Polystyrene resin foamed sheet and polystyrene resin laminated foamed sheet

Abstract

To improve an appearance by solving the problem in which, although an inner or outer surface of a molded container is required to have an attractive appearance, simply covering the surface of a foam layer with a non-foamed layer does not prevent the foam layer from affecting an appearance (such as gloss).SOLUTION: A foamed sheet has a foamed layer, which includes a first unit foamed layer and a second unit foamed layer positioned on one side of the first unit foamed layer. The surface of the first unit foamed layer forms one surface of the foamed layer, and the surface of the second unit foamed layer forms the other surface of the foamed layer. The average cell diameter of the first unit foamed layer is smaller than the average cell diameter of the second unit foamed layer.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a polystyrene-based resin foam sheet and a laminated polystyrene-based resin foam sheet. [Background technology]

[0002] Containers having a foamed layer of a polystyrene-based resin (foamed containers) are known as containers for food, etc. Examples of methods for manufacturing such containers include a method of thermoforming a polystyrene-based resin foamed sheet having a foamed layer of a polystyrene-based resin.

[0003] A polystyrene-based resin laminated foam sheet (sometimes referred to as a "laminated foam sheet") is known, which has a foamed layer of heat-resistant polystyrene resin and a non-foamed layer of polyolefin-based resin or the like on one or both sides of the foamed layer, with the aim of improving the heat resistance of foam containers. For example, a polystyrene-based resin foam sheet has been proposed that is made of a mixture containing less than 50% by mass of recycled material derived from a polystyrene-based resin foam sheet containing methacrylic acid, the mixture being mainly composed of styrene, and has a foam layer that is foamed containing methacrylic acid and a rubber component (for example, Patent Document 1). According to the invention described in Patent Document 1, the strength of a polystyrene-based resin foam sheet formed from a recycled material containing methacrylic acid is improved. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2021-046466 Summary of the Invention [Problem to be solved by the invention]

[0005] In foam containers, the interior or exterior surface of the container is required to be beautiful. The decorative surface (interior or exterior) that is required to be beautiful varies depending on the use of the container. Simply covering the surface of a foamed layer with a non-foamed layer to enhance aesthetic appeal will have an adverse effect on the appearance (gloss, etc.). For this reason, improvements in the appearance of foamed layers are required on surfaces that require aesthetic appeal (surfaces intended for decoration). Therefore, an object of the present invention is to provide a polystyrene resin foam sheet that can have a more beautiful appearance. [Means for solving the problem]

[0006] The present invention has the following aspects. <1> a foam layer having a first unit foam layer and a second unit foam layer located on one surface of the first unit foam layer, the surface of the first unit foam layer forms one side of the foam layer; the surface of the second unit foam layer forms the other surface of the foam layer; A polystyrene-based resin foam sheet, wherein the first unit foam layer has an average cell diameter smaller than the average cell diameter of the second unit foam layer. <2> The difference between the average cell diameter of the first unit foam layer and the average cell diameter of the second unit foam layer is 10 to 100 μm. <1> The polystyrene resin foam sheet according to claim 1. <3> The softening point of the first unit foam layer is lower than the softening point of the second unit foam layer. <1> or <2> The polystyrene resin foam sheet according to claim 1. <4> The difference between the softening point of the first unit foam layer and the softening point of the second unit foam layer is 0 to 25°C. <3> The polystyrene resin foam sheet according to claim 1. <5> the first unit foam layer contains a polystyrene-based resin and a polyphenylene ether-based resin, the second unit foam layer contains a polystyrene-based resin and a polyphenylene ether-based resin, a content ratio of the polyphenylene ether-based resin to the total mass of the resin of the first unit foam layer is lower than a content ratio of the polyphenylene ether-based resin to the total mass of the resin of the second unit foam layer; <1> ~ <4> 10. The polystyrene resin foam sheet according to claim 9, wherein the polystyrene resin foam sheet is a foam sheet having a diameter of 100 mm.

[0007] <6> <1> ~ <5> and a first non-foamed layer located on the one surface of the polystyrene-based resin foam sheet. [Effects of the Invention]

[0008] The polystyrene-based resin foam sheet of the present invention can suppress defects in appearance and has excellent impact resistance. [Brief explanation of the drawings]

[0009] [Figure 1] 1 is a cross-sectional view of a polystyrene-based resin foam sheet according to one embodiment of the present invention. [Figure 2] FIG. 2 is a cross-sectional view of a polystyrene-based resin foam sheet according to another embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0010] (Foam sheet) The polystyrene resin foamed sheet of the present invention (hereinafter, sometimes simply referred to as "foamed sheet") comprises a foamed layer. A foam sheet has a non-foamed layer on at least one side thereof to form a polystyrene-based resin laminated foam sheet (hereinafter, sometimes simply referred to as a "laminated foam sheet"). When the laminated foam sheet is molded into a container or the like, the side of the container that is required to be aesthetically pleasing (decorative side) is used. For example, if the container is for cooked food, the side with the non-foamed layer is used as the inner surface of the container. Also, for example, if the container is a bowl or the like, the side with the non-foamed layer is used as the outer surface of the container. That is, the surface of the foamed sheet on which the non-foamed layer is provided and which is required to have beauty after being formed into a container is designated as the surface to be decorated.

[0011] A foamed sheet according to one embodiment of the present invention will be described with reference to FIG. 1 is composed of a foam layer. The foam layer has a first unit foam layer 12 and a second unit foam layer 14 located on one side of the first unit foam layer 12. The first unit foam layer 12 forms one surface 13 of the foam layer 10. The second unit foam layer 14 forms the other surface 15 of the foam layer 10. In this embodiment, the one surface 13 is the surface to be decorated.

[0012] The thickness t10 of the foamed sheet 10 is determined appropriately taking into consideration the intended use, etc. The thickness t10 is, for example, preferably 0.5 to 3.0 mm, more preferably 1.0 to 2.5 mm, and even more preferably 1.0 to 2.0 mm. When the thickness t10 is equal to or greater than the above lower limit, the impact resistance and rigidity can be further improved. When the thickness t10 is equal to or less than the above upper limit, the reproducibility of the shape can be improved and poor appearance of the container surface can be prevented when the foamed sheet is thermoformed into a container, etc. (i.e., moldability can be improved). The thickness t10 is determined by, for example, measuring 10 points in an arbitrary direction (for example, the TD direction) using a dial thickness gauge, and averaging the measured values.

