The abnormal phenomenon of the solvent-free composite process of flexible packaging is usually caused by objective factors such as paper, film , ink, adhesive, machinery and equipment, as well as subjective factors such as temperature, pressure, speed, gluing amount, and customer use. Based on the actual application of our company's single-component FC-7146 and two-component FC-7201 / CK7302 adhesives in the composite process, the causes and treatment methods of several common abnormal phenomena are summarized. It is hoped that it can bring some technical references to production enterprises using solvent-free composite processes.
First, the phenomenon of paper and plastic detachment
The essence of paper-plastic composite is to use adhesive as an intermediate medium. On the drum of the laminator, under the action of heat and pressure, the paper fiber and the plastic non-polar polymer film and the ink layer are bidirectional. Wetting, penetrating, and drying of the oxidized conjunctiva, so as to produce an effective adsorption force, which makes the paper and plastic adhere firmly.
The paper-plastic detachment phenomenon mainly manifests as insufficient peel strength of the composite film, the adhesive is not dry, and the paper printed matter is detached from the adhesive layer on the plastic film. This phenomenon is easy to occur in products with large printing areas and large field products. Due to the thick ink layer on the surface, the glue is difficult to wet, spread and penetrate.
1. The main reasons
There are many factors that affect the separation of paper and plastic. The paper's smoothness, uniformity, moisture content, various properties of plastic films, the thickness of printed ink layers, the amount of auxiliary materials, the temperature and pressure when paper and plastic are combined, and the production environment. Hygienic conditions as well as temperature and relative humidity will all have an impact on the final results of paper-plastic composites.
(1) The ink layer of the ink is too thick, causing the penetration and diffusion of the adhesive, causing the paper and plastic to detach. The treatment method is to increase the coating amount of the adhesive and increase the pressure.
(2) When the ink layer is not dried or is not completely dried, the residual solvent component in the ink layer weakens the adhesive force and forms paper and plastic. The processing method is to wait for the product ink to dry and then compound.
(3) Residual dust on the surface of printed matter will also hinder the adhesion of paper and plastic film to form paper and plastic. The processing method is to use mechanical and manual methods to erase the powder on the surface of the printed matter before compounding.
(4) The operation process is not standardized, the pressure is too small, and the machine speed is fast, resulting in the separation of paper and plastic. The treatment method is to strictly operate according to the process specifications, appropriately increase the pressure of the film and reduce the machine speed.
(5) Adhesive is absorbed by paper and printing ink, and paper and plastic are separated due to insufficient coating amount. The adhesive should be re-formulated and the sizing amount determined according to the manufacturer's requirements.
(6) The corona treatment on the surface of the plastic film is insufficient or exceeds the service life, causing the paper and plastic to detach due to the failure of the treated surface. The plastic substrate should be coronad or the plastic film should be renewed according to the corona standard of the film coating.
(7) When using single-component adhesives, paper and plastic detachment due to insufficient air humidity should be artificially humidified according to the humidity requirements of the single-component adhesive processing technology.
(8) Ensure that the adhesive is within the shelf life, and is stored and used according to the manufacturer's requirements. For example, the two-component automatic mixing machine is in good condition to ensure accurate, uniform and sufficient proportioning.
Second, the phenomenon of aluminum transfer
The aluminized film not only has the characteristics of a plastic film, but also replaces the aluminum foil to a certain extent, which plays a role in improving the grade of the product and has a relatively low cost. However, in the production process, the problem of aluminum plating layer transfer often occurs, which leads to a decrease in the peeling strength of the composite film, a decrease in product performance, and a serious impact on the quality of packaging contents.
The root cause of the aluminum plating transfer is that the bonding force between the aluminum plating layer and the substrate is smaller than the bonding force between the aluminum plating layer and the glue layer, which causes the overall peel strength of the composite film to decrease. As a result, the aluminum plating layer is largely detached from the substrate to the glue layer Migration phenomenon.
