JP2023100351A - Composite resin particle, and foamed molded product - Google Patents

Abstract

To provide a foamed molded product produced from composite resin particles capable of reducing environmental load, and foam-molding with a comparatively low vapor pressure by using a recycled product of a polyolefin resin (a recycled polyolefin resin), and containing a polyolefin resin and a polystyrene resin.SOLUTION: A composite resin particle for producing a foamed particle contains a polyolefin resin and a polystyrene resin, where the total content of the polyolefin resin and the polystyrene resin is 90 mass% or more with respect to a mass of the composite resin particle, the content of the polystyrene resin in the composite resin particle is 50-800 pts. mass with respect to 100 pts. mass of a content of the polyolefin resin, and the content of a recycled polyolefin resin is 20-100 mass% in the polyolefin resin.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to composite resin particles, foamed moldings, and the like.

Foam molded products made of polystyrene resins are often used as packaging materials and heat insulating materials because they are excellent in rigidity, heat insulation, light weight, water resistance and foam moldability, but have low chemical resistance and impact resistance. On the other hand, a foamed molded article made of a polyolefin resin is excellent in chemical resistance and impact resistance, but is inferior in retention of a foaming agent. Therefore, it is difficult to transport expandable particles containing a blowing agent from raw material manufacturers to molding manufacturers. Expanded particles obtained by preexpanding expandable particles (also called preexpanded particles). ), but the bulk of the foamed particles increases the manufacturing cost. Further, it is known that a foam molded article made of polyolefin resin is inferior in rigidity to a foam molded article made of polystyrene resin. Therefore, in order to utilize the excellent properties of both resins, a foamed molded article obtained from composite resin particles of a polystyrene resin and a polyolefin resin has been devised (Patent Document 1).

Also, the amount of plastic waste is increasing year by year. Most of the plastic waste is disposed of by incineration or landfill, but it is becoming a big social problem such as environmental pollution, global warming, and lack of landfill sites. Therefore, there is a strong social demand to recycle plastic waste. While various recycling methods have been proposed, material recycling, which reuses plastic waste as plastic components for products, is attracting attention from the viewpoint of resource circulation and environmental load reduction. , such material recycling is being studied (Patent Documents 2 and 3).

WO2007/138916 JP-A-06-087973 Japanese Patent Application Laid-Open No. 2000-219765

Composite resin particles containing polyolefin-based resin and polystyrene-based resin that reduce environmental load by using recycled polyolefin-based resin (recycled polyolefin-based resin) and can be foam-molded at relatively low steam pressure There has been a demand for the provision of manufactured foamed moldings.

The present invention typically includes the following aspects.
Item 1.
Composite resin particles for producing expanded beads containing a polyolefin resin and a polystyrene resin,
The total content of the polyolefin-based resin and the polystyrene-based resin is 90% by mass or more of the mass of the composite resin particles,
The polystyrene resin content in the composite resin particles is 50 to 800 parts by mass with respect to 100 parts by mass of the polyolefin resin content,
The content of the recycled polyolefin resin in the polyolefin resin is 20 to 100% by mass,
Composite resin particles.
Item 2.
Item 2. The composite resin particles according to Item 1, wherein the polyolefin-based resin is a polyethylene-based resin.
Item 3.
Item 3. The composite resin particle according to item 2, wherein the polyethylene-based resin is (1) polyethylene or (2) polyethylene and ethylene-vinyl acetate copolymer.
Item 4.
Item 4. Expandable particles containing the composite resin particles according to any one of Items 1 to 3 and a blowing agent.
Item 5.
Item 5. Expanded beads which are pre-expanded products of the expandable beads according to item 4.
Item 6.
Item 6. A foam-molded product which is an in-mold foam-molded product of the foamed particles according to item 5.

According to the present invention, the use of recycled polyolefin-based resin makes it possible to manufacture a foamed molded article with steam having a relatively low steam pressure while contributing to the reduction of environmental load.

