JP4806551B2 - Expandable polystyrene resin particles and process for producing the same, pre-expanded particles, foamed molded product, and food packaging - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a foamable polystyrene-based resin particle which gives a foamed molded article capable of preventing an oil and a pigment from oozing out and is excellent in foamability, to provide its production method, to provide a pre-foamed particle obtained from the particle, to provide a foamed molded article, and to provide a food package prepared by receiving and packaging a food or the like in a container comprising the foamed molded article. <P>SOLUTION: The foamable polystyrene-based resin particle for foaming molding, prepared by polymerizing a cross-linkable monomer and a styrenic monomer on the surface of the polystyrene-based resin particle to form a surface layer, and then impregnating the surface with an easily evaporable foaming agent, is characterized in that the thickness of the surface layer is 3 to 100 &mu;m, when the resin is saturated and swollen with tetrahydrofuran, and tetrahydrofuran-insoluble gel content is 10 to 50 mass% based on the total amount of the resin particle. <P>COPYRIGHT: (C)2007,JPO&amp;INPIT

Description

  The present invention relates to expandable polystyrene resin particles and a method for producing the same, pre-expanded particles manufactured using the expandable polystyrene resin particles, a foam molded product, and a food packaging in which food is packaged in a container comprising the foam molded product. About the body.

  Conventionally, expandable polystyrene resin particles obtained by impregnating a foaming agent into styrene resin particles are pre-expanded to produce pre-expanded 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. It is not what is heat-sealed entirely at the contact portion between the particles, but is 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 caused by the non-thermally fused portion in the contact portion of the contact portion in the inside and outside direction is continuous, a fine capillary that cannot be visually confirmed is formed so as to penetrate between the inside and outside 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 through the capillary formed between the foam particles. This can be confirmed from the occurrence of the phenomenon.

  When such a foam molded container is used as a cup for beverages such as coffee, there is no practical problem, but oily foods such as donuts, hamburgers, fried chicken, margarine are contained in the foam molded container. When foods containing salad oil, fats and oils 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, when storing and storing the curry powder containing instant noodles together with instant noodles in the foam molded container, 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, There was a problem that merchandise value was impaired.

  Therefore, in Patent Document 1, the surface of the expandable polystyrene resin particles is covered with a skin layer, and this skin layer is formed from zinc stearate 0.3 to 0.3 parts by mass with respect to 100 parts by mass of the expandable polystyrene resin particles. An expandable polystyrene system comprising 0.6 part by mass and 0.1 to 0.4 part by mass of a polyethylene glycol aqueous solution containing 20 to 50% by mass of polyethylene glycol having a weight average molecular weight of 100 to 600 Resin particles have been proposed.

  However, the foamed molded product obtained by foaming the expandable polystyrene resin particles has a certain degree of oil content prevention effect, but the molded product has insufficient oil resistance, and therefore has a long period of time. In the storage of oil, it was insufficient to prevent oil from seeping out.

  In order to provide a certain degree of oil resistance in the polystyrene resin particles, a method of giving a crosslinked structure to the polystyrene resin can be mentioned. Although prevention of oil oozing out from a molded product has not been performed directly, attempts have been made to impart a crosslinked structure to polystyrene resin particles.

  Patent Document 2 discloses a polymerization consisting of 0.05 to 1.0% by mass of divinylbenzene and 99.95 to 99.0% by mass of styrene monomer for the purpose of producing an expandable polystyrene resin that can be mixed and molded with a polyethylene resin. In the aqueous medium in which the expandable polystyrene particles are suspended, the expandable polystyrene mixture is gradually added so that the expandable polystyrene resin particles are 90 to 50% by mass and the polymerizable monomer mixture is 10 to 50% by mass. There has been proposed a method for producing expandable polystyrene resin particles which is added and polymerized in the presence of a polymerization catalyst to form a styrene-divinylbenzene copolymer on the surface of the expandable polystyrene.

In this method, the surface layer portion can have a crosslinked structure, but the polystyrene resin is swollen by the foaming agent, and when the styrene monomer containing the crosslinkable monomer is included therein, the particle center is relatively The styrene monomer penetrates to the part, and although the degree of crosslinking is lower than that of the particle surface layer part, the inside of the particle also has a crosslinked structure.
When the resin particle has a small particle diameter, which is usually used as a cup noodle packaging container, crosslinking proceeds more remarkably to the inside of the particle. In order to maintain the foaming ability of such particles, a good foaming ability is not obtained unless there is a component that can serve as a solvent, such as unreacted styrene monomer. However, those containing a lot of solvent components are not suitable as containers for containing food.

