JP7372860B2 - High-density polyethylene resin particles, composite resin particles, foam particles, and foam molded products - Google Patents

Description

The present invention relates to high-density polyethylene resin particles, composite resin particles, foam particles, and foam molded products.

Foam molded articles made of polystyrene resins have excellent rigidity, heat insulation, light weight, water resistance, and foam moldability, but are known to have low chemical resistance and impact resistance. On the other hand, foam molded products made of polyolefin resins have excellent chemical resistance and impact resistance, but they are expensive to manufacture due to poor foaming agent retention, and compared to foam molded products made of polystyrene resins. It is known to have poor rigidity. Therefore, a foam molded article obtained from composite resin particles of a polystyrene resin and a polyolefin resin has been devised in order to take advantage of the excellent properties of both resins.

Composite resin particles are generally manufactured by using a base resin such as a polyethylene resin as a seed particle (also referred to as a core particle), adding a styrene monomer to the seed particle, and then polymerizing the seed particle. However, in composite resin particles containing polyethylene resin as seed particles, the mechanical properties of the resulting foamed molded product are highly temperature dependent. For this reason, composite resin particles using high-density polyethylene as a polyethylene resin have been reported for the purpose of suppressing this temperature dependence (Patent Document 1).

Furthermore, in order to improve the impact resistance of foam molded products obtained by high-magnification foaming of composite resin particles using high-density polyethylene, we have added seed particles containing a specific ethylene copolymer in addition to high-density polyethylene. has been reported to be used (Patent Document 2).

On the other hand, by further blending an ethylene-vinyl acetate copolymer and an acrylonitrile-styrene copolymer into the seed particles containing linear low-density polyethylene, the weak point of the expandable particles obtained from the seed particles containing polyethylene can be improved. It has been reported that an attempt was made to improve the low foaming agent retention that existed in the prior art (Patent Document 3).

Japanese Patent Application Publication No. 2012-025347 Japanese Patent Application Publication No. 2015-189912 International Publication No. 2007/138916

Steam is used in foam molding using seed particles containing high-density polyethylene and specific ethylene copolymers, but if moldability can be maintained even if the steam pressure is lowered, it would save money in terms of equipment, costs, etc. Improvement is expected.

Foamed molded articles using seed particles containing linear low-density polyethylene, ethylene-vinyl acetate copolymer, and acrylonitrile-styrene copolymer had room for improvement in dimensional change rate and flame retardancy.

The present invention provides a foam molded product that has a high thermal fusion rate of heat-expanded particles and a low dimensional change rate even when the water vapor pressure during molding is low, and high-density polyethylene resin particles for producing the same. , composite resin particles, and expanded particles.

In view of the above-mentioned problems, the inventors of the present invention reduced the water vapor pressure during molding by using high-density polyethylene resin particles containing specific high-density polyethylene and styrene-acrylonitrile copolymer as seed particles. It is possible to obtain a foamed molded product with sufficient molding processability (high fusion rate of heat-expanded particles) even when the foamed molded product is obtained, the rate of dimensional change of the foamed molded product obtained from this is small, and the foamed molded product obtained from this is small. They discovered that it has excellent impact resistance, flame retardance, chemical resistance, etc., and completed the present invention.

The present invention typically includes the following aspects.
Item 1.
High-density polyethylene resin particles used as seed particles for producing composite resin particles for producing expanded particles,
The high-density polyethylene resin particles contain high-density polyethylene and a styrene-acrylonitrile copolymer,
The high-density polyethylene resin particles contain 5 to 100 parts by mass of the styrene-acrylonitrile copolymer based on 100 parts by mass of the high-density polyethylene,
The high density polyethylene has a softening temperature of 115 to 130°C.
High-density polyethylene resin particles.
Item 2.
Item 2. The high-density polyethylene resin particles according to Item 1, further comprising 50 to 400 parts by mass of the ethylene copolymer based on 100 parts by mass of the high-density polyethylene.
Item 3.
Item 3. The high-density polyethylene-based resin particles according to item 2, wherein the high-density polyethylene-based resin particles contain 5 to 50 parts by mass of the styrene-acrylonitrile copolymer based on 100 parts by mass of the high-density polyethylene.
Item 4.
Item 2 or 3, wherein the ethylene copolymer is a copolymer of ethylene and at least one monomer selected from acrylic acid alkyl ester, methacrylic acid alkyl ester, and aliphatic saturated vinyl monocarboxylate. High-density polyethylene resin particles.
Item 5.
Composite resin particles obtained by impregnating and polymerizing the high-density polyethylene resin particles according to any one of Items 1 to 4 with a styrene monomer,
Containing a high-density polyethylene resin derived from the high-density polyethylene resin particles and a styrenic polymer obtained by polymerizing the styrenic monomer,
Composite resin particles.
Item 6.
Item 5. The composite resin particles according to Item 5, which contain 100 to 500 parts by mass of the styrene polymer based on 100 parts by mass of the high-density polyethylene resin.
Section 7.
Item 7. The composite resin particle according to Item 5 or 6, further comprising a flame retardant.
Section 8.
Item 8. The composite resin particles according to item 7, wherein the content of the flame retardant is 1.5 to 6% by mass based on the total mass of the high-density polyethylene resin and the styrene polymer.
Item 9.
Item 9. The composite resin particle according to item 7 or 8, wherein the flame retardant is a halogen-based flame retardant.
Item 10.
Item 10. The composite resin particle according to any one of Items 7 to 9, further comprising a flame retardant aid.
Item 11.
Item 6. The composite resin particles according to item 5 or 6, which do not contain a halogen flame retardant.
Item 12.
Expanded particles obtained by foaming the composite resin particles according to any one of Items 5 to 11.
Item 13.
Item 13. A foam molded article obtained by foam molding the expanded particles according to item 12.
Section 14.
Item 14. The foam molded article according to Item 13, which has a density of 20 to 50 kg/m ³ .
Item 15.
Item 15. The foamed molded article according to Item 13 or 14, wherein the dimensional change rate upon heating at 80° C. and 168 hours is 10/1000 or less.
Section 16.
Item 16. The foam molded article according to any one of Items 13 to 15, which has a burning rate of 80 mm/min or less in the FMVSS302 combustion test using a foam molded specimen having a density of 33 kg/m ³ or is self-extinguishing.

