JP5690621B2 - Expandable polystyrene resin particles, expanded particles and expanded molded articles - Google Patents

Description

  The present invention relates to expandable polystyrene resin particles, expanded particles, and expanded molded articles. More specifically, the present invention relates to an expandable polystyrene resin particle capable of giving a foamed molded product that can be attached even with a low-adhesive label, and a foamed particle and a foamed molded product obtained therefrom.

Conventionally, a foam-molded article composed of a polystyrene-based resin has been used as a transport container for food and agricultural products, a food container, and the like. Such a foamed molded body is usually provided with a pattern on the surface for improving design properties, displaying contents, and the like. As a method of providing a pattern, there is a method of attaching a label printed with a pattern.
The affixed label may peel from the foamed molded product. In that case, it is necessary to press the label again. Therefore, it is desired to provide a foamed molded product in which the peeling of the label is suppressed.
As a method for suppressing the peeling of the label, there is a method described in JP-A-10-15777 (Patent Document 1). This method is a method for preventing the peeling of the label by improving the smoothness of the surface of the foam molded product without providing a steam slit mark on the outer surface of the foam molded product.

JP-A-10-15777

However, in the method described in the above publication, it is necessary to newly provide a molding die having a structure that does not give the slit mark to the foamed molded product, and it is high in order to improve the appearance and fusion property of the foamed molded product. There is a problem that heat is required, which is disadvantageous in terms of cost.
Therefore, there is no need to install a molding die, there is no problem in cost, and a foamed molded product that can be attached with a low-adhesive label and expandable styrene resin particles that can provide this foamed molded product are provided. Was desired.

The inventors of the present invention reviewed the production procedure of the foam molded article and the additives used during the production. As a result, it has been found that the label is easily peeled off when the amount of the fusion accelerator used is increased. Since this fusion accelerator is used for the purpose of improving the fusing property of the foamed particles constituting the foamed molded article, it is difficult to reduce the amount of use.
Therefore, the inventors of the present invention have focused on the powder component present before washing the expandable polystyrene resin particles. The inventors believe that this powder component is produced in the production process of expandable polystyrene resin particles and is mainly composed of a fine polystyrene resin, a dispersant and the like. Since this powder component was generally considered to be an unnecessary component, it is removed as much as possible by washing. However, it is surprisingly found that the expandable polystyrene resin particles in which the powder component and the fusion accelerator are present on the surface in a specific range can give a foamed molded article that can be attached with a low-adhesive label. This led to the present invention.

Thus, according to the present invention, expandable polystyrene containing at least polystyrene resin particles, a foaming agent present in the polystyrene resin particles, and a fusion accelerator and a powder component present on the surface of the polystyrene resin particles. Resin particles,
The expandable polystyrene resin particles have an average particle diameter of 0.5 to 1.2 mm,
The powder component is included in an amount of 0.008 to 0.025 parts by mass with respect to 100 parts by mass of the expandable polystyrene resin particles,
The fusion promoter and the powder component are present in a ratio of 2 to 7.5: 1 (mass ratio) ;
It said powder component, expandable polystyrene resin particles is provided, which comprises have a mean particle size of less 100 [mu] m.

Moreover, the foamed particle obtained by foaming the said expandable polystyrene-type resin particle is provided.
Furthermore, a foam molded article obtained by foam molding of the foamed particles is provided.

According to the present invention, it is possible to attach a label having a low adhesive strength (for example, 700 gf / 25 mm or less) without using a special mold, and a foamed molded article having excellent fusion property and the foamed product. A molded body can be provided, and expandable styrene-based resin particles and expanded particles in which blocking during preliminary foaming is suppressed can be provided.
In addition, since the powder component has an average particle diameter of 100 μm or less, it is possible to attach a label having a lower adhesive strength, and expandable polystyrene resin particles capable of giving a foamed molded article having excellent fusion property. Can be provided.
Furthermore, since the fusion accelerator is contained in an amount of 0.035 to 0.075 parts by mass with respect to 100 parts by mass of the expandable polystyrene resin particles, a label having a lower adhesive strength can be attached. It is possible to provide expandable polystyrene resin particles that can provide a foamed molded article having excellent fusing property.

