JPH0711043A - Polystyrenic foamed granule - Google Patents

Abstract

PURPOSE:To obtain polystyrenic foamed granules excellent in crack resistance, appearance characteristics and foaming gas holdability by dispersing butadiene polymer rubber particles containing polystyrenic resin small particles in the continuous phase of a polystyrenic resin in a flat state in the surface direction. CONSTITUTION:A rubber-modified polystyrenic resin comprising the continuous phase 3 of a polystyrenic resin and the dispersed phases of a butadiene resin 5 containing a polystyrenic resin 4 in a small particle state, the intrinsic viscosity of the continuous phase being 0.6-0.9 (at 30 deg.C in toluene) and the swelling index of the dispersed phases being 6.5-13.5 (at 25 deg.C in toluene), is melt-blended with a foaming agent in an extruder, held at a temperature of >=130 deg.C under a pressure of 50-300kg/cm<2>G for 15min, extruded and subsequently cut into a granular shape to provide the objective polystyrenic foamed granules in which the dispersed phases are dispersed in a flat state in the direction of the cell membrane surface 2 and in plural layers in the cross section of thickness direction, and which has relations: a/c=0.1-0.2 and b/a=10-70 wherein (a) is the dimension of the dispersed phase in the thickness direction; (b) is its dimension in the surface direction; and (c) is the dimension of the cell membrane in the thickness direction.

Description

Detailed Description of the Invention

[0001]

FIELD OF THE INVENTION This invention relates to expanded particles of rubber-modified polystyrene resin with improved performance and a method of making the same. More specifically, it relates to expanded particles having good crack resistance, good appearance characteristics, and improved retention of a blowing agent gas.

[0002]

BACKGROUND OF THE INVENTION Expanded particles made of polystyrene are molded into various forms and are widely used as packaging materials, cushioning materials and the like. However, the polystyrene foamed particle molded article is not sufficiently resistant to cracking and chipping, and if it is used as a cushioning material for relatively heavy packaged cargo, cracking will occur due to shock during transportation, and repeated shocks may occur. There was a risk of damaging the product. If the thickness of the cushioning material is increased in order to prevent cracking due to impact, the size of the package becomes large, resulting in a decrease in transportation efficiency. As a solution to that problem, it has been proposed to make expanded particles of a resin by adding a butadiene component to polystyrene.

Japanese Unexamined Patent Publication (Kokai) No. 56-67344 discloses expanded particles having improved impact resistance, which are composed of a resin in which non-oriented rubber particles are dispersed in polystyrene. However, since the rubber particles are non-oriented, the rubber particles are less likely to be deformed. Therefore, the rubber particles are easily exposed from the surface of the foam film in the thin foam film forming the foam, and particularly in the pre-expanded particles having a high expansion ratio, the retention of the foaming agent gas is insufficient due to the exposure of the rubber particles. there were.

Japanese Unexamined Patent Publication (Kokai) No. 63-175043 discloses a styrene-based polymer foam having a uniform cell size obtained by polymerizing a solution of a styrene-butadiene block copolymer dissolved in a styrene monomer. ing. Also,
Japanese Unexamined Patent Publication (Kokai) No. 2-311542 discloses a styrene-based polymer foam having improved strength obtained by dissolving styrene-soluble rubber in styrene and polymerizing the styrene-soluble rubber. But,
These foams were still insufficient in improving crack resistance. That is, the crack resistance of the foam is expressed by a plurality of physical property factors such as compressive strength, tensile elongation, and foam structure of the foam, and these physical properties are the rubber particles in the foam film constituting the foam. It depends on the distributed structure of.

Japanese Unexamined Patent Publication No. 3-182529 discloses a resin foam obtained by mechanically mixing high-impact polystyrene and a hydrogenated styrene-butadiene block copolymer. However, since the foam contains a mechanically mixed rubber component, if the mixed rubber component is insufficiently dispersed, the rubber component dispersion in the foam cell of the foam becomes non-uniform, and bubbles are likely to communicate with each other. This tendency is remarkable especially when the magnification is high, and the expansion force of the high-magnification expanded particles is reduced, so that voids between particles are observed in the expanded particle molded product, and the appearance of the molded product is poor.

[0006]

SUMMARY OF THE INVENTION The present invention solves such a problem and has good retention of the blowing agent gas after pre-foaming,
It is an object of the present invention to provide foamed particles which have a high closed cell ratio even when expanded by a high number of times and have excellent cracking resistance when formed into a foamed particle molded body and have a good appearance.

[0007]

DISCLOSURE OF THE INVENTION The present invention provides a foamed particle composed of a rubber-modified polystyrene-based resin in which a butadiene-based polymer rubber particle containing a polystyrene-based resin in the form of small particles is dispersed in a continuous phase of the polystyrene-based resin. And the intrinsic viscosity of the continuous phase of the rubber-modified polystyrene resin is 0.6
Is 0.9 or more, the swelling index of the gel component of the rubber-modified polystyrene-based resin is 6.5 or more and 13.5 or less, and the apparent density of the expanded particles is 0.014 g / cm ³ or more, 0.100 g. / Cm ³ or less, the rubber particles are flatly dispersed in the surface direction of the foam film of the expanded particles,
When the bubble film is viewed in a cross section in the thickness direction, a plurality of rubber particles exist in a layered form in the thickness direction, and the dimension (a) of the rubber particles in the bubble film thickness direction and the dimension of the rubber particles in the bubble film surface direction ( b)
And the bubble film thickness dimension (c), a / c is 0.0
It relates to expanded beads having a ratio of 1 or more and 0.2 or less and ab / a of 10 or more and 70 or less.

The present invention will be described in detail below with reference to the drawings. FIG. 1 is a schematic explanatory view showing a cross section of a foamed film of foamed particles according to the present invention as seen in a cross section in a thickness direction. 6 is foamed particles, 5 is butadiene-based component part of rubber particles, 4 is polystyrene-based component part of rubber particles, 3 is polystyrene-based continuous phase,
Reference numeral 1 indicates a bubble film cross section, and 2 indicates a bubble film surface. a is the dimension of the rubber particles in the thickness direction of the bubble membrane, and b is the dimension of the rubber particles in the dimension of the bubble membrane surface, which is the dimension of the largest portion.

2 and 3 are schematic explanatory views of a bubble film.
That is, the cell membrane cross section (1) is a section in the thickness direction of the cell membrane (9), and the cell membrane (9) forms the cell (8) of the foamed particle section (7). FIG. 3 is an enlarged view of a broken line portion of FIG.

The cracking resistance of the rubber-modified polystyrene resin is expressed by the fact that the rubber phase suppresses the propagation of cracks generated in the matrix phase when the resin is impacted. Therefore, even in the crack resistance of the foamed particle molded product made of the rubber-modified polystyrene resin, the propagation of cracks that occur when the molded product is impacted is expressed by suppressing the rubber particles present in the foam film. Conceivable. However, the shape of the rubber particles dispersed in the resin continuous phase, the orientation state of the rubber particles, the orientation state of the resin, and the like are completely different between the resin and the foam cell, and the resin and the cell membrane have crack resistance. The rubber phase dispersion structure suitable for is different.

