JP5401083B2 - Pre-expanded particles, method for producing the same, and foam molded article - Google Patents

Description

  The present invention relates to pre-expanded particles, a method for producing the same, and a foam-molded product. More specifically, the present invention relates to pre-expanded particles having good antistatic properties, a method for producing the same, and a foam-molded article.

  Expandable polystyrene resin particles imparted with foaming performance are obtained by impregnating polystyrene resin particles with a volatile foaming agent such as propane, butane, or pentane. Expandable polystyrene resin particles have good retention of the foaming agent and can be stored at room temperature or in a refrigerated state. Accordingly, it is possible to heat the expandable polystyrene resin particles at appropriate times to obtain pre-expanded particles, which are filled in a mold of a molding machine and heated to obtain a foam molded product. Since this foamed molded article is excellent in heat insulation, buffer and lightness, it is widely used as a food container such as a fish box, a shock absorber for home appliances, a heat insulator for building materials, and the like. However, this foamed molded product has a problem that it is easily broken by an impact or the like, and there has been a limit to expansion of applications.

On the other hand, in addition to the features of foamed molded products made of polystyrene resin, foamed molded products made of polyolefin resins such as polyethylene resins and polypropylene resins are flexible and resistant to cracking (excellent crack resistance). It has been known. However, since polyolefin resin particles are inferior in retention of the foaming agent, there is a problem that they cannot be stored in the state of expandable resin particles. In addition, since it is necessary to precisely control the foam molding conditions, there is a problem that the manufacturing cost is high.
In order to solve the above-mentioned problems, expandable composite resin particles in which polystyrene resin is modified with polyethylene resin by impregnating and polymerizing polyethylene resin particles with polyethylene resin particles in an aqueous medium have been proposed ( For example, International Publication No. 2004-90029 pamphlet: Patent Document 1).

Pamphlet of International Publication 2004-90029

In the above publication, the composite resin particles are impregnated with the antistatic agent when the foaming agent is impregnated.
Although the foamable composite resin particles of the above publication can be used to obtain a foamed molded article having sufficient antistatic properties, for example, in applications such as packaging materials for electronic parts, further improvement of antistatic properties, particularly one foamed molding. It has been desired to suppress variation in antistatic properties of a plurality of parts in the body.

Thus, according to the present invention, after the foamable composite resin particles are isolated by impregnating the composite resin particles containing the polystyrene resin and the polyolefin resin with the volatile foaming agent, Before pre-foaming, the foamable composite resin particles are impregnated with an antistatic agent by contacting with 0.1 to 2 parts by weight of a solution-like or liquid antistatic agent with respect to 100 parts by weight of the composite resin particles. And then pre-expanding the expandable composite resin particles impregnated with the antistatic agent to obtain the pre-expanded particles.
Moreover, according to this invention, the pre-expanded particle obtained by the said method is provided.
Furthermore, according to this invention, the foaming molding which shape | molded the said pre-expanded particle in the type | mold is provided.

  The pre-expanded particles of the present invention can provide a foam-molded article that provides improved antistatic properties over conventional pre-expanded particles. In particular, the foamed molded product obtained from the pre-expanded particles of the present invention has antistatic properties in which variation is suppressed at a plurality of sites in one foamed molded product.

The inventors of the present invention perform the impregnation of the antistatic agent into the expandable composite resin particles (hereinafter referred to as the expandable composite resin particles) containing the polystyrene resin and the polyolefin resin, simultaneously with the impregnation of the foaming agent, The reason why the antistatic property of the foamed molded product can be improved by impregnating with the foaming agent and before preliminary foaming is presumed to be as follows.
That is, since the expandable composite resin particles contain a polyolefin resin therein, it is known that the dispersibility of the volatile foaming agent is higher than that of the resin particles made of only polystyrene. Therefore, when the antistatic agent is impregnated simultaneously with the foaming agent, the antistatic agent is extruded into the foaming agent that dissipates from the foamable composite resin particles between the impregnation and the prefoaming, and the antistatic property of the foamable composite resin particles It is considered that the amount of the agent retained decreases. Therefore, the inventors of the present invention may be able to suppress a decrease in the amount of the antistatic agent held in the foamable composite resin particles by impregnating the antistatic agent after impregnation with the foaming agent and before preliminary foaming. As a result, it was possible to improve the antistatic property when actually carried out, and the present invention was made.

The present invention will be described below in the order of steps.
(1) First, a composite resin particle containing a polystyrene resin and a polyolefin resin is impregnated with a volatile foaming agent to obtain expandable composite resin particles.
It does not specifically limit as polyolefin-type resin, A well-known resin can be used. The polyolefin resin may be cross-linked. For example, polyethylene resins such as branched low-density polyethylene, linear low-density polyethylene, medium-density polyethylene, high-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-methyl methacrylate copolymer, and cross-linked products of these polymers And polypropylene resins such as propylene homopolymer, ethylene-propylene random copolymer, propylene-1-butene copolymer, and ethylene-propylene-butene random copolymer. 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. The medium density is an intermediate density between these low density and high density.

