Paper and film type self-adhesive label printing process
Self-adhesive labels, also known as self-adhesive labels, timely stickers, instant stickers, pressure sensitive paper, etc., are paper, film or special materials as the fabric, the back is coated with adhesive, and the silicon coated paper is used as the bottom paper. The composite material is processed into a finished label after printing, die cutting and the like. When it is applied, it can be peeled off from the base paper and attached to the surface of various substrates with a single push. It can also be automatically labeled on the production line using a labeling machine.
Compared with the traditional label, the self-adhesive label does not need to be glued, does not need paste, does not need to be drowned, has no pollution, saves labeling time, and is convenient and quick to be applied in various occasions. Different types of labels for fabrics, adhesives and liners can be applied to materials that are not suitable for general paper labels.
The printing of self-adhesive labels is quite different from the traditional label printing. Self-adhesive labels are usually printed on the label linkage, and the multi-process is completed once, as shown in the figure, die-cutting, waste-cutting, cutting or re-cutting. Volume and so on. That is, one end is input to the raw material of the whole roll, and the other end is the output of the finished product. The finished product is divided into single or rolled labels, and the finished label can be directly applied to the product. Therefore, the self-adhesive label printing process is more complicated, and the requirements for equipment performance and printing staff quality are also higher.
The basic structure of the self-adhesive material and the function of each part. The structure of the self-adhesive material is composed of three parts, namely surface material, adhesive and base paper, but from the perspective of manufacturing process and quality assurance, the self-adhesive material consists of seven parts:
1, surface coating
Used to change the surface properties of the facestock. Such as improving the surface tension, changing the color, adding a protective layer, etc., to better accept the ink and easy to print, to prevent dirt, increase the adhesion of the ink and prevent the printed graphics from falling off. Surface coating is mainly used for non-absorbent materials such as aluminum foil, aluminized paper and various film materials.
2. The surface material, that is, the surface material, is a material that receives the printed image on the front side and the adhesive on the back side and is finally applied to the object to be pasted.
In general, any material that can be flexibly deformed can be used as a material for self-adhesive materials, such as commonly used paper, film, composite foil, various textiles, thin metal sheets and rubber. The type of facestock depends on the final application and the printing process. The face material should be able to adapt to printing and printing, have good ink repellency, and have sufficient strength to accept various processing such as die cutting, waste discharge, slitting, punching and labeling.
3, the bottom layer
Like the surface coating, it is simply applied to the back side of the facestock. The main purpose of the primer layer is to:
(1) Protect the surface material from penetration of the adhesive.
(2) increasing the opacity of the fabric;
(3) increasing the adhesion between the adhesive and the face material;
(4) Prevent the plasticizer in the plastic surface material from penetrating into the adhesive, affecting the performance of the adhesive, resulting in a decrease in the adhesive force of the label and a peeling of the label.
4, the adhesive
The adhesive is the medium between the label material and the bonded substrate and acts as a bond. According to its characteristics, it can be divided into two types: permanent and removable. It is available in a variety of formulations for different facets and different occasions. Adhesives are the most important component in the technology of self-adhesive materials and are the key to label application technology.
5, release coating (silicon coating) is to apply a layer of silicone oil on the surface of the paper, coating silicone oil can make the paper into a very low surface tension, very smooth surface, the role is to prevent the adhesive bond on the bottom paper on.
6, the bottom paper
The role of the backing paper is to accept the release agent coating, protect the adhesive on the back side of the face material, support the surface material, so that it can be die-cut, waste and label on the labeling machine.
7, back or back printing
The back coating is a protective coating on the back side of the backing paper to prevent waste, and the adhesive around the re-rolled label is bonded to the bottom paper. Another role is to make multi-layer labels. The back printing function is to print the manufacturer's registered trademark or pattern on the back of the bottom paper for publicity and anti-counterfeiting.
