JP2008144025A - Method for producing styrene-based resin foam sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a styrene-based resin foam sheet, remarkably reduced in weight, compared with conventional sheets and producing a styrene-based resin foam sheet having good secondary formability and excellent also in strength and appearance. <P>SOLUTION: The method for producing the styrene-based resin foam sheet comprises adding 0.005-0.8 mass% at least either one selected from epoxidized soybean oil and epoxidized linseed oil and 0-0.5 mass% higher fatty acid metal salt to a resin composition containing a styrene-methacrylic acid copolymer having 0.2-4.0 mass% methacrylic acid unit content, heat-melting the mixture and extruding the melted material. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for producing a styrene resin foam sheet, a styrene resin foam sheet produced by the method, and a food packaging container formed by molding the styrene resin foam sheet.

  Styrenic resin extruded foam sheets are widely molded into food trays, lunch boxes, instant noodle containers, cups, etc., taking advantage of features such as buffering and heat barrier properties, mainly from the viewpoint of cost reduction, There is a demand for improved productivity during molding as well as weight reduction. Such an extruded foam sheet is generally produced by using an extruder, melting and mixing a nucleating agent such as talc or calcium carbonate into a styrenic resin, press-fitting the foaming agent, and then extruding and foaming from a circular die. .

  In order to reduce the weight of the styrene-based resin foam sheet, that is, to increase the expansion ratio, it is necessary to increase the amount of the foaming agent added at the time of foam sheet extrusion. However, when the amount of foaming agent added increases, the resin viscosity in the extruder decreases due to the plasticizing effect of the foaming agent, the pressure in the die at the tip of the extruder decreases, foaming occurs in the die, and the appearance is reduced. There is a problem that gets worse. Therefore, for weight reduction, a material having a higher molecular weight is required for higher viscosity, but there is a limit to the molecular weight that can be economically produced by the conventional technology. Moreover, the higher the molecular weight, the greater the degree of molecular weight reduction due to thermal degradation in the extruder and the lower the efficiency.

  Furthermore, when the weight is reduced, the amount of resin constituting the foamed sheet is reduced, so that the strength of the sheet and the molded product is reduced, and cracking and tearing are liable to occur during secondary molding from the sheet to the molded product. There's a problem.

  As an improvement measure, a method of using a polystyrene resin obtained by polymerizing a styrene monomer using an organic peroxide having a specific chemical structure as a polymerization initiator (see Patent Documents 1 to 3) is proposed. However, the balance between weight reduction, secondary formability, strength, and appearance is not sufficient, and there is a limit to weight reduction.

JP 2003-49033 A JP-A-6-279612 Japanese Patent Laid-Open No. 11-246624

  The present invention can produce a styrene resin foam sheet that can be significantly reduced in weight compared to the prior art, and can produce a styrene resin foam sheet having good secondary formability and excellent strength and appearance. It is an object to provide a method, a styrene resin foam sheet produced by the method, and a food packaging container formed by molding the styrene resin foam sheet.

  In order to achieve the above object, the present invention has been intensively studied. As a result, at least one of epoxidized soybean oil and epoxidized linseed oil was added to a resin composition containing a styrene-methacrylic acid copolymer. Then, it was found that it is possible to reduce the weight of the styrene-based resin foam sheet by heating and melting and then extruding, and the present invention was completed.

  That is, the method for producing a styrene-based resin foam sheet of the present invention is 0% relative to a resin composition containing a styrene-methacrylic acid copolymer having a methacrylic acid unit content of 0.2 to 4.0% by mass. Adding at least one selected from 0.005 to 0.8% by mass of epoxidized soybean oil and epoxidized linseed oil and 0 to 0.5% by mass of a higher fatty acid metal salt, followed by heating and melting, and then extruding. Features.

  According to the production method of the present invention, the molecular weight can be increased when the styrene resin foam sheet is extruded. As a result, even if the amount of foaming agent added is increased to increase the expansion ratio, the pressure inside the die at the tip of the extruder can be kept at a level that does not foam in the die, and the weight can be reduced with the same appearance as before. It becomes. Moreover, the fall of intensity | strength can be suppressed by the increase in molecular weight. In addition, since the component on the high molecular weight side (Z average molecular weight) can be increased, secondary moldability is also improved.

