JP5882070B2 - Expandable polystyrene resin particles, method for producing the same, and foam molded article - Google Patents

Description

  The present invention relates to an expandable polystyrene resin particle obtained by a melt extrusion method, a method for producing the same, and an expanded molded body manufactured from the expandable polystyrene resin particle.

  A foaming agent is press-fitted and kneaded into the polystyrene resin melted in the extruder, and the foaming agent-containing molten resin is extruded directly into the cooling liquid through a small hole in the die attached to the tip of the extruder. With respect to a method for producing expandable polystyrene resin particles by a so-called melt extrusion method, the extrudate is cooled and solidified by contact with a liquid to obtain expandable polystyrene resin particles. Techniques disclosed in Patent Documents 1 and 2 have been proposed.

  In Patent Document 1, a melt-kneaded product of a foaming agent-containing thermoplastic resin is introduced into a pelletizing die, and a flow path is made to flow toward the extrusion hole of the die. A process for producing expandable thermoplastic resin particles, characterized in that after flowing into a large flow path, it passes through an extrusion hole, extruded into a pressurized liquid from its outlet, immediately cut into particles, and then cooled. It is disclosed.

  In Patent Document 2, a thermoplastic resin (A), a foaming agent (B), and 1.5 parts by weight or less of inorganic powder (C) with respect to 100 parts by weight of the thermoplastic resin (A) are melt-kneaded. Then, this is extruded into a pressurized liquid from an extrusion hole of a die head, immediately cut, and then cooled, and then a method for producing expandable thermoplastic resin particles is disclosed.

JP-A-6-136176 JP-A-6-298893

In the production methods described in Patent Documents 1 and 2, when foamable polystyrene resin particles are produced, the foamable polystyrene resin particles obtained have a low foaming capacity and produce a foamed molded article having a high expansion ratio. There is a problem that is difficult. In addition, the foam molded body produced from the resin particles has a problem that the mechanical strength is inferior. Furthermore, the foam molded article produced from the resin particles has a poor appearance, and it has been difficult to obtain a foam molded article having a beautiful appearance.
Further, when a recycled material is used as the polystyrene-based resin, each of the above-mentioned problems may be increased, and therefore, it is not suitable for use of the recycled material.

  The present invention has been made in view of the above circumstances, and can use recycled raw materials when producing expandable polystyrene resin particles by a melt extrusion method, has excellent foamability, has a short molding cycle, has a good appearance, and is a sufficient machine. An object of the present invention is to provide expandable polystyrene resin particles capable of producing a well-balanced foamed molded article having strength.

  In order to achieve the above object, the present invention is an expandable polystyrene resin particle in which a polystyrene resin containing a foaming agent is in the form of particles, and the weight average molecular weight Mw of the polystyrene resin is in the range of 120,000 to 320,000. The foaming agent contains 2 to 8 parts by mass of butane as an essential component with respect to 100 parts by mass of polystyrene resin, and the composition of butane is isobutane: normal butane = 10: 90 by mass ratio. Expandable polystyrene resin particles having a range of ˜80: 20 are provided.

  In the expandable polystyrene resin particles of the present invention, the polystyrene resin preferably has a weight average molecular weight Mw in the range of 140,000 to 270,000.

  In the expandable polystyrene resin particles of the present invention, the polystyrene resin preferably has a weight average molecular weight Mw in the range of 140,000 to 215,000.

  In the expandable polystyrene resin particles of the present invention, the polystyrene resin preferably has a weight average molecular weight Mw in the range of 140,000 to 185,000.

  The expandable polystyrene resin particles of the present invention are prepared by press-fitting and kneading a foaming agent into a polystyrene resin melted in an extruder and cooling the foaming agent-containing molten resin directly from a small hole in a die attached to the tip of the extruder. It was obtained by a melt extrusion method in which extrudates were extruded with a high-speed rotary blade at the same time as extrusion and the extrudates were cooled and solidified by contact with the liquid to obtain expandable polystyrene resin particles. It is preferable.

  The present invention also provides a foam molded product obtained by heating the expandable polystyrene resin particles to be pre-expanded particles and foam-molding the pre-expanded particles in a mold.

  In the foam molded article of the present invention, it is preferable that the average cell diameter of the foamed particles in the foam molded article is in the range of 50 μm to 300 μm.

  Further, the present invention is a method in which a foaming agent is press-fitted and kneaded into a polystyrene resin melted in an extruder, and the foaming agent-containing molten resin is extruded directly into a cooling liquid from a small hole of a die attached to the tip of the extruder, Simultaneously with extrusion, the extrudate is cut with a high-speed rotary blade, and the extrudate is cooled and solidified by contact with a liquid to obtain expandable polystyrene resin particles. In the production method of polystyrene resin, the weight average molecular weight Mw of the polystyrene resin is 120,000 to The foaming agent contains 2 to 8 parts by mass of butane as an essential component with respect to 100 parts by mass of polystyrene resin, and the composition of the butane is isobutane: normal butane by mass ratio. A method for producing expandable polystyrene resin particles in the range of 10:90 to 80:20 is provided.