It is a figure which shows the relationship between the fusion accelerator amount of Example 1-5 and Comparative Examples 1-2, and the amount of powder components, and a fusion rate x peeling prevention rate.

(Expandable polystyrene resin particles)
Expandable polystyrene resin particles (hereinafter also referred to as expandable particles) include at least a foaming agent, a fusion accelerator, and a powder component.
(1) Polystyrene resin Expandable polystyrene resin particles contain a polystyrene resin as a base resin.
The polystyrene resin is not particularly limited, and for example, a styrene monomer such as styrene, α-methylstyrene, paramethylstyrene, vinyltoluene, chlorostyrene, ethylstyrene, i-propylstyrene, dimethylstyrene, bromostyrene, or the like. Examples thereof include a polymer or a copolymer thereof.
Examples of the polystyrene resin include a copolymer of a styrene monomer and a vinyl monomer copolymerizable with the styrene monomer.

Examples of the vinyl monomer copolymerizable with the styrenic monomer include alkyls having 1 to 8 carbon atoms such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, and cetyl (meth) acrylate (meta ) Acrylate, (meth) acrylonitrile, dimethyl maleate, dimethyl fumarate, diethyl fumarate, ethyl fumarate, difunctional monomers such as divinylbenzene, alkylene glycol dimethacrylate, maleic anhydride, N-vinylcarbazole, etc. Can be mentioned.
In the polystyrene resin, it is preferable that a component derived from a styrene monomer occupies a main component (50 mass% or more, preferably 80 mass% or more, more preferably 99.8 mass% or more). Furthermore, the polystyrene resin preferably contains 50% by mass or more of a component derived from styrene, and more preferably consists of only polystyrene.

  Furthermore, the weight average molecular weight in terms of styrene of the polystyrene resin is preferably 200,000 to 500,000. If it is less than 200,000, the mechanical strength of the foamed molded product obtained by foaming the expandable polystyrene resin particles may decrease. On the other hand, if it is larger than 500,000, the foamability of the expandable polystyrene resin particles may be reduced, and a high-magnification foamed molded article may not be obtained. A more preferable molecular weight is 240,000 to 400,000.

(2) Foaming agent The foaming agent is present in the expandable polystyrene resin particles.
As the foaming agent, a gaseous or liquid organic compound having a boiling point equal to or lower than the softening point of the polystyrene resin and normal pressure is suitable. For example, hydrocarbons such as propane, normal butane, isobutane, normal pentane, isopentane, neopentane, cyclopentane, cyclopentadiene, normal hexane, petroleum ether, ketones such as acetone and methyl ethyl ketone, alcohols such as methanol, ethanol and isopropyl alcohol, Low boiling point ether compounds such as dimethyl ether, diethyl ether, dipropyl ether, methyl ethyl ether, halogen-containing hydrocarbons such as HCFC-141b, HCFC-142b, HCFC-124, HFC-134a, HFC-152a, carbon dioxide, nitrogen And inorganic gases such as ammonia. These foaming agents may be used alone or in combination of two or more. Among these, it is preferable to use hydrocarbons from the viewpoint of preventing the destruction of the ozone layer and from the viewpoint of quickly replacing with the air and suppressing the time-dependent change of the foamed molded product. Among the carbon hydrogens, hydrocarbons having a boiling point of −45 to 40 ° C. are more preferable, and propane, normal butane, isobutane, normal pentane, isopentane and the like are more preferable.
The amount of the foaming agent used is preferably 1 to 10 parts by mass, more preferably 2 to 7 parts by mass with respect to 100 parts by mass of the expandable polystyrene resin particles.

