Application of composite packaging materials and adhesives

With the improvement of people's living standards, the awareness of quality assurance and health guarantee of commodity packaging is also growing. In many cases, it is difficult for a single packaging material to meet a number of special needs. Therefore, a solid product composed of two or more independent physical phases, including a binding material (matrix) and pellets, fibers, or sheet materials, that is, a composite material emerges.

The most important feature of composite materials is that the composite material properties are superior to those of the individual materials that make up the composite material. The composite packaging material is based on the combination of strengths and weaknesses in the microstructure, exerts the advantages of the constituent materials, expands the scope of use, and improves economic efficiency, making it a more practical and complete packaging material, making use of their excellent comprehensiveness. Performance to meet the requirements of commodity packaging. In addition, the performance of the composite packaging material is also related to the adhesive used in compounding, and the adhesive must be selected in consideration of its adhesiveness, medium resistance, heat resistance, hygienic properties, and the like. Therefore, an excellent composite packaging material can not be separated from high quality adhesives.

Composite packaging materials

1, commonly used composite packaging materials

Commonly used composite packaging materials are mainly composite films. The so-called "composite film" refers to a flexible composite packaging material with comprehensive properties obtained by various composite processing methods using flexible packaging materials such as paper, cellophane, plastic film, and metal foil as base materials. Specifically include: cellophane/plastic, paper/plastic, plastic/plastic, paper/metal foil, plastic/metal foil, cellophane/plastic/metal foil, etc. In addition, there are dry paper/plastic, dry paper/plastic/other materials, etc.

2, commonly used compound method

Composite packaging materials According to different contents, different structural materials and different composite technologies can be used, and the correct selection of composite technologies not only relates to the composite quality of the composite materials, but also affects the composite production efficiency.

â—Ž coating method

This method refers to the method of applying a fluid substance to the surface of the film to form a film that closely adheres to the surface of the film. The film can improve the thermal adhesion, moisture resistance, gas barrier properties, UV absorption and antistatic properties. For example, in order to improve the thermal adhesiveness and gas barrier property of the stretched polypropylene film (OPP), the vinylidene chloride resin solution is applied and dried, and this method is used.

â—Ž Dry compound method

The dry compounding method is also called dry laminating compounding. The process is: applying a solvent-based adhesive on a base film (composite base material with higher strength) and bonding the adhesive layer material through a hot tunnel The solvent in the agent is completely volatilized and then compounded with the second substrate by warming and pressurizing. This composite is not only suitable for the compounding between plastic films (such as polypropylene and polyethylene, polyester and polyethylene, nylon and polyethylene, etc.), but also for the combination of plastic film and aluminum foil and paper (such as two-way pull Stretch polypropylene, aluminum foil and polyethylene three-layer composite, glass paper, aluminum foil and polyethylene three-layer composite, etc.). The binder used in the dry compounding method is prepared with a relatively volatile organic solvent, and its softening point temperature should not affect the properties of the film, and it has good adhesive properties, and it will not be peeled off when reheated. This method is the most commonly used method for producing aluminum foil composite packaging materials. Its composite materials are widely used in the packaging of chocolates, cigarettes, medicines and cooking foods.

â—Ž wet compound method

The wet compounding method is also called wet laminating compounding. The process is: the surface of the first layer substrate (such as plastic film, aluminum foil, etc.) is coated with a water-soluble or water-emulsifying adhesive, and it is in the wet state and the second The layered substrates (such as paper, cellophane, etc.) are extruded and compounded together by a composite device, and then dried by hot air drying to remove the solvent and combine the two substrates together. The adhesive used in this process is mostly water-based solvent viscose liquid or emulsion, mainly polyvinyl alcohol, sodium silicate, starch, polyvinyl acetate, ethylene-vinyl acetate copolymer, polyacrylate , natural resins, etc. Due to the water-solubility of the adhesive used in wet blending, at least one layer of its substrate should be paper or dry paper or cellophane, and it cannot be deformed by water soaking.

â—ŽExtrusion compound method

Extrusion compounding is to melt thermoplastic materials, such as PP, PE, etc., in an extruder and squeeze it into a flat sheet of hot melt film as an adhesive. The hot melt film is stretched to a specified thickness. With the additional substrate, the compounding is completed in a squeezing device composed of a metal cooling roller and a rubber covered roller. This method is simple, no adhesive, but one of the processing materials must be plastic (resin), otherwise it is difficult to form.

