I. Introduction
Since the composite film can combine the excellent properties of the film materials of each layer, the composite material is widely used in the packaging industry, as well as in other industries such as workers, agriculturists, and the like.
In the packaging industry, a commonly used bag composite is a composite of paper/PE/aluminum foil/PE four-layer material. Many factories use adhesives at three interfaces in this composite structure, and in some cases three different process procedures or in-sequence layers are used to bond the four substrates. Complete the compounding process on the machine. Some factories compound paper onto metal foil through an extrusion process. At the same time, the composite material is also subjected to an extrusion coating process of the PE layer, or an adhesive lamination is performed between the original substrate and the PE layer.
In the pharmaceutical industry, a commonly used composite material is a combination of polyester/PE/aluminum foil/PE. This combined processing situation is similar to the above. The composite structure of all four substrates can be processed by an adhesive lamination process. Perhaps the difference is that polyester/PE composites can use new co-extruded lamination processes. The final process of this composite structure may still be extrusion coating or adhesive lamination, and the PE layer is compounded.
From the above two application examples, it can be seen that this composite structure film material is a distinctive processing mode. At the same time, the composite material contains a PE layer, so there is bound to be such a problem, how to choose the most appropriate processing operations and methods. In addition, the PE may be a single layer or may be a multi-layer; and the introduction of the PE material may be using a PE film in adhesive lamination, or using PE particles in an extrusion process.
Second, the characteristics of composite film processing
There are many processing methods for multi-layer composite films, which can be summarized as coating method, laminating method and co-extrusion method. In processing and preparing such a composite material, a plastic film may be used in combination with another plastic film or paint, or may be bonded to non-plastic materials such as paper, cloth, and metal foil (such as aluminum foil) by heating or bonding. together.
Commonly used in the coating method are a roll coating method and an extrusion coating method. The roller coating method uses a roller coater to apply a viscous coating quantitatively to the film surface. The lower roller picks up the coating from the coating tank and transfers it to the second roller or directly onto the moving film. The film at this time is sandwiched between the coating roller and the pressure roller. The thickness of the coating depends on the viscosity of the coating. And the gap between the two rolls through which the film passes. In order to accurately control the thickness of the coating, when a very thin coating is made, a three-roll or four-roll coater can be used. The role of the remaining two rolls is to accurately calculate the amount of coating and is therefore called a metering roll. The coating thickness control depends on factors such as the gap between the metering roll and the speed of the roll. Extrusion coating is a process of compounding a molten extrusion layer onto a substrate. The substrate may be paper, metal foil or plastic film as long as they all withstand the temperature of the extruded molten polymer. The molten polymer is actually a highly viscous liquid that can flow on the substrate. It is due to this flow that the polymer can completely and evenly cover the entire surface of the substrate. For a porous substrate such as paper, it can also enter into voids that are not smooth. Both of these physical phenomena are very important for improving adhesion.
The common legalities in layer legalization include the legalization of extrusion and the legalization of thin film layers. The process of extrusion lamination is the compounding of two substrates by melting the polymer. In this compounding process, the extrudate enters the gap between the two rollers and is joined together. Both substrates also pass through each roller into the gap. Therefore, the extrudate is in the middle of the two substrates. From this process, it can be seen that the extrusion layer is the same as the extrusion coating method. The polymer flow, the substrate uniformity, and the unique adhesion force are the control of the degree of recombination and performance of the final three-layer structure of the composite material. The main factor.
The legal processing of thin film layers is completely different from the above-mentioned several kinds of processing techniques. This method uses a laminating adhesive to combine one layer of thin film with another layer of thin film, paper or metal foil. The adhesive is applied to the surface of the laminated substrate. If it contains solvent or water, it needs to be dried on a stove, and then it is pressed in a heated roller gap to make it with another base. Combination of wood. If the final composite exceeds more than two layers, additional lamination processes are required. The adhesive force during film layer processing operations depends on the properties of the laminating adhesive. First, it must have sufficient cohesive strength and the necessary bond strength to ensure that each substrate is firmly bonded to one another. In addition, other parameters, such as coating weight, nip temperature, and operating level, also affect the final degree of bonding of the composite.
