Current situation and development of the most popu

2022-08-22
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Current situation and development of color printing plastic flexible packaging (II)

IV. analysis of plastic film composite process flow

plastic film composite process is an important means of manufacturing composite materials. Through the composite process, two or more kinds of plastic films with different functions can be processed into a new type of composite film with the same body, so as to achieve the purpose of developing strengths and avoiding weaknesses and complementing advantages and heat

at present, the main plastic film compounding process is the gluing compounding process, which is a process of drying after gluing to turn the liquid adhesive layer into a solid adhesive film and then compounding. Compared with the "wet compounding method" in which the solid polymer materials of the extrusion compounding process become viscous flow after being subjected to high temperature and high pressure, and are evenly sprayed on the printed film, it is often called "dry compounding process" by insiders. In fact, as far as the research of the whole composite technology is concerned, that is, the degumming composite process should also be called "that is, the degumming wet composite process". 2. It is only right when checking the mechanical properties. Only in this way can the adhesive used be liquid, the diluent and dispersant added be liquid, and the adhesive layer coated on the base film be the liquid phase, which can reflect its process flow in the "wet" state. The real dry composite process should be that all raw materials used, including adhesives, are solid, which is the dry composite process of hot melt adhesive pre coating developed, applied and popularized in recent years. In addition to the ecological change of the work of compounding and the completion of compounding, there should be no substances with the concept of "wet" in the process of other work

(I) that is, the process flow chart of gluing wet compounding

(II) preparation of base film

first, a composite structure that can fully meet the customer's requirements, is easy to process and has low cost should be designed according to the customer's packaging of goods that are fresh-keeping, frozen or need to be cooked at high temperature, as well as the mode of transportation, the length of shelf life, cost requirements, etc. For example, some should use OPP/PE, some should use OPA/CPP, some should use OPP/Al/PE, some should use PETP/Al/CPP, and some should use PETP/Al/CPP. It is more demanding to introduce a market-oriented ecological and environmental protection promotion mechanism, use PETP/Al/OPA/CPP or use the newly developed VMCPP materials in the world at present. VMCPP contains a thin aluminized layer, and its air permeability is 10 times lower than that of BOPP and CPP

secondly, once the base material is determined, the width of the base material or the arrangement direction of the layout should be selected according to the size of the bag required by the customer, in order to maximize the function and efficiency of the existing equipment, reduce the waste of the base material, reduce costs and improve benefits

third, the surface of the base film to be compounded must be clean, dry, flat, dust-free and oil-free. For non-polar polyolefin materials with dense and smooth surface, it must be treated in advance to change their surface state, and the surface tension should be increased to 40mn/m, at least more than 38mn/m. In this way, printing and adhesive can achieve a certain fastness

non polar materials such as polyethylene and polypropylene have a dense and smooth surface and low surface energy. They are very inert. If surface treatment is not carried out, it is difficult for adhesives to infiltrate them. Like polytetrafluoroethylene (plastic king), they are difficult to stick. In order to change this situation, various methods can be used to deal with it, among which corona treatment is the most effective and feasible

after corona treatment, the surface tension of the film can be increased from about 3.0mn/m to more than 38mn/m, up to 40mn/m, which is very good for printing and bonding

why can corona treatment affect the surface of thin films

(1) under the high-voltage electric field of the high-frequency high-voltage power generator, the electron flow will have a strong impact on the surface of the plastic film, and will increase with the increase of voltage and current, making the surface hairy, 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 will form a very complex penetration combination with the roughened grooves of the plastic film, which will be intertwined and increase the bonding fastness. This is a physical action

(2) under high-voltage electric field, oxygen in the air turns into ozone, and ozone will decompose into oxygen and new ecological oxygen atoms:

3O2 → 2O3

O3 → o2+[o]

while new ecological oxygen atoms are very strong oxidants, which oxidize a-carbon in polyethylene or polypropylene molecules and turn it into carbonyl or hydroxyl:

with this structure, molecular polarity increases and surface tension increases, It has great affinity and attraction for adhesives with great polarity, and increases the bonding fastness. In addition, due to the production of carbonyl, new a-carbon is produced in the molecular chain, and new active hydrogen can react with isocyanate (- NCO), the active substrate in polyurethane adhesive, so that a chemical bond is formed between the bonded material and the adhesive, and its bonding fastness is increased. From the infrared spectrum detection, it can be found that there are carbonyl or hydroxyl absorption peaks on the spectrum line on the surface of polyolefin after corona treatment, which proves that the above chemical action exists