According to the present invention, by using seed particles containing high-density polyethylene and styrene-acrylonitrile copolymer, low pressure (e.g., gauge pressure of 0.11 MPa or less, 0.10 MPa or less, 0.09 Pa or less, or It is possible to obtain expanded particles having excellent moldability (eg, high fusion rate of expanded particles) in a medium (eg, water vapor) at a pressure of .08 MPa or less. Since foam molding can be performed using a low-pressure medium, the energy required for foam molding can be reduced, the equipment required for foam molding can be simplified, and the cost required for foam molding can be reduced (in other words, it has excellent productivity).
According to the present invention, by using seed particles containing high-density polyethylene and a styrene-acrylonitrile copolymer, a foamed molded article with a small dimensional change rate can be obtained.
According to the present invention, by using seed particles containing high-density polyethylene and a styrene-acrylonitrile copolymer, it is possible to obtain a foamed molded article having excellent impact resistance, flame retardance, and the like.
In the present invention, by using seed particles that further contain an ethylene copolymer, it is possible to obtain a foamed molded article with an even smaller dimensional change rate.
In the present invention, by using seed particles that further contain an ethylene copolymer, it is possible to obtain a foamed molded article with even better impact resistance.
In the present invention, by using seed particles that further contain an ethylene copolymer, it is possible to obtain a foamed molded article with even better flame retardancy.

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

(High-density polyethylene resin particles)
High-density polyethylene resin particles are used as seed particles (also referred to as core particles) for producing foam particles for producing foam molded articles.
The base resin constituting the high-density polyethylene resin particles is high-density polyethylene and a styrene-acrylonitrile copolymer.

(high density polyethylene)
The high-density polyethylene may be a resin made of an ethylene homopolymer or a copolymer of ethylene and an α-olefin having 3 to 8 carbon atoms. From the viewpoint of heat resistance, the α-olefin is preferably a carbon atom having 3 to 4 carbon atoms, such as propylene or 1-butene.

High-density polyethylene is not particularly limited, and commercially available resins can be used. For example, it is available from Tosoh, Braskem, Nippon Polyethylene, etc. On the other hand, linear low-density polyethylene such as Nipolon Z ZF260 (manufactured by Tosoh Corporation) and Nipolon LM50 (manufactured by Tosoh Corporation) are commercially available, but these linear low-density polyethylenes are used instead of high-density polyethylene. Even so, flame retardancy is low.

The softening temperature of high density polyethylene is preferably 115 to 130°C, more preferably 117 to 129°C, and even more preferably 117 to 120°C. When the softening temperature is within the above range, it is advantageous in that heat resistance is improved while maintaining moldability, and in addition, since the softening temperature is appropriately softened during seed polymerization, more styrene monomer is absorbed inside the seed particles. This is advantageous in that it is easy to use. Furthermore, generation of polymerized powder during seed polymerization can be suppressed. The softening temperature is the temperature specified by the method described in the Examples.

The melt mass flow rate (also referred to as MFR) of high density polyethylene is not particularly limited, but is preferably 1.8 to 2.4 g/10 minutes, more preferably 1.9 to 2.3 g/10 minutes. When the MFR is within the above range, it is advantageous in that the molding processability is improved and the seed particles are easily sphericalized during polymerization. MFR is a value specified by the method described in Examples.

The melting point of high-density polyethylene is not particularly limited, but is preferably 122 to 140°C, more preferably 124 to 135°C, and even more preferably 125 to 130°C. When the melting point is within the above range, it is advantageous in that moldability and dimensional stability are excellent. The melting point is a value determined by the method described in the Examples.

The density of high-density polyethylene is not particularly limited, but 930 to 960 kg/m ³ is preferable, and 935 to 955 kg/m ³ is more preferable. The density can also be greater than 945 kg/m ³ and less than 960 kg/m ³ , or from 950 to 960 kg/m ³ . When the density is within the above range, it is advantageous in that mechanical strength and dimensional stability are excellent. The density is a value specified by the method described in the Examples.

The content ratio of high density polyethylene in the high density polyethylene resin particles is, for example, 10 to 96% by mass, 10 to 70% by mass, 10 to 60% by mass, 10 to 50% by mass with respect to the total mass of the high density polyethylene resin particles. The amount may be 10 to 40% by weight, preferably 15 to 50% by weight, and more preferably 20 to 50% by weight. When the content ratio of high-density polyethylene is within the above range, it is advantageous in that foamability and moldability can be improved while maintaining mechanical strength.

(Styrene-acrylonitrile copolymer)
Composite resin particles with polystyrene obtained by subjecting high-density polyethylene resin particles containing high-density polyethylene and a styrene-acrylonitrile copolymer to seed polymerization are obtained by subjecting particles containing high-density polyethylene to seed polymerization. Compared to composite resin particles with polystyrene, it has the heat resistance of the latter, but it has improved the disadvantage of the latter, which is that the fusion rate of the expanded particles decreases when a low-pressure medium is used for foam molding. Ru. Furthermore, since the seed particles contain a styrene-acrylonitrile copolymer, they also have excellent dimensional stability.

The softening temperature of the styrene-acrylonitrile copolymer is preferably 90 to 120°C, more preferably 95 to 110°C. When the softening temperature is within the above range, it is advantageous in that both dimensional stability and moldability can be achieved. The softening temperature is the temperature specified by the method described in the Examples.

The MFR of the styrene-acrylonitrile copolymer is not particularly limited, but is preferably 7 to 20 g/10 minutes, more preferably 10 to 17 g/10 minutes. When the MFR is within the above range, the seed particles tend to become spherical during polymerization, which is advantageous in that the ability to fill the mold with expanded particles during molding improves. MFR is a value specified by the method described in Examples.

The density of the styrene-acrylonitrile copolymer is not particularly limited, but 900 to 1200 kg/m ³ is preferable, and 950 to 1100 kg/m ³ is more preferable. When the density is within the above range, it is advantageous in that mechanical strength is improved and deterioration in foamability can be suppressed. The density is a value specified by the method described in the Examples.

The content of the styrene-acrylonitrile copolymer in the high-density polyethylene resin particles can be, for example, 5 to 100 parts by mass, preferably 5 to 50 parts by mass, based on 100 parts by mass of high-density polyethylene.

(ethylene copolymer)
Preferably, the high-density polyethylene resin particles contain an ethylene copolymer. Ethylene copolymers do not include the high-density polyethylene. The ethylene copolymer is, for example, a copolymer of ethylene and an ester monomer. The ethylene copolymer preferably has a -COO- bond or an -OCO- bond in the molecule.

