Part F Glazing process and analysis of quality factors
The glazing process is a technique and method for applying a layer of uncoated transparent coating on the surface of the printed product, after leveling, drying, calendering, and forming a thin and uniform transparent bright layer on the surface of the printed matter.
UV glazing process knowledge and troubleshooting
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Seven, UV glazing mode
There are many UV glazing methods, and there are many classification methods. There are mainly the following classification methods:
1. According to the relationship between the glazing machine and the printing machine, it can be divided into two types: offline glazing and online glazing. (1) Off-line glazing: Off-line glazing uses a special glazing machine to illuminate the printed matter, that is, printing and glazing are performed on their respective dedicated devices. This glazing method is more flexible and convenient, and the investment in glazing equipment is small, which is more suitable for professional post-press processing manufacturers. However, this glazing method increases the transportation transfer between the printing and glazing processes, and the production efficiency is low.
(2) On-line glazing: On-line glazing directly connects the glazing unit to the printing unit, ie printing and glazing are carried out on the same machine. The speed is fast, the production efficiency is high, the processing cost is low, and the handling of printed matter is reduced. Overcoming all kinds of quality faults caused by dusting is the future development direction. However, on-line glazing has high requirements for glazing technology, glazing oil, drying equipment and glazing equipment.
2. According to the glazing method, it can be divided into two types: roll coating and printing.
(1) Roll coating
Roll coating is the most common glazing method, and the coating varnishes the varnish on the surface of the print to uniformly coat the entire surface.
(2) Printing glazing
The printing glaze is applied to the printed matter by the glazing plate, so that partial glazing can be performed. Currently used are gravure glazing, flexographic glazing, offset glazing and screen glazing.
3. According to the classification of glazing products, it can be divided into: full-surface light, partial glazing, matt glazing and artistic glazing.
(1) Full-surface light
The main function of the full-surface light is to protect the printed matter and improve the surface gloss of the printed matter. The full-surface light is generally carried out by means of roll coating.
(2) Partial glazing
Partial glazing generally illuminates the portion of the image to be emphasized on the printed matter, and the high-gloss picture of the glazing portion is compared with the low-gloss picture without the glazing portion, producing a wonderful artistic effect. Partial glazing is carried out by means of printing glazing. The film obtained by screen printing is thicker, the effect is more obvious than other methods, and the cost is lower. Currently, it is used more in China, but its production efficiency is generally Lower.
(3) matt glazing
The matt glazing uses UV matt oil, which is opposite to the effect of ordinary glazing. It reduces the gloss of the printed surface and produces a special effect. Because the gloss is too high, it has a certain degree of stimulation to the human eye. Therefore, matt glazing is a popular glazing method.
(4) Art glazing
The role of artistic glazing is to achieve a special artistic effect on the surface of the glazing product. If UV glazing varnish is used to glaze on the surface of the printed matter, the surface of the printed matter will have a pearlescent effect, making the printed matter look magnificent, noble and elegant.
UV glazing often has the following problems:
1. "Pee"
the reason:
a, the ink has crystallized.
b. The surface tension value is large, and the ink layer is not well wetted.
solve:
a. Add 5% lactic acid to the UV oil to destroy the Changhua film, remove the oil or roughen the hair.
b. Reduce the surface tension value and add a surfactant or a solvent with a low surface tension value.
2. Streaks and wrinkles
Reason: The UV oil is too thick and the coating amount is too large, mainly in the roll coating.
Solution: Reduce the viscosity of the UV oil and dilute with an appropriate amount of alcohol solvent.
3. Orange peel
the reason:
a, UV oil viscosity is high, leveling is poor.
b. The coating roller is too thick and not smooth and the coating amount is too large.
c, the pressure is not uniform.
solve:
a, reduce viscosity, national leveling agent and appropriate solvent.
b. Use a thin coating roller and reduce the amount of coating.
c. Adjust the pressure.
4. Sticky
the reason:
a, the UV light intensity is insufficient or the machine speed is too fast.
b, UV varnish storage time is too long.
c. The diluent that does not participate in the reaction is added too much.
solve:
a. When the curing speed is less than 0.5 second, the ultraviolet power should be no less than 120w/cm.
b. Add a certain amount of UV varnish curing accelerator or replace varnish.
c. Pay attention to the rational use of thinner.
5. Can't be painted or flowered
the reason:
a, the surface of the printed ink produces crystallized oil, dusting, and the like.
b. Too much ink and dry oil in the ink.
c. The viscosity of the UV varnish is too low or the coating is too thin.
d. The rubberized anilox roller is too thin.
e. The photocuring conditions are not suitable.
f. UV varnish itself has poor adhesion and poor adhesion of printed materials.
solve:
a. Eliminate the crystallized layer, roughen, remove grease or add 5% lactic acid.
b. Select the ink auxiliary material that matches the UV oil process parameters, or wipe with a cloth.
c. Use a high viscosity UV varnish to increase the coating amount.
d. Replace the anilox roller that matches the UV varnish.
e. Check if the UV lamp is aging, or the machine speed does not match, and choose the appropriate drying conditions.
f. Apply primer or replace special UV varnish or choose good surface performance.