Single machine glazing
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Single-machine glazing uses a special glazing machine to glaze the surface of the printed matter, that is, printing and glazing are performed on separate dedicated devices. Single-machine glazing has its own unique advantages in large-scale glazing, and has a high degree of flexibility, and can be matched with several different types of printing presses. In addition, it can meet different glazing requirements, provide a variety of special glazing effects, and can be used in a wide range of applications, such as commercial printing, such as corporate samples, calendars, annual reports, etc., as well as trademarks and various types. The package is glazed. The investment in single-machine glazing equipment is small, which is more suitable for professional post-press processing manufacturers.
Consumables and process parameters
In the process of glazing, there are many factors affecting the quality of single-machine glazing, such as light plate, glazing oil, printing material, printing ink, glazing temperature and so on.
1. The impact of the glazing version
The glazing is divided into overall glazing and partial glazing. The main function of the overall glazing is to protect the printed matter and improve the surface gloss of the printed matter. Generally, the method of roller coating is used for the glazing; the partial glazing is generally emphasized on the printed matter. The illuminating part of the image is glazed, and the high-gloss picture of the glazing portion is compared with the unglazed portion to produce a wonderful artistic effect.
Since there is basically no registration problem in the overall glazing, and the partial glazing pattern must be accurately registered, the difficulty is high, so we have more talk about the choice of the partial glazing version. First of all, it should have a clear understanding of the structure of the glazing part of the local glazing product. According to the distribution of the local graphic, the size of the graphic area, the thickness of the line and the characteristics of the glazing oil (the most important leveling), etc. Material selection. For example, when glazing on a partial fine pattern, it is not suitable to use a resin plate or a blanket as a glazing plate. The anilox roller with different number of lines should be selected according to the requirements of the product for the brightness of the glazing, and the thickness of the varnish must be controlled.
2. The effect of varnish
According to everyone's reflection, in the process of glazing, the most important factor affecting the quality of glazing is glazing oil. Therefore, we will start discussions on glazing oil, and put forward the matters that should be paid attention to when choosing the varnish for the current situation of varnish on the market, to help you buy.
For solvent-based varnish and water-based varnish, the current printing technology used by printing manufacturers is relatively uniform and relatively stable and mature; for UV varnish, the problem is relatively more.
All kinds of glazing oils may have poor gloss, poor leveling and poor drying. These phenomena are related to the quality of the varnish and the operation. Poor gloss, should pay attention to the resin composition ratio of varnish and the quality of the plate and glazing roller of the oil machine during operation. The main reason for the poor leveling property is that the drying time is too long or the light power is too large, and the glazing oil is too sticky. If the varnish is not dry well, the glazing oil will not dry thoroughly enough, and there is no over-base. That is to say, the surface is dry and the inner layer is not dry. The drying time and light intensity should be adjusted. At the same time, the viscosity of the varnish should be paid attention to. Dilution. In addition, the crystallization of the varnish has a relatively large influence on the quality of the glazing. Because the printing time is too long, the ink area of the printed product is too large, and the dry oil is added too much, the glazing oil will not be printed or the phenomenon of "flower face" and "pitting" will occur. Generally, 5% lactic acid can be added to the glazing oil and used after stirring.
These three different varnishes also present different problems during the drying process. Solvent-based varnishes can be odorous during drying. The oily solvent contains a resin and toluene. After heat-curing, the alcohol glazing coating and the solvent will chemically act on the ink layer. The solution is to increase the intensity and speed of infrared and heat-sensitive curing. Proper thermal energy and control of operating speed promote solvent volatilization, improve drying, reduce residue, and reduce odor and discoloration. In the drying process, the water-based glazing oil should avoid the chemical action of the thinner on the ink layer and the paper coating and the influence on the smoothness of the paper surface, and further avoid environmental pollution. The UV varnish uses the spectral range of the ultraviolet light source, the power of the light source, and the corresponding transfer width and effective curing speed to complete the drying. If there is solvent residue after curing, the oil phenomenon will occur. Therefore, attention should be paid when curing.
The varnish currently on the market mainly has the following problems:
(1) The dilution ratio range is too large, and it is difficult to grasp the best point in operation;
(2) There is a general problem of leveling instability, which is mainly manifested in the appearance of obvious oil marks at the edges of local glazing;
(3) The gloss of varnish is unstable;
(4) Drying performance is difficult to control, and the drying degree of different batches of the same varnish is different;
(5) The hot stamping performance of varnish is unstable, especially UV varnish;
(6) odor of varnish;
(7) The viscosity is high (easy to stick), the most important thing is that the friction test cannot be passed;
(8) The environmental performance of varnish is not very good.