  Patent Document 3 proposes styrene-based polymer beads modified with a styrene-divinylbenzene copolymer for the purpose of improving the strength of a cup-molded product. However, although the strength of the molded product is improved by this method, the entire particle is relatively uniformly modified by the crosslinked structure, so that the foaming ability is poor and extra heating is required to obtain a molded product having a good appearance. As a result, productivity was impaired.

Further, in Patent Document 4, the styrene polymer seed particles are added by continuously or intermittently adding a styrene monomer and a polymerization initiator to an aqueous suspension containing styrene polymer seed particles. The styrenic monomer is polymerized to obtain styrene polymer particles, and the styrene polymer particles are impregnated with a readily volatile foaming agent. When the total amount of the amount of styrene polymer seed particles and the amount of styrene monomer necessary to obtain the desired styrene polymer particles is 100 parts by mass, the styrene polymer seed particles From the time when the total amount of the styrene monomer added to the amount is 90 parts by mass, the addition of the styrene monomer is completed and the polymerization reaction is completed. Against 0.005 to 0.02 parts by mass Preparation of expandable polystyrene polymer particles added the bridge monomer (seed polymerization method) is disclosed.
However, the expandable polystyrene polymer particles produced by the production method are effective in closing the gap between the pre-expanded particles of the foam molded product obtained using the expandable polystyrene polymer particles. However, the above-mentioned problem that oil and yellow pigment ooze out to the outside through the capillary tube formed in the foam-molded container is a sufficient solution because the resistance to oil is insufficient. It did not bring.
JP 2005-8797 A Japanese Patent Publication No. 48-44656 Japanese Patent Laid-Open No. 62-181344 JP-A-9-221563

  As a result of intensive research, the inventors of the present invention have found that the heat-sealed portions of the foam particles are wavy and wrinkled at locations where oil and yellow pigment ooze out in the foam-molded container. On the other hand, in the part where the oil or yellow dye does not ooze out, the wavy phenomenon does not occur in the heat-sealed part of the foamed particles, and there is no distortion. It was found that it was not altered by the pigment. Furthermore, in order to prevent oil and yellow pigment from oozing out in the foam molded container, it is necessary to improve the oil resistance of the foam molded product, particularly the oil resistance of the heat-sealed part between the foam particles of the foam molded product. I found out.

  The present invention is a case where a pigment such as oil or curry powder contained in food is stored inside for a long period of time, or a liquid containing a surfactant or the like is stored inside for a predetermined time. Foamed polystyrene resin particles having excellent foamability and a method for producing the same, and foamed molding produced using the foamable polystyrene resin particles. It is an object of the present invention to provide a product and a food package in which food is packaged in a container made of the foam-molded product.

In order to achieve the above object, the present invention is provided with a surface layer formed by polymerizing a crosslinkable monomer and a styrene monomer on the surface of polystyrene resin particles, and these are easily volatile foaming agents. Expandable polystyrene resin particles for foam molding, impregnated with
The surface layer thickness when the resin particles are saturatedly swollen in tetrahydrofuran is in the range of 3 to 100 μm, and the tetrahydrofuran-insoluble gel content is in the range of 10 to 40 % by mass with respect to the total amount of the resin particles. An expandable styrenic resin particle is provided.

Further, in the present invention, after 100 parts by mass of seed particles made of a styrene resin are dispersed in an aqueous medium, 15 to 25 parts by mass of a styrene monomer with respect to 100 parts by mass of the seed particles in the dispersion, And 0.03 to 1.0 parts by mass of a crosslinkable monomer, and absorbed and polymerized in the seed particles to obtain styrene resin particles, and then impregnated with a readily volatile foaming agent. A method for producing styrene resin particles, wherein the expandable styrene resin particles according to claim 1 are obtained by setting the ratio of the styrene resin in the growing particles during the polymerization in the range of 80 to 96 mass%. A method for producing expandable styrene-based resin particles is provided.

The present invention also provides pre-expanded particles obtained by pre-expanding the expandable polystyrene resin particles according to the present invention.
The present invention also provides a foam-molded article obtained by foam-molding the pre-expanded particles according to the present invention.

  Moreover, this invention provides the food packaging body by which the foodstuff which contains an oil-based food or edible oil and fat, and a pigment | dye is packaged in the container which consists of the said foaming molding which concerns on the said invention.

The expandable polystyrene resin particles of the present invention can contain a food containing oil in a foamed molded product obtained by foaming the prefoamed particles obtained by prefoaming for a long period of time or have a surface activity. Even when a liquid containing an agent is stored, the thermal fusion interface between the expanded particles is not affected by oil, a dye, a surfactant, or the like. Therefore, it is possible to prevent a problem that oil, a pigment, a liquid containing a surfactant, or the like oozes out from the outer surface of the foam molded product through the heat fusion interface between the foam particles.
Furthermore, the foamed molded article of the present invention is excellent in appearance and has excellent surface printability because there are few voids between the foamed particles on the surface.