The co-extrusion process is a relatively new process that combines a plurality of polymer melts from a special die into a thin film-like melt stream composed of multiple layers of different polymer melts. Two, three or more layers of coextruded composite film material are obtained. Because each resin is melted in a separate extruder and then passed through a co-extrusion die and the melt is kept in uniform layers without mixing, the co-extrusion process and its special tooling are designed. The polymer rheology theory and techniques must be applied well. The co-extrusion method is often combined with the use of several extruders of different sizes to deliver the melt into the die at the same time. Therefore, the die structure is a key device, in addition, the extruder size and screw speed, melt pressure, melt temperature Extruder power, etc. will affect the thickness of each layer in the composite film.
Third, make full use of the coating function
For the coating method, laminating method and co-extrusion method mentioned above, it involves a very important factor in the operation of the extrusion process - the use of a coating to increase the composite adhesive force, and therefore it is also referred to as an adhesive layer. . Taking the composite film polyester/PE/aluminum foil/PE commonly used in pharmaceutical packaging as an example, this is actually a simplified representation. The structure of the composite film material should be polyester/coating/PE/ Aluminum foil / coating / PE. To make the polyester layer firmly adhered to the PE layer, it is necessary to add a layer of paint between the two, and similarly, there must also be a coating between the aluminum foil layer and the PE layer in order to be between the two layers of the substrate. Form a strong enough bond.
Applying the coating on a substrate requires some special equipment, such as a coater and a dryer, before the composite operation process. In many cases, laminating adhesives such as polyurethanes or polyesters can be used as coatings. According to general experience, it is known that when used as a binder, the amount thereof is about half that of ordinary paint. In addition, polymers such as polyethyleneimine or ethylene acrylic acid can also be used for special binder coatings.
Co-extrusion can eliminate the step of applying the adhesive compared to the processes such as the coating method and the lamination method, or can greatly reduce the amount of the binder so that the binder can be effectively prevented from drying out. Solvent contamination or serious fire ignition defects, therefore, the co-extrusion process has the potential to replace other composite processes. However, many layers of material are co-extruded together. If the viscosity between the two polymers is insufficient, the overall adhesive effect of the final film product is affected, that is, under sufficient external force, there is still between layers. Possible consequences of separation. In this case, it is necessary to increase the adhesive layer, that is, the paint. By tightly bonding the two material layers, the structural integrity of the multilayer material can be guaranteed. The adhesive layer must also be melted in a dedicated extruder and fed into the mold as a separately added layer. In the composite structure, in addition to the co-extruded three-layer structure film, that is, an adhesive layer is added between the two substrates as a bonding material, more than four co-extruded films are also common. For example, it is known that EVOH film material has excellent moisture resistance, and if it is used as a moisture-proof layer, it should be sandwiched between two layers of polymer film, plus two layers of adhesive coating, In fact, this composite structure consists of five layers. Although the resin melt from a single extruder can supply coextruded films in two or more layers, each new resin must have a dedicated extruder.
Fourth, processing method selection factors
How to choose a suitable composite plastic film is a relatively complicated issue. When selecting a composite film processing method, the following factors must be considered.
1. The first choice is the determination of the processing method, which depends on the existing equipment. If the packaging material factory currently only configures laminating film production lines, the composite film material can only be processed by laminating according to this equipment. In the same way, if only a factory with an extruder must use an extrusion coating or an extrusion layer to process the films of various composite structures. However, for those factories that have both laminators and extruders, it is necessary to seriously consider what kind of processing technology should be chosen. In this case, economic efficiency is always the first priority.
