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    Home > Coatings News > Paints and Coatings Market > Adhesive introduction and bonding process.

    Adhesive introduction and bonding process.

    • Last Update: 2020-10-04
    • Source: Internet
    • Author: User
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    Glue is a method of firmly connecting the same or different materials by a substance with adhesion. Substances with adhesive capacity are called adhesives or adhesives, and the objects that are glued are called adhesives, and the components made up of adhesives are called glue joints.
    its main advantages are simple operation, high productivity, flexible, fast and simple process, reliable, solid, beautiful product structure and processing process is simple, material saving, labor-saving, low cost, small deformation

    . Easy to achieve old-fashioned waste connection technology can be effectively applied to different kinds of metals or non-metallic connections.
    the composition and classification of adhesives
    1, the composition of adhesives
    are now used adhesives are using a variety of components of synthetic resin adhesives, a single component of adhesives can not meet the requirements in use. Synthetic adhesives are composed of main agents and additives, also known as main agents, substitums or adhesives, additives have curing agents, thinners, plasticizers, fillers, coupling agents, triggers, thickeners, anti-age agents, inhibitors, stabilizers, compounds, emulsifiers, etc., according to requirements and uses can also include flame retardants, foaming agents, defoamers, colorants and mold inhibitors.
    1.1 main agent
    main agent is the main component of adhesive, leading the adhesive bonding performance, but also an important mark to distinguish the adhesive category. The main agent is generally composed of one or two or even three kinds of high-polymers, which require good adhesion and wetting. The usual adhesives used are:
    1) natural polymer compounds
    e.g. protein, leather gum, fish glue, pine, peach gum, bone glue and so on.
    2) Synthesis of polymer compounds
    (1) thermosterone resins, such as epoxy resins, phenolic resins, polyurethane resins, formaldehyde resins, silicone resins, etc.
    (2) thermoplastic resins, such as polyethylene acetate, polyethylene alcohol and acetaldehyde resins, polystyrene and so on.
    (3) elastic materials, such as butyl rubber, neoprene, polysulfur rubber and so on.
    (4) a variety of synthetic resins, synthetic rubber mixtures or branches, mosaics and co-polymers.
    2. Additives
    In order to meet specific physical and chemical characteristics, various auxiliary compositions are added called additives, e.g., in order to allow the body viscose to form a mesh or body structure, increase the cohesion strength of the adhesive layer and add a curing agent (they react with the main adhesive and produce an interlinking effect); In order to improve the resistance to atmospheric aging, thermal aging, arc aging, ozone aging and other properties, add anti-aging agents, in order to give the adhesive specific properties, reduce costs and fillers, to reduce the rigidity of the adhesive layer, increase toughness and add tougheners, in order to improve the process to reduce viscosity, extend the service life of the addition of thinners. Including:
    2) curing agent
    curing agent also known as hardener, is to promote the bonding substance through chemical reactions to speed up curing of the composition, it is the most important adhesive material. Its role is to react directly with the main polymer directly or through a catalyst, cure the curing agent molecules into the resin, so that the original thermoplastic line body polymer into a tough and hard mesh structure.
    variety of chemical curing agents, different resins, different requirements to use different curing agents. The process and performance of the glue are determined by the performance and quantity of the curing agent.
    3) The active group of the
    toughener is directly involved in the curing reaction of the adhesive and enters into the chain structure of a large molecule eventually formed by the curing product. After the adhesive has not been added to the toughener, its performance is more brittle, easy to crack, poor practicality. The adhesives added to the tougheners have better impact strength and peeling resistance. Different tougheners can also reduce their internal stress, curing shrinkage and improve low temperature performance to varying degrees

    4) Diluent
    diluent, also known as solvent, the main role is to reduce the viscosity of the adhesive, increase the immersion capacity of the adhesive, improve process performance. Some can reduce the activity of adhesives, thereby prolonging the use of. However, too much addition will reduce the adhesive bonding strength, heat resistance, media resistance.
    commonly used in the united states are acetone, paint and other solvents compatible with the adhesive.
    5) Fillers
    Fillers generally do not occur chemical reactions in adhesives, the use of fillers can improve the strength of the glue joints, impact toughness, wear resistance, aging resistance, hardness, maximum temperature and heat resistance, reduce line expansion coefficient, curing shrinkage and cost. Common fillers are copper oxide, magnesium oxide, silver powder, porcelain powder, mica powder, asbestos powder, talcum powder and so on.