[0013] The basis weight of the foam sheet 10 is 50 to 250 g / m 2 is preferable, and 100 to 200 g / m 2 When the basis weight is equal to or greater than the lower limit, the impact resistance and rigidity can be further improved, and when the basis weight is equal to or less than the upper limit, the moldability can be improved. The basis weight can be measured by the following method. Excluding 20 mm from both ends of the width direction (TD direction) of the foam sheet 10, ten pieces of 10 cm x 10 cm are cut out at equal intervals in the width direction, and the mass (g) of each piece is measured to the nearest 0.001 g. The average mass (g) of each piece is calculated as 1 m 2 The value converted into the mass per unit area is used as the basis weight (g / m) of the foam sheet 10. 2 )

[0014] The apparent density of the foamed sheet 10 is, for example, 0.055 to 0.716 g / cm 3 is preferable, and 0.086 to 0.540 g / cm 3 More preferably, 0.130 to 0.363 g / cm 3 When the apparent density of the foamed sheet 10 is equal to or greater than the above lower limit, the impact resistance can be further improved. When the apparent density of the foamed sheet 10 is equal to or less than the above upper limit, the molded product can be made lighter and the heat insulating properties can be further improved.

[0015] The apparent density of foam sheet 10 can be measured in accordance with JIS K7222:2005 "Foamed plastics and rubber - Determination of apparent density." Specifically, the mass and apparent volume of a test piece of the foamed sheet 10 cut without changing the original cell structure are measured, and the mass and apparent volume are calculated using the following formula (1). Apparent density (g / cm 3 ) of the foam sheet 10 3 ) = mass of test piece (g) / apparent volume of test piece (cm 3 )···(1)

[0016] The arithmetic surface roughness Ra of one surface 13 is preferably 10 μm or less, and more preferably 6 μm or less. If the arithmetic mean roughness Ra of surface 13 is equal to or less than the above upper limit, the surface will be more beautiful. The lower limit of the arithmetic mean roughness Ra of surface 13 is substantially 2 μm or more. The arithmetic mean surface roughness Ra of the surface 13 can be measured in accordance with the method described in JIS B0601:2013.

[0017] The arithmetic surface roughness Ra of the other surface 15 is not particularly limited, but is preferably 20 μm or less, and more preferably 13 μm or less. The lower limit of the arithmetic mean roughness Ra of the surface 13 is substantially 6 μm or more. The arithmetic mean surface roughness Ra of surface 15 can be measured in the same manner as the arithmetic mean surface roughness Ra of surface 13 .

[0018] The arithmetic mean surface roughness Ra of the surface 13 is preferably equal to or smaller than the arithmetic mean surface roughness Ra of the surface 15 .

[0019] The glossiness of the one surface 13 is preferably 10 to 40%, more preferably 15 to 30%. When the glossiness is equal to or greater than the lower limit, the surface is more beautiful. When the glossiness is equal to or less than the upper limit, the formability is further improved. The gloss of surface 13 is measured by the method described in JIS Z8741:1997 "Specular Glossiness - Measurement Method." That is, using a handy gloss meter, Gloss Checker IG-320 (manufactured by Horiba, Ltd.), measurements are taken at five points across the width of the surface of the measurement sample (the outer surface of the foamed sheet) at a 60-degree angle of incidence (60 degrees), and the average value is taken as the gloss.

[0020] The glossiness of the other surface 15 is not particularly limited, but is preferably 3 to 30%, more preferably 3 to 20%. When the glossiness is equal to or greater than the lower limit, the surface is more beautiful. When the glossiness is equal to or less than the upper limit, the formability is further improved. The gloss of surface 15 can be measured in the same manner as the gloss of surface 13 .

[0021] The glossiness of surface 13 is preferably equal to or greater than the glossiness of surface 15 .

[0022] <First unit foam layer>

[0023] The first unit foam layer 12 contains a resin (first foam layer resin). The first unit foam layer 12 is a layer formed by foaming a first foamable resin composition containing a first foam layer resin and a foaming agent, and has bubbles formed in the layer. The first foam layer resin may contain a polystyrene-based resin (component (A1)). Examples of the resin other than component (A1) in the first foam layer resin include a first optional resin such as a polyphenylene ether resin (component (B1)) or a polyolefin resin.

[0024] Examples of the component (A1) include homopolymers of styrene-based monomers such as styrene, α-methylstyrene, vinyltoluene, chlorostyrene, ethylstyrene, i-propylstyrene, dimethylstyrene, and bromostyrene, as well as copolymers thereof. Examples of polystyrene-based resins include copolymers of styrene-based monomers and vinyl monomers polymerizable therewith, copolymers of styrene-based monomers and rubber components such as butadiene, and mixtures or polymers of homopolymers of styrene-based monomers or copolymers thereof, or copolymers of styrene-based monomers and vinyl monomers with diene-based rubber polymers, such as so-called high impact polystyrene (HIPS); and styrene-(meth)acrylic acid copolymers.

[0025] Component (A1) may be made from recycled materials in part or in whole. Examples of recycled materials include used polystyrene resin foam molded articles, such as fish boxes, cushioning materials for home appliances, and food packaging trays, which are recovered and regenerated using a limonene dissolution method or a thermal volume reduction method. Another example of recycled materials is scraps generated after punching food packaging containers from a foam sheet, which are crushed, melt-kneaded, and re-pelletized. Usable recycled raw materials include those obtained by recycling molded bodies such as used foam containers, as well as non-foamed polystyrene resins separated and recovered from home appliances (e.g., televisions, refrigerators, washing machines, air conditioners, etc.), office equipment (e.g., copiers, facsimiles, printers, etc.), etc. Component (A1) may be a virgin material other than a recycled material. Examples of virgin materials include general-purpose polystyrene resin (GPPS), commercially available polystyrene-based resins, and polystyrene-based resins newly prepared by methods such as suspension polymerization.

[0026] The weight average molecular weight Mw of the component (A1) is, for example, preferably 120,000 to 450,000, and more preferably 150,000 to 400,000. The weight average molecular weight Mw is a value measured by gel permeation chromatography (GPC) and converted based on a calibration curve using standard polystyrene.

