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The use of liquid colorants lowers material costs due to lower letdown ratios. Less liquid colorant is required to achieve the same final color as pelletized or powdered colorants, since liquid colorants generally disperse easier in the melt stage of processing, than solid colorants. Liquid color is commonly used in tinted clear resins and translucent parts; and opaque parts with letdown ratios of less than 2.0%.

Components associated with liquid color dosing equipment:

• Delivery vessel for liquid color: Since this vessel will be ‘tapped’ for removing the liquid color, it is an important element of the process and typically remains on the production floor, near the process. Common sizes are full sized poly drums as well as 5 gallon containers.
• Pickup lance or wand: This is inserted into the supply vessel by the user, the wand sucks the colorant from the drum when called upon by the pumping system.
• Color pump: A peristaltic, or roller pump, is the standard positive displacement pump used for pumping liquid colorants. The colorant is drawn from the storage container into a flexible tube fitted inside a circular pump casing, which can be located on the drum, in between, or on the machine throat, depending upon the manufacturer. A rotor with a number of "rollers" rotates and compresses the flexible tube. The part of tube under compression closes (or "occludes") forcing the colorant to move through the tube at the time and rate selected on the metering or blending controller.

A new style of pump, recently introduced, uses a compressed air controlled diaphragm to move the liquid colorant. This type of pump is installed directly onto the delivery vessel for maximum cleanliness and precludes the need to ‘tap’ the vessel when starting the coloring process. The pump is pre-installed onto the drum by the liquid colorant supplier, significantly improving cleanliness.

• Metering control: Metering can include at-the-throat units that fit below the standard material supply hopper and work in conjunction with the molding cycles of the processing machine. In these applications, the metering control is coordinated with molding machine operation to feed colorant for a specific duration at a specific time in the machine cycle for proper let-down. The liquid color may also be fed to a multi-component automatic blender to be combined with other materials into a common blend.
• Throat adaptor: When at the throat metering is to be utilized, a nozzle for the introduction of the liquid colorant into the material stream is installed below the material supply hopper on the machine. This component is not required when the metering equipment will be installed on a blender. In this instance the blender is equipped with a liquid color nozzle for connection to the pump.

Liquid Color Sources/Delivery

In the past, liquid color has been often thought of as difficult to handle prior to processing, it is still widely used in various industries due to its unique properties. Recently introduced methods for delivery of the colorant to processors, have brought higher levels of convenience, cleanliness and eco-consciousness.

Traditional Delivery Methods

Traditional delivery methods for color concentrate are typical liquid vessels including poly barrels and smaller quantities in 5 gallon containers. When delivered in this manner, the user provides a pump for pulling the colorant from the supply drum and metering it into the process. Metering can include at-the-throat units that fit below the standard material supply hopper and work in conjunction with the molding cycles of the processing machine. In these applications, the liquid pump control is coordinated with molding machine operation to feed colorant for a specific duration at a specific time in the machine cycle for proper let-down. The liquid color may also be fed to a multi-component automatic blender to be combined with other materials into a common blend.

A peristaltic, or roller pump, is the standard positive displacement pump used for pumping liquid colorants. The colorant is drawn from the storage container into a flexible tube fitted inside a circular pump casing. A rotor with a number of "rollers" rotates and compresses the flexible tube. The part of tube under compression closes (or "occludes") forcing the colorant to move through the tube at the time and rate selected on the metering or blending controller.

When using traditional delivery methods, the user is responsible for connecting their pump to the delivery vessel and then, when the vessel is empty, retrieving the siphoning tube in the cleanest possible way. Preventing spills, dribbles, contamination and fully emptying the supply drum are issues traditionally associated with liquid coloring.

New Liquid Color Delivery and Cleanliness

New methods for the delivery and pumping of liquid color have reignited this thought-to-be-messy coloring method. The concept is based upon maximizing the user’s efficiency and cleanliness by placing a pumping system into a proprietary drum which is initially delivered by the liquid colorant manufacturer and then replaced as needed. The unique diaphragm pumping system maximizes the draining of each barrel by the use of a pump made specifically for that barrel (or other vessel).

With each delivery, the user is provided with another liquid pump, built right into the delivery vessel (drum). If metering at the throat, the user is equipped with a mating control (which stays on site) so each new drum may be simply connected to the control, and turned on for reliable, consistent liquid metering with no need to ever actually touch or otherwise deal with the colorant. The proprietary control is easily set for the metering let-down ratio, or the pump/metering system may be connected to a batch blender as an additional ingredient for the blend.

The system not only delivers liquid color in a convenient and clean way, but is also eco-friendly, by eliminating the waste associated with empty color delivery containers. Each container (with its on-board pump) is recycled back to the supplier for re-use.