  The expandable styrene resin particles of the present invention are provided with a surface layer formed by polymerizing a crosslinkable monomer and a styrene monomer on the surface of the polystyrene resin particles. Expanded polystyrene resin particles for foam molding which are impregnated, and the resin layer has a surface layer thickness of 3 to 100 μm when saturated and swelled in tetrahydrofuran (hereinafter referred to as THF) at 25 ° C. under normal pressure. And the THF-insoluble gel content is in the range of 10 to 50% by mass with respect to the total amount of the resin particles.

  The polystyrene resin constituting the portion other than the surface layer of the expandable polystyrene resin particles of the present invention is not particularly limited. For example, styrene, α-methylstyrene, vinyltoluene, chlorostyrene, ethylstyrene, i-propylstyrene, Examples thereof include homopolymers of styrene monomers such as dimethylstyrene or copolymers thereof. Further, the polystyrene resin constituting the seed particle portion may be a copolymer of the styrene monomer and a vinyl monomer copolymerizable with the styrene monomer. Examples of the monomer include alkyl (meth) acrylates such as methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, and cetyl (meth) acrylate, (meth) acrylonitrile, dimethyl maleate, and dimethyl fumarate. Rate, diethyl fumarate, ethyl fumarate and the like.

  The polystyrene resin constituting the surface layer is formed by polymerizing a styrene monomer containing a crosslinkable monomer. The crosslinkable monomer is not particularly limited as long as it can give a crosslink structure to the expandable polystyrene resin particles, and examples thereof include alkylene glycol dimethacrylate such as divinylbenzene and polyethylene glycol dimethacrylate. And polyfunctional monomers such as divinylbenzene are preferred. The polystyrene resin constituting the resin surface layer may be a copolymer of the crosslinkable monomer, the styrene monomer, and a vinyl monomer copolymerizable with the styrene monomer. Well, as such a vinyl monomer, for example, methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, alkyl (meth) acrylate such as cetyl (meth) acrylate, (meth) acrylonitrile, Examples thereof include dimethyl maleate, dimethyl fumarate, diethyl fumarate, and ethyl fumarate. That is, the vinyl monomer may be supplied to a monomer solution containing a styrene monomer, a crosslinkable monomer, and a polymerization initiator.

  In the expandable styrene resin particles of the present invention, the surface layer thickness is in the range of 3 to 100 μm, preferably in the range of 5 to 80 μm, more preferably in the range of 5 to 70 μm, and most preferably in the range of 10 to 50 μm. It is a range. When the surface layer thickness is less than 3 μm, the oil resistance of the foam molded product is lowered, and a liquid containing an oil, a pigment, a surfactant, or the like is liable to exude outside through the foam molded product. On the other hand, when the surface layer thickness exceeds 100 μm, the secondary foamability is lowered, the fusion rate between the foamed particles is lowered, and there arises a problem that the oil is oozed and the strength of the molded product is lowered.

As shown in FIG. 1, as the process of the method for measuring the surface layer thickness,
(1) The resin particles 1 are saturated and swelled by being immersed in THF at 25 ° C. under normal pressure (see FIG. 1A).
(2) Next, the saturated and swollen resin particles 2 are separated from THF (see FIG. 1B),
(3) Next, the separated resin particles 2 are immersed in methyl methacrylate (hereinafter referred to as MMA) (see FIG. 1 (c)), and the THF inside the saturated and swelled resin particles 2 is replaced with MMA ( FIG. 1 (d))
(4) Next, MMA is polymerized to form polymethylmethacrylate (hereinafter referred to as PMMA) solidified body 3, and resin particles are fixed in the PMMA solidified body 3 in a swollen state (see FIG. 1 (e)).
(5) Next, the PMMA solidified body 3 is cut along a plane passing through the center of the resin particles (see FIG. 1 (f)),
(6) Next, it is desirable to carry out by observing the cut surface 4 and measuring the surface layer thickness of the resin particles (see FIG. 1G).

FIG. 2 is an enlarged view of the main part of the cut surface of the PMMA solidified body 3 produced by the measurement method. In this figure, reference numeral 5 is a surface layer of fixed resin particles, 6 is a PMMA phase outside the particles, and 7 is particles. Each of the internal PMMA phases is shown.
As shown in FIG. 2, the expandable styrene resin particles of the present invention are processed by sequentially performing the steps (1) to (6), so that the surface layer 5 remains on the cut surface of the PMMA solidified body 3, It is possible to measure the thickness by magnifying.

