Discussion on the Problems of Adhesion and Debonding of Printing Products

The packaging and printing products produced by packaging and printing companies often have the following problems:

1. Packaging and printing products do not have problems during the printing or use during the cold season, but they may stick to each other when printed or used in high temperature seasons.

2. Packaging and printing products. There is no problem when filming in high temperature season and when it is used in low temperature season. There will be film degumming of the commodity packaging.

The author believes that the former is due to the fact that the thermoplastic softening point in the ink system is too low or that excessive amounts of slow-drying solvents in the ink remain in the printed ink film. The latter is caused by improper or excessive use of dispersion aids in the ink or compounding system. This article will be discussed, only for reference of colleagues in the industry.

1. Use pressure to solve the problem of adhesion caused by too thick ink layer and adhesive layer.

By pressurizing the printing machine and the adhesive coating machine, the adhesion between the printing ink film layer and the coating adhesive layer can be brought into close cooperation and the ink and the glue can flow under pressure. The molecules of the system and the molecules of the glue system diffuse and penetrate to increase the adhesion strength between the ink and the substrate, the glue and the printing ink film.

Of course, the pressure should be such that the ink film and the glue film are not deformed into degrees. In other words, the purpose of pressurization is also to discharge excess ink or rubber to reduce the thickness of the ink layer and the adhesive layer so as to ensure that the entire ink layer and the adhesive layer are uniform in thickness and dense, and prevent voids caused by partial under ink or underfill. Prevents certain inks and adhesives from generating bubbles due to volatiles during heat curing or cooling and maturation.

2. Use a hair dryer to solve the problem of solvent residue.

Usually, we use infrared drying, ultraviolet drying, air-blast cooling, or even drying in the drying process in the packaging and printing process. The aim is to increase the volatilization of solvent in the ink and glue system to facilitate the operation of the ink filming and glue compounding process. Also allows ink and glue to fully wet the surface of the substrate. It facilitates its diffusion, infiltration and adsorption. Therefore, inks and glues containing solvents need to be fully blown, infrared-baked, etc. in order to promote solvent evaporation and evaporation completely. Solvent-free ink and glue. It can be coated and bonded immediately after printing and gluing.

The cooling time of IR, UV, air blowing, baking, etc. depends on the volatilization rate and evaporation rate of the solvent while the UV type depends on the light intensity. Time should not be too long. In order to avoid the ink film and film hardening (curing), poor adhesion, bonding is not strong. Should not be too short, so that solvent evaporation, evaporation or cross-linking is not enough, resulting in poor adhesion of the ink and the coating strength of the glue is reduced.

We know that printing and laminating can be performed at room temperature, under infrared, ultraviolet, heat curing or cold air curing, or alternatively between infrared heating and cold blowing, and between infrared and ultraviolet process alternately. This depends on the curing (curing) temperature of the ink and glue. In particular, it is scientific to wait until the film of the ink is formed and the compound glue matures (cured) before it is covered.

3. Wet dispersants solve the problem of leveling adhesion of inks and glues.

Practice tells us. No matter what happens to the interface between the ink and the composite glue, the complete infiltration of the surface of the adhesive material (substrate or substrate) by the ink and the compound glue is a prerequisite for obtaining the adhesive strength, but the factors that affect the moisture are mainly the ink and The properties of the composite adhesive are followed by the roughness of the adherend, the porosity, the degree of contamination of the adsorbent layer, and the length of the wetting time.

In order to improve the wet efficiency of inks and compound glues, when selecting packaging printing inks and compound adhesives, high-solid, low-inking inks and compound adhesives should be used. Also according to the characteristics of ink and compound adhesives. Select the appropriate wetting agent and coupling agent. Because inks and adhesives are a heterogeneous dispersion between organic pigments and inorganic pigments, between organic fillers and inorganic fillers, between pigments and fillers, between fillers and binders (resins), and between resins and solvents. Competition will occur between the adsorption, so be sure to pay attention to pigments, fillers, resin surface adsorption order of addition and the ink, adhesive and substrate surface adsorption strength.

From the adsorption theory, we can see that the thinner the ink layer and the composite glue coating layer of packaging and printing products are. The greater the adhesion, the higher the bond strength. Therefore, the ink layer and the adhesive layer should be as thin as possible under the premise of ensuring that the dot of the printing ink film is not lost or the composite coating is not glued. It is generally believed that the thickness of the ink layer and the adhesive layer should be controlled at 8-100 μm.

If the degree of drilling of the binder or composite glue in the ink system is too large, not only is it not easy to uniformly apply the sizing, but also it is not conducive to the penetration and diffusion of the printing ink to the substrate or ink on the printed ink film.
In addition, the adhesion strength is also related to the degree of surface roughness. A truly smooth solid surface for inks or compound glues is not an ideal adhesion surface. Only a certain degree of roughness can increase the adhesion area and combine with ink or compound.