2, from the perspective of reducing costs and improving efficiency, the extrusion process is suitable for long-term operation. Sometimes, material processing plants need to complete small batch production tasks, even in a matter of hours. In this case, applying a film layer legal process is a suitable method of choice. Because, the extrusion process production line must have a long time of non-stop operation to get better economic benefits. To make all process parameters in the extrusion process in a relatively harmonized and balanced condition, the necessary time is always much longer than the legal process of the thin film adhesive layer. Therefore, whenever the extrusion process line reaches the equilibrium coordination state, it has to keep running continuously for as long as possible.
3. For a material processing factory that is trying to purchase new processing equipment, the designed production line can use thin-film layers and can also use the process method. At this time, the application of economic theory analysis will certainly play a large role. Although the investment costs for extrusion process equipment are more expensive than simple film lamination process equipment, large-scale film lamination equipment with multiple options or auxiliary equipment may be more expensive than most common extrusion lines.
However, the extrusion process may provide a wide range of opportunities for material processing plants to use diverse polymers. The film use department is limited by the type of film supplied by the film processing department. The factory equipped with an extruder can choose various types of PE materials. They can use co-extruders, or even mixes, thus gaining more material selection opportunities.
4. When a material processing plant selects thin-film composite processing technology, the number of processes and times to be completed is also a very important factor. The laminating process is likely to require more processing than the extrusion process when producing multilayer thin-film structural materials, which is especially true when compared to co-extrusion. Coextrusion processing is actually the combination of two or more molten polymers into a single extrudate. Co-extrusion has many advantages, including the possible use of high-grade polymers, the use of recycled polymers, and the reduction of film thickness. It is worth pointing out that a prominent advantage of the co-extrusion process is that it can reduce the number of processes necessary to process the final composite film material. In theory, a single extruder can produce many different layers of composite film material under the condition that the number of open molds is constant.
Taking a close look at the processing methods and characteristics of the various composite film materials discussed above, many factors must be taken into consideration to achieve a reasonable choice. This means that it is difficult to say that there is an optimal method for processing any specially packaged composite film material. Therefore, it is very necessary to comprehensively and carefully analyze various influencing factors when selecting the best processing method.
Since the composite film can combine the excellent properties of the film materials of each layer, the composite material is widely used in the packaging industry, as well as in other industries such as workers, agriculturists, and the like.
In the packaging industry, a commonly used bag composite is a composite of paper/PE/aluminum foil/PE four-layer material. Many factories use adhesives at three interfaces in this composite structure, and in some cases three different process procedures or in-sequence layers are used to bond the four substrates. Complete the compounding process on the machine. Some factories compound paper onto metal foil through an extrusion process. At the same time, the composite material is also subjected to an extrusion coating process of the PE layer, or an adhesive lamination is performed between the original substrate and the PE layer.
In the pharmaceutical industry, a commonly used composite material is a combination of polyester/PE/aluminum foil/PE. This combined processing situation is similar to the above. The composite structure of all four substrates can be processed by an adhesive lamination process. Perhaps the difference is that polyester/PE composites can use new co-extruded lamination processes. The final process of this composite structure may still be extrusion coating or adhesive lamination, and the PE layer is compounded.
From the above two application examples, it can be seen that this composite structure film material is a distinctive processing mode. At the same time, the composite material contains a PE layer, so there is bound to be such a problem, how to choose the most appropriate processing operations and methods. In addition, the PE may be a single layer or may be a multi-layer; and the introduction of the PE material may be using a PE film in adhesive lamination, or using PE particles in an extrusion process.
Second, the characteristics of composite film processing
There are many processing methods for multi-layer composite films, which can be summarized as coating method, laminating method and co-extrusion method. In processing and preparing such a composite material, a plastic film may be used in combination with another plastic film or paint, or may be bonded to non-plastic materials such as paper, cloth, and metal foil (such as aluminum foil) by heating or bonding. together.