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There are five types of self-adhesive materials:
Classified according to the characteristics of adhesives, can be divided into permanent self-adhesive materials and removable adhesive materials;
According to the adhesive coating technology classification, it can be divided into hot-melt adhesive materials, solvent-based self-adhesive materials and emulsion-type self-adhesive materials; (not very understandable)
Classified according to adhesive and chemical properties, divided into rubber-based and acrylic-based adhesive materials;
According to the characteristics of the bottom paper, it is divided into three kinds of self-adhesive materials: opaque base paper, translucent base paper and transparent base paper;
Classified according to the characteristics of the surface material, it is divided into paper self-adhesive materials, film self-adhesive materials and special self-adhesive materials.
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Finally, we will talk about the specific printing and processing technology of self-adhesive film material labels for self-adhesive paper according to the classification of surface materials:
First, the printing process of paper-based self-adhesive labels
1, printing process flow
Different types of materials, labels for different uses, and different process flows are used. The general label printing machine is a multi-functional equipment, and the processing factory can formulate the printing processing technology according to the requirements of the customer. The self-adhesive label printing process is as follows:
(1) Unwinding
A intermittent type: There is no tension change when the roll paper is unwound, so no adjustment is needed. It is applied on the flat flat and round flat labeling machine, and the unwinding speed is slow. Since such equipment does not have a paper positioning correction device, the end face of the web is required to be clean and tidy, ensuring accurate overprinting during printing.
B continuous type: applied to the round transformation circular labeling machine. Since the paper has a tension change when the web diameter speed changes, the device has a tension automatic or manual control mechanism, and a web correction correcting device to ensure smooth paper feeding and ensure print quality.
(2) Hot stamping
Flat flattening: applied to round flattening, flat flat labeling machine, low speed.
Round pressing circle: It is applied on the circular pressing label printing machine. It has fast speed and can be used for continuous hot stamping. It is rarely used, and the gold printing process is generally used instead of hot stamping.
(3) Printing
Flat flat: suitable for small areas, simple pattern printing, such as price tags, barcodes, etc.
Round flattening: suitable for label printing with solid, general pattern, for simple color mesh printing.
The round pressing circle is suitable for printing all kinds of pattern labels, especially suitable for high-grade color mesh label printing.
UV printing: In the above three printing methods, after UV drying, the film self-adhesive material can be printed.
(4) first hot stamping, after printing
On ordinary equipment without UV drying, the disadvantage is that the design of the printed pattern is limited.
(5) printing first, then bronzing
It is applied to the equipment with UV drying device. After the ink is quickly dried, the ink is bronted on the ink. The bronzing pattern is designed freely and is not restricted by the ink. It is suitable for the printing of high-grade labels. It is an advanced production process.
(6) glazing
Field glazing: Coating a layer of varnish on the surface of the ink to protect the ink layer, moisture, water and surface gloss. It can replace the lamination process and adopt UV drying.
(7) laminating
Filming on paper or film material to protect the ink, waterproof, moisture-proof, increase label strength, and increase pattern
Three-dimensional. The laminating film is divided into a bottomed paper laminating film and a bottomless paper laminating film. Due to the low cost of the latter, it is currently widely used. According to the requirements of the process, there are two kinds of composite transparent film and matt film, the former is more common.
(8) Punch
Applications are not common and are primarily used for computer-printed labels. The requirement is to locate the drive hole on both sides of the label, or the label applied on the price tag. It is required to punch holes in the middle of the label for positioning and driving.
(9) Die cutting
The die-cutting of the self-adhesive label is a semi-cutting process, that is, only the surface material is cut through and the backing paper is retained. Divided into two processing methods:
Such as flat die-cutting, suitable for all kinds of label printing machines, manual plate making, low cost, short plate making cycle, but low viscosity, suitable for short-run printing. At present, almost all domestic label factories use flat die cutting. The other is circular die-cutting, which is applied on a circular-circular labeling device. It has a high speed and high die-cut viscosity, which is suitable for long-running. The disadvantage is that the plate-making cost is large and the cycle is long. At present, the die-cutting rolls of domestic manufacturers are generally processed abroad.