The present invention provides a continuous phase of polystyrene resin,
By specifying the dispersion structure of the rubber particles in the foam film of the foamed particles made of the rubber-modified polystyrene resin in which the butadiene polymer rubber particles in which the polystyrene resin is encapsulated in the form of small particles are specified, crack resistance is improved. It is shown that the foamed particles are excellent, the gas-retaining property of the foaming agent is also excellent, the closed cells have a high closed cell ratio even when expanded by a high number of times, and the molded particles have a good appearance.

In the present invention, the aspect ratio (b / a) showing the flat state of the rubber particles in the cross section of the bubble film is calculated as the average value of the aspect ratios of 20 randomly selected rubber particles, and the value is 10. It is preferably 70 or more and 70 or less.
Further, it is more preferably 10 or more and 40 or less. (B /
When a) is less than 10, the rubber particles are likely to be exposed from the surface of the cell membrane, and the retention of the blowing agent gas is reduced. Also,
When (b / a) exceeds 70, the particles become too flat and the rubber phase becomes thin so that it is difficult to suppress the propagation of cracks and the crack resistance of the foam decreases.

In the present invention, (a / c) is the bubble film thickness and (a / c) of 20 randomly selected rubber particles.
It is calculated as an average value of the values and is preferably 0.01 or more and 0.2 or less. Further, it is more preferably 0.01 or more and 0.1 or less. When (a / c) is less than 0.01, the rubber phase becomes smaller than the film thickness, making it difficult to suppress the propagation of cracks,
The crack resistance of the foam decreases. Further, (a / c) is 0.
If it exceeds 2, the rubber particles are likely to be exposed from the surface of the foam film, and the retention of the foaming agent gas is deteriorated. The thickness of the bubble film in the cross section of the bubble film is preferably 0.2 μm or more and 10 μm or less, more preferably 0.3 μm or more and 5 μm or less.

In the present invention, when the bubble film is viewed in a cross section in the thickness direction, a plurality of rubber particles are present in a layered form in the thickness direction. The number of layers is preferably 2 or more and 20 or less in the thickness direction, and more preferably 2 or more and 10 or less. When the bubble film is viewed in a cross section in the thickness direction, if a plurality of rubber particles do not exist in the thickness direction, it is difficult to suppress the propagation of cracks and cracks easily.

According to the present invention, when the bubble film is viewed in a cross section in the thickness direction, a square having a thickness of the bubble film as one side,
It is preferable that at least a part of the rubber particles is present and the number of the rubber particles is 2 or more and 70 or less. More preferably, it is 5 or more and 50 or less. The values of a, b and c can be measured as follows. That is, after preparing expanded particles having a cut-out cross section of expanded particles, immersing in expanded 2% osmium tetroxide solution for 24 hours and washing with distilled water,
The values of a, b, and c can be clearly measured by embedding in a room temperature curing type epoxy resin, preparing an ultrathin section using an ultramicrotome, and observing this section with an electron microscope.

The shape of the rubber particles in the cross section of the bubble film is not particularly limited, and may be, for example, a circle, an ellipse, or an irregular shape. Further, in the present invention, the shape of the expanded particles is not particularly limited, for example, spherical, elliptic spherical,
There is a columnar shape.

In the present invention, the apparent density of the expanded beads is preferably 0.012 g / cm ³ or more and 0.1 g / cm ³ or less. A more preferable range is 0.014 g / cm ³ or more and 0.07 or less. Apparent density is 0.014g / cm ³
When it is less than 1, the closed cell ratio of the expanded beads decreases and the strength of the expanded particle molded article decreases. On the other hand, if the apparent density exceeds 0.1 g / cm ³ , it is economically disadvantageous to use the molded product as a packaging material and a cushioning material because of its large weight.

In the present invention, the rubber particles in the cross section of the cell membrane have a specific flat shape because the polystyrene is a continuous phase in the process of foaming the resin, that is, in the process of stretching the cell membrane as the cell expands. This means that the rubber particles in the dispersed phase are appropriately stretched with the extension of the resin. This is achieved by specifying the viscoelastic combination of the continuous phase polystyrene resin and the dispersed phase rubber particles in the foaming process. The viscoelasticity of the rubber component is the degree of crosslinking of the rubber component,
It depends on the molecular weight of the rubber component. Further, the viscoelasticity of the polystyrene resin, which is the continuous phase, varies depending on the molecular weight of the resin and the like. In the present invention, the intrinsic viscosity of the continuous phase of the rubber-modified polystyrene resin is 0.6 or more and 0.9 or less,
The swelling index of the crosslinked rubber component of the rubber-modified polystyrene-based resin is preferably 6.5 or more and 13.5 or less.
The limiting viscosity referred to here is the converted viscosity vs. concentration (g / dl)
It is the viscosity when the curve is extrapolated to zero concentration, and the swelling index is the swelling index in a 25 ° C. toluene solvent.

When the intrinsic viscosity of the continuous phase is less than 0.6, the molecular weight of the continuous phase is small, the fluidity is increased, and the strength of the resin is reduced. If the intrinsic viscosity of the continuous phase exceeds 0.9, it is difficult to produce a rubber-modified polystyrene resin.
A particularly preferable range of the intrinsic viscosity of the continuous phase is 0.65 or more and 0.85 or less.

When the swelling index of the crosslinked rubber component is less than 6.5, the degree of crosslinking is too high and the rubber particles are less likely to be flattened during the foaming process. Further, when the swelling index exceeds 13.5, the degree of crosslinking is small, the elongation as a rubber is insufficient, and the crack resistance is poorly expressed. A particularly preferable range of the swelling index of the crosslinked rubber component is 8.5 or more and 12.5 or less.

In the present invention, the rubber phase is crosslinked as follows. That is, styrene monomer in which rubber is dissolved
After the solution is polymerized and the polymerization is completed, the rubber is crosslinked when the temperature is raised to a high temperature (150 ° C. or higher) under reduced pressure to recover the unreacted monomers and the solvent.

The rubber-modified polystyrene resin of the present invention is obtained by dispersing rubber particles in the polystyrene resin. The method for dispersing the rubber particles in the polystyrene resin is (1) polymerizing a solution in which a butadiene rubber component is dissolved in a styrene monomer, and allowing the rubber particles to exist as a dispersed phase in the continuous phase of the polystyrene resin. There is a method and (2) a method of mechanically mixing a butadiene rubber component with a polystyrene resin.

The method (1) is preferable because the rubber component can be dispersed as independent rubber particles. In the method (2), since the rubber component is mechanically mixed, the rubber component becomes amorphous,
It is difficult to finely disperse, and the dispersion tends to be non-uniform.

