Fourth, plastic film composite process analysis
Plastic film composite process is an important means of manufacturing composite materials. Through the compounding process, two or more plastic films with different functions can be processed into a new composite film of the same body, which achieves the purpose of avoiding weaknesses and complementing heat.
At present, the plastic film compounding process mainly used is a compounding process, ie, a glue compounding process, which is dried after the glue is applied, so that the liquid glue layer becomes a solid film and then compounded. Compared to the extrusion-composite technology, the solid polymer materials are often referred to in the industry as "dry compound processes" because they become "wet-process compound methods" in which they become viscous and fluid-like even after being subjected to high temperature and high pressure. . In fact, as far as the research of the composite arts is concerned, that is, the de-adhesive compounding process should also be called the “Deliminating and Wetting Compound Processâ€. Only in this way can it be used that the adhesive used is liquid, the dilute dispersant added is liquid, and the glue layer applied to the base film is the liquid phase, which reflects its process flow in the “wet†state. The real dry compounding process should be solid materials for all kinds of raw materials, including adhesives. It is a hot melt adhesive precoating film dry compounding process that has been developed and applied in recent years. In addition to compounding the work to make ecological changes, in addition to the completion of the compound, there should not be any "wet" concept material appearing in other work processes.
(I) Flow chart of glued wet compound process
(B) Base film preparation
First of all, according to the customer packaged goods are fresh, frozen or to be cooked at high temperature, as well as the mode of transport, the length of the shelf life, the cost requirements, etc., to design a combination that can fully meet customer requirements, easy processing, and low cost Structures come. For example, some use OPP/PE, some use OPA/CPP, some use OPP/AL/PE, some use PETP/AL/CPP, and more require PETP/AL/OPA/ CPP or using the newly developed VMCPP material in the world. VMCPP contains a thin layer of aluminum plating. Compared with BOPP and CPP, VMCPP has 10 times lower air permeability.
Second, once it has been determined which substrate to use, the width of the substrate or the layout direction of the layout should be selected according to the size of the customer's request for the bag, in order to maximize the use of existing equipment performance, efficiency and reduce the substrate Edge material loss, reduce costs, increase efficiency.
Third, the base film to be composited must have a clean, dry, flat, dust-free, and oil-free surface. For non-polar, dense, smooth polyolefin materials, it must be treated in advance to make it. The surface state changes, the surface tension increases to 40mN/m, and at least 38mN/m, so that printing and gluing can reach a certain degree of fastness.
Non-polar materials such as polyethylene and polypropylene have a dense and smooth surface, a very low surface energy, and are very inert. If surface treatment is not performed, the adhesive hardly infiltrates it, like PTFE (plastic king). , is a hard-to-stick material. In order to change this situation, it can be processed in various ways, of which the most effective one is corona treatment.
After corona treatment, the surface tension of the film can be increased from about 3.0 mN/m to 38 mN/m or more, and the height can be as high as 40 mN/m, which is a great benefit for printing and bonding.
Why does corona treatment work on the surface of the film?
(1) High-frequency high-voltage power generator In the high-voltage electric field, the electron current will make a strong impact on the surface of the plastic film, and it will increase as the voltage and current increase, making the surface fluffy, becoming rough and increasing the surface area. When the adhesive is in contact with its surface, it can produce a good wetting effect, and the adhesive can form an extremely complicated infiltration combination with the grooved groove where the plastic film is pulled, and the packing is disordered and the adhesiveness is increased. This is a physical effect.
(2) Under high-voltage electric fields, the oxygen in the air turns into ozone, which in turn decomposes into oxygen and new ecological oxygen atoms:
3O2→2O3
O3→O2+[O]
The new ecological oxygen atom is a very strong oxidant, which oxidizes the a-carbon in the polyethylene or polypropylene molecules to make them carbonyl or hydroxyl:
With this structure, the polarity of the molecule increases and the surface tension increases, resulting in a great affinity and attractiveness for the adhesive with a very large polarity, and increasing the adhesive fastness. In addition, due to the generation of carbonyl groups, new a-carbons are produced in the molecular chain, and new active hydrogen appears to be able to react chemically with the active substrate isocyanate (-NCO) in the polyurethane adhesive to make the material to be adhered. Chemical bonds are formed between the adhesive and it increases its adhesiveness. From infrared spectroscopy, it can be found that the surface of the polyolefin after corona treatment has carbonyl or hydroxyl absorption peaks on the line, which proves that the above-mentioned chemical action exists.