  Further, the present invention is a method in which a foaming agent is press-fitted and kneaded into a polystyrene resin melted in an extruder, and the foaming agent-containing molten resin is extruded directly into a cooling liquid from a small hole of a die attached to the tip of the extruder, At the same time as extruding, the extrudate is cut with a high-speed rotary blade, and the extrudate is cooled and solidified by contact with a liquid to obtain expandable polystyrene resin particles. The expandable polystyrene resin particles are heated to form pre-expanded particles. In the method for producing a foamed molded product obtained by foam-molding the pre-expanded particles into a mold, the polystyrene-based resin has a weight average molecular weight Mw in the range of 120,000 to 320,000, and the foaming agent is an essential component. As a ratio of 2 to 8 parts by mass of butane with respect to 100 parts by mass of polystyrene resin, and the composition of the butane is isobutane: normal butane = 10: 90 to 8 in mass ratio. : Provides a method for producing a foamed molded in the range of 20.

  The present invention also relates to a foam molded product obtained by heating expandable polystyrene resin particles to pre-expanded particles and foam-molding the pre-expanded particles in a mold, and the polystyrene-based resin has a weight average molecular weight Mw of 120,000. The foaming agent contains isobutane and normal butane in the range of the total amount of 0.1 to 3.0 parts by mass with respect to 100 parts by mass of the polystyrene-based resin as essential components. A foamed molded product is provided.

  In the foamed molded product, the composition of isobutane and normal butane is preferably in the range of isobutane: normal butane = 30: 70 to 99: 1 in terms of mass ratio.

  In the foamed molded article, the expandable polystyrene resin particles are preferably the expandable polystyrene resin particles according to the present invention described above.

  The expandable polystyrene resin particles of the present invention use an appropriate ratio of isobutane and normal butane as a foaming agent, and by incorporating them in the expandable polystyrene resin particles, they have excellent foamability and a short molding cycle. A foam-molded article having sufficient mechanical strength can be produced. Further, if the weight average molecular weight Mw of the polystyrene resin is in the range of 120,000 to 320,000, it is possible to produce a foamed molded article having excellent foamability, a short molding cycle, and sufficient mechanical strength. As recycled material can be used.

  The foamed molded product of the present invention is obtained by heating the expandable polystyrene resin particles into pre-expanded particles, and the pre-expanded particles are obtained by in-mold foam molding. It is possible to provide a foamed molded article having excellent strength and good appearance.

The method for producing expandable polystyrene resin particles of the present invention is capable of producing a foamed molded product having a high expansion ratio, easily producing expandable polystyrene resin particles capable of producing a foamed molded product having excellent strength and good appearance. can do.
In addition, according to the method for producing expandable polystyrene resin particles of the present invention, a foamed molded article having a strength close to that of a virgin material and having a good appearance can be obtained by using a recycled material of polystyrene resin. -Based polystyrene resin particles can be produced.

It is a block diagram which shows an example of the manufacturing apparatus used for the manufacturing method of the expandable polystyrene-type resin particle of this invention.

  The expandable polystyrene resin particles of the present invention are expandable polystyrene resin particles in which a polystyrene resin containing a foaming agent is made into particles, and the weight average molecular weight Mw of the polystyrene resin is in the range of 120,000 to 320,000. The foaming agent contains 2 to 8 parts by mass of butane as an essential component with respect to 100 parts by mass of polystyrene resin, and the composition of butane is isobutane: normal butane = 10: 90 by mass ratio. It is characterized by being in the range of ˜80: 20.

  In the expandable polystyrene resin particles of the present invention, the polystyrene resin is not particularly limited. For example, styrene, α-methylstyrene, vinyltoluene, chlorostyrene, ethylstyrene, i-propylstyrene, dimethylstyrene, bromostyrene. Homopolymers of styrene monomers such as these or copolymers thereof, and the like, polystyrene resins containing 50% by mass or more of styrene are preferable, and polystyrene is more preferable.

Further, the polystyrene resin may be a copolymer of the styrene monomer and a vinyl monomer copolymerizable with the styrene monomer, the main component of which is the styrene monomer. As, for example, alkyl (meth) acrylate such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, cetyl (meth) acrylate, (meth) acrylonitrile, dimethyl maleate, dimethyl fumarate, diethyl In addition to fumarate and ethyl fumarate, bifunctional monomers such as divinylbenzene and alkylene glycol dimethacrylate are exemplified.
If a polystyrene resin is the main component, other resins may be added. Examples of the resin to be added include polybutadiene, styrene-butadiene copolymer to improve the impact resistance of the foam molded article. Examples thereof include rubber-modified polystyrene resins to which a diene rubbery polymer such as a polymer, ethylene-propylene-nonconjugated diene three-dimensional copolymer is added, so-called high impact polystyrene. Alternatively, a polyethylene resin, a polypropylene resin, an acrylic resin, an acrylonitrile-styrene copolymer, an acrylonitrile-butadiene-styrene copolymer, and the like can be given.

  In the expandable polystyrene resin particles of the present invention, the polystyrene resin used as a raw material is a recycled raw material such as a commercially available ordinary polystyrene resin or a polystyrene resin newly produced by a method such as suspension polymerization. Non-polystyrene resin (hereinafter referred to as virgin polystyrene) can be used, and recycled material obtained by reprocessing used polystyrene resin foam moldings or non-foamed polystyrene resin moldings is used. be able to. As this recycled material, used polystyrene-based resin foam moldings such as fish boxes, household appliance cushioning materials, food packaging trays, etc. are collected and recycled using the limonene dissolution method or heating volume reduction method, or household appliances. Non-foamed polystyrene resin moldings separated and collected from products (eg, televisions, refrigerators, washing machines, air conditioners, etc.) and office equipment (eg, copiers, facsimiles, printers, etc.) are crushed and melt-kneaded. From the re-pelleted recycled materials, materials having a weight average molecular weight Mw in the range of 120,000 to 320,000 can be selected as appropriate, or a plurality of recycled materials having different weight average molecular weights Mw can be used in appropriate combination.

