JP4480435B2 - Expandable styrene resin particles, method for producing the same, and foam molded product - Google Patents

Description

  The present invention relates to an expandable styrene resin particle, an expanded molded article obtained by using the expandable styrene resin particle, and a method for producing the expandable styrene resin particle.

  Conventionally, pre-expanded particles are produced by pre-expanding expandable styrene resin particles obtained by impregnating a foaming agent into styrene-based resin particles, and the pre-expanded particles are filled in a mold of a molding machine. A foam-molded container having a desired shape has been manufactured by heating and foaming and fusing together.

  As described above, the foam-molded container is formed by thermally fusing together the foam particles obtained by foaming the pre-foamed particles by the foaming pressure of the pre-foamed particles themselves. The particles are not entirely heat-sealed at the opposed portions of the particles, but are only partially heat-sealed and integrated.

  Therefore, even if the foam-molded container is in a state where the foam particles are in good condition, that is, in a state where the surfaces of the foam particles are completely heat-sealed and integrated in the cross section of the foam-molded container, As the gap due to the non-heat-sealed part in the opposite part of the slab is continuous in the inner and outer directions, a fine capillary that cannot be visually confirmed is formed in a state penetrating between the inner and outer surfaces of the foam molded container. .

  This is because if the dye water containing the surfactant is put in the foam molded container and left for a predetermined time, the dye water in the foam molded container oozes out to the outside through the capillary formed between the foam particles. A phenomenon occurs, and the presence of the capillary can be confirmed by this phenomenon.

  When such a foam molded container is used as a drinking cup such as coffee, there is no practical problem, but oil-based foods such as donuts, hamburgers, fried chicken, margarine are contained in the foam molded container. When foods containing salad oil, fats, etc. are stored for a long period of time, the oil contained in these oily foods oozes out through capillaries formed in foam molded containers There was a point.

  Similarly, if the foamed container contains the noodles containing curry powder together with the instant noodles, the yellow pigment of the curry powder oozes out to the outer surface of the foam molded container through the capillary of the foam molded container. As a result, there was a problem that the commercial value was impaired.

  Therefore, in Patent Document 1, the styrene polymer is added by continuously or intermittently adding a styrene monomer and a polymerization initiator to an aqueous suspension containing styrene polymer seed particles. A method for producing expandable styrene polymer particles by polymerizing the styrene monomer on seed particles to obtain styrene polymer particles, and impregnating the styrene polymer particles with a readily volatile foaming agent, When the total amount of the amount of the styrenic polymer seed particles and the amount of the styrene monomer necessary for obtaining the target styrene polymer particles is 100 parts by weight, the styrenic polymer seed particles From the time when the total amount of the styrene monomer added to 90 parts by weight until the addition of the styrene monomer is completed and the polymerization reaction is completed, the total amount of 100 0.005 to 0.02 parts by weight with respect to parts by weight Preparation of expandable styrene polymer particles added a bridge agent (seed polymerization method) is disclosed.

However, although the expandable styrene polymer particles produced by the above production method are effective means for improving the appearance of the foam molded product obtained using the expandable styrene polymer particles, The above-described problem that oil and yellow pigment ooze out to the outside through a capillary tube formed in a foam molded container has not been sufficiently solved.
Japanese Patent No. 3474995

  Therefore, the present inventor has intensively studied, and in the portion where the oil component and the yellow pigment ooze out in the foam molded container, the heat-sealed portion of the foam particles is wavy and wrinkled. On the other hand, in the parts where no oil or yellow pigment oozes out, there is no waviness phenomenon in the heat-sealed part of the expanded particles, and there is no distortion. In order to prevent oil and yellow pigment from seeping out in the foam molded container, the oil resistance of the foam molded product, in particular, the oil resistance of the heat-sealed part between the foam particles of the foam molded product is known. I found it necessary to improve.

  Even in the case where the oil contained in food or the like and the pigment such as curry powder are stored in the interior for a long period of time or the liquid containing the surfactant is stored in the interior for a predetermined time. Provided is an expandable styrenic resin particle having excellent foamability, a foamable styrenic resin particle that can be obtained without exuding to the outside, and a foamed styrene resin particle molded using the expandable styrenic resin particle. .

The expandable styrene resin particles of the present invention have a gel fraction of 10 to 50% by weight and a bulk density of 0.025 to 0.06 g / min when pre-foamed by being immersed in water at 100 ° C. for 5 minutes. In the pre-foamed particles that are cm ³ and pre-foamed by steam at a bulk magnification of 10 times, the average bubble diameter of the surface layer portion is 10 to 70 μm, and the average bubble diameter of the surface layer portion and the central portion The ratio of the bubble to the average bubble diameter satisfies the following formula.
0.4 ≦ average bubble diameter of bubbles in the surface layer portion / average bubble diameter of bubbles in the central portion ≦ 0.8

  The styrene resin constituting the expandable styrene resin particles of the present invention is not particularly limited, and examples thereof include styrene, α-methyl styrene, vinyl toluene, chlorostyrene, ethyl styrene, i-propyl styrene, and dimethyl styrene. Examples include homopolymers of styrene monomers or copolymers thereof.

  The styrenic resin is a copolymer of the styrenic monomer and a vinyl monomer copolymerizable with the styrenic monomer, the main component of which is the styrenic monomer. Examples of such vinyl monomers include alkyl (meth) acrylates such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, and cetyl (meth) acrylate, (meth) Examples include acrylonitrile, dimethyl maleate, dimethyl fumarate, diethyl fumarate, and ethyl fumarate. In addition, 150,000-400,000 are preferable and, as for the weight average molecular weight of the said styrene resin, 250,000-350,000 are more preferable.