The rubber-modified polystyrene resin in which the rubber particles obtained by the method (1) are dispersed as independent rubber particles and the butadiene rubber component are mechanically mixed as in the method (2). There is also a method of obtaining a rubber-modified polystyrene resin. In this case, the mechanically mixed butadiene rubber component preferably has a small amount of independent rubber particle components obtained by the method (1). The butadiene-based rubber component used at this time is preferably a styrene-butadiene copolymer, more preferably a styrene-butadiene block copolymer. The butadiene rubber component to be mixed is preferably mixed to the extent that the effects of the present invention are not impaired. For example, it is preferable that the weight of the butadiene rubber component is 10 or less with respect to 90 of the rubber modified polystyrene resin obtained by the method (1).

The structure of the rubber particles obtained by the method (1) has a so-called core-shell structure in which a single polystyrene-based particle is enclosed inside a particle having a rubber component as an outer shell and a butadiene-based component as an outer shell. There is a so-called salami structure in which a plurality of polystyrene particles are included inside the particles.

The butadiene rubber particles of the present invention may have a core-shell structure, a salami structure, or a mixture of both. Among these rubber structures,
The particle size is 0.1 μm or more and 1 μm or less, more preferably 0.
Having a core-shell structure of 1 μm or more and 0.5 μm or less,
And 80w with a core-shell structure having a particle size of 1 μm or less
A mixture of t% or more and a salami structure of 20 wt% or less is particularly preferable. The rubber particles having a core-shell structure having a particle diameter of 1 μm or less can uniformly disperse the rubber component in the foam cell. In particular, since foamed particles having a high expansion ratio have a small bubble film thickness, rubber particles having a small particle size are suitable for uniform dispersion. In this case, the diameter of the rubber particles is 0.1μ
m or more and 10 μm or less, more preferably 0.1 μm or more and 0.5 μm or less. On the other hand, in the salami structure in which the rubber particles include a plurality of polystyrene-based resin components, the diameter of the rubber particles is relatively large at 1 μm or more, and it is difficult to uniformly disperse the rubber component in the bubble film.

In the present invention, the shape of the rubber particles in the rubber-modified polystyrene before foaming is not particularly limited, and may be, for example, spherical, elliptic spherical, or irregular.

In the present invention, the weight of the expanded beads is not particularly limited, but the average weight per expanded beads is preferably 0.2 mg to 2 mg, preferably 0.4 mg.
It is 1.2 mg. Here, the average weight per expanded particle refers to an average value of 200 randomly selected expanded particles.

Next, a method for producing expanded polystyrene particles of the present invention will be described. A preferred method for obtaining expanded particles from the rubber-modified polystyrene of the present invention is a production method comprising the following steps.

(1) A rubber-modified polystyrene-based resin comprising a continuous phase of polystyrene-based resin and a dispersed phase of butadiene-based rubber particles, wherein the continuous phase has an intrinsic viscosity of 0.6 dl.
/ G or more and 0.9 dl / g or less, and a step of mixing a rubber-modified polystyrene-based resin having a swelling index of the rubber component of 6.5 or more and 13.5 or less in an extruder in a molten state by heating.

(2) The molten mixture is placed in an extruder,
A step of holding at a temperature of 130 ° C. or more for 15 minutes or more under a pressure of 50 kg / cm ² G or more and 300 kg / cm ² G or less. (3) A step of extruding a rubber-modified polystyrene impregnated with a foaming agent from an extruder and then cutting the granulated product into granules. (4) A step of heating the obtained expandable particles.

The rubber-modified polystyrene resin used in the present invention can be produced by a usual method such as bulk polymerization, bulk suspension combined use polymerization, and irradiation polymerization. Bulk polymerization is generally carried out as follows. First, a butadiene-based polymer is dissolved in a styrene-based monomer, and this solution is polymerized while heating and stirring.

Polybutadiene (low cis polybutadiene and high cis polybutadiene: cis 1-4 addition 35%, trans 1-4 addition 52%, 1-2 addition 13% to low cis polybutadiene as the butadiene-based polymer.
including. In addition, cis 1-4 addition 90 to 98%, trans 1-4 addition 1 to 4%, 1-2 for high cis polybutadiene
Addition 1 to 6%), styrene-butadiene copolymer (random and block SBR), polyisoprene, butadiene-isoprene copolymer and the like, among which polybutadiene and styrene-butadiene copolymer are preferable. These may be used alone or as a mixture of two or more kinds.

In addition to styrene, the styrenic monomers include nuclear alkyl-substituted styrenes such as o-methylstyrene, p-methylstyrene, m-methylstyrene, 2,4-dimethylstyrene, ethylmethylstyrene, and α-methyl. Α-Alkyl-substituted styrenes such as styrene and nuclear halogenated styrenes such as o-chlorostyrene, which may be used alone or as a mixture of any two or more thereof.

In the present invention, the polystyrene resin forming the continuous phase is a homopolymer of a single monomer.
Besides, a styrene-based copolymer containing a styrene-based monomer component in an amount of 50 wt% or more can also be used. Examples of the copolymerization monomer include acrylonitrile, methyl methacrylate, maleic anhydride and the like.

During the polymerization reaction, a solvent may be added, and the solvent may be an aromatic hydrocarbon such as toluene, xylene or ethylbenzene, or a mixture of two or more thereof. The polymerization solution can be polymerized at a temperature of 100 to 180 ° C., but a polymerization initiator is used to improve the quality.

As polymerization initiators that can be used, peroxyketals such as 1,1-bis (t-butylperoxy) cyclohexane, dialkyl peroxides such as di-t-butyl peroxide, and dialper peroxides such as benzoyl peroxide. There are oxides, other peroxydicarbonates, peroxyesters, ketone peroxides, and hydroperoxides.

Examples of the chain transfer agent include α-methylstyrene dimer, n-dodecyl mercaptan, t
-Mercaptans such as dodecyl mercaptan, 1-phenylbutene-2-fluorene, dipentene and chloroform, terpenes, halogen compounds and the like can be used.

The polymerization reaction is carried out at a temperature of 50 to 170 ° C., preferably 90 to 155 ° C., at a constant temperature or in a stepwise gradual temperature increase of 2 or more.
/ Min, more preferably 0.4 to 1.5 ° C / min. )
Then, after the polymerization is advanced to a predetermined conversion rate, the unreacted monomer and the solvent are removed by a reduced pressure treatment under heating or the like to obtain a rubber-modified polystyrene resin.

This resin is continuously supplied to an extruder, and is extruded in a filament form from the pores provided in the die of the extruder while being heated and melted in the extruder, and immediately cooled in a cooling bath containing water to move up and down 2 It is sandwiched by a book drive roll, and while being pulled, it is cut in the lengthwise direction by a rotary cutter to obtain resin particles.

