Expandable polystyrene resin particles for cushioning filling

Abstract

To provide an expandable polystyrene-based resin particle for cushioning material padding, having excellent flowability and anti-blocking property as the expandable polystyrene-based resin particle, and excellent flowability and anti-static property of an expandable particle produced using the expandable polystyrene-based resin particle, and capable of providing a cushioning material excellent in touch feeling as the final product.SOLUTION: An expandable polystyrene-based resin particle for cushioning material padding is composed of a resin particle body having a polystyrene-based resin as the base resin, a foaming agent contained in the resin particle body, and a coating material coating the resin particle body. An average particle diameter of the resin particle body is 0.3 mm or more and 0.5 mm or less, and the coating material contains metal stearate A, stearic acid amide and an anti-static agent. The metal stearate A comprises 40 mass% or more and 100 mass% or less of magnesium stearate, and 0 mass% or more and 60 mass% or less of zinc stearate (the total of both is 100 mass%). Based on 100 pts.mass of the resin particle body, a coating amount of the metal stearate A is 0.1 pt.mass or more and less than 0.4 pt.mass, a coating amount of the stearic acid amide is 0.01 pt.mass or more and 0.5 pt.mass or less, and a coating amount of the anti-static agent is 0.2 pt.mass or more and 0.8 pt.mass or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to expandable polystyrene resin particles for use as padding for cushioning materials. [Background technology]

[0002] Conventionally, cushioning materials with cushioning properties have been known, in which foam particles such as foamed polystyrene resin particles are filled inside a bag made of fabric or the like, and such cushioning materials are used as cushions, sofas, mattresses, etc. For example, Patent Document 1 discloses foamed resin particles for filling cushioning materials, which are composed of foamed resin particles with an average particle size of 400 to 900 μm and a flow promoter such as zinc stearate. The foamed resin particles for filling cushioning materials are specified to contain 0.4 to 1.5 parts by weight of the flow promoter per 100 parts by weight of the foamed resin particles, and it is explained that this can suppress abnormal noise caused by friction between the foamed resin particles packed in the cushioning material as they flow.

[0003] Furthermore, Patent Document 2 proposes expandable polystyrene resin particles for providing expanded polystyrene resin particles for use as stuffing in bead cushion materials. The expandable polystyrene resin particles are specified to contain, on the particle surface, predetermined amounts of magnesium stearate, fatty acid monoglyceride, and hydroxyalkylamine per 100 parts by weight of the base resin. Patent Document 2 explains that the expandable polystyrene resin particles are less likely to cause blocking during expansion when produced, and that the produced expanded beads are less likely to suffer from deterioration in antistatic properties and fluidity due to moisture absorption. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] WO2003 / 032783 publication [Patent Document 2] Patent Publication No. 2021-155517 Summary of the Invention [Problem to be solved by the invention]

[0005] Expandable polystyrene resin particles for use as padding for cushioning materials have specific problems that differ from those for use in in-mold molding. For example, since the particle diameter of expandable polystyrene-based resin particles for filling cushioning materials is smaller than that of expanded particles for in-mold molding, problems such as the expandable polystyrene-based resin particles adhering to and remaining in corners of a hopper in a high-temperature, high-humidity environment, and the particles sticking to each other and causing blocking when the expandable polystyrene-based resin particles are expanded, tend to occur more easily than with expandable polystyrene-based resin particles for in-mold molding.When a cushioning material is produced by filling a bag with expanded particles in a blocked state, there are problems such as poor feel and fit of the cushioning material.

[0006] Furthermore, if the expanded beads are significantly charged, when the expanded beads are filled into a bag using a filling machine, a large number of the expanded beads may cling to the filling port of the filling machine or the outer surface of the bag, making it difficult to carry out the filling operation smoothly. Furthermore, when the cushioning material is used, the expanded beads filled inside may rub against each other and become charged, which may make the cushioning material more susceptible to attracting dust and the like. In addition, if the fluidity of the expanded beads is poor, there is a problem that the feel and fit of the cushioning material may be poor.

[0007] According to the investigations of the present inventors, it has been found that expandable polystyrene-based resin particles or expanded beads made therefrom that contain an antistatic agent to an extent sufficient to sufficiently improve the electrostatic property of expanded beads used as padding for cushioning and that sufficiently suppress blocking tend to have insufficient fluidity. In other words, it has been difficult with conventional techniques to provide expandable polystyrene-based resin particles or expanded beads that exhibit good antistatic property, antiblocking property, and fluidity.

[0008] That is, Patent Document 1 does not mention at all the problems of fluidity and blocking related to expandable polystyrene resin particles for producing expanded beads, and there is also room for improvement in the fluidity of expanded beads. In particular, Patent Document 1 does not consider expanded beads that exhibit high fluidity and also exhibit antistatic effects. Furthermore, although Patent Document 2 examines the problem of blocking during the foaming process and the fluidity and antistatic properties of the foamed particles, there is room for further investigation into how to improve all of these blocking, fluidity, and antistatic properties in a balanced manner.

[0009] The present invention has been made in view of the above background, and provides expandable polystyrene-based resin particles for cushioning filling, which have good fluidity and anti-blocking properties as expandable polystyrene-based resin particles, and which have good fluidity and anti-static properties for expanded beads produced using the expandable polystyrene-based resin particles, and which can provide a cushioning material with an excellent feel to the touch as a final product. [Means for solving the problem]

[0010] The expandable polystyrene-based resin particles for cushioning filling of the present invention are expandable polystyrene-based resin particles for cushioning filling, which are composed of resin particle bodies having a polystyrene-based resin as a base resin, a blowing agent contained in the resin particle bodies, and a coating agent coating the resin particle bodies, and are characterized in that the average particle diameter of the resin particle bodies is 0.3 mm or more and 0.5 mm or less, the coating agent contains metal stearate A, stearamide, and an antistatic agent, and the metal stearate A consists of 40% by mass or more and 100% by mass or less magnesium stearate and 0% by mass or more and 60% by mass or less zinc stearate (the total of both is 100% by mass), and the coating amount of the metal stearate A is 0.1 parts by mass or more and less than 0.4 parts by mass, the coating amount of the stearamide is 0.01 parts by mass or more and 0.5 parts by mass or less, and the coating amount of the antistatic agent is 0.2 parts by mass or more and 0.8 parts by mass or less, relative to 100 parts by mass of the resin particle bodies. [Effects of the Invention]

