Polystyrene-based resin particle and method for producing the same

Abstract

To provide a method for producing polystyrene-based resin particles in a hot cutting system, which more surely prevents clogging of a dice.SOLUTION: A method for producing polystyrene-based resin particles cuts a polystyrene-based resin composition while extruding the polystyrene-based resin composition to a cooling medium from a dice for granulation, and obtains polystyrene-based resin particles, wherein the polystyrene-based resin composition contains a resin containing a polystyrene-based resin and a fatty acid metal salt having 8 to 22 carbon atoms, as for a content of the fatty acid metal salt, a metal element constituting the fatty acid metal salt is 20 to 500 mg with respect to 1 kg of the total mass of the polystyrene-based resin composition, and a mass of 100 particles of the group of the polystyrene-based resin particles is 30 mg or less.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to polystyrene-based resin particles and a method for producing the same. [Background technology]

[0002] Polystyrene resin particles are impregnated with a foaming agent or subjected to suspension polymerization to form expandable particles, which are used as a raw material for expanded polystyrene beads. Examples of methods for producing polystyrene resin particles include a strand cutting method, an underwater cutting method, and a hot cutting method. In the underwater cutting method, polystyrene resin is put into an extruder, extruded through small holes in a die, and cut underwater with a rotary cutter or the like to obtain polystyrene resin particles.

[0003] For example, Patent Document 1 proposes an invention in which, in an underwater cutting method, the water temperature is set within a specific range, and the shear rate when passing through a specific position after the start of operation is set to 0.5 to 0.9 times the shear rate 5 minutes after the start of operation (the discharge rate is increased at the start of operation).The invention described in Patent Document 1 aims to prevent clogging of the die. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 6962694 Summary of the Invention [Problem to be solved by the invention]

[0005] However, in the underwater cutting method, it is required to be able to more reliably prevent clogging of the die. Therefore, an object of the present invention is to provide a method for producing polystyrene resin particles that can more reliably prevent clogging of the die. [Means for solving the problem]

[0006] <1> A method for producing polystyrene-based resin particles, comprising extruding a polystyrene-based resin composition through a granulation die into a cooling medium while cutting the composition to obtain polystyrene-based resin particles, the polystyrene-based resin composition comprises a resin containing a polystyrene-based resin and a metal salt of a fatty acid having 8 to 22 carbon atoms; The fatty acid metal salt is contained in an amount of 20 to 500 mg of a metal element constituting the fatty acid metal salt per kg of the total mass of the polystyrene-based resin composition, The method for producing polystyrene-based resin particles, wherein the mass of 100 particles in the group of polystyrene-based resin particles is 30 mg or less. <2> The fatty acid metal salt includes a metal stearate. <1> 1. A method for producing polystyrene-based resin particles according to claim 1. <3> The polystyrene-based resin contains recycled materials. <1> or <2> 1. A method for producing polystyrene-based resin particles according to claim 1.

[0007] <4> Polystyrene-based resin particles containing a resin containing a polystyrene-based resin and a metal salt of a fatty acid having 8 to 22 carbon atoms, a part or all of the fatty acid metal salt is present inside; The fatty acid metal salt is contained in an amount of 20 to 500 mg of metal elements constituting the fatty acid metal salt per kg of the total mass of the polystyrene-based resin particles, Polystyrene resin particles having a mass of 30 mg or less per 100 particles. [Effects of the Invention]

[0008] According to the method for producing polystyrene-based resin particles of the present invention, clogging of the die can be more reliably prevented. [Brief explanation of the drawings]

[0009] [Figure 1] FIG. 1 is a schematic diagram illustrating an example of a production apparatus for polystyrene-based resin particles. [Figure 2] FIG. 2 is a side cross-sectional view of the granulating die of FIG. 1. DETAILED DESCRIPTION OF THE INVENTION

[0010] (Polystyrene resin particles) The polystyrene-based resin particles (hereinafter sometimes referred to as "PS particles") of the present invention are particles containing a resin and a fatty acid metal salt. The shape of the PS particles is, for example, spherical, approximately spherical, oval spherical, cylindrical, or cylindrical with a bulging center (drum-like). In the PS particles, part or all of the fatty acid metal salt is present inside the PS particles, which means that the PS particles of the present invention are different from particles coated with a fatty acid metal salt on the outer surface.

