JP4912583B2 - Method for producing expandable styrene resin particles - Google Patents

Description

The present invention relates to a method for producing expandable styrenic resin particles for producing foamed molded articles such as bottomed cylindrical foam containers for packaging and cooking such as instant cup noodles.

  Conventionally, a bottomed cylindrical foam container is used as a container for instant cup noodle packaging and cooking. This foaming container is manufactured by filling pre-expanded particles obtained by pre-expanding expandable styrene resin particles in a mold, and heating and foaming.

  As such expandable styrene resin particles, Patent Document 1 discloses that 3 to 6% by weight of pentane and 0.01 to 1% by weight of propane with respect to 100% by weight of expandable styrene resin particles as an essential component of the foaming agent. %. Expandable styrenic resin particles characterized in that it is contained, and a cup-shaped foamed molded article excellent in top and bottom compression strength can be obtained by foaming the expandable styrene resin particles. Is disclosed.

  On the other hand, in recent years, with increasing social interest in environmental sanitation, there has been a great interest in the effects of various chemical substances on the human body. The same is true for the cup noodle container described above, and the content of aromatic compounds such as styrene monomer, toluene, xylene, ethylbenzene, propylbenzene in the expandable styrene resin particles that are the raw materials of the container. There is a demand for reduction.

  However, since the aromatic compound has the effect of plasticizing the styrene resin, when only reducing the aromatic compound contained in the expandable styrene resin particles of Patent Document 1, styrene is used. As a result of the reduced flexibility of the resin, the extensibility of the foamed particles obtained by foaming the expandable styrene resin particles is reduced, and the thickness of the foamed container is very low, about 1.5 to 3.0 mm. When the stress which deform | transforms this upper end opening part into a flat state is added to the upper end opening part of a foam container, another problem that a crack generate | occur | produces easily in the upper end opening part of the foam container occurred.

  Therefore, it is conceivable to reduce the expansion ratio of the foam container, but if the expansion ratio of the foam container is decreased, there arises a problem that the light weight of the foam container is impaired.

  Patent Document 2 discloses a coating containing a fluorine-containing vinyl monomer having a specific structural formula, a fluorine-containing vinyl monomer obtained by polymerizing a vinyl monomer, and a polyvinyl alcohol resin. Expandable styrene resin particles with the surface of the expandable styrene resin particles are proposed, and the foamed containers obtained using the expandable styrene resin particles are said to have less leaching of contents. ing.

  However, the fluorine-containing vinyl copolymer is expensive, and there is a problem that the production cost of the resulting expandable styrene resin particles is increased. Therefore, an attempt was made to produce a foam container using expandable styrene resin particles obtained by coating the surface of the expandable styrene resin particle body with only polyvinyl alcohol resin without using a fluorine-containing vinyl copolymer. As a result, the effect of preventing the contents from exuding in the foamed container is insufficient, and since the fluorine-containing vinyl copolymer is not contained, the releasability from the mold of the foamed container is poor, and the release is difficult. There was a problem of frequent mold defects.

JP 2003-82149 A JP 2003-138555 A

The present invention provides a foam molded article, in particular, a bottomed body that can smoothly absorb the stress that deforms the upper end opening into a flat state and can substantially prevent the upper end opening from being damaged, and has little exudation of the contents. Provided is a method for producing expandable styrene resin particles , which can easily produce a cylindrical foam container and is excellent in releasability of the resulting foam molded product.

The method for producing expandable styrene resin particles of the present invention is a method for producing expandable styrene resin particles for pre-foaming, filling into a mold and foaming to form a foam molded product. , styrene monomer, ethylbenzene, toluene, n- propylbenzene, the total amount of one or two or more aromatic compounds selected from the group consisting of i- propylbenzene and xylene Ri 0~500ppm der relative to the total weight and the expandable styrene resin particles 100 parts by weight of the particle diameter of only greater than 0.600mm below 0.300 mm, Ri viscosity 7 ~ 52 mPa · s der at 20 ° C. at the time of 4 wt% aqueous solution and polyethylene glycol degree of saponification 0.001 parts by weight 70 to 90 mol% der Ru polyvinyl alcohol and the weight average molecular weight of 200 to 600 0.02 to 0.20 after mixing the mixture liquid obtained by mixing parts by weight, in the expandable styrene resin particles in which the liquid mixture is applied to the surface, zinc fatty acid obtained by the direct method 0.3 to 1.2 parts by weight of zinc stearate obtained by a direct method as a salt and having an average particle diameter of 3 to 25 μm is added, and the polyvinyl alcohol and the polyethylene glycol are added to the surface of the expandable styrene resin particles. And a coating made of zinc stearate obtained by the direct method and having an average particle diameter of 3 to 25 μm, and the surface of the expandable styrenic resin particles is coated with a skin layer made of the coating. And

  The styrene resin constituting the expandable styrene resin particles is not particularly limited. For example, styrene, α-methyl styrene, vinyl toluene, ethyl styrene, i-propyl styrene, t-butyl styrene, dimethyl styrene, bromo Examples thereof include homopolymers of styrene monomers such as styrene and chlorostyrene or copolymers thereof.