(10) Receiving paper
It can be roughly divided into cut-sheet delivery and folding delivery.
2, paper type self-adhesive label processing method
(1) Sheet of paper
In the printing method of such self-adhesive materials, offset printing accounts for 95%, embossing accounts for 2%, silk screen accounts for 2%, and computer and printing accounts for 1%. Self-adhesive label printing of sheetfed paper is the same as ordinary printed matter, and each process is completed on a single machine, which has low production efficiency, high cost and high cost, but good printing quality. If the offset printing process is used, the quality of the four-color printed label is much better than that of the label printing machine. However, since the self-adhesive product of the sheet-fed paper is in the form of a single sheet of paper and cannot be re-rolled, such products can only be manually labeled and cannot be automatically labeled on the automatic labeling machine. Sheet-fed printing is suitable for large-area self-adhesive color prints. Such as posters, posters, large-area labels, etc., are not limited to label products. It can be said that sheetfed sticker printing is an important part of the self-adhesive printing industry.
(2) web
Among the printing methods of web-type self-adhesive materials, embossing currently accounts for 97%, silk screen accounts for 1%, offset printing accounts for 1%, and flexo printing accounts for 1%.
Thanks to the use of web printing, all processes are carried out on one machine, resulting in high production efficiency, low consumption and low cost. At present, China's label printing machine is in the form of letterpress printing, which has few functions. It is only suitable for printing simple color blocks, and the labels of line-like patterns are not as good as the labels of sheet-fed offset printing. However, labels processed using web can be re-rolled into rolls, which can be applied to automatic labeling machines, bar code printers, electronic scales, etc., to facilitate automated production. Web-printed self-adhesive labels are currently the mainstream of self-adhesive printing in the world.
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Second, the film-type self-adhesive printing process
Compared with ordinary paper, film materials have many advantages, and film material printing is the direction of self-adhesive printing in the future. We briefly introduce the structural properties of the film material, printability and post-press processing:
1. Structure and characteristics of film materials
(1) Structure
The film material has the same structure as the paper material, the only difference being that the surface of the material needs to be treated.
(2) Surface characteristics and treatment methods
The principle of the ink layer forming a pattern on the printed matter is penetration, volatilization, conjunctiva, and curing. Due to the high density of the film, the ink only volatilizes and conjunctiva. There is no penetration during the curing process, so the surface of the film needs special treatment. The effect of the surface treatment is to increase the surface tension of the film to be greater than the surface tension of the ink to achieve the correct combination of ink and film material. Surface treatment usually has the following methods:
A corona treatment: discharge treatment to the surface of the film by high-voltage electric charge, and finally achieve the purpose of increasing surface energy, that is, surface tension. Corona treatment is generally carried out at the film manufacturing facility. Since the surface tension is time-limited, it is required to be strictly tested before printing. Therefore, some advanced equipment has a pre-press corona treatment device for printing high quality film products.
B printing process: chemically change the surface characteristics of the film to make it suitable for ink printing or ribbon printing.
C surface coating: Coating with a chemical on the surface of the film to increase the surface tension and change the surface characteristics.
2. Printing process of film material
(1) Printing process of film material
The basic printing methods include gravure printing: gravure solvent ink printing and gravure aqueous ink printing; offset printing: UV offset ink printing; embossing: divided into ordinary resin ink printing and UV embossing ink printing; flexo: divided into water Ink printing, solvent ink printing and UV ink printing; silk screen: divided into UV ink printing and solvent ink printing; combined printing: divided into embossing + silk screen, embossing + flexo, flexo + silk screen, offset + embossing Printing method. Here are a few more specific printing methods:
A, ordinary resin ink printing. This is currently the most common method. Due to the drying problem, there are two drying methods: cutting a single sheet and drying it on the shelf. This method has a long drying time, a large area and is easy to smear.