[0011] The mass of 100 particles in the group of PS particles is preferably 30 mg or less, more preferably 15 to 28 mg, and even more preferably 19 to 23 mg. The mass of 100 particles is a value obtained by randomly selecting 100 PS particles from a group of PS particles and measuring their total mass using a precision electronic balance.

[0012] <Resin> The resin is a thermoplastic resin including a polystyrene-based resin. Examples of polystyrene-based resins include homopolymers of styrene-based monomers such as styrene, α-methylstyrene, vinyltoluene, chlorostyrene, ethylstyrene, i-propylstyrene, dimethylstyrene, and bromostyrene, as well as copolymers thereof. Examples of polystyrene-based resins also include copolymers of styrene-based monomers and vinyl monomers polymerizable therewith, copolymers of styrene-based monomers and rubber components such as butadiene, and so-called high impact polystyrene (HIPS), which are mixtures or polymers of homopolymers of styrene-based monomers, copolymers thereof, or copolymers of styrene-based monomers and vinyl monomers with diene-based rubber polymers.

[0013] The polystyrene resin may be partially or entirely made from recycled materials. Examples of recycled materials include used polystyrene resin foam molded articles, such as fish boxes, cushioning materials for home appliances, and food packaging trays, which are recovered and regenerated by a limonene dissolution method or a thermal volume reduction method. Examples of recycled materials include waste materials generated after punching food packaging containers from a foam sheet, which are crushed, melt-kneaded, and re-pelletized. Usable recycled raw materials include those obtained by recycling molded bodies such as used foam containers, as well as non-foamed polystyrene resins separated and recovered from home appliances (e.g., televisions, refrigerators, washing machines, air conditioners, etc.), office equipment (e.g., copiers, facsimiles, printers, etc.), etc. The polystyrene resin may be a virgin material other than a recycled material. Examples of the virgin material include general-purpose polystyrene resin (GPPS), commercially available polystyrene resins, and polystyrene resins newly prepared by methods such as suspension polymerization.

[0014] The content of the polystyrene resin relative to the total mass of the resins is preferably 50% by mass or more, more preferably 75% by mass or more, even more preferably 95% by mass or more, and may be 100% by mass.

[0015] As long as the resin is mainly composed of a polystyrene resin (50% by mass or more of the total mass of the resin), it may contain other resins such as polyethylene resins, polypropylene resins, and acrylic resins.

[0016] <Fatty acid metal salts> The fatty acid metal salt is a metal salt of a fatty acid having 8 to 22 carbon atoms, and is a so-called metal soap. Examples of metal salts include alkali metal salts, alkaline earth metal salts, and transition metal salts. Examples of the alkali metal salt include potassium salt and sodium salt. Examples of alkaline earth metal salts include calcium salts, magnesium salts, and barium salts. Examples of transition metals include zinc salts. As the fatty acid metal salt, metal stearates are preferred, and magnesium stearate, zinc stearate, etc. are preferred.

[0017] The PS particles preferably contain 20 to 500 mg, more preferably 20 to 250 mg, and even more preferably 20 to 150 mg of fatty acid metal salt per kg of total mass of the PS particles. That is, the content of fatty acid metal salt in the PS particles is preferably 20 to 500 mg, more preferably 20 to 250 mg, and even more preferably 20 to 150 mg, in terms of metal element equivalent, per kg of total mass of the PS particles. The content of the metal elements constituting the fatty acid metal salt in the PS particles can be measured by inductively coupled plasma emission spectrometry (ICP).

[0018] <Optional ingredients> The PS particles may contain any component other than the resin and the fatty acid metal salt. Examples of optional components include additives such as binding inhibitors, cell control agents, crosslinking agents, fillers, flame retardants, flame retardant assistants, lubricants, and colorants. It is preferable that the PS particles of this embodiment do not contain a foaming agent.

[0019] (Method of producing polystyrene-based resin particles) The method for producing PS particles of the present invention is a so-called underwater cutting method. That is, in the method for producing PS particles, a polystyrene-based resin composition (PS composition) is extruded through a granulating die into a cooling medium and cut into PS particles.

