JP4990585B2 - Polystyrene resin foam sheet - Google Patents

Description

  The present invention relates to a polystyrene-based resin foam sheet and a polystyrene-based resin laminated foam sheet excellent in heat secondary moldability. More specifically, the present invention relates to a polystyrene-based resin foam sheet and a polystyrene-based resin laminated foam sheet excellent in secondary moldability that can provide a good deep-drawn molded container excellent in light weight and heat insulation.

  Polystyrene resin foam sheets are used in various food containers because of their light weight, heat insulation, and moldability. In addition, containers such as instant noodles are molded into various shapes using their moldability.

  Especially for containers such as instant noodles, a polystyrene resin laminated foam sheet made by laminating a non-foamed layer made of thermoplastic resin on the surface of a polystyrene resin foam sheet is lightweight, highly heat-insulating, and excellent in moldability. It is used more than it is. In addition, from the viewpoint of design properties, many are used which are printed on the outside of the molded container.

  In these food containers, there is a strong demand for price reduction from consumers. In response to this requirement, container molding manufacturers are taking measures such as increasing the number of containers per sheet area and reducing the weight per container.

  However, increasing the number of containers per sheet area or reducing the weight of the sheet to reduce the weight of the container leads to a marked increase in the difficulty of molding. As a result, there may occur problems such as occurrence of minute cracks on the surface of the foamed layer called “inner cracks” at the time of molding, or occurrence of locally reduced strength on the side walls of the resulting molded container. .

  Although the overall strength of the container is satisfactory at the part where the strength of the molded container side wall is reduced, when printing is performed on the outside of the container side wall, the part where the strength is locally reduced with respect to the pressure during printing is indented. As a result, problems such as missing prints may occur.

  On the other hand, in recent years, the demand for deep-drawn molded containers has been increasing from the viewpoint of designability and increase in contents. In forming such a deep-drawn container, the degree of difficulty in forming becomes higher, it is difficult to ensure the strength of the resulting container, and the above-mentioned problems tend to appear remarkably.

  In response to these problems, a method of obtaining a deep-drawn molded container that does not reduce the strength is disclosed. For example, a method for adjusting the density and tensile breaking elongation of the surface layer portion of the foamed sheet has been proposed (Patent Document 1). In this method, although the strength of the container can be secured, there may be a case where a portion where the strength is locally reduced is observed on the side wall of the container as described above.

  On the other hand, in food containers made of polystyrene resin, styrene dimer and styrene trimer contained in the base resin have been suspected as exogenous endocrine disrupting substances. When a food containing oil such as hot tempura udon was put in a molded container of a polystyrene-based resin foam sheet, it was recognized that styrene dimer and styrene trimer were eluted into the food, which became a social problem. However, although these substances have been removed from the list of endocrine disrupting substances of the Environment Agency, there is a strong demand for reduction of these substances from a social point of view, and the styrene dimer and styrene trimer contained in the resin are strongly desired. Attempts have been made to reduce it.

Among them, the polystyrene resin foam sheet in which styrene dimer and styrene trimer are reduced has a problem that elongation at the time of molding deteriorates. In order to improve the moldability, a measure for improving the moldability has been proposed by the molecular weight distribution of the polystyrene-based resin and the presence of fine cells in the foamed sheet (Patent Document 2). Even in the polystyrene-based resin foam sheet with improved moldability in Patent Document 2, although the elongation is improved, there may be a portion where the local strength is weak as described above.
JP 2006-130881 JP 2000-355083 A

  An object of this invention is to provide the polystyrene-type resin foam sheet and polystyrene-type resin laminated foam sheet excellent in deep drawing moldability.

  When the inventors of the present invention have improved the elongation in the secondary molding of the polystyrene-based resin foam sheet, local elongation occurs on the side wall of the container having the largest elongation during the secondary molding, and as a result, the local strength is increased. It was found that the lowered portion is likely to occur. In addition, an internal crack may occur due to poor elongation during secondary molding of a polystyrene resin foam sheet having poor elongation.

  As a result of intensive research focusing on the above points, the present inventors have adjusted the viscosity at the time of melting of the base resin of the molded container, that is, the base resin of the polystyrene resin foam sheet used for molding, and stretched. By balancing the above, it has been found that a portion where the strength is locally lowered on the side wall of the container can be prevented, and no internal cracking has occurred, and the present invention has been completed.