[0027] The melt flow rate (MFR) of component (A1) is preferably 0.5 to 6.0 g / 10 min, and more preferably 0.7 to 3.0 g / 10 min. When the MFR of component (A1) is at least the lower limit, impact resistance can be further improved. When the MFR of component (A1) is at most the upper limit, moldability can be further improved. In this specification, MFR refers to a value measured in accordance with Method B described in JIS K7210:1999 "Test methods for melt mass-flow rate (MFR) and melt volume-flow rate (MVR) of plastics - thermoplastics" under conditions of a test temperature of 200°C, a test load of 49.03 N, and a preheating time of 5 minutes.

[0028] The content of the (A1) component in the first foam layer resin is preferably 70 to 98 mass %, more preferably 70 to 90 mass %, and even more preferably 80 to 90 mass %, based on the total mass of the first foam layer resin. When the content of the (A1) component is equal to or greater than the lower limit, rigidity can be further increased. When the content of the (A1) component is equal to or less than the upper limit, heat resistance can be further increased.

[0029] Component (B1) is a polyphenylene ether resin (PPE). Examples of component (B1) include poly(2,6-dimethylphenylene-1,4-ether), poly(2,6-diethylphenylene-1,4-ether), and poly(2,6-dichlorophenylene-1,4-ether).

[0030] The content of the (B1) component in the first foam layer resin (PPE content) is preferably 2 to 17 mass%, more preferably 5 to 17 mass%, and even more preferably 5 to 15 mass%. When the content of the (B1) component is equal to or greater than the above lower limit, the heat resistance of the first unit foam layer 12 can be improved. When the content of the (B1) component is equal to or less than the above upper limit, the rigidity of the first unit foam layer 12 can be improved.

[0031] The softening point of the first foam layer resin (i.e., the softening point of the first unit foam layer 12) is preferably 100 to 130°C, more preferably 105 to 120°C, and even more preferably 105 to 115°C. When the softening point of the first unit foam layer 12 is equal to or higher than the above lower limit, the heat resistance can be further improved. When the softening point of the first unit foam layer 12 is equal to or lower than the above upper limit, the average cell diameter can be suppressed, resulting in a more beautiful appearance.

[0032] The sum of the (A1) component and the (B1) component in the first foam layer resin is preferably 80% by mass or more, more preferably 95% by mass or more, and even more preferably 98% by mass or more, based on the total mass of the first foam layer resin, and may be 100% by mass.

[0033] The first optional resin may be a polyolefin resin, a hydrogenated styrene thermoplastic elastomer, or the like. Examples of polyolefin resins include polyethylene resins and polypropylene resins. Examples of hydrogenated styrene-based thermoplastic resin elastomers include styrene-butadiene-butylene-styrene block copolymer (SBBS), styrene-ethylene-butylene-styrene block copolymer (SEBS), styrene-ethylene-propylene-styrene block copolymer (SEPS), and styrene-ethylene-propylene-styrene block copolymer (SEEPS).

[0034] The first expandable resin composition contains a blowing agent (first blowing agent). Examples of the first blowing agent include hydrocarbons such as propane, butane, and pentane; and halogenated hydrocarbons such as tetrafluoroethane, chlorodifluoroethane, and difluoroethane. Hydrocarbons are preferred as the first blowing agent, and butane is preferred. As the butane, normal butane or isobutane may be used alone, or normal butane and isobutane may be used in combination in any ratio. These first blowing agents may be used alone or in combination of two or more.

[0035] The content of the first foaming agent in the first foamable resin composition is, for example, preferably 0.1 to 10 parts by mass, more preferably 1 to 7 parts by mass, and even more preferably 1 to 5 parts by mass, per 100 parts by mass of the first foam layer resin.

[0036] The first foamable resin composition may contain components other than the first foam layer resin and the foaming agent (hereinafter also referred to as "optional components of the first foam layer"). Examples of the optional components of the first foam layer include a cell regulator, a stabilizer, an ultraviolet absorber, an antioxidant, a colorant, a deodorizer, a lubricant, a flame retardant, an antistatic agent, and carbon. The type of optional component of the first foam layer is determined in consideration of the physical properties required for the first unit foam layer 12. The optional component of the first foam layer may be one type alone or a combination of two or more types.

[0037] The cell adjusting agent may be, for example, a mixture of inorganic powder such as talc or silica, etc. These cell adjusting agents can increase the closed cell ratio of the first unit foam layer 12. Examples of the stabilizer include calcium zinc-based heat stabilizers, tin-based heat stabilizers, and lead-based heat stabilizers. Examples of the ultraviolet absorber include cesium oxide-based ultraviolet absorbers and titanium oxide-based ultraviolet absorbers. Examples of antioxidants include cerium oxide, cerium oxide / zirconia solid solution, cerium hydroxide, titanium oxide, and fullerene. Examples of colorants (excluding carbon) include titanium oxide, carbon black, titanium yellow, iron oxide, ultramarine, cobalt blue, calcined pigments, metallic pigments, mica, pearl pigments, zinc oxide, precipitated silica, and cadmium red. Examples of deodorizing agents include silica, zeolite, zirconium phosphate, and calcined hydrotalcite. Examples of carbon include carbon, carbon nanotubes, carbon black, etc. By including carbon, the design properties can be further improved.

[0038] The content of the optional component for the first foam layer in the first foamable resin composition is, for example, preferably 0.05 to 20 parts by mass, more preferably 0.1 to 10 parts by mass, and even more preferably 0.3 to 5.0 parts by mass, per 100 parts by mass of the resin for the first foam layer. When the content of the optional component for the first foam layer is equal to or greater than the above-mentioned lower limit, the effects derived from the optional component for the first foam layer can be exhibited. When the content of the optional component for the first foam layer is equal to or less than the above-mentioned upper limit, clogging of the die or the like can be more effectively prevented, and the appearance of the foam sheet 10 can be improved.

[0039] The thickness t12 of the first unit foam layer 12 can be determined in consideration of the intended use, and is, for example, preferably 250 to 1500 μm, more preferably 500 to 1000 μm. The thickness t12 of the first unit foam layer 12 is the average value of thicknesses at 10 points randomly selected by cross-sectional observation.

[0040] The basis weight of the first unit foam layer 12 is 25 to 150 g / m 2 is preferable, and 35 to 100 g / m 2 When the basis weight is equal to or greater than the lower limit, the impact resistance and rigidity can be further improved, and when the basis weight is equal to or less than the upper limit, the moldability can be improved when a molded article is formed by thermoforming. The basis weight of the first unit foam layer 12 can be measured in the same manner as the basis weight of the foam sheet 10 .

