We have printed an insert on matte paper and with a matte varnish. The customer is complaining that they do not work on the insert machine. There is no problem when printed on gloss paper and varnished with gloss varnish. What is the difference?

There may be very significant difference in surface roughness between the matte and gloss inserts. The matte insert has a high coefficient of static friction (the ratio of force between two surfaces in contact--the higher the value the greater the frictional force acting between the surfaces) and is getting hung up in the insert machine.

}