The polyolefin resin is branched low density polyethylene, linear low density polyethylene or ethylene-vinyl acetate copolymer, and the polystyrene resin is polystyrene, styrene-alkyl acrylate copolymer or styrene-methacrylic acid. More preferably, it is an alkyl ester copolymer.
Examples of polystyrene resins include polystyrene or styrene (and substituted styrene: the substituent includes lower alkyl, halogen atom (especially chlorine atom), etc.) as a main component and other monomers copolymerizable with styrene. It is a copolymer. The main component means that styrene accounts for 70% by weight or more of the total monomers. Examples of the substituted styrene include chlorostyrenes, vinyltoluenes such as p-methylstyrene, and α-methylstyrene. Other monomers include α-methylstyrene, p-methylstyrene, acrylonitrile, methacrylonitrile, acrylic acid, methacrylic acid, acrylic acid alkyl ester (alkyl moiety having about 1 to 8 carbon atoms), methacrylic acid alkyl ester (alkyl (Partial carbon number of about 1 to 8), divinylbenzene, ethylene glycol mono- or diacrylic acid or methacrylic acid ester, maleic anhydride, N-phenylmaleide, etc.) polyethylene glycol dimethacrylate and the like.

The polystyrene resin is preferably contained in the composite resin particles in the range of 120 to 560 parts by weight with respect to 100 parts by weight of the polyolefin resin.
When there is more content of a polystyrene-type resin than 560 weight part, the crack resistance of a foaming molding may fall. On the other hand, if the amount is less than 120 parts by weight, the crack resistance is greatly improved, but the dissipation of the foaming agent from the surface of the expandable composite resin particles tends to be accelerated. Therefore, the bead life of the foamable composite resin particles may be shortened due to a decrease in the retention of the foaming agent. A more preferable content of the polystyrene resin is 140 to 450 parts by weight, and a more preferable content is 150 to 400 parts by weight.

  The average particle size of the composite resin particles is preferably 800 to 2400 μm. Composite resin particles having an average particle diameter of less than 800 μm tend to have a reduced bead life due to a decrease in foam retention. If it exceeds 2400 μm, the filling property to the mold tends to be poor when molding a foamed molded product having a complicated shape. A preferable average particle diameter is 1200-2000 micrometers.

As the volatile foaming agent, various known foaming agents can be used. Examples thereof include propane, n-butane, isobutane, n-pentane, isopentane, industrial pentane, petroleum ether, cyclohexane, cyclopentane and the like alone or as a mixture. Of these, propane, n-butane, isobutane, n-pentane, isopentane and cyclopentane are preferred.
The content of the foaming agent is preferably 7.5 to 11% by weight with respect to the foamable composite resin particles. If the content of the foaming agent is less than 7.5% by weight, the foamability of the foamable composite resin particles may be lowered. When foamability is lowered, it becomes difficult to obtain low-bulk density pre-expanded particles having a high bulk ratio, and the foam-molded product obtained by molding the pre-expanded particles in a mold has a lower fusion rate and is resistant to cracking. May decrease. On the other hand, when the content exceeds 11% by weight, the bubble size in the pre-expanded particles tends to be excessive, and the moldability may be deteriorated and the strength characteristics such as compression and bending of the obtained foamed molded article may be deteriorated. A more preferable content of the blowing agent is in the range of 8.0 to 10.5% by weight.

The composite resin particles can be obtained, for example, by impregnating and polymerizing a styrene monomer in a polyolefin resin particle to produce a polystyrene resin.
The polyolefin resin particles can be obtained by a known method. For example, polyolefin resin particles can be prepared by first melt-extruding a polyolefin resin using an extruder and then granulating it by underwater cutting, strand cutting, or the like. Usually, the shape of the polyolefin resin to be used is, for example, a true sphere, an oval (egg), a column, a prism, a pellet, or a granular. Hereinafter, the polyolefin resin particles are also referred to as micropellets.

  The polyolefin resin may contain a radical scavenger. The radical scavenger may be added to the polyolefin resin in advance, or may be added simultaneously with melt extrusion. The radical scavenger is preferably a compound having an action of scavenging radicals such as a polymerization inhibitor (including a polymerization inhibitor), a chain transfer agent, an antioxidant, a hindered amine light stabilizer, and the like, which is difficult to dissolve in water. .

As the polymerization inhibitor, t-butylhydroquinone, paramethoxyphenol, 2,4-dinitrophenol, t-butylcatechol, sec-propylcatechol, N-methyl-N-nitrosoaniline, N-nitrosophenylhydroxylamine, triphenyl Phosphite, tris (nonylphenyl phosphite), triethyl phosphite, tris (2-ethylhexyl) phosphite, tridecyl phosphite, tris (tridecyl) phosphite, diphenyl mono (2-ethylhexyl) phosphite, diphenyl monodecyl phosphite Phyto, diphenyl mono (tridecyl) phosphite, dilauryl hydrogen phosphite, tetraphenyl dipropylene glycol diphosphite, tetraphenyl tetra ( Rideshiru) phenol-based polymerization inhibitor such as pentaerythritol diphosphite, nitroso-based polymerization inhibitor, an aromatic amine-based polymerization inhibitor, a phosphite-based polymerization inhibitor, a thioether-based polymerization inhibitor, and the like.
Examples of chain transfer agents include β-mercaptopropionic acid 2-ethylhexyl ester, dipentaerythritol hexakis (3-mercaptopropionate), tris [(3-mercaptopropionyloxy) -ethyl] isocyanurate, and the like. Is done.