In order to make the dispersed rubber particles a core-shell type, it is preferable to use, for example, a styrene-butadiene block copolymer during the polymerization. When polymerizing a solution in which a styrene-butadiene block copolymer is dissolved in a styrene-based monomer, the styrene blocks have a good affinity with the styrene-based polymer phase of the matrix, so that they are collected together, and the butadiene blocks are formed between the butadiene blocks. Collectively, it is believed to form the core mold.

The butadiene component of the styrene-butadiene block copolymer used for making the dispersed rubber particles into the core-shell type is preferably 20 to 80%. In order to make the dispersed rubber particles have a core-shell structure, the affinity of the butadiene-based polymer used for the polystyrene-based resin is increased, the viscosity of the polymerization solution is adjusted, the stirring speed and time are adjusted,
This can be achieved by selecting many manufacturing conditions such as using a homogeneous stirring device (for example, disclosed in JP-A-60-130613).

On the other hand, in order to make the dispersed rubber particles into a salami type, it is preferable to use, for example, polybutadiene during the polymerization. It is considered that when polymerizing a solution in which polybutadiene is dissolved in a styrene-based monomer, the styrene-based polymer enters inside the dispersed rubber particles to form a salami type.

Also, bulk suspension combination polymerization can be used. In this method, first, the reaction in the first half is carried out in a lump and the reaction in the second half is carried out in a suspended state. That is, according to this method, a butadiene-based polymer is dissolved in a styrene-based monomer and then polymerized in the same manner as in the bulk polymerization to prepare one of the monomers.
After partially polymerizing 0 to 40%, the partially polymerized mixture is dispersed in an aqueous medium with stirring in the presence of a suspension stabilizer and a surfactant, and the latter half of the reaction is subjected to suspension polymerization. Is completed, washed, dried and, if necessary, pelletized or powdered. If necessary, additives such as dyes and pigments, lubricants, fillers, release agents, plasticizers, antistatic agents, foam nucleating agents, and ultraviolet stabilizers can be added to the obtained resin.

In the present invention, the method for obtaining the expandable resin particles, the expanded particles, and the molded product thereof is as follows. First, as a method for impregnating the rubber-modified polystyrene resin obtained above with a foaming agent to obtain expandable particles, an extrusion impregnation method or a suspension impregnation method can be used.

In the extrusion impregnation method, the rubber-modified polystyrene-based resin particles obtained above are heated and melted in an extruder, and then a volatile foaming agent is press-fitted through a foaming agent supply line separately connected to the extruder to obtain a molten state. Was sufficiently mixed with the resin in Example 1 and further retained in a molten state at 130 ° C. or higher for 15 minutes or longer, preferably 20 minutes or longer, and then extruded in a filament form through pores provided in the die of the extruder to immediately store water. While being cooled in a cooling bath, it is sandwiched between two upper and lower drive rolls, and while being pulled, it is cut in the lengthwise direction by a rotary cutter to obtain expandable resin particles.

Further, an underwater extrusion cut method can be used. The underwater extrusion cutting method is preferable because the particle shape after cutting becomes spherical. The pressure in the extruder in the molten state at 130 ° C or higher is preferably 50 to 300 kg / c.
m ² G, more preferably 100 to 200 kg / cm ² G
Is. When the pressure exceeds 300 kg / cm ² G, the cost of the extruder becomes high. If it is less than 300 kg / cm ² G, the extrusion rate will be low and the productivity will be poor.

The resin and the foaming agent are mixed and melted at 130 ° C. or more in the extruder and allowed to stay under the pressure of 15 minutes or more in order to balance the viscoelasticity of the rubber particles and the polystyrene resin during the foaming process. It is effective as a method. The reason for this is not clear, but it is considered that the foaming agent impregnates the rubber component or the polystyrene-based resin portion sufficiently uniformly, and the rubber component is appropriately plasticized.
To extend the residence time in the molten state, a conduit may be provided between the extruder and the die and adjusted by the length of the conduit. Alternatively, the residence time can be adjusted by adjusting the extrusion rate.

In the suspension impregnation method, the rubber-modified polystyrene-based resin particles obtained above are dispersed in an aqueous medium with stirring in the presence of a suspension stabilizer and a surfactant to impregnate a foaming agent. It is what makes me. Even in this method, it is important to make the impregnation temperature and time sufficiently long.

The volatile blowing agent used in the present invention has a boiling point in the range of −30 to + 100 ° C. under normal pressure, for example, aliphatic hydrocarbon such as propane, butane, pentane, hexane, heptane, petroleum ether and the like. And cycloaliphatic hydrocarbons such as cyclopentane and dichlorohexane, and halogenated hydrocarbons such as methyl chloride, ethyl chloride, methyl bromide, dichlorodifluoromethane, 1,2-dichlorotetrafluoroethane and monochlorotrifluoroethane. Etc. can be mentioned.

The amount of the foaming agent impregnated in the expandable resin particles before foaming is preferably such that 0.3 gmol to 1.7 gmol of the foaming agent is impregnated into 100 g of the rubber-modified polystyrene resin, 0.6 gmol to 1.5 gmol. 10
What is impregnated with 0 g of rubber-modified polystyrene resin is more preferable.

Next, the expandable resin particles impregnated with the foaming agent are expanded by steam in a known expander for polystyrene foam beads to form expanded particles. As for the foaming conditions, the heating temperature is 95 to 104 ° C., and the foaming holding time at this temperature is 10 to 150 seconds, preferably 20 to 60 seconds.

The foaming agent-impregnated resin particles may be annealed in warm water and then expanded to make the size of the bubbles in the expanded particles uniform. The foamed resin particles thus obtained can be fused and integrated in a molding die built in a known automatic molding machine for polystyrene foam beads to obtain a foamed molded body.

[0054]

The present invention will be described in more detail with reference to the following examples, but the present invention is not limited thereto.
The properties of the resins, expanded particles and expanded particle molded products in Examples and Comparative Examples were measured as follows.

(1) Apparent Density of Expanded Particles Expanded particles of about 5 g are weighed at the second decimal place. Then, minimum scale unit containing water of 50 to 100 cm ³ within 200 cm ³ glass measuring cylinder is 1 cm ^3, which in a slightly smaller circular metal mesh plate than the diameter of the graduated cylinder, the length at the center thereof The wire with a diameter of 15 to 30 cm is erected and the pressed tool for foamed particles is submerged, and the water level at that time is H1c.
Read m ³ . Next, remove the pressing tool, put the weighed expanded particles into a graduated cylinder, and read the water level H2 cm ^{3 in} the state of being completely submerged by the pressing tool, and calculate the apparent density ρ (g / cm ³ of the expanded particles by the following formula. ) Was asked. ρ = W / (H2 -H1) However, W: weight of the expanded particles (g) H1: before the water level to put the foamed particles (cm ³⁾ H2: water levels after the submerged foamed particles (cm ^3).

