Current situation of label printing technology in

2022-09-22
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Current situation of in mold label printing technology

in mold label is a special label paper processed with PP or PE synthetic paper on the surface and coated with special hot-melt adhesive on the back, which is printed and made into a trademark. Use the manipulator to suck up the printed label and place it in the mold, and the vacuum hole on the mold will firmly absorb the label in the mold. When the raw material of the plastic bottle is heated and sagged in the shape of a hose, the mold with the label is quickly closed, and the air is blown into the hose to make it close to the mold wall. At this time, the temperature in the whole mold is still relatively high, and the label solid adhesive close to the prototype of the bottle begins to melt and combine with the plastic bottle in the mold. So when the mold is opened again, the plastic bottle is formed, and the label and the bottle are integrated. The beautifully printed trademark is firmly embedded on the surface of plastic products, and the label and plastic bottle are on the same surface. It feels that there is no label, and color graphics and texts are directly printed on the surface of the bottle

in mold labels can be used for labeling thermoformed containers such as blow molding and injection molding. They have good performance, making them a packaging method with great development potential. Different printing manufacturers can use different printing processes and post press processing processes to produce in mold labels according to their own equipment conditions

currently, plastic film substrate is widely used for in mold labels, which is suitable for a variety of printing processing methods and different inks, including silk printing, UV relief printing, flexographic printing, gravure printing and offset lithography. Before selecting the ink, the adhesion, scratch resistance, chemical resistance and other properties of the ink on the label material in the mold should be tested according to the requirements of the final application

there are two printing methods for in mold labels: web printing and sheet fed printing

1. web printing processing: it is divided into online one-time processing and extension multiple processing. These two processing methods are related to the factory's own equipment and label design requirements. If the labels with bronzing patterns are printed and processed, and the printing machine is equipped with circular pressing, bronzing and die cutting devices, the processed labels can be formed at one time; If there is only a separate stamping machine and die-cutting machine, the label can only be processed many times. It is characterized by fast production speed and high efficiency, but due to the high cost of roll making, it is more suitable for mass production

2. sheet fed printing processing: usually silk screen printing and flat offset printing. In this way, multiple processes are completed on multiple equipment. The printing process is related to process design. The processing is more flexible, and the plate making cost is lower than that of the drum method, which is suitable for small batch production; The printing effect is good. The effect of silk screen printing and offset printing is better than that of web printing

printing needs of in mold labels:

1 Material

the technical content of in mold labels is very high, and the first embodiment is the material. The first one to enter the Chinese market is Japan Yupo in mold label, which is known as the most successful in mold label material in the world. Now, the internal standard of French Polyart blow molding mold has also entered the Chinese market, and some local enterprises are also stepping up the research and development of this material

in mold labels must first have good printability to ensure that the ink is firmly attached to the surface. In the post-processing process, they must have good processability, such as die cutting and cold stamping. Secondly, this material should meet the use characteristics and be integrated with the plastic bottle during blow molding

in mold label materials are divided into two categories: paper and plastic film. The former will deform in case of water or moisture, reducing its use value, but its advantage is that there is no electrostatic interference, reducing the loss of absorbing labels when blowing bottles. In addition, it is not the same material as plastic bottles, which is not convenient for recycling. Now, plastic film in mold label materials are generally used at home and abroad

in mold label material structure is composed of printing surface, intermediate layer and adhesive layer. The function of printing surface is to receive ink and form color pictures and texts; The middle layer supports the printing surface, gives the material enough stiffness and transparency, does not deform on the printing machine and under the action of high temperature, and ensures the accuracy of overprint. The adhesive layer will melt under the action of high temperature, so that the label material and the plastic container become one, ensuring that the label and the plastic bottle are firmly adhered together

there are generally three kinds of printing materials: PE, BOPP and PE +pp. At present, most plastic containers are made of PE, so the use of PE in mold labels is more conducive to recycling, because they are homogeneous materials. In the production of in mold labels, in order to improve the ink affinity of printing surface materials, it is generally necessary to coat the surface coating or improve the surface energy by corona discharge

there are two kinds of structures on the surface of the adhesive layer: flat textured structure and textured structure. The former is in direct contact with the blank when in use, natural exhaust, suitable for small area labels. The latter is embossed with a grain structure on the surface. When in use, the gas exhausts through the exhaust channel of the grain, avoiding the production of bubbles. The adhesive layer also has antistatic property to prevent double sheets during printing; In addition, it also has sliding property, which ensures the smooth separation of labels and the smooth printing process

2. Printing of in mold labels

different printing manufacturers can choose different printing processes according to their own equipment conditions. Offset printing, flexo printing, embossing and gravure printing can print in mold labels. At present, offset printing and flexo printing are in the majority

