In the research and development and quality control of gravure printing inks, printability and dryness are two key indicators. Gravure proofers simulate the actual printing process, providing a repeatable testing environment for ink color, transfer, leveling, and drying rates. The purpose of this paper is to explore how to construct a comprehensive evaluation method using gravure proofing mechanism to quantify the printing performance and drying behavior of ink on specific substrates.
Test equipment and materials
The test uses a standard gravure proofing machine, with electro-engraved copper plate or chrome plate, and the number of lines added to the net can be adjusted between 150-300 lpi. The substrate is coated with a dosage of 80 g/m² and a film substrate of 70 g/m². Ink samples are provided by the supplier and contain solvent-based systems with different volatilization rates, and the viscosity is uniformly adjusted to 20-25 seconds (coated with No. 4 cup, 25°C). The dryness is determined by infrared temperature measurement and placement method.
Printability evaluation index
Printability is mainly quantified from the following dimensions:
1. Dot clarity: Use a magnifying glass to observe the sharpness of the dot edge, and use image analysis software to calculate the deformation rate of dot area to reduce subjective deviation.
2. Transfer rate: The transfer amount is calculated by weighing the difference between the quality of the plate roller and the substrate before and after proofing, and the transfer amount is considered to be poor transfer if the transfer amount is less than 70%.
3. Leveling: Under the conditions of relative humidity of 50% and temperature of 23°C, the surface roughness of the ink is visually measured within 30 seconds after proofing, and the number of bubbles retained is recorded.
Dryness evaluation method
The dryness test adopts the stratified determination method, and the specific steps are as follows:
a. Set the speed of the proofing machine to 30 m/min and adjust the imprinting force to 1.5 kN/m.
b. Touch the surface of the ink film with filter paper every 5 seconds after proofing until there is no color transfer, and record the complete drying time.
c. Auxiliary use of infrared thermometer to monitor the temperature change of the ink film surface, when the difference between the temperature and the ambient temperature does not exceed 0.5°C, it is considered to be dry.
Summary of key data
After multiple batches of testing, the typical data obtained is summarized in the table below.
| Ink sample | Transfer rate (%) and complete drying time (s) |
| Solvent type A | 76%； Drying time 35 |
| Solvent type B | 82%； Drying time 42 |
| Water-based type C | 68%； Drying time 25 |
| Water base type D | 71%； Drying time 28 |
It can be seen from the table that the transfer rate of solvent-based inks is higher overall, but the drying time is slightly longer than that of water-based inks. Although the water-based type dries quickly, the transfer characteristics are more significantly affected by the surface energy of the substrate.
Comprehensive evaluation process
Printability and dryness data are normalized and then weighted scores are calculated. The weight setting should be combined with the actual application requirements: for high-speed gravure printing production lines, the dryness weight can be set to 0.6, and the transfer rate and dot quality account for 0.2 each. The full score is 100 points, and if it is less than 60 points, it will be judged as not up to standard. This process allows for the selection of ink formulations that meet both transfer efficiency and curing rate.
Discussion of influencing factors
The working parameters of the gravure proofing machine have a significant impact on the test results. Too high the imprinting force can easily lead to the expansion of the dots, and too low will lead to insufficient transfer. In addition, the ink layer thickness can be controlled within the range of 2-4 μm when the squeegee angle is adjusted to 60°-70°, which is close to the actual gravure plate printing process. Ambient temperature and humidity should also be strictly monitored, especially water-based inks can double the drying time when the humidity is too high.
Experimental limitations and suggestions
This method is mainly implemented under laboratory conditions, and although it is highly controllable, it does not fully reflect the continuous printing state of mass production. It is recommended to compare and verify the actual long-distance printing loss after obtaining the basic data. In the future, laser thickness measurement or spectral reflectance can be introduced to further improve the detection accuracy.
Cited source
1. Research Report on the Association between Rheology and Printability of Gravure Inks, China Academy of Printing Science and Technology, 2022.
2. Comparative analysis of drying kinetics of solvent-based and water-based inks, Academic Journal of Packaging Engineering, Vol. 43, No. 5, 2023.
3. Technical Manual of Printed Quality Inspection and Control, Light Industry Press, 2019.