(III) properties of adhesives for composites

that is, the wet bonding process can compound the sheet materials of different materials such as paper/plastic, plastic/plastic, plastic/paper/plastic, plastic/aluminum/plastic into one composite material, which mainly uses adhesives to have the bonding properties of these participating materials and various composite materials at the same time. At present, there are mainly two kinds of single component rubber adhesive and two-component polyurethane adhesive

one component rubber adhesive has the same bonding performance to these various materials involved in the composite. At present, there are mainly two kinds of single component rubber adhesives and two-component polyurethane adhesives

one component rubber adhesive is still prepared by dissolving and synthesizing SBS (styrene butadiene styrene block material) elastomer, terpene resin, polymerized rosin and other tackifiers, antioxidants, antioxidants and other additives with organic solvents. It has adhesion to a variety of materials. It can be widely used in BOPP/PE, PET/PE, BOPP/PET, BOPP/CPP, BOPP/paper, plastic/metal sheet and other structures. The requirements for the surface state of the adherend are not high, and many non-polar materials can stick firmly with small surface tension. At the same time, because it is a single component, it will not be crosslinked and cured, and there is no need to add solid agent, so it is simple to use and convenient to clean. The prepared adhesive is not easy to deteriorate in storage. As long as it is sealed and airtight, it will not deteriorate in storage for a long time. At the same time, the price is low, the production cost is small, and it is easy to be accepted by manufacturers that realize the completion and delivery of the plant, install the equipment, and process and produce color printing plastic flexible packaging within the next year

however, since one component adhesives are made of elastomer materials as the main material, they also need additives such as tackifiers to change the fluidity and initial adhesion of elastomer materials. These changes in properties and the synthesis of solid materials into liquid adhesives can only be achieved with the help of the dissolution of organic solvents. The organic solvents used are mostly aromatic benzene or ester, alcohol substances. Due to the existence of these substances, the adhesive not only has peculiar smell, but also has toxicity. At the same time, the adhesive cannot be completely dried and cured, which seems to be dry rather than dry. In essence, it is a kind of sub sensitive adhesive. Therefore, the adhesive force is not high, and quality problems such as blistering are easy to occur

two component polyurethane adhesive is required to make plastic flexible packaging bags that can withstand high temperature cooking. This adhesive is composed of two components: main agent and curing agent. The main agent and curing agent are composed of two components. The main agent and curing agent are packed and stored separately. When used, they are mixed in a certain proportion, and then diluted to a certain concentration with solvent before gluing

the main agent of two-component polyurethane adhesive is composed of many active hydrogen, such as hydroxyl, amino and other substances, while the curing agent is composed of many isocyanate compounds. When the isocyanate in the curing agent contacts with the active hydrogen in the main agent schizon, it will automatically carry out the addition reaction to generate the structure of hydrogen formate, so that the main agent and the curing agent are combined with each other, and the molecular weight is doubled, and even the cross-linking product with a square structure with a branched chain structure is generated, which has the characteristics of high and low temperature resistance, medium erosion resistance, and high adhesion

polyurethane molecules contain a large number of polar genes, with huge dipoles and great affinity for bonded materials, so they can bond a variety of materials at the same time

polyurethane molecules contain a large number of polar genes, with huge dipoles and great affinity for bonded materials, so they can bond a variety of materials at the same time

after full crosslinking and curing, polyurethane adhesive has high cohesion, tough and soft film, good heat resistance and medium erosion resistance. The composite material made of it can package foods with various properties, such as those containing acid, spicy, salty, sweet and oily

because of so many excellent properties, polyurethane has been used in the world for 60 years, and it has been used in composite materials for food packaging for nearly 50 years. China began to produce polyurethane adhesives for food composite packaging in 1984

polyurethane adhesives used in food composite packaging materials include aromatic and aliphatic

(IV) that is, the synthesis of glue

at present, there are two kinds of film covering production processes in China. One is the wet compounding process of gluing, and the other is the dry compounding process of hot melt adhesive pre coating

that is, the adhesives used in the wet bonding process are rubber solvent type, rubber resin solvent type, acrylic ester solvent type, synthetic resin lotion polymerization adhesive, and copolymer resin melt type adhesive used in the pre coating dry bonding process. Although they are all synthetic adhesives that are coated and cured in the state of melt, solution or colloidal dispersion, due to different component compositions, the production process is different, During the film covering production, the use methods and production conditions of adhesives in various processes are also different. With this processing process, the rheological properties of synthetic adhesives in Chinese patients with lumbar spondylosis have exceeded 200million. And their changes with temperature and pressure will inevitably have different effects

synthetic adhesive is a new kind of fine chemical products. It is a new discipline formed by the mutual penetration and integration of polymer chemistry, surface chemistry, material mechanics and other disciplines

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 carry out molecular design according to the action requirements, and different processes can be used to change its structure by controlling the mixing process without changing the chemical properties of the polymer, so as to produce thermosetting, thermoplastic rubber type, hot-melt type and other synthetic adhesives with different uses, different properties and different effects (hereinafter referred to as adhesives)

the adhesive used for film covering is alkene (solvent) adhesive. Most of them are rubber resin type. The main components are SBS and tackifying resins modified and purified by rubber, such as terpene resin, rosin and antioxidant antioxidant. If these different kinds of substances want to be mixed into glue, they need to be softened and dissolved by olefins first, and then reacted for a long time under high temperature conditions, so as to synthesize liquid glue and apply it to film covering. The process includes the sequence of feeding and mastering the process parameters such as the heat and weight during feeding

film covering glue is made of two or two

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