  If the gel fraction of the expandable styrene resin particles is low, the oil resistance of the foam molded product obtained by using the expandable styrene resin particles is lowered, and a liquid containing oil, pigment, surfactant, etc. Ooze out to the outside through the foam molded product, while if it is high, the foamability of the expandable styrenic resin particles will be reduced, and it will be necessary to heat the foamable styrenic resin particles for a long time, resulting in lower production efficiency. Therefore, it is limited to 10 to 50% by weight, and preferably 20 to 35% by weight.

In addition, the gel fraction of expandable styrene resin particle means what was measured in the following way. That is, the expandable styrene resin particles are heated in an oven at 140 ° C. for 1 hour, the foaming agent in the expandable styrene resin particles is removed to prepare a measurement sample, and the weight W _{1 of the} measurement sample is calculated. taking measurement.

Next, the measurement sample was immersed in 100 g of toluene and refluxed at 140 ° C. for 20 hours, followed by filtration using an 80-mesh wire mesh. The residue on the wire mesh was supplied into a desiccator and supplied at 140 ° C. for 2 hours. After drying under reduced pressure under a reduced pressure of 7.98 × 10 ⁴ Pa over time, it was naturally cooled to room temperature in a desiccator, and the weight W _{2 of the} dried residue was measured and calculated by the following formula.
Gel fraction (% by weight) = 100 × W ₂ / W ₁

If the bulk density when the foamable styrene resin particles are pre-foamed by immersing them in water at 100 ° C. for 5 minutes is too low, the foamability of the foamable styrene resin particles is too high, and a foam molded product is obtained. After that, it takes extra time to cool the foamed particles until they no longer expand, whereas if it is high, the foamability of the foamable styrene resin particles is reduced, and the heating time during foam molding takes a long time. , limited to ^{0.025~0.06g / cm 3, 0.027~0.04g / cm} 3 are preferred.

Here, in the present invention, the bulk density of the pre-expanded particles obtained by pre-expanding the expandable styrenic resin particles refers to those measured in the following manner. That is, the bulk density of the pre-expanded particles is measured in accordance with JIS K6911: 1995 “General Test Method for Thermosetting Plastics”. First, Wg was sampled from pre-expanded particles as a measurement sample, this measurement sample was naturally dropped into a graduated cylinder, and the volume Vcm ³ of the measurement sample dropped into the graduated cylinder was measured using an apparent density measuring instrument based on JIS K6911. The bulk density of the pre-expanded particles was measured based on the following formula.
Bulk density of pre-expanded particles (g / cm ³ )
= Weight of measurement sample (W) / Volume of measurement sample (V)

  In addition, what was produced in the following way is used for the measurement sample at the time of measuring the bulk density when foaming styrene resin particles are immersed in water at 100 ° C. for 5 minutes and pre-foamed. First, expandable styrenic resin particles are immersed in water at 100 ° C. for 5 minutes to be pre-expanded, and the obtained pre-expanded particles are separated from water using an 80-mesh wire mesh, and then on the wire mesh at 40 ° C. What was dried for 20 hours is used as a measurement sample.

  Further, if the average cell diameter of the surface layer portion of the pre-expanded particles obtained by pre-expanding the expandable styrene resin particles with steam to 10 times the bulk ratio is small, a foam-molded product is formed using the expandable styrene resin particles. When molding, the bubbles are broken by the heat during molding, and the appearance of the foamed molded product is deteriorated.On the other hand, if the foamed product is large, the gloss of the foamed molded product obtained using the expandable styrenic resin particles is impaired. It is limited to 70 μm, and preferably 20 to 60 μm. The bulk magnification of the pre-expanded particles is obtained by dividing the density of the styrenic resin constituting the expandable styrene-based resin particles by the bulk density of the pre-expanded particles.

In addition, the ratio of the average cell diameter of the cells in the surface layer to the average cell size of the cells in the central part of the pre-expanded particles obtained by pre-expanding the expandable styrene resin particles with a bulk ratio of 10 times by steam (hereinafter referred to as “average cell size”). The diameter ratio ”needs to satisfy the following formula 1, and preferably satisfies the following formula 2.
0.4 ≦ (average bubble diameter of the bubbles in the surface layer portion / average bubble diameter of the bubbles in the center portion) ≦ 0.8... 10.6 ≦ (average bubble diameter of the bubbles in the surface layer portion / the bubbles in the center portion) Average bubble diameter) ≤ 0.8 Formula 2

  This is because when the average cell diameter ratio is small, the foamability in the surface layer portion of the expandable styrene resin particles is lowered, and the foaming pressure necessary for heat-sealing the expanded particles cannot be obtained. If the average cell diameter ratio is large, the foamable styrenic resin may result in insufficient heat fusion between the liquids and the liquid containing oil, pigment, or surfactant may ooze out through the foamed molded product. This is because the oil resistance of the foam molded product obtained using the particles is lowered, and there is a possibility that a liquid containing an oil component, a pigment or a surfactant may ooze out through the foam molded product.

  Here, the surface layer part and the center part of the pre-expanded particles pre-expanded to 10 times the bulk magnification by steam and the average cell diameter of these bubbles are determined as follows. That is, the expandable styrenic resin particles are pre-foamed with steam at a bulk magnification of 10 times. Then, the pre-expanded particles that have been pre-expanded to a bulk magnification of 10 times are cut so that the weight of the pre-expanded particles is bisected on the surface passing through the center of gravity.