  Antioxidants include 2,6-di-t-butyl-4-methylphenol (BHT), n-octadecyl-3- (3,5-di-t-butyl-4-hydroxyphenyl) propionate, pentaerythris Lithyl-tetrakis [3- (3,5-di-tert-butyl-4-hydroxyphenyl) propionate], 1,3,5-tris (3,5-di-tert-butyl-4-hydroxybenzyl) isocyanurate 1,3,5-trimethyl-2,4,6-tris (3,5-di-t-butyl-4-hydroxybenzyl) benzene, 3,9-bis [2- {3- (3-t- Butyl-4-hydroxy-5-methylphenyl) propionyloxy} -1,1-dimethylethyl] -2,4,8,10-tetraoxaspiro [5.5] undecane, distearyl pentae Thritol diphosphite, tris (2,4-di-t-butylphenyl) phosphite, bis (2,4-di-t-butylphenyl) pentaerythritol diphosphite, tetrakis (2,4-di-t -Butylphenyl) 4,4'-biphenylenediphosphonite, bis (2-t-butyl-4-methylphenyl) pentaerythritol diphosphite, 2,4,8,10-tetra-t-butyl-6- [3- (3-methyl-4-hydroxy-5-t-butylphenyl) propoxy] dibenzo [d, f] [1,3,2] dioxaphosphine, phenyl-1-naphthylamine, octylated diphenylamine, 4,4-bis (α, α-dimethylbenzyl) diphenylamine, N, N′-di-2-naphthyl-p-phenylenediamine, etc. Nord antioxidants, phosphorus antioxidants, etc., an amine-based antioxidant may be exemplified.

Examples of hindered amine light stabilizers include bis (2,2,6,6-tetramethyl-4-piperidyl) sebacate, bis (1,2,2,6,6-pentamethyl-4-piperidyl) sebacate, and bis (1 , 2,2,6,6-pentamethyl-4-piperidyl) -2- (3,5-di-t-butyl-4-hydroxybenzyl) -2-n-butylmalonate and the like.
The amount of the radical scavenger used is preferably 0.005 to 0.5 parts by weight with respect to 100 parts by weight of the polyolefin resin.

  Polyolefin resins include talc, calcium silicate, calcium stearate, synthetic or naturally produced silicon dioxide, ethylene bis-stearic acid amide, methacrylic acid ester copolymer and the like, hexabromocyclododecane, It may contain a flame retardant such as triallyl isocyanurate hexabromide, or a colorant such as carbon black, iron oxide or graphite.

Next, the micropellets are dispersed in an aqueous medium in a polymerization vessel and polymerized while impregnating the styrenic monomer into the micropellets. In addition, when the water-soluble resin component (for example, polyvinyl acetate) is contained in the micropellet, the amount may be small.
Examples of the aqueous medium include water and a mixed medium of water and a water-soluble solvent (for example, alcohol). A solvent (plasticizer) such as toluene, xylene, cyclohexane, ethyl acetate, dioctyl phthalate, or tetrachloroethylene may be added to the styrene monomer.

A preferable amount of the styrene monomer used is 120 to 560 parts by weight with respect to 100 parts by weight of the polyolefin resin particles. More preferably, it is 140-450 weight part, More preferably, it is 150-400 weight part.
If the amount of the styrene monomer used exceeds 560 parts by weight, the polystyrene resin particles may be generated without being impregnated into the polyolefin resin particles. In addition, not only the crack resistance of the foamed molded product is lowered, but also the chemical resistance may be lowered. On the other hand, if it is less than 120 parts by weight, the ability to hold the foaming agent of the foamable composite resin particles may be lowered. If it falls, it will become difficult to make it highly foamed. In addition, the rigidity of the foamed molded product may be reduced.

The impregnation of the polyolefin resin particles with the styrene monomer may be performed while polymerizing, or may be performed before the polymerization is started. Of these, it is preferable to carry out the polymerization. When the polymerization is performed after impregnation, polymerization of the styrene monomer near the surface of the polyolefin resin particles tends to occur, and the styrene monomer not impregnated in the polyolefin resin particles is polymerized alone. In some cases, a large amount of fine particle polystyrene resin particles are produced.
When the impregnation is carried out while polymerizing, the polyolefin resin particles for calculating the content are particles composed of a polyolefin resin, an impregnated styrene monomer, and an impregnated polystyrene resin that has already been impregnated. Means.
In order to maintain the content ratio at 0 to 35% by weight, the styrenic monomer can be continuously or intermittently added to the aqueous medium in the polymerization vessel. In particular, it is preferable to gradually add the styrene monomer to the aqueous medium.