  The styrenic resin foam sheet of the present invention is significantly lighter than conventional ones, is excellent in strength and appearance, and is economically superior. Moreover, since the secondary moldability is also good, it becomes possible to improve productivity when molding food packaging containers and the like.

  First, the manufacturing method of this invention is demonstrated.

  The resin composition used in the production method of the present invention contains a styrene-methacrylic acid copolymer.

  Content of the methacrylic acid unit of a styrene-methacrylic acid copolymer is 0.2-4.0 mass%, Preferably it is 0.5-2.0 mass%, More preferably, it is 0.7-1.5. % By mass. If it is less than 0.2% by mass, the effect of increasing the molecular weight in the extruder is small, and it is difficult to reduce the weight of the foamed sheet. Moreover, when it exceeds 4 mass%, compatibility with the polystyrene which is a homopolymer of styrene will deteriorate. Therefore, there arises a problem that a conventional styrene resin foamed sheet mainly composed of polystyrene and a return material (such as a sheet waste) cannot be collected. In addition, content of a methacrylic acid unit can be measured by neutralization titration.

  The melt mass flow rate (MFR) of the styrene-methacrylic acid copolymer measured at 200 ° C. under a load of 49 N is preferably 0.5 to 3.0 g / 10 minutes, more preferably 1.0 to 2. 0.0 g / 10 min. If it is less than 0.5 g / 10 min, it may be difficult to economically produce a styrene-methacrylic acid copolymer, and if it exceeds 3.0 g / 10 min, foaming may occur due to insufficient resin viscosity. It may be difficult to reduce the weight of the seat. The melt mass flow rate can be measured based on JIS K-7210.

  Although there is no restriction | limiting in particular about the molecular weight of a styrene-methacrylic acid copolymer, It is preferable to set so that the molecular weight of a foamed sheet may become the range mentioned later.

  The styrene-methacrylic acid copolymer may contain a small amount of polymerizable monomers other than styrene and methacrylic acid as long as the properties of the copolymer are not impaired.

  Examples of the polymerization method of the styrene-methacrylic acid copolymer include known styrene polymerization methods such as a bulk polymerization method, a solution polymerization method, and a suspension polymerization method. As the solvent, for example, alkylbenzenes such as benzene, toluene, ethylbenzene and xylene, ketones such as acetone and methyl ethyl ketone, aliphatic hydrocarbons such as hexane and cyclohexane, and the like can be used.

  In the polymerization of the styrene-methacrylic acid copolymer, a polymerization initiator and a chain transfer agent can be used as necessary. As polymerization initiators, organic oxides such as benzoyl peroxide, t-butylperoxybenzoate, 1,1-di (t-butylperoxy) cyclohexane, 1,1-bis (t-butylperoxy)- 3,3,5-trimethylcyclohexane, t-butylperoxyisopropyl carbonate, dicumyl peroxide, t-butylcumyl peroxide, t-butylperoxyacetate, t-butylperoxy-2-ethylhexanoate, 2 , 2-bis (4,4-di-t-butylperoxycyclohexyl) propane, polyether tetrakis (t-butylperoxycarbonate), ethyl-3,3-di (t-butylperoxy) butyrate, t- Examples include butyl peroxyisobutyrate. As the chain transfer agent, for example, aliphatic mercaptan, aromatic mercaptan, pentaphenylethane, α-methylstyrene dimer, terpinolene and the like can be used.

  The styrene-methacrylic acid copolymer-containing resin composition may contain 0 to 70% by mass of polystyrene. In addition, rubber-reinforced components such as HI-PS resin and MBS resin and aromatic vinyl-based thermoplastic elastomers such as SBS may be contained in an amount of several percent as other components containing rubber if necessary. good. In this case, it is preferable that the content of the methacrylic acid unit of the styrene-methacrylic acid copolymer in the styrene-methacrylic acid copolymer-containing resin composition is 0.2% by mass or more for the above reason.