  And the scanning electron micrograph of magnification 80-80 times is obtained for the whole cut surface of this pre-expanded particle of 10 times the bulk magnification using a scanning electron microscope. A perfect circle (outer circle) with the smallest diameter is drawn that surrounds the entire cut surface of the pre-expanded particles shown in this scanning electron micrograph.

  A perfect circle (center circle) centered on the center of the outer circle and having a radius that is 1/3 of the diameter of the outer circle is drawn, and the pre-foamed particle portion existing in the center circle is defined as the center portion. Optionally, 20 bubbles are extracted from the existing bubbles. It should be noted that the target bubbles are those in which the entire bubble is contained in the central portion, and any bubbles protruding outside the central portion are excluded. If the number of bubbles present in the central portion is less than 20, all the bubbles present in the central portion are targeted.

  Next, the maximum chord length of each extracted bubble is measured, and the arithmetic average of the maximum chord length of each bubble is taken as the average bubble diameter of the bubbles in the center. Note that the maximum chord length of a bubble is the longest straight line when any part of the inner surface of the bubble wall that forms this bubble is connected with a straight line when a single bubble is focused (however, even a part of the bubble passes outside the bubble) The length R of the straight line (excluding the dotted straight line in FIG. 1) (see FIG. 1).

  On the other hand, a perfect circle (surface layer circle) centered on the center of the outer circle and having a radius 2/5 of the diameter of the outer circle is drawn, and the pre-expanded particle portion existing between the surface layer circle and the outer circle is drawn. As the surface layer portion, 20 bubbles are arbitrarily extracted from the bubbles existing in the surface layer portion. The target bubbles are those in which the entire bubbles are included in the surface layer portion, and any bubbles that protrude outside the surface layer portion are excluded. When the number of bubbles existing in the surface layer portion is less than 20, all the bubbles existing in the surface layer portion are targeted. Next, the maximum chord length of each extracted bubble is measured, and the arithmetic average of the maximum chord length of each bubble is taken as the average bubble diameter of the bubbles in the center.

  Next, the manufacturing method of the said expandable styrene resin particle is demonstrated. First, a dispersion liquid in which styrene resin seed particles are dispersed in water is prepared. As a method for producing the styrene-based resin seed particles, a general-purpose method is used. For example, a styrene-based monomer is added to the styrene-based monomer as necessary, followed by suspension polymerization in water and styrene. A method of producing a styrene-based resin seed particle, a method of supplying the styrene-based resin to an extruder, melt-kneading, extruding it into a strand from the extruder and cutting it at a predetermined length, and the like Is mentioned.

  Then, the styrenic monomer is continuously or intermittently supplied into a dispersion obtained by dispersing the styrenic resin seed particles in water, and seed polymerization is performed in the presence of a polymerization initiator to produce a styrenic Resin seed particles are grown as seed particles to produce styrene resin particles. In the present invention, resin particles that are in the process of growth using styrene resin seed particles as seed particles are referred to as “styrene resin growth particles”. Further, the vinyl monomer copolymerizable with the styrene monomer may be supplied together with the styrene monomer into the dispersion.

  At this time, the total amount of the styrene monomer and the styrene resin seed particles already supplied in the dispersion (hereinafter referred to as “total amount supplied”) is the same as the styrene resin seed particles and the styrene resin particles. When the total amount of styrene monomer required for production (hereinafter referred to as “total amount required for supply”) is 60% by weight or more and less than 90% by weight, preferably 75 to 85% by weight At that time, the crosslinkable monomer is started to be fed into the dispersion.

  This is because, when the total amount supplied is less than 60% by weight of the total amount required for supply, when the crosslinkable monomer is started to be fed into the dispersion, the inside of the resulting expandable styrene resin particles is unnecessarily crosslinked. When the foamability of the expandable styrenic resin particles is reduced, and when the total amount supplied is 90% by weight or more of the total supply amount, the supply of the crosslinkable monomer into the dispersion liquid, The surface part of the resin particle is cross-linked more than necessary, the foamability of the surface part of the expandable styrene resin particle is lowered, and the thermal fusion between the expanded particles is insufficient, and a good foam molded product is obtained. Because it is not possible.

  Here, the crosslinkable monomer is not particularly limited as long as the crosslinkable structure can be imparted to the expandable styrenic resin particles. For example, alkylene such as divinylbenzene and polyethylene glycol ditaacrylate is used. Examples thereof include polyfunctional monomers such as glycol dimethacrylate, and divinylbenzene is preferred.

  Then, the supply of the crosslinkable monomer into the dispersion liquid is started at the above timing, and then continuously or intermittently until the supply of the styrenic monomer into the dispersion liquid is completed. Done. Specifically, after the supply of the crosslinkable monomer into the dispersion liquid is started at the above-mentioned timing, the styrene monomer is further supplied into the dispersion liquid and the supplied total amount is the total supply amount required. After reaching 90% by weight or more, the crosslinkable monomer is continuously or intermittently supplied into the dispersion.

  In addition, if the crosslinkable monomer is supplied in the dispersion even after the supplied total amount becomes 90% by weight or more of the total supply required, the point of completion of the supply of the crosslinkable monomer into the dispersion And the completion of the supply of the styrenic monomer into the dispersion liquid may not match, and the completion of the supply of the crosslinkable monomer into the dispersion liquid may It may be earlier than the completion of the supply to the liquid.

  Thus, even after the supplied total amount reaches 90% by weight or more of the total supply required amount, a predetermined thickness portion in the surface portion of the expandable styrene resin particles can be obtained by supplying the crosslinkable monomer into the dispersion. The gel fraction (crosslinking degree) suitable for foaming can be obtained.