Lamination. Wrap the undried ink between the films, and pay attention to avoid publishing the film and preventing the film from failing.
B, UV ink embossing. This method has good printing quality and high efficiency. It is the most developed and most suitable printing process in China. Since the domestic embossing equipment generally does not have a UV device, the film printing is limited, so the equipment is updated and the transformation is a necessary condition for printing the film.
C, solvent ink flexo.
This is a traditional printing method with good quality. Due to the low surface tension of the solvent ink, the surface tension of the film is not as strict as other inks, so the ink layer is strong and the process is relatively simple. However, solvents affect the environment and are harmful to the human body. It is a printing method that is about to be eliminated.
D, water-based ink flexo printing. This is the most advanced printing method in the world today, with low cost, good quality and no pollution. However, the process requirements are strict, the surface tension of the film must be above 40 dynes, and the pH and viscosity of the ink are strictly required. This process is a process that is vigorously developed in China, but it is slow to develop due to equipment limitations.
E, UV ink flexo printing. Features the same as UV embossing, high cost, but the film surface tension requirements are relatively less strict. Most manufacturers use water-based ink printing, UV glazing can reduce costs and increase printing results.
F, UV ink silk screen printing. This new process can be used for single or roll printing, with high cost and good quality. Single-sheet printing does not need to be racked to dry, and the roll printing can be performed at high speed.
G, solvent ink silk screen printing. This is a traditional process, usually a single sheet is printed by hand, and the web material is printed by a joint machine. More than 95% is single-sheet printing, with good results and low cost. However, solvent screen printing ink is harmful to the human body and pollutes the environment.
H, UV offset printing ink. Since the glue uses a resin ink, the ordinary offset printing cannot print the film. Some manufacturers use a single overprint when printing PVC, drying on the shelf, and finally laminating. However, since the ink is not easy to dry and is easily smeared, it is wasteful and the productivity is low. With UV offset printing, all of the above problems are avoided, and high-level layered film products can be printed.
I, gravure printing. Gravure prints very little adhesive, but print quality is the best of all printing methods and is a promising printing method. As long as the post-press processing is solved in the country, the existing equipment can completely print high-quality self-adhesive labels.
J, combination printing, also known as composite printing, is the most advanced printing method in the world's packaging printing industry. According to different pattern design, several methods are used to print on the same pattern to achieve the best visual effect. Such equipment is very common in foreign countries. There are two types in China: SR-520B of LINTEC in Japan and F-330 of SHIKY. The former is embossed + silk screen, and the latter is offset + embossed.
(2) ink drying method
The ink on the film is classified into drying characteristics: oxidative polymerization drying (tree fingering ink), evaporation of the conjunct film drying (solvent ink), evaporation of the conjunct film drying (aqueous ink), and photocuring drying (UV ink).
Drying methods are divided into: hot air drying, electric drying (far infrared), ultraviolet curing and drying.
Requirements for drying: The ink is sufficiently dry; it does not affect the physical and chemical properties of the film; it does not affect the properties of the adhesive; it has no effect on the backing paper.
Ways to improve the effect of ink drying:
A. Use additives to improve the drying speed of the ink. Such as resin ink plus dry oil; water-based ink plus special additives, solvent ink plus low boiling point solvent. However, it should be noted that the additive will change the brightness and brightness of the ink, and the adhesion strength of the ink to the film cannot be affected by the additive.
B. Change the running speed of the film material.
C. Change the temperature inside the drying box or change the intensity of the ultraviolet light source.
D. Choose a suitable film material.
(3) Post-press processing
The post-press processing of the film material is substantially the same as the post-printing process of the paper label. Such as bronzing, laminating, punching, folding, cutting, rewinding, waste disposal, die cutting, etc. are used for post-press processing of film-type self-adhesive labels.
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