Flexible packaging plays an extremely important role in the packaging and printing industry, such as food packaging bags. The appearance and quality of the flexible packaging can clearly reflect the overall processing capability of the printing plant and even reflect the quality of the printing staff.
Printed flexible packaging undergoes a series of processes such as printing, compounding, slitting, and bag making. Each process must strictly guard the quality of the goods, so as to produce qualified products. This article will discuss the causes of bubbles and their solutions in order to discuss them with related personnel.
The dry compounding method is to apply a layer of solvent-based adhesive on the plastic film (the adhesive is divided into single-component hot-melt adhesives and two-component reactive adhesives), and the solvent is volatilized and dried after being dried by the compounder. , and then bonding with other composite materials under hot pressing to form a smooth composite material. The composite film combines the excellent properties of each layer of the film, such as moisture resistance, barrier properties, heat resistance, and heat sealability, to meet the packaging needs of various commodities.
What needs to be added is that during the drying process in the drying tunnel, the solvent in the adhesive is required to be volatilized as clean as possible. Because the solvent does not volatilize, its volume will gradually increase after winding. The gradual accumulation of residual solvent will leave tiny pinholes on the cooled composite material. This tiny pinhole is the bubble we talk about, seriously affecting the product quality, and even failing to meet the requirements of customers, resulting in product scrapping. .
Bubbles tend to occur in products that use one-component hot melt adhesives for compounding, and of course do not exclude two-component reactive adhesives.
The degree of evaporation of the solvent is related to many factors, such as the temperature of the drying tunnel, the speed of the machine, the temperature and humidity of the room, and even the adhesive itself. In the actual work, it should be able to accurately determine the distinction and give it a solution.
1. Over temperature effect
The drying tunnel is divided into three areas: evaporation zone, hardening zone, and exclusion odor zone. The energy consumption in the three regions is almost equal and should be adjusted at any time according to the condition of the substrate to be compounded in the actual work. In general, the evaporation zone temperature is controlled at 50-60°C, the hardening zone temperature should be controlled at 70-80°C, and the odor-suppressing zone temperature should be controlled at 80-100°C. Smooth composites can only be achieved if the substrate runs smoothly and the tension between the composite and the substrate is appropriate. With proper temperature control, it is beneficial to the volatilization of the solvent in the adhesive.
2. Speed ​​and indoor temperature and humidity
The speed of the machine also indirectly affects the volatilization of the solvent. In practical work. It is necessary to have a good grasp of the speed and solvent evaporation rate. The speed is too fast, not conducive to solvent evaporation, which affects the amount of residual solvent; too slow machine speed will reduce production efficiency.
At the same time, the vertical and horizontal extension of the substrate should also be considered to prevent distortion and deformation.
The temperature of the compound shop is controlled at 25°C and the relative temperature is controlled at 50%-60%.
3. The relationship between two-component reactive adhesives and bubbles
Two-component adhesives are based on polyurethane adhesives, and two-component reactive adhesives are more commonly used. It has a good bonding strength, room temperature can be cured, heating can also be cured, I plant currently using Zhejiang Huangyan Huaguang Resin Co., Ltd. Pu-1950 main agent, adhesive agent-based ratio: curing agent: ethyl acetate =1:0.2:1.7. The curing time is generally 24-48 hours.
Experience tells us that if the curing time is not enough, there will be tiny bubbles, and even affect the peeling fastness.
The preparation of two-component adhesive must be mixed evenly, so that the curing agent is full of activity, evenly dispersed, which is conducive to the affinity with the printed substrate, reducing bubbles. Curing room temperature is generally controlled at 50-60 °C is appropriate. Our factory operations are more formal, the interiors are clean, and the environment is good. These are the factors that reduce bubbles.
4. Influence of other factors and solutions
In dry compounding, defective rollers are also the cause of air bubbles. The selection of the rubber roller and the hot roller is very important. When selecting, the roller needs to be delicate, smooth, no fine pits and lines, etc.
The hot roller pressure is also related to the generation of air bubbles. It must be compacted and adjustable according to the actual situation.
The generation of bubbles is also related to the gluing roller. In summer, hot weather, long-term use of two-component adhesive prone to anilox roller jamming, so pay attention to cleaning. Our factory adopts the powerful release agent produced by Shanghai Shenda Technology Co., Ltd. for cleaning, with good results.
In addition, the amount of glue is too small, the concentration of lean is also the cause of bubbles, then, increase the amount of glue, increase the concentration ratio can eliminate bubbles.
When compounding in the winter, if the air conditioning device is not installed in the room, the temperature is low, the humidity is lower than 40%, and the adhesive is not well dispersed, which can also cause air bubbles. At this time, the prepared adhesive is preheated for 1-2 hours and satisfactory results can be obtained. However, attention must be paid to safety. There must be special care for warming up.