  As for the supply of the crosslinkable monomer into the dispersion, the crosslinkable monomer may be supplied into the dispersion separately from the styrenic monomer, but the residual not yet supplied into the dispersion. All the crosslinkable monomers supplied in the dispersion are dissolved in the total amount of the styrene monomer, and the styrene monomer in which the crosslinkable monomer is dissolved is supplied in the dispersion. Is preferred.

  In this way, when the crosslinkable monomer is dissolved in the styrene monomer and then supplied to the dispersion, the styrene resin seed particles are used as seed particles to crosslink in the growing styrene resin growing particles. The ratio of the polymerizable monomer and the styrene monomer can be kept substantially constant during the seed polymerization, and the gel fraction in the resulting expandable styrene resin particles can be foamed from the surface over a predetermined thickness. It can be made suitable and substantially uniform, and the foamed molded article obtained can have excellent oil resistance while ensuring foamability of the expandable styrene resin particles.

  And if the total amount of the styrene monomer required for the production of the styrene resin particles is small, the amount of the styrene monomer to be polymerized by one seed polymerization may decrease, which may be uneconomical. If the amount is too large, the time required for seed polymerization may become long and the productivity may be lowered. Therefore, it is preferable to adjust the styrene resin seed particles to 10 to 90% by weight in the styrene resin particles. It is more preferable to adjust so that it may become 20 to 80 weight%.

Further, if the total amount of the crosslinkable monomer supplied to the dispersion is small, the gel fraction of the expandable styrene resin particles is lowered, and the oil resistance of the obtained foamed molded product may be lowered. On the other hand, if the amount is too large, the gel fraction of the expandable styrenic resin particles may become too high and the foamability may decrease. Therefore, after the supply of the crosslinkable monomer is started in the dispersion, And 0.25 to 0.50 parts by weight, more preferably 0.25 to 0.45 parts by weight based on 100 parts by weight of the styrene monomer required for the production of styrene resin particles.

  In addition, if the content of the styrene monomer in the styrene resin growing particles after the supply of the crosslinkable monomer into the dispersion liquid is small, the surface portion of the expandable styrene resin particles is necessary. While the cross-linking is carried out as above, the moldability of the expandable styrene resin particles is lowered. On the other hand, the styrene monomer is impregnated more than necessary inside the styrene resin growth particles. As the styrene resin-grown particles are impregnated inside, the crosslinkable monomer is also impregnated inside the styrene-resin-grown particles, and the entire expandable styrene resin particles are crosslinked, Since the foaming property is lowered, it is necessary to adjust to 3 to 15% by weight, preferably 3 to 12% by weight.

  In addition, content of the styrene-type monomer in a styrene-type resin growth particle means what was measured in the following way. That is, the styrene-based resin growth particles are taken out from the dispersion, and the water adhering to the surface of the styrene-based resin growth particles is wiped off using gauze.

  Then, 0.08 g of styrene resin growing particles are collected, and the collected styrene resin growing particles are dissolved in 25 ml of toluene to prepare a toluene solution. Next, 10 ml of Wis reagent, 30 ml of 5% by weight potassium iodide aqueous solution and 30 ml of 1% by weight starch aqueous solution are supplied into this toluene solution, and titrated with an N / 40 sodium thiosulfate solution. Set the drop constant (milliliter). The Wis reagent is obtained by dissolving 8.7 g of iodine and 7.9 g of iodine trichloride in 2 liters of glacial acetic acid.

  On the other hand, without dissolving the styrene-based resin growth particles, 10 ml of Wis reagent, 30 ml of 5 wt% potassium iodide aqueous solution and 30 ml of 1 wt% starch aqueous solution were supplied in 25 ml of toluene, and N / 40 Titrate with sodium thiosulfate solution to blank titration (in milliliters).

And the amount of styrene-type monomers in a styrene-type resin growth particle is computable based on a following formula.
Amount of styrene monomer in styrene resin growth particles (wt%)
= 0.1322 × (blank drop constant−sample drop constant) / sample drop constant

  The polymerization initiator used when the styrene monomer is impregnated into the styrene resin seed particles and seed polymerization is not particularly limited, and examples thereof include benzoyl peroxide, lauryl peroxide, and t-butyl. Peroxybenzoate, t-butyl peroxide, t-butyl peroxypivalate, t-butyl peroxyisopropyl carbonate, t-butyl peroxyacetate, 2,2-t-butylperoxybutane, t-butylperoxy- Organic peroxides such as 3, 3, 5 trimethylhexanoate, di-t-butylperoxyhexahydroterephthalate, and azo compounds such as azobisisobutyronitrile, azobisdimethylvaleronitrile, etc. Or may be used in combination with a half-life of 10 hours A polymerization initiator having a decomposition temperature of 50 ° C. or higher and lower than 80 ° C. and a polymerization initiator having a decomposition temperature of 80 ° C. or higher and 120 ° C. or lower to obtain a half-life of 10 hours may be used in combination. preferable. In addition, as addition amount of a polymerization initiator, 0.01-3 weight part is preferable with respect to 100 weight part of styrene-type monomers.

  In addition, a suspension stabilizer or a stabilizing aid may be added to the dispersion to improve the dispersion stability of the styrene-based seed particles and the styrene resin-grown particles that are growing using the seed particles as seed particles. .

  Examples of the suspension stabilizer include water-soluble polymers such as polyvinyl alcohol, methyl cellulose, polyacrylamide, and polyvinyl pyrrolidone, and poorly soluble inorganic compounds such as tribasic calcium phosphate and magnesium pyrophosphate. When an is used, an anionic surfactant is usually used in combination.

