Wet-dry variation and color properties of offset printing ink on offset paper

Offset printing is still the mainstream printing method at present. In this printing process, the ink needs a certain drying time on the paper. In this process, the colors printed by different types of paper and ink are different. People often want to be able to accurately predict the final color effect of the printing ink after drying. This article provides data reference through relevant experiments and tests, from which readers can learn the trend of color data change from wet to dry of offset printing ink on offset paper and the time required for the final color to stabilize.

Testing purposes

The offset printing process will be affected by many factors, resulting in different printing effects. Among them, the influence of paper and ink on printing effect is particularly important, so people in the printing industry are very concerned about the color characteristics of different papers and different inks. In particular, there is no complete reference test data for the color change trend and final stabilization time of traditional inks during the curing process, and this information is very important for some printing workshop personnel. the final color effect. To this end, we have carried out relevant data tests and obtained a large amount of data, hoping that these data can help the printing workshop personnel to reduce the color adjustment time, reduce production waste, and promote the standardization of color adjustment.

Test Materials, Equipment, Instruments and Processes

Test materials: 70g double-adhesive paper, mineral ink, soybean ink, ptfe powder hp indigo ink Jinyang blanket, OURPRESS alcohol-free process.
Paper white data: L* is 90.48; a* is 1.00; b* is -5.76; C* is 5.85; h° is 279.82.

Printing equipment: KOMORI LITHRONE S29 four-color offset press.
Printing color sequence: KCMY.
Test instruments and software: MetaVue VS3200 non-contact imaging spectrophotometer, i1PRO2 spectrophotometer, i1iO2 automatic scanning reader, Color iQC color quality control software, i1PUBLISHPRO 2 color management system.

Parameter setting: chromaticity data is D50 light source, 2° viewing angle, M0 state. Density is in the T state, including paper white.
Test process: After the printing is completed, some color tables are measured every 10 minutes, and the continuous measurement is about 3 hours; some color tables are measured every 3 hours, and the continuous measurement is about 72 hours.

Printing environment temperature and humidity: The printing environment temperature is 21℃, and the printing environment humidity is 45%.
Measurement of ambient temperature and humidity: the measurement ambient temperature is 16°C to 20°C, and the measurement ambient humidity is 30% to 48%.

Density and chromaticity changes of ink during drying
This part is measured by MetaVue VS3200 non-contact imaging spectrophotometer and Color iQC color quality control software, and the color changes in the first 3 hours and the first 72 hours are measured respectively. The first part measures 8 solids and solid overprint, and the second measures 16 patches.

1. Use mineral ink to print, select the first 8 solid color blocks (C100, M100, Y100, K100, M100Y100, C100Y100, C100M100, C100M100Y100). The trends of color and density changes (in hours) in the first 3 hours or so of recording are shown in Figures 3 to 10.

There is a steady and smooth change in color throughout the time period, with rapid changes in the first 1 hour. There is a small change in shades, the hue is slightly reddish, and the saturation is significantly reduced. Although the data varies greatly, this variation is not obvious to the human eye.

There is a steady and smooth change in color throughout the time period, with rapid changes in the first 1.5 hours. The lightness increases, the hue slightly leans towards yellow, and the saturation decreases significantly. This difference will also be apparent visually.

The color changes steadily and smoothly throughout the time period, with the first 1.5 hours being relatively rapid. The brightness increases, the hue slightly leans towards purple, and the saturation decreases significantly. This change is not visually apparent.

There is a steady and smooth change in color throughout the time period, with rapid changes in the first 2 hours. The main reason is that the brightness becomes higher and the color becomes lighter, and this change will be very obvious visually.

The color changes steadily and smoothly throughout the time period, with the first 2 hours changing faster. Brightness increases, hue leans toward red, and saturation decreases significantly.

There is a steady and smooth change in color throughout the time period, with rapid changes in the first 1.5 hours. Brightness increases, hue tends to blue, and saturation decreases significantly.

The color has a relatively stable and smooth change throughout the entire time period. Brightness is significantly increased, hue changes are minor, and saturation is significantly reduced.

It can be seen from Figure 10 that the color has a relatively stable and smooth change in the entire time period, and the change in the first 2 hours is rapid, mainly because the brightness increases and the saturation decreases slightly.

2. Printing with soybean ink, select 16 color blocks (C100, M100, Y100, K100, M100Y100, C100Y100, C100M100, C100M100Y100, C50, M50, Y50, K50, M50Y50, C50Y50, C50M50, C50M50Y50), the initial measurement is about printing Completed within 30 minutes, and then measured every 3 hours. The trend graph of color and density changes (time in hours) within 74 hours is shown in Figures 11 to 26.

The yellow had a drastic color change within the first 2 hours and stabilized after 23 hours.

Magenta had a noticeable color change within the first 5 hours and leveled off after 23 hours.

Cyan had a drastic color change in the first 2 hours, followed by a slow change and stabilized after 29 hours.

Black had a drastic color change in the first 5 hours, followed by a slow change and leveled off after 47 hours.

The change was evident in the first 17 hours and stabilized after 56 hours.

The change was obvious in the first 14 hours and stabilized after 20 hours.

The change was evident in the first 14 hours and leveled off after 56 hours.

The change was evident in the first 11 hours and stabilized after 44 hours.

The change is obvious in the first 5 hours, and then tends to be stable, and the data is greatly affected by the measurement location.

The change is obvious in the first 5 hours, and then tends to be stable, and the data is greatly affected by the measurement location.

The changes were obvious in the first 2 hours, and then tended to be stable.

The changes were obvious in the first 3 hours, and then tended to be stable.

The changes are obvious in the first 3 hours, and then tend to be stable, and the data is greatly affected by the measurement location.

The changes were obvious in the first 3 hours, and then tended to be stable.

The changes were obvious in the first 3 hours, and then tended to be stable.

The changes are obvious in the first 3 hours, and then tend to be stable, and the data is greatly affected by the measurement location.

04Color gamut changes during ink drying

This part uses i1PRO2 spectrophotometer with i1iO measuring table and i1Profiler software to measure the color table of soybean ink P2P25X, measured once every 24 hours, and its L* value is CIELab color gamut at 75, 50, and 25, respectively.

It can be seen that during the drying process, the color gamut decreases and the saturation decreases in the dark tone area, but in the bright tone area, the color gamut increases in some areas.

05 Conclusion

1. The drying time of different ink colors and the degree and trend of color change before and after drying are different, among which the changes of black and magenta are the most significant (the change of mineral ink in 3.8 hours DE2000 is 2.77 and 1.82, respectively).

2. The solid color changes rapidly in the first 2 hours, then slows down, and becomes basically stable after 24 hours.

3. The change of color is mainly the decrease of saturation (C*) and the increase of lightness (L*).

4. Due to the difference in optical structure, there is a certain difference between the data of MetaVue VS3200 and eXact and i1PRO2. This difference is within the controllable range, and the author thinks that it will not affect the trend of color change.

5. Limited by the actual conditions, the initial measurement time of each color block has a certain difference.

6. The data measurement is performed in a windowless, air-conditioned room, which may differ from the actual production environment. Since the color block is fully exposed to the air and continuous measurement is performed, the light source of the instrument will continue to illuminate the color table, and these factors will have a certain impact on the drying time.