JP2009120703A - Regenerated expandable styrenic resin particle and its manufacturing method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a regenerated expandable styrenic resin particle capable of being also used for a foodstuff vessel regenerated from a recovered foamed polystyrene, and to provide a manufacturing method of the regenerated expandable styrenic resin particle for manufacturing the regenerated expandable styrenic resin particle capable of being also used for the foodstuff vessel from the recovered foamed polystyrene with much foreign matter of a fish box made of waste foamed polystyrene or the like. <P>SOLUTION: The regenerated expandable styrenic resin particle has an inner layer obtained by suspension-polymerizing a solution produced by dissolving a recovered polystyrene in a virgin styrene monomer, and a surface layer comprising a polymer of the virgin styrene monomer, and is impregnated with a foaming agent. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method for producing regenerated expandable styrene resin particles regenerated from used expanded styrene resin (expanded polystyrene), and in particular, a polystyrene box fish box recovered in a fish market or the like is reused again as expanded polystyrene. The present invention relates to a method for producing regenerated expandable styrene resin particles.

  Conventionally, after being used once, polystyrene foam is incinerated or heat-shrinked and reused as recovered polystyrene. However, the rate of reuse is insufficient, and increasing the reuse rate is a social issue in the future.

  A technique for recovering a foamed polystyrene molded product as a shredded mass has already been completed. In 2005, about 42% of the amount of polystyrene foam in Japan is recycled as a heat shredded mass. However, it is rarely reused in Japan, and mostly used overseas for bulking purposes such as miscellaneous goods by injection molding and building materials by extrusion molding.

  Thus, at present, the recycled polystyrene is still insufficiently recycled and used, and there is an urgent need to expand the scope of utilization of the recovered material and develop applications by developing new technologies.

  From the definition of recycling, it is preferable to recycle foamed styrenic resin as foamed polystyrene instead of foaming styrenic resin, which is finally used as foamed polystyrene, as polystyrene.

  In particular, in Japan, foamed polystyrene boxes that are in great demand are heat-reduced after use and are mainly exported to China as recovered polystyrene, but waste polystyrene boxes are reused as foamed polystyrene boxes. Industrial technology development is delayed and there are very few examples of application.

  On the other hand, several recovery systems have already been proposed in which the shrinkage of the foamed styrene resin molded product used as the packing material is once again used as a cushioning material for home appliances, etc., as a recycled foamable styrene resin. .

  For example, in Patent Document 1, styrene resin particles obtained by non-stretching melt and pulverizing a shrinkage of a foamed styrene resin molded product are dispersed in an aqueous medium containing an organic dispersant, and a readily volatile foaming agent is obtained. There has been proposed a method for producing regenerated expandable styrene-based resin particles by impregnating styrene.

  In Patent Document 2, modified foamable styrene resin particles in which styrene resin particles obtained by improving and pulverizing Patent Document 1 are returned to the reaction vessel and polymerization (seed polymerization) is performed while impregnating styrene monomers again. There has been proposed a method of manufacturing.

  Patent Document 3 proposes a method for producing a regenerated foamable styrene resin by pelletizing while supplying a foaming agent to an extruder in a process of supplying recovered polystyrene to the extruder and pelletizing to a certain size. Has been.

JP-A-6-87973 JP 2002-284916 A JP 2002-337138 A

  The collection systems of Patent Literatures 1 and 2 were effective as a method for returning the foamed styrene resin molded product used as the packaging material to the foamed styrene packaging material again. However, the recovered styrene resin made from a waste polystyrene foam fish box contains a large number of foreign substances such as paper labels, label adhesives, printing inks, coloring materials, and fish oil as impurities. Therefore, when producing a regenerated foamable styrene resin by these methods using such a fish box as a raw material, the production is not stable and the quality of the obtained regenerated foamable styrene resin particles contains a large amount of moisture. There are many problems, and stable supply is difficult.

  The production method of Patent Document 3 has an excellent feature that it is possible to obtain regenerated expandable styrene resin particles directly from recovered polystyrene. However, in the case of a recovered resin made from waste polystyrene foam fish boxes, it is necessary to remove the foreign substances previously exemplified, so there are restrictions on the application, and further due to differences in raw material varieties and heating volume reduction methods Applicable sources of recovered polystyrene had to be limited, such as having to absorb the difference in flowability of recycled resin due to the difference in molecular weight reduction.