  In the expandable polystyrene resin particles of the present invention, the weight average molecular weight Mw of the polystyrene resin constituting the expandable polystyrene resin particles is in the range of 120,000 to 320,000, preferably in the range of 140,000 to 270,000. The range of 140,000 to 215,000 is more preferable. When the weight average molecular weight Mw of the polystyrene resin is less than the above range, the high-pressure moldability of the expandable polystyrene resin particles may be deteriorated, and the mechanical strength of the obtained foamed molded product may be decreased. When the weight average molecular weight Mw of the polystyrene resin exceeds the above range, the low-pressure moldability is deteriorated, and it is difficult to shorten the heating time of the foam molding.

  In the expandable polystyrene resin particles of the present invention, the foaming agent contained in the polystyrene resin contains 2 to 8 parts by mass of butane as an essential component with respect to 100 parts by mass of the expandable styrene resin particles. However, it is the range of isobutane: normal butane = 10: 90-80: 20 by mass ratio. The butane (butane composition) may be contained alone in the polystyrene resin, or other volatile foaming agents, solvents, and plasticizers may be added as auxiliary components. Examples of the volatile blowing agent as an auxiliary component that can be added to the butane include aliphatic hydrocarbons such as propane, normal pentane, and isopentane, and halogenated hydrocarbons. Solvents and plasticizers that can be added to the butane include terpene hydrocarbons such as limonene and pinene, aromatic hydrocarbons such as styrene, toluene, ethylbenzene and xylene, and alicyclic carbons such as cyclopentane and cyclohexane. Examples thereof include ester compounds such as hydrogen, adipic acid esters such as diisobutyl adipate and diisononyl adipate, and sebacic acid esters such as dibutyl sebacate and dioctyl sebacate.

  The ratio of isobutane and normal butane in this blowing agent is in the range of isobutane: normal butane = 10: 90 to 80:20, and preferably in the range of isobutane: normal butane = 20: 80 to 70:30, The range of isobutane: normal butane = 30: 70 to 50:50 is more preferable. When the ratio of isobutane and normal butane in this foaming agent is larger than the range of the mass ratio, or when only isobutane is used, when producing a foam molded article from expandable polystyrene resin particles, After heating and heating steam into the mold cavity filled with pre-expanded particles inside, the cooling time for cooling the foamed molded product to a temperature at which the foamed molded product can be taken out becomes extremely long, resulting in poor productivity. End up. On the other hand, when there is more normal butane than the range of the said mass ratio, or when only normal butane is used, the mechanical strength of the foaming molding obtained will fall.

  In the expandable polystyrene resin particles of the present invention, the amount of the foaming agent contained in the polystyrene resin is 2 to 8 parts by mass of the butane (butane composition) with respect to 100 parts by mass of the polystyrene resin. Yes, preferably in the range of 3-7 parts by mass, more preferably in the range of 4-6 parts by mass. When the amount of butane is less than the above range, a sufficient expansion ratio may not be reached when the expandable polystyrene resin particles are foam-molded. On the other hand, if the amount of butane exceeds the above range, the improvement of foaming performance will reach its peak, and the time required for the cooling process in the production process of styrene resin foam moldings using expandable styrene resin particles will be increased. May be reduced).

  In addition to the foaming agent, the expandable polystyrene resin particles of the present invention may have other additives commonly used in the production of expandable polystyrene resin particles, such as talc, calcium silicate, Foaming nucleating agents such as silicon dioxide, ethylenebisstearic acid amide, methacrylic acid ester-based copolymer, hexabromocyclododecane, tetrabromobisphenol A-bis (2,3-dibromo-2-methyl) produced synthetically or naturally Additives such as flame retardants such as propyl ether) and triallyl isocyanurate hexabromide, and colorants such as carbon black, iron oxide, and graphite can be added to the polystyrene resin.

  The surface of the expandable polystyrene resin particles of the present invention is coated with a surface treatment agent such as a fatty acid metal salt, a fatty acid ester, or an antistatic agent, as is usually done for conventional expanded styrene resin particles. It is also possible to improve the fluidity and pre-foaming characteristics of the resin particles (beads) by coating the surface treatment agent. The total amount of the surface treatment agent is preferably about 0.01 to 2.0 parts by mass with respect to 100 parts by mass of the expandable polystyrene resin particles.

The particle size of the expandable polystyrene resin particles of the present invention is not particularly limited, but usually the average particle size is preferably in the range of 0.3 to 2.0 mm, and in the range of 0.5 to 1.4 mm. More preferably.
Moreover, the shape of the expandable polystyrene resin particles of the present invention is not particularly limited, but it is preferably spherical or close to a sphere.

The expandable polystyrene resin particles of the present invention are excellent in foaming performance, can be pre-foamed by heating to a high foaming factor, and a low-density foamed molded product can be produced.
In order to produce a foam molded article from the expandable polystyrene resin particles of the present invention, it can be carried out by a normal in-mold foam molding method using expandable polystyrene resin particles. That is, expandable polystyrene resin particles are heated to form pre-expanded particles, and the pre-expanded particles are filled into a cavity of a mold having a shape to mold the pre-expanded particles, and steam is blown into the mold for heating to perform in-mold foam molding. However, it can be produced by taking out the foamed molded product after cooling the mold.