  Furthermore, in the present invention, the THF-insoluble gel content of the expandable styrenic resin particles is in the range of 10 to 50% by mass, preferably in the range of 15 to 50% by mass, more preferably, with respect to the total amount of the resin particles. It is the range of 15-40 mass%. When the THF-insoluble gel content is less than 10% by mass, the oil resistance of the obtained foamed molded product is lowered, and the liquid containing the oil, the pigment, the surfactant or the like is likely to exude to the outside through the foamed molded product. Further, when the THF-insoluble gel content exceeds 50% by mass, the fusion of the pre-foamed particles is deteriorated during foam molding, not only the strength is reduced, but the voids between the pre-foamed particles are increased, and the content of the molded product is increased. There arises a problem that the product is easily dyed.

Next, the manufacturing method of the expandable styrene-type resin particle which concerns on this invention is demonstrated.
In order to produce the expandable styrene resin particles of the present invention, a known nuclear polymerization method (seed polymerization method) is used. As seed particles used in the present invention, those obtained by a conventionally known method for producing styrene resin particles can be used. For example, a method of producing a styrene resin seed particle by adding a crosslinkable monomer to the styrene monomer and then performing suspension polymerization in water, or supplying a styrene resin to an extruder to melt Examples thereof include a method of kneading, extruding into a strand shape or a substantially spherical shape from an extruder and cutting it at predetermined lengths to produce styrene resin seed particles. The weight average molecular weight of the styrene-based resin particles is preferably 150,000 to 400,000, more preferably 250,000 to 350,000, from the viewpoint of foam moldability and physical properties.

  It is desirable to improve the oil resistance of the surface of the foamed molded product in order to prevent the oils contained in foods and the like and pigments such as curry powder from leaching to the outside, which is a problem to be solved by the present invention. In order to improve the oil resistance of the foam molded product obtained by the foam molding method called the bead method as in the present invention, the surface layer of the expandable styrenic resin particles is often exposed on the surface of the foam molded product. It is necessary to increase the crosslink density on the surface of the resin particles. Furthermore, in order to give the foamable styrenic resin particles excellent foam moldability, the central part of the resin particles is preferably made of a styrene resin having a crosslink density as low as possible.

  And after disperse | distributing 100 mass parts of said seed particles in an aqueous medium, 15-100 mass parts styrene-type monomer and 0.03-1.0 mass part crosslinkable single monomer in this dispersion liquid After adding a body and absorbing and polymerizing the seed particles to obtain styrene resin particles, an easily volatile foaming agent is impregnated to produce expandable styrene resin particles. The production method of the present invention is characterized in that expandable styrene resin particles are obtained by setting the ratio of the styrene resin in the growing particles during the polymerization in the range of 80 to 100% by mass. Hereinafter, seed particles in the process of growth are referred to as “growth seed particles”.

  In the present invention, the crosslinkable monomer is added in the polymerization step, but it is desirable that the crosslinkable monomer is added after being dissolved in a part or all of the styrenic monomer. If the crosslinkable monomer and the styrene monomer are added separately, the crosslinked structure may be uneven, and uniform foamable styrene resin particles may not be obtained.

  The addition amount of the styrene monomer is in the range of 15 to 100 parts by mass with respect to 100 parts by mass of the seed particles. When the amount of the styrene monomer is less than 15 parts by mass, the resulting foamable styrene resin particles have a thin surface layer thickness, which causes a problem that sufficient oil resistance is not exhibited. Further, when the styrene monomer exceeds 100 parts by mass, it penetrates into the seed particles more than necessary, and the surface layer thickness of the obtained expandable styrene resin particles becomes too thick, thereby impairing the foaming ability. The problem is that the adhesion between the particles is weak, the oil content is exuded from between the particles, and the strength of the molded product is reduced.

  The addition amount of the crosslinkable monomer is in the range of 0.03 to 1.0 part by mass with respect to 100 parts by mass of the seed particles. When the crosslinkable monomer is less than 0.03 parts by mass, there is a problem that the surface layer of the finished expandable styrene resin particles is insufficient and sufficient oil resistance is not exhibited. On the other hand, when the crosslinkable monomer exceeds 1.0 part by mass, there is a problem that crosslinking is excessively performed, the foaming ability is impaired, the gap between the foamed particles of the molded product is widened, and oil exudation is increased.

