Do you know the techniques for mixing and using spot color ink?
The blending of spot color ink is an essential step in the printing process of adhesive labels. In this paper, the author will analyze several common problems in the deployment of spot color ink in the daily production process, hoping to give readers some reference.
Part 01
Control of the dosage of spot color ink
Before mixing spot color ink, the usage should be calculated. If the printing company has spot color management software, it can use a spectrophotometer to test the density of the printed color blocks, and then input the density, area, and total printing volume of the printed color blocks into the computer. The weight can be calculated through the spot color management software.
If printing companies do not have spot color management software, they can first use other colors to print spot color blocks and print dozens of them continuously; Secondly, weigh on an electronic scale, subtract the weight of the blank material from the printed weight, and then divide by the number of prints to calculate the weight of ink used for a single label; Finally, multiply the weight of ink used on a single label by the total printing quantity to obtain the total ink weight.
It should be noted that there is a certain degree of error in the ink weight calculated by the above two methods. In order to ensure printing quality and avoid color difference caused by multiple ink blending, it is recommended to add an additional 10% to 15% on top of the calculated ink weight. In addition, after the first production is completed, the weight of the ink can be accurately calculated, providing basic data for the next production. After several statistics are taken and averaged, the calculation will become relatively accurate.
Due to the fact that spot color ink is composed of multiple colors of ink, after calculating the total weight of the ink, we also need to allocate the total weight of the ink proportionally to each color of ink. So, how can we obtain this ratio?
It's actually quite simple. Printing companies with spot color management software can analyze the color ratio in the spot color ink through the software to obtain an approximate ratio. Printing companies without spot color management software can allow employees to first mix a small amount of ink, record the ratio of various colors of ink during the mixing process, and then mix a large amount of ink according to the accurate ratio.
Part 02
Color and saturation control of spot ink
We know that ensuring the accuracy of color is very important when blending spot color ink, and the presentation of color can be expressed through two parameters: hue and saturation. Hue, in fact, refers to the colors we usually refer to, such as red, green, blue, etc. Saturation mainly refers to the depth of the color. So, how can we obtain accurate hue and saturation? Professional tools (usually printing color cards) are needed here. There are two commonly used color cards in the self-adhesive label industry: Pantone color card and four-color printing chromatography.
Pantone color chart is an internationally recognized standard color chart, where all colors are numbered and the ink ratio that makes up the color is indicated below the number. Therefore, we can easily match the desired color based on the above guidance. However, it should be noted that the proportions indicated on the Pantone color chart are for reference only and may not be guaranteed to be very accurate. The specific proportions need to be flexibly controlled according to the actual situation during the mixing process. In general, many customers will specify a Pantone color code as the spot color. We only need to find the corresponding color on the color card. If the customer does not specify a specific Pantone color code but provides a sample, then we need to find the corresponding color code on the Pantone color card ourselves. Both methods are not difficult to operate.
Sometimes, the samples provided by customers are four-color prints, and the specified colors are printed in four colors. It is difficult to find the corresponding colors using a Pantone color chart. This is because Pantone color cards are only suitable for spot color printing, which requires the use of four-color printing chromatography to find the corresponding color, and then adjust the spot color according to the corresponding color ratio on the chromatography.
In short, as long as the corresponding color is found on the color chart, you will have a rough idea of the color matching ratio, and then adjust the spot color according to the actual ratio, basically achieving the desired ink hue. So, how should the saturation of ink be adjusted?
The same hue can also have differences in depth. Sometimes we may find that the blended ink matches the color hue requested by the customer, but it is much darker. This is because the customer's requested color saturation is not 100%. In this case, it is necessary to adjust the saturation of the spot color ink to meet the customer's color requirements. The specific method is to add a certain proportion of fading agent to the ink, and never add white ink, because fading agent will not change the color of the ink, only make the ink lighter, while white ink can change the color of the ink. The proportion of dilution agent needs to be added according to specific circumstances. It is recommended to add less at the beginning and gradually increase it, so as not to cause the ink to become too light due to adding too much dilution agent at once.
Part 03
Printing sequence of spot color ink
We know that there are certain principles for the color sequence arrangement in printing, and the general principle is to arrange them according to the color sequence of yellow, red, blue, and black. Of course, there are other principles besides this. So, where should the spot color ink be placed? Generally speaking, the following principles should be followed:
1. Printing area
If a label requires a large area for spot color printing, it is recommended to print it in the front because the large printing area is not easy to dry. Placing multiple sets of UV lamps in front can facilitate the complete drying of the spot color ink.
2. Is it overlapped with other colors
In principle, it is advisable to avoid overlapping of spot colors with other colors during design, as this not only affects the hue of the spot color ink, but also hinders drying. If it is necessary to overlap with other colors, it is recommended to place the color with a larger printing area at the front. Adhesive printing is dry overlay printing, which means that the first set of colors is dried by a UV lamp before printing the subsequent colors. Therefore, there will be no situation where the subsequent ink sticks off the previous ink. However, the larger printing area is printed first, and the smaller printing area is printed later. We can clearly see the effect of overlay printing. If there is a color change after overprinting, it can also be addressed by creating a missing pattern.
3. Depth of color
In principle, darker colors should be placed in the front as much as possible, because the darker the color, the less likely it is to dry. Printing in the front can be done with multiple sets of UV lamps, which is beneficial for quick drying.
4. Viscosity of spot color ink
Generally speaking, the viscosity of spot color ink is lower than that of the original box ink because the ink has thixotropy. Continuous stirring during the mixing process can reduce the viscosity of the ink, which in turn leads to an increase in the fluidity of the ink. Therefore, special attention should be paid to controlling the amount of ink during the printing process. If the amount of ink is too large, it is likely to cause sticking of the plate. If it is printing large-area spot color solid products, it is necessary to pay attention to deep ink thin printing, that is, to darken the spot color ink a little, and to thin the ink during the printing process so that the ink can dry as soon as possible. In addition, when printing small area spot color images and text, it is also necessary to minimize the ink volume as much as possible to avoid excessive ink volume causing plate sticking.
Part 04
Drying performance of spot color ink
For spot color ink, the darker the color, the less likely it is to dry. In terms of printing area, the larger the printing area, the less likely it is to dry. And many spot color images and text are printed on a large scale, so the drying problem is particularly prominent. In order to ensure the drying effect of the ink, when encountering large-scale solid spot color graphic printing, it is advisable to arrange the spot color sequence at the front as much as possible; The drying power of the UV lamp can be increased according to the actual situation to ensure the safe drying of spot ink; A certain proportion of dry oil can be added to dark spot color ink to promote rapid drying of the ink.
In addition, as mentioned above, the viscosity of spot color ink is usually lower, so it is best not to add too much ink to the ink hopper, because once the ink in the ink hopper increases, the ink will flow faster under pressure, which is not conducive to controlling the ink volume. It is best to add about half of the ink hopper and observe it at any time. If it is not enough, it will be easier to control the ink volume. At the same time, the color of dark ink can be darker, and the speed of the ink fountain roller can be increased during the printing process. By tightening the ink nail, the ink volume can be reduced, and the ink can be thinned to achieve the effect of deep ink thin printing, which is conducive to the rapid drying of the ink.