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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.

synopsisA direct relationship between polymer processing and metal adhesion is evident from studies of compression-molded isotactic polypropylene (PP). Cooling rate, nature of the mold surface, and after-plated annealing are shown to affect the peel adhesion of the plated components. This report described (1) the relation of compression molding variables to polymer surface morphology, (2) the oxidative cracking behavior of the surface due to pretreatment with chromic-sulfuric acid in terms of crystallite orientation and crystallinity, and (3) the effect of surface crack patterns on adhesion.The nature of the mold surface is the single most important variable for controlling the surface morphology of PP. Compression molding PP against oxidized aluminum or copper produces a spherulitic surface, whereas molding the polymer against Mylar or Teflon produces a transcrystalline surface. Surface etching of PP homopolymer produces sponge-like crack patterns characteristic of the morphology. Radial patterns are observed on spherulitic surfaces and random patterns, on transcrystalline ones. The various surface patterns are developed in the oxidative process by swelling of amorphous material followed by oxidative stress cracking and dissolution. Metal-to-polymer adhesion, as measured by the peel test, may involve failure a t the interface or within the polymer.(a) the geometry of the interface, (b) the diminished strength of the polymer surface arising from attack by the oxidizing acid, and (c) the crystallinity of the fissured polymer surface. The highest peel values are associated with conditions that lead to deep and frequent fissuring of the polymer surface and minimum oxidative damage.

The mechanism of adhesion failure of plated ABS and polypropylene (PP) plastics exposed to service conditions was determined. Adhesion failure, through the formation of blisters, proceeds by a corrosion mechanism which involves (a) the rapid lateral anodic dissolution of the thin electroless nickel layer at the plastic‐metal interface or (b) the relatively slower preferential dissolution of an electroless copper layer and the equally reactive adjacent electrodeposited copper layer. The rate of lateral development of blisters is related to the surface topography of the etched plastic substrate. The high‐density crack patterns and surface roughness of etched PP provide a greater path length for the anodic dissolution of the thin electroless nickel layer— thereby retarding the lateral undercutting more than with a plastic which has a relatively smooth etched surface (ABS). When the less reactive electroless copper is present in a copper‐nickel‐chromium system, the plastic substrate surface topography has no effect on the lateral rate of blister development. The weaker tendency toward blister formation is due to preferential corrosion of the relatively thick, two‐layered copper deposit.

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