How Much Masterbatch Is Used per Ton of Resin, and How Is the Dosing Calculated for Your Process?

The order of blue bags for the supermarket chain was on schedule until Thursday. The night shift found the film paler than the standard and raised the masterbatch feeder "a little" without recording by how much; the day shift found it dark and set it back to where they believed it had been. The customer received rolls in two different shades on the same pallet, and on Monday the warehouse reported that the concentrate budgeted for the month had run out a week early. The most basic question in the file was left unanswered: what percentage the line had been running at.

Masterbatch is typically dosed between 1% and 5%; one ton of resin takes on the order of 25 kg at 2.5%. The exact percentage is set by the technical data sheet and by laboratory testing.

What dosing by eye costs your plant

Masterbatch dosing is the plant variable that affects three results at once: the shade of the part, its cost and its performance. One percentage point above what is needed represents, in a ton of resin, ten kilograms of concentrate that you pay for and that the customer never perceives. One point below leaves the part pale, streaked or translucent where opacity was expected, and the lot is rejected for color. Between those two extremes lies the correct percentage, and the only way to hold it shift after shift is to have it in writing and to verify it in kilograms.

In the plants that consult us about shade variation, we frequently find the same scene. The formula exists, yet the feeder moves according to the operator's perception, and actual concentrate consumption is discovered only at the inventory close. The gap between what was budgeted and what was consumed then shows up as a shortfall of several thousand pesos that nobody knows which order to charge to, and the shade complaint arrives in the same week.

Let-down ratio: the proportion that defines the color

In the plastics industry, the proportion in which masterbatch is mixed with natural resin is known as the let-down ratio, or dilution ratio. It is expressed in two ways: as a percentage (2.5% means 2.5 kg of concentrate in every 100 kg of blend) or as a 1:X ratio (1:40 means one kilogram of concentrate for every forty kilograms of resin). Both notations describe the same idea, and confusing them is one of the most common sources of error on the plant floor.

In most color applications, typical dosing ranges between 1% and 5%. Within that range, the figure depends on how much pigment the concentrate carries, the shade being targeted and the thickness of the part. That is why the range is useful for budgeting, and the percentage for your part is defined during development.

Overdosing and underdosing: two failures with the same root

Excess concentrate raises the cost per part, can alter the flow of the blend and leaves pigment that the polymer matrix can no longer integrate; that surplus is the first to rise to the surface and transfer to whatever the part touches. Too little concentrate causes the opposite: a weak shade, streaks from incomplete dispersion and loss of opacity in thin film. Both failures originate at the same point, a percentage that nobody calculated or that nobody verified at the machine.

The calculation that turns a percentage into kilograms per shift

Calculating the dosing is simple arithmetic, provided you first define the basis on which the percentage is expressed. We propose the following three-step procedure, with example figures that you can replace with those of your line.

Step one: percentage of the blend or percentage of the resin

The base formula is kilograms of masterbatch = total blend weight × percentage ÷ 100. To prepare one ton of blend at 2.5%, you weigh 25 kg of concentrate and 975 kg of resin. If the technical data sheet expresses the percentage on the resin, the calculation changes slightly: 25 kg of concentrate are added to a full ton of resin, and the blend weighs 1,025 kg. The difference seems minor, but on a large order it accumulates and explains why two plants with the same formula report different consumption.

The 1:X ratio is converted with the same logic. At 1:40 there is one kilogram of concentrate for every forty of resin, that is, one kilogram in forty-one of blend: 2.44% of the blend, or 2.5% of the resin. Before programming the feeder, confirm with your supplier which of the two bases your technical data sheet uses.

Step two: from the percentage to the feeder

In extrusion, dosing translates into kilograms per hour. Using example figures, a film line processing 150 kg/h with a concentrate at 2% needs 3 kg/h of masterbatch; over an eight-hour shift, 24 kg. In injection molding, the calculation is made per shot: if each shot weighs 400 g including part and runner, at 2% the feeder must deliver 8 g of concentrate per cycle, and an order of 10,000 shots consumes 80 kg. With those figures, the warehouse knows how many bags to supply per shift and purchasing knows when to reorder, before the line stops.

Step three: how much pigment actually reaches the part

The masterbatch percentage and the pigment percentage in the part are two different figures. The second results from multiplying the pigment loading of the concentrate by the dosing. A hypothetical concentrate with 40% pigment, dosed at 2.5%, leaves 1% pigment in the part; a concentrate with a higher loading reaches that same concentration at a lower dosing. That is why a fair comparison between suppliers is made on cost per colored part. Our high-concentration masterbatches are formulated precisely on that criterion: greater tinting strength with lower dosing per kilogram of resin.

