JP2007031642A - In-mold expanded polystyrene resin molding and packaged food - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an in-mold expanded molding having excellent surface smoothness and high capability of being beautifully printed and to provide a packaged food using the same. <P>SOLUTION: The polystyrene resin in-mold expanded molding is one prepared by effecting the in-mold expansion of expandable polystyrene resin particles, wherein the centerline surface roughness (as specified in JIS B0601-1994) on the surface of the molding is in the range of 0.1 to 1.5 μm, and at least part of the surface is a printed surface. The packaged food is prepared by stowing food into the polystyrene resin in-mold expanded molding and packaging the food in the molding. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a polystyrene resin in-mold foam molded product and a food packaging body.

  Expandable resin particles made of polystyrene resin are widely used for producing foamed molded articles. In order to produce an in-mold foam-molded product from expandable resin particles, first, expandable particles are heated and foamed to produce polystyrene-based resin foam particles (pre-expanded particles), and then the pre-expanded particles are expanded by a foam molding machine. A method is employed in which the particles are heated in a mold, and the pre-foamed particles are further foamed in the mold, and the foamed particles are fused together to form an in-mold foam molded product. Therefore, the expandable resin particles are preferably operated in accordance with the purpose in the pre-foaming step for producing the pre-foamed particles and the in-mold foam molding step for fusing the pre-foamed particles in the mold. It is necessary to produce an in-mold foam molded product.

  In-mold foam molded products manufactured from expandable resin particles are made by fusion of expanded resin particles as described above, but the gaps between the expanded particles are difficult to fill and do not fully fill the surface of the molded product. There remains a gap. This gap exists as a V-shaped groove having a round cross section, and extends irregularly in a zigzag manner to intersect and present a net shape. In addition, since the groove has such a size that the groove width and the depth of the groove cannot be ignored, the surface of the in-mold foam-molded product is not smooth and the appearance is deteriorated.

  In particular, when used in a coffee container or instant noodle container, the surface of the in-mold foam-molded product is printed. When printing, only the gaps between the particles remain without being printed, resulting in printing unevenness, and thus the printing effect is significantly reduced. Therefore, it has been strongly demanded to make the gaps between the expanded particles as inconspicuous as possible.

Attempts have been made to make the gap as inconspicuous as possible. For example, an attempt to include more foaming agent in the expandable resin particles can increase the expansion force of the pre-expanded particles, so that the width and depth of the groove formed in the gap can be reduced. However, in this method, a large amount of foaming agent remains in the in-mold foam-molded product. Therefore, even after the obtained in-mold foam-molded product is taken out of the mold, the in-mold foam-molded product has a large foaming power. Therefore, it is necessary to sufficiently cool the in-mold foam-molded product in the mold, which causes a disadvantage that it takes more time for the foam-molding process and the foam-molding process cannot be performed efficiently. . At the same time, even if the inside of the mold is sufficiently cooled, the obtained in-mold foam-molded product also has a disadvantage that the central part of the foamed particles rises and the unevenness becomes remarkable.
In addition, depending on the foaming agent used, the foaming resin may be excessively softened, and the resin film may be destroyed when the molding is heated, thereby reducing the expansion force of the pre-expanded particles in the mold. There was also a case.
Attempts have also been made to use aromatic compounds such as styrene, xylene, toluene, and ethylbenzene as foaming aids. However, such aromatics are used for applications such as coffee containers and instant noodles that contain food directly. The compound should be as small as possible, and it is not preferable to use it as a foaming aid.

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

Although the appearance of the in-mold foam-molded product obtained by using the foamable styrene polymer particles produced by the production method is certainly improved, the improvement effect is still unsatisfactory for printing unevenness. It was insufficient.
Japanese Patent No. 3474995

  The present invention has been made in view of the above circumstances, and an object thereof is to provide an in-mold foam-molded product having excellent surface smoothness and high printing beauty and a food package using the same.