That is, the present invention
A foamed sheet made of a polystyrene resin, having a thickness of 1.3 to 2.5 mm, a basis weight of 150 to 400 g / m ² , an expansion ratio of 5 to 15 times, and 100 parts by weight of the polystyrene resin In addition, by adding 0.002 to 0.1 part by weight of a polymerization initiator and melt-kneading, the shear rate at 190 ° C. of the base resin is 6080 S ⁻¹ and the melt viscosity η _H (poise) is 122 S ⁻¹ . The polystyrene-based resin foam sheet (Claim 1), wherein the melt viscosity η _L (poise) of the resin is adjusted so as to satisfy the following conditional expressions (1) and (2):

(However, eta _H is a melt viscosity at a shear rate of 6080S ^-1 at 190 ° C. (poise), the melt viscosity at a shear rate of 122S ^-1 in eta _L is 190 ℃ (poise).)
The polystyrene-based resin foamed sheet according to claim 1, wherein a non-foamed layer is formed on at least one side of the polystyrene-based resin foamed sheet (claim 2), and styrene contained in the polystyrene-based resin foamed sheet. The polystyrene-based resin foamed sheet according to claim 1 or the polystyrene-based resin laminated foamed sheet according to claim 2, wherein the content of dimer and styrene trimer is 1600 ppm or less (claim 3).
About.

  By secondary molding of the polystyrene resin foam sheet or polystyrene resin laminated foam sheet according to the present invention, it is possible to obtain a good molded container free from defects such as internal cracks and without locally reduced strength. .

  In the present invention, the polystyrene resin means a styrene monomer alone or a copolymer resin, a copolymer resin of a styrene monomer and various vinyl monomers or divinyl monomers, an olefin homopolymer resin and a copolymer resin thereof, and styrene-butadiene. Examples thereof include graft polymerization resins of styrene monomers onto copolymer resins and the like, and mixed resins of these polymerization resins.

  As a production method for obtaining a polystyrene resin having a small content of styrene dimer and styrene trimer of 1600 ppm or less, the polystyrene resin produced by a general polymerization method is passed through an extruder equipped with a vacuum vent, and the styrene dimer and styrene trimer are obtained. The method of evaporating and removing by vacuum, the method of producing by suspension polymerization, and the like.

  In addition, the resin may be decomposed during the formation of the foam sheet to generate styrene dimers and styrene trimers. In such a case, the content of styrene dimer and styrene trimer in the obtained foamed sheet can be adjusted to 1600 ppm or less by adding, for example, a phenolic antioxidant or stabilizer.

  Here, content of a styrene dimer and a styrene trimer can be measured as follows. A polystyrene resin foam sheet 0.5 g is dissolved in chloroform 25 ml. By measuring the solution with GC / MC (manufactured by Agilent Technologies, GC-6890plus), the content of styrene dimer and styrene trimer in the polystyrene resin foam sheet base resin can be obtained.

  In the present invention, plasticizers such as liquid paraffin and fatty acid glyceride and lubricants such as fatty acid metal salts and amides may be added to the polystyrene resin in order to improve moldability and brittleness.

  The polystyrene resin foam sheet in the present invention can be obtained by extrusion foaming a polystyrene resin.

  The process for producing a foam sheet by extrusion foaming can be performed by a widely used method. For example, a resin composition in which a nucleating agent or the like is mixed with a polystyrene resin is melt-mixed using an extruder, a foaming agent is press-fitted, and the molten resin is further adjusted to a temperature suitable for foaming. The cylindrical shape is placed so as to be positioned inside the cylindrical foam so as to be extruded from a circular die having an annular slit to a low pressure region to obtain a cylindrical foam and then cooled from the inner surface side of the cylindrical foam. A method is known in which a foamed sheet can be obtained by stretching and cooling molding in a cooling cylinder and then cutting it open.

  Examples of the foaming agent used in the present invention include physical foaming agents such as propane, butane, and pentane, and chemical foaming agents such as sodium bicarbonate-citric acid. Also, industrially, physical foaming agents are preferably used from the viewpoint of availability and cost, and among them, butane is frequently used from the viewpoint of retention of foaming agents. Among them, from the viewpoint of securing the thermoformability of the sheet and the product life (period during which secondary molding can be performed after production), mixed butane composed of 70 to 100% by weight of isobutane and 0 to 30% by weight of normal butane is used. It is preferable.

