Abstract: Provided is an extruded polystyrene foam which is obtained by extrusion foaming using a polystyrene resin and a foaming agent, contains 0.5-8.0 parts by weight of a flame retardant based on 100 parts by weight of the polystyrene resin and has an apparent density of 20-45 kg/m3 and a closed cell ratio of 90% or more. The foaming agent contains HFO and an additional organic foaming agent. The amount of HFO is 0.030-0.125 mol/per 100 g of the polystyrene resin, polystyrene permeability of the additional organic foaming agent is 0.5×10?10 cc·cm/cm2·s·cmHg or more, an organic foaming agent having a polystyrene permeability of less than 0.5×10?10 cc·cm/cm2·s·cmHg is not included, and the total amount of HFO and the additional organic foaming agent is 0.105-0.300 mol/per 100 g of the polystyrene resin.

Abstract: A method for producing an extruded polystyrene foam in which when a foamable melted product, obtained by heat-melting a styrene resin composition and adding a foaming agent thereto in an extruder provided with a die slit section having an opening a (mm) in the thickness direction, is extrusion-foamed through the die slit section into a low pressure zone to form a plate-shaped foam, thereby obtaining an extruded polystyrene foam having a density of 20 kg/m3 or more and 45 kg/m3 or less, a closed cell ratio of 90% or more, and a thickness A (mm) of 10 mm or more and 150 mm or less, a foaming agent containing hydrofluoroolefin and other organic foaming agent is used, a thickness extension ratio A/a of an opening a in the thickness direction of the die slit section and a thickness A of the extruded polystyrene foam is adjusted to 18 or less, and a foamable melted product, just before the extrusion from the die slit section, is pressurized to 4.5 MPa or more and 10.0 MPa or less.

Abstract: An extruded polystyrene foam which is obtained by performing extrusion foaming using a styrene resin and a foaming agent, contains a flame retardant in a proportion of 0.5 parts by weight or more and 8.0 parts by weight or less based on 100 parts by weight of the styrene resin and has an apparent density of 20 kg/m3 or more and 45 kg/m3 or less and a closed cell ratio of 90% or more, in which the foaming agent at least contains HFO and another organic foaming agent, (i) the blended amount of the HFO is 0.030 mol or more and 0.125 mol or less based on 100 g of the styrene resin, (ii) an organic foaming agent having a polystyrene permeability of 0.5×10?10 cc·cm/cm2·s·cmHg or more is contained as the another organic foaming agent, (iii) an organic foaming agent having a polystyrene permeability of less than 0.5×10?10 cc·cm/cm2·s·cmHg is not contained as the another organic foaming agent, and (iv) the total blended amount of the HFO and the another organic foaming agent is 0.105 mol or more and 0.