  In order to achieve the above object, the present invention provides an in-mold foam molded product obtained by foaming polystyrene resin expanded particles in a mold, and the center line average roughness of the surface of the molded product (however, the center line average roughness is A polystyrene-based resin characterized in that the centerline average roughness defined in JIS B0601-1994 is in the range of 0.1 to 1.5 μm, and at least a part of the surface is a printing surface. Provide in-mold foam molded products.

  In the polystyrene-based in-mold molded product of the present invention, the center line average roughness of the molded product surface is preferably in the range of 0.1 to 1.0 μm.

  In the polystyrene-based in-mold molded product of the present invention, the gel fraction of the polystyrene-based resin is preferably in the range of 5 to 50% by mass.

  In the polystyrene-based in-mold foam molded product of the present invention, the polystyrene-based resin preferably contains 0.3 to 1.0% by mass of zinc stearate.

  In the polystyrene-based in-mold foam-molded product of the present invention, the molded product preferably has a cup shape.

  One or two or more aromatic compounds selected from the group consisting of a styrene monomer, ethylbenzene, toluene, n-propylbenzene, i-propylbenzene and xylene in the polystyrene resin internal foam molded product of the present invention It is preferable that the total amount of the organic compound consisting of is in the range of 0 to 500 ppm of the total amount of the foamed molded product in the polystyrene resin mold.

  The present invention also provides a food package characterized in that food is contained and packaged in a container made of the polystyrene-based in-mold foam molded product.

  The polystyrene resin-in-mold foam-molded product of the present invention has a center line average roughness of the molded product surface in the range of 0.1 to 1.5 μm, and the surface has a small gap between the particles, particularly a coffee container or When printing on the surface as an instant noodle container, it becomes difficult to cause a problem that only the gaps between the particles are not printed, and a molded product having a beautiful printing surface is obtained.

  The polystyrene resin-in-mold foam-molded product of the present invention is characterized in that the center line average roughness of the surface of the molded product is in the range of 0.1 to 1.5 μm, and at least a part of the surface is a printing surface. And

  The centerline average roughness of the surface was measured as follows. The center line average roughness was measured using a surface roughness meter Handy Surf E-35A manufactured by Tokyo Seimitsu Co., Ltd. This Handy Surf E-35A measures the cross-sectional curve of the sample surface, and from the result, automatically calculates based on the method specified in JIS B0601-1994 "Surface Roughness-Definition and Display", It has a function of outputting the center line average roughness. In all cases, the measurement conditions were such that the surface of the in-mold foam molded product was measured, the cut-off value was 0.8 mm, and the measurement length was 4 mm, which is five times the cut-off value.

  Here, the center line average roughness is preferably as small as possible, and is in the range of 0.1 to 1.5 μm, and more preferably 0.1 to 1.0 μm. When the center line average roughness exceeds 1.5 μm, the particle gap is conspicuous, and the smoothness and printing beauty of the molded product are not exhibited. In addition, it is impossible to achieve a center line average roughness of less than 0.1 μm in an in-mold foam molded product molded using foamable resin particles.

  The gel fraction of the polystyrene resin constituting the polystyrene resin-in-mold foam-molded product of the present invention is limited to the range of 5 to 50% by mass, and preferably in the range of 15 to 35% by mass. When the gel fraction is lower than 5% by mass, the oil resistance of the in-mold foam molded product obtained using the expandable polystyrene resin particles is lowered, and the liquid containing the oil, the pigment, the surfactant or the like is molded. There is a risk of oozing out through the inner foam molding. On the other hand, if the gel fraction is higher than 50% by mass, the foamability of the expandable polystyrene resin particles is lowered, and a long heating time is required at the time of in-mold foam molding of the expandable polystyrene resin particles. May fall.