Mechanical "meshing" occurs between glues.

Of course, simply think that the surface of the substrate is rough. It is also unscientific that good adhesion of inks or adhesives can be achieved. Because the surface is too rough or even has obvious unevenness, it is disadvantageous for the film-forming adsorption of the ink and the adhesion of the composite adhesive. If the interface of the substrate or printing ink film is too rough, the interface will not be able to contact with defects. These defects can make the ink or adhesive unable to enter the adhesion, but will cause stress concentration and greatly reduce the ink and substrate. Adhesive strength of adhesive and printing ink film. For the above surface with a little less ink, the graphic ink dot will be lost if the amount of sizing is too small, and the lack of glue will also reduce the adhesive strength of the coating.

4. Infiltrate the surface porosity of the substrate with ink and compound glue.

Some substrates (including the printed ink film surface) have many open pores that are invisible to the naked eye. If the ink or adhesive can impregnate the pore walls, the air must be excluded from the pores and “embedded” in the pores. It helps to improve the adhesion strength.

The depth of the ink or composite glue penetrating into the hole is related to the shape and size of the pores, and also the fineness of the ink adhesion force of the ink to the substrate and the composite glue on the surface of the packaged printing ink film, and the degree of drilling and curing time of the composite glue, etc. Factors related.

5. Control the degree of drilling and plasticizer usage of inks and adhesives.

The degree of adhesion of substrates and printed graphics has a great relationship with the degree of ink and adhesive tape. Therefore, this index must be controlled.

Substrate, printing graphics ink film contains some oligomers, such low molecular weight fluidity is very easy to seep out of the surface of the substrate, or very easy to see through the surface of the printing ink film, so that the surface tension is reduced. In order to prevent and eliminate these effects, the surface of the substrate and the surface of the printing ink film must be processed before or after the printing.

The purpose of using plasticizers in inks and adhesives is to obtain toughness of the ink ink film and composite adhesive layer. Secondly. For large-scale inks and adhesives can also reduce the cohesion of the system base material to increase the diffusion of the system base material to improve the adhesive strength. However, when choosing plasticizers, the compatibility of plasticizers with base materials and substrates should be taken into account. Also, the amount of plasticizers should be taken into consideration. In ink and compound glue. The amount of plasticizer should generally be controlled at less than 10% but will reduce the product's adhesion.

6. With a proper amount of filler to make up for the lack of ink and glue.

The use of fillers in printing inks and adhesives can not only save the base material, reduce the cost of materials, but also reduce the shrinkage of the adhesive joints of inks and adhesives, greatly improving the bonding strength of the printing ink film and the composite adhesive. The commonly used fillers are: reduced silver powder or electrolytic silver powder, zinc oxide powder, active silica (white carbon black), mica powder, calcium carbonate, and the like.

In addition, in order to prevent the adverse effects of inks and adhesives, their storage time should also be controlled.

The adhesion of inks and adhesives tends to decrease with the increase of the storage period. This is because the inks and adhesives undergo surface aging during the storage period if they are exposed to air. This aging phenomenon will be even more serious. Therefore, the ink and adhesive should be stored in a container that is isolated from the air, and the time should not be too long.

7. Master curing temperature and improve adhesion.

The increase of the curing temperature increases the thermal motion of the binder molecules in the ink and compounding system, which accelerates the diffusion, facilitates the infiltration and adsorption, enhances the adhesion and improves the bonding strength.

Of course, the curing temperature is not as high as possible. It is necessary to ensure that the softening point (temperature) of the substrate is not exceeded so as to avoid deformation of the printed composite material. If the temperature is too high. When the ink and compound gel flow into the microvoids, they easily generate bubbles and reduce their adhesive strength.

On the other hand, the bond strength between packaging printing inks and printing materials and composite adhesives and packaging printing graphics ink film tends to increase as the curing time increases, but after reaching a certain value. Its adhesive strength will no longer increase. Curing temperature and curing time are short-term constraints. Increasing temperature, increasing light energy and light intensity can shorten curing time. Lowering the temperature and reducing the light intensity will increase the curing time.

8. Use anti-static additives to solve the problem of difficult ink and difficult sizing.

In the modern packaging and printing process technology, especially in the process of continuous printing and continuous sizing coating, static electricity is often generated due to the friction between the substrate and the printing machine and the coating machine, and some substrates are also used. The electrostatic charge of electrical insulators will accumulate more and more. Eventually due to static electricity, it will not be easy to deposit ink, resulting in the loss of dots of printed graphics and the difficulty in uniform coating of the glue, and even deinking, degumming, and release. For this reason, it is recommended to add an appropriate amount of antistatic agent to the printing ink and glue system to improve the ink transfer rate and glue coating quality. .

Reprinted from: Printed in China