[0011] The expandable polystyrene-based resin particles for filling cushion materials of the present invention have good flowability and anti-blocking properties, and are easy to handle when used in the production of expanded beads. Furthermore, the expandable polystyrene-based resin particles for filling cushion materials of the present invention contribute to the provision of expanded beads having good flowability and anti-static properties, and also make it possible to provide a cushion material having an excellent feel to the touch as a final product. DETAILED DESCRIPTION OF THE INVENTION

[0012] As a result of intensive research into the above-mentioned problems, the present inventors have discovered that by using a combination of stearate metal salt A and stearic acid amide as flow promoters in a coating agent that coats the resin particle bodies, it is possible to improve the anti-blocking properties and fluidity of expandable polystyrene-based resin particles in a balanced manner, and further improve the antistatic properties and fluidity of the expanded particles obtained by expanding the expandable polystyrene-based resin particles in a balanced manner, thereby completing the present invention.

[0013] The expandable polystyrene resin particles for cushioning padding of the present invention are composed of a resin particle body having a polystyrene resin as a base resin, a blowing agent contained in the resin particle body, and a coating agent that coats the resin particle body. In the present invention, the resin particle body has an average particle diameter of 0.3 mm or more and 0.5 mm or less, and the coating agent contains a metal stearate A, stearamide, and an antistatic agent. The metal stearate A is composed of 40% by mass or more and 100% by mass or less of magnesium stearate and 0% by mass or more and 60% by mass or less of zinc stearate. In the metal stearate A, the total of the magnesium stearate and zinc stearate is 100% by mass. The coating amount of metal stearate A relative to 100 parts by mass of the resin particle body is in the range of 0.1 parts by mass or more but less than 0.4 parts by mass, the coating amount of stearamide is in the range of 0.01 parts by mass or more but less than 0.5 parts by mass, and the coating amount of antistatic agent is in the range of 0.2 parts by mass or more but less than 0.8 parts by mass.

[0014] In the following description, the expandable polystyrene-based resin particles for cushioning filling of the present invention may be simply referred to as the expandable resin particles of the present invention, and the polystyrene-based resin expanded particles produced using the expandable resin particles of the present invention may be simply referred to as expanded particles. Furthermore, in the present invention, cushioning materials refer to cushions, sofas, mattresses, pillows, stuffed toys, and other components that have cushioning properties and contain expanded particles within a bag made of fabric or the like. The cushioning materials include a bag made of fabric or the like and expanded particles filled inside the bag. The shape of the bag is not particularly limited, and examples of the material for the bag include woven or knitted fabrics, nonwoven fabrics, resin sheets, genuine leather, artificial leather, and the like, each having a basis weight sufficient to prevent the expanded particles from leaking out.

[0015] The expandable resin particles of the present invention having the above-described configuration have good fluidity and are sufficiently prevented from blocking. Furthermore, expanded particles produced using the resin particles of the present invention have excellent antistatic properties and fluidity, which prevents the expanded particles from adhering to the filling machine or the outer surface of the bag when filling the cushioning material, and makes it possible to provide a cushioning material that is comfortable to the touch. In other words, the expandable resin particles of the present invention contribute to the provision of expanded particles that exhibit the above-described desirable effects. The expandable resin particles of the present invention will be described in more detail below.

[0016] [Resin particle body] The resin particle body in the present invention is composed of a polystyrene-based resin as a base resin. Here, the term "polystyrene-based resin is the base resin" means that the resin particle body is mainly composed of a polystyrene-based resin, and may optionally contain other resins or materials. The optional materials will be described later.

[0017] In the present invention, polystyrene-based resin refers to a resin containing 50% by mass or more of structural units derived from styrene. Examples of polystyrene-based resins include polystyrene (general-purpose polystyrene: GPPS), styrene-methacrylic acid copolymer, styrene-methacrylic acid-methyl methacrylate copolymer, styrene-acrylic acid copolymer, styrene-maleic anhydride copolymer, styrene-methyl methacrylate copolymer, styrene-butyl acrylate copolymer, styrene-acrylonitrile copolymer, and high-impact polystyrene (HIPS) containing a rubber component such as butadiene rubber or styrene-butadiene rubber. Polystyrene-based resins may also contain structural units derived from branching agents such as divinylbenzene or polyfunctional macromonomers. Among these, polystyrene is particularly preferred as the polystyrene-based resin.

[0018] (Average particle size) The average particle diameter of the resin particle body in the present invention is 0.3 mm to 0.5 mm. If it is less than 0.3 mm, production may be difficult, and if it exceeds 0.5 mm, the feel of the cushioning material formed by using the expanded beads produced using them as a padding material may be reduced. In the present invention, the average particle diameter of the resin particle body is the cumulative 63% diameter (i.e., d63) calculated based on the particle size distribution on a volume basis. A particle size distribution measuring device is used to measure the average particle diameter.

[0019] [Foaming agent] In the present invention, a foaming agent is contained in the resin particle body. The blowing agent is appropriately selected from blowing agents used to produce expanded polystyrene resin beads. Preferably, the blowing agent contains at least one selected from butane, pentane, and cyclohexane, more preferably both butane and pentane, and even more preferably all of butane, pentane, and cyclohexane. By selecting such a blowing agent, the amount of residual styrene monomer in the expandable resin beads can be appropriately kept low, thereby appropriately keeping the residual styrene monomer and volatile organic compound emissions from expanded beads produced using the expandable resin beads low. Therefore, when such expanded beads are used to form a cushioning material, the generation of unpleasant odors during use can be prevented. In the following, residual styrene monomer may be referred to as R-SM, and volatile organic compounds may be referred to as VOCs.