[0020] An example of a production apparatus used in the method for producing PS particles will be described with reference to the drawings. In the manufacturing apparatus 100 and the granulating die 1, the side from which the resin is extruded will be referred to as the "front" or "tip," and the opposite side will be referred to as the "rear" or "rear end," and these terms will be used consistently in the following description. The PS particle production apparatus 100 shown in FIG. 1 is a production apparatus for granulating PS particles by an underwater cutting method. The manufacturing apparatus 100 has an extruder 2 (resin supply device) having a granulation die 1 at its tip, a chamber 4 housing a cutter 3, piping 5, a pump 6, a water tank 7, a dehydration treatment section 8, and a container 9. A chamber 4 is connected to the tip of the granulating die 1 of the extruder 2 . A pipe 5 for carrying a circulating cooling medium is connected to the chamber 4, and one end of this pipe 5 (upstream of the chamber 4) is connected to a water tank 7 via a pump 6. The other end of the pipe 5 (downstream of the chamber 4) is provided with a dehydration treatment unit 8 that separates the PS particles from the cooling medium, dehydrates them, and dries them. The PS particles separated, dehydrated, and dried in the dehydration treatment unit 8 are sent to a container 9.

[0021] In FIG. 1, symbol S denotes a sensing unit for measuring the temperature and pressure of the cooling medium in the manufacturing apparatus 100. The temperature and pressure of the cooling medium can be measured using conventionally known temperature and pressure measuring devices. The temperature of the cooling medium is controlled by a heater or cooler installed at an appropriate location in the circulating water supply path, and the pressure and amount are controlled by the pressure setting of pump 6.

[0022] The extruder 2 has a hopper 21 and a granulating die 1 at the tip. The extruder 2 may be, for example, either an extruder using a screw or an extruder not using a screw. Examples of extruders using a screw include a single-screw extruder, a multi-screw extruder, a vent extruder, and a tandem extruder. Examples of extruders not using a screw include a plunger extruder and a gear pump extruder. A static mixer can be used with either extruder. Of these extruders, an extruder using a screw is preferred from the viewpoint of productivity. The chamber 4 may be a conventionally known one used in the underwater cutting method.

[0023] The granulation die 1 in Fig. 2 has a die body 10 (also called a die plate) and a die holder 11 provided between the die body 10 and the extruder 2. The die body 10 is connected to the tip side of the die holder 11 by a plurality of bolts.

[0024] The die holder 11 is provided in communication with the cylinder of the extruder 2, and is formed with a rear-end passage 11a and a front-end passage 11b in this order from the rear end to the front end. The die body 10 has a conical protrusion 10a formed in the center of the rear end face, protruding rearward. With the die body 10 and the die holder 11 connected, the conical protrusion 10a is inserted into the front-end passage 11b of the die holder 11 with a predetermined gap.

[0025] The die body 10 has a resin discharge surface 13 whose tip surface is in contact with a cooling medium, multiple resin flow paths 14 for transporting the PS composition 20 extruded from the extruder 2 toward the resin discharge surface 13, multiple nozzles 15 provided at the tips of the multiple resin flow paths 14 and opening in the resin discharge surface 13, a heat insulating material 16 provided at the center of the resin discharge surface 13, a cartridge heater 17 located closer to the extruder 2 than the resin discharge surface 13 for heating the resin discharge surface 13 and the tip sides of the resin flow paths 14, and a short heater 18 for heating the rear ends of the resin flow paths 14.

[0026] The cartridge heater 17 and short heater 18 can be appropriately selected from conventionally known cartridge heaters according to the size and shape of the die body 10. In addition, the means for heating the die body 10 is not limited to rod-shaped heaters such as cartridge heaters 17 and short heaters 18, but may also be formed inside the die body 10 to pass a heat transfer medium such as thermo oil, and the die body 10 may be heated by the heated heat transfer medium.

[0027] The resin discharge surface 13 of the die body 10 has a heat insulating material 16 with a circular cross section arranged in the center, and the discharge openings of a plurality of nozzles 15 are positioned along concentric circles radially outward from the heat insulating material 16.