In addition, the gel fraction of an expandable polystyrene-type resin particle says what was measured by the following summary.
That is, the expandable polystyrene resin particles are heated in an oven at 140 ° C. for 1 hour, the foaming agent in the expandable polystyrene resin particles is removed to prepare a measurement sample, and the mass W _{1 of the} measurement sample is calculated. taking measurement.
Next, after immersing the measurement sample in 100 g of toluene and refluxing at 140 ° C. for 20 hours, the sample is filtered using an 80-mesh wire mesh, and the wire mesh residue is supplied into a desiccator and supplied at 140 ° C. for 2 hours. After drying under reduced pressure at −60 cmHg over time, it was naturally cooled to room temperature with a desiccator, the mass W _{2 of the} dry residue was measured, and calculated from the following formula.
Gel fraction (mass%) = 100 × W ₂ / W ₁

  The polystyrene resin constituting the polystyrene resin mold in the present invention is not particularly limited. For example, styrene, α-methylstyrene, vinyltoluene, chlorostyrene, ethylstyrene, i-propylstyrene, dimethylstyrene. , Homopolymers of styrene monomers such as bromostyrene or copolymers thereof.

  The polystyrene resin is a copolymer of the styrene monomer as a main component and the styrene monomer and a vinyl monomer copolymerizable with the styrene monomer. Examples of such vinyl monomers include methyl (meth) acrylate, ethyl (meth) acrylate, butyl (meth) acrylate, alkyl (meth) acrylates such as cetyl (meth) acrylate, and (meth) acrylonitrile. Dimethyl maleate, dimethyl fumarate, diethyl fumarate, ethyl fumarate and the like.

  Next, the manufacturing method of the said polystyrene-type in-mold foam-molded article is demonstrated. First, a dispersion liquid in which polystyrene resin seed particles are dispersed in water is prepared. As a method for producing the polystyrene-based resin seed particles, a general-purpose method is used. For example, a vinyl monomer is added to the styrene-based monomer as necessary, and suspension polymerization is performed in water. Method for producing polystyrene resin seed particles, Method for producing polystyrene resin seed particles by supplying the polystyrene resin to an extruder, melt-kneading, extruding into a strand form from the extruder and cutting it at a predetermined length Etc. The weight average molecular weight of the polystyrene resin particles is preferably in the range of 150,000 to 400,000, and more preferably in the range of 250,000 to 350,000.

Then, a monomer solution containing a styrene monomer, a crosslinkable monomer and a polymerization initiator is continuously or intermittently supplied into a dispersion in which the polystyrene resin seed particles are dispersed in water. Then, the monomer is seed polymerized in the presence of a polymerization initiator, and a polystyrene resin outer layer is grown on the surface of the polystyrene resin seed particles to produce polystyrene resin particles.
At this time, it is desirable that the crosslinkable monomer is dissolved and added to a part or all of the styrene monomer. If the crosslinkable monomer and the styrene monomer are added separately, the cross-linked structure may be uneven.

  Here, the crosslinkable monomer is not particularly limited as long as the crosslinkable structure can be imparted to the expandable polystyrene resin particles. For example, alkylene such as divinylbenzene and polyethylene glycol dimethacrylate is used. Examples thereof include polyfunctional monomers such as glycol dimethacrylate, among which divinylbenzene is preferable. The polystyrene resin constituting the resin outer 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.

  And the addition amount of the said crosslinkable monomer has the desirable range of 0.1-1.0 mass% with respect to the mass of the styrene-type monomer to add. If it is less than 0.1% by mass, the cross-linked structure is insufficient, the resin film when in-mold molding is broken, and a molded product with a beautiful appearance is difficult to obtain. On the other hand, if it exceeds 1.0% by mass, it will be too cross-linked and the foaming ability will be impaired, making it difficult to obtain a molded product with a beautiful appearance.

