Method for producing expandable styrenic resin particle, and expandable styrenic resin particle

Abstract

To provide a method for producing expandable styrenic resin particles containing an inorganic substance which can produce expandable styrenic resin particles excellent in expandability, moldability and heat insulation performance.SOLUTION: A method for producing expandable styrenic resin particles includes a step of preparing a molten resin containing a styrenic base material resin, an inorganic matter and an expanding agent, and a step of extruding the molten resin from a die having a plurality of small holes into pressurized circulation water, and cutting the molten resin with a rotation cutter and making the cut molten resin into particles, wherein the base material resin contains at least a first styrenic resin having 3 to 20% of a constitutional unit derived from a (meth)acrylic acid.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present disclosure relates to a method for producing expandable styrene-based resin particles, and to expandable styrene-based resin particles. [Background technology]

[0002] Since foam molded products using polystyrene as a base resin have excellent light weight and heat insulating properties, they are widely used as heat insulating materials for housing, etc. As one measure for imparting heat insulating properties to the foam molded products, inorganic substances such as graphite are contained in the foam molded products as radiation heat transfer inhibitors (e.g., Patent Documents 1 and 2).

[0003] On the other hand, from the viewpoint of heat resistance, polystyrene foam molded products have a large dimensional change rate when heated, so they may be difficult to use in contact with high-temperature parts (for example, the surface of a hot water tank, etc.) As one measure to address this problem, a styrene-acrylic acid copolymer is used as the base resin to impart heat resistance.

[0004] In addition, it is known that expandable styrene resin particles can be molded into foams of unspecified shapes according to the mold used, and therefore have a wide range of applications.In order to utilize this advantage, it is preferable that the expandable styrene resin particles have excellent moldability.For example, it is desired that the expandable styrene resin particles can always obtain high-quality foamed molded products without being significantly affected by the conditions during pre-expansion or molding.

[0005] Patent Document 3 describes matters related to expandable styrene-based resin particles containing a styrene-(meth)acrylic acid copolymer, polystyrene, graphite, and a blowing agent. The expandable styrene-based resin particles are obtained by impregnating styrene-based polymer seed particles containing a styrene-(meth)acrylic acid copolymer and graphite with styrene, polymerizing the particles, and then impregnating the particles with a blowing agent. It is said that this produces a styrene-based resin expanded bead molding having few gaps between particles and a good shape. On the other hand, when the expandable styrene-based resin particles are produced only by melt-kneading a styrene-(meth)acrylic acid copolymer and a polystyrene resin without impregnating the seed particles with styrene and polymerizing the particles, it is not possible to mold an expanded molded product, or only an expanded molded product having large gaps between the expanded particles is obtained, and the moldability is significantly inferior (Comparative Example 1-3). [Prior art documents] [Patent documents]

[0006] [Patent Document 1] International Publication No. 2019 / 198790 [Patent Document 2] JP 2020-033481 A [Patent Document 3] JP 2014-148558 A Summary of the Invention [Problem to be solved by the invention]

[0007] In general, expandable resin particles containing a resin and an inorganic substance have a lower foaming moldability than those not containing an inorganic substance. In detail, the presence of an inorganic substance in the resin makes the cell membrane more likely to break during foaming due to the inorganic substance. Then, the cell membrane breaks and the closed cell ratio decreases, so that the foaming agent remaining in the expanded particles is more likely to dissipate. As a result, the moldability also decreases, making it difficult to obtain a molded product with excellent fusion and surface beauty. This is not limited to graphite, but can occur with all inorganic substances including talc and the like.

[0008] In addition, methacrylic acid-modified styrene-based resins such as styrene-(meth)acrylic acid copolymers have a higher glass transition temperature than simple styrene-based resins such as styrene homopolymers, and therefore require a high amount of heat during foam molding. For this reason, when methacrylic acid-modified styrene-based resins are used, there is a problem that the processability of foam molding is reduced, making it difficult to obtain molded products with excellent fusion and surface beauty. Here, it is predicted that the foam moldability will be further reduced if an inorganic material such as graphite is contained in the methacrylic acid-modified styrene-based resin. Patent Document 3 also points out the problem that the foamability is significantly deteriorated when a filler such as graphite is mixed into a molten mixture of styrene-(meth)acrylic acid copolymer and polystyrene (paragraph

[0005] ).

[0009] However, when manufacturing expandable styrene-based resin particles containing inorganic substances, it is difficult to incorporate inorganic substances that are not dispersed in water using conventional polymerization methods, and the inorganic substances aggregate in water, so that the particle size of the inorganic substances tends to increase when incorporated into the resin. Therefore, cell membrane breakage during foaming due to the inorganic substances tends to occur, and moldability is reduced. As in the technology described in Patent Document 3, there is a method in which inorganic substances are incorporated into seed particles and resin that does not contain inorganic substances is polymerized onto the seed particles, but with this method, the inorganic substances are present only in the seed particles, making it difficult to effectively express heat insulating performance.

[0010] Therefore, an object of the present disclosure is to provide a method for producing expandable styrene-based resin particles containing an inorganic substance, which can produce expandable styrene-based resin particles that have excellent expandability, moldability, and heat insulating performance. [Means for solving the problem]

[0011] One aspect of the present disclosure is a method for producing expandable styrene-based resin particles, the method including the steps of preparing a resin melt containing a styrene-based base resin, an inorganic substance, and a blowing agent, and extruding the resin melt through a die having a plurality of small holes into pressurized circulating water and cutting the resin melt with a rotary cutter to form particles, the base resin including at least a first styrene-based resin having 3 to 20% of structural units derived from (meth)acrylic acid.

