Adhesives reactive liquids

These applications are a domain that is shared by UV and EB processes, because both can directly convert reactive liquids into solids almost instantly. There are specific areas where EB irradiation is more suitable than the UV curing process. In general, these include applications where thick layers of coatings or adhesives are applied. Other instances are coatings with high levels of inorganic pigments or fillers, which usually cannot be cured by UV radiation because of their opacity. As pointed... 

Ihe polymers of the 2-cyanoacrylic esters, more commonly known as the alkyl 2-cyanoacrylates, are hard glassy resins that exhibit excellent adhesion to a wide variety of materials. The polymers are spontaneously formed when their liquid precursors or monomers are placed between two closely fitting surfaces. Tile spontaneous polymerization of these very reactive liquids and the excellent adhesion properties of the cured resins combine to make these compounds a unique class of single-component, ambient-temperature-curing adhesive of great versatility (Table 3). The materials that can be bonded run the gamut from metals, plastics, most elastomers, fabrics, and woods to many ceramics. 

In principle, an equality between the thermodynamic work of adhesion of liquid-solid systems and the work needed to separate an interface might be expected for simple systems and this has been observed for failure of adhesive-polymer interfaces bonded by van der Waals forces, (Kinloch 1987). Similarly, empirical correlations of interfacial strengths and work of adhesion values of solidified interfaces have been reported for some nominally non-reactive pure metal/ceramic systems. However, mechanical separation of such interfaces is a complex process that usually involves plastic deformation of the lattices, and hence their works of fracture are often at least ten and sometimes one hundred times larger than the works of adhesion, (Howe 1993). Nevertheless, for non-reactive metal/ceramic couples, it is now widely recognised that the energy dissipated by plasticity (and as a result the fracture energy of the interface) scales with the thermodynamic work of adhesion (Reimanis et al. 1991, Howe 1993, Tomsiaet al. 1995). 

Adhesives are nonmetaUic substances used to join two surfaces by means of surface adherence (adhesion) and inherent strength (cohesion), DIN 16920. This definition of adhesives does not cover water glass adhesives, adhesive ceramics, or adhesive mortars. The substances used as adhesives are polymers that go through a liquid phase at least once (reactive adhesives) or more than once (hotmelts, thermally activated adhesives). The liquid phase can also be achieved by dissolution in suitable solvents (nonreactive adhesives). In dispersion adhesives, the polymer molecules are dispersed (finely distributed) in a liquid - usually water - whereby the polymer molecules themselves are not dissolved. Fig. 6. These adhesives are also known as water-based or aqueous adhesives. It must be remembered that solvents are contained in these adhesives in addition to the water. Genuine aqueous adhesives contain less than 5% solvents in the liquid phase. The dispersions crnitain, in contrast to the solute adhesive molecules, additional substances, disposal of which requires specific additional measures. Since the dispersions represent stable systems in water, the water-resistance of such adhesives is reduced. Their thermal and water resistance can be increased by additional crosslinking (usually with isocyanates). 

Microencapsulated adhesive Reactive adhesive mixture, with the (liquid) components encapsulated by a protective skin in the form of finest drops, preventing a reaction during storage. Only after the destruction of the capsule wall, for example, by screwing a nut onto a suchlike coated screw, does a chemical reaction set in and an adhesive layer develop. 

The acrylic core-shell polymers are considered to offer superior ultraviolet-light and thermal-oxidative aging properties than does the more conventional reactive liquid polymeric toughener, CTBN. Hence, there is current interest in the use of acrylic core-shell polymers as tougheners for adhesives and composite matrices that possess a relatively high glass-transition temperature. 

In this paper/ we shall describe the development of adhesives during the last several years and the trends for further advances. In general/ traditionally used / solvent-borne systems (4) will be gradually replaced by waterborne systems/ hot-meltS/ nonvolatile solid (or liquid) systems/ two-part adhesiveS/ radiation-curable adhesiveS/ and powder and reactive liquid systems (Table 1). 