  In the foamed molded product of the present invention, the average cell diameter of the foamed particles is preferably in the range of 50 μm to 300 μm, and more preferably in the range of 80 μm to 250 μm. When the average cell diameter is less than the above range, there is a risk that the foamed molded product obtained has a larger particle gap during foam molding and the appearance may be impaired.) When the average cell diameter exceeds the above range, foaming is obtained. There exists a possibility that the intensity | strength of a molded object may fall.

Moreover, this foaming molding normally has a density of 0.015-0.2 g / cm < ³ >. Preferably, the density is in the range of 0.0166~0.05g / cm ^3, more preferably, the density is in the range of 0.02~0.033g / cm ^3. If the density of the foamed molded product is less than 0.015 g / cm ³ , the strength of the foamed molded product obtained by foaming the pre-expanded particles is unfavorable. On the other hand, if the density of the foamed molded product is larger than 0.2 g / cm ³ , the mass of the foamed molded product obtained by foaming the pre-expanded particles is not preferable. In addition, when this density is expressed in terms of expansion ratio, since expansion ratio (times) = 1 / density (g / cm ³ ), this foamed molded article has a expansion ratio of 5 to 67 (times), which is preferable. The expansion ratio is 20 to 60 (times), and a more preferable expansion ratio is 30 to 50 (times).
The foamed molded product of the present invention is a foamed molded product obtained by heating foamable polystyrene resin particles into pre-expanded particles, and foam-molding the pre-expanded particles in a mold. Is in the range of 120,000 to 320,000, and the foaming agent contains isobutane and normal butane as essential components in an amount of 0.1 to 3.0 parts by mass with respect to 100 parts by mass of the polystyrene resin. It is characterized by being.
In the foamed molded product of the present invention, the weight-average molecular weight Mw of the polystyrene resin constituting the foamed molded product is in the range of 120,000 to 320,000, preferably in the range of 140,000 to 270,000, and 140,000 to 21.5. A range of 10,000 is more preferred. If the weight-average molecular weight Mw of the polystyrene-based resin is less than the above range, the high-pressure moldability may be deteriorated, and the mechanical strength of the foamed molded product may be reduced. When the weight average molecular weight Mw of the polystyrene resin exceeds the above range, the low-pressure moldability is deteriorated, and it is difficult to shorten the heating time of the foam molding.
In the foam molded article of the present invention, as a foaming agent to be contained in the polystyrene resin constituting the foam molded article, the total amount of isobutane and normal butane is 0.1 to 100 parts by mass of polystyrene resin particles as essential components. It is the range of 3.0 mass parts, Preferably it is the range of 0.1-2.0 mass parts, More preferably, it is the range of 0.3-1.0 mass part. When the total amount of isobutane and normal butane is less than the above range, it may not be possible to reach a sufficient expansion ratio when producing a foam molded article by in-mold foam molding. On the other hand, if the total amount of isobutane and normal butane exceeds the above range, the time required for the cooling step in the production process may be increased when producing a foamed molded article by in-mold foam molding, which may reduce productivity.
In the foamed molded article of the present invention, the composition of the blowing agent isobutane and normal butane is preferably in the range of isobutane: normal butane = 30: 70 to 99: 1 by mass ratio, The range is more preferable, and the range of 90:10 to 99: 1 is most preferable. When the ratio of isobutane and normal butane in this foaming agent is larger than the range of the mass ratio, or when only isobutane is used, it is possible to produce a foamed molded product in a short time by in-mold foam molding. May be difficult to manufacture. On the other hand, when there is more normal butane than the range of the said mass ratio, or when only normal butane is used, there exists a possibility that the mechanical strength of a foaming molding may fall.

  The expandable polystyrene resin particles of the present invention can be manufactured by conventionally known methods for producing expandable polystyrene resin particles, for example, suspension polymerization, melt extrusion, etc. It is preferable to manufacture by a melt extrusion method because the conductive polystyrene resin particles can be manufactured. In the melt extrusion method, a foaming agent is press-fitted and kneaded into a polystyrene-based resin melted in an extruder, and the foaming agent-containing molten resin is extruded directly into a cooling liquid from a small hole in a die attached to the tip of the extruder. Simultaneously with extrusion, the extrudate is cut with a high-speed rotary blade, and the extrudate is cooled and solidified by contact with a liquid to obtain expandable polystyrene resin particles.

FIG. 1 is a block diagram showing an example of a production apparatus used in the method for producing expandable polystyrene resin particles of the present invention. The manufacturing apparatus of this example includes an extruder 1, a die 2 having a large number of small holes attached to the tip of the extruder 1, a raw material supply hopper 3 for introducing a resin raw material into the extruder 1, an extruder 1 is provided so that cooling water is brought into contact with the high-pressure pump 4 for press-fitting the foaming agent into the molten resin 1 through the foaming agent supply port 5 and the resin discharge surface in which the small holes of the die 2 are formed. Is circulated and supplied, a cutter 6 rotatably provided in the cutting chamber 7 so as to cut the resin extruded from the small hole of the die 2, and a cooling water flow accompanying the cutting chamber 7. The foamable particles carried in this manner are separated from the cooling water and dehydrated and dried to obtain foamable particles. The dehydrating dryer 10 with a solid-liquid separation function, and the cooling water separated by the dehydrating dryer 10 with a solid-liquid separation function Water tank 8 for storing water, and in this water tank 8 A high pressure pump 9 that sends the cooling water in the cutting chamber 7, is configured by a storage container 11 for storing the dewatered dried effervescent grains at the solid-liquid separation function dehydrating dryer 10.
As the extruder, either an extruder using a screw or an extruder not using a screw can be used. Examples of the extruder using a screw include a single-screw extruder, a multi-screw extruder, a vent-type extruder, and a tandem extruder. Examples of the extruder that does not use a screw include a plunger type extruder and a gear pump type extruder. Moreover, any extruder can use a static mixer. Among these extruders, an extruder using a screw is preferable from the viewpoint of productivity.

