Let-down ratio

This is also the time to establish with the customer the desired let-down-ratio the ratio of the colorant system to the polymer (e.g., 25 1, 50 1, 100 1). The first number in the ratio represents the amount of uncolored polymer, the second number the amount of colorant. Let-down-ratios are also expressed in parts per hundred. For example, 1 pph means 1 part of colorant system to 100 parts of uncolored polymer. 

The melt flow test is routinely used as an indicator of whether or not a color concentrate will be adequately distributed throughout the natural in injection molding applications. A simple rule of thumb is to design the melt flow of the concentrate to be about 1.5-2 times higher than that of the natural resin. The assumption is that the colorant will flow slightly faster than the natural and readily blend in with it. At traditional let-down ratios of 20 1 and 25 1, this rule of thumb has served the indus-... 

A film produced by employing the resin concentrate let-down 5 1 embrittled in 22 hr while a commercial product believed to be let-down 50 1 ( ) embrittled with a 112 hr xenon irradiation. A film of the resin concentrate embrittled in 6 hr therefore, variation of the let-down ratio can control and vary the lifetime of the polystyrene during outdoor use. 

While some parts, as a cost-saving measure, could be molded with less color than others, the mixing of several batches with different let-down ratios is generally considered impractical. 

Liquid color contains colorant in a liquid base. It eliminates some of the handling problems associated with dry color, but requires a pump for accurate delivery. The percentage of colorant in the liquid carrier may be quite high so that only a minimal let down ratio (around 1%) is necessary. 

The color concentrates (masterbatches) used for ABS are of the universal or of the ABS-based types. A typical let down ratio (concentration) for the universal type is 1 to 2% whereas a ratio of between 3 to 7% is used for the ABS based master-batch. Before using a universal masterbatch it is important to ascertain it s compatibility with ABS. Pastel shades can now be readily achieved due to the availability of polymers with a lighter (i.e. whiter) base color. Back pressure is often used with masterbatches so as to assist in the dispersion of the pigment within the polymer melt. 

The usual let-down ratio is 10 1 to as high as 30 1. The let-down ratio will depend on the compatibility of the colorant with the polymeric resin, and it will also depend on the L-D ratio of the press or extruder. The higher the L-D ratio, the greater will be the let-down. Other factors that have an influence are the speed of the screw, particularly in an extruder (too fast a screw will lower the let-down ratio), and the temperature profile of the barrel. Increasing the temperature at the feed section slightly is said sometimes to result in a higher let-down ratio. 

Concentrates or masterbatches are consistent, simple, and safe. They usually come in a granular form, in which the concentrated pigment is dispersed in a polymer carrier (such as polyethylene) that is compatible with the matrix resin. The let-down ratio is usually 0.5-2%, depending on colour, host material, and part thickness. 

Additive masterbatches with fragrance have been developed by Clariant Masterbatches. Five flavours are available, initially for use with polyethylene, with let-down ratios of 2-10%. Formulations for other plastics are under development. 

Firex 300C is recognized under the Conqtonent Program of Underwriters Laboratories Inc. for UL 94V-2 Flammability standard covering all colors and all melt flows of Homopolymer Polypropylene in a minimum 1 10 let-down ratio. 

The incorporation of the HDPE resin and the slip additive into the film base resin, at the appropriate let-down ratios, can be done by dryblending in a tumbler mixer, or other suitable vessels. An antioxidant may also be incorporated in the film base resin at a ratio from 0.03 to 0.2 parts by weight per 100 parts of the film base resin. The relatively well-blended mixture can then be extruded and converted into films or bags. After dryblending, as the composition cools down, the HDPE resin will give rise to the formation of larger crystals, which will be uni-... 

A masterbatch is developed using best elastomers from the Dow to control the CLTE and shrinkage of the D143.00 at the injection molding machine. The talc level in the talc masterbatch is maximised to 70-75% talc and only 25-30% masterbatch carrier of a INSiTE type elastomer. This masterbatch carrier allows easy dispersion of the talc at minimum let down ratio (LDR). 

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