(3) Fusion promoter The fusion promoter is present on the surface of the expandable polystyrene resin particles.
Examples of the fusion accelerator include 12-hydroxystearic acid triglyceride, 12-hydroxystearic acid amide, stearic acid amide and the like.
Further, the fusion accelerator is present in a ratio of 2 to 7.5: 1 (mass ratio) in terms of the ratio between the fusion accelerator and the powder component. When the ratio of the fusion accelerator is less than 2, the fusion of the foamed particles constituting the foamed molded product may be insufficient. When it is larger than 7.5, the adhesiveness of the label is lowered, and it may be peeled off. A more preferable ratio between the fusion accelerator and the powder component is 2.5 to 7: 1.
The fusion promoter is preferably used in an amount of 0.035 to 0.075 parts by mass with respect to 100 parts by mass of the expandable polystyrene resin particles. When the amount used is less than 0.035 parts by mass, a sufficient fusion promoting effect may not be obtained. When the amount used exceeds 0.075 parts by mass, the adhesiveness of the label is lowered and may be peeled off. The amount used is more preferably 0.04 to 0.06 parts by mass.

(4) Powder component The powder component is present on the surface of the expandable polystyrene resin particles.
The inventors believe that the powder component is produced in the production process of the expandable polystyrene resin particles, and is mainly composed of a fine polystyrene resin, a dispersant and the like.
The powder component preferably has an average particle size of 100 μm or less. If it is larger than 100 μm, the appearance of the molded product may be deteriorated. A more preferable average particle diameter is 10 to 50 μm.

  The powder component is usually contained in an amount of about 0.008 to 0.025 parts by mass with respect to 100 parts by mass of the expandable polystyrene resin particles. In order to reduce the content of the powder component from 0.008 parts by mass, the number of washing steps is large, and the production time becomes long. If the amount exceeds 0.025 parts by mass, the fusion is hindered, so a large amount of a fusion accelerator is required, and as a result, label peeling is caused, which is not preferable. A more preferable content of the powder component is 0.01 to 0.02 parts by mass.

(5) Other components Expandable polystyrene resin particles may contain other known components. Examples of other components include an anti-blocking agent, a foaming aid, a flame retardant, a flame retardant aid, a bubble regulator, a filler, a lubricant, and a colorant.
Examples of the antiblocking agent include zinc stearate. It is preferable that 0.07-0.15 mass part of antiblocking agent is contained with respect to 100 mass parts of expandable polystyrene resin particles. If the content is less than 0.07 parts by mass, the anti-blocking effect may not be sufficient. If the amount is more than 0.15 parts by mass, the anti-blocking agent may fall off from the surface of the expandable polystyrene resin particles and adhere to the inside of the transport pipe, which may block the pipe and inhibit fusion during molding. May be. A more preferable content is 0.09 to 0.12 parts by mass.

Examples of the foaming aid include toluene, xylene, cyclohexane, ethyl acetate, dioctyl phthalate, and tetrachloroethylene.
Examples of the flame retardant include tetrabromocyclooctane, hexabromocyclododecane, trisdibromopropyl phosphate, tetrabromobisphenol A, and the like.
Moreover, as a flame retardant adjuvant, the organic peroxide like a dicumyl peroxide is mentioned, for example.

(6) Shape of expandable polystyrene resin particles The shape of the expandable polystyrene resin particles is not particularly limited, and any shape such as a spherical shape, a cylindrical shape, or an indefinite shape can be taken. Among these, considering the filling property into the mold, it is preferably spherical or cylindrical.
The expandable polystyrene resin particles have an average particle diameter of 0.5 to 1.2 mm. If the average particle size is smaller than 0.5 mm, the foaming agent may not be retained and foaming may not be achieved up to a desired expansion ratio. If the average particle diameter is larger than 1.2 mm, the particle diameter of the foamed particles becomes large, so that the filling ability into the mold may be inferior. A more preferable average particle diameter is 0.6 to 1.0 mm.

(7) Production Method of Expandable Polystyrene Resin Particles Expandable polystyrene resin particles can be obtained, for example, by impregnating polystyrene resin particles with a foaming agent and washing them to a predetermined powder component amount.
As the polystyrene resin particles, those produced by a known method can be used. For example,
(1) A method of extruding a polystyrene resin melt-kneaded by an extruder into a strand shape and cutting the strand,
(2) Suspension in which an aqueous medium, a styrene monomer and a polymerization initiator are supplied into an autoclave, and the styrene monomer is suspension-polymerized while heating and stirring in the autoclave to produce polystyrene resin particles. Polymerization method,
(3) After supplying seed particles of aqueous medium and polystyrene resin into the autoclave and dispersing the seed particles in the aqueous medium, the styrene monomer is continuously or intermittently heated and stirred in the autoclave. And polystyrene resin particles obtained by a seed polymerization method or the like for producing polystyrene resin particles by polymerizing in the presence of a polymerization initiator while absorbing styrene monomers in seed particles. It is done. The seed particles can be obtained by classifying the particles obtained by the suspension polymerization method (2).