  In addition, the polymerization initiator used when seed polymerization is performed by impregnating the styrene monomer into polystyrene resin seed particles is not particularly limited, and examples thereof include benzoyl peroxide, lauryl peroxide, and t-butyl. Peroxybenzoate, t-butyl peroxide, t-butyl peroxypivalate, t-butyl peroxyisopropyl carbonate, t-butyl peroxyacetate, 2,2-t-butylperoxybutane, t-butylperoxy- Examples include organic peroxides such as 3,3,5-trimethylhexanoate and di-t-butylperoxyhexahydroterephthalate, and azo compounds such as azobisisobutyronitrile and azobisdimethylvaleronitrile. These polymerization initiators may be used alone or in combination. However, a polymerization initiator having a decomposition temperature of 50 ° C. or higher and less than 80 ° C. for obtaining a half-life of 10 hours, It is preferable to use a polymerization initiator having a decomposition temperature of 80 ° C. or higher and 120 ° C. or lower in order to obtain a half-life. In addition, as an addition amount of a polymerization initiator, the range of 0.01-3 mass parts is preferable with respect to 100 mass parts of styrene-type monomers.

  In order to improve the dispersion stability of the polystyrene-based resin seed particles and the growing polystyrene-based resin growing particles using these as seed particles, a suspension stabilizer and a stabilizing aid are added to the dispersion. Also good.

  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 hardly 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.

  Next, the polystyrene resin particles obtained by the seed polymerization are impregnated with a foaming agent to produce expandable polystyrene resin particles.

  As the 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- Examples thereof include CFC-based blowing agents such as difluoroethane (HFC-152a), and among these, aliphatic hydrocarbons are preferable. In addition, a foaming agent may be used independently and may use 2 or more types together.

  In addition, general-purpose additives such as bubble regulators such as thiodipropionic acid esters, thiodibutyric acid esters, ethylenebisstearic acid amides, ultraviolet absorbers, extenders, and colorants are added to the expandable polystyrene resin particles. May be.

  The obtained expandable polystyrene resin particles are coated with 0.3 to 1.0% by mass of zinc stearate. By coating with zinc stearate, it is possible to improve the sliding property between the pre-expanded particles and the molding die at the time of in-mold molding, thereby obtaining a molded article having a more beautiful appearance. When the coating amount of zinc stearate is less than 0.3% by mass, it is difficult to obtain the effect of improving the appearance beauty. Moreover, even if it uses more than 1.0 mass%, an effect will not appear any more and it is unpreferable from the point that an excessive zinc stearate will fall off during the process of foam molding, and a production line will be dirty. .

  Moreover, as a mixer used for the coating of zinc stearate, a V-type mixer, a double conical mixer, a conical screw mixer, a high-speed fluidized mixer, or the like is used.

The expandable polystyrene resin particles thus obtained are pre-expanded with a pre-foaming machine to form polystyrene-based resin foam particles (pre-foamed particles). After being filled in, it is foamed by a heating medium such as heating steam, and is heat-fused and integrated with each other by a foaming pressure to obtain an in-mold foam molded product having a desired shape. The bulk density of the pre-expanded particles is preferably in the range of 0.015 to 0.20 g / cm ³ , but is not limited thereto.

  The in-mold foam-molded product may be in various forms, but in-mold foam-molded containers such as cups, bowls, trays, boxes and the like effectively exhibit the functions and effects of the present invention. This is preferable.

  In the polystyrene-based in-mold foam molded product of the present invention, at least a part of the surface is a printing surface. The method for printing on the surface of the in-mold foam-molded product is not particularly limited, and includes various types such as letterpress printing, planographic printing, offset printing, dry offset printing, intaglio printing, gravure printing, screen printing, ink jet printing, and stamp printing. The printing method can be used, and among these, relief printing and dry offset printing are particularly preferable. The ink used for this printing is not particularly limited, and can be appropriately selected from commercially available various inks conventionally used for printing on polystyrene-based resin-molded foam-molded containers such as instant noodles.

  The polystyrene resin-in-mold foam-molded product of the present invention has a center line average roughness of the molded product surface in the range of 0.1 to 1.5 μm, and the surface has a small gap between the particles, particularly a coffee container or When printing as an instant noodle container, it becomes difficult to cause a problem that only the gaps between the particles are not printed, and a molded product having a beautiful printing surface is obtained.