(III) Performance of Composite Adhesives
That is, the wet glue compounding process can be used to composite composite materials of paper/plastic, plastic/plastic, plastic/paper/plastic, and plastic/aluminum/plastic material materials with different materials, mainly by using adhesives. Composite materials also have the bonding properties. At present, it is mainly composed of one-component rubber adhesive and two-component polyurethane adhesive.
One-component rubber-based adhesives have the same adhesive properties to these various materials that are involved in compounding. At present, it is mainly composed of one-component rubber adhesive and two-component polyurethane adhesive.
One-component rubber adhesives are still based on SBS (styrene-butadiene-styrene block) elastomers, together with tackifiers such as terpene resins, polymerized rosins, and antioxidants and antioxidants. , It is synthesized and dissolved by organic solvent and has adhesiveness to various materials. Can be widely used in BOPP / PE, PET / PE, BOPP / PET, BOPP / CPP, BOPP / paper, plastic / metal sheet and other structures. The surface condition of the adherend is not high, and many non-polar materials and small surface tension can be firmly bonded. At the same time, because it is a single component, it will not be cross-linked and cured, and it is not necessary to add a solid agent, so it is simple to use and easy to clean. With a good adhesive storage does not deteriorate, as long as the airtight sealed, stored for a long time will not degenerate. At the same time, the price is low, the production cost is relatively low, and it is easily accepted by the manufacturers of color printing plastic flexible packaging processing and production.
However, one-component adhesives are made of elastomer materials as the main material, and they also need tackifiers and other additives to change the fluidity and initial tack ability of the elastomer materials, and these properties change and the solid materials are synthesized into liquid adhesives. , all need to rely on the dissolution of organic solvents can be achieved. Most of the organic solvents used are aromatic benzenes or esters and alcohols. Due to the existence of these substances, not only the adhesive smell, some of the toxicity, but also make the adhesive can not be completely dry and solid, like dry and non-dry, in essence, is a kind of sub-sensitive glue. Therefore, the adhesive force is not high and the quality problems such as blistering are liable to occur.
For high temperature cooking plastic flexible packaging bags, two-component polyurethane adhesives are required. This adhesive consists of two components: the main agent and the curing agent. The main agent and curing agent are two components. The main agent and curing agent are separately packaged and stored. When used, they are mixed according to a certain proportion, and then diluted with a solvent to a certain concentration and then used for gumming.
The main component of the two-component polyurethane adhesive is composed of many active hydrogens, such as hydroxyl and amino groups, and the curing agent is composed of many isocyanate compounds. When the isocyanate in the curing agent is in contact with the active hydrogen in the main agent splitter, an addition reaction is automatically performed to generate a hydrogen carbamate structure, so that the main agent and the curing agent are combined with each other, and the molecular weight is multiplied. It even produces cross-linked products with a cube-like structure with a branched structure, which is characterized by high and low temperature resistance, resistance to media erosion, and high adhesion.
Polyurethane molecules contain a large number of polar genes, which are extremely dipolar and have a great affinity for the adherent materials, so they can simultaneously bind a variety of materials.
Polyurethane molecules contain a large number of polar genes, which are extremely dipolar and have a great affinity for the adherent materials, so they can simultaneously bind a variety of materials.
After the polyacrylic acid adhesive has been fully cross-linked and cured, it has high cohesion, the film is tough and soft, and has good heat resistance and resistance to media erosion. The composite material made of it can package various properties. Foods such as acid, spicy, salty, sweet, and oily can be used.
It is precisely because of so many excellent properties that polyurethane has been used in the world for 60 years. The time for composites used in food packaging is also nearly 50 years. It was only in 1984 that polyurethanes began to produce polyurethanes for food packaging. adhesive.
Polyurethane adhesives used in food composite packaging materials include aromatics and aliphatics.
(d) The synthesis of glue
At present, there are two kinds of film production processes in China. One is a wet compounding process, and the other is a dry compounding process of a hot melt adhesive precoating film.
That is, the glue used in the glue-coating wet compounding process is a rubber-based adhesive, a rubber-resin solvent-based, an acrylic-based solvent-based, a synthetic resin emulsion polymerization adhesive, and a precoating film dry-type compounding process. Although all are synthetic adhesives that are applied in a melted, solution, or colloidal dispersion state and cured, due to the different composition of the components and the different production processes, various processes are used for the adhesives when coating the films. The production conditions are also different. The rheological properties of synthetic adhesives with this process. And their changes with temperature, pressure, the effect is also necessarily different.
