JP6962761B2 - Composite resin particles, their manufacturing methods, foamable particles, foamed particles and foamed molded products - Google Patents

Description

The present invention relates to composite resin particles, a method for producing the same, foamable particles, foamed particles, and a foamed molded product. The present invention relates to foamed particles having improved antistatic performance and composite resin particles capable of giving a foamed molded product, a method for producing the same, foamable particles, foamed particles having improved antistatic performance, and a foamed molded product.

A foam molded product made of a polystyrene resin has excellent cushioning and heat insulating properties, but has insufficient impact resistance and flexibility. On the other hand, a foam molded product made of a polyolefin resin is excellent in impact resistance and flexibility, but has insufficient rigidity. Therefore, a foam molded product using composite resin particles, which has the features of the two resins by using two different resins in combination, has been proposed. This foam molded product is often used as a cushioning material during transportation of various articles.
By the way, the foam molded product is known to have high chargeability. The high chargeability causes a problem that static electricity is accumulated in the foamed molded product, and the accumulated static electricity attracts dust. This dust adheres to the article during transportation and reduces the commercial value of the article. Further, when the article is an electronic device, a defect may occur in the electronic device due to a short circuit due to adhesion of dust or electrostatic destruction due to accumulated static electricity. Therefore, it has been required to reduce the chargeability of the foam molded product. In response to this request, a technique for coating a foam molded product with an antistatic agent has been proposed (Japanese Unexamined Patent Publication No. 2014-193949: Patent Document 1).
Patent Document 1 states that a foam molded product having suppressed antistatic properties can be obtained by applying or spraying a solution containing an antistatic agent on the foam molded product.

Japanese Unexamined Patent Publication No. 2014-193949

However, since the solution containing the antistatic agent is inferior in wettability to the foamed molded product, the foamed molded product cannot be uniformly covered with the antistatic agent, and there is a drawback that the suppression of antistatic property becomes non-uniform. Further, since the antistatic agent is only attached to the surface of the foamed molded product, it may be easily transferred to the article. This transition has also led to the drawback of corroding the metal wiring that makes up the electronic device when the article is an electronic device.
Therefore, it is desired to provide a foamed molded product capable of uniformly suppressing the chargeability and preventing the transfer of the antistatic agent to the article, and composite resin particles, foamable particles and foamed particles capable of giving the foamed molded product. Was there.

As a result of diligent studies, the inventor of the present invention can produce a foamed molded product having excellent antistatic properties by using composite resin particles containing a boron-containing compound as an antistatic agent in a specific range from the surface layer to the center. This has led to the completion of the present invention.
Thus, according to the present invention, the production of foamed particles containing a polyolefin-based resin and a polystyrene-based resin in the ranges of 38.8 to 17.9 % by mass and 61.2 to 82.1% by mass, respectively, based on the total of these. It is a composite resin particles of use,
A foamed molded product having a size of 100 mm × 100 mm × 30 mm obtained from the composite resin particles as an antistatic agent corresponding to an amount of boron of 1.0 to 15.0 mg per kg of the composite resin particles. Contains boron-containing compounds so that the amount of boron transferred to ultrapure water is 0.20 mg / L or less when immersed in 100 mL of ultrapure water at 25 ° C. for 72 hours with skins on both sides. , The boron-containing compound is present from the surface layer to the center of the composite resin particles , and
When the composite resin particles expose the foamed molded product obtained from the composite resin particles to the foamed molded product in an environment of a temperature of 65 ° C. and a humidity of 90% for 500 hours , the surface resistance of the ^{foamed molded product is 1 × 10 10 Ω or less.} Composite resin particles are provided that are characterized by giving a value.

Further, according to the present invention, there is a method for producing the composite resin particles.
Seed particles are obtained by cutting a boron-containing compound or a masterbatch made of a polyolefin-based resin containing a boron-containing compound and a melt of the polyolefin-based resin.
Provided is a method for producing composite resin particles, which comprises obtaining composite resin particles by impregnating and polymerizing the seed particles with a styrene-based monomer.
Further, according to the present invention, foamable particles containing the composite resin particles and a volatile foaming agent are provided.
Further, according to the present invention, foamed particles obtained by foaming the foamable particles are provided.
Further, according to the present invention, there is provided a foam molded product obtained by foam molding the above foam particles.

According to the present invention, it is possible to provide foamed particles having improved antistatic performance and composite resin particles capable of giving a foamed molded product, a method for producing the same, foamable particles, foamed particles having improved antistatic performance, and a foamed molded product.
In any of the following cases, it is possible to provide foamed particles having improved antistatic performance and composite resin particles capable of giving a foamed molded product.
(1) For the composite resin particles, a foamed molded product having a size of 100 mm × 100 mm × 30 mm obtained from the composite resin particles was immersed in 100 ml of ultrapure water at 25 ° C. for 72 hours with skins on both sides thereof. At that time, the boron-containing compound is contained so that the amount of boron transferred to ultrapure water is 0.20 mg / L or less.
(2) The boron-containing compound is a donor-acceptor-based molecular compound obtained by reacting a semi-polar organoboron compound as a donor component with a basic nitrogen compound as an acceptor component.
(3) The composite resin particles have a surface resistance ^{of 1 × 10 10} Ω or less when the foamed molded product obtained from the composite resin particles is exposed to the foamed molded product in an environment of a temperature of 65 ° C. and a humidity of 90% for 500 hours. Give a value.
(4) The polyolefin-based resin is selected from ethylene-vinyl acetate copolymer, high-density polyethylene, linear low-density polyethylene, and a mixture thereof.

(Composite resin particles)
The composite resin particles are used for producing foamed particles. Further, the composite resin particles contain a polyolefin resin and a polystyrene resin in the range of 50 to 10% by mass and 50 to 90% by mass, respectively, with respect to the total of these. Further, the composite resin particles contain a boron-containing compound as an antistatic agent corresponding to an amount of boron of 1.0 to 15.0 mg per kg thereof. Furthermore, the boron-containing compound is present from the surface layer to the center of the composite resin particles.