As used herein, the phrase "comprising" is intended to encompass the phrase "consisting essentially of" and the phrase "consisting of".

A composite resin particle is typically obtained by impregnating a base resin particle (seed particle) with a styrene-based monomer and polymerizing the styrene-based monomer. The base resin is typically a polyolefin resin.

(polyolefin resin)
The polyolefin-based resin is not particularly limited, and known resins such as polyethylene-based resins and polypropylene-based resins can be used. Moreover, the polyolefin resin may be crosslinked.

Examples of polyolefin resins include linear or branched low density polyethylene, linear or branched medium density polyethylene, linear or branched high density polyethylene, ethylene copolymer (ethylene-vinyl acetate copolymer , ethylene-methyl methacrylate copolymer, etc.), polyethylene resins such as crosslinked polymers of these polymers; propylene homopolymer, ethylene-propylene random copolymer, propylene-1-butene copolymer, ethylene-propylene-butene Examples include polypropylene resins such as random copolymers. Among these examples, low density may be 0.91-0.94 g/cm ³ , 0.91-0.93 g/cm ³ , and the like. The high density may be 0.95-0.97 g/cm ³ , 0.95-0.96 g/cm ³ . Medium density is a density intermediate between these low and high densities. Polyolefin-based resins may be used alone or in combination of two or more.

The polyolefin-based resin is preferably a recycled polyolefin-based resin, that is, a recycled polyolefin-based resin. The recycled polyolefin-based resin may be resin from which impurities and the like have been removed by recovering polyolefin-based resin products. Recycled polyolefin-based resins include, for example, G1030 (manufactured by Hong-en Group) as linear low-density polyethylene, L2040 (manufactured by Hong-en Group) as low-density polyethylene, and B3001-1 (manufactured by Hong-en Group) as high-density polyethylene. ), polypropylene may be P1001-1 (manufactured by Hong Eun Group), and the like. The amount of the recycled polyolefin resin in the polyolefin resin may be 20 to 100% by mass, 30 to 100% by mass, 50 to 100% by mass, etc., based on the mass of the polyolefin resin.

The ethylene copolymer may be a copolymer of ethylene and at least one ester-based monomer such as an alkyl acrylate, an alkyl methacrylate, or an aliphatic saturated vinyl monocarboxylate. The ester-based monomer may be at least one selected from the group consisting of alkyl acrylates, alkyl methacrylates, and saturated aliphatic vinyl monocarboxylates. It may be at least one selected from the group consisting of vinyl monocarboxylate, may be aliphatic saturated vinyl monocarboxylate, and may be an ethylene-vinyl acetate copolymer.

The alkyl acrylate is, for example, a C1-C4 alkyl ester of acrylic acid, and is preferably at least one selected from the group consisting of methyl acrylate and ethyl acrylate.

The methacrylic acid alkyl ester is, for example, a C1-C4 alkyl ester of methacrylic acid, and is preferably at least one selected from the group consisting of methyl methacrylate and ethyl methacrylate.

The aliphatic saturated vinyl monocarboxylate is preferably at least one selected from the group consisting of vinyl acetate and vinyl propionate, more preferably vinyl acetate.

The proportion of the ester-based monomer-derived component in the ethylene copolymer may be 1 to 20% by mass, 1 to 14% by mass, 1 to 10% by mass, or the like.

The content of the polyolefin resin in the composite resin particles may be 10 to 70% by mass, 20 to 60% by mass, etc., based on the mass of the composite resin particles.

(Inorganic component)
The seed particles may contain an inorganic component in addition to the polyolefin resin. When the seed particles or the composite resin particles contain an inorganic component, the air bubbles are easily made finer. Examples of inorganic components include inorganic cell control agents such as talc, silica, calcium silicate, calcium carbonate, sodium borate and zinc borate, and talc and silica are suitable for homogenizing cell sizes.
The inorganic component can be, for example, 0.01 to 5% by mass, preferably 0.1 to 1% by mass, based on the mass of the polyolefin resin.
An inorganic component may be added to the polyolefin resin.

