Patent ID: 7923081

Claim:
A recording medium for water-based ink, comprising a paper base and an ink receptive layer formed on a surface of said paper base, the ink receptive layer comprising a porous layer containing an inorganic pigment and also containing a substance reactive with an ink colorant, the recording medium being to be recorded using water-based ink containing the ink colorant, wherein: a droplet of 4 μl distilled water dropped onto a surface of the ink receptive layer is absorbed in a first absorbing stage of absorbing the droplet at a first absorbing speed (V 1 ) (μl/sec) within one second after the dropping, a second absorbing stage of absorbing the droplet at a second absorbing speed (V 2 ) (μl/sec) for at least 2 seconds after the first absorbing stage, and a third absorbing stage of absorbing the droplet at a third absorbing speed (V 3 ) (μl/sec) after the second absorbing stage, the droplet absorption in the first to third absorbing stages satisfying the following relationships: 0<V2<V1 0<V2<V3, the second absorbing speed (V 2 ) (μl/sec) being higher than 0.01 (μl/sec) and lower than 0.32 (μl/sec), and given that an inflection point from the first to the second absorbing stage is (a), an inflection point from the second to the third absorbing stage is (b), a final point of the third absorbing stage is (c), absorption quantities at the points (a), (b) and (c) are (qa), (qb) and (qc), respectively, and the times up to the points (a), (b) and (c) are (ta), (tb) and (tc), respectively, the absorption quantity (qa) at the inflection point, (a), is not smaller than 1.3 μl and smaller than 2.0 μl, and the absorption quantity (qb) at the inflection point, (b), is not smaller than 2.0 μl and smaller than 2.5 μl, wherein the ink receptive layer has a pH B satisfying the following relationship: 5<pH B ≦7 and the paper base has a pH A and the ink receptive layer has the pH B both satisfying the following relationship: 1<(pH B −pH A )<4.