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Label printing
Aug 13, 2018

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The wide application of labels and the continuous development of label varieties have naturally promoted the development of label printing technology. Label printing covers all printing methods such as flat, convex, concave and net, and the application situation varies from country to country. However, it can be seen from the development trend of global labels in recent years that flexographic printing, narrow-width rotary printing and digital printing have become the new highlights of label printing in Europe and the United States, and also the development trend of label printing.


Folding prepress

In terms of prepress processing, many customers design orders are mainly offset or gravure. If the original is printed in flexo, there will be many quality problems in the sample, such as the color is not in place, the level is not obvious, and the hard appears. Wait a minute. Therefore, to solve such problems, it is necessary to communicate with customers in a timely manner.


a) Today's label printing is hand-printed, and there are many single-color or machine-printed ones (which can improve production efficiency. Although many of the newly developed label printers have low printing accuracy, they improve printing efficiency and print quality needs to be improved.


Folding plate making process

Label printing covers several major printing methods. In the plate making stage, different printing methods are selected according to different product properties, and the plate making process is different for different printing methods. This article gives a brief introduction to the flexographic plate making process.


The flexographic plate making process is as follows: the original one film (negative film) is exposed, washed, dried, and processed.


1. Original. The original design suitable for flexible printing should have the following characteristics: more color number, but less overprinting; no special small details are required to be reproduced; the network cable is not too high, but the color printing effect can be obtained; the packaging processing can be performed online.


2. Film (negative film). In line with the needs of plate making, the picture is clear, the size and size are accurate; with frosted film, the density of the four corners of the film is required to be consistent; the film is used as the word; the density measured by the transmission density meter, the white bit density is below 0.06; the black bit density is above 3.5.


3. Exposure includes back exposure and main exposure.


1 back exposure. The support film of the photosensitive resin plate is upward, and the protective film is laid down in the exposure drawer for exposure. The ultraviolet light passes through the support film to cure the photosensitive adhesive layer to establish a stable substrate, and also controls the depth of the plate to strengthen the bonding force between the support film and the photosensitive resin layer. The back exposure time is determined by the required substrate thickness.


2 main exposure. Also known as frontal exposure, the photosensitive resin support film faces down and the protective film faces up. Tiled in the exposure drawer. The protective film is peeled off once in a row, and then the film surface of the film is attached to the photosensitive resin plate. How to produce a vacuum film flat female 1 female A test method covered in film (non-medicine The membrane is vacuumed to make the film and the photosensitive resin layer closely adhered. The ultraviolet light is transmitted through the vacuum film and the transparent portion of the film to cure and cure the photosensitive portion of the plate. The length of the main exposure time is determined by the type of the plate material and the intensity of the light source. Short will make the text slope too straight, the lines are curved, and the small characters and small dots are washed away. On the contrary, if the exposure time is too long, the plate will be applied and the writing will be blurred. If there are big and small, thick and thin lines on the same plate The black film can be used to cover the exposure separately. The small part will not be lost due to the rinse to ensure the quality of the plate.


4. Rinse. The unexposed portion is washed and dissolved, and the photopolymerized relief is retained. The length of the plate-washing time is determined by the thickness of the plate and the depth of the print. The plate-washing time is too short. The plate will leave unsensitive resin and affect the plate-making depth. If the plate-washing time is too long, the plate will expand, resulting in fine deformation or Fall off.


5. Drying. Remove the washing solvent to restore the original size to the plate. The baking temperature is between 50 and 60 °C. The baking time is determined by the thickness of the plate and the length of the plate washing time. Generally, the thick plate is two hours and the thin plate is one hour. If the baking time is too long, the baking temperature will be too high and the plate will become brittle and affect the printing life. If the baking temperature is too low, the drying time will be prolonged, the baking time will be too short, and the printing will appear bad.


6. Post processing. That is, except for sticking and post exposure. The photosensitive resin is completely hardened (polymerized) to the desired hardness index, and the plate tack is eliminated to facilitate ink transfer. The post-treatment time was obtained from the test, and the purpose was not to crack or stick.