  The food package of the present invention is such that food is contained and packaged in an in-mold foam-molded container made of the above-mentioned polystyrene resin in-mold foam-molded product. The food contained in the in-mold foam-molded container is not particularly limited. For example, vegetable oil such as soybean oil, rapeseed oil, perilla oil, olive oil, sesame oil, safflower oil, corn oil, lard (tallow) and head (beef tallow) ) Animal fats, instant noodles (including oysters) containing them, stew, mayonnaise, dressing sauce, curry roux, butter, margarine, white sauce, yogurt, ice cream, donut, hamburger, fried chicken, etc. Foods, fat foods, aqueous solutions containing surfactants, and the like can be accommodated. 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 in-mold foam molded product. For example, when using in-mold foam-molded containers such as cups, bowls, trays, etc., fill the container with food, seal the lid with a lid and seal it as necessary. Can be packaged with a synthetic resin film or the like.

Hereinafter, although an Example demonstrates further in detail, this invention is not limited by these.
Moreover, the total content of the organic compounds of the polystyrene-based in-mold molded articles in Examples and Comparative Examples was measured as follows.

<Amount of organic compound>
After precisely weighing 1.0 g of a polystyrene resin in-mold foam-molded product, 1 mL of a dimethylformamide solution containing 0.1% by volume of cyclopentanol was added as a standard solution to the accurately weighed in-mold foam-molded product, Further, dimethylformamide was added to make 25 mL, and this solution was allowed to stand for 24 hours to prepare a measurement solution. The insoluble matter is removed from this measurement solution, 1.8 mL is supplied to a 230 ° C. sample vaporization chamber to obtain the organic compound to be measured from the gas chromatograph, and the calibration of the organic compound to be measured has been measured in advance. Based on the line, the amount of organic compound is calculated from the chart. The target organic compounds are styrene monomers, ethylbenzene, toluene, n-propylbenzene, i-propylbenzene, and xylene. These totals should be as small as possible, especially for in-mold foam molded products for packaging foods, preferably 500 ppm or less, and more preferably 400 ppm or less.

The content of the organic compound in the polystyrene-based resin-molded foam-molded product can be measured using a gas chromatograph (trade name “GC-14A” manufactured by Shimadzu Corporation) under the following measurement conditions.
Detector: FID
Column: GL Sciences Inc. (3mm diameter x 2.5m)
Liquid phase: PEG-20M PT 25% by mass
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 In Table 1, “organic compound amount” is shown.

[Example 1]
In a stainless steel 5 L autoclave equipped with a stirrer, 1.5 L of ion-exchanged water, 1.5 kg of polystyrene seed particles having an average particle diameter of 0.3 mm and a weight average molecular weight of 280,000, and 20 g of magnesium pyrophosphate 1 g of sodium dodecylbenzenesulfonate was supplied and stirred at 300 revolutions per minute to prepare a dispersion.

  On the other hand, after dissolving 0.2 g of sodium dodecylbenzenesulfonate in 500 g of ion-exchanged water, 2.0 g of divinylbenzene as a crosslinkable monomer and benzoyl peroxide (with a 10-hour half-life of 74 ° C.) A solution prepared by dissolving 0 g and 1.0 g of t-butyl peroxybenzoate (10 hour half-life of 104 ° C.) in 500 g of styrene monomer was added to agitation and emulsion to prepare a styrene emulsion.

  The dispersion was kept at 85 ° C., and the inside of the reactor was replaced with nitrogen gas, and then the styrene emulsion was continuously supplied into the dispersion in 2 hours. Then, after hold | maintaining at 85 degreeC for further 1 hour, it heated up to 125 degreeC and hold | maintained for 1 hour, and superposition | polymerization was completed.

  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.

  Thereafter, 5 g of zinc stearate (average pulverized product length: 20 μm) was stirred for 2 minutes in a high-speed fluidized mixer to 1.0 kg of the expandable polystyrene resin particles produced as described above. Next, 1 g of polyethylene glycol was supplied, stirred for another 2 minutes, and coated with zinc stearate. Thereafter, it was stored in a cool and dark place for 3 days.