The ethylene copolymer is preferably a copolymer of ethylene and at least one ester monomer such as an acrylic acid alkyl ester, a methacrylic acid alkyl ester, or aliphatic saturated vinyl monocarboxylate. The ester monomer is preferably at least one selected from the group consisting of acrylic acid alkyl esters, methacrylic acid alkyl esters, and aliphatic saturated vinyl monocarboxylate; At least one selected from the group consisting of vinyl acids is more preferred, and aliphatic saturated vinyl monocarboxylate is even more preferred. As the ethylene copolymer, ethylene-vinyl acetate copolymer is particularly preferred.

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

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

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

The proportion of the component derived from the ester monomer in the ethylene copolymer is preferably 1 to 20% by mass, more preferably 1 to 15% by mass.

The softening temperature of the ethylene copolymer is preferably 70 to 95°C, more preferably 80 to 92°C. When the softening temperature is within the above range, it is advantageous in that foamability and moldability are improved. The softening temperature is the temperature specified by the method described in the Examples.

The MFR of the ethylene copolymer is not particularly limited, but is preferably 0.1 to 5.0 g/10 minutes, more preferably 0.1 to 4.0 g/10 minutes, and 0.1 to 1.4 g. /10 minutes is more preferred, and 0.1 to 0.8 g/10 minutes is particularly preferred. When the MFR is within the above range, it is advantageous in that the foamability is improved and the seed particles are more likely to be spherical during polymerization. MFR is a value specified by the method described in Examples.

The melting point of the ethylene copolymer is not particularly limited, but is preferably 85 to 140°C, more preferably 90 to 115°C. When the melting point is within the above range, it is advantageous in terms of improved moldability, efficient absorption of styrene monomer into seed particles during polymerization, and dimensional stability. The melting point is a value determined by the method described in the Examples.

The content ratio of the ethylene copolymer in the high-density polyethylene resin particles can be, for example, 0 to 400 parts by mass, 5 to 400 parts by mass, 10 to 400 parts by mass, and 20 to 400 parts by mass, based on 100 parts by mass of high-density polyethylene. Parts by weight are preferred, and 50 to 380 parts by weight are more preferred. When the content ratio of the ethylene copolymer is within the above range, it is advantageous in that it can be expected to improve foaming properties, moldability, and slow combustion properties.

(other ingredients)
The high-density polyethylene resin particles may contain other components in addition to high-density polyethylene, styrene-acrylonitrile copolymer, and ethylene copolymer. Other ingredients include colorants, nucleating agents, stabilizers, fillers (reinforcing materials), higher fatty acid metal salts, flame retardants, antistatic agents, lubricants, natural or synthetic oils, waxes, ultraviolet absorbers, and weathering stabilizers. , anti-fogging agents, anti-blocking agents, slip agents, coating agents, neutron shielding agents and the like. The content of other components is preferably 10% by mass or less based on the total mass of the high-density polyethylene resin particles.

(Production method of high-density polyethylene resin particles)
High-density polyethylene resin particles can be obtained by a known method used for producing seed particles for forming a foamed molded body. For example, a strand is obtained by melt-kneading and extruding a resin component (high-density polyethylene, styrene-acrylonitrile copolymer, ethylene copolymer, etc.) in an extruder, and the resulting strand is cut in air. , a method of granulating by cutting in water, or cutting while heating. The resin components may be mixed in a mixer before being fed into the extruder.

The shape of the high-density polyethylene resin particles may be any known shape, but is preferably cylindrical, elliptical (ovoid), or spherical. Further, the shape is more preferably ellipsoidal or spherical in order to improve the filling property of expanded particles obtained from high-density polyethylene resin particles into a mold.
The high density polyethylene resin particles preferably have an average particle diameter of 0.5 to 1.4 mm.

(composite resin particles)
The composite resin particles include a resin component derived from high-density polyethylene resin particles (herein also referred to as high-density polyethylene resin, and includes at least high-density polyethylene and a styrene-acrylonitrile copolymer), and a styrene-based resin component. Contains a resin component (styrenic polymer) derived from a monomer. The composite resin particles can be obtained, for example, by a seed polymerization method (impregnating seed particles with a styrene monomer and polymerizing them).

In the seed polymerization, the styrene monomer can be used in an amount of 100 to 500 parts by mass based on 100 parts by mass of the high-density polyethylene resin particles. The content of the styrenic polymer in the composite resin particles approximately corresponds to the amount of the styrene monomer added. Therefore, the proportion of the styrene polymer contained in the composite resin particles can be 100 to 500 parts by mass based on 100 parts by mass of the resin component (high-density polyethylene resin) derived from the high-density polyethylene resin particles. The proportion of the styrene polymer is preferably 100 to 400 parts by mass, more preferably 100 to 300 parts by mass.

Examples of the styrenic polymer include polymers derived from styrene monomers such as styrene, α-methylstyrene, p-methylstyrene, and t-butylstyrene. Furthermore, the styrenic polymer may be a polymer composed of a styrene monomer and another monomer copolymerizable with the styrene monomer. Examples of other monomers include polyfunctional monomers such as divinylbenzene, and alkyl (meth)acrylates that do not contain a benzene ring in their structure, such as butyl (meth)acrylate. Components derived from these other monomers may be contained in the styrenic polymer in an amount not exceeding 5% by mass.

The composite resin particles may also contain a flame retardant. Moreover, since the composite resin particles of the present invention have relatively high flame retardancy even without containing a flame retardant, they do not need to contain a flame retardant (eg, a halogen flame retardant). Composite resin particles that do not contain a flame retardant can suppress deterioration in chemical resistance, impact resistance, and heat resistance caused by containing a flame retardant.

Examples of the flame retardant include known halogen flame retardants, phosphorus flame retardants, and inorganic flame retardants. One type of flame retardant may be used alone, or two or more types may be used in combination. 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 to impart high flame retardancy to foamed molded products in small amounts. It is preferable from the viewpoint that it can be applied.

Examples of halogen flame retardants include tetrabromobisphenol A, its derivatives (for example, tetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl ether), tetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl ether), tetrabromobisphenol A-bis(2,3-dibromo-2-methylpropyl ether), propyl ether), tetrabromobisphenol A-bis(allyl ether)), triallylisocyanurate hexabromide, tris(2,3-dibromopropyl)isocyanurate, tetrabromocyclooctane, hexabromocyclododecane, and the like.