[0012] Preferably, the inorganic material includes a radiation heat transfer inhibitor.

[0013] Preferably, the inorganic material includes a carbon-based radiation heat transfer inhibitor.

[0014] Preferably, the inorganic substance has an average particle size of 2 μm or more and 12 μm or less.

[0015] Preferably, the temperature of the pressurized circulating water is 60°C or higher and 99°C or lower.

[0016] Preferably, the pressure of the pressurized circulating water is 0.5 MPa or more and 2.0 MPa or less.

[0017] One aspect of the present disclosure is expandable styrene-based resin particles obtained by the above-mentioned method for producing expandable styrene-based resin particles. Effect of the Invention

[0018] According to the present disclosure, it is possible to provide a method for producing expandable styrene-based resin particles containing an inorganic substance, which can produce expandable styrene-based resin particles having excellent expandability, moldability, and heat insulating performance. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] The method for producing expandable styrene-based resin particles according to one embodiment of the present disclosure includes a step of preparing a resin melt using a styrene-based resin as a base resin, and a step of granulating the resin melt. Hereinafter, each element constituting the expandable styrene-based resin particles to be produced will be described first, and then the production process will be described.

[0020] <Expandable styrene resin particles> The resin melt used in the method for producing expandable styrene-based resin particles according to one embodiment of the present disclosure, and the resin particles to be produced, contain a styrene-based base resin, an inorganic substance, and a foaming agent.

[0021] <Base resin> The styrene-based base resin in the present disclosure contains at least a first styrene-based resin having 3 to 20% (3% by weight or more and 20% by weight or less) of structural units derived from (meth)acrylic acid. The first styrene-based resin is, in other words, a styrene-(meth)acrylic acid copolymer having 3 to 20% of structural units derived from (meth)acrylic acid. The structural units derived from (meth)acrylic acid in the first styrene-based resin are usually 3 to 20%, preferably 4 to 15%, and more preferably 4 to 12%. The first styrene-based resin may be of only one type, or may be a combination of two or more types having different ratios of structural units derived from (meth)acrylic acid.

[0022] The content ratio of the first styrene resin to the entire base resin is not particularly limited, but is preferably 70% by weight or more. The content ratio may be 80% by weight or more, 90% by weight or more, or 100% by weight (total amount). By making the content ratio of the first styrene resin 70% by weight or more, a foamed molded product with excellent heat resistance can be obtained.

[0023] The Vicat softening temperature of the first styrene resin is not particularly limited, but is preferably 110° C. or higher and 130° C. or lower, and more preferably 110° C. or higher and 125° C. or lower. When the Vicat softening temperature of the first styrene resin is 110° C. or higher, a foamed molded product having excellent heat resistance can be obtained, and when it is 130° C. or lower, a good foamed molded product can be obtained using a general EPS (bead method polystyrene foam) molding machine.

[0024] The base resin has the first styrene-based resin as an essential component, but may further contain a resin other than the first styrene-based resin. The resin other than the first styrene-based resin may be only one type, or may be two or more types. The resin is preferably a styrene-based resin of a type different from the first styrene-based resin. In particular, it is preferable that the resin is at least one type selected from the group consisting of styrene homopolymer, styrene-acrylonitrile copolymer, styrene-methyl (meth)acrylate copolymer, and styrene-butyl (meth)acrylate copolymer, because it is relatively inexpensive among styrene-based resins, can be foamed with low-pressure steam without using a special method, and has an excellent balance of heat insulation, flame retardancy, and cushioning properties.

[0025] In one preferred embodiment, the base resin further contains a second styrene-based resin having a glass transition temperature of 95° C. or more and 110° C. or less, different from the first styrene-based resin. Examples of the second styrene-based resin include the above-mentioned styrene homopolymer, styrene-acrylonitrile copolymer, styrene-methyl (meth)acrylate copolymer, and styrene-butyl (meth)acrylate copolymer. The glass transition temperature of the second styrene-based resin is preferably 95° C. or more and 110° C. or less, and more preferably 100° C. or more and 110° C. or less. If the glass transition temperature of the second styrene-based resin is 95° C. or more, heat resistance is not impaired, and if it is 110° C. or less, moldability is not impaired.

[0026] In one preferred embodiment, the second styrene-based resin contains a styrene homopolymer. Also, in one preferred embodiment, the base resin is composed of the first styrene-based resin and the second styrene-based resin.

[0027] <Inorganic substances> The inorganic substance in the present disclosure is added, for example, as a radiation heat transfer inhibitor. In one preferred embodiment, the inorganic substance contains a radiation heat transfer inhibitor. This makes it possible to obtain a foamed molded article having high thermal insulation properties. Here, the "radiation heat transfer inhibitor" refers to a substance that has the property of reflecting, scattering, or absorbing light in the infrared region (for example, a wavelength region of about 0.7 μm to 1000 μm).

[0028] The radiation heat transfer inhibitor is not particularly limited, but a carbon-based radiation heat transfer inhibitor is preferred from the viewpoints of dispersibility in polystyrene resins and cost. That is, in one preferred embodiment, the inorganic material contains a carbon-based radiation heat transfer inhibitor.