(1) Polyolefin-based resin The polyolefin-based resin is not particularly limited, and known resins can be used. Moreover, the polyolefin resin may be crosslinked. For example, polyethylene-based resins such as branched low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-methylmethacrylate copolymer, and crosslinked products of these polymers. , Polyethylene homopolymer, propylene-vinyl acetate copolymer, ethylene-propylene random copolymer, propylene-1-butene copolymer, ethylene-propylene-butene random copolymer and other polypropylene-based resins. In the above example, low density is preferably 0.91~0.94g / cm ^3, more preferably 0.91~0.93g / cm ^3. High density is preferably 0.95~0.97g / cm ^3, more preferably 0.95~0.96g / cm ^3. Medium density is an intermediate density between these low and high densities. The polyolefin-based resin can be preferably selected from ethylene-vinyl acetate copolymer, high-density polyethylene, linear low-density polyethylene, and mixtures thereof.

(2) Polystyrene-based resin The polystyrene-based resin is not particularly limited as long as it is a resin containing a styrene-based monomer as a main component, and examples thereof include styrene or a styrene derivative alone or a copolymer.
Examples of the styrene derivative include α-methylstyrene, vinyltoluene, chlorostyrene, ethylstyrene, isopropylstyrene, dimethylstyrene, bromostyrene and the like. These styrene-based monomers may be used alone or in combination.

The polystyrene-based resin may be a combination of a styrene-based monomer and a copolymerizable vinyl-based monomer.
Examples of the vinyl-based monomer include divinylbenzene such as o-divinylbenzene, m-divinylbenzene, and p-divinylbenzene, and alkylene glycol di (meth) acrylate such as ethylene glycol di (meth) acrylate and polyethylene glycol di (meth) acrylate. Polyfunctional monomers such as meta) acrylate; (meth) acrylonitrile, methyl (meth) acrylate, butyl (meth) acrylate and the like can be mentioned. Among these, polyfunctional monomers are preferable, ethylene glycol di (meth) acrylate, polyethylene glycol di (meth) acrylate having 4 to 16 ethylene units, and divinylbenzene are more preferable, and divinylbenzene and ethylene glycol di (divinylbenzene). Meta) acrylate is particularly preferred. The monomer may be used alone or in combination of two or more.
When a monomer is used in combination, the content thereof is preferably set so that the styrene-based monomer is the main component (for example, 50% by mass or more).

(3) Content ratio of resin component The polyolefin-based resin and the polystyrene-based resin are contained in the range of 50 to 10% by mass and 50 to 90% by mass, respectively, with respect to the total of these.
If the polystyrene-based resin is less than 50% by mass, the foamability and molding processability may be insufficient. On the other hand, when the polystyrene-based resin is more than 90% by mass, the impact resistance and flexibility may be insufficient.
The polyethylene-based resin and the polystyrene-based resin are preferably contained in the ranges of 40 to 15% by mass and 60 to 85% by mass, respectively, with respect to the total of these.

(4) Boron-Containing Compound The boron-containing compound functions as an antistatic agent and is not particularly limited as long as it contains boron. For example, a boron-containing compound composed of an acceptor component and a boron-containing donor component can be mentioned.
Accepter components include, for example, ammonium cation, pyridinium cation, pyrazinium cation, quinolium cation, isoquinolium cation, oxonium cation, pyrylium cation, sulfonium cation, sulfoxonium cation, phosphonium cation, iodonium cation, iodine. Examples thereof include xonium cation, imidazolium cation, oxazolium cation, thiazolium cation, benzoimidazolium cation, benzoxazolium cation and benzothiazolium cation.
Examples of the donor component include a component in which four substituents are bonded to a boron atom. Examples of the four substituents include a hydrogen atom, an alkyl group, an alkenyl group, an alkynyl group, an alkoxy group, an aryl group and a heterocyclic group, which are the same or different. Of the four substituents, two adjacent substituents may be bonded to form a ring together with the boron atom.
Suitable boron-containing compounds include compounds represented by the following formula (1).

The above compound is a donor-acceptor-based molecular compound obtained by reacting a semi-polar organoboron compound as a donor component with a basic nitrogen compound as an acceptor component. This donor-acceptor-based molecular compound can impart the desired antistatic property to the foamed molded article in a relatively small amount. Therefore, it is a compound that does not easily adversely affect the process from obtaining the foamed molded product from the composite resin particles.
In the above formula, R1 to 4 are alkyl groups which may have the same or different substituents. The number of carbon atoms of the alkyl group is preferably 1 to 4 (however, the number of carbon atoms constituting the substituent is not included). Alkyl groups include structural isomers. Examples of the substituent include a hydroxyl group and an alkylcarbonyloxy group having 1 to 20 carbon atoms. Examples of R5 include a bond, an alkylene group (for example, 1 to 4 carbon atoms) and the like.
Specific examples of R1 and R2 include R _f- CO-OCH _2- (R _f is an alkyl group having 1 to 20 carbon atoms) and HOCH _2- . As R3 and _{R4, CH 3 -, C 2} H 5 -, HOCH 2 -, HOC 2 H 4 - and HOCH ₂ CH (CH ₃₎ -, and the like. Examples of R5 include a bond, −CH ₂ −, −C ₂ H ₄ − and −C ₃ H ₆ −.
Examples of the compound represented by the formula (1) include a biomicelle series manufactured by Boron Research Institute. In particular, biomicelle BN-105 is suitable.

The amount of boron in the composite resin particles is 1.0 to 15.0 mg per 1 kg of the composite resin particles. The composite resin particles contain an amount of boron-containing compound corresponding to the amount of boron. If the amount of boron is less than 1.0 mg, the antistatic effect may not be sufficiently obtained. If the amount of boron is more than 15.0 mg, the process from obtaining the foamed molded product from the composite resin particles may be adversely affected. The amount of boron is preferably 2.0 to 11.0 mg, more preferably 3.0 to 8.0 mg.
The boron-containing compound is present from the surface layer to the center of the composite resin particles. Therefore, in the foamed molded product obtained from the composite resin particles, the desorption of the boron-containing compound is suppressed. The presence state of the boron-containing compound in the composite resin particles may be uniformly present from the surface layer to the central portion as long as desorption can be suppressed, or may be unevenly distributed.