Thereafter, the expandable polystyrene resin particles were supplied to a pre-foaming machine and pre-expanded to a bulk density of 0.1 g / cm ³ using water vapor to obtain polystyrene-based resin expanded particles (pre-expanded 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 with 0.2 MPa of water vapor for 6 seconds so that the internal volume is 450 cm ³ . A cup-shaped in-mold foam-molded container having a wall thickness of 2 mm was obtained. Note that the cup-shaped in-mold foam-molded container has a shape formed by projecting a peripheral wall portion having a fixed height obliquely upward from the outer peripheral edge of the bottom surface portion having a flat circular shape.
The centerline average roughness, gel fraction, and amount of organic compound of this in-mold foam-molded container were measured, and the results are shown in Table 1.

Next, the cup-shaped in-mold foam-molded container obtained was coated and printed on the surface of the molded product with 6 cups of FLASH DRY FDC medium, which is an ink manufactured by Toyo Ink Co., Ltd., using CUP PRINTER KH-6100 manufactured by Hubei Seiko Co., Ltd. A printed cup-shaped in-mold foam-molded container was obtained by forming a coating film by ultraviolet drying with an eye ultraviolet curing power supply device manufactured by Eye Graphics.
The aesthetics of printing were determined as follows by visually observing the unprinted portions of the gaps between the foam particles.
Particles are inconspicuous ... ◎
Particles are hardly noticeable ... ○
Somewhat noticeable between particles ... △
Conspicuous between particles ... ×

[Example 2]
In a 5 L stainless steel autoclave equipped with a stirrer, 1.1 L of ion-exchange water, 1.1 kg of polystyrene seed particles having an average particle diameter of 0.3 mm and a weight average molecular weight of 280,000, and 20 g of magnesium pyrophosphate 1 g of sodium dodecylbenzenesulfonate was supplied and stirred at 300 revolutions per minute to prepare a dispersion.

  On the other hand, after dissolving 0.2 g of sodium dodecylbenzenesulfonate in 900 g of ion-exchanged water, 3.6 g of divinylbenzene, 3.6 g of benzoyl peroxide and t-butylperoxybenzoate 1 as a crosslinkable monomer are used. A solution prepared by dissolving 0.0 g in 900 g of styrene monomer was added, and the mixture was stirred and emulsified to prepare a styrene emulsion.

  The dispersion was kept at 85 ° C. and the inside of the reactor was replaced with nitrogen gas, and then the styrene emulsion was continuously supplied into the dispersion in 3 hours. Then, after hold | maintaining at 85 degreeC for further 1 hour, it heated up to 125 degreeC and hold | maintained for 1 hour, and superposition | polymerization was completed.

  Subsequent procedures were performed in the same manner as in Example 1. The centerline average roughness, gel fraction, and amount of organic compound of the obtained in-mold foam-molded container were measured, and the printing beauty was evaluated after printing. The results are shown in Table 1.

[Example 3]
In a 5 L stainless steel autoclave equipped with a stirrer, 1.65 L of ion-exchanged water, 1.65 kg of polystyrene seed particles having an average particle diameter of 0.3 mm and a weight average molecular weight of 280,000, and 20 g of magnesium pyrophosphate 1 g of sodium dodecylbenzenesulfonate was supplied and stirred at 300 revolutions per minute to prepare a dispersion.

  On the other hand, after dissolving 0.2 g of sodium dodecylbenzenesulfonate in 350 g of ion-exchanged water, 1.8 g of divinylbenzene, 1.4 g of benzoyl peroxide and t-butylperoxybenzoate 1 are used as a crosslinkable monomer. 0.0 g dissolved in 350 g of styrene monomer was added, and the mixture was stirred and emulsified to prepare a styrene emulsion.

  The dispersion was kept at 85 ° C., and the inside of the reactor was replaced with nitrogen gas, and then the styrene emulsion was continuously fed into the dispersion in 1 hour. Then, after hold | maintaining at 85 degreeC for further 1 hour, it heated up to 125 degreeC and hold | maintained for 1 hour, and superposition | polymerization was completed.