  The styrenic resin may be a copolymer of the styrenic monomer having the styrenic monomer as a main component and a vinyl monomer copolymerizable with the styrenic monomer. Examples of vinyl monomers include methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, 2-ethylhexyl (meth) acrylate, alkyl (meth) acrylate such as cetyl (meth) acrylate, and (meth) acrylonitrile. In addition to dimethyl maleate, dimethyl fumarate, diethyl fumarate, and ethyl fumarate, bifunctional monomers such as divinylbenzene, alkylene glycol dimethacrylate, and polyethylene glycol di (meth) acrylate are exemplified. In addition, 200,000-400,000 are preferable and, as for the weight average molecular weight by GPC (gel permeation chromatography) method of the said styrene resin, 250,000-350,000 are more preferable.

  Here, as a method for producing the expandable styrene resin particles, a general-purpose production method is used. During the suspension polymerization of the styrene resin, a foaming agent is contained in the aqueous suspension, and foaming is performed in the styrene resin particles. For producing expandable styrene resin particles by impregnating with an agent, and for producing styrene resin particles by producing styrene resin particles by a general-purpose method and impregnating the styrene resin particles with a foaming agent Etc. In addition, when impregnating a foaming agent at the time of suspension polymerization of a styrene-type resin, it is preferable to contain a foaming agent in aqueous suspension when the polymerization conversion rate of a monomer is 85 weight% or more.

  In addition, a polymerization initiator is used at the time of suspension polymerization of the styrene resin. As the polymerization initiator, a general-purpose one is used, for example, benzoyl peroxide, lauroyl peroxide, octanoyl peroxide, orthochloro. Benzoyl peroxide, orthomethoxybenzoyl peroxide, methyl ethyl ketone peroxide, diisopropyl peroxydicarbonate, cumene hydroperoxide, cyclohexanone peroxide, t-butyl hydroperoxide, t-butyl peroxybenzoate, t-butyl peroxybivalate , T-butylperoxyisopropyl carbonate, t-butylperoxyacetate, 2,2-t-butylperoxybutane, diisopropylbenzene hydroperio Peroxide-based polymerization initiators such as side, 2,2′-azobisisobutyronitrile, 2,2′-azobis (2,4-dimethylvaleronitrile), 2,2′-azobis (2,3- Dimethylbutyronitrile), 2,2'-azobis (2-methylbutyronitrile), 2,2'-azobis (2,3,3-trimethylbutyronitrile), 2,2'-azobis (2-isopropyl) Butyronitrile), 1,1′-azobis (cyclohexane-1-carbonitrile), 2,2′-azobis (4-methoxy-2,4-dimethylvaleronitrile), 2- (carbamoylazo) isobutyronitrile 4,4′-azobis (4-cyanovaleric acid), dimethyl-2,2′-azobisisobutyrate and the like.

  And the total content in the expandable styrene resin particles of one or two or more aromatic compounds selected from the group consisting of the styrene monomer, ethylbenzene, toluene, n-propylbenzene, i-propylbenzene and xylene (Total weight) is limited to 0 to 500 ppm, preferably 0 to 400 ppm, based on the total weight of the expandable styrene resin particles.

  That is, one or more aromatic compounds selected from the group consisting of styrene monomer, ethylbenzene, toluene, n-propylbenzene, i-propylbenzene and xylene are not contained in the expandable styrene resin particles. Or one or more aromatic compounds selected from the group consisting of styrene monomers, ethylbenzene, toluene, n-propylbenzene, i-propylbenzene and xylene are contained in the expandable styrene resin particles. The total amount of the aromatic compound is limited to 500 ppm or less, preferably 400 ppm or less, based on the total weight of the expandable styrene resin particles.

  Thus, by making the total content of aromatic compounds in the expandable styrene resin particles 0 to 500 ppm with respect to the total weight of the expandable styrene resin particles, the expandable styrene resin particles are obtained by foaming. Foamed molded products such as bottomed cylindrical foam containers that are low in the generation of volatile components and excellent in environmental hygiene, and suitable for food applications such as instant cup noodles that require cooking with hot water Can be used.

  And in order to make the total content of the aromatic compound in the expandable styrene resin particles be 0 to 500 ppm with respect to the total weight of the expandable styrene resin particles, the above-mentioned is described at the time of manufacturing the expandable styrene resin particles. It is preferable not to add the aromatic compound separately as a plasticizer.

  However, in the production of expandable styrenic resin particles, although no plasticizer is added separately, as an impurity in the styrene monomer used as the raw material of expandable styrene resin particles, ethylbenzene, toluene, i- The foamable styrene resin particles are plasticized by containing a large amount of propylbenzene, n-propylbenzene and xylene or by leaving a large amount of unreacted styrene monomer in the foamable styrene resin particles. There is a possibility that the chemical component is contained outside the above range.