(5) Physical Properties The composite resin particles are obtained by immersing a foamed molded product having a size of 100 mm × 100 mm × 30 mm obtained from the composite resin particles in 100 mL of ultrapure water at 25 ° C. for 72 hours with skins on both sides thereof. It is preferable to contain a boron-containing compound so that the amount of boron transferred to ultrapure water is 0.20 mg / L or less. When the amount of boron is 0.20 mg / L or less, it means that the boron-containing compound contained in the foamed molded product obtained from the composite resin particles is hard to fall off. As a result, it is possible to provide a foam molded product capable of uniformly suppressing the antistatic property and preventing the transfer of the antistatic agent to the article. The amount of boron is more preferably 0.15 mg / L or less, and further preferably 0.10 mg / L or less. The lower limit of the amount of boron is 0 mg / L.
The composite resin particles are foam-molded when the foamed molded product obtained from the composite resin particles is exposed to an environment of a temperature of 65 ° C. and a humidity of 90% for 500 hours as an accelerated test for measuring deterioration of antistatic properties. It is preferable to give the body a surface resistance value of 1 × 10 ^{10 Ω or less.} Having this surface resistance value means that the boron-containing compound contained in the composite resin particles does not adhere to the surface and exists from the surface layer to the central portion. In addition, having this surface resistance value means that if the composite resin particles of the present invention are used in the production of foamed particles, the antistatic performance can be maintained for a long period of time, and an antistatic agent for other articles in contact with the foamed molded product. It means that the transition of can be suppressed.
The composite resin particles preferably have an average particle size of 1.0 to 2.0 mm. The average particle size is more preferably 1.2 to 1.6 mm.
The mass average molecular weight of the composite resin particles: Mw is about 250,000 to 450,000. The mass average molecular weight can be measured using gel permeation chromatography (GPC).

(6) Production method The composite resin particles are not particularly limited, but can be produced by, for example, a seed polymerization method. (A) Seed polymerization method In the seed polymerization method, the seed particles generally absorb the monomer and then absorb the monomer. Alternatively, composite resin particles can be obtained by polymerizing the monomers while absorbing them. It is also possible to obtain effervescent particles by impregnating the composite resin particles with a foaming agent after or while polymerizing.

Specifically, first, the composite resin particles are obtained by allowing the seed particles to absorb the styrene-based monomer in an aqueous medium, and then polymerizing the styrene-based monomer after or while absorbing the styrene-based monomer.
As for the styrene-based monomer, it is not necessary to supply all the monomers constituting the styrene-based monomer into the aqueous medium at the same time, and all or a part of the monomers may be supplied into the aqueous medium at different timings. When the additive is contained in the composite resin particles, the additive may be added to the styrene-based monomer or the aqueous medium, or may be contained in the seed particles.
The amounts of the monomer and the resin are almost the same.

The polymerization of the styrene-based monomer can be carried out, for example, by heating at 60 to 150 ° C. for 2 to 40 hours.
In the polymerization step, it is preferable to keep the polymerization temperature for a long time, that is, to anneal.
In the steps leading up to the annealing step, the styrene-based monomer and the polymerization initiator absorbed in the seed particles have not completely completed the reaction, and there are not a few unreacted substances inside the composite resin particles. doing. Therefore, when a foamed molded product is obtained using the composite resin particles obtained without annealing, the mechanical properties and heat resistance of the foamed molded product deteriorate due to the influence of low molecular weight unreacted substances such as styrene-based monomers. Odor caused by volatile unreacted substances becomes a problem. Therefore, by introducing the annealing step, it is possible to secure a time for the unreacted product to cause a polymerization reaction and remove the remaining unreacted product so as not to affect the physical properties of the foamed molded product.
Examples of the styrene-based monomer are given in the section of composite resin particles, and the amount used thereof is within the range described in the section of composite resin particles.

(B) Seed particles The seed particles include a polyolefin resin and a boron-containing compound. Seed particles can be obtained, for example, by mixing a polyolefin resin and a boron-containing compound, melt-kneading them, extruding them into strands, and cutting them to a desired particle size. The boron-containing compound may be used in the production of seed particles in the form of a masterbatch previously mixed with a polyolefin-based resin. By using the boron-containing compound in this form, the boron-containing compound can be more uniformly dispersed in the seed particles.
The particle size of the seed particles can be appropriately adjusted according to the average particle size of the composite resin particles. The preferred particle size is in the range of 0.2 to 1.5 mm, the average mass of which is 10 to 100 mg / 100 particles. The shape thereof includes a true sphere, an elliptical sphere (egg-like), a columnar shape, a prismatic shape, and the like.

(C) Aqueous medium Examples of the aqueous medium include water, a mixed medium of water and a water-soluble solvent (for example, a lower alcohol such as methyl alcohol or ethyl alcohol).

(D) Dispersant As the aqueous medium, a dispersant may be used to stabilize the dispersibility of the droplets of the styrene-based monomer and the seed particles. Examples of such dispersants include organic dispersants such as partially saponified polyvinyl alcohol, polyacrylate, polyvinylpyrrolidone, carboxymethyl cellulose, and methyl cellulose; magnesium pyrophosphate, calcium pyrophosphate, calcium phosphate, calcium carbonate, magnesium phosphate, and the like. Examples thereof include inorganic dispersants such as magnesium carbonate and magnesium oxide. Among these, an inorganic dispersant is preferable because it may be possible to maintain a more stable dispersed state.
When an inorganic dispersant is used, it is preferable to use a surfactant in combination. Examples of such a surfactant include sodium dodecylbenzene sulfonate, sodium α-olefin sulfonate and the like.

(E) Polymerization Initiator A styrene-based monomer is usually polymerized in the presence of a polymerization initiator. The polymerization initiator is usually impregnated into seed particles at the same time as the styrene-based monomer.
The polymerization initiator is not particularly limited as long as it has been conventionally used for polymerization of styrene-based monomers. For example, benzoyl peroxide, t-butyl peroxybenzoate, t-butyl peroxypivalate, t-butyl peroxy-2-ethylhexyl monocarbonate, t-butyl peroxyisopropyl carbonate, t-butyl peroxyacetate, 2, 2-t-Butylperoxybutane, t-Butylperoxy-3,3,5-trimethylhexanoate, di-t-butylperoxyhexahydroterephthalate, 2,5-dimethyl-2,5-bis (benzoyl) Peroxy) Organic peroxides such as hexane and dicumyl peroxide can be mentioned. These polymerization initiators may be used alone or in combination of two or more. The amount of the polymerization initiator used is, for example, in the range of 0.1 to 5 parts by mass with respect to 100 parts by mass of the styrene-based monomer.