  Subsequent procedures were performed in the same manner as in Example 1. The centerline average roughness, gel fraction, and amount of organic compound of the obtained in-mold foam-molded container were measured, and the printing beauty was evaluated after printing. The results are shown in Table 1.

[Example 4]
In a stainless steel 5 L autoclave equipped with a stirrer, 1.75 L of ion-exchanged water, 1.75 kg of polystyrene seed particles having an average particle diameter of 0.3 mm and a weight average molecular weight of 280,000, and 20 g of magnesium pyrophosphate 1 g of sodium dodecylbenzenesulfonate was supplied and stirred at 300 revolutions per minute to prepare a dispersion.

  On the other hand, 0.2 g of sodium dodecylbenzenesulfonate was dissolved in 250 g of ion-exchanged water, and then 2.5 g of divinylbenzene, 1.0 g of benzoyl peroxide and t-butylperoxybenzoate 1 were used as a crosslinkable monomer. A solution prepared by dissolving 0.0 g in 250 g of styrene monomer was added and stirred to make an emulsion, thereby preparing a styrene emulsion.

  The dispersion was kept at 85 ° C., and the inside of the reactor was replaced with nitrogen gas, and then the styrene emulsion was continuously fed into the dispersion in 1 hour. Then, after hold | maintaining at 85 degreeC for further 1 hour, it heated up to 125 degreeC and hold | maintained for 1 hour, and superposition | polymerization was completed.

  Subsequent procedures were performed in the same manner as in Example 1. The centerline average roughness, gel fraction, and amount of organic compound of the obtained in-mold foam-molded container were measured, and the printing beauty was evaluated after printing. The results are shown in Table 1.

[Example 5]
The same procedure as in Example 1 was performed except that 8 g of zinc stearate was changed. The gel fraction, centerline average roughness, and amount of organic compound of the obtained molded product were measured, and the results are shown in Table 1.

[Comparative Example 1]
The procedure was the same as in Example 1 except that divinylbenzene was not used and that 8 g of zinc stearate was used. The centerline average roughness, gel fraction, and amount of organic compound of the obtained in-mold foam-molded container were measured, and the printing beauty was evaluated after printing. The results are shown in Table 1.

[Comparative Example 2]
The same procedure as in Example 1 was performed except that the amount of divinylbenzene used was 0.2 g and that zinc stearate was 8 g. The gel fraction, centerline average roughness, and amount of organic compound of the obtained molded product were measured, and the results are shown in Table 1.

[Comparative Example 3]
The same procedure as in Example 1 was performed except that 2 g of zinc stearate was changed. The centerline average roughness, gel fraction, and amount of organic compound of the obtained in-mold foam-molded container were measured, and the printing beauty was evaluated after printing. The results are shown in Table 1.

[Comparative Example 4]
The same procedure as in Example 2 was performed except that the amount of divinylbenzene used was 13.5 g. The centerline average roughness, gel fraction, and amount of organic compound of the obtained in-mold foam-molded container were measured, and the printing beauty was evaluated after printing. The results are shown in Table 1.

[Comparative Example 5]
In a 5 L stainless steel autoclave equipped with a stirrer, 0.9 L of ion-exchanged water, 0.9 kg of polystyrene seed particles having an average particle diameter of 0.3 mm and a weight average molecular weight of 280,000, and 20 g of magnesium pyrophosphate 1 g of sodium dodecylbenzenesulfonate was supplied and stirred at 300 revolutions per minute to prepare a dispersion.

  On the other hand, after dissolving 0.2 g of sodium dodecylbenzenesulfonate in 1100 g of ion-exchanged water, 2.8 g of divinylbenzene, 4.4 g of benzoyl peroxide and t-butylperoxybenzoate 1 are used as a crosslinkable monomer. A solution prepared by dissolving 0.0 g in 250 g of styrene monomer was added and stirred to make an emulsion, thereby preparing a styrene emulsion.