  The polymerization initiator used when the styrenic monomer is absorbed in the seed particles and polymerized is not particularly limited, and examples thereof include benzoyl peroxide, lauryl peroxide, t-butylperoxybenzoate, t- Butyl peroxide, t-butyl peroxypivalate, t-butyl peroxyisopropyl carbonate, t-butyl peroxyacetate, 2,2-t-butylperoxybutane, t-butylperoxy-3,3,5 trimethyl Examples include organic peroxides such as hexanoate and di-t-butylperoxyhexahydroterephthalate, and azo compounds such as azobisisobutyronitrile and azobisdimethylvaleronitrile. These may be used alone or in combination. can do.

  As the polymerization initiator, a decomposition temperature for obtaining a half-life of 10 hours is 50 ° C. or more and less than 80 ° C., and a decomposition temperature for obtaining a half-life of 10 hours is 80 ° C. or more and It is preferable to use together with a polymerization initiator at 120 ° C. or lower. In addition, as an addition amount of a polymerization initiator, 0.01-3 mass parts is preferable with respect to 100 mass parts of styrene-type monomers.

  Moreover, in order to improve the dispersion stability of styrene seed particles and seed particles, a suspension stabilizer or a stabilizing aid may be added to the dispersion.

  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 tricalcium phosphate and magnesium pyrophosphate. When using a poorly soluble inorganic compound, 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.

  In the present invention, the content of the styrene resin in the growing seed particles during the polymerization is 80 to 100% by mass, preferably 85 to 100% by mass, and more preferably 90 to 100% by mass, from the start to the end of the polymerization. Keep in the range. The means for maintaining the range can be adjusted by the temperature of the reaction system, the supply rate of the styrene monomer, the amount of the polymerization initiator, and the like. For example, the reaction temperature depends on the type of polymerization initiator, but is preferably 80 to 110 ° C. When the temperature is less than 80 ° C., the polymerization rate becomes slow, the styrene monomer easily penetrates into the seed particles, and crosslinking is not efficiently performed on the surface layer. When the temperature exceeds 110 ° C., the polymerization proceeds before the added styrene monomer is absorbed into the seed particles, the absorption efficiency into the seed particles deteriorates, and the production efficiency becomes unusable powder. It is not preferable because it gets worse.

The content of the styrene resin in the growing seed particles is measured by the following method.
A small amount of the growing seed particles during the polymerization reaction is taken out from the polymerization vessel and separated from the aqueous medium, and then the moisture on the surface of the growing seed particles is removed with gauze or the like to obtain a measurement sample.
Then, 0.08 g is precisely weighed from the measurement sample and dissolved in 24 mL of toluene.
10 mL of a Wis reagent, 30 mL of a 5% by mass potassium iodide aqueous solution, and about 30 mL of a 1% by mass starch aqueous solution are added to this solution, and titrated with an N / 40 sodium thiosulfate solution to obtain a sample titer constant (mL). The Wis reagent is prepared by dissolving 8.7 g of iodine and 7.9 g of iodine trichloride in 2 L of glacial acetic acid.
On the other hand, titration is performed in the same manner as described above without dissolving the sample, and a blank titer (mL) is obtained.
Then, the content of the styrene monomer in the growing seed particles is calculated by the following formula.
Styrene monomer content (mass%) = 0.1322 × (blank drop constant−sample drop constant) / measured sample mass (g)

This operation is performed on samples collected at intervals of 10 minutes from the start of polymerization to the end of polymerization to determine the styrene monomer content.
Subsequently, an amount obtained by subtracting the amount of the styrene monomer from the mass of the growing particles is defined as the amount of the styrene resin in the growing seed particles, and the content (% by mass) in the growing particles is calculated by the following formula.
Styrenic resin content (mass%) = 100 × (measurement sample mass−styrene monomer content) / measurement sample mass

  Next, the styrene resin particles obtained by the nuclear polymerization are impregnated with a readily volatile foaming agent to produce expandable styrene resin particles.

  As the readily volatile foaming agent, general-purpose ones are used. 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 -Freon-based blowing agents such as difluoroethane (HFC-152a) are mentioned, and aliphatic hydrocarbons are preferred. The readily volatile foaming agent may be used alone or in combination. In addition, 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, but when the foam molded product is a foam molded container and the thickness is small, the average particle size is set to a range of 0.2 to 1 mm. The thickness is preferably 0.2 to 0.8 mm, more preferably 0.3 to 0.7 mm, but is not limited thereto.

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 0.20 g / cm ^3, but is not limited thereto.

  Examples of the foamed molded product include various forms, and cup-shaped, bowl-shaped, tray-shaped, box-shaped and other foam-molded containers are preferable in that the effects and effects of the present invention are effectively exhibited.

  In this foamed container, beef fat, soybean oil, rapeseed oil, perilla oil, olive oil, sesame oil, safflower 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.