At present, the most commonly used aluminized films are VMCPP and VMPET, and the corresponding composite film structures are OPP / VMCPP, PET / VMCPP, PET / VMPET and so on. In practical applications, the most problematic is PET composite VMPET, because it is often used in middle-level composite. This is because as the aluminized substrate, CPP and PET have great differences in tensile properties. PET has a high rigidity. Once it is compounded with a material that also has great rigidity, during the curing and molding process of the adhesive, The presence of cohesion can easily cause the adhesion of the aluminized layer to be damaged, thereby causing the aluminized layer to migrate.
Main reasons and treatment methods:
(1) The sizing amount is too large. The sizing amount should be appropriate. If the sizing amount is too small, it will undoubtedly result in a small compound fastness and easy peeling. However, if the sizing amount is too large, it will volatilize and dry. Secondly, a large amount of glue is applied, and the curing time is long, and the penetration effect on the aluminum plating layer is strong. Therefore, it is necessary to determine reasonable process parameters and choose a reasonable sizing amount according to the substrate and use through small tests.
(2) The ripening conditions are bad, mainly because the ripening temperature is too high. Controlling the curing time and appropriately reducing the curing temperature can reduce the transfer of aluminum plating.
(3) The mixing ratio of glue is incorrect. Reducing the curing agent ratio within a certain range can improve the aluminum plating transfer. The specific method is to reduce the amount of curing agent when the working glue is prepared, so that the degree of cross-linking reaction between the main agent and the curing agent is reduced, thereby reducing the adhesive film. The brittleness allows it to maintain good flexibility and stretchability to control the transfer of the aluminum coating.
(4) Adhesive selection is incorrect. Use a suitable or special adhesive. In the composite aluminized film, do not use adhesives with too low viscosity, because the low-viscosity adhesive has a small molecular weight, weak intermolecular forces, and strong molecular activity easily penetrates into the aluminization and affects the aluminization adhesion. ,
(5) The quality of the substrate itself is poor. Change to a suitable substrate.
(6) The operating tension is too large, which will cause a change in elasticity due to a strain on the aluminized film, resulting in transfer. Control the tension. When unwinding aluminizing, the tension must be controlled. The reason is that the aluminized film will stretch under the action of tension and cause elastic deformation. Correspondingly, the aluminum plating layer is easily loosened, and the adhesion is relatively reduced.
(7) Excessive residual solvent will destroy the aluminum plating, because the aluminum plating layer of the aluminum plating film is relatively thin, it is inevitable that there will be some pinholes, and the residual solvent penetrates into the aluminum plating layer to destroy the aluminum layer and cause aluminum plating transfer.
Third, the bubble phenomenon
The so-called bubble refers to the incomplete adhesion of the two layers of film, the composite film and the substrate have gaps, and the presence of gas. When the aluminum-plated film is compounded, a white point like a needle tip will occur. The essence is that the applied glue is not enough to fill the voids of the ink layer in the composite film and the pits on the surface of the material, which is also called air bubbles. Bubbles do not have to be bulging, and they can exist in other forms. As long as the two films are not fully fitted, there will be a difference in transparency, which will present what we often call "bubbles".
1. The main reasons
Different types of composite substrates have very different physical properties (such as air permeability), and have a great relationship to the formation of bubbles in the composite film. Generally speaking, it is compounded between a substrate with good air permeability (such as BOPP, CPP, CPE, LDPE) or a composite substrate with poor air permeability (such as PVDC, BOPA) and another composite substrate with good air permeability It is not easy to produce bubbles. However, if the permeability of both substrates is poor, when they are compounded, bubbles are easily generated, such as the compound between PVDC and BOPA. This is due to the poor air permeability of the two composite substrates, and the adhesive inevitably mixed with a small amount of air on the composite unit gluing system. At the same time, the isocyanate-based adhesive itself is crosslinked and cured at the curing stage of the composite film, and also produces gas by-products such as carbon dioxide (CO2). In this way, a large number of fine bubbles are generated, which affects the apparent quality of the composite film. At the same time, in order to make the composite substrate have a certain surface tension, a certain treatment must be performed on the surface properties of the substrate, such as corona treatment, to improve the wettability and roughness of the surface of the composite substrate, but the roughness exceeds At a certain limit, it is difficult to be filled with viscous glue. In this way, large and small bubbles are formed between these minute engaging surfaces.