(other ingredients)
The seed particles may contain other components in addition to the polyolefin resin. Other ingredients include colorants, nucleating agents, stabilizers, fillers (reinforcing materials), higher fatty acid metal salts, antistatic agents, lubricants, natural or synthetic oils, waxes, UV absorbers, weather stabilizers, and anti-fogging agents. agents, anti-blocking agents, slip agents, coating agents, neutron shielding agents and the like. The content of other components may be 10% by mass or less, preferably 5% by mass or less, and particularly preferably 0% by mass (no other components are contained) with respect to the mass of the polyolefin resin. is.

(Manufacturing method of seed particles)
The seed particles can be obtained by a known method used for producing seed particles for forming foamed molded articles. For example, a base resin (polyolefin resin, etc.) is melt-kneaded and extruded in an extruder to obtain a strand, and the resulting strand is cut in air, cut in water, or cut while being heated. Thus, a method of granulating is exemplified. The resin components may be mixed by a mixer before being charged to the extruder.

The seed particles may have any known shape, but are preferably cylindrical, ellipsoidal (egg-shaped), or spherical. Further, the shape is more preferably oval or spherical from the viewpoint that the expanded particles obtained from the seed particles can be easily filled into a mold.
The seed particles may have an average particle size of 0.5 to 1.4 mm.

(Composite resin particles)
The composite resin particles contain, as resin components, a polyolefin-based resin derived from the base resin and a polystyrene-based resin derived from a styrene-based monomer. The composite resin particles are obtained, for example, by a seed polymerization method (impregnating and polymerizing seed particles with a styrene-based monomer).

In the seed polymerization, the amount of the styrene-based monomer used may be 50 to 800 parts by mass, 100 to 400 parts by mass, etc. with respect to 100 parts by mass of the polyolefin resin contained in the seed particles. In this specification, the content of the polystyrene-based resin in the composite resin particles corresponds to the amount of the styrene-based monomer used. For this reason, for example, the polystyrene resin content in the composite resin particles obtained by polymerizing 100 parts by mass of the styrene monomer with respect to 100 parts by mass of the polyolefin resin contained in the seed particles is 100 parts by mass with respect to 100 parts by mass of the polyolefin resin.
The content of the polystyrene resin in the composite resin particles may be 50 to 800 parts by mass, 100 to 400 parts by mass, etc. with respect to 100 parts by mass of the polyolefin resin. When the polystyrene resin content in the composite resin particles is 50 parts by mass or more with respect to 100 parts by mass of the polyolefin resin content, it is advantageous in that the foaming power of the expanded beads is high and the rigidity of the foam molded article is high. be. When the polystyrene-based resin content in the composite resin particles is 800 parts by mass or less with respect to the polyolefin-based resin content of 100 parts by mass, the styrene-based monomers that have not impregnated into the seed particles are polymerized on the surfaces of the composite resin particles. It is advantageous in that it is possible to suppress the formation of white particles by squeezing, cracking of the foam molded product is suppressed, and deterioration in chemical resistance is suppressed.
The content of the polystyrene-based resin in the composite resin particles may be 30 to 90% by mass, 40 to 80% by mass, etc. relative to the mass of the composite resin particles.

Examples of polystyrene resins include polymers derived from styrene monomers such as styrene, α-methylstyrene, p-methylstyrene and t-butylstyrene. The polystyrene-based resin may be a polymer composed of a styrene-based monomer and another monomer copolymerizable with the styrene-based monomer. Examples of other monomers include polyfunctional monomers such as divinylbenzene, and (meth)acrylic acid alkyl esters having no benzene ring in the structure such as butyl (meth)acrylate. . Components derived from these other monomers may be contained in the polystyrene resin in an amount not exceeding 5% by mass.

