Making a Mark with Liquid Colorant
They're not exactly new, but liquid colorants are growing more popular with processors looking for a competitive advantage. They can offer more economical letdown ratios and work especially well with heat-sensitive materials. But are they right for you?
October 1, 2012 by Mark Stephen, editor
Any plastics processor out there who doesn’t want to gain a competitive advantage, raise your hand. Nobody, right? Well, interest in one potential advantage is on the rise: A growing number of molders are considering liquid colorants as a way to improve overall production efficiencies while reducing the total coloring cost.
Yes, we know — liquid colors have seen their popularity rise before, which means you’ve probably heard the hype. But what’s the reality? Are liquid color concentrates really a win-win solution — all upside, no downside? Is liquid color the right solution for every application?
Before trying to answer that, here’s a quick backgrounder. First brought to market 20-odd years ago, liquid color concentrates are free-flowing pre-dispersions of pigments in carriers that are compatible with the base resin being processed. They are most commonly produced using one of two methods. First, by mixing base pigments in a liquid carrier with a high-speed mixer to achieve the desired color. Additives are often used to minimize the tendency of the pigment to settle out of suspension; the suspension may also require agitation just prior to use to ensure good color consistency in production. The second method involves milling or breaking down the pigments to very fine particles, then dispersing the color into the liquid carrier. This method is recommended when working with organic colorants, and is said to achieve the best color dispersion possible while increasing shelf stability.
The use of liquid color concentrates requires technology to meter and pump the material from its storage container into the process to be mixed with the resin material. There are various ways to accomplish this, ranging from simple volumetric systems using peristaltic pumps to more sophisticated and highly accurate gravimetric systems employing computer-controlled metering. A downside? The equipment to do the metering and pumping, which you probably don’t have. “Whatever method is used, it’s important to note that liquid color will require additional equipment to deploy the liquid into your system,” said George Cooke, vice president of sales for Vortex Liquid Color.
The bite for the new equipment aside, liquid color concentrates offer several advantages over other coloring options. “Because of the physical properties of a liquid, volumetric liquid systems are inherently more accurate than the gravimetric systems typically used for solid colorants,” said Bjoern Klaas, director of new product and technology development for ColorMatrix Group. How accurate? “Our proprietary liquid dosing systems allow for careful dosing control, to levels as low as 0.001 per cent accuracy,” he said.
The liquid also lends itself to dispersion within the base polymer more effectively than other forms of color, enabling processors to achieve good color dispersion throughout their finished products.
And from the machine operating perspective, there’s an added benefit. “In some cases, the easy mixing can lead to lower back pressure and lower cycle times to get a homogenous mix for injection molding or extrusion,” said George Cooke.
You might also need less liquid than pellets or powdered mixtures to achieve comparable results. “Liquid color can be loaded much higher than masterbatch. We can run liquid colorants at 0.02 per cent to 0.05 per cent, whereas masterbatch typically runs at two per cent,” Cooke continued. “This translates into higher letdown ratios for a given application and can provide a processor with great efficiencies in the coloring operation.” Even with heat-sensitive materials? “The fact that liquid does not require melting prior to mixing with the resin is especially advantageous when working with heat-sensitive resins,” said Bjoern Klaas.
And here’s a benefit not to be overlooked in today’s brave new world of bean counters: cost. “Liquid colorant pricing isn’t tied to resin swings,” George Cooke said. “Resin is at over 80 per cent global capacity utilization, which is pushing the prices up. Liquid color is independent of that, and therefore more stable in pricing over the long term. Also, some liquid producers have flat pricing, which means there’s no penalty for buying in smaller quantities, as there usually is with masterbatch.”
And from the finished-appearance standpoint, the results are usually the runway models of plastics parts. “Liquid typically has more gloss, especially for bright colors, and that gloss becomes part of the finished matrix,” Cooke said. “And it has less heat history on it, which also gives you a bigger bang out of your regrind because it hasn’t been diluted as much.”
But despite big strides forward in the two decades that liquid colorants have been on the scene, some challenges remain. In some applications, for example, the liquid carrier may bloom to the surface if not completely compatible with the base resin; or if they’re past their shelf life, the potential exists for the pigments to fall out of suspension, leading to inconsistent coloring. This last point has become less of an issue recently, however. “In the past, shelf life was a concern because a lot of the liquid manufacturers relied on the customer to finish developing the color,” Cooke said. “Today’s liquid color companies provide a more complete development of the product.”
Handling the material can be a concern, too. As with that can of paint you bought at the local hardware store, there’s almost always some residual colorant left in the container that most metering equipment is unable to extract. Depending on the equipment being used, this material can represent up to 10 per cent of the total volume of color — which makes for a lot of waste. But it doesn’t have to be that way. One method to extract as much as possible involves combining unused colorant with fresh containers of material — it works, but it’s not exactly labor-free, often involving someone physically lifting bulky and awkward containers. A second involves cutting a deal with your supplier. “In some instances, we can give the customer a net credit for residual material,” Cooke said.
And with today’s increased regulatory environment, disposal of the spent containers might not be easy. Depending upon the local jurisdiction of your plant, liquid colorant can be considered hazardous material, with all of the associated costs and headaches to dispose of it in a lawful manner. And even if the colorant isn’t considered hazardous, many waste haulers won’t touch it, or will do so only for an additional cost.
Lastly, there are some applications that liquid colorants just aren’t right for, period. “One processing area that we’ve been trying to get into for years is film,” Cooke said. “The difficulty is that the film is so thin and the liquid can be too slippery, causing the film to extrude improperly and even breaking the bubble and shutting down the line. It’s an issue that we’re still working to solve.”
Film manufacturers aside, companies wanting to make the move from pellets and powders to liquid colorants might find it well worth the hassles. “If a processor is switching from solids to liquid colorants systems, they’ll need to consider a number of change factors, primarily around handling and operational procedures for dosing liquids, managing inventory status, and matching new colors on their machines,” said Bjoern Klaas. “These would be important, but not onerous, considerations. In the long term, the changes required to switch are generally offset very quickly by the benefits.”
ColorMatrix Group (Cleveland, Ohio);
Vortex Liquid Color (Sheboygan, Wis.);