(2) Bulk Density of Expanded Particle Molded Article The bulk density D (g / cm ³ ) of the expanded particle molded article was determined by the following formula in accordance with JIS K6767. D = G / V where, G: the weight of the expanded-particle molded product (g) V: the volume of the expanded-particle molded product (cm ³ ) V is a part of the molded product cut into a rectangular parallelepiped, and the length, width, and height of the rectangular parallelepiped. Measure the dimensions and measure "vertical" x "horizontal" x "height"
It is calculated by. Measuring tools and accuracy are JI
According to SK6767.

(3) Closed cell ratio The true volume of about 24 cm ³ of foam, which is foamed particles having a known apparent density (g / cm ³ ), was measured using an air-comparison hydrometer 930 manufactured by Toshiba Beckman Co., Ltd. Measure and calculate the closed cell ratio [S, (%)] from the following formula (ASTM D-
2856). S = (Vx−W / ρ) × 100 / (Va−W / ρ)
(%) Vx: Sum of the volume of the base resin constituting the foam and the total volume of the closed cells in the foam (cm ³ ) Va: The volume of the base resin constituting the foam and the inside of the foam Sum of closed cells and total volume of open cells (cm)
³ ) W: The weight of the foam in which the content of the foaming agent gas is 0.5 wt% or less by fully replacing the foaming agent gas in the foam with air (g) ρ: The density of the base resin of the foam (g / Cm ³ ) Symbol evaluation scale ◎ Closed cell ratio 90% or more ○ 85% or more and less than 90% △ 80% or more and less than 85% × less than 80%.

(4) Average particle size and particle size distribution of rubber particles: An ultrathin section of rubber-modified polystyrene resin obtained in the polymerization step was dyed with osmium tetroxide and photographed with an electron microscope. 500 rubber particles were taken. The particle size of is measured and calculated by the following formula. D: Average particle diameter D = Σni · Di / ni R: Particle diameter distribution D1 = Σni · Di / ni D2 = Σni · (Di) ⁴ / ni · (Di) ³ R = D2 / D1 Here, Di is 0 It is the value of the particle size measured in units of 1 μm (rounding down to the first decimal place). Also, ni is the particle size Di
Is the number of particles. When the rubber particles have a non-circular cross-sectional shape and are indefinite, the particle diameter is determined by first determining the maximum diameter L1 of the cross-sectional shape, and then determining the minimum diameter L2 of the cross-sectional diameter passing through the center point of L1, Let (L1 + L2) / 2 be the particle size of the rubber particles.

(5) Intrinsic viscosity value of rubber-modified polystyrene To 1 g of rubber-modified polystyrene expanded particles was added a mixed solvent of 18 ml of methyl ethyl ketone and 2 ml of methanol.
Shake at 2 ° C. for 2 hours and centrifuge at 5 ° C. and 18000 rpm for 30 minutes. The supernatant was taken out, the resin component was precipitated with methanol, and then dried.

0.1 g of the resin thus obtained was dissolved in toluene to give a solution having a concentration of 0.5 g / dl, and 10 ml of this solution was placed in a Canon-Fenske viscometer.
At 30 ° C., the solution flow seconds t ₁ was measured. On the other hand, the flowing down time t ₀ of pure toluene was separately measured with the same viscometer, and the converted viscosity η _sp / c was calculated by the following mathematical formula (polymer
Concentration of 0.5 g / dl converted viscosity). η _sp / c = (t ₁ −t ₀ ) / (t ₀ · c) where c is the polymer concentration (g / dl). next,
The converted viscosities when c is 1.0 g / dl and 1.5 g / dl are similarly determined. Further, the intrinsic viscosity [η] which is the viscosity when the relational expression of the converted viscosity vs. the polymer concentration is extrapolated to zero polymer concentration is obtained.

(6) Swelling index of rubber-modified polystyrene About 0.5 g of rubber-modified polystyrene foam was added with 30 parts of toluene.
After adding ml, the mixture is immersed at 25 ° C. for 24 hours, shaken for 5 hours, and centrifuged at 5 ° C. and 18,000 rpm for 1 hour.
After removing the supernatant liquid by decantation, 30 ml of toluene was newly added, and the mixture was shaken at 25 ° C. for 1 hour, and 5 ° C.
Centrifuge for 1 hour at 18,000 rpm. Remove the supernatant and weigh it (W1). Then 100
Vacuum dry at 2 ° C for 2 hours and weigh the residue (W2).

The swelling index B (%) is calculated by the following formula. B = 100 * (W1-W2) / W2.

(7) Foaming agent retention performance Expandable particles are foamed by a foaming machine to give an apparent density of 0.03.
After forming expanded particles of ³ g / cm ^3, the expanded particles are treated at 23 ° C.
The foamed particles were left in the dried container for about 24 hours to remove moisture on the surface and inside of the foamed particles, and then taken out. Immediately, the foaming agent content was confirmed by the method for measuring the foaming agent content. The method for measuring the content of the foaming agent is as follows. About 5 g of expanded beads are weighed to the nearest 0.01 g. The expanded particles are placed in a glass flask having a volume of 1000 cm ³ .
Further, the weight of the glass flask containing the expanded particles is 0.0
Measure in units of 1 g. And 60 mmHg at 180 ° C
Degas under reduced pressure for 60 minutes under (absolute pressure). Then, the degassed glass flask is taken out, cooled to room temperature, returned to atmospheric pressure, and then weighed. The foaming agent content is calculated by the following formula.

G = 100 × (G ₁ −G ₂ ) / (G ₁ −G ₀ ), where G ₀ is the weight of the glass flask, and G ₁ is the total weight of the foamed particles and the glass flask before degassing under reduced pressure. , G ₂ is the total weight of the expanded beads and the glass flask after degassing under reduced pressure.

Further, the content of the foaming agent was confirmed every 3 hours by the same method, and the time required for reducing the content of the foaming agent from 4 (g / 100g resin) to 2 (g / 100g resin) by half was confirmed. The foaming agent retention performance was determined as follows. The expanded particles having apparent densities of 0.018, 0.023 and 0.040 g / cm ³ were also evaluated in the same manner. Symbol Required time (hours) ◎ 100 or more ○ ○ 75 or more and less than 100 △ 60 or more and less than 75 × less than 60.

(8) Appearance of molded body The number of voids between particles observed per 25 cm ² of the surface of the molded body, which is 1/2 or more of the particle size, was measured,
The value is used to evaluate the following scale. Symbol Number of voids on the surface Remarks ◎ 0 to 2 Very good appearance of molded article ○ 3 to 5 Almost good appearance of molded article 6 to 10 Somewhat poor appearance of molded article × 11 to 11 Bad appearance of molded article.

