To eliminate a wrong judge at the time of leak check, and to enable the measurement in a short time by measuring the swelled amount of a bottom part on the basis of the existence of the intrusion of air into a container through a pin hole.
When an upper part of a paper container (a) is covered by a holder 2, a pressurizing means 4 supplies air to a closed space 3 and pressurized to a predetermined constant pressure condition, and thereafter, the pressurizing means 4 maintains this constant pressure condition for a predetermined time. When the pressure of the closed space 3 formed by the holder 2 is raised to be under constant pressure condition by the pressurizing means 4, a measuring means 7 measures the downward expanded variable of an air bottom plate (f). The difference of the inner pressure of the paper container (a) is remarkably large between the case where air is fed into the paper container (a) from the closed space 3, in which a pin hole is generated in a heat seal closing part, and the case where the air is fed into the paper container (a) from the closed space 3, in which a pin hole is not generated. A judging means 8 compares the measured value of the measuring means 7, namely, the expanded amount with a preset value so as to judge the quality of the paper container (a).
HIRAYAMA TAKAHISA
ARITA YOSHIKI
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