In order to uniformly absorb the polymerization initiator from the seed particles or the growing particles, the polymerization initiator was suspended or emulsified and dispersed in the aqueous medium in advance when the polymerization initiator was added to the aqueous medium. It is preferable to add the above to the dispersion, or to dissolve the polymerization initiator in the styrene-based monomer in advance and then add it to the aqueous medium.

The preferable amount of the polymerization initiator added is 0.1 to 0.9 parts by mass per 100 parts by mass of the styrene-based monomer.
If the amount of the polymerization initiator added is less than 0.1 parts by mass, the molecular weight may become too high and the foamability may decrease. On the other hand, if the amount of the polymerization initiator added exceeds 0.9 parts by mass, the polymerization rate becomes too high, and the polystyrene-based resin particles may not be able to control the dispersion state in the polyolefin-based resin. A more preferable amount of the polymerization initiator is 0.2 to 0.5 parts by mass.

(F) Other components The composite resin particles include a plasticizer, a bond inhibitor, a bubble conditioner, a cross-linking agent, a filler, a lubricant, a colorant, a fusion accelerator, and a spread as long as the physical properties are not impaired. Additives such as a lubricant, a flame retardant and a flame retardant aid may be added.

The composite resin particles may contain a plasticizer having a boiling point of more than 200 ° C. under 1 atm in order to maintain good foam moldability even when the pressure of water vapor used during heat foaming is low.
Examples of the plasticizer include glycerin fatty acid esters such as phthalates, glycerin diacet monolaurate, glycerin tristearate, and glycerin diacet monostearate, adipates such as diisobutyl adipate, and plasticizers such as coconut oil. ..
The content of the plasticizer in the composite resin particles is preferably 0.1 to 3.0% by mass.

Examples of the bond inhibitor include calcium carbonate, silica, zinc stearate, aluminum hydroxide, ethylene bisstearate amide, tricalcium phosphate, dimethyl silicon and the like.
Examples of the bubble adjusting agent include ethylene bisstearic acid amide and polyethylene wax.
Examples of the cross-linking agent include 2,2-di-t-butylperoxybutane, 2,2-bis (t-butylperoxy) butane, dicumyl peroxide, and 2,5-dimethyl-2,5-di-t. -Organic peroxides such as butylperoxyhexane can be mentioned.
Examples of the filler include synthetically or naturally produced silicon dioxide and the like.
Examples of the lubricant include paraffin wax and zinc stearate.

Colorants include furnace black, ketjen black, channel black, thermal black, acetylene black, carbon black such as graphite and carbon fiber, chromate such as yellow lead, zinc yellow and barium yellow, and ferrocyanide such as dark blue. , Cadmium yellow, sulfides such as cadmium red, oxides such as iron black and red husks, silicates such as ultramarine, inorganic pigments such as titanium oxide, monoazo pigments, disazo pigments, azolakes, condensed azo pigments, chelate azo Examples thereof include azo pigments such as pigments, and organic pigments such as phthalocyanine-based, anthraquinone-based, perylene-based, perinone-based, thioindigo-based, quinacridone-based, dioxazine-based, isoindolinone-based, and quinophthalone-based polycyclic pigments.

Examples of the fusion accelerator include stearic acid, stearic acid triglyceride, hydroxystearic acid triglyceride, stearic acid sorbitan ester, polyethylene wax and the like.
Examples of the spreading agent include polybutene, polyethylene glycol, silicone oil and the like.

(Effervescent particles)
The foamable particles contain composite resin particles and a volatile foaming agent, and can be produced by impregnating the composite resin particles with a volatile foaming agent by a known method.
If the temperature at which the composite resin particles are impregnated with the volatile foaming agent is low, impregnation may take time and the production efficiency of the foamable particles may decrease, while if the temperature is high, the foamable particles may coalesce. Since it may occur in a large amount, it is preferably 50 to 130 ° C, more preferably 60 to 100 ° C.

(1) Foaming agent The volatile foaming agent is not particularly limited as long as it has been conventionally used for foaming polystyrene-based resins, and is, for example, isobutane, n-butane, isopentane, n-pentane, neopentane and the like. Examples thereof include volatile foaming agents such as aliphatic hydrocarbons having 5 or less carbon atoms, and butane-based foaming agents and pentane-based foaming agents are particularly preferable. Pentane can also be expected to act as a plasticizer.

The content of the volatile foaming agent in the effervescent particles is usually in the range of 5 to 13% by mass, preferably in the range of 8 to 12% by mass, and particularly preferably in the range of 9 to 11% by mass.
If the content of the volatile foaming agent is small, for example, less than 5% by mass, it may not be possible to obtain a low-density foamed molded product from the foamable particles, and the effect of increasing the secondary foaming force during in-mold foam molding. The appearance of the foamed molded product may be deteriorated because the foamed molded product is not obtained. On the other hand, if the content of the volatile foaming agent is large and exceeds, for example, 13% by mass, the time required for the cooling step in the manufacturing process of the foamed molded product using the foamable particles becomes long, and the productivity may decrease.

(2) Foaming aid The effervescent particles can contain a foaming aid together with the foaming agent.
The foaming aid is not particularly limited as long as it is conventionally used for foaming polystyrene-based resins, and examples thereof include aromatic organic compounds such as styrene, toluene, ethylbenzene, and xylene, cyclohexane, and methylcyclohexane. Examples thereof include solvents such as cyclic aliphatic hydrocarbons, ethyl acetate, and butyl acetate having a boiling point of 200 ° C. or lower under 1 atmospheric pressure.

The content of the foaming aid in the foamable particles is usually in the range of 0.3 to 3.5% by mass, preferably in the range of 0.5 to 2% by mass.
If the content of the foaming aid is small, for example, less than 0.3% by mass, the plasticizing effect of the polystyrene resin may not be exhibited. On the other hand, if the content of the foaming aid is large and exceeds 3.5% by mass, the foamed molded product obtained by foaming the foamable particles shrinks or melts to deteriorate the appearance, or the foamable particles are formed. The time required for the cooling step in the manufacturing process of the foamed molded product used may become long.