  In order to produce the expandable polystyrene resin particles of the present invention using this production apparatus, first, a raw material polystyrene resin and desired additives such as a foam nucleating agent are weighed and the raw material supply hopper 3 is used as an extruder. 1 in. The raw polystyrene resin may be pelletized or granulated and mixed well in advance and then fed from one raw material supply hopper. For example, when multiple lots are used, the supply amount for each lot may be reduced. A plurality of adjusted raw material supply hoppers may be charged and mixed in an extruder. Also, when using a combination of recycled materials from multiple lots, mix the raw materials from multiple lots in advance and remove foreign matter using appropriate sorting methods such as magnetic sorting, sieving, specific gravity sorting, and air blowing sorting. It is preferable to keep it.

  After supplying polystyrene resin into the extruder 1, this resin is heated and melted, and the foaming agent is press-fitted by the high-pressure pump 4 from the foaming agent supply port 5, and the foaming agent is mixed into the melt. The melt is moved to the tip side while further kneading through a foreign matter removing screen provided according to the above, and the melt added with the foaming agent is pushed out from the small hole of the die 2 attached to the tip of the extruder 1.

  The resin discharge surface in which the small holes of the die 2 are drilled is disposed in the cutting chamber 7 in which cooling water is circulated and supplied into the chamber, and the resin extruded from the small holes of the die 2 is placed in the cutting chamber 7. A cutter 6 is provided so as to be rotatable. Extruding the melt with the blowing agent added through a small hole in the die 2 attached to the tip of the extruder 1 causes the melt to be cut into granules, and at the same time, brought into contact with cooling water and rapidly cooled to solidify while suppressing foaming. Thus, expandable polystyrene resin particles are obtained.

  The formed expandable polystyrene resin particles are transferred from the cutting chamber 7 to the dewatering dryer 10 with a solid-liquid separation function along with the flow of the cooling water, where the expandable polystyrene resin particles are separated from the cooling water. And dehydrated and dried. The dried expandable polystyrene resin particles are stored in the storage container 11.

  The expandable polystyrene resin particles of the present invention use an appropriate ratio of isobutane and normal butane as a foaming agent, and by incorporating them in the expandable polystyrene resin particles, they have excellent foamability and a short molding cycle. A foam-molded article having sufficient mechanical strength can be produced. Further, if the weight average molecular weight Mw of the polystyrene resin is in the range of 120,000 to 320,000, it is possible to produce a foamed molded article having excellent foamability, a short molding cycle, and sufficient mechanical strength. As recycled material can be used.

[Example 1]
(Manufacture of expandable polystyrene resin particles)
0.3 parts by mass of fine powder talc was added to 100 parts by mass of recycled raw material having a weight average molecular weight of 18,000, and these were continuously supplied to a single screw extruder having a diameter of 90 mm at 130 kg per hour. As the temperature inside the extruder, the maximum temperature was set to 210 ° C., and after melting the resin, 6 parts by weight of butane (isobutane: normal butane = 30: 70 (mass ratio)) with respect to 100 parts by weight of the resin as a foaming agent. Was press-fitted from the middle of the extruder. The resin and foaming agent are kneaded and cooled in the extruder, the resin temperature at the tip of the extruder is maintained at 170 ° C., the pressure at the resin introduction part of the die is maintained at 15 MPa, the diameter is 0.6 mm, and the land length is 3 From the die having 200 small holes of 0.0 mm, the foaming agent-containing molten resin is extruded into the cutting chamber connected to the discharge side of this die and circulating water at 30 ° C. The extrudate was cut with a high-speed rotary cutter having a blade. While the cut particles were cooled with circulating water, they were conveyed to a particle separator, and the particles were separated from the circulating water. Further, the collected particles were dehydrated and dried to obtain expandable polystyrene resin particles. The obtained expandable polystyrene resin particles were almost perfect spheres without the occurrence of deformation or beard, and the average particle size was about 1.1 mm.
Polyethylene glycol 0.03 parts by mass, zinc stearate 0.15 parts by mass, stearic acid monoglyceride 0.05 parts by mass, hydroxystearic acid triglyceride 0.05 parts by mass with respect to 100 parts by mass of the obtained expandable polystyrene resin particles. The part was uniformly coated on the entire surface of the expandable polystyrene resin particles.