  An oil-soluble radical polymerization initiator can be used for the polymerization of the styrene monomer. As this polymerization initiator, a polymerization initiator generally used for the polymerization of styrene monomers can be used. For example, benzoyl peroxide, lauroyl peroxide, t-butyl peroxy octoate, t-hexyl peroxy octoate, t-butyl peroxy benzoate, t-amyl peroxy benzoate, t-butyl peroxybivalate, t- Butyl peroxyisopropyl carbonate, t-hexyl peroxyisopropyl carbonate, t-butyl peroxy-3,3,5-trimethylcyclohexanoate, di-t-butylperoxyhexahydroterephthalate, 2,2-di-t- Examples thereof include organic peroxides such as butyl peroxybutane, di-t-hexyl peroxide, and dicumyl peroxide, and azo compounds such as azobisisobutyronitrile and azobisdimethylvaleronitrile. These oil-soluble radical polymerization initiators may be used alone or in combination.

Various methods can be used as a method of adding the polymerization initiator to the aqueous medium in the polymerization vessel. For example,
(A) A method in which a polymerization initiator is dissolved and contained in a styrene monomer in a container different from the polymerization container, and the styrene monomer is supplied into the polymerization container.
(B) A solution is prepared by dissolving the polymerization initiator in a part of a styrene monomer, a solvent such as isoparaffin, or a plasticizer. A method of simultaneously supplying this solution and a predetermined amount of styrenic monomer into the polymerization vessel,
(C) A dispersion in which a polymerization initiator is dispersed in an aqueous medium is prepared. Examples thereof include a method of supplying the dispersion and the styrene monomer into a polymerization vessel.
In general, the polymerization initiator is preferably added in an amount of 0.02 to 2.0% by weight based on the total amount of the styrene monomer used.

It is preferable to dissolve a water-soluble radical polymerization inhibitor in the aqueous medium. The water-soluble radical polymerization inhibitor not only suppresses the polymerization of the styrene monomer on the surface of the polyolefin resin particles, but also prevents the styrene monomer floating in the aqueous medium from being polymerized alone. This is because the generation of fine particles can be reduced.
As the water-soluble radical polymerization inhibitor, a polymerization inhibitor that can dissolve 1 g or more in 100 g of water can be used. For example, thiocyanate such as ammonium thiocyanate, zinc thiocyanate, sodium thiocyanate, potassium thiocyanate, and aluminum thiocyanate. Nitrate, mercapto Ethanol, monothiopropylene glycol, thioglycerol, thioglycolic acid, thiohydroacrylic acid, thiolactic acid, thiomalic acid, thioethanolamine, 1,2-dithioglycerol, 1,3-dithioglycerol, etc. Water-soluble sulfur-containing organic compounds, may be mentioned addition of ascorbic acid, ascorbic acid sodium or the like. Of these, nitrite is particularly preferable.
As the usage-amount of the said water-soluble radical polymerization inhibitor, 0.001-0.04 weight part is preferable with respect to 100 weight part of water of an aqueous medium.

In addition, it is preferable to add a dispersant to the aqueous medium. Examples of such a dispersant include organic dispersants such as partially saponified polyvinyl alcohol, polyacrylate, polyvinyl pyrrolidone, carboxymethyl cellulose, and methyl cellulose, magnesium pyrophosphate, calcium pyrophosphate, calcium phosphate, calcium carbonate, and magnesium phosphate. And inorganic dispersants such as magnesium carbonate and magnesium oxide. Of these, inorganic dispersants are preferred.
When an inorganic dispersant is used, it is preferable to use a surfactant in combination. Examples of such surfactants include dodecyl benzene sulfonic acid soda and α-olefin sulfonic acid soda.

The shape and structure of the polymerization vessel are not particularly limited as long as they are conventionally used for suspension polymerization of styrene monomers.
Further, the shape of the stirring blade is not particularly limited, and specifically, a paddle blade such as a V-shaped paddle blade, a fiddler blade, an inclined paddle blade, a flat paddle blade, a pull margin blade, a turbine blade, a fan turbine blade, etc. Examples include a turbine blade and a propeller blade such as a marine propeller blade. Of these stirring blades, paddle blades are preferred. The stirring blade may be a single-stage blade or a multi-stage blade. A baffle may be provided in the polymerization container.

The temperature of the aqueous medium when polymerizing the styrene monomer in the micropellet is not particularly limited, but is preferably in the range of −30 to + 20 ° C. of the melting point of the polyolefin resin to be used. More specifically, 70-140 degreeC is preferable and 80-130 degreeC is more preferable. Furthermore, the temperature of the aqueous medium may be a constant temperature from the start to the end of the polymerization of the styrenic monomer, or may be increased stepwise. When raising the temperature of an aqueous medium, it is preferable to make it raise at the temperature increase rate of 0.1-2 degree-C / min.
Furthermore, when using particles comprising a crosslinked polyolefin resin, the crosslinking may be performed in advance before impregnating the styrene monomer, or while impregnating and polymerizing the styrene monomer in the micropellets. Alternatively, it may be performed after impregnating and polymerizing a styrenic monomer in a micropellet.

