Adhesive flow characteristics

Blister Detection Large area metal-to-metal bonding to ascertain adhesive flow characteristics during bonding. Conventional lap shear specimens are machined from the bonded sheet and are tested. The specimens are examined for evidence of air entrapment ( blistering ). 

It is difficult to generalize concerning the flow characteristics of granular materials. Each material has its own transport characteristics based on cohesive and adhesive forces, density, size of the particles, shape and perhaps other unknown characteristics. For a material of a given composition, humidity represents a day to day or hour to hour variable which could supercede the other characteristics. For on-line sensing of granular materials, the main... 

Control of Viscosity. To ensure that adhesives and sealants function well during their application and end use, the formulator must be able to control the flow properties of the product. The challenge that faces the formulator is that the adhesive or sealant may need different flow characteristics at different times. For example, adhesives must flow readily so that they can be evenly applied to a substrate and wet out the surface. Yet, there should not be an excess of penetration into porous substrates, nor should the adhesive run or bleed to create a starved joint. Certain adhesives and sealants must be capable of convenient flow application by trowel or extrusion, but they must also exhibit sag and slump resistance, once applied. Therefore, the flow properties, or rheology, of the material must fit the desired method of application. 

Flow characteristics can be regulated by the incorporation of fillers, by the use of scrims or woven tapes as internal shims within the adhesive itself, or by the careful regulation of the cure cycle. All these options along with a few more are available to the adhesive for-mulator and end user. Generally, fillers are incorporated to control the viscosity of the adhesives as well as other properties such as thixotropy and sag resistance. 

Silk screen application is often used when the adhesive has to be applied to specific controlled areas. The liquid adhesive is forced through pores in a cloth or screen. It is possible to coat only selected areas by masking parts of the screen so that adhesive does not pass through in the unwanted areas. Adhesives generally must be specifically formulated for silk screen processing. Very low-viscosity adhesives, with flow characteristics similar to those of coatings, are best for silk screening operations. 

Kiss No backup roll coater is in light contact with substrate contact is controlled by web tension. Best with adhesives having good flow characteristics and relatively slow drying rates... 

Internal lubricants are added as part of the formulation during plastics processing. Depending on their compatibility with the resin they can have a more pronounced internal lubrication effect mainly interacting with the molecules of the polymer melt or they can have a more pronounced external effect, i.e. additionally reduce friction at the interface between processed plastic melt and metallic machinery parts [121, 151-153]. Lubricants in resin systems improve flow characteristics and reduce adhesion in the polymer melt. Added in very small quantities... 

The most widely used thermoplastic polymer is the ethylene—vinyl acetate copolymer, which is obtainable in a wide range of molecular weights as well as in a variety of compositions. Often flexibilizers or plasticizers are added in order to improve both the mechanical shock resistance and the thermal properties of the adhesive. Polybutenes, phthalates, and tricresyl phosphate have been used as plasticizers. Tackifying agents can also be added. Because hot-melt adhesives are frequendy ethylene-based, they are subject to oxidation if, as in a typical situation, the adhesive sits in an applicator for long periods before use. Thus, antioxidants such as hindered phenols are often used, as are fillers. Fillers are added to opacify or to modify the adhesive s flow characteristics, as well as to reduce cost. Wax is also a very important component. Wax alters surface characteristics by decreasing both the liquid adhesive s surface tension and its viscosity in the melt. Upon solidification, however, the wax acts to increase the strength of the adhesive. Both paraffin and microcrystalline wax are used (see Waxes). 

OTHER COMMENTS used as an intermediate in the synthesis of pharmaceuticals, dyes, and insecticides used to provide better flow characteristics and film integrity used to increase wetting ability and electrostatic spraying properties used to ensure greater pigment dispersion used as a solvent in vinyl and epoxy coatings, nitrocellulose, chlorinated rubbers, printing inks, and adhesives. 

Particle size change, crystalline form change, viscosity, loss of consistency and flow characteristics (caking, coalescence, bleeding), drug release rate change In-vitro release rate leakage peel and adhesive forces... 

Retain adhesion while the circuit is flexed Wet and bond well to both the polymer film and the copper foil Have low moisture absorption Have good dielectric properties Have low or no-flow characteristics Be thermally resistant to solder-reflow temperatures... 

Virtually all rubber materials, and plastic materials, can be made into an adhesive or sealant compound. This is because many elastomers begin as monomers dispersed in water or solvent and are polymerized in situ. Latex products can remain so, while solid elastomers that are extracted from either water or solvent systems can be solvated with an appropriate organic solvent system. In addition, most solid elastomers exhibit thermal flow characteristics which can make them suitable for hot-melt formulations. And since there are many different rubber polymer families, it stands to reason that there will be many different rubber-based adhesives to identify and describe. Some, however, have... 

The rheological properties of adhesives and sealants are important in many applications. When these products must be pumped or applied through automated equipment, the flow characteristics at pertinent shear rates are critical. Sophisticated rheological measurements can be performed to predict performance. The rheology of silicone adhesives and sealants can be tailored through adjustment of polymer viscosity, filler loading, and incorporation of various additives. 

Features Exc. cure spe, exc. adhesion to metal and plastic, good wetting and flow characteristics UV/EB or conventional cure improved tensile and modulus props, while maintaining flexibility exc. thin-film adhesion to electrocoated steel... 

Adhesives are designed for specific applications. For example, a honeycomb structure adhesive (requiring good filleting around the cells) would have different flow characteristics than one used for metal-to-metal joining. In addition, the type of stress (e.g., shear or peel) on the bonded area varies and will depend upon the design of the structure. 

Amino molding compounds can be fabricated by economical molding methods. Because of their poorer flow characteristics, the urea resins are usually compression-molded, but transfer molding is common with the melamines. Amino resins exhibit relatively high mold shrinkage. Product applications for amino resins include dinnerware, buttons, toilet seats, knobs, handles, ashtrays, food utensils, mixing bowls, and military equipment. Parts are typically joined with adhesives and fasteners. 

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