Adhesive formulations, uncured

A filler should be dry, nonreactive with the uncured resin, and of a neutral or only slightly basic pH. Adsorbed water, which is present in some degree in most fillers, inhibits dispersion. Thus, most fillers must be dried before they are added to the adhesive formulation. The drying process will drive off adsorbed moisture and gases from the surface of the filler. The filler should generally be nonreactive with the base resins or curing agents that... 

The most commonly used tests for properties of the materials used in epoxy adhesive formulation and uncured mixed adhesives are viscosity, shelf life, percent of solids, and moisture content. These are generally applied to the resinous components. 

Since epoxy adhesive formulation represents a surprisingly broad area of technology, a road map to the use of this book may be valuable. Chapters 1 through 3 discuss the synthesis of raw materials, epoxy chemistry in general, and the physical and chemical properties that are important for an epoxy adhesive. These properties are important during the three primary phases or conditions of an adhesive (1) uncured, (2) during cure, and (3) fully cured. 

One of the tests is maintaining strength through a gap. This can be affected by air inhibition, as well as by the diffusion of accelerators. In another test, air was beaten into several adhesive formulations. The aerobic adhesives were only marginally affected by air inclusion when cured between surfaces. Like anaerobics, fillets or adhesive squeezed outside of a bonded joint will remain uncured unless exposed to UV light. 

One property common to UV-cure.d acrylate formulations as was discussed earlier is relatively poor surface-cure due to oxygen inhibition (see Fig. 1). This effect is most predominant at low photoinitiator concentrations, in thin coatings. Adhesive formulations can benefit from this property by enhancing surface tack via the presence of residual uncured resin. Post-cure, from residual cross-linking, or other anaerobic chemistry, can later result in enhanced bond strength. 

Anaerobic adhesive formulations vary substantially depending upon the properties sought in the cured and uncured composition. Typical formulations contain (meth)acrylate... 

Owing to their curing properties, anaerobic adhesives remain uncured outside the joint assembly this allows removal with solvent Some formulations now include sensitizers, which allow drying of the excess with UV light. 

Silicone adhesives are generally applied in a liquid and uncured state. It is therefore the physical and chemical properties of the polymers, or more precisely of the polymer formulation, that guide the various processes leading to the formation of the cured silicone network. The choice of the cure system can be guided by a variety of parameters that includes cure time and temperature, rheological properties in relation with the application process, substrates, the environment the adhesive joints will be subjected to and its subsequent durability, and of course, cost. 

In this reaction, no by-products are evolved, and the crosslinking reactions occur within the bulk of the material. A typical hydrosilylation crosslinking system is depicted in Scheme 11, where n and y can vary depending on the required viscosity of the uncured formulation and the final targeted properties of the cured adhesive. 

When formulating a silicone adhesive, sealant, or coating, based on hydrosilylation addition cure, one must consider the following properties of the uncured product pot life, dispensing technique, rheology, extrusion rate, cure performance. These characteristics directly affect the processing properties of the polymer base or crosslinker parts. The degree of cure conversion at the temperature of interest is determined by properties such as tack free time, cure profile and cure time. Once... 

S.2.2.2. Composite adherends. Composite adherends are bonded in both the cured and uncured states. Wherever possible the adhesive and all adherends are cured simultaneously to avoid the added cost of additional autoclave cure cycles. In many cases this is not practical due to part size and complexity. Cured parts can be bonded to uncured parts, which is known as cobonding, and fully cured parts can be bonded together, which is known as secondary bonding. Adhesives for composites are formulated to be compatible with matrix resins in either cured or uncured states. 

Proper formulation of epoxy adhesives requires knowledge of the chemical reactions that lead to polymerization as well as the chemical and physical properties of both the uncured mixture and the cured material. This chapter reviews the general principles of epoxy resin chemistry including synthesis of the epoxy monomer itself and its possible polymerization reactions. 

