In-Mold Label Printing Technology

The in-mold label is processed on the surface with PP or PE synthetic paper, and a special label paper processed with a special hot-melt adhesive on the back is printed and made into a trademark. Use a robot hand to suck up the printed label and place it in the mold. The vacuum hole on the mold will firmly hold the label in the mold. When the raw material of the plastic bottle is heated and hangs down in a hose shape, the mold with the label quickly closes and the air is blown into the hose to make it closely adhere to the mold wall. At this time, the temperature in the entire mold is relatively high, and the bottle body is tightly adhered to the bottle body. The initial shape of the solid adhesive starts to melt and is combined with the plastic bottle in the mold. When the mold is opened again, the plastic bottle body is formed and the label and the bottle body are integrated into one body. The well-printed brand is firmly embedded on the surface of the plastic product. The label and the plastic bottle are on the same surface and do not feel labeled. The color image is printed directly on the surface of the bottle body.

The in-mold label can be used for labeling of thermoformed containers such as blow molding and injection molding, and has good performance, which makes it a packaging method with great development potential. Different printing manufacturers can use different printing processes and post-printing processes to produce in-mold labels according to their own equipment conditions.

In-mold labels are currently commonly used plastic film substrates, suitable for a variety of printing methods and different inks, including: screen printing, UV letterpress printing, flexographic printing, gravure printing and lithographic offset printing. Before selecting the ink, the adhesion, scratch resistance, and chemical resistance of the ink on the in-mold label material should be tested according to the requirements of the final application.

There are two kinds of printing processing methods for in-mold labels: web printing and sheet-fed printing.

1. Web printing processing: divided into on-line processing and extension multiple processing. These two processing methods are related to the factory's own equipment and label design requirements. If the printing process is carried out with a label with gilt pattern and the printing press is equipped with round round hot stamping and die cutting device, the processed label can be formed at one time; if there is only a separate hot stamping machine and die cutting machine, the label can only be processed multiple times. carry out. It is characterized by high production speed and high efficiency, but due to the high cost of the roller, it is more suitable for mass production.

2. Sheet-fed printing process: usually silk screen and offset printing. In this way, multiple processes are performed on multiple machines. The printing process is related to the process design. The process is more flexible, the plate making cost is lower than the reeling mode, and it is suitable for small batch production. The printing effect is good, and the screen printing field and the offset printing layer are printed. Both are better than web printing.

In-mould label printing needs:

1. Material

The technical content of in-mold labels is very high, and the first thing that comes out is the material. The earliest entry into the Chinese market was the Japanese YUPO in-mold label, known as the most successful in-mold label material in the world. Now, the French Polyart blow mold internal standard also entered the Chinese market, and some local companies are also stepping up the development of this material.

The in-mold label must first have good printability to ensure that the ink is firmly attached to the surface, and in the post-processing process, good processability is ensured, such as die-cutting and cold stamping processability. Second, this material must meet the use characteristics and be integrated with plastic bottles during blow molding.

In-mold labels are divided into paper and plastic films. The former is deformed by water or moisture, which reduces the use value, but its advantage is that there is no static electricity interference, which reduces the loss of the label when it is blown. In addition, it is not a homogeneous material with the plastic bottle, and it is not easy to recycle. At present, plastic film in-mold label materials are generally used at home and abroad.

The in-mold label material structure consists of a printing surface, an intermediate layer, and an adhesive layer. The role of the printing surface is to accept ink, forming a color image; the middle layer supports the printing surface, giving the material a sufficient degree of stiffness and transparency, not deformed on the printing press and under the effect of high temperature, to ensure accurate overprinting. The adhesive layer will melt under the effect of high temperature, so that the label material and the plastic container are integrated, and the label and the plastic bottle are firmly adhered.

There are three kinds of printing surface materials: PE, BOPP and PE +PP. Since most plastic containers are PE materials at present, the use of PE in-mold labels is more conducive to recycling because they are all homogeneous materials. In the production of in-mold labels, in order to improve the ink receptivity of the printing surface material, it is generally necessary to apply a surface coating or to increase the surface energy using a corona discharge method.

There are two kinds of structures on the surface of the adhesive layer: planar no-grain structure and textured structure. The former is in direct contact with the blank during use, and is naturally exhausted, suitable for small area labels. The latter is embossed with a textured structure on the surface. During use, the gas is exhausted through the exhaust channel of the mesh, avoiding the production of bubbles. The adhesive layer also has anti-static properties to prevent double-printing during printing; in addition, it also has a slippery nature, which ensures the smooth separation of labels and enables smooth printing processing.

2. Printing of in-mold labels

Different printing manufacturers can choose different printing processes according to their own equipment conditions. Offset, flexo, emboss, and gravure can all be used to print in-mold labels. Currently, offset and flexo are mostly used.