  As the nucleating agent used in the present invention, porous inorganic powders such as calcium carbonate, barium sulfate, silica, titanium oxide, clay, aluminum oxide, bentonite, diatomaceous earth, talc and the like can be used. Further, if necessary, in order to improve the dispersion of the nucleating agent in the resin, a fatty acid metal salt such as ethylene bisstearylamide and magnesium stearate, a lubricant such as a fatty acid ester, and the like may be added.

  The number of cells of the polystyrene-based resin foam sheet in the present invention is preferably 10 or more and less than 25 in the thickness direction of the sheet. When the number of cells is 10 or less, the heat insulation may be inferior, and when 25 or more, the container strength may be inferior. The number of cells can be adjusted by the amount of nucleating agent added.

  The expansion ratio of the polystyrene resin foam sheet in the present invention is preferably 5 times or more and less than 15 times. When the foaming ratio is less than 5 times, the thickness is thin and inferior in container strength obtained by secondary molding. When the foaming ratio is 15 times or more, the thickness is so thick that heating takes time during secondary molding and the productivity is inferior. There is.

  In the polystyrene-based resin foam sheet of the present invention, the magnification and thickness increase by heating during secondary molding.

Basis weight of the polystyrene-based resin foam sheet of the present invention is preferably less than 150 g / ^{m 2} or more 400 g / ^{m 2,} less than 200 g / ^{m 2} or more 350 g / ^{m 2} is more preferable. When the basis weight of the polystyrene-based resin foam sheet is less than 150 g / m ² , a container satisfying the container strength may not be obtained. In addition, an increase in the basis weight of the polystyrene-based resin foam sheet leads to an improvement in the strength of the container, but increases the cost. Therefore, it is preferable to set it to less than 400 g / m ² .

  The amount of the remaining foaming agent of the polystyrene-based resin foam sheet in the present invention is mainly determined by the amount of the foaming agent injected during the production by extrusion foaming of the polystyrene-based resin and the resin temperature of the polystyrene-based resin at the time of foaming. The greater the amount of residual foaming agent (gas) in the polystyrene resin foam sheet, the higher the gas pressure in the cell of the polystyrene resin foam sheet and the better the container strength. In order to obtain a sufficiently strong container, the amount of residual foaming agent is preferably 1.5 to 3.2% by weight, and more preferably 2.0 to 3.0% by weight. If the residual foaming agent amount is less than 1.5% by weight, the container strength of the resulting container tends to decrease. In addition, when the amount of the remaining foaming agent exceeds 3.2% by weight, the foaming agent gas is dissipated from the polystyrene-based resin foam sheet during lamination with the polystyrene-based resin non-foamed film, and voids are generated at the lamination interface between the two. When the molding is heated, the interface between the non-foamed polystyrene resin film and the foamed polystyrene resin sheet is peeled off, causing a so-called blistering phenomenon, and the container appearance tends to be greatly impaired.

The closed cell ratio of the polystyrene resin foam sheet in the present invention is preferably 85% or more, and 90% in order to suppress the dissipation of the foaming agent gas in the polystyrene resin laminated foam sheet and maintain the strength properties over a long period of time. The above is more preferable. When the closed cell ratio is less than 85%, the remaining foaming agent in the foam sheet is quickly dissipated, the pressure inside the bubbles cannot be maintained, the strength is greatly reduced, and the secondary foaming force due to heating during molding is also reduced. Since it falls, there exists a tendency for favorable shaping | molding to become impossible.
The closed cell ratio of the polystyrene resin foam sheet can be measured using an Air Comparison Pycnometer (for example, model 1930, manufactured by BECKMAN).

  The melt viscosity of the base resin of the polystyrene resin foam sheet according to the present invention satisfies the following two conditional expressions.

(However, eta _H is a melt viscosity at a shear rate of 6080S ^-1 at 190 ° C. (poise), the melt viscosity at a shear rate of 122S ^-1 in eta _L is 190 ℃ (poise).)
If Conditional Expression (1) is not satisfied, internal cracks tend to occur inside the container obtained by secondary molding. If Conditional Expression (2) is not satisfied, partial strength reduction is caused on the side of the container. May occur.

  In addition, the melt viscosity of the base resin of the polystyrene resin foam sheet in the present invention can be measured using a capillograph (manufactured by Toyo Seiki Co., Ltd., capillograph).

