Offset Printing Kraft Paper Notes

Kraft paper is mainly used to print document bags, envelopes, document boxes, product packaging, handbags, information bags, portfolios, financial statement covers, etc. It has 60g/m2, 70g/m2, 80g/m2, 100g/m2. 120g/m2, 150g/m2 or even 250 ~ 450g/m2 and other specifications. The kraft paper has the advantages of hard and strong texture, good toughness, wear resistance, and not easily tearing and breaking. However, the whiteness, smoothness and flatness of the kraft paper are poor, and the surface of the paper is rough, which is prone to upturning, falling down, hair loss, and powder removal. Therefore, if you want to print kraft paper with offset press, you should master the following points.

1. The kraft paper is hanged and humidified before printing. First, the scrap paper and surface uneven paper removed, and then clean the paper surface of the paper ash, impurities, and then hang hanging treatment, so that the temperature and humidity of kraft paper and Offset Printing shop's temperature and humidity consistent. This prevents the paper from curling up and down due to uneven water content. After the paper is hung and humidity-controlled, the paper plywood is pressed on the paper basket and compacted with iron plates and large stones to prevent the paper from fluffy and unreal.

2. Select the model. For thicker kraft paper above 80g/m2, it is best not to use a small four- or eight-open offset press. Because 80g/m2 or more kraft paper is thicker, the suction nozzle often cannot absorb the paper when feeding. In addition, due to the small size of the paper, double-sheet or multiple-sheet failures are likely to occur, or the paper is skewed on the paper feeder. The use of off-set offset printing presses or full-open offset presses for printing thick kraft paper of 80g/m2 or more will be effective.

3. Adjust the offset printing system. Due to the thicker kraft paper, the suction volume of the suction nozzle should be adjusted. At the same time, the paper thickness is also likely to cause rolling stop accidents, so before the start of printing must be double-sheet control, skew control, punching control and other electrical devices to adjust the right, to prevent kraft paper sheet rolling machine. In addition, the paper separator and the feed nozzle should use rubber aprons with large diameter and thickness.

4. When the kraft paper is printed, the center distance between the plate cylinder and the blanket cylinder is kept unchanged, and only the center distance between the impression cylinder and the blanket cylinder is adjusted. When printing 250-450g/m2 kraft paper, the center distance can be increased by 0.2-0.4mm. Kraft paper has a rough surface and poor smoothness. The tightness of the paper is far inferior to that of coated paper and offset paper. Therefore, when printing kraft paper, the printing pressure must be increased accordingly.

Such as printing 400g/m2 kraft paper, the gap between the plate cylinder and the blanket cylinder is 3.95mm, the gap between the blanket cylinder and the impression cylinder is adjusted to 3.40mm, the total lineage of the plate cylinder is 0.65~0.75mm, the total length of the blanket cylinder The lining is 3.15 to 3.35mm. If the paper is thick and thin during printing, the reduced thickness of the lining should be removed from the lining of the plate and added to the lining of the squeegee; if the paper is thin to thick, the increased thickness should be drawn from the squeegee. The lining is added to the lining of the plate cylinder.

5. The surface of the kraft paper is loose and rough, and the paper is easy to lose wool and remove powder. Therefore, the blanket cylinder and the Printing Plate cylinder should be scrubbed frequently during printing to avoid the paper hair and paper powder adhering to the blanket cylinder and the plate cylinder to affect the ink transfer. Graphically out of print, missing pens. If the kraft paper loses its hair and the powder is severely degraded, if it is printed in a single color, if it is in the summer, it can be printed with a layer of clear water before printing. This can reduce paper lint and powder and make the paper more smooth.