Generally, when a halogen flame retardant is contained, flame retardancy and moldability are improved, but the heat resistance of the foam is reduced. The foamed molded product obtained by the present invention has relatively high flame retardancy and excellent moldability, so even if the content of halogenated flame retardant is reduced or it does not contain halogenated flame retardant, it has excellent flame retardancy. It has good flame retardancy and moldability, and is unlikely to cause a decrease in the heat resistance of the foam due to the addition of flame retardants.

The flame retardant can be used in an amount of, for example, 1.5 to 6.0% by mass, and 1.5 to 4.0% by mass based on the total mass of the resin component derived from the high-density polyethylene resin particles and the styrene polymer. Preferably, 2.0 to 3.5% by weight is more preferable. When the content of the flame retardant is within the above range, deterioration of the chemical resistance, impact resistance, and heat resistance of the foam molded article due to the addition of the flame retardant is suppressed.

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

The shape of the composite resin particles may be any known shape, but cylindrical, approximately spherical, and spherical shapes are preferable, and approximately cylindrical, approximately spherical, and spherical shapes are preferred, since the expanded particles formed from the composite resin particles can be easily filled into a mold. Spherical or spherical shapes are more preferred. The average particle diameter of the composite resin particles is preferably 0.6 to 1.8 mm.

(Production method of composite resin particles)
The method for producing composite resin particles is not particularly limited as long as the composite resin particles described above can be obtained. As an example, composite resin particles can be obtained by the following manufacturing method.
That is, composite resin particles can be obtained by polymerizing the styrene monomer impregnated into seed particles. This method is a so-called seed polymerization method.

An example of a method for producing composite resin particles using a seed polymerization method will be described below.
First, seed particles, a styrene monomer, and, if necessary, a polymerization initiator are dispersed in an aqueous suspension. In addition, when using a polymerization initiator, the styrene monomer and the polymerization initiator may be mixed in advance.

As the polymerization initiator, those generally used as initiators for suspension polymerization of styrenic monomers can be used. For example, benzoyl peroxide, di-t-butyl peroxide, t-butyl peroxybenzoate, dicumyl peroxide, 2,5-dimethyl-2,5-di-t-butyl peroxyhexane, t-butyl peroxy These include organic peroxides such as -3,5,5-trimethylhexanoate and t-butyl-peroxy-2-ethylhexyl carbonate, and azo compounds such as azobisisobutyronitrile and azobisdimethylvaleronitrile. These polymerization initiators can be used alone or in combination of two or more. Note that dicumyl peroxide can also act as a flame retardant aid.
Examples of the aqueous medium constituting the aqueous suspension include water and a mixed medium of water and a water-soluble solvent (eg, lower alcohol).

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

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

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

Next, a styrene monomer is polymerized. The polymerization is preferably carried out at 115 to 150°C, preferably 120 to 140°C, for 1.5 to 5 hours, although there is no particular limitation. Polymerization is usually carried out in a pressurizable closed container. Note that it is preferable to carry out the impregnation and polymerization of the styrene monomer in multiple steps. By dividing the process into multiple times, the generation of styrene resin polymer powder can be minimized. Furthermore, in consideration of the decomposition temperature of the polymerization initiator, the polymerization may be carried out while impregnating the seed particles with the styrene monomer instead of starting the polymerization after impregnating the seed particles with the styrene monomer.
When the polymerization is divided into multiple steps, in the second and subsequent polymerization steps, it is preferable to carry out the polymerization while adding the styrene monomer at a rate of 1.0 parts by mass/second or less per 100 parts by mass of the seed particles.

Composite resin particles containing a flame retardant and a flame retardant aid can be produced by a method in which the flame retardant and a flame retardant aid are impregnated into seed particles together with a styrene monomer, a method in which particles are impregnated after polymerization, and the like.

(expandable particles)
The expandable particles include the above composite resin particles and a foaming agent.

Examples of the blowing agent 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 blowing agents can be used alone or in combination of two or more. As the organic gas, any one of n-butane, isobutane, n-pentane, isopentane, or a combination thereof is suitable.
The content of the blowing agent is preferably 5 to 25 parts by mass based on 100 parts by mass of the composite resin particles.

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

(foamed particles)
Expanded particles (generally referred to as pre-expanded particles) are particles obtained by pre-expanding composite resin particles. For example, expanded particles can be obtained by foaming expandable particles impregnated with a foaming agent.

Further, the bulk density of the expanded particles is preferably 15 to 50 kg/m ³ , more preferably 22 to 40 kg/m ³ . If the bulk density is within this range, the closed cell ratio will be good when foamed, and as a result, the foamed molded product will have high strength and also be lightweight.

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

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

(Foam molded product)
The foamed molded product is a foamed product made of a fused product of foamed particles, and is obtained, for example, by foam-molding the above-mentioned foamed particles. Since the foamed molded article uses the above composite resin particles as a raw material, it has excellent flame retardancy, dimensional stability, and moldability (weldability at low pressure).

The density of the foamed molded product is preferably 20 to 100 kg/m ³ , more preferably 20 to 50 kg/m ³ , and even more preferably 20 to 40 kg/m ³ . The density of the foamed molded product is a value specified by the method described in the Examples. When the density is within the above range, both lightness and strength are excellent.

Foam molded products have excellent dimensional stability. The heating dimensional change rate of the foam molded article at 80° C. and 168 hours is preferably 10/1000 or less. The heating dimensional change rate is a value specified by the method described in Examples.

The foamed molded article has relatively excellent flame retardancy even if it does not contain a flame retardant. It is preferable that the combustion rate in the FMVSS302 combustion test using a foam molded product test piece with a density of 33 kg/m ³ is 80 mm/min or less, or that the foam molded product has self-extinguishing properties in the same combustion test. suitable.

Foam molded products have excellent impact resistance. The falling ball impact value of the foam molded product is preferably 30 cm or more, more preferably 32.5 to 50 cm. The falling ball impact value is a value specified by the method described in the Examples.

The foamed molded article can be obtained by filling a mold of a foam molding machine with foamed particles, and heat-sealing the foamed particles to each other while foaming the foamed particles. Steam can be suitably used as the heating medium.

The expanded particles obtained from the high-density polyethylene resin particles of the present invention can be sufficiently expanded and fused even in a low-pressure medium (eg, water vapor) of 0.11 MPa (gauge pressure) or less. Therefore, the energy required for foam molding can be reduced, the equipment required for foam molding can be simplified, and the cost required for foam molding can be reduced (that is, excellent productivity).
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, etc. to be used.

