Adhesion problems

Thus far, the discussion has dealt with the versatility of urethane adhesives, the wide variety of substrates urethanes can bond, and the infinite variations of one-component and two-component urethanes. Some substrates have posed particular challenges for urethanes. Many adhesion problems have been discussed, but not all can be covered in this brief synopsis. However, two of the more common problems, with possible solutions, will be mentioned. 

Solventless urethanes These are similar to solventless epoxies but can be applied in even thicker films without adhesion problems. They are considered to have better water and abrasion resistance than the epoxy but cost more and application is even more critical. Their main use would be for large areas requiring abrasion resistance. 

So far as iron and steel are concerned, the adhesion problem is simple, and the oleoresinous coatings which are generally applied to them form a good bond with them. Mechanical pretreatments are always extremely useful. 

Bullett, T. R. and Prosser, J. L., Adhesion Problems with Paint and Powder Coalings, Chap. 7, Industrial Adhesion Probiems, Orbitai Press (1985)... 

Although the DMT theory attempts to incorporate distance-dependent surface interactions into the adhesion problem, it does not take into account the effect surface forces have on the elastic deformation. In other words, it does not predict the neck formation predicted by JKR. 

D. M. Brewis and D. Briggs, eds., Industrial Adhesion Problems, Wiley, New York, 1985. 

Polysilicon subtrates are usually encountered during MOS device fabrication for defining gate structures. For submicrometer CMOS processing, adhesion problems encountered with this substrate are even more severe. 

The single ply roof membrane industry uses various rubber-based adhesives to bond the seams at which adjacent rolls of membrane overlap. Since such roofs frequently carry 20-year warranties, maximizing adhesion is always desirable. The adhesion problem is exacerbated in that the membranes used are based on highly... 

The basic concept of the c-BN nucleation by ion-beam-deposition has been described by Weissmantel et al. in 1980 [197, 198]. Adhesion problems and difficulties in analytical characterization have caused large problems. A breakthrough of nano-cBN coatings and their various applications seems to be possible. 

Due to its inert surface, PE suffers from a large number of adhesion problems, which can be overcome by well known surface modification tech-... 

In order to minimize adsorption during standard curve and QC preparations, aliquots of the stock solutions were spiked promptly into the control blank plasma to prepare the standards and QCs. Once the compounds were in an environment of protein solutions, the adsorption problem was alleviated. The de-proteinized extracted samples did not show an adhesion problem, as reflected by the stability data of the extracts. There was very little tailing of the compound peaks, indicating that they were not adhering to the LC-MS/MS system. 

Industrial Adhesion Problems, ed. by D.M. Brews and D. Briggs, Chapter 4, Orbital Press, Oxford, 1985. 

In order make an effort to bring the polyimide-metal adhesion problem to an even more fundamental level, we have previously proposed that model molecules, chosen as representative of selected parts of the polyimide repeat unit, may be used to predict the chemical and electronic structure of interfaces between polyimides and metals (12). Relatively small model molecules can be vapor deposited in situ under UHV conditions to form monolayer films upon atomically clean metal substrates, and detailed information about chemical bonding, charge transfer and molecular orientation can be determined, and even site-specific interactions may be recognized. The result of such studies can also be expected to be relevant in comparison with the results of studies of metal-polymer interfaces. Another very important advantage with this model molecule approach is the possibility to apply a more reliable theoretical analysis to the data, which is very difficult when studying complex polymers such as polyimide. 

Microelectronic device fabrication currently relies primarily upon photoresist processing for integrated circuit pattern delineation. Adhesion of polymeric photoresist patterns, especially those of micron and submicron dimensions, to the required fabrication substrates is of paramount importance. Photoresist image adhesion problems encountered in device fabrication have been solved by chemical interfacial treatments. Current new trends in microelectronic adhesion technology will be described and discussed with emphasis upon the chemical nature of the interface involved as determined by ESCA. 

PPFMs, particularly, Teflon AF and polytetrafluoro ethylene Excellent electrical Properties (Eowest dielectric constant among most polymers < 2) Poor thermal stability Adhesion problems High thermal expansion coefficients... 

The devices are reasonably simple to construct as their dimensions are not critical. Unfortunately the maximum oscillation will occur at the junction of the optical element and the piezoelectric plate. This can cause adhesion problems leading to static strain in the optical element and joint disruption during modulation. 

Figure 30.9. LPCAT treatment under stronger plasma conditions for a longer time yields the more wettable surface. However, the sessile droplet contact angle of a paint on Parylene C surface (resident time 0) is low and minimal change occurred with LTCAT treatment. Thus, the adhesion problem is not due to the wetting difficulty.

Separation of plasma from blood can be used to remove toxic substances with high molecular weights in body fluid which is important in the treatment of many fatal diseases [Nose et al., 1983] and to collect plasma for blood banks to produce plasma fractionates [Dceda et al., 1986]. Organic polymeric membranes with a mean pore diameter finer than 0.5 pm have been employed to some extent for these purposes. However, their wide pore size distributions and protein adhesion problems make their permeate flux quickly decline and their separation efficiency low. In addition, polymeric membranes generally can not withstand sterilization by autoclaves or chemical cleaning. 

Nakasaki et al.146 addressed the tungsten-oxide adhesion problem using reactively sputtered TiN as adhesion layer. A minimum thickness of 100 A TiN was needed for adhesion. 

Brewis, D. M.j Briggs, D., Industrial Adhesion Problems. Orbital Press, 1985. 

Polydimethyltetrafluoropropylmethacrylate (FPM) was actually used for direct fabrication of a 256 kBit RAM with 1 urn design rule (20). FPM shows good adhesion and better dry-etching durability, but the sensitivity was reduced by a factor of 10 compared with FBM (7). Adhesion problems in submicron FBM resist patterns were solved by the copolymerization with a small amount of glycidylmethacrylate, whose homopolymer is actually used as... 

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