[0029] Examples of carbon-based radiation heat transfer inhibitors include graphite, carbon black, activated carbon, graphene, carbon nanotubes, etc., with graphite being more preferably used. That is, when the inorganic material is used as a radiation heat transfer inhibitor, it is particularly preferable that the inorganic material contains graphite as a main component. Here, "containing as a main component" refers to a content ratio of more than 50% by weight. In a preferred embodiment, the content ratio of graphite relative to the entire inorganic material is more than 50% by weight, more preferably 80% by weight or more, even more preferably 90% by weight or more, and particularly preferably 100% by weight (total amount).

[0030] Examples of the graphite include flake graphite, earthen graphite, spherical graphite, and artificial graphite. In the present disclosure, the term "flake" also includes scaly, flaky, or plate-like graphite. These graphites can be used alone or in combination of two or more. Among these, a graphite mixture mainly composed of flake graphite is preferred, and flake graphite is more preferred, in terms of its high radiation heat transfer suppression effect.

[0031] Examples of radiation heat transfer inhibitors other than carbon-based radiation heat transfer inhibitors include aluminum-based compounds, zinc-based compounds, magnesium-based compounds, titanium-based compounds, heat ray reflectors, metal sulfates, antimony-based compounds, metal oxides, heat ray absorbers, metal particles, etc. Specific examples include titanium oxide, aluminum, copper, etc.

[0032] The above-mentioned radiation heat transfer inhibitors (inorganic substances) may be used alone or in combination of two or more kinds.

[0033] Examples of inorganic substances other than the radiation heat transfer inhibitor include inorganic particles such as talc, silica, kaolin, zeolite, mica, alumina, etc. These inorganic particles are added, for example, as a bubble adjusting agent.

[0034] The average particle size of the inorganic substance is not particularly limited, but is preferably 12 μm or less and 2 μm or more, more preferably 10 μm or less and 2 μm or more, and even more preferably 7 μm or less and 2 μm or more. By setting the average particle size to 12 μm or less, the moldability during foam molding of the resin particles becomes good, and by setting it to 2 μm or more, it can be handled without impairing the handleability. The average particle size of the inorganic substance referred to here refers to the particle size D50 (i.e., 50% volume cumulative particle size) when the cumulative volume of the total particles is 50% 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 Z8825-1.

[0035] The amount of inorganic substance used is not particularly limited, but for example, the inorganic substance can be contained in the expandable styrene-based resin particles produced such that the inorganic substance is contained in an amount of 2 parts by weight or more and 20 parts by weight or less per 100 parts by weight of the base resin. The inorganic substance may be contained in an amount of 3 parts by weight or more and 15 parts by weight or less, 3 parts by weight or more and 10 parts by weight or less, 4 parts by weight or more and 10 parts by weight or less, etc., per 100 parts by weight of the base resin. If the content of the inorganic substance is 20 parts by weight or less, it is easy to control the expansion ratio when producing a foamed molded product, and it is easy to obtain a high expansion ratio. In addition, when the inorganic substance is a radiation heat transfer inhibitor, if the content of the inorganic substance is 2 parts by weight or more, it is possible to achieve the desired heat insulation. In addition, the amount of inorganic substance used can be such that the content ratio of the inorganic substance to the entire resin particles in the expandable styrene-based resin particles produced is 2.0% by weight or more and 10.0% by weight or less, 3.0% by weight or more and 8.0% by weight or less, etc.

[0036] <Foaming agent> The foaming agent in the present disclosure is not particularly limited, but from the viewpoint of a good balance between foaming property and product life and easy to achieve a high expansion ratio when actually used, a volatile foaming agent is preferred, saturated hydrocarbons are more preferred, and among them, aliphatic hydrocarbons having 4 or 5 carbon atoms are even more preferred. Examples of such hydrocarbons include normal butane, isobutane, normal pentane, isopentane, neopentane, cyclopentane, etc. These foaming agents may be used alone or in combination of two or more. In one preferred embodiment, the foaming agent contains an aliphatic hydrocarbon having 4 carbon atoms and / or an aliphatic hydrocarbon having 5 carbon atoms. In one preferred embodiment, the foaming agent contains at least an aliphatic hydrocarbon having 5 carbon atoms, and the content ratio of the aliphatic hydrocarbon having 5 carbon atoms to the entire foaming agent is 50% by weight or more, more preferably 70% by weight or more.

[0037] The amount of the blowing agent used is not particularly limited, but for example, when the expandable styrene-based resin particles to be produced are assumed to be a mixture of all components constituting the resin particles except for the blowing agent, the amount of the blowing agent is 4.0 parts by weight or more and 10.0 parts by weight or less per 100 parts by weight of the mixture, preferably 4.5 parts by weight or more and 9.5 parts by weight or less, more preferably 5.0 parts by weight or more and 9.0 parts by weight or less per 100 parts by weight of the mixture.

[0038] <Other ingredients> In the method for producing expandable styrene-based resin particles according to the present disclosure, the resin melt may contain other components, such as a bromine-based flame retardant or a heat stabilizer, as long as the performance of the produced resin particles is not impaired.

[0039] The bromine-based flame retardant is not particularly limited, and various bromine-based flame retardants can be used. In one preferred embodiment, a bromine-based flame retardant having a 1% weight loss temperature in thermogravimetric analysis of 210°C or more and 280°C or less and a bromine content of 60% by weight or more and less than 70% by weight is used.

