Stability requirements adhesive

One of the means used to modify monomers and polyester acrylates further is to amine modify them. This is normally done using a Michael addition reaction between the acrylate and an amine. The benefits of amine modification are normally seen with increased cure speed since this will tend to overcome the effects of oxygen inhibition in the cure process. Amine oligomers and synergists can also be low viscosity and give improved flexibility to a film. One disadvantage of these materials maybe that perhaps they do not possess the stability required of UV inkjet ink formulations. They are also very prone to yellowing and are unstable with some forms of adhesion promoters. 

If one examines the future needs of high performance IC processing (Table 1.3), more than seven levels of interconnects may be required. Such schemes will be implemented using CMP methods to planarize at each level. Estimate the impact of building multilayers on stresses in underlying layers and its and CMP s impact on adhesion stability requirements. 

Development of planar solid oxide fuel cells (SOFCs) and other electrochemical devices, such as oxygen generators and sensors, makes it necessary to elaborate sealant materials for hermetization in high-temperature zone. The sealants should satisfy numerous requirements, including chemical stability, good adhesion and thermal expansion. 

Table 6.4 presents a typical formulation for emulsion polymerization. The principal monomers present low water solubihty and the ratio between hard (leading to high Tg polymers) and soft (leading to low Tg polymers) monomers is chosen to achieve the Tg required for the application. Minor functional monomers provide some special characteristics, such as improved latex stability and adhesion. Crosslinking agents and chain transfer agents (CTAs) are used to control the chain architecture and the MWD of the polymer. 

Manufacturing of metal OTEs has been desaibed in detail by Bauhofer [362], Apart from the demands of the optical and electrical performance and the purity of the materials, the OTE-substrate system must meet the mechanical and chemical stability requirements (including the adhesion of the film to the substrate). To obtain a well-ordered, clean single-crystal metal surface (Pt, Ir Au,) the sample can be sputtered with Ar" ions, oxidized in 10 mbar of oxygen at 1000 K to remove surface carbon, and annealed at 1400 K [661, 662],... 

The cross-linked nature of UV/EB-cured adhesives results in good chemical, heat, and abrasion resistance toughness dimensional stability and adhesion to many substrates. Unlike thermal curing, EB or UV curing requires pure raw material grades. The use of dual-curing systems allows opaque substrates to be cured. 

Unmodified rosins from all sources are highly unsaturated because their main constituent is abietic acid, which contains a conjugated double bond. Thus they are subject to degradation by oxygen, UV light, and heat. Therefore, the natural rosins must be modified to meet the stability requirements of the hot adhesives. Improved stability can be developed by several... 

ISO 11600 2003 Building construction. Jointing products. Classification and requirements for sealants ISO 15908 2002 Adhesives for thermoplastic piping systems. Test method for the determination of thermal stability of adhesives... 

Plastisol foam stabilizers (Section 14.5) may also function as viscosity depressants. With foamed plastisols, these factors must be considered together. Conversely, the viscosity depressants listed above typically also function as air release agents. SUicone additives can assist in all three areas, but must be used with caution if operations, even on other lines, involve appUcations requiring adhesion, printing, or decorating. It makes no sense to have unreasoning prejudice against such additives, but rather to be certain that they are used properly. 

Poly(vinyl acetate) emulsions can be made with a surfactant alone or with a protective coUoid alone, but the usual practice is to use a combination of the two. Normally, up to 3 wt % stabilizers may be included in the recipe, but when water sensitivity or tack of the wet film is desired, as in some adhesives, more may be included. The most commonly used surfactants are the anionic sulfates and sulfonates, but cationic emulsifiers and nonionics are also suitable. Indeed, some emulsion compounding formulas require the use of cationic or nonionic surfactants for stable formulations. The most commonly used protective coUoids are poly(vinyl alcohol) and hydroxyethyl cellulose, but there are many others, natural and synthetic, which are usable if not preferable for a given appHcation. 

Cyanoacrylate adhesives cure by anionic polymerization. This reaction is catalyzed by weak bases (such as water), so the adhesives are generally stabilized by the inclusion of a weak acid in the formulation. While adhesion of cyanoacrylates to bare metals and many polymers is excellent, bonding to polyolefins requires a surface modifying primer. Solutions of chlorinated polyolefin oligomers, fran-sition metal complexes, and organic bases such as tertiary amines can greatly enhance cyanoacrylate adhesion to these surfaces [72]. The solvent is a critical component of these primers, as solvent swelling of the surface facilitates inter-... 

Other polymers used in the PSA industry include synthetic polyisoprenes and polybutadienes, styrene-butadiene rubbers, butadiene-acrylonitrile rubbers, polychloroprenes, and some polyisobutylenes. With the exception of pure polyisobutylenes, these polymer backbones retain some unsaturation, which makes them susceptible to oxidation and UV degradation. The rubbers require compounding with tackifiers and, if desired, plasticizers or oils to make them tacky. To improve performance and to make them more processible, diene-based polymers are typically compounded with additional stabilizers, chemical crosslinkers, and solvents for coating. Emulsion polymerized styrene butadiene rubbers (SBRs) are a common basis for PSA formulation [121]. The tackified SBR PSAs show improved cohesive strength as the Mooney viscosity and percent bound styrene in the rubber increases. The peel performance typically is best with 24—40% bound styrene in the rubber. To increase adhesion to polar surfaces, carboxylated SBRs have been used for PSA formulation. Blends of SBR and natural rubber are commonly used to improve long-term stability of the adhesives. 

One key consideration in developing radiation curable adhesive systems is the thermal stability and volatility of any photoinitiators used. These chemicals are designed for liquid systems where these issues do not arise. Few of the commercial photoinitiators have adequate thermal stability at the highest hot melt temperatures (180-200°C) and many are too volatile. Reduced application temperatures and special antioxidant packages are often required. 

Polymerization inhibitors are key additives which prevent premature gelation of the adhesive. The foimulator must carefully balance shelf stability and the required cure on demand. Due to its high propagation rate, MMA is difficult to inhibit. Some comments on specific inhibitors follow. The most common inhibitor to be found in component monomers is 4-methoxyphenol, which is also called the methyl ether of hydroquinone. This inhibitor is effective only in the presence of oxygen. A mechanism has been proposed, and is illustrated in Scheme 13 [128]. 

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