Do you know the techniques for mixing spot color inks and using them?

Do you know the techniques for mixing spot color inks and using them?

In the process of printing adhesive labels, mixing spot color ink is an indispensable step. In this article, I will analyze several common issues in mixing spot color inks during daily production, hoping to provide readers with some reference.

Part 01

Control the amount of spot color ink used

Before mixing spot color ink, the amount used must be calculated. If the printing company has spot color management software, it can use a spectrometer to test the density of printed color blocks, then input the density, area, and total print volume of the printed color blocks into a computer, and use the spot color management software to calculate the weight.

If the printing company does not have spot color management software, first, you can print spot color blocks with other colors and print dozens of them continuously; Next, weigh on an electronic scale, subtract the weight of the blank material from the printed weight, then divide by the number of prints to calculate the weight of ink for each label; Finally, the total ink weight is calculated by multiplying the weight of ink used on a single label by the total number of prints.

It should be noted that the ink weight calculated by both methods has some error. To ensure printing quality and avoid color differences caused by multiple ink mixes, it is recommended to add an additional 10%~15% to the calculated ink weight. Additionally, after the first production is completed, the ink weight can be calculated more accurately, providing basic data for the next production. After several counts and averaging, the calculations become relatively accurate.

Since spot color ink is made from multiple colors, after calculating the total ink weight, we also need to proportionally distribute the total ink weight to each color. So, how can you get this ratio?

Actually, it's quite simple. Printing companies with spot color management software can analyze the color ratios in spot color inks and get an approximate ratio. Printing companies without spot color management software can have employees prepare a small amount of ink first, record the mixing ratios of various ink colors during the process, and then mix a large amount of ink according to the exact ratio.

Part 02

Color and saturation control of spot ink

We know that ensuring color accuracy is crucial when mixing spot color ink, and color presentation can be expressed through two parameters: hue and saturation. Hue refers to what we usually call colors, such as red, green, blue, etc. Saturation mainly refers to the depth of the color. So, how can you achieve accurate hue and saturation? This is where professional tools are needed (usually printed color swatches are commonly used). There are two commonly used color charts in the self-adhesive label industry: one is the Pantone color chart, and the other is the four-color printing color spectrum.

The Pantone color chart is an internationally recognized standard color chart. All colors on the chart are numbered, and below the number, the ink proportions that make up each color are indicated. Therefore, we can easily follow the above instructions to match the desired colors. However, it is important to note that the proportions indicated on the Pantone color chart are for reference only and may not be completely accurate. The specific proportions should be flexibly adjusted during the blending process according to actual conditions. Generally, many clients specify a Pantone color code as a spot color. We only need to find the corresponding color on the color chart. 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 chart ourselves. Both methods are not difficult to operate.

Sometimes, the sample provided by the client is a four-color printed product, where the specified color is printed from the four colors, and it is difficult to find the corresponding color using a Pantone color card. This is because Pantone color charts only target spot color printing, so a four-color printing spectrum is needed to find the corresponding colors, and then the spot colors are adjusted according to the color proportions on the spectrum.

In short, as long as you find the corresponding color on the color chart, you can roughly know the color mixing ratios, then adjust the spot colors based on the actual ratio, basically achieving the desired ink hue. So, how should ink saturation be balanced?

Even the same hue can vary in depth. Sometimes we find that the blended ink matches the customer's desired color hue, but it is much darker. This is because the saturation required by the client is not 100%. In this case, the saturation of the spot color ink needs to be adjusted to meet the customer's color requirements. The specific approach is to add a certain proportion of diluent to the ink, but never add white ink, because the diluent does not change the ink's hue; it only lightens it, whereas white ink can alter the hue. The proportion of diluent should be added according to the specific situation. It is recommended to add a small amount at the start and gradually increase the amount, so that adding too much diluent at once can cause the ink to be too shallow.

Part 03

The printing sequence of spot color inks

We know that printing color order follows certain principles. Generally, the color order is yellow, red, blue, and black, but there are other principles as well. So, where should spot color inks be ranked? Generally, the following principles should be followed:

1. Printing area

If a label requires a large spot color printing area, it is recommended to print it at the front, as the larger print area is less likely to dry. Placing several UV lamps in front helps ensure the spot color ink dries completely.

2. Whether it is overprinted with other colors

In principle, during design, avoid overprinting spot colors with other colors, as this not only affects the hue of spot color ink but also makes drying easier. If you must print with other colors, it is recommended to place the larger print area color at the front. Self-adhesive printing uses dry overprinting, where the first set of colors is dried by a UV lamp before printing the following colors. Therefore, the ink at the back will not stick to the previous ink, but printing with a larger print area and printing later with a smaller area allows us to clearly see the effect after overprinting. If the color changes after overprinting, it can also be addressed by making a blank plate.

3. Color depth

In principle, place darker colors at the front as much as possible, because the darker the color, the less likely it is to dry. Printing on the front allows for more UV lamps, which helps with quick drying.

4. Viscosity of spot color ink

Generally, spot color inks have lower viscosity than original box inks because the ink is thixotropic. Continuous stirring during mixing can reduce ink viscosity, which in turn increases ink flowability. Therefore, special attention must be paid to controlling the ink amount during printing; if the ink is too high, it can easily cause plate pasting. If printing large-area spot color products, pay attention to dark ink thinning, meaning the spot color ink is slightly darker and thinned during printing so the ink can dry quickly. Additionally, when printing small-area spot color graphics and text, try to keep the ink amount to a minimum to avoid excessive ink causing plate pasting.

Part 04

Drying performance of spot color ink

For spot color inks, generally, the darker the color, the harder it is to dry; for the printing area, the larger the print area, the less likely it is to dry. Many spot color graphics and text are printed on large areas, making drying issues particularly prominent. To ensure ink drying performance, when printing large areas of spot color graphics, place the spot color sequence at the front as much as possible; You can increase the drying power of the UV lamp according to actual conditions to ensure the spot color ink dries safely; You can add a certain proportion of drying oil to dark-colored spot inks to promote rapid ink drying.

Additionally, as mentioned above, spot color inks usually have lower viscosity, so it's best not to add too much ink to the foul. Once the ink in the fountain increases, it will flow faster under pressure, making it harder to control the ink amount. It's best to fill it to about half the foul and observe it regularly, then add more if it's not enough. This makes it easier to control the ink amount. At the same time, you can make the dark ink color a bit darker, speed up the ink hopper roller during printing, and reduce ink output by tightening the ink staples, thinning the ink to achieve a deep ink thin print, which helps the ink dry quickly.