more concentrated, more efficient

Thanks to the development efforts of concentrate manufactures and additive suppliers, plastic processors may be able to reduce raw material costs by using more highly loaded color concentrates.

“Most applications that I see in the automotive business can now run at a 50:1 or 2 percent letdown,” reports Dave Graham, technical service representative with concentrate supplier Uniform Color. “This can be achieved as long as the proper equipment and materials are used.”

While 50:1 may be common, 300:1 or even 400:1 is possible in some cases.

“There have been a number of situations, especially with our Color Spheres product, where customers can use up to 300:1 ratios,” reports Jim Cafferty, Teknor Color. “With transparent colors you can go even higher than that.”

The increasingly low letdown ratios are the result of enhancements to pigments, use of better equipment by concentrate formulators, and improved lot-to-lot consistency in the natural base resin. More highly loaded concentrates allow the processor to reduce receiving, handling and warehousing functions. Also, overall material costs are generally lower if a more concentrated product is substituted for a conventional color concentrate. Teknor Color cites savings of 59 percent for its Ultracolor super-concentrate compared with conventional color for medium blue polycarbonate (see table below for details).

“But it is not as simple as pouring in the new color concentrate and saying ‘Okay, now you can use one-quarter as much as you used last week’,” says Dave McDonald, technical manager with Clariant Masterbatches Canada. The processor has to be committed to cost savings through using a more concentrated masterbatch, and may have to investigate tweaking his process or upgrading equipment, says McDonald. “At least half of our customers want to reduce the amount of masterbatch they are using, but at the same time, they are recognizing there are problems in their process that don’t permit the proper distribution of the colorant.”

Worn equipment won’t do

Based on his experience as a technical service representative, Dave Graham has concluded that equipment capability is usually the limiting factor in converting to more highly loaded concentrates.

“A stable process is very important for achieving good quality colored parts. Newer injection molding machines have excellent process control capability, but internal wear in the screw and barrel is detrimental to good mixing.”

“Auxiliary equipment is a big part of why color concentrates can be used at lower percentages now,” he adds. “The use of weigh scale blenders and accurate volumetric feeders ensures the proper amount of concentrate gets to each shot.”

“Since there are fewer color pellets being added to the resin, dispersion of the pellets is the big trick. Good dispersion can be achieved in most injection machines if all conditions are perfect, such as: screw and barrel conditions, proper number of shots in the barrel (3-5), proper heat control and back pressure control. Recharging should be as slow as possible without affecting the cycle time,” Graham advises.

If dispersion is a problem, he suggests a specially designed mixing screw may be an option, albeit a costly one. One of the more cost effective fixes Graham has found is the addition of a static mixing head, such as those produced by Koch-Glitsch, that can be easily installed in place of the injection molding machine nozzle. These mixers can be used for almost all materials and can be replaced with a standard nozzle very quickly.

Dispersion improved with new products

Another option now available from some concentrate suppliers is to have the concentrate produced as micro-beads. At Teknor Color, these smaller beads measure 1/32 in. instead of the more typical 1/16 in. The smaller beads mean there are more pellets to be distributed in the resin. For example, Cafferty says there are about 27,000 beads per pound if the beads measure 1/8 in. each. With 1/32 in. beads, there are about 645,000 beads per pound. However, the smaller beads require a volumetric feeding device to be accurately dispensed.

McDonald reports that Clariant has also performed a lot of research and development aimed at the formulation of the carrier resin to improve mixing and facilitate melting.

“Processors are switching (to more concentrated masterbatches), little by little,” says Cafferty. But volume of colorant usage is also a limiting factor.

“If you only require a small amount of concentrate for a given job, a custom formulation in a super-concentrate will add too much cost,” he explains. “Ideally, you probably need a 500 lb. minimum order before a super-concentrate formulation becomes economical.”CPL

The bottom line on more efficient concentrates

Two examples of the costs associated with conventional color concentrates and Teknor Color’s Ultracolor super-concentrate, calculated for polycarbonate and polypropylene.

All figures in US dollars. Information provided by Teknor Color.

Raw materials developments provide better color

Some credit for lower-letdown concentrates goes to the pigment and additive manufacturers, who have developed new products that directly or indirectly lead to better color with less concentrate.

Day-Glo Color, for example, recently introduced GloPrill daylight fluorescent colorants. New technology has virtually eliminated the problem of plateout at the blow pin and in the mold cavity. This means fluorescent concentrate and masterbatch formulations no longer need additives to control plateout, and the concentrate can contain more colorant.

“In the past, because of the need for processing aids, fluorescent concentrates could contain a maximum colorant loading of 25 to 30 percent,” explains Dennis Reis, marketing manager. “With GloPrill, formulators should be able to bring that colorant loading up to 50 percent without using processing aids.”

The resulting concentrate has a higher loading of colorant, so less is needed to attain the desired effect, and it is more easily processed due to the greatly reduced plateout.

Used as a dispersing aid, waxes can also contribute to improved color strength and dispersion of the pigment in the concentrate. Clariant’s Ceridust micronized waxes have particle sizes from 8.5 to 18 microns, compared with conventional waxes, which can have particles up to 2 mm (2000 microns). During the manufacture of the color concentrate, the smaller particles are more easily distributed, melt more quickly, are more efficient for wetting and coating of the pigment, and act as a “distance keeper” to prevent the pigment particles from agglomerating. The result is better color yield from the pigment, which may allow
concentrate suppliers to substitute some quantity of less expensive pigment to achieve the same color strength. The micronized waxes are more expensive than conventional waxes, but the benefits can outweigh the added cost. Clariant’s Owen Iversen reports that formulators generally get the best value for their dollar by substituting Ceridust at a ratio of 1:2.

BASF Color has enhanced some of its single pigment flushes, making the products easier to disperse. The single pigment flushes contain 50 to 60 percent pigment loadings, and are used mainly in the film and fibres markets. To improve dispersion, the particle size range has been reduced (particles are a more uniform size), and in some cases additives are present to aid dispersion. With BASF’s single pigment flushes, the net result is that concentrate manufacturers will require less energy to disperse the pigment, the potential for formulation inconsistencies is reduced, and the drawbacks associated with handling a powder are eliminated.

Holland Colours Canada has introduced Holcoprill for PVC profiles. The new pigment dispersion contains an average of 50 percent organic pigment or 80 percent inorganic pigment in a low-temperature release point carrier. The melting point is approximately 85C, resulting in excellent distribution into the base compound. It is suitable for dark-colored PVC profiles, using low dosing levels, and has also been used successfully in white opaque PET applications. Holcoprill is a free-flowing, dust-free spherical granule, two mm in diameter, which can be added on-line, via color feeder or in a mixer.