Defining molded color for a cosmetic cap involves identifying both the plastic and the color concentrate mixed into it. For a project with SamBound New Material Technology Company Ltd., whose website is sambound.com, keeping those inputs distinct makes the color specification easier to reproduce and review. A masterbatch addition rate describes one input to that mixture; it does not directly state the pigment content of the finished cap.

Identify the base resin

Sambound packaging sample showroom. Context photograph.

Record the proposed polymer and its grade. The base resin provides the starting material for the molded component, but the behavior of the finished part also depends on the concentrate, other ingredients, processing and geometry. Choosing a resin family alone does not establish the properties of the final colored assembly.

Identify the complete masterbatch grade

A conventional solid color masterbatch contains concentrated pigment or additives dispersed in a carrier. The carrier is part of the material being introduced, so its suitability for the receiving resin matters. Plastics Consultancy Network's explanation of masterbatches describes this carrier-to-base-material relationship.

The grade reference identifies a formulated product. It should not be reduced to a carrier name or a general rating of dispersion quality: different grades can also use different pigments, concentrations and additives. Keep the concentrate supplier's technical reference and recommended application conditions with the specification.

State what the addition rate is based on

A percentage needs a denominator. It may describe masterbatch mass as a fraction of the complete blend, or an addition expressed relative to the uncolored base resin. Those conventions give different percentages for the same mixture. State the basis rather than expecting a number alone to identify it.

Avient's PEI masterbatch bulletin labels its listed percentages as recommended addition rates and makes them specific to the selected colorant grades. Those recommendations concern the products in that bulletin; they are not a recipe for cosmetic caps or a universal colorant dosage.

Connect addition rate with pigment contribution

When addition is defined as masterbatch mass divided by total blend mass, its contribution to the blend's pigment mass fraction is the addition fraction multiplied by the pigment fraction within that masterbatch. A rate expressed relative to base resin alone must first be converted to the same total-blend basis.

This accounts for pigment introduced by that concentrate. Precolored resin or another color-bearing ingredient would need its own contribution included. Two concentrates used at the same addition rate therefore need not supply the same pigment amount. Different pigment chemistry and dispersion also mean that pigment mass alone does not predict an identical visual shade.

Retain the approved material combination

Keep the base grade, concentrate grade, addition basis and approved component together in the project record. Review a proposed substitution on representative molded samples, including the relevant appearance and functional requirements. This connects an agreed color with an identifiable material combination, rather than treating a color code or pellet photograph as the complete formulation.

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