  Accordingly, a styrene monomer having a small amount of impurities is selected so that the total content of the aromatic compound in the expandable styrene resin particles is 0 to 500 ppm based on the total weight of the expandable styrene resin particles. It is necessary to adjust the production conditions of the expandable styrene resin particles. Examples of a method for adjusting the production conditions of expandable styrene resin particles for suppressing the content of the aromatic compound within a predetermined range include, for example, a decomposition temperature as a polymerization initiator used for suspension polymerization of styrene resin. First, suspension polymerization of a styrene resin is performed using a polymerization initiator having a low decomposition temperature, and then a suspension of the styrene resin is performed using a polymerization initiator having a high decomposition temperature. For example, a method of continuously performing turbid polymerization may be mentioned. In the above method, among the two types of polymerization initiators having different decomposition temperatures, the polymerization initiator having a high decomposition temperature is preferably a polymerization initiator having a half-life of 10 hours at a temperature of 90 to 120 ° C. Examples of such a polymerization initiator include t-butyl peroxybenzoate, t-butyl peroxybivalate, t-butyl peroxyisopropyl carbonate, t-butyl peroxyacetate, 2,2-t-butyl peroxy Examples include butane.

  In addition, content of the aromatic compound in an expandable styrene-type resin particle is measured in the following way. That is, 1 g of expandable styrene resin particles was precisely weighed, and 1 ml of a dimethylformamide solution containing 0.1% by volume of cyclopentanol was added as an internal standard solution to the precisely weighed expandable styrene resin particles. Thereafter, dimethylformamide solution is further added to dimethylformamide solution to prepare 25 mL of a measurement solution, and 1.8 μL of this measurement solution is supplied to a sample vaporization chamber at 230 ° C., and an aromatic to be measured from a gas chromatograph. A chart of the compound is obtained, and the amount of the aromatic compound is calculated from the chart based on the calibration curve of the aromatic compound to be measured that has been measured in advance.

In addition, content of the aromatic compound in an expandable styrene-type resin particle can be measured on the following measuring conditions using a gas chromatograph (Shimadzu Corporation brand name "GC-14A").
Detector: FID
Column: GL Sciences Inc. (3mm diameter x 2.5m)
Liquid phase: PEG-20M PT 25% by weight
Carrier: Chromosorb W AW-DMCS
Mesh: 60/80
Column temperature: 100 ° C
Detector temperature: 230 ° C
Inlet temperature: 230 ° C
Carrier gas: Nitrogen Carrier gas flow rate: 40 ml / min

  And as a foaming agent used by this invention, if it is conventionally used for manufacture of an expandable styrene-type resin particle, it will not specifically limit, For example, aliphatic hydrocarbons, such as propane, butane, and 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-difluoroethane (HFC-152a) and the like, and aliphatic hydrocarbons are preferable. In addition, a foaming agent may be used independently or may be used together.

  If the content of the foaming agent in the expandable styrene resin particles is small, the fusion of the expanded particles obtained by foaming the expandable styrene resin particles is insufficient, and the mechanical strength of the foam molded product is low. On the other hand, if the amount is too large, the size of the foamed particles obtained by foaming the expandable styrene resin particles becomes too large. The depth of the concave portion is increased, the smoothness of the foam container surface is impaired, and the appearance of the foam container and the appearance when printing is performed on the foam container surface may be reduced, so 2 to 6% by weight is preferable. 4 to 5 weight% is more preferable.

  Here, the content of the foaming agent in the expandable styrene-based resin particles refers to that measured in the following manner. That is, the foamable styrene resin particles are supplied to a heating furnace at 180 ° C. to obtain a chart of the foaming agent to be measured from the gas chromatograph, and based on the calibration curve of the foaming agent to be measured that has been measured in advance. Then, the amount of the foaming agent in the expandable styrene resin particles is calculated from the chart.

In addition, content of the foaming agent in an expandable styrene-type resin particle can be measured on condition of the following using a gas chromatograph (Shimadzu Corporation brand name "GC-14B").
Detector: FID
Heating furnace: Product name “PYR-1A” manufactured by Shimadzu Corporation
Column: Shinwa Kako Co., Ltd. (3mm diameter x 3m)
Liquid phase: Squalane 25% by weight
Carrier: Shimalite 60-80 NAW
Heating furnace temperature: 180 ° C
Column temperature: 70 ° C
Detector temperature: 110 ° C
Inlet temperature: 110 ° C
Carrier gas: Nitrogen Carrier gas flow rate: 60 ml / min

In addition, when the expandable styrene resin particles are mixed with the expandable styrene resin particles having a small particle diameter, the foamed styrene resin particles are obtained when a bottomed cylindrical foam container is manufactured using the expandable styrene resin particles. While there is a possibility that the mechanical strength of the opening of the container may be reduced, if the expandable styrene resin particles having a large particle diameter are mixed, the pre-expanded particles obtained by pre-expanding the expandable styrene resin particles Since the filling property into the mold is lowered, the particles having a particle diameter larger than 0.300 mm and not more than 0.600 mm, that is, expandable styrene resin particles having a particle diameter larger than 0.600 mm and a particle diameter Is limited to those containing no expandable styrene resin particles of 0.300 mm or less.

  And, as a method for obtaining expandable styrene resin particles having a particle diameter larger than 0.300 mm and not more than 0.600 mm, the expandable styrene resin particles produced in the above-mentioned manner are defined in JIS. A method of classifying using a sieve having an opening of 0.300 mm and a sieve having an opening of 0.600 mm, and a styrenic resin particle before impregnating with a foaming agent are used as a sieve and an opening of 0.300 mm according to JIS. A method of classifying using a sieve having an opening of 0.600 mm and impregnating the classified styrene resin particles with a foaming agent can be mentioned.