[0041] The apparent density of the first unit foam layer 12 is, for example, 0.055 to 0.716 g / cm 3 is preferable, and 0.086 to 0.540 g / cm 3 More preferably, 0.130 to 0.363 g / cm 3 When the apparent density of the first unit foam layer 12 is equal to or greater than the above lower limit, the impact resistance can be further improved. When the apparent density of the first unit foam layer 12 is equal to or less than the above upper limit, the molded body can be made lighter and the heat insulating property can be further improved. The apparent density of the first unit foam layer 12 can be measured in the same manner as the apparent density of the foam sheet 10 .

[0042] The expansion ratio of the first unit foam layer 12 is, for example, preferably 2 to 18 times, more preferably 5 to 15 times, and even more preferably 3 to 10 times. When the expansion ratio of the first unit foam layer 12 is equal to or greater than the above lower limit, the molded article can be made lighter and the heat insulating properties can be further improved. When the expansion ratio of the first unit foam layer 12 is equal to or less than the above upper limit, the impact resistance can be further improved. The expansion ratio is the value obtained by dividing 1 by the apparent density.

[0043] The average cell diameter of the first unit foam layer 12 is preferably 100 to 300 μm, more preferably 150 to 300 μm, and even more preferably 150 to 200 μm. When the average cell diameter of the first unit foam layer 12 is equal to or greater than the above lower limit, moldability can be further improved. When the average cell diameter of the first unit foam layer 12 is equal to or less than the above upper limit, aesthetics can be further improved. The average cell diameter can be adjusted by the content of component (B1), the type and amount of a cell regulator, or a combination thereof. The method for determining the average cell diameter of the first unit foam layer 12 will be described later.

[0044] The softening point of the first unit foam layer 12 (i.e., the softening point of the first foam layer resin) is preferably 100 to 130°C, more preferably 105 to 120°C, and even more preferably 105 to 115°C. When the softening point of the first unit foam layer 12 is equal to or higher than the lower limit, deformation of the container during heating can be more effectively suppressed. When the softening point of the first unit foam layer 12 is equal to or lower than the upper limit, the surface to be decorated can be made more beautiful.

[0045] The softening point of the first unit foam layer 12 is a value measured as a glass transition temperature (Tg) by the following measurement method.

[0046] <Method for measuring glass transition temperature> The method for measuring the glass transition temperature will be described below. <Pretreatment> A sample of 5 to 6 g is weighed out from the first unit foam layer 12, sandwiched between two polytetrafluoroethylene sheets, and pressed in the following manner to defoam (pretreatment). Press equipment: Small press equipment "Lab Press 10T" manufactured by Toyo Seiki Co., Ltd. Temperature: Upper heater 180℃, lower heater 180℃. Pressing process: Pressing is performed at 0.54 MPa for 3 minutes, followed by 5 cycles of pressing at 0.54 MPa for 2 seconds and pressure release for 2 seconds. Then, pressing is performed at 15.5 MPa for 2 minutes.

[0047] <Measurement of glass transition temperature (Tg)> The glass transition temperature (midpoint glass transition temperature) of the pretreated sample is measured by the method described in JIS K7121:1987 "Method for measuring transition temperature of plastics." However, the sampling method and temperature conditions shall be as follows: Using a differential scanning calorimeter "DSC6220" (manufactured by SII NanoTechnology Inc.), approximately 6 mg of sample is packed into the bottom of an aluminum measurement container so that there are no gaps. The sample is heated from 30°C to 220°C at a heating rate of 20°C / min under a nitrogen gas flow rate of 20 mL / min. After heating, the sample is held for 10 minutes, then quickly removed and allowed to cool in an environment of 25±10°C. After cooling, the sample is heated from 30°C to 220°C at a heating rate of 20°C / min, and the midpoint glass transition temperature is calculated from the DSC curve obtained. In this case, alumina is used as the reference material. The midpoint glass transition temperature is determined according to the standard (9.3 "Determination of glass transition temperature").

[0048] <Second unit foam layer> The second unit foam layer 14 is a layer formed by foaming a second foamable resin composition containing a second foam layer resin and a foaming agent (second foaming agent), and has bubbles formed in the layer. The second foam layer resin may contain a polystyrene-based resin (component (A2)). Examples of the resin other than component (A2) in the second foam layer resin include a second optional resin such as a polyphenylene ether resin (component (B2)) or a polyolefin resin.

[0049] The component (A2) is the same as the component (A1). The component (A2) may be the same as or different from the component (A1).

[0050] The content of the (A2) component in the second foam layer resin is preferably 50 to 90 mass %, more preferably 60 to 90 mass %, and even more preferably 70 to 90 mass %, based on the total mass of the second foam layer resin. When the content of the (A2) component is equal to or greater than the lower limit, rigidity can be further increased. When the content of the (A1) component is equal to or less than the upper limit, heat resistance can be further increased.

[0051] The component (B2) is the same as the component (B1). The component (B2) may be the same as or different from the component (B1).

[0052] The content of component (B2) in the resin for the second foam layer (PPE content) is preferably 10 to 40 mass %, more preferably 10 to 35 mass %, and even more preferably 25 to 35 mass %, based on the total mass of the resin for the second foam layer. When the content of component (B2) is equal to or greater than the lower limit, heat resistance can be further improved. When the content of component (B2) is equal to or less than the upper limit, rigidity can be further improved.

[0053] The content of component (B2) in the resin for the second foam layer (B2 mass%) is preferably greater than the content of component (B1) in the resin for the first foam layer (B1 mass%). The difference in content (B2 mass%), expressed as [B2 mass%] - [B1 mass%], is preferably 6 to 17, more preferably 6 to 14, and even more preferably 3 to 10. When the difference in content is within the above range, the decorative surface of the resulting container can be made more beautiful and moldability can be improved. If the difference in content is too large, the difference in softening point between the first unit foam layer 12 and the second unit foam layer 14 becomes too large during secondary foaming of the foam sheet 10, resulting in delamination between the layers.

[0054] The type and content of the second blowing agent are the same as those of the first blowing agent, and may be the same as or different from those of the first blowing agent.