  In the production method of the present invention, at least one selected from epoxidized soybean oil and epoxidized linseed oil is added to the styrene-methacrylic acid copolymer-containing resin composition.

  Epoxidized soybean oil and epoxidized linseed oil are added singly or in combination, and the addition amount is 0.005 to 0.8% by mass with respect to the styrene-methacrylic acid copolymer-containing resin composition, preferably It is 0.01-0.5 mass%, More preferably, it is 0.05-0.3 mass%. When the addition amount is less than 0.005 mass%, the effect of increasing the molecular weight is not sufficient, and it is difficult to reduce the weight of the foamed sheet. When the addition amount exceeds 0.8% by mass, a gel-like substance is generated and the appearance deteriorates.

  There are no particular restrictions on the method of adding epoxidized soybean oil or epoxidized linseed oil, and it may be added directly to the feed hole of the extruder alone or with a styrene-methacrylic acid copolymer-containing resin composition. You can also. Also, a master batch based on polystyrene or the like, which is a homopolymer of styrene, can be prepared and supplied using the master batch. Moreover, it can also supply using the rubber | gum reinforcement | strengthening styrene resin and styrene thermoplastic elastomer which were previously mix | blended with epoxidized soybean oil and epoxidized linseed oil.

  In the production method of the present invention, a higher fatty acid metal salt can be used in combination in order to promote the reaction between the epoxidized soybean oil or epoxidized linseed oil and the styrene-methacrylic acid copolymer. The addition amount is 0 to 0.5% by mass, preferably 0.02 to 0.2% by mass, based on the styrene-methacrylic acid copolymer-containing resin composition. If the addition amount exceeds 0.5% by mass, dirt is likely to occur on the die, which is not preferable.

  Examples of the higher fatty acid metal salt include higher fatty acid zinc having 8 to 22 carbon atoms, higher fatty acid magnesium, higher fatty acid calcium, higher fatty acid lithium, and higher fatty acid aluminum. Higher fatty acid zinc and higher fatty acid magnesium which are highly effective in promoting the reaction between epoxidized soybean oil or epoxidized linseed oil and styrene-methacrylic acid copolymer are particularly preferred.

  There is no restriction | limiting in particular about the addition method of a higher fatty acid metal salt, You may add directly to the supply hole of an extruder directly, and can also add with a styrene-methacrylic acid copolymer containing resin composition. Also, a master batch based on polystyrene or the like, which is a homopolymer of styrene, can be prepared and supplied using the master batch. Moreover, it can also supply using the rubber | gum reinforcement | strengthening styrene-type resin and styrene-type thermoplastic elastomer which were previously mix | blended with the higher fatty acid metal salt.

  However, when a high-fatty acid metal salt is supplied to an extruder using a masterbatch pre-blended with epoxidized soybean oil or epoxidized linseed oil, the effect of increasing the molecular weight of epoxidized soybean oil or epoxidized linseed oil becomes poor. Therefore, it is preferable that the higher fatty acid metal salt and the epoxidized soybean oil or epoxidized linseed oil are not subjected to heat history in advance.

  In the production method of the present invention, after adding epoxidized soybean oil or the like, the foamed sheet is produced by heating and melting and then extruding.

  In the production method of the present invention, as a blowing agent, aliphatic hydrocarbons such as propane, normal butane, isobutane, pentane and hexane, cycloaliphatic hydrocarbons such as cyclobutane and cyclopentane, trichlorofluoromethane, dichlorodifluoromethane, Use physical blowing agents such as halogenated hydrocarbons such as 1,1-difluoroethane, 1,1-difluoro-1-chloroethane, 1,1,1,2-tetrafluoroethane, methyl chloride, ethyl chloride, methylene chloride can do. Also, decomposable foaming agents such as azodicarbonamide, dinitrosopentamethylenetetramine, azobisisobutyronitrile, sodium bicarbonate and citric acid, inorganic gases such as carbon dioxide and nitrogen, and water can be used. These foaming agents can be used by mixing them appropriately, but industrially, butane is often used, and from the viewpoints of foam extrudability, secondary formability of foamed sheets, and retention of foaming agents, isobutane and normal It is preferable to use mixed butane composed of rubbutane. The addition amount of a foaming agent is 1-10 mass% normally with respect to the resin composition supplied to an extruder.