[0020] Among these, it is particularly preferred that the foaming agent contains all of butane, pentane, and cyclohexane, the total content of butane, pentane, and cyclohexane in the expandable polystyrene resin particles is 4% by mass or more and 8% by mass or less based on 100% by mass of the expandable resin particles, and the mass ratio of the sum of the butane and the pentane to the cyclohexane is 1:0.1 to 1:0.5. As described above, expandable resin particles containing butane, pentane, and cyclohexane as foaming agents within a specified range not only suppress the odor of the final cushioning material product, but also effectively improve the blocking properties and foaming properties of the expandable resin particles, and contribute to providing expanded particles that are less likely to collapse.

[0021] The butane may be n-butane, isobutane, or a mixture thereof. The butane is a gas at 25°C and 1 atm, and has a boiling point of about -11°C. The pentane may be n-pentane, isopentane, or a mixture thereof. Pentane is a liquid at 25°C and 1 atm, and has a boiling point of about 35°C. The cyclohexane is a cyclic aliphatic hydrocarbon, which is liquid at 25°C and 1 atm, and has a boiling point of about 81°C.

[0022] [Coating material] The expandable resin particles of the present invention are composed of a resin particle body containing a blowing agent and a coating agent that coats the resin particle body. The coating agent contains a metal stearate A, stearic acid amide, and an antistatic agent.

[0023] (Metallic stearate A) The metal stearate A is coated in an amount of 0.1 to less than 0.4 parts by mass, preferably 0.2 to 0.4 parts by mass, per 100 parts by mass of the resin particle body.

[0024] In the present invention, metal stearate A is composed of 40% by mass to 100% by mass of magnesium stearate and 0% by mass to 60% by mass of zinc stearate, with the total of these being 100% by mass. If the magnesium stearate is less than 40% by mass in 100% by mass of metal stearate A, the fluidity and anti-blocking properties of the expandable resin particles may not be improved satisfactorily. From the viewpoint of realizing better fluidity of the expandable resin particles, it is preferable that the metal stearate A consists of 60% by mass or more and 80% by mass or less of magnesium stearate and 20% by mass or more and 40% by mass or less of zinc stearate (provided that the total of both is 100% by mass).

[0025] From the viewpoint of more fully exerting the effect of the coating of metal stearate A, it is preferable that the coating amount of magnesium stearate is 0.1 parts by mass or more but less than 0.4 parts by mass, and the coating amount of zinc stearate is less than 0.2 parts by mass (including 0 parts by mass) per 100 parts by mass of the resin particle body, and it is more preferable that the coating amount of magnesium stearate is 0.13 parts by mass or more but less than 0.35 parts by mass, and the coating amount of zinc stearate is less than 0.17 parts by mass (including 0 parts by mass) per 100 parts by mass of the resin particle body.

[0026] (Stearic acid amide) The amount of stearic acid amide coated relative to 100 parts by mass of the resin particle body is 0.01 parts by mass or more and 0.5 parts by mass or less, and more preferably 0.03 parts by mass or more and 0.3 parts by mass or less. In the present invention, the resin particle bodies are coated with stearic acid amide in combination with metal stearate A. When metal stearate A is contained as a coating agent without stearic acid amide, it is difficult to exhibit desirable flowability and anti-blocking properties. According to the studies of the present inventors, it has been found that the use of stearic acid amide as a coating agent can significantly improve the fluidity of expandable resin particles, but tends to promote the occurrence of blocking during foaming. Here, the combined use of stearate metal salt A and stearic acid amide as coating agents tends to further improve the fluidity of expandable resin particles while effectively suppressing blocking.

[0027] In the coating agent of the present invention, in the relationship of the coating amount described above, the mass ratio of metal stearate A to stearamide can be 1:0.02 to 1:1.5, preferably 1:0.03 to 1:1.5, more preferably 1:0.05 to 1:1.5, and even more preferably 1:0.1 to 1:1.5. By satisfying this ratio, the fluidity of the expandable resin particles can be more sufficiently improved, and the feel of the cushioning material as a final product can be improved.

[0028] (antistatic agent) The expandable resin particles of the present invention contain an antistatic agent to improve the electrostatic property of the expanded resin particles produced using the same. The coating amount of the antistatic agent is 0.2 parts by mass or more and 0.8 parts by mass or less, and more preferably 0.3 parts by mass or more and 0.5 parts by mass or less, per 100 parts by mass of the resin particle body.

[0029] The antistatic agent can be appropriately selected from antistatic agents that can be used to prevent static electricity in expanded particles, and preferred examples include fatty acid monoglycerides such as stearic acid monoglyceride, palmitic acid monoglyceride, and lauric acid monoglyceride, hydroxyamine, polyethylene glycol, etc.

[0030] Among these, in order to exhibit a more desirable antistatic effect in the present invention, stearic acid monoglyceride and hydroxypropyl stearic acid monoglyceride are used as antistatic agents. Shea Preferably, the stearic acid monoglyceride and hydroxyamine are contained in the hydroxyamine-containing oil, and the mass ratio of stearic acid monoglyceride to hydroxyamine is more preferably 1:1.5 to 1:10, further preferably 1:1.5 to 1:8, and particularly preferably 1:1.5 to 1:5.

[0031] [Optional material] The expandable resin particles of the present invention may further contain or be coated with any material. The any material can be appropriately selected within the scope of the present invention, and for example, the resin particle body may contain a polymer other than the polystyrene resin as the base resin within the scope of the intended purpose of the present invention. Examples of other polymers include thermoplastic resins such as polyolefin resins, polyester resins, and polyamide resins, and thermoplastic elastomers such as styrene elastomers and olefin elastomers. When other polymers are contained in the resin particle body in addition to the polystyrene resin that is the base resin, the content thereof is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less, per 100 parts by mass of the polystyrene resin.

[0032] The bulk density of the expandable resin particles is preferably 16 to 50 kg / m 3 , more preferably 20 to 35 kg / m 3 is.

