Pressure Filter Value (FPV) for Pigment & Filler Dispersion

In plastic compounding and masterbatch production, pigments and fillers (e.g., TiO₂, carbon black, calcium carbonate) must be dispersed uniformly down to sub-micron scales. Poorly dispersed particles form agglomerates that clog screen packs, cause thread breakages in fiber spinning, and create surface defects in thin films. The Filter Pressure Value (FPV) is the international standard test method used to quantify masterbatch dispersion quality. Compounding units operated by Indian firms like Plastiblends and Cabot India use FPV testing to qualify batches before shipping them to manufacturers.

• Explain the principle of the Filter Pressure Value (FPV) test for masterbatch qualification.
• Describe the layout of an FPV test extruder (feed screw, gear pump, melt temperature sensor, filter mesh).
• Calculate the FPV ($F_p$) value from pressure difference ($\Delta P$) and pigment mass parameters.
• Evaluate how filter mesh size influences test sensitivity and results.
• Identify DIN EN 13900-5 as the standard governing FPV measurements.

3.1 Principle of the FPV Test

The FPV test measures the pressure rise upstream of a test filter screen while a mixture of masterbatch and virgin polymer is extruded at a constant flow rate. Agglomerates in the masterbatch block the filter mesh, reducing the open flow area and causing a pressure increase. A small pressure rise indicates excellent pigment dispersion, while a steep pressure jump indicates poor dispersion.

3.2 FPV Extruder Setup

The test apparatus consists of:

1. Single Screw Extruder: Melts and homogenises the compound.
2. Melt Pump (Gear Pump): Guarantees a constant volumetric flow rate ($Q$) regardless of viscosity variations.
3. Pressure Sensor: Positioned directly upstream of the test filter.
4. Test Filter (Screen): Specialized wire mesh. Standard mesh sizes are defined by DIN EN 13900-5 (typically 14 $\mu$m, 25 $\mu$m, or 40 $\mu$m).

3.3 FPV Calculation Formula

According to DIN EN 13900-5, the Filter Pressure Value ($F_p$, bar/g of pigment) is:

$$F_p = \frac{P_{max} - P_0}{m_{pigment}}$$

Where:

• $P_{max}$: Maximum pressure recorded during injection of the masterbatch blend (bar)
• $P_0$: Baseline pressure with virgin polymer melt alone (bar)
• $m_{pigment}$: Total mass of dry pigment passing through the filter during the test (g):

$$m_{pigment} = m_{blend} \times w_{masterbatch} \times w_{pigment}$$

Evaluation Limits (typical for PP fibre grades):

• $F_p < 1.0$ bar/g: Excellent dispersion (suitable for ultra-fine spun fibres).
• $1.0 \le F_p \le 2.5$ bar/g: Acceptable (suitable for films and blow-moulded parts).
• $F_p > 2.5$ bar/g: Poor dispersion (unsuitable; will clog spinnerets).

<div className="problem-statement">

Problem: An FPV test is performed to qualify a blue masterbatch containing $30\%$ copper phthalocyanine pigment. A test blend of 1.0 kg total mass containing $10\%$ masterbatch and $90\%$ virgin PP is passed through a 14 $\mu$m filter screen. The data is:

• Baseline pressure with virgin PP: $P_0 = 42.0$ bar
• Peak pressure during the test: $P_{max} = 78.5$ bar Calculate:

1. The mass of pigment ($m_{pigment}$) that passed through the filter.
2. The Filter Pressure Value ($F_p$) in bar/g.
3. Determine if the masterbatch is suitable for fiber spinning (limit $F_p < 1.0$ bar/g).

</div> <div className="solution-step">

Solution:

1. Calculate the pigment mass $m_{pigment}$:

$$m_{pigment} = m_{blend} \times w_{masterbatch} \times w_{pigment}$$ $$m_{pigment} = 1000 \text{ g} \times 0.10 \times 0.30 = \textbf{30.0 grams of pigment}$$

1. Calculate $F_p$:

$$F_p = \frac{P_{max} - P_0}{m_{pigment}} = \frac{78.5 - 42.0}{30.0} = \frac{36.5 \text{ bar}}{30.0 \text{ g}} = \textbf{1.217 bar/g}$$

1. suitability check: The calculated $F_p = 1.22$ bar/g is above the 1.0 bar/g limit. Therefore, this batch is not suitable for fine fiber spinning as it may cause thread breakages. It can, however, be qualified for structural injection moulding or profile extrusion where clearances are larger.

Plastiblends India Limited (Daman/Mumbai) is a major masterbatch manufacturer. They use FPV testing on dedicated lab-scale single screw extruders equipped with melt pumps to certify their additive and color masterbatch grades for Indian packaging and textile processors.

Indian fiber manufacturers (e.g., producing PP bags or polyester geotextiles) require an FPV test certificate from masterbatch suppliers to protect their high-speed melt spinning lines from screen clogging.

• FPV (Filter Pressure Value): Metric quantifying pigment dispersion based on back-pressure rise per gram of pigment.
• DIN EN 13900-5: The international standard specifying FPV testing equipment and calculation methods.
• Melt Pump: Gear pump delivering constant volume flow rate, eliminating viscosity-driven pressure drops.
• Agglomerates: Clusters of pigment particles that failed to separate during compounding.
• Zeta Potential: (Not applicable, latex parameter).

1. DIN EN 13900-5 — Pigments and extenders — Methods of dispersion and assessment of dispersibility in plastics — Part 5: Determination of filter pressure value
2. ISO 2393 — Rubber testing guidelines (Not applicable to thermoplastics FPV)
3. ASTM D3218 — Standard Specification for Polyolefin Monofilaments (refers to dispersion checks)

1. Explain the role of the gear pump in the FPV test apparatus. Why can a simple extruder screw alone without a gear pump yield unreliable pressure curves?
2. How does the choice of filter screen size (e.g., 14 $\mu$m vs. 25 $\mu$m) impact the FPV value and test sensitivity for masterbatches destined for agricultural films?
3. Discuss how compound moisture or thermal degradation can affect FPV pressure readouts, potentially leading to false-positive or false-negative results.

Q1. The Filter Pressure Value (FPV) is calculated as the pressure rise divided by the:

• B) Mass of active pigment passed through the filter

Q2. Which standard governs the determination of FPV for pigments and fillers in plastics?

• C) DIN EN 13900-5

Q3. An FPV value of 0.8 bar/g is considered:

• A) Excellent (suitable for fine fiber extrusion)

Q4. What is the purpose of the gear pump in the FPV testing extruder?

• C) To maintain a constant volumetric melt flow rate

Q5. Which Indian masterbatch compounding company uses FPV tests to qualify batches in Daman?

• B) Plastiblends India Limited