PVC (Polyvinyl Chloride) Injection Molding

PVC (Polyvinyl Chloride) is a widely used thermoplastic in injetion molding. It’s versatile, has good chemical resistance and is cost efficient. A range of applications are using PVC, such as medical devices, electrical applications and even construction components.
PVC offers a good balance of performance and affordability.

This guide will help to understand what exactly PVC is and how it can be processes via injection molding.

Table of Contents

Basic Properties of PVC

PVC material advantages

  • Chemical resistance
  • Non-hygroscopic (negligible moisture absorption)
  • Electrical insulation
  • Can be solvent bonded
  • Flame resistance
  • High impact and tensile strength
  • Resin cost is relatively low
pvc material

Disadvantages of molded PVC

  • Susceptibility to thermal degradation
  • Low heat deflection temperature

Types of PVC

There are 2 main types of PVC material that have completely different applications due to its flexibility and softness.

Rigid PVC (RPVC / H-PVC)

  • PVC-U (unplasticized): The most widely used grade, also denoted as uPVC.
  • PVC-M (Modified): More ductile and tough.
  • PVC-O (oriented PVC): Produced by extrusion and post-stretching; not typically manufactured via conventional injection molding.
  • CPVC (Chlorinated Polyvinyl Chloride): Rigid, high-temperature grade with added chlorine for heat resistance (functional operating range ~100°C).

Applications: Pipe fittings, electrical boxes, window profiles, chemical tank components, construction hardware, medical equipment.

Flexible PVC (PVC-P / FPVC)

  • Incorporates plasticizers to enhance flexibility.

Applications: Flexible gaskets, soft tool grips, electrical connector boots, flexible tubing fittings, automotive interior trim.

PVC molding what to follow

PVC is heat- and shear-sensitive during molding. Prolonged exposure to processing temperatures or high shear from resin flowing through narrow areas (such as gates) can cause melt degradation. PVC is corrosive to the mold and molding machine.

General Safety

PVC and acetal (POM) must never be mixed, even in trace amounts within the same machine. When heated, PVC generates acidic decomposition products that catalyze rapid acetal degradation, leading to violent gas release. Standard purging is insufficient for contamination; best practice is to not run these materials on the same machine.

PVC resin dust can cause skin, eye, and respiratory irritation.

Control Measures

Ventilate the molding machine area. Wear chemical-resistant gloves and goggles. Use a respirator during high-fume/dust tasks (e.g., machine startup, thermal degradation events).

Resin Storage

Store PVC resin in a dry, well-ventilated area with sealed containers. Avoid excessive heat for long-term storage.

pvc material storage

Mold Design

Stainless steel is recommended for mold steel (resists HCl corrosion), such as 420SS.

Streamlined sprue and gate geometry to minimize shear and stagnant zones.

Hot runners: Use cautiously (open nozzles only, short hot sprue/hot runner setups). PVC must be purged after intermittent delays; the machine/mold must allow purging the hot runner while the mold is open.

Processing Parameters

Regrind

PVC may be reground in some applications, but cumulative heat history must be considered (repeated thermal cycles cause degradation).

Resin Drying

  • Non-hygroscopic (no moisture absorption; dry only to remove surface moisture).
  • Refer to the resin data sheet for drying parameters (e.g., 2 hours at 50°C for some grades).
  • Use direct-feed drying systems to avoid moisture re-accumulation on cooled pellets.
  • Excessive drying causes degradation (reduced mechanical properties, discoloration).
plastic resin dryer

Melt Temperature

Some PVC resins process at 200°C; verify actual melt temperature with a probe pyrometer (pull the injection unit to take an “air shot” sample, then insert the probe into the molten resin).

Screw RPM & Back Pressure

Adequate back pressure (75 psi is a good starting point) removes air bubbles and ensures uniform melt temperature. Excessive back pressure or high RPM causes shear-induced degradation; settings vary by screw type.

Injection Speed

Profile injection speed slower for the runner and initial 5% of the part, then increase speed to fill to 98% full. Ensure the process is not pressure-limited (actual injection pressure must stay below the set pressure limit to maintain speed).

Packing & Holding

  • Fill the last 2% of the part at a slower speed.
  • Start with low packing pressure and incrementally increase until part appearance is acceptable.
  • Determine holding time by incrementally increasing until part weight stabilizes (gate freeze time).

