Adhesion fluorocarbon polymers

If silica particles are anchored to or embedded in a surface, the submicroscopic roughness and polarity of the surface are increased and adhesion of a second material is generally improved on the other hand, if the silica is present as a loose, friable coating, or is applied as a mixture with a silicone or fluorocarbon polymer, adhesion is reduced. 

In this paper, we report the studies on the adhesion between metals and fluorocarbon polymer films. Fluorocarbon polymer has a dielectric constant of 2.1, lower than that of polyimide, 3.2-3.5, and is attractive to packaging. We have studied the adhesion of Cu to bulk Teflon, a polytetrafluoroethylene (PTFE) polymer, and found enhanced adhesion using a presputtering treatment of the Teflon prior to the deposition of Cu (4). Further analysis shows that the morphological changes of the Teflon due to the sputtering treatment could be a major contributor to the enhanced adhesion observed (5). 

In summary, several fluorocarbon polymer films are compared for their adhesion to metals. A strong adhesion, as measured by the peel strength, is obtained for Ti and Cr bonding to the polymers with a high concentration of carbon atoms with three fluorine neighbors. 

Adhesion of metals to polymers has been an intensively studied subject over the past decades This is due to the wide application of polymers to electronic packaging and, to a lesser extent, to device inter-connect The increasing demand in density for devices and speed for packaging, in turn, prompts searches for polymers with reduced dielectric constants than that of the widely used polyimide. Some fluorocarbon polymers, notably Teflon, have lower dielectric constants, 2.1, vis-i-vi the values of 3.0-3.5 for polyimides. The fluorocarbon polymers, however, have very weak adhesion to metals. An enhancement in adhesion is thus a primary requirement for the application of such polymers to technologies. A wide range of studies have been made in the past to understand and enhance the adhesion between metals and fluorocarbon polymers In this paper we review some of our earlier work, and present new observations related to the enhanced adhesion between metals and fluorocaiton polymers. We present results address three contributions to enhanced adhesion between metals and fluorocarbon polymers chemical, mechanical, and thermal. 

The thermal treatments of the metal/fluorocarbon polymer systems show both stable structures and enhanced peel strengths. Such information is important to the application of fluorocarbon polymers to the packaging uses. Differently enhanced adhesion is noted for samples using mixed polymers, which may serve further purposes to technologies depending on the specific uses. 

Other related articles are as follows Contact angles and interfacial tension. Infrared spectroscopy. Pre-treatment of fluorocarbon polymers. Primers for adhesive bondii. Roughness of surfaces. Surface analysis. 

Silica particles are embedded into the surface of polyethylene Him to improve the adhesion of coatings of thermoplastic polymers (595). A fluorocarbon polymer surface is made cementable by coating it with the mixture of dispersed polytetrafluo-roethylene and colloidal silica, and heating the surface to over 500°C for a few minutes (596). On glassine paper used to separate uncured sheets of rubber, adhesion is needed on one surface but not on the other. One side of the paper is treated with 0.04-0.6 lb of colloidal silica per 1000 ft so that rubber sheeting will stick only to the treated surface when stored as a roll (597). 

Polyolefins and fluorocarbon polymers have low values of 7 and are said to have low energy surfaces these materials are difficult to wet and bond. Metals, ceramics and polar polymers have high value of 7 (high energy surfaces), can be readily wet by many organic adhesives, and exhibit good bondability. 

Low surface energy solids such as polyolefins and fluorocarbon polymers are difficult to bond with conventional polar adhesives. Various methods have been developed to modify their surfaces to overcome this problem. Common to all of them is surface oxidation. 

Simple abrasion is usually a very poor surface treatment for fluorocarbon polymers. This may be seen from the results shown in Table 4.2 where joint strengths for PTFE and PCTFE, bonded using an epoxy-polyamide adhesive, are given and the fluorocarbons have been pretreated by either abrasion or a... 

Like the fluorocarbon polymers discussed above, polyolefins such as low- and high-density polyethylene, polypropylene and poly (4-methyl 1-pentene) cannot usually be joined by adhesives to give reproducible high strengths unless some form of surface pretreatment is first employed. 

As mentioned earlier, other plastics such as poly(vinyl chloride), poly (ethylene terephthalate), polyacetals, nylons and polyimides do not present such a severe problem to the adhesives technologist as do fluorocarbon polymers or polyolefins. Nevertheless, in order to obtain very high joint strengths approaching the cohesive strength of the substrate, some form of surface pretreatment is often necessary. 

The primers given in Table 4.18 were also shown to be effective when bonding copper with other adhesives and to polymeric films, such as fluorocarbon polymers, polyolefins, polyester and polyamides, to produce laminates. 

Sealants, while sharing many similarities with adhesives, tend to be made from different materials and include those based on polysulfides (often for uses in contact with fuel), silicones, polyurethanes, acrylics in both solvent-based and latex-based materials, and sealants based on butyl and fluorocarbon polymers. In addition to adhesive and sealant types, this chapter reviews methods for testing and qualifying these materials. 

Liquid or solid films which reduce or prevent adhesion between surfaces solid-solid, solid-paste, solid-liquid. Waxes, metallic soaps, glycerides (particularly stearates), polyvinyl alcohol, polyethene, silicones, and fluorocarbons are all used as abherents in metal, rubber, food, polymer, paper and glass processing. 

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