That is, a capillograph cylinder having an inner diameter of 9.6 mm and a length of 350 mm, to which an orifice having a hole diameter of 0.1 cm, a length of 1.0 cm and an inflow angle of 45 degrees is attached at the tip is heated at 180 ° C. Fill with 20 g and preheat for 5 minutes. After preheating, the molten polystyrene resin is extruded at a speed of 10 mm / min using a piston having the same diameter as the cylinder. Next, extrusion is performed at a speed of 500 mm / min. In that case, the load concerning the piston in the speed of each piston can be detected from the load cell connected with the piston.
Here, the shear rate of the molten polystyrene resin passing through the orifice when the piston speed is 10 mm / min is 122 S ⁻¹ , and the shear rate of the molten polystyrene resin passing through the orifice when the piston speed is 500 mm / min is 6080 S. ^-1 .

The melt viscosity at each piston speed can be obtained by calculating from the obtained load using the following calculation formula (3). That is, the load applied to the obtained piston is F (kg), the piston speed as a measurement condition is V (mm / min), the inner radius of the cylinder is R, the length of the orifice is L (mm), the hole of the orifice When the radius is r (mm), the melt viscosities η _H and η _L are calculated by the calculation formula (3).

As a method of adjusting the melt viscosity of the base resin of the polystyrene type resin foamed sheet of the present invention, in producing a polystyrene resin at a polymerization, to be within the scope of formula, polymerization Po polystyrene resin how to melt kneading by adding initiator. From the adjustment can be easily performed in terms of melt viscosity during extrusion of the port polystyrene-based resin foam sheet, a method of adding a heavy initiator is needed use.

In the method of mixing the polymerization initiator, representative examples of the polymerization initiator used include, for example, benzoyl peroxide, lauroyl peroxide, t-butyl perbenzoate, t-butyl perpivalate, and t-butyl peroxide. Oxyisopropyl carbonate, t-butyl peroxyacetate, 2,2-di-t-butylperoxybutane, t-butylperoxy-3,3,5-trimethylcyclohexanoate, di-t-butylperoxyhexahydro Examples thereof include organic oxides such as terephthalate and 1,1-di-t-butylperoxy-3,3,5-trimethylcyclohexane, and azo compounds such as azobisisobutyronitrile and azobisdimethylvaleronitrile. The addition amount of the polymerization initiator is limited to 0.002 to 0.1 parts by weight with respect to 100 parts by weight of the polystyrene resin. If it is 0.002 parts by weight or less, the effect of the melt viscosity due to the addition thereof is difficult to be exhibited, and if it is 0.1 parts by weight or more, the melt viscosity is greatly lowered and may be out of the range of the formula (2).

  In this invention, the required intensity | strength of the container obtained by secondary shaping | molding is securable by laminating | stacking a styrene resin non-foaming film on at least one surface of the polystyrene resin foam sheet surface.

  In the present invention, as the resin of the styrene resin non-foamed film laminated on the surface of the polystyrene resin foam sheet, those exemplified as the styrene resin used in the styrene resin foam sheet can be used. The same kind of resin as the foamed sheet or a different kind of resin may be used. Among them, styrene resin film containing a rubber component made of copolymer resin with styrene monomer and diene monomer, especially film made from high impact polystyrene resin, has the adhesiveness to foamed sheet and the impact resistance of the film. From the viewpoint of

  As a method for laminating the polystyrene resin non-foamed film on the surface of the polystyrene resin foam sheet, a known dry laminating method, extrusion laminating method, co-extrusion method or the like can be used and is not particularly limited. However, the extrusion laminating method, that is, the method of extruding and laminating a thermoplastic resin in a molten state on the surface of the polystyrene resin foam sheet using a T die is preferable from the viewpoint of securing moldability. .

  Only one non-foamed extruded film layer of polystyrene-based resin may be laminated on the surface of the polystyrene-based resin foamed sheet, or a thermoplastic resin non-foamed film may be laminated on the outer surface through the extruded film layer. .

  In the lamination method by the extrusion lamination method, it is preferable to appropriately select the temperature of the film-like polystyrene resin extruded from the T-die according to the fluidity of the resin used. If the resin temperature of the film-like polystyrene-based resin is too low relative to the temperature required for melt-compression bonding with the polystyrene-based resin foam sheet, there is a tendency that the adhesive force with the polystyrene-based resin foam sheet cannot be secured. On the other hand, if it is too high, fine bubbles are generated on the surface of the polystyrene resin foam sheet on the side where the polystyrene resin film is bonded due to the heat of the film-like polystyrene resin, causing blistering during molding. In addition, other thermoplastic resin non-foamed films laminated on the outer surface tend to expand and contract to cause wrinkles. For example, in the case of a high impact polystyrene resin, the temperature is preferably 210 to 240 ° C.