  The dispersion was kept at 85 ° C., and the inside of the reactor was replaced with nitrogen gas, and then the styrene emulsion was continuously fed into the dispersion in 1 hour. Then, after hold | maintaining at 85 degreeC for further 1 hour, it heated up to 125 degreeC and hold | maintained for 1 hour, and superposition | polymerization was completed.

  Subsequent procedures were performed in the same manner as in Example 1. The centerline average roughness, gel fraction, and amount of organic compound of the obtained in-mold foam-molded container were measured, and the printing beauty was evaluated after printing. The results are shown in Table 1.

[Comparative Example 6]
The procedure was the same as in Example 2 except that the amount of divinylbenzene used was 0.36 g. The centerline average roughness, gel fraction, and amount of organic compound of the obtained in-mold foam-molded container were measured, and the printing beauty was evaluated after printing. The results are shown in Table 1.

[Comparative Example 7]
In a 5 L stainless steel autoclave equipped with a stirrer, 1.85 L of ion-exchanged water, 1.85 kg of polystyrene seed particles having an average particle diameter of 0.3 mm and a weight average molecular weight of 280,000, and 20 g of magnesium pyrophosphate 1 g of sodium dodecylbenzenesulfonate was supplied and stirred at 300 revolutions per minute to prepare a dispersion.

  On the other hand, after dissolving 0.2 g of sodium dodecylbenzenesulfonate in 150 g of ion exchange water, 1.2 g of divinylbenzene, 0.6 g of benzoyl peroxide and t-butylperoxybenzoate 1 A solution prepared by dissolving 0.0 g in 150 g of styrene monomer was added and stirred to make an emulsion to prepare a styrene emulsion.

  The dispersion was kept at 85 ° C., and the inside of the reactor was replaced with nitrogen gas, and then the styrene emulsion was continuously fed into the dispersion in 1 hour. Then, after hold | maintaining at 85 degreeC for further 1 hour, it heated up to 125 degreeC and hold | maintained for 1 hour, and superposition | polymerization was completed.

  Subsequent procedures were performed in the same manner as in Example 1. The centerline average roughness, gel fraction, and amount of organic compound of the obtained in-mold foam-molded container were measured, and the printing beauty was evaluated after printing. The results are shown in Table 1.

  From the results of Table 1, the in-mold foam-molded containers of Examples 1 to 5 according to the present invention had a surface centerline average roughness of 1.5 μm or less, and had good printing beauty.

On the other hand, the in-mold foam-molded containers of Comparative Examples 1 to 7 had a surface centerline average roughness of more than 1.5 μm and were inferior in printing beauty, and Comparative Example 4 could not be molded.

Claims (7)

  An in-mold foam-molded product obtained by foaming polystyrene resin foam particles in a mold, wherein the center line average roughness of the surface of the molded product (however, the center line average roughness is a center line average defined in JIS B0601-1994) The polystyrene-based in-mold foam-molded product, wherein the roughness is in the range of 0.1 to 1.5 μm, and at least a part of the surface is a printing surface.   The polystyrene-based in-mold foam-molded product according to claim 1, wherein the center line average roughness of the surface of the molded product is in the range of 0.1 to 1.0 µm.   The polystyrene resin in-mold foam-molded product according to claim 1 or 2, wherein the gel fraction of the polystyrene resin is in the range of 5 to 50 mass%.   The polystyrene resin in-mold foam-molded product according to any one of claims 1 to 3, wherein the polystyrene resin contains 0.3 to 1.0 mass% of zinc stearate.   5. The polystyrene-based in-mold foam-molded product according to any one of claims 1 to 4, which has a cup shape.   The total amount of the organic compound consisting of one or two or more aromatic compounds selected from the group consisting of styrene monomer, ethylbenzene, toluene, n-propylbenzene, i-propylbenzene and xylene is foamed in the polystyrene resin mold. The polystyrene-based in-mold foam-molded product according to any one of claims 1 to 5, wherein the total amount of the molded product is in the range of 0 to 500 ppm. A food package comprising a container made of the polystyrene-based in-mold foam-molded product according to any one of claims 1 to 6, wherein food is contained and packaged.