As described above, the foamed molded product is obtained by foaming predetermined foamable styrene resin particles, and thus the foamed particles are firmly heat-sealed and integrated at their interfaces. The interface portion where the foamed particles are heat-sealed has high crosslink density and excellent oil resistance.
Therefore, when food containing oil or a pigment such as curry powder is stored in the foamed molded product for a long period of time, or liquid containing a surfactant is stored in the foamed 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. The problem that liquid or the like oozes on the outer surface of the foam molded product can be solved. Furthermore, a foamed molded article having a beautiful appearance, excellent printability, and excellent strength can be obtained.

  The food package according to the present invention is obtained by packaging an oil-based food or a food containing edible fats and pigments in a foam-molded container made of the foam-molded product. The type of food to be filled in the foam molded container is not particularly limited as long as it contains fats and oils. However, instant noodles (including oysters) containing stew, mayonnaise, dressing sauces, curry roux as described above. Oily foods such as butter, margarine, white sauce, yogurts, ice cream, donuts, hamburgers, and fried chicken, or foods containing edible fats and pigments are preferred in that the effects and effects of the present invention are effectively exhibited. The packaging form of the food package is not particularly limited, and an appropriate packaging form can be selected according to the shape of the foam molded product. For example, when using foamed containers such as cups, bowls, trays, etc., fill the container with food, seal the lid with a lid and seal it, and if necessary, synthesize the whole. It can be set as the form packaged with a resin film.

  Since the food package according to the present invention is formed by packaging an oil-based food or a food containing edible fats and pigments in a foam-molded container made of the foam-molded product, such as food containing oil or curry powder. Even if food containing pigments is stored in the foam molded container for a long period of time, oil, pigments, liquids containing surfactants, etc. ooze out to the outer surface of the foam molded container through the heat fusion interface between the foamed particles. Can be prevented.

  Hereinafter, although an Example demonstrates further in detail, this invention is not limited by these.

[Example 1]
In a 5 L autoclave equipped with a stirrer, 2.0 L of ion-exchanged water, 1600 g of polystyrene seed particles having an average particle diameter of 0.3 mm and a weight average molecular weight of 280,000, 20 g of magnesium pyrophosphate, and dodecylbenzenesulfonic acid 1 g of sodium was supplied and stirred to prepare a dispersion.

  As a crosslinking monomer, 1.4 g of divinylbenzene, 2.0 g of benzoyl peroxide (with a 10-hour half-life of 74 ° C.) and 1.0 g of t-butylperoxybenzoate (with a 10-hour half-life of 104 ° C.) of 400 g A substance dissolved in the styrene monomer was added, and the mixture was stirred and emulsified with a homomixer to prepare a styrene solution.

And the said dispersion liquid was hold | maintained at 90 degreeC, and the said styrene solution was continuously supplied in 1.5 hours in this dispersion liquid. Thereafter, the temperature was further maintained at 90 ° C. for 1 hour, and then the temperature was raised to 125 ° C. and maintained for 1 hour to complete the polymerization.
During the polymerization, the proportion of the styrene resin in the growing seed particles was measured. As a result, the minimum ratio of the resin in the grown particles was 88%.

  Thereafter, while maintaining the temperature at 125 ° C., 110 g of normal pentane and 30 g of isopentane were supplied and maintained for 3 hours. Then, it cooled to 30 degreeC over 2 hours, the dispersion medium was removed, wash | cleaned, and dried and the expandable polystyrene resin particle was obtained.

  The obtained expandable styrene resin particles were subjected to (1) surface layer thickness measurement and (2) THF-insoluble gel content measurement.

(1) Surface layer thickness measurement (a) From the obtained expandable styrenic resin particles, those having a diameter of 0.3 to 0.4 mm are selected, accurately weighed 1.00 g, and immersed in 100 ml of THF.
(B) After immersion, the mixture was allowed to stand at 25 ° C. and atmospheric pressure for 24 hours, and saturated and swollen in THF.
(C) After 24 hours, the mixture was filtered using an 80-mesh wire mesh to obtain swollen resin particles.
(D) In a state where the above-mentioned swelling resin particles are swollen in a commercially available test tube having an outer diameter of 17 mm, a length of 105 mm and a capacity of 10 ml, the swelling resin particles 2 g, MMA 3 g, 2,2 azobis (2,4 -Dimethylvaleronitrile) 0.003 g was added, and the swelling resin particles were immersed in MMA.
(E) The MMA soaked product was heated in a thermostatic bath at 40 ° C. for 20 hours in a sealed state.
(F) After heating, it was cooled with cold water, and PMMA during polymerization was taken out from the test tube so as not to be deformed.
(G) The obtained PMMA in the middle of polymerization was sliced with a cutter knife along a plane passing through the center of the resin particles fixed inside.
(H) The sliced material was reheated in an oven at 70 ° C. for 2 hours.
(I) After reheating, the surface layer thickness of the resin particles in the PMMA solidified body was measured with an electron microscope.
(J) The average value of the numerical values measured at 10 locations was defined as the surface layer thickness (μm).
As a result of this measurement, the surface layer thickness of the expandable polystyrene resin particles of Example 1 was 15 μm.