Pay attention to the following when choosing varnish:
(1) Understand the type, nature, effect and varnish of varnishes when they are formulated with other solvents;
(2) Select a suitable varnish for the substrate and ink surface properties of the substrate;
(3) Pay attention to the drying performance of the varnish, and whether the drying temperature range and the drying time have an influence on the substrate;
(4) Consider the post-processing adaptability of the glazing material, such as hot stamping performance, rub resistance, pressure resistance during die-cutting die-cutting, etc.;
(5) When testing a batch of varnish, check whether the varnish is sticky by heating and whether the color of the printed pattern changes;
(6) A varnish with high transparency and low odor should be used.
3. Influence of printing materials
The influence of printing materials on glazing is manifested in two aspects. One is unprinted paper, which is mainly reflected by the influence of paper smoothness on glazing quality. Paper with high smoothness is effective after glazing, while paper with low smoothness is less effective after glazing because the glazing oil is almost completely absorbed by the rough surface. To solve this problem, you can use the primer or the last two lights before glazing. In addition, the paper is too thin or the paper is too bad for the glazing. The paper is too thin to wrinkle, the paper is too poor, the glazing oil will leak, and the gloss is not good. The second is the printed paper, which is mainly reflected in the following aspects:
(1) If there are substances such as talcum powder and additives on the surface of the printed matter, it needs to be treated before glazing.
(2) When printing gold, silver ink or large-area field printing (such as black, dark brown, dark green, etc.), in order to avoid sticking, it is necessary to spray a large amount of powder. Before the single machine is glazed, it must be wiped cleaned to remove the powder. Light.
4. The influence of printing ink
Printing inks used in products that need to be glazed after printing must have solvent resistance and heat resistance, otherwise the graphics will be discolored or wrinkled. In selecting the printing ink, the following principles should be adhered to: the use of alcohol-resistant, ester-resistant solvents, acid and alkali resistant, long-lasting discoloration, good gloss and good adhesion to paper.
Human Factors
When the operator glazes the product, he must understand the glazing requirements of the glazing product, be familiar with the mechanical properties of the glazing machine and operate it strictly according to the operating procedures. At the same time, the performance of the varnish must be clearly understood. It is necessary to reach the parameters of the glazing oil during operation to be officially started.
The correct method of operation can improve efficiency, reduce time and waste of resources in the production process, and the quality is further guaranteed. The method of operation has a direct impact on the glazing effect:
(1) The temperature and time control of the drying system of the glazing machine does not meet the requirements, which will result in incomplete drying of the glazing oil. Sticky flowers will appear after the overlap of the printing products; excessive drying will cause the varnish to appear on the surface of the printed product. Bad or bursting.
(2) Pay attention to the selection of the plate when glazing. If the plate is improperly selected, it will directly affect the brightness thickness of the glazing and fail to meet the product quality requirements.
(3) Dilution is not strictly carried out according to the dilution ratio of varnish, which has a direct impact on the drying performance, brightness, leveling and wear resistance of the varnish.
Since the operator plays a more important role in the operation, the operator is required to:
(1) Must be rigorous, prudent and meticulous in the course of operation;
(2) The operation must be in place to test the gloss and color;
(3) Enhance the quality awareness of the product;
(4) The problems that arise during the work must be resolved quickly and accurately.
In addition, the operator should take different measures according to the type, thickness and quality of the printed product, the depth of the ink, the dryness of the surface and the amount of dust spray to ensure the glazing effect. If the operation method is improper, it will directly affect the glazing effect. If the temperature is too high, the paper will be deformed, yellow, brittle or even vitrified. If the temperature is too low, the brightness will be insufficient and it will stick. The amount of oil will also affect the upper part. The quality of light.
5. The effect of temperature
The temperature of the glazing is generally controlled at 18 to 20 ° C, which can achieve better results. The glazing temperature is too high, which on the one hand causes waste of resources, and on the other hand, it also affects the printing materials. When the temperature is too low, the glazing oil is easily solidified, and the surface layer of the product after glazing is not uniform. Therefore, the varnish should be stored in a place where it is kept warm; if the temperature of the varnish is too low, a hot solvent can be added.
Unresolved issue
In addition to the problems mentioned above during the glazing process, frontline operators have encountered some difficult problems, including online glazing and single glazing. They asked us to seek help from a wide range of readers. We hope that everyone can contribute ideas, solve existing problems, jointly promote the improvement of glazing quality, and print more exquisite products.
Problem 1: When the glazing is carried out on the plain laser coated paper, the varnish is dry and not sticky. At present, the large domestic glazing oil producers and agents are seeking solutions and have not yet solved them.
Question 2: After a product of a company is glazed, its light film layer is slightly yellow and the gloss is not enough. After the coated UV varnish is cured, the color of the printed matter is unstable and discolored, which is very different from the original. For example: 200g/m2 coated paper is applied to UV varnish after printing, and the color changes greatly after printing for less than one month, especially the blue and red colors are more obvious. This type of UV glazing is first applied to the base oil and then to the UV varnish. The amount of sizing used in the crepe process is also moderate.