  The polymerization initiator used in the suspension polymerization method and the seed polymerization method is not particularly limited, and examples thereof include benzoyl peroxide, lauryl peroxide, t-butyl peroxybenzoate, t-butyl peroxide, and t-butyl peroxide. Oxypivalate, t-butyl peroxyisopropyl carbonate, t-butyl peroxy-2-ethylhexyl monocarbonate, isopropyl carbonate, t-butyl peroxyacetate, 2,2-bis (t-butylperoxy) butane, t- Organic peroxides such as butylperoxy-3,3,5 trimethylhexanoate and di-t-butylperoxyhexahydroterephthalate, and azo compounds such as azobisisobutyronitrile and azobisdimethylvaleronitrile It is done. These may be used alone or in combination of two or more.

An aqueous suspension obtained by dispersing polystyrene resin particles in an aqueous medium may be obtained by using the reaction liquid after polymerization by the suspension polymerization method or seed polymerization method as an aqueous suspension, or by using the suspension weight described above. An aqueous suspension may be formed by separating the polystyrene resin particles obtained by the combination method or the seed polymerization method from the reaction solution and suspending the polystyrene resin particles in an aqueous medium separately prepared.
It does not specifically limit as an aqueous medium, For example, water, alcohol, etc. are mentioned. Of these, water is preferred.

In the suspension polymerization method or the seed polymerization method, a suspension stabilizer may be used to stabilize the dispersibility of the styrene monomer droplets or the polystyrene resin seed particles when the styrene monomer is polymerized. Good. Examples of such suspension stabilizers include water-soluble polymers such as polyvinyl alcohol, methyl cellulose, polyacrylamide, and polyvinyl pyrrolidone, and poorly water-soluble inorganic salts such as tricalcium phosphate and magnesium pyrophosphate. When using a poorly water-soluble inorganic salt, an anionic surfactant is usually used in combination.
Examples of the anionic surfactant include alkyl sulfates such as sodium lauryl sulfate, alkylbenzene sulfonates such as sodium dodecylbenzene sulfonate, higher fatty acid salts such as sodium oleate, and β-tetrahydroxynaphthalene sulfonate. Can be mentioned. Of these, alkylbenzene sulfonates are preferred.

In order to stabilize the dispersibility of the polystyrene resin particles even when the aqueous suspension is formed by suspending the polystyrene resin particles obtained by the suspension polymerization method or the seed polymerization method in a separately prepared aqueous medium. The above-mentioned suspension stabilizer and anionic surfactant may be added to the aqueous medium.
Under the present circumstances, it is preferable that the addition amount to the aqueous medium of a slightly water-soluble inorganic salt is 0.2-2 mass parts with respect to 100 mass parts of aqueous media. When the amount is less than 0.2 parts by mass, the dispersibility of the polystyrene resin particles in the aqueous medium may be reduced, and the polystyrene resin particles may be agglomerated. When the amount is more than 2 parts by mass, the viscosity of the aqueous medium in which the polystyrene resin particles are dispersed may increase, and the polystyrene resin particles may not be uniformly dispersed in the aqueous medium.

  The impregnation of the foaming agent into the polystyrene resin particles may be performed on the particles after polymerization of the styrene monomer, or may be performed on the growing particles. Impregnation during the polymerization can be performed by a method of impregnation in an aqueous medium (wet impregnation method). The impregnation after polymerization can be carried out by a wet impregnation method or a method of impregnation in the absence of a medium (dry impregnation method). Moreover, it is preferable to perform the impregnation in the middle of the polymerization usually in the latter stage of the polymerization.