The variables that move the percentage in your process

Two parts of the same color may require very different dosing. These are the variables the laboratory reviews before proposing a figure:

• Wall thickness: a thin film needs more concentrate to reach opacity than a thick-walled injection-molded part, where the same shade is achieved with less pigment.

• Target opacity or translucency: a translucent shade allows low dosing; a solid shade that must hide the contents of the package requires a higher loading.

• Pigment type: organic pigments offer greater brightness and tinting strength at lower dosing; inorganic pigments contribute opacity and resistance to heat and light, and many formulas combine both.

• Base resin: a natural resin with a clean tone and a recycled resin with its own base tone respond differently to the same concentrate.

• Process and temperature: our basic line is formulated for HDPE, LDPE and PP in injection molding, film extrusion, extrusion blow molding and compression molding, with a processing range of 150 °C to 250 °C; outside that range, dosing stops being the only factor that controls the shade.

Each of these variables is recorded during development, and the recommended dosing comes from their combination. When one of them changes, for example a new resin supplier or a different film gauge, it is advisable to review the percentage with the laboratory before starting the run.

Three plant errors that throw dosing off

Even with the correct percentage on the data sheet, the actual dosing can drift from the programmed one. These are the three mechanisms we find most often when we review a lot with shade variation.

Dosing by volume with materials of different density

A volumetric feeder delivers a constant volume of pellets, and masterbatch pellets and resin pellets rarely share the same bulk density or the same shape. If the equipment was calibrated with another material, the actual percentage drifts from the programmed one without anyone noticing. The correction is simple: weigh what the feeder delivers over one minute, compare it with what it should deliver according to the calculation, and adjust. A gravimetric feeder solves the problem at the root because it doses by weight.

Drum premixing and segregation in the hopper

When the concentrate is premixed with the resin in a drum, pellets of different sizes tend to separate during transfer and inside the hopper. The result is a part with more color at the start of the load and less at the end, or streaks that appear and disappear throughout the run. Direct dosing at the machine throat, with a calibrated feeder, eliminates that variation.

Shift adjustments without a record

The case in the opening is the most frequent. Every adjustment an operator makes to correct the shade changes the actual percentage, and if it is made without a record, the next person starts from an unknown point. The solution is procedural: the percentage written on the production order, verification by weight at the start of every shift, and any shade deviation reported to the laboratory before the feeder is moved.

Who defines the exact percentage for your part

The 1% to 5% range is useful for budgeting; the percentage for your part is defined by the concentrate's technical data sheet and by laboratory testing. At Delta Pigmentos, dosing is adjusted to your machine through the technical proposal that accompanies every quote. The laboratory starts from your shade reference (a physical sample, a Pantone code or the material you use today), your polymer, your process and the thickness of the part, and formulates the concentrate with the pigment loading that case requires.

You then test the sample on your own machine, with your material and your conditions, and confirm the shade at the recommended dosing before committing volume. We carry out color matching as an authorized Pantone partner, and our manufacturing procedures are certified under ISO 9001-2015, which is what ensures that the dosing approved today delivers the same shade on next quarter's order.

Frequently asked questions

Can I lower the dosing to reduce cost?

Only with prior validation. If the shade and the opacity hold at a lower percentage, the savings are real; if they drop, the savings are paid for in rejects. The safest route is a concentrate with a higher pigment loading, which reaches the same shade with fewer kilograms per ton. The laboratory can evaluate both options with your part.

How do I convert a 1:50 ratio to a percentage?

Divide one by the sum of the two parts: 1 ÷ 51 gives 1.96% of the blend. If the technical data sheet expresses the percentage on the resin, 1 ÷ 50 gives 2%. Always confirm which of the two bases your supplier uses before programming the feeder.

Does the dosing change if I work with recycled resin?

Frequently, yes. Recycled resin brings its own base tone and can vary between lots, so the percentage that worked with natural resin may fall short or overshoot. It is advisable to develop the color on the actual resin that will be used in production and to measure each new lot against the standard.

At Delta Pigmentos we have been manufacturing masterbatch for 24 years, with our own laboratory and ISO 9001-2015 certified procedures. If you need to confirm the correct percentage for a new part, or your concentrate consumption is already drifting from the budget, write to us on WhatsApp with your polymer, your process, the thickness of the part and your shade reference; we will respond with a technical proposal and a recommended dosing. Every request is reviewed within the following 24 business hours.