  Specifically, the expandable styrene resin particles were sieved using a sieve having an opening of 0.600 mm specified in JIS, and the expandable styrene resin particles that passed through the sieve were collected, and then collected. The expandable styrene resin particles are sieved using a sieve having an opening of 0.300 mm specified in JIS, and the expandable styrene resin particles remaining on the sieve are collected, whereby the particle diameter is larger than 0.3 mm. In addition, expandable styrene resin particles consisting only of 0.6 mm or less can be obtained.

  When the styrene resin particles are classified, the styrene resin particles after classification are impregnated with a foaming agent to obtain expandable styrene resin particles. Before and after impregnating the styrene resin particles with the foaming agent, the resin Since the particle diameter of the particles hardly changes, the particle diameter of the styrene resin particles may be the particle diameter of the expandable styrene resin particles in the present invention.

  And on the surface of the above-mentioned expandable styrene-based resin particles, polyvinyl having a viscosity at 20 ° C. of 1 to 60 mPa · s with respect to 100 parts by weight of expandable styrene-based resin particles as a 4 wt% aqueous solution. A skin layer comprising 0.001 to 0.1 parts by weight of alcohol, 0.02 to 0.20 parts by weight of polyethylene glycol, and 0.3 to 1.2 parts by weight of a zinc salt of a fatty acid obtained by a direct method. It is covered.

In the polyvinyl alcohol constituting the skin layer, when the viscosity at 20 ° C. when the polyvinyl alcohol is made into a 4% by weight aqueous solution exceeds 60 mPa · s, foam molding obtained by using expandable styrenic resin particles Since the releasability of the product is lowered, it is limited to 7 to 52 mPa · s. Here, the viscosity of polyvinyl alcohol at 20 ° C. when it was made into a 4 wt% aqueous solution was measured using a B-type viscometer after leaving a 4 wt% aqueous solution of polyvinyl alcohol in a constant temperature room at 20 ° C. for 24 hours. Say. The B-type viscometer is commercially available from, for example, Tokyo Keiki Co., Ltd.

  And if there is little content in the skin layer of polyvinyl alcohol, while the mechanical strength of the opening part of a bottomed cylindrical foam container obtained using an expandable styrene-type resin particle will fall, the content in a foam container While the effect of suppressing the exudation of the product is reduced, if it is more, the releasability from the mold of the foam molded product such as a foam container obtained using the foamable styrene resin particles is lowered. It is limited to 0.001 to 0.1 parts by weight with respect to 100 parts by weight of the particles, and 0.005 to 0.05 parts by weight is preferable.

If the degree of saponification of the polyvinyl alcohol is small, the flowability of the styrene resin pre-expanded particles obtained by pre-expanding the expandable styrene resin particles becomes poor, and the styrene resin pre-expanded particles from the pre-foaming machine Since discharge may take time, it is limited to 70 to 90 mol% .

  Further, if the content of polyethylene glycol in the skin layer is small, the effect of suppressing the exudation of the contents in the foamed container obtained by using the foamable styrene resin particles is lowered, whereas if the content is large, the foamable styrene system is used. Since the releasability from the mold of foamed molded articles such as foamed containers obtained using resin particles is reduced, the amount is limited to 0.02 to 0.20 parts by weight with respect to 100 parts by weight of expandable styrene resin particles. 0.05 to 0.10 parts by weight is preferable.

When the weight average molecular weight of the polyethylene glycol is small, the skin layer of the expandable styrene resin particles tends to fall off, whereas when the weight average molecular weight is large, the styrene resin prefoamed obtained by prefoaming the expandable styrene resin particles. Since the fluidity of the particles deteriorates and it takes time to discharge the styrene resin pre-foamed particles from the pre-foaming machine, it is limited to 200 to 600.

  Furthermore, the fatty acid zinc salt constituting the skin layer is one produced by the direct method, and zinc stearate produced by the direct method is preferably used. Conventionally, the zinc salt of a fatty acid has been produced by the direct method or the metathesis method. However, if the zinc salt of the fatty acid produced by the metathesis method is used, the foamed molded product obtained using the expandable styrene resin particles is used. Since the releasability from the mold becomes extremely poor, a zinc salt of a fatty acid obtained by a direct method is used in the present invention.

  Here, the direct method refers to heating and melting fatty acid, adding zinc oxide or zinc hydroxide to the molten fatty acid, and allowing the reaction to proceed until there is no water to obtain a zinc salt of the fatty acid. A method for producing a zinc salt of a fatty acid by pulverizing the salt after cooling and solidification. Examples of reaction formulas for producing a zinc salt of a fatty acid by a direct method are shown in Formulas 1 and 2.

  Furthermore, when manufacturing the zinc salt of a fatty acid by a direct method, it does not specifically limit as a fatty acid used as a raw material, Although beef tallow and palm oil are used, a foam-molded article is manufactured using expandable styrene resin particles. Palm oil is preferable because the mold becomes less dirty.

