Analysis and Research on Adhesion of IMD Technology Inks (I)

1 Introduction

IMD technology is the abbreviation for In-Mould Decoration, which is mainly used for the surface decoration and functional panels of home appliances and other electronic products. It covers various industries such as home appliances, electronics, automobiles, and communications, and has become a social life of human beings. The indispensable component.

The essence of IMD technology is a new type of technology that combines printing technology and injection molding technology. First, it prints on a transparent film, completes graphic transfer, and then forms and processes the surface, and finally prints and shapes the finished decorative sheet. Into the injection mold, the resin is injected on the back of the formed sheet, so that the resin and the sheet are joined into one body to complete the production of the IMD product.

At present, the development of China's IMD technology is still in its infancy. The main problem is that the product quality is not high enough to meet the requirements for use. For this reason, in addition to improving the level of molding and injection molding technology, how to improve the adhesion of printing ink is also an important issue of concern in the industry.

The adhesion of printing ink to the surface of the printing surface of the sheet is one of the important performance indicators of the IMD product and is an important factor that affects the quality of the product. This article focuses on the selection of printing inks and the surface treatment of the sheet.

2 ink selection

In IMD technology, printing inks generally use VOC (volatile organic compounds) inks, which are mainly composed of colorants, resins and solvents. Among them, the resin and the solvent have a direct influence on the adhesion of the ink. Therefore, strict requirements should be placed on the choice of ink resins and solvents.

1) Effect of resin on ink adhesion

1 The relative molecular weight of the resin

The relative molecular weight of the resin should be similar to the relative molecular weight of the film sheet. If the relative molecular weight of the resin is too small, the cohesive force and compatibility will not meet the requirements, and the adhesion effect will be poor. On the contrary, if the relative molecular weight of the resin is too large, the melting point will increase, and the resin will not dissolve in the solvent, nor Advantages of ink adhesion, but also cause the waste of solvents. Therefore, the relative molecular weight of the resin should be matched with the printing film.

2 resin components

Since the functional groups, branching structures, and the like in the resin molecules directly affect the adhesion of the ink and the thin film, the corresponding inks are selected for different thin films. In general, a binary or ternary copolymer resin is used in the ink, and an ink having a good texture can be prepared by a method of modifying the resin. Therefore, proper control of the components of the resin plays an important role in the good adhesion of the ink.

3 resin monomer content

By changing the content of a certain element of the synthetic resin monomer, the performance of the resin can be improved, so that a new resin can be synthesized to achieve a good adhesion of the ink and the sheet.

4 The polarity and crystallinity of the resin

The presence of polarity will help improve the adhesion of the ink, but if the polarity is too high, the ink will crystallize, which will affect the adhesion of the ink. Therefore, the polarity of the resin should be controlled within a reasonable range.

5 resin structure

The resin is generally a linear high-molecular polymer. The molecular ends of the resin are easily diffused into the film. This diffusion is sensitive to temperature. Increasing the temperature can promote the Brownian motion of macromolecules, and it is beneficial to increase the speed and capability of diffusion. Helps improve ink and film adhesion.

2) Effect of solvent on ink adhesion

If the solvent is used improperly, it will directly affect the adhesion of the ink.

On the one hand, the solubility parameter of the solvent should be close to that of the resin, which is beneficial to the dissolution of the resin; on the other hand, the solubility parameter of the film should be similar to the solvent in order to improve the solvent's ability to dissolve the film, so that the surface of the film is slight. The swelling will help the binder penetrate into the molecular structure on the surface of the film, forming a layer of unbounded intermediate layer after mixing, leading to the disappearance of the interface and forming a firm bond between the ink and the film.

It should be pointed out that because of the aesthetic requirements of the product, it is also necessary to prevent the solvent from excessively eroding the surface of the film (even resulting in deformation of the film). Therefore, it is not possible to match their solubility parameters blindly, otherwise it would be counterproductive. For this purpose, mixed solvents can be used to give them a certain volatilization gradient.

3 surface structure and processing of the film

According to the adhesion mechanism between the printing ink and the substrate, in order for the ink to successfully adhere to the surface of the film, the surface tension of the ink must be equal to or less than the surface energy of the film, so that the ink can achieve a desired adhesion effect.

The matching of the two can be achieved by changing the surface tension of the ink or the surface energy of the film. In practical applications, the surface tension of the ink is generally used as a fixed value, but the surface tension of the ink can also be changed by changing the solvent or adding a surfactant and a silicone organic resin. At this time, the ink manufacturer should be negotiated because it is not appropriate. Changing the surface tension of the ink is likely to affect the printing effect. In addition, the surface of the film can be surface-treated to improve its surface structure to improve the adhesion of the ink to the film. The film sheets commonly used in IMD technology include PET, PVC, PC and PE.

Different sheet materials should use different surface treatment methods, mainly including the following: chemical etching, radiation, plasma, corona treatment, ultraviolet irradiation and de-esterification.


(to be continued)