Metalized fluoroplastics

A number of companies offer metallized fluoroplastic films. For example, Sheldahl Corp. provides a family of metallized FEP films as shown in Table 14.13. WL Gore markets a metallized film, based on its Gore-Tex film, which is selectively image-metallized and has a continuous metal phase in the direction of the z-axis (thickness). Crane Polyflonmarkets electroplated PTFE shaped articles for applications such as micro-wave communications and magnetic resonance imaging (MRI).[129]... 

The construction materials for the plates include most corrosion-resistant metals, usually 304SS, 316SS, titanium, Incoloy 825 , Hastelloy , and others, plus nonmetallic fused graphite, and fluoroplastic Diabon F . Typical gaskets between the plates include nitrile rubber, butyl, and EPDM elastromers, Hypalon and Viton , based on the various manufacturers literature. 

Examples of external lubricants are metal soaps, paraffin waxes, silicones and fluoroplastics. 

Chemical etching requires immersion of the part into a bath for a period of time, then rinsing and drying. This process is more expensive than most other surface treatments, such as flame treatment, thus it is used when other methods are not sufficiently effective. Fluoroplastics are often etched chemically because they do not respond to other treatments, ABS are usually etched for metallic plating, and so on. 

Combination of metal to be deposited with water repellent powder. In composite plating, the characteristics of particles to be codeposited are the most important. Water repellent fluoroplastic powder represented by Polytetrafluoro-ethylene (PTFE) has various unique and interesting characteristics such as non-adhesiveness, self-lubricity and chemical resistance, as well as water repellency. Incorporation of such powder into the composite plating would give a surface with quite different characteristics from those obtained by conventional surface treatments. Representative water repellent powders used in this study of composite plating are graphite fluoride [(CF) ] and PTFE. 

This property is an important consideration in the design of parts from fluoroplastics because they deform substantially over time when subjected to load. Metals similarly deform at elevated temperatures. Creep (also called cold flow) is defined as the total deformation under stress after a period of time, beyond the instantaneous deformation upon the application of load. Significant variables that affect creep are chemical structure of resin, load, time under load, and temperature. Creep is measured under various conditions tensile, compressive, and torsional. 

In another example, ] a problem with poor physical properties of molded fluoroplastics was overcome. Transfer molded material was found to have low modulus of elasticity above 150°C and was prone to irreversible cold flow. The solution involved embedding a metal or plastic insert as a core material in the mold. The choice of the core material depended on the end use performance requirements. 

Wear resistance of the polyacetal-metal friction pair can be improved considerably by the introduction of higher fat acids or realizing their S3mthesis conditions in the friction zone. Passivation of metal surface layers by phos-phating formulations and epilamens may elevate wear resistance of friction bodies in which polyacetal, polyamide, fluoroplastics, and other substances rub against copper alloys, aluminum, chrome or titanium [108,117,118]. 

In general, rigid plastics are superior to elastomers in radiation resistance but are inferior to metals and ceramics. Examples of materials, which will respond satisfactorily in the range of 10 and 10 erg per gram, are fluoroplastics, glass fiber-filled phenolics, certain epoxies, polyurethane, polystyrene, mineral-filled polyesters, silicone, and fiirane resins. The next group of resins in order of radiation resistance includes polyethylene, melamine, urea formaldehyde resins, unfilled phenolic, and silicone resins. Those materials, which have poor radiation resistance, include methyl methacrylate, imfilled polyesters, cellulosics, polyamides, and fluorocarbons (Tables 9.16 and 9.17). 

The effect of the sohd body surface on the structure of the polymer boimdary layers has been considered in detail in a great number of pubhcations and we wiU not consider this issue in detail. We point out only that a number of pubhcations have reported correlation between the structure of the boimdary layer and the adhesion strength for couples such as metal—polycaproamide coating [33], fluoroplastic— steel [34], and epoxy rubber polymers-metals [35]. 

One of the principal reasons for failure of the adhesion bonds is a specific adsorption reaction of the medium with the material to be cemented at the boundary with the adhesive. There is an adsorption substitution of adhesive-substrate bonds by medium-substrate bonds. Surface structural defects that are present in each solid are the first to be subjected to adsorption. It is to be expected that the probability of appearance of such defects is higher at an interface of two materials with different properties. The rate of penetration of the medium along the polymer-substrate interface frequently substantially exceeds the rate of diffusion of the medium in pure polymer [212]. Adsorption substitution of the polymer macromolecules by water molecules on the metal surface explains the low water resistance of such adhesive-bonded joints as fluoroplastic-steel or polyethylene-steel [34]. The adhesion strength, which decreases during hold-up of adhesive-bonded joints in water, is frequently reestablished after the joints are dried [213]. 

Antiblocking agents can be applied externally or internally and include such materials as waxes, metallic salts, fatty adds, fumed siUcas, and even other plastics (e.g., polyvinyl alcohol, polysiloxanes, and fluoroplastics). Silicates and silicas can... 