(Manufacture of foam moldings)
The expandable polystyrene resin particles produced as described above are placed in a 15 ° C. cool box and allowed to stand for 72 hours, and then supplied to a cylindrical batch type pre-foaming machine to generate steam with a blowing pressure of 0.05 MPa. To obtain pre-expanded particles. The obtained pre-expanded particles had a bulk density of 0.02 g / cm ³ (bulk expansion ratio: 50 times).
Subsequently, the pre-expanded particles obtained were allowed to stand at room temperature for 24 hours, and then the pre-expanded particles were filled into a mold having a rectangular cavity of length 400 mm × width 300 mm × height 50 mm. Thereafter, the inside of the cavity of the mold is heated with water vapor at a gauge pressure of 0.08 MPa for 20 seconds, and then cooled until the pressure in the cavity of the mold reaches 0.01 MPa. Opened, a rectangular foam molded body having a length of 400 mm, a width of 300 mm, and a height of 50 mm was taken out. The obtained foamed molded article had a density of 0.02 g / cm ³ (foaming factor: 50 times).

  The following evaluation tests were performed on the polystyrene resin, the expandable polystyrene resin particles, the pre-expanded particles, and the foamed molded product of Example 1 manufactured by the method as described above.

<Measurement of weight average molecular weight>
About polystyrene resin used as a raw material to be fed into an extruder and polystyrene resin constituting expandable polystyrene resin particles produced by a melt extrusion method, about 4 mg of each resin is dissolved in 4 mL of THF (tetrahydrofuran), and non-aqueous After filtration with a 0.45 μm chromatodisc, the polystyrene equivalent molecular weight was measured using HLC-8320GPC (built-in RI detector) manufactured by Tosoh Corporation. The measurement conditions were TOSOH TSKgel SuperMultiporeHZ-H (φ4.6 × 150mm) made by Tosoh Corp., and TOSOH TSKguardSuperMP (HZ) -H (φ4.6 × 20mm) made by Tosoh Corp. Temperature (40 ° C), mobile phase (THF), mobile phase flow rate (0.2ml / min), pump temperature / detector (40 ° C), detection (RI), injection volume (20μL), standard curve calibration standard PS (Showa) (Shodex) molecular weight Mw was 5,620,000, 3,120,000, 1,250,000, 442,000, 131,000, 54,000, 20,000, 7,590, 3,450 and 1,320). )

<Measurement of foaming agent content and foaming agent composition>
After the expandable polystyrene resin particles obtained in the examples (and comparative examples) were allowed to stand for 72 hours in a 15 ° C. cool box, the amount of foaming agent in the expandable polystyrene resin particles (of isobutane and normal butane) The total content, unit: mass%) and the blowing agent composition (mass ratio of isobutane and normal butane) were measured using gas chromatography under the following conditions.
Gas chromatography (GC): GC-14B manufactured by Shimadzu Corporation
-Detector: FID-Heating furnace: Shimadzu PYR-1A
Column: Shinwa Kako Co., Ltd. (diameter 3 mm × length 3 m) liquid phase 1 squalane 25%, carrier lShimalite 60-80 NAW
-Heating furnace temperature: 180 ° C
-Column temperature: 70 ° C

<Bulk expansion ratio of pre-expanded particles>
The mass (a) of about 5 g of pre-expanded particles was weighed in the second decimal place. Next, weighed pre-expanded particles in a 500 cm ³ graduated cylinder with a minimum scale unit of 5 cm ³ , and a round resin plate slightly smaller than the caliber of the graduated cylinder. Apply a pressing tool in which a rod-shaped resin plate of about 30 cm is fixed upright, read the volume (b) of the pre-expanded particles, and calculate the bulk expansion ratio of the pre-expanded particles by the formula (b) / (a) It was.

<Evaluation of molding cycle>
Pre-expanded particles are filled into a mold having a rectangular cavity of length 400 mm × width 300 mm × height 50 mm, and then the inside of the mold cavity is steamed with water at a gauge pressure of 0.08 MPa for 20 seconds. Then, the cooling time until the pressure in the mold cavity reaches 0.01 MPa is measured, and the following evaluation criteria:
Particularly good (◎): less than 210 seconds. Good (○): 210 seconds or more and less than 300 seconds. Bad (x): molding cycles were evaluated based on 300 seconds or more.

<Measurement of average bubble diameter>
The foamed molded body obtained in the examples (and comparative examples) is cut with a razor blade, and the cut surface is photographed with a scanning electron microscope (S-3000N manufactured by Hitachi, Ltd.) at a magnification of 30 times. The photographed image was printed on A4 paper, and the average chord length (t) of the bubbles was calculated from the number of bubbles on an arbitrary straight line (length: 60 mm) by the following formula. However, the arbitrary straight lines were made so that the bubbles did not contact only at the contact points as much as possible (included in the number of bubbles if contacted). The measurement was performed at 10 locations, and after obtaining the average chord length, the bubble diameter was calculated to obtain the average bubble diameter D (μm).
Average string length t = 60 / (number of bubbles × photo magnification)
Bubble diameter D = t / 0.616 × 1000

<Strength evaluation>
About the foaming molding obtained in the Example (and comparative example), bending strength was measured according to the method of JISA9511: 2006 "foaming plastic heat insulating material". That is, using a Tensilon universal testing machine UCT-10T (manufactured by Orientec Co., Ltd.), the specimen size is 75 mm × 300 mm × 50 mm, the compression speed is 10 mm / min, the tip jig is a pressure wedge 10R, and a support base 10R. Measurement was performed under the condition of a distance between fulcrums of 200 mm, and the bending strength was calculated by the following formula. The number of test pieces was three, and the average value was obtained.
Bending strength (MPa) = 3FL / 2bh ²
(Here, F represents the maximum bending load (N), L represents the distance between supporting points (mm), b represents the width (mm) of the test piece, and h represents the thickness (mm) of the test piece. )
In this way, the average value of the bending strength is obtained, and the following evaluation criteria:
Particularly good (◎): bending strength is 0.28 MPa or more Good (◯): bending strength is 0.25 MPa or more and less than 0.28 MPa Bad (x): strength was evaluated based on bending strength less than 0.25 MPa.