(1). Offset printing

offset printing has the advantages of light weight in fine dot printing, but its line, field printing effect and printing saturation are not as good as other printing methods. Offset printing cannot realize inline printing processing like flexo printing, so offline die cutting, cold pressing, polishing and other processes must be carried out after printing. However, offset printing is suitable for small batch label printing, with short cycle and strong flexibility

offset printing is superior to other printing methods in the printing quality of small dots. For short edition business, the production cost of offset printing is lower than that of other printing methods. The printing effect and color saturation of strip and field are not as good as other printing methods. Offset printing is more difficult to control the color difference clearly required by relevant laws and regulations in China than other printing methods

(2). Gravure printing

field printing and printing color saturation are better than offset printing, which is not suitable for printing small dots and rich layers of trademarks. But color difference control is more convenient. On concave 2 and carbon nanotube printing machines, the paper path of label materials in the mold is longer than that of other printing methods, so there is a greater chance of static electricity. Gravure plate making has high cost and long cycle, so it is suitable for long plate in mold label printing

gravure printing is superior to offset printing in the field printing effect and the degree of color saturation. It is inferior to other printing methods in the printing quality of small dots and the richness of image levels, and is superior to offset printing and relief printing in the control of color difference. Because the paper path of gravure printing is longer than other printing methods, it is easier to generate static electricity than other printing methods. Gravure printing takes a long time and costs a lot, so it is not suitable to use gravure printing in the label printing business of medium and short plates

There are "mean value", "standard deviation", etc. based on the test results of each experimental piece, calculate the value of statistical processing

(3) Embossing

embossing is suitable for printing field and line trademarks. The effect of printing small dots is not ideal. It is also easier to control the color difference of the same batch of products, but ink bars will appear. In terms of cost, it is cheaper than gravure printing and flexo printing

relief printing is inferior to other printing methods in the quality of printing fine points. The printing resistance of the printing plate is lower than that of gravure and flexo. It is easier to control the printing color difference than offset printing, but the effect is not as good as that of gravure printing and flexo printing, and it is easy to have ink bars. The cost and cycle of plate making are lower than that of gravure printing and flexo printing

(4). Flexographic printing

the outstanding advantage of flexographic printing is that the printing and post-processing processes can be completed at one go. The front end is the feeding end, and the back end obtains the final printing and processing products, realizing the online production of printing and post-processing. Now, with the improvement of flexographic plate making technology, the dot printing quality has made great progress. Flexographic printing of in mold labels has been recognized by some manufacturers, but printing with environmental friendly water-based ink is not mature. At present, experienced manufacturers use UV ink with good fluidity, which has become the trend of in mold label printing

flexographic printing is the mainstream packaging printing method in Europe and America. Combined with CDI plate making technology, flexographic printing can obtain better dot printing quality and saturated printing color

(5). Silk screen printing

silk printing is not as economical as printing labels in the mold directly on the bottle

3. The printing process of in mold label is the key to the use of ink

although various printing methods can choose different types of inks to print in mold labels, the good adhesion of UV ink on the surface of in mold label materials and its drying characteristics are undoubtedly the first choice for all kinds of printing processes. The balance between water and ink in UV offset printing process is the key to obtain high-quality printed labels and high yield. The key to using UV ink in other printing processes is to choose UV ink with high color intensity and good leveling performance. Therefore, in large-area printing thick real-time, on the corresponding color ink, an appropriate amount of antistatic agent can be used to remove the static electricity in the printing process

4. Polishing of in mold label

in order to reduce the failure of in mold label labeling, if vacuum adsorption in mold label method is used, antistatic agent should be properly added and the smoothness of varnish should be adjusted during polishing; Use electrostatic adsorption in mold label method, Polish should not add antistatic agent. If the label in the mold needs to be bronzed after printing, the bronzing should be done with a hot UV varnish. If the varnish is added with additives, it should be tested before each batch of polishing to avoid the scrapping of the whole batch of products

5. Die cutting of in mold labels

for roll shaped printing semi-finished products, if the die cutting method is adopted after sheet breaking, the needle position movement will often occur when sheet breaking, and the needle position movement will directly affect the efficiency of the whole production process and the final yield. The first method to solve the clockwise movement of broken tension is to maintain the stability of tension and eliminate the cumulative error of broken tension in time; Method 2: when making plates, make trapezoidal needle position lines, and then sort different needle position lines

(1) in mold label off-line die-cutting can use CNC automatic die-cutting machine, semi-automatic trademark die-cutting machine, semi-automatic die-cutting machine to die-cutting molding

(2) in mold label wiring die cutting: in mold label manufacturers are prone to disordered labels when using flexographic printing machines for die cutting. Disordered labels are mainly caused by static electricity on labels and poor label handover. Therefore, when there is disordered bidding, the collection and sorting of finished products should pay attention to check whether there is reverse bidding and reverse bidding

6. In mold label bronzing process

different bronzing processes can be used for bronzing on in mold label materials, such as ironing before oiling, or oiling before ironing. Hot stamping and cold stamping can be used

the main factors affecting the effect of hot stamping are: anodized aluminum, stamping temperature, stamping pressure, stamping speed

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