Synthetic adhesives are a new type of fine chemical products. It is a new discipline formed by the mutual penetration and synthesis of polymer chemistry, surface chemistry, and material mechanics.
Synthetic adhesives are made of synthetic polymers or prepolymers and monomers. With the development of science and technology, molecular weight determination, molecular weight publication, microstructure analysis and other methods can be used to perform molecular design according to the requirements. Different processes are adopted to control the mixing process to change its structure, without altering the chemical properties of the polymer and producing thermosetting properties. , Thermoplastic rubber type, hot-melt type synthetic adhesives with different uses, different properties, and different effects (hereinafter referred to as glue).
The glue used for the film is an encapsulant (solvent) type glue. Most are rubber-resin types. The main components are rubber-modified SBS and tackifying resins such as terpene resins, rosin and antioxidant antioxidants. If these different kinds of substances are to be blended and geled, they must be softened and dissolved by the olefins, and then reacted under a high temperature for a long time to synthesize the liquid glue and apply them to the film. The process includes the sequence of feeding and the process parameters such as the temperature and weight of the material during the feeding.
The coating film adhesive is a composite composed of two or more resins and containing a filler. The synthesis of the gum can only be guaranteed if the filler is optimally distributed between the phases. The best distribution of the orientation distribution establishes a degree of microscopic heterogeneity in order to obtain the maximum reinforcing effect. It can not only guarantee the most favorable conditions for stress relaxation, but also effectively hinder the growth of destructive cracks, resulting in an increase in strength properties and fatigue resistance.
The mechanical properties of this plastic depend to a large extent on the shape and size of the supramolecular structure produced during the production of the gel.
In the radical body, solution and suspension polymerization of vinyl monomers, when the initiator concentration is constant, in order to increase the reaction speed, the temperature must be increased. The reaction of solvent-based gel synthesis is the temperature generated by steam heat or electric heat. The increase in the reaction temperature will accelerate the decomposition of the initiator and increase the total free radical concentration. Since the chain termination rate is proportional to the square of the free radical concentration, the chain termination rate increases significantly as the total free radical concentration increases, which inevitably leads to a decrease in the average molecular weight of the polymer and a decrease in performance; in turn, the polymer must be increased. With regard to the average molecular weight, it is necessary to lower the reaction temperature, which in turn reduces the reaction rate. That is to say,
Plastic film composite process is an important means of manufacturing composite materials. Through the compounding process, two or more plastic films with different functions can be processed into a new composite film of the same body, which achieves the purpose of avoiding weaknesses and complementing heat.
At present, the plastic film compounding process mainly used is a compounding process, ie, a glue compounding process, which is dried after the glue is applied, so that the liquid glue layer becomes a solid film and then compounded. Compared to the extrusion-composite technology, the solid polymer materials are often referred to in the industry as "dry compound processes" because they become "wet-process compound methods" in which they become viscous and fluid-like even after being subjected to high temperature and high pressure. . In fact, as far as the research of the composite arts is concerned, that is, the de-adhesive compounding process should also be called the “Deliminating and Wetting Compound Processâ€. Only in this way can it be used that the adhesive used is liquid, the dilute dispersant added is liquid, and the glue layer applied to the base film is the liquid phase, which reflects its process flow in the “wet†state. The real dry compounding process should be solid materials for all kinds of raw materials, including adhesives. It is a hot melt adhesive precoating film dry compounding process that has been developed and applied in recent years. In addition to compounding the work to make ecological changes, in addition to the completion of the compound, there should not be any "wet" concept material appearing in other work processes.
(I) Flow chart of glued wet compound process
(B) Base film preparation
First of all, according to the customer packaged goods are fresh, frozen or to be cooked at high temperature, as well as the mode of transport, the length of the shelf life, the cost requirements, etc., to design a combination that can fully meet customer requirements, easy processing, and low cost Structures come. For example, some use OPP/PE, some use OPA/CPP, some use OPP/AL/PE, some use PETP/AL/CPP, and more require PETP/AL/OPA/ CPP or using the newly developed VMCPP material in the world. VMCPP contains a thin layer of aluminum plating. Compared with BOPP and CPP, VMCPP has 10 times lower air permeability.
Second, once it has been determined which substrate to use, the width of the substrate or the layout direction of the layout should be selected according to the size of the customer's request for the bag, in order to maximize the use of existing equipment performance, efficiency and reduce the substrate Edge material loss, reduce costs, increase efficiency.