Examples of the crosslinking agent used for crosslinking the polyolefin resin include 2,2-di-t-butylperoxybutane, dicumyl peroxide, 2,5-dimethyl-2,5-di-t-butylperoxy. An organic peroxide such as hexane may be mentioned. In addition, a crosslinking agent may be individual or may be used together 2 or more types. Moreover, the usage-amount of a crosslinking agent has preferable 0.05-1.0 weight part normally with respect to 100 weight part of polyolefin resin particles (micro pellet).
As a method of adding a crosslinking agent, for example, a method of directly adding a crosslinking agent to a polyolefin resin, a method of adding a crosslinking agent after dissolving it in a solvent, a plasticizer or a styrene monomer, and dispersing the crosslinking agent in water For example, a method of adding after adding them. Among these, the method of adding after dissolving a crosslinking agent in a styrene-type monomer is preferable.

  It is possible to obtain expandable composite resin particles by impregnating the composite resin particles after impregnation of the styrene monomer and polymerization with a foaming agent. Impregnation with the blowing agent can be performed by a method known per se. For example, the impregnation during the polymerization can be performed by performing the polymerization reaction in a sealed container and press-fitting a foaming agent into the container. The impregnation after the completion of the polymerization is performed by press-fitting a foaming agent in a sealed container.

(2) Next, after isolating the foamable composite resin particles impregnated with the volatile foaming agent, the foamable composite resin particles obtained are impregnated with a specific amount of antistatic agent.
The antistatic agent is not particularly limited, and any known antistatic agent can be used. For example, a surfactant having antistatic properties can be mentioned. Specific surfactants include alkyl monoethanolamines, alkyl polyetheramines, polyethylene glycol fatty acid esters, alkyl diethanolamides, alkyl diethanol amines, polyalkylene glycol derivatives, and other nonionic surfactants, alkyl sulfonates, and alkyl benzenes. Anionic surfactants such as sulfonates and alkyl phosphates, cationic surfactants such as aliphatic alkyl quaternary ammonium salts and trialkylbenzylammonium salts, amphoteric surfactants such as alkylbetaines and alkylimidazolium betaines, etc. Can be mentioned. In addition, although it changes with kinds of surfactant, it is preferable to use surfactant with a total carbon number of 5-20 as an antistatic agent.

The antistatic agent can be brought into contact with the expandable composite resin particles in the form of a solution or liquid. The solution state means a state in which a solid or liquid antistatic agent is dissolved or dispersed in an aqueous medium, and the liquid state means that the antistatic agent itself is a liquid.
Among these, nonionic surfactants are preferable, and alkyl mono or diethanolamine and alkyl polyether amine are more preferable from the viewpoint of good antistatic properties. Here, the alkyl preferably has 8 to 18 carbon atoms. In particular, an antistatic agent that is liquid at a temperature of 10 to 30 ° C. is preferable in that the foamable composite resin particles can be impregnated with the antistatic agent in a short time without being dissolved in an aqueous medium. Examples of such an antistatic agent include N-hydroxyethyl lauryl amine and polyoxyethylene lauryl amine (polyoxyethylene preferably has a range of 2 to 10 oxyethylene units).

The usage-amount of an antistatic agent is 0.1-2.0 weight part with respect to 100 weight part of expandable composite resin particles, Preferably it is 0.5-1.5 weight part. When the amount is less than 0.1 part by weight, desired antistatic properties may not be imparted to the foamed molded product. On the other hand, if it exceeds 2.0 parts by weight, the foamable composite resin particles and the pre-foamed particles are sticky, which may make handling difficult. In addition, it becomes difficult to fill the pre-expanded particles into the molding die, and the foamed molded product obtained may become sticky, and on the contrary, dust may easily adhere.
The impregnation with the antistatic agent is preferably performed at an atmospheric temperature of 30 to 90 ° C. for 5 to 90 seconds. Outside these temperature and time ranges, insufficient antistatic properties, reduced productivity, and stickiness of foamable composite resin particles may occur. In addition, you may perform the impregnation of an antistatic agent under pressure as needed.

  In addition, the impregnation of the foamable composite resin particles with the antistatic agent is performed in the form of a solution in a container used for prefoaming in consideration of the relatively fast dissipation of the volatile foaming agent from the foamable composite resin particles. Alternatively, it is preferable to carry out by spraying the liquid antistatic agent on the foamable composite resin particles or immersing the foamable composite resin particles in a solution or liquid antistatic agent. When spraying, the spray position with respect to the container is not particularly limited. However, it is preferable that the position is as close as possible to the expandable composite resin particles because the antistatic agent can be prevented from adhering to the container and the stirring blade, and the antistatic agent can be efficiently brought into contact with the expandable resin particles. . Here, the close position is more preferably a position of 80 cm or less from the upper surface of the expandable resin particle.