(9) Practical Buffer Drop Test According to JIS-Z-0202, a drop test of packaged cargo is performed. As shown in FIG. 4, the object to be packaged (14) is formed of four rubber-modified polystyrene resin foam pads, that is, pads (1
0), pad (11), pad (12), pad (1
Buffer-wrap in 3). The bulk density of the foam is 0.033g
/ Cm ³ , 0.018, 0.023, 0.040 g / cm ³
In case of, the weight of the packaged object is 30 kg, 10 kg, 2 respectively.
It was set to 0 kg and 35 kg. The pad has a static stress of 0.0 on each of the six pad surfaces on the front, back, left, right, and top.
A shape-designed one with a weight of 8 to 0.12 kg / cm ³ is used. Further, the buffer-wrapped packaged product is stored in the corrugated cardboard box (17) as it is.

When the package is dropped, first the corner (1
5) Drop with the downward direction. In this case, the pad (10) receives the largest load. Next, each of the three edges (16) of the cardboard box is dropped downward once,
Further, after dropping each of the six sides of the corrugated board box downward once, the corrugated board box is opened and the damage state of the four pads is observed.

The damaged state of the pad is a: no cracking at all,
The evaluation is performed according to the following categories: b: local small crack, c: half crack of molded body thickness, d: large crack, e: disjointed state.

Further, the damage level of the four pads after dropping on the six sides was determined by the following evaluation scale. Mark evaluation scale ◎ All four pads are a or b or c, and there are two or more a or b. O Other than the above, four are a or b or c. Other than the above item 2, there is d in four and there is no e. × All except the above 3 items.

(10) Comprehensive Evaluation The following scales are used for evaluation according to the crack resistance, the appearance of the molded product, and the results of the practical buffer drop test. Rating scale ◎ A rating of ◎ in all evaluations ○ A rating of ○ or higher in all evaluations other than the above △ A rating of △ or higher in all evaluations other than the above 2 X All evaluations other than the above 3

Example 1 (Preparation of rubber-modified polystyrene resin) A styrene-butadiene block copolymer having a butadiene content of 60 wt% was dissolved in a styrene monomer to prepare a 12 wt% solution. Ethylbenzene 5 was added to 100 parts by weight of this dissolved solution.
By weight, 1,1-bis (t-butylperoxy) cyclohexane (0.05 parts by weight) and t-dodecylmercaptan (0.05 parts by weight) are added to prepare a polymerization raw material liquid. The polymerization raw material liquid was sent to the polymerization vessel to carry out polymerization.

The polymerization temperature was raised to 105 ° C. for 3 hours, the temperature was raised to 130 ° C. for 2 hours, and the temperature was further raised to 145 ° C. for 1 hour to carry out polymerization, and then the obtained polymerization solution was sent to a devolatilizer under heating vacuum. Unreacted styrene monomer and ethylbenzene were removed to obtain a polymer. The obtained polymer was supplied to an extruder, a strand was drawn from the pores of the die, immediately cooled with water, and then cut into pellets. The obtained resin is HIPS-1
And When the content of the butadiene component of HIPS-1 was calculated from the mass balance of the styrene-butadiene block copolymer and styrene, it was 9 wt%.

HIPS-1 was mixed with polystyrene resin and then melt-mixed in a 30 mmφ uniaxial extruder. The resin thus obtained was designated as HIPS-2. When the content of the butadiene component of HIPS-2 was measured, it was 7 wt%. In addition, except that the styrene monomer solution concentration of the styrene-butadiene block copolymer was set to 14.5%, HIP
Polymerization similar to that of S-1 was performed to obtain HIPS-3. HI
The amount of butadiene component in PS-3 was 10.5%. H
The rubber particles dispersed in IPS-1, 2 and 3 were core-shell type and all had an average particle size of 0.2 μm. Further, the intrinsic viscosity value (hereinafter represented by [η]) of each continuous phase resin, the swelling index of the crosslinked rubber component (hereinafter represented by SWI) and the like are shown in Table 1. Further, Table 2 also shows resins used in Comparative Examples described later.

(Preparation of Expandable Particles) The above HIPS-1 has a pressure-supplying device for a foaming agent, and is connected so that a connection line from the pressure-supplying device leads to a melt-kneading section in a cylinder of an extruder. Further, the resin is supplied to an extrusion impregnation device equipped with a resin cooling device and a die device having a large number of outflow holes (diameter 0.7 mm) in the forehead, while melting in the extruder,
Isopentane resin 100g from the blowing agent pressure supply device
Regarding the amount, 0.13 g molar ratio was supplied by a constant amount by a pump, kneading and mixing with the resin, and further retained in a molten state at 130 ° C. for 20 minutes, then cooled to an appropriate temperature by a cooling device and provided in a die device. While being extruded into water at 60 ° C. from the resulting large number of pores, the product was cut with a rotary cutter to obtain expandable resin particles. The average particle size of the obtained particles was 1.1 mm. H
Expandable resin particles were similarly obtained for IPS-2 and 3.

(Pre-expansion and in-mold molding) The expandable resin particles obtained were expanded by a steam expansion machine. The heating conditions of the steam for foaming are as follows. First, after preheating the inside of the foaming machine with a steam, the expandable particles were charged and the steam was introduced. Air in the foaming machine for 20 seconds
The steam was filled in the machine while being expelled from the page pipe for which an orifice was provided, and the machine temperature was set to 102 ° C. (gauge pressure: 0.1 kg / cm ² G). 1 at 102 ° C
After holding for 7 seconds, the steam was purged.

The expanded beads recovered from the foaming machine were aged in a room at 20 ° C. for 24 hours. The resulting expanded beads had an apparent density of 0.033 g / cm ³ . HIPS-1, HI
The average weight per particle of PS-2 and HIPS-3 particles was 0.70 mg, 0.68 mg, and 0.69 mg, respectively. The cross section of the foamed film of the foamed particles was observed with an electron microscope. The observed b / a value, a / c value, the presence or absence of the layered structure of the rubber particles in the cross section of the foam film, the foaming agent retention property,
The closed cell rate is shown in Table 3. In addition, HIPS-1, 2, 3
The number of rubber particles (hereinafter, NR) is at least a part of the rubber particles in a square having the thickness of the foam film as one side when the foam film of the foamed particles obtained in (1) is viewed in a cross section in the thickness direction. , 20 pieces, 16 pieces, and 24 pieces. Further, the obtained expanded particles were fused and integrated in a molding die built in a molding machine for Styrofoam, and had a density of 0.020 g / c.
m ^3, and a predetermined shape, and forming a 30kg CRT monitor packaging cushioning packaging material.

(Crack resistance of molded product, appearance evaluation) The practical molded product was evaluated for practical drop cracking property and appearance. The results are shown in Table 3. All were good.