[0040] Examples of brominated flame retardants include brominated bisphenol compounds, brominated styrene-butadiene copolymers, and brominated isocyanurate compounds. Specific examples of brominated bisphenol compounds include 2,2-bis[4-(2,3-dibromo-2-methylpropoxy)-3,5-dibromophenyl]propane (also known as tetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl ether)), 2,2-bis[4-(2,3-dibromopropoxy)-3,5-dibromophenyl]propane (also known as tetrabromobisphenol A-bis(2,3-dibromopropyl ether)), and the like. Brominated styrene-butadiene copolymers include brominated styrene-butadiene block copolymers, brominated random styrene-butadiene copolymers, and brominated styrene-butadiene graft copolymers. Examples of brominated isocyanurate compounds include tris(2,3-dibromopropyl)isocyanurate, etc. Other compounds include tetrabromocyclooctane, etc. These brominated flame retardants may be used alone or in combination of two or more.

[0041] The amount of the brominated flame retardant used is not particularly limited, but for example, in the expandable styrene resin particles produced, the content ratio of the brominated flame retardant to the entire resin particles can be 0.8% by weight or more and 5.0% by weight or less. If the content ratio of the brominated flame retardant is 0.8% by weight or more, the desired flame retardant performance can be achieved. If the content ratio of the brominated flame retardant is 5.0% by weight or less, the adverse effect on the foam moldability can be suppressed.

[0042] By further including a heat stabilizer, it is possible to suppress the deterioration of flame retardancy due to the decomposition of the bromine-based flame retardant in the manufacturing process and the deterioration of the expandable styrene-based resin particles. There is no particular limitation on the heat stabilizer, and it is appropriately selected depending on the type of base resin, the type and content of the foaming agent, the type and content of the inorganic substance such as the radiation heat transfer inhibitor, the type and content of the bromine-based flame retardant, etc. Examples of the heat stabilizer include hindered amine compounds, phosphorus-based compounds, epoxy compounds, etc., and hindered amine compounds and phosphorus-based compounds are particularly preferred. These heat stabilizers may be used alone or in combination of two or more.

[0043] Examples of further components other than the bromine-based flame retardant and the heat stabilizer include a radical generator, a processing aid, a light resistance stabilizer, a nucleating agent, a foaming aid, an antistatic agent, and a colorant such as a pigment.

[0044] <Method of producing expandable styrene-based resin particles> A method for producing expandable styrene-based resin particles according to one embodiment of the present disclosure (hereinafter sometimes abbreviated as "a method for producing resin particles") basically includes at least the following two steps (a) and (b). (a) preparing a resin melt containing a styrene-based base resin, an inorganic material, and a foaming agent; and (b) extruding the resin melt through a die having a plurality of small holes into pressurized circulating water and cutting it with a rotating cutter to form particles.

[0045] In step (a), a resin melt containing a styrene-based base resin, an inorganic substance, and a foaming agent is prepared. For example, the base resin, the inorganic substance, and other components as necessary are melt-kneaded in an extruder. Next, the foaming agent is dissolved and dispersed in the melt-kneaded mixture by the extruder or a mixing facility provided after the extruder to obtain a resin melt.

[0046] In step (a), a general extruder can be used as the extruder, and specific examples thereof include a single-screw extruder, a twin-screw extruder, and a tandem extruder. Examples of the tandem extruder include a combination of two single-screw extruders, and a combination of a twin-screw extruder and a single-screw extruder. Dispersion equipment such as an extruder, a static mixer, and an agitator without a screw may also be used in combination.

[0047] Regarding the resin temperature during resin melt kneading, the resin temperature of the resin melt at the tip of the extruder is preferably 130°C or more and 250°C or less, more preferably 140°C or more and 240°C or less, and even more preferably 150°C or more and 220°C or less. The resin temperature of the resin melt at the tip of the extruder is a value measured by a temperature sensor attached to the tip of the extruder. When two or more extruders are attached upstream of the die, the tip temperature of the most downstream extruder is taken as the resin temperature of the resin melt at the tip of the extruder. If the resin temperature is 130°C or more, the resin viscosity decreases and sufficient melt kneading in the extruder is possible. If the resin temperature exceeds 250°C, there is a risk of decomposition of the styrene-based resin and additives used in combination as necessary, which may result in deterioration of the expandable styrene-based resin particles and lead to a decrease in the expansion performance.

[0048] The extruder tip pressure is preferably 8 MPa or more and 30 MPa or less, more preferably 10 MPa or more and 25 MPa or less, and even more preferably 12 MPa or more and 20 MPa or less. The extruder tip pressure referred to here is a value measured by a pressure sensor attached to the tip of the extruder. When two or more extruders are attached upstream of the die, the tip pressure of the most downstream extruder is taken as the extruder tip pressure. If the extruder tip pressure is 8 MPa or more, the foaming agent is easily dissolved and dispersed in the resin during melt kneading, and expandable styrene-based resin particles can be obtained stably. On the other hand, if the extruder tip pressure is 30 MPa or less, shear heat generation during melt kneading can be suppressed, and decomposition of the styrene-based resin and additives used in combination as necessary is less likely to occur.

[0049] In step (b), the resin melt prepared in step (a) is extruded through a die having a plurality of small holes into pressurized circulating water (pressurized circulating cooling water) and cut into particles by a rotating cutter. Step (b) can be called a granulation step.

[0050] The die used in step (b) is not particularly limited as long as it has a plurality of small holes, and examples thereof include those having a plurality of small holes with a diameter of 0.3 mm to 2.0 mm, preferably 0.35 mm to 1.0 mm.