The composite resin particles may contain a flame retardant. Flame retardants include known halogen-based flame retardants, phosphorus-based flame retardants, inorganic flame retardants, and the like. A flame retardant may be used individually by 1 type, and may use 2 or more types together. When the composite resin particles contain a flame retardant, halogen-based flame retardants such as brominated flame retardants, chlorine-based flame retardants, and chlorine-bromine-containing flame retardants can be used as the flame retardant. It is preferable from the viewpoint that it can be imparted.

Halogenated flame retardants include, for example, tetrabromobisphenol A, derivatives thereof (eg, tetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl ether), tetrabromobisphenol A-bis(2,3-dibromo propyl ether), tetrabromobisphenol A-bis(allyl ether)), triallyl isocyanurate hexabromide, tris(2,3-dibromopropyl) isocyanurate, tetrabromocyclooctane, hexabromocyclododecane and the like.

The flame retardant can be, for example, 1.5 to 6.0% by mass, preferably 1.5 to 4.0% by mass, and 2.0 to 3.5% by mass with respect to the mass of the polyolefin resin. It is more suitable.

When the composite resin particles contain a flame retardant, the composite resin particles preferably contain a flame retardant aid. By including the flame retardant aid, the flame retardancy provided by the flame retardant can be further enhanced. Flame retardant aids include organic peroxides such as dicumyl peroxide (DCP), cumene hydroperoxide, diacyl peroxide, 2,3-dimethyl-2,3-diphenylbutane (also known as biscumyl), 3,4 -dimethyl-3,4-diphenylhexane and the like.
The flame retardant auxiliary is preferably contained in an amount of, for example, 50 parts by mass or less, preferably 10 to 40 parts by mass, and more preferably 15 to 25 parts by mass with respect to 100 parts by mass of the flame retardant. When the content of the flame retardant auxiliary is within the above range, the decrease in impact resistance and heat resistance of the foam molded product is suppressed.

The shape of the composite resin particles may be any known shape, but cylindrical, substantially spherical, and spherical shapes are preferable. A spherical or spherical shape is more preferred. The average particle diameter of the composite resin particles is preferably 0.6 mm to 1.8 mm.

(Method for producing composite resin particles)
The method for producing the composite resin particles is not particularly limited as long as the composite resin particles described above can be obtained. For example, composite resin particles can be obtained by a seed polymerization method in which a styrene-based monomer impregnated in seed particles is polymerized.

In the seed polymerization, the amount of the styrene-based monomer used may be 50 to 800 parts by mass, 100 to 400 parts by mass, etc. with respect to 100 parts by mass of the polyolefin resin contained in the seed particles.

An example of a method for producing composite resin particles using a seed polymerization method will be described below.
First, seed particles, a styrenic monomer, and, if necessary, a polymerization initiator are dispersed in an aqueous suspension. In addition, when using a polymerization initiator, you may mix a styrene-type monomer and a polymerization initiator previously, and may use it.

As the polymerization initiator, those generally used as an initiator for suspension polymerization of styrenic monomers can be preferably used. For example, benzoyl peroxide, di-t-butyl peroxide, t-butyl peroxybenzoate, dicumyl peroxide, 2,5-dimethyl-2,5-di-t-butylperoxyhexane, t-butylperoxy organic peroxides such as -3,5,5-trimethylhexanoate and t-butyl-peroxy-2-ethylhexyl carbonate; and azo compounds such as azobisisobutyronitrile and azobisdimethylvaleronitrile. One or more of these polymerization initiators can be used. Dicumyl peroxide can also act as a flame retardant aid.
Examples of the aqueous medium that constitutes the aqueous suspension include water, a mixed medium of water and a water-soluble solvent (eg, lower alcohol), and the like.

The amount of the polymerization initiator used is preferably 0.01 to 0.9 parts by mass, more preferably 0.1 to 0.5 parts by mass, per 100 parts by mass of the styrene-based monomer.

A dispersant may be added to the aqueous suspension as needed. The dispersant is not particularly limited, and any known dispersant can be used. Specific examples include sparingly soluble inorganic substances such as calcium phosphate, magnesium pyrophosphate, sodium pyrophosphate and magnesium oxide. Additionally, surfactants such as sodium dodecylbenzenesulfonate may be used.

