another 24 hours, the minimum oxygen index was measured in accordance with JIS K7201, and a value of 26 or higher was considered acceptable.

[0046] <Ingredients> The following raw materials were used in the examples and comparative examples. (Styrene resin) (A1) Styrene homopolymer [Manufactured by PS Japan Co., Ltd., 680] (A2) Styrene-methacrylic acid polymer [Manufactured by PS Japan Co., Ltd., G9001] (A3) Styrene-methacrylic acid polymer [Manufactured by PS Japan Co., Ltd., MR100] (A4) Styrene-methacrylic acid polymer [Manufactured by PS Japan Co., Ltd., MA100] (A5) Styrene-polyphenylene ether polymer [SABIC, PKN-4752]

[0047] (Graphite) (B) Graphite [(Manufactured by Marutoyo Casting Materials Co., Ltd., flake-type graphite SGP-40B)] (Bromine-based flame retardant) (C) 2,2-Bis[4-(2,3-dibromo-2-methylpropoxy)-3,5-dibromophenyl]propane [manufactured by Daiichi Kogyo Seiyaku Co., Ltd., SR-130, bromine content = 66% by weight]

[0048] (Heat stabilizer) (D1) Tetrakis(2,2,6,6-tetramethylpiperidyloxycarbonyl)butane [(Manufactured by ADEKA Corporation, LA-57)] (D2) Bis(2,6-di-t-butyl-4-methylphenyl)pentaerythritol diphosphite [(Manufactured by ADEKA Corporation, PEP-36)] (others) (E) Ethylene bis-stearamide [Manufactured by NOF Corporation, AL-FLOW H-50S]

[0049] The following describes the manufacturing methods of the masterbatches used in the examples and comparative examples.

[0050] (Manufacturing Example 1) (Graphite Masterbatch (F)) 49 parts by weight of polystyrene resin (A1), 50 parts by weight of graphite (B), and 1 part by weight of ethylenebis-stearate amide (E) were placed in a Banbury mixer and melt-kneaded for 20 minutes under a load of 5 kgf / cm2 without heating or cooling. The mixture was fed into a ruder and extruded at 250 kg / hr through a die with small holes attached to the tip. The strand-like resin was cooled and solidified in a 30°C water bath, and then cut to obtain a masterbatch (F). The graphite content in the masterbatch (F) was 50% by weight.

[0051] (Manufacturing Example 2) (Masterbatch (G) of a mixture of brominated flame retardant and heat stabilizer) Polystyrene resin (A1) was supplied to a twin-screw extruder and melted and kneaded. Then, a mixture of brominated flame retardant (C), heat stabilizers (D1) and (D2) was supplied from the middle of the extruder and further melted and kneaded. The weight ratio of each material was (A1):(C):(D1):(D2) = 70.0:28.5:0.6:0.9, and (A1)+(C)+(D1)+(D2) = 100% by weight. The strand-like molten material extruded at a discharge rate of 300 kg / hr through a die with small holes attached to the tip of the extruder was cooled and solidified in a 20°C water bath, and then cut to obtain a masterbatch (G) of the mixture of brominated flame retardant and heat stabilizer.

[0052] (Example 1) <Manufacturing of styrene-based resin particles> Polystyrene resin (A2), masterbatch (G), and graphite masterbatch (F) were each placed in a blender and blended for 10 minutes to obtain a resin mixture. The weight ratio of each material was (A2):(G):(F) = 83.67:8.33:8.00, and (A2)+(G)+(F) = 100% by weight. The obtained resin mixture was supplied to a 50 mm diameter coaxial twin-screw extruder and melted and kneaded at a set temperature of 210°C and a screw rotation speed of 200 rpm. The strand-shaped resin was extruded at a discharge rate of 70 kg / hour through a die with 30 holes of 1.2 mm in diameter attached to the tip of the extruder. After cooling and solidifying the strand in a 30°C water bath, it was cut with a strand cutter to obtain styrene resin particles with a particle weight of 0.9 mg / particle.