(Foam particles)
The foamed particles are obtained by foaming the foamable particles to a predetermined bulk density by a known method, and examples thereof include batch type foaming in which steam is introduced, continuous foaming, and release foaming under pressure.
The foamed particles preferably have a bulk density in the range of 20 to 200 kg / m ^3. If the bulk density of the foamed particles ^{is less than 20 kg / m 3} , the foamed molded product tends to shrink and the appearance may be impaired. On the other hand, if the bulk density of the foamed particles ^{exceeds 200 kg / m 3} , the merit of weight reduction as a foamed molded product may be impaired. The preferred bulk density of effervescent particles is in the range of ^{20-100 kg / m 3.}
In foaming, air may be introduced at the same time as steam when foaming, if necessary.

(Foam molded product)
The foamed molded product is obtained by a known method, for example, by filling the mold of the foam molding machine with the foamed particles and heating the foamed particles again to foam the foamed particles while heat-sealing the foamed particles to each other.
The foam molded product preferably has a density in the range of 20 to 200 kg / m ^3. If the density of the foam molded product ^{is less than 20 kg / m 3} , the slow flame resistance and impact resistance may not be sufficient. On the other hand, if the density of the foamed molded product ^{exceeds 200 kg / m 3} , the mass of the foamed molded product increases and the transportation cost increases, which may not be preferable. The preferred foam molding density is in the range of ^{20-100 kg / m 3.}
Foam moldings are used for cushioning materials (cushion materials) for home appliances, electronic parts, various industrial materials, transport containers for foods, etc., and impact energy for automobile-related parts (for example, core materials for vehicle bumpers, cushioning materials for door interiors, etc.) It can be used as an absorbent material, a shock absorbing material for lower limbs, a floor raising material, a tool box, etc.

Hereinafter, the present invention will be specifically described with reference to Examples and Comparative Examples, but the following Examples are merely examples of the present invention, and the present invention is not limited to the following Examples.
In Examples and Comparative Examples, the obtained composite resin particles, foamed particles and foamed molded product were evaluated as follows.
<Analysis of boron content and metal element content of composite resin particles (ICP measurement)>
(Pretreatment method)
Approximately 1.0 g of the sample was precisely weighed, ashed at 450 ° C. × 3 hr, 2 mL of concentrated hydrochloric acid was added, and then the insoluble matter was No. 7 Filtered with filter paper. The obtained filtrate was scalpel-up to 50 mL, the boron (B) concentration was measured under the following conditions, and the amount of B in the sample was calculated from the calibration curve.
B amount (mg / kg) = B concentration (μg / mL) x 50 (mL) ÷ sample weight (g)
(ICP measurement conditions)
Measuring device: Shimadzu multi-type ICP emission spectroscopic analyzer ICPE-9000
Element to be measured: B (249.773 nm)
Observation direction = axial direction, high frequency output = 1.20 kW, carrier flow rate = 0.7 L / min, plasma flow rate = 10.0 L / min, auxiliary flow rate = 0.6 L / min, exposure time = 30 seconds Standard solution for calibration line : US SPEX XSTC-8 (general-purpose mixed standard solution) 13-element mixture (base 5% HNO ₃ ) -Approximately 10 mg / L each diluted appropriately with ultrapure water, 5 ppm, 2.5 ppm, 1 ppm, 0.25 ppm A standard solution was prepared.
(Ashes condition)
Measuring device: Electric furnace Muffle furnace STR-15K (manufactured by Isuzu)
Ashification conditions: 450 ° C x 3 hr (sample amount = about 1.0 g)

<Volume density and bulk factor of foamed particles>
The bulk density of the foamed particles is measured as follows.
First, the foamed particles are filled in a graduated ^{cylinder up to a scale of 500 cm 3.} However, when the measuring cylinder is visually inspected from the horizontal direction and even one of the foamed particles ^{reaches the scale of 500 cm 3} , filling is completed. Next, the mass of the foamed particles filled in the graduated cylinder is weighed with two significant figures after the decimal point, and the mass is defined as W (g). The bulk density of the foamed particles is calculated by the following formula.
Bulk density (kg / m ³ ) = W ÷ 500 × 1000
The bulk multiple is 1000 times the reciprocal of the bulk density.

<Density of foam molded product and multiple of foam>
The density of the foam molded product is measured by the method described in JIS A9511: 1995 "Foam plastic heat insulating plate".
A test piece of 10 cm × 10 cm × 3 cm (300 cm ³ ) is cut out from the obtained foamed molded product, and its mass W (g) is weighed in two decimal places.
From the mass W of the obtained foamed molded product and the volume of the foamed molded product, the foaming multiple (times) is calculated by the following formula.
Density of foam molded product (kg / m ³ ) = W ÷ 300 × 1000
1000 times the reciprocal of the density is a multiple.

<Surface specific resistance value of foam molded product>
Measurement was performed by the method described in JIS K 6911: 1995 "General Test Method for Thermosetting Plastics". That is, using a test device (Advantest digital ultra-high resistance / micro ammeter R8340 and resiliency chamber R12702A), the electrode was crimped to the sample sample with a load of about 30 N, and the resistance after charging at 500 V for 1 minute. The value was measured. The surface resistivity was calculated from the measured values by the following formula.
ρs = π (D + d) / (D−d) × Rs
ρs: Surface resistivity (MΩ)
D: Inner diameter (cm) of the annular electrode on the surface
d: Outer shape of the inner circle of the surface electrode (cm)
Rs: Surface resistance (MΩ)
Sample The sample had a size of 100 mm × 100 mm × thickness 10 mm or less, and was cut out from the same foam molded product.
The sample sample was stored in an environment of 20 ° C. and 65% humidity for about 24 hours, and then the resistance value of the sample sample was measured.