  Furthermore, when the regenerated styrene resin is used as a food container, an inner bag may be added to the container so as not to come into direct contact with food, leading to an increase in cost. Therefore, even if a resin regenerated from waste foamed polystyrene, such as a fish box, is used, it has been required to improve reliability so that it can be used as it is as a food container.

  An object of the present invention is to provide regenerated expandable styrene resin particles that can also be used in food containers regenerated from recovered expanded polystyrene. Another object of the present invention is to provide a method for producing regenerated expandable styrene resin particles for producing regenerated expandable styrene resin particles that can also be used in food containers from recovered expanded polystyrene having a large amount of foreign matter such as waste polystyrene foam fish boxes. That is.

According to the present invention, the following regenerated foamable styrene resin particles, a method for producing the same, and the like can be provided.
1. An inner layer obtained by suspension polymerization of a solution obtained by dissolving the recovered polystyrene in styrene monomer of virgin;
It has a surface layer made of a polymer of virgin styrene monomer,
Regenerated foamable styrene resin particles impregnated with a foaming agent.
2. The weight average molecular weight of the surface layer is higher than the weight average molecular weight of the inner layer;
2. The regenerated expandable styrene resin particles according to 1, wherein the surface layer occupies 5% by weight or more and 30% by weight or less of the regenerated expandable styrene resin particles.
3. The regenerated foaming styrene system according to 1 or 2, wherein the foaming agent is an aliphatic hydrocarbon, an alicyclic hydrocarbon, or a mixture thereof, and the impregnation amount is 3.5 wt% or more and 8.0 wt% or less. Resin particles.
4). The recovered polystyrene is dissolved in virgin styrene monomer,
Filtering the lysate;
Suspension polymerization of the filtered solution as it is,
At a polymerization rate of 70% or more, while maintaining the oxygen concentration in the polymerization system at 5% by volume or less, virgin styrene monomer was added to form a styrene resin layer as a surface layer,
Impregnating with blowing agent,
A method for producing regenerated expandable styrene resin particles.
5). Filtration of the lysate is performed using a filter having pores having a diameter of 50 μm or less, or filtration of the lysate is performed using a filter having pores having a diameter exceeding 50 μm, and the filtrate is further precipitated and separated. 4. A process for producing regenerated expandable styrene resin particles according to 4.
6). 6. The production of regenerated expandable styrene resin particles according to 4 or 5, wherein the recovered polystyrene has a weight average molecular weight of 100,000 to 300,000 and the amount dissolved in the styrene monomer is 3% to 40% by weight. Method.
7. Regenerated styrene resin foam beads obtained by foaming the regenerated expandable styrene resin particles according to any one of 7.1 to 3.
A regenerated expanded styrene resin molded product obtained by expansion molding the regenerated styrene resin expanded beads described in 8.7.

  ADVANTAGE OF THE INVENTION According to this invention, the reproduction | regeneration foaming styrene-type resin particle which can be used also for the food container reproduced | regenerated from the collection foamed polystyrene can be provided. ADVANTAGE OF THE INVENTION According to this invention, the manufacturing method of the reproduction | regeneration foaming styrene resin particle which manufactures the reproduction | regeneration foaming styrene resin particle | grains which can be used also for a food container from collection | recovery polystyrene foams with many foreign materials, such as a waste polystyrene foam fish box, can be provided.

  Regenerated foamable styrene resin particles of the present invention have an inner layer obtained by suspension polymerization of a solution obtained by dissolving recovered polystyrene in virgin styrene monomer, and a surface layer made of a polymer of virgin styrene monomer, Impregnated with foaming agent.

Preferably, the weight average molecular weight of the surface layer is higher than the weight average molecular weight of the inner layer. By increasing the weight average molecular weight of the surface layer, even a recycled product can have almost the same physical properties as a virgin product.
Preferably, the surface layer occupies 5% by weight or more and 30% by weight or less with respect to the entire regenerated foamable styrene resin particles. If it is less than 5% by weight, it may be difficult to confirm the formation of a clear surface layer. If it exceeds 30% by weight, the target recycling rate will be lowered, which is not preferable. Preferably, it occupies 10 wt% or more and 20 wt% or less.