[0033] The resin particle body may contain conventionally known additives such as a cell adjusting agent, a plasticizer, an antibacterial agent, and a flame retardant in the base resin. Examples of the cell regulator include polyethylene wax, talc, silica, ethylene bisstearylamide, methyl methacrylate copolymers, and silicone. Examples of the plasticizer include liquid paraffin, glycerin diacetomonolaurate, glycerin tristearate, di-2-ethylhexyl phthalate, and di-2-ethylhexyl adipate. Examples of antibacterial agents include organic antibacterial agents such as 3-iodo-2-propynyl butylcarbamate (IPBC), thiabendazole (TBZ), carbendazim (BCM), and chlorothalonil (TPN), and inorganic antibacterial agents such as silver-based, copper-based, and titanium oxide-based antibacterial agents. Examples of the flame retardant include organic flame retardants such as bromine-based flame retardants and phosphorus-based flame retardants, and inorganic flame retardants such as aluminum hydroxide, magnesium hydroxide, and antimony trioxide. The resin particle body may also contain a colorant such as a pigment or dye.

[0034] The coating agent may contain other coating components in addition to the metal stearate A, stearic acid amide and antistatic agent, as long as the intended object of the present invention is not impaired. Examples of other coating components include conventionally known coating components such as silicone oil and higher fatty acid ester. Among these, it is preferable that the coating agent contains dimethylpolysiloxane, since this can effectively prevent the metal stearate A, stearic acid amide, and antistatic agent from being detached from the resin particle body. The amount of dimethylpolysiloxane to be coated is preferably 0.01 to 1.0 parts by mass, more preferably 0.03 to 0.08 parts by mass, per 100 parts by mass of the resin particle body. Examples of commercially available dimethylpolysiloxane include, but are not limited to, silicone oil (KF96) manufactured by Shin-Etsu Chemical Co., Ltd. The coating agent may also contain a metal salt of a fatty acid other than metal stearate A, or a fatty acid amide other than stearic acid amide. Other examples of fatty acid metal salts include higher fatty acid metal salts, which are metal salts of fatty acids having 12 to 24 carbon atoms, such as metal stearates such as barium stearate, aluminum stearate, and lithium stearate, and metal laurates such as zinc laurate and barium laurate. These fatty acid metal salts may be used alone, or two or more fatty acid metal salts may be used in combination. Other examples of fatty acid amides include compounds such as stearic acid amide and N-stearyl stearic acid amide. The content of other fatty acid metal salts in the coating agent is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, per 100 parts by mass of metal stearate A. The content of other fatty acid amides is preferably 10 parts by mass or less, more preferably 5 parts by mass or less, per 100 parts by mass of stearic acid amide.

[0035] (Blowing agent content of expandable resin particles) The expandable resin particles are dissolved in dimethylformamide (hereinafter referred to as DMF) to obtain a solution, which is then subjected to gas chromatography analysis to measure the content of each blowing agent in the expandable resin particles. Quantitative determination of blowing agents using gas chromatography can be performed as follows: First, approximately 5 g of cyclopentanol is weighed accurately to three decimal places and placed in a 100 mL volumetric flask. DMF is then added to make a total of 100 mL. The DMF solution obtained in this way is further diluted 100 times with DMF to create an internal standard solution. Next, approximately 1 g of the expandable resin particles to be measured is weighed accurately to three decimal places. The precisely weighed expandable styrene-based resin particles are dissolved in approximately 18 mL of DMF to create a solution. 2 mL of the internal standard solution is accurately measured using a volumetric pipette and added to the solution to create the sample solution. 1 μL of this sample solution is introduced into a gas chromatography analyzer using a microsyringe to obtain a chromatogram. The peak areas of each blowing agent component and internal standard substance are calculated from the obtained chromatogram, and the concentration of each blowing agent contained in the expandable resin particles is calculated using the following formula (1): [Number 1] Concentration of each blowing agent (mass%) = [(Wi / 10000) × 2] × [An / Ai] × Fn ÷ Ws × 100 (1) The symbols in the above formula (1) have the following meanings: Wi: Mass (g) of cyclopentanol in the internal standard solution Ws: Mass of expandable resin particles dissolved in DMF (g) An: Peak area of ​​each foaming agent component calculated from the chromatogram Ai: Peak area of ​​the internal standard calculated from the chromatogram Fn: Correction coefficient for each blowing agent component obtained from a previously prepared calibration curve

[0036] (Bulk density of expanded particles) Bulk density of foam particles (kg / m 3 ) is measured by filling a measuring cylinder with expanded beads and stabilizing the filling height of the expanded beads at the 1 L mark. Next, the mass (unit: g) of the expanded beads in the measuring cylinder is measured. The mass of the expanded beads per 1 L of bulk volume (unit: g / L) thus obtained is converted into units to obtain the bulk density (unit: kg / m 3 ) can be calculated.

[0037] (Touch) A stretchy, bag-shaped cushioning material (110cm x 125cm x 150cm) made from polyester fiber is filled with 2.2L of foam particles to create a rectangular cushioning material, which is then placed on a test table. Panelists place their palms on top of the cushioning material and press downward to check the feel, allowing the feel to be evaluated using specified evaluation criteria.

[0038] [Method for producing expandable resin particles] The method for producing the expandable resin particles of the present invention is not particularly limited. For example, the expandable resin particles of the present invention can be produced by suspension polymerization in the same manner as general expandable styrene-based resin particles. More specifically, a dispersion medium such as water, a resin material such as styrene monomer, a dispersant, a polymerization initiator, a cell regulator, etc. are charged into an autoclave (sealed container) equipped with a stirrer, and the mixture is stirred. A blowing agent is added at an appropriate timing while suspension polymerization is carried out to obtain pre-expandable resin particles composed of resin particle bodies and a blowing agent. The pre-expandable resin particles are dried and then classified to obtain pre-expandable resin particles having a desired average particle size. The pre-expandable resin particle bodies are then coated with a coating agent to produce expandable polystyrene-based resin particles. The coating method for the coating agent is not particularly limited; for example, the resin particle bodies and the components constituting the coating agent can be fed into a mixer and mixed by stirring.

[0039] The dispersion medium is exemplified by aqueous dispersion media such as water and deionized water. Examples of the dispersant include calcium phosphate such as tricalcium phosphate, disodium hydrogen phosphate, potassium persulfate, and sodium alkyldiphenyletherdisulfonate. Examples of the polymerization initiator include benzoyl peroxide, t-butylperoxy 2-ethylhexyl monocarbonate, lauryl peroxide, and t-butyl peroxybenzoate. The components used in suspension polymerization may be used alone or in combination. The components are not limited to the examples given above. At least a portion of these components may be contained in the produced expandable resin particles.