  Examples of the nucleating agent for foaming include inorganic powders such as talc, calcium carbonate, and clay. Single or a mixture can be used. Talc is most preferable in that it has a large effect of reducing the bubble diameter and is inexpensive. The method for adding the nucleating agent is not particularly limited, and it may be added directly to the supply hole of the extruder or may be added together with the styrene-methacrylic acid copolymer-containing resin composition. A master batch based on polystyrene or the like, which is a homopolymer of styrene, can be prepared and supplied using the master batch. The addition amount of the nucleating agent is usually 0.1 to 5% by mass with respect to the resin composition supplied to the extruder.

  In addition, you may mix | blend a higher fatty acid metal salt beforehand in a nucleating agent containing masterbatch. Further, lubricants such as ethylene bisstearyl amide, spreading agents such as liquid paraffin and silicone oil, other surfactants, antistatic agents, antioxidants, plasticizers, light fasteners, pigments and the like may be contained.

  As a production apparatus used in the production method of the present invention, a known extruded foam sheet production apparatus is suitable. That is, a known melt-kneading apparatus such as a single screw extruder or a twin screw extruder can be used alone or in combination of two or more. From the viewpoint of residence time for sufficiently proceeding with the reaction, it is preferable to use two or more extruders in series. Specifically, after a foaming agent is pressed into and mixed with the resin composition heated and melted by the first extruder, the resin temperature is adjusted to 120 to 180 ° C. by cooling with the second extruder. A method of extruding a foam sheet into the air from a circular die is preferable. The thickness of the foam sheet can be adjusted by operating conditions such as equipment structure such as a die structure, resin processing flow rate, sheet take-up speed, and the like. Moreover, the density of a foam sheet can be adjusted with the addition amount etc. of a foaming agent.

  In the production method of the present invention, the set temperature of the first extruder cylinder until the foaming agent is press-fitted is important, and is preferably set to 200 to 270 ° C, more preferably 220 to 250 ° C. If it is lower than 200 ° C., the reaction does not proceed sufficiently, the effect of increasing the molecular weight is reduced, and it may be difficult to reduce the weight of the styrene resin foam sheet. On the other hand, when the temperature is higher than 270 ° C., it becomes difficult to cool in the second extruder, the resin temperature cannot be lowered sufficiently, and foaming in the die may occur.

  Next, the styrene resin foam sheet of the present invention will be described.

  The foam sheet of the present invention is produced by the production method of the present invention.

  The thickness of the foam sheet of the present invention is 1 to 3 mm. When the thickness of the sheet is less than 1 mm, the strength and heat insulating properties of the container obtained by secondary molding of the foamed sheet are lowered. When it exceeds 3 mm, temperature unevenness tends to occur inside and outside the foamed sheet, and a container that reproduces the shape of the mold cannot be obtained. The thickness of the foam sheet can be measured using a dial gauge or a micrometer, and the thickness can also be measured by cutting the foam sheet vertically and observing the cross section with a microscope or the like.

The density of the foamed sheet of the present invention is 50 to 80 kg / m ³ , preferably 60 to 70 kg / cm ³ . If the density of the foam sheet is less than 50 kg / m ³ , the rigidity of the container after the secondary molding is insufficient, and if it exceeds 80 kg / m ³ , the container cannot be reduced in weight. The density D (kg / cm ³ ) of the foamed sheet can be calculated as D = S / T from the basis weight S (g / m ² ) and the thickness T (mm) of the foamed sheet.

  Further, the polystyrene-equivalent weight average molecular weight (Mw) of the foamed sheet is 300,000 to 550,000, and the ratio (Mz / Mw) of the Z average molecular weight (Mz) to the weight average molecular weight (Mw) is 2.1 to 4.0. Preferably there is. When the weight average molecular weight (Mw) is less than 300,000 and Mz / Mw is less than 2.1, the strength of the foamed sheet and the molded product is insufficient, and cracking and tearing occur when secondary molding of the styrene resin foamed sheet. It becomes easy to do. If the weight average molecular weight (Mw) exceeds 550,000, a gel-like substance may be generated and the appearance may deteriorate. The weight average molecular weight (Mw) and the Z average molecular weight (Mz) can be measured using gel permeation chromatography (GPC).