  In the method for producing regenerated expandable styrene resin particles of the present invention, in order to remove foreign substances contained in the recovered polystyrene, the recovered polystyrene is dissolved in virgin styrene monomer (solvent) and filtered.

Preferably, the recovery of polystyrene is pulverized compacted material, for example, an average particle diameter 10mm below pulverized bulk density 0.3 g ^/ cm 3 volume reduction of ~0.6g / cm ^3. The recovered polystyrene may be a pellet that is melt-mixed by an extruder.

  The weight average molecular weight of the recovered polystyrene is preferably 100,000 or more and 300,000 or less, more preferably 150,000 or more and 250,000 or less. If the weight average molecular weight is too large, the viscosity of the solution increases, and if it is too small, the physical properties of the molded product may be deteriorated.

  The amount of recovered polystyrene dissolved in the styrene monomer is preferably 5% by weight or more and 40% by weight or less, and particularly preferably 5% by weight or more and 30% by weight or less. If it is less than 5% by weight, the effect as a recycled material is small, and if it exceeds 30% by weight, the workability of filter filtration may deteriorate.

  The styrene monomer used in the present invention is styrene alone or styrene as a main component, a small amount of styrene derivatives such as α-methylstyrene and vinyltoluene, methacrylic acid esters and acrylic acid esters such as methyl methacrylate, ethyl methacrylate, and butyl acrylate, It is a mixture with other polymerizable monomers such as vinyl cyanide such as acrylonitrile and methacrylonitrile.

  In the step of dissolving the recovered polystyrene with respect to the styrene monomer, it is preferable to introduce a polymerization inhibitor into the dissolution tank. Particularly in the summer, when the outside air temperature becomes high, gelation is likely to occur in the piping, so that it is preferable to add a polymerization inhibitor. As such a polymerization inhibitor, conventionally known polymerization inhibitors such as catechols and hydroquinones can be used. The blending amount is preferably about 10 to 100 ppm, but is not limited because it varies depending on working conditions, temperature conditions, and the like.

  Filtration can be performed using a filter. Since most of the foreign matter contained in the recovered polystyrene is insoluble in the styrene monomer, it can be separated by filter filtration. As the filter, those conventionally used for filtering paints and liquid resins, such as bag filters and cartridge filters, can be used as they are.

  The opening (diameter) of the filter is preferably 50 μm or less, particularly preferably 1 μm or more and 20 μm or less. Even with a filter exceeding 50 μm, about 90% of foreign matter can be removed. However, since a pulp breakage or printing ink crushed material passes through, it is not preferable because the stability of the particle diameter in the suspension polymerization reaction is impaired. If the opening of the filter is less than 1 μm, the filtration workability may be reduced, and the amount of the fish box ingot that can be dissolved may be insufficient.

  Even if the filter has a relatively large opening size exceeding 50 μm, the ruptured product of pulp and crushed printing ink can settle and be removed by allowing the solution after filtration to stand still. Therefore, it is also effective to use a filter exceeding 50 μm in combination with sedimentation separation. Preferably, a filter of 100 μm or less is used. In this case, only the settled and separated solution may be diluted again as necessary and filtered using a microporous filter, so that the filter workability is greatly improved.

  The method for producing the reclaimable foamable styrene resin of the present invention is a recycling technique applicable to, for example, waste foamed polystyrene (for example, a fish box) having a high contamination of about 0.1% by weight or more. The recovered polystyrene used in the method is not limited to waste polystyrene foam fish boxes. It is also possible to use recovered polystyrene other than waste polystyrene foam fish boxes, or recovered polystyrene mixed with waste polystyrene fish boxes and other raw material source recovered polystyrene.

