Residues on molds

Interfacial layers were formed on the surfaces of molds used with nitrile butadiene rubber compounds. These layers help to reduce adhesion to mold and remove molded part. Stearic acid is the major component of this layer which was measured to be 6 nm thick on the surface of steel mold. The parting occurs within this interlayer but most of the residue remains on steel. 

Application of UV light for mold surface cleaning was evaluated.  

It is pertinent that this area desires additional woik, results of which may help to base evaluation of problems related to residues of surface active agents on basis of data rather than on limited experimentation being used now. 

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Many more suppHers and information about their product line can be obtained from compilations such as the Modem Plastics Pmyclopedia (1) and the Thomas Register of Mmerican Manufacturers (2). The choice of a release agent depends on the process conditions involved and the nature of the contacting substrates (3). Apart from the obvious ease of release, other important requirements are minimal buildup of residues on mold substrate, minimal effect on the molded article, adequate film-forming abiHty, compatibiHty with secondary operations and other processing parameters, health and safety requirements, and cost. 

OUTSTANDING PROPERTIES low vapor pressure, chemical inertness, leaves no deposit or residue on mold, thermal, chemical shear stability, lubricating action ... 

Stearic acid used as mold release in polyurethane foams was essential in lowering pull-out force (see Figure 10.15). Later analysis did not find residue on mold surface. Stearic acid was also not detected on the part surface, therefore it was assumed that it was absorbed into the bulk of polyurethane. ... 

PDMS is a popular and frequently used elastomer not only because of its cost-effectiveness, but also because of the ease of use and its specific molding characteristics. For instance, PDMS can form conformal contact with a substrate and it can be released again easily from complex or fragile substrates. In addition, due to its low interfacial free energy (ca. 21.6 dyn cm ) and its low reactivity, it does not adhere irreversibly to other substrates such as polymers, silicon, etc. [14,15]. It does, however, bind to photoresist residues on the silicon template. Thus, careful photoresist removal is advised before casting the elastomer on its template. 

Sodium bicarbonate is also used in cleaning products on both a household and industrial level. Many householders use commercial baking soda, such as that sold by the Arm Hammer company, to clean kitchen and bathroom appliances, such as sinks, stoves, and toilet bowls. Industries also use sodium bicarbonate filters to remove sulfur dioxide and other pollutants in flu gases released from factory smokestacks. The compound is also used in the treatment of wastewater to maintain proper acidity, remove certain odors (such as those of sulfur dioxide), and destroy bacteria. Some communities have used aqueous solutions of sodium bicarbonate sprayed at high pressure to remove graffiti paint soot and smoke residues and mold from buildings, walls, and other public structures. 

Potential adverse effects adhesion to hot metal surface, bubbling, increased mold cleaning frequency, lack of adhesion in joining processes, residue on the product surface, transfer to a material in contact, welding impairment... 

In order to work efficiently, the mechanical properties of the layer should be tailored. A thin residual layer reduces the shear stress needed to induce failure, while the use of a brittle polymer allows for a cleaner failure of the layer and, consequently, smoother surface and sidewalls of the final transferred structures than if a ductile polymer is used. The quality of the process depends as well on mold design molds with sharp edges induce failure of the residual layer in a specific location, while molds where protrusions edges are not sharp lead to nonspecific layer failure and, consequently, patterned features with rough edges [31]. 

Figure 10.15 shows data from direct estimation of the effect of release agent on the force required for separation of polyurethane from cold rolled steel.As consistent with other data presented on release forces, the increased coverage by a surface agent reduced the force required for part separation, but only until a certain critical surface coverage is achieved. When this concentration is reached no further changes in pull-out forces are recorded. It was calculated for stearic acid that this critical concentration allows the formation of 17 monolayers on the mold surface. Similar effect of stearate residues on adhesion to the mold was found for nitrile butadiene rubber. ... 

The first step is to coat the mold with a mold release agent so that the cured item can be removed from the mold without damage. Fluorocarbons are preferably used for this purpose although silicones are used when the surface finish is not of primary importance. Silicones leave residues on... 

Uses Biological hard surf, cleaner, odor eliminator, sanitizer for bathroom fixtures, sinks, toilets, drain lines, septic systems, waste treatment facilities Features Degrades residual organics environmentally friendly effective on mold and mildew... 

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