Foamed molded products can be used for cushioning materials, packaging materials, construction materials, shoe parts, and sporting goods. Specifically, midsole members, insole members, or outsole members of shoes; core materials of hitting tools for sports equipment such as rackets and bats; protective gear for sports equipment such as pads and protectors; medical products such as pads and protectors. , Nursing care, welfare or health care products; Tire core materials for bicycles, wheelchairs, etc.; Interior materials, seat core materials, shock absorbing members, vibration absorbing members, etc. for transportation equipment such as automobiles, railway vehicles, airplanes; Fender materials; Floats It can be used for toys; flooring materials; wall materials; beds; cushions; electronic parts, various industrial materials, containers for transporting foods, etc.
Preferably, it is an interior material of an automobile, a shock absorbing member, or a vibration absorbing member.

EXAMPLES Hereinafter, the present invention will be specifically explained with reference to Examples, but the present invention is not limited thereto.
The methods for measuring various physical properties in Examples and the like are described below.

<Density of polyethylene resin and styrene-acrylonitrile copolymer>
The density of the polyethylene resin was measured by the density gradient tube method in accordance with JIS K6922-1:1998.

<Melt flow rate (MFR) of polyethylene resin and ethylene copolymer>
MFR was measured at 190° C. under a load of 2.16 kg in accordance with JIS K6922-1:1998.

<Melt flow rate (MFR) of styrene-acrylonitrile copolymer>
MFR was measured in accordance with ISO 1133 at 200° C. under a load of 50 kg.

<Melting point of polyethylene resin and ethylene copolymer>
The melting point was measured by the method described in JIS K7122:1987 "Method for measuring heat of transition of plastics". That is, using a differential scanning calorimeter RDC220 model (manufactured by Seiko Electronics Industries, Ltd.), a measurement container was filled with 7 mg of the sample, and the temperature was heated at 10°C/min between room temperature and 220°C under a nitrogen gas flow rate of 30 mL/min. The temperature was raised, lowered, and raised repeatedly according to the speed of temperature rise and fall, and the melting peak temperature of the DSC curve at the second temperature rise was taken as the melting point. Moreover, when there were two or more melting peaks, the lower peak temperature was taken as the melting point.

<Vicat softening temperature of polyethylene resin, styrene-acrylonitrile copolymer and ethylene copolymer>
It was measured by the method described in JIS K7196:1991 "Softening temperature test method by thermomechanical analysis of thermoplastic films and sheets". That is, after crushing the resin particles to a thickness of 2 mm by heat pressing, a film-like test piece with a flat rectangular shape measuring 10 mm long x 20 mm wide x 2 mm thick was prepared. , trade name "TMA/SS6200"), in needle insertion test mode (needle tip area 1 mm ² ), with a load of 50 g, the needle was applied to the film-like test piece, and the temperature was raised at a heating rate of 5°C/min. The temperature at which distortion occurred in the film-like test piece was defined as the softening temperature of the resin particles.

<Average cell diameter of expanded particles>
The average cell diameter of the expanded particles was measured as follows.
A plane passing near the center of the foamed particles was cut out with a razor blade, and the cut surface was photographed using a scanning electron microscope (manufactured by JEOL Ltd., model: JSM-6360LV) at 100 times magnification. In addition, when photographing the cut surface, a range including the surface layer part of the foamed particles, a range including the center part of the foamed particles, and a range including an arbitrary part (three locations) were photographed.
The surface layer part of the foamed particle refers to the area within 50% of the radius from the outermost layer film, and the center area of the expanded particle refers to the area within 50% of the radius from the center of the expanded particle.
Next, print the photographed images one by one on A4 paper, draw a straight line with a length of 60 mm on the image of the cut surface of the foam particle, and calculate the average chord of the bubbles from the number of bubbles existing on this straight line. The length (t) was calculated using the following formula.
Average chord length t (μm) = (60 x 1,000) / (number of bubbles x photo magnification)
However, any straight line was drawn as much as possible so that the straight line and the bubble did not touch only at the point of contact (if they did, it was included in the number of bubbles). Furthermore, if both ends of the straight line were located within the bubble without penetrating the bubble, the bubble in which both ends of the straight line were located was also included in the number of bubbles.
Then, based on the calculated average chord length t, the average bubble diameter (D) is calculated using the following equation.
Average bubble diameter D (μm) = t/0.616
The average value of a total of 5 images for each sample is defined as the average bubble diameter.

<Bulk density of expanded particles>
The bulk density of the expanded particles was measured as follows. The expanded particles were filled into a measuring cylinder to a scale of 500 cm ³ . However, the measuring cylinder was visually observed from the horizontal direction, and if even one foamed particle reached the scale of 500 cm ³ , filling was completed. Next, the weight of the foamed particles filled in the graduated cylinder was weighed to two significant figures below the decimal point, and the weight was defined as W (g). The bulk density of the expanded particles was calculated using the following formula.
Bulk density (kg/m ³ )=(W/500)×1000

<Fusion rate of foam molded product>
A cut line with a length of 300 mm and a depth of approximately 5 mm was made along the horizontal direction with a cutter on the top surface of a rectangular parallelepiped foam molded product with a top surface of 400 mm long x 300 mm wide and a thickness of 30 mm. The foamed molded product was divided into two parts and the fractured surface was observed. Set an arbitrary range that includes 50 or more foamed particles on the fracture surface, and count (a) the number of foamed particles (strongly heat-fused foamed particles) that are broken inside the foamed particles instead of on the surface within this range. Then, the number (b) of foamed particles broken at the interface between the foamed particles (foamed particles weakly thermally fused) was counted, and the fusion rate (%) was calculated using the following formula.
Fusion rate (%) = (a/(a+b)) x 100

<Moldability (water vapor pressure)>
The foamed particles were filled into a 300 mm x 400 mm x 30 mm mold of a foam molding machine, and heated with water vapor to foam the foamed particles, while thermally fusing the foamed particles to each other. During heating with water vapor (for 50 seconds), the resulting foam molded product melted when the steam pressure of the water vapor was changed from 0.08 MPa to 0.25 MPa in 0.01 MPa increments. The arrival rate was calculated. Evaluation was made according to the following criteria based on the lowest steam pressure value (minimum steam pressure value) at which the fusion rate was 90% or more. Note that if a foam molded article with good fusion bonding is obtained at the low pressure mentioned above, the molding equipment can be simplified and the manufacturing energy can be reduced, resulting in lower manufacturing costs and improved productivity.
High moldability (○): A molded article with a fusion rate of 90% or more was obtained at a steam pressure of 0.11 MPa or less.
Low moldability (×): A steam pressure exceeding 0.11 MPa is required to obtain a molded article with a fusion rate of 90% or more, and productivity is found to be difficult.