The expandable polystyrene resin particles are appropriately washed after impregnation with the foaming agent in order to obtain a predetermined powder component amount. Here, when an inorganic salt is used as the dispersion stabilizer during the production process, it is preferable to remove the inorganic salt as a water-soluble salt with a strong acid such as hydrochloric acid.
Next, the expandable particle | grains of this invention are obtained by apply | coating a fusion accelerator to the particle | grain surface to expandable polystyrene type resin particle. As an application method, it is preferable to stir the expandable polystyrene resin particles together with the fusion accelerator in a stirrer. As the stirrer, a stirrer such as a tumbler mixer or a Redige mixer is used.

(Foamed particles)
Foamed particles can be obtained by foaming expandable polystyrene resin particles. The foamed particles for food containers preferably have a bulk density in the range of 0.014 to 0.033 g / cm ³ . When the bulk density exceeds 0.033 g / cm ³ , productivity may be reduced. If it is less than 0.014 g / cm ³ , the strength of the molded product may be lowered. A more preferable bulk density is in the range of 0.015 to 0.025 g / cm ³ .

(Foamed molded product)
In the foamed molded product, the expanded particles (pre-expanded particles) are filled into a closed mold having a large number of small holes, heated and foamed again with pressurized steam, etc., filling the gaps between the expanded particles, and the expanded particles mutually. It can be manufactured by being integrated by fusing.
Since the surface of the obtained foamed molding is derived from the surface of the expandable particles, the amount of the fusion accelerator and the powder component is equal to the amount of the expandable particles. Therefore, even a low adhesive label having an adhesive strength of 700 gf / 25 mm or less can be easily attached.
The foamed molded product can be used in a wide range of applications such as food containers such as agricultural boxes and fishery boxes, and containers for material transportation.

EXAMPLES Hereinafter, although this invention is demonstrated in detail based on an Example, this invention is not limited by these Examples. Various measurement methods in the examples are described below.
<Average particle size>
The average particle diameter is a value expressed by D50. Specifically, sieve opening 4.00 mm, opening 3.35 mm, opening 2.80 mm, opening 2.36 mm, opening 2.00 mm, opening 1.70 mm, opening 1.40 mm, opening 1.18 mm, opening 1.00 mm, opening 0.85 mm, opening 0.71 mm, opening 0.60 mm, opening 0.50 mm, opening 0.425 mm, opening 0.355 mm, opening 0. Particle size with a cumulative mass of 50% based on the cumulative mass distribution curve obtained by classification using a JIS standard sieve with 300 mm, 0.250 mm mesh, 0.212 mm mesh, and 0.180 mm mesh (Median diameter) is referred to as the average particle diameter.

<Weight average molecular weight>
A weight average molecular weight means the styrene conversion weight average molecular weight measured in the following ways.
That is, 30 mg of polystyrene resin is dissolved in 10 ml of chloroform. The resulting solution is filtered through a non-aqueous 0.45 μm chromatographic disk, and the average molecular weight is measured under the following conditions using a chromatograph.
Gas chromatograph: Product name “Detector 484, Pump 510” manufactured by Water
Column: Showa Denko Corporation trade name “Shodex GPC K-806L (φ8.0 × 300 mm)” Column temperature: 40 ° C.
Carrier gas: Chloroform Carrier gas flow rate: 1.2 ml / min injection / pump temperature: room temperature detection: UV254 nm
Injection amount: standard polystyrene for 50 microliter calibration curve: trade name “shodex” manufactured by Showa Denko KK: weight average molecular weight: 1030000 and weight average molecular weight manufactured by Tosoh Corporation: 5480000, 3840000, 355000, 102000, 37900, 9100, 2630,495 Polystyrene

<Amount of powder component>
1 liter of the expandable polystyrene resin particle dispersion is weighed. The dispersion is provided in a beaker in which holes are provided on the side surfaces and a nylon net having a mesh opening of 0.18 mm is attached to the holes. Attach a stirrer to the beaker and stir at 270 rpm. By pouring an aqueous solution of sodium alkylbenzene sulfonate having a concentration of 50 ppm under stirring, the powder component adhering to the expandable polystyrene resin particles is separated and dispersed in the liquid. A polycup is installed at the flow outlet of the beaker, and 6 liters of the powder component dispersion is collected.
A glass fiber filter paper GA-200 is laid on a Buchner funnel, and the powder component dispersion is suction filtered. The filtered powder is dried together with the filter paper in an oven at 45 ° C. for 24 hours.
Further, the expandable polystyrene resin particles from which the powder component remaining in the beaker is separated are dried.
The mass of the expandable polystyrene resin particles from which the powder component is separated is A, the mass of the glass filter paper is B, the mass of the powder component after drying including the glass filter paper is C, and the amount of the powder component is measured by the following formula. .
Powder component amount (parts by mass) = (C−B) / (A + C−B) × 100

