Coater

A coater for coating a running paper or cardboard web, comprising:

• wall means defining a coating chamber having an inlet end and an opposite outlet end, the chamber having an inlet opening at its inlet end for introducing coating substance into the chamber and being open against the web at its outlet end, the wall means including a web entrance wall that bounds the chamber in the upstream direction with respect to the path of movement of the web and its spaced from the web so as to define a slot for the web to enter the chamber, and a back wall structure that bounds the chamber in the opposite, downstream direction, said back wall structure including a doctor member that engages the web for forming a coating layer on the web, the distance between the web entrance wall and the doctor member at the outlet end of the chamber being such that, at normal web running speed, the web moves from the entrance wall to the doctor member in a time of at most 0.3 s, and the inlet opening being closer to the web entrance wall than to the back wall structure, whereby the flow of coating substance introduced into the coating chamber by way of the inlet opening is, at a position close to the web entrance wall, divided into two branches, of which a first branch follows the web in its running direction toward the back wall structure and a second branch, which is of a considerably greater volume flow rate than the first branch, flows out from the coating chamber through the slot,
• a partition wall located in said coating chamber between the web entrance wall and the back wall structure and spaced from the web, said partition wall defining passageways for the coating substance in said chamber, thereby leading the flow in said chamber, firstly, mainly along said web entrance wall, thereafter in the direction of the movement of the web, and thereafter along said back wall structure of the coating chamber away from the web, there being a pressure equalizing opening in the partition wall connecting the region of the coating chamber that is between the back wall structure and the partition wall with the region of the coating chamber that is between the web entrance wall and the partition wall, and
• supply means connected to the inlet opening of the coating chamber for delivering pressurized coating substance into the coating chamber, the slot defined between the web entrance wall and the web being sufficiently narrow to limit the flow of coating substance from the coating chamber and thereby maintain the coating substance in the coating chamber under pressure.

A coater for coating a running paper or cardboard web, comprising:

• wall means defining a coating chamber having an inlet end and an opposite outlet end, the chamber having an inlet opening at its inlet end for introducing coating substance into the chamber and being open against the web at its outlet end, the wall means including a web entrance wall that bounds the chamber in the upstream direction with respect to the path of movement of the web and is spaced from the web so as to define a slot for the web to enter the chamber, and a back wall structure that bounds the chamber in the opposite, downstream direction, said back wall structure including a doctor member that engages the web for forming a coating layer on the web, the distance between the web entrance wall and the doctor member at the outlet end of the chamber being such that, at normal web running speed, the web moves from the entrance wall to the doctor member in a time of at most 0.3 s,
• a partition wall located in said coating chamber between the web entrance wall and the back wall structure and spaced from the web, said partition wall dividing the coating chamber into a first region between the web entrance wall and the partition wall and a second region between the partition wall and the back wall structure, and there being a pressure equalizing opening in the partition wall connecting the first and second regions of the coating chamber, the inlet opening being between the web entrance wall and the partition wall so that coating substance introduced into the coating chamber by way of the inlet opening flows firstly mainly along said web entrance wall, and the flow is divided at a position close to the web entrance wall into a first branch, which follows the web in its direction towards the back wall structure and thereafter flows away from the web along the back wall structure, and a second branch, which is of a considerably greater volume flow rate than the first branch and flows out from the coating chamber through the slot.