  Waste polystyrene foam boxes generated in the fish market are reduced in volume to become reduced volume. This reduced volume is called a fish box ingot, and is generally known as a recycled resin that contains a large amount of foreign matter. This is because a large amount of waste foamed polystyrene is discharged in a short time in the fish market, and the bulky waste fish box needs to be subjected to volume reduction processing in a short time. For this reason, about 0.1 wt%-0.5 wt% of foreign matter is mixed in the fish box ingot in addition to polystyrene. The main component of the foreign matter is pulp that is considered to be labels and corrugated pieces, but there are many other types such as printing ink, fish oil, coloring materials (dyes), and label adhesives.

  Therefore, when polystyrene having a large amount of foreign matter such as a fish box ingot is used as the recovered polystyrene, the volume-reduced product is roughly pulverized and then washed with water, hot water, or boiling water as necessary. Thereafter, the dehydrated pulverized product is dissolved in styrene monomer and filtered.

  The water washing, hot water washing, or boiling water washing described above is not an essential process, but this process can remove odors derived from fish oil and foreign substances having affinity for water such as soap components, dust, and coloring materials. . For example, if hot water of about 80 ° C. is used, a cleaning time of about 1 hour is sufficient.

  The filtrate from which foreign substances have been removed by filtration and, if necessary, washing and filtration can be directly transferred to suspension polymerization. Since the solvent removal step can be omitted, the manufacturing cost can be reduced. Specifically, the filtrate is supplied to the reaction vessel as it is and becomes oil droplets in suspension polymerization. Preferably, immediately before the polymerization, a polymerization initiator such as an organic peroxide and a bubble forming agent for adjusting bubbles when the foam is formed are additionally dissolved. For the formation of oil droplets, a conventionally known suspension polymerization method can be applied as it is.

  Usable organic peroxides include compounds that act as both polymerization initiators and decolorizers, such as benzoyl peroxide, which is most commonly used, peroxyketal peroxides and azobisisoptilo A compound that does not have a decolorizing action but can be a polymerization initiator, such as nitrile, can be used.

  In addition, two or more polymerization initiators having different decomposition temperatures can be used in combination for the completion of the polymerization reaction, and a polyfunctional polymerization initiator can be used in combination for adjusting the molecular weight.

  Examples of such a polymerization initiator include benzoyl peroxide, t-butyl perbenzoate, di-t-butyl peroxycyclohexane, di-t-hexyl peroxycyclohexane, t-butyl peroxy isopropyl carbonate, and t-butyl-2. -Ethylhexyl peroxycarbonate, azobisisobutyronitrile and the like.

  The addition amount of the polymerization initiator varies depending on the molecular weight setting of the obtained regenerated foamable styrene resin. For example, in order to set the weight average molecular weight for an ordinary foamable resin to 180,000 to 400,000, it is appropriately selected from the range of 0.15 wt% to 0.5 wt%.

  As the bubble forming agent, a conventionally known compound having a bubble adjusting action can be used as it is. Examples of such bubble forming agents include monoamide compounds such as oleic acid amide and stearic acid amide, bisamide compounds such as methylene bisstearyl amide and ethylene bisstearyl amide, polyethylene wax having a molecular weight of 100 to several thousand, and the like. The amount of the bubble-forming agent added varies depending on the blended amount of the recovered polystyrene, but is generally appropriately selected from a blending amount of about 0.1% by weight or less.

  The recovered polystyrene and, if necessary, the styrene solution containing a polymerization initiator, a polymerization inhibitor and a bubble regulator are pre-stirred and gradually poured into an aqueous medium containing a dispersant to form styrene oil droplets. Can do. After the oil droplet diameter is stabilized, the polymerization reaction can be started by heating. At this time, the reactor is a pressure-resistant reactor capable of adjusting the temperature, and preferably includes a baffle bar or baffle plate and a stirring blade capable of stirring the reactor uniformly.

  Deionized water can be used as the aqueous medium. The dispersant is not particularly limited as long as it is used for suspension polymerization. Examples thereof include organic dispersants such as polyvinyl alcohol, polyvinyl pyrrolidone, and methyl cellulose, and inorganic dispersants such as magnesium phosphate and tricalcium phosphate.

  When an inorganic dispersant is used, a surfactant can be used in combination. As the surfactant, sodium oleate, sodium dodecylbenzenesulfonate, and other anionic surfactants and nonionic surfactants commonly used in suspension polymerization can be used.

