Bag-making method

1. A bag-making method for producing a bag by melt-bonding and thereby integrating a mouth member formed of a preliminarily heated synthetic resin and a bag unit formed of a flexible film, said method comprising;

a preliminary heating step of softening the synthetic resin of the mouth member at the part to be melt-bonded to the bag unit, which is a melt-bonding part of mouth member, while preventing the synthetic resin of the mouth member at the end part in the bag side, which is an end part of mouth member, from being softened at the preliminary heating, and

a melt-bonding step of inserting the preliminarily heated mouth member into the opening of the bag unit and pressing them by a sealing mold to melt-bond the melt-bonding part of the mouth member to the opening,

wherein the temperature of the sealing mold is higher than a melting point of a bag unit resin by 10° C. or more, and time period after the preliminary heating step until the pressing by the sealing mold is 1 to 4 seconds.

2. The bag-making method as claimed in claim 1 , wherein radiation heat is used for the preliminary heating.

3. The bag-making method as claimed in claim 1 , wherein the end part of the mouth member has a length of 5 mm or less.

4. The bag-making method as claimed in claim 1 , wherein the end part of the mouth member is prevented by heat insulating means from being heated at the preliminary heating.

5. The bag-making method as claimed in claim 1 , wherein in the melt-bonding step, the melt-bonding is performed not to heat the mouth member in the region at least 0.5 mm from the lowermost portion of the end part.

6. The bag-making method as claimed in claim 1 , wherein a mouth member supported by a cylindrical body is inserted into the opening of a bag unit and the mouth member and the bag unit are melt-bonded while the bag unit is depressurized.

7. A medical container produced by the bag-making method claimed in claim 1 .