[0028] The resin flow paths 14 have a circular cross section, extend in a direction perpendicular to the resin discharge surface 13, and are arranged at regular intervals along a circumference (a circumference drawn on the resin discharge surface 13) centered on the central axis of the die body 10. The number of resin flow paths 14 is not particularly limited and may be, for example, 4 to 12.

[0029] The nozzles 15 are arranged at predetermined intervals along the circumference of the resin discharge surface 13 . The nozzle 15 has a plurality of openings. The number of openings per nozzle is, for example, 5 to 50. The diameter of the opening of the nozzle 15 is determined appropriately depending on the particle diameter of the desired PS particles, and is set to, for example, 0.3 to 1.0 mm.

[0030] The heat insulating material 16 is provided on the resin discharge surface 13 on the inner side of the circumference where the multiple nozzles 15 are arranged, and serves to prevent heat from the die body 10 from escaping into the water in the chamber 4, thereby suppressing a drop in temperature of the die body 10. A heat insulating material that is water-resistant and has a high surface hardness is preferred as the heat insulating material 16. The die body 10 is provided with a temperature measuring element 19 such as a thermocouple.

[0031] A method for producing PS particles using the production apparatus 100 will be described. Pump 6 is started to circulate the cooling medium through pipe 5. The cooling medium flows into chamber 4 from inlet 4a, flows through chamber 4, and flows out from outlet 4b.

[0032] Examples of the cooling medium include water and a mixture of water and an organic solvent. The temperature of the cooling medium is, for example, preferably 50 to 90°C, more preferably 70 to 80°C. When the temperature of the cooling medium is equal to or higher than the above lower limit, the molten PS composition 20 is cooled by the cooling medium at the tip of the nozzle 15, preventing clogging of the nozzle. When the temperature of the cooling medium is equal to or lower than the above upper limit, the PS particles cut by the cutter 3 are cooled appropriately, preventing the PS particles from coalescing together.

[0033] The flow rate of the cooling medium is preferably, for example, 150 to 300 L / min, and more preferably 180 to 250 L / min. When the flow rate of the cooling medium is equal to or greater than the lower limit, the PS particles cut by the cutter 3 are immediately swept away by the water flow, preventing the PS particles from coalescing together. When the amount of the cooling medium is equal to or less than the upper limit, the die is prevented from being cooled by the cooling medium, and nozzle clogging is suppressed. The flow rate of the cooling medium is, for example, the flow rate flowing into the chamber 4, and is measured using a conventionally known flow meter.

[0034] The raw materials for the PS composition (resins including polystyrene-based resins, fatty acid metal salts, and optional components as necessary) are fed from a hopper 21 into an extruder 2, where the raw materials for the PS composition are melt-kneaded to form a PS composition. The melt-kneaded PS composition flows from the extruder 2 into a granulation die 1. Within the granulating die 1, the PS composition 20 flows through the rear-end flow path 11a, the front-end flow path 11b, and the resin flow path 14 in this order, and is discharged from the nozzle 15 onto the resin discharge surface 13. The PS composition 20 discharged from the nozzle 15 is immediately cut by the cutter 3 to form PS particles. At this time, since the PS composition contains a fatty acid metal salt, it flows smoothly through the flow path and prevents clogging of the nozzle 15.

[0035] The resin contained in the PS composition is the resin contained in the PS particles, and the content of the resin contained in the PS composition is the same as the content of the resin contained in the PS particles. The fatty acid metal salt contained in the PS composition is the fatty acid metal salt contained in the PS particles, and the content of the fatty acid metal salt in the PS composition is the same as the content of the fatty acid metal salt in the PS particles. The optional components contained in the PS composition are the optional components contained in the PS particles, and the content of the optional components contained in the PS composition is the same as the content of the optional components contained in the PS particles.

[0036] The temperature (resin temperature) of the PS composition in the extruder 2 is, for example, preferably 180 to 250°C, more preferably 210 to 230°C. When the resin temperature is equal to or higher than the above lower limit, the fluidity of the PS composition can be further improved. When the resin temperature is equal to or lower than the above upper limit, the PS particles cut by the cutter 3 can be more reliably cooled by the cooling medium, preventing the PS particles from coalescing together.

