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 applications in different countries are not the same. 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 European and American countries, and are also the trend of label printing.
Prepress processing
In terms of prepress processing, many customers design orders based on offset or gravure printing. If this type of manuscript is used for flexographic printing, proofs will have many quality problems. For example, the color is not in place, the level is not obvious, and there is hard evidence. Waiting. Therefore, to solve such problems, it is necessary to communicate with customers in a timely manner.
a) Today's label printing has manual printing, and there are many monochromatic or machine-printing (which can improve the production efficiency. Although many newly-developed label printers do not have high overlay accuracy, the printing efficiency is improved, and the printing quality needs to be improved.
Platemaking process
Label printing covers several major printing methods at the plate making stage. According to the nature of different products, different printing methods are selected. For different printing methods, the plate making process is also different. This article gives a brief introduction to the flexography process.
The process flow of the flexographic plate making process is as follows: the manuscript film (negative film) is exposed, processed, rinsed, dried, and processed.
1. Originals. The manuscript for flexible printing should have the following characteristics: more colors. However, there are few overprints; no special details are required to be reproduced; the cable is not too high, but color printing can be achieved; packaging can be done online.
2. Film (negative film). In accordance with the needs of plate making, graphic and clear, accurate size and size specifications; with frosted film, film density requirements for the same film; the use of positive film; measured by transmission densitometer, the density of white bits below 0.06; black density of 3.5 or more.
3. Exposure includes back exposure and main exposure.
1 back exposure. The support film of the photosensitive resin plate is up and the protective film is laid down in the exposure drawer to receive exposure. Ultraviolet light penetrates the support film to cure the photosensitive adhesive layer. In order to establish a stable base, the depth of platewashing can also be controlled, and the binding force between the support film and the photosensitive resin layer can be strengthened. The back exposure time is determined based on the required substrate thickness.
2 main exposure. Also known as front exposure, the photosensitive resin plate is supported with the film facing down and the protective film facing up. Tiling in exposure drawer. The protective film was peeled off once and then the film surface of the film was pasted on the photosensitive resin plate. The vacuum film flat 1 woman's high yield * female A inspection method covered with film (non-membrane vacuum, so that the film and the photosensitive resin layer close together. Ultraviolet light through the vacuum film and film light transmission part, so that the photosensitive material Partial polymerization curing.The length of the main exposure is determined by the type of the material and the light source strength.If the exposure time is too short, the graphic gradient will be too straight, the lines will be bent, the small prints and small dots will be washed out, otherwise the exposure time will be too long. If you have large and small lines on the same plate, thick and thin lines may be covered with a black film to cover the exposure. Small parts will not be lost due to flushing to ensure plate quality.
4. rinse. The unexposed part is washed and dissolved, leaving the photopolymerized relief. Washing time depends on the thickness of the printing plate and the depth of the impression. If the washing time is too short, the unsensitized resin will remain on the plate, which will affect the plate-making depth. If the plate-washing time is too long, the plate will swell, resulting in deformation of the fine part or Fall off.
5. drying. Remove the wash solvent and return the plate to its original size. Baking temperature between 50-60 °C. The baking time is determined by the thickness of the plate and the length of the plate-washing time, generally two hours thick and one hour thin. Too long baking time and too high baking temperature will make the printing plate 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 be rotted.
6. Post-processing. That is, in addition to sticking and post exposure. The photosensitive resin is completely hardened (polymerized) to achieve the required hardness index, and eliminate the tackiness of the printing plate to facilitate ink transfer. The post-processing time was obtained from the test with the aim of not cracking or sticking.
(b)
Printing ink
With the development of economy, the wide application of labels on commodities has led to the rapid development of the label printing industry. But people's understanding of label printing ink is far less than the understanding of the label material, printing methods and other aspects, label printing inks such as a mysterious field need us to recognize and explore.
There are many types of label printing inks, which can be divided into three categories based on the solvents used: water-based label printing inks, solvent-based label printing inks, and UV label printing inks.
(three)
Combination of multiple processes
At present, domestic label printing mainly adopts several methods of letterpress printing, offset printing, flexo printing, and screen printing. From the technical point of view, these printing methods have their own advantages and disadvantages, and each has its own inherent advantages and disadvantages. There is no alternative printing method. A printing method.
Offset printing is a relatively wide range of printing methods. The domestic sheetfed printing is basically the world of offset printing. This type of printing method has high speed, high printing definition, accurate overprinting, and full printing layers, but its durability is poor and the ink layer is relatively poor. Light, not suitable for printing brightly colored label products.
The letterpress printed copy has good definition, higher printing speed, stronger color strength and durability than offset printing, and is slightly inferior to screen printing, but the level of expression and registration are stronger than screen printing and flexo printing. Most of the use of letterpress printing methods for label production.
The biggest advantages of screen printing are the heavy ink layer and good hiding power, but its slow speed, poor leveling, and low degree of registration (this refers to the general level in China, and screen printing machine research and development in recent years. The precision has reached 10 silks and the speed is up to 6,000 prints per hour, so the screen printing machine can be used to print labels with weak sense of hierarchy.
