Electroplating on crystalline polypropylene. II. Injection molding and adhesion

Abstract

SynopsisThis paper describes the effect of injection molding conditions (melt temperature, mold temperature, and fill time) and etch conditions on metal adhesion in electroplated isotactic polypropylene (PP). It is found that injection molding PP homopolymer produces a lamellar surface morphology which can consistently develop after-plated peel strengths of 30 lb/in or better as measured by the Jacquet peel test. Surface etching of PP homopolymer prior to plating develops crack patterns characteristic of injection molding; a directional crack pattern is always evident in specimen surfaces crystallized under shear. The surface pattern is developed in the oxidative process by swelling of amorphous material, followed by oxidative dissolution and oxidative stress cracking. Additionally, the depth and number of the surface cracks is a function of the solvent swell and acid etch times. Crack depth increases in lamellar surfaces as the sample immersion times are increased; however, as crack depth increases, crack density decreases.Metal-to-polymer adhesion, as measured by the peel test, represents a balance between crack depth and diminished surface strength incurred in the oxidative cracking process. Although peel adhesion usually increases with crack depth, overetching may actually reduce adhesion even though the crack depth has been increased. Any advantage from deeper cracks may, therefore, be offset by a loss in the surface strength of the polymer. Comparison of the surface and cross-sectional crack patterns in TiOZ-filled PP indicates that the surface morphology is similar to that of unfilled polymer. Molding conditions that produce the desired morphology are important for high peel adhesion values but appear to be less critical than in unfilled PP. A propyleneet,hylene copolymer (90/10) developed 12-15 lb/in. peel adhesion-50% lower than for the filled and unfilled homopolymer when molded under similar conditions; peel adhesion in this composite system is, however, relatively insensitive to changes in molding conditions. Aging of 2-3 weeks after plating is required for maximum peel adhesion in all samples studied.

Effect of Chain Extender on Phase Mixing and Coating Properties of Polyurethane Ureas

“…Since the substrate-induced crystallites constitute the interfacial area between the two materials, their characteristics affect the adhesion of the coating to the substrate. [10][11][12][13][14][15] Of equal importance is the preparation of surfaces and its nature, the coating application process, and, very often, the environmental conditions during application and drying of the coating. 16,17 Chatterjee et al 18 suggested that a substrate may have active sites such as cracks or fissures that increase the bonding of the polymer to the substrate at these sites.…”

“…When such material cures on a solid surface, heterogeneous nucleation at a plethora of nucleation sites, such as defects, craters, fewer, crevice, hills, and contaminants on the substrate surface, may take place. Since the substrate-induced crystallites constitute the interfacial area between the two materials, their characteristics affect the adhesion of the coating to the substrate. − Of equal importance is the preparation of surfaces and its nature, the coating application process, and, very often, the environmental conditions during application and drying of the coating. , Chatterjee et al suggested that a substrate may have active sites such as cracks or fissures that increase the bonding of the polymer to the substrate at these sites. Cui et al reported that the difference in adhesion development and moisture diffusion rate in isocyanate reactive hot melt adhesives is owed to a difference in crystalline structure.…”

Tailoring the surface morphology of polyimide for improved adhesion

“…The rms roughness for PMDA-ODA is measured to be less than 1 nm for a typical film cured to 400°C using a standard thermal cycle [31]. Surface roughness in the 10~' to 10"-/im range is reported to enhance (mechanical) adhesion between polymers, such as i-PP, acrylonitrile-butadiene-styrene, high-density polyethylene (HDPE), and metals such as nickel, copper, and aluminum [11][12][13][32][33][34]. Improved adhesion on a roughened surface is due to mechanical interlocking and an increased surface area at the interface.…”

“…A metal can be electrolessly plated onto a rough polymer surface using palladium as a seed [12,13], or the polymer may be deposited by melt (or solution) processing onto a roughened metal surface [11,33]. The roughness in semicrystalline polymers such as i-PP, HDPE, and nylon is achieved by relying on a differential rate of etching of crystalUne and amorphous regions [12,13,34]. Polymer/metal adhesion improves as the size of the surface features decreases from a l-fim to a OA-fim scale [35].…”

“…Simply modifying the surface topography [11][12][13] is not sufficient to improve adhesion, since polymer morphology (features 2 and 3, above) also plays an important role. These morphological attributes were previously reported, as mentioned below, but their relation to poor adhesion was not appreciated.…”