<Comprehensive evaluation>
Regarding the evaluation results of the <evaluation of molding cycle> and <evaluation of strength>, the following evaluation criteria:
Especially good (◎): Both evaluations are ◎
Good (○): One evaluation is ◎, the other evaluation is ○
Defect (x): Either or both of the evaluations are x
Based on this, a comprehensive evaluation was made.

  About Example 1, the measurement of the weight average molecular weight mentioned above, the measurement of foaming agent content, the evaluation of a shaping | molding cycle, the measurement of an average bubble diameter, evaluation of intensity | strength, and comprehensive evaluation are performed, and the result is described in Table 1.

[Example 2]
In place of the recycled material having a weight average molecular weight of 1870,000 used in Example 1, a recycled material having a weight average molecular weight of 208,000 was used in the same manner as in Example 1 except that An evaluation test was conducted. The results are shown in Table 1.

[Example 3]
In place of the recycled raw material having a weight average molecular weight of 1870,000 used in Example 1, a recycled raw material having a weight average molecular weight of 250,000 was used in the same manner as in Example 1, and each of the items described above was used. An evaluation test was conducted. The results are shown in Table 1.

[Example 4]
In place of the recycled material having a weight average molecular weight of 1870,000 used in Example 1, a recycled material having a weight average molecular weight of 283,000 was used in the same manner as in Example 1 except that An evaluation test was conducted. The results are shown in Table 1.

[Example 5]
The evaluation test of each item mentioned above was done like Example 1 except having set it as the composition of isobutane: normal butane = 50: 50 (mass ratio) as a foaming agent. The results are shown in Table 1.

[Example 6]
The evaluation test of each item mentioned above was done like Example 1 except having set it as the composition of isobutane: normal butane = 70: 30 (mass ratio) as a foaming agent. The results are shown in Table 1.

[Example 7]
Except that the composition was 4 parts by weight of butane (isobutane: normal butane = 30: 70 (mass ratio)) and 2 parts by weight of pentane (isopentane: normal pentane = 30: 70 (mass ratio)) as the blowing agent. In the same manner as in Example 1, the above-described evaluation tests for each item were performed. The results are shown in Table 1.

[Example 8]
Example 1 except that the composition was 6 parts by weight of butane (isobutane: normal butane = 30: 70 (mass ratio)) as a blowing agent and 1 part by weight of diisobutyl adipate (DIBA) as a solvent / plasticizer. Then, an evaluation test of each item described above was performed. The results are shown in Table 1.

[Comparative Example 1]
Example 1 was used except that virgin polystyrene having a weight average molecular weight of 340,000 (brand name: G9305) was used instead of the recycled material having a weight average molecular weight of 1870,000 used in Example 1. Similarly, the evaluation test of each item mentioned above was conducted. The results are shown in Table 1.

[Comparative Example 2]
In place of the recycled material having a weight average molecular weight of 1870,000 used in Example 1, a recycled material having a weight average molecular weight of 106,000 was used in the same manner as in Example 1 except that An evaluation test was conducted. The results are shown in Table 1.

[Comparative Example 3]
The evaluation test of each item mentioned above was done like Example 1 except having used only isobutane (isobutane: normal butane = 100: 0) as a foaming agent. The results are shown in Table 1.

[Comparative Example 4]
The evaluation test of each item mentioned above was done like Example 1 except having used only normal butane (isobutane: normal butane = 0: 100) as a foaming agent. The results are shown in Table 1.

From the results of Table 1, a polystyrene resin having a weight average molecular weight Mw in the range of 120,000 to 320,000 is used, and as a foaming agent, butane in the range of isobutane: normal butane = 10: 90 to 80:20 is a main component. The expandable polystyrene resin particles obtained in Examples 1 to 7 used as the above have excellent foaming performance, and can be produced in a short time when producing a foamed molded article by in-mold foam molding. The evaluation of the cycle was particularly good or good.
Moreover, the foaming moldings obtained in Examples 1 to 7 were particularly good with a bending strength of 0.28 MPa or more.
Moreover, the foaming molding obtained in Examples 1-8 had few particle | grain gap | intervals, and the external appearance was beautiful and favorable.
On the other hand, Comparative Example 1 using a polystyrene-based resin having a weight average molecular weight Mw exceeding the range of the present invention is difficult to produce in a short time when producing a foamed molded article by in-mold foam molding, and evaluation of the molding cycle. Became defective.
Moreover, the comparative example 2 using the polystyrene-type resin whose weight average molecular weight Mw is less than the range of this invention became weak in the intensity | strength of the obtained foaming molding, and became poor in bending strength. Further, in Comparative Example 3 using only isobutane as a foaming agent, it was difficult to produce in a short time when producing a foamed molded article by in-mold foam molding, and the evaluation of the molding cycle was poor.
Further, in Comparative Example 4 in which only normal butane was used as the foaming agent, the strength of the obtained foamed molded article was weak and the bending strength was poor.