If you want to get the ideal compound product, you must have a serious and responsible attitude in the actual work, and you should also have the habit of summing up experience.
Printed flexible packaging undergoes a series of processes such as printing, compounding, slitting, and bag making. Each process must strictly guard the quality of the goods, so as to produce qualified products. This article will discuss the causes of bubbles and their solutions in order to discuss them with related personnel.
The dry compounding method is to apply a layer of solvent-based adhesive on the plastic film (the adhesive is divided into single-component hot-melt adhesives and two-component reactive adhesives), and the solvent is volatilized and dried after being dried by the compounder. , and then bonding with other composite materials under hot pressing to form a smooth composite material. The composite film combines the excellent properties of each layer of the film, such as moisture resistance, barrier properties, heat resistance, and heat sealability, to meet the packaging needs of various commodities.
What needs to be added is that during the drying process in the drying tunnel, the solvent in the adhesive is required to be volatilized as clean as possible. Because the solvent does not volatilize, its volume will gradually increase after winding. The gradual accumulation of residual solvent will leave tiny pinholes on the cooled composite material. This tiny pinhole is the bubble we talk about, seriously affecting the product quality, and even failing to meet the requirements of customers, resulting in product scrapping. .
Bubbles tend to occur in products that use one-component hot melt adhesives for compounding, and of course do not exclude two-component reactive adhesives.
The degree of evaporation of the solvent is related to many factors, such as the temperature of the drying tunnel, the speed of the machine, the temperature and humidity of the room, and even the adhesive itself. In the actual work, it should be able to accurately determine the distinction and give it a solution.
1. Over temperature effect
The drying tunnel is divided into three areas: evaporation zone, hardening zone, and exclusion odor zone. The energy consumption in the three regions is almost equal and should be adjusted at any time according to the condition of the substrate to be compounded in the actual work. In general, the evaporation zone temperature is controlled at 50-60°C, the hardening zone temperature should be controlled at 70-80°C, and the odor-suppressing zone temperature should be controlled at 80-100°C. Smooth composites can only be achieved if the substrate runs smoothly and the tension between the composite and the substrate is appropriate. With proper temperature control, it is beneficial to the volatilization of the solvent in the adhesive.
2. Speed ​​and indoor temperature and humidity
The speed of the machine also indirectly affects the volatilization of the solvent. In practical work. It is necessary to have a good grasp of the speed and solvent evaporation rate. The speed is too fast, not conducive to solvent evaporation, which affects the amount of residual solvent; too slow machine speed will reduce production efficiency.
At the same time, the vertical and horizontal extension of the substrate should also be considered to prevent distortion and deformation.
The temperature of the compound shop is controlled at 25°C and the relative temperature is controlled at 50%-60%.
3. The relationship between two-component reactive adhesives and bubbles
Two-component adhesives are based on polyurethane adhesives, and two-component reactive adhesives are more commonly used. It has a good bonding strength, room temperature can be cured, heating can also be cured, I plant currently using Zhejiang Huangyan Huaguang Resin Co., Ltd. Pu-1950 main agent, adhesive agent-based ratio: curing agent: ethyl acetate =1:0.2:1.7. The curing time is generally 24-48 hours.
Experience tells us that if the curing time is not enough, there will be tiny bubbles, and even affect the peeling fastness.
The preparation of two-component adhesive must be mixed evenly, so that the curing agent is full of activity, evenly dispersed, which is conducive to the affinity with the printed substrate, reducing bubbles. Curing room temperature is generally controlled at 50-60 °C is appropriate. Our factory operations are more formal, the interiors are clean, and the environment is good. These are the factors that reduce bubbles.
4. Influence of other factors and solutions
In dry compounding, defective rollers are also the cause of air bubbles. The selection of the rubber roller and the hot roller is very important. When selecting, the roller needs to be delicate, smooth, no fine pits and lines, etc.
The hot roller pressure is also related to the generation of air bubbles. It must be compacted and adjustable according to the actual situation.
The generation of bubbles is also related to the gluing roller. In summer, hot weather, long-term use of two-component adhesive prone to anilox roller jamming, so pay attention to cleaning. Our factory adopts the powerful release agent produced by Shanghai Shenda Technology Co., Ltd. for cleaning, with good results.
In addition, the amount of glue is too small, the concentration of lean is also the cause of bubbles, then, increase the amount of glue, increase the concentration ratio can eliminate bubbles.
When compounding in the winter, if the air conditioning device is not installed in the room, the temperature is low, the humidity is lower than 40%, and the adhesive is not well dispersed, which can also cause air bubbles. At this time, the prepared adhesive is preheated for 1-2 hours and satisfactory results can be obtained. However, attention must be paid to safety. There must be special care for warming up.
If you want to get the ideal compound product, you must have a serious and responsible attitude in the actual work, and you should also have the habit of summing up experience.
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