[0040] [Method of manufacturing foam beads] The expandable resin particles produced as described above are placed in an expansion machine and heated by supplying a heating medium such as steam, thereby expanding the expandable resin particles and obtaining expanded polystyrene resin particles. The foamed polystyrene resin particles produced as described above are filled into a bag using an air filling machine or the like to produce a cushioning material. [Example]

[0041] The present invention will be described in detail below with reference to examples, but the present invention is not limited thereto. In the tables, the foaming agents butane, pentane, and cyclohexane are represented as C4, C5, and CH, respectively. Magnesium stearate is represented as MgSt, zinc stearate as ZnSt, calcium stearate as CaSt, stearamide as SA, erucamide as EA, stearic acid monoglyceride as GMS, and hydroxypropyl methylcellulose as hydroxypropylcellulose. Shea In the table, the amount of each component of the coating agent is shown as the amount (parts by mass) based on 100 parts by mass of the resin particle body. Example 1 First, 300 kg of deionized water, 1.39 kg of tribasic calcium phosphate, 0.08 kg of disodium hydrogen phosphate, 3.5 g of potassium persulfate, and 1.5 g of sodium alkyldiphenyl ether disulfonate (Pelex SSH, manufactured by Kao Corporation) were charged into a 760 L autoclave (sealed container) equipped with a stirrer. Next, while the contents of the autoclave were being stirred, 0.25 kg of a foam regulator (polyethylene wax 1000, manufactured by Toyochem Co., Ltd.), 5 kg of cyclohexane as a blowing agent, and 252 kg of a polymerization initiator and styrene were charged into the autoclave. As a polymerization initiator, 0.94 kg of benzoyl peroxide ("Niper (registered trademark) BW" manufactured by NOF Corporation) and 0.54 kg of t-butylperoxy 2-ethylhexyl monocarbonate ("Perbutyl (registered trademark) E" manufactured by NOF Corporation) were used in combination. The contents of the autoclave were stirred at room temperature for 5 minutes, and then the temperature inside the autoclave was increased to 90°C over 30 minutes. After the temperature inside the autoclave reached 90°C, this temperature was maintained for 330 minutes (first half of the first-stage polymerization step). Next, the temperature inside the autoclave was heated to 96°C over 25 minutes and maintained at this temperature for 52 minutes (second half of the first-stage polymerization step). Next, the temperature inside the autoclave was increased to 120°C over 96 minutes and maintained at this temperature for 200 minutes (second-stage polymerization step). Thereafter, the temperature inside the autoclave was cooled to 25°C over 140 minutes. In this manner, the styrene inside the autoclave was polymerized. In the first half of the first-stage polymerization step, a blowing agent was supplied into the autoclave. Specifically, the supply of the blowing agent into the autoclave was started 364 minutes after the temperature inside the autoclave reached 90°C, and the supply was completed 60 minutes later. As described above, 7.6 kg of pentane (100% isopentane) and 7.6 kg of butane (a mixture of about 70% by mass of normal butane and about 30% by mass of isobutane) were used in combination as the blowing agent supplied in the first half of the first-stage polymerization step.

[0042] After cooling of the autoclave was completed, the pre-expandable resin particles containing a blowing agent in the resin particle body were removed from the autoclave. The pre-expandable resin particles were dehydrated and washed using a centrifuge, and then water adhering to the surface of the pre-expandable resin particles was removed using an airflow dryer. The dried pre-expandable resin particles were then classified to obtain pre-expandable resin particles with an average particle diameter of 0.4 mm. The average particle diameter of the pre-expandable resin particles was equal to the average particle diameter of the particle body. Next, the surfaces of the pre-expandable resin particles obtained as described above were coated with a coating agent. Specifically, 0.1 parts by mass of zinc stearate ("Zn-St" manufactured by Nitto Kasei Kogyo Co., Ltd.), 0.2 parts by mass of magnesium stearate ("Mg-St" manufactured by Nitto Kasei Kogyo Co., Ltd.), 0.1 parts by mass of glycerin monostearate ("Rikemal S-100P" manufactured by Riken Vitamin Co., Ltd.), 0.35 parts by mass of hydroxyalkylamine (Antista 80FS manufactured by Tanaka Chemical Research Institute Co., Ltd.), 0.05 parts by mass of stearic acid amide ("Fatty Acid Amide S" manufactured by Kao Corporation), and 0.05 parts by mass of dimethylpolysiloxane ("KF-96-100CS" manufactured by Shin-Etsu Chemical Co., Ltd.) were added to a container containing the dried pre-expandable resin particles, relative to 100 parts by mass of the resin particle bodies, and the mixture was stirred and mixed to coat the surfaces of the resin particle bodies, thereby obtaining expandable resin particles. This was designated Example 1.

[0043] [Preparation of foam particles] The expandable resin particles of Example 1 obtained as described above were placed in a pressure foaming machine (DYHL500U, manufactured by Daisen Kogyo Co., Ltd.), and steam was supplied into the pressure foaming machine to expand the expandable resin particles and obtain expanded particles.

[0044] Examples 2 to 16 Expandable resin particles were produced as Examples 2 to 16 in the same manner as in Example 1, except that the contents of Example 1 were changed as shown in Table 1 or Table 2. In addition, expandable resin particles of Examples 2 to 16 were produced in the same manner as in the production of expandable beads using the expandable resin particles of Example 1.

[0045] (Comparative Examples 1 to 6) Comparative Examples 1 to 6 were produced by the same method as in Example 1, except that the contents of Example 1 were changed as shown in Table 3. Furthermore, in Comparative Examples 1 to 6, expanded beads were produced using the expandable resin beads in the same method as in Example 1. The calcium stearate used in Comparative Example 1 was "Ca-St" manufactured by Nitto Kasei Kogyo Co., Ltd., and the erucamide used in Comparative Example 5 was "Fatty Acid Amide E" manufactured by Kao Corporation.