[0055] The second foamable resin composition may contain other components (hereinafter also referred to as "second foam layer optional components") in addition to the second foam layer resin and the second foaming agent. The second foam layer optional components are the same as the first foam layer optional components. The second foam layer optional components may be the same as or different from the first foam layer optional components.

[0056] The content of the optional component for the second foam layer in the second foamable resin composition is the same as the content of the optional component for the first foam layer in the first foamable resin composition. The content of the optional component for the second foam layer in the second foamable resin composition may be the same as or different from the content of the optional component for the first foam layer in the first foamable resin composition.

[0057] The thickness t14 of the second unit foam layer 14 is the same as the thickness t12 of the first unit foam layer 12. The thickness t14 of the second unit foam layer 14 may be the same as or different from the thickness t12 of the first unit foam layer 12. The thickness t14 of the second unit foam layer 14 can be measured in the same manner as the thickness t12 of the first unit foam layer 12.

[0058] The basis weight of the second unit foam layer 14 is 25 to 150 g / m 2 is preferable, and 35 to 100 g / m 2 When the basis weight is equal to or greater than the lower limit, the impact resistance and rigidity can be further improved, and when the basis weight is equal to or less than the upper limit, the moldability can be improved when a molded article is formed by thermoforming. The basis weight of the second unit foam layer 14 can be measured in the same manner as the basis weight of the foam sheet 10 .

[0059] The apparent density of the second unit foam layer 14 is, for example, 0.055 to 0.716 g / cm 3 is preferable, and 0.086 to 0.540 g / cm 3 More preferably, 0.130 to 0.363 g / cm 3When the apparent density of the second unit foam layer 14 is equal to or greater than the above lower limit, the impact resistance can be further improved. When the apparent density of the second unit foam layer 14 is equal to or less than the above upper limit, the molded body can be made lighter and the heat insulating property can be further improved. The apparent density of the second unit foam layer 14 can be measured in the same manner as the apparent density of the foamed sheet 10 .

[0060] The expansion ratio of the second unit foam layer 14 is, for example, preferably 2 to 20 times, more preferably 10 to 20 times, and even more preferably 10 to 18 times. When the expansion ratio of the second unit foam layer 14 is equal to or greater than the above lower limit, the molded article can be made lighter and the heat insulating properties can be further improved. When the expansion ratio of the second unit foam layer 14 is equal to or less than the above upper limit, the impact resistance can be further improved.

[0061] The average cell diameter of the second unit foam layer 14 is preferably 120 to 400 μm, more preferably 200 to 400 μm, and even more preferably 200 to 300 μm. When the average cell diameter of the second unit foam layer 14 is equal to or greater than the lower limit, moldability can be improved. When the average cell diameter of the second unit foam layer 14 is equal to or less than the upper limit, the other surface 15 can be made beautiful. The average cell diameter can be adjusted by the content of component (B2), the type and amount of the cell regulator, or a combination thereof. The average cell diameter of the second unit foam layer 14 can be measured in the same manner as the average cell diameter of the first unit foam layer 12 .

[0062] The softening point of the second unit foam layer 14 (i.e., the softening point of the second foam layer resin) is preferably 105 to 135°C, more preferably 110 to 130°C, and even more preferably 115 to 125°C. When the softening point of the second unit foam layer 14 is equal to or higher than the lower limit, deformation of the container during heating can be more effectively suppressed. When the softening point of the second unit foam layer 14 is equal to or lower than the upper limit, moldability can be improved. The softening point of the second unit foam layer 14 can be measured in the same manner as the softening point of the first unit foam layer 12 .

[0063] The softening point of the second unit foamed layer 14 is higher than that of the first unit foamed layer 12. Since the softening point of the second unit foamed layer 14 is higher than that of the first unit foamed layer 12, the surface to be decorated can be made beautiful. The Tg difference represented by [the softening point of the second unit foamed layer 14] - [the softening point of the first unit foamed layer 12] is preferably 0 to 25°C, more preferably 2 to 20°C, still more preferably 5 to 20°C, and particularly preferably 5 to 15°C. When the Tg difference is within the above range, the surface to be decorated can be made more beautiful. If the Tg difference is too large, when the foamed sheet 10 is secondarily foamed, the difference in softening points between the first unit foamed layer 12 and the second unit foamed layer 14 is too large, resulting in delamination between the layers.

[0064] The average cell diameter of the second unit foamed layer 14 is preferably 120 to 400 μm, more preferably 200 to 400 μm, and still more preferably 200 to 300 μm. When the average cell diameter of the second unit foamed layer 14 is at least the above lower limit value, the formability can be further enhanced. When the average cell diameter of the second unit foamed layer 14 is at most the above upper limit value, the decorative surface of the container can be made more beautiful. The average cell diameter can be adjusted by the content of the (B2) component, the type and amount of the cell regulator, and combinations thereof. The average cell diameter of the second unit foamed layer 14 can be measured in the same manner as the average cell diameter of the first unit foamed layer 12.

[0065] The average cell diameter r1 of the first unit foamed layer 12 is smaller than the average cell diameter r2 of the second unit foamed layer 14. Since the average cell diameter r1 is smaller than the average cell diameter r2 (r1 < r2), the surface to be decorated can be made beautiful. The cell diameter difference represented by [average cell diameter r2] - [average cell diameter r1] is preferably 10 to 100 μm, more preferably 30 to 90 μm, and still more preferably 30 to 70 μm. When the cell diameter difference is at least the above lower limit value, the decorative surface of the container can be made more beautiful. When the cell diameter difference is at most the above upper limit value, the adhesive strength between the first unit foamed layer 12 and the second unit foamed layer 14 can be further enhanced.

[0066] <Method for manufacturing the foamed sheet> An example of the method for manufacturing the foamed sheet 10 will be described. The first foamable resin composition is melt-kneaded, and the kneaded mixture is extruded into a sheet and foamed to obtain the first foamed layer unit 12. In this case, the component (B1) may be blended in the form of a masterbatch, which is a mixture with the component (A1). The second foamable resin composition is melt-kneaded, and the kneaded mixture is extruded into a sheet and foamed to obtain the second foamed layer unit 14. In this case, the component (B2) may be blended in the form of a masterbatch, which is a mixture with the component (A2). Next, the first unit foam layer 12 and the second unit foam layer 14 are bonded together to form the foam layer 10. As a method for bonding the first unit foam layer 12 and the second unit foam layer 14 together, for example, a method for heat-sealing the first unit foam layer 12 and the second unit foam layer 14 can be mentioned.