(3) Further, the foamable composite resin particles impregnated with the antistatic agent are prefoamed to obtain prefoamed particles.
Pre-expanded particles can be obtained by heating the expandable composite resin particles impregnated with the antistatic agent using a heating medium such as water vapor and pre-expanding to a predetermined bulk density, if necessary.
The pre-expanded particles preferably have a bulk multiple of 5 to 60 times (bulk density 0.016 to 0.2 g / cm ³ ). A more preferable bulk factor is 10 to 55 times. When the bulk multiple is larger than 60 times, the closed cell ratio of the expanded particles is lowered, and the strength of the foamed molded product obtained by foaming the pre-expanded particles may be decreased. On the other hand, if it is less than 5 times, the weight of the foamed molded product obtained by foaming the pre-foamed particles may increase.

(4) Manufacturing method of foam molded body The above-mentioned pre-foamed particles are filled in a mold of a molding machine, heated and subjected to secondary foaming, and the pre-foamed particles are fused and integrated to form a foam molded body having a desired shape. Can be obtained. As the molding machine, there can be used an EPS molding machine or the like used when producing a foam molded body from polystyrene resin pre-foamed particles.
The obtained foamed molded article has good antistatic properties. Therefore, a foaming molding can be used for uses, such as transfer containers (packing material), such as buffer materials (cushion material), such as household appliances, an electronic component, various industrial materials, and foodstuffs. It can also be used as an impact energy absorbing material such as a vehicle bumper core and a door interior cushioning material.

The present invention will be further described below with reference to examples, but the present invention is not limited to these examples.
<Bulk multiple of pre-expanded particles>
The weight (a) of about 5 g of pre-expanded particles is weighed at the second decimal place. Next, weighed pre-expanded particles in a 500 cm ³ graduated cylinder with a minimum memory unit of 5 cm ³ , and a round resin plate slightly smaller than the caliber of the graduated cylinder, about 1.5 cm wide at the center, The volume (b) of the pre-expanded particles is read by applying a pressing tool in which a rod-shaped resin plate having a length of about 30 cm is fixed upright, and the bulk density (g) of the pre-expanded particles is calculated according to the formula (a) / (b). / Cm ³ ). The bulk multiple is the reciprocal of the bulk density, that is, the formula (b) / (a).

<Multiple of foam molding>
The weight (a) and volume (b) of a test piece (example 75 × 300 × 35 mm) cut out from a foamed molded product (after being molded and dried at 40 ° C. for 20 hours or more) each have three or more significant figures. Then, the density (g / cm ³ ) of the foamed molded product is obtained by the formula (a) / (b). The multiple is the reciprocal of the density, that is, the formula (b) / (a).

<Average surface resistivity>
Measured by the method described in JIS K6911: 1995 “General Test Method for Thermosetting Plastics”. That is, using a test device (advantest digital long high resistance / microammeter R8340 and resiliency chamber R12702A), an electrode is pressure-bonded to a sample sample with a load of about 30 N, and the resistance value after charging for 500 V for 1 minute is obtained. taking measurement. The surface resistivity is calculated from the measured value by the following formula.
ρs = π (D + d) / (D−d) × Rs
ρs: Surface resistivity (MΩ)
D: Inner diameter of surface annular electrode (cm)
d: Outline of inner circle of surface electrode (cm)
Rs: Surface resistance (MΩ)
The sample sample has a size of 100 mm × 100 mm × thickness 10 mm or less, and 10 pieces are cut out from the same foamed molded article. Ten cut sample samples are stored in an environment of 20 ° C. and 65% humidity for about 24 hours, and then the resistance values of the ten sample samples are measured. The average surface resistivity is an average value of 10 surface resistivities.

<Standard deviation>
The 10 surface resistivity values are each returned as a logarithm (1 log ₁₀ ), and the standard deviation is obtained using the obtained logarithm.
<Evaluation of antistatic properties>
When the average surface resistivity is less than 10 ¹² and the standard deviation is 1.0 or less, it is evaluated as a non-defective product (◯) with little variation in surface resistivity.

Example 1 (Reference Example)
(Manufacture of composite resin particles)
To 100 parts by weight of ethylene-vinyl acetate copolymer resin particles (LV-211, manufactured by Nippon Polyethylene Co., Ltd., melt flow rate 0.3 g / 10 min, vinyl acetate content 6.2% by weight), calcium silicate 0 as a foam regulator .3 parts by weight and 0.1 part by weight of calcium stearate were added and kneaded uniformly with an extruder to obtain granulated pellets by an underwater cutting method (ethylene-vinyl acetate copolymer resin particles per 100 grains). Adjusted to 80 mg).
Add 40 parts by weight of the above pellets, 120 parts by weight of pure water, 0.45 parts by weight of magnesium pyrophosphate, and 0.02 parts by weight of sodium dodecylbenzenesulfonate to a pressure-resistant container with a stirrer having an internal volume of 100 liters, and stir pure water. Suspended in.
Next, a mixed solution obtained by dissolving 0.03 part by weight of dicumyl peroxide as a radical polymerization initiator in 20 parts by weight of styrene monomer was dropped into this suspension over 30 minutes. After maintaining for 30 minutes after dropping, the temperature of the reaction system was increased to 135 ° C., maintained for 2 hours, and then cooled to room temperature.