  The ratio of the recovered polystyrene solution and the aqueous medium containing the dispersant in the initial stage of suspension polymerization is usually 1.2 to 2.0 (weight ratio) with respect to 1.0 of the styrene solution. . If the ratio is less than 1.2, the stability of the styrene oil droplet diameter is inferior, and if it exceeds 2.0, the productivity is inferior.

  The suspension polymerization temperature is usually equal to or slightly lower than the polymerization temperature of the virgin material alone. When volatile components remain in the recovered polystyrene, the stability of oil droplets is inferior, so the temperature is lower than that of suspension polymerization using only a virgin material.

  Formation of a surface layer composed of virgin styrene monomer is carried out by quantitatively supplying virgin styrene monomer dropwise to the reaction vessel when the polymerization rate in suspension polymerization is 70% or more and 99% or less.

  If the polymerization rate is less than 70%, the absorption of the styrene monomer into the resin particles becomes faster than the polymerization rate, so that it is difficult to form a clear surface layer. On the other hand, even if added after completion of polymerization, the polymerization initiator is completely decomposed and the concentration of polymerization radicals is low, so that it is absorbed by the resin particles earlier than the polymerization reaction, so that a clear surface layer cannot be formed. In order to form the surface layer more clearly, a styrene monomer is preferably added at a polymerization rate of 80% to 95%.

  The preferred amount of styrene monomer added in the second half of suspension polymerization is based on the sum of the amount of regenerated styrene monomer and virgin styrene monomer used in the initial stage of suspension polymerization and the amount of virgin styrene monomer added in the second half of polymerization. 5% by weight or more and 30% by weight or less.

  The styrene monomer dropping step for forming the virgin material surface layer is performed when the oxygen concentration in the reaction vessel is 5% by volume or less. The quality of recycled products tends to be lower than that of virgin products. In the case of polystyrene foam, its quality tends to depend on the properties of the surface layer.

  Usually, in the dropping step of the styrene monomer, since a low temperature raw material is introduced into the reaction tank, a negative pressure is likely to be generated and the oxygen concentration is likely to be high. Therefore, it is preferable to manage to 5 volume% or less. If it exceeds 5% by volume, the physical properties and appearance of the resulting expanded polystyrene molded product are deteriorated, and the quality is inferior to that of a virgin product. The deterioration in quality can be recovered by adjusting the density of the foamed molded product. However, the density adjustment leads to an increase in the weight per molded product, which is an essential purpose of using recycled materials. The contribution to the decrease is reduced.

  The foaming agent impregnation is usually performed by press-fitting a readily volatile foaming agent into the reactor after the virgin surface layer is formed by suspension polymerization or after the polymerization is completed. As the foaming agent, a readily volatile hydrocarbon that does not dissolve or slightly swell resin particles obtained by suspension polymerization, specifically, propane, normal butane, isobutane, normal pentane, Aliphatic hydrocarbons such as isopentane and normal hexane, alicyclic hydrocarbons such as cyclohexane and cyclopentane, or mixtures thereof are used. These blowing agents are usually used so as to be impregnated in an amount of 3.5 to 8.0% by weight based on the total amount of resin obtained by polymerization.

  The regenerated foamable styrenic resin particles obtained are generally classified by particle size after dehydration and drying, and then coated with a conventionally known surface coating material.

  Although fine powder particles of 1 to 3% by weight are usually generated by classification for each particle size, since there is no demand as a polystyrene foam, when re-dissolving in the styrene monomer, which is the first step of the present invention, There is no waste of resources.

  As the surface coating agent, those used for conventionally known expandable styrene resin particles can be applied. For example, zinc stearate, stearic acid triglyceride, stearic acid monoglyceride, castor oil, silicones, and various other antistatic agents can be used in combination depending on the application.

  According to the production method of the present invention, regenerated expandable styrenic resin particles can be stably obtained from recovered polystyrene obtained by reducing the volume of waste expanded polystyrene fish boxes that have been difficult to reuse as regenerated expanded polystyrene. . Furthermore, since the regenerated expandable styrene resin particles of the present invention have a surface layer made of a virgin material, they can be used again for food containers such as fish boxes.