[0067] Alternatively, the first and second foamable resin compositions may be melt-kneaded, co-extruded, and cooled to produce the foamed sheet 10 having the first unit foam layer 12 and the second unit foam layer 14.

[0068] According to the foamed sheet of the present embodiment, the average cell diameter of the first unit foam layer is smaller than the average cell diameter of the second unit foam layer, so that the surface to be decorated can be made beautiful. In addition, by making the softening point of the first foamed layer unit lower than that of the second foamed layer unit, the surface to be decorated can be made more beautiful.

[0069] (Polystyrene resin laminated foam sheet) The polystyrene resin laminate foam sheet (laminated foam sheet) of the present invention has a non-foamed layer on one surface (the surface to be decorated) or on both surfaces of the foam sheet of the present invention.

[0070] A laminated foam sheet according to one embodiment of the present invention will be described with reference to FIG. The laminated foam sheet 1 in Figure 2 has a foam sheet 10, a first non-foamed layer 20 located on one surface (the surface to be decorated) 13 of the foam sheet 10, and a second non-foamed layer 30 located on the other surface 15 of the foam sheet 10. In this embodiment, the foam sheet (foam layer) 10 is in close contact with the first non-foam layer 20 and the second non-foam layer 30.

[0071] The thickness t1 of the laminated foam sheet 1 is, for example, preferably 1.0 to 3.0 μm, more preferably 1.3 to 2.3 μm. When the thickness t1 is equal to or greater than the above lower limit, rigidity can be increased. When the thickness t1 is equal to or less than the above upper limit, moldability can be increased. The thickness t1 of the laminated foam sheet 1 can be measured in the same manner as the thickness t10 of the foam sheet 10.

[0072] <First non-foamed layer> In this embodiment, the first non-foamed layer 20 is located on the intended decoration surface 13 of the foamed layer 10. By including the first non-foamed layer 20, the laminated foamed sheet 1 can further improve aesthetics and moldability.

[0073] The first non-foamed layer 20 is a layer formed by curing a first non-foamable resin composition containing a first non-foamed layer resin. The first non-foamed layer 20 may be a non-stretched film, a stretched film, or a laminate thereof. That is, the first non-foamed layer 20 may be a single layer or may have a multi-layer structure of two or more layers. When the first non-foamed layer 20 is multi-layered, for example, it may be a combination of an unstretched polypropylene-based resin film (surface) and an unstretched polystyrene-based resin film (side 13). When the first non-foamed layer 20 is multi-layered, a printed layer may be located between the layers.

[0074] Examples of the resin for the first non-foamed layer include polyolefin resins, polystyrene resins, and polyester resins. Examples of polyolefin resins include polypropylene resins and polyethylene resins. Examples of the polystyrene resin include those similar to those used for the component (A1). The polystyrene resin of the first non-foamed layer resin may be the same as or different from the component (A1). Examples of polyester resins include polyethylene terephthalate resins. The above-mentioned first non-foamed layer resin may be used alone or in combination of two or more.

[0075] The first non-foamable resin composition may contain optional components (optional components for the first non-foamable layer) other than the resin for the first non-foamable layer. Examples of optional components of the first non-foamed layer include stabilizers, ultraviolet absorbers, antioxidants, colorants, deodorants, lubricants, flame retardants, antistatic agents, and carbon. The type of optional component of the first non-foamed layer is determined taking into consideration the physical properties required for the first unit non-foamed layer 22. The optional component of the first non-foamed layer may be one type alone or a combination of two or more types.

[0076] The thickness t20 of the first non-foamed layer 20 is determined appropriately taking into consideration the intended use, etc. The thickness t20 is, for example, preferably 10 to 80 μm, more preferably 10 to 60 μm, even more preferably 20 to 60 μm, and particularly preferably 20 to 45 μm. When the thickness t20 is equal to or greater than the above lower limit, strength can be increased and the product can be made more beautiful. When the thickness t20 is equal to or less than the above upper limit, moldability can be increased and environmental impact can be reduced. The thickness t20 can be measured in the same manner as the thickness t10.

[0077] The basis weight of the first non-foamed layer 20 is 10 to 100 g / m 2 is preferable, and 20 to 70 g / m 2 When the basis weight is equal to or greater than the lower limit, the impact resistance and rigidity can be further improved, and when the basis weight is equal to or less than the upper limit, the moldability can be improved. The basis weight of the first non-foamed layer 20 can be measured in the same manner as the basis weight of the foamed sheet 10 .

[0078] <Second non-foamed layer> The second non-foamed layer 30 of this embodiment is located on the other surface 15 of the foamed layer 10. By including the second non-foamed layer 30, the laminated foamed sheet 1 can further improve its strength.

[0079] The second non-foamed layer 30 is similar to the first non-foamed layer 20. The second non-foamed layer 30 may be the same as the first non-foamed layer 20 or may be different.

[0080] The thickness t30 of the second non-foamed layer 30 is the same as the thickness t20 of the first non-foamed layer 20. The thickness t30 of the second non-foamed layer 30 may be the same as or different from the thickness t20 of the first non-foamed layer 20.

[0081] The basis weight of the second non-foamed layer 30 is the same as the basis weight of the first non-foamed layer 20. The basis weight of the second non-foamed layer 30 may be the same as or different from the basis weight of the first non-foamed layer 20.

[0082] <Manufacturing method> An example of a method for producing the laminated foam sheet 1 will be described.

[0083] A first non-foamed layer 20 is provided on one surface 13 of the foamed sheet 10 . The first non-foamed layer 20 may be formed by extruding the first non-foamed resin composition onto one surface 13 using a T-die and curing the extruded first non-foamed resin composition. Alternatively, a non-foamed sheet is obtained by a conventional method, and this non-foamed sheet is fused to the foamed sheet 10 by heat fusion or the like to form the first non-foamed layer 20 .

[0084] A second non-foamed layer 30 is provided on the other surface 15 of the foamed sheet 10 . The second non-foamed layer 30 may be formed by extruding the second non-foamed resin composition onto the other surface 15 using a T-die and curing the extruded second non-foamed resin composition. Alternatively, a non-foamed sheet may be obtained by a conventional method, and this non-foamed sheet may be fused to the foamed sheet 10 by heat fusion or the like to form the second non-foamed layer 30 .

