Discussion on the Problems of Printed Matte Adhesion and Film Degumming
Packaging and printing products produced by packaging and printing enterprises often have the following problems:
1 For packaging and printing products, there is no problem in the printing or using process in the low temperature season, but when printing or using in the high temperature season, the phenomenon of graphic ink film sticking to each other will occur.
2 There is no problem when packaging and printing products are coated in the high-temperature season, and when the product is used in the low-temperature season, the film degumming phenomenon of the product packaging will occur.
The author believes that the former is caused by the low softening point of the thermoplastic coconut in the ink system or the excessive slow-drying solvent in the ink remaining in the printed graphic ink film. The latter is caused by improper or excessive use of the dispersion aid in the ink or compound adhesive system. This article will be discussed for reference only by colleagues in the industry.
1 Use pressure to solve the adhesion problem caused by the thick ink layer and adhesive layer.
By pressurizing the printing machine and the compound adhesive coating machine, the adhesion between the printed graphic ink film layer and the coated compound adhesive layer can be closely matched, and the ink and glue can flow under pressure, which is beneficial to the ink The molecules of the system and the molecules of the glue system diffuse and penetrate to improve the adhesion and adhesion strength of the ink and the substrate, the glue and the printed graphic ink film.
Of course, the pressure should be such that the ink film and glue film are not deformed. That is to say, the purpose of pressurization is also to discharge excess ink or glue to reduce the thickness of the ink layer and glue layer to ensure that the thickness of the entire ink layer and glue layer is uniform and dense, and to prevent voids caused by local under-ink or under-glue. Prevent some inks and compound adhesives from generating bubbles due to the discharge of volatiles when heated and solidified or cooled and matured.
2 Solve the residual solvent problem with a blower, etc.
Usually we use infrared drying, ultraviolet drying, air cooling and even drying in the packaging and printing process. The purpose of drying is to increase the volatility of the solvent in the ink and glue system. It is convenient for the operation of the ink film forming and glue compound process. It also allows 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 baking, etc., to promote solvent evaporation and evaporation. Solvent-free inks and glues can be laminated and bonded immediately after printing and gluing.
The cooling time of infrared, ultraviolet, blowing, baking, etc. depends on the evaporation 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 the film from hardening (curing), the adhesion is not good, the adhesion is not strong, or it is not too short, so that the solvent evaporates, evaporates or crosslinks are not enough, resulting in poor adhesion fastness and glue The strength of the coating decreases.
We know that printing and laminating can be carried out at room temperature, under infrared, ultraviolet, heating and baking curing or cold blowing aging, or alternately between infrared heating and cold blowing, or between infrared and ultraviolet process alternately. This depends on the curing (curing) temperature of the ink and glue. In particular, it is scientific to remove the film after the ink film is formed and the compound glue is cured (cured).
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3 Use the wetting and dispersing agent to solve the problem of leveling and adhesion of ink and glue.
Practice tells us that no matter what happens to the interface between the ink and the composite glue, the complete wetting of the surface of the adhesive material (substrate or substrate) by the ink and the composite glue is a prerequisite for obtaining the adhesion strength, but the main factors affecting the wetting It is the inherent characteristics of the ink and the composite adhesive, followed by the roughness of the adherend, the porosity, the degree of contamination of the adsorption layer, and the length of the wetting time.
In order to improve the wetting efficiency of inks and compound glues, when selecting packaging printing inks and compound glues, inks and compound glues with high solid content and low drilling degree should be used. The corresponding wetting agent and coupling agent should also be selected according to the characteristics of the ink and compound adhesive.
Because the ink and compound glue are a multi-phase dispersion between organic pigments and inorganic pigments, between organic fillers and inorganic fillers, between pigments and fillers, between fillers and connecting base materials (resins), resins and solvents There will be competitive adsorption between them, so we must pay attention to the order of addition of pigments, fillers, resin surface adsorbents, and the strength of the adsorption of ink, compound glue and substrate surfaces.
From the adsorption theory, it can be known that the thinner the ink layer of the packaging and printing product and the coating glue layer of the composite glue, the greater the adhesion and the higher the bonding strength. Therefore, the ink layer and the adhesive layer should be as thin as possible under the premise of ensuring that the dots of the printed graphic ink film are not lost or the composite coating is not under-adhesive. It is generally believed that the thickness of the ink layer and the glue layer should be controlled at 8-100 microns.
If the drilling degree of the binder or compound glue in the ink system is too large, it is not only difficult to make the sizing coating uniform, but also not conducive to the penetration and diffusion of the printing ink to the substrate or the glue to the printed graphic ink film.
In addition, the adhesion strength is also related to the surface roughness. A solid surface that is really smooth for ink or compound glue is not an ideal adhesion surface. Only with a certain degree of roughness can the adhesion area be increased and combined with ink or compound
Mechanical "meshing" occurs between glues.