[0053] <Manufacturing of expanded polystyrene resin particles> Next, 200 parts by weight of deionized water, 1 part by weight of tricalcium phosphate, 0.03 parts by weight of sodium dodecylbenzenesulfonate, and 3 parts by weight of sodium chloride were added to a 6 L autoclave equipped with a stirring device for 100 parts by weight of the obtained styrene-based resin particles, and the pressure vessel was sealed. After adding 6.5 parts by weight of mixed pentane (a mixture of 80% n-pentane and 20% isopentane) and 1.5 parts by weight of mixed butane (a mixture of 70% n-butane and 30% isobutane) as blowing agents to the pressure vessel, the temperature was raised to 118°C and maintained at that temperature for 10 hours. After cooling to room temperature, the resin particles impregnated with the blowing agents were removed from the autoclave, pickled with hydrochloric acid, washed with water, dehydrated using a centrifuge, and then dried to remove moisture adhering to the surface of the resin particles using an air-flow dryer to obtain foamed polystyrene-based resin particles. To 100 parts by weight of the obtained foamed polystyrene resin particles, 0.2 parts by weight of zinc stearate and 0.07 parts by weight of castor wax were applied, and then the mixture was stored at 10°C.

[0054] Pre-foamed particles and foamed molded bodies were prepared using the procedures described above for <Preparation of Pre-Foamed Particles> and <Preparation of Foamed Molded Bodies>, and various evaluations were conducted. The evaluation results are shown in Table 1.

[0055] (Example 2) In the <Production of Expandable Polystyrene Resin Particles>, expandable polystyrene resin particles, pre-expanded particles, and in-mold foamed molded articles were obtained by the same procedure as in Example 1, except that (A3) was used instead of (A2) for the polystyrene resin. The evaluation results are shown in Table 1.

[0056] (Example 3) In the <Production of Expandable Polystyrene Resin Particles>, expandable polystyrene resin particles, pre-expanded particles, and in-mold foamed molded articles were obtained by the same procedure as in Example 1, except that (A4) was used instead of (A2) for the polystyrene resin. The evaluation results are shown in Table 1.

[0057] (Comparative Example 1) In the <Production of Expandable Polystyrene Resin Particles>, the weight ratio of each material was set to (A2):(A1):(G):(F) = 83.67:8.00:8.33:0.00, and (A2)+(A1)+(G)+(F) = 100% by weight. Except for these conditions, the same procedure as in Example 1 was used to obtain expandable polystyrene resin particles, pre-expanded particles, and in-mold foamed molded articles. The evaluation results are shown in Table 1.

[0058] (Comparative Example 2) In the <Production of Expandable Polystyrene Resin Particles>, the weight ratio of each material was set to (A2):(A1):(G):(F) = 83.67:8.33:0.00:8.00, and (A2)+(A1)+(G)+(F) = 100% by weight. Except for these conditions, the same procedure as in Example 1 was followed to obtain expandable polystyrene resin particles, pre-expanded particles, and in-molded foamed molded articles. The evaluation results are shown in Table 1.

[0059] (Comparative Example 3) In the <Production of Expandable Polystyrene Resin Particles>, the weight ratio of each material was set to (A3):(A1):(G):(F) = 63.67:20.00:8.33:8.00, and (A3)+(A1)+(G)+(F) = 100% by weight. Except for these conditions, the same procedure as in Example 1 was used to obtain expandable polystyrene resin particles, pre-expanded particles, and in-mold foamed molded articles. The evaluation results are shown in Table 1.

[0060] (Comparative Example 4) In the <Production of Expandable Polystyrene Resin Particles>, expandable polystyrene resin particles, pre-expanded particles, and in-mold foamed molded articles were obtained by the same procedure as in Example 1, except that (A1) was used instead of (A2) as the styrene resin. The evaluation results are shown in Table 1.

[0061] (Comparative Example 5) In the <Production of Expandable Polystyrene Resin Particles>, the weight ratio of each material was set to (A5):(A1):(G):(F) = 28.60:55.07:8.33:8.00, (A5)+(A1)+(G)+(F) = 100% by weight, and the twin-screw extruder temperature was set to 250°C. Except for these conditions, the same procedure as in Example 1 was followed to obtain expandable polystyrene resin particles, pre-expanded particles, and in-mold foamed molded articles. The evaluation results are shown in Table 1.