[0085] As described above, the laminated foam sheet of this embodiment has a foam layer having a first unit foam layer forming one side and a second unit foam layer forming the other side, the average cell diameter of the first unit foam layer is smaller than the average cell diameter of the second unit foam layer, and the first non-foamed layer is located on one side of the foam layer. Therefore, a container having the first non-foamed layer as a decorative surface is beautiful.

[0086] The laminated foam sheet of this embodiment is suitable as a sheet for thermoforming. Examples of thermoforming methods include conventionally known thermoforming methods such as vacuum forming, pressure forming, and their applications, such as free drawing forming, plug and ridge forming, ridge forming, matched mold forming, straight forming, drape forming, reverse draw forming, air slip forming, plug assist forming, and plug assist reverse load forming.

[0087] (Other embodiments) In the above-described embodiment, the foam layer has a two-layer structure, but the present invention is not limited thereto, and the foam layer may have three or more layers as long as the first unit foam layer forms one side and the second unit foam layer forms the other side. However, from the viewpoints of moldability and productivity of the foam sheet, the layer structure of the foam layer is preferably 1 to 3 layers, more preferably 1 to 2 layers.

[0088] In the above-described embodiment, the non-foamed layer is located on both sides of the foam sheet. However, the present invention is not limited to this, and the laminated foam sheet may have a non-foamed layer only on one side (the surface to be decorated) of the foam sheet. [Example]

[0089] The present invention will be explained in more detail below with reference to examples, but the present invention is not limited to these examples. In the tables, "-" indicates that the component was not blended. (Raw materials used) <Resin> -PS (polystyrene): Product name "HRM26", manufactured by Toyo Styrene Co., Ltd. PPE-MB: "Noryl EFN4230" (product name) manufactured by Sabic Corporation. Polyphenylene ether (PPE) = 70% by mass, polystyrene = 30% by mass. Talc MB: Kneaded masterbatch (product name "DSM1401M"), manufactured by Toyo Styrene Co., Ltd. Talc = 40% by mass, polystyrene = 60% by mass. <Foaming agent> Mixed butane: a mixture of isobutane and normal butane in a ratio of 70 / 30 by mass.

[0090] (Examples 1 to 9, Comparative Examples 1 to 4) A foamed sheet similar to foamed sheet 10 in FIG. 1 was obtained by the following procedure. Two tandem extruders were prepared, each consisting of a single-screw extruder with a screw diameter of 90 mm and a single-screw extruder with a screw diameter of 150 mm arranged in series, with the single-screw extruder with a screw diameter of 90 mm positioned upstream. These extruders were connected to a circular die via a merging die. That is, the first foamable resin composition was supplied to the first tandem extruder of the two tandem extruders and melt-kneaded therein, and the second foamable resin composition was supplied to the second tandem extruder and melt-kneaded therein, and the melt-kneaded products discharged from these tandem extruders were prepared so as to be co-extruded from a circular die.

[0091] According to the composition in Table 1, the resins of the first expandable resin composition were charged into a batch mixer and mixed, and then the mixture was supplied to the upstream extruder (screw diameter 90 mm) of the first tandem extruder system. In the upstream extruder, the maximum cylinder temperature was set to 290°C, and the amount of foaming agent shown in the table was added midway through the process, and the foaming agent was melt-kneaded with the resin to form a molten mixture (first foamable resin composition), which was then supplied to the downstream extruder. In the downstream extruder, the first expandable resin composition fed from the upstream extruder was fed to the joining die at a rate of 120 kg / h.

[0092] Furthermore, according to the composition in Table 1, the resin of the second expandable resin composition was charged into a batch mixer, mixed, and then the mixture was supplied to the upstream extruder (screw diameter 90 mm) of the second tandem extruder system. In the upstream extruder, the maximum cylinder temperature was set to 300°C, and the amount of foaming agent shown in the table was added midway through the process, and the foaming agent was melt-kneaded with the resin to form a molten mixture (second foamable resin composition), which was then supplied to the downstream extruder. In the downstream extruder, the second expandable resin composition fed from the upstream extruder was fed to the joining die at a rate of 120 kg / h.

[0093] The first and second foamable resin compositions were joined in a joining mold, laminated, and then extruded (co-extruded) into a cylindrical shape through a circular die with a diameter of 175 mm so that the first foamable resin composition was on the outside and the second foamable resin composition was on the inside. Immediately after this, air was blown onto the inside and outside of the extrusion foam to cool it down and form a cylindrical foam. The air temperature was set to 27°C, and the amount of air blown was set to 0.08 m on the outside (first foamable resin composition side). 3 / m 2 and 0.06 m on the inside (second resin composition side). 3 / m 2 It was decided. After cooling, the cylindrical foam was cut open to obtain a foam sheet consisting of only the foam layer. In Comparative Example 2, a single-layer foamed sheet was used. The foam sheets were stored for 14 days after production to allow for replacement of the foaming gas. Then, a film (CPP / CPS 45 μm plain (product name)) dry-laminated with 25 μm CPP (non-oriented polypropylene) and 20 μm CPS (Oishi Sangyo SPH) was laminated to one side (the side of the first unit foam layer), and a CPS (non-oriented polystyrene) film (20 μm thick, Oishi Sangyo SPH) was heat-laminated to the other side (the side of the second unit foam layer) of the foam sheet to obtain laminated foam sheets for each example.

[0094] For each unit foam layer of the obtained foamed sheet, the average cell diameter, PPE content, glass transition temperature (Tg), expansion ratio, thickness, basis weight, average cell diameter difference, Tg difference, gloss, and arithmetic surface roughness Ra were determined and are shown in the table. In addition, the laminated foam sheet of each example was evaluated for heat resistance, appearance and moldability, and the results are shown in the table.

