Dry compounding is a process in which a dry compounding apparatus is used and adhesives are bonded together using two or more films. The amount of binder used in dry compounding is small, but it has a very important influence on the quality performance of the composite film. It determines the peel strength, heat resistance, and medium resistance of the composite film, so the choice and use of the adhesive by the compounding company is still very prudent. Generally, two main aspects are considered. One is the choice of adhesive type, and the different requirements of the product, the choice of different types of adhesives; the second is to specify different coating amounts for different requirements (dry basis) . These two tasks are done well, and the quality control of the dry compound film is also basically guaranteed. According to investigations, at present domestic composite companies often overlook another important indicator - adhesive coating status. The coating state of the adhesive has a great influence on the peel strength, transparency, heat seal strength and the like. Many apparent defects are often caused by poor coating conditions, such as the occurrence of defects such as bubbles and spots. One of the major causes is the poor coating state.
The state of application of the adhesive refers to the distribution of the adhesive on the film. The standard state should be that the adhesive forms a uniform, transparent, defect-free film on the surface of the film, but due to the complexity of the actual production, many factors in the production process will affect the coating state of the adhesive. It is very difficult to reach the ideal standard state. The work we have to do is take appropriate measures to put the quality of this film. Here, I would like to start from the equipment coating control system, raw materials, workshop environment and process factors, and discuss with friends the factors that affect the adhesive coating state and the corresponding solutions.
First, equipment coating control system The equipment itself affects the coating status of the system has the following four parts:
1. Rubber Roller - Net Roller - Scraper - Glue Slot System This system determines the amount of adhesive applied, and ensures that the adhesive spreads on the surface of the carrier film with a certain distribution density. The adhesive coating is the most important It is determined by this system.
2. Flattening the roll and flattening the roll can further evenly coat the adhesive and eliminate traces of part of the screen.
3. The Oven oven system temperature and ventilation conditions affect the solvent volatilization rate and the binder hardening rate.
4. Composite Roller - Rubber Roller This system provides a certain temperature and pressure that not only further activates the adhesive, but also allows the adhesive to spread further, further eliminating subtle defects in the glue.
Second, raw materials 1. Adhesives In general, general-purpose adhesives have better leveling than cooking adhesives. Different manufacturers produce adhesives that vary in leveling. In order to ensure excellent coating conditions, compounding Manufacturers should carefully identify and use.
2. The surface tension of the carrier film and the bottom film or bottom film is too low, and the difference between the surface tension of the adhesive and the surface tension of the adhesive is too small, which can cause the adhesive to be insufficiently dispersed and affinity on the surface, and the surface tension of the film in general. The difference between the surface tension and the adhesive is 12 more than dyne. Below this value, the coating state may be problematic. Precipitation of the auxiliary agent on the carrier film or the base film should also be noted. At present, compound manufacturers have a deeper understanding of the precipitation of additives with a long storage time for PE films with a thickness of 60 μm, but the understanding of the precipitation of additives for PET and NY is not enough. It is generally believed that the surface tensions of PET and NY are high and dry compound There will be no problem, but PET and NY also add a lot of additives during production, and there will also be sales of auxiliary additives precipitated, which will seriously affect the spread and affinity of the adhesive on the film surface. As composite manufacturers are happy to use PET and NY as carrier films, this must be taken seriously. Random corona treatment is a better solution.
3. Ethyl acetate ethyl acetate is passed through a binder diluent. The content of water or alcohol in the ethyl ester has a relatively large influence on the coating state of the adhesive. The volatilization rate of water is much lower than the volatilization rate of ethyl ester. Excessive water content will seriously reduce the volatilization rate of the solvent, affect the spreading rate and hardening rate of the adhesive, and the adhesive itself cannot be infiltrated by water. The surface of the film. In addition, the curing agent with water or alcohol in the adhesive can quickly generate CO2, not only limiting the adhesion of the infiltration, but also produce more serious bubbles.
Third, process factors 1. The working concentration of the binder and the matching of the network roller are generally solved by increasing the working concentration of the binder (that is, the working solid content) in order to increase the amount of sizing. However, it must be considered that only with the combination of the number of lines of the roller, consideration will be given to a good coating effect, and the adjustment of the working concentration alone cannot meet the requirements. Generally speaking, such a principle can be followed. The higher the working concentration is, the greater the coating viscosity is, and the smaller the number of lines that should be selected, namely the mesh roller with a large mesh volume. Usually 75% solids content, viscosity in the 3000-5000CPS, 25 °C adhesive (ordinary adhesive is generally in this range), 100 using 100-150 wire roller, the working concentration in the range of 30% adjustment to meet The coating amount is within 2.0-3.5g/m2 (dry base coating weight), while the high temperature cooking concentration is large. Generally, the viscosity is 3000-4000CPS at 50% solids content, 25°C. If the coating amount is required to be 4.5-5.5g/m2 (dry base coating amount), it is difficult to ensure a good coating state by using a network cable roller with more than 100 lines. At this time, an 80-line cable roller should be used. It is suggested that the compound manufacturer will be equipped with three sets of cable roller, so that almost all dry products can be produced, that is, one set of 80 lines for high temperature cooking bag products or products requiring a coating weight greater than 4.5 g/m2 (dry); 100-120 One set of wire, used for boiling, ordinary aluminum foil bags, general medium or vacuum product production coating amount between 3.0-4.0g/m2 (dry); 130-150 line set, for common products Production, the coating amount is allowed to be below 3.0g/m2.