The use of elastomeric or flexibilizing modifiers occurred and grew with epoxy resins first. Various aspects of toughened epoxy adhesives have been covered in reviews by the present authors (2,3), where the elastomeric modifiers have essentially been carboxylic, liquid and solid butadiene/acrylonitrile polymers. There has not been a systematic review, however, of these and other reactive liquid polybutadiene/acrylonitriles in the burgeoning areas of acrylic, anaerobic and radiation-curable systems. Thus, this paper s intent. 

Ralph Drake has degrees from Case-Western Research University. He has been with B. F. Goodrich Chemical Group for 26 years and spent much of that time associated with new products, many of them adhesive raw materials. He is currently Marketing Manager for Reactive Liquid Polymers. He has over 40 patents and technical publications. 

These are liquid ingredients added to an adhesive to reduce the concentration of the binder component. Diluents are added principally to lower the viscosity and to modify the processing conditions of some adhesives. Reactive diluents do not evaporate, as would solvents. They react with the binder during the cure cycle and are incorporated in the cured adhesive. 

Reactive— liquid components chemically react with each other to form a solid (two-component epoxy adhesives, cyanoacrylates or super glues react with water, some adhesives react on exposure to light or radiation)... 

Reactive liquid polymers (RLPs) The Uquid rubbers most often used in epoxy adhesives are those based on acrylonitrile-butadiene copolymers or on long-chain polyethers. To act as effective tougheners, however, they cannot be directly added to the formulation but have to be prereacted with some of the epoxy resin, or sometimes with the amino hardeners in two component paste adhesives (adduct fonnatiou). To achieve this, only RLPs with reactive eud groups are used by the formulator. 

Single-component solventless reactive liquid adhesives where the diisocyanate group is the key bonding element in a prepolymer base. 

The most common textile adhesives are available as solutions in water or solvent, as dispersions in water, or as solids that melt under the appUcation of heat. However, 100% reactive liquid adhesives such as epoxies and moisture-cured urethanes are also used. 

Reactive liquid adhesives can be chemically cross-linked to form durable, three-dimensional molecular structures. These bind chemically and/or mechanically with the fabric surface to generate high joint strength. They are generally one-part elevated-temperarnre-setting or two-part room-temperature-setting polymer systems. However, one-part systems that cure at room temperature when in contact with the substrates are also available (e.g., cyanoacrylates). 

Reactive liquid adhesives can consist of waterborne emulsion- or solvent-based adhesives. These are adhesive systems similar to those described above but here a cross-linking agent is added to the formulation. They most notably are acrylics and PUs where a cross-linking agent is added to the adhesive immediately before application to provide improved heat and chemical resistance. 

Adhesive materials are applied as thin layers of polymeric materials capable of transmitting stresses between two substrates. They can be classified according to their functions into physical or chemical adhesive forms. Adhesives must behave as fluids before they set and become solid. Thus, the solid adhesive is formed from (a) its solution by solvent evaporation, (b) hot-melting by coohng and (c) reactive liquid precursor by in-situ thermosetting reactions. The purpose of adhesives is the transmission of forces from one adherent to the other. Thus, adhesive performance is always described in terms of mechanical adhesion in which the strength of the polymer interface with the adherents is evaluated. The distribution of stresses in bonded joints depends on the overall bond geometry and on the loads applied to the bonded structnre. The initiation and development of failure is most certainly associated with stress distribntion. 

The -R groups in the APES and AAMS contain amines, which would make them reactive with epoxide adhesives or liquid resins. As GPMS contains epoxide groups, it would react with amine groups in adhesives or resins. The carbon-carbon double bonds in MPMS of VMS would copolymerise with styrene and unsaturated polyester in liquid resins, by a free radical mechanism. 

The attempt to blend natural rubber with epoxy resins resulted from the abundance of natural rubber and that it was a renewable resource. Nevertheless, interfacial adhesion between natural rubber and epoxy resins was weak due to the hydrophobic nature of natural rubber. Thus, it was an interesting experiment to blend the toughened epoxy resins with synthetic reactive liquid rubber. In order to achieve an efficient stress transfer between rubber and the... 

Hycai Reactive Liquid Polymers Preliminary Data Sheet AB-16, Hycai Reactive Liquid Polymer Modified Epoxy Adhesives Polyether Diamine Hardeners, BFGoodrich, August 1983. 

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