Example 2 High-cis polybutadiene rubber was dissolved in styrene monomer to prepare a 9.5 wt% solution. To 100 parts by weight of this solution, 0.04 parts by weight of 1,1-bis (t-butylperoxy) cyclohexane and 0.06 parts by weight of t-dodecyl mercaptan were added, and polymerization was initiated at 110 ° C. with stirring. After a lapse of time, the temperature was raised at 135 ° C. for 2 hours and then at 150 ° C. for 2 hours to carry out polymerization. Finally, the polymerization solution was sent to a devolatilizer under heating and vacuum to remove unreacted styrene to obtain a polymer solid HIPS-4. Butadiene component in HIPS-4 resin is 12.3 wt%, [η] is 0.80, SW
I was 9.5. The dispersed rubber particles had a salami structure and the average particle diameter was 1.3 μm. The polymerization was carried out in the same manner as HIPS-4 except that the polystyrene content in the styrene monomer was set to 5.5 wt% and the polymerization temperature conditions were changed.
PS-5 was obtained. Table 1 shows the properties of HIPS-5.

HIPS-4 and 5 were fed into an extrusion impregnation apparatus similar to that used in Example 1, isopentane was added in an amount of 0.13 per 100 g of resin while being melted in the extruder.
A constant amount of pressure was supplied by a pump to the molar ratio of g mol, and the mixture was kneaded and mixed with the resin and allowed to stay in a molten state at 130 ° C. for 25 minutes, then cooled to an appropriate temperature by a cooling device, and a large number of units were installed in the die device. The resin was extruded through pores into water at 60 ° C. and cut with a rotary cutter to obtain expandable resin particles.

The expandable resin particles obtained were foamed and aged in the same manner as in Example 1 to give an apparent density of 0.033 g / cm ^3.
Foamed particles. The average weight of the obtained expanded beads was 0.
It was 75 mg. Table 3 shows the properties of the expanded beads.
In addition, the NR of the expanded particles is 7 for HIPS-4, H
There were 6 of IPS-5. Further, the obtained expanded particles were molded in the same manner as in Example 1 and had a density of 0.020.
30 kg of a cushion packaging material for CRT monitor packaging having a predetermined shape of g / cm ³ was molded. The performance of the obtained molded product is shown in Table 2. All were good.

Example 3 A styrene-butadiene block copolymer having a butadiene content of 60 wt% was dissolved in a styrene monomer, and 1
It was a 2 wt% solution. A rubber-modified polystyrene (I) having an average particle diameter of 0.2 μm, a core-shell structure, and a butadiene component in the resin of 9 wt% and a 1-4 cis content of 96 were obtained by polymerizing this solution under stirring. % High cis polybutadiene dissolved in styrene monomer,
It was set to 9 wt%. An average particle size obtained by polymerizing this solution under stirring is 1.4 μm and has a salami structure,
Rubber-modified polystyrene (II) having a butadiene component in the resin of 12 wt% was mixed in a ratio of (I) 9 to (II) 1,
The resin thus obtained was designated as HIPS-6.

A rubber-modified polystyrene (III) having an average particle diameter of 0.3 μm and a core-shell structure and a butadiene component in the resin of 8 wt% and a salami structure having an average particle diameter of 1.7 μm Rubber modified polystyrene (IV) containing 8 wt% of butadiene component of (III) 8 vs. (IV) 2
The resulting resin was mixed with each other at a ratio of HIPS-7.
Using HIPS-6 and 7, expandable resin particles, expanded particles, and expanded particle molded bodies were produced in the same manner as in Example 1, and their properties were evaluated.
The performance is shown in Table 3. All were good. The average weight of the expanded beads was 0.64 mg and 0.62 mg for HIPS-6 and HIPS-7, respectively.

Example 4 Using HIPS-1, in the same manner as in Example 1, expandable particles impregnated with a foaming agent were produced. The resulting expandable resin particles were foamed under the same conditions as HIPS-1 except that the holding time at 102 ° C. was 30 seconds (condition 1), 20 seconds (condition 2), and 15 seconds (condition 3), and an apparent appearance was obtained. Density is 0.018g / c
m ³ (condition 1), 0.023 g / cm ³ (condition 2),
Foamed resin particles of 0.040 g / cm ³ (condition 3) were produced. Foamed particles having an apparent density of 0.018 g / cm ³ were molded in the same mold as in Example 1 to give a bulk density of 0.11 g / c.
A molded body of m ³ was obtained. Also, apparent density 0.023 g /
The foamed particles cm ³ to obtain a molded body having a bulk density of 0.14 g / cm ^3. The foamed particles of apparent density 0.040 g / cm ³ to obtain a molded body having a bulk density of 0.24 g / cm ^3. Table 4 shows the properties and performance of each foamed particle, molded product.

Example 5 Using HIPS-4, expanded particles were prepared in the same manner as in Example 4.
A molded body was produced. Table 4 shows the properties and performance of each foamed particle, molded product.

Comparative Example 1 Rubber-modified polystyrene [η] was 0.52 and SWI was 1.
Foamed particles and molded bodies were produced in the same manner as in Example 1 except that HIPS-8 of 0.5 was used. Each foamed particle,
Table 5 shows the properties and performance of the molded product. The average weight of the obtained expanded beads was 0.65 mg, and b /
The a value was 8, and the gas retention of the expanded beads, the crack resistance of the molded product, and the appearance were poor.

Comparative Example 2 Foamed particles and a molded product were prepared in the same manner as in Example 1 except that HIPS-9 having [η] of rubber-modified polystyrene of 0.92 and SWI of 8.5 was used. Each foamed particle,
Table 5 shows the properties and performance of the molded product. The average weight of the obtained expanded beads was 0.68 mg, and the crack resistance of the molded product was slightly inferior.

Comparative Example 3 Foamed particles and a molded body were produced in the same manner as in Example 1 except that HIPS-10 having [η] of rubber-modified polystyrene and SWI of 0.85 was used. Table 5 shows the properties and performance of each foamed particle, molded product. The average weight of the obtained expanded particles was 0.70 mg, the b / a value of the expanded particle cell membrane was 7, and the gas retention of the expanded particles, the crack resistance of the molded product, and the appearance were poor. .

Comparative Example 4 [η] of rubber-modified polystyrene was 0.62 and SWI was 1.
Expanded particles and a molded body were produced in the same manner as in Example 1 except that HIPS-11 of 4.5 was used. Table 5 shows the properties and performance of each foamed particle, molded product. The average weight of the obtained expanded beads was 0.68 mg, and the crack resistance and appearance of the molded product were somewhat inferior.

Comparative Example 5 HIPS-1, 4, and 6 were used, and the temperature was 130 ° C. during extrusion impregnation.
Expanded particles and a molded body were produced in the same manner as in Example 1 except that the residence time was 5 minutes. Table 5 shows the properties and performance of each foamed particle, molded product. The average weight of the obtained expanded beads was 0.70 mg and 0.69 for HIPS-1, 4 and 6, respectively.
mg, 0.70 mg, and b / a of the foamed particle cell membrane
The values of HIPS-1, 4, and 6 are 7, 6 and 7, respectively,
The performance of the expanded beads and the molded product was slightly inferior.