  A conventionally well-known system can be applied as it is for foaming and molding of the recyclable styrene resin particles obtained by the present invention. In general, expanded polystyrene is produced by obtaining expanded particles in a pre-expanding step for determining the density of the foam, filling the expanded particles in a mold, and then heating with steam. The same applies to the case of recycled expandable styrene resin particles. Most of the regenerated expandable styrene resin particles are distributed as expanded polystyrene molded products, but some are distributed in the state of expanded particles before molding depending on the application.

In order to describe the present invention in more detail, examples are shown below, but the present invention is not limited to these examples.
(Preparation of styrene monomer solution)
A fish box ingot obtained by reducing the volume of a used polystyrene foam fish box by frictional heat and mixed with light brown and blue was pulverized to a particle size of 10 mm or less to obtain a granular recovered polystyrene (weight average molecular weight 250,000). 3 kg of tap water and 2 kg of crushed and recovered polystyrene were placed in a 10 L washing tank equipped with a stirrer, and stirred at 80 ° C. for 1 hour for washing. After washing, dehydration and drying were performed to obtain recovered polystyrene having a light blue color.

  Subsequently, 4 kg of styrene monomer (virgin) was added to a 10 L dissolution tank equipped with a stirrer, and while stirring, 1000 g of recovered polystyrene and 1.5 g of a styrene monomer (virgin) solution containing 10% by weight of t-butylcatechol were added. Stirring was continued for a time to prepare a 20% recovered styrene solution.

The dissolved solution was filtered through a filter bag having an opening (diameter) of 70 to 100 μm to remove insoluble matters. The weight of insoluble matter remaining on the filter was about 3 g.
When the recovered polystyrene solution was allowed to stand for 1 day, a brownish brown precipitate was generated at the bottom, so that only the precipitate was removed to obtain 4500 g of a light blue colored transparent solution.

(Suspension polymerization)
In a pressure-resistant reaction tank having an internal volume of 4 L having a stirring blade and a baffle plate, 1650 g of deionized water, 25 g of 3% calcium phosphate slurry and 3.3 g of 1% aqueous solution of dodecylbenzene were stirred as an aqueous medium.
Subsequently, 2.100 g of benzoyl peroxide, 0.55 g of t-butyl perbenzoate and 0.55 g of polyethylene wax (Mw = 1000) were dissolved and dispersed in 1100 g of the 20% recovered styrene solution thus prepared, and then a pressure resistant reactor And used as an oil droplet component of suspension polymerization.

  While stirring, the temperature was raised to 90 ° C. and the heat retention was started, and 10 g each of 10% slurry of tricalcium phosphate was added 1.5 hours and 2.0 hours later. After 4.5 hours, resin particles with a polymerization rate of 90% were obtained. Subsequently, after pressurizing and releasing with nitrogen twice, the oxygen concentration in the reaction vessel space was set to 3% by volume, and then 100 g of styrene monomer (virgin) was added dropwise over 1 hour.

  After completion of dropping, the temperature was raised to 110 ° C. and held for 2 hours, and 96 g of pentane with iso / normal = 3/7 was injected as a blowing agent over 1 hour. The suspension was further maintained for 8 hours to finish the suspension polymerization and impregnation of the foaming agent into the resin particles.

(Post-processing)
After cooling, the resin particles were taken out, the dispersant was removed by pickling and washing, and after further dehydrating and drying, sieving was performed according to particle size. 1000 g of particles of 0.6 to 1.4 mm were collected for quality evaluation, and 0.8 g of zinc stearate, 0.3 g of monostearyl glyceride, 0.3 g of tristearyl glyceride, polyethylene glycol 400 as a surface coating agent. 1 g was mixed to obtain recycled expanded styrene resin particles.

(analysis)
The obtained recycled expanded styrene resin particles had an average particle size of 1.05 mm, a residual styrene content of 0.15% by weight, a foaming agent impregnation amount of 6.7% by weight, and a water content of 1.8% by weight. .

  In order to confirm the formation of the surface virgin layer, the obtained regenerated expanded styrene resin particles were expanded in boiling water for 3 minutes to obtain expanded resin particles having a bulk density of 14 to 12.5 g / L, and then Kelpermeation chromatography (GPC). ) The molecular weight distribution of the surface layer (up to 100 μm), the inner layer, and the entire particle was measured by the method, and the weight average molecular weight of each part was 483,000, 236,000, 298,000. It was. Therefore, it was confirmed that the resin of the inner layer and the resin of the surface layer are clearly different resins.