  Examples of such anionic surfactants 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. Etc.

  Next, the styrenic resin particles obtained by the seed polymerization are impregnated with a foaming agent, or the styrenic resin growth particles are impregnated with the foaming agent in the course of the seed polymerization to obtain expandable styrenic resin particles. To manufacture.

  As the blowing agent, general-purpose ones are used. For example, aliphatic hydrocarbons such as propane, butane, pentane; 1,1-dichloro-1-fluoroethane (HCFC-141b), 1-chloro-1,1 -Difluoroethane (HCFC-142b), 2-chloro-1,1,1,2-tetrafluoroethane (HCFC-124), 1,1,1,2-tetrafluoroethane (HFC-134a), 1,1- Examples thereof include CFC-based blowing agents such as difluoroethane (HFC-152a), and aliphatic hydrocarbons are preferable. In addition, a foaming agent may be used independently or may be used together. Furthermore, general-purpose additives such as bubble regulators such as thiodipropionic acid ester, thiodibutyric acid ester, ethylenebisstearic acid amide, ultraviolet absorbers, extenders, and colorants are added to the expandable styrene resin particles. May be.

  The average particle diameter of the expandable styrenic resin particles is adjusted depending on the use of the obtained foam molded product. When the foam molded product is a foam molded container and the thickness is thin, 0.2 to 1 mm is used. preferable.

The expandable styrenic resin particles thus obtained are pre-foamed by a pre-foaming machine to be pre-foamed particles, and the pre-foamed particles obtained are filled in a mold of the foam molding machine and heated. It is foamed by a heating medium such as steam, and is heat-fusion integrated with each other by foaming pressure to obtain a foamed molded product having a desired shape. The bulk density of the pre-expanded particles is preferably 0.015 to 0.500 g / cm ³ .

  In addition, the foamed molded article includes various forms, but is preferably a cup-shaped, bowl-shaped, tray-shaped, box-shaped or other foam-molded container in that the effects and effects of the present invention are effectively exhibited. In this foamed container, beef tallow, soybean oil, rapeseed oil, sesame oil, olive oil, sesame oil, bean flower oil, corn oil and other vegetable oils, lard, instant noodles, stew, mayonnaise, dressing sauce, curry roux, butter, margarine, white Oily foods such as sauces, yogurts, ice creams, donuts, hamburgers, and fried chicken, fat foods, aqueous solutions containing surfactants, and the like can be stored.

  The foamed molded product is obtained by foaming predetermined foamable styrene resin particles as described above, and therefore, the foamed particles are firmly heat-sealed and integrated at the interface between them. At the same time, the interface part where the foamed particles are heat-sealed has high crosslink density and excellent oil resistance.

  Therefore, when food containing oil or pigments such as curry powder is stored in the foam molded product for a long period of time, or liquid containing a surfactant is stored in the foam molded product. However, the thermal fusion interface between the expanded particles is not affected by the oil, the dye, or the surfactant, and therefore the oil, the dye, and the surfactant are included through the thermal fusion interface between the expanded particles. It is possible to substantially prevent the situation that the liquid oozes out from the outer surface of the foam molded product.

The expandable styrene resin particles of the present invention have a gel fraction of 10 to 50% by weight and a bulk density of 0.025 to 0.06 g / min when pre-foamed by being immersed in water at 100 ° C. for 5 minutes. In the pre-foamed particles that are cm ³ and pre-foamed with steam at a bulk magnification of 10 times, the average cell diameter of the bubbles in the surface layer portion is 10 to 70 μm, and the average cell diameter of the bubbles in the surface layer portion and the central portion Since the ratio of a certain bubble to the average bubble diameter is within a predetermined range, it has excellent foamability, and a foam molded product obtained by foaming the expandable styrene resin particles is excellent in that. The foam particles are firmly heat-sealed and integrated with each other by sufficient foaming pressure due to the foaming property, and the heat-sealed part between the foam particles is formed by foaming the surface portion of the foamable styrene resin particles. Because it is a thing, its high Demonstrates excellent oil resistance derived from the water fraction.

  Therefore, even when a food containing oil is stored for a long period of time in a foamed molded product or a liquid containing a surfactant is stored, the heat-sealed portion between the foamed particles of the foamed molded product However, the oil or surfactant contained in the foamed molded product hardly oozes out and the foamed product is practically problematic. Can be used.

  And in the said expandable styrene resin particle, when the gel fraction is 20 to 35% by weight, this expandable styrene resin particle is maintained while maintaining the excellent foamability of the expandable styrene resin particle. The foamed molded product obtained by foaming has further excellent oil resistance at the heat fusion interface between the foamed particles.

  Furthermore, in the foam molded product obtained by foaming the expandable styrene resin particles, the heat-sealed portion between the expanded particles is derived from the surface portion having a high gel fraction in the expandable styrene resin particles. Therefore, it has excellent oil resistance. Therefore, when a food containing oil is stored for a long period of time in a foamed molded product or a liquid containing a surfactant is stored. However, the heat-sealed part between the foamed particles of the foamed molded product is not altered by the oil or surfactant, and the liquid containing the oil or surfactant contained in the foamed molded product oozes out to the outside. There is almost no such thing, and the foamed molded product can be used practically without any problem.