<Density of foam molded product>
The weight (a) and volume (b) of a test piece (75 mm x 300 mm x 35 mm) cut out from a foamed molded product (dried at 50 ° C for 4 hours after molding) were calculated to have three or more significant digits. The density (kg/m ³ ) of the foamed molded product was determined using the formula (a)/(b).

<Heating dimensional change rate of foam molded product>
The heating dimensional change rate of the foamed molded product was measured by method B described in JIS K 6767:1999 "Foamed plastic - polyethylene - test method". A test piece measuring 150 mm long x 150 mm wide x 20 mm high was cut out from the foam molded product. On the surface of the test piece, three straight lines with a length of 50 mm oriented in the vertical direction are drawn parallel to each other at intervals of 50 mm, and three straight lines oriented in the horizontal direction with a length of 50 mm are drawn parallel to each other at 50 mm intervals. Fill in each interval. After that, the test piece was left in a hot air circulation dryer at 80°C for 168 hours, taken out, and placed in a place under standard conditions (20 ± 2°C, humidity 65 ± 5%) for 1 hour. I left it alone. Next, the lengths of six straight lines drawn on the surface of the test piece were measured, and the arithmetic average value L1 of the lengths of the six straight lines was calculated. The degree of change S was calculated based on the following formula, and the absolute value of the degree of change S was taken as the heating dimensional change rate (%).
S (%) = 100 x (L1-50)/50

<Evaluation criteria for heating dimensional change rate>
Low dimensional change rate (◎): 0≦S<10.0: Very good dimensional stability Low dimensional change rate (○): 10.0≦S≦11.0: Good dimensional stability High dimensional change rate (×): S>11.0: Practically difficult to use

<Burning rate>
The burning rate (mm/min) was measured in accordance with the US automobile safety standard FMVSS 302. The test piece (bulk expansion ratio: 30 times) was 350 mm x 100 mm x 12 mm (thickness), and skin was present on at least two sides measuring 350 mm x 100 mm.

<Flame retardancy>
Flame retardancy was evaluated based on the burning rate using the following criteria.
High flame retardancy (○): When the burning rate is 80 mm/min or less, or when the flame is self-extinguishing (that is, the flame extinguishes before reaching the measurement starting point).
Low flame retardancy (×): When the burning rate is greater than 80 mm/min.

<Falling ball impact value>
The falling ball impact strength was measured in accordance with the method described in JIS K7211:1976 "General Rules for Testing Methods for Falling Weight Impact on Hard Plastics."
After drying the foamed molded product (volume multiple 40 times) at a temperature of 50°C for 1 day, a strip-shaped test piece (without skin on all 6 sides) of 40 mm x 215 mm x 20 mm (thickness) was cut out from this foamed molded product. Ta.
Next, both ends of the test piece were fixed with clamps so that the distance between the supporting points was 150 mm, and a rigid ball weighing 321 g was dropped from a predetermined height onto the center of the test piece to check whether the test piece was broken or not. Observe.
The test was performed by changing the falling height (test height) of the rigid ball at 5 cm intervals from the lowest height at which all five test pieces were destroyed to the highest height at which all five test pieces were not destroyed, and the falling ball impact value (cm), that is, 50%. The fracture height was calculated using the following formula.
H50=Hi+d[Σ(i・ni)/N±0.5]
The symbols in the formula mean the following.
H50: 50% fracture height (cm)
Hi: Test height (cm) when the height level (i) is 0, the height at which the test piece is predicted to break d: Height interval (cm) when raising and lowering the test height
i: Height level that increases or decreases by one, with 0 when it is Hi (i=...-3, -2, -1, 0, 1, 2, 3...)
ni: Number of test pieces that broke (or did not break) at each level, whichever is larger (if the number is the same, you can use either one)
N: Total number of test specimens that were destroyed (or not destroyed) (N = Σni), whichever data is larger is used (in case of the same number, either can be used)
±0.5: Negative (-) number is used when using destroyed data, positive (+) number is used when using undestroyed data

The resulting falling ball impact values were evaluated based on the following criteria. The larger the falling ball impact value, the greater the impact resistance of the foamed molded product.
〇 (Excellent): Falling ball impact value is 30 cm or more × (Not acceptable): Falling ball impact value is less than 30 cm

The meanings of terms used in the examples are as follows.
Resin type 1: Polyethylene resin HDPE1:
High-density polyethylene (Tosoh Corporation, product number 10S65B, density 940 kg/m ³ , MFR 2.0 g/10 minutes, melting point 126°C, softening temperature 118°C)
HDPE2:
High-density polyethylene (Braskem, product number SGE7252, density 953 kg/m ³ , MFR 2.2 g/10 min, melting point 131°C, softening temperature 128°C)
LDPE1:
Low density polyethylene (Japan Polyethylene Co., Ltd., product number NF444A, density 912 kg/m ³ , MFR 2 g/10 min, melting point 121°C, softening temperature 93°C)
Resin type 2: Styrene-acrylonitrile copolymer AS: Styrene-acrylonitrile copolymer (Daicel Polymer Co., Ltd., product number 020SF, density 1.07 g/cm ³ , MFR 13 g/10 minutes, softening temperature 101°C)
Resin type 3: Ethylene copolymer EVA:
Ethylene-vinyl acetate copolymer (Japan Polyethylene Co., Ltd., product number LV115, MFR 0.3 g/10 min, melting point 108°C, softening temperature 80°C, vinyl acetate content 4% by mass)
EEA:
Ethylene-ethyl acrylate copolymer (Japan Polyethylene Co., product number A1100, MFR 0.4 g/10 min, melting point 104°C, softening temperature 83°C, ethyl acrylate content 10% by mass)
TAIC6B:
Triallylisocyanurate hexabrominated compound (Manac, product number EB-70)
DCP:
Dicumyl peroxide (NOF Corporation, product number Percmil D)

Example 1
[Preparation of seed particles]
HDPE1, AS, and EVA were put into a tumbler mixer at a mass ratio of 30:10:60 and mixed for 10 minutes to obtain a resin mixture. The resin mixture is supplied to an extruder, melted and kneaded at a temperature of 230 to 250°C, and granulated by an underwater cutting method and cut into elliptical spheres (ovals) to obtain a high-density polyethylene resin made of HDPE1, AS, and EVA. Particles (seed particles, average weight 0.6 mg) were obtained.