In the polystyrene-based resin laminated foam sheet of the present invention, when only one extruded film is laminated as a polystyrene-based resin non-foamed film, the basis weight of the non-foamed film is preferably 160 to 210 g / m ² , and 180 to 200 g / m ^2. m ² is more preferable. When the basis weight of the non-foamed film is less than 160 g / m ² , the curved surface printing suitability tends to be impaired. On the other hand, if it exceeds 210 g / m ² , the cost increases, but the container strength tends not to be improved as much as the increase in the basis weight of the non-foamed film.

  In the polystyrene resin laminated foam sheet of the present invention, the material of the thermoplastic resin non-foamed film laminated on the outer surface through the extruded film layer is not only styrene resin but also polyolefin resin such as polyethylene and polystyrene, polyethylene terephthalate Any material that can be applied to food packaging applications such as can be used.

  In a polystyrene resin laminated foam sheet, a thermoplastic resin non-foamed film laminated on the outer surface through an extruded film layer is produced by a known method such as a T-die method or an inflation method. In this case, since the film is stretched to some extent, the effect of improving the container strength can be expected by laminating the thermoplastic resin non-foamed film.

  In the polystyrene resin laminated foam sheet of the present invention, it is also possible to impart design properties to the molded container by laminating the thermoplastic resin non-foamed film film that has been previously printed by a known method such as a gravure method. It is.

In a polystyrene-based resin laminate foam sheet, the basis weight of the thermoplastic resin non-foamed film laminated via the extruded film layer is preferably from 20 to 40 g / ^{m 2,} more preferably 25 to 35 g / ^{m 2,} a polystyrene resin the basis weight of the total non-foamed film layer is preferably 160~210g / ^{m 2,} and more preferably 180-200 g / ^{m 2.} When the basis weight of the thermoplastic resin non-foamed film is less than 20 g / m ² , the thermoplastic resin non-foamed film tends to be wrinkled during lamination, and stable production tends to be difficult. Further, if it exceeds 40 g / m ² , the cost of the film itself tends to increase. The polystyrene-based resin foam sheet and the polystyrene-based resin laminated foam sheet obtained by the present invention are widely used as a heat forming method. Can be molded into a container. That is, after heating with an infrared heater or the like to secondarily foam the polystyrene-based resin laminated foam sheet, the container is shaped by fitting with a mold and then punching out the container from the sheet. Specific examples of thermoforming include plug molding, match molding, straight molding, drape molding, plug assist molding, plug assist reverse draw molding, air slip molding, snapback molding, reverse draw molding, and free molding. Although methods such as drawing molding, plug-and-ridge molding, and ridge molding can be mentioned, match molding is preferred from the standpoint of container shape and surface properties.

  In general, the appropriate secondary foam thickness of the polystyrene-based resin laminated foam sheet is determined by the mold design used for thermoforming. Generally, when thermoforming to obtain a molded body having a bowl shape, the secondary thickness of the polystyrene-based resin laminated foam sheet is required to be about 3.0 to 6.0 mm. It is necessary to determine the primary thickness of the resin laminated foam sheet.

  In order to sufficiently bring out the strength of the polystyrene-based resin laminated foam sheet, the secondary thickness is about 80 to 90% of the maximum secondary thickness of the laminated foam sheet (secondary foam thickness immediately before heating and burning of the sheet). It is desirable to perform molding by heating so that the thickness of the polystyrene-based resin laminated foam sheet is preferably 1.7 to 3.0 mm, and more preferably 2.0 to 2.8 mm. If the thickness of the polystyrene-based resin laminated foam sheet is less than 1.7 mm, it is necessary to increase the heating at the time of molding, which tends to cause a decrease in container strength and an appearance defect due to excessive heating. On the other hand, when the thickness exceeds 3.0 mm, sufficient heating cannot be performed at the time of molding, and due to insufficient heating, the elongation of the polystyrene-based resin laminated foam sheet tends to be insufficient, and molding defects tend to occur.

