How To Choose And Use UV Ink Effectively? Read Quickly At This Article

How to choose and use UV ink effectively? Read quickly at this article

UV ink is widely used in label printing due to its vivid colors, high gloss, water resistance, solvent resistance, wear resistance, and fast curing speed. It is widely used in letterpress, flexograph, offset printing, and more. Selecting and using UV ink well, especially by comprehensively understanding the factors affecting UV ink curing, assessment methods, and solutions, is crucial for reducing printing failures and improving label printing quality.

01

Current application status of UV ink

1. The quality of UV ink varies greatly

Currently, the quality of UV ink varies widely in the domestic label printing market, so common issues during printing include dry rollers, ink stacking, ink splatter, and dirty plates; UV-printed label products also commonly suffer from poor ink adhesion, low gloss, and insufficient coverage, with low white ink covering being especially prominent. These are often faults caused by the use of low-end UV inks, which not only affect printing efficiency but also clearly fail to meet quality requirements for label products.

To minimize potential problems caused by UV ink and to meet the quality requirements of different printing materials, application fields, and printing processes, UV ink suppliers have been continuously improving and launching new products.

2. There is no unified standard for UV light sources

The curing effect of UV ink is directly affected by the UV light source. Since there is currently no unified standard for the spectral range of UV light sources, the spectral range and power of commercially available UV light sources vary greatly. If the UV light source and ink are not well matched, it will cause incomplete curing of the UV ink or excessive surface curing, ultimately leading to poor ink adhesion and other quality issues.

02

How to choose UV ink

Ink curing performance is the most critical factor determining the quality of UV printing products. Therefore, when selecting UV ink, the main consideration is whether the emission wavelength of the UV lamp used in the company's printing equipment matches the trigger wavelength of the photoinitiator in the ink. Additionally, different manufacturers offer different UV ink models with different curing speeds and adhesion key properties. Generally, as long as white and black inks meet the requirements, other color series inks generally have no major issues, so black and white inks should be carefully examined.

1. Performance characteristics of UV light sources

UV light has a wavelength range of 200~600nm, but ozone is produced at 254nm, while heat is generated above 400nm. Ozone pollutes the environment and harms workers' health; Heat not only causes unstable print dimensions and even severe deformation, but also leads to energy waste-both of which we do not want to happen in UV printing. Low-energy UV (HUV/LEC) lamps have emission wavelengths between 280~600nm. Although they avoid the ozone band, they still contain a significant amount of heat-generating bands, and LED lamps perfectly solve this problem. Single-wavelength LED lamps can use wavelengths of 365nm, 385nm, and 395nm, avoiding the ozone and heat-generating bands. Moreover, the light energy of the single-wavelength light source is highly concentrated, resulting in high ink curing efficiency and safer operation.

2. Select UV ink based on compatibility with the UV light source

The prerequisite for UV ink curing is UV light exposure, and the photoinitiators in the ink can absorb its energy and generate free radicals. Under the action of free radicals, the resin in the ink and the single-molecule compounds can undergo crosslinking reactions, causing the ink to cure.

Generally, the trigger wavelength of the photoinitiator for traditional UV inks is 220~580nm, for low-energy UV inks is 280~400nm, and for LED-UV inks, the photoinitiator mainly absorbs UV light at wavelengths of 365~405nm. When selecting UV ink, first consider whether the wavelength range sensitive to the ink corresponds to the emission wavelength range of the UV lamp used by the company. At the same time, take into account the actual curing energy of the UV curing system, and combine both factors to determine the specific model of UV ink.

3. Choose UV ink based on the curing performance of black or white ink

Color also affects the curing speed of UV ink. Different ink colors cure at different speeds, mainly because different pigments absorb UV light at different wavelengths at different rates. Among them, magenta ink is the easiest to cure among all color palettes, while black ink is the hardest to cure.

This is because, although black theoretically absorbs all light and should have high curing efficiency, pigment particles block light, hindering the curing of deep ink. Therefore, black UV ink requires higher curing energy, so black and various dark-colored inks cure more slowly.

White ink curing requires high energy because white pigments can fully reflect all visible light, making thorough curing of white UV ink difficult and slow. The curing efficiency of an ink series is directly related to white and black ink. As long as white and black inks are fine, other colored inks can generally be used with confidence.

03

A few basic knowledge you need to know about UV printing

Choosing the UV ink brand and model suitable for your company's production conditions is only the first step to success. Next, it is necessary to understand the performance characteristics of UV ink and the factors influencing performance changes, as well as the reasons behind it, so that UV ink can be used effectively and the quality of label UV printing improved. The following focuses on the characteristics of composite color reproduction related to digital management of printing colors, as well as how to determine whether the UV ink layer has fully cured.

1. Why do composite colors differ in printed colors?

To ensure stable quality of printed products, color management during the printing process must be extremely strict. Printing factories manage printing colors digitally based on Lab values. During printing, it is common to encounter monochrome inks with the same Lab value, but inconsistent composite colors after overprinting.

The main reason for this phenomenon is the difference in ink transparency, because printing reproduces colors based on the principle of subtractive color mixing. The lower the transparency of the ink in subsequent overprinting, the more heavily it obscures the previous color, and the more the mixed colors lean toward the latter. Taking Lab values for magenta inks from different manufacturers as an example, when the lab values are similar, the color after overprinting can vary significantly.

Using the same principle for spot color mixing, the new ink obtained after mixing multicolor inks has lower brightness but higher saturation, making it easier to achieve uniform and thick ink colors, which is commonly used in packaging and label printing.

2. How to determine whether UV ink has fully cured

Whether UV ink can fully cure determines the adhesion fastness of the printing ink layer, color reproduction, and gloss of the printing ink layer. It is very important for the production site to quickly make accurate judgments on these points. Therefore, various methods have been summarized in practice, which can be classified as appearance observation, physical testing, and chemical testing.

The appearance observation method does not require any tools; it is determined by observing whether the UV ink layer has a bright surface. A fully cured UV ink layer is very bright.

There are two commonly used physical testing methods. Method 1: lay a sheet of paper on the UV ink layer of the printed material, press the paper with your hand, and rub it against the UV ink layer. If the curing is incomplete, the surface of the ink layer will be damaged. Method 2: Use a pin to cut open the surface of the UV ink layer, then observe the scratches under a 200x magnifying glass. If the scratches are jagged, it indicates the UV ink layer has fully cured.

Chemical testing methods use acetone solvent to drop it onto the UV ink layer; if the ink layer can dissolve, it means it has not fully cured.

Above, I have shared some key points to pay attention to when selecting and using UV ink from three perspectives: current applications, how to choose, and some common knowledge you need to know. I hope this is helpful to everyone. In the next article, I will share some common issues and solutions in UV ink printing. Stay tuned!