<Boron amount metal element elution test (ICP measurement) by water extraction test of foamed molded product>
(Pretreatment method (dissolution test of molded product))
(1) The foam molded product was cut into 100 (mm) × 100 (mm) × thickness 30 (mm) (with double-sided skin).
(2) The above sample was placed in a zipper bag, 100 mL of ultrapure water was added, and the sample was allowed to stand on a horizontal surface and left in an environment of 25 ° C. for 3 days.
(3) The obtained boron (B) concentration (mg / L) in ultrapure water was measured under the following conditions and calculated from the calibration curve. The amount of boron below the measurement limit is indicated as "ND".
When the amount of boron in ultrapure water was 0.20 mg / L or less, it was evaluated as “◯”, and when it exceeded 0.20 mg / L, it was evaluated as “x”.
(ICP measurement conditions)
Measuring device: Shimadzu multi-type ICP emission spectroscopic analyzer ICPE-9000
Element to be measured: B (249.773 nm)
Observation direction = axial direction, high frequency output = 1.20 kW, carrier flow rate = 0.7 L / min, plasma flow rate = 10.0 L / min, auxiliary flow rate = 0.6 L / min, exposure time = 30 seconds Standard solution for calibration line : US SPEX XSTC-8 (general-purpose mixed standard solution) 13-element mixture (base 5% HNO ₃ ) -Approximately 10 mg / L each diluted appropriately with ultrapure water, 5 ppm, 2.5 ppm, 1 ppm, 0.25 ppm A standard solution was prepared.

Example 1
(Preparation of composite resin particles)
100 parts by mass of polyethylene resin (linear low density polyethylene LLDPE: Harmorex NF366A manufactured by Japan Polyethylene Corporation) and 5 parts by mass of master batch (Biomicelle BN-105 manufactured by Boron Research Institute) containing an antistatic agent are used in a tumbler mixer. It was charged and mixed for 10 minutes.
Next, this resin mixture is supplied to a single-screw extruder (model: CER40Y 3.7MB-SX, manufactured by Hoshi Plastic Co., Ltd., diameter 40 mmφ, die plate (diameter 1.5 mm)) and melt-kneaded at a temperature of 230 to 250 ° C. , Cut into a cylindrical shape of 0.40 to 0.60 mg / piece (average 0.5 mg / piece) with a fan cutter (manufactured by Hoshi Plastic Co., Ltd., model: FCW-110B / SE1-N) by the strand cut method, and seed particles. Got
Biomicelle BN-105 is a masterbatch containing a donor-acceptor-based molecular compound as an antistatic agent in a polyethylene-based resin, and is a white granular solid having an active ingredient of 99% or more. In the donor-acceptor-based molecular compound, in the above formula (1), R1 and R2 are CH ₃ (CH ₂ ) _16- CO-OCH ₂ or HOCH ₂ , and at least one of them is CH ₃ (CH ₂ ) _16- CO. -OCH ₂ , R3 and R4 are CH ₃ , C ₂ H ₅ , HOCH ₂ , HOC ₂ H ₄ , or HOCH ₂ CH (CH ₃ ), and R 5 is the compound of the acceptor.
Next, 30 g of magnesium pyrophosphate and 0.15 g of sodium dodecylbenzenesulfonate were dispersed in 1.9 kg of pure water in a 5 liter autoclave equipped with a stirrer to obtain a dispersion medium.

400 g of the seed particles were dispersed in a dispersion medium at 30 ° C. and held for 10 minutes, and then the temperature was raised to 60 ° C. to obtain a suspension.
Further, 200 g of a styrene monomer in which 0.50 g of dicumyl peroxide as a polymerization initiator was dissolved was added dropwise to this suspension over 30 minutes. The seed particles were impregnated with the styrene monomer by holding for 60 minutes after the dropping. After impregnation, the temperature was raised to 135 ° C., and polymerization (first polymerization) was carried out at this temperature for 2 hours.

Next, in a suspension cooled to 115 ° C., an aqueous solution prepared by dissolving 0.65 g of sodium dodecylbenzenesulfonate in 0.1 kg of pure water was added, and then 4.8 g of t-butylperoxybenzoate was dissolved. 1400 g of styrene monomer was added dropwise over 4 hours. The total amount of styrene monomer was 400 parts by mass with respect to 100 parts by mass of seed particles. After the dropping, 3.4 g of ethylene bisstearic acid amide was added as a bubble adjusting agent, and the mixture was kept at 115 ° C. for 1 hour to impregnate the linear low-density polyethylene-based resin particles with the styrene monomer. After impregnation, the temperature was raised to 140 ° C., and the temperature was maintained at this temperature for 2 hours for polymerization (second polymerization). As a result of this polymerization, composite resin particles could be obtained.

(Preparation of effervescent particles)
Then, the mixture was cooled to 30 ° C. or lower, and the composite resin particles were taken out from the autoclave. 2 kg of composite resin particles, 2 liters of water and 0.50 g of sodium dodecylbenzene sulfonate were placed in a 5 liter autoclave with a stirrer. Further, 520 ml (300 g) of butane (n-butane: isobutane = 7: 3 (mass ratio)) was placed in the autoclave as a foaming agent. After that, the temperature was raised to 70 ° C. and stirring was continued for 3 hours to obtain effervescent particles.
Then, the temperature was cooled to 30 ° C. or lower, and the effervescent particles were taken out from the autoclave and dehydrated and dried.

(Preparation of foamed particles and foamed molded product)
Then, the obtained foamable particles were foamed to a bulk density of 50 kg / m ³ to obtain foamed particles. The obtained foamed particles were allowed to stand at room temperature (23 ° C.) for 1 day, and then placed in a molding die having a size of 400 mm × 300 mm × 30 mm. Then, 0.10 MPa (gauge pressure) of water vapor is introduced for 50 seconds to heat the foamed molded product, and then the foamed molded product is cooled until the surface pressure of the foamed molded product drops to 0.01 MPa to obtain a foamed molded product ^{having a density of 50 kg / m 3.} Got
The appearance and fusion of the obtained foamed molded product were both good.