  The foamed sheet of the present invention is heated and molded simultaneously with secondary foaming, so that it is secondarily molded into various shapes and widely used in food packaging containers such as food trays, lunch boxes, instant noodle containers, and cups. be able to.

  EXAMPLES Hereinafter, although an Example is given and this invention is demonstrated concretely, this invention is not limited to these Examples.

<Manufacture of polymer>
First, the polymerization initiator used for manufacture of a polymer is shown below.
Polymerization initiator 1: 2,2-bis (4,4-t-butylperoxycyclohexyl) propane (Nippon Yushi Co., Ltd., Pertetra A)
Polymerization initiator 2: 1,1-bis (t-butylperoxy) cyclohexane (manufactured by NOF Corporation, Perhexa C)

(1) Polymer T1
The polymerization reactor was configured by connecting in series a first reactor that was a complete mixing tank, a second reactor, and a third reactor that was a plug flow reactor with a static mixer. The capacity of each reactor was 39 liters for the first reactor, 39 liters for the second reactor, and 16 liters for the third reactor.

  A mixed solution of 90.2% by mass of styrene, 9.0% by mass of ethylbenzene, and 0.8% by mass of methacrylic acid was prepared, and 200 ppm of polymerization initiator 1 was mixed on a mass basis with respect to the total amount of styrene and methacrylic acid. A raw material solution was obtained.

  This raw material solution was continuously supplied to the first reactor at a rate of 13.5 kg per hour. The reaction temperature of each reactor is 120 ° C in the first reactor, 125 ° C in the second reactor, 125 ° C in the third reactor, with a temperature gradient along the flow direction, 135 ° C in the middle part, and at the outlet part. The temperature was adjusted to 140 ° C.

Subsequently, the solution containing the polymer continuously taken out from the third reactor was introduced into a vacuum devolatilization tank with a preheater constituted of two stages in series, and after separating unreacted styrene and ethylbenzene, a strand shape After being extruded and cooled, it was cut into pellets. The temperature of the first stage preheater is set to 200 ° C., the pressure of the vacuum devolatilization tank is set to 6.67 × 10 ⁴ Pa (500 torr), and the temperature of the second stage preheater is set to 250 ° C. The pressure in the vacuum devolatilization tank was 6.67 × 10 ² Pa (5 torr).

  The properties of the obtained polymer T1 were evaluated by the following methods. The results are shown in Table 1.

a) Melt Mass Flow Rate The melt mass flow rate under the conditions of 200 ° C. and 49 N load was measured based on JIS K-7210.

b) Methacrylic acid content At room temperature, 0.5 g of the polymer was weighed and dissolved in a mixed solution of toluene / ethanol = 8/2 (volume ratio), and then in a potassium hydroxide 0.1 mol / L ethanol solution. Japanese titration is performed, the end point is detected, and the content of methacrylic acid based on mass is calculated from the amount of potassium hydroxide ethanol solution used. In addition, it measured with the potentiometric automatic titrator (Kyoto Electronics Industry Co., Ltd. make, AT-510).

c) Molecular weight The number average molecular weight (Mn), the weight average molecular weight (Mw), and the Z average molecular weight (Mz) were measured under the following conditions using gel permeation chromatography (GPC). Each molecular weight is calculated as a molecular weight in terms of polystyrene by calculating the molecular weight at each elution time from the elution curve of monodisperse polystyrene.

GPC model: Shodex GPC-101 manufactured by Showa Denko KK
Column: Polymer Laboratories PLgel 10 μm MIXED-B, 300 × 7.5 mm
Mobile phase: tetrahydrofuran 1.0 ml / min
Sample concentration: 0.2% by mass
Temperature: 40 ° C oven, 35 ° C inlet, 35 ° C detector
Detector: Differential refractometer

(2) Polymers T2 to T6, G1
Polymers T2 to T6 and G1 were produced in the same manner as the polymer T1, except that the reaction conditions shown in Table 1 were used. The properties of the obtained polymer are shown in Table 1.