    6) modifier
    modifier is to improve the performance of a certain aspect of the adhesive to meet special requirements and add some parts, such as in order to increase the strength of the glue, can be added to the couple agent, but also add preservatives, mold inhibitors, flame retardants and stabilizers.
    1.2 adhesive classification
    adhesive variety, composition is different, different uses, classification methods are as follows.
    1. By source can be divided into natural adhesives and synthetic adhesives.
    natural adhesive raw materials mainly come from natural, such as animal glue has bone glue, insect glue, fish glue, etc. ; Synthetic adhesives are adhesives made from synthetic resins or synthetic rubbers as the main raw materials, such as thermo-solid adhesive epoxy, phenolic aldehyde, acrylic lipids, silicones, unsaturated polyesters and so on. Rubber adhesives have neoprene, butyl rubber, silicone rubber and so on. Thermoplastic adhesives are polyvinyl acetate, ethylene, vinyl acetate and so on.
    2. By use can be divided into general adhesives and special adhesives.
    general glue has a certain glue strength, the general material can be glued, such as epoxy resin. Special adhesives have metal, wood, glass, rubber, polyethylene foam and other adhesives.
    3. According to the strength of the glue can be divided into structural adhesives and non-structural adhesives.
    structure glue joint shearing strength of up to 7MPa, not only has enough shear strength, but also has a high uneven tearing strength, can withstand vibration, fatigue and shock loads for a long time, but also has a certain degree of heat resistance and weather resistance. Unstructured adhesives have a certain strength at lower temperatures, and the bonding strength decreases rapidly as the temperature increases, so these adhesives are mainly used for parts that are not important for bonding, or for temporary fixation.
    4. According to the adhesive curing temperature can be divided into room temperature curing adhesive, medium temperature curing adhesive, high temperature curing adhesive. Room temperature refers to the temperature is less than 30 degrees C, the medium temperature refers to 30 to 99 degrees C, the high temperature refers to more than 100 degrees C can cure the adhesive.
    5. According to the adhesive base material can be divided into resin type, rubber type, inorgeable and natural adhesive.
    6. According to other special properties can be divided into conductive, magnetic conductive, spot welding adhesive and so on.
    II, glue process
    glue process includes pre-glue preparation, joint design, preparation of adhesives, coating, close, curing and quality testing.
    2.1 Pre-glue preparation
    the size of the adhesive to the glued material bond strength, mainly depends on the mechanical connection between the adhesive and the adhesive, the physical adsorption between molecules, mutual diffusion and the formation of chemical bonds and other factors combined results. The structural state of the surface of the glue has a direct effect on the strength of the glue joint.
    , transport, storage process, the surface will be oxidation, oil, dust and other impurities, etc. , must be removed before the glue.
    commonly used surface removal methods are skimming treatment, mechanical treatment and chemical treatment.
    1. Surface degreasing treatment method
    organic solvent degreasing, the current use of degreasing method is organic solvent method, lye method and surfactant method. Commonly used degreasing solvents are acetone, toluene, xylene, tetvinyl tetrachloride, acetic acid, banana water, gasoline and so on. For large quantities of small glue joints, trenchloroethylene vapor tank can be placed in about half a minute to remove grease. For large areas of adhesive surfaces, wash from top to bottom or from left to right. When using solvent degreasing, there should be a certain drying time to prevent the glue surface residual solvent affecting the strength of the connector. For the glue surface washed with lye, after cleaning must be washed with hot water, cold water to the surface of the lye in the net, after drying with hot air.
    after use, the surface is easy to absorb or deposit oil. If high temperature treatment is allowed, the glue can be placed in a hot air drying tank of 200 to 250 degrees C, so that the grease seeps out, and then used for cleaning cotton yarn rub, and then with solvent de-oiling. Special emphasis is placed on the need for solvents to leave the source of the fire in case of an accident.
    2. Mechanical treatment method
    mechanical treatment commonly used manual tools are wire brush, copper brush, scraper, sandpaper, wind tools, etc. ; The mechanical method is used to treat the surface, which provides the appropriate roughness to the surface, increases the effective glue area and improves the glue performance.
    3. Chemical treatment
    chemical treatment has two treatment methods: acidic solution and alkaline solution. Chemically treated metals can form a uniform dense, solid active layer on the surface, which can easily wet and expand the adhesive, which can significantly improve the strength of the bonding. For chemically treated polymers, such as Teflon, polyethylene, polypropylene, fluoroelas rubber, etc., the surface can be turned into a polar group, improve the surface's free energy, increase wetting, can greatly improve the strength of the glue.