[Example 9]
After the foamed molded product obtained in Example 1 was left in a room at 23 ° C. ± 5 ° C. for 30 days and 90 days, the following <measurement of foaming agent content and foaming agent composition in the foamed molded product > And the foaming agent content and composition were analyzed, and the strength of the foamed molded product was measured and evaluated according to the above <Evaluation of Strength>.

<Measurement of foaming agent content and foaming agent composition in foamed molded article>
A rectangular parallelepiped having a size of 35 mm in the length direction, 5 mm in the width direction, and 5 mm in the thickness direction is cut out from the substantially center part of the foamed molding obtained in the examples, and the weight of the test piece is measured. And the said test piece is supplied to a 180 degreeC heating furnace, foaming agent content (total content of isobutane and normal butane, unit: mass%) in a foaming molding, and a foaming agent composition (isobutane and normal butane). (Mass ratio) was measured using gas chromatography under the following conditions.
Gas chromatography (GC): GC-14B manufactured by Shimadzu Corporation
-Detector: FID-Heating furnace: Shimadzu PYR-1A
Column: Shinwa Kako Co., Ltd. (diameter 3 mm × length 3 m) liquid phase 1 squalane 25%, carrier lShimalite 60-80 NAW
-Column temperature: 70 ° C
-Heating furnace temperature: 180 ° C

The amount of foaming agent after 30 days (total content of isobutane and normal butane) was 0.4% by mass, the ratio of isobutane and normal butane was isobutane: normal butane = 98: 2, and the strength evaluation was particularly good (◎) there were.
The foaming agent amount after 90 days (total content of isobutane and normal butane) was 0.4% by mass, the ratio of isobutane and normal butane was isobutane: normal butane = 98: 2, and the strength evaluation was particularly good (◎). there were.

[Example 10]
The foaming agent content was measured and the strength was evaluated in the same manner as in Example 9 except that the foamed molded product obtained in Example 6 was used as the foamed molded product.
The amount of blowing agent after 30 days (total content of isobutane and normal butane) was 0.6% by mass, the ratio of isobutane and normal butane was isobutane: normal butane = 98: 2, and the strength evaluation was particularly good (◎). there were.
The amount of foaming agent after 90 days (total content of isobutane and normal butane) was 0.6% by mass, the ratio of isobutane and normal butane was isobutane: normal butane = 98: 2, and the strength evaluation was particularly good (◎). there were.

  From the results of Examples 9 and 10, in the foamed molded product produced using the expandable polystyrene resin particles according to the present invention, the composition of butane (isobutane + normal butane) added as a foaming agent was a foamed molded product. In the case where 30 days or more have passed after the production, isobutane accounted for the majority.

  TECHNICAL FIELD The present invention relates to expandable polystyrene resin particles, a method for producing the same, and a foamed molded product. In particular, when producing expandable polystyrene resin particles by a melt extrusion method, recycled raw materials can be used, and foamability is excellent. The present invention relates to an expandable polystyrene resin particle capable of producing a well-balanced foamed molded article having a short cycle, good appearance, and sufficient mechanical strength, and a method for producing the same. The foam molded product obtained using the expandable polystyrene resin particles is used for applications such as a buffer material, a container, and a heat insulating material.

  DESCRIPTION OF SYMBOLS 1 ... Extruder (resin supply apparatus), 2 ... Die, 3 ... Raw material supply hopper, 4 ... High pressure pump, 5 ... Foam supply port, 6 ... Cutter, 7 ... Cutting chamber, 8 ... Water tank, 9 ... High pressure pump, 10: Dehydration dryer with solid-liquid separation function, 11: Storage container.

Claims (4)

Expandable polystyrene resin particles having a polystyrene resin containing a foaming agent in the form of particles,
A foaming agent is press-fitted and kneaded into the polystyrene resin melted in the extruder, and the foaming agent-containing molten resin is extruded directly into the cooling liquid through a small hole in the die attached to the tip of the extruder. Is obtained by a melt extrusion method in which an extrudate is cooled and solidified by contact with a liquid to obtain expandable polystyrene resin particles.
The polystyrene-based resin has a weight average molecular weight Mw in the range of 120,000 to 320,000, and the foaming agent contains 2 to 8 parts by mass of butane as an essential component with respect to 100 parts by mass of the polystyrene-based resin. Expandable polystyrene resin particles in which the composition of butane is in the range of isobutane: normal butane = 10: 90 to 80:20 by mass ratio. A foam-molded product obtained by heating the expandable polystyrene resin particles according to claim 1 into pre-expanded particles and foam-molding the pre-expanded particles in a mold. The foamed molded product according to claim 2 , wherein an average cell diameter of the foamed particles in the foamed molded product is in the range of 50 µm to 300 µm.   A foaming agent is press-fitted and kneaded into the polystyrene resin melted in the extruder, and the foaming agent-containing molten resin is extruded directly into the cooling liquid through a small hole in the die attached to the tip of the extruder. In the production method in which the extrudate is cooled and solidified by contact with a liquid to obtain expandable polystyrene resin particles, the weight average molecular weight Mw of the polystyrene resin is in the range of 120,000 to 320,000. Yes, the foaming agent contains 2 to 8 parts by mass of butane as an essential component with respect to 100 parts by mass of polystyrene resin, and the composition of the butane is isobutane: normal butane = 10: 90 to mass ratio. A process for producing expandable polystyrene resin particles in the range of 80:20.

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