  In addition, the measuring method of the polymerization rate in an Example, a weight average molecular weight, and a foaming agent impregnation amount is shown below.

(I) Polymerization rate The polymerization rate during the polymerization was measured by measuring the specific gravity of styrene oil droplets using a specific gravity liquid, and converted as a polymerization rate of 0% = specific gravity of 0.91 and a polymerization rate of 100% = specific gravity of 1.05. .

(Ii) Weight average molecular weight The weight average molecular weight was measured by GPC method (mixed gel column for polymer measurement) using polystyrene as a standard substance. Measuring device: manufactured by Hitachi, Ltd., eluent: THF (tetrahydrofuran), flow rate: 2 ml / min, detector: UV 220 nm, column: two GL-R400M manufactured by Hitachi Chemical Co., Ltd.

(Foam molding)
The obtained regenerated expandable styrene resin particles were pre-expanded into 18 g / L expanded beads by heating with steam using a foaming machine for expanded styrene resin (HBP-500LW manufactured by Hitachi Chemical Technoplant). Thereafter, after aging for about 18 hours, a foamed styrene resin molded product (20 g / L) was obtained by molding at a molding pressure of 0.08 mpa using a foamed styrene resin molding machine (Daisen Kogyo vs-300). . As a result of evaluating the JISA9511 bending strength, as shown in Table 1, it was equivalent to the bending strength of the virgin material (Comparative Example 1).

Comparative Example 1
An example of virgin material is shown for comparison.
(Suspension polymerization)
As in Example 1, 1650 g of deionized water, 25 g of tricalcium phosphate 10% slurry, and 3.3 g of 1% aqueous solution of dodecylbenzene were placed in a 4 L internal pressure-resistant reaction vessel having a stirring blade and a baffle plate. Stir.
Subsequently, 2.75 g of benzoyl peroxide, 0.55 g of t-butyl perbenzoate and 0.55 g of polyethylene wax (mw = 1000) were dissolved and dispersed in 1200 g of styrene monomer (virgin), and then charged into a pressure resistant reactor. An oil droplet component of suspension polymerization was used.

  While stirring, the temperature was raised to 90 ° C. and the heat retention was started, and 10 g each of 10% slurry of tricalcium phosphate was added 2.5 hours and 3.0 hours later. After 7 hours, resin particles having a polymerization rate of 93% were obtained. After raising the temperature to 110 ° C. and holding it for 1 hour, 96 g of pentane of iso / normal = 3/7 was injected as a blowing agent over 1 hour. The suspension was further maintained for 8 hours to finish the suspension polymerization and impregnation of the foaming agent into the resin particles.

(Post-processing)
After cooling, the resin particles were taken out, the dispersant was removed by pickling and washing, and after further dehydrating and drying, sieving was performed according to particle size.
1000 g of particles of 0.6 to 1.4 mm were collected for quality evaluation, and 0.8 g of zinc stearate, 0.3 g of monostearyl glyceride, 0.3 g of tristearyl glialide, and 0 of polyethylene glycol 400 were used as surface coating agents. 0.1 g was mixed to obtain expandable styrene resin particles of virgin material.

(analysis)
The obtained expandable styrene resin particles had an average particle size of 0.95 mm, a residual styrene content of 0.11% by weight, a foaming agent impregnation amount of 6.8% by weight, a water content of 0.25% by weight, and a weight average. The molecular weight was 285,000.

(Foam molding)
Foam molding was performed in the same manner as in Example 1 to obtain a foamed styrene resin molded product, and the bending strength was evaluated. The evaluation results are shown in Table 1.

