The thermal expansion member adjusts the opening degree of the variable restriction so that a change in kinematic viscosity of the feed liquid by a change in environmental temperature is compensated by thermal expansion to make the flow rate of the feed liquid almost fixed. この熱膨張部材は、熱膨張により環境温度変化による原液の動粘度の変動を補償し、原液流量を略一定にするように可変絞りの開度を調節する。 - 特許庁