(1) Offset printing

The advantages of offset printing in fine dot printing are outstanding, but lines, solid printing effects, and printing saturation are inferior to other printing methods. Offset cannot achieve inline printing like flexo printing. Therefore, off-line die cutting, cold lapping, and glazing must be performed after printing. However, offset printing is suitable for the printing of small batches of labels, which has a short cycle and high flexibility.

Offset printing in fine dots is superior to other printing methods. For short-run business, the production cost of offset printing is lower than other printing methods. In the line, the actual printing effect and the saturation of the color are less than other printing methods. Offset printing on the color difference is more difficult than other printing methods.

(2) Gravure

The field printing and printing color saturation is better than offset printing, and it is not suitable for printing small outlets and layers of rich trademarks. However, the color difference control is more convenient. In the gravure printing machine, the paper path of the in-mold label material is longer than other printing methods, so the chance of static electricity is greater. The gravure platemaking cost is high and the cycle is long, so it is suitable for the long version of the in-mold label printing.

Gravure printing method is better than offset printing in field printing effect and color saturation. It is inferior to other printing methods in fine dot printing quality and image level richness. It is superior to offset printing and letterpress printing in the control of color difference. Since the gravure printing path is longer than other printing methods, static electricity is more easily generated than other printing methods. Intaglio printing plates have a long production time and cost, so medium and short-run in-mold label printing businesses are not suitable for gravure printing.

(3) Embossing

Embossing is suitable for printing on-the-spot and line logos. The effect of printing small dots is unsatisfactory. The control of the color difference of the same batch of products is also relatively easy, but ink bars will appear. From a cost perspective, it is cheaper than gravure and flexo.

The letterpress printing method is inferior to other printing methods in the printing of small dots. The printing plate has lower resistance than the gravure and flexographic printing plates. It is easier to control the printing color difference than offset printing, but the effect is not as good as gravure printing and flexographic printing. Easy to have ink bars, plate making costs and cycles lower than gravure and flexo printing.

(4) Flexo

The outstanding advantage of flexographic printing is that the printing and subsequent processing can be performed at one go. The front end is the feed end, and the back end obtains the final printing processing product, which realizes the connection production of printing and post-processing. Now, with the improvement of flexo platemaking technology, dot printing quality has made great progress, and in-mold labels have been flexographically recognized by some manufacturers, but printing with environment-friendly water-based inks is not yet mature. Currently, there are experienced manufacturers. The use of very good UV inks, and become the trend of in-mold label printing.

The flexographic printing method is the mainstream packaging and printing method in Europe and America. With the CDI platemaking technology, the flexographic printing method can obtain better dot printing quality and saturated printing colors.

(5) screen printing

Screen printing is not as economic as printing direct labels on bottles.

3, in-mold label printing process is the key to the use of ink

Although various printing methods can use different types of inks to print in-mold labels, the good adhesion of the UV ink to the surface of the in-mold label material and its drying characteristics are undoubtedly the best choice for various printing processes. The ink balance of the UV offset printing process is the key to high-quality printing of labels and high yields. The key to using UV inks in other printing processes is the selection of UV inks with both high color intensity and good leveling performance. Therefore, in the large-area printing thick real-time, in the appropriate color ink on the appropriate and appropriate amount of antistatic agent knot printing process will be a certain degree of elimination of static electricity.

4, coating the in-mold label

In order to reduce the failure of in-mold labeling, if using the vacuum adsorption in-mold labeling method, the anti-static agent and the smoothness of the varnish should be properly added to the varnish, and the varnish should not be used when using the electrostatic adsorption in-mold labeling method. Add antistatic agent. If the in-mold labels need to be gilded after printing, bronzing should be done with hot UV varnish. If the varnish is added with additives, it should be tested before each batch of glazing to prevent the entire batch of products from being scrapped.

5, die cutting of in-mold labels

For roll-shaped printing semi-finished products, if a die-cutting method is adopted after cutting, the pin-position movement phenomenon often occurs when the sheet is cut off. The movement of the needle position directly affects the efficiency of the entire production process and the final yield. To solve the problem of pin position movement when cutting Zhang Zhang: maintain tension stability, eliminate cumulative error of Zhang Zhang in time; Method 2: Make trapezoidal needle bit line at the time of plate making, and then select and classify different needle bit lines.

(1) In-mold labels Off-line die-cutting can use die-cutting machine, semi-automatic trademark die-cutting machine and semi-automatic die-cutting machine.

(2) In-mold Label Wiring Die Cutting: In-mold label makers are prone to disorderly marking when using a flexographic printing press to perform in-line die-cutting. The generation of disordered labels is mainly caused by the static nature of labels and the incomplete transfer of labels. Therefore, when disorder occurs, the collection and arrangement of finished products should pay attention to checking whether there is a phenomenon of inversion or back-marking.

6, in-mold label bronzing process