<Average particle size of powder component>
An aperture having a pore size of 400 μm is attached to Multisizer 3 manufactured by Beckman Coulter, an appropriate amount of the filtrate containing the powder component obtained in the measurement of the amount of the powder component is supplied, and the average particle size is measured.

<Bulk density>
The bulk magnification of the pre-expanded particles is measured according to JIS K6911: 1995 “General Test Method for Thermosetting Plastics”. Specifically, first, Wg is collected using pre-expanded particles as a measurement sample, and this measurement sample is naturally dropped into a measuring cylinder. The volume Vcm ³ of the measurement sample dropped into the graduated cylinder is measured using an apparent density measuring instrument based on JIS K6911. By substituting Wg and Vcm ³ into the following formula, the bulk density of the pre-expanded particles is calculated.
Bulk density of pre-expanded particles (g / cm ³ ) = mass of measurement sample (W) / volume of measurement sample (V)

<Bonded amount of pre-expanded particles>
W1g of pre-expanded particles are prepared, the pre-expanded particles are sieved with a sieve having an opening of 0.5 cm, and the mass W2g of the pre-expanded particles remaining on the sieve is measured. The value obtained by substituting W1 and W2 into the following formula is defined as the degree of bonding of the pre-expanded particles. Note that a degree of bond of 1% by mass or less is evaluated as “◯”, and a value exceeding 1% by mass is evaluated as “x”.
Bonding degree of pre-expanded particles (% by mass) = 100 × W2 / W1
<Density of foam molding>
The mass (a) and the volume (b) of the test piece (example 75 × 300 × 35 mm) cut out from the foamed molded product (after being molded and dried at 40 ° C. for 20 hours or more) each have three or more significant figures. And the density (kg / m ³ ) of the foamed molded product is obtained from the formula (a) / (b).

<Fusion molding fusion rate>
A cutting line having a depth of about 5 mm is made with a cutter knife along the center of the foam molded body. Thereafter, the foamed molded product is manually divided into two along the cut line. Regarding the foamed particles in the fracture surface, the number (a) of particles broken in the particles and the number (b) of particles broken at the interface between the particles in an arbitrary range of 100 to 150 are counted. A value obtained by substituting the result into the formula [(a) / ((a) + (b))] × 100 is defined as a fusion rate (%). A fusion rate of 80% or more is evaluated as ○, and a less than 80% is evaluated as ×.

<Label peeling evaluation>
A label having an adhesive strength of 600 gf / 25 mm is attached to the side surface of the foam molded product. After pasting, leave for 24 hours. Thereafter, the number (a) of foam molded products in which peeling occurs on the tape attached to the side surface with respect to 100 arbitrary foam molded products and the number (b) of foam molded products in which peeling does not occur are counted. A value obtained by substituting the result into the formula [(b) / ((a) + (b))] × 100 is defined as a peeling prevention rate (%). Evaluation is made with a peel prevention rate of 80% or more as ◯ and less than 80% as x.