<Manufacture of master batch>
(1) Epoxidized soybean oil masterbatch (ESO 4% MB)
The polymer G1 and epoxidized soybean oil (Nippon Yushi Co., Ltd., Neusizer 510R) are mixed well at 96/4 (mass ratio), and then screwed using a twin screw extruder (Toshiba Machine Co., Ltd., TEM26SS). The mixture was melt kneaded and pelletized under the conditions of a rotation speed of 300 rpm, a barrel temperature of 220 ° C., and a discharge amount of 30 kg / hr.

(2) Epoxidized linseed oil masterbatch (ELO 4% MB)
Polymer G1 and epoxidized linseed oil (Nippon Yushi Co., Ltd., Neusizer 512) were mixed well at 96/4 (mass ratio), and then screwed using a twin screw extruder (Toshiba Machine Co., Ltd., TEM26SS). The mixture was melt kneaded and pelletized under the conditions of a rotation speed of 300 rpm, a cylinder temperature of 220 ° C., and a discharge amount of 30 kg / hr.

(3) Talc master batch (talc MB-A)
Polymer G1, talc (manufactured by Kihara Kasei Co., Ltd., SP-GPSS), magnesium stearate, and liquid paraffin were mixed in a tumbler at 50/45/3/2 (mass ratio) for 5 minutes. Using an extruder (OCM100, manufactured by Nagata Seisakusho), the mixed composition was subjected to conditions of a kneader rotation speed of 250 rpm, a kneader cylinder temperature of 150 to 180 ° C., a ruder rotation speed of 60 rpm, a ruder cylinder temperature of 180 ° C., and a discharge amount of about 400 kg / hr. And kneaded and pelletized.

(4) Talc master batch (talc MB-B)
Polymer G1, talc (manufactured by Kihara Kasei Co., Ltd., SP-GPSS), magnesium stearate, and liquid paraffin were mixed at 52/45/1/2 (mass ratio) with a tumbler for 5 minutes. Using an extruder (OCM100, manufactured by Nagata Seisakusho), the mixed composition was subjected to conditions of a kneader rotation speed of 250 rpm, a kneader cylinder temperature of 150 to 180 ° C., a ruder rotation speed of 60 rpm, a ruder cylinder temperature of 180 ° C., and a discharge amount of about 400 kg / hr. And kneaded and pelletized.

(5) Talc master batch (talc MB-C)
Polymer G1, talc (manufactured by Kihara Kasei Co., Ltd., SP-GPSS), and liquid paraffin were mixed at 53/45/2 (mass ratio) with a tumbler for 5 minutes. Using an extruder (OCM100, manufactured by Nagata Seisakusho), the mixed composition was subjected to conditions of a kneader rotation speed of 250 rpm, a kneader cylinder temperature of 150 to 180 ° C., a ruder rotation speed of 60 rpm, a ruder cylinder temperature of 180 ° C., and a discharge amount of about 400 kg / hr. And kneaded and pelletized.

<Example 1>
Polymer T1: composition consisting of 93.0% by mass, ESO 4% MB: 5.0% by mass, talc MB: 2.0% by mass (based on polymer T1, epoxidized soybean oil 0.2% by mass, Magnesium stearate 0.06% by mass) was supplied to a 115 mm diameter single screw extruder (cylinder temperature 230 ° C.) at 150 kg / hour, melt-mixed, and then 60/40 (mass ratio) consisting of isobutane and normal butane as blowing agents. About 5% by mass with respect to the resin composition supplied to the extruder. Thereafter, the resin was transferred to a 180 mm diameter single screw extruder, cooled to 150 ° C. at the extruder outlet, and extruded from a circular die for foaming.

  The characteristics of the obtained foam sheet were evaluated by the following methods. The results are shown in Table 2.

(1) Thickness The thickness of the foam sheet was measured with a dial gauge so as not to deform the sample.

