Application of the hottest composite packaging mat

Application of composite packaging materials and adhesives

with the improvement of people's living standards, the awareness of commodity packaging quality assurance and hygiene assurance is also increasing. In many cases, a single packaging material is difficult to meet many special needs. Therefore, composite materials, a solid product composed of two or more independent physical phases, including bonding materials (matrix) and granular, fiber or sheet materials, came into being

the biggest feature of the composite is that the material properties after composite are better than those of the single materials that make up the composite. Composite packaging materials, which follow the combination of strengths and weaknesses in the microstructure, give full play to the advantages of the constituent substances, expand the scope of use, improve economic benefits, and make it a more practical and complete packaging material, using their excellent comprehensive properties to meet the requirements of commodity packaging. In addition, the performance of composite packaging materials is also related to the adhesives used in compounding. The selection of adhesives must consider its adhesion, medium resistance, heat resistance, hygiene and so on. Therefore, a good composite packaging material cannot be separated from high-quality adhesives

composite packaging materials

1. Common composite packaging materials

common composite packaging materials are mainly various composite films. The so-called composite film refers to the flexible composite packaging material with comprehensive properties, which is based on paper, cellophane, plastic film, metal foil and other flexible packaging materials and obtained through various composite processing methods. 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. Common composite methods

composite packaging materials can use different structural materials and different composite processes according to different contents, and the correct selection of composite process is not only related to the composite quality of composite materials, but also affects the production efficiency of composite

◎ coating method

this method refers to a method of coating a fluid substance on the surface of the film to make the surface of the film form a close contact with the skin film. It can improve the thermal adhesion, moisture resistance, gas isolation, UV absorption and antistatic properties of the film. For example, this method is used to coat vinylidene chloride resin solution and dry it in order to improve the thermal adhesion and gas isolation of stretched polypropylene film (OPP)

◎ dry compounding method

dry compounding method is also called dry lamination. Its process is: apply solvent-based adhesive on the basic film (composite base material with high strength), evaporate the solvent in the adhesive on the adhesive layer material through a hot drying channel, and then compound with the second base material by heating and pressing. This kind of composite is not only suitable for the composite between plastic films (such as the composite between polypropylene and polyethylene, polyester and polyethylene, nylon and polyethylene, etc.), but also suitable for the composite between plastic films and aluminum foil and paper (such as biaxial tensile polypropylene, three-layer composite between aluminum foil and polyethylene, three-layer composite between cellophane, aluminum foil and polyethylene, etc.). The adhesive used in the dry compounding method is prepared with highly volatile organic solvents. Its softening point temperature should not affect the properties of the film, and it has good adhesion, and will not peel off when reheated. This method is the most commonly used method in the production of aluminum foil composite packaging materials. Its composite materials are widely used in the packaging of chocolate, cigarettes, drugs and cooked food

◎ wet compounding method

wet compounding method is also called wet lamination compounding. Its process is: the surface of the first layer of substrate (such as plastic film, aluminum foil, etc.) is coated with water-soluble or water emulsion adhesives. In a wet state, it is extruded and compounded with the second layer of substrate (such as paper, cellophane, etc.) through a compounding device, and then dried through a hot drying channel to remove the solvent, so that the two layers of substrate are compounded together. The adhesives used in this process are mostly viscose or emulsion with water as the solvent, mainly including polyvinyl alcohol, sodium silicate, starch, polyvinyl acetate, ethylene vinyl acetate copolymer, polypropylene, natural resin, etc. Because the adhesive used for wet compounding is water-soluble, at least one layer of its substrate should be paper, dry paper or cellophane, and it cannot be soaked in water and cause deformation

◎ extrusion compounding method

extrusion compounding is to extrude thermoplastic materials, such as PP, PE, etc., into a flat die after melting in the extruder, and form a sheet of hot-melt film as the adhesive. This hot-melt film is stretched to the specified thickness, and then compounded with other substrates in the extrusion device composed of metal cooling roll and rubber wrapping roll. This method is simple and does not need adhesives, but one of the processing materials must be plastic (resin), otherwise it is difficult to form