Third, the base film to be composited must have a clean, dry, flat, dust-free, and oil-free surface. For non-polar, dense, smooth polyolefin materials, it must be treated in advance to make it. The surface state changes, the surface tension increases to 40mN/m, and at least 38mN/m, so that printing and gluing can reach a certain degree of fastness.
Non-polar materials such as polyethylene and polypropylene have a dense and smooth surface, a very low surface energy, and are very inert. If surface treatment is not performed, the adhesive hardly infiltrates it, like PTFE (plastic king). , is a hard-to-stick material. In order to change this situation, it can be processed in various ways, of which the most effective one is corona treatment.
After corona treatment, the surface tension of the film can be increased from about 3.0 mN/m to 38 mN/m or more, and the height can be as high as 40 mN/m, which is a great benefit for printing and bonding.
Why does corona treatment work on the surface of the film?
(1) High-frequency high-voltage power generator In the high-voltage electric field, the electron current will make a strong impact on the surface of the plastic film, and it will increase as the voltage and current increase, making the surface fluffy, becoming rough and increasing the surface area. When the adhesive is in contact with its surface, it can produce a good wetting effect, and the adhesive can form an extremely complicated infiltration combination with the grooved groove where the plastic film is pulled, and the packing is disordered and the adhesiveness is increased. This is a physical effect.
(2) Under high-voltage electric fields, the oxygen in the air turns into ozone, which in turn decomposes into oxygen and new ecological oxygen atoms:
3O2→2O3
O3→O2+[O]
The new ecological oxygen atom is a very strong oxidant, which oxidizes the a-carbon in the polyethylene or polypropylene molecules to make them carbonyl or hydroxyl:
With this structure, the polarity of the molecule increases and the surface tension increases, resulting in a great affinity and attractiveness for the adhesive with a very large polarity, and increasing the adhesive fastness. In addition, due to the generation of carbonyl groups, new a-carbons are produced in the molecular chain, and new active hydrogen appears to be able to react chemically with the active substrate isocyanate (-NCO) in the polyurethane adhesive to make the material to be adhered. Chemical bonds are formed between the adhesive and it increases its adhesiveness. From infrared spectroscopy, it can be found that the surface of the polyolefin after corona treatment has carbonyl or hydroxyl absorption peaks on the line, which proves that the above-mentioned chemical action exists. (III) Performance of Composite Adhesives
That is, the wet glue compounding process can be used to composite composite materials of paper/plastic, plastic/plastic, plastic/paper/plastic, and plastic/aluminum/plastic material materials with different materials, mainly by using adhesives. Composite materials also have the bonding properties. At present, it is mainly composed of one-component rubber adhesive and two-component polyurethane adhesive.
One-component rubber-based adhesives have the same adhesive properties to these various materials that are involved in compounding. At present, it is mainly composed of one-component rubber adhesive and two-component polyurethane adhesive.
One-component rubber adhesives are still based on SBS (styrene-butadiene-styrene block) elastomers, together with tackifiers such as terpene resins, polymerized rosins, and antioxidants and antioxidants. , It is synthesized and dissolved by organic solvent and has adhesiveness to various materials. Can be widely used in BOPP / PE, PET / PE, BOPP / PET, BOPP / CPP, BOPP / paper, plastic / metal sheet and other structures. The surface condition of the adherend is not high, and many non-polar materials and small surface tension can be firmly bonded. At the same time, because it is a single component, it will not be cross-linked and cured, and it is not necessary to add a solid agent, so it is simple to use and easy to clean. With a good adhesive storage does not deteriorate, as long as the airtight sealed, stored for a long time will not degenerate. At the same time, the price is low, the production cost is relatively low, and it is easily accepted by the manufacturers of color printing plastic flexible packaging processing and production.
However, one-component adhesives are made of elastomer materials as the main material, and they also need tackifiers and other additives to change the fluidity and initial tack ability of the elastomer materials, and these properties change and the solid materials are synthesized into liquid adhesives. , all need to rely on the dissolution of organic solvents can be achieved. Most of the organic solvents used are aromatic benzenes or esters and alcohols. Due to the existence of these substances, not only the adhesive smell, some of the toxicity, but also make the adhesive can not be completely dry and solid, like dry and non-dry, in essence, is a kind of sub-sensitive glue. Therefore, the adhesive force is not high and the quality problems such as blistering are liable to occur.
For high temperature cooking plastic flexible packaging bags, two-component polyurethane adhesives are required. This adhesive consists of two components: the main agent and the curing agent. The main agent and curing agent are two components. The main agent and curing agent are separately packaged and stored. When used, they are mixed according to a certain proportion, and then diluted with a solvent to a certain concentration and then used for gumming.
