For example, a thermal insulation material produced by binding a talc powder and pulp using Portland cement is known as a thermal insulation material which is cut prior to use to have a shape corresponding to a device shape or the like, and for which high strength is required during use (e.g., a thermal insulation material that is used as a thermal insulation material for a hot press, a rubber vulcanizing machine, and an injection molding machine, and a casing for an induction furnace) (see Patent Document 1 (JP-A-61-109205)).
However, since the above thermal insulation material is produced using only pulp as reinforced fibers, the above thermal insulation material shows a significant decrease in mechanical strength and a significant dimensional change due to heating, and exhibits insufficient toughness. Specifically, the above thermal insulation material exhibits good cutting workability, but cracks and breakage (chipping) easily occur when a high load or an impact load is applied to the thermal insulation material.
Patent Document 2 (JP-A-2012-166358) discloses a composite sheet having a thickness of 3 mm that is formed by bringing two glass wool prepreg mats including an uncured urea-phenolic resin and having a thickness of 50 mm into contact with each other to obtain a laminate, and compression-molding the laminate at 200° C. for 5 minutes in a state in which melamine resin-impregnated paper having a thickness of 0.1 mm is provided on each side of the laminate.
However, the composite sheet disclosed in Patent Document 2 is designed for use as a decorative sheet, and it is difficult to use the composite sheet disclosed in Patent Document 2 as a thermal insulation material for a hot press, a rubber vulcanizing machine, and an injection molding machine due to poor toughness and bending strength.
Therefore, a thermal insulation material that exhibits excellent toughness, higher bending strength, and excellent thickness accuracy has been desired.