Of course, it is unscientific to simply think that as long as the substrate surface is rough, good adhesion of ink or compound glue can be achieved. Because the surface is too rough and even has obvious unevenness, it is also unfavorable for the ink film adsorption and the adhesion of the composite adhesive. If the interface of the printing material or the printing ink film is too rough, defects will be formed where the interface cannot contact. These defects can prevent the ink or compound glue from entering and can not play the role of adhesion. Instead, it will generate stress concentration and greatly reduce the ink and the printing material. The adhesion strength of the compound glue and the printing ink film. If the amount of ink used on the surface is slightly less, the graphic ink dots will be lost. If the amount of sizing is too small, the under-glue will be formed and the bonding strength of the film will also be reduced.
4 Infiltrate the surface porosity of the substrate with ink and compound glue.
Some substrates (including the surface of printed graphic ink film) have many open capillary pores that are invisible to the naked eye. If ink or compound glue can infiltrate the pore wall, it is necessary to exclude air from penetrating into the pores and "embedding" in the pores. Helps to improve the adhesion strength.
The depth of the ink or compound glue penetrating into the hole is related to the shape and size of the pore, and the adhesion of the ink to the substrate, the compound glue to the surface of the packaging printing ink film, the fineness of the ink, the drilling degree and the curing time of the compound glue, etc. Factors.
5 Control the drilling degree of the ink and compound glue and the amount of plasticizer.
The adhesion degree of the substrate and the printed graphics has a great relationship with the drilling degree of the ink and compound glue. Therefore, this index must be well controlled.
The printing material and the printed graphic ink film contain some oligomers. The fluidity of such low molecular weight materials is very easy to seep out of the surface of the printing material, or it is easy to seep on the surface of the printed 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 treated before printing or before compounding.
The purpose of using plasticizers in inks and compound adhesives is to make the ink film and compound adhesive layer tough. Secondly, it can also reduce the cohesion of the system base material, increase the diffusion capacity of the system base material, and improve the adhesion strength. However, when choosing to use plasticizers, the compatibility of the plasticizer with the base material and the substrate should be considered, and the amount of plasticizer should be paid attention to. The amount of plasticizer used in inks and compound adhesives should generally be controlled to less than 10%, but it will reduce the adhesion of the product.
6 Make up for the shortage of ink and glue with appropriate amount of filler.
The use of fillers in printing inks and compound adhesives can not only save base materials and reduce material costs, but also reduce the shrinkage rate of the bonding seam of inks and compound adhesives, which greatly improves the bonding strength of printing ink films and compound adhesives.
The commonly used fillers are: reduced silver powder or electrolytic silver powder, zinc oxide powder, activated silica (white carbon black), mica powder, calcium carbonate, etc.
In addition, in order to prevent the adverse effects of inks and compound adhesives, their storage time should also be controlled.
The adhesion of ink and compound adhesive tends to decrease with the increase of storage period. This is because the surface aging of ink and compound adhesive during storage period will be more serious if exposed to air. Therefore, the ink and compound glue should be stored in a container isolated from the air, and the time should not be too long.
7 Master the curing temperature to improve adhesion.
The increase in curing temperature increases the ability of the thermal movement of the base molecules in the ink and compound adhesive system to accelerate the diffusion rate, which is beneficial to wetting and adsorption, enhances adhesion and improves bonding strength.
Of course, the higher the curing temperature, the better. Make sure not to exceed the softening point (temperature) of the substrate to avoid deformation of the composite material. If the temperature is too high, the ink and compound glue flow into the micro-voids, it is easy to generate bubbles and reduce its adhesion strength.
On the other hand, the bonding strength between packaging printing ink and printing material and compound adhesive and packaging printing graphic ink film tends to increase with the curing time, but when a certain value is reached, its adhesion strength will not Increased again. The curing temperature and the curing time are mutually restrictive. In short, increasing the temperature and increasing the light energy and light intensity can shorten the curing time. To lower the temperature and lower the light intensity, it is necessary to extend the curing time.
8 Use antistatic additives to solve the problem of not easy to ink and sizing.
In modern packaging and printing technology, especially in the process of continuous printing and continuous sizing, due to the friction between the printing material and the relevant parts of the printing machine and the coating machine, static electricity is often generated, and due to some printing materials The electrostatic charge of the electrical insulator will accumulate more and more, and it will eventually lose the dots of the printed graphics and text due to static electricity, and it is difficult to apply the glue evenly, even deinking, degumming, and stripping. For this reason, it is recommended to add antistatic agent in the printing ink and glue system in an appropriate amount to improve the ink transfer rate and glue coating quality.
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