[0046] The expandable resin particles of the Examples and Comparative Examples obtained as described above were measured or evaluated as follows. The results are shown in Tables 1 to 3. In the evaluations shown below, ratings A and B were determined to be practical.

[0047] (Average particle size of expandable resin particles) Using a particle size distribution measuring device (manufactured by Nikkiso Co., Ltd., product name: Millitrac JPA), the cumulative 63% diameter (d63) of the expandable resin particles calculated based on the particle size distribution on a volume basis was measured, and this was taken as the average particle diameter.

[0048] (Amount of volatile matter in expandable resin particles) Approximately 1 g of expandable resin particles was prepared and weighed accurately to four decimal places to determine the pre-heating mass (W1). After weighing, the expandable resin particles were dried for 4 hours in a hot air dryer set at 120°C. After cooling the dried expandable resin particles to room temperature, the expandable resin particles were weighed to determine the post-heating mass (W2). The total volatile content was calculated from the mass change rate before and after heating, as shown in formula (2) below. Next, the content of volatile components was calculated by subtracting the moisture content of the expandable resin particles before heating from the total volatile content, as shown in formula (3) below. Note that for this measurement, five precisely weighed samples were prepared, and the procedure was performed for each sample. The arithmetic mean of these measured values ​​was taken as the volatile content of the expandable resin particles. The method for measuring the moisture content will be described later. [Number 2] Total volatile content (mass%) = [W1 (g) - W2 (g)] ÷ W1 (g) × 100 (2) [Number 3] Volatile content (mass%) = Total volatile content (mass%) - Water content (mass%) (3)

[0049] (Water content of expandable resin particles) The moisture content of the expandable resin particles was measured using a Karl Fischer moisture meter. Specifically, approximately 0.28 g of expandable resin particles was prepared and accurately weighed to four decimal places. This was used as a sample. The sample was heated at 160°C using a moisture vaporizer to vaporize the moisture in the sample, and the vaporized moisture was introduced into a Karl Fischer moisture meter, where the moisture content in the sample was measured by coulometric titration. Five precisely weighed samples were prepared for this measurement, and the procedure was performed for each sample. The arithmetic mean of these measured values ​​was used as the moisture content of the expandable resin particles. The moisture vaporizer used was a "CHK-501" manufactured by Kyoto Electronics Manufacturing Co., Ltd., and the Karl Fischer moisture meter used was a "MKC-610" manufactured by Kyoto Electronics Manufacturing Co., Ltd.

[0050] (Blowing agent content of expandable resin particles) The foaming agent content of the expandable resin particles of Examples and Comparative Examples was measured according to the method for measuring the foaming agent content of the expandable resin particles described above. Specifically, five precisely weighed samples were prepared, and the foaming agent content of each sample was measured, and the arithmetic mean value of these measured values ​​was taken as the foaming agent content of the expandable resin particles. The detailed analytical conditions for the gas chromatograph were as follows: Analytical equipment: Shimadzu Corporation, Gas chromatograph GC-6AM Detector: FID (Flame Ionization Detector) Column material: Glass column with an inner diameter of 3 mm and a length of 5000 mm Column packing material: [Liquid phase name] FFAP (free fatty acids), [Liquid phase impregnation rate] 10% by mass, [Carrier name] Chomasorb W diatomaceous earth for gas chromatography, [Carrier particle size] 60 / 80 mesh, [Carrier treatment method] AW-DMCS (water washing, calcination, acid treatment, silane treatment), [Packaging volume] 90 mL Inlet temperature: 250℃ Column temperature: 120℃ Detector temperature: 250°C Carrier gas: N2, flow rate 40 ml / min

[0051] (R-SM amount of expandable resin particles) The content of unreacted styrene (R-SM) in the expandable resin particles was measured using a headspace gas chromatograph mass spectrometer. Three standard solutions were prepared, each containing 5 ppm, 50 ppm, or 500 ppm styrene by mass in DMF. 0.2 g of each standard solution was weighed and placed in a 20 ml vial, which was then sealed with 1 ml of DMF. The gas phase of the vial was measured using a gas chromatograph mass spectrometer, and a calibration curve was created from the resulting chromatogram. Next, 0.2 g of expandable resin particles was weighed and placed in a 20 ml vial with 1 ml of DMF, which was then sealed. The vial was kept at room temperature for one day until the expandable resin particles were completely dissolved in the DMF. The gas phase of the vial was then measured using a gas chromatograph mass spectrometer. The content of unreacted styrene (ppm by mass) in the expandable resin particles was determined from the resulting chromatogram and a previously prepared calibration curve. For this measurement, five of the above samples were prepared, the procedure was performed for each sample, and the arithmetic mean value of these measured values ​​was taken as the R-SM amount of the expandable resin particles.The measurement conditions for gas chromatography mass spectrometry were as follows. Gas chromatograph mass spectrometer: Shimadzu Corporation GCMS-QP2020 Headspace sampler: Shimadzu Corporation HS-20 Capillary column: Stabilwax manufactured by GL Sciences, inner diameter 0.32 mm, length 30 m Headspace sampler incubation conditions: 90°C, 1 hour Column temperature: 50°C x 2 min → (heating rate: 10°C / min) → 90°C → (heating rate: 5°C / min) → 120°C → (heating rate: 20°C / min) → 230°C x 2 min Ion source temperature: 200℃ Carrier gas: Helium, column flow rate: 2 ml / min Split ratio: 1 / 10

[0052] (Weight average molecular weight of expandable resin particles) The weight-average molecular weight of the expandable resin particles was measured by gel permeation chromatography (GPC) using polystyrene as a standard substance. The chromatograms were obtained using a Tosoh HLC-8320GPC EcoSEC. Each expandable resin particle sample was dissolved in tetrahydrofuran (THF) to prepare a sample solution with a concentration of 0.1% by mass. The measurement samples were then separated by gel permeation chromatography (GPC) according to molecular weight differences under the following conditions to obtain chromatograms. The retention times in the chromatograms were converted to molecular weights using a calibration curve created using standard polystyrene to obtain differential molecular weight distribution curves. The weight-average molecular weight (Mw) of the measurement samples was calculated from the differential molecular weight distribution curves. Columns: One TSKguardcolumn SuperH-H and two TSK-GEL SuperHM-H columns were connected in series. Eluent: tetrahydrofuran Tetrahydrofuran flow rate: 0.6 ml / min