Example 1
In a stainless steel 100 liter autoclave equipped with a stirrer, 32,000 parts by weight of ion exchange water, 20000 parts by weight of polystyrene seed particles having an average particle size of 0.3 to 0.5 mm and a weight average molecular weight of 280,000, pyrroline 200 parts by weight of magnesium oxide and 8 parts by weight of sodium dodecylbenzenesulfonate were supplied and stirred to prepare a dispersion.

  On the other hand, after dispersing 1 part by weight of sodium dodecylbenzenesulfonate and 10 parts by weight of magnesium pyrophosphate in 6000 parts by weight of ion-exchanged water, benzoyl peroxide (decomposition temperature for obtaining a half-life of 10 hours: 74 ° C.) 70 parts by weight and 15 parts by weight of t-butyl peroxybenzoate (decomposition temperature for obtaining a half-life of 10 hours: 104 ° C.) dissolved in 5000 parts by weight of styrene were further added and stirred to be emulsified. A styrene emulsion was prepared.

  And after heating the said dispersion liquid to 85 degreeC, the said styrene emulsion is supplied in this dispersion liquid, and immediately after hold | maintaining the said dispersion liquid at 85 degreeC for 40 minutes, this dispersion liquid is 85 degreeC. In the dispersion liquid, 5000 parts by weight of styrene was continuously dropped over 40 minutes and dropped at the same dropping rate to perform seed polymerization.

  Thereafter, while maintaining the above dispersion at 85 ° C., a styrene solution in which 25 parts by weight of divinylbenzene was dissolved in 10000 parts by weight of styrene was continuously added to this dispersion over 80 minutes at the same dropping rate. The seed polymerization was conducted dropwise. Subsequently, after the dispersion was held at 85 ° C. for 1 hour, the temperature was raised to 125 ° C. over 50 minutes, and the dispersion was held at 125 ° C. for 2 hours to complete the polymerization. The dispersion was cooled to 90 ° C. and held. In addition, the styrene content in the growing polystyrene particles was measured every 20 minutes from the start of supplying divinylbenzene into the dispersion using the polystyrene seed particles as seed particles. Moreover, all the styrene supplied in the dispersion was used for seed polymerization.

  On the other hand, 10 parts by weight of dilauryl thiodipropionate and 0.5 parts by weight of sodium dodecylbenzenesulfonate were supplied to 500 parts by weight of ion-exchanged water and stirred and dispersed.

  Thereafter, 2240 parts by weight of normal pentane and 560 parts by weight of isopentane are injected into the autoclave containing the above dispersion, heated to 115 ° C. over 30 minutes, held for 2 hours, and then cooled to 30 ° C. Then, after separating and removing water, drying was performed to obtain expandable polystyrene particles having an average particle diameter of 450 μm. In addition, the scanning electron micrograph image | photographed when measuring the average cell diameter ratio of the pre-expanded particle obtained by pre-expanding expandable polystyrene particle | grains with water vapor | steam by 10 times the bulk magnification was shown in FIG.

(Example 2)
The dispersion prepared in the same manner as in Example 1 was heated to 85 ° C., and then the styrene emulsion prepared in the same manner as in Example 1 was supplied into the dispersion. Immediately after being held for 40 minutes, 10000 parts by weight of styrene was continuously added dropwise to the dispersion over the course of 80 minutes while maintaining the dispersion at 85 ° C.

  Thereafter, while maintaining the dispersion at 85 ° C., a styrene solution prepared by dissolving 15 parts by weight of divinylbenzene in 5,000 parts by weight of styrene was continuously taken over 40 minutes at the same dropping rate. The seed polymerization was conducted dropwise. Thereafter, the same procedure as in Example 1 was carried out to obtain expandable polystyrene particles having an average particle diameter of 450 μm. All styrene supplied in the dispersion was used for seed polymerization.

(Example 3)
The dispersion prepared in the same manner as in Example 1 was heated to 85 ° C., and then the styrene emulsion prepared in the same manner as in Example 1 was supplied into the dispersion. Immediately after being held for 40 minutes, while maintaining this dispersion at 85 ° C., a styrene solution prepared by dissolving 40 parts by weight of divinylbenzene in 15,000 parts by weight of styrene was taken over 120 minutes at the same dropping rate. Seed polymerization was carried out by dripping continuously. Thereafter, the same procedure as in Example 1 was carried out to obtain expandable polystyrene particles having an average particle diameter of 450 μm. Note that all styrene supplied in the dispersion was used for seed polymerization.

Example 4
In a 100 liter stainless steel autoclave equipped with a stirrer, 32,000 parts by weight of ion-exchanged water, 32,000 parts by weight of polystyrene seed particles having an average particle size of 0.3 to 0.5 mm and a weight average molecular weight of 280,000, pyrroline 200 parts by weight of magnesium oxide and 8 parts by weight of sodium dodecylbenzenesulfonate were supplied and stirred to prepare a dispersion.

  On the other hand, 1 part by weight of sodium dodecylbenzenesulfonate and 10 parts by weight of magnesium pyrophosphate were dispersed in 6000 parts by weight of ion-exchanged water, and then 28 parts by weight of benzoyl peroxide and 15 parts by weight of t-butylperoxybenzoate were added to styrene 2000. What was melt | dissolved in the weight part was further added, and it agitated and emulsified and produced the styrene emulsion.

  And after heating the said dispersion liquid to 85 degreeC, the said styrene emulsion is supplied in this dispersion liquid, and immediately after hold | maintaining the said dispersion liquid at 85 degreeC for 40 minutes, this dispersion liquid is 85 degreeC. The styrene solution prepared by dissolving 27 parts by weight of divinylbenzene in 6000 parts by weight of styrene was continuously dropped over 60 minutes at the same dropping rate to carry out seed polymerization. Thereafter, the same procedure as in Example 1 was carried out to obtain expandable polystyrene particles having an average particle diameter of 400 μm. All styrene supplied in the dispersion was used for seed polymerization.