And if the average particle diameter of the zinc salt of fatty acid obtained by the direct method is small, the heat-fusibility between the foamed particles of foamed molded articles such as foamed containers obtained using foamable styrene resin particles is reduced. On the other hand, if it is large, the adhesion of the zinc salt of the fatty acid on the surface of the expandable styrene resin particles becomes non-uniform. As a result, when supplying the expandable styrene resin particles to the pre-foaming machine, the expandable styrene resin When supplying pre-expanded styrene resin particles obtained by pre-expanding the particles into the mold, the fatty acid adhered to the particle surface in the flow pipe through which the expandable styrene resin particles or styrene resin pre-expanded particles circulate The zinc salt may fall off and the inner surface of the flow pipe may be contaminated, so it is limited to 3 to 25 μm .

  In addition, the average particle diameter of the zinc salt of fatty acid can be measured in the following manner. That is, the average particle diameter of the fatty acid zinc salt is measured by an electrical resistance method. Specifically, an aperture tube having electrodes disposed on both sides of the aperture (pore) is used as a zinc salt of the fatty acid to be measured. Is immersed in a suspension obtained by suspending in the electrolyte.

  An electric current is passed between the electrodes of the aperture tube through the suspension, and the electric resistance between the electrodes is measured. When the zinc salt of the fatty acid in the suspension is sucked and passes through the aperture, the electrolyte corresponding to the volume of the zinc salt of the fatty acid is replaced, and the electrical resistance between the electrodes changes. Since the amount of change in electrical resistance is proportional to the size of the particles, the volume of the particles can be calculated by converting the amount of change in electrical resistance into a voltage pulse, amplifying and detecting the volume. The diameter of the true sphere corresponding to the volume is the particle diameter of the fatty acid zinc salt.

  The average particle diameter of the fatty acid zinc salt can be calculated by taking the average particle diameter of the zinc salt of each fatty acid measured as described above, that is, the average particle diameter of the fatty acid zinc salt. Means the volume average particle diameter.

  The average particle diameter of the fatty acid zinc salt can be measured, for example, using a measuring apparatus commercially available from Beckman Coulter, Inc. under the trade name “Coulter Multisizer II”.

  Furthermore, if the content of the fatty acid zinc salt obtained by the direct method in the skin layer is small, the effect of suppressing the exudation of the contents in the foamed container obtained using the foamable styrenic resin particles is reduced. If the amount is too large, the heat-fusability between the expanded particles obtained by secondary foaming of the styrene resin pre-expanded particles obtained by pre-expanding the expandable styrene-based resin particles is reduced. It is limited to 0.3 to 1.2 parts by weight with respect to 100 parts by weight, and preferably 0.5 to 0.8 parts by weight.

  Here, when the zinc salt of the fatty acid produced by the metathesis method is used, the reason why the releasability from the mold of the foam molded article is not clearly clarified as described above, but according to the metathesis method, Fatty acid sodium salt is formed as an intermediate product, and this sodium salt remains as an impurity in the fatty acid zinc salt in an unreacted state, and can be released from the mold of the foamed molded product by interaction with polyvinyl alcohol. Is considered to be extremely bad.

  In the metathesis method, sodium hydroxide is reacted with fatty acid to prepare a sodium salt of the fatty acid, and this aqueous solution is maintained at 70 to 95 ° C. in an aqueous solution containing 5 to 10% by weight of the sodium salt of the fatty acid. In this state, a zinc chloride aqueous solution is gradually added to precipitate a fatty acid zinc salt to produce a fatty acid zinc salt.

As a coating method for coating the surface of the expandable polystyrene resin particles with a skin layer composed of polyvinyl alcohol having a predetermined viscosity, polyethylene glycol, and a zinc salt of a fatty acid obtained by a direct method, an expandable styrene resin A supermixer is prepared by mixing particles and 0.001 to 0.1 parts by weight of polyvinyl alcohol and 0.02 to 0.20 parts by weight of polyethylene glycol with respect to 100 parts by weight of the expandable styrene resin particles. , a Henschel mixer, after mixing are supplied to a general-purpose mixer such as a Loedige mixer, a zinc salt of the expandable styrene fatty acids obtained by the direct method in the resin particles in which the liquid mixture is applied to the surface 0.3 to 1.2 parts by weight are added, and the surface of the expandable styrenic resin particles is added to the polyvinyl alcohol and the polyester. Apply the entire surface uniformly with a coating composed of lenglycol and the zinc salt of the fatty acid obtained by the direct method, and evenly cover the surface of the expandable styrene resin particles entirely with the skin layer composed of the coating. The method of coating is mentioned.

  Next, a procedure for molding a foam molded product such as a bottomed cylindrical foam container using the expandable styrene resin particles will be described. First, expandable styrene resin particles are pre-expanded with a pre-foaming machine to form styrene resin pre-expanded particles, and the obtained pre-foamed particles are filled in a mold of a foam molding machine and heated with heating steam or the like. It is possible to produce a foamed molded article such as a bottomed cylindrical foaming container by heating and foaming with a medium and heat-fusion-integrating with each other by foaming pressure.

  The expansion ratio of the foam molded product obtained by foaming the expandable styrene resin particles of the present invention is not particularly limited, but is preferably 5 to 15 times, and more preferably 8 to 12 times. The expansion ratio of the foam molded product refers to a value obtained by dividing the specific gravity of the styrene resin constituting the foam molded product by the specific gravity of the foam molded product.

