The packaging and printing products produced by packaging and printing companies often have the following problems:
1 Packaging printing products, no problem during the printing or use during the cold season, but when printing or using in high temperature seasons, the phenomenon of mutual adhesion of the graphic ink film will occur.
2 Packaging printing products are not problematic when filmed in high temperature seasons, but will appear in the packaging film degumming phenomenon when used in the cold season.
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 adhesion problem 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. It also allows the ink and glue to fully wet the surface of the substrate to facilitate its diffusion, penetration 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 inks and glues can be film-laminated 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. The time should not be too long to prevent the ink film and film hardening (curing), poor adhesion, adhesion should not be too short, so that solvent evaporation, evaporation or cross-linking is not enough, resulting in poor adhesion of the ink and glue The coating strength 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 Use a wet dispersant to solve the problem of leveling adhesion of inks and glues.
Practice tells us that no matter what happens to the adhesion interface of ink and composite glue, the complete infiltration of ink and composite glue on the surface of its adherent material (substrate or substrate) is a prerequisite for obtaining adhesive strength, but the main factors affecting moisture are The inherent characteristics of the ink and 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. The corresponding wetting agents and coupling agents should also be selected according to the characteristics of the ink and the compound adhesive.
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, the thinner the ink layer of the packaging and printing product and the coating layer of the composite glue, the greater the adhesion force is. 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, it is purely considered that as long as the surface of the substrate is rough, it is unscientific that good adhesion of the ink or the adhesive 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.