    2.2 glue connector design
    . 1. Several forms of force of the glue joint
    a glue joint in the actual use, will not be only by one direction of force, but a collection of one or several forces. In order to facilitate force analysis, the actual glue joint force is simplified to shear force, pull force, peeling, split several forms (Figure 1).
    several forms of force of the glue connector in Figure 1
    . 2. The design of the glue joint should abide by the following principles
    manufacturing a high-quality glue joint is mainly related to the performance of the adhesive, reasonable bonding process and the correct form of the glue joint. The following points should be considered when designing the glue connector.
    1) As far as possible, the glue joint layer is pressurized, stretched and sheared, do not let the joint be stripped and split, as shown in Figure 2. Figure 2 (b) The joint glue layer is more stressed than Figure 2 (a). For those that are inevitably peeled and cracked, the measures shown in Figure 3 should be used to reduce the peeling and cracking of the adhesive layer.
    2 joint force comparison
    Figure 3 reduce the peeling and cracking measures of the glue layer
    2) reasonable design of a larger area of the joint, improve the joint carrying capacity.
    3) In order to further improve the carrying capacity of the glue joint, the joint form of the composite joint such as glue-welding, glue-riveting, glue-bolt should be adopted, as shown in Figure 4.
    4 composite joint form
    4) design of the glue joint should be easy to process, Table 1 is a few commonly used forms of glue joint.
    2.3 adhesive preparation and application
    . 1. The preparation of adhesive
    the performance of adhesive preparation will directly affect the practical performance of the adhesive joint, therefore, the preparation of adhesive should be scientific and reasonable, preparation should be carried out in a reasonable order.
    adhesive has a single component, two components and multi-components and other types. Single-part adhesives can be used directly. When adhesives with two or more parts are made, the quality error of the quality children who must accurately calculate and claim each part must not exceed 2% to 5%. Too much curing agent does not make the adhesive layer brittle, and the curing of the adhesive is incomplete if the amount is insufficient.
    , the adhesive should be placed in a closed container with a temperature of 15 to 25 degrees C (with the exception of special varieties), dark opaque, and no destructive effect on the adhesive.
    the preparation of adhesive depends on the dosage. Small dosing can be used by hand stirring, when the dosing is large, should choose an electric mixer for stirring. The ingredients must be evenly and consistent in stirring. For some adhesives with poor compatible, lots of fillers and long storage time, re-mixing should be carried out before use. For the viscosity to become larger also need to add human solvent dilution and stirring.
    2. Application of adhesive
    is the use of appropriate methods and tools to apply adhesive to the surface of the adhesive site. Application methods are brushing, immersion, spraying, scraping, etc.
    according to the purpose of adhesive use, the viscosity of the adhesive, the nature of the adhesive, can choose a different method of coating. If the temperature at the time of preparation is too low, the adhesive is too large, you can use water bath heating or first put the glue in the oven to preheat.
    apply the glue layer to be uniform, in order to avoid adhesion after the glue layer memory air, when applying glue are applied from one direction to the other direction, the speed of 2 to 4 cm /s is appropriate. The thickness of the glue layer is generally 0.08 to 0.15mm.
    to solvent-based adhesives and perforated adhesives, need to be applied 2 to 3 times, before applying the second road, to accurately grasp the first glue solvent volatile completely and then applied a second time. If too much solvent remains in the adhesive layer, the bonding strength will be reduced, but the excessive drying of the adhesive layer will lose adhesion.
    For solvent-free thermostate adhesives, bond immediately after application to avoid prolonged placement of moisture absorbed in the air or volatilization of curing agents such as epoxy adhesive fatty amine curing agents.
    2.4 Curing of adhesives
    The so-called curing is the process by which the adhesive becomes solid through the physical effects of solvent volatilization, melt cooling, emulsion condensation, etc., or through chemical reactions such as condensation, amerization, crosslinking, and collation.
    the glue is closed together, in order to obtain the desired joint strength after hardening, the process and parameters such as pressure, temperature and time in the curing process must be accurately grasped.
    1. Curing pressure
    pressurization is conducive to the adhesive to the surface of the full immersion, discharge of solvents or low molecular volatiles in the adhesive layer, control the thickness of the adhesive layer, prevent the contraction caused by poor contact between the adhesive, improve the mobility of the adhesive.
    moderate pressure can be a good control of the thickness of the adhesive layer, give full play to the adhesive bonding effect, to ensure that there are no pores in the adhesive layer. The size of the pressure is related to the adhesive and the type of adhesive, for brittle materials or plastics that are easily deformed after pressurized.
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