One aspect of eluent compatibility with EC detection is that there should be no effect on the components of the detector. Detector cell bodies are now routinely constructed of PTFE, other fluoroplastics, glass or stainless steel, and seem stable to most eluents. Nevertheless electrodes are vulnerable to chemical attack. Problems with the longer term use of some eluents at potentials around +1 V vs Ag/AgCl have been experienced. For example, ammonium acetate buffers have caused flaking of the surface of glassy carbon electrodes held at as little as +0.1 V for one batch of electrodes. Noble metal electrodes are easily contaminated by a number of eluents unless the electrode is cleaned by pulsing the applied voltage as in carbohydrate analysis (Chapter 3, Section 6). 

Fluoroplastics have been used as wire coatings in military and aerospace applications since their discovery. They have also found their way into wire and cable applications that required extreme performance based on thermal extremes (cryogenic and high temperature applications), chemical resistance, etc., but the major market expansion in fluoroplastic use in the wire and cable industry occurred in North America when the National Electric Code (NEC) allowed polymers with low smoke-generation and flame-spread to be installed in building plenums without metal conduits. 

The adiabatic combustion temperature of Ti/PTFE is depicted in Figure 5.15. Tarasov has investigated the reactivity of a special titanium aUoy (87% Ti rest aluminium and transition metals Cr, Fe, Cd, Mo and Ta) towards Fluoroplast -42 [21]. The DSC shows a distinct onset of an exothermal reaction at 345 °C (Figure 5.16). 

Rotational molding (Fig. 9.1) involves the external heating of a thin-walled hollow metal mold containing a polymer powder. Heating occurs while the mold is rotated multiaxially. The powder melts and coats, or sinters, onto the interior wall of the cavity. The mold is then cooled which allows the part to solidify and crystallize in the case of fluoroplastics. Finally, the part is removed and the mold is charged to repeat the cycle. 

In another example,1 1 a problem with poor physical properties of molded fluoroplastics was overcome. Transfer molded material was found to have low modulus of elasticity above 150°C and prone to irreversible cold flow. The solution involved embedding a metal or plastic insert as a core material in the mold. The choice of the core material depended on the end use performance requirements. An engineering plastic core was found preferable examples included polyetherether ketone (PEEK), polyphenylene sulfide (PPS), and polyether imide (PEI). Polytetrafluoroethylene bearers were placed in the mold to keep the core material away from the walls of the mold. No special cavity modifications were required. Any hot-melt fluoroplastic could be molded surrounding the insert examples include PVDF, FEP, ETFE, PFA, ECTFE, and PCTFE. 

Other than poor thermal conductivity, fluoroplastics have much higher coefficients of linear thermal expansion than metals. This means that any type of heat buildup will cause significant expansion of the part at that point resulting in over-cuts or undercuts, thus deviating from the desired part design. 

Surface preparation of fluoroplastics can be achieved by a number of methods.h i] The plastic surface can be roughened by blasting with water. Other methods include corona bombardment, cross-linking by activated inert gas species, molten metal alloy treatment, sodium hydride treatment, and sodium etching. The treated layer is at most 1 pm thick and does not alter the bulk properties of the fluoroplastic. Surface... 

Fluoroplastic films such as FEP can be metallized by vacuum deposition. Metal adhesion is enhanced if the surface has been treated for adhesion by sodium etching or other procedures. Untreated general purpose FEP film may be vacuum-metallized for some applications depending upon the specific metal and deposition process. Copper, aluminum, silver, gold, and some metallic oxides have been applied to FEP film by vacuum metallization.f ]... 

Encapsulation of metal parts can be easily achieved with fluoroplastics. These parts are used in applications where extreme mechanical integrity and rigidity combined with chemical resistance are required such as butterfly valves. 

Fluid handling systems and ultra-purity water (UPW) systems are flushed with UPW, acids, or bases to extract ions and remove the loose particles from surfaces. Diluted hydrofluoric acid is effective in leaching out metals from fluoroplastics. Ultra pure water removes anions and particles. It is not unusual to flush a system with several hundred liters of water. 

In the remainder of this seetion, examples of impurity data for different fluoropolymers are listed. An important aspect of these measurements is the detection limit of each technique when measured by ICP-MS, of whieh examples are shown in Tables 15.10 and 15.11. Deteetion limit to less than 100 ppt (part per trillion, or 1 in 10 ) and part per quadrillion (1 in 10 ) is being diseussed as a near future need. Current detection limits for leaching metals from fluoroplastics resins, in a mixture of 80% by volume hydrofluoric acid (49% by weight solution in water) and 20% by volume /-propanol, are summarized in Table 15.11. 

Table 15.15. Effect of Two Consecutive Extractions (16 hours each) on Metal Extraction (10% HCI) Results of a Fluoroplastic Filter...

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