[0062] (Comparative Example 6) In a 6L autoclave equipped with a stirrer, 110 parts by weight of water, 0.105 parts by weight of tricalcium phosphate, 0.0075 parts by weight of sodium α-oleinsulfonate, and 0.3 parts by weight of di-t-butyl peroxyhexahydroterephthalate: Kaya Ester HTP-65W (manufactured by Nurion) and 0.2 parts by weight of 1,1-bis(t-butylperoxy)cyclohexane): Perhexa C (manufactured by NOF Corporation) as polymerization initiators, 0.2 parts by weight of α-methylstyrene dimer: MSD (manufactured by NOF Corporation) as a chain transfer agent, tetrabromobisphenol-A-bis(2,3-dibromo-2-methylpropyl) ether; Pyroguard SR-130 (manufactured by Daiichi Kogyo Seiyaku Co., Ltd.) as a flame retardant, along with a flame retardant aid and a plasticizer, were charged and deoxidized to a gauge pressure of -0.06 MPa using a vacuum pump. Subsequently, stirring was started using a stirrer, and 71 parts by weight of styrene monomer, 5 parts by weight of alpha-methylstyrene monomer, and 24 parts by weight of acrylonitrile monomer were added and stirred for 30 minutes. Then, the temperature was raised to 90°C and held at 90°C for 5 hours and 30 minutes to carry out the first polymerization. After that, 5 parts by weight of mixed butane (a mixture of 70% normal butane and 30% isobutane) was added, the temperature was raised to 102°C, and foaming agent impregnation and second polymerization were carried out for 8 hours. After that, it was cooled to 40°C, dehydrated, and dried to obtain foamed polystyrene resin particles. 0.3 parts by weight of zinc stearate was applied to 100 parts by weight of the obtained foamed polystyrene resin particles, and then stored at 10°C. The evaluation results are shown in Table 1.

[0063] [Table 1]

Claims

1. These are foamed polystyrene resin particles containing a resin composition comprising a base resin, a brominated flame retardant, and graphite. The base resin includes a styrene copolymer resin containing styrene monomer units as constituent units. The resin composition has a glass transition temperature of 105°C or higher and 125°C or lower. The styrene monomer content is less than 0.03% by weight. The styrene copolymer resin comprises styrene monomer units and acrylic monomer units as constituent units. Expandable polystyrene resin particles in the resin composition wherein the content of styrene resin, which consists solely of styrene monomer units as constituent units, is less than 20 parts by weight per 100 parts by weight of the resin composition.

2. The foamed polystyrene resin particle according to claim 1, wherein the ratio (L / D) of the length in the long axis direction (L) to the length in the short axis direction (D) of the particle shape is 0.8 or more.

3. Expandable polystyrene resin particles according to claim 1 or claim 2, wherein the weight-average molecular weight is 180,000 or more and 250,000 or less.

4. The foamed polystyrene resin particles according to any one of claims 1 to 3, wherein the content of the brominated flame retardant is 2 parts by weight or more and 4 parts by weight or less per 100 parts by weight of the base resin.

5. The foamed polystyrene resin particles according to any one of claims 1 to 4, wherein the graphite content is 2 parts by weight or more and 8 parts by weight or less per 100 parts by weight of the base resin.

6. The foamed polystyrene resin particles according to any one of claims 1 to 5, wherein the foamed polystyrene resin particles are pre-foamed 50 times, and the average chord length of the bubbles in the molded foamed product is 20 μm or more and 150 μm or less.

7. The foamed polystyrene resin particles according to any one of claims 1 to 6, wherein when foamed polystyrene resin particles are pre-foamed 50 times and molded to form a foamed molded article, the following conditions (a), (b), and (c) are met. (a) The dimensional change rate after heating at 95°C for 168 hours is less than 2%. (b) The thermal conductivity is 0.033 W / mK or less. (c) The minimum oxygen index is 26 or higher.

8. Pre-foamed particles obtained by pre-foaming the foamable polystyrene resin particles described in any one of claims 1 to 7.

9. A foamed molded body obtained by molding the pre-foamed particles described in claim 8.

10. An insulating material for a hot water storage tank comprising the foamed molded body described in claim 9.

Images