odor
There are two indicators for evaluating the odor of UV ink. One is the odor during construction. The main source is the residual solvent in the UV ink. Under normal circumstances, the residual solvent content is less than 2%. In special cases, such as cigarette pack UV ink The requirement is less than 0.5%, but today, when the price of oil is soaring, many suppliers add a large amount of solvents, such as alcohol and toluene, to reduce the cost of UV inks, and the highest can reach 25%. Protection is unfavorable.
Another indicator for evaluating the odor of UV ink is the residual odor of UV ink after construction. It will not disappear after being left for a long time. The main source is the improper selection of UV ink. Some odorous but cheap chemicals are used. It is difficult to improve fundamentally, mainly because of the cost and the choice of suitable materials.
UV ink discoloration or ink discoloration
UV ink is sensitive to ultraviolet 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, which is a defect of UV ink itself. For conventional UV inks, it is currently impossible to fundamentally improve, but the degree of yellowing of UV inks of different suppliers is different, unless specific non-yellowing or special white UV inks are used.
The main reason for the ink discoloration after UV ink glazing is the ink problem. There are some pigments in the ink, such as light blue, which is a blue acid lake pigment. It is an organic dye triphenylmethane dyed on body pigments such as aluminum hydroxide to form a water-insoluble pigment pigment. The price is low and the hue is low. Bright, but its light resistance, solvent resistance and alkali resistance are poor. When it encounters solvents such as alcohols or alkali, the red phase is easily dissolved, weakened or disappeared. These pigments, such as used in book inks (the surface is no longer glazed after printing) are feasible, but if used in color box inks, it is very dangerous, because most color boxes are post-processed. The detection method is to drop a drop of primer and ink on the surface of the ink. It is very obvious to see whether the ink has changed color after 1 hour.
For the printed paper, if the ink changes color, you can use forced ink drying, such as drying or a little more time to solve, or use a neutral primer, solvent-free UV ink, solvent-free book UV ink, etc. Ways to reduce ink discoloration tendency.
Oil burst and scratches
UV ink explosion oil refers to the phenomenon of UV ink cracking in embossed paper, folding, beer box or daily use after glazing. Scratch is the UV ink after construction, when it is scraped on the surface with nails or hard objects, it is partially powdered. The root cause of the above two phenomena is caused by too high UV ink hardness or poor adhesion of UV oil to the substrate. Specific reasons and solutions are:
1. The UV ink is over-exposed or the hardness is too high. At this time, pay attention to the appropriate exposure (40mj / cm2 ～ 70mj / cm2). It is best to choose a UV ink with good flexibility;
2. The UV ink construction is too thick, the thicker the coating film is, the easier it is to burst;
3. The paper quality is too poor, easy to burst, the strength of UV ink is not enough to resist the cracking strength of paper;
4. The base oil is too hard and too thick, which is not very helpful to prevent the UV oil from cracking or play a negative role;
5. Ink powdering, poor cohesive strength, paper, ink, primer, UV ink cannot form an organic whole. At this time, especially in winter, it is most likely to cause scratches.
Bronzing
Bronzing is a process of heat transfer. Under the action of heat and pressure, the substance on the PET substrate is transferred to paper or other printed substrates. The most commonly used material is anodized aluminum. To solve the bronzing process, it is best to first explain the structure of anodized aluminum. As shown in Figure 1, it is divided into 5 layers: the first layer is a PET (polyester) film base; the second The layer is an isolation layer, which can be detached from the PET film base under the effect of hot pressing. The commonly used materials are silicone grease or other adhesives with low adhesion; the third layer is a dyeing layer, which is composed of resin and pigment, and protects the aluminum powder after bronzing , And give color and luster; the fourth layer is a vacuum aluminum plating layer to provide reflectivity; the fifth layer is an adhesive layer, mainly acrylic resin and some other tackifying resins, which are bonded to the substrate under the effect of hot pressing This layer is the most critical layer to determine the adaptability of bronzing. Its bonding force directly determines what kind of substrate can be applied to the anodized aluminum, such as BOPP, grinding oil absorption, water oil, UV ink and other substrates. .
Conventional UV oil is a thermosetting material, it will not soften when heated, and a large amount of silicone and wax substances are added to the UV oil, these substances are not easy to be bonded, so the conventional UV oil is the first in the anodized aluminum Five-layer adhesive, that is to say, conventional UV ink can not be gilded.
The composition of bronzable UV ink is very different from conventional UV ink, mainly because it has the characteristics of heat softening but not melting and high surface tension, so it can be bronzed. Conversely, if a layer of anodized aluminum uses an adhesive similar to the performance of UV color box glue, it is believed that conventional UV inks can also be gilded.
Book UV Ink
In terms of formulation design and chemical structure, the book UV oil is a very special UV oil, which is a special UV oil for books and periodicals developed for offset paper. It has good adhesion without primer. , Anti-penetration, sticky box, hot stamping and other properties. Books and periodicals UV oil also has a certain adaptability when applied to ordinary cardboard, but it is best to be tested before use.
Other properties of paper UV oil, such as stick marks, orange peel, pinholes, shrinkage holes, pitting, etc., and some special-purpose products, such as gravure UV oil, silk screen UV oil, etc., due to space limitations , Not introduced 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 worthy of focus in the future:
1. High gloss and high wear resistance UV ink: Under certain premises, high gloss and high wear resistance are in conflict. How to improve the wear resistance and scratch resistance of UV inks under the premise of high gloss is a technical problem.
2. Harmless and tasteless food-grade UV oil: Because UV ink contains a large number of small molecules with a molecular weight of less than 1000, and curing occurs in an instant (within 1 second), there will inevitably be some small molecules that cannot fully participate in the reaction. How to make these small molecules The complete response is also a subject that the industry counterparts need to face.
3. Water-based UV ink: This is a product that realizes the true environmental protection of UV ink. At present, the technical barriers have been overcome, but it will take time to reduce the production cost and achieve large-scale production.
This product was launched in 2019.
It's been 3 years, very popular in China and Europe.
The main ingredient is PEG-PLLA-PEG, balanced salt and water.
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Let me explain here. Poly (L-lactic acid) PLLA is a high molecular polymer.
It is insoluble in water. So Reborn PLLA Dermal Filler is a milky white mixture after mixing. PLLA microspheres are mixed in solution and then injected into the human body to stimulate collagen. But Reborn PLLA Hydrogel Filler, which is a liquid gel.
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