[0053] (Evaluation of fluidity of expandable resin particles) The expandable resin particles coated with the coating agent were placed in a 100 ml disposable cup to a level of 100%. The disposable cup was then placed in a thermo-hygrostat chamber at 60°C and 60% humidity and allowed to stand for 1 hour. The disposable cup was then removed from the chamber, the opening of the disposable cup was covered with a concentrically graduated scale mount, and the cup was slowly moved up and down so that the opening faced downward. The bottom of the mount was placed on the top surface of the test table. The cup was then positioned so that the center of the opening coincided with the center of the concentric scale. Then, while still placed on the test table, the disposable cup was slowly lifted vertically upward, and the diameter of the expandable resin particles spread on the scale mount (the point passing through the center of the scale and measuring the largest distance from the outer edge of the expandable resin particles) was measured. Based on the diameter of the expandable resin particles spread on the mount, the fluidity of the expandable resin particles was evaluated according to the following criteria. A: The diameter was 85 mm or more. B: The diameter was 75 mm or more and less than 85 mm. C: Diameter is less than 75 mm or lumps are visually observed in the expandable resin particle group.

[0054] (Evaluation of blocking occurrence of expandable resin particles) Approximately 4200 g of expanded particles immediately after being removed from the expansion machine were sieved through a mesh with 2.8 mm square holes, and the mass of the expanded particles remaining on the mesh was measured and the mass ratio of the expanded particles remaining on the mesh was calculated. Based on this ratio, the occurrence of blocking of the expandable resin particles was evaluated according to the following criteria. A: The ratio was less than 0.1%. B: The ratio was 0.1% or more and less than 0.2%. C: The ratio was 0.2% or more.

[0055] (Evaluation of Expandability of Expandable Resin Particles) The expandable resin particles were heated in a foaming machine using steam at a gauge pressure of 3 kPa (G) for 270 seconds to expand the expandable resin particles, producing expanded particles. The expanded particles were air-dried for a day and night, and then the bulk density (unit: kg / m) of each expanded particle was measured in the same manner as in the measurement of the bulk density of the expanded particles described above. 3 The expandability of the expandable resin particles was evaluated according to the following criteria based on the bulk density of the expanded particles when the expandable resin particles were expanded under certain conditions. A: The bulk density was 12 g / L or more and less than 15 g / L. B: The bulk density was 15 g / L or more and less than 30 g / L. C: The bulk density was 30 g / L or more.

[0056] The expanded beads produced by expanding the expandable resin beads of each Example and Comparative Example were measured or evaluated as follows. The results are shown in Tables 1 to 3. In the evaluations shown below, ratings A, B, and C were judged to be practical.

[0057] (Measurement of bulk density of expanded particles) Following the measurement of the bulk density of the expanded beads described above, the bulk density (unit: kg / m 3 ) was sought.

[0058] (Evaluation of fluidity of expanded beads) Except for using expanded beads instead of expandable resin beads, the fluidity of each expanded bead was confirmed in the same manner as described above for confirming the fluidity of expandable resin beads, and the diameter of the expanded bead group spread on the backing paper was measured and evaluated according to the following criteria. A: The diameter was 85 mm or more. C: Diameter is less than 85 mm or lumps are visually observed in the foam particles.

[0059] (Measurement of the settling rate of foamed beads) The foamed particles with a bulk volume of 330 ml have an inner diameter of 7.8 cm and a volume of 61.6 cm 3The expanded beads were placed in a cylindrical metal container. Using a metal disc-shaped tool with a diameter of 7.7 cm, the expanded beads were compressed from the top at a speed of 10 m / min until a compression load of 650 N was reached, and this was repeated 100 times. After the repeated compression was completed, the bulk volume of the expanded beads in the container was measured, and the settling rate (volume reduction rate) was calculated using the following formula (4). The testing machine used for the repeated compression operation was an Autograph AG-X plus 100 kN manufactured by Shimadzu Corporation. [Number 4] Settling rate = (bulk volume before test - bulk volume immediately after test) ÷ volume before test × 100 (4)

[0060] (Evaluation of the amount and property of electrostatic charge of foamed beads) The expanded particles were placed in a constant temperature and humidity chamber at a temperature of 23°C and a humidity of 50% and cured for 24 hours. After curing, the expanded particles had a bulk volume of 330 ml and an inner diameter of 7.8 cm and a volume of 61.6 cm. 3 The foamed beads were placed in a cylindrical metal container. A Mascot static eliminator (manual static eliminator) was used to eliminate static electricity while the foamed beads were placed. The initial charge was set to 0 V at a position 10 mm from the surface of the foamed beads. Using a 7.7 cm diameter metal disc-shaped jig, the foamed beads were compressed from above at a compression rate of 60 mm / min until a compression load of 650 N was reached. This process was repeated 100 times. Thirty seconds after the end of the repeated compression, the charged voltage [V] was measured 25 mm above the top surface of the foamed beads in the container. The test machine used for the repeated compression was an Autograph AG-X plus 100 kN manufactured by Shimadzu Corporation. The withstand voltage was measured using a digital low-potential meter KSD-3000 manufactured by Kasuga Electric Co., Ltd. The chargeability of the foamed beads was evaluated based on the charge measured as described above, as follows: A: The charge amount was between -10V and +10V. B: The charge amount was -25V or more and less than -10V. C: The charge was less than -25V.

[0061] (R-SM amount of expanded particles) The R-SM amount (ppm by mass) of the expanded beads was measured in the same manner as in the measurement of the R-SM amount of the expandable resin beads described above, except that the sample used was changed from expandable resin beads to expanded beads.

[0062] (VOC emission amount of foam particles) First, the foamed particles were placed in a constant temperature and humidity chamber at a temperature of 23°C and a humidity of 50% and cured for two days. Following JISA1901:2015, the cured foamed particles were placed on the bottom of a small 20 L stainless steel chamber with a surface area of ​​320 cm. 2 The test load rate was 1.6m 2 / m 3 The amount of VOCs emitted from the foam particles under the conditions (μg / m 3 ) was measured.

