A rigid polymer foam having specific characteristics in terms of resin absorption, and a structural element made from such rigid polymer foam and adapted to be used as a core layer in a multilayer structural element.

In one embodiment, a method of forming an extruded board includes mixing a resin and a foaming agent, melting the mixed resin and foaming agent to form a uniformly colored extrudate, differentially expanding voids formed from the foaming agent within the uniformly colored extrudate by passing the uniformly colored extrudate through a breaker plate, forming a board with the differentially expanded voids and uniformly colored extrudate, and forming lightened portions on an outermost surface of the formed board.

In one embodiment, a method of forming an extruded board includes mixing a resin and a foaming agent, melting the mixed resin and foaming agent to form a uniformly colored extrudate, differentially expanding voids formed from the foaming agent within the uniformly colored extrudate by passing the uniformly colored extrudate through a breaker plate, forming a board with the differentially expanded voids and uniformly colored extrudate, and forming lightened portions on an outermost surface of the formed board.

A process for producing split crosslinked polyolefin sheets comprises producing a crosslinked polyolefin foam sheet having an opposing first surface region and second surface region, and an intermediate region disposed therebetween, wherein the intermediate region is configured to have a gel content lower than an average gel content of the first surface region and the second surface region, and an average cell size larger than an average cell size of the first surface region and the second surface region; and applying a splitting force to the crosslinked foam sheet such that a controlled tear propagation travels through the intermediate region until a first side of the crosslinked polyolefin foam sheet and a second side of the crosslinked polyolefin foam sheet are separated to produce two split polyolefin foam sheets. The split crosslinked polyolefin foam sheets may comprise a skin side comprising a closed cell surface, and a split side comprising an open cell surface having peak heights of about 150 ?m to about 550 ?m.

The present invention is a phenolic resin foam board having a thickness of 40 mm or more to 300 mm or less, when the phenolic resin foam board is sliced into n pieces (n5) at approximately equal intervals of 8 mm or more to 10 mm or less, a density of an n-th specimen is d.sub.n, an average density of n pieces of specimens is d.sub.ave, a lowest density among the densities of n pieces of specimens is d.sub.min, 0(d.sub.aved.sub.min)/d.sub.ave0.12 is established, and when values for D.sub.i=(d.sub.i+d.sub.(i+1))/2 are calculated, D.sub.i values are plotted and points corresponding to the D.sub.i values are connected, resulting in a density distribution curve, no straight line parallel to the horizontal axis intersects the density distribution curve at four points.

In one embodiment, a method of forming an extruded board includes mixing a resin and a foaming agent, melting the mixed resin and foaming agent to form a uniformly colored extrudate, differentially expanding voids formed from the foaming agent within the uniformly colored extrudate by passing the uniformly colored extrudate through a breaker plate, forming a board with the differentially expanded voids and uniformly colored extrudate, and forming lightened portions on an outermost surface of the formed board.

A structural element for use as a core layer in a sandwich composite element, wherein the structural element (2) is formed from a plurality of mutually welded body segments (4, 5) made from an extrusion foamed thermoplastic, and wherein the structural element (2) has a first face side (1) for bonding to a cover layer, wherein a surface of the first face side (1) that can be loaded with a resin (8) has open pores (6), wherein the surface of the first face side (1) is created by hot-element cutting, in such a manner that the surface is thermally sealed to some extent, wherein a gloss value of the surface of the first face side (1), measured at 60 in accordance with DIN 67530-1982 is between 2 and 10 gloss units.

In order to provide a manufacturing method of an elongated foam sheet capable of manufacturing the elongated foam sheet with highly-precise thickness without being limited by the material and thickness of foam material, a method of manufacturing an elongated foam sheet includes performing a slice process in which a foam sheet is created by slicing a foam block and a sheet pasting process in which a large number of foam sheets are arranged and pasted onto one side of an elongated base material sheet to manufacture the elongated foam sheet where the large number of foam sheets are lined up in a longitudinal direction of the base material sheet.