Next, the resulting dispersion is heated to a temperature at which the styrene-based monomer is not substantially polymerized to impregnate the seed particles with the styrene-based monomer. The time for impregnating the seed particles with the styrenic monomer is not particularly limited, but is preferably 20 minutes to 4 hours, more preferably 30 minutes to 2 hours.

Then, the styrene-based monomer is polymerized. The polymerization is not particularly limited, but is preferably carried out at 80° C. to 150° C., preferably 85° C. to 140° C., for 1.5 hours to 5 hours. Polymerization is usually carried out in a pressurizable closed vessel. In addition, it is preferable to carry out the impregnation and polymerization of the styrene-based monomer in multiple steps. By dividing into multiple times, generation of styrene-based resin polymer powder can be reduced as much as possible. Further, in consideration of the decomposition temperature of the polymerization initiator, the polymerization may be performed while impregnating the seed particles with the styrene-based monomer instead of starting the polymerization after the seed particles are impregnated with the styrene-based monomer.
When the polymerization is divided into a plurality of times, in the second and subsequent polymerization steps, the styrene-based monomer may be added at a rate of 0.1 parts by mass/second or less per 100 parts by mass of the seed particles. preferred.

A composite resin particle containing a flame retardant and a flame retardant auxiliary can be produced by a method of impregnating a seed particle with a flame retardant and a flame retardant auxiliary together with a styrene-based monomer, a method of impregnating particles after polymerization, or the like.

(Expandable particles)
The expandable particles contain the composite resin particles and a blowing agent.
Examples of foaming agents include organic gases such as propane, n-butane, isobutane, n-pentane, isopentane, cyclopentane, n-hexane, and isohexane, and inorganic gases such as carbon dioxide, nitrogen, helium, argon, and air. can be used. These foaming agents can be used alone or in combination of two or more. As the organic gas, n-butane, isobutane, n-pentane, isopentane, or a combination thereof is suitable. As the inorganic gas, carbon dioxide and nitrogen are preferred, and carbon dioxide is more preferred.
The content of the foaming agent may be 5 to 25 parts by mass with respect to 100 parts by mass of the composite resin particles.

Expandable particles can be obtained, for example, by impregnating composite resin particles during or after polymerization with a foaming agent. Impregnation can be carried out by methods known per se. For example, impregnation during polymerization can be carried out by carrying out the polymerization reaction in a closed container and forcing the blowing agent into the container. The impregnation after completion of the polymerization can be performed, for example, by pressurizing the foaming agent into a sealed container containing the composite resin particles.

(foamed particles)
Expanded particles (generally also referred to as pre-expanded particles) are particles obtained by pre-expanding composite resin particles. For example, expanded beads can be obtained by impregnating composite resin particles with a blowing agent to produce expandable beads, and pre-expanding the expandable beads.

The bulk density of the expanded particles is preferably 15 kg/m ³ to 200 kg/m ³ , more preferably 20 kg/m ³ to 100 kg/m ³ , and even more preferably 20 kg/m ³ to 50 kg/m ³ . . When the bulk density is within this range, it is advantageous in that the strength of the foam molded article is high and the foam molded article is lightweight. Bulk density can be determined by the method described in the Examples.

The shape of the expanded particles is preferably spherical to approximately spherical. The average particle diameter is preferably 1.0 mm to 9.0 mm, more preferably 2.0 mm to 6.4 mm.

Expanded particles can be obtained by expanding expandable particles to a desired bulk density by a known method. Foaming can be obtained by expanding the expandable particles using heating steam of preferably 0.05 MPa to 0.20 MPa (gauge pressure), more preferably 0.06 MPa to 0.15 MPa.

(Foam molding)
The foamed molded article is a foamed body composed of a fused body of expanded particles, and is obtained, for example, by foam-molding the above-mentioned expanded particles. Since the foam molded article uses the composite resin particles as a raw material, the environmental load is low.

