In pad printing technology, the correct restoration of color plays an important role in print quality. In color matching, the color matching problem associated with color measurement equipment is an objective scientific problem, which can be expressed by data; and the device-independent color matching problem is subjective, subject to the limitations of artistic cultivation and observation. How to establish the relationship between ink color in printing, in order to correctly express the color, has a relationship with subjectivity, even if it is strictly according to the correct method, using the most color matching method to produce the customer's own visual defects (such as color blindness or eye fatigue) Rejected. Therefore, in order to meet the needs of customers, it is necessary to consider the influence of objective data when printing, and to consider the desired artistic effect.
We know that observing the target, observing the light source or the light and the observer (human vision or a color measuring device) are the three essential elements necessary to form a certain color. The observer's ability to feel the color is affected by many factors. Limitations, almost all variables are included in the three elements of the observed color, these variables affect the ability to match the color, any change in the variable will have an effect on the color of the image after the transfer, the impact of these variables will be introduced below.
1 Influence of printing materials
The color that a customer needs is usually from a color matching (color matching) system such as Pantone or a standard color swatch. However, due to the limitations of the bearing, the color transferred in the printing is not a complete reflection of the color in the color sample. For the impact of substrates, the following four aspects are mainly considered:
(1) Influence of substrate color and surface characteristics of the substrate or medium
(2) Number of prints required to achieve a certain hiding power
(3) Influence of ink additives, diluents and catalysts
(4) Produce a printing method (offset, silk screen or pad printing) that is compatible with a certain color standard.
1.1 color and surface characteristics of the substrate
The surface color of the printing material is an important factor affecting the image color reproduction of the fingerprint printing technology. When observing the printed color, the color seen is formed by the reflection of light from the surface of the substrate and the overprinting layer of the printing ink into the human eye. Since the ink layer deposited on the substrate in the pad printing is thick, the light usually passes through the ink layer to reach the substrate, and then reflects on the surface of the substrate, passes through the ink layer again, and is reflected into the human eye. The amount of light reflected on the substrate of the substrate is related to the color of the material itself, especially the darkness of the substrate itself, and the effect is more pronounced when observing the lighter shades printed thereon.
The surface properties of the substrate such as smoothness or flatness and porosity play an important role in color reproduction. Observing the same color on two media of the same color but different flatness, the visual effect obtained is Different: The color printed on a smooth base looks brighter and sharper; the same color printed on a porous, rough surface such as fabric is gray. This is caused by the difference in the reflected light of the two hostages. When the light hits the smooth and flat surface of the medium, most of the light is reflected at the same angle, so most of the reflected light is incident on the human eye; on the contrary, rough, The porous surface light is reflected from different angles and emits much less light into the human eye.
Therefore, the tighter the color of the printed and the printed matter, the better the printing effect: a certain color can be reproduced on the coated or uncoated white paper medium, and in the darker plastic medium. The reproducibility is very poor.
In addition, under certain specific printing conditions, one or more layers of white ink are pre-printed as the base color, otherwise a better matching effect will not be obtained. For example, for transparent glossy pigments, in order to avoid losing features, a layer of white ink should be pre-printed before any color is printed.
1.2 number of printing
As mentioned earlier, while observing the color on the print, the color of the substrate itself is also seen. In order to reduce the influence of the substrate, the ink selected should be as opaque as possible. At the time of pad printing, the thickness of the printing ink layer after drying is about 20% of the etching depth of the printing plate. If the etch depth is 0.001 inches, then the film thickness after drying is between 0.0002 inches and 0.00025 inches, which is much thinner than silk screen, so a too thin film layer is not sufficient to mask the effect of the color of the substrate. One of the solutions is to increase the etching depth, but when the depth exceeds 0.0015 inches, the effective transferability of the ink is greatly reduced, the image becomes blurred, and the paste starts to be applied. Therefore, only another method can be adopted to increase the number of printings in the printing. This process is called double printing or multiple printing.
The use of multiple prints will undoubtedly extend production time, so before taking multiple prints, determine if this will achieve the required productivity, even if a single print does not achieve the desired color match, not necessarily at the expense of production time. Multiple printing at the expense can be achieved by reducing the amount of diluent in the ink or adding pigment. In addition, before using multiple printings, it should be determined whether the image can still maintain good detail clarity in the case of increasing the number of printings, and will not be deformed or bent during the printing process.