The properties of epoxy adhesives in their uncured condition will determine primarily how easily the adhesive can be processed, applied, and cured. They will also determine, to some extent, the performance characteristics of the cured joint. The properties of the individual components as well as that for the mixed formulation are important. 

Properties often used by epoxy resin manufacturers to specify particular grades of resin include the epoxy content, viscosity or softening point, and color. In addition, properties such as density, vapor pressure, flash point, refractive index, solubility characteristics, and hydroxyl content are often reported. The important properties of uncured epoxy formulations with regard to most adhesive applications are... 

In general, the elastomer must be prereacted (adducted) with the epoxy for the toughening effect to take place. Adducts reduce the likelihood of early phase separation and maintain the solubility of the elastomer in the uncured resin system. For CTBN the reaction is carried out at high temperatures (150 to 160°C) and usually in the presence of a catalyst, such as tris-dimethylamino phenol or piperidine. The resulting epoxy-CTBN adducts are available from several suppliers, and they can be easily formulated into epoxy adhesives. 

Solid epoxy adhesives generally rely on high-molecular-weight epoxy resin for the solid appearance of the uncured adhesive. This epoxy resin is generally formulated with either ... 

A wide range of epoxy resins as well as a wide range of curing agents and catalysts are available for formulating solid epoxy adhesives. Resins with different viscosities, amounts of reactive groups, and structures are available. Additives that change the uncured resin viscosity, reduce brittleness, or impart some other property are also available. 

Physical-property tests are used to measure the properties of adhesives in the liquid or gelled states prior to curing and in the solid state after curing. Tests for the uncured state such as viscosity, visual examination, and surface energy or contact angle assure that fillers, if used, have not settled out, that the material has not exceeded its pot life or shelf life, and that the supplier has not changed the formulation. Visual examination and density after cure are performed to verify that voids are not present or, if present, meet specification requirements. Finally, light transmission and index of refraction measurements are important for adhesives used in optoelectronic applications. 

The density of a material is mass per unit volume reported as g/cm. The density of uncured adhesives is useful in verifying the correct portion of liquid resin and filler ingredients of a formulation. The density of a cured adhesive is an indicator of the specific formulation and of completeness of cure. 

The density of uncured liquid formulations is measured as specified in ASTM D1875, Density of Adhesives in Fluid Form. A weight-per-gaUon cup whose volume is exactly 83.2 ml at 25 °C is weighed to the nearest 0.1 g, filled with adhesive, and reweighed.The net weight of adhesive divided by the volume of the cup gives the density. 

Uses Biocide microbiostatpresenrative for aq. formulations, latex emulsions, adhesives, metalworking fluids, aq. paints, casein and rosin disps., textile spin finishes, pesticides, inks, slurries, food-pkg. adhesives, polishes, leather processing sol ns. antimicrobial in cosmetics preservative for animal hides and skins preservative in paper/paper-board in contact with aqTfatty/dry foods slimicide in food-contact pa-per/paperboard biocide in food-contact uncured liq. rubber latex Regulatory FDA 21CFR 175.105,176.170,176.180,176.300 Mam JDistrib. Avecia PMC Spec. Sinochem Jiangsu Wuxi Troy... 

MDI Prepolymers with a High Content of Isocyanate This type of adhesive was formulated on the basis of MDI-prepolymer with a relatively high concentration of isocyanate in the uncured adhesive (around 15-16%). This also means a low molecular weight (around 500-600 g/mol). This adhesive type is often used to bond wood. In standard practice, the adhesive is applied under pressure so that most of it flows out between the wood members the thickness of the adhesive layer is virtually zero. 

The rate of cure is temperature dependent and many formulations stop curing altogether below a temperature of about 5 °C. If carefully formulated the change in volume between the uncured resin-hardener system and the fully cured polymer can be very low. This property, together with their relatively high strength and claimed resistance to moisture and chemical attack, forms the basis of the use of epoxy resins as structural adhesives. 

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