[0051] The device for cutting the molten resin extruded into the pressurized circulating water is not particularly limited, but examples thereof include a device in which the molten resin is cut and formed into small pellets by a rotating cutter that comes into contact with a die, and the small pellets are transported to a centrifugal dehydrator without foaming in the pressurized circulating water, where they are dehydrated and collected.

[0052] The temperature and other conditions of the pressurized circulating water can be appropriately selected depending on the type and content of the resin, additives, foaming agent, etc. that constitute the resin melt, but conditions that suppress foaming of the molten resin extruded from the die and allow it to be stably cut by the cutter are preferred. Specifically, the temperature condition of the pressurized circulating cooling water is preferably 60°C or higher and 99°C or lower, more preferably 65°C or higher and 95°C or lower, and even more preferably 70°C or higher and 90°C or lower.

[0053] The pressure of the pressurized circulating water can be appropriately selected depending on the type of foaming agent used, etc., but is preferably 0.5 MPa or more and 2.0 MPa or less, more preferably 0.6 MPa or more and 1.8 MPa or less, and even more preferably 0.7 MPa or more and 1.6 MPa or less.

[0054] In the method for producing resin particles according to the present disclosure, a base resin, an inorganic substance, and a foaming agent are kneaded in an extruder or the like to disperse the inorganic substance in the resin. Therefore, it is considered that the increase in particle size of the inorganic substance in the resin can be suppressed. As a result, it is possible to provide expandable resin particles that exhibit excellent quality in foaming moldability, fusion, and heat insulation performance without breaking cells during foaming.

[0055] <Expandable styrene resin particles> The present disclosure includes expandable styrene-based resin particles obtained by the above-mentioned method for producing expandable styrene-based resin particles. The apparent density of the expandable resin particles is 1020 kg / m 3 More than 1070kg / m 3 It is preferable that the saturation temperature is 1025 kg / m or less, and more preferable that the saturation temperature is 1025 kg / m or less. 3 More than 1065kg / m 3 More preferably, it is 1030 kg / m or less. 3 More than 1060kg / m 3 The apparent density is 1020 kg / m 3 By setting the apparent density at or above 1070 kg / m, it is possible to suppress micro-bubbles during extrusion and to suppress a decrease in the closed cell ratio, resulting in excellent foaming performance. 3 By setting the amount of the foamed beads to the amount below 100, the cell structure of the foamed beads does not become extremely enlarged, and it becomes possible to obtain a foamed molded article having excellent heat insulating properties. The amount of the foaming agent in the expandable resin particles is not particularly limited, but is preferably 4.0% by weight or more and 10.0% by weight or less. More preferably, it is 4.5% by weight or more and 9.5% by weight or less, and even more preferably, it is 5.0% by weight or more and 9.0% by weight or less. When the amount of the foaming agent is 4.0% by weight or more, excellent foaming performance is obtained. On the other hand, when the amount of the foaming agent is 10.0% by weight or less, the plasticizing effect of the foaming agent is not extremely large, and shrinkage of the expanded particles immediately after foaming is unlikely to occur.

[0056] <Method of manufacturing styrene resin foam molded product> A known method can be used to manufacture a foamed molded article using expandable styrene-based resin particles (hereinafter sometimes abbreviated as "a method for manufacturing a foamed molded article"). For example, the expandable styrene-based resin particles are pre-expanded to prepare pre-expanded resin particles. Next, the pre-expanded resin particles are molded using a molding machine to manufacture a styrene-based resin foamed molded article.

[0057] <Pre-expanded particles> The pre-expanded resin particles can be produced, for example, by expanding expandable styrene-based resin particles 10 to 110 times with heated steam. The pre-expanded resin particles are used for molding after being cured for a certain period of time as necessary. The obtained pre-expanded resin particles are molded (for example, molded in a mold) with steam using a known molding machine to produce a foamed molded product. Depending on the shape of the mold used, a molded product with a complex shape and a block-shaped molded product can be obtained.

[0058] The present disclosure includes the following items (1) to (11).

[0059] (1) A method for producing expandable styrene-based resin particles, comprising the steps of: A step of preparing a resin melt containing a styrene-based base resin, an inorganic material, and a foaming agent; The resin melt is extruded through a die having a plurality of small holes into pressurized circulating water, and cut into particles by a rotary cutter. The method for producing expandable styrene-based resin particles, wherein the base resin contains at least a first styrene-based resin having 3 to 20% of structural units derived from (meth)acrylic acid.

[0060] (2) The method for producing expandable styrene-based resin particles according to (1), wherein the inorganic substance includes a radiation heat transfer inhibitor.

[0061] (3) The method for producing expandable styrene-based resin particles according to (1), wherein the inorganic material includes a carbon-based radiation heat transfer inhibitor.

[0062] (4) The method for producing expandable styrene-based resin particles according to any one of (1) to (3), wherein the inorganic substance has an average particle size of 2 μm or more and 12 μm or less.

[0063] (5) The method for producing expandable styrene-based resin particles according to any one of (1) to (4), wherein the temperature of the pressurized circulating water is 60° C. or higher and 99° C. or lower.

[0064] (6) The method for producing expandable styrene-based resin particles according to any one of (1) to (5), wherein the pressure of the pressurized circulating water is 0.5 MPa or more and 2.0 MPa or less.

[0065] (7) The method for producing expandable styrene-based resin particles according to any one of (1) to (6), wherein the expandable styrene-based resin particles contain 2 parts by weight or more and 20 parts by weight or less of the inorganic substance per 100 parts by weight of the base resin.