Comparative Example 6 Rubber-modified polystyrene particles having an average rubber particle diameter of 0.12 μm
Expanded particles and a molded body were produced in the same manner as in Example 1 except that HIPS-12 of m was used. Table 6 shows the properties and performance of each foamed particle, molded product. The average weight of the obtained expanded particles was 0.70 mg, and the a / c of the expanded particle foam film was
The value was 0.009, and the crack resistance of the molded product was poor.

Comparative Example 7 Rubber Particles of Rubber Modified Polystyrene The average rubber particle size is 3.3.
Foamed particles and a molded body were produced in the same manner as in Example 1 except that HIPS-13 having a thickness of μm was used. Each foamed particle,
Table 6 shows the properties and performance of the molded product. The average weight of the obtained expanded beads was 0.75 mg, and a /
The c value was 0.21 and the performance of the expanded beads and the molded product was poor.

Comparative Example 8 HIPS-1 was mixed with polystyrene resin and then melt-mixed in an extruder. The obtained resin is HIPS-14.
And When the content of the butadiene component of HIPS-14 was measured, it was 3% by weight. Foamed particles and a molded body were produced in the same manner as in Example 1 except that HIPS-14 was used. Table 6 shows the properties and performance of each foamed particle, molded product. The average weight of the obtained expanded beads was 0.66 mg, the rubber particles in the foam film cross section of the expanded beads did not form a layered structure, and the crack resistance of the molded product was slightly inferior.

Comparative Example 9 Apparent densities of 0.018 g / cm ³ and 0.023 g / c were obtained in the same manner as in Example 4 except that HIPS-10 was used.
m ^3, the foamed resin particles 0.040 g / cm ^3, and bulk density of ^{0.11g / cm 3, 0.14g / cm} 3, 0.2
A molded body of 4 g / cm ³ was obtained. Table 6 shows the properties and performance of each foamed particle, molded product. The average weight of the obtained expanded particles was 0.72 mg, and the b / a of the cross section of the bubble film was
All the values were less than 10, and the performance of the molded product was inferior.

[0095]

[Table 1]

[0096]

[Table 2]

[0097]

[Table 3]

[0098]

[Table 4]

[0099]

[Table 5]

[0100]

[Table 6]

[0101]

EFFECTS OF THE INVENTION The molded article molded using the expanded particles of the rubber-modified polystyrene resin of the present invention is suitably used as a cushioning material for packaged cargo, which is expected to have a relatively large weight and a high impact frequency. To be Since the molded product has excellent crack resistance, the amount of cushioning material used can be reduced. Further, it is also useful as a heat insulating material for houses and tanks by taking advantage of the flexibility due to the rubber component blending. The expanded beads and expanded beads molded product of the present invention can be produced at relatively low cost by using general equipment,
In addition, the expanded particles have good gas retention for the foaming agent, and therefore, the expanded ability of the expanded particles is great, resulting in excellent appearance such as good appearance of the molded product. It has the advantage that it can be riveted. As described above, the expanded beads of the present invention are extremely useful in the field of foam molding processing.

[Brief description of drawings]

FIG. 1 is a schematic explanatory view showing a dispersed state of rubber particles in a cross section of a bubble film according to the present invention.

FIG. 2 is a schematic explanatory view showing a cross-sectional state of the expanded beads of the present invention.

FIG. 3 is an enlarged view of a broken line portion of FIG.

FIG. 4 is a schematic explanatory view showing a packaging form of a practical drop test in the present invention.

[Explanation of symbols]

 1 Cell cross-section 2 Cell membrane surface 3 Polystyrene continuous phase 4 Polystyrene component part of rubber particles 5 Butadiene component part of rubber particles 6 Foamed particles 7 Foamed particle cross section 8 Bubbles 9 Cell membrane

Claims (8)

[Claims] 1. A foamed particle composed of a rubber-modified polystyrene-based resin in which a butadiene-based polymer rubber particle in which the polystyrene-based resin is encapsulated in the form of small particles is dispersed in a continuous phase of the polystyrene-based resin, wherein the rubber particle is The foamed particles are flatly dispersed in the plane direction of the bubble film, and when the bubble film is viewed in the cross section in the thickness direction, the rubber particles are present in a plurality of layers in the thickness direction, and the rubber particles have a layer thickness direction. (A), the dimension (b) of the rubber particles in the bubble film surface direction, and the bubble film thickness dimension (c) have a / c of 0.01 or more and 0.2 or less, and b / A is 10 or more and 70 or less polystyrene-based expanded particles. 2. The apparent density of expanded particles is 0.014 g /
It is not less than cm ^{3 and not} more than 0.100 g / cm ^3.
Expanded polystyrene-based particles. 3. The intrinsic viscosity of the continuous phase of the rubber-modified polystyrene-based resin in toluene at 30 ° C. is 0.6 or more and 0.9 or less, and the gel content of the rubber-modified polystyrene-based resin in toluene at 25 ° C. The expanded polystyrene particles according to claim 1 or 2, having a swelling index of 6.5 or more and 13.5 or less. 4. The expanded polystyrene particles according to claim 1, wherein the butadiene-based polymer rubber particles are a styrene-butadiene block copolymer or polybutadiene. 5. The expanded polystyrene particles according to claim 1, wherein the polystyrene resin forming the continuous phase is polystyrene or a styrene copolymer containing 50% by weight or more of a styrene component. 6. The expanded polystyrene particles according to claim 1, wherein the butadiene-based polymer rubber particles have a core-shell structure containing a single polystyrene-based resin particle. 7. A butadiene-based polymer rubber particle having a core-shell structure of 80 wt% or more and a salami structure of 20
The expanded polystyrene particles according to any one of claims 1 to 6, which are mixed particles of not more than wt%. 8. A method for producing expanded beads from a rubber-modified polystyrene resin, comprising the following steps. (1) A rubber-modified polystyrene-based resin comprising a continuous phase of polystyrene-based resin and a dispersed phase of butadiene-based rubber particles, wherein the continuous phase has an intrinsic viscosity of 0.6 or more and 0.9 or less in toluene at 30 ° C. And the swelling index of the butadiene rubber particles in toluene at 25 ° C. is 6.5 or more, 13.
A step of mixing a rubber-modified polystyrene resin of 5 or less with a foaming agent in a heating and melting state in an extruder to obtain a molten mixture (2) The molten mixture in an extruder is 50 kg /
Under a pressure of not less than cm ² G and not more than 300 kg / cm ² G,
A step of obtaining a rubber-modified polystyrene resin impregnated with a foaming agent by holding at a temperature of 130 ° C. or more for 15 minutes or more (3) Extruding the rubber-modified polystyrene resin impregnated with the foaming agent, and then cutting it into granules (4) A method of impregnating a rubber-modified polystyrene resin with a foaming agent, which comprises the step of heating the expandable particles.