(Example 5)
While a dispersion was prepared in the same manner as in Example 1, a styrene emulsion was prepared in the same manner as in Example 1 except that 90 parts by weight of benzoyl peroxide was used instead of 70 parts by weight.

  The dispersion is heated to 85 ° C., and then the styrene emulsion is supplied into the dispersion. Immediately after the dispersion is held at 85 ° C. for 40 minutes, 10,000 weight of styrene is added to the dispersion. The solution is continuously dropped over 90 minutes at the same dropping rate, and while the styrene is being supplied into the dispersion, the temperature of the dispersion is kept constant at a rate of 0.2 ° C./min. The temperature rose.

  Thereafter, a styrene solution prepared by dissolving 20 parts by weight of divinylbenzene in 5,000 parts by weight of styrene is continuously dropped over 30 minutes into the above dispersion at the same dropping rate. During the supply to the inside, the temperature of the dispersion was increased at a constant temperature increase rate of 0.2 ° C./min to perform seed polymerization. Thereafter, the same procedure as in Example 1 was carried out to obtain expandable polystyrene particles having an average particle diameter of 450 μm. All styrene supplied in the dispersion was used for seed polymerization.

(Comparative Example 1)
Expandable polystyrene particles having an average particle diameter of 450 μm were obtained in the same manner as in Example 1 except that 10000 parts by weight of styrene was dropped into the dispersion instead of the styrene solution. In addition, the styrene content in the growing polystyrene particles 40 minutes after the start of dropping styrene into the dispersion instead of the styrene solution, and every 20 minutes thereafter, using the polystyrene seed particles as seed particles. Was measured. Further, FIG. 3 shows a scanning electron micrograph taken when measuring the average cell diameter ratio of the pre-expanded particles obtained by pre-expanding the expandable polystyrene particles with water vapor to 10 times the bulk magnification.

(Comparative Example 2)
As the styrene solution, expandable polystyrene particles having an average particle diameter of 450 μm were obtained in the same manner as in Example 1 except that a styrene solution obtained by dissolving 7 parts by weight of divinylbenzene in 10000 parts by weight of styrene was used.

(Comparative Example 3)
As the styrene solution, expandable polystyrene particles having an average particle diameter of 450 μm were obtained in the same manner as in Example 1 except that a styrene solution obtained by dissolving 60 parts by weight of divinylbenzene in 10,000 parts by weight of styrene was used.

(Comparative Example 4)
The dispersion prepared in the same manner as in Example 1 was heated to 85 ° C., and then the styrene emulsion prepared in the same manner as in Example 1 was supplied into the dispersion. Immediately after being held for 40 minutes, 12,000 parts by weight of styrene was continuously added dropwise to the dispersion at the same dropping rate for 100 minutes while maintaining the dispersion at 85 ° C.

  Thereafter, while maintaining the above dispersion at 85 ° C., a styrene solution prepared by dissolving 9 parts by weight of divinylbenzene in 3000 parts by weight of styrene was continuously taken over 20 minutes and continuously at the same dropping rate. The seed polymerization was carried out by dripping the solution. Thereafter, the same procedure as in Example 1 was carried out to obtain expandable polystyrene particles having an average particle diameter of 450 μm. All styrene supplied in the dispersion was used for seed polymerization.

(Comparative Example 5)
Expandable polystyrene particles having an average particle diameter of 450 μm were obtained in the same manner as in Example 1 except that the temperature of the dispersion before raising the temperature to 125 ° C. was 75 ° C. instead of 85 ° C. In addition, the scanning electron micrograph image | photographed when measuring the average bubble diameter ratio of the pre-expanded particle obtained by pre-expanding expandable polystyrene particles with water vapor | steam by 10 times the bulk magnification was shown in FIG.

(Comparative Example 6)
A dispersion was prepared using 15000 parts by weight of polystyrene particles instead of 20000 parts by weight, while a styrene emulsion was prepared using 90 parts by weight of benzoyl peroxide instead of 70 parts by weight.

  And after heating the said dispersion liquid to 85 degreeC, the said styrene emulsion is supplied in this dispersion liquid, and immediately after hold | maintaining the said dispersion liquid at 85 degreeC for 40 minutes, this dispersion liquid is 85 degreeC. The styrene solution obtained by dissolving 60 parts by weight of divinylbenzene in 20000 parts by weight of styrene was continuously dropped over 160 minutes in the dispersion and continuously dropped at the same dropping rate to perform seed polymerization. . Subsequently, after the dispersion was held at 85 ° C. for 1 hour, the temperature was raised to 125 ° C. over 50 minutes, and the dispersion was held at 125 ° C. for 2 hours to complete the polymerization. The dispersion was cooled to 90 ° C. and held. Thereafter, the same procedure as in Example 1 was carried out to obtain expandable polystyrene particles having an average particle diameter of 500 μm. All styrene supplied in the dispersion was used for seed polymerization.