[0037] The discharge rate of the PS composition from the granulating die 1 is, for example, preferably 50 to 200 kg / h, more preferably 60 to 100 kg / h. When the discharge rate is equal to or greater than the lower limit, clogging of the die can be prevented. When the discharge rate is equal to or less than the upper limit, PS particles with a small particle size can be easily obtained.

[0038] The die pressure is appropriately determined depending on the type of PS composition, the particle size of the group of PS particles, and the like. The die pressure is measured at the resin introduction section into the granulation die 1.

[0039] The smaller the rate of increase in die pressure, the better. Preventing clogging reduces the rate of increase in die pressure, enabling long-term continuous production of PS particles and preventing the PS particles from becoming enlarged. The die pressure increase rate after 2 hours from the start of production is, for example, preferably 18% or less, more preferably 10% or less, and even more preferably 5% or less. When the die pressure increase rate is equal to or less than the upper limit, nozzle clogging is reduced, PS particle enlargement is suppressed, and productivity is improved. The die pressure increase rate can be calculated using the following formula (1). Die pressure increase rate (%) = ([Die pressure 2 hours after the start of production] - [Die pressure at the start of production]) ÷ [Die pressure at the start of production] × 100 (1)

[0040] The cooling medium containing the PS particles is transferred from chamber 4 through pipe 5 to dehydration treatment unit 8. The PS particles are separated, dehydrated, dried, and sent to container 9 in dehydration treatment unit 8. The cooling medium is separated in dehydration treatment unit 8 and transferred to water tank 7.

[0041] According to the method for producing PS particles of this embodiment, PS particles having a specific mass of 100 particles are produced using a PS composition containing a fatty acid metal salt, thereby suppressing nozzle clogging and increasing productivity. [Example]

[0042] (Measurement method) <Metal element content> The metal element (zinc and magnesium) content in the recovered pellets of used polystyrene resin used as the raw material in each example was measured as follows. A weighed 0.5 g sample was heated at 475°C for 3 hours and incinerated. The resulting ash was mixed with 2 mL of concentrated hydrochloric acid (Ultrapur-100, ultra-high purity reagent, manufactured by Kanto Chemical Co., Ltd.). The insoluble matter in the mixture was filtered through ADVANTEC No. 7 filter paper, and the filtrate was diluted to 50 mL with pure water to prepare the test solution. The metal element concentrations in the test solution were measured under the following conditions. The metal element concentrations were determined from the calibration curve. The amount of metal element in the sample was calculated using the following formula (2). The lower limit of quantitation was 1 mg / kg. Amount of metal element (mg / kg) = Metal element concentration (μg / mL) x 50 (mL) ÷ Measured sample mass (g) (2)

[0043] <ICP measurement conditions> Measurement equipment: Shimadzu Corporation's "ICPE-9000" multi-type ICP optical emission spectrometer. Measured elements = Zn (202.548nm), Mg (285.213nm). Observation direction = axial, high frequency output = 1.20 kW, carrier flow rate = 0.7 L / min. Plasma flow rate = 10.0 L / min., auxiliary flow rate = 0.6 L / min., exposure time = 30 seconds. Standard solution for calibration curve = SPEX USA "XSTC-13X" general-purpose mixed standard solution 31 elements mixed (base 5% HNO3): each approximately 10 mg / L. The standard solution for the calibration curve was diluted with pure water to prepare standard solutions of 5 ppm, 2.5 ppm, 1 ppm, and 0.25 ppm, and measurements were performed.

[0044] ≪Ashing conditions≫ Measurement equipment: Yamato Scientific Muffle Furnace FP-410. Ashing conditions: 475°C x 3 hours (sample weight: approximately 0.5 g).

