One-component reactive adhesives

One-component reactive adhesives are applied to the adherends only in the form of one (the resin) component. That the curing of an adhesive layer still occurs is due to the fact that the reactive conditions required for the curing of the resin component in the glueline are given. Such conditions may be, for example  

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Adhesives that cure without the admixture of a second component, since the latter is already determined by the chemical state of the adherend surface or diffuses into the glueline, for example, water molecules (one-component reactive adhesives). 

One-component reactive adhesives have to be distinguished from the physically setting adhesives described in Chapter 5, which generally occur only in the form of one component, namely, the already finished polymer, for example, in the case of hot-melt adhesives, dispersion adhesives and solvent-based adhesives. They are called one-component adhesives. 

Control of viscosity, density, solid content and color, if required, for additional adhesive identification. In the case of one-component reactive adhesives, the viscosity test allows the verification of a probable exceedance of pot life (geli-hcation). 

One-component polyurethane adhesive Adhesive containing isocyanates ernes on exposure to moisture or to heat, when latent hardener is included Primer Special coating designed to improve adhesion between adhesive and substrate - applied before adhesive application Reactive adhesives Adhesives that cure or set when exposed to heat, moisture, radiation, etc. 

Temperature during storage Some very reactive adhesives such as epoxy one component film adhesives or some cyanoacrylates should be stored in refrigerators at — 10 or — 20°C before utilization in order to increase storage life. At these temperatures they may be stored several months, while at 20°C they could only be stored a few weeks. Suppliers always indicate the shelf life of their A and S. 

Due to the existence of different adhesive systems and the potential hazards associated with each system, there are different types of pack ing as well as stor e conditions and shelf fives. Adhesives can be differentiated based on specific criterion and properties. In the literature, one can find various classifications based on the assembly process, delivery form, adhesion mechanism, or application. Within the same adhesive group, the adhesives can be further differentiated based on their physical states or characteristics liquid, paste, or solid (throi viscosity measurements and rheological characterization), and solvent based, water based, or those without volatile content (through solid content measurements). Another classification can be made based on the adhesion mechanism physically dried adhesives from solution, solidified hot-melt adhesive, or chemically cross-linked single- and two-component reactive adhesives. 

These subgel prepolymers have been manufactured by industry for some time and used in two-component adhesives or coating materials. For one-component materials, storage below the actual Tg, whenever applicable, is the most efficient method for blocking the reactivities. This kind of blocking is used in powder coatings. 

Reactivity can also be increased by externally heating the epoxy formulation to a preselected curing temperature. Epoxy resin reactions roughly obey Arrhenius law that for every 10°C rise in temperature, the reaction rate doubles. Certain epoxy resin systems must be heated for any reaction to take place at all. This is beneficial in that these latent adhesive formulations are one-component products that do not require metering or mixing yet have long, practical shelf lives. 

The lower reactivity of the aromatic amines in adhesive formulations is an advantage in that epoxy resin mixtures can be B-staged at room temperature (react to a glassy but fusible and thermoplastic intermediate structure) and will not fully cure for months. In this way, dry films and solid powders can be formulated as elevated-temperature curing, one-component adhesives with long shelf life. 

The separate phases will be rich in one component but may have the other present as a minor component. In order to control compatibility the elastomer may have reactive end groups to enhance interfacial adhesion. A common example in epoxy-resin technology is the carboxy-terminated butadiene-acrylonitrile copolymer (CTBN). The structure is shown in Scheme 1.47. In this resin the solubility in the epoxy resin is conferred by the acrylonitrile group, and an increase in the fraction present decreases the upper critical solution temperature, with 26% acrylonitrile conferring total miscibility of CTBN with a DGEBA-based epoxy resin (Pascault et al, 2002). 

Another possibility of applying reactive adhesives in the form of only one component without mixing will be given, if the components A and B do not react with each other after mixing, because due to their chemical composition they are too... 

Their main field of application are sealing compounds (silicone rubber) for which they are sold in the form of reactive one-component systems (mainly in cartridges) (RTV-l-systems, room-temperature vulcanization). Just like the one-component polyurethanes described in Section 4.2.2, they cure under the influence of moisture from the ambient air. In certain formulations, this reaction leads to the separation of acetic acid perceptible by its characteristic odor. Adhesive and sealing layers on a silicone basis show the following characteristics ... 

The work discussed here has shown that suspensions of platelets and red cells in a physiological medium can provide information for platelet surface interactions. Evidence is provided on the dynamic features of platelet-surface adhesion and detachment which indicates that more than one sequence of adhesion, detachment and re-adhesion can lead to the same net platelet adhesion. Surface generated substances, such as A DP and serotonin from platelets and thrombin from the coagulation pathway, may strongly influence the function of platelets approaching a surface. The supply of these substances depends on the presence of flow and continued arrival of platelets at a surface. The reactivity of surface-bound protein may be altered by platelet adhesion and detachment. This may occur as a result of deposition of cell membrane components, replacement of the original substrate with protein secreted from platelets or possibly by enzymatic digestion of surface bound protein. 

Flexible circuit boards consist primarily of polyimide-based carriers. The problem of bonding the copper foil on the polyimide carrier has not yet been solved satisfactorily. Due especially to their low bonding strength at elevated temperatures, the production of such materials is very limited. Nevertheless, adhesives for copper-polyimide systems were developed, where one-component epoxy resins (e.g., epoxy-polyester mixtures) and reactive hot melts (e.g., phenolic resin-nitrile rubbers) reached importance. 

CH3CH2CH2CH2)2Sn[COOCHCHCOOC8Hi7]2 Properties M.w. 687.46 ref. index 1.145 Toxicology TSCA listed HMIS Health 2, Flammability 2, Reactivity 0 Uses Heat stabilizer for PVC catalyst for one-component RTV s good adhesion to metal substrates... 

One-part epoxy adhesives include solvent-free liquid resins, solutions in solvent, liquid resin pastes, fusible powders, sticks, pellets and paste, supported and unsupported films, and preformed shapes to fit a particular joint. Two-part epoxy adhesives are usually comprised of the resin and the curing agent, which are mixed just prior to use. The components may be liquids, putties, or liquid and hardener powder. They may also contain plasticizers, reactive diluents, fillers, and resinous modifiers. The processing conditions are determined by the curing agent employed. In general, two-part systems are mixed, applied within the recommended pot life (a few minutes to several hours), and cured at room temperature for up to 24 hours, or at elevated temperatures to reduce the cure time. Typical cure conditions range from 3 hours at 60°C to 20 minutes at 100 C. ... 

Two-component reactive quasi-prepolymer liquid adhesives where one component forms the polyol prepolymer stream and the other the diisocyanate prepolymer stream. 

Adhesives can set or cure by carrier (solvent or water) evaporation, chemical reaction, or thermal activation. Chemically reactive adhesives solidify primarily by a chemical reaction of one or more components in the adhesive formulation. It should be noted that solvent welding cementing processes or solvent-borne adhesives are in disfavor due to environmental, safety, and health concerns and regulations. As a result, waterborne adhesives and heat-activated adhesives are replacing solvent-based adhesives in many applications. 

One component of a two-part urethane adhesive typically contains an NCO-terminated prepolymer and possibly fillers. The second component consists of polyfunctional, NCO-reactive materials, such as polyols and/or polyamines, and may also contain fillers and catalysts. The work life and rate of cure can be adjusted by the selection of catalysts, the catalyst level, and the starting materials used to prepare the resins. Table III lists the cure times for three adhesives which have identical bond strengths when cured, but different work lives. Two-part urethane systems usually cure at room temperature, but the cure can be accelerated by the use of heat. Although... 

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