3.4 Smell
There are two indicators for evaluating the odor of UV oil. One is the odor during construction. The main source is the residual solvent in the UV oil. Normally, the residual solvent content is less than 2%. In special cases, such as cigarette pack UV oil 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 oil. The highest can reach 25%. This will affect the long-term development and environment of UV oil. Protection is unfavorable.
Another indicator for evaluating the odor of UV oil is the residual odor of UV oil after construction. It will not disappear after a long period of time. The main source is the improper selection of UV oil. The use of some tasteful but cheap chemicals, this It is difficult to improve fundamentally, mainly because of the cost and the choice of suitable materials.
3.5UV oil discoloration or ink discoloration
UV oil is sensitive to ultraviolet light. If the UV oil after construction continues to be exposed to ultraviolet light (such as sunlight and fluorescent lamps), the UV oil will continue to react and turn yellow, which is a defect of the UV oil itself. For conventional UV oils, it is currently impossible to fundamentally improve, but the degree of yellowing of UV oils from different suppliers is different, unless specific non-yellowing or special white UV oils are used.
The main reason for the ink discoloration after UV oil 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 are feasible if they are used in book inks (the surface is no longer polished after printing), but if used in color box inks, they are very dangerous because most color boxes are post-processed. The detection method is to drop a drop of base oil and UV oil on the surface of the ink. It is very obvious to see whether the ink changes 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 oil, solvent-free book UV oil, etc. Ways to reduce ink discoloration tendency.
3.6 Explosion and scratches
UV oil explosion oil refers to the phenomenon that the UV oil cracks in the embossed bumps, folding, beer box or daily use of the glazed paper. The scratch is the UV oil after construction, when it is scratched 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 oil hardness or poor adhesion of UV oil to the substrate. Specific reasons and solutions are:
* The UV oil is over-exposed or the hardness is too high. At this time, pay attention to the appropriate exposure (40-70mj / cm2). It is best to choose a UV oil with good flexibility;
* UV oil construction is too thick, the thicker the coating film is, the easier it is to burst;
* The quality of the paper is too poor, easy to burst, the strength of the UV oil is not enough to resist the cracking strength of the paper;
* 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;
* Ink powderization, poor cohesive strength, paper, ink, primer, UV oil cannot form an organic whole. At this time, especially in winter, it is most likely to cause scratches.
3.7 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 gold foil , 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 strength directly determines what kind of substrate can be applied to the anodized aluminum, such as BOPP, grinding oil absorption, water oil, UV oil and other substrates. .
Conventional UV oil is a thermosetting material that 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. 5 layers of adhesive, that is to say, conventional UV oil cannot be gilded.
The composition of bronzable UV oil is very different from conventional UV oil, mainly because it has the characteristics of heat softening but not melting and high surface tension, so it can be bronzed. Conversely, if the fifth layer of anodized aluminum uses an adhesive similar to the performance of UV color box glue, I believe that conventional UV oil can also be gilded.
3.8 Books UV Oil
In terms of formula design and chemical structure, the book UV oil is a very special UV oil. It 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.
4. The development prospect of paper UV oil
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:
* High gloss and high wear resistance UV oil: Under certain premises, high gloss and high wear resistance are in conflict. How to improve the wear resistance and scratch resistance of UV oil under high light is a technical problem.
* Harmless and tasteless food-grade UV oil: Because UV oil 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 completely Response is also a subject that industry colleagues need to face.
* Water-based UV oil: This is a product that realizes the true environmental protection of UV oil. At present, the technical barriers have been overcome, but it will take time to reduce the production cost and achieve large-scale production.
Limited by personal level, if the above is not available, I hope all readers, industry experts and seniors can point out and discuss and make progress together.
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