[Preparation of composite resin particles]
40 g of magnesium pyrophosphate (dispersant), 0.6 g of sodium dodecylbenzenesulfonate (surfactant), and 2 kg of pure water were placed in an autoclave with an internal volume of 5 liters equipped with a stirrer to obtain a dispersion medium. 800 g of seed particles were dispersed in a dispersion medium at 30°C, held for 10 minutes, and then heated to 60°C to obtain a suspension. Furthermore, while heating this suspension to 65°C, a solution prepared by dissolving 0.8 g of dicumyl peroxide (polymerization initiator) in 400 g of styrene monomer was added dropwise over 30 minutes, and then held for 30 minutes. By doing so, the styrene monomer was impregnated into the seed particles. After impregnation, the temperature was raised to 140°C, and polymerization was carried out at this temperature for 2 hours (first polymerization).

Next, a dispersion of 3 g of sodium dodecylbenzenesulfonate dispersed in 20 g of pure water was added dropwise into the reaction solution whose temperature had been lowered to 115° C. over 10 minutes. Next, a solution prepared by dissolving 3 g of t-butyl peroxybenzoate (polymerization initiator) in 800 g of styrene monomer was added dropwise over 4 hours. After dropping, the mixture was maintained at 115° C. for 1 hour to impregnate the styrene monomer into the modified high-density polyethylene resin particles. Thereafter, a dispersion medium prepared by dispersing 3 g of ethylene bisstearamide (bubble control agent) in 100 g of pure water was added dropwise over 30 minutes, and after the dropwise addition, it was kept at 115°C for 1 hour to form the seed particles. Impregnated with styrene and foam control agent. After impregnation, the temperature was raised to 140° C. and maintained at this temperature for 3 hours for polymerization (second polymerization) to produce composite resin particles. The mixture was cooled to 30° C. or below, and the composite resin particles (styrene composite polyethylene resin particles) were taken out from the autoclave. The mass ratio of seed particles to polystyrene was 40/60.

[Preparation 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 placed in an autoclave with an internal volume of 5 liters and equipped with a stirrer. Furthermore, 300 g (15 parts by mass, 520 mL) of butane (normal butane: isobutane = 7:3 (volume ratio)) as a foaming agent was introduced into the autoclave until the internal pressure of the autoclave reached 3.0 MPa in terms of gauge pressure. Expandable particles could be obtained by heating the autoclave to 70° C. while maintaining the pressure inside the autoclave at 3.0 MPa and continuing stirring for 4 hours. Thereafter, the mixture was cooled to 30° C. or lower, and after cooling was completed, the autoclave was depressurized, the surfactant was immediately washed with distilled water, and the mixture was dehydrated and dried to obtain expandable particles.

[Preparation of expanded particles]
The obtained expandable resin particles were put into a cylindrical pre-foaming machine with an internal volume of 50 L and equipped with a stirrer, and heated with water vapor of 0.02 MPa while stirring, resulting in foaming with bulk densities of 33 kg/m ³ and 25 kg/m ³ . Particles were prepared. The average cell diameter of the expanded particles was 0.26 mm.

[Preparation of foam molded product]
The obtained expanded beads were left at 23° C. for one day, and then filled into a mold (length 400 mm x width 300 mm x thickness 30 mm) of an automatic foam bead molding machine (manufactured by DABO Japan, DPM-7454). After heating and foaming the foamed particles by introducing water vapor of 0.09MPa into the mold for 50 seconds, the foamed molded product was cooled until the maximum surface pressure decreased to 0.01MPa, resulting in a density of 33kg/ ^m3. A foamed molded product weighing 25 kg/m ³ was obtained. A foamed molded product with a density of 33 kg/m ³ was used for the combustion test, and a foamed molded product with a density of 25 kg/m ³ was used in the other tests. The results are shown in Table 1.

Example 2
[Preparation of seed particles]
HDPE2, AS, and EEA were placed in a tumbler mixer at a mass ratio of 50:10:40 and mixed for 10 minutes to obtain a resin mixture. The resin mixture is supplied to an extruder, melted and kneaded at a temperature of 230 to 250°C, and granulated by an underwater cutting method and cut into elliptical spheres (ovals) to produce a high-density polyethylene resin made of HDPE2, AS, and EEA. Particles (seed particles, average weight 0.6 mg) were obtained.

[Preparation of composite resin particles]
40 g of magnesium pyrophosphate (dispersant), 0.6 g of sodium dodecylbenzenesulfonate (surfactant), and 2 kg of pure water were placed in an autoclave with an internal volume of 5 liters equipped with a stirrer to obtain a dispersion medium. 600 g of seed particles were dispersed in a dispersion medium at 30°C, held for 10 minutes, and then heated to 60°C to obtain a suspension. Furthermore, while heating this suspension to 65°C, a solution prepared by dissolving 0.6 g of dicumyl peroxide (polymerization initiator) in 300 g of styrene monomer was added dropwise over 30 minutes, and then held for 30 minutes. By doing so, the styrene monomer was impregnated into the seed particles. After impregnation, the temperature was raised to 140°C, and polymerization was carried out at this temperature for 2 hours (first polymerization).
Next, a dispersion of 3 g of sodium dodecylbenzenesulfonate dispersed in 20 g of pure water was added dropwise into the reaction solution whose temperature had been lowered to 115° C. over 10 minutes. Next, a solution prepared by dissolving 5 g of t-butyl peroxybenzoate (polymerization initiator) in 1100 g of styrene monomer was added dropwise over 4 hours. After dropping, the mixture was maintained at 115° C. for 1 hour to impregnate the styrene monomer into the modified high-density polyethylene resin particles. Thereafter, a dispersion medium prepared by dispersing 3 g of ethylene bisstearamide (bubble control agent) in 100 g of pure water was added dropwise over 30 minutes, and after the dropwise addition, it was kept at 115°C for 1 hour to form the seed particles. Impregnated with styrene and foam control agent. After impregnation, the temperature was raised to 140° C. and maintained at this temperature for 3 hours for polymerization (second polymerization) to produce composite resin particles. The mixture was cooled to 30° C. or below, and the composite resin particles (styrene composite polyethylene resin particles) were taken out from the autoclave. The mass ratio of seed particles to polystyrene was 30/70.
Using these composite resin particles, expandable particles, expanded particles, and a foamed molded article were produced in the same manner as in Example 1, and subjected to various measurements, evaluations, and the like. The results are shown in Table 1.