1.3 ink additives
The additive component of the ink component also affects the color of the ink. The diluent, catalyst, and flow agent are generally colorless, which may result in a decrease in ink hiding power. For example, adding a certain catalyst (such as a hardener) to the ink in a ratio of 2:1 will reduce the hiding power by 50%, which is almost as obvious as the difference between single printing and multiple printing. Therefore, it is important for the person performing the color matching to know the required additives and the specific proportions at the time of addition so that the correct addition can be done before coloring.
1.4 color sample production
Standard color samples are a guarantee for proper printing. Since the thickness of the obtained ink film layer is different in each printing mode, the color sample is obtained by silk screen printing or offset printing, and must be corrected in use. The color samples used for reference in pad printing are also subject to correction.
2 observation environment
Light is generated by electromagnetic radiation, so light is derived from the partial electromagnetic spectrum. The range of spectra that can be observed by the human eye is called seeing light, from red light in the longer band to blue-violet light in the shorter band. Since the light color seen by the human eye is only a certain wavelength of light in the visible light range, the light conditions in the observation environment have a great influence on the observation result. If the color to be matched is observed during the day and the color matching is obtained under fluorescent conditions, then this match is not a truly accurate match.
In addition, the environment in which the target turnover is observed also has an effect on the color of the observed image. For example, the color perception obtained by observing the same image on a darker background with a darker background is different. This is more important when presenting samples to customers for comments. It is important to ensure that the customer's observation conditions are consistent with the environmental conditions at which the ink process is established during printing, or that the lighting conditions during production are changed to be consistent with the customer's observation conditions.
3 The observer can be a human observer or a color measurement device (such as a spectrophotometer)
It is impossible for any type of observer to observe the same image in the same way. Human vision can distinguish ten million colors, and the individual's psychological state affects his or her feelings about color. When a person's card is in a healthy state, the color that is observed is different from the color feeling that he gets when he is tired, sick, or depressed; the feelings of adults are not the same as those of children. Moreover, a particular class of people is less sensitive to color changes in a certain wavelength range, and some are even color-blind patients. Therefore, judging whether a color is correct or not is based on the visual characteristics of multiple people.
Color measuring devices, such as spectrophotometers, are represented by a set of color stimuli in a simulated three-dimensional color model, also known as a color space, by measuring reflected light from an object. During the measurement process, each device is calibrated under certain given conditions to complete the color measurement of the color swatch. These given conditions include lighting conditions or types of light sources, viewing angles, whether or not to consider the effects of gloss, and the like.
In theory, the results of different device measurements under the same environmental conditions will have the same color matching performance in the color space. But in reality, there are differences between different devices, and the results are different. Even the same device itself, the continuous two measurements may be different without changing any conditions. In most cases, these subtle differences do not have much impact on the results, but problems arise for different devices under different conditions or when the specified color tolerance is too small. Although the printing department and the customer may use the same equipment, there is often a difference because we cannot guarantee that the equipment will be observed in the same way after the correction process, and the measurement is completed. For example, for a person who specifies or sets a color, the gloss factor is taken into account when measuring the color sample, and the printer is observing the color matching condition, and does not consider the gloss factor when measuring the color sample, then, although the naked eye observes The matching result is acceptable, but it will be unacceptable from the instrument measurement results. Therefore, when matching a color within a specific tolerance range generated by a computer, it is important to ensure that the measuring device is viewed in the same environment as the device used to set the color.
Color measurement plays an important role in color matching. The measurement results can generate a lot of useful information, which can directly indicate the position of the matched color in the color space, and help the reliable matching. However, in other cases, although the matching effect is good from the measurement results, it is not ideal from the viewpoint of visual effect or artistic effect. This is because in the evaluation of color matching, human vision still occupies a dominant position, so it is necessary to consider not only the role of measurement tools in color matching, but also the subjective sensibility of human vision.
When comprehensively considering the factors involved in the observation target and the effects of the observation environment and the role of the observation subject (measurement equipment and humans), color management becomes simple, and with the understanding and implementation of effective control of the variables, The color matching of headaches becomes easier and more efficient. I believe that in the near future, the ability to control color will be more powerful.
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