(2) Density The density D (kg / cm ³ ) of the foam sheet was calculated as D = S / T from the basis weight S (g / m ² ) and the thickness T (mm) of the foam sheet. The basis weight S (g / m ² ) was calculated by cutting the foam sheet into 10 cm length and 10 cm width, and measuring the mass per 100 cm ² area of the foam sheet.

(3) Molecular weight The weight average molecular weight (Mw) and the Z average molecular weight (Mz) of the foam sheet were measured by the same method as the molecular weight measurement method for the polymer.

(4) Surface state The appearance of the foam sheet was visually observed, and the appearance was evaluated in three stages: ○: good appearance, Δ: slightly bad appearance, ×: poor appearance.

(5) Tensile test From the foam sheet, an SD-type lever-type sample cutter (manufactured by Dumbbell, SDL-200) and a super dumbbell cutter (manufactured by Dumbbell, SDK-600-D) are used for tensile tests. A sample was created. The test piece conforms to JIS K-6732, and has a dumbbell shape with a parallel part width of 10 mm, a parallel part length of 40 mm, a grip part width of 25 mm, and a total length of 120 mm. Two types of test pieces were prepared so that the tensile direction of the tensile test was the sheet flow direction (MD) and the vertical direction (TD).

  When the obtained test piece is set in a tensile tester at room temperature so that the distance between chucks (between grippers) is 70 mm, a tensile test is performed at a tensile speed of 5 mm / min, and the test piece breaks. The tensile fracture strength (MPa) and the displacement until failure (mm) were determined. The test was performed using five test pieces, and the average value was obtained as the test result.

(3) Secondary formability The foamed sheet is heated by a vacuum forming machine at a heater temperature of 260 ° C. for a predetermined time, softened and subjected to secondary foaming, and then immediately subjected to vacuum forming to form a circular punch having an inner diameter of 100 mm and a depth of 50 mm. A container was obtained.

  Observe the occurrence of cracks on the inner surface of the container, out of 100 molded containers, the number of cracks observed is 0, ◎ less than 5, ≧ 5 and less than 10 △ and 10 or more cases were evaluated as x, and the secondary formability (deep drawing property) was evaluated.

<Examples 2-12, Comparative Examples 1-8>
A foamed sheet was produced in the same manner as in Example 1 except that the formulations shown in Tables 2 and 3 were used. The characteristics of the obtained foamed sheet are shown in Tables 2 and 3.

  In Comparative Example 3, when an attempt was made to produce a foamed sheet, a large amount of gel-like substance was generated, making it difficult to take up the foamed sheet, and production was impossible.

  As shown in Tables 2 and 3, the styrene resin foam sheet produced by the production method of the present invention has a low density and a light weight, is excellent in sheet appearance, and is excellent in secondary formability. Moreover, the displacement until a test piece breaks is large from the tensile test result of a foamed sheet, and it is excellent also in intensity | strength.

Claims (6)

  0.005-0.8 mass% epoxidized soybean oil and epoxy with respect to the resin composition containing the styrene-methacrylic acid copolymer whose methacrylic acid unit content is 0.2-4.0 mass% A method for producing a styrene-based resin foam sheet, comprising adding at least one selected from modified linseed oil and 0 to 0.5% by mass of a higher fatty acid metal salt, followed by heating and melting, and then extruding.   2. The styrene according to claim 1, wherein the styrene-methacrylic acid copolymer has a melt mass flow rate (MFR) measured at 200 ° C. under a load of 49 N of 0.5 to 3.0 g / 10 minutes. Of manufacturing a resin-based resin foam sheet.   The method for producing a styrene-based resin foamed sheet according to claim 1 or 2, wherein the resin composition contains 0 to 70 mass% of polystyrene. A styrenic resin foamed sheet produced by the production method according to any one of claims 1 to 3, having a thickness of 1 to 3 mm and a density of 50 to 80 kg / m ³ .   The polystyrene-reduced weight average molecular weight (Mw) is 300,000 to 550,000, and the ratio (Mz / Mw) of the Z average molecular weight (Mz) to the weight average molecular weight (Mw) is 2.1 to 4.0. The styrene resin foam sheet according to claim 4.   A food packaging container formed by molding the styrenic resin foam sheet according to claim 4 or 5.