  The polystyrene-based resin foam sheet and molded article of the present invention are excellent in secondary moldability that can provide a good deep-drawn molded container excellent in light weight and heat insulation, and therefore used in food containers, particularly instant noodle containers. Can do.

  Hereinafter, specific examples will be described.

  The evaluation methods for the polystyrene-based resin laminated foam sheets or containers obtained in Examples and Comparative Examples are shown below.

(Measurement of thickness of polystyrene resin foam sheet)
At an arbitrary point in the flow direction of the obtained polystyrene-based resin foam sheet, the thickness was measured with calipers at intervals of 50 mm in the width direction, and the arithmetic average value at each measurement point was taken as the sheet thickness.

(Measurement of basis weight of polystyrene resin foam sheet)
A 10 cm square sample was cut out from the obtained polystyrene-based resin foam sheet in the width direction, the weight was measured, and the weight was calculated from the arithmetic average value of the obtained sample weights.

(Measurement of expansion ratio of polystyrene resin foam sheet)
In the above, the value obtained by dividing the measured basis weight by the volume calculated from the thickness is calculated as the density, and the value obtained by dividing the base resin density (1.05 g / cm ³ ) by the obtained density is the expansion ratio. It was.

(Measurement of residual foaming agent amount of polystyrene resin foam sheet)
A 10 × 10 cm sample was cut out from the polystyrene-based resin foam sheet obtained by extrusion foaming, and calculated from the change in weight of the foam sheet before and after heating for 30 minutes in a dryer at 150 ° C.

(Measurement of styrene dimer and styrene trimer content)
A 0.5 g sample is cut out from the polystyrene resin foam sheet obtained by extrusion foaming and dissolved in 25 ml of chloroform. From this solution, the amounts of styrene dimer and styrene trimer were measured using GC / MC (manufactured by Agilent Technologies, GC-6890plus). The measurement conditions are as follows: apparatus: Agilent Technologies, GC-6890plus, column: J & W Scientific, DB-5MS (0.25 m × 30 m, film thickness: 0.25 μm), column temperature: 100 ° C. to 20 ° C. / min to 280 ° C. (6 min), inlet temperature: 250 ° C., detection port temperature: 280 ° C., carrier gas: helium (150 kPa).

(Measurement of melt viscosity)
25 g of a sample was cut out from the polystyrene-based resin foam sheet obtained by extrusion foaming, heated in a vacuum drying oven (vacuum VEN VOS-450SD manufactured by EYLEA) at 180 ° C. for 1 hour, and then melt viscosity A resin sample for measurement was used.
The melt viscosity of the obtained sample was measured by the following procedure using a capillograph (manufactured by Toyo Seiki Co., Ltd., capillograph). A cylinder with an inner diameter of 9.6 mm and a length of 350 mm, fitted with an orifice with a hole diameter of 0.1 cm, a length of 1.0 cm and an inflow angle of 45 degrees, is heated at 180 ° C. and filled with about 20 g of a polystyrene resin, Preheat for 5 minutes. After preheating, the molten polystyrene resin is extruded at a speed of 10 mm / min using a piston having the same diameter as that of the cylinder. Next, extrusion is performed at a speed of 500 mm / min. A load applied to the piston at each piston speed can be detected from a load cell connected to the piston. The melt viscosity at each piston speed can be obtained by calculating from the obtained load using the following formula.
The shear rate of the molten polystyrene resin passing through the orifice when the piston speed is 10 mm / min is 122 S ⁻¹ , and the shear rate of the molten polystyrene resin passing through the orifice when the piston speed is 500 mm / min is 6080 S ^{−. 1} .

(Calculation of melt viscosity)
The load applied to the piston obtained by the measurement is F (kg), the piston speed as a measurement condition is V (mm / min), the inner radius of the cylinder is R, the length of the orifice is L (mm), the hole of the orifice When the radius is r (mm), the melt viscosities η _H and η _L are calculated by the following equation (3).