The characteristics of the flexographic prints are relatively central, and foreign labels are often printed in this way. However, this technique requires high requirements for the processing of the anilox roll and the technical level of the workers. Although the machine is relatively simple, the process is quite complicated. Domestic print labels in this way are few.
In order to print the most exquisite labels, it is necessary to combine various processes effectively in the printing process and integrate the advantages of various printing methods to form a greater advantage combination.
The purpose of combining multiple processes:
(1) Effective anti-counterfeiting effect: Use a variety of process effects to print on the same label product, especially on some easily fake cosmetics and food packaging labels. This allows consumers to pass a label. Seeing the authenticity of the product, thus protecting the interests of the product manufacturers and consumers, has 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 mode can ensure the printing effect of printed materials to the greatest degree, thereby satisfying people’s growing sensory requirements. Improve the printing quality of the printing factory so as to bring more living resources to it. Improve production efficiency and reduce costs. Combination of multiple processes also includes a combination of printing and post-printing processes. Printing and post-printing are completed in the production process, and the finished products can be directly exported, which can greatly reduce costs.
Multi-process combined machines have the following two forms:
(1) One is a combination of stand-alone machines: In the trademark printing press, we usually use a ramp-back type machine to print, bronze, die-cut, and waste-discharge on a single machine, but because it is a stand-alone printing , print size will be affected.
(2) The other is the combination of the unit into a production line: It is a printing production line that consists of printing and post-printing processing units such as embossing, screen printing, flexo printing, bronzing, die-cutting, etc. to produce a variety of processes on the same product. Combined effect. This modular printing production method adapts to the needs of the development of the label market, and the grade of printed matter has been greatly improved. At the same time, it has brought huge profits to the printing manufacturers. The development of the unit-type production line in China has been increasingly Look good.
The combination of letterpress, flexo and screen printing in label printing
Combine a practical example of label production to illustrate the multiple process combinations in the production process. We need to print a label with a color gradation, a blue field, a portrait of a person, and a corresponding textual description. In the above comparison we know that printing patterns with rich color gradations are more prominent in label printing than flexographic printing. The sense of hierarchy is stronger, and the best choice for the printing of real map texts is screen printing. We can choose flexographic printing for the characters' portraits. So on this label we have combined the letterpress, flexo, and screen printing to form a production line that produces beautiful labels. In the label printing, the combination of such relief printing, flexographic printing, and screen printing is a typical representation of multi-process integration.
The process arrangement in multi-process integration is also a science and requires a lot of practical experience, such as the slowness 　of screen printing and drying. Therefore, comprehensive consideration must be taken when combining.
(d)
common problem
When people talk about laser tags, they must think of the word “be careful” because it is difficult to produce and transport. Of course it is a great product and the market has great demand for it. But if you can replace it with other tags, then give up laser tags.
One problem is overheating. The heat of fusion on the laser printer is 250-300 degrees Fahrenheit. To produce a good label, the film base, adhesive, and lining must all be combined. Even if all kinds of raw materials are well matched, if the label moves too slowly in the printing, it will be thermally damaged. The other is the problem of the tag corner - this means that the tag is invalid. After the product is damaged, it should be repaired at the printing factory.
Before the label is shipped to the user, the paper supplier and the manufacturer must solve the above problem.
Laser tags are generally processed on rotary flexographic printing equipment. According to Heinl, vice president of RLP, Iowa. "Laser labels are difficult to produce on the press."
Paper suppliers need to understand the moisture control requirements for laser labels so that they can solve the problems of curling and printer jamming. Whether crimping occurs on 81/2 or 11 die cuts, it will be difficult for manufacturers to solve this problem.
Adhesives are another factor. Heinl said, "If it is too thin, it will be on the product drum, and it will be expensive to repair. Unless you use a suitable blade for trimming, dust will accumulate on the roller and cause the printer to get stuck."
In addition, care should be taken in the packaging of finished products to avoid label folding and damage to the printer's information data.
According to Illinois State Co. CD Sales Coordinator F, the company uses special anti-roll linings and sealable plastic bags to package the laser labels so that they are protected against moisture (tide and heat will curl the product). Since the adhesive is only dry after one year, the label's shelf life is written on the package. F said that when the user feeds the laser tag to the machine, he or she can put it into the feeding tray with his hands to avoid curling, which can avoid malfunctions.
Precautions
1. For cylindrical bottles, especially if the diameter is less than 30mm, choose materials carefully.
2. If the label size is too large or too small, practical tests should be performed.
3. If the attached object is an irregular surface or even a spherical surface, there are specific considerations for the type, thickness, and adhesive of the label material.
4. Some rough surfaces, such as corrugated cartons, can affect labeling, and the varnish on the surface of corrugated cartons can also have an effect.
5. Automatic labeling machine labeling, if necessary, can be labeling test.
6. Even if the label is labelled at room temperature, it should be noted whether the export is experiencing high temperatures during transit and during use.
7. Multi-water or multi-oil environment will affect the properties of adhesives. Attention should be paid to the labeling environment and temperature.