CPVC molding processes – Differences from PVC

While comparing it to the PVC molding process, we will introduce the points to note when molding CPVC (extrusion molding, injection molding, profile extrusion molding) and the recommended settings for the molding machine.

Can molding machines for PVC be used for CPVC molding?

The molding processes for CPVC and PVC are very similar.

CPVC molding processes such as extrusion and injection molding can generally use equipment and tools for PVC molding.

However, it is necessary to set the molding machine appropriately, such as by setting the temperature and screw to match the material characteristics.

The Sekisui Chemical Group is itself a molding manufacturer and has high technological capabilities in the field of molding, including extrusion and injection molding.
In addition to selling CPVC compounds, we can also offer process proposals based on our knowledge as a molding manufacturer.

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CPVC Compound (powder, pellet)

Molding (Photo: Extrusion molding)

Molded product (pipes, etc.)

CPVC pipes

What Is the Main Difference Between CPVC and PVC Processing?

The main differences between PVC and CPVC are thermal stability and viscosity.

Thermal stability

CPVC will not melt without the application of moderate heat and will not exhibit excellent physical properties.
On the other hand, it will decompose if exposed to excessively high temperatures.

The diagram on the right is a reference material that shows the crystallization melting points of PVC and CPVC.

Key Points

PVC and CPVC materials have different thermal stabilities:

  • The residence time of CPVC in the molding machine must be as short as possible.
  • Temperature setting is important to ensure melting and gelling of the material.
This is a reference document and does not guarantee the content.

Viscosity (Fluidity)

In general, the viscosity of CPVC is higher than that of PVC. In the case of PVC, the viscosity (=K-value) is set simply by the degree of polymerisation. In the case of CPVC, on the other hand, the viscosity (=K-value) is set by a combination of degree of polymerisation and chlorination.

Key Points

PVC and CPVC materials have different thermal stabilities:

The structure of the screw and mould tools is an important factor. Molding equipment must be suitable for CPVC molding.

The screw undergoes shear heating. Temperature control is therefore required to keep the material at the correct temperature.

Differences in molding processes (CPVC vs. PVC)

Extrusion molding

Twin-screw extruderScrew motor:High torque
Screw:Parallel φ60-170
    Conical φ50-85
Screw mortar:High torque
Screw:Parallel φ60-135
    Conical φ50-70
Screw rotationLower than PVC
Condition (Barrel Temp.)300 – 340℉340 – 410℉
Mold typeStainless steelStainless steel
Small quantity (flow channel section)
Mold angle: acute angle
*We cannot guarantee these reference values.

Injection molding

Injection machineScrew mortar: High torque
Barrel cooling: Blower
Screw mortar: High torque
Barrel cooling: Blower
Barrel zone: 4-5 zone
Nozzle: Short nozzle、φ:Larger than PVC
Screw rotation9-14 m/sec8-13 m/sec
(lower than PVC)
Condition (Barrel Temp.)320 – 365℉320 – 392℉
Condition (holding pressure)100 – 170 MPa100 – 170 MPa
Mold typeStainless steel
Gate: Direct gate
Stainless steel
Gate: Direct gate
*We cannot guarantee these reference values.

Deformed extrusion molding

Single screw extruderSingle screw machine
Screw: Dulmage, Fullfight
Single screw machine
Screw: Fullfight recommended (Dulmage)
L/D = 22 – 25
Compression ratio: 2.5 – 3.2
Screw rotation15~ rpm (65 mm single)15–25 rpm (65 mm single)
Condition (Barrel Temp.)284 – 338℉300 – 370℉
Mold typeStainless steelStainless steel
*We cannot guarantee these reference values.


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