  If the thickness of the bottomed cylindrical foam container is thin, the mechanical strength of the foam container may be reduced. On the other hand, if the thickness is thick, the lightweight property of the foam container may be reduced or the upper end opening of the foam container may be reduced. Since the adaptability when a flat stress for deforming into a flat state is applied and the upper end opening of the foam container may easily crack, 1.5 to 3.5 mm is preferable. -3.0 mm is more preferable.

  Moreover, since the expandable styrene resin particles have a very small content of the aromatic compound of 0 to 500 ppm, the foam container can be suitably used for food applications and can be developed for various applications. It is.

The expandable styrene resin particles obtained by the method of the present invention are expandable styrene resin particles for pre-expanding, filling into a mold and foaming to form a foam molded product, The total amount of one or more aromatic compounds selected from the group consisting of styrene monomers, ethylbenzene, toluene, n-propylbenzene, i-propylbenzene and xylene is based on the total weight of the expandable styrene resin particles. The viscosity of the expandable styrene resin particles is 0 to 500 ppm, and the viscosity at 20 ° C. when the surface of the expandable styrene resin particles is 4% by weight with respect to 100 parts by weight of the expandable styrene resin particles is 1 to 60 mPa · s. 0.001 to 0.1 parts by weight of polyvinyl alcohol, 0.02 to 0.20 parts by weight of polyethylene glycol, and zinc salts of fatty acids obtained by the direct method 0.3 to 1. It is characterized by being covered with a skin layer consisting of parts by weight, so that the top opening of the foam container is deformed into a flat state despite the absence or reduction of aromatic compounds. It shows excellent adaptability to stress, and even when flat stress is applied to the upper end opening, it can generally prevent cracks from occurring in the upper end opening of the foam container, and can also be an aromatic compound. Since it is not contained or reduced, it can be suitably used for food applications.

And the foamed container obtained using the said expandable styrene-type resin particle hardly bleeds outside through the foamed container, and can expand | deploy to the various food use.

Furthermore, since the foamed container obtained using the above expandable styrene resin particles is excellent in releasability from the mold at the time of manufacture, the foam container is efficiently manufactured using expandable styrene resin particles. can do.

  Further, when the above expandable styrene resin particles are composed of expandable styrene resin particles having a particle diameter larger than 0.3 mm and not more than 0.6 mm, the foamable styrene resin particles can be obtained. The bottomed cylindrical foamed container shows better adaptability to the flat stress applied to the upper end opening, and cracks occur in the upper end opening even when flat stress is applied to the upper end opening. Can be almost prevented.

(Examples 1-6, Comparative Examples 1-7)
40 kg of ion exchange water is supplied into a 100 liter autoclave made of stainless steel equipped with a stirrer, and 40 kg of styrene monomer and tricalcium phosphate (manufactured by Boudenheim) are stirred into the ion exchange water. "C13-09") 40 g, potassium persulfate 0.5 g, benzoyl peroxide 140 g having a purity of 75% by weight and t-butyl peroxybenzoate 30 g were supplied to prepare a suspension.

  Next, the suspension was heated to 90 ° C. over 1 hour while stirring at a stirring speed of 200 rpm, and the suspension was held at 90 ° C. for 6 hours to polymerize. 40 g of tribasic calcium phosphate and 0.4 g of α-olefin sulfonate (product name “Lipolane PJ-400” manufactured by Lion Corporation) were added, and 1600 g of n-pentane and 400 g of i-pentane were injected into the suspension. The temperature was raised to 40 ° C. over 40 minutes and left at 130 ° C. for 3 hours.

  Thereafter, the suspension was cooled and hydrochloric acid was added until the pH of the suspension was 2, to decompose tricalcium phosphate. Subsequently, the suspension was washed with water for 10 minutes with a dehydrator, dehydrated, and then air-dried to obtain expandable polystyrene particles.

  The obtained expandable polystyrene particles were sieved with a sieve having an opening defined by JIS of 0.600 mm, and the expandable polystyrene particles that passed through the sieve were collected. Next, the collected expandable polystyrene particles are sieved with a sieve having an opening defined by JIS of 0.300 mm, and the expandable polystyrene particles remaining on the sieve are collected to obtain a particle diameter of 0.3 mm or more. Expandable polystyrene particles consisting only of 0.6 mm or less were obtained.

  On the other hand, polyvinyl alcohols 1 to 5 of the types shown in Tables 1 and 2 and polyethylene glycol (trade name “PEG-300” manufactured by NOF Corporation, weight average molecular weight: 300) are given in the predetermined amounts shown in Tables 1 and 2. A mixed solution obtained by uniformly mixing the mixture and 100 parts by weight of expandable polystyrene particles were supplied to a super mixer and stirred for 2 minutes, and then zinc stearate obtained by a direct method (average particle size: 17 μm). ) Or zinc stearate (average particle size: 16 μm) obtained by the metathesis method is added in a predetermined amount as shown in Tables 1 and 2 and further stirred for 2 minutes. The mixture and zinc stearate All of the coating agent made of was applied uniformly over the entire surface of the expandable polystyrene particles to obtain expandable polystyrene particles whose entire surface was uniformly coated with the skin layer made of the coating agent.