The density of the foam molded product is preferably 15 kg/m ³ to 200 kg/m ³ , more preferably 20 kg/m ³ to 100 kg/m ³ , and even more preferably 20 kg/m ³ to 50 kg/m ³ . . When the density is within the above range, both lightness and strength are excellent. The density of the foam molded article can be specified by the method described in Examples.

The fusion rate of the foam molded product may be 60% or more, 70% or more, 80% or more, 90% or more, and the like. The fusion rate of the foam molded product can be specified by the method described in the Examples.

A foam molded article can be produced by a known method. For example, it can be obtained by filling the mold of a foam molding machine with expanded particles, heating the expanded particles to expand them, and thermally bonding the expanded particles to each other. Water vapor can be suitably used as a medium for heating. Other manufacturing conditions such as process temperature, process pressure and process time in each manufacturing process are appropriately set according to the manufacturing equipment, raw materials and the like to be used.

Foam molded articles can be used for cushioning materials, packing materials, building materials, shoe members, and sporting goods. More specifically, midsole members, insole members, or outsole members of shoes; core materials of striking tools for sporting goods such as rackets and bats; protective gear for sporting goods such as pads and protectors; medical equipment such as pads and protectors , nursing care, welfare or health care products; tire core materials for bicycles, wheelchairs, etc.; interior materials for transport equipment such as automobiles, railroad vehicles, and airplanes, seat core materials, shock absorption members, vibration absorption members, etc.; fenders; floats toys; underfloor materials; wall materials; beds; cushions;
Preferably, it is an automobile interior material, a shock absorbing member, a vibration absorbing member, or a parts packaging material.

Hereinafter, one embodiment of the present invention will be described in more detail with reference to examples and the like, but the present invention is not limited to these.
Methods for specifying various physical properties in Examples and the like are described below.

(Density of polyolefin resin)
The density of the polyolefin resin is measured by the density gradient tube method according to JIS K6922-1:1998.

(Melt flow rate (MFR) of polyolefin resin)
MFR was measured at 190° C. under a load of 2.16 kg according to JIS K6922-1:1998.

(Melting point of polyolefin resin)
The melting point was measured by the method described in JIS K7122:1987 "Method for measuring transition heat of plastic". That is, using a differential scanning calorimeter RDC220 type (manufactured by Seiko Electronics Industries Co., Ltd.), 7 mg of the sample was filled in the measurement container, and the nitrogen gas flow rate was 30 mL / min. The temperature was raised, lowered, and raised according to the rate of temperature elevation and temperature decrease, and the melting peak temperature of the DSC curve at the time of the second temperature increase was taken as the melting point. When there are two or more melting peaks, the peak temperature on the lower side was taken as the melting point.

(Bulk density of expanded particles)
The expanded particles were filled into a graduated cylinder to the mark of 500 cm ³ . However, when the graduated cylinder was viewed from the horizontal direction and even one foamed particle reached the scale of 500 cm ³ , the filling was completed. Next, the mass of the foamed particles filled in the graduated cylinder was weighed to two significant figures after the decimal point, and the mass was defined as W (g). The bulk density of the expanded particles is calculated by the following formula.
Bulk density (kg/m ³ ) = (W/500) x 1000

(Density of foam molded body)
The mass (a) and volume (b) of a test piece (75 mm × 300 mm × 35 mm) cut out from a foamed molded product (dried at 50 ° C. for 4 hours or more after molding) should be at least three significant figures. , and the density (g/cm ³ ) of the foamed molded product was determined by the formula (a)/(b).