  The gel fraction of the expandable polystyrene particles obtained as described above and the bulk density when pre-expanded by immersing in water at 100 ° C. for 5 minutes (in Table 1, simply “bulk density”), foamability The average cell diameter of bubbles in the surface layer part of the pre-expanded particles obtained by pre-expanding polystyrene particles at a bulk magnification of 10 times (referred to as “surface layer average cell diameter” in Table 1), the average of the bubbles in the surface layer part of the pre-expanded particles The ratio of the bubble diameter to the average bubble diameter in the central part (average bubble diameter in the surface layer / average bubble diameter in the central part) (average bubble diameter ratio), as well as during the production of expandable polystyrene particles Maximum styrene monomer content in polystyrene-grown particles (referred to as “maximum styrene content” in Table 1), minimum styrene monomer content (referred to as “minimum styrene content” in Table 1), and divinylbenzene supply Start point The styrene monomer content in the styrene-grown particles (referred to as “starting styrene content” in Table 1) was measured as described above, and the oil leaching property and surfactant leaching property were measured as follows. The results are shown in Table 1.

  Table 1 also shows the percentage of the total supply amount at the time when divinylbenzene began to be supplied into the dispersion (referred to as “supply time” in Table 1) and the supply of divinylbenzene into the dispersion. Describes the converted amount of divinylbenzene supplied to the dispersion when the total amount of styrene supplied to the dispersion after conversion to 100 parts by weight was started (referred to as “supply amount” in Table 1). did.

(Oil exudation)
2000 g of expandable polystyrene particles and 4 g of zinc stearate (ground product, average maximum length of 20 μm) as a surface treatment agent were supplied to a supermixer and stirred for 2 minutes. Next, 0.8 g of polyethylene glycol (weight average molecular weight: 300) is supplied into the super mixer and stirred for 5 minutes to uniformly attach zinc stearate and polyethylene glycol to the surface of the expandable polystyrene particles. It was.

Thereafter, the expandable polystyrene particles were supplied to a pre-foaming machine and pre-foamed to a bulk density of 0.1 g / cm ³ using water vapor to obtain pre-foamed particles. The pre-expanded particles were left to dry at room temperature for 1 day.

Next, the pre-expanded particles are supplied and filled into a mold of a foam molding machine, and the pre-expanded particles are heated and foamed with 0.2 MPa of water vapor for 6 seconds, so that the internal volume is 450 cm ^3. And a cup-shaped foam-molded container having a wall thickness of 2 mm was obtained. In addition, the cup-shaped foam-molded container was formed by protruding a peripheral wall portion having a certain height from the outer peripheral edge of the bottom surface portion having a flat circular shape toward the upper diagonally outward direction.

  Then, in the obtained foam molded container, the seasoning used in instant noodles, containing the seasoning and curry containing curry powder, is supplied until it is full, and then the foam molded container is entirely covered with a stretched polypropylene film. did. Next, the foam-molded container was left in an oven maintained at 60 ° C. for 48 hours.

Next, copy the entire outer surface of the peripheral wall portion of the foam-molded container onto paper, and copy the yellow pigment portion of curry powder that has oozed out on the outer peripheral surface of the foam-molded container onto the paper, and copy the peripheral wall portion of the foam-molded container While measuring the weight W ₃ of the paper corresponding to the entire outer surface, the weight W ₄ of the paper corresponding to the copied yellow pigment part was measured, and the percentage was calculated by the following formula, and judged according to the following criteria.
Oil exudation (%) = 100 × W ₄ / W ₃

◎ ・ ・ ・ less than 10% ○ ・ ・ ・ 10% or more and less than 20% × ... 20% or more

(Surfactant leaching property)
First, 1.0 g of a nonionic surfactant (trade name “Kao Emulgen 810” manufactured by Kao Corporation) and 0.05 g of black colorant (trade name “Eriochrome Black T” manufactured by Wako Pure Chemical Industries, Ltd.) in 1 liter of water. Was uniformly dissolved and dispersed to prepare colored water.

Then, the colored water is supplied to the foam molded container prepared in the same manner as the measurement of oil leaching until it fills up, and the colored water oozes out to the outer surface of the peripheral wall portion of the foam molded container. Then, after supplying colored water into the foam molded container, the time until it was confirmed that the colored water first oozed out on the outer surface of the peripheral wall portion of the foam molded container was measured and judged according to the following criteria.
◎ ・ ・ ・ 30 minutes or more ○ ・ ・ ・ 20 minutes or more and less than 30 minutes × ・ ・ ・ less than 20 minutes

It is the schematic diagram which showed an example of the maximum chord length of a bubble. 2 is a scanning electron micrograph at a magnification of 80 times showing a cut surface of pre-expanded particles obtained using the expandable polystyrene particles of Example 1. FIG. 2 is a scanning electron micrograph at a magnification of 80 times showing a cut surface of pre-expanded particles obtained using the expandable polystyrene particles of Comparative Example 1. FIG. 6 is a scanning electron micrograph at a magnification of 100, showing a cut surface of pre-expanded particles obtained using the expandable polystyrene particles of Comparative Example 5. FIG.

Claims (3)

The gel fraction is 10 to 50% by weight and the bulk density when pre-foamed by immersion in water at 100 ° C. for 5 minutes is 0.025 to 0.06 g / cm ³ , and the bulk magnification is 10 by steam. In the pre-expanded particles that have been pre-expanded twice, the average cell diameter of the cells in the surface layer portion is 10 to 70 μm, and the ratio between the average cell diameter of the cells in the surface layer portion and the average cell diameter of the bubbles in the center portion is Expandable styrenic resin particles characterized by satisfying
0.4 ≦ (Average bubble diameter of bubbles in the surface layer portion / Average bubble diameter of bubbles in the center portion) ≦ 0.8 The expandable styrenic resin particles according to claim 1, wherein the gel fraction is 20 to 35% by weight. A foam-molded article obtained by pre-expanding the expandable styrenic resin particles according to claim 1 or 2 and foaming the obtained pre-expanded particles.