[0066] (8) The method for producing expandable styrene-based resin particles according to any one of (1) to (7), wherein the base resin further contains a second styrene-based resin different from the first styrene-based resin, and the second styrene-based resin has a glass transition temperature of 95° C. or higher and 110° C. or lower.

[0067] (9) The method for producing expandable styrene-based resin particles according to any one of (1) to (8), wherein the resin melt further contains a brominated flame retardant.

[0068] (10) The method for producing expandable styrene-based resin particles according to any one of (1) to (9), wherein the foaming agent contains an aliphatic hydrocarbon having 4 carbon atoms and / or an aliphatic hydrocarbon having 5 carbon atoms.

[0069] (11) Expandable styrene-based resin particles obtained by the method for producing expandable styrene-based resin particles according to any one of (1) to (10).

[0070] (12) A styrene-based resin foamed molded article obtained by pre-expanding the expandable styrene-based resin particles according to (11) above and foaming the pre-expanded particles. EXAMPLES

[0071] The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

[0072] First, the raw materials used in each experimental example are listed below. <Styrene-based resin> (A1) Styrene-methacrylic acid copolymer [PS Japan Co., Ltd., G9001, glass transition temperature 123°C, methacrylic acid 8% by mass] (A2) Styrene homopolymer [PS Japan Co., Ltd., 680, glass transition temperature 103°C] Incidentally, (A1) corresponds to the first styrene-based resin, and (A2) corresponds to the second styrene-based resin.

[0073] <Carbon-based radiation heat transfer inhibitor> (B) Graphite [Marutoyo Foundry Manufacturing Co., Ltd., flake graphite SGP-40B, average particle size D50 = 5.8 μm]

[0074] <Brominated flame retardants> (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]

[0075] <Heat stabilizer> (D1) Tetrakis(2,2,6,6-tetramethylpiperidyloxycarbonyl)butane [ADEKA Corporation, LA-57] (D2) Bis(2,6-di-t-butyl-4-methylphenyl)pentaerythritol diphosphite [ADEKA Corporation, PEP-36]

[0076] <Foaming agent> (E1) Normal pentane [Wako Pure Chemical Industries, Ltd.] (E2) Isopentane [Wako Pure Chemical Industries, Ltd.]

[0077] <Mixture of brominated flame retardants and heat stabilizers> Brominated flame retardant (C), heat stabilizers (D1) and (D2) were mixed in a mixer to obtain a mixture (F) of brominated flame retardant and heat stabilizer (hereinafter sometimes abbreviated as mixture (F)). The weight ratio (weight %) of each material was (C):(D1):(D2) = 94.7:2.1:3.2 ((C) + (D1) + (D2) = 100 weight %). For example, 2.5 g of mixture (F) contains 2.375 g of brominated flame retardant (C).

[0078] (Experimental Example 1) 1. Preparation of expandable styrene resin particles The styrene resin (A1), graphite (B), and mixture (F) were fed by feeders to a tandem-type two-stage extruder consisting of a 40 mm diameter twin-screw extruder (first extruder) and a 90 mm diameter single-screw extruder (second extruder) connected in series, and melt-kneaded at a set temperature of 200°C and a rotation speed of 167 rpm for the first extruder. The weight ratio of each material was (A1):(B):(F) = 93:4.5:2.5, and the total feed rate was 55.7 kg / h.

[0079] 80 parts by weight of normal pentane (E1) and 20 parts by weight of isopentane (E2) were mixed to prepare a mixed pentane. The mixed pentane was injected at a ratio of 8.0 parts by weight per 100 parts by weight of the melt of the resin mixture from the middle of the first extruder. Then, the mixed pentane was fed to the second extruder through a continuation pipe set at 210°C.

[0080] After the temperature of the molten resin was cooled to 160°C in the second extruder, the molten resin was extruded from a die having 60 small holes with a diameter of 0.65 mm and a land length of 5.0 mm attached to the tip of the second extruder set at 255°C into pressurized circulating water at a temperature of 84°C and 1.0 MPa. The extruder tip pressure at this time was 15.8 MPa, and the resin temperature of the molten material (i.e., the resin temperature of the molten resin at the tip of the extruder) was 157°C. The extruded molten resin was cut and pelletized using a rotary cutter with eight blades that contacted the die, and transferred to a centrifugal dehydrator to obtain expandable styrene-based resin particles. At this time, the residence time in the first extruder was 2 minutes, and the residence time in the second extruder was 5 minutes.

[0081] 2. Preparation of Pre-expanded Particles The obtained expandable styrene resin particles were stored at 15°C for more than one week. 0.1 parts by weight of zinc stearate and 0.1 parts by weight of hydroxystearic acid triglyceride, which are external additives, were added to 100 parts by weight of the expandable styrene resin particles, and dry blended. 400 g of the expandable styrene resin particles containing the external additives were placed in a pre-expander [batch-type pre-expander manufactured by Daikai Kogyo Co., Ltd.], the pressure inside the can was set to 0.020 MPa to 0.030 MPa, and steam of 0.12 MPa was introduced into the pre-expander to expand to a bulk ratio of 50 times, thereby obtaining pre-expanded particles. The expansion ratio of the obtained pre-expanded particles was 50 times.