  Further, 0.16 part by weight of sodium dodecylbenzenesulfonate was added to this suspension, and then the temperature of the reaction system was raised to 90 ° C., and 0.3 parts by weight of benzoyl peroxide and radical polymerization initiator were used. A mixture of 0.02 parts by weight of t-butyl peroxybenzoate and 0.8 parts by weight of dicumyl peroxide dissolved in 40 parts by weight of styrene monomer is dropped over 2 hours, and polymerization is performed while absorbing the styrene monomer. went. Then, after maintaining at 90 ° C. for 3 hours, the temperature was raised to 135 ° C. and maintained at that temperature for 3 hours to complete the polymerization. After completing the above series of polymerizations, it was cooled to room temperature to obtain composite resin particles.

(Manufacture of expandable composite resin particles)
100 parts by weight of composite resin particles and 0.5 parts by weight of diisobutyl adipate were charged into a V-type blender having an internal volume of 50 liters that can be sealed and sealed, and 14 parts by weight of butane were press-fitted while stirring and stirring. And after maintaining the temperature in a blender at 60 degreeC for 4 hours, it cooled to 25 degreeC and took out the expandable composite resin particle.
(Impregnation with antistatic agent)
100 parts by weight of the above expandable composite resin particles were put into a batch type foaming machine (SKK-70 manufactured by Sekisui Koki Seisakusho Co., Ltd.), and polyoxyethylene alkylamine as an antistatic agent (ELEGAN S-100 manufactured by NOF Corporation: Oxygen) The number of ethylene unit repetitions was about 1 to 4: the carbon number of the alkyl was about 10 to 14) 0.3 parts by weight were added over 30 seconds with stirring, and stirring was maintained at 60 ° C. for 30 seconds. The addition position of the antistatic agent was the upper surface of the batch type foaming machine (about 80 cm above the upper surface of the charged foamed resin particles).

(Manufacture of pre-expanded particles)
After the addition, while stirring, steam is introduced at a setting of about 0.05 MPa, heating is started, and the foamable composite resin particles are pre-foamed aiming at a bulk ratio of 15 times, so that a reserve of about 15 times the bulk ratio is obtained. Expanded particles were obtained.
(Manufacture of foam moldings)
The obtained pre-expanded particles were placed in a molding die having a size of 400 mm (length) × 300 mm (width) × 30 mm (thickness). The mold was heated by introducing 0.06 MPa of water vapor for 25 seconds and then cooled for 120 seconds to take out a foamed molded article having a multiple of about 15 times. The obtained foamed molded article was dried for about 8 hours in a drying chamber at 40 ° C.
The average surface resistivity and standard deviation of the obtained foamed molded product were obtained, and the obtained results are shown in Table 1 together with the evaluation of chargeability.

Example 2
A foamed molded article was obtained in the same manner as in Example 1 except that the addition amount of the antistatic agent was 0.9 parts by weight.
The average surface resistivity and standard deviation of the obtained foamed molded product were obtained, and the obtained results are shown in Table 1 together with the evaluation of chargeability.
Example 3
A foamed molded article was obtained in the same manner as in Example 1 except that the addition amount of the antistatic agent was 1.5 parts by weight.
The average surface resistivity and standard deviation of the obtained foamed molded product were obtained, and the obtained results are shown in Table 1 together with the evaluation of chargeability.

Example 4
A polypropylene resin (F-744NP manufactured by Prime Polymer Co., Ltd.) was supplied to the extruder, melted and kneaded, and granulated pellets were obtained by a strand cut method (the polypropylene resin particles were adjusted to 80 mg per 100 particles).
Add 40 parts by weight of the above pellets, 120 parts by weight of pure water, 1 part by weight of magnesium pyrophosphate and 0.03 parts by weight of sodium dodecylbenzenesulfonate to a pressure-resistant container with a stirrer having an internal volume of 100 liters, and stir in pure water. Suspended. The resulting suspension was held for 10 minutes with stirring.
Next, a mixed solution in which 0.04 part by weight of dicumyl peroxide as a radical polymerization initiator was dissolved in 20 parts by weight of styrene monomer was dropped into this suspension over 30 minutes. After dropping, the mixture was held for 30 minutes, the styrene monomer was absorbed by the polyethylene resin particles, the temperature of the reaction system was raised to 135 ° C., and then the styrene monomer was polymerized by holding for 2 hours.

Further, 0.08 part by weight of sodium dodecylbenzenesulfonate was added to this suspension, and then a mixed solution in which 0.18 part by weight of dicumyl peroxide was dissolved in 40 parts by weight of styrene monomer as a radical polymerization initiator. Was added dropwise over 4 hours, and polymerization was carried out while the styrene monomer was absorbed by the polyethylene resin particles. Thereafter, the temperature was raised to 120 ° C., held at that temperature for 1 hour, then heated to 140 ° C. and held at that temperature for 3 hours to complete the polymerization. Then, it cooled to normal temperature and took out the composite resin particle.
Thereafter, in the same manner as in Example 2, expandable composite resin particles, pre-expanded particles, and foamed molded articles were obtained.
The average surface resistivity and standard deviation of the obtained foamed molded product were obtained, and the obtained results are shown in Table 1 together with the evaluation of chargeability.