Commonly used in the coating method are a roll coating method and an extrusion coating method. The roller coating method uses a roller coater to apply a viscous coating quantitatively to the film surface. The lower roller picks up the coating from the coating tank and transfers it to the second roller or directly onto the moving film. The film at this time is sandwiched between the coating roller and the pressure roller. The thickness of the coating depends on the viscosity of the coating. And the gap between the two rolls through which the film passes. In order to accurately control the thickness of the coating, when a very thin coating is made, a three-roll or four-roll coater can be used. The role of the remaining two rolls is to accurately calculate the amount of coating and is therefore called a metering roll. The coating thickness control depends on factors such as the gap between the metering roll and the speed of the roll. Extrusion coating is a process of compounding a molten extrusion layer onto a substrate. The substrate may be paper, metal foil or plastic film as long as they all withstand the temperature of the extruded molten polymer. The molten polymer is actually a highly viscous liquid that can flow on the substrate. It is due to this flow that the polymer can completely and evenly cover the entire surface of the substrate. For a porous substrate such as paper, it can also enter into voids that are not smooth. Both of these physical phenomena are very important for improving adhesion.
The common legalities in layer legalization include the legalization of extrusion and the legalization of thin film layers. The process of extrusion lamination is the compounding of two substrates by melting the polymer. In this compounding process, the extrudate enters the gap between the two rollers and is joined together. Both substrates also pass through each roller into the gap. Therefore, the extrudate is in the middle of the two substrates. From this process, it can be seen that the extrusion layer is the same as the extrusion coating method. The polymer flow, the substrate uniformity, and the unique adhesion force are the control of the degree of recombination and performance of the final three-layer structure of the composite material. The main factor.
The legal processing of thin film layers is completely different from the above-mentioned several kinds of processing techniques. This method uses a laminating adhesive to combine one layer of thin film with another layer of thin film, paper or metal foil. The adhesive is applied to the surface of the laminated substrate. If it contains solvent or water, it needs to be dried on a stove, and then it is pressed in a heated roller gap to make it with another base. Combination of wood. If the final composite exceeds more than two layers, additional lamination processes are required. The adhesive force during film layer processing operations depends on the properties of the laminating adhesive. First, it must have sufficient cohesive strength and the necessary bond strength to ensure that each substrate is firmly bonded to one another. In addition, other parameters, such as coating weight, nip temperature, and operating level, also affect the final degree of bonding of the composite.
The co-extrusion process is a relatively new process that combines a plurality of polymer melts from a special die into a thin film-like melt stream composed of multiple layers of different polymer melts. Two, three or more layers of coextruded composite film material are obtained. Because each resin is melted in a separate extruder and then passed through a co-extrusion die and the melt is kept in uniform layers without mixing, the co-extrusion process and its special tooling are designed. The polymer rheology theory and techniques must be applied well. The co-extrusion method is often combined with the use of several extruders of different sizes to deliver the melt into the die at the same time. Therefore, the die structure is a key device, in addition, the extruder size and screw speed, melt pressure, melt temperature Extruder power, etc. will affect the thickness of each layer in the composite film.
Third, make full use of the coating function
For the coating method, laminating method and co-extrusion method mentioned above, it involves a very important factor in the operation of the extrusion process - the use of a coating to increase the composite adhesive force, and therefore it is also referred to as an adhesive layer. . Taking the composite film polyester/PE/aluminum foil/PE commonly used in pharmaceutical packaging as an example, this is actually a simplified representation. The structure of the composite film material should be polyester/coating/PE/ Aluminum foil / coating / PE. To make the polyester layer firmly adhered to the PE layer, it is necessary to add a layer of paint between the two, and similarly, there must also be a coating between the aluminum foil layer and the PE layer in order to be between the two layers of the substrate. Form a strong enough bond.
Applying the coating on a substrate requires some special equipment, such as a coater and a dryer, before the composite operation process. In many cases, laminating adhesives such as polyurethanes or polyesters can be used as coatings. According to general experience, it is known that when used as a binder, the amount thereof is about half that of ordinary paint. In addition, polymers such as polyethyleneimine or ethylene acrylic acid can also be used for special binder coatings.