Example 2
A foamed molded product was obtained in the same manner as in Example 1 except that the amount of the masterbatch added was 10 parts by mass and the bulk density of the foamed particles and the density of the foamed molded product were 33.3 kg / m ^3. The appearance and fusion of the obtained foamed molded product were both good.
Example 3
A foamed molded product was obtained in the same manner as in Example 1 except that the amount of the masterbatch added was 15 parts by mass and the bulk density of the foamed particles and the density of the foamed molded product were 25.0 kg / m ^3. The appearance and fusion of the obtained foamed molded product were both good.
Example 4
First polymerization using polyethylene resin (high density polyethylene HDPE: TOSOH-HMS grade name: 10S65B, density 0.940 g / cm ³ , mp126 ° C, MFR 2.0 g / 10 minutes) instead of LLDPE. The amount of seed particles at the time was 600 g, the amount of styrene monomer was 240 g, the amount of styrene monomer at the time of the second polymerization was 1160 g, the temperature at the time of the second polymerization was 125 ° C., and t-butylper. A foamed molded product was obtained in the same manner as in Example 1 except that the oxybenzoate was changed to dicumyl peroxide and the bulk density of the foamed particles and the density of the foamed molded product were 33.3 kg / m ^3. The appearance and fusion of the obtained foamed molded product were both good.
Example 5
Using HDPE of Example 4 instead of LLDPE, the amount of the master batch added was 10 parts by mass, the amount of seed particles at the time of the first polymerization was 600 g, the amount of styrene monomer was 240 g, and the second Foam molding in the same manner as in Example 1 except that the amount of styrene monomer at the time of polymerization was 1160 g, the temperature at the time of the second polymerization was 125 ° C., and t-butyl peroxybenzoate was changed to dicumyl peroxide. I got a body. The appearance and fusion of the obtained foamed molded product were both good.

Example 6
The HDPE of Example 4 was used instead of the LLDPE, the amount of the master batch added was 15 parts by mass, the amount of seed particles at the time of the first polymerization was 600 g, the amount of the styrene monomer was 240 g, and the second The amount of styrene monomer at the time of polymerization was set to 1160 g, the temperature at the time of the second polymerization was changed to 125 ° C., t-butylperoxybenzoate was changed to dicumyl peroxide, and the bulk density of the foamed particles and the density of the foamed molded product were changed. A foamed molded product was obtained in the same manner as in Example 1 except that the value was 33.3 kg / m ^3. The appearance and fusion of the obtained foamed molded product were both good.
Example 7
A polyethylene resin (ethylene-vinyl acetate copolymer EVA: NUC-3450 manufactured by NUC) was used instead of LLDPE, and the amount of seed particles at the time of the first polymerization was 800 g and the amount of styrene monomer was 336 g. The same as in Example 1 except that the amount of styrene monomer at the time of the second polymerization was 864 g, the temperature at the time of the second polymerization was 90 ° C., and t-butylperoxybenzoate was changed to benzoyl peroxide. A foamed molded product was obtained. The appearance and fusion of the obtained foamed molded product were both good.
Example 8
EVA of Example 7 was used instead of LLDPE, the amount of the master batch added was 10 parts by mass, the amount of seed particles at the time of the first polymerization was 800 g, the amount of styrene monomer was 336 g, and the second The amount of styrene monomer at the time of polymerization was set to 864 g, the temperature at the time of the second polymerization was changed to 90 ° C., t-butylperoxybenzoate was changed to benzoyl peroxide, and the bulk density of the foamed particles and the density of the foamed molded product were changed. A foamed molded product was obtained in the same manner as in Example 1 except that the weight was 33.3 kg / m ^3. The appearance and fusion of the obtained foamed molded product were both good.
Example 9
EVA of Example 7 was used instead of LLDPE, the amount of the master batch added was 15 parts by mass, the amount of seed particles at the time of the first polymerization was 800 g, the amount of styrene monomer was 336 g, and the second The amount of styrene monomer at the time of polymerization was set to 864 g, the temperature at the time of the second polymerization was changed to 90 ° C., t-butylperoxybenzoate was changed to benzoyl peroxide, and the bulk density of the foamed particles and the density of the foamed molded product were changed. A foamed molded product was obtained in the same manner as in Example 1 except that the weight was 33.3 kg / m ^3. The appearance and fusion of the obtained foamed molded product were both good.

Example 10
EVA of Example 7 was used instead of LLDPE, the amount of the master batch added was 10 parts by mass, the amount of seed particles at the time of the first polymerization was 200 g, the amount of styrene monomer was 100 g, and the second The amount of styrene monomer at the time of polymerization was set to 1700 g, the temperature at the time of the second polymerization was changed to 90 ° C., t-butylperoxybenzoate was changed to benzoyl peroxide, and the bulk density of the foamed particles and the density of the foamed molded product were changed. A foamed molded product was obtained in the same manner as in Example 1 except that the weight was 33.3 kg / m ^3. The appearance and fusion of the obtained foamed molded product were both good.
Example 11
EVA of Example 7 was used instead of LLDPE, the amount of the master batch added was 20 parts by mass, the amount of seed particles at the time of the first polymerization was 200 g, the amount of styrene monomer was 100 g, and the second The amount of styrene monomer at the time of polymerization was set to 1700 g, the temperature at the time of the second polymerization was changed to 90 ° C., t-butylperoxybenzoate was changed to benzoyl peroxide, and the bulk density of the foamed particles and the density of the foamed molded product were changed. A foamed molded product was obtained in the same manner as in Example 1 except that the weight was 25.0 kg / m ^3. The appearance and fusion of the obtained foamed molded product were both good.
Example 12
The amount of the master batch added was 10 parts by mass, the amount of seed particles during the first polymerization was 300 g, the amount of styrene monomer was 150 g, and the amount of styrene monomer during the second polymerization was changed to 1550 g. A foamed molded product was obtained in the same manner as in Example 1 except that the bulk density of the foamed particles and the density of the foamed molded product were 25.0 kg / m ^3. The appearance and fusion of the obtained foamed molded product were both good.
Example 13
The amount of the master batch added was 15 parts by mass, the amount of seed particles during the first polymerization was 300 g, the amount of styrene monomer was 150 g, and the amount of styrene monomer during the second polymerization was changed to 1550 g. A foamed molded product was obtained in the same manner as in Example 1 except that the bulk density of the foamed particles and the density of the foamed molded product were 33.3 kg / m ^3. The appearance and fusion of the obtained foamed molded product were both good.