The main component of the two-component polyurethane adhesive is composed of many active hydrogens, such as hydroxyl and amino groups, and the curing agent is composed of many isocyanate compounds. When the isocyanate in the curing agent is in contact with the active hydrogen in the main agent splitter, an addition reaction is automatically performed to generate a hydrogen carbamate structure, so that the main agent and the curing agent are combined with each other, and the molecular weight is multiplied. It even produces cross-linked products with a cube-like structure with a branched structure, which is characterized by high and low temperature resistance, resistance to media erosion, and high adhesion.
Polyurethane molecules contain a large number of polar genes, which are extremely dipolar and have a great affinity for the adherent materials, so they can simultaneously bind a variety of materials.
Polyurethane molecules contain a large number of polar genes, which are extremely dipolar and have a great affinity for the adherent materials, so they can simultaneously bind a variety of materials.
After the polyacrylic acid adhesive has been fully cross-linked and cured, it has high cohesion, the film is tough and soft, and has good heat resistance and resistance to media erosion. The composite material made of it can package various properties. Foods such as acid, spicy, salty, sweet, and oily can be used.
It is precisely because of so many excellent properties that polyurethane has been used in the world for 60 years. The time for composites used in food packaging is also nearly 50 years. It was only in 1984 that polyurethanes began to produce polyurethanes for food packaging. adhesive.
Polyurethane adhesives used in food composite packaging materials include aromatics and aliphatics.
(d) The synthesis of glue
At present, there are two kinds of film production processes in China. One is a wet compounding process, and the other is a dry compounding process of a hot melt adhesive precoating film.
That is, the glue used in the glue-coating wet compounding process is a rubber-based adhesive, a rubber-resin solvent-based, an acrylic-based solvent-based, a synthetic resin emulsion polymerization adhesive, and a precoating film dry-type compounding process. Although all are synthetic adhesives that are applied in a melted, solution, or colloidal dispersion state and cured, due to the different composition of the components and the different production processes, various processes are used for the adhesives when coating the films. The production conditions are also different. The rheological properties of synthetic adhesives with this process. And their changes with temperature, pressure, the effect is also necessarily different.
Synthetic adhesives are a new type of fine chemical products. It is a new discipline formed by the mutual penetration and synthesis of polymer chemistry, surface chemistry, and material mechanics.
Synthetic adhesives are made of synthetic polymers or prepolymers and monomers. With the development of science and technology, molecular weight determination, molecular weight publication, microstructure analysis and other methods can be used to perform molecular design according to the requirements. Different processes are adopted to control the mixing process to change its structure, without altering the chemical properties of the polymer and producing thermosetting properties. , Thermoplastic rubber type, hot-melt type synthetic adhesives with different uses, different properties, and different effects (hereinafter referred to as glue).
The glue used for the film is an encapsulant (solvent) type glue. Most are rubber-resin types. The main components are rubber-modified SBS and tackifying resins such as terpene resins, rosin and antioxidant antioxidants. If these different kinds of substances are to be blended and geled, they must be softened and dissolved by the olefins, and then reacted under a high temperature for a long time to synthesize the liquid glue and apply them to the film. The process includes the sequence of feeding and the process parameters such as the temperature and weight of the material during the feeding.
The coating film adhesive is a composite composed of two or more resins and containing a filler. The synthesis of the gum can only be guaranteed if the filler is optimally distributed between the phases. The best distribution of the orientation distribution establishes a degree of microscopic heterogeneity in order to obtain the maximum reinforcing effect. It can not only guarantee the most favorable conditions for stress relaxation, but also effectively hinder the growth of destructive cracks, resulting in an increase in strength properties and fatigue resistance.
The mechanical properties of this plastic depend to a large extent on the shape and size of the supramolecular structure produced during the production of the gel.
In the radical body, solution and suspension polymerization of vinyl monomers, when the initiator concentration is constant, in order to increase the reaction speed, the temperature must be increased. The reaction of solvent-based gel synthesis is the temperature generated by steam heat or electric heat. The increase in the reaction temperature will accelerate the decomposition of the initiator and increase the total free radical concentration. Since the chain termination rate is proportional to the square of the free radical concentration, the chain termination rate increases significantly as the total free radical concentration increases, which inevitably leads to a decrease in the average molecular weight of the polymer and a decrease in performance; in turn, the polymer must be increased. With regard to the average molecular weight, it is necessary to lower the reaction temperature, which in turn reduces the reaction rate. That is to say,
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