Adeka Argus Chemical Co., Ltd.

Asahi Denka Kogyo Kabushiki Kaisha

Syuji Iwakura

Mitsuo Akutsu

Keiji Oya

Keiji Tabata

A process for treating paper to prevent discoloration when exposed to light which comprises adding 1% to 10% by weight of hypophosphorous acid or its salt based on the paper at any stage during or after paper making and maintaining said hypophosphorous acid or its salt therein. The invention also provides paper which contains hypophosphorous acid or its salt to prevent discoloration when exposed to light.

Method for preventing the discoloration of paper and paper treated to

A heat-sensitive recording material wherein a color-forming layer comprising a coupling substance which is usually colorless or light-colored and a developer which gives rise to color in the coupling substance upon heating further contains, as a sensitizer, a tetrahydronaphthalene compound of the following general formula (I): ##STR1## wherein X represents an alkylene group, --O--CO--O--, --O--CO-- or --O--R'.sub.n Y--, n represents 1 or 2, Y represents --O-- or --S--, R' represents an alkylene group, and R represents a phenyl, alkylphenyl or tetrahydronaphthyl group.

Heat-sensitive recording material

A heat-sensitive recording material wherein 1,2-bis(3,4-dimethylphenyl)ethane is contained as a sensitizer in a color-forming layer comprising a usually colorless or light-colored coupling substance and a developer which causes coloring of the coupling substance upon heating.

An optical recording material having excellent light stability, shelf stability and solubility in a solvent comprises, as an indispensable constituent, a compound of the following general formula: ##STR1## wherein R represents a cycloalkyl group having 3 to 12 carbon atoms, X.sup.- represents a halide anion, a perchlorate anion or a quencher anion, rings A and B each represent a benzene or naphthalene ring which may be substituted with a halogen atom, and n represents 1 to 4.

Optical recording material

A heat-sensitive recording material which comprises a usually colorless or light-colored coloring material together with one or more compounds selected from among bissulfonate compounds, 2-substituted cyclohexyl sulfonate derivatives and biscycloalkyl aryldisulfonate derivatives.

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Saitama, Japan

Syuji Iwakura