Example 3
Seed particles were produced in the same manner as in Example 1, except that the resin type and resin usage amount were changed as shown in Table 1. Next, the steps up to the second polymerization were performed in the same manner as in Example 1. After the particles after the second polymerization were cooled to 30° C. or lower, 50 g of triallylisocyanurate hexabrominated compound (flame retardant) and 10 g of dicumyl peroxide (flame retardant aid) were added to the autoclave. After raising the temperature to 130°C, this temperature was maintained for 2 hours to produce flame retardant-containing composite resin particles. Thereafter, the mixture was cooled to 30° C. or lower, and the composite resin particles (styrene composite polyethylene resin particles) were taken out from the autoclave. The mass ratio of seed particles to polystyrene was 40/60.
Using these composite resin particles, expandable particles, expanded particles, and a foamed molded article were produced in the same manner as in Example 1, and subjected to various measurements, evaluations, and the like. The results are shown in Table 1.

Example 4
Seed particles, composite resin particles, expandable particles, foamed particles, and foamed molded bodies were produced in the same manner as in Example 3, except that the resin type and resin usage amount were changed to those listed in Table 1, and various measurements, evaluations, etc. Served. The results are shown in Table 1.

Example 5
Seed particles, composite resin particles, expandable particles, Expanded particles and foamed molded articles were manufactured and subjected to various measurements, evaluations, etc. The results are shown in Table 1.
[Preparation of expandable particles]
2 kg (100 parts by mass) of composite resin particles were charged into an autoclave having an internal volume of 5 liters. Further, carbon dioxide gas was introduced as a foaming agent and was pressurized until the internal pressure of the autoclave reached 3.0 MPa in terms of gauge pressure. Expandable particles were obtained by allowing the autoclave to stand for 12 hours while maintaining the pressure inside the autoclave at 3.0 MPa. Thereafter, the autoclave was depressurized to obtain expandable particles.

Examples 6-7 and Comparative Examples 1-2
Seed particles, composite resin particles, expandable particles, foam particles, and foamed molded bodies were produced in the same manner as in Example 1, except that the resin type, resin usage amount, and blowing agent type were changed to those listed in Table 1. It was used for measurement, evaluation, etc. The results are shown in Table 1.

By using seed particles containing high-density polyethylene and styrene-acrylonitrile copolymer, a foam molded product that can be molded at low steam pressure and has a low dimensional change rate was obtained (Example 3). It was confirmed that it can be produced at low cost and has excellent dimensional stability.
The foam molded product of Example 3 can be molded at lower steam pressure compared to the foam molded product (Comparative Example 1) using seed particles containing high-density polyethylene and ethylene-vinyl acetate copolymer. It was confirmed that it can be produced at low cost. The foamed molded article of Example 3 had better dimensional stability than the foamed molded article (Comparative Example 2) using seed particles containing low-density polyethylene, styrene-acrylonitrile copolymer, and ethylene-vinyl acetate copolymer. It was confirmed that it is excellent.

Good results were obtained in various evaluations whether the styrene-acrylonitrile copolymer content in the seed particles was one-twentieth or one-half of the high-density polyethylene content (Example 6 and 7).

Foam molded articles using seed particles containing high-density polyethylene, styrene-acrylonitrile copolymer, and ethylene-vinyl acetate copolymer showed good flame retardancy even without flame retardant (conducted). Example 1).

Claims (16)

High-density polyethylene resin particles used as seed particles for producing composite resin particles for producing expanded particles,
The high-density polyethylene resin particles contain high-density polyethylene and a styrene-acrylonitrile copolymer,
The high-density polyethylene resin particles contain 5 to 100 parts by mass of the styrene-acrylonitrile copolymer based on 100 parts by mass of the high-density polyethylene,
The high density polyethylene has a softening temperature of 115 to 130°C,
The styrene-acrylonitrile copolymer has a softening temperature of 95 to 110°C.
High-density polyethylene resin particles. The high-density polyethylene resin particles according to claim 1, further comprising 50 to 400 parts by mass of an ethylene copolymer based on 100 parts by mass of the high-density polyethylene. The high-density polyethylene-based resin particles according to claim 2, wherein the high-density polyethylene-based resin particles contain 5 to 50 parts by mass of the styrene-acrylonitrile copolymer based on 100 parts by mass of the high-density polyethylene. 4. The ethylene copolymer is a copolymer of ethylene and at least one monomer selected from acrylic acid alkyl ester, methacrylic acid alkyl ester, and aliphatic saturated vinyl monocarboxylate. High-density polyethylene resin particles. Composite resin particles obtained by impregnating and polymerizing the high-density polyethylene resin particles according to any one of claims 1 to 4 with a styrene monomer,
Containing a high-density polyethylene resin derived from the high-density polyethylene resin particles and a styrenic polymer obtained by polymerizing the styrenic monomer,
Composite resin particles. The composite resin particles according to claim 5, containing 100 to 500 parts by mass of the styrene polymer based on 100 parts by mass of the high-density polyethylene resin. The composite resin particle according to claim 5 or 6, further comprising a flame retardant. The composite resin particles according to claim 7, wherein the content of the flame retardant is 1.5 to 6% by mass based on the total mass of the high-density polyethylene resin and the styrene polymer. The composite resin particle according to claim 7 or 8, wherein the flame retardant is a halogen-based flame retardant. The composite resin particles according to any one of claims 7 to 9, further comprising a flame retardant aid. The composite resin particles according to claim 5 or 6, which do not contain a halogen flame retardant. Expanded particles obtained by foaming the composite resin particles according to any one of claims 5 to 11. A foam molded article obtained by foam molding the foam particles according to claim 12. The foamed molded article according to claim 13, having a density of 20 to 50 kg/m ³ . The foamed molded article according to claim 13 or 14, which has a dimensional change rate under heating of 10/1000 or less under conditions of 80° C. and 168 hours. The foam molded article according to any one of claims 13 to 15, which has a burning rate of 80 mm/min or less in the FMVSS302 combustion test using a foam molded specimen having a density of 33 kg/m ³ or is self-extinguishing.