Calculating Substrate Compression Ratios in Embossing Operations
Substrate compression ratio measures z-axis compaction, balancing tool impression depth against fiber strain limits to maximize embossing height without shearing.
Impression Dwell Time
Press Parameter
Duration of contact between the printing substrate and the transfer surface determines the efficiency of ink transfer and the depth of the resulting image. Impression dwell time is calculated as a function of the press speed and the width of the nip where the pressure is applied. Contact time allows the ink to bridge the gap between the plate or blanket and the microscopic valleys of the paper surface.
In flexographic and gravure printing, this period is extremely short, often measured in milliseconds.
High-speed Rotation
High-speed rotation of the cylinders reduces the available window for the liquid ink to penetrate the coating layer of the board. Increasing the pressure can sometimes compensate for a shorter contact period, but this risks distorting the halftone dots or crushing the fluting of corrugated materials. The viscosity of the ink must be tuned to match the speed of the line to ensure complete coverage without splashing or ghosting.
Longer contact periods are generally preferred for heavy flood coats or when printing on highly textured uncoated papers. Adjusting the diameter of the impression cylinder or the hardness of the rubber backing can subtly alter the nip width to optimize the result.
Monitoring the Relationship
Monitoring the relationship between machine speed and ink density prevents variations in color throughout a long production run. If the speed fluctuates without a corresponding adjustment in pressure, the ink transfer becomes inconsistent. Precise control over this variable ensures that the final print meets the required optical density specifications.