  There are four types of polyvinyl alcohol used above. Specifically, polyvinyl alcohol 1 (trade name “GOHSENOL GM-14” manufactured by Nippon Synthetic Chemical Industry Co., Ltd., viscosity: 23 mPa · s, saponification degree: 88 mol%) , Polyvinyl alcohol 2 (trade name “GOHSENOL KP-08” manufactured by Nippon Synthetic Chemical Industry Co., Ltd., viscosity: 7 mPa · s, saponification degree: 72 mol%), polyvinyl alcohol 3 (trade name “GOHSENOL GH- manufactured by Nippon Synthetic Chemical Industry Co., Ltd.”) 23 ”, viscosity: 52 mPa · s, saponification degree: 88 mol%) and polyvinyl alcohol 4 (trade name“ GOHSENOL AH-26 ”manufactured by Nippon Synthetic Chemical Industry Co., Ltd., viscosity: 26 mPa · s, saponification degree: 98 mol%) there were. Here, in Tables 1 and 2, the polyvinyl alcohol is simply expressed as “PVA”, and the viscosity of the aqueous polyvinyl alcohol solution at 20 ° C. when the polyvinyl alcohol is a 4 wt% aqueous solution is simply expressed as “viscosity”.

  In each of the expandable polystyrene particles whose entire surface is coated with the skin layer, the weight ratio of the expandable polystyrene particles, polyvinyl alcohol, polyethylene glycol and zinc stearate is the expandable polystyrene particles, polyvinyl alcohol, The weight ratio was the same as that of polyethylene glycol and zinc stearate.

(Example 7)
Instead of a sieve with an opening specified in JIS of 0.300 mm, a sieve with an opening specified in JIS of 0.250 mm was used, and instead of a sieve with an opening specified in JIS of 0.600 mm In addition, expandable polystyrene particles having a particle diameter larger than 0.250 mm and not more than 0.710 mm were used in the same manner as in Example 1 except that a sieve having an opening of 0.710 mm defined in JIS was used. Manufactured.

  And using the above-mentioned expandable polystyrene particles, as the polyvinyl alcohol, polyvinyl alcohol 5 (trade name “GOHSENOL GH-20” manufactured by Nippon Synthetic Chemical Industry Co., Ltd., viscosity at 20 ° C. when made into a 4 wt% aqueous solution: 43 mPa · s In the same manner as in Example 1 except that a degree of saponification: 88 mol%) was used, expandable polystyrene particles having the entire surface uniformly coated with a skin layer made of a coating agent were obtained.

  Release property, lip strength and leaching property of the bottomed cylindrical foam container obtained by using the obtained expandable polystyrene particles, and the particle size of the expandable styrene resin particles before the surface is coated with the skin layer The distribution was measured as shown below, and the results are shown in Tables 1 and 2.

(Releasability)
Expandable polystyrene particles whose entire surface was coated with a skin layer were pre-expanded using a rotary stirring pre-foaming machine to obtain polystyrene pre-expanded particles having a bulk ratio of 9 times. The polystyrene pre-expanded particles thus obtained were allowed to stand at room temperature for 24 hours, and then the polystyrene pre-expanded particles were filled in a cavity of a male and female mold and steamed with a gauge pressure of 0.2 MPa for 7 seconds. A bottomed cylindrical foam container was formed by heating and secondary foaming.

  Then, after cooling the male and female molds, the male and female molds are opened, and release air is blown from the female mold toward the foaming container, thereby releasing the foaming container from the female mold and a bottomed cylinder. A foamed container was obtained.

  The above-mentioned bottomed cylindrical foam container has a cross-sectional shape as shown in FIG. 1, and specifically, the foam container A is a planar circle having a diameter of 68 mm and a thickness of 2.8 mm. It is formed from a bottom surface portion 1 having a shape and a cylindrical peripheral wall portion 2 (open end inner diameter: 178 mm, height: 100 mm, thickness 2 mm) that gradually increases in diameter from the outer periphery of the bottom surface portion 1 obliquely upward. It was. In addition, a planar annular flange 21 having a thickness of 3 mm is projected in the horizontal direction at the upper end of the peripheral wall 2, and the outer diameter of the upper end of the cylindrical peripheral wall 2 including the flange 21 is as follows. It was 192 mm.

  The foaming container was continuously produced 500 times as described above, and during this production, the number of mold release failures that occurred when the foaming container was released from the mold was measured and judged according to the following criteria. In Tables 1 and 2, the number of mold release failures (in the table, simply indicated as “number of failures”) is shown in parentheses. Here, mold release failure refers to the case where the foam container is in close contact with the male mold and does not separate, and the foam container is detached from the female mold even if the release air is blown from the female mold. It was assumed that there was not.

○: 0 to 5 times △: 6 to 20 times ×: 21 times or more

(Lip strength)
Expandable polystyrene particles whose entire surface was covered with a skin layer were pre-expanded using a rotary stirring pre-expanding machine to obtain polystyrene pre-expanded particles having a bulk magnification of 9 times and 10 times. Then, using polystyrene pre-expanded particles having a bulk magnification of 9 times, 10 bottomed cylindrical foam containers having the same shape and the same size were obtained in the same manner as in the measurement of releasability. Similarly, ten polystyrene foam containers having the same shape and the same size were obtained using polystyrene pre-expanded particles having a bulk magnification of 10 times in the same manner as in the measurement of releasability.