(2) Measurement of THF-insoluble gel content The THF-insoluble gel content is a value measured under the following conditions.
A measurement sample W ₁ (exactly weighed with 1.00 g ± 0.02 g) of expandable polystyrene resin particles is immersed in 100 ml of THF at 25 ° C. under normal pressure for 24 hours. After soaking, the mixture is filtered using an 80-mesh wire mesh, and the residue is dried under reduced pressure at 80 ° C. and −60 cmHg for 2 hours. After drying, it is naturally cooled to room temperature in a desiccator, and the mass W _{2 of the} dry residue is measured.
From the above measured value, the THF-insoluble gel content is calculated from the following formula.
THF-insoluble gel content (mass%) = 100 × W ₂ / W ₁
As a result of this measurement, the THF-insoluble gel content of the expandable polystyrene resin particles of Example 1 was 32% by mass.

Furthermore, the obtained expandable polystyrene resin particles are subjected to foam molding, and (3) measurement of the fusion rate of the molded product and (4) evaluation of oil exudation prevention property are performed on the obtained foam molded product. did.
First, expandable polystyrene resin particles were foam-molded under the following conditions to produce a foam-molded container.
To 1.0 kg of expandable styrene resin particles, 3 g of zinc stearate (average size of pulverized product, maximum length: 20 μm) was stirred for 2 minutes in a high-speed fluidized mixer. Next, 1 g of polyethylene glycol was supplied, and the mixture was further stirred for 2 minutes and coated with zinc stearate. Thereafter, it was stored in a cool and dark place for 3 days.
Thereafter, the expandable styrene resin 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 stored at room temperature for 1 day and dried.
Next, the pre-expanded particles are supplied and filled in a mold in a foam-molding machine, and the pre-expanded particles are heated and foamed using 0.20 MPa water vapor for 6 seconds, and the internal volume is 450 cm ³ . Moreover, a cup-shaped foam-molded container having a wall thickness of 2 mm was obtained. Note that the cup-shaped foam-molded container is formed by projecting 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.

(3) Measurement of molded product fusion rate The fusion rate between the foamed particles of the obtained foam molded container (molded product fusion rate) was measured by the following method.
The side wall of the foam-molded container is divided into two by hand, and regarding the foamed particles in the fracture surface, the number of particles broken within the particles (a) and the number of particles broken at the interface between the particles (b) And the value obtained by substituting into the formula [(a) / ((a) + (b))] × 100 was defined as the fusion rate (%). Evaluation was performed by the following evaluation method.
A: The fusion rate is 80% or more, and the fusion rate of the molded product is extremely good.
A: The fusion rate is 50% or more and less than 80%, and the fusion rate of the molded product is good.
X: The fusion rate is less than 50%, and the fusion rate of the molded product is poor.

  As a result of this measurement, the fusion rate of the molded product in the foam molded container of Example 1 was 90%, and the evaluation was 評 価.

(4) Evaluation of oil leaching prevention property In the obtained foamed container (with an internal volume of 450 cm ³ ), the seasoning and curry containing curry powder, which are used for commercial instant noodles (curry taste), are used. No. 8 (volume 360 cm ³ ), wrap the entire container with a commercially available food wrap film, put this packaging container in an oven maintained at 60 ° C., and curry oil and fat content on the outer surface of the packaging container The oozing time was measured.
The oil leaching prevention property was evaluated by the following evaluation method.
A: After 48 hours, curry oil and fat did not bleed out, and the oil leaching prevention property was extremely good.
○: Cured oil and fat ooze out for 24 hours or more and less than 48 hours, and the oil oozing prevention property is good.
X: The curry oil and fat exudes in less than 24 hours, and the oil exudation preventing property is poor.

As a result of this measurement, the evaluation of the oil leaching prevention property in the foam-molded container of Example 1 was ◎.
These results are shown in Table 1.

[Example 2]
The same procedure as in Example 1 was performed except that the styrene monomer solution was continuously supplied in 2.0 hours. The results are shown in Table 1.

[Example 3]
The same procedure as in Example 1 was performed except that the styrene monomer solution was continuously supplied in 0.5 hours. The results are shown in Table 1.

