Difference between drying (curing) principle and equipment
UV varnish relies on the initiator in the varnish to absorb ultraviolet light, generate free radicals, and initiate monomer and oligomer reaction and curing. A domestic laboratory curing equipment can be 20,000 RMB, domestic production equipment is about 200,000 to 300,000 RMB.
EB varnish is under the strong bombardment of the electron beam, the double bonds on the monomer and oligomer are forced to open, generate free radicals and complete the polymerization. An imported laboratory EB curing equipment costs about US $ 100,000-200,000, while the production equipment is between US $ 500,000-800,000.
At present, the core technology of EB curing equipment is in the hands of a few foreign companies. Because the mass production of such equipment is small, the price is relatively high. I believe that if this technology is generally used, the reasonable price should be between 300,000 and 500,000 US dollars If the manufacturing technology of the equipment is mastered by Taiwanese or domestic counterparts, I believe the price will be lower.
· The difference between smell
Both UV oil and EB oil do not contain solvents, so the odor problem during construction does not exist. The so-called odor mainly refers to the odor remaining on the surface of the printed matter. There are two sources of residual odor of UV oil, one is the residual initiator and active monomer, and the other is other small molecular substances generated after the reaction of the initiator. Improve the initiator of UV oil, and increase the degree of reaction, the smell will be improved, but it can not be completely removed.
There is no initiator in EB varnish, and the reaction degree exceeds 98%, so it will not have the problem of residual odor like UV oil.
· The difference between yellowing resistance
We know that the paper that has been coated with UV oil will gradually turn yellow after being left for a long time. The main reason is that the residual initiator and the initiator product absorb ultraviolet light. Use expensive initiators or add ultraviolet absorbers to the UV oil It will help, but it can't be completely non-yellowing. EB varnish does not use an initiator, so this problem will not exist.
· The problem of ink discoloration
While the UV lamp generates ultraviolet rays, it also generates infrared rays, which makes the surface temperature of the varnished paper higher. Since the production efficiency must be guaranteed, the paper is stacked together before the temperature drops. The inner layer of the paper will be 30- Keep it at 60 ℃ for a period of time, then some inks with poor heat resistance will change color. In addition to the influence of temperature, the initiator in the UV oil will still maintain a certain activity at a relatively high temperature, and it may have a chemical reaction with some active substances in the ink. One. By improving the UV lamp, reflector, and cooling system, the problem of ink discoloration will be solved to a certain extent, but it is also a solution to the symptoms.
In the curing process of EB varnish, the curing equipment does not generate infrared rays during the process of generating electron beams, and the temperature problem is well solved. Therefore, electron beam curing is a real cold energy source and will be more suitable for some heat-sensitive substrates.
· Comparison of curing degree
In order to understand the degree of curing of UV oil and UV oil, the concept of gel rate is introduced here. The measuring method is: make varnish into a coating film with a thickness of 100 μm, record the quality W0 of the coating film after curing, use acetone After 48 hours of extraction, vacuum drying at 50 ° C for 8 hours, and note the mass Wg after extraction. Then calculate as follows:
Gel rate = Wg / W0 × 100%
The higher the gel rate, the higher the degree of curing. The following figure is a comparison of the curing degree of typical EB varnish and UV varnish.
It can be seen that the UV oil increases the energy anyway, and the curing degree is only about 75%. The normal construction energy of UV oil is 50-100mJ / cm2, which means that the UV oil we currently use will have 25% -30% on the surface of the printed product. The residual of small molecular substances, these small molecular substances, on the one hand, reduce the physical properties of the product, on the one hand, there are serious hidden dangers in safety, if it may cause human skin allergies, etc.
The curing energy of EB varnish reaches 40kGy (the unit of electron beam energy), the degree of curing can reach more than 98%, and the physical properties and safety have been well solved. [next]
· Differences between scratch resistance, wear resistance and explosion-proof wire
Scratch resistance: Because the curing degree of EB varnish is much higher than that of UV varnish, plus the reason of oxygen inhibition during UV curing, the curing degree of the surface of UV varnish is lower than that of the interior. Under the condition of hardness, the scratch resistance of UV varnish is far inferior to that of EB varnish. Of course, increasing the hardness of the UV varnish, adding wear-resistant fillers and additives, etc. can improve the scratch resistance of the UV oil, but this will also bring the sacrifice of the linearity of the UV oil explosion-proof.
Wear resistance: We know that wear resistance is related to the flexibility of the coating film. The greater the toughness, the more wear-resistant the coating film, such as automobile tires (SBS rubber material) and sports soles (PU polyurethane material), etc., due to UV Insufficient curing of varnish can not obtain a coating film with good flexibility. Therefore, the wear resistance of UV varnish cannot be compared with EB varnish.