[0045] Example 1 The zinc content of recycled pellets of used polystyrene resin (hereinafter simply referred to as "recycled pellets") was measured, and zinc stearate was added to adjust the zinc content to 130 mg / kg. The pellets were then fed into a 90 mm diameter single-screw extruder and mixed while heated and melted. The molten PS composition was then kneaded and cooled to 218 °C and extruded through 312 0.5 mm diameter orifices at a rate of 79.4 kg / h into a chamber filled with circulating water (cooling medium) at 70 °C and 200 L / min. A high-speed rotating cutter with 10 circumferential blades was attached to the resin outlet surface, and the extruded PS composition was cut at 4,500 rpm to produce PS particles. The PS particles were dehydrated in a centrifugal dehydrator. The resin temperature at the resin inlet of the granulation die was 235 °C. The rate of increase in die pressure after 2 hours from the start of production was determined, and the results are shown in Table 1. In addition, after confirming that the mass of 100 PS particles immediately after the start of production was 30 mg or less, the mass of 100 PS particles after 2 hours from the start of production was determined, and the results were evaluated according to the following evaluation criteria.

[0046] (Examples 2 to 5, Comparative Examples 1 and 2) PS particles were obtained in the same manner as in Example 1, except that zinc stearate or magnesium stearate was added in an amount to adjust the zinc element content or magnesium element content as shown in Table 1, and the resin temperature, circulating water temperature, and discharge rate were set as shown in Table 1. The magnesium element content was measured in the recovered pellets, and adjusted by adding magnesium stearate so as to achieve the magnesium element content shown in Table 1. The rate of increase in die pressure after 2 hours from the start of production was determined, and the results are shown in Table 1. In addition, after confirming that the mass of 100 PS particles immediately after the start of production was 30 mg or less, the mass of 100 PS particles after 2 hours from the start of production was determined, and the results were evaluated according to the following evaluation criteria.

[0047] (Evaluation criteria) ○: The mass of 100 PS particles 2 hours after the start of production is 30 mg or less. ×: The mass of 100 PS particles exceeds 30 mg 2 hours after the start of production.

[0048] [Table 1]

[0049] As shown in Table 1, in Examples 1 to 5 in which the present invention was applied, the die pressure increase rate 2 hours after the start of production was 2.0 to 16.3%, and the mass of 100 PS particles was 30 mg or less. In Comparative Example 1, which used a PS composition containing no fatty acid metal salt, the die pressure increase rate after 2 hours from the start of production was 29.0%, and the mass of 100 PS particles was 33 mg. In Comparative Example 2, in which the content of metal elements constituting the fatty acid metal salt was 520 mg / kg, the die pressure increase rate 2 hours after the start of production was 18.4%, and the mass of 100 PS particles was 36 mg. From the above, it was confirmed that clogging can be more reliably prevented by applying the present invention. [Explanation of symbols]

[0050] 100 Manufacturing equipment, 1 Granulation die, 2 Extruder (resin supply device), 3 Cutter, 4 Chamber, 5 Piping, 6 Pump, 7 Water tank, 8 Dehydration treatment unit, 9 Container, 21 Hopper, S Sensing unit, 10 Die body, 11 Die holder, 13 Resin discharge surface, 14 Resin flow path, 15 Nozzle, 16 Heat insulating material, 17 Cartridge heater, 18 Short heater, 19 Temperature measuring element

Claims

1. A method for producing polystyrene-based resin particles, comprising extruding a polystyrene-based resin composition through a granulation die into a cooling medium while cutting the composition to obtain polystyrene-based resin particles, the polystyrene-based resin composition comprises a resin containing a polystyrene-based resin and a metal salt of a fatty acid having 8 to 22 carbon atoms; The fatty acid metal salt is contained in an amount of 20 to 500 mg of a metal element constituting the fatty acid metal salt per kg of the total mass of the polystyrene-based resin composition, The method for producing polystyrene-based resin particles, wherein the mass of 100 particles in the group of polystyrene-based resin particles is 30 mg or less.

2. The method for producing polystyrene-based resin particles according to claim 1 , wherein the fatty acid metal salt includes a stearate metal salt.

3. The method for producing polystyrene-based resin particles according to claim 1 or 2, wherein the polystyrene-based resin contains recycled materials.

4. Polystyrene-based resin particles containing a resin containing a polystyrene-based resin and a metal salt of a fatty acid having 8 to 22 carbon atoms, a part or all of the fatty acid metal salt is present inside; the fatty acid metal salt is contained in an amount of 20 to 500 mg of a metal element constituting the fatty acid metal salt per kg of the total mass of the polystyrene-based resin particles; Polystyrene-based resin particles having a mass of 30 mg or less per 100 particles.

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