Co-extrusion can eliminate the step of applying the adhesive compared to the processes such as the coating method and the lamination method, or can greatly reduce the amount of the binder so that the binder can be effectively prevented from drying out. Solvent contamination or serious fire ignition defects, therefore, the co-extrusion process has the potential to replace other composite processes. However, many layers of material are co-extruded together. If the viscosity between the two polymers is insufficient, the overall adhesive effect of the final film product is affected, that is, under sufficient external force, there is still between layers. Possible consequences of separation. In this case, it is necessary to increase the adhesive layer, that is, the paint. By tightly bonding the two material layers, the structural integrity of the multilayer material can be guaranteed. The adhesive layer must also be melted in a dedicated extruder and fed into the mold as a separately added layer. In the composite structure, in addition to the co-extruded three-layer structure film, that is, an adhesive layer is added between the two substrates as a bonding material, more than four co-extruded films are also common. For example, it is known that EVOH film material has excellent moisture resistance, and if it is used as a moisture-proof layer, it should be sandwiched between two layers of polymer film, plus two layers of adhesive coating, In fact, this composite structure consists of five layers. Although the resin melt from a single extruder can supply coextruded films in two or more layers, each new resin must have a dedicated extruder.
Fourth, processing method selection factors
How to choose a suitable composite plastic film is a relatively complicated issue. When selecting a composite film processing method, the following factors must be considered.
1. The first choice is the determination of the processing method, which depends on the existing equipment. If the packaging material factory currently only configures laminating film production lines, the composite film material can only be processed by laminating according to this equipment. In the same way, if only a factory with an extruder must use an extrusion coating or an extrusion layer to process the films of various composite structures. However, for those factories that have both laminators and extruders, it is necessary to seriously consider what kind of processing technology should be chosen. In this case, economic efficiency is always the first priority.
2, from the perspective of reducing costs and improving efficiency, the extrusion process is suitable for long-term operation. Sometimes, material processing plants need to complete small batch production tasks, even in a matter of hours. In this case, applying a film layer legal process is a suitable method of choice. Because, the extrusion process production line must have a long time of non-stop operation to get better economic benefits. To make all process parameters in the extrusion process in a relatively harmonized and balanced condition, the necessary time is always much longer than the legal process of the thin film adhesive layer. Therefore, whenever the extrusion process line reaches the equilibrium coordination state, it has to keep running continuously for as long as possible.
3. For a material processing factory that is trying to purchase new processing equipment, the designed production line can use thin-film layers and can also use the process method. At this time, the application of economic theory analysis will certainly play a large role. Although the investment costs for extrusion process equipment are more expensive than simple film lamination process equipment, large-scale film lamination equipment with multiple options or auxiliary equipment may be more expensive than most common extrusion lines.
However, the extrusion process may provide a wide range of opportunities for material processing plants to use diverse polymers. The film use department is limited by the type of film supplied by the film processing department. The factory equipped with an extruder can choose various types of PE materials. They can use co-extruders, or even mixes, thus gaining more material selection opportunities.
4. When a material processing plant selects thin-film composite processing technology, the number of processes and times to be completed is also a very important factor. The laminating process is likely to require more processing than the extrusion process when producing multilayer thin-film structural materials, which is especially true when compared to co-extrusion. Coextrusion processing is actually the combination of two or more molten polymers into a single extrudate. Co-extrusion has many advantages, including the possible use of high-grade polymers, the use of recycled polymers, and the reduction of film thickness. It is worth pointing out that a prominent advantage of the co-extrusion process is that it can reduce the number of processes necessary to process the final composite film material. In theory, a single extruder can produce many different layers of composite film material under the condition that the number of open molds is constant.
Taking a close look at the processing methods and characteristics of the various composite film materials discussed above, many factors must be taken into consideration to achieve a reasonable choice. This means that it is difficult to say that there is an optimal method for processing any specially packaged composite film material. Therefore, it is very necessary to comprehensively and carefully analyze various influencing factors when selecting the best processing method.
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