Explosion-proof linearity: Once tested, the initiator in the UV oil formula was removed and changed to EB varnish. It was found that the anti-explosion linearity of EB varnish is not as good as that of UV oil. Because the degree of curing of EB varnish is nearly 30% higher than that of UV oil, the higher the degree of curing, the greater the hardness of the product, the easier it is to be broken, and the anti-explosion linearity will become worse.
To truly compare the explosion-proof linearity of the two, you must adjust the formula of the two so that their hardness or scratch resistance is the same. At this time, you will find that the explosion-proof linearity of EB varnish will be better.
· The difference of anti-sticky flower
In the impression of ordinary people, there is no sticky flower in UV oil, but in some special cases, such as, UV oil is required to have a good explosion-proof linearity, then the cross-linking density of UV oil will be reduced as much as possible to make UV oil It has better flexibility and will not break when the paper is bent. However, due to the incomplete curing of UV oil, it may bring the risk of UV oil sticking to flowers.
In addition, in the silk screen UV oil, in order to obtain good flexibility and adhesion to the film, the varnish is filled with thermoplastic resins, such as polyisobutyl acrylate, etc. These resins not only do not participate in curing themselves, but will Blocking the curing of other monomers and resins, this type of UV oil is more insufficiently cured, and the possibility of sticking flowers is greater.
In EB varnish, due to the violent bombardment of the electron beam, the monomers and resins that can react will fully react, and the possibility of sticking flowers is very small.
· The difference between solvent resistance
In some cases, varnish will have solvent resistance requirements. For example, if you put PVC or PET film on the skylight above the color box, because the color box glue contains a small amount of solvent, if the UV oil has poor solvent resistance, it may cause UV oil. Stick to the film. In addition, the surface coating of film furniture also requires solvent resistance.
The measurement method of solvent resistance is as follows: a cotton cloth dipped in MEK (methyl ethyl ketone), one round trip, until the coating film is scratched. Figure 3 below is the difference between the solvent resistance of EB varnish and UV varnish, the coating thickness is 4 microns.
Under the same thickness, the solvent resistance of EB varnish is more than 4 times that of UV varnish. As the coating becomes thicker, the solvent resistance of EB varnish will become more obvious.
· Whether EB varnish and UV oil need to be primed
First, we need to understand why UV oil needs to be primed. In UV oil, the molecular weight of the active monomer is very small (about 300), the molecular weight of the oligomer is also very limited (about 500-1000), and the solvent type Compared with resin in varnish (20,000) and resin in water and oil (5000-100,000), the molecular weight is very different. When UV oil is applied to cardboard, monomers and oligomers will penetrate into the paper fibers In the loss of light on the surface. In order to ensure that the UV oil does not penetrate into the paper and all stay on the surface of the paper, high molecular weight products such as water oil are required for primer. At the same time, in order to ensure that the primer and UV oil have good adhesion, the primer also needs special design and matching .
EB varnish and UV varnish are very similar in formulation and selection, so EB varnish also needs a primer, but due to the sufficient curing of EB varnish, higher molecular weight resins can be used in EB varnish, which is not suitable for design. The EB varnish that needs to be primed provides greater possibilities and flexibility.
· The difference in cost
I believe everyone will ask this question. UV oils used on packaging materials that are not sensitive to odor requirements do not use expensive ultraviolet light initiators. Compared with EB oils, these types of UV oils are comparable in price. However, for some of the more demanding UV oils used in gift packaging, medicine, tobacco, alcohol, food and other outer packaging, the price of UV varnish will be higher than that of EB varnish, but due to the need for nitrogen or carbon dioxide gas protection during the construction of EB varnish, The overall cost may be the same, and since there is no industrial production material, an accurate answer cannot be given yet.
Summary of the advantages of EB varnish
Efficient: The curing speed of the single-curtain EB curing equipment can reach 900 meters per minute (calculated value), which is higher than the UV curing equipment with 3 UV lamps connected in series (about 200 meters per minute), and also higher than the current The fastest printing speed (726 m / min, calculated value, German Manroland 75 printing machine, 75,000 sheets), so EB varnish is the fastest drying varnish at present, and will not be used to improve printing efficiency Obstacles; enhance the added value of the product: the curing degree of EB varnish is much higher than that of UV varnish, which can make the product have better wear resistance, scratch resistance, solvent resistance, yellowing resistance and good smell, these Performance is unattainable by UV oil, water oil and other varnishes.
Safety and environmental protection: The surface of the printed matter after construction with EB varnish has no residual small molecular chemicals. Its safety and environmental protection are also unattainable by UV oil, and can be safely used in food packaging, tobacco and alcohol packaging , Packaging of medicines or articles in contact with the human body.
in conclusion
EB varnish has obvious advantages in performance compared to UV coatings. When processing high-document products or products with special requirements, such as food packaging, tobacco and alcohol packaging, and packaging for items that contact human bodies, etc., EB varnish is a better select.
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