Purging

Purging material depends on PVC grade (examples: Dyna-Purge D2, ABS, Polystyrene, LDPE). Purge material must have a melt temperature similar to the PVC grade being processed.

Mold Storage

For mold storage, spray the mold with an acid neutralizer (to neutralize HCl residues from PVC degradation) followed by a rust preventative to protect mold integrity.

mold storage pvc

Top PVC Resin Manufacturers

Name Country / Origin Trademark Names Website
Shin-Etsu Japan Shin-Etsu PVC (grade series such as TK-xxx) https://www.shinetsu.co.jp/en/products/infrastructure-materials/polyvinyl-chloride-pvc/
Westlake Chemical USA Westlake PVC Resin (grades such as 1091, 1185B, 1195B, 1230P) https://www.westlake.com/pvc-resin
Formosa Plastics Taiwan Formolon® PVC https://www.fpcusa.com/products/formolon-suspension-polyvinyl-chloride-resins/
INEOS Inovyn UK / Europe INOVYN™ PVC https://www.ineos.com/industry/products/polymers/pvc/
Vynova Belgium VYNOVA™ PVC https://www.vynova-group.com/products/pvc/commercial-information
KEM ONE France Lacovyl®, Kemaia® https://www.kemone.com/en/general-purpose-pvc/
GEON USA GEON® PVC Compounds, GEON® Rigid, GEON® Flex https://www.geon.com/materials/polyvinyl-chloride-pvc
Xinjiang Zhongtai Chemical China Zhongtai PVC Resin (commodity grades SG3, SG5, SG8 etc.) http://www.zhongtaiint.com/
Xinjiang Tianye China Tianye PVC Resin (SG-series commodity grades) http://www.xj-tianye.com
Tianjin Dagu Chemical China Dagu PVC Resin (DG-series grades such as DG700, DG800) http://www.tjdagu.com
Beiyuan Group China Beiyuan PVC Resin (SG-series grades) http://www.sxbeiyuan.com
LG Chem South Korea HRTP PVC, BCB PVC, PCR PVC, general PVC https://www.lgchem.com/product-detail/pvc
Orbia (Vestolit) Germany / Mexico VESTOLIT® PVC, PRIMEX® PVC https://www.vestolit.com
Hanwha Solutions South Korea Hanwha PVC Resin, CPVC specialty line https://hcc.hanwha.co.kr/en/business/pvc-pvc-resin

Molding Machines for PVC

  • Haitian HA-PVC Series (https://www.haitian.com.tr/en/uploads/docs/ha-pvc-serisi.pdf)
  • Arburg corrosion-resistant, low-compression screws (https://www.arburg.com/media/daten/publications/brochures/arburg_service_plasticising_526421_en_gb.pdf)
  • Milacron Q-Series CPVC (https://www.milacron.com/wp-content/uploads/2025/08/Q-Series-CPVC-MI0825.pdf)
  • FCS HT-PVC machine (https://www.fcs.com.tw/products_i_special-imm-for-pvc-fittings)
  • YIZUMI UPVC & PPR Pipe Fitting Special Injection Molding Machine
  • DKM-PVC series (https://www.dakumar.com/PVC-Injection-Molding-Machine.html)
  • Bole BLD400EK-PVC (https://www.bolemachinery.com/pvc-special-injection-moulding-machine/39919647.html)
pvc molding machines

Machine Components

Machine Throat

Avoid premature material softening to prevent bridging and inconsistent flow to the screw.

Barrels

  • Size should be chosen so that the shot is 60% of barrel capacity (mitigates excessive residence time).
  • Air cooling added to the barrel.
  • Bimetallic construction: Inner layer for corrosion/wear resistance; outer layer for structural strength.

Screws

  • PVC screws produce lower shear and gentler melting (general-purpose screws generate high shear that degrades PVC).
  • Optimized length-to-diameter (L/D) ratio for PVC.
  • Milder compression zone to minimize shear.
  • Non-return mechanisms (e.g., smear tip style) to reduce shear (avoid tight-clearance valve gates).
  • Corrosion-resistant material to resist HCl-induced corrosion.
  • High-torque, low-RPM motor capability.

End Cap & Nozzle

End caps and nozzles are optimized to eliminate stagnant areas and reduce shear.

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We have been making various PVC molds and building up a vast knowledge on how to deal with the different properties of it during the molding process.

Let us know if you need help with your project.

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