A new binder is provided. The binder is composed of a polyvinyl alcohol polymer having an average saponification degree of 85.0 mol% to 89.0 mol% measured according to JIS K6726 and satisfying the following requirement (A). Requirement (A): The detector is a charged particle detector, and the column is Acclaim TM300 (catalog number: 060266, carbon content: 8%, maximum pressure: 4500 psi, particle size: 3 μm, pore size: 300 Å, stationary phase, Thermo Scientific). : C18, surface area: 100 m2 / g, length: 150 mm, diameter: 4.6 mm, pH: 2.5 to 7.5, material: Glass Lined Tubing (glass lining tube)) using the following liquid chromatography: In the relationship between the retention time and the detection intensity obtained after measuring the polyvinyl alcohol polymer under the measurement conditions and performing the baseline correction, the retention time is 5.0 minutes to 12.0 minutes when the data sampling period is 500 milliseconds. When the detection intensity at the retention time Ti [minutes] in all the data obtained during the period is Pi [pA], it is calculated based on the equations (1) and (2) and is represented by the equation (3). The value to be set is 22 or more. [Measurement conditions] -Polyvinyl alcohol polymer aqueous solution concentration: 0.1% by mass-Polyvinyl alcohol polymer aqueous solution injection amount: 2 μL-Column temperature: 50 ° C-Flow rate: 1.0 ml / min-Eluent: water and methanol Gradient conditions of mixed solvent / eluent: The mixing ratio of water and methanol in the eluent changed at a constant rate from 95: 5 to 15:85 in the measuring time of 0 to 10 minutes, and the measuring time of 10 The mixing ratio of water and methanol in the eluent from 15 minutes to 15 minutes is constant at 15:85. [Formula] Tn = Σ (Ti × Pi) / Σ (Pi) Formula (1) Tw = Σ (Ti2 × Pi) / Σ (Ti × Pi) Formula (2) {(Tw / Tn) -1} × 1000 Formula (3) 新規な結合剤を提供する。結合剤を、ＪＩＳ Ｋ６７２６に従って測定した平均けん化度８５．０モル％～８９．０モル％を有し、下記要件（Ａ）を充足するポリビニルアルコール系重合体で構成する。 要件（Ａ）：検出器が荷電化粒子
