Paper UV ink technical standards

UV ink discoloration or ink discoloration

UV inks are sensitive to UV light. If the UV ink after construction continues to be exposed to ultraviolet light (such as sunlight and fluorescent lamps), the UV ink will continue to react and turn yellow. This is a defect of the UV ink itself. For conventional UV inks, there is currently no fundamental improvement, but the degree of yellowing of UV inks from different suppliers is not the same unless a specific non-yellowing or ultra-white UV ink is used.

The main reason for ink discoloration after UV ink coating is the ink problem. There are some pigments in the ink, such as blue light, which is a blue acid lake pigment. It is an organic dye triphenylmethane dyed on an organic pigment such as aluminum hydroxide. It forms insoluble pigment pigments in water. The price is low. Hue Bright, but its light resistance, solvent resistance and poor resistance to alkali, when met with solvents such as alcohol or alkali, the red phase is easily dissolved, weakened or disappeared. These pigments, such as those used in book inks (the surface is no longer glossed on after printing), are feasible, but if used in boxed inks, they are very dangerous because most color boxes are post-processed. The test method is to drop a drop of base oil and ink on the surface of the ink. After 1 hour, it is very obvious whether the ink is discolored.

For printed paper, if the ink is discolored, forced ink drying can be used, such as drying or adding a little time to solve, or using neutral base oil, solvent-free UV ink, solvent-free UV ink, etc. Ways to reduce the tendency of ink discoloration.

Bursting and scratching

UV ink burst refers to the phenomenon of UV ink cracking after embossing, folding, beer box or daily use. Scratching is a phenomenon in which the UV ink after construction is partially pulverized when a nail or a hard object is scratched on the surface. The root cause of the above two phenomena is UV ink hardness is too high or UV oil on the substrate adhesion caused by the specific reasons and solutions are:

1.UV ink overexposure or hardness is too high, this time should pay attention to the amount of exposure (40mj/cm2 ~ 70mj/cm2), the best choice for flexible UV ink;

2.UV ink construction is too thick, the thicker the coating film is, the easier it is to burst.

3. Poor paper quality, explosive cracks, UV ink strength is not enough to resist the paper cracking force;

4. The base oil is too hard and thick to help protect the UV oil from cracking or vice versa.

5. Ink powdering, poor cohesive strength, paper, ink, base oil, UV ink can not form an organic whole. At this time, especially in winter, the phenomenon of scratching occurs most easily.

Hot stamping

Hot foil stamping is a heat transfer process in which the material on the PET substrate is transferred to paper or other printed substrates under the influence of heat and pressure. The most commonly used material is galvanized aluminum. To understand the bronzing process, it is best to first understand the structure of the galvanized aluminum and divide it into five layers: the first layer is the PET (polyester) film base; the second layer is the isolation layer, in the hot pressing It can be separated from the PET film base. The commonly used material is silicone grease or other low-viscosity adhesives. The third layer is a dyed layer composed of resin and pigment. After the gold foil is protected, the aluminum powder is protected and the color and gloss are imparted. The 4th layer is a vacuum aluminum plating layer, providing reflection; the 5th layer is an adhesive layer, mainly acrylic resin and other tackifying resins, which are bonded to the substrate under the effect of hot pressing. This layer is determined to be hot The most critical layer of adaptability, the size of its adhesive force, directly determines the substrate on which the anodized aluminum can be hot, such as BOPP, grinding oil, water oil, and UV ink.

Conventional UV oils are thermosetting materials that do not soften when heated, and a large amount of organic silicon and wax species are added to the UV oil. These materials are not easily bonded, so conventional UV oils cannot be used in anodized aluminum. The five-layer adhesive, that is to say conventional UV inks cannot be hot stamped.

The composition of the bronzing UV ink is very different from that of the conventional UV ink, and is mainly characterized by heat softening but not melting and high surface tension, so it can be gilded. On the contrary, if the fifth layer of anodized aluminum adopts a kind of adhesive similar to the performance of UV color box adhesive, it is believed that the conventional UV ink can also be hot stamped.

Books UV ink

From the aspect of formula design and chemical structure, the publication UV oil is a very special UV oil. It is a special UV oil developed for offset paper and has good adhesion without primer. , anti-infiltration, sticky boxes, hot stamping and other properties. UV oil is also adaptable when it is applied to plain paper, but it is best to test it before use.

Other properties of paper UV oil, such as stick marks, orange peel, pinholes, shrinkage holes, pitting, etc., as well as some special-purpose products, such as gravure UV oil, screen UV oil, due to space limitations , not one by one here.

Paper UV ink development prospects

Under the environment of environmental protection, high efficiency, high performance and energy saving, UV oil will be further promoted and applied in the printing industry. From a personal point of view, the following UV oil products are worth focusing on in the future:

1. High-gloss, high wear-resistance UV ink: Under certain conditions, there is a conflict between high light and high abrasion resistance. How to improve the abrasion resistance and scratch resistance of UV ink under the premise of high light is a technical problem.

2. Harmless and odorless food grade UV oil: Since UV inks contain a large number of small molecules with a molecular weight of less than 1000, and curing occurs instantaneously (within 1 second), some small molecules will inevitably not fully participate in the reaction. How to make these small molecules Complete response is also a subject that the industry peers need to face.

3. Water-based UV inks: This is a product that realizes the real environmental protection of UV inks. At present, technical barriers have been overcome. However, it remains to be seen how to significantly reduce its production costs and achieve large-scale production.