[0095] (Measurement method) <Average bubble diameter> The average cell diameter of the foamed sheet was determined as follows. The foamed sheet was cut perpendicular to the surface from the center in the width direction along the MD direction (extrusion direction) and the TD direction (direction perpendicular to the extrusion direction). The cross section was photographed at 50x magnification using a scanning electron microscope (SU1510, Hitachi High-Technologies Corporation). The microscope images were taken so that the desired magnification would be obtained when two images (a total of four images) were printed side by side on a single A4 sheet of paper in landscape orientation. Specifically, 60-mm arbitrary lines parallel to each of the MD and TD directions and a 60-mm line perpendicular to each direction (VD direction) were drawn on the image. Microscopic images of two fields of view for each cross section cut along the MD direction (MD cross section) and the TD cross section (TD cross section), totaling four fields of view, were captured and printed on A4 paper. Three arbitrary lines (60 mm long) parallel to the MD direction were drawn on each of the two MD cross section images, and three arbitrary lines (60 mm long) parallel to the TD direction were drawn on each of the two TD cross section images. Three lines (60 mm long) parallel to the VD direction were also drawn on one MD cross section image and one TD cross section image, and six 60-mm arbitrary lines parallel to the MD, TD, and VD directions were drawn in each direction. The lines were drawn with care to avoid contact with air bubbles at their contact points as much as possible. If contact did occur, these air bubbles were also counted. The number of bubbles D counted along six arbitrary straight lines in each of the MD, TD, and VD directions was calculated as the arithmetic mean, and the number of bubbles in each direction was calculated. The average chord length t of the bubbles was calculated using equation (s1) from the image magnification at which the number of bubbles was counted and the number of bubbles.

[0096] Average chord length t (mm) = 60 / (number of bubbles × image magnification) (s1)

[0097] The image magnification was calculated by measuring the scale bar on the image to 1 / 100 mm using a Digimatic caliper (Mitutoyo Corporation) and using the following formula: Image magnification = Actual scale bar value (mm) / Displayed scale bar value (mm).

[0098] The bubble diameter in each direction was calculated using equation (s2). Bubble diameter D (mm) = t / 0.616 (s2)

[0099] Furthermore, the cube root of the product of these values ​​was defined as the average bubble diameter (equation (s3)). Average bubble diameter (mm) = (DMD x DTD x DVD) 1 / 3 (s3) DMD: bubble diameter in MD direction (mm). DTD: bubble diameter in TD direction (mm). DVD: Bubble diameter in the VD direction (mm).

[0100] <Appearance> The foamed sheet of each example was visually observed and evaluated for appearance according to the following evaluation criteria. <Evaluation Criteria> ◯: No resin lumps or streaks are formed on the surface, and the appearance is beautiful. ×: Resin lumps and streaks were observed on the surface, and the appearance was beautiful.

[0101] <Heat resistance> Using the laminated foam sheets of each example, a bowl-shaped container was produced with an opening inner diameter of 160 mm, a bottom inner diameter of 110 mm, a depth of 50 mm, and a drawing ratio of 0.31. A foamed container was produced by continuously supplying a foamed sheet to a press molding device having a cavity (concave mold) with 5 x 5 = 25 recesses corresponding to the outer shape of the foamed container and a plug (convex mold) with the same number of protrusions corresponding to the inner shape of the container. The molding conditions were a molding cycle of 10.0 seconds for one shot (=25 pieces), a heater temperature setting of 320°C on the cavity side, and a heater temperature setting of 350°C on the plug side. The timing of molding was set so that the cavity and the plug came into contact with the laminated polystyrene resin foam sheet at almost the same time, and molding was initiated. The appearance of the sample heated with a heater was visually inspected and evaluated according to the following evaluation criteria.

[0102] <Evaluation Criteria> ○: The appearance is smooth and good. ×: Blisters and the like occurred, and the product was defective.

[0103] <Moldability> The laminated foam sheet of each example was fed into a preheating device equipped with heaters, and both sides of the laminated foam sheet were heated to soften it. The laminated foam sheet was then deformed along a mold to produce a container. The heaters of the preheating device faced both sides of the laminated foam sheet. At this time, the other surface was thermoformed so as to become the inside of the container. The container was a rectangular tray with a long side of 200 mm, a short side of 100 mm, and a depth of 30 mm. The appearance of the resulting container was visually inspected and evaluated according to the following evaluation criteria.

[0104] <Evaluation Criteria> A: The inside of the container is smooth, there are no cracks or breaks in the container, and the thickness is uniform throughout when visually inspected (no locally thin areas are visible). B: There are no cracks or breaks in the container, but it is poorly stretched and has thin areas. C: Surface cracks called "naki" have occurred on the inner surface of the container, or the first and second unit foam layers have peeled off from each other, making the container unusable.

[0105] [Table 1]

[0106] As shown in Table 1, the appearance of all of Examples 1 to 9 to which the present invention was applied was evaluated as "good." Comparative Examples 1 to 3, in which the average cell diameter difference was 0, and Comparative Example 2, which was a single layer, were evaluated as "x" in terms of appearance. [Explanation of symbols]

[0107] 1 Polystyrene resin laminated foam sheet 10 Polystyrene resin foam sheet 12 First unit foam layer 14 Second unit foam layer 20 First non-foam layer 30 Second non-foam layer

Claims

1. a foam layer having a first unit foam layer and a second unit foam layer located on one surface of the first unit foam layer, the surface of the first unit foam layer forms one side of the foam layer; the surface of the second unit foam layer forms the other surface of the foam layer; A polystyrene-based resin foam sheet, wherein the first unit foam layer has an average cell diameter smaller than the average cell diameter of the second unit foam layer.

2. 2. The polystyrene-based resin foam sheet according to claim 1, wherein a difference between an average cell diameter of the first unit foam layer and an average cell diameter of the second unit foam layer is 10 to 100 μm.

3. The polystyrene-based resin foam sheet according to claim 1 , wherein the first unit foam layer has a softening point lower than that of the second unit foam layer.

4. 4. The polystyrene-based resin foam sheet according to claim 3, wherein a difference between a softening point of the first unit foam layer and a softening point of the second unit foam layer is 0 to 25°C.

5. the first unit foam layer contains a polystyrene-based resin and a polyphenylene ether-based resin, the second unit foam layer contains a polystyrene-based resin and a polyphenylene ether-based resin, 2. The polystyrene-based resin foam sheet according to claim 1, wherein a content ratio of the polyphenylene ether-based resin to a total mass of resins of the first unit foam layer is lower than a content ratio of the polyphenylene ether-based resin to a total mass of resins of the second unit foam layer.

6. A laminated polystyrene resin foam sheet comprising: the polystyrene resin foam sheet according to any one of claims 1 to 5; and a first non-foamed layer located on the one surface of the polystyrene resin foam sheet.

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