Why does screen printing produce color casts? If we put aside the mixture of several colors and consider only one color, it may be simpler to discuss the causes of color cast. This article shares several factors that affect color deviation in screen printing. The content is for reference by friends who purchase and supply the Youpin packaging material system:

Listed below are some of the most common factors that cause color deviation in screen printing: ink preparation, mesh selection, mesh tension, pressure, drying, substrate characteristics, observation conditions, etc.

 

01 Ink preparation
Ink blending Assuming that the pigment of the ink used is a standard pigment, the biggest cause of color deviation is the addition of solvents such as ink mixing oil to the ink. In a workshop with good color control equipment, ink can be mixed according to the control equipment. However, for most printing companies, it is impossible to have these facilities. They only rely on the experience of the master workers when mixing ink.

Generally, ink-adjusting oil is added to make the ink more suitable for printing. However, once adjusting oil is added to the ink, the concentration of pigments in the ink will change, which will lead to changes in the color characteristics of the ink during printing. In addition, excess solvent in the ink will form a thin film of ink after drying, which will reduce the brightness of the color.

There is also the problem of ink being diluted before inking. For example, workers in the ink shop make judgments based on their formula when mixing or diluting ink. This leads to inevitable color deviation. If the ink is mixed a few days ago, If you print with good ink, the color cast caused by this situation will be more obvious. Therefore, it is almost impossible to completely avoid color cast.

 

02 Mesh selection
If you think that the mesh size of the screen is the only factor that affects ink transfer, you will encounter a lot of trouble. Mesh diameter and wrinkles also affect ink transfer. Generally, the more ink attached to the ink holes of the screen, the more ink will be transferred to the substrate during the printing process.

In order to estimate in advance how much ink can be transferred by each mesh, many screen suppliers provide the theoretical ink transfer volume (TIV) of each mesh. TIV is a parameter indicating the size of the ink transfer amount of the screen. It refers to the amount of ink transferred in a certain How much ink will be transferred by each mesh under specific printing conditions. Its unit is the volume of ink per unit area.

To ensure consistent tones in printing, it is not enough to keep the mesh number of the screen unchanged, but also to ensure that the diameter of the screen and its waviness remain constant. Changes in any parameter of the screen will result in changes in the thickness of the ink film during printing, resulting in color changes.

 

03 Net tension
If the tension of the net is too small, it will cause the film to peel off. If there is too much ink staying in the mesh, the printed matter will become dirty.

This problem can be solved by increasing the distance between the screen and the substrate. However, increasing the distance between the screen and the substrate requires increasing the pressure, which will cause more ink to transfer to the substrate. to change the density of the color. The best way is to keep the tension of the stretch net uniform, so as to ensure the consistency of the color.

 

04 Pressure level
Proper pressure settings are crucial to maintaining consistent color, and ensuring uniform pressure levels during the printing process is critical. Especially in high-volume, repetitive printing jobs.

When it comes to pressure, the first thing to consider is the hardness of the squeegee. The hardness of the squeegee is small, which is good for the contact rate, but it is not good for bending resistance. If the hardness is too high, the friction on the screen will also be large during printing, thus affecting the printing accuracy. The second is the angle of the squeegee and the squeegee speed. The angle of the ink knife has a significant impact on the amount of ink transfer. The smaller the angle of the ink knife, the greater the amount of ink transfer. If the ink knife speed is too fast, it will cause insufficient ink filling and incomplete imprinting, thus affecting the quality of the print.

Once you have obtained the correct pressure settings for a print job and recorded them accurately, as long as you follow these settings correctly during the printing process, you will get a satisfactory print product with consistent colors.

 

05 dry
Sometimes, the color looks consistent just after printing, but the color changes after the finished product is found. This is often caused by incorrect settings of the drying equipment. The most common cause is that the dryer temperature is set too high, causing the ink color on the paper or cardboard to change.

 

06 Substrate characteristics
One issue that screen printing masters often overlook is the surface properties of the substrate. Paper, cardboard, plastic, etc. are all produced in batches, and high-quality substrates can ensure stable and consistent surface properties. But this is not the case. Small changes in the surface properties of the substrate will cause color deviations in printing. Even if the printing pressure is uniform and even each process is operated correctly, inconsistencies in the surface properties of the substrate will also cause larger color shifts in printing. Color cast.

When the same product is printed on different substrates with the same printing equipment, the influence of the surface properties of the substrate on the color is particularly obvious. Customers may require window advertisements to be printed on plastic or other cardboard. And clients may require consistent colors for the same piece.

In situations like this, the only solution is to make accurate color measurements. Use a spectrophotometer or spectral densitometer to measure color density. If there is a color shift, the densitometer can clearly reflect it, and you can overcome this color shift by controlling other processes.

 

07 Observation conditions

Human eyes are very sensitive to subtle changes in color, and can only distinguish colors under lighting conditions. Because of this, make sure to compare colors under the same lighting conditions. Otherwise, adjusting the ink volume or pressure will produce more ink. Large color cast.

All in all, the key to maintaining consistent color lies in the stable control of each process to ensure stable performance of the ink. The selection of mesh size, tension and pressure of the stretch screen, surface characteristics of the substrate and observation conditions all have a certain impact on color deviation. However, Accurate setting records and stable control of each process are the keys to ensuring consistent screen printing colors.