To provide a manufacturing method of a lightweight bathtub stabilized in its quality, having good post-processability and excellent in impact resistance.
A male mold is covered with a thermoplastic resin molded product while a female mold is arranged on the side opposite to the male mold so as to leave a predetermined interval from the thermoplastic resin molded product to form a cell and, in a state that the peripheral part of the thermoplastic resin molded product and the peripheral part of the male mold are sealed to clamp the male and female molds, a resin mixed liquid, which contains a polymerizable resin raw material, at least one kind of an inorganic filler selected from the group consisting of glass balloons, aluminum hydroxide and silica and a phosphoric ester containing a (meth)acryloyloxy group represented by the formula (1) (wherein R1 is H or CH3 and n is 1 or 2), is injected in the cell and cured to form a reinforcing material layer.
Ishibashi Masayuki
Shinichi Iwata
Masaaki Ogata
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