◎ hot melt compounding method

this method is to heat and melt the hot melt adhesive into a flowing state, then apply it, and immediately press and stick other films for compounding. Compared with dry compounding and wet compounding, it has the advantages of no need for hot drying, short compounding time, energy saving, low cost, and no solvent pollution. Suitable for laminating paper, plastic and aluminum foil. The hot melt method can adopt the following three processing methods to complete the compounding operation: the first is curtain flow compounding, which is to pump the hot melt from the storage tank to the "die head" (the seam width is less than 0.5mm), form a uniform curtain flow of hot melt through air processing, and then compound with the substrate, which can be carried out many times. The second is seam mold compounding. The hot melt is sprayed directly onto the back roll (the surface is covered with substrate) through the "die" of the seam mold, and the coating amount is controlled according to the different uses of the material variety. The third kind is roll compounding, and the roll coater used is roughly the same as that in the paper industry

adhesives

◎ selection of adhesives

when designing product packaging based on the quality of tensile machine, in addition to the correct selection of various substrates, the selection of adhesives is very important. Composite packaging is made of multi-layer film bonding, which is mostly used in food and drug packaging bags. Therefore, the adhesive is required to be soft, heat-resistant, low temperature resistant, non-toxic and tasteless, resistant to various media corrosion, and good bonding ability. In the domestic market, the composite packaging adhesive is mainly two-component polyurethane adhesive, which has superior physical and chemical properties. It is mainly reflected in: (1) polyurethane adhesive contains isocyanate group (- NCO) and carbamate group (- nhcoo -) with high polarity, which has excellent adhesion with materials containing active hydrogen. Polyurethane adhesive also produces hydrogen bond with the bonded materials, thus making the adhesion more firm. (2) The polyurethane formula can be adjusted, and the adhesive layer can be adjusted from flexibility to rigidity, so as to meet the needs of bonding different materials. (3) Polyurethane adhesive can be cured by heating and can also be cured at room temperature. New energy vehicles are also vigorously trying and promoting spray free materialization, and the process is simple. (4) There are no side effects when the polyurethane adhesive is cured, so it is not easy to cause defects in the adhesive film, except for Guo Daodi, a professor at the school of metallurgy and energy engineering, Kunming University of science and technology. (5) In addition to good bonding strength and medium impact strength, polyurethane adhesive has good oil resistance, chemical resistance, low temperature resistance, non-toxic, tasteless and softness

polyurethane two-component adhesive has two components: A and B. Component A is polyester or polyether containing polyhydroxy (- OH) as the main agent; Component B contains polyisocyanate group as curing agent. When used, a (main agent), B (curing agent) and diluent are mixed in a certain proportion. Due to the reaction between (- NCO) in polyisocyanate group and polyhydroxy (- OH) in polyester or polyether, a crosslinked cured polyurethane adhesive layer containing a certain amount of isocyanate group is generated. For example, the reaction between the main agent of polyester or polyether containing two hydroxyl groups and the curing agent containing three isocyanate groups is:

ho-r-oh + 2ocn-r-nco → ocn-r-nhco-r-cohn-r-nco

◎ bonding mechanism

the bonding mechanism of two-component polyurethane adhesive is that the main agent is composed of substances containing many active hydrogen, such as hydroxyl, amino, etc. The curing agent is composed of polyisocyanate compounds. When the isocyanate in the curing agent contacts with the active hydrogen in the main agent, it will automatically carry out the addition reaction to form the structure of carbamate, which will combine the main agent with the curing agent, and the molecular weight will be doubled, and even the crosslinked product with branched chain structure will be generated, which has the characteristics of high adhesion. Because polyurethane molecules contain a large number of polar groups, with large dipole moment and great affinity for bonded materials, it can bond a variety of materials at the same time. In addition, the isocyanate group (- NCO) in the curing agent is a very active reactive group. In addition to reacting with the active hydrogen in the main agent, it can also react with the active hydrogen in the surface material molecules of the bonded material to form a chemical structure, so that the adhesive molecules can bridge the friction between the adhesive molecules and the driven needle on the bonded device at the same time, producing a good adhesive force. After full crosslinking and curing, the adhesive has high cohesion, the adhesive film is strong, tough and soft, and the adhesive force is stronger

composite packaging materials are suitable for modern people's fast pace of life and are deeply loved by people because of their excellent characteristics, such as protection, operability, merchantability, hygiene, oil resistance, etc. In recent years, composite packaging materials have developed rapidly, and countries all over the world are competing to develop them. With the continuous emergence of new composite processes, composite substrates and better adhesives, composite packaging materials will write a more brilliant chapter for the world packaging industry

reprinted from: Shenzhen packaging