The viscosity of the adhesive is also an important cause of air bubbles. Generally speaking, the viscosity of the adhesive is related to the molecular weight of the adhesive, the plasticizer, and the type of the diluent, and the adhesive is generally high in viscosity and poor in fluidity at room temperature. Therefore, in order to reduce the viscosity and improve the fluidity, it is necessary to Keep warm at temperature. The higher the use temperature of the two-component adhesive, the shorter the mixing and storage time, and the larger the proportion of the main agent and the curing agent, the greater the viscosity of the adhesive, the less conducive to the formation of bubbles, and the easier it is to form bubbles. Bubbles of the same size can be eliminated by low-viscosity glues, while high-viscosity glues may not be possible, because high-viscosity glues have large molecular weights and poor leveling properties.
(1) Bubbles caused by insufficient sizing amount and uneven coating are actually blank spots without sizing, which can be eliminated by appropriately increasing the sizing amount. Insufficient sizing amount is a relative concept. In addition to peel strength, the leveling factor of coating is an important factor. In addition to the effect of sizing amount on it, whether to use it? The surface tension of the homogenizing roller, the substrate, the adhesive, and the viscosity of the adhesive will affect it. The comprehensive conditions are good, and the sizing amount can be appropriately reduced. This is even more pronounced on the composite of aluminized and white printed films.
(2) Air bubbles caused by excessive humidity. The reason is that the carbon dioxide gas generated by the reaction between the NCO component of the adhesive and water vapor is too late to precipitate the film and accumulate between the films. This phenomenon is solved by properly controlling the ambient humidity during production. Generally the relative humidity is below 70%.
(3) Due to insufficient ripening temperature and failure to eliminate air bubbles, the ripening temperature should be appropriately increased. The temperature of the aging room is not higher than 50 ° C and not lower than 35 ° C. It is rare that the composite film has no bubbles at the time of curing, and curing can eliminate small bubbles, because the two-component polyurethane adhesive that has not been cured, the higher the temperature and the greater the fluidity, the "secondary leveling" can eliminate bubbles to a certain extent.
(4) Air bubbles generated due to insufficient drying of the ink solvent are caused by the residual solvent of the printing film. Generally appear in the part with high overprint rate of ink, and the part with low overprint rate has few bubbles. During production, it should be guaranteed to be completely dry before recombination. It can also deal with printed film or reduce laminating speed.
(5) For the bubbles caused by the equipment process, if there is damage or foreign objects on the rollers in the compound part or the glue application part, the steel rollers should be replaced and the foreign objects should be removed.
(6) Bubbles caused by production processes. It mainly refers to controlling some process parameters, mainly including compound pressure, winding tension, coating temperature and compound temperature. If the compound pressure is too low, the rubber roller pressure should be increased appropriately. The compounding speed is too fast, you can reduce the compounding speed appropriately, or increase the temperature of the nip roller to increase the fluidity of the adhesive. Bubbles caused by dust and impurities on the film surface should improve the environmental sanitation of the production workshop.
Fourth, the conclusion
Because of its energy-saving, high-efficiency, safety, and environmental protection characteristics, especially the advantages of cost savings, the solvent-free composite process is being used by more and more flexible packaging companies. It is not easy to use the solvent-free composite process. . It has particularly high requirements for the standardized operation of flexible packaging enterprise employees. When enterprises introduce solvent-free composite technology, they must fully consider this point.