(Fusion evaluation of foam molded product)
In the upper surface of a rectangular parallelepiped foam molded product having an upper surface of 400 mm long x 300 mm wide and a thickness of 30 mm, a cut line with a length of 300 mm and a depth of about 5 mm was made along the horizontal direction with a cutter. The foamed molded product was divided into two parts by using the same method, and the fracture surface was observed. An arbitrary range containing 50 or more expanded beads is set on the fracture surface, and the number of expanded beads (strongly heat-fused expanded beads) that are broken not on the surface but inside the expanded beads within this range (a) Then, the number (b) of broken expanded beads (weakly heat-fused expanded beads) at the interface between the expanded beads was counted, and the fusion rate (%) was calculated by the following formula.
Fusion rate (%) = (a/(a+b)) x 100
Evaluation was made according to the following criteria based on the numerical value of the fusion rate.
◎: The fusion rate is 80% or more and 100% or less ○: The fusion rate is 60% or more and less than 80% ×: The fusion rate is less than 60%

(polyolefin resin)
Polyolefin-based resins used in Examples and the like are as follows.
Polyethylene: Linear low-density polyethylene (manufactured by Nippon Polyethylene Co., Ltd., product name NF444A, density 912 kg/m ³ , MFR 2.0 g/10 minutes, melting point 121°C;)
Recycled polyethylene: Recycled linear low-density polyethylene (manufactured by Hong Eun Group, product name G1030)

Example 1
[Preparation of seed particles]
Polyethylene and recycled polyethylene were put into a tumbler mixer at a mass ratio of 80:20 and mixed for 10 minutes.
The obtained resin mixture is supplied to an extruder (manufactured by Toshiba Machine Co., Ltd., model: SE-65), melted and kneaded at a temperature of 230 ° C. to 250 ° C., and granulated by an underwater cutting method to form an ellipsoid (egg). It was cut into three pieces to obtain polyethylene resin particles (seed particles, average mass 0.6 mg).

[Production of composite resin particles]
40 g of magnesium pyrophosphate (dispersant), 0.6 g of sodium dodecylbenzenesulfonate (surfactant), and 2 kg of pure water were charged into an autoclave with a stirrer having an internal volume of 5 liters (manufactured by Nitto Koatsu Co., Ltd.) to obtain a dispersing medium. Obtained. 600 g of seed particles were dispersed in a dispersing medium at 30° C., held for 10 minutes, and then heated to 60° C. to obtain a suspension. Furthermore, while this suspension was maintained at 60° C., a liquid obtained by dissolving 0.6 g of dicumyl peroxide (polymerization initiator) in 300 g of styrene was added dropwise over 30 minutes, and then maintained for 30 minutes. Styrene was impregnated into the seed particles. After the impregnation, the temperature was raised to 140° C., and polymerization was carried out at this temperature for 2 hours (first polymerization).

Next, a dispersion liquid prepared by dispersing 3 g of sodium dodecylbenzenesulfonate in 20 g of pure water was added dropwise to the reaction liquid cooled to 115° C. over 10 minutes. Then, a solution prepared by dissolving 4 g of t-butyl peroxybenzoate (polymerization initiator) in 1100 g of styrene was added dropwise over 4 hours and 30 minutes. After that, a dispersion medium prepared by dispersing 3 g of ethylene bis-stearic acid amide (cell control agent) in 100 g of pure water was added dropwise over 30 minutes, maintained at 115°C for 1 hour, and then heated to 140°C. Composite resin particles were produced by holding at the temperature for 3 hours. Then, it was cooled to 30° C. or less, and the composite resin particles were taken out from the autoclave. The mass ratio of the polyolefin-based resin and the polystyrene-based resin in the composite resin particles was 30:70.

[Production of expandable particles]
2 kg (100 parts by mass) of composite resin particles, 2 kg of water, and 2.0 g of sodium dodecylbenzenesulfonate (surfactant) were put into an autoclave equipped with a stirrer and having an internal volume of 5 liters. Furthermore, 300 g (15 parts by mass, 520 mL) of butane (normal butane:isobutane=7:3 (volume ratio)) was added as a foaming agent, and was pressurized until the internal pressure of the autoclave reached 0.8 MPa in terms of gauge pressure. While maintaining the inside of the autoclave at 0.8 MPa, the temperature was raised to 70° C., and stirring was continued for 4 hours to produce 2200 g of expandable particles. Thereafter, the mixture was cooled to 30° C. or lower, and after the completion of cooling, the autoclave was depressurized, and the surfactant was immediately washed with distilled water, followed by dehydration and drying to obtain expandable particles.