[0082] 3. Preparation of styrene-based resin foam molded body The obtained pre-expanded particles were cured at 30°C for 24 hours, then filled into a mold for in-mold molding (length 400mm x width 400mm x thickness 25mm) attached to a polystyrene foam molding machine [KR-57, manufactured by Daisen Kogyo Co., Ltd.], and 0.12 MPa of water vapor was introduced to cause in-mold foaming, and water was sprayed onto the mold to cool it. The foam molded body was held in the mold until the pressure of the foam molded body pressing the mold reached 0.03 MPa (gauge pressure), and then the foam molded body was removed to obtain a styrene-based resin foam molded body. Hereinafter, the styrene-based resin foam molded body may be abbreviated as "foam molded body".

[0083] (Experimental Example 2) In Experimental Example 2, a styrene-based resin (A1) and a styrene-based resin (A2) were used together as the base resin. The weight ratio of each material was (A1):(A2):(B):(F)=74.4:18.6:4.5:2.5 ((A1) / (A2)=80 / 20). The other operations were the same as in Experimental Example 1 to obtain expandable styrene-based resin particles. The extruder tip pressure was 15.1 MPa, and the resin temperature of the molten material was 159°C. In the preparation of the pre-expanded particles, the same operations were performed as in Experimental Example 1, except that the pressure inside the can was set to 0.015 MPa to 0.025 MPa. In the preparation of the styrene-based resin foamed molded body, the same operations were performed as in Experimental Example 1, except that the pressure of the introduced steam was set to 0.10 MPa.

[0084] (Experimental Example 3) In Experimental Example 3, a styrene-based resin (A1) and a styrene-based resin (A2) were used together as the base resin. The weight ratio of each material was (A1):(A2):(B):(F)=65.1:27.9:4.5:2.5 ((A1) / (A2)=70 / 30). The other operations were the same as in Experimental Example 1 to obtain expandable styrene-based resin particles. The extruder tip pressure was 13.5 MPa, and the resin temperature of the molten material was 158°C. In the preparation of the pre-expanded particles, the same operations were performed as in Experimental Example 1, except that the pressure inside the can was set to 0.015 MPa to 0.025 MPa. In the preparation of the styrene-based resin foamed molded body, the same operations were performed as in Experimental Example 1, except that the pressure of the introduced steam was set to 0.09 MPa.

[0085] To summarize the base resin, in Experimental Example 1, the base resin was composed only of the styrene-based resin (A1). In Experimental Example 2, the base resin was composed of the styrene-based resin (A1) and the styrene-based resin (A2), and the content ratio of the first styrene-based resin (styrene-based resin (A1)) to the entire base resin was 80% by weight. In Experimental Example 3, the base resin was composed of the styrene-based resin (A1) and the styrene-based resin (A2), and the content ratio of the first styrene-based resin (styrene-based resin (A1)) to the entire base resin was 70% by weight.

[0086] In Experimental Examples 1 to 3, 4.5 parts by weight of the radiation heat transfer inhibitor (B) was contained per 93 parts by weight of the base resin, so 4.8 parts by weight of the radiation heat transfer inhibitor (B) was contained per 100 parts by weight of the base resin. Also, in Experimental Examples 1 to 3, 4.5 g of the radiation heat transfer inhibitor (B) was contained in 108 g of the resin melt, so the content of the radiation heat transfer inhibitor (B) in the entire resin melt was 4.2 wt %.

[0087] In Experimental Examples 1 to 3, 2.375 g of the brominated flame retardant (C) was contained in 108 g of the molten resin, and therefore the content of the brominated flame retardant (C) in the entire molten resin was 2.2% by weight.

[0088] In Experimental Examples 1 to 3, 8.0 parts by weight of mixed pentane as a foaming agent was contained per 100 parts by weight of the total of the styrene-based resin (A1), the styrene-based resin (A2), the radiation heat transfer inhibitor (B), and the mixture (E).

[0089] The various properties of the expandable styrene resin particles and the styrene resin foamed molded articles produced in each experimental example were measured and evaluated by the following methods.

[0090] <Method for measuring the apparent density of expandable styrene resin particles> A measurement sample of W (kg) of expandable styrene resin particles is taken, and this measurement sample is allowed to fall naturally into a measuring cylinder containing ethanol, and its mass (kg) and volume V (m 3 ) was measured, and the apparent density was calculated based on the following formula: Apparent density (kg / m 3 ) = weight of sample (W) / volume of sample (V)

[0091] <Method for measuring the amount of blowing agent in expandable styrene resin particles> The weight W1 (g) of the expandable styrene resin particles was measured, heated in an oven at 150°C for 30 minutes, cooled at room temperature in a desiccator for 30 minutes, and then the weight W2 (g) was measured again. The value calculated by the following formula was regarded as the amount of blowing agent in the expandable styrene resin particles. Amount of foaming agent in expandable styrene resin particles (wt%) = (W1-W2) / W1 x 100

[0092] <Expansion ratio of styrene resin foam molded products> The styrene-based resin foam molded body removed from the mold was dried at 30°C for 24 hours, after which the weight (g) of the foam molded body was measured, and the length, width, and thickness were measured using a vernier caliper. The volume (cm3) of the foam molded body (test piece) was calculated from each measured dimension. 3 ) was calculated, and the expansion ratio was calculated according to the following formula. Expansion ratio (cm 3 / g) = test piece volume (cm 3 ) / test piece weight (g) The expansion ratio of styrene-based resin foamed moldings is conventionally expressed as "cm 3 It is also expressed as " / g".

[0093] <Thermal conductivity of styrene-based resin foam molded bodies> The styrene-based resin foam molded body was left to stand at 60°C for 48 hours, and then a sample of 300 mm length x 300 mm width x 25 mm was cut out. The sample was left to stand at 23°C for 24 hours, and then the thermal conductivity was measured at an average temperature of 23°C and a temperature difference of 20°C by the heat flow meter method using a thermal conductivity measuring device (HC-074, manufactured by Eiko Seiki Co., Ltd.) in accordance with JIS A1412-2:1999.