(Molding evaluation)
A sample of 520 × 520 mm was cut out from the obtained polystyrene-based resin foamed sheet and polystyrene-based resin laminated foamed sheet, and a small vacuum / pressure forming machine (manufactured by Wakisaka Engineering, FVS-500P) equipped with a frame having an opening of 400 × 400 mm was used. Using a mold having a drawing ratio of 0.85 (a mouth inner diameter of 130 mmφ and a bottom mouth diameter of 86 mmφ × depth of 110 mm), molding was performed by a match mold method to obtain a molded body. However, at the time of molding, a 400 × 400 × 1 mm thick Teflon (registered trademark) sheet with a 180 mmφ hole in the center so as to be concentric with the mold is overlapped on the upper surface of the polystyrene resin foam sheet and used in a single molding machine. Introduced, heated and molded. With this Teflon (registered trademark) sheet, the heater heating in the heating furnace of the single molding machine is heated and molded only in the 180 mmφ hole portion of the Teflon (registered trademark) sheet. Under the present circumstances, the heating conditions were adjusted so that the secondary foaming thickness at the time of shaping | molding by the match mold method of a polystyrene-type resin foam sheet might be 5.4-5.6 mm.
Moreover, when shape | molding a polystyrene-type resin laminated foam sheet, it shape | molded so that the polystyrene-type resin non-foamed film lamination surface of a polystyrene-type resin laminated foam sheet might become the outer side of a container.

(Formability: Crack evaluation)
The presence or absence of occurrence of cracks (a phenomenon in which cells are broken) inside the container of the polystyrene-based resin foam sheet molding container obtained by the above method was evaluated visually. The evaluation criteria at that time are as follows.
○: No cracking is observed.
X: Generation | occurrence | production of a crack is recognized.

(Moldability: Local strength reduction part)
The central part of the side wall of the molded resin laminated foam sheet obtained by the above method is strongly sandwiched between the thumb and index finger at intervals of about 1 cm in the circumferential direction of the container side wall, and locally soft. It was judged whether there was a felt part.
○: No local strength decrease is observed.
X: The local strength fall part is recognized.

  Below, it describes about the raw material used for the Example and the comparative example.

(Polystyrene resin A)
A reactor equipped with a stirrer was charged with 100 parts by weight of pure water and 0.15 part by weight of calcium phosphate as a suspension stabilizer, stirred to form an aqueous suspension, and then a polymerization initiator was added to 100 parts by weight of styrene monomer. As a solution, 0.15 part by weight of benzoyl peroxide and 0.13 part by weight of 1,1-bistributylbutyl peroxy-3,3,5-trimethylcyclohexane were added to the reactor and heated to 98 ° C. Polymerization took place over 4 hours. Subsequently, after heating up to 120 degreeC and hold | maintaining for 2 hours and 30 minutes, it cooled, the content was taken out, it dehydrated and dried, and the polystyrene resin A was obtained.
(Polystyrene resin B) G0002, manufactured by PS Japan
(Polystyrene resin C) manufactured by PS Japan, HIPS475D
(Initiator) manufactured by Nippon Oil & Fat Co., Ltd., Perhexa 25B
(Foaming agent) Butane-based gas in which isobutane / normal butane is mixed at a ratio of 85/15% by weight

(Reference Example 1)
A mixture of 0.4 parts by weight of talc to 100 parts by weight of a polystyrene resin mixture (50 parts by weight of polystyrene resin A and 50 parts by weight of polystyrene resin B) is put into a 65 mmφ uniaxial-90 mmφ uniaxial tandem extruder. Then, the mixture was melted in a first stage extruder heated to a set temperature of 200 ° C., and the butane gas as a foaming agent was added to 3 parts by weight of polystyrene resin at a position in the middle of the first stage extruder. 4 parts by weight were injected. Next, the resin introduced into the second-stage extruder is cooled so that the resin pressure at the tip of the second-stage extruder is 22 MPa, and then air is passed through a circular die having a circular slit of 75 mmφ (set temperature: 145 ° C.). It was extruded and foamed inside. While blowing air at 30 ° C. onto the surface of the extruded cylindrical foam that is not in contact with the cooling cylinder with an air volume of 3.0 m ³ / hr, it is applied to the cooling cylinder to perform drawing and cooling, and a take-off speed of 5 It was taken up at 0.7 m / min and cut into a sheet-like foam by a cutter to obtain a polystyrene resin foam sheet having a width of 640 mm.
Table 1 shows the evaluation results regarding the obtained polystyrene-based resin foam sheet and the obtained container.

(Reference Example 2)
A polystyrene-based resin foam sheet was obtained in the same manner as in Reference Example 1 except that 0.35 parts by weight of talc, 3.2 parts by weight of the foaming agent, and the take-up speed were 5.0 m / min.
Table 1 shows the evaluation results regarding the obtained polystyrene-based resin foam sheet and the obtained container.