[Example 1]
(Manufacture of resin particles)
Into a polymerization vessel equipped with a stirrer having an internal volume of 100 liters, 40000 g of water, 100 g of calcium triphosphate as a suspension stabilizer and 2.0 g of calcium dodecylbenzenesulfonate as an anionic surfactant are stirred and 40000 g of styrene monomer and a polymerization initiator are stirred. After adding 96.0 g of benzoyl peroxide and 28.0 g of t-butylperoxybenzoate, the temperature was raised to 90 ° C. to polymerize. And it hold | maintained at this temperature for 6 hours, and also, after heating up to 125 degreeC, it cooled after 2 hours, and obtained the polystyrene-type resin particle (a).
The polystyrene resin particles (a) were sieved to obtain polystyrene resin particles (b) having a particle diameter of 0.5 to 0.71 mm as seed particles.
Next, 40000 g of water, 10000 g of polystyrene resin particles (b), 120.0 g of magnesium pyrophosphate as a suspension stabilizer, and calcium dodecylbenzenesulfonate 6 as an anionic surfactant are placed in a polymerization vessel equipped with a stirrer having an internal volume of 100 liters. 0.0 g was supplied and the temperature was raised to 75 ° C. while stirring.

Next, 110.0 g of benzoyl peroxide and 4.0 g of t-butyl peroxybenzoate as a polymerization initiator dissolved in 2000 g of styrene monomer were supplied to the polymerization vessel having an internal volume of 100 liters. Hold for 60 minutes.
After 60 minutes, the reaction solution was heated to 110 ° C. in 150 minutes, and 28000 g of styrene monomer was fed into the polymerization vessel by a fixed amount in 150 minutes, and then heated to 120 ° C. for 2 hours. After cooling to 70 ° C., polystyrene resin particles (c) were obtained (weight average molecular weight 300,000).

(Foaming agent impregnation)
Subsequently, 180.0 g of cyclohexane as a foaming aid was placed in a polymerization vessel, sealed and heated to 100 ° C. Next, 3600 g of n-butane as a foaming agent was pressed into a polymerization vessel containing 30000 g of polystyrene resin particles (c) and held for 3 hours. Thereafter, the mixture was cooled to 30 ° C. or lower and taken out from the polymerization vessel, and 300 ml of hydrochloric acid of 20 mol / L hydrochloric acid was added and stirred. Subsequently, it dehydrated with a wire mesh having a mesh opening of 0.5 mm, and again poured 40 liters of water, stirred, and then dehydrated with a metal mesh having a mesh opening of 0.5 mm. The process from water injection to dehydration was the cleaning process, and the cleaning process was carried out three times to make the adhered powder component 0.015% by mass. After dehydrating and drying, it was left in a thermostatic chamber at 13 ° C. for 5 days to obtain expandable polystyrene resin particles (a).
Subsequently, the surface of the expandable polystyrene resin particles (a) was coated with 0.1% by mass of zinc stearate as an antiblocking agent and 0.05% by mass of 12-hydroxystearic acid triglyceride as a fusion accelerator. By the coating treatment, expandable polystyrene resin particles (b) having an adhering powder component amount of 0.015% by mass and a fusion accelerator amount of 0.05% by mass were obtained.

(Pre-foaming)
Next, the expandable polystyrene resin particles (b) were prefoamed to a bulk density of 0.017 g / cm ³ using a prefoaming apparatus and then aged at 20 ° C. for 24 hours to obtain prefoamed particles. The bonding amount of the pre-expanded particles was as good as 0.40% by mass.
(Manufacture of foam moldings)
Subsequently, the obtained pre-expanded particles were put into a cavity of a mold, and the pre-expanded particles were vaporized at a vapor pressure of 0.7 kgf / cm ² using a molding machine “ACE-30QS” (manufactured by Sekisui Koki Co., Ltd.). A foamed molded article was obtained by heating for 17 seconds. Next, the foamed molded body in the cavity of the molding die was water-cooled for 5 seconds, and then allowed to cool under reduced pressure to take out a box-shaped foamed molded body having a width of 300 mm × length of 430 mm × height of 130 mm × thickness of 20 mm.
The obtained foamed molded article had no shrinkage and had a heat fusion rate of 90% and a good heat fusion property.

(Labeling process)
Subsequently, after the foamed molded product was naturally dried for 24 hours, an OPS label made by Sato Co., Ltd. having a width of 370 mm and a length of 80 mm was attached to the long side using a labeler (manufactured by Sekisui Chemical Co., Ltd.). Table 1 shows the peeling prevention rate.