[0094] <Evaluation of adhesion of styrene-based resin foam molded bodies> The obtained styrene-based resin foam molded article was broken. The fracture surface was visually observed to determine the area of ​​the entire fracture surface where the particles themselves, not the particle interfaces, were broken. The ratio (%) of the area of ​​the entire fracture surface where the particles themselves were broken was determined.

[0095] <Dimensional change rate of styrene resin foam molded body> The dimensional change rate was measured according to the B method for dimensional stability at high temperatures specified in JIS K6767. A sample of 150 mm length x 150 mm width x 25 mm height was cut out from the styrene resin foam molded body. After leaving the sample at 23°C for 24 hours, three straight lines parallel to each other in the vertical and horizontal directions were drawn on the sample at 50 mm intervals. The lengths of the three lines in the vertical and horizontal directions were measured, and the average value (mm) was taken as the initial dimension. The sample was heated at 90°C for 168 hours, removed, and left at 23°C for 1 hour, after which the lengths of the three lines in the vertical and horizontal directions were measured, and the average value (mm) was taken as the dimension after heating. The thermal dimensional change rate S (%) was calculated according to the following formula. S = (L1-L0) / L0 x 100 In the formula, S represents the rate of dimensional change due to heating (%), L0 represents the initial dimension (mm), and L1 represents the dimension after heating (mm).

[0096] <Flame retardancy evaluation of styrene resin foam molded products - oxygen index> The obtained foamed molded article was allowed to stand at 70° C. for 168 hours and then at 23° C. for 24 hours, after which the oxygen index was measured in accordance with JIS K7201.

[0097] The formulation, manufacturing conditions, and measurement results for each item in each experimental example are shown in Table 1.

[0098] [Table 1]

[0099] In all the experimental examples, foamed molded articles with high performance in all items including fusion (moldability), thermal conductivity (thermal insulation), thermal dimensional change rate, and oxygen index (flame retardancy) were obtained. There were no problems even in the experimental example 1, in which the base resin was made only of styrene-methacrylic acid copolymer.

[0100] In this embodiment, the reason why excellent foam moldability was obtained is not clear, but it is possible that, by melt-kneading inorganic substances such as graphite with a twin-screw extruder while the foaming agent is melted in the base resin, aggregation of the inorganic substances is less likely to occur, and the particle size of the inorganic substances dispersed in the resin is reduced, thereby suppressing the deterioration of foam moldability. In other words, by kneading in the presence of a foaming agent, it is possible to maintain high dispersibility of the inorganic substances, and it can be inferred that even in the case of a methacrylic acid-modified styrene-based resin with low processability in foam molding, it is possible to obtain a foam molded product with excellent foam moldability and high fusion.

[0101] Further consideration will be given in comparison with the experimental results described in Patent Document 3 (JP Patent Publication 2014-148558 A). Comparative Examples 1-3 (hereinafter simply referred to as Comparative Examples) of Patent Document 3 are common to the above experimental examples in that inorganic substances (graphite) are contained in advance in the resin melt, but differ from the above experimental examples in that the resin melt does not contain a foaming agent. That is, in the Comparative Examples, first, the resin melt not containing a foaming agent is extruded into a strand shape, cooled and cut to obtain resin particles. Next, the resin particles are impregnated with a foaming agent to obtain expandable styrene-based resin particles. However, according to the expandable styrene-based resin particles of Comparative Examples 1-3, it was not possible to mold an expanded molded product, or only an expanded molded product with large gaps between the expanded particles was obtained, and the moldability was significantly poor (Table 3 of Patent Document 3).

[0102] In contrast, the expandable styrene-based resin particles produced in the above experimental examples were excellent in expandability and moldability, and could even achieve an expansion ratio of 50. This effect was obtained by the above-mentioned difference, i.e., by kneading the molten resin in the presence of a foaming agent and incorporating the foaming agent into the molten resin, and is an advantageous and unique effect that cannot be obtained in the comparative examples.

Claims

1. A method for producing expandable styrene-based resin particles, comprising the steps of: A step of preparing a resin melt containing a styrene-based base resin, an inorganic material, and a foaming agent; The resin melt is extruded through a die having a plurality of small holes into pressurized circulating water, and cut into particles by a rotary cutter. The method for producing expandable styrene-based resin particles, wherein the base resin contains at least a first styrene-based resin having 3 to 20% of structural units derived from (meth)acrylic acid.

2. The method for producing expandable styrene-based resin particles according to claim 1 , wherein the inorganic substance contains a radiation heat transfer inhibitor.

3. The method for producing expandable styrene-based resin particles according to claim 1 , wherein the inorganic substance contains a carbon-based radiation heat transfer inhibitor.

4. The method for producing expandable styrene-based resin particles according to claim 1, wherein the inorganic substance has an average particle size of 2 to 12 μm.

5. The method for producing expandable styrene-based resin particles according to claim 1, wherein the temperature of the pressurized circulating water is 60°C or higher and 99°C or lower.

6. 2. The method for producing expandable styrene-based resin particles according to claim 1, wherein the pressure of the pressurized circulating water is 0.5 MPa or more and 2.0 MPa or less.

7. 7. Expandable styrene-based resin particles obtained by the method for producing expandable styrene-based resin particles according to claim 1.

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