2. Hardness adjustment of the rubber roller The rubber roller in the coating system provides a certain pressure to force the adhesive out of the mesh and disperse on the surface of the film. The hardness of the roller affects the dispersion of the adhesive. There are two aspects worth noting. First of all, the domestic hardness of the rubber roller is generally not high, and the hardness of the products of different manufacturers is relatively large; secondly, the hardness of the rubber roller will decrease with the extension of the use time.
3. The cleaning of the system's cleaning wire roller is very important. The degree of clogging of the mesh affects the coating effect of the adhesive and the uniform-continuity of the film, with particular attention to two aspects. First of all, we must adhere to regular cleaning, here refers to the use of net roller cleaning agent for thorough cleaning, and to use a standard operating method; Second, before replacing different types of adhesive, it must be carefully cleaned to prevent the adhesive from contaminating each other Affects adhesive properties and coating results.
4. During the mixing and stirring process, the adhesive of the circu- lation system sizing air suction system will trap a large amount of air and it will not be easily dissipated. This is especially true of high-temperature cooking adhesives. A large amount of air is also entrained during the pouring of the adhesive into the tank. The presence of air not only restricts the spreading of the adhesive, but also causes the composite film to generate a large amount of air bubbles in severe cases. If a circulation suction system is installed, on the one hand, it is possible not to use a pouring method to reduce the entrainment of air; on the other hand, it is also possible to extract the trapped air and ensure the uniform application of the adhesive.
Fourth, the environment of the workshop The humidity of the humidity workshop also seriously affects the coating state of the adhesive. Generally, the humidity of more than 70% will not guarantee the normal coating state. Especially in summer, the temperature of the workshop is high, and the ethyl ester is volatilized in the coating system, resulting in a rather low temperature of the system. A large amount of water vapor condenses on the rubber roller and the wire roller portion to destroy the coating state of the adhesive, and the adhesive is severely reduced. performance.
2. The dust in the air of the dust workshop will adhere to the film and cannot be removed. This will damage the film evenly and continuously. In particular, at the air outlet of the oven, strong air current will trap dust particles and spread it to the film. Affect the appearance. Therefore, in addition to the cleaning of the workshop, the filter at the air outlet must be cleaned frequently.
Above we discussed some of the factors that affect the coating state of the adhesive and improve the coating effect. The normal production process is more complex. When analyzing a certain quality problem, it needs to be more comprehensively considered. (From "China Packaging Industry" 2001 12)
The state of application of the adhesive refers to the distribution of the adhesive on the film. The standard state should be that the adhesive forms a uniform, transparent, defect-free film on the surface of the film, but due to the complexity of the actual production, many factors in the production process will affect the coating state of the adhesive. It is very difficult to reach the ideal standard state. The work we have to do is take appropriate measures to put the quality of this film. Here, I would like to start from the equipment coating control system, raw materials, workshop environment and process factors, and discuss with friends the factors that affect the adhesive coating state and the corresponding solutions.
First, equipment coating control system The equipment itself affects the coating status of the system has the following four parts:
1. Rubber Roller - Net Roller - Scraper - Glue Slot System This system determines the amount of adhesive applied, and ensures that the adhesive spreads on the surface of the carrier film with a certain distribution density. The adhesive coating is the most important It is determined by this system.
2. Flattening the roll and flattening the roll can further evenly coat the adhesive and eliminate traces of part of the screen.
3. The Oven oven system temperature and ventilation conditions affect the solvent volatilization rate and the binder hardening rate.
4. Composite Roller - Rubber Roller This system provides a certain temperature and pressure that not only further activates the adhesive, but also allows the adhesive to spread further, further eliminating subtle defects in the glue.
Second, raw materials 1. Adhesives In general, general-purpose adhesives have better leveling than cooking adhesives. Different manufacturers produce adhesives that vary in leveling. In order to ensure excellent coating conditions, compounding Manufacturers should carefully identify and use.
2. The surface tension of the carrier film and the bottom film or bottom film is too low, and the difference between the surface tension of the adhesive and the surface tension of the adhesive is too small, which can cause the adhesive to be insufficiently dispersed and affinity on the surface, and the surface tension of the film in general. The difference between the surface tension and the adhesive is 12 more than dyne. Below this value, the coating state may be problematic. Precipitation of the auxiliary agent on the carrier film or the base film should also be noted. At present, compound manufacturers have a deeper understanding of the precipitation of additives with a long storage time for PE films with a thickness of 60 μm, but the understanding of the precipitation of additives for PET and NY is not enough. It is generally believed that the surface tensions of PET and NY are high and dry compound There will be no problem, but PET and NY also add a lot of additives during production, and there will also be sales of auxiliary additives precipitated, which will seriously affect the spread and affinity of the adhesive on the film surface. As composite manufacturers are happy to use PET and NY as carrier films, this must be taken seriously. Random corona treatment is a better solution.