[Example 4]
1720 g of polystyrene seed particles, 1.0 g of divinylbenzene, 1.3 g of benzoyl peroxide and 0.3 g of t-butylperoxybenzoate were dissolved in 280 g of styrene monomer to prepare a styrene solution. The procedure was the same as in Example 1 except that the supply was made in 5 hours. The results are shown in Table 1.

[Example 5]
A polystyrene solution was prepared by dissolving 1200 g of polystyrene seed particles, 2.8 g of divinylbenzene, 3.8 g of benzoyl peroxide and 0.8 g of t-butylperoxybenzoate in 800 g of styrene monomer. The procedure was the same as in Example 1 except that the supply was made in 0 hours. The results are shown in Table 1.

[Example 6]
A styrene solution was prepared by dissolving 1050 g of polystyrene seed particles, 3.3 g of divinylbenzene, 4.4 g of benzoyl peroxide and 0.95 g of t-butylperoxybenzoate in 950 g of styrene monomer. The procedure was the same as in Example 1 except that the supply was made in 0 hours. The results are shown in Table 1.

[Comparative Example 1]
The same procedure as in Example 1 was performed except that divinylbenzene was not used. The results are shown in Table 1.

[Comparative Example 2]
The same procedure as in Example 1 was performed except that the styrene solution was supplied in 4 hours. The results are shown in Table 1.

[Comparative Example 3]
1800 g of polystyrene seed particles, 0.7 g of divinylbenzene, 1.0 g of benzoyl peroxide and 0.2 g of t-butylperoxybenzoate were dissolved in 200 g of styrene monomer to prepare a styrene solution. The procedure was the same as in Example 1 except that the supply was performed in 5 hours. The results are shown in Table 1.

[Comparative Example 4]
A styrene solution was prepared by dissolving 1050 g of polystyrene seed particles, 3.3 g of divinylbenzene, 4.6 g of benzoyl peroxide and 1.0 g of t-butylperoxybenzoate in 950 g of styrene monomer. The procedure was the same as in Example 1 except that the supply was made in 0 hours. The results are shown in Table 1.

From the results in Table 1, the expandable polystyrene resin particles of Examples 1 to 6 according to the present invention and the foam molded container manufactured using the same have excellent molded product fusion rate and oil exudation prevention property. You can see that
On the other hand, the comparative example 1 which did not use a crosslinkable monomer was inferior in the oil exudation prevention property of the obtained foam-molded container.
Further, Comparative Examples 2 and 3 in which the surface layer thickness was less than the range of the surface layer thickness in the present invention were 1 μm, and the oil leaching prevention property of the foam molded container was also poor.
Furthermore, Comparative Example 4 in which the surface layer thickness was 110 μm, which was thicker than the range of the surface layer thickness in the present invention, was poor in both the molded product fusion rate and the oil leaching prevention property.

It is a schematic block diagram which shows the procedure of the surface layer thickness measurement of an expandable polystyrene-type resin particle. It is an enlarged view which shows the surface layer of the resin particle fixed to the PMMA solidified body.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1, 2 ... Resin particle, 3 ... PMMA solidified body, 4 ... Cut surface, 5 ... Surface layer, 6 ... PMMA phase outside particle | grains, 7 ... PMMA phase inside particle | grains.

Claims (5)

Expandable polystyrene for foam molding in which a surface layer formed by polymerizing a crosslinkable monomer and a styrene monomer is provided on the surface of polystyrene resin particles, and these are impregnated with a readily volatile foaming agent. Resin particles,
The surface layer thickness when the resin particles are saturatedly swollen in tetrahydrofuran is in the range of 3 to 100 μm, and the tetrahydrofuran-insoluble gel content is in the range of 10 to 40 % by mass with respect to the total amount of the resin particles. Expandable styrenic resin particles. After dispersing 100 parts by mass of seed particles made of styrene resin in an aqueous medium, 15 to 25 parts by mass of styrene monomer with respect to 100 parts by mass of the seed particles in this dispersion, and 0.03 to 0.03 After adding 1.0 part by mass of a crosslinkable monomer, the seed particles are absorbed and polymerized to obtain styrene resin particles, and then impregnated with a readily volatile foaming agent to obtain expandable styrene resin particles. A foaming method characterized in that the foaming styrene resin particles described in claim 1 are obtained by setting the ratio of the styrene resin in the growing particles during the polymerization in the range of 80 to 96 mass%. For producing conductive styrene resin particles. Pre-expanded particles obtained by pre-expanding the expandable polystyrene resin particles according to claim 1 . A foam-molded article obtained by foam-molding the pre-expanded particles according to claim 3 . 5. A food package comprising an oily food or a food containing edible oils and pigments and a container comprising the foamed molded product according to claim 4 .

Images