To provide a lid member whose specific gravity is small, which is excellent in molding property, transparency and dimension stability and which has a visibility correction function by copolymerizing a monomer containing a specified phosphate group and mixed monomer with a monomer which can be copolymerized with the monomer and containing an ionic metal component in it.
The monomer containing phosphate group represented by a formula I is copolymerized with the monomer which can be copolymerized with the monomer. Then, an acrylic copolymer whose hygroscopic property is small and which is superior in heat resistance, dimension stability and adhesive strength against a package is obtained. Here, the group R of the formula I is polymerized functional group shown by a formula II and (n) becomes '1' or '2'. Then, X in the formula II shows a hydrogen atom or a methyl group, and (m) is the integer of 0-5. The ionic metal group whose main component is set to be copper ions is contained in the acrylic copolymer which is thus obtained at an appropriate rate. Consequently, the lid member absorbing the liquid of a near-infrared area at high efficiency and having a satisfactory visibility correction function is obtained.
OGIWARA TAKEO
SHOJI MASUHIRO
KATONO HIROKI
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