Example 1
In the same manner as in Reference Example 1 , except that a resin obtained by mixing 0.45 parts by weight of talc and 0.005 parts by weight of initiator perhexa 25B with respect to 100 parts by weight of polystyrene resin A was charged into the extruder. -Based resin foam sheet was obtained.
Table 1 shows the evaluation results regarding the obtained polystyrene-based resin foam sheet and the obtained container.

(Reference Example 3)
On one side of the polystyrene-based foamed sheet obtained in Reference Example 2 , a film using high impact polystyrene resin C (manufactured by PS Japan, HIPS475D) by extrusion lamination using a T die is shown in Table 1. Was laminated to obtain a polystyrene-based resin laminated foam sheet.
In addition, as a result of measuring the surface temperature of the extruded film-like polystyrene resin at the time of extrusion lamination using the non-contact-type surface thermometer (PT-3LF made from APTUS), it was 225 +/- 3 degreeC in the width direction.
The evaluation results regarding the obtained polystyrene-based resin laminated foam sheet and the obtained container are shown in Table 1.

(Comparative Example 1)
A polystyrene resin foam sheet was obtained in the same manner as in Reference Example 1 except that the raw polystyrene resin was changed to 100 parts by weight of polystyrene resin B.
Table 1 shows the evaluation results regarding the obtained polystyrene-based resin foam sheet and the obtained container.

(Comparative Example 2)
A polystyrene resin foam sheet was obtained in the same manner as in Reference Example 1 , except that the raw polystyrene resin was changed to 100 parts by weight of polystyrene resin A.
Table 1 shows the evaluation results regarding the obtained polystyrene-based resin foam sheet and the obtained container.

(Comparative Example 3)
A polystyrene resin foam sheet was obtained in the same manner as in Reference Example 2 , except that the raw polystyrene resin was changed to 100 parts by weight of polystyrene resin B.
Polystyrene resin C was laminated on the obtained polystyrene resin foam sheet in the same manner as in Reference Example 3 to obtain a polystyrene resin foam sheet laminated sheet.
Table 1 shows the evaluation results regarding the obtained polystyrene-based resin foam sheet and the obtained container.

(Comparative Example 4)
A polystyrene resin foam sheet was obtained in the same manner as in Reference Example 2 , except that the raw polystyrene resin was changed to 100 parts by weight of polystyrene resin A. Furthermore, the polystyrene-type resin C was laminated | stacked on the obtained polystyrene-type resin foam sheet by the method similar to the reference example 3, and the polystyrene-type resin foam sheet laminated sheet was obtained.
Table 1 shows the evaluation results regarding the obtained polystyrene-based resin foam sheet and the obtained container.

  Compared to Comparative Examples 1 and 3 in which elongation was poor and internal cracks occurred, and Comparative Examples 2 and 4 in which elongation was too good and local strength was weak on the side wall of the container, the melt viscosity was within the range described herein. It can be seen that in the examples adjusted to the above, there are no internal cracks or portions with weak local strength.

The graph which showed the melt viscosity of base-material resin of a polystyrene-type resin foam sheet, and the relationship with Formula 1 or Formula 2. FIG.

Claims (3)

A foamed sheet made of a polystyrene resin, having a thickness of 1.3 to 2.5 mm, a basis weight of 150 to 400 g / m ² , an expansion ratio of 5 to 15 times, and 100 parts by weight of the polystyrene resin In addition, by adding 0.002 to 0.1 part by weight of a polymerization initiator and melt-kneading, the shear rate at 190 ° C. of the base resin is 6080 S ⁻¹ and the melt viscosity η _H (poise) is 122 S ⁻¹ . The polystyrene-based resin foamed sheet is characterized in that the melt viscosity η _L (poise) is adjusted so as to satisfy the following conditional expressions (1) and (2).

(However, eta _H is a melt viscosity at a shear rate of 6080S ^-1 at 190 ° C. (poise), the melt viscosity at a shear rate of 122S ^-1 in eta _L is 190 ℃ (poise).)   The polystyrene-based resin laminated foam sheet according to claim 1, wherein a non-foamed layer is formed on at least one surface of the polystyrene-based resin foam sheet.   The polystyrene resin foam sheet according to claim 1 or the polystyrene resin laminate foam sheet according to claim 2, wherein the content of styrene dimer and styrene trimer contained in the polystyrene resin foam sheet is 1600 ppm or less.

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