[0063] A rectangular cushioning material was created by filling a stretchable bag (110cm x 125cm x 150cm) made of polyester fiber with foamed particles with a bulk volume of 2.2 L. This was placed on a test table, and panelists placed their palms on the top of the cushioning material and pressed downward to check the feel, evaluating the feel according to the following criteria. Ten randomly selected panelists evaluated the feel of the cushioning material using the following criteria: an "A" rating was given for a total score of 27 or more by the ten panelists, a "B" rating was given for a total score of 20 to 26 points by the ten panelists, and a "C" rating was given for a total score of 19 or less by the ten panelists. 3 points: Highly fluid and has a smooth feel. 2 points: Fluid, but sometimes feels gritty. 1 point: Low fluidity and rough texture.

[0064] [Table 1]

[0065] [Table 2]

[0066] [Table 3]

[0067] The present invention described above encompasses the following technical ideas. (1) Expandable polystyrene-based resin particles for filling cushioning materials, which are composed of a resin particle body having a polystyrene-based resin as a base resin, a blowing agent contained in the resin particle body, and a coating agent coating the resin particle body, The average particle diameter of the resin particle body is 0.3 mm or more and 0.5 mm or less, the coating agent comprises a metal stearate A, stearic acid amide, and an antistatic agent; The metal stearate A comprises 40% by mass or more and 100% by mass or less of magnesium stearate and 0% by mass or more and 60% by mass or less of zinc stearate (the total of both is 100% by mass), Expandable polystyrene-based resin particles for filling cushioning material, wherein the coating amount of the metal stearate A is 0.1 parts by mass or more but less than 0.4 parts by mass, the coating amount of the stearic acid amide is 0.01 parts by mass or more but 0.5 parts by mass or less, and the coating amount of the antistatic agent is 0.2 parts by mass or more but 0.8 parts by mass or less, relative to 100 parts by mass of the resin particle body. (2) Expandable polystyrene-based resin particles for filling cushioning material according to (1) above, in which the amount of coating of the magnesium stearate is 0.1 parts by mass or more but less than 0.4 parts by mass, and the amount of coating of the zinc stearate is less than 0.2 parts by mass (including 0 parts by mass) per 100 parts by mass of the resin particle body. (3) Expandable polystyrene-based resin particles for cushioning filling according to (1) or (2) above, wherein the metal stearate A is composed of 60% by mass or more and 80% by mass or less of magnesium stearate and 20% by mass or more and 40% by mass or less of zinc stearate (the sum of the two is 100% by mass). (4) Expandable polystyrene resin particles for filling of cushioning material according to any one of the above (1) to (3), wherein the mass ratio of the metal stearate A to the stearic acid amide is 1:0.05 to 1:1.5. (5) The antistatic agent is a stearic acid monoglyceride and a hydroxy Shea The expandable polystyrene resin particles for padding of cushioning material according to any one of (1) to (4) above, which contain stearic acid monoglyceride and hydroxyamine, and the mass ratio of the stearic acid monoglyceride to the hydroxyamine is 1:1.5 to 1:10. (6) Expandable polystyrene-based resin particles for filling cushioning material according to any one of (1) to (5) above, wherein the foaming agent contains butane, pentane, and cyclohexane, the total content of butane, pentane, and cyclohexane in the expandable polystyrene-based resin particles is 4% by mass or more and 8% by mass or less relative to 100% by mass of the expandable resin particles, and the mass ratio of the sum of butane and pentane to cyclohexane is 1:0.1 to 1:0.5.

Claims

1. The expandable polystyrene-based resin particles for use in filling a cushioning material are composed of a resin particle body having a polystyrene-based resin as a base resin, a blowing agent contained in the resin particle body, and a coating agent coating the resin particle body, the average particle diameter of the resin particle body is 0.3 mm or more and 0.5 mm or less, the coating agent comprises a metal stearate A, stearic acid amide, and an antistatic agent; The metal stearate A comprises 40% by mass or more and 100% by mass or less of magnesium stearate and 0% by mass or more and 60% by mass or less of zinc stearate (the total of both is 100% by mass), Expandable polystyrene-based resin particles for filling cushioning material, wherein the coating amount of the metal stearate A is 0.1 parts by mass or more but less than 0.4 parts by mass, the coating amount of the stearic acid amide is 0.01 parts by mass or more but 0.5 parts by mass or less, and the coating amount of the antistatic agent is 0.2 parts by mass or more but 0.8 parts by mass or less, relative to 100 parts by mass of the resin particle body.

2. 2. Expandable polystyrene-based resin particles for cushioning filling according to claim 1, wherein the amount of coating of the magnesium stearate is 0.1 parts by mass or more but less than 0.4 parts by mass, and the amount of coating of the zinc stearate is less than 0.2 parts by mass (including 0 parts by mass) per 100 parts by mass of the resin particle body.

3. 3. The expandable polystyrene-based resin particles for cushioning filling according to claim 1 or 2, wherein the metal stearate A comprises 60% by mass or more and 80% by mass or less of magnesium stearate and 20% by mass or more and 40% by mass or less of zinc stearate (the sum of the two being 100% by mass).

4. 4. The expandable polystyrene-based resin particles for filling cushion materials according to claim 1, wherein the mass ratio of said metal stearate A to said stearamide is 1:0.05 to 1:1.

5.

5. The expandable polystyrene-based resin particles for cushioning filling according to any one of claims 1 to 4, wherein the antistatic agent comprises stearic acid monoglyceride and hydroxyamine, and the mass ratio of the stearic acid monoglyceride to the hydroxyamine is 1:1.5 to 1:

10.

6. The expandable polystyrene-based resin particles for cushioning filling according to any one of claims 1 to 5, wherein the foaming agent contains butane, pentane, and cyclohexane, the total content of butane, pentane, and cyclohexane in the expandable polystyrene-based resin particles is 4% by mass or more and 8% by mass or less relative to 100% by mass of the expandable resin particles, and the mass ratio of the sum of the butane and pentane to cyclohexane is 1:0.1 to 1:0.5.

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