The Solutions to Poor Curing of UV Ink

Jul

1.Understanding the Curing of UV Ink
2.Common UV Ink Curing Problems
3.How to Judge UV Ink Curing is Poor
4.Solutions To Poor Curing Of UV Ink

UV (ultraviolet curing) ink refers to an imaging material that uses ultraviolet light of different wavelengths and energies to polymerize the monomers in the ink binder into polymers under ultraviolet light, and then solidifies into a film and dries.

In the printing process, we often encounter undesirable phenomena such as UV ink not being completely cured, weak adhesion, roller pile, dry roller, and ink flying, which affect the gradation, color, clarity, etc. of the image on the surface of the printed product.

In this article, based on many years of work experience, we will analyze the causes and solutions to the problem of poor curing of UV ink during the printing process for your reference.

Understanding the Curing of UV Ink

1. The drying of UV ink is called curing, which is different from the oxidation and penetration drying mode of traditional ink.

2. UV printing must use UV ink and UV light source to make the ink cure instantly.

3. Excessive UV energy will lead to over-curing, resulting in ink brittleness or easy peeling.

4. Insufficient UV energy directly affects insufficient ink curing and various poor adhesion problems.

5. The color of the ink and the thickness of the ink layer (single color or double color) will greatly affect the curing result. The darker or opaque the ink, the less likely the UV energy will pass through, and the worse the curing result.

6. Opaque white ink printing is sometimes more difficult to cure than black ink because UV light is not easy to penetrate or penetrate deeply.

7. Printing speed directly affects the amount of UV energy received by the ink on the material. The higher the speed, the less energy received.

8. Experiments have shown that in the process of UV ink curing, oxygen has a restrictive effect on UV curing. In an environment without oxygen, less UV energy is required to achieve the same curing effect.

9. UV ink is easier to cure at higher temperatures than at lower temperatures.

10. The light initiator in the ink needs to be matched with the UV lamp spectral energy band to achieve the most economical and optimal drying and curing effect.

Common UV Ink Curing Problems

If UV ink is not completely cured, the adhesion of the ink layer is relatively poor. During the printing process, the printed ink layer will stick to the back of the adjacent printed product, resulting in dirty printed products.

At the same time, the surface of the ink layer is not resistant to friction and is easily scratched during subsequent processing and use of printed products, seriously affecting the printing quality.

In the process of large-area solid printing, due to the large amount of ink and the thick ink layer, the ink cannot be completely dried when the printed product is dried by the UV lamp, and the surface of the ink will be dry while the bottom layer will not be completely dry. We call this the false drying phenomenon of the ink.

Especially when printing dark colors such as white and black, due to the slow curing speed, it is easy to produce a false drying phenomenon, resulting in poor ink curing.

On the one hand, this is because white can fully reflect all visible light, and requires higher energy during curing, so white ink is more difficult to cure;

On the other hand, although black and dark colors can absorb all light in theory, due to the shielding effect of pigment particles on light, it also hinders the deep curing of ink and requires higher energy, so the curing speed of dark color inks such as black is slower.

How to Judge UV Ink Curing is Poor

Whether the UV ink is completely cured determines the adhesion of the printed ink layer, the reproduction of the printed color, and the glossiness of the printed ink layer. Therefore, it is very important to quickly and accurately judge whether the UV ink is cured at the production site.

After years of production practice, we have summarized a variety of judgment methods, which can be roughly summarized as appearance observation method, physical test method, and chemical test method.

(1) Appearance observation method
The appearance observation method does not require any external tools, and directly judges by observing whether the UV ink layer has a shiny surface.
Generally speaking, a completely cured UV ink layer has a shiny surface.

(2) Physical test method
There are two commonly used physical test methods.

Method 1: Place a piece of paper on the UV ink layer on the surface of the printed product, press the paper with your hand and rub it back and forth on the UV ink layer several times.

If the surface of the UV ink layer on the surface of the printed product is found to be damaged, then the UV ink layer is not completely cured.

Method 2: Use a pin to scratch the surface of the UV ink layer on the surface of the printed product, and then observe the scratches under a 200x magnifying glass.

If the scratches on the UV ink layer are found to be jagged under magnification, it means that the UV ink layer has been completely cured.

(3) Chemical test method
The chemical testing method requires the use of acetone (CH3COCH3) solvent for testing. The specific method is to drop acetone solvent on the UV ink layer. If the UV ink layer is found to be dissolved, it means that the UV ink layer has not been completely cured.

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Solutions To Poor Curing Of UV Ink

Anyone with printing experience knows that poor UV ink curing during the printing process mainly occurs when printing film products, and poor ink drying is less common when printing paper products.

This is mainly due to the low surface tension of film products, and the ink is not easy to adhere firmly to the surface of such products.

The most thorough way to solve the problem of poor UV ink curing is to replace UV ink with a faster curing speed;
You can also replace ink with a higher color concentration to achieve the expected color reproduction with a thinner ink layer, that is, by thinning the ink layer, improving the curing efficiency of the ink, and making the ink completely cured.

In some cases, you can also not change the ink, and improve the curing efficiency of the UV ink by adding an appropriate amount of surface slip additives or an appropriate amount of curing additives to achieve complete curing of the ink layer.

However, in general, the method of adding additives is not recommended to prevent chemical reactions.

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