Control of the printing process
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The importance of color control bars
The color control bar is a quality verification tool that helps different departments in the printing process to understand the color of the finished product, so that when the quality problems occur, they know how to solve it. It is also an objective reference for understanding the color performance of different devices in the production process and for monitoring and stabilizing production quality.
For example, if a foreign customer attaches a digital manuscript to an electronic document, and you see the image with blue, then it is the idea of design, or where there is a problem. If there is a color control bar on the drawing, you can know what it means. way.
In fact, every buyer wants their suppliers to have a stable product. The color control bar is the pointer to the quality control of the printed product. This can also improve the ability to predict problems if the daily color control bar data can be graphed.
Solidink density (SID)
Field density is the most important data, as a basic physical quantity for measuring tonal values, and the first part of color verification. The field can indicate that the ink on the sheet can achieve the highest color saturation; in fact, the thickness of the ink film in a steady state. The relationship between the thickness of the ink film and its reflection density is complicated. When the ink film is thin, the relationship is not established. When the thickness of the ink film is saturated, the relationship is not established. That is to say, the density does not increase indefinitely.
At the same time, these solid color densities indicate the color gamut boundary of this color, and the color gamut can print more saturated colors, so there is more attractive dark detail. In printing, the Ink key is used to control the thickness of the ink to adjust the color change.
Print contrast-PC
The contrast of printing is to compare the amount of reflection of each color ink and its 75% dot (also using 70% dot). If the difference of the amount of reflection is large, the naked eye can easily distinguish between the ground and the 75% mesh, and the details of the dark part will be detailed. On the contrary, the difference in light amount is small, and the details of the dark part are not good. Note that we do not need to compare the contrast of 25%, 50%, etc. Because the dot gain in offset printing appears in the entire tone curve, it only makes the details of the dark part disappear because the dot becomes full. A higher printing contrast means higher quality printing. The principle is that high printing contrast must match the saturated solid density, so that the dark part of the printed matter has a better level, and the image has the feeling of jumping out of the paper, that is, the so-called three-dimensional feeling. Strong.
From the contrast, you can basically grasp:
1. Ink inking situation
2. Value added in the dark part of the print
3. Increase the influence of ink concentration (Ink Density) on this
Tone valueincrease-TVl
Dot gain-DG
There are three parts that affect the color change in the printing process:
1. Pre-press: The change in the pre-press process to generate the dot. If the film is added or subtracted by the film, the dot will become larger or thinner, or the compensation curve on the film output will change the dot.
2. Mechanical dot gain: All the mechanical influences in the printing process cause the dots printed on the paper to be larger than the value of the dots on the zinc plate.
3. Optical dot gain: The optical effect caused by scattering on the surface of the paper, resulting in the same dots appearing different sizes on different papers.
In the United States, the 50% flat screen is used to increase the printed value. As a parameter, if the printed mark is 72%, the outlet of the factory is increased by 22%. In Europe, 40% and 80% of the location measurement is based on the physical characteristics of printing. Although it is impossible to make it a perfect zero value, it can be monitored by the color control bar to maintain the stability of value added. Compensation is applied in the separation of color separations to offset problems arising from value added. Since the change in hue does not necessarily have a dot, the term Tone value increase is also used in recent years.
Increased dot size caused by printing failure
Slurring: It means that when the paper comes into contact with the tape, there is a slight movement, which causes the ink to be dragged, so the dots appear in the same direction.
Doubling: When the tape is in contact with the paper, the viscosity of the ink is large. Therefore, when the paper and the tape are separated, the ink is pulled and bounced back onto the tape, and the excess ink is printed on the next paper. An irregular dot is formed.
Overprinting rate (Ink trapping)
The overprint ratio is a case where the ink films are successively printed on the paper, and the factors affecting the overprint include the thickness of the ink layer, the viscosity of the ink, the color sequence of the printing, the interval between the two colors, and the like.