Taking a fresh look at LIQUID COLORANTS
Canadian PlasticsResearch & Development Plastics: Design Plastics: Technology Advances
All plastics processors out there who don’t want to gain a competitive advantage, raise your hands. Nobody, right? Well, interest in one such solution is spiking right now: a growing number of processors are considering liquid colorants...
All plastics processors out there who don’t want to gain a competitive advantage, raise your hands. Nobody, right? Well, interest in one such solution is spiking right now: a growing number of processors are considering liquid colorants to take advantage of their potential 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 and no drawbacks? Is liquid color the right solution for every application?
First, a backgrounder. 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 achieves the best color dispersion possible while increasing shelf stability.
The use of liquid color concentrate requires equipment 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. “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 with Vortex Liquid Color.
And no matter which type of production method is used to make them, 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 product development and operations with ColorMatrix Group. How accurate? “Our proprietary liquid dosing systems allow for careful dosing control, to levels as low as 0.001 per cent accuracy,” she added.
The liquid also lends itself to dispersion within the base polymer more effectively than other forms of color, enabling processors to achieve excellent 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 concentrate 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 said. “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: cost. “Liquid colorant pricing isn’t tied to resin swings,” Cooke continued. “Resin is at over 80 per cent global capacity utilization, which is pushing resin and concentrates 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, meaning that there’s no penalty for buying smaller quantities as there usually is with masterbatch.”
The end result can be a great looking part. “Liquid typically has more gloss, especially for bright colors, and the gloss becomes part of the finished matrix,” Cooke said. “It also has less heat history on it, which also gives a bigger bang out of your regrind because it hasn’t been diluted as much.”
But despite some big steps forward in the 20 years since liquid colorants were first developed, 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 is becoming less of an issue all the time, 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,” George 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 buy at the local hardware store, there’s almost always residual colorant left in the container that most metering equipment is unable to extract. Depending on the equipment being used, this residual material can represent up to 10 per cent of the total volume of color – which makes for a huge potential for wasted material. 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 physically lifting bulky and awkward containers. A second involves cutting a deal with your supplier. “In some instances, we can give a net credit for whatever residual is left and there is no waste whatsoever,” said George Cooke.
And with today’s increased regulatory environment, disposal of the spent containers might not be easy either. Depending upon the local jurisdiction of your plant, liquid colorant can be considered hazardous material with all of the associated additional costs to dispose of it in a lawful manner. Even if the colorant isn’t considered hazardous, many waste haulers will not handle it, or 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.”
Filmmakers aside, companies wanting to make the move from pellets and concentrates to liquid colorants might find it well worth the hassles. “If a processor is switching from solid to liquid colorants systems, they will 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 the their machines,” said Bjoern Klaas. “These would be important but not onerous considerations. In the long term, the changes required to switch are generally quickly off-set by the benefits of utilizing liquid systems.”