  On the other hand, a pressing tool 3 was prepared in which a groove portion 31 having a width of 4 mm, a depth of 4 mm, a length of 60 mm and an opening at both ends was formed on a flat lower end surface (see FIG. 2). Then, the foam container A was placed on the support plate in a state where the bottom surface portion 1 faced the vertical direction. Thereafter, the uppermost portion of the flange portion 21 in the horizontally placed foam container A is fitted into the central portion in the length direction of the groove portion 31 of the pressing tool 3, and the pressing tool 3 is moved at a speed of 50 mm / min. Then, it was moved vertically downward to apply a flat stress to the opening of the foaming container in the vertical direction, and the opening of the foaming container was deformed into a flat state as shown in FIG.

  Then, the pressing tool 3 was moved vertically downward until a crack penetrating in the inner and outer directions occurred at the opening end of the foam container A, and the maximum pressing strength at this time was measured. Ten foaming containers A are prepared. Among the maximum pressing strengths of the ten foaming containers A, the arithmetic average value of the maximum pressing strengths excluding the maximum value and the minimum value is defined as the lip strength of the foaming container A. Judgment based on. In Tables 1 and 2, specific values of lip strength are shown in parentheses.

In Example 7, when polystyrene pre-expanded particles obtained by pre-expanding expandable polystyrene particles at 9 times the bulk magnification were evaluated as 1.44 × 10 ⁵ Pa, the evaluation was “◯”. If using polystyrene pre-expanded particles comprising prefoamed polystyrene particles bulk 10X magnification, evaluated as 1.31 × 10 ⁵ Pa is "△", the bubbling container a high expansion ratio of a bulk magnification 10 times It was insufficient to obtain.

○: 1.40 × 10 ⁵ Pa or more Δ: 1.30 × 10 ⁵ or more and less than 1.40 × 10 ⁵ Pa ×: less than 1.30 × 10 ⁵

(Exudation)
In the bottomed cylindrical foaming container obtained in the same manner as the measurement of releasability, after supplying the seasoning and curry containing curry powder used for instant noodles until full, The foam container was entirely covered with stretched polypropylene film. Next, the foamed container was left in an oven maintained at 60 ° C. for 48 hours.

Then, copy the entire outer surface of the foam container to the paper and copy the yellow pigment part of the curry powder that has oozed out to the outer surface of the foam container onto the paper, corresponding to the entire outer surface of the foam container. While measuring the weight W ₁ of the portion of the paper, the weight W ₂ of the portion of the paper corresponding to the copied yellow pigment portion was measured, the percentage was calculated by the following formula, and judged according to the following criteria. In Tables 1 and 2, specific values of exudation are shown in parentheses.
Exudability (%) = 100 × W ₂ / W ₁

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

(Particle size distribution)
The particle size distribution of the expandable polystyrene particles classified using two sieves was measured as follows. Plural kinds of sieves having different openings defined in JIS (opening 0.600 mm, opening 0.500 mm, opening 0.425 mm, opening 0.355 mm, opening 0.300 mm, opening 0.250 mm And 25 g of the classified expanded polystyrene was sieved with a sieve so that the mesh size was changed from a large sieve to a small sieve. As a result, the expandable polystyrene particles could not pass through a sieve having a predetermined opening according to the particle diameter of each particle, and remained on each sieve.

Next, the weight W ₃ of the expandable polystyrene particles remaining on the sieve is measured for each sieve, and the weight ratio (% by weight) of the expandable polystyrene particles remaining on the sieve to the total expandable polystyrene particles is determined for each sieve. Calculated.

It is the longitudinal cross-sectional view which showed the foaming container obtained in the Example. (A) It is the bottom view which showed the pressing tool. (B) It is the longitudinal cross-sectional view which showed the pressing tool. It is the side view which showed the state which changed the upper end opening part of the foaming container into the flat state.

Explanation of symbols

  A foaming container

Claims (1)

A method for producing foamable styrene resin particles for pre-foaming, filling into a mold and foaming to form a foamed molded article, comprising a styrene monomer, ethylbenzene, toluene, n-propylbenzene, i- and particle size Ri 0~500ppm der total amount of the total weight of propyl benzene and one or two or more aromatic compounds selected from the group consisting of xylene only greater 0.600mm less than 0.300mm expandable styrene resin particles 100 parts by weight, 4 wt% viscosity at 20 ° C. when the aqueous solution is 7-52 and saponification degree Ri mPa · s der is Ru 70-90 mol% der polyvinyl alcohol consisting of 0.001 parts by weight and the weight average molecular weight is a mixture of polyethylene glycol 0.02 to 0.20 parts by weight of 200 to 600 mixture After mixing, to the expandable styrene resin particles in which the liquid mixture is applied to the surface, and an average particle size obtained by the direct method as the zinc salt of fatty acids obtained by direct method of 3~25μm stearic 0.3 to 1.2 parts by weight of zinc acid is added, and the surface of the expandable styrene resin particles is stearin obtained by the polyvinyl alcohol, the polyethylene glycol and the direct method and having an average particle diameter of 3 to 25 μm. A method for producing expandable styrene resin particles, wherein a coating agent comprising zinc acid is applied, and the surface of the expandable styrene resin particles is coated with a skin layer comprising the coating agent.

Images