Example 2
A foam molded article was obtained in the same manner as in Example 1 except that the amount of the fusion accelerator was 0.07% by mass. Table 1 shows the fusion rate and the peeling prevention rate. The amount of pre-expanded particles bound was as good as 0.50% by mass.
Example 3
A foam molded article was obtained in the same manner as in Example 1 except that the amount of the fusion accelerator was 0.04% by mass. Table 1 shows the fusion rate and the peeling prevention rate. The amount of pre-expanded particles bonded was as good as 0.40% by mass.

Example 4
A foamed molded article was obtained in the same manner as in Example 1 except that the washing step after impregnation with the foaming agent was performed twice so that the amount of the powder component was 0.02% by mass. The results are shown in Table 1. The amount of pre-expanded particles bound was as good as 0.50% by mass.
Example 5
A foamed molded article was obtained in the same manner as in Example 1 except that the washing step after impregnation with the foaming agent was performed 5 times to make the amount of the powder component 0.008% by mass. Table 1 shows the fusion rate and the peeling prevention rate. The amount of pre-expanded particles bound was as good as 0.50% by mass.

Comparative Example 1
A foam molded article was obtained in the same manner as in Example 1 except that the amount of the fusion accelerator was 0.012% by mass. Table 1 shows the fusion rate and the peeling prevention rate. The amount of pre-expanded particles bonded was as good as 0.80% by mass.
Comparative Example 2
Foam molding in the same manner as in Example 1 except that the washing step after impregnation with the foaming agent is performed twice so that the amount of the powder component is 0.02% by mass and the amount of the fusion accelerator is 0.03% by mass. Got the body. Table 1 shows the fusion rate and the peeling prevention rate. The amount of pre-expanded particles bound was 0.40% by mass.

Comparative Example 3
A foamed molded article was obtained in the same manner as in Example 1 except that the amount of the powder component was changed to 0.044% by mass by performing the washing step after impregnation with the foaming agent. Table 1 shows the fusion rate and the peeling prevention rate. The amount of pre-expanded particles bound was as good as 0.60% by mass.
Comparative Example 4
Foam molding is performed in the same manner as in Example 1 except that the amount of the powder component is 0.04% by mass and the amount of the fusion accelerator is 0.015% by mass by setting the cleaning process after impregnating the foaming agent once. Got the body. Table 1 shows the fusion rate and the peeling prevention rate. The amount of pre-expanded particles bonded was 1.10% by mass, which was a large amount of bonded.

Further, for Examples 1 to 5 and Comparative Examples 1 and 2, the relationship between the amount of fusion accelerator / the amount of powder components and the fusion rate × the delamination prevention rate is shown in FIG. The reason why only Comparative Examples 1 and 2 are shown in FIG. 1 is that the amount of fusion accelerator and the amount of powder components are close to those of Examples 1 to 5. Further, a higher value of fusion rate × peeling prevention rate means that fusion and prevention of peeling can be achieved at a higher level.
It can be seen from Table 1 and FIG. 1 that if the amount of the fusion accelerator and the amount of the powder component are in a specific range, a foamed molded product having a high fusion rate and a high label peeling prevention rate can be obtained.

Claims (5)

Expandable polystyrene resin particles comprising at least polystyrene resin particles, a foaming agent present in the polystyrene resin particles, a fusion accelerator and a powder component present on the surface of the polystyrene resin particles,
The expandable polystyrene resin particles have an average particle diameter of 0.5 to 1.2 mm,
The powder component is included in an amount of 0.008 to 0.025 parts by mass with respect to 100 parts by mass of the expandable polystyrene resin particles,
The fusion promoter and the powder component are present in a ratio of 2 to 7.5: 1 (mass ratio) ;
It said powder component, expandable polystyrene resin particles characterized by have a mean particle size of less 100 [mu] m. 2. The expandable polystyrene resin particles according to claim 1 , wherein the fusion accelerator is contained in an amount of 0.035 to 0.075 parts by mass with respect to 100 parts by mass of the expandable polystyrene resin particles. Foamed particles obtained by foaming the expandable polystyrene resin particles according to claim 1 or 2 . A foam-molded product obtained by foam-molding the foamed particles according to claim 3 . The foamed molded product according to claim 4 , wherein a label having an adhesive strength of 700 gf / 25 mm or less can be attached.

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