3. Ethyl acetate ethyl acetate is passed through a binder diluent. The content of water or alcohol in the ethyl ester has a relatively large influence on the coating state of the adhesive. The volatilization rate of water is much lower than the volatilization rate of ethyl ester. Excessive water content will seriously reduce the volatilization rate of the solvent, affect the spreading rate and hardening rate of the adhesive, and the adhesive itself cannot be infiltrated by water. The surface of the film. In addition, the curing agent with water or alcohol in the adhesive can quickly generate CO2, not only limiting the adhesion of the infiltration, but also produce more serious bubbles.
Third, process factors 1. The working concentration of the binder and the matching of the network roller are generally solved by increasing the working concentration of the binder (that is, the working solid content) in order to increase the amount of sizing. However, it must be considered that only with the combination of the number of lines of the roller, consideration will be given to a good coating effect, and the adjustment of the working concentration alone cannot meet the requirements. Generally speaking, such a principle can be followed. The higher the working concentration is, the greater the coating viscosity is, and the smaller the number of lines that should be selected, namely the mesh roller with a large mesh volume. Usually 75% solids content, viscosity in the 3000-5000CPS, 25 °C adhesive (ordinary adhesive is generally in this range), 100 using 100-150 wire roller, the working concentration in the range of 30% adjustment to meet The coating amount is within 2.0-3.5g/m2 (dry base coating weight), while the high temperature cooking concentration is large. Generally, the viscosity is 3000-4000CPS at 50% solids content, 25°C. If the coating amount is required to be 4.5-5.5g/m2 (dry base coating amount), it is difficult to ensure a good coating state by using a network cable roller with more than 100 lines. At this time, an 80-line cable roller should be used. It is suggested that the compound manufacturer will be equipped with three sets of cable roller, so that almost all dry products can be produced, that is, one set of 80 lines for high temperature cooking bag products or products requiring a coating weight greater than 4.5 g/m2 (dry); 100-120 One set of wire, used for boiling, ordinary aluminum foil bags, general medium or vacuum product production coating amount between 3.0-4.0g/m2 (dry); 130-150 line set, for common products Production, the coating amount is allowed to be below 3.0g/m2.
2. Hardness adjustment of the rubber roller The rubber roller in the coating system provides a certain pressure to force the adhesive out of the mesh and disperse on the surface of the film. The hardness of the roller affects the dispersion of the adhesive. There are two aspects worth noting. First of all, the domestic hardness of the rubber roller is generally not high, and the hardness of the products of different manufacturers is relatively large; secondly, the hardness of the rubber roller will decrease with the extension of the use time.
3. The cleaning of the system's cleaning wire roller is very important. The degree of clogging of the mesh affects the coating effect of the adhesive and the uniform-continuity of the film, with particular attention to two aspects. First of all, we must adhere to regular cleaning, here refers to the use of net roller cleaning agent for thorough cleaning, and to use a standard operating method; Second, before replacing different types of adhesive, it must be carefully cleaned to prevent the adhesive from contaminating each other Affects adhesive properties and coating results.
4. During the mixing and stirring process, the adhesive of the circu- lation system sizing air suction system will trap a large amount of air and it will not be easily dissipated. This is especially true of high-temperature cooking adhesives. A large amount of air is also entrained during the pouring of the adhesive into the tank. The presence of air not only restricts the spreading of the adhesive, but also causes the composite film to generate a large amount of air bubbles in severe cases. If a circulation suction system is installed, on the one hand, it is possible not to use a pouring method to reduce the entrainment of air; on the other hand, it is also possible to extract the trapped air and ensure the uniform application of the adhesive.
Fourth, the environment of the workshop The humidity of the humidity workshop also seriously affects the coating state of the adhesive. Generally, the humidity of more than 70% will not guarantee the normal coating state. Especially in summer, the temperature of the workshop is high, and the ethyl ester is volatilized in the coating system, resulting in a rather low temperature of the system. A large amount of water vapor condenses on the rubber roller and the wire roller portion to destroy the coating state of the adhesive, and the adhesive is severely reduced. performance.
2. The dust in the air of the dust workshop will adhere to the film and cannot be removed. This will damage the film evenly and continuously. In particular, at the air outlet of the oven, strong air current will trap dust particles and spread it to the film. Affect the appearance. Therefore, in addition to the cleaning of the workshop, the filter at the air outlet must be cleaned frequently.
Above we discussed some of the factors that affect the coating state of the adhesive and improve the coating effect. The normal production process is more complex. When analyzing a certain quality problem, it needs to be more comprehensively considered. (From "China Packaging Industry" 2001 12)
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