â—ŽHot melt composite method

In this method, the hot melt adhesive is heated and dissolved in a flow state, coated, and pressure-bonded to other films for compounding. Compared with dry compounding and wet compounding, the advantage is that there is no need for drying in the hot tunnel, the compounding time is short, energy is saved, the cost is low, and there is no solvent hazard. Suitable for composites such as paper, plastic and aluminum foil. The hot-melt method can take the following three processing methods to complete the compounding work: The first is the curtain flow compounding, which is to transfer the hot-melt material from the storage trough to the “die” (slit width is less than 0.5mm) by air. Processing to form a uniform curtain of hot melt, and then composite with the substrate can be carried out multiple times. The second type is the slit mold compounding. The hot melt is passed through the “die” of the slot die and directly sprayed onto the back roller (the substrate is covered on the surface), and the coating amount can be grasped according to the different uses of the material type. The third type is roll-type compounding. The roll coater used is almost the same as the coating machine in the paper industry.

adhesive

â—ŽAdhesive selection

In the design of product packaging, in addition to the right choice of a variety of substrates, the choice of adhesive is of utmost importance. Composite packaging is a multi-layer film bonding, mostly for food, pharmaceutical packaging bags, so the adhesive requirements of soft, heat-resistant, low temperature, non-toxic, odorless, resistant to various media corrosion, good bonding ability. In the Chinese market, compound packaging adhesives are mainly based on two-component polyurethane adhesives, which have superior physical and chemical properties. Mainly reflected in: (1) Polyurethane adhesive contains highly polar isocyanate groups (-NCO) and carbamate groups (-NHCOO-), and has excellent adhesion with active hydrogen-containing materials, and polyurethane adhesives are also bonded with Hydrogen bonding occurs between the composite materials, thereby making the bonding more robust. (2)Adjustable polyurethane formula, adhesive layer from flexible to rigid can be arbitrarily adjusted to meet the needs of different materials bonding. (3) Polyurethane adhesive can be cured by heating or room temperature, and the process is simple. (4) No side effects occur when the polyurethane adhesive cures, and thus it is not easy to cause defects in the adhesive film. (5) In addition to having good adhesive strength and >medium strike strength, polyurethane adhesives are oil-resistant, chemical-resistant, low-temperature resistant, non-toxic, odorless, and soft.

Polyurethane two-component adhesive A, B two components used for reconciliation. The A component is a polyhydroxy (-OH)-containing polyester or polyether as a main agent; the B component is a polyisocyanate group as a curing agent, and A (main agent), B (curing agent) and diluent are used when used. Mix by a certain percentage. Due to the reaction between (-NCO) in the polyisocyanate group and polyhydroxy (-OH) in the polyester or polyether, a crosslinked and cured urethane adhesive layer containing a certain amount of isocyanate groups is formed. For example, the reaction between the main agent of a polyester or polyether containing two hydroxyl groups and a curing agent containing three isocyanate groups is:

HO-R-OH+2OCN-R-NCO→OCN-R-NHCO-R-COHN-R-NCO.

â—Ž Bonding mechanism

The bonding mechanism of the two-component polyurethane adhesive is that the main agent is composed of substances containing many active hydrogens such as hydroxyl, amino, and the like. Curing agents consist of polyisocyanate compounds. When the isocyanate in the curing agent is in contact with the active hydrogen in the main agent, an addition reaction is automatically performed to generate a urethane structure, so that the main agent and the curing agent are combined, the molecular weight is multiplied, and even a branched chain is generated. The cross-linked product of the three-dimensional structure of the structure has a characteristic of high adhesion. Because the polyurethane molecule contains a large number of polar groups, the dipole moment is large, and it has a great affinity for the adherent material, so it can play a binding role for many kinds of materials at the same time. In addition, the isocyanate group (-NCO) in the curing agent is a very reactive group that can react with the active hydrogen in the surface material molecules of the adhered material in addition to the active hydrogen in the main agent. Generation of chemical build-up enables the adhesive molecules to bridge the two materials being adhered at the same time, resulting in good adhesion. After the adhesive has been fully cross-linked and cured, it has a high cohesive force and the film is strong and soft, resulting in a stronger adhesive force.

The composite packaging material is suitable for the fast pace of life of modern people and has excellent characteristics such as protection, operability, merchandise, sanitation, oil resistance, etc. and it is deeply loved by people. In recent years, the development of composite packaging materials has been rapid. Countries around the world are competing to develop. With the continuous emergence of new composite technologies, composite substrates and better adhesives, composite packaging materials will surely be more brilliant for the world packaging industry. Chapters.

Reprinted from: Shenzhen Packaging Network