[Preparation of expanded beads]
The obtained expandable particles are put into a cylindrical pre-expanding machine with a stirrer (manufactured by Kasahara Kogyo Co., Ltd., model: PSX40) with an internal volume of 50 L, and 0.04 MPa steam is introduced into the machine while stirring to obtain foaming properties. The particles were heated. Thereby, the expandable particles were pre-expanded to a bulk density of 25 kg/m ³ to produce expanded particles (also referred to as pre-expanded particles).

[Preparation of foam molded product]
The resulting expanded beads were allowed to stand at 23° C. for 1 day, and then filled into a molding die (length 400 mm×width 300 mm×thickness 30 mm) of an automatic expanded bead molding machine (DPM-7454, manufactured by DABO Japan). After introducing 0.07 MPa steam into the mold for 20 seconds to heat and expand the foamed particles, the foamed molded product was cooled until the maximum surface pressure was reduced to 0.01 MPa, resulting in a density of 25 kg/m ³ . was obtained. The resulting foamed molded article was subjected to a fusion rate measurement test. Table 1 shows the results.

Examples 2 and 3
A foamed molded article was obtained in the same manner as in Example 1, except that all of the polyethylene was replaced with recycled polyethylene, or part of the polyethylene was replaced with the amount of recycled polyethylene shown in Table 1 to prepare the seed particles, and the mixture was fused. It was subjected to a rate measurement test. Table 1 shows the results.

Reference example 1
A foamed molded article was obtained in the same manner as in Example 1 except that polyethylene was used instead of recycled polyethylene, that is, the seed particles were made of only polyethylene, and subjected to a fusion rate measurement test. Table 1 shows the results.

The foam molded articles of Example 1, in which 20% of the recycled polyolefin resin was used, and Example 2, in which 40% of the recycled polyolefin resin was used, contributed to the reduction of the environmental load, while the fusion performance was lower than that of Reference Example 1 (no use of recycled polyolefin). ) was equivalent to The vapor pressure of the heating steam used in the foam molding process is relatively low at 0.07 MPa, which is not favorable for fusion bonding. A fusion rate of 90% or more means that foam molding is possible with low steam pressure, and therefore foam molding with low energy is possible. In other words, the expanded beads of Examples 1 and 2 are excellent in moldability.
The foam molded article of Example 3, in which 100% of the recycled polyolefin resin is used, greatly contributes to the reduction of the environmental load, and exhibits a fusion rate of 60% or more in foam molding with 0.07 MPa heating steam. rice field. If the fusion rate is 60% or more, it can withstand practical use. Even with recycled polyethylene alone, it was possible to obtain a foam molded article with a sufficient fusion rate with low energy consumption.

Claims (6)

Composite resin particles for producing expanded beads containing a polyolefin resin and a polystyrene resin,
The total content of the polyolefin-based resin and the polystyrene-based resin is 90% by mass or more of the mass of the composite resin particles,
The polystyrene resin content in the composite resin particles is 50 to 800 parts by mass with respect to 100 parts by mass of the polyolefin resin content,
The content of the recycled polyolefin resin in the polyolefin resin is 20 to 100% by mass,
Composite resin particles. The composite resin particles according to claim 1, wherein the polyolefin-based resin is a polyethylene-based resin. 3. The composite resin particles according to claim 2, wherein the polyethylene-based resin is (1) polyethylene or (2) polyethylene and ethylene-vinyl acetate copolymer. Expandable particles containing the composite resin particles according to any one of claims 1 to 3 and a blowing agent. An expanded bead that is a pre-expanded product of the expandable bead according to claim 4 . A foam-molded product which is an in-mold foam-molded product of the foamed particles according to claim 5 .