Example 2
(Preparation of styrene monomer solution)
The recovered polystyrene lump (fish box ingot) mixed with brown and blue, in which the volume of used polystyrene foam fish box was reduced by frictional heat, was pulverized to a particle size of 10 mm or less to obtain a granular recovered polystyrene (weight average molecular weight 20 to 20). 250,000). Subsequently, while adding 4.25 kg of styrene monomer (virgin) to a 10 L dissolution tank equipped with a stirrer and stirring, 750 g of recovered polystyrene and 1.5 g of a styrene (virgin) solution containing 10% by weight of t-butylcatechol were added. Stirring was continued for 4 hours to prepare a 15% recovered styrene solution.

The dissolved solution was filtered through a cartridge filter having an opening (diameter) of 10 μm to remove insoluble matters. The weight of insoluble matter remaining on the filter was about 3 g.
The recovered polystyrene solution was allowed to stand for 1 day, but a transparent solution colored brown-blue with no precipitate was obtained.

(Suspension polymerization)
In Example 1, suspension polymerization was performed in the same manner as in Example 1 except that the 15% by weight recovered styrene solution was used instead of the 20% by weight recovered styrene solution.

(Post-processing)
The same operation as in Example 1 was performed.

(analysis)
The obtained regenerated expanded styrene resin particles had an average particle size of 1.15 mm, a residual styrene content of 0.10% by weight, a foaming agent impregnation amount of 6.7% by weight, and a water content of 3.1% by weight. .

  In order to confirm the formation of the surface virgin layer, the obtained regenerated expanded styrene resin particles were expanded in boiling water for 3 minutes to obtain expanded resin particles having a bulk density of 14 to 12.5 g / L. As a result of measuring the molecular weight distribution of the surface layer (up to 100 μm), the inner layer, and the entire particle, the weight average molecular weight of each part was 480,000, 250,000, and 310,000. Therefore, it was confirmed that the resin of the inner layer and the resin of the surface layer are clearly different resins.

(Foam molding)
The regenerated foamable styrene resin particles obtained were molded in the same manner as in Example 1 to obtain a foamed styrene resin molded product. As a result of evaluating the bending strength, as shown in Table 1, it was almost equal to the bending strength of the virgin material.

  The production method of the present invention can be used to reuse foamed polystyrene having a dirt like a foamed polystyrene box, which has been difficult to reuse. The recycled foamable styrene resin particles obtained by the production method of the present invention can be used for packaging materials, food containers, and heat insulating building materials, but are particularly suitable for food containers.

Claims (8)

An inner layer obtained by suspension polymerization of a solution obtained by dissolving the recovered polystyrene in styrene monomer of virgin;
It has a surface layer made of a polymer of virgin styrene monomer,
Regenerated foamable styrene resin particles impregnated with a foaming agent. The weight average molecular weight of the surface layer is higher than the weight average molecular weight of the inner layer;
The regenerated expandable styrene resin particles according to claim 1, wherein the surface layer occupies 5 wt% or more and 30 wt% or less of the regenerated expandable styrene resin particles.   The regenerative foaming property according to claim 1 or 2, wherein the foaming agent is an aliphatic hydrocarbon, an alicyclic hydrocarbon, or a mixture thereof, and the impregnation amount is 3.5 wt% or more and 8.0 wt% or less. Styrenic resin particles. The recovered polystyrene is dissolved in virgin styrene monomer,
Filtering the lysate;
Suspension polymerization of the filtered solution as it is,
At a polymerization rate of 70% or more, while maintaining the oxygen concentration in the polymerization system at 5% by volume or less, virgin styrene monomer was added to form a styrene resin layer as a surface layer,
Impregnating with blowing agent,
A method for producing regenerated expandable styrene resin particles. Filtration of the lysate is performed using a filter having pores having a diameter of 50 μm or less, or filtration of the lysate is performed using a filter having pores having a diameter exceeding 50 μm, and the filtrate is further precipitated and separated. The manufacturing method of the regenerated expandable styrene-type resin particle of Claim 4.   The regenerated expandable styrene resin particles according to claim 4 or 5, wherein the recovered polystyrene has a weight average molecular weight of 100,000 to 300,000 and the amount dissolved in the styrene monomer is 3% to 40% by weight. Manufacturing method.   Regenerated styrene resin foam beads obtained by foaming the regenerated expandable styrene resin particles according to claim 1.   A regenerated expanded styrene resin molded product obtained by expansion molding of the regenerated styrene resin expanded beads according to claim 7.