Example 5
A foamed molded article was obtained in the same manner as in Example 2 except that the addition position of the antistatic agent was added from about 20 cm above the top surface of the expandable resin particles so as not to adhere to the container and the stirring blade.
The average surface resistivity and standard deviation of the obtained foamed molded product were obtained, and the obtained results are shown in Table 1 together with the evaluation of chargeability.
Example 6
A foamed molded article was obtained in the same manner as in Example 2 except that the antistatic agent was changed to N-hydroxyethyllaurylamine (Nymine L201 manufactured by NOF Corporation).
The average surface resistivity and standard deviation of the obtained foamed molded product were obtained, and the obtained results are shown in Table 1 together with the evaluation of chargeability.

Comparative Example 1
A foamed molded article was obtained in the same manner as in Example 1 except that the addition amount of the antistatic agent was 0.05 parts by weight.
The average surface resistivity and standard deviation of the obtained foamed molded product were obtained, and the obtained results are shown in Table 1 together with the evaluation of chargeability.

Comparative Example 2
After the foaming agent impregnation, the foamed molded article was obtained in the same manner as in Example 1 except that the antistatic agent was not impregnated before the preliminary foaming, and the antistatic agent was impregnated at the time of foaming agent impregnation as follows.
In a V-type blender with an internal volume of 50 liters that can be sealed with pressure resistance, 100 parts by weight of composite resin particles, 0.5 parts by weight of diisobutyl adipate, 0.3 parts by weight of polyoxyethylene alkylamine (ELEGAN S-100 manufactured by NOF Corporation) Was sealed, and 14 parts by weight of butane was press-fitted while stirring. And after maintaining the temperature in a blender at 60 degreeC for 4 hours, it cooled to 25 degreeC and took out the expandable composite resin particle.
The average surface resistivity and standard deviation of the obtained foamed molded product were obtained, and the obtained results are shown in Table 1 together with the evaluation of chargeability.

Comparative Example 3
A foamed molded article was obtained in the same manner as in Comparative Example 2 except that the addition amount of the antistatic agent was 1.5 parts by weight.

From Table 1, in the examples, the antistatic agent was added after impregnation with the volatile foaming agent and before the preliminary foaming, so that the average surface resistivity was compared with Comparative Examples 2 and 3 added at the time of impregnation with the volatile foaming agent. It can be seen that it is possible to obtain a foamed molded article having a low standard deviation and a low standard deviation indicating a variation in surface resistivity.
From the examples and comparative example 1, when the amount of the antistatic agent used is 0.1 to 2 parts by weight, the foamed molded product has a low average surface resistivity and a low standard deviation showing variations in the surface resistivity. It can be seen that
From the above, in the Examples, a foamed molded article having excellent antistatic properties and small variations in antistatic properties can be obtained.

Claims (9)

After isolating the foamable composite resin particles by impregnating the composite resin particles containing polystyrene resin and polyolefin resin with a volatile foaming agent, The foamable composite resin particles are charged by contact with a solution or liquid nonionic surfactant as an antistatic agent in an amount of 0.5 to 1.5 parts by weight based on 100 parts by weight of the resin particles. A method for producing pre-expanded particles, comprising a step of impregnating an inhibitor and then pre-expanding the expandable composite resin particles impregnated with the anti-static agent to obtain pre-expanded particles.   When the foamable composite resin particles are impregnated with the antistatic agent, the solution-like or liquid antistatic agent is sprayed on the foamable composite resin particles in the container used for the preliminary foaming, or the solution-like or liquid-state. The method for producing pre-expanded particles according to claim 1, which is performed by immersing the expandable composite resin particles in an antistatic agent. The method for producing pre-expanded particles according to claim 1 or 2 , wherein the antistatic agent is an alkylethanolamine or an alkyl polyetheramine. The method for producing pre-expanded particles according to any one of claims 1 to 3 , wherein the antistatic agent is impregnated for 5 to 90 seconds at 30 to 90 ° C with stirring. The method for producing pre-expanded particles according to any one of claims 1 to 4 , wherein the volatile blowing agent is selected from propane, n-butane, isobutane, n-pentane, isopentane, and cyclopentane. The method for producing pre-expanded particles according to any one of claims 1 to 5 , wherein the volatile foaming agent is used in a ratio of 10 to 30 parts by weight with respect to 100 parts by weight of the composite resin particles. The method for producing pre-expanded particles according to any one of claims 1 to 6 , wherein the composite resin particles include 100 parts by weight of a polyolefin-based resin and 120 to 560 parts by weight of a polystyrene-based resin. Pre-expanded particles obtained by the method according to any one of claims 1 to 7 . A foam molded article obtained by in-mold molding the pre-expanded particles according to claim 8 .