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mini corrugated and solid cardboard |
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To laminate mini corrugated and solid cardboard, in general the same type of machines are used (Assitrade, Universal, Tünkers, etc) with supply of adhesive from the top onto a two roller system.
Below an example of the settings of a laminating machine.
Machine speed: 60-100 m/min
Amount adhesive: ±26 g/m² (wet adhesive)
Pressing time: ±45 s (at 80 m/min)
The pressing time depends on the length of the pressing belt. Sometimes there is no pressing belt, but the sheets are stacked and then pressed at the same time. The first sheet needs the longest pressing time as this lies on the bottom of the stack.
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These are the general requirements for mini corrugation and solid cardboard adhesives:
- good bonding of paper to cardboard: often both surfaces are varnished paper qualities;
- high solid content: the cardboard is often only laminated on one side which means that the moisture content of only one side increase which can result in curling/tubing of the cardboard (this is mostly the case for solid cardboard laminating);
- high wet tack: after the first pressing, the sheet comes loose momentarily. In no case is the top sheet allowed to curl;
- set time/open time is depending on the machine and customer requirements (e.g. some laminators want sealing after the pressing belt).
The development of air bubbles between the paper and cardboard can have different causes which can be related to either the adhesive, the paper or the process. Often it is a combination of these:
- the wet tack and the setting speed of the adhesive: if the wet tack or the setting speed of the glue is too low, the paper is insufficiently held together in the wet, non set state;
- the Cobb-value of the paper and cardboard: paper with a high Cobb-value can give problems. As soon as it comes into contact with liquid absorption takes place and the paper can swell up. On the other hand, paper with a very low Cobb-value can also give problems because of the slow speed of absorption. Often it is this difference in Cobb-values between paper and cardboard that leads to complaints;
- the quantity of glue applied: the application of too much adhesive has consequences for the wet tack, the set time and for the amount of fluid applied;
- the pressing: if insufficient pressure is applied or for a too short period, the setting of the glue is negatively influenced.
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