Between layer adhesion

One of the practical remedies used to reduce blocking is to cover blocking substances with a layer which prevents blocking. This method is frequently used in plasticized PVC in which plasticizer migration causes between-layer-adhesion. This adhesion can be easily eliminated by kiss-coating with lacquers (e.g., films, coated fabrics, etc.)."... 

Reduced adhesion to other materials, deterioration of between layers adhesion, effect on paintability are all influenced by the presence of additives on surface. Still, only a limited data were published so far. 

Adhesion between layers of plastic sheets in contact condition arises during storage or use when components are under pressure. 

Additional drawbacks to the use of polyimide insulators for the fabrication of multilevel structures include self- or auto-adhesion. It has been demonstrated that the interfacial strength of polyimide layers sequentially cast and cured depends on the interdiffusion between layers, which in turn depends on the cure time and temperature for both the first layer (Tj) and the combined first and second layers (T2) [3]. In this work, it was shown that unusually high diffusion distances ( 200 nm) were required to achieve bulk strength [3]. For T2 > Tj, the adhesion decreased with increasing T. However, for T2 < Tj and Tj 400 °C, the adhesion between the layers was poor irrespective of T2. Consequently, it is of interest to combine the desirable characteristics of polyimide with other materials in such a way as to produce a low stress, low dielectric constant, self-adhering material with the desirable processabiHty and mechanical properties of polyimide. 

The two predominant mechanisms of failure in adhesively bonded joints are adhesive failure or cohesive failure. Adhesive failure is the interfacial failure between the adhesive and one of the adherends. It indicates a weak boundary layer, often caused by improper surface preparation or adhesive choice. Cohesive failure is the internal failure of either the adhesive or, rarely, one of the adherends. 

Priming is the process of applying a dilute solution of the adhesive mixed with an organic solvent on the adherend to a dried film thickness between 0.0015 and 0.005 mm (0.00006 to 0.002 in). Priming protects the surface from oxidation, improves wetting, helps prevent adhesive peeling, and serves as a barrier layer to prevent undesirable reactions between the adhesive and the adherent. 

Even if pigments are completely stable to wet treatments, there is the potential for starch adhesive joins and fills adhered with starch to give way. In addition, delaminations between layers may also occur, or increase if already present. It has also been observed that tapa may decrease in strength while wet, and can be stretched and distorted if not carefully supported. 

The main difference between primers and adhesion promoters is that primers are liquids that are applied to the substrate as a relatively heavy surface coating prior to application of the adhesive. Adhesion promoters, on the other hand, are liquids that form a very thin (usually monomolecular) layer between the substrate and the adhesive. Usually chemical bonds are formed (1) between the adhesion promoter and the adhesive and (2) between the adhesion promoter and the substrate surface. These bonds are stronger than the internal chemical bonds within the adhesive. These new bonds also provide an interface region that is more resistant to chemical attack from the environment. Adhesion promoters are also sometimes referred to as coupling agents. 

Metal thin films deposited on polymers are widely used in various industrial domains such as microelectronics (capacitors), magnetic recording, packaging, etc. Despite much attention that has been paid in the recent literature on the adhesive properties of metals films on polyimide (PI)( 1 - 5 ) and polyethyleneterephtalate (PET)((L) it appears that a better knowledge of the metal/polymer interface is needed. In this paper we focus ourself on the relationship between the adhesion and the structural properties of the aluminum films evaporated (or sputtered) on commercial bi-axially stretched PET (Du Pont de Nemours (Luxembourg) S.A.). A variety of treatment (corona, fluorine,etc.) have been applied in order to improve the adhesion of the metallic layer to the polymer. The crystallographic... 

Fleischauer has carried out a detailed analysis of the electronic structure of molybdenum disulphide. This analysis showed that all the accessible orbital electrons for both molybdenum and sulphur are used in intralaver bonding, leaving only high-energy antibonding orbitals available for bonding between layers or for basal surface adhesion to substrates. There are no accessible orbital electrons on either... 

Laminating adhesive is always behind a barrier film layer. The thickness of this layer, the levels of crystallinity as well as polymer type all influence the migration rates of adhesive components through this layer. The rate of permeation of food or food simulant into the packaging is also controlled by the nature of the food contact layer. Because of the presence of this barrier layer between the adhesive and the food, it is only low molecular weight mobile chemical species that have the potential to contaminate food. 

A potentially important development for the future of biomimetic research was published recently. Using a procedure developed by Whitesides, nucleophiles micropattemed on a gold surface were used as initiators to prepare poly(Y-benzyl-L-glutamate). Thus, an array of poly(amino acid) layers covalently attached to the surface was obtained. These would potentially act as mediators of biomimetic reactions. German workers have described the production of protein-DNA double and triple layers adsorbed on smfaces. Adhesion between layers was provided by biotin-streptavadin interactions and binding was detected by a quartz crystal microbalance. These studies may have some relevance to the understanding of protein DNA interactions at interfaces in biological systems. 

PFM experiments performed with surface-modified tips allow steady imaging of polymer blends with respect to the pull-off forces. Comparing non-modified, hydrophilic tips with modified hydrophobic tips reveals the inversion of the difference between the adhesive forces, indicating even an inversion of the strength of interactions between hydrophilic and hydrophobic polymer surfaces and the SFM tip or silica particles. It could also be shown that the hardness of the silane layer influences the measured pull-off forces. The harder HMDS modification leads to lower adhesive forces, like the softer PDMS modification, confirming the results obtained for toner-silica particles. 

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