Comparative Example 1
A foamed molded product was obtained in the same manner as in Example 1 except that the amount of the masterbatch added was 4 parts by mass and the bulk density of the foamed particles and the density of the foamed molded product were 33.3 kg / m ^3. The appearance and fusion of the obtained foamed molded product were both good.
Comparative Example 2
HDPE of Example 4 was used instead of LLDPE, the amount of the master batch added was 2.5 parts by mass, the amount of seed particles at the time of the first polymerization was 600 g, the amount of styrene monomer was 240 g, and the first The amount of styrene monomer at the time of polymerization of 2 was set to 1160 g, the temperature at the time of second polymerization was changed to 125 ° C., t-butylperoxybenzoate was changed to dicumyl peroxide, and the bulk density of foamed particles and the foamed molded product were changed. A foamed molded product was obtained in the same manner as in Example 1 except that the density of the mixture was 33.3 kg / m ^3. The appearance and fusion of the obtained foamed molded product were both good.
Comparative Example 3
EVA of Example 7 was used instead of LLDPE, the amount of the master batch added was 2 parts by mass, the amount of seed particles at the time of the first polymerization was 800 g, the amount of styrene monomer was 336 g, and the second Foam molded article in the same manner as in Example 1 except that the amount of styrene monomer at the time of polymerization was 864 g, the temperature at the time of the second polymerization was 90 ° C., and t-butylperoxybenzoate was changed to benzoyl peroxide. Got The appearance and fusion of the obtained foamed molded product were both good.
Comparative Example 4
The amount of the master batch added was 3 parts by mass, the amount of seed particles during the first polymerization was 300 g, the amount of styrene monomer was 150 g, and the amount of styrene monomer during the second polymerization was changed to 1550 g. A foamed molded product was obtained in the same manner as in Example 1 except that the bulk density of the foamed particles and the density of the foamed molded product were 33.3 kg / m ^3. The appearance and fusion of the obtained foamed molded product were both good.

Comparative Example 5
Perestat 300 (manufactured by Sanyo Kasei Co., Ltd.) was used for the master batch, the amount of the master batch added was 20 parts by mass, the amount of seed particles at the time of the first polymerization was 600 g, and the amount of styrene monomer was 240 g. As a result of changing the amount of the styrene monomer at the time of polymerization of No. 2 to 1160 g, a large number of bonded particles were generated during the polymerization step, and good composite resin particles could not be obtained.

Comparative Example 6
A polyethylene resin (ethylene-vinyl acetate copolymer EVA: NUC-3450 manufactured by NUC) was used instead of LLDPE, the amount of the master batch added was 0 parts by mass, and the amount of seed particles at the time of the first polymerization was set. 800 g, the amount of styrene monomer is 336 g, the amount of styrene monomer at the time of the second polymerization is 864 g, the temperature at the time of the second polymerization is 90 ° C., and t-butylperoxybenzoate is changed to benzoyl peroxide. A foamed molded product was obtained in the same manner as in Example 1 except that it was changed. The appearance and fusion of the obtained foamed molded product were both good.
On the surface used for the measurement, apply a boron-based compound solution "Antista H (Boron Laboratory, an aqueous solution with a boron-based antistatic agent concentration of 1%)" to the surface surface of the molded body so that the boron-based compound is 30 g / m ² . It was sprayed evenly with a mist. Table 2 shows the surface specific resistance value and the result of the water extraction test.

Comparative Example 7
Polystyrene foamable resin particles were pre-foamed by a usual method and foam-molded in a mold to prepare a polystyrene-based foamed molded product (300 mm × 400 mm × 30 mm (t)) having ^{a molded product density of 33.3 kg / m 3.} On the surface used for the measurement, apply a boron-based compound solution "Antista H (Boron Laboratory, an aqueous solution with a boron-based antistatic agent concentration of 1%)" to the surface surface of the molded body so that the boron-based compound is 30 g / m ² . It was sprayed evenly with a mist. Table 2 shows the surface specific resistance value and the result of the water extraction test.
Tables 1 and 2 show the manufacturing conditions and various physical properties of Examples and Comparative Examples.
In addition, Examples 10 to 13 are reference examples.

From Tables 1 and 2, if the amount of boron is in the range of 1.0 to 15.0 mg per 1 kg of composite resin particles, a foam molded product having a high surface specific resistance value (high antistatic effect) can be obtained. I understand.

Claims (8)

The composite resin particles for producing foamed particles containing a polyolefin-based resin and a polystyrene-based resin in the ranges of 38.8 to 17.9 % by mass and 61.2 to 82.1% by mass, respectively, based on the total amount thereof.
A foamed molded product having a size of 100 mm × 100 mm × 30 mm obtained from the composite resin particles as an antistatic agent corresponding to an amount of boron of 1.0 to 15.0 mg per kg of the composite resin particles. Contains boron-containing compounds so that the amount of boron transferred to ultrapure water is 0.20 mg / L or less when immersed in 100 mL of ultrapure water at 25 ° C. for 72 hours with skins on both sides. , The boron-containing compound is present from the surface layer to the center of the composite resin particles , and
When the composite resin particles expose the foamed molded product obtained from the composite resin particles to the foamed molded product in an environment of a temperature of 65 ° C. and a humidity of 90% for 500 hours , the surface resistance of the ^{foamed molded product is 1 × 10 10 Ω or less.} Composite resin particles characterized by giving a value. The composite resin particles according to claim 1, wherein the boron-containing compound is a donor-acceptor-based molecular compound obtained by reacting a semi-polar organoboron compound as a donor component with a basic nitrogen compound as an acceptor component. The composite resin particles according to claim 1 or 2 , wherein the polyolefin-based resin is selected from an ethylene-vinyl acetate copolymer, high-density polyethylene, linear low-density polyethylene, and a mixture thereof. The method for producing composite resin particles according to any one of claims 1 to 3.
Seed particles are obtained by cutting a boron-containing compound or a masterbatch made of a polyolefin-based resin containing a boron-containing compound and a melt of the polyolefin-based resin.
A method for producing composite resin particles, which comprises obtaining composite resin particles by impregnating and polymerizing the seed particles with a styrene-based monomer. Foamable particles containing the composite resin particles according to any one of claims 1 to 3 and a volatile foaming agent. Foamed particles obtained by foaming the foamable particles according to claim 5. A foamed molded product obtained by foam-molding the foamed particles according to claim 6. The foamed molded product according to claim 7 , wherein the foamed molded product is a cushioning material for transporting electronic devices.