(two)

Folding printing ink

With the development of the economy, the wide application of labels on commodities has driven the rapid development of the label printing industry. However, people's understanding of label printing inks is far less than the understanding of label materials, printing methods, etc. Label printing inks, such as a mysterious field, are waiting for us to recognize and explore.


There are many types of label printing inks, which can be divided into three categories according to the solvent used - water-based label printing ink, solvent-based label printing ink and UV label printing ink.


(three)

Folding multi-process combination

At present, domestic label printing mainly adopts several methods of letterpress printing, offset printing, flexographic printing and screen printing. From a technical point of view, these printing methods have their own advantages, and each has its own advantages and disadvantages. No printing method can replace another. A printing method.


Offset printing is a widely used printing method. Domestic sheetfed printing is basically the world of offset printing. This printing method is fast, high in printing definition, accurate in overprinting, and full in printing, but the durability is poor and the ink layer is relatively thin. Light, not suitable for printing bright color label products.


The graphic reproduction of the letterpress printing has good definition, high printing speed, stronger color strength and durability than offset printing, and slightly worse than screen printing, but the level of expression and registration are stronger than screen printing and flexo printing. Most of them use letterpress printing for label production.


The biggest advantage of screen printing is that the ink layer is thick and the hiding power is good, but the speed is slow, the level is poorly reflected, and the registration degree is low (this refers to the general level in China, and the screen printing machine register developed by Wanli in recent years) The precision has reached 10 filaments and the speed is up to 6000 prints per hour), so the screen printer can be used to print labels with less layering.


The printing characteristics of flexographic printing are relatively central. Printing labels are widely used in foreign countries. However, this technology requires high processing of anilox rolls and the technical level of workers. Although the machine is simple, the process is quite complicated. There are not many domestic labels printed in this way.


In order to print the most exquisite labels, it is necessary to effectively combine various processes in the printing process, and integrate the advantages of various printing methods to form a larger combination of advantages.


The purpose of combining multiple processes:

(1) Effective anti-counterfeiting effect: printing on a same label product using a variety of process effects, especially on some labels that are easy to counterfeit cosmetics and food packaging, can make consumers look through the label It is seen that the true and false products of the products guarantee the interests of the manufacturers and consumers of the products, and have also won an excellent reputation for the printing factory.


(2) Improve the quality of printed matter: The combination of multiple processes combines the advantages of various printing processes, so this combined printing method can ensure the printing effect of printed materials to the greatest extent, thus meeting the growing sensory requirements of people. Improve the printing quality of the printing house, thus bringing more living resources to it. Improve production efficiency and reduce costs. The combination of various processes also includes the combination of printing and post-press technology. The printing and finishing of the products are completed once, and the finished products can directly reduce the cost.


There are two forms of multi-process combined machines:

(1) One is a combination of single machine: In the trademark printing machine, we are more common is the hatchback machine, which can complete printing, bronzing, die cutting, waste discharge, etc. on one machine, but because it is single machine printing The print size will be affected.


(2) The other is that the units are combined into a production line: the printing and production processes of embossing, screen printing, flexo printing, bronzing, die-cutting, etc. are combined into a production line for printing production, and various processes are realized on the same product. The combined effect. This combined printing production method has adapted to the needs of the development of the label market. The grade of printed materials has been greatly improved, and it has also brought huge profits to the printing manufacturers. The development of the unit-type production line in China is increasingly being I am optimistic.


Combination of letterpress, flexo and screen printing in label printing

Combining a practical example of label production to illustrate the multi-process combination in the production process. We want to print a label with color levels, blue solids and character avatars and corresponding text descriptions. In the above comparison, we know that the printing color is richer in the pattern. In label printing, letterpress printing is more flexible than flexographic printing. The layering is stronger. The best choice for printing the map is the screen printing. The character avatar can be flexographic. So on this label we put together the letterpress, flexo and screen printing to form a production line that produces beautiful labels. This type of combination of letterpress, flexographic and screen printing in label printing is a typical representation of a multi-process combination.


The process arrangement in the multi-process combination is also a matter of learning, and requires a lot of practical experience, such as the problem of slow drying of screen printing, so comprehensive and comprehensive considerations should be made when combining.


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